CAUFOR ilA EAHTK LIBRARY DANA'S SERIES OF MINERALOGIES System of Mineralogy Sixth edition, entirely rewritten. With Appendices I and II, completing the work to 1909. 1333 pages, 6f by 10, over 1400 figures Half leather, net $15.00. Third Appendix to the Sixth Edition of Dana's System of Mineralogy Completing the Work to 1915. By William E. Ford, Pro- fessor of Mineralogy, Sheffield Scientific School of Yale University, 87 pages, 6f by 10 Cloth, net $2.00 A Text-book of Mineralogy With an extended Treatise on Crystallography and Physical Mineralogy. By Edward Salisbury Dana, Professor of Physics and Curator of Mineralogy, Yale University. New edition, entirely rewritten and reset. By William E. Ford (1922). 720 pages, 6 by 9, nearly 1000 figures . Cloth, net $5.00 Minerals, and How to Study Them A book for beginners in Mineralogy. By Prof. E. S. Dana. 380 pages, 319 figures. Cloth, net $2.00 BY DANA AND FORD Manual of Mineralogy For the Student of Elementary Mineralogy, the Mining Engineer, the Geologist, the Prospector, the Collector, etc. Thirteenth edition, entirely revised and rewritten, by Wil- liam E. Ford. 460 pages, 5 by yj, 357 figures, and 10 plates. Cloth, net $3.00 Flexible binding, net $3.50 A TEXT-BOOK OF MINERALOGY WITH AN EXTENDED TREATISE ON CRYSTALLOGRAPHY AND PHYSICAL MINERALOGY BY EDWARD SALISBURY DANA ft Professor Emeritus of Physics and Curator of Mineralogy Yale University THIRD EDITION, REVISED AND ENLARGED BY WILLIAM E. FORD Professor of Mineralogy, Sheffield Scientific School of Yale University TOTAL ISSUE, TWENTY-SEVEN THOUSAND NEW YORK JOHN WILEY & SONS, INC. LONDON: CHAPMAN & HALL, LIMITED 1922 COPYRIGHT, 1898 BY EDWARD S. DANA. COPYRIGHT, 1922 BY EDWARD S. DANA AND WILLIAM E. FORD. TECHNICAL COMPOSITION CO. CAMBRIDGE, MASS., U. S. A. EARTH SCIENCES LIBRARY PREFACE TO THE THIRD EDITION The first edition of this book appeared in 1877 and approximately twenty years later (1898) the second and revised edition was published. Now, again after more than twenty years, comes the third edition. The changes involved in the present edition are chiefly those of addition, the general character and form of the book having been retained unchanged. In the section on Crystallography the important change consists in the introduction of the methods employed in the use of the stereographic and gnomonic pro- jections. A considerable portion of the section on the Optical Characters of Minerals has been rewritten in the endeavor to make this portion of the book simpler and more readily understood by the student. In the section on Descriptive Mineralogy all species described since the previous edition have been briefly mentioned in their proper places. Numerous other changes and corrections have, of course, been made in order to embody the results of mineral investigation during the last two decades. Only minor changes have been made in the order of classification of the mineral species. It was felt that as this book is so closely related to the System of Mineralogy it was unwise to attempt any revision of the chemical classification until a new edition of that work should appear. The description of the methods of Crystal Drawing given in Appendix A has been largely rewritten. A new table has been added to. Appendix B in which the minerals have been grouped into lists according to their important basic elements. Throughout the book the endeavor has been to present in a clear and concise way all the information needed by the elementary and advanced student of the science. The editor of this edition is indebted especially to the published and un- published writings of the late Professor Samuel L. Penfield for much ma- terial and many figures that have been used in the sections of Crystallog- raphy and The Optical Character of Minerals. He also acknowledges the cordial support and constant assistance given him by Professor Edward S. Dana. WILLIAM E. FORD NEW HAVEN, CONN., Dec. 1, 1921. 469105 m PREFACE TO THE SECOND EDITION THE remarkable advance in the Science of Mineralogy, during the years that have elapsed since this Text-Book was first issued in 1877, has made it necessary, in the preparation of a new edition, to rewrite the whole as well as to add much new matter and many new illustrations. The work being designed chiefly to meet the wants of class or private instruction, this object has at once determined the choice of topics discussed, the order and fullness of treatment and the method of presentation. In the chapter on Crystallography, the different types of crystal forms are described under the now accepted thirty-two groups classed according to their symmetry. The names given to these groups are based, so far as possible, upon the characteristic form of each, and are intended also to suggest the terms formerly applied in accordance with the principles of hemihedrism. The order adopted is that which alone seems suited to the demands of the elementary student, the special and mathematically simple groups of the isometric system being described first. Especial prominence is given to the " normal group" under the successive systems, that is, to the group which is relatively of most common occurrence and which shows the highest degree of symmetry. The methods of Miller are followed as regards the indices of the different forms and the mathematical calculations. In the chapters on Physical and Chemical Mineralogy, the plan of the former edition is retained of presenting somewhat fully the elementary prin- ciples of the science upon which the mineral characters depend; this is par- ticularly true in the department of Optics. The effort has been made to give the student the means of becoming practically familiar with all the modern methods of investigation now commonly applied. Especial attention is, therefore, given to the optical properties of crystals as revealed by the micro- scope. Further, frequent references are introduced to important papers on the different subjects discussed, in order to direct the student's attention to the original literature. The Descriptive part of the volume is essentially an abridgment of the Sixth Edition of Dana's System of Mineralogy, prepared by the author (1892). To this work (and future Appendices) the student is, therefore, referred for fuller descriptions of the crystallographic and optical properties of species, for analyses, lists of localities, etc.; also for the authorities for data here quoted. In certain directions, however, the work has been expanded when the interests VI PREFACE TO THE SECOND EDITION of the student have seemed to demand it; for example, in the statement of the characters of the various isomorphous groups. Attention is also called to the paragraph headed "Diff.," in the description of each common species, in which are given the distinguishing characters, particularly those which serve to separate it from other species with which it might be easily confounded. The list of American localities of minerals, which appeared as an Appendix in the earlier edition, has been omitted, since in its present expanded form it requires more space than could well be given to it; further, its reproduc- tion here is unnecessary since it is accessible to all interested not only in the System of Mineralogy but also in separate form. A full topical Index has been added, besides the usual Index of Species. The obligations of the present volume to well-known works of other au- thors particularly to those of Groth and Rosenbusch are too obvious to require special mention. The author must, however, express his gratitude to his colleague, Prof. L. V. Pirsson, who has given him material aid in the part of the work dealing with the optical properties of minerals as examined under the microscope. He is also indebted to Prof. S. L. Penfield of New Haven and to Prof. H. A. Miers of Oxford, England, for various valuable suggestions. EDWARD SALISBURY DANA NEW HAVEN, CONN., Aug. 1, 1898. TABLE OF CONTENTS PAGE INTRODUCTION 1 PART I. CRYSTALLOGRAPHY GENERAL MORPHOLOGICAL RELATIONS OF CRYSTALS 7 GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 26 I. ISOMETRIC SYSTEM 52 1. Normal Class (1). Galena Type , 52 2. Pyritohedral Class (2). Pyrite Type 63 3. Tetrahedral Class (3). Tetrahedrite Type 66 4. Plagiohedral Class (4). Cuprite Type 71 5. Tetartohedral Class (5). Ullmannite Type 72 Mathematical Relations of the Isometric System 72 II. TETRAGONAL SYSTEM 77 1. Normal Class (6). Zircon Type 77 2. Hemimorphic Class (7). lodosuccinimide Type . 84 3. Pyramidal Class (8). Scheelite Type 85 4. Pyramidal-Hemimorphic Class (9). Wulfenite Type 86 5. Sphenoidal Class (10). Chalcopyrite Type 87 6. Trapezohedral Class (11). Nickel Sulphate Type 89 7. Tetartohedral Class (12) 89 Mathematical Relations of the Tetragonal System 90 III. HEXAGONAL SYSTEM 94 A. Hexagonal Division 95 1. Normal Class (13). Beryl Type 95 2. Hemimorphic Class (14). Zincite Type 98 3. Pyramidal Class (15). Apatite Type 100 4. Pyramidal-Hemimorphic Class (16). Nephelite Type 101 5. Trapezohedral Class (17) 102 B. Trigonal or Rhombohedral Division 103 1. Trigonal Class (18). Benitoite Type 103 2. Rhombohedral Class (19). Calcite Type. 104 3. Rhombohedral-Hemimorphic Class (20). Tourmaline Type 109 4. Trirhombohedral Class (21). Phenacite Type 110 5. Trapezohedral Class (22). Quartz Type 112 6. 7. Other Classes (23) (24) 114 Mathematical Relations of the Hexagonal System 115 IV. ORTHORHOMBIC SYSTEM 121 1. Normal Class (25). Barite Type 121 2. Hemimorphic Class (26). Calamine Type 126 3. Sphenoidal Class (27). Epsomite Type 128 Mathematical Relations of the Orthorhombic System 128 vii yiii TABLE OF CONTENTS PAGE V. MONOCLINIC SYSTEM 133 1. Normal Class (28). Gypsum Type 133 2. Hemimorphic Class (29). Tartaric Acid Type 138 3. Clinohedral Class (30). Clinohedrite Type '138 Mathematical Relations of the Monoclinic System 139 VI. TRICLINIC SYSTEM 143 1. Normal Class (31). Axinite Type 144 2. Asymmetric Class (32). Calcium Thiosulphate Type 147 Mathematical Relations of the Triclinic System 148 MEASUREMENT OP THE ANGLES OF CRYSTALS 152 COMPOUND OR TWIN CRYSTALS 160 Examples of Important Methods of Twinning 165 Regular Grouping of Crystals 172 IRREGULARITIES OF CRYSTALS 174 1. Variations in the Forms and Dimensions of Crystals 174 2. Imperfections of the Surfaces of Crystals 176 3. Variations in the Angles of Crystals 178 4. Internal Imperfection and Inclusions 178 CRYSTALLINE AGGREGATES 182 PART II. PHYSICAL MINERALOGY PHYSICAL CHARACTERS OF MINERALS 185 I. Characters depending upon Cohesion and Elasticity 186 II. Specific Gravity, or Relative Density ' 195 III. Characters depending upon Light 200 General Principles of Optics 200 Optical Instruments and Methods 241 General Optical Characters of Minerals . . / , 246 1. Diaphaneity - 247 2. Color 247 3. Luster 249 Special Optical Characters of Minerals belonging to the different Systems 251 A. Isometric Crystals 252 B. Uniaxial Crystals 253 General Optical Relations 253 Optical Examination of Uniaxial Crystals 259 C. Biaxial Crystals 270 General Optical Relations 270 Optical Examination of Biaxial Crystals 278 IV. Characters depending upon Heat 303 V. Characters depending upon Electricity and Magnetism 306 VI. Taste and Odor 310 PART III. CHEMICAL MINERALOGY GENERAL PRINCIPLES OF CHEMISTRY AS APPLIED TO MINERALS 311 CHEMICAL EXAMINATION OF MINERALS 327 Examination in the Wet Way 328 Examination by Means of the Blowpipe 329 TABLE OF CONTENTS IX PART IV. DESCRIPTIVE MINERALOGY PAGE NATIVE ELEMENTS 344 SULPHIDES, SELENIDES, TELLURIDES, ETC 357 SULPHO-SALTS 383 CHLORIDES, BROMIDES, IODIDES, FLUORIDES 394 OXIDES 402 CARBONATES 436 SILICATES 454 TlTANO-SlLICATES, TlTANATES 583 NIOBATES, TANTALATES 587 PHOSPHATES, ARSENATES, VANADATES, ETC 592 NITRATES 619 BORATES 619 URANATES ' 623 SULPHATES, CHROMATES, ETC 624 TUNGSTATES, MoLYBDATES 641 OXALATES, MELLATES 644 HYDROCARBON COMPOUNDS 645 APPENDIX A. ON THE DRAWING OF CRYSTAL FIGURES 649 APPENDIX B. TABLES TO BE USED IN THE DETERMINATION OF MINERALS 663 GENERAL INDEX 695 INDEX TO SPECIES. . 703 INTRODUCTION 1. THE SCIENCE OF MINERALOGY treats of those inorganic species called minerals, which together in rock masses or in isolated form make up the material of the crust of the earth, and of other bodies in the universe so far as it is possible to study them in the form of meteorites. 2. Definition of a Mineral. A Mineral is a body produced by the proc- esses of inorganic nature, having a definite chemical composition and, if formed under favorable conditions, a certain characteristic molecular structure which is exhibited in its crystalline form and other physical properties. This definition calls for some further explanation. First of all, a mineral must be a homogeneous substance, even when minutely examined by the microscope; further, it must have a definite chemical composition, capable of being expressed by a chemical formula. Thus, much basalt appears to be homogeneous to the eye, but when examined under the microscope in thin sections it is seen to be made up of different substances, each having characters of its own. Again, obsicftan, or volcanic glass, though it may be essentially homogeneous, has not a definite composition corresponding to a specific chemical formula, and is hence classed as a rock, not as a mineral species. Further, several substances, as tachylyte, hyalome- lane, etc., which at one time passed as minerals, have been relegated to petrology, because it has been shown that they are only local forms of basalt, retaining an apparently homogeneous form due to rapid cooling. Again, a mineral has in all cases a definite molecular structure, unless the conditions of formation have been such as to prevent this, which is rarely true. This molecular structure, as will be shown later, manifests itself in the physical characters and especially in the external crystalline form. It is customary, as a matter of convenience, to limit the name mineral to those compounds which have been formed by the processes of nature alone, while compounds made in the laboratory or the smelting-furnace are at most called artificial minerals. Further, mineral substances which have been pro- duced through the agency of organic life are not included among minerals, as the pearl of an oyster, the opal-silica (tabasheer) secreted by the bamboo, etc. Finally, mineral species are, as a rule, limited to solid substances; the only liquids included being metallic mercury and water. Petroleum, or mineral oil, is not properly a homogeneous substance, consisting rather of several hydrocarbon compounds; it is hence not a mineral species. It is obvious from the above that minerals, in the somewhat restricted sense usually adopted, constitute only a part of what is often called the Mineral Kingdom. 3. Scope of Mineralogy. In the following pages, the general subject of mineralogy is treated under the following heads : (1) Crystallography. This comprises a discussion of crystals in general and especially of the crystalline forms of mineral species. 1 INTRODUCTION (2) Physical Mineralogy. This includes a discussion of the physical characters of minerals, that is, those depending upon cohesion and elasticity, density, light, heat, electricity, and so on. (3) Chemical Mineralogy. Under this head are presented briefly the general principles of chemistry as applied to mineral species; their charac- ters as chemical compounds are described, also the methods of investigating them from the chemical side by the blowpipe and other means. (4) Descriptive Mineralogy. This includes the classification of minerals and the description of each species with its varieties, especially in its relations to closely allied species, as regards crystalline form, physical and chemical characters, occurrence in nature, and other points. 4. Literature. Reference is made to the Introduction to the Sixth Edition of Dana's System of Mineralogy, pp. xlv-lxi, for an extended list of independent works on Mineralogy up to 1892 and to its Appendices I, II and III for works published up to 1915; the names are also given of the many scientific periodicals which contain original memoirs on mineralogical subjects. For the convenience of the student the titles of a few works, mostly of a general character, are given here. Further references to the literature of Mineralogy are introduced through the first half of this work, particularly at the end of the sections dealing with special subjects. Crystallography and Physical Mineralogy EARLY WORKS * include those of Rome de Flsle, 1772; Haiiy, 1822; Neumann, Krys- tallonomie, 1823, and Krystallographie, 1825; Kupffer, 1825; Grassmann, Krystallonomie, 1829; Naumann, 1829 and later; Quenstedt, 1846 (also 1873); Miller, 1839 and 1863; Grailich, 1856; Kopp, 1862; von Lang, 1866; Bravais, Etudes Crist., Paris, 1866 (1849); Schrauf, 1866-68; Rose-Sadebeck, 1873. RECENT WORKS include the following: Bayley. Elementary Crystallography, 1910. Beale. Introduction to Crystallography, 1915. Beckenkamp. Statische und kinetische Kristalltheorien, 1913-. Bruhns. Elemente der Krystallographie, 1902. Goldschmidt. Index der Krystallformen der Mineralien; 3 vols., 1886-91. Also Anwendung der Linearprojection zum Berechnen der Krystalle, 1887. Atlas der Krystall- formen, 1913-. Gossner. Kristallberechnung Und Kristallzeichnung, 1914. Groth. Physikalische Krystallographie und Einleitung in die krystallographische Kenntniss der wichtigeren Substanzen, 1905. Klein. Einleitung in die Krystallberechnung, 1876 Lewis. Crystallography, 1899. Liebisch. Geometrische Krystallographie, 1881. Physikalische Krystallographie, 1891. Mallard. Traite de Cristallographie geometrique et physique; vol. 1, 1879; vol. 2, 1884. Moses. Characters of Crystals, 1899. Reeks. Hints for Crystal Drawing, 1908. Sadebeck. Angewandte Krystallographie (Rose's Krystallographie, II. Band), 1876. Sohncke. Entwickelung einer Theorie der Krystallstruktur, 1879. Sommerfeldt. Physikalische Kristallographie, 1907; Die Kristallgruppe, 1911. Story-Maskelyne. Crystallography: the Morphology of Crystals, 1895. Tutton. Crystalline Structure and Chemical Constitution, 1910; Crystallography and Practical Crystal Measurement, 1911. Viola. Grundziige der Kristallographie, 1904. Walker. Crystallography, 1914. * The full titles of many of these are given in pp. li-lxi of Dana's System of Miner- alogy, 1892. INTRODUCTION 3 Wallerant. Cristallographie, 1909. Websky. Anwendung der Linearprojection zum Berechnen der Krystalle (Rose's Krystallographie III. Band), 1887. Williams. Elements of Crystallography, 1890. Wulfing. Die 32 krystallographischen Symmetrieklassen und ihre einfachen Formen, 1914. In PHYSICAL MINERALOGY the most important general works are those of Schrauf (1868), Mallard (1884), Liebisch (1891), mentioned -in the above list; also Rosenbusch, Mikr. Physiographic, etc. (1892). Important later works include the following. Davy-Farnham. Microscopic Examination of the Ore Minerals, 1920. Duparc and Pearce. Traite de Technique Mineralogique et Petrographique, 1907. Groth. Physikalische Krystallographie, 1905. Groth- Jackson. Optical Properties of Crystals, 1910. Johannsen. Determination of Rock-Forming Minerals, 1908. Manual of Petrographic Methods, 1914. Murdoch. Microscopical Determination of the Opaque Minerals, 1916. Nikitin, translated into French by Duparc and de Dervies. La Methode Universelle de Fedoroff, 1914. Winchell. Elements of Optical Mineralogy, 1909. Wright. The Methods of Petrographic-Microscopic Research, 1911. General Mineralogy Of the many works, a knowledge of which is needed by one who wishes a full acquaint- ance with the historical development of Mineralogy, the following are particularly im- portant. Very early works include those of Theophrastus, Pliny, Linnaeus, Wallerius, Cronstedt, Werner, Bergmann, Klaproth. Within the nineteenth century: Hauy's Treatise, 1801, 1822; Jameson, 1816, 1820; Werner's Letztes Mineral-System, 1817; Cleaveland's Mineralogy, 1816, 1822; Leonhard's Handbuch, 1821, 1826; Mohs's Min., 1822; Haidinger's translation of Mohs, 1824; Breit- haupt's Charakteristik, 1820, 1823, 1832; Beudant's Treatise, 1824, 1832; Phillips's Min., 1823, 1837; Shepard's Min., 1832-35, and later editions; yon Kobell's Grundzuge, 1838; Mohs's Min., 1839; Breithaupt's Min., 1836-1847; Haidinger's Handbuch, 1845; Nau- mann's Min., 1846 and later; Hausmann's Handbuch, 1847; Dufrenoy's Min., 1844-1847 (also 1856-1859); Brooke & Miller, 1852; J. D. Dana's System of 1837, 1844, 1850, 1854,. 1868. More RECENT WORKS are the following: Bauer. Lehrbuch der Mineralogie, 1904. Bauerman. Text-Book of Descriptive Mineralogy, 1884. Baumhauer. Das Reich der Krystalle, 1889. Bayley. Descriptive Mineralogy, 1917. Blum. Lehrbuch der Mineralogie, 4th ed., 1873-1874. Brauns. Das Mineralreich, 1903. English, translation by Spencer, 1912. Clarke. The Data of Geochemistry, 1916. Dana, E. S. Dana's System of Mineralogy, 6th ed., New York, 1892. Appendix I, 1899; II, 1909; III, 1915. Also (elementary) Minerals and How to study them, New York, 1895. Dana-Ford. Manual of Mineralogy, 1912. Des Cloizeaux. Manuel de Mineralogie; vol. 1, 1862; vol. 2, ler Fasc., 1874; 2me. 1893. Groth. Tabellarische Uebersicht der Mineralien, 1898. Hintze. Handbuch der Mineralogie, 1889-1915. Iddings. Rock Minerals, 1906. Kraus. Descriptive Mineralogy, 1911. Lacroix. Mineralogie de la France et de ses Colonies, 5 vols., 1893-1913. Miers. Mineralogy, 1902. Moses and Parsons. Mineralogy, Crystallography and Blowpipe Analysis, 1916. Merrill. The Non-metallic Minerals, 1904. Phillios. Mineralogv, 1912. Rogers. Study of Minerals, 1912. Schrauf. Atlas der Krystall-Formen des Mineralreiches, 4to, vol. 1, A-C, 1865-1877. Tschermak. Lehrbuch der Mineralogie, 1884; 5th cd., 1897. 4 INTRODUCTION Weisbach. Synopsis Mineralogica, systematische Uebersicht des Mineralfeiches, 1875. Zirkel. 13th edition of Naumann's Mineralogy, Leipzig, 1897. Wiilfing. Die Meteoriten in Sammlungen, etc., 1897 (earlier works on related subjects, see Dana's System, p. 32). For a catalogue of localities of minerals in the United States and Canada see the volume (51 pp.) reprinted from Dana's System, 6th ed. See also the volumes on the Mineral Re- sources of the United States published (since 1882) under the auspices of the U. S. Geo- logical Survey. Chemical and Determinative Mineralogy Bischoff. Lehrbuch der chemischen und physikalischen Geologic, 1847-54; 2d ed., 1863-66. (Also an English edition.) Blum. Die Pseudomorphosen des Mineralreichs, 1843. With 4 Nachtrage, 1847-1879. Brush-Penfield. Manual of Determinative Mineralogy, with an Introduction on Blow- pipe Analysis, 1896. Doelter. Allgemeine chemische Mineralogie, Leipzig, 1890. Handbuch der Mineral- chemie, 1912-. Duparc and Monnier. Traite de Technique Mineralogique et Petrographique, 1913. Eakle. Mineral Tables for the Determination of Minerals by their Physical Properties, 1904. Endlich. Manual of Qualitative Blowpipe Analysis, New York, 1892. Kobell, F. von. Tafeln zur Bestimmung der Mineralien mitteist einfacher chemischer Versuche auf trockenem und nassem Wege, lite Auflage, 1878. Kraus and Hunt. Tables for the Determination of Minerals, 1911. Lewis. Determinative Mineralogy, 1915. Rammelsberg. Handbuch der krystallographisch-physikalischen Chemie, Leipzig, 1881-82. Handbuch der Mineralchemie, 2d ed., 1875. Erganzungsheft, 1, 1886; 2, 1895. Roth. Allgemeine und chemische Geologic; vol. 1, Bildung u. Umbildung der Minera- lien, etc., 1879; 2, Petrographie, 1887-1890. Websky. Die Mineral Species nach den fiir das specifische Gewicht derselben ange- nommenen und gefundenen Werthen, Breslau, 1868. Weisbach. Tabellen zur Bestimmung der Mineralien nach ausseren Kennzeichen, 3te Auflage, 1886. Also founded on Weisbach's work, Frazer's Tables for the determina- tion of minerals, 4th ed., 1897. Artificial Formation of Minerals Dittler. Mineralsynthetisches Praktikum, 1915. 'Gurlt. Uebersicht der pyrogeneten ktinstlichen Mineralien, namentlich der krystal- lisirten Hiittenerzeugnisse, 1857. Fuchs. Die. kiinstlich dargestellten Mineralien, 1872. Daubree. Etudes synthetique de Geologic experimentale, Paris, 1879. Fouque and M. Levy. Synthese des Mineraux et des Roches, 1882. Bourgeois. Reproduction artificielle des Mineraux, 1884. Meunier. Les methodes de synthese en Mineralogie. Vogt. Die Silikatschmelzlozungen, 1903-1904. Mineralogical Journals The following Journals are largely devoted to original papers on Mineralogy: Amer. Min. The American Mineralogist, 1916. Bull. Soc. Min. Bulletin de la Societe Francaise de Mineralogie, 1878-. Centralbl. Min. Centralblatt fiir Mineralogie, Geologie und Palseontologie, 1900-. Fortschr. Min. Fortschritte der Mineralogie, Kristallographie und Petrographie, 1911- . Jb. Min. Neues Jahrbuch fiir Mineralogie, Geologie und Palaeontologie, etc., from 1833. Min. Mag. The Mineralogical Magazine and Journal of the Mineralogical Society of Gt. Britain, 1876-. Min. Mitth. Mineralogische und petrographische Mittheilungen, 1878- ; Earlier, from 1871, Mineralogische Mittheilungen gesammelt von G. Tschermak. Riv. Min. Ri vista di Mineralogia e Crystallografia, 1887-. Zs. Kr. Zeitschrift fiir Krystallographie und Mineralogie. 1877-. INTRODUCTION 5 ABBREVIATIONS Ax. pi. Plane of the optic axes. H. Hardness. Bx, Bx a . Acute bisectrix (p. 277). Obs. Observations on occurrence, etc. Bxo. Obtuse bisectrix (p. 277). O.F. Oxidizing Flame (p. 331). B.B. Before the Blowpipe (p. 330). Pyr. Pyrognostics or blowpipe and Comp. Composition. allied characters. Diff. Differences, or distinctive char- R.F. Reducing Flame (p. 331). acters. Var. Varieties. G. Specific Gravity. The sign A is used to indicate the angle between two faces of a crystal, as am (100 A 110) = 44 30'. PART I. CRYSTALLOGRAPHY GENERAL MORPHOLOGICAL RELATIONS OF CRYSTALS 5. Crystallography. The subject of Crystallography includes the description of the characters of crystals in general; of the various forms of crystals and their division into classes and systems; of the methods of study- ing crystals, including the determination of the mathematical relations of their faces, and the measurement of the angles between them; finally, a de- scription of compound or twin crystals, of irregularities in crystals, of crystal- line aggregates, and of pseudomorphous crystals. 6. Definition of a Crystal. A crystal * is the regular polyhedral form, bounded by smooth surfaces, which is assumed by a chemical compound, under the action of its intermodular forces, when passing, under suitable conditions, from the state of a liquid or gas to that of a solid. As expressed in the foregoing definition, a crystal is characterized, first, by its definite internal molecular structure, and, second, by its external form. A crystal is the normal form of a mineral species, as of all solid chemical com- pounds; but the conditions suitable for the formation of a crystal of ideal perfection in symmetry of form and smoothness of surface are never fully realized. Further, many species usually occur not in distinct crystals, but in massive form, and in some exceptional cases the definite molecular struc- ture is absent. 7. Molecular Structure in General. By definite molecular structure is meant the special arrangement which the physical units, called molecules,^ assume under the action of the forces exerted between them during the forma- tion of the solid. Some remarks are given in a later article (p. 22 et seq.) in regard to the kinds of molecular arrangement theoretically possible, and their relation to the symmetry of the different systems and classes of crystals. The definite molecular structure is the essential character of a crystal, and the external form is only one of the ways, although the most important, in which this structure is manifested. Thus it is found that all similar direc- tions in a crystal, or a fragment of a crystal, have like physical characters,}: * In its original signification the term crystal was applied only to crystals of quartz, which the ancient philosophers believed to be water congealed by intense cold. Hence the term, from KpvaraXXos, ice. t Recent studies, particularly those made by the use of the X-ray, would indicate that the unit of crystalline structure is the atom rather than the molecule. The grouping of the atoms to form a molecule is extended in the analogous grouping of the molecules to form a crystal. t This subject is further elucidated in the chapter devoted to Physical Mineralogy, where it is also shown that, with respect to many, but not all, of the physical characters, the r^ r r r " T>co ~- f t.hi^ prop nation is true, viz., that unlike directions in a crystal have in general unlike properties. 7 8 CRYSTALLOGRAPHY as of elasticity, cohesion, action on light, etc. This is clearly shown by the cleavage, or natural tendency to fracture in certain directions, yielding more or less smooth surfaces; as the cubic cleavage of galena, or the rhombohedral cleavage of calcite. It is evident, therefore, that a small crystal differs from a large one only in size, and that a fragment of a crystal is itself essentially a crystal in all its physical relations, though showing no crystalline faces. Further, the external form without the corresponding molecular structure does not make a crystal of a solid. A model of glass or wood is obviously not a crystal, though having its external form, because there is no relation between form and structure. Also, an octahedron of malachite, having the form of the crystal of cuprite from which it has been derived by chemical alteration, is not a crystal of malachite, but what is known as a pseudomorph (see Art. 478) of malachite after cuprite. On the other hand, if the natural external faces are wanting, the solid is not called a crystal. A cleavage octahedron of fluorite and a cleavage rhom- bohedron of calcite are not properly crystals, because the surfaces have been yielded by fracture and not by the natural molecular growth of the crystal. 8. Crystalline and Amorphous. When a mineral shows no external crystalline form, it is said to be massive. It may, however, have a definite molecular structure, and then it is said to be crystalline. If this structure, as shown by the cleavage, or by optical means, is the same in all parallel direc- tions through the mass, it is described as a single individual. If it varies from grain to grain, or fiber to fiber, it is said to be a crystalline aggregate* since it is in fact made up of a multitude of individuals. Thus in a granular mass of galena or calcite, it may be possible to separate the fragments from one another, each with its characteristic cubic, or rhom- bohedral, cleavage. Even if the individuals are so small that they cannot be separated, yet the cleavage, and hence the crystalline structure, may be evi- dent from the spangling of a freshly broken surface, as with fine-grained statu- ary marble. Or, again, this aggregate structure may be so fine that the crystalline structure can only be resolved by optical methods with the aid of the microscope. In all these cases, the structure is said to be crystalline. If optical means show a more or less distinct crystalline structure, which, however, cannot be resolved into individuals, the mass is said to be crypto- crystalline; this is true of some massive varieties of quartz. If the definite molecular structure is entirely wanting, and all directions in the mass are sensibly the same, the substance is said to be amorphous. This is true of a piece of glass, and nearly so of opal. The amorphous state is rare among minerals. A piece of feldspar which has been fused and cooled suddenly may be in the glass-like amorphous condition as regards absence of definite molecular structure. But even in such cases there is a tendency to go over into the crystalline condition by molecular rearrange- ment. A transparent amorphous mass of arsenic trioxide (AsaOa), formed by fusion, becomes opaque and crystalline after a time. Similarly the steel beams of a railroad bridge may gradually become crystalline and thus lose some of their original strength because of the molecular rearrangement made possible by the vibrations caused by the frequent jar of passing trains. The microscopic study of rocks reveals many cases in which an analogous change in molecular structure has taken place in a solid mass, as caused, for example, by great pressure. * The consideration of the various forms of crystalline aggregates is postponed to the end of the present chapter. GENERAL MORPHOLOGICAL RELATIONS OF CRYSTALS 9 9. External Form. A crystal -is bounded by smooth plane surfaces, called faces or planes,* showing in their arrangement a certain characteristic symmetry, and related to each other by definite mathematical laws. Thus, without inquiring, at the moment, into the exact meaning of the term symmetry as applied to crystals, and the kinds of symmetry possible, which will be explained in detail later, it is apparent that the accompanying figures, 1-3, show the external form spoken of. They represent, therefore, certain definite types. Galena Vesuvianite Chrysolite 10. Variation of Form and Surface. Actual crystals deviate, within certain limits, from the ideal forms. First, there may be variation in the size of like faces, thus producing what are defined later as distorted forms. In the second place, the faces are rarely absolutely smooth and brilliant; commonly they lack perfect polish, and they may even be rough or more or less covered with fine parallel lines (called striations), or show minute elevations, depressions or other peculiarities. Both the above subjects are discussed in detail in another place. It may be noted in passing that the characters of natural faces, just alluded to, in general make it easy to distinguish between them and a face artificially ground, on the one hand, like the facet of a cut gem; or, on the other hand, the splintery uneven surface commonly yielded by cleavage. 11. Constancy of the Interfacial Angles in the Same Species. The angles of inclination between like faces on the crystals of any species are essentially constant, wherever they are found, and whether products of nature or of the laboratory. These angles, therefore, form one of the im- portant distinguishing characters of a species. Thus, in Fig. 4, of apatite, the angle between the adjacent faces x and m (130 18') is the same for any two like faces, similarly situated with reference to each other. Further, this angle is constant for the species no matter what the size of the crystal may be or from what locality it may come. Moreover, the angles between all the faces on crystals of the same species (cf . Figs. 5-8 of zircon below) are more or less closely connected together by certain definite mathematical laws. m,' m Apatite * This latter word is usually limited to cases where the direction, rather than the definite surface itself, is designated. 10 CRYSTALLOGRAPHY 12. Diversity of Form, or Habit. While in the crystals of a given species there is constancy of angle between like faces, the forms of the crystals may be exceedingly diverse. The accompanying figures (5-8) are examples of a few of the forms of the species zircon. There is hardly any limit to the number of faces which may occur, and as their relative size changes, the habit, as it is called, may vary indefinitely. Zircon 13. Diversity of Size. Crystals occur of all sizes, from the merest microscopic point to a yard or more in diameter. It is important to under- stand, however, that in a minute crystal the development is as complete as with a large one. Indeed the highest perfection of form and transparency is found only in crystals of small size. A single crystal of quartz, now at Milan, is three and a quarter feet long and five and a half in circumference, and its weight is estimated at eight hundred and seventy pounds. A single cavity in a vein of quartz near the Tiefen Glacier, in Switzerland, discovered in 1867, afforded smoky quartz crystals, a considerable number of which had a weight of 200 to 250 pounds. A gigantic beryl from Acworth, New Hampshire, measured four feet in length and two and a half in circumference; another, from Graf ton, was over four feet long, and thirty-two inches in one of its diameters, and weighed about two and a half tons. 14. Symmetry in General. The faces of a crystal are arranged according to certain laws of symmetry, and this symmetry is the natural basis of the division of crystals into systems and classes. The symmetry may be defined in relation to (1) a plane of symmetry, (2) an axis of symmetry, and (3) a center of symmetry. These different kinds of symmetry may, or may not, be combined in the same crystal. It will be shown later that there is one class, the crystals of which have neither center, axis, nor plane of symmetry; another where there is only a center of symmetry. On the other hand, some classes have all these elements of^symmetry represented. 15. Planes of Symmetry. A solid is said to be geometrically * sym- metrical with reference to a plane of symmetry when for each face, edge, or solid angle there is another similar face, edge, or angle which has a like posi- tion with reference to this plane. Thus it is obvious that the crystal of am- phibole, shown in Fig. 9, is symmetrical with reference to the central plane of symmetry indicated by the shading. * The relation between the ideal geometrical symmetry and the actual crystallographic symmetry is discussed in Art. 18. GENERAL MORPHOLOGICAL RELATIONS OF CRYSTALS 11 In the ideal crystal this symmetry is right symmetry in the geometrical sense, where every point on the one side of the plane of symmetry has a cor- responding point at equal distances on the other side, measured on a line normal to it. In other words, in the ideal geometrical symmetry, one half of the crystal is the exact mirror-image of the other half. A crystal may have as many as nine planes of sym- metry, three of one set and six of another, as is illustrated by the cube * (Fig. 16). Here the planes of the first set pass through the crystal parallel to the cubic faces; they are shown in Fig. 10. The planes of the second set join the opposite cubic edges; they are shown in Fig. 11. 16. Axes of Symmetry. If a solid can be revolved through a certain number of degrees about some line as an axis, with the result that it again occupies precisely the same position in space as at first, that axis is said to be an axis of symmetry. There are four different kinds of axes of symmetry among crystals; they are de- fined according to the number of times which the crystal repeats itself in ap- pearance during a complete revolution of 360. Amphibole Symmetry Planes in the Cube (a) A crystal is said to have an axis of binary, or twofold, symmetry when a revolution of 180 produces the result named above; in other words, when it repeats itself twice in a complete revolution. This is true of the crystal shown in Fig. 12 with respect to the vertical axis (and indeed each of the horizontal axes also). (6) A crystal has an axis of trigonal, or threefold, symmetry when a revo- lution of 120 is needed; that is, when it repeats itself three times in a com- plete revolution. The vertical axis of the crystal shown in Fig. 13 is an axis of trigonal symmetry. (c) A crystal has an axis of tetragonal, or fourfold, symmetry when a revolution of 90 is called for; in other words, when it repeats itself four times in a complete revolution. The vertical axis in the crystal shown in Fig. 14 is such an axis. (d) Finally, a crystal has an axis of hexagonal, or sixfold, symmetry when a revolution of 60 is called for; in other words, when it repeats itself six times in a complete revolution. This is illustrated by Fig. 15. * This is the cube of the normal class of the isometric system. 12 CRYSTALLOGRAPHY The different kinds of symmetry axes are sometimes known as diad, triad, tetrad and hexad axes. 12 13 14 16 Chrysolite Calcite Rutile Beryl The cube * illustrates three of the four possible kinds of symmetry with respect to axes of symmetry. It has six axes of binary symmetry joining the middle points of opposite edges (Fig. 16). It has four axes of trigonal symmetry, joining the opposite solid angles (Fig. 17). It has, finally, three axes of tetragonal symmetry joining the middle points of opposite faces (Fig. 18). 16 17 18 -v Symmetry Axes in the Cube 17. Center of Symmetry. Most crystals, besides planes and axes of symmetry, have also a center of symmetry. On the other hand, a crystal, though possessing neither plane nor axis of symmetry, may yet be sym- Rhodonite Heulandite metrical with reference to a point, its center. This last is true of the triclinic crystal shown in Fig. 19, in which it follows that every face, edge, and solid angle has a face, edge, and angle similar to it in the opposite half of the crystal. This is again the cube of the normal class of the isometric system. GENERAL MORPHOLOGICAL RELATIONS OF CRYSTALS 13 18. Relation of Geometrical to Crystallographic Symmetry. Since the symmetry in the arrangement of the faces of a crystal is an expression of the internal molecular structure, which in general is alike in all parallel direc- tions, the relative size of the faces and their distance from the plane or axis of symmetry are of no moment, their angular position alone is essential. The crystal represented in Fig. 20, although its faces show an unequal develop- ment, has in the crystallographic sense as truly a vertical plane of symmetry (parallel to the face 6) as the ideally developed crystal shown in Fig. 21. The strict geometrical definition of symmetry would, however, apply only to the second crystal.* 22 23 24 Cube Distorted Cubes Also in a normal cube (Fig. 22) the three central planes parallel to each pair of cubic faces are like planes of symmetry, as stated in Art. 15. But a crystal is still crystallographically a cube, though deviating widely from the requirements of the strict geometrical definition, as shown in Figs. 23, 24, if only it can be proved, e.g., by cleavage, by the physical nature of the faces, or by optical means, that the three pairs of faces are like faces, independently of their size, or, in other words, that the molecular structure is the same in the three directions normal to them. 25 26 Cube and Octahedron Further, in the case of a normal cube, a face of an octahedron on any solid angle requires, as explained beyond, similar faces on the other angles. It is not necessary, however, that these eight faces should be of equal size, for in the crystallographic sense Fig. 25 is as truly symmetrical with reference to the planes named as Fig. 26. * It is to be noted that the perspective figures of crystals usually show the geometrically ideal form, in which like faces, edges, and angles have the same shape, size, and position. In other words, the ideal crystal is uniformly represented as having the symmetry called for by the strict geometrical definition. 14 CRYSTALLOGRAPHY 19. On the other hand, the molecular and hence the crystallographic symmetry is not always that which the geometrical form would suggest. Thus, deferring for the moment the consideration of pseudo-symmetry, an illustration of the fact stated is afforded by the cube. It has already been implied and will be fully explained later that while the cube of the normal class of the isometric system has the symmetry described in Arts. 15, 16, a cube of the same geometrical form but belonging molecularly, for example, to the tetrahedral class, has no planes of symmetry parallel to the faces but only the six diagonal planes; further, though the four axes shown in Fig. 17 are still axes of trigonal symmetry, the cubic axes (Fig. 18) are axes of binary symmetry only, and there are no axes of symmetry corresponding to those represented in Fig. 16. Other more complex cases will be described later. Further, a crystal having interf acial angles of 90 is not necessarily a cube : in other words, the angular relations of the faces do not show in this case whether the figure is bounded by six like faces; or whether only four are alike and the other pair unlike; or, finally, whether there are three pairs of unlike faces. The question must be decided, in such cases, by the molecular structure as indicated by the physical nature of the surfaces, by the cleavage, or by other physical characters, as pyro-electricity, those connected with light phenomena, etc. Still, again, the student will learn later that the decision reached in regard to the symmetry to which a crystal belongs, based upon the distribution of the faces, is only preliminary and approximate, and before being finally accepted it must be confirmed, first, by accurate measurements, and, second, by a minute study of the other physical characters. The method based upon the physical characters, which gives most conclusive results and admits of the widest application, is the skillful etching of the surface of the crystal by some appropriate solvent. By this means there are, in general, produced upon it minute depressions the shape of which conforms to the symmetry in the arrangement of the mole- cules. This process, which is in part essentially one involving the dissection of the molecu- lar structure, is more particularly discussed in the chapter on Physical Mineralogy. 20. Pseudo-symmetry. The crystals of certain species approximate closely in angle, and therefore in apparent symmetry, to the requirements of a system higher in symmetry than that to which they actually belong: they are then said to exhibit pseudo-symmetry. Numerous examples are given under the different systems. Thus the micas have been shown to be truly monoclinic in crystallization, though in angle they seem to be in some cases rhombohedral, in others orthorhombic. It will be shown later that compound, or twin, crystals may also simulate by their regular grouping a higher grade of symmetry than that which belongs to the single crystal. Such crystals also exhibit pseudo-symmetry and are specifically called mimetic. Thus aragonite is an example of an orthorhombic species, whose crystals often imitate by twinning those of the hexagonal system.* Again, a highly complex twinned crystal of the monoclinic species, phillipsite, may have nearly the form of a rhombic dodecahedron of the iso- metric system. This kind of pseudo-symmetry also occurs among the classes of a single system, since a crystal belonging to a class of low sym- metry may by twinning gain the geometrical symmetry of the corresponding * The terms pseudo-hexagonal, etc., used in this and similar cases explain themselves. GENERAL MORPHOLOGICAL RELATIONS OF CRYSTALS 15 form of the normal class. This is illustrated by a twinned crystal of scheelite like that figured (Fig. 416) in the chapter on twin crystals. Pseudo-symmetry of still another kind, where there is an imitation of the symmetry of another system of lower grade, is particularly common in crystals of the isometric system (e.g., gold, copper). The result is reached in such cases by an abnormal development of " distortion " in the direction of certain axes of symmetry. This subject is discussed and illustrated on a later page. 21. Possible Classes of Symmetry. The theoretical consideration of the different kinds of symmetry possible among crystals built up of like mole- cules, as explained in Arts. 30-32, has led to the conclusion that there are thirty-two (32) types in all, differing with respect to the combination of the different symmetry elements just described. Of these thirty-two natural classes among crystals based upon their symmetry, seven classes include by far the larger number of crystallized minerals. Besides these, some thirteen or fourteen others are distinctly represented, though several of these are of rare occurrence. The remaining classes, with possibly one or two excep- tions, are known among the crystallized salts made in the laboratory. The characters of each of the thirty-two classes are given under the discussion of the several crystalline systems. 22. Crystallographic Axes. In the description of a crystal, especially as regards the position of its faces, it is found convenient to assume, after the methods of analytical geometry, certain lines passing through the center of the ideal crystal, as a basis of reference. (See further Art. 34 et seq.) These lines are called the Crystallographic axes. Their direction is to a greater or less extent fixed by the symmetry of the crystals, for an axis of symmetry is in almost all cases * a possible Crystallographic axis. Further, the unit lengths assigned to these axes are fixed sometimes by the symmetry, sometimes by the position of the faces assumed as fundamental, i.e., the unit forms in the sense defined later. The broken lines shown in Fig. 18 are the Crystallographic axes to which the cubic faces are referred. 23. Systems of Crystallization. The thirty-two possible crystal classes which are distinguished from one another by their symmetry, are classified in this work under six systems, each characterized by the relative lengths and inclinations of the assumed Crystallographic axes. These are as follows : I. ISOMETRIC SYSTEM. Three equal axes at right angles to each other. II. TETRAGONAL SYSTEM. Three axes at right angles to each other, two of them the horizontal axes equal, the third the vertical axis longer or shorter. III. HEXAGONAL SYSTEM. Four axes, three equal horizontal axes in one plane intersecting at angles of 60, and a vertical axis at right angles to this plane and longer or shorter. IV. ORTHORHOMBIC SYSTEM. Three axes at right angles to each other, but all of different lengths. V. MONOCLINIC SYSTEM. Three axes unequal in length, and having one of their intersections oblique, the two other intersections equal to 90. VI. TRICLINIC SYSTEM. Three unequal axes with mutually oblique intersections. * Exceptions are found in the isometric system, where the axes must necessarily be the axes of tetragonal symmetry (Fig. 18), and cannot be those of binary or trigonal symmetry (Figs. 16, 17). 16 CRYSTALLOGRAPH 24. Each one of the six systems, as will be understood from Art. 21, embraces several classes differing among themselves in their symmetry. One of these classes is conveniently called the normal class, since it is in general the common one, and since further it exhibits the highest degree of symmetry possible for the given system, while the others are lower in grade of symmetry. It is important to note that the classes comprised within a given system are at once essentially connected together by their common optical characters, and in general separated * from those of the other systems in the same way. Below is given a list of the six systems together with their subordinate classes, thirty-two in all. The order and the names given first are those that are used in this book while in the following parentheses are given other equivalent names that are also in common use. Under nearly all of the classes it is possible to give the name of a mineral or an artificial compound whose crystals serve to illustrate the characters of that particular class. There is some slight variation between different authors in the order in which the crystal systems and classes are considered but in the main essentials all modern discussions of crystallography are uniform. ISOMETRIC SYSTEM (Regular, Cubic System) 1. NORMAL CLASS. (Hexoctahedral. Holohedral.) Galena Type. 2. PYRITOHEDRAL CLASS. (Dyakisdodecahedral. Pentagonal Hemihe- dral.) Pyrite Type. 3. TETRAHEDRAL CLASS. (Hextetrahedral. Tetrahedral Hemihedral.) Tetrahedrite Type. 4. PLAGIOHEDRAL CLASS. (Pentagonal Icositetrahedral. Plagiohedral Hemihedral.) Cuprite Type. 5. TETARTOHEDRAL CLASS. (Tetrahedral Pentagonal Dodecahedral.) Sodium Chlorate Type. TETRAGONAL SYSTEM 6. NORMAL CLASS. (Ditetragonal Bipyramidal. Holohedral.) Zircon Type. 7. HEMIMORPHIC CLASS. (Ditetragonal Pyramidal. Holohedral Hemi- morphic.) lodosuccinimide Type. 8. TRIPYRAMIDAL CLASS. (Tetragonal Bipyramidal. Pyramidal Hemi- hedral.) Scheelite Type. 9. PYRAMIDAL-HEMIMORPHIC CLASS. (Tetragonal Pyramidal. Hemihe- dral Hemimorphic.) Wulfenite Type. 10. SPHENOIDAL CLASS. (Tetragonal Sphenoidal. Sphenoidal Hemihe- dral. Scalenohedral.) Chalcopyrite Type. 11. TRAPEZOHEDRAL CLASS. (Tetragonal Trapezohedral. Trapezohe- dral Hemihedral.) Nickel Sulphate Type. 12. TETARTOHEDRAL CLASS. (Tetragonal Bisphenoidal.) Artif. 2 CaO.Al 2 3 .SiO 2 Type. * Crystals of the tetragonal and hexagonal systems are alike in being optically unaxial; but the crystals of all the other systems have distinguishing optical characters, GENERAL MORPHOLOGICAL RELATIONS OF CRYSTALS 17 HEXAGONAL SYSTEM A. HEXAGONAL DIVISION 13. NORMAL CLASS. (Dihexagonal Bipyramidal. Holohedral.) Beryl Type. 14. HEMIMORPHIC CLASS. (Dihexagonal Pyramidal. Holohedral Hemi- morphic.) Zincite Type. 15. TRIPYRAMIDAL CLASS. (Hexagonal Bipyramidal. Pyramidal Hemi- hedral.) Apatite Type. 16. PYRAMIDAL-HEMIMORPHIC CLASS. (Hexagonal Pyramidal. Pyrami- dal Hemihedral Hemimorphic.) Nephelite Type. 17. TRAPEZOHEDRAL CLASS. (Hexagonal Trapezohedral. Trapezohedral Hemihedral.) /3-Quartz Type. B. TRIGONAL OR RHOMBOHEDRAL DIVISION (Trigonal System) 18. TRIGONAL CLASS. (Ditrigonal Bipyramidal. Trigonal Hemihedral.) Benitoite Type. 19. RHOMBOHEDRAL CLASS. (Ditrigonal Scalenohedral. Rhombohedral Hemihedral.) Calcite Type^ 20. RHOMBOHEDRAL HEMIMORPHIC CLASS. (Ditrigonal Pyramidal. Tri- gonal Hemihedral Hemimorphic.) Tourmaline Type. 21. TRI-RHOMBOHEDRAL CLASS. (Rhombohedral. Rhombohedral Te- tartohedral.) Phenacite Type. 22. TRAPEZOHEDRAL CLASS. (Trigonal Trapezohedral. Trapezohedral Tetartohedral.) Quartz Type. 23.' (Trigonal Bipyramidal. Trigonal Tetar- tohedral. 24. (Trigonal Pyramidal. Trigonal Tetarto- hedral Hemimorphic.) Sodium Periodate Type. ORTHORHOMBIC SYSTEM (Rhombic or Prismatic System) 25. NORMAL CLASS. (Orthorhombic Bipyramidal. Holohedral.) Barite Type. 26. HEMIMORPHIC CLASS. (Orthorhombic Pyramidal.) Calamine Type. 27. SPHENOIDAL CLASS. (Orthorhombic Bisphenoidal.) Epsomite Type. MONOCLINIC SYSTEM (Oblique System) 28. NORMAL CLASS. (Prismatic. Holohedral.) Gypsum Type. 29. HEMIMORPHIC CLASS. (Sphenoidal.) Tartaric Acid Type. 30. CLINOHEDRAL CLASS. (Domatic. Hemihedral.) Clinohedrite Type. TRICLINIC SYSTEM (Anorthic System) 31. NORMAL CLASS. (Holohedral. Pinacoidal.) Axinite Type. 32. ASYMMETRIC CLASS. (Hemihedral.) Clacium Thiosulphate Type. 18 CRYSTALLOGRAPHY 25. Symmetry of the Systems. In the paragraphs immediately fol- lowing, a synopsis is given of the symmetry of the normal class of each of the different systems, and also that of one subordinate class of the hexagonal system, which is of so great importance that it is also often conveniently treated as a sub-system even when, as in this work, the forms are referred to the same axes as those of the strictly hexagonal type a usage not adopted by all authors. I. ISOMETRIC SYSTEM. Three like axial * planes of symmetry (principal planes) parallel to the cubic faces, and fixing by their intersection the crystal- lographic axes; six like diagonal planes of symmetry, passing through each opposite pair of cubic edges, and hence parallel to the faces of the rhombic dodecahedron. Further, three like axes of tetragonal symmetry, the crystallographic axes normal to the faces of the cube; four like diagonal axes of trigonal sym- metry, normal to the faces of the octahedron; and six like diagonal axes of binary symmetry, normal to the faces of the dodecahedron. There is also obviously a center of symmetry.! These relations are illustrated by Fig. 27 also by Fig. 35; further by Figs. 92 to 125. 27 28 29 \m Galena Rutile a Rutile II. TETRAGONAL SYSTEM. Three axial planes of symmetry : of these, two are like planes intersecting at 90 in a line which is the vertical crystallo- graphie axis, and the third plane (a principal plane) is normal to them and hence contains the horizontal axes. There are also two diagonal planes of symmetry, intersecting in the vertical axis and meeting the two axial planes at angles of 45. Further, there is one axis of tetragonal symmetry, a principal axis ; this is the vertical crystallographic axis. There are also in a plane normal to this four axes of binary symmetry like two and two those of each pair at right angles to each other. Fig. 28 shows a typical tetragonal crystal, and Fig. 29 a basal projection of it, that is, a projection on the principal plane of sym- metry normal to the vertical axis. See also Fig. 36 and Figs. 170-192. * Two planes of symmetry are said to be like when they divide the ideal crystal into halves which are identical to each other; otherwise, they are said to be unlike. Axes of symmetry are also like or unlike. If a plane of symmetry includes two of the crystallo- graphic axes, it is called an axial plane of symmetry. If the plane includes two or more like axes of symmetry, it is called a principal plane of symmetry ; also an axis of symmetry in which two or more like planes of symmetry meet is a principal axis of symmetry. t In describing the symmetry of the different classes, here and later, the center of symmetry is ordinarily not mentioned when its presence or absence is obvious. GENERAL MORPHOLOGICAL RELATIONS OF CRYSTALS 19 III. HEXAGONAL SYSTEM. In the Hexagonal Division there are four axial planes of symmetry; of these three are like planes meeting at angles of 60, their intersection-line being the vertical crystallographic axis; the fourth plane (a principal plane) is at right angles to these. There are also three other diagonal planes of symmetry meeting the three of the first set in the vertical axis, arid making with them angles of 30. Further, there is one principal axis of hexagonal symmetry; this is the vertical crystallographic axis; at right angles to it there are also six binary axes. The last are in two sets of three each. Fig. 30 shows a typical hex- agonal crystal, with a basal projection of the same. See also Fig. 37 and Figs. 220-227. 32 m m ! -L ,---S Miorosoinmite Cabito Chrysolite In the Trigonal or Rhombohedral Division of this system there are three like planes of symmetry intersecting at angles of 60 in the vertical axis. Further, the forms belonging here have a vertical principal axis of trigonal symmetry, and three horizontal axes of binary symmetry, coinciding with the horizontal crystallographic axes. Fig. 31 shows a typical rhombohedral crystal, with its basal projection. See also Figs. 243-269. IV. ORTHORHOMBIC SYSTEM. Three unlike planes of symmetry meeting at 90, and fixing by their intersection-lines the position of the crystallo- graphic axes. Further, three unlike axes of binary symmetry coinciding with the last-named axes. Fig. 32 shows a typical orthorhombic crystal, with its basal projection. See also Fig. 38 and Figs. 298-320. V. MONOCLINIC SYSTEM. One plane of symmetry which contains two of the crystallographic axes. Also one axis of binary symmetry, normal to this plane and coinciding with the third crystallographic axis. See Fig. 33; also Fig. 39 and Figs. 333-347. VI. TRICLINIC SYSTEM. No plane and no axis of symmetry, but sym- metry solely with respect to the central point. Figs. 34 and 40 show typical triclinic crystals. See also Figs. 359-366 20 CRYSTALLOGRAPHY 26. The relations of the normal classes of the different systems are further illustrated both as regards the crystallographic axes and symmetry by the accompanying figures, 35-40. The exterior form is here that bounded by faces each of which is parallel to a plane through two of the crystallographic axes indicated by the central broken lines. Further, there is shown, within this, the combination of faces each of which joins the extremities of the unit lengths of the axes. 34 Pyroxene Axinite The full understanding of the subject will not be gained until after a study of the forms of each system in detail. Nevertheless the student will do well to make himself familiar at the outset with the fundamental relations here illustrated. 35 37 Isometric Tetragonal Hexagonal It will be shown later that the symmetry of the different classes can be most clearly and easily exhibited by the use of the different projections ex- plained in Art. 39 et seq. GENERAL MORPHOLOGICAL RELATIONS OF CRYSTALS 21 27. Models. Glass (or transparent celluloid) models illustrating the different sys- tems, having the forms shown in Figs. 35-40, will be very useful to the student, especially in learning the fundamental relations as regards symmetry. They should show within, the crystallographic axes, and by colored threads or wires, the outlines of one or more simple forms. Models of wood are also made in great variety and perfection of form; these are indispensable to the student in mastering the principles of crystallography. Orthorhombic Monoclinic Triclinic 28. So-called Holohedral and Hemihedral Forms. It will appear later that each crystal form * of the normal class in a given system embraces all the faces which have a like geometrical position with reference to the crystallograpfeic axes; such a form is said to be holohedral (from bXos, com- plete, and Mpz, face). On the other hand, under the classes of lower sym- metry, a certain form, while necessarily having all the faces which the sym- metry allows, may yet have but half as many as the corresponding form of the normal class ; these half -faced forms are sometimes called on this account hemihedral. Furthermore, it will be seen that, in such cases, to the given holohedral form there correspond two similar and complementary hemihedral forms, called respectively positive and negative (or right and left), which together embrace all of its faces. 41 43 Octahedron Positive Tetrahedron Negative Tetrahedron A single example will help to make the above statement intelligible. In the normal class of the isometric system, the octahedron (Fig. 41) is a " holohedral" form with all the possible faces eight in number which are alike in that they meet the axes at equal distances. In the tetrahedral class of the same system, the forms are referred to the same crystallographic axes, but the symmetry defined in Art. 19 (and more fully later) calls for but four similar faces having the position described. These yield a four-faced, or "hemi- hedral/' form, the tetrahedron. Figures 42 and 43 show the positive and negative tetra- hedron, which together, it will be seen, embrace all the faces of the octahedron, Fig. 41. * The use of the word/orw is defined in Art. 37 22 CRYSTALLOGRAPHY ' In certain classes of still lower symmetry a given crystal form may have ut one-quarter of the faces belonging to the corresponding normal form, and, after the same method, such a form is sometimes called tetartohedral. The development of the various possible kinds of hemihedral (and tetarto- hedral) forms under a given system has played a prominent part in the crystal- lography of the past, but it leads to much complexity and is distinctly less simple than the direct statement of the symmetry in each case. The latter method is systematically followed in this work, and the subject of hemihe- drism is dismissed with the brief (and incomplete) statements of this and the following paragraphs. 29. Hemimorphic Forms. In several of the systems, forms occur under the classes of lower symmetry than that of the normal class which are characterized by this : that the faces present are only those belonging to one extremity of an axis of symmetry (and crystallographic axis) . Such forms are conveniently called hemimorphic (half-form). A simple example under the hexagonal system is given in Fig. 44. It is obvious that hemi- morphic forms have no center of symmetry. 30. Molecular Networks. Much light has re- cently been thrown upon the relations existing between the different types of crystals, on the one hand, and of these to the physical propertied of crystals, on the other, by the consideration of the various possible methods of grouping of the molecules of which the crystals are supposed to be built up. This subject, very early treated by Haiiy and others (including J. D. Dana), was discussed at length by Frankenheim and later by Bravais. More recently it has been extended and elaborated by Sohncke, Wulff, Schonflies, Fedorow, Barlow, and others. All solid bodies, as stated in Art. 7, are believed to be made up of definite physical units, called the physical, or crystal, molecules. Of the form of the molecules nothing is definitely known, and though theory has something to say about their size, it is enough here to understand that they are almost infinitely small, so small that the surface of a solid e.g., of a crystal may appear to the touch and to the eye, even when assisted by a powerful microscope, as perfectly smooth. The molecules are further believed to be not in contact but separated from one another if in contact, it would be impossible to explain the motion to which the sensible heat of the body is due, or the transmission of radiation (radiant heat and light) through the mass by the wave motion of the ether, which is believed to penetrate the body. When a body passes from the state of a liquid or a gas to that of a solid, under such conditions as to allow perfectly free action to the forces acting between the molecules, the result is a crystal of some definite type as regards symmetry. The simplest hypothesis which can be made assumes that the form of the crystal is determined by the way in which the molecules group themselves together in a position of equilibrium under the action of the inter- molecular forces. As, however, the forces between the molecules vary in magnitude and direction from one type of crystal to another, the resultant grouping of the molecules must also vary, particularly as regards the distance between them Zincite GENERAL MORPHOLOGICAL RELATIONS OF CRYSTALS 23 and the angles between the planes in which they lie. This may be simply represented by a series of geometrical diagrams, showing the hypothetical groupings of points which are strictly to be regarded as the centers of gravity of the molecules themselves. Such a grouping is named a network, or point- system, and it is said to be regular when it is the same for all parallel lines and planes, however they be taken. For the fundamental observed fact, true in all simple crystals, that they have like physical properties in all parallel directions, leads to the conclusion that the grouping of the molecules must be the same about each one of them (or at least about each unit group of them), and further the same in all parallel lines and planes. 1 - - l) ^^MSra^r" ; " 1 'ill! i I H si: -fe H : . i i #Hf i 1 r H u Crystal Networks The subject may be illustrated by Figs. 45, 46 for two typical cases, which are easily understood. In Fig. 45 the most special case is represented where the points are grouped at equal distances, in planes at right angles to each other. The structure in this case obviously corresponds in symmetry to the cube described in Arts. 15 and 16, or, in other words, to the normal class of the isometric system. Again, in Fig. 46, the general case is shown where the molecules are unequally grouped in the three directions, and further these directions are oblique. The symmetry is here that of the normal class of the triclinic system. If, in each of these cases, the, figure be bounded by the simplest possible arrangement of eight points, the result is an elementary parallelepiped, which obviously defines the molecular structure of the whole. In the grouping of these parallelepipeds together, as described, it is obvious that in whatever direction a line be drawn through them, the points (molecules) will be spaced alike along it, and the grouping nbout any one of these points will be the same as about any other. 31. Certain important conclusions can be deduced from a consideration of such regular molecular networks as have been spoken of, which will be enumerated here though it is impossible to attempt a full explanation. (1) The prominent crystalline faces must 1x3 such as include the largest number of points, that is, those in which the points are nearest together. Thus in Fig. 47, which represents a section of a network conforming in symmetry to the structure of a normal orthorhombic crystal, the common crystalline faces would be expected to be those having the position 66, aa, mm, 24 CRYSTALLOGRAPHY then II, nn, and so on. This is found to be true in the study of crystals, for the common forms are, in nearly all cases, those whose position bears some simple relation to the assumed axes; forms whose position is complex are usually present only as small faces on the simple predominating forms, that is, as modifications of them- So-called vicinal forms, that is, forms taking the place of the simple fundamental forms to which they approximate very closely in angular position, are exceptional. Orthorhombic Point System (2) When a variety of faces occur on the same crystal, the numerical rela- tion existing between them (that which fixes their position) must be rational and, as stated in (1), a simple numerical ratio is to be expected in the common cases. This, as explained later, is found by experience to be a fundamental law of all crystals. Thus, in Fig. 47, starting with a face meeting the section in mm, II would be a common face, and for it the ratio is 1 : 2 in the directions b and a; nn would be also common with the ratio 2:1. (3) If a crystal shows the natural easy fracture, called cleavage, due to a minimum of cohesion, the cleavage surface must be a surface of relatively great molecular crowding, that is, one of the common or fundamental faces. This follows (and thus gives a partial, though not complete, explanation of cleavage) since it admits of easy proof that that plane in which the points are closest together is farthest separated from the next molecular plane. Thus in Fig 47 compare the distance separating two adjoining planes parallel to bb or aa, then two parallel to mm, II, nn, etc Illustrations of the above will be found under the special discussion of the subject of cleavage. GENERAL MORPHOLOGICAL RELATIONS OF CRYSTALS 25 32. Kinds of Molecular Groupings. The discussion on the basis just described shows that there are fourteen possible types of arrangement of the molecules. These agree as to their symmetry with the seven classes defined in Art. 25 as representing respectively the normal classes of the six systems with also that of the trigonal (or the rhombohedral) division of the hex- agonal system. Of the fourteen, three groupings belong to the iso- metric system (these are shown, for sake of illustration, in Fig. 48 from Groth; a, cube lattice; &, cube- centered lattice; c, face centered Isometric Lattices cube lattice) ; two to the tetragonal; one each to the hexagonal and the rhombohedral; four to the orthorhombic system; two to the monoclinic, and one to the triclinic. In its simplest form, as above outlined, the theory fails to explain the ex- istence of the classes under the several systems of a symmetry lower than that of the normal class. It has been shown, however, by Sohncke and later by Fedorow, Schonflies and Barlow, that the theory admits of extension. The idea supposed by Sohncke is this: that, instead of the simple form shown, the network may consist of a double system, one of which may be conceived of as having a position relative to the other (1) as if pushed to one side, or (2) as if rotated about an axis, or finally (3) as if both rotated as in (2) and displaced as in (1) The complexity of the subject makes it impossible to develop it here. It must suffice to say that with this extension Sohncke concludes that there are 65 possible groups. This number has been further extended to 230 by the other authors named, but it still remains true that these fall into 32 distinct types as regards symmetry, and thus all the observed groups of forms among crystals, described under the several systems, have a theoretical explanation, Literature. A complete understanding of this subject can only be gained by a careful study of the many papers devoted to it. An excellent and very clear summary of the whole subject is given by Groth in the fourth edition of his Physikalische Krystallographie, 1905, and by Sommerfeldt, in his Physi- kalische Kristallographie, 1907. 33. X-Rays and Crystal Structure. In 1912, while attempting to prove a similarity in character between X-rays and light, Dr. Laue, of the University of Zurich conceived the idea of using the ordered arrangement of the molecules or atoms of a crystal as a " diffraction grating " for their analysis By placing a photographic plate behind a crystal section which in turn lay in the path of a beam of X-rays he found that not only did the developed plate show a dark spot in its center where the direct pencil of the X-rays had hit it but it also showed a large number of smaller spots arranged around the center in a regular geometrical pattern. This pattern was formed by the interference of waves which had been diffracted in different directions by the molecular structure of the crystal. In this way he succeeded in proving that X-rays belong to the same class of phenomena as light but with a much shorter wave length. The experiment showed indeed that the wave lengths of the X-rays must be comparable to the distances between the layers of molecular particles of crystals. Another, and, from the crystallographic point of view, a very important, result of this investigation was the furnishing of a 26 CRYSTALLOGRAPHY method for the study of the internal structure of crystals. The position of the smaller dark spots in the Laue photographs corresponded to that of various planes existing in the crystal network parallel to possible crystal faces and their arrangement indicated the symmetry of the crystal. Following these investigations of Laue and his colleagues another fruitful method of investigation of crystal structure by means of X-rays was devised by W. H. and W. L. Bragg. In this method the beam of X-rays meets the crystal section with varying acute angles of incidence and the reflection of the rays is studied. The X-rays are not reflected from the surface of the section like light rays but because of their short wave lengths penetrate the crystal section and are reflected from the successive layers of its molecular structure. In studying the reflection phenomena we have to consider the effect upon each other of these different wave trains originating from the different layers of the crystal. In general these various reflected waves would be in different phases of vibration and so would tend to interfere with each other with the consequent cessation of all vibrations. But with a cer- tain angle of incidence and reflection it would happen that the different re- flected rays would possess on emergence from the crystal the same phase of vibration and would therefore reinforce each other. This angle would vary with the wave length of the X-ray used (for it has been found that the wave length of X-rays varies with the metal that is used as the anticathode in the X-ray bulb) and with the spacing between the molecular layers of the mineral used. It is also obvious that there might be other angles of incidence at which the successive wave trains would each differ in phase by two or even more whole wave lengths from the preceding one and a similar strong re- flected beam obtained. By the use of a special X-ray spectrometer the angles at which these reflections take place can be accurately measured. If the character of the X-ray used is therefore kept constant these angles of reflec- tion give the data necessary for calculating the distance between the succes- sive molecular layers in the particular mineral used and for the direction perpendicular to the surface used for reflection. The spacing of the molec- ular layers was found to vary with different substances and in different directions in the same substance and by making a series of observations it has been possible to arrive at some very interesting conclusions as to the character of the molecular structure of certain minerals as well as to the relationship existing between the structures of different but related com- pounds. The possibilities lying in these methods of attack are very great and unquestionably much new information concerning crystal structure will soon be available. An excellent summary of the methods employed and the results already obtained will be found in " X-rays and Crystal Structure " by W. H. and W. L. Bragg, 1915. GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 34. Axial Ratio, Axial Plane. The crystallographic axes have been defined (Art. 22) as certain lines, usually determined by the symmetry, which are used in the description of the faces of crystals, and in the determination of their position and angular inclination. With these objects in view, certain GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 27 49 lengths of these axes are assumed as units to which the occurring faces are referred. The axes are, in general, lettered a, b, c, to correspond to the scheme in Fig. 49. If two of the axes are equal, they are designated a, a, c; if the three are equal, a, a, a. In one system, the hexagonal, there are four axes, lettered a, a, a, c. Further, in the systems other than the isometric, one of the horizontal axes is taken as the unit to which the other axes are referred; hence the lengths of the axes express strictly the axial ratio. Thus for sulphur (orthorhombic, see Fig. 49) the axial ratio is a : b : c = 0'8131 : 1 : 1'9034. For rutile (tetragonal) it is a : c = 1 : 0'64415, or, simply, c = 0'64415. The plane of any two of the axes is called an axial plane, and the space included by the three axial planes is an octant, since the total space about the center is thus divided by the three axes into eight parts. In the hexagonal system, how- ever, where there are three horizontal axes, the space about the center is divided into 12 parts, or sectants. 35. Parameters, Indices, Symbol. Parameters. The parameters of a plane consist of a series of numbers which express the relative intercepts of that plane upon the crys- tallographic axes. They are given in terms of the estab- lished unit lengths of those axes. For example, in Fig. 50 let the lines OX, OY, OZ be taken as the directions of the crystallographic axes, and let OA, OB, OC represent their unit lengths, designated (always in the same order) by the letters a, b, c. Then the Orthorhombic Crystal Axes intercepts for the plane (1) HKL are OH, OK, OL; for the plane (2) ANM they are OA, ON, OM. But in terms of the unit lengths of the axes these give the following parameters, and (1) (2) la 2c. It is to be noted that since the two planes HKL and MNA are parallel to each other and hence crystallographically the same, these two sets of parameters are considered to be identical. Obviously each of them may be changed into the other by multiplying (or dividing) by 4. 28 CRYSTALLOGRAPHY Indices and Symbol. Simplified and abbreviated expressions which have been derived from the parameters of a crystal form are commonly used to give its relations to the crystallographic axes. These are known as indices. A number of different methods of deriving indices have been devised and several are in use at present. The so-called Miller indices are most widely employed and will be exclusively used in this work.* Below, a description of the other important systems of indices is given together with the neces- sary directions for transforming one type into another. The Miller indices may be derived from the parameters of any form by taking their reciprocals and clearing of fractions if necessary. For instance take the two sets of parameters as given above. (1) \a : |6 : \c, and (2) la : |6 : 2c. By inversion of these expressions we obtain (1) 4a : 36 : 2c, and (2) la : |6 : ic. In the case of (2) it is necessary to clear of fractions, giving (2) 4a : 36 : 2c. The indices of this form then are 4 a : 3 6 : 2 c. The letters indicating the different axes are commonly dropped and the indices in this case would be written simply as 432, the intercepts on the different axes being indicated by the order in which the numbers are given. A general expression frequently used for the indices of a form belonging to any crystal system which has three crystallographic axes is hkl. In the hexagonal system, which has four axes, this becomes hkil. If the parameters of a form be written so that they are fractions with the numerators always unity then the denominators will become the same as the corresponding in- dices. The general expression in this case would therefore be T r 7 rl K L The symbol of a given form is the indices of the face of that form which has the simplest relations to the crystallographic axes. The symbol is com- monly used to designate the whole form. Various examples are given below illustrating the relations between param- eters and indices. Parameters Miller's Symbol } = %a : kb : Ic = 221 fe la }a la la la la 16 16 26 006 GO6 16 26 006 l c l = 2c/ ooci ooc : %c = 212 : jc = 201 ) = \a : & :fc = 210 ooc = ja : 6 : c = 100 If the axial intercepts are measured in behind on the a axis, or to the left on the 6 axis, or below on the c axis, they are called negative, and a minus sign is placed over the corresponding number of the indices; as Parameters Indices -\a -io -\b : \c = 221 201 *In the hexagonal system the indices used are those adapted by Bravais after the method of Miller. GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 29 Different Systems of 'Indices. The Weiss indices are the same as the parameters described above. The different axes are represented by the letters a, b and c, each being preceded by a number indicating the relative intercept of the face in question upon that particular axis. For instance, a possible orthorhombic pyramid face might be represented as la : 26 : fc. The Weiss indices may be converted into the Miller indices by inversion and clearing of fractions, the above symbol becoming then 213. In the Naumann indices the unit pyramidal form is indicated by O in the isometric system where the three crystal axes all have the same unit lengths or by P where the axes differ in their unit lengths. For other forms the indices become mPn (or mOn) in which m gives the intercept upon the vertical axis, c, and n the intercept upon one of the horizontal axes (a or 6), the intercept upon the other horizontal axis being always at unity. To which particular horizontal axis this number refers may be indicated by a mark over it as n for the b axis, ft or n' for the a axis. If the intercept m or n is unity it is omitted from the indices. The pyramid face used as an example above would therefore in the Naumann notation be represented by |P2. Other examples are given in the table below. J. D. Dana modified the Naumann indices by substituting a hyphen for the letter P or O and i for the infinity sign, oo . He designated the fundamental pyramid form simply by 1. When the only parameter differ- ing from unity was that one which referred to the intercept upon the vertical axis, it was written alone; for example the pyramid face having the parameter relations of la : 16 : 2c would be indicated by 2. The Naumann and Dana indices are easily converted into the Miller indices by arranging them in the proper order, inverting and then clearing of frac- tions. Goldschmidt has proposed another method of deriving indices. This has the advantage that the indices for any particular face can be derived directly from the position of its pole on the gnomonic projection. The first number gives the linear position of the pole in respect to the left to right medial line of the projection and in terms of the unit pace distance of the projection (see Art. 84). The second figure similarly gives the position of the pole in reference to the front to back medial line. These two figures con- stitute the Goldschmidt indices of the face. If the two numbers should be the same the second is omitted. The Goldschmidt indices are easily converted into the Miller indices by adding 1 as the third figure and clearing of fractions and eliminating any oo sign. The relations between the Miller and the Miller-Bravais indices for the hexagonal system are given in Art. 169. EXAMPLES OF INDICES ACCORDING TO VARIOUS SYSTEMS OF NOTATION Weiss Naumann Dana Goldschmidt Miller la 16 2c. . 2P 2 2 221 \a 26 lc OP2 1-2 ii 212 la 006 2c 2Poo 2-i 20 201 la ?,b ooc oo P2 i-2 2oo 210 la 006 ooc oo Poo i-i ooO 100 36. Law of Rational Indices. The study of crystals has established the general law that the ratios between the intercepts on the axes for the different faces on a crystal can always be expressed by rational numbers. These ratios may be 1:2, 2:1, 2:3, 1 : oo, etc., but never 1 : V2, etc. Hence the values of hkl in the Miller symbols must always be either whole numbers or zero. If the form whose intercepts on the axes a, 6, c determine their assumed unit lengths the unit form as it is called is well chosen, these numerical values of the indices are in most cases very simple. In the Miller symbols, and the numbers from 1 to 6 are most common. The above law, which has been established as the result of experience, in fact follows from the consideration of the molecular structure as hinted at in an earlier paragraph (Art. 31). 30 CRYSTALLOGRAPHY 37. Form. A form in crystallography includes all the faces which have a like position relative to the planes, or axes, of symmetry. The full meaning of this will be appreciated after a study of the several systems. It will be seen that in the most general case, that of a form having the symbol (hkl), whose planes meet the assumed unit axes at unequal lengths, there must be forty-eight like faces in the isometric system * (see Fig. 121), twenty-four in the hexagonal (Fig. 226), sixteen in the tetragonal (Fig. 187), eight in the orthorhombic (Fig. 51), four in the monoclinic, and two in the triclinic. In the first four systems the faces named yield an enclosed solid, and hence the form is called a closed form; in the remaining two systems this is not true, and such forms in these and other cases are called open forms. Fig. 298 shows a crystal bounded by three pairs of unlike faces; each pair is hence an open form. Figs. 52-55 show open forms. The unit or fundamental form is one where parameters cor- respond to the assumed unit lengths of the axes. Fig. 51 shows the unit pyramid of sulphur whose symbol is (111); it has eight similar faces, the position of which determines the ratio of the axes given in Art. 34. 52 53 Basal Pinacoid (001) 54 Prism (110) (/i/cO) Dome (101), (MM) Dome (Oil), (OW) * The normal cla,ss is referred to in each case. GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 31 56 The forms in the isometric system have special individual names, given later. In the other systems certain general names are employed in this book which may be briefly men- tioned here. A form whose faces are parallel to two of the axes * is called a pinacoid (from Trufa^j a board). It is shown in Fig. 52. One whose faces are parallel to the vertical axis but meet both the horizontal axes is called a prism, as Fig. 53. If the faces are parallel to one horizontal axis only, it is a dome (Figs. 54, 55) . If the faces meet all the axes, the form is a pyramid (Fig. 51); this name is given even if there is only one face belonging to the form. In Fig. 56, a(100), 6(010) are pinacoids; w(110), s(120) are prisms; d(101) and fc(021) are domes; all these are open forms. Finally, e(lll) is a pyramid, this being a closed form. The relation existing in each of these cases between the symbol and the position of the faces to the axes should be carefully studied. As shown in the above cases, the symbol of a form is usually included in parentheses, as (111), (100); or it may be in brackets [111] or UH \. 38. Zone. A zone includes a series of faces on a crystal whose inter- section-lines are mutually parallel to each other and to a common line drawn through the center of the crystal, called the zone-axis. This parallelism means simply that the given faces are either all parallel to one of the crystallographic axes or that their parameters have a constant ratio for two of the axes. Some simple numerical relation exists, in every case, between all the faces in a zone, which is expressed by the zonal equation (see Art. 45). The faces m, s, b (Fig. 56) are in a zone; also, b and k. If a face of a crystal falls simultaneously in two zones, it follows that its symbol is fixed and can be determined from the two zonal equations, without the measurement of angles. Further, it can be proved that the face correspond- ing to the intersection of two zones is always a possible crystal face, that is, one having rational values for the indices which define its position. In many cases the zonal relation is obvious at sight, but it can always be determined, as shown in Arts. 45, 46 by an easy calculation. Illustrations will be given after the methods of representing a crystal by the various projections have been explained. Chrysolite 39. Horizontal Projections. In addition to the usual perspective figures of crystals, projections on the basal plane (or more gener- ally the plane normal to the prismatic zone) are very conveniently used. These give in fact a map of the crystal as viewed from above looking in the direction of the axis of the prismatic zone. Figs. 30-33 give simple examples. In these the successive faces may be indicated by accents, as in Fig. 56, passing around in the direction of the axes a, 6, a, that is, counter-clockwise. On the construction of these projections see the Appendix A. 40. Spherical Projection. The study of actual crystals, particularly as regards the angular and zonal relations of their faces, is much facilitated by the use of various projections. The simplest of these and the one from which the others may be derived is known as the spherical projection. In making a spherical projection of a crystal it is assumed that the crystal lies within a sphere, the center of which coincides with the center of the * In the tetragonal system the form (100) is, however, called a prism and (101) a pyramid. 32 CRYSTALLOGRAPHY crystal (i.e. the point of intersection of its crystallographic axes). From this common center normals are drawn to the successive faces of the crystal and continued until they meet the surface of the sphere. The points in which these normals touch that surface locate the poles of the respective faces and together form the spherical projection of the crystal. The method of formation and the character of the spherical projection is shown in Fig. 57. It is to be noted that all the poles of faces which lie in the same zone on the crystal, i.e. faces whose in- tersection lines are mutually parallel, fall upon the same great circle on the sphere. TTulTls illustrated in the figure in the case of the zone a-d-a and a-o-d. Con- versely, of course, all faces whose poles fall on the same great circle of the spherical projection must lie in the same zone. A face whose pole falls at the intersection of two or more great circles lies in two or more inde- Spherical Projection (after Penfield) pendent zones, as for instance o(lll), in Fig. 57. The angular relations between the faces on the crystal are of course preserved in the angles exist- ing between their respective poles on the spherical projection. The angles between the poles, however, are the supplementary angles to those between the faces on the crystal, as shown in Fig. 58. The supplementary angles are those which are commonly measured and recorded when studying a crystal, see Art. 230. The spherical projection is very useful in getting a mental picture of the relations existing between the various faces and zones upon a crystal but because of its nature does not permit of the close study and ac- curate measurements that may be made on the other projections described below which are made on plane surfaces. 41. The Stereographic Projection. The stereo- graphic projection may be best considered as derived from the spherical projection in the following man- s ioi j [ projection * ner. The plane of the projection is commonly taken as the equatorial plane of the sphere. Imaginary lines are drawn from the poles of the spheri- cal projection to the south pole of the sphere. The points in which these lines pierce the plane of the equator locate the poles in the stereographic pro- jection. The relation between the two projections is shown in Fig. 59. GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 33 oft 111 010 Fig. 60 shows the same stereographic projection without the foreshortening of Fig. 59. Commonly only the poles that lie in the northern hemisphere, including those on the equator, are transferred to the stereographic projection. Certain facts concerning the stereographic projection need to be noted. Its most important charac- -* ter is that all circles or cir- cular arcs on the spherical projection are projected as arcs of true circles on the stereographic projection.* The poles of all crystal faces that are parallel to the vertical crystallogra- phic axis fall on the equa- tor of the spherical pro- jection and occupy the same positions in the stere- ographic projection. The pole of a horizontal face will fall on the center of the stereographic projec- tion. All north and south meridians of the spherical projection will appear as straight radial lines in the stereographic projection (i.e. as arcs of circles hav- ing infinite radii). Other Relation between Spherical and Stereographic Projections great circles on the spher- ical projection, as already stated, will be transferred to the stereographic as circular arcs. Examples of all these are shown in Fig. 60. The angular relations between the poles of the various faces are preserved in the stereographic projection but the linear distance corresponding to a degree of arc naturally increases from the center of the projection toward its circumference. This is illustrated in Fig. 61 where the circle represents a vertical section through the spherical projection and the line A-B represents the trace of the horizontal plane of the stereographic projection. A point 20 from N on the sphere is projected to the point a on the stereographic projection, a point 45 from N is projected to b, etc. In this way a protractor can be made by means of which angular distances from the center of the stereographic projection can be readily determined. Fig. 62 represents such a protractor which was devised by Penfield.f The mathematical relation between the linear distance from the center of the projection and its angular value is seen by study of Fig. 61. If the radius of the circle of the projection is taken as unity the distance from its center to any desired point is equal to the tangent of one half of the angle represented. For instance the distance * For proof of this statement see Penfield, Am. Jour. Sci., 11, 10, 1901. f This protractor and the other protractors and scales used by Penfield ? pan be ob- tained from the Mineralogical Laboratory of the Sheffield Scientific School of Yale Uni- versity, New Haven, Ct. 34 CR YSTALLO GR APH Y 60 duo dlio a 01 a 010 a 100 Stereographic Projection of the Isometric Forms, Cube, Octahedron, and Dodecahedron 61 from the center to the point a is equivalent to the tangent of 10, to point c the tangent of 35, etc. Fig. 63 represents a chart used by Penfield for making stereographic projections. The circle has a diameter of 14 cm. and is graduated to de- grees. With it go certain scales that are very useful in locating the desired points and zonal circles. These will be briefly described later. GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 35 For detailed descriptions of the principles of the stereographic projection and the methods of its use the reader is referred to the various books and articles, the titles of which are given beyond. It is possible here to give only a brief outline of the more important methods of construction used. 62 Stereographic Protractor for plotting Stereographic Projections (after Penfield; reduced one-half) (1) . To locate the pole of a face lying on a known north and south great circle, its angular distance from the center or a point on the circumference of the pro- jection being given. The stereographic protractor, Fig. 62, or the tangent rela- tion as stated above, gives the proper distance. The poles labeled o (iso- metric octahedron), Fig. 60, may be located in this way. (2) To locate the projection of the arc of a great circle which is not a north and south meridian or the equator. The projections of three points on the arc must be known. Then, since the projection of the circle will be still a circular arc, its position can be determined by the usual geometric construc- tion for a circle with three points on its arc given. If, as is commonly the case, the points where the great circle crosses the equator and the angle it makes with the equator are known it is possible to get the radius of the pro- jected arc directly from Scale No. 1, Fig. 63. The location of such a desired arc is shown in Fig. 64. The arcs shown in Fig. 60 were also located in this way. (3) To locate the position of the pole of a face lying on a known great circle, which is not a north and south meridian, its angle from a point on the circum- ference of the projection being known. The projected arc of a small vertical circle, whose radius is the known angle, is drawn about the point on the cir- cumference of the projection and since all points on this arc must have the required angular distance from the given point the intersection of this circle with the known great circle will give the desired point. The radius of the projected arc of the small vertical circle can be determined by finding the position of three points on the projection which have the required angular distance from the point given on the circumference of the projection and then obtaining the center of the required circle in the usual way. Or by the use of Scale No. 2, Fig. 63, the required radius is obtained directly. It is to be noted that the known point on the circumference of the projection, while the stereographic center of the small circle, is not the actual center of the projected arc. The center will lie outside the circumference on a con- tinuation of the radial line that joins the given point with the center of the projection. Therefore, even if the radius of the required arc is taken from 36 CRYSTALLOGRAPHY s i II 3 E E a r- 3- P GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 37 Scale No. 2, it will be necessary to establish at least one point on the re- Zed circle in order to find its center. These methods of construction are trated in Fig. 65, in which the position is determined of the pole n (iso- Location of the arc of a great circle in the Stereographic Projection at a given angle above the equator a Oil dllQ Location of pole of trapezohedron, n(211), in Stereographic Projection metric trapezohedron) which lies on the great circle passing through the poles a (isometric cube) and o (isometric octahedron), and makes a known angle (35J) with a. 38 CRYSTALLOGRAPHY (4) To locate the position of the pole of a face given the angles between it and two other faces whose poles lie within the divided circle. Circumscribe about the poles of the two known points small circles with the proper radii and the desired point will be located at their intersection. The two small circles may touch at only a single point or they may intersect in two points. In the latter case both points will meet the required conditions. The positions of the projected small circles are readily found by drawing radii from the center of the projection through the two known poles and then laying off on these radii points on either side of the known poles with the required angular distances. The center is then found between these two points in each case and a circle drawn through them. This line of this circle will then be every- where the required number of degrees away from the known pole. The re- quired points may be found readily by means of the Stereographic Protrac- tor, Fig. 62, remembering that the zero point on the protractor must always lie at the center of the projection. This construction is illustrated in Fig. 66, in which the points s (isometric hexoctahedron), are 22 12' and 19 5' from the points o (isometric octahedron), and d (isometric dodecahedron). It is to be noted here, also, that while the points o and d are the stereographic centers of the circles about them, the actual centers are points which are somewhat farther out from the center of the projection. a 010 duo a loo Location of two poles of hexoctahedron, s, in Stereographic Projection (5) To measure the angle between two given points on the stereographic projection. If the two points lie on the circumference of the projection the angle between them is read directly from the divisions of the circle. If they lie on the same radial line in the projection, the angle is given by the use of the Stereographic Protractor, Fig. 62. In other cases it is necessary first to find the arc of a great circle upon which the two points lie. This is most easily accomplished by the use of a transparent celluloid protractor upon which the arcs of great circles are given, Fig. 67. Place this protractor over the projection with its center coinciding with the center of the projection and turn it about until the required great circle is found. Note the points where this circle intersects the circumference of the projection. Then place a second transparent protractor on which small vertical circles are given, Fig. 68, over the projection with its ends on the points of the circumference GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 39 just determined. Now note the angular distance between the two given points. The whole operation may also be done by use of a third trans- parent protractor, on which the arcs of both great and small circles are given. 67 Stereograph! c Protractor, giving the great circles of every alternate degree (second, fourth, etc.) (After Penfield, reduced one-half) Stereograph] c Protractor, giving small circles for every degree measured from a given point on the circumference. (After Penfield, reduced one-half) (6) To measure the angle between the arcs of two great circles on the stereo- graphic projection. This is most conveniently accomplished by construct- ing the arc of a great circle which shall have a 90 radius about the point at which the two arcs in question cross each other and then measuring the angular distance between the two points at which they intersect this great circle. Fig. 69, after Penfield, will serve to illustrate the method. First, if it is wished to measure the angle between the divided circle and the arc of the great circle that crosses it at C it is only necessary to draw a straight line through the center of the projection, N, which shall intersect the divided circle at points 90 distant from C. This line will be the projection of the arc of a great circle about the sphere at 90 distant from C. The angle at C is then determined by measuring with the stereographic protractor the angle between u and v. In the case of the angle between two great circles that meet at some point within the divided circle as at A, Fig. 69, it is necessary to construct the projected arc of the great circle 90 distant from this point This is done 40 CRYSTALLOGRAPHY 69 by drawing the radial line through N and A and measuring with the stereo- graphic protractor an angle of 90 from A to the point B. The required arc will pass through this point and the points p and p f which are each 90 away from the points at which the line A-N-B crosses the divided circle. The angle between x and y measured on this great circle gives the value of the required angle at A. This is most readily measured by the use of the transparent protractor showing small circles, Fig. 68. This is placed across the projection from p to p' and the angle between x and y read directly from it. Wiilfing has described a stereo- graphic net, which gives both great and small circles for every two de- grees. Over this is placed a sheet of tracing paper upon which the stereo- graphic projection is made. If the paper is fastened at the center of the drawing so that it can be turned into various positions in respect to the stereographic net below, the various great and small circles needed can be sketched directly upon the drawing. Or the required points can be trans- ferred from the net to a separate drawing by means of three point dividers. Examples of the use of the stereographic projection will be given later under each crystal system. 70 no ^100 Relation between Spherical and Gnomonic Projections 42. The Gnomonic Projection. The characters of the gnomonic pro- jection can best be understood by considering it to be derived from the spherical projection (see Art. 40). In the case of the gnomonic projection the plane of the projection is usually taken as the horizontal plane which , GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 41 lies tangent to the north pole of the sphere of the spherical projection. Im- aginary lines are then taken from the center of the sphere through the poles of the crystal faces that lie on its surface and extended until they touch the plane of the projection. The points in which these lines touch that plane constitute the gnomonic projection of the forms represented. Fig. 70 shows the relations between the spherical and gnomonic projections, using the same isometric crystal forms (cube, octahedron and dodecahedron) as were em- ployed to illustrate the principles of the Stereographic Projection (Art. 41). Fig. 71 shows the gnomonic projection of the same set of forms. 100 Gnomonic Projection of Cube, Octahedron and Dodecahedron The following features of the gnomonic projection are important. All great circles on the spherical projection become straight lines when trans- ferred to tho gnomonic. The poles of a series of crystal faces which belong in the same zone will, therefore, on the gnomonic projection, lie on a straight line. This primary distinction between the stereographic and gnomonic pro- jections will be readily seen by a comparison of Figs. 60 and 71. The pole of a horizontal crystal face (like the top face of the cube) will fall at the center of the projection. The poles of vertical crystal faces will lie on the plane of projection only at infinite distances from the center. This is shown by a consideration of Fig. 70. Such faces are commonly indicated on the pro- jection by the use of radial lines or arrows which indicate the directions in which their poles lie. This is illustrated in the case of the vertical cube and dodecahedron faces in Fig. 71. Crystal faces having a steep inclination with the horizontal plane must frequently be indicated in the same way. 42 CRYSTALLOGRAPHY A simple relation exists between the linear distance from the center of the projection to a given point and the angular distance represented. This is shown in Fig. 72 where the circle is assumed to be a vertical cross-section of the sphere of the spherical projection and the line A-B represents the trace of the plane of the gnomonic projection. It is evident from this figure that if the radius of the circle is taken as unity d' B the linear distances N-a', N-b', etc., are the tangents of the angles 20, 35, etc. Conse- quently in the gnomonic projection the distance of a given pole from the center of the projection, considering the funda- mental distance 0-A r , Fig. 72, to be unity, is equal to the tangent of the angle represented. In the case of the stereo- graphic projection this distance is equal to the tangent of one half the angle, see Art. 41. The stereographic scale, used hi trie stereographic protractor, Fig. 62, can therefore be adapted for use in the gnomonic projection by taking the point on it reading at twice the desired angle. The simplest method of plotting, however, is to make a direct use of the tangent relation. The distance 0-N t Fig. 72, is taken at some convenient length and then by multiplying this distance by the natural tangent of the angle desired the linear distance of the pole in question from the center of the projection is obtained. Frequently the distance 0-N is taken as 5 cm. In making a gnomonic projection a circle is commonly drawn about the center of the projection, known as the fundamental circle, with a radius equal to this chosen dis- tance. Points th at have an angular distance of 45 with the center point of the projection will lie on the circumference of this circle. Measurement of angle between any two poles Commonly also the gnomonic pro- (Ai, A 2 ) on the Gnomonic Projection jection is surrounded by a square border of two parallel lines on which is indicated the directions in which lie the poles that cannot appear on the projection because of the vertical or steeply inclined position of their faces. These characters are shown in Fig. 71. To measure the angle between two poles on the gnomonic projection. In GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 43 Fig. 73 let Ai and A 2 be any two points the angle between which is desired. First draw a straight line through them or, in other words, find the direction of the zonal line upon which they lie. Next erect the line 0-A perpendicular to this zonal line and passing through the center of the projection. On this line establish the point N, the distance A-N being equal to the hypo- thenuse of the right triangle A OP or the distance A-P. The point TV is known as the angle-point of the zone Ai-Az. The angle AiNAz is equal to the desired angle between the points AI and A 2 . In the case of zonal lines that pass through the center of the projection this angle-point will lie on the circumference of the fundamental circle at the terminus of a radius which is at right angles to the zonal line in question. In the case of vertical crystal faces whose poles lie at an infinite distance the center of the projec- tion is itself the angle-point. The explanation of the above method may be given as follows. In Fig. 74 let the circle represent a vertical section through the sphere of the spherical projection and the line N-A the trace of the plane of the gnomonic projection. Let the line A-C represent the intersection of a zonal plane lying at right angles to the plane of the drawing. The zonal line representing the intersection of this zonal plane with the plane of the gnomonic pro- jection would therefore be a straight line through point A which would be 74 perpendicular to the plane of the draw- ing. The angle between any two poles N O A lying on this zonal line would be deter- mined by the angle formed by the lines drawn from these poles to the point C. Ifj we consider this zonal line which passes through A perpendicular to the drawmg as an axis around which we may revolve its zonal plane, the point C may be moved so that it will lie 'in the plane of the gnomonic projection and fall at N, the distance A-N being equal to A-C. The character of the point C has not been changed by this transfer and the point N becomes the angle-point of the zonal line running through A and the angle between any two poles on this line may be determined by running lines from them to this point and measuring the included angle. The point N lies on the line running through O (center of the gnomonic projection) and the distance A-N is equal to the hypothenuse, A-C, of the right triangle one side of which is equal to A-O and the other to O-C (the raclius of the fundamental circle). To measure the angle between parallel zonal lines on the gnomonic projection. In Fig. 75 let the two lines Zone 1 and Zone 2 represent two parallel zonal lines the angle between which is desired. Draw the. radial line trom the center of the projection, 0, at right angles to these zonal lines intersecting them at the points AI and A 2 . Make 0-P at right angles to 0-AiA 2 . The angle AiPAz will give the angle between the two zones. The construction will be readily understood if the figure is supposed to be turned on the line 0-AiAz as on an axis until the point P becomes the center of the spherical projection The broken arc now represents a vertical cross section of the sphere of the spherical projection and the points i and 02 the points where the two zonal lines cross it. The angle at P is obviously the angle between the two zones. The angle between Zone 2 and the prism zone, the line of which lies at infinity on the gnomonic projection, is given in Fig. 75 by the angle A%PN which is the same as 44 CRYSTALLOGRAPHY A gnomonic net, similar in character to the stereographic net described in Art. 41, is useful in plotting the points of a projection or in making meas- urements upon it. The straight lines upon it represent the projection of the arcs of great circles of the spherical projection, while the hyperbola curves represent those of the small vertical circles. The gnomonic projection is most commonly used in connection with the measurement of crystal angles by means of the two-circle goniometer. This use will be explained later, see Art. 232. For more detailed descrip- tions of the principles and uses of the gnomonic projection the reader is referred to the literature listed below. References on the Stereographic and Gnomonic Projections. In addition to the descriptions of these Measurement of the angle between parallel projections that are given in many general zones on the Gnomonic Projection crystallographic texts the following books and papers are of value. Boecke, H. E. Die Anwendung der stereographischen Projektion bei kristallographi- schen Untersuchungen, 1911. Die gnomonische Projektion in ihrer Anwendung auf kris- tallographische Aufgaben, 1913. Evans, J. W. Gnomonic Projections in two planes. Min. Mag., 14, 149, 1905. Goldschmidt, V. Uber Projektion und graphische Kristallberechnung, 1887. Gossner, B. Kristallberechnung und Kristallzeichnung, 1914. Hilton, H. The Gnomonic Net, Min. Mag., 14, 18-20, 1904. The Construction of Crystallographic Projections, Min. Mag., 14, 99-103, 1905. Some Applications of the Gnomonic Projection to Crystallography, Min. Mag., 14, 104-108, 1905. Hutchinson, A. On a protractor for use in constructing stereographic and gnomonic projections of the sphere, Min. Mag., 15, 94-112, 1908. Palache, Charles. The Gnomonic Projection. Amer. Min., 6, 67, 1920. Penfield, S. L. The Stereographic Projection and Its Possibilities from a Graphical Standpoint, Am. J. Sci., 9, 1-24, 115-144, 1901. On the Solution of Problems in Crystal- lography by Means of Graphical Methods based upon Spherical and Plane Trigonometry. Am. J. Sci., 14, 249-284, 1902. On the Drawing of Crystals from Stereographic and Gnomonic Projections, Am. J. Sci., 21, 206-215, 1906. Smith, G. H. H. On the Advantages of the Gnomonic Projec- tion and its use in the Drawing of Crystals, Min. Mag., 13, 309-321, 1903. 43. Angles between Faces. The angles most con- veniently used with the Miller symbols, and those given in this work, are the normal angles, that is, the angles be- tween the poles or normals to the facts, measured on arcs of great circles joining the poles as shown on the stereo Chrysolite graphic projection. These normal angles are the supple- ments of the actual interfacial angles, as has been explained. The relations between these normal angles, for example in a given zone, is much simpler than those existing between the actual interfacial angles. Thus it is always true that, for a series of faces in the same zone, the normal angle between two end faces is equal to the sum of the angles of faces falling between. Thus (Figs. 76, 77) the normal angle of GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 45 06(100 A 010) is the sum of aw(100 A 110), ms(110 A 120), and s6(120 A 010). This relation holds true in all the systems. Furthermore, it will be seen that, supposing oca! (Fig. 77) is a plane of symmetry as in the orthorhombic system, the angle 100 A 110, or am (Fig. 76), is half 77 the angle 110 A 110(rara'"). Similarly 010 A 120(6s) is half the angle 120 A 120(ss')j again, 100 A lll(ae) is the complement of half the angle 111 A 111(66') and 010 A lll(6e) the_comple- ment of half the angle 111 A 111(60. Here, as throughout this work, the sign A is used to represent the angle between two faces, usually designated by letters. 44. Use of the Stereographic Projection to Exhibit the Sym- metry. The symmetry of any one of the crystalline classes may be readily exhibited by the help of the stereographic projection. The axes of binary, trigonal, tetragonal and hexagonal sym- metry are represented respec- tively by the following signs: fcoio 010 ft . Further, a plane of stereographic Projection of Faces on Chrysolite symmetry is represented by a full Crystal, Fig. 76 line (zone-circle), while a dotted line indicates that the plane of symmetry is wanting. The position of the crystallographic axes is shown by arrows at the extremities of the lines. The pole of a face in the upper half of the crystal (above the plane of pro- jection) is represented by a cross; one below by a circle. If two like faces fall in a vertical zone a double sign is used, a cross within the circle. Figs. 91, 128, 140, etc., give illustrations. 45. General Relations be- tween Planes in the Same Zone. - Certain important relations Y exist between the indices of faces that lie in the same zone. All faces to belong to the same zone, tautozonal faces as they are called, must have their mutual intersec- tions parallel to a given direction, see Art. 38. This direction is known as the axis of the zone. The position of this zonal axis can be expressed by what is known as the zonal symbol. Consider Fig. 78, where is represented two crystal faces, ABC, and CDE, intersecting the crystallographic axes X, Y and Z. In the illustration, for simplicity, both faces have been assumed to pass through 46 CRYSTALLOGRAPHY the point C on the axis Z. This, of course, is possible since any crystal plane may be moved parallel to itself without altering its relative intercepts on the crystal axes. These two planes intersect in the line C-W, which then becomes the direction of the zonal axis for the zone in which they lie. Let the line 0P which has been drawn parallel to this direction represent that axis. In the parallelogram of which it is the diagonal the length of the edge 0-S and its parallel edges have been taken as equal to the distance 0-C. The point P on the zonal axis and therefore the direction of the axis itself is fixed by the three coordinates, 0-M, 0-R, and 0-S. By means of the consideration of similar triangles it is possible to prove that the values of these coordinates may be expressed by, 0-M = (Ar - lq)a; 0-R = (Ip - hr)b; 0-S = (hq - kp)c, where a, 6, c represent the unit lengths of the three crystallographic axes, X, Y, Z and (hkl) and (pqr) represent the indices of the two faces ABC and CDE. These expressions are usually simplified by substituting u = kr Iq, v = Ip hr, w = hq kp, giving 0-M = ua, 0-R = vb and 0-S = we. The three figures [uvw] are said to be the symbol of the zone in question. They represent the reciprocals of the values of the three coordinates, or in other words are the indices of a point, P, on the zonal axis. They may most readily be obtained by a system of cross-multiplication and subtraction according to the following scheme. Write the indices of one face twice in their proper order and directly under them the corresponding indices of the second face. Cross off the first and last number of each series. Then mul- tiply the figures joined by the cross lines, see below, and substract the prod- uct of the two joined by light lines from that of those joined by heavy lines, working from left to right. The three numbers obtained will in their order correspond to u,.v and w. P k I h k XXX q r p q I u = kr Iq, v = Ip hr, w = hq kp. Since the zonal symbol for a given zone may be obtained from the indices of any two faces lying in that zone it follows that the indices of every pos- sible face in that zone must have definite relations to the zonal symbol. For a given face with indices (xyz), in a zone having the symbol [uvw] the follow- ing equation, known as the zonal equation, must hold true. ux -\- vy + wz = 0. In this way it can be readily shown whether or not a given face can lie in a certain zone. Further if [uvw] be the symbol of one zone and [efg] that of another inter- secting it, then the point of intersection will always be the pole of a possible crystal face. Its indices (hkl) must satisfy the equations of both zones and may be obtained by combining them or the same result may be had by tak- ing the symbols of the two zones and subjecting them to the same sort of cross- multiplication by which they were themselves originally derived. GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 47 46. Examples of Zones and Zonal Relations. The following are cases in which the zonal equation is seen at once. In Figs. 76 and 77 the faces a(100), ra(110), s(120), 6(010) form a vertical zone with mutually parallel intersections, since they are all parallel to the vertical axis; that is, for all faces in this zone it must be true that I = 0. Again, the faces a(100), d(101), c(001) are in a zone, all being parallel to the horizontal axis 6; hence for them and all others in this zone k = 0. Also 6(010), fc(ti21), /i(011), c(001) are in a zone, all being parallel to the axis a, so that h = 0. Also the faces /(121), e(lll), d(101), e' ''(111), /"'(121) are in a zone, since they have a common ratio for the axes arc. With them, obviously, h = I. The faces c(001), e(lll), m(110) are also in a zone, and again c(001), /(121), s(120), though intersections do not happen to be made between c and e in the one case, and c and / in the other. For each of these zones it is true that there is a common ratio of the hori- zontal axes, that is, of h to k in the indices. For the first it may be shown that h = k; for the second, that 2h = k. All the relations named may be obtained at once from the 79 above scheme. For example, for the faces s(120) and /(121) the scheme gives XXX 2. T, 0; .'. 2h - k = 0, or 2h = k. The symbol of a face lying at once in two zones, as stated above, must satisfy the zonal equation of each; these symbols are hence easily obtained either by combining the equations or by a scheme of multiplication like that given above. For example, in Fig. 79, of sulphur, the face lettered x is in the zone (l)_with 6(010) andsdlS), als9 in zone (2) with p(lll) and n(01T). These zones give, respectively: 01 1 (2) 1 Sulphur (1) 3 1 1 v = 0, w = 1. 6=0, 9 1. Hence for (1) the zonal equation is 3h = I: for (2) k = I. Combining these, we obtain h = 1, k = 3, -I = 3. The symbol of the face x is, therefore, 133. The same result is given by multiplying the zonal symbols Oil, 301, together after the same method, thus; 01 10 11 133 Hence, again, x = 133. This method of calculation belongs to all the different systems. In the hexagonal system, in which there are four indices, one of the three referring to the horizontal axes (usually the third) is omitted when the zonal relations are applied. See Art. 166. 47. Methods of Calculation. In general the angles between the poles can be calculated by the methods of spherical trigonometry from the tri- angles shown in the spherical projection which for the most part are right- angled. Certain fundamental relations connect the axes with the elemental angles of the projection; the most important of these are given under the individual systems. Some general relations only are explained here. 48 CRYSTALLOGRAPHY 80 48. Relations between the Indices of a Plane and the Angle made by it with the Axes. In Fig. 80 let the three lines, X, Y, and Z represent three crystallographic axes making any angles with each other and let a, b and c represent their unit lengths. Assume any face HKL cutting these axes with the intercepts 0-H, O-K and 0-L. Let 0-p-P be a normal to the plane HKL intersecting the plane at p and the enveloping surface of the spherical pro- jection at P. Let hkl represent the indices of the given form. Since the line 0-p is normal to the plane HKL the triangles HOp, KOp and LOp are right angles and the following relations hold true. - cos HOp; Qr = cos KOp; = cos LOp. The angles HOp, KOp, and LOp are equal, respectively, to the angles repre- sented on the spherical projection by the arcs PX, PY and PZ and OH = ^, = 7 , OL = = . By substituting we have, OP = h = cos PY = j cos PZ. n I This equation is fundamental, and several of the relations given beyond are deduced from it. 81 no The most useful application is that when the axial angles are 90, as represented in Fig. 81; then X, Y, Z are the normals to 100, 010, 001, respectively. Also if the plane HKL is taken as a face of the unit pyramid, that is, if its intercepts on the axes are taken as the unit lengths OH = a, OK = b, OL = c. Then the lines HK, HL, KL give also the intersections of the planes 110, 101, Oil on the three axial planes, and their poles are hence at the points fixed by normals to these GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 49 lines drawn from O. It will be obvious from this figure, then, that the following relations hold true: tan (100 A 110) = ^ ; tan (001 A 101) = - ; tan (001 A Oil) = ^- These values are often used later. 49. Cotangent and Tangent Relations. In the case of four faces in a zone concerning which we know, either the angles between all the faces and the indices of three of them, or the angles between three faces and all the indices, it is possible by either a simple graphical method of plotting or by ^calculation to determine the missing angle or indices. To illustrate the graphic method first let Fig. 82 represent a cross section perpendicular to the prism zone of a rhodonite crystal. The traces upon the plane of the drawing of the faces a(100) and 6(010) provide the direction of the lines of reference X and Y. It is assumed that the position of the third face w(110) is known and a line drawn parallel to its trace upon the plane of the drawing from the point X will give its relative intercepts upon the two lines of reference. These intercepts do not correspond to the unit lengths of the axes a and 6 since, rhodonite being triclinic, these axes do not lie in the plane of the drawing but they represent rather the unit lengths of these axes as foreshortened by projection upon that plane. This makes no dif- ference, however, since it will still be true that all faces lying in the prism zone of rhodonite must intercept these two lines in distances which will have rational relations to the lengths of the intercepts of w(110). It is now as- sumed that a fourth face / has the indices (130) and its angular position in respect to the other faces in the zone is required. From its indices it must intercept the two lines of reference X-X' and Y-Y' in the ratio of 1 to ^. Let OX equal 1 on X-X' and OZ equal f on Y-Y'. Then a line joining these two points will give the direction of the trace of / upon the plane of the drawing and so determine the angles it will make with the other faces in the zone. If, on the other hand, the angles between / and the other faces in the zone were known, the position of the trace of / upon the plane of the drawing could be found, and so its relative intercepts (and indices) upon the two lines of reference be determined. If the method of calculation is used let P, Q, S and R be the poles of four faces in a zone (Fig. 83) taken in such an order * that PQ < PR and let the indices of these faces be respectively P Q R S fs hkl pqr uvw xyz Then it may be proved that cot PS - cot PR = (P.Q) (S.R) cot PQ - cot PR (Q.R) (P.S) * In the application of this principle it is essential that the planes should be taken in the proper order, as shown above ; to accomplish this it is often ne_cessary to use th& in- dices and corresponding angles, not of (hkl), but the face opposite (h k F), etc. r 50 CRYSTALLOGRAPHY where (P.Q) (Q.R) (S.R) (P.S) 123 "P, hkl~ Q, pqr Q, pqr _R, uvw_ 123 R, uvw P, hkl _S, xyz] 1 X 2 2X3 3 X 1 hq kp _ kr Iq _ Ip hr pv qu qw rv ru pw 2X3 yw zv kz - ly 3 X 1 Ix - hz If one of these fractions reduces to an indeterminate form, -, then one of the others must be taken in its place. This formula is chiefly used in the monoclinic and triclinic systems; and some special cases are referred to under these systems. The cotangent relation becomes much simplified for a rectangular zone, that is, a zone between a pinacoid and a face lying in a zone at right angles to it so that the angle PR, becomes 90. In Fig. 83 let P(hkl) and Q(pgr) be two faces lying in the zone between a(100) and d(011) with the angle a A d = 90. Let Pa and Qa represent the angles between the two faces and the pinacoid a. Then the following holds true. h tan Pa k I "*\s : ___. _ p tan Qa q r or the faces P and Q lie in zones with the other pinacoids 6(010) or c(001) the expression becomes h k . . tan P6 I P k tan Pb q tan Q6 h _ k _ I tan PC pqr tan Qc If the zone in question lies between two pinacoids which are at right angles to each other so that the indices of the faces P and Q become either hkQ and p#0, hQl and pOr or OH and Qqr, we have tan (100 A hkQ) = k tan (100 A pqQ) h tan (001 A MM) = h r_ . tan (001 A pQr) ~ I ' p ' tan (001 A Qkl) = k r tan (001 A Qqr) ~ I ' q ' These equations are the ones ordinarily employed to determine the symbol of any pris- matic plane or dome. The most common and important application of this tangent principle is where the positions of the unit faces 110, 101, Oil are known, then the relation becomes p. q ' Also, tan (100 A fe/cO) = k tan (100 A 110) h' tan (001 A MM) = h tan (001 A 101) ~ I ' tan (010 A hkO) = h tan (010 A 110) k' tan (001 A 0/cQ = k tan (001 A Oil) ~ I GENERAL MATHEMATICAL RELATIONS OF CRYSTALS 51 Thus the tangents of angles between the base, 001, and 102, 203, 302, 201, etc., are respectively |, f, |, 2 times the tangent of the angle between 001 and 101. Again, the tangent of the angle 100 A 120 is twice the tangent of 100 A 110 (here v = 2 V and one- half the tangent of 010 A 110. These last relations are shown clearly in Fig. 84 which represents a cross-section of a barite crystal showing the macrodome zone between a(100) and c(001). It is assumed that the angles between the faces a, u, d, I and c have been measured and the positions of their poles deter- mined as indicated in the figure. The broken lines drawn from a point x on the line represent- ing the a crystallographic axis show the direction of the traces of these faces upon the plane of the a and c axes. If the face u is assumed to be the unit dome (101) it will intersect the two axes at distances proportional to their unit lengths, namely O-X and O-Y. The other faces d and I are seen to intersect the c axis at | and i the distance O-Y, giving them the indices (102) and (104). But the intercepts on O-Y for the three faces u, d and I are proportional to the tangents of the angles between their poles and that of c(001) as shown below. tan 58 10%' = 1.6112 = 1 tan 38 5H' = .8056 = % tan 21 56|' = .4028 = i 52 CRYSTALLOGRAPHY I. ISOMETRIC SYSTEM (Regular or Cubic System) 50. THE ISOMETRIC SYSTEM embraces all the forms which are referred to three axes of equal lengths and at right angles to each other. Since these axes are mutually interchangeable it is customary to designate them all by 85 the letter a. When properly orientated (i.e. placed in the commonly accepted position for study) one of a 3 these axes has a vertical position and of the two which lie in the horizontal plane, one is perpendicular and the other parallel to the observer. The order in which the axes are referred to in giving the relations ^^ -i of any face to them is indicated in Fig. 85 by lettering o x a * them ai, 0% and a s . The positive and negative ends of each axis are also shown. There are five classes here included; of these the normal class,* which possesses the highest degree of Isometric Axes symmetry for the system and, indeed, for all crystals, is by far the most important. Two of the other classes, the pyritohearal and tetrahedral, also have numerous representatives among minerals. 1. NORMAL CLASS (1). GALENA TYPE (Hexoctahedral or Holohedral Class) 51. Symmetry. The symmetry of each of the types of solids enumer- ated in the following table, as belonging to this class, and of all their com- binations, is as follows. Axes of Symmetry. There are three principal axes of tetragonal sym- metry which are coincident with the crystallographic axes and are some- times known as the cubic axes since they are perpendicular to the faces of the cube. There are three diagonal axes of trigonal symmetry which emerge in the middle of the octants formed by the cubic axes. These are known as the octahedral axes since they are perpendic ular to the faces of the octahedron. Lastly there are six diagonal axes of binary symmetry which bisect the plane angles made by the cubic axes. These are perpendicular to the faces of the dodecahedron and are known as the dodecahedral axes. These symmetry axes are shown in the Figs. 86-88. Planes of Symmetry. There are three principal planes of symmetry which are at right angles to each other and whose intersections fix the posi- * It is called normal, as before stated, since it is the most common and hence by far the most important class under the system ; also, more fundamentally, because the forms here included possess the highest grade of symmetry possible in the system. The cube is a pos- sible form in each of the five classes of this system, but although these forms are alike geo- metrically, it is only the cube of the normal class that has the full symmetry as regards molecular structure which its geometrical shape suggests. If a crystal is said to belong to the isometric system, without further qualification-, it is to be understood that it is included here. Similar remarks apply to the normal classes of the other systems. ISOMETRIC SYSTEM 53 tion of planes Fig. 90 the crystallographic axes, Fig. 89. In addition there are six diagonal of symmetry which bisect the angles between the principal planes, 87 Axes of Tetragonal Symmetry Axes of Trigonal Symmetry Axes of Binary Symmetry (Dodecahedral Axes) (Cubic Axes) (Octahedral Axes) 90 Principal Symmetry Planes The accompanying stereographic projection (Fig. 91), constructed in accordance with the principles explained in Art. 44, shows the dis- tribution of the faces of the general form, hkl (hexoctahedron) and hence represents clearly the symmetry of the class. Compare also the projections given later. 52. Forms. The various possible forms belonging to this class, and possessing the symmetry denned, may be grouped under seven types of solids. These are enumerated in the following table, comiQencing with the sim- plest. Diagonal Symmetry Planes Symmetry of Normal Class, Isometric System 54 CRYSTALLOGRAPHY 1. Cube (100) 2. Octahedron (Ill) 3. Dodecahedron .' (110) 4. Tetrahexahedron (AfcQ) as, (310) 5. Trisoctahedron (hhl) as, (331) 6. Trapezohedron (hll) as, (311) Indices (210); (320), etc. (221); (332), etc. (211); (322), etc. 7. Hexoctahedron (hkl) as, (421); (321), etc. Attention is called to the letters uniformly used in this work and in Dana's System of Mineralogy (1892) to designate certain of the isometric forms.* They are: Cube: a. Octahedron: o. Dodecahedron: d. Tetrahexahedrons: e = 210; / = 310; g = 320; h = 410. Trisoctahedrons: p = 221; q = 331; r = 332; p = 441. Trapezohedrons: m = 311; n = 211; /3 = 322. Hexoctahedrons: s = 321; t = 421. 53. Cube. The cube, whose general symbol is (100), is shown in Fig. 92. It is bounded by six similar faces, each parallel to two of the axes. Each face is a square, and the interfacial angles are all 90. The faces of the cube are parallel to the principal or axial planes of symmetry. 92 ^^\ ,001 010 100 ._._, ,^.. . ,--'' ...._. ^ Cube Octahedron Dodecahedron 54. Octahedron. The octahedron, shown in' Fig. 93, has the general symbol (111). It is bounded by eight similar faces, each meeting the three axes at equal distances. Each face is an equilateral_ triangle with plane angles of 60. The normal interfacial angle, (111 A 111), is 70 31' 44". 55. Dodecahedron. The rhombic dodecahedron, f shown in Fig. 94, has the general symbol (110). It is bounded . by twelve faces, each of which meets two of the axes at equal distances and is parallel to the third axis. Each face is a rhomb with plane angles of 7Q and 109 J. The normal in- terfacial angle is 60. The faces of the dodecahedron are parallel to the six auxiliary, or diagonal, planes of symmetry. * The usage followed here (as also in the other systems) is in most cases that of Miller (1852). t The dodecahedron of the crystallographcr is this fc commonly found on crystals of garnet. Geometricians reco by twelve similar faces; of these the regular (pentagonal) portant. In crystallography this solid is impossible th< mates to it. (See Art. 68.) rhombic shaped faces various solids bounded ledron is the most im- pyritohedron approxi- ISOMETRIC SYSTE!^ 55 It will be remembered that, while the forms described are designated respectively by the symbols (100), (111), and (110), each face of any one of the forms has its own indices. Thus for the cube the six faces have the indices 100, 010, 001, TOO, OTO, 001. For the octahedron the indices of the eight faces are: Above 111, 111, TTl, Below 111, 111, 111; ITT. For the dodecahedron the indices of the twelve faces are: 110, 110, 101, Toi, Oil, Oil, no, Toi, on; 110, 101, on. These should be carefully studied with reference to the figures (and to models), and also to the projections (Figs. 125, 126). The student should become thoroughly familiar with these individual indices and the relations to the axes which they express, so that he can give at once the indices of any face required. 95 96 Cube and Octahedron Cube and Octahedron Octahedron and Cube 100 Dodecahedron and Cube Octahedron and Dodecahedron Dodecahedron and Octahedron 56. Combinations of the Cube, Octahedron, and Dodecahedron. Figs. 95, 96, 97 represent combinations of the cube and octahedron; Figs. 98, 101 of the cube and dodecahedron; Figs. 99, 100 of the octahedron and dodecahedron; finally, Figs. 102, 103 show combinations of the three forms. The predominating form, as the cube in Fig. 95, the octahedron in Fig. 97, etc., is usually said to be modified by the faces of the other forms. In Fig. 96 the cube and octahedron are sometimes said to be "in equilibrium," since the faces of the octahedron meet at the middle points of* the edges of the cube. 56 CRYSTALLOGRAPHY It should be carefully noticed, further, that the octahedral faces replace the solid angles of the cube, as regular triangles equally inclined to the adja- cent cubic faces, as shown in Fig. 95. Again, the square cubic faces replace the six solid angles of the octahedron, being equally inclined to the adjacent octahedral faces (Fig. 97) . The faces of the dodecahedron truncate * the twelve similar edges of the cube, as shown in Fig. 101. They also truncate the twelve edges of the octahedron (Fig. 99). Further, in Fig. 98 the cubic faces replace the six tetrahedral solid angles of the dodecahedron, while the octahedral faces replace its eight trihedral solid angles (Fig. 100). 101 102 103 ^--^ /if ^ a i i ] L \ a \ d c ^' J \ I , _ W Cube and Dodeca- hedron Cube, Octahedron and Dodecahedron Octahedron, Cube and Dodecahedron The normal interfacial angles for adjacent faces are as follows: Cube on octahedron, ao. 100 A 111 = 54 44' 8". Cube on dodecahedron, ad, 100 A 110 = 45 0' 0". Octahedron on dodecahedron, od, 111 A 110 = 35 15' 52". 67. As explained in Art. 18 actual crystals always deviate more or less widely from the ideal solids figured, in consequence of the unequal development of like faces. Such crystals, therefore, do not satisfy the geometrical definition of right symmetry relatively to the three principal and the six auxiliary planes mentioned on p. 53 but they do conform to the con- ditions of crystallographic symmetry, requiring like angular position for similar faces. Again, it will be noted that in a combination form many of the faces do not actually meet the axes within the crystal, as, for example, the octahedral face o in Fig. 95. It is still true, however, that this face would meet the axes at equal distances if produced; and since the axial ratio is the essential point in the case of each form, and the actual lengths of the axes are of no importance, it is not necessary that the faces of the different forms in a crystal should be referred to the same actual axial lengths. The above remarks will be seen to apply also to all the other forms and combinations of forms described in the pages following. 58. Tetrahexahedron. The tetrahexahedron (Figs. 104, 105, 106) is bounded by twenty-four faces, each of which is an isosceles triangle. Four of these faces together occupy the position of one face of the cube (hexahe- dron) whence the name commonly applied to this form. The general symbol is (hkQ), hence each face is parallel to one of the axes while it meets the other two axes at unequal distances which are definite multiples of each other. There are two kinds of edges, lettered A and C in Fig. 104; the interfacial angle of either edge is sufficient to determine the symbol of a given form (see below). The angles of some of the common forms are given on a later page (p. 63). * The words truncate, truncation, are used only when the modifying face makes equal with the adjacent similar faces. ISOMETRIC SYSTEM 57 There may be a large number of tetrahexahedrons, as the ratio of the intercepts of the two axes, and hence of h to k varies; for example (410) (310), (210), (320), etc. The form (210) is shown in Fig. 104; (410) in Fig. 105, and (530) in Fig. 106. All the tetrahexahedrons fall in a zone with a cubic face and a dodecahedral face. As h increases relatively to k the form approaches the cube (in which h : k = : 1 or 1 : 0), while as it dimin- ishes and becomes more and more nearly equal to k in value it approaches the dodecahedron; for which h = k. Compare Fig. 105 and Fig. 106; also Figs. 125, 126. The special symbols belonging to each face of the tetra- hexahedron should be carefully noted. 106 107 Tetrahexahedrons 108 109 Cube and Tetrahexa- hedron Octahedron and Tetrahexahedron Dodecahedron and Tetrahexahedron The faces of the tetrahexahedron bevel * the twelve similar edges of the cube, as in Fig. 107; they replace the solid angles of the octahedron by four faces inclined on the edges (Fig. 108;/ = 310), and also the tetrahedral solid angles of the dodecahedron by four faces inclined on the faces (Fig. 109; h = 410). 59. Trisoctahedron. The trisoctahedron (Fig. 110) is bounded by twenty-four similar faces; each of these is an isosceles triangle, and three together occupy the position of an octahedral face, whence the common name. Further, to distinguish it- from the trapezohedron (or tetragonal trisoctahedron), it is sometimes called the trigonal trisoctahedron. There are two kinds of edges, lettered A and B in Fig. 110, and the interfacial angle corresponding to either is sufficient for the determination of the special symbol. * The word bevel is used when two like faces replace the edge of .a form and hence are inclined at equal angles to its adjacent similar faces. 58 CRYSTALLOGRAPHY The general symbol is (hhl)', common forms are (221), (331), etc. Eacn face of the trisoctahedron meets two of the axes at a distance less than unity and the third at the unit length, or (which is an identical expression*) it meets two of the axes at the unit length and the third at a distance greater than unity. The indices belonging to each face should be carefully noted. The normal interfacial angles for some of the more common forms are given on a later page. Ill 112 Trisoctahedron Cube and Trisoctahedron Octahedron and Trisoctahedron 60. Trapezohedron. The trapezohedron f (Figs. 113, 114) is bounded by twenty-four similar faces, each of them a quadrilateral or trapezium. It also bears in appearance a certain relation to the octahedron, whence the name, sometimes employed, of tetragonal trisoctahedron. There are two kinds of edges, lettered B and C, in Fig. 113. The general symbol is hll\ common forms are (311), (211), (322), etc. Of the faces, each cuts an axis at a distance less than unity, and the other two at the unit length, or (again, an identical expression) one of them intersects an axis at the unit length and the other two at equal distances greater than unity. The indices belonging to each face should be carefully noted. The normal interfacial angles for some of the common forms are given on a later page. Another name for this form is icositetrahedron. 61. The combinations of these forms with the cube, octahedron, etc., should be carefully studied. It will be seen (Fig. Ill) that the faces of the trisoctahedron replace the solid angles of the cube as three faces equally inclined on the edges; this is a combination which has not been observed on crystals. The faces of the trapezohedron appear as three equal triangles equally inclined to the cubic faces (Fig. 115). Again, the faces of the trisoctahedron bevel the edges of the octahedron, Fig. 112, while those of the trapezohedron are triangles inclined to the faces at the extremities of the cubic axes, Fig. 119; m(311). Still again, the faces of the trapezohedron n(211) truncate the edges of the dodecahedron (110), as shown in Fig. 118; this can be proved to follow at once from the zonal * Since \a : %b : {c = la : 16 : 2c. The student should read again carefully the ex- planations in Art. 35. t It will be seen later that the name trapezohedron is also given to other solids whose faces are trapeziums conspicuously to the tetragonal trapezohedron and the trigonal trapezohedron. ISOMETRIC SYSTEM 59 relations (Arts. 45, 46), cf. also Figs. 125, 126. The position of the faces of the form m(311), in combination with o, is shown in Fig. 119; with d in Fig. 120. 113 114 Trapezohedrons It should be added that the trapezohedron n(211) is a common form both alone and in combination; m(311) is common in combination. The trisoc- tahedron alone is rarely met with, though in combination (Fig. 112) it is not uncommon. 115 Analcite. Cube and Trapezohedron 118 Analcite. Trapezohedron Garnet. Trapezohedron and and Octahedron Dodecahedron 119 Garnet. Dodecahedron and Trapezohedron Spinel. Octahedron and Trapezohedron Magnetite. Dodecahedron and Trapezohedron 62. Hexoctahedron, The hexoctahedron. Figs. 121, 122, is the gen- eral form in this system; it is bounded by forty-eight similar faces, each of which is a scalene triangle, and each intersects the three axes at unequal 60 CRYSTALLOGRAPHY distances. The general symbol is (hki)\ common forms are s(321), shown in Fig. 121, and (421), in Fig. 122 The indices of the individual faces, as shown in Fig. 121 and more fully in the projections (Figs. 125, 126), should be carefully studied The hexoctahedron has three kinds of edges lettered A, B, C (longer, middle, shorter) in Fig. 122; the angles of two of these edges are needed to fix the symbol unless the zonal relation can be made use of In Fig. 124 the faces of the hexoctahedron bevel the dodecahedral edges, and hence for this form h = k + 1; the form s has the special symbol (321). The hexocta- hedron alone is a very rare form, but it is seen in combination with the cube (Fig 123, fluorite) as six small faces replacing each solid angle. Fig. 124 is common with garnet. 123 Fluorite Cube and Hexoctahedron Garnet Dodecahedron and Hexoctahedron 64. Pseudo-symmetry in the Isometric System. Isometric forms, by development in the direction of one of the cubic axes, simulate tetragonal forms. More common, and of greater interest, are forms simulating those of rhombohedral symmetry by extension, or by flattening; in the direction of an octahedral axis. Both these cases are illustrated later. Conversely, certain rhombohedral forms resemble an isometric octahedron in angle. 65. Stereographic and Gnomonic Projections. The stereographic projection, Fig 125, and gnomonic projection, Fig. 126, show the positions of the poles of the faces of the cube (100), octahedron (111), and dodecahe- dron (110); also the tetrahexahedron (210), the trisoctahedron (221), the trapezohedron (211), and the hexoctahedron (321). ISOMETRIC SYSTEM 61 126 110 010 H Stereographic Projection of Isometric Forms (Cube (100), Octahedron (111), Dodecanedron (110), Tetrahexahedron (210), Trisoctahedron (221), Trapezohedron (211), Hexocta- hedron (321)) Finally, note the prominent zones of planes; for example, the zone between two cubic faces including a dodecahedral face and the faces of all possible tetrahexahedrons. Again, the zones from a cubic face (as 001) through an octahedral face (as 111) passing through the trisoctahedrons, as 113, 112, 223, and the trapezohedrons 332, 221, 331, etc. Also the zone from one dodecahedral face, as 110, to another, as 101, passing through 321, 211, 312, etc. At the same time compare these zones with the same zones shown on the figures already described. A study of the relations illustrated in Fig. 127 will-^e found useful. From it is seen that any crystal face falling in the zone between the cube and dodecahedron must belong to a tetrahexahedron; any face falling in the zone between the cube and octa- hedron must belong to a trapezohedron; and any face falling in the zone between the octahedron and dodecahedron must belong to a trisoctahedron, further any face falling outside these three zones must belong to a hexoctahedron. 62 CRYSTALLOGRAPHY 126 821 321 120 321 Gnomonic Projection of Isometric Forms (Cube (100), Octahedron (111), Dodecahedron (110), Tetrahexahedron (210), Trisoctahedron (221), Trapezohedron (211), Hexocta- hedron (321)) 128 UOO) Symmetry of Pyritohedral class ISOMETRIC SYSTEM 66. Angles of Common Isometric Forms.* TETRAHEXAHEDRONS. 63 Cf. Fig. 104. 410 310 520 210 530 320 430 540 Edge A 210 A 201, 19 45' 25 50* 30 27 36 52} 42 40 46 11} 50 12* 52 251 EdgeC etc. 210 A 120 61 55- 4 53 17^ 46 23; 36 52; 28 4; 22 37; 16 15i 12 40^ Angle on etc. a(100) 14 2}' 18 26 21 48 26 34 30 571 33 41* 36 52} 38 39* Angle on 0(111) 45 33f 43 5} 41 22 39 14 37 37 36 48* 36 4} 35 45* TRISOCTAHEDBONS. /-^ Edge 4\. Edge B Angle on Angle on 221 552 331 772 441 27 16 33 33* 37 511 40 59 43 20* etc. 221 A 221, 50 28| 38 56* 31 35} 26 31* 22 50f 20 21 etc. a(100) 50 14}' 48 11 47 7* 46 30* 46 7* 45 52 0(111) 10 1*' 15 47* 19 28i 22 23 50* 25 14* TRAPEZOHEDRONS. Cf. Fig. 113. 411 722 EdgeB 211 A 2ll, 27 16' 30 43} EdgeC etc 211 A 121, 60 0' 55 501 Angle on etc. a(100) 19 28} 22 Angle on 0(111) 35 15f 32 44 311 35 51 50 281 25 14} 29 291 522 40 45 43 20* 29 291 25 14} 211 48 11* 33 33* 35 151 19 28} 322 58 2 19 45 43 181 11 25} HEXOCTAHEDRONS. , . Edge A EdgeB Edge C Angle on Angle on Ct. Fig. 121. 321 A 312, etc. 321 A 321, etc. 321 A 231, etc. o(100) o(lll) 17 45}' 25 12*' 35 57' 29 12*' 28 f4' 531 27 39* 19 271 27 39* 32 18| 28 331 321 21 47} 31 0^ 21 47} 36 42 22 12* 432 15 5* 43 36f 15 5* 42 11 15 13* 431 32 .12} 22 37f 15 56* 38 191 25 4 2. PYRITOHEDRAL CLASS (2). PYRITE TYPE (Dyakisdodecahedral or Pentagonal Hemihedral Class) 67. Typical Forms and Symmetry. The typical forms of the pyrito- hedral class are the pyritohedron, or pentagonal dodecahedron, Figs. 129, 130, and the d^plo^d, or dyakisdodecahedron, Fig. 135. The symmetry of these forms; as of the class as a whole, is as follows: The three crystallographic axes are axes of binary symmetry only; there are also four diagonal axes of trigonal symmetry coinciding with the octahedral axes. There are but three planes of symmetry; these coincide with the planes of the crystallographic axes and are parallel to the faces of the cube. The stereographic projection in Fig. 128 shows the distribution of the faces of the general form (hkl), diploid, and thus exhibits the symmetry of the class. This should be carefully compared with the corresponding pro- * A fuller list is given in the Introduction to Dana's System of Mineralogy, 1892, pp. xx-xxiii. 64 CRYSTALLOGRAPHY jection (Fig. 91) for the normal class, so that the lower grade of symmetry here present be thoroughly understood. In studying the forms described and illustrated in the following pages, this matter of symmetry, especially in relation to that of the normal class, should be continually before the mind. It will be observed that the faces of both the pyritohedron (Fig. 129) and the diploid (Fig. 135) are arranged in parallel pairs, and on this account these forms have been sometimes called parallel hemihedrons. Further, those authors who prefer to describe these forms as cases of hemihedrism call this type parallel-faced hemihedrism or pentagonal hemihedrism. 68. Pyritohedron. The pyritohedron (Fig. 129) is so named because it is a typical form with the common species, pyrite. It is a solid bounded by twelve faces, each of which is a pentagon, but with one edge (A, Fig. 129) longer than the other four similar edges (C). It 4s often called a pentagonal dodecahedron, and indeed it resembles closely the regular dodecahedron of geometry, in which the faces are regular pentagons. This latter form is, however, an impossible form in crystallography. 129 130 Pyritohedrons Showing Relation between Pyritohedron and Tetra- hexahedron The general symbol is (MO) or like that of the tetrahexahedron of the normal class. Hence each face is parallel to one of the axes and meets the other two axes at unequal distances. Common forms are (410), (310), (210), (320), etc. Besides the positive pyritohedron, as (210), there is also the com- plementary negative form * shown in Fig. 130; the symbol is here (120). Other common forms are (250), (230), (130), etc. The positive and negative pyritohedrons together embrace twenty-four faces, having the same position as the twenty-four like faces of the tetra- hexahedron of the normal class. The relation between the tetrahexahedron and the pyritohedron is shown in Fig. 131, where the alternate faces of the tetrahexahedron (indicated by shading) are extended to form the faces of the pyritohedron. 69. Combinations. The faces of the pyritohedron replace the edges of the cube as shown in Fig. 132; this resembles Fig. 101 but here the faces make unequal angles with the two adjacent cubic faces. On the other hand, when the pyritohedron is modified by the cube, the faces of the latter truncate the longer edges of the pentagons. * The negative forms in this and similar cases have sometimes distinct letters, some- times the same as the positive form, but are then distinguished by a subscript accent, as e(210) and e 4 (120). ISOMETRIC SYSTEM 65 Fig. 133 shows the combination of the pyritohedron and octahedron, and m Fig. 134 these two forms are equally developed. The resulting combina- tion bears a close similarity to the icosahedron, or regular twenty-faced solid of geometry Here, however of the twenty faces, the eight octahedral are equilateral triangles, the twelve others belonging to the pyritohedron are isosceles triangles. 132 Cube and Pyritohedron 134 Octahedron and Pyritohedron Octahedron and Pyritohedron Diploid 70. Diploid. The diploid is bounded by twenty-four similar faces, each meeting the axes at -unequal distances; its general symbol is hence (hkl), and common forms are s(321), 2(421), etc. The form (321) is shown in Fig. 135; the symbols of its faces, as giveii, should be carefully studied. As seen in the figure, the faces are quadrilaterals or trapeziums; moreover, they are grouped in pairs, hence the common name diploid. It is also sometimes called a dyakisdodecahedron. The complementary negative form bears to the positive form of Fig. 135 the same relation as the negative to the positive pyritohedron. Its faces have the symbols 312, 231, 123, in the front octant, and similarly with the proper negative signs in the others. The positive and negative forms together obviously embrace all the faces of the hexoctahedron of the normal class. The diploid can be considered to be derived from the hexoctahedron by the extension of the alternate faces of the latter and the omission of the remaining faces, exactly as in the case of the pyritohedron and tetrahexahedron (Art. 68). In Fig. 136 the positive diploid is shown in combination with the cube. Here the three faces replace each of its solid angles. This combination form resembles that of Fig. Ill, but the three faces are here unequally inclined upon two adjacent cubic faces. Other combinations of the diploid with the cube, octahedron, and pyritohedron are given in Figs. 137 and 138. 71. Other Forms. If the pyritohedral type of symmetry be applied to planes each parallel to two of the axes, it is seen that this symmetry calls for six of these, and the resulting form is obviously a cube. This cube cannot be distinguished geometrically from the cube of the normal class, but it has its own characteristic molecular symmetry. Corresponding to this ijb is com- mon to find cubes of pyrite with fine lines (striations) parallel to the alter- nate edges, as indicated in Fig. 139. These are due to the partial develop- 66 CRYSTALLOGRAPHY ment of pyritohedral faces (210). On a normal cube similar striations, if present, must be parallel to both sets of edges on each cubic face. 136 Cube and Diploid Cube, Octahedron and Diploid Cube, Diploid and Pyritohedron Similarly to the cube, the remaining forms of this pyritohedral class, namely, (111), (110), (hhl), (Ml), have the same geometrical form, respectively, as the octahedron, dodecahedron, the trisoctahedrons and trapezohedrons of the normal class. In molecular structure, however, these forms are distinct, each having the symmetry described in Art. 67. Pyrite. Striated Cube ^ 2> A^g* 68 - The following tables contain the angles of some common forms. PYBITOHEDRONS. Cf. Fig. 129. Edge A 210 A 210, etc. Edge C 210 A 102, etc. 410 28 4J' 76 23|' 310 36 52| 72 32^ 520 43 36 69 49| 210 53 7f 66 25i 530 61 55f 63 49i 320 67 22| 62 30| 430 73 44 61 19 540 650 77 19i 79 36| 60 48i 60 32^ Angle on a(100) 14 2J' 18 26 21 48 26 34 30 57| 33 41 36 52 38 3 39 48 Angle on o(lll) 45 6 33f 43 5| 41 22 39 14 37 37 36 48 36 4i 35 45 35 35f DlPLOIDS. Edge A Edge B Edge C Cf. Fig. 135. 321 A 321, etc. 321 A 321, etc. 321 A 213, etc. 421 51 45|' 25 12' 48 114' 532 58 14| 37 51f 35 20 531 60 56| 19 27f 19 27f 851 63 36f 12 6 53 55i 321 64 37 31 0| 38 12i 432 67 42^ 43 36^ 26 m 431 72 4| 22 37 J 43 3 3. TETRAHEDRAL CLASS (3). TETRAHEDRITE TYPE (Hextetrahedral, Tetrahedral Hemihedral Class) 73. Typical Forms and Symmetry. The typical form of this class, and that from which it derives its name, is the tetrahedron, shown in Figs. bigle on Angle on a(100) 29 12*' 0(111) 28 6*' 35 47f 20 30f 32 18| 32 30| 28 33| 31 34 36 42 22 12| 42 If 15 13* 38 19f 25 4 ISOMETRIC SYSTEM 67 141, 142. There are also three other distinct forms, shown in Figs. 149, 150, 151. The symmetry of this class is as follows. There are three axes of binary symmetry which coincide with the crystallographic axes. There are also four diagonal axes of trigonal symmetry which coincide with the octahedral axes. There are six diagonal planes of sym- metry. There is no center of symmetry. The stereographic projection (Fig. 140) shows the distribution of the faces of the general form (hkl), hextetrahedron, and thus exhibits the symmetry of the class. It will be seen at once that the like faces are all grouped in the alternate octants, and this will be seen to be characteristic of all the forms peculiar to this class. The relation between the sym- metry here described and that of the normal class must be carefully studied. In distinction from the pyritohedral forms whose faces were in parallel pairs, the faces of the tetrahedron and the analogous solids are inclined to each other, and hence they are Symmetry of Tetrahedral Class sometimes spoken of as inclined hemihedrons, and the type of so-called hemi- hedrism here illustrated is then called inclined or tetrahedral hemihedrism. 74. Tetrahedron. The tetrahedron,* as its name indicates, is a four- faced solid, bounded by planes meeting the axes at equal distances. Its general symbol is (lll)_,_and_the_four faces of the positive form (Fig. 141) have the symbols 111, 111, 111, 111. These correspond to four of the faces of the octahedron of the normal class (Fig. 93). The relation between the two forms is shown in Fig. 143. Positive Tetrahedron Negative Tetrahedron Showing Relation between Octahedron and Tetrahedron Each of the four faces of the tetrahedron is an equilateral triangle; the (normal) interfacial angle is 109 29' 16". The tetrahedron is the regular triangular pyramid of geometry, but crystallographically it must be so placed that the axes join the middle points of opposite edges, and one axis is vertical. * This is one of the five regular solids of geometry, which include also the cube, octa- hedron, the regular pentagonal dodecahedron, and the icosahedron; the last two, as already noted, are impossible forms among crystals. 68 CRYSTALLOGRAPHY There are two possible tetrahedrons: the positive tetrahedron (111), designated by the letter o, which has already been described, and the nega- tive tetrahedron, having the_same_geometrica_l form and symmetry, but the indices of its four faces are 111, 111, 111, 111. This second form is shown in Fig. 142; it is usually designated by the letter o,. These two forms are, as stated above, identical in geometrical shape, but they may be distinguished in many cases by the tests which serve to reveal the molecular structure, particularly the etching-figures; also in many cases by pyro-electricity (see under boracite, p. 306), Art. 438. It is probable that the positive and negative tetrahedrons of sphalerite (see that species) have a constant differ- ence in this particular, which makes it possible to distinguish them on crystals from different localities and of different habit. 144 145 146 \/ Positive and Negative Tetrahedrons Cube and Tetrahedron Tetrahedron and Cube If both tetrahedrons are present together, the form in Fig. 144 results. This is geometrically an octahedron when the two forms are equally de- veloped, but crystallographically it is always only a combination of two unlike forms, the positive and negative tetrahedrons, which can be distin- guished as already noted. 147 Tetrahedron and Dodecahedron Boracite. Cube, Dodecahedron with Positive and Negative Tetrahedrons The tetrahedron in combination with the cube replaces the alternate solid angles as in Fig. 145. The cube modifying the tetrahedron truncates its edges as shown in Fig 146. The normal angle between adjacent cubic and tetrahedral faces is 54 44'. In Fig. 147 the dodecahedron is shown modify- fnL -t P l? S ^ 1Ve tet hedr n ' whlle m Fl S- 148 the cube is the predominating form with the positive and negative tetrahedrons and dodecahedron. ISOMETRIC SYSTEM gg 75. Other Typical Forms. - There are three other distinct types of solids in this class, having the general symbols (hhl), (hll), and (hkl) The first of these is shown in Fig 149; here the symbol is 221). There are twelve faces each a quadrilateral belonging to this form, distributed as determined by the tetrahedral type of symmetry. They correspond to twelve of the faces of the trisoctahedron, namely, all those falling in alternate octants I his type of solid is sometimes called a tetragonal tristetrahedron, or a deltoid dodecahedron It does not occur alone among crystals, but its faces are observed modifying other forms Tetragonal Tristetrahedron Trigonal Tristetrahedron Hextetrahedron There is also a complementary negative form, corresponding to the posi- tive form, related to it in precisely the same way as the negative to the posi- tive tetrahedron. Its twelve faces are those of the trisoctahedron which belong to the other set of alternate octants. 152 Tetrahedrite Sphalerite Boracite Another form, shown in Fig. 150, has the general symbol (hll), here (211); it is bounded by twelve like triangular faces, distributed after the type de- manded by tetrahedral symmetry, and corresponding consequently to the faces of the alternate octants of the form (hU) the trapezohedron of the normal class. This type of solid is sometimes called a trigonal tristetrahedron or trigondodecahedron.* It is observed both alone and in combination, * It is to be noted that the tetragonal tristetrahedron has faces which resemble those of the trapezohedron (tetragonal trisoctahedron), although it is related not to this but to the trisoctahedron (trigonal trisoctahedron). On the other hand, the faces of the trigonal tris- tetrahedron resemble those of the trisoctahedron, though in fact related to the trapezo- hedron. 70 CR YST ALLO GR APH Y especially with the species tetrahedrite; it is much more common than the form (hhl). There is here again a complementary negative form. Fig. 152 shows the positive form n(211) with the positive tetrahedron, and Fig. 153 the form m(311) with a(100), o(lll), and d(110). In Fig. 154, the negative form 71X211) is present. The fourth independent type of solids in this class is shown in Fig. 151. It has the general symbol (hkl), here (321), and is bounded by twenty-four faces distributed according to tetrahedral symmetry, that is, embracing all the faces of the alternate octants of the forty-eight-faced hexoctahedron. This form is sometimes called a hextetrahedron or hexakistetrahedron. The complementary negative form (hkl) embraces the remaining faces of the hexoctahedron. The positive hextetrahedron, 0(531), is shown in Fig. 154 with the cube, octahedron, and dodecahedron, also the negative trigonal tristetrahedron n t (2 1 1 ) . 76. If the tetrahedral symmetry be applied in the case of planes each parallel to the two axes, it will be seen that there must be six such faces. They form a cube similar geometrically to the cube both of the normal and pyritohedral class but differing in its molecular structure, as can be readily proved, for example, by pyro-electricity (Art. 438). Similarly in the case of the planes having the symbol (110), there must be twelve faces forming a rhombic dodecahedron bearing the same relation to the like geometrical form of the normal class. The same is true again of the planes having the position expressed by the general symbol (hkQ); there must be twenty-four of them and they together form a tetrahexahedron. In this class, therefore, there are also seven types of forms, but only four of them are geometrically distinct from the corresponding forms of the normal class. 77. Angles. The following tables contain the angles of some com- mon forms : TETRAGONAL TRISTETRAHEDRONS. Cf. Fig. 149. Edge A 221 A 212, etc. Edge B 221 A 212, etc. 332 17 20' 97 50i' 221 27 16 90 552 33 33 84 41 331 37 51f 80 55 TRIGONAL TRISTETRAHEDRONS. Cf. Fig. 150 411 Edge B Edge C 211 A 211, etc. 211 A 121, etc. 3856f 60 0' 722 44 0; 55 50| 311 50 28i 50 28! 522 58 59^ 43 20 211 70 31i 33 33^ 322 86 37i 19 45 HEXTETRAHEDRONS. Angle on o(100) 50 14J' 48 111 47 1\ 46 Angle on o(100) 19 28i' 22 25 14i 29 29| 35 15f 43 18f Angle on o(lll) 10 If 15 47| 19 28| 22 Angle on o(lll) 35 15f ' 32 44 29 29f 25 14 19 28 11 25| Cf. Fig. 151. 531 321 432 431 Edge A 321 A 312, etc. 27 39|' 21 47i 15 5i 32 12J EdgeB EdgeC Angle on Angle on 321 A 312 etc. 321 A 231, etc. o(100) o(lll) 57 7i' 27 39f 32 18f 28 33f r 69 4i 21 47i 36 42 22 124 82 4f 15 5 42 If 15 13* 67 22f 15 56| 38 19| 25 4 ISOMETRIC SYSTEM 71 4. PLAGIOHEDRAL CLASS (4). CUPRITE TYPE. (Pentagonal Icositetrahedral, Plagiohedral Hemihedral Class) 78. Typical Forms and Symmetry. - The fourth class under the iso- metric system is called the plagiohedral or gyroidal class because the faces of the general form (hkl) are arranged in spiral order. This is shown on the stereographic projection, Fig. 155, and also in Figs. 156, 157, which represent the single typ- ical form of the class. These two complemen- tary solids together embrace all the faces of the hexoctahedron. They are distinguished from one another by being called respectively right- handed and left-handed pentagonal icositetra- hedrons. The other forms of the class are geometrically like those of the normal class. The symmetry characteristic of the class in general is as follows: There are no planes of symmetry and no center of symmetry. There are, however, three axes of tetragonal symmetry normal to the cubic faces, four axes of trigonal symmetry normal to the octahedral faces, and six axes of binary symmetry normal to the faces of the dodecahedron. In other words, it has all the axes of symmetry of the normal class while without planes or center of symmetry. Symmetry of Plagiohedral Class 156 168 Right and Left-handed Pentagonal Icositetrahedrons Cuprite 79. It is to be noted that the two forms shown in Figs. 156, 157 are alike geometrically, but are not superposable; in other words, they are related to one another as is a right- to a left-hand glove. They are hence said to be enantiomorphous, and, as explained elsewhere, the crystals belonging here may be expected to show circular light polarization. It will be seen that the complementary positive and negative forms of the preceding classes, unlike those here, may be superposed by being rotated 90 about one of the crystallographic axes. This distinction between positive and negative forms, and between right- and left-handed enantiomorphous forms, exists also in the case of the classes of several of the other systems. This class is rare among minerals; it is represented by cuprite, sal am- 72 CR YSTALLO GR APH Y moniac, sylvite, and halite. It is usually shown by the distribution of the small modifying faces, or by the form of the etching figures. Fig. 158 shows a crystal of cuprite from Cornwall (Pratt) with the form 2(13' 10' 12). 5. TETARTOHEDRAL CLASS (5). ULLMANNITE TYPE. (Tetrahedral Pentagonal Dodecahedral Class) 80. Symmetry and Typical Forms. The fifth remaining possible class under the isometric system is illustrated by Fig. 160, which represents the twelve-faced solid corresponding to the general symbol (hkl). The distri- bution of its faces is shown in the projection, Fig. 159. This form is sometimes called a tetrahedral-pentagonal dodecahedron. It is seen to have one-fourth as many faces as the form (hkl) in the normal class, hence there are four similar solids which together embrace all the faces of the hexoctahedron. These four solids, which are distinguished as right-handed (positive and negative) and left-handed (posi- circular polarization. The remaining forms of the class are (besides the cube and rhombic Symmetry of Tetartohedral Class dodecahedron) the tetrahedrons, the pyritohe- drons, the tetragonal and trigonal tnstetrahe- drons; geometrically they are like the solids of the same names already described. This class has no plane of symmetry and no center of symmetry. There are three axes of binary symmetry normal to the cubic faces, and four axes of trigonal symmetry normal to the faces of the tetrahedron. 160 This group is illustrated by artificial crystals of barium nitrate, stron- tium nitrate, sodium chlorate, etc. Further, the species ullmannite, which shows sometimes pyritohedral and again tetrahedral forms, both having the same composition, must be regarded as belonging here. MATHEMATICAL RELATIONS OF THE ISOMETRIC SYSTEM 81. Most of the problems arising in the isometric system can be solved at once by the right-angled triangles in the sphere of projection (Fig. 125) without the use of any special formulas. ISOMETRIC SYSTEM 73 It will be remembered that the angles between a cubic face, as 100, and the adjacent face of a tetrahexahedron, 310, 210, 320, etc can be obtained at once, since the > tangent ' of this angle is equal to ->->-> or in general r o 6 h tan (hkO A 100) = ~ 162 ac 6c Z k = 1 ft = 2 c = 90 Z a&c (100) A (210) = 26 34' This relation is illustrated in Fig. 162, which also shows the method of graphically determining the indices of a tetrahexahedron, the angle between one of its faces and an adjacent cube face being given. Since all the forms of a given symbol under different species have the same angles, the tables of angles already given are very useful. These and similar angles may be calculated immediately from the sphere, or often more simply by the formulas given in the following article. 82. Formulas. (1) The distance of the pole of any face P(hkl) from the cubic faces is given by the following equations. Here Pa is the distance between (hkl) and (100); Pb is the distance between (hkl) and (010); and PC that between (hkl) and (001). These equations admit of much simplification in the various special cases, for (hkQ), (hfd), etc.: (2) The distance between the poles of any two faces P(hkl) and Q(pqr) is given by the following equation, which in special cases may also be more or less simplified: hp + kq+ Ir cosPQ (p* (3) The calculation of the supplement interfacial or normal angles for the several forms may be accomplished as follows: Trisoctahedron. The angles A and B are, as before, the supplements of the interfacial angles of the edges lettered as in Fig. 110. V + 2hl. 9/,2_/2 cos A = , 2 , 2 , cos B = For the tetragonal-tristetrahedron (Fig. 149), cos B = Trapezohedron (Fig. 113). B and C are the supplement angles of the edges as lettered in the figure. cos B = T0 , ^ 70 J cos C For the trigonal-tristetrahedron (Fig. 150), cos B = Tetrahexahedron (Fig. 104). cos A = , 2 . ^ 2 >* cos C = 74 CR YST ALLO GR APH Y h 2 k 2 hk Forthepyritohedron(Fig. 129), cos A = ^ 2 _^_ fc2 >' cos C = ^rqrp* Hexoctahedron (Fig. 122). - I 2 cos A = / + y;v ^ B = ; 2 ;^ + ; 8 ; c OS c = /;y; p - For the diploid (Fig. 135), cos A - M , M , n ; cos C = ,, For the hextetrahedron (Fig. 151), cos B = h 2 - 2kl h 2 + k 2 + I 2 83. To determine the indices of any face (fcfel) of an isometric form, given the posi- tion of its pole on the stereographic projection. As an illustrative example of this problem the hexoctahedron (321) has been taken, It is assumed that the angles 100 A 321 = 36 42' ISOMETRIC SYSTEM 75 and 111 A 321 = 22 12' are given. The methods by which the desired pole is located from these measurements have been described on page 38 and are illustrated in Fig. 163. Having located the pole (hkl) a line is drawn through it from the center O of the projec- tion. This line O-P represents the intersection with' the horizontal plane (which is the plane of the horizontal crystal axes, a and 6) of a plane which is normal to the crystal face (hkl) . Since two planes which are at right angles to each other will intersect a third plane in lines that are at right angles to each other, it follows that the plane of the hexoctahedral face will intersect the plane of the horizontal axes in a line at right angles to O-P. If, therefore, the distance 0-M be taken as representing unity on the a axis and the line M-P-N be drawn at right angles to O-P the distance 0-N will represent the intercept of the face in question upon the 6 axis. 0-N is found in this case to be f 0-M in value. The intercepts upon the two horizontal axes are, therefore la, |6. The plotting of the intercept upon the c axis is shown in the upper left hand quadrant of the figure. The angular distance from to the pole (hkl) is measured by the stereographic protractor as 74 30'. This angle is then laid off from the line representing the c axis and the line repre- senting the pole (hkl) is drawn. The distance O-P. is transferred from the lower part of the figure. Then we can construct the right triangle, the vertical side of which is the c axis, the horizontal side is this line O-P (the intersection of the plane which is normal to the crystal face with the horizontal plane) and the hypothenuse is a line lying in the face and therefore at right angles to the pole of the face. This line would intersect the c axis at a distance equal to 30-M. The same relation may be shown by starting this last line from a point on the c axis which is at a distance from the center of the figure equal to 0-M. In this case the intercept on the horizontal line O-P would be at one third its total length. By these constructions the parameters of the face in question are shown to be la, |6, 3c, giving (321) as its indices. 84. To determine the indices of the faces of teometac their poles on the gnomonic projection. - As an illustrative m 2 lower right hand quadrant of the gnomonic projection of ^ometric forn^ Fig 126 been taken and reproduced in Fig. 164. The lines O-M and ( re at ""* each other and may represent the horizontal ?3^^^^^ pole of the projection lines are drawn perpendicular to ^ these two axial seen that the intercepts made upon these lines have rational relations to 76 CRYSTALLOGRAPHY since we are dealing with the isometric system in which the crystallographic axes are all alike and interchangeable with each other, it follows that the different intercepts upon O-M and O-N are identical. The distance O-R (i.e. the distance from the center to the 45 point of the projection) must equal the unit length of the axes. That this is true is readily seen by the consideration of Fig. 165. The intercepts of the lines drawn from the different poles to the lines O-M and O-N are found to be |, 5, f, 1, |, 2 and 3 times this unit distance. To find the Miller indices of any face represented, it is only necessary to 165 Plane of Gnomonic Projection take the intercepts of the two lines drawn from its pole upon the two axes a\ and ct 2 , place these numbers in their proper order and add a 1 as a third figure and then if necessary clear of fractions. Take for exa'mple the hexoctahedrqn face with indices 312. The lines drawn from its pole intercept the axes at lai and a 2 , which gives the expression | \ 1, which, again, on clearing of fractions, yields 312, the indices of the face in question. In the case of a face parallel to the vertical axis, the pole of which lies at infinity on the gnomonic projection, the indices may be obtained by taking any point on the radial line that points to the position of the pole and dropping perpendiculars to the lines representing the two horizontal axes. The relative intercepts formed upon these axes will give the first two numbers of the required indices while the third number will necessarily be 0. TETRAGONAL SYSTEM 77 II. TETRAGONAL SYSTEM 85. THE TETRAGONAL SYSTEM includes all the forms which are referred to three axes at right angles to each other of which the two horizontal axes are equal to each other in length and interchangeable and the third, the vertical axis, is either shorter or longer. The horizontal axes are desig- nated by the letter a; the vertical axis by c (see Fig. 166). The length of the vertical axis expresses properly the axial ratio of a : c, a being uniformly taken as equal to unity. The axes are orientated and their opposite ends designated by plus and minus signs exactly as in the case of the Isometric System. Seven classes are embraced in this system. Of these the normal class is common and important among minerals; two others have several represen- tatives, and another a single one only. It may be noted that in four of the classes the vertical axis is an axis of tetragonal symmetry; in the remaining three it is an axis of binary symmetry only. 1. NORMAL CLASS (6). ZIRCON TYPE (Ditetragonal Bipyramidal or Holohedral Class) 86. Symmetry. The forms belonging to the normal class of the tetragonal system (cf . Figs. 170 to 192) have one principal axis of tetragonal symmetry (whence name of the system) which coincides with the vertical crystallographic axis, c. There are also four horizontal axes of binary sym- metry, two of which coincide with the horizontal crystallographic axes while the other two are diagonal axes bisecting the angles between the first two. 166 167 eta Axes of Tetragonal Mineral, Octahedrite a : c = 1 : 178 Symmetry of Normal Class Tetragonal System Further they have one principal plane of symmetry, the plane of the horizontal crystallographic axes. There are also four vertical planes of symmetry which pass through the vertical crystallographic axis c and make angles of 45 with each other. Two of these latter planes include the hori- zontal crystallographic axes and are known as axial planes of symmetry. The other two are known as diagonal planes of symmetry. 78 CRYSTALLOGRAPHY The axes and planes of symmetry are shown in Figs. 168 and 169. The symmetry and the distribution of the faces of the general form, hkl, is shown in the stereographic projection, Fig. 167. 87. Forms. The various possible forms under the normal class of this system are as follows: Symbols 1. Base or basal pinacoid (001) 2. Prism of the first order (110) 3. Prism of the second order (100) 4. Ditetragonal prism (hkO) as, (310) ; (210) f (320), etc. 5. Pyramid of the first order (hhl) as, (223); (111); (221), etc. 6. Pyramid of the second order (hQl) as, (203) ; (101) ; (201), etc. 7. Ditetragonal pyramid (hkl) as, (421); (321); (122), etc. 168 169 Symmetry of Normal Class, Tetragonal System 88. Base or Basal Pinacoid. The 6ase is that form which includes the two similar faces which are parallel_to the plane of the horizontal axes. These faces have the indices 001 and 001 respectively; it is an "open form," as they do not inclose a space, consequently this form can occur only in com- bination with other forms. Cf. Figs. 170-173, etc. This form is always lettered c in this work. 170 OQL 4- i 171 172 no First Order Prism 001 100 010 Second Order Prism First and Second Order Prisms 89. Prisms. Prisms, in systems other than the isometric, have been defined to be forms whose faces are parallel to the vertical axis (c) of the crystal, while they meet the two horizontal axes; in this system the four- faced form whose planes are parallel both to the vertical and one horizontal TETRAGONAL SYSTEM 79 axis is also called a prism. There are hence three types of prisms here included. 90. Prism of First Order. The prism of the first order includes the four faces which, while parallel to the vertical axis, meet the horizontal axes at equal distances; its general symbol is consequently (110). It is a square prism, with interfacial angles of 90. It is shown in combination with the base in Fig. 170. It is uniformly designated by_the letter m. The in- dices of its faces, taken in order, are 110, 110, 110, 110. 91. Prism of Second Order. The prism of the second order shown* in combination with the base in Fig. 171 includes the four faces which are parallel at once to the vertical and to a horizontal axis; it has, therefore, the general symbol (100). It is a square prism with an angle between any two adjacent faces of 90. It is uniformly designated by _the letter a, and its faces, taken in order, have the indices 100, 010, 100, 010. It will be seen that the combination of this form with the base is the analogue of the cube of the isometric system. The faces of the prism of the first order truncate the edges of the prism of the second order and vice versa. When both are equally developed, as in Fig. 172, the result is a regular eight-sided prism, which, however, it must be remembered, is a combination of two distinct forms. It is evident that the two prisms described do not differ geometrically from one another, and furthermore, in a given case, the symmetry of this class allows either to be made the first order, and the other the second order, prism according to the position assumed for the horizontal axes. If on crys- tals of a given species both forms occur together equally developed (or, on the other hand, separately on different crystals) and without other faces than the base, there is no means of telling them apart unless by minor char- acteristics, such as striations or other markings on the surface, etchings, etc. 92. Ditetragonal Prism. The ditetragonal prism is the form which is bounded by eight similar faces, each one of which is parallel to the vertical axis while meeting the two horizontal axes at unequal distances. It has the general symbol (hkQ). It is shown in Fig. 173, where (hkO) = (210). The successive faces_ have here the indices 210, 120, 120, 210, 210, 120, 120, 210. In Fig. 185 a combination is shown of this form (y = 310) with the second order prism, the edges of which it bevels. In Fig. 189 (h = 210) it bevels the edges of the first order prism m. In Fig. 190 (I = 310) it is combined with both Ditetragonal Prism orders of prisms. 93. Pyramids. There are three types of pyramids in this class, cor- responding, respectively, to the three prisms which have just been described. * In Figs. 170-173 the dimensions of the form are made to correspond to the assumed length of the vertical axis (here c = 178 as in octahedrite) used in Fig. 177. It must be noted, however, that in the case of actual crystals of these forms, while the tetragonal symmetry is usually indicated by the unlike physical character of the face c as compared with the faces a, m, etc., in the vertical prismatic zone, no inference can be drawn as to the relative length of the vertical axis. This last can be determined only when a pyramid is present; it is fixed for the species when a particular pyramid is chosen as fundamental or unit form, as explained later. 173 001 | i_ ~z* 4 210 fl 120 -210 ^^^ \ -U *' 80 CRYSTALLOGRAPHY As already stated, the name pyramid is given (in systems other than the iso- metric) to a form whose planes meet all three of the axes; in this system the form whose planes meet the axis c and one horizontal axis while parallel to the other is also called a pyramid. The pyramids of this class are strictly double pyramids (bipyramids of some authors). 94. Pyramid of First Order. A pyramid of the first order, is a form whose eight similar faces intersect the two horizontal axes at equal distances and also intersect the vertical axis. It has the general symbol (hhl). It is a square pyramid with equal interfacial angles over the terminal edges, and the faces replace the horizontal, or basal, edges of the first order prism and the solid angles of the second order prism. If the ratio of the vertical to the horizontal axis for a given first order pyramid is the assumed axial ratio for the species, the form is called the fundamental form, and it has the symbol (lll)_as in_Fig. 174. The indices of its_faces_ me oned in order are: Above 111, 111, 111, 111; below 111, 111, 111, 111. 175 176 177 in in First Order Pyramid Zircon, First Order Prism and Pryamid Zircon, First Order Prism and Pyramids Apophyllite, Second Order Prism and First Order Pyramid Obviously the angles of the first order pyramid, and hence its geometrical aspect, vary widely with the length of the vertical axis. In Figs. 174 and 182 the pyramids shown have in both cases the symbol (111) but in the first case (octahedrite) c = 1.78, while in the second (vesuvianite), c = 0.64. For a given species there may be a number of second order pyramids, varying in position according to the ratio of the intercepts upon the vertical and horizontal axes. Their symbols, passing from the base (001) to the unit prism (110), may thus be (115), (113), (223), (111), (332), (221), (441), etc. In the general symbol of these forms (hhl), as h diminishes, the form approx- imates more and more nearly to the base (001), for which h = 0- as h in- creases, the form passes toward the first order prism. In Fig. 176 two pvra- mids of this order are shown, p(lll) and w(331). 95. Pyramid of Second Order. The pyramid of the second order is the iorm, .big. 178, whose faces are parallel to one of the horizontal axes while meeting the other two axes. The general symbol is (hOl) . These faces replace the basal edges of the second order prism (Fig. 179), and the solid angles of the first order prism (cf. Fig. 180). It is a square pyramid since its' basal section is a square, and the interfacial angles over the four terminal TETRAGONAL SYSTEM 81 edges, above and below, are equal. The successivejaces of the form (101) are as follows: Above 101, Oil, 101, Oil; below 101, Oil, 101, Oil. If the ratio of the intercepts on the horizontal and vertical axes is the assumed axial ratio of the species, the symbol is (101), and the form is desig- nated by the letter e. This ratio can be deduced from the measurement of either one of the interfacial angles (y or z, Fig. 178) over the terminal or basal edges, as explained later. In the case of a given species, a number of second 180 Second Order Pyramid Second Order Prism and Pyramid Rutile, First and Second Order Prisms and Pyra- mids order pyramids may occur, varying in the ratio of the axes a and c. Hence there is possible a large number of such forms whose symbols may be, for example, (104), (103), (102), (101), (302), (201), (301), etc. Those men- tioned first come nearest to the base (001), those last to the second order prism (100); the base is therefore the limit of these pyramids (hQl) when h = 0, and the second order prism (100) when h = 1 and I = 0. Fig. 186 shows the three second order pyramids w(105), 6(101), g(201). 182 183 Vesuvianite First Order Prism, Pyramid and Base Vesuvianite First Order Pyramid and First and Scond Order Prisms Cassiterite First and Second Order Pyramids A second order pyramid truncating the pyramidal edges of a given first order pyramid as in Fig. 183 has the same ratio as , it Jor >h to I Thus ( truncates the terminal edge of (111); (201) of (221), etc. This is obvious because each face has the same position as the corresponding edge of the other form (see Fig. 183, when - 111 and e = 101; also Figs. 186, 191, where r = 115, u = 105). Again, if a first order pyramid truncates the pyramidal edges of a given second order pyramid, its ratio for h to I is half 82 CRYSTALLOGRAPHY that of the other form; that is, (112) truncates the pyramidal edges of (101); (111) of (201), etc. This relation is exhibited by Fig. 186, where p(lll) truncates the edges of 0(201). In both cases the zonal equations prove the relations stated. 186 184 185 m Vesuvianite First and Second Order Prisms, First Order Pyr- amid and Base Apophyllite Second Order Prism, Dite- tragonal Prism, First Order Pyramid and Base Octahedrite Two First Order Pyra- mids, First Order Prism, Three Second Order Pyramids and Base 96. Ditetragonal Pyramid. The ditetragonal pyramid, or double eight- sided pyramid, is the form each of whose sixteen similar faces meets the three axes at unequal distances. This is the most general case of the symbol (hkl), where h, k, I are all unequal and no one is equal to 0. That there are sixteen faces in a single form is evident. Thus, for example, for the form (212) the face 212 is similar to 122, the two lateral axes being equal (not, however, to 221). Hence there are two like faces in each octant. Similarly the indices of all the faces in the successive octants are, therefore, as follows: Above 212 122 122 212 212 122 122 212 Below 212 122 122 212 212 122 122 212 187 188 189 190 Ditetragonal Pyramid Zircon Cassiterite Rutile First and Second Order Prisms, First Order Pyramid, Ditetrag- onal Pyramid This form is common with the species zircon, and is hence often called a zirconoid. It is shown in Fig. 187- It is not observed alone, though some- TETRAGONAL SYSTEM 83 times, as in Figs. 188 (x = 311) and 189 (z = 321), it is the predominating form. In Fig. 190 two ditetragonal pyramids occur, namely, /(313) and Z\OZ\.), -g- 97. In addition to the perspective figures already given, a basal projection (Fig. 191) is added of the crystal of octahedrite already referred to (Fig. 186) ; also a stereographic (Fig. 192) and gnomonic (Fig. 193) projections of the same with the faces of the forms w(22l) and $(313) added. These exhibit well the general relations of this normal class of the tetragonal system. The symmetry here is to be note tt is more Convenient to use a formula 113. Formulas. It is sometimes convenient to have the normal interfacial angles expressed directly in terms of the axis c and the indices h, k, and I Thus ' the pole 223, and the calculated angle 313 A 223 is half the angle 313 A 133 If a laree given bek>w r ^ "* tO ** Calculated > tt is more Convenient to use a formula These may also be expressed in the form P& = |Ti ', tan 2 PC '- <- /C 2 C 2 2 (2) For the distance between the poles of any two faces (hkl), (pqr), we have in general cos PQ = : -^ v [(# + k 2 )c 2 + I 2 ] [(p 2 -f o 2 )c 2 + r z ] The above equations take a simpler form for special cases often occurring; for example, for hkl and the angle of the edge y of Fig. 187. 114. Prismatic Angles. The angles for the commonly occurring ditetragonal prisms are as follows* Angle on Angle on Angle on Angle on 0(100) w(110) o(100) w(llO) 410 14 21' 3057f 530 30 57*' 14 21' 310 18 26 26 34 320 33 41J 11 18| 210 26 34 18 26 430 36 521 8 7| 115. To determine, by plotting, the axial ratio, a : c, of a tetragonal mineral from the stereographic projection of its crystal forms. As an illustrative example it has been assumed that the angles between the faces on the crystal of rutile, represented in Fig 180, have been measured and from these measurements the poles of the faces in one octant located on the stereographic projection, see Fig. 215. In determining the axial ratio of a tetragonal crystal (or what is the same thing, the length of the c axis, since the length of the a axes are always taken as equal to 1) it is necessary to assume the indices of some pyramidal form. It is customary to take a pyramid which is prominent upon the crystals of the mineral and assume that it is the fundamental or unit pyramid of either the first or second order and has as its symbol either (111) or (101). In the example chosen both a first order and a second order pyramid are present and from their zonal relations it is evi- dent that if the symbol assigned to the first order form be (111) that of the second order form must be (101), In order to determine the relative length of the c axis in respect to the length of the a axis for rutile therefore, it is only necessary to plot the intercept of either of these forms upon the axes. In the case of the second order pyramid it is only necessary to construct a right angle triangle (see upper left hand quadrant of Fig. 215) in which the horizontal side shall equal the length of the a axis, (1), the vertical side shall represent the c axis and the hypothenuse shall show the proper angle of slope of the face. The angle between the center of the projection and the pole e(101) is measured by the stereographic protractor and a line drawn making that angle with the line representing the c axis. The hypothenuse of the triangle must then be at right angles to this pole. Its intercept upon the vertical side of the triangle, when expressed in relation to the distance (0-M) which was chosen as representing unity on the a axis, will therefore give the length of the c axis. In rutile this is found to be 0.644. The same value is obtained when the position of the pyramid of the first order s(lll) is used. In this case the line M-P-N is first drawn at right angles to the radial line 0-P drawn through the pole s(lll). The triangle to be plotted in this case has the distance O-P as the length of its horizontal side. Its hypothenuse must be at right angles to the line representing the pole to (111). The intercept on the c axis is the same as in the first case. CRYSTALLOGRAPHY 216 H010 TETRAGONAL SYSTEM 93 116. To determine, by plotting, the indices of any face (hkl) of a tetragonal form from the position of its pole on the stereographic projection. The solution of this problem is like that given in a similar case under the -Isometric System, see p. 74, except that the intercept of the face on the vertical axis must be referred to the established unit length of that axis and not to the length of the a axis. The method is exactly the reverse of the one used in the problem discussed directly above. 117. To determine, by plotting, the axial ratio, a : c, of a tetragonal mineral from the gnomonic projection of its crystal forms. As an illustrative example consider the crystal of rutile, Fig. 180, the poles to the faces of which, are shown plotted in gnomonic projec- tion in Fig. 216. The pyramids of the first and second order present are taken as the unit forms with the symbols, s(lll) and e(101). The lines O-M and O-N represent the two horizontal axes a\ and az and the distance from the center O to the circumference of the fundamental circle is equal to unity on these axes. The intercepts on O-M and O-N made by the poles of e (101) or the perpendiculars drawn from the poles of s(lll) give the unit length of the vertical axis, c. In this case this distance, when expressed in terms of the assumed length of the horizontal axes (which in the tetragonal system always equals 1) is equal to 0.64. That the above relation is true is -obvious from a consideration of Fig. 216. This rep- resents a vertical section through the spherical and gnomonic projection including the horizontal axis, 02. The slope of the face e(011) is plotted with its intercepts on the a 2 and c axes and the position of its pole in both the spherical and gnomonic projections is shown. It is seen through the two similar triangles in the figure that the distance from the center to the pole e(011) in the gnomonic projection must be the same as the intercept of the face e upon the vertical axis c. And as e is a unit form this must represent unity on c. 118. To determine, by plotting, the indices of any face of a tetragonal form from the position of its pole on the gnomonic projection. It is assumed that in this case a mineral is being considered whose axial ratio is known. Un- 217 der these conditions draw perpendiculars from the pole in question to the lines representing the two horizontal axes. Then space off on these lines distances equivalent to the length of the c axis, remem- bering that it must be expressed in terms of the length of the horizontal axes which in turn is equal to the distance from the center of the projection to the circumference of the fundamental circle. Give the intercepts of the lines drawn from the pole of the face to the axes a\ and a 2 in terms of the length of the vertical axis, add a 1 as the third figure and if necessary clear of fractions and the required indices are the result. This is illustrated in Fig. 217, which is the lower right hand quadrant of the gno- monic projection of the forms shown on the rutile e dttetragonal pyramid ,(321), Perpendiculars drawn from its pole .interact as - h sr 94 CRYSTALLOGRAPHY the indices of the face in question. The indices of a prism face like (310) can be readily obtained in exactly the same manner as described under the Isometric System, Art. 84. p. 75. III. HEXAGONAL SYSTEM 119. The HEXAGONAL SYSTEM includes all the forms which are referred to four axes, three equal horizontal axes in a common plane intersecting at angles of 60, and a fourth, vertical axis, at right angles to them. Two sections are here included, each embracing a number of distinct classes related among themselves. They are called the Hexagonal Division and the Trigonal (or Rhombohedral) Division. The symmetry of the former, about the vertical axis, belongs to the hexagonal type, that of the latter to the trigonal type. Miller (1852) referred all the forms of the hexagonal system to three equal axes parallel to the faces of the fundamental rhombohedron, and hence intersecting at equal angles, not 90. This method (further explained in Art. 169) had the disadvantage of failing to bring out the relationship between the normal hexagonal and tetragonal types, both characterized by a principal axis of symmetry, which (on the system adopted in this book) is the vertical crystallographic axis. It further gave different symbols to faces which are crystallq- graphically identical. It is more natural to employ the three rhombohedral axes for tri- gonal forms only, as done by Groth (1905), who includes these groups in a Trigonal System; but this also has some disadvantages. The indices commonly used in describing hexagonal forms are known as the Miller-Bravais indices, since they were adopted by Bravais for use with the four axes from the scheme used by Miller in the other crystal systems. 120. Symmetry Classes. There are five possible classes in the Hex- agonal Division. Of these the normal class is much the most important, and two others are also of importance among crystallized minerals. In the Trigonal Division there are seven classes; of these the rhombo- hedral class or that of the Calcite Type, is by far the most common, and three others are also of importance. 121. Axes and Symbols. The position of the four axes taken is shown in Fig. 218; the three horizontal axes are called a, since they are equal and Interchangeable, and the vertical axis is c, since it has a different length, 218 being either longer or shorter than the horizontal axes. The length of the vertical axis is expressed in terms of that of the horizontal axes which in turn is always taken as unity. Further, when it is de- sirable to distinguish between the horizontal axes they may be designated i, a 2 , a 3 . When properly orientated one of the horizontal axes (a 2 ) is par- allel to the observer and the other two make angles of 30 either side of the line perpendicular to him. The axis to the left is taken as ai, the one to the right as a 3 . The positive and negative ends Hexagonal Axes of ^ e axes are shown in Fig. 218. The general position of any plane may be expressed in a manner analogous to that applicable in the other systems, viz.- 1111 h^'-k^'-i"*''!*' . ; The corresponding indices for a given plane are then h, k, i, I; these always refer to the axes named in the above scheme. Since it is found convenient HEXAGONAL SYSTEM 95 to consider the axis a 3 as negative in front and positive behind, the general symbol becomes hkll. Further, as following from the angular relation of the three horizontal axes, it can be readily shown to be always true that the algebraic sum of the indices h, k f i. is equal to zero: h + k + i = 0. A. Hexagonal Division 1. NORMAL CLASS (13). BERYL TYPE (Dihexagonal Bipyramidal or Holohedral Class) 122. Symmetry. Crystals belonging to the normal class of the Hex- agonal Division have one principal axis of hexagonal, or sixfold, symmetry, which coincides with the vertical crystallographic axis; also six horizontal axes of binary symmetry; three of these coincide with the horizontal crystal- lographic axes, the others bisect the angles between them. There is one principal plane of symmetry which is the plane of the horizontal crystallo- graphic axes and six vertical planes of symmetry 219 which meet in the vertical crystallographic axis. Three of these vertical planes include the hori- zontal crystallographic axes and the other three bisect the angles between the first set. The symmetry of this class is exhibited in the accompanying stereographic projection, Fig. 219, and by the following crystal figures. The analogy between this class and the normal class of the tetragonal system is obvious at once and will be better appreciated as greater familiarity is gained with the indi- vidual forms and their combinations. 123. Forms. - The possible forms in this of Normal claas class are as follows: MUler-Bravaia. 1. Base (0001) 2. Prism of the first order (1010) 3. Prism of the second order (1120) 4. Dihexagonal prism (hkiG) as, (2130) 5. Pyramid of the first order (M)W)_as, (1011); (2021) etc. 6. Pyramid of the second order (h-h-Zh-l) as, (1122) 7. Dihexagonal pyramid (ftM) as, (2131) In the above h > k, and h + k = i. 124. Base. The base, or basal pinacoid, includes the two faces, 0001 and OOOT, parallel to the plane of the horizontal axes. It is uniformly d nated by the letter c; see Fig. 220 et seq. . 125, Prism of the First Order. There are three types of prisms, or forms in which the faces are parallel to the vertical axis. 96 CRYSTALLOGRAPHY The prism of the first order. Fig. 220, includes six faces, each one of which is parallel to the vertical axis and meets two adjacent horizontal axes at equal distances, while i^is parallel to the third horizontal axis. It has hence the general symbol (1010) and is uniformly designated by the letter m; the indices of its six faces taken in order (see Figs. 220 and 229, 230) are: 10TO, OlTO, TlOO, 1010, 0110, lIOO. 221 220 a. J^- 0001 V, r i i ; i iiu If -n<: 10 0, r,, ^ r _. 2110 T<~~ i 1120 --1210 First Order Prism Second Order Prism Dihexagonal Prism 126. Prism of the Second Order. The prism of the second order, Fig. 221, has six faces, each one of which is parallel to the vertical axis, and meets the three horizontal axes, two alternate axes at the unit distance, the intermediate axis at one-half this distance; or, which is the same thing, it meets the last-named axis at the unit distance, the others at double this distance.* The general symbol is (1120) and it is uniformly designated by the letter a; the indices of the six faces (see Figs. 221 and 229, 230) in order are: 1120, 1210, 2110, 1120, 1210, 2110. The first and second order prisms are not to be distinguished geometric- ally from each other since each is a regular hexagonal prism with normal interfacial angles of 60. They are related to each other in the same way as the two prisms ra(110) and a(100) of the tetragonal system. The relation in position between the first order prism (and pyramids) on the one hand and the second order prism (and pyramids) on the other will be understood better from Fig. 223, repre- senting a cross section of the two prisms parallel to the base c. 127. Dihexagonal Prism. The dihexagonal prism, Fig. 222, is a twelve-sided prism bounded by twelve faces, each one of which is parallel to the vertical axis, and also meets two adjacent horizontal axes at unequal distances, the ratio of which always lies between 1 : 1 and 1:2. This prism has two unlike_ edges, lettered x and y, as shown in Fig. 222. The general symbol is (hkzO) and the indices of the faces of a given form, as (2130), are: * Since lai : la-j : |a 3 : a> c is equivalent to 2ai : 2a 2 : Ia 3 : HEXAGONAL SYSTEM 97 2130, 1230, 1320, 2310, 3210, 3120, 2130, 1230, 1320, 2310, 32lO, 3l20. 128. Pyramids of the First Order. Corresponding to the three types of prisms just mentioned, there are three types of pyramids A pyramid of the first order, Fig. 224, is a double six-sided pyramid (or bipyramid) bounded by twelve similar triangular faces six above and six below which have the same position relative to the horizontal axes as the faces of the first order prism, while they also intersect the vertical axis above and below. The general symbol is hence (hOhl). The faces of a given form, as 1011), are: Above 1011, 0111, 1101, 1011, 0111, 1101. Below 1011, 0111, 1101,, 1011, 0111, lIOl. On a given species there may be a number of pyramids of the first order, differing in the ratio of the intercepts on the horizontal to the vertical axis, and thus forming a zone between the base (0001) and the faces of the unit prism (1010). Their symbols, passing from the base (0001) tojthe unit prism (1010), would be, for example, 1014, 1012, 2023, 1011, 3032, 2021, etc. In Fig. 228 the faces p_and u are first order pyramids and they have the symbols respectively (1011) and (2021), here c = 0.4989. As shown in these cases the faces of the first order pyramids replace the edges of the first order prism. On the other hand, they replace the solid angles of the second order prism a(112Q). 224 226 First Order Pyramid Second Order Pyramid Dihexagonal Pyramid 129. Pyramids of the Second Order. The pyramid of the second order (Fig. 225), is a double six-sided pyramid including the twelve similar faces which have the same position relative to the horizontal axes as the faces of the second order prism, and which also intersect the vertical axis. They have the general symbol (h'h-2h-l). The indices of the faces of the form (1122) are: Above 1122, 1212, 2112, 1122, 1212, 2112. Below 1122, 1212, 2112, 1122, 1212, 2112. The faces of the second order pyramid replace the edges between the faces of the second order prism and_the base. Further, they replace the solid angles of the first order prism m(1010). There may be on a single crystal: a .num- ber of second order pyramids forming a zone between the base c(0( 98 CRYSTALLOGRAPHY the faces_of the second order prism a(1120), as, naming them in order: JL 124, 1122, 2243, 1121, etc. In Fig. 227, s is the second order pyramid (1121). 130. Dihexagonal Pyramid. The dihexagonal pyramid, Fig. 226, is a double twelve-sided pyramid, having the twenty-four similar faces embraced under the general symbol (hk'd). It is bounded by twenty-four similar faces, each meeting the vertical axis, and also meeting two adjacent hori- zontal axes at unequal distances, the ratio of which always lies between 1 : 1 and 1:2. Thus the form (2131) includes the following twelve faces in the upper half of the crystal: 2131, 1231, 1321, 2311, 3211, 3121, 2131, 1231, 1321, 2311, 3211, 3121. And similarly below with I (here 1) negative, 2131, etc. The dihexagonal pyramid is often called a berylloid because a common form with the species beryl. The dihexagonal pyramid v(2131) is shown on Figs. 224, 225. 131. Combinations. Fig. 227 of beryl shows a combination of the 227 Beryl base_c(0001) and prism m(1010) with the_first order pyramids p(10ll) and tt(2Q21); the second order pyramid s(1121) and the dihexagonal pyramid p(2131). Both the last forms lie in a zone between m and s, for which it is true that k = I. The basal projection of a similar crystal shown in Fig. 228 is very instructive as exhibiting the symmetry of the normal hexagonal class. This is also true of the stereographic and gnomonic projections in Figs. 229 and 230 of a like crystal with the added form 0(1122). 2. HEMIMORPHIC CLASS (14). ZINCITE TYPE (Dihexagonal Pyramidal or Holohedral Hemimorphic Class) 132. Symmetry. This class differs from the normal class only in having no horizontal plane of principal symmetry and no horizontal axes of binary symmetry. It has, however, the same six vertical planes of sym- metry meeting at angles of 30 in the vertical crystallographic axis which is 0110 2110 1100 1010 100 CRYSTALLOGRAPHY an axis of hexagonal symmetry. There is no center of symmetry. The symmetry is exhibited in the stereographic projection, Fig. 231. 133. Forms. - - The forms belonging to this class are the two basal planes, 0001 and 0001, here distinct forms, the positive (upper) and negative (lower) pyramids of each of the three types; also the three prisms, which last do not differ geometrically from the prisms of the normal class. An example of this class is found in zincite, Fig. 44, p. 22. lodyrite, greenockite and wurtzite are also classed here. Symmetry of Hemimorphic Class 3. TRIPYRAMIDAL CLASS (15). APATITE TYPE (Hexagonal Bipyramidal or Pyramidal Hemihedral Class) 134. Typical Forms and Symmetry. This class is important because it includes the common species of the Apatite Group, apatite, pyromorphite, mimetite, vanadinite. The typical form is the hexagonal prism (hklO) and the hexagonal pyramid (hktl), each designated as of the third order. These forms which are shown in Figs. 233 and 234 may be considered as derived from the corresponding dihexagonal forms of the normal class by the omis- sion of one half of the faces of the latter. They and the other forms of the class have only one plane of symmetry, the plane of the horizontal axes, and also one axis of hexagonal symmetry (the vertical axis). The symmetry is exhibited in the stereo- graphic projection (Fig. 232). It is seen here, as in the figures of crystals given, that, like the tripyramidal class under the tetragonal system, the faces of the general form (hk~l) present are half of the possible planes belong- ing to each sectant, and further that those above and below fall in the same vertical zone. 135. Prism and Pyramid of the Third Order. The prism of the third order (Fig. 233) has six like faces embraced under the general symbol (hkiQ) , and the form is a regular hexagonal prism with angles of 60, not to be distinguished geometrically, if alone, from the Symmetry of Tripyramidal Class other hexagonal prisms; cf. Figs. 220, 221, p. 96. The six faces of the right-handed form (2130) have the indices 2130, 1320, 3210, 2l30, 1320, 32lO. The faces of the complementary left-handed form have the indices: 1230, 23lO, 3120, 1230, 2310, 3l20 As already stated these two forms together embrace all the faces of the dihexagonal prism (Fig. 222). 233 HEXAGONAL SYSTEM 234 101 236 Third Order Prism Third Order Pyramid The pyramid is also a regular double hexagonal pyramid of the third order, and in its relations to the other hexagonal pyramids of the class (Figs. 224, 225) it is analogous to the square pyramid of the third order met with in the corresponding class of the_ tetragonal system (see Art. 100). The faces of the right-handed form (2131) are: Above 2131, 1321, 3211, 2131, 1321, 3211. Below 2131, 1321, 3211, 2131, 1321, 3211. There is also a complementary left-handed form, which with this embraces all the faces of the dihexagonal pyramid. The cross section of Fig. 235 shows in outline the position of the first order prism, and also that of the right- handed prism of the third order. The prism and pyramid just described do not often appear on crystals as predominating forms, though this is sometimes the case, but commonly these faces are present modifying other fundamental forms. 136. Other Forms. The remaining forms of the class are geometri- cally like those of the normal class, viz., the base (0001) ; the first order prism (1010); the second order prism (1120);_ the first order pyramids (hQhl); and the second order pyramids (h'h'2h'l). That their molecular struc- ture, however, corresponds to the symmetry of this class is readily proved, for example, by etching. In this way it was shown that pyromorphite and mimetite belonged in the same group with apatite (Baumhauer), though crystals with the typical forms had not been observed. This class is given its name of Tripyramidal because its forms include three distinct types of pyramids. 137. A typical crystal of apatite is given_ in Fig. 236. It shows the third order pjism ft(2130), and the third order pyramids, M_(2131), n_(3141); also the first order pyramids r(1012), z(1011), (--AA-H V ? % / Symmetry of Trapezohedral Class Hexagonal Trapezohedron Fig. 240), which are enantiomorphous, and the few crystallized salts falling in this class show circular polarization. A modification of quartz known as HEXAGONAL SYSTEM 103 /3-quartz is also described as belonging here. The indices of the right form (2131) are as follows: Above 2131, 1321, 3211, 2131, 1321, 32ll. Below 1231, 2311, 3121, 1231, 23ll, 3l2l. B. Trigonal or Rhombohedral Division (Trigonal System) 140. General Character. As stated on p. 19, the classes of this division are characterized by a vertical axis of trigonal, or threefold, symmetry. There are seven classes here included of which the rhombohedral class of the Calcite Type is by far the most important. 1. TRIGONAL CLASS (18). BENITOITE TYPE (Ditrigonal Bipyramidal, Trigonal Hemihedral or Trigonotype Class) 141. Typical Forms and Symmetry. This class has, besides the ver- tical axis of trigonal symmetry, three horizontal axes of binary symmetry which are diagonal to the crystallographic axes. There are four planes of symmetry, one horizontal, and three vertical diagonal planes intersecting at angles of 60 in the vertical axis. The symmetry and the distribution of the faces of the positive ditrigonal pyramid is shown in Fig. 241. The char- acteristic forms are as follows. Trigonal prism consisting of three faces comprising one half the faces of the hexagonal prism of the first_order. They are of two types, called positive (1010) and negative (0110). Trigonal 241 242 Symmetry of Trigonal Class Benitoite (Palache) pyramid, a double three-faced pyramid, consisting of six faces corresponding to one half the faces of the hexagonal pyramid of the first order. The faces of the upper and lower halves f alj_ in vertical zones with each other. There are two types, called positive (1011) and negative (0111). Ditrigonal prism consists of six vertical faces arranged in three similar sets of two faces and having therefore the alternate edges of differing character. It may be de- rived from the dihexagonal prism by taking alternating pairs of faces. Ditri- gonal pyramid consists of twelve faces, six above and six below. It, like the prism, may be derived from the dihexagonal form by taking alternate pairs of faces of the latter. The faces of the upper and lower halves fall in vertical 104 CRYSTALLOGRAPHY zones. The only representative of this class known is the rare mineral benitoite, a crystal of which is represented in Fig. 242. This crystal shows the trigonal prisms m(1010) and ^(01 10), the hexagonal_ prism of_the second order, a(1120), the trigonal pyramids, p(1011] and Tr(Olll); 6(0112) and the hexagonal pyramid of the second order, x(2241) 2. RHOMBOHEDRAL CLASS (19). CALCITE TYPE . (Ditrigonal Scalenohedral or Rhombohedral Hemihedral Class) 142. Typical Forms and Symmetry. The typical forms of the rhom- bohedral class are the rhombohedron (Fig. 244) and the scalenohedron (Fig. 259). These forms, with the projections, 243 Figs. 243 and 269, illustrate the symmetry >.-- I -^ ! characteristic of the class. There are three planes of symmetry only; these are diangoal to the horizontal crystallographic axes and intersect at angles of 60 in the vertical crystal- lographic axis. This axis is with these forms an axis of trigonal symmetry; there are, further, three horizontal axes diagonal to the crystallographic axes of binary symmetry. Compare Fig. 244, also Fig. 245 et seq. By comparing Fig. 269 with Fig. 229, p. 99, it will be seen that all the faces in half the sectants are present. This group is hence analogous to the tetrahedral class of the iso- metric system, and the sphenoidal class of the tetragonal system. 143. Rhombohedron. Geometrically described, the rhombohedron is a solid bounded by six like faces, each a rhomb. It has six like lateral edges forming a zigzag line about the crystal, and six like terminal edges, three above and three in alternate position below. The vertical axis joins the two trihedral solid angles, and the horizontal axes join the middle points of the opposite sides, as shown in Fig. 244. 244 245 246 Symmetry of Rhombohedral Class Positive Rhombohedron Calcite Negative Rhombohedron Positive Rhombohedron Hematite The general symbol of the rhombohedron is (hQhl), and the successive faces of the unit form (1011) have the indices: Above, lOll, IlOl, Olll; below, OlIT, Toil, llol. HEXAGONAL SYSTEM 105 The geometrical shape of the rhombohedron varies widely as the angles change, and consequently the relative length of the vertical axis c (expressed in terms of the horizontal axes, a = 1). As the vertical axis diminishes, the rhombohedrons become more and more obtuse or flattened; and as it increases they become more and more acute. A cube placed with an octahedral axis vertical is obviously the limiting case between the obtuse and acute forms where the interfacial angle is 90. In Fig. 244 of calcite the normal rhom- bohedral angle is 74 55' and c = 0-854, while for Fig. 246 of hematite this angle is 94 and c = 1-366. Further, Figs. 246-251 show other rhombohe- drons of calcite, namely, I (0112), (0554), /(0221), M(4041), and p(16-0-16-l) ; here the vertical axes are in the ratio of J, f , 2, 4, 16, to that of the funda- mental (cleavage) rhombohedron of Fig. 244, whose angle determines the value of c. 247 249 250 261 253 254 Figs. 247-252, Calcite Figs. 253-254, Gmelinite 144. Positive and Negative Rhombohedrons. To every positive rhombohedron there may be an inverse and complementary form, identical geometrically, but bounded by faces falling in the_ alternate sectants. Thus the negative form of the unit rhombohedron (0111) shown in Fig. 245 has the faces: Above, Olll, 1011, 1101; below, 1101, 0111, 1011. The position of these in the projections (Figs. 269, 270) should be care- fully studied. Of the figures already referred to Figs .244, 246, 250 are positive, and Figs. 245, 247, 248, 249 negative, rhombohedrons; Fig. 251 shows both forms. . , It will be seen that the two complementary positive and negative rhom- bohedrons of given axial length together embrace all the like faces of the double six-sided hexagonal pyramid of the first order. When these two rhombohedrons are equally developed the form is geometrically .identical with this pyramid. This is illustrated by Fig. 254 of gmelimte r(1011), 106 CRYSTALLOGRAPHY p(0111) and by Figs. 284, 285, p. 113, of quartz, r(1011), 3(0111).* In each case the form, which is geometrically a double hexagonal pyramid (in Fig. 254 with c and m), is in fact a combination of the two unit rhombohedrons, positive and negative. Commonly a difference in size between the two forms may be observed, as in Figs. 253 and 286, where the form taken as the posi- tive rhombohedron predominates. But even if this distinction cannot be established, the two rhombohedrons can always be distinguished by etching, or, as in the case of quartz, by pyro-electrical phenomena. 145. Of the two series, or zones, of rhombohedrons the faces of the posi- tive rhombohedrons replace the edges between the base (0001) and the first order prism (1010). Also the faces of the negative rhombohedrons replace the alternate edges of the same forms, that is, the edges between (0001) and (0110) (compare Figs. 253, 254, etc.). Fig. 255 shows the rhombohed_ron in combination with the base. Fig. 256 the same with the prism a(1120). When the angle between the two forms happens to approximate to 70 32' the crystal simulates the aspect of a regular octahedron. This is illustrated by Fig. 257; here co = 69 42', also oo = 71 22', and the crystal resembles closely an octahedron with truncated edges (cf. Fig. 99, p. 55). 255 257 258 Figs. 255, 256, Hematite Coquimbite Eudialyte 146. There is a very simple relation between the positive and negative rhombohedrons which it is important to remember. The form of one series which truncates the terminal edges of a given form of the other will have one half the intercept on the vertical crystallographic axis of the latter. This ratio is expressed in the values of the indices of the two forms. Thus (0112), truncates the terminal edges of the positive unit rhombohedron (1011); (1014) truncates the terminal edges_of (0112),_(1015) of (2025). Again (1011) truncates the edges of (0221), (4041) of _(0221), etc. This is illustrated by Fig. 252 with the forms r(1011) and /(0221). Also in Fig. 258,_a basal pro- jection^ 2(1014) truncates the edges of e(0112); c(0112) of r(1011); r(1011) of s(0221). 147. Scalenohedron. The scalenohedron, shown in Fig. 259, is the general form for this class corresponding to the symbol hkll. It is a solid, bounded by twelve faces, each a scalene triangle. It has roughly the shape of a double six-sided pyramid, but there are two sets of terminal edges, one more obtuse than the other, and the lateral edges form a zigzag edge around the form like that of the rhombohedron. It may be considered as derived from the dihexagonal pyramid by taking the alternating pairs of faces of * Quartz serves as a convenient illustration in this case, none the less so notwithstand- ing the fact that it belongs to the trapezohedral class of this division. HEXAGONAL SYSTEM 107 an that form. It is to be noted that the faces in the lower half of the form do not fall in vertical zones with those of the upper half. Like the rhombohe- drons, the scalenohedrons may be either positive or negative. The positive forms correspond in position to the positive rhombohedrons and conversely. The positive scalenohedron (2131), Fig. 259, has the fol- lowing indices for the several faces: Above 2131, 2311, 3211, 1231, 1321, 3l21 Below 1231, 1321, 3121, 2131, 2311, 3211. For the complementary negative scalenohedron (1231) the indices of the faces are: Above 1231, 1321, 3121, 2131, 2311, 32ll. Below 2311, 3211, 1231, 1321, 3l2l, 2131. 148. Relation of Scalenohedrons to Rhombohedrons. It was noted above that the scalenohedron in general has a series of Q , X , zigzag lateral edges like the rhombohedron. It is obvious, further, bcaler that for every rhombohedron there will be a series or zone of scalenohedrons having the same lateral edges. This is shown in Fig. 262, where the scalenohedron 260 261 262 263 264 Figs. 260-263, Calcite 265 266 267 Figs. 264, 265, Corundum Figs. 266, 267, Spangolite* w(2l3l) bevels the lateral edges of the fundamental rhombohedron r(10Tl); the same would be true of the scalenohedron (3251), etc. Further, in Fig. 263, the negative scaleno- hedron 3(1341) bevels the lateral edges of the negative rhombohedron /(0221). The rela- tion of the indices which must exist in these cases may be shown to be, for example, for the rhombohedron r(lOTl), h - k + l\ again for /(0221), h + 21 = k, etc. See also the pro- jections, Figs. 269, 270. Further, the position of the scalenohedron may be defined with reference to its parent rhombohedron. For example in Fig. 262 the scalenohedron y (2 131) has three times the vertical axis of the unit rhombohedron r(1011). Again in Fig. 263 re (1341) has twice the vertical axis of /(0221). * Spangolite belongs properly to the next (hemimorphic) group, but this fact does not destroy the value of the illustration. 108 CR YSTALLO GR APH Y 149. Other Forms. The remaining forms of the normal class of the rhombohedral division are geometrically like those of the corresponding class of the hexa- gonal division viz._, the base c(0001); the prisms ra(lOlO), a(1120), (teO); also the second order pyramids, as (1121). Some of these forms are shown in the accompanying figures. For further illustrations reference may be made to typical rhombohedral species, as calcite, hema- tite, etc. With respect to the second order pyramid, it is interesting to note that if it occurs alone (as in Fig. 264, n = 2243) it is impossible to say, on geometrical grounds, whether it has the trigonal symmetry of the rhombohedral type or the hexagonal symmetry of the hexagonal type. In the latter case, 2110 Calcite m l 1120 1010 m Calcite the form might be made a first order pyramid by exchanging the axial and diagonal planes of symmetry. The true symmetry, however, is often indi- HEXAGONAL SYSTEM 109 cated, as with corundum, by the occurrence on_ other crystals_^)f rhombo- hedral faces, as r(1011) in Fig. 265 (here z = 2241, co = 14-14-28-3). Even if rhombohedral faces are absent (Fig. 266), the etching-figures (Fig. 267) will often serve to_ reveal the true trigonal molecular symmetry; here o = (1124), p = (1122). 150. A basal projection of a somewhat complex crystal of calcite is given in Fig. 268, and stereographic and gnomonic projections of the same forms in Figs. 269 and 270; both show well the symmetry in the distribution 270 of the faces. Here the forms are: prisms, a(l_120), ra(10lO); rhombohedrons, positive, r(lOll), negative, e(0112), /(0221); scalenohedrons. positive, 3. RHOMBOHEDRAL-HEMIMORPHIC CLASS (20). TOURMALINE TYPE (Ditrigonal Pyramidal or Trigonal Hemihedral Hemimorphic Class) 151. Symmetry. A number of prominent rhombohedral species, as tourmaline, pyrar- gyrite, proustite, belong to a hemimorphic class under this division. For them the symmetry in the grouping of the faces differs at the two extremities of the vertical axis. The forms have the same three diagonal planes of symmetry meeting at angles of 60 in the vertical axis, Symmetry of Rhombohedral-Hemimorphic Class 110 CRYSTALLOGRAP which is an axis of trigonal symmetry. There are, however, no hori- zontal axes of symmetry, as in the rhombohedral class, and there is no center of symmetry. Cf. Fig. 271. 152. Typical Forms. In this class the basal planes (0001) and (0001) are distinct Jorms. The other characteristic forms are the two trigonal prisms ra(1010) and ra/0110) of the first order series; also the four trigonal first order pyramids, corresponding respectively to the three upper and three lower faces of a positive rhombohedron, and the three upper and three lower faces of the negative rhombohedron; also the hemimorphic second order hexagonal pyramid; finally, the four ditrigonal pyramids, corresponding to the . upper and lower faces respectively of the positive and negative scalenohedrons. Figs. 272-275 illustrate these forms. Fig. 274 is a basal section with r/0111^ and e/1012) below. 272 274 275 276 Figs. 272-275, Tourmaline 4. TRI-RHOMBOHEDRAL CLASS (21). PHENACITE TYPE (Rhombohedral or Rhombohedral Tetartohedral Class) 153. Symmetry. This class, illustrated by the species dioptase, phenacite, willemite, dolomite, ilmenite, etc., is an important one. It is characterized by the absence of all planes of symmetry, but the vertical axis is still an axis of trigonal symmetry, and there is a center of symmetry. Cf. Fig. 276. 154. Typical Forms. The distinctive forms of the class are the rhombohedron of the second order and the hexagonal prism and rhombo- hedron, each of the third order. The class is thus characterized by three rhombohedrons of distinct types (each + and - ), and hence the name given to it. ^ The second order rhombohedron may be de- rived by taking one half the faces of the nor- mal hexagonal pyramid of the second order. There will be two complementary forms known as positive and negative. For example, in a given case the indices of the faces for the positive and negative forms are: Positive (above) 1122, 2112, 1212; (below) 12l2, Il22, 2ll2 Negative (above) 1212, 1122, 2112; (below) 2112, 1212, 1122! ;.._..,. v_... Symmetry of Tri-Rhombohedral Class HEXAGONAL SYSTEM 111 The rhombohedron of the third order has the general symbol (hkll), and may be derived from the normal dihexagonal pyramid, Fig. 226, by taking one quarter of the faces of the latter. There are therefore four complementary third order rhombohedrons, dis- tinguished respectively as positive right-handed (2131), positive left-handed (3121), negative right-handed (1321), and negative left-handed (1231). The indices of the six like faces of the positive right-handed form (2131) are: Above 2131, 3211, 1321; below 1321, 2l3l, 3211. The hexagonal prism of the third order may be derived from the normal dihexagonal prism, Fig. 219, by taking one half the faces of the latter. There are two complementary forms known as right- and left-handed. The faces of these forms in a given case (2130) have the indices: Right 2130, 1320, 3210, 2130, 1320, 32lO Left 1230 2310 3120 1230 2310, 3l20. 155. The remaining forms are geometrically like those of the rhombo- hedral class, viz. : Base c(0001) ; first order prism m(1010) ;_ second order prism a(1120); rhombohedrons of the first order, as (1011) and (0111), etc. 156. The forms of this group are illustrated by Figs. 277-279. Fig. 277 is of dioptase and shows the hexagonal prism_of the second order a(1120) with a negative first order rhombohedron, s(0221) and the third order rhom- bohedron #(1341). Figs. 278 and 279 show the horizontal and clinographic 279 Dioptase Phernacite projections of a crystal of phenacite with_the following forms: first order prism, ra(1010); _second order prism, a(1120); third _order rhombohedrons, x(1232) and s(2131); first order rhombohedrons, r(1011) and d(0112). In order to make clearer the relation of the faces of the different types of forms under this class, Fig. 280 is added. Here the zones of the positive and negative rhombohedrons of the first order are indicated (+R and R) also the general positions of the four types of the third order rhombohedrons (_l_p f I I l\ The following scheme may also be helpful in connection with Fig. 280. It 112 CRYSTALLOGRAPHY loio 280 1100 10J50 shows the distribution of the faces of the four rhombohedrons of the third ojder (+r, +/, r, I) relatively to the faces of the unit hexagonal prism (1010). PHENACITE TYPE +1 +r 3121 2131 -I -r 1231 1321 +1 +T 2311 3211 -I -r 3121 2131 +1 +r 1231 1321 -/ -r 2311 3211 1010 OlTO IlOO 1010 olio 1TOO -I -r 3121 2131 +Z +r 1231 1321 -I -r 2311 3211 +1 +r 3121 2131 -I -r 1231 1321 +Z +r 2311 3211 5. TRAPEZOHEDRAL CLASS (22). QUARTZ TYPE (Trigonal Trapezohedral or Trapezohedral Tetartohedral Class) 157. Symmetry. This class includes, among minerals, the species quartz and cinnabar. The forms have no plane of symmetry and no center of symmetry; the vertical axis is, however, an axis of trigonal symmetry, and there are also three horizontal axes of binary symmetry, coinciding in direction with the crystallographic axes; cf. Fig. 281 281 282 283 o \ r * Symmetry of Trapezohedral Class Trigonal Trapezohedrons HEXAGONAL SYSTEM 113 158. Typical Forms. The characteristic form of the cJass is the trigonal trapezohedron shown in Fig. 282. This is the general form corre- sponding to the symbol (hkil), the faces being distributed as indicated in the accompanying stereographic projection (Fig. 281). The faces of this form correspond to one quarter of the faces of the normal dihexagonal pyramid, Fig. 226. There are therefore four such trapezohedrons, two positive, called respectively right-handed (Fig. 282) and left-handed (Fig. 283), and two simi- lar negative forms, also right- and left-handed (see the scheme given in Art. 160). It is obvious that the two forms of Figs. 282, 283 are enantio- morphous, and circular polarization is a striking character of the species belonging to the class as elsewhere discussed. The indices of the six faces belonging to each of these will be evident on consulting Figs. 281 and 229 and 230. The complementary positive form (r and I) of a given symbol include the twelve faces of a positive scalenohe- dron, while the faces of all four as already stated include the twenty-four faces of the dihexagonal pyramid. Corresponding to these trapezohedrons there are_two ditrigonal prisms, respectively right- and left-handed, as (2130) and (3120). The remaining characteristic forms are the right- and left-handed trigonal prism a(H20) and_a(2110); also the right- and left-handed trigonal pyramid, as (1122) and (2112). They may be derived by taking respectively one half the faces of the hexagonal prism of the second order (1120) or of the corre- sponding pyramid (1122); these are shown in Figs. 221 and 225. 159. Other Forms. The other forms of the class are geometrically like those of the normal class. They are the base c(0001), the hexagonal first order prism ra(1010), and the positive and negative rhombohedrons as (1011) and (0111). These cannot be distinguished geometrically from the normal forms. 160. Illustrations. The forms of this class are best shown in the species quartz. As already remarked (p. 106), simple crystals often appear to be of normal hexagonal symmetry, the rhombohedrons r(1011) and 2(0111) being equally developed (Figs. 284, 285). In many cases, however, a differ- ence in molecular character between them can be observed, and more com- 284 285 288 Figs. 284-288, Quartz monly one rhombohedron, r(1011), predominates in size; the distinction can always be made out by etching. Some crystals, like Fig. 286, show as modifying faces the right trigonal pyramid *(ll2l), with a right positive trapezohedron, as z(5161). Such crystals are called right-handed and rotate 114 CRYSTALLOGRAPHY the plane of polarization of light transmitted in the direction of the vertical axis to the right. A crystal, like Fig. 287, with _the left trigonal pyramid s(2111) and one or more left trapezohedrons, as x(6151), is called left-handed, and as regards light has the opposite character to the crystal of Fig. 286. Fig. 288 shows a more complex right-handed crystal with several positive and negative rhombohedrons, several positive right trapezohedrons and the negative left trapezohedron, N. The following scheme shows the distribution of the faces of the four trapezohedrons (+r, -\-l, r, I) relatively to the faces of the unit hex- agonal prism (lOlO); it is to be compared with the corresponding scheme, given in Art. 156, of crystals of the phenacite type. _In the case of the nega- tive forms some authors prefer to make the faces 2131, 1231, etc., right, and 3121, 1321, etc., left. QUARTZ TYPE +1 +r 3121 2131 -I -r 1231 1321 +1 +r 2311 3211 -I -r 3121 2131 +1 +r 1231 1321 -I -r 2311 3211 1010 0110 TlOO 1010 olio 1100 -r -I 3121 2131 +r +1 1231 1321 -r -I 2311 3211 +r +1 3121 2131 -r -I 1231 1321 -fr +1 2311 32TT 161. Other Classes. The next class (23) is known as the Trigonal Bipyramidal or Trigonal Tetartohedral class. It has one plane of sym- metry that of the horizontal axes, and one axis of trigonal symmetry the vertical axis. There is no center of symmetry. Its characteristic forms are the three types of trigonal prisms and the three corresponding types of trigonal pyramids. Cf. Fig. 289. This class has no known representation among crystals. The last class (24) of this division is known as the Trigonal Pyramidal or Trigonal Tetartohedral Hemimorphic class. It has no plane of symmetry 289 290 Symmetry of Trigonal Bipyramidal Class Symmetry of the Trigonal Pyramidal Class and no center of symmetry, but the vertical axis is an axis of trigonal sym- metry. The forms are all hemimorphic, the prisms trigonal prisms, and the pyramids hemimorphic trigonal pyramids. Cf. Fig. 290. The crystals of sodium periodate belong to this class. HEXAGONAL SYSTEM 115 MATHEMATICAL RELATIONS OF THE HEXAGONAL SYSTEM. 162. Choice of Axis. The position of the vertical crystallographic axis is fixed in all the classes of this system since it coincides with the axis of hexagonal symmetry in the hexagonal division and that of trigonal symmetry in the rhombohedral division. The three horizontal axes are also fixed in direction except in the normal class and the subordinate hemimorphic class of the hexagonal division; in these there is a choice of two positions according to which of the two sets of vertical planes of symmetry is taken as the axial set. 163. Axial and Angular Elements. The axial element is the length of the vertical axis, c, in terms of a horizontal axis, a; in other words, the axial ratio of a : c. A single measured angle (in any zone but the prismatic) may be taken as the fundamental angle from which the axial ratio can be obtained. The angular element is usually taken as the angle between tfhe base c(0001) and the unit first order pyramid (1011), that is, 0001 A 1011. The relation between this angle and the axis c is given by the formula tan (0001 A lOll) X - Vs = c. The vertical axis is also easily obtained from the unit second order pyramid, since tan (0001 A 1122) = c. These relations become general by writing them as follows: tan (0001 A hOhl) X-^3 = -Xc; 2i I tan (0001 A h'h'2h'l) = X c. In general it is easy to obtain any required angle between the poles of two faces on the spherical projection either by the use of the tangent (or cotangent) relation, or by the solution of spherical triangles, or by the application of both methods. In practice most of the triangles used in calculation are right-angled. 164. Tangent and Cotangent Relations. The tangent relation holds good in any zone from c(0001) to a face in the prismatic zone. For example: tan (0001 A hOhl) = h. tan (0001 A h'h'2Ji'l) _ 2h tan (0001 A lOll) I ' tan (0001 A 1122) " l" In the prismatic zone, the cotangent formula takes a simplified form; for example, lor a dihexagonal prism, hklQ, as (2130) : cot (1010 A M*0) = ^ cot (1120 A feHO) = M L The sum of the angles (lOlO A hkiO) and (1120 A MnO) is equal to 30. Further, the last equations can be written in a more general form, applying to any pyramid (hkil) in a zone, first between 1010 and a face in the zone 0001 to 0110, where the angle between 1010 and this face is known; or_again, for the same pyramid, in a zone between 1120 and a face in the zone 0001 to 1010, the angle between 1120 and this face being given. For example (cf. _Fig. 229, p. 99), if the first-mentioned zone is lOlO'/iEZ-OlIl and the second is llSfrAHMOll, then cot (10TO A hM) = cot (lOlO A Olll) . ^ and cot (1120 A Mil) = cot (1120 A lOll) . j-p Also similarly for other zones, cot (1010 A MB) = cot (1010 A 0221) . f-> etc. 116 CRYSTALLOGRAPHY cot (1120 A hkil) = cot (1120 A 2021) . ~7 etc. 165. Other Angular Relations. The following simple relations are of frequent use: (1) For a hexagonal pyramid of the first order, tan \ (lOTl A OlTl) = sin Vj, where tan = c, and in general tan \ (hOhl A Qhhl) = sin ,V|, where tan ,= ^-c. (2) For a hexagonal pyramid of the second order, as (1122), 2 sin \ (1122 A I2l2) = sin , and tan = c. (3) For a rhombohedron sin (lOTl A TlOl) = sin a Vf, where a = (0001 A lOTl); in general sin \ (hOhl A hhOl) = sin a, Vf , where a, = (0001 A 166. Zonal Relations. The zonal equations, described in Arts 45, 46, apply here as in other systems, only that it is to be noted that one of the indices referring to the horizontal axes, preferably the third, i, is to be dropped in the calculations and only the other three employed. Thus the indices (u, v, w) of the zone in which the faces (hkil), (pqft) lie are given by the scheme I XXX where u = kt Iq, v = lp ht, w = hq kp. For example (Fig. 226) the face n lies in the zone mv, IOTO'2131 and^ also in the zone au, 1120 ' 2021. For the_first zone the values obtained are: u = 0, v = I, w = 1; for the second zone, e = !,/=!, = 2. Combining these zone symbols according to the usual scheme 1 \ The face n has, therefore, the indices 314i, since further i = (h + k). 167. Formulas. The following formulas in which c equals the unit length of the vertical axis are sometimes useful: (1) The_distances (see Fig. 229) of the pole of any face (hkil) from the poles of the faces (10TO), (0110), (1100), and (0001) are given by the following equations, cos (hkil) (1010) = cos (M#) (OlTO) = cos (hkil) (TlOO) = cos (hkil) (0001) c (k + 2h) + 4c 2 (h 2 + k 2 + hk) c (2k + h) _ + 4c 2 (/i 9 - + k 2 + hk) c (h - k) 4c 2 (As hk) v 3? 2 + 4c 2 (A 2 + fc 2 4- A/c) (2) The distance (PQ) between the poles of anv two faces P(hkil) and Q(pqrt) is given by the equation HEXAGONAL SYSTEM 117 W, + 2c 2 (hq + pk + 2hp + 2kq) cos PQ = -7= v [3J 2 + 4c 2 (h 2 + k 2 (3) For special cases the above formula becomes simplified; it serves to give the value of the normal angles for the several forms in the system. They are as follows: (a) Pyramid of First Order (hQhl), Fig. 224: cos X (terminal) cos Z (basal) = 3/ 2 (6) Pyramid of Second Order (h'h'2fcl), Fig. 225: cos Y (terminal) = (c) Dihexagonal Pyramid (hkil) : P + 4W' cosZ ( basal )- P + 4^ Q/2 I O~2 /J,2 _|_ ]fZ . cos X (see Fig. 226) - ^ 2 + J ( ^ fc2 ; - , 3l 2 + 2c 2 (2h 2 + 2hk - k 2 ) cos Y (see Fig. 226) = . 3. + 4^ fr, + &. + M.) = 3/ 2 + 4c 2 (h 2 + k 2 + hk) ' cos Z (basal) (d) Dihexagonal Prism (hkiQ), Fig. 222: cos X (axial) = ^^^ . (e) Rhombohedron (1011): cos X (terminal) = (f) Scalenohedron (hkil): cos X (see Fig. 259) = cos Y (diagonal) 2ft 2 + 2hk - 2 (h* + A; 2 + 2c (2A: 2 + 2hk - Cft . cos Y (see Fig. 259) 3/2 3Z 2 + 2c 2 (2h* == & + 4** (h* + k* + hk) 2c 2 (W + 168. Angles. The angles for some commonly occurring dihexagonal prisms with the n second order risms are iven in the following table: first and second order prisms are given 169. 5160 4150 3140 5270 2130 3250 5490 The Miller Axes and Indices. 291 w(1010) 8 57' 10 53^ 54 6 owng a(1120) 21 19 61 16 6 13 54 10 53^ 13 16 19 23 24i 26 19{ The forms of the hexagonal system were referred by Miller to a set of three equal oblique axes which were taken parallel to the edges of the unit positive rhombohedron of the species. Fig. 291 represents such a rhombohedron with the position of the Miller axes shown. This choice of axes for hexa- gonal forms has the grave objec- tion that in several cases the faces of the same form are rep- resented by two sets of different indices; for example the faces of .the pyramid of the first order would have the indices, 100, 221,010, 122, 001, 2l2. This objection, however, disappears if the 118 CRYSTALLOGRAPHY Miller axes and indices are used only for forms in the Rhombohedral Division, that is for forms belonging to classes which are characterized by a vertical axis of trigonal symmetry. It is believed, however, that the mutual relations of all the classes of both divisions of the hex- agonal system among themselves (as also to the classes of the tetragonal system), both morphological and physical are best brought out by keeping throughout the same axes, namely those of Fig. 218, Art. 121. The Miller method has, however, been adopted by a number of authors and consequently it is necessary to give the following brief description. (1120) 110 0210) Oil (1010) Miller and Miller-Bravais Indices Compared Fig. 292 shows in stereographic projection the common hexagonal-rhombohedral forms .vith their Miller indices and in parentheses the corresponding indices when the faces are referred to the four axial system. It will be noted that the faces of the unit positive rhom- bohedron have the indices 100, 010, and 001 and those of the negative unit rhombohedron have 221, 122, 212. These two forms together give the faces of the hexagonal pyramid_of the first order (see above). The hexagonal prism of the first order is represented by 211, etc., while the second order prism has 101, etc. The dihexagonal pyramid has also two sets of indices (hid) and (efg) ; of these the symbol (hkl) belongs to the positive scaleno- hedron and (efg) to the negative form. In this as in other cases it is true that e = 2h + 2k - I, f = 2h - k + 21, g = - h + 2k + 21. For example, the faces of the form 201, etc., belong in the Rhombohedral Division of this system to the_scalenohedron (2131) while the complementary negative form would have the indices 524, etc. The relation between the Miller-Bravais and the Miller indices for any form can be HEXAGONAL SYSTEM 119 obtained from the following expression, where (hktt) represents the first and (pqr) the second. h k i _ p - q p -r r -p~p The relation between the Miller indices for hexagonal forms and those of isometric forms should be noted. If we conceive of the isometric cube as a rhombohedron with interfacial angles of 90 and change the orientation so that the normal to the octahedral face (111) becomes vertical we get a close correspondence between the two. This will be seen by a comparison of the two stereographic projections, Figs. 292 and 125. 170. To determine, by plotting, the length of the vertical axis of a hexagonal mineral, given the position on the stereographic projection of the pole of a face with known indices. To illustrate this problem it is assumed that the mineral in question is beryl and that the position of the pole p(10ll) is known, Fig. 293. Let the three lines ai, a 2 , a 3 represent the horizontal axes with their unit lengths equalling the radius of the circle. Draw a line from the center of the projec- tion through the pole p. Draw another line (which will be at right angles to the first) joining the ends of ai and 3 . This will be parallel to a 2 and will represent the intercept of p(1011) upon the plane of the horizontal axes. In order to plot the intercept of p upon the vertical axis construct in the upper left-hand quadrant of the figure a right-angle triangle the base of which shall be equal to O-P, the vertical side of which shall represent the c axis and the hypothenuse shall show the slope^ of the face and give its intercept upon the c axis. The direction of the hypothe- nuse is determined by locating the normal to p from the angle measured from the center of the projection to its pole. Since the face has been as- sumed to have an unit intercept on the vertical axis the dis- tance O-M. which equals 0-49 Determina tion of unit length of c axis, having given the (in terms of the length of the position of p(10Tl) horizontal axes, which equals 1*00), gives the unit length of the c axis for beryl. 171. To determine the indices of a face of a hexagonal form of a known mineral, given the position of its pole on the stereographic projection. In Fig. 294 it is assumed that the position of the pole v of a crystal face on calcite is known. To determine its indices, first draw a radial line through the pole and then erect a perpendicular to it, starting the line from the end of one of the horizontal axes. This line will represent the direction of the intersection of the crystal face with the horizontal plane and its relative intercepts on the horizontal axes will give the first three numbers of the parameters of the face, namely lai, 2a 2 , 3-3- To determine the relative intercept on the c axis transfer the distance O-P to the upper left- hand quadrant of the figure, then having measured the angular distance between the center of the projection and v by means of the stereographic protractor draw the pole to^tne face in the proper position. Draw then a line at right angles to this pole starting from the point P'. This line gives the intercept of the face upon the line representing the vertical axis. In this case the intercept has a value of 17 when the length of the horizontal axes is taken as equal to I'O. This distance 17 is seen to be twice the unit length of the c axis for calcite, 0'85. Therefore the parameters of the face in question upon the four axes are lai, 2a 2 , | a 3 , 2c, which give 2131 for the indices of the face v. 120 CRYSTALLOGRAPHY 2 e =1,70 294 Determination of the indices for v on calcite 172. To determine, by plotting, the indices of hexagonal forms, given the position of 295 then: poles on the gno- monic projection. To illustrate this problem one sectant of the gno- monic projection of the important forms of beryl, Fig. 228, is reproduced in Fig. 295. The directions of the three horizontal axes, ai, 02 and 3 are in- dicated by the heavy lines. From the poles of the faces perpendiculars are drawn to these three axes. It will be noted that the va- rious intercepts made upon the axes by these lines have simple rational relations to each other. One of these intercepts is chosen as having the length of 1 (this length will be equivalent to the unit length of the c crys- tallographic axis, see below) and the others are then given in terms of it. ORTHORHOMBIC SYSTEM 121 The indices of each face are obtained directly by taking these intercepts upon the three horizontal axes in their proper order and by adding a 1 as the fourth figure If necessarv clear of fractions, as in the case of the second order pyramid, 1122. 173. To determine the axial ratio of a hexagonal mineral from the gnomonic projection of its forms. The gnomonic projection of the beryl forms, Fig. 295, may be used as an illustrative example. The radius of the fundamental circle, a, is taken as equal to the length of the horizontal axes and is given a value of 1. Then the length of the funda- 296 in the same manner as in the case of the tetragonal system, see Art. 117, p. IV. ORTHORHOMBIC SYSTEM (Rhombic or Prismatic System) 174. Crystallographic Axes. The orthorhombic system includes all the forms which are referred to three axes at right angles to each other, all of different lengths. Any one of the three axes may be taken as the vertical axis, c. Of the two horizontal axes the longer is always taken as the b or macro-axis * and when orientated is parallel to the observer. The a or brachy-axis is the shorter of the two horizontal axes and is perpendicular to the observer. The length of the b axis is taken as unity and the lengths of the other axes are expressed in terms of it. The axial ratio for barite, for instance, is a : b : c = 0*815 : TOO : 1*31. Fig. 296 shows the crystallographic axes for barite. 1. NORMAL CLASS (25). BARITE TYPE Orthorhombic Axes (Barite) 297 (Orthorhombic Bipyramidal or Holohedral Class) 175. Symmetry. The forms of the normal class of the orthorhombic system are characterized by three axes of binary sym- metry, which directions are coincident with the crystallographic axes. There are also three unlike planes of symmetry at right angles to each other in which lie the crystal- lographic axes. The symmetry of the class is exhibited in the accompanying stereographic projection, Fig. 297. This should be compared with Fig. 91 (p. 53) and Fig. 167 (p. 77), representing the symmetry of the normal classes of the isometric and tetragonal systems respec- tively. It will be seen that while normal iso- metric crystals are developed alike in the three axial directions, those of the tetragonal type have a like development only in the direction of the two horizontal axes, and Symmetry of Normal Class Orthorhombic System this system (and also in the triclinic system) are * The prefixes brachy- and macro- used in this system ( from the Greek words, ppaxvs, short, and MKPOS, long. 122 CRYSTALLOGRAPHY those of the orthorhombic type are unlike in the three even axial directions. Compare also Figs. 92 (p. 54), 171 (p. 78) and 298 (p. 122). 176. Forms. The various forms possible in this class are as follows : jr>^ Indices 1. Macropinacoid or a-pinacoid (100) 2. Brachypinacoid or 6-pinacoid (010) 3. Base or c-pinacoid (001) 4. Prisms (hkO) 5. Macrodomes . (hQl) 6. Brachydomes (OfcZ) 7. Pyramids (hkl) In general, as defined on p. 31, a pinacoid is a form whose faces are parallel to two of the axes, that is, to an axial plane; a prism is one whose faces are parallel to the vertical axis, but intersect the two horizontal axes; a dome * (or horizontal prism) is one whose faces are parallel to one of the horizontal axes, but intersect the vertical axis. A pyramid is a form whose faces meet all the three axes. These terms are used in the above sense not only in the orthorhombic system, but also in the monoclinic and triclinic systems; in the last each form consists of two planes only. 177. Pinacoids. The macropinacoid includes two faces, each of which is parallel both to the macro-axis b and to the vertical axis c; their indices are respectively 100 and 100. This form is uniformly designated by the letter a, and is conveniently and briefly called the a-face or the a-pinacoid. The brachypinacoid includes two faces, each of which is parallel both to the brachy-axis a and to the vertical axis c; they have the indices 010 and 010. This form is designated by the letter 6; it is called the b-face or the b-pinacoid. The base or basal pinacoid includes the two faces parallel to the plane of the horizontal axes, and having the indices 001 and 001. This form is desig- nated by the letter c; it is called the c-face or the c-pinacoid. Each one of these three pinacoids is an open-form,! but together they make the so-called diametral prism, shown in Fig. 298, a solid which is the analogue of the cube of the isometric system. Geometrically it cannot be distinguished from the cube, but it differs in having the symmetry unlike in 299 300 ! no" , \ iib~~ I j H * Prism and Basal Pinacoid 120- - 110 120 n \ Macro-, Brachy- and Basal Pinacoids the three axial directions; this may be shown by the unlike physical char- acter of the faces, a, 6, c, for example as to luster, striations, etc.; or, again, by the cleavage. Further, it is proved at once by optical properties. This * From the Latin domus, because resembling the roof of a house; cf. Figs. 301, 302. J feee p. 30. ORTHORHOMBIC SYSTEM 123 diametral prism, as just stated, has three pairs of unlike faces. It has three kinds of edges, four in each set, parallel respectively to the axes a, 6, and c; it has, further, eight similar solid angles. In Fig. 298 the dimensions are arbitrarily made to correspond to the relative lengths ojkthe chosen axes, but the student will understand that a crystal of this shape gives no informa- tion as to these values. 178. Prisms. The prisms proper include those forms whose faces are parallel to the vertical axis, while they intersect both the horizontal axes; their general symbol is, therefore, (hkQ). These all belong to one type of rhombic prism, in which the interfacial angles corresponding to the two un- like vertical edges have different values. The unit prism, (110), is that form whose faces intersect the horizontal axes in lengths having a ratio corresponding to the accepted axial ratio of a : b for the given species; in other words, the angle of this unit prism fixes the unit lengths of the horizontal axes . This form is shown in combination with the basal pinacoid in Fig. 299; it is uniformly designated by the letter m. The four faces of the unit prism have the indices 110, IlO, TlO, iTO. There is, of course, a large number of other possible prisms whose inter- cepts upon the horizontal axes are not proportionate to their unit lengths. These may be divided into two classes as follows: macroprisms, whose faces lie between those of the macropinacoid and the unit prism, brachyprisms with faces between those of the brachypinacoid and the unit prism. A macroprism has the general symbol (hkQ) in which h > k and is represented by the form Z(210), Fig. 300. A brachyprism has the general symbol (hkQ) with h < k and is represented by n(120), Fig. 300. 301 302 303 101 Brachydqme and Macropinacoid Pyramid Macrodome and Brachypinacoid 179. Macrodomes, Brachydomes. The macrodomes are forms whose faces are parallel to the macro-axis b, while they intersect the vertical axis c and the horizontal axis a; hence the general symbol is (hOl). The angle of the unit macrodome, (101), fixes the ratio of the axes a : c. This form is shown in Fig. 301 combined (since it is an open form) with the brachypinacoid. In the macrodome zone between the base c(001) and the macropinacoid a (100) there may be a large number of macrodomes having the symbols, taken in the order named, (103), (102), (203), (101), (302), (201), (301) ; etc. Cf. Figs. 318 and 319 described later. The brachydomes are forms whose faces are parallel to the brachy-axis, a, while they intersect the other axes c and 6; their general symbol is (0/cZ). The angle of the unit brachydome, (Oil), which is shown with a(100) in Fig. 302, determines the ratio of the axes b : c. The brachydome zone between c(001) and 6(010) includes the forms (013), (012), (023), (Oil), (032), (021), (031), etc. Cf. Figs. 318 and 319. 124 CRYSTALLOGEAPHY Both sets of domes are often spoken of as horizontal prisms. The pro- priety of this expression is obvious, since they are in fact prisms in geo- metrical form; further, the choice of position for the axes which makes them domes, instead of prisms in the narrower sense, is more or less arbitrary, as already explained elsewhere. 180. Pyramids. The pyramids in this system all belong to one type, the double rhombic pyramid, bounded by eight faces, each a scalene triangle. This form has three kinds of edges, x, y, z (Fig. 303), each set with a different interfacial angle; two of these angles suffice to determine the axial ratio. The symbol for this, the general form for the system, is (hkl). The pyramids may be divided into three groups corresponding respec- tively to the three prisms just described, namely, unit pyramids, macro- pyramids, and br achy pyramids. The unit pyramids are characterized by the fact that their intercepts on the horizontal axes have the same ratio as those of the unit prism; that is, the assumed axial ratio (a : b) for the given species. For them, therefore, the general symbol becomes (hhl). There may be different unit pyramids on crystals of the same species with different intercepts upon the vertical axis, and these form a zone of faces lying between the base c(001) and the unit prism m(110). This zone would include the forms, (119), (117), (115), (114), (113), (112), (111). In the symbol of all of the forms of this zone h = k, and the lengths of the vertical axes are hence, in the example given, ^, \, , J, f , J of the vertical axis c of the unit pyramid. The macropyramids and brachypyramids are related to each other and to the unit pyramids, as were the macroprisms and brachyprisms to themselves and to the unit prism. Further, each vertical zone of macropyramids (or brachypyramids), having a common ratio for the horizontal axes (or of h : k in the symbol), belongs to a particular macroprism (or brachy prism) char- acterized by the same ratio. Thus the macropyramids (214), (213), (212), (421), etc., all belong in a common vertical zone between the base (001) and the prism (210). Similarly the brachypyramids (123), (122), (121), (241), etc., fall in a common vertical zone between (001) and (120). 181. Illustrations. The following figures of barite (304-311) give 305 306 307 Barite Crystals excellent illustrations of crystals of a typical orthorhombic species, and show also how the habit of one and the same species may vary. The axial ratio for this species is a : b : c = 0'815 : 1 : 1'314. Here d is the macrodome ORTHORHOMBIC SYSTEM 125 (102) and o the brachydome (Oil); m is, as always, the prism (110). Figs. 304-307 and 309 are described as tabular j| c; Fig. 308 is prismatic in habit in the direction of the macro-axis (6), and 310, 311 prismatic in that of the brachy-axis (a). Figs. 312-314 of native sulphur show a series of crystals of pyramidal habit with the dome n(011), and the pyramids p(lll), s(113). Note n trun- cates the terminal edges of the fundamental pyramid p. In general it should 314 315 Sulphur Crystals 316 317 Staurolite Figs. 316-318, Topaz be remembered that a macrodome truncating the edge of a pyramid must have the same ratio oth:l', thus, (201) truncates the edge of (221), etc. Similarly of .the brachydomes: (021) truncates the edge of (221), etc. Ji. Figs. 319-321. Again, Fig. 315, of staurolite, shows the pinacoids 6(010), c(001), the prism m(110), and the macrodome r(101). Figs. 316-318 are prismatic crystals of topaz. Here m is the prism (110); I and n are the prisms (120), (140); d and p are the macrodomes (201) and (401); /and y are the brachydomes (021) and (041); i, u, and o are the pyramids (223), (111), (221). 182. Projections. - - Basal, stereographic, and gnomonic projections are given in Figs. 319-320a, on pp. 125, 126, 127 for a crystal of the species topaz. Fig. 319 is the basal projection Topaz 126 CR YST ALLO GR APH Y of the crystal shown in *ig. 318. Figs. 320 and 320a give the stereographic and gnomonic projections of these forms present upon it. 110 Stereographic Projection Topaz Crystal 2. HEMIMORPHIC CLASS (26). CALAMINE TYPE (Orthorhombic Pyramidal Class) 183. Class Symmetry and Typical Forms. The forms of the ortho- rhombic-hemimorphic class are characterized by two unlike planes of sym- metry and one axis of binary symmetry, the line in which they intersect; there is no center of symmetry. The forms are therefore .hemimorphic, as defined in Art. 29. For example, if, as is usually the case, the vertical axis is made the axis of symmetry, the two planes of symmetry are parallel to the pinacoids a(100) and 6(010). The prisms are then geometrically like those of the normal class, as are also the macropinacoid and brachypinacoid; but the two basal planes become independent forms, (001) and (001). . There are also two macrodomes, (101) and (101), or in general (hQl) and (MM); and similarly two sets, for a given symbol, of brachydomes and pyramids. The general symmetry of the class is shown in the stereographic projec- 120 120 041 r 010 Gnomonic Projection Topaz Crystal 321 322 -*^ Symmetry of Hernimorphic Class Calamine Struvite (127) 128 CR YSTALLO GR APH Y 324 325 tion Fig 321. Further, Figs. 322, of calamine, and 323, of struvite, represent typical crystals of this class. In Fig. 322_the forms present are (301), i(031), t>(12l); in Fig. 323 they are 8(101), i(101), 0(011). 3. SPHENOIDAL CLASS (27). EPSOMITE TYPE. (Orthorhombic Bisphenoidal Class) 184. Symmetry and Typical Forms. The forms of the remaining class of the system, the ortho- rhombic-sphenoidal class, are char- acterized by three unlike rec- tangular axes of binary symme- try which coincide with the crys- tallographic axes, but they have no plane and no center of sym- metry (Fig. 324). The general form hkl here has four faces only, and the corresponding solid is a rhombic sphenoid, analogous to the sphenoid of the tetragonal system. The complementary pos- itive and negative sphenoids are Symmetry of Sphenoidal Class Epsomite enantiomorphous. Fig. 325 represents a typical crystal, of epsomite, with the positive sphenoid, z(lll). Other crystals of this species often show both positive and negative complementary forms , but usually unequally developed. MATHEMATICAL RELATIONS OF THE ORTHORHOMBIC SYSTEM 186. Choice of Axes. As explained in Art. 175, the three crystallographic axes are fixed as regards direction in all orthorhombic crystals, but any one of them may be made the vertical axis, c; and of the two horizontal axes, which is the longer (6) and which the snorter (a) cannot be determined until it is decided which faces to assume as the funda- mental, or unit, pyramid, prism, or domes. The choice is generally so made, in a given case, as to best bring out the relation of the crystals of the species in hand to others allied to them in form or in chemical composition, or in both respects; or, so as to make the cleavage parallel to the fundamental form; or, as suggested by the common habit of the crystals, or other considerations. 186. Axial and Angular Elements. The axial elements are given by the ratio of the lengths of the three axes in terms of the macro-axis, b, as unity. For example, with barite the axial ratio is a : 6 : c = 0'81520 : 1 : 1'31359. The angular elements are usually taken as the angles between the three pinacoids and the unit faces in the three zones between them. Thus, again for barite, these elements are 100 A 110 = 39 11' 13", 001 A 101 = 58 10' 36", 001 A Oil = 52 43' 8". ' Two of these angles obviously determine the third angle as well as the axial ratio. The degree of accuracy to be attempted in the statement of the axial ratio depends upon the character of the fundamental measurements from which this ratio has been deduced. There is no good reason for giving the values of a and c to many decimal places if the probable error of the measurements amounts to many minutes. In the above case the measurements (by Helmhacker) are supposed to be accurate within a few seconds. It is convenient, how- ever, to have the angular elements correct, say, within 10", so that the calculated angles obtained from them will not vary from those derived direct from the measured angles by more than 30" to 1'. ORTHORHOMBIC SYSTEM 129 187. Calculation of the Axes. The following simple relations (cf . Art. 48) connect the axes with the angular elements : tan (100 A 110) = a, tan (001 A Oil) = c, tan (001 A 101) = - These equations serve to give either the axes from the 'angular elements, or the angular elements from the axes. It will be noted that the axes are not needed for simple purposes of calculation, but it is still important to have them, for example to use in comparing the morphological relations of allied species. In practice it is easy to pass from the measured angles, assumed as the basis of calculation (or deduced from the observations by the method of least squares), to the angular elements, or from either to any other angles by the application of the tangent principle (Art. 49) to the pinacoidal zones, and by the solution of the right-angled spherical triangles given on the sphere of projection. Thus any face hkl lies in the three zones, 100 and Qkl, 010 and hOl, 001 and hkO. For example, the position of the face 312 is fixed if the positions of two of the poles, 302, 012, 310, are known. These last are given, respec- tively, by the equations Stibnite tan (001 A 302) = f x tan (001 A 101), tan (001 A 012) = \ x tan (001 A Oil) tan (100 A 310) = \ X tan (100 A 110). m' :010 Stereographic Projection Stibnite Crystal 130 CRYSTALLOGRAPHY 188 Example. Fig. 326 represents a crystal of stibnite from Japan and Fig. 327 the stereographic projection of its forms, p(lll), r(343), 77(353), co 3 (5-10'3), ra(110) and 6(010). On this the following measured angles were taken as fundamental: 7777' (353 A 353) =55 1' 0", 7777'" (353 A 353) = 99 39' 0". Hence, the angles 353 A 010 = 40 10*' and 353 A 053 = 27 30|' are known with- out calculation. The right-angled spherical triangle * 010'053'353 yields the angle (010 A 053) and hence (001 A 053); also the angle at 010, which is equal to (001 A 101). But tan (001 A Oil) = f X tan (001 A 053), and tan (001 A Oil) = c. Also, since tan (001 A 101) = --, the axial ratio is thus known, and two of the angular elements. The third angular element (001 A 110) can be calculated independently, for the angle at 001 in the triangle 001'053'353 is equal to (010 A 350) and tan (010 A 350) x f = (010 A 110), the complement of (100 A 110). Then since tan (100 A 110) = a, this can be used to check the value of a already obtained. The further use of the tangent principle with the occasional solution of a right- angled triangle will serve to give any desired angle from either the fundamental angles direct, or from the angular elements. Again, the symbol of any unknown face can be readily calculated if two measured angles of tolerable accuracy are at hand. For example, for the face co, suppose the meas- ured angles to be 6co (010 A hkl) = 30 15', coco' (hkl A hkl) = 51 32'. The solution of the triangle b'u'Okl gives the angle (010 A Okl) = 16 25' 20", and tan (001 A Okl) _ tan 73 34|' = k tan (001 A Oil) ~ tan 45 30^' I ' But the ratio of k : I must be rational and the number derived agrees most closely with 10 : 3. Again, the angle (001 A hOl) may now be calculated from the same triangle and the value 59 38 f obtained. From this the ratio of h to I is derived since tan (001 A hOl ) = tan 59 38f ' = _ = h tan (001 A 101) tan 45 43J' I ' This ratio is nearly equal to 5 : 3, and the two values thus obtained give the symbol 5'10'3. If, however, from the triangle 001' Okl'u, the angle at 001 is calculated, the value 26 42f is obtained, which is also the angle (010 A MO). From this the ratio h : k is deduced, since tan (010 A 110) tan 45 12f = k tan (010 A hkO) ~ tan 26 42f " ~ h ' The value of -r is hence closely equal to 2; this combined with that first obtained f =- = -5- J gives the same symbol 5" 10*3. This symbol being more than usually complex calls for fairly accurate measurements. How accurate the symbol obtained is can best be judged by comparing the measured angles with those calculated from the symbol. For example, in the given case the calculated angles for u(5'10'3) are 6(010 A 5'10'3) = 30 16', coco'(5'10-3) = 51 35'. The correctness of the value deduced is further established if it is found that the given face falls into prominent zones. It will be understood further that the zonal relations, explained on pp. 45-47, play an important part in all calculations. For example, in Fig. 326, if the symbol of r were un- known, it could be obtained from a single angle (as br), since for this zone h = I. 189. Formulas. Although it is not often necessary to employ formulas in calculations, a few are added here for sake of completeness. Here a and c in the formulas are the lengths of the two axes a and c. * The student in this as in every similar case should draw a projection, cf. Fig. 327 (not necessarily accurately constructed), to show, if only approximately, the relative posi- tion of the faces present. ORTHORHOMBIC SYSTEM 131 (1) For the distance between the pole of any face P(hkl) and the pinacoids a, 6, c, we have in general: cos 2 Pa = cos 2 (Md A 100) = cos 2 P6 = cos 2 (Md A 010) = cos 2 PC = cos 2 (Md A 001) = he 2 + k 2 a?c 2 + I 2 a? Me* + A; 2 a 2 c 2 + Pa? ' _ Pa? We 2 + /c 2 a 2 c 2 + I 2 a? ' 102 Oil 111 (2) For the distance (PQ) between the poles of any two faces (Md) and (par) hpc 2 + kqa?c 2 + Ira 2 cos PQ = , ' V(h 2 c 2 + & 2 a 2 c 2 + Z 2 a 2 ] [p 2 c 2 + ? 2 a 2 c 2 + r 2 a 2 ] 190. To determine, by plotting, the axial ratio of an orthorhombic crystal, having given the stereographic projection of its forms. In order to solve this problem it is necessary that the position of the pole of a pyramid face of known indices be given or the position of the faces of a prism and one dome or of both a macro- and a brachydome. For illus- tration it is assumed that a crystal of barite, such as represented in Fig. 305, has been measured on the goniometer and the poles of its faces plotted in the stereographic projec- tion. The lower right- hand quadrant of this projection is shown in Fig. 328. The forms present are common ones on bar- ite crystals and have been given the symbols, ro(110), d(102), o(011), c(001). The ratio of a : 6 can be determined readily from the position of the pole m(110). A radial line is drawn to the pole of the face and then a perpendicular erected to it from the end of the line representing the b crys- tallographic axis. The intercept of this perpen- dicular on the line repre- senting the a axis, when expressed in terms of the assumed unit length of the b axis, gives the length of a. It is to be noted that the fact that this line in the present case passes very nearly through the pole 111 is wholly accidental. The length of the vertical axis can be determined from the position of the pole of either d(102) or o(011). given^n 8 the upper left- hand quadrant of the . , . ,. figure. If the brachydome, o(011), is used the sloping line that gives the inchnA- tion of the face is started from a distance on the horizontal line equivalent to the length of the 6 axis, or 1, and its intercept .on the c axis will equal the unit length of that axis. If however, the position of d(102) is used the base line of the triangle must be made equal to the unit length of the a axis as already established and the intercept on the c axis will equal ? of the Tatter's unit length. Determination of the Axial Ratio for Barite 132 CRYSTALLOGRAPHY The problem could have been wholly solved from the position of the pyramid face, 111, if that form had been present on the crystal. The construction in this case is also illustrated. 191. To determine, by plotting, the indices of a face upon an orthorhombic crystal, given the position of iis 329 pole upon the stereographic projection and the axial ratio of the mineral. To illustrate this problem it is assumed that the position of the pole in the stereographic projection of the face o, Fig. 329, upon a topaz crystal is known. First draw a radial line through the pol e o . Next erect a perpendicular to this line, starting it from the distance selected as repre- senting 1 on the b crystallo- graphic axis. The intercept of this line upon the line representing the a axis when expressed in terms of the unit length of the b axis is 0'53. This is equivalent to the established unit length of the a axis and therefore the parameters of the face o on the horizontal crystallo- graphic axes are la, 16. Next the distance O-P is transfer- red into the upper left-hand quadrant of the figure. The position of the normal to the face is determined by measuring with a protractor the angular distance between O and o. The line giving the slope of the face is next drawn perpendicu- lar to this normal and its intercept upon the line representing the vertical axis determined. This distance when expressed in terms of the length of the 6 axis is 0'95. This is twice the established length of the c axis (0'476) and consequently the third parameter of the face o is 2c. This gives the indices 221 for the face. 192. To deter mine, by plotting, the axial ratio of an orthorhombic crystal having given the gnomonic projection of its forms. To illus- trate this problem the gnomonic projection of the crystal of topaz already given in Fig. 320a will be used. In Fig. 330 one quadrant of this projection is reproduced. From each pole lines are drawn perpendicular to the two lines representing the a and b crystal- lographic axes. It will be found that the intercepts made in this way upon the a axis have rational relations to each other. The same is true of the intercepts upon the 6 axis. The intercepts upon the two axes, however, are irrational in respect to each other. A convenient intercept upon each axis is chosen as 1 and the other intercepts upon that axis are then expressed in terms of this length. Of 2< MONOCLINIC SYSTEM 133 course with a known mineral, whose forms have already had indices assigned to them, the intercept that shall be considered as 1 is fixed. If we take r as equivalent to the radius of the fundamental circle of the projection, q as equal to the chosen intercept upon the 6 crystallographic axis and p that upon the a axis, then the axial ratio can be derived from the following expressions: b r . a r c q c p The proof of these relationships is similar to that already given under the Tetragonal System, Art. 117, p. 93. 193. To determine, by plotting, the indices of a face upon an orthorhombic crystal, given the position of its pole upon the gnomonic projection and the axial ratio of the min- eral. The method of construction in this case is the reverse of that given in the problem above and is essentially the same as given under the Isometric and Tetragonal Systems, Arts. 84 and 118. In the case of an orthorhombic mineral the intercepts of the perpendicu- lars drawn from the pole of the face to the a and b axes must be expressed in each case in terms of the unit intercept on that axis. These values, p and q, can be determined from the equations given in the preceding problem. V. MONOCLINIC SYSTEM (Obliqw System) 331 i 194. Crystallographic Axes. The monoclinic system includes all the forms which are referred to three unequal axes, having one of their axial inclinations oblique. The axes are designated as follows: the inclined or clino-axis is a; the ortho-axis is b, the ver- tical axis is c. The acute angle between the axes a and c is rep- resented by the letter (3; the angles between a and b and b and c are right angles. See Fig. 331. When properly orientated the inclined axis, a, dopes dawn .toward S^Omi^^W 1 the observer, the b axis is hori- zontal and parallel to the observer and the c axis vertical. 1. NORMAL CLASS (28). GYPSUM TYPE (Prismatic or Holohedral Class) 195. Symmetry. In the normal class of the monoclinic system there is one plane of sym- metry and one axis of binary symmetry normal to it. The plane of symmetry is always the plane of the axes a and c, and the axis of sym- metry coincides with the axis b, normal to this plane. The position of one axis (6) and that of the plane of the other two axes (a and c) is thus fixed by the symmetry; but the latter axes may occupy different positions in this plane. Fig. 332 Symmetry of Normal Class sn ows the typical stereographic projection, pro- jected on the plane of symmetry. Figs. 347, 348 are the projections of an actual 134 CR YST ALLO GR APH Y crystal of epidote; here, as is usual, the plane of projection is normal to the prismatic zone. 196. Forms. The various forms * belonging to this class, with their symbols, are given in the following table. As more particularly explained later, an orthodome includes two faces only, and a pyramid four only. Symbols Orthopinacoid or a-pinacoid (100) Clinopinacoid or 6-pinacoid (010) Base or c-pinacoid (001) Prisms (hkO) Orthodomes.. ' (/ ^ 1. 2. 3. 4. 5. 6. Clinodomes. . 7. 197. Pinacoids. The pinacoids are the orthopinacoid, clinopinacoid, and the basal plane. The orthopinacoid, (100), includes the two faces parallel to the plane of the ortho-axis b and the vertical axis c. They have the indices 100 and 100. This form is designated by the letter a, since it is situated at the extremity of the a axis; it is hence conveniently called the a-face or a-pinacoid. The clinopinacoid, (010), includes the two faces parallel to the plane of symmetry, that is, the plane of the clino-axis a and the axis c. They have the indices 010 and 010. The clinopinacoid is designated by the letter 6, and is called the b-face or b-pinacoid. The base or basal pinacoid, (001), includes the two terminal faces, above and below, parallel to the plane of the axes a, 6; they have the indices 001 and 001. The base is designated by the letter c, and is often called the c-face or c-pinacoid. It is obviously inclined to the orthopinacoid, and the normal angle between the two faces (100 A 001) is the acute axial angle 0. 333 335 101 I Ortho-, Clmo - and Basal Pinacoids Prism and Basal Pinacoid Orthodomes and Clinopinacoid The diametral prism, formed by these three pinacoids, taken together, Fig. 333, is the analogue of the cube in the isometric system. It is bounded by three sets of unlike faces; it has four similar vertical edges; also four similar edges parallel to the axis a, but the remaining edges, parallel to the axis b, are of two sets. Of its eight solid angles there are two sets of On the general use of the terms pinacoid, prisms, domes, pyramids, see pp. 31, 122. MONOCLINIC SYSTEM 135 four each; the two above in front are similar to those below behind, and the two below in front to those above in behind. 198. Prisms. -- The prisms are all of one type, the oblique rhombic prism. They may be divided into three classes as follows: the unit prism, (110), designated by the letter m, shown in Fig. 334; the orthoprisms, (hkQ), where h > k, lying between a(100) and m(110), and the clinoprisms, (MO) where h < k, lying between m(110) and 6(010). The orthoprisms and clino- prisms correspond respectively to the macroprisms and brachyprisms of the orthorhombic system, and the explanation on p. 123 will hence make their rela- tion clear. Common cases of these prisms are shown in the figures given later, 199. Orthodomes. The four faces parallel to the ortho-axis 6, and meeting the other two axes, fall into two sets of two each, having the general symbols (hOl) and (hOl). These forms are called orthodomes; they are strictly hemiprthodomes. For example, the unit orthodome (101) has the faces 101 and 101; they would replace the two obtuse edges between a(100) and c(001) in Fig. 333. The other unit orthodome (101) has the faces 101 and 101, and they would replace the acute edges between a(100) and c(001). These two independent forms are shown _together, with 6(010), in Fig. 33_5. Similarly the faces 201, 201 belong tq_the form (201), and 201, 201 to the independent but complementary form (201). 200. Clinodomes. The clinodomes are the forms whose faces are parallel to the inclined axis, a, while intersecting the other two axes. Their general symbol is hence (Qkl) and they lie between the base (001) and the clinopinacoid (010). Each form has Jour Jaces ; thus for the unit clinodome these have the symbols, Oil, Oil, Oil, Oil. The form n(021) in Fig. 342 is a clinodome. 201. Pyramids. The pyramids in the monoclinic system are all hemi- pyramids, embracing four faces only in each form, corresponding to the general symbol (hkl) . This obviously follows from the symmetry; it is shown, for example, in the fact already stated that the solid angles of the diametral prism (Fig. 333, see above), which are replaced by these pyramids, fall into two sets of four each. Thus any general symbol, as (321), includes the two independent forms (321) and (321) with the faces 321, 321, 321, 321, and 321, 321, 321, 321 336 337 339 The pyramids may also be divided into three classes as unit pyramids, (hhl)' orthopyramids, (hkl), when h > fc; or clinopyramids, (hkl), when h < k. These correspond respec- tively to the three prisms already named. They are analogous also to the unit pryamids, rnacropyramids, anTf brachypyramids of the orthorhombic system, and the explanation given on p. 124, should serve to make their relations clear. But it must be remembered that each general symbol 7 embraces two forms, (hhl) and (hkl) with four faces each, as above explained. Pyroxene 136 CRYSTALLOGRAPHY 202. Illustrations. Figs. 336-339 of pyroxene (a : b : c = 1'092 : 1 : 0-589, ft = 74 = o(100) A c(001)) show typical monoclinic forms. Fig. 336 shows the diametral prism. Of the other forms, m is the unit prism (110); p(101) is an orthodome; w(lll), 0(221), s(lll) are pyramids; for other figures see p. 475. Again, Figs. 340-342 represent common crystals of orthoclase (aj b : c = 0'659 : 1 : 0'555, ft = 64). Here z (130) is a prism; #(101) and 2/(201) are orthodomes ; n(021) is a clinodome; 0(111) a pyramid. Since (Fig. 340) c and x happen to make nearly equal angles with the vertical edge of the prism m, the combination often simulates an orthorhombic crystal. 340 341 342 Orthoclase Fig. 343 shows a monoclinic crystal, epidote, prismatic in the direction of the ortho-axis; the forms are a(100), c(001), r(101) and w(Ill). Fig. 344 of gypsum is flattened || 6(010); it shows the unit pyramid /(111) with the unit prism w(110). Epidote Epidote 203. Projections. Fig. 345 shows a projection of a crystal of epidote (cf. Fig. 897, p. 531) on a plane normal to the prismatic zone, and Fig. 346 one of a similar crystal on a plane parallel to 6(010) ; both should be care- fully studied, as also the stereographic and gnomonic projections of the same species, Figs. 347, 348. The symbols of the prominent faces are given in the latter figures. Stereographic Projection of Epidote Crystal 210 IV 211 10211 a 100 Gnomonic Projection of Epidote Crystal (137) 138 CRYSTALLOGRAPHY 2. HEMIMORPHIC CLASS (29). TARTARIC ACID TYPE (Sphenoidal Class) 204. The monoclinic-hemimorphic class is characterized by a single axis of binary symmetry, the 349 350 crystallographic axis 6, but ^ it has no plane of sym- metry. It is illustrated X. ^^ 7^ by the stereographic pro- jection (Fig. 349) made upon a plane parallel to 6(010). Fig. 350 shows a common form of tartaric acid; sugar crystals also belong here. The hemi- morphic character is dis- tinctly shown in the distribution of the clino- domes and pyramids; cor- responding to this the Tartaric Acid Symmetry of Hemimorphic Class artificial salts belonging here often exhibit marked pyroelectrical pheno- mena. 3. CLINOHEDRAL CLASS (30). CLINOHEDRITE TYPE (Domatic or Hemihedral Class) 205. The monoclinic-clinohedral class is characterized by a single plane of symmetry, parallel to the clinopinacoid, 6(010), but it has no axis of sym- metry. This symmetry is shown in the stereographic projection made upon a plane parallel to 6(010), Fig. 351. In this class, therefore, the forms parallel to the 6 axis, viz., c(001), a(100), and the orthodomes, are represented by a 353 Symmetry of Clinohedral Class Clinohedrite single face only. The other forms have each two faces, but it is to be noted that, with the single exception of the clinopinacoid 6(010), the faces of a given form are never parallel to each other. The name given to the class is based on this fact. Several artificial salts belong here in their crystallization, but the only MONOCLINIC SYSTEM 139 known representative among minerals is the rare silicate, clinohedrite (H 2 CaZnSiO 5 ),* a complex crystal of which is shown in two positions in Figs. 352, 353. As seen in these figures, the crystals of the group have a hemi- morphic aspect with respect to their development in the direction of the vertical axis, although they cannot properly be called hemimorphic since this is not an axis of symmetry. The forms shown in Figs. 352 353 are as follows: pinacoid, b (010) ;_ prisms, w(110), Wi(IlO), fc(3_20), n_(120), Z(130); orthodomes, e(10_l), ei(l_01); pyramids, p(lll), Pi(lll), tf(lll), r(331), s(551), *(771), w(531), o(131), z(131), y(121). It is to be noted that crystals of the common species pyroxene (also of segirite and titanite) occasionally show this habit in the distribution of their faces, but it is not certain that this may not be accidental^ MATHEMATICAL RELATIONS OF THE MONOCLINIC SYSTEM 206. Choice of Axes. It is repeated here (Art. 196) that the fixed position of the plane of symmetry establishes the direction of the plane of the a and c crystallographic axes and also of the axis b which is the symmetry axis and lies at right angles to this plane. The a and c axes, however, may have varying positions in the symmetry plane according to which faces are taken as the pinacoids a(100) and c(001), and which the unit pyramid, prism, or domes. 207. Axial and Angular Elements. The axial elements are the lengths of the axes a and c in terms of the unit axis b, that is. the axial ratio, with also the acute angle of inclination of the axes a and c, called /3. Thus for orthoclase the axial elements are: a : b : c = 0'6585 : 1 : 0'5554 = 63 56f. The angular elements are usually taken as the angle (100 A 001) which is equal to the angle /3; also the angles between the three pinacoids 100, 010, 001, respectively, and the unit prism 110, the unit orthodome (101 or 101) and the unit clinodomeOll. Thus, again, for orthoclase, the angular elements are: 001 A 100 = 63 56f , 100 A 110 = 30 36'. 001 A 101 = 50 16', 001 A Oil = 26 31'. 208. The mathematical relations connecting axial and angular elements are given in the following equations in which a, b, and c represent the unit lengths of the respective crystallographic axes. a = tan (10 A 110) or tan (100 A 110)= a. sin 0; (1) sin /3 = tan (001 A Oil) Qr t an (001 A Oil) = c . sin /3; (2) sin.tf a . tan (001 A 101) . (m A 101) sin ? - cos . tan (001 A 101) a + c . cos a. tan (001 A 101) . or t an (001 A 101) = (3) ( = : Ul UCkU ^vyv/i /\ J.WA/ sin + cos . tan (001 A 101) a - c . cos These relations may be made more general by writing in the several cases i in (1) MO for 110 and ^ a for a; in (2) OW for Oil and Before; in (3) hOl for 101 and j- c for c.. , 38, 115, ,889. 140 CRYSTALLOGRAPHY Also c = sin (001 A 101) = sin (001 A 101) ; a sin (100 A 101) sin (TOO A TOl)' and more generally h c sin (001 A hOl) = sin (001 A hQl) a ' I ~ sin (100 A hOl) ~ sin (TOO A hQl) Note also that tan = a and tan f = c, where is the angle (Fig. 347) between the zone-circles (001, 100) and (001, 110); also f is the angle between (100, 001) and (100, Oil). All the above relations are important and should be thoroughly understood. 209. The problems which usually arise have as their object either the deducing of the axial elements, i.e., the angle /3 and the values of a and c in terms of 6(= 1), from three measured angles, or the finding of any required interfacial angles from these elements or from the fundamental angles. The simple relations of the preceding article connect the angular and axial elements, and beyond this all ordinary problems can be solved * either by the solution of spherical triangles on the sphere of projection, or by the aid of the cotangent (and tangent) relation. It is to be noted, in the first place, that all great circles on the sphere of projection (see the stereographic projection, Fig. 347) from 010 cut the zone circle 100, 001, 100 at right angles, but those from 100 cut the zone circles 010, 001, 010 obliquely, as also those from 001 cutting the zone circle 100, 010, 100. 210. Tangent and Cotangent Relations. The simpje tangent relation holds good for all zones from 010 to any pole on the zone circle 100, 001. 100; in other words, for the prisms, clinodomes, and also zones of pyramids in which the ratio of h : I is constant (from 001 to hOl or to (M). Thus it is still true, as in the orthorhombic system, that the tangents of the angles of the prisms 210, 110, 120, 130 from 100 are in the ratio of * : 1 : 2 : 3, or, more generally, that tan (100 A MO) = k tan (010 A hkO) _ h tan (100 A 110) ~~ h tan (010 A 110) ~ k' Also for the clinodomes the tangents of the angles of 012, Oil, 021 from 001 are in the ratio of \ i : 1 : 2, etc. A^similar relation holds for the tangents of the angles of pyramids in the zones mentioned, as 121, 111, 212, etc. For zones other than those mentioned as from 100 to a clinodome, or from 001 to a prism, the more general cotangent formula given in Art. 49 must be employed. This rela- tion is simplified for certain common cases. For any zone starting from 001, as the zone 001, 100, or 001, 110, or 001, 210, etc.; if two angles are known, viz., the angles between 001 and those two faces in the given zone which fall (1) in the zone 010, 101, and (2) in the prismatic zone 010, 100; then the angle between 001 and any other face in the given zone can be calculated. Thus, Let 001 A 101 = PQ and 001 A 100 = PR, or " 001 A 111 = PQ " 001 A 110 = PR, or " 001 A 212 = PQ 001 A 210 = PR, etc. Then for these, or any similar cases, the angle (PS) between 001 and any face in the given zone (as 201, or 221, or 421, etc., or in general hQl, hhl, etc.) is given by the equation cot PS - cot PR = l_ cotPQ - cot PR ~ h For the corresponding zones from 001 to 100, to 110, to 210, etc., the expression has the same value; but here PQ = 001 A TOl, PR = 001 A TOO, PS = 001 A hOl, or 001 A Til, etc., 001 A TlO, etc., 001 A hhl, etc. * The general formulas, from which it is possible to calculate directly the angles between any face and the pinacoids, or the angle between any two faces whatever, are so complex as to be of little value. MONOCLINIC SYSTEM 141 If, however, 100 is the starting-point, and 100 A 101 or 100 A 111 then the relation becomes 100 A 001 100 A Oil PR, PR, etc., cot PS - cot PR cot PQ - cot PR 211 To determine, by plotting, the axial elements of a monoclinic crystal eiven the stereographjc projection of its forms. As an example of this problem t [fassumld that an orthoclase crystal similar to the one shown in Fig 341 has been measured andThe pol?s of its faces located on the stenographic projection, Fig. 354. The inclination of the a axis or the angle is given directly by measuring, by means of the stenographic protractor the angular distance between the poles of a(100) and c(001). In the present case the a(100) form does not actually occur on the crystal, p is measured as 64 If thp basp ii rmt present upon the crystal it will be usualfy possible to locate its position by mean^ of some zone circle on which it must he In the present case the great circle of the zone of m'(TlO), the oie m to the base "^ t0 ba k llne (Z ne f the orthodomes ) at ^ point of mllO fc'oio* 6010 a 100 Determination of Axial Elements of Orthoclase from Stereographic Projection The ratio between the lengths of the a and b axes can be readily determined from the position of the pole, m(110). Draw the radial line O-P from the center of the projection to m(110). From the end of the b axis draw a line at right angles to O-P. This repre- sents the intersection of the prism face with the horizontal plane and the distance O-R gives the intercept of the prism upon the horizontal projection of the a axis. The distance O-R therefore is not the unit length of the a axis but is that distance foreshortened some- what because of the inclination of that axis. The construction by which the true length of the a axis is obtained is shown in Fig. 355. The line R-O-S-T represents the horizontal projection of the a axis upon which the distance O-R is transferred from Fig. 354. As the prism face is vertical its intercept upon the 'a axis can be found by dropping a perpendicu- lar from R to intersect the line which represents the a axis. The inclination of this last 142 CRYSTALLOGRAPHY line is found by use of the angle ft, which has been already determined. The length of the a axis when expressed in terms of the b axis (TOO) was found to be 0' 66. The length of the c axis can be found best from the inclination of the ?/(201) face. This face will intersect the negative end of the a axis and the upper end of the c axis at either \a, Ic or la, 2c. The angle between the center of the projection, O, Fig. 354, and the pole y is measured by means of the stereographic protractor. From this angle the position of the normal to y, as shown in Fig. 355, is determined. The line representing the slope of the face is drawn at right angles to this normal, starting from the negative unit length of the inclined a axis. The intercept on the c axis was found to be equal to I'll, which, as it is equal to 2c, would give the unit length of the c axis as, 0'55. The length of the c axis could also be determined from the inclination of the pyramid face, o(Tll). The method of construction would be similar to that described in the prob- lem below. 212. To determine the indices of a face upon a monoclinic crystal, having given the position of its pole upon the stereographic projection and the axial elements of the min- eral. The pyramid face o on orthoclase will be used to illustrate the problem. First, see Fig. 354, a radial line is drawn through the pole o and a perpendicular S-T erected to it, starting from the unit length of the b axis. It is to be noted that the point T is the inter- section of the face o with the horizontal projection of the a axis Transfer the distance Determination of Axial Elements, etc. of Orthoclase O-S to the horizontal line in Fig. 355 and locate the position of the normal to o by the angle, Fig. 354, between O and o. The line giving the slope of the face can then be drawn from the point S (Fig. 355) perpendicular 'to the normal. This line intersects the line representing the vertical axis at a distance equal to its unit length. Two points of inter- section of the pyramid face with the plane of the a and c axes have now been determined, namely Ic and T. A line joining these two points will give the intersection of the two planes and the point where it crosses the line representing the a axis will therefore give the intercept of the pyramid upon that axis. This is also found to be at the unit length and therefore the indices of o must be 111. 213. To determine, by plotting, the axial elements of a monoclinic crystal, having given the gnomonic projection of its forms. The construction by which this problem is solved is shown in Fig. 356. The poles of the unit forms (101), (Oil), (001) and (111) are located (in this case tor pyroxene) and the zonal lines drawn. The angle /S is complementary to TRICLINIC SYSTEM 143 the angle from the center of the projection to 001. This can be measured directly bv means of the gnomonic tangent scale. Then construct the triangles CST and XYZ The angles p and *, and [ v and .are measured. This can most easily be done by means of the divided circle and the fact that an angle at the circumference of Lircle ?s mL?ureTby one half its subtended arc. The following relations will then yield the axial ratio sin p. sin TT' sin v sin v the explanation f the 366 Determination of Axial Elements of Pyroxene from Gnomonic Projection 214. To determine, by plotting, the indices of a face on a monoclinic crystal, having given the position of its pole upon the gnomonic projection. There is no essential differ- ence between the orthorhombic and monoclinic systems in the determination of indices from the gnomonic projection. The intercepts of perpendiculars from the poles of the faces upon th< front to back and left to right zonal lines running through the pole of c(001) give directly the first two numbers of the indices. The gnomonic projection of the epi- dote crystal already given (Fig. 348) will serve to illustrate this problem. VI. TRICLINIC SYSTEM (Anorthic System) 215. Crystallographic Axes. The tridinic system includes all the forms which are referred to three unequal axes with all their intersections oblique. When orientated in the customary manner one axis has a vertical posi- 144 CRYSTALLOGRAPHY 357 Triclinic Axes tion and is called the c axis (cf. Fig. 357), a second axis lies in the front-to- back plane, sloping down toward the observer, and is called the a axis. The remaining axis is designated as the b axis. Usually the a and b axes are so chosen that the a axis is the shorter and, like in the orthorhombic system, is sometimes called the brachy-axis. In that case the 6 axis is longer and is known as the macro- axis. But this is not invariably true; thus with rho- donite the ratio of a :b = 1*073 : 1. The angle between the axes b and c is called a, that between a and c is 0, and that between a and b is 7 (Fig. 357). It is to be noted that there is no necessary relation between the values of a, p, and 7, any one may be greater or less than 90; this is determined by the choice of the fundamental forms. 1. NORMAL CLASS (31). AXINITE TYPE (Holohedral or Pinacoidal Class) 216. Symmetry. The normal class of the triclinic system is character- ized by a center of symmetry, the point of intersection of the three axes, but there is no plane and no axis of symmetry. This symmetry is shown in the accompanying stereographic projection (Fig. 358). 358 Symmetry of Normal Class Triclim'c Pinacoids 217. Forms. Each form of the class includes two faces, parallel to one another and symmetrical with reference to the center of symmetry. This is true as well of the form with the general symbol (hkl) as of one o the special forms, as, for example, the a-pinacoid (100). __ Hence, as shown in the following table, the four pjismatic faces 110, TlO, 10, 110 include two forms, namely, 110, 110, and 110, 110. The same is true of the domes._ Further, _any eight corresponding pyramidal faces, as, for example, 111, 111_,_111,_111, 111, _1_11, 111, 111 belong to four distinct forms, namely, 111, 111; 111, 111; Hi, lll;-in, 111, and similarly in general. TRICLINIC SYSTEM The various types of forms are given in the following table: Indices Macropinacoid or a-pinacoid (100) Brachypinacoid or 6-pinacoid ' " (010) Base or c-pinacoid (001) Prisms { >, W I (MO) MacrodomeS (P) BrahydomeB (g 145 Pyramids I (hkl) \(hkl) In the above table it is assumed that the axial ratio is such that a < b. If the oppo- site were true the names brachy- and macro- would be interchanged. 218. The explanations given under the two preceding systems make it unnecessary to discuss in detail the various forms individually, except as illustrated in the case of crystals belonging to certain typical triclinic species. It may be mentioned, however, that Fig. 359 shows the diametral prism, which is bounded by three sets of unlike faces, the pinacoids a, 6, and c. This is the analogue of the cube of the isometric system, but here the like faces, edges, and solid angles include only a given face, edge, and angle, and that opposite to it. 219. Illustrations. A typical triclinic crystal is shown in_Fig. 360 of axinite. Here a (100) is the macropinacoid; m(110)_and M(110) the two unit prisms; s(201) a macrodome, and z(lll) and r(lll) two unit pyramids. The axial ratio is as follows: a : b : c = 0'49 : 1 : 0'48, a = 82 54', ft = 91 52', 7 = 131 32'. Figs. 361, 362 show two crystals of rhodonite, a species which is allied to pyroxene, and which approximates to it in angle and habit. Here the faces 361 362 Rhodonite are: Pina_coids a(l_00), 6(010), c(001); prisms m(110), M(lTO); pyramids Further illustrations are given by Fig. 363 of albite and Fig. 364 of anor- thite. The symbols of the faces, besides the pinacoids and the unit prisms, 146 CRYSTALLOGRAPHY are as follows: Fig. 363, z(101); _Fig. 364, prisms /(1 30), z(130); domes *(207), t/(201), e(021), r(061), n(021); pyramids m(lll), a(lll), o(lll), 363 365 &0104 &010 mllO a 100 MllQ Stereographic Projection of an Axinite Crystal . In Fig. 364 of anorthite the similarity of the crystal to one of ortho- clase is evident on slight examination (cf. Figs. 340, 341), and careful study TRICLINIC SYSTEM 147 with the measurement of angles shows that the correspondence is very close Hence in this case the choice of the fundamental planes is readily made. Fig. 365 represents a crystal of axinite; Figs. 366 and 367 its stereo- graphic and gnomonic projections. 367 M110 6010-4 K110 Gnomonic Projection of an Axinite Crystal a 100 368 2. ASYMMETRIC CLASS (32). CALCIUM THIOSULPHATE TYPE (Hemihedral Class) 220. Besides the normal class of the triclinic system there is another possible class, possessing symmetry neither with respect to a plane, axis nor center; in it a given form has one face only. This class finds ^- * .. examples among a number of artificial salts. One of these is calcium thiosulphate (CaS 2 O 3 .6H 2 O) ; as yet no mineral species is known to be included here. This is the most general of all the thirty-two types of forms classified according to their symmetry and comes first, therefore, if the classes are arranged in order according to the degree of symmetry characterizing them. This class is one of those whose crystals may show circular polarization. This is true of eleven of the classes which have Symmetry of Asymmetric Class been described in the preceding pages. \ 148 CRYSTALLOGRAPHY MATHEMATICAL RELATIONS OF THE TRICLINIC SYSTEM 221. Choice of Axes. It is obvious, from what has been said as to the symmetry of this system, that any three faces of a triclinic crystal may be chosen as the pinacoids, or the faces which fix the position of the axial planes and the directions of the axes; moreover, there is a like liberty in the choice of the unit prisms, domes or pyramids which further fix the lengths of the axes. When the crystal in hand is allied in form or composition to other species, whether of the same or different systems, this fact simplifies the problem and makes the choice of the fundamental forms easy. This is well illustrated, as already noted, by the triclinic feldspars (e.g., albite and anorthite, Figs. 363, 364) which are near in angle to the allied monoclinic species orthoclase. Rhodonite (Figs. 361, 362), the triclinic member of the pyroxene group, is another good example. In other cases, where no such relationship exists, and where varied habit makes different orientations plausible, there is but little to guide the choice. This is illustrated in the case of axinite (Fig. 360), where at least ten distinct positions have been assumed by different authors. 222. Axial and Angular Elements. The axial elements of a triclinic crystal are : (1) the axial ratio, which expresses the lengths of the axes a and c in terms of the third axis, 6; and (2) the angles between the axes a, 3, 7 (Fig. 357). There are here five quanti- ties to be determined which obviously require the measurement of five independent angles between the faces. The angular elements are usually taken as the angles between the pinacoids and, in addition, those between each pinacoid and the unit face lying in the zone of the other pina- coids; that is, ac, 100 A 001, be, 010 A 001; 001 A 101, 001 A Oil; 100 A 010, also am 100 A 110, or, instead, any one or all of these, aM, 100 A 110, 001 A 101, 001 A Oil. Of these six angles taken, one is determined when the others are known. 223. The mathematical relations existing between the axial angles and axial ratio, on the one hand, and the angles between the faces on the other, admit of being drawn out with great completeness, but they are necessarily complex and in general have little practical value. In fact, most of the problems likely to arise can be solved by means of the triangles of the spherical projection, together with the cotangent formula connecting four planes in the same zone (Art. 49, p. 49); this will often be laborious and may require some ingenuity but in general involves no serious difficulty. In connection with the use of the cotangent formula, it is to be noted that in certain commonly occurring cases its form is much simpli- fied; some of these have already been explained under the monoclinic system (Art. 210). The formulas given there are of course equally applicable here. 224. The first problem may be to find the axial elements from measured angles. Since these elements include five unknown quantities, viz., the three axial angles a /3 7 and the lengths of the axes a and c in terms of b, five measured angles are required, as already stated. Fig. 369 represents the crystallographic axes of the triclinic mineral rhodonite The positive ends of the three axes are joined by lines forming three triangles the angles of which are very important. In the triangle, for instance, which has the b and c axes for two of its sides since the length of the b axis is taken as I'O, it is only necessary to know the angle a and either p or ?r in order to determine the length of the c axis. In the triangle that has the a and b axes for two of its sides it is necessary to know the value of 7 and either a or T in order to deter- mine the length of the a axis. And lastly in the triangle formed between the a and c axes, if the length of either of of the other can be determined from the angle and either'f orT &S*? ^af a TRICLINIC SYSTEM 149 a ioo ^*k i{ rhodonite ? ho *j D the , for ms o(100), 6(010), c(001) and p(lll), see Fie 370, has bee^me^ural and^e poles of the faces plotted in the stereogr^hic'projectio^ great circles which connect these 371 poles are the same as those shown 100 in the triangles built upon the crystallographic axes, Fig. 369. With the angles between the different crys- tal faces known by measurement, it is easy, by the formulas of spherical trigonometry, to calculate the value of these other angles and from them obtain the axial ratio. That the angles shown on the stere- ographic projection, Fig. 371, are identical with those in Fig. 369 may be proved as follows. Let Fig. 372 represent a vertical section cut through the spherical projection of rhodonite in such a way as to include the 6 and c crystallographic axes. The triangle, which has these axes as two sides and the three angles a, -K and p, lies therefore in the plane of the figure. The nor- mals to all faces parallel to the c axis, i.e. the prism zone, would lie in a plane at right angles to that axis. This plane would intersect the sphere of the spher- ical projection in a great circle which is represented on the stereographic pro- jection, Fig. 371, by the divided circle. On Fig. 372 this great circle would appear in orthographic projection as the line C-C' lying at right angles to the c axis. In the same way all faces lying parallel to the b axis, i.e. the zone (100)- (101)- (001), would have their normals in a plane which would be foreshortened to the line B-B' in Fig. 372. Since the lines C-C' and B-B' are at right angles respectively to the c and b axes the angle between them must equal the axial angle, a. This same angle will appear therefore on the stereographic projection, Fig. 371, between the great circles of the two zones, the faces of which are parallel respectively to the c and b axes. Further the normals to all faces which intersect the b and c axes at their unit lengths would lie in a plane at right angles to the line b-c, Fig. 372. This plane would appear in orthographic projection as the line P-P'. On the stereographic 372 projection, Fig. 371, this would be represented as the zonal circle passing through (100), (111), (Oil), (100). The angle between B-B' and P-P' will by construction equalV and that between C-C' and P-P' will equal p. These same angles will appear therefore in the stereographic projection between the corresponding zone circles. In the same way the identity of the angles j, a, T, 0, n and v in Figs. 369 and 371 can be proved. With the necessary number of these angles given the formulas required for the calculation of the axial lengths are given below. The angles T', a', t>', //, if' and p' are the corresponding angles to T, o-, etc.. in the adjacent quadrants, see Fig. 373. 373 150 CRYSTALLOGRAPHY sin T _ sin T' _ a sin v _ sin v' _ c sin -w _ sin TT' _ c sin sin MO sin MO' I la h tt sin TTO _ sin TH/ _ c _ k c sin PO sin p ' I, I b Thus for the face 321 the formulas become sin TO _ a^ _ 2_a sin v _ 3c sin XQ _ 2c ^ sin (TO |6 36 sin MO a sin po b It is also to be noted that a = 180 - A, ft = 180 - B, 7 = 180 - C, where A, B, C are the angles in the pinacoidal spherical triangle IOO'010'OOI at these poles respectively. That is, A = * + P = TO + PO = (180 - a); B = ^+ M = ^ + /io= (180 -0); C = T-f- and p of Goldschmidt) measured, respec- tively, in the vertical and horizontal circles from an assumed pole and merid- ian, which are fixed, in most cases, by the symmetry of the crystal. In prac- tice the crystal is usually so mounted that its prismatic zone is perpendicular to the vertical circle. A plane at right angles to this zone, i.e., the basal plane in the first four systems, is known as the polar plane and its position when reflecting the signal into the telescope establishes the zero position for the horizontal circle. The position of a pinacoid, usually the 010 plane, in the prism zone establishes the zero position for the vertical circle. For example, with an orthorhombic crystal, for the pyramid 111, the angle (measured on the vertical circle) is equal to 010 A 110 and p (measured on the horizontal circle) is equal to 001 A 111. Goldschmidt has shown that this instrument is directly applicable to the system of indices and methods of calculation and projection adopted by him, which admit of the deducing of the elements and symbols of a given crystal with a minimum of labor and calculation.* Fedorow has also shown that this in- strument, with the addition of the appliances devised by him, can be most conveniently used in the crys- tallographic and optical study of crystals. The following hints as to the methods of using this instrument may prove helpful. The telescope and colhmator tube are placed at some convenient angle to each other (usually about 70) and then clamped in position. The next step is to find the polar posi- tion of the horizontal circle, i.e., the position at which a crystal plane lying at right angles to the axis of the vertical circle will throw the reflected beam of light on to the cross-hairs of the telescope. Obviously the plane under these conditions must be normal to the bisector of the angle between the axes of the collimator and telescope, the line B-P Fig 382. The method by which this polar position is found is as follows: Some reflecting sur- face is mounted upon the end of the post h, Figs. 381, 382, making some small inclined angle to the plane normal to that post. Then by turning the instrument in both the hori- * See Goldschmidt's Krystallographische Winkeltabellen (432 pp., Berlin, 1897). 9Q TTa e a -? les rec * ulre( i b T his , g y stem f <* all known species. See also Zs. Kryst., wnrV angles are measured. If the pinacoid 010 is not present it is usually possible to determine its theoretical position from the position of other faces in the prism zone or in the zone between 010 and 100. 2. // there is no basal plane present upon the crystal but a good prism zone. Under these cir- cumstances the horizontal circle is turned until it is exactly 90 away from its determined polar angle and then the crystal adjusted by means of the tipping scr ews until the signals from the faces of the prism zone all fall on the vertical cross-hair as the vertical circle of the goniometer is turned. 3. // neither basal plane or prism zone is available but there are two or more faces present which are equally inclined to a theoretical basal plane. First adjust the crystal as nearly as possible in the proper position and then obtaining reflections from these faces note the horizontal circle reading in each case. Take an average of these read- ings and adding or subtracting this angle from the polar angle of the horizontal scale place the instrument in this position. Then by tipping the crystal try to bring it into such a position that all of these faces will successively reflect the sig- nal into the telescope as the vertical circle is turned. The operation may have to be re- peated two or three times before the final adjustment is made. If the angle between the inclined faces and the theoretical base is known the instrument can be set in the proper position at once and the crystal brought into adjustment very quickly. Other problems wil arise in practice but their solution will be along similar lines to those suggested above. It may frequently happen that more than one method of adjustment may be used with a given crystal. In that , rase H 6010 [0=0; p=90 120 43 24; P90 in all possible ways before making the measurements. 160 CRYSTALLOGRAPHY After these adjustments have been completed the crystal is turned about both the horizontal and vertical planes so that each face upon it successively reflects the signal into the telescope. The horizontal and vertical readings are made in each case. The forms present can then be readily plotted in either the stereographic or gnomonic projec- tions. Fig. 383 shows how the forms of a simple crystal of topaz could be plotted in the stereographic projection from the and p angles obtained from it the two circle goni- ometer measurements. For each face the vertical circle angle, <, is plotted on the divided circle, the position of 6(010) giving the zero point while the horizontal circle angle is plotted on a radial line from the center of the projection, the position of c(001) giving its zero point. COMPOUND OR TWIN CRYSTALS 233. Twin Crystals. Twin crystals are those in which one or more parts regularly arranged are in reverse position with reference to the other part or parts. They often appear externally to consist of two or more crystals symmetrically united, and sometimes have the form of a cross or star. They also exhibit the composition in the reversed arrangement of part of the faces, 384 386 Thenardite Columbite Fluorite in the striae of the surface, and in re-entering angles; in certain cases the compound structure can only be surely detected by an examination in polar- ized light. The above figures (Figs. 384-386) are examples of typical kinds of twin crystals, and many others are given on the pages following. To illustrate the relation of the parts in a twin crystal, Figs. 387, 388 are given. Fig. 387 shows a regular octahedron divided into halves by a plane parallel to an octahedral face. If now the lower half be supposed to be re- volved 180 about an axis normal to this plane, the twinned octahedron of Fig. 388 results. This is a common type of twin in the isometric system, and the method here employed to describe the position of the parts of the crystal to one another is applicable to nearly all twins. 234. Distinction between Twinning and Parallel Grouping. It is important to understand that crystals, or parts of crystals, so grouped as to occupy parallel positions with reference to each other that is, those whose similar faces are parallel are not called twins; the term is applied only where the crystals or parts of them are united in their reversed position in accordance with some deducible mathematical law. Thus Fig. 389, which represents a cluster of partial crystals of analcite, is a case of parallel grouping simply (see Art. 252); but Fig. 407 illustrates twinning, and this is COMPOUND OR TWIN CRYSTALS 161 true of Fig. 416 also. Since though in these cases the axes remain parallel the similar faces (and planes of symmetry) are reversed in position. 235. Twinning-Axis. The relative position of the parts of a twinned crystal can be best described as just explained, by reference to that line or axis called the twinning-axis, a revolution of 180 about which would serve to 388 Twinned Octahedron Analei'te bring the twinned part parallel to the other, or in other words, which would cause one of the parallel parts to take a twinned position relatively to the other. The twinning-axis is always a possible crystalline line that is, either a crystallographic axis or the normal to some possible face on the crystal, usually one of the common fundamental forms. It is not to be supposed that ordinary twins have actually been formed by such a revolution of the parts of crystals, for all twins (except those of second- ary origin, see Art 242) are the result of regular molecular growth or enlarge- ment, like that of the simple crystal. This reference to a revolution, and an axis of revolution, is only a convenient means of describing the forms. In certain rare cases, particularly of certain pseudo-hexagonal species, a revolution of 60 or 120 about a normal to the base has been assumed to explain the complex group observed. 236. T winning-Plane. The plane normal to the axis of revolution is called the twinning-plane. The axis and plane of twinning bear the same relation to both individuals in their reversed position; consequently, in the majority of cases, the twinned crystals are symmetrical with reference to the twinning-plane. The twinning-plane is, with rate exceptions, parallel to a possible occurring face on the given species, and usually one of the more frequent or fundamental forms. The exceptions occur only in the triclinic and monoclinic systems, where the twinning-axis is sometimes one of the oblique crystallographic axes, and then the plane of twinning normal to it is obviously not necessarily a crystallographic plane; this is conspicuously true in albite. 237. Composition-Plane. The plane by which the reversed crystals are united is the composition-plane. This and the twinning-plane very com- monly coincide; this is true of the simple example given above (Fig. 388), where the plane about which the revolution may be conceived to take place (normal to the twinning-axis) and the plane by which the semi-individuals are united are identical. When not coinciding, the two planes are generally at right angles to each other that is, the composition-plane is parallel to the axis of revolution. Examples of this are given below. Still again, where the 162 CRYSTALLOGRAPHY crystals are not regularly developed, and where they interpenetrate, the con- tact surface may be interrupted, or may be exceedingly irregular. In such cases the axis and plane of twinning have, as always, a definite position, but the composition-plane loses its significance. Thus in quartz twins the interpenetrating parts have often no rectilinear boundary, but mingle in the most irregular manner throughout the mass, showing this composite irregularity by abrupt variations in the character of the surfaces. This irregular internal structure, found in many quartz crystals, even the common kinds, is well brought out by means of polarized light; also by etching with hydrofluoric acid. The composition-plane has sometimes a more definite signification than the twinning-plane. This is due to the fact that in many cases, whereas the former is fixed, the twinning-axis (and twinning-plane) maybe exchanged 390 for another line (and plane) at right angles to each, respectively, 7v since a revolution about the second axis will also satisfy the * c ' ' conditions of producing the required form. An example of this is furnished by Fig. 390, of orthoclase; the composition-plane is here fixed namely, parallel to the crystal face, 6(010). But the axis of revolution may be either (1) parallel to this face and normal to a (100), which is then consequently the twinning-plane, though the axis does not coincide with the crystallographic axis; or (2) the twinning-axis may be taken as __ coinciding with the vertical axis, and then the twinning-plane Orthoclase normal to it is not a crystallographic face. In other simpler cases, also, the same principle holds good, generally in con- sequence of the possible mutual interchange of the planes of twinning and composition. In most cases the true twinning-plane is evident, since it is parallel to some face on the crystal of simple mathematical ratio. 238. An interesting example of the possible choice between two twinning-axes at right angles to each other is furnished by the species staurolite. Fig. 439 shows a prismatic twin from Fannin Co., Ga. The measured angle for bb was 70 30'. The twinning-axis deduced from this may be normal to the face (230), which would then be the twinning-plane. Or, instead of this axis, its complementary axis at right angles to it may be taken, which would equally well produce the observed form. Now in this species it happens that the faces, 130 and 230 (over 100), are almost exactly at right angles with each other, and, according to the latter supposition, 130 becomes the twinning-plane, and the axis of revolution is normal to it. Hence, either 230 or 130 may be the twinning-plane, either supposition agreeing closely with the measured angle (which could not be obtained with great accuracy). The former method of twinning (tw. pi. 230) conforms to the other twins observed on the species, and hence it may be accepted. What is true in this case, however, is not always true, for it will seldom happen that of the two complementary axes each is so nearly normal to a face of the crystal. In most cases one of the two axes conforms to the law in being a normal to a possible face, and the other does not, and hence there is no doubt as to which is the true twinning-axis. Another interesting case is that furnished by columbite. The common twins of the species are similar to Fig. 385, p. 160, and have e(021) as the twinning-plane; but twins also occur like Fig. 434, p. 169, where the twinning-plane is g(023). The two faces, 021 and 023, are nearly at right angles to each other, but the measured angles are in this case sufficiently exact to prove that the two kinds cannot be referred to one and the same law. 239. Contact- and Penetration-Twins. In contact-twins, when nor- mally formed, the two halves are simple connate, being united to each other by the composition-plane; they are illustrated by Figs. 385, 388, etc. In actual crystals the two parts are seldom symmetrical, as demanded by theory, but one may preponderate to a greater or less extent over the other; COMPOUND OR TWIN CRYSTALS 163 in some cases only a small portion of the second individual in the reversed position may exist. Very great irregularities are observed in nature in this respect. Moreover, the re-entering angles are often obliterated by the abnor- mal developments of one or other of the parts, and often only an indistinct line on some of the faces marks the division between the -two individuals. Penetration-twins are those in which two or more complete crystals inter- penetrate, as it were crossing through each other. Normally, the crystals have a common center, which is the center of the axial system for both ; practically, however, as in contact-twins, great irregularities occur. Examples of twins of this second kind are given in the annexed figures, Figs. 386 and 391 of fluorite, Fig. 392 of tetrahedrite, and Fig. 393 of chabazite. Other examples occur in the pages following, as, for instance, of the species staurolite (Figs. 438-441), the crystals of which sometimes occur in nature with almost the perfect symmetry demanded by theory. It is obvious that the distinction between contact- and penetration-twins is not of great import- ance, and the line cannot always be clearly drawn between them. 392 393 Fluorite Tetrahedrite Chabazite 240. Paragenic and Metagenic Twins. The distinction of paragenic and metagenic twins belongs rather to crystallogeny than crystallography. Yet the forms are often so obviously distinct that a brief notice of the distinction is important. In ordinary twins, the compound structure had its beginning in a nucleal compound molecule, or was compound in its very origin; and whatever 394 inequalities in the result, these are only irregularities in the devel- opment from such a nucleus. But in others, the crystal was at first simple; and afterwards, through some change in itself or in the condition of the material supplied for its increase, received new layers, or a continuation, in a reversed position. This mode ot twinning is metagenic, or a result subsequent to the origin of the crystal; while the ordinary mode is paragenic. One form ot it is illustrated in Fig. 394. The middle portion had attained a length of half an inch or more, and then became geniculated simultaneously at either extremity. These geniculations are often repeated in rutile, and the ends of the crystal are thus bent into one another, and occasionally produce nearly regular prismatic forms. This metagenic twinning is sometimes presented by the successive layers of deposition in a crystal, as in some quartz crvstals, especia amethyst, the inseparable layers, exceedingly thin, being of oppos kinds. In a similar manner, crystals of the triclmic feldspars, by oscillatory composition, Rutile albite, etc., _- ., are often made up of thin plates parallel to 6(010) by osc and the face c(001), accordingly, is finely striated parallel to the edge 241. Repeated Twinning, Polysynthetic and Symmetrical. In the preceding paragraph one case of repeated twinning has been mentioned, that of the feldspars; it is a case of parallel repetition or parallel grouping in re- versed position of successive crystalline lamellae. This kind of twinning is 164 CRYSTALLOGRAPHY often called polysynthetic twinning, the lamellae in many cases being extremely thin, and giving rise to a series of parallel lines (striations) on a crystal face or a surface of cleavage. The triclinic feldspars show in many cases polysyn- thetic twinning and not infrequently on both c(001) and 6(010), cf. p. 172. It is also observed with magnetite (Fig. 474) , pyroxene, barite, etc. Another kind of repeated twinning is illustrated by Figs. 395-400, where the successively reversed individuals are not parallel. In these cases the axes may, however, lie in a zone, as the prismatic twins of aragonite, or they may be inclined to each other, as in Fig. 397 of staurolite In all such cases the repetition of the twinning tends to produce circular forms, when the angle between the two axial systems is an aliquot part of 360 (approximately). Thus six-rayed twinned crystals, consisting of three individuals (hence called trillings), occur with chrysoberyl (Fig. 395), or cerussite (Fig. 396), or staurolite (Fig. 397), since three times the angle of twinning in each case is not far from 360. Again, five-fold twins, or fivelings, occur in the octahedrons of gold and 397 Spinel Rutile Phillipsite spinel (Fig 398), since 5 X 70 32' = 360 (approx.). Eight-fold twins, or eigktlings, of rutile (Figs. 399, 413) occur, since the angle of the axes in twinned position goes approximately eight times in 360. Repeated twinning of the symmetrical type often serves to give the com- pound crystal an apparent symmetry of higher grade than that of the simple individual, and the result is often spoken of as a kind of pseudo-symmetry (Art. 20) , cf. Fig. 431 of aragonite, which represents a basal section of a pseudo-hexagonal crystal. Fig. 400 of phillipsite (cf. Figs. 452-454) is an inter- EXAMPLES OF IMPORTANT METHODS OF TWINNING 165 esting case, since it shows how a multiple twin of a monoclinic crystal may simulate an isometric crystal (dodecahedron). Compound crystals in which twinning exists in accordance with two laws at once are not of common occurrence; an excellent example is afforded by staurolite, Fig. 441. They have also been observed with albite, orthoclase, and in other cases. 242. Secondary Twinning. When there is reason to believe that the twinning has been produced subsequently to the original formation of the crystal, or crystalline mass, as, for example, by pressure, it is said to be secondary. Thus the calcite grains of a crystalline limestone often show such secondary twinning lamellae. The same are occasionally observed (||c, 001) in pyroxene crystals. Further, the poly synthetic twinning of the triclinic feldspars is often secondary in origin. This subject is further discussed on a later page, where it is also explained that in certain cases twinning may be produced artificially in a crystal individual e.g., in calcite (see Art. 282). EXAMPLES OF IMPORTANT METHODS OF TWINNING 243. Isometric System. With few exceptions the twins of the normal class of this system are of one kind, the twinning-axis an octahedral axis, and the twinning-plane consequently parallel to an octahedral face; in most cases, also, the latter coincides with the composition-plane. Fig. 388, p. 161,* 401 402 403 Galena Hauynite Sodalite shows this kind as applied to the simple octahedron; it is especially common with the spinel group of minerals, and is hence called in general a spinel-twin. * It will! be noted that here and elsewhere the letters used to designate the faces on the twinned parts of crystals are distinguished by a subscript line. 166 CRYSTALLOGRAPHY Fig. 401 is a similar more complex form; Fig. 402 shows a cube twinned by this method, and Fig. 403 represents the same form but shortened in the direction of the octahedral axis, and hence having the anomalous aspect of a triangular pyramid. All these cases are contact-twins. Penetration-twins, following the same law, are also common. A simple case of fluorite is shown in Fig. 391, p. 163; Fig. 404 shows one of galena; Fig. 405 is a repeated octahedral twin of haiiynite, and Fig. 406 a dodecahedral twin of sodalite. 244. In the pyritohedral class of the isometric system penetration-twins ot the type shown in Fig. 407 are common (this form of pyrite is often called the iron cross). Here the cubic axis is the twinning-axis, and obviously such a twin is impossible in the normal class. Figs. 408 and 409 show analogous forms with par- allel axes for crystals belonging to the tetrahedral class. The peculiar development of Fig. 408 of tetrahedrite is to be noted. Fig. 410 is a twin of the ordinary spinel type of another tetrahedral species, sphalerite; with it, complex forms with repeated twinning are not uncommon and sometimes polysynthetic twin lamellae are noted. Pyrite 408 409 410 Tetrahedrite Eulytite Sphalerite 245. Tetragonal System. The most common method is that where the twinning-plane is parallel to a face of the pyramid, e(101) . It is especially characteristic of the species of the rutile group viz., rutile and cassiterite: 411 413 Cassiterite Zircon Rutile also similarly the allied species zircon. This is illustrated in Fig. 411, and EXAMPLES OF IMPORTANT METHODS OF TWINNING 167 again in Fig. 412. Fig. 413 shows a repeated twin of rutile, the twinning according to this law; the vertical axes of the successive six individuals lie in a plane, and an inclosed circle is the result. Another repeated twin of rutile according to the same law is shown in Fig. 399; here the successive vertical axes form a zigzag line; Fig. 414 shows an analogous twin of hausmannite. Another kind of twinning with the twinning-plane parallel to a face of the pyramid (301) is shown in Fig. 415. 246. In the pyramidal class of the same system twins of the type of Fig. 416 are not rare. Here the vertical axis, c, is the twinning-axis; such a crystal may simulate one of the normal class. 414 415 416 Hausmannite Rutile Scheelite 417 In chalcopyrite, of the sphenoidal class, twinning with a face of the unit pyramid, /(111), as the twinning-plane is common (Fig. 417). As the angles differ but a small fraction of a degree from those of a regular octahedron, such twins often resemble closely spinel-twins. The face 6(101) may also be a twinning- plane and other rarer types have been noted. 247. Hexagonal System. In the hexagonal divis- ion of this system twins are rare. An example is furnished by pyrrhotite, Fig. 418, where the twinning- plane is the pyramid (1011), the vertical axes of the individual crystals being nearly at right angles to each other (since 0001 A 1011 = 45 8'). 248. In the species belonging to the trigonal or Chalcopyrite rhombokedral division, twins are common. Thus the twinning-axis may be the vertical axis, as in the contact-twins of Figs. 419 and 420, or the penetration- twin of Fig. 393. Or the twinning-plane may be the obtuse rhombohedron e(0112), as in Fig. 421, the vertical axes crossing at angles of 127 2 and 52i. Again, the twinning-plane may be r(10ll) as in Figs. 422-425, the_ vertical axes nearly at right angles (90f); or (0221), as in Fig. 426, the axes inclined 53f and 126| . Pvrrhotite 5. tne axes inclined 004 auu j.^ 4 . In the trapezohedral class, the species quartz shows several methods twinning. In Fig. 427 the twinning-plane is the pyramid {(1122}, the axes crossing at angles of 84| and 95i- In Fig. 428 the twmmng-axis is c, the 168 CRYSTALLOGRAPHY axes hence parallel, the individuals both right- or both left-handed but un- symmetrical, r(]0ll) then parallel to and coinciding with 2(0111). The re- 420 421 422 Figs. 419-426, Calcite suiting forms, as in Fig. 428, are mostly penetration-twins, and the parts are often very irregularly united, as shown by dull areas (z) on the plus rhombo- hedral face (r); otherwise these twins are recognized by pyro-electrical phenomena. In Fig. 429 the twinning-plane is a(1120) the Brazil law the individuals respectively right- and left-handed and the twin symmetrical with reference to an a-face; these are usually irregular penetration-twins; in these twins r and r, also z and z, coincide These twins often show, in con- 427 428 429 Figs. 427-429, Quartz verging polarized light, the phenomenon of Airy's spirals. It may be added that pseudo-twins of quartz are common that is, groups of crystals which EXAMPLES OF IMPORTANT METHODS OF TWINNING 169 430 431 nearly conform to some more or less complex twinning law, but where the grouping is nevertheless only accidental 249. Orthorhombic System. In the orthorhombic system the commonest method of twinning is that where the twinning-plane is a face of a prism of 60, or nearly 60. This is well shown with the species of the aragonite group. In accord- ance with the principle stated in Art. 241, the twinning after this law is often repeated, and thus forms with pseudo- hexagonal symmetry result. Fig. 430 shows a simple twin of aragonite; Fig. 431 \ shows a basal section of an aragonite triplet which although it resembles a hexagonal Aragonite prism reveals its twinned character by the striations on the basal plane and by irregularities on its composite prism faces due to the fact that the pris- matic angle is not exactly 60. With witherite (and bromlite), apparent hexagonal pyramids are common, but the true complex twinning is revealed in polarized light, as noted later. Twinning of the same type, but where a dome of 60 is twinning-plane, is common with arsenopyrite (tw. pi. e(101)), as shown in Figs. 432, 433; also 434 Arsenopyrite Columbite Fig. 434 of columbite, but compare Fig. 385 and remarks in Art 238, Another example is given in Fig. 395 of alexandrite (chrysoberyl) . Chrysolite, man- 435 436 437 Marcasite Arsenopyrite ganite, humite, are other species with which this kind of twinning is common. Another common method of twinning is that where the twinning is parallel 170 CRYSTALLOGRAPHY to a face of a prism of about 70J, as shown in Fig. 435. With this method symmetrical fivelings not infrequently occur (Figs. 436, 437). The species staurolite illustrates three kinds of twinning. In Fig. 438 the twinning-plane is (032), and since (001 A 032) = 45 41', the crystals cross nearly at right angles. In Fig. 439 the twinning-plane is the prism (230). In Fig. 440 it is the pyramid (232) ; the crystals then crossing at angles of about 60, stellate trillings occur (see Fig. 397), and indeed more complex forms. In Fig. 441 there is twinning according to both (032) and (232). 440 Staurolite 441 Staurolite Struvite In the hemimorphic class, twins of the type shown in Fig. 442, with c(001) as the twinning-plane, are to be noted. 250. Mpnoclinic System. In the monoclinic system, twins with the ver- tical axis as twinning-axis are common ; this is illustrated by Fig. 443 of augite (pyroxene), Fig. 444 of gypsum, and Fig. 445 of orthoclase (see also Fig. 390, 443 444 445 Augite Gypsum y Orthoclase p. 162). With the latter species these twins are called Carlsbad twins (because common in the trachyte of Carlsbad, Bohemia) ; they may be contact-twins EXAMPLES OF IMPORTANT METHODS OF TWINNING 171 (Fig. 390), or irregular penetration-twins (Fig. 445). In Fig. 390 it is to be noted that c and x fall nearly in the same plane. In Fig. 446, also of orthoclase, the twinning-plane is the clinodome (021), and since (001 A 021) = 44 56^', this method of twinning yields nearly square prisms. These twins are called Baveno twins (from a prominent locality at Baveno, Italy) ; they are often repeated (Fig. 447). In Fig. 448 a 446 447 448 Orthoclase Manebach twin is shown; here the twinning-plane is c(001). Other rarer types of twinning have been noted with orthoclase. Polysynthetic twinning with c(001) as twinning-plane i& common with pyroxene (cf. Fig. 461, p. 173). Twins of the aragonite-chrysoberyl type are not uncommon with mono- clinic species, having a prominent 60 prism (or dome), as in Fig. 449. Stellate twins after this law are common with chondrodite and clinohumite. An analogous twin of pyroxene is shown in Fig. 450; here the pyramid (122) is the twinning-plane, and since (010 A 122) = 59 21', the crystals cross at angles of nearly _60; further, the orthopinacoids fall nearly in a common zone, since (100 A 122) = 90 9'. In Fig. 451 the twinning-plane is the orthodome 449 450 461 Wolframite Pyroxene Pyroxene (101) Phillipsite and harmotome exhibit multiple twinning, and the crystals often show pseudo-symmetry. Fig. 452 shows a cruciform fourling with c(001) as twinning-plane, the twinning shown by the stnations on the side face. This is compounded in Fig. 453 with twinning-plane (Oil), making nearly square prisms, and this further repeated with ra(110) as twinning-plane 172 CR YST ALLO GR APH Y yields the form in Fig. 454, or even Fig. 400, p. 164, resembling an isometric dodecahedron, each face showing a fourfold striation. 452 453 454 Phillipsite 251. Triclinic System. The most interesting twins of the triclinic system are those shown by the feldspars. Twinning with 6(010) as the twinning-plane is very common, especially polysynthetic twinning yielding thin parallel lamellae, shown by the striations on the face c (or the correspond- ing cleavage-surface), and also clearly revealed in polarized light. This is known as the albite law (Figs. 455, 456). Another important method (Fig. 457) is that of the pericline law; the twinning-axis is the crystallographic axis b. Here the twins are united by a section (rhombic section) shown in the figure and further explained under the feldspars. Polysynthetic twinning after this law is common, and hence a cleavage-mass may show two sets of striations, one on the surface parallel to c(001) and the other on that parallel to 6(010). The angle made by these last striations with the edge 001/010 is character- istic of the particular triclinic species, as noted later. 455 456 457 Albite Twins of albite of other rarer types also occur, and further twins similar 458 to the Carlsbad, Baveno, and Manebach twins of ortho- clase. Fig. 458 shows twinning according to both the albite and Carlsbad types. REGULAR GROUPING OF CRYSTALS 252. Parallel Grouping. Connected with the sub- ject of twin crystals is that of the parallel position of associated crystals of the same species, or of different species. Crystals of the same species occurring together are very commonly in parallel position. In this way large Albite EXAMPLES OF IMPORTANT METHODS OF TWINNING 173 459 460 crystals, as of calcite, quartz, fluorite, are sometimes buiJt up of smaller individuals grouped together with corresponding faces parallel. This parallel grouping is often seen in crystals as they lie on the supporting rock. On glancing the eye over a surface covered with crystals a reflection from one face will often be accompanied by reflections from the corres- ponding face in each of the other crystals, showing that the crystals are throughout similar in their positions. With many species, complex crystalline forms result from the growth of parallel partial crystals in the direction of the crystallographic axes, or axes of symmetry. Thus dendritic forms, resembling branch- ing vegetation, often of great del- icacy, are seen with gold, copper, argentite, and other species, espe- cially those of the isometric sys- tem. This is shown in Fig. 459 (ideal), and again in Fig. 460, where the twinned and flattened cubes (cf. Fig. 403, p. 165) are grouped in directions corresponding to the diagonals of an octahedral Co face which is the twinning-plane. 253. Parallel Grouping of Unlike Species. Crystals of different spe- cies often show the same tendency to parallelism in mutual position. This is true most frequently of species which are more or less closely similar in form and composition. Crystals of albite, implanted on a surface of orthoclase, are sometimes an example of this; crystals of amphibole and pyroxene (Fig. 461), of zircon and xenotime (Fig. 462), of va- rious kinds of mica, are also at times observed associated in par- allel position. The same relation of position also occasionally occurs where there is no connection in composi- tion, as the crystals of rutile on tabular crystals of hematite, the vertical axes of the former coinciding with the horizontal Amphibole enclosing Xenotime enclosing zircon ax es of the latter. Crystals of pyroxene in parallel in parallel position calcite have been observed whose position rhombohedral faces had a series of quartz crystals upon them, all in parallel position; sometimes three such quartz crystals, one on each rhombohedral face, entirely envelop the calcite, and unite with re-entering angles to form pseudo-twins (rather trillings) of quartz after calcite. Parallel growths of the sphenoidal chalcopyr- ite upon the tetrahedral sphalerite are common, the similarity in crystal structure of the two species controlling the position of the crystals of chal- copyrite. 461 462 174 CRYSTALLOGRAPHY IRREGULARITIES OF CRYSTALS 254. The laws of crystallization, when unmodified by extrinsic causes, should produce forms of exact geometrical symmetry, the angles being not only equal, but also the homologous faces of crystals and the dimensions in the directions of like axes. This symmetry is, however, so uncommon that it can hardly be considered other than an ideal perfection. The various possible kinds of symmetry, and the relation of this ideal geometrical symmetry to the actual crystallographic symmetry, have been discussed in Arts. 14 and 18 et seq. Crystals are very generally distorted, and often the fundamental forms are so completely disguised that an intimate familiarity with the possible irregularities is required in order to unravel their complexities. Even the angles may occasionally vary rather widely. The irregularities of crystals may be treated under several heads: 1, Variations of form and dimensions; 2, Imperfections of surface; 3, Varia- tions of angles; 4, Internal imperfections and impurities. 1. VARIATIONS IN THE FORMS AND DIMENSIONS OF CRYSTALS 255. Distortion in General. The variations in the forms of crystals, or, in other words, their distortion, may be irregular in character, certain faces being larger and others smaller than in the ideal geometrical solid. On the other hand, it may be symmetrical, giving to the distorted form the symmetry of a group or system different from that to which it actually belongs. The former case is the common rule, but the latter is the more interesting. 256. Irregular Distortion. As stated above and on p. 13, all crystals show to a greater or less extent an irregular or accidental variation from the ideal geometrical form. This distortion, if not accompanied by change in the interfacial angles, has no particular significance, and does not involve any deviation from the laws of crystallographic symmetry. Figs. 463, 464 show distorted crystals of quartz ; they may be compared with the ideal form, Fig. 284, p. 113. Fig. 465 is an ideal and Fig. 466 an actual crystal of lazulite. 463 464 465 466 Quartz Lazulite The correct identification of the forms on a crystal is rendered much more difficult because ol this prevailing distortion, especially when it results in the entire obliteration of urtain laces by the enlargement of others. In deciphering the distorted crystalline forms it must be remembered that while the appearance of the crystals may be entirely altered, e intertacial angles remain the same; moreover, like faces are physically alike that is IRREGULARITIES OF CRYSTALS 175 alike in degree of luster, in striations, and so on. Thus the prismatic faces of quartz show almost always characteristic horizontal striations. In addition to the variations in form which have just been described, still greater irregularities are due to the fact that, in many cases, crystals in nature are attached either to other crystals or to some rock surface, and in consequence of this are only partially developed. Thus quartz crystals are generally attached by one extremity of the prism, and hence have only one set of pyra- midal faces; perfectly formed crystals, having the double pyramid complete, are rare. 257. Symmetrical Distortion. The most interesting examples of the symmetrical distortion of crystalline forms are found among crystals of the isometric system. An elongation in the direction of one cubic axis may give the appearance of tetragonal symmetry, or that in the direction of two cubic axes of orthorhombic symmetry; while in the direction of an octahedral axis a lengthening or shortening gives rise to forms of apparent rhombohedral symmetry. Such cases are common with native gold, silver, and copper. A cube lengthened or shortened along one axis becomes a right square prism, and if varied in the direction of two axes is changed to a rectangular prism. Cubes of pyrite, galena, fluorite, etc., are often thus distorted. It is very unusual to find a cubic crystal that is a true symmetrical cube. In some species the cube or octahedron (or other iso- metric form) is lengthened into a capillary crystal or needle, as happens in cuprite and pyrite. An octahedron flattened parallel to a face that is, in the direction of a trigonal sym- metry axis is reduced to a tabular crystal resembling a rhombohedral crystal with basal plane (Fig. 467). If lengthened in the same direction (i.e. along line A-B, Fig. 468), to the obliteration of the terminal octahedral faces, it becomes an acute rhombohedron. When an octahedron is extended in the direction of a line between two opposite edges, 467 468 469 470 Distorted Octahedrons 471 472 473 Distorted Dodecahedrons or that of a binary symmetry axis, it has the general form of a rec f tan ^ la f, oct ^ he( }f. on j still farther extended, as in Fig. 469, it resembles a combination of two orthorhombic d (spinel, fluorite, magnetite). n domes 176 CRYSTALLOGRAPHY The dodecahedron lengthened in the direction of a trigonal symmetry axis becomes a six-sided prism with three-sided summits, as in Fig. 470. If shortened in the same direc- tion, it becomes a short prism of the same kind (Fig. 471). Both resemble rhombohedral forms and are common in garnet. When lengthened in the direction of one of the cubic axes, the dodecahedron becomes a square prism with pyramidal summits (Fig. 472), and shortened along the same axis it is reduced to a square octahedron, with truncated angles (Fig. 473). The trapezohedron elongated in the direction of an octahedral (trigonal) axis assumes rhombohedral (trigonal) symmetry. If the elongation of the trapezohedron takes place along a cubic axis, it becomes a double eight-sided pyramid with four-sided summits; or if these summit planes are obliterated by a farther extension, it becomes a complete eight-sided double pyramid. Similarly the trisoctahedron, tetrahexahedron and hexoctahedron may show distortion of the same kind. Further examples are to be found in the other systems. 2. IMPERFECTIONS OF THE SURFACES [OF CRYSTALS 258. Striations Due to Oscillatory Combinations. The parallel lines or furrows on the surfaces of crystals are called strice or striations, and such surfaces are said to be striated. Each little ridge on a striated surface is inclosed by two narrow planes more or less regular. These planes often correspond in position to different faces of the crystal, and these ridges have been formed by a continued oscillation in the operation of the causes that give rise, when acting uninter- ruptedly, to enlarged faces. By this means, the surfaces of a crystal are marked in parallel lines, with a succession of narrow planes meeting at an angle and constituting the ridges referred to. This combination of different planes in the formation of a surface has been termed oscillatory combination. The horizontal striations on prismatic crystals of quartz are examples of this combination, in which the oscillation has- taken place between the prismatic and rhombohedral faces. Thus crystals of quartz are often tapered to a point, without the usual pyramidal terminations. Other examples are the striations on the cubic faces of pyrite parallel to the intersections of the cube with the faces of the pyritohedron; also the striations on magnetite due to the oscillation between the octahedron and do- decahedron. Prisms of tourmaline are very com- monly bounded vertically by three convex surfaces, owing to an oscillatory combination of the faces in the prismatic zone. 259. Striations Due to Repeated Twinning. The striations of the basal plane of albite and other triclinic feldspars, also of the x rhombohedral surfaces of some calcite, have been explained in Art. 241 as Magnetite due to polysynthetic twinning. This is illustrated by Fig. 474 of magnetite from Port Henry, N. Y. (Kemp.) 260. Markings from Erosion and Other Causes. The faces of crys- tals are often uneven, or have the crystalline structure developed as a con- sequence of etching by some chemical agent. Cubes of galena are frequently thus uneven, and crystals of lead sulphate (anglesite) or lead carbonate (cerus- site) are sometimes present as evidence with regard to the cause. Crystals of numerous other species, even of corundum, spinel, quartz, etc., sometimes show the same result of partial change over the surface often the incipient IRREGULARITIES OF CRYSTALS 177 stage in a process tending to a final removal of the whole crystal. Interesting investigations have been made by various authors on the action of solvents on different minerals, the actual structure of the crystals being developed in this way. This method of etching is fully discussed, with illustrations in another place (Art. 286). The markings on the surfaces of crystals are not, however, always to be ascribed to etching. In most cases such depressions, as well as the minute elevations upon the faces having the form of low pyramids (so-called vicinal prominences) , are a part of the original molecular growth of the crystal, and often serve to show the successive stages in its history. They may be imper- fections arising from an interrupted or disturbed development of the form, the perfectly smooth and even crystalline faces being the result of completed action free from disturbing causes. Examples of the markings referred to occur on the crystals of most minerals, and conspicuously so on the rhombo- hedral faces of quartz. Faces of crystals are often marked with angular elevations more or less distinct, which are due to oscillatory combination. Octahedrons of fluorite are common which have for each face a surface of minute cubes, proceeding from an oscillation between the cube and octahedron. Sometimes an examina- tion of such a crystal shows that though the form is apparently octahedral, there are no octahedral faces present at all. Other similar cases could be mentioned. Whatever their cause, these minute markings are often of great importance as revealing the true molecular symmetry of the crystal. For it follows from the symmetry of crystallization that like faces must be physically alike that is, in regard to their surface character; it thus often happens that on all the crystals of a species from a given locality, or perhaps from all localities, the same planes are etched or roughened alike. There is much uniformity on the faces of quartz crystals in this respect. 261. Curved surfaces may result from (a) oscillatory combination; or (6) some independent molecular condition producing curvatures in the laminae of the crystal ; or (c) from a mechanical cause. Curved surfaces of the first kind have been already mentioned (Art. 258). A singular curvature of this nature is seen in Fig. 475, of calcite; in the lower 476 476 Calcite Diamond Beryl part traces of a scalenohedral form are apparent which was in oscillatory com- bination with the prismatic form. 178 CRYSTALLOGRAPHY Curvatures of the second kind sometimes have all the faces convex. This is the case in crystals of diamond (Fig. 476), some of which are almost spheres. The mode of curvature, in which all the faces are equally convex, is less common than that in which a convex surface is opposite and parallel to a corresponding concave surface. Rhombohedrons of dolomite and siderite are usually thus curved. The feathery curves of frost on windows and the flagging-stones of pavements in winter are other examples. The alabaster rosettes from the Mammoth Cave, Kentucky, are similar. Stibnite crystals sometimes show very remarkable curved and twisted forms. A third kind of curvature is of mechanical origin. Sometimes crystals appear as if they had been broken transversely into many pieces, a slight displacement of which has given a curved form to the prism. This is common in tourmaline and beryl. The beryls of Monroe, Conn., often present these interrupted curvatures, as represented in Fig. 477. Crystals not infrequently occur with a deep pyramidal depression occupy- ing the place of each plane, as is often observed in common salt, alum, and sulphur. This is due in part to their rapid growth. 3. VARIATIONS IN THE ANGLES OF CRYSTALS 262. The greater part of the distortions described in Arts 256, 257 occasion no change in the interfacial angles of crystals. But those imper- fections that produce convex, curved, or striated faces necessarily cause such variations. Furthermore, circumstances of heat or pressure under which the crystals were formed may sometimes have resulted not only in distortion of form, but also some variation in angle. The presence of impurities at the time of crystallization may also have a like effect. Still more important is the change in the angles of completed crystals which is caused by subsequent pressure on the matrix in which they were formed, as, for example, the change which may take place during the more or less complete metamorphism of the inclosing rock. The change of composition resulting in pseudomorphous crystals (see Art. 273) is generally accompanied by an irregular change of angle, so that the pseudomorphs of a species vary much in angle. In general it is safe to affirm that, with the exception of the irregularities arising from imperfections in the process of crystallization, or from the sub- sequent changes alluded to, variations in angles are rare, and the constancy of angle alluded to in Art. 11 is the universal law. In cases where a greater or less variation in angle is observed in the crystals of the same species from different localities, the cause for this can usually be found in a difference of chemical composition. In the case of isomorphous compounds it is well known that an exchange of corresponding chemically equivalent elements may take place without a change of form, though usually accompanied with a slight variation in the fundamental angles. The effect of heat upon the form of crystals is alluded to in Art. 433. 4. INTERNAL IMPERFECTIONS AND INCLUSIONS 263. The transparency of crystals is often destroyed by disturbed crystal- lization; by impurities taken up from the solution during the process of crystallization; or, again, by the presence of foreign matter resulting from IRREGULARITIES OF CRYSTALS 179 partial chemical alteration. The general name, inclusion, is given to any foreign body inclosed within the crystal, whatever its origin. These inclusions are extremely common; they may be gaseous, liquid, or solid; visible to the unaided eye or requiring the use of the microscope. Rapid crystallization is a common explanation of inclusions. This is illustrated by quartz crystals containing large cavities full or nearly full of water (in the latter case, these showing a movable bubble); or, they may contain sand or iron oxide in large amount. In the case of calcite, crystalliza- tion from a liquid largely charged with a foreign material, as quartz sand, may result in the formation of crystals in which the impurity makes up as much as two-thirds of the whole mass; this is seen in the famous Fontainebleau limestone, and similarly in that from other localities. 264. Liquid and Gas Inclusions. Attention was early called by Brewster to the presence of fluids in cavities in certain minerals, as quartz, topaz, beryl, chrysolite, etc. In later years this subject has been thoroughly studied by Sorby, Zirkel, Vogelsang, Fischer, Rosenbusch, and others. The nature of the liquid can often be determined, by its refractive power, or by special physical test (e.g., determination of the critical point in the case of CO 2 ), or by chemical examination. In the majority of cases the observed liquid is simply water; but it may be the salt solution in which the crystal was formed, and not infrequently, especially in the case of quartz, liquid carbon dioxide (CO 2 ), as first proved by Vogelsang. These liquid inclusions are marked as such, in many cases, by the presence in the cavity of a movable bubble of gas. Occasionally cavities contain two liquids, as water and liquid carbon dioxide, the latter then inclosing a bubble of the same sub- stance as gas (cf. Fig. 478). Interesting exper- iments can be made with sections showing such inclusions (cf. literature, p. 181). The mixture of gases yielded by smoky quartz, meteoric iron, and other substances, on the application of heat, has been analyzed by Wright. In some cases the cavities appear to be empty; if they then have a regular form determined by the crystallization of the species, they are often called negative crystals. Such cavities are com- monly of secondary origin, as remarked on a later Beryllonite pase. 265. Solid Inclusions. The solid inclusions are almost infinite in their variety. Sometimes they are large and distinct, and can be referred to known mineral species, as the scales of gothite or hematite, to which the peculiar character of aventurine feldspar is due. Magnetite is a very common impurity in many minerals, appearing, for example, in the Pennsbury mica; quartz is also often mechanically mixed, as in staurolite and gmelinite the other hand, quartz crystals very commonly inclose foreign material, such as chlorite, tourmaline, rutile, hematite, asbestus, and many other minerals. (Cf. also Arts. 266, 267.) , , , The inclusions may consist of a heterogeneous mass of material; << granitic matter seen in orthoclase crystals in a porphyntic granite; or the feldspar, quartz, etc., sometimes inclosed in large coarse crystals of beryl or spodumene, occurring in granite veins. 180 CRYSTALLOGRAPHY 266. Microlites, Crystallites. The microscopic crystals observed as inclusions may sometimes be referred to known species, but more generally their true nature is doubtful. The term microlites, proposed by Vogelsang, is often used to designate the minute inclosed crystals; they are generally of needlelike form, sometimes quite irregular, and often very remarkable in their arrangement and groupings; some of them are exhibited in Fig. 484 and Fig. 485, as explained below. Where the minute individuals belong to known species they are called, for example, feldspar microlites, etc. Crystallites is an analogous term used by Vogelsang to cover those minute forms which have not the regular exterior form of crystals, but may be con- sidered as intermediate between amorphous matter and true crystals. Some of the forms are shown in Figs. 479-483; they are often observed in glassy volcanic rocks, and also in furnace-slags. A series of names has been given to varieties of crystallites, such as globulites, margarites, etc. Trichite and belonite are names introduced by Zirkel; the former name is derived from i, hair; trichites, like that in Fig. 483, are common in obsidian. 479 480 481 482 Crystallites The microscopic inclusions may also be of an irregular glassy nature; this kind is often observed in crystals which have formed from a molten mass, as lava or the slag of an iron furnace. 267. Symmetrically Arranged Inclusions. In general, while the solid inclusions sometimes occur quite irregularly in the crystals, they are more generally arranged with some evident reference to the symmetry of the form, or external faces of the crystals. Examples of this are shown in the following 484 486 Augite (Zirkel) Leucite (Zirkel) Garnet inclosing quartz (Heddle) figures. Fig. 484 exhibits a crystal of augite, inclosing magnetite, feldspar and nephelite microlites, etc. Fig. 485 shows a crystal of leucite, a species IRREGULARITIES OF CRYSTALS 181 whose crystals very commonly inclose foreign matter, tion of a crystal of garnet, containing quartz. Fig. 486 shows a sec 487 488 Andalusite Another striking example is afforded by andalusite (Fig. 487), in which the inclosed carbonaceous impurities are of considerable extent and remarkably arranged, so as to yield symmetrical figures of various forms. Staurolite occasionally shows analogous carbonaceous impurities symmetrically dis- tributed. The magnetite common as an inclusion in muscovite, alluded to above, is always symmetrically disposed, usually parallel to the directions of the percussion-figure (Fig. 491, p. 189). The asterism of phlogopite is explained by the presence of symmetrically arranged inclusions (cf, Art, 368). Fig. 488 shows an interesting case of symmetrically arranged inclusions due to chemical alteration. The original mineral, spodumene, from Branchville, Conn., has been altered to a substance apparently homogeneous to the eye, but found under the microscope to have the structure shown in Fig. 488. Chemical analysis proves the base to be albite and the inclosed hexagonal mineral to be a lithium silicate (LiAlSO 4 ) called eucryptite. It has not yet been identified except in this form. LITERATURE Eucryptite in Albite Some of the most important works on the subject of microscopic inclusions are referred to here; for a fuller list of papers reference may be made to the work of Rosenbusch (1904) ; also that of Zirkel and others mentioned on pp. 3 and 4. Brewster. Many papers, published mostly in the Philosophical Magazine, and the Edinburgh Phil. Journal, from 1822-1856. Blum, Leonhard, Seyfert, and Sochting. Die Einschlusse von Mineralien in krystalli- sirten Mineralien. Haarlem, 1854. (Preisschrift.) Sorby. On the microscopical structure of crystals, etc. Q. J. G. Soc., 14, 453, 1858 (and other papers). Sorby and Butler. On the structure of rubies, sapphires, diamonds, and some other minerals. Proc. Roy. Soc., No. 109, 1869. Reusch. Labradorite. Pogg. Ann., 120, 95, 1863. Vogelsang. Labradorite. Arch. Neerland, 3, 32, 1868. Fischer. Kritische-microscopische mineralogische Studien. Freiburg in Br., 64 pp., 1869; Ite Fortsetzung, 64 pp., 1871; 2te Forts., 96 pp., 1873 Kosmann. Hypersthene. Jahrb. Min., 532, 1869; 501, 1871. Schrauf. Labradorite. Ber. Ak. Wien, 60 (1) 996, 1869. Vogelsang. Die Krystalliten. 175 pp., Bonn, 1875. Vogelsang and Geissler. Ueber die Natur der Flussigkeitsemschlusse in gewissen Mineralien. Pogg. Ann, 137, 56, 257, 1869 Hartley. Liquid CO 2 in cavities, etc. J. Chem. Soc., 1, 137; 2, 237, 1876, 1, 241, 2, 271, 1877; also, Proc. Roy. Soc, 26, 137, 150, 1877 _ Gumbel. Enhydros. Ber. Ak. Miinchen, 10, 241, 1880; 11, 321, 1881. Hawes. Smoky quartz (CO.). Am. J. Sc 21,203, 1881 A. W. Wright. Gases in smoky quartz. Am J. fee, 21, 209, l? Rutley. Notes on Crystallites. Mm. MM., t, 2W-, 18M. Vater. Das Wesen der Krystalliten, Zs. Kr, 27, 505, 189b. 182 CEYSTALLOGBAPHY CRYSTALLINE AGGREGATES 268. The greater part of the specimens or masses of minerals that occur may be described as aggregations of imperfect crystals. Many specimens whose structure appears to the eye quite homogeneous, and destitute internally of distinct crystallization, can be shown to be composed of crystalline grains. Under the above head, consequently, are included all the remaining varieties of structure among minerals. The individuals composing imperfectly crystallized individuals may be: 1. Columns, or fibers, in which case the structure is columnar or fibrous. 2. Thin lamince, producing a lamellar structure. 3. Grains, constituting a granular structure. 269. Columnar and Fibrous Structure. A mineral possesses a col- umnar structure when it is made up of slender columns, as some amphibole. When the individuals are flattened like a knife-blade, as in cyanite, the struc- ture is said to be bladed. The structure again is called fibrous when the mineral is made up of fibres, as in asbestus, also the satin-spar variety of gypsum. The fibres may or may not be separable. There are many gradations between coarse columnar and fine fibrous structures. Fibrous minerals have often a silky luster. The following are properly varieties of columnar or fibrous structure : Reticulated: when the fibers or columns cross in various directions and produce an appearance having some resemblance to a net. Stellated: when they radiate from a center in all directions and produce star-like forms. Ex. stilbite, wavellite. Radiated, divergent: when the crystals radiate from a center without producing stellar forms. Ex. quartz, stibnite. 270. Lamellar Structure. The structure of a mineral is lamellar when it consists of plates or leaves. The laminae may be curved or straight, and thus give rise to the curved lamellar and straight lamellar structure. Ex. wollastonite (tabular spar), some varieties of gypsum, talc, etc. If the plates are approximately parallel about a common center the structure is said to be concentric. When the laminae are thin and separable, the structure is said to be foliaceous or foliated. Mica is a striking example, and the term micaceous is often used to describe this kind of structure. 271. Granular Structure. The particles in a granular structure differ much in size. When coarse, the mineral is described as coarse-granular; when fine, fine-granular; and if not distinguishable by the naked eye, the structure is termed impalpable. Examples of the first may be observed in granular crys- talline limestone, sometimes called saccharoidal; of the second, in some varie- ties of hematite; of the last, in some kinds of sphalerite. The above terms are indefinite, but from necessity, as there is every degree of fineness of structure among mineral species, from perfectly impalpable, through all possible shades, to the coarsest granular. The term phanero-crys- talline has been used for varieties in which the grains are distinct, and crypto- crystalline for those in which they are not discernible, although an indistinct crystalline structure can be proved by the microscope. Granular minerals, when easily crumbled in the fingers, are said to be friable. f -272. Imitative Shapes. The following are important terms used in describing the imitative forms of massive minerals. CRYSTALLINE AGGREGATES 183 Reniform: kidney-shaped. The structure may be radiating or concentric Ex. hematite. Botryoidal: consisting of a group of rounded prominences. The name is derived from the Greek Corpus, a bunch of grapes. Ex. limonite, chalcedony prehnite. Mammillary: resembling the botryoidal, but composed of larger promi- nences. Ex. malachite. Globular: spherical or nearly so; the globules may consist of radiating fibres or concentric coats. When attached, as they usually are, to the surface of a rock, they are described as implanted globules. Nodular: in tuberose forms, or having irregular protuberances over the surface. Amygdaloidal: almond-shaped, applied often to a rock (as diabase) con- taining almond-shaped or sub-globular nodules. Coralloidal: like coral, or consisting of interlaced flexuous branchings of a white color, as in the variety of aragonite called flos ferri. Dendritic: branching tree-like, as in crystallized gold. The term den- drites is used for similar forms even when not crystalline, as in the dendrites of manganese oxide, which form on surfaces of limestone or are inclosed in "moss-agates." Mossy: like moss in form or appearance. Filiform or Capillary: very slender and long, like a thread or hair; con- sists ordinarily of a succession of minute crystals. Ex. millerite. Acicular: slender and rigid, like a needle. Ex. stibnite. Reticulated: net-like. See Art. 269. Drusy: closely covered with minute implanted crystals. Ex. quartz. Stalactitic: when the mineral occurs in pendent columns, cylinders, or elongated cones. Stalactites are produced by the percolation of water, hold- ing mineral matter in solution, through the rocky roofs of caverns. The evaporation of the water produces a deposit of the mineral matter, and grad- ually forms a long pendent cylinder or cone. The internal structure may be imperfectly crystalline and granular, or may consist of fibres radiating from the central column, or there may be a broad cross-cleavage. The most famil- iar example of stalactites is afforded by calcite. Chalcedony, gibbsite, limonite, and some other species, also present stalactitic forms. The term amorphous is used when a mineral has not only no crystalline form or imitative shape, but does not polarize the light even in its minute particles, and thus appears to be destitute wholly of a crystalline structure internally, as most opal. Such a structure is also called colloid or jelly-like, from the Greek /coXXa (see p. 8), for glue. The word amorphous is from a privative, and MP??, shape. 273. Pseudomorphous Crystals. Every mineral species has, when distinctly crystallized, a definite and characteristic form. Occasionally, however, crystals are found that have the form, both as to angles and general habit, of a certain species, and yet differ from it entirely in chemical composi- tion. Moreover, it is often noted in such cases that, though in outward form complete crystals, in internal structure they are granular, or waxy, and have no regular cleavage. Even if they are crystalline in structure the optical characters do not conform to those required by the symmetry of the faces. 1 84 CR YSTALLO GR APH Y Such crystals are called pseudomorphs, and their existence is explained by the assumption, often admitting of direct proof, that the original mineral has been changed into the new compound; or it has disappeared through some agency, and its place been taken by another chemical compound to which the form does not belong. In all these cases the new substance is said to be a pseudomorph after the orginal mineral. Common illustrations of pseudomorphous crystals are afforded by mala- chite in the form of cuprite, limonite in the form of pyrite, barite in the form of quartz, etc. This subject is further discussed in the chapter on Chemical Mineralogy. PART II. PHYSICAL MINERALOGY 274. The PHYSICAL CHARACTERS of minerals fall under the following heads : I. Characters depending upon Cohesion and Elasticity viz., cleavage, fracture, tenacity, hardness, elasticity, etc. II. Specific Gravity, or the Density compared with that of water. III. Characters depending upon Light viz., color, luster, degree of trans- parency, special optical properties, etc. IV. Characters depending upon Heat viz., heat-conductivity, change of form and of optical characters with change of temperature, fusibility, etc. V. Characters depending upon Electricity and Magnetism. VI. Characters depending upon the action of the senses viz., taste, odor, feel. 275. General Relation of Physical Characters to Molecular Structure. It has been stated on pp. 7, 8 that the geometrical form of a crystallized min- eral is the external evidence of the internal molecular structure. A full knowledge in regard to this structure, however, can only be obtained by the study of the various physical characters included in the classes enumerated above. Of these characters, the specific gravity merely gives indication of the atomic mass of the elements present, and further, of the state of molecular aggregation. The first of these points is illustrated by the high specific gravity of compounds of lead; the second, by the distinction observed, for example, between carbon in the form of the diamond, with a specific gravity of 3' 5, and the same chemical substance as the mineral graphite, with a specific gravity of only 2. All the other characters (except the relatively unimportant ones of Class VI) in general vary according to the direction in the crystal; in other words they have a definite orientation. For all of them it is true that directions which are crystallographically identical have like physical characters. In regard to the converse proposition viz., that in all directions crystal- lographically dissimilar there may be a variation in the physical characters, an important distinction is to be made. This proposition holds true for all crystals, so far as the characters of Class I are concerned; that is, those depending upon the cohesion and elasticity, as shown in the cleavage, hard- ness, the planes of molecular gliding, the etching-figures, etc. It is also true in the case of pyro-electricity and piezo-electricity. It does not apply in the same way with respect to the characters which involve the propagation of light (and radiant heat), the change of volume with change of temperature; further, electric radiation, magnetic induction, etc. 185 186 PHYSICAL MINERALOGY Thus, although it will be shown that the optical characters of crystals are in agreement in general with the symmetry of their form, they do not show all the variations in this symmetry. It is true, for example, that all directions are optically similar in a crystal belonging to any class under the isometric system; but this is obviously not true of its molecular cohesion, as may be shown by the cleavage. Again, all directions in a tetragonal crystal at right angles to the vertical axis are optically similar; but this again is not true of the cohesion. These points are further elucidated under the description of the special characters of each group. I. CHARACTERS DEPENDING UPON COHESION AND ELASTICITY \ 276. Cohesion, Elasticity. The name cohesion is given to the force of attraction existing between the molecules of one and the same body, in con- sequence of which they offer resistance to any influence tending to separate them, as in the breaking of a solid body or the scratching of its surface. Elasticity is the force which tends to restore the molecules of a body back into their original position, from which they have been disturbed, as when a body has suffered change of shape or of volume under pressure. The varying degrees of cohesion and elasticity for crystals of different minerals, or for different directions in the same crystal, are shown in the prominent characters: cleavage, fracture, tenacity, hardness; also in the gliding-planes, percussion-figures or pressure-figures, and the etching-figures. 277. Cleavage. Cleavage is the tendency of a crystallized mineral to break in certain definite directions, yielding more or less smooth surfaces. It obviously indicates a minimum value of cohesion in the direction of easy fracture that is, normal to the cleavage-plane itself. The cleavage parallel to the cubic faces of a crystal of galena is a familiar illustration. An amor- phous body (p. 8) necessarily can show no cleavage. As stated in Art. 31, the consideration of the molecular structure of crystals shows that a cleavage-plane must be a direction in which the mole- cules are closely aggregated together; while normal to this the distance between successive layers of molecules must be relatively large, and hence this last is the direction of easy separation. It further follows that cleavage can exist only parallel to some possible face of a crystal, and, further, that this must be one of the common fundamental forms. Hence in cases where the choice in the position of the axes is more or less arbitrary the presence of cleavage is properly regarded as showing which planes should be made funda- mental. Still again, cleavage is the same in all directions in a crystal which are crystallographically identical. Cleavage is defined, (1) according to its direction, as cubic, octahedral, rhomobohedral, basal, prismatic, etc. Also, (2) according to the ease with which it is obtained, and the smoothness of the surface yielded. It is said to be perfect or eminent when it is obtained with great ease, affording smooth, lustrous surfaces, as in mica, topaz, calcite. Inferior degrees of cleavage are spoken of as distinct, indistinct -or imperfect, interrupted, in traces, difficult. These terms are sufficiently intelligible without further explanation. It may be noticed that the cleavage of a species is sometimes better developed in some of its varieties than in others. CHARACTERS DEPENDING UPON COHESION AND ELASTICITY 187 278. Cleavage in the Different Systems. (1) In the ISOMETRIC SYSTEM, cleavage is cubic, when parallel to the faces of the cube; this is the common case, as illustrated by galena and halite, it is also often octahedral that is, parallel to the octahedral faces as with fluonte and the diamond. Less frequently it is dodecahedral, or parallel to the faces of the rhombic dodecahedron, as with sphalerite. In the TETRAGONAL SYSTEM, cleavage is often basal, or parallel to the basal plane, as with apophylhte; also prismatic, or parallel to one (or both) of the square prisms as with rutile and wernerite; less frequently it is pyramidal, or parallel to the faces of the square pyramid, as with scheelite. In the HEXAGONAL SYSTEM, cleavage is usually either basal, as with beryl, or prismatic, parallel to one of the six-sided prisms, as with nephelite; pyramidal cleavage, as with pyromorphite, is rare and imperfect. In the RHOMBOHEDRAL DIVISION, besides the basal and prismatic cleavages rhombo- hedral cleavage, parallel to the faces of a rhombohedron, is also common, as with calcite and the allied species. In the ORTHORHOMBIC SYSTEM, cleavage parallel to one or more of the pinacoids is common. Thus it is basal with topaz, and in all three pinacoidal directions with anhydrite. Prismatic cleavage is also common, as with barite; in this case the arbitrary position assumed in describing the crystal may make this cleavage parallel to a "horizontal prism," or dome. In the MONOCLINIC SYSTEM, cleavage parallel to the clinopinacoid, is common, as with orthoclase, gypsum, heulandite and euclase; also basal, as with the micas and orthoclase, or parallel to the orthopinacoid; also prismatic, as with amphibole. Less frequently cleavage is parallel to a hemi -pyramid, as with gypsum. In the TRICLINIC SYSTEM, it is usual and proper to so select the fundamental form as to make the cleavage directions correspond with the pinacoids. 279. In some cases cleavage which is ordinarily not observed may be developed by a sharp blow or by sudden change of temperature. Thus, quartz is usually conspicuously free from cleavage, but a quartz crystal heated and plunged into cold water often shows planes of separation * parallel to both the + and rhombohedrqns and to the prism as well. Similarly, the prismatic cleavage of pyroxene is observed with great distinctness in thin sections, made by grinding, while not so readily noted in large crystals. When the cleavage is parallel to a closed form that is, when it is cubic, octahedral, dodecahedral, or rhombohedral (also pyramidal in the tetragonal, hexagonal, and ortho- rhombic systems) solids resembling crystals may often be broken out from a single crystalline" individual, and all the fragments have the same angles. It is, in general, easy to distinguish such a cleavage form, as a cleavage octahedron of fluorite, from a true crystal by the splintery character of the faces of the former. 280. Cleavage and Luster. The face of a crystal parallel to which there is perfect cleavage often shows a pearly luster (see p. 249), due to the partial separation of the crystal into parallel plates. This is illustrated by the basal plane of apophyllite. the clinopina- coid of stilbite and heulandite. An iridescent play of colors is also often seen, as with calcite, when the separation has been sufficient to produce the prismatic colors by interference. 281. Gliding-planes. Closely related to the cleavage directions in their connection with the cohesion of the molecules of a crystal are the gliding- planes, or directions parallel to which a slipping of the molecules may take place under the application of mechanical force, as by pressure. This may have the result of simply producing a separation into layers in the given direction, or, on the other hand, and more commonly, there may be a revolution of the molecules into a new twinning-position, so that secondary twinning-lamellce are formed. Thus, if a crystal of halite, or rock salt, be subjected to gradual pressure in the direction of a dodecahedral face, a plane of separation is developed normal to this and hence in the direction of another face of the same form. There are six such directions of molecular slipping and separation in a crystal of this substance. Certain kinds of mica of the biotite class often show * Lehmann (Zs. Kr., 11, 608, 1886) and Judd (Min. Mag., 8, 7, 1888^ regard these as gliding-planes (see Art. 281). 188 PHYSICAL MINERALOGY Biotite pseudo-crystalline faces, which are undoubtedly secondary in origin that is, have been developed by pressure exerted sub- sequently to the growth of the crystal (cf. Fig. 489). In stibnite, the base, c(001), normal to the plane of perfect cleavage, is a gliding-plane. Thus a slipping of the molecules without their separation may be made to take place by pressure in a plane (||c) normal to the direction of perfect cleavage (||6). A slender prismatic crystal supported near the ends and pressed downward by a dull edge is readily bent, or knicked, in this direction without the parts beyond the support being affected. 282. Secondary Twinning. - - The other case mentioned in the preceding article, where molecular slipping is accompanied by a half -re volution (180) of the molecules into a new twinning-position (see p. 160 et seq.)jis well illus- trated by calcite. Pressure upon a cleavage-fragment may result in the forma- tion of a number of thin lamella in twinning-position to the parent mass, the twinning-plane being the obtuse negative rhombohedron, 0(0112). Second- ary twinning-lamellaB similar to these are often observed in natural cleavage- masses of calcite, and particularly in the grains of a crystalline limestone, as observed in thin sections under the microscope. Secondary twinning-lamellse may also be produced (and are often noted in nature) in the case of the triclinic feldspars, pyroxene, barite, etc. A secondary lamellar structure in quartz has been observed by Judd, in which the lamellae consisted of right-handed and left-handed portions. By the proper means a complete calcite twin may be artificially produced by pressure. Thus, if a cleavage-fragment of prismatic form, say fr-8 mm. in length and 3-6 mm. in breadth, be placed with the obtuse edge on a firm horizontal support, and pressed by the blade of an ordinary tableknife on the other obtuse edge (at a, Fig. 490), the result is that a portion of the crystal is reversed in position, as if twinned parallel to the plane (0112) which in the figure lies in a vertical position. If skillfully done, the twinning surface is perfectly smooth, and the re-entrant angle corresponds exactly with that required by theory. 490 Artificial Twinning in Calcite 283. Parting. The secondary twinning-planes described are often directions of an easy separation conveniently called parting which may be mistaken for cleavage.* The basal parting of pyroxene is a common example of such pseudo-cleavage; it was long mistaken for cleavage. The basal and rhombohedral (1011) and the less distinct prismatic (1120) parting of corundum; the octahedral parting of magnetite (cf. Fig. 474, p. 176), are other examples. An important distinction between cleavage and parting is this : parting can exist only in certain definite planes that is, on the surface of a twinning-lamel- la while the cleavage may take place in any plane having the given direction. 284. Percussion-figures. Immediately connected with the gliding- planes are the figures called percussion-figures f produced upon a crystal * The lamellar structure of a massive mineral, without twinning, may also be the cause of a fracture which can be mistaken for cleavage. t The percussion-figures are best obtained if the crystal plate under investigation be supported upon a hard cushion and a blow be struck with a light hammer upon a steel rod the slightly rounded point of which is held firmly against the surface. CHARACTERS DEPENDING UPON COHESION AND ELASTICITY 189 section by a blow or pressure with a suitable point. In such cases, the method described serves to develop more or less well-defined cracks whose orientation varies with the crystallographic direction of the surface. Thus upon the cubic face of a crystal of halite a four-rayed, star-shaped figure is produced with arms parallel to the diagonals that is, parallel to the dodecahedral faces. On an octahedral face a three- rayed star is obtained. The percussion-figures in the case of the micas have been often investigated, and, as remarked later, they form a means of fixing the true orientation of a cleavage-plate having no crystalline outlines. The figure (Fig. 491) is here a six-rayed star one of whose branches is parallel to the clinopinacoid (6), the others approximately parallel to the intersection edges of the prism (m) and base (c).* Pressure upon a mica plate produces a less distinct six-rayed star^diagonal to that just named; this is called a pressure-figure. 285. Solution-planes. In the case of many crystals, it is possible to prove the ex- istence of certain directions, or structure-planes, in which chemical action takes place most readily for example, when a crystal is under great pressure. These directions of chemi- cal weakness have been called solution-planes. They often manifest themselves by the presence of a multitude of oriented cavities of crystalline outline (so-called negative crystals) in the given direction. These solution-planes in certain cases, as shown by Judd, are the same as the directions of secondary lamellar twinning, as is illustrated by calcite. Connected with this is the schillerization (see Art. 369), observed in certain minerals in rocks (as diallage, schillerspar). 286. Etching-figures. Intimately connected with the general sub- jects here considered, of cohesion in relation to crystals, are the figures pro- duced by etching on crystalline faces; these are often called etching-figures. This method of investigation, developed particularly by Baumhauer, is of high importance as revealing the molecular structure of the crystal faces under examination, and therefore the symmetry of the crystal itself. The etching is performed mostly by solvents, as by water in some cases, more generally the ordinary mineral acids, or caustic alkalies, also by steam at a high pressure and hydrofluoric acid; the last is especially powerful in its action, and is used frequently with the silicates. The figures produced are in the majority of cases angular depressions, such as low triangular or quadrilateral pyramids, whose outlines may run par- allel to some of the crystalline edges. In some cases the planes produced can be referred to occurring crystallographic faces. They appear alike on similar faces of crystals, and hence serve to distinguish different forms, perhaps in appearance identical, as the two sets of faces in the ordinary double pyramid of quartz; so, too, they reveal the corn- Quartz, right- Quartz, left- pound twinning-structure common on handed crystal handed crystal some crystals, as quartz and aragonite. * Cf. Walker, Am. J. Sc., 2, 5, 1896, and G. Friedel, Bull. Soc. Min., 19, 18, 1896. Walker found the angle opposite 6(010) (x in Fig. 491) to be 53 to 56 for muscovite, 59 for lepidolite, 60 for biotite, and 61 to 63 for phlogopite. 492 493 190 PHYSICAL MINERALOGY Further, their form in general corresponds to the symmetry of the group to which the given crystal belongs. They thus reveal the trape- zohedral symmetry of quartz and the difference between a right-handed and left-handed crystal (Figs. 492, 493); the distinction between calcite and dolomite (Figs. 496, 497) ; the distinctive character of apatite, pyromorphite, etc.; the hemimorphic symmetry of calamine and nephelite (cf. Fig. 237, p. 102), etc.; they also prove by their form the monoclinic crystallization of muscovite and other micas (Fig. 495). Fig. 494 shows the etching-figures formed on a basal plane (cleavage) of topaz by fused caustic potash; Fig. 495, those on a cleavage-plate of muscovite by hydrofluoric acid; Fig. 496, upon a rhombohedral face of calcite, and Fig. 497, on one of dolomite by dilute hydro- chloric acid. 494 495 497 Topaz Muscovite Calcite 499 Dolomite 500 Spangolite The shape of the etching-figures may vary with the same crystal with the nature of the solvent employed, though their symmetry remains constant. For example, Fig. 498 shows the figures obtained with spangolite 601 502 by the action of sulphuric acid, Fig. 499 by the same diluted, and Fig. 500 by hydrochloric acid of different degrees of concentration. Of the same nature as the etching-figures artificially produced, in their relation to the symmetry of the crystal, are the markings of ten observed on the natural faces of crys- tals. These are sometimes secondary, caused by a natural ,, etching process, but are more rften an irregularity in the crystalline development of the crystal. The inverted triangular depressions often seen on the octahedral faces of diamond crystals are an example. Fig. 501 shows natural depressions, rhombohedral C h 1 aracter ' observed on corundum crystals from Montana (Pratt). Fig. shows a twin crystal of fluorite with natural etching-figures (Pirsson) - Corundum Fluorite CHARACTERS DEPENDING UPON COHESION AND ELASTICITY 191 these are minute pyramidal depressions whose sides are parallel to the faces of the trapezohedron (311). 287. Corrosion Forms. If the etching process spoken of in the pre- ceding article whether natural or artificial is continued, the result may be to destroy the original crystalline surface and to substitute for it perhaps a multitude of minute elevations, more or less distinct; or, further, new faces may be developed, the crystallographic position of which can often be deter- mined, though the symbols may be complex. The mere loss of water in some cases produces certain corrosive forms. Penfield subjected a sphere of quartz (from a simple right-handed individual) to the prolonged action of hydrofluoric acid. It was found that it was attacked rapidly in the direction of the vertical axis, but barely at all at the -\- extremities of the horizontal axes. Figs. 503, 504 show the form remaining after the sphere had been etched for seven weeks; Fig. 503 is a basal view; Fig. 504, a front view; the circle shows the original form of the sphere, the dotted hexagon the position of the axes. 288. Fracture. The term fracture is used to define the form or kind of surface obtained by breaking in a direction other than that of cleavage in crystallized minerals, and 503 in any direction in mas- sive minerals. When the cleavage is highly perfect in several direc- tions, as the rhombo- hedral cleavage of calcite, fracture is often not readily obtainable. Fracture is defined as : (a) Conchoidal; when a mineral breaks with Etched Sphere of Quartz SS?dS"1ft l ^S3tod from the resemblance of the concavity to the valve of a shell, from concha, a shell. This is well illustrated by obsidian, also by flint. If the resulting forms are small, the fracture is said to be smaK-con- choidal- if only partially distinct, it is subconchoidal. (6) aL,when the surface of fracture, though rough with numerous small elevations and depressions, still approximates to a plane surface. (c) Uneven; when the surface is rough and entirely irregular, t f f Hackf when the elevations are sharp or jagged; broken iron. SffitS^i^t 1 ,*^ by the re- sista'nc^ wS n a e smooth surface offers to abrasion. V*&* determined by observing the comparative ease or difficulty with that of talc impressible by he fingeaa, to that ofthe diamond. To this character, a scale of hardness was introduced by scale of Mohs is now universally accepted. 192 PHYSICAL MINERALOGY 1. Talc. 6. Orthoclase. 2. Gypsum 7. Quartz. 3. Caltite. 8. Topaz. 4. Fluorite. 9. Corundum. 5. Apatite. 10. Diamond. Crystalline varieties with smooth surfaces should be taken so far as possible. If the mineral under examination is scratched by the knife-blade as easily as calcite its hardness is said to be 3; if less easily than calcite and more so than fluorite its hardness is 3' 5. In the latter case the mineral in question would be scratched by fluorite but would itself scratch calcite. It need hardly be added that great accuracy is not attainable by the above methods, though, indeed, for purposes of the determination of minerals, exactness is quite unnecessary. It should be noted that minerals of grade 1 have a greasy feel to the hand; those of grade 2 are easily scratched by the finger-nail; those of grade 3 are rather readily cut, as by a knife; of grade 4, scratched rather easily by the knife; grade 5, scratched with some difficulty; grade 6, barely scratched by a knife, but distinctly by a file moreover, they also scratch ordinary glass. Minerals as hard as quartz (H. = 7), or harder, scratch glass readily but are little touched by a file; the few species belonging here are enumerated in Appendix B; they include all the gems. 290. Sclerometer. Accurate determinations of the hardness of min- erals can be made in various ways, one of the best being by use of an instru- ment called a sclerometer. The mineral is placed on a movable carriage, with the surface to be experimented upon horizontal ; this is brought in contact with a steel point (or diamond point), fixed on a support above; the weight is then determined which is just sufficient to move the carriage and produce a scratch on the surface of the mineral. By means of such an instrument the hardness of the different faces of a given crystal has been determined in a variety of cases. It has been found that different faces of a crystal (e.g., cyanite) differ in hardness, and the same face may differ as it is scratched in different directions. In general, differ- ences in hardness are noted only with crystals which show distinct cleavage; the hardest face is that which is intersected by the plane of most complete cleavage. Further, of a single face, which is intersected by cleavage-planes, the direction perpendicular to the cleavage-direction is the softer, those parallel to it the harder. This subject has been investigated by Exner (p. 194), who has given the form of the cwrves of hardness for the different faces of many crystals. These curves are obtained as follows: the least weight required to scratch a crystalline surface in different directions, for each 10 or 15, from to 180, is determined with the sclerometer; these directions are laid off as radii from a center, and the length of each is made proportional to the weight fixed by experiment that is, to the hardness thus determined; the line connecting the extremities of these radii is the curve of hardness for the given face. The following table gives the results obtained * (see literature) in comparing the hard- ness of the minerals of the scale from corundum, No. 9, taken as 1000, to gypsum, No. 2. Pfaff used the method of boring with a standard point, the hardness being determined by the number of rotations; Rosiwal used a standard powder to grind the surface, Jaggar employed his micro-scle rometer, the method being essentially a modification of that of * The numbers are here given as tabulated by Jaggar. CHARACTERS DEPENDING UPON COHESION AND ELASTICITY 193 Pfaff. By means of this instrument he is able to test the hardness of the minerals present in a thin section under the microscope. Measurements of absolute hardness have also been made by Auerbach. Holmquist has recently made many hardness tests by the grinding method. His results with regard to the minerals of the scale of hardness agree fairly well with those ot Rosiwal given below but show considerable discrepancies with the results obtained by the other methods. He, like Rosiwal, finds that topaz is lower in the scale than quartz. Pfaff, 1884 Rosiwal, 1892 Jaggar, 1897 9. Corundum 1000 1000 1000 8. Topaz 459 138 152 7. Quartz 254 149 40 6. Orthoclase 191 287 25 5. Apatite :... 53'5 6'20 1'23 4. Fluorite 37'3 470 75 3. Calcite 15'3 2'68 '26 2. Gypsum 12'03 '34 '04 291. Relation of Hardness to Chemical Composition. Some general facts of impor- tance can be stated * in regard to the connection between the hardness of a mineral and its chemical composition. 1. Compounds of the heavy metals, as silver, copper, mercury, lead, etc., are soft, their hardness seldom exceeding 2 '5 to 3. Among the compounds of the common metals, the sulphides (arsenides) and oxides of iron (also of nickel and cobalt) are relatively hard (e.g., for pyrite H. = 6 to 6'5; for hematite H. = 6, etc.); here belong also columbite, iron niobate;- tantalite, iron tantalate; wolframite, iron tungstate. 2. The sulphides are mostly relatively soft (except as noted in 1), also most of the carbonates, sulphates, and phosphates. 3. Hydrous salts are relatively soft. This is most distinctly shown among the silicates e.g., compare the feldspars and zeolites. 4. The conspicuously hard minerals are found chiefly among the oxides and silicates; many of them are compounds containing aluminium e.g., corundum, diaspore, chryso- beryl, and many alumino-silicates. Outside of these the borate, boracite, is hard (H. = 7); also iridosmine. On the relation of hardness to specific gravity, see Art. 302. 292. Practical Suggestions. Several points should be regarded hi the trials of hardness: (1) If the mineral is slightly altered, as is often the case with corundum, garnet, etc., the surface may be readily scratched when this would be impossible with the mineral itself; a trial with an edge of the latter will often give a correct result in such a case. (2) A mineral with a granular surface often appears to be scratched when the grains have been only torn apart or crushed. (3) A relatively soft mineral may leave a faint white ridge on a surface, as of glass, which can be mistaken for a scratch if carelessly observed. (4) A crystal, as of quartz, is often slightly scratched by the edge of another of the same species and like hardness. (5) The scratch should be made in such a way as to disfigure the specimen as little as possible. 293. Tenacity. Minerals may be either brittle, sectile, malleable, or flexible. (a) Brittle; when parts of a mineral separate in powder or grains on attempting to cut it, as calcite. (b) Sectile; when pieces may be cut off with a knife without falling to powder, but still the mineral pulverizes under a hammer. This character is intermediate between brittle and malleable, as gypsum. (c) Malleable; when slices may be cut off, and these slices flattened out under a hammer; native gold, native silver. * See further in Appendix B. 194 PHYSICAL MINERALOGY (d) Flexible; when the mineral will bend without breaking, and remain bent after the bending force is removed, as talc. The tenacity of a substance is properly a consequence of its elasticity. 294. Elasticity. The elasticity of -a solid body expresses at once the resistance which it makes to a change in shape or volume, and also its tendency to return to its original shape when the deforming force ceases to act. If the limit of elasticity is not passed, the change in molecular position is proportional to the force acting, and the former shape of volume is exactly resumed; if this limit is exceeded, the deformation becomes permanent, a new position of molecular equilibrium having been assumed; this is shown in the phenomena of gliding-planes and secondary twinning, already discussed. The magni- tude of the elasticity of a given substance is measured by the coefficient of elasticity, or, better, the coefficient of restitution. This is denned as the rela- tion, for example, between the elongation of a bar of unit section to the force acting to produce this effect; similarly of the bending or twisting of a bar. The subject was early investigated acoustically by Savart; in recent years, Voigt and others have made accurate measures of the elasticity of many sub- stances and of the crystals of the same substance in different directions. The elasticity of an amorphous body is the same in all directions, but it changes in value with change of crystallographic direction in all crystals. The distinction between elastic and inelastic is often made between the species of the mica group and allied minerals. Muscovite, for example, is described as " highly elastic/' while phlogopite is much less so. In this case it is not true in the physcial sense that muscovite has a high value for the coefficient of elasticity; its peculiarity lies rather in the fact that its elasticity is displayed through unusually wide limits. LITERATURE Hardness Seebeck. Sklerometer. Programm d. Coin Realgymnasiums, 1833. Franz. Pogg., 80, 37, 1850. Grailich u. Pekarek. Ber. Ak. Wien, 13, 410, 1854. Pfaff. Mesosklerometer. Ber. Ak. Munchen, 13, 55, 1883. Sohncke. Halite. Pogg., 137, 177, 1869. Exner. Ueber die Harte der Krystallflachen, 166 pp. Vienna, 1873 (Preisschrift Wiener. Akad.). Auerbach. Wied. Ann., 43, 61, 1891; 45, 262, 277, 1892; 68, 357, 1896. Rosiwal. Verb. G. Reichs., 475, 1896. T. A. Jaggar, Jr. Microsclerometer. Am. J. Sc., 4, 399, 1897. Schroeder van der Kolk. Ueber Harte in Verland mit Spaltbarkeit, Verb. Ak. Am- sterdam, 8, 1901. Holmquist. Ueber den Relativen Abnutzungswiderstand der Mineralien der Harte- skala. Geol. For. Forh., 33, 281, 1911. Die Schleifharte der Feldspathe, ibid., 36, 401, 1914. Die Hartestufe, 4-5, ibid., 38, 501, 1916. Etching-figures, etc. Goldschmidt and Wright. Ueber Aetzfiguren, Lichtfiguren und Losungskorper. With exhaustive references to the literature. N. Jb. Min. Beil-Bd., 17, 355-390, 1903. Gliding-planes, Secondary Twinning, etc. )be," halite, calcite. Pogg. Ann., 132, 441, 1867. Mica, ibid., 136, 130, 632, 1869. Gypsum, ibid., p. 135. Ber. Ak., Berlin, 440, 1873. ~ 61 \ vSoMfe' Pogg< Ann -' 138 > 337 ' 1869 > Zs " G - Ges -> 26 137 1874 - Galena, L., 1, L6&, SPECIFIC GRAVITY OR RELATIVE DENSITY 195 Baumhauer. Calcite. Zs. Kr., 3, 588, 1879. 1 7 898 Caldte> augite > stibnite > etc. Jb. Min., 1, 32, 1883; 2, 13, 1883. Also ibid., LiJ* ^ J U ? d< Solution-planes etc. Q. J. G. Soc., 41, 374, 1885; Min. Mag., 7, 81, 1887. Structure planes of corundum, Min. Mag., 11, 49 1895 Voigt. See below. Elasticity Savart. Ann. Ch. Phys., 40, 1, 113, 1829; also in Pogg. Ann., 16, 206, 1829. Neumann. Pogg. Ann., 31, 177, 1834. Angstrom. Pogg. Ann., 86, 206, 1852. Baumgarten. Calcite. Pogg. Ann., 152, 369, 1874. Groth. Halite. Pogg. Ann., 157, 115, 1876. Coromilas. Gypsum, mica. Inaug. Diss., Tubingen, 1877 (Zs. Kr., 1, 407, 1877) Reusch. Ice. Wied. Ann., 9, 329, 1880. Klang. Fluorite. Wied. Ann., 12, 321, 1881. Koch. Halite, sylvite. Wied. Ann., 18, 325, 1883. Beckenkamp. Alum. Zs. Kr., 10, 41, 1885. Voigt. Pogg. Ann., Erg. Bd., 7, 1, 177, 1876. Wied. Ann., 38, 573, 1889. Calcite, 39, 412, 1890. Dolomite, ibid., 40, 642, 1890. Tourmaline, ibid., 41, 712, 1890; 44, 168 1891. Also papers in Nachr. Ges. Wiss. Gottingen. Tutton. The Elasmometer. Crystalline Structure and Chemical Constitution, 1910. II. SPECIFIC GRAVITY OR RELATIVE DENSITY 295. Definition of Specific Gravity. The specific gravity of a mineral is the ratio of its density * to that of water at 4 C. (39'2 F.). This relative density may be learned in any case by comparing the ratio of the weight of a certain volume of the given substance to that of an equal volume of water; hence the specific gravity is often defined as: the weight of the body divided by the weight of an equal volume of water. The statement that the specific gravity of graphite is 2, of corundum 4, of galena 7'5, etc., means that the densities of the minerals named are 2, 4, and 7'5, etc., times that of water; in other words, as familiarly expressed, any volume of them, a cubic inch for example, weighs 2 times, 4 times, 7*5 times, etc., as much as a like volume, a cubic inch, of water. Strictly speaking, since the density of water varies with its expansion or contraction under change of temperature, the comparison should be made with water at a fixed temperature, namely 4 C. (39'2 F.), at which it has its maxi- mum density. If made at a higher temperature, a suitable correction should be introduced by calculation. Practically, however, since a high degree of accuracy is not often called for, and, indeed, in many cases is impracticable to attain in consequence of the nature of the material at hand, in the ordinary work of obtaining the specific gravity of minerals the temperature at which the observation is made can safely be neglected. Common variations of tem- perature would seldom affect the value of the specific gravity to the extent of one unit in the third decimal place. * The density of a body is strictly the mass of the unit volume. Thus if a cubic centi- meter of water (at its maximum density, 4 C. or 39'2 F.) is taken as the unit of mass, the density of any body as gold is given by the number of grams of mass (about 19) in a cubic centimeter; in this case the same number, 1.9, gives the relative density or specific gravity. If, however, a pound is taken as the unit of mass, and the cubic foot as the unit of volume, the mass of a cubic foot of water is 62'5 Ibs., that of gold about 1188 Ibs., and the specific gravity is the ratio of the second to the first, or, again, 19. 196 PHYSICAL MINERALOGY For the same reason, it is not necessary to take into consideration the fact that the observed weight of a fragment of a mineral is less than its true weight by the weight of air displaced. Where the nature of the investigation calls for an accurate determination of the specific gravity (e.g., to four decimal places), no one of the precautions in regard to the purity of material, exactness of weight-measurement, temper- ature, etc., can be neglected.* The accurate values spoken of are needed in the consideration of such problems as the specific volume, the relation of molec- ular volume to specific gravity, and many others. 296. Determination of the Specific Gravity by the Balance. The direct comparison by weight of a certain volume of the given mineral with an equal volume of water is not often practicable. By making use, however, of a familiar principle in hydrostatics, viz., that a solid immersed in water, in consequence of the buoyancy of the latter, loses in weight an amount which is equal to the weight of an equal volume of the water (that is, the volume it dis- places) the determination of the specific gravity becomes a very simple process. The weight of the solid in the air (w) is first determined in the usual man- ner; then the weight in water is found (w')] the difference between these weights that is, the loss by immersion (w w f ) is the weight of a volume 505 of water equal to that of the solid ; finally, the quotient of the first weight (w) by that of the equal volume of water as determined (w w') is the specific gravity (G). Hence, w . w w' A common method of obtaining the specific gravity of a firm fragment of a mineral is as follows: First weigh the specimen accurately on a good chemical balance. Then suspend it from one pan of the balance by a horse- hair, silk thread, or, better still, by a fine platinum wire, in a glass of water conveniently placed beneath, and take the weight again with the same care; then use the results as above directed. The platinum wire may be wound around the specimen, or where the latter is small it may be made at one end into a little spiral support. 297. The Jolly Balance. Instead of using an ordin- ary balance and determining the actual weight, the spiral balance of Jolly, shown in Fig. 505, maybe conveniently employed; this is also suitable when the mineral is in the form of small grains. The instrument consists of a spiral spring at the lower end of which are suspended two pans for'spedSfGravitv or ^ baskets > ' and d, Fig. 505. Upon the movable stand -B rests a beaker filled with water. When in adjust- ment for reading this stand has such a position that the pan d is immersed in the water while c hangs above it. Upon the upright A there is a mirror upon which is marked a scale. The position of the balance at any time is obtained by so placing the eye that the bead, m, and its reflection in the mirror coincide Spring or Jolly Balance * Cf. Earl of Berkeley in Min. Mag., 11, 64, 1895. SPECIFIC GRAVITY OR RELATIVE DENSITY 197 and then reading the position of the top of the bead upon the scale. The first step in the operation consists in getting the position of the spring alone, having the pan d immersed in the water in the beaker. Let this reading be represented by n. The mineral whose specific gravity is to be determined is then placed on the pan or basket, c, and the platform B raised until d is properly immersed in the water. The position of the bead m is again read. Let this value be represented by NI. If from N\ be subtracted the number n, expressing the amount to which the scale is stretched by the weight of spring and pans alone, the difference will be proportional to the weight of the mineral. Next, the mineral is placed in the lower pan, d, immersed in the water, and again the corresponding scale number, Nz, read. The difference between these readings (Ni Nz) is a number proportional to the loss of weight in water. The specific gravity is then Nj-n . It is obviously necessary to have the wires supporting the lower pan immersed to the same depth in the case of each of the three determinations. If care is taken the specific gravity can be obtained accurately to two decimal places. 298. The Beam Balance. A beam balance described by Penfield is another very simple and quite accurate device for measuring the specific gravity. It is illustrated in Fig. 506, which will make clear its essential parts. The beam is so balanced by a weight on its shorter end that it is very nearly in equilibrium when the lower pan is immersed in water. An exact balance is then obtained by the small rider d. When the beam is once balanced this rider is kept stationary and its position disregarded in the subsequent readings. The mineral is first placed in the upper pan and the beam balanced by another rider of such a weight that its position will be near the outer end of the beam. 506 Beam Balance for Specific Gravity, th Natural Size (after Penfield) The position of this rider is then read from the scale engraved upon the beam. Let this value be equal to Ni. The mineral is next transferred to the lower pan and the beam again brought into balance by moving this same rider back. The second reading may be represented by N 2 . The formula for obtaining the specific gravity is now: n Nl . = N^^" 2 299. Pycnometer. If the mineral is in the form of grains or small fragments, the specific gravity may be obtained by use of the pycnometer. 198 PHYSICAL MINERALOGY This is a small bottle (Fig. 507) having a stopper which fits tightly and ends in a tube with a very fine opening. The bottle is filled with distilled water, the stopper inserted, and the overflowing water carefully removed 607 with a soft cloth and then weighed. The weight of the water is obviously the difference between this last weight and that of the bottle and mineral together, as first determined. The mineral whose density is to be determined is also weighed. Lastly the bottle is weighed with the mineral in it and filled with water as described above.* The weight of the water displaced by the mineral is obviously the difference between this last weight and that of the bottle filled with water plus the weight of the mineral. The specific gravity of the min- eral is equal to its weight alone divided by the weight of the equal volume of water thus determined. Where this method is followed with sufficient care, especially avoiding any change Pycnometer of temperature in the water, the results may be highly accurate. If the mineral forms a porous mass, it may be first reduced to powder, but it is to be noted that it has been shown by Rose that chemical precipitates have uniformly a higher density than belongs to the same substance in a less finely divided state. This increase of density also characterizes, though to a less extent, a mineral in a fine state of mechanical subdivision. It is explained by the condensation of the water on the surface of the powder. 300. Use of Liquids of High Density. It is often found convenient both in the determination of the specific gravity and in the mechanical separa- tion of fragments of different specific gravities (e.g., to obtain pure material for analysis, or again in the study of rocks) to use a liquid of high density that is, a so-called heavy solution. One of these is the solution of mercuric iodide in potassium iodide, called the Sonstadt or Thoulet solution. When made with care it has a maximum density of nearly 3 '2, which by dilution may be lowered at will. A second solution, often employed, is the Klein solution, the borotungstate of cadmium, having a maximum density of 3*6. This again may be lowered at will by dilution, observing certain necessary precautions. Still a third solution of much practical value is that proposed by Brauns, methylene iodide, which has a specific gravity of 3*324. A number of other solutions, more or less practical, have also been suggested.! When one of these liquids is to be used for the determination of the specific gravity of fragments of a certain mineral it must be diluted until the fragments just float and the specific gravity then obtained, most conveniently by the Westphal balance (Art. 301). When, on the other hand, the liquid is to be used for the separation of the fragments of two or more minerals mixed together, the material is first reduced to the proper degree of fineness, the dust and smallest fragments being sifted out, then it is introduced into the solution and this diluted until one con- stituent after another sinks and is removed. For the convenient application * Care should be taken to prevent air-bubbles being included among the mineral particles. This may be accomplished by placing the bottle under an air-pump and ex- hausting the air or by suspending the bottle for a short time in a beaker filled with boiling water and then allowing it to cool again before weighing. t Johannsen, Manual of Petrographic Methods, p. 519 et seq., gives in detail an account of the various solutions, the methods of their preparation, etc. SPECIFIC GRAVITY OR RELATIVE DENSITY 199 of this method a suitable tube is called for and certain precautions must be observed; compare the papers noted in the literature (p. 200), especially one by Penfield. 301. Westphal's Balance. -The Westphal balance is conveniently used to determine ^A. SP Q e n^ C g i? Y ? i a qm< ? ? n nd 5 ence j a mineral when a heavy solution is employed (Art. 300). It consists essentially of a graduated steelyard arm, upon which the weights in the form of riders are placed. These must be so adjusted that the sinker is freely sus- pended m the given liquid while the index at the end points to the zero of the scale and shows that the arm is horizontal (cf. Johannsen, p. 533). The graduation usually allows of the specific gravity being read off directly without calculation. 302. Relation of Density to Hardness, Chemical Composition, etc. The density or specific gravity, of a solid depends, first, upon the nature of the chemical substances which it contains, and, second, upon the state of molecular aggregation. Thus, as an illustration of the first point, all lead compounds have a high density (G. = about 6), since lead is a heavy metal, or, chemically expressed, has a high atomic weight (206'4). Similarly, barium sulphate, barite, has a specific gravity of 4'5, while for calcium sulphate or anhydrite the value is only 2'95 {atomic weight for barium 137 for calcium about 40). On the other hand, while aluminium is a metal of low density (G. = 2'5 and atomic weight = 27), its oxide, corundum, has a remarkably high density (G. = 4) and is also very hard (H. = 9). Again, carbon (atomic weight = 12) has a high density in the diamond (G. = 3'5) and low in graphite (G. = 2); also, the first is hard (H. = 10), the second soft (H. = 1'5). In these and similar cases the high density signifies great molecular aggrega- tion, and hence it is natural that it should be accompanied by great hardness and resistance to the attack of acids. As bearing upon this point, it is to be noted that the density of many substances is altered by fusion. Again, the same mineral in different states of molecular aggregation may differ (but only slightly) in density. Furthermore, minerals having the same chemical composition have sometimes different densities, corresponding to the different crystalline forms in which they appear. Thus in the case of calcium carbonate (CaCO 3 ), calcite has G. = 27, aragonite has G. = 2'9. 303.- Average Specific Gravities. It is to be noted that among minerals of NON- METALLIC LUSTER the average specific gravity ranges from 2'6 to 3. Here belong quartz (2'66), calcite (27), the feldspars (2'6-275), rmiscovite (2'8). A specific gravity of 2'5 or less is low, and is characteristic of soft minerals, and often those which are hydrous (e.g., gypsum, G. = 2'3). The common species fluorite, tourmaline, apatite, vesuvianite, amphi- bole, pyroxene, and epidote lie just above the limit given, namely, 3'0 to 3'5. A specific gravity of 3'5 or above is relatively high, and belongs to hard minerals (as corundum, see Art. 302), or to those containing a heavy metal, as compounds of strontium, barium, also iron, tungsten, copper, silver, lead, mercury, etc. With minerals of METALLIC LUSTER, the average is about 5 (here belong pyrite, hematite, etc.), while if below 4 it is relatively low (graphite 2, stibnite 4'5); if 7 or above, relatively high (as galena, 7 '5). Tables of minerals arranged according to their specific gravity are given in Appendix B. 304. Constancy of Specific Gravity. The specific gravity of a mineral species is a character of fundamental importance, and is highly constant for different specimens of the same species, if pure, free from cavities, solid inclusions, etc., and if essentially constant in composition. In the case of many species, however, a greater or less variation exists in the chemical composition, and this at once causes a variation in specific gravity. The different kinds of garnet illustrate this point; also the various minerals intermediate between the tantalate of iron (and manganese) and the niobate, varying from G. = 7'3 to G. = 5'3. 305. Practical Suggestions. It should be noted that the determination of the specific gravity has little value unless the fragment taken is pure and is free from impurities, internal and external, and not porous. Care must be taken to exclude air-bubbles, and it will often be found well to moisten the surface of the specimen before inserting it in the water, and sometimes boiling (or the use of the air-pump) is necessary to free it from air. If it absorbs water this latter process must be allowed to go on till the substance is fully saturated. No accurate determinations can be made unless the changes of temperature are rigorously excluded and the actual temperature noted. In a mechanical mixture of two constituents in known proportions, when the specific gravity of the whole and of one are known, that of the other can be readily obtained. This method is often important in the study of rocks. 200 PHYSICAL MINERALOGY It is to be noted that the hand may be soon trained to detect a difference of specific eravitv if like volumes are taken, even in a small fragment thus the difference between calcite or albite and barite, even the difference between a small diamond and a quartz crystal, can be detected. LITERATURE. Specific Gravity General: Beudant. Pogg. Ann., 14, 474, 1828. Jenzsch. Pogg. Ann., 99, 151, 1856. Jolly. Ber. Ak. Miinchen, 1864, 162. Gadolin. Pogg., 106, 213, 1859. G. Rose. Pogg. Ann., 73, 1; 75, 403, 1848. Scheerer. Pogg. Ann., 67, 120, 1846. Schroder. Pogg. Ann., 106, 226, 1859. Jb. Min., 561, 932, 1873; 399, 1874, etc. Tschermak. Ber. Ak. Wien, 47 (1), 292, 1863. Websky. Die Mineralien nach den fur das specifische Gewicht derselben angenom- menen und gefundenen Werthen. 170 pp. Breslau, 1868. Use of Heavy Solutions, etc.: Sonstadt. Chem. News, 29, 127, 1874. Thoulet. Bull. Soc. Min., 2, 17, 189, 1879. Breon. Bull. Soc. Min., 3, 46, 1880. Goldschmidt. Jb. Min., Beil.-Bd., 1, 179, 1881. D. Klein. Bull. Soc. Min., 4, 149, 1881. Rohrbach. Jb. Min., 2, 186, 1883. Gisevius. Inaug. Diss., Bonn., 1883. Brauns. Jb. Min., 2, 72, 1886; 1, 213, 1888. Retgers. Jb. Min., 2, 185, 1889. Salomon. Jb. Min., 2, 214, 1891. Penfield. Am. J. Sc., 50, 446, 1895. Merwin. Am. J. Sc., 32, 425, 1911. III. CHARACTERS DEPENDING UPON LIGHT GENERAL PRINCIPLES OF OPTICS 306. Before considering the optical characters of minerals in general, and more particularly those that belong to the crystals of the different systems, it is desirable to review briefly some of the more important principles of optics upon which the phenomena in question depend. For a fuller discussion of the optics of crystals, special reference is made to the works of Groth (translation by Jackson), Liebisch, Mallard, Duparc and Pearce, Rosenbusch (translation by Iddings), Iddings, Johannsen, Winchell, mentioned on p. 3 also to the various advanced text-books of Physics. 307. The Nature of Light. Light is now considered to be an electro- magnetic phenomenon due to a periodicJvariation in the energy given off by vibrating electrons. This energy is transmitted by a series of periodic changes that show all the characters of ordinary wave phenomena. The light waves, as they are commonly called, possess certain short wave-lengths that are of the correct magnitude to affect the optic nerves. Other similar waves with longer or shorter wave-lengths belong to the same class of phenomena. Immediately beyond the violet end of the visible spectrum come the so-called " ultra- violet" waves with still shorter wave-lengths and on beyond these we have the X-rays and the " gamma" rays produced by radium. Of the waves having greater lengths than those of light waves we have the waves that give CHARACTERS DEPENDING UPON LIGHT 201 rise to the sensation of heat and the Hertzian waves used in wireless All of these vibrations, while varying enormously in their wave-lengths, belong to the same order of phenomena and obey the same laws. The proportion that the section of the series which produces the effect of light bears to the whole may be strikingly shown when we say that if ordinary white light is broken up into a spectrum a yard long and this then considered to be extended on either end so as to include all known electro-magnetic waves the entire spectrum would be over five million miles in length. The transmission of light through interstellar space, through liquids and transparent solids, has for some time been explained by the assumption that a medium, called the luminiferous ether, pervades all space, including the intermodular space of material bodies. In this medium the vibrations of light waves are assumed to take place. For the purposes of the present work, however, it is unnecessary to consider closely the exact nature of light or the mode of its transmission. It will assist greatly, however, in obtaining a clear idea of the behavior of light in crystals if we assume that light waves are me- chanical in nature and consist of periodic vibrations in an all-prevailing ether. 308. Wave-motion in General. A familiar example of wave-motion is given by the series of concentric waves which on a surface of smooth water go out from a center of disturbance, as the point where a pebble has been dropped in. These surface-waves are propagated by a motion of the water- particles which is transverse to the direction in which the waves themselves travel; this motion is given from each particle to the next adjoining, and so on. Thus the particles of water at any one spot oscillate up and down,* while the wave moves on as a circular ridge of water of constantly increasing diameter, but of diminishing height. The ridge is followed by a valley, indeed both together properly constitute a wave in the physical sense. This compound wave is followed by another wave and another, until the original impulse has exhausted itself. Another familiar kind of wave-motion is illustrated by the sound-waves which in the free air travel outward from a sonorous body in the form of concentric spheres. Here the actual motion of the layers of air is forward and back that is, in the direction of propagation of the sound and the effect of the transfer of this impulse from one layer to the next is to give rise alternately to a condensed and rarefied shell of air, which together constitute a sound-wave and which expand in spherical waves of constantly decreasing intensity (since the mass of air set in motion continually increases). Sound- waves, as of the voice, may be several feet in length, and they travel at a rate of 1120 feet per second at ordinary temperatures. 309. It is important to understand that in both the cases mentioned, as in every case of free wave-motion, each point on a given wave may be considered as a center of disturbance from which a system of new waves tend to go out. These individual wave-systems ordinarily destroy each other except so far as the onward progression of the wave as a whole is concerned. This is further discussed and illustrated in its application to light-waves (Art 312 and Figs. 509, 510). In general, therefore, a given wave is to be considered as the resultant of all these minor wave-systems. If, however, a wave encounters an obstacle in its path, as a narrow opening (i.e., one narrow in comparison with the length * Strictly speaking, the path of each particle approximates closely to a circle. 202 PHYSICAL MINERALOGY of the wave) or a sharp edge, then the fact just mentioned explains how the waves seem to bend about the obstacles, since new waves start from them as centers. This principle has an important application in the case of light- waves, explaining the phenomena of diffraction (Art. 331). 310. Still another case of wave-motion may be mentioned, since it is particularly help- ful in giving a correct apprehension of light-phenomena. If a long rope, attached at one end, be grasped at the other, a quick motion of the hand, up or down, will give rise to a half wave-form in one case a crest, in the other a trough which will travel quickly to the other end and be reflected back with a reversal in its position; that is, if it went forward as a hill-like wave, it will return as a trough. If, just as the wave has reached the end. a second like one be started, the two will meet and pass in the middle, but here for a brief interval the rope is sensibly at rest, since it feels two equal and opposite impulses. This will be seen later to be a case of the simple interference of two like waves opposed in phase. Again, a double motion of the hand, up and down, will produce a complete wave, with crest and trough, as the result, and this again is reflected back as in the simpler case. Still again, if a series of like motions are continued rhythmically and so timed that each wave is an even part of the whole rope, the two systems of equal and opposite waves passing in the two directions will interfere and a system of so-called stationary waves will be the result, the rope seeming to vibrate in segments to and fro about the position of equilibrium. Finally, if the end of the rope be made to describe a small circle at a rapid, uniform, rhythmical rate, a system of stationary waves will again result, but now the vibrations of the string will be sensibly in circles about the central line. This last case will be seen to roughly indicate the kind of transverse vibrations by which the waves of circularly polar- ized light are propagated, while the former case represents the vibrations of waves of what is called plane-polarized light. All these cases of waves obtained with a rope deserve to be carefully considered and studied by experiment, for the sake of the assistance they give to an understanding of the complex phenomena of light-waves. 311. Light-waves. In the discussion that follows, in order to make the explanations simpler and clearer, light waves have been treated as if they consisted of mechanical disturbances in a material medium called the ether. The vibrations in the ether caused by the transmission of a light wave take place in directions transverse to the direction of the movement of the wave. These oscillations have the following characters. When an ether par- ticle is set vibrating it moves from its original position with gradually decreas- ing velocity until the position of its maximum displacement is reached. Then with gradually increasing velocity it returns to its original position and since it is moving without friction it will continue in the same direction on past this point. Its velocity will then again diminish until it has reached a displace- ment equal but opposite in direction to its first swing, when it will start back on its course and repeat the oscillation. The varying velocity of such an oscillation would be the same as that shown by a particle moving around a circle with uniform speed if the particle was observed in a direction lying in the plane of the circle. Under these conditions the particle would appear to move forward and backward along a straight line with constantly changing velocity. Such a motion is called simple harmonic motion. The motion of one ether particle is communicated to another and so on, each, in order, falling a little behind in the time of its oscillation. Conse- quently, while the individual particles move only back and forth in the same line the wave disturbance moves forward. If, at a given instant of time, the positions of successive particles in their oscillations are plotted, a curve, such as shown in Fig. 508, will be formed. Such a curve is known as a harmonic curve. The oscillatory motion of the particles in a light wave is called a periodic motion since it repeats itself at regular intervals. The maximum dis- CHARACTERS DEPENDING UPON LIGHT 203 D placement of a particle from its original position of rest is called the amplitude of the wave (distance C-D, Fig. 508). The phase of a particle at a given instant is its position in the vibration and the 608 direction in which it is moving. /^ The distance between / any particle and the next / which is in a like position r i.e., of like phase, as A \ and B is the wave-length; \~ j\l I/ and the time required for this completed movement Harmonic Curve is the time of vibration, or vibration-period. The wave-system therefore travels onward the distance of one wave-length in one vibration-period. The intensity of the light varies with the amplitude of the vibration, and the color, as explained in a later ar- ticle, depends upon the length of the waves; the length of the violet waves is about one-half the length of the red waves. In ordinary light the transverse vibrations are to be thought of as taking place in all planes about the line of propagation. In the above figure, vibra- tions in one plane only are represented ; light that has only one direction of transverse vibration is said to be plane-polarized. Light-waves have a very minute length, only 0'000023 of an inch for the yellow sodium flame, and they travel with enormous velocity, 186,000 miles per second in a vacuum; thus light passes from the sun to the earth in about eight minutes. The vibration-period, or time of one oscillation, is conse- quently extremely brief; it is given by dividing the distance traveled by light in one second by the number of waves included.* 312. Wave-front. In an isotropic medium, as air, water, or glass that is, one in which light would be propagated in all directions about a lumi- nous point with the same velocity the waves are spherical in form. The wave-front is the continuous surface, in this case spherical, which includes all particles that commence their vibration at the same moment of time. Obvi- ously the curvature of the wave-front diminishes as the distance of the source of light increases, and when the light comes from an indefinitely great distance (as the sun) the wave-front becomes sensibly a plane surface. Such waves are usually called plane waves. These cases are illustrated by Figs. 509 and 510. In Fig. 509 the luminous point is supposed to be 0, and the medium being isotropic, il is obvious that the wave-front, as ABC . . . G, is spherical. It is also made clear by this figure how, as briefly stated in Art. 309, the resultant of all the individual impulses which go out from the successive points, as A, B, C, etc., as centers, form a new wave-front, abc . . . g, concentric with ABC G. In Fig. 510 the luminous body is supposed to be at a great dis- * "On account of the tremendous speed at which light travels the rapidity of vibration, or "frequency " of light as it passes through a fixed point, is extremely great. About eight hundred trillion waves of violet light would pass through such a point in a second. Ine extreme brevity of the interval of time required for the passage of a single wave of this sort may perhaps be realized better when it is said that one eight-hundred-trillionth of a second is a vastly smaller part of a second than a second is of the whole of historic time. Comstock and Troland, "The Nature of Matter and Electricity, p. 157. 204 PHYSICAL MINERALOGY tance, so that the wave-front AB . 609 F is a plane surface. Here also the individual impulses from A, B, etc., unite to form the wave-front ab . . . / parallel to AB . . . F. 313. Light-ray. The study of light-phenomena is, in certain cases, facilitated by the conception of a light-ray, a line drawn from the luminous point to the wave-front, and whose direction is taken so as to represent that of the wave itself. 510 A V a > B Y b ^ C /v y D V \A d^ E x \ J 1 F \ A f . / / In Fig. 509 OA, OB, etc., are diverging light-rays, and in Fig. 510 OA, OB, etc., are parallel light-rays. In both these cases, where the medium is assumed to be isotropic, the light-ray is normal to the wave- front. This is equivalent to saying that the light-wave moves onward in a direction normal to the wave-front. It must be understood that the " light-ray" has no real existence and is to be taken only as a convenient method of representing the direction of motion of the light-waves under varying conditions. Thus when by appro- priate means (e.g., the use of lenses) the curvature of the wave-front is altered for example, if from being a plane surface it is made sharply convex then the light-rays, at first parallel, are said to be made to diverge. Again, if the convex wave-front is made plane, the diverging light-rays are then said to be made parallel. 314. Wave-length. Color. White Light. Notwithstanding the very small length of the waves of light, they can be measured with great precision. The visual part of the waves going out from a brilliantly incandescent body, as the glowing carbons of an electric arc-light, may be shown to consist of waves of widely varying lengths. They include red waves whose length is 0*0007604 mm. ( about nAA of an inch ) and waves whose length constantly \ oy,uuu / diminishes without break, through the orange, yellow, green, and blue to the violet, whose minimum length (0'0003968 mm.) is 'about half of that of the red. The colo of light is commonly said to depend upon its wave-length and will be so spoken of here. This is not strictly true, however, because, since the velocity of light varies with the medium through which it is traveling CHARACTERS DEPENDING UPON LIGHT 205 constant under all conditions, it follows mpL ^ ave ; 1 , en g t . h of "fht of the same color must be different in different media. It is, therefore, rather the frequency with which the light waves reach the eye tLat determines the color sensation. Commonly a given color t produced by the combination of several different wave-lengths of light It I strictly monochromatic only when it corresponds to one definite wave-length this is nearly true of the bright-yellow sodium line, though strictly TpeS this consists of two sets of waves of slightly different lengths. The effect of white light" is obtained if all the waves from the red to the violet come together to the eye simultaneously; for this reason a piece of platinum at a temperature of 1500 C. appears " white hot" The radiation from the sources named, either the sun, the electric carbons or the glowing platinum, includes also longer waves which do not affect the eye, but which, like the light-waves, produce the effect of sensible heat when received upon an absorbing surface, as one of lamp- black. There are also, particularly in the radiation from the sun, waves shorter than the violet which also do not affect the eye. The former are called infra-red, the latter ultra-violet waves. The brightness of light depends upon the am- plitude of its vibrations and varies directly as the square of this distance. 315. Complementary Colors. - - The sensation of white light mentioned above is also obtained when to a given color ^ \r \^ \,< \^ ^X M , i . T 1 "* V ** x n * T"* /T * that is, light-waves of given wave-length - - is combined a certain other so - called complementary color. Thus certain shades of pink and green combined, as by the rapid rotation of a card on which the colors form segments, produce the effect of white. Blue and yellow of certain shades are also complementary. For every shade of color in the spectrum there is another one complementary to it in the sense here defined. The most perfect illustration of complementary colors is given by the examination of sections of crystals in polarized light, as later explained. 316. Reflection. When light- waves come to the boundary which separates one medium from another, as a surface of water, or glass in air, they are, in general, in part reflected or returned back into the first medium. The reflection of light-waves is illustrated by Figs. 511 and 512. In Fig. 511, MM is the reflecting surface here a plane surface and the light- waves have a plane wave-front (Abcde); in other words, the light-rays (OA, Ob, etc.) are parallel. It is obvious that the wave-front meets the sur- face first at A and successively from point to point to E. These points are to be regarded as the centers of new wave-systems which unimpeded would be propagated outward in all directions and at a given instant would have traveled through distances equal to the lines Aa', Bb' , etc. Hence the com- 206 PHYSICAL MINERALOGY mon tangent fghkE to the circular arcs drawn with these radii from A, B, etc., represents the direction of the new or reflected wave-front. But geomet- 512 rically the angle eAE is equal to fEA, or the in- cident and reflected wave- fronts make equal angles with the reflecting surface. If NA is a normal at A, the angle OAN - - called the angle of incidence is equal to NAF, the angle of reflection. Hence the familiar law: The angle of incidence is equal to the angle of reflec- tion. Furthermore, the " in- cident and reflected rays" both lie in the same plane with the normal .to the reflecting surface. In Fig. 512, where the luminous point is at 0, the waves going out from it will meet the plane mirror MM first at the point A and successively at points, as B, C, D, etc., farther away to the right (and left) of A. Here also it is easy to show that all the new impulses, which have their centers at A, B, C, etc., must together give rise to a series of reflected waves whose center is at 0', at a distance equally great from MM measured on a normal to the surface (OA = O'A}. Now the lines OA, OB, etc., which are perpendicular to the wave-front, represent certain incident light-rays, and the eye placed in the direction BE, CF, etc., will see the luminous point as if at 0' . It follows from the construc- tion of the figure and can be proved by experiment that if BN, CN', etc., are normals to the mirror the angles of incidence, OBN, OCN' ', etc., are equal to the angles of reflection, NBE, N'CF, etc., respectively. Hence the above law applies to this case also. If the reflecting surface is not plane, but, for example, a concave surface, as that of a spherical or parabolic mirror, there is a change in the curvature of the wave-front after reflection, but the same law still holds true. The proportion of the reflected to the incident light increases with the smoothness of the surface and also as the angle of incidence diminishes. The intensity of the reflected light is a maximum for a given surface in the case of perpendicular incidence (OA, Fig. 512). If the surface is not perfectly polished, diffuse reflection will take place, and there will be no distinct reflected ray. It is the diffusely reflected light which makes the reflected surface visible; if the surface of a mirror were absolutely smooth the eye would see the reflected body in it only, not the surface itself. Optically expressed, the surface is to be considered smooth if the distance between the scratches upon it is considerablv less (say one-fourth) than the wave-length of light. 317. Refraction. When light passes from one medium into another there is, in general, an increase or decrease in its velocity, and this commonly results in the phenomenon of refraction that is, a change in the direction of propagation. The principles applicable here can be most easily shown in the CHARACTERS DEPENDING UPON LIGHT 207 513 case of light-waves with a plane wave-front, as shown in Fig 513 that is where the light-rays OA, OB, etc., are parallel. Suppose, for example, that a light-wave, part of whose wave- front is Abcde, passes from air obliquely into glass, in which its velocity is about two-thirds as great as it was in the air and suppose the surface of the glass to be plane. At the moment that the ray 0-A enters the glass the ray 0-E has reached the point e. During the time that the latter ray travels from e to E, the ray 0-A will have advanced in the glass a distance equal to %e-E, or to some point on an arc having this distance as a radius (A-f). In the same way during the time ray 0-E passes from the point p to E, ray 0-B will have traveled in the glass the distance B-g, equal to f p-E. In this way arcs may be drawn about each one of the points A, B, C, etc., and the position of the new wave-front in the glass determined by their common tangent, Ekhgf. It is seen that there is a change of direction in the wave-front, or otherwise stated, in the light-ray, the magnitude of which depends on the ratio between the light-velocities in the two media, and, as discussed later, also upon the wave-length of the light. The light-ray is here said to be broken or refracted, and for a medium like glass, optically denser than air (i.e., with a lower value of the light- velocity), the refraction is toward the perpendicular with the angle of refraction, r, smaller than the angle of incidence, i. In the opposite case when light passes into an optically rarer medium the refraction is away from the perpendicular and the angle of refraction is larger than that of incidence (Art. 323). 318. Refractive Index. It is obvious from the figure that whatever the direction of the wave-front that is, of the light-rays relatively to the given surface, the ratio of eE to Af, which determines the direction of the new wave-front (i.e., the direction of a refracted ray, AF) is constant. This ratio y is equal to where V is the value of the light-velocity for the first medium (here air) and v for the second (as glass). This constant ratio is commonly represented by n and is known as the index of refraction. Therefore eE In Fig. 513, by construction, / eAE = / i and / AEf = / r. Al eE Also, Therefore, sn sin r and eE_ AE = eE Af Af AE 208 PHYSICAL MINERALOGY sin ^ , The law of refraction then is given by the expression, n = - - , or may be olll / formulated as follows: The sine of the angle of incidence bears a constant ratio to the sine of the angle of refraction. In the case of light passing from air into crown glass this ratio is found to 3in ^ = T608, and this number consequently gives the value of the be, sin r refractive index, or 514 for this kind of glass. The above relation holds true for any wave-system of given wave- length in passing from one medium into another, whatever the wave- front or shape of the bounding sur- face. In Fig. 514 the luminous point is at 0, and it can be readily shown that the new wave-front propagated in the second me- dium (of greater optical density) has a flattened curvature and corresponding to this a center at 0' f where ^4^ = ). Here the OA v incident rays OB, OC, are re- fracted at J3*and C, the correspond- ing refracted rays being BE and CF. For this case also the relation holds good, n sin i sinr sin i sin r -, , etc. If the bounding surface is not plane but curved, as in lenses, there is a change in the curvature of the wave-front in the second medium, but the simple law, n = - > holds true here also, so long as the medium is isotropic. The relation between wave-length and refractive index is spoken of in Art. 328. 319. Relation of Refractive Index to Light- velocity. The discussion of the preceding article shows that if n is the refractive index of a given sub- stance for waves of a certain length, referred to air, V the velocity in air and v the velocity in the given medium, then V n = v For two media whose indices are n\ and n z respectively, it consequently follows that n\ _ v% t nz v\ CHARACTERS DEPENDING UPON LIGHT 209 Therefore, The indices of refraction of two given media for a certain wave- length are inversely proportional to their relative light-velocities. In other words, if the velocity of light in air is taken as equal to 1 and the velocity of the same light is found to be one half as great when passing through a given substance, the index of refraction, or n, of that substance when referred to air (n = TO) will be equal to 2*0. 320. Principal Refractive Indices. The refractive index has, as stated, a constant value for every substance, referred, as is usual, to air (or it may be to a vacuum). In regard to solid media, it is evident from Art. 318 and will be further explained later that those which are isotropic, viz., amorphous substances and crystals of the isometric system, can have but a single value of this index. Crystals of the tetragonal and hexagonal systems have, as later explained, two principal refractive indices, e and co, corresponding to the velocities of light-propagation in certain definite directions in them. Further, all orthorhombic, monoclinic, and triclinic crystals have similarly three principal indices, a, |S, 7. In the latter 'cases of so-called anisotropic media, the mean refractive index is taken, namely, as the arithmetical mean 321. Effect of Index of Refraction upon Luster, etc. The luster and general appearance of a transparent substance depend largely upon its refrac- tive index. For instance the peculiar aspect of the mineral cryolite, by means of which it is usually possible to readily identify the substance, is due to its low index of refraction. If cryolite is pulverized and the powder poured into a test tube of water it will disappear and apparently go into solution. It is quite insoluble, however, but becomes invisible in the water because its index of refraction (about 1*34) is near that of water (T335). The light will travel with practically the same velocity through the cryolite as through the water and consequently suffer little reflection or refraction at the surfaces between the two. On the other hand powdered glass with a higher index of refraction than that of water appears white under the same conditions because of the reflection of light from the surfaces of the particles. Substances having an unusually high index of refraction have an appear- ance which it is hard to define, and which is generally spoken of as an adaman- tine luster. .This kind of luster may be best comprehended by examining specimens of diamond (n = 2*419) or of cerussite (n = 1*98). They have a flash and quality, sometimes almost a metallic appearance, which is not possessed by minerals of a low refractive index. Compare, for example, spec- imens of cerussite and fluorite (n = 1'434). The usual index of refraction for minerals may be said to range not far from 1*55, and gives to minerals a luster which has been termed vitreous. Quartz, feldspar, and halite show good examples of vitreous luster. Below is given a list of common minerals arranged according to their indices of refraction. For minerals other than those of the isometric system the average value (as defined in the preceding article) is given here. Water ........... 1 ' 335 Muscovite ....... 1 582 Fluorite ......... 1'434 Beryl ........... 1'582 Orthoclase ....... 1523 Calcite .......... T601 Gypsum ......... 1'524 Topaz ........... 1622 Quartz .......... 1 "547 Tremolite ....... 1 '622 210 PHYSICAL MINERALOGY Dolomite ........ 1626 Anglesite ........ T884 Aragonite ....... 1 633 Zircon ........... 1 952 Apatite ......... 1 633 Cerussite ........ T 986 Barite ........... 1640 Cassiterite ....... 2'029 Diopside ........ T 685 Sulphur .......... 2'077 Cyanite .......... 1'723 Sphalerite ........ 2369 Epidote .......... 1750 Diamond ........ 2 419 Corundum ....... 1 765 Rutile ........... 2 711 Almandite ....... 1*810 Cuprite .......... 2849 Malachite ........ 1 ' 880 Cinnabar ........ 2 969 322. Relations between Chemical Composition, Density, and Refractive Index. That definite relations exist between the chemical composition of a substance, its specific gravity, and its index of refraction, has been conclusively shown in many cases. With the plagio- clase feldspar group, for instance, the variation in composition which the different members show is accompanied by a direct variation in density and refractive index. Attempts have been made to express these relations in the form of mathematical statements. The two most satisfactory expressions are the one proposed by Gladstone and Dale,* l -^ = constant, and the one proposed independently by Lorentz f and Lorenz,t n 2 ~ -. = constant. In these n is equal to the mean refractive index and d to the density. These were originally proposed for use with gases and solutions and for these bodievS have been found to serve about equally well. When attempts are made, however, to apply them to crystalline solids the results are at the best only approximate. This is probably because the formulas do not take into consideration the modifications that the crystal structure must introduce. 323. Total Reflection. Critical Angle. In regard to the principle stated in Art. 318 and expressed by the equation n = - , two points are to be noted. First, if the angle i = 0, then sin i 0, and obviously also r = 0; in other words, when the ray of light (as OA, Fig. 514) coincides with the per- pendicular, no change of direction takes place, the ray proceeds onward (AD) into the second medium without deviation, but with a change of velocity. Again, if the angle i = 90, then sin i = 1, and the equation above becomes n = - or sin r = -. Asn has a fixed value for every substance, it is obvi- sin T 7i ous that there will also be a corresponding value of the angle r for the case mentioned. From the above table it is seen that for water, sin r = VT^H 1 OOO r = 48 31'; for crown glass (n = 1'608), sin r = and r = 38 27'; for diamond, sin r = ^r - and r = 24 25'. This fact, that for each substance at a particular value of the angle r~the angle i becomes equal to 90, has an important bearing on the behavior of light when it is passing from an optically denser into an optically rarer medium. * Phil. Trans., 153, 317, 1863. t Wiedem. Ann., 9, 641, 1880. J Wiedem. Ann., 11, 70, 1880. E. S. Larsen, Am. Jour. Sci., 28, 263, 1909. See also Cheneveau, Ann. Chem. Phys., 12) 145, '28 J, 1907. CHARACTERS DEPENDING UPON LIGHT 211 515 B In Fig. 515 we may assume that light rays coming from various directions meet the surface between a block of glass and the air at the point A. Light traveling along the path O-A will pass out into the air without a change in its direction but with an increase in its velocity. If it emerges from the glass at any other angle than 90 the ray on entering the air will be bent away from the perpendicular and the angle of deviation will vary with the angle at which the ray touched the surface and with the index of refraction of the glass. The same law holds true in this case as in the case of a ray entering from the air, except that the formula nows reads n = . , where r = the angle the ray in szn v air makes with the normal to the surface and i = the angle that the ray makes within the glass to the same normal. In Fig. 515 the ray C-A will pass out into the air along the line A-D. But the angle i for the ray E-A = 38 27' and, as shown in the preceding paragraph, for glass, where n = 1*608, the angle r in the air will be 90 and the ray will travel along the surface of the glass in the direction A-F. Consequently any ray, such as G-A, which meets the surface of the glass at an angle greater than 38 27', will be unable to pass out into the air and will suffer total reflection at the surface, passing back into the glass in the direction A-G', with angle GAG = angle GAG'. The angle at which total reflection takes place for any substance is known as its critical The phenomenon of total reflection is taken advantage of in the cutting of gem stones. According to common practice such a stone is cut with a flat surface on top and with a number of inclined facets on the bottom. The light that enters the stone from above is in a large measure totally reflected from the sloping planes below and comes back to the eye through the stone. The amount of light reflected in this way and the consequent brilliancy of the gem increases with its index of refraction. Two stones cut exactly alike, one from diamond and the other, perhaps, from quartz, would have very different 516 517 Total Reflection in Fluorite n = 1.43 Total Reflection in Diamond n = 2.42 appearances due to this difference in the amount of light totally reflected from their lower facets. This principle is illustrated in Figs. 516 and 517. They 212 PHYSICAL MINERALOGY represent cross sections of two hemispheres cut, one from fmorite and the other from diamond. It is assumed that light from all directions is focused on the center of the plane surface of each hemisphere. All the light that meets this surface at an angle greater than the critical angle for the mineral will be totally reflected back through the spherical surface. The shaded areas of the figures show the amount of light in each case that would be so reflected and clearly illustrate the optical difference between the two substances. 324. Effect of Index of Refraction upon Microscopic Phenomena. In the study of minerals, especially in thin sections under the microscope, varia- tions in the index of refraction give effects which are of importance. In Fig. 518 let it be assumed that L is the objective lens of a compound microscope, and that the instrument is exactly focused upon a point O, Fig. 518, A. If now we imagine that a section of some mineral of mean index of refraction is 518 ; Cover glass br~~Section in balsam A-Glass slide placed under the lens, Fig. 518, B, the point O' will now be in focus, or as in Fig. 518, C, where the mineral is supposed to have a high index of refraction, the focus will be at O". Thus it is that with two sections of equal thickness and with the lens in the same position, one looks deeper into the mineral of higher index of refraction. Consequently, when there are two minerals in the same section, the one having a high and the other a low index of refraction (for example, a crystal of zircon, n = 1.95, embedded in quartz, n = 1.55), the one having the higher index of refraction will apparently have the greater thickness and will appear to stand up in relief above the surface of the mineral of lower index. The apparent relief is furthermore augmented by other properties to be explained below. In preparing thin sections of minerals or rocks for study with the micro- scope the process, in brief, is to make first a flat surface upon the mineral or rock by grinding it upon a plate supplied with some abrasive. This flat surface is then cemented to a piece of glass by means of Canada balsam and the re- mainder of the mineral is ground away until only a thin film remains, which in the best rock sections is not over 0'03 mm. in thickness. The section is finally embedded in balsam, n about 1'54, and over it a thin cover glass is laid. In CHARACTERS DEPENDING UPON LIGHT 213 the preparation of a section the surfaces are not polished, hence, from the nature of the abrasive, they must be pitted and scratched and it may be assumed that in cross section such a preparation would be somewhat as repre- sented in Fig. 518, D. When a thin section is examined under the microscope the light enters the section from below, having been reflected up into the microscope tube by an inclined mirror. Before it reaches the section it will have passed through a nicol prism and through a slightly converging lens. Let it be assumed that the mineral at a, Fig. 518, D, is one of mean refractive index. The convergent light entering the section will pass with little or no refraction from the mineral into the balsam because their refractive indices are nearly alike. Hence the roughness of the surface of the section is not apparent and the mineral appears as if polished. If there is a crack, as at 6, so much light penetrates it that it is scarcely visible when the convergent lens is close to the object, but when the latter is lowered, and especially when the light is restricted by the use of an iris diaphragm inserted into the micro- scope tube, the nearly parallel rays of light will suffer some total reflection along the line of the crack and so make it visible. On the other hand, if the mineral has a high index of refraction there will be innumerable places all over the section where the surfaces are so inclined that the light will suffer total reflection in attempting to pass from the optically dense mineral into the rarer balsam. Hence the uneven surface of the section due to its grinding is plainly visible. This effect is more pronounced if the convergent lens is lowered. The cracks that may exist in a mineral of high index of refraction are for the same reasons much more distinct than in a mineral of low index. Further, if a mineral of high index of refraction is embedded in one of low, c, Fig. 518, D, there will be places along its outer edge where total reflection will take place, thus causing its outline to be dark and distinct. This effect combined with the roughened aspect of the surface and the apparent increase in thickness, as described in the preceding paragraph, all tend to make a mineral of high index of refraction stand out conspicuously in relief. 325. Determination of the Indices of Refraction of Mineral Grains under the Microscope. The considerations of the preceding article sug- gest a means of determining the indices of refraction of mineral grains under the microscope. If a grain is immersed in a liquid of known index of refrac- tion it is possible to determine whether it has a higher or lower index of refraction than the liquid and by the use of a series of liquids of varying refractive indices it is possible to determine with considerable accuracy the index of refraction of the mineral. A list of liquids * in common usejfor such purposes, with their indices of refraction is given below. Mixtures of refined petroleum oils and turpentine 1 450-1 '475 Turpentine and ethylene bromide or clove oil 1 480-1 ' 535 Clove oil and a-monobromnaphthalene 1 540-1 ' 635 Petroleum oils and a-monobromnaphthalene 1 475-1 ' 650 a-monobromnaphthalene and methylene iodide 1' 650-1 ' 740 Sulphur dissolved in methylene iodide 1 740-1 790 Mixtures of methylene iodide with iodides of antimony, arsenic and tin, also sulphur and iodof orm (see Merwin) ... 1 740-1 870 Methylene iodide and arsenic trisulphide (see Merwin) 1 740-2 280 Resin-like substances formed from mixtures of piperine and * Wright, Methods of Petrographic-Microscopic Research, p. 98; Merwin, Jour. Wash. Acad. Sc., 3, 35, 1913. 214 PHYSICAL MINERALOGY the tri-iodides of arsenic and antimony. These fuse easily and mineral grains can be thus embedded in a thin film of the material 1 '680-2 ' 10 The indices of refraction of the test liquids can be determined either b the use of the total refractometer or by filling a hollow glass prism with th liquid and using the metho'ds employed with ordinary mineral prisms, se Art. 327. A series of these liquids should be prepared which for most purposes migh conveniently show differences in the indices of the different liquids of 0*01 For more exacting work smaller differences betw.een the indices of the member of the series would be of advantage. If these are kept in well stopperei bottles and are protected from the light they will show very little change ove considerable periods of time. It is advisable, however, to check their indice at least once a year. The mineral to be studied should be broken down into uniform sma] grains. (0'05 mm. is usually a good diameter) and then a few grains place< upon a glass slide. A drop of liquid with a known index of refraction is the] placed upon the grains and the whole covered with a thin cover glass. Whei a mineral grain is immersed in a liquid of closely the same index of refractio] it loses its sharpness of outline and if the mineral is colorless and the corre spondence of the two indices exact it will quite disappear. Certain tests however, are commonly used to determine the relative indices of the minera and the liquid which with proper care can distinguish differences as small a O'Ol or with practice and especial care as small as O'OOl. To make these test the condenser below the microscope stage should be lowered and, if the instru ment has a sub-stage iris diaphragm, this should be partly closed. Unde: these conditions the obliquity of the light is reduced and only a small penci of light composed of nearly parallel rays enters the section. Let Fig. 511 represent a mineral grair illuminated in this way wher immersed in a liquid o1 higher index of refraction The light rays as the} pass from the mineral intc the higher refracting liquic above will be bent awa^ from the perpendicular. In the opposite case, Fig. 520, where the mineral has the higher index the reverse wil] be true and the light rays will be bent toward the perpendicular. This will produce in one case a brighter illumination of the borders of the mineral grain of its. center. This dif- 519 520 Grain with Low Refractive Grain with High Refractive Index immersed in Liquid Index immersed in Liquid of High Refractive Index of Low Refractive Index and in the other a brighter illumination _ _ __. _ ^ ference in illumination is, however, commonly so slight as to be cer- tainly detected only with difficulty. The so-called Becke Test is commonly used under these circumstances. This consists in focusing upon the grain with a high power objective and then slowly raising or lowering the micro- CHARACTERS DEPENDING UPON LIGHT 215 scope tube. In the case illustrated by Fig. 519, when the tube is raised, a narrow line of light will be seen to move outward from the mineral, while when the tube is lowered this line will move inward. In the case illustrated in Fig. 520 the opposite conditions will prevail. A convenient rule to remem- ber is that when the microscope tube is raised the Becke line will move toward the material of higher refractive index and when the tube is lowered this line will move toward the material of lower index. This makes a very satisfactory and quite delicate test for distinguishing differences in refractive indices. Some- times two lines will appear moving in opposite directions and it may be diffi- cult to decide which is the Becke line. This is usually obviated by lowering the condenser or decreasing the aperture in the iris diaphragm. For the use of the Becke test in rock sections, see Art. 326. The test upon mineral grains immersed in a liquid may also be made by means of oblique illumination. An oblique pencil of rays may be obtained most conveniently by placing a pencil, a finger, or a piece of cardboard between the reflecting mirror and the polarizer in such a way as to darken one-half of the field of vision. The best results will be obtained by the use of an objective of medium magnifying power. When a mineral grain is viewed under these conditions it will be noted that one of its edges is more brightly illuminated than the other. With the condenser lens lowered and mineral with a lower index of refraction than the liquid, the bright edge of the mineral will be away from the shadow, while if the mineral has a higher index than the liquid the bright edge will be on the side toward the shadow. These conditions are pre- sented in Fig. 521, where L and H represent grains with indices respectively lower and higher than the liquid in which they are immersed. If the con- denser lens is raised effects exactly op- posite to those described above will be noted. It is wise, at first at least, to test the apparatus used by observing mineral fragments of known indices and taking note of the effects produced. Commonly the liquids used have a higher dispersion than the mineral to be tested. In other words the liquid will have distinctly different indices of refraction for red and for blue light. If the mineral should have an index intermediate between those for red and blue light in the liquid the grain when illuminated in oblique light will show colored borders. With the con- denser lens lowered the edge of the mineral next to the shadow will be colored an orange-red while the edge away from the shadow will be pale blue. If the amount of the dispersion in the liquid (i.e., the difference between the indices for blue and red light) is not too great this effect gives very closely the refrac- tive index of the mineral. It should be pointed out here that all minerals, except those of the isometric system, show different indices of refraction depending upon the crystal direc- tion in which the light is passing through the mineral. Consequently un- orientated grains of a mineral, unless it belongs to the isometric system, will show a variation in the refractive indices depending upon their position on Darker >/\ .... . ( L ^Brighter 216 PHYSICAL MINERALOGY 522 12 11 10 7 8 9654 3 2 the slide. Sometimes it is possible to determine the crystal orientation of a grain due to some significant cleavage or structure and so obtain the index for some particular crystal direction, but ordinarily all that can be determined is the mean index of refraction of the mineral. 326. The Becke Test in Rock Sections. The Becke test can be often used in a rock section to determine the relative indices of refraction of two different minerals lying in contact with each other. Their contact plane should be nearly vertical in order to give clear results. The position of this plane can be determined by focusing on the surface of the section and then when the microscope tube is lowered note whether or not the position of the dividing line between the two minerals remains stationary or moves. If it remains stationary or moves only a little, the dividing plane is vertical or nearly so. Under these conditions assume that the cone of light entering from below is focused at point O, Fig. 522, lying on the dividing plane between L (mineral with lower index) and H (mineral with higher index). The light rays 1-6 passing as they do from a mineral of lower index into one of higher will suffer no total reflection and all emerge from the section on the side of H. On the other hand, rays 7-12 attempting to pass from H to L will only in part pass across the dividing plane while the others will be totally reflected and add them- selves to rays 1-6 on the side of H. H will there- fore show a brighter illumination than L. In this case also when the tube of the microscope is raised the Becke line will be seen moving toward the mineral of higher index or when the tube is lowered toward that of lower index. The best results will be obtained by using an objective of high magnification and the condenser lens must be lowered. 327. Determination of the Index of Refraction by Means of Prisms or Plates. For the more accurate determination of the indices of refraction of minerals a natural or cut prism or plate of the mineral is used. In all cases, except minerals of the isometric system, the prism or plate used must have a certain crystallographic orientation. This matter, however, will be discussed when the optical characters of such minerals are given. For the present, we will assume that the mineral whose index of refraction is to be determined is isometric in its crystallization. There are two chief methods of determining the index of refraction by the use of a prism. 1. The Method of Perpendicular Incidence. This method, although not 12 3456 CHARACTERS DEPENDING UPON LIGHT 217 the one most generally employed, is an excellent one to become acquainted with, as it may be used to advantage in some cases and from it the formula necessary for making the calculations is readily derived. It is necessary to have a prism of the mineral which has two plane surfaces meeting at a small angle. This angle should be small enough so that the light may pass freely through the prism and not suffer any total reflection as it attempts to pass out into the air. For in- stance with fluorite in which n = 1*434, the prism angle must be less than 44 12', for at a this angle total reflection would take place. For a mineral of higher index the angle would have to be smaller still, as with dia- mond, n = 2 '4 19, where total reflection would take place at 24 24'. On the other hand, more accurate results will be obtained Refraction of Light through a Prism if the prism angle is fairly near to the limit Method of Perpendicular Incidence for the mineral being used.* Let Fig. 523 represent the cross section of such a prism. Let a-b represent a ray of light striking the face of this prism at 90 incidence. It will suffer no deviation in its path on entering the prism but will proceed with somewhat diminished velocity until it reaches c. In passing out of the prism at this point, from a denser to a rarer medium, the light will be deflected away from the normal to the surface, P-P', making a. deviation 5 in the direction o-d. The data necessary for the calculation of the index of refraction under these conditions are the angle of the prism, a, and that of the deviation in the path of the light, 5. It is easy to see from the figure that a and a' are equal, for they are both parts of right-angled triangles having the angle bP'c in common, and a" is equal to a! because they are opposite angles. The angle of incidence, as defined in Art. 317, is equal to a + 8 and the angle of refraction is equal to a. Therefore the usual formula - - n becomes here sin r Sm . a = n. In order to make a determination of the index of refraction, sin a therefore, it is necessary to measure these two angles, a and 5. The prism is mounted on a one-circle reflection goniometer and its angle a measured in the same way as an angle upon a crystal. The instrument is then adapted to the uses of a refractometer. For this purpose it is necessary to note that the telescope and vernier are both fastened to the outer rim of the instrument and move together. The graduated circle being clamped, the telescope tube is first moved to the position T', Fig. 524, so that the rays from the collimator tube, C, passing the edge of the prism, cause the light signal to fall on the vertical cross-hair of the telescope. The inner Circle being clamped the telescope is next moved through an arc of exactly 60 to position T" and then clamped. Next the prism is turned to the first position so that the light from C is reflected from its right-hand face and the signal s falls on the cross-hair of T". In this position the normal, N, to the prism face, must bisect the angle between the axes of C and T". The prism is now turned through an angle of exactly 60 to its second position, which brings the normal A T exactly in line with the axis of the collimator tube. When this has been 218 PHYSICAL MINERALOGY accomplished the graduated circle is securely clamped. The telescope may 524 now be undamped and moved without altering the position of the prism, and somewhere between T' and T" a position T'" will be found where the refracted ray falls on the cross-hair of the telescope. The move- ment of the telescope from the position T"' back to T' gives the angle of devia- tion, or 5, of the light ray that has been refracted by the prism. In practice it is well to repeat the measurements both of a and d several times and to go through all the opera- tions of shifting the posi- tions of the prism and telescope. If white light is used for illumination the refracted ray seen at T" f will appear as a narrow spectrum. To make an exact determination a mono- chromatic light (sodium light is best) must be employed. 2. The Method of Min- imum Deviation. - - This is the method that is most of refraction by the use of 525 Determination of Index of Refraction Method of Perpendicular Incidence generally employed for determining indices prisms. It depends upon the principle that when a beam of light, abed, Fig. 525, traverses a prism in such a way that the angles i and i' are equal, the beam suffers the minimum amount of deviation in its path of any possible course through the prism. This fact may be proven empirically by experi- mentation on the refrac- tometer. In order to make a determination, the angle a of the prism is first measured on the goniometer. The angle of the prism with this method may be considerably larger than when the method of perpendicular 526 CHARACTERS DEPENDING UPON LIGHT 219 incidence is used. in the position & . _, W110 telescope undamped and moved until the refracted ray appears in it. Now, turn the central post with the prism on it toward the left and follow the signal with the telescope. The position of minimum deviation is soon reached, when, on turning the prism, the signal seems to remain stationary for a moment and then moves away to the right, no matter in which direction the prism is turned. A little practice is needed to determine exactly the position of min- imum deviation and the measurement should be made in a monochromatic light. When the telescope is properly placed at this point the graduated circle is clamped and the telescope turned until the direct signal from the collimator tube is fixed upon the vertical cross- hair. The angle between these two positions of the telescope is the same as the angle of deviation, or 5. The for- mula for making the necessary calcu- lation from these measurements follows very simply from a comparison of Figs. 525 and 523. It may be imagined that Fig. 525 is composed of two prisms like Fig. 523 placed back to back. This results in doubling the angles a and 5 so that the formula now becomes sn 8) sn -J-a 3. The Method of Total Reflection. This method is based upon the prin- ciple that light cannot always pass from an optically dense into an optically rarer medium but at a certain angle, known as the critical angle, will suffer total reflection. The critical angle for any substance varies with the index of refraction of that substance as explained in Art. 323. Consequently if we can measure this critical angle we can calculate the index of refraction of the substance. This method is particularly useful because the measurement can be made upon a single polished surface, which may be quite small in area. This measurement is made by means of an instrument, known as the Total Refractometer, a description of which will be found in Art. 352. The essential feature of this instrument is a hemisphere of glass with a known, high index of refraction. The upper surface of the hemisphere is plane and should be accurately adjusted in a horizontal position. The mineral to be tested may be of any shape provided that some surface upon it has been ground plane and polished. A drop of some liquid of high index of refraction is placed be- tween the surface of the glass hemisphere and the flat surface of the mineral. This serves to unite the two substances and dispel the thin layer of air that would otherwise separate them. The liquid should have an index of refraction intermediate between that of the glass and that of the mineral. As the liquid 220 PHYSICAL MINERALOGY lies between the two substances in the form of a thin film with parallel surfaces whatever optical effect it has upon the light as it enters will be balanced by the opposite effect as the light leaves the film. So the optical effect of the liquid can be ignored. Fig. 527 represents a cross section of such a hemi- sphere with a mineral plate resting upon it. Let it be now supposed that by means of a mirror a beam of monochromatic light is thrown upon the apparatus from the direction of X. Rays 1 and 2 will suffer partial refraction at the 527 dividing plane between the glass and the mineral to rays 1' and 2' and also partial reflection to rays 1" and 2". Ray 3 strikes the mineral at the critical angle for the combination of the glass and mineral and will in part be refracted at a 90 angle and emerge as ray 3', just grazing the surface of the hemisphere. The greater part of ray 3 will however be reflected as ray 3". Beyond this point, all the light must be totally reflected, thus 4 to 4". If the optical axis of a telescope is now brought to the direction 3", what appears to be a marked One side will be illuminated by the Determination of Index of Refraction Method of Total Reflection, I. 528 shadow will appear in the field of vision. total reflection of all rays beyond those of the critical angle while the other side will be distinctly darker since here a considerable amount of the light passed out into the mineral. The angle between the position of the shadow and the normal to the surface of the hemisphere, /*, Fig. 527, will be the critical angle for the combina- tion of glass and mineral. As the index of refraction of the glass is known it is possible to calculate what the index of refraction of the mineral must be. If the mineral plate is transparent enough so that light may pass through it into the glass hemisphere another method of illumination may be used, as illustrated Fig. 528. The reflecting m mirror Determination of Index of Refraction Method of Total Reflection, II. is so arranged that the light comes from the direction X. Rays 1 and 2 will be refracted to 1' and 2' and 3 which just grazes the surface to 3'. Beyond this point no light will pass into the hemisphere and a telescope placed with its axis along the line 3' will show in its field a dark shadow. The contrast CHARACTERS DEPENDING UPON LIGHT 221 between the light and dark portions of the field, by this method of illumination, is much stronger than by the one first described. The telescope is so placed that the line of the shadow exactly divides the angle between the diagonal cross-hairs of the eyepiece. The telescope is attached to a graduated circle from which the angle M can be directly read. With each of these instruments comes ordinarily a table giving the indices of refraction corresponding to the different possible values of ju. This table can easily be converted into a curve plotted on co-ordinate paper in such a way that the index of refraction for a particular angle can be read at a glance. Further, the calculation can be made having given the index of refraction of the glass of the hemisphere and the value of fji for a special mineral plate. Let n' equal the index of refraction of the glass of the hemisphere and // the critical angle measured; then the index of refraction of the mineral, n, = sin ju X n'.* 328. Dispersion. Thus far the change in direction which light suffers in reflection and refraction has alone been considered. It is further true that the amount of refraction differs for light of different wave-lengths, being greater for blue than for red. In consequence of this fact, if ordinary light be passed through a prism, as in Fig. 525, it will not only be refracted, but it will also suffer dispersion or be separated into its component colors, thus forming the prismatic spectrum. This variation for the different colors depends directly upon their wave- lengths; the red waves are longer, their transverse vibrations are slower, and it may be shown to follow from this that they suffer less change of velocity on entering the new medium than the violet Waves, which are shorter and whose velocity of transverse vibration is greater. Hence the refractive index for a given substance is greater for blue than for red light. The following are values of the refractive indices for diamond determined by Schrauf : 2-40845 red (lithium flame). 2*41723 yellow (sodium flame). 2*42549 green (thallium flame). 329. Spectroscope. The instrument most commonly used for the analysis of the light by dispersion is familiar to all as the spectroscope. There * The derivation of this formula follows. From the ordinary law for the index of re- n - But when the critical angle h reached i = 90 and sin i 1. Therefore we may substitute and have n = -- = - -, or velocity of light in mineral = - . Further, we may derive velocity of light in mineral n in the same svay for the highly refracting glass of the hemisphere whose refractive index, n 1 , is known, the expression, velocity of light in glass = . Further, we have in the case of the light attempting to pass from the glass (optically denser medium) into the mineral the expression, velocity of light in mineral _ sin 90 velocity of light in glass sin /x (measured on instrument). By substituting this becomes n _ sin 90 _ 1 1 sin n sin n n' or - = or n = sin /n X ' sin M n 222 PHYSTCAL MINERALOGY are a number of varieties of spectroscopes made, the simplest of which consists of a glass prism mounted at the center of the instrument with two tubes pointing away from it. The light from the given source is received through a narrow slit in the end of one tube and made to fall as a plane-wave (that is, as a " pencil of parallel rays ") upon one surface of a prism at the center. The light is dispersed by its passage through the prism and the spectrum produced is viewed through a suitable telescope at the end of the second tube. If the light from an incandescent solid which is ''white hot" (Art. 314) is viewed through the spectroscope, the complete band of colors of the spectrum is seen from the red through the orange, yellow, green, blue, to the violet. If, however, the light from an incandescent vapor is examined, it is found to give a spectrum consisting of bright lines (or bands) only, and these in a definite position characteristic of it as the yellow line (double line) of sodium vapor; the more complex series of lines and bands, red, yellow, and green, characteristic of barium; the multitude of bright lines due to iron vapor (in the intensely hot electric arc), and so on. 330. Absorption. Of the light incident upon the surface of a new medium, not only is part reflected (Art. 316) and part transmitted and re- fracted (Art. 317), but, in general, part is also absorbed at the surface and part also during the transmission. Physically expressed, absorption in this case means the transformation of the ether-waves into sensible heat, that is, into the motion of the molecules of the body itself. The color of a body gives an evidence of this absorption. Thus a sheet of red glass appears red to the eye by transmitted light, because in the trans- mission of the light-waves through it, it absorbs all except those which to- gether produce the effect of red. For the same reason a piece of jasper appears red by reflected light, because it absorbs part of the light-waves at the surface, or, in other words, it reflects only those which together give the effect of this particular shade of red. Absorption in general is selective absorption; that is, a given body absorbs particular parts of the total radiation, or, more definitely, waves of a definite wave-length only. Thus, if transparent pieces of glass of different colors are held in succession in the path of the white light which is passing into the spectroscope, the spectrum viewed will be that due to the selective absorption of the substance in question. A layer of blood absorbs certain parts of the light so that its spectrum consists of a series of absorption bands. Certain rare substances, as the salts of didymium, etc., have the property of selective absorption in a high degree. In consequence of this, a section of a mineral containing them often gives a characteristic absorption spectrum. This latter property may be made use of in testing certain minerals, more especially those that contain the rare earths or uranium. These give char- acteristic absorption bands in the spectrum. They may be tested by passing a strong white light through a thin section of the mineral and observing the resulting spectrum by means of a direct vision spectroscope. Often a better result will be obtained by illuminating the surface of the mineral and testing the reflected light for absorption bands. The light will have sufficiently penetrated the mineral before reflection to have had some of it absorbed. These tests can be made best by some sort of a microspectroscope, which will give a clear spectrum superimposed upon a scale of wave-lengths.* *' For details of this method of testing minerals see Wherry. Smithsonian Misc. Coll.. 66, No. 5, 1915. CHARACTERS DEPENDING UPON LIGHT 223 The dark lines of the solar spectrum, of which the so-called Fraunhofer lines are the most prominent, are due to the selective absorption exerted by the solar atmosphere upon the waves emitted by the much hotter incandescent mass of the sun. 331. Diffraction. When monochromatic light is made to pass through a narrow slit, or by the sharp edge of an opaque body, it suffers diffraction, and there arise, as may be observed upon an appropriately placed screen, a series of dark and light bands, growing fainter on the outer limits. Their presence is explained (see Arts. 335, 336) as due to the interference, or mutual reaction, of the adjoining systems of waves of light, that is, the initial light-waves, and further, those which have their origin at the edge or sides of the slit in question. It is essential that the opening in the slit should be small as com- pared with the wave-length of the light. If ordinary light is employed, the phenomena are the same, and for the same causes, except that the bands are successive colored spectra. Diffraction spectra, explained on the principles alluded to, are obtained from diffraction gratings. These gratings consist of a series of extremely fine parallel lines (say, 15,000 or 20,000 to an inch) ruled with great regularity upon glass, or upon a polished surface of speculum metal. The glass grating is used with transmitted, and the speculum grating with reflected, light; the Rowland grating of the latter kind has a concave surface. Each grating gives a number of spectra, of the first, second, third order, etc. These spectra have the advantage, as compared with those given by prisms, that the dispersion of the different colors is strictly proportional to the wave-length. 332. Double Refraction. As implied in Art. 320, all crystallized sub- stances may be divided into two principal optical classes, viz. : isotropic, in which light has the same velocity no matter what the direction of its propaga- tion, and anisotropic, in which the velocity of light in general varies with the direction of propagation. The anisotropic class is further divided into uniaxial, which includes crystals of the tetragonal and hexagonal systems, and biaxial, which includes crystals of the orthorhombic, monoclinic, and triclinic systems. The characters of these various optical classes will be explained in detail further on. In the discussion of Art. 317, applying to isotropic media, it was shown that light-waves passing from one medium into another, which is also isotropic, suffer simply a change in wave-front in consequence of their change in velocity. In anisotropic media, however, which include all crystals but those of the isometric system, there are, in general, two wave-systems propagated with different velocities and only in certain limited cases is it true that the light- ray is normal to the wave-front. This subject cannot be adequately explained until the optical properties of these media are fully discussed, but it must be alluded to here since it serves to explain the familiar fact that, while with glass, for example, there is only one refracted ray, many other substances give two refracted rn rays, or, in other words, show double refraction. I The most familiar example of this property is fur- / nished by the mineral calcite, also called on account of this property "doubly-refracting spar." If mnop (Fig. 529) be a cleavage piece of calcite, and a ray of light meets it at b, it will, in passing through, be divided into two rays, be, bd. For this reason, a dark spot or a line seen through a piece of calcite ordinarily appears double. As implied above, the same property is enjoyed by all crystallized 224 PHYSICAL MINERALOGY minerals, except those of the isometric system. The wide separation of the two refracted rays by calcite, which makes the phenomenon so striking, is a consequence of the large difference in the values of its indices of refraction; in other words, as technically expressed, it is due to the strength of its double refraction, or its birefringence. 333. Double refraction also takes place in the anisotropic media just mentioned, in the majority of cases, even when the incident light is perpen- dicular to the surface. If the medium belongs to the uniaxial class (see p. 253, et seq.), one of the rays always retains its initial direction normal to the sur- face; but the other, except in certain special cases, is more or less deviated from it. With a biaxial substance, further, both rays are usually refracted and bent from their original direction. In the case of both uniaxial and biaxial media, however, it is still true that the normal to the wave-front remains unre- fracted with perpendicular incidence. 334. Interference of Waves in General. The subject of 'the inter- ference of light-waves, alluded to in Art. 331, requires detailed discussion. It is one of great importance, since it serves to explain many common and beauti- ful phenomena in the optical study of crystals. Referring again to the water-waves spoken of in Art. 308, it is easily understood that when two wave-systems, going out, for example, from two centers of disturbance near one another, come together, if at a given point they meet in the same phase (as crest to crest), the result is to give the particle in question a double amplitude of motion. On the other hand, if at any point the two wave-systems come together in opposite phases, that is, half a wave- length apart, the crest of one corresponding to the trough of the other, they interfere and the amplitude of motion is zero. Under certain conditions, therefore, two sets of waves may unite to form waves of double amplitude; on the other hand, they may mutually interfere and destroy each other. Obvi- ously an indefinite number of intermediate cases lie between these extremes. What is true of the waves mentioned is true also of sound-waves and of wave- motion in general. A very simple case of interference was spoken of in con- nection with the discussion of the waves carried by a long rope (Art. 310). 335. Interference of Light-waves. Interference phenomena can be most satisfactorily studied in the case of light-waves. The extreme cases are as follows: If two waves of like length and intensity, and propagated in the same direction, meet in the same phase, they unite to form a wave of double intensity (double amplitude). This, as stated in Art. 311, will cause an increase in the intensity of the light. If, however, the waves differ in phase by half a wave-length, or an odd multiple of this, they interfere and extinguish each other and no light results. For other relations of phase they are also said to interfere, forming a new resultant wave, differing in amplitude from each of the component waves. In the above cases monochromatic light- waves were assumed (that is, those of like length). If ordinary white light is used interference for certain wave-lengths may result with the consequent sub- traction of the corresponding color from the white light and so give rise to various spectrum colors. 336. Illustrations of Interference. A simple illustration is afforded by the bright colors of very thin films or plates, as a film of oil on water, a soap- bubble, and like cases,. To understand these, it is only necessary to remember that the incident light-waves are reflected in part from the upper and in part from the lower surface of the film or plate. The rays that are reflected from CHARACTERS DEPENDING UPON LIGHT 225 531 the under surface of the very thin film (see Fig. 530) having traveled a greater distance and with a different velocity will, when they unite with those rays reflected from the upper surface, show in general a different phase. For some partic- ular wave-length of light this difference is likely to be exactly a half wave-length or some odd multiple of this amount and so the corresponding color will be eliminated (assuming that ordinary white light is being used) and its complementary color will be seen. It is to be noted that the phenom- ena of interference by reflection are some- what complicated by the fact that there is a reversal of phase (that is, a loss of half a wave-length) at the surface that separates the medium of greater optical density from the rarer one. Hence the actual relation in phase of the two reflected rays, as AC, BD (sup- posing them of the same wave-length) is that determined by the retardation. due to the greater length of path trav- ersed by BD, together with the loss of a A half wave-length due to the reversal of phase spoken of. As shown in the figure, there are also two transmitted waves which also interfere in like manner. A plano-convex lens of long curvature, resting on a plane glass surface (Fig. 531), and hence separated from it, except at the center, by a film of air of varying thickness, gives by reflected monochromatic light a dark center and about this a series of light and dark rings, called Newton's rings. The dark center is due to the interference of the incident and reflected waves, the later half a wave-length behind the former. The light rings correspond to the distances where the two sets of reflected waves meet in the same phase, that is (noting the explanation above) where the retardation of those having the longer path is a half wave-length or an odd multiple of this (JX, fX, fX, etc.). Similarly the dark rings fall between these and correspond to the points where the two waves meet in opposite phase, the retardation being a wave-length or an even multiple of this. The rings are closer together with blue than with red because of the smaller wave-length of blue light. In each of the cases described the ring is properly the intersection on the plane surface of the cone of rays of like retardation. In ordinary white light we get, instead of the alternate light and dark rings described above, a series of colored bands. If the illumination was originally by sodium light the position of the dark rings indicates where light for that particular wave-length has been extinguished through interference. When white light is used the conditions in respect to its component having the yellow sodium-light wave-length have not changed and this light will still be eliminated at the same points, but now, instead of dark rings, we get rings having the complementary color blue. If our original illumination was by means of a red light the dark rings would have had different positions from those pro- duced in sodium light. And again when white light is used red light is elim- inated at those points and its complementary color shows. In this way we obtain a series of colored rings, each showing the successive colors of the spectrum. The series of the spectrum colors are repeated a number of times 226 PHYSICAL MINERALOGY due to successive interferences produced by differences of phase of J, 1J, 2|, etc., wave-lengths. The different series are distinguished as of the first, second, third, etc., order; for a given color, as red, may be repeated a number of times. The interference rings for different colored lights are not evenly spaced, the rings shown in blue light being, for instance, closer together than for red. Consequently after three or four repetitions of the spectrum bands the different interference rings begin to overlap one another and the resulting colors become fainter and less pure. Ultimately this overlapping becomes so general that the effect of color is lost and white light, the so-called white of the higher orders, is shown. Another most satisfactory illustration of the interference of light-waves is given by means of the diffraction gratings spoken of in Art. 331. Other cases of the composition of two systems of light-waves will be con- sidered after some remarks on polarized light. 337. Polarization and Polarized Light. Ordinary light is propagated by transverse vibrations of the ether which may take place in any direction as long as it is at right angles to the line of propagation. The direction of vibra- tion is constantly changing and the resulting disturbance of the ether is a complex one. A ray of ordinary light will be symmetrical, therefore, only to the line of its propagation. Plane-polarized light, on the other hand, as stated briefly in Art. 311, is propagated by ether-vibrations which take place in one plane only. The change by which ordinary light is converted into a polarized light is called polarization, and the plane at right angles to the plane of transverse vibration is called the plane of polarization* Polarization may be accomplished (1) by reflection and by single refrac- tion, and (2) by double refraction. Polarization by Reflection and Single Refraction. In general, light which has suffered reflection from a surface like that of polished glass is more or less completely po- larized; that is, the reflected waves are propagated by vibrations to a large extent limited to a single plane, viz., (as assumed) the plane normal to the plane of incidence, which last is hence the plane of polarization. Furthermore, in this case, the light transmitted and refracted by the reflecting medium is also in like manner partially polarized; that is, the vibrations are more or less limited to a single plane, in this case a plane at right angles to the former and hence coinciding with the plane of incidence. For instance, in Fig. 532, let a-b rep- resent an incident light ray in which the vibrations are taking place in all possible transverse directions as represented > * It is necessary to keep clear the distinction between the plane of polarization and the plane in which the vibrations take place. All ambiguity is avoided by speaking uniformly of the vibration-plane of the light. 338. 532 CHARACTERS DEPENDING UPON LIGHT 227 by the arrows, x-x, y-y, and z-z. When this ray strikes the polished surface at 6 light with vibrations parallel to x-x will be reflected along b-c and other vibrations near to x-x in direction will be shifted to this direction so that the reflected ray will be largely polarized. In a similar manner the light having z- vibrations will enter the transparent substance as the refracted ray b-d and other vibrations will be shifted to this direction so that the re- fracted ray is also largely polarized and in a plane at right angles to that of the reflected ray. Light reflected from a polished and transparent sur- face is not completely polarized but there is Brewster's Law an angle of incidence for every substance at which the amount of polarization will be at its maximum. This will hap- pen, as illustrated in Fig. 533, when the angle between the reflected and refracted rays A B and AC equals 90. It is evident from a consideration of the figure that the angle r is the complement of i\ hence the formula ? - = n becomes in this case sin i : = tan i = n. cos ^ This law, established by Brewster, may be stated as follows : The angle of incidence for maximum polarization is that angle whose tangent is the index of refraction of-the reflecting substance. For crown glass this angle is about 57 (see Fig. 533) . If light suffers repeated reflections from a series of thin glass plates, the polarization is more complete, though its intensity is weakened. Metallic surfaces polarize the light very slightly. 339. Polarization by Double Refraction. When light in passing through a crystalline medium is doubly refracted (Art. 332) or divided into two sets of waves, it is always true that both are completely polarized and in planes at right angles to each other. This subject can only be satisfactorily explained after a full discussion of the properties of anisotropic crystalline media, but it. may be alluded to here since this principle gives the most satis- factory method of obtaining polarized light. For this end it is necessary that one of the two wave-systems should be extinguished, so that only that one due to a single set of vibrations is transmitted. This is accomplished by natural absorption in the case of tourmaline plates and by artificial means in the nicol prisms of calcite. 340. Polarized Light by Absorption. Light passing through a strongly colored but transparent thin section of a tourmaline crystal the section being cut parallel to the vertical crystallographic axis will be almost completely polarized. This can be easily demonstrated in the following way. Select a polished floor surface, or a table top and stand in such a position that light from a window is reflected from the polished wood to the eye. Look at this reflected light through the tourmaline section, holding it first with the 228 PHYSICAL MINERALOGY direction 'of the c crystal axis in a horizontal position and then turning the section until the c axis becomes vertical. The light passing into the tour- maline section is in considerable part polarized through its reflection from the wood surface and possesses a horizontal vibration direction. It will be noted that when the c axis of the tourmaline is horizontal the section readily transmits light but when this axis is vertical the section becomes practically opaque. The crystal structure of the tourmaline is such that light entering it is broken up into two rays (i.e., it is doubly refracted), one of which has its vibrations parallel to the c axis, while the vibrations of the other lie in the plane of the horizontal crystal axes. From the foregoing experiment it is obvious that the light vibrating parallel to the c axis is readily transmitted by the crystal but that the other ray, vibrating in the horizontal axial plane, is almost completely absorbed. Under these conditions it is clear that the trans- mitted light belongs almost wholly to one ray, the vibrations of which take place in a single direction. In other words, the light transmitted by such a tourmaline section is polarized. If two such sections of tourmaline are available it is instructive to make the following experiment with them. Place them together, first with their c axes parallel to each other, and then turn one section upon the other until these axes are at right angles to each other. In the first case, the light comes through the sections because the vibration planes of the transmitted rays in the two sections are parallel to each other. In the second case, all light is cut off because now these two vibration planes are at right angles to each other, the light that did get through the first section being wholly absorbed in the second. 341. Polarized Light by Double Refraction. Calcite, as already stated in Art. 332, possesses in an unusual degree the power to doubly refract light. If we take a cleavage block of clear calcite (Iceland spar) and look at an image through it, such as a dot or line drawn on a piece of paper, the image will appear double. If we take a card and make in it a pinhole, place the card upon one face of a cleavage rhombohedron and, looking through the calcite, hold it up against a source of light, we will observe two bright dots. Now if we look in the same way at the light reflected from a polished wooden surface, as described in the preceding article, we will find that when a line bisecting the acute angles of the rhombic face of the cleavage block is horizontal one of these images is bright while the other is almost invisible. If we then turn the block so that the line bisecting the obtuse angles of the rhombic face is horizontal the first image will fade while the second becomes bright. Remem- bering that the light reflected from the polished wooden surface is largely polarized with a horizontal vibration direction, it becomes evident from this experiment that the two rays into which the light is broken up in passing through the calcite are polarized and that their planes of vibration are at right angles to each other and respectively bisect the angles of the rhombic face of the cleavage block. As the double refraction of calcite is strong, it follows that the indices of refraction of the two rays show considerable differ- ences. This fact is taken advantage of in constructing a prism from calcite in such a way as to wholly eliminate one of these rays and so, as only the other ray can come through the prism, effectively polarizing the light that emerges. The prism referred to above is called the Nicol Prism or simply the nicol. A full explanation of the nicol cannot be made at this time, as there would be required a knowledge of the optical properties of hexagonal crystals, but a CHARACTERS DEPENDING UPON LIGHT 229 535 description may be given enabling one to understand its construction and uses. In Fig. 534 is represented a cleavage rhombohedron of calcite with its edges vertical. Let d represent a point of light underneath the rhombo- hedron. Light coming from d will be broken into two rays whose paths through the rhombohedron are shown by the lines o and e. As shown above, these two rays are polarized, with vibration directions as indicated .by the double arrows in the top view in Fig. 534. In the construction of a nicol, the top and bottom surfaces of such a cleavage rhombohedron are ground and polished so that they make angles of 68 with the vertical edges. Then the block is cut in two along the diagonal a-/, as shown in Fig. 535. These two surfaces, after being polished, are cemented together by means of a thin layer of Canada balsam. Let us assume that a ray of light enters the prism from below, as shown in Fig. 535. It is broken up into the rays o and e. The ray o travels with the slower velocity, has therefo're the higher index of refraction, and shows a greater deviation from the original path. The Canada balsam Nico1 Prism has a lower index of refraction than ray a, which, therefore, when it strikes the layer of balsam, is attempting to pass from an optically dense into a rarer medium. The construction of the prism is such that this ray meets the layer of balsam at an angle greater than the critical angle for. this optical combination and suffers therefore total reflection toward the side of the prism, and will be absorbed by whatever fastening holds the nicol. The second ray e passes through the prism with almost no deviation from its original course. Its index of refraction and that of the Canada balsam are nearly the same, hence the ray suffers almost no deflection at this point and passes out of the upper face of the prism. The light, therefore, that emerges from a nicol belongs wholly to one ray and is all vibrating parallel to the shorter diagonal of the rhombic end surface. It should be noted, however, that some prisms are made in a different way and that the above statement concerning the plane of vibration of the light emerging from the prism may not always hold true. It is always wise to test the plane of vibration of a nicol by looking through it at the floor or a table top as previously described. The prism will show bright when its plane of vibration is horizontal, thus corresponding to the plane of vibration of the reflected light. 342. Polariscope. Polarizer. Analyzer. The combination of two nicols, or other polarizing contrivances, between which transparent mineral sections may be examined in polarized light is called, in general, a polariscope; the common forms of which are described later. In any polariscope the lower prism, or other contrivance, which polarizes the light given from the outside source is called the polarizer; the upper prism is the analyser. If these prisms 230 PHYSICAL MINERALOGY have their vibration-planes at right angles to each other, they are said to be crossed; the incident light polarized by the polarizer will then be extinguished by the analyzer; briefly, under these conditions it is said to suffer extinction. 343. Interference of Plane-polarized Waves. Interference Colors. When sections of doubly refracting minerals are examined in polarized light certain interference effects are commonly obtained that are of great impor- tance. As shown in Art. 341, calcite when it doubly refracts light also polarizes the two rays and in planes that are at right angles to each other. In general, this is true of sections of doubly refracting minerals. Consider, then, what takes place when a general section of a doubly refracting mineral is placed in a polariscope between the polarizer and analyzer the planes of vibration of which are at right angles to each other. In Fig. 536 let the rectangular out- line represent such a section. The double arrows marked o and e show the two possible directions of vibration of light in the section. The direction P-P' represents the plane of vibration of light which emerges from the polar- izer below and A- A' shows the direction in which light must vibrate when it emerges from the analyzer above. In the first case to be considered the directions o and e are taken as parallel to P-P' and A- A' respectively. The light that enters the section from below must all vibrate parallel to the direc- tion P-P'. It enters the mineral section and must vibrate there as the ray labeled o. There will be no ray in the mineral vibrating parallel to the direc- tion e, as a vibration parallel to o cannot be resolved into another at right angles to it. The light will leave the section, therefore, still vibrating parallel to P-P' and enter the analyzer above. It will, however, be entirely reflected in the analyzer at the'layer of balsam since only light vibrating parallel to A- A', which is at right angles to P-P', can emerge from the analyzer. Consequently, when such a section has its planes of vibration parallel to those of the polar- izer and analyzer, the section will appear dark. The same reasoning holds true when the section is turned to a position at 90 from the first. Con- sequently with such a section there are four positions at 90 to each other in which it appears dark during its complete rotation upon the stage of the polariscope. At such positions the section, is said to be extinguished. 636 537 A' 538 -P' P Next consider what happens when the vibration directions of the section are at oblique angles to those of the polarizer and analyzer. In Fig. 537 let o and e represent the directions of vibration in a section which makes some oblique angle. with the directions P-P' and A- A'. In Fig. 538A let the line P-P' represent the direction and amplitude of the vibration of the light enter- CHARACTERS DEPENDING UPON LIGHT 231 ing the mineral section having come through the polarizer below. The light must vibrate in the mineral in directions parallel to o and e, Fig. 537. The vibration P-P' will therefore be resolved into two vibrations at right angles to each other which will be parallel respectively to o and e. In Fig. 538A the lines o and e representing the direction and amplitudes of such vibrations are found by the application of the principle of the parallelogram of forces. The two rays emerge from the mineral section vibrating in these two planes and enter the analyzer above. Since the planes of vibration in the analyzer are parallel to A- A' and P-P' these two rays o and e will resolve each into two new rays which will vibrate now parallel to A-A' and P-P'. The two rays labeled P and P' in Fig. 5385 will be absorbed by the analyzer but the rays marked A and A' will emerge and meet the eye. The section in this position, therefore, will be illuminated. Consequently the section will be illuminated in all possible positions in which the directions of vibration of the light in the mineral make inclined angles with the directions of vibration of the polarizer and analyzer. It is easy to prove that this illumination will be at its maxi- mum when the angle between the directions o and e and A-A' and P-P' is 45. In addition to being illuminated, the section, if thin, will also be colored. This interference color, as it is called, of mineral sections when examined in a polariscope, now needs explanation. The amount of refraction which any ray of light suffers on entering a mineral depends upon two things, namely, the angle of incidence at which the light enters and the index of refraction of the mineral. In the case of a doubly refracting mineral we have a light ray entering the section at a given angle of incidence and then being broken up into two polarized rays which have differ- ent angles of refraction and so travel different paths. Consequently the indices of refraction for these rays must be different and from this it follows that the two rays must have different velocities and will therefore emerge from the mineral in different phases. Light waves having different phases will in a greater or less degree interfere with each other and in case of light of certain wave-lengths, i.e., light of some particular color, the interference may lead to extinguishment of that particular wave-length. If one particular color is subtracted in this way from white light the result will be to produce the complementary color and under such conditions the section will no longer be white but colored. The color of thin sections of minerals when seen under the polariscope is known as their interference color. To develop this subject further use will be made of an accessory of the microscope known as the Quartz Wedge. The Quartz Wedge consists simply of a very thin tapering wedge the faces of Which are approximately parallel to the prism of a quartz crystal. It is mounted on a narrow glass plate, Fig. 539, A. The plate is generally marked with the letter Q (quartz) and with an arrow. If the wedge is cut, as is usually the case, with its longer direction at right angles to the vertical axis of a quartz crystal, the arrow is marked X (or a), which indicates that of the two directions of vibration of light in the wedge the one which is parallel to this direction is that of the ray which is propagated with greater velocity. Some wedges are cut with their longer direction parallel to the vertical axis of quartz, and the arrow in this case would be marked Z (or c), which indicates that this is the direction of vibration of the slower ray. It is abso- lutely essential that the optical orientation of the wedge be known. The quartz wedge furnishes a prismatic section of varying thickness and 232 PHYSICAL MINERALOGY of known orientation and may be used to study the effects of polarized light on plates (short sections of the wedge) of different thicknesses. Take the simplest form of polariscope, a combination of polarizer and analyzer without 539 A r 1 + H- + 4 P X** -e ! i : ! i ! Q Quartz Wedge lenses, and arrange it so that the vibration planes of the instrument are crossed. Illuminate with ordinary light and on the stage of the instrument place a quartz wedge with its X direction parallel to the plane of vibration of the polarizer. The light in entering the quartz will vibrate parallel to the X direction and without changing its plane of vibration will pass through the quartz and up into the upper nicol where it will suffer total reflection. Hence the wedge in this position will appear dark throughout its length. A similar result will be obtained when the X direction of the wedge is placed parallel to the vibration plane of the analyzer. But if the wedge is turned so that its X direction makes an angle of about 45 with the plane of vibration of the polarizer the wedge will exhibit a series of beautiful interference colors, arranged in transverse bands, the nature of which will be discussed in a later paragraph. If the wedge is turned from this 45 position the colors become less and less brilliant as the position of extinction is neared. i As preliminary to another experiment, paste a narrow strip of paper, P-P, Fig. 539, B, on the top, but to one side, of a quartz wedge. Place this on the stage of a polariscope (without lenses) and illuminate with diffused sodium light. When the wedge is examined under these conditions it will be found that it shows extinction when its vibration directions are parallel to those of the polariscope but at the 45 position it will show transverse dark bands upon a yellow field. The number of these bands will depend upon the thickness of the wedge; usually there will be two or three, although for this experiment it is interesting to have a longer and proportionally thicker wedge than those commonly supplied, so as to have more bands appearing. Mark on the strip of paper the position of each band, as illustrated in Fig. 539, B and number them, starting at the band nearest the thinner end of the wedge. The number 1 band marks the place where the faster of the two rays, into which the quartz breaks up the sodium light, has gained exactly one wave length in its phase over the slower ray. At the point marked 2 the gain is two wave- lengths, etc. In explaining the phenomenon just described, reference is made to Fig. 540 in which it is assumed that P-P' is the plane of the polarizer and A- A 1 CHARACTERS DEPENDING UPON LIGHT 233 is the plane of the analyzer, and a quartz wedge is between them at such an angle that the direction of the vertical crystal axis lies parallel to C-C'. If we explain the action of light in the wedge in a purely mechanical way we may say, let the amplitude of vibration of an ether particle before the light has entered the wedge be represented in the figure by the line 0-p. The vibration may be likened to that of a pendulum', swinging back and forth from p to p'. If the impact, or disturbance, of an ether particle is communicated to the ether particles of the quartz when it is at at the middle of an oscillation from p to p', there will result two disturbances, one to r parallel to C-C' and the other to s at right angles thereto. The amplitude of the vibrations repre- sented by 0-r and 0-s are determined by the parallelogram of forces, as indi- cated by the dotted lines in the figure.^ During the passage of these two rays through the quartz the one whose vibrations are represented by s-s' travels the faster and it is assumed that the thickness of the quartz wedge at the place under consideration is such that, on emerging, this ray is just one wave-length ahead of the one whose vibrations are parallel to r-r'. Now, when one ray is exactly one wavelength ahead of another (it may be two, three or any exact number of wavelengths) the conditions are such, that, at the middle of the vibration, when an ether particle of the ray s-s' is just starting from to s, an ether particle of the ray r-r' will be just starting from to r. Now con- sider the effects produced by the simultaneous impacts in the directions to s and to r upon the ether particles of the calcite constituting the analyzer. A* vibration from s' to s acting at will displace the ether particles of the calcite to a and a'. Likewise a vibration from r' to r acting at will displace the ether particles to p and p'. Two of these resulting disturbances, namely 0-- First Order -A^ Second Order Interference Colors with Quartz Wedge noted that at the very thin end of the wedge before any interference can have taken place the color is white. Also the thicker end of the wedge is white because here there is an overlapping of the various points of interference of the different colors. The thickness of the wedge at the different points is given in millimeters in Fig. 544. 344. Sensitive Tint. Among the accessories of the polarizing micro- scope is a thin plate of gypsum mounted between two plates of glass. It is commonly marked S. T. and also with an arrow marked either X (o) or Z (c), indicating respectively the direction of vibration of the faster or slower ray. If this is placed on the microscope stage in the 45 position with the nicols crossed, the interference color shown is reddish violet, the same as that close to the red of the first order of the quartz wedge. It is an interesting experi- ment to first put a quartz wedge under the microscope and focus on the red- violet, just beyond the red of the first order and then cover it with the sensi- tive tint arranged in such a way that its X direction is at right angles to the X direction of the quartz wedge. The resulting color will be gray. The explanation of this is simple. Whatever gain the faster ray had made over the slower in passing through the quartz has been overcome or neutralized by passing through a layer of gypsum of opposite optical orientation- and of suit- able thickness to produce the same interference as the quartz. The name Sensitive Tint is given to this gypsum plate because a slight increase of the double refraction which it shows will give a blue color while a corresponding slight decrease will change the color to yellow. Numerous uses of the sensi- tive tint will be given in subsequent articles. 345. Interference Colors of Mineral Sections. The interference col- ors of mineral sections depend upon three things. 1. On the strength of the birefringence of the mineral, or in other words upon the amount of double refraction that the mineral shows. The greater the birefringence the higher the order of interference color, the other influenc- ing factors remaining constant. 2. The thickness of the section. The thicker the section the greater will be the amount of double refraction and consequently the higher the order of the interference color. CHARACTERS DEPENDING UPON LIGHT 237 3. The crystallographic orientation of the section. This will be explained later when the optical characters of the different crystal systems are described 346. Determination of the Order of the Interference Color of a Min- eral Section. It is often important to determine to which order (see last paragraph of Art. 343) the interference color of a given section belongs. If, as is often the case, the section has somewhere a tapering wedge-like edge, the successive bands of color shown there can be counted and the order of the color of the surface of the section determined. In other words the order of the color can be told in the same way as upon the quartz wedge itself. If such an edge cannot be found the quartz wedge is used as described below. Suppose a certain mineral section showed an interference color of orange- red and it was desired to ascertain whether this color belonged to the first or second order. Under the microscope with crossed nicols find a position of extinction of the section and then turn it upon the stage of the microscope through an angle of 45. By doing this the vibration directions of the section are brought into such a position that they make angles of 45 with the vibra- tion directions of the polarizer and analyzer. Then insert above the section and below the analyzer a quartz wedge, the optical orientation of which is known. A slot running through the microscope tube just above the objective and making an angle of 45 to the cross-hairs is provided for this purpose. Under these conditions there are two possibilities. Either the optical orientation of the section and the quartz wedge agree; i.e., the X direction of the section is parallel to the X direction of the wedge, or these two directions are at right angles to each other. The effect of the introduction of the wedge above the section will be either to increase or decrease the amount of double refraction of the light due to the mineral section. If the double refraction is increased, the optical effect will be as if the mineral section had been thickened and in this case its interference color will rise in its order. On the other hand, if the double refraction of the light is decreased by the introduction of the quartz wedge the effect will be as if the mineral section had been thinned and the interference color will fall in its order. In the first case the red interfer- ence color of the section would be changed as the wedge is pushed in, first to blue and then to green. In the second case it would change to orange, then to yellow and green. Arrange the section, therefore, so that upon the intro- duction of the quartz wedge the interference color will fall in its order. Then gradually continue to push in the wedge, noting the successive colors that occur as the amount of the double refraction is decreased. Finally the point will be reached where the thickness of the wedge will give practically the same amount of double refraction as the mineral section. The two having oppo- site optical orientations the result will be to eliminate all interference and a gray color of the first order will result. When this condition arises the quartz wedge is said to compensate the mineral. By noting the succession of colors that occurs until this point is reached the order of the original color of the section can be determined. 347. Determination of Strength of Birefringence. The birefringence, or amount of double refraction, varies with different minerals. It is expressed numerically by a figure that is the difference between the greatest and least indices of refraction of a given mineral. In the case of calcite, for instance, the index of refraction for one ray is 1'486 and for the other is T658. The birefringence of calcite therefore equals 0'172. This is much higher than for most minerals, the strength of the birefringence of quartz being only 0*0091. 238 PHYSICAL MINERALOGY An accurate estimation of the strength of the birefringence of a mineral is to be made only by determining the greatest and least indices of refraction. An approximate determination, however, can often be made in a thin section under the microscope. The order of the interference color of a section, as stated in Art. 345, varies with the thickness of the mineral, its crystallographic orienta- tion and the strength of its birefringence. If the first two factors are known the birefringence can be estimated by noting the interference color of the' section. Fig. 545 will aid in this determination. The thickness of the sec- tion is shown in the column at the left. The strength of the birefringence is expressed along the top and right-hand side of the figure. Suppose that a given section was 0*03 mm. in thickness and showed an orange-red interference color of the first order. By following the diagonal line that crosses the hori- zontal line marked 0*03 mm. at a point lying in the middle of the orange-red of the first order it will be seen that the birefringence of the mineral must be about Q'015. This method of determining birefringence is most commonly used in the case of minerals observed in rock sections. In the case of the best rock sections the thickness of the section is usually about 0'03 to 0'04 mm. The thickness of the section can also be judged from the interference color shown by some known mineral, like quartz or feldspar, which is to be observed in the section. As the strength of the birefringence of a mineral varies with its crystallographic orientation it is necessary always to look over the rock section and use in the observations that section of the mineral which shows the highest order of interference color. The birefringence of a mineral is always 545 | I \ .1 0.06 0.05 0.04 0.03 0.02 0.01 0.00 I! 11 I * 3 O /* ill ,OP^P3O .><= s,i |MfS -i .2o SS3 g "S .2 >o'w oo o He>^ o II ll , i^jtf I .1^3122 ffl diii &-M o^^dtf'S^S o White of higher order. 0.045 0.050 0.055 0.060 0.065 0.070 0.100 0.120 0.160 0.200 0.300 Determination of the Strength of Birefringence (after Pirsson and Robinson) expressed as the maximum difference between the indices of refraction. Con- sequently, with a uniform thickness, such as is obtained in a rock section, that CHARACTERS DEPENDING UPON LIGHT 239 section of a mineral which shows the highest order of interference color most nearly approaches the proper orientation for the maximum birefringence. The order of the interference color of a given section is to be determined by the method of compensation as explained in Art. 346. Special quartz wedges are made with scales upon them giving the birefringence produced by the varying thicknesses of the wedge. If such a wedge is available it is only necessary to note the birefringence corresponding to that thickness of the quartz which produced compensation. This will obviously equal the bire- fringence of the section being tested. For a detailed description of the various wedges and compensators used for this purpose the reader must be referred to more special text-books.* 348. Determination of the Relative Optical Character of the Extinc- tion Directions of any Section of a Doubly Refracting Mineral. It fre- quently becomes important to determine which of the two rays of light in a doubly refracting mineral is being propagated with the greater or less velocity; in other words, to determine which of the two directions of vibration corre- sponds to the X and which to the Z direction. Place the given section under the microscope with the nicols crossed. Find a position of extinction and then turn the section through an arc of 45 so that its vibration directions make that angle with the planes of vibration of the nicols. If the section in this position shows a strong color or white of the higher order the quartz wedge is used. The optical orientation of the wedge must be known, i.e., which are its X and Z directions. The wedge is then pushed through the slot above the objective lens, the thin end of the wedge being introduced first. The vibra- tion directions of the wedge and the section will now coincide and the effect of the gradual introduction of the wedge above the mineral will be to slowly increase or decrease the birefringence due to the section. The result will be to either raise or lower the order of the interference color obtained. If the X directions of the wedge and the section coincide the effect will be additive in character and the color will rise in its order. If the optical directions of the two are opposed to each other the birefringence is decreased and the color will fall. By noting which effect takes place the X and Z directions of the section are determined. In this use of the quartz wedge the following precaution must be observed. If the section originally showed a color of the first order and the wedge was introduced in the opposed position the effect would be to cause the color to fall rapidly to gray of the first order. The optical effect of the quartz wedge would thus quickly compensate that of the section. From this point on as the quartz wedge is pushed further in, the optical effect of the wedge will more and more preponderate over that of the section and the interference colors will now appear in ascending order. Under these conditions, if the first effect of the quartz wedge was overlooked, a wrong deduction would be made. It is always best to repeat the test with the section rotated 90 from the first posi- tion. The two results should be of opposite character and so serve to confirm each other. Frequently a thick section of a mineral will show a tapering edge somewhere which will show bands of color. When the quartz wedge is introduced above the section these color bands will move, either toward the center of the section, * See Johannsen, Manual of Petrographic Methods; Wright, The Methods of Petro- graphic-Microscopic Research. 240 PHYSICAL MINERALOGY or go off toward the edge. When the color bands move up on the section it means that the effect of the quartz wedge is such that a thicker part of the section is now showing the same interference as a thinner part did originally. In other words, the result is as if the section had been thinned. If this is so, then the X and Z directions of the section and the wedge must be opposed to each other. On the other hand, if the color bands move off the section it means that a thinner part of the section is showing the same interference effect that a thicker portion did originally. The introduction of the quartz wedge has in effect thickened the section and therefore the similar optical directions of the two coincide. This test is particularly useful for determin- ing the X and Z directions of deeply colored minerals, as the natural color of the mineral may, over the thicker portion of the section, completely mask the interference color. If a mineral section shows an interference color of white or gray of the first order the sensitive tint will give better results than the quartz wedge. If the similar optical directions of the section and the sensitive tint coincide the effect will be to raise the color of the sensitive tint (red of the first order) to blue. On the other hand, if the optical orientations of the two are opposed the color will fall to yellow. This test can be made to advantage only when the birefringent effect of the section is small enough to just raise or lower the color of the sensitive tint respectively to blue or yellow. \ 349. Circularly and Elliptically Polarized Light. In the preceding articles the two interfering light-rays, after emerging from the second nicol, were assumed to be polarized in the same plane; for them the resulting phe- nomena as indicated are comparatively simple. If, however, two plane- polarized rays propagated in the same direction have their vibration-directions at right angles to each other, and if they differ one-quarter of a wave-length (JX) in phase (assuming monochromatic light), then it may be shown that the composition of these two systems results in a ray of circularly polarized light. Briefly expressed, this is a ray that, looked at end-on, would seem to be propagated by ether-vibrations taking place in circles about the line of transmission. From the side, the onward motion would be like that of a screw, and either right-handed or left-handed. If, again, two light-rays meet as above described, with a difference of phase differing from JX (but not equal to an even multiple of |X), then the resulting composition gives rise to elliptically polarized light, that is, a light-ray propa- gated by ether-motions taking place in ellipses. The above results are obtained most simply by passing plane-polarized light through a doubly refracting medium of the proper thickness (e.g., a mica plate) which is placed with its vibration-planes inclined 45 to that of the polarizer. If the thickness is such as to give a difference in phase of JX or an odd multiple of this, the light which emerges is circularly polarized. If the phase differs from \\ (but is not equal to |X or X), the emergent light is ellip- tically polarized. 350. Rotation of Plane of Polarization. In the case of certain doubly refracting crystallized media (as quartz), and also of certain solutions, (as of sugar), it can be shown that the light is propagated by two sets of ether- vibrations which take place, not in definite transverse planes as in plane- polarized light but in circles; that is, each ray is circularly polarized, one being right-handed, the other left-handed. Further, of these rays, one will uniformly gain with reference to the other. The result is, that if a ray of CHARACTERS DEPENDING UPON LIGHT 241 plane-polarized light fall upon such a medium (assuming the simplest case, as of a section of quartz cut normal to the vertical crystal axis), it is found that the two rays circularly polarized within unite on emerging to a plane-polar- ized ray, but the plane of polarization has suffered an angular change or rota- tion, which may be either to the right (to one looking in the direction of the ray), when the substance is said to be right-handed, or to the left, when it is called left-handed. This phenomenon is theoretically possible with all crystals of a given system belonging to any of the classes of lower symmetry than the normal class which show a plagiohedral development of the faces *; or, more simply, those in which the corresponding right and left (or + and ) typical forms are enantiomorphous (pp. 71, 112), as noted in the chapter on crystallography. In mineralogy, this subject is most important with the common species quartz, of the rhombohedral-trapezohedral class, and a further discussion of it is postponed to a later page (Art. 394). OPTICAL INSTRUMENTS AND METHODS 351. Measurement of Refractive Indices. Refractometer. For the determination of the refractive indices of crystallized minerals various methods are employed. The most accurate results, when suitable material is at hand, may be obtained by the ordinary refractometer. This requires the observa- tion of the angle of minimum deviation (5) of a light-ray on passing through a prism of the given material, having a known angle (a}, and with its edge cut in the proper direction. The measurements of a and 5 can be made with an ordinary refractometer or with the horizontal goniometer described in Art. 231. For the latter instrument, the collimator is made stationary, being fastened to a leg of the tripod support, but the observing telescope with the verniers moves freely. Further, for this object the graduated circle is clamped, and the screw attachments connected with the axis carrying the support, and the vernier circle and observing telescope are loosened. Light from a mono- chromatic source passes through an appropriate slit and an image of this is thrown by the collimator upon the prism. With a doubly refracting substance two images are yielded and the angle of minimum deviation must be measured for each ; the proper direction for the edge of the prism in this case is discussed later. When a and 5 are known the formula in Art. 327 is used. 352. Total Refractometer. The principle of total reflection (Art. 323) may also be made use of to determine the refractive index. No prism is re- quired, but only a small fragment having a single polished surface; this may have any direction with an isometric crystal, but in other cases must have a definite orientation, as described later. A number of different instruments have been devised by means of which indices of refraction may be measured by the use of total reflection. A type widely used at present is represented in Fig. 546. This particular instrument was made by Leiss. It consists of a hemisphere of glass (H) having a high refractive index which is mounted upon a glass post through which light may be reflected from the mirror Sp. The * Of the thirty-two possible classes among crystals, the following eleven may be char- acterized by circular polarization: Class 4, p. 71; 5, p. 72; 11 and 12, p. 89; 17, p. 102; 22, p. 112; 23 and 24, p. 114; 27, p. 128; 29, p. 138; 32, p. 147. 242 PHYSICAL MINERALOGY 546 tube P contains a nicol prism so that when a thin section of a mineral is placed upon the plane surface of the hemisphere it is possible to obtain its optical orientation in the same manner as with the polarizing microscope. The polished mineral sur- face is placed upon the plane surface of H with a film of some high refract- ing oil between them. Then a beam of light from some source of illumination, usually a mono- chromatic light, is reflected by means of the mirror Bl in such a way as to produce a total reflec- tion shadow down on the opposite side of the hemisphere. For further details of the operation see Art. 327. The tel- escope F is attached to the disk V which in turn carries a scale on its edge. The telescope is moved up or down until the line between the light and dark portions of the field lies on the cross-hairs. The angle which is read on the scale under these conditions is the desired critical angle for the combination of the glass of the hemisphere and the mineral plate. Knowing this angle and the index of refraction of the glass of the hemisphere it is possible to calculate the index of refraction of the mineral ; see Art. 327. Usually a table is furnished with the total ref ractometer by means of which the desired refractive index is obtained directly from the value of the measured critical angle. The post carrying the glass hemisphere may be revolved in the horizontal plane and the angle of rotation measured on the scale K. This permits the measurement of indices corresponding to different vibration direc- tions in the mineral. L is an eye lens which in combination with the other lenses of the tube F makes a low power microscope, which is used in the pre- liminary operations in order to center the mineral plate, etc. In the tube A is an iris diaphragm and usually a small nicol prism that may be pushed in or out of the tube. Fig. 547 represents a small total refractometer devised by G. F. H. Smith which depends upon the same principle. The mineral plate is placed upon the glass surface shown on the top of the instrument. The instrument is so Total Refractometer CHARACTERS DEPENDING UPON LIGHT 243 held that light enters at the forward end, and the totally reflected light is sent by means of an inclined mirror to the eyepiece. A scale is placed in the instru- 647 Smith Total Refractometer (Actual Size) ment in such a way that the boundary between the light and dark areas is seen superimposed upon it and so yields directly the value of the refractive index. For rapid and approximate determinations this instrument is very useful. 353. Tourmaline Tongs. A very simple form of polariscope for con- verging light is shown in Fig. 548; it is convenient in use, but of limited appli- cation. Here the polarizer and analyzer are two tourmaline plates such as were described in Art. 340. They are mounted in pieces of cork and held in a kind of wire pincers. The object to be examined is placed between them and supported there by the spring in the wire. In use they are held close to the eye, and in this position the crystal section is viewed in converging polarized light, with the result of showing (under proper conditions) the axial inter- ference-figures (Arts. .389 and 407) . Tourmaline Tongs 354. Polariscope. Conoscope. The common forms of polariscopes employing nicol prisms are shown in Figs. 549 and 550.* Fig. 549 represents the instrument arranged for converging light, which is often called a conoscope. The essential parts are the mirror S, reflecting the light, which after passing through the lens e is polarized by the prism p. It is then rendered strongly converging by the system of lenses nn, before passing through the section under examination placed on a plate at k. This plate can be revolved * These figures are taken from the catalogue of Fuess. 244 PHYSICAL MINERALOGY through any angle desired, measured on its circumference. The upper tube contains the converging system oo, the lens t, and the analyzing prism q. The arrangements for lowering or raising the tubes need no explanation, nor 649 550 Conoscope Polariscope indeed the special devices for setting the vibration-planes of the nicols at right angles to each other. The accompanying tube (Fig. 550) shows the arrangement for observations in parallel light, the converging lenses having been removed. CHARACTERS DEPENDING UPON LIGHT 245 561 Fig. 551 represents in cross-section a simple, inexpensive but quite efficient form of polariscope. The polarizing device, P, is in the form of two or three thin glass sheets, the back of the bottom one being blackened. These glass plates are set at the appropriate angle to secure the maximum amount of polarization of the light reflected from them up through the opening in the stage K. M represents an adjustable mirror by means of which light is reflected upon P. The analyzer, A, is a small nicol prism which is held over the opening in the stage by means of the stand- ard S. A double series of lenses may be placed upon the stage of the instrument and so convert it into a conoscope. 355. Polarization -Microscope. The investigation of the form and optical properties of minerals when in microscopic form has been much facilitated by the use of microscopes * specially adapted for this purpose. First arranged with reference to the special study of minerals as seen in thin sections of rocks, they have now been so elaborated as largely to take the place of the older optical instruments. They not only allow of the determination of the optical properties of minerals with greater facility, but are applicable to many cases where the crystals in hand are far too small for other means. A highly serviceable microscope is the Laboratory Model made by the Bausch and Lomb Optical Co., and illustrated in Fig. 552. The essential arrangements of this instrument are as follows: The eyepiece at A, which is removable, contains the cross-hairs with an eye lens adjustable for focusing upon them. At B is a Bertrand lens that slides in and out of the tube, with an iris diaphragm immediately above it. At C is the analyzer box which slides in and out of the body tube. This prism may be revolved through a quarter turn. D is a slot in the microscope tube with a dust-proof shutter for the introduction of various accessories, such as the quartz wedge, etc. At E is the nosepiece which can be centered by the two screws which work at right angles in the N and E positions. The objective F is held in place by a spring clamp and is quickly detached. The stage, G, revolves and carries a scale graduated into degrees, the attached vernier permitting the reading of angles to one-tenth degree. The substage at H carries condensing lenses, iris dia- phragm and the polarizing prism. It can be moved upward and downward by means of a screw-head and when at its lowest point can be sprung to one side, out of the optical axis. The mirror at / is adjustable and has both a plane and concave surface. The coarse focusing adjustment is at J, while the milled head at K provides a fine adjustment by means of which a vertical movement of 0'0005 mm. can be read. * For detailed descriptions of the polarizing microscope and its accessories see Johannsen, Manual of Petrographic Methods; Wright, The Methods of Petrographic Research; etc. Polariscope (| natural size) 246 PHYSICAL MINERALOGY 356. The Research Model of the Bausch and Lomb microscope is illus- trated in Fig. 553. This instrument is patterned after one described by 552 553 Petrographical Microscope (Laboratory Model, Bausch and Lomb, | actual size) Petrographical Microscope (Research Model, Bausch and Lomb j actual size) Wright to whose papers reference is made for a more detailed account. The outstanding features of the instrument may be briefly summarized as follows : It has a large body-tube within which are always contained the analyzer and the Bertrand lens, both when they lie in or outside the optical axis of the micro- scope. The two nicols may be connected by means of the upright bar and rotated simultaneously through an arc of 90. This enables the measurement of extinction angles, etc., to be made without the necessity of revolving the stage and the consequent difficulty in keeping the mineral grain under observa- tion exactly centered in the field. This bar carries verniers that lie against the scale engraved upon the stage so that the angle of rotation of the nicols can be accurately measured. The polarizing prism can be entirely removed from the optical axis. A revolvable carrier for a sensitive plate is attached to the iris diaphragm mount of the substage. GENERAL OPTICAL CHARACTERS OF MINERALS 357. There are certain characteristics belonging to all minerals alike, crystallized and non-crystallized, in their relation to light. These are: 1. DIAPHANEITY: depending on the relative quantity of light transmitted. CHARACTERS DEPENDING UPON LIGHT 247 2. COLOR: depending on the kind of light reflected or transmitted, as determined by the selective absorption. 3. LUSTER: depending on the power and manner of reflecting light. 1. DIAPHANEITY 358. Degrees of Transparency. The amount of light transmitted by a solid varies in intensity, or, in other words, more or less light may be absorbed in the passage through the given substance (see Art. 330). The amount of absorption is a minimum in a transparent solid, as ice, while it is greatest in one which is opaque, as iron. The following terms are adopted to express the different degrees in the power of transmitting light : Transparent: when the outline of an object seen through the mineral is perfectly distinct. Subtransparent, or semi-transparent: when objects are seen, but the outlines are not distinct. Translucent: when light is transmitted, but objects are not seen. Subtranslucent: when merely the edges transmit light or are translucent. When no light is transmitted, even on the thin edges of small splinters, the mineral is said to be opaque. This is properly only a relative term, since no substance fails to transmit some light, if made sufficiently thin. Magnetite is translucent in the Pennsbury mica. Even gold may be beaten out so thin as to be translucent, in which case it transmits a greenish light. The property of diaphaneity occurs in the mineral kingdom, from nearly perfect opacity to transparency, and many minerals present, in their numerous varieties, nearly all the different degrees. 2. COLOR 359. Nature of Color. As briefly explained in Art. 314, the sensation of color depends, in the case of monochromatic light, solely upon the length of the waves of light which meet the eye. If the light consists of various wave-lengths, it is to the combined effect of these that the sensation of color is due. Further, since the light ordinarily employed is essentially white light, that is, consists of all the wave-lengths corresponding to the successive colors of the spectrum, the color of a body depends upon the selective absorption (see Art. 330) which it exerts upon the light transmitted or reflected by it. A yellow mineral, for instance, absorbs all the waves of the spectrum with the exception of those which together give the sensation of yellow. In general, the color which the eye perceives is the result of the mixture of those waves which are not absorbed. 360. Streak. The color of the powder of a mineral as obtained by scratching the surface of the mineral with a knife or file, or, still better, if the mineral is not too hard, by rubbing it on an unglazed porcelain surface, is called the streak. The streak is often a very important quality in distinguish- ing minerals. This is especially true with minerals having a metallic luster, as defined in Art. 364. 361. Dichroism; Pleochroism. The selective absorption, to which the color of a mineral is due, more especially by transmitted light, often varies with the crystallographic direction in which the light passes through the mineral. It is hence one of the special optical characters depending upon the 248 PHYSICAL MINERALOGY crystallization, which are discussed later. Here belong dichroism or pleochro- ism, the property of exhibiting different colors in different crystallographic directions by transmitted light. This subject is explained further in Arts. 396 and 411. 302. Varieties of Color. The following eight colors were selected by Werner as fundamental, to facilitate the employment of this character in the description of minerals: white, gray, black, blue, green, yellow, red, and brown. (a) The varieties of METALLIC COLORS recognized are as follows: 1. Copper-red: native copper. 2. Bronze-yellow: pyrrhotite. 3. Brass-yellow: chalcopyrite. 4. Gold-yellow: native gold. 5. Silver-while: native silver, less distinct in arsenopyrite. 6. Tin-white: mercury; cobaltite. 7. Lead-gray: galena, molybdenite. 8. Steel-gray: nearly the color of fine-grained steel on a recent fracture; native plati- num, and palladium. (6) The following are the varieties of NON-METALLIC COLORS: A. WHITE. 1. Snow-white: Carrara marble. 2. Reddish white, 3. Yellowish white and 4. Grayish white: all illustrated by some varieties of calcite and quartz. 5. Greenish white: talc. 6. Milk white: white, slightly bluish; some chalcedony. B. GRAY. 1. Bluish gray: gray, inclining to dirty blue. 2. Pearl-gray: gray, mixed with red and blue; cerargyrite. 3. Smoke-gray: gray, with some brown; flint. 4. Greenish gray: gray, with some green; cat's-eye; some varieties of talc. 5. Yellowish gray: some varieties of compact limestone. 6. Ash-gray: the purest gray color; zoisite. C. BLACK. 1. Grayish black: black, mixed with gray (without green, brown, or blue tints); basalt; Lydian stone. 2. Velvet-black: pure black; obsidian, black tourmaline. 3. Greenish black: augite. 4. ' Brownish black: brown coal, lignite. 5. Bluish black: black cobalt. p. BLUE. 1. Blackish blue: dark varieties of azurite. 2. Azure-blue: a clear shade of bright blue; pale varieties of azurite, bright varieties of lazulite. 3. Violet-blue: blue, mixed with red; amethyst, fluorite. 4. Lavender-blue: blue, with some red and much gray. 5. Prussian-blue, or Berlin blue: pure blue; sapphire, cyanite. 6. Smalt-blue: some varieties of gypsum. 7. Indigo-blue: blue, with black and green; blue tourmaline. 8. Sky-blue: pale blue, with a little green; it is called mountain-blue by painters. E. GREEN. 1. Verdigris-green: green, inclining to blue; some feldspar (amazon-stone). 2. Celandine-green: green, with blue and gray; some varieties of talc and beryl. It is the color of the leaves of the celandine. 3. Mountain-green: green, with much blue; beryl. 4. Leek-green: green, with some brown; the color of leaves of garlic; distinctly seen in prase, a variety of quartz. 5. Emerald-green: pure deep green; emerald. 6-. Apple-green: light green with some yellow; chrysoprase. 7. Grass-green: bright green, with more yellow; green diallage. 8. Pistachio-green: yellowish green, with some brown; epidote. 9. Asparagus-green: pale green, with much yellow; asparagus stone (apatite). 10. Blackish green: serpentine. 11. Olive-green: dark green, with much brown and yellow; chrysolite. 12. Oil-green: the color of olive-oil; beryl, pitchstone. 13. Siskin-green: light green, much inclining to yellow; uranite. F. YELLOW. 1.. Sulphur-yellow: sulphur. 2. Straw-yellow: pale yellow; topaz. 3. Wax-yellow: grayish yellow with some brown; sphalerite, opal. 4. Honey-yellow: yellow, with some red and brown; calcite. 5. Lemon-yellow: sulphur, orpiment. 6. Ocher-yellow: yellow, with brown; yellow pcher. 7. Wine-yellow: topaz and fluorite. 8. Cream-yellow: some varieties of kaolinite. 9. Orange-yellow: orpiment. G. RED. 1. Aurora-red: red, with much yellow; some realgar. 2. Hyacinth-red: red, with yellow and some brown; hyacinth garnet. 3. Brick-red: polyhalite, some jas- per. 4. Scarlet-red: bright red, with a tinge of yellow; cinnabar. 5. Blood-red: dark red, with some yellow; pyrope. 6. Flesh-red: feldspar. 7. Carmine-red: pure red; ruby sapphire. 8. Rose-red: rose quartz. 9. Crimson-red: ruby. 10. Peachblossom- red: red, with white and gray; lepidolite. 11. Columbine-red: deep red, with some blue; garnet. 12. Cherry-red: dark red, with some blue and brown; spinel, some jasper. 13. Brownish-red: jasper, limonite. H. BROWN. 1. Reddish brown: garnet, zircon. 2. Clove-brown: brown, with red and some blue; axinite. 3. Hair-brown: wood-opal. 4. Broccoli-brown: brown, with blue, red, and gray; zircon. 5. Chestnut-brown: pure brown. 6. Yellowish brown: jasper. 7. Pinchbeck-brown: yellowish brown, with a metallic or metallic-pearly luster; several varieties of talc, bronzite. 8. Wood-brown: color of old wood nearly rotten; some CHARACTERS DEPENDING UPON LIGHT 249 specimens of asbestus- 9. Liver-brown: brown, with some gray and green; jasper. - 10. Blackish brown: bituminous coal, brown coal. 3. LUSTER 363. Nature of Luster. The luster of minerals varies with the nature 5- 1* surfaces - A variation in the quantity of light reflected produces different degrees of intensity of luster; a variation in the nature of the reflect- ing surface produces different kinds of luster. 364. Kinds of Luster. The kinds of luster recognized are as follows: 1. METALLIC: the luster of the metals, as of gold, copper, iron, tin. In general, a mineral is not said to have metallic luster unless it is opaque in the mmeralogical sense, that is, it transmits no light on the edges of thin splinters. Some minerals have varieties with metallic and others with non- metallic luster; this is true of hematite. Imperfect metallic luster is expressed by the term sub-metallic, as illus- trated by columbite, wolframite. Other kinds of luster are described briefly as NON-METALLIC. 2. NON-METALLIC. A. Adamantine: the luster of the diamond. When also sub-metallic, it is termed metallic-adamantine, as cerussite, pyrargyrite. Adamantine luster belongs to substances of high refractive index. This may be connected with their relatively great density (and hardness), as with the diamond, also corundum, etc. ; or because they contain heavy molecules, thus most compounds of lead, not metallic in luster, have a high refractive index and an adamantine luster. B. Vitreous: the luster of broken glass. An imperfectly vitreous luster is termed sub-vitreous. The vitreous and sub-vitreous lusters are the most common in the mineral kingdom. Quartz possesses the former in an eminent degree; calcite, often the latter. C. Resinous: luster of the yellow resins, as opal, and some yellow varieties of sphalerite. D. Greasy: luster of oily glass. This is near resinous luster, but is often quite distinct, as nephelite. E. Pearly: like pearl, as talc, brucite, stilbite, etc. When united with sub-metallic, as in hypersthene, the term metallic-pearly is used. Pearly luster belongs to the light reflected from a pile of thin glass-plates; similarly it is exhibited by minerals, which, having a perfect cleavage, may be partially separated into successive plates, as on the basal plane of apophyllite. It is also shown for a like reason by foliated minerals, as talc and brucite. F. Silky: like silk; it is the result of a fibrous structure. Ex. fibrous cal- cite, fibrous gypsum. The different degrees and kinds of luster are often exhibited differently by unlike faces of the same crystal, but always similarly by like faces. For example, the basal plane of apophyllite has a pearly luster wanting in the pris- matic faces, which have a vitreous luster. As shown by Haidinger, only vitreous, adamantine, and metallic luster belong to faces perfectly smooth and pure. In the first, the refractive index of the mineral is I'S-l'S; in the second, l'9-2'5; in the third, about 2'5. The true difference between metallic and vitreous luster is due to the effect which the different surfaces have upon the reflected light; in general, the luster is produced by the union of two simultaneous impressions made upon the eye. If the light reflected from a metallic surface be examined by a nicol prism (or the dichroscope of Haidinger, Art. 393), it will be found that both rays, that vibrating in the plane of incidence and that whose vibrations are normal to it, are alike, each having the 250 PHYSICAL MINERALOGY color of the material, only differing a little in brilliancy; on the contrary, of the light reflected by a vitreous substance, those rays whose vibrations are at right angles to the plane of incidence are more or less polarized, and are colorless, while those whose vibrations are in this plane, having penetrated somewhat into the medium and suffered some absorp- tion, show the color of the substance itself. A plate of red glass thus examined will show a colorless and a red image. Adamantine luster occupies a position between the others. 365. Degrees of Luster. The degrees of intensity of luster are classi- fied as follows: 1. Splendent: reflecting with brilliancy and giving well-defined images, as hematite, cassiterite. 2. Shining: producing an image by reflection, but not one well-defined, as celestite. 3. Glistening: affording a general reflection from the surface, but no image, as talc, chalcopyrite. 4. Glimmering: affording imperfect reflection, and apparently from points over the surface, as flint, chalcedony. A mineral is said to be dull when there is a total absence of luster, as chalk, the ochers, kaolin. 366. Play of Colors. Opalescence. Iridescence. The term play of colors is used to describe the appearance of several prismatic colors in rapid succession on turning the mineral. This property belongs in perfection to the diamond, in which it is due to its high dispersive power. It is also observed in precious opal, where it is explained on the principle of interference; in this case it is most brilliant by candle-light. The expression change of colors is used when each particular color appears to pervade a larger space than in the play of colors and the succession pro- duced by turning the mineral is less rapid. This is shown in labradorite, as explained under that species. Opalescence is a milky or pearly reflection from the interior of a specimen. Observed in some opal, and in cat's-eye. Iridescence means the exhibition of prismatic colors in the interior or on the surface of a mineral. The phenomena of the play of colors, iridescence, etc., are sometimes to be explained by the presence of minute foreign crystals, in parallel positions; more generally, however, they are caused by the presence of fine cleavage-lamellae, in the light reflected from which interference takes place, analogous to the well-known Newton's rings (see Art. 336). 367. Tarnish. A metallic surface is tarnished when its color differs from that obtained by fracture, as is the case with specimens of bornite. A surface possesses the steel tarnish when it presents the superficial blue color of tempered steel, as columbite. The tarnish is irised when it exhibits fixed prismatic colors, as is common with the hematite of Elba. These tarnish and iris colors of minerals are owing to a thin surface or film, proceeding from different sources, either from a change in the surface of the mineral or from foreign incrustation; hydrated iron oxide is one of the most common sources of it and produces the colors on anthracite and hematite. 368. Asterism. This name is given to the peculiar star-like rays of light observed in certain directions in some minerals. This is seen by reflected light in the form of a six-rayed star in sapphire, and is also well shown by transmitted light (as of a small flame) with the phlogopite mica from South Burgess, Canada. In the former case it is explained by the presence of thin twinning-lamellse symmetrically arranged. In the other case it is due to the presence of minute inclosed crystals, also symmetrically arranged, which are probably rutile or tourmaline in most cases. Crystalline faces which have CHARACTERS DEPENDING UPON LIGHT 251 been artificially etched also sometimes exhibit asterism. The peculiar light- figures sometimes observed in reflected light on the faces of crystals either natural or etched, are of similar nature. 369. Schillerization. The general term schiller is applied to the pecu- liar luster, sometimes nearly metallic, observed in definite directions in certain minerals, as conspicuously in schiller-spar (an altered variety of bronzite) also in diallage, hypersthene, sunstone, and others. It is explained by the reflection either from minute inclosed plates in parallel position or from the surfaces of minute cavities (negative crystals) having a common orientation In many cases it is due to alteration which has developed these bodies (or the cavities) in the direction of solution-planes (see Art. 285). The process by which it has been produced is then called schillerization. 370. Fluorescence. The emission of light from within a substance while it is being exposed to direct radiation, or in certain cases to an electrical discharge in a vacuum tube, is called fluorescence. It is best exhibited by fluorite, from which the phenomenon gained its name. Thus, if a beam of white light be passed through a cube of colorless fluorite a delicate violet color is called out in its path. This effect is chiefly due to the action of the ultra- violet rays, and is connected with a change of refrangibility in the transmitted light. The electrical discharge from the negative pole of a vacuum tube calls out a brilliant fluorescence not only with the diamond, the ruby, and many gems, but also with calcite and other minerals. Such substances may continue to emit light, or phosphoresce, after the discharge ceases. 371. Phosphorescence. The continued emission of light by a sub- stance (not incandescent) produced especially after heating, exposure to light or to an electrical discharge, is called phosphorescence. Fluorite becomes highly phosphorescent after being heated to about 150 C. Different varieties give off light of different colors; the chlorophane variety, an emerald-green light; others purple, blue, and reddish tints. This phosphorescence may be observed in a dark place by subjecting the pulverized mineral to a heat below redness. It may even be produced by a sharp blow with a hammer. Some varieties of white limestone or marble, after slight heating, emit a yellow light; so also tremolite, danburite, and other species. The X-ray and ultra-violet light will produce phosphorescence in willemite, kunzite, and some diamonds. The fact that willemite glows when exposed to ultra-violet light is made use of in testing the residues from a willemite ore to make certain the separation has been complete. Radium emanations cause certain minerals to phosphoresce, as willemite and wurtzite. Exposure to the light of the sun produces very apparent phosphorescence with many diamonds, but some specimens seem to be destitute of this power. This property is most striking after exposure to the blue rays of the spectrum, while in the red rays it is rapidly lost. A mixture of calcium sulphide and bismuth will phosphoresce for a considerable period after being exposed to sunlight. SPECIAL OPTICAL CHARACTERS BELONGING TO CRYSTALS OF THE DIFFERENT SYSTEMS 372. All crystallized minerals may be grouped into three grand classes, which are distinguished by their physical properties, as well as their geometri- cal form. These three classes are as follows: 252 PHYSICAL MINERALOGY A. Isometric class, embracing crystals of the isometric system, which are referred to three equal rectangular axes. B. Isodiametric class, embracing crystals of the tetragonal and hexagonal systems., referred to two, or three, equal horizontal axes and a third, or fourth, axis unequal to them at right angles to their plane. Crystals of this class have a fixed principal axis of crystallographic symmetry. C. Anisometric class, embracing the crystals of the orthorhombic, mono- clinic, and triclinic systems, referred to three unequal axes. Crystals of this class are without a fixed axis of crystallographic symmetry. 373. Isotropic Crystals. Of the three classes, the ISOMETBIC CLASS includes all crystals which, with respect to light and related phenomena involv- ing the ether, are isotropic (from the Greek, signifying equal turning) ; that is, those which have like optical properties in all directions. Their distinguishing characteristic is that light travels through them with equal velocity in all directions, provided their molecular equilibrium is not disturbed by external pressure or internal strain. If it be imagined therefore that light starts from a point within an isotropic medium at a given moment of time the resulting wave surface will be a sphere. It must be emphasized here, however, that such a crystal is not isotropic with reference to those characters which depend directly upon the molecular structure alone, as cohesion and elasticity. (See Art. 275.) Further, amorphous bodies, as glass and opal, which are destitute of any orientated molecular structure that is, those in which all directions are sensi- bly the same are also isotropic, and not only with reference to light, but also as regards their strictly molecular properties. 374. Anisotropic Crystals ; Uniaxial and Biaxal. Crystals of the ISO- DIAMETRIC and ANISOMETRIC CLASSES, on the other hand, are in distinction anisotropic (from the Greek, signifying unequal turning) . Their optical prop- erties are in general unlike in different directions, or, more particularly, the velocity with which light is propagated varies with the direction. Further, in crystals of the isodiametric class that variable property of the light-ether upon which the velocity of propagation depends remains constant for all directions which are normal to, or, again, for all those equally inclined to, the vertical crystallographic axis. In the direction of this axis there is no double refraction; it is hence called the optic axis, and the crystals of this class are said to be uniaxial. Crystals of the third or anisometric class have more complex optical rela- tions requiring special explanation, but in general it may be stated that in them there are always two directions analogous in character to the single optic axis spoken of above; hence, these crystals are said to be optically biaxial. A. ISOMETRIC CRYSTALS 375. It has been stated that crystals of the isometric system are optically isotropic, and hence light travels with the same velocity in every direction in them. Light can, therefore, suffer only single refraction in passing into an isotropic medium; or, in other words, there can be but one value of the refractive index for a given wave-length. If this be represented by n, while V is the velocity of light in air and v that in the given medium, then V V n = , or v = v n CHARACTERS DEPENDING UPON LIGHT 253 The wave-front for light-waves propagated from any point within such an isotropic medium is, as already stated, a sphere. The sphere, therefore, may be taken to represent the optical properties of an isotropic medium. Sec- tions of a sphere normal to any diameter will always be circles. These cir- cular sections with like radii in all directions correspond to the fact that the optical character of an isotropic substance is the same in all directions normal to the line of light propagation. Or, in other words, light vibrations may take place in any direction normal to the direction of transmission; i.e., the light is not polarized. Further its velocity remains uniform no matter what may be the direction of its vibration. This statement holds true of all the classes of isometric crystals. In other words, a crystal of maximum symmetry, as fluorite, and one having the restricted symmetry characteristic of the tetrahedral or pyritohedral divisions, have alike the same isotropic character. Two of the classes, however, namely, the plagiohedral and the tetartohedral classes, differ in this particular: that crystals belonging to them may exhibit what has already been defined (Art. 350) as circular polarization. 376. Behavior of Sections of Isometric Crystals in Polarized Light. In consequence of their isotropic character, isometric crystals exhibit no special phenomena in polarized light. As a section of an isotropic substance (isometric crystal or some amorphous material) has no polarizing or doubly refracting effect upon light it does not change at all the character of light that enters it from the polarizer of a polariscope. Therefore thin sections of iso- tropic media when examined in a polariscope or polarizing microscope with the nicols crossed will appear dark in all positions. In other words, they are always extinguished. Further, when a colored mineral is examined without the analyzer there will be no change in its color when the section is revolved with the stage of the microscope. Some anomalies are mentioned on a later page, (Art. 429). The single refractive index of an isotropic substance may be determined by means of a prism (see Art. 327) with its edge cut in any direction whatever. B. UNI AXIAL CRYSTALS General Optical Relations 377. The crystallographic and optical relations of crystals belonging to crystals of the tetragonal and hexagonal systems have already been briefly summarized (Art. 374); it now remains to develop their optical characters more fully. This can be done most simply by making frequent use of the familiar conception of a light-ray to represent the character and motion of the light-wave. 378. Behavior of Light in Uniaxial Minerals. Light entering a uni- axial mineral is in general broken up into two rays which are polarized in planes perpendicular to each other and which travel with different velocities and therefore have different indices of refraction. One of the two rays derived from a single incident ray always vibrates in the plane of the horizontal crys- tallographic axes. The other ray vibrates at right angles to the first and always in a vertical plane that includes the vertical crystallographic axis. The optical character of a uniaxial mineral is uniform for all directions lying in the horizontal crystallographic plane and therefore the ray whose vibra- tions lie in this plane will have uniform velocity no matter what its direction 254 PHYSICAL MINERALOGY of transmission. This ray will therefore have a single and constant index of refraction, commonly designated by co. Since this ray follows the usual law as to the constant ratio between the sines of the angles of incidence and refrac- tion and in general behaves in an ordinary way it is called the ordinary ray. The ray which vibrates in a plane that includes the vertical crystallographic axis will have the direction of its vibration constantly changing as the direc- tion of its path through the crystal changes and its velocity will correspond- ingly vary. Its index of refraction will therefore depend upon the direction of its propagation and it will not in general obey the usual sine law. This ray is therefore called the extraordinary ray. When light travels in a uniaxial mineral in a direction parallel to the vertical crystallographic axis, since all its vibrations must take place in the horizontal plane, it behaves wholly as the ordinary ray with a single velocity and refractive index. There can be no double refraction of light, therefore, along this direction and in this case the mineral will behave like an isotropic substance. This direction of no double refraction, coincident with the ver- tical crystal axis, is known as the optic axis and as there is only one such direc- tion in this optical group the latter is called uniaxial. As soon as the direc- tion of transmission becomes inclined to the vertical crystal axis the light is doubly refracted and as the inclination increases the direction of vibration of the light of the extraordinary ray departs more and more from the plane of vibration of the ordinary ray with a corresponding change in its velocity and refractive index. The difference between the refractive indices of the two rays becomes a maximum when the light passes through the mineral in a horizontal direction with the direction of vibration of the extraordinary ray parallel to the vertical crystal axis or in other words as divergent as possible from the horizontal plane. The value of the refractive index of the extra- ordinary ray when at its maximum difference from the constant index of the ordinary ray is the one always quoted and is indicated by"e. These two indices, w and e, are called the principal indices of a uniaxial crystal. A principal section of a uniaxial crystal is a section passing through the vertical axis. 379. Positive and Negative Crystals. Uniaxial crystals are divided into two classes, depending upon whether the velocity of the extraordinary ray is greater or less than that of the ordinary ray. Those in which the refractive index of the ordinary ray, co, is less than that of the extraordinary ray, e (co < e), are called positive. This is illustrated by quartz for which (for yel- low sodium light) : co = T544. e = 1-553. On the other hand, if e is less than co (e < co), the crystal is said to be negative* Calcite is an example for which (for sodium light) co = T658. e = 1-486. Other examples are given later (Art. 383) . 380. Determination of the Refractive Indices in Uniaxial Crystals. The indices of refraction of uniaxial minerals are measured in much the same * It will assist in remembering these relations to note that the first vowel in the words positive and negative agrees with the symbol used fo* the smaller index of refraction in each case. CHARACTERS DEPENDING UPON LIGHT 255 way as in the case of isotropic substances. With uniaxial crystals, however, the prism or plate used must have a definite crystallographic orientation. If a prism is employed its edge should be parallel to the optic axis, or in other words parallel to the vertical crystal axis of the mineral. When such a prism is examined on the refractometer two refracted rays are seen, the angles of refraction of which can be measured by either the method of minimum devia- tion or perpendicular incidence as described in Art. 327. The two rays are polarized, the ordinary ray vibrating in the horizontal plane and the extra- ordinary ray vibrating in the vertical plane, i.e., parallel to the edge of the prism. The plane of vibration of each ray must be determined by the use of a nicol prism held in front of the eyepiece of the refractometer. When the plane of the nicol is horizontal the image belonging to the ordinary ray will be visible and when the plane of the nicol is vertical only that of the extraordi- nary ray will appear. In this way the indices of the two rays are determined and the positive or negative character of the mineral is established. It is pos- sible to obtain these measurements in prisms with different crystallographic orientation but the difficulties attending their preparation are so great that such prisms are very seldom used. If the method of >total reflection is used a single plate will suffice, provided it lies either in the prism zone of the crystal, or is parallel to the basal plane. In each case two shadows will be observed, corresponding in their position to the angles of total reflection of the two rays: When the plate is cut parallel to a face in the prism zone one of these shadows, that belonging to the ordi- nary ray, will remain stationary as the plate is revolved on the hemisphere of the total refractometer while the shadow of the extraordinary ray will vary from being coincident with that of the ordinary ray to a certain maximum divergence from that position. This maximum difference in position, which may yield a greater or less angle than that of the ordinary ray, depending upon the optical character of the mineral, is the angle corresponding to the true value of the refractive index of the extraordinary ray. There will be two positions at 180 apart during the complete revolution of the section at which this value may be measured. If the plate was cut parallel to the basal plane of the crystal the two shadows would both be stationary during such a revolu- tion and the value of the angle for both rays can be measured in any position of the plate. 381. Wave-surface. Remembering that the velocity of light-propa- gation is always inversely proportional to the corresponding refractive index, it is obvious that the velocity of the ordinary ray for all directions in a uniaxial crystal must be the same, being uniformly proportional to . In other words, supposing light originates at a point within a uniaxial crystal the ordinary ray would travel out in all directions with uniform velocity and its wave-front would form a sphere. For the extraordinary ray, however, the velocity varies with the direction, being proportional to - in a horizontal direction and becoming sensibly equal to when nearly coincident with the direction of the vertical axis. The CO law of the varying change of velocity between these values, - and -, is given 256 PHYSICAL MINERALOGY by an ellipse whose axes (OC, OA, Figs. 554, 555) are respectively proportional to the above values. 554 555 c 00:OA=- The wave-front of the extraordinary ray is then a spheroid, or an ellipsoid of revolution whose axis coincides with the vertical crystallographic axis, that is, the optic axis. In the direction of the vertical axis it is obvious that the wave-fronts of the ordinary and extraordinary rays will coincide. Figures 556 and 557 represent vertical sections of the combined wave- 666 557 Negative crystal, Positive crystal, ox: e. surfaces for both "rays. Fig. 556 gives that for a negative crystal like calcite (e < e or e co, is also given; this measures the birefringence or strength of the double refraction. It may be remarked that in some species both + and varieties have been observed. Certain crystals of apophyllite are positive for one end of the spectrum and negative for the other, and consequently for some color between the two extremes it has no double refraction. The same is true for some other species (e.g., chabazite) of weak double refraction. NEGATIVE CRYSTALS Proustite. . 2 '979 Tourmaline '638 Corundum 768 Beryl 584 Vesuvianite "720 Nephelite 54? Apatite. . . 634 2711 1-486 1'620 1-760 1-578 1715 1-538 1-631 CO 0-268 0-172 0-018 0-008 0'006 0-005 0-004 0-003 POSITIVE CRYSTALS Rutile 2-616 2-903 6 CO 0'287 Cassiterite 1-997 2-093 0-096 Zircon 1-923 1-968 0'045 Brucite 1-559 1-580 0'021 Phenacite 1-654 1-670 0'016 Quartz 1-544 1-553 0'009 Apophyllite 1-535 1-533 0'002 Leucite 1-508 1-509 o-ooi * From tables by E. S. Larsen. CHARACTERS DEPENDING UPON LIGHT 259 Examination of Uniaxial Crystals in Polarized Light 384. Section Normal to the Axis in Parallel Polarized Light. Sup- pose a section of a uniaxial crystal to be cut perpendicular to the vertical crystallographic axis. It has already been shown that light passing through the crystal in this direction suffers no double refraction; consequently, such a section examined in parallel polarized light behaves as a section of an isotropic substance. If the nicols are crossed it appears dark, or extinguished, and re- mains so when revolved. 385. Section Parallel to the Axis. A section cut parallel to the verti- cal axis, as already explained,, has two directions of light- vibration, one parallel to this axis, that of the extraordinary ray, and the other at right angles to it, that of the ordinary ray. A ray of light falling upon such a section with perpendicular incidence is divided into the two rays, ordinary and extraor- dinary, which travel on in the same path through the crystal, but one of them retarded relatively to the other. When such a section is examined in polar- ized light with crossed nicols it will appear dark, or be extinguished, when its vibration directions lie parallel to the vibration directions of the nicols. Assume that the section abed, Fig. 560, lies with the direction of its vertical crystallographic axis parallel to P-P, which represents the vibration direction of the polarizer. The light entering the section under these conditions will be vibrating parallel to the vertical axis of the crystal and will therefore pass into the mineral wholly as the extraordinary ray, there being no vibration 560 < A I t d . ft c r- ( 'A possible in the direc- tion of the ordinary ray. The light will, therefore, leave the section with the same direction of vibration as when it entered and will be entirely lost by reflection in the an- alyzer. If the section is turned at an angle of 90, as aWd', Fig. 560, similar conditions prevail, although in this case the light will vibrate in the section as the ordinary ray. Therefore in such a section there will be four positions during its complete revolution on the stage of the polariscope or microscope when it will be extinguished. If the section stand obliquely, as abed in Fig. 561, it will appear light to the eye (and usually colored), for the vibrations parallel to P-P that have passed through the polarizer have upon resolution a component in the direc- tion of each of the vibration-planes of the section. Again, each of these components can be resolved along the direction of the vibration-plane of the upper nicol, A- A. Therefore, two rays will emerge from the analyzer, both having the same vibration-plane, but one more or less retarded with reference to the other, the amount of retardation increasing with the birefringence and the thickness of the section. In general, therefore, these rays will interfere, and if the thickness of the section is sufficient (and not too great) it will appear colored in white light and, supposing the thickness uniform, of the same color throughout. 260 PHYSICAL MINERALOGY 386. Parallel Extinction. When the vibration directions of a section coincide with those of the polarizer and analyzer, assuming them to be crossed, the section appears dark and it is said to be in the position of extinction. If a section extinguishes when its crystallographic axis or axial plane is -parallel to one of the planes of vibration of the nicols it is said to show parallel extinction. If, on the other hand, no such parallelism exists between the crystallographic directions and the directions of vibration in the mineral the section is said to show inclined extinction. In the case of uniaxial minerals, since the vibration directions always lie in some crystallographic axial plane, all sections of such minerals will show parallel extinction. 387. Determination of the Relative Character of the Extinction Direc- tions of a Given Uniaxial Mineral. The relative characters of the ex- tinction directions of a section of a uniaxial mineral are to be determined by the use of the quartz wedge or the sensitive tint as described in Art. 348. If the orientation of the section is known so that it can be told which of the directions of vibration belongs to the ordinary and which to the extraor- dinary ray the positive or negative character of the mineral can be determined. For instance, if the ordinary ray is proved to be the faster of the two (i.e., the X direction) it follows that its index is the smaller, i.e., co < e, and the mineral is positive. 388. Interference Colors of Uniaxial Minerals. Birefringence. The interference color of any section of a uniaxial mineral depends upon the fol- lowing: first upon the thickness of the section, second upon the strength of the double refraction of the mineral, i.e., its birefringence, this being measured by the difference between the indices of refraction of the two rays in the sec- tion, and third upon the crystallographic orientation of the section. A section cut parallel to the basal plane shows no double refraction and therefore cannot exhibit any interference color. The strength of the birefringence, the other conditions remaining uniform, increases as the inclination of the section to the basal plane increases. The highest birefringence of a given mineral is therefore shown by its prismatic sections. The following table * gives the thickness (in millimeters) of sections of a few uniaxial crystals which yield red of the first order: Birefringence Thickness in (03 e) or (e o>) Millimeters Rutile 0-287 0'0019 Calcite 0172 0'0032 Zircon 0'062 0*0089 Tourmaline 0'023 0'0240 Quartz 0'009 0*0612 Nephelite 0*004 01377 Leucite 0*001 0*5510 Again, as another example, it may be noted that with zircon (e co = 0*062), a thick- ness of about 0'009 mm. gives red of the first order; of 0'017 red of the second order: of 0*026 red of the third order. The methods ordinarily used to determine the birefringence of a section (not J_ c axis) of a uniaxial crystal, as also to fix the relative value of its two vibration-directions, have already been discussed, see Arts. 347 and 348. 389. Effects of Convergent Polarized Light upon Sections of Uniaxial Minerals. Uniaxial Interference Figures. When certain sections of uni- * See further, Rosenbusch (Mikr. Phys. Min., 1904, p. 292), from whom these are taken. CHARACTERS DEPENDING UPON LIGHT 261 axial minerals are observed in convergent polarized light they show what are known as interference figures. A symmetrical interference figure is obtained in uniaxial minerals by allowing converging polarized light to pass through a basal section of the crystal. Parallel polarized light entering such a section would suffer no double refraction and consequently give no interference. To convert the parallel polarized light that comes from the polarizer into con- vergent light a lens is placed between the polarizer and the section. Under these conditions a sharply converging cone of light rays enters the section. Another lens is placed above the section to change these oblique rays back again into a parallel postion. Such an instrument is known as a conoscope and may be obtained by placing a pair of lenses between the polarizer and analyzer of a polariscope, or, in case the polarizing microscope is used, the small converging lens that lies above the polarizer is swung into position by a lever and at the same time a small lens known as the Bertrand lens is introduced into the microscope tube. Under such conditions the light entering the section is composed of a 562 converging system of rays polarized and vibrating in the plane P-P, Fig. 562. Let B-B (Fig. 562, A) be a vertical cross section of the mineral section along the line B-B, Fig. 562, B. Consider any ray, as a, entering the section. Since the ray enters the section obliquely it will be doubly a refracted into the rays o and e. 563 ( i B oe e o B ' V \ I The mineral being taken as calcite the extraordinary ray (calcite being negative) will have the greater velocity and be least refracted. As the light enters the section in the form of a cone the traces of the two rays as they emerge from the section will be circles, Fig. 562, B. Now consider in a similar case the action of the two rays a and b or a' and V (Fig. 563) upon each other. Ray a on entering the section is doubly refracted and polarized into the rays e and o which are considered as emerging from the section at the points e and r. Ray b also on entering the section is doubly refracted and polarized. Suppose the extraordinary ray derived from b emerges from the section at the same point as the ordinary ray derived from a, that is at r. Since it travels with a greater velocity the extraordinary ray emerging at this point will have advanced in its phase over that of the ordinary ray. In that case they would be in a condition to interfere with each other except that they are vibrating in planes perpendicular to each other and so cannot. The two rays travel on, vibrating in planes at right angles to each other and maintaining 262 PHYSICAL MINERALOGY this difference in phase until they reach the upper 'nicol; there they are each resolved into rays vibrating in the plane A-A, Fig. 562, B, and are now in condition to interfere with each other. Let it be assumed that the conditions are right for the extraordinary ray to emerge from the section just one wave- length ahead of the ordinary ray. Their components in the upper nicol will have opposite phases and therefore compensate each other, see Art. 335. If the section is viewed in a monochromatic light (for instance, sodium light) this interference will result in a black point. But as these rays are converging in the form of a cone they will make, when they strike the section, a circular trace upon its surface and their interference will result in a dark ring. Going out from the center of the section there will be a succession of these rings corresponding to the interference of waves 1, 2, 3, 4, 5, etc., wave-lengths apart. As the distance from the center of the section is increased, the paths of the refracted rays in the section are lengthened and the points of inter- ference are brought closer together. This will cause the interference rings to lie nearer together as the distance from the center of the figure increases. Fig. 564 is a top view of the section without taking into consideration the effects of the upper nicol. Let the two circles represent the traces of the emergence of the two rays e and o into which one incident conical ray is divided ; e, being the least refracted (for calcite), will be the inner one. The plane of vibration of e is always parallel to some plane passing through the vertical axis of the crystal, therefore the trace of its plane of vibration upon the surface of the section will always be in a radial direction. The plane of vibration of o is at right angles to that of the extraordinary ray and parallel to the horizontal axes of the crystal, therefore the trace of its plane of vibra- tion upon the surface of the section will always be in a tangential direction, see Fig. 564. Along the line P-P, Fig. 564, only light vibrating in a radial plane or that of the extraordinary ray can come through the section, since the light entering the section cannot be resolved into the vibrations of the ordinary ray. The intensity and direction of vibration of the light that emerges from the section along the line P-P is represented by the double arrow on that line. Along the line A-A, since the light entering the section is still vibrating in the plane P-P, all the light passing through the section must vibrate as the ordinary ray. It is evident, therefore, that along these two directions, P-P and A-A the plane of vibration of the light is not changed by passage through the section and consequently such light will be completely absorbed in the CHARACTERS DEPENDING UPON LIGHT 263 upper nicol. In this way dark brushes will be formed along the lines P-P and A- A. A dark spot will also be formed in the center of the field because any light entering the section at this point must enter in the direction of the optic axis and therefore will not be doubly refracted and consequently will also be absorbed in the analyzer. Now consider point B, Fig. 564, which lies 45 away from P and A. Here the directions of vibration of e and o would be equally inclined to the planes of vibration of the polariscope, A-A and P-P. Light striking the section at B would be vibrating in the plane P-P but by resolution a component vibrating in the direction B-B would come through the section as the ray e; in the same manner a component vibrating in a direction at right angles to B-B would emerge as o. The intensities and directions of vibration of these two rays at this point are represented by the double arrows. When these rays meet the analyzer above they would again each be resolved and their components which vibrate in the plane A-A would emerge from the analyzer. In this way it is seen that, except at the special points where complete interference takes place, light will result in the interference figure at all points away from the center of the figure and from the lines P-P and A-A. From the consideration of Fig. 564 it is evident that the greatest amount of light will come through the section at the 45 points, such as B. When viewed in monochromatic light, therefore, the interference figure consists of a series of concentric dark and light rings crossed by a vertical and a horizontal dark brush in- tersecting in the center of the field of the microscope, like Fig. 565. If a basal section of a uniaxial mineral while in the conoscope is viewed in daylight colored rings will take the place of the light and dark rings observed in the monochro- matic light. The change will be like that Uniaxial Interference Figure shown by the quartz wedge in the similar case described in Art. 343. Where the first few dark rings near the center of the figure were formed by the interference of rays having the wave-length of sodium, light colored rings will result in the daylight illumination. These rings will be composed of all the components of white light with the yellow of sodium subtracted. The other colors are obtaind in a similar manner by the elimination though interference of some particular wave-length of light. While the interference figure when illuminated in the monochromatic light showed a large number of distinct black rings in day- light, the corresponding colored rings are limited in number and their colors, gradually becoming fainter as the distance from the center of the figure increases, finally merge into the white of the higher order. This is due to the overlapping of the interference rings of the various colors in the same manner as observed in the quartz wedge, see Art. 343. The interference figure viewed in daylight will of course retain the black cross and center since these are due to the cutting out of all the light by the analyzer and are not the result of interference. The distance of each successive ring from the center of the interference 264 PHYSICAL MINERALOGY figure obviously depends upon the birefringence, or the difference between the refractive indices, for the ordinary and extraordinary ray, and also upon the thickness of the plate. The stronger the double refraction and the thicker the plate, the smaller the angle of the light-cone which will give a certain amount of retardation, or, in other words, the nearer the circles will be to the center. Further, for the same section the circles will be nearer for blue light than for red, because of their shorter wave-length. When the plate is either quite thin or quite thick only the black brushes will be distinctly seen. 390. Determination of the Positive or Negative Character of the Bire- fringence of a Uniaxial Mineral from Its Interference Figure. Use of the Mica Plate. For the identification of a uniaxial mineral it is naturally important to determine whether the character of its birefringence is positive or negative. This can usually be best accomplished by tests made upon its interference figure. One of the common ways of making this 'test is by the use of a sheet of muscovite mica, cleaved so thin that, of the two rays of light passing through it, one has gained one quarter of a wave-length in phase over the other. The mica is usually mounted between long and narrow glass plates and is known as the one quarter wave-length mica plate. It is commonly marked 1 /4M with an arrow indicating the Z optical direction. In testing an interference figure by means of the mica plate the latter is inserted somewhere between the polarizer and analyzer (in the microscope commonly through the slot just above the objective) and is so orientated that the Z direction makes an angle of 45 with the planes of vibra- tion of the nicols. In Fig. 566 let P-P rep- resent the plane of vibra- tion of the polarizer and A-A the plane of vibration of the analyzer of a conoscope. Let be the point of emer- gence of the optic axis of a positive uniaxial mineral. Suppose a single conical ray of light enters the section. It is broken up in the mineral into two rays, o and e, which emerge from the section along the arcs of the circles shown in Fig. 566. The trace of the ordinary ray, o, will be within that of the extraordinary ray, e, because in a positive mineral the o ray travels the faster and is less refracted. The directions of vibration of these two rays at the 45 points R and R' are represented by the double-headed arrows. When these rays reach the analyzer they will be resolved into components vibrating parallel to A-A . There are an infinite number of such rays entering and pass- ing through the mineral section with varying angles of inclination and there- fore varying lengths of path. At some certain distance out from the center two rays will emerge on the same circle with a difference of phase of one CHARACTERS DEPENDING UPON LIGHT 265 whole wave-length and when resolved in the upper nicol into rays vibrating in the same plane will interfere with each other and produce the first dark ring of the interference figure as it is viewed in monochromatic light. If the mica plate is introduced above the section a change in the inter- ference figure is noted. The optical character of the mica cannot be fully explained at this point. It is sufficient for present purposes to know that it is a doubly refracting mineral which breaks light up into two rays which are polarized in planes at right angles to each other and which, traveling with different velocities through the mica, will emerge from it with different phases. As stated above, the mica plate is cleaved to the requisite thickness so that the two rays emerge from it with a difference of phase of one quarter of a wave- length. Consider what takes place when such a plate is introduced above the section represented in Fig. 566 in such a position that its vibration direction Z is parallel to the direction R-O-R of the figure. Consider what takes place at the points R. There the vibration direction of the e ray coincides with the vibration direction Z of the mica plate. These vibration directions in each case are those of the rays traveling with the smaller velocity. On the other hand, at the same point the vibration direction of the o ray in the mineral coincides with the vibration direction X in the plate, both of these being of the rays with the greater velocity. So at this point the effect of the mica plate is to increase the difference of phase between o and e and to produce the same result as if the mineral section had been thickened. Consequently the interference rings along the line R-O-R are increased in number and drawn toward the center of the figure. At the points R' the opposite is true. The vibration direction of e coincides now with that of X in the mica plate; the direction of least velocity in the mineral with that of the greatest in the mica. Also the vibration direction of o coincides with that of Z\ that of the greater velocity in the mineral with the less velocity in the mica. So at this point the mica will decrease the difference in phase between o and e and produce the effect of thinning the section and so spreading the interference rings farther apart along the line R'-O-R'. In quadrants 2 and 4, therefore, the rings will be drawn nearer the center, while in quadrants 1 and 3 they will be spread farther apart. Another effect caused by the introduction of the mica plate is even more pronounced. In quadrants 1 and 3, in the case illustrated in Fig. 566, black dots will appear near the center of the figure. In the interference figure, before the introduction of the mica plate, there were points in quadrants 1 and 3 at short distances from the center, 0, where the two rays, o and e, emerged from the section with a difference of phase of one quarter wave-length. Under these conditions no interference could take place and these spots were light. The effect of the mica plate in these two quadrants is to everywhere reduce the birefringence due to the mineral by one quarter of a wave-length. Therefore at these two points the difference of phase caused by the birefring- ence of the mineral is annulled by the mica plate and consequently at these points interference will result and black dots appear. The mica plate produces still other effects. The brushes which were dark in the interference figure be- come light. Light coming from the crystal section along the lines of the brushes is vibrating only in the vibration direction of the polarizer and ordinarily is wholly cut out by the analyzer above. But with the mica plate intervening this light is broken up in the mica into two rays which vibrate in the vibration planes of the mica and as these are inclined to the plane of the analyzer a portion of the light will come through to the eye. As the light coming from 266 PHYSICAL MINERALOGY the section along the lines of the brushes had only a single velocity (was entirely either the ordinary or extraordinary ray) there are only two rays emerging from the mica plate along these directions and their difference of phase is one quarter of a wave-length. Under these conditions there can be no interference and white brushes result. In the same way the dark center of the interference figure becomes light. 667 Determination of Optical Character with Mica Plate Fig. 567, A, is a diagrammatic representation of the interference figure of a positive mineral as affected by the insertion of the mica plate, the direction of the arrow indicating the direction Z of the mica, i.e., the direction of vibra- tion of the ray having the smaller velocity. In the case of a negative mineral the conditions as described above will be completely reversed. Fig. 567, B, represents the appearance of an interference figure of a negative mineral when the mica plate is used. Therefore, to determine the optical character of a uniaxial mineral from its interference figure insert a mica plate above the section with its Z direction making 45 with the vibration planes of the nicols. Then, if this direction Z is at right angles to a line joining the two black dots that appear near the cen- ter of the figure (i.e., the two lines form a plus sign), the mineral is positive; if, on the other hand, these two directions coincide (form together a minus sign) the mineral is negative. Use of the Sensitive Tint. The sensitive tint, see Art. 344, is used to deter- mine the positive or negative character of a uniaxial mineral from its inter- ference figure when the mineral section is so thin, or the mineral possesses such a low birefringence, as to show in the figure only a black cross without any rings. Under such conditions the mica plate would not give a decisive test. The sensitive tint is usually so mounted that its longer direction coin- cides with the direction of the vibration of the faster ray, i.e., the direction X. The sensitive tint is introduced somewhere between the polarizer and ana- lyzer in such a position that its vibration directions are at 45 with the planes of vibration of the nicols. Let it be assumed that we have the interference figure from a positive mineral, such as is represented in Fig. 566. If the sensitive tint is introduced in such a position that its X direction is parallel to the line R-O-R the X direction of the sensitive tint will be parallel to the direction of vibration of the e ray in the mineral. Since the mineral is positive the e ray will have the smaller velocity and therefore in quadrants 2 and 4 the CHARACTERS DEPENDING UPON LIGHT 267 optical orientation of the mineral and the sensitive tint will be opposed to each other. The sensitive tint alone would produce an interference color of red of the first order. But if the effect of the birefringence of the mineral is such as to subtract from the birefringence of the sensitive tint the color will change to yellow. Consequently in these quadrants yellow spots will appear near the center of the field at the points where the effect of the mineral has been sufficient to lower the interference color to that extent. In the other quadrants, 1 and 3, the faster and slower rays of the mineral and sensitive tint coincide in their directions and the effect of the two substances is an addi- tive one. Con- sequently in these two 568 quadrants the color will rise to blue. In making the above test with the sensitive tint it is convenient to follow the rule that if the direction X of the sensitive tint crosses a line uniting the two blue dots (makes a plus sign) the mineral is positive ; if, on the other hand, these two directions coincide ( make to- gether a minus sign) the mineral is negative 391. Interference Figures from Inclined Sections of Uniaxial Minerals. 569 Determination of Optical Character with Sensitive Tint These conditions are illustrated Eccentric Uniaxial Interference Figures 268 PHYSICAL MINERALOGY 570 An interference figure obtained from such an inclined section will of course be eccentric to the microscope field. If the section is inclined only a little to the basal plane, the center of the figure (i.e., the point of emergence of the optic axis) will still be within the field of vision and will move in a circle about the center of the field wtien the section is revolved upon the microscope stage. Fig. 569, A, shows the successive positions of such an interference figure during revolution. If the section is more sharply inclined the center of the inter- ference figure may be quite outside the field. As the section is turned on the stage the four arms of the interference cross will traverse the field in succession. They will move across the field as straight bars and, provided the section has been cut not too highly inclined to the optic axis, will move across the field parallel to the cross-hairs of the microscope. This fact is of importance in order to distinguish such a uniaxial interference figure from certain biaxial figures. The latter will often show similar bars which, however, will always curve as they cross- the field of the microscope. If the first of these bars in the uniaxial figure moves from left to right across the field, the second will move from the top to the bottom, the third from right to left and the last from the bottom to the top, etc. Fig. 569, B, shows the different position of such a figure during one quarter of a revolution. The positive or negative character of the mineral can usually be deter- mined from an eccentric figure if care is taken to make certain . which quadrant is visible when the test is made. For instance, in Fig. 570 is shown how the test is made with the sensitive tint upon the eccentric interference figure of a positive mineral. In examining unorientated sections of a mineral, such as the random section found in a rock section or the small fragments of a mineral placed upon a glass slide, it is advis- able always to hunt for that section that gives the lowest interference color. The amount of birefringence shown in various sections of a uniaxial mineral decreases as the section approaches the orientation of the basal plane. Consequently that section showing the lowest interference color will yield the most nearly symmetrical interference figure. 392. Interference Figure from a Prismatic Section of a Uniaxial Mineral. When a prismatic section of a uniaxial mineral is examined for an interference figure an indefinite result is obtained. The figure is analo- gous to one obtained in the case of biaxial crystals. The reasons for this resemblance will be pointed out in a later article. The two types of figures cannot be in this case easily differentiated. Two dark and usually indefinite hyperbolas approach each other as the section is turned on the microscope stage, form an indistinct cross, and rapidly separate. These bars differ from those obtained in a biaxial interference figure in that they rapidly fade out as they move away from the crossed position. This type of interference figure can be obtained easily from the quartz wedge. wu 393: Absor P tion Phenomena of Uniaxial Crystals. Dichroism. When light enters colored minerals as rays of white light, i.e., containing vibra- Sensitive Tint with Eccentric Interference Figure CHARACTERS DEPENDING UPON LIGHT 269 P 1 Vertical Axis ^ tions of all wave-lengths from that of violet light at one end of the spectrum to that of red light at the other, certain wave-lengths will be absorbed during the passage of the light through the mineral, so that the light, as it emerges, has a definite color. It happens in certain deeply colored minerals that the amount and character of this absorption depends upon the direction of the light vibration. For instance in the case of uniaxial minerals, the ordinary and extraordinary rays may emerge from the section with distinctly different colors. Take, for instance, a prismatic section of a brown colored tourmaline and observe it in plane polarized light without the use of the upper nicol. As the section is revolved upon the stage of the polariscope the color may change from a dark brown to a light yellow-brown. The greatest difference in the color occurs at positions 90 apart and when the crystallographic directions of the section, i.e., the vertical crystallographic axis and the trace of the plane of the horizontal axes, are either parallel or perpendicular to the vibration plane of the polarizer. In other words, these extremes of color occur when the directions of the vibration of the ordinary and extraordinary rays in the section are parallel or perpendicular to the vibration plane of the light entering the section. In Fig. 571, A, let P-P represent the vibration direction of the light entering the section. The mineral section is so placed that the direction of the vertical crystal axis is perpendicular to P-P. The light on entering the section will therefore vibrate in the plane of the horizontal axes or as the ordinary ray, o. In this position the tourmaline section is dark colored and con- sequently it is seen that light vibrating in the mineral as the ordinary ray is largely absorbed. Now turn the section through a 90 angle to the position shown in Fig. 571, B. In this position the light must vibrate in the section wholly as the extraordinary ray, e, and the color is a light yellow-brown. There- fore the extraordinary ray is only slightly absorbed. This difference in the absorption or the color of the two rays is known as dichroism. Either the ordinary or the extraordinary ray may be the most absorbed and the two cases are expressed as either o > e (o> > e) or e > o (e > co). In uniaxial minerals dichroism is to be best observed in prismatic sections where it attains its full intensity. Basal sections show no dichroism, since light passing through the section parallel to the optic axis must all vibrate in the horizontal axial plane and belong wholly to the ordinary ray. An instrument called a dichroscope, contrived by Haidinger, is sometimes used for examining this property of crystals. An oblong rhombohedron of Iceland spar is placed in a metallic cylindrical case, having a convex lens at one end, and a square hole at the other. On looking through it, the square hole appears double; one image belongs to the ordinary and the other to the extraordinary ray. When a pleochroic crystal is examined with it by transmitted light, on revolving it the two squares, at intervals of 90 in the revo- lution, have different colors, corresponding to the vibration-planes of the ordinary and extraordinary ray in calcite. Since the two images are situated side by side, a very slight difference of color is perceptible. A similar device is sometimes used as an ocular in the microscope. 1 i > e \ Light fellow 270 PHYSICAL MINERALOGY 394. Circular Polarization. The subject 9f elliptically polarized light and circular polarization has already been briefly alluded to in Art. 350. This phenomenon is most dis- tinctly observed among minerals in the case of crystals belonging to the rhombohedral- trapezohedral class, that is, quartz and cinnabar. It has been explained that a section of an ordinary uniaxial crystal cut normal to the vertical (optic) axis appears dark in parallel polarized light for every position between crossed nicols. If, however, a similar section of quartz, say 1 mm. in thickness, be examined under these conditions, it appears dark in monochromatic light only, and that not until the analyzer has been rotated so that its vibration-plane makes for sodium light an angle of 24 with that of the polarizer. In other words, this quartz section has rotated the plane of vibration some 24, and here either to the right or to the left, looking in the direction of the light. The amount of this rotation increases with the thickness of the section, and, as the wave-length of the light diminishes (for red this angle of rotation for a section of 1 mm. is about 19, for blue 32). The direction of the rotation is to the right or left, as denned above according as the crystal is crystallographically right-handed or left-handed (p. 113). If the same section of quartz (cut perpendicular to the axis) be viewed between crossed nicols in converging polarized light, it is found that the interference-figure differs from that of an ordinary uniaxial crystal. The central portion of the black cross has disappeared, and instead the space within the inner ring is brilliantly colored.* Furthermore, when the analyzing nicol is revolved, this color changes from blue to yellow to red, and it is found that in some cases this change is produced by revolving the nicol to the right, and in other cases to the left; the first is true with right-handed crystals, and the second with left-handed. If sections of a right-handed and left-handed crystal are placed together in the polariscope, the center of the interference-figure is occupied with a four-rayed spiral curve, called, from the discoverer, Airy's spiral. Twins of quartz crystals are not uncommon, consisting of the combination of right- and left-handed individuals (according to the Brazil law) which show these spirals of Airy. With cinnabar similar phenomena are observed. Twins of this species also not infrequently show Airy's spirals in the polariscope. 395. Summary of the Optical Characters of Uniaxial Crystals. All sections of uniaxial crystals show double refraction except those that are cut parallel to the basal plane. All doubly refracting sections show parallel ex- tinction. When viewed in convergent polarized light with crossed nicols all sections show a characteristic uniaxial interference figure except those that lie in the prism zone of the crystal or that are only slightly inclined to that zone. All doubly refracting sections have two refractive indices correspond- ing to the two extinction directions : one of these is always co and the other has a value (c') ranging from co to e, dependent on the inclination of the section to the optic axis. Dark colored minerals may show dichroism. Tetragonal and hexagonal substances cannot be distinguished from each other by optical tests. They may be at times told apart by characteristic cross sections of their crystals. C. BIAXIAL CRYSTALS General Optical Relations The crystals of the remaining systems, i.e., the orthorhombic, monoclinic, and triclinic belong optically to what is known as the Biaxial Group. 396. The Behavior of Light in Biaxial Crystals. In biaxial crystals there are three especially important directions at right angles to each other which are designated as X, Y, and Z (also a, fo, and c). These three direc- tions are sometimes spoken of as axes of elasticity in reference to certain assumed differences in the ether along them. The nature of these three direc- tions is as follows. Light which results from vibrations parallel to X (axis of greatest elasticity) is propagated with the maximum velocity; that from vibra- * Very thin sections of quartz, however, show (e.g., with the microscope) the dark cross of an ordinary uniaxial crystal. CHARACTERS DEPENDING UPON LIGHT 271 572 tions parallel to Z (axis of least elasticity) with minimum velocity; and that from- vibrations parallel to Y with an intermediate velocity. It is to be emphasized that these directions, X, Y, and Z refer to directions of vibration and not to directions of propagation. Corresponding to the maximum inter- mediate and minimum light velocities are three principle indices of refraction designated respectively as a, ft and y. Of these a, belonging to light with the maximum velocity, will have the least value and 7 belonging to light with the minimum velocity, will have the greatest value. The value of B will be inter- mediate between the other two, sometimes being nearer to a and at other times being nearer to 7; it is not the arithmetical mean between them. The various methods of deter- mining the values of these three principal indices of refraction will be consid- ered in a later article. In studying the prop- agation of light within a biaxial crystal let it be assumed that Fig. 572 represents a rectangular parallelopiped in which the front to back axis is the direction X, the left to right axis is Y, and the vertical axis is Z. In connection with the figure and those which follow it is helpful to make use of a model (a pasteboard box would answer) orientated so that its longer edge runs from front to back, its mean edge from left to right and its shortest edge vertical, corresponding to the X, Y, and Z directions of the figure. In the development of the figures that follow it has been assumed that the three principle indices of refraction are a = 1.5, (3 = 1.6, 7 = 2.5, a difference between a and 7 far exceeding anything observed in actual crystals. In general, this difference does not exceed 0.1; hence it is necessary to greatly exaggerate the actual values in order that the phenomena may be distinctly shown by diagrams drawn on a small scale. In the discussion that follows it will be assumed that light originates at the center of a crystal, 0, Fig. 572, and the endeavor will be made to determine the character of the rays which radiate from in all directions. The simplest directions, and the ones which in reality are the most important, are those that lie in the axial planes of the figure, XOY, YOZ, and XOZ. These will be considered first. Consider the plane of the X and Y directions, Fig. 572. Light will radiate from toward X and Y and in all intermediate directions with vibrations parallel to Z and hence traveling with a uniform and at the same time mini- mum velocity, 1/7. The distance such light will travel in a given moment of time may be plotted by drawing a circle about with the radius, 1/7, Fig. 573. In the direction OX there must also travel a second polarized ray result- 272 PHYSICAL MINERALOGY 573 ing from vibrations parallel to OF, hence traveling with mean velocity 1/0. Likewise in the direction OF there will be a ray resulting from vibrations parallel to OX, hence travel- ing with the maximum velocity, I/a. In all direc- tions intermediate between X and F the light velocities will be proportional to the radii of an ellipse having 1/0 and I/ a respectively as its semi-minor and semi-major diameters, Fig. 573. In the plane of the X and F directions, therefore, in a given moment of time light will radiate from the center as ordinary and extraordinary rays, the wave fronts being represented by a circle within an ellipse. Consider next the plane of the F and Z directions, Fig. 572. Light will radiate from toward F and Z and in all intermediate directions resulting from vibrations parallel to OX. It will therefore travel with uniform and the maximum velocity, I/a. The distance traveled in a given moment of time may be plotted by drawing a circle about with the radius I/a, Fig. 574. Likewise there will travel in the direction OF a second ray resulting from vibrations parallel to OZ, hence mov- ing with the minimum velocity, l/y. Also in the direction OZ there will be a ray resulting from vibrations parallel to OF with the velocity 1/0. In directions intermediate between F and Z the light velocities will be proportional to the radii of an ellipse having l/y and 1/0 respectively as its semi- minor and semi-major diameters, Fig. 574. In the plane of the F and Z directions, therefore, in a given moment of time, light will radiate from the center as ordinary and extraordinary rays, the wave fronts being represented by an ellipse within a circle. CHARACTERS DEPENDING UPON LIGHT 273 The last and most important plane to be considered is that of the X and Z directions, Fig. 572. Light will radiate from toward X and Z and all in- termediate directions with vibrations parallel to OF, hence traveling with a uniform and intermediate veloc- ity, 1/jS. The distance traveled in a given moment of time is represented in Fig. 575 by the circle with the radius 1/0. There will likewise travel in the direction OZ a ray resulting from vibrations parallel to OX, hence moving with the max- imum velocity, I/a. Also a ray will travel in the direction OX with vibrations parallel to OZ, hence having the minimum velocity, l/y. In intermediate positions the light velocity will be proportional to the radii of an ellipse with I/a and l/y respectively as its semi-major and semi-minor diameters, Fig. 575. In the plane of the X and Z directions, therefore, in a given moment of time, light will radiate from the center as or- dinary and extraordinary rays, the wave fronts represented, by a circle intersecting an ellipse. It is to be noted that in this last plane there are four points where the two wave fronts coincide. In other words, light traveling along the radial lines connecting these points will be moving with uniform velocity and consequently along these directions there will be no double refraction. These directions are known as the optic axes of the crystal and since there are two of them the optical group is spoken of as biaxial. The character of these optic axes will be more fully developed in a later article. In the above paragraphs the wave fronts for light moving in the three prin- cipal optical planes of the crystal have been discussed. Fig. 576 represents the wave fronts in these three planes as they appear when bounding one octant. The complete wave Ellipse 274 PHYSICAL MINERALOGY surfaces for light propagated in all directions consist of warped figures which conform to the circular or elliptical wave fronts already described in the three principal planes and have intermediate positions elsewhere. The only satisfactory way to represent these complete surfaces is by means of a model. 397. Biaxial Indicatrix. It is found further that the optical structure of a biaxial crystal can be represented by an ellipsoid, .known as the indicatrix, having as its axes three lines which are at right angles to each other and proportional in length to the indices a, /3, 7. This is analogous to the similar figure for uniaxial crystals described in Art. 382. This ellipsoid, whose axes represent in magnitude the three principal refractive indices, a /3, 7 (where a < |8 < 7), (see Fig. 577), not only exhibits the character of the optical symmetry, but from it may be derived the direction, velocity and plane of vibration of any light ray traversing the crystal. In general it may be stated that the character of the two light rays which result from a single incident, ray may be derived from a study of that elliptical section of the indicatrix which is normal to the incident ray. If this section happens to be one of the three principal sections of the indicatrix, A BAB, ACAC, or BCBC, Fig. 577, its major, and minor diameters give the directions of vibration and their semi-lengths the indices of refrac- tion of the two rays. If the incident ray has some direction different from the directions of the three axes of the indicatrix ellipsoid the derivation of the character of the two refracted rays is not as simple. Let Fig. 578 represent such an elliptical section normal to the inclined ray L-L. In this case the major and minor diameters R-O-R and r-0-r of the elliptical section lie in the vibration L planes of the two rays but the directions of vibration of the latter will be somewhat inclined to the elliptical section. These directions of vibration may be obtained by erecting normals to the surface of the indicatrix at the points R and r where the major and minor diameters of the elliptical section meet that surf ace. These normals RN and rn, when extended to the line of the incident ray L-L, yield the directions of vibration and the refractive indices of the two refracted rays. Their direc- tions of transmission (the lines OS and OT) will be perpendicular to these normals and since neither of the latter lie in the elliptical section both rays will be refracted and behave as extraordinary rays. There are two special sections of the indicatrix that require notice. The Biaxial Indicatrix CHARACTERS DEPENDING UPON LIGHT 275 line B-O-B (Fig. 577) is longer than the line A-O-A but shorter than the line C-O-C. Obviously, in some position intermediate between A-O-A and C-O-C there will be a diameter of the ellipse AC AC which will be equal in length to B-O-B. There are two such lines, as S-O-S and S'-O-S' in Fig. 577. The major and minor diameters of these sections of the indicatrix, BSBS and BS'BS', are equal and the sections therefore become circles. Con- sequently light passing through a section of a crystal cut parallel to either of these circular sections of its indicatrix will have a uniform velocity and may vibrate in any transverse direction. In other words, there will be no double refraction along the lines normal to these two sections. These lines consti- tute what are known as the primary optic axes of the crystal; see further in Art. 398. The major and minor diameters of any section of the indicatrix yield the traces upon that section of the planes of vibrations of the two rays into which the ray normal to the section is refracted. In other words, the major and minor diameters of the elliptical section of the indicatrix give the directions of extinc- tion of a crystal section having this optical orientation. Further, these extinction directions bisect the angles made by the traces upon the section of two planes, each of which includes the pole of the section and one of the two optic axes. This may be demonstrated by aid of Fig. 579 which represents a general elliptical section of an indicatrix. A- A and B-B are the major and minor diameters of the ellipse and so represent the extinction directions of the mineral section. C-C and C'-C' represent the intersections of the two circu- lar sections of the indicatrix with this elliptical section. As these lines are diameters of equal circles they must be equal in length and it therefore follows from the geometrical nature of an ellipse that the angles AOC and AOC' are equal. Let the line P-P represent the intersection with this elliptical section of a plane in which lie the normal to the section and one of the optic axes. Since this plane includes an optic axis it must be perpendicular to the circular section of the indicatrix of which the line C'-C' is a diameter. Also since this plane includes the normal to the elliptical section under consid- eration it must be at right angles to the latter plane. Under these conditions it is obvious that the lines P-P and C'-C' in Fig. 579 must be at right angles to each other. In the same way it can be proved that the lines P'-P' and C-C are also at right angles to each other. Since the angles AOC and AOC' are equal and the angles POC' and P'OC are also equal it follows that the angles A OP* and A OP' are likewise equal. In other words the lines A-A and B-B representing the directions of extinction of the section bisect the angles made by the traces upon the section of the two planes which respectively pass through each optic axis and the normal to the section. This fact will be made use of later, see Art. 407, in explaining the characters of the biaxial interference figure. 579 276 PHYSICAL MINERALOGY 580 Primary and Secondary Optic Axes. It has already been stated (Art. 397) that there are two directions, namely, those normal to the circular cross sections of the indicatrix (SS, S'S', Fig. 577) in which all light is propagated with uniform velocity. Hence in these directions there can be no double refraction within a crystal; nor is there when the ray emerges. These two directions bear so close an analogy to the optic axes of a uniaxial crystal that they are also called optic axes, and the crystals here considered are hence named biaxial. In Fig. 575, which represents a cross section of the wave-surfaces in the plane of the X and Z directions, these optic axes have the direction SS, S'S' normal to the tangent planes tt, t't', and the direction of the external wave is given by the normal Str (Fig. 580). Properly speaking the directions mentioned are those of the primary optic axes, for there are also two other somewhat analogous directions, PP, P'P', of Fig. 575, called for sake of distinction the secondary optic axes. The properties of the latter directions are obvious from the following considerations. In the section of the wave-surface shown in Fig. 575 (also enlarged, in Fig. 580), corresponding to the axial plane XZ, it is seen that the circle with radius - intersects the ellipse whose major and minor axes are - and - in the four points P, P, P f , P'. Corresponding to these directions the velocity of propa- gation is obviously the same* for both rays. Hence within the crystal these rays travel together without double refraction. Since, however, there is no common wave-front for these two rays (for the tangent for one ray is repre- sented by mm and for the other by nn, Fig. 580) they do suffer double refrac- tion on emerging; in fact, two external light-waves are formed whose directions are given by the normals Pju and Pv. These directions, PP, P'P', therefore, have a relatively minor interest, and whenever, in the pages following, optic axes are spoken of, they are always the primary optic axes, that is, those having the directions SS, S'S' (Fig. 575), or OS, Fig. 580. In practice, however, as remarked in the next article, the angular variation between the two sets of axes is usually very small, perhaps 1 or less. 399. Interior and Exterior Conical Refraction. The tangent plane to the wave-surface drawn normal to the line OS through the point S (Fig. 580) may be shown to meet it in a small circle on whose circumference lie the points S and T. This circle is the base .of the interior cone of rays SOT, whose remarkable properties will be briefly hinted at. If a section of a biaxial crystal be cut with its faces normal to OS, those parallel rays belonging to a cylinder having this circle as its base, incident upon it from without, will be propagated within as the cone SOT. Conversely, rays from within corresponding in position to the surface of this cone will emerge parallel and form a circular cylinder. This phenomenon is called interior conical refraction. On the other hand, if a section be cut with its faces normal to OP, those rays having the direction of the surface of a cone formed by perpendiculars to mm and nn will be propa- gated within parallel to OP, and emerging on the other surface form without a similar cone on the other side. This phenomenon is called exterior conical refraction. In the various figures given (573-580) the relations are much exaggerated for the sake CHARACTERS DEPENDING UPON LIGHT 277 of clearness; in practice the relatively small difference between the indices of refraction a and 7 makes this cone of small angular size, rarely over 2. 400. Optic Axial Angle. Bisectrices. Positive and Negative Biaxial Crystals. The optic axes always lie in the plane of the X and Z optical directions; this plane is called the optic axial plane (or, briefly, ax. pi.). It is obvious from a consideration of the indicatrix ellipsoid that the position of its circular sections and consequently of the optic axes normal to them, will vary with a variation in the relative values of the indices of refraction. As already stated the index is not an arithmetical mean between a and 7 but may at times be nearer to a than to 7 or the reverse. As these relations change, the shape of the indicatrix and the position of its circular sections and the angle between the optic axes will also change. The mathematical relations between the optic axial angle and the principle refractive indices are given in the next article. From the above it is obvious that for certain relative values of the refractive indices, the optic angle must be 90.* Such a case, however, is rarely observed and when it occurs it is true for light of a certain color f (wave-length) only and not for others. The X and Z optical directions bisect the angles between the optic axes and are therefore known as bisectrices. The one that bisects the acute axial angle is called the acute bisectrix (or Bx a ) while the one bisecting the obtuse angle is the obtuse bisectrix (or Bx ) . If the word bisectrix is used alone with- out special qualification it is always to be understood as referring to the acute bisectrix. Either X or Z may be the acute bisectrix. If X is the acute bisectrix the substance is said to be optically negative, while if Z is the acute bisectrix it is optically positive. Roughly expressed, the optic axes will lie nearer to Z than to X that is, Z will be the bisectrix when the value of the intermediate index, /3, is nearer to that of a than to that of 7. It is obvious (cf . Fig. 575) that in this case, as the angle diminishes and becomes nearly equal to zero, the form of the ellip- soid then approaches that of the prolate spheroid of the positive uniaxial crystal as its limit (Fig. 557, p. 256) ; this shows the appropriateness of the + sign here used. On the other hand, the optic axes will lie nearer to X than to Z that is, X will be the bisectrix if the value of the mean index is nearer to that of 7 than to that of a. Such a crystal, for which Bx a = X, is called optically negative. In this case the smaller the angle the more the ellipsoid approaches the oblate spheroid of the negative uniaxial crystal (Fig. 556, p. 256). The following are a few examples of positive and negative biaxial crystals: Positive (+). Negative (-). Sulphur. Aragonite. Enstatite. Hypersthene. Topaz. Muscovite. Barite. Orthoclase. Chrysolite. Epidpte. Albite. Axinite. * The axial angle will equal 90 when the indices satisfy the following equation: 1 _! - I 1 a 2 j8 2 ft 2 7 2 ' t For danburite axial angle = 89 14' for green (thallium) and 90 14' for blue (CuSO 4 ). 278 PHYSICAL MINERALOGY 401. Relation of the Axial Angle to the Refractive Indices. If in a given case the values of a, 0, and 7 are known, the value of the interior optic axial angle known as 2V; see also Art. 408, can be calculated from them by the following formulas: 11 11 cos 2 F P 7 2 a 2 7 2 or tan 2 V = 681 Examination of Biaxial Crystals in Polarized Light 402. Sections in Parallel Polarized Light with Crossed Nicols. Interference Colors. Thin sections of biaxial crystals when examined between crossed nicols in general show some interference color. This color will depend upon the following factors : the thickness of the section, the thicker the sec- tion the higher the order of color; the birefringence of the substance, the higher the birefringence (i.e., the greater the difference between the values of a and 7) the higher the order of color; the optical orientation of the section, in gen- eral, the nearer the section comes to being parallel to the optic axial plane, in which he the vibration directions of the fastest and slowest rays, the higher will be its birefringence and the order of its interference color. Extinction Directions. A section which, in general, is colored will show dur- ing a complete revolution on the microscope stage four positions at 90 inter- vals in which it appears dark. These are the positions of extinction, or are those positions in which the vibration planes of the section coincide with those of the nicols. When the directions of extinction of a section are parallel or at right angles to a crystallographic axis or to the trace, upon the section, of a crystallographic axial plane it is said to show parallel extinction. If the extinction directions are not parallel to these crystallographic directions the extinction is said to be inclined. For example, in Fig. 581, let the two larger rectangular arrows represent the vibration ., 6 ' directions for the two nicols, and between which suppose a section of a biaxial crystal, ^-P abed, to be placed so that one edge of a known crystallographic plane coincides with the direc- tion of one of these lines. The vibration directions of the section are indicated by the dotted arrows and as in this position of the section these directions do not coincide with the vibration directions of the nicols the section will appear light. The section will have to be turned to the position a'b'c'd' in order to achieve this coincidence and so bring about extinction. The angle (indicated in the figure) which it has been necessary to revolve the plate to obtain the effect described, is the angle which one of the vibration directions in the given plate makes with the given crystallographic edge ad', it is called the extinction angle. 403. Measurement of the Extinction Angle. It frequently becomes important to measure as accurately as possible the extinction angle of a sec- CHARACTERS DEPENDING UPON LIGHT 270 tion. This is most commonly done with a microscope which is provided with a revolving stage having a graduated circle for measuring angles of rotation. In order to measure an extinction angle it is of course necessary to be able to locate in the section some definite crystallographic direction. This is usually provided by some crystal outline or cleavage crack. This crystallography direction is brought parallel to one of the cross-hairs of the microscope and the angular position of the microscope stage noted. Then the stage is rotated until the section shows its maximum darkness. The angle between these two positions is the angle of extinction desired. The difficulty in the measure- ment lies in the accurate determination of the position of maximum extinction. Frequently it is possible to rotate the microscope stage through an arc of one to two degrees without any appreciable brightening of the field. It will help in determining the point of maximum extinction if the plate is turned beyond the point of extinction until the first faint illumination is observed and then back in the other direction until the same strength of illumination occurs. The point half way between these two positions should be very close to the point desired. The measurements should be repeated a number of times and the average taken. It is also advisable to make the measurements on both sides of the position of the crystallographic direction. The illumination in most cases had better be in the monochromatic sodium-light. Various devices are used at times in order to increase the accuracy with which the position of maximum extinction can be determined.* The sensi- tive tint is sometimes used for this purpose. If this is inserted in the diagonal slot of the microscope tube below the analyzer the field will be uniformly colored red of the first order when the section on the microscope stage is at the position of extinction. But if the section is turned, even very slightly, from this position it will also affect the light and change the interference color observed. The sensitive tint in specially favorable cases can be used in this way to advantage but it has been shown that in the majority of cases its use does not materially increase the accuracy of the measurements. The power of quartz plates cut normal to the vertical crystallographic axis to rotate the plane of polarization of light (see Art. 394) is used in other devices to increase the accuracy of the measurement of the angle of extinction. The Bertrand ocular contains four such sectors of quartz; two of these placed diagonally opposite to each other are from a right-handed quartz crystal while the other two are from a left-handed crystal. This ocular is inserted in the microscope tube in place of the regular ocular; the analyzer is pushed out of the microscope tube and a nicol prism mounted in an appropriate holder is placed over the ocular. If this upper nicol is turned about in various positions it will be noted that, in general, opposite quadrants of the field are colored alike but differ in color from the adjacent quadrants, see Fig. 582. But when the plane of the cap nicol is exactly at right angles to the plane of the polarizer below all four quadrants show the same color. If a double refracting mineral be placed on the stage of the microscope with its vibration Bertrand~Ocular directions parallel to those of the nicols, since in this position it has no birefringent effect upon the light, the field will still remain uniformly colored. But if the section is turned from its * Detailed descriptions of these various devices with comment on their accuracy are given by F. E. Wright in The Methods of Petrographic-Microscopic Research. 280 PHYSICAL MINERALOGY position of extinction its birefringent effect is added to that of the two opposite quadrants of the ocular and subtracted from that of the remaining two. Consequently adjacent quadrants become differently colored. A very slight rotation of the section is sufficient to produce an appreciable effect. Another microscope accessory using the same principle as the Bertrand ocular is the so-called bi-quartz wedge plate described by Wright. This con- sists of two adjacent plates of quartz cut normal to the c crystal axis, one from a left-handed and the other from a right-handed crystal. Above these are placed two wedges of quartz, a right-handed wedge above the left-handed plate, etc. At the point where the wedge is equal in thickness to the plate beneath there will be zero rotation of the light and between crossed nicols this will produce a dark line across the field. As the distance increases from this point the amount of rotation of the light increases equally but in opposite directions on either side of the central dividing line of the plate. Both halves of the plate will be equally illuminated if the mineral section is in the position of extinction, but if the latter is turned so that it adds or subtracts its bire- fringent effect to that of the quartz plate the two halves become differently illuminated. By moving the plate in or out a position can be found where this change in illumination is most marked. This quartz plate is used with a special ocular provided with a slot in such a position that the quartz plate may be introduced into the microscope tube at the focal plane of the ocular and with the medial line of the plate parallel to the plane of vibration of the polarizer. A cap nicol is used above the ocular. 404. Determination of the Birefringence with the Microscope. The value of the maximum birefringence (7 a) is obviously given at once when the refractive indices are known. It can be approximately estimated for a section of proper orientation and of measured thickness by noting the inter- ference-color as described in Art. 347. 405. Determination of the Relative Refractive Power. The relative refractive power of the two vibration-directions in a thin section is readily determined with the microscope (in parallel polarized light) by the method of compensation. This Is applicable to any section, whatever its orientation and whether uniaxial or biaxial. The methods employed have already been described in Art 348. A crystal-section is said to have positive elongation if its direction of exten- sion approximately coincides with the ether-axis Z; if with X the elongation is negative. The same terms are also used, in general, according to the relative refractive power of the two directions. 406. Determination of the Indices of Refraction of a Biaxial Mineral. The indices of refraction of a biaxial mineral are determined by the same methods as outlined previously, see Art. 327, the only modification introduced being necessitated by the fact that three principal indices, a, ft and 7, are to be determined. Measurement of the Angles of Refraction by Means of Prisms. Two or three prisms must be used to determine the three indices. If three prisms are used they are cut so that their edges are parallel respectively to the X, F, and Z directions of the mineral. In the case of an orthorhombic mineral, in which these directions are parallel to the directions of the three crystallo- graphic axes, the prism edges would have to be respectively parallel to the a, b, and c crystal axes. In crystals of the monoclinic and triclinic systems the proper orientation of the three prisms is a matter of considerable difficulty. CHARACTERS DEPENDING UPON LIGHT 281 Each such prism will yield two refracted and polarized rays but only the one whose light has its vibrations parallel to the edge of the prism (to be deter- mined by the use of a nicol) is considered. In certain cases all three indices may be obtained from two prisms. If one prism is cut so that not only is its edge parallel to one of the directions X, Y, and Z but so that its medial plane contains not only this direction but one other, then by the use of the method of minimum deviation an index may be determined from each of the two refracted rays. Or with a small angle prism cut so that one of its faces con- tains two of these directions the corresponding two indices may be determined when the method of perpendicular incidence is used upon this face. In mak- ing these measurements it is important to note the crystallographic directions parallel to which the different rays vibrate. In this way the optical orienta- tion in respect to the crystallographic directions can be determined. Method of Total Reflection. The method of total reflection for determining the indices of refraction of a biaxial mineral has the obvious advantage that only polished plates of the mineral are required instead of carefully orientated prisms. In general, the plane surface of a plate will give with the total refractometer two boundaries of total reflection. Both of these shadows move when the section is rotated. Four readings should be taken corresponding to the maximum and minimum positions of each boundary. The largest and smallest angles read will give on calculation the values for the greatest and least indices of refraction, i.e., j and a. The mean index of refraction, 0, can be derived from one of the other measurements. There are certain more or less complicated methods by which these two intermediate readings can be tested in order to prove which is the correct one for the index |8. It is com- monly simpler to make use of another plate having a different crystallographic orientation. It will be found that in the second plate one of the intermediate angles corresponds with one already observed on the first plate while the second angle shows no such correspondence. The angle that is common to the two plates is the one desired. If the plate is orientated so that its plane contains two of the three optical directions, X, Y and Z, all three indices can be obtained easily from the single plate. In this case one of the boundaries of total reflection is stationary for different positions of the plate. This corresponds to the ray whose vibrations are normal to the surface of the plate. The other boundary will vary its position as the plate is rotated and yield at its maximum and minimum positions the angles corresponding to the other two indices of refraction. 407. Sections of Biaxial Crystals in Convergent Polarized Light. - In general, sections of biaxial crystals when examined in convergent polarized light show interference figures. The best and most symmetrical figures are to be observed when the section has been cut perpendicular to a bisectrix, and preferably to the acute bisectrix. If such a section is examined under the conditions described in the case of uniaxial crystals, see Art. 389, figures similar to those shown in Fig. 583 will be observed. When the axial plane, i.e., the plane including the two optic axes, lies parallel to the direction of vibration of the polarizer the figure is similar to that of Fig. 583, A. When these two directions are inclined at a 45 angle the figure is like that shown in Fig. 583, B. First consider the interference figure in the parallel position, Fig. 583, A and when viewed in monochromatic light. It consists of two black bars that form a cross somewhat similar to the cross of a uniaxial figure. The horizon- 282 PHYSICAL MINERALOGY tal bar is thinner and better denned than the vertical one. About two points on the horizontal bar, there will be observed a concentric series of dark ellip- tical curves which, as they enlarge, coalesce, forming first a figure eight and 583 Biaxial Interference Figures then a double curve. As the section is rotated on the microscope or polar- iscope stage, the black bars forming the cross separate at the center and curve across the field pivoting on these points until at the 45 position, Fig. 583, B, they form the two arms of a hyperbola. A biaxial mineral has two directions, the directions of the optic axes, along which light travels with no double refraction. At these points there would be no birefringence and consequently dark spots would result. As the paths of the light rays become inclined to the directions of the optic axes the light suffers double refraction and in increasing degree as the amount of inclination becomes greater. Consequently at short distances away from these points the light must be refracted into two rays which have a difference of phase of one wave-length for a certain colored light, the yellow of the sodium flame in this case. The result will be extinguishment at such points. The assem- blage of all points where the difference of phase equals one wave-length yields the first dark elliptical-like curve, called a lemniscate, shown in the figure. Further out will be found curves embracing the points where the difference o" phase is two wave-lengths, three wave-lengths, etc. If the interference figure is viewed in daylight instead of the monochr niatic light the black curves will be replaced by colored ones. Each colored curve is produced by the elimination from the white light of some particular wave-length of light on account of the interference explained above. The convergent bundle of light rays that pass through the section will each have its own particular plane of vibration. The directions of the planes of vibration for light emerging from the section at any given point can be found, as explained in Art. 397, by bisecting the angles made by two lines connecting this point with the two points of emergence of the optic axes. Fig. 584 shows how the direction of vibration of the two rays emerging from given points can be obtained in this way. These directions of vibration vary over the field and consequently some of them must always be parallel or very nearly so to the planes of vibration of the nicol prisms. When this happens the light is extinguished and darkness results. This explains the formation of the black bars of the interference figure. Fig. 585 shows the bars in the crossed position ire. i TOV CHARACTERS DEPENDING UPON LIGHT 283 and Fig. 586 when separated into the hyperbola arms. As the section is turned the vibration directions of new points successively become parallel to the planes of the nicols and so the dark bars sweep and curve across the field. 584 585 586 With a thick section or one of a mineral of high birefringence, the number of colored curves (when the figure is viewed in daylight) is greater than with a thinner section or one with low birefringence. An instructive experiment can be made by noting the changes in the interference figure obtained from a section of muscovite as the mineral is cleaved into thinner and thinner sheets. In most rock sections the minerals are ground so thin that their interference figures do not show any colored curves but rather only the dark hyperbola bars. The biaxial interference figure varies in appearance with the change in the angle between the optic axes. Where this angle is very small the figure becomes practically the same as that of a uniaxial crystal. Where this angle becomes greater than 60 the points of the emergence of the optic axes will commonly lie outside the microscope field. In the latter case the hyper- bola arms will appear as the section is brought into the parallel position, form a cross, and then as the section is further revolved will curve out of the field again. The larger the axial angle the more rapidly will the bars disappear from the field. A comparative measurement of the axial angles of two minerals can be made by noting the angle through which the microscope stage has to be turned in order to cause the bars to leave the field. The system of lenses must be kept the same for the two experiments. Or by experimenting with various minerals with known axial angles a scale could be derived for a certain microscope and system of lenses so that the axial angle of any other mineral could be approximately measured in this way. A symmetrical interference figure may also be obtained from a section cut perpendicular to the obtuse bisectrix. In general, the obtuse axial angle is considerably larger than the acute angle and the interference figure will differ therefore in this respect from that obtained from the section cut perpendicular to the acute bisectrix. It is important to be able to recognize the biaxial interference figures which are obtained from inclined sections. They are chiefly characterized by the fact that the hyperbola bars curve as they cross the field. This charac- teristic distinguishes the figure from an eccentric uniaxial figure in which the bars of the cross move in straight lines as the section is turned. Fig. 587 shows in the row A a series illustrating the appearance in different positions 284 PHYSICAL MINERALOGY of the figure when the section is slightly inclined to the bisectrix. In row B, a series where the section is cut perpendicular to an optic axis and the hyper- bola bar revolves in the field as upon a pivot. In this case the bar curves 687 Eccentric Biaxial Interference Figures with its convex side toward the acute bisectrix. If the axial angle was 90 there would be no distinction between acute and obtuse bisectrices and the bar would then revolve as a straight line. Therefore such a figure indicates by the amount of the curvature of the bar the size of the axial angle. The figures given by planes cut nearly normal to an optic axis are often of great use in the optical examination of a mineral. Sections which will furnish them are easily found by noting those sections of the mineral that remain dark or nearly so during their rotation between crossed nicols. If the single bar shown in such a figure exhibits a decided curvature it indicates that the direction of the acute bisectrix is not very much inclined to the plane of the section and consequently its character, whether X or Z, can be determined by noting the character of that extinction direction which symmetrically bisects the curve. From this observation the positive or negative character of the mineral can be determined. In row C, Fig. 587, is shown a series of figures where the section has a still greater inclination. A section cut parallel to the axial plane does not give a decisive interference figure. Often it is difficult to distinguish it from the figure obtained from a section cut parallel to the optic axis of a uniaxial mineral, see Art. 392. It should be pointed out that, while in general the interference figures of these two optical classes are to be clearly distinguished from each other, cases may arise in which such differentiation is difficult if not impossible. 408. Measurement of the Axial Angle. The determination of the angle made by the optic axes is most accurately accomplished by use of the instru- ment shown in Fig. 588. The section of the crystal, cut at right angles to the bisectrix, is held in the pincers at p, with the plane of the axes horizontal, and making an angle of 45 with the vibration-plane of the nicols. There is a cross-wire in the focus of the eyepiece, and as the pincers holding the section are turned by the screw at the top (here omitted) one of the axes, that is, one black hyperbola, is brought in coincidence with the vertical cross-wire, and CHARACTERS DEPENDING UPON LIGHT 285 then, by a further revolution, the second. The angle which the section has been turned from one axis to the second, as read off at the vernier on the graduated circle above, is the apparent angle for the axes of the given crystal 688 Axial Angle Apparatus as seen in the air (aca = 2E, Fig. 589). It is only the apparent angle, for, on passing from the section of the crystal to the air, the true axial angle is more or less increased, according to the refractive power of the given crystal. The relation between the real interior angle and the measured angle is given below. If the axial angle is large, the axes may suffer total reflection. In this case some oil or liquid with a high refractive power is interposed so that the axes will no longer be totally reflected but emerge into the liquid and thence into the air. In the instrument described a small receptacle holding the oil is brought between the tubes, as seen in the figure, and the pincers holding the section are immersed in this and the angle measured as before. In the majority of cases it is only the acute axial angle that it is practicable to measure; but sometimes, especially when Measurement of Axial Angle oil (or other liquid) is made use of, the obtuse angle can also be determined from a second section normal to the obtuse bisectrix. If E = the apparent semi-acute axial angle in air (Fig. 589), H a = " " u " in oil, Ho = " " semi-obtuse angle in oil, V a = the (real or interior) semi-acute angle, 286 PHYSICAL MINERALOGY V = the (real or interior) semi-obtuse angle, n = refractive index for the oil or other medium, |8 = the mean refractive index for the given crystallized substance, the following simple relations connect the various quantities mentioned: Bin E = sin 7; sin E = n sin H a ; sin V a = ^ sin H a ; sin V = ^ sin H . These formulas give the true interior angle (2F) from the measured apparent angle in air (2E) or in oil (2H) when the mean refractive index (0) is known. 409. Axial Angle Measured with the Microscope. Approximate measurements of the axial angle may be made by various methods with the microscope. In most cases some sort of a micrometer ocular is used which contains an engraved scale. By means of this scale the distance between the points of emergence of the optic axes can be determined. Mallard * showed that the distance of any point from the center of the interference figure as observed in the microscope is very closely the same as the sine of the angle which the ray emerging at this point makes with the axis of the microscope. The Mallard equation for the derivation of the axial angle is D = K sin E, in which D equals one half the meas- ured distance between the optic axes and K a constant which varies with the microscope and the system of lenses used. K for a given set of lenses may be determined by observing the interference figures derived from plates of minerals with known axial angles and then substituting the values for D and E in the above equation. The angular values of the divisions on the micrometer scale of the ocular may also be determined directly by the use of an instrument known as the apertometer. The measurement of an axial angle by means of the microscope is naturally most easily accomplished when the points of emergence of both optic axes are visible in the field. It is possible, however, by various ingenious methods to determine its value when only one optic axis is in view. These methods are too com- plicated and too seldom used to be explained here and the reader is referred to the text books on the methods of petrographic investigation- for their details, f 410. Determination of the Optical Character of a Biaxial Mineral from Its Interference Figure. Use of the Quartz Wedge. If the section is turned until its interference figure is in the 45 position and then the quartz wedge inserted above the section through the 45 slot in the microscope tube the vibration directions of the section along a line that joins the optical axes and a line at right angles to this through the center of the figure will be paral- lel to the vibration directions of the quartz-wedge. Under these circum- stances the effect of the introduction of the quartz wedge will be to gradually increase or diminish along these lines the birefringence due to the section alone. If the directions of vibration of the faster and slower rays in the quartz coin- cide with the vibration directions of the similar rays in the section, the total birefringence will be increased and the effect upon the interference figure will be as if the section had been thickened. Complete interference will take place with rays of less obliquity and the colored curves will be drawn closer together. They will move, as the quartz wedge is pushed in over the section, as indicated by the arrows shown in Fig. 590. On the other hand, if the quartz wedge is so placed that its optical orientation is opposed to that of the section, the effect will be the same as if the section was being gradually thinned. The colored rings about the points of the optic axes will expand until they meet in the cen- ter as a figure eight and then grow outwards as a continuous curve. The directions of their movements are shown by the arrows in Fig. 591. There- fore, by knowing the optical orientation of the quartz-wedge and noting the * Bull. Soc. Min., 6, 7787, 1882. t See especially Wright, The Methods of Petrographic Microscopic Research, and Johannsen, Manual of Petrographic Methods. CHARACTERS DEPENDING UPON LIGHT 287 effect of its introduction over a section upon the interference figure, it is pos- sible to determine the relative character of the two important extinction directions of the sections; that is, to determine whether the ray vibrating in the plane which includes the optic axes is faster or slower than the one which vibrates in the plane at right angles to this direction. In the case of a positive mineral the acute bisectrix, which in a sym- metrical interference figure is the direction normal to the section, is the direction Z. Consequently the direction of the line in the section which passes through the points of emergence of the two optic axes is the direction of the obtuse bisectrix, or in this case the direction X. The direction Y then will lie in the plane of the section and at right angles to the line joining the points of emergence of the optic axes. In the case, therefore, of a positive Determination of Optical Character of Biaxial Mineral with Quartz Wedge mineral, the faster ray has its vibrations lying in the optical axial plane With a negative mineral the direction X becomes the acute bisectrix and will be normal to the section, while the direction Z will lie in the section along the line connecting the points of emergence of the optic axes. With a negative mineral, therefore, the vibration direction which lies in the optical axial plane is of the slower ray. By finding, therefore, the relative character of these two vibration directions the optical char- acter of the mineral is determined. The effects produced by an interference figure which is perpendicular to an obtuse bisectrix would be exactly opposite to those described above. It is imperative, therefore, that the positions of the two bisectrices be definitely known. With sections that are very thin or with minerals of low birefringence the interference figure may show only the black hyperbolas without any colored rings. In such cases, frequently the introduction of the quartz wedge in such a position that its optical orientation is parallel to that of the section will suffice to so thicken the section in effect as to cause the appearance of colored rings. Further, with such sections it is possible to establish the directions in the section that are parallel and at right angles to the trace upon the section of the optical axial plane. Then, by use of the sensitive tint, when the convergent lens has been removed the character of the vibrations parallel to these two directions is easily determined. 288 PHYSICAL MINERALOGY 411. Absorption Phenomena of Biaxial Crystals. Pleochroism. Colored biaxial crystals like similar uniaxial crystals may show different de- grees or kinds of absorption of the light passing through them depending upon the direction of vibration of the light. In biaxial crystals there may be three different degrees of absorption corresponding to three different directions of vibration lying at right angles to each other. In general, these directions co- incide with the optical directions X, F, and Z. Variations from this parallel- ism may be observed, however, in crystals of the monoclinic and triclinic systems. It is customary, however, to describe the absorption as it is ob- served parallel to the directions X, Y, and Z. If light vibrating parallel to X is the most absorbed and light vibrating parallel to Z is the least absorbed these facts are expressed asX > Y > Z. There are various other possibili- ties, such as X > Y = Z, Z > X > F, etc. Further, according to the kind of selective absorption, the crystal may show distinctly different colors for ' light vibrating in the different directions, or in general show pleochr9ism. The character of the pleochroism is stated by giving the colors correspond- ing to the vibrations parallel to X, F, and Z. For instance, in the case of riebeckite, X = deep blue, F = light blue, Z = yellow-green. In order to investigate the absorption properties of a biaxial crystal at ( least two sections must be obtained in which will lie the directions X, F, and Z. These sec- tions are examined on the stage of the polariscope or microscope without the upper nicol. They will show as they are rotated upon the stage, variations in absorption and in color as the light passing through them vibrates parallel to first one and then the other of their vibration directions. See the discussion of dichroism in uniaxial minerals, Art. 393. When a section cut normal to an optic axis of a crystal characterized by a high degree of color-absorption is examined by the eye alone (or with the microscope) in strongly con- verging light, it often shows the so-called epoptic figures, polarization-brushes, or houppes somewhat resembling the ordinary axial interference-figures. This is true of andalusite, epidote, iolite, also tourmaline, etc. A cleavage section of epidote ||c(001) held close to the eye and looked through to a bright sky shows the polarization-brushes, here brown on a green ground. These figures are caused by the light being differently absorbed as it passes through the section with different degrees of inclination. In certain minerals small circular or elliptical spots may be observed in which the pleo- chroism is stronger than in the surrounding mineral. These are commonly spoken of as pleochroic halos. They are found to surround minute inclusions of some other mineral. There have been many diverse theories to account for these ''halos" but recently it has been shown that they are probably due to some radioactive property of the inclosed crystal. Pleochroic halos have been observed in biotite, iolite, andalusite, pyroxene, hornblende, tourmaline, etc., while the included crystals belong to allanite, rutile, titanite, zircon, apa- tite, etc. Special Optical Characters of Orthorhombic Crystals 412. Position of the Ether-axis. In the ORTHORHOMBIC SYSTEM, in accordance with the symmetry of the crystallization, the three axes of the indicatrix, that is, the directions X, F, and Z, coincide with the three crystal- lographic axes, and the three crystallographic axial planes of symmetry cor- respond to the planes of symmetry of the ellipsoid. Further than this, there is no immediate relation between the two sets of axes in respect to magnitude, for the reason that, as has been stated, the choice of the crystallographic axes is arbitrary so far as relative length and position are concerned, and hence made, in most cases, without reference to the optical character. Sections of an orthorhombic crystal parallel to a pinacoid plane (a (100), 6(010), or c(001)) appear dark between crossed nicols, when the axial directions CHARACTERS DEPENDING UPON LIGHT 289 coincide with the vibration-planes of the nicols; in other words, such sections show parallel extinction. The same is true of all sections that are parallel to one of the three crys- tallographic axes, i.e., sections lying in the prism, macrodome and brachydome zones. Sections, however, that are inclined to all three crystallographic axes, i.e., pyramidal sections, will show inclined extinction. 413. Determination of the Plane of the Optic Axes. The plane of the optic axes, that is, the plane including the directions X and Z, must be parallel to one of the three pinacoids. Further, the acute bisectrix must be normal to one of the two pinacoids that are at right angles to the optic axial plane while the obtuse bisectrix is normal to the other such pinacoid. The optical orientation, i.e., the relation between the principal optical and crystal- lographic directions, can be easily determined by the examination of sections of a crystal which are cut parallel to the three pinacoids. To illustrate by an example, let it be assumed that such sections of the mineral aragonite are available. These are represented in Fig. 592, A, B, and C. If the relative 100 C _ Slower ray _, ^ t ] 1 X 592 a axis 010 ^ J & f Y , Slower ray y y I X 6 axis Optical Orientation of Aragonite characters of the vibration directions of each section are determined it will be found that light vibrating parallel to the c axis in sections parallel to (100) and (010) is in both cases moving with the greater velocity, that light vibrat- ing parallel to the 6 axis in (100) and (001) is in both cases the slower ray, and that light vibrating parallel to the a axis is the faster ray in (001) but the slower ray in (010). From this it is seen that the a axis must coincide with the direc- tion of vibration of the ray having the intermediate velocity, or be the same as the optical direction Y. Also it follows that c axis = X and b axis = Z. The optic axial plane, therefore, since it must include X and Z, lies parallel to (100). If the sections parallel to (001) and (010) are examined in convergent light both will show biaxial interference figures with the points of emergence of the optic axes lying as illustrated in B and C, Fig. 592. The axial angle observed with the section parallel to (001) is much smaller than that obtained from (010). Consequently the acute bisectrix is normal to the base (001) and since it is the direction X the mineral is optically negative. These facts of optical orientation may be summarized in the statements: optically , Ax.pl. ||a(100), Bxa.1 c(001). 290 PHYSICAL MINERALOGY 414. Dispersion of the Optic Axes in Orthorhombic Crystals. In determining the indices of refraction of a crystal by means of the prism method it is to be noted that when the incident ray is of white light the refracted ray will in general show this white light dispersed into its primary colors. The amount of this dispersion is usually small but in certain substances becomes considerable. Obviously since the angle of refraction varies in this way with the different wave-lengths of light the indices of refraction will also vary. In biaxial minerals, as already stated, the optic axial angle is directly depend- ent upon the relative values of the three indices of refraction, a, 0, and y. As these indices may show considerable differences, depending upon the wave-length of the refracted ray, it follows that the optic axial angle will also vary with the color of the light used. In other words, the optic axes may be dispersed. Fig. 593 represents such a case in which the angle between the optic axes for red light is greater than that for blue. The opposite condition may hold, in which the angle for blue is greater than for red. From this it follows that the interference figure when observed in blue light will not exactly co- incide with that produced by rod light. The bisectrices of both figures will be the same but the position of the points where the optic axes emerge will be different and consequently the positions of the hyper- bolas and lemniscate curves will also be orthorhombic Ditpemoo different. In the case of orthorhombic crystals the dispersion will always be symmetrical to the two symmetry planes of the indicatrix that pass through the acute bisectrix, i.e., the direc- tions M-M and N-N 594 595 in Figs. 594 and 595. A A This particular type of dispersion is said to be Orthorhombic Disper- sion, in order to distin- guish it from that ob- served in biaxial crys- tals of other systems. The two possible cases of orthorhombic disper- sion are shown in Figs. 594 and 595. In expres- sing these two cases the Orthorhombic Dispersion Greek letters p (for red) and v (for violet) are used. When the axes for red light are more dispersed than those for blue that fact is expressed as p > v or in the reverse case it is p < v. In the majority of cases the effect produced upon the interference figure by the dispersion of the optic axes is too slight to be noted. In exceptional cases where the amount of dispersion is large the effects are clearly seen. The hyperbola bars, which are ordinarily black throughout, will, when the figure N CHARACTERS DEPENDING UPON LIGHT 291 is observed in white light, be seen, near the center, to be bordered on one side by a red fringe and on the other by a blue one. The first one or two of the colored lemniscates will also be broadened out along the line joining the two optic axes. As already stated these changes in the appearance of the figure will always be symmetrical in respect to the traces of the two symmetry planes 596 597 'Blue -Red Orthorhombic Dispersion lying at right angles to each other. In the case, Fig. 594, where the axes for red light are farther apart than those for blue (p > v), the hyperbolas in the interference figure for the two different wave-lengths of light will not coincide and the ones where the red light is extinguished will be farther out than those for blue light. When red light is taken out of the white light, blue remains, and conversely when blue is subtracted the resultant color is red. Conse- quently in this case the hyperbola bars will be bordered on their concave sides by blue and on their convex sides by red, Fig. 596. In the other case, where p < v, the hyperbolas will be bordered on their concave sides by red and on their convex sides by blue, Fig. 597. In other words, if blue light shows at the larger angle it means that red light has been eliminated from these positions and the optic axes for red are more dispersed than those for blue, etc. Special Optical Characters of Monoclinic Crystals 415. Optical Orientation of Monoclinic Crystals. In monoclinic crys- stals there is one axis of symmetry, the b crystallographic axis, and one plane of symmetry, the plane of the a and c crystallographic axes. These are the only crystallographic elements that are definitely fixed in position. One of the three chief optical directions, X, Y, or Z, is coincident with the 6 crystal- lographic axis, while the other two lie in the symmetry plane, (010), but not parallel to any crystal direction. There are obviously three possible cases. If Y coincides with the axis b (and this is apparently the most common case) the directions X and Z will lie in the crystal symmetry plane, which therefore becomes the optic axial plane. If X or Z coincides with the" 6 axis the optic axial plane will be at right angles to (010) and either the acute or obtuse bisec- trix -will be normal to that plane. This clino-pinacoid of a monoclinic crystal is usually the best plane upon which to study its optical orientation. Fig. 598 represents such a section cleaved from an ordinary crystal of gypsum. The cleavages parallel to (100) and (111) will serve to give its crystallo- graphic orientation. Examination of the section in convergent light fails to show a distinct interference figure, consequently it is to be assumed that the section itself is parallel to the optic axial plane and that the direction Y is 292 PHYSICAL MINERALOGY 598 (100) to (111) Optical Orientation of Gypsum normal to the section. When the section is rotated on the microscope stage between crossed nicols its extinction directions are seen to be inclined to the direction of the c crystallographic axis, the angle of inclination being measured as 52J. The relative character of the two extinction directions can be easily determined by the use of the quartz wedge and so the position of X and Z established. In this way the orientation of the X, Y and Z directions can be determined. It is also pos- sible from this section to determine whether the mineral is optically positive or negative. If the section is viewed in convergent light a some- what vague interference figure is observed. When the section is turned from its position of extinction it will be noted that faint dark hyperbolas rapidly move out of the field. Careful observation will show that they disappear more slowly into one set of -quadrants than into the other. The line bisecting the opposite quadrants into which the hyperbola bars disappear more slowly is the direction of the acute bisectrix. The X or Z character of this direction can be determined and from this the positive or negative character of the mineral. In a similar way the clino-pinacoid section of crystals belonging to the two other possible classes would yield data concerning their optical orientations. 416. Extinction in Monoclinic Crystals. Since only one of the three principal optical directions, X, F, or Z, of a monoclinic crystal coincides with a crystallographic axis, namely the symmetry axis 6, it follows that only sec- tions that are parallel to this axis, i.e., sections in the orthodome zone, will show parallel extinction. All other sections will exhibit inclined extinction. 417. Dispersion in Monoclinic Crystals. - As previously stated there are three possible optical orientations of a monoclinic crystal. In the first case the vibration direction Y coincides with that of the symmetry axis 6 and the optic axial plane coincides with the symmetry plane (010). In the other cases either the vibration direction X or Z coincides with the crystal- lographic axis b and the optic axial plane is at right angles to "the crystallographic symmetry plane. Under these conditions either the acute or obtuse bisectrix may coincide with the axis b. Each of these three possibilities may produce a different kind of dispersion. It should be em- phasized that the phenomenon of dispersion is seldom to be clearly observed and then com- monly only in unusually thick mineral sections. Inclined Dispersion Case 1. Inclined Dispersion. Inclined dispersion is observed in the case 599 CHARACTERS DEPENDING UPON LIGHT 293 where the direction Y coincides with the axis 6. This is illustrated in Fig. 599. In this case not only may the axial angles vary for light of different wave-lengths but -the bisectrices of these angles may lie along different lines. 600 601 f 602 r all Colon Red Inclined Dispersion, p=*v So, here, both the optical axes and the bisectrices may be dispersed. In Fig. 599 with p > v the angle between the optic axes for red light is greater than that for blue. But because of the dispersion of the bisectrices it follows that on one side the point of emergence of the optic axis for red light lies beyond that for blue, while on the other side the conditions are reversed. Also the optic axes for red and blue will be farther apart on one side of the interfer- ence figure than on the other side. With this sort of dispersion the interfer- ence figure will be symmetrical only in respect to the line which is the trace upon the section of the optic axial plane, N-N, Fig. 600, but is unsymmetrical to J the line at right angles to it, M-M. Inclined dispersion is shown in the interference figure by the fact that the colored borders to the hyperbola bars are reversed in the two cases, i.e., if blue is on the concave side of one, red will be on the concave side of the other. Further, tho amount of dispersion shown is much greater with one bar than with the other. Fig. 601 represents a case of inclined dispersion. Case 2. Horizontal Dispersion. In this case the crystallographic axis b coincides with the obtuse bisectrix which may be either the X or Z direction, depending upon whether the crystal is optically positive or negative in charac- ter. In this case the direction of the obtuse bisectrix is fixed for light of all wave-lengths. The angle between the optic axes may vary and further the position of the acute bisectrix may vary as long as it lies in the crystallographic symmetry plane. In other words, the axial planes may be dispersed, see Fig. 602. The points of emergence of the optic axes, when p > v, for blue and red light, might therefore be like that shown in Fig. 603. It will be noted that in this case the interference figure (obtained of course from a section approx- Horizontal Dispersion 294 PHYSICAL MINERALOGY imately perpendicular to the acute bisectrix) is symmetrical to the line M-M but unsymmetrical in respect to the line N-N. Fig. 604 shows the effect of horizontal dispersion upon the interference figure. 603 604 Axis for Red p Axis for Blue P Horizontal Dispersion. p>v Case 3. Crossed 605, ion. In Blue Red r all Colors this case the crystallographic axis b coincides with the acute bisectrix, which may be either the X or Z direc- tion depending upon the optical char- acter of the crystal. In this case the direction of the acute bisectrix is fixed for light of all wave-lengths. The angle between the optic axes may vary and further the position of the axial planes for different wave-lengths may vary as long as they remain perpendic- ular to the crystallographic symmetry plane. A case of this sort is shown in Fig. 605. The points of emer- gence of the optic axes when p > v f or blue and red light might therefore be like that shown in Fig. 606. It will be seen that in this case the figure is sym- metrical to neither the line M-M nor N-N but only to the central point of the figure, i.e., the point of emergence of the acute bisectrix. Fig. 607 shows Crossed Dispersion the effect of crossed dispersion upon the interference figure. 606 607 Crossed Dispersion p>v CHARACTERS DEPENDING UPON LIGHT 295 Special Optical Characters of Triclinic Crystals 418. Optical Orientation of Triclinic Crystals. The center of the optical ellipsoidal figure coincides with the center of the system of crystallo- graphic axes but there is no further correspondence between optical and crys- tallographic directions. 419. Extinction in Triclinic Crystals. Since there is no parallel rela- tion existing between optical and crystallographic directions in triclinic crys- tals all sections will show inclined extinction. 420. Dispersion in Triclinic Crystals. Because of the lack of coinci- dence between any optical and crystallographic direction in triclinic crystals it follows that the optic axes and bisectrices for different wave-lengths of light may be dispersed in any direction. Consequently the dispersion shown in an interference figure obtained from a triclinic crystal is irregular and without symmetry. 421. Suggestions as to Methods and Order of Optical Tests upon an Unknown Mineral. Preparation of Material. The size and character of the fragments or section of a mineral to be studied will depend upon various circumstances. In the majority of cases it will probably be most convenient to crush the mineral into small uniform sized fragments. In other cases a cleavage flake of the mineral will serve, and under still other conditions it may be preferable to cut an unorientated or, better, an orientated section. For at least the preliminary examination small irregular fragments of varying orienta- tion will most often be used. Take a few of these mineral grains and place them upon an object glass and immerse ^them either in Canada balsam or in some oil with known refractive index and cover with a piece of thin cover glass. In the majority of cases it will prove more expeditious and conven- ient to place the fragments in an oil. Order of Optical Tests. Below is given a brief outline of the natural order of observations and tests to be made upon the mineral. 1. Observations in plane polarized light without the upper nicol. a. Note color of mineral, whether uniform or not. b. By rotating slide on microscope stage test for possible pleochroism. If the mineral exhibits pleochroism it cannot be isotropic. Con- nect as far as possible the directions of absorption with crystal- lographic directions. c. Note crystal outline, if any; cleavage cracks, etc. d. Note any inclusions, their shape and arrangement. e. Index of refraction. Determine approximately the refractive index. Note character of relief and determine whether mineral has a higher or lower index than the medium in which it is immersed (see Art. 325). 2. Observations in plane polarized light with crossed nicols. a. If the section is dark between crossed nicols and remains so during the rotation of the stage the mineral is either isotropic or orientated perpendicular to an optic axis. In the latter case test as indicated below under 3a. b. If the section is alternately light and dark during the rotation of the stage the mineral is anisotropic. c. Note position of extinction directions. If they are inclined to some known crystallographic direction measure the angle of inclina- tion. 296 PHYSICAL MINERALOGY d. Determine the relative character of the two vibration directions of the section (i.e., the two extinction directions), as to which cor- responds to the faster and which to the slower ray. Test to be made with quartz wedge or sensitive tint, see Art. 348. e. Find the grain showing the highest order of interference color and so approximately determine the strength of the mineral's bire- fringence. /. By immersion in oils of known refractive indices determine as accurately as possible the range of the refractive indices shown by the mineral. It may be possible in connection with tests made under 3 to determine the values for certain of the prin- . cipal refractive indices. 3. Observations in convergent polarized light with crossed nicols. a. Note whether the mineral shows an interference figure, and if so whether it is uniaxial or biaxial. 6. If mineral is uniaxial determine the position of the optic axis in respect to the plane of the given section and if possible determine the positive or negative character of the mineral. c. If the mineral is biaxial determine the position of the axial plane in respect to the section. Determine, if possible, the positive or negative character of the mineral. Obtain, if possible, an approx- imate idea as to the size of the axial angle. Note any evidences of dispersion. Note. In making the above tests it is helpful to keep, as far as possible, a graphic record of the results, something like that illustrated in Fig. 592. 422. Effect of Heat upon Optical Characters. The general effects of heat upon crystals as regards expansion, etc., are spoken of later. It is con- venient, however, to consider here, briefly, the changes produced by this means in the special optical characters. It is assumed that no alteration of the chemical composition takes place and no abnormal change in molecular structure. In general, the effect of a temperature change causes a change in the refractive indices. In the majority of cases the indices decrease in value with rise of temperature but in certain cases the reverse is true. It is consequently important in any exact statement of a refractive index to give the temperature at which it was determined. The particular facts for the different optical classes are as follows : (1) Isotropic crystals remain isotropic at all temperatures. Crystals, how- ever, which, like sodium chlorate (NaClO 3 of Class 5, p. 72), show circular polarization may have their rotatory power altered; in this substance it is in- creased by rise of temperature. (2) Uniaxial crystals similarly remain uniaxial with rise or fall of tempera- ture; the only change noted is a variation in the relative values of co and e, that is, in the strength of the double refraction. This increases, for example, with calcite and grows weaker with beryl and quartz. It is, further, interesting to note that the rotatory power of quartz increases with rise of temperature, but the relation for all parts of the spectrum remains sensibly the same. (3) With Biaxial crystals, the effect of change of temperature varies with the system to which they belong. The axial angle of biaxial crystals may be measured at any required temperature by the use of a metal air-bath. This is placed at P (Fig. 588) and extends beyond the instrument on either side, so as to allow of its being heated with gas-burners; a thermometer inserted CHARACTERS DEPENDING UPON LIGHT 297 in the bath makes it possible to regulate the temperature as may be desired. This bath has two openings, closed with glass plates, corresponding to the two tubes carrying the lenses, and the crystal-section, held as usual in the pincers, is seen through these glass windows. Suitable accessories to the refractometer also allow of the measurement of the refractive indices at different temperatures. In the case of orthorhombic crystals, the position of the three rectangular ether-axes cannot alter, since they must always coincide with the crystallo- graphic axes. The values of the refractive indices, however, may change, and hence with them also the optic axial angle; indeed a change of axial plane or of the optical character is thus possible. With monodinic crystals, one ether-axis must coincide at all temperatures with the axis of symmetry, but the position of the other two in the plane of symmetry may alter, and this, with the possible change in the value of the refractive indices, may cause a variation in the degree (or kind) of dispersion as well as in the axial angle. With triclinic crystals, both the positions of the ether-axes and the values of the refractive indices may change. The observed optical characters may therefore vary widely. A striking example of the change of optical characters with change of temperature is furnished by gypsum, as investigated by Des Cloizeaux. At ordinary temperatures, the dispersion is inclined, the optic axial plane is || 6(010) and 2E r = 95. As the temperature rises this angle diminishes; thus, at 47, 2E r = 76; at 95, 2E r = 39; and at 116, 2E r = 0. At this last temperature the axes for blue rays have already separated in a plane _1_ 6(010); at 120 the axes for red rays also separate in this plane (_L 6) and the dispersion becomes horizontal. The motion toward the center of one red axis is more rapid than that of the other, namely, between 20 and 95, one axis moves 33 55' while the other moves only 22 38'; thus Bx r moves 5 38'. Another interesting case is that of glauberite. Its optical characters under normal con- ditions are described as follows: Optically . Ax. pi. J_ 6(010), Bx a . r A c axis = 31 3', Bxa.y A c axis = -30 46', Bx a .bi A c axis = -30 10'. The optical character (-) and the position of the axes of elasticity remain sensibly constant between and 100. The ax. pi., however, at first _l_ 6(010) with horizontal dispersion and v < p becomes on rise of temperature 1 1 6 with inclined dispersion and v > p. The axial angle accordingly diminishes to at a temperature depending upon the wave-length and then increases in the new plane. In white light, therefore, the interference-figures are abnormal and change with rise in temperature. Des Cloizeaux found that the feldspars, when heated up to a certain point, suffer a change in the position of the axes, and if the heat becomes greater and is long continued they do not return again to their original position, but remain altered. In addition to the typical cases referred to, it is to be noted that when eleva- tion of temperature is connected with change of chemical composition wide changes in optical characters are possible. This is illustrated by the zeolites and related species, where the effect of loss of water has been particularly investigated. Further, with some crystals, heat serves to bring about a change of molec- ular structure and with that a total change of optical characters. For exam- ple, the greenish-yellow (artificial) orthorhombic crystals of antimony iodide (SbI 3 ) on heating (to about 114) change to red uniaxial hexagonal crystals. Note also the remarks made later in regard to the effect of heat upon leucite and boracite (Art. 429). 423. Some Peculiarities in Axial Interference-figures.* In the case of uniaxial crys- tals, the characteristic interference-figure varies but little from one species to another, such * Variations in the axial figures embraced under the head .of optical anomalies are spoken of later (Art. 429). 298 PHYSICAL MINERALOGY variation as is observed being usually due 19 the thickness of the section and the bire- fringence. In some cases, however, peculiarities are noted. For example, the interference- figure of apophyllite is somewhat peculiar, since its birefringence is very weak, and it may be optically positive for one part of the spectrum and negative for the other. In the case of biaxial crystals, peculiarities are more common. The following are some typical examples: Brookite is optically + and the acute bisectrix is always normal to a (100). While, how- ever, the axial plane is || c(001) for red and yellow, with 2E T = 55, 2E V = 30, it is com- monly || 6(010) for green and blue, with 2E gr = 34. Hence a section 1 1 a(100) in the cono- scope shows a figure somewhat resembling that of a uniaxial crystal but with four sets of hyperbolic bands. Titanite also gives a peculiar interference-figure with colored hyperbolas because of the high color-dispersion, p > v, the variation between 2E for red and green light being approximately 10; the dispersion of the bisectrices is, however, very small. The most striking cases of peculiar axial figures are afforded by twin crystals (Art. 425). 424. Relation of Optical Properties to Chemical Composition. The effect of varying chemical composition upon the optical characters has been minutely studied in the case of many series of isomorphous salts, and with important results. It is, indeed, only a part of the general subject of the rela- tion between crystalline form and molecular structure on the one hand and chemical composition on the other, one part of which has been discussed in Art. 322. It was shown there that the refractive index can often be approx- imately calculated from the chemical composition. Among minerals, the most important examples of the relation between composition and optical characters are afforded by the triclinic feldspars of the albite-anorthite series. Here, as explained in detail in the descriptive part of this work, the relation is so close that the composition of any intermediate member of this isomorphous group can be pre- dicted from the position of its ether-axes, or more simply from the vibration directions on the fundamental cleavage-directions, || c(001) and || 6(010). The effect of varying amounts of iron protoxide (FeO) is illustrated in the case of the monoclinic pyroxenes, where, for example, the angle Bx a A c axis is 38 in diopside (2'9 p. c. FeO) and 47 in hedenbergite (26 p. c. FeO). This is also shown in the closely related orthorhombic species of the same group, enstatite, MgSiOs with little iron, and hypersthene, (Mg,Fe)SiO 3 with iron to nearly 30 p. c. With both of these species the axial plane is parallel to 6(010), but the former is optically + (Bxa = Z) and the dispersion p < v, the latter is optically (Bxa = A^) and dispersion p > v. In other words,the optic axial angle changes rapidly with the FeO percentage, being about 90 for FeO = 10 p. c. In the case of the chrysolites, the epidotes, the species triphylite and lithiophilite, and others, analogous relations have been made out.- 425. Optical Properties of Twin Crystals. The examination of sec- tions of twin crystals of any other than the isometric system in polarized light serves to establish the compound character at once a'nd also to show the relative orientation of the several parts. This is most distinct in the case of contact-twins, but is also well shown with penetration-twins, though here the parts are usually not separated by a sharp line. Thus the examination of a section parallel to 6(010) of a twin crystal of gypsum, of the type of Fig. 608, makes it easy not only to establish the fact of the twinning but also to fix the relative positions of the ether-axes in the two parts. The measurement can in such cases be made between the extinc- tion-directions in the two halves, instead of between one of these and some definite crystallographic line, as the vertical axis. The polysynthetic twinning of certain species, as the triclinic feldspars, appears with great distinctness in polarized light. For example, in the case of a section of albite, parallel to the basal cleavage, the alternate bands extinguish together and assume the same tint when the quartz section is inserted. Hence the angle between these directions is easily measured, and this is obviously double the extinction-angle made with the edge 6(010) A c(001). A basal section of microcline in the same way shows its compound twinning CHAEACTERS DEPENDING. UPON LIGHT 299 according to both the albite and pericline laws, the characteristic grating structure being clearly revealed in polarized light. Fig. 609 of a section of chondrodite (from Des Cloizeaux) shows how the compound structure is shown by optical examination; the position of the 609 001 axial plane is indicated in the case of the successive polysynthetic lamellae. The complex penetration-twins of right- and left-handed crystals of quartz (see the description of that species) also have their character strikingly revealed in polarized light. 610 612 Witherite Bromlite (Des Cloizeaux) Still again, the true structure of complex multiple twins, exhibiting pseudo-symmetry in their external form, can only be fully made out in this way. This is illustrated by Fig. 610, a basal section of an apparent hexagonal pyramid of witherite. The analogous six- 613 614 615 Stilbite (Lasaulx) sided pyramid of bromlite (Fig. 611) has a still more complex structure, as shown in Fig. 612. Fig. 613 shows a simple crystal of stilbite; Fig. 614 is the common type of twin- crystal, and Fig. 615 illustrates how the complex structure (||6010) is revealed in polarized 300 PHYSICAL MINERALOGY light. Other illustrations are given in Art. 429. It will be understood that the axial interference-figures of twin crystals, where the parts are superposed, often show many peculiarities; the Airy spirals of quartz (p. 270) will serve as an illustration. 426. A particularly interesting case, related to the subject discussed in the preceding article, is that of the special properties of superposed cleavage- sections of mica. If three or more of these, say of rectangular form, be super- posed and so placed that the lines of the axial planes make equal angles of 60 (45, etc.) with each other the effect is that polarized light which has passed through the center suffers circular polarization, with a rotation to right or left according to the way in which the sections are built up. The inter- ference-figure resembles that of a section of quartz cut normal to the axis. If the sections are numerous and very thin the imitation of the phenomena of quartz is closer. These facts throw much light upon the ultimate molec- ular structure of a crystallized medium showing circular polarization. Fur- ther, it is easy from this to understand how it is possible to have in sections of certain crystals (e.g., of clinochlore) portions which are biaxial and others that are uniaxial, the latter being due to an intimate twinning after this method of biaxial portions. 427. Optical Properties of Crystalline Aggregates. The special optical phenomena of the different kinds of crystalline aggregates described on pp. 182, 183, and the extent to which their optical characters can be determined, depend upon the distinctness in the development of the individuals and their relative orientation. The case of ordinary granu- lar, fibrous, or columnar aggregates needs no special discussion. Where, however, the doubly refracting grains are extremely small, the microscope may hardly serve to do more than to show the aggregate polarization present. A case of special interest is that of spherulites, that is, aggregates spherical in form and radiated or concentric in structure; such aggregates occur with calcite, various chlorites, feldspars, etc. If they are formed of a doubly refracting crystalline mineral, or of an amorphous substance which has birefringent characters due to internal tension, they com- monly exhibit a dark cross in the microscope between crossed nicols; further, this cross, as the section is revolved on the stage, though actually stationary, seems to rotate backward. A distinct and more special case is that of spherical aggregates of a mineral optically uniaxial (or biaxial with a small angle) . Sections of these (not central) in parallel polarized light show more or less distinctly the interference-figure of a uniaxial crystal. The objec- tive must be focussed on a point a little removed from the section itself, say on the surface of the sphere of which it is a part. In such cases the + or character of the double refraction can be determined as usual. 428. Change of Optical Character Induced by Pressure. As the difference between the optical phenomena exhibited by an isometric crystal on the one hand and a uniaxial or biaxial crystal on the other is referred to a difference in molecular structure modifying the properties of the ether, it would be inferred that if an amorphous substance were subjected to conditions tending to develop an analogous difference in its molecular structure it would also show doubly refracting properties. This is found to be the case. Glass which has been suddenly cooled from a state of fusion, and which is therefore characterized by strong internal tension, usually shows marked double refraction. Further, glass plates subjected to great mechanical pressure in one direction show in polarized light more or less distinct interference-curves. Gelatine sections, also, under pressure exhibit like phenomena. Even the strain in a glass block developed under the influence of unlike charges of electricity of great difference of potential on its opposite sides is sufficient to make it doubly refracting. In an analogous manner the double refraction of a crystal may be changed by the appli- cation of mechanical force. Pressure exerted normal to the vertical axis of a section of a tetragonal or hexagonal crystal which has been cut _L c axis, changes the uniaxial inter- ference-figure into a biaxial, and with substances optically positive, the plane of the optic axes is parallel, and with negative substances normal, to the direction of pressure. The o.uartz crystals in rocks, which have been subjected to great pressure, are often found to be in an abnormal state of tension, showing an undulatory extinction in polarized light. CHARACTERS DEPENDING UPON LIGHT 301 429. Optical An6malies. Since the early investigations of Brewster, Herschel, and others (1815 et seq.) it has been recognized that many crystals exhibit optical phenomena which are not in harmony with the apparent symmetry of their external form. Crystals of many isometric species, as analcite, alum, boracite, garnet, etc., often show more or less pronounced double refraction, and sometimes they are distinctly uniaxial or biaxial. A section examined in parallel polarized light may show more or less sharply denned doubly refracting areas, or parallel bands or lamellae with varying extinction. Occasionally, as noted by Klein in the case of garnet, while most crystals are normally isotropic, others show optical characters which seem to be determined by the external bounding faces and edges; thus, a dodecahedron may appear to be made up of twelve rhombic pyramids (biaxial) whose apices are at the center; a hexoctahedron similarly may seem to be made up of forty- eight triangular pyramids, etc. Similarly, crystals of many common tetragonal or hexagonal species, as vesuvianite, zircon, beryl, apatite, corundum, chabazite, etc., give interfer- ence-figures resembling those of biaxial crystals. Also, analogous contra- dictions between form and optical characters are noted with crystals of orthorhombic and monoclinic species, e.g., topaz, natrolite, orthoclase, etc. All cases such as those mentioned are embraced under the common term of optical anomalies. This subject has been minutely studied by many investigators in recent years and important additions have been made to it both on the practical and the theoretical side. The result is that, though doubtful cases still remain, many of the typical ones have found a satisfactory explanation. No single theory, however, can be universally applied. The chief question involved has been whether the anomalies are to be considered as secondary and non-essential, or whether they belong to the inherent molecular structure of the crystals in question. On the one hand, it has been urged that internal tension suffices (Art. 428) to call out double refraction in an isotropic substance or to give a uniaxial crystal the typical optical structure of a biaxial crystal. On the other hand, it is equally clear that twinning often produces pseudo-symmetry in external form, and at the same time conceals or changes the optical characters. From the simplest case, as that of aragonite, we pass to more complex cases, as witherite (Fig. 610), bromlite (Figs. 611, 612), phillipsite (Figs. 400, 452-454), which last is some- times pseudo-isometric in form though optical study shows the monoclinic character of the individuals.* Reasoning from the analogy of these last cases, Mallard was led (1876) to the theory that the optical anomalies could in most cases be explained by the assumption of a similar but still more intimate grouping of molecules which themselves without this would unite to form crys- tals of a lower grade of symmetry than that which their complex twinned crystals actually simulate. In regard to the two points of view mentioned, it seems probable that internal tension (due to pressure, sudden cooling, or rapidity of growth, etc.) can be safely appealed to to explain the anomalous optical character of many species, as diamond, halite, beryl, quartz, etc. Again, it has been fully proved that the later growth of isomorphous layers of varying composition may * Crystals showing pseudo-symmetry of highly complex type are called mimetic crystals by Tschermak. 302 PHYSICAL MINERALOGY produce optical anomalies, probably here also to be referred to tension. Alum is a striking example. The peculiarities of this species were early investigated by Biot and made by him the basis of his theory of " lamellar polarization," but the present explanation is doubtless the true one. Fig. 616 (from Brauns) shows the appearance in polarized light of a section || 0(111) from a crystal in which the successive layers have different composition. Further, according to Brauns, the optical peculiarities of many other species may be referred to this same cause. He includes here, particularly, those cases (as with some garnets) in which the optical characters seem to depend upon the external form, as noted above. Here belongs also apophyllite, a section of which (from Golden, Col., by Klein) is shown in Fig. 617. The section has been cut || c(001) 616 617 618 Alum, || 111 Apophyllite, || 001 Leucite, || 100 through the center of the crystal and is represented as it appears in parallel polarized light. Another quite distinct but most important class is that including species such as boracite and leucite, which are dimorphous; that is, those species which at a certain elevation of temperature (300 for boracite and 500 to 600 for leucite) become strictly isotropic. Under ordinary conditions, these species are anisotropic, but the fact stated makes it probable that originally their crystalline form and optical characters were in harmony. The relations for leucite deserve to be more minutely stated. Leucite usually shows very feeble double refraction: to = 1'508, e = 1'509. This anomalous double refraction, early noted (Brewster, Biot), was variously explained. In 1873, Rath, on the basis of careful measurements, referred the seemingly isometric crystals to the tetragonal system, the trapezohedral face 112 being taken as 111 and 211, 121 as 421, 241 ; respectively; also 101, Oil as 201, 021. Later Weisbach (1880), on the same ground, made them orthorhombic; Mallard, however, referred them (1876), chiefly on optical grounds, to the monoclinic system, and Fouque and Levy (1879) to the triclinic. The true symmetry, corresponding to the molecular structure which they possess or tend to possess at ordinary temperatures, is in doubt, but it has been shown (Klein, Penfield) that at 500 to 600 sections become isotropic; and further (Rosenbusch) that the twinning striations disappear on heating, to reappear again in new position on cooling. Sections ordinarily show twinning-lamellae |j d(110); in some cases a bisectrix (+) is normal to what corresponds to a cubic face, the axial angle being very small. The structure corresponds in general (Klein) to the interpenetration of three crystals, in twinning position || d, which may be equally or unequally developed; or there may be one fundamental individual with inclosed twinning-lamellse. Fig. 618 shows a section of a crystal (|| a, 100) which is ap- parently made up by the twinning of three individuals. Still again, in a limited number of cases, it can be shown that -the inter- growth of lamellae having slightly different crystallographic orientation is the cause of the optical peculiarities. Prehnite is a conspicuous example of this class. CHARACTERS DEPENDING UPON HEAT 303 After all the various possible explanations have been applied there still remain, however, many species about which no certain conclusion can be reached. To many of these species the theory of Mallard may probably be applicable. Indeed it may be added that much difference of opinion still exists as to the cause of the " optical anomalies " in a considerable number of minerals. LITERATURE . Optical Anomalies * Brewster. Many papers in Phil. Trans., 1814, 1815, and later; also in Ed. Trans., Ed. Phil. J., etc. Biot Recherches sur la polarisation lamellaire, etc. C. R., 12, 967, 1841: 13. 155, 391, 839, 1841; in full in Mem. de I'Institut, 18, 539. Volger. Monographic des Boracits. Hannover, 1857. Marbach. Ueber die optischen Eigenschaf ten einiger Krystalle des tesseralen Systems. Pogg. Ann., 94, 412, 1855. Pfaff. Versuche iiber den Einfluss des Drucks auf die optischen Eigenschaften der Krystalle. Pogg. Ann., 107, 333, 1859; 108, 598, 1859. Des Cloizeaux. Ann. Mines 11, 261, 1857; 14, 339, 1858, 6, 557, 1864. Also Nou- velles Recherches, etc., 1867. Reusch. Ueber die sogennante Lamellarpolarisation des Alauns. Pogg. Ann., 132, 618, 1867. Rumpf. Apophyllite. Min. petr. Mitth., 2, 369, 1870. Hirschwald. Leucite. Min. Mitth., 227, 1875. Lasaulx. Tridymite. Zs. Kr., 2, 253, 1878. Mallard. Application des phenomenes optiques anomaux que presentent un grand nombre de substances cristallisees. Annales des Mines (Ann. Min.) 10, pp. 60-196, 1876 (Abstract in Zs. Kr., 1, 309-320). See also Bull. Soc. Min., 1, 107, 1878. Sur les pro- prietes optiques des melanges de substances isomorphes et sur les anomalies optiques des cristaux. Bull. Soc. Min., 3, 3, 1880, Also ibid., 4, 71, 1881; 5, 144, 1882. Bertrand. Numerous papers in Bull. Soc. Min., 1878-1882. Becke. Chabazite. Min. petr. Mitth., 2, 391, 1879. Baumhauer. Perovskite. Zs. Kr., 4, 187, 1879. Tschermak. " Mimetische Formen." Zs. G. Ges., 31, 637, 1879. Jannettaz. Diamond. Bull. Soc. Min., 2, 124, 1879; alum, ibid., 2, 191; 3, 20. Bucking. Ueber durch Druck hervorgerufene optische Anomalien. Zs. G. Ges., 32, 199, 1880. Also, Zs. Kr., 7, 555, 1883. Arzruni and S. Kock. Analcite. Zs. Kr., 5, 483, 1881. Klocke. Ueber Doppelbrechung regularer Krystalle. Jb. Min., 1, 53, 1880 (also 2, 97, 13 ref.; 1, 204, 1881, and Verh. nat. Ges. Freiburg, 8, 31). Ueber einige optische Eigenschaften optisch anomaler Krystalle und deren Nachahmung durch gespannte und gepresste Colloide. Jb. Min., 2, 249, 1881. C. Klein. Boracite. Jb. Min., 2, 209, 1880; 1, 239, 1881; 1, 235, 1884. Garnet. Nachr. Ges. Gottingen, 1882; Jb. Min., 1, 87, 1883. Apophyllite (influence of heat). Jb. Min., 2, 165, 1892. Garnet, vesuvianite, etc. Ibid., 2, 68, 1895. W. Klein. Beitrage zur Kenntniss der optischen Aenderungen in Krystallen unter dem Einflusse der Erwarmung. Zs. Kr., 9, 38, 1884. Brauns. Die optischen Anomalien der Krystalle. (Preisschrift), Leipzig, 1891. Also earlier papers: Jb. Min., 2, 102, 1883; 1, 96, 1885; 1, 47, 1887. Ben Saude. Beitrag zu einer Theorie der Optischen Anomalien der regularen Krys- talle. Lisbon, 1894. Also earlier: Analcite, Jb. Min., 1, 41, 1882. Perovskite (Preiss- chrift), Gottingen, 1882. Wallerant. Theorie des anomales optiques, de 1'isomorphisme et du polymorphisme. Bull. Soc. Min., 21, 188, 1898. IV. CHARACTERS DEPENDING UPON HEAT 430. The more important of the special properties of a mineral species with respect to heat include the following: Fusibility; conductivity and expansion, * A complete bibliography is given in the memoir by Brauns (1891), see above. 304 PHYSICAL MINERALOGY especially in their relation to crystalline structure; change in optical charac- ters with change of temperature; specific heat; also diathermancy, or the power of transmitting heat radiation. The full discussion of these and other related subjects lies outside of the range of the present text-book. A few brief remarks are made upon them, and beyond these reference must be made to text-books on Physics and to special memoirs, some of which are mentioned in the literature (p. 305). 431. Fusibility. The approximate relative fusibility of different min- erals is an important character in distinguishing different species from one another by means of the blowpipe. For this purpose a scale is conveniently used for comparison, as explained in the articles later devoted to the blowpipe. Accurate determinations of the fusibility are difficult, and though of little importance for the above object, they are interesting from a theoretical stand- point. They have been attempted by various authors by the use of a number of different methods. The following are the approximate melting-point values for the minerals used in von KobelPs scale (Art. 491) : Stibnite, 525 : natrolite, 965; almandite, 1200; actinolite, 1296; orthoclase, 1200; bronzite, 1380; also for quartz, about 1600. 432. Conductivity. The conducting power of different crystallized media was early investigated by Senarmont. He covered the faces of the sub- stance under investigation with wax and observed the form of the figure melted by a hot wire placed in contact with the surface at its middle point. Later investigations have been made by Rontgen (who modified the method of Senarmont), by Jannettaz, and others. In general it Is found that, as regards their thermal conductivity, crystals are to be divided into the three classes noted on p. 252. In other words, the conductivity for heat seems to follow the same general laws as the propagation of light. It is to be stated, however, that experiments by S. P. Thompson and 0. J. Lodge have shown a different rate of conductivity in tourmaline in the opposite directions of the vertical axis. 433. Expansion. Expansion, that is, increase in volume upon rise of temperature, is a nearly universal property for all solids. The increment of volume for the unit volume in passing from to 1 C. is called the coefficient of expansion. This quantity has been determined for a number of species. Further, the relative expansion in different directions is found to obey the same laws as the light-propagation. Crystals, as regards heat-expansion, are thus divided into the same three classes mentioned on p. 252 and referred to in the preceding article. The amount of expansion varies widely, and, as shown by Jannettaz, is influenced particularly by the cleavage. Mitscherlich found that in calcite there was a diminution of 8' 37" in the angle of the rhombohedron on passing from to 100 C., the form thus approaching that of a cube as the tempera- ture increased. The rhombohedron of dolomite, for the same range of tem- perature, diminishes 4' 46"; and in aragonite, for a rise in temperature from 21 to 100, the angle of the prism diminishes 2' 46". In some rhombohedrons, as of calcite, the vertical axis is lengthened (and the horizontal shortened), while in others, like quartz, the reverse is true. The variation is such in both cases that the birefringence is diminished with the increase of temperature, for calcite possesses negative double refraction, and quartz, positive. It is to be noted that in general the expansion by heat, while it may serve to alter the angles of crystals, other than those of the isometric system, does CHARACTERS DEPENDING UPON HEAT 305 Oeberg 01291 01645 01758 0-1861 Orthoclase Albite Amphibole, black Beryl Calcite 0'2034 Aragonite Joly Oeberg 01869 0-1877 01983 0-1976 0-1963 Augite 01830 0-2066 0-1979 - 0-2044 0*2042 0-2036 not alter the zone-relations and the crystalline symmetry. In certain cases, however, the effect of heat may be to give rise to twinning-lamellse (as in anhydrite) or to cause their disappearance (as in calcite). Rarely heat serves to develop a new molecular structure; thus, as explained in Art. 429, boracite and leucite, which are anisotropic at ordinary temperatures, become isotropic when heated, the former to 300 the latter to 500 or 600. The change in the optical properties of crystals produced by heat has already been noticed (Art. 422). 434. Specific Heat. Determinations of the specific heat of many minerals have been made by Joly, by Oeberg, and others. Some of the results reached are as follows: Joly Galena, cryst. 0'0541 Chalcopyrite 01271 Pyrite 01306 Hematite 01683 Garnet, red cryst. 01780 01793 Epidote G'1877 435. Diathermancy. Besides the slow molecular propagation of heat in a body, measured by its thermal conductivity, there is also to be considered the rapid propagation of what is called radiant heat through it by the wave- motion of the ether which surrounds its molecules. This is merely a part of the general subject of light-propagation already fully discussed, since heat- waves, in the restricted sense, differ from light-waves only in their relatively greater length * The degree of absorption exerted by the body is measured by its diathermancy, which corresponds to transparency in light. In this sense halite, sylvite, and fluorite are highly diathermanous, since they absorb but little of the heat-waves passing through them; on the other hand, gypsum and, still more, alum are comparatively athermanous, since while transparent to the short light-waves they absorb the long heat-waves, transforming the energy into that of sensible heat. Measurements of the diathermancy were early made by Melloni, later by Tyndall, Langley, and others. LITERATURE Heat Mitscherlich. Pogg. Ann., 1, 125, 1824; 10, 137, 1827. F. E. Neumann. Gypsum. Pogg. Ann., 27, 240, 1833. Senarmont. Ann. Ch. Phys., 21, 457, 1847; 22, 179, 1848; also in Pogg. Ann., 73, 191; 74, 190; 75. 50, 482. Angstrom. Pogg. Ann., 86, 206, 1852. Grailich and von Lang. Ber. Ak. Wien, 33, 369, 1858. Fizeau. Thermal expansion. C. R., 58, 923, 1864. Ann. Ch. Phys., 2, 143, 1864; 8, 335, 1866; also C. R., 1864-1867. C. Neumann. Pogg. Ann., 114, 492, 1868. Pape. Thermic axes of blue vitriol. Wied. Ann., 1, 126, 1877. Rontgen. Pogg. Ann., 151, 603, 1874; Zs. Kr., 3, 17, 1878. Jannettaz. Conductivity of crystals. Bull. Soc. Geol., (3) 1, 117, 252; 2, 264; 3, 499; 4, 116, 554; 9, 196. Bull. Soc. Min., 1, 19, 1879. C. R., 1848, 114, 1352, 1892. O. J. Lodge. Thermal conductivity. Phil. Mag., 5, 110, 1878. S. P. Thompson and O. J. Lodge. Conductivity of tourmaline. Phil. Mag., 8, 18, 1879. Arzruni. Effect of heat on refractive indices of barite, etc. Zs. Kr., 1, 165, 1877. Beckenkamp. Expansion'of monoclinic and triclinic crystals. Zs. Kr., 5, 436, 1881. H. Dufet. Effect of heat on refractive indices of gypsum. Bull. Soc. Min., 4, 113, 191, 1881. 306 PHYSICAL MINERALOGY A. Schrauf. Sulphur. Zs. Kr., 12, 321, 1887; TiO 2 , ibid., 9, 433, 1884. L. Fletcher. Expansion of crystals. Zs. Kr., 4, 337, 1880. Joly. Meldometer. Ch. News, 65, 1, 16, 1892, and Proc. Roy. Irish Acad., 2, 38, 1891. Specific heat. Proc. Roy. Soc., 41, 250, 352, 1887. f^. 1 Ct C. " f^ e A 1 Ctj._-l_t_ TVT_ O /IO 1OOC Oeberg. Specifn Doelter. For m chemie, 1, 628 et seq. X. kJfJV/V-'ll.lV-' AXV/C*V -1. J.W. -*.vv^ . F Oeberg. Specific heat. Oefv. Ak. Stockh., No. 8, 43, 1885. Doelter. For methods and results in fusing silicates, see Handbuch der Mineral- V. CHARACTERS DEPENDING UPON ELECTRICITY AND MAGNETISM 1. ELECTRICITY 436. Electrical Conductivity. The subject of the relative conducting power of different minerals is one of minor interest.* In general most min- erals, except those having a metallic luster among the sulphides and oxides, are non-conductors. Only the non-conductors can show pyro-electrical phenom- ena, and only the conductors can give a thermo-electric current. 437. Frictional Electricity. The development of an electrical charge on many bodies by friction is a familiar subject. All minerals become electric by friction, although the degree to which this is manifested differs widely. There is no line of distinction among minerals, dividing them into positively electric and negatively electric ; for both electrical states may be presented by different varieties of the same species, and by the same variety in different states. The gem& are in general positively electric only when polished; the diamond, however, exhibits positive electricity whether polished or not. It is a familiar fact that the electrification of amber upon friction was early observed (600 B. C.), and indeed the Greek name (^Xe/crpo*/) later gave rise to the word electricity. 438. Pyro-electricity. The simultaneous development of positive and negative charges of electricity on different parts of the same crystal when its temperature is suitably changed is called pyro-electricity. Crystals exhibiting such phenomena are said to be pyro-electric. This phenomenon was first observed in the case of tourmaline, which is rhombohedral-hemimorphic in crystallization, and it is particularly marked with crystals belonging to groups of relatively low symmetry, especially those of the hemimorphic type. It is possible, of course, only with non-conductors. This subject was early inves- tigated by Riess and Rose (1843), later by Hankel, also by C. Friedel, Kundt. and others (see literature). In all cases it is true that directions of like crystallographic symmetry show charges of like sign, while unlike directions may exhibit opposite charges. Substances not crystallized cannot show pyro-electricity. A few of the many possible examples will serve to bring out the most essential points. Boracite (isometric-tetrahedral, p. 66) on heating exhibits + electricity on one set of tetrahedral faces and electricity on the other. Cf. Fig. 619. Tourmaline (rhombohedral-hemimorphic, p. 109) shows opposite charges at the opposite extremities of the vertical axis corresponding to its hemimorphic crystallization. In this and in other similar cases, the extremity which * On the conductivity of minerals, see Beijerinck, Jb. Min., Beil.-Bd., 11, 403, 1898. CHARACTERS DEPENDING UPON ELECTRICITY AND MAGNETISM 307 becomes positive on heating has been called the analogous pole, and that which becomes negative has been called the antilogous pole. Calamine and struvite (orthorhombic-hemimorphic, p. 126) exhibit phenom- ena analogous to those of tourmaline. Quartz (rhombohedral-trapezohedral, p. 112) shows + electricity on heating at the three alternate prismatic edges and electricity at the three remaining edges; the distribution for right-handed crystals is opposite to that of left- handed. Twins may exhibit a high degree of complexity. Cf. Figs. 620, 621. Axinite (triclinic, p. 144), when heated to 120 or 130, has an analogous 619 620 621 pole (Riess & Rose) at the solid angle rxM'; the antilogous pole at the angle mr'M' near plane n. A very convenient and simple method for investigating the phenomena is the following, which is due to Kundt: First heat the crystal or section care- fully in an air-bath; pass it several times through the flame of an alcohol lamp and then place it on a little upright cylinder of brass to cool. While cooling, a mixture of red lead and sulphur finely pulverized and previously agitated is dusted over it through a fine cloth from a suitable bellows. The positively electrified red lead collects on the parts having a negative charge, and the negatively electrified sulphur on those with a positive charge. This is illustrated by Figs. 619-621, and still better by the illustrations given by Kundt and others. (Cf. Plate III of Groth, Phys. Kryst., 1905.) 439. Piezoelectricity. The name piezo-electricity has been given to the development of electrical charges on a crystallized body by pressure. This is shown by a cleavage mass of calcite, also by topaz. This phenomenon is most interesting where a relation can be established between the electrical excitement and the molecular structure, as is conspicuously true with quartz, tourmaline, and some other species. This subject has been investigated by Hankel, Curie, and others, and discussed theoretically by Lord Kelvin (see literature). Hankel has also employed the term actino-electricity ', or, better, photo-electricity, for the phe- nomenon of producing an electrical condition by the influence of direct radiation; fluorite is a conspicuous example. 440. Thermo-electricity. The contact of two unlike metals in gen- eral results in electrifying one of them positively and the other negatively. If, further, the point of contact be heated while the other parts, connected with a wire, are kept cool, a continuous current of electricity shown, for example, by a suitable galvanometer is set up at the expense of the heat-energy sup- plied. If, on the other hand, the point of junction is cooled, a current is set up in the reverse direction. This phenomenon is called thermo-electricity , 308 PHYSICAL MINERALOGY and two metals so connected constitute a thermo-electric couple. Further it is found that different conductors can be arranged in order in a table a so-called thermo-electric series according to the direction of the current set up on heating and according to the electromotive force of this current. Among the metals, bismuth (+) and antimony () stand at the opposite ends of the series; the current passes through the connecting wire from antimony to bismuth. This subject is so far important for mineralogy, as it was shown by Bunsen that the natural metallic sulphides stand farther off in the series than bismuth and antimony, and consequently by them a higher electromotive force is produced. The thermo-electrical relations of a large number of minerals were determined by Flight. It was early observed that some minerals have varieties which are both -f- and . Rose attempted to establish a relation between the positive and negative pyritohedral forms of pyrite and cobaltite, and the positive or nega- tive thermo-electrical character. Later investigations by Schrauf and Dana have shown, however, that the same peculiarity belongs also to glaucodot, tetradymite, skutterudite, danaite, and other minerals, and it is demonstrated by them that it cannot be dependent upon crystalline form, but rather upon chemical composition. LITERATURE * Pyro-electricity, etc. Rose. Tourmaline. Pogg. Ann., 39, 285, 1836. Riess and Rose. Pogg. Ann., 59, 353, 1843: 61. 659, 1844. Kobell. Pogg. Ann., 118, 594, 1863. Hankel. Pogg. Ann., 49, 493; 50, 237, 1840; 61, 281, 1844. Many important papers in Abhandl. K. Sachs. Ges., 1865 and later; also Wied. Ann., 2, 66, 1877; 11, 269, 1880, etc. J. and P. Curie. C. R., 91, 294, 383, 1880; 92, 186, 350, 1881; 93, 204, 1882. Kundt. Ber. Ak. Berlin, 421, 1883; Wied. Ann., 20, 592, 1893. Kolenko. Quartz. Zs. Kr., 9, 1, 1884. C. Friedel. Sphalerite, etc. Bull. Soc. Min., 2, 31, 1879. C. Friedel and Curie. Sphalerite, boracite. Bull. Soc. Min., 6. 191, 1883. Mack. Boracite. Zs. Kr., 8, 503, 1883. Voigt. Abhandl. Ges. Gottingen, 36, 99, 1890. Kelvin. Phil. Mag., 36, 331, 453, 1893. G. S. Schmidt. Photo-electricity of fluorite. Wied. Ann., 62, 407, 1897. Thermo-electricity Marbach. C. R., 45, 705, 1857. Bunsen. Pogg. Ann., 123, 505, 1864. Friedel. Ann. Ch. Phys., 17, 79, 1869; C. R., 78, 508, 1874. Rose. Pyrite and cobaltite. Pogg. Ann., 142, 1, 1871. Schrauf and E. S. Dana. Ber. Ak. Wien, 69 (1), 142, 1874; Am. J. Sc., 8, 255, 1874. 2. MAGNETISM 441. Magnetic Minerals. Natural Magnets. A few minerals in their natural state are capable of being attracted by a strong steel magnet; they are said to be magnetic. This is conspicuously true of magnetite, the magnetic oxide of iron; also of pyrrhotite or magnetic pyrites, and of some varieties of native platinum (especially the variety called iron-platinum). A number of other minerals, as hematite, franklinite, etc., are in some * See Liebisch Phys. Krystallographie, 1891, for a full discussion of the topics briefly touched upon in the preceding pages, also for references to original articles. CHARACTERS DEPENDING UPON ELECTRICITY AND MAGNETISM 309 cases attracted by a steel magnet, but probably in most if not all cases because of admixed magnetite (but see Art. 443). Occasional varieties of the three minerals mentioned above, as the lodestone variety of magnetite, exhibit them- selves the attracting power and polarity of a true magnet. They are then called natural magnets. In such cases the magnetic polarity has probably been derived from the inductive action of the earth, which is itself a huge magnet. 442. Paramagnetism. Diamagnetism. In a very strong magnetic field, as that between the poles of a very powerful electromagnet, all minerals, as indeed all other substances, are influenced by the magnetic force. Accord- ing to their behavior they are divided into two classes, the paramagnetic and diamagnetic; those of the former appear to be attracted, those of the latter to be repelled. For purposes of experiment the substance in question, in the form of a rod, is suspended on a horizontal axis between the poles of the magnet. If paramagnetic, it takes a position parallel to the magnetic axis; if diamag- netic, it sets transversely to it. Iron, cobalt, nickel, manganese, platinum are paramagnetic; silver, copper, bismuth are diamagnetic. Among minerals compounds of iron are paramagnetic, as siderite, also diopside; further, beryl, dioptase. Diamagnetic species include calcite, zircon, wulfenite, etc. By the use of a sphere it is possible to determine the relative amount of magnetic induction in different directions of the same substance. Experiment has shown that in isometric crystals the magnetic induction is alike in all directions; that in those optically uniaxial, there is a direction of maximum and, normal to it, one of minimum magnetic induction; that in biaxial crystals, there are three unequal magnetic axes, the position of which may be determined. In other words, the magnetic relations of the three classes of crystals are analogous to their optical relations. 443. Corresponding to the facts just stated, that all compounds of iron are paramagnetic, it is found that a sufficiently powerful electromagnet attracts all minerals containing iron, though, except in the cases given in Art. 441, a bar magnet has no sensible influence upon them; hence the efficiency of the electromagnetic method of separating ores. Plucker * determined the magnetic attraction of a number of substances compared with iron taken as 100,000. For example, for magnetite he obtained 40,227; for hematite, crystallized, 533, massive, 134; limonite, 71; pyrite, 150. LITERATURE Magnetism Plucker. Pogg. Ann., 72, 315, 1847; 76, 576, 1849; 77, 447, 1849; 78, 427, 1849; 86, 1, 1852. Plucker and Beer. Pogg. Ann., 81, 115, 1850; 82, 42, 1852. Faraday. Phil. Trans., 1849-1857, and Experimental Researches, Series XXII, XXVI, XXX. W. Thomson (Lord Kelvin). Theory of Magnetic Induction. Brit. Assoc., 1850, pt. 2, 23; Phil. Mag., 1, 177, 1851, etc. Reprint of Papers on Electrostatics and Magnetism, 1872. Tyndall. Phil. Mag., 2, 165, 1851; 10, 153, 257, 1855; 11, 125, 1856; Phil. Trans., 1855, 1. Researches on diamagnetism and magne-crystallic action. London, 1870. Knoblauch and Tyndall. Pogg. Ann., 79, 233; 81, 481, 1850 (Phil. Mag., 36, 37, 1850). Rowland and Jacques. Bismuth, Calcite. Am. J. Sc., 18, 360, 1879. Tumlirz. Quartz. Wied. Ann., 27, 133, 1886. Koenig. Wied. Ann., 31, 273, 1887. Stenger. Calcite. Wied. Ann., 20, 304, 1883; 35, 331, 1888. * Pogg. Ann., 74, 343, 1848. 310 PHYSICAL MINERALOGY VI. TASTE AND ODOR In their action upon the senses a few minerals possess taste, and others under some circumstances give off odor. 444. Taste belongs only to soluble minerals. The different kinds of taste adopted for reference are as follows : 1. Astringent: the taste of vitriol. 2. Sweetish astringent: taste of alum. 3. Saline: taste of common salt. 4. Alkaline: taste of soda. 5. Cooling: taste of saltpeter. 6. Bitter: taste of Epsom salts. 7. Sour: taste of sulphuric acid. 445. Odor. Excepting a few gaseous and soluble species, minerals in the dry unchanged state do not give off odor. By friction, moistening with the breath, and the elimination of some volatile ingredient by heat or acids, odors are sometimes obtained which are thus designated : 1. Alliaceous: the odor of garlic. Friction of arsenopyrite elicits this odor; it may also be obtained from arsenical compounds by means of heat. 2. Horse-radish odor: the odor of decaying horse-radish. This odor is strongly perceived when the ores of selenium are heated. 3. Sulphurous: friction elicits this odor from pyrite, and heat from many sulphides. 4. Bituminous: the odor of bitumen. 5. Fetid: the odor of sulphureted hydrogen or rotten eggs. It is elicited by friction from some varieties of quartz and limestone. 6. Argillaceous: the odor of moistened clay. It is obtained from serpen- tine and some allied minerals, after moistening them with the breath; others, as pyrargillite, afford it when heated. 446. Feel. The FEEL is a character which is occasionally of some importance; it is said to be smooth (sepiolite), greasy (talc), harsh, or meager, etc. Some minerals, in consequence of their hygroscopic character, adhere to the tongue when brought in contact with it. PART III. CHEMICAL MINERALOGY GENERAL PRINCIPLES OF CHEMISTRY AS APPLIED TO MINERALS 447. Minerals, as regards their chemical constitution, are either the uncombined elements in a native state, or definite compounds of these elements formed in accordance with chemical laws. It is the object of Chemical Min- eralogy to determine the chemical composition of each species; to show the chemical relations of different species to each other where such exist; and also to explain the methods of distinguishing different minerals by chemical means. It thus embraces the most important part of Determinative Mineralogy. In order to understand the chemical constitution of minerals, some knowl- edge of the fundamental principles of Chemical Philosophy is required; and these are here briefly recapitulated. 448. Chemical Elements. Chemistry recognizes about eighty sub- stances which cannot at will be decomposed, or divided into others, by any process of analysis at present known ; these substances are called the chemical elements. A list of them is given in a later article (452) ; common examples are: Oxygen, nitrogen, hydrogen, chlorine, gold, silver, sodium, etc. 449. Atom. Molecule. The study of the chemical properties of sub- stances and of the laws governing their formation has led to the belief that there is for each element a definite, indivisible mass, which is the smallest particle which can play a part in chemical reactions; this indivisible unit is called the atom. With some rare exceptions, the atom cannot exist alone, but unites by the action of what is called chemical force, or chemical affinity, with other atoms of the same or different kind to form the molecule. The molecule, in the chemical senso, may be defined as the smallest particle into which a given kind of substance can be subdivided without undergoing chemical decomposi- tion. For example, two atoms of hydrogen unite to form a molecule of hydro- gen gas. Again, one atom of hydrogen and one of chlorine form a molecule of hydrochloric acid gas; two atoms of hydrogen and one of sulphur form a molecule of the gas hydrogen sulphide. 450. Atomic Weight. The atomic weight of an element is the weight, or, better expressed, the mass of its atom compared with that of the element hydrogen taken as the unit or with the weight of an atom of oxygen taken as 16. Of the methods by which the relation between the masses of the atoms is determined it is unnecessary here to speak ; the results that have been obtained are given in the table on p. 312. 311 312 CHEMICAL MINERALOGY 451. Symbol. Formula. The symbol of an element is the initial letter, or letters, often of its Latin name, by which it is represented when expressing in chemical notation the constitution of substances into the compo- sition of which it enters. Thus O is the symbol of oxygen, H of hydrogen, Cl of chlorine, Fe (from ferrum) of iron, Ag (from argentum) of silver, etc. Fur- ther, this symbol is always understood to indicate that definite amount of the given element expressed by its atomic weight; in other words, it represents one atom. If twice this quantity is involved, that is, two atoms, this is indicated by a small subscript number written immediately after the symbol. Thus, Sb 2 S 3 means a compound consisting of two atoms of antimony and three of sulphur, or of 2 X 120 parts by weight of antimony and 3 X 32 of sulphur. This expression, Sb 2 S 3 , is called the formula of the given compound, since it expresses in briefest form its composition. Similarly the formula of the mineral albite is NaAlSisOg. Strictly speaking, such formulas are merely empirical formulas, since they express only the actual result of analysis, as giving the relative number of atoms of each element present, and make no attempt to represent the actual constitution. A formula developed with the latter object in view is called a rational, structural, or constitutional formula (see Art. 469). 452. Table of the Elements. The following table gives a list of all the definitely established elements with their accepted symbols and also their atomic weights.* Of the elements given in this list more than eighty in all only a very small number, say twelve, play an important part in making up the crust of the earth and the water and air surrounding it. The common elements con- cerned in the composition of minerals are: Oxygen, sulphur, silicon, alu- minium, iron, calcium, magnesium, sodium, potassium. Besides these, hydro- gen is present in water, nitrogen in the air, and carbon in all animal and vegetable substances. Only a very few of the elements occur as such in nature, as native gold, native silver, native sulphur, etc. Of the elements, oxygen, hydrogen, nitrogen, chlorine, and fluorine are gases; bromine is a volatile liquid; mercury is also a liquid, but the others are solids under ordinary conditions. = 16 Symbol At. Weieht ' Symbol 0=16 At. Wpio-h Aluminium, Aluminum Al 27-1 Columbium, see Niobium Antimony (Stibium) Sb 120-2 Copper (Cuprum) Cu 63-6 Argon Arsenic A As 39-9 74-9 Dysprosium Erbium Dy Er 162-5 1677 Barium Ba 137-4 Europium Eu 152-0 Beryllium. Glucinum Be (or Gl) 9-1 Fluorine F 19-0 Bismuth Bi 208-0 Gadolinium Gd 157-3 Boron B 11-0 Gallium Ga 69-9 Bromine Br 79-9 Germanium Ge 72-5 Cadmium Cd 112-4 Glucinum, see Beryllium Caesium Cs 132-8 Gold (Aurum) Au 197-2 Calcium Ca 40-1 Helium He 4-0 Carbon C 12-0 Holmium Ho 163-5 Cerium Ce 140-2 Hydrogen H 1-0 Chlorine Cl 35-5 Indium In 114-8 Chromium Cr 52-0 Iodine I 126*9 Cobalt Co 59-0 Iridium Ir 193-1 * These correspond in value to those commonly accepted, and are given accurate to one decimal place. GENERAL PRINCIPLES OF CHEMISTRY AS APPLIED TO MINERALS 313 Symbol Iron (Ferrum) Fe 0=16 At. Weight 55-8 Ruthenium Symbol Ru 0=16 At. Weight 1017 Krypton Kr 82-9 Samarium Sa 150-4 Lanthanum La 139-0 Scandium Sc 44-1 Lead (Plumbum) Pb 207-2 Selenium Se 79-2 Lithium Li 6-9 Silicon Si 28-3- Lutecium Lu 175-0 Silver (Argentum) Ag 107-9 Magnesium Mg 24-3 Sodium (Natrium) Na 23-0 Manganese Mn 54-9 Strontium Sr 87-6 Mercury (Hydrargyrum) Hg 200-6 Sulphur S 32-0 Molybdenum Mo 96-0 Tantalum Ta 181-5 Neodymium Nd 144-3 Tellurium Te 127-5 Neon Ne 20-2 Terbium Tb 159-2 Nickel Ni 58-7 Thallium Tl 204-0 Niobium Nb 93-1 Thorium Th 232-4 Niton Nt 222-4 Thulium Tm 168-5 Nitrogen N 14-0 Tin (Stannum) Sn 1187 Osmium Os 190-9 Titanium Ti 48-1 Oxygen Palladium O Pd 16-0 106-7 Tungsten (Wolframium) Uranium W U 184-0 238-2 Phosphorus P 31:0 Vanadium V 51-0 Platinum Pt 195-2 Xenon Xe 130-2 Potassium (Kalium) K 39-1 Ytterbium Yb 173-5 Praseodymium Pr 140-9 Yttrium Yt 887 Radium Ra 226-0 Zinc Zn 65-4 Rhodium Rh 102-9 Zirconium Zr 90-6 Rubidium Rb 85-5 453. Metals and Non-metals. The elements may be divided into two more or less distinct classes, the metals and the non-metals. Between the two lie a number of elements sometimes called the semi-metals. The metals, as gold, silver, iron, sodium, are those elements which, physically described, possess to a more or less perfect degree the fundamental characters of the ideal metal, viz.: malleability, metallic luster (and opacity to light), conductivity for heat and electricity; moreover, chemically described, they commonly play the part of the positive or basic element in a simple compound, as later denned (Arts. 462-465). The non-metals, as sulphur, carbon, silicon, etc., also the gases, as oxygen, chlorine, etc., have none of the physical charac- ters alluded to: they are, if solids, brittle, often transparent to light-radiation, are poor conductors for heat and electricity. Chemically expressed, they usually play the negative or acid part in a simple compound. The so-called semi-metals, or metalloids, include certain elements, as tellurium, arsenic, antimony, bismuth, which have the physical characters of a metal to a less perfect degree (e.g., they are more or less brittle); and, more important 4 han this, they often play the part of the acidic element in the compound into which they enter. These points are illustrated later. It is to be understood that the distinctions between the classes of the elements named cannot be very sharply applied. Thus the typical metallic characters mentioned are possessed to a very unequal degree by the different substances classed as metals; for example, by silver and tin. Corresponding to this a number of the true metals, as tin and manganese, play the part of an U in acid in numerous salts. Further, the mineral magnetite, FeFe 2 O 4 , is often described as an iron ferrate; so that in this compound the same element would play the part of both acid and base. 454. Positive and Negative Elements. It is common to make a dis- tinction between the electro-positive and electro-negative element hi a compound. 314 CHEMICAL MINERALOGY The passage of a sufficiently strong electrical current through a chemical com- pound in many cases results in its decomposition (or electrolysis) into its ele- ments or parts. In such cases it is found that for each compound the atoms of one element collect at the negative pole (the cathode) and those of the other at the positive pole (the anode). The former is called the electro-positive element and the latter the electro-negative element. Thus in the electrolysis of water (H 2 0) the hydrogen collects at the cathode and is hence called posi- tive, and the oxygen at the anode and is called negative. Similarly, in hydro- chloric acid (HC1) the hydrogen is thus shown to be positive, the chlorine negative. This distinction is also carried to complex compounds, as copper sulphate (CuSO 4 ), which by electrolysis is broken into Cu, which is found to be electro-positive, and SO 4 (the last separates into SO 3 , forming H 2 SC>4 and free oxygen). For reasons which will be explained later, the positive element is said to play the basic part, the negative the acidic. The metals, as already stated, in most cases belong to the former class, the non-metals to the latter, while the semi-metals may play both parts. It is common in writing the formula to put the positive or basic element first, thus H 2 O, H 2 S, HC1, H 2 SO 4 , Sb 2 S 3 , As 2 O 3 , AsH 3 , NiSb, FeAs 2 . Here it will be noted that antimony (Sb) and arsenic (As) are positive in some of the compounds named but negative in the others. 455. Periodic Law. In order to understand the relations of the chief classes of chemical compounds represented among minerals, as still more their further subdivision, down finally to the many isomorphous groups groups of species having analogous composition and closely similar form, as explained in Art. 471 the fundamental relations and grouping of the ele- ments must be understood, especially as developed of recent years and shown in the so-called Periodic Law. Although the subject can be only briefly touched upon, it will be useful to give here the general distribution of the elements into Groups and Series, as presented in the Principles of Chemistry (Engl. Ed., 1891) of D. Mendeleeff, to whom is due more than any one else the development of the Periodic Law. When the elements are arranged according to the values of their atomic weights it is seen that they fall more or less into groups consisting of eight elements each, or double groups containing sixteen elements. The corresponding members of each group show similar chemical characters. The table given below will illustrate these relationships. For the thorough explanation of this subject, more particularly as regards the periodic or progressive relation between the atomic weights and various properties of the elements, the reader is referred to the work above mentioned or to one of the many other excellent modern text-books of chemistry. The relations of some of the elements of the first group are exhibited by the isomorphism (see Art. 471, also the description of the various groups and species here referred to, which are given in Part IV of this work) of NaCl, KC1, AgCl; or again of LiMnP0 4 and NaMnPO 4 , etc. In the second group, reference may be made to the isomorphism of the carbonates and sulphates (p. 322) of calcium, barium, and strontium; while among the sulphides, ZnS, CaS, and HgS are doubly related. In the third group, we find boron and aluminium often replacing one another among silicates. In the fourth group, the relations of silicon and titanium are shown in the titano-silicates, while the compounds Ti0 2 , SnO 2 , Pb0 2 (and MnO 2 ), also ZrSiO 4 and ThSi0 4 , have GENERAL PRINCIPLES OF CHEMISTRY AS APPLIED TO MINERALS 315 II II O 02 II 5 3 43 6 ^ II 23 ffl ii H 8 8 J u 316 CHEMICAL MINERALOGY closely similar form. In the fifth group, many compounds of arsenic, anti- mony, and bismuth are isomorphous among metallic compounds, while the relations of phosphorous, vanadium, arsenic, also antimony, are shown among the phosphates, vanadates, arsenates, and antimonates; again the mutual relations of the niobates and tantalates are to be noted. In the sixth group, the strongly acidic elements, sulphur, selenium, tellurium, are all closely related, as seen in many sulphides, selenides, tellu- rides; further, the relations of sulphur and chromium, and similarly of both of these to molybdenum and tungsten, are shown among many artificial sul- phates, chromates, molybdates, and tungstates. In the seventh group the relations of the halogens are too well understood to need special remark. In the eighth group, we have Fe, Co, Ni alloyed in meteoric iron, and their phosphates and sulphates are in several cases closely isomorphous; further, the relation of the iron series to that of the platinum series is exhibited in the isomorphism of FeS 2 , FeAsS, FeAs 2 , etc., with PtAs 2 and probably RuS 2 . 456. Combining Weight. Chemical investigation proves that the mass of a given element entering into a compound is always proportional either to its atomic weight or to some simple multiple of this; the atomic weight is hence also called the combining weight. Thus in rock salt, sodium chloride, the masses involved of sodium and chlorine present are found by analysis to be equal to 39'4 and 60'6 in 100 parts, and these numbers are in proportion to 23 : 35*4, the atomic weights of sodium and chlorine; hence it is concluded that one atom of each is present in the compound. The formula is, therefore, NaCl. In calcium chloride, by the same method the masses pres- ent are found to be proportional to 39'9 : 70*8, that is, to 39'9 : 2 X 35'4; hence the formula is CaCl 2 . Still again, a series of compounds of nitrogen with oxygen is known in which the ratios of the masses of the two elements are as follows: (1) 28 : 16, (2) 14 : 16, (3) 28 : 48, (4) 14 : 32, (5) 28 : 80. It is seen at once that these must have the formulas (1) N 2 O ; (2) NO, (3) N 2 O 3 , (4) NO 2 , (5) N 2 O 6 . On the contrary, atmospheric air which contains these elements in about the ratio of 76 '8 to 23 '2 cannot be a chemical compound of these elements, since (aside from other considerations) these numbers are not in the ratio of n X 14 : m X 16 where n and m are simple whole numbers. 457. Molecular Weight. The molecular weight is the weight of the molecule of the given substance, expressed in terms of the mass of the hydro- gen atom as unit. The molecular weight of hydrogen is 2 because the mole- cule can be shown to consist of two atoms. The molecular weight of hydro- chloric acid (HC1) is 36*4, of water vapor (H 2 O) 18, of hydrogen sulphide (H 2 S) 34. Since, according to the law of Avagadro, like volumes of different gases under like conditions as to temperature and pressure contain the same number of molecules, it is obvious that the molecular weight of substances in the form of gas can be derived directly from the relative density or specific gravity. If the density is referred to hydrogen, whose molecular weight is 2, it will be always true that the molecular weight is twice the density in the state of a gas and vice versa. Thus the observed density of carbon dioxide (CO 2 ) is 22, hence its molecular weight must be 44. It is this principle that makes it possible in the case of a gas to fix the constitution of the molecule when the ratio in number of the atoms entering into it has been determined by analysis. In the case of solids, where the constitution of the molecule in general cannot GENERAL PRINCIPLES OF CHEMISTRY AS APPLIED TO MINERALS 317 be fixed, it is best, as already stated, to write the molecular formula in its simplest form, as NaAlSi 3 Os for albite. The sum of the weights of the atoms present is then taken as the molecular weight. 458. Valence. The valence of an element is given by a number representing the capacity of its atoms to combine with the atoms of some unit element like hydrogen or chlorine. Thus, using the examples of Art. 456, in NaCl, since one atom of sodium unites with one of chlorine, its valence is one; or, in other words, it is said to be univalent. Further, calcium (as in CaCl 2 ), also barium, etc., are bivalent; aluminium is triva- lent; silicon is tetravalent, etc. The valence may be expressed by the number of bonds by which one element in a compound is united to another, thus: Na-Cl, Ba = Cl 2 , Au=Cl 3 , SniiCU, etc. A considerable number of the elements show a different valence in different compounds. Thus both Sb 2 3 and Sb 2 O 5 are known; also FeO and Fe 2 p 3 ; CuCl and CuCl 2 . These possible variations are indicated in the following table which gives the valences for the common elements. Univalent: H, Cl, Br, I, F; Li, Na, K, Rb, Cs, Ag, Hg, Cu, Au. Bivalent: O, S, Se, Te; Be, Mg, Ca, Sr, Ba, Pb, Hg, Cu, Zn, Co, Ni, Fe, Mn, Cr, C, Sn. Trivalent: B, Au, Al, Fe, Mn, Cr, Co, Ni, N, P, As, Sb, Bi. Tetravalent: C, Si, Ti, Zr, Sn, Mn, Pb. Pentavalent: N, P, As, Sb, V, Bi, Nb, Ta. 459. Chemical Reactions. When solutions of two chemical sub- stances are brought together, in many cases they react upon each other with the result of forming new compounds out of the elements present; this phe- nomenon is called a chemical reaction. One of the original substances may be a gas, and in many cases similar results are obtained from a liquid and a solid, or less often from two solids. For example, solutions of sodium chloride (NaCl) and silver nitrate (AgNO 3 ) react on each other and yield silver chloride (AgCl) and sodium nitrate (NaNO 3 ). This is expressed in chemical language as follows: NaCl + AgNO 3 = AgCl + NaN0 3 . This is a chemical equation, the sign of equality meaning that equal weights are involved both before and after the reaction. Again, hydrochloric acid (HC1) and calcium carbonate (CaCO 3 ) yield calcium chloride (CaCl 2 ) and carbonic acid (H 2 CO 3 ) ; which last breaks up into water (H 2 O) and carbon dioxide (CO 2 ), the last going off as a gas with effervescence. Hence CaCO 3 + 2HC1 = CaCl 2 + H 2 O + C0 2 . 460. Radicals. A compound of two or more elements according to their relative valence in which all their bonds are satisfied is said to be satu- rated. This is true of H 2 O, or, as it may be written, H OH. If, however, one or more bonds is left unsatisfied, the resulting combination of elements is called a radical. Thus O H, called briefly hydroxyl, is a common radical, having a valence of one, or, in other words, univalent ; NH 4 is again a univalent radical; so, too, (CaF), (MgF) or (A10). Radicals often enter into a com- pound like a simple element; for example, in ammonium chloride, NH 4 C1, the univalent radical NH 4 plays the same part as the univalent element Na in NaCl. In the chemical composition of mineral species, the commonest radical 318 CHEMICAL MINERALOGY is hydroxyl ( H) already defined. Other examples are (CaF) in apatite (see Art. 471), (MgF) in wagnerite, (A1O) in many basic silicates, etc. 461. Chemical Compound. A chemical compound is a combination of two or more elements united by the force of chemical attraction. It is always true of it, as before stated (Art. 456), that the elements present are combined in the proportion of their atomic weights or some simple multiples of these. A substance which does not satisfy this condition is not a compound, but only a mechanical mixture. Examples of the simpler class of compounds are afforded by the oxides, or compounds of oxygen with another element. Thus, among minerals we have Cu 2 O, cuprous oxide (cuprite); ZnO, zinc oxide (zincite); A1 2 3 , alumina (corundum); SnO 2 , tin dioxide (cassiterite) ; SiO 2 , silicon dioxide (quartz); As 2 O 3 , arsenic trioxide.(arsenolite). Another simple class of compounds are the sulphides (with the selenides, tellurides, arsenides, antimonides, etc.), compounds in which sulphur (selen- ium, tellurium, arsenic, antimony, etc.) plays the same part as oxygen in the oxides. Here belong Cu 2 S, cuprous sulphide (chalcocite) ; ZnS, zinc sulphide (sphalerite); PbTe, lead telluride (altaite); FeS 2 , iron disulphide (pyrite); Sb 2 S 3 , antimony trisulphide (stibnite). 462. Acids. The more complex chemical compounds, an understanding of which is needed in a study of minerals, are classed as acids, bases, and salts; the distinctions between them are important. An acid is a compound of hydrogen, or hydroxyl, with a non-metallic element (as chlorine, sulphur, nitrogen, phosphorus, etc.), or a radical con- taining these elements. When dissolved in water they all give the positive hydrogen ion and a negative ionic substance such as Cl, SO 4 , etc. The hydrogen atoms of an acid may be replaced by metallic atoms; the result being then the formation of a salt (see Art. 464). Acids in general turn blue litmus paper red and have a sharp, sour taste. The following are familiar examples: HC1, hydrochloric acid, HNO 3 , nitric acid. H 2 CO 3 , carbonic acid. H 2 S0 4 , sulphuric acid. H 2 Si0 3 , metasilicic acid. H 3 PO4, phosphoric acid. H 4 Si04, orthosilicic acid. It is to be noted that with a given acid element several acids are possible. Thus normal, or orthosilicic, acid is H 4 SiO 4 , in which the bonds of the ele- ment silicon are all satisfied by the hydroxyl (HO). But the removal of one molecule of water, H 2 O, from this gives the formula H 2 SiO 3 , or metasilicic acid. Acids which, like HN0 3 , contain one atom of hydrogen that may be replaced by a metallic atom (e.g., in KNO 3 ) are called monobasic. If, as in H 2 CO 3 and H 2 SO 4 , there are two atoms or a single bivalent atom, (e.g., in CaC0 3 , BaSO 4 ) the acids are dibasic. Similarly, H 3 PO 4 is tribasic, etc. Most acids are liquids (or gases), and hence acids are represented very sparingly among minerals; B(OH) 3 , boric acid (sassolite), is an illustration. 463. Bases. The bases, or hydroxides, as they are also called, are compounds which may be regarded as formed of a metallic element (or radical) GENERAL PRINCIPLES OF CHEMISTRY AS APPLIED TO MINERALS 319 and the univalent radical hydroxyl, (OH) ; or, in other words, of an oxide with water. Thus potash, K 2 O, and water, H 2 O, form 2K(OH), or potassium hydroxide; also CaO + H 2 O similarly give Ca(OH) 2 , or calcium hydroxide. In general, when soluble in water, bases give an alkaline reaction with turmeric paper or red litmus paper, and they also neutralize an acid, as explained in the next article. Further, the bases yield water on ignition, that is, at a temperature sufficiently high to break up the compound. Among minerals the bases are represented by the hydroxides, or hydrated oxides, as Mg(OH) 2 , magnesium hydrate (brucite); A1(OH) 2 , aluminium hydrate (gibbsite); also, (A1O)(OH), diaspore, etc. 464. Salts. A third class of compounds are the salts; these may be regarded as formed chemically by the reaction of a base upon an acid, or, in other words, by the neutralization of the acid. Thus calcium hydrate and sul- phuric acid give calcium sulphate and water: Ca(OH) 2 -f H 2 S0 4 = CaSO 4 + 2H 2 O. Here calcium sulphate is the salt, and in this case the acid, sulphuric acid, is said to be neutralized by the base, calcium hydroxide. It is instructive to compare the formulas of a base, an acid, and the corresponding salt, as follows : Base, Ca(OH) 2 ; Acid, H 2 S0 4 ; Salt, CaS0 4 . Here it is seen that a salt may be simply described as formed from an acid by the replacement of the hydrogen atom, or atoms, by a metallic element or radical. 465. Typical Salts. The commonest types of salts represented among minerals are the following: Chlorides: salts of hydrochloric acid, HC1; as AgCl, silver chloride (cerar- gyrite). Nitrates: salts of nitric acid, HN0 3 ; as KNO 3 , potassium nitrate (niter). Carbonates: salts of carbonic acid, H 2 C0 3 ; as CaC0 3 , calcium carbonate (calcite and aragonite). Sulphates: salts of sulphuric acid, H 2 S0 4 ; as CaS0 4 , calcium sulphate (anhydrite). Phosphates: salts of phosphoric acid, H 3 P0 4 ; as Ca 3 (PO 4 ) 2 , calcium phos- phate. Silicates: several classes of salts are here included. The most common are the salts of metasilicic acid, H 2 SiO 3 ; as MnSi0 3 , manganese metasilicate (rhodonite). Also salts of orthosilicic acid, H 4 Si0 4 ; as Mn 2 Si0 4 , manganese orthosilicate (tephroite) . Numerous other classes of salts are also included among mineral species; their composition, as well as that of complex salts of the above types, is explained in the descriptive part of this work. 466. Normal, Acid, and Basic Salts. A neutral or normal salt is one in which the basic element completely neutralizes the acid, or, in other words, one of the type already given as examples, in which all the hydrogen atoms of the acid have been replaced by metallic atoms or radicals. Thus, K 2 SO 4 is normal potassium sulphate, but HKSO 4 , on the other hand, is acid potassium sulphate, since in the acid H 2 SO 4 only one of the bonds is taken by the basic element potassium. Salts of this kind are called acid salts. The formula in 320 CHEMICAL MINERALOGY such cases may be written * as if the compound consisted of a normal salt and an acid; thus, for the example given, K 2 SO 4 . H 2 SO 4 . A basic salt is one in which- the acid part of the compound is not sufficient to satisfy all the bonds of the base. Thus malachite is a basic salt basic carbonate of copper its composition being expressed by the formula _ f^r\ Cu 2 (OH) 2 C0 3 . This may be written CuCO 3 . Cu(OH) 2 , or (Cu 2 ) = ^g^ The majority of minerals consist not of simple salts, as those noted above, but of more or less complex double salts in which several metallic elements are present. Thus common grossular garnet is an orthosilicate containing both calcium and aluminium as bases; its formula is Ca 3 Al 2 (SiO 4 ) 3 . 467. Sulpho-salts. The salts thus far spoken of are all oxygen salts. There are also others, of analogous constitution, in which sulphur takes the place of the oxygen; they are hence called sulpha-salts. Thus normal sulph- arsenious acid has the formula H 3 AsS 3 , and the corresponding silver salt is AgsAsS 3 , the mineral proustite. Similarly the silver salt of the analogous antimony acid is Ag 3 SbS 3 , the mineral pyrargyrite. From the normal acids named, a series of other hypothetical acids may be derived, as HAsS 2 , H 4 As 2 S 5 , etc. ; these acids are not known to exist, but their salts are important minerals. Thus zinkenite, PbSb 2 S4, is a salt of the acid H 2 Sb 2 S4, and jamesonite, Pb 2 Sb 2 S 5 , of the acid H4Sb 2 S 5 , etc. 468. Water of Crystallization. As stated in Art. 463, the hydroxides, or bases, and further basic salts -in general, yield water when ignited. Thus calcium hydroxide Ca(OH) 2 breaks up on heating into CaO and H 2 O, as expressed in the chemical equation 2Ca(OH) 2 = 2CaO + H 2 0. So also the basic cupric carbonate, malachite, Cu 2 (OH) 2 C0 3 , yields water on ignition; and the same is true of the complex basic orthosilicates, like zoisite, whose formula is (HO)Ca 2 Al 3 (Si04) 3 . It is not to be understood, however, in these or similar cases, that water as such is present in the substance. On the other hand, there is a large number of mineral compounds which yield water readily when heated, and in which the water molecules are regarded as present as so-called water of crystallization. Thus, the formula of gypsum is written CaSO 4 + 2H 2 O, and the molecules of water (2H 2 O) are considered as water of crystallization. So, too, in potash alum, KA1(S0 4 ) 2 + 12H 2 O, the water is believed to play the same part. 469. Formulas of Minerals. The strictly empirical formula expresses the kinds and numbers of atoms of the elements present in the given com- pound, without attempting to show the way in which it is believed that the atoms are combined. Thus, in the case of zoisite the empirical formula is HCa2Al 3 Si 3 Oi 3 . While not attempting to represent the structural formula (which will not be discussed here), it is convenient in certain cases to indicate the atoms which there is reason to believe play a peculiar relation to each other. Thus the same formula written (HO)Ca 2 Al 3 (SiO 4 ) 3 shows that it is regarded as a basic orthosilicate, in other words, a basic salt of orthosilicic acid, H 4 SiO 4 . * This early form of writing the composition explains the name often given to the com- pound, namely, in this case, "bisulphate of potash." GENERAL PRINCIPLES OF CHEMISTRY AS APPLIED TO MINERALS 321 Again, the empirical formula of common apatite is Ca 5 FP 3 Oi 2 ; but if this is written (CaF)Ca 4 (PO 4 )3, it shows that it is regarded as a phosphate of the acid H 3 PO4, that is, H^PO^s, in which the nine hydrogen atoms are replaced by four Ca atoms together with the univalent radical (CaF). In another kind of apatite the radical (CaCl) enters in the same way. Similarly to this the formula of pyromorphite is (PbCl)Pb 4 (PO 4 )3, of vanadinite (PbCl)Pb 4 (VO 4 ) 3 . Further, it is often convenient to employ the method of writing the form- ulas in vogue under the old dualistic system. For example, CaO.CO 2 for CaCO 3 , 3CaO . A1 2 O 3 . 3SiO 2 for Ca 3 Al 2 Si 3 Oi 2 , 3Ag 2 S . Sb 2 S 3 for Ag 3 SbS 3 , etc. It is no longer believed, however, that the molecular groups CaO, A1 2 3 , etc., actually exist in the molecule of the substance. But in part because these groups are what analysis of the substance affords directly, and in part because so easily retained in the memory, this method of writing is still often used. 470. Calculation of a Formula from an Analysis. The result of an analysis gives the proportions, in a hundred parts of the mineral, of either the elements themselves, or of their oxides or other compounds obtained in the chemical analysis. In order lo obtain the atomic proportions of the elements : Divide the percentages of the elements by the respective ATOMIC WEIGHTS; or, for those of the oxides: Divide the percentage amounts of each by their MOLECULAR WEIGHTS; then find the simplest ratio in whole numbers for the numbers thus obtained. . Example. An analysis of bournonite from Wolfsberg gave C. Bromeis the results under (1) below. These percentages divided by the respective atomic weights, as indicated, give the numbers under (2). Finally the ratio of these numbers gives very nearly 1 : 3 : 1 : 1. Hence the formula derived is CuPbSbS 3 . The theoretical values called for by the formula are added under (4). (1) (2) (3) (4) Sb 24'34 -r- 120 = 0'203 1 247 S 1976 * 32 = 0'617 3 19'8 Pb 42-88 -5- 206-4 = 0'208 1 42'5 Cu 13-06 -r- 63-2 = 0-207 1 13'0 100-04 lOO'O Second Example. The mean of two analyses of a garnet from Alaska gave Kountze the results under (1) below. Here, as usual, the percentage amounts of the several molecular groups (SiO 2 , A1 2 O 3 , etc.) are given instead of those of the elements. These amounts divided by the respective niolecular weights give the numbers under (2). In this case the amounts of the protoxides are taken together and the ratio thus obtained is 3 '09 : 1 : 2 "92, which corresponds approximately to the formula 3FeO.Al 2 O 3 .3SiO 2 , or Fe 3 Al2(SiO 4 ) 3 . The magnesium in this garnet would ordinarily be explained by the presence of the pyrope molecule (Mg 3 Al 2 [SiO 4 ] 3 ) together with the simple almandite molecule whose composition is given above. (1) (2) (3) SiO 2 39-29 -5- 60 = 0'655 3'09 A1 2 O 3 21-70 -5- 102 = 0-212 1 Fe 2 3 tr. FeO 30-82 H- 71 -9 = 0'429 MnO 1-51 -f- 70-8 = 0'022 L. A1Q 9 . Q9 MgO 5-26 -^40 = 0-132 l CaO 1-99 -J- 55-9 = 0'036 100-57 It is necessary, when very small quantities only of certain elements (as MnO, MgO, CaO above) are present, to neglect them in the final formula, reckoning them in with the elements 322 CHEMICAL MINERALOGY which they replace, that is, with those of the same quanti valence. The degree of corre- spondence between the analysis and the formula deduced, if the latter is correctly assumed, depends entirely upon the accuracy of the former. i ! 471. Isomorphism. Chemical compounds which have an analogous composition and a closely related crystalline form are said to be isomorphous. This phenomenon, called ISOMORPHISM, was first clearly brought out by Mit- scherlich. Many examples of groups of isomorphous compounds will be found among the minerals described in the following pages. Some examples are mentioned here in order to elucidate the subject. In the brief discussion of the periodic classification of the chemical ele- ments of Art. 455, attention has been called to the prominent groups among the elements which form analogous compounds. Thus calcium, barium, and strontium, and also lead, form the two series of analogous compounds, Aragonite Group Barite Group CaCO 3 , aragonite. Also CaSO 4 , anhydrite. BaC0 3 , witherite. BaS0 4 , barite. SrCO 3 , strontianite. SrS0 4 , celestite. PbCO 3 , cerussite, PbSO 4 , anglesite. Further, the members of each series crystallize in closely similar forms. The carbonates are orthorhombic, with axial ratios not far from one another; thus the prismatic angle approximates to 60 and 120, and corresponding to this they all exhibit pseudo-hexagonal forms due to twinning. The sulphates also form a similar orthorhombic series, and though anhydrite deviates somewhat widely, the others are close together in angle and in cleavage. Again, calcium, magnesium, iron, zinc, and manganese form a series of car- bonates with analogous composition as shown in the list of the species of the Calcite Group given on p. 437. This table brings out clearly the close relation in form between the species named. Further it is also generally true with an isomorphous series that the various molecules may enter in greater or less degree into the constitution of one of the members of the series without causing any marked change in the crystal characters. For instance, in the Calcite Group, calcite itself may contain small percentages of MgCO 3 , FeCO 3 and MnCO 3 . These different molecules may assume in the crystal structure of the mineral the same functions as the corresponding amounts of CaC0 3 which they have replaced. The molecules of magnesite and siderite, MgCO 3 and FeCO 3 , may replace each other in any proportion and the same is true with siderite and rhodochrosite, MnC0 3 . Various intermediate mixtures of these latter molecules have been described and given distinctive names to which definite formulas have been assigned. It is doubtful, however, if these compounds have any real existence but merely represent certain points in the complete isomorphous series that lies between the end members. Dolomite, CaMg(CO 3 ) 2 , on the other hand, is a definite compound and not an isomorphous mixture of CaCO 3 and MgCO 3 . It may, however, contain varying amounts of FeCO 3 , MnCO 3 and also an excess of CaCO 3 or MgCO 3 , all of which enter the regular molecule in the form of isomorphous replacements. The Apatite Group forms another valuable illustration since in it are represented the analogous compounds, apatite and pyromorphite, both phos- phates, but respectively phosphates of calcium and lead; also the analogous GENERAL PRINCIPLES OF CHEMISTRY AS APPLIED TO MINERALS 323 lead compounds pyromorphite, mimetite, and vanadinite respectively lead phosphate, lead arsenate, and lead vanadate. Further, in all these compounds the radical (RC1) or (RF) enters in the same way (see Art. 469). Thus the formulas for the two kinds of apatite and that for pyromorphite are as follows : (CaF)Ca 4 (P0 4 )3, (CaCl)Ca 4 (PO 4 )3, (PbCl)Pb 4 (PO 4 ) 3 . Some of the more important isomorphous groups are mentioned below. For a discus- sion of them, as well as of many others that might be mentioned here, reference must be made to the descriptive part of this work. Isometric System. The Spinel group, including spinel, MgAl 2 O 4 ; also magnetite, chromite, franklinite, gahnite, etc. The Galena group, as galena, PbS; argentite, Ag->S, etc. The Garnet group, as grossularite, CasAiiSiiOn, etc. Tetragonal System. Rutile group, including rutile, TiO2,' cassiterite, SnC>2. The Scheelite group, including scheelite, CaWO 4 ; stolzite, PbW0 4 ; wulfenite, PbMoO 4 . Hexagonal System. Apatite group, already mentioned, including apatite, pyromor- phite, mimetite, and vanadinite. Corundum group, corundum, A1 2 O 3 ; hematite, FesOs. Calcite group, already mentioned. Phenacite group, etc. Orthorhombic System. Aragonite group, and Barite group, both mentioned above. Chrysolite group, (Mg,Fe)2SiO 4 ; Topaz group, etc. Monodinic System. Copperas group, including melanterite, FeSO 4 + THizO; bieberite, CoSO 4 + 7H 2 O, etc. Pyroxene and Amphibole groups, and the Mica group. Monodinic and Triclinic Systems. Feldspar group. 472. Isomorphous Mixtures. It is important to note that the inter- mediate compounds in the case of an isomorphous series, such as those spoken of in the preceding article, often show a distinct gradation in crystalline form, and more particularly in physical characters (e.g., specific gravity, optical properties, etc.). This is illustrated by the species of the calcite group already referred to; also still more strikingly by the group of the triclinic feldspars as fully discussed under the description of that group. See further Art. 424. The feldspars also illustrate two other important points in the subject, which must be briefly alluded to here. The triclinic feldspars have been shown by Tschermak to be isomorphous mixtures of the end compounds in varying proportions : Albite, NaAlSi 3 O 8 . Anorthite, CaAl 2 Si 2 O 8 . Here it is seen that these compounds have not an analogous composition in the narrow sense previously illustrated, and yet they are isomorphous and form an isomorphous series. Other examples of this are found among the pyroxenes, the scapolites, etc. Further, the Feldspar group in the broader sense includes several other species, conspicuously the monoclinic orthoclase, KAlSi 3 Os, which, though belonging to a different system, still approximates closely in form to the triclinic species. 473. Variation in Composition of Minerals. Isomorphous Replacement and Solid Solution. The idea that a mineral must rigidly conform in its chemical composition to a theoretical composition derived from its formula can no longer be strictly held. It is true that the majority of minerals do show a close correspondence to that theory, commonly within the limits of possible errors in the analyses. On the other hand, many minerals show slight and certain ones considerable variations from their theoretical compositions. These variations. can usually be explained by the principle of isomorphism. An instructive example is the case of sphalerite. Note in the analyses quoted below how the percentages of zinc diminish and those of iron correspondingly increase. It is evident from these analyses that iron, and in a much smaller 324 CHEMICAL MINERALOGY degree other metals, may enter into the chemical compound and while replac- ing the zinc perform the same function as it, in the crystalline structure of the mineral. The iron is therefore spoken of as being isomorphous with the zinc or the iron sulphide molecule as isomorphous with the zinc sulphide molecule. There is no definite ratio between the amounts of the iron and zinc that may be present but there is a constant ratio (1 : 1) between the sum of the atoms of the metals and the atoms of sulphur. That is, although the composition may vary, the atomic ratios and the crystalline structure remain constant. In some cases this interchange between elements or radicals may be complete, in other cases there may be distinct limitations to the amount by which any element or radical may be replaced by another. For instance in sphalerite the maximum percentage of the isomorphous iron seems to be about 16 to 18 per cent. Colorless Sphalerite Brown Sphalerite Black Sphalerite S 32.93 S 33.36 S 33.25 Zn 66.69 Zn 63.36 Zn 50.02 Fe 0.42 Fe 3.60 Fe 15.44 moi 100.32 Cd 0.30 100.02 Further, we have cases where a compound may, in a certain sense, dissolve another unrelated substance and form what is known as a solid solution. This kind of phenomenon is well recognized among artificial salts and has recently been definitely proved with certain minerals. For instance, it has been shown experimentally that the artificial iron sulphide, FeS, correspond- ing to pyrrhotite, can dissove an excess of sulphur up to about 6 per cent. Natural pyrrhotite always contains an excess of sulphur over that required by the formula, FeS, and various formulas such as Fe 7 S 8 , Fe n S n +i, etc., have been assigned to the mineral. This extra sulphur in the mineral varies in amount but also has as its maximum about 6 per cent. In view of the experimental data there is no doubt but that pyrrhotite should be considered as the mono- sulphide of iron containing varying small amounts of excess sulphur in the form of a solid solution. Another case of solid solution is undoubtedly shown by nephelite which commonly contains a small excess of SiO 2 . It is very probable that further investigation will show that many minerals have this power of holding in solid solution small amounts of foreign substances and that many hitherto inexplicable discrepancies in their analyses may be explained in this way. Such an assumption should not be made, however, without convincing proof of its probability, since many analytical discrepancies are undoubtedly due to either faulty analyses or to impure material. 474. Colloidal Minerals or Mineral Gels.* It has been recognized recently that our amorphous hydrated minerals frequently do not conform in their analyses to the usually accepted formulas and cannot be regarded in the strict sense as definite chemical compounds. They show rather the proper- ties of solid colloids or as they are commonly called mineral gels. A colloidal solution may be conceived as being intermediate in its characters between a true solution and the case where the mineral material is definitely in suspen- * For a resume of the subject of gel minerals and a complete bibliography reference is made to articles by Marc and Himmelbauer, Fortschritte Min. Krist. Pet., 3, 11, 33, 1913. GENERAL PRINCIPLES OF CHEMISTRY AS APPLIED TO MINERALS 325 sion in a liquid. It is probable that all gradations between these two extremes may occur. The mineral gels, or hydrogels, as they are sometimes called, since water is the liquid involved, are apparently formed from such colloidal solutions by some process of coagulation. They are considered therefore to consist of a micro-heterogeneous mixture of excessively minute particles of mineral material and water. These mineral gels are formed at low temperatures and pressures and are characteristically found among the products of rock weathering and in the oxidized zone of ore deposits. Some of them also occur in hot spring deposits. These minerals ordinarily assume botryoidal, reniform or stalactitic shapes, although, when the conditions of formation do not permit free growth, they may be earthy or dendritic. Frequently a mineral originally colloidal may become more or less crystalline in character through a molecular rearrange- ment and develop a fibrous" or foliated structure. These have been designated as meta-colloids. One important character of the gel minerals is their power to adsorb foreign materials. If through some change in condition one of these hydrogels should lose a part of its water content the remaining material would have a finely divided and porous structure exactly adapted to exert a strong power of adsorption. Consequently, although in many cases the main mass of the mineral may have a composition closely similar to some definite crystallized mineral, it will commonly show a considerable range in composition due both to the non-molecular relations of the contained water and to this secondary adsorption. Common mineral gels or substances derived from them are opal, bauxite, psilomelane, various members of the phosphate and arsenate groups, etc. As suggested above, gel varieties of minerals that occur also in crystal- line forms are thought to exist. For example some authors speak of bauxite as the gel form of hydrargillite, stilpnosiderite as the gel form of goethite, chrysocolla of dioptase, and further give new names, such as gelvariscite, gelpyrophyllite, etc., to the gel phases of the corresponding crystalline minerals. 475. Dimorphism. Isodimorphism. A chemical compound, which crystallizes in two forms genetically distinct, is said to be dimorphous; if in three, trimorphous, or in general pleomorphous. This phenomenon is called DIMORPHISM Or PLEOMORPHISM. An example is given by the compound calcium carbonate (CaCO 3 ), which is dimorphous : appearing as calcite and as aragonite. As calcite it crystallizes in the rhombohedral class of the^ hexagonal system, and, unlike as its many crystalline forms are, they may be all referred to the same fundamental axes, and, what is more, they have all the same cleavage and the same specific gravity (27) and, of course, the same optical characters. As aragonite, cal- cium carbonate appears in orthorhombic crystals, whose optical characters are entirely different from those of calcite; moreover, the specific gravity of aragonite (2'9) is higher than that of calcite (27). Many other examples might be given: Titanium dioxide (TiO 2 ) is tri- morphous, the species being called rutile, tetragonal (c = 0'6442), G. = 4*25; octahedrite, tetragonal (c = 1778), G. = 3 '9; and brookite, orthorhombic, G. = 4' 15. Carbon appears in two forms, in diamond and graphite. Other familiar examples are pyrite and marcasite (FeS 2 ), sphalerite and wurtzite (ZnS), etc. When two or more analogous compounds are at the same time isomorphous and dimorphous, they are said to be isodimbrphous, and the phenomenon is 326 CHEMICAL MINERALOGY called ISODIMORPHISM. An example of this is given in the Pyrite and Mar- casite groups described later. Thus we have in the isometric Pyrite Group, pyrite, FeS 2 , smaltite, CoAs 2 ; in the orthorhombic Marcasite Group, marcas- ite, FeS 2 , safflorite, CoAs 2 , etc. 476. Chemical and Microchemical Analysis. The analysis of min- erals is a subject treated of in chemical works, and need not be touched upon here except so far as to note the convenient use of certain qualitative methods, as described in the later part of this chapter. Of more importance are the microchemical methods applicable to sections under the microscope and often yielding decisive results with little labor. This subject has been particularly developed by Boricky, Haushofer, Behrens, Streng, and others. Reference is made to the discussion by Rosenbusch. (Mikr. Phys., 1904, p. 435 et seq.), to Johannsen (Manual of Pet. Methods, 559, et seq., including a bibliography). Microchemical methods used upon polished surfaces of opaque minerals are described by Murdock (Micro. Deter. Opaque Min., 1916) and by Davy-Farnham (Micro. Exam, of the Ore Min., 1920). 477. Mineral Synthesis. The occurrence of certain mineral com- pounds (e.g., the chrysolites) among the products of metallurgical furnaces has long been noted. But it has only been in recent years that the formation of artificial minerals has been made the subject of minute systematic experi- mental study. In this direction the French chemists have been particularly successful, and now it may be stated that the majority of common minerals quartz, the feldspars, amphibole, mica. etc. have been obtained in crystal- lized form. Even the diamond has been formed in minute crystals by Moissan. These studies are obviously of great importance particularly as throwing light upon the method of formation of minerals in nature. The chief results of the work thus far done are given in the volumes mentioned in the Introduction, p. 4. 478. Alteration of Minerals. Pseudomorphs. The chemical altera- tion of mineral species under the action of natural agencies is a subject of great importance and interest, particularly when it results in the change of the original composition into some other equally definite compound. A crystal- lized mineral which has thus suffered change so that its form no longer belongs to its chemical composition has already been defined (Art. 273, p. 183) as a pseudomorph. It remains to describe more fully the different kinds of pseudo- morphs. Pseudomorphs are classed under several heads : 1. Pseudomorphs by substitution. 2. Pseudomorphs by simple deposition, and either by (a) incrustation or (b) infiltration. 3. Pseudomorphs by alteration; and these may be altered (a) without a change of composition, by paramorphism; (b) by the loss of an ingredient; (c) by the assumption of a foreign substance; (d) by a partial exchange of constituents. 1. The first class of pseudomorphs, by substitution, embraces those cases where there has been a gradual removal of the original material and a cor- responding and simultaneous replacement of it by another, without, however, any chemical reaction between the two. A common example of this is a piece of fossilized wood, where the original fiber has been replaced entirely by CHEMICAL EXAMINATION OF MINERALS 327 silica. The first step in the process was the filling of the pores and cavities by the silica in solution, and then as the woody fiber, by gradual decomposi- tion, disappeared the silica further took its place. Other examples are quartz after fluorite, calcite, and many other species; cassiterite after orthoclase; native copper after aragonite, etc. 2. Pseudomorphs by incrustation form a less important class. Such are the crusts of quartz formed over fluorite. In most cases the removal of the original mineral has gone on simultaneously with the deposition of the second, so that the resulting pseudomorph is properly one of substitution. In pseudo- morphs by infiltration a cavity made by the removal of a crystal has been filled by another mineral. 3. The third class of pseudomorphs, by alteration, includes a considerable proportion of the observed cases, of which the number is very large. Con- clusive evidence of the change which has gone on is often furnished by a nucleus of the original mineral in the center of the altered crystal e.g., a kernel of cuprite in a pseudomorphous octahedron of malachite; also of chrysolite in a pseudomorphous crystal of serpentine, etc. (a) An example of paramorphism that is, of a change in molecular con- stitution without change of chemical substance is furnished by the change of aragonite to calcite (both CaCO 3 ) at a certain temperature ; also the paramorphs of rutile after brookite (both TiO 2 ) from Magnet Cove, Arkansas. (6) An example of the pseudomorphs in which alteration is accompanied by a loss of ingredients is furnished by crystals of native copper in the form of cuprite. (c) In the change of cuprite to malachite e.g., the familiar crystals from Chessy, France an instance is afforded of the assumption of an ingredient viz., carbon dioxide (and water). Pseudomorphs of gypsum after anhydrite occur where there has been an assumption of water alone. (d) A partial exchange of constituents in other words, a loss of one and gain of another takes place in the change of feldspar to kaolin, in which the potash silicate disappears and water is taken up; pseudomorphs of limonite after pyrite or siderite, of chlorite after garnet, pyromorphite after galena, are other examples. The chemical processes involved in such changes open a wide and impor- tant field for investigation. Their study has served to throw much light on the chemical constitution of mineral species and the conditions under which they have been formed. For the literature of the subject see the Introduc- tion, p. 4 (Blum, Bischof, Roth, etc.). CHEMICAL EXAMINATION OF MINERALS 479. The complete investigation of the chemical composition of a min- eral includes, first, the identification of the elements present by qualitative analysis, and, second, the determination of the relative amounts of each by quantitative analysis, from which last the formula can be calculated. Both processes carried out in full call for the equipment of a chemical laboratory. An approximate qualitative analysis, however, can, in many cases, be made quickly and simply with few conveniences. The methods employed involve either (a) the use of acids or other reagents " in the wet way," or (6) the use 328 CHEMICAL MINERALOGY of the blowpipe, or of both methods combined. Some practical instructions will be given applying to both cases. EXAMINATION IN THE WET WAY 480. Reagents, etc. The most commonly employed chemical re- agents are the three mineral acids, hydrochloric, nitric, and sulphuric acids. To these may be added ammonium hydroxide, also solutions of barium chlo- ride, silver nitrate, ammonium molybdate, ammonium oxalate; finally, dis- tilled water in a wash-bottle. A few test-tubes are needed for the trials and sometimes a porcelain dish with a handle called a casserole; further, a glass funnel and filter-paper. The Bunsen gas-burner (p. 330) is the best source of heat, though an alcohol lamp may take its place. It is unnecessary to remark that the use of acids and the other reagents requires much care to avoid injury to person or clothing. In testing the powdered mineral with the acids, the important points to be noted are: (1) the degree of solubility, and (2) the phenomena attending entire or partial solution; that is, whether (a) a solution is obtained quietly, without effervescence, and, if so, what its color is; or (6) a gas is evolved, producing effervescence; or (c) an insoluble constituent is separated out. 481. Solubility. In testing the degree of solubility hydrochloric acid is most commonly used, though in the case of many metallic minerals, as the sulphides and compounds of lead and silver, nitric acid is required. Less often sulphuric acid and aqua regia (nitro-hydrochloric acid) are resorted to. The trial is usually made in a test-tube, and in general the fragment of mineral to be examined should be first carefully pulverized in an agate mortar. In most cases the heat of the Bunsen burner must be employed. (a) Many minerals are completely soluble without effervescence; among these are some of the oxides, as hematite, limonite, gothite, etc.; some sul- phates, many phosphates and arsenates, etc. Gold and platinum are soluble only in aqua regia or nitro-hydrochloric acid. A yellow solution is usually obtained if much iron is present; a blue or greenish blue solution (turning deep blue on the addition of ammonium hy- droxide in excess) from compounds of copper; pink or pale rose from cobalt, etc. (b) Solubility with effervescence takes place when the mineral loses a gaseous ingredient, or when one is generated by the mutual reaction of acid and mineral. Most conspicuous here are the carbonates, all of which dissolve with effervescence, giving off the odorless gas carbon dioxide (C0 2 ), though some of them only when pulverized, or, again, on the addition of heat. In applying this test dilute hydrochloric acid is employed. Hydrogen sulphide (H 2 S) is evolved by some sulphides when dissolved in hydrochloric acid: this is true of sphalerite, stibnite, etc. This gas is readily recognized by its offensive odor. Chlorine is evolved by oxides of manganese and also chromic and vanadic acid salts when dissolved in hydrochloric acid. Nitrogen dioxide (NO 2 ) is given off, in the form of red suffocating fumes, by many metallic minerals, and also some of the lower oxides (cuprite, etc.), when treated with nitric acid. (c) The separation of an insoluble ingredient takes place: With many silicates, the silica separating sometimes as a fine powder, and again as a jelly; in the latter case the mineral is said to gelatinize (sodalite, analcite). In order to test this point the finely pulverized silicate is digested with strong hydro- CHEMICAL EXAMINATION OF MINERALS 329 chloric acid, and the solution afterward slowly evaporated nearly to dryness. With a considerable number of silicates the gelatinization takes place only after the mineral has been previously fused; while some others, which ordi- narily gelatinize, are rendered insoluble by ignition. With many sulphides (as pyrite) a separation of sulphur takes place when they are treated with nitric acid. Some compounds of titanium and tungsten are decomposed by hydro- chloric acid with the separation of the oxides of the elements named (TiO2, WO 3 ) . The same is true of salts of molybdic and vanadic acids, only that here the oxides are soluble in an excess of the acid. Compounds containing silver, lead, and mercury give with hydrochloric acid insoluble residues of the chlorides. These compounds are, however, soluble in nitric acid. When compounds containing tin are treated with nitric acid, the tin dioxide (SnO 2 ) separates as a white powder. A corresponding reaction takes place under similar circumstances with minerals containing arsenic and antimony. Insoluble Minerals. A large number of minerals are not sensibly attacked by any of the acids. Among these may be named the following oxides: corundum, spinel, chromite, diaspore, rutile, cassiterite, quartz; also cerar- gyrite; many silicates, titanates, tantalates, and niobates; some of the sul- phates, as barite, celestite; many phosphates, as xenotime, lazulite, childrenite, amblygonite; also the borate, boracite. 482. Examination of the Solution. If the mineral is difficultly, or only partially, soluble, the question as to solubility or insolubility is not always settled at once. Partial solution is often shown by the color given to the liquid, or more generally by the precipitate yielded, for example, on the addi- tion of ammonium hydroxide to the liquid filtered off from the remaining powder. The further examination of the solution yielded, whether from par- tial or complete solution, after the separation by filtration of any insoluble residue, requires the systematic laboratory methods of qualitative analysis. It may be noted, however, that in the case of sulphates the presence of sulphur is shown by the precipitation of a heavy white powder of barium sulphate (BaSOO when barium chloride is added. The presence of silver in solution is shown by the separation of a white curdy precipitate of silver chloride (AgCl) upon the addition of any chlorine compound; conversely, the same precipitate shows the presence of chlorine when silver nitrate is added to the solution. Again, phosphorus may be detected if present, even in small quantity, in a nitric acid solution of a mineral by the fine yellow powder which separates, sometimes after standing, when ammonium molybdate has been added. EXAMINATION BY MEANS OF THE BLOWPIPE* 483. The use of the blowpipe, in skilled hands, gives a quick method of obtaining a partial knowledge of the qualitative composition of a mineral. The apparatus needed includes the following articles : * The subject of the blowpipe and its use is treated very briefly in this place. The student who wishes to be fully informed not only in regard to the use of the various instru- ments, but also as to all the valuable reactions practically useful in the identification of minerals, should consult a manual on the subject. The Brush-Penfield Manual of Deter- minative Mineralogy, with an introduction on Blowpipe Analysis, is particularly to be recommended. 330 CHEMICAL MINERALOGY 622 Blowpipe, lamp, forceps, preferably with platinum points, platinum wire, charcoal, glass tubes; also a small hammer with sharp edges, a steel anvil an inch or two long, a horseshoe magnet, a small agate mortar, a pair of cutting pliers, a three-cornered file. Further, test-paper, both turmeric and blue litmus paper; a little pure tin-foil; also in small wooden boxes the fluxes: borax (sodium tetraborate) , soda (anhydrous sodium carbonate), salt of phosphorus or microcosmic salt (sodium-ammonium phosphate), acid potassium sulphate (HKS0 4 ); also a solution of cobalt nitrate in a dropping bulb or bottle; further, the three acids mentioned in Art. 480. 484. Blowpipe and Lamp. A good form of blowpipe is shown in Fig. 622. The air-chamber, at a, is essential to stop the condensed moisture of the breath, the tip (6), which is removable, is usually of brass, (c) is a remov- able mouthpiece which may or may not be used as preferred. The most convenient form of lamp is that furnished by an ordinary Bunsen gas-burner * (Fig. 623), provided with a tube, 6, which when inserted cuts off the air supply at a; the gas then burns at the top with the usual yellow flame. This flame should be one to one and a half inches high. The tip of the blow-pipe is held near (or just within the flame, see beyond), and the air blown through it causes the flame to take the shape shown in Fig. 625. It is necessary to learn to blow continuously, that is, to keep up a blast of air from the compressed reservoir in the mouth-cavity while respiration is maintained through the nose. To accomplish this successfully and at the same time to produce a clear flame without unnecessary fatiguing effort calls for some practice. When the tube, 6, is removed, the gas burns with a colorless flame and is used for heating glass tubes, test- tubes, etc. 485. Forceps. Wire. The for- ceps (Fig. 624) are made of steel, nickel-plated, and should have a spring strong enough to support firmly the small fragment of mineral between the platinum points at d. The steel points at the other end are used to pick up small pieces of minerals, but must not be inserted in the flame. Care must be taken not to injure the platinum by allow- ing it to come in contact with the fused mineral, especially if this contains antimony, arsenic, lead, etc. Cheaper forceps, made of steel wire, etc., while not so convenient, will also serve reasonably well. A short length of fairly stout platinum wire to be used in the making of bead tests should be available. A similar length of finer wire for making flame tests is also desirable. * Instead of this, a good stearin candle will answer, or an oil flame with flat wick. CHEMICAL EXAMINATION OF MINERALS 331 486. Charcoal. The charcoal employed should not snap and should yield but little ash; the kinds made from basswood, pine or willow are best. It is most conveniently employed in rectangular pieces, say four inches long, an inch wide, and three-quarters of an inch in thickness. The surface must always be perfectly clean before each trial. 487. Glass Tubes. The glass tubes should be preferably of two grades; a hard glass tubing with about 5 mm. interior diameter to be cut in five inch lengths and used in open tube tests and a soft glass tubing with about 624 3 mm. interior diameter to be in about six inch lengths, each length yielding two closed tubes. 488. Blowpipe Flame. The blowpipe flame, shown in Fig. 625, consists of three cones : an inner of a blue color, c, a second pale violet cone, b, and an outer invisible cone, a. The cone c consists of unburned gas mixed with air from the blowpipe. There is no 625 combustion in this cone and therefore no heat. The cone b is the one in which combus- tion is taking place. This cone contains carbon monoxide which is a strong reducing agent, see below. Cone a is merely a gas envelope composed of the final products of combustion, C0 2 and Blowpipe Flame R ^ The ^ ^ mogt intense near the tip of the cone 6, and the mineral is held at this point when its fusibility is to be tested. The point o, Fig. 625, is called the OXIDIZING FLAME (O.F.) ; it is character- ized by the excess of the oxygen of the air and has hence an oxidizing effect upon the assay. This flame is best produced when the jet of the blowpipe is inserted a very little in the gas flame; it should be entirely non-lu- minous. The cone 6 is called the REDUCING FLAME (R.F.); it is characterized by the excess of the carbon or hydrocarbons of the gas, which at the high tem- perature present tend to combine with the oxygen of the mineral brought into it (at r), or, in other words, to reduce it. The best reducing flame is produced when the blowpipe is held a little distance from the gas flame; it should retain the yellow color of the latter on its upper edge. 489. Methods of Examination. The blowpipe investigation of min- erals includes their examination, (1) in the forceps, (2) in the closed and the open tubes, (3) on charcoal or other support, and (4) with the fluxes on the platinum wire. 1. EXAMINATION IN THE FORCEPS 490. Use of the Forceps. Forceps are employed to hold the fragment of the mineral while a test is made as to its fusibility; also when the presence of a volatile ingredient which may give the flame a characteristic color is tested for, etc. The following practical points must be regarded: (1) Metallic minerals, especially those containing arsenic or antimony, which when fused might injure the platinum of the forceps, 332 CHEMICAL MINERALOGY should first be examined on charcoal; * (2) the fragment taken should be thin, and as small as can conveniently be held, with its edge projecting well beyond the points; (3) when decrepitation takes place, the heat must be applied slowly, or, if this does not prevent it, the mineral may be powdered and a paste made with water, thick enough to be held in the forceps or on the platinum wire; or the paste may, with the same end in view, be heated on charcoal; (4) the fragment whose fusibility is to be tested must be held in the hottest part of the flame, just beyond the extremity of the blue cone. 491. Fusibility. All grades of fusibility exist among minerals, from those which fuse in large fragments in the flame of the candle (stibnite, see below) to those which fuse only on the thinnest edges in the hottest blowpipe flame (bronzite) ; and still again there are a considerable number which are entirely infusible (e.g., corundum). The exact determination of the temperature of fusion is not easily accom- plished (cf Art. 431 p. 304), and for purposes of determination of species it is unnecessary. The approximate relative degree of fusibility is readily fixed by referring the mineral to the following scale, suggested by von Kobell: 1. Stibnite. 4. Actinolite. 2. Natrolite (or Chalcopyrite). 5. Orthoclase. 3. Almandite Garnet. 6. Bronzite. 492. In connection with the trial of fusibility, the following phenomena may be observed: (a) coloration of the flame (see Art. 493); (b) swelling up (stilbite), or exfoliation of the mineral (vermiculite) ; or (c) glowing without fusion (calcite); and (d) intumescence, or a spirting out of the mass as it fuses (scapolite). The color of the mineral after ignition is to be noted; and the nature of the fused mass is also to be observed, whether a clear or blebby glass is obtained, or a black slag; also whether the bead or residue is magnetic or not (due to iron, less often nickel, cobalt), etc. The ignited fragment, if nearly or quite infusible, may be moistened with the cobalt solution and again ignited, in which case, if it turns blue, this indicates the presence of aluminium (as with cyanite, topaz, etc.) ; but note that zinc silicate (calamine) also assumes a blue color. If it becomes pink, this indicates a compound of magnesium (as brucite). Also, if not too fusible, it may, after treatment in the forceps, be placed upon a strip of moistened turmeric paper, in which case an alkaline reaction proves the presence of an alkali, sodium, potassium; or an alkaline earth, calcium, barium, strontium. 493. Flame Coloration. The color often imparted to the outer blow- pipe flame, while the mineral held in the forceps is being heated, makes pos- sible the identification of a number of the elements. The colors which may be produced, and the substances to whose presence they are due, are as follows: Color Substance Carmine-red Lithium. Purple-red Strontium. Orange-red Calcium. Yellow. Sodium. Yellowish green Barium. Siskine-green Boron. * Arsenic, antimony, and easily reducible metals like lead, also copper, form more or less fusible alloys with platinum. CHEMICAL EXAMINATION OF MINERALS 333 Emerald-green Oxide of copper. Bluish green Phosphoric acid (phosphates). Greenish blue Antimony. Whitish blue Arsenic. Azure-blue Chloride of copper; also selenium. Violet Potassium. A yellowish green flame is also given by the oxide or sulphide of molybdenum; a bluish green flame (in streaks) by zinc; a pale bluish flame by tellurium; a blue flame by lead. 494. Notes. The presence of soda, even in small quantities, produces a yellow flame, which (except in the spectroscope) more or less completely masks the coloration of the flame due to other substances, e.g., potassium. A filter of blue glass held in front of the flame will shut out the monochromatic yellow of the sodium flame and allow the charac- teristic violet color of the potassium to be observed. Silicates are often so difficultly decomposed that no distinct color is obtained even when the substance is present; in such cases (e.g., potash feldspar) the powdered mineral may be fused on the platinum wire with an equal volume of gypsum, when the flame can be seen (at least through blue glass). Again, a silicate like tourmaline fused with a mixture of fluorite and acid potassium sul- phate yields the characteristic green flame of boron. Phosphates and borates give the green flame in general best when they have been pulverized and moistened with sulphuric acid. Moistening with hydrochloric acid makes the coloration in many cases (as with the carbonates of calcium, barium, strontium) more distinct. 2. HEATING IN THE CLOSED AND OPEN TUBES 495. The tubes are useful chiefly for examining minerals containing volatile ingredients, given off at the temperature of the gas flame. In the case of the closed tube, the heating goes on practically uninfluenced by the air present, since this is driven out of the tube in the early stages of the process. In the open tube, on the other hand, a continual stream of hot air, that is, of hot oxygen, passes over the assay, tending to produce oxidation and hence often materially changing the result. 496. Closed Tube. A small fragment is inserted, or a small amount of the powdered mineral in this case with care not to soil the sides of the tube and heat is applied by means of the ordinary Bunsen flame. The presence of a volatile ingredient is ordinarily shown by the deposit, or subli- mate, upon the tube at some distance above the assay where the tube is rela- tively cool. Independent of this, other phenomena may be noted, namely: decrepita- tion, as shown by fluorite, calcite, etc.; glowing, as exhibited by gadoliriite; phosphorescence, of which fluorite is an example; change of color (limonite), and here the color of the mineral should be noted both when hot, and again after cooling; fusion; giving off oxygen, as mercuric oxide; yielding acid or alkaline vapors, which should be tested by inserting a strip of moistened litmus or turmeric paper in the tube. Of the sublimates which form in the tube, the following are those with which it is most important to be familiar: Substance Sublimate in the Closed Tube Water (H 2 0) Colorless liquid drops. Sulphur (S) ; Red to deep yellow, liquid ; pale yellow, solid. Tellurium dioxide (TeO 2 ) Pale yellow to colorless, liquid; colorless or white, solid. Arsenic sulphide (As 2 S 3 ) Dark red, liquid; reddish yellow, solid. Antimony oxysulphide (Sb 2 S 2 O) Black to reddish brown on cooling, solid. Arsenic (As) Black, brilliant metallic to gray crystalline, solid Mercury sulphide (HgS) Deep black, red when rubbed very fine. Mercury (Hg) Gray metallic globules. In addition to the above: Tellurium gives black fusible globules; selenium the same, but 334 CHEMICAL MINERALOGY in part dark red when very small; the chloride of lead and oxides of arsenic and antimony give white solid sublimates. 497. Open Tube. The small fragment is placed in the tube about an inch from the lower end, the tube being slightly inclined (say 20), but not enough to cause the mineral to slip out, and heat applied beneath. The cur- rent of air passing upward through the tube during the heating process has an oxidizing effect. The special phenomena to be observed are the formation of a sublimate and the odor of the escaping gases. The acid or alkaline character of the vapors is tested for in the same way as with the closed tube. The most common gas to be obtained in this way is sulphur dioxide, S0 2 , when sulphides are being oxidized. This gas is to be recognized by its irritating, pungent odor and its acid reaction upon moistened blue litmus paper. The more important sublimates are as follows: Substance Sublimate in the Open Tube Arsenic trioxide (AsaOa) White, crystalline, volatile. Antimony antimonate (Sb 2 O 4 ) Straw-yellow, hot; white, cold. Infusible, non-volatile, amorphous, settling along bottom of tube. Obtained from compounds containing sulphur as stibnite, also the sulphantimonites (e.g., bournonite) as dense white fumes. Usually accompanied by the following: Antimony trioxide (Sb 2 O 3 ) . . . White, crystalline, slowly volatile, forming as a ring on walls of tube. Tellurium dioxide (TeO 2 ) White to pale yellow globules. Selenium dioxide (SeO 2 ) White, crystalline, volatile. Molybdenum trioxide (MoO 3 ) Pale yellow, hot; white, cold. Mercury (Hg) Gray metallic globules, easily united by rubbing. It is also to be noted that if the heating process is too rapid for full oxidation, subli- mates, like those of the closed tubes, may be formed, especially with sulphur (yellow), arsenic (black), arsenic sulphide (orange), mercury sulphide (black), antimony oxysulphide (black to reddish brown). 3. HEATING ON CHARCOAL 498. The fragment (or powder) to be examined is placed near one end of the piece and this so held that the flame passes along its length. If the mineral decrepitates, it may be powdered, mixed with water, and then the material employed as a paste. The reducing flame is employed if it is desired to reduce a metal (e.g.., silver, copper) from its ores : this is the common case. If, however, the min- eral is to be roasted, that is, heated in contact with the air so as to oxidize and volatilize, for example, the sulphur, arsenic, antimony present, the oxidizing flame is needed and the mineral should be in powder and spread out. The points to be noted are as follows : (a) The odor given off after short heating. In this way the presence of sulphur, arsenic (garlic or alliaceous odor), and selenium (odor of decayed horseradish) may be recognized. (b) Fusion. In the case of the salts of the alkalies the fused mass is absorbed into the charcoal; this is also true, after long heating, of the car- bonates and sulphates of barium and strontium. (Art. 501.) (c) The Sublimate. By this means the presence of many of the metals may be determined. The color of the sublimate, both near the assay (N) and at a distance (D) , as also when hot and when cold, is to be noted. The important sublimates are the following: CHEMICAL EXAMINATION OF MINERALS 335 Substance Sublimate on Charcoal Arsenic trioxide (As 2 O 3 ) White, very volatile, distant from the assay; also garlic fumes. Antimony oxides (SbaOe and Sb2C>4) Dense white, volatile; forms near the assay. Zinc oxide (ZnO) Canary-yellow, hot; white, cold; moistened with cobalt nitrate and ignited (O.F.) becomes green. Molybdenum trioxide (MoO 3 ) Pale yellow, hot; yellow, cold; touched for a moment with the R.F. becomes azure-blue. Also a copper- red sublimate (MoO 2 ) near the assay. Lead oxide (PbO) Dark yellow, hot; pale yellow, cold. Also (from sulphides) dense white (resembling antimony), a mixture of oxide, sulphite, and sulphate of lead. Bismuth trioxide (I^Os) Dark orange-yellow (N), paler on cooling; also bluish white (D). See further, p. 338. Cadmium oxide (CdO) Nearly black to reddish brown (N) and orange-yellow (D) ; often iridescent. To the above are also to be added the following: Selenium dioxide, SeO 2 , sublimate steel-gray (N) to white tinged with red (D) ; touched with R.F. gives an azure-blue flame; also an offensive selenium odor. Tellurium dioxide, TeOz, sublimate dense white (N) to gray (D); in R.F. volatilizes with green flame. Tin dioxide, SnO2, sublimate faint yellow hot to white cold; becomes bluish green when moistened with cobalt solution and ignited. Silver (with lead and antimony), sublimate reddish (d) The Infusible Residue. This may (1) glow brightly in the O.F., indi- cating the presence of calcium, strontium, magnesium, zirconium, zinc, or tin. (2) It may give an alkaline reaction after ignition: alkaline earths. (3) It may be magnetic, showing the presence of iron (or nickel). (4) It may yield a globule or mass of a metal (Art. 499) . 499. Reduction on Charcoal. In many cases the reducing flame alone suffices on charcoal to separate the metal from the volatile element present, with the result of giving a globule or metallic mass. Thus silver is obtained from argentite (Ag 2 S) and cerargyrite (AgCl) ; copper from chalcocite (Cu 2 S) and cuprite (Cu 2 0), etc. The process of reduction is always facilitated by the use of sodium carbonate or borax as a flux, and this is in many cases (sulph- arsenites, etc.) essential. The finely pulverized mineral is intimately mixed with two or three times its volume of soda, and a drop of water added to form a paste. This is placed in a cavity in the charcoal, and subjected to a strong reducing flame. More soda is added as that present sinks into the coal, and, after the process has been continued some time, a metallic globule is often visible, or a number of them, which can be removed and separately examined. If not distinct, the remainder of the flux, the assay, and the surrounding coal are cut out with a knife, and the whole ground up in a mortar, with the addition of a little water. The charcoal is carefully washed away and the metallic globules, flattened out by the process, remain behind. Some metallic oxides are very readily reduced, as lead, while others, as copper and tin, require considerable skill and care. The metals obtained (in globules or as a metallic mass) may be: copper, color red; bismuth, lead-gray, brittle; gold, yellow, not soluble in nitric acid; silver, white, soluble in nitric acid, the solution giving a silver chloride pre- cipitate (p. 340); tin, white, harder than silver, soluble in nitric acid with separation of white powder (Sn0 2 ); lead, lead-gray (oxidizing), soft and fusible. The coatings (see the list of sublimates above) often serve to identify the metal present. 336 CHEMICAL MINERALOGY 500. Detection of Sulphur in Sulphates. By means of soda on char- coal the presence of sulphur in the sulphates may be shown, in the following manner. Fuse the powdered mineral with soda and charcoal dust. The latter acting as a strong reducing agent changes the sulphate to a sulphide with the formation of sodium sulphide. When the fused mass is placed with a drop of water upon a clean silver surface a black or yellow stain of silver sulphide will be formed. A similar reaction would of course be obtained from a sulphide. The latter can however be readily distinguished by roasting in the open tube or upon charcoal and noting the formation of SO 2 . 4. TREATMENT ON THE PLATINUM WIRE 501. Use of the Fluxes. The three common fluxes are borax, salt of phosphorus, and carbonate of soda (p. 330). They are generally used with the platinum wire, less often on charcoal (see p. 335) . If the wire is employed it must have a small loop at the end; this is heated to redness and dipped into the powdered flux, and the adhering particles fused to a bead; this operation is repeated until the loop is filled. Sometimes in the use of soda the wire may at first be moistened a little to cause it to adhere. When the bead is ready, it is, while hot, brought in contact with the pow- dered mineral, some of which will adhere to it, and then the heating process may be continued. Very little of the mineral is in general required, and the experiment should be commenced with a minute quantity and more added if necessary. The bead must be heated successively first in the oxidizing flame (O.F.) and then in the reducing flame (R.F.), and in each case the color noted when hot and when cold. The phenomena connected with fusion, if it takes place, must also be observed. Minerals containing sulphur or arsenic, or both, must be first roasted (see p. 334) till these substances have been volatilized. If too much of the mineral has been added and the bead is hence too opaque to show the color, it may, while hot, be flattened out with the hammer, or d'rawn out into a wire, or part of it may be removed and the remainder diluted with more of the flux . With salt of phosphorus, the wire should be held above the flame so that the escaping gases may support the bead ; this is continued till quiet fusion is attained. It is to be noted that the colors vary much with the amount of material present ; they are also modified by the presence of other metals. 502. Borax. - - The following list enumerates the different colored beads obtained with borax, both in the oxidizing (O.F.) and reducing flames (R.F.), and also the metals to the presence of whose oxides the colors are due. Com- pare further the reactions given in the list of elements (Art. 504). Color in Borax Bead Substance 1. OXIDIZING FLAME Colorless, or opaque white. . . Silica, calcium, aluminium; also silver, zinc, etc. Iron, cold (pale yellow, hot, if in small amount). Ked, red-brown to brown Chromium (CrO 3 ), hot (yellowish green, cold). Manganese (Mn 2 O 3 ), amethystine-red (violet, hot). Iron (Fe 2 O 3 ), hot (yellow, cold) if saturated. Nickel (NiO) red-brown to brown, cold (violet, hot). Uranium (UO 3 ), hot (yellow, cold). Green Copper (CuO), hot (blue, cold, or bluish green if highly saturated). Chromium (CrO 3 ), yellowish green, cold (red, hot). CHEMICAL EXAMINATION OF MINERALS 337 Yellow Iron (Fe 2 O 3 ), hot (pale yellow to colorless, cold) but red-brown and yellow if saturated. Uranium (UOs), hot, if in small amount; paler on cooling. Chromium (CrO 3 ), hot and in small amount (yellowish green, cold). Blue Cobalt (CoO), hot and cold. Copper (CuO), cold if highly saturated (green, hot). Violet ,. . Nickel (NiO), hot (red-brown, cold). Manganese (Mn 2 O 3 ), hot (amethystine-red, cold). 2. REDUCING FLAME (R.F.) Colorless Manganese (MnO), or a faint rose color. Red Copper (Cu 2 O, with Cu), opaque red. Green Iron (FeO), bottle-green. Chromium (CrjOs), emerald-green. Uranium (U^Os), yellowish green if saturated. Blue Cobalt (CoO), hot and cold. Gray, turbid Nickel (Ni). 503. Salt of Phosphorus. This flux gives for the most part reactions similar to those obtained with borax. The only cases enumerated here are those which are distinct, and hence those where the flux is a good test. With silicates this flux forms a glass in 'which the bases of the silicate are dissolved, but the silica itself is left insoluble. It appears as a skeleton readily seen floating about in the melted bead. The colors of the beads, and the metals to whose oxides these are due, are : Color Substance Red : Chromium in O.F., hot (fine green when cold). Green Chromium in O.F. and R.F., when cold (red in O.F., hot). Molybdenum in R.F., dirty green, hot; fine green, cold (yellow-green in O.F.). Uranium in R.F., cold; yellow-green, hot. Vanadium, chrome-green in R.F., cold (brownish red, hot). In O.F., dark yellow, hot, paler on cooling. Yellow Molybdenum, yellowish green in O.F., hot, paler on cooling (in R.F., dirty green, hot; fine green, cold). Uranium in O.F. , hot; yellowish green, cold (in R.F. , yellowish green, hot; green, cold). Vanadium in O.F., dark yellow, hot, paler on cooling (in R.F., brownish red, hot; chrome-green, cold). Violet Titanium (TiO 2 ) in R.F., yellow, hot. (Also in O.F., yellow, hot; color- cold.) CHARACTERISTIC REACTIONS OF THE IMPORTANT ELEMENTS AND OF SOME OF THEIR COMPOUNDS 504. The following list contains the most characteristic reactions, chiefly before the blowpipe and in some cases also in the wet way, 'of the different elements and their oxides. It is desirable for every student to gain familiarity with them by trial with as many minerals as possible. Many of them have already been briefly mentioned in the preceding pages. For a thoroughly full description of these and other characteristic tests (blowpipe and otherwise) reference should be made to the volume by Brush and Penfield referred to on p. 329. It is to be remembered that while the reaction of a single substance may be perfectly distinct if alone, the presence of other substances may more or 338 CHEMICAL MINERALOGY less entirely obscure these reactions; it is consequently obvious that in the actual examination of minerals precautions have to be taken, and special methods have to be devised, to overcome the difficulty arising from this cause. These will be gathered from the "pyrognostic characters" (Pyr.) given in con- nection with the description of each species in the Fourth Part of this work. Aluminium, The presence of aluminium in most infusible minerals, containing a con- siderable amount, may be detected by the blue color which they assume when, after being heated, they are moistened with cobalt solution and again ignited (e.g., cyanite, andalusite, etc.). Very hard minerals (as corundum) must be first finely pulverized. The test is not conclusive with fusible minerals since a glass colored blue by cobalt oxide may be formed. It is to be noted that the infusible calamine (zinc silicate) also assumes a blue color when treated with cobalt nitrate. From solutions aluminium will be precipitated as a flocculent white or colorless precipitate on the addition of ammonium hydroxide in excess. Antimony. Antimonial minerals roasted on charcoal give dense white odorless fumes; metallic antimony and its sulphur compounds give in the open tube a white sublimate of oxide of antimony (see p. 334). Antimony sulphide (stibnite), also many sulpharitimonites, give in a strong heat in the closed tube a sublimate of antimony oxysulphide, black when hot, brown-red when cold. See also p. 333. In nitric acid, compounds containing antimony deposit white insoluble metantimonic acid. Arsenic. Arsenides, sulpharsenites, etc., give off fumes when roasted on charcoal, usually easily recognized by their peculiar garlic odor. In the open tube they give a white, volatile, crystalline sublimate of arsenic trioxide. In the closed tube arsenic sulphide gives a sublimate dark brown-red when hot, and red or reddish yellow when cold; arsenic and some arsenides yield a black mirror of metallic arsenic in the closed tube. In arsenates the arsenic can be detected by the garlic odor yielded when a mixture of the powdered mineral with charcoal dust and sodium carbonate is heated (R.F.) on charcoal. Barium. A yellowish green coloration of the flame is given by all barium salts, except the silicates; an alkaline reaction is usually obtained after intense ignition. In solution the presence of barium is proved by the heavy white precipitate (BaSO 4 ) formed upon the addition of dilute sulphuric acid. Bismuth. On charcoal alone, or better with soda, bismuth gives a very characteristic orange-yellow sublimate; brittle globules of the reduced metal are also obtained (with soda). Also when treated with 3 or 4 times the volume of a mixture in equal parts of potassium iodide and sulphur, and fused on charcoal, a beautiful red sublimate of bismuth iodide is obtained; near the mineral the coating is yellow. Boron. Many compounds containing boron (borates, also the silicates, datolite, dan- burite, etc.) tinge the flame intense yellowish green, especially if moistened with sulphuric acid. For some .silicates (as tourmaline) the best method is to mix the powdered mineral with one part powdered fluorite and two parts potassium bisulphate. The mixture is moistened and placed on platinum wire. At the moment of fusion the green color appears, but lasts but an instant. A clilute hydrochloric acid solution containing boron gives a reddish brown color to turmeric paper which has been moistened with it and then dried at 100; the color changes to black when ammonia is poured on the paper. Cakium. Many calcium minerals (carbonates, sulphates, etc.) give an alkaline reaction on turmeric paper after being ignited. A yellowish red color is given to the flame by some compounds (e.g., calcite after moistening with HG1) ; the strontium flame is a much deeper red. In weakly acid or alkaline solutions calcium is precipitated as oxalate by the addition of ammonium oxalate. Cadmium. On charcoal with soda, compounds of cadmium give a characteristic sub- limate of the reddish brown oxide. Carbonates. All carbonates effervesce with dilute hydrochloric acid, yielding the odor- less gas CO 2 (e.g., calcite); many require to be pulverized, and some need the addition of heat (dolomite, sidente). Carbonates of lead should be tested with nitric acid. LMprides. If a small portion of a mineral containing chlorine (a chloride, also pyro- morphite, etc.) is added to the bead of salt of phosphorus, saturated with copper oxide, the bead when heated is instantly surrounded with an intense purplish flame of copper chloride. In solution chlorine gives with silver nitrate a white curdy precipitate of silver chloride which darkens in color on exposure to the light; it is insoluble in nitric acid, but entirely soluble m ammonia. CHEMICAL EXAMINATION OF MINERALS 339 Chromium. Chromium gives with borax a bead which (O.F.) is yellow to red (hot) and yellowish green (cold) and R.F. a fine emerald-green. With salt of phosphorus in O.F. the bead is dirty green (hot) and clear green (cold); in R.F. the same. Cf. Vanadium beyond (also pp. 336, 337). Cobalt. A beautiful blue bead is obtained with borax in both flames from minerals containing cobalt. Where sulphur or arsenic is present the mineral should first be thoroughly roasted on charcoal. Copper. On charcoal, at least with soda, metallic copper can be reduced from most of its compounds. In the case of sulphides the powdered mineral should be roasted first in order to eliminate the major part of the sulphur before fusion with soda. With borax it gives (O.F.) a green bead when hot, becoming blue when cold; also (R.F.), if saturated, an opaque red bead containing Cu 2 O and often Cu is obtained. Copper chloride, obtained by moistening the mineral with hydrochloric acid (in the case of sulphides the mineral should be previously roasted) yields a vivid azure-blue flame; copper oxide gives a green flame. Most metallic compounds are soluble in nitric acid. Ammonia in excess produces an intense blue color in the solution. Fluorine. Heated in the closed tube with potassium bisulphate and powdered glass produces a white sublimate of SiO 2 . This sublimate and the hydrofluosilicic acid present form a volatile combination. But if the lower end of the tube is broken off and the open tube then dipped in a test tube of water so that the acid is removed, the deposit of SiO 2 which will appear when the tube is dried will be found to be no longer volatile. Heated gently in a platinum crucible with sulphuric acid, many compounds (e.g., fluorite) give off hydrofluoric acid, which corrodes the exposed parts of a glass plate placed over it which has been coated with wax and then scratched. Iron. Minerals which contain even a small amount of iron yield a magnetic mass when heated in the reducing flame. With borax iron gives a bead (O.F.) which is yellow to brownish red (according to quantity) while hot, but is colorless to yellow on cooling; R.F. becomes bottle-green (see pp. 336', 337). Lead. With soda on charcoal a malleable globule of metallic lead is obtained from lead compounds; the coating has a yellow color near the asay; the sulphide gives also a white coating (PbSO 3 ) farther off (p. 335). On being touched with the reducing flame the coat- ing disappears, tingeing the flame azure-blue. In solutions dilute sulphuric acid gives a white precipitate of lead sulphate; when delicacy is required an excess of the acid is added, the solution evaporated to dryness, and water added; the lead sulphate, if present, will then be left as a residue. Lithium. Lithium gives an intense carmine-red to the outer flame, the color somewhat resembling that of the strontium flame but is deeper; in very small quantities it is evident in the spectroscope. Magnesium. Moistened, after heating, with cobalt nitrate and again ignited, a pink color is obtained from some infusible compounds of magnesium (e.g., brucite). In solution the addition of ammonium hydroxide in large excess and a little hydrogen sodium phos- phate produces a white granular precipitate of NH 4 MgPO 4 . Elements precipitated by ammonium hydroxide or ammonium oxalate should be removed first. Manganese. With borax manganese gives a bead violet-red (O.F.), and colorless (R.F.). With soda (O.F.) it gives a bluish green bead; this reaction is very delicate and may be relied upon, even in presence of almost any other metal. Mercury. In the closed tube a sublimate of metallic mercury is yielded when the mineral is heated with dry sodium carbonate. In the open tube the sulphide gives a mirror of metallic mercury; in the closed tube a black lusterless sublimate of HgS, red when rubbed, is obtained. Molybdenum. On charcoal molybdenum sulphide gives near the assay a copper-red stain (O.F.), and beyond a white coating of the oxide; the former becomes azure-blue when for a moment touched with the R.F. The salt of phosphorus bead (O.F.) is yellowish green (hot) and nearly colorless (cold); also (R.F.) a fine green. Nickel. With borax, nickel oxide gives a bead which (O.F.) is violet when hot and red-brown on cooling; (R.F.) the glass becomes gray and turbid from the separation of metallic nickel. Niobium (Columbium). An acid solution boiled with metallic tin gives a blue color. The reactions with the fluxes are not very satisfactory. Nitrates. These detonate when heated on charcoal. Heated in a tube with sulphuric acid they give off red fumes of nitrogen dioxide (NO 2 ). been Phosphorus. Most phosphates impart a green color to the flarne, especially after having n moistened with sulphuric acid, though this test may be rendered unsatisfactory by 340 CHEMICAL MINERALOGY the presence of other coloring agents. If they are used in the closed tube with a fragment of metallic magnesium or sodium, and afterward moistened with water, phosphureted hydrogen is given off, recognizable by its disagreeable odor. A few drops of a nitric acid solution, containing phosphoric acid, produce in a solu- tion of ammonium molybdate a pulverulent yellow precipitate of ammonium phospho- molybdate. Potassium. Potash imparts a violet color to the flame when alone. The flame is best observed through a blue glass filter which will eliminate the sodium flame color which will almost invariably be present. It is best detected in small quantities, or when soda or lithia is present, by the aid of the spectroscope. See also p. 333. Selenium. On charcoal selenium fuses easily, giving off brown fumes with a peculiar disagreeable organic odor; the sublimate on charcoal is volatile, and when heated (R.F.) gives a fine azure-blue flame. Silicon. A small fragment of a silicate in the salt of phosphorus bead leaves a skeleton of silica, the bases being dissolved. If a silicate in a fine powder is fused with sodium carbonate and the mass then dissolved in hydrochloric acid and evaporated to dryness, the silica separates as a gelatinous mass and on evaporation to dryness is made insoluble. When strong hydrochloric acid is added and then water to the dry residue in the test tube, the bases are dissolved and the silica left behind. Many silicates, especially those which are hydrous, are decomposed by strong hydro- chloric acid, the silica separating as a powder or, after evaporation, as a jelly (see p. 328). Silver. On charcoal in O.F. silver gives a brown coating. A globule of metallic silver may generally be obtained by heating on charcoal in O.F., especially if soda is added. Under some circumstances it is desirable to have recourse to cupellation. From a solution containing any salt of silver, the insoluble chloride is thrown down when hydrochloric acid is added. This precipitate is insoluble in acid or water, but entirely so in ammonia. It changes color on exposure to the light. Strontium. Compounds of strontium are usually recognized by the fine crimson-red which they give to the blowpipe flame; many yield an alkaline reaction after ignition. (Cf. barium.) Sodium. Compounds containing sodium in large amount give a strong yellow flame. Sulphur, Sulphides, Sulphates. In the closed tube some sulphides give off sulphur; in the open tube they yield sulphur dioxide, which has a characteristic odor and reddens a strip of moistened litmus paper. In small quantities, or in sulphates, sulphur is best detected by fusion on charcoal with soda and charcoal dust. The fused mass, when sodium sulphide has thus been formed, is placed on a -clean silver coin and moistened; a distinct black stain on the silver is thus obtained (the precaution mentioned on p. 336 must be exercised). A solution of a sulphate in hydrochloric acid gives with barium chloride a white insoluble precipitate of barium sulphate. Tellurium. Tellurides heated in the open tube give a white or grayish sublimate, fusible to colorless drops (p. 334). On charcoal they give a white coating and color the R.F. green. Tin. Minerals containing tin (e.g., cassiterite), when heated on charcoal with soda or potassium cyanide, yield metallic tin in minute globules; these are malleable, but harder than silver. Dissolved in nitric acid, white insoluble stannic oxide separates out. Titanium. Titanium gives in the R.F. with salt of phosphorus a bead which is violet when cold. Fused with sodium carbonate and dissolved with hydrochloric acid, and heated with a piece of metallic tin, the liquid takes a violet color, especially after partial evaporation. Tungsten. Tungsten oxide gives a blue color to the salt of phosphorus bead (R.F.). Fused and treated as titanium (see above) with the addition of zinc instead of tin, gives a fine blue color. Uranium. Uranium compounds give to the salt of phosphorus bead (O.F.) a greenish yellow bead when cool; also (R.F.) a fine green on cooling (p. 337). Vanadium. With borax (O.F.) vanadates give a bead yellow (hot) changing to yellow- ish green and nearly colorless (cold) ; also (R.F.) dirty green (hot), fine green (cold). With ri P hos P horus (O.F.) a yellow to amber color (thus differing from chromium); also (R.F.) fine green (cold). Zinc. On charcoal in the reducing flame compounds of zinc give a coating which is yellow while hot and white on cooling, and moistened by the cobalt solution and again heated becomes a fine green. Note, however, that the zinc silicate (calamine) becomes blue when heated after moistening with cobalt solution. CHEMICAL EXAMINATION OF MINERALS 341 Zirconium. A dilute hydrochloric acid solution, containing zirconium, imparts an orange-yellow color to turmeric paper, moistened by the solution. DETERMINATIVE MINERALOGY 505. Determinative Mineralogy may be properly considered under the general head of Chemical Mineralogy, since the determination of minerals depends mostly upon chemical tests. But crystallographic and all the physi- cal characters have also to be carefully observed. There is but one exhaustive way in which the identity of an unknown mineral may in all cases be fixed beyond question, and that is by the use of a complete set of determinative tables. By means of such tables the mineral in hand is referred successively from a general group into a more special one, until at last all other species have been eliminated, and the identity of the one given is beyond doubt. A careful preliminary examination of the unknown mineral should, how- ever, always be made before final recourse is had to the tables. This examina- tion will often suffice to show what the mineral in hand is, and in any case it should not be omitted, since it is only in this way that a practical familiarity with the appearance and characters of minerals can be gained. The student will naturally take note first of those characters which are at once obvious to the senses, that is: crystalline form, if distinct; general struc- ture, cleavage, fracture, luster, color (and streak), feel; also, if the specimen is not too small, the apparent weight will suggest something as to the specific gravity. The characters named are of very unequal importance. Structure, if crystals are not present, and fracture are generally unessential except in distinguishing varieties; color and luster are essential with metallic, but generally very unimportant with nonmetallic, minerals. Streak is of impor- tance only with colored minerals and those of metallic luster (p. 247) . Crystal- line form and cleavage are of the highest importance, but may require careful study. The first trial should be the determination of the hardness (for which end the pocket-knife is often sufficient in experienced hands). The second trial should be the determination of the specific gravity. Treatment of the pow- dered mineral with acids may come next; by this means (see pp. 328,329) a carbonate is readily identified, and also other results obtained. Then should follow blowpipe trials, to ascertain the fusibility; the color given to the flame, if any; the character of the sublimate given off in the tubes and on charcoal; the metal reduced on the latter; the reactions with the fluxes, and other points as explained in the preceding pages. How much the observer learns in the above way, in regard to the nature of his mineral, depends upon his knowledge of the characters of minerals in general, and upon his familiarity with the chemical behavior of the various elementary substances with reagents and before the blowpipe (pp. 338 to 341). If the results of such a preliminary examination are sufficiently definite to suggest that the mineral in hand is one of a small number of species, reference may be made. to their full description in Part. IV of this work for the final decision. A number of tables, in which the minerals included are arranged according to their crystalline and physical characters, are added in the Appendix. They 342 CHEMICAL MINERALOGY will In many cases aid the observer in reaching a conclusion in regard to a specimen in hand. The first of these tables gives lists of minerals arranged primarily accord- ing to their principle basic elements and secondarily according to their acid radicals. The second of these tables is intended to include all well-defined species, grouped according to the crystalline system to which they belong and arranged under each system in the order of their specific gravities; the hardness is also added in each case. The relative importance of the individual species is shown by the type employed. Following this are minor tables enumerating species characterized by some one of the prominent crystalline forms; that is, those crystallizing in cubes, octahedrons, rhombohedrons, etc. Other tables give the names of species prominent because of their cleavage; structure of different types; hardness; luster; the various colors, etc. The student is recommended to make frequent use of these tables, not simply for aid in the identification of specimens, but rather because they will help him in the difficult task of learning the prominent characters of the more important minerals. PART IV. DESCRIPTIVE MINERALOGY 506. Scope of Descriptive Mineralogy. It is the province of De- scriptive Mineralogy to describe each mineral species, as regards: (1) form and structure; (2) physical characters; (3) chemical composition including blowpipe and chemical tests; (4) occurrence in nature with reference to geo- graphical distribution and association with other species; also in connection with the above to show how it may be distinguished from other species. Fur- ther, it should classify mineral species into more or less comprehensive groups according to those characters regarded as most essential. Other points which may or may not be included are the investigation of the methods of origin of minerals; the changes that they undergo in nature and the results of such alteration; also the methods by which the same compounds may be made in the laboratory; finally, the uses of minerals as ores, for ornament and in the arts. 507. Scheme of Classification. The method of classification adopted in this work, and the one which can alone claim to be thoroughly scientific, is that which places similar chemical compounds together in a common class and which further arranges the mineral species into groups according to the more minute relations existing between them in chemical composition, crystalline form and other physical properties. Upon this basis there are recognized eight distinct chemical classes, begin- ning with the Native Elements; these are enumerated on the following page. Under each of these, sections of different grades are made, also based on chem- ical relationships. Finally, the mineral species themselves are arranged, as far as possible, in isomorphous groups, including those 'which have, at once, analogous chemical composition and similar crystallization (see Art. 471). It is unnecessary to take the space here to develop the entire scheme of classi- fication in detail, since a survey of the successive sub-classes under any one of the divisions will make the principles followed entirely clear. A few remarks, only, are added for sake of illustration. Under the Oxides, for example, the classification is as follows: First, the Oxides of silicon (quartz, tridymite, opal). Second, the Oxides of the semi- metals, tellurium, arsenic, antimony, bismuth, also molybdenum, tungsten. Third, the Oxides of the metals, as copper, zinc, iron, manganese, tin, etc. The third section is then subdivided into the anhydrous and hydrous species. Further, the former fall into the four divisions : Protoxides, RoO and RO ; Ses- quioxides, R 2 O 3 ; Intermediate oxides, RO,R 2 O 3 ; Dioxides, RO 2 . Under each of these heads come finally the individual species, arranged so far as possible in isomorphous groups. Thus we have the Hematite group, the Rutile group, etc. 343 344 DESCRIPTIVE MINERALOGY In regard to the various classes of salts it may be stated that, in general, they are separated into anhydrous, acid, basic and hydrous sections; the special subdivisions called for, however, vary in the different cases. For an explanation of the abbreviations used in the description of species, see p. 5. SCHEME OF CLASSIFICATION I. NATIVE ELEMENTS. II. SULPHIDES, SELENIDES, TELLURIDES, ARSENIDES, ANTIMONIDES. III. Sulpho-salts. SULPHARSENITES, SULPHANTIMONITES, SULPHO- BISMUTHITES. IV. Haloids. CHLORIDES, BROMIDES, IODIDES J FLUORIDES. V. OXIDES. VI. Oxygen Salts. 1. CARBONATES. 2. SILICATES, TITANATES. 3. NIOBATES, TANTALATES. 4. PHOSPHATES, ARSENATES, VANADATES; ANTIMONATES. NITRATES. 6. BORATES. URANATES. 6. SULPHATES, CHROMATES, TELLURATES. 7. TUNGSTATES, MOLYBDATES. VII. Salts of Organic Acids: Oxalates, Mellates, etc. VIII. HYDROCARBON COMPOUNDS. I. NATIVE ELEMENTS The NATIVE ELEMENTS are divided into the two distinct sections of the Metals and the Non-metals, and these are connected by the transition class of the Semi-metals. The distinction between them as regards physical characters and chemical relations has already been given (Art. 453) . The only non-metals present among minerals are carbon, sulphur, and selenium; the last, in one of its allotropic forms, is closely related to the semi-metal tellurium. The native semi-metals form a distinct group by themselves, since all crystallize in the rhombohedral class of the hexagonal system with a funda- mental angle differing only a few degrees from 90, as shown in the following list: Tellurium, rr r = 93 3'. Arsenic, rr' = 94 54'. Antimony, rr' = 92 53'. Bismuth, rr' = 92 20'. An artificial form of selenium is known with metallic luster and rhombo- hedral in crystallization, with rr' = 93. Zinc (also only artif .) is rhombohe- dral (rr' = 93 46') and connects the semi-metals to the true metals. Metallic tantalum has been described in cubic crystals. Among the metals the isometric GOLD GROUP is prominent, including gold, silver, copper, mercury, amalgam (AgHg), and lead. NATIVE ELEMENTS 345 Another related isometric group includes the metals platinum, iridium, palladium, and iron. An allot ropic form of palladium and also iridosmine (IrOs) are both rhombohedral. DIAMOND. Isometric, tetrahedral, but with the + and forms usually equally devel- oped and not to be distinguished from each other. Commonly showing octahe- dral, hexoctahedral, and other forms ; faces frequently rounded or striated and with triangular depressions (on o(lll)). Twins common with tw. pi. 0(111). Crystals often distorted. In spherical forms; massive. 627 628 Cleavage: o( 111) highly perfect. Fracture conchoidal. Brittle. H. = 10. G. = 3-516-3-525 crystals. Luster adamantine to greasy. Color white or colorless; occasionally various pale shades of yellow, red, orange, green, blue, brown; rarely deeply colored; sometimes black. Usually transparent; also translucent, opaque. Refractive and dispersive power high; index n = 2-4195. (See Art. 328.) Var. -- 1 . Ordinary. In crystals usually with rounded faces and varying from those which are colorless and free from flaws (first water) through many faint shades of color, yellow being the most common; often full of flaws and hence of value only for cutting pur- poses. 2. Bort or Boort; rounded forms with rough exterior and radiated or confused crystal- line structure. 3. Carbonado or Carbon; black diamond. Massive, crystalline, granular to compact, without cleavage. Color black or grayish black. Opaque. Obtained chiefly from Bahia, Brazil. Comp. Pure carbon; the variety carbonado yields on combustion a slight ash. Pyr., etc. Unaffected by heat except at very high temperatures, when (in an oxygen atmosphere) it burns to carbon dioxide (CO 2 ) ; out of contact with the air transformed into a kind of coke. Not acted upon by acids or alkalies. Diff. Distinguished (e.g., from quartz crystal) by its extreme hardness and brilliant adamantine luster; the form, cleavage, and high specific gravity are also distinctive charac- ters; it is optically isotropic ; transparent to X-rays. Artif. Minute diamonds have been formed artificially in several ways. Moissan first produced them by dissolving carbon in molten iron and then cooling the mass suddenly under pressure; they have been formed by dissolving graphite in fused olivine or artificial magnesium silicate melts; they have been formed when an electric current was passed through an iron spiral embedded in carbon while under high pressure in an atmosphere of hydrogen. Obs. The diamond occurs chiefly in alluvial deposits of gravel, sand, or clay, asso- ciated with quartz, gold, platinum, zircon, octahedrite, rutile, brookite, hematite, ilmenite, and also andalusite, chrysoberyl, topaz, corundum, tourmaline, garnet, etc.; the associated minerals being those common in granitic rocks or granitic veins. Also found in quartzose 346 DESCRIPTIVE MINERALOGY conglomerates, and further in connection with the laminated granular quartz rock or quartzose hydromica schist, itacolumite, which in thin slabs is more or less flexible. This rock occurs at the mines of Brazil and the Ural Mts.; and also in Georgia and North Caro- lina, where a few diamonds have been found. It has been reported as occurring in situ in a pegmatite vein in gneiss at Bellary in India. It occurs further in connection with an eruptive peridotite in South Africa and in a similar formation in Pike County, Ark. It has been noted as grayish particles forming one per cent of the meteorite which fell at Novo-Urei, Russia, Sept. 22, 1886; also in the form of black diamond (H. = 9) in the meteorite of Carcote, Chile; in the meteoric iron of Canon Diablo, Ariz. India was the chief source of diamonds from very early times down to the discovery of the Brazilian mines ; the yield is now small. Of the localities, that in southern India, in the Madras presidency, included the famous "Golconda mines." The diamond deposits of Brazil have been worked since the early part of the 18th century, and have yielded very largely, although at the present time the amount obtained is small. The most important region was that near Diamantina in the province of Minas Geraes; also from Bahia, etc. The discovery of diamonds in South Africa dates from 1867. They were first found in the gravel of the Vaal river; they occur from Potchefstroom down to the junction with the Orange river, and along the latter as far as Hope Town. More recently they have been found in gravels in the Somabula Forest, Rhodesia and at Liideritzbucht, German South West Africa. These river diggings are now of much less importance than the dry diggings, discovered in 1871. The latter are chiefly in Griqualand-West, south of the Vaal river, on the border of the Orange Free State. There are here near Kimberley a number of limited areas approxi- mately spherical or oval in form, with an average diameter of some 200 to 300 yards, of which the Kimberley, De Beer's, Dutoitspan and Bultfpntein mines are the most important. A circle 3 miles in diameter encloses these four principal mines. The general structure is similar: a wall of nearly horizontal black carbonaceous shale with upturned edges enclos- ing the diamantiferous area. The upper portion of the deposit consists of a friable mass of little coherence of a pale yellow color, called the "yellow ground." Below the reach of atmospheric influences, the rock is more firm and of a bluish green or greenish color; it is called the "blue ground" or simply "the blue." This consists essentially of a serpentinous breccia: a base of hydrated magnesian silicate penetrated by calcite and opaline silica and enclosing fragments of bronzite, diallage, also garnet, magnetite, and ilmenite, and less commonly smaragdite, pyrite, zircon, etc. The diamonds are rather abundantly dissemi- nated through the mass, in some claims to the amount of 4 to 6 carats per cubic yard. The original rock seems to have been a peculiar type of peridotite. These areas are believed to be volcanic pipes, and the occurrence of the diamonds is obviously connected with the eruptive outflow, they having probably been brought up from underlying rocks. Other important mines, similar in character to those near Kimberley, are the Jagersfontein mine in Orange Free State and the Premier, near Pretoria, Transvaal. The South African mines up to the beginning of 1914 are estimated to have yielded about 120 million carats (26 tons) of diamonds valued at nearly 900 million dollars. Diamonds are also obtained in Borneo, associated with platinum, etc.; in Australia, and the Ural Mts. In the United States a few stones have been found in gravels in N. C., Ga., Va,, Col., Cal. and Wis. Reported from Idaho and from Oregon with platinum. In 1906 diamonds were found in Pike County, Ark., both loose in the soil and enclosed in a peridotite rock. Considerable exploration work has been done at this locality and probably between two and three thousand stones found. The stones have been of good color but usually small. Some of the famous diamonds of the world with their weights are as follows: the Kohi- noor, which weighed when brought to England 186 carats, and as recut as a brilliant, 106 carats; the Orloff, 194 carats; the Regent or Pitt, 137 carats; the Florentine or Grand Duke of Tuscany, 133 carats. The "Star of the South" found in Brazil weighed before and after cutting respectively 254 and 125 carats. Also famous because of the rarity of their color are the green diamond of Dresden, 40 carats, and the deep blue Hope diamond from India, weighing 44 carats. at the Premier mine. It was named the Cullinan and was presented by the Transvaal Assembly to King Edward VII of England. When found it weighed 3,025 carats or over li Ibs. It has since been cut into 105 separate stones, the two largest weighing 516 and 309 NATIVE ELEMENTS 347 carats, respectively, being the largest cut stones in existence. The history of the above stones and of others is given in many works on gems. Use. In addition to its use as a gem, the diamond is extensively used as an abrasive. Crystal fragments are used to cut glass. The fine powder is employed in grinding and polishing gem stones. The noncrystalline, opaque varieties, especially the carbonado, are used in the bits of diamond drills. The diamond is also used in wire drawing and in the making of tungsten filaments for electric lights. CLIFTONITE. Carbon in minute cubic and cubo-octahedral crystals. H. = 2'5. G. = 2' 12. Color and streak black; from the Youndegin, West Australia, meteoric iron, found in 1884, and other meteoric irons. GRAPHITE. Plumbago. Black Lead. Rhombohedral. In six-sided tabular crystals. Commonly in embedded foliated masses, also columnar or radiated; scaly or slaty; granular to con> pact; earthy. Cleavage: basal, perfect. Thin laminae flexible, inelastic. Feel greasy. H. = 1-2. G = 2'09-2'23. Luster metallic, sometimes dull, earthy. Color iron-black to dark steel-gray. Opaque. A conductor of electricity. Comp. Carbon, like the diamond; often impure from the presence of ferric oxide, clay, etc. Pyr., etc. At a high temperature some graphite burns more easily than diamond, other varieties less so. B.B. infusible. Unaltered by acids. Diff. Characterized by its extreme softness (soapy feel); iron-black color; metallic luster; low specific gravity; also by infusibility. Cf. molybdenite, p. 360. Artif. It is a common furnace product being formed from the fuel. It is produced extensively by heating coke in the electric furnace. Obs. Graphite is most commonly formed through the metamorphism of carbona- ceous deposits and is most frequently found in metamorphic rocks, contact metamorphic deposits, etc. Coal beds may be largely converted into graphite by intense metamorphism It is not always of organic origin, however, as is shown by its occurrence in meteorites, in pegmatite deposits and as a magmatic separation in various igneous rocks. Frequently its origin is obscure. Found as beds and embedded masses, as laminae or scales in granite, gneiss, mica schist, quartzite, crystalline limestone. The deposits of crystalline graphite which are of the greatest commercial importance have formed as veins along rock fractures. Important localities are: Island of Ceylon from which the largest part of the world's supply comes; Passau district in Bavaria; southern Bohemia; Korea; Madagascar; Sonora in Mexico ; eastern Ontario and adjacent portions of Quebec in Canada. The most productive locality in the United States is in the eastern and southeastern Adirondack region in Essex, Warren, Saratoga and Washington Counties, N. Y. It occurs here in graphitic quartzites, with quartz in small veins running through gneiss and in pegmatite veins. Also found in metamorphosed Carboniferous rocks near Providence and Tiverton, R. I.; in granite and schists in Clay, Chilton and Coqsa Counties, Ala.; as amorphous graphite near Raton, N. M.; in irregular veins near Dillon, Mon.; near Turret, Chaff ee Co., Col. Use. Its chief uses are for making crucibles and other refractory products, in lubri- cants, paint, tove polish, "lead" pencils and for foundry facings. The name black lead, applied to this species, is inappropriate, as it contains no lead. The name graphite, of Werner, is derived from ypacu>, to write, alluding to its use for pencils. QUISQUEITE. A black lustrous material composed chiefly of carbon and sulphur from the vanadium ores of Minasragra, Peru. SULPHUR. Orthorhombic. Axes a : b : c = 0'8131 : 1 : 1-9034. Crystals commonly acute pyramidal; sometimes thick tabular || c(001). See also Fig. 79, p. 47. Also massive, in reniform shapes, incrusting, stalac- titic and stalagmitic; in powder. Cleavage: c(001), m(110), 'p(lll) imperfect. Fracture conchoidal to uneven. Rather brittle to imperfectly sectile. H. = 1/5-2 -5. G. = 2 '05- 348 DESCRIPTIVE MINERALOGY 2-09. Luster resinous. Color sulphur-yellow, straw- and honey-yellow, yellowish brown, greenish, reddish to 629 630 yellowish gray. Streak white. Trans- parent to translucent. A non-con- ductor of electricity; by friction neg- atively electrified. A poor conductor of heat. Optically + . Double refrac- tion strong. Ax. plane || 6(010). Bx _L c(001). Dispersion p < v. 2 V = 695'. Refractive indices, a = 1-958, j8 = 2-038, 7 = 2 -245. Comp. - - Pure sulphur; often contaminated with clay, bitumen, and ofher impurities. Sulphur may also be obtained in the laboratory in other allotropic forms; a monoclinic form is common. Pyr., etc. Melts at 108 C., and at 270 burns with a bluish flame yielding sulphur dioxide. Insoluble in water, and not acted on by the acids, but soluble in carbon disulphide. Diff. Readily distinguished by the color, fusibility and combustibility. Obs. The great repositories of sulphur are either beds of gypsum and the associate rocks, or the regions of active and extinct volcanoes. Sulphur may have several different modes of origin. At times it is a volcanic sublimate formed by reactions between sulphur dioxide and hydrogen sulphide gases. It occurs fre- quently around mineral springs where it has been formed by the incomplete oxidation of hydrogen sulphide. Where such waters act upon limestone rocks both gypsum and sul- phur may be formed. In a small way it is formed in many coal deposits and elsewhere by the slow decomposition of pyrite and other sulphides. Found in large amounts on the Island of Sicily, often in fine crystals and associated with celestite, calcite, aragonite, gypsum, and barite. Important deposits are found in the volcanic districts of Japan, Hawaii, Mexico, and western South America. In the United States the most productive deposits are in Louisiana and Texas. In Calcasieu Parish, Louisiana, a bed of sulphur 100 ft. in thickness is found at a depth of between 300 and 400 ft. It is underlain by beds of gypsum and salt. A similar deposit occurs near Freeport in Brazoria Co., Texas. It is found in numerous other Western localities; Utah, at Sulphurdale, Beaver Co., in a rhyolitic tuff; Wy., in limestones near Cody and Ther- mopolis and about the fumeroles of the Yellowstone Park; Nev., in Esmeralda Co. near Luning and Cuprite, near Rosebud, Humbolt Co., sometimes in crystals and at Eureka, Eureka Co.; Cal., in Colusa, Lake, San Bernadino and other Counties, at the geysers of Napa Valley, Sonoma Co., on Lassen Peak, Tehema Co.; Col., at Vulcan, Gunnison Co., and in Mineral Co. Use. In manufacture of sulphuric acid, in the process of making paper from wood pulp, in making matches, gun powder, fireworks, insecticides, for vulcanizing rubber, for medicinal purposes, etc. Sulphuric acid is now largely derived from the oxidation of pyrite. Selensulphur. Contains sulphur and selenium, orange-red or reddish brown; from the islands Vulcano and Lipari. ARSENIC. Rhombohedral. Generally granular massive; sometimes reticulated, reniform, stalactitic. Cleavage: c(0001) highly perfect. Fracture uneven and fine granular. Brittle. H. = 3'5. G. = 5'63-573. Luster nearly metallic. Color and streak tin-white, tarnishing to dark gray. Comp. Arsenic, often with some antimony, and traces of iron, silver, gold, or bismuth. P yf' ~~ *:i' B> . on cnarcoa l volatilizes without fusing, coats the coal with white arsenic tnoxide, and affords a garlic odor; the coating treated in R.F. volatilizes, tingeing the flame blue. In the closed tube gives a volatile sublimate of arsenic. NATIVE ELEMENTS 349 Micro. In polished section shows white color similar to galena. Smooth surface. With HNOs slowly effervesces, turning dark. Changes color in same way with Feds. Unaffected by KCN and HC1. Obs. Occurs in veins in crystalline rocks and the older schists, often accompanied by ores of antimony, the ruby silvers, realgar, sphalerite, and other metallic minerals. Thus in the silver mines of Saxony; also Andreasberg, Harz Mts., Germany; Joachimstal and Pfibram, Bohemia; in Hungary; Norway; Zmeov, Siberia; Prov. Echizen, Japan, etc. Abundant at Chanarcjllo, Chile. In the United States sparingly at Haverhill and Jackson, N. H.; near Leadville, Col.; Washington Camp, Santa Cruz Co., Ariz. In Canada at Watson Creek, British Columbia; Montreal, Quebec. Use. An ore of arsenic. Allemontite. Arsenical Antimony, SbAs 3 . In reniform masses. G. = 6'203. Luster metallic. Color tin-white or reddish gray. From Allemont, France; Pfibram, Bohemia, etc. Tellurium. Rhombohedral. In prismatic crystals; commonly columnar to fine-gran- ular massive. Perfect prismatic cleavage. H. = 2-2'5. G. = 6'2. Luster metallic. Color and streak tin- white. B.B. wholly volatile. In warm concentrated sulphuric acid gives red solution. From Transylvania, West Australia, and a number of places in Colorado. ANTIMONY. Rhombohedral. Generally massive, lamellar and distinctly cleavable; also radiated; granular. Cleavage: c(0001) highly perfect; also other cleavages. Fracture uneven; brittle. H = 3-3'5. G. = 6'65-672. Luster metallic. Color and streak tin-white. Comp. Antimony, containing sometimes silver, iron, or arsenic. Pyr. B.B. on charcoal fuses very easily and is wholly volatile giving a white coating. The white coating tinges the R.F. bluish green. Crystallizes readily from fusion. Obs. Occurs near Sala in Sweden; Andreasberg in the Harz Mts., Germany; Alle- mont, Dauphine, France; Pfibram, Bohemia; Mexico; Chile; Borneo. In the United States, at Warren, N. J., rare; in Kern Co., and at South Riverside, Cal. At South Ham, Quebec; Prince William parish, York Co., New Brunswick. Use. An ore of antimony. BISMUTH. Rhombohedral. Usually reticulated, arborescent; foliated or granular. Cleavage: c(0001) perfect. Sectile. Brittle, but when heated somewhat malleable. H. = 2-2*5. G. = 970-9-83. Luster metallic. Streak and color silver-white, with a reddish hue; subject to tarnish. Opaque. Comp. Bismuth, with traces of arsenic, sulphur, tellurium, etc. Pyr., etc. B.B. on charcoal fuses very easily and entirely volatilizes, giving a coating orange-yellow while hot, lemon-yellow on cooling. With potassium iodide and sulphur B.B. on charcoal gives a brilliant red coating. Dissolves in nitric acid; subsequent dilu- tion causes a white precipitate. Crystallizes readily from fusion. Micro. In polished section shows creamy white color with pink tinge. Smooth and metallic surface. With HC1 slowly darkens and dissolves. Rapidly darkens with effer- vescence with HNO 3 and aqua regia. Obs. Occurs in veins in gneiss and other crystalline rocks and clay slate, accom- panying various ores of silver, cobalt, lead and zinc. Thus at the mines of Saxony and Bohemia, etc.; Meymac, Correze, France. Also at Modum, Norway; at Falun, Sweden. In Cornwall and Devonshire; near Copiapo, Chile; Bolivia. Occurs at Monroe, Conn.; Brewer's mine, Chesterfield district, S. C.; near Cummins City, and elsewhere in Col. Abundant with silver ores at Cobalt, Ontario. Use. An ore of bismuth. Zinc. Probably does not occur in the native state. In the laboratory it is obtained in hexagonal prisms with tapering pyramids; also in complex crystalline aggregates. It also appears to crystallize in the isometric system, at least in various alloys. Tantalum. Isometric. In cubic crystals and fine grains. Color grayish yellow. 350 DESCRIPTIVE MINERALOGY Found containing small amounts of niobium in the gold washings of the Ural and Altai Mis. Gold Group GOLD. Isometric. Distinct crystals rare, 0(111) most common, also d(110) and ra(311); crystals often elongated in direction of an octahedral axis, giving rise to'rhombohedral-like forms, and arborescent shapes; also in plates flattened || o(lll), and branching at 60 parallel either to the edges or diag- onals of an o face (see pp. 172, 173). Twins: tw. plane o. Skeleton crystals 633 634 common; edges salient or rounded; in filiform, reticulated, dendritic shapes. Also massive and in thin laminae; often in flattened grains or scales. Cleavage none. Fracture hackly. Very malleable and ductile. H. = 2*5-3. G. = 15-6-19-3, 19'33 when pure. Luster metallic. Color and streak gold-yellow, sometimes inclining to silver-white and rarely to orange-red. Opaque. Comp. Gold, but usually alloyed with silver in varying amounts and sometimes containing also traces of copper or iron. Var. 1. Ordinary. Containing up to 16 p. c. of silver. Color varying accordingly from deep gold-yellow to pale yellow, and specific gravity from 19'3 to 15'5. The ratio of gold to silver of 3 : 1 corresponds to 15'1 p. c. silver. For G. = 17'6, Ag = 9 p. c.; G. = 16'9, Ag = 13'2; G. = 14'6, Ag = 38'4. The purest gold which has been described is that from Mount Morgan, in Queensland, which has yielded 99'7 to 99'8 of gold, the remainder being copper with a little iron; silver is present only as a minute trace. 2. Argentiferous; Electrum. Color pale yellow to yellowish white; G = 15'5-12'5. Ratio for the gold and silver of 1 : 1 corresponds to 36 p. c. of silver; 1| : 1, to 26 p. c.; 2 : 1, to 21 p. c.; 1\ : 1, to 18 p. c. The word in Greek means also amber; and its use for this alloy probably arose from the pale yellow color it has as compared with gold. Varieties have also been described containing copper up to 20 p. c. from the Ural Mts.; palladium to 10 p . c. (porpezite), from Porpez, Brazil; bismuth, including the black gold of Australia (maldonite); also rhodium (?). Pyr., etc. B.B. fuses easily (at 1100 C.). Not acted on by fluxes. Insoluble in any single acid; soluble in aqua regia, the separation not complete if more than 20 p. c. Ag is present. Diff. Readily recognized (e.g., from other metallic minerals, also from scales of yel- low mica) by its malleability and high specific gravity, which last makes it possible to sepa- rate it from the gangue by washing ; distinguished from chalcopyrite and pyrite since both sulphides are brittle and soluble in nitric acid. Micro. In polished section shows a golden yellow color with a smooth, metallic sur- face. Unaffected by reagents except KCN, with which it quickly darkens and its surface becomes rough. Obs. Gold is widely distributed in the earth's crust. It has been found in various igneous rocks, more commonly in the acid types, and sometimes in visible particles. It occurs in sedimentary rocks and quite frequently in connection with metamorphic rocks. NATIVE ELEMENTS 351 It is a constituent of sea water. It is most frequently found in notable amounts in quartz veins and in the various forms of placer deposits. The gold, when occurring in quartz, is often irregularly distributed, in strings, scales, plates, and in masses which are sometimes an agglomeration of crystals. Frequently the scales are invisible to the naked eye. The associated minerals are: pyrite, which far exceeds in quantity all others, and is generally auriferous; next, chalcopyrite, galena, sphalerite, arsen- opyrite, each frequently auriferous; often tetradymite and other tellurium ores, native bismuth, native arsenic, stibnite, cinnabar, magnetite, hematite; sometimes barite, scheelite, apatite, fluorite, siderite, chrysocolla. The quartz at the surface, or in the upper part of a vein, is usually cellular and rusted from the more or less complete disappearance of the pyrite and other sulphides by decomposition; but below, it is commonly solid. The gold of the world wasearly gathered, not directly from the quartz veins (the "quartz reefs" of Australia and Africa), but from the gravel and sand deposited in the valleys in auriferous regions, or on the slopes of the mountains or hills, whose rocks contain in some part, and generally not far distant, gold bearing veins. Such deposits are known as placer deposits. The gold is obtained by some method involving the use of a current of water and the separation of the gold from the sand and gravel by means of its high specific gravity. These hydraulic methods have been very extensively used in California and Alaska and indeed most of the gold of the Ural Mts., Brazil, Australia, and many other gold regions has come from such alluvial washings. At the present time, however, placer deposits are much less depended upon and in many regions all the gold is obtained directly from the rock. The alluvial gold is usually in flattened scales of different degrees of fineness, the size depending partly on the original condition in the quartz veins, and partly on the distance to which it has been transported and assorted by running water. The rolled masses when of some size are called nuggets; in rare cases these occur very large and of great value. The Australian gold region has yielded many large nuggets; one of these found in 1858 weighed 184 pounds, and another (1869) weighed 190 pounds. In the auriferous sands, crystals of zircon are very common; also garnet and cyanite in grains; often also monazite, diamond, topaz, corundum, iridosmine, platinum. Besides the free gold of the quartz veins and gravels, much gold is also obtained from auriferous sulphides or the oxides produced by their alteration, especially pyrite', also arsenopyrite, chalcopyrite, sphalerite, marcasite, etc. The only minerals containing gold in combination are the rare tellurides (sylvanite, calaverite, etc.). Gold is widely distributed over the earth. It occurs under many different conditions and with many different rocks, being, however, more commonly associated with the acid types. A brief summary of the more important districts follows. Europe. The gold deposits of Europe are to be found chiefly in three great districts, namely the Ural mountains, eastern Hungary and a less important Alpine district reaching from Carinthia through the Austrian Tyrol^and the Italian Alps to the Pyrenees. There are three gold districts in Hungary. Two of these are of minor importance and lie one to* the north of Buda-Pesth and the other near the Galician frontier. The third district, which is the most important district in Europe, is in Transylvania, lying in the southeastern portion of the Bihar mountains. Its important centers are Offenbanya, Verespatak, Nagyag (largely tellurides), Boicza and Ruda. Asia. In Siberia gold is found on the eastern slope of the Ural mountains for a distance of 500 miles. The important districts from north to south are Bogoslov, Nizhni Tagilsk, Beresov and other localities near Ekaterinburg, Syserstk and Kyshtimsk, the Miask dis- trict including Zlatoust and Mt. Ilmen, Kotchkar and at the southern limit of the fields, Orsk. Siberia also has the important placer districts in Tomsk, which include Altai and Marinsk, and in Yeniseisk, the Atchinsk, Minusinsk and the north and south Yenisei dis- tricts. . Farther east there are deposits in Transbaikalia and the Lena district in Yakutsk. In India the chief districts are the Kolar field near Bangalore in Mysore and the Gadag and Hutti districts a little further north. Gold has been mined in China in Chili, Shantung Weihaiwei, Szechuen, Yuman and Fo-Kien. In Manchuria on the Lua.u-tung Peninsula. In Korea principally at Unsan. Gold-quartz veins, many of which have been worked for a long time, occur on a number of the Japanese islands. Australasia. The most important districts in New Zealand lie on the Hauraki Penin- sula with the Waihi mine as the most famous. Other districts are the West Coast area on the western slopes of the Alps of the South Island and the Otago area. In Queensland the districts of Charter Towers and the Mount Morgan mine are important. There are many gold districts in New South Wales among which are Hillgrove, Mount Bpppy and Hill End. Rich districts in Victoria are the Bendigo and Ballarat. The principal gold fields of Tasmania are Beaconsfield, Mathinna and the copper deposits at Mount Lyell. The chief gold field in West Australia is near Kalgoorlie where the ores are largely tellurides. 352 DESCRIPTIVE MINERALOGY Africa. Gold is found in Egypt in the section between the Nile and the Red Sea. Some of these deposits were worked in very early days. Gold has been produced for a long time from the Gold Coast district on the Gulf of Guinea. Important deposits are found in Matabeleland and Mashonaland in Southern Rhodesia. The most important gold district in the world is that of the Witwatersrand in the Transvaal. The mines occur in an east and west belt, some sixty miles in length, near Johannesburg. The gold is found scattered in small amounts through a series of steeply dipping quartz conglomerate rocks. South America. Colonlbia has in the past produced large amounts of gold. The chief districts today are in the states of Antioquia and Cauca. Comparatively small amounts are produced at the present time in the other northern countries. The important deposits of Brazil lie 200 miles to the north of Rio de Janeiro in Minas Geraes along the Sierra do Espinhaco. The gold deposits in Chile lie chiefly in the coast ranges in the northern and central parts of the country. Mexico. While Mexico is chiefly noteworthy for its silver output it produces also con- siderable gold. Important districts are as follows: Altar, Magdalena and Arizpe in Sonora; various places in Chihuahua, especially about Parral, and the Dolores mine on the western border of the state; the El pro mines in the state of Mexico; the Pachuca district in Hidalgo; also various places in Guanajuato and Zacatecas. Canada. The three important placer districts of Canada are the Klondike in Yukon Territory and the Atlin and Cariboo in British Columbia. The most productive vein deposits are found in British Columbia in the West Kootenay and Yale districts. Gold is also found in Ontario and Nova Scotia. , - United States. Gold occurs in the United States chiefly along the mountain ranges in the western states. Smaller amounts have been found along the Appalachians in the states of Virginia, North and South Carolina and Georgia. The more important localities in the western states are given below, the states being arranged approximately in the order of their importance. California. At the present time about two thirds of the state's out- put comes from the lode mines and one third from placer deposits. The quartz veins are chiefly found in what is known as the Mother-Lode belt that lies on the western slope of the Sierra Nevada and stretches from Mariposa County for more than 100 miles toward the north. The veins occur chiefly in a belt of slates. The lode mines are found chiefly in Amador, Calaveras, Kern, Nevada, Shasta, Sierra and Tuolumne Counties. The important placer mines are located in Butte, Sacramento and Yuba Counties. About 90 per cent of the placer gold is obtained by the use of dredges. Colorado. Gold is mined in various districts in Gilpin County, from the Leadville district and others in Lake County, in the region of the San Juan mountains in the Sneffels, Silverton and Telluride districts, Cripple Creek district (telluride ores) in Teller County, placer deposits in the Breckenridge district in Summit County. Alaska. The most important lode mines are in the Juneau district, while the chief placer deposits are those of Fairbanks and Iditarod in the Yukon basin and the Nome district on the Seward Peninsula. Nevada. The most important districts are those of Goldfield in Esmeralda County and Tonapah in Nye County. South Dakota. The output is chiefly from the Homestake mine at Lead in Lawrence County. Montana. There are various producing districts, the more important being in Madison (largely placers), Deer Lodge and Silver Bow Counties. Arizona. The important counties are Mohave and Cochise. Utah. Gold is produced chiefly from the Bingham and Tintic districts in Salt Lake County and from Juab County. Use. The chief ore of gold. SILVER. Isometric. Crystals commonly distorted, in acicular forms, reticulated or arborescent shapes; coarse to fine filiform; also massive, in plates or flattened scales. Cleavage none. Ductile and malleable. Fracture hackly. H. = 2'5-3. G. = 10-1-11 -1, pure 10*5. Luster metallic. Color and streak silver-white, often gray to black by tarnish. Comp. Silver, with some gold (up to 10 p. c.), copper, and sometimes platinum, antimony, bismuth, mercury. r ? y 5'?i et , C * ~ B - B - on charcoal fuses easily to a silver-white globule, which in O.F. gives a faint dark red coating of silver oxide; crystallizes on cooling; fusibility about 1050 C. Soluble in nitric acid, and deposited again by a plate of copper. Precipitated from its solutions by hydrochloric acid in white curdy forms of silver chloride. NATIVE ELEMENTS 353 Diff. Distinguished by its malleability, color (on the fresh surface), and specific gravity. Micro. In polished section shows a creamy white color with a metallic, smooth surface. With aqua regia and FeCl 3 tarnishes quickly with bright iridescent color-s Blackens with HNO ? . Obs. Native silver occurs in masses, or in arborescent and filiform shapes, in veins traversing gneiss, schist, porphyry, and other rocks. Also occurs disseminated, but usually invisibly, in native copper, galena, chalcocite, etc. It is commonly of secondary origin having been derived from the reduction of sulphides and other compounds of silver. Native silver is found at a great many localities, some of the most famous of which follow: Kongsberg, Norway, in magnificent specimens and in very large masses; Freiberg Schneeberg, etc., in Saxony; Pribram and Joachimstal in Bohemia; Andreasberg in the Harz Mts., Germany; Allemont in Dauphine, France; at various points in Cornwall England. At Chanarcillo and other localities in Chile; in large masses at Huantaya' Peru. In many places in Mexico, especially at Batopilas in Chihuahua; in Zacatecas and Guanajuato. A very important district is at Cobalt, Ontario, where native silver occurs in masses up to 1000 pounds in weight; it occurs there associated with various cobalt and nickel minerals. In the United States it has been found with native copper in the Lake Superior copper district; at Silver Islet, Lake Superior; at Butte and the Elkhorn mine in Mon.; at the Poor Man's Lode in Idaho; in Col., with various sulphide deposits, especially at Aspen. Use. An ore of silver. COPPER. Isometric. The tetrahexahedron a common form (Fig. 635) ; also in octa- hedral plates. Distinct crystals rare. Frequently irregularly distorted and passing into twisted and wirelike forms; filiform and arborescent. Massive; as sand. Twins: tw. pi. o (111), very common, often flattened or elongated to spear-shaped forms. Cf. p. 173. Cleavage none. Fracture hackly. Highly ductile and malleable. H. = 2-5-3. G. = 8'8-8'9. Luster metallic. Color copper-red. Streak metallic shining. Opaque. An excellent conductor for heat and electricity. (410). Comp. Pure copper, often containing some silver, bismuth, mercury, etc. Pyr., etc. B.B. fuses readily; on cooling becomes covered with a coating of black oxide. Dissolves readily in nitric acid, giving off red nitrous fumes, and produces a deep azure-blue solution with excess of ammonia. Fusibility 780 C. Micro. In polished section shows pink color with smooth, metallic surface. With cone. HNp 3 dissolves and shows iridescent tarnish. With FeCl 3 blackens and shows a solution pit. Obs. Copper is usually, if not always, secondary in its origin. It has either been deposited from solution by some reducing agent which is commonly a compound of iron or by the gradual reduction of some solid compound. Pseudomorphs of copper after cu- prite, azurite, chalcocite, etc., are well known. It is associated with other copper ores, especially cuprite, malachite and azurite in the upper zone of copper veins; also with the sulphides, chalcopyrite, chalcocite, etc.; often abundant in the vicinity of dikes of igneous rocks; also in clay slate and sandstone. Occurs in crystals at Bogoslovsk, Nijni Tagilsk and elsewhere in the Ural Mts. In Nassau, Germany. Common in Cornwall, England. Occurs in Brazil, Chile, and Peru. Found in pseudomorphs after the pseudo-hexagonal twins of aragonite at Corocoro, Bolivia. Abundant at Wallaroo, South Australia and at Broken Hill, New South Wales. Occurs at various places in Mexico. Occurs native throughout the red sandstone region of the eastern United States, spar- ingly in Mass., Conn., and more abundantly in N. J. Near New Haven, Conn., a mass was found in the drift weighing nearly 200 pounds; smaller isolated masses have also been found. Found in minor amounts at Bisbee, Ariz, (in branching crystal groups) ; at George- 354 DESCRIPTIVE MINERALOGY town N M (pseudomorphs after azurite) ; Ducktown, Tenn.; Cornwall, Pa.; and Frank- lin N J. The most important region in the world for native copper is the Lake Superior copper district on the Keweenaw peninsula, northern Mich. The rocks of this district con- sist of a series of interbedded lava flows, sandst9nes and conglomerates which dip steeply to the northwest. The copper is obtained practically all in the native state, sometimes m immense masses. It occurs as (1) a cement filling the interstices in the sandstone and conglomerate, sometimes replacing in large part the grains and pebbles themselves, (2) fill- ing the amygdaloidal cavities in the diabase and (3) in veins that traverse all kinds of rock. The copper was probably brought into the district by the igneous rocks. It is associated with native silver, calcite, prehnite, datolite, analcite, etc. Use. An ore of copper. MERCURY. Quicksilver. In small fluid globules scattered through its gangue. G = 13 '6. Luster metallic, brilliant. Color tin-white. Opaque. Comp. Pure mercury (Hg) ; with sometimes a little silver. Pyr., etc. B.B. entirely volatile, vaporizing at 350 C. Becomes solid at 40 C., crystallizing in regular octahedrons with cubic cleavage; G. = 14 '4. Dissolves in nitric Obs. Mercury in the metallic state is a rare mineral, and is usually associated with the sulphide cinnabar, from which the supply of commerce is obtained. The rocks afford- ing the metal and its ores are chiefly clay shales or schists of different geological ages. Also found in connection with hot springs. See cinnabar. LEAD. Isometric. Crystals rare. Usually in thin plates and small globular masses. Very malleable, and somewhat ductile. H = 1-5. G. = 11*4. Luster metallic. Color lead-gray. Opaque. Comp. Nearly pure lead; sometimes contains a little silver, also antimony. Pyr. B.B. fuses easily, coating the charcoal with a yellow to white oxide. Fusi- bility 330 C. Dissolves easily in dilute nitric acid. Obs. Of rare occurrence. Found at Pajsberg, Harstig, and Langban in Sweden; similarly at Nordmark; also in the gold washings of the Ural Mts.; reported elsewhere, but localities often doubtful. In the United States, occurs at Breckinridge and Gunnison, Col.; Wood River district, Idaho; Franklin, N. J. AMALGAM. Isometric. Common habit dodecahedral. Crystals often highly modified. Also massive in plates, coatings, and embedded grains. Cleavage: dodecahedral in traces. Fracture conchoidal, uneven. Rather brittle to malleable. H. = 3-3'5. G, = 1375-14-1. Luster metallic, bril- liant. ^Color and streak silver-white. Opaque. Comp. (Ag,Hg), silver and mercury, varying from Ag 2 Hg 3 to Ag 36 Hg. Var. Ordinary amalgam, Ag 2 Hg 3 (silver 26'4 p. c.) or AgHg (silver 35-0); also Ag 5 Hg 3 , etc. Arquerite, Agi 2 Hg (silver 86 "6); G. = 10'8; malleable and soft. Kongsber- gite, AgasHg or Ag 36 Hg. Pvr., etc. B.B. on charcoal the mercury volatilizes and a globule of silver is left. In the closed tube the mercury sublimes and condenses on the cold part of the tube in minute globules. Dissolves in nitric acid. Rubbed on copper it gives a silvery luster. Obs. From Germany in the Rhine-Palatinate at Moschel-Landsberg and at Jriednchssegen, Nassau; from Sala, Sweden; Kongsberg, Norwav; Allemont, Dauphine", France; Almaden, Spain; Chile; Vitalle Creek, British Columbia (arquerite). . . T m '~ Native tin has been reported from several localities. The only occurrence fairly above doubt is that from the washings at the headwaters of the Clarence river, near >ban, New bouth Wales. It has been found here in grayish white rounded grains, with platinum, mdosmine, gold, cassiterite, and corundum PLATINUM. NATIVE ELEMENTS 355 Platinum-Iron Group Isometric. Crystals rare; usually in grains and scales. Cleavage none. Fracture hackly. Malleable and ductile. H. = 4-4-5. G. = 14-19 native; 21-22 chem. pure. Luster metallic. Color and streak whitish steel-gray; shining. Sometimes magnetic and occasionally shows polarity. Comp. Platinum alloyed with iron, iridium, rhodium, palladium, osmium, and other metals. Most platinum yields from 8 to 15 or even 18 per cent of iron, 0*5 to 2 p. c. palladium, 1 to 3 p. c. each of rhodium and iridium, a trace of osmium and finally 0'5 to 2 p. c. or more of copper. Var. 1. Ordinary. Non-magnetic or only slightly magnetic. G. = 16'5-18'0 mostly. 2. Magnetic. G. about 14. Much platinum is magnetic, and occasionally it has polarity. The magnetic property seems to be connected with high percentage of iron (iron-platinum), although this distinction does not hold without exception. Pyr., etc. B.B. infusible. Not affected by borax or salt of phosphorus, except in the state of fine dust, when reactions for iron and copper may be obtained. Soluble only in heated aqua regia. Diff. Distinguished by its color, malleability, high specific gravity, infusibility and insolubility in ordinary acids. Obs. The platinum of commerce comes almost exclusively from placer deposits. Its original source, however, is in the basic igneous rocks, usually peridotites. The associated minerals are commonly chrysolite, serpentine and chromite. Platinum was first found in pebbles and small grains, associated with iridium, gold, chromite, etc., in the alluvial de- posits of the river Pinto, in the district of El Choco, Colombia ; South America, where it received its name platina (platina del Pinto) from plala, silver. The greater part of the world's supply comes from Russia (discovered in 1822) where it occurs in alluvial material in the Ural Mts. at Nijni Tagilsk, and with chromite in a serpentine probably derived from a peridotite; also in the Goroblagodat and Bisersk districts. Also found in Borneo; in New Zealand, from a region characterized by a chrysolite rock with serpentine; in New South Wales, at the Broken Hill district, and in gold washings at various points. In Cal. in small amounts in the gold placers, chiefly in Trinity Co.; at Port Orfqrd in Ore. At various points in Canada, the most important being the Tulameen District in British Columbia Use. Practically the only ore of platinum. Iridium. Platin-iridium. Iridium alloyed with platinum and other allied metals. Occurs usually in angular grains of a silver-white color. H. = 6-7. G. = 22 '6-22 '8. With the platinum of the Ural Mts. and Brazil. IRIDOSMINE. Osmiridium. Rhombohedral. Usually in irregular flattened grains. Cleavage: c(0001) perfect. Slightly malleable to nearly brittle. H. = 6-7. G. = 19-3-21 -12. Luster metallic. Color tin-white to light steel- gray. Opaque. Comp. Iridium and osmium in different proportions. Some rhodium, platinum, ruthenium, and other metals are usually present. Var. 1. Nevyanskite. H. = 7; G. = 18'8-19'5. In flat scales; color tin-white. Over 40 p. c. of iridium. 2. Siserskite. In flat scales, often six-sided, color grayish white, steel-gray. G. = 20-21'2. .Not over 30 p. c. of iridium. Less common than the light- colored variety. Diff. Distinguished from platinum by greater hardness and by its lighter color. Obs. Occurs with platinum in South America; in the Ural Mts.; in auriferous drift in New South Wales. Rather abundant in the auriferous beach-sands of northern Cali- fornia and Oregon. Palladium. Isometric. Palladium, alloyed with a little platinum and iridium. 356 DESCRIPTIVE MINERALOGY Mostly in grains. H. = 4'5-5. G. = 11 '3-11 '8. Color whitish steel-gray. Occurs with platinum in Brazil; also from the Ural Mts. Allopalladium. Palladium under the hexagonal-rhombohedral class (?). From Til- kerode in the Harz Mts. in small hexagonal tables with gold. IRON. Isometric. Usually massive, rarely in crystals. Cleavage: a( 100), perfect; also a lamellar structure || 0(111) and || d(110). Fracture hackly. Malleable. H. = 4-5. G. = 7-3-7-8. Luster metallic. Color steel-gray to iron-black. Strongly magnetic. Var. 1. Terrestrial Iron. Found in masses, occasionally of great size, as well as in small embedded particles, in basalt at Blaafjeld, Oyifak (or Uifak), Disko Island, West Greenland; also elsewhere on the same coast. This iron contains 1 to 2 p. c. of Ni. In small grains with pyrrhotite in basalt from near Kassel, Hesse Nassau, Germany. In minute spherules in feldspar from Cameron Township, Nipissing Dist., Ontario. Some other occurrences, usually classed as meteoric, may be in fact terrestrial. A nickeliferous metallic iron (FeNi 2 ) called awaruite occurs in the drift of the Gorge river, which empties into Awarua Bay on the west coast of the south island of New Zea- land; associated with gold, platinum, cassiterite, chromite; probably derived from a partially serpentinized peridotite. Josephinite is a nickel-iron (FeNia) from Oregon, occur- ring in stream gravel. Similar material from near Lillooet on the Fraser river, British Co- lumbia, has been called soucsite. Native iron also occurs sparingly in some basalts; reported from gold or platinum washings at various points. 2. Meteoric Iron. Native iron also occurs in most meteorites, forming in some cases (a) the entire mass (iron meteorites) ; also (6) as a spongy, cellular matrix in which are embedded grains of chrysolite or other silicates (siderolites)} (c) in grains or scales dissemi- nated more or less freely throughout a stony matrix 636 (meteoric stones). Rarely a meteorite consists of a single crystalline individual with numerous twinning lamellse !(o(lll). Cubic cleavage sometimes observed: also an octahedral, less often dodecahedral, lamellar structure. Etching with dilute nitric acid (or iodine) commonly develops a crystalline structure (called Widmanstdtten figures) (Fig. 636); usually consisting of lines or bands crossing at various angles according to the direction of the section, at 60 if || 0(111), 90 |! a(100), etc. They are formed by the edges of crystalline plates, usually 1 1 o, of the nickeliferous iron of different composition (kamacite, tcenite, plessite), as shown by the fact that they are differently attacked by the acid. Irons with cubic structure and with twinning lamellse have a series of fine lines correspond- ri 4. iv/rSb, Ag 4 (Sb,As) 3 , etc. By some authors classed with chalcocite. Pyr., etc. B.B. on charcoal fuses (1'5) to a globule, coating the coal with white anti- mony trioxide and finally giving a globule of almost pure silver. Soluble in nitric acid, leaving antimony trioxide. Obs. Occurs near Wolfach, Baden; Andreasberg in the Harz Mts., Germany; Alle- mont, France. Noted at Cobalt, Ontario, Canada. Also from Mexico arid Chile. Named from dvffKpacrts, a bad alloy. HENTILITE, ANIMIKITE. The ores from Silver Islet, Lake Superior, apparently contain a silver arsenide (huntilite, Ag 3 As?) and perhaps also a silver antimonide (animikite, Ag 9 Sb?), the latter probably a mixture. Horsfordite. A silver-white, massive copper antimonide, probably Cu 6 Sb (Sb 24 p. c.). G. = 8'8. Asia Minor, near Mytilene. Domeykite. Copper arsenide, Cu 3 As. Reniform and botryoidal; also massive, dissem- inated. G. = 7'2-775. Luster metallic. Color tin-white to steel-gray, readily tarnished. From several Chilian mines; also Zwickau, Saxony. In North America, with niccolite at Michipicoten Island, Lake Superior. Microscopic examination shows this mineral to be an intimate mixture of two unknown constituents. Usually identical with algodonite. Mohawkite. Like domeykite, Cu 3 As, with Ni and Co. Massive, fine granular to compact. Color gray with faint yellow tinge; tarnishes to dull purple. H. = 3'5. Brittle. G. = 8 '07. Microscopic examination, shows it to be a mixture. From Mohawk mine, Keweenaw Co., Mich. Ledouxite from the Mohawk minesaid to be Cu 4 As has been shown to be a mixture. Algodonite. Copper arsenide, Cu 6 As (As 16'5 p. c.); G. = 7'62. Resembles domey- kite. From Chile; also Lake Superior. Microscopic examination shows this mineral to be a mixture of two constituents. Whitneyite. Copper arsenide, Cu 9 As (As 11'6 p. e). G. = 8'4-8'6. Color pale red- dish white. From Houghton Co., Mich.; Sonora, Lower California. Chilenite. Perhaps Ag 6 Bi. Copiapo, Chile. COCINERITE. Copper, silver sulphide, Ci^AgS. Massive. Color silver-gray, tarnish- ing black, H = 2'5. G. = 6*1. From Cocinera mine, Ramos, San Luis Potosi, Mexico. Stiitzite. A rare silver telluride (Ag 4 Te?). Probably from Nagyag, Transylvania. Rickardite. Cu 4 Te 3 . Massive. H. = 3'5. G. = 7'5. Color deep purple, dulling on exposure. Fusible. Found at Vulcan, Col. Maucherite. Ni 3 As 2 . Tetragonal. Habit, square tabular. H. =5. G. = 7'83. Color reddish silver-white tarnishing to gray copper-red. Streak blackish gray. Easily fusible. From Eisleben, Thuringia. The furnace product, placodine, is identical wfth maucherite. B. Monosulphides, Monotellurides,* etc., R 2 S, RS, ETC. 1. Galena Group. Isometric. Galena PbS Argentite Ag 2 S Also, (Pb,Cu 2 )S, (Cu 2 ,Pb)S Jalpaite (Ag,Cu) 2 S Altaite PbTe Hessite Ag 2 Te Clausthalite PbSe Aguilarite Ag 2 Se Naumannite (Ag 2 ,Pb)Se The following, known only in massive form, probably also belong here: Berzelianite Cu 2 Se Zorgite (Pb,Cu2,Ag 2 )Se? Lehrbachite (Pb,Hg 2 )Se t Crookesite (Cu,Tl,Ag) 2 Se Eucairite Cu 2 Se.Ag2Se SULPHIDES, SELENIDES, TELLURIDES, ARSENIDES, ANTIMONIDES 363 The GALENA GROUP embraces a number of monosulphides, etc., of the related metals, silver, copper, lead, and mercury. These crystallize in the normal class of the isometric system, and several show perfect cubic cleavage. These characters are most distinctly exhibited in the type species, galena. GALENA. GALENITE. Lead glance. Isometric. Commonly in cubes, or cubo-octahedrons, less often octa- hedral. Also in skeleton crystals, reticulated, tabular. Twins: tw. pi. o(lll), both contact- and penetration-twins (Figs. 401, 404, p. 165), sometimes repeated; twin crystals often tabular || o. Also other tw. planes giving poly- synthetic tw. lamellae. Massive cleavable, coarse or fine granular, to impal- pable; occasionally fibrous or plumose. 641 642 643 644 ! ! ! a p(221), w Cleavage: cubic, highly perfect; less often octahedral. Fracture flat sub- conchoidal or even. H. = 2-5-275. G. = 7*4-7 '6. Luster metallic. Color and streak pure lead-gray. Opaque. Comp. Lead sulphide, PbS = Sulphur 13'4, lead 86'6 = 100. Often contains silver, and occasionally selenium, zinc, cadmium, antimony, bismuth, copper, as sulphides; besides, also, sometimes nativ,e silver and gold. Var. 1. Ordinary, (a) Crystallized; (6) somewhat fibrous and plumose; (c) cleav- able, granular coarse or fine; (d) crypto -crystalline. The variety with octahedral cleavage is rare; in it the usual cubic cleavage is obtained readily after heating to 200 or 300; the peculiar cleavage may be connected with the bismuth usually present. One variety showing octahedral cleavage contained a small amount of tellurium. 2. Argentiferous. All galena is more or less argentiferous, and no external characters serve to distinguish the kinds that are much so from those that are not. The silver is detected by cupellation, and may amount from a few thousandths of one per cent to one per cent or more; when mined for silver it ranks as a silver ore. 3. Containing arsenic, or antimony , or a compound of these metals, as impurity. Here belong bleischweif f rom Claustal, Harz'Mts., with 0'22 Sb, and steinmannite from PHbram, Bohemia, with both arsenic and antimony. Pyr. In the open tube gives sulphurous fumes. B.B. on charcoal fuses, emits sul- phurous fumes, coats the coal yellow near the assay (PbO) and white with a bluish border at a distance (PbSO 3 , chiefly), and yields a globule of metallic lead. Decomposed by strong nitric acid with the separation of some sulphur and the formation of lead sulphate. Diff. Distinguished, except in very fine granular varieties, by its cubic cleavage; the color and the high specific gravity are characteristic; also the blowpipe reactions. Micro. In polished section shows white color with smooth surface usually showing triangular pits. With HNO 3 blackens; with FeCl 3 becomes bright, iridescent. Artif. Crystallized galena has been formed in numerous ways. In nature it is appar- ently commonly formed by hydrochemical reactions perhaps similar to the following labora- tory methods : galena was produced by allowing a mixture of lead chloride, sodium bicar- bonate and a solution of hydrogen sulphide to remain in a sealed tube for several months. 364 DESCRIPTIVE MINERALOGY Pyrite or marcasite heated with a solution of lead chloride will produce galena; a solution of lead nitrate when heated with ammonium sulphydrate will yield galena. Galena is fre- quently observed in furnace slags. Obs. One of the most widely distributed of the metallic sulphides. Occurs in beds and veins, both in crystalline and uncrystalline rocks. Very commonly found together with zinc ores in connection with limestone rocks. It is often associated with pyrite, marcasite, sphalerite, chalcopyrite, arsenopyrite, etc., in a gangue of quartz, calcite, barite or fluorite, etc.; also with cerussite, anglesite, and other salts of lead, which are frequent results of its alteration. It is also common with gold, and in veins of silver ores. A few of the notable localities at which galena has been found are as follows: At Freiberg in Saxony in veins in gneiss; at Claustal and Neudorf, etc., in the Harz Mts., and at Pribram in Bohemia, it forms veins in clay slate; similarly in Styria; in limestone at Bleiberg, Carinthia; in Silesia, Prussia; at Gonderbach near Laasphe, Westphalia; at Schemnitz, Kapnik, etc., Hungary; Joachimstal, Bohemia; at Poullaouen and Huelgoet, Brittany, France; in Moresnet district in Belgium; in province of Cagliari, Sardinia; in Spain, in granite at Linares, also in Catalonia, Grenada, and elsewhere; in veins through the graywacke of Leadhill, Scotland, and the contact hornstones of Cornwall; filling cavities in the limestone of Derbyshire, Cumberland, and the northern districts of England, associated with calcite, dolomite, fluorite, barite, witherite, calamine and sphalerite; in many places in Australia, Chile, Bolivia, Peru, etc. Extensive deposits of this ore in the United States exist in Missouri, Illinois, Iowa, and Wisconsin. The ore occurs usually filling cavities or chambersin stratified limestone, of different periods, from Silurian to Carboniferous. It is associated with sphalerite, smith- sonite, calcite, pyrite, etc. The Missouri mines are situated in three districts in the southern part of the state, (1) Southeastern, chiefly in St. Francis, Washington and Madison counties, (2) Central, (3) Southwestern or Joplin district, the latter producing chiefly zinc. Other districts in the upper Mississippi Valley are found in southwestern Wis., eastern Iowa and northwestern 111. Also occurs in N. Y., at Rossie, St. Lawrence Co., in crystals with calcite and chalcopyrite; in Pa., at Phcenixyille and elsewhere. In Col., at Leadville and Aspen, there are productive mines of argentiferous galena, also at Georgetown, the San Juan dis- trict and elsewhere. Mined for silver in the Cceur d'Alene region in Idaho; at the Park City and Tintic districts in Utah. The name galena is from the Latin galena (ya\i)t>rj), a name 'given to lead ore or the dross from melted lead. Use. The most important ore of lead and frequently a valuable ore of silver. CUPROPLUMBITE. A massive mineral, from Chile, varying in characters from galena to those of chalcocite and covellite; composition, Cu 2 S.2PbS(?). Material classed here from Butte, Mon., gave formula, 5Cu 2 S.PbS. Alisonite is massive, deep indigo-blue quickly tarnishing; corresponds to 3(?u 2 S.PbS. From Mina Grande, Chile. Whether these and similar minerals represent definite homogeneous compounds, or only ill-defined alteration- products, is uncertain, and if so it is not clear whether they should be classed with isometric galena or with orthorhombic chalcocite. Altaite. Lead telluride, PbTe. Rarely in cubic or octahedral crystals, usually massive with cubic cleavage. G. = 8 '16. Color tin-white, with yellowish tinge tarnishing to bronze-yellow. From the Altai Mts., with hessite; Coquimbo, Chile; Cal., Col., British Columbia. ( Clausthalite. Lead selenide, PbSe. Commonly in fine granular masses resembling galena. Cleavage: cubic. G. = 7 '6-8 -8. Color lead-gray, somewhat bluish. From Claustal, Harz Mts., Germany; Cacheuta mine, Mendoza River, Argentina. Tilkerodite is a cobaltiferous variety. Naumannite. Silver-lead telluride (Ag2,Pb)Se. In cubic crystals; also massive, granular, in thin plates. Cleavage: cubic. G. = 8'0. Color and streak iron-black. From Tilkerode in the Harz Mts , Germany. ARGENTITE. Silver Glance. Isometric. Crystals often octahedral, also cubic; often distorted, fre- quently grouped in reticulated or arborescent forms; also filiform. Massive; embedded; as a coating. Cleavage: a(100), d(110) in traces. Fracture small subconchoidal. Per- fectly sectile. H. = 2-2-5. G. = 7'20-7'36. Luster metallic. Color and streak blackish lead-gray; streak shining. Opaque. Comp. Silver sulphide, AgaS = Sulphur 12-9, silver 871 = 100. SULPHIDES, SELENIDES, TELLURIDES, ARSENIDES, ANTIMONIDES 365 Pyr., etc. In the open tube gives off sulphurous fumes. B.B. on charcoal fuses with intumescence in O.F., emitting sulphurous fumes, and yielding a globule of silver. Diff. Distinguished from other sulphides by being readily cut with a knife; also by yielding metallic silver on charcoal. Micro. In polished section shows grayish white color with a smooth surface which is easily scratched. Turns brown with HNO 3 ,KCN and FeCl 3 ; with cone. HC1 tarnished iridescent by fumes and blackened by acid. Artif. Argentite is very easily prepared artificially and in numerous ways. Sulphur, sulphur dioxide or hydrogen sulphide will act upon metallic silver or any of its common compounds, either in solution or as solids, to. produce silver sulphide. Obs. Found at Freiberg, etc., Saxony; Andreasberg, Harz Mts., Germany; Schemnitz, Hungary: Joachimstal, Bohemia; Kongsberg, Norway; Sardinia. In South America at sil- ver mines in Chile, Peru and Bolivia. In Mexico in the states of Chihuahua, Guanajuato, etc. Important ore at Comstock Lode, Tonapah, etc., Nev.; Aspen, Leadville, etc. Col. Found at Port Arthur on north shore of Lake Superior. Use. An important ore of silver. JALPAITE is a cupriferous argentite from Jalpa, Mexico. Hessite. Silver telluride, Ag2Te. Isometric. Usually massive, compact or fine- grained. Cleavage indistinct. Somewhat sectile. H. = 2*5-3. G. = 8 '31-8 '45. Color between lead-gray and steel-gray. From the Altai Mts.; at Nagyag, Botes and Rezbdnya in Transylvania; Chile near Arqueros, Coquimbo. In Mexico at San Sebastian, Jalisco. In the United States, Calaveras Co., Cal.; Boulder Co., Col.; Utah. This species also often contains gold and thus graduates toward petzite. Petzite. (Ag,Au) 2 Te with Ag : Au = 3 : 1. Massive; granular to compact. Slightly sectile to brittle H. = 2*5-3. G. = 8 '7-9 '02. Color steel-gray to iron-black ; tarnishing. From Nagyag, Transylvania; Kalgoorlie, West Australia; Yale District, British Columbia; Col.; Poverty Hill, Tuolumne Co., and elsewhere, Cal. Aguilarite. Silver selenide, Ag 2 S and Ag 2 (S,Se). In skeleton dodecahedral crystals. Sectile. G. = 7'586. Color iron-black. From Guanajuato, Mexico. Berzelianite. Copper selenide, Cu 2 Se. In thin dendritic crusts and disseminated. G. = 671. Color silver-white, tarnishing. From Skrikerum, Sweden; Lehrbach, in the Harz Mts., Germany. Lehrbachite. Selenide of lead amd mercury, PbSe with HgSe. Massive, granular. G. = 7'8. Color lead-gray to iron-black. From Lehrbach, in the Harz Mts., Germany. Eucairite. Cu 2 Se.Ag 2 Se. Massive, granular. G. = 7-50. Color between silver- white and lead-gray. From the Skirkerum copper mine, Sweden; also Chile. Zorgite. Selenide of lead and copper in varying amounts. Perhaps a mixture. Mas- sive, granular G. = 7-7 '5. Color dark or light lead-gray. From the Harz Mts., Germany; Cacheuta, Argentina. Crookesite. Selenide of copper and thallium, also silver (1-5 p. c.), (Cu,Tl,Ag) 2 Se. Massive, compact. G. = 6*9. Luster metallic. Color lead-gray. From the mine of Skirkerum, Sweden. Umangite. CuSe.Cu 2 Se. Massive, fine-granular to compact. H. =3. G. = 5-620. Color dark cherry-red. From La Rioja, Argentina. 2. Chalcocite Group a :b : c Chalcocite Cu 2 S 0'5822 : 1 0'9701 Stromeyerite Ag 2 S.Cu 2 S 0'5822 : 1 0.9668 Sternbergite Ag 2 S.Fe 4 S 5 0-5832 : 1 0.8391 Frieseite 0-5970 : 1 0-7352 Acanthite Ag 2 S 0-6886 : 1 0-9944 The species of the CHALCOCITE GROUP crystallize in the orthorhombic system with a prismatic angle approximating to 60; they are hence pseudo- hexagonal in form, especially when twinned. The group is parallel to the Galena Group, since Cu 2 S appears in isometric form in cuproplumbite and Ag 2 S also in argentite. Some authors include dyscrasite here (see p. 361). 366 DESCRIPTIVE MINERALOGY CHALC0CITE. Copper Glance. Redruthite. Orthorhombic. Axes a : b : c = 0'5822 : 1 110 A 110 = 60 25'. dd'f (021) A 021 = 125 28'. 645 0-9701. p, 001 A 111 = 62 35*'. pp" r , 111 A 111 =53- 646 647 Crystals pseudo-hexagonal in angle, also by twinning (tw. pi. w(110)). Often massive, structure granular to compact and impalpable. Cleavage: m(110) indistinct; etching of orientated crystals develops cleav- ages parallel to the three pinacoids. Fracture conchoidal. Rather sectile. H. = 2-5-3. G. = 5-5-5-8. Luster metallic. Color and streak blackish lead-gray, often tarnished blue or green, dull. Opaque. Comp. Cuprous sulphide, Cu 2 S = Sulphur 20*2, copper 79'8 = 100. Sometimes iron in small amount is present, also, silver. Pyr., etc. In the open tube gives sulphurous fumes. B.B. on charcoal melts to a globule, which boils with spirting; the fine powder roasted at a low temperature on charcoal, then heated in R.F., yields a globule of metallic copper. Soluble in'nitric acid. Diff. Resembles argentite but much more brittle; bornite has a different color on the fresh fracture and becomes magnetic B.B. Micro. In polished section shows grayish or bluish white color with smooth surface. With HNO 3 effervesces and etches, turning more or less blue, and develops cleavage direc- tions; wibh KCN blackens and etches. Artif . Chalcocite has been prepared artificially by heating the vapors of cuprous chloride and hydrogen sulphide or by the treatment of cupric oxide with hydrogen sulphide; also by the heating of cupric solutions with ammonium sulphocyanate in a sealed tube. Obs. Chalcocite is an important ore of copper. It is usually secondary in its origin, being found in the upper, enriched portions of copper veins. It is commonly associated with chalcopyrite, bornite, pyrite, cuprite, malachite, azurite, etc. Cornwall affords splendid crystals, especially the districts of Saint Just, Camborne, and Redruth (redruthite). Occurs at Joachimstal, Bohemia; Tellemarken, Norway; compact and massive varieties in Siberia; Saxony; Mte. Catini mines in Tuscany; Mexico; South America. In the United States, Bristol, Conn., has afforded large and brilliant crystals ; also found at Simsbury and Cheshire; at Schuyler's mines, *N. J.; in Nev., in Washoe, Humboldt, Churchill and Nye counties; at Clifton, Ariz.; in Mon., massive at Butte in great amounts. Notable deposit at Kennecott, Copper River District, Alaska. Found in Canada, with chalcopyrite and bornite at the Acton mines and elsewhere in the province of Quebec. Use. An important ore of copper. Stromeyerite. (Ag,Cu) ? S, or Ag 2 S.Cu 2 S. Rarely in orthorhombic crystals, often twinned. Commonly massive, compact. H. = 2 '5-3. G. = 6'15-6'3. Luster metallic. Color and streak dark steel-gray. From the Zmeinogorsk mine, Siberia; Silesia; also Chile, Zacatecas, Mexico; Cobalt, Ontario; the Heintzelman mine in Ariz.; Col. Chalmersite. Cu 2 S.Fe 4 S 5 . Orthorhombic. Axial ratio near that of chalcocite. In thin elongated prisms vertically striated. Twins cdmmon with ra(110) as tw. pi. resem- bling chalcocite. H. = 3'5. G. = 47. Color brass- to bronze-yellow. Strongly mag- netic. From the Morro Velho gold mine, Minas Geraes, Brazil. SULPHIDES, SELENIDES, TELLURIDES, ARSENIDES, ANTIMONIDES 367 STERNBERGITE Orthorhombic. Crystals tabular || c(001). Commonly in fan-like aggre- gations; twins, tw. pi. ra(110). Cleavage : c(001), highly perfect. Thin laminae flexible, like tin-foil. H. = 1-1*5. G. = 4-215. Luster metallic. Color pinchbeck-brown. Streak black. Opaque. Comp. AgFe 2 S 3 or Ag 2 S.Fe 4 S 5 = Sulphur 30.4, silver 34.2, iron 35.4 = 100. Obs. Occurs with pyrargyrite and stephanite at Joachimstal, Bohemia, and Johann- georgenstadt, Saxony. FRIESEITE. Near sternbergite. In thick tabular crystals. H. = 2 '5; G. = 4 '22. .Color dark gray. Composition Ag 2 Fe 5 S 8 . Occurs with marcasite at Joachimstal, Bohemia. Acanthite. Silver sulphide, Ag 2 S, like argentite. In slender prismatic crystals (or- thorhornbic) . Sectile. G. = 7'2-7'3. Color iron-black. Occurs at Joachimstal, Bohemia; also at Freiberg and Schneeberg, Saxony; at Rico, Col. It has been suggested that acanthite may be only argentite in distorted isometric crys- tals. Sphalerite Group. Sphalerite ZnS Metacinnabarite HgS Guadalcazarite (Hg,Zn)S Tiemannite HgSe RS. Isometric-tetrahedral Onofrite Hg(S,Se) Alabandite MnS Cotoradoite HgTe Massive The SPHALERITE GROUP embraces a number of sulphides, selenides, etc., of zinc, mercury, and manganese. These are isometric-tetrahedral in crystal- lization. * SPHALERITE, ZINC BLENDE or BLENDE. Black-Jack, Mock-Lead, False Galena. Isometric-tetrahedral. Often in tetrahedrons. Twins common: tw. pi. 648 649 650 m = (311) o(lll); twinning often repeated, sometimes as polysynthetic lamellae. Com- monly massive cleavable, coarse to fine granular and compact; also foliated, sometimes fibrous and radiated or plumose; also botryoidal and other imita- tive shapes. Cryptocrystalline to amorphous, the latter sometimes as a powder. Cleavage: dodecahedral, highly perfect. Fracture conchoidal. Brittle. H. = 3-5-4. G. = 3-9-4-1; 4-063 white, N. J. Luster resinous to adaman- tine.. Color commonly yellow, brown, black; also red, green to white, and when pure nearly colorless. Streak brownish to light yellow and white. Transparent to translucent. Refractive index high: n = 2-3692. Comp. Zinc sulphide, ZnS = Sulphur 33, zinc 67 = 100. Often con- taining iron and manganese, and sometimes cadmium, mercury and rarely lead 368 DESCRIPTIVE MINERALOGY and tin. Also sometimes contains traces of indium, gallium and thallium; may be argentiferous and auriferous. Var. 1. Ordinary. Containing little or no iron; from colorless white to yellowish brown, sometimes green; G. = 4-0-4 '1. The red or reddish brown transparent crystallizec kinds are sometimes called ruby blende or ruby zinc. The massive cleavable forms are the most common, vary ing from coarse to fine granular; also cryptocrystalline. Schalenblende is a closely compact variety, of a pale liver-brown color, in concentric layers with reniform surface; galena and marcasite are often interstratified. The fibrous forms are chiefly wurtzite. A soft white amorphous form of zinc sulphide occurs in Cherokee Co., Kan. 2. Ferriferous: Marmatite. Containing 10 p. c. or more of iron; dark-brown to black; G. = S'9-4'05. The proportion of FeS to ZnS varies from 1 : 5 to 1 : 2, and the last ratio is that of the christophitc of Breithaupt, a brilliant black sphalerite from St. Christophe mine, at Breitenbrunn, having G. = 3 '91-3 '923. 3. Cadmiferous: Pribramite, Przibramite. The amount of cadmium present in any sphalerite thus far analyzed is less than 5 per cent. Pyr., etc. Difficultly fusible. In the open tube sulphurous fumes, and generally changes color. B.B. on charcoal, in R.F., gives a coating of zinc oxide, which is yellow while hot and white after cooling. If cadmium is present a reddish brown coating of cadmium oxide will form first. With cobalt solution the zinc oxide coating gives a green color when heated in O.F. Most varieties, after roasting, give with borax a reaction for iron. Dissolves in hydrochloric acid with evolution of hydrogen sulphide. Diff. Varies widely in color and appearance, but distinguished by the resinous luster in all but deep black varieties; usually exhibits distinct cleavage; nearly infusible B.B.; yields a zinc oxide coating on charcoal. Micro. In polished section shows a grav'color with smooth surface. Transparent, yellow to brown with oblique illumination. /HiVith HNOs becomes slowly brown, often showing crystal structure; with aqua regia effervesces and blackens. Arttf . Sphalerite has been artificially formed by heating zinc solutions in hydrogen sulphide inclosed in a sealed tube; also by passing hydrogen sulphide over heated zinc chloride. Obs. Sphalerite is the most important ore of zinc. It occurs in both crystalline and sedimentary rocks, being especially common in the limestones, where it often occurs as beds of considerable size. It is frequently associated with galena, also with chalcopyrite, pyrite, barite. fluorite, siderite, etc. Commonly found with silver ores. Of the two forms of zinc sulphide, sphalerite is the form which crystallizes below 1020 while wurtzite is deposited at higher temperatures. Zinc sulphide is deposited from alkaline solutions as sphalerite; from acid solutions both forms are deposited, the amount of sphalerite increas- ing with the temperature while that of wurtzite increases with the acidity of the solution. Some of the chief localities for crystallized sphalerite are: Alston Moor in Cumberland and at St. Agnes and elsewhere in Cornwall, England; Andreasberg and Neudorf in the Harz Mts., Freiberg, and other localities in Saxony; Pfibram, and Schlackenwald in Bohe- mia; Kapnik, Schemnitz and Felsobanya, in Hungary; Nagyag and Rodna in Transyl- vania; the Binnental in Switzerland, isolated crystals of great beauty, yellow to brown, in cavities of dolomite. A beautiful transparent variety . yielding large cleavage masses is brought from Picos de Europa, Santander, Spain, where it occurs in a brown limestone. A similar variety with golden brown to green colors from Chivera mine, Cannanea, Mexico. Large crystals from Ani copper mines, Ugo, Japan. Fibrous varieties (see wurtzite) are obtained at Pribram; Geroldseck in Baden; Raibl, Carinthia; also in Cornwall. The origi- nal marmatite is from Marmato near Popayan, Italy. The important zinc ore districts of the United States in which sphalerite is the chief zinc mineral are found in Missouri, Colorado, Montana, Wisconsin, Idaho and Kansas, borne localities noteworthy for the specimens they have produced are as follows: In Conn., ?in, i y 'j N * J- ' a white varie ty (cleiophane) at Franklin Furance. In Pa., at the Wheatley and Perkiomen lead mines, in crystals; near Friedensville, Lehigh Co., a grayish waxy variety. In 111., near Rosiclare, with galena and calcite; at Marsden' diggings, near Galena, m stalacites, with crystallized marcasite, and galena; at Warsaw. In Wis., at Mineral Point, in fine crystals. In Ohio, at Tiffin. In Mo., in beautiful crystallizations with galena, marcasite and calcite at Joplin and other points in the southwestern part of the state; deposits here occur in limestone and are of great extent and value; also in adjoining parts of Kan. In Col., at many places. Named blende because, while often resembling galena, it yielded no lead, the word in German meaning blind or deceiving. Sphalerite is from cr0aXepds, treacherous. use. ine most important ore of zinc. SULPHIDES, SELENIDES, TELLURIDES, ARSENIDES, ANTIMONIDES 369 Metacinnabarite. Mercuric sulphide, HgS. In composition like cinnabar, but occurs in black tetrahedral crystals; also massive. G. = 77. In Cal., from the Reddington mine, Lake county, with cinnabar, quartz and marcasite; and from San Joaquin, Orange Co. Found also at Idria in Austria. Guadalcazarite. Near metacinnabarite, but contains zinc (up to 4 p. c.). Guadal- cazar, Mexico. Probably a mixture. Tiemannite. Mercuric selenide, HgSe. Isometric-tetrahedral. Commonly massive' compact. G. = 8'19 Utah; 8'30-8'47 Claustal. Luster metallic. Color steel-gray to blackish lead-gray. Streak nearly black. Occurs at Claustal in the Harz Mts.; Cal., in the vicinity of Clear lake; MarysVale, Piute Co., Utah. Onofrite. Hg(S,Se) with Se = 4'5 to 6'5 p. c. San Onofre, Mexico; Marysvale, Utah. Coloradoite. Mercuric telluride, HgTe. Massive. Conchoidal fracture. H. = 2'5. G. = 8'07 (Kalgoorlie). Color iron-black. Originally found sparingly in Colorado. Rather abundant at the Kalgoorlie district, West Australia. Material called kalgoorlite is a mixture of coloradoite and petzite. * Alabandite. Manganese sulphide, MnS. Isometric-tetrahedral; usually granular massive. Cleavage: cubic, perfect. G. = 3 '95-4 '04. Luster submetallic. Color iron- black. Streak green. Occurs at Nagyag, Transylvania; Kapnik, Hungary; Mexico; Peru; crystallized and massive on Snake River, Summit county, Col.; Tombstone, Ariz. Oldhamite. Calcium sulphide, CaS. In pale brown spherules with cubic cleavage in the Busti meteorite. Also noted in Allegan meteorite. PENTLANDITE. Isometric. Massive, granular. Cleavage: octahedral. Fracture uneven. Brittle. H. = 3*5^. G. = 5-0. Luster metallic. Color light bronze- yellow. Streak light bronze-brown. Opaque. Not magnetic. Comp. A sulphide of iron and nickel, (Fe,Ni)S. In part, 2FeS.NiS = Sulphur 36-0, iron 42-0, nickel 22-0 = 100. Obs. Occurs with chalcopyrite near Lillehammer, Norway. Also from Sudbury, Ontario, where it is intimately associated with nickeliferous pyrrhotite. It can be dis- tinguished from the latter by its cleavage. 4. Cinnabar-Wurtzite-Millerite Group. Rhombohedral or Hexagonal c Cinnabar HgS Rhombohedral-Trapezohedral 1*1453 Covellite CuS 1-1466 c c Greenockite CdS Hexagonal-Hemimorphic 0*8109 or 0*9364 Wurtzite ZnS " 0*8175 0*9440 Millerite NiS Rhombohedral 0*9883 Niccolite NiAs " 0*8194 0*9462 Breithauptite NiSb 0'8586 0*9915 Arite Ni(Sb,As) Pyrrhotite FenSw, etc. Hexagonal 0*8701 1*0047 Troilite FeS This fourth group among the monosulphides includes several subdivisions, as shown in the scheme above, and the relations of the species are not in all cases perfectly clear. It is to be noted that the sulphides of mercury and zinc, already represented in the sphalerite group, appear here again. If, as suggested by Groth, the prominent pyramids of wurtzite, greenockite, etc., be made pyramids of the second series (e.g., x = 1122, instead of 1011), then the values of c in the second column are obtained, which correspond to millerite. The form of several of these species, however, is only imperfectly known. A rhombohedral form for greenockite has been suggested. 370 DESCRIPTIVE MINERALOGY CINNABAR. Rhombohedral-trapezohedral. Axis c = 11453. rr' 1011 A 1011 = 87 23'. u', 4045 A 4045 = 78 0'. cr, 0001 A 1C11 = 52 54'. Crystals usually rhombohedral or thick tabular in habit, rarely showing trapezohedral faces; in rhombohedral penetration twins; also acicular pris- matic. In crystalline incrustations, granular, massive; sometimes as an earthy coating. Cleavage: ra(1010) perfect. Fracture subconchoidal, uneven. Some- what sectile. H. = 2-2;5. G..= 8-0-8-2. Luster adamantine, inclining to metallic when dark-colored, and to dull in friable varieties. Color cochineal- red, often inclining to brownish red and lead-gray. Streak scarlet. Trans- parent to opaque. Optically + . Indices: o> r = 2 -82, e r = 3 '14. See Art. 394. Var. 1. Ordinary: either (a) crystallized; (b) massive, granular embedded or com- pact; bright red to reddish brown in color; (c) earthy and bright red. 2. Hepatic. Of a fiver-brown color, with sometimes a brownish streak, occasionally slaty in structure, though commonly granular or compact. Comp. Mercuric sulphide, HgS = Sulphur 13'8, mercury 86'2 = 100. Usually impure from the admixture of clay, iron oxide, bitumen. Pyr. In the closed tube alone a black sublimate of mercuric sulphide, but with sodium carbonate one of metallic mercury. Carefully heated in the open tube gives sulphurous fumes and metallic mercury, which condenses in minute globules on the cold walls of the tube. B.B. on charcoal wholly volatile, but only when quite free from gangue. Diff. Characterized by its color and vermilion streak, high specific gravity (reduced, however, by the gangue usually present), softness; also by the blowpipe characters (e.g., in the closed tube) . Resembles some varieties of hematite and cuprite. Artif. Cinnabar has been produced artificially by several methods which are, how- ever, in general modifications of the two following types: (1) When the black mercury sul- phide formed byjthe direct union of mercury and sulphur is sublimed, cinnabar is the prod- uct; (2) the black sulphide when treated with solutions of alkaline sulphides is converted into cinnabar. In general cinnabar is formed under alkaline conditions and metacinnabarite under acidic conditions. Obs. Cinnabar is the only common mineral of mercury and with rare exceptions constitutes the ore of the metal. It occurs in veins filling fissures and cavities in rocks which are commonly sedimentary in character, being often slates, shales, sandstones or limestones. While infrequently occurring in igneous rocks such rocks are commonly near by and are thought to have been the source of the metal. Cinnabar is deposited from hot alkaline solutions or as the result of solfataric action. Pyrite and marcasite, sulphides of copper, stibnite, realgar, gold, etc., are associated minerals; calcite, quartz or opal, also barite, fluorite, are gangue minerals; a bituminous mineral is common. The most important European deposits are at Almaden in Spain, and at Idria in Car- niola, where it is usually massive; also at Bakmut.in southern Russia. Crystallized at Moschellandsberg and Wolf stein in the Palatinate and at the mines of Mt. Avala, near Belgrade, Servia; at Ripa in Tuscany; at Als6sajo, Hungary; in the Ural Mts., the Ner- chinsk region in Transbaikalia; in large twinned rhombohedrons from Province of Kwei- chow, China; Japan; Mexico; Huancavelica, Peru; Chile. In the United States forms extensive mines in Cal., the most important at New Almaden and the vicinity, in Santa Clara Co.; also at Altoona, Trinity Co.; it is now forming by solfataric action at Sulphur Bank, Cal., and Steamboat Springs, Nev.; has been found in southern Utah; important deposits occur in Brewster Co., Texas; also mined in Nev. and Ariz. The name cinnabar is supposed to come from India, where it is applied to the red resin, dragon's blood. The native cinnabar of Theophrastus is true cinnabar; he speaks of its affording quicksilver. The Latin name of cinnabar, minium, is now given to red lead, a substance which was early used for adulterating cinnabar, and so got at last the name. Only comparatively few localities have furnished the mineral in quantity. Use. The most important ore of mercury. SULPHIDES, SELENIDES, TELLURIDES, ARSENIDES, ANTIMONIDES 371 COVELLITE. Monoclinic ? Pseudohexagonal through twinning. Crystals usually thin hexagonal plates. Often massive. CleaVage: basal, perfect. H. = T5-2. G. = 4'6. Luster submetallic to resinous. Color indigo-blue or darker. Often shows fine purple color when moistened with water. Streak lead-gray to black. Opaque. Comp. Cupric sulphide, CuS = Sulphur 33'6, copper 66'4 = 100. Pyr., etc. Fusible at 2' 5 yielding sulphurous fumes. After roasting and moistening with hydrochloric acid gives azure-blue flame. Much sulphur in C.T. Macro. In polished section shows blue color with smooth surface. With KCN be- comes instantly deep violet which rubs off, leaving a yellow coating and rough surface. Artif. Covellite has been prepared artificially by heating in sealed tubes a cupric solution with ammonium sulphocyanate and by heating sphalerite in a solution of copper sulphate. Obs. Covellite is a mineral of secondary origin found in the enriched portions of copper sulphide veins, associated with chalcocite, bornite, etc. Found in small amounts in many places. Noteworthy localities are as follows: various places in Germany; in exceptional crystals at Bor in Timoker Kreis, Servia; on the lavas of Vesuvius; in Chile; Province of Rikuchu, Japan. In the United States at the Butte district, Mon.; Summitville, Col.; La Sal district, Utah; Kennecott, Alaska, etc. GREENOCKITE. Hexagonal-hemimorphic. Rarely in hemimorphic crystals; also as a coating. Cleavage: a(1120) distinct, c(0001) imperfect. Fracture conchoidal. Brittle. H. = 3-3'5. G. = 4'9-5*0. Luster adamantine to resinous. Color honey-, citron-, or orange-yellow. Streak between orange-yellow and brick-red. Nearly transparent. Optically + . co = 2-506, e = 2*529. Comp. Cadmium sulphide, CdS = Sulphur 22'3, cadmium 77-7 = 100. Pyr., etc. In the closed tube assumes a carmine-red color white hot, fading to the original yellow on cooling. In the open* tube gives sulphurous fumes. B.B. on charcoal, either alone or with soda, gives in R.F. a reddish brown coating. Soluble in hydrochloric acid, affording hydrogen sulphide. Artif. Greenockite has been prepared artificially in sev- eral ways. Precipitated cadmium sulphide when fused with potassium carbonate and sulphur produced greenockite crystals; also when cadmium sulphate, calcium fluoride and barium sulphide were fused together. Greenockite is formed when cadmium oxide is heated in sulphur vapor. Obs. Occurs with prehnite at Bishopton, Renfrewshire, and elsewhere in Scotland. At Pfibram in Bohemia, as a coating on sphalerite; similarly at other points; so too in the United States near Friedensville, Pa., and in the zinc region of southwestern Mo.; in Marion Co., Ark., it colors smithsonite bright yellow; noted at Franklin, N. J. Not un- common as a furnace product. Use. An ore of cadmium. Wurtzite. Zinc sulphide, ZnS, like sphalerite, but in hemimorphic hexagonal crystals; also fibrous and massive. G. = 3 '98. Color brownish black. See under sphalerite, p. 368, for the conditions of its formation. From a silver-mine near Oruro in Bolivia; Portugal; at Mies, Bohemia; Peru. In crystals with sphalerite and quartz at the "Original Butte" mine, Butte, Mon. In crystals from Joplin, Mo.; from near Frisco, Beaver Co., Utah. The massive fibrous forms of "Schalenblende" occur at Pfibram, Bohemia; Liskeard, Cornwall, etc. Other forms, from Stolberg, Wiesloch, Altenberg, Germany, are in part wurtzite, in part sphalerite. 372 DESCRIPTIVE MINERALOGY MILLERITE. Capillary Pyrites. Rhombohedral. Usually in very slender to capillary crystals, often in delicate radiating groups; sometimes interwoven like a wad of hair. Also in columnar tufted coatings, partly semi-globular and radiated. The rhombohe- dron (0112) is a gliding plane and artificial twins may be formed. Cleavage perfect parallel to (1011) and (0112). Fracture uneven. Brittle; capillary crystals elastic. H. = 3-3 '5. G. = 5 '3-5 '65. Luster metallic. Color brass-yellow, .inclining to bronze-yellow, with often a gray iridescent tarnish. Streak greenish black. Comp. Nickel sulphide, NiS = Sulphur 35'3, nickel 64-7 = 100. Pyr., etc. In the open tube sulphurous fumes. B.B. on charcoal fuses to a globule. When roasted, gives with borax and salt of phosphorus a violet bead in O.F., becoming gray in R.F. from reduced metallic nickel. On charcoal in R.F. the roasted mineral gives a coherent metallic mass, attractable by the magnet. Most varieties also show traces of copper, cobalt, and iron with the fluxes. Artif . Crystals of millerite have been formed artificially by treating under pressure a solution of nickel sulphate with hydrogen sulphide. Obs. Found at Joachimstal and Pfibram in Bohemia; in Germany at Johann- georgenstadt and Freiberg, Saxony; Wissen, Prussia; in Cornwall, England. In the United States, at Antwerp, N. Y., in cavities in hematite; in Lancaster Co., Pa., at the Gap mine, in thin velvety coatings of a radiated fibrous structure. With calci'te, dolomite and fluorite, forming delicate tangled hair-like tufts, in geodes in limestone, often penetrating the calcite crystals, at St. Louis, Mo.; similarly near Milwaukee, Wis. At Orford, Quebec. Use. An ore of nickel. BEYRICHITE. NiS like millerite, but with lower specific gravity (4 '7). Laspeyres con- siders all millerite as formed by paramorphism from beyrichite. Found in Westerwald, Rhine-Prussia. HAUCHECORNITE. Perhaps Ni(Bi,Sb,S). In tabular tetragonal crystals. H. = 5. G. = 6*4. Color light bronze-yellow. From Hamm a. d. Sieg, Germany. NICCOLITE. Copper Nickel. Hexagonal. Crystals rare. Usually massive, structure nearly impal- pable; also reniform, columnar; reticulated, arborescent. Fracture uneven. Brittle. H. = 5-5'5. G. = 7'33-7'67. Luster metallic. Color pale cop- per-red. Streak pale brownish black. Opaque. Comp. Nickel arsenide, NiAs = Arsenic 56'1, nickel 43*9 = 100. Usually contains a little iron and cobalt, also sulphur; sometimes part of the arsenic is replaced by antimony, and then it graduates toward breithauptite. The intermediate varieties have been called write. Pyr., etc. In the closed tube on intense ignition gives a faint sublimate of arsenic. In the open tube a sublimate of arsenic trioxide, with a trace of sulphurous fumes, the assay becoming yellowish green. On charcoal gives arsenical fumes and fuses to a globule, which, treated with borax glass, affords, by successive oxidation, reactions for iron, cobalt, and nickel; the antimonial varieties give also reactions for antimony. Soluble in aqua regia. Obs. Accompanies cobalt, silver and copper ores in Germany in the Saxon mines of Annaberg, Schneeberg, Mansfield, etc.; also in Thuringia, Hesse, and in Styria; at Alle- mont, Dauphine, at Balen in the Basses Pyrenees, France (arite) ; at the Ko mines in Nord- mark, Sweden; occasionally in Cornwall, Chile: abundant at Mina de la Rioja, Oriocha, Argentina. In the United States, sparingly at Franklin Furnace, N. J., Silver Cliff, Col. In Canada, at Cobalt, Ontario. Use. An ore of nickel. TEMISKAMITE. Described as having composition Ni 4 As 3 , has been shown to be a mix- ture of niccolite, maucherite and a little cobaltite. Breithauptite. Nickel antimonide, NiSb. Rarely in hexagonal crystals; usually massive, arborescent, disseminated. G. = 7'54. Color light copper-fed. From Andreas- berg in the Harz Mts., Germany. SULPHIDES, SELENIDES, TELLURIDES, ARSENIDES, ANTIMONIDES 373 PYRRHOTITE. Magnetic Pyrites. Hexagonal, c = 0'8701. 652 cs, 0001 A 1011 = 45 8'. cu, 0001 A 4041 _ =76 0'. XC~ cy, 0001 A (20-0-20-3) = 81 30*'. gg Twins: tw. pi. s(10ll), with vertical axes nearly at \ right angles (Fig. 418, p. 167). Distinct crystals rare, commonly tabular; also acute pyramidal with faces striated horizontally. Usually massive, with granular structure. Parting: c(0001), sometimes distinct. Fracture uneven to subconchoidal. Brittle. H. = 3 -5-4-5. G. = 4-58-4-64. Luster metallic. Color between bronze-yellow and copper-red, and subject to speedy tarnish. Streak dark grayish black. Magnetic, but varying much in intensity; sometimes possess- ing polarity. Comp. Ferrous sulphide containing variable amounts of dissolved sulphur. Analyses show variation from FesSe to FeieSi?. Often also contains nickel. Fe 7 S 8 = Sulphur 39'6, iron 60'4 = 100. (Cf. Art. 473, p. 323.) Pyrrhotite differs from troilite in containing more or less of dissolved sulphur, while troilite, occurring in meteorites where there is always an excess of iron, may form the pure monosulphide. Pyr., etc. Unchanged in the closed tube. In the open tube gives sulphurous fumes. On charcoal in R.F. fuses to a black magnetic mass; in O.F. is converted into red oxide, which with fluxes gives only an iron reaction when pure, but many varieties yield small amounts of nickel and cobalt. Decomposed by hydrochloric acid, with evolution of hydro- gen sulphide. Diff. Distinguished by its peculiar reddish bronze color; also by its magnetic prop- erties. Micro. In polished section shows a cream color with a shiny and pitted surface. With hot HC1 tarnishes quickly, giving bright colors, then blackens and dissolves; with aqua regia effervesces, becomes iridescent in center of drop and brown at the edge. Artif. Pyrrhptite has been synthesized by the direct union of iron and sulphur and also when pyrite is heated in an atmosphere of hydrogen sulphide at 550. Pyrrhotite exists in two crystalline modifications, hexagonal at ordinary temperatures and ortho- rhombic-above 138. Obs. Occurs at Kongsberg, Modum, Kristiania, etc., in Norway; Falun, Sweden; Andreasberg in the Harz Mts., Germany; Schneeberg, Saxony; Leoben and Lavantal, Carinthia; Minas Geraes in Brazil, in large tabular crystals; the lavas of Vesuvius; Corn- wall. In North America, in Me., at Standish with andalusite; in Ver., at Stafford, etc. In N. Y., near Diana, Lewis Co.; Orange Co.; at Tilly Foster mine, Brewsters. In Pa., at the Gap mine, Lancaster Co., nickeliferous. In Tenn ., at Ducktown mines, abundant. In Canada, in large veins at St. Jerome, Elizabethtown , Ontario; large deposit mined for nickel at Sudbury, Ontario. Named from irvpporw, reddish. Use. Often becomes a valuable ore of nickel. Troilite. Ferrous sulphide, FeS, occurring in nodular masses and in thin veins in many iron meteorites. G. = 4 -75-4*82. Color tombac-brown. Considered to be the end member of the pyrrhotite series. See above. C. Intermediate Division Polydymite. A nickel sulphide, perhaps Ni 4 S 8 . In octahedral crystals; frequently twinned. G. = 4'54-4'81. Color gray. From Griinau, Westphalia, Germany. Sychnodymite. Essentially (Co,Cu) 4 S 6 . Isometric, in small steel-gray octahedrons. From the Siegen district, Germany. 374 DESCRIPTIVE MINERALOGY The following species are sometimes regarded as Sulpho-salts, namely, Sulpho-ferrites, etc. BORNITE. Peacock Ore. Purple Copper Ore. Variegated Copper Ore. Erubescite. Isometric. Habit cubic, faces often rough or curved. Twins: tw. pi. o(lll), often penetration-twins. Crystals rare. Usually massive, structure granular or compact. Cleavage : o (1 1 1) , in traces. Fracture small conchoidal, uneven. Brittle. H. = 3. G. = 4-9-5-4. Luster metallic. Color between copper-red and pinchbeck-brown on fresh fracture, speedily iridescent from tarnish. Streak pale grayish black. Opaque. Comp. A sulphide of copper and iron. Cu 5 FeS 4 . Copper 63-3, iron 11-1, sulphur 25-6=100. The mineral often contains small amounts of chalcocite, etc., and therefore shows con- siderable variation in its percentage composition, giving from 50 to 70 p. c. of copper and 15 to 6*5 p. c. of iron. Pyr., etc. In the closed tube gives a faint sublimate of sulphur. In the open tube yields sulphurous fumes. B.B. on charcoal fuses in R.F. to a brittle magnetic globule. The roasted mineral gives with the fluxes the reactions of iron and copper, and with soda a metallic globule. Soluble in nitric acid with separation of sulphur. Diff. Distinguished (e.g., from chalcocite) by the peculiar reddish color on the fresh fracture and by its brilliant tarnish; B.B. becomes strongly magnetic. Micro. In polished section shows a pinkish brown color with smooth surface. With HNO 3 becomes quickly golden-brown with effervescence. Artif. Bornite has been obtained by fusing pyrite, copper and sulphur together; by heating a mixture of cuprous, cupric and ferric oxides in hydrogen sulphide at 100 to 200. Obs. Bornite is often a primary mineral of magmatic origin, being frequently found in igneous rocks. It is also often a secondary mineral, occurring with chalcocite, etc., in the enriched portions of copper sulphide veins. It is usually associated with other copper ores, and is a valuable ore of copper. Crystalline varieties are found in Cornwall, called by the miners "horse-flesh ore." Occurs massive at Ross Island, Killarney, Ireland; Monte Catini, Tuscany; the Mansfeld district, Germany; in Norway, Sweden, Siberia, Silesia, and Hungary. It is the principal copper ore at some Chilian mines; also common in Peru, Bolivia, and Mexico. In the United States, found at the copper mine in Bristol, Conn.; massive at Mahoopeny, near Wilkesbarre, Pa.; in western Idaho; Butte, Mon., etc. A common ore in Canada, at the Acton and other mines. Named after the mineralogist Ignatius von Born (1742-1791). Use. An ore of copper. Linnaeite. A sulphide of cobalt, Co 3 S 4 = CqS.Co 2 S 3 , analogous to the spinel group. Also contains nickel (var. siegenite). Commonly in octahedrons; also massive. H. = 5 '5. G. = 4*8-5. Color pale steel-gray, tarnishing copper-red. Occurs at Bastnaes, etc., Sweden; Mtisen, near Siegen, Prussia; at Siegen (siegenite), in octahedrons. In the United States at Mine la Motte, Mo.; Mineral Hill, Md. Daubreelite. An iron-chromium sulphide, FeS.Cr 2 S 3 , occurring with troilite in some meteoric irons. Color black. G. = 5 '01. CUBANITE. Described as an iron-copper sulphide, perhaps CuFe 2 S 4 = CuS.Fe 2 S 3 . Examination of specimens from several localities show it to be a mixture of pyrite or pyrrho- tite with chalcopyrite. CARROLITE. A copper-c9balt sulphide, CuCo 2 S 4 = CuS.Co 2 S 3 . Isometric; rarely in octahedrons. Usually massive. G. = 4*85. Color light steel-gray, with a faint reddish hue. From Carroll Co., Md., near Finksburg. Probably linnseite with intergrown bornite and chalcopyrite. Badenite. (Co,Ni,Fe) 2 (As,Bi) 3 . Massive granular to fibrous. G. = 7'1. Metallic. Color steel-gray. Fusible. From near Badeni-Ungureni, Neguletzul valley, Roumania. CHALCOPYRITE. Copper Pyrites. Yellow Copper Ore. Tetragpnal-sphenoidal. Axis c = 0-98525. pp f , 111 A 111 = 108 40'. PPl , 111 A 111 = 70 7i'. ce, 001 A 101 = 44 34|'. SULPHIDES, SELENIDES, TELLURIDES, ARSENIDES, ANTIMONIDES 375 Crystals commonly tetrahedral in aspect, the sphenoidal faces p(lll) large, dull or oxidized; p/111) small and brilliant. Sometimes both forms equally developed, and then octahedral in form. Twins: (1) tw. pi. p(lll), 663 654 655 656 2(201), 8(513) resembling spinel-twins (Fig. 417, p. 167); sometimes repeated as a five- ling (Fig. 655). (2) Tw. pi. and comp.-face e(101) (Fig. 656,) often in repeated twins. (3) Tw. pi. w(110), tw. axis c, complementary penetration twins. Often massive, compact. Cleavage: 2(201), sometimes distinct; c(001), indistinct. Fracture un- even. Brittle. H. = 3*5-4. G. = 4-1-4-3. Luster metallic. Color brass- yellow; often tarnished or iridescent. Streak greenish black. Opaque. Comp. A sulphide of copper and iron, CuFeS 2 = Sulphur 35-0, cop- per 34-5, iron 30 '5 = 100. Analyses often show variations from this formula, often due to mechanical admixture of pyrite. Sometimes auriferious and argentiferous; also contains traces of selenium and thallium. Pyr., etc. In the closed tube often decrepitates, and gives a sulphur sublimate, in the open tube sulphurous fumes. On charcoal fuses to a magnetic globule; the residue mois- tened with hydrochloric acid and then touched with blowpipe flame gives intense blue flame color. Decomposed by nitric acid giving free sulphur and a green solution; ammonia in excess changes the green color to a deep blue, and precipitates red ferric hydroxide. Diff. Distinguished from pyrite by its inferior hardness and deeper yellow color. Resembles gold when disseminated in minute grains in quartz, but differs in being brittle and in having a black streak; further it is soluble in nitric acid. Micro. In polished section shows a bright brass-yellow color with smooth surface. With hot HNO 8 tarnishes and dissolves. Unaffected by KCN, differing from gold. Artif. Chalcopyrite has been artificially prepared (1) by fusing pyrite and copper sulphide together; (2) by gently heating cupric and ferric oxides in an atmosphere of hy- drogen sulphide. Obs. -^Chalcopyrite is the most common and important mineral containing copper. It is commonly of primary origin and from it, by various alteration processes, many other copper minerals are derived. It has repeatedly been observed as an original constituent of igneous rocks and the ultimate source of the copper of our ore deposits is to be found in rocks of this type. It occurs widely disseminated in metallic veins and nests in gneiss and crystalline schists, also in serpentine rocks; often intimately associated with pyrite, also with siderite, tetrahedrite, etc., sometimes with nickel and cobalt sulphides, pyrrhotite, etc. Observed coated with tetrahedrite crystals in parallel position, also as a coating over the latter. Frequently associated with sphalerite, its crystals often lying with parallel orienta- tion upon the latter mineral. Chalcopyrite is so widely distributed as an ore mineral that it is possible to mention here only those occurrences which are exceptional either because of their size or because of the quality of the minerals found in them. It is the principal ore of copper at the Cornwall mines; there associated with cassiterite, galena, bornite, chalcocite, tetrahedrite, sphalerite. At Falun, Sweden, it occurs in large masses embedded in gneiss. At Rammelsberg, near Goslar in the Harz Mts., Germany, it 376 DESCRIPTIVE MINERALOGY forms a bed in argillaceous schist; occurs with nickel and cobalt ores in the Kupferschiefer of Mansfield. In Germany the Kurprinz mine at Freiberg affords well-defined crystals; also Horhausen, Dillenburg, Neudorf, Musen. Common elsewhere as at Mte. Catini in Tuscany; Rio Tin to, Spain; in New. South Wales; Chile; Japan, etc. In the United States it is found in large crystals associated with quartz at Ellenville, N. Y.; in exceptional crystals at the French Creek mines, Chester Co., Pa., associated with pyrite, magnetite, etc.; in Mo., with sphalerite at Joplin; at various localities in Gilpin and other counties in Col. The most important sulphide deposits of copper in many of which chalcopyrite is the chief ore are found in the states of Arizona, Montana, Utah, Alaska, Nevada, New Mexico, California, and Tennessee. In Canada there are important copper deposits in British Columbia, Ontario arid Quebec, Use. The most important ore of copper. Named from XO\KOS, brass, and pyrites, by Henckel (1725). D. Bisulphides, Diarsenides, etc. The disulphides, diarsenides, etc., embrace two distinct groups. The prominent metals included are the same in both, viz. : iron, cobalt and nickel. The groups present, therefore, several cases of isodimorphism, as is shown in the lists of species below. These sulphides are all relatively hard, H. = 5-6; they hence strike fire with a steel, and this has given the familiar name pyrites applied to most of them. The color varies between pale brass-yellow and tin-white. Pyrite Group. RS^RAs^RSb^ Isometric-pyritohedral Pyrite FeS 2 Gersdorffite Arsenoferrite FeAs2 Corynite Cobaltnickelpyrite (Co,Ni,Fe)S 2 Ullmannite Hauerite MnS 2 [Smaltite CoAs 2 , also (Co,Ni)As 2 Sperrylite | Chloanthite NiAs 2 , also (Ni,Co)As 2 Laurite Cobaltite CoS 2 .CoAs 2 NiS 2 .NiAs 2 NiS 2 .Ni(As,Sb)j NiS 2 .NiSb 2 (isometric- tetartohedral) PtAs 2 RuS 2 ? Marcasite Group. RS 2 , RAS 2 , etc. Orthorhombic a 07662 0-6689 c 1-2342 1-2331 110 A 110 74 55' 67 33' 101AI01 116 20' 123 3' 0-6773 : 1 : 1-1882 68 13' 120 38' 0-6942 : 1 : 1-1925 69 32' 119 35' Marcasite FeS 2 Lollingite FeAs 2 Leucopyrite Fe 3 As 4 Arsenopyrite FeS 2 .FeAs 2 Danaite (Fe,Co)S 2 . (Fe,Co) As 2 Safflorite CoAs 2 Rammelsbergite NiAs 2 Glaucodot (Co,Fe)S 2 . (Co,Fe) As 2 Alloclasite (Co,Fe) (As,Bi)S Wolfachite NiS 2 .Ni(As,Sb) 2 The PYRITE GROUP includes, besides the compounds of Fe, Co, Ni, also others of the related metals Mn and Pt. The crystallization is isometric- pyntohedral. The species of the MARCASITE GROUP crystallize in the orthorhombic system with prismatic angles of about 70 and 110 and a prominent macro- dome of about 60 and 120. Hence fivefold and sixfold repeated twins are common with several species, in the one case the prism and in the other the macrodome named being the twinning-plane. SULPHIDES, SELENIDES, TELLURIDES, ARSENIDES, ANTIMONIDES 377 Pyrite Group PYRITE. Iron Pyrites. Isometric-pyritohedral. Cube and pyritohedron e(210) the common forms, the faces of both often with striations || edge a(100)/e(210), due to oscillatory combination of these forms and tending to produce rounded faces; pyritohedral faces also striated J_ to this edge; octahedron also common. See Figs. 657-662, also Figs. 133-138, pp. 65, 66. Twins: tw. ax.= a crystal axis, usually penetration-twins with parallel axes (Fig. 407, p. 166); rarely contact-twins. Frequently massive, fine granular; sometimes subfibrous radiated; reniform, globular, stalactitic. 657 658 660 661 Cleavage: a(100), o(lll), indistinct. Fracture conchoidal to uneven. Brittle. H. = 6-6-5. G. = 4-95-5-10; 4-967 Traversella, 5-027 Elba. Lus- ter metallic, splendent to glistening. - Color a pale brass-yellow, nearly uni- form. Streak greenish black or brownish black. Opaque. Comp. Iron disulphide, FeS 2 = Sulphur 53'4, iron 46*6 = 100. Nickel, cobalt, and thallium, and also copper in small quantities, sometimes replace part of the iron, or else occur as mixtures; selenium is sometimes present in traces. Gold is sometimes distributed invisibly through it, auriferous pyrite being an important source of gold. Arsenic is 1 rarely present, as in octahedral crystals from French Creek, Pa. (0'2 p. c. As). Pyr., etc. Easily fusible, (2'5-3). Becomes magnetic on heating and yields sulphur dioxide. Gives nn abundant sublimate of sulphur in the closed tube. Insoluble in hydro- chloric acid. The fine powder is completely soluble in strong nitric acid . Diff. Distinguished from chalcopyrite by its greater hardness and paler color; in form and specific gravity different from marcasite, which has also a whiter color. Micro. In polished section shows a cream color with a scratched and dull surface. With HNOa effervesces slowly becoming faintly brown. Alteration. Pyrite readily changes by oxidation to an iron sulphate or to the hy- drated oxide, limonite, with sulphuric acid set free. Crystals of pyrite which have been changed on their surfaces to limonite are common. This change may continue until tho original mineral has completely disappeared. Large masses of pyrite lying near the surface may be altered to a cellular mass of limonite tHe iron gossan of the miners while the sulphuric acid set free travels downward and enters into various important reactions with the unaltered minerals below. The alteration of pyrite to limonite may be continued until hematite is formed. Gbs. Experiments show that pyrite is formed in neutral or alkaline solutions and at high temperatures. Marcasite, on the other hand, is deposited from acid solutions and 378 DESCRIPTIVE MINERALOGY is stable only at temperatures below 450 C. These sulphides can be formed through the action of hydrogen sulphide, although the reducing action of carbonaceous materials may also at times be of importance. Pyrite occurs in rocks of all ages and types, being most common in the metamorphic and sedimentary rocks, but it is also frequently found as a minor acces- sory constituent of igneous rocks. When disseminated in the rocks it usually occurs in small crystals, cubes, octahedrons, pyritohedrons, etc., but in veins it may occur in crystals or with a granular or radiating massive structure. At times it is in nodular or concre- tionary forms. Pyrite is very widespread in its occurrence, being the most common sulphide mineral. At times it is found in very large amounts and is mined for its sulphur content or because it contains small amounts of some valuable metal, like copper, gold, etc. It is frequently found in crystals with a fine luster. Some of ^the more notable localities for its occurrence are given below. Important commercial deposits of pyrite are found in Norway, Germany, France, Italy, Spain and Portugal. The mines at Rio Tinto, Spain, are especially noteworthy. The mineral has been mined in the United States in Louisa and Prince William Cos., Va.; in St: Lawrence Co., N. Y.; at Davis, Mass., etc. The following localities furnish exception- ally fine crystallized specimens: Cornwall, England; Traversella and Brosso, Piedmont Italy; Island of Elba; Ardennes, France, in distorted cubes; Minden, Prussia, in inter- penetration twins; in various localities in Bohemia, Hungary, Germany, Sweden, etc.; at Firmeza, Cuba; at French Creek, Pa., in pyramids with apparently tetragonal or ortho- rhombic symmetry; at Rossie and Scoharie, N. Y.; Roxbury, Conn.; Franklin, N. J.; Gilpin Co. and at Leadville, Col.; Bin^ham Canyon, Utah. The name pyrite is derived from irvp, fire, and alludes to the sparks formed when the mineral is struck with a hammer; hence the early name pyrites, p. 376. Use. Pyrite often carries small amounts of copper or gold and becomes an impor- tant ore of these metals. It is also mined for its sulphur content which is used in the form of sulphur dioxide (used in the preparation of wood pulp for manufacture into paper), as sul- phuric acid (used for many purposes, especially in the purification of kerosene and in the preparation of mineral fertilizers), and as the ferrous sulphate, copperas (used in dyeing, in inks, as a wood preservative, and as a disinfectant). Bravdite (Fe,Ni)S 2 . Contains nearly 20 per cent nickel. In small grains and crystal fragments, apparently octahedral. Pale yellow with a faint reddish tarnish. Occurs dis- seminated through the vanadium ores at Minasragra, Peru. Cobaltnickelpyrite.l Iron sulphide with about 20 per cent cobalt and nickel, (Co,Ni,Fe)S 2 . In minute pyritohedral crystals. Steel-gray color. Gray-black streak. H. = 5. G. = 4-716. Found. at Musen, Germany. Arsenoferrite. Iron arsenide, probably FeAs 2 . Isometric-pyritohedral. In small crystals. Color dark brown. Fine splinters transparent with ruby-red color. From the Binnental, Switzerland. Hauerite. Manganese disulphide, MnS 2 . In octahedral or pyritohedral crystals; also massive. G. = 3'46. Color reddish brown or brownish black. From Kalinka, Hungary; Raddusa, Catania, Sicily. SMALTITE-CHLOANTHITE. Isometric-pyritohedral. Commonly massive; in reticulated and other imitative shapes. Cleavage: o(lll) distinct; a (100) in traces. Fracture granular and uneven. Brittle. H. = 5'5-6. . G. = 6*4 to 6-6. Luster metallic. Color tin-white, inclining, when massive, to steel-gray, sometimes iridescent, or grayish from tarnish. Streak grayish black. Opaque. Comp. SMALTITE is essentially cobalt diarsenide, CoAs2 = Arsenic 71;8, cobalt 28-2 = 100. CHLOANTHITE is nickel diarsenide, NiAs 2 = Arsenic 71-9, nickel 28'1 = 100. Cobalt and nickel are usually both present, and thus these two species graduate into each other, and no sharp line can be drawn between them. Iron is also present in varying amount ; the variety of chloanthite containing much iron has been called chathamite. Fur- ther sulphur is usually present, but only in small quantities. Many analyses do not conform even approximately to the formula RAs 2 , the ratio rising from less than 1 : 2 to 1 : 2 '5 and nearly 1 : 3, thus showing a tendency toward skutterudite (RAs 3 ), perhaps due to either molecular or mechanical mixture. Microscopic examination of polished specimens shows SULPHIDES, SELENJDES, TELLURIDES, ARSENIDES, ANTIMONIDES 379 probable zoning of different members of the group. Material known as keweenawite is a mixture of smaltite, niccolite and domeykite. Much that has been called smaltite is shown by the high specific gravity to belong to the orthorhombic species safRorite. Pyr., etc. In the closed tube gives a sublimate of metallic arsenic; in the open tube a white sublimate of arsenic trioxide, and sometimes traces of sulphur dioxide. B.B. on charcoal gives a coating of As 2 O 3 , the arsenical odor, and fuses to a globule, which, treated with successive portions of borax-glass, affords reactions for iron, cobalt, and nickel. Obs. Usually occurs in veins, accompanying ores of cobalt or nickel, and ores of silver and copper; also, in some instances, with niccolite and arsenopyrite. Found at the Saxon mines; Joachimstal, Bohemia; Wheal Sparnon, Cornwall; Riechelsdorf, Hesse, Germany; Tunaberg, Sweden; Allemont, Dauphine, France; Cobalt, Ontario. In the United States, at Chatham, Conn., the chathamite occurs in mica slate, with arsenopyrite and niccolite; at Franklin Furnace, N. J. Use. Ores of cobalt and nickel. COBALTITE. Isometric-pyrithohedral. Commonly in cubes, or pyritohedrons, or com- binations resembling common forms of pyrite. Also granular massive to compact. Cleavage: cubic, rather perfect. Fracture uneven. Brittle. H. = 5-5. G. = 6-6 -3. Luster metallic. Color silver-white, inclined to red; also steel- gray, with a violet tinge, or grayish black when containing much iron. Streak grayish black. Comp. Sulpharsenide of cobalt, CoAsS or CoS 2 .CoAs2 = Sulphur 19'3, arsenic 45'2, cobalt 35'5 = 100. Iron is present, and in the variety ferrocobaltite in large amount. Pyr., etc. Unaltered in the closed tube. In the open tube gives sulphurous fumes, and a crystalline sublimate of arsenic trioxide. B.B. on charcoal gives off sulphur and arsenic oxides, and fuses to a magnetic globule; with borax a cobalt-blue color. Soluble in warm nitric acid, with the separation of sulphur. Obs. Occurs at Tunaberg and Hakansbo in Sweden; at the Nordmark mines; also at Skutterud in Norway; at Schladming, Styria; Siegen in Westphalia; Botallack mine, near St. Just, in Cornwall; Khetri mines, Rajputana, India; Cobalt, Ontario, Canada. Use. An ore of cobalt. Gersdorffite. Sulpharsenide of nickel, NiAsS or NiS 2 .NiAs 2 . Iron, and sometimes cobalt, replace more or less of the nickel. Isometric-pyritohedral; usually massive. H. = 5*5. G. = 5'6-6'2. Color silver-white to steel-gray. From Loos, Sweden; the Harz Mts., and Lobenstein, Reuss-Schleiz, Germany; Schladming, Styria; Sudbury and Algoma districts, Ontario; Rossland, British Columbia. CORYNITE is near gersdorffite, but contains also antimony. Probably represents a mix- ture. From Olsa, Carinthia. Willyamite. CoS 2 .NiS 2 .CoSb2.NiSb2. Cleavage cubic. Color tin-white to steel-gr.ay. Broken Hill mines, New South Wales. Villamaninite. Sulphide of Cu,Ni with smaller amounts of Co,Fe. H = 4'5. G. = 4-4-4-5. Color, iron-black. In irregular groups of cubo-octahedral crystals and in radiating nodular masses. In dolomite from Carmenes district, near Villamanm, Prov. Leon, Spain. UUmannite. Sulphantimonide of nickel, NiSbS or NiS 2 .NiSb 2 ; arsenic is usually present in small amount. Isometric-tetartohedral; both pyritohedral and tetrahedral forms occur. Usually massive, granular. H. = 5-5 '5. G. = 6 '2-6 7. Color steel-gray to silver-white. Occurs in the mines of Siegen, Prussia; Lolling, Carinthia (tetrahedral); Monte Narba, Sarrabus, Sardinia (pyritohedral). KALLILITE. Ni(Sb,Bi)S or NiS 2 .Ni(Sb,Bi) 2 . Massive, color light bluish gray. From the Friedrich mine near Schonstein a. d. Sieg, Germany. Sperrylite. Platinum diarsenide, PtAs 2 . In minute cubes, or cubo-octahedrons with at times small pyritohedral or diploid faces. H. = 6-7. G. = 10*6. Luster metallic. Color tin-white. Streak black. Found at the Vermillion mine, 22 miles west of Sudbury, Ontario, Canada; also in Macon Co., N. C. Found associated with covellite at the Rambler mine, Medicine Bow Mts., Wy. This is the only known native compound of platinum. 380 DESCRIPTIVE MINERALOGY Laurite. Sulphide of ruthenium and osmium, probably essentially RuS 2 . In minute octahedrons; in grains. H. = 7 '5. G. = 6 '99. Luster metallic. Color dark iron-black. From the platinum washings of Borneo. Also reported from Oregon. ^ Skutterudite. Cobalt arsenide, CoAs 3 . Isometric-pyritohedral. Also massive granu- lar. Cleavage: a(100), distinct. H. = 6. G. = 672-6 '86. Color between tin-white and pale lead-gray. From Skutterud, Norway; the Turtmanntal, Switzerland. NICKEL-SKUTTERUDITE. (Ni,Co,Fe)As 3 . Massive, granular. Color gray. From near Silver City, N. M. BISMUTO-SMALTITE. Co(As,Bi) 3 . A skutterudite containing bismuth. Color tin- white. G. = 6 '92. Zschorlau, near Schneeberg, Saxony. Marcasite Group For the list of species and their relations, see p. 376. MARCASITE. White iron pyrites. Orthorhombic. Axes a : b : c = 07662 : 1 : 1*2342. mm"', 110 A 110 = 74 55'. II', Oil A Oil = 101 58'. ee', 101 A 101 = 116 20'. cs, 001 A 111 = 63 46'. Twins: tw. pi. m(110), sometimes in stellate fivelings (Fig. 436, p. 169, cf. Fig. 664); also tw. pi. e(101), less common, the crystals crossing at angles of nearly 60. Crystals commonly tabular || c(001), also pyramidal;- the bra- chydomes striated edge 6(010) /c(001). Of- ten massive; in stalac- tites ; also globular, ren- iform, and other imi- tative shapes. Cleavage: m(110) Folkestone rather distinct; Z(Oll) in traces. Fracture uneven. Brittle. H. = 6-6*5. G = 4-85-4-90. Luster metallic. Color pale bronze-yellow, deepening on exposure. Streak grayish or brownish black. Opaque. Comp. Iron disulphide, like pyrite, FeS 2 = Sulphur 53'4, iron 46'6 = 100. Arsenic is sometimes present in small amount. Var- The varieties named depend mainly on state of crystallization. Radiated: Radiated; also the simple crystals. Cockscomb Pyrite: Aggregations of flattened twin crys- tals in crest-like forms. Spear Pyrite: Twin crystals, with re-entering angles a little like the head of a spear in form. (Fig. 664.) Capillary: In capillary crystallizations. Pyr., etc. Like pyrite. Very liable to decomposition, more so than pyrite. Diff. Resembles pyrite, but has a lower specific gravity, and the color when fresh e.g., after treatment with acid) is paler: when crystallized easily distinguished by the forms. ore subject to tarnish and final decomposition than pyrite. Marcasite can be distinguished chemically from pyrite by the following methods. When both minerals are finely powdered and treated with a little concentrated nitric acid, first in the cold and later, after vigorous action has ceased, by warming, it will be found that in the case of pyrite the greater part of the sulphur of the mineral has been oxidized and taken into solution as sulphuric acid, while in the case of marcasite most of the sulphur has sep- arated in a free state. The Stokes method, which can be used quantitatively to determine the amounts of the two minerals in a mixture, depends upon the difference in their behavior when boiled with a standard solution of ferric sulphate. In the case of pyrite about 52 per cent pj the sulphur is oxidized to sulphuric acid, while with marcasite only about 12 per cent is oxidized. (e. M tfr~^ polished sections shows a cream color with a scratched and dull surface. With HNO 3 slowly turns brown to black with effervescence. SULPHIDES, SELENIDES, TELLURIDES, ARSENIDES, ANTIMONIDES 381 Alteration. Marcasite being relatively unstable is easily altered. Specimens often disintegrate with the formation of ferrous sulphate and sulphuric acid. It also alters to pyrite, limonite, etc. Obs. Marcasite is a much more unstable compound than pyrite and is formed under comparatively limited conditions. Experiments have shown that it is deposited at tem- peratures below 450 C. and in acid solutions. The higher the temperature the more acid must the solution contain. At ordinary temperatures marcasite may be deposited from nearly neutral solutions. Marcasite is formed in general under surface conditions, while in deep veins where the minerals are deposited from ascending hot and usually alkaline waters only pyrite is found. Marcasite occurs abundantly at Littmitz near Carlsbad, Bohemia. Found at several localities in the Harz Mts., Germany. In its cockscomb form occurs at Tavistock in Devon- shire and as Spear Pyrites in the chalk-marl between Folkestone and Dover, England. In the United States a notable locality is at Galena, 111., where it occurs in stalactites with concentric layers of sphalerite and galena. In fine crystals at Mineral Point, Wis.; in crystals altered to limonite from Richland Co., Wis. Frequently associated with galena, sphalerite and dolomite from the Joplin district, Mo. The word marcasite, of Arabic or Moorish origin (and variously used by old writers, for bismuth, antimony), was the name of common crystallized pyrite among miners and min- eralogists in later centuries, until near the close of the eighteenth. It was first given to this species by Haidinger in 1845. Lb'llingite. Essentially iron diarsenide, FeAs2, but passing into FesAs4 (leucopyrite) ; also tending toward arsenopyrite (FeAsS) and safflorite (CoAs2). Bismuth and antimony are sometimes present. Usually masswe. H. = 5-5*5. G. = T'0-7'4 chiefly, also 6*8. Luster metallic. Color between silver-white and steel-gray. Streak grayish black. Occurs in the Lolling-Huttenberg district in Carinthia. Found also sparingly in a number of other districts. GEYERITE is near lollingite, but contains sulphur; from Geyer, Saxony. ARSENOPYRITE, or MISPICKEL. Orthorhombic. Axes a : b : c = 0'6773 : mm'", 110 A 110 = 101 A 101 uu', nn f , 014 A 014 = 012 A 012 = Oil A Oil = 1 : 1-1882. 68 13'. 120 38'. 33 5'. 61 26'. 99 50'. 665 Twins: tw. pi. ra(110), sometimes repeated like marcasite (Figs. 667 and 437, p. 109); e(101) cruciform twins, also trillings (Figs. 432, 433, p. 169). Crystals prismatic m(110) or flattened vertically by the oscillatory combina- tion of brachydomes. Also columnar, straight, and divergent; granular, or compact. Cleavage: ra(110) rather distinct; c(001) in faint traces. Fracture uneven. Brittle. H. = 5*5-6. G. = 5'9-6'2. Luster metallic. Color sil- ver-white, inclining to steel-gray. Streak dark grayish black. Opaque. Comp. Sulpharsenide of iron, FeAsS or FeS 2 .FeAs2 = Arsenic 46 '0, sul- 382 DESCRIPTIVE MINERALOGY phur 197, iron 34 -3 = 100. Part of the iron is sometimes replaced by cobalt, as in the variety danaite (3 to 9 p. c. Co). Pyr., etc. In the closed tube may give at first a little yellow sulphide of arsenic and then a conspicuous sublimate of metallic arsenic which is of bright gray crystals near the heated end and of a brilliant black amorphous deposit farther away. In the open tube gives sulphurous fumes and a white sublimate of arsenic trioxide. B.B. on charcoal gives arsenical fumes and a magnetic globule. Decomposed by nitric acid with the separation of sulphur. Diff. Characterized by its hardness and "tin-white color; closely resembles some of the sulphides and arsenides of cobalt and nickel, but identified, in most cases easily, by its blowpipe characters. Lollingite does not give a decided sulphur reaction. Micro. In polished sections shows a white color with scratched and dull surface. With HNO 3 darkens quickly through iridescent colors to brown, showing rough surface. Obs. Found principally in crystalline rocks, its usual mineral associates being ores of silver, lead, and tin, also pyrite, chalcopyrite, and sphalerite. Abundant at Freiberg, etc., in Saxony; at Andreasberg, Harz Mts., Germany; Sala, Sweden; Skutterud, Norway; at several points in Cornwall. In crystals in the Binnental, Switzerland. Crystals of danaite from Sulitjelma, Finland. In the United States, in N. H., in gneiss, at Franconia (danaite). In Conn., at Mine Hill, Roxbury, with siderite. In crystals at Canton, Ga.; Leadville, Col. In twin crys- tals in quartz ore veins at Deloro, Hastings Co., Ontario. The name mispickel is an old German term of doubtful origin. Danaite is from J. Free- man Dana of Boston (1793-1827), who made known the Franconia locality. Use. An ore of arsenic. Safflorite. Like smaltite, essentially cobalt diarsenide, CoAs 2 . Form near that of arsenopyrite. Usually massive. H. = 4'5-5. G. = 6'9-7*3. Color tin-white, soon tar- nishing. From Germany at Schneeberg, Saxony; Bieber, Hesse; Wittichen, Baden; from Tunaberg, Sweden. Rammelsbergite. Essentially nickel diarsenide, NiAs 2 , like chloanthite. Crystals resembling arsenopyrite; also massive. G. = 6'9-7'2. Color tin-white with tinge of red. Occurs at Schneeberg, Saxony, and at Riechelsdorf, Hesse, Germany. Glaucodot. Sulpharsenide of cobalt and iron, (Co,Fe)AsS. In orthorhombic crystals (axes, etc., p. 376). Also massive. H. = 5. G. = $-90-6'01. Luster metallic. Color grayish tin-white. Occurs in the province of Huasco, Chile; at Hakansbo, Sweden. Named from yXavnos, blue, because used for making smalt. ALLOCLASITE. Probably glaucodot containing bismuth and other impurities. Com- monly in columnar to hemispherical aggregates. H. = 4'5. G. =6'6. Color steel-gray. From Orawitza, Hungary. Wolfachite. Probably Ni(As,Sb)S, near corynite. In small crystals resembling arse- nopyrite; also columnar radiated. H. = 4 '5-5. G. = 6 "372. Color silver-white to tin- white. From Wolfach, Baden, Germany. Melonite. A nickel telluride, NiTe 2 . In indistinct granular and foliated particles. Color reddish white, with metallic luster. From the Stanislaus mine, Cal.; probably also m Boulder Co., Col. Found at Worturpa, New South Wales. The following species are tellurides of gold, silver, etc. SYLVANITE. Graphic Tellurium. _ Monoclinic. a : b : c = 1-6339 : 1 : M265; = 89 35'. Often in branch- ing arborescent forms resembling written characters; also bladed and imper- iectly columnar to granular. Cleavage: 6(010) perfect. Fracture uneven. Brittle. H. = 1-5-2. ~' ~ 7 '9-8 -3. Luster metallic, brilliant. Color and streak pure steel-era v to silver-white, inclining to yellow. Comp. Telluride of gold and silver (Au,Ag)Te 2 with Au : Ag = 1 : 1: this requires: Tellurium 62-1, gold 24-5, silver 134 = 100. . , Pyr *' e j?- ~ When a little of the powdered mineral is heated in concentrated sulphuric da reddish violet color is given to the solution. When treated with nitric acid is decom- 1 leaving residue of rusty colored gold. A few drops of hydrochloric acid added to this SULPHO-SALTS 383 solution yield an abundant precipitate of silver chloride. In the open tube gives a white sub- limate of tellurium dioxide which near the assay is gray; when treated with the blowpipe flame the sublimate fuses to clear transparent drops. B.B. on charcoal fuses to a dark gray globule, covering the coal with a white coating, which treated in R.F. disappears, giving a bluish green color to the flame; after long blowing a yellow, malleable metallic globule is obtained. Obs. With gold, at OffenMnya, Transylvania; also at Nagyag. With calaverite at Kalgoorlie district, West Australia. In CaL, Calaveras Co., at the Melones and Stanislaus mines. In Boulder Co., at Cripple Creek and elsewhere in Col. Named from Transyl- vania, where first found, and in allusion to sylvanium, one of the names at first proposed for the metal tellurium. Use. An ore of gold Krennerite. A telluride of gold and silver (Au,Ag)Te 2 like sylyanite. In prismatic crystals (orthorhombic), vertically striated. G. = 8 '353. Color silver-white to brass- yellow. From Nagyag, Transylvania; Cripple Creek, Col. Calaverite. A gold telluride, AuTe 2 with small amounts of silver. Monoclmic. In small lath-shaped crystals striated parallel to their length. Massive granular to crystalline. H. = 2'5. G: = 9*043. Color silver-white with often a faint yellow tinge. Tests similar to those for sylvanite with smaller amount of silver showing. Occurs with petzite at the Stanislaus mine, Calaveras county, Cal. An important gold ore at the Cripple Creek dis- trict, Col. Found elsewhere in that state. Occurs abundantly at Kalgoorlie, West Australia. Muthmannite. (Ag,Au)Te. In tabular crystals usually elongated in one direction. One perfect cleavage parallel to elongation. H. = 2 '5. Color bright brass-yellow, on fresh fracture gray-white. Probably from Nagyag, Transylvania. Empressite, AgTe, from the Empress-Josephine mine, in the Kerber Creek District, Col., is probably a gold-free variety. Massive. H. = 3-3 '5. G. = 7'5. Color pale bronze. Nagyagite. A sulpho-telluride of lead and gold; some analyses show also about 7 p. c. of antimony which was probably due to impurities. Orthorhombic. Crystals tabular || 6(010); also granular massive, foliated. Cleavage: b perfect; flexible. H. = 1-1 '5. G. = 6'85-7'2. Luster metallic, splendent. Streak and color blackish lead-gray. Opaque. From Nagyag, Transylvania; and at Offenbanya. Reported] from Colorado and Tararu Creek, New Zealand. Oxysulphides Here are included Kermesite, Sb 2 S 2 O, and Voltzite, Zn 5 S 4 0. Kermesite. Pyrostibite. Antimony oxysulphide, Sb 2 S 2 O or 2Sb 2 S 3 .Sb 2 O 3 . Mono- clinic. Usually in tufts of capillary crystals. Cleavage: a(100) perfect. H. = 1-1 -5. G. = 4'5-4'6. Luster adamantine. Color cherry-red. Results from the alteration of stibnite. Occurs at Malaczka, Hungary; Braunsdorf, Saxony: Allernont, Dauphine, France. At South Ham, Wolfe Co., Quebec, Canada; with native antimony and stibnite at the Prince William mine, York Co., New Brunswick. Named from kermes, a name given (from the Persian qurmizq, crimson) in the older chemistry to red amorphous antimony trisulphide, often mixed with antimony trioxide. Voltzite. Zinc oxysulphide, Zn 6 S 4 O or 4ZnS.ZnO. In implanted spherical globules. H. = 4-4'5. G. = 3'66-3'80. Color dirty rose-red, yellowish. Occurs near Pontgibaud, Puy-de-D6me, France; Joachimstal, Bohemia; Marienberg, Saxony, Germany. IH. SULPHO-SALTS I. Sulpharsenites, Sulphantimonites, Sulphobismuthites. H. Sulpharsenates, Sulphostannates, etc. I. Sulpharsenites, Sulphantimonites, etc. In these sulphosalts, as further explained on p. 320, sulphur takes the place of the oxygen in the commoner and better understood oxygen acids (as carbonic acid, H 2 C0 3 , sulphuric acid, H 4 S0 4 , phosphoric acid, H 3 PO 4 , etc.). The species included are salts of the sulpho-acids of trivalent arsenic, antimony and bismuth. The most important acids are the ortho-acids, 384 DESCRIPTIVE MINERALOGY H 3 AsS 3 , etc., and the meta-acids, H 2 AsS 2 , etc.; but H 4 As 2 S 5 , etc., and a series of others are included. The metals present as bases are chiefly copper, silver, lead; also zinc, mercury, iron, rarely others (as nickel, cobalt} in small amount. In view of the hypothetical character of many of the acids whose salts are here represented, there is a certain advantage, for the sake of comparison, in writi ig the composition after the dualistic method, RS.As 2 S 3 , 2RS.As 2 S 3 , etc. As a large part of the species here included are rare and hence to be men- tioned but briefly, the classification can be only partially developed. The divisions under the first and more important section of sulpharsenites, etc., with the prominent species under each, are as follows: A. Acidic Division. RS : (As,Sb,Bi) 2 S 3 = 1 : 3, 1 : 2, 2 : 3, 3 : 4, 4 : 5. B. Meta- Division. RS : (As,Sb,Bi) 2 S 3 = 1:1. General formula: RAs 2 S 4 ,RSb 2 S4,RBi 2 S 4 . ; : Zinkenite Group Zinkenite . PbS.Sb 2 S 3 Emplectite CuoS.Bi 2 S 3 Sartorite PbS.As 2 S 3 Chalcostibite Cu 2 S.Sb 2 S 3 , etc. Also Miargyrite Ag 2 S.Sb 2 S 3 Lorandite Tl 2 S.As 2 S 3 C. Intermediate Division. RS : (As,Sb,Bi) 2 S 3 = 5 : 4, 3 : 2, 2 : 1, 5 : 2 Here belong Plagionite 5PbS.4Sb 2 S 3 . Schirmerite 3(Ag 2 ,Pb)S.2Bi 2 S 3 Klaprotholite 3Cu 2 S.2Bi 2 S 3 , etc. Jamesonite Group Jamesonite 2PbS.Sb 2 S 3 Cosalite 2PbS.Bi 2 S 3 , etc. Dufrenoysite 2PbS.As 2 S 3 Also Freieslebenite 5(Ag 2 ,Pb)S.2Sb 2 S 3 Boulangerite 5PbS.2Sb 2 S 3 D. Ortho- Division. RS : (As,Sb,Bi) 2 S 3 =3:1 General formula: R 3 AsS 3 ,R 3 SbS 3 ; R 3 As 2 S 6 ,R 3 Sb 2 S 6 , etc. Bournonite Group Bournonite 3(Cu 2 ,Pb)S.Sb 2 S 3 Wittichenite 3Cu 2 S.Bi 2 S 3 Seligmannite 3(Cu 2 ,Pb)S.As 2 S 3 LiUianite 3PbS.Bi 2 S 3 , etc. Aikmite 3(Pb,Cu 2 )S.Bi 2 S 3 Pyrargyrite Group Pyrargyrite 3Ag 2 S.Sb 2 S 3 Proustite 3Ag 2 S.As 2 S 3 E. Basic Division. RS : (As,Sb,Bi) 2 S 3 = 4 : 1, 5 : 1, 6 : 1, 9 : 1, 12 : 1 Tetrahedrite Group Tetrahedrite 4Cu 2 S.Sb 2 S 3 Tennantite SULPHO-SALTS 385 Jordanite Group Jordanite 4PbS.As 2 S 3 Meneghinite 4PbS.Sb 2 S 3 Also Geocronite 5PbS.Sb 2 S 3 Stephanite 5Ag 2 S.Sb 2 S 3 Kilbrickenite 6PbS.Sb 2 S 3 Beegerite 6PbS.Bi 2 S 3 Polybasite Group Polybasite 9Ag 2 S.Sb 2 S 3 Pearceite Polyargyrite 12Ag 2 S.Sb 2 S 3 A. Acidic Division Eichbergite. (Cu,Fe) 2 S.3(Bi,Sb) 2 S8. Color iron-gray. H. > 6. G. = 5*36. From Eichberg, Semmering district, Austria. Livingstonite. HgS.2Sb 2 S 3 . Resembles stibnite in form. Color lead-gray; streak red. H. =2. G. = 4'81. From Huitzuco, Mexico. Histrixite. 5CuFeS2.2Sb2S3.7Bi 2 S3. Orthorhombic. In radiating groups of prismatic crystals. H. = 2. Color and streak steel-gray. Found at Ringville, Tasmania. Chiviatite. 2PbS.3Bi 2 S 3 . Foliated massive. Color lead-gray. From Chiviato, Peru. Cuprobismutite. Probably 3Cu 2 S.4Bi 2 S 3 , in part argentiferous. Resembles bismuth- inite. G. = 6*3-67. From Hall valley, Park Co., Col. Rezbanyite. 4PbS.5Bi 2 S 3 . Fine-granular, massive. Color lead-gray. G. = 6' 1-6*4. From Rezbanya, Hungary. B. Meta- Division. RS.As 2 S 3 , RS.Sb 2 S 3 , etc. Zinkenite Group. Orthorhombic ZINKENITE. Zinckenite. Orthorhombic. Axes a : b : c = 0'5575 : 1 : 0*6353. Crystals seldom dis- tinct ; sometimes in nearly hexagonal forms through twinning. Lateral faces longitudinally striated. Also columnar, fibrous, massive. Cleavage not distinct. Fracture slightly uneven. H. = 3-3*5. G. = 5*30-5*35- Luster metallic. Color and streak steel-gray. Opaque. . Comp. PbSb 2 S 4 or PbS.Sb 2 S 3 = Sulphur 22*3, antimony 41*8, lead 35*9 = 100. Arsenic sometimes replaces part of the antimony. Pyr., etc. Decrepitates and fuses very easily; in the closed tube gives a faint subli- mate of sulphur, and antimony trisulphide. In the open tube sulphurous fumes and a white sublimate of oxide of antimony; the arsenical variety gives also arsenical fumes. On charcoal is almost entirely volatilized, giving a coating which on the outer edge is white, and near the assay dark yellow; with soda in R.F. yields globules of lead. Soluble in hot hydrochloric acid with evolution of hydrogen sulphide and separation of lead chloride on cooling. Obs. Occurs at Wolfsberg in the Harz Mts.; Kinzigtal, Baden; Val Sugana, Tyrol; Oruro, Bolivia; Sevier County, Ark.; San Juan Co., Col. Andorite. Ag 2 S.2PbS.3Sb 2 S 3 . In prismatic, Orthorhombic crystals. H. = 3-3'5. G. = 5*5. Color dark gray to black. From Felsobanya, Hungary; Oruro, Bolivia. Webnerite and Sundtite are identical with andorite. Sartorite. PbS. As 2 S 3 . In slender, striated crystals, probably monoclinic. G. = 5'4. Color dark lead-gray. Occurs in the dolomite of the Binnental. Platynite. PbS.Bi 2 Se 3 . Rhombohedral. Basal and rhombohedral cleavages. H. = 2-3. G. = 7'98. Color like graphite. Streak shining. In small lamellae in quartz at Falun, Sweden. 386 DESCRIPTIVE MINERALOGY Emplectite. Cu 2 S.Bi 2 S 3 . In thin striated prisms. G. = 6'3-6'5. Color grayish white to tin-white. Occurs in quartz at Schwarzenberg and Annaberg, Saxony. Chalcostibite. Wolfsbergite. Cu 2 S.Sb 2 S 3 . In small aggregated prisms; also fine granular, massive. G. = 475-5 '0. Color between lead-gray and iron-gray. From Wolfs- berg in the Harz Mts.; from Huanchaca, Bolivia. Guejarite from Spain is the same species. Galenobismutite. PbS.Bi 2 S 3 ; also with Ag,Cu. Crystalline columnar to compact. Color lead-gray to tin-white. G. = b'9. From Nordmark, Sweden; Poughkeepsie Gulch, Col. (alaskaite, argentiferous) ; material from Falun, Sweden, containing selenium has been named weibullite and given the formula, 2PbS.Bi 4 S 3 Se 3 . Berthierite. FeS.Sb 2 S 3 . Fibrous massive, granular. G. = 4'0. Color dark steel- gray. From Chazelles and Martouret, Auvergne, France; Charbes, Val de Ville, Alsace; Braunsdorf, Saxony, etc. Matildite. Ag 2 S.Bi 2 S 3 . In slender, prismatic crystals. G. = 6-9. Color gray. From Morochoca, Peru; Lake] City, Col. PLENARGYRITE, from Schapbach, Baden, similar in composition, has been shown to be a mixture. Miargyrite. Ag 2 S.Sb 2 S 3 . In complex monoclinic crystals, also massive. H. = 2-2-5. G. = 5'1-5'30. Luster metallic-adamantine. Color iron-black to steel-gray, in thin splin- ters deep blood-red. Streak cherry-red. From Braunsdorf, Saxony; Felsobanya and Nagybanya, Hungary; Pfibram, Bohemia; Zacatecas, Mexico; Bolivia. Smithite. Ag 2 S.Sb 2 S 3 . Monoclinic. Crystals resemble a flattened hexagonal pyra- mid. One perfect cleavage. H. = T5^2. G. = 4'9. Color light red changing to orange- red on exposure to light. Streak vermilion. From the Binnental, Switzerland. Trechmanite. Ag 2 S.As 2 S 3 . Rhombohedral, tetartohedral. Crystals minute with pris- matic habit. Good rhombohedral cleavage. H. = T5-2. Color and streak scarlet- vermilion. From the Binnental, Switzerland. Lorandite. A sulpharsenide of thallium, TlAsS 2 . Monoclinic. Color cochineal-red. From Allchar, Macedonia; Rambler mine, Encampment, Wy. Vrbaite. TlAs 2 SbS 5 . Orthorhombic. H. = 3'5. G. = 5'3. Color gray-black to dark red in thin splinters. Streak light red. From Allchar, Macedonia. Hutchinsonite. (Tl,Ag,Cu) 2 S.As 2 S 3 +PbS.As 2 S 3 (?). Orthorhombic. In flattened rhom- bic prisms. Cleavage o(100) good. H. = 1-5-2. G. = 4'6. Color scarlet to red. From the Binnental, Switzerland. C. Intermediate Division Baumhauerite. 4PbS.3As 2 S 3 . Monoclinic. In complex crystals with varied habit One perfect cleavage. H. = 3. G. = 3 -3. Metallic. Color lead to steel-gray. From the Binnental, Switzerland. Schirmerite. 3(Ag 2 ,Pb)S.2Bi 2 S 3 . Massive, granular. G. = 674. Color lead-gray. Treasury lode, Park Co., Col. KLAPROTHOLITE. 3Cu 2 S.Bi 2 S 3 . In furrowed prismatic crystals. G. = 4'6. Color steel-gray. Wittichen, Baden. Probably a mixture and not a definite species. Rathite. 3PbS.2As 2 S 3 . Orthorhombic, in prismatic crystals. Cleavage, 6(010). H. = 3. G. = 5'41. From the Binnental, Switzerland. Wiltshireite is the same species. Jamesonite Group. 2RS.As2S 3 , 2RS.Sb 2 S 3 , etc. Monoclinic JAMESONITE. Monoclinic. Q Axes: a : b : c = 0'8316 : 1 : 0-4260. = 88 36'. mm'" 110 A 110 = 79 28'. In acicular crystals; common in capillary forms; also fibrous massive, parallel or divergent; compact massive. Cleavage: basal, perfect. Fracture uneven to conchoidal. Brittle. - 2-3- G. = 5-5-6-0. Luster metallic. Color steel-gray to dark lead- gray. Streak grayish black. Opaque. Comp. Pb 2 Sb 2 S 5 or 2PbS.Sb 2 S 3 = Sulphur 197, antimony 29'5, lead SULPHO-SALTS 387 50-8 = 100. Most varieties show a little iron (1 to 3 p. c.), and some contain also silver, copper, and zinc. It has been suggested that the iron shown by the analyses is an integral part of the mineral and that the formula should be 4PbS.FeS.3Sb 2 S 3 and that the usual jamesonite for- mula, 2PbS.Sb2S3, belongs to the material commonly called plumosite. Pyr. Same as for zinkenite, p. 385. Obs. Occurs principally in Cornwall; also in Siberia; Hungary; at Valentia d* Al- cantara in Spain; at the antimony mines in Sevier Co., Ark.; from Bolivia. Named after Prof. Robert Jameson of Edinburgh (1774-1854). The feather ore occurs at Wolfsberg, etc., in the Harz Mts.; Freiberg, Germany; Schem- nitz, Hungary; in Tuscany, near Bottino, Italy. These so-called feather ores may be di- vided into flexible and brittle, all the latter being referred to jamesonite and the former to either zinkenite, plumosite, boulangerite, or meneghinite. Warrenite has been shown to probably be a mixture of jamesonite and zinkenite. Dufrenoysite. 2PbS.As 2 S 3 . In highly modified crystals; also massive. Cleavage- 6(010) perfect. H. =3. G. = 5'55-5'57. Color blackish lead-gray. From the Bin- nental, Switzerland, in dolomite. Cosalite. 2PbS.Bi 2 S 3 . Usually massive, fibrous or radiated. G. = 6'39-675. Color lead- or steel-gray. Cosala, Province of Sinaloa, Mexico; Bjelke mine (bjelkite), Nord- mark, Sweden; Deer Park, Wash.; Col. Kobellite. 2PbS.(Bi,Sb) 2 S 3 . Fibrous radiated or granular massive. G. = 6'3. Color lead-gray to steel-gray. From Hvena, Sweden; Ouray, Col. BRONGNIARDITE. Lead, silver, antimony sulphide. Shown in some cases to be a mixture. A doubtful species. Plagionite. Heteromorphite. Semseyite. Lead, antimony sulphides ranging from 5PbS4.Sb 2 S 3 to 9PbS.4Sb 2 S 3 . Perhaps a morphotropic series with the vertical crystallo- graphic axis increasing in length with increase in the percentage of lead. Monoclinio. G. = 5'4-5'9. Plagionite from Wolfsberg, Harz Mts.; heteromorphite from Arnsberg, Westphalia; semseyite from Felsobanya, Hungary and Wolfsberg. Liveingite from the Binnental, Switzerland, is said to have the same composition as plagionite. Bismuto- plagionite, a variety containing bismuth instead of antimony. From Wickes, Jefferson Co., Mon. SCHAPBACHITE. A lead, silver, bismuth sulphide. From Schapbach, Baden. Shown to be a mixture. FREIESLEBENITE. Monoclinic. Axes a : b : c = 0-5871 : 1 : 0-9277; ft = 87 46'. Habit prismatic. G. = 6-2-6-4. Luster metallic. Color and streak light steel- gray inclining to silver-white, also to blackish lead-gray. Comp. (Pb,Ag 2 ) 5 Sb 4 Sii or 5(Pb,Ag 2 )S.2Sb 2 S 3 . Obs. From Freiberg, Saxony; Kapnik and Felsobanya, Hungary; Hiendelencina, Spain; also from the Augusta Mt., Gunnison Co., Col. Diaphorite. Like freieslebenite in composition but orthorhombic in form. G. = 5'9. From Pfibram, Bohemia; Lake Chelan district, Wash. BOULANGERITE. Orthorhombic. Axes a : b : c = 0*5527 : 1 : 0*7478. In prismatic or tabu- lar crystals or crystalline plumose masses; granular, compact. H. = 2*5-3. G. = 6-18. Luster metallic. Color bluish lead-gray; often covered with yellow spots from oxidation. Opaque. Comp. Pb 5 Sb 4 Sn or 5PbS.2Sh>S 3 = Sulphur 18'9, antimony 25*7, lead 55-4 = 100. Pyr. Same as for zinkenite, p. 385. Obs. In good crystals from Sala, Sweden; Molieres, Depart, du Gard, France; at Nerchinsk, Siberia; Wolfsberg in the Harz Mts. Pfibram, Bohemia; near Bottino, Tus- cany, Italy. Echo District, Union county, Nev. Embrithite and plumbostib are from Nerchinsk; they correspond nearly to 10PbS.3Sb 2 Sj, but the material analyzed may not have been quite pure. 388 DESCRIPTIVE MINERALOGY Mullanite. 5PbS.2Sb 2 S 3 . In slender orthorhombic (?) prisms. Cleavage, c(001) and 6(010). Color, steel-gray. Streak, brownish black H. = 3'5. G = 6'35. Found at Gold Hunter mine, near Mullan, Idaho, and at Iron Mountain mine, near Superior, Mon. D. Ortho- Division. 3RS.As 2 S 3 , 3RS.Sb 2 S 3 , etc. Bournonite Group. Orthorhombic. Prismatic angle 86 to 87 BOURNONITE. Wheel Ore. Orthorhombic. Axes: a : b mm"' 110 A 110 = 86 co, 001 A 101 = 43 C : c = 0-9380 20' 43' 669 Harz Kapnik steel-gray, 1 : 0-8969. en, 001 A Oil = 41 53' cu, 001 A 112 = 33 15' Twins: tw. pi. ra(110), often repeated, forming cruciform and wheel shaped crystals. Also massive; granular, compact. Cleavage: 6(010) imper- fect; a(100), c(001) less distinct. Fracture sub- conchoidal to uneven. Rather brittle. H. = 2-5-3. G. = 5-7-5-9. Lustermetal- inclining to blackish lead- lie, brilliant. Color and streak gray or iron-black. Opaque. Comp. (Pb,Cu 2 ) 3 Sb 2 S 6 or 3(Pb,Cu 2 )S.Sb 2 S 3 = PbCuSbS 3 (if Pb : Cu 2 = 2:1) = Sulphur 19'8, antimony 247, lead 42*5, copper 13*0 = 100. Pyr., etc. In the closed tube decrepitates, and gives a dark red sublimate. In the open tube gives sulphur dioxide, and a white sublimate of oxide of antimony. B.B. on char- coal fuses easily, and at first coats the coal white; continued blowing gives a yellow coating of lead oxide; the residue, treated with soda in R.F., gives a globule of copper. Decom- posed by nitric acid, affording a blue solution, and leaving a residue of sulphur, and a white powder containing antimony and lead. Obs. From Neudorf in the Harz Mts.; also Wolfsberg, Claustal, and Andreasberg; Pfibram, Bohemia; Kapnik and Nagybanya, Hungary; Horhausen, Prussia; Liskeard, Cornwall. In the United States at the Boggs mine, Yavapai Co., Ariz.; also Montgomery Co., Ark.; reported from San Juan Co., Col; Austin, Ney. In Canada, in the township of Marmora, Hastings Co., and Darling, Lanark Co., Ontario. Seligmannite. (Pb,Cu2) 3 As 2 S6 isomorphous with bournonite. Orthorhombic. a : b : c = 0*9233 : 1 : 0'8734. In small complex crystals. Commonly twinned with m(110) as tw. pi. Color lead-gray. Chocolate streak. H. = 3. Found at Lengenbach quarry, Binnental, Switzerland; reported from Emery, Mon. Aikinite. 2PbS.Cu 2 S.Bi 2 S 3 . Acicular crystals; also massive. G. = 6'l-6'8. Color blackish lead-gray. From Berezov near Ekaterinburg, Ural Mts. Wittichenite. 3Cu 2 S.Bi 2 S 3 . Rarely in crystals resembling bournonite; also massive. G. = 4*5. Color steel-gray or tin-white. Wittichen, Baden, etc. Stylotypite. 3(Cu 2 ,Ag 2 ,Fe)S.Sb 2 S 3 . In orthorhombic crystals, in cruciform twins like bournonite. G. = 47-5'2. Color iron-black. Copiapo, Chile; Peru. Lfflianite. 3PbS.BiSbS 3 and 3PbS.Bi 2 S 3 . Orthorhombic. Crystalline and massive. Color steel-gray. Gladhammar, Sweden; Leadville, Col. (argentiferous). Guitermanite. Perhaps 3PbS.As 2 S 3 . Massive, compact. G. = 5-94. Color bluish gray. Zufii mine, Silvertqn, Col. Lengenbachite. 7[Pb,(Ag,Cu) 2 ]S.2As 2 S 3 . Probably triclinic. In thin blade-shaped crystals. One perfect cleavage. Soft. G. = 5*8. Color steel-gray. Streak black. From the Lengenbach quarry, Binnental, Switzerland. SULPHO-SALTS 389 670 671 TAPALPITE. A sulpho-telluride of bismuth and silver, perhaps 3Ag2(S,Te).Bii(S,Te) 8 . Study of polished specimen shows it to be a mixture of unknown components. Massive, granular. G. = 7 '80. Sierra de Tapalpa, Jalisco, Mexico. Pyrargyrite Group. Rhombohedral-hemimorphic PYRARGYRITE. Ruby Silver Ore. Dark Red Silver Ore. Rhombohedral-hemimorphic. Axis: c = 07892; 0001 A 1011 = 4220J.' ee', 0112 A 1012 = 42 5' tw', 2131 A 2311 = 74 25' rr f , 1011 A 1101 = 71 22' yyv, 2131 A 3121 = 35 12' Crystals commonly prismatic. Twins: tw. pi. a(1120), very com- mon, the c axes parallel; also common. Also massive, compact. Cleavage: r(1011) distinct; e(0112) imperfect. Fracture conchoidal to uneven. Brittle. H. = 2-5. G. = 577- 5*86; 5-85 if pure. Luster metallic- adamantine. Color black to grayish black, by transmitted light deep red. Streak purplish red. Nearly opaque, ' = T970. e = 2-650. Comp. Mercurous chloride, HgCl = Chlorine 15 -1, mercury 84 -9 = 100. Pyr., etc. In the closed tube volatilizes without fusion, condensing in the cold part of the tube as a white sublimate; with soda gives a sublimate of metallic mercury. B.B. on charcoal volatilizes, coating the coal white. Insoluble in water, but dissolved by aqua regia; blackens when treated with alkalies. Obs. Usually associated with cinnabar. Thus at Moschellandsberg in the Palatinate, Germany; at Idria in Carniola, Austria; Almaden in Spain; at Mt. Avala near Belgrade in Servia. In crystals with many forms from Terlingua, Tex. Calomel is an old term of uncertain origin and meaning, perhaps from KO\OS, beautiful, and /zeXi, honey, the taste being sweet, and the compound the Mercurius dulcis of early chemistry; or from /caXos and /xeXas, black. Kleinite. Mercurammonite. A mercury ammonium chloride of uncertain composition. Hexagonal. Crystals short prismatic. Basal cleavage. H. = 3*5. G. = 8'0. Color yellow to orange, darkening on exposure. Volatile. From Terlingua, Tex. Nantokite. Cuprous chloride, CuCl. Granular, massive. Cleavage cubic. H. = 2-2*5. G. = 3*93. Luster adamantine. Colorless to white or grayish. From Nantoko, Chile; Broken Hill, New South Wales. Marshite. Cuprous iodide, Cul. Isometric- tetrahedral. Cleavage dodecahedral. H. = 2'5. G.=5'59. Color oil-brown.. n = 2'346. Broken Hill mines, New South Wales. Halite Group. RC1, RBr, RI. Isometric Halite NaCl Embolite Sylvite KC1 Bromyrite Sal Ammoniac (NH 4 )C1 lodobromite Cerargyrite AgCl Miersite Ag(Cl,Br) AgBr Ag(Cl,Br,I) Agl The HALITE GROUP includes the halogen compounds of the closely related metals, sodium, potassium, and silver, also ammonium (NH 4 ). They crystal- lize in the isometric system, the cubic form being the most common. Sylvite and sal-ammoniac are plagiohedral, and the same may be true of the others. HALITE. COMMON or ROCK SALT. Isometric. Usually in cubes; crystals sometimes distorted, or with cavern- ous faces. Also massive, granular to compact; less often columnar. 676 Cleavage: cubic, perfect. Frac- ture conchoidal. Rather brittle. H. = 2-5. G. = 2-1-2-6; pure crystals 2-135. Luster vitreous. Colorless or white also yellowish, reddish, bluish, purplish. Transpar- ent to translucent. Soluble; taste saline, n = 1-5442. Highly dia- thermanous. 396 DESCRIPTIVE MINERALOGY Comp. - Sodium chloride, NaCl = Chlorine 60 -6, sodium 39 -4 = 100. Commonly mixed with calcium sulphate, calcium chloride, magnesium chlo- ride, and sometimes magnesium sulphate, which render it liable to deliquesce. Pyr., etc. In the closed tube fuses, often with decrepitation; when fused on the platinum wire colors the flame deep yellow. After intense ignition the residue gives an alkaline reaction upon moistened test paper. Nitric acid solution gives precipitate of silver chloride upon addition of silver nitrate. Dissolves readily in three parts of water. Diff. Distinguished by its solubility (taste), softness, perfect cubic cleavage. Obs. Common salt occurs in extensive but irregular beds in rocks of various ages, associated with gypsum, poly halite, anhydrite, carnallite, clay, sandstone, and calcite; also in solution forming salt springs' similarly in the water of the ocean and salt seas. The deposits of salt have been formed by the gradual evaporation and ultimate drying up of enclosed bodies of salt water. Salt beds formed in this way are subsequently covered by other sedimentary deposits and gradually buried beneath the rock strata thus formed. The salt strata range from a few feet up to more than one hundred feet in thickness and have been found at depths of two thousand feet and more beneath the earth's surface. The principal salt mines of Europe are at Stassfurt, near Magdeburg, Saxony; Wie- liczka, in Galicia; at Hall, in Tyrol, Austria; and along the range through Reichental in Bavaria, Hallein in Salzburg, Hallstadt, Ischl, and Ebensee, in Upper Austria, and Aussee in Styria; in Hungary, at Marmoros and elsewhere; Transylvania; Wallachia, Galicia, and Upper Silesia; in southern and southeastern Russia; Vic and Dieuze in France; Valley of Cardona and elsewhere in Spain; Bex in Switzerland; and Northwich in Cheshire, England. Salt also occurs, forming hills and covering extended plains, near Lake Urumia, the Caspian Sea, etc. In Algeria; in Abyssinia. In India in enormous deposits in the Salt Range of the Punjab. In China and Asiatic Russia; in South America, in Peru, and at Zipaquera and Nemocon, the former a large mine long explored in the Cordilleras of Colombia; clear salt is obtained from the Cerro de Sal, San Domingo. In the United States, salt has been found in large amount in central and western N. Y. Salt wells had long been worked in this region, but rock salt is now known to exist over a large area from Ithaca at the head of Cayuga Lake, Tompkins Co., and Canandaigua Lake, Ontario Co., through Livingston Co., also Genesee, Wyoming, and Erie Cos. The salt is found in beds with an average thickness of 75 feet, but sometimes much thicker (in one instance 325 feet), and at varying depths from 1000 to 2000 feet and more; the depth increases southward with the dip of the strata. The rocks belong to the Salina period of the Upper Silurian. Extensive deposits of salt occur in Mich., chiefly in Saginaw, Bay, Midland, Isabella, Detroit, Wayne, Manistee and Mason Counties. Salt has also been found near Cleveland, Ohio, associated with gypsum; in Kan.; in La., extensive beds occur in the southern portion of the state at and in the neighborhood of Petite Anse island. Salt has also been obtained from Nev., Utah, Ariz, and Cal. In Utah and Cal. salt is chiefly obtained by the evaporation of the waters of Great Salt Lake and the ocean. Brine springs are very numerous in the Middle and Western States. Vast lakes of salt water exist in many parts of the world. The Great Salt Lake in Utah is 2000 square miles in area; L. Gale found in this water 20 '196 per cent of sodium chloride. The Dead and Caspian seas are salt, and the waters of the former contain 20 to 26 parts of solid matter in 100 parts. Sodium chloride is the prominent salt present in the ocean. Use. The chief uses of salt are for culinary and preservative purposes. Soda ash is also made from it, being employed in the manufacture of glass, soap, bleaching, prepara- tion of other sodium compounds, etc. Villiaumite. NaF. Isometric. In small carmine colored grains. Soft. G. = 2'8. Refractive index = 1'33. Found in nepheline-syenite from the Islands of Los. Huantajayite. 20NaCl.AgCl. In cubic crystals and as an incrustation. H. = 2. Wot sectile. Color white. From Huantajaya, Tarapaca, Chile. SYLVITE. Isometric-plagiohedral. Also in granular crystalline masses; compact. Cleavage: cubic, perfect. Fracture uneven. Brittle. H. = 2. G. = 1-97-1-99. Luster vitreous. Colorless, white, bluish or yellowish red from inclusions. Soluble; taste resembling that of common salt, but bitter. n = 1'490. Comp. Potassium chloride, KC1 = Chlorine 47-6, potassium 52'4 = 100. Sometimes contains sodium chloride. HALOIDS. CHLORIDES, BROMIDES, IODIDES; FLUORIDES 397 Pyr., etc. B.B. in the platinum loop fuses, and gives a violet color to the outer flame Dissolves completely in water (saline taste). After ignition residue reacts alkaline upon moistened test paper. Solution in nitric acid gives precipitate of silver chloride with silver nitrate. Obs. Occurs at Vesuvius, about the fumaroles of the volcano. Also in Germany at Stassfurt, Saxony; and at Leopoldshall (leopoldite) , Anhalt; at Kalusz in Galicia. Use. A source of potash compounds used as fertilizers. Sal Ammoniac. Ammonium chloride, NH 4 C1. n = 1'642. Observed as a white in- crustation about volcanoes, as at Etna, Vesuvius, etc. Cerargyrite Group. Isometric-Normal An isomorphous series of silver haloids in which silver chloride, bromide and iodide may mix in varying proportions. The suggestion has been made that the name cerargyrite be kept as the group name and that the different sub-species be named as follows: chlorargyrite, AgCl; bromargyrite, AgBr: embolite, Ag(Cl,Br); iodembolite, Ag(Cl,Br,I). CERARGYRITE. Horn Silver. Isometric. Habit cubic. Twins: tw. pi. o(lll). Usually massive and resembling wax; sometimes columnar; often in crusts. Cleavage none. Fracture somewhat conchoidal. Highly sectile. H. = 1-1*5. G. = 5 -552. Luster resinous to adamantine. Color pearl-gray, grayish green, whitish to colorless, rarely violet-blue; on exposure to the light turns violet-brown. Transparent to translucent, n = 2-0611. Comp. Silver chloride, AgCl = Chlorine, 24-7, silver 75-3 = 100. Some varieties contain mercury. Pyr., etc. In the closed tube fuses without decomposition. B.B. on charcoal gives a globule of metallic silver. Added to a bead of salt of phosphorus, previously saturated with oxide of copper and heated in O.F., imparts an intense azure-blue to the flame. Insoluble in nitric acid, but soluble in ammonia. Obs. Cerargyrite and the related minerals are products of secondary action and are commonly found in the upper parts of silver deposits. Descending waters containing chlorine, bromine or iodine act upon the oxidation products of the primary silver minerals and so precipitate' these relatively insoluble compounds. Commonly associated with other silver minerals, with lead, copper and zinc ores and their usual alteration products. The largest masses are brought from Peru, Chile, Bolivia, and Mexico, where it occurs with native silver. Also once obtained from Johanngeorgenstadt and Freiberg, Saxony; occurs in the Altai Mts.; at Kongsberg in Norway. In the United States, in Col., near Leadville, Lake Co.; near Breckenridge, Summit Co., and elsewhere. In Nev. near Austin, Lander Co.; at mines of Comstock lode; Tonapah. In Idaho, at the Poorrnan mine, in crystals; also at various other mines. In Utah, in Beaver, Summit and Salt Lake counties. At Tombstone, Ariz. Named from /cepas, horn, and apyvpos, silver. Use. An ore of silver. Embolite. Silver chloro-bromide Ag(Br,Cl), the ratio of chlorine to bromine vary- ing widely. Usually massive. Resembles cerargyrite, but color grayish green to yellowish green and yellow, n = 2*15. Abundant in Chile. Found also at Broken Hill, New South Wales; Tonapah, Nev.; Leadville, Col.,; Yuma County, Ariz.; Georgetown, N. M. Bromyrite. Silver bromide, AgBr. G. = 5*8-6. Color bright yellow to amber-yel- low; slightly greenish, n = 2'25. From Mexico; Chile. lodobromite. 2AgCl.2AgBr.AgI. Isometric. G. = 5713. Color sulphur-yellow, greenish, n = 2'2. From near Dernbach, Nassau; Broken Hill, New South Wales. Miersite. Silver, copper iodide, 4AgI.CuI. Isometric; tetrahedral. G. = 5'64. In bright yellow crystals from the Broken Hill Silver Mines, New South Wales. Cupro- iodargyrite from Huantajaya, Peru, belongs here also. lodyrite. Silver iodide, Agl. Hexagonal-hemimorphic; usually in thin plates; pale 398 DESCRIPTIVE MINERALOGY yellow or green. G. = 5'5-57. Lake Valley, Sierra Co., N. M. Tonapah, Nev. Optically + . co = 2 '182. From Mexico, Chile, etc. In crystals from Broken Hill, New South Wales, and ii ii RF 2 ,RC1 2 Fluorite Group. The species here included are Fluoritel CaF 2 T and the rare Hydrophilite, CaCl 2 . Both are isometric, habit cubic. V^ 4 FLUORITE or FLUOR SPAR. Isometric. Habit cubic; less frequently octahedral or dodecahedral ; forms /(310), e(210) (fluoroids) common; also the vicinal form f (321-0?), producing striations on a(100) (Fig. 682) ; hexoctahedron 2(421) also common with the cube (Fig. 681). Cubic crystals sometimes grouped in parallel position, thus forming a pseudo-octahedron. Twins: tw. pi. 0(111), com- 678 679 681 682 monly penetration-twins (Fig. 682). Also massive; granular, coarse or fine- rarely columnar; compact. Cleavage: o(lll) perfect. Fracture flat-conchoidal; of compact kinds splintery. Brittle. H. = 4 G. = 3-01-3-25; 318 cryst. Luster vitreous. Color white, yellow, green, rose- and crimson- red, violet-blue, sky-blue, and brown; wine-yellow, greenish blue, violet-blue, most common; red, rare. Streak white. Transparent - - subtranslucent. Sometimes shows a bluish fluor- escence. Some varieties phos- phoresce when heated (p. 251) n = 1-4339. Fluorine 48'9, calcium 511 = 100. A Comp. --.- Calcium fluoride, CaF 2 - nuorme 3 Oniorme is sometimes present in minute quantities ipitates and sometimes phosphoresces. B. B. in the rm, octahedral cleavage, relative softness (as i, also with the feldspars); etching power when effervesce with acid like calcite on test compared with certain treated with sulphuric Fused b a closed HALOIDS. CHLORIDES, BROMIDES, IODIDES; FLUORIDES 399 Obs. Fluorite occurs most commonly as a vein mineral either in deposits in which it is the chief constituent or as a gangue mineral with various metallic ores, especially those of lead and zinc. It is common in sedimentary rocks, being often found in dolomites and limestones. It is also found as a minor accessory mineral in granite and other acid igneous rocks. It occurs as a sublimation product in connection with volcanic rocks. In the North of England, it is the gangue of the lead veins, which intersect the coal formation in Northumberland, Cumberland, Durham, and Yorkshire. In Derbyshire it is abundant, and also in Cornwall, where the veins intersect metamorphic rocks. The Cumberland and Derbyshire localities especially have afforded magnificent specimens. Common in the mining district of Saxony; from Stolberg, Harz Mts.; fine near Kongsberg in Norway. In the dolomites of St. Gothard occurs in pink octahedrons; from Brienz, Switzerland. From Rabenstein, Tyrol, Austria. Rarely in volcanic regions, as in the Vesuvian lava. In colorless transparent crystals from Madoc, Hastings Co., Ontario, Canada. Some localities in the United States are, Trumbull, Conn, (chlorophane) ; Muscolonge Lake, Jefferson Co., N. Y., and Macomb, St. Lawrence Co., both in very large sea-green cubes; Franklin Furnace, N. J.; Amelia Court House, Va. ; Westmoreland, Ver. Fluorite has been mined in the United States chiefly from Western Kentucky and adjacent sections in Hardin and Pope counties, 111. Also obtained from Jamestown, Boulder County; Ever- green, Jefferson County, and near Rosita, Custer County, Col.; from ten miles north of Deming, N. M.; from Smith, Trousdale and Wilson counties, Tenn.; from Castle Dome district, Ariz. Use. As a flux in the making of steel; in the manufacture of opalescent glass; in enameling cooking utensils; the preparation of hydrofluoric acid; sometimes as an orna- mental material. Hydrophilite. Chlorocalcite. Calcium chloride, CaCl 2 . In white cubic crystals or as an incrustation at Vesuvius. Bceumlerite is same material intergrown with halite and tachhydrite from Leinetal, Germany. The following are from Vesuvius: Chloromagnesite, MgCl 2 ; Scacchite. MnCl 2 ; ChloraUuminite, A1C1 3 .6H 2 O; Molysite, FeCl 3 ; Chlormanganokalite, 4KCl.MnCl 2 . Sellaite. Magnesium fluoride, MgF 2 . In prismatic tetragonal crystals. H. = 5. G. = 2 '97-3 15. Colorless. Optically + . co = 1'378. From the moraine of theGebrou- laz glacier in Savoie, France. Belonesite is the same species. Lawrencite. Ferrous chloride, FeCl2. Occurs in meteoric iron. Rinneite. FeCl 2 .3KCl.NaCl. Rhombohedral. In coarse granular masses. Prismatic cleavage. H. =3. G. = 2'3. Colorless, rose, violet or yellow when fresh, becomes brown on exposure due to oxidation. o> = 1'59. Easily fusible. Astringent taste. Found in Germany at Nordhausen and elsewhere in Saxony and at Diekholzen, Hannover. Cotunnite. Lead chloride, PbCl2. In acicular crystals (orthorhombic) and in semi- crystalline masses. Soft. G. = 5 '24. Color white, yellowish. Optically + . 8 = 2 '2 17. From Vesuvius; also Tarapaca, Chile. Tysonite. Fluoride of the cerium metals, (Ce,La,Di)Fs. In thick hexagonal prisms, and massive. Cleavage: c(001), perfect. H. = 4*5-5. G. = 6'13. Color pale wax- yellow, changing to yellowish and reddish brown. From the granite of Pike's Peak, El Paso Co., Col. Fluocerite, from Osterby, Sweden, is propably the same species. Yttrofluorite. (Ca 3 ,Y 2 )F 6 , near yttrocerite. Isometric. In granular masses. Imperfect octahedral cleavage. H. = 4*5. G. = 3'55. Color yellow, also with brown or green shades, n 1*46. Found in pegmatite in northern Norway. CRYOLITE. Monoclinic. |8 = 89 49'. mm'", 110 A 1TO = 88 cm, 001 A 110 = 89 cv, 001 A 101 = 55 683 Axes a : b : c = 0'9663 : 1 : 1'3882; 2'. 52'. 2'. ck, 001 A T01 = 55 17'. cr, 001 A Oil = 54 14'. cp, 001 A 111 = 63 18'. Crystals often cubic in aspect and grouped in paral- lel position; often with twin lamellae. Massive. Parting at times due to j/winning lamellae parallel to c(001), ra(110) and /c(101). Fracture uneven. Brittle. H. = 2'5. G. = 2-95-3-0. Luster vitreous to greasy; somewhat pearly on c(001). Colorless to snow-white, 400 DESCRIPTIVE MINERALOGY sometimes reddish or brownish to brick-red or even black. Transparent to translucent. Optically +. Mean index, 1-364. p_ Comp. A fluoride of sodium and aluminium^ Na 3 AlF 6 lor 3NaF.AlF 3 = Fluorine 54*4, aluminium 12'8, sodium 32*8 = !D6>----rAr-nttle iron sesqui- oxide is sometimes present as impurity. Pyr., etc. Fusible in small fragments in the flame of a candle. Heated in C. T. with potassium bisulphate gives fluorine reaction. In the forceps fuses very easily, coloring the flame yellow. On charcoal fuses easily to a clear bead, which on cooling becomes opaque; after long blowing, the assay spreads out, the fluoride of sodium is absorbed by the coal, a suffocating odor of fluorine is given off, and a crust of alumina remains, which, when heated with cobalt solution in O.F., gives a blue color. Soluble in sulphuric acid, with evolution of hydrofluoric acid. Diff. Distinguished by its extreme fusibility. Because of its low index of refraction the powdered mineral becomes almost invisible when placed in water. Its planes of part- ing (resembling cubic cleavage) and softness are characteristic. Obs. Occurs in a bay in Arksukfiord, in West Greenland, at Ivigtut (or Evigtok), about 12 m. from the Danish settlement of Arksuk, where it constitutes a large bed in a granitic vein in a gray gneiss. Cryolite and its alteration products, pachnolite, thom- senolite, prosopite, etc., also occur in limited quantity at the southern base of Pike's Peak, El Paso county, Col., north and west of Saint Peter's Dome. Named from Kpvos, frost, X9os, stone, hence meaning ice-stone, in allusion to the trans- lucency of the white masses. Use. In the manufacture of sodium salts, certain kinds of glass and porcelain, and as a flux in the electrolytic process for the production of aluminum. Cryolithionite is a variety of cryolite with half the sodium replaced by lithium. G. = 278. Refractive index T34. Associated with cryolite at Ivigtut. Chiolite. 5NaF.3AlF 3 . In small pyramidal crystals (tetragonal); also massive granu- lar. Cleavages, c(001) perfect, p(lll) distinct. H. = 3'5-4. G. = 2'84-2'90. Color snow-white. Optically . co = 1*349.. From near Miask in the Ilmen Mts., Russia; also with the Greenland cryolite. Hieratite. A fluoride of potassium and silicon. In grayish stalactitic concretions; isometric. From the fumaroles of the crater of Vulcano, Lipari Islands. ATACAMITE. Orthorhombic. 684 II. Oxychlorides, Oxyfluorides Axes a :b : c = 0-6613 : 1 : 07515. mm", 110 A 110 = 66 57'. rr'" t 111 A 111 = 52 48'. ee', Oil A Oil = 73 51'. mr, 110 A 111 = 36 16*'. Commonly in slender prismatic crystals, vertically striated. Twins according to a complex law. (Paratacamite is twinned atacamite.) In confused crystalline aggregates; also massive, fibrous or granular to compact; as sand. Cleavage: 6(010) highly perfect. Fracture conchoidal. Brittle. H. = 3-3-5. G. = 375-377. Luster adamantine to vitreous. Color bright green of various shades, dark emerald-green to blackish green. Streak apple-green. Transparent to translucent. Optically . a = T831 = T861. 7 = 1-880. Comp. Cu 2 ClH 3 3 or CuCl 2 .3Cu(OH) 2 = Chlorine 16'6, copper 14'9, cupnc oxide 55-8, water 12-7 = 100. on charcoal _ . owmsn w. u ^ Viiv , UIMI^I gioijriBii wince, uuiiuiiueu uiowuig yieias a gioouie oi met sflv C ? a uj ngs ' touched ^h the R.F., volatilize, coloring the flame azure-blue. In HALOIDS. CHLORIDES, BROMIDES, IODIDES; FLUORIDES 401 Obs. Originally from Atacama in the northern part of Chile; also found at Colla- hurasi, Tarapaca and elsewhere in Chile and Bolivia; at Wallaroo and Bimbowrie, in South Australia; at Gloncurry, Queensland; at St. Just in Cornwall. In the United States, with cuprite, etc., at the United Verde mine, Jerome, Ariz. Percylite. A lead-copper oxychloride, perhaps PbCl 2 .CuO.H 2 O. In sky-blue cubes. From Sonora, Mexico; Atacama, Chile; Bolivia, etc. Boleite. 9PbCl 2 .8CuO.3AgC1.9H 2 O. Tetragonal, pseudo-isometric. Twinned to form pseudo cubes. Pseudo-boleite. 5PbCl 2 .4CuO.6H 2 O. Tetragonal. Cumengite. 4PbCl 2 .4CuO.5H 2 O. Tetragonal. Pseudo-boleite and cumengite occur in parallel growth upon crystals of boleite. Boleite and pseudo-boleite have pearly luster on cleavage, while cumengite has not. All three deep blue in color, the first two showing a greenish tinge in powder. Found at Boleo, near Santa Rosalia, Lower California. Matlockite. Lead oxychloride, Pb 2 OCl 2 . In tabular tetragonal crystals. G. = 7-21. Luster adamantine to pearly. Color yellowish or slightly greenish. Optically . co =2 '15. From Cromford, near Matlock, Derbyshire. Mendipite. Pb 2 O 2 Cl 2 or PbCl 2 .2PbO. In fibrous or columnar masses; often radiated. H. =2-5-3. G. = 7-7'l. Color white. Index, 1'93. From the Mendip Hills, Somer- setshire, England; near Brilon, Westphalia. Lorettoite. 6PbO.PbCl 2 . Tetragonal? Coarse fibers or blades. Perfect basal cleavage. G. = 7-6. H. = 3. Fusible at 1. Color honey-yellow. Uniaxial, -. Indices, 2'37- 2-40. From Loretto, Tenn. Laurionite. PbClOH or PbCl 2 .Pb(OH) 2 . In minute prismatic colorless crystals (ortho- rhombic), in ancient lead slags at Laurion, Greece. Optically . /3 = 2-116. Para- laurionite. Same composition as laurionite but monoclinic. From Laurion. Rafaelite from Chile is the same mineral. Suggested that laurionite is the same as paralaurionite but owing to submicroscopic twinning has apparently orthorhombic symmetry. Fiedlerite, associated with laurionite, is probably also a lead oxychloride; in colorless monoclinic crystals. Penfieldite. Pb 3 OCl 2 or PbO.2PbCl 2 . In white hexagonal crystals. Laurion, Greece. Daviesite. A lead oxychloride of uncertain composition. In minute colorless pris- matic crystals (orthorhombic) from the Mina Beatriz, Sierra Gorda, Atacama, Chile. Schwartzembergite. Probably Pb(I,Cl) 2 .2PbO. In druses of small crystals; also in crusts. G. = 6"2. Color honey-yellow. Desert of Atacama, Chile. Nocerite. Perhaps 2(Ca,Mg)F 2 (Ca,Mg)O(?). In white hexagonal acicular crystals from bombs in the tufa of Nocera, Italy. Koenenite. An oxychloride of aluminium and magnesium. Rhombohedral. Perfect cleavage yielding flexible folia. Very soft. G. = 2'0. Color red, due to included hema- tite. From near Volpriehausen in the Soiling, Germany. Daubreeite. An earthy yellowish oxychloride of bismuth. From Bolivia. The following are oxychlorides of mercury from the mercury deposits at Terlingua, Texas. Associated minerals are montroydite, calomel, native mercury and calcite. Eglestonite. Hg 4 Cl 2 O. Isometric in minute crystals of dodecahedral habit. Many forms observed. H. = 2-3. G. = 8' 3. Luster adamantine to resinous. Color brownish yellow darkening on exposure to black, n = 2*49. Volatile. Terlinguaite. Hg 2 ClO. Monoclinic. In small striated prismatic crystals elongated parallel to the 6-axis. Many forms observed. Cleavage perfect. H. = 2-3. G = 87. Luster adamantine. Color sulphur-yellow changing to olive-green on exposure. III. Hydrous Chlorides, Hydrous Fluorides, etc. CARNALLITE. Orthorhombic. Crystals rare. Commonly massive, granular. No distinct cleavage. Fracture conchoidal. Brittle. H. = 1. G = 1-60. Luster shining, greasy. Color milk-white, often reddish. Transparent to translucent. Strongly phosphorescent. Optically + 2 V = 70. a = 1 -466. = 1-475. T = 1-494, Taste bitter. Deliquescent. Comp. KMgCl 3 .6H 2 O or KCl.MgCl 2 .6H 2 O = Chlorine 38'3, potas- sium 14-1, magnesium 87, water 39'0 = 100. 402 DESCRIPTIVE MINERALOGY Obs. Occurs at Stassfurt, in beds, alternating with thinner beds of common salt and kieserite. In large crystals from Beienrode, near Konigshiitte, Silesia. U se . Carnallite is a source of potash compounds used in fertilizers. DOUGLASITE, associated with carnallite, is said to be 2KCl.FeCl 2 .2H 2 O. Bischofite. MgCl 2 .6H 2 O. Crystalline-granular; colorless to white. Optically +. /3 = 1-507. From Leopoldshall and Stassfurt, Prussia. Kremersite. KCl.NH 4 Cl.FeCl 2 .H 2 O. In red octahedrons. From Vesuvius and Mt. Etna, Sicily. Mosesite. A mercury-ammonium compound containing chlorine, sulphur trioxide and water. Near kleinite in composition. Isometric. Minute octahedrons. Spinel twins. H. = 3 + . Color yellow. Doubly refracting at ordinary temperatures. Found sparingly at Terlingua, Texas. Erythrosiderite. 2KCl.FeCl3.H 2 O. In red tabular crystals. Vesuvius. Tachhydrite. CaCl 2 .2MgCl 2 .12H 2 O. In wax- to honey-yellow masses. From Stass- furt, Germany. Fluellite. A1F 3 .H 2 O. In colorless or white rhombic, pyramids. Index, 1'47. From Stenna Gwyn, Cornwall. ' Prosopite. CaF 2 .2Al(F,OH) 3 . In monoclinic crystals, or granular massive. H. = 4'5. G. = 2-88. Colorless, white, grayish. = 1'502. From Altenberg, Saxony; St. Peter's Dome near Pike's Peak, Col.; Utah. Pachnolite and Thomsenolite, occurring with cryolite in Greenland, Col., and Ural Mts., have the same composition, NaF.CaF 2 .AlF3.H 2 O. Both occur in monoclinic prismatic crystals; prismatic angle for pachnolite, 98 36', crystal twins, orthorhombic in aspect. /3 = 1-413. For thomsenolite, 89 46', crystals often resembling cubes, also prismatic; distinguished by its basal cleavage; also massive. /3 = T414. Gearksutite. CaF 2 .Al(F,OH) 3 .H 2 O. Earthy, clay-like. Index, T448. Occurs with cryolite. Ralstonite. (Na 2 ,Mg)F 2 .3Al(F,OH) 3 .2H 2 O. In colorless to white, isometric, octa- hedrons. H. = 4-5. G. = 2-56-2-62. n = 1'43. With the Greenland cryolite. Creedite. 2CaF 2 .2Al(F,OH) 3 .CaSO 4 .2H 2 O. Monoclinic. In grains, prismatic crys- tals and radiating masses. Usually colorless, rarely purple. H. = 3'5. G. = 2*71. Perfect cleavage. Indices, 1-46-1-49. 2 V = 64. Y = b axis. Fusible with intumescence. Soluble in acids. Found near Wagon Wheel Gap, Creed Quadrangle, Col. Tallingite. A hydrated copper chloride from the Botallack mine, Cornwall; in blue globular crusts. Yttrocerite. (Y,Er,Ce)F 3 .5CaF 2 .H 2 O. Massive-eleavable to granular and earthy. H. = 4-5. G. = 3'4. Color violet-blue, gray, reddish brown. From near Falun, Sweden, etc. V. OXIDES I. Oxides of Silicon, n. Oxides of the Semi-Metals : Tellurium, Arsenic, Antimony, Bismuth ; also Molybdenum, Tungsten. III. Oxides of the Metals. The Fifth Class, that of the OXIDES, is subdivided into three sections, according to the positive element present. The oxides of the non-metal silicon are placed by themselves, but it will be noted that the compounds of the related element titanium are included with those of the metals proper. This last is made necessary by the fact that in one of its forms Ti0 2 is isomor- phous with MnO 2 and Pb0 2 . A series of oxygen compounds which are properly to be viewed as salts, e.g., the species of the Spinel Group and a few others, are for convenience also included in this class. OXIDES I. Oxides of Silicon 403 QUARTZ. Rhombohedral-trapezohedral. rr f , 1011 A TlOl = 85 46'. rz, 1011 A 0111 = 46 16'. mr, 1010 A 1011 = 38 13'. 685 686 Axis: c = 1-09997. mz, 1010 A 0111 = 66 52'. ms, 1010 A 1121 = 37 58'. mx, 1010 A. 5161 = 12 1'. 687 688 Crystals commonly prismauc, with the m(10TO) faces horizontally striated; terminated commonly by the two rhombohedrons, r(1011) and 2(0111), in nearly equal development, giving the appearance of a hexagonal pyramid; when one rhombohedron predominates it is in almost all cases r. Often in double six-sided pyramids or quartzoids through the equal develop- ment of r and 2; when r is relatively large the form then has a cubic aspect (rr f = 85 46'). Crystals frequently distorted, when the correct orientation may be obscure except as shown by the striations on m. Crystals often elon- gated to acicular 'forms, and tapering through the oscillatory combination of successive rhombohedrons with the prism. Occasionally twisted or bent. Frequently in radiated masses with a surface of pyramids, or in druses. Simple crystals are either right- or left-handed. On a right-handed crystal (Fig. 690) the right trigonal pyramid, s(1121), if present, lies to the right of the m face, which is below the predominating positive rhombohedron r, and with this belong the positive right trapezohedrons, as (5161). On a left-handed crystal (Fig. 691), s lies to the left of the m below r. The right- and left-handed forms occur together only in twins. In the absence of trapezohedral faces the striations on s (|| edge r/m), if distinct, serve to dis- tinguish the faces r and z, and hence show the right- and left-handed character of the crystals. The right- and left-handed character is also revealed by etching (Art. 286) and by pyro-electricity (Art. 438). Thermal study of quartz shows that it exists in two modifications, known as a- and /3-quartz. a-quartz is apparently hexagonal, trapezohedral-tetartohedral and is formed at temperatures below 575 while /3-quartz is hexagonal, trapezohedral-hemihedral and forms at temperatures ranging from 575 to 800. Above 800 tridymite is formed. The crystal angles of a-quartz change with increase of temperature up to? 575, the inver- sion point to /3-quartz, while beyond this point they remain nearly constant. In a similar 404 DESCRIPTIVE MINERALOGY manner at this point there is a sudden marked lowering of the refractive indices and birefrin- gence, a-quartz occurs in veins and geodes and large pegmatites while the /3 modification is found in graphite granite, granite pegmatites, and porphyries. Tridymite when heated to about 1470 passes over into cristobalite. Quartz, tridymite and cristobalite are prob- ably to be considered as polymers of the fundamental molecule, SiO 2 . Twins: (1) tw. axis c, all axes parallel. (2) Tw. pi. a, sometimes called the Brazil law, usually as irregular penetration-twins (Fig. 692). (3) Tw. pi. (1122), contact-twins, the axes crossing at angles of 84 33'_and with a prism face in common to the two individuals. (4) Tw. pi. r(1011). See further p. 168 and Figs. 427^429. Massive forms common and in great variety, pass- ing from the coarse or fine granular and crystalline kinds to those which are flint-like or cryptocrystalline. Sometimes mammillary, stalactitic, and in concretionary forms; as sand. Cleavage not Distinctly observed; sometimes fracture surfaces (|| r(1011), 2(0111) and m(1010), developed by sudden cooling after being heated (see Art. 279). Fracture conchoidal to subconchoidal in crystallized forms, uneven to splintery in some massive kinds. Brittle to tough. H. = 7. G. = 2-653- 2-660 in crystals; cryptocrystalline forms somewhat lower (to 2 -60) if pure, but impure massive forms (e.g., jasper) higher. Luster vitreous," sometimes greasy; splendent to nearly dull. Colorless when pure; often various shades of yellow, red, brown, green, blue, black. Streak white, of pure varieties; if impure, often the same as the color, but much paler. Transparent to opaque. Optically +. Double refraction weak. Polarization circular; right- handed or left-handed, the optical character corresponding to right- and left-handed character of crystals, as defined above; in twins (law 2), both right and left forms sometimes united, sections then often showing Airy's spirals in the polariscope (cf. Art. 394, p. 270, and Fig. 692). Ro- tatory power proportional to thickness of plate. Refractive indices for the D line, co = 1-54418, e = 1-55328; also rotatory power for section of l mm thickness, a = 21 71 (D line). Pyroelectric; also electric by pressure or piezo-electric.- See Arts. 438, 439. On etching-figures, see Arts. 286, 287. Comp. Silica, or silicon dioxide, = Oxygen 53'3, silicon 467 = 100. 692 Basal section in polarized light, show- mg interpenetration of right- and left-handed portions. Des Cloi- In massive varieties often mixed with a little opal silica. Impure varieties contain- iron oxide, calcium carbonate, clay, sand, and various minerals as inclusions. Artif. Quartz has been produced artificially in numerous ways. Recently crystals have been obtained at temperatures below 760 from melts containing dissolved silica which were composed of (1) a mixture of potassium and lithium chlorides, (2) vanadic acid, (3) sodium tungstate. At higher temperatures tridymite crystals formed. Var ~A-, PHENOCRYSTALLINE: Crystallized, vitreous in luster. B. CRYPTOCRYSTAL- LINE: Flint-like, massive. The first division includes all ordinary vitreous quartz, whether having crystalline faces 1 he varieties under the second are in general acted upon somewhat more by rition and by chemical agents, as hydrofluoric acid, than those of the first. In all kinds made up of layers, as agate, successive layers are unequally eroded. OXIDES 405 A. PHENOCRYSTALLINE OR VITREOUS VARIETIES Ordinary Crystallized; Rock Crystal. Colorless quarts, or nearly so, whether in dis- tinct crystals or not. Here belong the Bristol diamonds, Lake George diamonds, Brazilian pebbles, etc. Some variations from the common type are : (a) cavernous crystals; (6) cap- quartz made up of separable layers or caps; (c) drusy quartz, a crust of small or minute quartz crystals; (d) radiated quartz, often separable into radiated parts, having pyramidal terminations; (e) fibrous, rarely delicately so, as a kind from Griqualand West, South Africa, altered from crocidolite (see cat's-eye below, also crocidolite, p. 493). Asteriated; Star-quartz. Containing within the crystal whitish or colored radiations along the diametral planes. Occasionally exhibits distinct asterism. Amethystine; Amethyst. Clear purple, or bluish violet. Color perhaps due to man- ganese. Rose. Rose-red or pink, but becoming paler on exposure. Commonly massive. Luster sometimes a little greasy. Color perhaps due to titanium. Yellow; False Topaz or Citrine. Yellow and pellucid; resembling yellow topaz. Smoky; Cairngorm Stone. Smoky yellow to dark smoky brown, and often trans- parent; varying to brownish black. Color is probably due to some organic compound (Forster). Called cairngorms from the locality at Cairngorm, southwest of Banff, in Scotland. The name morion is given to nearly black varieties. Milky. Milk-white and nearly opaque. Luster often greasy. Siderite, or Sapphire-quartz. Of indigo or Berlin-blue color; a rare variety. Sagenitic. Inclosing acicular crystals of rutile. Other included minerals in acicular forms are: black tourmaline; gothite; stibnite; asbestus; actinolite; hornblende; epidote. Cat's-eye exhibits opalescence, but without prismatic colors, especially when cut en ca- bochon, an effect sometimes due to fibers of asbestus. Also present in the siliceous pseudo- morphs, after crocidolite, called tiger-eye (see crocidolite). The highly-prized Oriental cat's-eye is a variety of chrysoberyl. Aventurine. Spangled with scales of mica, hematite, or other mineral. Impure from the presence of distinct minerals distributed densely through the mass. The more common kinds are those .in which the impurities are: (a) ferruginous, either red or yellow, from anhydrous or hydrous iron sesquioxide; (6) chloritic, from some kind of chlorite; (c) actinolitic; (d) micaceous; (e) arenaceous, or sand. Containing liquids in cavities. The liquid, usually water (pure, or a mineral solution), or some petroleum-like compound. Quartz, especially smoky quartz, also often contains inclusions of both liquid and gaseous carbon dioxide. B. CRYPTOCRYSTALLINE VARIETIES Chalcedony. Having the luster nearly of wax, and either transparent or translucent. G. = 2'6-2'64. Color white, grayish, blue, pale brown to dark brown, black. Also of other shades, and then having other names. Often mammillary, botryoidal, stalactitic, and occurring lining or filling cavities in rocks. It often contains some disseminated opal- silica. The thermal study of chalcedony shows that it differs from quartz and may be therefore a distinct species. The name enhydros is given to nodules of chalcedony con- taining water, sometimes in large amount. Embraced under the general name chalcedony is the crystalline form of silica which forms concretionary masses with radial-fibrous and concentric structure, and which, as shown by Rosenbusch, is optically negative, unlike true quartz. It has n = 1*537; G. = 2'59-2'64. Often in spherulites, showing the spheru- litic interference-figure . Lussatite of Mallard has a like structure, but is optically + and has the specific gravity and refractive index of opal. It may be a fibrous form of tridymite. See also quartzine, p. 407. Carnelian. Sard. A clear red chalcedony, pale to deep in shade; also brownish red to brown. Chrysoprase. An apple-green chalcedony, the color due to nickel oxide. Prase. Translucent and dull leek-green. Plasma. Rather bright green to leek-green, and also sometimes nearly emerald-green, and subtranslucent or feebly translucent. Heliotrope, or Blood-stone, is the same stone essentially, with small spots of red jasper, looking like drops of blood. Agate. A variegated chalcedony. The colors are either (a) banded; or (6) irregu- larly clouded ; or (c) due to visible impurities as in moss agate, which has brown moss-like or dendritic forms, as of manganese oxide, distributed through the mass. The bands are delicate parallel lines, of white, pale and dark brown, bluish and other shades; they are sometimes straight, more often waving or zigzag, and occasionally concentric circular. 406 DESCRIPTIVE MINERALOGY The bands- are the edges of layers of deposition, the agate having been formed by a deposit of silica from solutions intermittently supplied, in irregular cavities in rocks, and deriving their concentric waving courses from the irregularities of the walls of the cavity. The layers differ in porosity, and therefore agates may be varied in color by artificial means, and this is done now to a large extent with the agates cut for ornament. There is also agatized wood; wood petrified with clouded agate. Onyx. Like agate in consisting of layers of different colors, white and black, white and red, etc., but the layers in even planes, and the banding straight, and hence its use for cameos. Sardonyx. Like onyx in structure, but includes layers of carnelian (sard) along with others of white or whitish, and brown, and sometimes black colors. Agate-jasper. An agate consisting of jasper with veinings of chalcedony. Siliceous -sinter. Irregularly cellular quartz, formed by deposition from waters con- taining silica or soluble silicates in solution. See also under opal, p. 408. Flint. Somewhat allied to chalcedony, but more opaque, and of dull colors, usually gray, smoky, brown, and brownish black. The exterior is often whitish, from mixture with lime or chalk, in which it is embedded. Luster barely glistening, subvitreous. Breaks with a deeply conchoidal fracture, and a sharp cutting edge. The flint of the chalk forma- tion consists largely of the remains of diatoms, sponges, and other marine productions. The coloring matter of the common kind is mostly carbonaceous matter. Flint implements play an important part among the relics of early man. Hornstone. Resembles flint, but is more brittle, the fracture more splintery. Chert is a term often applied to hornstone, and to any impure flinty rock, including the jaspers. Basanite; Lydian Stone, or Touchstone. A velvet-black siliceous stone or flinty jasper, used on account of its hardness and black color for trying the purity of the precious metals. The color left on the stone after rubbing the metal across it indicates to the experienced eye the amount of alloy. It is not splintery like hornstone. Jasper. Impure opaque. colored quartz; commonly red, also yellow, dark green and grayish blue. Striped or riband jasper has the colors in broad stripes. Porcelain jasper is nothing but .baked clay, and differs from true jasper in being B.B. fusible on the edges. C. Besides the above there are also: Granular Quartz, Quartz-rock, or Quartzite. A rock consisting of quartz grains very firmly compacted; the grains often hardly distinct. Quartzose Sandstone, Quartz-con* glomerate. A rock made of pebbles of quartz with sand. The pebbles sometimes are jasper and chalcedony, and make a beautiful stone when polished. Itacolumite, or Flexible Sandstone. A friable sand-rock, consisting mainly of quartz-sand, but containing a little mica, and possessing a degree of flexibility when in thin laminae. Buhrstone, or Burrstone. A cellular, flinty rock, having the nature in part of coarse chalcedony. Pseudomorphous Quartz. Quartz appears also under the forms of many of the mineral species, which it has taken through either the alteration or replacement of crystals of those species. The most common quartz pseudomorphs are those of calcite, barite, fluorite, and siderite. Silicified wood is quartz pseudomorph after wood (p. 326). Pyr., etc. B.B. unaltered; with borax dissolves slowly to a clear glass; with soda dissolves with effervescence; unacted upon by salt of phosphorus. Insoluble in hydro- chloric acid, and only slightly acted upon by solutions of fixed caustic alkalies, the crypto- crystalline varieties to the greater extent. Soluble only in hydrofluoric acid. When fused and cooled it becomes opal-silica having G. = 2'2. Diff. Characterized in crystals by the form, glassy luster, and absence of cleavage; also in general by hardness and inf usibility. Micro. Easily recognized in rock sections by its low refraction (" low relief," p. 212) and low birefringence (e - co = 0'009); the interference colors in good sections not rising above yellow of the first order; also by its limpidity and the positive uniaxial cross yielded by basal sections (p. 270, note), which remain dark when revolved between crossed nicols. Commonly in formless grains (granite), also with crystal outline (porphyry, etc.). Obs. Quartz is an essential component of certain igneous rocks, as granite, granite- porphyry quartz-porphyry and rhyolite in the granite group; in such rocks it is com- nonly in tormless grains or masses filling the interstices between the feldspar, as the last product of crystallization. Further it is an essential constituent in quartz-diorite, quartz- diorite porphyry and dacites in the diorite group; in the porphyries frequently in distinct crystals. It occurs also as an accessory in other feldspathic igneous rocks, such as syenite and trachyte. Among the metamorphic rocks it is an essential component of certain varieties of gneiss, of quartzite, etc. It forms the mass of common sandstone. It occurs as the vein-stone m various rocks, and forms a large part of mineral veins; as a foreign min- OXIDES 407 eral in some limestones, etc., making geodes of crystals, or of chalcedony, agate, carnelian, etc.; as embedded nodules or masses in various limestones, constituting the flint of the Chalk formation, the hornstone of other limestones these nodules sometimes becoming con- tinuous layers; as masses of jasper occasionally in limestone. It is the principal material of the pebbles of gravel-beds, and of the sands of the seashore, and sandbeds everywhere. In graphic granite (pegmatite) the quartz individuals are arranged in parallel position in feldspar, the angular particles resembling written characters. The quartz grains in a fragmental sandstone are often found to have undergone a secondary growth by the depo- sition of crystallized silica with like orientation to the original nucleus. From a general study of the chemical and mineralogical character of the rocks of the earth's crust it has been estimated that quartz forms about twelve per cent of their constituents. Switzerland; Dauphine, France; Piedmont, Italy; the Carrara quarries, Italy; and numerous other foreign localities afford fine specimens of rock crystal; also Japan, from which are cut the beautiful crystal spheres, in rare cases up to 6 inches in diameter; also interesting twin crystals from Kai, Japan; Bourg d'Oisans, Dauphine, France. Smoky quartz crystals of great beauty, and often highly complex in form, occur at many points in the central Alps, also at Cairngorm, Scotland. The most beautiful amethysts are brought from India, Ceylon, and Persia, Nova Scotia, Brazil, Guanajuato, Mexico; inferior speci- mens occur in Transylvania. The finest carnelians and agates are found in Arabia, India, Brazil, Uruguay, Surinam, also formerly at Oberstein and Saxony. Scotland affords smaller but handsome specimens (Scotch pebbles). The banks of the Nile afford the Egyptian jasper; the striped jasper is met with in Siberia, Saxony, and Devonshire. In N. Y., quartz crystals are abundant in Herkimer Co., at Middleville, Little Falls, etc., loose in cavities hi the Calciferous sand-rock, or embedded in loose earth. Fine quartzoids, at the beds of hematite in Fowler, Herman, and Edwards, St. Lawrence Co., also at Antwerp, Jefferson Co. On the banks of Laidlaw Lake, Rossie, large implanted crystals; at Ellenville lead mine, Ulster Co., in fine groups. At Paris, Me., handsome crystals of brown or smoky quartz. Beautiful colorless crystals occur at Hot Springs, Ark. Alexander Co., N. C., has afforded great numbers of highly complex crystals, with rare modifications. Fine crystals of smoky quartz come from the granite of the Pike's Peak region, Col. Geodes of quartz crystals, also enclosing calcite, sphalerite, etc., are common in the Keokuk limestone of the west. Rose quartz occurs at Hebron, Albany, Paris, Me. ; Acworth, N. H. ; Southbury, Conn. ; Custer Co., S. D. Amethyst, in trap, at Keweenaw Point, Lake Superior; Specimen Mt., Yellowstone Park; Jefferson Co., Mon.; in Pa., at East Bradford, Chester, and Provi- dence (one fine crystal over 7 Ibs. in weight), in Chester Co.; at the Prince vein, Lake Superior; large crystals, near Greensboro, N. C.; crystallized green quartz, in talc, at Providence, Delaware Co., Pa. Chalcedony and agates abundant and beautiful on north- west shore of Lake Superior. Red jasper is found on Sugar Loaf Mt., Me.; in pebbles on the banks of the Hudson at Troy, N. Y.; yellow, with chalcedony, at Chester, Mass. Agatized and jasperized wood of great beauty and variety of color is obtained from the petrified forest called Chalcedony Park, near Carrizo, Apache Co., Ariz.; also from the Yellowstone Park; near Florissant and elsewhere in Col.; Amethyst Mt., Utah; Napa Co., Cal. Moss agates from Humboldt Co., Nev., and many other points. The word quartz is of German provincial origin. Agate is from the name of the river Achates, in Sicily, whence specimens were brought, as stated by Theophrastus. Use. In its various colored forms as ornamental material; for abrading purposes; manufacture of porcelain, of glass; as wood filler; in paints, scouring soaps, etc.; as sand in mortars and Cements; as quartzite, sandstone, etc., for building stone, etc.; as an acid flux in certain smelting operations. QUARTZINE is a name which has been given to a form of silica which is present in chalcedony and is inferred to be triclinic in crystalline structure. Lutecite belongs here. TRIDYMITE. Hexagonal or pseudo-hexagonal. Axis c = 1*6530. Crystals usually minute, thin tabular || c(0001); often in twins; also united in fan-shaped groups. Cleavage: prismatic, not distinct; parting 1 1 c, sometimes observed. Frac- ture conchoidal. Brittle. H. = 7. G. = 2*28-2*33. Luster vitreous, on c pearly. Colorless to white. Transparent. Optically +. co = 1*477. e = 1'479. Often exhibits anomalous refraction phenomena. 408 DESCRIPTIVE MINERALOGY Comp. Pure silica, SiO 2 , like quartz. Tridymite is formed above 800 C. See further under Quartz, p. 403. Pyr., etc. Like quartz, but soluble in boiling sodium carbonate. Obs. Occurs chiefly in acidic volcanic rocks, rhyolite, trachyte, andesite, liparite, less often in dolerite; usually in cavities, often associated with sanidine, also hornblende, augite, hematite; sometimes in opal. First observed in crevices and druses in an augite- andesite from the Cerro San Cristobal, near Pachuca, Mexico; later proved to be rather generally distributed. Thus in trachyte of the Siebengebirge, Germany; of Euganean Hills in northern Italy; Puy Capucin (Mont-Dore) in Central France, etc. In the ejected masses from Vesuvius consisting chiefly of sanidine. In the lavas of Mt. Etna, Sicily, and Mt. Pelee, Martinique. From Kibosan, Prov. Higo, Japan. With quartz, feldspar, fayalite in lithophyses of Obsidian cliff, Yellowstone Park. In the andesite of Mt. Rainier, Washington. Named from rpiSu/zos, threefold, in allusion to the common occurrence in trillings. ASMANITE. A form of silica found in the meteoric iron of Breitenbach, in. very minute grains, probably identical with tridymite; by some referred to the orthorhombic system. CRISTOBALITE. Christobalite. Silica in white octahedrons (pseudo-isometric?). G. = 2'27. n = 1*486. With tridymite in andesite of the Cerro S. Cristobal, Pachuca, Mexico, Also noted in lava at May en, Germany, and in meteorites. For thermal relations to quartz and tridymite see under quartz, p. 403. MELANOPHLOGITE. In minute cubes and spherical aggregates. Occurring with calcite and celestite implanted upon an incrustation of opaline silica over the sulphur crystals of Girgenti, Sicily. Consists of SiO 2 with 5 to 7 p. c. of S0 3 , perhaps SiO 2 with SiS 2 . The mineral turns black superficially when heated B.B. OPAL. Amorphous. Massive; sometimes small reniform, stalactitic, or large tuberose. Also earthy. H. = 5-5-6-5. G. = 1-9-2-3; when pure 2-1-2-2. Luster vitreous, fre- quently subvitreous; often inclining to resinous, and sometimes to pearly. Color white, yellow, red, brown, green, gray, blue, generally pale; dark colors arise from foreign admixtures; sometimes a rich play of colors, or different colors by refracted and reflected light. Streak white. Transparent to nearly opaque, n = 1-44-1-45. Often shows double refraction similar to that observed in colloidal substances due to tension. The cause of the play of color in the precious opal was investigated by Brewster, who ascribed it to the presence of microscopic cavities. Behrends, however, has given a monograph on the subject (Ber. Ak. Wien, 64 (1), 1871), and has shown that this explana- tion is incorrect; he refers the colors to thin curved lamellae of opal whose refractive power may differ by O'l from that of the mass. These are conceived to have been originally formed in parallel position, but have been changed, bent, and finally cracked and broken in the solidification of the groundmass. Comp. Silica, like quartz, with a varying amount of water, Si0 2 .nH 2 0. The water is sometimes regarded as non-essential. The opal condition is one of lower degrees of hardness and specific gravity, and, as generally believed, of incapability of crystallization. The water present varies from 2 to 13 p. c. or more, but mostly from 3 to 9 p. c. Small quantities of ferric oxide, alumina, lime magnesia, and alkalies are usually present as impurities. Var. Precious Opal Exhibits a play of delicate colors. Fire-opal Hyacinth-red to honey-yellow colors, with fire-like reflections, somewhat insed on turning. Gir'asol. Bluish white, translucent, with reddish reflections in a bright light. Common Opal In part translucent; (a) milk-opal, milk-white to greenish, yellowish, bluish; (6) Resin-opal, wax-, honey- to ocher-yellow, with a resinous luster; (c) dull olive- green and mountain-green ; (d) brick-red. Includes Semiopal; (e) Hydrophane, a variety which becomes more translucent or transparent in water. Cacholong. Opaque, bluish white, porcelain-white, pale yellowish or reddish. Upal-agate. Agate-like in structure, but consisting of opal of different shades of color. Memlite. In concretionary forms; opaque, dull grayish. OXIDES 409 J asp-opal. Opal-jasper. Opal containing some yellow iron oxide and other impurities, and having the color of yellow jasper, with the luster of common opal. Wood-opal. Wood petrified by opal. Hyalite. Muller's Glass. Clear as glass and colorless, constituting globular concre- tions, and crusts with a globular or botryoidal surface; also passing into translucent, and whitish. Less readily dissolved in caustic alkalies than other varieties. Schaumopal. A porous variety from the Virunga district, German East Africa. Fiorite, Siliceous Sinter. Includes translucent to opaque, grayish, whitish or brownish incrustations, porous, to firm in texture; sometimes fibrous-like or filamentous, and, when so, pearly in luster (then called Pearl-sinter)', deposited from the siliceous. waters of hot springs. Geyserite. Constitutes concretionary deposits about the geysers of the Yellowstone Park, Iceland, and New Zealand, s _presenting white or grayish, porous, stalactitic, fila- mentous, cauliflower-like forms, often of great beauty: also compact-massive, and scaly- massive. Float-stone. In light porous concretionary masses, white or grayish, sometimes cavernous, rough in fracture. Tripolite. Formed from the siliceous shells of diatoms (hence called diatomite) and other microscopic species, and occurring in extensive deposits. Includes Infusorial Earth, or Earthy Tripolite, a very fine-grained earth looking often like an earthy chalk, or a clay, but harsh to the feel, and scratching glass when rubbed on it. Pyr., etc. Yields water. B.B. infusible, but becomes opaque. Some yellow vari- eties, containing iron oxide, turn red. Soluble in hydrofluoric acid somewhat more readily than quartz; also soluble in caustic alkalies, but more readily in some varieties than in others. Obs. Occurs filling cavities and fissures or seams in igneous rocks, as trachyte, por- phyry, where it has probably resulted from the action of hot, magmatic waters upon the silicates of the rocks, the liberated silica being deposited in the cavities in the form of opal. Also in some metallic veins. Also embedded, like flint, in limestone, and sometimes, like other quartz concretions, in argillaceous beds; formed from the siliceous waters of some hot springs; often resulting from the mere accumulation, or accumulation and partial solution and solidification, of the siliceous shells of infusoria, of sponge spicules, etc., which consist essentially of opal-silica. The last mentioned is the probable source of the opal of limestones and argillaceous beds (as it is of flint in the same rocks), and of part of that in igneous rocks. It exists in most chalcedony and flint. Precious opal occurs in porphyry at Czerwenitza, near Kashau in Hungary; at Gracias a Dios in Honduras; Queretaro in Mexico; a beautiful blue opal on Bulla Creek, Queens- land; from White Cliffs, New South Wales, as filling openings in sandstone, in fossil wood, in the material of various fossil shells and bones and in aggregates of radiating pseudo- morphic crystals. Fire-opal occurs at Zimapan in Mexico; the Faroe Islands; near San Antonio, Honduras. Gem opal, often of "black opal" type, comes from Humboldt Co., Nev. Common opal is abundant at Telkebanya in Hungary; near Pernstein, etc., in Moravia; in Bohemia; Stenzelberg in Siebengebirge, Germany; in Iceland. Hyalite occurs in amygdaloid at Schemnitz, Hungary; in clinkstone at Waltsch, Bohemia; at San Luis Potosi, Mexico; Kamloops, British Columbia. In the United States, hyalite occurs sparingly in connection with the trap rock of N. J. and Conn. A water-worn specimen of fire-opal has been found on the John Davis river, in Crook Co., Ore. Common opal is found at Cornwall, Lebanon Co., Pa.; at Aquas Calientes, Idaho Springs, Col.; a white variety at Mokelumne Hill, Calaveras Co., Cal., and on the Mt. Diablo range. Geyserite occurs in great abundance and variety in the Yellowstone region (cf. above); also siliceous sinter at Steamboat Springs, Nev. Use. In the colored varieties as a highly prized gem-stone. II. Oxides of the Semi-Metals; also Molybdenum, Tungsten Arsenolite. Arsenic trioxide, As2Os. In isometric octahedrons; in crusts and earthy. Colorless or white. G. = 37. n = 1755. Occurs with arsenical ores. Claudetite. Also As 2 O 3 , but monoclinic in form. In thin plates. Senarmontite. Antimony trioxide. Sb 2 O 3 . In isometric octahedrons; hi crusts and granular massive. G. = 5;3. Colorless, grayish, n = 2 P 087. Occurs with ores of anti- mony. From Algeria; South Ham, Quebec. 410 DESCRIPTIVE MINERALOGY Valentinite. Sb 2 O 3 , in prismatic orthorhombic crystals. Index = 2-34. From South Ham, Quebec. Bismite. Bismuth trioxide, Bi 2 O 3 . Pulverulent, earthy; color straw-yellow. From Goldfield, Nevada, in minute silvery white, pearly scales that are hexagonal, rhombo- hedral; optically . Analyses of a number of so-called bismites show them to be bis- muth hydroxide or other compounds. Tellurite. Tellurium dioxide, TeO 2 . In white to yellow slender prismatic crystals. Molybdite. Molybdenum trioxide, MoO 3 . In capillary tufted forms and earthy. Color straw-yellow. Analyses of molybdic ocher from various localities show it to be not the oxide but a hydrous ferric molybdate, Fe 2 O 3 .3MO3.7H 2 O. Indices, 178-1 '90. Tungstite. Tungsten trioxide, WO 3 . Pulverulent, earthy; color yellow or yellowish green. Indices, 2'09-2'26. Analysis of tungstic ocher from Salmo, B. C., prove it to have the composition WO 3 .H 2 O; perhaps identical with meymacite (a hydrated tungstic oxide from Meymac, Correze, France). Cervantite. Sb 2 O 3 .Sb 2 O 6 . In yellow to white acicular crystals; also massive, pul- verulent. Stibiconite. H 2 Sb 2 O 6 . Massive, compact. Color pale yellow to yellowish white. Index, 1-83. HI. Oxides of the Metals A. ANHYDROUS OXIDES I. Protoxides, R 2 O and RO. H. Sesquioxides, R^Oa. ii in m. Intermediate, RR-A or RO.RgOg, etc. IV. Dioxides, RO 2 . The Anhydrous Oxides include, as shown above, three distinct divisions, the Protoxides, the Sesquioxides and the Dioxides. The remaining Inter- mediate division embraces a number of oxygen compounds which are properly to be regarded chemically as salts of certain acids (aluminates, ferrates, etc.) ; here is included the well-characterized SPINEL GROUP. Among the Protoxides the only distinct group is the PERICLASE GROUP, which includes the rare species Periclase, MgO, Manganosite, MnO, and Bunsenite, NiO. All of these are isometric in crystallization. The Sesquioxides include the well-characterized HEMATITE GROUP, R 2 O 3 , The Dioxides include the prominent RUTILE GROUP, R0 2 . Both of these groups are further defined later. I. 'Protoxides, RaO and RO CUPRITE. Red Copper Ore. Isometric-plagiohedral. Commonly in octahedrons; also in cubes and dodecahedrons, often highly modified. Plagiohedral faces sometimes distinct (see p. 71). At times in capillary crystals. Also massive, granular; some- times earthy. Cleavage: o(lll) interrupted. Fracture conchoidal, uneven. Brittle. H. = 3*5-4. G. = 5'85-6*15. Luster adamantine or submetallic to earthy. Color red, of various shades, particularly cochineal-red, sometimes almost black; occasionally crimson-red by transmitted light. Streak several shades of brownish red, shining. Subtransparent to subtranslucent. Refractive index, n = 2*849. OXIDES 411 Var. 1. Ordinary, (a) Crystallized; commonly in octahedrons, dodecahedrons, cubes, and intermediate forms; the crystals often with a crust of malachite; (6) massive. 2. Capillary; Chalcotrichite. Plush Copper Ore. In cap- illary or acicular crystallizations, which are sometimes cubes elongated in the direction of the cubic axis. 3. Earthy; Tile Ore. Brick-red or reddish brown and earthy, often mixed with red oxide of iron; sometimes nearly black. , Comp. Cuprous oxide, Cu 2 O = Oxygen 11*2, copper 88'8 = 100. Pyr., etc. Unaltered in the closed tube. B.B. hi the forceps fuses and colors the flame emerald-green. On char- coal first blackens, then fuses, and is reduced to metallic copper. With the fluxes gives reactions for copper. Soluble in concentrated hydrochloric acid, and a strong solution when Arizona cooled and diluted with cold water yields a heavy, white precipitate of cuprous chloride. Diff . Distinguished from hematite by inferior hardness, but is harder than cinnabar and proustite and differs from them in the color of "the streak; reactions for copper, B.B., are conclusive. Micro. In polished sections shows white with shining surface, usually pitted. With oblique illumination, transparent deep red. With HNO 3 instantly plated with metallic copper which blackens and dissolves. On drying a thin film of copper remains. With HC1 darkens and is coated with white, seen by oblique light. Obs. Cuprite is a mineral of secondary origin. It is often formed as a furnace prod- uct and has been rioted as a coating upon ancient copper or bronze objects. Occurs at Kamsdorf in Thuringia; in Cornwall, in fine crystals, at Wheal Gorland and other mines; in Devonshire near Tavistock; in isolated crystals, more or less altered to malachite, at Chessy, near Lyons, France; in the Ural Mts.; South Australia; also abundant in Chile, Peru, Bolivia. In the United States observed at Somerville, etc., N. J.; at Cornwall, Lebanon Co., Pa.; in the. Lake Superior region. From Ariz, with malachite, limonite, etc., at the Cop- per Queen mine, Bisbee, sometimes in fine crystals; beautiful chalcotrichite at Morenci; at Clifton, Graham Co., in crystals, and massive. Use. An ore of copper. Ice. H 2 O. Hexagonal. Familiarly known in six-rayed snow crystals; also coating ponds in whiter, further as glaciers and icebergs. Periclase Group Periclase. Magnesia, MgO. In cubes or octahedrons, and in grains. Cleavage cubic'. H. =6. G. = 3'67-3'90. n = 174. Artif. Crystallized from a melt containing magne- sium chloride and silica. Occurs in white limestone at Mte. Somma, Vesuvius; at the Kitteln manganese mine, Nordmark, Sweden. Manganosite Manganese protoxide, MnO. In isometric octahedrons. Cleavage cubic. H. = 5-o. G. = 5'18. n = 2'18. Color emerald-green, becoming black on ex- posure. From Langban and Nordmark, Sweden; Franklin Furnace, N. J. Bunsenite. Nickel protoxide, NiO. In green octahedrons. From Johanngeorgen- stadt, Germany. Cadmium oxide. Isometric. In minute octahedrons. Forms a thin coating of black color and brilliant metallic luster upon calamine from Monte Poni, Sardinia. Also formed artificially. ZINCITE. Red Oxide of Zinc. Hexagonal-hemimprphic. Axis c = 1*5870. Natural crystals rare (Fig. 44, p. 22) ; usually foliated massive, or in coarse particles and grains; also with granular structure. 412 DESCRIPTIVE MINERALOGY Cleavage: c(0001) perfect; prismatic, sometimes distinct. Fracture sub- conchoidal. Brittle. H. = 4-4'5. G. = 5-43-57. Luster subadamantine. Streak orange-yellow. Color deep red, also orange-yellow. Translucent to subtranslucent. Optically +. Comp. Zinc oxide, ZnO = Oxygen 197, zinc 80*3 = 100. Manga- nese protoxide is sometimes present. Pyr., etc. B.B. infusible; with the fluxes, on the platinum wire, gives reactions for manganese, and on charcoal in R.F. gives a coating of zinc oxide, yellow while hot, and white on cooling. The coating, moistened with cobalt solution and treated in O.F., as- sumes a green color. Soluble in acids. Diff. Characterized by its color, particularly that of the streak; by cleavage; by reactions B.B. Artif. Zincite is often formed as a furnace product. It is also produced when zinc chloride and water vapor act upon lime at red heat. Obs. Occurs with franklinite and willemite, at Sterling Hill near Ogdensburg, and at Mine Hill, Franklin Furnace, Sussex Co., N. J., sometimes in -lamellar masses in pink calcite. Has been reported from Poland. A not uncommon furnace product. Use.' An ore of zinc. Massicot. Lead monoxide, PbO. Massive, scaly or earthy. Color yellow, reddish. Probably orthorhombic. Index, 1735. Optically. Tenorite. Cupric oxide, CuO. In minute black scales with metallic luster; from Vesuvius. Also black earthy massive (melaconite) ; occurring with ores of copper as at Ducktown, Tenn., and Keweenaw Point, Lake Superior. Pitchy black material asso- ciated with cuprite, chrysocolla and malachite from Bisbee, Ariz., has been called melano- chaldte. Paramelaconite is essentially cupric oxide, CuO, occurring in black pyramidal crystals referred to the tetragonal system. From the Copper Queen mine, Bisbee, Ariz. Montroydite. HgO. Orthorhombic. In minute highly modified crystals. H. = T5-2. Color and streak orange-red. Index, 2'55. Volatile. Found at Terlingua, Tex. Hematite Group. R 2 3 . Rhombohedral rr' c Corundum A1 2 3 93 56' 1*3630 Hematite Fe 2 O 3 94 0' 1*3656 Ilmenite (Fe,Mg)O.Ti0 2 Tri-rhombohedral 94 29' 1*3846 Pyrophanite MnO.Ti0 2 " 94 5J' 1'3692 The HEMATITE GROUP embraces the sesquioxides of aluminium and iron. These compounds crystallize in the rhombohedral class, hexagonal system, with a fundamental rhombohedron differing but little in angle from a cube. Both the minerals belonging here, Hematite and Corundum, are hard. To these species the titanates of iron (and magnesium) and manganese, Ilmenite and Pyrophanite, are closely related in form though belonging to the tri-rhombohedral class (phenacite type) ; in other words, the relation between hematite and ilmenite may be regarded as analogous to that between calcite and dolomite. It is to be noted, further, that hematite often contains tita- nium, and an artificial isomorphous compound, Ti 2 3 , has been described. Hence the ground for writing the formula of ilmenite (Fe,Ti) 2 O 3 , as is done by some authors. It is shown by Penfield, however, that the formula (Fe,Mg)Ti0 2 is more correct. OXIDES 413 CORUNDUM. Rhombohedral. 694 Axisc = 1-3630. 695 697 cr, 0001 A 1011 = 57 34' en, 0001 A 2243 = 6l 11' rr' 1011 A 1101 = 93 56' nn', 2243 A 2423 = 51 58' w', 4483 A 4843 = 57 38' zz', 2241 A 2421 = 58 55' Twins: tw. pi. r(10ll), sometimes penetration-twins; often polysynthetic, and thus producing a laminated structure. Crystals usually rough and rounded. Also massive, with nearly rectangular parting or pseudo-cleavage; granular, coarse or fine. Parting: c(0001), sometimes perfect, but interrupted; also r(1011) due to twinning, often prominent; a(1120) less distinct. Fracture uneven to conchoidal. Brittle, when compact very tough. H. =9. G. = 3-95-4-10. Luster adamantine to vitreous; on c sometimes pearly. Occasionally show- ing asterism. Color blue, red, yellow, brown, gray, and nearly white; streak uncolored. Pleochroic in deeply colored varieties. Transparent to trans- lucent. Normally uniaxial, negative; for sapphire co = 17676 to 1*7682 and e = 17594 to 17598. Often abnormally biaxial. Var. There are three subdivisions of the species prominently recognized in the arts, but differing only in purity and state of crystallization or structure. VAR. 1. SAPPHIRE, RUBY. Includes the purer kinds of fine colors, transparent to translucent, useful as gems. Stones are named according to their colors: Sapphire blue; true Ruby, or Oriental Ruby, red; Oriental Topaz, yellow; Oriental Emerald, green; Oriental Amethyst, purple. The term sapphire is also often used as a general term to indicate corun- dum gems of any color except red. A variety having a stellate opalescence when viewed in the direction of the vertical axis of the crystal is the Asteriated Sapphire or Star Sapphire. 2. CORUNDUM. Includes the kinds of dark or dull colors and not transparent, colors light blue to gray, brown, and black. The original adamantine spar from India has a dark grayish smoky brown tint, but greenish or bluish by transmitted light, when translucent. 3. EMERY. Includes granular corundum, of black or grayish black color, and contains magnetite or hematite intimately mixed. Sometimes associated with iron spinel or hercy- nite. Feels and looks much like a black fine-grained iron ore, which it was long considered to be. There are gradations from the evenly fine-grained emery to kinds in which the corun- dum is in distinct crystals. Comp. Alumina, A1 2 O 3 = Oxygen 47' 1, aluminium 52'9 = 100. The crystallized varieties are essentially pure; analyses of emery show more or less impurity, chiefly magnetite. Artif . Crystallized corundum has been produced artificially in a number of differ- ent ways. Alumina dissolved in molten sodium sulphide, in a fused mixture of a fluoride and potassium carbonate or in fused lead oxide, will separate out as crystallized corundum. 414 DESCRIPTIVE MINERALOGY Gem material has been produced in this way, colored red, with a chromium salt, or blue by cobalt. Crystallized material can also be produced by fusing alumina in an electric arc. The artificial abrasive, alundum, is made by heating bauxite to 5000-6000 in an electric furnace. Pear-shaped drops of gem material are made by fusing together small fragments of natural or artificial stones. Gems cut from them are known as. "recon- structed " stones and have the crystalline and other physical properties of the natural mineral. Pyr., etc. B.B. unaltered; slowly dissolved in borax and salt of phosphorus to a clear glass, which is colorless when free from iron; not acted upon by soda. The finely pulverized mineral, after long heating with cobalt solution, gives a beautiful blue color. Not acted upon by acids, but converted into a soluble compound by fusion with potassium bisulphate. Diff. Characterized by its hardness (scratching quartz and topaz), by its adaman- tine luster, high specific gravity and infusibility. The massive variety with rhombohedral parting resembles cleavable feldspar but is much harder and denser. Micro, In thin sections appears nearly colorless with high relief and low interfer- ence colors. Obs. Usually occurs in crystalline rocks, as granular limestone or dolomite, gneiss, granite, mica slate, chlorite slate. The associated minerals often include some species of the chlorite group, as prochlorite, corundophilite, margarite, also tourmaline, spinel, cyanite, diaspore, and a series of aluminous minerals, in part produced from its alteration. Occasionally found as an original constituent of igneous rocks containing high percentages of alumina. In the Ural Mts. are found an anorthite rock containing nearly 60 per cent of corundum, a corundum syenite with 18 per cent, and a pegmatite with 35 per cent. A corundum anorthosite and corundum syenites are found in Canada. Important deposits of corundum in North Carolina and Georgia are associated with dunite rocks. Rarely observed as a contact-mineral. The fine sapphires are usually obtained from the beds of rivers, either in modified hexagonal prisms or in rolled masses, accompanied by grains of magnetite, and several kinds of gems, as spinel, etc. The emery of Asia Minor occurs in granular limestone. The best rubies come from the mines in Upper Burma, north of Mandalay, in an area covering 25 to 30 square miles, of which Mogok is the center. The rubies occur in situ in crystalline limestone, also in the soil of the hillsides and in gem-bearing gravels of the Irra- waddy River. Blue sapphires are brought from Ceylon from the Ratnapura and Rakwena districts, often as rolled pebbles, also as well-preserved crystals. Corundum occurs in the Carnatic on the Malabar coast, on the Chantibun hills in Siam, and elsewhere in the East Indies; also near Canton, China; from Naegi, Mino, Japan. At St. Gothard, Switzerland, it occurs of a red or blue tinge in dolomite, and near Mozzo in Piedmont, Italy, in white compact feldspar. Adamantine spar is met with in large, coarse, hexagonal pyramids in Gellivara, Sweden. Other localities are in Bohemia, near Petschau, in Russia, in the Ilmen mountains, not far from Miask and in the gold-washings northeast of Zlatoust. Corundum, sapphires, and less often rubies occur in rolled pebbles in the diamond gravels on the Cudgegong river, at Mudgee and other points in New South Wales. Emery is found in large bowlders at Naxos, Nicaria, and Samos of the Grecian islands ; also in Asia Minor, 12 m. E. of Ephesus, near Gumuchdagh and near Smyrna, associated with margarite, chloritoid, pyrite. -> In North America, in Mass., at Chester, with magnetite, diaspore, ripidolite, 'mar- garite, etc., was mined for use as emery. In Conn, near Litchfield. In N. Y., at Warwick, bluish and pink, with spinel; Amity, in granular limestone; emery with magnetite and green spinel (hercynite) in Westchester Co., near Cruger's Station, and elsewhere. In N. J., at Newton, blue crystals in granular limestone; at Vernon, at Sparta and elsewhere in Sussex Co. In Pa., in Delaware Co., in Aston, near Village Green, in large crystals; at Mineral Hill, in loose crystals; in Chester Co., at Unionville, abundant in crystals; in large crystals loose m the soil at Shimersville, Lehigh Co. In Va., in the mica schists of Bull Mt., Patrick Co. Common at many points along a belt extending from Virginia across western North and South Carolina and Georgia to Dudleyville, Alabama; especially in Madison, Buncombe, Haywood, Jackson, Macon, Clay, and Gaston counties in N. C. The localities at which most work has been done are the Culsagee mine, Corundum hill, near Franklin, Macon Co., ik U ' 1 ! md 26 miles S E. of this, at Laurel Creek, Ga. The corundum occurs in beds in chrysolite (and serpentine) and hornblendic gneiss, associated with a species of the chlorite group, also spinel, etc., and here as elsewhere with many minerals resulting from its altera- tion. Some fine rubies have been found. Fine pink crystals of corundum occur at Hia- OXIDES 415 wassee, Towns Co., Ga. In Col., small blue crystals occur in mica schist near Salida Chaffee Co. Gem sapphires are found near Helena, Mon., in gold-washings and in bars in the Missouri river, especially the Eldorado bar; at Yogo Gulch on the Judith river and at other points in the state. 1 hese latter occur embedded in an igneous dike that cuts through the limestone formation. In Cat, in Los Angeles Co., in the drift of San Francisqueto Pals. In Canada, at Burgess, Ontario, red and blue crystals; in a syenite from Renfrew Co Ontario. Use. Clear varieties of corundum form valuable gem stones as noted above. Also formerly largely used as an abrasive; at present various artificial abrasives are mostlv used instead. * HEMATITE. Rhombohedral. Axis c = 1*3656. cr, 0001 A 1011 = 57 37'. rr', 1011 A 1101 = 94 0'. dd',0112 A 1012 = 64 51'. uu', 10T4 A 1104 = 37 2'. nn', 2243 A 2423 = 51 59'. en, 0001 A 2243 = 61 13'. 700 Twins: tw. pi. (1) c(0001), penetration-twins; (2) r (0112), less common, usually as polysynthetic twin- ning lamellae, producing a fine striation on c(0001), and giv- ing rise to a distinct parting or pseudo-cleavage \\ r(1011). Crystals often thick to thin tabular j \ c, and grouped in paral- lel position or in rosettes;_c faces striated \\ edge c/d (0112) and other forms due to oscillatory combination; also in cube-like rhombohedrons; rhombohedral faces w(1014) horizontally striated and often rounded over in 701 702 703 convex forms. Also columnar to granular, botryoidal, and stalactitic shapes; also lamellar, laminae joined parallel to c, and variously bent, thick or thin; also granular, friable, earthy or compact. Parting: c(0001), due to lamellar structure; also r(1011), caused by twin- ning. Fracture subconchoidal to uneven. Brittle in compact forms; elastic in thin laminae; soft and unctuous in some loosely adherent scaly varieties. H. = 5'5-6'5. G. = 4'9-5'3; of crystals mostly 5'20-5'25; of some compact varieties, as low as 4'2. Luster metallic and occasionally splendent; some- times dull. Color dark steel-gray or iron-black; in very thin particles blood- red by transmitted light; when earthy, red. Streak cherry-red or reddish brown. Opaque, except when in very thin laminae. Var. 1. Specular. Luster metallic, and crystals often splendent, whence the name specular iron. When the structure is foliated or micaceous, the ore is called micaceous hematite: some of the micaceous varieties are soft and unctuous. Some varieties are magnetic, but probably from admixed magnetite (Arts. 441, 443). 416 DESCRIPTIVE MINERALOGY 2. Compact Columnar; or fibrous. The masses often long radiating; luster submetallic to metallic; color brownish red to iron-black. Sometimes called red hematite, to contrast it with limonite and turgite. Often in reniform masses with smooth fracture, called kidney ore. 3. Red Ocherous. Red and earthy. Reddle and red chalk are red ocher, mixed with more or less clay. 4. Clay Iron-stone; Argillaceous hematite. Hard, brownish black to reddish brown, often in part deep red; of submetallic to nonmetallic luster; and affording, like all the preceding, a red streak. It consists of oxide of iron with clay or sand, and sometimes other impurities. Comp. Iron sesquioxide, Fe 2 3 = Oxygen 30, iron 70 = 100. Some- times contains titanium and magnesium, and is thus closely related to ilmenite, p. 417. Pyr., etc. B.B. infusible; on charcoal in R.F. becomes magnetic; with borax gives the iron reactions. With soda on charcoal in R.F. is reduced to a gray magnetic powder. Slowly soluble in hydrochloric acid. Diff. Distinguished from magnetite by its red streak, also from limonite by the same means, as well as by its not containing water: from turgite by its greater hardness and by not decrepitating B.B. It is hard in all but some micaceous varieties (hence easily dis- tinguished from the black sulphides); also infusible, and B.B. becomes strongly magnetic. Micro. In polished sections shows white color with a shining, pitted surface. Un- affected by reagents. Artif . Crystals of hematite have been made by decomposing ferric chloride by steam at a high temperature; also by the action of heated air and hydrochloric acid upon iron. Hematite has been crystallized from various artificial magmas, which must contain little or no ferrous iron. Obs. This ore occurs in rocks of all ages. The specular variety is mostly confined to crystalline or metamorphic rocks, but is also a result of igneous action about some vol- canoes, as at Vesuvius. Many of the geological formations contain the argillaceous variety or clay iron-stone, which is mostly a marsh-formation, or a deposit over the bottom of shallow, stagnant water; but this kind of clay iron-stone (that giving a red powder) is less common than the corresponding variety of limonite. The beds that occur in meta- morphic rocks are sometimes of very great thickness, and, like those of magnetite in the same situation, have resulted from the alteration of stratified beds of ore, originally of marsh origin, which were formed at the same time with the enclosing rocks, and underwent metamorphism, or a change to the crystalline condition, at the same time. Beautiful crystallizations of this species are brought from the island of Elba, which has afforded it from a very remote period; the surfaces of the crystals often present an irised tarnish and brilliant luster. St. Gothard in Switzerland affords beautiful specimens, com- posed of crystallized tables grouped in the form of rosettes; near Limoges, France, in large crystals; fine crystals are the result of volcanic action at Etna and Vesuvius. Arendal in Norway, Langban and Nordmark in Sweden; Dognacska, Hungary; Framont in Lorraine, Dauphine, France; Binnental and Tavetsch, Switzerland; also Cleator Moor in Cumber- land, and Minas Geraes, Brazil, afford splendid specimens. Crystals from Ascension Island and from Cernero do Campo, Brazil. Red hematite occurs in reniform masses of a fibrous concentric structure, near Ulverstone in Lancashire, in Saxony, Bohemia, and the Harz Mts., Germany. In North America, widely distributed, and sometimes in beds of vast thickness in rocks of the Archaean age. Very extensive and important hematite deposits are found along the southern and northwestern shores of Lake Superior. The various districts are known as ranges and are located as follows : The Marquette and Menominee Ranges in northern Mich., the Penokee-Gogebic Range in Northern Wis., the Mesabi, Vermilion and Cuyuna Ranges in Minn. Another district, the Michipico en, is farther north in Canada. The ore bodies are the results of the concentration in favorable localities of the iron content of the original sedimentary rocks. These rocks contained cherty iron carbonates, pyrite-bearmg iron carbonates and ferrous silicates. The ore bodies vary widely in form, many of them lying in trough-like structures formed by the deformation of an impervious rock strata. The character of the ores varies from hard specular hematites to soft earthy ores. The latter are often mined by the use of steam shovels. Hematite is found in Wyoming in schist formations in Lararnie and Carbon Counties. In N. Y., in Oneida, Herkimer, Madison, Wayne Cos., a lenticular argillaceous variety, constituting one or two beds in the Clinton group of the Upper Silurian; the same in Pa., and as far south as Ala., and in Canada, and Wis., to the west; in Ala. there are extensive OXIDES 417 beds; prominent mines are near Birmingham. Besides these regions of enormous beds, there are numerous others of workable value, either crystallized or argillaceous. Some of these localities, interesting for their specimens, are in northern N. Y., at Gouverneur, Antwerp, Hermon, Edwards, Fowler, Canton, etc.; Woodstock and Aroostoqk, Me.; at Hawley, Mass., a micaceous variety; in N. and S. C. a micaceou variety in schistose rocks, constituting the so-called specular schist, or itabirite. Hematite is mined in Nova Scotia and Newfoundland. Named hematite from cu^a, blood. Use. The most important iron ore. Used also in red paints, as polishing rouge, etc. MARTITE. Iron sesquioxide under an isometric form, occurring in octahedrons or dodecahedrons like magnetite, and believed to be pseudomorphous after magnetite; perhaps in part also after pyrite. Parting octahedral like magnetite. Fracture conchoidal. H. = 6^7. G. = 4 '8-5*3. Luster submetallic. Color iron-black, sometimes with a bronzed tar- nish. Streak reddish brown or purplish brown. Not magnetic, or only feebly so. The crystals are sometimes embedded in the massive sesquioxide. They are distinguished from magnetite by the red streak, and very feeble, if any, action on the magnetic needle. Found in the Marquette iron region south of Lake Superior, where crystals are common in the ore; Monroe, N. Y.; Twin Peaks, Milliard Co., Utah; Digby Co., N. S.; at the Cerro de Mer- cado, Durango, Mexico, in large octahedrons; in the schists of Minas Gera s, Brazil; near Rittersgriin, Saxony. ILMENITE or MENACCANITE. Titanic Iron Ore. Tri-rhombohedral; Axis c = 1'3846. cr, 0001 A 1011 = 57 58*'. rr', 1011 A TlOl = 94 29'. en, 0001 A 2243 = 61 33'. Crystals usually thick tabular; also acute rhombohedral. Often in thin plates or laminae. Massive, compact ; in embedded grains, 704 705 also loose as sand. Fracture conchoidal. H. - 5-6. G. = 4-5-5. Luster submetallic. Color iron-black. Streak submetallic, powder black to brownish red. Opaque. Influences slightly the magnetic needle. Comp. If normal, FeTi0 3 or FeO,Ti0 2 = Oxygen 31-6, titanium 31-6, iron 36 *8 = 100. Sometimes written (Fe,Ti) 2 O 3 , but probably to be regarded as an iron titanate. Sometimes also contains magnesium (picrotitanite) , replacing the ferrous iron; hence the general formula (Fe,Mg)O.Ti02 (Pen- field). (Compare geikielite, p. 586.) Pyr., etc. B.B. infusible in O.F., although slightly rounded on the edges in R.F. With borax and salt of phosphorus reacts for iron in O.F., and with the latter flux assumes a more or less intense brownish red color in R.F.; this treated with tin on charcoal changes to a violet-red color when the amount of titanium is not too small. The pulverized mineral, heated with hydrochloric acid, is slowly dissolved to a yellow solution, which, filtered from the undecomposed mineral and boiled with the addition of tin-foil, assumes a beautiful blue or violet color. Decomposed by fusion with bisulphate of sodium or potassium. Diff. Resembles hematite, but has a submetallic, nearly black, streak; not magnetic like magnetite. Obs. Occurs, as an accessory component, in many igneous rocks in grams, assuming the place of magnetite, especially in gabbros and diorites. In these occurrences, it is often found in veins or large segregated masses near the borders of the igneous rock where it is supposed to have formed by local differentiation or fractional crystallization in the molten mass. It is also found at tunes in metamorphic rocks. Some principal European localities are St. Cristophe, Dauphine, France (cricktonite) ; Miask in the Ilmen Mts. (ilmenite)} in 418 DESCRIPTIVE MINERALOGY th'e form of sand at Menaccan, Cornwall (menaccanite) ; Gastein in Tyrol (kibdelophane) ; Binnental, Switzerland. One of the most remarkable is at Kragero, Norway, where it occurs in veins or bed 3 in diorite, which sometimes afford crystals weighing over 16 pounds. Others are Egersund, Arendal, Snarum in Norway; St. Gothard, Switzerland, etc. Fine crystals, sometimes an inch in diameter, occur in Warwick, Amity, and Monroe, Orange Co., N. Y.; Litchfield, Conn, (washingtonite) . Crystals from Chester and Quincy, Mass. Vast deposits or beds of titanic ore occur at Bay St. Paul in Quebec, Canada, in tyenite; also in the Seignory of St. Francis, Beauce Co. Grains are found in the gold sand of California. The titanic iron of massive rocks is extensively altered to a dull white opaque substance, called leucoxene by Gumbel. This for the most part is to be identified with titanite. Senaite. (Fe,Mn,Pb)O.TiO 2 . Tri-rhombohedral. H. =6. G. = 5'3. Color black. Streak brownish, black. Found in the diamond-bearing sands of Diamantina, Brazil. Arizonite. Fe 2 O 3 .3TiO 2 . Monoclinic? Crystal faces rough. H. = 5'5. G. = 4'25. Color dark steel-gray. Streak brown. Decomposed by hot concentrated sulphuric acid. Found with gadolinite, 25 miles southeast of Hackberry, Ariz. Pyrophanite. Manganese titanate, MnTiOa. In thin tabular rhombohedral crystals and scales, near ilmenite in form (p. 417). H. = t 5. G. = 4'537. Luster vitreous to sub- metallic. Color deep blood-red. Streak ocher-yellow. From the Harstig mine, Pajsberg, Sweden. SITAPARITE. 9Mn2O 3 .4Fe 2 O3.MnO2.3CaO. Notary stallized. Good cleavage. H. == 7. G. = 5*0. Color deep bronze. Streak black. Weakly magnetic. Found at Sitapdr, District Chhindwara, India. VREDENBURGITE. 3Mn 3 O 4 .2Fe 2 O 3 . Cleavage parallel to octahedron or tetragonal pyramid. H. = 6 - 5. G. = 4 '8. Color bronze to dark steel-gray. Streak dark brown. Strongly magnetic. Completely soluble in acids. Found at Beldongri, District Ndgpur and at Gravidi, District Vizagapatam, India. III. Intermediate Oxides The species here included are retained among the oxides, although chem- ically considered they are properly oxygen-salts, aluminates, ferrates, manga- nates, etc., and hence in a strict classification to be placed in section 5 of the Oxygen-salts. The one well-characterized group is the Spinel Group. ii in ii in Spinel Group. RR 2 4 or RO.R 2 O 3 . Isometric Spinel MgO.Al 2 O 3 Ceylomte (Mg,Fe)O.Al 2 O 3 Chlorospinel MgO. (Al,Fe) 2 O 3 Picotite (Mg,Fe)0.(Al,Cr) 2 3 Hercynite FeO.Al 2 O 3 Gahnite (Automolite) ZnO.Al 2 O 3 Dysluite (Zn,Fe,Mn)0.(Al,Fe) 2 O 3 Kreittonite (Zn,Fe,Mg)0.(Al,Fe) 2 O 3 Magnetite FeO.Fe 2 O 3 (Fe,Mg)O.Fe 2 3 Magnesioferrite MgO.Fe 2 O 3 Franklinite (Fe,Zn,Mn)O.(Fe,Mn) 2 O 3 Jacobsite (Mn,Mg)O.(Fe,Mn) 2 O 3 Chromite FeO.Cr 2 3 (Fe,Mg)0.(Cr,Fe) 2 3 OXIDES 419 The species of the Spinel Group are characterized by isometric crystalli- sation, and, further, the octahedron is throughout the common form. All of the species are hard; those with nonmetallic luster up to 7*5-8, the others from 5*5 to 6*5. SPINEL. Isometric. Usually in octahedrons, sometimes with dodecahedral trunca- tions, .rarely cubic. Twins: tw. pi. and comp. face o(lll) common (Fig. 707), hence often called spinel-twins; also repeated and polysynthetic, pro- ducing tw. lamellae. Fracture conchoidal. Brittle. H. = 8. 706 707 Cleavage: o(lll) imperfect. G. = 3'5-4'L Luster vitreous; splendent to nearly dull. Color red of various shades, passing into blue, green, yellow, brown and black; occasionally almost white. Streak white. Transparent to nearly opaque. Refractive index : n= 17155. Comp. Magnesium alumin- ate, MgAl 2 O 4 or MgO.Al 2 O 3 = Alumina 71*8, magnesia 28*2 = 100. The magnesium may be in part replaced by ferrous iron or man- ganese, and the aluminium by ferric iron and chromium. . Var. RUBY SPINEL or Magnesia Spinel. Clear red or reddish; transparent to translucent; sometimes subtranslucent. G. = 3 '63-3 71. Compo ition normal, with little or no iron, and sometimes chromium oxide to which the red color has been ascribed. The varieties are: (a) Spinel-Ruby, deep red; b) Balas-Ruby, rose-red; (c) Rubicette, yellow or orange^red; (d) Almandine, violet. CEYLONITE or Pleonaste, Iron-Magnesia Spinel. Color dark green, brown to black, mostly opaque or nearly so. G. = 3 '5-3 '6. Contains iron replacing the magnesium and perhaps also the aluminium, hence the formula (Mg,Fe)O.Al2C>3 or (Mg,Fe)O.(Al,Fe)2O 3 . CHLOROSPINEL or Magnesia-Iron Spinel. Color grass green, owing to the presence of copper. G. = 3'591-3*594. Contains iron replacing the aluminium, MgO.(Al,Fe 3 O 3 . PICOTITE or Chrome-Spinel. Contains chromium and also has the magnesium largely repla ed by iron (Mg,Fe)O.(Al,Cr) 2 O 3 , hence lying be ween spinel prope and chromite. G. = 4 '08. Color dark yellowish brown or greenish brown Translucent to nearly opaque. Pyr., etc. B.B. alone infusible. Slowly soluble in borax, more readily in salt of phosphorus, with which it gives a reddish bead while hot, becoming faint chrome-green on cooling. Black varieties give reactions for iron with the fluxes. Soluble with difficulty in concentrated sulphuric acid. Decomposed by fusion with potassium bisulphate. Diff. Distinguished by its octahedral form, hardness, and inf usibility ; zircon Jias a higher specific gravity; the true ruby (p. 413) is harder and is distinguished optically; garnet is softer and fusible. Micro. In thin section shows light color and high relief. Isotropic. Artif . Artificial spinel crystals may be obtained by direct crystallization from the pure melt fused in the electric arc. They also form from melts of the oxides or fluorides of magnesium and aluminium dissolved in boric acid. The addition of chromium and iron oxides will produce various colors. Obs. Spinel occurs embedded in granular limestone, and with calcite hi serpentine, gneiss, and allied rocks. Ruby spinel is a common associate of the true ruby. Common spinel is often associated with chondrodite. It also occupies the cavities of masses ejected from some volcanoes. Spinel (common spinel, also picotite and chromite, occurs as an accessory constituent in many basic igneous rocks especially those of the peridotite group; it is the result of the crystallization of a magma very low in silica, high in magnesia and con- taining alumina; since, as in many of the peridotites alkalies are absent, feldspars cannot form, and the A1 2 O 3 and Cr 2 Os (also Fe 2 O 3 perhaps) are compelled to form spinel (or corun- dum). The serpentines which yield spinel are altered peridotites. 420 DESCRIPTIVE MINERALOGY In Ceylon, in Siam, and other eastern countries, occurs with beautiful colors, as rolled pebbles; in upper Burma with the ruby (cf. p. 414)* Plepnaste is found at Candy, in Ceylon; at Aker, in Sweden, a pale blue and pearl-gray variety in limestone; small black splendent crystals occur in the ancient ejected masses of Monte Somma, Vesuvius; also at Pargas, Finland, with chondrodite, etc.; in compact gehlenite at Monzoni, in the Fassa valley, Austria. From Amity, N. Y., to Andover, N. J., a distance of about 30 miles, is a region of gran- ular limestone and serpentine, in which localities of spinel abound; colors, green, black, brown, and less commonly red, along with chondrodite and other minerals. Localities are numerous about Warwick, and also at Monroe and Cornwall; Gouverneur, 2 m. N. and f m. W. of Somerville, St. Lawrence Co.; green, blue, and occasionally red varieties occur at Bolton, Boxborough, etc., Mass. Franklin, N. J., affords crystals of various shades of black, blue, green, and red: Newton, Sterling, Sparta, Hamburgh and Vernon, N. J., are other localities. With the corundum of N. C. as at the Culsagee mine, near Franklin, Macon Co.; similarly at Dudleyville, Ala. Spinel ruby at Gold Bluff, Humboldt Co., Cal. Good black spinel is found in Burgess, Ontario; a bluish spinel having a rough cubic form occurs at Wakefield, Ottawa Co.; blue with clintonite at Daillebout, Joliette Co., Quebec. Use. The colored transparent varieties are used as gems. . Hercynite. Iron Spinel, FeAl 2 O 4 . Isometric; massive, fine granular. H. = 7-5-8. G. = 3 '9 1-3 '95. Color black. From Ronsberg, at the eastern foot of the Bohmerwald, Bohemia. A related iron-alumina spinel, with about 9 p. c. MgO, occurs with magnetite and corundum in Cortlandt township, Westchester Co., N. Y. From the tin drift, Moorina, Tasmania. GAHNITE. Zinc-Spinel. Isometric. Habit octahedral, often with faces striated || edge between dodecahedron and octahedron; also less commonly in dodecahedrons and modified cubes.- Twins: tw. pi. 0(111). Cleavage: o(lll) indistinct. Fracture conchoidal to uneven. Brittle. H. = 7-5-8. G. = 4-0-4-6. n gr = 1'82 (Finland). Luster vitreous, or some- what greasy. Color dark green, grayish green, deep leek-green, greenish black, bluish black, yellowish, or grayish brown; streak grayish. Subtrans- parent to nearly opaque. Comp. Zinc aluminate, ZnAl 2 4 = Alumina 55-7, zinc oxide 44-3 = 100. The zinc is sometimes replaced by manganese or ferrous iron, the aluminium by ferric iron. Var. AUTOMOLITE, or Zinc Gahnite. ZnAl 2 O 4 , with sometimes a little iron. G. = 4-1-4 '6. Colors as above given. DYSLUITE, or Zinc-Manganese-Iron Gahnite. (Zn,Fe,Mn)O.(Al,Fe) 2 O 3 . Color yellow- ish brown or grayish brown. G. = 4-4*6. KREITTONITE, or Zinc-Iron Gahnite. (Zn,Fe,Mg)O.(Al,Fe) 2 O 3 . In crystals, and granular massive. H. = 7-8. G. = 4 '48-4 '89. Color velvet-black to greenish black; powder grayish green. Opaque. Pyr., etc. Gives a coating of zinc oxide when treated with a mixture of borax and soda on charcoal; otherwise like spinel. Obs. Occurs at Falun and Farila parish, Helsingland, Sweden (automolite) ; Trask- bole, Finland; at Tiriola, Calabria, Italy; at Bodenmais, Bavaria (kreittonite) ', Minas Geraes, Brazil; Ambatofisikely, Madagascar. In the United States, at Franklin Furnace, N. J., with franklinite and willemite; also at Sterling Hill, N. J. (dysluite); with pyrite at Rowe, Mass.; at a feldspar quarry in Delaware Co., Pa.; sparingly at the Deake mica mine, Mitchell Co., N. C.; at the Canton Mine, Ga.; with galena, chalcopyrite, pyrite at the Cotopaxi mine, Chaffee Co., Col. In Canada at Raglan, Renfrew Co., Ontario. Named after the Swedish chemist Gahn. The name Automolite, of Ekeberg, is from , a deserter, alluding to the fact of the zinc occurring in an unexpected place. MAGNETITE. Magnetic Iron Ore. Isometric. Most commonly in octahedrons, also in dodecahedrons with faces striated || edge between dodecahedron and octahedron (Fig. 710); in dendrites between plates of mica; crystals sometimes highly modified; cubic OXIDES 421 forms rare. Twins: tw. pi. o(lll), sometimes as polysynthetic twinning lamellae, producing striations on an octahedral face and often a pseudo-cleav- 708 709 710 age (Fig. 474, p. 176). Massive with laminated structure; granular, coarse or fine; impalpable. Cleavage not distinct; parting octahedral, often highly developed. Frac- ture subconchoidal to uneven. Brittle. H. = 5 '5-6*5. G. = 5-168-5-180, crystals. Luster metallic and 711 splendent to submetallic and rather dull. Color iron- black. Streak black. Opaque, but in thin dendrites in mica nearly transparent and pale brown to black. Strongly magnetic; sometimes possessing polarity (lodestone) . ii in Comp. FeFe 2 O 4 or FeO.Fe 2 O 3 = Iron sesquioxide 69.0, iron protoxide 31 '0 = 100; or, Oxygen 27-6, iron 72 '4 = 100. The ferrous iron sometimes replaced by magnesium, and rarely nickel; also sometimes contains titanium (up to 6 p. c. TiO 2 ). Var. Ordinary. (a) In crystals. (&) Massive, with pseudo-cleavage, also granular, coarse or fine, (c) As loose sand, (d) Ocherous: a black earthy kind. Ordinary magne- tite is attracted by a magnet but has no power 6f attracting particles of iron itself. The property of polarity which distinguishes the lodestone (less properly written loadstone) is exceptional. Magnesian. G. = 4-41-4*42; luster submetallic; weak magnetic; in crystals from Sparta, N. J., and elsewhere. Manganesian. Containing 3'8 to 6 '3 p. c. manganese (Manganmagnetite). From Vester Silfberg, Sweden. Pyr., etc. B.B. very difficultly fusible. In O.F. loses its influence on the magnet. With the fluxes reacts like hematite. Soluble in hydrochloric acid and solution reacts for both ferrous and ferric iron. Diff. Distinguished from other members of the spinel group, as also from garnet, by its being attracted by the magnet, as well as by its high specific gravity; franklinite and chromite are only feebly magnetic (if at all), and have a brown or blackish brown streak; also, when massive, by its black streak from hematite and limonite; much harder than tetrahedrite. Micro. In polished sections shows white color with a shining, pitted surface.. With cone. HC1 slowly turns brown. Artif. Magnetite is frequently formed as a furnace product. It is easily formed in artificial magmas when they are low in the percentage of silica. It is formed by the breaking down of various minerals or by interreactions among minerals in processes simi- lar to those of contact metamorphism. Obs. Magnetite is mostly confined to crystalline rocks, and is most abundant in metamorphic rocks, though widely distributed also in grainy in eruptive rocks. It is found most abundantly in the ferro-magnesian rocks, occurring at times in large segregated 422 DESCRIPTIVE MINERALOGY masses. These are often highly titaniferous. In the Archaean rocks the beds are of im- mense extent, and occur under the same conditions as those of hematite. It is an ingre- dient in most of the massive variety of corundum called emery. The earthy magnetite is found in bogs like bog-iron ore.- Occurs in meteorites, and forms the crust of meteoric irons. Present in dendrite-like forms in the mica of many localities following the direction of the lines of the percussion-figure, and perhaps of secondary origin. A common alteration- product of minerals containing iron protoxide, e.g., present in veins in the serpentine resulting from altered chrysolite. The beds of ore at Arendal, Norway, and nearly all the celebrated iron mines of Sweden, consist of massive magnetite, as at Dannemora and the Taberg in Smaland. Falun, in Sweden, and Corsica, afford octahedral crystals, embedded in chlorite slate. Splendid dodecahedral crystals occur at Nordmark in Wermland. The most powerful native magnets are found in Siberia, and in the Harz Mts., Germany; they are also obtained on the island of Elba. Other localities for the crystallized mineral are Traversella in Piedmont, Italy; Achmatoysk in the Ural Mts.; Scalotta, near Predazzo, at Rothenkopf and Wild- kreuzjoch, Austrian Tyrol; the Binnental, Switzerland; Sannatake, Bufen, Japan. In North America, it constitutes vast beds in the Archaean, in the Adirondack region, Warren, Essex, and Clinton Cos., in Northern N. Y., while in St. Lawrence Co. the iron ore is mainly hematite; fine crystals and masses showing" broad parting surfaces and yield- ing large pseudo-crystals are obtained at Port Henry, Essex Co.; similarly in N J.; in Canada, in Hull, Greenville, Madoc, etc.; at Cornwall in Pa., and Magnet Cove, Ark. It occurs also in N. Y., in Saratoga, Herkimer, Orange, and Putnam Cos.; at the Tilly Foster iron mine, Brewster, Putnam Co., in crystals and massive accompanied by chondrodite, etc. In N. J., at Hamburg, near Franklin Furnace and elsewhere. In Pa., at Goshen, Chester Co., and at the French Creek mines; delineations forming hexagonal figures in mica at Pennsbury. Good lodestones are obtained at Magnet Cove, Ark. In Cal., in Sierra Co., abundant, massive, and in crystals; in Plumas Co.; and elsewhere. In Wash., in large deposits. In crystals from Millard Co., Utah. Fine crystals from Fiqrmeza, Cuba. Named from the loc. Magnesia bordering on Macedonia. But Pliny favors Nicander's derivation from Magnes, who first discovered it, as the fable runs, by finding, on taking his herds to pasture, that the nails of his shoes and the iron ferrule of his staff adhered to the ground. Use. An important ore of iron. FRANKLINITE. Isometric. Habit octahedral; edges often rounded, and crystals passing into rounded grains. Massive, granular, coarse or fine to compact. Pseudo-cleavage, or parting, octahedral, as in magnetite. Fracture con- choidal to uneven. Brittle. H. = 5'5-6'5. G. = 5-07-5-22. Luster metallic, sometimes dull. Color iron-black. Streak reddish brown or black. Opaque. Slightly magnetic. Comp. (Fe,Zn,Mn)O.(Fe,Mn) 2 O 3 , but varying rather widely in the relative quantities of the different metals present, while conforming to the general formula of the spinel group. Pyr., etc. B.B. infusible. With borax in O.F. gives a reddish amethystine bead (manganese), and in R.F. this becomes bottle-green (iron). With soda gives a bluish green manganate, and on charcoal a faint coating of zinc oxide, which is much more marked when a mixture with borax and soda is used. Soluble in hydrochloric acid, sometimes with evolution of a small amount of chlorine. Diff. Resembles magnetite, but is only slightly attracted by the magnet, and has a dark brown streak; it also reacts for zinc on charcoal B.B. bs> T"* 1 ^ ( ^ erman y occurs in cubic crystals near Eibach in Nassau; in amorphous masses at Altenberg, near Aix-la-Chapelle. Abundant at Mine Hill, Franklin Furnace JN. J., with wulemite and zmcite in granular limestone; also at Sterling Hill, two miles distant, associated with willemite. Use. An ore of zinc. *;' Ma g nof ernte. MgFe ? O 4 . In octahedrons. H. = 6-6'5 G. = H4t>54. Luster color, and streak as in magnetite. Strongly magnetic. Formed about the fumaroles of Vesuvius-, and especially those of the eruption of 1855; also found at iviont jJor OXIDES 423 Jacobsite. (Mn,Mg)O.(Fe,Mn) 2 O 3 . Isometric; in distorted octahedrons. H. = 6. Color deep black. Magnetic. _ From Jakobsberg, in Nordmark, Wermland, G. = 475. and at Langban, Sweden. Reported from Bulgaria. CHROMITE. Isometric. In octahedrons. Commonly massive; fine granular to compact. Fracture uneven. Brittle. H. = 5-5. G. = 4-32-4-57. Luster sub- metallic to metallic. Color between iron-black and brownish black, but sometimes yellowish red in very thin sections. Streak brown. Translucent to opaque. Sometimes feebly magnetic. Comp. FeCr 2 O 4 or FeO.Cr 2 O 3 = Chromium sesquioxide 68'0, iron protoxide 32-0 = 100. The iron may be replaced by magnesium; also the chromium by alu- minium and ferric iron. The varieties containing but little chromium (up to 10 p. c.) are hardly more than varieties of spinel and are classed under picotite, p. 419. Pyr., etc. B.B. in O.F. infusible; in R.F. slightly rounded on the edges, and becomes magnetic. With borax and salt of phosphorus gives beads which, while hot, show only a reaction for iron, but on cooling become chrome-greeny the green color is heightened by fusion on charcoal with metallic tin. Not acted upon by acids, but decomposed by fusion with potassium or sodium bisulphate. Diff. Distinguished from magnetite by feeble magnetic properties, streak and by yielding the reaction for chromic acid with the blowpipe. Artif. Chromite can be prepared artificially by fusing together chromic, ferric and boric oxides. Obs. Occurs in peridotite rocks and the serpentines derived from them, forming veins, or in embedded masses. It is one of the earliest minerals to crystallize in a cooling magma and its large ore bodies are probably formed during the solidification of the rock by the process of magmatic differentiation. It assists in giving the variegated color to verde-antique marble. Not uncommon in meteoric irons, sometimes in nodules as in the Coahuila iron, less often in crystals (Lodran). Occurs in the Gulsen mountains, near Kraubat in Styria; in crystals in the islands of Unst and Fetlar, in Shetland; in the province of Trondhjem in Norway; in the Department du Var in France; in Silesia and Bohemia; abundant in Asia Minor; in the Eastern and Western Ural Mts.; in New Caledonia, affording ore for commerce. In Md. at Baltimore, in the Bare Hills, in veins or masses in serpentine; also in Mont- gomery Co., etc. In Pa., Chester Co., near Unionville, abundant; at Wood's Mine, near Texas, Lancaster Co., very abundant. Massive and in crystals at Hoboken, N. J., in ser- pentine and dolomite. In various localities in N. C. In the southwestern part of the town of New Fane, etc., Vt. A magnesian variety (mitchellite) from Webster, N. C. In Cal., in Monterey Co.; 'also Santa Clara Co., near the New Almaden mine. Use. An ore of chromium; used in refractory bricks for metallurgical furnace linings; as source of certain red and yellow pigments and dyes. CHROMITITE. Material in minute octahedral crystals occurring in sand at Zeljin Mt., Servia, said to have composition, FeCrO 3 . 712 .. CHRYSOBERYL. Cymophane. Orthorhombic. Axes a : b : c = 0-4701 1:1: 0-5800. mm'", 110 A 110 = 50 21'. ss', 120 A 120 = 93 32'. XX', 101 A 101 = 101 57'. ii'J Oil A Oil = 60 14'. PP', 031 A 031 = 120 14'. 00', 111 A Til = 93 44'. oo'", 111 A 111 = 40 7'. nn' t 121 A 121 = 77 43'. Twins: tw. pi. p(031), both contact- and penetration-twins; often re- peated and forming pseudo-hexagonal crystals with or without re-entrant 424 DESCRIPTIVE MINERALOGY angles (Fig. 395, p. 164) . Crystals generally tabular 1 1 a(100) . Face a striated vertically, in twins a feather-like striation (Fig. 713). Cleavage: "(QH) quite distinct; 6(010) imperfect; a(100) more so. Frac- ture uneven to conchoidal. Brittle. H. = 8-5. G. = 3'5-3'84. Luster vitreous. Color asparagus-green, grass-green, emerald-green, greenish white, and yellowish green; greenish brown; yellow; sometimes raspberry- or colum- bine-red by transmitted light. Streak uncolored. Transparent to trans- lucent. Sometimes a bluish opalescence or chatoyancy, and asteriated. Pleochroic, vibrations || Y (= b axis) orange-yellow, Z (= c axis) emerald- green, X ( = a axis) columbine-red. Optically +. Ax. pi. || 6(010). Bx. _L c(001). a = 1747. = 1748. 7 = 1'757. 2E = 84 43'. Var. 1. Ordinary. Color pale green, being colored by iron; also yellow and trans- parent and then used as a gem. 2. Alexandrite. Color emerald-green, but columbine-red by transmitted light; valued as a gem. G. = 3 '644, mean of results, ^upposed to be colored by chromium. Crystals often very large, and in twins, like Fig. 395, either six-sided or six-rayed. 3. Cat's-eye. Color greenish and exhibiting a fine chatoyant effect; from Ceylon. Comp. Beryllium aluminate, BeAl 2 O 4 or BeO.Al 2 3 = Alumina 80'2, glucina 19 '8 = 100. Pyr., etc. B.B. alone unaltered; with soda, the surface is merely rendered dull. With borax or salt of phosphorus fuses with great difficulty. Ignited with cobalt solu- tion, the powdered mineral gives a bluish color. Not attacked by acids. Diff. Distinguished by its extreme hardness, greater than that of topaz; by its in- fusibility; also characterized by its tabular crystallization, in contrast with beryl. Obs. In Minas Geraes, Brazil, in rolled pebbles; from Ceylon in pebbles and crystals; at Marschendorf in Moravia; in the Ural Mts., 85 yersts from Ekaterinburg, in mica slate with beryl and phenacite, the variety alexandrite; in the Orenburg district, southern Ural Mts., yellow; in the Mourne Mts., Ireland. In the United States at Haddam, Conn., in granite traversing gneiss, with tourmaline, garnet, beryl; at Greenfield, near Saratoga, N. Y., with tourmaline, garnet, and apatite; has been found in crystals in the rocks of New York City; in Me. at Norway, in granite with garnet and at Stoneham, with fibrolite, at Topsham, Buckfield and Greenwood. Chrysoberyl is from xpvvos, golden, ftrjpvXXos, beryl. Cymophane, from Kv/j.a, wave, and aij>a), appear, alludes to a peculiar opalescence the crystals sometimes exhibit. Alexandrite is after the Czar of Russia, Alexander I. Use. As a gem stone; see under Var. above. Hausmannite. Mn 3 O 4 or MnO. Mn 2 O 3 . In tetragonal octahedrons and twins (Fig. 414, E. 167); also granular massive, particles strongly coherent. H. = 5-5'5. G. = 4'856. uster submetallic. Color brownish black. Streak chestnut-brown. Occurs near Ilme- nau in Thuringia, Germany; .Ilefeld in the Harz Mts., Germany; Filipstad, Langban, Nordmark, in Sweden; from Brazil. Coronadite. (Mn,Pb)Mn 3 O 7 . Massive with delicate fibrous structure. H. = 4. G. = 5'2. Color black. Streak brownish black. Occurs in Coronado vein of the Clifton- Morenci district, Arizona. Hollandite is a similar manganate of manganese, barium 'and ferric iron from the Kaljlidongri manganese mine, Central India. Cesllrolite. H 2 PbMn 3 O 8 . In cellular masses. Color, steel-gray. H. = 4'5. G. = 5'29. From Sidi-Amer-bers-Salem, Tunis. Minium. Pb 3 4 or 2PbO.PbO 2 . Pulverulent, as crystalline scales. G. = 4'6. Color vivid red, mixed with yellow; streak orange-yellow. Occurs in Germany at Bleialf in the Jjjifel; Badenweiler in Baden, etc. Crednerite. Cu 3 Mn 4 O 9 or 3CuO.2Mn 2 O 3 . Foliated crystalline. H. = 4'5. G. = 4'9- 5*1. Luster metallic. Color iron-black to steel-gray. Streak black, brownish. From Fnednchroda, Germany. Pseudobrookite. Probably Fe 4 (TiO 4 ) 3 . Usually in minute orthorhombic crystals, tab- ular || a(100) and often prismatic || the macro-axis. G. = 4-4-4'98. Color dark brown to black, btreak ocher-yellow. Found with hypersthene (szaboite) in cavities of the andesite ot Aranyer Berg, Transylvania, and elsewhere; on recent lava (1872) from Vesuvius; at Havredal, Bamle, Norway, embedded in kjerulfine (wagnerite) altered to apatite. OXIDES 425 BRAUNITE. Tetragonal. Axis c = 0;9850. Commonly in octahedrons, nearly iso- metric in angle (pp f 111 A 111 = 70 7'). Also massive. Cleavage : p(lll) perfect. Fracture uneven to subconchoidal. Brittle. H. = 6-6-5. G. = 4-75-4-82. Luster submetallic. Color and streak, dark brownish black to steel-gray. Comp. 3Mn 2 3 .MnSiO 3 = Silica lO'O, manganese protoxide 11 '7, man- ganese sesquioxide 78 -3 = 100. Pyr., etc. B.B. infusible. With borax and salt of phosphorus gives an amethystine bead in O.F., becoming colorless in R.F. With soda gives a bluish green bead. Dissolves in hydrochloric acid leaving a residue of gelatinous silica. Marceline gelatinizes with acids. Obs. Occurs in veins traversing porphyry, at Oehrenstock, near Ilmenau, Thuringia, and near Ilefeld in the Harz Mts., Germany; St. Marcel in Piedmont, Italy; at Elba; at Botnedal, Upper Tellemark, in Norway; at the manganese mines of Jakobsberg, also at Langban, and at the Sjo mine, Grythyttan, Orebro, Sweden. Marceline (heterocline) from St. Marcel, Ptedmont, is impure braunite. Bixbyite. Essentially FeO.MnO 2 . In black isometric crystals. H. = 6-6'5. G. = 4'945. Occurs with topaz in cavities in rhyolite; from Utah. IV. Dioxides, RO 2 . Rutile Group. Tetragonal c c Cassiterite SnO 2 0-6723 Rutile TiO 2 0-6442 Polianite MnO 2 0'6647 Plattnerite PbO 2 0'6764 ' The RUTILE GROUP includes the dioxides of the elements tin, manganese, titanium, and lead. These compounds crystallize in the tetragonal system with closely similar angles and axial ratio; furthermore in habit and method of twinning there is much similarity between the two best known species included here. Chemically these minerals are sometimes considered as salts of their respective acids, as stannyl metastannate, (SnO)SnO 3 , for cassiterite and titanyl metatitanate, (TiO)TiO 3 , for rutile. With the Rutile Group is also sometimes included Zircon. ZrO 2 SiO 2 ; c = 0'6404. In this work, however, Zircon is classed among the silicates, with the allied species Thorite, ThO 2 .SiO 2 , c = 0-6402. A tetragonal form, approximating closely to that of the species of the Rutile Group, belongs also to a number of other species, as Xenotime, YPO4; Sellaite, MgF2; Tapiolite, Fe(Ta,Nb) 2 O 6 . It may be added that ZrO 2 , as the species Baddeleyite, crystallizes in the monoclinic system. CASSITERITE. Tin-stone, Tin Ore Tetragonal. Axis c = 0-6723. ee', 101 A Oil = 46 28'. ms, 110 A 111 = 46 27'. ee", 101 A 101 = 67 50'. zz', 321 A 231 = 20 53' ', 111 A 111 = 58 19'. zzv, 321 A 321 = 61 42'. ss", 111 A 111 = 87 7' Twins common: tw. pi. e(101); both contact- and penetration-twins (Fig. 717); often repeated. Crystals low pyramidal; also prismatic and acutely terminated. Often in reniform shapes, structure fibrous divergent; also mas- sive, granular or impalpable; in rolled grains. 426 DESCRIPTIVE MINERALOGY Cleavage: a(100) imperfect; 8(111) more so; m(110) hardly distinct. Fracture subconchoidal to uneven. Brittle. H. = 6-7. G. = 6-8-71. Luster adamantine, and crystals usually splendent. Color brown or black; some- 714 715 716 717 times red, gray, white, or yellow. Streak white, grayish, brownish. Nearly transparent to opaque. Optically + . Indices: co = 1-9966, e = 2-0934. Var. Ordinary. Tin-stone. In crystals and massive. Wood-tin. In botryoidal and reniform shapes, concentric in structure, and radiated fibrous internally, although very compact, with the color brownish, of mixed shades, looking somewhat like dry wood in its colors. Toad's-eye tin is the same, on a smaller scale. Stream- tin is the ore in the state of sand, as it occurs along the beds of streams or in gravel. Comp. Tin dioxide, Sn0 2 = Oxygen 21'4, tin 78'6 = 100. A little Ta2O 5 is sometimes present, also Fe 2 O 3 . Pyr., etc. B.B. alone unaltered. On charcoal with soda reduced to metallic tin, and gives a white coating. With the fluxes sometimes gives reactions for iron and manganese. Only slightly acted upon by acids. Artif . Cassiterite has been artificially prepared by the action of aqueous vapor upon tin tetrachloride in a heated tube and by other similar methods employing heated vapors. Obs. Cassiterite has been noted as an original constituent of igneous rocks but usu- ally it occurs in veins traversing granite, rhyolite, quartz porphyry, pegmatite, gneiss, mica schist, chlorite or clay schist; also in finely reticulated veins forming the ore-deposits called stockworks, or simply impregnating the enclosing rock. It is most commonly found in quartz veins traversing granite, accompanied by minerals containing boron and fluorine which indicates a pneumatolytic origin. The commonly associated minerals are quartz, wolframite, scheelite; also mica, topaz, tourmaline, apatite, fluorite; further pyrite, arsenopyrite, sphalerite; molybdenite, native bismuth, etc. Formerly very abundant, now less so, in Cornwall, in fine crystals, and also as wood-tin and stream-tin; in Devonshire, near Tavistock and elsewhere; in pseudomorphs after feldspar at Wheal Coates, near St. Agnes, Cornwall; in fine crystals, often twins, at Schlackenwald, Graupen, Joachimstal, Zinnwald, etc., in Bohemia, and at Ehrenfrieders- dorf, Altenberg, etc., in Saxony; at Limoges, France, in splendid crystals; Sweden, at Fmbo; Finland, at Pitkaranta. In the East Indies, on the Malay peninsula of Malacca and the neighboring islands, Banca, and Bilitong near Borneo. In New South Wales abundant over an area of 8500 sq. miles, also in Victoria, Queensland and Tasmania. In Bolivia in veins containing silver, lead, and bismuth; Mexico, in Durango, Guanajuato, Zacatecas, Jalisco. In the United States, in Me., sparingly at Paris, Hebron, etc. In Mass., at Chesterfield and Goshen, rare. In N. H., at Jackson. In Va.. on Irish Creek, Rockbridge Co., with wolframite, etc. In N. C. and S. C. In Ala., in Coosa Co. In S. D., near Harney Peak and near Custer City in the Black Hills, where it has been mined. In Wy., in Crook Co.; in Mon., near Dillon. In Cal., in San Bernardino Co., at Temescal. Has been mined in the York district, Seward Peninsula, Alaska. Use. The most important ore of tin. OXIDES 427 Polianite. Manganese dioxide, MnO 2 . In composite parallel groupings of minute crystals; also forming the outer shell of crystals having the form of manganite. H. = 6-6'5. G. = 4'992. Luster metallic. Color light steel-gray or iron-gray. Streak black. From Flatten, Bohemia. It is distinguished from pyrolusite by its hardness and its anhydrous character. Like pyrolusite it is often a pseudomorph after manganite. RUTILE. Tetragonal. vu, ee' t ee", 718 Axis_c = 0-64415. 310 A 310 =* 36 54'. 101 A Oil = 45 2'. 101 A 101 = 65 34*'. ss', 111 A 111 = 56 25|'. ", 111 A 111 = 84 40'. it', 313 A 133 = 29 6'. 719 720 721 Twins: tw. pi. (1) e(101); often geniculated (Figs. 720, 721) ; also contact-twins of very varied habit, sometimes sixlings and eightlings (Fig. 399, p. 164; Fig. 413, p. 166). (2) v(301) rare, contact-twins (Fig. 415, p. 167). Crys- tals commonly prismatic, vertically striated or fur- rowed; often slender acicular. Occasionally compact, massive. Cleavage: a(100) and w(110) distinct; s(lll) in traces. Fracture sub- conchoidal to uneven. Brittle. H. = 6y6'5. G. = 4'18-4'25; also to 5'2. Luster metallic-adamantine. Color reddish brown, passing into red; some- times yellowish, bluish, violet, black, rarely grass-green; by transmitted light deep red. Streak pale brown. Transparent to opaque. Optically +. Refractive indices high: co = 2-6158, e = 2-9029. Birefringence very high. Sometimes abnormally biaxial. Comp. Titanium dioxide, Ti0 2 = Oxygen 40'0, titanium 60'0 = 100. A little iron is usually present, sometimes up to 10 p. c. While the iron present is often reported as ferric the probability is that in the unaltered mineral it existed in the ferrous state. The formula for rutile may be written as a titanyl metatitanate (TiO)TiO 3 With this the ferrous titanate FeTiO 3 may be considered isomorphous and so account for the iron frequently present. It has been suggested that the tapiolite molecule, FeO.Ta 2 O 5 is also isomorphous and that tapiolite belongs in the same group as rutile and cassiterite, see ilmenorutile, below. Var. Ordinary. Brownish red and other shades, not black. G. = 4* lS-4'25. Trans- parent quartz (sagenite) is sometimes penetrated thickly with acicular or capillary crystals. Dark smoky quartz penetrated with the acicular rutile or "rutilated quartz," is the Filches d'amour Fr. (or Venus hair-stone). Acicular crystals often implanted in parallel position on tabular crystals of hematite; also somewhat similarly on magnetite. Ferriferous, (a) Nigrine is black in color, whence the name; contains up to 30 p. c. of ferrous titanate. (b) Ilmenorutile is a black variety from the Ilmen Mts., Russia; contain- ing iron in the form of ferrous titanate, niobate and tantalate. G. = 5'14. Struverite is the same mineral with greater amounts of the niobate present, (c) Iserine from Iserweise, Bohemia, formerly considered to be a variety of ilmenite is probably also a ferriferous rutile. 428 DESCRIPTIVE MINERALOGY pyr e tc. B.B. infusible. With salt of phosphorus gives a colorless bead, which in R.F. assumes a violet color on cooling. Most varieties contain iron, and give a brownish yellow or red bead in R.F., the violet only appearing after treatment of the bead with metallic tin on charcoal. Insoluble in acids; made soluble by fusion with an alkali or alkaline carbonate. The solution containing an excess of acid, with the addition of tin- foil, gives a beautiful violet color when concentrated. Diff. Characterized by its peculiar sub-adamantine luster and brownish red color. Differs from tourmaline, vesuvianite, augite in being entirely unaltered when heated alone B.B. Specific gravity about 4, of cassiterite 6'5. Micro. In thin sections shows red-brown to yellow color, very high relief and high order of interference color. Artif . Rutile has been formed artificially by heating titanic oxide with boric oxide, with sodium tungstate, etc. Rutile, octahedrite and brookite have all been formed by heat- ing potassium titanate and calcium chloride in a current of hydrochloric acid gas and air. RutUe is formed at the highest temperature, brookite at lower temperatures, and octahedrite at the lowest of all. Obs. Rutile occurs as an accessory mineral in granite, gneiss, mica schist, and sye- nitic rocks, and sometimes in granular limestone and dolomite; common, as a secondary product, in the form of microlites in many slates. A dike rock from Nelson Co., Va., con- sists essentially of rutile and apatite. It is generally found in embedded crystals, often in masses of quartz or feldspar, and frequently in acicular crystals penetrating quartz ; also in phlqgopite (which see), and has been observed in diamond. It has also been met with in hematite and limenite, rarely in chromite. It is common in grains or fragments in many auriferous sands. Prominent localities are: Arendal and Kragero in Norway; Horrsjoberg, Sweden, with lazulite and cyanite; Saualpe, Carinthia; in the Ural Mts.; in the Tyrol, Austria; at St. Gothard and Binnental, Switzerland; at Yrieux, near Limoges in France; at Ohlapian in Transylvania, nigrine in pebbles; in large crystals in Perthshire, Scotland; in Donegal Co., Ireland. In Me., at Warren. In Ver., at Waterbury; also in loose bowlders in middle and northern Vermont, acicular, some specimens of great beauty in transparent quartz. In Mass., at Barre, in gneiss; at Shelburne, in mica slate, at Chester. In N. Y., in Orange Co., Edenville; Warwick; east of Amity. In Pa., at Sudsbury, Chester Co., and the adjoining district in Lancaster Co.; at Parksburg, Concord, West Bradford, and Newlin, Chester Co.; at the Poor House quarry, Chester Co. In N. J., at Newton, with spinel. In N. C., at Crowder's Mountain; at Stony Point, Alexander Co., in splendent crystals. In Ga., in Habersham Co.; in Lincoln Co., at Graves' Mountain, with lazulite in large and splendent crystals. In Ark., at Magnet Cove, commonly in twins, with brookite and perovskite, also as paramorphs after brqokite. Fine specimens of "rutilated quartz," from Minas Geraes, Brazil; Madagascar; Tavetch and elsewhere, Switzerland; West Hartford, Ver.; Alexander Co., N. C. Use. A source of titanium. Plattnerite. Lead dioxide, PbO 2 . Rarely in prismatic crystals, usually massive. H. = 5-5*5. G. = 8'5. Luster submetallic. Color iron-black. Streak chestnut-brown. From Leadhill and Wanlockhead, Scotland. Also at the "As You Like" mine, Mullan, Cceur d'Alene Mts., Idaho. Baddeleyite. Zirconium dioxide, ZrO 2 . In tabular monoclinic crystals. H. = 6'5. t. = 5-5-6-0. Colorless to yellow, brown and black. Index, 174. From Ceylon; from Brazil near Caldas, Minas Geraes and Jacupiranga, (brazilite) where it is associated with zirkelite, (Ca,Fe)0.2(Zr,Ti,Th)O 2 . Noted at Mte. Somma, Vesuvius. Also near Boseman, Mon. Various minerals occurring as rolled pebbles in the diamond sands of Brazil are known as favas (beans). Some of them consist of nearly pure TiO 2 others of nearly pure ZrO 2 , while others are various phosphates. Paredrite is a "fava," composed of TiO 2 with a little water. Uhligite. Ca(Ti Zr)0 5 .Al(Ti,Al)0 6 . Isometric. Octahedral. Color black. Brown and transparent on thin edges. Found in a nepheline syenite on the shore of Lake Magad, ri.QQt. A TT1OQ OCTAHEDRITE. Anatase. Tetragonal. Axis c = 17771. Commonly octahedral in habit, either acute (p, 111), or obtuse (v, 117); OXIDES 429 also tabular, c(001) predominating; rarely prismatic crystals; frequently highly modified. ee',. 101 A Oil = ee", 101 A 101 = pp f , 111 A 111 = pp",Ul A 111 = zz', 113 A 113 = vv' 117 A 117 = 76 5' 121 16' 82 9' 136 36' 54 1' 27 39' 722 723 Cleavage: c (001) and p (111) perfect. Fracture subconchoidal. Brittle. H. = 5-5-6. G. = 3-82-3-95; sometimes 4-11-4-16 after heating. Luster adamantine or metallic-ad- amantine. Color various shades of brown, passing into indigo-blue, and black; greenish yellow by transmitted light. Streak uncolored. Transparent to nearly opaque. Optically . Birefringence rather high. Indices: o> = 2-554, e = 2-493. Sometimes abnor- mally biaxial. Comp. Titanium dioxide, TiO 2 = Oxygen 40'0, titanium 60*0 = 100. Pyr., etc. Same as for rutile. Artif. See under rutile. Obs. Most abundant at Bpurg d'Oisans, in Dauphine, France, with feldspar, axinite, and ilmenite; near Hof in the Fichtelgebirge, Germany; at Selva and Naderanertal, Swit- zerland; Norway; the Ural Mts.; in chlorite in Devonshire, near Tavistock; with brookite at Tremadoc, in North Wales ; in Cornwall, near Liskeard and at Tintagel Cliffs ; in Brazil in quartz, and in detached crystals. In Switzerland in the Binnental the variety wiserine, long supposed to be xenotime; also Cavradi, Tavetsch; Rauris, Salzburg, in the Eastern Alps; also at Pfitsch Joch. In the United States, at the Dexter lime rock, Smithfield, R. L, in dolomite; from granite pegmatite, Quincy, and from Somerville, Mass.; in the washings at Brindletown, Burke Co., N. C., in transparent tabular crystals; at Magnet Cove, Ark.; in unusual crystals from Beaver Creek, Gunnison Co., Col. BROOKITE. Orthorhombic. Axes a : b : c = 0-8416 : 1 : 0-9444. mm'", 110 A lIO = 80 10'. ee', 122 A 122 = 44 23'. zz', 112 A 112 = 53 48'. ee'", 122 A 122 = 78 57'. zz"' 112 A 112 = 44 46'. me, 110 A 122 = 45 42'. 725 726 727 Only in crystals, of varied habit. Cleavage: w(110) indistinct; c(001) still more so. Fracture subcon- choidal to uneven. Brittle. H. = 5-5-6. G. = 3-87-4-08. Luster metallic- adamantine to submetallic. Color hair-brown, yellowish; reddish, reddish 430 DESCRIPTIVE MINERALOGY brown and translucent; also brown to iron-black, opaque. Streak uncolored to grayish or yellowish, a = 2-583. = 2*586. 7 = 2741. Other optical characters, see p. 298. Comp. Titanium dioxide, TiO 2 = Oxygen 40*0, titanium 60'0 == 100. Pyr. Same as for rutile. Obs.' Occurs at Bourg d'Oisans in Dauphine, France; in Switzerland at St. Gothard, with albite and quartz, and Maderanertal; in the Ural Mts.; district of Zlatoust, near Miask, and in the gold-washings in the Sanarka river and elsewhere; at Fronolen, near Tremadoc, Wales. From Companhia, Lencoes, Bahia, Brazil. In the United States in thick black crystals (arkansite) at Magnet Cove, Ozark Mts., Ark. with elaeolite, black garnet, schorlomite, rutile, etc.; in small crystals from the gold- washings of N. C.; at the lead mine at Ellenville, Ulster Co., N. Y., on quartz, with chal- copyrite and galena; at Paris, Me., Somerville, Mass. Named after the English mineralogist, H. J. Brooke (1771-1857). PYROLUSITE. Orthorhombic, but perhaps only pseudomorphous. Commonly columnar, often divergent; also granular massive, and frequently in reniform coats. Soft, often soiling the fingers. H. = 2-2-5. G. = 473-4-86. Luster metallic. Color iron-black, dark steel-gray, sometimes bluish. Streak black or bluish black, sometimes submetallic. Opaque. Comp. Manganese dioxide, MnO 2 , like polianite (p. 427). Commonly contains a little water (2 p. c.), it having had usually a pseudomorphous origin (after manganite). It is uncertain whether pyrolusite is an independent species, with a crystalline form of its own, or only a secondary mineral derived chiefly from the dehydration of manganite; also from polianite (Breith.). Pseudomorphous crystals having distinctly the form of manganite are common. I^r., etc. Like polianite, but most varieties yield some water in the closed tube. Diff. Hardness less than that of psilomelane. Differs from iron ores in its reaction for manganese B.B. Easily distinguished from psilomelane by its inferior hardness, and usually by being crystalline. Its streak is black; that of manganite is more or less brown. Obs. Manganese ore deposits in general are secondary in origin, the manganese content of the rocks having been concentrated in favorable places. They often occur as irregular bodies in residual clays. Pyrolusite is extensively worked at Elgersberg near Ilmenau, and other places in Thuringia, Germany; at Vorderehrensdorf in Moravia; at Flatten in Bohemia, and elsewhere; near Johanngeorgenstadt, at Hirschberg in West- phalia, Germany; Matzka, Transylvania; in Australia; in India. Occurs in the United States' with psilomelane, abundantly in Ver., at Brandon, etc.; at Plainfield and West Stockbridge, Mass.; Augusta Co., Va.; Pope, Pulaski, Montgomery Cos., Ark. Negaunee, Mich.; Lake Co., N. M. In New Brunswick, 7 m. from Bathurst. In Nova Scotia, at Teny Cape; at Walton, etc. The name is from -nvp, fire, and \oveiv, to wash, because used to discharge the brown and green (FeO) tints of glass; and for the same reason it is whimsically entitled by the French le savon de verriers. Use. An ore of manganese; as an oxidizing agent in manufacture of chlorine, bro- mine and oxygen; as a drier in paints, a decolorizer in glass and in electric batteries, as color- ing material in bricks, pottery, glass, etc. B. HYDROUS OXIDES. ddes the DIASPORE Gi 3 of aluminium, iron an in formula is properly written RO(OH). The three species here included are Among the hydrous oxides the DIASPORE GROUP is well characterized. Here belong the hydroxides of aluminium, iron and manganese. The general OXIDES 431 orthorhombic in crystallization with related angles and axial ratios; this rela- tion is deviated from by manganite in the prismatic zone. Another less prominent group is the BRUCITE GROUP, including the rhombohedral species Brucite, Mg(OH), and Pyrochroite, Mn(OH). Gibbsite, A1(OH) 3 , and Sassolite, B(OH) 3 , are also related, and further Hydrotalcite and Pyroaurite. . TTT Diaspore Group. p. RO(OH) or R 2 3 .H 2 0. a :b Orthorhombic. c : c a A1 2 3 .H 2 o- 9372 1 :0 6039 or 6443 Fe 2 O 3 .H 2 O 0' 9185 1 :0 6068 or 6606 Mn 2 O 3 .H 2 O 6- 8441 1 :0 5448 or 6463 Diaspore Gothite Manganite DIASPORE. Orthorhombic. Axes: a : b : c = 0-9372 : 1 : 0-6039. Crystals prismatic, mm'", 110 A 110, = 86 17'; usually thin, flattened || 6(010); sometimes acicular. Also foliated massive and in thin scales; sometimes stalactitic. Cleavage: 6(010) eminent; A(210) less perfect. Fracture conchoidal, very brittle. H. = 6*57. G. = 3 "3 3*5. Luster brilliant; 'pearly on cleav- age-face, elsewhere vitreous. Color whitish, grayish white, greenish gray, hair-brown, yellowish, to colorless. Pleochroic. Transparent to subtrans- lucent. Optically + . Birefringence high. Ax. pi. || 6(010). Bx. J_ a(100). Dispersion p < v, feeble. 2 V = 84. a = 1-702. = 1-722. 7 = 1750. Comp. AIO(OH) or A1 2 3 .H 2 O = Alumina 85'0, water 15'0 = 100. Pyr., etc. In the closed tube usually decrepitates strongly, separating into white pearly scales, and at a high temperature yields water. Infusible; ignited with cobalt solution gives a deep blue color. Not attacked by acids, but after ignition soluble in sulphuric acid. Diff. Distinguished by its hardness and pearly luster; also (B.B.) by its decrepitation and yielding water; by the reaction for alumina with cobalt solution. Resembles some varieties of hornblende, but is harder. Artif . Diaspore crystals have been artificially formed by heating in a steel tube aluminium oxide in sodium hydroxide to temperatures less than 500. Obs. Commonly found with corundum or emery. Occurs near Kossoibrod, in the Ural Mts.; at Schemnitz, Hungary; with corundum in dolomite* at Campolongo, Tessin, in Switzerland; Greiner in the Zillertal, Austria. In the United States, with corundum and margarite at Newlin, Chester Co., Pa.; at the emery mines of Chester, Mass.; in cavities in massive corundum at the Culsagee mine, near Franklin, Macon Co., N. C.; with alunite forming rock masses at Mt. Robinson, Rosita Hills, Col. Named by Haiiy from dtaaTre'ipeiv, to scatter, alluding to the usual decrepitation before the blowpipe. GOTHITE. 72 ? Orthorhombic. Axes a : b : c = 0*9185 : 1_ : 0*6068. mm'", 110 A 110 = 85 8'. pp', 111 A 111 = 58 55'. ee', Oil A Oil = 62 30'. pp"', 111 A ill = 53 42'. In prisms vertically striated, and often flattened into scales or tables || 6(010). Also fibrous; foliated or in scales; massive, reniform and stalactitic, with concentric and radiated structure. Cleavage: 6(010) very perfect. Fracture uneven. Brittle. H. = 5-5-5. G. = 4*28. Luster imperfect adamantine. Col- or yellowish, reddish, and blackish brown. Often blood-red by transmitted light. Streak brownish yellow to ocher-yellow. a = 2 -26. ]8 = 2-39. 7 = 2-4. Only weakly pleochroic. 432 DESCRIPTIVE MINERALOGY Var. In thin scale-like or tabular crystals, usually attached by one edge. Also in acicular or capillary (not flexible) crystals, or slender prisms, often radiately grouped: the Needle-Ironstone. It passes into a variety with a velvety surface; the Przibramite (Sammet- blende) of Pfibram, Bohemia, is of this kind. Also columnar, fibrous, etc., as above. Comp. FeO(OH) or Fe 2 3 .H 2 O = Oxygen 27'0, iron 62'9, water 101 = 100, or Iron sesquioxide 89*9, water 10*1 = 100. Pyr., etc. In the closed tube gives off water and is converted into red iron sesqui- oxide. With the fluxes like hematite; most varieties give a manganese reaction, and some, treated in the forceps in O.F., after moistening in sulphuric acid, impart a bluish green color to the flame (phosphoric acid). Soluble in hydrochloric acid. Diff. Distinguished from hematite by its yellow streak; from limonite by crystalline nature; it also contains less water than limonite. . Obs. Found with the other oxides of iron,^ especially hematite or limonite. Occurs at Eiserfeld near Siegen, in Nassau, Germany; Pfibram, Bohemia; at Clifton, near Bristol, England; in Cornwall. In the United States, at the Jackson Iron mine, Negaunee, Lake Superior; in Conn., at Salisbury; in Pa., near Easton; in the Pike's Peak region and at Crystal Peak, Col. Named Gothite (Goethite) after the poet-philosopher Goethe (1749-1832) . A colloidal form of iron hydroxide having the composition of goethite and occurring as pseudomorphs after pyrite has been called ehrenwerthite. Use. An ore of iron. Lepidocrocite. A dimorphous form of goethite. Orthorhombic but with different axial ratio. Scaly, fibrous. G = 4'09. = 2*20. Strongly pleochroic. MANGANITE. Orthorhombic. Axes a : b : c = 0*8441 729 730 1 : 0-5448. hh'", 410 A 410 = 23 50'. mm'", 110 A 110 = 80 20'. ee', 205 A 205 = 28 57'. ee', Oil A Oil = 57 10'. pp f , 111 A Til = 59 5|'. Crystals commonly prismatic, the faces deeply striated vertically; often grouped in bundles. Twins: tw. pi. e(011). Also columnar; stalactitic. Cleavage: 6(010) very perfect; w(110) perfect. Fracture uneven. Brittle. H. = 4. G. = 4-2-4-4. Luster sub- metallic. Color dark steel-gray to iron-black. Streak reddish brown, sometimes nearly black. Opaque; in minute splinters sometimes brown by transmitted light. Comp. MnO(OH) or Mn 2 O 3 .H 2 = Oxygen 27'3, manganese 62'4, water 10'3 = 100, or Manganese sesquioxide 897, water 10-3 = 100. Pyr., etc. In the closed tube yields water; manganese reactions with the fluxes, p. 339, Obs. Occurs in Germany at Ilefeld in the Harz Mts.; Ilmenau in Thuringia; Lang- ban and Bolet, Sweden; Cornwall, at various places; also in Cumberland, etc. In the Lake Superior mining region at the Jackson mine, Negaunee; Devil's Head, Douglas Co., Col. In Nova Scotia, at Cheverie, Hants Co., and Walton. In New Brunswick, at Shep- ody mountain, Albert Co., etc. Sphenomanganite is a variety of manganite from Langban, Sweden, showing sphenoidal forms. Use. An ore of manganese. LIMONITE. Brown Hematite. Not crystallized. Usually in stalactitic and botryoidal or mammillary torms, having a fibrous or subfibrous structure; also concretionary, massive- and occasionally earthy. OXIDES 433 H. = 5-5*5. G. = 3'6-4-0. Luster silky, often submetallic; sometimes dull and earthy. Color of surface of fracture various shades of brown, com- monly dark, and none bright; sometimes with a nearly black varnish-like exterior; when earthy, brownish yellow, ocher-yellow. Streak yellowish brown. Opaque. Var. (1) Compact, Submetallic to silky in luster; often stalactitic, botryoidal, etc. (2) Ocherous or earthy, brownish yellow to ocher-yellow, often impure from the presence of clay, sand, etc. (3) Bog ore. The ore from marshy places, generally loose or porous in texture, often petrifying leaves, wood, nuts, etc. (4) Brown clay-ironstone, in compact masses, often in concretionary nodules. Comp. Approximately 2Fe 2 3 .3H 2 O = Oxygen 257, iron 59'8, water 14'5 = 100, or Iron sesquioxide 85 '5, water 14*5 = 100. The water content varies widely and it is probable that limonite is essentially an amorphous form of goethite with adsorbed and capillary water. In the bog ores and ochers, sand, clay, phosphates, oxides of manganese, and humic or other acids of organic origin are very common impurities. Pyr., etc. Like gpthite. Some varieties leave a siliceous skeleton in the salt of phos- phorus bead, and a siliceous residue when dissolved in acids. Diff . Distinguished from hematite by its yellowish streak, inferior hardness, and its reaction for water. Does not decrepitate B.B., like turgite. Not crystallized like gothite and yields more water. Obs. In all cases a result of the alteration of other ores, or minerals containing iron, through exposure to moisture, air, and carbonic or organic acids; derived largely from the change of pyrite, magnetite, siderite, ferriferous dolomite, etc.; also various species (as mica, pyroxene, hornblende, etc.), which contain iron in the ferrous state (FeO). Waters containing iron in solution when brought into marshy places deposit the metal usually in the form of limonite. The evaporation of the carbonic acid in the water which held the iron in solution is one cause for the separation of the iron oxide. This separation is also aided by the so-called "iron bacteria" which absorb the iron from the water and later deposit it again as ferric hydroxide. Limonite consequently occupies, as a bog ore, marshy places, into which it has been borne by streamlets from the hills around. It is also found in deposits associated with iron-bearing limestones where the original iron con- tent of the rock has been largely dissolved and redeposited later in some favorable spot. Limonite forms the capping or gossan, iron hat, of many metallic veins. It is often asso- ciated with manganese ores. Limonite is a common ore in Bavaria, the Harz Mts., Ger- many, Luxemburg, Scotland, Sweden, etc. Abundant in the United States. Extensive beds exist at Salisbury and Kent, Conn., also in the neighboring towns of N. Y., and in a similar situation in Berkshire Co., Mass., and in Ver.; in Pa., widely distributed; also in Tenn., Ala., Ohio, etc. Named Limonite from Xei/icoi>, meadow. Use. An ore of iron; as a yellow pigment. TURGITE. Hydrohematite. Approximately 2Fe 2 O3.H 2 O. Probably to be considered as a solid solution of goethite with hematite together with enclosed and adsorbed water. Resembles limonite but has a red streak. G. = 4'14-4'6. Decrepitates B.B. From the Turginsk mine in the Ural Mts., etc.; also from Salisbury, Conn. Intermediate between hematite and limonite. HYDRO GOETHITE. 3Fe 2 03.4H 2 0. Orthorhombic, radiating fibrous. H. =4. G. = 37. Color and streak brick-red. With limonite at various localities in Tula, Russia. Xanthosiderite. Fe 2 O 3 .2H 2 O. In fine needles or fibers, stellate and concentric; also as an ocher. Color golden yellowish, brown to brownish red. Associated with manganese ores at Ilmenau, Thuringia, Germany, etc. Esmeraldaite. Fe 2 3 .4H 2 O. In small pod-shaped masses enclosed in limonite. Con- choidal fracture. H. = 2'5. G. = 2 '58. Color coal black. Yellow-brown streak. From Esmeralda Co., BAUXITE. Beauxite. In round concretionary disseminated grains. Also massive, oolitic; and earthy, clay-like. G. = 2'55. Color whitish, grayish, to ocher-yeHow, brown, and red. 434 DESCRIPTIVE MINERALOGY Var. 1. In concretionary grains, or oolitic; bauxite. 2 Clay-like, wocheinite; the purer kind grayish, clay-like, containing very little iron oxide; also red from the iron oxide present. Comp. Essentially A1 2 3 .2H 2 O = Alumina 73'9, water 26'1 = 100; some analyses, however, give A1 2 O 3 .H 2 O like diaspore. Bauxite is probably a mixture of varying character but containing large amounts of a colloidal form of Al 2 Os.H 2 O. This substance has been called sporogelite or diasporogelite, ' cliachite and alumogel. Iron sesquioxide is usually present, sometimes in large amount, in part replacing alumina, in part only an impurity. The name hematogelite has been suggested for this colloidal form of ferric oxide. Silica, phosphoric acid, carbonic acid, lime, magnesia are common impurities. Obs. Bauxite is a product of the decomposition of certain rocks, particularly those rich in plagioclase feldspars, and has been found under various conditions. The later ites of India, etc., are probably similar in origin and might be considered as iron-rich bauxites. Bauxite is certainly not a definite mineral species but consists of a mixture of several different materials. From Baux (or Beaux), near Aries, and elsewhere in France, dissemi- nated in grains in compact limestone, and also oolitic. Wocheinite occurs in Carniola, Austria, between Feistritz and Lake Wochein. The purest bauxite is used for the manu- facture of aluminium (aluminum), and is called aluminum ore. In the United States, bauxite occurs in Saline and Pulaski Cos., Ark.; also in Cherokee and Calhoun Cos., Ala., and in Floyd, Barton and Walker Cos., Ga. Use. As an aluminum ore. Brucite Group. R(OH) 2 . Rhombohedral BRUCITE. Jlhombohedral. Axis c = 1-5208; cr 0001 A 1011 = 60 20i', rr' 1011 A 1101 = 97 37J'. Crystals usually broad tabular. Also commonly foliated massive; fibrous, fibers separable and elastic. H. = 2-5. G. = 2-38-2-4. Cleavage: c(0001) eminent. Folia separable and flexible, nearly as in gypsum. Sectile. Luster || c pearly, elsewhere waxy to vitreous. Color white, inclining to gray, blue, or green. Transparent to translucent. Optically + . Indices: o> r = 1-559, e r = 1-5795. Comp. --Magnesium hydroxide, Mg(OH) 2 or MgO.H 2 O = Magnesia 69*0, water 31*0 = 100. Iron and manganese protoxide are sometimes present. Var - Ordinary, occurring in plates, white to pale greenish in color; strong pearly luster on the cleavage surface. Nemalite is a fibrous variety containing 4 to 5 p. c. iron protoxide, with G. = 2 "44. Manganbrucite contains manganese; occurs granular; color honey-yellow to brownish red. Ferrobrucite contains iron. Pyr., etc. In the closed tube gives off water, becoming opaque and friable, sometimes turning gray to brown; the manganesian variety becomes dark brown. B.B. infusible, glows with a bright light, and the ignited mineral reacts slightly alkaline to test-paper. ignited with cobalt solution gives the pale pink color of magnesia. The pure mineral is soluble in acids without effervescence. i, P^vT D / S i tingU i S ^ by - its . infusib ility, softness, cleavage, and foliated structure. Is harder than talc and differs in its solubility in acids; the magnesia test and optical char- acters separate it from gypsum, which is also somewhat softer. ln f^'r^- A r secon dary mm f a. 1 accompanying other magnesian minerals in serpentine, also found m limestone. At Swmaness in Unst, Shetland Isles; at the iron mine of Cogne Aosta Italy; near Fihpstadt in Sweden. At Hoboken, N. J, in serpentine; at the Tilly Foster iron nime, Brewster N. Y, well crystallized; Richmond Co , N. Y.; at Wood's e *' m ? 5 r m - asses ' and often crystallizations several inches across, hydjomagnesite From Crestmore, Riverside Co., Cal. Nemalite, ur the fibrvHHp rom resmore, verse o., a. Nemalite, the fibrous variety, occurs at Hoboken, N. J., and at Xettes in the Vosges Mts. Mangos OXIDES 435 brucite occurs with hausmannite and other manganese minerals in the granular limestone of Jakobsberg, Nordmark, Sweden. Named after the early American mineralogist, A. Bruce (1777-1818). Pyrochroite. Manganese hydroxide, Mn(OH) 2 . Usually foliated, like brucite. Lus- ter pearly. Color white, but growing dark on exposure, to = 1723. e = 1'681. In Sweden occurs in magnetite at Pajsberg, also at Nordmark and Langban; in N. J. at Franklin Furnace. Backstromite. Manganese hydroxide, Mn(OH) 2 . Orthorhombic. From Langban, Sweden. GIBBSITE. Hydrargillite. Monoclinic. Axes a : b : c = 17089 : 1 : 1-9184; = 85 29'. Crystals- tabular | c(001), hexagonal in aspect. Occasionally in spheroidal concretions. Also stalactitic, or small mammillary, incrusting, with smooth surface, and often a faint fibrous structure within. Cleavage: c(001) eminent. Tough. H. = 2-5-3 -5. G. = 2-3-2-4. Color white, grayish, greenish, or reddish white. Luster of c(001) pearly; ot other faces vitreous; of surface of stalactites faint. Translucent; sometimes transparent in crystals. Indices, 1-535-1-558. A strong argillaceous odor when breathed on. Comp. Aluminium hydroxide, A1(OH) 3 or A1 2 3 .3H 2 = Alumina 65-4, water 34-6 = 100. Pyr., etc. In the closed tube becomes white and opaque, and yields water. B.B. in- ''usible, whitens, and does not impart a green color to the flame. Ignited with cobalt solution gives a deep blue color. Soluble in concentrated sulphuric acid. Artif . When solutions of sodium aluminate are slowly decomposed by carbon dioxide gibbsite is precipitated. Obs. The crystallized gibbsite (hydrargillite) occurs in the Shishimsk mountains near Zlatoust in the Ural Mts. ; also in crystals filling cavities in natrolite at Langesundfiord, Norway; Ouro Preto, Minas Geraes, Brazil. Occurs in nodular plates at Kodikanal, Palni Hills, Madras, and at Talevadi, Bombay, India. In the United States, in stalactitic form at Richmond, Mass., in a bed of limonite ; at the Clove Mine, Union Vale, Dutchess Co., N. Y., on limonite; in Orange Co., N. Y. Named after Col. George Gibbs. Sassolite. Boric acid, B(OH) 3 . Crystals tabular || c(001) (triclinic). Usually small, white, pearly scales. G. = 1'48. Index, 1*46. From the waters of the Tuscan lagoons of Monte Rotondo and Castelnuovo, Italy. Exists also in other natural waters, as at Clear Lake, in Lake Co., Cal. Occurs also abundantly in the crater of Vulcano, Lipari isles. Hydrotalcite. Perhaps Al(OH) 3 .3Mg(OH) 2 .3H 2 O. Lamellar-massive, or foliated, some- what fibroiR. H. =2. G. = 2 -04-2 '09. Color white. Luster pearly. Uniaxial, -. w = 1'47. Occurs at the mines of Shishimsk, district of Zlatoust, Ural Mts.; at Snarum, Norway, in serpentine. Pyroaurite. Perhaps Fe(OH) 3 .3Mg(OH) 2 .3H 2 O. Rhombohedral. Thin tabular crys- tals. H. = 2-3. G. = 2-07. Luster pearly to greasy. Color yellow to yellow-brown. Optically . Occurs at the Langban iron-mine, Wermland, Sweden, in gold-like sub- metallic scales (pyroaurite) . From the Moss mine, Norway. In thin seams of a silvery white color in serpentine in the island Haaf-Grunay, Scotland (igelstromite). Chalcophanite. Hydrofranklinite. (Mn,Zn)O.2MnO 2 .2H 2 O. In druses of minute tabular rhombohedral crystals; sometimes octahedral in aspect. Also in foliated aggre- gates; stalactitic and plumose. G. = 3 '907. Luster metallic, brilliant. Color oluish black to iron-black. Streak chocolate-brown, dull. Occurs at Sterling Hill, near Ogdens- burg, Sussex Co., N. J. From Leadville, Col. Hetserolite. 2ZnO.2Mn 2 O 3 .lH 2 O. In radiating botryoidal masses. Black. Brown- black streak. H. =5. G. = 4 '85. From Franklin, N. J., and Leadville, Col. (Wolf- tonite). 436 DESCRIPTIVE MINERALOGY ALAITE. V^Oe.H^O. Rare. Found in dark bluish red moss-like masses in Alai Mts., Turkestan. SHANYAVSKWE. A1 2 O 8 .4H 2 O. Amorphous, transparent material found in dolomite, near Moscow, Russia. PSILOMELANE. Massive and botryoidal; reniform; stalactitic. H. = 5-6. G. = 37-4-7. Luster submetallic, dull. Streak brownish black, shining. Color iron-black, passing into dark steel-gray. Opaque. Comp. A hydrous manganese manganate in wjrich part of the man- ganese is often replaced by barium or potassium, perhaps conforming to H 4 Mn0 6 . The material is generally very impure, and the composition hence doubtful. Pyr., etc. In the closed tube most varieties yield water, and all lose oxygen on igni- tion; with the fluxes reacts for manganese. Soluble in hydrochloric acid, with evolution of chlorine. Obs. A common but impure ore of manganese; frequently in alternating layers with pyrolusite. From Devonshire and Cornwall. In Germany at Ilefeld in the Harz Mts., at Ilmenau, Siegen, etc. From the Crimea, Russia; also various localities in India. Forms mammillary masses at Brandon, etc., Vt. In Independence Co., and elsewhere in Ark. With pyrolusite at Douglas, Hants Co., Nova Scotia. Named from ^i\6s, smooth or naked, and ne\as, black. Use. An ore of manganese. The following mineral substances here included are mixtures of various oxides, chiefly of manganese (MnO 2 , also MnO), cobalt, copper, with also iron, and from 10 to 20 p. c. water. These are results of the decomposition of other ores partly of oxides and sul- phides, partly of manganesian carbonates, and can hardly be regarded as representing distinct mineral species. WAD. In amorphous and reniform masses, either earthy or compact; also in crusting or as stains. Usually very soft, soiling the fingers; less often hard to H. =6. G. = 3'0- 4-26; often loosely aggregated, and feeling very light to the hand. Color dull black, bluish or brownish black. BOG MANGANESE consists mainly of oxide of manganese and water, with some oxide of iron, and often silica, alumina, baryta. ASBOLITE, or Earthy Cobalt, contains oxide of cobalt, which sometimes amounts to 32 p. c. LAMPADITE, or Cupreous Manganese, is a wad containing 4 to 18 p. c. of oxide of copper, and often oxide of cobalt also. SKEMMATITE. 3MnO 2 .2Fe 2 O 3 .6H 2 q. Color black. Streak dark brown. H. = 5'5-6. Fusible to magnetic globule. Alteration product of pyroxmangite. From Iva, Anderson Co., S. C. BELDONGRITE. 6Mn 3 6 .Fe2O 3 .8H 2 0. Luster pitchy. Color black. From Beldongri, District Ndgpur, India. VI. OXYGEN-SALTS The Sixth Class includes the salts of the various oxygen acids. These fall into the following seven sections: 1. Carbonates; 2. Silicates and Titanates; 3. Niobates and Tantalates; 4. Phosphates, Arsenates, etc.; also the Nitrates; 5. Borates and Uranates; 6. Sulphates, Chromates and Tellurates; 7. Tungstates and Molybdates. 1. CARBONATES A. Anhydrous Carbonates The Anhydrous Carbonates include two distinct isomorphous groups, the CALCITE GROUP and the ARAGONITE GROUP. The metallic elements CARBONATES 437 present in the former are calcium, magnesium, iron, manganese, zinc and cobalt; in the latter, they are calcium, barium, strontium and lead. The species included are as follows: 1. Calcite Group. RCO 3 . Rhombohedral Calcite Dolomite Normal Dolomite Ankerite Magnesite Breunnerite Mesitite Pistomesite Siderite Oligonite Rhodochrosite Manganosiderite Manganocalcite pt. Smithsonite Monheimite Sphaerocobaltite CaC0 3 (Ca,Mg)C0 3 CaC0 3 .MgC0 3 CaC0 3 .(Mg,Fe)C0 3 MgC0 3 (Mg,Fe)C0 3 2MgC0 3 .FeC0 3 MgCO 3 .FeCO 3 FeCO 3 (Fe,Mn)C0 3 MnCO 3 (Mn,Fe)C0 3 (Mn,Ca)CO 3 ZnCO 3 (Zn,Fe)C0 3 CoCO 3 Tri-rhombohedral rr' c 74 55' 0-8543 73 45' 0-8322 73 48' 0-8332 72 36' 0-8112 72 46' -8141 72 42' 0-8129 73 0' 0-8184 73 0' 0-8184 72 20' 0-8063 This list gives not only the prominent species of this group, but also some of the isomor- phous intermediate compounds. The CALCITE GROUP is characterized by rhombohedral crystallization. All the species show, when distinctly crystallized, perfect rhombohedral cleavage, the angle varying from 75 (and 105) in calcite to 73 (and 107) in siderite. This is exhibited in the table above. 2. Aragonite Group. RC0 3 . Orthorhombic Aragonite Bromlite Witherite Strontianite Cerussite CaCO 3 (Ca,Ba)CO, BaCO 3 SrC0 3 PbC0 3 mm'" 63 48' 62 12' 62 41' 62 46' a : b : c 0-6224 : 1 : 07206 0-6032 : 1 : 07302 0-6090 : 1 : 0*7239 0-6100 : 1 : 07230 The species of the ARAGONITE GROUP crystallize in the orthorhombic system, but the relation to those of the Calcite Group is made more close by the fact that the prismatic angle varies a few degrees only from 60 (and 120) and the twinned forms with the fundamental prism as twinning-plane are pseudo-hexagonal in character. 438 DESCRIPTIVE MINERALOGY 1. Calcite Group. RC0 3 . Rhombohedral CALCITE. Calc Spar; Calcareous Spar. Rhombohedral. Axis c = 0*8543. 731 732 733 734 735 cr* ce, me, rr'. MM', ff', 0001 A 1011 = 44 36'. 0001 A 0112 = 26 15'. 1010 A 0112 = 63 45'. 1011 A 1101 = 74 55'. 4041 A 4401 = 114 10'. 0112 A 1012 = 45 3' 0554 A 5054 = 84 324'. 0221 A 2021 = 101 9'. w', 2131 A 2311 = 75 22'. wv, 2131 A 3121 = 35 36'. wvi, 2131 A 1231 = 47 1|'. yy' t 3251 A 3521 = 70 59'. yyv, 3251 A 5231 = 45 32'. yy*, 3251 A 2351 = 29 16'. v , 2134 A 3124 = 20 36f '. wv, 3145 A 4135 = 16 0'. * See the stereographic projection, Fig. 269, p. 108. CARBONATES 439 Habit of crystals very varied, as shown in the figures, from obtuse to acute rhombohedral ; from thin tabular to long prismatic; and scalenohedral of many types, often highly modified. Twins (see Figs. 419-426, p. 168): (1) Tw. pi. c(0001), common, the crys- tals having the same vertical axis. (2) Tw. pi. 6(0112), very common, the vertical axes 750 inclined 127 29 J' and 52 30 J'; often producing twinning lamellae as in Iceland Spar, which are, in many cases, of secondary origin as in granular limestones (Fig. 750) ; this twinning may be produced artificially (see p. 188). (3) Tw. pi. r(10Tl), not common; the vertical axes inclined 90 46' and 89 14'. (4) Tw. pi. /(0221), rare; the axes intersect at angles of 53 46' and 126 14'. Also fibrous, both coarse and fine; sometimes lamellar; often granular; from coarse to impal- Section of crystalline limestone pable, and compact to earthy. Also stalactitic, in polarized light, tuberose, nodular, and other imitative forms. Cleavage: r(1011) highly perfect. Parting || e(0112) due to twinning. Fracture conchoidal, obtained with difficulty. H. = 3, but varying with the direction on the cleavage face; earthy kinds softer. G. = 2'714, in pure crystals, but varying somewhat widely in impure forms, as in those contain- ing iron, manganese, etc. Luster vitreous to sub vitreous to earthy. Color white or colorless; also various pale shades of gray, red, green, blue, violet, yellow; also brown and black when impure. Streak white or grayish. Transparent to opaque. Optically . Birefringence very high. Refractive indices for the D line : co = 1-65849, e = 1-48625. Comp. Calcium carbonate, CaC0 3 = Carbon dioxide 44'0, lime 56*0 = 100. Small quantities of magnesium, iron, manganese, zinc, and lead may be present replacing the calcium. Var. The varieties are very numerous, and diverse in appearance. They depend mainly on the following points: differences in crystallization and structural condition, presence of impurities, etc., the extremes being perfect crystals and earthy massive forms; also on composition as affected by isomorphous replacement. A. VARIETIES BASED CHIEFLY UPON CRYSTALLIZATION AND ACCIDENTAL IMPURITIES 1. Ordinary. In crystals and cleavable masses, the crystals varying very widely in habit as already noted. Dog-tooth Spar is an acute scalenohedral form; Nail-head Spar, a composite variety having the form suggested by the name. The transparent variety from Iceland, used for polarizing prisms, etc., is called Iceland Spar or Doubly-refracting Spar. As regards color, crystallized calcite varies from the kinds which are perfectly clear and colorless through yellow, pink, purple, blue, to brown and black. The color is usually pale except as caused by impurities. These impurities may be pyrite, native copper, malachite, sand, etc.; they are sometimes arranged in symmetrical form, as depending upon the growth of the crystals and hence produce many varieties. Fontainebleau limestone, from Fontainebleau and Nemours, France, contains a large amount of sand, some 50 to 63 p. c* Siliceous calcite crystals come from S. D., Wy., Cal., etc. 2. Fibrous and lamellar kinds. Satin Spar is fine fibrous, with a silky luster; resembles fibrous gypsum, also called satin spar, but is much harder than gypsum and effervesces with acids. Lublinite is a fibrous variety, probably pseudomorphous after some organic material. 440 DESCRIPTIVE MINERALOGY Argentine is a pearly lamellar calcite, the lamellae more or less undulating; color white, grayish, yellowish. Aphrite, in its harder and more sparry variety, is a foliated white pearly calcite, near argentine; in its softer kinds it approaches chalk, though lighter, pearly in luster, silvery white or yellowish in color, soft and greasy to the touch, and more or less scaly in structure. Aphrite has been thought to be aragonite pseudomorphous after gypsum. 3. Granular massive to cryptocrystalline kinds: Limestone, Marble, Chalk. Granular limestone or Saccharoidal limestone, so named because like loaf sugar in frac- ture, varying from coarse to very fine granular, and hence to compact limestone; colors are various, as white, yellow, reddish, green; usually they are clouded and give a handsome effect when the material is polished. When such limestones are fit for polishing, or for architectural or ornamental use, they are called marbles. Many varieties have special names. Shell-marble consists largely of fossil shells; Lumachelle or fire-marble is a dark brown shell-marble, with brilliant fire-like or chatoyant internal reflections. Ruin-marble is a kind of a yellow to brown color, showing, when polished, figures bearing some resem- blance to fortifications, temples, etc., in ruins, due to infiltration of iron oxide, etc. Lithographic stone is a very even-grained compact limestone, of buff or drab color; as that of Solenhofen, Bavaria. Hydraulic limestone is an impure limestone which after igni- tion sets, i.e., takes a solid form under water, due to the formation of a silicate. The French varieties contain 2 or 3 p. c. of magnesia, and 10 to 20 of silica and alumina (or clay). The varieties in the United States contain 20 to 40 p. c. of magnesia, and 12 to 30 p. c. of silica and alumina. Hard compact limestone varies from nearly pure white, through grayish, drab, buff, yellowish, and reddish shades, to bluish gray, dark brownish gray, and black, and sometimes variously veined. Many kinds make beautiful marble when pol- ished. Red oxide of iron produces red of different shades. Shades of green are due to iron protoxide, chromium oxide, iron silicate. Chalk is white, grayish white, or yellowish, and soft enough to leave a trace on a board. It is composed of the shells of minute sea organisms. Calcareous marl is a soft earthy deposit, with or without distinct fragments of shells; it generally contains much clay, and graduates into a calcareous clay. Oolite is a granular limestone, its grains minute concretions, looking somewhat like the roe of fish, the name coming from u6i>, egg. Pisolite consists of concretions as large often as a small pea, or larger, having usually a distinct concentric structure. Deposited from calcareous springs, streams, or in caverns, etc. (a) Stalactites are cal- careous cylinders or cones that hang from the roofs of limestone caverns, and which are formed from the waters that drip through the roof; these waters hold some calcium bicarbonate in solution, and leave calcium carbonate to form the stalactite when evapora- tion takes place. Stalactites vary from transparent to nearly opaque; from a crystalline structure with single cleavage directions to coarse or fine granular cleavable and to radi- ating fibrous; from a white color and colorless to yellowish gray and brown. (6) Stalag- mite is the same material covering the floors of caverns, it being made from the waters that drop from the roofs, or from sources over the bottom or sides; cones of it sometimes rise from the floor to meet the stalactites above. It consists of layers, irregularly curved, or bent. Stalagmite, or a solid kind of travertine (see below) when on a large scale, is the alabaster stone of ancient writers, that is, the stone of which ointment vases, of a certain form called alabasters, were made. A locality near Thebes, now well known, was largely explored by the ancients, and the material has often been hence called Egyptian alabaster. It was also formerly called onyx and onychites because of its beautiful banded structure. In the arts it is often now called Oriental alabaster or onyx marble. Very beautiful marble of this kind is obtained in Algeria. Mexican onyx is a similar material obtained from lecah, Puebla, Mexico; also in a beautiful brecciated form from the extinct crater of Zem- poaltepec in southern Mexico. Similar kinds occur in Missouri, Arizona, San Luis Obispo Co., California, (c) Calc-sinter, Travertine, Calc Tufa. Travertine is of essentially the same origin with stalagmite, but is distinctively a deposit from springs or rivers, especially where m large deposits, as along the river Anio, at Tivoli, near Rome, where the deposit is icores ot feet in thickness. Similar material is being deposited at the Mammoth Hot Springs, Yellowstone Park, (d) Agaric mineral; Rock-milk is a very soft white material, breaking easily m the fingers, deposited sometimes in caverns, or about sources holding lime in solution, (e) Rock-meal is white and light, like cotton, becoming a powder on the slightest pressure. B. VARIETIES BASED UPON COMPOSITION These include: Dolomitic calcite. Contains magnesium carbonate, thus graduating toward true dolomite. Also baricalcite (which contains some BaCO 3 ); similarly, stron- CARBONATES 441 tianocalcite (SrCO 3 ), ferrocalcite (FeCO 3 ), manganocalcite (MnCOa) (see under agnolite, p. 582), zincocalcite (ZnCO 3 ), plumbocalcite (PbCOs), cobal'ocalcite (CoCO 3 ). Pyr., etc. B.B. infusible, glows, and colors the flame reddish yellow; after ignition the assay reacts alkaline; moistened with hydrochloric acid imparts the characteristic lime color to the flame. In the solid mass effervesces when moistened with hydrochloric acid, and fragments dissolve with brisk effervescence even in cold acid. See further under aragonite, p. 447. Diff. Distinguishing characters: perfect rhombohedral cleavage; softness, can be scratched with a knife; effervescence in cold dilute acid; infusibility. Less hard and of lower specific gravity than aragonite (which see). Resembles in its different varieties the other rhombohedral carbonates, but is less hard, of lower specific gravity, and more readily attacked by acid. Also resembles some varieties of barite, but has lower specific gravity; it is less hard than feldspar and harder than gypsum. Micro. Recognized in thin sections by its low refraction and very high birefringence, the polarization colors in the thinnest sections attaining white of the highest order. The negative interference figure, with many closely crowded colored rings, is also character- istic. The rhombohedral cleavage is often shown in the fine fracture lines; systems of twinned lamellae often conspicuous (Fig. 750), especially in crystalline limestone. Artif . Crystals of calcite are formed when a solution of calcium carbonate in dilute carbonic acid is evaporated slowly at ordinary temperatures. Calcite is formed when aragonite is heated, the transformation being complete at 470. Obs. Calcite, in its various forms, is one of the most widely distributed of minerals. Beds of sedimentary limestone, formed from organic remains, shells, crinoids, corals, etc., yield on metamorphism crystalline limestone or marble, and in connection with these crystallized calcite and also deposits in caves of stalactites and stalagmites often occur. Common with the zeolites in cavities and veins of igneous rocks as a result of alteration, and similarly though less abundant with granite, syenite, etc. A frequent mineral in metalliferous deposits, with lead, copper, silver, etc. Deposited from lime- bearing waters as calc sinter, travertine, etc., especially in connection with hot springs as at the Mammoth Hot Springs in the Yellowstone region. Some of the best known localities for crystallized calcite are the following: Andreas^- berg in the Harz Mts.; the mines of Freiberg, Schneeberg, etc., in Saxony; Kapnik in Hungary; Aussig in Bohemia; Bleiberg in Carinthia; Traversella in Piedmont, Italy; Elba. In England at Alston Moor and Egremont in Cumberland; Matlock, Derbyshire; Beer Alston in Devonshire; at numerous points in Cornwall; Weardale in Durham; Stank mine, Lancashire, In twin crystals of great variety and beauty at Guanajuato, Mexico. The Iceland spar has been obtained from Iceland near Helgustadir on the Eske- fiord. It occurs in a large cavity in basalt. The crystals, usually showing the fundamental rhombohedron, are often coated with tufts of stilbite. In the United States, crystallized calcite occurs in N. Y., in St. Lawrence Co., especially at the Rossie lead mine; in Jefferson Co., near Oxbow; dog-tooth spar, in Niagara Co., near Lockport, with pearl spar, celestite, etc.; in Lewis Co., at Leyden nd Lowville, and at the Martinsburg lead mine; at Anthony's Nose on the Hudson, formerly groups of large tabular crystals; twins from Union Springs, Cayuga Co In N. J., at Bergen, yel- low calcite with datolite, etc. In Va., at Wier's cave, stalactites of great beauty; also in the large caves of Ky. In pyramidal crystals from Kelly's Island, Lake Erie. At the Lake Superior Copper mines, complex crystals often containing scales of native copper. At Warsaw, 111., in great variety of form, lining geodes and implanted on quartz crystals; at Quincy. In Mo., with dolomite, near St. Louis; also with sphalerite at Joplin and other points in the zinc region in the south-western part of the state, the crystals usually scaleno- hedral and of a wine-yellow color. Wis., from Hazel Green. From the Bad Lands, S. p. In Nova Scotia, at Partridge Island, a wine-colored calcite, and other interesting varieties. Use. In the manufacture of mortars and cements; as a building and ornamental material; as a flux in metallurgical operations; Iceland spar is used to make polarizing prisms; chalk as a fertilizer, in whitewash, etc. THINOLITE. A tufa deposit of calc um carbonate occurring on an enormous scale in north-western Nev.; also occurs about Mono Lake, Cal. It forms layers of interlaced crystals of a pale yellow or light brown color and often skeleton structure except when covered by subsequent deposit of calcium carbonate. 442 DESCRIPTIVE MINERALOGY DOLOMITE. Pearl Spar pt. Tri-rhombohedral. Axis c = 0-8322. or 0001 A 10T1 = 43 52'. MM', 4041 A 4401 = 113 53'. rr\ lOll A Ilt)l = 73 45'. Habit rhombohedral, usually r(10ll) or M(4041); the presence of rhom- bohedrons of the second or third 751 752 series after the phenacite type very characteristic. The r faces com- monly curved or made up of sub- individuals, and thus passing into saddle-shaped forms (Fig. 752). Also granular, coarse or fine, resembling ordinary marble. Cleavage: r(1011) perfect. Fracture subconchoidal. Brittle. H. = 3-5-4. G. = 2-8-2-9. Luster vitreous, inclining to pearly in some vari- eties. Color white, reddish, or greenish white; also rose-red, green, brown, gray and black. Transparent to translucent. Optically . w = 1-68174. e = 1-50256. Comp. Carbonate of calcium and magnesium (Ca,Mg)CO 3 ; for nor- mal dolomite CaMgC 2 O 6 or CaC0 3 MgCO 3 = Carbon dioxide 47-9, lime 30-4, magnesia 21'7 = 100, or Calcium carbonate 54-35, magnesium carbonate 45*65 = 100. Varieties occur in which the ratio of the two carbonates varies from 1:1. The carbonates of iron and manganese also frequently enter replacing the magnesium carbonate and grading to ankerite ; rarely cobalt and zinc carbonates. Pyr. t e tc. B.B. acts like calcite. In solution gives tests for magnesium and usually for iron. Fragments thrown into cold acid, unlike calcite, are only very slowly acted upon, if at all, while in powder in warm acid the mineral is readily dissolved with effervescence. The ferriferous dolomites become brown on exposure. Diff. Resembles calcite (see p. 441), but generally to be distinguished in that it does not effervesce readily in the mass in cold acid. Artif. Artificial dolomite has been formed in several ways. The results of many ex- periments would indicate that heat and pressure are favorable for its formation. Sea water in contact with calcium carbonate when heated in a sealed tube produced dolomite. It has been observed that such reactions take place more readily with aragonite than with calcite, indicating the possibility of coral deposits (aragonite) being transformed into dolomite. Micro. Similar to calcite in thin sections except that it more often shows crystal outlines and less commonly polysynthetic twinning. Obs. Massive dolomite constitutes extensive strata, called limestone strata, in various regions, as in the dolomite region of the southern Tyrol. Crystalline and compact varieties are often associated with serpentine and other magnesian rocks, and with ordinary lime- stones. Dolomite, as a rock, is of secondary origin, having been transformed from ordinary limestone by the action of solutions containing magnesium. This change, called dolomiti- zaiion, may take place in various ways. The more favorable conditions would involve heat, pressure, high magnesium content of waters and long periods of time. Consequently the older and more deeply buried in the earth's crust the greater is the probability of a lime- stone being converted into dolomite. Dolomite is also commonly a vein mineral, frequently occurring with various metallic ores. Some prominent localities are: Leogang in Salzburg, Austria; Schemnitz and Kapnik in Hungary; Freiberg in Saxony, Germany. In Switzer- land, at Bex, in crystals; also in the Binnental; Traversella in Piedmont and Campolongo, Italy. In unusual dark colored crystals from Teruel, Spain. In the United States, in Ver., at Roxbury. In N. J., at Hoboken. In N. Y. at Lock- port, Niagara Falls, etc.; at the Tilly Foster iron mine, Brewster, Putnam Co., with mag- netite, chondrodite. In Pa. at Phoenixville. In saddle-shaped crystals with the sphalerite CARBONATES 443 of Joplin, Mo. In N. C. at Stony Point, Alexander Co. In fine crystals from Alamosa, Alaska. Named after Dolomieu (1750-1801), who announced some of the marked characteristics of the rock in 1791 its not effervescing with acids, while burning like limestone, and solubility after heating in acids. Use. As a building and ornamental stone; for the manufacture of certain cements; for the production of magnesia used in the preparation of refractory linings in metallurgical furnaces . Ankerite. CaCO 3 .(Mg,Fe,Mn)CO 3 ,_or for normal ankerite 2CaCO 3 .MgCO 3 .FeCO 3 . In rhombohedral crys als; rr' 1011 A 1101 =73 48' also crystalline massive, granular, compact. G. = 2 -95-31. Color white, gray, reddish. Occurs with siderite at the Styrian mines. From Traversella, Italy. With the hematite of northern New York/ MAGNESITE. Rhombohedral Axis: c = 0-8112. rr' 1011 A TlOl = 72 36'. Crystals rare, usually rhombohedral, also prismatic. Commonly massive; granular cleavable to very compact; earthy. Cleavage: r(1011) perfect. Fracture flat conchoidal. Brittle. H. = 3-5- 4-5. G. = 3-0-3-12, cryst. Luster vitreous; fibrous varieties sometimes silky. Color white, yellowish, or grayish white, brown. Transparent to opaque. Optically . co = 1*717. c = 1*515. Comp. Magnesium carbonate, MgC0 3 = Carbon dioxide 52'4, mag- nesia 47-6 = 100. Iron carbonate is often present. Breunnerite contains several p. c. of FeO; G. = 3-3 '2; white, yellowish, brownish, rarely black and bituminous; often becoming brown on exposure, and hence called Brown Spar. Pyr., etc. B.B. resembles calcite and dolomite, and like the latter is but slightly acted upon by cold acids; in powder is readily dissolved with effervescence in warm hydro- chloric acid. In solution gives strong test for magnesium with little or no calcium. Obs. Found as a secondary mineral formed by the alteration of various magnesian minerals; in talcose schist, serpentine and other magnesian rocks, also gypsum; as veins in serpentine, or mixed with it so as to form a variety of verd-antique marble. Occurs at Hrubschiitz in Moravia; at Kraubat and Maria-ZeU, Styria; Greiner in the Zillertal, Tyrol, Austria; Snarum, Norway. In the United States, in Mass., at Bolton; at Roxbury, veining serpentine; in Md., at- Barehills, near Baltimore; in Pa., in crystals, at West Goshen, Chester Co., near Texas, Lancaster Co.; in Cal. it is mined in Tulare, Kern, Santa Clara, Sonoma Cos. and else- where. A white saccharqidal magnesite resembling statuary marble has been found as loose blocks on an island in the St. Lawrence River, near the Thousand Island Park. In small prismatic crystals from Orangedale, Nova Scotia. Use. In the preparation of magnesite brick for the linings of metallurgical furnaces; in the manufacture of various chemical compounds, as epsom salts, magnesia, etc. Intermediate between magnesite and siderite are: MESITITE. 2MgCO 3 .FeCO 3 . rr' lOll A TlOl = 72 46'. G. = 3-35-3-36. Usually in flat rhombohedrons (e, 0112) with rounded faces. Traversella, Piedmont, Italy. PISTOMESITE. MgCOs.FeCOs = Magnesium carbonate 42'0, iron carbonate 58'0 = 100. rr' 1011 A TlOl = 72 42'. G. = 3 '42. Thurnberg, Salzburg, Austria; also Traversella, Italy. SIDERITE. Chalybite, Spathic Iron. Rhombohedral. Axis c = 0-8184. cr, 0001 A lOTl = 43 23'. rr', 1011 A 1101 = 73 0'. cM, 0001 A 4041 = 75 11'. MM', 4041 A 4401 = 113 42'. cs, 0001 A 0551 = 78 3'. ss', 0551 A 5051 = 115 50'. cd, 0001 A 0881 = 82 28'. dd', 0881 A 8081 = 118 18'. Crystals commonly rhombohedral r (1011) or e(0112) the faces, often curved and built up of sub-individuals like dolomite. Often cleavable massive 444 DESCRIPTIVE MINERALOGY to coarse or fine granular. Also in botryoidal and globular forms, subfibrous within, occasionally silky fibrous; compact and earthy. Cleavage: r(1011) perfect. Fracture uneven or subconchoidal. Brittle. H. = 3'5-4. G. = 3-83-3-88. Luster vitreous, inclining to pearly. Color ash-gray, yellowish gray, greenish gray, also brown and brownish red, rarely green; and sometimes white. Streak white. Translucent to subtranslucent. Optically -. = 1'873. = 1-633. Comp. Iron protocarbonate, FeC0 3 = Carbon dioxide 37-9, iron pro- toxide 62-1 = 100 (Fe = 48'2 p. c.). Manganese may be present (as in oligonite, manganospherite) , also magnesium and calcium. Pyr., etc. In the closed tube decrepitates, gives off CO 2 , blackens and becomes mag- netic. B.B. blackens and fuses at 4 '5-5. With the fluxes reacts for iron, and with soda and niter on platinum foil generally gives a manganese reaction. Only slowly acted upon by cold acid, but dissolves with brisk effervescence in hot hydrochloric acid. Exposure to the atmosphere darkens its color, rendering it often of a blackish brown or brownish red color. Diff. Characterized by rhombohedral form and cleavage. Specific gravity higher than that of calcite, dolomite and ankerite. Resembles some sphalerite but lacks the resinous luster, differs in cleavage angle and yields COa (not H^S) with hydrochloric acid. Obs. ,Siderite may form as " bog ore " by the action, out of contact with the air, of organic matter in a bicarbonate solution. It may also be formed by the action of ferrous solutions upon limestones. It frequently occurs also as a vein mineral. It occurs in many of the rock strata, in gneiss, mica slate, clay slate, and as clay iron-stone in connection with the Coal formation and many other stratified deposits. It is often associated with metallic ores. At Freiberg, Saxony, it occurs in silver mines. In Cornwall it accompanies tin. It is also found accompanying copper and iron pyrites, galena, chalcocite, tetrahedrite. Occa- sionally it is to be met with in trap rocks as spherosiderite in globular concretions. Exten- sive deposits occur in the Eastern Alps, in Styria and Carinthia at Tavetsch, Switzerland. At Harzgerode and elsewhere in the Harz Mts., it occurs in fine crystals in gray-wacke; also in Cornwall of varied habit at many localities; at Alston-Moor, and Tavistock, Devon- shire. In large rhombohedrons from Allevard, France. Fine cleavage masses occur with cryolite in Greenland. In the United States, in Ver., at Plymouth. In Mass., at Sterling. In Conn., at Rox- bury, an extensive vein in quartz, traversing gneiss. In N. Y., a series of deposits occur in Columbia Co.; at the Rbssie iron mines, St. Lawrence Co. In N. C., at Fentress and Har- lem mines. The argillaceous carbonate, in nodules and beds (clay ironstone), is abundant in the coal regions of Pa., Ohio, and many parts of the country. In a clay-bed under the Tertiary along the west side of Chesapeake Bay for 50 m. Use. An ore of iron. RHODOCHROSITE. Dialogite. Rhombohedral. Axis c = 0-8184, rr' 1011 A TlOl =_73 0'. Distinct crystals not common; usually the rhombohedron r(1011); also e(0112), with rounded striated faces. Cleavable, massive to granular-massive and compact. Also globular and botryoidal, with columnar structure, sometimes indistinct; incrusting. Cleavage: r(10Tl) perfect. Fracture uneven. Brittle. H. = 3-5-4-5. G. = 3-45-3*60 and higher. Luster vitreous, inclining to pearly. Color shades of rose-red; yellowish gray, fawn-colored, dark red, brown. Streak white. Translucent to subtranslucent. Optically -. co = 1-820. e = 1*600. Comp. Manganese protocarbonate, MnCO 3 = Carbon dioxide 38'3, manganese protoxide 61-7 = 100. Iron carbonate is usually present even up to 40 p. c , as in manganosiderite; sometimes the carbonate of calcium, as in manganocalcite, also magnesium, zinc, and rarely cobalt. green manganate. CARBONATES 445 effervescence in warm hydrochloric acid. On exposure to the air changes to brown, and some bright rose-red varieties become paler. Diff. Characterized by its pink color, rhombohedral form and cleavage, effervescence in acids. Obs. Occurs commonly in veins along with ores of silver, lead and copper, and with other ores of manganese. Found at Schemnitz and Kapnik in Hungary ; Nagyag in Tran- sylvania; ponite is a ferriferous variety from Roumania; in Germany at Freiberg in Sax- ony; at Diez near Oberneisen in Nassau; at Daaden, Rheinprovinz ; in Belgium at Moet-Fontaine in the Ardennes. A variety containing 45 per cent of zinc carbonate from Rosseto, Elba, has been called zincorodochrosite. In the United States at Branchville, Conn.; in N. J., with franklinite at Mine Hill, Franklin Furnace. In Col., at the John Reed mine, Alicante, Lake Co., in beautiful clear rhombohedrons ; also at the Oulay mine, near Lake City and Alma, Park Co.; in Chaff ee, Gilpin and Ouray Cos. In Mon., at Butte City. Abundant at the silver mines of Austin, Nev. At Placentia Bay, Newfoundland. Named rhodochrosite from podov, a rose, and xpoxris, color; and dialogite, from 5ux\oyrj, doubt. Use. A minor ore of manganese. SMITHSONITE. Calamine pt. Dry-bone ore Miners. Rhombohedral. Axis c = 0-8063. rr f lOll A IlOl = 72 20'. Rarely well crystallized; faces r(1011) generally curved and rough. Usually reni- form, botryoidal, or stalactitic, and in crystalline incrustations; also granular, and sometimes impalpable, occasionally earthy and friable. Cleavable: r(1011) perfect. Fracture uneven to imperfectly conchoidal. Brittle. H. = 5. G. = 4*30-4 '45. Luster vitreous, inclining to pearly. Streak white. Color white, often grayish, greenish, brownish white, some- times green, blue and brown. Subtransparent to translucent. Optically . co = 1-818. e - 1-618. Comp. Zinc carbonate, ZnCO 3 = Carbon dioxide 35-2, zinc protoxide 64-8 = 100. Iron carbonate is often present (as in monheimite) ', also manga- nese and cobalt carbonates; further calcium and magnesium carbonates in traces; rarely cadmium and indium. Pyr., etc. In the closed tube loses carbon dioxide, and, if pure, is yellow while hot and white on cooling. B.B. infusible, giving characteristic zinc flame; moistened with co- balt solution and heated in O.F. gives a green color on cooling. With soda on charcoal coats the coal with the oxide, which is yellow while hot and white on cooling; this coating, moistened with cobalt solution, gives a green color after heating in O.F. Soluble in hydrochloric acid with effervescence. Diff. Distinguished from calamine, which it often closely resembles, by its efferves- cence in acids. Obs. Found both in veins and beds, especially in company with galena and sphalerite; also with copper and iron ores. It usually occurs in calcareous rocks, and is generally asso- ciated with calamine, and sometimes with limonite. It frequently replaces limestone, pseu- domorphs after calcite crystals being often observed. Commonly a secondary mineral and is often produced by the action of carbonated waters upon zinc sulphide. Often is in a porous, honey-comb-like material, known commonly as "dry-bone" ore. Found at Nerchinsk in Siberia; at Dognaczka in Hungary; Bleiberg and Raibel in Carinthia; Wiesloch in Baden and at AJtenberg, Germany. Moresnet in Belgium and Altenberg. In the province of Santander, Spain, at Puente Viesgo. In England, at Roughten Gill, Alston Moor, near Matlock, in the Mendip Hills, and elsewhere; in Ireland, at Donegal. At Laurion, Greece, varieties of many colors; from Sardinia. From Broken Hill, New South Wales. In the United States, in Pa., at Lancaster abundant, the variety called "dry-bone"; at the Ueberroth mine, near Bethlehem, in scalenohedrons. In Wis., at Mineral Point, Shullsburg, etc., pseudomorphs after sphalerite and calcite. In la., at Swing's diggings, N. W. of Dubuque, etc. In south-western Mo., associated with sphalerite and calamine. In Ark., at Calamine, Lawrence Co.; in Marion Co. A pink cobaltiferous variety occurs at Boleo, Lower California. In N. M. from Socorro Co. and in translucent green botryoidal masses from Kelly. In Tooele Co., Utah. 446 DESCRIPTIVE MINERALOGY Named after James Smithson (1754-1829), who founded the Smithsonian Institution in Washington. The name calamine is frequently used in England, cf. calamme, p. 539. Use. An ore of zinc. Sphserocobaltite. Cobalt protocarbonate, CoCO 3 . Rhombohedral In small spheri- cal masSs with crystalline surface, rarely in crystals. G. = 4 '02-4-13. Color rose-red. From Schneeberg, Saxony. From Boleo, Lower California. 2. Aragonite Group. RC0 3 . Orthorhombic For list of species, see p. 437. ARAGONITE. Orthorhombic. Axes a : b : c = 0'62244 : 1 : 072056. mm"', 110 A 110 = 63 48'. kk' Oil A Oil = 71 33'. pp' 111 A 111 = 86 24'. pp"', 111 A 111 = 50 27'. Crystals often acicular, and characterized by the presence of acute domes or pyramids. Twins: tw. pi. ra(110) commonly repeated, producing pseudo- 763 ' 754 755 756 757 \ m \ hexagonal forms (see Figs. 755-757) . Also globular, renif orm, and coralloidal shapes; sometimes columnar, straight or divergent; alsostalactitic; incrusting. Cleavage: 6(010) distinct; also ra(110); fc(Oll) imperfect. Fracture subconchoidal. Brittle. H. = 3'5^. G. = 2*93-2-95. Luster vitreous, inclining to resinous on surfaces of fracture. Color white; also gray, yel- low, green and violet; streak uncolored. Transparent to translucent. Op- tically -. Ax. pi. || a(100). Bx J_ c(001). Dispersion p > v small. 2 E = 30 54'. a = 1-531. = 1-682. 7 = 1-686. Comp. Calcium carbonate, CaCO 3 = Carbon dioxide 44'0, lime 56*0 = 100. Some varieties contain a little strontium, others lead, and rarely zinc. Aragonite changes to calcite at 470. Var. Ordinary, (a) Crystallized in simple or compound crystals, the latter much the most common; often in radiating groups of acicular crystals. Columnar; also fine fibrous with silky luster, (c) Massive. Stalactitic or stalagmitic: Either compact or fibrous in structure, as with calcite; Spru- delstein is stalactitic from Carlsbad, Bohemia. Coralloidal: In groupings of delicate inter- lacing and coalescing stems, of a snow-white color, and looking a little like coral; often called Flosferri. Tarnowitzite is a kind containing lead carbonate (4 to 8 p. c.), from Tarnowitz in Silesia; with G. = 2 '99. Zeyringite is a calcareous sinter, probably aragonite, colored greenish white or sky-blue with nickel, from Zeyring, Styria. Nicholsonite is aragonite containing zinc from Leadville, Col., and the Tintic District, Utah. CARBONATES 447 Pyr., etc. B.B. whitens and falls to pieces, and sometimes, when containing strontia, imparts a more intensely red color to the flame than lime; otherwise reacts like calcite. When immersed in cobalt nitrate solution powder turns lilac and the color persists on boiling while calcite under like conditions remains uncolored or becomes blue on long boiling. It is stated that these tests are not always strictjy reliable. DM. Distinguished from calcite by higher specific gravity and absence of rhombo- hedral cleavage; from the zeolites (e.g., natrolite), etc., by effervescence in acid. Stron- tianite and witherite are fusible, higher in specific gravity and yield distinctive flames B.B. The resinous luster on fracture surfaces is to be noted. Artif . Aragonite will form when solutions of calcium carbonate are evaporated at temperatures from 80 to 100; it will form at lower temperatures if the solution contains some sulphate or small amounts of the carbonates of strontium or lead. Obs. The most common repositories of aragonite are beds of gypsum; also beds of iron ore, as the Styrian mines, where it occurs in coralloidal forms, and is denominated flos- ferri, "flower of iron"', in cavities in basalt and lavas ; often associated with copper and iron pyrites, galena, and malachite. It constitutes the pearly layer of shells and the skeleton material of corals. First discovered in Aragon, Spain (whence its name), at Molina and Valencia, in six- sided prisms, with gypsum, similarly at Dax, France. Prominent localities are Bilin, Bohemia; Racanbunto, Silesia; Leogang in Salzburg, Austria; Herrengrund, Hungary; with sulphur in Sicily in fine prisms; also at Alston Moor and elsewhere, England, fine frequently replaced by native copper from Coro-Coro, Bolivia. In fibrous crusts at Hoboken, N. J.; at Edenville and Rossie, N. Y.; Wood's Mine, Lancaster Co., Pa.; Warsaw, 111., lining geodes; Mine-la-Motte, Mo., in crystals. Flos- ferri in the Organ Mts., N. M.; from Bisbee, Ariz. Ktypeite is calcium carbonate in the form of pisolites from Carlsbad, Bohemia, and Hammam-Meskoutine, Algeria. G. = 2'58-270. Decrepitates when heated and changes to calcite. WITHERITE. Orthorhombic. Axes a : b : c = 0-6032 : 1 : 07302. Crystals always re- peated twins, simulating hexagonal pyramids. Also massive, columnar or granular. Cleavage: 6(010)distinct; m(110) imperfect. Fracture uneven. Brittle. H. = 33*75. G. = 4'27-4'35. Luster vitreous, inclining to resinous on sur- faces of fracture. Color white, yellowish, grayish. Streak white. Subtrans- parent to translucent. Optically -. a = 1'529. = 1-676. 7 = 1-677. Comp. Barium carbonate, BaCO 3 = Carbon dioxide 22*3, baryta 77 -7 = 100. Pyr., etc. B.B. fuses at 2 to a bead, coloring the flame yellowish green; after fusion reacts alkaline. B.B. on charcoal with soda fuses easily, and is absorbed by the coal. Solu- ble in dilute hydrochloric acid; this solution, even when very much diluted, gives with sul- phuric acid a white precipitate which is insoluble in acids. Diff. Distinguished by its high specific gravity; effervescence in acid; green colora- tion of the flame B.B. Barite is insoluble in hydrochloric acid. Obs. Occurs at Alston Moor in Cumberland, with galena; at Fallowfield near Hex- ham in Northumberland; Tarnowitz in Silesia. Leogang in Salzburg, Austria. Near Lexington, Ky., with barite. In a silver-bearing vein near Rabbit Mt., Thunder Bay, Lake Superior. From Tsubaki mine, Prov. Ugo, Japan. Use. A minor source of barium compounds. Bromlite. (Ba,Ca)CO 3 . In pseudohexagonal pyramids (Figs. 611, 612, p. 299). In- dices, 1*525-1 '670. Bromley Hill, near Alston, Cumberland, England. STRONTIANITE. Orthorhombic. Axes a : b : c = 0-6090 : 1 : 07239. Crystals often acicular or acute spear-shaped, like aragonite. Twins: tw. pi. m(110) common. Also columnar, fibrous and granular. Cleavage: ra(110) nearly perfect; 6(010) in traces. Fracture uneven. Brittle. H. = 3-5-4. G. = 3-680-3-714. Luster vitreous; inclining to 448 DESCRIPTIVE MINERALOGY resinous on faces of fracture. Color pale asparagus-green, apple-green; also white, gray, yellow, and yellowish brown. Streak white. Transparent to translucent. Optically -. Ax. pi. || Z>(&10). Bx _L c(001). Dispersion p < v small. 2E r = 12 17'. a = t'52f6. (3 = T667. y = T667. Comp. Strontium carbonate, SrCOs = Carbon diozide 29*9, strontia 70-1 = 100. A little calcium is sometimes present. Pyr., etc. B.B. swells up, throws out minute sprouts, fuses only on the thin edges, and colors the flame strontia-red; the assay reacts alkaline after ignition. Moistened with hydrochloric acid and treated either B.B. or in the naked lamp gives an intense red color. Soluble in hydrochloric acid; the mediumly dilute solution when treated with sulphuric acid gives a white precipitate. Diff. Differs from related minerals, not carbonates, in effervescing with acids; has a higher specific gravity than aragonite and lower than witherite; colors the flame red B.B. Obs. Occurs at Strontian in Argyllshire and in Yorkshire, England; Claustal in the Harz Mts., Germany; Braunsdorf, near Freiberg, Saxony; Leogang in Salzburg, Austria; near Brixlegg, Tyrol, Austria (calciostrontianite) ; in Westphalia, Germany in fine crystals near Hamm, and at the Wilhelmine mine near Altahlen. In the United States, occurs in N. Y. at Schoharie, at Muscalonge Lake, Chaumont Bay and Theresa, in Jefferson Co.; Mifflin Co., Pa. Use. A minor source of strontium compounds. CERUSSITE. White Lead Ore. Orthorhombic. 758 Axes a : 6 : c = 0-60997 : 1 : 072300. mm'", 110 A 110 = 62 46'. 759 760 J*', oil A Oil = 71 44'. ii', 021 A 021 = 110 40'. cp, 001 A 111 = 54 14'. pp'j 111 A 111 = 87 42'. pp'", 111 A 111 = 49 59'. Simple crystals often tabular || 6(010), pris- matic || caxis; also pyr- amidal. Twins: tw. pi. m(110) very common, contact- and penetration- twins, often repeated yielding six-rayed stellate groups. Crystals grouped in clusters, and aggregates. Rarely fibrous, often granular massive and compact- earthv Sometimes stalactitic. Cleavage: m(110) and {(021) distinct; 6(010) and z(012) in traces. Fracture conchoidal. Very brittle. H. = 3-3-5. G. = 6-46-6-574. Luster adamantine, inclining to vitreous, resinous, or pearly; sometimes submetallic. Color white gray, grayish black, sometimes tinged blue or green (copper); streak uncolored. Transparent to subtranslucent. Optically-. Ax. nil 6(010). Bx _L c(001). Dispersion p > v large. 2 V = 8 14'. a = 1-804 p = 2*076. 7 = 2-078. Q rF m i P nVT~ Lead carbonate > p bC0 3 = Carbon dioxide 16-5, lead oxide oo.o = 1UU- at - ecr epitates, loses carbon dioxide, turns first yellow, and n yellow on coolin ^ B ' B ' on cha al d ' Soluble in dilute nitric acid with Aiding CAEBONATES 449 Artif . Cerussite has been produced artificially by the slow diffusion of a carbonate solution into a lead solution through a porous membrane; by the action of a carbonate solution upon a lead plate. Obs. A secondary mineral occurring in connection with other lead minerals, and is formed from galena, which, as it passes to a sulphate, may be changed to carbonate by means of solutions of calcium bicarbonate. It is tound in Germany at Johanngeorgenstadt in beautiful crystals; Friedrichssegen, Nassau; Badenweiler, Baden; at Claustal in the Harz Mts. Other important localities are Monte Poni, Sardinia; at Bleiberg in Carinthia; at Mies and Pfibram, Bohemia; in England, in Cornwall; at East Tamar mine, Devonshire; near Matlock and Wirksworth, Derbyshire; at Leadhill and Wanlockhead, Scotland. Fine crystals from Broken Hill, New South Wales. Found in Pa., at Phenixyille. In Va., at Austin's mines, Wythe Co. In N. C., in King's mine. In lead mines of Wis. but rarely in crystals; at Hazelgreen, crystals coating galena. In Col., at Leadyille, and elsewhere. In Ariz., at the Flux mine, Pima Co., in large crys- talline masses; in crystals at the Red Cloud mine, Yuma Co. In Utah from Flagstaff mine; in Idaho at Wardner and Kingston. Use. An ore of lead. BARYTOCALCITE. Monoclinic. Axes a : b : c = 07717 : 1 : 0-6254; /3 = 73 52'. In crys- tals; also massive. Cleavage: ra( 110) perfect; c(001) less so. Fracture uneven to subcon- choidal. Brittle. H. = 4. G. = 3 -64-3 '66. Luster vitreous, inclining to resinous. Color white, grayish, greenish or yellowish. Streak white. Trans- parent to translucent. Optically -. a = 1-525. = 1'684. 7 = 1-686. Comp. Carbonate of barium and calcium, BaCO 3 .CaCO 3 = Carbon dioxide 29'6, baryta 51 '5, lime 18'9 = 100. Pyr., etc. B.B. colors the flame yellowish green, and at a high temperature fuses on the thin edges and assumes a pale green color; the assay reacts alkaline after ignition. Soluble in dilute hydrochloric acid with effervescence. Dilute solution gives an abundant precipitate, BaSO 4 , with a few drops of sulphuric acid. Obs. Occurs at Alston Moor in Cumberland, England, in limestone with barite and fluorite. ROSASITE. 2CuO.3CuC0 3 .5ZnC0 3 ?. Mammillary fibrous of a bright green to sky- blue color. From Rosas mine at Sulcis, Sardinia. Bismutospharite. Bi 2 (CO3)3.2Bi 2 O3. In spherical forms with radiated structure. G. = 7 '42. Color yellow to gray or blackish brown. From Schneeberg, Saxony. Also sparingly at Willimantic and Portland, Conn., as a result of the alteration of bismuthinite. From the Stewart mine, Pala, San Diego Co., Cal. Rutherfordine. Uranyl carbonate, UO 2 CO 3 . A yellow ocher resulting from alteration of uraninite. G. = 4*8. From Uruguru Mts., German East Africa. Parisite. A fluocarbonate of the cerium metals, [(Ce,La,Di)F] 2 Ca(C0 3 )2. Rhombo- hedral. Crystals small and slender. Habit pyramidal or prismatic. Crystals horizontally grooved due to oscillatory combination of faces. H. = 4'5. G. = 4*358. Color brownish yellow. Optically + . co = 1*676. e = 1757. From the emerald mines, Muso, Colom- bia; Ravalli, Mon.; Quincy, Mass.; Montorfano, Italy; Narsarsuk, Greenland (syn- chisite) . Cordylite is a parisite containing barium from Narsarsuk, South Greenland. Other material from Narsarsuk thought to be a new species and named synchisite is parisite. Bastnasite. Hamartite. A fluocarbonate of the cerium metals (RF)COs. H. = 4 '5- G. = 4 '948. Color wax-yellow to reddish brown. Uniaxial, +. Strong birefringence. cc = 1715. From the Bastnas mine, Riddarhyttan, Sweden. Also in parallel growth with tysonite in the granite of the Pike's Peak region in Colorado. Found to the east of Ambo- sitra, Madagascar. Ancylite. 4Ce(OH)CO 3 .3SrCO 3 .3H 2 O. Orthorhombic. In small pyramids with curved faces and edges. H. =4'5. G. = 3 '9. Color light yellow, orange, brown, gray. Infu- sible. From Narsarsuk, Greenland. WeibyeUe is a related mineral. Ambatoarinite. A carbonate of strontium and the rare earths. Orthorhombic? In crystals with parallel axes, forming skeleton-like groups. Index, > 1'66. From Arnba- toarina, near Ambositra, Madagascar. 450 DESCRIPTIVE MINERALOGY PHOSGENITE. Tetragonal. Axis c = 1-0876. Crystals prismatic; sometimes tabular Cleavage: m(110), a(100) distinct; also c(001). Rather sectile. H. = 275-3. G. = 6-0-6-3. Luster adamantine. Color white, gray, and yellow. Streak white. Transparent to translucent. Optically +. w = 2-114. e = Comp. Chlorocarbonate of lead, (PbCl) 2 CO 3 or PbCO 3 .PbCl 2 = Lead carbonate 49'0, lead chloride 51*0 = 100. Pyr., etc. B.B. melts readily to a yellow globule, which on cooling becomes white and crystalline. On charcoal in R.F. gives metallic lead, with a white coating of lead chloride. Dissolves with effervescence in dilute nitric acid and solution reacts for chlorine with silver nitrate. Obs. At Cromford near Matlock in Derbyshire; at Gibbas, Monte Pom and Monte- vecchio in Sardinia. From Broken Hill, New South Wales; Dundas, Tasmania. Northupite. MgCO 3 .Na 2 CO3.NaCl. In isometric octahedrons. H. = 3'5-4. G. = 2'38. White to yellow or gray, n = T514. From Borax Lake, San Bernardino Co., Cal. Tychite. 2MgCO 3 .2Na 2 CO3.Na2SO4. Isometric. Octahedral habit. H. = 3'5. G. = 2'5. n = l;51. Very rare. From Borax Lake, San Bernardino Co., Cal., associated with northupite. B. ACID, BASIC, AND HYDROUS CARBONATES Teschemacherite. Acid ammonium carbonate, HNH 4 CO 3 . Orthorhombic. In yel- lowish to 'white crystals. G. = 1'45. Indices, 1'423-1'536. From guano deposits of Africa, Patagonia, the Chincha Islands. MALACHITE. Monoclinic. Axes a : b : c = 0-8809 : 1 : 0-4012; $ = 61 50'. Crystals rarely distinct, usually slender, acicular prisms (mm"' 110 A 110 = 75 40'), grouped in tufts and rosettes. Twins: tw. pi. a(100) common. Commonly massive or incrusting, with surface botryoidal, or stalactitic, and structure divergent; often delicately compact fibrous, and banded in color; frequently granular or earthy. Cleavage: c(001) perfect; 6(010) less so. Fracture subconchoidal, un- even. Brittle. H. = 3-5-4. G. = 3-9-4-03. Luster of crystals admantine, inclining to vitreous; of fibrous varieties more or less silky; often dull and earthy. Color bright green. Streak paler green. Translucent to sub- translucent to opaque. Optically . /3 = 1'88. Comp. Basic cupric carbonate, CuC0 3 .Cu(OH) 2 = Carbon dioxide 19-9, cupric oxide 71-9, water 8'2 = 100. Pyr., etc. In the closed tube blackens and yields water. B.B. fuses at 2, coloring the flame emerald-green; on charcoal is reduced to metallic copper; with the fluxes reacts like cuprite. Soluble in acids with effervescence. Diff. Characterized by green color and -copper reactions B.B.; differs from other copper ores of a green color in its effervescence with acids. Artif. Malachite has been formed artificially by heating precipitated copper carbon- ate with a solution of ammonium carbonate for several days. Obs. Common with other ores of copper and as a product of their alteration ; thus as a pseudomorph after cuprite and azurite. Occurs abundantly in the Ural Mts.; at Chessy in France; in Cornwall and in Cumberland, England; in Germany at Rheinbreit- bach; Dillenburg, Nassau; Betzdorf near Siegen. At the copper mines of Nizhni Tagilsk, Russia; with the copper ores of Cuba; Chile; at the Cobar mines and elsewhere in New bouth Wales; South Australia; Rhodesia. In crystals from Katanga, Congo, and Min- douh, French Congo. CARBONATES 451 Occurs in N. J., at Schuyler's mines, and at New Brunswick. In Pa., at Cornwall, Lebanon Co.; at the Perkiomen and Phenixville lead-mines. In Wis., at the copper mines, of Mineral Point, and elsewhere. Abundantly in fine masses and acicular crystals, with calcite at the Copper Queen mine, Bisbee, Cochise Co., Ariz.; also in Graham Co., at Morenci (6 m. from Clifton), in stalactitic forms of malachite and azurite in concentric bands. At the Santa Rita mines, Grant Co., and elsewhere in N. M. Tintic district, Utah. In pseudomorphs from Good Springs, Nev. Named from naXaxi), mallows, in allusion to the green color. Use. An ore of copper; at times as an ornamental stone. AZURITE. Monoclinic. Axes a : b : c = 0-8501 : 1 : 0-8805; = 87 36'. 761 762 763 mm'", 110 A 110 = 80 41'. ac, 100 A 001 = 87 36'. ca, 001 A 101 = 44 46'. II', 023 A 023 = 60 47'. pp f , 021 A 021 = 120 47'. cm, 001 A 110 = 88 10'. cd, 001 A 243 = 54 29'. hh f , 221 A 221 = 73 56'. Crystals varied in habit and highly modified. Also massive, and present- ing imitative shapes, having a columnar composition; also dull and earthy. Cleavage: p(021) perfect but interrupted; a(100) less perfect; ra(HO) in traces. Fracture conchoidal. Brittle. H. = 3-5-4. G. = 3-77-3-83. Lus- ter vitreous, almost adamantine. Color various shades of azure-blue, passing into Berlin-blue. Streak blue, lighter than the color. Transparent to sub- translucent, a = 1730. 0-= 1-758. 7 = 1-838. Comp. Basic cupric carbonate, 2CuCO 3 .Cu(OH) 2 = Carbon dioxide 25-6, cupric oxide 69-2, water 5 -2 = 100. Pyr., etc. Same as in malachite. Diff. Characterized by its blue color; effervescence in nitric acid; copper reactions B.B. Artif . Azurite has been formed by allowing a solution of copper nitrate to lie in con- tact with fragments of calcite for several years. Obs. Occurs in splendid crystallizations in France at Chessy, near Lyons, whence it derived the name Chessy Copper or chessylite. Also in fine crystals in Siberia; Moldawa in the Banat, Hungary; at Wheal Buller, near Redruth in Cornwall; in Devonshire and Derby- shire, England; at Broken Hill and elsewhere in New South Wales; South Australia. Occurs in Pa., at Phenixville, in crystals. In N. J., near New Brunswick. In Wis., near Mineral Point. In Ariz., at the Longfellow and other mines in Graham Co.; with malachite in beautiful crystals at the Copper Queen mine, Bisbee; at Morenci. In Grant Co., N. M. At the Mammoth mine in the Tintic district and in Tooele Co., Utah. In Cal., Calaveras Co., at Hughes's mine, in crystals. Use. An ore of copper. Aurichalcite. A basic carbonate of zinc and copper, 2(Zn,Cu)CO 3 ,.3(Zn,Cu)(OH) 2 . Orthorhombic? In drusy incrustations. G. = 3'54-3'64. Luster pearly. Color pale green to sky-blue. Indices, 1 '634^1 '682. From the Altai Mts., Mongolia; Chessy, near Lyons, France; Rezbdnya, Hungary; Ondarroa, Vizcaya, Spain; Chihuahua, Mexico. In the United States, at Lancaster, Pa.; Salida, Col.; the Santa Caterina Mts., Ariz.; Beaver Co., Utah; Kelly, N. M. Hydrozincite. A basic zinc carbonate, perhaps ZnCO 3 .2Zn(pH) 2 . Massive, fibrous, earthy or compact, as incrustations. G. = 3'58-3'8. Color white, grayish or yellowish. 452 DESCRIPTIVE MINERALOGY Index, 1-695. Occurs at mines of zinc, as a result of alteration. In great quantities at the Dolores mine, Santander, Spain. From Chihuahua, Mexico; Bleyberg, Belgium; Mal- fidano, Sardinia. In the United States at Friedensville, Pa.; at Linden, in Wis.; Granby, Mo. OTAVITE. A basic cadmium carbonate of uncertain composition. In crusts showing min- ute rhombohedral crystals. Color white to reddish. From the Otavi district, German Southwest Africa. Hydrocerussite. A basic lead carbonate, probably 2PbCO 3 .Pb(pH) 2 . In thin color- less hexagonal plates. Index, 2 '07. Occurs as a coating on native lead, at Langban, Sweden; with galena at Wanlockhead, Scotland. Dundasite. A basic carbonate of lead and aluminium, Pb(AlO)2(CO 3 )2.4H 2 O. In small spherical aggregates of radiating acicular crystals. Color white. From Dundas and Mt. Read, Tasmania, and from near Trefriw, Carnarvonshire, Wales; Wensley, Derbyshire; near Maam, County Gal way, Ireland. Dawsonite. A basic carbonate of aluminium and sodium, Na 3 Al(CO 3 ) 3 .2Al(OH)3. Orthorhombic. In thin incrustations of white radiating bladed crystals. Perfect cleavage, ra(110). G. = 2-40. Indices, 1-466-1-596. Found on a feldspathic dike near McGill College, Montreal. From the province of Siena, Pian Castagnaio, Tuscany, Italy Thermonatrite. Hydrous sodium carbonate, Na 2 CO 3 .H 2 O. G. = l'S-1'6. Occurs m various lakes, and as an efflorescence over the soil in many dry regions. Nesquehonite. Hydrous magnesium carbonate, MgCO 3 .3H 2 O. In radiating groups of prismatic crystals. G. = 1 '83-1-85. Colorless to white. Biaxial, . Indices, 1-495- 1'526. From a coal mine at Nesquehoning, Schuylkill Co., Pa. See lansfordite, p. 453. Natron. Hydrous sodium carbonate, Na 2 CO 3 .10H 2 O. Occurring in nature only in solution, as in the soda lakes of Egypt, and elsewhere, or mixed with the other sodium carbonates. Pirssonite. CaCO 3 .Na 2 CO 3 .2H 2 O. In prismatic crystals, orthorhombic-hemimorphic. H. =3. G. = 2'35. Colorless to white. Optically +. Indices, I'504-r575. Borax Lake, San Bernardino, Cal. GAY-LUSSITE. Monoclinic. Axes a : b : c = 1 -4897 : 1 764 765 : 1-4442; = _78 27'. mm'", 110 A UO = 111 10'. ee', Oil A Oil = 109 30'. me, 110 A Oil = 42 21'. rr f , 112 A 112 = 69 29'. Crystals often elongated || a axis; also flattened wedge-shaped. Cleavage: m (110) perfect; c (001) rather difficult. Fracture conchoidal. Very brittle. H. = 2-3. G. = 1-93-1-95. Luster vitreous. Color white, yellowish white. Streak uncolored to grayish. Translu- cent. Optically . a = 1*444 6 = T517., 7 = 1-518. Comp. Hydrous carbonate of calcium and sodium, CaCO 3 .Na2CO 3 . Calcium carbonate 33-8, sodium carbonate 35-8, water 30-4 = 100. Pyr., etc. Heated in a closed tube decrepitates and becomes opaque. B.B. fuses brisk y effervesoen e ^^'l ""Vu^ the flame inten ^ly yellow. Dissolve! in acids with a brisk effervescence; partly soluble in water, and reddens turmeric paper. the botton" of r^ll a V La ? Un ^ a ^ Merida > in Venezuela, in crystals disseminated at Lake or So iM ' 'SV 1 & ^ f day ' coverm g tr ona. Also abundant in Little Salt tion of the ttPr 'F n th % Cars f m Desert near Ragtown, Nev, deposited upon the evapora- cms 1850) Sweetwater VaUey ' Wv ' Named after Gay Lussac, the French CARBONATES 453 Lanthanite. La 2 (CO 3 ) 3 .9H 2 O. In thin tabular orthorhombic crystals; also granular, earthy. G. = 2 '605. Color grayish white, pink, yellowish. Optically . Found coat- ing cerite at Bastnas, Sweden; with zinc ores of the Saucon valley, Lehigh Co., Pa.; at the Sandford iron-ore bed, Moriah, N. Y. TRONA.' Urao. Monoclinic. Axes a : b : c = 2-8460: 1: 2-9700; = 77 23'. ca, 001 A 100 = 77 23'. co, 001 A Til = 75 53^. 766 oo", 111 A 111 = 47 35|'. Often fibrous or columnar massive. . . Cleavage: a (100) perfect; o (111) ; c (001) in traces. \ Fracture uneven to subconchoidal. H. = 2*5-3. \ G. = 2-11-2-14. Luster vitreous, glistening. Color gray or yellowish white. Translucent. Taste alkaline. Optically. Index, 1-507. Comp. Na2CO3.HNaCO3.2H 2 O or 3Na2O.4CO 3 .5H 2 = Carbon diox- ide 38-9, soda 41-2, water 19-9 = 100. Chatard established the above composition for urao, and showed that trona, sometimes called " sesquicarbonate of soda," is an impure form of the same compound. Pyr., etc. In the closed tube yields water and carbon dioxide. B.B. imparts an intensely yellow color to the flame. Soluble in water, and effervesces with acids. Reacts alkaline with moistened test-paper. Obs. Found in the province of Fezzan, Africa, forming thin superficial crusts; Na- troun lakes, Egypt; from Vesuvius; at the bottom of a lake at Lagunilla, Venezuela. Efflorescences of trona occur near the Sweetwater river, Rocky Mountains. An extensive bed in Churchill Co., Nev. In fine crystals at Borax lake, San Bernardino Co., Cal., with hanksite, glauberite, thenardite, etc. Hydromagnesite. Basic magnesium carbonate, 3MgCO 3 .Mg(OH) 2 .3H 2 O. Crystals small, tufted. Also amorphous; as chalky crusts. Color and streak white. Index, 1 '530. Often occurs with serpentine; thus at Hrubschiitz, in Moravia; at Kraubat, Styria, etc. Also similarly near Texas, Pa.; Hoboken, N. J. Material closely similar from saline crusts on lava at Alpharoessa, Santorin Island, has been called giorgiosite. Hydrogiobertite. MgCO 3 .Mg(OH) 2 .2H 2 O. In light gray spherical forms. From the neighborhood of Pollena, Italy. Deposited from Phillips Springs, Napa Co., Cal. Artinite. MgCO 3 .Mg(OH) 2 .3H 2 O. Orthorhombic. Radiating fibrous. H. = 2'0. G. = 2-0. White, ft = 1'54. From Val Laterna and Emarede, Val Aosta, Piedmont, Italy. Lansfordite. 3MgCO 3 .Mg(OH) 2 .21H 2 O. Biaxial -. Indices, 1'42-1-503. Occurs as small stalactites in the anthracite mine at Nesquehoning near Lansford, Schuylkill Co., Pa.; changed on exposure to nesquehonite. Brugnatellite. MgCO 3 .5Mg(OH) 2 .Fe(OH) 3 .4H 2 O. Micaceous/ lamellar. Perfect cleav- age. Color flesh-pink, co = T53. Found in an old asbestos mine at Torre Santa Maria, Val Malenco, Lombardy, Italy. GAJITE. A basic hydrous calcium, magnesium carbonate. Rhombqhedral cleavage. Granular structure. H. = 3'5. G. = 2'62. Color, white. Strong birefringence. Found near Plesce, in the district Gorskikotar, Croatia. Stichtite. 2MgCO 3 .5Mg(OH) 2 .2Cr(OH) 3 . Micaceous. In scales. G.= 2'16. Color lilac. Optically uniaxial or feebly biaxial. Optically . Index, 1'54. An alteration product of serpentine from Dundas, Tasmania. Zaratite. Emerald Nickel. NiCO 3 .2Ni(OH) 2 .4H 2 O. Inmammillary incrustations; also massive, compact. Color emerald-green. Occurs on chromite at Texas, Lancaster Co., Pa.; at Swinaness, Unst, Shetland; Igdlokunguak, Greenland. Remingtonite. A hydrous cobalt carbonate. A rose-colored incrustation, soft and earthy. From a copper mine near Finksburg, Carroll Co., Md.; Boleo, Lower California. 454 DESCRIPTIVE MINERALOGY Tengerite. A supposed yttrium carbonate. In white pulverulent coatings. On gado- linite at Ytterby, Sweden. A similar mineral is associated with the gadolinite of Llano Co., Tex. Bismutite. A basic bismuth carbonate, perhaps Bi 2 O3.CO2.H 2 O. Incrusting, or earthy and pulverulent; amorphous. G. = 6'86-6'9 Breith.; 7 '67 Rg. Color white,- green, yel- low and gray. Index, 2'25. Occurs in Germany, at Schneeberg and Johanngeorgenstadt, with native bismuth, and at Joachimstal, Bohemia. In the United States, in S. C., at Brewer's mine; hi Gaston Co., N. C. Uranothallite. 2CaCO 3 .U(CO 3 )2.10H 2 O. In scaly or granular crystalline aggregates. Color siskin-green. Occurs on uraninite at Joachimstal, Bohemia. Liebigite. A hydrous carbonate of uranium and calcium. In mammillary concretions, or thin coatings. Color apple-green. Occurs on uraninite near Adrianople, Turkey; also Johanngeorgenstadt, Germany, and Joachimstal, Bohemia. Voglite. A hydrous carbonate of uranium, calcium and copper. In aggregations of crystalline scales. Color emerald-green to bright grass-green. From the Elias mine, near Joachimstal, on uraninite, Bohemia. Oxygen Salts 2. SILICATES The Silicates are in part strictly anhydrous, in part hydrous, as the zeolites and the amorphous clays, etc. -Furthermore, a large number of the silicates yield more or less water upon ignition, and in many cases it is known that they are, therefore, to be regarded as basic (or acid) silicates. The line, however, between the strictly anhydrous and hydrous silicates cannot be sharply drawn, since with many species which yield water upon ignition the part played by the elements forming the water is as yet uncertain. Furthermore, in the cases of several groups, the strict arrangement must be deviated from, since the relation of the species is best exhibited by introducing the related hydrous species immediately after the others. This chapter closes with a section including the Titanates, Silico-titanates, Titano-niobates, etc., which connect the Silicates with the Niobates and Tantalates. Some Titanates have already been included among the Oxides. Section A. Chiefly Anhydrous Silicates I. Disilicates, Polysilicates II. Metasilicates III. Orthosilicates IV. Subsilicates The DISILICATES, RSi 2 5 , are salts of disilicic acid, H 2 Si 2 O 5 , and have an oxygen ratio of silicon to bases of 4 : 1, as seen when the formula is written after the dualistic method, RO.2Si0 2 . The POLYSILICATES, R 2 Si 3 8 , are salts of polysilicic acid, H 4 Si 3 O 8 , and have an oxygen ratio of 3 : 1, as seen in 2R0.3Si0 2 . The METASILICATES, RSiO 3 , are salts of metasilicic acid, H 2 SiO 3 , and have an oxygen ratio of 2 : 1. They have hence been called bisilicates. The ORTHOSILICATES, R 2 Si0 4 , are salts of orthosilicic acid, H 4 Si0 4 , and have an oxygen ratio of 1 : 1. They have hence been called unisilicates. The majority of the silicates fall into one of the last two groups. SILICATES 455 Furthermore, there are a number of species characterized by an oxygen ratio of less than 1:1, e.g., 3 : 4, 2 : 3, etc. These basic species are grouped as SUBSILICATES. Their true position is often in doubt; in most cases they are probably to be regarded as basic salts belonging to one of the other groups. The above classification cannot, however, be carried through strictly, since there are many species which do not exactly conform to any one of the groups named, and often the true interpretation of the composition is doubtful. Furthermore, within the limits of a single group of species, connected closely in all essential characters, there may be a wide variation in the proportion of the acidic element. Thus the triclinic feldspars, placed among the polysili- cates, range from the true polysilicate, NaAlSisOg, to the orthosilicate, CaAl 2 Si 2 O 8 , with many intermediate compounds, regarded as isomorphous mixtures of these extremes. Similarly of the scapolite group, which, how- ever, is included among the orthosilicates, since the majority of the compounds observed approximate to that type. The micas form another example. I. Disilicates, RSi 2 5 . Polysilicates, R 2 Si 3 8 PETALITE. Monoclinic. Crystals rare (castorite). Usually massive, foliated cleavable (petalite) . Cleavage: c (001) perfect; o (201) easy; z (905) difficult and imperfect. Fracture imperfectly conchoidal. Brittle. H. = 6-6-5. G. = 2-39-2*46. Luster vitreous, on c (001) pearly. Colorless j white, gray, occasionally reddish or greenish white. Streak uncolored. Transparent to translucent, a = 1-504. ft = 1-510. y = 1-516. Comp. LiAl(Si 2 O 5 ) 2 or Li 2 O.Al 2 O 3 .8SiO 2 = Silica 78'4, alumina 167, lithia, 4-9 = 100. Pyr., etc. Gently heated emits a blue phosphorescent light. B.B. fuses quietly at 4 and gives the reaction for lithia. With borax it forms a clear, colorless glass. Not acted on by acids. Obs. Petalite occurs at the iron mine of Uto, Sweden, with lepidolite, tourmaline, spodumene, and quartz; on Elba (castorite). In the United States, at Bplton, Mass., with scapolite; at Peru, Me., with spodumene in albite. The name petalite is from TreraXov, a leaf, alluding to the cleavage. Milarite. HKCa 2 Al2(Si 2 O 5 ) 6 . In hexagonal prisms. H. = 5'5-6. G. = 2'55-2'59. Colorless to pale green, glassy. From Val Giuf, Grisons, Switzerland. Eudidymite. HNaBeSisOs. Monoclinic. In white, glassy, twinned crystals, tabular in habit. H. =6. G. = 2 '553. Optically +. Indices, 1 '545-1 '551. Occurs very spar- ingly in elaeolite-syenite on the island Ovre-Aro, in the Langesundfiord, Norway; from Nar- sarsuk, Greenland. Epididymite. Same composition as eudidymite. Orthorhombic. Tabular || c (001). Cleavage, 6(010) and c(001), perfect. H. = 5 '5. G. = 3 "55. Optically -. Indices, 1-565-1-569. Narsarsuk, Greenland. RIVAITE. (Ca,Na 2 )Si 2 O 5 . Monoclinic? In fibrous aggregates. H. =5. G. = 2*55. Color, pale lavender to dark blue. Fibers show parallel extinction with positive elongation. Easily fusible. Insoluble in hydrochloric acid. Found in loose nodules on Vesuvius. 456 DESCRIPTIVE MINERALOGY Orthoclase Soda-Orthoclase Hyalophane Celsian Microcline Soda-microcline Anorthoclase Feldspar Group a. Monoclinic Section a KAlSi 3 O 8 0-6585 { (K,Na) AlSi 3 O 8 \(Na,K)AlSi 3 O 8 (K 2 ,Ba)Al 2 Si 4 Oi 2 0*6584 BaAl 2 Si 2 8 0-657 j8. Triclinie Section KAlSi 3 O 8 (K,Na)AlSi 3 O 8 (Na,K)AlSi 3 O 8 : 0'5554 0'5512 0'554 116 3' 115 35' 115 2' Albite-anorthite Series. Plagioclase Feldspars Albite NaAlSi 3 8 0' 6335 :'l: 0*5577 94* 3' 116 29' 88 9' Oligoclasej 0'6321: 1:0'5524 93 4' 116 23' 90 5' Andesine ( n f a f!?J?9v 8 ^ 0'6357 : 1 : 0'5521 93 23' 116 29' 89 59' Labra- dorite J Anorthite CaAl 2 Si 2 8 0-6377:1:0-5547 0-6347:1:0-5501 93 31' 116 3' 8954J' 93 13' 115 55' 91 12' The general characters of the species belonging in the FELDSPAR GROUP are as follows : 1, Crystallization in the monoclinic or triclinie systems, the crystals of the different species resembling each other closely in angle, in general habit, and in methods of twinning. The prismatic angle in all cases differs but a few degrees from 60 and 120. 2, Cleavage in two similar directions parallel to the base c (001) and clino- pinacoid (or brachypinacoid) 6 (010), inclined at an angle of 90 or nearly 90. 3, Hardness between 6 and 6'5. 4, Specific Gravity varying between 2"5 and 2'9, and mostly between 2-55 and 275. 5, Color white or pale shades of yellow, red or green, less commonly dark. 6, In composition silicates of alu- minium with either potassium, sodium, or calcium, and rarely barium, while magnesium and iron are always absent. Furthermore, besides the several distinct species there are many intermediate compounds having a certain independence of character and yet connected with each other by insensible gradations; all the members of the series showing a close relationship not only in composition but also in crystalline form and optical characters. The species of the Feldspar Group are classified, first as regards form, and second with reference to composition. The monoclinic species include (see above) : ORTHOCLASE, potassium feldspar, and SODA-ORTHOCLASE, potassium- sodium feldspar; also HYALOPHANE and CELSIAN, barium feldspars. The triclinie species include : MICROCLINE and ANORTHOCLASE, potassium- sodium feldspars; ALBITE, sodium feldspar; ANORTHITE, calcium feldspar. Also intermediate between albite and anorthite the isomorphous sub- species, sodium-calcium or calcium-sodium feldspars: OLIGOCLASE, ANDESINE, LABRADORITE. SILICATES a. Monoclinic Section ORTHOCLASE. Monoclinic. Axes a : b : c = 0*6585 : 1 : 0-5554; 767 768 769 457 63 57'. 770 m mm'", 110 A 110 = 61 13'. zz', 130 A 130 = 58 48'. ex, 001 A 101 = 50 16|'. cy, 001 A 201 = 80 18'. m cn, 001 A 021 = 44 nn', 021 A 021 = 89 53 cm, 001 A 110 = 67 47 co, 001 A Til = 55 14 Twins: tw. pi. (1) a (100), or tw. axis c, the common Carlsbad twins, either of irregular penetratipm (Fig. 772) or contact type; the latter usually with b (010) as composition-face, often then (Fig. 773) with c (001) and x (101) nearly in a plane, but to be distinguished by luster, cleavage, etc. (2) n (021), the Baveno ..twins forming nearly square prisms (Fig. 774), since cn = 44 SGJ'^and hence cc = 89 53'; often repeated as fourlings (Fig. 447, p. 171), /also in*square prisms, elongated || a axis. (3) c (001), the Manebach 773 771 772 774 776 twins (Fig. 775), usually contact-twins with c as comp.-face. Also other rarer laws. Crystals often prismatic || c axis; sometimes orthorhombic in aspect (Fig. 770) since c (001) and x (101) are inclined at nearly equal angles to the vertical axis ; also elongated || a axis (Fig. 771) with b (010) and c (001) nearly equally developed; also thin tabular || 6 (010): rarely tabular || a (100), a face not often observed. Often massive, coarsely cleavable to granular; sometimes lamellar. Also compact crypto-crystalline, and flint-like or jasper-like. Cleavage: c (001) perfect; 6 (010) somewhat less so; prismatic m (110) imperfect, but usually more distinct parallel to one prismatic face than to the other. Parting sometimes distinct parallel to a (100), also to a hemi-ortho- dome, inclined a few degrees to the orthopinacoid; this may produce a satin- like luster or schiller (p. 251), the latter also often present when the parting 458 DESCRIPTIVE MINERALOGY is not distinct. Fracture conchoidal to uneven. Brittle. H. =6. G. = 2'57. Luster vitreous; on c (001) often pearly. Colorless, white, pale yellow and flesh-red common, gray; rarely green. Streak uncolored. Optically negative in all cases (Fig. 776). Ax. pi. usually J_ b (010), sometimes 1 1 6, also changing from the former to the latter on increase of tem- ,*m<-,\ ?i .7. ___ T->__ A . !ro i -i r ID,, A perature (see p 776 297). For adularia Bx a . r Ac axis = - 69 11', Bx a .w A c axis = 69 37'. Hence Bx a and the.extinction- direction (Fig. 776) inclined a few degrees only to a axis, or the edge b/c; thus +3 to +7 usually, or up to +10 or +12 in varieties rich in Na20. Dispersion p >v\ also horizontal, strongly marked, or inclined, according to position of ax. pi. Axial angles variable. Birefringence low, 7 - a = 0-007 - 0-005. For adularia a y = 1-5190, fty = 1-5237, y y = 1'5260. /. 2V y = 69 43', 2E y = 121 6'. Comp. A silicate of aluminium and potas- sium, KAlSi 3 8 or K 2 O.Al 2 O 3 .6SiO2 = Silica 647, alumina 18-4, potash 16'9 = 100. Sodium is often also present, replacing part of the potassium, and sometimes exceeds it in amount; these varieties are embraced under the name soda-orthoclase (the name barbierite has been proposed for this material whose existence, as a distinct though rare mineral, seems to have been proven). Var. The prominent varieties depend upon crystalline habit and method of occur- rence more than upon difference of composition. 1. Adularia. The pure or nearly pure potassium silicate. Usually in crystals, like Fig. 770 inhabit; often with vicinal planes; Baveno twins common. G. = 2 '565. Trans- parent or nearly so. Often with a pearly opalescent reflection or schiller or a delicate play of colors; some moonstone is here included, but the remainder belongs to albite or other of the triclinic feldspars. The original adularia (Adular) is from the St. Gothard region in Switzerland. Valencianite, from the silver mine of Valencia, Mexico, is adularia. 2. Sanidine or glassy feldspar. Occurs in crystals, often transparent and glassy, embedded in rhyolite, trachyte (as of the Siebengebirge, Germany), phonolite, etc. Habit often tabular || 6 (010) (hence named from (ravls, a tablet, or board) ; also in square prisms (6, c) ; Carlsbad twins common. Most varieties contain sodium as a prominent constituent, and hence belong to the soda-orthoclase. Natronsanidine is a sanidine-like soda-ortho- clase from a soda liparite from Mitrowitza, Servia. Rhyacolite. Occurs in glassy crystals at Monte Somma, Vesuvius; named from pva, stream (lava stream). 3. Isothose is said to be a variety having a different optical orientation than normal orthoclase. 4. Ordinary. In crystals, Carlsbad and other twins common; also massive or cleavable, varying in color from white to pale yellow, red or green, translucent; sometimes avent urine. Here belongs the common feldspar of granitoid rocks or granite veins. Usually contains a greater or less percentage of soda (soda-orthoclase). Compact cryptocrystalline orthoclase makes up the mass of much felsite, but to a greater or less degree admixed with quartz; of various colors, from white and brown to deep red. Much of what has been called ortho- clase, or common potash feldspar, has proved to belong to the related triclinic species, microcline. Cf. p. 461 on the relations of the two species. Chesterlite and Amazon stone are microcline; also most aventurine orthoclase. Loxoclase contains sodium in considerable amount (7 '6 Na 2 O); from Hammond, St. Lawrence Co., N. Y. Murchisonite is a flesh- red feldspar similar to perthite (p. 460), with gold-yellow reflections in a direction _|_ b (010) and nearly parallel to 701 or 801 (p. 457) ; from Dawlish and Exeter, England. The spherulities noted in some volcanic rocks, as in the rhyolite of Obsidian Cliff in the Yellowstone Park, are believed to consist essentially of orthoclase needles with quartz. SILICATES 459 (from Iddings; much magnified) 777 778 Pyr., etc. B.B. fuses at 5; varieties containing much soda are more fusible. Loxo- clase fuses at 4. Not acted upon by acids. Mixed with powdered gypsum and heated B. B. gives violet potassium flame visible through blue glass. Diff . Characterized by its crystalline form and the two cleavages at right angles to each other; harder than barite and calcite; not attacked by acids; difficultly fusible. Mas- sive corundum is much harder and has a higher specific gravity. Micro. Distinguished in rock sections by its low refraction (low relief) and low'inter- f erence-colors, which last scarcely rise to white of the first order hence lower than those of quartz; also by its biaxial character in convergent light and by the distinct cleavages. It is colorless in ordinary light and may be limpid, but is frequently turbid and brownish from the presence of very minute scales of kaolin due to alteration from weathering; this change is especially common in the older granular rocks, as granite and gneiss. Artif. Orthoclase has not been produced artificially by the methods of dry fusion. It can, however, be crystallized from a dry melt when certain other substances, like tungstic acid, alkaline phosphates, etc., are added. The function of these additions in the reactions is not clear. Orthoclase is more easily formed by hydrochemical methods. It has been produced by heating gelatinous silica, alumina, caustic potash and water in a sealed tube. Orthoclase has also been formed by heating potassium silicate and water together with muscovite. Obs. Orthoclase in its several varieties belongs especially to the crystalline rocks, occurring as an essential constituent of granite, gneiss, syenite, also porphyry, further (var., sanidine) trachyte, phonolite, etc. In the massive granitoid rocks it is seldom in distinct, well-formed, separable crystals, except in veins and cavities; such crystals are more com- mon, however, in volcanic rocks like trachyte. Adularia occurs in the crystalline rocks of the central and eastern Alps, associated with smoky quartz and albite, also titanite, apatite, etc.; the crystals are often coated with chlorite; also ^n Elba. Fine crystals of orthoclase, often twins, are obtained from Baveno, Lago Maggiore, Italy; the Fleimstal, Tyrol, Austria, a red variety; Bodenmais, Carlsbad, and Elbogen in Bohemia; Striegau, etc., in Silesia. Also Arendal in Norway, and near Shaitansk in the Ural Mts.; Land's End and St. Agnes in Cornwall; the Mourne Mts., Ireland, with beryl and topaz. From Tamagama Yama, Japan, with topaz and smoky quartz. Moonstone is brought from Ceylon. Crystals of gem quality from Itrongahy, Madagascar Valencianite from Guanajuato, Mexico. Crystals from Eganville, Ontario. In the United States, orthoclase is common in the crystalline rocks of New England, also of States south, further Colorado, California, etc. Thus at the Paris tourmaline locality, Me. In N. H., at Acworth. In Mass., at South Royalston and Barre. In Conn., at Haddam and Middletown, in large coarse crystals. In N. Y., in St. Lawrence Co., at Rossie; at Hammond (loxoclase)', in Lewis Co., in white limestone near Natural Bridge; at Amity and Edenville. In Pa., in crystals at Leiperville, Mineral Hill, Delaware Co.; sun- stone in Kennett Township. In N. C., at Washington Mine, Davidson Co. In Col., at the summit of Mt. Antero, Chaffee Co., in fine crystals, often twins; at Gunnison; Black 460 DESCRIPTIVE MINERALOGY Hawk; Kokomp, Summit Co., Robinson, also at other points. Also similarly in Nev. and Cal. Large twin crystals from Barringer Hill, Llano Co., Texas. Alter. Orthoclase is frequently altered, especially through the action of carbonated or alkaline waters; the final result is often the removal of the potash and the formation of kaolin. Steatite, talc, chlorite, leucite, mica, laumontite, occur as pseudomorphs after orthoclase; and cassiterite and calcite often replace these feldspars by some process of solu- tion and substitution. Use. In the manufacture of porcelain, both in the body of the ware and in the glaze on its surface. PERTHITE. As first described, a flesh-red aventurine feldspar from Perth, Ontario, Canada, called a soda-orthoclase, but shown by Gerhard to consist of interlaminated ortho- clase and albite. Many similar occurrences have since been noted, as also those in which microcline and albite are similarly interlaminated, the latter called microcline-perthite, or microcline-albite-perthite; this is true in part of the original perthite. When the structure is discernible only with the help of the microscope it is called microperthite. Brogger has investigated not only the microperthites of Norway, but also other feldspars characterized by a marked schiller; he assumes the existence of an extremely fine interlamination of albite and orthoclase || 801, not discernible by the microscope (cryptoperthite), and connected with secondary planes of parting || 100 or || 801, which is probably to be explained as due to incipient alteration. Hyalophane. (K 2 ,Ba)Al 2 (SiO 3 )4 or K 2 O.BaO.2Al 2 O 3 .8SiO 2 . Silica 51 '6, alumina 21'9, baryta 16*4, potash 101 = 100. In crystals, like adularia in habit (Fig. 770, p. 457); also massive. Cleavage: c (001) perfect; b (010) somewhat less so. H. = 6-6*5. G. =2*805. Optically -. a. = 1*542. ft = 1*545. 7 = 1-547. Occurs in a granular dolomite in the Binnental, Switzerland; also at the manganese mine of Jakobsberg, Sweden. Some other feldspars containing 7 to 15 p. c. BaO have been described. Celsian. BaAl 2 Si 2 Og, similar in composition to anorthite, but containing barium in- stead of calcium. Monoclinic. In crystals showing a number of forms; twinned according to Carlsbad, Manebach and Baveno laws. Usually cleavable massive. H. = 6-6*5. G. = 3'37. Extinction on 6 (010) = 28 3'. Colorless. Optically + . a = 1*584. ft = 1*589. 7 = 1*594. From Jakobsberg, Sweden. Name baryta-orthoclase given to mixtures of celsian and orthoclase. Paracelsian from Candoglia, Piedmont, Italy, is the same species. ft. Triclinic Section MICROCLINE. 779 Triclinic. Near orthoclase in angles and habit, but the angle be (010 A 001) = about 89 30'. Twins: like orthoclase, also polysynthetic twinning according to the albite and pericline laws (p. 464), common, producing two series of fine lamellae nearly at right angles to each other, hence the characteristic grating- structure of a basal section in polarized light (Fig. 779). Also massive cleavable to granular compact. Cleavage: c(001) perfect; 6(010) some- what less so; M (1TO) sometimes distinct; m (110) also sometimes distinct, but less easy. Fracture uneven. Brittle. H. = 6-6'5. G = 2'54-2*57 Luster vitreous, on c (001) sometimes pearly. Color white to pale cream-yellow also red, green Transparent to translucent. Optically -. Ax. pi. nearly perpendicular (82-83) to 6 (010). Bx inclined 15 26' to a normal to 6 *' Bx - Extinction-angle on c (001), +15 . = 1-522. SILICATES 461 The essential identity of orthoclase and microcline has been urged by Mallard and Michel-Levy on the ground that the properties of the former would belong to an aggregate of submicroscopic twinning lamellae of the latter, according to the albite and pericline laws. Comp. Like orthoclase, KAlSi 3 O 8 or K 2 O.Al 2 O3.6Sip2 = Silica 647, alumina 18 -4, potash 16*9 = 100. Sodium is usually present in small amount: sometimes prominent, as in soda-microcline. Pyr. As for orthoclase. Diff. Resembles orthoclase but distinguished by optical characters (e.g., the grating structure in polarized light, Fig. 779); also often shows fine twinning-striations on a basal surface (albite law). Micro. In thin sections like orthoclase but usually to be distinguished by the grating- like structure in polarized light due to triclinic twinning. Obs. Occurs under the same conditions as much common orthoclase. The beautiful amazonstone from the Ural Mts., also that occurring in fine groups of large crystals of deep color in the granite of Pike's Peak, Col., is microcline. Crystals from Ivigtut, Greenland. From Antsongombato and Antoboko (amazonstone), Madagascar. Chesterlite from Poor- house quarry, Chester Co., Pa., and the aventurine feldspar of Mineral Hill, Pa., belong here. A pure variety occurs at Magnet Cove, Ark. Ordinary microcline is common at many points. Use. Same as for orthoclase; sometimes as an ornamental material (amazonstone). Anorthoclase. Soda-microcline. A triclinic feldspar with a cleavage-angle, be, 010 A 001, varying but little from 90. Form like that of the ordinary feldspars. Twinning as with orthoclase; also polysynthetic according to the albite and pericline laws; but in many cases the twinning laminae very narrow and hence not distinct. Rhombic section (see p. 462) inclined on 6 (010) 4 to 6 to edge b/c. G. = 2 '57-2 "60. Cleavage, hardness, luster, and color as with other members of the group. Optically ._ Extinction-angle on c (001) +5 45' to +2; on b (010) 6 to 9.8. Bx a nearly _L y (201). Dispersion p > v; hor- izontal distinct, a = 1'523. /3 = 1'529. 7 = 1'531. Axial angle variable with tem- perature, becoming in part monoclinic in optical symmetry between 86 and 264 C., but again triclinic on cooling; this is true of those containing little calcium. Chiefly a soda-potash, feldspar NaAlSisOs and KAlSi 3 p 8 , the sodium silicate usually in larger proportion (2 : 1, 3 : 1, etc.), as if consisting of albite and orthoclase molecules. Cal- cium (CaAl 2 Si 2 p8) is also present in relatively very small amount. These triclinic soda-potash feldspars are chiefly known from the andesitic lavas of Pantelleria. Most of these feldspars come from a rock, called pantellerite. Also prominent from the augite-syenite of southern Norway and from the " Rhomben-porphyr " near Chris- tiania. Here is referred also a feldspar in crystals, tabular j| c (001), and twinned according to the Manebach and less often Baveno laws occurring in the lithophyses of the rhyolite of Obsidian Cliff. Yellowstone Park. It shows the blue opalescence in a direction parallel with a steep orthodome (cf. p. 457). Albite-Anorthite Series. Plagioclase Feldspars * Between the isomorphous species ALBITE NaAlSisOg Ab ANORTHITE CaAl 2 Si 2 08 An there are a number of intermediate subspecies, regarded, as urged by Tscher- mak, as isomorphous mixtures of these molecules, and defined according to the ratio in which they enter; their composition is expressed in general by the formula Ab n An m . They are: OLIGOCLASE Ab 6 Ani to Ab 3 Ani ANDESINE Ab 3 Ani to LABRADORITE AbiAni to and Bytownite AbiAn 3 to AbiAn 6 From albite through the successive intermediate compounds to anorthite with the progressive change in composition (also specific gravity, melting * The triclinic feldspars of this series, in which the two cleavages 6 (010) and c (001) are oblique to each other, are often called in general plagioclase (from Tr\ayios, oblique). 462 DESCRIPTIVE MINERALOGY points, etc.), there is also a corresponding change in crystallographic form, and in certain fundamental optical properties. Crystalline Form. The axial ratios and angles given on p. 456 show that these triclinic feldspars 780 781 approach orthoclase close- ly in form, the most ob- vious difference being in the cleavage-angle 6c010 A 001, which is 90 in orthoclase, 86 24' in albite, and 85 50' in anorthite. There is also a change in the axial angle 7, which is 88 in albite, about 90 in oligoclase and andesine, and 91 in anorthite. This transition appears still more strikingly in the position of the " rhombic section," by which the twins according to the pericline law are united as explained below. Twinning. The plagioclase feldspars are often twinned in accordance with the Carlsbad, Baveno, and Manebach laws common with orthoclase (p. 457). Twinning is also almost universal according to the albite law twinning plane the brachypinacoid; this is usually polysynthetic, i.e., repeated in the form of thin lamellae, giving rise to fine striations on the basal cleavage surface (Figs. 780, 781). Twinning is also common according to the pericline law twinning axis the macrodiagonal axis 6; when polysynthetic this gives another series of fine striations seen on the brachypinacoid. The composition-plane in this pericline twinning is a plane passing through the crystal in such a direction that its intersections with the prismatic faces and the brachypinacoid make equal plane angles with each other. The position of this rhombic section and the consequent direction of the striations on the brachypinacoid change rapidly with a small variation in the angle 7. In general it may be said to be approximately parallel to the base, but in albite it is inclined backward (+, Figs. 782 and 784) and in anorthite to the front ( , Fig. 783) ; for the intermediate species its position varies progressively with the composition. 782 783 784 Plagioclase with twinning lamellae. Fig. 780 section || c (001) showing vibration-directions (cf. Fig. 784), ordin- ary light; Fig. 781 section in polarized light. Fig. 782, Rhombic section in albite. 783, Same in anorthite. 784, Typical form showing + and extinction-directions on c (001) and 6 (010). Thus for the angle between the trace of this plane on the brachypinacoid and the edge 6/c, we have for Albite +22 to +20; for Oligoclase +9 to +3; for Andesine +1 to -2; for Labradorite -9 to -10; for Anorthite -15 to -17. SILICATES 463 785 the togeth of microline. Optical Characters. There is also a progressive change in the position of the ether- axes and the optic axial plane in passing from albite to anorthite. This is most simply exhibited by the position of the planes of light- vibration, as observed in sections parallel to the two cleavages, basal c and brachy-pinacoidal 6, in other words the extinction-angle formed on each face with the edge b/c (cf. Fig. 784). _ The approximate position of the ether-axes for the different feldspars is shown in Fig. 785 (after Iddings). The axis Z does not vary very Projection of the optical directions X, Y and Z upon much from the zone bc\ b (010). 1, Albite; 2, Oligoclase; 3, Andesine; 010 A 001, but the axis X 4 Labradorite; 5, Anorthite. (After Iddings.) varies widely, and hence the axial plane has an entirely different position in albite from what it has in anorthite. Furthermore albite is optically pos- 786 Albife or*. Andesine Anorthite +20 -10 -20 -30 -40 Ab 100 90 80 70* 60 50 40 30 20 An 10 20 30 40 50 60 70 80 90 100 Extinction Angles on (001) and (010) in the Lime-soda feldspars. (After Iddings.) 464 DESCRIPTIVE MINERALOGY itive, that is Z Bx, while anorthite is negative or X = Bx; for certain andesines the axial angle is sensibly 90. Fig. 786 (after Iddings) shows the variation in the extinction angles on the cleavage faces, c (001) and b (010), for the different mixtures of the albite and anorthite molecule. Micro. In rock sections the plagioclase feldspars are distinguished by their lack of color, low refractive relief, and low interference-colors, which in good sections are mainly dark gray and scarcely rise into white of the first order; also by their biaxial character in converging light. In the majority of cases they are easily told by the parallel bands or fine lamellae which pass through them due to the multiple twinning according to the albite law; one set of bands or twin lamellae exhibits in general a different interference-color from the other (cf. Figs. 780, 781). They are thus distinguished not only from quartz and orthoclase, with which they are often associated, but from all the common rock-making minerals. To distinguish the different species and sub-species from one another, as albite from laboradorite or andesine, is more difficult. In sections having a definite orientation (|| c (001) and || 6 (010) ) this can generally be done by determining the extinction angles (cf . p. 462 and Fig. 784). In general in rock sections special methods are required; these are discussed in the various texts devoted to this subject. ALBITE. Triclinic. = 88 9'. Axed a : b : c = 0*6335 : 1 : 0-5577; a = 94 3', (3 = 116 29', 787 788 be, 010 A 001 = 86 24'. mM, 110 A 110 = 59 14'. bm, 010 A 110 = 60 26'. cm, 001 A 110 = 65 17'. cM, 001 A 110 = 69 10'. ex, 001 A 101 = 52 16'. Twins as with orthoclase; also very common, the tw. pi. b (010), albite law (p. 462), usually contact-twins, and polysynthetic, consisting of thin lamellae and with con- sequent fine striations on c(001) (Fig. 790); tw. axis b axis, peridine law, contact-twins whose compos- ition-face is the rhombic section (Figs. 782 and 792); often polysynthetic and showing fine striations which on 6 (010) are inclined backward +22 to the edge b/c. Crystals often tabular || b (010); also elongated || 6 axis as in the variety pericline. Also massive, either lamellar or granular; the laminae often curved, sometimes divergent; granular varieties occasionally quite fine to impalpable. Cleavage: c(001) perfect; 6(010) somewhat less so; m (110) imperfect. Fracture uneven to conchoidal. Brittle. H. = 6-6*5. G. = 2-62-2-65. Luster vitreous; on a cleavage surface often pearly. Color white; also occa- sionally bluish, gray, reddish, greenish, and green; sometimes having a bluish opalescence or play of colors on c (001). Streak uncolored. Transparent to sub- translucent. SILICATES 465 Optically-!-. Extinction-angle with edge b/c =4-4 30' to 2 on c, and = +20 to 15 on b (Fig. 782). Dispersion for Bx a , p < v; also in- clined, horizontal; for Bx , ^91 ^ 92 p > v, inclined, crossed. a=l-531. J3 = l' 1-540. 2V= 77. fringence weak, y a = 0-009. Comp. A silicate of aluminium and sodium, Pericline NaAlSi 3 O 8 or NaaO.Al 2 0. 6SiO 2 = Silica 687, alumina 19'5, soda 11 -8 =100. Calcium is usually present in small amount, as anorthite (CaAl 2 Si 2 O8), and as this in- creases it graduates through oligoclase-albite to oligoclase (cf. p. 466). Potas- sium may also be present, and it is then connected with anorthoclase and microcline. Var. Ordinary. In crystals and massive. The crystals often tabular || b (010). The massive forms are usually nearly pure white, and often show wavy or curved laminae. Per- isterite is a whitish adularia-like albite, slightly iridescent, named from Trepto-repa, pigeon. Aventurine and moonstone varieties also occur. Pericline from the chloritic schists of the Alps is in rather large opaque white crystals, with characteristic elongation in the direction of the 6 axis, as shown in Figs. 791 and 792, and commonly twinned with this as the twinning axis (pericline law). Pyr., etc. B.B. fuses at 4 to a colorless or white glass, imparting an intense yellow to the flame. Not acted upon by acids. Diff. Resembles barite in some forms, but is harder and of lower specific gravity; does not effervesce with acid (like calcite). Distinguished optically and by the common twinning striations on c (001) from orthoclase; from the other tri clinic feldspars partially by specific gravity and better by optical means (see p. 463). Artif. Albite acts, in regard to its artificial formation, like orthoclase, which see. Obs. Albite is a constituent of many igneous rocks, especially those of alkaline type, as granite, elaeolite-syenite, diorite, etc.; also in the corresponding feldspathic lavas. In perthite (p. 460) it is interlaminated with orthoclase or microcline, and similar aggrega- tions, often on a microscopic scale, are common in many rocks. Albite is common also in gneiss, and sometimes in the crystalline schists. Veins of albitic granite are often repositories of the rarer minerals and of fine crystallizations of gems, including beryl, tour- maline, allanite, columbite, etc. It is found in disseminated crystals in granular limestone. Some of the most prominent European localities are in cavities and veins in the granite or granitoid rocks of the Swiss and Austrian Alps, associated with adularia, smoky quartz, chlorite, titanite, apatite, and many rarer species : it is often implanted in parallel position upon the orthoclase. Thus in the Alps the St. Gothard region; Roc Tourne near Modane, Savoie; on Mt. Skopi (pericline); Tavetschtal; in Austria at Schmirnand Greiner, Tyrol; also Pfitsch, Rauris, the Zillertal, Krimml, Schneeberg in Passeir, Tyrol, in simple crystals. Also in DaupLine, France, in similar association; Elba. Also Hirschberg in Silesia; Penig in Saxony; with topaz at Mursinka in the Ural Mts. and near Miask in the Ilmen Mts.; Cornwall, England; Mourne Mts. in Ireland. Fine crystals from Greenland. In the United States, in Me., at Paris, with red and blue tourmalines, also at Topsham. In Mass., at Chesterfield, in lamellar masses (cleavelandite) , slightly bluish, also fine granu- lar. In N. H., at Acworth and Alstead. In Conn., at Haddam; at the Middletown feld- spar quarries, at Branchville, in fine crystals and massive. In N. Y., at Moriah, Essex Co., of a greenish color; at Diana, Lewis Co., and Macomb, St. Laurence Co. In Pa., at Union ville, Chester Co. In Va., at the mica mines near Amelia Court-House in splendid crystallizations. In Col., in the Pike's Peak region with smoky quartz and amazonstone. The name albite is derived from albus, white, in allusion to its common color. Use. Same as orthoclase but not so commonly employed; some varieties which show an opalescent play of colors when polished form the ornamental material known as moonstone. 466 DESCRIPTIVE MINERALOGY Oligoclase. Triclinic. Axes, see p. 456. be, 010 A 001 = 86 32'. Twins observed according to the Carlsbad, albite, and pericline laws. Crystals not common. Usually massive, cleavable to compact. Cleavage: c (001) perfect; 6 (010) somewhat less so. Fracture conchoidal to uneven. Brittle. H. = 6-6 -5. G. = 2 1-65-2 '67. Luster vitreous to some- what pearly or waxy. Color usually whitish, with a faint tinge of grayish green, grayish white, reddish white, greenish, reddish; sometimes aventurine. Transparent, subtranslucent. Optical characters, see p. 463. Comp. Intermediate between albite and anorthite and corresponding to Ab 6 Ani to Ab 2 Ani, but chiefly to Ab 3 Ani, p. 461. Var. 1. Ordinary. In crystals or more commonly massive, cleavable. The varieties containing soda up to 10 p. c. are called oligoclase-albite. 2. Aventurine oligoclase, or sun- stone, is of a grayish white to reddish gray color, usually the latter, with internal yellowish or reddish fire-like reflections proceeding from disseminated crystals of probably either hematite or gothite. Pyr., etc. B.B. fuses at 3-5 to a clear or enamel-like glass. Not materially acted upon by acids. Diff. See orthoclase (p. 459) and albite (p. 465); also pp. 456, 463. Obs. Occurs in porphyry, granite, syenite, and also in different effusive rocks, as andesite. It is sometimes associated with orthoclase in granite or other granite-like rock. Among its localities are Danviks-Zoll near Stockholm, Sweden; Pargas in Finland; Shai- tansk, Ural Mts.; in syenite of the Vosges Mts., France; at Albula in Orisons, Switzerland; Marienbad, Bohemia; in France at Chalanches in Allemont, and Bourg d'Oisans, Dauphine; as sunstone at Tvedestrand, Norway; at Hittero, Norway; Lake Baikal, Siberia. In the United States, at Fine and Macomb, St. Lawrence Co., N. Y., in good crystals; at Danbury, Conn., with orthoclase and danburite; Haddam, Conn.; at the emery mine, Chester, Mass., granular; at Unionville, Pa., with euphyllite and corundum; Mineral Hill, Delaware Co., Pa.; at Bakersville, N. C., in clear glassy masses, showing cleavage but no twinning. Named in 1826 by Breithaupt from 0X1705, little, and /cXao-is, fracture. Andesine. Triclinic. Axes, see p. 456. be, 010 A 001 = 86 14'. Twins as with albite. Crystals rare. Usually massive, cleavable or granular. Cleavage: c (001) perfect; b (010) less so; also M (110) sometimes observed. H. = 5-6. G. = 2'68-2'69. Color white, gray, greenish, yellow- ish, flesh-red. Luster subvitreous to pearly. Optical characters, see p. 463. Comp. Intermediate between albite and anorthite, corresponding to Ab : An in the ratio of 3 : 2, 4 : 3 to 1 : 1, see p. 461. _ r., etc. Fuses in thin splinters before the blowpipe. Imperfectly soluble in acids: Obs. Observed in many granular and volcanic rocks; thus occurs in the Andes, at Marmato, Colombia, as an ingredient of the rock called andesite; in the porphyry of 1 JLsterel, Dept. du Var, France; in the syenite of Alsace in the Vosges Mts.; at Vapnefiord, Iceland; Bodenmais, Bavaria; Frankenstein, Silesia. Sanford, Me., with vesuvianite Common in the igneous rocks of the Rocky Mts. Crystals from Sardinia and Greenland. Labradorite. Labrador Feldspar. Triclinic. Axes, see p. 456. Cleavage angle be 010 A 001 = 86 4'. Forms and twinning similar to the other plagioclase species. Crystals often very thin tabular 1 1 b (010) ; and rhombic in outline bounded by cy or ex (Fig. 455, p. 172). Also massive, cleavable or granular; sometimes crvptocrvstal- hne or hornstone-like. Cleavage: c (001) perfect; b (010) less so; M (110) sometimes distinct. *T ~~ 5 ~ b< G< = 270-272. Duster on c pearly, passing into vitreous; else- where vitreous or subresinous. Color gray, brown, or greenish; sometimes SILICATES 467 colorless and glassy; rarely porcelain- white; usually a beautiful change of colors in cleavable varieties, especially || 6 (010). Streak uncolored. Trans- lucent to subtranslucent. Optical characters, see p. 463. Play of colors a common character, but sometimes wanting as in some colorless crys- tals. Blue and green are the predominant colors; but yellow, fire-red, and pearl-gray also occur. Vogelsang regards the common blue color of labradorite as an interference-phenom- enon due to its lamellar structure, while the golden or reddish schiller, with the other colors, is due to the presence of black acicular microlites and yellowish red microscopic lamellae, or to the combined effect of these with the blue reflections. Schrauf has examined the inclu- sions, their position, etc., and given the names microplakite and microphyllite to two groups of them. (See references on p. 181.) Comp. Intermediate between albite and anorthite and corresponding chiefly to Ab : An in a ratio of from 1 : 1 to 1 : 3, p. 461. The feldspars which lie between labradorite proper and anorthite have been embraced by Tschermak under the name bytownite. The original bytownite of Thomson was a greenish white feldspathic mineral found in a boulder near Bytown (now Ottawa) in Onta- rio, Canada. Pyr., etc. B.B. fuses at 3 to a colorless glass. Decomposed with difficulty by hydro- chloric acid, generally leaving a portion of undecomposed mineral. Diff. The beautiful play of colors is a common but not universal character. Other- wise distinguished as are the other feldspars (pp. 459, 465). Obs. Labradorite is an essential constituent of various igneous rocks, especially of the basic kinds, and usually associated with some member of the pyroxene or amphibole groups. Thus with hypersthene in norite, with diallage in gabbro, with some form of pyroxene in diabase, basalt, dolerite, also andesite, tephrite, etc. Labradorite also occurs in other kinds of lava, and is sometimes found in them in glassy crystals, as in those of Etna, Vesuvius, at Kilauea, Hawaiian Islands. The labradoritic massive rocks are most common among the formations of the Archaean era. Such are part of those of British America, northern New York, Pennsylvania, Arkan- sas; those of Greenland, Norway, Finland, Sweden, and probably of the Vosges Mts. On the coast of Labrador, labradorite is associated with hornblende, hypersthene, and magnetite. It is met with in many places in Quebec. Occurs abundantly through the cen- tral Adirondack region in northern N. Y.; in the Wichita Mts., Ark. Labradorite was first brought from the Isle of Paul, on the coast of Labrador, by Mr. Wolfe, a Moravian missionary, about the year 1770. Use. The varieties showing a play of colors are used as ornamental material. MASKELYNITE. In colorless isotropic grains in meteorites; composition near labradorite. ANORTHITE. Indianite. Triclinic. Axes a : b : c = 0-6347 7 = 91 12'. be, 010 A 001 = 85 50'. mM, 110 A 110 = 59 29'. bm, 010 A 110 = 58 4'. cm, 001 A 110 = 65 53'. cM, 001 A 110 = 69 20'. cy, 001 A 201 = 81 14'. Twins as with albite (p. 462 and p. 464). Crystals usually prismatic || c axis (Fig. 793, also Fig. 364, p. 146), less often elon- gated 1 1 b axis, like pericline (Fig. 794). Also massive, cleavable, with granular or coarse lamellar structure. Cleavage: c (001) perfect; b (010) somewhat less so. Fracture conchoidal 1 : 0-5501; a = 93 13', ft = 115 55|', 793 794 468 DESCRIPTIVE MINERALOGY to uneven. Brittle. H. = 6-6'5. G. = 2-74-276. Color white, grayish, reddish. Streak uncolored. Transparent to translucent. Optically -. Ax. pi. nearly _L e (021), and its trace inclined 60 to the edge c/e from left above behind to right in front below. Extinction-angles on c (001), -34 to -42 with edge 6/c; on b (010), -35 to -43 (Fig. 784, p. 462). Dispersion p < v, also inclined. 2 V = 78. a = 1'576. j8 = 1*584. 7 = 1*588. Birefringence stronger than with albite. Comp. A silicate of aluminium and calcium, CaAl 2 Si 2 O 8 or CaO.Al 2 3 . 2SiO 2 = Silica 43'2, alumina 367, lime 20-1 = 100. Soda (as NaAlSi 3 O 8 ) is usually present in small amount, and as it increases there is a gradual transi- tion through bytownite to labradorite. Var. Anorthite was described from the glassy crystals of Mte. Somma, Vesuvius; and christianite and biotine are the same mineral. Thiorsauite is the same from Iceland. In- dianite is a white, grayish, or reddish granular anorthite from India, where it occurs as the gangue of corundum, first described in 1802 by Count Bournon. Cyclopite occurs in small, transparent, and glassy crystals, tabular ||- b (010), coating cavities in the dolerite of the Cyclopean Islands and near Trezza on Etna. Amphodelite, lepolite, latrobite also belong to anorthite. Pyr., etc. B.B. fuses at 5 to a colorless glass. Anorthite from Mte. Somma, and indianite from the Carnatic, India, are decomposed by hydrochloric acid, with separation.of gelatinous silica. Artif. Anorthite is the easiest of the feldspars to be formed artificially. Unlike the alkalic feldspars it can be easily formed in a dry fusion of its constituents. This method becomes progressively more difficult as the albite molecule is added to the composition. Anorthite is frequently observed in slags and is easily produced in artificial magmas. It further is often produced when more complex silicates are broken down by fusion. Obs. Occurs in some diorites; occasionally in connection with gabbro and serpentine rocks; in some cases along with corundum; in many volcanic rocks, andesites, basalts, etc.; as a constituent of some meteorites ( Juvenas, Stannern) . Anorthite (christianite and biotine) occurs at Mount Vesuvius in isolated blocks among the old lavas in the ravines of Monte Somma; in the Albani Mts.; on the Pesmeda Alp, Monzoni, Tyrol, as a contact mineral; Aranyer Berg, Transylvania, in andesite; in Ice- land; near Bogoslovsk in the Ural Mts. In the Cyclopean Islands (cyclopite). In the lava of the island of Miyake, Japan. In crystals from Franklin, N. J.; from Phippsburg, Me. Anorthite was named in 1823 by Rose from avopdos, oblique, the crystallization being triclinic. Anemousite. A feldspar having the composition, Na 2 O.2CaO.3Al 2 O3.9SiO 2 . This does not agree with any possible member of the albite-anorthite series. This is explained by assuming the presence in small amount of a sodium-anorthite molecule, Na 2 O.Al 2 O 3 .2SiO 2 , to which the name carnegieite has been given. Cleavage angle = 85 59'. G. = 2 '68. a = 1-555. j8 = 1-559. 7 = 1'563. 2 V = 82 48'. Found as loose crystals on Mte. Rosso, Island of Linosa. Name derived from the ancient Greek name of the island. Car- negieite is named in honor of Andrew Carnegie. ;H. Metasilicates. RSiO 3 Salts of Metasilicic Acid, H^SiOs; characterized by an oxygen ratio of 2 : 1 for silicon to bases. The Division closes with a number of species, in part of somewhat doubtful composition, forming a transition to the Orthosilicates. The metasilicates include two prominent and well-characterized groups, viz., the Pyroxene Group and the Amphibole Group. There are also others less important. SILICATES 469 Leucite Group. Isometric In several respects leucite is allied to the species of the FELDSPAR GROUP, which imme- diately precede. Leucite KAl(SiO 3 ) 2 Isometric at 500 Pseudo-isometric at ordinary temperatures. Pollucite H 2 Cs4Al 4 (Si03)9 Isometric LEUCITE. Amphigene. Isometric at 500 C.; pseudo-isometric under ordinary conditions (see p. 302). Commonly in crystals varying in angle but little from the tetragonal trisoctahedron n (211), sometimes with a (100), and d (110) as subordinate forms. Faces often showing fine striations due to twinning (Fig. 795). Also in disseminated grains; rarely massive granular. Cleavage: d (110) very imperfect. Fracture conchoidal. Brittle. H. = 5'5-6. G. = 2-45-2-50. Luster vitreous. Color white, ash-gray or smoke- gray. Streak uncolored. Translucent to opaque. Usually shows very feeble double refraction: co = 1-508,6 = 1-509 (p. 302). Comp. KAl(Si0 3 ) 2 or K 2 O.Al 2 O 3 .4Si0 2 = Silica 55*0, alumina 23'5. potash 21'5 = 100. Soda is present only in small quantities, unless as introduced by alteration; traces of lithium, also of rubidium and caesium, have been detected. Leucite and analcite are closely related chemically as is shown by the fact that the two species can be converted into each other when heated with sodium or potassium chlorides or carbonates. Pyr., etc. B.B. infusible; with cobalt solution gives a blue color (aluminium). De- composed by hydrochloric acid without gelatinization. Diff . Characterized by its trapezohedral form, absence of color, and inf usibility. It is softer than garnet and harder than analcite; the latter yields water and fuses. Micro. Recognized in thin sections by its extremely low refraction, isotropic charac- ter, and the symmetrical arrangement of inclusions (Fig. 796; also Fig. 485, p. 180). Larger 796 Leucite crystals from the leucitite of the Bearpaw Mts., Montana (Pirsson). These show the progressive growth from skeleton forms to complete crystals with glass inclusions . crystals are commonly not wholly isotropic and, further, show complicated systems of twinning-lines (Fig. 795); the birefringence is, however, very low, and the colors scarcely rise above dark gray; they are best seen by introduction of the quartz or gypsum plate yielding red of the first order. The smaller leucites, which lack this twinning or the inclu- sions, are only to be distinguished from sodalite or analcite by chemical tests. Artif . Leucite is easily prepared artificially by simply fusing together its constitu- ents in proper proportion and allowing the melt to crystallize slowly. The addition of potassium vanadate produces larger crystals. Leucite has been formed when microcline and biotite were fused together and also when muscovite was fused alone. Obs. Leucite occurs only in igneous rocks, and especially in recent lavas, as one of the products of crystallization of magmas rich in potash and low in silica (for which reason this species rather than orthoclase is formed) . The larger embedded crystals are commonly anisotropic and show twinning lamellae; the smaller ones, forming the groundmass, are isotropic and without twinning. Found in leucitites and leucite-basalts, leucitophyres, leucite-phonolites and leucite-tephrites; also in certain rocks occurring in dikes. Very rare 470 DESCRIPTIVE MINERALOGY in intruded igneous rocks, only one or two instances being known; but its former presence under such conditions is indicated by pseudomorphs, often of large size (pseudoleucite) consisting of neph elite and orthoclase, also of anal cite. The prominent localities are, first of all, Vesuvius and Mte. Somma, where it is thickly disseminated through the lava in grains, and in large perfect crystals; also in ejected masses; also near Rome, at Capo di Bove, Rocca Monfina, etc. Further in leucite-tephrite at Proceno near Lake Bolsena in central Italy; in Germany about the Laacher See and at several points in the Eifel; at Riedennear Andernach; at Meichesin the Vogelsgebirge; in the Kaiserstuhlgebirge; Wiesental, Bohemia. Occurs in Brazil, at Pinhalzinho. From the Cerro de las Virgines, Lower California. In the United States it is present in a rock in the Green River Basin at the Leucite Hills, Wy. ; also in the Absaroka range, in north- western Wy.; in the Highwood and Bearpaw Mts., Mon. (in part pseudoleucite). On the shores of Vancouver Island, where magnificent groups of crystals have been found as drift boulders. Pseudoleucite (see above) occurs in the phonolite (tinguaite) of the Serra de Tingua, Brazil; at Magnet Cove, Ark.; near Hamburg, N.J.; Mon.; also in the Cariboo District, British Columbia. Named from Xewcos, white, in allusion to its color. Pollucite. Essentially H 2 O.2Cs2O.2Al 2 O3.9SiO2. Isometric; often in cubes; also mas- sive. H. = 6'5. G. = 2-901. Colorless, n = 1-525. Occurs very sparingly in the island of Elba, with petalite (castorite); also at Hebron and Rumford, Me. Ussingite. HNa 2 Al(Si0 3 ) 3 . Triclinic. Three cleavages. G. = 2-5. H. = 6-7. Color reddish violet. Indices, 1-50-1 '55. Easily fusible. Soluble in hydrochloric acid. Found in rolled masses from pegmatite at Kangerdluarsuk, Greenland. Pyroxene Group Orthorhombic, Monoclinic, Triclinic Composition for the most part that of a metasilicate, RSiO 3 , with R = Ca,Mg,Fe chiefly, also Mn,Zn. Further RSiO 3 with R(Fe,Al) 2 SiO 6 , less often containing alkalies (Na,K), and then RSiO 3 with RAl(Si0 3 ) 2 . Rarely includ- ing zirconium and titanium, also fluorine. . Orthorhombic Section _, a : b : c or b : a * c Enstatite MgSi0 3 0'9702 : 1 : 0'5710 1'0307 1 0'5885 Bronzite (Mg,Fe)Si0 3 Hypersthene (Fe,Mg)SiO 3 0'9713 : 1 : 0'5704 T0319 : 1 : 0'5872 ut the similarity of the form to the 0. Monoclinic Section Pyroxene .1-0921 1 1 ': 0-5893 74 10' I. NON-ALUMINOUS VARIETIES: 1. DIOPSIDE {CaMg(Si0 3 ) 2 Ayr , r , . iCa(Mg,Fe)(Si0 3 ) 2 Malacohte, Sahte, Diallage, etc. 2. HEDENBERGITE CaFe(SiO 3 ) 2 Manganhedenbergite Ca(Fe,Mn) (SiO 3 ) 2 3. SCHEFFERITE (Ca,Mg) (Fe,Mn)(SiO 3 ) 2 Jeffersomte (Ca,Mg) (Fe,Mn,Zn) (Si0 3 ) 2 SILICATES 471 II. ALUMINOUS VARIETIES.- 4 AUGITE {Ca(Mg,Fe)(Si0 3 ) 2 (with (Mg,Fe)(Al,Fe) 2 Si0 6 Leucaugite, Fassaite, ^Egirite-augite. AcmiteU^Sgiritel NaFe(SiO 3 ) 2 1'0996 : 1 : 0'6012 73 11' Spodumene LiAl(SiO 3 ) 2 1*1238 : 1 : 0'6355 69 40' Jadeite NaAl(Si0 3 ) 2 1*103 : 1 : 0'613 72 44|' a : b : c /8 WoUastonite CaSiO 3 1'0531 : 1 : 0'9676 84 30' Pectolite HNaCa(SiOi)s 1'1140 : 1 : 0'9864 84 40' 7- Triclinic Section Rhodonite MnSiO 3 1-0729 :' 1 ': 0-6213 103 18' 108 44' 81 39' also (Mn,Ca)Si0 3 (Mn,Fe)SiO 3 (Mn,Zn,Fe,Ca)Si0 3 Babingtonite (Ca,Fe,Mn)SiO 3 .Fe 2 (Si0 3 ; 3 1-0691 : 1 : 0-6308 104 21|' 108 31' 83 34' The rare species Rosenbuschite, Layenite, Wohlerite also belong under the monoclinic section and Hiortdahlite under the triclinic section of this group. The PYROXENE GROUP embraces a number of species which, while falling in different systems orthorhombic, monoclinic, and triclinic are yet closely related in form. Thus all have a fundamental prism with an angle of 93 and 87, parallel to which there is more or less distinct cleavage. Further, the angles in other prominent zones show a considerable degree of similarity. In composition the metasilicates of calcium, magnesium, and ferrous iron are ii m i most prominent, while compounds of the form R(Al,Fe) 2 SiOe, RAl(Si0 3 ) 2 are also important. The species of the pyroxene group are closely related in composition to the corresponding species of the amphibole group, which also embraces members in the orthorhombic, monoclinic, and triclinic systems. In a number of cases the same chemical compound appears in each group; furthermore, a change by paramorphism of pyroxene to amphibole is often observed. In form also the two groups are related, as shown in the axial ratio; also in the parallel growth of crystals of monoclinic amphibole upon or about those of pyroxene (Fig. 461, p. 173). The axial ratios for the typical monoclinic species are: Pyroxene a : b :c = 1'0921 : 1 : 0'5893 /3 = 74 10' Amphibole a : 6 : c = M022 : 1 : 0-5875 /? = 73 58' See further on p. 486. The optical relations of the prominent members of the Pyroxene Group, especially as regards the connection between the position of the ether-axes and the crystallographic axes are exemplified in the following figures (Cross). A corresponding exhibition of the prominent amphiboles is given under that group, Fig. 826, p. 486, 472 DESCRIPTIVE MINERALOGY 797 I, Enstatite, etc. II, Spodumene. Ill, Diopside, etc. IV, Hedenbergite, Augite. V, Augite. VI, Acmite. 798 a. Orthorhombic Section ENSTATITE. Orthorhombic. Axes a : b : c = 0'9702 : 1 : 0'5710. mm'", 110 A 110 = 88 16'. rr', 223 A 223 = 40 16^. qq f , 023 A 023 = 241 41'. XT'", 223 A 223 = 39 H'. Twins rare: tw. pi. h (014) as twinning lamellae; also tw. pi. (101) as -stel- late twins cros'sing at angles of nearly 60, sometimes six-rayed. Distinct crystals rare, habit prismatic. Usually massive, fibrous, or lamellar. Cleavage: m (110) rather easy. Parting || 6 (010); also a (100). Frac- ture uneven. Brittle. H. = 5*5. G. = 31-3-3. Luster, a little pearly on cleavage-surfaces to vitreous; often metalloidal in the bronzite variety. Color grayish, yellowish or greenish white, to olive-green and brown. Streak uncolored, grayish. Translucent to nearly opaque. Pleochroism weak, more marked in varieties relatively rich in iron. Optically +. Ax. pi. 1 1 b (010) . Bx a J_ c (001) . Dispersion p < v weak. Axial angle large and variable, increasing with the amount of iron, usually about 90 for FeO = 10 p. c. j8 = 1-669; 7 - a = 0'009. Comp. MgSiO 3 or MgO.SiO 2 = Silica 60, magnesia 40 = 100. Also (Mg,Fe)SiO 3 with Mg : Fe = 8 : 1, 6 : 1, 3 : 1, etc. Var. 1. With little or no iron; Enstatite. Color white, yellowish, grayish, or green- ish white; luster vitreous to pearly; G. = 3'10-3'13. Chladnite (Shepardite of Rose), which makes up 90 p. c. of the Bishopville meteorite, belongs here and is the purest kind. Victorite, occurring in the Deesa meteoric iron in rosettes of acicular crystals, is similar. 2. Ferriferous; Bronzite. Col- or grayish green to olive-green and brown. Luster on cleav- ,-, ., .- age-surface often adamantine- ^nstatite (Bronzite) Hypersthene pearly to submetallic or bronze-like; this, however, is usually of secondary origin and is Bamle 799 800 001 100 001 100 x^-H *K h- t SILICATES 473 not essential. With the increase 9f iron (above 12 to 14 p. c.) bronzite passes to hyper- sthene, the optic axial angle changing so that in the latter X = Bxa _L (100). This is illustrated by Figs. 799, 800. Pyr., etc. B.B. almost infusible, being only slightly rounded on the thin edges; F. = 6. Insoluble in hydrochloric acid. Artif . Enstatite is formed from a melt having the proper composition at temperatures slightly under 1100. At higher temperatures the monoclinic pyroxenes appear. Enstatite has also been formed by fusing olivine with silica. When serpentine is melted it breaks down into enstatite and olivine. Micro. In thin sections is colorless or light yellow or green; marked relief; prominent cleavage with parallel extinction; little pleochroism but becoming stronger with increase of iron; inclusions common lying parallel to brachypinacoid, producing characteristic schiller of mineral. Obs. Enstatite (including bronzite) is a common constituent of peridotites and the serpentines derived from them; it also occurs in crystalline schists. It is often associated in parallel growth with a monoclinic pyroxene, e.g., diallage. A common mineral in mete- oric stones often occurring in chondrules with eccentric radiated structure. Occurs near Aloystal in Moravia, in serpentine; at Kupferberg in Bavaria; at Baste in the Harz Mts., Germany (protobastite) ; in the so-called olivine bombs of the Dreiser Weiher in the Eifel, Germany; in immense crystals, in part altered, at the apatite deposits of Kjorrestad near Bamle, Norway; in the peridotite associated with the diamond deposits of South Africa. In. the United States, in N. Y. at the Tilly Foster magnetite mine, Brewster, Putnam Co., with chondrodite and at Edwards; Texas, Pa.; bronzite from Webster, N. C.; Bare Hills, Baltimore, Md. Named from evaaTT-rjs, an opponent, because so refractory. The name bronzite has priority, but a bronze luster is not essential, and is far from universal. HYPERSTHENE. Orthorhombic. Axes a : b : c = 0-9713 : 1 : 0-5704. mm hh', 110 A 110 = 88 20'. 014 A 014 = 16 14'. oo'", 111 A 111 = 52' uu'" t 232 A 232 = 72< 23'. 50'. Crystals rare, habit prismatic, often tabular || a (100), less often || b (010). Usually foliated massive ; sometimes in embedded spherical forms. Cleavage: b (010) perfect; m (110) and a (100) distinct but interrupted. Fracture uneven. Brittle. H. = 5-6. G. = 3 '40-3 '50. Luster somewhat pearly on a Cleavage-surface, and sometimes metalloidal. Color dark brown- ish green, grayish black, greenish black, pinchbeck-brown. Streak grayish, 801 802 803 Figs. 801, Amblystegite, Laacher See. 802, Malnas. 803, Section || 6 (010) showing inclu- sions; the exterior transformed to actinolite; from Lacroix. brownish gray. Translucent to nearly opaque. Pleochroism often strong, especially in the kinds with high iron percentage; thus 1 1 X or a axis brownish red, Y or b axis reddish yellow, Z or c axis green. Optically . Ax. pi. || b (010). Bx a J_ a (100). Dispersion p > v. Axial angle rather large and 474 DESCRIPTIVE MINERALOGY variable, diminishing with increase of iron, cf . enstatite, p. 472, and Figs. 799, 800, p. 472. = 1702; y - a = 0-013. Hypersthene often encloses minute tabular scales, usually of a brown color, arranged mostly parallel to the basal plane (Fig. 803), also less frequently vertical or inclined 30 to c axis; they may be brookite (gothite, hematite), but their true nature is doubtful. They are the cause of the peculiar metalloidal luster or schiller, and are often of secondary origin, being developed along the so-called " solution-planes" (p. 189)'. Comp. (Fe,Mg)SiO 3 with Fe : Mg = 1 : 3(FeO = 167 p. c.), 1 . 2 (FeO = 217 p. c.) to nearly 1 : l(FeO = 31 '0 p. c.). Alumina is sometimes present (up to 10 p. c.) and the composition then approximates to the alu- minous pyroxenes. Of the orthorhombic magnesium-iron metasilicates, those with FeO > 12 to 15p. c. are usually to be classed with hypersthene, which is further characterized by being optically negative and having dispersion p > v. Pyr., etc. B.B. fuses to a black enamel, and on charcoal yields a magnetic mass; fuses more easily with increasing amount of iron. Partially decomposed by hydro- chloric acid. Micro. In thin sections similar, to enstatite except shows distinct reddish or greenish color with stronger pleochroism and is optically . Artif . Similar to enstatite, which see. Obs. Hypersthene, associated with a triclinic feldspar (labradorite), is common in certain granular eruptive rocks, as norite, hyperite, gabbro, also in some andesites (hyper- sthene-andesite) , a rock shown to occur rather extensively in widely separated regions. It occurs at Isle St. Paul, Labrador; in Greenland; at Farsund and elsewhere in Nor- way; Elfdalen in Sweden; Penig in Saxony; Ronsberg in Bohemia; the Tyrol; Neurode in Silesia; Bodenmais, Bavaria. Amblystegite is from the Laacher See, Germany. Sza- boite occurs with pseudobrookite and tridymite, in cavities in the andesite of the Aranyer Berg, Transylvania, and elsewhere. Occurs in the norites of the Cortlandt region on the Hudson river, N.' Y.; also common with labradorite in the Adirondack Archa3an region of northern N. Y. and northward in Canada.- In the hypersthene-andesites of Mt Shasta, Cal.; Buffalo Peaks, Col., and other points. Hypersthene is named from virep and os, very strong, or tough. BASTITE, or SCHILLER SPAR. An altered enstatite (or brqnzite) having approximately the composition of serpentine. It occurs in foliated form in certain granular eruptive rocks and is characterized by a bronze-like metalioidal 'luster or schiller on the chief cleavage-face 6 (010), which "schillerization" (p. 251) is of secondary origin. H. = 3'5-4. G. = 2 '5-2 '7. Color leek-green to olive- and pistachio-green, and pinchbeck-brown. Pleochroism not marked. Optically -. Double refraction weak. Ax. pi. || a (010) (hence normal to that of enstatite). Bx a b (010). Dispersion p > v. The original bastite was from Baste near Harzburg in the Harz Mts., Germany; also from Todtmoos in the Schwarzwald, Germany. PECKHAMITE, 2(Mg,Fe)SiO 3 .(Mg,Fe)SiO 4 . Occurs in rounded nodules hi the meteorite of Estherville, Emmet Co., Iowa, May 10, 1879. G. = 3 '23. Color light greenish yellow. )8. Monoclinic Section PYROXENE. Monoclinic. Axes_a : b : c = 1-0921 : 1 : 0-5893; J3 = 74 10'. mm'", 110 A 110 = 92 50'. ' &>, 001 A 221 = 49 54'. co, 001 A 100 = 74 10'. en, 001 A 110 = 79 9'. cp, 001 A 101 = 31 20'. a, 001 A Til = 42 2'. ee', Oil A Oil = 59 6'. uu', 111 A ill = 48 29'/ 22', 021 A 021 = 97 11'. SS f , 111 A TTl = 59 11'. cu, 001 A 111 = 33 49*'. oo', 221 A 221 = 84 11'. Twins: tw. pi. (1) a (100), contact-twins, common (Fig. 810), sometimes polysynthetic. (2) c (001), as twinning lamellae producing striations on the vertical faces and pseudocleavage or parting || c (Fig. 811); very common, SILICATES 475 often secondary. (3) y (101) cruciform-twins, not common (Fig. 451, p. 171). (4) W (122) the vertical axes crossing at angles of nearly 60; sometimes re- peated as a six-rayed star (Fig. 450, p. 171). Crystals usually prismatic in 804 805 806 807 808 813 100 habit, often short and thick, and either a square prism (a (100), 6 (010) prom- inent), or nearly square (93, 87) with m (110) predominating; sometimes a nearly symmetrical 8-sided prism with a, 6, m (Fig. 811). Often coarsely lamellar, || c (001) or a (100). Also granular, coarse or fine; rarely fibrous or columnar. Cleavage: m (110) sometimes rather perfect, but interrupted, often only observed in thin sections J_ caxis (Fig. 812). Parting || c (001), due to twinning, often prominent, especially in large crystals and lamellar masses (Fig. 811); also || a (100) less distinct and not so common. Fracture uneven to conchoidal. Brittle. H. = 5-6. G. = 3*2-3*6, varying with the compo- sition. Luster vitreous inclining to res- inous; often dull; sometimes pearly || c(001) in kinds showing parting. Color usually green of various dull shades, varying from nearly colorless, white, or grayish white to brown and black; rarely bright green, as in kinds containing chromium; also blue. Streak white to gray and grayish green. Transparent to opaque. Pleo- chroism usually weak, even in dark-colored varieties; sometimes marked, especially in violet-brown kinds containing titanium. (Violaite is name given to a highly pleochroic variety from the Caucasus Mts.) X 476 DESCRIPTIVE MINERALOGY v, Optically +. Birefringence strong, (7 a) = 0'02 0'03. Ax. pi. || b (010). Bx a or Z A c axis =^4-36 in diopside, to -j-52 in augite (which see), or Z A c (001) = 20 to gg, the angle in general increasing with amount of iron. For diopside 2 V = 59-. a = 1-673. = 1-680. 7 = 1702. Comp. For the most g^rt a normal metasilicate, RSiO 3 , chiefly of calcium and magnesium, also iron, less often manganese and zinc. The alkali metals potassium anc^ sodium present rarely, except in very small amount. Also in certain varieties containing the trivalent metals aluminium, ferric iron, and manganese. These last varieties may be most simply con- sidered as molecular compounds of Ca(Mg,Fe)Si 2 O 6 and (Mg,Fe)(Al,Fe) 2 Si0 6 , as suggested by Tschermak. Chromium is sometimes present in small amount; also titanium "replacing silicon. The name Pyroxene is from iryp, fire and evps, stranger, and records Haiiy's idea that the mineral was, as he expresses it, "a stranger in the domain of fire," whereas, in fact, it is, next to the feldspars, tjje most Tmiversal constituent of igneous rocks. The varieties are numerous and depend upon variations in composition chiefly; the more prominent of the varieties p*>perly rank as sub-species . Artif. The monoclinic pyroxene, MgSiOs, can be crystallized from a melt having the theoretical composition at temperatures about 1500 or at a lower temperature from solu- tion in molten calcium or magnesium vanadate. It is the most stable form of MgSiO?. It has no true melting point but af about 1550 breaks down into forsterite and silica. I. Containing little or no Aluminium 1. DIOPSIDE. Malacolite, Alalite. Calcium-magnesium pyroxene. For- mula CaM"g(Si0 3 ) 2 = Silica 55-6, lime 25-9, magnesia 18-5 = 100. Color white, yellowish, grayish white to pale green, and finally to dark green and nearly black; sometimes transparent and colorless, also rarely a fine blue. In prismatic crystals, often slender; also granular and columnar to lamellar mas- sive. G. = 3-2-3-38. Bx a A c axis = + 36 and upwards. 7 - a = 0-03. Iron is present usually in small amount as noted below, and the amount increases as it graduates toward true hedenbergite. The following belong here: Chrome-diopside, contains chromium (1 to 2'8 p. c. C^Oa), often a bright green. Malacolite, as originally described, was a pale-colored translucent variety from Sala, Sweden. Alalite occurs in broad right-angled prisms, colorless to faint greenish or clear green, from the Mussa Alp in the Ala valley, Piedmont, Italy. Traversellite, from Trayersella, Piedmont, Italy, is similar. Violan is a fine blue diopside from St. Marcel, Piedmont, Italy; occurring in prismatic crystals and massive. Canaanite is a grayish-white or bluish-white pyroxene rock occurring with dolomite at Canaan, Conn. Lavrovite is a pyroxene, colored green by vanadium, from the neighborhood of Lake Baikal, in eastern Siberia. Diopside is named from 6is, twice or double, and o^is, appearance. Malacolite is from na\otKos, soft, because softer than feldspar, with which it was associated. 2. HEDENBERGITE. Calcium-iron pyroxene. Formula CaFe(Si0 3 ) 2 = Silica 48'4, iron protoxide 29'4, lime 22'2 = 100. Color black. In crystals, and also lamellar massive. G. = 3-5-3-58. Bx a A c axis = + 48. Man- ganese is present in manganhedenbergite to 6 -5 p. c. Color grayish green. G. = 3'55. Between the two extremes, diopside and hedenbergite, there are numerous transitions jonformmg to the formula Ca(Mg,Fe)Si 2 O 6 . As the amount of iron increases the color langes irom light to dark green to nearly black, the specific gravity increases from 3 -2 to 3-6, and the angle Bx a A c axis also from 36 to 48. SILICATES 477 The following are varieties, coming under these two sub-species, based in part upon structure, in part on peculiarities of composition. Salite (Sahlite), color grayish green to deep green and black; sometimes grayish and yellowish white; in crystals; also lamellar (parting || c (001)), and granular massive; from Sala in Sweden. Baikalite, a dark dingy green variety, in crystals, with parting j| c (001), from Lake Baikal, in Siberia. Coccolite is a granular variety, embedded in calcite, also forming loosely coherent to compact aggregates; color varying from white to pale green to dark green, and then con- taining considerable iron; the latter the original coccolite. Named from KOKKOS, a grain. DIALLAGE. A lamellar or thin-foliated pyroxene, characterized by a fine lamellar structure and parting || a (100), with also parting |j 6 (010), and less often || c (001). Also a fibrous structure || c axis. Twinning || a (100), often poly synthetic ; interlamination with an orthorhombic pyroxene common. Color grayish green to bright grass-green, and deep green; also brown. Luster of surface a (100) often pearly, sometimes metalloidal or exhibiting schiller and resembling bronzite, from the presence of microscopic inclusions of secondary origin. Bx a A c axis = +39 to 40; = 1-681; y - a = 0;024. H. = 4; G. = 3'2-3'35. In composition near diopside, but often containing alumina and some- times in considerable amount, then properly to be classed with the augites. Often changed to amphibole, see smaragdite, and uralite, p. 490. Named from dta^Xayrj, difference, in allusion to the dissimilar planes of fracture. This is the characteristic pyroxene of gabbro, and other related rocks. Omphacite. The granular to foliated pyroxenic constituent of the garnet-rock called eclogite, often interlaminated with amphibole (smaragdite); color grass-green. Contains some A^Os. 3. SCHEFFERITE. A manganese pyroxene, sometimes also containing much iron. Color brown to black. In crystals, sometimes tabular || c (00_1), also with p (101) prominent, more often elongated in the direction of the zone b (010) : p (101), rarely prismatic, || c axis. Twins, with a (100) as tw. pi. very common. Also crystalline, massive. Cleavage prismatic, very distinct. Color yellowish brown to reddish brown; also black (iron-schefferite} .^Optically +. Bx a or Z A c axis = 44 25'. The iron-schefferite from.Pajsberg, Sweden, is black in color and has Z A c axis = + 49 to 59 for different zones in the same crystal. The brown iron-schefferite (urbanite) from Langban, Sweden, has Z A c axis = 69 3'. It resembles garnet in appearance. Jeffersonite is a manganese-zinc pyroxene from Franklin Furnace, N. J. (but the zinc may be due to impurity). In large, coarse crystals with edges rounded and faces uneven. Color greenish black, on the exposed surface chocolate-brown. Blanfordite. A pyroxene containing some sodium, manganese and iron. Strongly pleo- chroic (rose-pink to sky-blue). Found with manganese ores in the Central Provinces, India. Clinoenstatite has been suggested as the name for the monoclinic magnesium pyroxene. II. Aluminous 4. AUGITE. Aluminous pyroxene. Composition chiefly CaMgSi 2 Oe with (Mg,Fe)(Al,Fe) 2 SiO 6 , and occasionally also containing alkalies and then gradu- ating toward acmite. Titanium is also sometimes present. Here belong: a. LEUC AUGITE. Color white or grayish. Contains alumina, with lime and magnesia, and little or no iron. Looks like diopside. H. = 6'5; G. = 3*19. Named from Xeu/cos, white. b. FASSAITE. Includes the pale to dark, sometimes deep-green crystals, or pistachio- green and then resembling epidote. The aluminous kinds of diallage also belong here. Named from the locality in the Fassatal, Tyrol. Pyrgom is from irvpyu/jia, a tower. c. AUGITE. Includes the greenish or brownish black and black kinds, occurring mostly in eruptive rocks. It is usually in short prismatic crystals, thick and stout, or tabular || a (100); often twins (Figs. 809, 810). Ferric iron is here present, in a relatively large amount, and the angle Bx a A c axis becomes +50 to 52. = 1717; y a '= 0'022. TiO 2 is present in some kinds, which are then pleochroic. Named from avyij, luster. d. ALKALI- AUGITE. Here belong varieties of augite characterized by the presence of alkalies, especially soda; they approximate in composition and optically to acmite and ajgirite (Bx a A c axis = 60, Fig. 814), and are sometimes called aegirite-augite (cf. Fig. 818, 478 DESCRIPTIVE MINERALOGY 814 p. 480). -Known chiefly from rocks rich in alkalies, as elseolite-syenite, phonolite, leu- Pyr. etc. Varying widely, owing to the wide variations in composition in the differ- ent varieties, and often by insensible gradations. Fusibility, 3*75 in diopside; 3 '5 in salite, baikalite, and omphacite; 3 in jeffersonite and augite; 2 '5 in hedenbergite. Varieties rich in iron afford a mag- netic globule when fused on charcoal, and in general the fusibility varies with the amount of iron. Many varieties give with the fluxes reactions for man- ganese. Most varieties are unacted upon by acids. Diff. Characterized by monoclinic crystallization and the prismatic angle of 87 and 93, hence yield- ing nearly square prisms; these may be mistaken for scapolite if terminal faces are wanting or indistinct (but scapolite fuses easily B. B. with intumescence). The oblique parting (|| c (001), Fig. 811) often distinctive, also the common dull green to gray and brown colors. Amphibole differs in prismatic angle (55^ and 124|) and cleavage, and in having com- mon columnar to fibrous varieties, which are rare with pyroxene. (See also p. 486.) Micro. The common rock-forming pyroxenes are distinguished in thin sections by their high relief; usually greenish to olive tones of color; distinct system of interrupted cleavage-cracks crossing one another at nearly right angles in sections _L c axis (Fig. 812); high interference-colors; general lack of pleo- chroism; large extinction-angle, 35 to 50 and higher, for sections || b (010). The last- named sections are easily recognized by showing the highest interference colors; yielding no optical figures in convergent light and having parallel cleavage-cracks, the latter in the direction of the vertical axis. See also segirite, p. 480. A zonal banding is common, the successive laminae sometimes differing in extinction- angle and pleochroism; also thje hour-glass structure occasionally distinct (Fig. 815, from Lacroix). Obs. Pyroxene is a very common mineral in igneous rocks, being the most important of the ferromagnesian minerals. Some rocks consist almost entirely of pyroxene. It most commonly occurs in volcanic rocks but is found also, but less abundantly, in connection with granitic rocks. It is a common mineral in crystalline limestone and dolomite, in serpentine and metamorphic schists; sometimes forms large beds or veins, especially in Archaean rocks. It occurs also in meteorites. The pyroxene of limestone is mostly white and light green or gray in color, falling under diopside (malacoh'te, salite, coccolite); that of most other metamorphic rocks is sometimes white or colorless, but usually green of different shades, from pale green to greenish black, and occasionally black; that of serpentine is sometimes in fine crystals, but often of the foliated green kind called diallage; that of eruptive rocks is usually the black to greenish black augite. In limestone the associations are often amphibole, scapolite, vesuvianite, garnet, ortho- clase, titanite, apatite, phlogopite, and sometimes brown tourmaline, chlorite, talc, zircon, spinel, rutile, etc.; and in other metamorphic rocks mostly the same. In eruptive rocks it may be in distinct embedded crystals, or in grains without external crystalline form; it often occurs with similarly disseminated chrysolite (olivine), crystals of orthoclase (sani- dine), labradorite, leucite, etc.; also with a rhombic pyroxene, amphibole, etc. Pyroxene, as an essential rock-making mineral, is especially common in basic eruptive rocks. Thus, as augite, with a triclinic feldspar (usually labradorite), magnetite, often chrysolite, in basalt, basaltic lavas and diabase; in andesite; also in trachyte; in peridotite and pikrite; with nephelite in phonolite. Further with elseolite, orthoclase, etc., in elaeohte-syenite and augite-syenite; also as diallage in gabbro; in many peridotites and the serpentines formed from them; as diopside (malacolite) in crystalline schists. In limburg- ite, augitite and pyroxenite, pyroxene is present as the prominent constituent, while feld- spar is absent; it may also form rock masses alone nearly free from associated minerals. Diopside (alalite, mussite) occurs in fine crystals on the Mussa Alp in the Ala valley in Piedmont, Italy, associated with garnets (hessonite) and talc in veins traversing serpentine; in fine crystals at Traversella, Piedmont; at Zermatt in Switzerland; Schwarzenstein in the Zillertal, Ober-Sulzbachtal, and elsewhere in Tyrol and in the Salzburg Alps; Reichenstein, SILICATES 479 Silesia, Germany; Ober-Sulzbachtal and elsewhere in Tyrol and in the Salzburg Alps; Reichenstein Lake; Rezbanya, Hungary; Achmatoysk in the Ural Mts., with almandite, clinochlore; Lake Baikal (baikalite) in eastern Siberia; Pargas in Finland; at Nordmark, Sweden. Hedenbergite is from Tunaberg and Nordmark, Sweden; Arendal, Norway. Mangan- hedenbergite from Vester Silfberg, Sweden; schefferite from Langban, Sweden. Augite (including fassaite) occurs on the Pesmeda Alp, Mt. Monzoni, and elsewhere in the Fassatal, Tyrol, as a contact formation; at Carlsbad and Teplitz, Bohemia; Traversella, Piedmont, Italy; the Laacher See, Eifel and Sasbach in the Kaiserstuhl, Germany; in Italy at Vesuvius, white rare, green, brown, yellow to black, Frascati, Etna; the Azores and Cape Verde Islands; the Hawaiian Islands, and many other regions of volcanic rocks. In North America, occurs in Me., at Raymond and Rumford, diopside, salite, etc. In Vt., at Thetford, black augite, with chrysolite, in bowlders of basalt. In Conn., at Canaan, white crystals, often externally changed to tremolite, in dolomite; also the pyroxenic rock called canaanite. In N. Y., at Warwick, fine crystals; in Westchester Co., white, at the Sing Sing quarries; in Orange Co., in Monroe, at Two Ponds, crystals, often large, in lime- stone; near Greenwood furnace, and also near Edenville; in Lewis Co., at Diana, white and black crystals; in St. Lawrence Co., at Fine, in large crystals; at De Kalb, fine diopside; also at Gouverneur, Rossie, Russell, Pitcairn; at Moriah, coccolite, in limestone. In N. J., Franklin Furnace, Sussex Co., good crystals, also jeffersonite. In Pa., near Attleboro, crystals, and granular; in Pennsbury, at Burnett's quarry, diopside; at the French Creek mines, Chester Co., chiefly altered to fibrous amphibole. In Tenn., at the Ducktown mines. In Canada, at Calumet Island, grayish green crystals in limestone; in Bathurst, color- less or white crystals; at Grenville, dark green crystals, and granular; Burgess, Lanark Co.; Renfrew Co., with apatite, titanite, etc.; crystals from Adams Lake, Ontario; Orford, Sherbrooke Co., white crystals, also of a chrome-green color with chrome garnet; at Hull and Wakefield, white crystals with nearly colorless garnets, honey-yellow vesuvianite, etc. At many other points in the Archaean of Quebec and Ontario, especially in connection with the apatite deposits. Pyroxene undergoes alteration in different ways. A change of molecular constitution without essential change of composition, i.e., by paramorphism (using the word rather broadly), may result in the formation of some variety of amphibole. Thus, the white pyroxene crystals of Canaan, Conn., are often changed on the exterior to tremolite; sim- ilarly with other varieties at many localities. See uralite, p. 490. Also changed to steatite, serpentine, etc. PIGEONITE, is the name given to a pyroxene with small and variable axial angle from Pigeon Point, Minn. ACMITE. Monoclinic. Axes: a : b : c = 1-0996 : 1 : 0-6012; = 73 11'. Twins: tw. pi. a (100) very common; crystals often polysynthetic, with enclosed twinning lamellae. Crystals long prismatic, vertically striated or channeled; acute terminations very characteristic. The above applies to ordinary acmite. For cegirite, crystals prismatic, bluntly termi- nated; twins not common; also in groups or tufts of slender acicular to capillary crystals, and in fibrous forms. Cleavage: m (110) distinct; 6 (010) less so. Fracture uneven. Brittle. H. = 6-6*5. G. = 3-50-3-55. Luster vitreous, inclining to resinous. Streak pale yellowish gray. Color brownish or reddish brown, green; in the fracture blackish green. Subtransparent to opaque. Optically . Ax. pi. || b (010). Bx a or X A c axis = +2| acmite, to 6 segirite. a = 1-763. = 1799, 7 = 1-813. Var. Includes acmite in sharp-pointed crystals (Fig. 816) often twins. Bx a A c axis = 5|-6. Also cegirite (Fig. 817)' in crystals bluntly terminated, twins rare, Bx a A c axis = 2-3*. Crystals of acmite often show a marked zonal structure, green within and brown on the exterior, particularly || a (100), b (010), p (101), s (111). The brown portion (acmite) is feebly pleochroic, the green (agirite) strongly pleochroic. Both have absorption X > Y > Z, but the former has X light brown with tinge of green, Y greenish yellow with tinge of 480 DESCRIPTIVE MINERALOGY Acmite ^Egirite brown, Z brownish yellow; the latter has X deep grass-green, Y lighter grass-green, Z yel- lowish brown to yellowish. With some authors (vom Rath, etc.) s = (Oil) and X A c axis = - 2 to 6, as in Fig. 819. Fig. 818 shows the optical orientation according to Brogger. Ill Comp. Essentially NaFe(SiO 3 ) 2 or Na 2 O.Fe 2 O 3 .4Si0 2 = Silica 52'0, iron sesquioxide 34'6, soda 13'4 = 100. Ferrous iron is also present. Pyr.. etc. B.B. fuses at 2 to a lustrous black mag- netic globule, coloring the flame deep yellow; with the fluxes reacts for iron and sometimes manganese. Slightly acted upon by acids. Micro. ^Egirite is characterized in thin sections by its grass-green color; strong pleochroism in tones of green and yellow; the small extinction-angle in sections || &(010). Distinguished from common green hornblende, with which it might be confounded, by the fact that in such sections the direction of extinction lying near the cleavage is neg- ative (X), while the same direction in hornblende is pos- itive (Z). Artif . Acmite can be produced artificially by fusing together its constituent oxides but usually under such conditions only a glass containing crystals of magnetite is formed. Obs. The original acmite occurs in a pegmatite vein; at Rundemyr, east of the little lake called Rokebergskjern, in the parish of Eker, near Kongsberg, Norway. It is in slender crystals, sometimes a foot long, embedded in feldspar and quartz. jEgirite occurs especially in igneous rocks rich in soda and containing iron, commonly in rocks containing leucite or. nephelite; thus in aegirite-granite, nephelite-syenite, and some varieties of phonolite; often in such cases iron-ore grains are wanting in the rock, their place being taken by aegirite crystals. In the sub-variety of phonolite called tinguaite, the rock has often a deep greenish color due to the abundance of minute crystals of aegirite. Large crystals are found in the pegmatite facies of nephelite- syenites as in West Greenland, Southern Norway, the peninsula Kola in Russian Lapland, Ditro in Transylvania. Prominent American occurrences are the following: Magnet Cove, ' Ark. (large crystals); Salem and Quincy, Mass.; Libertyville, N. J. (dike); Trans Pecos district in Texas; Black Hills, S. D.; Cripple Creek, Col.; Bearpaw Mts., Judith Mts. and the Crazy Mts. in Mon.; also vanadium-bearing aegirites from Libby, Mon., also at Montreal, Canada. Acmite is named from &KM, point, in allusion to the pointed extremities of the crystals; Mginte is from ^Egir, the Icelandic god of the sea. SPODUMENE. Triphane. Monoclinic. Axes a : b : c = 1-1238 : 1 : 0*6355; = 69 40'. Twins: tw. pi. a (100). Crystals prismatic (mm'" 110 A HO = 93 0'), often flattened || a (100); the vertical planes striated and furrowed;' crystals , sometimes very lar,ge. Also massive, cleavable. Cleavage m (110) perfect. A lamellar structure || a (100) sometimes very 818 SILICATES 481 820 Norwich, Mass Hiduenite prominent, a crystal then separating into thin plates. Fracture uneven to subconchoidal. Brittle. H. = 6'5-7. G. = 3-13-3-20. Luster vitreous, on cleavage surfaces somewhat pearly. Color greenish white, grayish white, yellowish green, emerald-green, yellow, ame- thystine purple. Streak white. Transparent to translucent. Pleochroism strong in deep green varieties. Optically + . Ax. pi. || b (010). Bxa A c axis = + 26. Dispersion p > v, horizontal. 2 V = 58. a = 1-651. j8 = 1-669. 7 = 1-677. Hiddenite has a yellow-green to emerald-green color; the latter variety is used as a gem. In small ( to 2 inches long) slender prismatic crystals, faces often etched. Kunzite is a clear lilac-colored variety found near Pala, San Diego Co., California, and also at Vanakarata, Madagascar . The unaltered material from Branch ville, Conn., shows the same color. Used as a gem stone. Comp. LiAl(SiO 8 ) 2 or Li 2 O.Al 2 O 3 .4SiO2 = Silica 64-5, alumina 27-4, lithia 8*4 = 100. Generally contains a little sodium; the variety hiddenite also chromium, to which the color may be due. Pyr., etc. B.B. becomes white and opaque, swells up, imparts a purple-red color (lithia) to the flame (sometimes obscured by sodium), and fuses at 3 '5 to a clear or white glass. Not acted upon by acids. Kunzite shows strong phosphorescence with an orange- pink color when excited by an oscillating electric discharge, by ultra violet rays, X-rays, or radium emanations. Diff. Characterized by its perfect parting || a (100) (in some varieties) as well as by prismatic cleavage; has a higher specific gravity and more pearly luster than feldspar or scapolite. Gives a red flame B.B. Less fusible than amblygonite. Alter. Spodumene undergoes very commonly alteration. First by the action of solu- tions containing soda it is changed to a mixture of eucryptite, LiAlSiO 4 , and albite, NaAl SisOg. Later through the influence of potash salts the eucryptite is changed to muscovite. This resulting mixture of albite and muscovite is known as cymatolite, having a wavy fibrous structure and silky luster . These alteration products are well shown in the specimens from Branch ville, Conn. Artif . An artificial spodumene has been obtained together with other silicates by fusing together lithium carbonate, alumina and silica. This spodumene differs, however, from the natural mineral in its optical properties and has been called ^-spodumene. The natural mineral, or spodumene, is transformed into the /3 modification on heating to 1000. Obs. Spodumene occurs in pegmatite veins, sometimes in crystals of very great size. Crystals from the Etta tin mine, S. D., with faces up to 40 feet in length have been reported. Occurs on the island of Uto, Sweden; at Killiney Bay, Ireland; in small transparent crystals of a pale yellow in Brazil, province of Minas Geraes. Variously colored spodumene from Madagascar. In the United States, in granite at Goshen, Mass.; also at Chesterfield, Chester, Hunt- ington (formerly Norwich), and Sterling, Mass.; at Windham, Me., with garnet and stau- rolite and at Peru, with beryl, triphylite, petalite. In Conn., at Branchville, the crystals often of immense size; near Stony Point, Alexander Co., N. C. (hiddenite)', in S. D. at the Etta tin mine in Pennington Co. Kunzite from Pala, Cal. The name spodumene is from awodios, ash-colored. Hiddenite is named for W. E. Hidden and Kunzite for Dr. G. F. Kunz. Use. The colored transparent varieties are used as gem stones; see above. JADEITE. Monoclinic. Axes, see p. 471. Cleavage and optical characters like pyroxene. Usually massive, with crystalline structure, sometimes granular, also obscurely columnar, fibrous foliated to closely compact. 482 DESCRIPTIVE MINERALOGY Cleavage: prismatic, at angles of about 93 and 87; also || a (100) diffi- cult. Fracture splintery. Extremely tough. H. = 6'5-7. G. = 3-33-3-35. Luster subvitreous, pearly on surfaces of cleavage. Color apple-green to nearly emerald-green, bluish green, leek-green, greenish white, and nearly white; sometimes white with spots of bright green. Optically + . Bx a A c axis = 30 to 40. 2 V = 72. 0=1-654. Streak uncolored. Trans- lucent to subtranslucent. Comp. Essentially a metasilicate of sodium and aluminium corre- sponding to spodumene, NaAl(SiO 3 ) 2 or Na 2 O.Al 2 O3.4SiO2 = Silica 59*4, alumina 25 -2, soda 15 -4 = 100. Chloromelanite is a dark green to nearly black kind of jadeite (hence the name), contain- ing iron sesquioxide and not conforming exactly to the above formula. Pyr., etc. B.B. fuses readily to a transparent blebby glass. Not attacked by acids after fusion, and thus differing from saussurite. Obs. Occurs chiefly in eastern Asia, thus in the Mogoung district in Upper Burma, in a valley 25 miles southwest of Meinkhoom, in rolled masses in a reddish clay; in Yung- chang, province of Yunnan, southern China; in Thibet. Much uncertainty prevails, how- ever, as to the exact localities, since jadeite and nephrite have usually been confused with each other. May occur also on the American continent, in Mexico and South America ; perhaps also in Europe. Jadeite has long been highly prized in the East, especially in China, where it is worked into ornaments and utensils of great variety and beauty. It is also found with the relics of early man, thus in the remains of the lake-dwellers of Switzerland, at various points in France, in Mexico, Greece, Egypt, and Asia Minor. A pyroxene, resembling jadeite in structure and consisting of the molecules of jadeite, diopside, and acmite in nearly equal proportions, occurs at the manganese mines of St. Marcel, Italy. Use. As the material jade, is used as an ornamental stone. See below. JADE is a general term used to include various mineral substances of tough, compact texture and nearly white to dark green color used by early man for utensils and ornaments, and still highly valued in the East, especially in China. It includes properly two species only; nephrite, a variety of amphibole (p. 489), either tremolite or actinolite, with G. = 2 '95-3-0. and jadeite, of the pyroxene group and in composition a soda-spodumene, with G. = 3-3-3-35; easily fusible. The jade of China belongs to both species, so also that of the Swiss lake-habitations and of Mexico. Of the two, however, the former, nephrite, is the more common and makes the jade (ax stone or Punamu stone) of the Maoris of New Zealand; also found in Alaska. The name jade is also sometimes loosely used to embrace other minerals of more or less similar characters, and which have been or might be similarly used thus sillimanite, pec- tolite, serpentine; also vesuvianite, garnet. Bowenite is a jade-like variety of serpentine. The "jade tenace" of de Saussure is now called saussurite. WOLLASTONITE. Tabular Spar Monoclinic. Axes a : b : c = 1-0531 : 1 : 0*9676; = 84 30'. 822 mm"', 110 A 110 = 92 42'. hh f ", 540 A 540 = 79 58'. gg' t Oil A Oil = 87 51'. co, 001 A 101 = 40 3'. cr, 001 A 301 = 74 59'. ct, 001 A 101 = 45 5'. Diana, N. Y. Twins: tw. pi. a (100). Crystals commonly tabular || a (100) or c (001); also short prismatic. Usually cleavable mas- sive to fibrous, fibers parallel or reticulated; also compact. Cleavage: a (100) perfect; also c (001); t (101) less so. Fracture uneven, brittle. H. = 4-5-5. G. = 2-8-2-9. Luster vitreous, on cleavage surfaces pearly. Color white, inclining to gray, yellow, red, or brown. Streak white, bubtransparent to translucent. Optically -. Bx a A c axis = + 32. Dis- SILICATES 483 persion p > v, inclined distinct. Ax. pi. || b (010). 2E = 70; a = T621. ft = 1-633. 7 = 1*635. Comp. Calcium metasilicate, CaSi0 3 or CaO.SiO 2 = Silica 51*7, lime 48-3, = 100. When wollastonite is heated above 1190 C. it develops a basal cleavage, becomes pseudo- hexagonal, optically positive, nearly uniaxial but probably monoclinic. This material has been called pseudowollastonite. Pyr., etc. B.B. fuses quietly to a white, almost glassy globule. With hydrochloric acid decomposed with separation of silica; most varieties effervesce slightly from the pres- ence of calcite. Often phosphoresces. Micro. In thin sections wollastonite is colorless with a moderate relief and medium birefringence. The plane of the optic axes is usually normal to the elongation of the crystals. Artif . Wollastonite may be obtained artificially by heating a glass of the composition CaSiOs to between 800 and 1000. At higher temperatures the pseudowollastonite modi- fication is obtained. Obs. Wollastonite is found especially in granular limestone, and in regions of granite, as a contact formation; it is very rare in eruptive rocks. It is often associated with a lime garnet, diopside, etc. Occurs in Hungary in the copper mines of Cziklowa in the Banat; at Pargas in Finland; at Harzburg in the Harz Mts., Germany; at Auerbach, Hesse, Germany, in granular lime- stone; at Vesuvius, rarely in fine crystals; on the islands of Elba and Santorin. In the United States, in N. Y., at Willsborough ; Diana, Lewis Co.; Bonaparte Lake, Lewis Co. In Pa., Bucks Co., 3m. west of Attleboro; in Cal., at Crestmore. In Canada, at Grenville; at St. Jerome and Morin, Quebec, with apatite. Named after the English chemist, W. H. Wollaston (1766-1828). Alamosite. Lead metasilicate, PbSiOs. Closely related to wollastonite in crystal forms. Monoclinic. In radiating fibrous aggregates. Cleavage || 6 (010). G. = 6'5. H. = 4'5. Colorless or white. Refractive index about T96. Found near Alamos, Sonora, Mexico. PECTOLITE. Moneclinic. Axes a : b : c = 1-1140 : 1 : 0-9864; ft = 84 40'. Commonly in close aggregations of acicular crystals; elongated || b axis, but rarely terminated. Fibrous massive, radiated to stellate. Cleavage: a (100) and c (001) perfect. Fracture uneven. Brittle. H. = 5. G. = 2 '68-2 -78. Luster of the surface of fracture silky or subvitreous. Color whitish or grayish. Subtranslucent to opaque. Optically +. Ax. pi. and Bx a _L b (010); Bx nearly _L a (100). 2 V = 60. ft = 1-61. Comp. HNaCa2(SiO 3 ) 3 or H 2 O.Na2O.4CaO.6Si0 2 = Silica 54-2, lime 33-8, soda 9 -3, water 27 = 100. Pectolite is sometimes classed with the hydrous species allied to the zeolites. Pyr., etc. - In the closed tube yields water. B.B. fuses at 2 to a white enamel. De- composed in part by hydrochloric acid with separation of silica as a jelly. Often gives out light when broken in the dark. Obs. A secondary mineral, occurring like the zeolites mostly in basic eruptive rocks, in cavities or seams; occasionally in metamorphic rocks. Found in Scotland near Edin- burgh; at Kilsyth, Corstorphine Hill (walkerite); Island Skye. Also at Mt. Baldo and Mt. Monzoni in the Tyrol; at Niederkirchen, Bavaria (osmelite). Occurs also at Bergen Hill, Paterson and Great Notch, N. J.; Lehigh Co., Pa.; compact at Isle Royale, Lake Superior; at Magnet Cove, Ark., in elseqlite-syenite (manganpectolite with 4 p. c. MnO); compact, massive in Alaska, where used, like jade, for implements. Schizolite. Like manganpectolite, HNa(Ca,Mn)2(SiOs)3, but triclinic. In prismatic crystals. Two cleavages. H. = 5-5 '5. G. = 3'0-3'1. Color light red to brown. From the nepheline syenite of Julianehaab, southern Greenland. Rosenbuschite. Near pectolite, but contains zirconium. Index, 1-65. From Norway. In nephelite-syenite-porphyry, Red Hill, Moultonboro, N. H. 484 DESCRIPTIVE MINERALOGY Wohlerite. A zirconium-silicate and niobate of Ca, Na, etc. In prismatic, tabular crystals, yellow to brown. Indices, 1700-1 726. Occurs in elseolite-syenite^ on several islands of the Langesund fiord, near Brevik, in Norway. In syenite from Red Hill, N. H. Lavenite. A complex zirconuim-silieate of Mn, Ca, etc., containing also F, Ti, Ta. etc. In yellow to brown prismatic crystals. Index, 1750. Found on the island Laven in the .Langesund fiord, southern Norway; also elsewhere in eheolite-syemte. 7. Triclinic Section RHODONITE. Triclinic. Axes a : b : c = 1*07285 : 1 : 0-6213; a = 103 18'; ]8 = 108 44'- y = 81 39'. Crystals usually large and rough with rounded edges. Commonly tabular 1| c (001); sometimes resembling pyroxene in habit. Commonly massive, cleavable to compact; also in_ embedded grains. Cleavage: m (110), M (110) perfect; c (001) less perfect. Fracture con- choidal to uneven; very tough when compact. H. = 5-5-6-5. G. = 3-4- 3-68. Luster vitreous; on cleavage surfaces somewhat pearly. Color light brownish red, flesh-red, rose-pink; sometimes greenish or yellowish, when impure; often black outside from exposure. Streak white. Transparent to translucent. Optically . .0 = 173. Comp. Manganese metasilicate, MnSiOa or MnO.SiO 2 = Silica 45-9, manganese protoxide 54-1 = 100. Iron, calcium (in bustamite), and occasion- ally zinc (in 'fowlerite) replace part of the manganese. 823 824 825 Franklin Furnace, N. J. db, 100 A 010 = 94 26'. mM, 110 A 110 = 92 28|'. ac, 100 A 001 = 72 36*'. en, 001 A 221 = 73 52'. be, 010 A 001 = 78 42i'. ck, 001 A 221 = 62 23'. am, 100 A 110 = 48 33'. kn, 221 A 221 = 86 5'. Pyr., etc. B.B. blackens and fuses with slight intumescence at 2'5; with the fluxes gives reactions for manganese; fowlerite gives with soda on charcoal a reaction for zinc. Slightly acted upon by acids. The calciferous varieties often effervesce from mechanical admixture of calcium carbonate. In powder, partly dissolves in hydrochloric acid, and the insoluble part becomes of a white color. Darkens on exposure to the air, and some- times becomes nearly black. Diff. Characterized by its pink color; distinct cleavages; hardness; fusibility and manganese reactions B.B. Obs. Occurs in Sweden at Langban, Wermland ; in iron-ore beds, in broad cleavage- plates, and also granular massive, and at the Pajsberg iron mines near Filipstad (paisbergite) sometimes in small brilliant crystals; in the district of Ekaterinburg in the Ural Mts., mas- sive like marble, whence it is obtained for ornamental purposes; with tetrahedrite at Kap- nik and Rezbanya, Hungary; St. Marcel, Piedmont, Italy; Mexico (bustamite, containing CaO). In crystals from Broken Hill, New South Wales. Occurs in Cummington, Mass.; on Osgood's farm, Blue Hill Bay, Me.; fowlerite (con- SILICATES 485 taining ZnO) at Mine Hill, Franklin Furnace, and Sterling Hill, near Ogdensburgh, N. J., usually embedded in calcite and sometimes in fine crystals. Named from podov, a rose, in allusion to the color. Rhodonite is often altered chiefly by oxidation of the MnO (as in marceline, dyssnite); also by hydration (stratopeite, neotocite, etc.); further by introduction of CO 2 (allagite, photidte, etc.). Use. Rhodonite at times is used as an ornamental stone. Pyroxmangite. A triclinic, manganese-iron pyroxene. In cleavage masses. Indices, 175-1 -76. H. = 5-5-6. G. = 3'8. Color, amber to dark brown. Easily fusible to black magnetic globule. Alters to skemmatite. Found near Iva, Anderson Co., South Carolina. Babingtonite. (Ca,Fe,Mn)SiO 3 with Fe 2 (SiO3)a. In small black triclinic crystals, near rhodonite in angle (axes on p. 471). H. = 5'5-6. G. = 3'35-3'37. Index, 172. From Arendal, Norway; at Herbornseelbach, Nassau, Germany; at Baveno, Italy. From Somer- ville and Athol, Mass.; in the zeolite deposits of Passaic Co., N. J. Hiortdahlite. Essentially (Na2,Ca) (Si,Zr)Oa, with also fluorine. In pale yellow tab- ular crystals (triclinic). Index, 1'695. Occurs sparingly on an island in the Langesund fiord, southern Norway. Sobralite. A triclinic pyroxene. Optically + . Colorless. From eulysite rock at Sodermanland, Sweden. 3. Amphibole Group Orthorhombic, Monoclinic, Triclinic Composition for the most part that of a metasilicate, RSi0 3 , with R = Ca,Mg,Fe chiefly, also Mn,Na 2 ,K 2 ,H 2 . Further often containing aluminium and ferric iron, in part with alkalies as NaAl(Si0 3 ) 2 or NaFe(SiO 3 )2; perhaps ii in also containing RR 2 SiOe. a. Orthorhombic Section a :b Anthophyllite (Mg,Fe)SiO 3 0-5138 : 1 GEDRITE (Mg,Fe)Si0 3 with (Mg,Fe)Al 2 Si0 6 0. Monoclinic Section a : b : c /3 Amphibole . 0-5511 : 1 : 0-2938 73 58' I. NONALUMINOUS VARIETIES. 1. TREMOLITE CaMg 3 (SiO 3 ) 4 2. ACTINOLITE Ca(Mg,Fe) 3 (SiO 3 ) 4 Nephrite, Asbestus, Smaragdite, etc. Cummingtonite (Fe,Mg)SiO 3 Dannemorite (Fe,Mn,Mg)SiO 3 Grtinerite FeSiO 3 3. RICHTERITE (K 2 ,Na2Mg,Ca,Mn) 4 (SiO 3 )4 II. ALUMINOUS VARIETIES- 4. HORNBLENDE Edenite Pargasite and Common Hornblende Chiefly Ca(Mg,Fe) 3 (SiO 3 ) 4 with Na 2 Al 2 (SiO 3 ) 4 and (Mg,Fe) 2 (Al,Fe) 4 Si 2 Oi 2 486 DESCRIPTIVE MINERALOGY Glaucophane Riebeckite Crocidolite Arfvedsonite NaAl(Si0 3 ) 2 .(Fe,Mg)Si0 3 a : b : c /3 2NaFe(SiO 3 ) 2 .FeSiO 3 0'5475 : 1 : 0'2925 = 76 10' NaFe(Si0 3 ) 2 .FeSi0 3 Na 8 (Ca,Mg) 3 (Fe,Mn) 14 (Al,Fe) 2 Si 21 045 0-5509 : 1 : 0*2378 = 73 2' 7. Triclinic Section ^Enigmatite. The only species included under the triclinic section is the rare and im- perfectly known aenigmatite (cossyrite). The AMPHIBOLE GROUP embraces a number of species which, while falling in different systems, are yet closely related in form as shown in the common prismatic cleavage of 54 to 56 - also in optical characters and chemical com- position. As already noted (see p. 471), the species of this group form chem- ically a series parallel to that of the closely allied Pyroxene Group, and between them there is a close relationship in crystalline form and other characters. The Amphibole Group, however, is less fully developed, including fewer species, and those known show less variety in form. The chief distinctions between pyroxene and amphibole proper are the following: Prismatic angle with pyroxene 87 and 93; with amphibole 56 and 124; the prismatic cleavage being much more distinct in the latter. With pyroxene, crystals usually short prismatic and often complex, structure of massive kinds mostly lamellar or granular; with amphibole, crystals chiefly long prismatic and simple, columnar and fibrous massive kinds the rule. The specific gravity of most of the pyroxene varieties is higher than of the like varieties of amphibole. In composition of corresponding kinds, magnesium is present in larger amount in amphibole (Ca : Mg = 1 : 1 in diopside, = 1 : 3 in tremolite) ; alkalies more frequently play a prominent part in amphibole. The optical relations of the prominent members of the group, as regards the position of the ether-axes, is exhibited by the following figures (Cross) ; compare Fig. 797, p. 472, for a similar representation for the corresponding members of the pyroxene group. I. Anthophyllite. II. Glaucophane. III. Tremolite, etc. IV. Hornblende. V. Arfvedsonite. VI. Riebeckite. a. Orthorhombic Section ANTHOPHYLLITE. Orthorhombic. Axial ratio a : b = 0*5137 : 1. Crystals rare, habit pris- matic (mm"' 110 A 110 = 54 23). Commonly lamellar, or fibrous massive; fibres often very slender; in aggregations of prisms. SILICATES 487 Cleavage: prismatic, perfect; b (010) less so; a (100) sometimes distinct. H. = 5 -5-6. G. = 3 1-3 -2. Luster vitreous, somewhat pearly on the cleavage face. Color brownish gray, yellowish brown, clove-brown, brownish green, emerald-green, sometimes metalloidal. Streak uncolored or grayish. Transparent to subtranslucent. Sometimes pleochroic Usually optically + ; also + for red, for yellow, green. Ax. pi. always || b (010). Bx a usually J_ c (001) ; also _L c (001) for red, J_ a (100) for yellow, green. 2 V = 84. a = 1-633. = 1'642. 7 = 1-657. Comp. (Mg,Fe)SiO 3 , corresponding to enstatite-bronzite-hypersthene in the pyroxene group. Aluminium is sometimes present in considerable amount. There is the same relation in optical character between anthophyl- lite (+) and gedrite ( ) as between enstatite and hypersthene (cf. Figs. 799 803, p. 472). Var. ANTHOPHYLLITE, Mg : Fe = 4 : 1, 3 : 1, etc. For 3 : 1, the percentage compo- sition is: Silica 55*6, iron protoxide 16'6, magnesia 27 '8 = 100. Anthophyllite sometimes occurs in forms resembling asbestus. Aluminous, GEDRITE. Iron is present in larger amount, and also aluminium; it hence corresponds nearly to a hypersthene, some varieties of which are highly aluminous. Ferroanthophyllite is a name given to an iron anthophyllite from Idaho and elsewhere. Hydrous anthophyllites have been repeatedly described, but in most cases they have been shown to be hydrated monoclinic amphiboles. Pyr., etc. B.B. fuses with difficulty to a black magnetic enamel; with the fluxes gives reactions for iron; unacted upon by acids. Micro. In sections colorless, non-pleochroic. Parallel extinction. Commonly fibrous. Artif . Anthophyllite is formed artificially when magnesium metasilicate is heated considerably above its melting point and then quickly cooled. Obs. Anthophyllite occurs in mica schist near Kongsberg in Norway: at Hermann- schlag, Moravia. In the United States, at the Jenks corundum mine, Franklin, Macon Co., N. C.; from Rockport, Mass. A colorless or pale red variety from Edwards, N. Y., has been called valleite. The original gedrite is from the valley of Heas, near Gedres, France. Named from anthophyllum, clove, in allusion to the clove-brown color. 13. Monoclinic Section AMPHIBOLE. Monoclinic. mm ca, cp, Hornblende. Axes a : b : c = 0*5511 110 A 110 = 55 49'. 001 A 100 = 73 58'. 001 A 101 = 31 0'. : 0-2938; = 73 58'. rr', Oil A Oil = 31 32'. ii, 031 A 031 = 80 32'. pr, 101 A Oil = 34 25'. Twins: (1) tw. pi. a (100), common as contact-twins; rarely polysyn- 827 829 830 831 thetic. (2) c (001), as tw. lamellae, occasionally producing a parting analogous to that more common with pyroxene (Fig. 461, p. 173). Crystals commonly 488 DESCRIPTIVE MINERALOGY prismatic; usually terminated by the low clinodome, r (Oil), sometimes by r and p (101) equally developed and then suggesting rhombohedral forms (as of tourmaline). Also columnar or fibrous, coarse or fine, fibres often like flax; rarely lamellar; also granular massive, coarse or fine, and usually strongly coherent, but sometimes friable. Cleavage: m (110) highly perfect; a (100), b (010) sometimes distinct. Fracture subconchoidal, uneven. Brittle. H. = 5-6. G. = 2-9-3-4, vary- ing with the composition. Luster vitreous to pearly on cleavage faces ; fibrous varieties often silky. Color between black and white, through various shades of green, inclining to blackish green; also dark brown; rarely yellow, pink, rose-red. Streak uncolored, or paler than color. Sometimes nearly trans- parent; usually subtranslucent to opaque. Pleochroism strongly marked in all the deeply colored varieties, as described beyond. Absorption usually Z > Y > X. Optically , rarely -f . Ax. pi. || b (010). Extinction-angle on b (010), or Z A c axis = + 15 to 18 in most cases, but varying from about 1 up to 37; hence also Bx a A c axis = 75 to 72, etc. See Fig. 832. Dispersion p < v. Axial angles variable; see beyond. Optical characters, particularly indices of refraction, birefringence and extinction angles vary with change in composition, particularly with the total amount of iron present. In general the indices and extinction angles increase with increase of iron content while the birefringence decreases. Comp. In 'part a normal metasilicate of calcium and magnesium, RSi0 3 , usually with iron, also manganese, and thus in general analogous to the pyroxenes. The alkali metals, sodium and potassium, also present, and more commonly so than with pyroxene. In part also aluminous, corresponding to the aluminous pyroxenes. Titanium sometimes is present and also rarely fluorine in small amount. The aluminium is in part present as NaAl(SiO 3 ) 2 , but many amphiboles containing aluminium or ferric iron are more basic than a normal metasilicate; they may sometimes be n m explained as containing R(Al,Fe) 2 SiO 6 , but the exact nature of the compound is often doubtful. The amphibole formulas are in many cases double the corresponding ones for 832 833 pyroxene Thus, for most tremolite and actinolite, Ca : Mg(Fe) = 1 kte is CaMgaSuOw, while diopside is CaMgSi 2 6 , etc. 3, and hence tremo- SILICATES 489 Rammelsberg has shown that the composition of most aluminous amphiboles may be expressed in the general form mRSiO3.nAl 2 O 3 ; while Scharizer, modifying this view, pro- poses to regard the amphiboles as molecular compounds of Ca(Mg,Fe) 3 Si 4 Oi2 (actinolite), i ii in and the orthosilicate (R2,R) 3 R2Si 3 Oi2, for which he uses Breithaupt's name syntagmatite, originally given to the Vesuvian hornblende. Penfield concludes that (1) amphibole is a metasilicate, (2) that fluorine and hydroxyl are isomorphous with the protoxides and (3) that the presence of sesquioxides is explained by their introduction into the molecule in the form of various bivalent radicals. The crystallographic position here adopted is that suggested by Tschermak, which best exhibits the relation between amphibole and_pyroxeme. Some authors retain the former position, according to which p = (001), r = (111), etc. Fig. 833 shows the corresponding optical orientation. I. Containing little or no Aluminium 1. TEEMOLITE. Grammatite, nephrite in part. Calcium-magnesium amphibole. Formula CaMg 3 (SiO 4 ) 3 = Silica 577, magnesia 28*9, lime 13'4 = 100. Ferrous iron, replacing the magnesium, present only sparingly, up to 3 p. c. Colors white to dark gray. In distinct crystals, either long-bladed or short and stout.. In aggregates long and thin columnar, or fibrous; also com- pact granular massive (nephrite, below). G. = 2'9-3'l. Sometimes trans- parent and colorless. Optically . Extinction-angle on b (010), or Z A c axis = +16 to 18, hence Bx a A c axis = - 74 to - 72. 2V = 80 to 88. a = 1-609. (3 = 1-623. 7 = 1'635. Tremolite was named by Pini from the Tremola valley on the south side of the St. Gothard. Winchite is the name given to a blue amphibole near tremolite from the manganese mines of Central India. 2. ACTINOLITE. Calcium-magnesium-iron amphibole. Formula Ca(Mg,Fe) 3 (Si0 3 ) 4 . Color bright green and grayish green. In crystals, either shortx- or long-bladed, as in tremolite; columnar or fibrous; granular massive. G. = 3-3 '2. Sometimes transparent. The variety in long bright-green crystals is called glassy actinolite; the crystals break easily across the prism. The fibrous and radiated kinds are often called asbestiform actinolite and radiated actinolite. Actinolite owes its green color to the ferrous iron present. Pleochroism distinct, increasing as the amount of iron increases, and hence the color becomes darker; Z emerald-green, Y yellow-green, X greenish yellow. Absorption Z > Y > X, Zillertal. Optically . Extinction-angle on b (010), Z A c axis = + 15 and Bx a A c axis = - 75. 2V = 78; p < v, a = 1-611. (3 = 1-627. 7 = 1-636. Named atfinolite from a/cris, a ray, and XZ0os, stone, a translation of the German Strahlslein or radiated stone. Name changed to actinote by Haiiy, without reason. NEPHRITE. Jade in part. A tough, compact, fine-grained tremolite (or actinolite). breaking with a splintery fracture and glistening luster. H. = (M5'5. G. = 2'96-3'l. Named from a supposed efficacy in diseases of the kidney, from >ep6s, kidney. It varies in color from white (tremolite) to dark green (actinolite), in the latter, iron protoxide being present up to 6 or 7 p. c. The latter kind sometimes encloses distinct prismatic crystals of actinolite. A derivation from an original pyroxenic mineral has been suggested in some cases. Nephrite or jade was brought in the form of carved ornaments from Mexico or Peru soon after the discovery of America. A similar stone comes from Eastern Asia, New Zea- land and Alaska. See jadeite, p. 481; jade, p. 482. Szechenyiite is an amphibole occurring with jadeite from Central Asia. ASBESTUS. Asbestos. Tremolite, actinolite, and other varieties of amphibole, except- ing those containing much alumina, pass into fibrous varieties, the fibers of which are some- times very long, fijie, flexible, and easily separable by the fingers, and look like flax. These kinds are called asbestus (from the Greek for incombustible) . The colors vary from white to 490 DESCRIPTIVE MINEEALOGY green and wood-brown. The name amianthus is applied usually to the finer and more silky kinds. Much that is popularly called asbestus is chrysotile, or fibrous serpentine, containing 12 to 14 p. c. of water. Byssolite is a stiff fibrous variety. Mountain leather is in thin flexible sheets, made of interlaced fibers; and mountain cork the same in thicker pieces; both are so light as to ftoat on water, and they are often hydrous, color white to gray or yellowish. Mountain wood is compact fibrous, and gray to brown in color, looking a little like dry wood. SMARAGDITE. A thin-foliated variety of amphibole, near actinolite in composition but carrying some alumina. It has a light grass-green color, resembling much common green diallage. In many cases derived from pyroxene (diallage) by uralitization, see below. It retains much of the structure of the diallage and also often encloses remnants of the original mineral. It forms, along with whitish or greenish saussurite, a rock called saussurite- gabbro, the euphotide of the Alps. The original mineral is from Corsica, and the rock is the verde di Corsica duro of the arts. URALITE. Pyroxene altered to amphibole. The crystals, when distinct, retain the form of the original mineral, but have the cleavage of amphibole. The change usually commences on the surface, transforming the outer layer into an aggregation of slender amphibole prisms, parallel in position to each other and to the parent pyroxene (cf . Fig. 803, p. 473). When the change is complete the entire crystal is made up of a bundle of amphibole needles or fibers. The color varies from white (tremolite) to pale or deep green, the latter the more common. In composition uralite appears to conform nearly to actinolite, as also in optical characters. The most prominent change in composition in passing from the original pyroxene is that corresponding to the difference existing between the two species in general, that is, an increase in the magnesium and decrease in calcium. The change, therefore, is not strictly a case of paramorphism, although usually so designated. Uralite was originally described by Rose in a rock from the Ural Mts. It has since been observed from many localities. The microscopic study of rocks has shown the process of "uralitiza- tion" to be very common, and some authors' regard many hornblendic rocks and schists to represent altered pyroxenic rocks on a large scale. CUMMINGTONITE. Amphibole-Anthophyllite. Iron-Magnesium Amphibole. Here be- long certain varieties of amphibole resembling anthophyllite and essentially identical with it in composition, but optically monoclinic. From Kongsberg, Norway; Greenland. The original cummingtonite is gray to brown in color; usually fibrous or fibre-lamellar, often radiated. G. = 3'l-3'32; from Cummington, Mass. DANNEMORITE. Iron-Manganese Amphibole. Color yellowish brown to greenish gray. Columnar or fibrous, like tremolite and asbestus. Contains iron and manganese. From Sweden. Juddite is a manganese amphibole found at Kacharwahi, India. GRUNERITE. Iron- Amphibole. Asbestiform or lamellar-fibrous. Luster silky; color brown; G. = 3713. Formula FeSiO 3 . 3. RICHTERITE. Sodium-Magnesium-Manganese Amphibole. (K 2 ,Na 2 ,M2;, Ca,Mn) 4 (Si0 3 ) 4 . In elongated crystals, seldom terminated. G. = 3 '09. Color brown, yellow, rose-red. Transparent to^ranslucent. Z A c axis = + 17-20; /3 = 1-63; 7 - a = 0'024. From Pajsberg and Langban, Sweden. Characterized by the presence of manganese and alkalies in relatively large amount. Imerinite is a soda-amphibole, related to soda-richterite from the province Imerina, Madagascar. Breislakite occurs in wool-like forms at Vesuvius and Capo di Bove, Italy. Color dark brown to black, pleochroism strongly marked. Inferred to belong near richterite. II. Aluminous. 4. ALUMINOUS AMPHIBOLE. Hornblende. Contains alumina or ferric iron, and usually both, with ferrous iron (sometimes manganese), magnesium, calcium, and alkalies. The kinds here included range from the light-colored edemte containing but little iron, through the light to dark green pargasite, to the dark-colored or black hornblende, the color growing darker with increase in amount of iron. Extinction-angle variable, from to 37, see below. Pleochroism strong. Absorption usually Z < Y < X. EDENTTE. Aluminous Magnesium-Calcium Amphibole. Color white to gray and pale SILICATES 491 green, and also colorless; G. = 3'0-3'059. Resembles anthophyllite and tremolite. Named from the locality at Edenville, N. Y. To this variety belong various pale-colored amphiboles, having less than 5 p. c. of iron oxides. Koksharovite is a variety from the neighborhood of Lake Baikal, Siberia, named after the Russian mineralogist, von Koksharov. Soretite is an aluminous amphibole from the anorthite-diorite rocks of Koswinsky in the northern Ural Mts. COMMON HORNBLENDE, PARGASITE. Colors bright or dark green, and bluish green to grayish black and black. G. = 3'05-3'47. Pargasite is usually made to include green and bluish green kinds, occurring in stout lustrous crystals, or granular; and Common horn- blende the greenish black and black kinds, whether in stout crystals or long-bladed, colum- nar, fibrous, or massive granular. But no line can be drawn between them. The extinction- angle on 6 (010), or Z A c axis = + 15 to 25 chiefly. Absorption Z > Y > X. Pargasite occurs at Pargas, Finland, in bluish green and grayish black crystals. Z A c axis = + 18; = 1'64; y - a = 0'019; 2V = 59. Pleochroism: Z greenish blue; Y emerald-green; X greenish yellow. The dark brown to black hornblendes from basaltic and other igneous rocks vary some- what widely in optical characters. The angle Z A c axis = to + 10 chiefly; = 1725; y a = 0'072 (maximum). Pleochroism: Z brown, Y yellow, X yellow-green, but variable. Speziaite, from Traversella, Italy, is an iron amphibole with strong pleochroism; X = green, Y = yellow-brown, Z = azure-blue, Z A c axis = 23. The Kataforite of Norway (Brogger) has Z A c axis = 30 to 60; absorption Y > Z > X; pleochroism: Z yellow, Z violet, X yellow-brown; it approximates toward arfvedsonite (p. 494). Kupfferite, from a graphite mine in the Tunkinsk Mts., near Lake Baikal, Siberia, is a deep green amphibole (aluminous) formerly referred to anthophyllite. Syntagmatite is the black hornblende of Vesuvius. Bergamaskite is an iron-amphibole containing almost no magnesia. From Monte Altino, Province of Bergamo, Italy. Kaersutite is a titaniferpus amphibole from Kaersut, Umanaks fiord, North Greenland. Hastingsite is an amphibole low in silica and high in iron and soda, from the nephelite- syenite of Dungannon, Hastings Co., Ontario. Philipstadite from Philipstad, Sweden, is an iron-magnesium amphibole showing unusual pleochroism. Pyr. Essentially the same as for the corresponding varieties of pyroxene, see p. 478. Diff. Distinguished from pyroxene (and tourmaline) by its distinct prismatic cleav- age, yielding angles of 56 and 124. Fibrous and columnar forms are much more common than with pyroxene, lamellar and foliated forms rare (see also pp. 478, 486). Crystals often long, slender, or bladed. Differs from the fibrous zeolites in not gelatinizing with acids. Epidote has a peculiar green color, is more fusible, and shows a different cleavage. Micro. In rock sections amphibole generally shows distinct colors, green, sometimes olive or brown, and is strongly pleochroic. Also recognized by its high relief; generally rather high interference-colors; by the very perfect system of cleavage-cracks crossing at angles of 56 and 124 in sections _L c axis (Fig. 834). In sections || b (010) (recognized by yielding no axial figure in convergent light, by showing the highest interference-colors, and by having parallel cleavage-cracks, || c axis), the extinction-direction for common hornblendes makes a small angle (12-15) with the cleavage-cracks (i.e., with c axis); further, this direction is positive Z (different from com- mon pyroxene and aegirite, cf. Figs. 813 and 818). Artif . Experiments on the artificial production of the amphiboles have shown that in general they are unstable at high temperatures and that their formation in igneous rocks is due either to the rapid cooling of the magma, to the presence of water or to some unusual conditions of pressure, etc. In general when the amphiboles are fused they are transformed into the corresponding pyroxenes. Obs. Amphibole occurs only sparingly in volcanic rocks but is found in many crys- talline limestones, and granitic and schistose rocks. Tremolite, the magnesia-lime vari- ety, is especially common in limestones, particularly magnesian or dolomitic; actinolite (also nephrite), the magnesia-lime-iron variety, in the crystal line schists, in steatitic rocks and with serpentine; and dark green and black hornblende, occurs in both igneous and meta- 492 DESCRIPTIVE MINERALOGY morphic rocks. It is found in granites, syenites, diorites and some varieties of peridotite, in gneisses and the hornblende schists. Hornblende-rock, or amphibolite, consists of massive hornblende ot a dark greenish black or black color, and has a granular texture. Occasionally the green hornblende, or actino- lite, occurs in rock-masses, as at St. Francis, in Canada. Hornblende-schist has the same composition as amphibolite, but is schistose or slaty in structure. It often contains a little feldspar. In some varieties of it the hornblende is in part in minute needles. Granite and syenite often contain hornblende, and with diorite it is a common constituent. This is also true of the corresponding forms of gneiss. In these cases it is usually present in small, irregular masses, often fibrous in structure; also as rough bladed crystals. Prominent foreign localities of amphibole are the following: Tremolite (grammatite) in dolomite at Campolongo, Switzerland; also at Orawitza, Rezbanya, Hungary; Gulsjo, Wermland, Sweden. Actinolite in the crystalline schists of the Central and Eastern Alps, especially at Greiner in the Zillertal, Tyrol; at Zoblitz in Saxony; Arendal, Norway. Asbestus at Sterzing, Zillertal, and elsewhere in Tyrol; in Savoie, France; also in the island of Corsica. Pargasite at Pargas, Finland; Saualpe in Carinthia. Hornblende at Arendal, Kongsberg and Kargero, Norway; in Sweden and Finland; at Vesuvius; Aussig and Tep- litz, Bohemia; etc. Nephrite, which in the form of " jade" ornaments and utensils is widely distributed among the relics of early man (see jade, p. 482), is obtained at various points in Central Asia. The most important source is that in the Karakash valley in the Kuen Lun Mts., on the southern borders of Turkestan; also other localities in Central Asia. In New Zealand. Nephrite has been found in Europe as a rolled mass at Schwemmsal near Leipzig; in Swiss Lake habitations and similarly elsewhere. In the United States, in Me., black crystals- occur at Thomaston; pargasite at Phipps- burg. In Ver., actinolite in the steatite quarries of Windham and New Fane. In Mass., tremolite at Lee; black crystals at Chester; asbestus at Pelham; cummingtonite at Cum- mington. In Conn., in large flattened white crystals and in bladed and fibrous forms (tremolite) in dolomite, at Canaan. In N. Y., Warwick, Orange Co.; near Eden ville; near Amity; at the Stirling mines, Orange Co.; in short green crystals at Gouverneur, St. Lawrence Co.; with pyroxene at Russell; a black variety at Pierrepont; at Macomb; Pit- cairn; tremolite at Fine; in Rossie, 2 miles north of Oxbow; in large white crystals at Diana, Lewis Co.; asbestus near Greenwood Furnace. Hudsonite from Cornwall, N. Y., formerly classed as a pyroxene has been shown to be an amphibole. In N. J., tremolite or gray amphibole in good crystals at Bryam, and other varieties of the species at Franklin and Newton, radiated actinolite. In Pa., actinolite at Mineral Hill, in Delaware Co. ; at Union- vllle; at Kennett, Chester Co. In Md., actinolite and asbestus at the Bare Hills in serpen- tine; asbestus is mined at Pylesville, Harford Co. In Va., actinolite at Willis's Mt., in Buckingham Co.; asbestus at Barnet's Mills, Fauquier Co. Nephrite occurs in Alaska. In Canada, tremolite is abundant in the Laurentian limestones, at Calumet Falls, Litch- field, Pontiac Co., Quebec; also at Blythfield, Renfrew Co., and Dalhousie, Lanark Co. Black hornblende at various localities in Quebec and Ontario with pyroxene, apatite, titanite, etc., as in Renfrew Co. Asbestus and mountain cork at Buckingham, Ottawa Co., Quebec; a bed of actinolite at St. Francis, Beauce Co., Quebec; nephrite has been found in British Columbia and Northwest Territory. GLAUCOPHANE. Mpnoclinic; near amphibole in form. Crystals prismatic in habit, usually indistinct ; commonly massive, fibrous, or columnar to granular. Cleavage: m (110) perfect. Fracture conchoidal to uneven. Brittle. L = 6-6-5. G. = 3-103-3-113. Luster vitreous to pearly. Color azure-blue, lavender-blue, bluish black, grayish. Streak grayish blue. Translucent. Plepchroism strongly marked : Z sky-blue to ultramarine-blue, Y reddish or bluish violet, X yellowish green to colorless. Absorption Z > Y > X. Opti- cally + . Ax. pi. 1 1 6 (010) . Z A c axis = 4 to 6, rarely higher values. 2V = 45. a = 1-621. 18 = 1-638. T = 1-638. Comp. Essentially NaAl(SiO) s .(Fe,Mg)SiQ,. If Mg : Fe = 2 : 1, the formula requires: Silica 57'6, alumina 16'3, iron protoxide 77, magnesia 8-5, soda 9-9 = 100. Obs. Occurs as the hornblendic constituent of certain crystalline schists, called icophane-schuts, or glaucophanite; also more or less prominent in mica schists, am- SILICATES 493 phibolites, gneiss, eclogites, etc. It is often associated with mica, garnet, diallage and omphacite, epidote and zoisite, etc. First described from the island of Syra, one of the Cyclades; since shown to be rather widely distributed, as on the southern slope of the Alps (gastaldite) , Corsica, Japan, etc. Rhodusite is a fibrous variety from the Island Rhodus and Asskys river, Minassinsk, Siberia. Holmquistite is a lithium-bearing variety from the Island of Uto. In the United States, glaucophane schists have been described from the Coast Ranges of California, as at Sulphur Bank, Lake Co. Glaucophane is named from yXavKos, bluish green, and ^atj/eo-tfm, to appear. Crossite. An amphibole intermediate in composition between glaucophane and riebeckite, being optically more nearly related to the latter. Occurs in lath shaped crystals. Color blue. Strongly pleochroic. Found in the crystalline schists of the Coast Ranges of California. RIEBECKITE. Monoclinic. Axes a : b : c = 0;5475 : 1 : 0-2925; = 76 10'. In em- bedded prismatic crystals, longitudinally striated. Cleavage : prismatic (56) perfect. Luster vitreous. Color black. Pleochroism very strongly marked : Z green, Y ( = b axis) deep blue, X (nearly 1 1 c axis) dark blue. Optically . Extinction-angle small, X A c axis = 4-5 (=b?). Axial angle large. = 1-687. in Comp. Essentially 2NaFe(Si0 3 ) 2 .FeSiO 3 = Silica 50-5, iron sesqui- oxide 26-9, iron protoxide 12-1, soda 10*5 = 100. It corresponds closely to acmite (segirite) among the pyroxenes. Obs. Originally described from the granite and syenite of the island of Socotra in the Indian Ocean, 120 m. N. E. of Cape Guardafui. the eastern extremity of Africa; occurs in groups of prismatic crystals, often radiating and closely resembling tourmaline; also in granophyre blocks found at Ailsa Crag and at other points in Scotland and Ireland. A simi- lar amphihqle occurs at Mynydd Mawr, Carnarvonshire, Wales. Also another in granu- lite in Corsica. Found at Narsarsuk. Greenland. From pegmatite at Quincy, Mass. A so-called arfvedsonite from St. Peter's Dome, Pike's Peak region, Col., occurring with astro- phyllite and zircon, is shown by Lacroix to be near riebeckite. Extinction-angle on 6, X A c axis = 3 to 4. A soda amphibole, related to riebeckite, from Bababudan Hills, Mysore, India, has been named bababudanite. CROCIDOLITE. Blue Asbestus. Fibrous, asbestus-like ; fibers long but delicate, and easily separable. Also massive or earthy. Cleavage: prismatic, 56. H. = 4. G. = 3-20-3-30. Luster silky; dull. Color and streak lavender-blue or leek-green. Opaque. Fibers somewhat elastic. Pleochroism: Z green, Y violet, X blue. Optically + . Extinction-angle on b (010) inclined 18 to 20 with c axis. 2E = 95 approx. 7 a = 0'025. in Comp. NaFe(SiO 3 ) 2 .FeSiO 3 (nearly) = Silica 49-6, iron sesquioxide 22-0, iron protoxide 19'8, soda 8'6 = 100. Magnesium and calcium replace part of the ferrous iron, and hydrogen part of the sodium. Pyr., etc. B.B. fuses easily with intumescence to a black magnetic glass, coloring the flame yellow (soda). With the fluxes gives reactions for iron. Unacted upon by acids. Obs. Occurs in South Africa, in Griqualand-West, north of the Orange river, in a range of quartzose schists called the Asbestos Mountains. In a micaceous porphyry near Framont, in the Vosges Mts. At Golling in Salzburg, Austria. In the United States, at Beacon Pole Hill, near Cumberland, R. I. Emerald Mine, Buckingham, and Perkin's Mill, Templeton, Ottawa Co., Ontario, Canada. Abriachanite is an earthy amorphous form occurring in the Abriachan district, near Loch Ness, Scotland. Crocidolite is named from KOOK'IS, woof, in allusion to its fibrous structure. 494 DESCRIPTIVE MINERALOGY The South African mineral is largely altered by both oxidation of the iron and infiltra- tion of silica, resulting in a compact siliceous stone of delicate fibrous structure, chatoyant luster, and bright yellow to brown color, popularly called tiger-eye (also cat's-eye). Many varieties occur forming transitions from the original blue mineral to the final product; also varieties depending upon the extent to which the original mineral has penetrated the quartz. ARFVEDSONITE. Monoclinic. Axes a : b : c = 0-5569 : 1 : 0*2978; = 73 2'. Crystals long prisms, often tabular || b (010), but seldom distinctly termi- nated; angles near those of amphibole; also in prismatic aggregates. Twins: tw. pi. a (100). Cleavage: prismatic, perfect; b (010) less perfect. Fracture uneven. Brittle. H. = 6. G. = 3 -44-3 -45 Luster vitreous. Color pure black; in thin scales deep green. Streak deep bluish gray. Opaque except in thin splinters. Pleochroism strongly marked: Z deep greenish blue, Y lavender, X pale greenish yellow. Absorption Z > Y > X; sections || a (100) are deep greenish blue, || b (010) olive-green. Optically - . Axial angle, large, a = 1'687. = 1707. 7 = 1708. Extinction-angle on b (010), with c axis = 14. Comp. A slightly basic metasilicate of sodium, calcium, and ferrous iron chiefly. The supposed arfvedsonite from Greenland has been shown to be segirite; that from Pike's Peak, Col., has been referred to riebeckite. Pyr., etc. B.B. fuses at 2 with intumescence to a black magnetic globule; colors the flame" yellow (soda) ; with the fluxes gives reactions for iron and manganese. Not acted upon by acids. Micro. In thin sections shows brown- or gray-green or gray- violet colors; strongly pleochroic in blue and green tints; negative elongation? Obs. Arfvedsonite and amphiboles of similar character, containing much iron and soda, are constituents of certain igneous rocks which are rich in alkalies, as nephelite-syenite, certain porphyries, etc. Large and distinct crystals are found only in the pegmatite veins in such rocks, as at Kangerdluarsuk, Narsarsuk, Greenland, where the associated minerals are sodalite, eudialyte, feldspar, etc. Arfvedsonite occurs also in the nephelite-syenites and related rocks of the Christiania region in southern Norway; on the Kola peninsula in Russian Lapland; Dungannon township, Ontario; Trans Pecos district, Texas. The re- lated brownish pleochroic amphiboles (cf. barkevikite) occur in similar rocks at Montreal, Canada; Red Hill, N. H.; Salem, Mass.; Magnet Cove, Ark.; Black Hills, S. D.; Square Butte, Mon. St. Peter's Dome, Col., etc. Osannite from an amphibole-gneiss at Cevadaes, Portugal, and Tschernichewite from a magnetite bearing quartzite in the northern Ural Mts., are near arfvedsonite. BARKEVIKITE. An amphibole near arfvedsonite but more basic. In prismatic crys- tals. Cleavage: prismatic (55 44f')- G. = 3*428. Color deep velvet-black. Pleochro- ism marked, colors brownish. Extinction-angle with c axis on b (010) = 12|. Occurs at the wohlerite locality near Barkevik, on the Langesund fiord, and elsewhere in southern Norway. In large crystals at Lugar, Ayrshire, Scotland. JEnigmatite. Cossyrite. Essentially a titano-silicate of ferrous iron and sodium, but containing also aluminium and ferric iron. In prismatic triclinic crystals. Cleavage: prismatic, distinct (66). G. = 3 74-3 "80. Color black, ^nigmatite is from the sodalite- syemte of Tunugdliarfik and Kangerdluarsuk, Greenland. Cossyrite occurs in minute crystals embedded in the liparite lavas of the island Pantellaria (ancient name Cossyra) ; also widespread in the rocks of East Africa. Rhonite is like senigmatite but contains much less ferrous oxide and alkalies with increase in alumina, ferric oxide, etc. From basaltic rocks in the Rhon district and elsewhere in Germany and Bohemia. ' WEINBERGERITE. Perhaps NaAlSiO 4 .3FeSiO 3 . Orthorhombic. In spherical aggregates of radiating fibers. Black color. From a meteoric iron at Codai Canal, Palni Hills, Madras, India. SILICATES 495 BERYL. Hexagonal. Axis c = 0*4989. Crystals usually long prismatic, often striated vertically, rarely trans- versely; distinct terminations exceptional. Occasionally in large masses, coarse columnar or granular to compact. Cleavage: c (0001), imperfect and indistinct. Fracture conchoidal to uneven. Brittle. H. = 7*5-8. G. = 2-63-2-80; usually 2-69-2-70. Lus- ter vitreous, sometimes resinous. Colors emerald-green, pale green, passing into light blue, yellow and white; also pale rose-red. Streak white. Trans- parent to subtranslucent. Dichroism more or less distinct. Optically . Birefringence low. Often abnormally biaxial, co = 1-5820, e = 1-5765, aquamarine. 835 836 837 V m m. ~y *N m \ m >^-& rn x- t 56 31 '*' cs, 0001 A 1121 = pp', 1011 A 0111 = 44 56' 2854i f m cp, 0001 A 1011 = 29 co, 0001 A 1122 = 26 31'. Var. 1. Emerald. Color bright emerald-green, due to the presence of a little chro- mium; highly prized as a gem when clear and free from flaws. 2. Ordinary; Beryl. Generally in hexagonal prisms, often coarse and large; green the common color. The principal kinds are : (a) colorless; (6) bluish green, called aquamarine; (c) apple-green; (d) greenish yellow to iron-yellow and honey-yellow; sometimes a clear bright yellow as in the golden beryl (a yellow gem variety from Southwest Africa has been called heliodor) ; (e) pale yellowish green; (/) clear sapphire blue; (g) pale sky-blue; (h) pale violet or reddish; (i) rose colored called morganite or vorobyevite; (j) opaque brownish yellow, of waxy or greasy luster. The oriental emerald of jewelry is emerald-coi- lored sapphire. Comp. Be 3 Al 2 (SiO 3 )6 or 3BeO.Al 2 3 .6SiO 2 = Silica 67-0, alumina 19-0, glucina 14-0 = 100. Alkalies (NagO, Li 2 O, Cs 2 O) are sometimes present replacing the beryllium, from 0'25 to 5 p. c.; also chemically combined water, including which the formula becomes H 2 Be 6 Al 4 Si 12 O 37 . Pyr., etc. B.B. alone, unchanged or, if clear, becomes milky white and clouded; at a high temp'erature the edges are rounded, and ultimately a vesicular scoria is formed. Fusibility = 5 '5, but somewhat lower for beryls rich in alkalies. Glass with borax, clear and colorless for beryl, a fine green for emerald. Unacted upon by acids. Diff. Characterized by its green or greenish blue color, glassy luster and hexagonal form; rarely massive, then easily mistaken for quartz. Distinguished from apatite by its hardness, not being scratched by a knife, also harder than green tourmaline; from chryso- beryl by. its form; from euclase and topaz by its imperfect cleavage. Artif . Crystals of beryl have been produced artificially by fusing a mixture of silica, alumina and glucina with boric oxide as a flux. Obs. Beryl is a common accessory mineral in granite veins, especially in those of a pegmatitic character. Emeralds occur in clay slate, in isolated crystals or in nests, near Muso, etc., 75 m. N.N.E. of Bogota, Colombia. Emeralds of less beauty, but larger, occur in Siberia, on the river Tokovoya, N. of Ekaterinburg, embedded in mica schist. Emeralds of large size, though not of uniform color or free from flaws, have been obtained in Alex- ander Co., N. C. 496 DESCRIPTIVE MINERALOGY Transparent beryls are found in Siberia, India and Brazil. In Siberia they occur at Mursinka and Shaitanka, near Ekaterinburg; near Miask with topaz; in the mountains of Adun-Chalon with topaz, in E. Siberia. A clear aquamarine crystal weighing 110'5 kg. was found at Marambaya, Minas Geraes, Brazil. Beautiful crystals also occur at Elba; the tin mines of Ehrenfriedersdorf in Saxony, and Schlackenwald in Bohemia. Other local- ities are the Mourne Mts., Ireland; yellowish green at Rubislaw, near Aberdeen, Scotland (davidsonite); Limoges in France; Finbo and Broddbo in Sweden; Tamela in Finland; Pfitsch-Joch, Tyrol; Bodenmais and Rabenstein in Bavaria; in New South Wales. Pink, alkali-rich beryls are found in Madagascar. In the United States, beryls of gigantic dimensions have been found in N. H., at Acworth and Grafton, and in Mass., at Royalston. In Me., at Albany; Norway; Bethel; at Hebron, a ca3sium beryl (Cs 2 O, 3*60 p. c.), associated with pollucite; in Paris, with black tourmaline; at Topsham, pale green or yellowish; at Stowe and Stoneham. In Mass., at Barre; at Goshen (goshenite), and at Chesterfield. In Conn., at Haddam, and at the Mid- dletown and Portland feldspar quarries; at New Milford, of a clear golden yellow to dark amber color; Branchville. In Pa., at Leiperville and Chester; at Mineral Hill. In ya., at Amelia Court House, sometimes white. In N. C., in Alexander Co., near Stony Point, fine emeralds; in Mitchell Co.; Morganton, Burke Co., and elsewhere. In Ala., Cposa Co., of a light yellow color. In Col., near the summit of Mt. Antero, beautiful aquamarines. In S. D., in the Black Hills in large crystals. Rose-pink crystals, often showing prominent pyramid faces, from San Diego Co., Cal., also colorless and aquamarine. Use. The transparent mineral is used as a gem stone; see above under Varieties. Eudialyte. Essentially a metasilicate of Zr,Fe(Mn),Ca,Na, etc. In red to brown tabular or rhombohedral crystals; also massive. H. = 5-5'5. G. = 2'9-3'0. Optically -J-. o> = 1'606. 6 = 1'611. From Kangerdluarsuk, West Greenland, etc., with arfved- sonite and sodalite; at Lujaor on the Kola peninsula, Russian Lapland, in elseolite-syenite, there forming a main constituent of the rock-mass. Eucolite, from islands of the Langesund fiord in Norway, is similar (but optically ). Eudialyte and eucolite also occur at Magnet Cove, in Ark., of a rich crimson to peach-blossom red color, in feldspar, with elseolite and aegirite. Elpidite. Na 2 O.ZrO 2 .6SiO 2 .3H 2 O. Massive, fibrous. H. = 7. G. = 2'54. Color white to brick-red. Biaxial, +. Indices = 1 '560-1 '574. Southern Greenland. ASTROLITE. (Na,K) 2 Fe(Al,Fe) 2 (SiO3) 5 .H 2 O?. In globular forms with radiating structure. H. = 3'5. G. = 2'8. Color green. Fusible, 3'5. Found in a diabase tuff near Neumark, Germany. The following are rare species of complex composition, all from the Lange- sund fiord region of southern Norway. Catapleiite. H 4 (Na 2) Ca)ZrSi 3 pii. In thin tabular hexagonal prisms. H. = 6. G. = 2-8. Color light yellow to yellowish brown. Biaxial, +. Indices, 1 '591-1 '627. Natron- catapleiite, or soda-catapleiite, contains only sodium; color blue to gray and white; on heat- ing the blue color disappears. Cappelenite. A boro-silicate of yttrium and barium. In greenish brown hexagonal crystals. Melanocerite. A fluo-silicate of the cerium and yttrium metals and calcium chiefly (also B, Ta, etc.). In brown to black tabular rhombohedral crystals. Caryocerite. Near melanocerite, containing ThO 2 . Steenstrupine (from Greenland) is allied to the two last-named species. Rhombohe- H. =4. G. = 3'4. Color dark brown to nearly black. Optically . Tritomite. A fluo-silicate of thorium, the cerium and yttrium metals and calcium, with boron. In dark brown crystals of acute triangular pyramidal form. The following are also from the same region : Leucophanite. Na(BeF)Ca(SiO 3 ) 2 . In glassy greenish tabular crystals (orthorhombic- sphenoidal). H. =4. G. = 2'96. Optically -. Indices, 1'571-1'598. Meliphanite. A fluo-silicate of beryllium, calcium, and sodium near leucophanite. In low square pyramids (tetragonal). Color yellow. H. = 5-5'5. G. = 3*01. Optically - Indices, 1 '593-1 '612. SILICATES 497 Custerite. Ca 2 (OH,F)SiO 3 . Monoclinic. In fine granular masses. Cleavages par- allel to base and prism, all making nearly 90 with each other. Twinning plane c (001), showing in twin lamellae. H. =5. G. = 2 -91. Color greenish gray. Transparent. Optically +. Bxa nearly perpendicular toe (001). Indices, 1 '58-1 '60. Difficultly fusible. Decomposed by hydrochloric acid. Found in limestone contact zone at the Empire mine, Custer Co., Idaho. Didymolite. 2CaO.3Al 2 O 3 .9SiO 2 . Monoclinic. In small twinned crystals. H. = 4-5. G. = 271. Color dark gray. Opaque. Index 1 '5. Difficultly fusible. Insoluble. Found as contact mineral in limestone from Tatarka River, Yenisei District, Siberia. IOLITE. Cordierite. Dichroite. Orthorhombic. Axes a : b : c = 0-5871 : 1 : 0;5585. Twins: tw. pi. m (110), also d (130), both yielding pseudo-hexagonal forms. prismatic (mm Habit short 60 50') (Fig. 838). As embedded grains; also massive, compact. Cleavage: b (010) distinct; a(100) and c(001) indistinct. Crys- tals often show a lamellar structure || c (001), especially when slightly altered. Fracture subconchoidal. Brittle. H. = 7-7 '5. G. = 2-60- 2*66. Luster vitreous. Color va- rious shades of blue, light or dark, smoky blue. Transparent to trans- lucent. Pleochroism strongly marked except in thin sections. Axial colors variable. Thus: Bodenmais Z (= b axis) dark Berlin-blue. yellowish white. 839 Y ( = a axis) light Berlin-blue. X ( = c axis) Absorption Z > Y > X. Pleochroic halos common, often bright yellow; best seen in sections || c axis. Exhibits idiophanous figures. Optically . Ax. pi. || a (100). Bx. J_ c (001). Dispersion feeble, p < v. 2V = 70 23' (also 40 to 84). Indices variable, from 1'534 to 1-599. Comp. H 2 (Mg,Fe) 4 Al 8 Siio0 3 7or H 2 O.4(Mg,Fe)O.4Al 2 O 3 .10SiO 2 . If Mg : Fe = 7 : 2, the percentage composition is: Silica 49*4, alumina 33'6, iron protoxide 5*3, magnesia 10-2, water 1-5 = 100. Ferrous iron re- places part of the magnesium. Calcium is also present in small amount. Pyr., etc. B.B. loses transparency and fuses at 5-5'5. Only partially decomposed by acids. Decomposed on fusion with alkaline carbonates. Diff. Characterized by its vitreous luster, color and pleochroism; fusible on the edges unlike quartz; less hard than sapphire. Micro. Recognized in thin sections by lack of color; low refraction and low inter- ference-colors; it is very similar to quartz, but distinguished by its biaxial character; in volcanic rocks commonly shows distinct crystal outlines and a twinning of three individuals like aragonite. In the gneisses, etc., it is in formless grains, but the common occurrence of inclusions, especially of sillimanite needles, the pleochroic halos of a yellow color around small inclusions, particularly zircons, and the constant tendency to alteration to micaceous pinite seen along cleavages, help to distinguish it. Obs. Occurs in granite, gneiss (cordierite-gneiss) , hornblendic, chloritic and talcose schist, and allied rocks, with quartz, orthoclase or albite, tourmaline, hornblende, andalu- site, sillimanite, garnet, and sometimes beryl. Less commonly in or connected with igne- ous rocks, thus formed directly from the magma, as in andesite, etc.; also in ejected masses 498 DESCRIPTIVE MINERALOGY (in fragments of older rocks) ; further formed as a contact-mineral in connection with erup- tive dikes, as in slates adjoining granite. Occurs at Bodenmais, Bavaria, in granite, with pyrrhotite, etc.; Orijarvi, in Finland (steinheilite)-; Tunaberg, in Sweden; from Switzerland; in colorless crystals from Brazil; Ceylon affords a transparent variety, the saphir d'eau of jewelers; from Ibity, Madagascar; from Greenland. In the United States, at Haddam, Conn., associated with tourmaline in a granitic vein in gneiss. In large altered crystals from Litchfield, Conn. AtBrimfield, Mass.; at Richmond N. H. Named I elite from 'lov, violet, and X10os, stone; Dichroite (from dixpoos, two-colored), from its dichroism; Cordierite, after Cordier, the French geologist (1777-1861). Alteration. The alteration of iolite takes place so readily by ordinary exposure, that the mineral is most commonly found in an altered state, or enclosed in the altered iolite. This change may be a simple hydration; or a removal of part of the protoxide bases by car- bon dioxide; or the introduction of oxide of iron; or of alkalies, forming pinite and mica. The first step in the change consists in a division of the prisms of iolite into plates parallel to the base, and a pearly foliation of the surfaces of these plates; with a change of color to grayish green and greenish gray, and sometimes brownish gray. As the alteration proceeds, the foliation becomes more complete; afterward it may be lost. The mineral in this altered condition has many names : as hydrous iolite ( including bonsdorffite and auralite) from Abo, Finland; fahlunite from Falun, Sweden, also pyrargillite from Helsingfors; esmarkite and praseolite from near Brevik, Norway, also raumite from Raumo, Finland, and peplolite from Ramsberg-, Sweden; chlorophyllite from Unity, Me.; aspasiolite and polychroilite from Kragero. There are further alkaline kinds, as pinite, cataspilite, gigantolite, iberite, belong- ing to the Mica Group. Use. Iolite is sometimes used as a gem. Jurupaite. H 2 (Ca,Mg) 2 Si 2 O7. Monoclinic? Radiating fibrous. White. H = 4 G. = 275. n = 1-57. Crestmore, Cal. The following are rare lead, zinc, and barium silicates: Barysilite. Pb 3 Si 2 O 7 . Rhombohedral. In embedded masses with curved lamellar structure. Cleavage: basal. H. = 3. G. = 611-6-55. Color white; tarnishing on exposure. From the Harstig mine, Pajsberg, and Langban, Sweden. Molybdophyllite. (Pb,Mg)SiO 4 .H 2 O. Hexagonal. In irregular foliated masses with perfect basal cleavage. H. = 3-4. G. = 47. Colorless to pale green, co = 1-81 Difficultly fusible. From Langban, Sweden. Ganomalite. Pb 4 (PbOH) 2 Ca4(Si 2 O 7 )3. In prismatic crystals (tetragonal); also mas- sive granular. H =3 G. =574. Colorless to gray. Indices, 1'83-1'93. From Langban, Sweden; also Jakobsberg. Nasonite. Closely related to ganomalite. Pb 4 (PbCl) 2 Ca 4 (Si 2 O 7 )3. Probably tetragonal. Massive, granular cleavable. H. =4. G. = 5'4. White. Fusible. From Franklin^N. J. Margarosanite. Pb(Ca,Mn) 2 (SiO 3 ) 3 . Triclinic. Slender prismatic crystals and cleav- able granular. Three cleavages, one perfect. Colorless and transparent with pearly lus- = 2-5-3. G. = 3-99. Easily fusible. From Franklin, N. J., and Langban, Sweden. Hardystonite. CasZnSisOr. Tetragonal. In granular masses. Three cleavages. H. = 3-4. G. = 3'4. Color white. From Franklin, N. J. Hydotekite. Approximately (Pb,Ba,Ca)B 2 (SiO 3 )i 2 . Massive; coarsely crystalline. U. = 5 -5-5. G. = 3-81. Color white to pearly gray. From Langban, Sweden. . Barylite. Ba^SiAt In groups of colorless prismatic orthorhombic crystals. ' I ; n- ' r ?' Lust T e r gr eas y- Optically +. ft = 1-685. Occurs with hedyphane in crystalline limestone at Langban, Sweden. ii in Taramellite. Ba 4 FeFe 4 Si 10 O 31 . Orthorhombic? Fibrous. Color reddish brown. Candoglia Italy K ^ t ^^ "** tO ^^ F Und ln lime - Roeblingite. ,H 2 CaSiO 4 ).2(CaPbSO 4 ). In dense, white, compact, crystalline n. 6. u. = 6 433. From Franklin Furnace N. J. masses. SILICATES 499 III. Orthosilicates. R 2 SiO 4 Salts of Orthosilicic Acid, H 4 SiO 4 ; characterized by an oxygen ratio of 1 : 1 for silicon to bases. The following list includes the more prominent groups among the Ortho- silicates. A number of basic orthosilicates are here included, which yield water upon ignition; also others which are more or less basic than a normal orthosilicate, but which are of necessity introduced here in the classification, because of their relationship to other normal salts. The MICA GROUP is so closely related to many Hydrous Silicates that (with also Talc, Kaolinite, and some others) it is described later with them. Nephelite Group. Hexagonal. Scapolite Group. Tetragonal- Soda lite Group. Isometric. pyramidal. Helvite Group. Isometric-tetrahe- Zircon Group. Tetragonal. draL Danburite Group. Orthorhom- Garnet Group. Isometric. bic. Chrysolite Group. Orthorhombic. Datolite Group. Monoclinic. Phenacite Group. Tri-rhombohe- Epidote Group. Monoclinic. dral. Nephelite Group. Hexagonal i Typical formula RAlSiO 4 Nephelite K^NaeA^C^ c = 0-8389 Soda-nephelite (artif.) NaAlSi0 4 Eucryptite LiAlSiO 4 Kaliophilite KAlSi0 4 Cancrinite H 6 Na 6 Ca(NaC0 3 )2Al 8 (SiO 4 )9 2c = 0'8448 Microsommite (Na,K)ioCa4Ali2Sii 2 5 2SCl 4 2c = 0'8367 The species of the NEPHELITE GROUP are hexagonal in crystallization and i have in part the typical orthosilicate formula RAlSi0 4 . From this formula nephelite itself deviates somewhat, though an artificial soda-nephelite, NaAlSiO 4 , conforms to it. The species Cancrinite and Microsommite are related in form and also in composition, though in the latter respect some- what complex. They serve to connect this group with the sodalite group following. NEPHELITE. Nepheline. Elseolite. Hexagonal-hemimorphic (p. 101). Axis c = 0-83893. In thick six- or twelve-sided prisms with plane or modified summits. Also massive compact, and in embedded grains; structure sometimes thin columnar. Cleavage: m (110) distinct; c (001) imperfect. Fracture subconchoidal. Brittle. H. = 5'5-6. G. = 2-55-2-65. Luster vitreous to greasy; a little opalescent in some varieties. Colorless, white, or yellowish; also, when mas- sive, dark green, greenish or bluish gray, brownish red and brick-red. Trans- parent to opaque. Optically . Indices: o> = 1-542, e = 1-538. Var. 1. Nephelite. Glassy. Usually in small glassy crystals or grains, transparent with vitreous luster, first found on Mte. Somma, Vesuvius. Characteristic particularly of 500 DESCRIPTIVE MINERALOGY younger eruptive rocks and lavas. 2. Elceolite. In large coarse crystals, or more com- monly massive, with a greasy luster, and reddish, greenish, brownish or gray in color. Usually clouded by minute inclusions. Characteristic of granular crystalline rocks, syenite, etc. Comp. NaAlSiO4. This is the composition of the artificial mineral. Natural nephelite always contains silica in varying excess and also small amounts of potash. The composition usually approximates to NaeK^AlgSigCV Synthetic experiments, yielding crystals like nephelite with the composition NaAlSiO 4 , lead to the conclusion that a natural soda-nephelite would be an orthosilicate with this formula, while the higher silica in the potash varieties may be explained by the presence, in molecular combination, of KAlSiO 4 and NaAlSi 3 O 8 (albite in hexagonal modification). The variation in composition may be more simply explained by considering normal nephe- lite, NaAlSiO 4 , to take up in solid solution silica or other silicate molecules. The other species of the group are normal orthosilicates, viz., eucryptite LiAlSiO 4 . and kaliophilite, Pyr. ? etc. B.B. fuses quietly at 3 '5 to a colorless glass, coloring the flame yellow. Gelatinizes with acids. Diff. Distinguished by its gelatinizing with acids from scapolite and feldspar, as also from apatite, from which it differs too in its greater hardness. Massive varieties have a characteristic greasy luster. Micro. Recognized in thin sections by its low refraction; very low interference- colors, which scarcely rise to gray; parallel extinction when in crystals; faint negative uniaxial cross yielded by basal sections in converging light. The negative character is best told by aid of the gypsum plate (see p. 266). Micro-chemical tests serve to distinguish non- characteristic particles from similar ones of alkali feldspar; the section is treated with dilute acid, and the resultant gelatinous silica, which coats the nephelite particles, stained with cosine or other dye. Artif. Nephelite is easily prepared artificially by fusing its constituents together in the proper proportions. Obs. Nephelite is rather widely distributed (as shown by the microscopic study of rocks) in igneous rocks as the product of crystallization of a magma rich in soda and at the same time low in silica (which last prevents the soda from being used up in the formation of albite). It is thus an essential component of the nephelite-syenites and phonolites where it is associated with alkali feldspars chiefly. It is also a constituent of more basic augitic rocks such as nephelinite, nephelite-basalts, nephelite-tephrites, theralite, etc., most of which are volcanic in origin. The variety elceolite is associated with the granular plutonic rocks, while the name nephelite was originally used for the fresh glassy crystals of the modern lavas; the terms have in this sense the same relative significance as orthoclase and sanidine. Modern usage, however, tends to drop the name elceolite. The original nephelite occurs in crystals in the older lavas of Mte. Somma, Vesuvius, with mica, vesuvianite, etc.; at Capo di Bove, near Rome; in the basalt of Katzenbuckel, near Heidelberg, Germany; Aussig in Bohemia; Lobau in Saxony. Occurs also in massive forms foyaite); Ditro, Hungary _ (in the rock ditroite) ; Pousac, France; Brazil; South Africa. Elaeolite occurs massive and crystallized at Litchfield, Me., with cancrinite; Salem, Mass.; Red Hill, N. H.; in the Ozark Bits., near Magnet Cove, Ark.; elseolite-syenite is also found near Beemersville, northern N. J.; near Montreal, Canada; at Dungannon township, Ontario, in enormous crystals. Nephelite rocks also occur at various points, as the Transpecos district, Texas; Pilot Butte, Texas; also in western North America, as in Col. at Cripple Creek; in Mon., in the Crazy Mts., the Highwood, Bearpaw and Judith |Cts.; Black Hills in S. D.; Ice River, British Columbia. Named nephelite from i/e^eXrj, a cloud, in allusion to its becoming cloudy when immersed in strong acid; elceolite is from eXaiov, oil, in allusion to its greasy luster. Gieseckite is a pseudomorph after nephelite. It occurs in Greenland in six-sided green- ish gray prisms of greasy luster; also at Diana in Lewis Co., N. Y. Dysyntribite from Diana is similar to gieseckite, as is also liebenerite, from the valley of Fleims, in Tyrol, Austria. See further FINITE under the MICA GROUP. Eucryptite. LiAlSi0 4 . In symmetrically arranged crystals (hexagonal), embedded, in albite and derived from the alteration of spodumene at Branchville, Conn, (see Fig. 488, p. 181). G. = 2-667. Colorless or white. SILICATES 501 Kaliophilite. KAlSiO 4 . Phacellite. Phacelite. Facellite. In bundles of slender acicular crystals (hexagonal), also in fine threads, cobweb-like. H. =6. G. = 2*493- 2'602. Colorless. Occurs in ejected masses at Mte. Somma, Vesuvius. CANCRINITE. _Hexagonal. Axis c = 04224; and mp 1010 A 1011 = 64, pp f 1011 A 0111 = 25 58'. Rarely in prismatic crystals with a low terminal pyramid. Usually massive. Cleavage: prismatic, m (1010) perfect; a (1120) less so. H. = 5-6. G. = 2 -42-2 -5. Color white, gray, yellow, green, blue, reddish. Streak uncolored. Luster subvitreous, of a little pearly or greasy. Transparent to translucent. Optically -. co = 1-524. e = 1-496. Comp. H 6 Na 6 Ca(NaC0 3 )2Al8(SiO4)9 or 3H 2 O.4Na 2 O.CaO.4Al 2 O 3 . 9Si0 2 .2C0 2 = Silica 387, carbon dioxide 6-3, alumina 29-3, lime 4-0, soda 17-8, water 3-9 = 100. Pyr., etc. In the closed tube gives water. B.B. loses color, and fuses (F. = 2) with intumescence to a white blebby glass, the very easy fusibility distinguishing it readily from nephelite. Effervesces with hydrochloric acid, and forms a jelly on heating, but not before. Micro. Recognized in thin sections by its low refraction; quite high interference- colors and negative uniaxial character. Its common association with nephelite, socialite, etc., are valuable characteristics. Evolution of CO 2 with acid distinguishes it from all other minerals except the carbonates, which show much higher interference-colors. Artif . Cancrinite has been prepared artificially by heating under pressure a mixture of sodium silicate, alumina and sodium carbonate; also by the treatment of nephelite and labradorite by sodium carbonate at high temperatures. Obs. Cancrinite occurs only in igneous rocks of the nephelite-syenite and related rock groups. It is in part believed to be original, i.e., formed directly from the molten mag- ma; in part held to be secondary and formed at the expense of nephelite by infiltrating waters holding calcium carbonate in solution. Prominent localities are Miask in the Ilmen Mte., Russia, in coarse-grained nephelite-syenite; similarly at Barkevik and other localities on the Langesund fiord in southern Norway; in the parish of Knolajarvi in northern Finland (where, associated with orthoclase, segirite and nephelite, it composes a mass of cancrinite- syenite); at Ditro, Transylvania, etc.; in nephelite-syenite of Sarna and Alno in Sweden, and in Brazil; also in small amount as an occasional accessory component of many phono- litic rocks at various localities. In the United States at Litchfield and West Gardiner, Me., with ela3olite and blue soda- lite. Named after Count Cancrin, Russian Minister of Finance. SULPHATIC CANCRINITE with nearly one-half the CO 2 replaced by SO 3 is found in an altered rock on Beaver Creek, Gunnison Co., Col. Has lower refractive indices and' bire- fringence than cancrinite. Microsommite. Near cancrinite; perhaps (Na,Et)i Ca4Ali 2 Sii2O52SCl 4 ). In minute colorless prismatic crystals (hexagonal. See Fig. 30, p. 19). From Vesuvius (Monte Somma). H. =6. G. = 2'42-2'53. co = 1-521. e = 1'529. Davyne. Near microsommite. From Mte. Somma; Laacher See, Germany. o> = 1-518. e = 1'521. Sodalite Group. Isometric Sodalite Na 4 (AlCl)Al 2 (SiO 4 )3 Haiiynite (Na 2 ,Ca) 2 (NaSO4.Al)Al 2 (Si04)3 Noselite Na 4 (NaSO4.Al)Al 2 (Si0 4 )3 Lazurite Na 4 (NaS 3 .Al)Al 2 (SiO 4 ) 3 The species of the Sodalite Group are isometric in crystallization and per- haps tetrahedral like the following group. In composition they are peculiar (like cancrinite of the preceding group) in containing radicals with Cl, S0 4 and S, which are elements usually absent in the silicates. These are shown in the 502 DESCRIPTIVE MINERALOGY formulas written above in the form suggested by Brogger, who shows that this group and the one following may be included with the garnets in a broad group characterized by isometric crystallization and a close resemblance in composition. See further under the GARNET GROUP proper, p. 505. The formulas are also often written as if the compound consisted of a sili- cate and chloride (sulphate, sulphide) thus for sodalite, 3NaAlSiO 4 + NaCl, etc. SODALITE. Isometric, perhaps tetrahedral. Common form the dodecahedron. Twins- tw. pi. o (111), forming hexagonal prisms by elongation in the direction of an octahedral axis (Fig. 406, p. 165). Also massive, in embedded grains; in concentric nodules resembling chalcedony, formed from elaeolite. Cleavage: dodecahedral, more or less distinct. Fracture conchoidal to uneven. Brittle. H. = 5-5-6. G. = 2'14-2'30. Luster vitreous, sometimes inclining to greasy. Color gray, greenish, yellowish, white; sometimes blue, lavender-blue, light red. Transparent to translucent. Streak uncolored. n = 1-4827. Comp. Na 4 (AlCl)Al 2 (SiO 4 )3 = Silica 37'2, alumina 31*6, soda 25'6, chlorine 7'3 = 1017, deduct (0 = 2C1) 17 = 100. Potassium replaces a small part of the sodium. The formula may also be written 3NaAlSiO 4 + NaCl. Pyr.. etc. In the closed tube the blue varieties become white and opaque. B.B. fuses with intumescence, at 3 '5-4, to a colorless glass. Soluble in hydrochloric acid and yields gelatinous silica upon evaporation. Diff. Distinguished from much analcite, leucite and haiiynite by chemical tests alone; dissolving the mineral in dilute nitric acid and testing for chlorine is the simplest and best. Micro. Recognized in thin sections by its very low refraction, isotropic character and lack of good cleavage; also, in most cases, by its lack of color. In uncovered rock sections the minerals of this group may be distinguished from each other by covering them with a little nitric acid which is allowed to evaporate slowly. With sodalite crystals of sodium chloride will form; with haiiynite crystals of gypsum; with noselite crystals of both com- pounds after the addition of calcium chloride; lazurite will evolve hydrogen sulphide which will blacken silver. Aftif. .Sodalite can be obtained by fusing nephelite with sodium chloride; also by the action of sodium carbonate and caustic soda upon muscovite at 500. It has been pro- duced also in various artificial magmas at temperatures below 700. Obs. Sodalite occurs only in igneous rocks of the nephelite-syenite and related rock groups, as a product of the crystallization of a magma rich in soda; also as a product asso- ciated with enclosed masses and bombs ejected with such magmas in the form of lava, as at Vesuvius. Often associated with nephelite (or elseolite), cancrinite and eudialyte. With sanidine it forms a sodalite-trachyte at Scarrupata in Ischia, Italy, in crystals. In Sicily, Val di Noto, with nephelite and analcite. At Vesuvius, in bombs on Monte Somma in white, translucent, dodecahedral crystals; massive and of a gray color at the Kaiserstuhl and near Lake Laach, Germany. A variety from Monte Somma containing 2 per cent of molybde- num trioxide has -been called molybdosodalite. At Ditro, Transylvania, in an elaeolite- syenite. In the foyaite of southern Portugal. At Miask, in the Ilmen Mts., Russia; in the augite-syenite of the Langesund-fiord region in Norway. Further in West Greenland in sodalite-syenite; the peninsula of Kola, Russia. A blue massive variety occurs at Litchfield and West Gardiner, Me. Occurs in the theralite of the Crazy Mts., Mon., also at Square Butte, Highwood Mts., and in the Bear- paw Mts., in tinguaite. Occurs also in the ela3olite-syenite of Brome, Brome Co., and of Montreal and Beloeil, province of Quebec; at Dungannon, Ontario, in large blue masses and in small pale pink crystals. At Kicking Horse Pass, Bristish Columbia. Hackmanite. . A sodalite containing about 6 per cent of the molecule Na 4 [Al(NaS)]Al 2 (biO 4 ) 3 trom a rock called tawite from the Tawa valley on the Kola peninsula, Lapland. SILICATES 503 HAUYNITE. Haiiyne. Isometric. Sometimes in dodecahedrons, octahedrons, etc. Twins: tw. pi. o (111); contact-twins, also poly synthetic; penetration- twins (Fig. 405, p. 165). Commonly in rounded grains, o ten looking like crystals with fused surfaces. Cleavage: dodecahedral, rather distinct. Fracture flat .conchoidal to uneven. Brittle. H. = 5*5-6. G. = 2-4-2 -5. Luster vitreous, to some- what greasy. Color bright blue, sky blue, greenish blue ; asparagus-green, red, yellow. Streak slightly bluish to colorless. Subtransparent to translu- cent; often enclosing symmetrically arranged inclusions (Fig. 840): n = T4961. Comp. Na2Ca(NaSO4.Al)Al 2 (SiO4)3. This is analogous to the garnet formula (Brogger) where the place of the R 3 is taken by Na 2 , Ca and the group Na-0-SO 2 -O-Al. The percentage composition is: Silica 32*0, sulphur trioxide 14-2, alumina 27 -2, lime 10*0, soda 16*6 = 100. The ratio of Na* : Ca also varies from 3:2; potassium may be present in small amount. The formula may also be wr tten 2(Na2,Ca)Al 2 (Si0 4 ) 2 + (Na ,Ca)SO 4 . Pyr., etc. In the closed tube retains its color. B.B. in the forceps fuses at 4*5 to a white glass. Soluble in hydrochloric acid and yields gelatinous silica upon evaporation. The solution gives a -test for the sulphate radical with barium chloride. Micro. Similar to sodalite, which see. Artif . Has been produced artificially in the same ways as with sodalite with the use of a sulphate instead of a chloride. Obs. Common in certain igneous rocks, thus in hauynophyre, in phonolite, tephrite ; very commonly associated with nephelite and leucite. Occurs in the Vesuvian lavas, on Mte. Somma; at Melfi, on Mt. Vultur, Naples; in the lavas of the Campagna, Rome, also Section of crystals of haiiynite (after Mohl) in a basalt tuff near Albano, Italy; at Niedermendig, in the Eifel, Germany; the phonolites of Hohentwiel, Baden, Germany. Noselite or Nosean. Near haiiynite, but contains little or no lime. Color grayish, bluish, brownish; sometimes nearly opaque from the presence of inclusions (cf. Fig. 840). n = 1-495. Not uncommon in phonolite. In Germany at Andernach, the Laacher See, and elsewhere. LAZURITE. LAPIS-LAZULI. Lasurite. Isometric. In cubes and dodecahedrons. Common y massive, compact. Cleavage: dodecahedral, imperfect. Fracture uneven. H. = 5-5*5. G. = 2-38-2-45. Luster vitreous. Color rich Berlin-blue or azure-blue, violet-blue, greenish blue. Translucent, n = 1*500. Comp. Essentia ly Na 4 (NaS .Al) Al 2 (SiO 4 ) 3 , but containing also in mo- lecular combination haiiynite and sodalite. The percentage composition of this ultramarine compound is as follows: Si ica 31*7, alumina 26*9, soda 27*3, sulphur 16*9 = 102*9, or deduct (O = S) 2*9 = 100. The heterogeneous character of what had long passed as a simple mineral under the name Lapis-lazuli was shown by Fischer (1869), Zirkel (1873), and more fully by Vogelsang (1873). 504 DESCRIPTIVE MINERALOGY amount ^ scapolite V plagioclase, orthoclase (microperthite?), apatite, titanite, zircon, and n undetermined' mineral optically + and probably uniaxial. Regarded by Brogger as a result of contact metamorphism in limestone. Micro. _ Similar to sodalite, which see. Pvr etc Heated in the closed tube gives off some moisture; the variety from Chile clows with a beetle-green light, but the color of the mineral remains blue on cooling Fuses easily (3) with intumescence to a white glass. Soluble in hydrochloric acid and yields gelati- nous silica upon evaporation and evolves hydrogen sulphide. Obs Occurs in Badakshan, India, in the valley of the Kokcha, a branch of the Oxus, a few miles above Firgamu. Also at the south end of Lake Baikal Siberia. Further, in Chile in the Andes of Ovalle. In ejected masses at Monte Somma, Vesuvius, rare. From Siberia and Persia. Use The richly colored varieties of lapis lazuli are highly esteemed for costly vases and ornamental furniture; also employed in the manufacture of mosaics; and when pow- dered constitutes the rich and durable paint called ultramarine. This has been replaced, however, by artificial ultramarine, now an important commercial product. >, Helvite Group. Isometric-tetrahedral Helvite (Mn,Fe) 2 (Mn 2 S)Be 3 (Si04) 3 Danalite (Fe,Zn,Mn) 2 ( (Zn,Fe) 2 S)Be 3 (Si0 4 )3 Eulytite Bi 4 (SiO 4 ) 3 Zunyite (Al(OH,F,Cl) 2 ) 6 Al 2 (SiO 4 ) 3 The HELVITE GROUP includes several rare species, isometric-tetrahedral in crystallization and in composition related to the species of the SODALITE GROUP and also to those of the GARNET GROUP which follows: HELVITE. Isometric-tetrahedral. Commonly in tetrahedral crystals ; also in spheri- cal masses. Cleavage: octahedral in traces. Fracture uneven to conchoidal. Brittle. H. = 6-6*5. G. = 3'16-3'36. Luster vitreous, inclining to resinous. Color honey-yellow, inclining to yellowish brown, and siskin-green, reddish brown. Streak uncolored. Subtransparent. n = 1 739. Pyroelectric. Comp. (Be,Mn,Fe) 7 Si 3 Oi 2 S. This may be written (Mn,Fe) 2 (Mn 2 S)Be 3 (SiO 4 ) 3 analogous to the Garnet Group, the bivalent group -Mn-S-Mn taking the place of a bivalent element, R, and 3Be corresponding to 2A1, cf. p. 505. Composition also written 3(Be,Mn,Fe) 2 SiO 4 .(Mn,Fe)S. Pyr., etc. Fuses at 3 in R.F. with intumescence to a yellowish brown opaque bead, becoming darker in R.F. With the fluxes gives the manganese reaction. Soluble in hydro- chloric acid, giving hydrogen sulphide and yielding gelatinous silica upon evap9ration. Obs. Occurs at Schwarzenberg and Breitenbrunn, in Saxony; at Kapnik, Hungary; also in the pegmatite veins of the augite-syenite of the Langesund fiord, Norway; in the Ilmen Mts., Russia, near Miask, in pegmatite. In the United States, with spessartite, at the mica mines near Amelia Court-House, Amelia Co., Va.; etc. Named by Werner, in allu- sion to its yellow color, from -Xios, the sun. Danalite. (Be,Fe,Zn,Mn) 7 Si 3 Oi2S. In octahedrons; usually massive. H. = 5'5-6. G. = 3-427. Color flesh-red to gray. Occurs in small grains in the Rockport granite, Cape Ann, Mass.; at the iron mine at Bartlett, N. H.; El Paso Co., Col. In England at Eulytite. Bi 4 Si 3 Oi 2 . Usually in minute tetrahedral crystals; also in spherical forms. H. = 4'5. G. = 6'106. Color dark hair-brown to grayish, straw-yellow, or colorless. n ^ 2?' Found witn native bismuth near Schneeberg, Saxony; also at Johanngeorgen- stadt, Germany, m crystals on quartz. SILICATES 505 Zunyite. A highly basic orthosilicate of aluminium, (Al(OH,F,Cl) 2 )6Al 2 Si 3 Oi2. In minute transparent tetrahedrons. H. =7. G. = 2*875. From the Zuni mine, near Sil- verton, San Juan Co., and on Red Mountain, Ouray Co., Col. 4. Garnet Group. Isometric or 3RO.R 2 O 3 .3Si0 2 . II II H III III R = Ca,Mg,Fe,Mn. Ill III Al,Fe,Cr,Ti. Garnet A. GROSSULARITE Ca 3 Al 2 (SiO 4 ) 3 B. PYROPE Mg 3 Al 2 (Si0 4 ) 3 C. ALMANDITE Fe 3 Al 2 (SiO 4 ) 3 D. SPESSARTITE Mn 3 Al 2 (SiO 4 ) 3 Schorlomite Ca 3 (Fe,Ti) 2 ( (Si,Ti)O 4 ) E. ANDRADITE Ca 3 Fe 2 (SiO 4 ) ; Also (Ca,Mg) 3 Fe 2 (SiO 4 ) 3 , Ca 3 Fe 2 ((Si,Ti)0 4 ) 3 F. UVAROVITE Ca 3 Cr 2 (Si0 4 ) 3 , The GARNET GROUP includes a series of important sub-species included under the same specific name. They all crystallize in the normal class of the isometric system and' are alike in habit, the dodecahedron and trapezo- hedron being the common forms. They have also the same general formula, and while the elements present differ widely, there are many intermediate varieties. Some of the garnets include titanium, replacing silicon, and thus they are connected with the rare species schorlomite, which probably also has the same general formula. Closely related to the GARNET GROUP proper are the species of the Sodalite and llelvite Groups (pp. 501, 504). All are characterized by isometric crystallization, and all are orthosilicates, with similar chemical structure. Thus the formula of the Garnet Group is Hill R 3 R 2 (SiO 4 )3; to this Sodalite conforms if written Na 4 (AlCl)Al 2 (SiO 4 ) 3 , where Na 4 and the bivalent radical A1C1 are equivalent to R 3 ; similarly for Noselite (Haliynite) if the presence of the bivalent group NaSO 4 -Al is assumed. In the Helvite Group, which is characterized by the tetrahedral character of the species (perhaps true also of the Sodalites), the chemical relation is less close but probably exists, as exhibited by writing the formula of Helvite (Mn,Fe)(Mn 2 S)Be 3 (SiO4) 3 , where the bivalent group -S-Mn-S- enters, and 3Be may be regarded as taking the place of 2A1. GARNET. Isometric. The dodecahedron and trapezohedron, n (211), the common 841 842 843 simple forms; also these in combination, or with the hexoctahedron s (321). Cubic and octahedral faces rare. Often in irregular embedded grains. Also 506 DESCRIPTIVE MINERALOGY massive; granular, coarse or fine, and sometimes friable; lamellar, lamellae thick and bent. Sometimes compact, cryptocrystalline like nephrite. Parting: d (110) sometimes rather distinct. Fracture subconchoidal to 844 845 846 uneven. Brittle, sometimes friable when granular massive; very tough when compact cryptocrystalline. H. = 6'5-7'5. G. = 3-15-4-3, varying with the composition. Luster vitreous to resinous. Color red, brown, yellow, white, apple-green, black; some red and green, colors often bright. Streak white. Transparent to subtranslucent. Often exhibits anomalous double refraction, especially grossularite (also topazolite, etc.), see Art. 429. Refractive index rather high, and varying directly with the composition. The different pure molecules have approximately the following indices. Pyrope 1705, Grossularite 1-735, Spessartite I'SOO, Almandite 1'830, Uvarovite 1'870, Andradite 1'895. II III Comp. An orthosilicate having the general formula R 3 R 2 (SiO 4 ) 3 , or 3RO.R20 3 .3Si0 2 . The bivalent element may be calcium, magnesium, ferrous iron or manganese; the trivalent element, aluminium, ferric iron or chro- mium, rarely titanium; further, silicon is also sometimes replaced by titanium. The different garnet molecules are isomorphous with each other although there are apparently definite limits to their miscibility. The greater majority will be found to have two or three component molecules ; in the case, however, where three are present one is commonly in subordinate amount. The index of refraction and specific gravity vary directly with the variation in composition. Var. There are three prominent groups, and various subdivisions under each, many of these blending into each other. I. Aluminium Garnet, including A. GROSSULARITE Calcium- Aluminium Garnet Ca 3 Al 2 (Si0 4 ) 3 B. PYROPE Magnesium- Aluminium Garnet Mg 3 Al 2 (SiO 4 ) 3 C. ALMANDITE Iron- Aluminium Garnet Fe 3 Al 2 (SiO 4 ) 3 D. SPESSARTITE Manganese- Aluminium Garnet Mn 3 Al 2 (SiO 4 ) 3 II. Iron Garnet, including E. ANDRADITE Calcium-Iron Garnet Ca 3 Fe 2 (SiO 4 )3 (1) Ordinary. (2) Magnesian. (3) Titaniferous. (4) Yttriferous, III. Chromium Garnet. F. UVAROVITE Calcium-Chromium Garnet Ca 3 Cr 2 (SiO 4 ) 3 The name Garnet is from the Latin granatus, meaning like a grain, and directly from pomegranate, the seeds of which are small, numerous, and red, in allusion to the aspect oi the crystals. SILICATES 507 A. GROSSULARITE. Essonite or Hessonite. Cinnamon-stone. Calcium- aluminium Garnet. Formula 3CaO.Al 2 O 3 .3Si0 2 = Silica 40 -0, alumina 227, lime 37 '3 = 100. Often containing ferrous iron replacing the calcium, and ferric iron replacing aluminium, and hence graduating toward groups C and E. G. = 3-53. Color (a) colorless to white; (6) pale green; (c) amber- and honey-yellow; (d) wine-yellow, brownish yellow, cinnamon-brown; (e) rose-red; rarely (/) emerald-green from the presence of chromium. Often shows optical anomalies (Art. 429). The original grossularite (wiluite in part) included the pale green from Siberia, and was so named from the botanical name for the gooseberry; G. = 3-42-372. Cinnamon-stone, or essonite (more properly hessonite), included a cinnamon-colored variety from Ceylon, there called hyacinth; but under this name the yellow and yellowish red kinds are usually included; named from fjvauv, inferior, because of less hardness than the true hyacinth which it resembles. Succinite is an amber-colored kind from the Ala valley, Piedmont, Italy. Romanzovite is brown. Pale green, yellowish, and yellow-brown garnets are not invariably grossularite; some (including topazolite, demantoid, etc.) belong to the group of Calcium-Iron Garnet, or Andradite. B. PYROPE. Precious garnet in part. Magnesium-aluminium Garnet. Formula 3MgO.Al 2 3 .3Si0 2 = Silica 44-8, alumina 25*4, magnesia 29*8 = 100. Magnesia predominates, but calcium and iron are also present; the original pyrope also contained chromium. G. = 3'51. Color deep red to nearly black. Often perfectly transparent and then prized as a gem. The name pyrope is from TTUPCOTTOS, fire-like. Rhodolite, of delicate shades of pale rose-red and purple, brilliant by reflected light, corresponds in composition to two parts of pyrope and one of almandite; from Macon Co., N. C. C. ALMANDITE. Almandine. Precious garnet in part. Common garnet in part. Iron-aluminium Garnet. Formula 3FeO.Al 2 3 .3SiO 2 = Silica 36 -2, alumina 20 '5, iron protoxide 43 '3 = 100. Ferric iron replaces the aluminium to a greater or less extent. Magnesium also replaces the ferrous iron, and thus it graduates toward pyrope, cf. rhodolite above. G. = 4-25. Color fine deep red, transparent, in precious garnet; brownish red, translucent or sub- translucent, in common garnet; black. Part of common garnet belongs to Andradite. The Alabandic carbuncles of Pliny were so called because cut and polished at Alabanda. Hence the name almandine or almandite, now in use. D. SPESSARTITE. Spessartine. Manganese-aluminium Garnet. Formula 3MnO.Al 2 O 3 .3SiO 2 = Silica 36'4, alumina 20'6, manganese protoxide 43'0 = 100. Ferrous iron replaces the manganese to a greater or less extent, and ferric iron also the aluminium. G. = 4-18. Color dark hyacinth-red, some- times with a tinge of violet, to brownish red. E. ANDRADITE. Common Garnet, Black Garnet, etc. Calcium-iron Garnet. Formula 3CaO.Fe 2 O 3 .3Si0 2 = Silica 35'5, iron sesquioxide 31 -5, lime 33*0 = 100. Aluminium replaces the ferric iron; ferrous iron, manganese and sometimes magnesium replace the calcium. G. = 375. Colors various: wine-, topaz- and greenish yellow, apple-green to emerald-green; brownish red, brownish yellow; grayish green, dark green; brown; grayish black, black. Named Andradite after the Portuguese mineralogist, d'Andrada, who in 1800 described and named one of the included subvarieties, Allochroite. Chemically there are the follow- ing varieties: 508 DESCRIPTIVE MINERALOGY 1 Simple Calcium-iron Garnet, in which the protoxides are wholly or almost wholly lime' Includes- (a) Topazolite, having the color and transparency of topaz, and also sometimes green; crystals often showing a vicinal hexoctahedron. Demantoid ! a grass-green o emerald-green variety with brilliant diamond-like luster, used as a gem. (6) Colophonite, a coarse granular kind, brownish yellow to dark reddish brown in color resinous in luster, and usually with iridescent hues; named after the resin colophony, (c) Melamte (from ueXas black] black, either dull or lustrous; but all black garnet is not here included. Pyreneite is grayish black melanite. (d) Dark green garnet, not distinguishable from some allochroite except by chemical trials. 2 Manganesian Calcium-iron Garnet, (a) Rothoffite. The original allochroite was a manganesian iron-garnet of brown or reddish brown color, and of fine-grained massive structure. Rothoffite, from Langban, Sweden, is similar, yellowish brown to liver-brown. Other common kinds of manganesian iron-garnet are light and dark, dusky green and black, and often in crystals. Polyadelphite is a massive brownish yellow kind, from Franklin Fur- nace N. J. Bredbergite, from Sala, Sweden, contains a large amount of magnesia. (6) Ap- lome (properly haplome) has its dodecahedral faces striated parallel to the shorter diagonal, whence Haiiy inferred that the fundamental form was the cube; and as this form is simpler than the dodecahedron, he gave it a name derived from airXoos, simple. Color of the origi- nal aplome (of unknown locality) dark brown; also found yellowish green and brownish green at Schwarzenberg in Saxony, and on the Lena in Siberia. 3. Titaniferous. Contains titanium and probably both TiO 2 and Ti 2 O 3 ; formula hence 3Ca6.(Fe,Ti,Al) 2 O 3 .3(Si,Ti)O 2 . It thus graduates toward schorlomite. Color black. 4. Yttriferous Calcium-iron Garnet. Contains yttria in small amount; rare. F. UVAROVITE. Ouvarovite. Uwarowit. Calcium-chromium Garnet. Formula 3CaO.Cr 2 3 .3SiO 2 = Silica 35'9, chromium sesquioxide 30*6, lime 33-5 = 100. Aluminium takes the place of the chromium in part. H. = 7 '5. G. = 3-41-3-52. Color emerald-green. Pyr. etc. Most varieties of garnet fuse easily to a light brown or black glass; F. = 3 in almandite, spessartite, and grossularite; 3 '5 in andradite and pyrope; but uvarovite, the chrome-garnet, is almost infusible, F. = 6. Andradite and almandite fuse to a magnetic globule. Reactions with the fluxes vary with the bases. Almost all kinds react for iron; strong manganese reaction in spessartite, and less marked in other varieties; a chromium reaction in uvarovite, and in most pyrope. Some varieties are partially decomposed by acids; all except uvarovite after ignition become soluble in hydrochloric acid, and generally yield gelatinous silica on evaporation. Decomposed on fusion with alkaline carbonates. The density of garnets is largely diminished by fusion. Thus a Greenland garnet fell from 3'90 to 3'05 on fusion, and a Vilui grossularite from 3'63 to 2'95. Diff. Characterized by isometric crystallization, usually in isolated crystals, dode- cahedrons or trapezohedrons; massive forms rare, then usually granular. * Also distin- guished by hardness, vitreous luster, and in the common kinds the fusibility. Vesuvianite Fuses more easily, zircon and quartz are infusible; the specific gravity is higher than for tourmaline, from which it differs in form; it is much harder than sphalerite. Micro. Distinguished in thin sections by its very high relief; lack of cleavage; iso- tropic character; usually shows a pale pink color; sometimes not readily told from some of the spinels. Artif. While members of the garnet group have been formed artificially their synthe- sis is difficult. Apparently they can be produced only under exact conditions of tempera- ture and pressure that are difficult to reproduce. Natural garnets when fused break down into various other minerals. Obs. Grossularite is especially characteristic of metamorphosed impure calcareous rocks, whether altered by local igneous or general metamorphic processes; it is thus com- monly found in the contact zone of intruded igneous rocks and in the crystalline schists. Almandite is characteristic of the mica schists and metamorphic rocks containing alumina and iron; it occurs also in some igneous rocks as the result of later dynamic and metamor- phic processes; it forms with the variety of amphibole called smaragdite the rock eclogite. Pyrope is especially characteristic of such basic igneous rocks as are formed from magmas containing much magnesia and iron with little or no alkalies, as the peridotites, dunites, etc.; also found in the serpentines formed from these rocks; then often associated with spinel, chromite, etc. Spessartite occurs in granitic rocks, in quartzite, in whetstone schists (Belgium) ; it has been noted with topaz in lithophyses in rhyolite (Colorado). The black variety of andradite, melanite, is common in eruptive rocks, especially with nephelite, leucite, thus in phonohtes, leucitophyres, nephelinites : in such cases often titaniferous or associated SILICATES 509 with a titaniferous garnet, sometimes in zonal intergrowth; it also occurs as a product of contact metamorphism. Demantoid occurs in serpentine. Uvarovite belongs particularly with chromite in serpentine; it occurs also in granular limestone. Garnet crystals often contain inclusions of foreign matter, but only in part due to altera- tion; as, vesuvianite, calcite, epidote, quartz (Fig. 486, p. 180); at times the garnet is a mere shell, or perimorph, surrounding a nucleus of another species. A black garnet from Arendal, Norway, contains both calcite and epidote; crystals from Tvedestrand, Norway, are wholly calcite within, there being but a thin crust of garnet. Crystals from East Woodstock, Me., are dodecahedrons with a thin shell of cinnamon-stone enclosing calcite; others from Raymond, Me., show successive layers of garnet and calcite. Many such cases have been noted. Garnets are often altered, thus to chlorite, serpentine; even to limonite. Crystals of pyrope are sometimes surrounded by a chloritic zone (kelyphite of Schrauf) not homogeneous, as shown in Fig. 847. Among prominent foreign localities of garnets, besides those already mentioned, are the following GROSS- ULARITE: Fine cinnamon-stone comes from Ceylon; on the Mussa-Alp in the Ala valley in Piedmont, Italy, with clinochlore and diopside; at Zermatt, Switzerland; pale yellow at Auerbach, Germany; brownish (romanzovite) at Kimito in Finland; honey- yellow octahedrons in Elba; pale greenish from the banks of the Vilui in Siberia, in serpentine with vesuvianite; also from Cziklowa and Orawitza in the Banat, Hungary; with vesu- vianite and wollastonite in ejected masses at Vesuvius; in white or colorless crystals in Tellemark, in Norway; also dark brown at Mudgee, New South Wales; dark honey-yellow at Guadalcazar, and clear pink or rose-red dodecahedrons at Xalostoc, Morelos, Mexico, called variously, landerite, xalostocite and rosolite. PYROPE: In serpentine (from peridotite) near Meronitz and the valley of Krems, in Bohemia (used as a gem); at Zoblitz in Saxony; in the Vosges Mts.; in the diamond dig- gings of South Africa ("Cape rubies"). ALMANDITE: Common in granite, gneiss, eclogite, etc., in many localities in Saxony, Silesia, etc.; at Eppenreuth near Hof, Bavaria; in large dodecahedrons at Falun in Sweden; hyacinth-red or brown in the Zillertal, Tyrol, Austria. Precious garnet comes in fine crystals from Ceylon, Pegu, British India, Brazil, and Green- land. SPESSARTITE: From Aschaffenburg in the Spessart, Bavaria; at St. Marcel, Pied- mont, Italy; near Chanteloube, Haute Vienne, France, etc. ANDRADITE: The beautiful green demantoid or "Uralian emerald" occurs in transparent greenish rolled pebbles, also in crystals, in the gold washings of Nizhni-Tagilsk in the Ural Mts.; green crystals occur at Schwarzenberg, Saxony; brown to green at Morawitza and Dognacska, Hungary; emerald-green at Dobschau, Hungary; in the Ala valley, Piedmont, Italy, the yellow to greenish topazolite. Allochroite, apple-green and yellowish, occurs at Zermatt, Switzerland; black crystals (melanite), also brown, at Vesuvius on Mte. Somma; near Bareges in the Hautes-Pyrenees, France, (pyreneite). Aplome occurs at Schwarzen- berg in Saxony, in brown to black crystals. Other localities are Pfitschtal, Tyrol, Austria; Langban, Sweden; Pitkaranta, Finland; Arendal, Norway. UVAROVITE: Found at Sara- novskaya near Bisersk, also in the vicinity of Kyshtymsk, Ural Mts., in chromic iron; at Jordansmuhl, Silesia; Pic Posets near Venasque in the Pyrenees on chromite. In North America, in Me., beautiful crystals of cinnamon-stone (with vesuvianite) occur at Parsonsfield, Phippsburg, and Rumford, at Raymond. In N. H., at Hanover, small clear crystals in gneiss; at Warren, cinnamon garnets; at Graf ton. In Ver., at New Fane, in chlorite slate. In Mass., in gneiss at Brookfield; in fine dark red or nearly black trape- zohedral crystals at Russell, sometimes very large. In Conn., trapezohedrons, in mica slate, at Reading and Monroe; dodecahedrons at Southbury and Roxbury; at Haddam, crystals of spessartite. In N. Y., brown crystals at Crown Point, Essex Co.; colophonite as a large vein at Willsboro, Essex Co.; in Middletown, Delaware Co., large brown crystals; a cinnamon variety at Amity. In N. J., at Franklin, black, brown, yellow, red, and green dodecahedral garnets; also near the Franklin Furnace (polyadelphite] . In Pa., in Chester Co., at Pennsbury, fine dark brown crystals; near Knauertown; at Chester, brown; in Concord, on Green's Creek, resembling pyrope; in Leiperville, red; at Mineral Hill, fine brown; at Avondale quarry, fine hessonite; uvarovite at Woods' chrome mine, Lancaster Co. In Va., beautiful transparent spessartite, used as a gem, at the mica mines at Amelia Court-House. In N. C., fine cinnamon-stone at Bakers ville; red garnets in the gold wash- ings of Burke, McDowell, and Alexander counties; rhodolite in Macon Co.; also mined near 510 DESCRIPTIVE MINERALOGY Morgantown and Warlich, Burke Co., to be used as "emery," and as " garnet-paper." In Ky., fine pyrope in the peridotite of Ellis Co. In Ark., at Magnet Cove, a titaniferous melanite with schorlomite. Large dodecahedral crystals altered to chlorite occur at the Spurr Mt. iron mine, Lake Superior, Mich. In Col., at Nathrop, fine spessartite crystals in lithophyses in rhyolite; in large dodecahedral crystals at Ruby Mt., Salida, Chaff ee Co., the exterior altered to chlorite. In Ariz., .yellow-green crystals in the Gila canon; pyrope on the Colorado river in the western part of the territory. N. M., fine pyrope on the Navajo reservation with chrysolite and a chrome-pyroxene. In Cal., green with copper ore, Hope Valley, El Dorado Co.; uvarovite, in crystals on chromite, at New Idria. Fine crystals of a rich red color and an inch or more in diameter occur in the mica schists at Fort Wrangell, mouth of the Stickeen river, in Alaska. In Canada, at Marmora, dark red; at Grenville, a cinnamon-stone; an emerald-green chrome-garnet, at Orford, Quebec, with millerite and calcite; fine colorless to pale olive- green, or brownish crystals, at Wakefield, Ottawa Co., Quebec, with white pyroxene, honey- yellow vesuvianite, etc., also others bright green carrying chromium; dark red garnet in the townships of Villeneuve (spessartite) and Templeton; at Hull, Quebec. Use. The various colored and transparent garnets are used as semiprecious gem s'ones. At times the mineral is also used as an abrasive. Schorlomite. Probably analogous to garnet, 3CaO.(Fe,Ti) 2 O 3 .3(Si,Ti)O 2 . Usually massive, black, with conchoidal fracture and vitreous luster. H. = 77 '5. G. = 3'81 3*88. From Magnet Cove, Ark.; in nepheline-syenite on Ice River, British Columbia. In small dull crystals (monoclinic). From the auriferous sands of Oldh- Partschinite. (Mn,Fe) 3 Al 2 Si 3 Oi 2 like spessartite. H. = 6-5-7. G. = 4-006. Color yellowish, reddish, pian, Transylvania. Agricolite. Same as for eulytite, Bi 4 Si 3 Oi 2 , but monoclinic. In globular or semi- globular forms. From Johanngeorgenstadt, Germany. Monticellite Forsterite Chrysolite Hortonolite Fayalite Knebelite Tephroite Chrysolite Group. R 2 Si0 4 . Orthorhombic GaMgSiO 4 Mg 2 SiO 4 (Mg,Fe) 2 SiO 4 (Fe,Mg,Mn) 2 SiO 4 Fe 2 SiO 4 (Fe,Mn) 2 SiO 4 Mn 2 Si0 4 mm" 1 110 A 110 hh' Oil A 01 I a b : c 46 54' 59 52' 0-4337 1 : 0-5758 49 51' 60 43' 0-4648 1 : 0-5857 49 57' 60 47' 0-4656 1 : 0-5865 49 15' 60 10' 0-4584 1 : 0-5793 49 24' 61 25' 0-4600 1 : 0-5939 The CHRYSOLITE GROUP includes a series .of orthosilicates of magnesium calcium, iron and manganese. They all crystallize in the orthorhombic system with but little variation in axial ratio. The prismatic angle is about 50 and hat of the unit brachydome about 60; corresponding to the latter threefold twms are observed. The type species is chrysolite (or olivine), which contains t^^ /V m Varylng P r P orti ns and is hence intermediate the comparatively rare magnesium and iron silicates SILICATES 511 CHRYSOLITE. Olivine. Peridot. Orthorhombic. Axes a : b : c = 0-46575 : 1 : 0-5865. mm'", 110 A 1TO = 49 57' ss' 120 A 120 = 94 4' dd', kk, ee f ", W", 101 A 101 021 A 021 111 A 111 121 A 121 103 6' 99 6' 40 5 72 13 848 /e\ a e \ m a in Twins rare: tw. pi. h (Oil) with angle between basal planes of the two individuals = 60 47', penetration-twins, sometimes repeated; tw. pi. w \ d \// (012), the vertical axes crossing at an angle of about 30. Crystals often flattened || a (100) or 6 (010), less commonly elongated || c axis. Massive, compact, or granular; in embedded grains. Cleavage: b (010) rather distinct; a (100) less so. Fracture conchoidal. Brittle. H. = 6'5-7. G. = 3-27-3-37, increasing with the amount of iron; 3'57 for hyalosiderite (30 p. c. FeO). Luster vitreous. Color green com- monly olive-green, sometimes brownish, grayish red, grayish green, becoming yellowish brown or red by oxidation of the iron. Streak usually uncolored, rarely yellowish. Transparent to translucent. Optically + . Ax. pi. || c (001), Bx J_ a (100). Dispersion p < v , weak. Axial angle large, a = 1-662. /? = 1-680. 7 = 1*699. Var. Precious. Of a pale yellowish green color, and transparent. G. = 3-441, 3'351. Occasionally seen in masses as large as "a turkey's egg," but usually much smaller. It has long been brought from the Levant for jewelry, but the exact locality is not known. Common; Olivine. Dark yellowish green to olive- or bottle-green. G. = 3 '26-3 '40. Disseminated in crystals or grains in basic igneous rocks, basalt and basaltic lavas, etc. Hyalosiderite is a highly ferruginous variety. Comp. (Mg,Fe) 2 Si0 4 or 2(Mg,Fe)O.Si0 2 . The ratio of Mg : Fe varies widely, from 16 : 1, 12 : 1, etc., to 2 : 1 in hyalosiderite, and hence pass- ing from forsterite on the one side to fayalite on the other. No sharp line can be drawn on either side. Titanium dioxide is sometimes present replacing silica; also tin and nickel in minute quantities. Pyr., etc. B. B. whitens, but is infusible in most cases; hyalosiderite and other varieties rich in iron fuse to a black magnetic globule; some kinds turn red upon heating. With the fluxes gives reactions for iron. Some varieties give reactions for titanium and manganese. Soluble in hydro- chloric acid and yields gelatinous silica upon evaporation. Diff. Characterized by its infusibility, the yellow-green color, granular form and cleavage (quartz has none). Micro. Recognized in thin sections by its high relief; lack of color; its few but marked rough cleavage-cracks; high interference-colors, which are usually the brilliant and pronounced tones of the second order; parallel extinction; biaxial character; charac- teristic outlines (usually with acute terminations) when in distinct crystals (Figs. 850-852), its frequent association with iron ore and augite, and its very common alteration, in a greater or less degree, to serpentine, the first stages being marked by the separation of iron-ore grains along the lines of fracture (Fig. 853). Artif . The different members of the Chrysolite Group have been easily synthesized in various ways. They are often observed in slags. 010 512 DESCRIPTIVE MINERALOGY Obs. Chrysolite (olivine) has two distinct methods of occurrence: (a) in igneous rocks, as peridotite, norite, basalt, diabase and gabbro, formed by the crystallization of magmas low in silica and rich in magnesia; from an accessory component in such rocks 852 853 the olivine may increase in amount until it is the mam rock constituent as in the dunites; also (6) as the product of metamorphism of certain sedimentary rocks containing magnesia and silica, as in impure dolomites. In the dunites and peridotites of igneous origin the chrysolite is commonly associated with chromite, spinel, pyrope, etc., which are valuable indications also of the origin of serpentines derived from olivine. In the metamorphic rocks the above are wanting, and carbonates, as dolomite, breunnerite, magnesite, etc., are the common associations; chrysolitic rocks of this latter kind may also occur altered to serpentine. Chrysolite also occurs in grains, rarely crystals, embedded in some meteoric irons. Also present in meteoric stones, frequently in spherical forms, or chondrules, sometimes made up of a multitude of grains with like (or unlike) optical orientation enclosing glass between. Among the more prominent localities are: Vesuvius in lava and on Monte Somma in ejected masses, with augite, mica, etc. In Germany observed in the so called sanidine bombs at the Laacher See; at Forstberg near May en in the Eifel and forming the mass of "olivine bombs" in the Dreiser Weiher near Daun in the same region; at Sasbach in the Kaiserstuhl, Baden (hyalosiderite) . In crystals of gem-quality from Egypt. In Sweden, with ore-deposits, as at Langban, Pajsberg, Persberg, etc. In serpentine at Snarum, Nor- way, in large crystals, themselves altered to the same mineral. Common in the volcanic rocks of Sicily, the Hawaiian Islands, the Azores, etc. In the United States, in Thetford and Norwich, Ver., in boulders of coarsely crystallized basalt, the crystals or masses several inches through. In olivine-gabbro of Waterville, in the White Mts., N. H.; at Webster, in Jackson Co., N. C., with serpentine and chromite; with chromite in Loudon Co., Va.; in Lancaster Co., Pa. In small clear olive-green grains with garnet at some points in Ariz, and N. M. In basalt in Canada, near Montreal, at Rougemont and Mounts Royal and Montarville, and in eruptive rocks at other points. Alteration of chrysolite often takes place through the oxidation of the iron; the mineral becomes brownish or reddish brown and iridescent. The process may end in leaving the cavity of the crystal filled with limonite or red oxide of iron. A very common kind of alteration is to the hydrous magnesium silicate, serpentine, with the partial removal of the iron or its separation in the form of grains of magnetite, also as iron sesquioxide; this change has often taken place on a large scale. See further under serpentine, p. 573. Chrysolite is named from xpvris, gold, and Al0os. The hyalosiderite, from oaXos, glass, and o-iSrjpos, iron. The chrysolithus of Pliny was probably our topaz ; and his topaz our chrysolite. Use. The clear, fine green varieties are used as a gem stone; usually caUed peridot. T^Y-* Fr m * the r ck ? armeloite of Carmelo Bay, Cal.; a silicate resembling an chrysolite, exact composition undetermined. Has been noted as a pseudomorph h* Mittelgebirge ' Bohemi a. Orthorhombic, foliated and cleavable^G SILICATES 513 The axial ratios of the other members of the Chrysolite Group are given in the table on p. 510. The species are briefly characterized as follows: Monticellite. CaMgSiO 4 . Occurs in colorless to gray crystals on Mte. Somma, Vesu- vius; in masses (batrachite) on Mt. Monzoni, Tyrol, Italy; in crystals or grains in lime- stone at Magnet Cove, Ark. G. = 3'03-3'25. Optically -. Indices, 1 '651-1 '668. Glaucochroite. CaMnSiO 4 . In embedded prismatic crystals. Crystal constants and optical properties near those of Chrysolite Group. Color, delicate bluish green. Found at Franklin Furnace, N. J. H. =6. G. = 3 '4. Forsterite. Mg 2 SiO 4 . Occurs in white crystals at Vesuvius; in greenish or yellowish embedded grains at Bolton, Mass, (boltonite). G. = 3'21-3'33. Optically +. ft = 1'659. Hortonolite. (Fe,Mg,Mn) 2 SiO 4 . In rough dark-colored crystals or masses. Occurs at the iron mine of Monroe, Orange Co., N. Y. ; Iron Mine Hill, Cumberland, R. I. G. = 3'91. Optically -. Indices, 1768-1 '803. Fayalite. Fe 2 SiO 4 . From the Mourne Mts., Ireland; the Azores; the Yellowstone Park; Rockport, Mass., etc. From Cuddia Mida, Island of Pantelleria, Italy. Crystals and massive, brown to black on exposure. G. = 4'1 Optically . Indices, 1 '824-1 '874. Manganfayalite is a manganese variety found at Sodermanland, Sweden. Knebelite. (Fe,Mn) 2 SiO 4 . From Dannemora, and elsewhere in Sweden. G. = 4-1. Tephroite. MnoSiO 4 ; also with zinc, in the variety roeppetite. From Sterling Hill and Franklin Furnace, N. J.; also from Sweden; from Benderneer, New South Wales. Color flesh-red to ash-gray. G. = 41. Optically . Index about T80. Phenacite Group. R 2 Si0 4 . Tri-rhombohedral rr' c Willemite Zn 2 SiO 4 64 30' 0-6775 Troostite (Zn,Mn) 2 SiO 4 Phenacite Be 2 SiO 4 63 24' 0-6611 The PHENACITE GROUP includes the above orthosilicates of zinc (man- ganese) and beryllium. Both belong to the tri-rhombohedral class of the trigonal division of the hexagonal system, and have nearly the same rhombo- hedral angle. The rare species trimerite, MnSiO 4 .BeSiO 4 , which is pseudo- hexagonal (triclinic) is probably to be regarded as connecting this group with the preceding Chrysolite Group. The following rare species are related: rr' c Dioptase H 2 CuSiO 4 Tri-rhombohedral 54 5' 0'5342 Friedelite H 7 (MnCl)Mn 4 (SiO 4 ) 4 56 17' 0'5624 Pyrosmalite H 7 ( (Fe,Mn)Cl)(Fe,Mn) 4 (SiO 4 ) 4 53 49' 0'5308 These species are very near to each other in form, as shown in the above axial ratios; they further approximate to the species of the Phenacite Group proper. They are also closely related among themselves in composition, since they are all acid orthosilicates, and have the general formula H 2 RSiO 4 = H 8 R 4 (SiO 4 )4, where (e.g. for Friedelite) in the latter form the place of one hydrogen atom is taken by the univalent radical (MnCl). WILLEMITE. Tri-rhombohedral. Axis c = 0*6775; rr' (1011) A (IlOl) = 64 30'; ee r (0112) A (1012) = 36 47'. In hexagonal prisms, sometimes long and slender, again short and stout; rarely showing subordinate faces distributed according to the phenacite type. Also massive and in disseminated grains; fibrous. Cleavage: c (000 1) easy, Moresnet; difficult, N. J.-; a (1120) easy, N. J. Fracture conchoidal to uneven. Brittle. H. = 5'5. G. = 3 -89-4 -18. Luster 514 DESCRIPTIVE MINERALOGY vitreo-resinous, rather weak. Color white or greenish yellow, when purest; apple-green, flesh-red, grayish white, yellowish brown- often dark brown 854 855 856 Figs. 854-857, New Jersey, e (0112), s (1123), u (2ll3), x (3121). when impure. Streak uncolored. Transparent to opaque. Optically + . va, a deceiver, in allusion to its having been mistaken for quartz. Trimerite. (Mn,Ca) 2 SiO 4 .Be 2 SiO 4 . In thick tabular prismatic crystals, pseudo- hexagonal (triclinic) in form and angle. H. = 6-7. G. = 3 '474. Color salmon-pink to nearly colorless in small crystals. Optically. Indices, 1715-1 725. From the Harstig mine, Wermland, Sweden. 861 JDioptase. H 2 CuSiO 4 or H 2 O.CuO.SiO 2 . Commonly in prismatic crystals (ss r 0221 A 2021 =84 33$') Also in crystalline aggregates; massive. Cleavage: r (lOTl) per- fect. Fracture conchoidal to uneven. H. = 5. G. = 3 '28-3 '35. Luster vitreous. Color emerald-green. Opti- cally +. co = 1-654. e = 1-707. Occurs in druses of well-defined crystals on quartz, occupying seams in a compact limestone west of the hill of Altyn-Tiibe in the Kirghiz Steppe, Russia; in the gold washings at several points in Siberia; atRezbanya, Hungary. From Copiapo, Chile, on quartz with other copper ores. In fine crystals at the Mine Mindouli, two leagues east of Comba, in the French Congo State. Also at the copper mines of Clifton, Graham Co., and from Metcalfe and near Florence, Ariz. Plancheite. H 2 Cu 7 (Cu.OH) 8 (SiO 3 )i 2 . Fibrous, often mammillary. Blue color. G, = 3'4. Found associated with dioptase, etc., at Mindouli, French Congo. Friedelite. H 7 (MnCl)Mn 4 Si 4 Oi 6 . Crystals commonly tabular \\ c (0001) ; also massive, cleavable to closely compact. H. = 4-5. G. = 3'07. Color rose-red. From the man- ganese mine of Adervielle, vallee du Louron, Hautes Pyrenees, France; from Sjo mine, Wermland, Sweden; from Franklin Furnace, N. J. Pyrosmalite. H 7 ((Fe,Mn)Cl)(Fe,Mn) 4 Si 4 Oi 6 . Crystals thick hexagonal prisms or tabular; also massive, foliated. H. = 4-4'5. G. = 3*06-3 '19. Color blackish green to pale liver-brown or gray. Index about 1'66. From the iron mines of Nordmark in Werm- land and at Dannemora, Sweden. Meionite Wernerite Scapolite Group. c = 0-4393 c = 0-4384 Tetragonal-pyramidal Mizzonite, Dipyre Marialite c = 0-4424 c = 0-4417 The species of the SCAPOLITE GROUP crystallize in the pyramidal class of the tetragonal system with nearly the same axial ratio. They are white or grayish white in color, except when impure, and then rarely of dark color. 516 DESCRIPTIVE MINERALOGY Hardness = 5-6*5; G. = 2-5-2-8. In composition they are silicates of aluminium with calcium and sodium in varying amounts; chlorine is also often present, sometimes only in traces. Iron, magnesia, potash are not present unless by reason of inclusions or of alteration. Carbon dioxide and sulphur trioxide have been noted in certain analyses. It has been suggested that these radicals enter into the composition in the same manner as the chlorine. The Scapolites are analogous to the Feldspars in that they form a series with a gradual variation in composition, the amount of silica increasing with the increase of the alkali, soda, being 40 p. c. in meionite and 64 p. c. in mari- alite. A corresponding increase is observed also in the amount of chlorine present. Furthermore there is also a gradual change in specific gravity, in the strength of the double refraction, and in resistance to acids, from the easily decomposed meionite, with G. = 2-72, to marialite, which is only slightly attacked and has G. = 2-63. Tschermak has shown that the variation in composition may be explained by the assumption of two fundamental end compounds, viz. : Meionite Ca 4 Al 6 Si6025 Me Marialite NaiAlgSigC^Cl Ma By the isomorphous combination of these compounds the composition of the species mentioned above may be explained; no sharp line can, however, be drawn between them. Optically the series is characterized by the decrease in the strength of the double refrac- tion in passing from meionite to marialite. Thus (Lacroix) for meionite e = 0'036' for typical wernerite 0'03-0-02; for dipyre 0'015. The tetragonal species melilite and gehlenite are near the Sca*polites in ' angle. The more common vesuvianite is also related. MEIONITE. Tetragonal. Axis c = 0-43925. In prismatic crystals (Fig. 201, "p. 86), either clear and glassy or milky white; also in crystalline grains and massive. Cleavage: a (100) rather perfect, m (110) somewhat less so. Fracture con- choidal. Brittle. H. = 5-5-6 G. = 2-70-2-74. Luster vitreous. Color- less to white. Transparent to translucent; often cracked within. Opticallv -. co = 1-597; e = 1-560. Comp. Ca 4 Al 6 Si 6 2 5or4CaO.3Al 2 O 3 .6Si02 = Silica 40-5, alumina 34-4, hme 25' 1 = 100. The varieties included here range from nearly pure meionite to those consisting: of rneiomte and marialite in the ratio of 3 : 1, i.e., Me : Ma = 3 : 1. No sharp line can be drawn between meionite and the following species. Obs. Occurs in small crystals in cavities, usually in limestone blocks, on Monte bomma Vesuvius. Also in ejected masses at the Laacher See, Germany. A mineral in h^11 "\ neiS u m * h l Black Foi> est, Germany, which is like meionite except for a basal cleavage has been called pseudomeionite. WERNERITE. COMMON SCAPOLITE. Tetragonal-pyramidal. Axis c = 0-4384. Crystals prismatic, usually coarse, with uneven faces and often large. The f the pyramidal class sometimes shown in the development of the SILICATES 517 faces z (311) and z x (131). Also massive, granular, or with a faint fibrous appearance; sometimes columnar. ee r , 101 A Oil = 32 59'. rr', 111 A 111 = 43 45'. mr, 110 A 111 = 58 12'. zz'", 311 A 311 = 29 43'. Cleavage: a (100) and m (110) rather dis- tinct, but interrupted. Fracture subconchoidal. Brittle. H. = 5-6. G. = 2-66-273. Luster vitreous to pearly externally, inclining to res- inous; cleavage and cross-fracture surface vitreous. Color white, gray, bluish, greenish, and reddish, usually light; streak uncolored. Transparent to faintly subtranslucent. Optically, co = 1-570. e = 1-549. Comp. Intermediate between meionite and marialite and correspond- ing to a molecular combination of these in a ratio 3 : 1 to 1 : 2. The silica varies from 46 to 54 p.c., and as its amount increases the soda and chlorine also increase. Scapolites with silica from 54 p. c. to 60 p. c. are classed with mizzonite; they correspond to Me : Ma from 1 : 2 to 1 : 3 and upwards. The percentage composition for a common compound is as follows: Me : Ma 3 : 1 SiO 2 46*10 A1 2 O 3 30'48 CaO 19'10 Na 2 O 3'54 Cl 1 -01 =100*23 Pyr., etc. B.B. fuses easily with intumescence to a white blebby glass giving a strong sodium flame color. Imperfectly decomposed by hydrochloric acid. Diff . Characterized by its square form and prismatic cleavage (90) : resembles feldspar when massive, but has a characteristic fibrous appearance on the cleavage surface; it is also more fusible, and has a higher specific gravity; also distinguished by fusibility with intumescence from pyroxene (which see, p. 478). Micro. Recognized in thin sections by its low refraction; lack of color; rather high interference-colors reaching the yellows and reds of the first order, sections showing which extinguish parallel to the cleavage; by the distinct negative axial cross of basal sections which show the cleavage-cracks crossing at right angles. Obs. Occurs in metamorphic rocks, crystalline schists, gneisses, amphibolites and most abundantly in granular limestone near its junction with the associated granitic or allied rocks; sometimes in beds of magnetite accompanying limestone. It is often asso- ciated with a light-colored pyroxene, amphibole, garnet, and also with apatite, titanite, zircon; amphibole is a less common associate than pyroxene, but in some cases has resulted from the alteration of pyroxene. Scapolite has been^sjjown also to be frequently. a com- ponent of basic igneous rocks, especially those rich in plaglOuLiuLj uiwitaining much lime; it is regarded as a secondary product through a certain kind of. alteration. The scapolites are easily altered; pseudormorphs of mica, more rarely other minerals, are com- mon. Prominent localities are at Pargas, Finland, where it occurs in limestone; Arendal in Norway, and Malsjo in Wermland, Sweden, where it occurs with magnetite in limestone. Passauite is from Obernzell, near Passau, in Bavaria. The pale blue or gray scapolite from Lake Baikal, Siberia, is called glaucolite. In the United States, occurs in Ver., at Marl- borough, massive. In Mass., at Bolton; at Chelmsford. In N. Y. in Orange Co., Essex Co., Lewis Co.; Grasse Lake, Jefferson Co.; at Gouverneur, in limestone. In N. J., at Franklin and Newton. In Pa., at the Elizabeth mine, French Creek, Chester Co. In Canada, at Calumet Island, massive; at Grenville; .Templeton; Wakefield, Ottawa Co.; at Bedford and Bathurst, Ont : Scapolite rocks occur at several points. Mizzonite. Dipyre. Here are included scapolites with 54 to 57 p. c. SiO 2 , correspond- ing to a molecular combination from Me : Ma = 1 : 2 to Me : Ma = 1:3. Mizzonite occurs in clear crystals in ejected masses on Mte. Somma, Vesuvius. Dipyre occurs in elongated square prisms, often slender, sometimes large and coarse, in limestone and crystalline schists, chiefly from the Pyrenees; also in diorite at Bamle, Nor- way; Saint-Nazaire, France; Algeria. Couseranite from the Pyrenees is a more or less altered form of dipyre. DESCRIPTIVE MINERALOGY Marialite Theoretically Na 4 Al 3 Si 9 O 24 Cl, see p. 516. Indices, 1- 541-1- 554. The actual iinerkl corresponds to Me : Ma = 1 : 4. It occurs in a basalt tuff, at Pianura, near Naples. Sarcolite. (Ca,Na,) 3 Al 2 (SiO 4 ) 3 . In small tetragonal crystals. H. = 6. G. = 2-545- 2-932. Color flesh-red. Indices, 1 '640-1 '656. From Monte Somma, Vesuvius. MELILITE. Tetragonal. Axis c = 0-4548. Usually in short square prisms (a (100)) or octagonal prisms (a, m (110)), also in tetragonal tables. Cleavage: c (001) distinct; a (100) indistinct. Fracture conchoidal to uneven. Brittle. H. = 5. G. = 2-9-3-10. Luster vitreous, inclining to resinous. Color white, pale yellow, greenish, reddish, brown. Pleochroism distinct in yellow varieties. Sometimes exhibits optical anomalies. Opti- cally -. co = 1-634. = 1-629. Comp. Perhaps R 12 R 4 Si 9 036 or Na 2 (Ca,Mg)i 1 (Al,Fe) 4 (Si0 4 )9 for meli- lite. If Ca : Mg = 8:3, and Al : Fe = 1 : 1, the percentage composition is: Silica 37-7, alumina 7'1, iron sesquioxide 11-2, lime 31-3, magnesia 8'4, soda 4'3 = 100. Potassium is also present. The composition of the melilite-gehlenite group can be explained as isomorphous mix- tures of the three compounds, sarcolite, 3CaO.Al 2 O 3 .3SiO 2 or soda-sarcolite 3Na 2 O.Al 2 O 3 . 3SiO 2 ; dkermanite, 8CaO.4MgO.9SiO 2 ; velardeiiite, 2CaO.Al 2 O 3 .SiO 2 . The last is noted in large amount in gehlenite from the Velardena mining district, Mexico. Artif. Melilite has been formed artificially by fusing together its constituent oxides. It is found in slags and has been produced in various artificial magmas. Pyr., etc. B.B. fuses at 3 to a yellowish or greenish glass. With the fluxes reacts for iron. Soluble in hydrochloric acid and yields gelatinous silica upon evaporation. Micro. Distinguished in thin sections by its moderate refraction; very low interfer- ence-colors, showing often the "ultra blue" (Capo di Bove); parallel extinction; negative character; usual development in tables parallel to the base and very common "peg struc- ture" due to parallel rod-like inclusions penetrating the crystal from the basal planes inward: this, however, is not always easily seen. Obs. Melilite is a component of certain igneous rocks formed from magmas very low in silica, rather deficient in alkalies, and containing considerable lime and alumina. In such cases melilite appears to crystallize in the place of the more acid plagioclase. Melilite of yellow and brownish colors is found at Capo di Bove, near Rome, in leucito- phyre with nephelite, augite, hornblende; at Vesuvius in dull yellow crystals (somervillite) ', not uncommon in certain basic eruptive rocks, as the melilite-basalts of Hochbohl near Owen in Wurttemberg, of the Swabian Alp, of Gorlitz, the Erzgebirge, Germany; also in the nephelite basalts of the Hegau, of Oahu, Hawaiian Islands, etc.; perovskite is a common associate. Occurs as chief constituent of rock on Beaver Creek, Gunnison Co., Col. Com- mon in furnace slags. Melilite is named from n f \t, honey, in allusion to the color. Humboldtilite occurs in cavernous blocks on Monte Somma, Vesuvius, with greenish mica, also apatite, augite; the crystals are often rather large, and covered with a calcareous coat- ing; less common in transparent lustrous crystals with nephelite, sarcolite, etc., in an augitic rock. Zurlite is impure humboldtilite. Deeckeite is a pseudomorph after melilite with the composition (H,K,Na) 2 (Mg,Ca)(Al,Fe) 2 (Si 2 O 6 )5.9H 2 O, found in a melilite basalt from the Kaiserstuhl, Baden, Germany. Cebollite. H 2 Ca5Al<>Si 3 Oi6. Orthorhombic (?). Fibrous. H. =5. G. = 2'96. Color white to greenish gray. Indices, 1 '59-1 '63. Fusible at 5. Soluble in acids. Found as an alteration product of melilite near Cebolla Creek, Gunnison Co., Col. ^ Gehlenite. Ca 3 Al 2 Si 2 Oi . Crystals usually short square prisms. Axis c = 0-4001. y- = 2 -9-3 '07. Different shades of grayish green to liver-brown. From Mount Monzoni, m the Fassatal, in Tyrol, Austria. From Velardena mining district, Mexico. FUGGERITE Corresponds to a member of the gehlenite-akermanite series, 3 ak : 10 geh. From Monzonite of Monzonital, Tyrol, Austria. SILICATES 519 AKERMANITE. Tetragonal, isomorphous with melilite and gehlenite. as. See further under Melilite. Found in certain VESUVIANITE. Idocrase. Tetragonal. Axis c = 0-5372. ce, 001 A 101 = 28 15'. cp, 001 A 111 = 37 13|'. ct, 001 A 331 = 66 18'. 865 pp 866 111 A Til = 50 39'. 311 A 311 = 31 38'. 867 Zermatt Sandford, Me. Often in crystals, prismatic or pyramidal. Also massive; columnar, straight and divergent, or irregular; granular massive; cryptocrystalline. Cleavage: m (110) not very distinct; a (100) and c (001) still less so. Fracture subconchoidal to uneven. Brittle. H. = 6*5. G. = 3 '35-3 '45. Luster vitreous; often inclining to resinous. Color brown to green, and the latter frequently bright and clear; occasionally sulphur-yellow, and also pale blue. Streak white. Subtransparent to faintly subtranslucent. Dichroism not usually strong. Optically ; also -+- rarely. Birefringence very low. Sometimes abnormally biaxial. Indices variable, from 1715 to 1720. Comp. A basic calcium-aluminium silicate, but of uncertain formula; perhaps Ca6[Al(OH,F)]Al 2 (SiO 4 )5. Ferric iron replaces part of the aluminium and magnesium the calcium. Fluorine and titanium may be present. Another general formula has been proposed, RtCayALzSieO^, in which R 4 may be Ca 2 ,(AlOH) 2 ,(A10 2 H) 4 , or H 4 . Pyr., etc. B.B. fuses at 3 with intumescence to a greenish or brownish glass. With the fluxes gives reactions for iron, and some varieties a strong manganese reaction. Cyprine, a blue variety, gives a reaction for copper with salt of phosphorus. Partially decomposed by hydrochloric acid, and completely when the mineral has been previously ignited. Diff. Characterized by its tetragonal form and easy fusibility. Resembles some brown varieties of garnet, tourmaline, and epidote. 520 DESCRIPTIVE MINERALOGY Micro. Recognized in thin sections by its high refraction producing a very strong relief and its extremely low birefringence; * also in general by its color, pleochroism, and uniaxial negative character; the latter, on account of the low birefringence, being difficult to determine. The low birefringence, however, aids in distinguishing it from epidote, with which at times it may be confounded. Obs. Vesuvianite was first found among the ancient ejections of Vesuvius and the dolomitic blocks of Monte Somma, whence its name. It commonly occurs as a contact mineral from the alteration of impure limestones, then usually associated with lime garnet (grossularite), phlogopite, diopside, wollastonite; also epidote; also in serpentine, chlorite schist, gneiss and related rocks. Prominent localities are Vesuvius; the Albani Mts.; in Switzerland at Zermatt, etc.; the Mussa Alp in the Ala valley, in Piedmont, Italy; Mt. Monzoni in the Fassatal, Austria; at Orawitza and Dognaczka, Hungary; Haslau near Eger in Bohemia (egeran); near Jordansmiihl, Silesia; on the Vilui river, near Lake Baikal, Siberia (sometimes called wiluite or viluite, like the grossular garnet from the same region); Achmatovsk, Ural Mts.; in Norway; at Arendal, " colophonite" ; at Egg, near Christiansand; at Morelos, Mexico. In North America, in Me. at Phippsburg and Rumford; at Sandford. In N. H., at Warren with cinnamon-stone. In N. Y., near Amity. In N. J., at Newton. In Lewis and Clark Co., Mon. In Cal. near San Carlos in Inyo Co.; at Crestmore, Riverside Co. In Canada, at Calumet Falls, Litchfield, Pontiac Co.; at Grenville in calcite; at Templeton, Ottawa Co., Quebec. A lavender-colored variety, known as mangan-vesuvianite comes from near Black Lake, Quebec. Californite is a closely compact variety of an olive-green to a grass-green color from Siskiyou, Fresno and Tulare Cos., Cal. Zircon Thorite Zircon Group. ZrSi0 4 ThSiO 4 . Tetragonal c = Q'6404 c = 0-6402 This group includes the orthosilicates of zirconium and thorium, both alike in tetragonal crystallization, axial ratio and crystalline habit. .These species are sometimes regarded as oxides and then included in the RUTILE GROUP (p. 425), to which they approximate closely in form. A similar form belongs also to the tantalate, Tapiolite, and to the phosphate, Xenotime; further, compound groups consisting of crystals of Xenotime and Zircon in parallel position are not uncommon (Fig. 462, p. 173) . ZIRCON. Tetragonal. Axis c = 0-64037. ee', 101 A Oil = 44 50' ee", 101 A 101 = 65 16'. pp', 111 A 111 = 56 40'. uu' 331 A 331 871 83 9' 872 mp 110 A 111 = 47 50'. mu, 110 A 331 = 20 12' xx, 311 A 311 = 32 57'. ax, 100 A 311 = 31 43'. 873 Frequently minerals which, like vesuvianite, melilite and zoisite, are doubly refract- ing but of extremely low birefringence and possibly (where they are positive for one color SILICATES 521 Twins: tw. pi. e (101), geniculated twins like rutile (Fig. 412, p. 166). Commonly in square prisms, sometimes pyramidal. Also in irregular forms and grains. 875 876 877 c 'Pi Colorado Cleavage: m (110) imperfect; p (111) less distinct. Fracture conchoidal. Brittle. H. = 7*5. G. = 4-68-470 most common, but varying widely to 4 '2 and 4 '86. Luster adamantine. Colorless, pale yellowish, grayish, yellowish green, brownish yellow, reddish brown. Streak uncolored. Transparent to subtranslucent and opaque. Optically +. Birefringence high, co = 1-9239, e = 1*9682, Ceylon. Sometimes abnormally biaxial. Hyacinth is the orange, reddish and brownish transparent kind used for gems. Jargon is a name given to the colorless jor smoky zircons of Ceylon, in allusion to the fact that while resembling the diamond in luster, they are comparatively worthless; thence came the name zircon. zirconia 67-2 = 100. A Comp. ZrSi0 4 or Zr0 2 .SiO 2 = Silica 32-8, little iron (Fe2O 3 ) is usually present. Pyr., etc. Infusible; the colorless varieties are unaltered, the red become colorless, while dark-colored varieties are made white; some varieties glow and increase in density by ignition. Not perceptibly acted upon by salt of phosphorus. In powder decomposed when fused with soda on the platinum wire, and if the product is dissolved in dilute hydro- chloric acid it gives the orange color characteristic of zirconia when tested with turmeric paper. Not acted upon by acids except in fine powder with concentrated sulphuric acid. Decomposed by fusion with alkaline carbonates and bisulphates. Diff. Characterized by the prevailing square pyramid or square prism; also by its adamantine luster, hardness, high specific gravity, and infusibility; the diamond is optically isotropic. Micro. Recognized in thin sections by its very high relief; very high interference- colors, which approach white of the higher order except in very thin sections; positive uniaxial character. It is distinguished from cassiterite and rutile only by its lack of color, and from the 1-itter also in many cases by method of occurrence. Artif . Zircon has been prepared artificially by heating zirconium oxide with quartz in gaseous silicon fluoride. Obs. A common accessory constituent of igneous rocks, especially those of the more acid feldspathic groups and particularly the kinds derived from magmas containing much soda, as granite, syenite, diorite, etc. It is one of the earliest minerals to crystallize from a cooling magma. Is generally present in minute crystals, but in pegmatitic facies often in large and well-formed crystals. Occurs more rarely elsewhere, as in granular limestone, chloritic and other schists; gneiss; sometimes in iron-ore beds. Crystals are common in most auriferous sands. Sometimes found in volcanic rocks, probably in part as inclusions derived from older rocks. Zircon in distinct crystals is so common in the pegmatitic forms of the nephelite-syenite but negative for another), do not show a gray color between crossed nicols but a curious blue, at times an intense Berlin blue, which is quite distinct from the other blues of the color scale and is known as the "ultra blue." 522 DESCRIPTIVE MINERALOGY and augite-syenite of southern Norway (with segirite, etc.) that this rock there and else- where has sometimes been called a " zircon-syenite." Found in alluvial sands in Ceylon; in the gold regions of the Ural Mts.; in Norway, at Laurvik, at Arendal, in the iron mines, at Fredriksyarn, and in veins in the augite-syenite of the Langesund fiord; Pfitschtal, Tyrol, Austria; in Germany in lava at Niedermendig in the Eifel, red crystals; from Madagascar; from Minas Geraes, Brazil. In North America, in Me., at Litchfield; in N. Y., in Moriah, Essex Co., cinnamon- red; near the outlet of Two Ponds, Orange Co., with scapolite, pyroxene and titantite; at Warwick, chocolate-brown, near Amity; in St. Lawrence Co.. in the town of Hammond; at Rossie, Fine, Pitcairn. In Pa., near Reading. In N. C., abundant in the gold sands of Burke, McDowell, Polk, Rutherford, Henderson, and other counties. In Col., with astro- phyllite, etc., in the Pike's Peak region in El Paso Co.; at Cheyenne Mt. In CaL, in auri ferous gravels. In Canada, at Grenville, Argenteuil Co.; in Templeton and adjoining townships in Ottawa Co., Quebec; in Renfrew Co., sometimes very large; in North Burgess, Lanark Co. Use. Zircon in its transparent varieties serves frequently as a gem stone; also as a source of zirconium oxide used in the manufacture of the incandescent gas mantles. Malacon is an altered zircon. Cyrtolite is related but contains uranium, yttrium and other rare elements. Naegite is apparently zircon with yttrium, niobium-tantalum, thorium, and uranium oxides. Occurs in spheroidal aggregates near Takoyama, Mino, Japan. Color green, gray brown. H. = 7'5. G. = 4'1. Thorite. Thorium silicate, ThSiO 4 , like zircon in form; usually hydrated, black in color, and then with G. = 4 '5-5; also orange-yellow and- with G. = 5 '19-5 -40 (orangite). From the Brevik region and Arendal, Norway. Auerlite. Like zircon in form; supposed to be a silico-phosphate of thorium. Hender- son Co., N. C. RR 2 (Si0 4 ) 2 or (RO)RSi0 4 Danburite-Topaz Group. Orthorhombic. Danburite CaB 2 (Si0 4 ) 2 a : b Topaz [Al(F,OH) 2 ]AlSiO 4 a : b Andalusite (A10)AlSiO 4 J b : a : f c = 0'5070 or a : b : c = 0'9861 c = G'5444 c = 0-5285 0-4807 0-4770 0-4749 0-7025 Sillimanite Cyanite a : b : c Al 2 SiO 5 Al 2 Si0 5 - 0-8994 : 1 : 07090; Orthorhombic Triclinic a = 90 5J', ft = 101 2' a :b = 0-970 : 1 7 = 105 44J'. DANBURITE. Orthorhombic. 878 in 28-4 Axes a : b : c =_0'5444 : 1 : 0-4807. mm'", 110 A 110 = 57 8'. dd', 101 A 101 = 82 53' II', 120 A 120 = 85 8'. ww', 041 A 041 = 125 3'.' Habit prismatic, resembling topaz. Also in indistinct embedded crystals, and disseminated masses. Cleavage: c (001) very indistinct. Fracture uneven to subconchoidal. Brittle. H. = 7-7-25. G. = 2*97- 3-02. Color pale wine-yellow to colorless, yellowish white, dark wine-yellow, yellowish brown. Luster vitreous to greasy, on crystal surfaces brilliant. Transparent to translucent. Streak white. . Optically - 2V = 88 a = 1-632. ft = 1-634. 7 = 1-636. i or CaO.B 2 O 3 .2SiO 2 = Silica 48'8, boron trioxide SILICATES 523 Pyr., etc. B.B. fuses at 3'5 to a colorless glass, and imparts a green color to the O. F. (boron). Not decomposed by hydrochloric acid, but sufficiently attacked for the solution to give the reaction of boric acid with turmeric paper. When previously ignited gelatinizes with hydrochloric acid. Phosphoresces on heating, giving a reddish light. Obs. Occurs at Danbury, Conn., with microcline and oligoclase in dolomite. At Russell, N. Y., in fine crystals. On the Piz Valatscha, the northern spur of Mt. Skopi south of Dissentis in eastern Switzerland, in slender prismatic crystals and elsewhere in Switzerland. In crystals from Takachio, Hinga, and from Obira, Bungo, Japan. From Mt. Bity and Maharitra, Madagascar. BARSOWITE. This doubtful species, occurring with blue corundum in the Ural Mts., is by some authors classed with danburite; composition CaAl 2 Si 2 Q8 like anorthite. TOPAZ. Orthorhombic. Axes a : b : c = 0-52854 : 1 : 047698. 879 880 881 882 ^ I p in T m P> I 1 Brazil mm'", 110 A 1TO = 55 43'. II, 120 A 120 = 89 49'. dd', 201 A 201 = 122 1'. XX', 043 A 043 = 64 55'. //', 021 A 021 = 87 18'. Japan Durango yy', 041 A 041 = 124 41'. ci, 001 A 223 = 34 14'. ^cu, 001 A 111 = 45 35'. co, 001 A 221 = 63 54'. Ural uu', 111 A Til = 78 20'. uu'", 111 A 111 = 39 0'. oo', 221 A 221 = 105 7'. oo'" 221 A 221 = 49 37*'. 883 884 Crystals commonly prismatic, m (110) predominating; or I (120) and the form then a nearly square prism resembling andalusite. Faces in the prismatic zone often vertically striated, and often show- ing vicinal planes. Also firm columnar; granular, coarse or fine. Cleavage: c (001) highly perfect. Fracture subconchoidal to uneven. Brittle. H. = 8. G. = 3 -4-3 -6. Luster vitreous. Color straw-yellow, wine- yellow, white, grayish, greenish, bluish, reddish. Streak uncolored. Trans- parent to subtranslucent. Optically +. Ax. pi. || 6 (010). Bx J_ c (001). Axial angles variable. 2V = 49 to 66. Refractive indices, Brazil: For D a = 1-62936 ft = 1 "63077 7 = 1 '63747 .'. 2V = 49 31' Var. Ordinary. In prismatic crystals usually colorless or pale yellow, less often pale blue, pink, etc. The yellow of the Brazilian crystals is changed by heating to a pale rose-pink. Often contains inclusions of liquid CCV Physalite, or pyrophysalite, is a coarse nearly opaque variety, from Finbo, Sweden; intumesces when heated, hence its name from Y > Z. Sections normal to an optic axis are idiophanous or show the polarization- brushes distinctly (p. 288). Optically . Ax. pi. || b (010). Bx J_ c (001). 2V = 85. a = T632. = 1*638. 7 = 1-643. Var. Chiastolite, or Made is a variety in stout crystals having the axis and angles of a different color from the rest, owing to a regular arrangement of carbonaceous impurities through the interior, and hence exhibiting a colored cross, or a tesselated appearance in a transverse section. Fig. 888 shows sections of a crystal. Viridine is a green variety con- taining some iron and manganese from near Darmstadt, Ger- many. Comp. Al 2 SiO 5 = (A1O) AlSiO 4 or Al 2 O 3 .SiO 2 = Silica 36-8, alumina 63*2 = 100. Manganese is sometimes present, as in manganandalusite. 100 *z Pyr., etc. B.B. infusible. With cobalt solution gives a blue color after ignition. Not decomposed by acids. De- composed on fusion with caustic alkalies and alkaline carbonates. Diff. Characterized by the nearly square prism, plepchroism, hardness, infusibility; reaction for alumina B.B. Micro. Distinguished in thin sections by its high relief; low interference-colors, which are only slightly above those of quartz; negative biaxial character; negative exten- sion of the crystals (diff . from sillimanite) ; rather distinct prismatic cleavage and the con- stant parallel extinction .(diff. from pyroxenes, which have also greater birefringence); also by its characteristic arrangement of impurities when these are present (Fig. 888). The pleochroism, which is often lacking, is, when present, strong and characteristic. 888 Obs. Most common in argillaceous schist, or other scnists imperfectly crystalline; also in gneiss, mica schist and related rocks; rarely in connection with serpentine. The variety chiastolite is commonly a contact mineral in clay-slates, e.g., adjoining granitic dikes. Sometimes associated with sillimanite with parallel axes. Found in Spain, in Andalusia; in Austria in the Tyrol, Lisens Alp; in Saxony, at Brauns- dorf ; Bavaria, at Wunsiedel, etc. In Brazil, province of Minas Geraes, in fine crystals and as rolled pebbles. Remarkable crystals of chiastolite from Mt. Howden, near Bimbowrie, South Australia. In North America, in Me., at Standish. N. H., White Mtn. Notch; Mass., at West- ford; Lancaster, both varieties; Sterling, chiastolite. Conn., at Litchfield and Washing- ton. Pa., in Delaware Co., near Leiperville, large crystals; Upper Providence. Named from Andalusia, the first locality noted. The name made is from the Latin macula, a spot. Chiastolite is from X*O"TOS, arranged diagonally, and hence from chi, the Greek name for the letter X. Use. When clear and transparent may serve as a gem stone. Guarinite. 2(K,Na) 2 O.8CaO.5(Al,Fe,Ce) 2 O 3 .10SiO 2 . Orthorhombic. In minute thin tables, flattened || b (010), nearly tetragonal in form. H. = 6'5. G. = 2 -9-3-3. Color sulphur-yellow, honey-yellow. Pleochroic, canary-yellow to colorless. Found in a grayish trachyte on Mte. Somma, Vesuvius. Axial ratio and optical properties agree closely with those of danburite. 526 DESCRIPTIVE MINERALOGY SILLIMANITE. Fibrolite. Orthorhombic. Axes a : b = 0'970 : 1. mm'" 110 A 110 = 88 15', hh' 230 A 230 = 69. Prismatic faces striated and rounded. Commonly in long slender crystals not distinctly terminated; often in close parallel groups, passing into fibrous and columnar massive forms; sometimes radiating. Cleavage: b (010) very perfect. Fracture uneven. H. = 6-7. G. = 3-23-3-24. Luster vitreous, approaching subadamantine. Color hair-brown, grayish brown, grayish white, grayish green, pale olive-green. Streak un- colored. Transparent to translucent. Pleochroism sometimes distinct. Optically +. Double refraction strong. Ax. pi. || b (010). Bx J_ c (001). Dispersion p > v. Axial angle and indices variable. 2V = 20 (approx.). a = 1-638. = 1-642. 7 = 1*653. Comp. Al 2 SiO 5 = (A10)AlSi0 4 , like andalusite. Silica 36'8, alumina 63'2 = 100. Sillimanite is the most stable of the three aluminium silicates. Both andalusite and cyanite are converted into sillimanite when strongly heated. Pyr. Same as andalusite. Diff. Characterized by its fibrous or columnar form; perfect cleavage; infusibility; reaction for alumina. Micro. In thin sections recognized by its form, usually with transverse fractures; parallel extinction; high interference-colors. Artif. Sillimanite has been made, artificially by fusing its oxides together. Both andalusite and cyanite are converted into sillimanite when strongly heated. Obs. Often present in the quartz of gneisses and sometimes granites in very slender, minute prisms commonly aggregated together and sometimes intergrown with andalusite; iolite is also a common associate; rarely as a contact mineral; often occurs with corundum. Observed in many localities, thus near Moldau in Bohemia; at Fassa in Tyrol, Austria (bucholziie) ; in the Carnatic, India, with corundum (fibrolite} ; at Bodenmais, Bavaria; Freiberg, Saxony; in France, near Pontgibaud and other points in Auvergne; forms rolled masses in the diamantiferous sands of Minas Geraes, Brazil. In the United States, in Mass., at Worcester. In Conn.; near Norwich, with zircon, monazite and corundum; at Willimantic. In N. Y., at Yorktown, Westchester Co.; in Monroe, Orange Co., (monrolite). In Pa., at Chester on the Delaware, near Queensbury forge; in Delaware Co.; Del., at Brandy wine Springs. With corundum in N. C. Named fibrolite from the fibrous massive variety; sillimanite. after Prof. Benjamin Silliman of New Haven (1779-1864). Bamlite, xenolite, worthite probably belong to sillimanite; the last is altered. CYANITE. Kyanite. Disthene. Triclinic. Axes a : b : c = 0-8994 : 1 : 07090; a = 90 5|', = 101 2', 7 = 105 44i'. ac, 100 A 001 = 78 30'; be, 010 A 001 = 86 45'. 889 Usually in long bladed crystals, rarely terminated. Also >, ^ coarsely bladed columnar to subfibrous. Cleavage : a (100) very perfect ; b (010) less perfect ; also parting 1 1 c (001). H. = 5-7 -25; the least, 4-5, on a (100) | caxis; 6-7 on a (100) || edge a (100)/ c (001); 7 on b (010). G. = 3-56-3-67. Luster vitreous to pearly. Color blue, white; blue along the center of the blades or crystals with white margins; also gray, green, black. Streak uncolored. Translucent to transparent. Pleo- chroism distinct in colored varieties. Optically . Ax. pi. nearly 1 a (100) and inclined to edge a/b on a about 30, and about 7i on 6 (010), cf. Fig. 889. 2V = 82. a = 1-717. B = 1722. 7 = 1'729. SILICATES 527 Comp. Empirical formula Al 2 SiO 6 or Al 2 3 .Si0 2 , like andalusite and sillimanite. Perhaps a basic metasilicate, (A10) 2 Si0 3 . Pyr., etc. Same as for andalusite. At a high temperature cyanite assumes the physical characters of sillimanite. Diff. Characterized by the bladed form; common blue color; varying hardness; in- fusibility; reaction -for alumina. Obs. Occurs principally in gneiss and mica schist (both the ordinary variety with muscoyite and also that with paragonite) often accompanied by garnet and sometimes by staurolite; also in eclogite schist. It is often associated with corundum. Found in transparent crystals at Monte Campione in the St. Gothard region in Switzer- land in paragonite schist; on Mt. Greiner, Zillertal, and in the Pfitschtal (rhcetizite, white) in Tyrol, Austria; in eclogite of the Saualpe, Carinthia; Horrsjoberg in Wermland, Sweden; Villa Rica, Brazil, etc. In Mass., at Chesterfield, with garnet in mica schist. In Conn., at Litchfield, Washing- ton, Canton, Barkhamstead, etc. In Ver., at Thetford. In Pa., in Chester Co. and in Delaware Co. In Va., Buckingham Co. In N. C., with rutile, lazulite, etc., at Crowder's Mt., Gaston Co.; in Gaston and Rutherford counties associated with corundum, damourite; beautiful clear green in Yancey Co. Named from KVCXVOS, blue. Datolite Group. Monoclinic ii in ii in Basic Orthosilicates. HRRSiO 5 or R 3 R2(SiO 5 ) 2 . Oxygen ratio for R : Si = 3 : 2. ii in R = Ca,Be,Fe, chiefly; R = Boron, the yttrium (and cerium) metals, etc. a Datolite 0'6345 HCaBSiO 5 or Ca(BOH)SiO 1 1-2657 89 51 1-2824 89 21' 4c ft 1-3330 79 44' T3215 89 26*' Homilite 0'6249 CaaFeBsSisOig or Ca 2 Fe(BO) 2 (Si0 4 ) 2 2a Euclase 0'6474 1 HBeAlSi0 5 or Be(A10H)Si0 4 a Gadolinite 0'6273 1 Be 2 FeY 2 Si 2 Oi or Be 2 Fe(YO) 2 (Si0 4 ) 2 The species of the DATOLITE GROUP are usually regarded as basic ortho- silicates, the formulas being taken in the second form given above. They all crystallize in the monoclinic system, and all but Euclase conform closely in axial ratio; with the latter there is also a distinct morphological relationship. DATOLITE. Monoclinic. Axes a : b : c = 0'6345 : 1 : 1-2657; ft = 89 51^'. mm'", 110 A HO = 64 47'. en, 001 A 111 = 66 57'. ac, 100 A 001 = 89 51'. cm, 001 A 110 = 89 53'. ax, 100 A 101 = 45 0'. ce, 001 A Tl2 = 49 49'. 012 A 012 = 64 39*'. nn', 111 A 111 = 59 4*'. Oil A Oil = 103 23'. ce', Tl2 A U2 = 48 19*'. Crystals varied in habit; usually short prismatic with either m (110) or w x (Oil) predominating; sometimes tabular || x (201); also of other types, and often highly modified (Figs. 890-893). Also botryoidal and globular, having a columnar structure; divergent and radiating; sometimes massive, granular to compact and crypto-crystalline. Cleavage not observed. Fracture conchoidal to uneven. Brittle. 528 DESCRIPTIVE MINERALOGY H =5-5-5. G. = 2-9-3-0. Luster vitreous, rarely subresinous on a surface of fracture. Color white; sometimes grayish, pale green, yellow, red, or ame- thystine, rarely dirty olive-green or honey-yellow. Streak white. Trans- 890 891 Bergen Hill parent to translucent; rarely opaque white. Optically -. 2V = 74. a 1-625. |8 = 1-653. 7 = 1*669. 893 Bergen Hill Andreasberg Var. 1. Ordinary. In glassy crystals of varied habit, usually with a greenish tinge. The angles in the prismatic and clinodome zones vary but little/e. g., 110 A 110 = 64 47, while Oil A Oil = 66 37', etc. 2. Compact massive. White opaque cream-colored, pink; breaking with the surface of porcelain or Wedge wood ware. From the Lake Superior region. 3. Betryoidal; Botryolite. Radiated columnar, having a botryoidal surface, and containing more water than the crystals, but optically identical. Comp. A basic orthosilicate of boron and calcium; empirically HCaBSiO 5 or H 2 0.2CaO.B 2 O3.2SiO 2 ; this may be written Ca(BOH)Si0 4 = Silica 37-6, boron trioxide 21-8, lime 35-0, water 5'6 = 100. Pyr., etc. In the closed tube gives off much water. B.B. fuses at 2 with intumescence to a clear glass, coloring the flame bright green. Gelatinizes with hydrochloric acid. Diff. Characterized by its glassy, greenish, complex crystals; easy fusibility and green flame B. B. Obs. Datolite is found chiefly as a secondary mineral in veins and cavities in basic eruptive rocks, often associated with calcite, prehnite and various zeolites; sometimes associated with danburite; also in gneiss, diorite, and serpentine; in metallic veins; some- times in beds of iron ore. Found in Scotland, in trap, at the Kilpatrick Hills, etc.; in a bed of magnetite at Arendal in Norway (botryolite) ; at Uto in Sweden; at Andreasberg, Germany, in diabase and in veins of silver ores; in Rhenish Bavaria (the humboMtite) ; at the Seisser Alp, Tyrol, Austria, and at Theiss, near Claussen, Hungary; in geodes in amygda- SILICATES 529 loid; in Italy, in granite at Baveno near Lago Maggiore, at Toggiana in Modena, in serpen- tine, at Monte Catini in Tuscany. In the United States not uncommon with the diabase of Conn, and Mass. Thus at the Rocky Hill quarry, Hartford, Conn.; at Middlefield Falls and Roaring Brook, Conn.; Westfield, Mass. In N. J., at Bergen Hill and Great Notch in splendid crystals; at Pater- son, Passaic Co. Both crystals and the opaque compact variety, in the Lake Superior region. Named from daTeurdai, to divide, alluding to the granular structure of a massive variety. Homilite. (Ca,Fe) 3 B 2 Si 2 Oi or (Ca,Fe) 3 (BO) 2 (SiO 4 )2. Crystals often tabular || c (001); angles near those of datolite. H. = 5. G. = 3'38. Color black, blackish brown. Index about T68. Found on Stoko and other islands, in the Langesund fiord, Norway. Euclase. HBeAlSiO 5 or Be(AlOH)SiO 4 . In prismatic crystals. Cleavage || 6 (010) perfect. H. = 7*5. G. = 3'05-3'10. Luster vitreous. Colorless to pale green or blue. Optically +. = 1'655. From Brazil, in the province of Minas Geraes; in the aurif- erous sands of the Orenburg district, southern Ural Mts., near the river Sanarka; in the Glossglockner region of the Austrian Alps; from Epprechtstein, Fichtelgebirge, Bavaria. Gadolinite. Be 2 FeY 2 Si 2 Oi or Be 2 Fe(YO) 2 (SiO 4 ) 2 . Crystals, often prismatic, rough and coarse; commonly in masses. Cleavage none. Fracture conchoidal or splintery. Brittle. H. = 6'5-7. G. = 4'0-4'5; normally 4'36-4 '47 (anisotropic), 4'24-4 '29 (isotropic and amorphous from alteration). Luster vitreous to greasy. Color black, greenish black, also brown. From near Falun and Ytterby, Sweden; Hittero, Norway; also in Llano Co., Texas, in nodular masses and rough crystals, sometimes up to 40 or 60 pounds in weight. Crystals from Kumak, East Greenland. The yttrium earths or " gadolinite-earths " (partly replaced by the oxides of cerium, lanthanum and didymium) form a complex group which contains considerable erbium, also several new elements (ytterbium, scandium, etc.) of more or less definite character. Yttrialite. A silicate of thorium and the yttrium metals chiefly. Massive; amor- phous. G. = 4-575. Color on the fresh fracture olive-green, changing to orange-yellow on surface. Associated with the gadolinite of Llano Co., Texas. Rowlandite. An yttrium silicate, occurring massive with gadolinite of Llano Co., Texas; color drab-green. Thalenite. An yttrium silicate. In tabular or prismatic monoclinic crystals. H. = 6*5. G. = 4'2. Color flesh-red. /3 = 174. Found in Sweden at Osterby in Dale- carlia and at Askagen in Wermland. Thortveitite. A silicate of the yttrium metals, (Sc,Y) 2 Si 2 O 7 . Orthorhombic. In radi- ating groups of large tapering crystals. Prismatic cleavage. H. = 6-7. G. = 3*57. Color grayish green to white when altered. Usually translucent. Difficultly fusible. Found in pegmatite in Iveland parish, Satersdalen, Norway. Mackintoshite. Silicate of uranium, thorium, cerium, etc. Massive. Color black. Llano Co., Texas. Epidote Group. Orthorhombic and Monoclinic ii in ii in in Basic Orthosilicates, HR^R 3 Si 3 O 13 or R 2 (ROH)R 2 (SiO 4 ) 3 ii ii in in in R = Ca,Fe; R = Al,Fe,Mn,Ce, etc. a. Orthorhombic Section a Zoisite Ca 2 (AlOH)Al 2 (SiO 4 ) 3 0'6196 1 0'3429 j8. Monoclinic Section mCa 2 (AlOH)Al 2 (SiO 4 ) 3 Piedmontite Ca2(AlOH)(Al,Mn) 2 (SiO 4 ) 3 1-6100 Allanite (Ca,Fe) 2 (A10H) (Al,Ce,Fe) 2 (SiO 4 ) 3 1*5509 1-8036 64 37' 1-8326 64 39' 1-7691 64 59' 530 DESCRIPTIVE MINERALOGY The EPIDOTE GROUP includes the above complex orthosilicates. The monoclinic species agree closely in form. To them the orthprhombic species zoisite is also related in angle, its prismatic zone corresponding to the mono- clinic orthodomes, etc. Thus we have: Zoisite mm'", 110 A 110 = 63 34'. Epidote cr, 001 A 101 = 63 42'. . uu', 021 A 021 = 68 54'. mm', 110 A 110 = 70 4', etc. There seems to be, however, a monoclinic calcium compound, having the com- position of zoisite, but monoclinic and strictly isomorphous with ordinary epidote; it is called dinozoisite. ZOISITE. J Orthorhombic. Axes a : b : c = 0'6196 : 1 : 0-34295. ^ mm'", 110 A HO = 63 34'. jf, Oil A Oil = 37 52'. dd', 101 A 101 = 57 56'. oo'", 111 A 111 = 33 24'. Crystals prismatic, deeply striated or furrowed vertically, and seldom distinctly terminated. Also massive; columnar to compact. Cleavage: b (010) very perfect. Fracture uneven to subconchoidal. Brittle. H. = 6-6 -5. G. = 3-25-3-37. Luster vitreous; on the cleavage- face, b (010), pearly. Color grayish white, gray, yellowish brown, greenish gray, apple-green; also peach-blossom-red to rose-red. Streak uncolored. Transparent to subtranslucent. i Pleochroism strong in pink varieties. Optically +. Ax. pi. usually || b (010); also || c (001). Bx _L a (100). Dispersion strong, p < v; also p > v. Axial angle variable even in the same crystal. 2V = 0-60. a = 1-700. = 1-703. 7 = 1*706. Var. 1. Ordinary. Colors gray to white and brown; also green. Usually in indistinct prismatic or columnar forms; also in fibrous aggregates. G. = 3'226-3'381. Unionite is a very pure zoisite. 2. Rose-red or Thulite. Fragile; pleochroism strong. 3. Compact, massive. Includes the essential part of most of the mineral material known as saussurite (e.g., in saussurite-gabbro), which has arisen from the alteration of feldspar. Comp. HCa 2 Al 3 Si 3 13 or 4CaO.3Al 2 O 3 .6SiO 2 .H 2 O = Silica 397, alu- mina 33-7, lime 24-6, water 2*0 = 100. The alumina is sometimes replaced by iron, thus graduating toward epidote, which has the same general for- mula. Pyr., etc. B.B. swells up and fuses at 3-3'5 to a white blebby mass. Not decom- posed by acids; when previously ignited gelatinizes with hydrochloric acid. Gives off water when strongly ignited. Diff. Characterized by the columnar structure; fusibility with intumescence; re- sembles some amphibole. Micro. Distinguished in thin sections by its high relief and very low interference- colors; lack of color and biaxial character. From epidote it is distinguished by its lack of color and low birefringence; from vesuvianite by its color and biaxial character. Thin sections frequently show the "ultra blue" (p. 520) between crossed nicols. Obs. Occurs especially in those crystalline schists which have been formed by the dynamic metamorphism of basic igneous rocks containing plagioclase rich in lime. Com- monly accompanies some one of the amphiboles (actinolite, smaragdite, glaucophane, etc.); thus in amphibolite, glaucophane schist, eclogite; often associated with corundum. The original zoisite is that of the eclogite of the Saualpe in Carinthia (saualpite] . Other localities are: Kauris in Salzburg; Sterzing, etc., in Tyrol, Austria; the Fichtelgebirge in Bavaria; Marschendorf in Moravia; Saastal in Switzerland; the island of Syra, one of the Cyclades, in glaucophane schist. In crystals from Chester, Mass.. Thulite occurs at Kleppan in Tellemarken, Norway, and at Traversella in Piedmont, Italy. SILICATES 531 EPIDOTE. Pistacite. Monoclinic. Axes a : b : c 1-5787 : 1 mm' ca, ce, cr, ar'. 894 110 A 110 = 109 56'. 001 A 100 = 001 A 101 = 001 A 101 = 100 A 101 = 64 37'. 34 43'. 63 42'. 51 41'. : 1-8036; 0_= 64 37'. d, 001 A 201 = 89 26' co, 001 A Oil = 58 28' en, 001 A 111 = 75 11' an"', 100 A 111 = 69 2' rm"', 111 A 111 = 70 29' 897 Twins: tw. pi. a (100) common, often as embedded tw. lamellae. Crystals usually prismatic || the ortho-axis b and terminated at one .extremity only; passing into acicular forms; the faces in the zone a (100) /c (001) deeply striated. Also fibrous, divergent or parallel; granular, particles of various sizes, sometimes fine granular, and forming rock-masses. Cleavage: c (001) perfect; a (100) imperfect. Fracture uneven. Brittle. H. = 6-7. G. = 3-25-3-5. Luster vitreous; on c (001) inclining to pearly or resinous. Color pistachio-green or yellowish green to brownish green, greenish black, and black; sometimes clear red and yellow; also gray and grayish white, rarely colorless. Streak uncolored, grayish. Transparent to opaque: generally subtranslucent. Pleochroism strong : vibrations 1 1 Z green, Y brown and strongly absorbed, X yellow. - Absorption usually Y > Z > X] but sometimes Z > Y > X in the variety of epidote common in rocks. Often exhibits idiophano-us figures; best in sections normal to an optic axis, but often to be observed in natural Crystals (Sulzbach), especially if flat- tened || r(101). (See p. 288.) Optically-. Ax. pi. || b (010). Bx.a.r A c axis = - 2 56'. Hence Z J_ a (100) nearly. Dispersion inclined, strongly marked; of the axes feeble, p > v. Axial angle large, a = 1-729. /3 = 1'754. 7 = 1-768. Var. Epidote has ordinarily a peculiar yellowish green (pistachio) color, seldom found in other minerals. But this color passes into dark and light shades black on one side and brown on the other; red, yellow and colorless varieties also occur. Var. 1. Ordinary. Color green of some shade, as described, the absent, (a) In crystals, (b) Fibrous, (c) Granular massive, (d) )istachio tint rarely >corza is epidote sand from the gold washings in Transylvania. The Arendal, Norway, epidote (Arendalite) is mostly in dark green crystals; that of Bourg d'Oisans, Dauphine, France, (Thallite, Del- 532 DESCRIPTIVE MINERALOGY phinite Oisanite) in yellowish green crystals, sometimes transparent. Puschkinite includes crystals from the auriferous sands of Ekaterinburg, Ural Mts. Achmatite is ordinary epi- dote from Achmatovsk, Ural Mts. A variety from Garda, Hoste Island, Terra del Fuego, is colorless and resembles zoisite. 2. The Bucklandite from Achmatovsk, Ural Mts., described by Hermann, is black with a tinge of green, and differs from ordinary epidote in having the crystals nearly symmetrical and not, like other epidote, lengthened in the direction of the ortho-axis. G. = 3 '51. 3. Withamite. Carmine-red to straw-yellow, strongly pleochroic; deep crimson and straw-yellow. H. = 6-6'5; G. = 3 '137; in small radiated groups. From Glencoe, in Argyleshire, Scotland. Sometimes referred to piedmontite, but contains little MnO. 4. Tawmanite is a chromium-bearing epidote from Tawman, Kachin Hills, Upper Burma. Deep green color and strong pleochroism, emerald-green to bright yellow. Comp. HCa*(Al,Fe) 8 SiOi8 or H 2 O.4CaQ.3(Al > Fe 8 ) 2 O 8 .6SiO2, the ratio of aluminium to iron varies commonly from 6 : 1 to 3 : 2. Percentage com- position: For Al : Fe = 3 : 1 SiO 2 37'87, A1 2 O 3 24'13, Fe 2 O 3 12'60, CaO 23'51, H 2 O 1'89 = 100 Clinozoisite is an epidote without iron, having the composition of zoisite; fouqueite is probably the same from an anorthite-gneiss in Ceylon. Picroepidote is supposed to contain Mg in place of Ca. Pyr., etc. In the closed tube gives water on strong ignition. B.B. fuses with in- tumescence at 3-3 '5 to a dark brown or black mass which is generally magnetic. Reacts for iron and sometimes for manganese with the fluxes. Partially decomposed by hydro- chloric acid, but when previously ignited, gelatinizes with acid. Decomposed on fusion with alkaline carbonates. Diff . Characterized often by its peculiar yellowish green (pistachio) color ; readily fusible and yields a magnetic globule B.B. Prismatic forms often longitudinally striated, but they have not the angle, cleavage or brittleness of tremolite; tourmaline has no distinct cleavage, is less fusible (in common forms) and usually shows its hexagonal form. Micro. Recognized in thin sections by its high refraction; strong interference-colors rising into those of the third order in ordinary sections; decided color and striking pleochro- ism; also by the fact that the plane of the optic axes lies transversely to the elongation of the crystals. Obs. Epidote is commonly formed by the metamorphism (both local igneous and of general dynamic character) of impure calcareous sedimentary rocks or igneous rocks con- taining much lime. It thus often occurs in gneissic rocks, mica schist, amphibole schist, serpentine; so also in quartzites, sandstones and limestones altered by neighboring igneous rocks. Often accompanies beds of magnetite or hematite in such rocks. Has also been found in granite (Maryland), and regarded as an original mineral. It is often associated with quartz, feldspar, actinolite, axinite, chlorite, etc. It some- times forms with quartz an epidote rock, called epidosite. A similar rock exists at Mel- bourne in Canada. A gneissoid rock consisting of flesh-colored orthoclase, quartz and epidote from the Unaka Mts. (N. C. and Tenn.) has been called unakyte. Beautiful crystallizations come from Bourg d'Oisans, Dauphine, France; the Ala valley and Traversella, in Piedmont, Italy; Elba; Zermatt, Switzerland; Zillertal in Tyrol, Austria; also in fine crystals from the Knappenwand in the Untersulzbachtal, Pinzgau, Austria, associated with asbestus, adularia, apatite, titanite, scheelite; further at Striegau, Silesia; Zoptau, Moravia; Arendal, Norway; the Achmatovsk mine near Zlatoust, Ural Mts. In North America, occurs in N. H., at Franconia and Warren. In Mass., at Hadlyme and Chester in crystals in gneiss; at Athol, in syenitic gneiss, in fine crystals; Newbury, Sr limestone - In Conn., at Haddam, in large splendid crystals. In N. Y., near Amity; Monroe, Orange Co.; Warwick, pale yellowish green, with titanite and pyroxene. In N. C., at Hampton's, Yancey Co.; White's mill, Gaston Co.; Franklin, Macon Co.; in crystals and crystalline masses in quartz at White Plains, Alexander Co. In Mich., in the Lake Superior region, at many of the mines. Crystals from Seven Devils mining district, Idaho; from Riverside, Cal.; from Sulzer, Prince of Wales Island, Alaska. (( Epidote was named by Haiiy, from the Greek e7ri5o Y > Z. Optically +. Ax. pi. || b (010). Bx a . r A c axis = + 82 34', X A caxis = - 6 to - 3. = 173. Occurs with manganese ores at St. Marcel, Pied- mont, Italy. In crystalline schists on lie de Groix, France; in glaucophane-schist in Japan. Occasionally in quartz porphyry, as in the antique red porphyry of Egypt, also that of South Mountain, Pa. Hancockite. Belongs in Epidote Group containing, PbO, MnO, CaO, SrO, MgO, A1 2 O 3 , Fe 2 O 3 , Mn 2 Os. Crystals which are very small and lath shaped show characteristic epidote habit and closely related angles. Brownish red. H. = 6-7. G. = 4'0. Found at Franklin, N. J. ALLANITE. Orthite. Monoclinic. Axes, p. 529. In angle near epidote. Crystals often tabu- lar 1 1 a (100) ; also long and slender to acicular prismatic by elongation 1 1 axis b. Also massive and in embedded grains. Cleavage: a (100) and c (001) in traces; also m (110) sometimes observed. Fracture uneven or subconchoidal. Brittle. H. = 5-5-6. G. = 3-0-4-2. Luster submetallic, pitchy or resinous. Color brown to black. Subtranslu- cent to opaque. Pleochroism strong: Z brownish yellow, Y reddish brown, X greenish brown. Optically . Ax. pi. || b (010). Bx a A caxis = 32J approx. j8 = 1*682. Birefringence variable. Also isotropic and amorphous by alteration analogous to gadolinite. Var.-^ Allanite. The original mineral was from East Greenland, in tabular crystals or plates. Color black or brownish black. G. = 3'50-3'95. Bucklandite is anhydrous allanite in small black crystals from a magnetite mine near Arendal, Norway. Bagration- ite occurs in black crystals which are like the bucklandite of Achmatovsk (epidote). Orthite included, in its original use, the slender or acicular prismatic crystals, containing some water, from Finbo, near Falun, Sweden. But these graduate into massive forms, and some orthites are anhydrous, or as nearly so as most allanite. The name is from 6p66s straight. ii in ii Comp. Like epidote HRR 3 Si 3 Oi 3 or H 2 0.4R0.3R 2 3 .6Si02 with R m = Ca and Fe, and R. = Al,Fe, the cerium metals Ce, Di, La, and in smaller amounts those of the yttrium group. Some varieties contain considerable water, but probably by alteration. Pyr., etc. Some varieties give much water in 1 the closed tube, and all kinds yield a small amount on strong ignition. B.B. fuses easily and swells up (F. = 2 '5) to a dark, blebby, magnetic glass. With the fluxes reacts for iron. Most varieties gelatinize with hydrochloric acid, but if previously ignited are not decomposed by acid. Obs. Occurs in albitic and common feldspathic granite, gneiss, syenite, zircon syenite, porphyry. Thus in Greenland; Norway; Sweden; Striegau, Silesia. Also in white lime- stone as at Auerbach on the Bergstrasse, Germany; often in mines of magnetic iron. Rather common as an accessory constituent in many rocks, as in andesite, diorite, dacite, rhyolite, the tonalite of Mt. Adamello, Austria, the scapolite rocks of Odegaarden, Norway, etc. Sometimes inclosed as a nucleus in crystals of the isomorphous species, epidote. From Madagascar. At Vesuvius in ejected masses with sanidine, sodalite, nephelite, hornblende, etc. Similarly in trachytic ejected masses at the Laacher See, Germany (bucklandite). In Mass., at the Bolton quarry. In N. Y., Moriah, Essex Co., with magnetite and apatite; at Monroe, Orange Co. In N. J., at Franklin Furnace with feldspar and mag- netite. In Pa., at South Mountain, near Bethlehem, in large crystals; at East Bradford; near Eckhardt's furnace, Berks Co., abundant. In Va., in large masses in Amherst Co.; also in Bedford, Nelson, and Amelia counties. In N. C., at many points. At the Devil's Head Mt., Douglas Co., Col. In Texas in Llano Co. 534 DESCRIPTIVE MINERALOGY AXINITE. Triclinic. Axes a : b : c = 04921 : 1 : 0-4797; a = 82 54', ft = 91 52', T = 131 32'. ftoa 900 901 M Dauphine" Poloma Bethlehem, P; am, 100 A 110 = 15 34'. aM, 100 A 110 = 28 55'. as, 100 A 201 = 21 37'. Mr, 110 A 111 = 45 15'. mr, 110 A 111 = 64 22'. ras, 110 A 201 = 27 57'. Also mas- Crystals usually broad and acute-edged, but varied in habit, sive, lamellar, lamellae often curved; sometimes granular. Cleavage: b (010) distinct. Fracture conchoidal. Brittle. H. = 6'5-' G. = 3-271-3-294. Luster highly glassy. Color clove-brown, plum-blue, and pearl-gray; also honey-yellow, greenish yellow. Streak uncoloi Transparent to subtranslucent. Pleochroism strong. Optically . Ax. pi. and Bx a approximately J_ x (111). Axial angles variable. 2V = 65-70. = 1-68 (approx.). Pyroelectric (p. 307). Comp. A boro-silicate of aluminium and catcium with varying amounts of iron and manganese. Formula, RyR^ (SiOJs. R = Calcium chiefly, sometimes in large excess, again in smaller amount and manganese prominent; iron is present in small quantity, also magnesium and basic hydro- gen. Pyr., etc. B.B. fuses readily with intumescence, imparts a pale green color to the O.F., and fuses at 2 to a dark green to black glass; with borax in O.F. gives an amethystine bead (manganese), which in R.F. becomes yellow (iron). Fused with a mixture of bisul- phate of potash and fluorite on the platinum loop colors the flame green (boric acid) . Not decomposed by acids, but when previously ignited, gelatinizes with hydrochloric acid. Obs. Axinite occurs in clove-brown crystals; near Bourg d'Oisans in Dauphine, France; at Andreasberg, Harz Mts., Germany; Striegau, Silesia; on Mt. Skopi, in eastern Switzerland; Elba; at the silver mines of Kongsberg, Norway; Nordmark, Sweden; near Miask in the Ural Mts.; in Cornwall, England, of a dark color, at the Botallack mine near St. Just, etc. From Obira, Japan. In the United States, at Phippsburg, Me.; Franklin Furnace, N. J., honey-yellow; at Bethlehem, Pa.; in Cal. at Bonsall, San Diego Co., at Riverside, Riverside Co., and at Consumers Mine, Amador Co. Named from a^lvij, an axe, in allusion to the form of the crystals. PREHNITE. Orthprhombic-hemimorphic. Axes a : b : c = 0-8401 : 1 : 0-5549. Distinct individual crystals rare; usually tabular || c (001); sometimes prismatic, mm 7 " (110) A (HO) = 80 4'; again acute pyramidal. Commonly SILICATES 535 in groups of tabular crystals, united by c (001) making broken forms, often barrel-shaped. Reniform, globular, and stalactitic with a crystalline surface. Structure imperfectly columnar or lamellar, strongly coherent; also compact granular or impalpable. Cleavage: c (001) distinct. Fracture uneven. Brittle. H. = 6-6 '5. G. = 2 -80-2 -95. Luster vitreous; on base weak pearly. Color light green, oil-green, passing into white and gray; often fading on exposure. Sub- transparent to translucent. Streak uncolored. Comp. An acid orthosilicate, H 2 Ca 2 Al 2 (Si04)3 = Silica 43*7, alumina 24-8, lime 27'1, water 4-4 = 100. Prehnite is sometimes classed with the zeolites, with which it is often associated; the, water here, however, has been shown to go off only at a red heat, and hence plays a differ- ent part. Pyr., etc. In the closed tube yields water. B.B. fuses at 2 with intumescence to a blebby enamel-like glass. Decomposed slowly by hydrochloric acid without gelatinizing; after fusion dissolves readily with gelatinization. Diff. B.B. fuses readily, unlike beryl, green quartz, and chalcedony. Its hardness is greater than that of the zeolites. Obs. Occurs chiefly in basic eruptive rocks, basalt, diabase, etc., as a secondary min- eral in veins and cavities, often associated with some of the zeolites, also datolite, pectolite, calcite, but commonly one of the first formed of the series; also less often in granite, gneiss, syenite, and then frequently associated with epidote; sometimes associated with native copper, as in the Lake Superior region. At St. Christophe, near Bourg d'Oisans in Dauphine, France; Fassatal, Tyrol, Austria; the Ala valley in Piedmont, Italy; in the Harz Mts. near Andreasberg, Germany; in granite at Striegau, Silesia; Arendal, Norway; ^Edelfors in Sweden (edelite)', at Corstorphine Hill, near Edinburgh, Scotland; Mourne Mts., Ireland. In the United States, finely crystallized at Farmington, Conn.; Paterson and Bergen Hill, N. J.; in syenite, at Somerville, Mass.; on north shore of Lake Superior, and the copper region. Named (1790) after Col. Prehn, who brought the mineral from the Cape of Good Hope. Harstigite. An acid orthosilicate of manganese and calcium. In small colorless pris- matic crystals. H. = 5'5. G. = 3 '049. Indices, 1 '678-1 '683. From the Harstig mine, near Pajsberg, Wermland, Sweden. Cuspidine. Contains silica, lime, fluorine, and from alteration carbon dioxide: formula perhaps Ca 2 Si(O,F 2 ) 4 . In minute spear-shaped crystals. H. = 5-6. G. = 2-853-2'860. Color pale rose-red. Indices, 1 '590-1 '602. From Vesuvius, in ejected masses in the tufa of Monte Somma. From Franklin, N. J. IV. Subsilicates The species here included are basic salts, for the most part to be referred either to the metasilicates or orthosilicates, like many basic compounds already included in the preceding pages. Until their constitution is definitely settled, however, they are more conveniently grouped by themselves as SUBSILICATES. It may be noted that those species having an oxygen ratio of silicon to bases of 2 : 3, like topaz, andalusite, sillimanite, datolite, etc., also calamine, car- pholite, and perhaps tourmaline, are sometimes regarded as salts of the hypo- thetical parasilicic acid, HeSiOs. The only prominent group in this subdivision is the HUMITE GROUP. 536 DESCRIPTIVE MINERALOGY Humite Group a :b 1-0803 : 1 : T8861 90 C 1-0863 6 1-0802 1 : 3-1447 90 C c 4-4033 T0803 : 1 : 5'6588 90 C Prolectite [Mg(F,OH)] 2 Mg[SiO 4 ]i? Monoclmic Chondrodite [Mg(F,OH)] 2 Mg 3 [Si0 4 ]2 Monoclmic Humite [Mg(F,OH)] 2 Mg5[Si0 4 ]3 Orthorhombic Clinohumite [Mg(F,OH)] 2 Mg 7 [SiO 4 ] 4 Monoclinic The species here included form a remarkable series both as regards crys- talline form and chemical composition. In crystallization they have sensibly the same ratio for the lateral axes, while the vertical axes are almost exactly in the ratio of the numbers 3:5:7:9 (see also below). Furthermore, though one species is orthorhombic, the others monoclinic, they here also correspond closely, since the axial angle in the latter cases does not sensibly differ from 90. In composition, as shown by Penfield and Howe (also Sjogren), the three species are basic orthosilicates in each of which the univalent g (MgF) or (MgOH) enters, while the Mg atoms present are in the rati<^; 3 : 5 : 7. The composition given for Prolectite is theoretical only, 1 -i that which would be expected from its crystallization. In physr characters these species are very similar, and several of them may o<|ij together at the same locality and even intercrystallized in pa lamellae. % . The species of the group approximate closely in angle to chrysolite and chrysoi The axial ratios may be compared as follows: Prolectite a Chondrodite. a Humite b Clinohumite a Chrysolite b Chrysoberyl b CHONDRODITE HUMITE CLINOHUMITE. Axial ratios as given above. Habit varied, Figs. 902 to 910. Twins common, the twinning planes inclined 60, also 30, to c (001) in the brachy- dome or clinodome zone, hence the axes crossing at angles near 60; often repeated as trillings and as polysynthetic lamellae (cf. Fig. 609, p. 299). Also twins, with c (001) as tw. plane. Two of the three species are often twinned together. Cleavage: c (001) sometimes distinct. Fracture subconchoidal to uneven. Brittle. H. = 6-6-5. G. = 3-1-3-2. Luster vitreous to resinous. Color white, light yellow, honey-yellow to chestnut-brown and garnet- or hyacinth- red. Pleochroism sometimes distinct. Optically .+ . Chondrodite. Absorption X > Z > Y. Optically +. Ax. pi. and Bx a J_ b (010). Bx A c axis = X A c axis = + 25 52' Brewster; 28 56' Kafveltorp; 30 approx., Mte. Somma. = 1-619; 7 - a = 0'031. 2V = 80. Humite. Ax. pi. || c (001). Bx J_ a (100). = 1'643. 7 - a = 0'035. Clinohumite. Ax. pi. and Bx a _L b (010). Bx A c axis = + 11-12; 7^ approx., Brewster. 2V = 76. = 1-670. 7 - a = 0'038. b : \c = 1-0803 -i 0-6287 6 :\c = 1-0863 1 0-6289 a :$c = 1-0802 1 0-6291 b : $c = 1-0803 -| 0-6288 2a : c = 1-0735 1 0-6296 2a: c = 1-0637 i 0-6170 % SILICATES 903 537 904 Figs. 902, 903, Chondrodite, Brewster, N. Y. 906 905 103 Chondrodite, Sweden 907 Projection on (001) Projection on (Olb) Figs. 905, 906, Chondrodite, Mte. Somma 908 Humite, Sweden 910 Humite, Vesuvius Clinohumite, Brewster Projection on (010) Clinohumite, Mte. Somma Comp. Basic fluosilicates of magnesium with related formulas as shown in the table above. Hydroxyl replaces part of the fluorine, and iron often takes the place of magnesium. Pyr., etc. B.B. infusible; some varieties blacken and then burn white. Fused with potassium bisulphate in the closed tube gives a reaction for fluorine. With the fluxes a reaction for iron. Gelatinizes with acids. Heated with sulphuric acid gives off silicon fluoride. 538 DESCRIPTIVE MINERALOGY Obs. -Chondrodite, humite, and elinohumite all occur at Vesuvius in the ejected masses both of limestone or feldspathic type found on Monte Somma. They are associated with chrysolite, biotite, pyroxene, magnetite, spinel, vesuvianite, calcite, etc.; also less often with sanidine, meionite, nephelite. Of the three species, humite is the rarest and elinohumite of most frequent occurrence. They seldom all occur together in the same mass, and only rarely two of the species (as humite and elinohumite) appear together. Occasionally elinohumite interpenetrates crystals of humite, and parallel intergrowths with chrysolite have also been observed. Chondrodite occurs at Mte. Somma, Vesuvius, as above noted; at Pargas, Finland, honey- yellow in limestone; at Kafveltorp, Nya-Kopparberg, Sweden, associated with chalcopyrite, galena, sphalerite. At Brewster, N. Y., at the Tilly Foster magnetic iron mine in deep garnet-red crystals. Also probably at numerous points where the occurrence of "chon- drodite" has been reported. Humite also occurs at the Ladu mine near Filipstadt, Sweden, with magnetite in crys- talline limestone. In crystalline limestone with elinohumite in Andalusia, Spain. Also in large, coarse, partly altered crystals at the Tilly Foster iron-mine at Brewster, N. Y. Noted at Franklin Furnace, N. J. Clinohumite occurs at Mte. Somma and in Andalusia; in crystalline limestone near Lake Baikal in East Siberia; at Brewster, N. Y., in rare but highly modified crystals. Hydroclinohumite is a titaniferous variety (originally called titanolivine) from Ala Valley, Piedmont, Italy. Prolectite is from the Kq mine, Nordmark, Sweden; very rare; imperfectly known. Numerous other localities of "chondrodite" have been noted, chiefly in crystalline limestone; most of them are probably to be referred to the species chondrodite, but the identity in many cases is yet to be proved. At Brewster large quantities of massive "chon- drodite" occur associated with magnetite, enstatite, ripidolite, and from its extensive alteration serpentine has been formed on a large scale. The granular mineral is common in limestone in Sussex Co., N. J., and Orange Co., N. Y., associated with spinel, and occa- sionally with pyroxene and corundum. Also in Mass., at Chelmsford, with scapolite; at South Lee, in limestone. In Canada, in limestone at St. Jerome, Grenville, etc., abundant. The name chondrodite is from xwSpos, a grain, alluding to the granular structure. Humite is from Sir Abraham Hume. Leucophcenicite. Mn 5 (MnOH) 2 (SiO4)3, similar to the humite type of formula. Monoclinic. In striated crystals elongated parallel to ortho-axis. Massive. H. = 5*5-6. G. = 3'8. Color light purplish red. Fusible. From Franklin, N. J. . ILVAITE. Lievrite. Yenite. Orthorhombic. Axes a : b : c = 0'6665 : 1 : 0*4427. oil mm'", 110 A lIO = 67 22'. rr' 101 A 101 = 67 11'. as', 120 A 120 = 73 45'. oo', 111 A Til = 62 33'. Commonly in prisms, with prismatic faces vertically striated. Columnar or compact massive. Cleavage: 6(010), c(001) rather distinct. Fracture uneven. Brittle. H. = 5-5-6. G. = 3'99-4'05. Luster submetallic. Color iron-black or dark grayish black. Streak black, inclining to green or brown. Opaque. ^ Comp. - - CaFe 2 (FeOH) (SiO 4 ) 2 or H 2 O.CaO.4FeO.Fe 2 O 3 . 4SiO 2 = Silica 29 -3, iron sesquioxide 19 -6, iron protoxide 35 -2, lime 137, water 2-2 = 100. Manganese may replace part of the ferrous iron. Pyr., etc. B.B. fuses quietly at 2'5 to a black magnetic bead. With the fluxes reacts lor iron. Some varieties give also a reaction for manganese. Gelatinizes with hydro- chloric acid. Obs. Found on Elba in dolomite; on Mt. Mulatto near Predazzo, Tyrol, Austria, in granite; Schneeberg, Saxony; Fossum, in Norway. In crystals from Siorarsiut, South Lrreenland. Reported as formerly found at Cumberland, R. I.; also at Milk Row quarry, SILICATES 539 Somerville, Mass. In fine crystals from South Mountain mine, Owyhee Co., Idaho. Named Ilvaite from the Latin name of the island (Elba). Ardennite. Dewalquite. A vanadio-silicate of aluminium and manganese; also con- taining arsenic. In prismatic crystals resembling ilvaite. H. = 6-7. G. = 3*620. Yel- low to yellowish brown. Index about 179. Found at Salm Chateau in the Ardennes, Belgium. Langbanite. Manganese silicate with ferrous antimonate; formula doubtful. Rhom- bohedral-tetartohedral. In iron-black hexagonal prismatic crystals. H. = 6'5. G. = 4'918. Luster metallic. From Langban, Sweden. The following are rare lead silicates. See also p. 498. Kentrolite. Probably 3PbO.2Mn 2 O3.3SiO 2 . In minute prismatic crystals; often in sheaf -like forms; also massive. H. =5. G. =6'19. Color dark reddish brown; black on the surface. From southern Chile; Langban and Jakobsberg, Sweden; Bena Padru, near Ozieri, Sardinia. Melanotekite. 3PbO.2Fe 2 O 3 .3SiO 2 or (Fe 4 O8)Pb 8 (SiO 4 )s. Orthorhombic; prismatic. Massive; cleavable. H. = 6'5. G. = 573. Luster metallic to greasy. Color black to blackish gray. Occurs with native lead at Langban, Sweden. Also in crystals resembling kentrolite at Hillsboro, N. M. Bertrandite. H 2 Be 4 Si?O 9 or H 2 O.4BeO.2SiO 2 . Orthorhombic-hemimorphic. In small tabular or prismatic crystals. H. = 6-7. G. = 2'59-2'60. Colorless to pale yellow. Optically . = T603. Usually occurs in feldspathic veins, often with other beryllium minerals as a result of the alteration of beryl. At the quarries of Barbin near Nantes, France; Pisek, Bohemia; Irkutka Mt., Altai Mts., Russia; Ireland, Southern Norway; Cornwall, England; Mt. Antero, Chaff ee Co., Col., with phenacite; Amelia Court-House, Va.; Oxford Co., Me. 07834 : 1 : 04778. 912 913 CALAMINE. Smithsonite. Hemimorphite. Orthorhombic-hemimorphic. Axes a : b : c mm'", 110 A 101 = 76 9'. ss', 101 A 101 = 62 46'. ', 301 A 301 = 122 41'. ee', Oil A Oil = 51 5'. w', 031 A 031 = 110 12'. w'", 121 A 121 = 78 26'. Crystals often tabular || b (010); also pris- matic; faces 6 vertically striated. Usually implanted and showing one extremity only. Often grouped in sheaf -like forms and form- ing drusy surfaces in cavities. Also stalac- titic, mammillary, botryoidal, and fibrous forms; massive and granular. Cleavage: m (110) perfect; s( 101) less so; c (001) in traces. Fracture uneven to subconchoidal. Brittle. H. the latter when crystallized. G. = 3 -40-3 -50. Luster vitreous; subpearly, sometimes adamantine. Color white; sometimes with a delicate bluish or greenish shade; also yellowish to brown. Streak white. Trans- parent to translucent. Optically +. 2V = 46. a = 1-614. (3 = 1*617. 7 = 1-636. Strongly pyroelectric. Comp. H 2 ZnSiO 5 or (ZnOH) 2 SiO 3 or H 2 O.2ZnO.SiO 2 = Silica 25-0, zinc oxide 67 -5, water 7-5 = 100. The water goes off only at a red heat; unchanged at 340 C. Pyr., etc. In the closed tube decrepitates, whitens, and gives off water. B.B. almost infusible (F. =6). On charcoal with soda gives a coating which is yellow while hot, and = 4-5-5, c (001) 540 DESCRIPTIVE MINERALOGY white on cooling Moistened with cobalt solution, and heated in O.F., this coating assumes a bright green color, but the ignited mineral itself becomes blue. Gelatinizes with acids even when previously ignited. . ,,..,. .,, ., f)iQ Characterized by its mfusibihty; reaction for zinc; gelatimzation with acids. Resembles some smithsonite (which effervesces with acid), also prehnite. Obs. Calamine and smithsonite are usually found associated in veins or beds in stratified calcareous rocks accompanying sulphides of zinc, iron and lead. Thus at Aix-la- Chapelle Germany; Raibel and Bleiberg, in Carinthia; Moresnet in Belgium; Rezbanya, and Schemnitz, Hungary. At Roughten Gill, in Cumberland; at Alston Moor, white; near Matlock, in Derbyshire; Leadhill, Scotland; at Nerchinsk, m eastern Siberia. From Santa Eulalia, Chihuahua, Mexico. In the United States occurs at Sterling Hill, near Ogdensburg, N. J., in fine clear crystal- line masses. In Pa., at the Perkiomen and Phenixville lead mines; at Friedensville. Abundant in Va., at Austin's mines in Wythe Co. With the zinc deposits of southwestern Missouri, especially about Granby, both as crystallized and massive calamine. Crystals from Leadville, Col; from Organ Mts., N. M.; Elkhorn Mts., Mon. At the Emma mine, Cottonwood Canon, Utah. The name Calamine (with Galmei of the Germans) is commonly supposed to be a cor- ruption of Cadmia. Agricola says it is from calamus, a reed, in allusion to the slender forms (stalactitic) common in the cadmia fornacum. Use. An ore of zinc. Clinohedrite. H 2 CaZnSiO 5 . Monoclinic-clinohedral (see Figs. 352, 353, p. 138). H. = 5'5. G. = 3'33. Colorless or white to amethystine. Index, 1 '67. From Franklin, N. J. Stokesite. Perhaps H^aSnSisOn. Orthorhombic. Prismatic cleavage. H. = 6. G. = 3'2. Colorless. = 1*61. From Roscommon Cliff, St. Just, Cornwall. Carpholite. H 4 MnAl s Si2O 10 . In radiated and stellated tufts. G. = 2'935. Color straw- to wax-yellow. Biaxial, . = 1*63. Occurs at the tin mines of Schlaggenwald, Bohemia; Wippra, in the Harz Mts., on quartz, etc. Lawsonite. H 4 CaAl2Si 2 Oio. In prismatic orthorhombic crystals; mm'", 110 A 110 = 67 16'. G. = 3*09. Luster vitreous to greasy. Colorless, pale blue to grayish blue. Optically -f-. /3 = 1'669. Occurs in crystalline schists of the Tiburn peninsula, Marin Co., Gal.; also in the schists of Pontgibaud, France, and New Caledonia. Hibschite. Same as for lawsonitc, H4CaAl 2 Si2Oio. In minute isometric crystals, usually octahedrons. H. = 6. G. = 3'0. Colorless or pale yellow. Refractive index, 1 '67. In- fusible. From the phonolite of Marienberg, Bohemia. Associated with melanite. Cerite. A silicate of the cerium metals chiefly, with water. Crystals rare; commonly massive; granular. H. = 5'5. G. = 4*86. Color between clove-brown and cherry-red to gray. Indices, 1 '83-1 '93. Occurs at Bastnas, near Riddarhyttan, Sweden. Toernebohmite. A silicate of the cerium metals, chiefly, R3(OH)(SiO 4 ) 2 . Monoclinic? Color, green to olive. /3 = 1'81. Biaxial, +. Strong dispersion, P < v. Pleochroic, rose to blue-green. From Bastnas, near Riddarhytta.n, Sweden. Beckelite. Ca3(Ce,La,Di) 4 Si3O 15 . Isometric Crystals small, often microscopic. Cubic cleavage. H. = 5. G. = 4*1. Color yellow. Infusible. Occurs with nepheline syenite rocks near Mariupol, Russia. Hellandite. A basic silicate chiefly of the cerium metals, aluminium, manganese and calcium. Monoclinic. Prismatic habit. H. = 5*5. G. = 37. Color brown. Fusible. Found in pegmatite near Kragero, Norway. Bazzite. A silicate of scandium with other rare earth metals, iron and a little soda. Hexagonal. In minute prisms, often barrel shaped. H. = 6*5. G. = 2'8. Color azure- i Transparent in small individuals. Optically -. Refractive indices, co = 1'626. e = rb05. Strongly dichroic, co = pale greenish yellow, e = azure-blue. Infusible. In- soluble m ordinary acids. Found at Baveno, Italy. ANGARALITE 2(Ca,Mg)0.5(Al,Fe) 2 O.,.6SiO 2 . In thin tabular hexagonal(?) crystals. U. - 2-b2. Color black from carbonaceous impurities. Uniaxial, +. In contact zone of limestone, southern part of Yenisei District, Siberia. TOURMALINE. Rhombohedral-hemimorphic._ Axis c = 0-4477. cr, 0001 A lOll = 27 20'. rr' 1011 A 1101 4fi W im' 39^1 A Q^91 AA T co, 0001 A 0221 = 45 57'. oof, oil A 20*1 = # %\ %i, l|i ^ 1} I 4 6 2 6 gj/ SILICATES 541 Crystals usually prismatic in habit, often slender to acicular; rarely flattened, the prism nearly wanting. Prismatic faces strongly striated ver- 914 515 916 917 918 ma 921 tically, and the crystals hence often much rounded to barrel-shaped. The cross-section of the prism three-sided (m, Fig. 921), six- sided (a), or nine-sided (m and a). Crystals commonly hemimorphic. Sometimes isolated, but more com- monly in parallel or radiating groups. Sometimes mas- sive compact; also columnar, coarse or fine, parallel or divergent. Cleavage : a (1 120) , r (101 1) difficult. Fracture sub- conchoidal to uneven. Brittle and often rather friable. H. = 7-7-5. G. = 2-98-3-20. Luster vitreous to res- inous. Colur black, brownish black, bluish black, most common; blue, green, red, and sometimes of rich shades; rarely white or colorless; some specimens red internally and green externally; and others red at one extremity, and green, blue or black at the other; the zonal arrangement of different colors widely various both as to the colors and to crystallographic directions. Streak uncolored. Trans- parent to opaque. Strongly dichroic, especially in deep-colored varieties; axial colors varying widely. Absorption for co much stronger than for e, thus sections 1 1 c axis trans- mit sensibly the extraordinary ray only, and hence their use (e.g., in the tour- maline tongs (p. 243) ) for giving polarized light. Exhibits idiophanous figures (p. 288). Optically . Birefringence rather high, co e = OO2. Indices: co y = 1-6366, ey = 1-6193 colorless variety; o>r = 1*6435, e r =. 1-6222 blue- 542 DESCRIPTIVE MINERALOGY green. Sometimes abnormally biaxial. Becomes electric by friction; also strongly pyroelectric. Var. Ordinary. In crystals as above described; black much the most common, (a) Rubellite; the red, sometimes transparent; the Siberian is mostly violet-red (siberite), the Brazilian rose-red; that of Chesterfield and Goshen, Mass., pale rose-red and opaque; that of Paris, Me., fine ruby-red and transparent. (6) Indicolite, or indigolite; the blue, either pale or bluish black; named from the indigo-blue color, (c) Brazilian Sapphire (in jewelry); Berlin-blue and transparent, (d) Brazilian Emerald, Chrysolite (or .Peridot) of Brazil; green and transparent, (e) Peridot of Ceylon; honey-yellow. (/) Achroite; color- less tourmaline, from Elba, (g) Aphrizite; black tourmaline, from Kragero, Norway. (h) Columnar and black; coarse columnar. Resembles somewhat common hornblende, but has a more resinous fracture, and is without distinct cleavage or anything like a fibrous appearance in the texture; it often has the appearance on a broken surface of some kinds of soft coal. Comp. A complex silicate of boron and aluminium, with also either magnesium, iron or the alkali metals prominent. A general formula may be written as HgAlaCB.OH^Si^ip (Penfield and Foote) in which the hyrogen may be replaced by the alkalies and also the bivalent elements, Mg,Fe,Ca. Fluorine is commonly present in small amounts. The varieties based upon composition fall into three prominent groups, between which there are many gradations: 1. ALKALI TOURMALINE. Contains sodium or lithium, or both; also potassium. G. = 3-0-3-1. Color red to green; also colorless. From pegmatites. 2. IRON TOURMALINE. G. = 3-1-3-2. Color usually deep black. Accessory mineral in siliceous igneous rocks and in mica schists, etc. 3. MAGNESIUM TOURMALINE. G. = 3-0-3'09. Usually yellow-brown to brownish black; also colorless. From limestone or dolomite. A chromium tourmaline also occurs. G. = 3*120. Color dark green. Pyr., etc. The magnesia varieties fuse rather easily to a white blebby glass or slag; the iron-magnesia varieties fuse with a strong heat to a blebby slag or enamel; the iron varieties fuse with difficulty, or, in some, only on the edges; the iron-magnesia-lithia varieties fuse on the edges, and often with great difficulty, and some are infusible; the lithia varieties are infusible. With the fluxes many varieties give reactions for iron and man- ganese. Fused with a mixture of potassium bisulphate and fluor-spar gives a distinct re- action for boric acid. Not decomposed by acids. Crystals, especially of the lighter colored varieties, show strong pyroelectricity. Diff. Characterized by its crystallization, prismatic forms usual, which are three-, six-, or nine-sided, and often with rhombohedral terminations; massive forms with colum- nar structure; also by absence of cleavage (unlike amphibole and epidote); in the common black kinds by the coal-like fracture; by hardness; by difficult fusibility (common kinds), compared with garnet and vesuvianite. The boron test is conclusive. Micro. Readily distinguished in thin sections by its somewhat high relief; rather u n u g i n i erence ~ colors ' ne "gative uniaxial character; decided colors in ordinary light in which basal sections often exhibit a zonal structure. Also, especially, by its remarkable -bsorption when the direction of crystal elongation is _]_ to the vibration-plane of the lower nicol; this with its lack of cleavage distinguishes it from biotite and amphibole, which alone among rock-making minerals show similar strong absorption. Ubs. Commonly found in granite and gneisses as a result of fumarole action or of legalizing gases m the fluid magma, especially in the pegmatite veins associated with icn rocks; at the periphery of such masses or in the schists, or altered limestones, gneisses, !tc., immediately adjoining them. It marks especially the boundaries of granitic masses, its associate minerals are those characteristic of such occurrences; quartz, albite, microcline muscovite etc. The variety in granular limestone or dolomite is commonly vn, tne bluish-black variety sometimes associated with tin ores; the brown with e lithium variety is often associated with lepidolite. Red or green varieties, d Ppn- CUr Q near kat ? F mb u rg in the Ural Mts - Elba ; Campolongo in Tessin, Switzer- ^lr ?: XOny; - * he P rovince Min as Geraes, Brazil; yellow and brown from A br ?T n netles rom Eibenstock, Saxony; the Zillertal, Tyrol, Austria; " i dal ' N . rwa y; Snarum and Kragero, Norway; pale yellowish brown at crystais ccur in c n at different iocaiities - SILICATES 543 variety from the chromite beds in Montgomery Co., Md. In N. C., Alexander e black crystals with emerald and hiddenite. In Cal., fine groups of rubellite in In the United States, in Me. at Paris and Hebron, magnificent red and green tourmalines with lepidolite, etc.; also blue and pink varieties; and at Norway; pink at Rumford, em- bedded in lepidolite; at Auburn in clear crystals of a delicate pink or lilac with lepidolite, etc.; at Albany, green and black. In Mass., at Chesterfield, red, green, and blue; at Goshen, blue and green; at Norwich, New Braintree and Carlisle, good black crystals. In N. H., Grafton, Acworth; at Orford, brownish black in steatite. In Conn., at Monroe, dark brown in mica-slate; at Haddam, black in mica slate; also fine pink and green; at New Milford, black. In N. Y., near Gouverneur, brown crystals, with tremolite, etc., in granular limestone; black near Port Henry, Essex Co.; near Edenville; splendid black crystals at Pierrepont, St. Lawrence Co.; colorless and glassy at De Kalb; dark brown at McComb. In N. J., at Hamburg and Newton, black and brown crystals in limestone, with spinel; also grass-green crystals in crystalline limestone near Franklin Furnace. In Pa., at Newlin, Chester Co.; near Unionville, yellow; at Chester, fine black; Middle- town, black; Marple, green in talc; near New Hope on thej)elaware, large black crystals. A chrome y Co., in fine lepidolite from Mesa Grande, Pala, etc. in San Diego Co. In Canada, in the province of Quebec, yellow crystals in limestone at Calumet Falls, Litchfield, Pontiac Co.; at Hunterstown; fine brown crystals at Clarendon, Pontiac Co.; black at Grenville and Argenteuil, Argenteuil Co. In Ontario, in fine crystals at North Burgess, Lanark Co.; Gal way and Stoney Lake in Dummer, Peterborough Co. The name turmalin from Turamali in Cingalese (applied to zircon by jewelers of Cey- lon) was introduced into Holland in 1703, with a lot of gems from Ceylon. Use. The variously colored and transparent varieties are used as gem stones; see under "Var." above. Dumortierite. A basic aluminium borosilicate, perhaps SAloOs^Os.GSiC^.HaO (Schaller) . The water and boric oxide have been considered as variable in amount and basic in charac- ter with the general formula, (AlO)i 6 Al 4 (SiO4) 7 (Ford). Orthorhombic. Prismatic angle approximately 60. Usually in fibrous to columnar aggregates. Cleavage: a (100), distinct; also prismatic, imperfect. H. =7. G. = 3'26- 3'36. Luster vitreous. Color bright smalt-blue to greenish blue. Transparent to trans- lucent. Pleochroism very strong: X deep-blue or nearly colorless, Y yellow to red- violet or nearly colorless, Z colorless or pistachio-green. Exhibits idiophanous figures, analogous to andalusite. Optically -. Ax. pi. || b (010). Bx J_ c (001). = 1-678. = 1'686. 7 = 1-689. Recognized in thin section by its rather high relief; low interference-colors (like those of quartz); occurrence in slender prisms, needles or fibers, with negative optical extension; parallel extinction; biaxial character and "especially by its remarkable pleochroism. Found embedded in feldspar in blocks of gneiss at Chaponost, near Lyons, France; from Wolfshau, near Schmiedeberg, Silesia; in the iolite of the gneiss of Tvedestrand, Norway; Rio de Janeiro, Brazil. In the United States, it occurs near Harlem, New York Island, in the pegmatoid portion of a biotite-gneiss ; in a quartzose rock at Clip, Yuma Co., Arizona; from San Diego Co., Cal.; Woodstock, Wash. STAUROLITE. Staurotide. Orthorhombic. Axes a : b : c mm"', 110 A 110 = 50 40'. rr', 101 A 101 = 110 32'. 922 0-4734 : 1 : 0-6828. cr, m,r, 001 A 110 A 101 101 923 = 55 16'. = 42 2'. 924 Twins cruciform: tw. pi. x (032), the crystals crossing nearly at right angles; tw. pi. z (232), crossing at an angle of 60 approximately; tw. pi. 010 544 DESCRIPTIVE MINERALOGY y (230) rare, also in repeated twins (cf. Figs. 397, p. 164; 439, 440, 441, p . 170). Crystals commonly prismatic and flattened || b axis; often with rough surfaces. Cleavage: b (010) distinct, but interrupted; m (110) m traces. Fracture subconchoidal. Brittle. H. = 7-7-5. G. = 3 '65-3 77. Subvitreous, inclin- ing to resinous. Color dark reddish brown to brownish black, and yellowish brown. Streak uncolored to grayish. Translucent to nearly or quite opaque. Pleochroism distinct : Z ( = c axis) hyacinth-red to blood-red, X, Y yellowish red; or Z gold-yellow, **&* x Y light yellow to colorless. Optically +. Ax. pi. || a (100). Bx _L c (001). 2V = 88 (ap- \ MI I / prox.). a = 1-736. ft = 1741. 7 = 1*746. Comp. HFeAl 5 Si 2 Oi3, which may be writ- ten (A10)4(AlOH)Fe(SiO4) 2 or H 2 O.2Fe0.5Al 2 O 3 . 010 4SiO 2 = Silica 26*3, alumina 55 '9, iron protoxide > x 15-8, water 2'0 = 100. Magnesium (also man- ganese) replaces a little of the ferrous iron; ferric iron part of the aluminium. Nordmarkite from Nordmark, Sweden, contains man- /\ ganese in large amounts. \ g Pyr., etc. B.B. infusible, excepting the manganesian & variety, which fuses easily to a black magnetic glass. Z With the fluxes gives reactions for iron, and sometimes for manganese. Imperfectly decomposed by sulphuric acid. Diff. Characterized by the obtuse prism (unlike andalusite, which is nearly square) ; by the frequency of twinning forms; by hardness and infusibility. Micro. Under the microscope, sections show a decided color (yellow to red or brown) and strong pleochroism (yellow and red); also characterized by strong refraction (high relief), rather bright interference-colors, parallel extinction and biaxial character (generally positive in the direction of elongation). Easily distinguished from rutile (p. 427) by its biaxial character and lower interference-colors. Obs. Usually found in crystalline schists, as mica schist, argillaceous schist, and gneiss, as a result of regional or contact metamorphism; often associated with garnet, silli- manite, cyanite, and tourmaline. Sometimes encloses symmetrically arranged carbon- aceous impurities like andalusite (p. 524) . Other impurities are also often present, especially silica, sometimes up to 30 to 40 p. c.; also garnet, mica, and perhaps magnetite, brookite. Occurs with cyanite in paragonite schist, at Mt. Campione, Switzerland; in the Zillertal, Tyrol, Austria; Goldenstein in Moravia; Aschaffenburg, Bavaria; in large twin crystals in the mica schists of Brittany and Scotland. In the province of Minas Geraes, Brazil. Abundant throughout the mica schists of New England. In Me., at Windham. In N. H., brown at Franconia; at Lisbon; on the shores of Mink Pond, loose in the soil. In Mass., at Chesterfield, in fine crystals. In Conn., at Bolton, Vernon, etc.; Southbury with garnets; at Litchfield, black crystals. In N. C., near Franklin, Macon Co.; also in Madi- son and Clay counties. In Ga., in Fannin Co., loose in the soil in fine crystals. In large crystals from Ducktown, Tenn. Named from (rravpos, a cross. Use. Occasionally a transparent stone is cut for a gem. Kornerupine. Near MgAl 2 SiO 6 . In fibrous to columnar aggregates, resembling silli- mamte. H. = 6'5. G. = 3'273 kornerupine; 3'341 prismatine. Colorless to white, or brown. Biaxial, -. Indices, 1 '669-1 '682. Kornerupine occurs at Fiskernas on the west coast of Greenland. Prismatine is from Waldheim, Saxony. Found in large, clear crystals of a sea-green color and gem quality trom near Betroka, Madagascar. Sapphirine. Mg 6 Ali 2 Si 2 O27. In indistinct tabular crystals. Usually in disseminated grains, or aggregations of grains. H. = 7'5. G. = 3'42-3'48. Color pale to dark blue or green. Biaxial, -. Indices, 1705-1711. From Fiskernas, southwestern Greenland. Occurs near Betroka, Madagascar. From St. Urbain, Quebec. r\ .p^didierite. A basic silicate of aluminium, ferric iron, magnesium, ferrous iron, etc. Orthornombic. In elongated crystals. Two cleavages. G. = 3'0. Color bluish green. SILICATES 545 /3 = 1-64. Strongly pleochroic. Found in pegmatite at Andrahomana in southern Madagascar. Serendibite. 10(Ca,Mg)O.5Al 2 p 3 .B 2 O 3 .6SiO 2 . In irregular grains showing polysyn- thetic twinning; probably monoclinic or triclinic. H. = 6*7. G. = 3*4. Color blue. Pleochroism marked. Refractive index, 17. Infusible. From Gangapitiya near Am- bakotte, Ceylon. Silicomagnesipfluorite. A fluosilicate of calcium and magnesium, perhaps, H 2 Ca 4 Mg 3 Si 2 O 7 Fi . Radiating fibrous in spherical forms. H. = 2'5. G. = 2'9. Color ash-gray, light greenish or bluish. Fusible. From Lupikko, near Pitkaranta, Finland. Grothine. A silicate of calcium with aluminium and a little iron of uncertain compo- sition. Orthorhombic. In small tabular crystals. Colorless. Transparent. G. = 3'09. Optically +. Infusible. Decomposed by sulphuric acid. Found with microsommite on limestone near Nocera and Sarno, Campagna, Italy. ALOISIITE. Luigite. A basic silicate containing ferrous oxide, lime, magnesia, and soda. Amorphous. Color, brown to violet. Acts as a cement in a tuff found at Fort Portal, Uganda. POCHITE. Hi6Fe 8 Mn 2 Si 3 O 2 9. Amorphous. H. = 3'5-4. G. = 370. Color reddish brown. Opaque. Found in iron ore near Vares, Bosnia. SILICATES Section B. Chiefly Hydrous Species The SILICATES of this second section include the true hydrous compounds, that is, those which contain water of crystallization, like the zeolites; also the hydrous amorphous species, as the clays, etc. There are also included certain species as the Micas, Talc, Kaolinite which, while they yield water upon ignition, are without doubt to be taken as acid or basic metasilicates, orthosili- cates, etc. Their relation, however, is so close to other true hydrous species that it appears more natural to include them here than to have placed them in the preceding chapter with other acid and basic salts. Finally, some species are referred here about whose chemical constitution and the part played by the water present there is still much doubt. The divisions recog- nized are as follows: I. Zeolite Division 1. Introductory Subdivision. 2. Zeolites II. Mica Division 1. Mica Group. 2. Clintonite Group. 3. Chlorite Group III. Serpentine and Talc Division Chiefly Silicates of Magnesium. IV. Kaolin Division Chiefly Silicates of Aluminium; for the most part belonging to the group of the clays. V. Concluding Division Species not included in the preceding divisions; chiefly silicates of the heavy metals, iron, manganese, etc. 546 DESCRIPTIVE MINERALOGY I. Zeolite Division 1. Introductory Subdivision Of the species here included, several, as Apophyllite, Okenite, etc., while not strictly ZEOLITES, are closely related to them in composition and method of occurrence. Pectolite (p. 483) and Prehnite (p. 534) are also sometimes classed "here. Inesite. H 2 (Mn,Ca)6Si 6 Oi 9 .3H 2 O. Crystals small, prismatic; also fibrous, radiated and spherulitic. H. = 6. G. = 3'029. Color rose- to flesh-red. Occurs at the manganese mines near Dillenburg, Germany. Rhodotilite is the same species from the Harstig mine, Pajsberg, Sweden. From Jakobsberg and Langban, Sweden ; Villa Corona, Durango, Mexico. Hillebrandite. Ca 2 SiO 4 .H 2 O. Orthorhombic; radiating fibrous. H. = 5'5. G.= 27. Refractive index = 1*61. Color white. Fusible with difficulty. Found in contact zone between limestone and diorite in the Velardena mining district, Mexico. Crestmoreite. Probably 4H 2 CaSiO 4 .3H 2 O. Compact. Color, snow-white. H. = 3. G. = 2'2. ft = T59. An alteration product of Wilkeite. From Crestmore, Riverside Co., Riversideite. 2CaSiO 6 .H 2 O. In compact fibrous veinlets. Silky luster. H. = 3. G. = 2-64. Indices, 1 "59-1 '60. Easily fusible. From Crestmore, Riverside Co., Cal. Ganophyllite. 7MnO.Al 2 O 3 .8SiO 2 .6H 2 O. In short prismatic crystals; also foliated, micaceous. Color brown. H. = 4~4'5. G. = 2'84. Biaxial, -. Indices, 17Q5-1730. From the Harstig mine, near Pajsberg, Sweden. Lotrite. 3(Ca,Mg)O.2(Al,Fe) 2 O 3 .4SiO 2 .2H 2 O. Massive, in an aggregate of small grains and leaves. One cleavage. H. = 7'5. G.= 3'2. Color green. Refractive index, 1'67. Found in small veins in a chlorite schist in the valley of the Lotru, Transylvania. . Okenite. H 2 CaSi 2 O 6 .H 2 O. Commonly fibrous; also compact. H. = 4'5-5. G. = 2'28- 2 '36. Color white, with a shade of yellow or blue. Biaxial, . Index, 1'556. Occurs in basalt or related eruptive rocks; as in the Faroe Islands; Iceland; Disko, Niorkornat, etc., Greenland; Poona, India. From Crestmore, Riverside Co., Cal. Gyrolite. H 2 Ca 2 Si 3 O 9 .H 2 O. Rhombohedral-tetartohedral. In white concretions, lamellar-radiate in structure. Optically -. co = 1'56. From the Isle of Skye, with stilbite, laumontite, etc.; in India, etc. With apophyllite of New Almaden, California; also Nova Scotia. Found also at various places in Bohemia; from Scotland and the Faroe Islands; Sao Paulo, Brazil. Reyerite from Greenland is similar to gyrolite. Zeophyllite is a similar species which may be identical with gyrolite. Rhombohedral. In spherical forms with radiating foliated structure. Perfect basal cleavage. H. = 3. G. = 2*8. Color white, u = 1'56. From various localities in Bohemia and elsewhere. APOPHYLLITE. Tetragonal. Axis c = 1 -2515. 926 927 928 929 ay, 100 A 310 cp, 001 A 111 18 26'. 60 32'. op, 100 A 111 pp', 111 A Til 52 0'. 76 0'. / it T aried ' in sc l uare P risms ( (100)) usually short and terminated by -) or by o and p (111), and then resembling a cube or cubo-octahedron; SILICATES 547 also acute pyramidal (p (111)) with or without c and a; less often thin tabu- lar II c. Faces c often rough; a bright but vertically striated; p more or less uneven. Also massive and lamellar; rarely concentric radiated. Cleavage: c (001) highly perfect; m (110) less so. Fracture uneven. Brittle. H. = 4-5-5. G. = 2-3-2-4. Luster of c pearly; of other faces vitreous. Color white, or grayish; occasionally with a greenish, yellowish, or rose-red tint, flesh-red. Transparent; rarely nearly opaque. Birefringence low; usually +, also . Often shows anomalous optical characters (Art. 429, Fig. 617). Indices, 1-535-1-537. Comp. H 7 KCa4(SiO 3 )8.4fH 2 or K 2 0.8Ca0.16SiO 2 .16H 2 = Silica 537, lime 25-0, potash 5-2, water 16*1 = 100. A small amount of fluorine replaces part of the oxygen. The above formula differs but little from H 2 CaSi 2 O6.H 2 O, in which potassium replaces part of the basic hydrogen. The form often accepted, H 2 (Ca,K)Si 2 O 6 .H 2 O, corresponds less well with the analyses. Pyr., etc. In the closed tube exfoliates, whitens, and yields water, which reacts acid. B.B. exfoliates, colors the flame violet (potash), and fuses to a white vesicular enamel. F. = 1*5. Decomposed by hydrochloric acid, with separation of slimy silica. Diff. Characterized by its tetragonal form, the square prism and pyramid the com- mon habits; by the perfect basal cleavage and pearly luster on this surface. Obs. Occurs commonly as a secondary mineral in basalt and related rocks, with various zeolites, also datolite, pectolite, calcite; also occasionally in cavities in granite, gneiss, etc. Greenland, Iceland, the Faroe Islands, and British India, especially at Poonah, afford fine specimens of apophyllite in amygdaloidal basalt or diabase. Occurs also at Andreasberg, Harz Mts., Germany, of a delicate pink; Radautal in the Harz Mts.; at Orawitza, Hungary, with wollastonite; Uto, Sweden; on the Seisser Alp in Tyrol, Austria; Guanajuato, Mexico, often of a beautiful pink upon amethyst. In the United States, large crystals occur at Bergen Hill, Paterson, West Paterson, and Great Notch, N. J.; in Pa., at the French Creek mines, Chester Co.; at the Cliff, Phoenix and other mines, Lake Superior region; Table Mt. near Golden, Col.; in Cal., at the mercury mines of. New Almaden often stained brown by bitumen; also from Nova Scotia at Cape Blomidon, and other points. Named by Haiiy in allusion to its tendency to exfoliate under the blowpipe, from airb and (f>v\\oi>, a leaf. Its whitish pearly aspect, resembling the eye of a fish after boiling, gave rise to the earlier name Ichthyophthalmite, from ixOvs, fish, 6da\iJi6s, eye, 2. Zeolites The ZEOLITES form a family of well-defined hydrous silicates, closely re- lated to each other in composition, in conditions of formation, and hence in mode of occurrence. They are often with right spoken of as analogous to the Feldspars, like which they are all silicates of aluminium with sodium and calcium chiefly, also rarely barium and strontium; magnesium, iron, etc., are absent or present only through impurity or alteration. Further, the com- position in a number of cases corresponds to that of a hydrated feldspar; while fusion and slow recrystallization result in the formation from some of them of aiiorthite (CaAl 2 Si 2 Og) or a calcium-albite (CaA^SieOie) as shown by Doelter. The Zeolites do riot, however, form a single group of species related in crystal- lization, like the Feldspars, but include a number of independent groups widely diverse in form and distinct in composition; chief among these are the monoclinic PHILLIPSITE GROUP; the rhombohedral CHABAZITE GROUP, and the orthorhombic (and monoclinic) NATROLITE GROUP. A transition in composition between certain end compounds has been more or less well- established in certain cases, but, unlike the Feldspars, with these species cal- cium and sodium seem to replace one another and an increase in alkali does not necessarily go with an increase in silica. 548 DESCRIPTIVE MINERALOGY Like other hydrous silicates they are characterized by inferior hardness, chiefly from 3-5 to 5-5, and the specific gravity is also lower than with corre- sponding anhydrous species, chiefly 2 -0 to 2 -4. Corresponding to these charac- ters; they are rather readily decomposed by acids, many of them' with gela- tinization. The intumescence B.B., which gives the name to the family (from fefi>, to boil, and \iBos, stone) is characteristic of a large part of the species. The Zeolites are all secondary minerals, occurring most commonly in cavities and veins in basic igneous rocks, as basalt, diabase, etc.; less fre- quently in granite, gneiss,, etc. In these cases the lime and the soda in part have been chiefly yielded by the feldspar; the soda also by elseolite, sodalite, etc. ; potash by leucite, etc. The different species of the family are often asso- ciated together; also with pectolite and apophyllite (sometimes included with the zeolites), datolite, prehnite and, further, calcite. Many of the zeolites have been produced synthetically by various hydrochemical reactions. In general they appear to have been formed in nature by reactions upon the feld- spar or feldspathoid minerals. Ptilolite. RAl 2 SiioO24.5H 2 O. Here R = Ca : K 2 : Na 2 = 6 : 2 : 1 approx. In short capillary needles, aggregated in delicate tufts. Colorless, white. Biaxial, +. Indices, 1 '480-1 '485. Occurs upon a bluish chalcedony in cavities in a vesicular augite-andesite found in fragments in the conglomerate beds of Green and Table mountains, Jefferson Co., and from Silver Cliff, Custer Co., Col., also from Elba and Iceland. Mordenite. - 3RAl 2 Si 10 p 24 .20H;.O, where R = K 2 : Na 2 : Ca = 1 : 1 : 1. In minute crystals resembling heulandite in habit and angles; also in small hemispherical or reniform concretions with fibrous structure. H. = 3-4. G. = 215. Color white, yellowish or pinkish. Occurs near Morden, King's Co., Nova Scotia, in trap; also in western Wyoming near Hoodoo Mt., on the ridge forming the divide between Clark's Fork and the East Fork of the Yellowstone river. Also from Seiseralpe, Tyrol, Austria and the Faroe Islands. HEULANDITE. Stilbite some authors. Monoclinic. Axes a : b : c = 0-4035 : 1 : 0-4293; = 88 34J'. mm'", 110 A 1TO = 43 56'. cs, 001 A 201 = 66 0'. ct, 001 A 201 = 63 40'. ex, 001 A 021 = 40 38|' v t Crystals sometimes flattened 1 1 b (010), the surface of pearly \ luster (Fig. 930; also Fig. 21, p. 12); form often suggestive of the orthorhombic system, since the angles cs and ct differ but little. Also in globular forms; granular. Cleavage: b (010) perfect. Fracture subconchoidal to un- even. Brittle. H. = 3-5-4. G. = 2-18-2-22. Luster of 6 strong pearly; of other faces vitreous. Color various shades of wmt e, passing into red, gray and brown. Streak white. Transparent to subtranslucent. Optically +. Ax. pi. and Bxa _L b (010). Ax. pi. and Bx for some localities nearly || c also for others nearly _L c in white light. Bx A c axis = + 57J Axial angle variable, from to 92; usually 2E r = 52. a = 1-498. P = 1-^:99. 7 = 1-505. Comp. H 4 CaAl 2 (Si0 3 ) 6 .3H 2 or 5H 2 O.CaO.Al 2 O 3 .6SiO 2 = Silica 59'2, alumina 16'8, lime 9'2, water 14'8 = 100. Strontia is usuaUy present, sometimes up to 3 '6 p. c. Pyr. As with stilbite, p. 551. SILICATES 549 Obs. Heulandite occurs principally in basaltic rocks, associated with chabazite, stil- bite and other zeolites; also in gneiss, and occasionally in metalliferous veins. The finest specimens of this species come from Berufiord, and elsewhere in Iceland; the Faroe Islands; in British India, near Bombay; also in railroad cuttings in the Bhor and Thul Ghats. Also occurs in the Kilpatrick Hills, near Glasgow; on the Island of Skye; Fassatal, Tyrol, Austria; Andreasberg, Harz Mts., Germany; Viesch and elsewhere, Switzerland. In the United States, in diabase at Bergen Hill, West Paterson and Great Notch, N. J.; on north shore of Lake Superior; with haydenite at Jones's Falls near Baltimore (beau- montite), Md. At Peter's Point, Nova Scotia; also at Cape Blomidon, and other points. Named after the English mineralogical collector, H. Heuland, whose cabinet was the basis of the classical work (1837) of Levy. Brewsterite. H 4 (Sr,Ba,Ca)Al 2 (SiO 3 ) 6 .3H 2 O. In prismatic crystals. H. =5. G. = 2-45. Color white, inclining to yellow and gray. Biaxial, +. Index, 1*45. From Strontian in Argyleshire, Scotland; near Freiburg in Breisgau, Germany. Epistilbite. Probably like heulandite, H 4 CaAl 2 (SiO 3 ) 6 .3H 2 O. Crystals monoclinic, uniformly twins; habit prismatic. In radiated spherical aggregations; also granular. G. = 2-25. Color white. Biaxial,-. Indices, 1 '502-1 '512. Occurs with scolecite at the, Berufiord, Iceland; the Faroe Islands; Poona, India; in small reddish crystals, at Mar- garet ville, Nova Scotia, etc. Reissite is from Santorin Island. Wellsite Phillipsite Harmotome Stilbite Phillipsite Group. Monoclinic a 6 c (Ba,Ca,K 2 )Al 2 Si 3 10 .3H 2 O 0-768 1 1-245 (K 2 ,Ca)Al 2 Si 4 12 .4iH 2 O 0-7095 1 1-2563 (K 2 ,Ba)Al 2 Si 5 O 14 .5H 2 0-7032 1 1-2310 (Na 2 ,Ca)Al 2 Si 6 O 16 .6H 2 O 0-7623 1 1-1940 53 55 55 50 27' 37' 10' 50' The above species, while crystallizing in the monoclinic system, are remark- able for the pseudo-symmetry exhibited by their twinned forms. Certain of these twins are pseudo-orthorhombic, others pseudo-tetragonal and more com- plex twins even pseudo-isometric. Fresenius has shown that the species of this group may be regarded as forming a series, in which the ratio of RO : A1 2 O 3 is constant (= 1 : 1), and that of SiO 2 : H 2 O also chiefly 1:1. The end compounds assumed by him are: RAl 2 Si 6 Oi 6 .6H 2 O; R 2 Al 4 Si 4 O 16 .6H 2 O. Here R = Ca chiefly, in phillipsite and stilbite, Ba in harmotome, while in wellsite Ba, Ca, and K 2 are present; also in smaller amounts Na 2 , Sr 2 . The first of the above compounds may be regarded as a hydrated calcium albite, the second as a hydrated anorthite. Pratt and Foote, however, show that the anorthite end compound more probably has the for- mula RAl 2 Si 2 O ; .2H 2 O (or this doubled) . The formulas given beyond are those correspond- ing to reliable analyses of certain typical occurrences. 931 932 Wellsite. RAl 2 Si 3 Oio.3H 2 O with R = Ca : Ba : K 2 = 3 : 1 : 3; Sr and Na also present in small amount. Percentage composition: SiO 2 42-9, A1 2 O 3 24-3, BaO6'6, CaO 7'3, K 2 O 6' 1, H 2 O 12-8 = 100. Monoclinic (axes above) ; in complex twins, analogous to those of phillipsite and harmotome (Figs. 931, 932). Brittle. No cleavage. H. = 4-4'5. G. = 2'278-2'366. Luster vitreous. Colorless to white. Optically +. Bx _L b (010). Birefringence weak. Occurs at the Buck Creek (Cullakanee) corundum mine in Clay Co., N. C.; in isolated crystals attached to feldspar, also to hornblende and corundum; intimately associated with chabazite. Also found at Kurzy near Simferopol, Crimea, Russia. 550 DESCRIPTIVE MINERALOGY PHILLIPSITE. Monoclinic. Axes a : b : c = 07095 : 1 : 1-2563; ft = 55 37'. mm"' 110 A HO = 60 42'. cm, 001 A 110 = 60 50'. a/, 100 A 101 = 34 23'. ee', Oil A Oil = 92 4'. 933 Crystals uniformly penetration-twins, but often simulating orthorhombic or tetragonal forms. Twins sometimes, but rarely, simple (1) with tw. pi. c (001) . and then cruciform so that diagonal parts on b (010) belong together, hence a fourfold striation, || edge b/m, may be often observed on b. (2) Double twins, the simple twins just noted united with e (Oil) as tw. pi., and, since ee' varies but little from 90, the result is a nearly square prism, terminated by what appear to be pyramidal faces each with a double series of striations away from the medial line. See Figs. 452-454, p. 172; also Fig. 400, p. 164. Faces 6 (010) often finely striated as just noted, but striations sometimes absent and in general not so distinct as with harmotome; also m (110) striated || edge b/m. Crystals either isolated, or grouped in tufts or spheres, radiated within and bristled with angles at surface. Cleavage: c (001), 6 (010), rather distinct. Fracture uneven. Brittle. H. = 4-4-5. G. = 2-2. Luster vitreous. Color white, sometimes reddish. Streak uncolored. Translucent to opaque. Optically +. Ax. pi. and Bx J_ b (010) . The ax. pi. lies in the obtuse angle of the a-c axes, and is usually inclined to a axis about 15 to 20, or 75 to 70 to the normal to c (001) . The position, however, is variable. 2H a . r = 71-84. Indices, 1-48-1-57. Comp. In some cases the formula is (K 2 ,Ca) Al 2 Si4Oi 2 .4H 2 O = Silica 48-8, alumina 207, lime 7-6, potash 6-4, water 16-5 = 100. Here Ca : K 2 = 2:1. Pyr., etc. B.B. crumbles and fuses at 3 to a white enamel. Gelatinizes with hydro- chloric acid. Obs. In translucent crystals in basalt, at the Giant's Causeway. Ireland; at Capo di Bove, near Rome; Aci Castello and elsewhere in Sicily; among the lavas of Mte. Somma, Vesuvius; in Germany at Stempel, near Marburg; Annerod, near Giessen; in the Kaiser- stuhl, with faujasite, at Salesl, Bohemia; in the ancient lavas of the Puy-de-D6me, France; from Richmond, Victoria. Pseudophillipsite, found near Rome, Italy, differs from phillips- ite only in the manner in which it loses water on heating. HARMOTOME. 934 Monoclinic. Axes a : b : c = 0*7031 : 1 : 1-2310; ft = 55 10'. Crystals uniformly cruciform penetration-twins with c (001) as tw. pi; either (1) simple twins (Fig. 934) or (2) united as fourlings with tw. pi. e (Oil). These double twins often have the aspect of a square prism with diag- onal pyramid, the latter with characteristic feather-like striations from the medial line. Also in more complex groups analogous to those of phillipsite. Cleavage: b (010) easy, c (001) less so. Fracture uneven to subconchoidal. Brittle. H. = 4-5. G. = 2-44- 2-50. Luster vitreous. Color white; passing into gray, yellow, red or brown. Streak white. Subtransparent to translucent, SILICATES 551 Ax. pi. and Bx a J_ b (010). Ax. pi. in obtuse angle a-c axes and inclined about 65 to a axis and 60 to c axis. Optically + . 2V = 43. a = 1-503. ft = 1-505. 7 = 1-508. Comp. In part H 2 (K 2 ,Ba)Al 2 Si5Oi5.4H 2 O or (K 2 ,Ba)O.Al 2 O 3 .5SiO 2 . 5H 2 O = Silica 47-1, alumina 16-0, baryta 20'6, potash 2-1, water 14-1 = 100. Pyr., etc. B.B. whitens, then crumbles and fuses without intumescence at 3'5 to a white translucent glass. Some varieties phosphoresce when heated. Decomposed by hydrochloric acid without gelatinizing. Obs. Occurs in basalt and similar eruptive rocks, also phonolite, trachyte; not infre- quently on gneiss, and in some metalliferous veins. AtStrontian, in Scotland; in a metal- liferous vein at Andreasberg in the Harz Mts., Germany; at Rudelstadt, Silesia; Oberstein, Germany, on agate in siliceous geodes; at Kongsberg, Norway. In the United States, in small brown crystals with stilbite on the gneiss of New York Island; near Port Arthur, Lake Superior. Named from ap/zos, joint, and r'env&v, to cut, alluding to the fact that the pyramid (made by the prismatic faces in twinning position) divides parallel to the plane that passes through the terminal edges. STILBITE. Desmine. Monoclinic. Axes a:b:.c = 0-7623 : 1 : 1-1940; ft = 50 50'. Crystals uniformly cruciform penetration-twins with tw. pi. c (001), analo- gous to phillipsite and harmotome. The apparent form a rhombic pyramid whose faces are in fact formed by the prism faces of the two individuals; the vertical faces being then the pinacoids 6 (010) and c (001) (cf. Figs. 613-615, p. 299). Usually thin tabular || b (010). These 935 compound crystals are often grouped in nearly parallel position, forming sheaf -like aggregates with the side face (b), showing its characteristic pearly luster, often deeply depressed. Also divergent or radiated; sometimes globular and thin lamellar- columnar. Cleavage: 6 (010) perfect. Fracture uneven. Brittle. H. = 3-5-4. G. = 2-094-2-205. Luster vitreous; of b (010) pearly. Color white; occasionally yellow, brown or red, to brick-red. Streak uncolored. Transparent to translucent. Optically . Ax. pi. || b (010). Bxa inclined 5 to axis a in obtuse angle a-c axes; hence Bx a A caxis = 55 50'. 2V = 33 (approx.). a = 1-494. ft = 1-498. 7 = I'SOO. Comp. For most varieties H4(Na2,Ca)Al 2 Si 6 Oi8.4H 2 O or (Na 2 ,Ca)O.Al 2 O 3 .6SiO 2 .6H 2 O = Silica 57-4, alumina 16-3, lime 7-7, soda 1-4, water 17 -2 = 100. Here Ca : Na, = 6 : 1. Some kinds show a lower percentage of silica, and these have been called hypostilbite. Pyr., etc. B.B. exfoliates, swells up, curves into fan-like or yermicular forms, and fuses to a white enamel. F. = 2-2*5. Decomposed by hydrochloric acid, without gelati- nizing. Diff. Characterized by the frequency of radiating or sheaf-like forms; by the pearly luster on the clinopinacoid. Does not gelatinize with acids. Obs. Stilbite occurs mostly in cavities in amygdaloidal basalt, and similar rocks. It is also found in some metalliferous veins, and in granite and gneiss. Abundant on the Faroe Islands; in Iceland; on the Isle of Skye, in amygdaloid ; also in Dumbartonshire, Scotland, in red crystals; the Giant's Causeway, Ireland; at Andreas- berg in the Harz Mts., Germany, and Kongsberg and Arendal in Norway, with iron ore; on the Seisser Alp in Tyrol, Austria, and at the Puflerloch (puflerite) ; on the granite of Striegau, Silesia. A common mineral in the Deccan trap area of British India. In North America, sparingly in small crystals at Chester and at the Somerville syenite quarries, Mass.; at Phillipstown, N. Y.; and at Bergen Hill, West Paterson and Great Notch, N. J.; also at the Michipicoten Islands, Lake Superior. In Nova Scotia at Part- ridge Island, also at Isle Haute, Two Islands, Digby Neck, Cape Blomidon, etc. The name stilbite is from arlX^rj, luster, and desmine from d'caw, a bundle. 552 DESCRIPTIVE MINERALOGY Flokite. H 8 (Ca,Na 2 )Al 2 Si 9 26 .2H 2 0. Monoclinic. In slender prismatic crystals. Perfect cleavages parallel to (100) and (010). H. = 5. G. = 2 -10. Colorless and trans- parent. Indices, 1 '472-1 '474. Fuses with intumescence. From Iceland. Gismondite. Perhaps CaAl 2 Si 2 O 8 .4H 2 O. In pyramidal crystals, pseudo-tetragonal. H = 4'5 G. = 2-265. Colorless or white, bluish white, grayish, reddish. Biaxial. -. Index 1-539. Occurs in the leucitophyre of Mt. Albano, near Rome, at Capo di Bove, and elsewhere, etc.; on the Gorner glacier, near Zermatt, Switzerland; Schlauroth near Gorlitz in Silesia; Salesl, Bohemia, etc. LAUMONTITE. Leonhardite. Caporcianite. Monoclinic. Axes a : b : c = M451 : 1 : 0-5906; = 68 46'. Twins- tw. pi. a (100). Common form the prism m (mm'" 110 A 110 = 93 440 with oblique termination e, 201 (ce 001 A 201 = 56 55'). Also columnar, radiating and divergent. Cleavage: 6 (010) and m (110) very perfect; a (100) imperfect. Fracture uneven. Not very brittle. H. = 3 -5-4. G. = 2-25-2-36. Luster vitreous, inclining to pearly upon the faces of cleavage. Color white, passing into yellow or gray, sometimes red. Streak uncolored. Transparent to trans- lucent; becoming opaque and usually pulverulent on exposure. Optically . Ax. pi. || b (010). Bx a A c axis = + 65 to 70. Dispersion large, p < v; inclined, slight. 2E r = 52 24'. a = 1-513. = 1'524. 7 = 1*525. Comp. H 4 CaAl 2 Si4Oi4.2H 2 =. 4H 2 O.CaO.Al 2 O 3 .4SiO 2 = Silica 51% alumina 217, lime 11-9, water 15-3 = 100. Var. Leonhardite is a laumontite which has lost part of its water (to one molecule), and the same is probably true of caporcianite. Schneiderite is laumontite from the serpen- tine of Monte Catini, Italy, which has undergone alteration through the action of magnesian solutions. Pyr., etc. B.B. swells up and fuses at 2'5-3 to a white enamel. Gelatinizes with hydrochloric acid. Obs. Occurs in the cavities of basalt and similar eruptive rocks; also in porphyry and syenite, and occasionally in veins traversing clay slate with calcite. Its principal localities are the Faroe Islands; Disko in Greenland; in Bohemia, at Eule in clay slate; St. Gothard in Switzerland; Baveno, Italy; Nagyag, Transylvania; the Fassatal, Tyrol, Austria; the Kilpatrick hills, near Glasgow, Scotland; the Hebrides, and the north of Ireland. In India, in the Deccan trap area, at Poona, etc. Peter's Point, Nova Scotia, affords fine specimens of this species. Found at Phipps- burg, Me. Abundant in many places in the copper veins of Lake Superior in trap, and on Isle Royale; on north shore of Lake Superior, between Pigeon Bay and Fond du Lac. Found also at Bergen Hill, N. J.; at the Tilly Foster iron mine, Brewster, N. Y. Laubanite. CaaAUSuOu.GHjjO. Resembles stilbite. H. = 4'5-5. G. = 2'23. Color snow-white. Occurs upon phillipsite in basalt at Lauban, Silesia. Chabazite Group. Rhombohedral rr'. c Chabazite (Ca,Na 2 )Al 2 Si 4 12 .6H 2 85 14' 1;0860 Gmelinite (Na 2 Ca)Al 2 Si 4 Oi 2 .6H 2 68 8' 07345 or fc = 1*1017 Levynite CaAl 2 Si 3 Oi .5H 2 73 56' 0'8357 fc = 1-1143 The Chabazite Group includes these three rhombohedral species. The fundamental rhombohedrons have different angles, but, as shown in the axial ratios above, they are closely related, since, taking the rhombohedron of Chabazite as_ the basis, that of Gmelinite has the symbol (2023) and of Levynite (3034). The variation in composition often observed in the first two species has led to the rather SILICATES 553 plausible hypothesis that they are to be viewed as isomorphous mixtures of the feldspar-like compounds (Ca,Na2)Al 2 Si 2 O 8 .4H 2 O, (Ca,Na 2 )Al 2 Si 6 Oi 6 .8H 2 O. CHABAZITE. Rhombohedral. Axis c = 1-0860; 0001 A 1011 = 51 25f. 936 937 938 Phacolite Twins: (1) tw. axis c axis, penetration-twins common. (2) Tw. pi. r(1011); contact-twins, rare. Form commonly the simple rhombohedron varying little in angle from a cube (rr f 1101 A 1101 = 85 14'); also r and e (0112), (ee f ' = 54 47'). Also in complex twins. Also amorphous. Cleavage: r (1011) rather distinct. Fracture uneven. Brittle. H. = 4-5. G. = 2-08-2-16. Luster vitreous. Color white, flesh-red; streak uncolored. Transparent to translucent. Optically ; also + (Andreas- berg, also haydenite). Birefringence low. The interference-figure usually confused; .sometimes distinctly biaxial; basal sections then divided into sharply defined sectors with different optical orientation. These anomalous optical characters probably secondary and chiefly conditioned by the variation in the amount of water present. Mean refractive index 1-5. Var. 1. Ordinary. The most common form is the fundamental rhombohedron, in which the angle is so near 90 that the crystals were at first mistaken for cubes. Acadialite, from Nova Scotia (Acadia of the French of 18th century), is a reddish chabazite; sometimes nearly colorless. Haydenite is a yellowish variety in small crystals from Jones's Falls, near Baltimore, Md. 2. Phacolite is a colorless variety occurring in twins of hexagonal form (Fig. 938), and lenticular in shape (whence the name, from 0a/c6s, a bean)', the original was from Leipa in Bohemia. Here belongs also herschelite (seebachite) from Richmond, Victoria; the composite twins of great variety and beauty. Probably also the original herschelite from Sicily. It occurs in flat, almost tabular, hexagonal prisms with rounded terminations divided into six sectors. Comp. Somewhat uncertain, since a rather wide variation is often noted even among specimens from the same locality. The ratio of (Ca,Na2,K 2 ) : Al is nearly constant (= 1 : 1), but of A1 2 : Si varies from 1 : 3 to 1 : 5 ; the water also increases with the increase in silica. The composition usually corresponds to (Ca,Na2)Al 2 Si4Oi 2 .6H2O, which, if calcium alone is present, requires: Silica 47 -4, alumina 20'2, lime 11-1, water 21 -3 = 100. If Ca : Nao = 1:1, the percentage composition is: Silica 47*2, alumina 20*0, lime 5-5, soda 6-1, water 21-2 = 100. Potassium is present in small amount, also sometimes, barium and strontium. Streng explains the supposed facts most satisfactorily by the hypothesis that the members of the group are isomorphous mixtures analogous to the feldspars, as noted above. Pyr., etc. B.B. intumesces and fuses to a blebby glass, nearly opaque. Decomposed by hydrochloric acid, with separation of slimy silica. 554 DESCRIPTIVE MINERALOGY Diff Characterized by rhombohedral form (resembling a cube). It is harder than calcite and does not effervesce with acid; unlike calcite and fluonte in cleavage; fuses B.B. with intumescence unlike analcite. Obs. Occurs mostly in basaltic rocks, and occasionally m gneiss, syenite, mica schist, hornblendic schist. Occurs at the Faroe Islands, Greenland, and Iceland, associated with chlorite and stilbite; at Aussig in Bohemia; in Germany at Oberstem, with harmotome, and at Annerod, near Giessen; at the Giant's Causeway, Antrim, Ireland, and Renfrew- shire, Scotland; Isle of Skye, etc. In Australia (phacolite) at Richmond, near Melbourne, etc In the United States, in syenite at Somerville, Mass.; at Bergen Hill and West Paterson, N. J., in crystals; at Jones's Falls near Baltimore, Md. (haydenite). In Nova Scotia, wine yellow or flesh-red (the last the acadialite), associated with heulandite, analcite and calcite, at Five Islands, Swan's Creek, Digby Neck, Two Islands, Wasson's Bluff, etc. The name chabazite is from x<*/3^os, an ancient name of a stone. GMELINITE. Rhombohedral. Axis c = 0*7345. Crystals usually hexagonal in aspect; sometimes p (0111) smaller than r(1011),_and habit rhombo- 939 940 hedral; rr' 10_11 A 1101 = 68 8', rp 1011 A 0111 = 37 44'. Cleavage: m (1010) easy; c (0001) sometimes distinct. Frac- ture uneven. Brittle. H. = 4*5. G. = 2-04-2-17. Luster vitreous. Colorless, yellowish white, green- ish white, reddish white, flesh- red. Transparent to translucent. Optically positive, also nega- tive. Birefringence very low. Interference-figure often disturbed, and basal sections divided optically into sections analogous to chabazite. Mean refrac- tive index, 1'47. Comp. In part (Na2,Ca)Al 2 Si40i2.6H 2 O. If sodium alone is present this requires: Silica 46-9, alumina 19-9, soda 12-1, water 21-1 = 100. See also p. 552. Pyr., etc. B.B. fuses easily (F. = 2'5-3) to a white enamel. Decomposed by hydro- chloric acid with separation of silica. Obs. Occurs in flesh-red crystals in amygdaloidal rocks at Montecchio Maggiore, Italy; at Andreasberg, Germany; in Transylvania; Antrim, Ireland; Talisker in Isle of Skye, in large colorless crystals. In Australia at Flinders, Victoria. In the United States in fine white crystals at Bergen Hill, Great Notch and Paterson, N. J. At Cape Blomidon, Nova Scotia (ledererite) ; also at Two Islands and Five Islands. Named Gmelinite after Prof. Gmelin of Tubingen (1792-1860). Levynite. CaAl 2 Si 3 Oi .5H.,p. In rhombohedral crystals. H. = 4-4'5. G. = 2'09-2'lG. Colorless, white, grayish, reddish, yellowish. Optically . co = T50. Found at Glen- arm and at Island Magee, Antrim, Ireland; at Dalsnypen, Faroe Islands, in Iceland; in East Greenland; in the basalt of Table Mountain near Golden, Col. Offretite. A potash zeolite, related to the species of the chabazite group. In basalt of Mont Simiouse, France. ANALCITE. Analcime. Isometric. Usually in trapezohedrons; also cubes with faces n (211); again the cubic faces replaced by a vicinal trisoctahedron. Sometimes in composite groups about a single crystal as nucleus (Fig. 389, p. 161). -Also massive granular; compact with concentric structure. SILICATES 555 942 Cleavage: cubic, in traces. Fracture subconchoidal. Brittle. H. = 5-5 -5. G. = 2-22-2-29. Luster vitreous. Colorless, white; occasionally grayish, greenish, yellowish, or reddish white. Transparent to nearly opaque. Often shows weak double refrac- tion, which is apparently con- nected with loss of water and consequent change in molecular structure (Art. 429). n = 1-4874. Comp. Na AlSi 2 O 6 H 2 O = Na20.Al 2 O3.4Si0 2 .2H 2 O = Silica 54.5, alumina 23-2, soda 14-1, water 8-2 = 100. Analyses show always a varying excess of silica and water above amounts required by formula. It has been assumed that a molecule containing the acid H 2 Si 2 O 6 is present in soild solution in small amounts. Pyr., etc. Yields water in the closed tube. B.B. fuses at 2'5 to a colorless glass. Gelatinizes with hydrochloric acid. Diff. Characterized by trapezohedral form, but is softer than garnet, and yields water B.B., unlike leucite (which is also infusible); fuses without intumescence to a clear glass unlike chabazite. From leucite and spdalite surely distinguished only by chemical tests, i.e., absence of chlorine in the nitric-acid test (see sodalite, p. 502), absence of much potash and abundance of soda in the solution, anol evolution of much water from the powder in a closed glass tube below a red heat. Micro. Recognized in thin sections by its very low relief and isotropic character; often shows optical anomalies. Obs. Occurs frequently with other zeolites., also prehnite, calcite, etc., in cavities and seams in basic igneous rocks, as basalt, diabase, etc.: also in granite, gneiss, etc. Recently shown to be also a rather widespread component of the groundmass of various basic igneous rocks, at times being the only alkali-alumina silicate present, as in the so-called analcite-basalts. Has been held in such cases to be a primary mineral produced by the crystallization of a magma containing considerable soda and .water vapor held under pres- sure. The Cyclopean Islands, near Catania, Sicily, afford pellucid crystals; also the Fassatal in Tyrol, Austria; other localities are, in Scotland, in the Kilpatrick Hills; Co. Antrim, etc., in Ireland; the Faroe Islands; Iceland; near Aussig, Bohemia; at Arendal, Norway, in beds of iron ore; at Andreasberg, in the Harz Mts., Germany, in silver mines. In the United States, occurs at Bergen Hill and West Paterson, N. J.; in gneiss near Yonkers, Westchester Co., N. Y.; abundant in fine crystals with prehnite, datolite, and calcite, in the Lake Superior region; at Table Mt. near Golden, Col., with other zeolites. Nova Scotia affords fine specimens. The name analcime is from avaXms, weak, and alludes to its weak electric power when heated or rubbed. The correct derivative is analcite, as here adopted for the species. Faujasite. Perhaps In isometric octahedrons. H. =5. G. = 1'923. Colorless, white, n = 1'48. Oc- curs with augite in the limburgite of Sasbach in the Kaiserstuhl, Baden, Germany, etc. Edingtonite. Perhaps BaAl 2 Si 3 Oio.3H2O. Crystals pyramidal in habit (orthorhombic, pseudo-tetragonal); also massive. H. = 4-4 -5. G. = 2*694. White, grayish white, pink. Optically . Indices, 1*538-1 '554. Occurs in the Kilpatrick Hills, near Glasgow, Scot- land, with harmotome. From Bohlet, Sweden. Natrolite Group. Orthorhombic and Monoclinic Natrolite Scolecite Mesolite Ca(A10H) 2 (SiO 3 )3.2H 2 O (Na 2 Al 2 Si 3 O 10 .2H 2 O [2[CaAl 2 Si 3 Oio.3H 2 O] a 0*9785 a 0-9764 0-3536 c 0-3434 89 18' 556 DESCRIPTIVE MINERALOGY The three species of the NATROLITE GROUP agree closely in angle, though varying m crystalline system; Natrolite is orthorhombic usually, also rarely monoclmic ; fecolecite is monoclinic, perhaps also in part triclinic; Mesolite seems to be both monoclmic and tn- clinic. Fibrous, radiating or divergent groups are common to all these species. The Natrolite Group includes the sodium silicate, Natrolite, with the empirical formula Na2Al 2 Si 3 Oi .2H 2 O; the calcium silicate, Scolecite, CaAlaSigOio.SHaO; also Mesolite , . \ mNa 2 Al2Si 3 Oio.2H 2 O intermediate between these and corresponding to n CaAl 2 Si3Oio.3H 2 O. NATROLITE. Orthorhombic.* 943 Axes a : b 944 c = 0-9785 : 1 : 0*3536. mm"', 110 A 1TO = 88' mo, 110 A 111 = 63 oo oo' 111 A 111 111 A 111 11'. 37 38'. 36 47'. Crystals prismatic, usually very slender to acicular; frequently divergent, or in stellate groups. Also fibrous, radiating, massive, gran- ular, or compact. Cleavage: m (110) perfect; b (010) imper- fect, perhaps only a plane of parting. Frac- ture uneven. H. = 5-5'5. G. = 2'20-2'25. Luster vitreous, sometimes inclining to pearly, especially in fibrous varieties. Color white, or colorless; to grayish, yellow- ish, reddish to red. Transparent to translucent. Optically +. Ax. pi. || 6 (010). Bx _L c (001). 2V = 63. a = 1'480. ft = T482. 7 = T493. Var. Ordinary. Commonly either () in groups of slender colorless prismatic crys- tals, varying but little in angle from square prisms, often acicular, or (6) in fibrous diver- gent or radiated masses, vitreous in luster, or but slightly pearly (these radiated forms often resemble those of thomsonite and pectolite) ; often also (c) solid amygdules, usually radiated fibrous, and somewhat silky in luster within; (d) rarely compact massive. Galactite is ordinarily natrolite, in colorless needles from southern Scotland. Bergmannite, spreustein, brevicite, are names which have been given to the natrolite from the augite-syenite of southern Norway, on the Langesund fiord, in the "Brevik" region, where it occurs, fibrous, massive, and in long prismatic crystallizations, and from white to red in color. Derived in part from elaeolite, in part from sodalite. Iron-natrolite is a dark green opaque variety, either crystalline or amorphous, from the Brevik region; the iron is due to inclusions. Comp. Na2Al 2 Si 3 Oio.2H 2 or Na 2 O.Al 2 3 .3Si0 2 .2H 2 = Silica 474, alu- mina 26-8, NasO 16-3, water 9-5 = 100. Pyr., etc. In the closed tube whitens and becomes opaque. B.B. fuses quietly at 2 to a colorless glass. Fusible in the flame of an ordinary wax candle. Gelatinizes with acids. Diff. Distinguished from aragonite and pectolite by its easy fusibility and gelati- nization with acid. Obs. Occurs in cavities in amygdaloidal basalt, and other related igneous rocks; sometimes in seams in granite, gneiss, and syenite. Found at Aussig and Teplitz in Bohe- mia; in fine crystals in Auvergne, France; Fassatal, Tyrol, Austria; Kapnik, Hungary. In red amygdules (crocalite) in amygdaloid of Ireland, Scotland and Tyrol; the amygdaloid of Bishopton, Scotland (galactite) and at Glen Farg (fargite) in Fifeshire. Common in the augite-syenite of the Langesund fiord, near Brevik, southern Norway. From various local- ities in Greenland. In North America, in the trap of Nova Scotia; at Bergen Hill and West Paterson, N. J.; at Copper Falls, Lake Superior; from benitoite locality, San Benito Co., Cal. Named Mesotype by Haiiy, from M es, middle, and TVTTOS, type, because the form of the crystal in his view a square prism was intermediate between the forms of stilbite * In rare cases the crystals seem to be monoclinic. SILICATES 557 and analcite. Natrolite, of Klaproth, is from natron, soda; it alludes to the presence of soda, whence also the name soda-mesotype, in contrast with scolecite, or lime-mesotype. SCOLECITE. Monoclinic. Axes a : b : c = 0-9764 : 1 : 0*3434; /3 = 89 18'. Crystals slender prismatic (mm'" 110 A 110 = 88 37%'), twins showing a feather-like striation on b '(010), diverging upward; also as penetration-twins. Crystals in divergent groups. Also massive, fibrous and radiated, and in nodules. Cleavage: m (110) nearly perfect. H. = 5-5-5. G. = 2-16-2-4. Luster vitreous, or silky when fibrous. Transparent to subtranslucent. Optically . Ax. pi. and Bx J_ b (010). Bx a A c axis = 15-16. 2V = 36 (approx.). a - 1-512. |8 = 1-519. 7 = 1'519. Comp. CaAl 2 Si 3 O 10 .3H 2 O or CaO.Al 2 O 3 .3SiO 2 .3H 2 = Silica 45'9, alu- mina 26-0, lime 14-3, water 13*8 = 100. Pyr., etc. B.B. sometimes curls up like a worm (whence the name from o-KuXqg, a worm, which gives scolecite, and not scolesite or scolezite)', other varieties intumesce but slightly, and all fuse at 2-2*2 to a white blebby enamel. Gelatinizes with acids like natrolite. Obs. Occurs in the Berufiord, Iceland; in Scotland in amygdaloid at Staffa Island and in Isle of Skye, at Talisker; near Eisenach, Saxony; in Auvergne, France; common in fine crystallizations in the Deccan trap area, in British India. In crystals from Karsanan- guit-Kakait, Greenland. In the United States, in Col. at Table Mountain near Golden in cavities in basalt. In Canada, at Black Lake, Megantic Co., Quebec. Mesolite. Intermediate between natrolite and scolecite (see p. 556). In acicular and capillary crystals; delicate divergent tufts, etc. G. = 2 -29. White or colorless. Indices, 1 '505-1 '506. In amygdaloidal basalt at numerous points. Crystals from Faroe Islands appear to be triclinic, pseudomonoclinic through twinning. Pseudomesolite is name given to a zeolite from Carlton Peak, Minn., like mesolite except for its optical characters. Gonnardite. (Ca,Na 2 )2Al 2 Si5Oi5.5H2O. In spherules with radiating structure. G. = 2-25-2-35. From basalt of Gignat, Puy-de-D6me, France. THOMSONITE. Orthorhombic. Axes a : b : c = 0-9932 : 1 : 1-0066. Distinct crystals rare; in prisms, mm'" 110 A ,110 = 89 37'. Commonly columnar, structure radiated; in radiated spherical concretions; also closely compact. Cleavage: 6 (010) perfect; a (100) less so; c (001) in traces. Fracture uneven to subconchoidal. Brittle. H. = 5-5*5. G. = 2-3-2-4. Luster vitreous, more or less pearly. Snow-white; reddish, green; impure varieties brown. Streak uncolored. Transparent to translucent. Pyroelectric. Op- tically + . Ax. pi. 1 1 c (001). Bx J_ 6 (010). Dispersion p > v strong. 2V = 54 (approx.). a = 1-497. ft = 1-503. 7 = 1'525. Var. 1. Ordinary, (a) In regular crystals, usually more or less rectangular in out- line, prismatic in habit. (6) Prisms slender, often vesicular to radiated, (c) Radiated fibrous, (d) Spherical concretions, consisting of radiated fibers or slender crystals. Also massive, granular to impalpable, and white to reddish brown, less often green as in Union- ite. The spherical massive forms also radiated with several centers and of varying colors, hence of much beauty when polished. Ozarkite is a white massive thomsonite from Arkan- sas. Comp. (Na 2 ,Ca) Al 2 Si 2 O 8 .2JH 2 or (Na 2 ,Ca)O.Al 2 O 3 .2SiO 2 .2iH 2 0. The ratio of Na 2 : Ca varies from 3 : 1 to 1 : 1. If Ca : Na^ = 3:1 the percentage composition requires: SiO 2 37'0, A1 2 O 3 31-4, CaO 12'9, NaaO 4-8, H 2 13'9 = 100. 558 DESCRIPTIVE MINERALOGY Pyr., etc. B.B. fuses with intumescence at 2 to a white enamel. Gelatinizes with hydrochloric acid. ' Diff. Resembles some natrolite, but fuses to an opaque, not to a clear glass. Obs. Found in cavities in lava in amygdaloidal igneous rocks, sometimes with elseolite as a result of its alteration. Occurs near Kilpatrick, Scotland; in the lavas of Mte Somma (comptonite) , Vesuvius; in basalt at the Pflasterkaute in Saxe Weimar, Ger- many in Bohemia, in phonolite; the Cyclopean islands, Sicily; near Brevik, Norway; the Faroe' Islands; Iceland (carphostilbite, straw-yellow); at Mt. Monzoni, Fassatal, Tyrol, Occurs at Peter's Point, Nova Scotia. In the United States, at West Paterson, N. J.; at Magnet Cove (ozarkite) in the Ozark Mts,, Ark.; in the amygdaloid of Grand Marais, Lake Superior, which yields the water-worn pebbles resembling agate, in part green (linton- ite) ; in the basalt of Table Mt. near Golden, Col. HYDROTHOMSONITE. (H 2 ,Na 2) Ca)Al2Si2O8.5H 2 O. An alteration product of thomsonite or scolecite from Tschakwa near Batum on the Black Sea. Arduinite. A zeolite containing lime and soda. In radiating fibrous aggregates. G. = 2-26. Color red. From Val dei Zuccanti, Venetia, Italy. Echellite. (Ca,Na 2 )O.2Al 2 O 3 .3SiO 2 ,4H 2 O. In radiating, fibrous, spheroidal masses. White. H. = 5. ft = T533. Elongated |[ Y. From Sextant Portage, Abitibi River, Northern Ontario. Epidesmine. Comp. same as for stilbite. Orthorhombic. In minute crystals, only the three pinacoids showing. Cleavages parallel to both vertical pinacoids. Colorless to yel- low. Index = 1 '50. Bx a perpendicular to c (001). Optically-. G. =2*16. Easily fusible with intumescence. Occurs as a crust on calcite from Schwarzenberg, Saxony. Stellerite. CaAl 2 Si 7 Oi 8 .7H 2 O. Orthorhombic. Crystals tabular parallel to b (010). Cleavage perfect parallel to b (010), imperfect parallel to a (100) and c (001). H. = 3 '5-4. G. = 2*12. Indices, 1 '48-1 '50. Found in cavity in a diabase tuff, Copper Island, Com- mander Islands. Erionite. H 2 CaK 2 Na 2 Al 2 Si 6 Oi 7 .5H 2 O. Orthorhombic. In aggregates of very slender fibers, resembling wool. G. = 1'997. White. Occurs in cavities in rhyolite from Durkee, Oregon. Bavenite. Ca 3 Al 2 (SiO3)6.H 2 O. Monoclinic. Fibrous-radiated groups of prismatic crystals. One cleavage. H. = 5'5. G. = 2*7. Color white. = 1'58. Occurs in peg- matitic druses in the granite of Baveno, Italy. Bityite. A hydrous silicate of calcium and aluminium, with small amounts of the alkalies. Pseudo-hexagonal. In minute hexagonal plates which in polarized light show division into six biaxial sectors. Cleavage parallel to base. H. = 5*5. G. = 3*0. In- dices 1 '62-1 '64. Found as crystal crusts in pegmatite veins at Maharitra, Madagascar. Hydronephelite. HNa 2 Al 3 Si 3 Oi 2 .3H 2 O. Massive, radiated. H. = 4'5-6. G. = 2'263. Color white; also dark gray. Index, 1'50. From Litchfield, Me.; said however to be a mixture of natrolite, hydrargillite and diaspore. Ranite from the Langesund fiord, Norway, is similar. II. Mica Division The species embraced under this Division fall into three groups: 1, the MICA GROUP, including the Micas proper; 2, the CLINTONITE GROUP, or the Brittle Micas; 3, the CHLORITE GROUP. Supplementary to these are the Vermiculites, hydrated compounds, chiefly results of the alteration of some one of the micas. All of the above species have the characteristic micaceous structure, that is, they have highly perfect basal cleavage and yield easily thin laminae. They belong to the monoclinic system, but the position of the bisectrix in general deviates but little from the normal to the plane of cleavage; all of them show on the basal section plane angles of 60 or 120, marking the relative position of the chief zones of forms present, and giving them the appearance of hex- SILICATES 559 agonal or rhombohedral symmetry; further, they are more or less closely related among themselves in the angles of prominent forms. The species of this Division all yield water upon ignition, the micas mostly from 4 to 5 p. c., the chlorites from 10 to 13 p. c.; this is probably to be regarded in all cases as water of constitution, and hence they are not properly hydrous silicates. More or less closely related to these species are those of the Serpentine and Talc Division and the Kaolin Division following, many of which show dis- tinctly a mica-like structure and cleavage and also pseudo-hexagonal sym- metry. 1. Mica Group. Monoclinic Muscovite Paragonite Lepidolite Zinnwaldite Biotite Phlogopite H 2 KAl 3 (Si0 4 ) 3 c = 0-57735 : 1 : 3-3128 H 2 NaAl 3 (SiO 4 )3 KLi[Al(OH,F) 2 ]Al(Si0 3 ) 3 in part. ft = 89 54' Potassium Mica a : b Sodium Mica Lithium Mica Lithium-iron Mica Magnesium-iron Mica (H,K) 2 (Mg,Fe) 2 (Al,Fe) 2 (SiO 4 ) 3 in part. a : b : c = 0-57735 : 1 : 3-2743 = 90 0' (H,K,(MgF)) 3 Mg 3 Al(Si0 4 ) 3 Magnesium Mica; usually containing fluorine, nearly free from iron. Lepidomelane Annite. Iron Micas. Contain ferric iron in large amount. The species of the MICA GROUP crystallize in the monoclinic system, but with a close approximation to either rhombohedral or orthorhombic symmetry; the plane angles of the base are in all cases 60 or 120. They are all charac- terized by highly perfect basal cleavage, yielding very thin, tough, and more or less elastic laminae. The negative bisectrix, X, is very nearly normal to the basal plane, varying at most but a few degrees from this; hence a cleavage plate shows the axial interference-figure, which for the pseudo-rhombohedral kinds is often uniaxial or nearly uniaxial. Of the species named above, biotite has usually a very small axial angle, and is often sensibly unaxial; the axial angle of phlogopite is also small, usually 10 to 12; for muscovite, para- gonite, lepidolite the angle is large, in air commonly from 50 to 70. The Micas may be referred to the same fundamental axial ratio with an angle of obliquity differing but little from 90; they show to a considerable extent the same forms, and their isomorphism is further indicated by their not infrequent intercrystallization in par- allel position, as biotite with muscovite, lepidolite with muscovite, etc. A blow with a somewhat dull-pointed instrument on a cleavage plate of mica develops in all the species a six-rayed percussion-figure (Fig. 945, also Fig. 491, p. 189), two lines of which are nearly par- allel to the prismatic edges ; the third, which is the most strongly characterized, is parallel to the clino- pinacoid or plane of symmetry. The micas are often divided into two classes, according to the position of the plane of the optic axes. In the first class 945 560 DESCRIPTIVE MINERALOGY belong those kinds for which the optic axial plane is normal to b (010), the plane of symmetry (Fig. 945) ; in the second class the axial plane is parallel to the plane of symmetry. The percussion figure serves to fix the crystallo- graphic orientation when crystalline faces are wanting. A second series of lines at right angles to those mentioned may be more or less distinctly developed by pressure of a dull point on an elastic surface, forming the so-called pressure- figure; this is sometimes six-rayed, more often shows three branches only, and sometimes only two are developed. In Fig. 945 the position of the pressure- figure is indicated by the broken lines. These lines are connected with gliding- planes inclined some 67 to the plane of cleavage (see beyond). The micas of the first class include : Muscovite, paragonite, lepidolite, also some rare varieties of biotite called anomite. The second class embraces: Zinnwaldite and most biotite, including lepidomelane and phlogopite. Chemically considered, the micas are silicates, and in most cases orthosili- cates, of aluminium with potassium and hydrogen, also often magnesium, ferrous iron, and in certain cases ferric iron, sodium, lithium (rarely rubidium and caesium); further, rarely, barium, manganese, chromium. Fluorine is prominent in some species, and titanium is also sometimes present. Other elements (boron, etc.) may be present in traces. All micas yield water upon ignition in consequence of the hydrogen (or hydroxyl) which they contain. MUSCOVITE. Common Mica. Potash Mica. Monoclinic. Axes a b : c = 0*57735 : 1 : 3-3128; /3 = 89 54'. Twins common according to the mica-law: tw. pi. a plane in the zone cM 001 A 221 normal to c (001) the crystals often united by c. Crystals rhombic or hexagonal in outline with plane angles of 60 or 120. Habit tabular, passing into tapering forms with planes more or less rough and strongly striated horizontally; vicinal forms common. Folia often very small and aggregated in stellate, plumose, or globular forms; or in scales, and scaly massive; also cryptocrystalline and compact massive. Cleavage : basal, eminent. Also planes of secondary cleavage as shown in the percussion-figure (see pp. 559 and 189) ; natural plates hence often yield cM, 001 A 221 = 85 36'. CM, 001 A 111 = 81 30'. MM', 221 A 221 = 59 48'. MM', HI A 111 = 59 16'. narrow strips or thin fibers || axis b, and less distinct in directions inclined 60 to this. Inin L laminae flexible and elastic when bent, very tough, harsh to the touch, passing into kinds which are less elastic and have a more or less unctuous or talc-like feel. Etching-figures on c (001) , monoclinic in symmetry (rig. 495, p. 190). .~~' T* i ^*' ^' = ^ '76-3. Luster vitreous to more or less pearly or Iky. Colorless, gray, brown, hair-brown, pale green, and violet, yellow, dark olive-green, rarely rose-red. Streak uncolored. Transparent to trans- lucent. Pleochroism usually feeble; distinct in some deep-colored varieties (see >eyond). Absorption in the direction normal to the cleavage plane (vibra- X , aj strong, much more so than transversely (vibrations 1 1 X) ; hence a 'i SILICATES 561 crystal unless thin is nearly or quite opaque in the first direction though translucent through the prism. Optically . Ax. pi. J_ b (010) and nearly J_ c (001). Bxa (= X) inclined about -- 1 (behind) to a normal to c (001). Dispersion p > v. 2V variable, usually about 40, but diminishing in kinds (phengite) relatively high in silica, a 1*561. ft = T590. 7 = T594. Var. 1. Ordinary Muscovite. In crystals as above described, often tabular || c (001), also tapering with vertical faces rough and striated; the basal plane often rough unless as developed by cleavage. More commonly in plates without distinct outline, except as developed by pressure (see above) ; the plates sometimes very large, but passing into fine scales arranged in plumose or other forms. In normal muscovite he thin laminae spring back with force when bent, the scales are more or less harsh to the touch, unless very small, and a pearly luster is seldom prominent. 2. DAMOURITE. Including margarodite, gilbertite, hydro-muscovite, and most HYDRO- MICA in general. Folia less elastic; luster somewhat pearly or silky and feel unctuous like talc. The scales are usually small and it passes into forms which are fine scaly or fibrous, as sericite, and finally into the compact crypto-crystalline kinds called oncosine, including much pinite. Often derived by alteration of cyanite, topaz, corundum, etc. Although often spoken of as hydrous micas, it does not appear that damourite and the allied varieties necessarily contain more water than ordinary muscovite; they may, however, give it off more readily. Margarodite, as originally named, was the talc-like mica of Mt. Greiner in the Zillertal, Tyrol, Austria; granular to scaly in structure, luster pearly, color grayish white. Gilbertite occurs in whitish, silky forms from the tin mine of St. Austell, Cornwall. Sericite is a fine scaly muscovite united in fibrous aggregates and characterized by its silky luster (hence the name from O-T/PIKOS, silky}. Comp. For the most part an orthosilicate of aluminium and potas- sium (H,K)AlSiO 4 . If, as in the common kinds, H : K = 2 : 1, this becomes H 2 KAl 3 (SiO 4 )3 = 2H 2 O.K 2 O.3Al 2 O 3 .6SiO 2 = Silica 45-2, alumina 38*5, potash 11-8, water 4-5 = 100. Some kinds give a larger amount of silica (47 to 49 p. c.) than corresponds to a normal orthosilicate, and they have been called phengite. As shown by Clarke, these acid mus- covites can be most simply regarded as molecular mixtures of H^KA^SiO^s and H 2 KAl 3 (Si 3 8 ) 3 . Iron is usually present in small amount only. Barium is rarely present, as in oellacherite. G. = 2'88-2*99. Chromium is also present in fuchsite from Schwarzenstein, Zillertal, Tyrol, and elsewhere. Pyr., etc. In the closed tube gives water. B.B. whitens and fuses on the thin edges (F. = 5'7) to a gray or yellow glass. With fluxes gives reactions for iron and sometimes manganese, rarely chromium.* Not decomposed by acids. Decomposed on fusion with alkaline carbonates. . Diff. Distinguished in normal kinds from all but the species of this division by the perfect basal cleavage and micaceous structure, the pale color separates it from most biotite; the laminae are more flexible and elastic than those of phlogopite and still more than those of the brittle micas and the chlorites. Micro. In thin sections recognized by want of color and by the perfect cleavage shown by fine lines (as in Fig. 951, p. 564) in sections _1_ c (001), in a direction parallel to c. By reflected light under the microscope the same sections show a peculiar mottled surface with satin-like luster; birefringence rather high, hence interference-colors bright. Obs. Muscovite is the most common of the micas. It is an essential constituent of mica schist and related rocks, and is a prominent component of certain common varieties of granite and gneiss; also found at times in fragmental rocks and limestones; in volcanic rocks it is rare and appears only as a secondary product. The largest and best developed crystals occur in the pegmatite dikes associated with granitic intrusions, either directly cutting the granite or in its vicinity. Often in such occurrences in enormous plates from which the mica or "isinglass" of commerce is obtained. It is then often associated with crystallized orthoclase, quartz, albite; also apatite, tourmaline, garnet, beryl, columbite, etc., and other mineral species characteristic of granitic veins. Further, muscovite often encloses flattened crystals of garnet, tourmaline, also quartz in thin plates between the sheets; further not infrequently magnetite in dendrite-like forms following in part the direc- tions of the percussion-figure. 562 DESCRIPTIVE MINERALOGY Some of the best known localities, are: Abiihl in the Sulzbachtal, Austrian Tyrol; with adularia; Rothenkopf in the Zillertal, Tyrol; Soboth, Styria; St. Gothard, Binnental, and elsewhere in Switzerland; Mourne Mts., Ireland; Cornwall; Uto, Falun, Sweden; Skut- terud, and Bamble, Norway. Obtained in large plates from Greenland and the East Indies. In Me., at Mount Mica in the town of Paris; at Buckfield, in fine crystals. In N. H., at Acworth, Graf ton. In Mass., at Chesterfield; South Royalston; at Goshen, rose-red. In Conn., at Monroe; at Litchfield, with cyanite; at the Middletown feldspar quarry; at Haddam; at Branch ville, with albite, etc.; New Milford. In N. Y., near Warwick; Eden- ville; Edwards. In Pa., at Pennsbury, Chester Co.; at Unionville, Delaware Co., and at Middletown. In Md., at Jones's Falls, Baltimore. In Va., at Amelia Court-Hquse. In N. C., extensively mined at many places in the western part of the state; the chief mines are in Mitchell, Yancey, Jackson and Macon Cos.; crystals from Lincoln Co. The mica mines have also afforded many rare species, as columbite, samarskite, hatchettolite, uran- inite, etc.; in good crystals in Alexander Co. In S. C., there are also muscovite deposits; also in Ga. and Ala. Mica mines have also been worked to some extent in the Black Hills, S. D.; in Wash., at Rockford, Spokane Co.; in Col. The important states for the production of mica are North Carolina, New Hampshire, Idaho, South Dakota, Virginia, Alabama, New York, Connecticut. Muscovite is named from Vitrum Muscoviticum or Muscovy-glass, formerly a popular name of the mineral. Use. As an insulating material in electrical apparatus; as a non-inflammable trans- parent material for furnace doors, etc.; in a finely divided form as a non-conductor of heat and fireproofing material; mixed with oil as a lubricant, etc. Finite. A general term used to include a large number of alteration-products especially of iolite, also spodumene, nephelite, scapolite, feldspar and other minerals. In composi- tion essentially a hydrous silicate of aluminium and potassium corresponding more or less closely to muscovite, of which it is probably to be regarded as a massive, compact variety, usually very impure from the admixture of clay and other substances. Characters as fol- lows: Amorphous; granular to cryptocrystalline. Rarely a submicaceous cleavage. H. = 2'5-3'5. G. = 2'6-2'85. Luster feeble, waxy. Color grayish white, grayish green, pea- green, dull green, brownish, reddish. Translucent to opaque. The following are some of the minerals also classed as pinite: gigantolite, gieseckite (see p. 500), liebenerite, dysyntribite, par ophite, rosite, polyargite, wilsonite, killinite. Agalmatolite (pagodite) is like ordinary massive pinite in its amorphous compact texture, luster, and other physical characters, but contains more silica, which may be from free quartz or feldspar as impurity. The Chinese has H. = 2-2'5; G. = 2785-2'815. Colors usually grayish, grayish green, brownish, yellowish. Named from aja\na, an image; pagodite is from pagoda, the Chinese carving the soft stone into miniature pagodas, images, etc. Part of the so-called agalmatolite of China is true pinite in composition, another part is compact pyrophyllite, and still another steatite (see these species). Paragonite. A sodium mica, corresponding to muscorite in composition; formula, HaNaAlsCSiCMs. In fine pearly scales; also compact. G. = 278-2-90. Index, 1'60. Color yellowish, grayish, greenish; constitutes the mass of the rock at Monte'Campione near Faido in Canton Tessin, Switzerland, containing cyanite and staurolite; called paragonite- schist. Occurs associated with tourmaline and corundum at Unionville, Delaware Co., Pa. Hallerite, a mica with an iridescent silver color and pearly luster. Perhaps a lithium-bear- ing paragonite. Found at Mesores, near Autun, France. BADDECKITE, an iron mica related to muscovite. In small scales with a copper-red color. From near Baddeck, Nova Scotia. LEPIDOLITE. LithiaMica. In aggregates of short prisms, often with rounded terminal faces. Crys- tals sometimes twins or trillings according to the mica law. Also in cleavable plates, but commonly massive scaly-granular, coarse or fine. Cleavage: basal, highly eminent. H. = 2-5-4. G. = 2 -8-2 -9. Luster pearly Color rose-red, violet-gray or lilac, yellowish, grayish white, white. Translucent Optically -. Ax. pi. usually b (010); rarely || 6. Bx a (X) i n Si 1 7oJ f d ' * nd T 33 *' " ellow to normal to c irom ou iZ , p = 1'5975. SILICATES 563 Comp. In part a metasilicate, R 3 Al(SiO 3 ) 3 or KLi[Al(OH,F) 2 ]Al(Si0 3 ) 3 . The ratio of fluorine and hydroxyl is variable. It has been suggested that the puro lepidolite molecule is represented by 3Li 2 O.2K 2 O. 3Al 2 O3.8F.12SiO 2 and that most lepidolites are mixtures of this and the muscovite molecule. Pyr., etc. In the closed tube gives water and reaction for fluorine. B.B. fuses with intumescence at 2-2 '5 to a white or grayish glass sometimes magnetic, coloring the flame purplish red at the moment of fusion (lithia) . With the fluxes some varieties give reactions for iron and manganese. Attacked but not completely decomposed by acids. After fusion, gelatinizes with hydrochloric acid. Obs. Occurs in granite and gneiss, especially in granitic veins; often associated with lithia-tourmaline; also with amblygonite, spodumene, cassiterite, etc.; sometimes associ- ated with muscovite in parallel position. Found near TJto in Sweden; Penig, Saxony; Rozena (or Rozna), Moravia; Madagascar, etc. In the United States, common in the western part of Me., in Hebron, Auburn, Paris, etc.; at Chesterfield, Mass.; Middletown and Haddam Neck, Conn.; with rubellite near San Diego, Cal. Named lepidolite from XeTm, scale, after the earlier German name Schuppenstein, allud- ing to the scaly structure of the massive variety of Rozena. Use. As a source of lithium compounds. COOKEITE is a micaceous mineral occurring in rounded aggregations on rubellite, also with lepidolite, tourmaline, etc., at Hebron, Me. An alteration of lepidolite or tourmaline. Composition Li[Al(OH) 2 l3(SiO 3 ) 2 . Zinnwaldite. An iron-lithia mica in form near biotite. Color pale violet, yellow to brown and dark gray. Occurs at Zinnwald and Altenberg, Germany; similarly in Corn- wall, England. From Narsarsuk, Greenland, and the York region, Alaska. Cryophyllite is a related lithium mica from Rockport, Mass. Polylithionite is a lithium mica from Kangerdluarsuk, Greenland. Irvingite is an alkalie mica containing lithium from near Wausau, Wis. Manandonite. A basic boro-silicate of lithium and aluminium, H 24 Li4Ali4B 4 Si6O53. Micaceous. In lamellar aggregates or mammillary crusts of hexagonal plates. Perfect basal cleavage. Color white. Luster pearly. Optically +. Axial angle small and vari- able. Easily fusible giving red flame. Unattacked by acids. Found in pegmatite at An- tandrokomby, near the Manandona River, Madagascar. BIOTITE. Monoclinic; pseudo-rhombohedral. Axes a : b : c = 0-57735 : 1 : 3 -2743; = 90. Habit tabular or short prismatic; the pyramidal faces often repeated in oscillatory combination. .Crystals often apparently rhombohedral in sym- metry since r (101) and z (132), z' (132), which are inclined to c (001) at sen- sibly the same angle, often occur together; further, the zones to which these faces belong are inclined 120 to each other, hence the hexagonal outline of basal sections. Twins, according to the mica law, tw. pi. a plane in the prismatic zone _L c (001) . Often in disseminated scales, sometimes in massive aggregations of cleavable scales. 948 M 960 co, 001 A 112 cM, 001 A 221 c/*, 001 A 111 73 1'. cr, 001 A T01 = 80 0'. 85 38'. cz, 001 A 132 = 80 0'. 81 19'. MM', 221 A 221 = 59 48*'. 564 DESCRIPTIVE MINERALOGY Cleavage: basal, highly perfect; planes of separation shown in the percus- sion-figure; also gliding-planes /> (205), , f (135) shown in the pressure-figure inclined about 66 to c (001) and yielding pseudo-crystalline forms (Fig. 489, p. 188). H. = 2-5-3. G. = 27-3-1. Luster splendent, and more or less pearly on a cleavage surface, and sometimes submetallic when black; lateral surfaces vitreous when smooth and shining. Colors usually green to black, often deep black in thick crystals, and sometimes even in thin laminae, unless the lamina? are very thin; such thin lamina? green, blood-red, or brown by transmitted light; also pale yellow to dark brown; rarely white. Streak uncolored. Transparent to opaque. Pleochroism strong; absorption Y = Z nearly, for X much stronger. Hence sections || c (001) dark green or brown to opaque; those J_ c lighter and deep brown or green for vibrations 1 1 c, pale yellow, green or red for vibrations J_ c. Pleochroic halos often noted, particularly about microscopic inclusions. Optically . Ax. pi. usually || b (010), rarely _L b. Bx a (=X) nearly coinci- dent with the normal to c (001), but inclined about half a degree, sometimes to the front, sometimes the reverse. Axial angle usually very small, and often sensibly uniaxial; also up to 50. Birefringence high, y a = 0*04 to 0-06. Comp. In most cases an orthosilicate, chiefly ranging between (H,K) 2 (Mg,Fe) 4 (Al,Fe) 2 (Si0 4 ) 4 and (H,K) 2 (Mg,Fe) 2 Al 2 (SiO 4 ) 3 . Of these the second formula may be said to represent typical biotite. The amount of iron varies widely. Var. Biotite is divided into two classes by Tschermak: I. MEROXENE. Axial plane || 6 (010). II. ANOMITE. Ax. pi. J_ 6 (010). Of these two kinds, meroxene includes nearly all ordinary biotite, while anomite is, so far as yet observed, of restricted occurrence, the typical localities being Greenwood Furnace, Orange Co., N. Y., and Lake Baikal in East Siberia. Meroxene is a name early given to the Vesu- vian biotite. Anomite is from aw^tos, contrary to law. Haughtonite and Siderophyllite are kinds of biotite containing much iron. Manganophyllite is a manganesian biotite. Occurs in aggregations of thin scales. Color bronze- to copper-red. Streak pale red. From Pajsberg and Langban, Sweden; Pied- mont, Italy. Pyr., etc. In the closed tube gives a little water. Some varieties give the reaction for fluorine in the open tube; some kinds give little or no reaction for iron with the fluxes, while others give strong reactions for iron. B. B. whitens and fuses on the thin edges. Completely decomposed by sulphuric acid, leaving the silica in thin scales. DM. Distinguished by its dark green to brown and black color and micaceous structure, usually nearly uniaxial. Micro. Recognized in thin sections by 'its ^ brown (or green) color; strong pleochroism and strong absorption parallel to the elongation (unlike tourmaline). Sections | c (001) are non-pleochroic, commonly exhibit more or less distinct hexagonal outlines and yield a negative sensibly uniaxial figure. Sections _|_ c are strongly pleochroic and are marked by fine parallel, cleavage lines (Fig. 951); they also have nearly parallel extinction, and show high ,. polarization colors; by reflected light they exhibit them from ^ro u 01 ' Vv h a 1 tered sheen which is vei T characteristic and aids in distinguishing ^i ~V? iotit r is an , im P rtant constituent of many different kinds of igneous rocks, illy those formed from magmas containing considerable potash and magnesia non in certain varieties of granites, syenite, diorite, etc., of the massive granular type; i rhyohte trachyte, and andesite among the lavas; in minettes, kersantites, etc. It .curs also as the product of metamorphic action in a variety of rocks. It is not infre- SILICATES 565 quently associated in parallel position with muscovite, the latter, for example, forming the outer portions of plates having a nucleus of biotite. Some of the prominent localities of crystallized biotite are as follows: Vesuvius, com- mon particularly in ejected limestone masses on Monte Somma, with augite, chrysolite, nephelite, humite, etc. The crystals are sometimes nearly colorless or yellow and then usually complex in form; also dark green to black; Mt. Monzoni in the Fassatal and Schwarzenstein, Zillertal, Tyrol, Austria; Rezbanya and Morawitza in Hungary; in Ger- many at Schelingen and other points in the Kaiserstuhl and the Laacher See; on the west side of Lake Ilmen near Miask, Russia. In the United States ordinary biotite is common in granite, gneiss, etc.; but notable localities of distinct crystals are not numerous. It occurs with muscovite (which see) as a more or less prominent constituent of the pegmatite veins in the New England States; also Pennsylvania, Virginia, North Carolina. From Greenwood, Orange Co., N. Y. Sidero- phyllite is from the Pike's Peak region, Col. CASWELLITE. An altered biotite from Franklin Furnace, N. J. PHLOGOPITE. Monoclinic. In form and angles near biotite. Crystals prismatic, taper- ing; often large and coarse; in scales and plates. Cleavage: basal, highly eminent. Thin laminae tough and elastic. H. = 2-5-3. G. = 278-2-85. Luster pearly, often submetallic on cleavage surf ace. Color yellowish brown to brownish red, with often something of a copper-like reflection; also pale brownish yellow, green, white, colorless. Often exhibits asterism in transmitted light, due to regularly arranged inclusions. Pleo- chroism distinct in colored varieties: Z brownish red, Y brownish green, X yellow. Absorption Z > Y > X. Optically-. Ax. pi. || b (010). Bx a nearly _!_ c (001). Axial angle small but variable even in the same specimen, from to 50. Dispersion p < v. The axial angle appears to increase with the amount of iron. Indices variable, from 1-541-1-638. Comp. A magnesium mica, near biotite, but containing little iron; potassium is prominent as in all the micas, and in most cases fluorine. Typi- i i cal phlogopite is R 3 Mg3Al(SiO 4 )3, where R = H,K,MgF. Obs. Phlogopite is especially characteristic of crystalline limestone or dolomite. It is often associated with pyroxene, amphibole, serpentine, etc. Thus as at Pargas, Fin- land; in St. Lawrence Co. and Jefferson Co., N. Y.; Franklin, N. J.; also Burgess, Ontario, and elsewhere in Canada. Named from Xoyco7r6s, fire-like, in allusion to the color. The asterism of phlogopite, seen when a candle-flame is viewed through a thin sheet, is a common character, particularly prominent in the kinds from northern New York and Canada. It has been shown to be due to minute acicular inclusions, rutile or tourmaline, arranged chiefly in the direction of the rays of the pressure-figure, producing a distinct six- rayed star: also parallel to the lines of the percussion-figure, giving a secondary star, usually less prominent than the other. Taeniolite. Essentially a potassium-magnesium silicate. Monoclinic, belonging to the mica group. Perfect basal cleavage. Folia somewhat elastic. H. = 2 '5-3. G. = 2 "9. Colorless. Fusible. From Narsarsuk, southern Greenland. Lepidomelane. Near biotite, but characterized By the large amount of ferric iron present. From Langesund fiord, Norway; Haddam, Conn. Annite from Cape Ann, Mass., belongs here. In small six-sided tables, or an aggregate of minute scales. H. = 3. G. = 3 '0-3 -2. Color black, with occasionally a leek-green reflection. Alurgite. A manganese mica from St. Marcel, Piedmont, Italy. Color copper-red. Index, 1'59. Mariposite may belong here. Roscoelite. A vanadium mica; essentially a muscovite in which vanadium has partly replaced the aluminium. In minute scales; structure micaceous. G. = 2'92-2'94. Color 566 DESCRIPTIVE MINERALOGY clove-brown to greenish brown. Indices, 1 '610-1 704. Occurs in Cal. at the gold mine at Granite Creek, Placerville, and elsewhere, El Dorado Co. 2. Clintonite Group. Monoclinic The minerals here included are sometimes called the Brittle Micas. They are near the micas in cleavage, crystalline form and optical properties, but are marked physically by the brittleness of the laminae, and chemically by their basic character. In several respects they form a transition from the micas proper to the chlorites. Margarite, or calcium mica, is a basic silicate of aluminium and calcium, while Chloritoid is a basic silicate of aluminium and ferrous iron (with magnesium), like the chlorites. MARGARITE. Monoclinic. Rarely in distinct crystals. Usually in intersecting or aggregated laminae; sometimes massive, with a scaly structure. Cleavage: basal, perfect. Laminae rather brittle. H. = 3 -5-4*5. G. = 2-99-3-08. Luster of base pearly, of lateral faces vitreous. Color grayish, reddish white, pink, yellowish. Translucent, subtranslucent. Optically . Ax. pi. J_ b (010). Bx a approximately J_ c (001), but vary- ing more widely than the ordinary micas. X A c axis = + 6^. Dispersion p < v. Axial angle large, from 76 to 128 in air. Refractive index ft =1-64- 1-65. Comp. H 2 CaAl 4 Si 2 Oi2 = Silica 30'2, alumina 51 '3, lime 14'0, water 4'5 = 100. Pyr., etc. Yields water in the closed tube. B.B. whitens and fuses on the edges. Slowly and imperfectly decomposed by boiling hydrochloric acid. Obs. Associated commonly with corundum, and in many cases obviously formed directly from it; thus at the emery deposits of Gumuch-dagh in Asia Minor, the islands Naxos, Nicaria, etc. Occurs in chlorite of Mt. Greiner, Sterzing, Tyrol. In the United States at the emery mine at Chester, Mass.; at Unionville, Chester Co., Pa.; with corun- dum in Madison Co. and elsewhere in N. C.; at Gainesville, Hall Co., Ga.; at Dudley ville, Ala. . Named Margarite from fj.apyapiTt]s, pearl. SEYBERTITE. Clintonite. Brandisite. Monoclinic, near biotite in form. Also foliated massive; sometimes lamellar, radiate. Cleavage: basal, perfect. Structure foliated, micaceous. Laminae brittle. Percussion- and pressure-figures, as with mica. H. = 4-5. G. = 3-3-1. Luster pearly submetallic. Color reddish brown, yellowish, copper-red. Streak uncolored, or slightly yellowish or grayish. Pleochroism rather feeble. Optically . Ax. pi. J_ 6 (010) seybertite; \\ b brandisite. Bx a nearly J_ c (001). Axial angles variable, but not large, a = 1*646. ft = 1-657. 7 = 1 '658. y**- ! The Amity seybertite (dintonite} is in reddish brown to copper-red brittle foli- ated masses; the surfaces of the folia often marked with equilateral triangles like some mica and chlorite. Axial angle 3-13. 2. Brandisite (disterrite) , from the Fassatal, Tyrol, is in hexagonal prisms of a yellowish ffT ?mm ^T^en lor to reddish gray; H. = 5 of base; of sides, 6-6-5. Ax. pi. || b (010). Axial angle 15-30. Some of it pseudomorphous, after fassaite. SILICATES 567 Comp. In part H 3 (Mg,Ca)5Al 5 Si 2 O 18 = 3H 2 0.10(Mg,Ca)0.5Al 2 O 3 . 4SiO 2 . Pyr., etc. Yields water. B.B. infusible but whitens. In powder acted on by con- centrated acids. Obs. Seybertite occurs at Amity, N. Y., in limestone with serpentine, associated with amphibole, spinel, pyroxene, graphite, etc.; also a chlorite near leuchtenbergite. Brandis- ite occurs on Mt. Monzoni in the Fassatal, Tyrol, Austria, in white limestone, with fassaite and black spinel. Xanthophyllite. Perhaps HsCMgjCa^Al^SisOsa. The original xanthophyllite is in crusts or in implanted globular forms. Optically negative. Axial angle usually very small, or sensibly uniaxial; sometimes 20. Indices, -1 '649-1 '661. From near Zlatoust in the Ural Mts. Found at Crestmore, Riverside Co., Cal. Waluewite is the same species occurring in distinct pseudo-rhombohedral crystals. Folia brittle. H. = 4'6. G. = 3 '093. Luster vitreous; on cleavage plane pearly. Color leek- to bottle-green. Transparent to translucent. Pleochroism rather feeble: || c axis fine green; _L c axis reddish brown. Optically . Ax. pi. || b (010). Bx sensibly J_ c (001). Axial angle 17 to 32. Found with perovskite and other species in chloritic schists near Achmatovsk, in the southern Ural Mts. CHLORITOID. Ottrelite. Phyllite. Probably triclinic. Rarely in distinct tabular crystals, usually hexagonal in outline, often twinned with the individuals turned in azimuth 120 to each other. Crystals grouped in rosettes. Usually coarsely foliated massive; folia often curved or bent and brittle; also in thin scales or small plates dis- seminated through the containing rock. Cleavage: basal, but less perfect than with the micas; also imperfect parallel to planes inclined to the base nearly 90 and to each other about 60 ; b (010) difficult. Laminae brittle. H. = 6'5. G. = 3'52-3'57. Color dark gray, greenish gray, greenish black, grayish black, often grass-green in very thin plates. Streak uncolored, or grayish, or very slightly greenish. Luster of surface of cleavage somewhat pearly. Pleochroism strong: Z yellow green, Y indigo-blue, X olive-green. Opti- cally + . Ax. pi. nearly || b (010). Bx a inclined about 12 or more to the nor- mal to c (001). Dispersion p > v, large, also horizontal. Axial angles, in air 65 to 120. = 175. Birefringence low, 7 - a = 0'007-0'016. Comp. For chloritoid H 2 (Fe,Mg)Al 2 Si0 7 . If iron alone is present, this requires: Silica 23 '8, alumina 40'5, iron protoxide 28*5, water 7-2 = 100. Micro. Recognized in thin sections by the crystal outlines and general micaceous appearance; high relief ; green colors; distinct cleavage; frequent twinning; strong phleo- chroism and low interference-colors. By the last character readily distinguished from the micas; also by the high relief and extinction oblique to the cleavage from the chlorites. Obs: Chloritoid (ottrelite, etc.) are characteristic of sedimentary rocks which have suffered dynan^c metamorphism, especially in the earlier stages; thus found in argillites, conglomerates, etc., which have assumed the schistose condition. With more advanced .degree of metamorphism it disappears.' Often grouped in fan-shaped, sheaf -like forms, also in irregular or rounded grains. The original chloritoid from Kosoibrod, near Ekaterinburg in the Ural Mts., is in large curving laminae or plates, grayish to blackish green in color, often spotted with yellow from mixture with limonite. Other localities are He le Groix (Morbihan), France; embedded in large crystals at Vanlup, Shetland; Ardennes, France, and Belgium, in schists with ottrelite; also from Upper Michigan; Leeds, Canada, etc. Sismondine (HnFeyAlieSigOs-i) is from St. Marcel, Piedmont, Italy; it occurs also with glaucophane at Zermatt in the Valais, Switzerland, and elsewhere. Salmite is a manganesian variety occurring in irregular masses, having a coarse saccha- roidal structure and grayish color. G. = 3'38. From Vielsalm, Belgium. Masonite, from Natic, R. I., is in very broad plates of a dark grayish green color, but bluish green in very thin laminae parallel to c (001) and grayish green at right angles to this; occurs in argillaceous schist. 568 DESCRIPTIVE MINERALOGY Ottrelite is generally classed with chloritoid, though it is not certain that they are iden- tical; it seems to have the composition H 2 (Fe,Mn)Al 2 Si 2 O 9 . It occurs in small, oblong, shining scales or plates, more or less hexagonal in form and gray to black in color; in argil- laceous schist near Ottrez, on the borders of Luxemburg, and from the Ardennes, France, and Belgium; also near Serravezza, Tuscany, Italy; Tintagel in Cornwall. Venasquite is from Venasque in the Pyrenees, and from Teule, Finistere, France. Phyllite is from the schists of New England. 3. Chlorite Group. Monoclinic The CHLORITE GROUP takes its name from the fact that a large part of the minerals included in it are characterize^ by the green color common with sili- cates in which ferrous iron is prominent. The species are in many respects closely related to the micas. They crystallize in the monoclinic system, but in part with distinct monoclinic symmetry, in part with rhombohedral symme- try, with corresponding uniaxial optical character. The plane angles of the base are also 60 or 120, marking the mutual inclinations of the chief zones of forms. The mica-like basal cleavage is prominent in distinctly crystallized forms, but the laminae are tough and comparatively inelastic. Percussion and pressure-figures may be obtained as with the micas and have the same orientation. The etching-figures are in general monoclinic in symmetry, in part also asymmetric, suggesting a reference to the triclinic system. Chemically considered the chlorites are silicates of aluminium with ferrous iron and magnesium and chemically combined water. Ferric iron may be present replacing the aluminium in small amount ; chromium enters similarly in some forms, which are then usually of a pink instead of the more common green color. Manganese replaces the ferrous iron in a few cases. Calcium and alkalies characteristic of all the true micas are conspicuously absent, or present only in small amount. The only distinctly crystallized species of the Chlorite Group are Clino- chlore and Penninite. These seem to have the same composition, but while the former is monoclinic in form and habit, the latter is pseudo-rhombohedral and usually uniaxial. Prochlorite (including some ripidolite) and Corundo- philite also occur in distinct cleavage masses. Besides the species named there are other kinds less distinct in form, occur- ring in scales, also fibrous to massive or earthy; they are often of more or less undetermined composition, but in many cases, because of their extensive occur- rence, of considerable geological importance. These latter forms occur as secondary minerals resulting from the alteration especially of ferro-magnesian silicates, such as biotite, pyroxene, amphibole; also garnet, vesuvianite, tc. I hey are often accompanied by other secondary minerals, as ser- pentine, hmonite, calcite, etc., especially in the altered forms of basic rocks. . The rock-making chlorites are recognized in thin sections by their charac- teristic appearance in thin leaves, scales or fibers, sometimes aggregated into irulites; by their greenish color; pleochroism; extinction parallel to the cleavage (unlike choritoid and ottrelite); low relief and extremely low inter- ference-colors, which frequently exhibit the " ultra-blue." By this latter char- ?r they are readily distinguished from the micas, which they strongly resemble and with which they are frequently associated. SILICATES 569 CLINOCHLORE. Ripidolite in part. Monoclinic. Axes a : b : c = 0-57735 : 1 : 2-2772; = 89 40'. 952 953 954 / m< Pfitsch Wchwarzenstem Zillertal 955 Achmatovsk Crystals usually hexagonal in form, often tabular || c (001). Plane angles of the basal section = 60 or 120, and since closely similar angles are found in the zones which are separated by 60, the symmetry approximates to that of the rhombohedral system. Twins: (1) Mica law, tw. pi. _L c (001) in the zone cmo 001 A 112; sometimes contact-twins with c as com- position face, the one part revolved 60 or a multiple of 60 in azimuth with reference to the other; also in three- fold twins. (2) Penninite law, tw. pi. c, contact-twins also united by c (Fig. 954); here corresponding faces differ 180 in position. Massive, coarse scaly granular to fine granular and earthy. Cleavage: c (001) highly perfect. Laminae flexible tough, and but slightly elastic. Percussion-figure and pressure-figures orientated as with the micas (p. 559). H. = 2-2*5. G. = 2-65-2-78. Luster of cleavage-face somewhat pearly. Color deep grass-green to olive-green; pale green to yellowish and white; also rose-red. Streak greenish white to uncolored. Transparent to translucent. Pleochroism not strong, for green varieties usually X green, Z yellow. Optically usually +. Ax. pi. in most cases || 6 (010). Bx a inclined somewhat to the normal to c (001), forward; for Achmatovsk 2 30'. Disper- sion p < v. Axial angles variable, even in the same crystal, 0-90; some- times sensibly uniaxial. Birefringence low. Indices approximately; a = 1-585. = 1-586. 7 = 1-596. Var. 1. Ordinary; green clinochlore, passing into bluish green; (a) in crystals, as described, usually with distinct monoclinic symmetry; (6) foliated; (c) massive. Leuchtenbergiie. Contains usually little or no iron. Color white, pale green, yellowish; often resembles talc. From near Zlatoust in the Ural Mts. Kotschubeite. Contains several per cent of chromium oxide. Crystals rhombohedral in habit. Color rose-red. From the southern Ural Mts. Manganiferous. Manganchlorite. A chlorite from the Harstig mine near Pajsberg, Sweden, is peculiar in containing 2 -3 p. c. MnO. Comp. Normally H 8 Mg 5 Al 2 Si 3 Oi8 = 4H 2 O.5MgO.Al 2 O 3 .3SiO2 = Silica 32-5, alumina 18-4, magnesia 36-1, water 13-0 = 100. Ferrous iron usually replaces a small part of the magnesia, and the same is true of manganese rarely; sometimes chromium replaces the aluminium. Pyr., etc. Yields water. B.B. in the platinum forceps whitens and fuses with diffi- culty on the edges to a grayish black glass. With borax, a clear glass colored by iron, and sometimes chromium. In sulphuric acid wholly decomposed. Micro. In thin sections characterized by pale green color and pleochroism; dis- tinctly biaxial and usually +. 570 DESCRIPTIVE MINERALOGY Orr-nrs in connection with chloritic'and talcose rocks or schists and serpen- tine; iswasSffislfii ^^u^Tys: ssr Texas Zermatt u Marienberg, Saxony; Zoptau, Moravia. A manganesian vanety occurs at ^n iS the r ilJted d States, at Westchester, Pa., in large crystals and plates; also Unionville and Tex^, Pa fat the magnetic iron mine at Brewster, N. Y, in part changed to serpen- tine; near' Lowell, Ver., in crystals. PENNINITE. Pennine. Apparently rhombohedral in form but strictly pseudo-rhombohedral and L ^abit C r'hombohedral: sometimes thick tabular with c (001) prominent, again steep rhombohedral; also in tapering six-sided pyramids. Rhombo- hedral faces often horizontally striated. Crystals often in crested groups. Also massive, consisting of an aggre- gation of scales; also compact crypto- crystalline. Cleavage: c (001) highly perfect. Laminae flexible. Percussion-figure and pressure-figure as with clinochlore but less easy to obtain; not elastic. H. = 2-2-5. G. = 2-6-2-85. Luster of cleavage-surface pearly; of lateral plates vitreous, and sometimes brilliant. Color emerald- to olive-green; also violet, pink, rose-red, grayish red; occasionally yellowish and silver- white. Transparent to subtranslucent. Pleochroism distinct: usually || c (001) green; _L c yellow. Optically +, also , and sometimes both in adja- cent lamina of the same crystal. Usually sensibly uniaxial, but sometimes distinctly biaxial (occasionally 2E = 61) and both in the same section. Sometimes a uniaxial nucleus while the border is biaxial with 2E = 36, the latter probably to be referred to clinochlore. Indices 1-576 and 1-579. Var. 1. Penninite, as first named, included a green crystallized chlorite from the Penninine Alps. Kammererite. In hexagonal forms bounded by steep six-sided pyramids. Color kermes-red; peach-blossom-red. Pleochroism distinct. Optically from Lake Itkul, Bisersk, Perm, Russia; + Texas, Pa. Uniaxial or biaxial with axial angle up to 20. Rho- dophyllite from Texas, Pa., and rhodochrome from Lake Itkul belong here. Pseudophite is compact massive, without cleavage, and resembles serpentine. Comp. Essentially the same as clinochlore, H8(Mg,Fe) 5 Al 2 Si3Oi8. Pyr., etc. In the closed tube yields water. B.B. exfoliates somewhat and is diffi- cultly fusible. With the fluxes all varieties give reactions for iron, and many varieties react for chromium. Partially decomposed by hydrochloric and completely by sulphuric acid. Micro. In thin sections shows pale green color and pleochroism ; usually nearly uniaxial, . Obs. Occurs with serpentine in the region of Zermatt, Valais, Switzerland, near Mt. Rosa, especially in the moraines of the Findelen glacier; crystals from Zermatt are sometimes 2 in. long and H in. thick; also at the foot of the Simplon Pass, Switzerland; at Ala, Piedmont, Italy, with clinochlore; at Schwarzenstein in Tyrol, Austria; at Taberg in Wermland, Sweden; at Snarum, Norway, greenish and foliated. Kammererite is found at the localities already mentioned; also near Miask in the Ural Mts.; at Haroldswick in Unst, Shetland Isles. In large crystals enclosed in the talc in crevices of the chromite from Kraubat, Styria. Abundant at Texas, Lancaster Co., Pa., along with clmochlore, some crystals being embedded in clinochlore, or the reverse. Also SILICATES 571 in N. C., with chromite at Culsagee, Macon Co.; Webster, Jackson Co.; and other points. From Washington, Cal. PROCHLORITE. Ripidolite in part. Monoclinic. In six-sided tables or prisms, the side planes strongly fur- rowed and dull. Crystals often implanted by their sides, and in divergent groups, fan-shaped, vermicular, or spheroidal. Also in large folia. Massive, foliated, or granular. H. = 1-2. G. = 278-2-96. Translucent to opaque; transparent only in very thin folia. Luster of cleavage surface feebly pearly. Color green, grass- green, olive-green, blackish green; across the axis by transmitted light some- times red. Streak uncolored or greenish. Laminae flexible, not elastic. Pleochroism distinct. Optically + in most cases. Bx inclined to the normal to c (001) some 2. Axial angle small, often nearly uniaxial; again 2E = 23- 30. Dispersion p < v. Comp. Lower in silicon than clinochlore, and with ferrous iron usu- ally, but not always, in large amount. Obs. Like other chlorites in modes of occurrence. Occasionally formed from amphi- bole. Sometimes in implanted crystals, as at St. Gothard, Switzerland, enveloping often adularia, etc.; Mt. Greiner in the Zillertal, Tyrol, Austria; Rauris in Salzburg, Austria; Traversella in Piedmont, Italy; at Mts. Sept Lacs and St. Cristophe in Dauphine, France; in Styria, Bohemia. Also massive in Cornwall, England, in tin veins; at Arendal in Nor- way; Salberg and Dannemora, Sweden; Dognacska, Hungary. In Scotland at various points. In the United States, near Washington, D. C.; on Castle Mt., Batesville, Va., a massive form resembling soapstone, color grayish green, feel greasy; Steele's mine, Mont- gomery Co., N. C.; also with corundum at the Culsagee mine, in broad plates of a dark green color and fine scaly; it differs from ordinary prochlorite in the small amount of ferrous iron. Corundophilite. A chlorite occurring in deep green laminae resembling clinochlore but more brittle; contains but 24 p. c. SiO 2 . /3 = 1'583. Occurs with corundum at Chester, Mass. AMESITE. H 4 (Mg,Fe)2Al 2 SiO9. Silica 21'4 p. c. In hexagonal plates, foliated, resem- bling the green talc from the Tyrol. H. = 2-5-3. G. = 271. Color apple-green. Luster pearly on cleavage face. Optically +, sensibly uniaxial. Occurs with diaspore at Chester, Mass. SHERIDANITE. A chlorite from Sheridan Co., Wy., containing only little iron. OTHER CHLORITES. Besides the chlorites already described which occur usually in distinct crystals or plates, there are, as noted on p. 568, forms varying from fine scaly to fibrous and earthy, which are prominent in rocks. In some cases they may belong to the species before described, but frequently the want of sufficient pure material has left their composition in doubt. These chlorites are commonly characterized by their green color, distinct pleochroism and low birefringence (p. 568). The follow, ng are names which have been given particularly to the chlorites filling cavities or seams in basic igneous rocks : aphrosiderite, diabantite, delessite, epichlorite, eural- ite, chlorophceite, hullite, pycnochlorite. The following are other related minerals. Moravite. 2FeO.2(Al,Fe)oO3.7SiO 2 .2H 2 O. In lamellar, scaly and granular forms with perfect basal cleavage. H. = 3"5. G. = 2'4. Color iron-black. Fuses difficultly. Found at iron mines of Gobitschau near Sternberg, Moravia. Cronstedite. 4FeO.2Fe 2 O3.3SiO2.4H 2 O. Occurs tapering in hexagonal pyramids; also in diverging groups; amorphous. Cleavage: basal, highly perfect. Thin laminae elastic. G. = 3 '34-3 '35. Color coal-black to brownish black; by transmitted light in thin scales emerald-green. Streak dark olive-green. /3 = 1*80. From Pfibram in Bohemia; also in Cornwall, England. Thuringite. 8FeO.4(Al,Fe) 2 O 3 .6SiO 2 .9H 2 O. Massive; an aggregation of minute pearly scales. Color olive-green to pistachio-green. /3 = 1*63. From near Saalfeld, in Thurin- gia; Hot Springs, Ark., etc.; from the metamorphic rocks on the Potomac, near Harper's 572 DESCRIPTIVE MINERALOGY Ferry (owenite). Stilpnochloran is name given to an alteration product of thuringite from Gobitschau, near Sternberg, Moravia. In yellow to bronze-red scales. Brunsvigite. 9(Fe,Mg)O.2Al 2 O 3 .6SiO 2 .8H 2 O. In cryptocrystalline and foliated masses sometimes forming spherical radiated aggregates. Under microscope folia show hexagonal outline. Color olive-green to yellow-green. H. = 1-2. G. = 3U Occurs in cavities in the gabbro of the Radautal in the Harz Mts., Germany. Griffithite. 4(Mg,Fe,Ca)O.(Al,Fe)2O3.5SiO 2 .7H 2 O. A member of the Chlorite Group. Color dark green. H. = 1. G. = 2 '31. Fusible to magnetic slag. Pleochroic, pale yel- low, olive-green, brown-green. Indices 1 '48-1 '57. Occurs in amygdaloidal cavities in a basalt from Cahuenga Pass, Griffith Park, Los Angeles, Cal. CHAMOSITE. Contains iron (FeO) with but little MgO. Occurs compact or oolitic with H. about 3; G. = 3-3'4; color greenish gray to black. From Chamoson, near St. Maurice, in the Valais, Switzerland. Stilpnomelane. An iron silicate. In foliated plates; also fibrous, or as a velvety coat- ing. G. = 2 '77-2 '96. Color black, greenish black. Occurs at Obergrund and elsewhere in Silesia; also hi Moravia; near Weilburg, Nassau, Germany. Chalcodite, from the Sterling Iron mine, in Antwerp, Jefferson Co., N. Y., coating hematite and calcite, is the same mineral in velvety coating of mica-like scales with a bronze color. Minguetite. A member of Chlorite Group. A silicate of ferric and ferrous iron, inter- mediate between stilpnomelane and lepidomelane. G. = 2'86. Color blackish green. Strongly pleochroic, light yellow to opaque black. Optically . Fuses to a black mag- netic enamel. Decomposed by hydrochloric acid. From Minguet mine, near Segre, Maine-et-Loire, France. Strigovite. H4Fe2(Al,Fe) 2 Si 2 Oii. In aggregations of minute crystals. Color dark green. Occurs as a fine coating over the minerals in cavities in the granite of Striegau in Silesia. Rumpfite. Probably a variety of clinochlore. Massive; granular, consisting of very fine scales. Color greenish white. Occurs with talc near St. Michael and elsewhere in Styria. Spodiophyllite. (Na2,K 2 )2(Mg,Fe)3(Fe,Al)2(SiO 3 )8. In rough hexagonal prisms. Mica- ceous cleavage. Laminae brittle. H. = 3-3'2. G. = 2 '6. Color ash-jgray. Fusible. From Narsarsuk, southern Greenland. APPENDIX TO THE MICA DIVISION. VERMICULITES. The VERMICULITE GROUP includes a number of micaceous minerals, all hydrated sili- cates, in part closely related to the chlorites, but varying somewhat widely in composi- tion. They are alteration-products chiefly of the micas, biotite, phlogopite, etc., and retain more or less perfectly the micaceous cleavage, and of ten-show the negative optical character and small axial angle of the original species.- Many of them are of a more or less indefinite chemical nature, and the composition varies, with that of the original mineral and with the degree of alteration. The laminae in general are soft, pliable, and inelastic; the luster pearly or bronze-like, and the color varies from white to yellow; and brown. Heated to 100-110 or dried over sulphuric acid most of the vermiculites lose considerable water, up to 10 p. c., which is probably hygroscopic; at 300 another portion is often given off; and at a red heat a some- what larger amount is expelled. Connected with the loss of water upon ignition is the common physical character of exfoliation; some of the kinds especially show this to a marked degree, slowly opening out, when heated gradually, into long worm-like threads. Ihis character has given the name to the group, from the Latin vermiculari, to breed worms. Ihe minerals included can hardly rank as distinct species and only their names can be given here: Jefferisite, vermiculite, culsageeite, kerrite, lennilite, hallite, philadelphite, vaalite, macomte, dudleyite, pyrosclerite. HI. Serpentine and Talc Division The leading species belonging here, Serpentine and Talc, are closely related Chlorite Group of the Mica Division preceding, as noted beyond. borne other magnesium silicates, in part amorphous, are included with them. SILICATES , 573 SERPENTINE. Monoclinic. In distinct crystals, but only as pseudomorphs. Sometimes foliated, folia rarely separable; also delicately fibrous, the fibers often easily separable, and either flexible or brittle. Usually massive, but microscopically finely fibrous and felted, also fine granular to impalpable or cryptocrystalline ; slaty. Crystalline in structure but often by compensation nearly isotropic; amorphous. Cleavage b (010), sometimes distinct; also prismatic (50) in chrysotile. Fracture usually conchoidal or splintery. Feel smooth, sometimes greasy. H. = 2-5-4, rarely 5-5. G. = 2-50-2-65; some fibrous varieties 2-2-2-3; retinalite, 2-36-2-55. Luster subresinous to greasy, pearly, earthy; resin-like, or wax-like; usually feeble. Color leek-green, blackish green; oil- and siskin- green; brownish red, brownish yellow; none bright; sometimes nearly white. On exposure, often becoming yellowish gray. Streak white, slightly shining. Translucent to opaque. Pleochroism feeble. Optically - , perhaps also + in chrysotile. Double refraction weak. Ax. pi. | a (100). Bx (X) J_ 6 (010) the cleavage surface; Z || elongation of fibers. Biaxial, angle variable, often large; 2V = 20 to 90. Indices variable, from 1*490-1' 571. Var. Many unsustained species have been made out of serpentine, differing in struc- ture (massive, slaty, foliated, fibrous), or, as supposed, in chemical composition; and these now, in part, stand as varieties, along with some others based on variations in texture, etc. A. IN CRYSTALS PSEUDOMORPHS. The most common have the form of chrysolite. Other kinds are pseudomorphs after pyroxene, amphibole, spinel, chondrodite, garnet, phlogopite, etc. Bastite or Schiller Spar is enstatite (hypersthene) altered more or less completely to serpentine. See p. 474. B. MASSIVE. 1. Ordinary massive, (a) Precious or Noble Serpentine is of a rich oil- green color, of pale or dark shades, and translucent even when in thick pieces. (b) Common Serpentine is of dark shades of color, and sub translucent. The former has a hardness of 2*5-3; the latter often of 4 or beyond, owing to impurities. Resinous. Retinalite. Massive, honey-yellow to light oil-green, waxy or resin-like luster. Bowenite (Nephrite Bowen) . Massive, of very fine granular texture, and much resembles nephrite, and was long so called. It is apple-green or greenish white in color; G. = 2 '594- 2*787; and it has the unusual hardness 5 "5-6. From Smithfield, R. I..; also a similar kind from New Zealand. Ricolite is a banded variety with a fine green color from Mexico. C. LAMELLAR. Antigorite, thin lamellar in structure, separating into translucent folia. H. = 2-5; G. = 2*622; color brownish green by reflected light; feel smooth, but not greasy. From Antigorio valley, Piedmont, Italy. D. THIN FOLIATED. Marmolite, thin foliated; the laminae brittle but separable. G. = 2*41; colors greenish white, bluish white to pale asparagus-green. From Hoboken, N. J. E. FIBROUS. Chrysotile. Delicately fibrous, the fibers usually flexible and easily separating; luster silky, or silky metallic; color greenish white, green, olive-green, yellow and brownish; G. = 2 -2 19. Often constitutes seams in serpentine. It includes most of the silky amianthus of serpentine rocks and much of what is popularly called asbestus (asbestos). Cf. p. 489. Picrolite, columnar, but fibers or columns not easily flexible, and often not easily sepa- rable, or affording only a splintery fracture; color dark green to mountain-green, gray, brown. The original was from Taberg, Sweden. Baltimorite is picrolite from Bare Hills, Md. Radiotine is like serpentine except in regard to its solubility and specific gravity. In spherical aggregates of radiating fibers from near Dillenburg, Nassau. F. SERPENTINE ROCKS. Serpentine often constitutes rock-masses. It frequently occurs mixed with more or less of dolomite, magnesite, or calcite, making a rock of clouded green, sometimes veined with white or pale green, called verd antique, ophiolite, or ophicalcite. Serpentine rock is sometimes mottled with red, or has something of the aspect of a red 574 DESCRIPTIVE MINERALOGY porphyry; the reddish portions containing an unusual amount of oxide of iron. Any ser- pentine rock cut into slabs and polished is called serpentine marble. Microscopic examination has established the fact that serpentine in rock-masses has been largely produced by the alteration of chrysolite, and many apparently homogeneous ser- pentines show more or less of this original mineral. In other cases it has resulted from the alteration of pyroxene or amphibole. Sections of the serpentine derived from chrysolite often show a peculiar structure, like the meshes of a net (Fig. 958) ; the lines marked by grains of magnetite also follow the original cracks and cleavage directions of the chrysolite (Fig. 959, a). The serpentine from amphibole and pyroxene commonly shows an analogous structure; the iron particles following the former cleav- 968 age lines. Hence the nature of the original mineral can often be inferred. Cf. Fig. 959, a, b, c (Pirsson). Comp. A magnesium silicate, H 4 Mg 3 Si 2 09 or 3MgO.2SiO 2 .2H 2 = Silica 44.1, magnesia 43-0, water 12-9 = 100. Iron protoxide often replaces a small part of the magnesium ; nickel in small amount is sometimes present. The water is chiefly expelled at a red heat. Pyr., etc. -<- In the closed tube yields water. B. B. fuses on the edges with difficulty. F. ==6. Gives usually an iron reaction. Decom- posed by hydrochloric and sulphuric acids. From chrysotile the silica is left in fine fibers. Diff. Characterized by softness, absence of cleavage and feeble waxy or oily luster; low specific gravity; by yielding much water B.B. Micro. Readily recognized in thin sections by its greenish or yellowish green color; low relief and aggregate polarization due to its fibrous structure. When the fibers are parallel, the interference-colors are not very low, but the confused aggregates may show ..Mife v\\ov, leaf, on account of the exfoliation when heated; Chrysotile, from XPWOS, golden, and rtXos, fibrous; Metaxite, from nerafe, silk; Marmolite, from juap/xmpco, to shine, in allu- sion to its peculiar luster. Use. As an ornamental stone; the fibrous variety furnishes the greater part of the heat insulating material known as asbestus. Deweylite. A magnesian silicate near serpentine but with more water. Formula perhaps 4MgO.3SiO 2 .6H 2 O. Amorphous, resembling gum arabic, or a resin. H. = 2-3 -5. G. = 2'0-2'2. Color whitish, yellowish, reddish, brownish. Index, 1/55. Occurs with serpentine in the Fleimstal, Tyrol, Austria; also at Texas, Pa., and the Bare Hills, Md. Gymnite of Thomson, named from yvnvos, naked, in allusion to the locality at Bare Hills, Md., is the same species. Genthite. Nickel Gymnite. A gymnite with pait of the magnesium replaced by nickel, 2NiO.2MgO.3SiO 2 .6H 2 O. Amorphous, with a delicate stalactitic surface, incrusting. H. = 3-4; sometimes very soft. G. = 2 -409. Luster resinous. Color pale apple-green, or yellowish. From Texas, Lancaster Co., Pa., in thin crusts on chromite. Nepouite. 3(Ni,Mg)O.2SiO 2 .2H 2 O. In microscopic crystal plates with hexagonal out- line. Good cleavages. H. = 2-2;5. G. = 2*5-3-2. Color pale to deep green. = 1'62- 1'63. Occurs in the nickel deposits of New Caledonia. Garnierite. Noumeite. An important ore of nickel, consisting essentially of a hy- drated silicate of magnesium and nickel, perhaps H 2 (Ni,Mg)SiO 4 + water, but very variable in composition, particularly as regards the nickel and magnesium; not always homogene- ous. Amorphous. Soft and friable. G. = 2'3-2'8. Luster dull. Color bright apple- green, pale green to nearly white. Index, 1/59. In part unctuous; sometimes adheres to the tongue. Occurs in serpentine rock near Noumea, capital of New Caledonia, associated with chromic iron and steatite, where it is extensively mined. A similar ore occurs at Riddle in Douglas County, southern Oregon; also at Webster, Jackson Co., N. C. TALC. Orthorhombic or monoclinic. Rarely in tabular crystals, hexagonal or rhombic with prismatic angle of 60. Usually foliated massive; sometimes in globular and stellated groups; also granular massive, coarse or fine; fibrous (pseudomorphous) ; also compact or cryptocrystalline. Cleavage: basal, perfect. Sectile. Flexible in thin laminse, but not elastic. Percussion-figure a six-rayed star, oriented as with the micas. Feel greasy. H. = 1-1-5. G. = 27-2-8. Luster pearly on cleavage surface. Color apple-green to white, or silvery white; also greenish gray and dark green; sometimes bright green perpendicular to cleavage surface, and brown 576 DESCRIPTIVE MINERALOGY and less translucent at right angles to this direction; brownish to blackish green and reddish when impure. Streak usually white; of dark green varie- ties lighter than the color. Subtransparent to translucent. Optically nega- tive Ax. pi. 1 1 a (100). Bx _L c (001). Axial angle small, variable. Indices approx.; a = 1'539. = 1-589. 7 = 1'589. Var. Foliated, Talc. Consists of folia, usually easily separated, having a greasy feel, and presenting ordinarily light green, greenish white, and white colors. G. = 2'55-278. Massive, Steatite or Soapstone. a. Coarse granular, grayish green, and brownish gray in color; H. = l-2'5. Pot-stone is ordinary soapstone, more or less impure. 6. Fine granu- lar or cryptocrystalline, and soft enough to be used as chalk; as the French chalk, which is milk-white with a pearly luster, c. Indurated talc. An impure slaty talc, harder than ordinary talc. Pseudomorphous. a. Fibrous, fine to coarse, altered from enstatite and tremohte. 6. Rensselaerite, having the form of pyroxene from northern New York and Canada. Comp. An acid metasilicate of magnesium, H 2 Mg 3 (SiO 3 )4 or H 2 O. 3MgO.4Si0 2 = Silica 63 -5, magnesia 317, water 4*8 = 100. The water goes off only at a red heat. Nickel is sometimes present in small amount. Pyr., etc. In the closed tube B.B., when intensely ignited, most varieties yield water. In the platinum forceps whitens, exfoliates, and fuses with difficulty on the thin edges to a white enamel. Moistened with cobalt solution, assumes on ignition a pale red color. Not decomposed by acids. Rensselaerite is decomposed by concentrated sulphuric acid. Diff. Characterized by extreme softness, soapy feel; common foliated structure; pearly luster; it is flexible but inelastic. Yields water only on intense ignition. Obs. Talc or steatite is a very common mineral, and in the latter form constitutes extensive beds in some regions. It is often associated with serpentine, talcose or chloritic schist, and dolomite, and frequently contains crystals of dolomite, breunnerite, also asbes- tus, actinolite, tourmaline, magnetite. Steatite is the material of many pseudomorphs, among which the most common are those after pyroxene, hornblende, mica, scapolite, and spinel. The magnesian minerals are those which commonly afford steatite by alteration; while those like scapolite and nephelite, which contain soda and no magnesia, most frequently yield pinite-like pseudomorphs. There are also steatitic pseudomorphs after quartz, dolomite, topaz, chiastolite, staurolite, cyanite, garnet, vesuvianite, chrysolite, gehlenite. Talc in the fibrous form is pseudomorph after enstatite and tremolite. Apple-green talc occurs at Mt. Greiner in the Zillertal, Tyrol, Austria; in the Valais and St. Gothard in Switzerland; in Cornwall, England, near Lizard Point, with serpentine; the Shetland islands. In North America, foliated talc occurs in Me., at Dexter. In Ver., at Bridgewater, handsome green talc, with dolomite; Newfane. In Mass., at Middlefield, Windsor, Blan- fprd, Andover, and Chester. In R. I., at Smithfield, delicate green and white in a crystal- line limestone. In N. Y., at Edwards, St. Lawrence Co., a fine fibrous talc (agalite) asso- ciated with pink tremolite; on Staten Island. In N. J., Sparta. In Pa., at Texas, Nottingham, Unionville; in South Mountain, ten miles south of Carlisle; at Chestnut Hill, on the Schuylkill, talc and also soapstone, the latter quarried extensively. In Md., at Cooptown, of green, blue, and rose colors. In N. C., at Webster, Jackson Co. The im- portant states for the production of talc and soapstone are New York, Vermont and Virginia. In Canada, in the townships Bolton, Button, and Potton, Quebec, with steatite in beds of Cambrian age; in the township of Elzevir, Hastings Co., Ontario, an impure grayish variety in Archaean rocks. Use. In the form of soapstone used for wash tubs, sinks, table tops, switchboards, hearth stones, furnace linings, etc.; the tips of gas burners, tailors' chalk, slate pencils, etc 3rnaments ' etc> ; m P ow dered form as filler in papers, as a lubricant, in toilet powders, % G ^?M is a PP a . rent ly a variety of talc, differing in the amount of water present and in its solubility in acids. From Gava valley, Italy. SEPIOLITE. Meerschaum. Compact, with a smooth feel, and fine earthy texture, or clay-like; also rarely fibrous. H. = 2-2-5. G. = 2. Impressible by the nail. In dry SILICATES 577 masses floats on water. Color grayish white, white, or with a faint yellowish or reddish tinge, bluish green. Opaque. Biaxial,. /3 = 1-55. Comp. H 4 Mg2Si3O 10 or 2H 2 O.2MgO.3SiO 2 = Silica 60-8, magnesia 27-1, water 12-1 = 100. Some analyses show more water, which is probably to be regarded as hygroscopic. Copper and nickel may replace part of the magnesium. Pyr., etc. In the closed tube yields first hygroscopic moisture, and at a higher tem- perature gives much water and a burnt smell. B.B. some varieties blacken, then burn white, and fuse with difficulty on the thin edges. With cobalt solution a pink color on ignition. Decomposed by hydrochloric acid with separation of silica. Obs. Occurs in Asia Minor, in masses in stratified earthy or alluvial deposits at the plains of Eskihi sher; at Hrubschitz in Moravia; in Morocco, called in French Pierre de Savon de Maroc; at Vallecas in Spain, in extensive beds. A fibrous mineral, having the composition of sepiolite, occurs in Utah. The word meerschaum is German for sea-froth, and alludes to its lightness and color. Sepiolite is from . Monoclinic. In acute pyramidal crystals. Perfect basal cleavage. H= 4-5-5. G. = 3*91. Color, bright pink to reddish brown. - 1 76. crepitates and then fuses readily. Soluble in acids. From Franklin, N. J. ran,??;* 6 ' ~ A 1 } ydro jf sjjicate of manganese, magnesium and zinc, 8RO.3SiO 2 .2H 2 O. In radiating groups of needle-like crystals. Colorless and transparent. From Franklin, N. J. G -^T^-Qi %&?*** i Mn0 - 3S KV3H 2 0. In stalactitic and reniform shapes. ~ olor brown. From the Harstig mine near Pajsberg, Sweden. allv d e erived e frnm &?!]* ? ica1 1 [ man S ane se and iron, of doubtful composition, usu- and liverTbro^n alteration of rhodonite. Amorphous. Color black to dark brown TITANO-SILICATES, TITANATES 583 Searlesite. NaB(SiO 3 )2.H 2 O. Monoclinic (?). In minute spherulites composed of radiating fibers. Color white. Indices, 1-52-1-53. Fusible. Decomposed by hydro- chloric acid. Found at Searles Lake, San Bernardino Co., Cal. Colerainite. 4MgO.Al 2 O 3 .2SiO2.5H 2 O. Hexagonal. In minute, thin, hexagonal plates. H. = 2-5-3. G. = 2-51. Colorless or white. Optically +. Index, 1*56. Found in Black Lake area, Coleraine township, Quebec. TARTARKAITE. A complex hydrous silicate of aluminium, magnesium, etc. Tabular crystals. G. = 27. Color dark gray to black. Uniaxial, +. In limestone on the Tar- tarka river, Yenisei District, Siberia. ITANO-SILICATES, TITANATES This section includes the common calcium titano-silicate, Titanite; also a number of silicates which contain titanium, but whose relations are not alto- gether clear; further the titanate, Perovskite, and niobo-titanate, Dysanalyte, which is intermediate between Perovskite and the species Pyrochlore, Micro- lite, Koppite of the following section. In general the part played by titanium in the many silicates in which it enters is more or less uncertain. It is probably in most cases, as shown in the preceding pages, to be taken as replacing the silicon; in others, however, it seems to play the part of a basic element; in schorlomite (p. 510) it may enter in both relations. TITANITE. Sphene. Monoclinic. Axes a 110 A 110 = 001 A 102 mm ex. b:c = 0-7547 66 29'. 21 0'. 1 : 0-8543; p = 60 ( nri 960 021 A 021 = 112 3'. Ill A 111 = 43 49'. IV, en, cm, d t Tl2 A 112 001 A 111 = 001 A 110 = 001 A 112 = 961 17'. 46 7*'. 38 16'. 65 30'. 40 34'. 962 963 964 Twins: tw. pi. a (100) rather common, both contact-twins and cruciform penetration-twins. Crystals very varied in habit; often wedge-shaped and 584 DESCRIPTIVE MINERALOGY flattened || c (001); also prismatic. Sometimes massive, compact; rarely 1 $} in f*l 1 1\ T* Cleavage- m (110) rather distinct; a (100), I (112) imperfect; in greeno- vite n (111) easy, t (111) less so. Parting often easy 1 1 77 (221) due to twinning lamellae. H. = 5-5'5. G. = 3 -4-3 -56. Luster adamantine to resinous. Color brown, gray, yellow, green, rose-red and black. Streak white, slightly reddish in greenovite. Transparent to opaque. Pleochroism in general rather feeble, but distinct in deep-colored kinds: Z red with tinge of yellow;. 7, yellow, often greenish; X, nearly colorless. Optically + . Ax. pi. || b (010). Bx nearly J_ x (102), i.e., Bx A c axis = + 51. Dispersion p > v very large, and hence the peculiarity of the axial interference-figure in white, light. Axial angles variable. 2V = 27. a = 1-900. ft = 1-907. 7 = 2-034. Var. Ordinary, (a) Titanite; brown to black, the original being thus colored, also opaque or subtranslucent. (6) Sphene (named from a^v, a wedge)', of light shades, as yellow, greenish, etc., and often translucent; the original was yellow. Ligurite is an apple- green sphene. Spinthere (or Semeline) a greenish kind. Lederite is brown, opaque, or sub- translucent, of the form in Fig. 960. Titanomorphite is a white mostly granular alteration-product of rutile and ilmemte, not uncommon in certain crystalline rocks; here also belongs most leucoxene (see p. 418). Manganesian; Greenovite. Red or rose-colored, owing to the presence of a little man- ganese; from St. Marcel, Piedmont, Italy; from Jothvad in Narukot, India. Containing yttrium or cerium. Here belong grothite, alshedite, eucolite-titanite. Comp. CaTiSiO 5 or CaO.TiO 2 .Si0 2 = Silica 30-6, titanium dioxide 40-8, lime 28*6 = 100. Iron is present in varying amounts, sometimes man- ganese and also yttrium in some kinds. Pyr., etc. B.B. some varieties change color, becoming yellow, and fuse at 3 with intumescence, to a yellow, brown or black glass. With borax they afford a clear yellowish green glass. Imperfectly soluble in heated hydrochloric acid; and if the solution be con- centrated along with tin, it assumes a fine violet color. With salt of phosphorus in R. F. gives a violet bead; varieties containing much iron require to be treated with the flux on charcoal with metallic tin. Completely decomposed by sulphuric and hydrofluoric acids. Diff. Characterized by its oblique crystallization, a wedge-shaped form common; by resinous (or adamantine) luster; hardness less than that of staurolite and greater than that of sphalerite. The reaction for titanium is distinctive, but less so in varieties containing much iron. Micro. Distinguished in thin sections by its acute-angled form, often lozenge-shaped; its generally pale brown tone; very high relief and remarkable birefringence, causing the section to show white of the higher order; by its biaxial character (showing many lemnis- cate curves); and by its great dispersion, which produces colored hyperbolas. Artif. Titanite is apparently produced artificially only with difficulty. It has been obtained by fusing together silica and titanic oxide with calcium chloride. Obs. Titanite, as an accessory component, is widespread as a rock forming mineral, though confined mostly to the acidic feldspathic igneous rocks; it is much more common in the plutonic granular types than in the volcanic forms. Thus it is found in the more basic hornblende granites, syenites, and diorites, and is especially common and character- istic in the nephelite-syenites. It occurs also in the metamorphic rocks and especially in the schists, gneisses, etc., rich in magnesia and iron and in certain granular limestones. It is also found in beds of iron ore; commonly associated minerals are pyroxene, amphibole, chlorite, scapolite, zircon, apatite, etc. In cavities in gneiss and granite, it often accom- panies adularia, smoky quartz, apatite, chlorite, etc. Occurs at various points in the Grisons, Switzerland, associated with feldspar and chlorite; Tavetsch; Binnental; in the St. Gothard region; Zermatt in the Valais ; Mader- anertal in Uri; also elsewhere in the Alps; in Dauphine (spinthere), France; in Italy at Ala (hgunte) and at St. Marcel, in Piedmont; at Schwarzenstein and Rothenkopf in the XT /uif i r' T y ro1 ' z P ta u, Moravia; near Tavistock, England; near Tremadoc, in JNorth Wales; from Kragero and in titanic iron at Arendal, Norway; with magnetite at TITANO-SILICATES, TITANATES 585 Nordmark, Sweden; Achmatovsk, Ural Mts. Occasionally found among volcanic rocks, as at Lake Laach (semeline) and at Andernach on the Rhine. In Me., in fine crystals at Sandford. In Mass., in gneiss, in the east part of Lee; at Bolton with pyroxene and scapolite in limestone. In N. Y., at Roger's Rock on Lake George, abundant in small brown crystals; at Gouverneur, in black crystals in granular limestone; in Diana near Natural Bridge, Lewis Co., in large dark brown crystals, among Statesville, Iredell Co., yellowish white with sunstone; also Buncombe Co., Alexander Co., and other points. Occurs in Canada in Quebec at Grenyille, Argenteuil Co.; also Buckingham, Templeton, Wakefield, Hull, Ottawa Co.; in Ontario at North Burgess, honey-yellow; near Eganville, Renfrew Co., in very large dark brown crystals with apatite, amphibole, zircon. Molengraaffite. A titano-silicate of lime and soda. Monoclinic (?). In imperfect pris- matic crystals. Cleavage (100) perfect. Color yellow-brown. Indices, 173-177. From a rock, "lujaurite," in Pilandsberg, near Rustenberg, Transvaal. Keilhauite. A titano-silicate of calcium, aluminium, ferric iron, and the yttrium metals. Crystals near titanite in habit and angles. H. = 6'5. G. = 3'52-377. Color brownish black. From near Arendal, Norway. Tscheffkinite. A titano-silicate of the cerium metals, iron, etc., but an alteration product, more or less heterogeneous, and the composition of the original mineral is very uncertain. Massive, amorphous. H. = 5-5'5. G. = 4'508-4'549. Color velvet-black. From the Ilmen mountains in the Ural Mts. Also from South India, Kanjamalai Hill, Salem district. An isolated mass weighing 20 Ibs. has been found on Hat Creek, near Mas- sie's Mills, Nelson Co., Va.; also found, south of this point, in Bedford Co. Astrophyllite. Probably R 4 R 4 Ti(SiO 4 ) 4 with R = H, Na, K, and R = Fe, Mn chiefly, including also Fe 2 O 3 . Orthorhombic. In elongated crystals; also in thin strips or blades; sometimes in stellate groups. Cleavage: 6 (010) perfect like mica, but laminae brittle. H. = 3. G. = 3 '3-3 '4. Luster submetallic, pearly. Color bronze-yellow to gold-yellow. Optically +. Indices, 1 '678-1733. Occurs on the small islands in the Langesund fiord, near Brevik, Norway, in elseolite- syenite, embedded in feldspar, with catapleiite, segirite, black mica, etc. Similarly at Kangerdluarsuk and Narsarsuk, Greenland. Also with arfvedsonite and zircon at St. Peter's Dome, Pike's Peak, El Paso Co., Col. Johnstrupite. A silicate of the cerium metals, calcium and sodium chiefly, with titan- ium and fluorine. In prismatic monoclinic crystals. G. = 3 '29. Color brownish green. Index, 1 -646. From near Barkevik, Norway. Mosandrite. Near Johnstrupite in form and composition and from the same region. Rinkite, also near Johnstrupite, is from Greenland. f Narsarsukite. A highly acidic titano-silicate of ferric iron and sodium. Tetragonal. In tabular crystals. Fine prismatic cleavage. H. =7. G. = 27. Color honey-yellow, on weathering brownish gray or ocher-yellow. w = T55. Fusible. In pegmatite at Narsarsuk, southern Greenland. Neptunite. A titano-silicate of iron (manganese) and the alkali metals. In prismatic monoclinic crystals. H. = 5-6. G. = 3 '23. Color black. Streak, cinnamon-brown. Mean index, 170. Pleochroic, yellow to deep-red. Found at Narsarsuk and elsewhere, southern Greenland, and at the benitoite locality in San Benito Co., Cal. (originally called carlosite) . Benitojte. BaTiSi 3 O 9 . Hexagonal, trigonal (ditrigonal-bipyramidal) . In crystals with p(1011) prominent. H. = 6'2-6'5. G .= 3'6. Color sapphire-blue to light blue and colorless. Transparent. Strongly dichroic, deep blue to colorless, co = 177. Fusible at 3. Found associated with neptunite and natrolite near the headwaters of the San Benito River in San Benito Co., Cal. Leucosphenite. Na 4 Ba(TiO)2(Si 2 O5)5. Monoclinic. In minute wedge-shaped crystals. Distinct cleavage. H. = 6'5. G. = 3'0. Color white. /8 = 1'66. Difficultly fusible. From Narsarsuk, southern Greenland. 586 DESCRIPTIVE MINERALOGY Lorenzenite. Nao(TiO) 2 Si 2 O 7 . Contains considerable zirconia. Orthorhombic. In minute acicular crystals. Distinct cleavage. H. = 6. G. = 3 -4. /3 about 1 '78. Fusible. From Narsarsuk, southern Greenland. Joaquinite. A titano-silicate of calcium and iron. Orthorhombic. Color, honey- yellow. Associated with benitoite from San Benito Co., Cal. PEROVSKITE. Perofskite. Isometric or pseudo-isometric. Crystals in general (Ural Mts., Zermatt, Switzerland) cubic in habit and often highly modified, but the faces often irregularly distributed. Cubic faces striated parallel to the edges and appar- ently penetration-twins, as if of pyritohedral individuals. Also in reniform masses showing small cubes. Cleavage: cubic, rather perfect. Fracture uneven to subconchoidal. Brittle. H. = 5*5. G. = 4-017-4-039. Luster adamantine to metallic-ada- mantine. Color pale yellow, honey-yellow, orange-yellow, reddish brown, grayish black. Streak colorless, grayish. Transparent to opaque. Usually exhibits anomalous double refraction. Mean index, about 2*38. Geometrically considered, perovskite conforms to the isometric system; optically, how- ever, it is uniformly biaxial and usually positive. The molecular structure (also as devel- oped by etching) seems to correspond to Orthorhombic symmetry. Cf. Art. 429. Comp. Calcium titanate, CaTiO 3 = Titanium dioxide 58-9, lime 41-1 = 100. Iron is present in small amount replacing the calcium. Pyr., etc. In the forceps and on charcoal infusible. With salt of phosphorus in O.F. dissolves easily, giving a greenish bead while hot, which becomes colorless on cooling; in R.F. the bead changes to grayish green, and on cooling assumes a violet-blue color. En- tirely decomposed by boiling sulphuric acid. Obs. Occurs in small crystals, associated with chlorite, and magnetic iron in chlorite slate, at Achmatovsk, near Zlatoust, in the Ural Mts.; at Schelingen in the Kaiserstuhl, Germany, in granular limestone; in the valley of Zermatt, Switzerland, near the Findelen glacier; at Wildkreuzjoch, between Pfitsch and Pfunders in Tyrol, Austria; various localities, Piedmont, Italy. Sometimes noted in microscopic octahedral crystals as a rock constituent; thus in nephelite- and melilite-basalts; also in serpentine (altered peridotite) at Syracuse, N. Y.; in igneous rocks, Beaver Creek, Gunnison Co., Col. Knopite. Near perovskite but contains cerium. In black isometric crystals. From Alno, Sweden. Dysanalyte. A titano-niobate of calcium and iron, like perovskite with lime replaced to some extent by iron, etc. Pseudo-isometric, probably Orthorhombic. In cubic crystals. Color, iron-black. From the granular limestone of Vogtsburg, Kaiserstuhl, Baden, Ger- many. Has previously been called perovskite, but is in fact intermediate between the titanate, perovskite, and the niobates, pyrochlore and koppite. From Mte. Somma, Vesuvius. A related mineral, which has also long passed as perovskite, occurs with magnetite, brookite, rutile, etc., at Magnet Cove, Ark. It is in octahedrons or cubo-octahedrons, black or brownish black in color and submetallic in luster. See also the allied titanate, bixbyite, mentioned on p. 425. Geikielite. Magnesium iron titanate, (Mg,Fe)TiO 3 . Hexagonal, rhombohedral. Usu- ally massive, as roUed pebbles. H. =6. G. = 4. Color bluish or brownish black. Index, very high. From Ceylon. Delorenzite. A titanate of iron, uranium and yttrium of uncertain composition. Or- thorhombic. Prismatic habit. Color black. Resinous luster. Found in pegmatite at Graveggia, Val Vigezzo, Piedmont, Italy. Yttrocrasite. A hydrous titanate of the yttrium earths and thorium. Orthorhombic. **_? 5 ' 5 ~6 ; G- = 4-8. Black color with pitchy to resinous luster. Infusible. Found in Burnet Co., three miles east of Barringer Hill, Texas. Brannerite. Essentially (UO,TiO,UO 2 )TiO 3 . Prismatic crystals or granular. Blank. Basin Idh greenish brown> H< = 4 ' 5> G " " 4 ' 5 - 5 ' 4 - F und in gold placers, Stanley NIOBATES, TANTALATES 587 Oxygen Salts 3. NIOBATES, TANTALATES The Niobates (Columbates) and Tantalates are chiefly salts of metaniobic and metatantalic acid, RNb 2 O 6 and RTa^A; also in part Pyroniobates, R 2 Nb 2 O7, etc. Titanium is prominent in a number of the species, which are hence intermediate between the niobates and titanates. Niobium and tanta- lum also enter into the composition of a few rare silicates, as wohlerite, laven- ite, etc. The following groups may be mentioned: The isometric PYROCHLORE GROUP, including pyrochlore, microlite, etc. The tetragonal FERGUSONITE GROUP, including fergusonite and sipylite. The orthorhombic COLUMBITE GROUP, including columbite and tantalite. Also the orthorhombic SAMARSKITE GROUP, including yttrotantalite, samarsk- ite, and annerodite. The species belonging in this class are for the most part rare, and are hence but briefly described. PYROCHLORE. Isometric. Commonly in octanedrons; also in grains. Cleavage : octahedral, sometimes distinct. Fracture conchoidal. Brittle. H. = 5-5-5. G. = 4 -2-4 -36. Luster vitreous or resinous, the latter on frac- ture surfaces. Color brown, dark reddish or blackish brown. Streak light brown, yellowish brown. Subtranslucent to opaque, Comp. Chiefly a niobate of the cerium metals, calcium and other bases, with also titanium, thorium, fluorine. Probably essentially a metanio- bate with a titanate, RNb 2 O 6 .R(Ti,Th)0 3 ; fluorine is also present. Obs. Occurs in elseolite-syenite at Fredriksvarn and Laurvik, Norway; on the island Lovo, opposite Brevik, and at several points in the Langesund fiord; near Miask in the Ural Mts. Named from -n-vp, fire, and x^wpos, green, because B.B. it becomes yellowish green. A variety of pyrochlore from near Wausau, Wis., has been called marignadte. Neotantalite. Composition near that of tantalite. Isometric, in octahedrons. H. = 5-6. G. = 5'2. Color clear yellow. Refractive index, 1*9. Found with kaolin at Colettes and Echassieres, Dept. PAllier, France, ii ii Chalcolamprite. RNb 2 OeF2.RSiO3. Isometric. In small octahedrons. H. = 5-5. G. = 3 '8. Color dark gray-brown. Crystal faces show a copper-red metallic iridescence. Occurs sparingly at Narsarsuk, South Greenland. Endeiolite is a similar mineral from the same locality supposed to have the same composition with the substitution of the hydroxyl group for the fluorine. Koppite. Essentially a pyroniobate of cerium, calcium, etc., near pyrochlore. In minute brown dodecahedrons. G. = 4'45-4'56. From Schelingen, Kaiserstuhl, Germany, embedded in limestone. Hatchettolite. A tantalo-niobate of uranium, near pyrochlore. In octahedrons with a (100) and m (311). G. = 477-4-90. Color yellowish brown. Occurs with samarskite, at the mica mines of Mitchell Co., N. C.; from Mesa Grande, Cal. Samiresite. A niobate of uranium, etc. Isometric. In octahedrons. G. = 5 24. Color golden-yellow. From Antsirabe, on Samiresy Hill, Madagascar. Microlite. Essentially a calcium pyrotantalate, CauTa2O7, but containing also nio- bium, fluorine and a variety of bases in small amount. Isometric. Habit octa- hedral; crystals often very small and highly modified. H. = 5'5. G. = 5'485-5'562; 6*13 Virginia. Color pale yellow to brown, rarely hyacinth-red, n = T94. From Chesterfield, Mass., in albite; Branchville, Conn.; Rumford, Me.; Uto, Sweden; Green- 588 DESCRIPTIVE MINERALOGY land. Also in fine crystals up to 1 in. in diameter at the mica mines at Amelia Court- House, Amelia Co., Va. PYRRHITE. Probably a niobate related to pyrochlore, and perhaps identical with microlite. Occurs in minute orange-yellow octahedrons. From Alabashka, near Mursinka in the Ural Mts.; from Mte. Somma, Vesuvius. RISORITE. A niobate of the yttrium metals. Isotropic. Color yellow-brown. H. = 5'5. G. = 4-18. In pegmatite at Risor, Norway. FERGUSONITE. Tyrite. Bragite Tetragonal-pyramidal. Axis c = T4643. Crystals pyramidal or pris- matic in habit. Cleavage: s (111) in traces. Fracture subconchoidal. Brittle. H. = 5-5-6. G. = 5-8, diminishing to 4 -3 when largely hydrated. Luster exter- nally dull, on the fracture brilliantly vitreous and submetallic. Color brown- ish black; in thin scales pale liver-brown. Streak pale brown. Subtrans- lucent to opaque. Index, 2-19. Comp. Essentially a metaniobate (and tantalate) of yttrium with erbium, cerium, uranium, etc., in varying amounts; also iron, calcium, etc. in in General formula R(Nb,Ta)O 4 with R = Y,Er,Ce. Water is usually present and sometimes in considerable amount, but probably not an original constituent; the specific gravity falls as the amount increases. Obs. From Cape Farewell in Greenland, in quartz; also at Ytterby and Kararfvet, Sweden. From near Beforona, Madagascar; South Africa; Australia; Ceylon; Taka- yama, Mino, Japan. Tyrite is associated with euxenite at Hampemyr on the island of Tromo, and Helle on the mainland, Norway; bragite is from Helle, Naresto, etc., Norway. Found in the United States, at Rockport, Mass., in granite; in the Brindletown gold district, Burke Co., N. C., in gold washings; with zircon in Anderson Co., S. C.; at the gadolinite locality in Llano Co., Texas, in considerable quantity. Sipylite. A niobate of erbium chiefly, also the cerium metals, etc., near fergusonite in form. Rarely in octahedral crystals. Usually in irregular masses. G. = 4 '89. Color brownish black to brownish orange. Occurs sparingly with allanite in Amherst Co., Va. COLUMBITE-TANTALITE. Orthorhombic. Axes a : b : c = 0'8285 : 1 : 0'8898. yy'", 210 A 2lO = 45 0'. ce, 001 A 021 = 60 40'. mm'", 110 A 110 = 79 17'. ao, 100 A 111 = 51 16'. gg', 130 A 130 = 43 50'. cu, 001 A 133 = 43 48'. cfc, 001 A 103 = 19 42'. uu', 133 A 133 = 29 57'. cq, 001 A 023 = 30 41'. uu"' , 133 A 133 = 79 54'. Twins: tw. pi. e (021) common, usually contact-twins, heart-shaped (Fig. 385, p. 160), also penetration-twins; further tw. pi. q (023) rare (Fig. 434, p. 169). Crystals short prismatic, often rectangular prisms with the three pina- coids prominent; also thin tabular || a (100); the pyramids often but slightly developed, sometimes, however, acutely terminated by u (133) alone. Also in large groups of parallel crystals, and massive. Cleavage: a (100) rather distinct; 6 (010) less so. Fracture subconchoidal to uneven. Brittle. H. = 6. G. = 5 -3-7 -3, varying with the composition (see below). Luster submetallic, often very brilliant, sub-resinous. Color iron-black, grayish and brownish black, opaque; rarely reddish brown and NIOBATES, TANTALATES 589 translucent; frequently iridescent. Streak dark red to black. Optically 4- .= 2-26. = 2-20. 7 = 2-34. 967 968 969 Middletown Black Hills Greenland Comp. Niobate and tantalate of iron and manganese, (Fe,Mn)(Nb, Ta) 2 6 , passing by insensible gradations from normal COLUMBITE, the nearly pure niobate, to normal TANTALITE, the nearly pure tantalate. The iron and manganese also vary widely. Tin and tungsten are present in small amount. The percentage composition for FeNb 2 O 6 = Niobium pentbxide 82-7, iron protoxide 17 '3 = 100; for FeTa^Oe = Tantalum pentoxide 86-1, iron protox- ide 13-9 = 100. In some varieties, manganocolumbite or manganotantalite, the iron is largely replaced by manganese. The connection between the specific gravity and the percentage of -metallic acids is shown in the following table: G. TaaOe 5 '36 3 '3 15'8 13 '8 13'4 lO'O Greenland Acworth, N. H. Limoges Bodenmais (Dianite) Haddam 5'65 570 574 5'85 Bodenmais Haddam Bodenmais Haddam G. 5 '92 6'05 6 '06 613 Ta 2 O 5 27-1 30-4 35-4 31-5 Tantalite 7-03 65-6 Diff. Distinguished (from black tourmaline, etc.) by orthorhombic crystallization, rectangular forms common; high specific gravity; submetallic luster, often with iridescent surface; cleavage much less distinct than for wolframite. Pyr., etc. For tantalite, B.B. alone unaltered. With salt of phosphorus dissolves slowly, giving an iron glass, which in R.F. is pale yellow on cooling; treated with tin on char- coal it becomes green. Decomposed on fusion with potassium bisulphate in the platinum spoon, and gives on treatment with dilute hydrochloric acid a yellow solution and a heavy white powder, which, on addition of metallic zinc, assumes a smalt-blue color; on dilution with water the blue color soon disappears. Columbite, when decomposed by fusion with caustic potash, and treated with hydrochloric and sulphuric acids, gives, on the addition of zinc, a blue color more lasting than with tantalite. Partially decomposed when the powdered mineral is evaporated to dryness with concentrated sulphuric acid, its color is changed to white, light gray, or yellow, and when boiled with hydrochloric acid and metallic zinc it gives a beautiful blue. Obs. Columbite occurs at Rabenstein and Bodenmais, Bavaria, in granite; Tam- mela, in Finland; Chanteloube, near Limoges, France, in pegmatite with tantalite; near Miask, in the Ilmen Mts., Russia, with samarskite; in the gold-washings of the Sanarka region in the Ural Mts.; in Greenland, in cryolite, at Ivigtut (or Evigtok), in brilliant crystals. In crystals from Ampangabe and Ambatofotsikely, Madagascar. In the United States, in Me., at Standish, in splendent crystals in granite; also at Stone- ham with cassiterite, etc., manganotantalite from Rumford. In N. H., at Acworth, at the mica mine. In Mass., at Chesterfield; Northfield. In Conn., at Haddam, in a granite vein; near Middletown; at Branch ville, Fairfield Co., in a vein of albitic granite, in large 590 DESCRIPTIVE MINERALOGY crystals and aggregates of crystals, also in minute translucent crystals (manganocolumbite} , upon spodumene. In N. Y., at Greenfield, with chrysoberyl. In Pa., Mineral Hill, Dela- ware Co. In Va., Amelia Co., in fine splendent crystals with microlite, monazite, etc. In N. C., with samarskite at the mica mines of Mitchell Co. In Col., on microcline at the Pike's Peak region; Turkey Creek, Jefferson Co. In S. D. in the Black Hills region, common in the granite veins. In Cal., King's Creek district, Fresno Co., from Rinc.on and manganotantalite from Pala. Mangantantalite (Nordenskiold) from Uto, Sweden, occurs with petalite, lepidolite, microlite, etc. Manganotantalite (Arzruni) is from gold-washings in the Sanarka region in the Ural Mts.; from Pilbarra district, West Australia. Massive tantalite occurs in Finland, in Tammela, at Harkasaari near Torro; in Kimito, at Skogbole; in Somero at Kaidasuo, and in Kuprtane at Katiala, with lepidolite, tourma- line, and beryl; in Sweden, near Falun, at Broddbo and Finbo; in France, at Chanteloube near Limoges, in pegmatite. In the United States, in Yancey Co., N. C.; Coosa Co., Ala.; also in the Black Hills, S. D.; in large masses near Canon City, Col. Use. Source of tantalum used in making filaments for incandescent electric lights. Tapiolite. Fe(Ta,Nb)aO6. Like tantalite, but occurring in square tetragonal octa- hedrons. Tapiolite shows close similarities with the minerals of the Rutile Group, in which some authors place it. G. = 7'496. Color pure black. From the Kulmala farm, Tammela, Finland. In twin crystals from Topsham, Me. Mossite, a niobium tapiolite. Found at Berg near Moss, Norway. Skogbolite and ixiolite are twinned varieties of tapio- lite. Stibio tantalite. (Sbp)2(Ta,Nb)2Oe. Orthorhombic, hemimorphic in direction of a axis. Polysynthetic twinning parallel to a (100). Cleavage a (perfect). H. = 5*5. G. = 6'0-7'4 (varying with composition). /S. = 2'40-2'42. Fusible. Color brown, reddish yellow, yellow. Luster adamantine to resinous. Originally found in tin-bearing sands of Greenbushes, Australia. In crystals from Mesa Grande, San Diego Co., Cal. b : c = 0-5412 : 1 : M330. Crystals prismatic, YTTROTANTALITE. Orthorhombic. Axes a mm'" 110 A 110 = 56 50'. Cleavage: b (010) very indistinct. Fracture small conchoidal. H. = 5-5-5. G. = 5 '5-5 -9. Luster submetallic to vitreous and greasy. Color black, brown, brownish yellow, straw-yellow. Streak gray to colorless. Opaque to subtranslucent. n m n in Comp. Essentially RR 2 (Ta,Nb) 4 Oi 5 .4H 2 O, with R = Fe, Ca, R = Y, Er, Ce, etc. The water may be secondary. The so-called yellow yttrotantalite of Ytterby and Kararfvet belongs to fergusonite. Obs. Occurs in Sweden at Ytterby, near Vaxholm, in red feldspar; at Finbo and Broddbo, near Falun, in southern Norway. SAMARSKITE. Orthorhombic. Axes a : b : c = 0*5456 Crystals rectangu- e (101) prominent). ee' 101 A 101 = 87. massive, and in flattened 1 : 0-5178. lar prisms (a (100), b (010), with Angles, mm'" 110 A 110 = 57 14'; Faces rough. Commonly embedded grains. Cleavage: b (010) imperfect. Fracture conchoidal. Brittle. H. = 5-6. G. = 5-6-5-8. Luster vitreous to resinous, splendent. Color velvet-black. Streak dark reddish brown. Nearly opaque. Index, 2*21. Comp; n RTRs(Nb,Ta) 6 O 2 i with R = Fe, Ca, U0 2 , m etc. ; R = cerium and yttrium metals chiefly. - In the closed tube decrepitates, glows, cracks open, and turns black. B.B, edges to a black glass. With salt of phosphorus in both flames an emerald- NIOBATES, TANTALATES 591 green bead. With soda yields a manganese reaction. Decomposed on fusion with potas- sium bisulphate, yielding a yellow mass which on treatment with dilute hydrochloric acid separates white tantalic acid, and on boiling with metallic zinc gives a fine blue color. In powder sufficiently decomposed on boiling with concentrated sulphuric acid to give the blue reduction test when the acid fluid is treated with metallic zinc or tin. Obs. Occurs in reddish brown feldspar, with seschynite and columbite in the Ilmen mountains, near Miask, Ural Mts.; from Antanamalaza, Madagascar. In the United States rather abundant and sometimes in large masses up to 20 Ibs. at the mica mines in Mitchell Co., N. C., intimately associated with columbite; sparingly elsewhere. Ampangabeite. A niobate of uranium, etc. In rectangular prisms, probably ortho- rhombic. Color brownish red. Luster greasy. H. = 4, G. = 3'97-4-29. Fuses to a black slag. Easily soluble in hydrochloric acid. Radioactive. Found in parallel growth with columbite at Ampangabe and Ambatofotsikely, Madagascar. Annerodite. Essentially a pyro-niobate of uranium and yttrium. In prismatic crys- tals, often resembling columbite. H. =6. G. = 5'7. Color black. From the pegmatite vein at Annerod, near Moss, Norway. Hielmite. A stanno-tantalate (and niobate) of yttrium, iron, manganese, calcium. Crystals (orthorhombic) usually rough; massive. G. = 5*82. Color pure black. From the Kararfvet mine, Falun, Sweden. ^Eschynite. A niobate and titanate (thorate) of the cerium metals chiefly, also in small amount iron, calcium, etc. Crystals prismatic, orthorhombic. Fracture small con- choidal. Brittle. H. = 5-6. G. = 4 -93 Hittero; 5 '168 Miask. Luster submetallic to resinous, nearly dull. Color nearly black, inclining to brownish yellow when translucent. From Miask in the Ilmen Mts., Russia, in feldspar with mica and zircon; also with euclase in the gold sands of the Orenburg District, Southern Ural Mts. From Hittero, Norway. Named from aurxwh, shame, by Berzelius, in allusion to the inability of chemical science, at the time of its discovery, to separate some of its constituents. Polymignite. A niobate and titanate (zirconate) of the cerium metals, iron, calcium. Crystals slender prisms, vertically striated. G. = 4'77-4'85. Color black. Occurs at Frederiksvarn, Norway. Euxenite. A niobate and titanate of yttrium, erbium, cerium and uranium. Crystals rare; commonly massive. H. = 6*5. G. = 47-5'0. Color brownish black. Occurs in Norway, at Jolster near Tvedestrand; at Alve, etc., near Arendal; from Greenland; from various localities in Madagascar. Loranskite and Wiikite are euxenite-like minerals from Impilaks, Finland. Usually in irregular masses but orthorhombic crystals are noted. H. =6. G. = 3'8-4'8. Color black to brown and yellow. Polycrase. A niobate and titanate of yttrium, erbium, cerium, uranium, like euxenite. Crystals thin prismatic, orthorhombic. Fracture conchoidal. H. = 5-6. G. = 4'97-5'04. Luster vitreous to resinous. Color black, brownish in splinters. From Hittero, Norway, in granite with gadolinite; at Slattakra, Smaland, Sweden. In the United States, in N. C., in the gold-washings on Davis land, Henderson Co., with zircon, monazite, xenotime, magnetite; also in S. C., four miles from Marietta in Greenville Co. Named from TTO\US, many, and /cpaais, mixture. Blomstrandine-Priorite. Niobates and titanates of yttrium, erbium, cerium and uranium, similar to the euxenite-poly erase series. The two series may be dimorphous. The ratio of Nb 2 O 6 : TiO 2 ranges from 1:2 in priorite to 1:6 in blomstrandine. Orthohombic. Crystals tabular parallel to b (010). Most prominent forms are 6 (010), c (001) and n (130). G. = 4'8-4'9. Color brownish black. Originally found in a pegmatite vein at Urstad, Island of Hittero, Norway. Also noted from Arendal and elsewhere in southern Norway and from Miask, Ilmen Mts., Russia. Betafite. A niobate and titanate of uranium, etc. Isometric with octahedron and dodecahedron. G. = 3 75-4 '17. Color, a greenish black. Opaque. Greasy luster. Found in pegmatites from various localities in Madagascar, including Ambolotara, near Betafo. 592 DESCRIPTIVE MINERALOGY Epistolite. A niobate of uncertain composition. Analysis shows chiefly SiO 2 , TiO 2 , Na^O, H 2 O. Monoclinic. In rectangular plates, also in aggregates of curved folia. Basal cleavage perfect. H. = 1-1 '5. G. = 2 '9. Color white, grayish, brownish. Refractive index 1 '67. Found in pegmatite veins or in massive albite from Julianehaab, Greenland. Plumboniobite. A niobate of yttrium, uranium, lead, iron, etc. Amorphous. H. = 5-5-5. G. = 4*81. Color dark brown to black. Found in mica mines at Morogoro, German East Africa. Oxygen Salts 4. PHOSPHATES, ARSENATES, VANADATES, ANTIMONATES A. Anhydrous Phosphates, Arsenates, Vanadates, Antimonates Normal phosphoric acid is H 3 PO 4 , and consequently normal phosphates i n m have the formulas R 3 P0 4 , R 3 (PO 4 )2 and RPO 4 , and similarly for the arse- nates, etc. Only a comparatively small number of species conform to this simple formula. Most species contain more than one metallic element, and in the prominent Apatite Group the radical (CaF), (CaCl) or (PbCl) enters; n in the Wagnerite Group we have similarly (RF) or (ROH). XENOTIME. 972 973 Tetragonal. Axisc = 0-6187, zz' (111 A 111) = 55 30', zz" (111 A Til) 82 22'. In crystals resembling zircon in habit; sometimes compounded with zircon in parallel position (Fig. 462, p. 173). In rolled grains. Cleavage: m (110) perfect. Fracture uneven and splintery. Brittle. H. = 4-5. G. = 4-45-4-56. Luster resinous to vitreous. Color yellowish brown, reddish brown, hair-brown, flesh-red, grayish white, wine-yellow, pale yellow; streak pale brown, yellow- ish or reddish. Opaque. Optically + . o> = 1 -72. e = 1*81. Comp. Essentially yttrium phosphate, YPO 4 or Y 2 03.P 2 O5 = Phosphorus pentoxide 38 -6, yttria = 100 The yttrium metals may include erbium m large amount; cerium is sometimes present; also silicon and thorium as in monazite. nl u moi ? tene , d with sulphuric acid colors the flame Diff PP Difficultly soluble m salt of phosphorus. Insoluble in acids. and D pfrfe7t ' ** ^^^ f rm ' but Distinguished by inferior hardness !? g ram ' te . veins ; sometimes in minute embedded uent if tfe musoovT^Hesof B, 6 S 1 ' Switzerland : An accessory constit- ously thought to ^taKgfaluSf of SO * & * fr m Braz " errone - Hender^n C I o lte Mftch t e n'Co t^f d shings of Clarksville, Ga, in N. C., Burke Co., ty S onite Ml Co - ^ "tile, etc, with' PHOSPHATES, ARSENATES, ETC. 593 MONAZITE Monoclinic. Axes a : b mm'", 110 A 110 = 86 34'. aw, 100 A 101 = 39 12'. a'x, 100 A 101 = 53 31'. ee', Oil A Oil = 83 56'. rr', 111 A 111 = 60 40'. vv', Til A Til = 73 19'. Norwich, Ct. Switzerland Crystals commonly small, often flattened || a (100) or elongated || axis 6; some- times prismatic by extension of v (111); also large and coarse. In masses yielding angular fragments; in rolled grains. Cleavage: c (001) sometimes perfect (parting?); also, a (100) distinct; 6 (010) difficult; sometimes showing parting || c (001), m (110). Fracture con- choidal to uneven. Brittle. H. = 5-5 -5. G. = 4-9-5-3; mostly 5*0 to 5-2. Luster inclining to resinous. Color hyacinth-red, clove-brown, reddish or yellowish brown. Subtransparent to subtranslucent. Optically + . Ax. pi. b (010) and nearly || a (100). Bx a Ac axis = + 1 to 4. Dispersion p < v weak; horizontal weak. 2V = 14. a = 1-786. ft = 1-788. 7 = 1-837. Comp. Phosphate of the cerium metals, essentially (Ce,La,Di)PO 4 . Most analyses show the presence of ThO 2 and SiO 2 , usually, but not always, in the proper amount to form thorium silicate; that this is mechanically present is not certain but possible. Pyr., etc. B.B. infusible, turns gray, and when moistened with sulphuric acid colors the flame bluish green. With borax gives a bead yellow while hot and colorless on cooling; a saturated bead becomes enamel-white on flaming. Difficultly soluble in hydrochloric acid. Obs. Rather abundantly distributed as an accessory constituent of gneissoid rocks in certain regions, thus in North Carolina and Brazil. Occurs near Zlatoust in the Ilmen Mts., Russia, in granite. In Norway, near Arendal, and at Annerod. In small yellow or brown crystals (turnerite] in Dauphine, France, and Switzerland. Found also in the gold washings of Antioquia, Colombia; in the diamond gravels of Brazil. In crystals from Trundle near Condobolin and Emmaville, New South Wales; California Creek, Queens- land; Olary, South Australia. In Madagascar at various localities. In the United States, formerly found with the sillimanite of Norwich, and at Portland, Conn.; also at Yorktown, N. Y. In large coarse crystals and masses in albitic granite with microlite, etc., at Amelia Court-House, Va. In Alexander Co., N. C., in splendent crystals; in Mitchell, Madison, Burke, and McDowell counties, obtained in large quantities in rolled grains by washing the gravels. In the gold sands of southern Idaho. Monazite is named from nova^iv, to be solitary, in allusion to its rare occurrence. Cryptolite occurs in wine-yellow prisms and grains in the green and red apatite of Aren- dal, Norway, and is discovered on putting the apatite in dilute nitric acid. It is probably monazite. Use. Monazite is the chief source of thorium oxide which is used in the manufacture of incandescent gaslight mantles. Berzeliite. R 3 As 2 O 8 (R = Ca,Mg,Mn,Na2). Isometric, usually massive. G. = 4-03. Color bright yellow. From Lungban, Sweden. Pyrrharsenite from the Sjo mines, Sweden, contains also antimony; color yellowish red. Caryinite, associated with berzeliite, is re- lated, but contains lead; massive (monoclinic). Monimolite. An antimonate of lead, iron, and sometimes calcium; in part, RsSbaOg. Usually in octahedrons; massive, incrusting. G. = 6 '58. Color yellowish or brownish green. From the Harstig mine, Pajsberg, Sweden. 594 DESCRIPTIVE MINERALOGY Carminite. Perhaps Pb 3 As 2 O 8 .10FeAsO4. In clusters of fine needles; also in sphe- roidal forms. G. = 4105. Color carmine to tile-red. From the Luise mine at Hor- hausen, Nassau, Germany. Georgiadesite. Pb 3 (AsO 4 ) 2 .3PbCl 2 . Orthorhombic. In small crystals with hexago- nal outline. H. = 3'5. G. = 7'1. Resinous luster. Color white, brownish yellow. Found on lead slags at Laurium, Greece. Pucherite. Bismuth vanadate, BiVO 4 . In small orthorhombic crystals. H. = 4. G. = 6-249. Color reddish brown. Optically -. = 2 -50. From the Pucher Mine, Schneeberg, Saxony; San Diego Co., Cal. Armangite. Mn 3 (AsO 3 ) 2 . Hexagonal-rhombohedral. Prismatic habit. H. = 4. G. = 4-23. Poor basal cleavage. Color black, streak brown. Optically -. High refractive index. From Langban, Sweden. Triphylite Group. Orthorhombic a : b : c Triphylite Li(Fe,Mn)P0 4 0'4348 : 1 : 0'5265 Lithiophilite Li(Mn,Fe)PO 4 Natrophilite NaMnPO 4 Orthophosphates of an alkali metal, lithium or sodium, with iron and man- ganese. TRIPHYLITE-LITHIOPHILITE. Orthorhombic. Axes a : b : c = 0-4348 : 1 : 0'5265. Crystals rare, usu- ally coarse and faces uneven. Commonly massive, cleavable to compact. Cleavage: c (001) perfect; b (010) nearly perfect; m (110) interrupted. Fracture uneven to subconchoidal. H. = 4-5-5. G = 3-42-3-56. Luster vitreous to resinous. Color greenish gray to bluish in triphylite; also pale pink to yellow and clove-brown in lithiophilite. Streak uncolored to grayish white. Transparent to translucent. Axial angle variable, 0-90. Mean index, 1-68. Comp. A phosphate of iron, manganese and lithium, Li(Fe,Mn)P0 4 , varying from the bluish gray TRIPHYLITE with little manganese to the salmon- pink or clove-brown LITHIOPHILITE with but little iron. Typical Triphylite is LiFePO 4 = Phosphorus pentoxide 45 '0, iron protoxide 45 '5, lithia 9'5 = 100. Typical Lithiophilite is LiMnPO4 = Phosphorus pentoxide 45 '3, manganese protoxide 45'1, lithia 9'6 = 100. Both Fe and Mn are always present. Pyr., etc. In the closed tube sometimes decrepitates, turns to a dark color, and gives off traces of water. B.B. fuses at T5, coloring the flame beautiful lithia-red in streaks, with a pale bluish green on the exterior of the cone of flame. With the fluxes reacts for iron and manganese; the iron reaction is feeble in pure lithiophilite. Soluble in hydro- chloric acid. Obs. Triphylite is often associated with spodumene; occurs at Rabenstein, near Zwiesel^in Bavaria; Keityo, Finland; Norwich, Mass.; Peru, Me.; Grafton, N. H. Named from Tpis, threefold, and v\ri, family, in allusion to its containing three phosphates. Lithiophilite occurs at Branch ville, Fairfield Co., Conn., in a vein of albitic granite, with spodumene, manganese phosphates, etc.; also at Norway, Me., in crystals from Pala, Cal. Named from lithium and t\6s, friend. Natrophilite. NaMnPO 4 . Near triphylite in form. Chiefly massive, cleavable. H. = 4-5-5. G. = 3-41. Color deep wine-yellow. Occurs sparingly at Branchville, Conn. Graftomte. (Fe,Mn,Ca) 3 P 2 O 8 . Monoclinic. H. =5. G. = 37. Color when fresh salmon-pink, usually dark from alteration. Fusible. Occurs in laminated intergrowths with tnphyllite in a pegmatite from Grafton, N. H. PHOSPHATES,- ARSENATES, ETC. 595 Beryllonite. A phosphate of sodium and beryllium, NaBePCX. Crystals short pris- matic to tabular, orthorhombic. H. = 5'5-6. G. = 2*845. Luster vitreous; on c (001) pearly. Colorless to white or pale yellowish. Optically . /3 = 1*558. From Stone- ham, Me. Apatite Group R 5 (F,Cl)[(P,As,V)0 4 ] 3 = (R(F,Cl))R 4 [(P,As,V)0 4 ] 3 ; (CaF)Ca 4 (PO 4 ) 3 Fluor-apatite c = 0-7346 or (CaCl)Ca 4 (PO 4 ) 3 Chlor-apatite (PbCl)Pb 4 (PO 4 ) 3 0-7362 (PbCl)Pb 4 (AsO 4 ) 3 0-7224 (PbCl)Pb 4 (VO 4 ) 3 0-7122 General formula Apatite Pyromorphite Mimetite Vanadinite In addition to the above species, there are also certain intermediate compounds contain- ing lead and calcium; others with phosphorus and arsenic, or arsenic and vanadium, as noted beyond. Further the rare calcium arsenate, Svabite, also seems to belong in this group. The radicals CaO, Ca.OH, may possibly replace the CaF radical in apatite. A probable member of the group, wilkeite, contains CO 3 , SiO 2 and SO 4 in addition to usual radicals. Fermorite contains strontium. The species of the APATITE GROUP crystallize in the hexagonal system, but all show, either by the subordinate faces, or in .etching-figures, that they belong to the pyramidal class (p. 100). They are chemically phosphates, arsenates, vanadates of calcium or lead (also manganese), with chlorine or fluorine. The latter element is probably present as a univalent radical CaF (or CaCl), etc., in general RF (or RC1), replacing one hydrogen atom in i n n the acid R 9 (P0 4 ) 3 , so that the general formula is (RF)R 4 (PO 4 ) 3 , and similarly for the arsenates. This is a more correct way of viewing the composition than the other method sometimes adopted, viz., 3R 3 (PO 4 ) 2 .RF 2 , etc. APATITE. Hexagonal-pyramidal. 976 977 Axis c = 07346. 978 979 cr, 0001 A 1012 = 22 59'. ex, 0001 A lOll = 40 18'. cy, 0001 A 2021 = 59 29'. rr', 1012 A 0112 = 22 31'. xx r , lOTl A 1011 = 37 88', 1121 A 1211 = 48 50'. m^ 1010 A 2131 = 30 20'. ms, 1010 A 1121 = 44 17'. Crystals varying from long prismatic to short prismatic and tabular. Also globular and reniform, with a fibrous or imperfectly columnar structure; massive, structure granular to compact. Cleavage: c (0001) imperfect; m (1010) more so. Fracture conchoidal 596 DESCRIPTIVE MINERALOGY and uneven. Brittle. H. = 5, sometimes 4-5 when massive. G = 3-17- 3-23 crystals. Luster vitreous, inclining to subresmous. btreak white. Color usually sea-green, bluish green; often violet-blue; sometimes white; occasionally yellow, gray, red, flesh-red and brown. Transparent to opaque. Optically -. Birefringence low. co = 1-6461, e = 1-6417. Var 1 Ordinary Crystallized, or cleavable and granular massive. Colorless to ereen blue yellow, flesh-red, (a) The asparagus-stone, originally from Murcia Spain is yellowish green. Moroxite, from Arendal, Norway, is in greenish blue and bluish crystals (6) Lasurapatite is a sky-blue variety with lapis-lazuli in Siberia, (c) Francohte, from Wheal Franco, near Tavistock, Devonshire, England, occurs in small crystalline stalactitic masses and in minute curving crystals. . Ordinary apatite is fluor-apatite, containing fluorine often with only a trace of chlorine, up to 0'5 p. c.; rarely chlorine preponderates, and sometimes fluorine is entirely absent. 2. Manganapatite contains manganese replacing calcium to 10'5 p. c. MnO; color dark 3 Voelckerite is name given to the possible isomorphous molecule, Ca 4 (CaO)(PO 4 ) 3 and . 4. Fibrous, concretionary, stalactitic. Phosphorite includes the fibrous concretionary and partly scaly mineral from Estremadura, Spain, and elsewhere. Eupyrchroite, from Crown Point, N. Y., belongs here; it is concentric in structure. Staffelite occurs incrust- ing the phosphorite of Staffel, Germany, in botryoidal, reniform, or stalactitic masses, fibrous and radiating. See p. 597. 5. Earthy apatite; Osteolite. Mostly altered apatite; coprolites are impure calcium phosphate. Comp. For Fluor-apatite (CaF)Ca 4 (PO 4 ) 3 ; and for Chlor-apatite (CaCl)Ca 4 (PO 4 )3; also written 3Ca 3 P 2 O8.CaF 2 and SCaaPaOs.CaCl;. There are also intermediate compounds containing both fluorine and chlorine. The percentage composition for these normal varieties is as follows : Fluor-apatite P 2 O 5 42'3 CaO 55'5 F 3'8 = 101'6 or Ca 3 P s O 8 92'25 CaF 2 775 = 100 Chlor-apatite P 2 O 5 41'0 CaO 53 '8 C16'8 = 101-6 or Ca 3 P 2 8 89'4 CaCl 2 10'6 = 100 Fluor-apatite is much more common than the other variety; here belongs the apatite of the Alps, Spain, St. Lawrence Co., N. Y., Canada. Apatites in which chlorine is promi- nent are rare; this is true of some Norwegian kinds. Pyr., etc. B.B. in the forceps fuses with difficulty on the edges (F. = 4-5-5), coloring the flame reddish yellow; moistened with sulphuric acid and heated colors the flame pale bluish green (phosphoric acid). Dissolves in hydrochloric and nitric acids, yielding with sulphuric acid a copious precipitate of calcium sulphate; the dilute nitric acid solution gives sometimes a precipitate of silver chloride on addition of silver nitrate. Most varieties will give a slight test for fluorine, when heat ed with potassium bisulphate in a closed tube. Diff. Characterized by the common hexagonal form, but softer than beryl, being scratched by a knife; does not effervesce in acid (like calcite) ; difficultly fusible; yields a green flame B.B. after being moistened with sulphuric acid. Micro. Recognized in thin sections by its moderately high relief; extremely low bire- fringence (hence not often showing a disti net axial figure in basal sections), the interference colors in ordinary sections scarcely rising above gray of the first order; parallel extinction and negative extension; columnar form; lack of color and cleavage; and by the rude cross parting seen as occasional cracks crossing the prism. Artif. Apatite may be prepared artificially by fusing sodium phosphate with calcium fluoride or calcium chloride. Obs. Apatite occurs in rocks of various kinds and ages, but is most common in meta- morphic crystalline rocks, especially in granular limestone and in many metalliferous veins, particularly those of tin, in gneiss, syenite, hornblendic gneiss, mica schist, beds of iron ore; occasionally in serpentine. In the form of minute microscopic crystals it has an almost universal distribution as an accessory rock-forming mineral. It is found in all kinds of igneous rocks and is one of the earliest products of crystallization. In larger crystals it is especially characteristic of the pegmatite facies of igneous rocks, particularly the granites, and occurs there associated with quartz, feldspar, tourmaline, muscovite, beryl, etc. It is sometimes present in ordinary stratified limestone, beds of sandstone or shale of the Silurian, Carboniferous, Jurassic, Cretaceous, or Tertiary. It has been observed as the petrifying matenal of wood. PHOSPHATES, ARSENATES, ETC. 597 Among its localities are Ehrenfriedersdorf in Saxony; Schwarzenstein, the Knappen- wand in Untersulzbachtal and Zillertal in the Tyrol, Austria; St. Gothard, Tavetsch, etc., in Switzerland; Mussa-Alp in Piedmont, Italy, white or colorless; Zinnwald and Schlacken- wald in Bohemia; at Gellivare, Sweden; in England, in Cornwall, with tin ores; in Cum- berland, at Carrock Fells; in Devonshire, cream-colored at Bovey Tracey, and at Wheal Franco (francolite). The asparagus-stone or spargelstein of Jumilla, in Murcia, Spain, is pale yellowish green in color. Large quantities of apatite are mined in Norway at Kragero; also at Odegaard, near Bamle, and elsewhere. In Me., on Long Island, Blue-hill Bay; in fine purple crystals of gem-quality from Auburn. In N. H., Westmoreland. In Mass., at Norwich; at Bolton abundant. In Conn., at Branch ville (manganapatite) , also greenish white and colorless; at Haddam Neck. In N. Y., common in St. Lawrence Co., in granular limestone, also Jefferson Co.; Sandford mine, East Moriah, Essex Co., in magnetite; near Edenville, Orange Co.; at Tilly Foster iron mine. In Pa., at Leiperville, Delaware Co.; in Chester Co. In N. C., at Stony Point, Alexander Co., etc. In lavender-colored crystals from Mesa Grande, Cal. In extensive beds in the Laurentian gneiss of Canada, usually associated with limestone, and accompanied by pyroxene, amphibole, titanite, zircon, garnet, vesuvianite and many other species. Prominent mines are in Ottawa County, Quebec, in the townships of Buck- ingham, Templeton, Portland, Hull, and Wakefield. Also in Renfrew county, Ontario, and in Lanark, Leeds, and Frontenac counties. Apatite was named by Werner from diraTaew, to deceive, older mineralogists having referred it to aquamarine, chrysolite, amethyst, fluorite, tourmaline, etc. Besides the definite mineral phosphates, including normal apatite, phosphorite, etc., there are also extensive deposits of amorphous phosphates, consisting largely of "bone phosphate" (CasPjOs), of great economic importance, though not having a definite chemi- cal composition, and hence not strictly belonging to pure mineralogy. Here belong the phosphatic nodules, coprolites, bone beds, guano, etc. Extensive phosphatic deposits also occur in North Carolina, Alabama, Florida, Tennessee, and in the western states, Idaho, Utah, and Wyoming. Guano is bone phosphate of lime, mixed with the hydrous phos- phates, and generally with some calcium carbonate, and often a little magnesia, alumina, iron, silica, gypsum, and other impurities. Use. Apatite and phosphate rock are used chiefly as sources of mineral fertilizers. Some clear finely colored varieties of apatite may be used as gem stones. The mineral is too soft, however, to permit of extensive use for this purpose. STAFFELITE. A carbonated calcium phosphate. Occurs incrusting the phosphorite of Staffel, Germany, in botryoidal or stalactitic masses, fibrous and radiating; it is the result of the action of carbonated waters. H. =4. G. = 3 '128. Color leek- to dark green, greenish yellow. Dahllite, from Bamle, Norway, is similar. Fermorite. A member of the Apatite Group. (Ca,Sr) 4 [Ca(OH,F)][(P,As)O 4 ] 3 . H. = 5. G. = 3-52. Color pale pinkish white to white. Uniaxial, - . Index = 1'66. Found with manganese ores at Sitapar, Chhindwara District, Central provinces, India. Wilkeite. 3Ca3(PO 4 )o.CaCO 3 .3Ca 3 ((SiO 4 )(SO 4 )].CaO. Probably a member of Apatite Group. Hexagonal. H. =5. G. = 3*23. Color pale rose-red, yellow. Optically . Index, 1-64. Fusible at 5 '5. Dissolves in acids with separation of silica. In crystalline limestone at Crestmore, Riverside Co., Cal. PYROMORPHITE. Green Lead Ore. Hexagonal pyramidal. Axis c = 07362. Crystals prismatic, often in rounded barrel-shaped forms; also in branching groups of prismatic crystals in nearly parallel position, tapering down to a slender point. Often globular, reniform, and botryoidal or in wart-like shapes, with usually a subcolumnar structure; also jibrous, and granular. Cleavage: m (1010), x (1011) in traces. Fracture subcon- choidal, uneven. Brittle. H. = 3-5-4. G. = 6-5-7-1 mostly, when pure; 5-9-6-5, when containing lime. Luster resinous. Color green, yellow, and brown, of different shades; sometimes wax-yellow and fine orange-yellow; also grayish white to milk-white. Streak white, sometimes yellowish. Subtransparent to subtranslucent. Optically . co = 2*050. e = 2-042. 598 DESCRIPTIVE MINERALOGY Var 1 Ordinary, (a) In crystals as described; sometimes yellow and in rounded forms resembling campylite (pseudo-campylite) . (6) In acicular and moss-like aggregations. (c) Concretionary groups or masses of crystals, having the surface angular, (d) Fibrous, (e) Granular massive. (/) Earthy; incrusting. 2 Polysphcerite. Containing lime; color brown of different shades, yellowish gray, pale yellow to nearly white; streak white; G. = 5'89-6'44. Rarely in separate crystals; usually in groups, globular, mammillary. Miesite, from Mies in Bohemia, is a brown variety Nussierite is similar and impure, from Nussiere, near Beaujeu, Prance; color yellow greenish or grayish; G. = 5'042. 3. Chromiferous; color brilliant red and orange. 4. Arseniferous; color green to white; G. = 5 '5-6 '6. 5. Pseudomorphous; (a) after galena; (6) cerussite. Comp. (PbCl)Pb 4 (PO 4 )3 or also written 3Pb 3 P 2 O8.PbCl 2 = Phosphorus pentoxide 157, lead protoxide 82-2, chlorine 2-6 = 100-5, or Lead phosphate 897, lead chloride 10-3 = 100. The phosphorus is often replaced by arsenic, and as the amount increases the species passes into mimetite. Calcium also replaces the lead to a considerable extent. Pyr., etc. In the closed tube gives a white sublimate of lead chloride. B.B. in the forceps fuses easily (F. = T5), coloring the flame bluish green; on charcoal fuses without reduction to a globule, which on cooling assumes a crystalline polyhedral form, while the coal is coated white from lead chloride and, nearer the assay, yellow from lead oxide. With soda on charcoal yields metallic lead; some varieties contain arsenic, and give the odor of garlic in R.F. on charcoal. Soluble in nitric acid. Diff. Distinguished by its hexagonal form; high specific gravity; resinous luster; blowpipe characters. Obs. Pyromorphite occurs principally in veins, and accompanies other ores of lead. At Poullaouen and Huelgoet in Brittany, France; at Zschopau and other places in Saxony, Germany; at Pfibram, Bleistadt, in Bohemia; in fine crystals at Ems, Braubach, in Nassau, Germany; also at Dernbach in Nassau; in Siberia at Beresov and in the Nerchinsk mining district; in England, in Cornwall, green and brown; Devon, gray; Derbyshire, green and yellow; Cumberland, golden yellow ; in Scotland, Leadhill, red and orange. From Broken Hill and elsewhere, New South Wales. In the United States, has been found very fine at Phenixville, Pa. ; also in Me., at Lubec and Lenox; in N. Y., a mile south of Sing Sing; in Davidson Co., N. C., also in Cabarrus and Caldwell Cos.; from Mullan, Burke, Wardner and Mace, Idaho. Named from irvp, fire, vopr), form, alluding to the crystalline form the globule assumes on cooling. This species passes into mimetite. Use. A minor ore of lead. MIMETITE. Hexagonal-pyramidal. Axis c = 07224. Habit of crystals like pyromorphite; sometimes rounded to globular forms. Also in mammillary crusts. Cleavage: x (1011) imperfect. Fracture uneven. Brittle. H. = 3-5. G. = 7-0-7-25. Luster resinous. Color pale yellow, passing into brown; orange-yellow; white or colorless. Streak white or nearly so. Sub trans- parent to translucent. Optically, co = 2-135. = 2-118. Var - 1- Ordinary, (a) In crystals, usually in rounded aggregates. (6) Capillary or filamentous, especially marked in a variety from St. Prix-sous-Beuvray, France; somewhat like asbestus, and straw-yellow in color, (c) Concretionary. Campylite, from Drygill in Cumberland, England, has G. = 7*218, and is in barrel- shaped crystals (whence the name, from K anirv\os, curved), yellowish to brown and brown- ish red; contains 3 p. c. P 2 O 6 . Comp. (PbCl)Pb 4 (AsO 4 ) 3 ; also written 3Pb 3 As 2 8 .PbCl 2 = Arsenic pentoxide 23'2, lead protoxide 74-9, chlorine 2-4 = 100'5, or Lead arsenate 90-7, lead chloride 9-3 = 100. Phosphorus replaces the arsenic in part, and calcium the lead. Endlichite (p. 599) is intermediate between mimetite and vanadinite. PHOSPHATES, ARSENATES, ETC. 599 982 m Pyr., etc. In the closed tube like pyromorphite. B.B. fuses at 1, and on charcoal gives m R.F. an arsenical odor, and is easily reduced to metallic lead, coating the coal at first with lead chloride, and later with arsenic trioxide and lead oxide. Soluble in nitric acid. Obs. Occurs in England near Redruth and elsewhere in Cornwall; Beer Alston Dev- onshire; in Cumberland; in France near Pontgibaud, Puy-de-D6me; in Germany at Johanngeorgenstadt, m fine yellow crystals, at Zinnwald; at Nerchinsk, Siberia; Langban, Sweden; from Santa Eulalia, Chihuahua, Mexico; at the Brookdale mine Phenixville Pa Eureka, Utah. Named from /it/z^r^s, imitator, it closely resembling pyromorphite. Use. A minor ore of lead. VANADINITE. Hexagonal-pyramidal. Axis c = 07122. Crystals prismatic, with smooth faces and sharp edges; sometimes cavern- ous, the crystals hollow prisms; also in rounded forms and in parallel group- ings like pyromorphite. In implanted globules or incrustations. Fracture uneven, or flat conchoidal. Brittle. H. = 275-3. G. '= 6'66- 7'10. Luster of surface of fracture resinous. Color deep ruby-red, light brownish yellow, straw-yellow, reddish brown. Streak white or yellowish. Subtranslucent to opaque. Opti- cally -. co = 2-354. e = 2-299. Comp.. - - (PbCl)Pb 4 (V0 4 ) 3 , also written 3Pb 3 V 2 O 8 .PbCl2 = Vanadium pentoxide 19-4, lead protoxide 78-7, chlorine 2-5 = 100*6, or Lead vanadate 90-2, lead chloride 9-8 = 100. Phosphorus is sparingly present, also sometimes arsenic, both* replacing vanadium. In endlichite the ratio of V : As = 1 : 1 nearly. Pyr., etc. In the closed tube decrepitates and yields a faint white sublimate. B.B. fuses easily, and on charcoal to a black lustrous mass, which in R.F. yields metallic lead and a coating of lead chloride; after completely oxidizing the lead in O.F. the black residue gives with salt of phosphorus an emerald-green bead in R.F., which becomes light yellow in O.F. Decomposed by hydrochloric acid. Obs. First discovered at Zimapan in Mexico. Later obtained at Wanlockhead in Dumfriesshire, Scotland; also at Berezov in the Ural Mts., with pyromorphite; and near Kappel in Carinthia, in crystals; at Undenas, Bolet, Sweden. In the Sierra de Cordoba, Argentine Republic. In the United States, sparingly near Sing Sing, N. Y. Abundant in the mining regions of Arizona and New Mexico, often associated with wulfenite and descloizite; in Ariz., at the mines in Yuma Co., in brilliant deep red crystals; Vulture, Phoenix, etc., in Maricopa Co.; the Mammoth gold mine, near Oracle, Pinal Co.; from Yavapai Co. In N. M. at Lake Valley, Sierra Co. (endlichite); and the Mimbres mines near Georgetown; Hillsboro; Magdalena. Use. A source of vanadium and a minor ore of lead. HEDYPHANE. From Langban, Sweden; has ordinarily been included as a calcium variety of mimetite. Massive, cleavable. Color yellowish white. From Harstig mine, Pajsberg, Sweden. Svabite. A calcium arsenate, related to the species of the Apatite Group. Crystals hexagonal prisms; colorless; c = 07143. H. =5. G. = 3 -52. From the Harstig mine, Pajsberg, and near Nordmark, Sweden. 6QO DESCRIPTIVE MINERALOGY Wagnerite Group. Monoclinic a :b : c ft Wagnerite (MgF)MgP0 4 1'9145 : 1 : 1'5059; 71 53' Triplite (RF)RP0 4 , R = Fe : Mn = 2 : 1, 1 : 1, etc. Triploidite ROH)RP0 4 , R = Mn : Fe = 3 : 1 T8572 : 1 : 1*4925; 71 46' AdSlte (MgOH)CaAs0 4 2'1978 : 1 : 1-5642; 73 15' Tilasite (MgF)CaAs0 4 Sarkinite (MnOH)MnAsO 4 2'0017 : 1 : 1 5154; 62 13*' Phosphates (and arsenates) of magnesium (calcium), iron and manganese containing fluorine (also hydroxyl). Formula R 2 FPO 4 or (RF)RPO 4 , etc. WAGNERITE. Monoclinic. Axes, see above. Crystals sometimes large and coarse. Also massive. Cleavage: a (100), m (110) imperfect; c (001) in traces. Fracture uneven and splintery. Brittle. H. = 5-5*5. G. = 3*07-3' 14. Luster vitreous. Streak white. Color yellow, of different shades; often grayish, also flesh-red, greenish. Translucent. Optically +. 2V = 26 (approx.). a = 1*569. ft = 1'570. 7 = 1*582. Comp. A fluo-phosphate of magnesium, (MgF)MgPO 4 or Mg 3 P 2 8 . MgF 2 = Phosphorus pentoxide 43 '8, magnesia 49*3, fluorine 11*8 = 104*9, deduct (O = 2F) 4'9 = 100. A little calcium replaces part of the magnesium. Pyr., etc. B.B. in the forceps fuses at 4 to a greenish gray glass; moistened with sulphuric acid colors the flame bluish green. With borax reacts for iron. On fusion with soda effervesces, but is not completely dissolved; gives a faint manganese reaction. Re- acts for fluorine. Soluble in nitric and hydrochloric acids. With sulphuric acid evolves fumes of hydrofluoric acid. Obs. Wagnerite (in small highly modified crystals) occurs in the valley of Hollen- graben, near Werfen, in Salzburg, Austria. Kjerulfine (massive, cleavable; also in coarse crystals) is from Kjorrestad, near Bamle, Norway. , Spodiosite. A calcium fluo-phosphate, perhaps (CaF)CaPO 4 . In flattened prismatic orthorhombic crystals. G. = 2 '94. Color ash-gray. From the Krangrufva, Wermland, and Nordmark, Sweden. TRIPLITE. Monoclinic. Massive, imperfectly crystalline. Cleavage: unequal in two directions perpendicular to each other, one much the more distinct. Frac- ture small conchoidal. H. = 4-5 -5. G. = 3'44-3'S. Luster resinous, inclin- ing to adamantine. Color brown or blackish brown. Streak yellowish gray or brown. Subtranslucent to opaque. Optically +. Mean index from 1 66- 1-68. . Comp. (RF)RP0 4 or R 3 P 2 8 .RF 2 with R = Fe and Mn, also Ca and Mg. The ratio varies widely from Fe : Mn = 1 : 1 to 2 : 1 (zwieselite) : 1:2; 1:7. Talktriplite is a variety from Horrsjoberg, Sweden; contains magnesium and calcium in large amount. Pyr. ? etc. B.B. fuses easily at 1*5 to a black magnetic globule; moistened with sulphuric acid colors the flame bluish green. With borax in O.F. gives an amethystine- colored glass (manganese) ; in R.F. a strong reaction for iron. With soda reacts for man- ganese. With sulphuric acid evolves hydrofluoric acid. Soluble in hydrochloric acid. D ~~ UMI by Alluaud at Limoges in France; Helsingfors, Finland; Stoneham, Me.; Branchville, Conn.; from Reagan mining district, White Pine Co., Nev. Zwieselite, a clove-brown variety, is from Rabenstein, near Zwiesel in Bavaria. GRIPHITE. A problematical phosphate related to triplite occurring in embedded reni- form masses. From the Riverton lode near Harney City, Pennington Co., S. D. PHOSPHATES, ARSENATES, ETC. 601 II PHOSPHOFERRITE. H 6 R9(PO 4 ) 3 : R = Fe, Mn,Ca, Mg. Columnar. White to yellow or pale green. H. = 4-5. G. = 3' 16. Habendorf, Bavaria. Triploidite. Like triplite, but with the F replaced by (OH). Monoclinic. Commonly in crystalline aggregates. Fibrous to columnar. H. = 4'5-5. G. = 3*697. Color yel- lowish to reddish brown. Optically + . = 1726. From Branchville, Fair-field Co., Conn. Adelite. (MgOH)CaAsO 4 . Monoclinic. Axes, see p. 600; also massive. H. = 5. G. = 374. Color gray or grayish yellow. Optically +. Mean index, 1 '67. From Nord- mark and Langban, Sweden. Tilasite. Like adelite, but contains fluorine. Monoclinic. Optically . /3 = 1*660. From Langban, Sweden, and Kajlidongri, Jhabua, India. Sarkinite. (MnOH)MnAsO 4 . In monoclinic crystals; also in spherical forms. G. = 4 '17. Color rose-red, flesh-red, reddish yellow. From the iron-manganese mines of Pajsberg, Sweden. Polyarsenite and Xantharsenite from the Sjo mine, Grythytte parish, Orebro, Sweden, and Chondrasenite from Pajsberg, Sweden, are essentially the same. Trigonite. Pb 3 MnH(AsO 3 )3. Monoclinic-clinohedral. In small wedge-shaped crystals. H. = 2-3. Perfect cleavage || (010). Color sulphur-yellow, a. = 2*08. 7 = 216. Ax. pi. | j (010) . From Langban, Sweden. Herderite. A fluo-phpsphate of beryllium and calcium, Ca[Be(F,OH)]PO4. In pris- matic crystals, monoclinic with complex twinning. H. =5. G. = 2 '99-3 *01. Luster vitreous. Color yellowish and greenish white. Optically, ft = T612. From the tin mines of Ehrenfriedersdorf, Saxony; from Epprechtstein, Bavaria; also at Stoneham, Auburn, Hebron, and Paris, Me. Hamlinite. A basic phosphate of aluminium, and strontium. In colorless rhombo- hedral crystals. H. = 4 '5. G. = 3* 16-3 '28. Optically +. o> = 1*620. Occurs with herderite, bertrandite, etc., at Stoneham, Me. In the diamond sands of Diamantina, Brazil. Found also in Binnental, Switzerland (originally thought to be a new species and named bowmannite) . Plumbogummite. A basic phosphate of lead and aluminium. In chemical group with hamlinite. Resembles drops or coatings of gum; as incrustations. Color yellowish, brown- ish. From Roughten Gill, Cumberland, England. Hitchcockite from Canton mine, Ga., is closely identical. The material from Huelgoet, Brittany, France, is a mixture. Florencite. A basic phosphate of aluminium and the cerium metals, closely analogous to hamlinite to which it is related in form. 3Al 2 O3.Ce2O3.2P 2 O6.6H2O. Hexagonal, rhom- bohedral. Habit rhombohedral. Basal cleavage. H. =5. G. = 3*58. Color pale yellow. Infusible. Found in sands from near Ouro Preto and Diamantina, Minas Geraes, Brazil. Georceixite. A basic phosphate of aluminium and barium (with smaller amounts of calcium and cerium) . BaO.2Al 2 p 3 .P 2 O 5 .5H 2 O. Microcrystalline, in rolled pebbles. H. = 6. G. = 3*1. Color brown and white. Refractive index, 1*63. From the diamond sands of Minas Geraes, Brazil. Geraesite is similar but more acidic in composition. Crandallite. 2CaO.4Al/) 3 .2P 2 O 5 .10H 2 O. In compact to cleavable masses. Micro- scopically fibrous. Color white to light gray. Indices, 1-58-1*60. Found at Brooklyn mine near Silver City, Utah. Harttite. A basic phosphate and sulphate of aluminium and strontium, (Sr,Ca)O. 2A1 2 O 3 .P 2 O 5 .SO 3 .5H 2 O. Hexagonal. Usually microcrystalline as rolled pebbles. H. = 4'5-5. G. = 3*2. Color flesh-red. From the diamond sands of Minas Geraes, Brazil. Jezekite. A fluo-phosphate of lime, soda, and alumina, Na 4 CaAl(AlO)(F,OH) 4 (Pp 4 ) 2 . Monoclinic. H. = 4*5. G. = 2*94. Cleavage perfect (100); imperfect (001). Indices, 1 '55-1 '59. Colorless or white. From Ehrenfriedersdorf, Saxony. Lacroixite. A fluo-phosphate of soda, lime, manganese oxide, and alumina. Na 4 (Ca,Mn) 4 Al 3 (F,OH) 4 P 3 Oi 6 .2H 2 O. Probably monoclinic. Pyramidal cleavage. H. = 4-1. G. = 3*13. Color pale yellow or green. Found at Ehrenfriedersdorf, Saxony. Durangite. A fluo-arsenate of sodium and aluminium, Na(AlF)AsO 4 . In monoclinic crystals. G. = 3*94-4*07. Color orange-red. Mean index, 1*673. From Durango, Mexico. 602 DESCRIPTIVE MINERALOGY AMBLYGONITE. Hebronite. Triclinic. Crystals large and coarse; forms rarely distinct. Usually cleavable to columnar and compact massive. Polysynthetic twinning lamellae common. Cleavage: c (001) perfect, with pearly luster; a_(100) somewhat less so, vitreous; e (021) sometimes equally distinct; M (110) difficult; ca (001) A (100) = 75 30', ce (001) A (021) = 74 40', cM (001) A (110) = 92 20'. Fracture uneven to subconchoidal. Brittle. H. = 6. G. = 3'01-3'09. Luster vitreous to greasy, on c (001) pearly. Color white to pale greenish, bluish, yellowish, grayish or brownish white. Streak white. Subtrans- parent to translucent. Optically -. a = 1'579. = 1*593. 7 = 1'597. Comp. A fluo-phosphate of aluminium and lithium, Li(AlF)PO 4 or AlPO 4 .LiF = Phosphorus pentoxide 47*9, alumina 34-4, lithia 10-1, fluorine 12-9 = 105-3, deduct (0 = 2F) 5*3 = 100. Sodium often replaces part of the lithium, and hydroxyl part of the fluorine. Pyr., etc. In the closed tube yields water, which at a high heat is acid and corrodes the glass. B.B. fuses easily (at 2) with intumescence, and becomes opaque white on cool- ing. Colors the flame yellowish red with traces of green; the Hebron variety gives an in- tense lithia-red; moistened with sulphuric acid gives a bluish green to the flame. With borax and salt of phosphorus forms a transparent colorless glass. In fine powder dissolves easily in sulphuric acid, more slowly in hydrochloric acid. Diff. Distinguished by its easy fusibility and by yielding a red flame B.B., from feld- spar, barite, calcite, etc.; also by the acid water in the tube from spodumene. Obs. Occurs near Penig in Saxony; Arendal, Norway; Montebras, Creuze, France. In the United States, in Me., at Hebron; also at Paris, Peru, etc.; Branchville, Conn., Pala, San Diego Co., Cal. The name amblygonite is from anftXls, blunt, and yow, angle. Fremontite. Natramblygonite. Natromontebrasite. (Na,Li)Al(OH,F)PO 4 . Mono- clinic. Crystals coarse with rough faces. Three cleavages. Usually in cleavage masses. Polysynthetic twinning shown under microscope. H. = 5'5. G. = 3 '04. Luster vitreous to greasy. Color, grayish white to white. Translucent to opaque. Optically. Bisec- trix nearly normal to basal cleavage. Easily fusible to a white enamel with strong sodium flame color. From a pegmatite near Canon City, Fremont County, Col. B. Basic Phosphates This section includes a series of well-characterized basic phosphates, a number of which fall into the Olivinite Group. Acid phosphates are repre- sented by one species only, the little known monetite, probably HCaPO 4 , see p. b06. Olivenite Group. Orthorhombic OUvenite Cu 2 (OH)AsO 4 0-9396 : 1 : 0-6726 Libethenite Cu 2 (OH)PO 4 0-9601 : 1 : 0-7019 Adamite Zn 2 (OH)AsO 4 0-9733 : 1 : 0-7158 Descloizite (Pb,Zn) 2 (OH)VO 4 a : b : c = 0-6368 : 1 : 0-8045 or fa : b : c = 0-9552 : 1 : 0-8045 Cuprodescloizite (Pb,Zn,Cu) 2 (OH)VO 4 The OLIVENITE GROUP includes several basic phosphates, arsenates, etc., of copper, zinc, and lead, with the general formula (ROH)RPO 4 ,(ROH)RAsO 4 , 1 hey crystallize in the orthorhombic system with similar form. It is to * , ? roup corres P n ds in a measure to the monoclinic Wagnerite Group, p. 600, which also includes basic members. PHOSPHATES, ARSENATES, ETC. 603 \ OLIVENITE. Orthorhombic. Axes a : b : c = 0*9396 : 1 : 0-6726. mm'", 110 A 110 = 86 26'. ee', Oil A Oil = 67 51'. w' f 101 A TOl = 71 1U'. ve, 101 A Oil = 47 34'. Crystals prismatic, often acicular. Also globular and reniform, indistinctly fibrous, fibers straight and divergent, rarely irregular; also curved lamellar and granular. Cleavage: m (110), 6(010), e (Oil) in traces. Fracture conchoidal' to uneven. Brittle. H. = 3. G. = 4-1-4-4. Luster adamantine to vitreous; of some fibrous varieties pearly. Color various shades of olive-green, passing into leek-, siskin-, pistachio-, and blackish green; also liver- and wood-brown; sometimes straw-yellow and grayish white. Streak olive-green to brown. Subtransparent to opaque. Mean index, 1-83. Var. (a) Crystallized, (b) Fibrous; finely and divergently fibrous, of green, yellow, brown and gray, to white colors, with the surface sometimes velvety or acicular; found investing the common variety or passing into it; called wood-copper or wood-arsenate. (c) Earthy; nodular or massive; sometimes soft enough to soil the fingers. Comp. Cu 3 As2O8Cu(OH) 2 or 4CuO.As2O 5 .H 2 = Arsenic pentoxide 407, cupric oxide 56-1, water 3-2 = 100. Pyr., etc. In the closed tube gives water. B.B. fuses at 2, coloring the flame bluish green, and on cooling the fused mass appears crystalline. B.B. on charcoal fuses with deflagration, gives off arsenical fumes, and yields a metallic arsenide which with soda yields a globule of copper. With the fluxes reacts for copper. Soluble in nitric acid. Obs. The crystallized varieties occur in Cornwall, at various mines; Tavistock, in Devonshire; in Tyrol, Austria; the Banat, Hungary; Nizhni Tagilsk in the Ural Mts.; Chile. In the United States, in Utah, at the American Eagle and Mammoth mines, Tintic district, both in crystals and wood-copper. The name olivenite alludes to the olive-green color. LIBETHENITE. Orthorhombic. Axes a : b : c = 0-9601 : 1 mm"', 110 A 110 = 87 40'. ee', Oil A Oil = 70 8'. 0-7019. Ill A 111 = 59 4'. Ill A 111 = 61 47|'. In crystals usually small, short prismatic in habit ; often united in druses. Also globular or reniform and compact. Cleavage: a (100), b (010) very indistinct. Fracture subconchoidal to uneven. Brittle. H. = 4. G. = 3-6- 3*8. Luster resinous. Color olive-green, generally dark. Streak olive-green. Translucent to subtranslucent. Mean index, 1'72. Comp. Cu 3 P 2 O 8 .Cu(OH) 2 or 4CuO.P 2 O 5 .H 2 O = Phosphorus pentoxide 29'8, cupric oxide 66*4, water 3'8 = 100. Pyr., etc. In the closed tube yields water and turns black, the flame emerald-green. B.B. fuses at 2 and colors On charcoal with soda gives metallic copper, sometimes also an arsenical odor. Fused with metallic lead on charcoal is reduced to metallic copper, with the formation of lead phosphate, which treated in R.F. gives a crystalline polyhedral bead on cooling. With the fluxes reacts for copper. Soluble in nitric acid. Obs. Occurs with chalcopyrite at Libethen, near Neusohl, Hungary; at Rhein- breitenbach and Ehl on the Rhine, Germany; at Nizhni Tagilsk in the Ural Mts.; from Viel-Salm, Belgium; in small quantities in Cornwall, England. In Clifton-Morenci dis- trict, Ariz. 604 DESCRIPTIVE MINERALOGY Tarbuttite, Zn 3 P 2 O 8 Zn(OH) 2 . Triclinic. Crystals striated and rounded, frequently in sheaf-like aggregates. Perfect basal cleavage. H. = 37. G. = 4'1. Colorless to pale yellow, brown, red, or green. Fusible. From Broken Hill, N. W. Rhodesia. Adamite. Zn 3 As->O 8 .Zn(OH) 2 . In small orthorhombic crystals, often grouped in crusts and granular aggregations. H. = 3'5. G. = 4'34-4'35. Color honey-yellow, violet, rose- red, green, colorless. Mean index, 173. From Chanarcillo, Chile; Cap Garonne, France; from Mte. Valerio, Campiglia Marittima, Italy; at the ancient zinc mines of Laurion, Greece. From Island of Thasos, Turkey. Varieties from Cap Garonne, Var, France, con- taining cobalt and copper have been called cobaltoadamiie and cuproadamite. Descloizite. R 2 V 2 O 8 .R(OH) 2 or 4RO.V 2 O 6 .H 2 O; R = Pb, Zn chiefly, and usually in the ratio 1 : 1 approx. In small orthorhombic crystals, often drusy; also massive, fibrous radiated with mammillary surface. H. = 3 '5. G. = 5'9-6'2. Color cherry-red and brownish red, to light or dark brown, black. Streak orange to brownish red or yellowish gray. Mean index, 1'83. From the Sierra de Cordoba, Argentina; Kappel in Carinthia. Abundant at Lake Valley, Sierra Co., N. M., also near Georgetown and at Magdalena; in Ariz, near Tomb- stone; in Yavapai Co.; at the Mammoth Gold mine, near Oracle, Final Co. A massive variety, containing copper (6'5 to 9 p. c.), in crusts, and reniform masses with radiated structure, occurs in San Luis Potosi, also in a vein of argentiferous galena in Zacatecas, Mexico; it has been variously named cuprodescloizite, tritochorite, ramirite. A similar variety (11 p. c. CuO) occurs as an incrustation on quartz at the Lucky Cuss mine, Tombstone, Cochise Co., and in stalactites at Shattuck Arizona mine, Bisbee, Ariz. From Camp Signal, San Bernardino Co., Cal. EUSYNCHITE may be identical with descloizite. Massive: in nodular, stalactitic forms. G. = 5 '596. Color yellowish red, reddish brown, greenish. From Hofsgrund near Frei- burg in Baden, Germany. The same may be true of arceoxene from Dahn near Nieder- Schlettenbach, Rhenish Bavaria, Germany. Pyrobelonite. 4PbO.7MnO.2V 2 O 5 .3H 2 O. Orthorhombic. In small acicular crystals. Fire-red color. H. = 3'5. G. = 5'377. High index. Probably related crystallographic- ally to descloizite. From Langban, Sweden. DECHENITE. Composition usually accepted as PbV 2 O 6 . Massive, botryoidal, nodular. G. = 5'6-5'81. Color deep red to yellowish red and brownish red. From Nieder-Schlet- tenbach in the Lautertal, Rhenish Bavaria, Germany. Calciovolborthite. Probably (Cu,Ca)sVXMChi,Ca)(OH) 8 . In thin green tables; also gray, fine crystalline granular. Mean index, 2 '05. From Friedrichsrode, Thuringia, Ger- many. Minerals from Richardson, southeastern Utah, and from near Baker City, Oregon, probably belong here. Higginsite. CuCa(OH)AsO 4 . Orthorhombic. Small prismatic crystals. H. = 4'5. G. = 4 '33. n = 1745. Pleochroic, green, yellow-green, blue-green. From Higgins mine, Bisbee, Ariz. Brackebuschite. Near descloizite (monoclinic?). From the State of Cordoba, Ar- gentina. TURANITE. A copper vanadate, 5CuO.V 2 O 5 .2H 2 O. Radiating fibrous. From Tyuya- Muyun, south of Andidjan, Alai Mts., Turkestan. Psittacinite. A vanadate of lead and copper, from the Silver Star District, Mon In thin coatings; also pulverulent. Color siskin- to olive-green. MOTTRAMITE. A vanadate of lead and copper; possibly identical with psittacinite; in velvety black incrustations. From Mottram St. Andrew's, Cheshire, England. Furnacite. A basic chrom-arsenate of lead and copper. In dark olive-green small .prismatic crystals. From Djocie, French Equatorial Africa. Tsumebite. Preslite. A basic lead and copper phosphate. Orthorhombic? In small tabular crystals. H = 3'5. G. = 6'1. Index, > 178. Color emerald-green. Pleochroic, blue-green to yellow-green. Easily fusible. From Tsumeb, Otavi, German o. W . Alrica. CLINOCLASITE. Aphanese. Monoclinic. Axes a : b : c = 1-9069 : 1 : 3-8507; = 80 30' Crystals prismatic (TO (110)); also elongated || 6 axis; of ten* grouped in PHOSPHATES, ARSENATES, ETC. 605 nearly spherical forms. Also massive, hemispherical or reniform; structure radiated fibrous. Cleavage: c (001) highly perfect. Brittle. H. = 2'5-3. G. = 4'19-4'37. Luster: c pearly; elsewhere vitreous to resinous. Color internally dark verdi- gris-green; externally blackish blue-green. Streak bluish green. Subtrans- parent to translucent. Comp. Cu 3 As 2 O 8 .3Cu(OH)2 or 6CuO.As 2 O 5 .3H 2 = Arsenic pentoxide 30'3, cupric oxide 62'6, water 71 = 100. Pyr., etc. Same as for olivenite. Obs. Occurs in Cornwall, with other ores of copper. In Utah, Tintic district, at the Mammoth mine. From Collahurasi, Tarapaca, Chile. Named in allusion to the basal cleavage being oblique to the sides of the prism. Erinite. Cu3As2O8.2Cu(OH) 2 . In mammillated crystalline groups. Color fine emer- ald-green. From Cornwall; also the Tintic district, Utah. Dihydrite. Cu3P2Og.2Cu(OH)2. In dark emerald-green crystals (monoclinic). H. = 4'5-5. G.= 4-4'4. From Ehl near Linz on the Rhine, Germany ; the Ural Mts., etc. Pseudomalachite. In part Cu 3 P2O8.3Cu(OH)2. Massive, resembling malachite in color and structure. Indices, 1*83-1*93. From Rheinbreitenbach, Germany; Nizhni Tagilsk, Russia, etc. Ehlite is closely allied. DUFRENITE. Kraurite. Orthorhombic. Crystals rare, small, and indistinct. Usually massive, in nodules; radiated fibrous with drusy surface. Cleavage: a (100), probably also b (010), but indistinct. H. = 3*5-4. G. = 3'2-3'4. Luster silky, weak. Color dull leek-green, olive-green, or blackish green; alters on exposure to yellow and brown. Streak siskin-green. Subtranslucent to nearly opaque. Strongly pleochroic. Indices, 1'83-1'93. Comp. Doubtful; in part FeP0 4 .Fe(OH) 3 = 2Fe 2 O3.P2O5.3H 2 O = Phosphorus pentoxide 27 -5, iron sesquioxide 62'0, water 10*5 = 100. Pyr., etc. Same as for vivianite, but less water is given out in the closed tube. B.B. fuses easily to a slag. Obs. Occurs near Anglar, Dept. of Haute Vienne, France; in Germany at Hirsch- berg in Westphalia and from the Rothlaufchen mine near Waldgirmes; St. Benigna, Bohemia; East Cornwall, England. In the United States, at Allentown, N. J.; in Rockbridge Co., Va., in radiated coarsely fibrous masses; from Graf ton, N. H. Dufreniberaunite is a variety intermediate in com- position between dufrenite and beraunite from Hellertown, Pa. LAZULITE. Monoclinic: Axes a : b : c = 0-9750 : 1 :_ 1-6483; = 89 14'. at, 100 A 101 = 30 24'. ee', Til A 111 = 80 20'. 986 pp f , 111 A 111 = 79 40'. pe, 111 A 111 = 82 30'. Crystals usually acute pyramidal in habit. Also massive, granular to compact. Cleavage: prismatic, indistinct. Fracture uneven. Brittle. H. = 5-6. G. = 3-057-3-122. Luster vitreous. Color azure-blue; commonly a fine deep blue viewed along one axis, and a pale greenish blue along another. Streak white. Subtranslucent to opaque. Optically . 2V = 69. a = 1-603. (3 = 1'632. 7 = 1-639. Comp. RAL(OH) 2 P 2 O 8 or 2AlPO 4 .(Fe,Mg)(OH) 2 with Fe : Mg(Ca) = 1 : 12, 1 : 6, 1 : 2, 2 : 3. For 1 : 2 the for- mula requires: Phosphorus pentoxide 45*4, alumina 32*6, iron protoxide 7*7, magnesia 8'5, water 5*8 = 100. 506 DESCRIPTIVE MINERALOGY Pyr etc In the closed tube whitens and yields water. In the forceps whitens, cracks open swells up, and without fusion falls to pieces, coloring the flame bluish green. B.B. with cobalt solution the blue color of the mineral is restored. The green color of the flame is made more intense by moistening the assay with sulphuric acid. With the fluxes gives an iron glass; with soda on charcoal an infusible mass. Unacted upon by acids, retaining perfectly its blue color. Obs. Occurs near Werfen in Salzburg, Austria; Kneglach, in Styna; also Horrs- joberg, Sweden; from Madagascar. Abundant with corundum at Crowder's Mt., Gaston Co., N. C.; and on Graves Mt., Lincoln Co., Ga., with cyanite, rutile, etc. The name lazulite is derived from an Arabic word, azw, meaning heaven, and alludes to the color of the mineral. Tavistockite. Ca 3 P 2 O 8 .2Al(OH) 2 . In microscopic acicular crystals, sometimes stellate groups. Color white. From Tavistock, Devonshire. Cirrolite. Perhaps Ca3Al(PO 4 )3.Al(OH) 3 . Compact. G. = 3'OS. Color pale yellow. Occurs at the iron mine at Westana, in Scania, Sweden. Arseniosiderite. Ca3Fe(AsO 4 ) 3 .3Fe(OH) 3 . In yellowish brown fibrous concretions. G. = 3'520. Index, 3'83. From Romaneche, near Macon, France; also at Schneeberg, Saxony. Allactite. Mn 3 As 2 O 8 .4Mn(OH) 2 . Monoclinic. In small brownish red prismatic crys- stals. Mean index, 1786. From the Moss mine, Nordmark, and at Langban, Sweden. Synadelphite. 2(Al,Mn)AsO 4 .5Mn(OH) 2 . In prismatic crystals; also in grains. G.= 3 '45-3 -50. Color brownish black to black. From the Moss mine, Nordmark, Sweden. Flinkite. MnAsO 4 .2Mn(OH) 2 . In minute orthorhombic crystals, tabular || c (001); grouped in feather-like aggregates. G. = 3 '87. Color greenish brown. From the Harstig mine, Pajsberg, Sweden. Hematolite. Perhaps (Al,Mn)AsO 4 .4Mn(OH) 2 . In rhombohedral crystals. G. = 3 -30-3 '40. Color brownish red, black on the surface. Mean Index, 1730. From the Moss mine, Nordmark, Sweden. Retzian. A basic arsenate of the yttrium earths, manganese and calcium. In ortho- rhombic crystals. H. =4. G. = 415. Color chocolate- to chestnut-brown. From the Moss mine, Nordmark, Sweden. n m ii ni Arseniopleite. Perhaps RgR^OH^AsO^e; R = Mn, Ca, also Pb, Mg; R = Mn, also Fe. Massive, cleavable. Color brownish red. Occurs at the Sjo mine, Grythytte parish, Sweden, with rhodonite in crystalline limestone. Manganostibiite. Hematostibiite. Highly basic manganese antimonates. In em- bedded grains. Color black. Manganostibiite occurs at Nordmark, Sweden; hematostibiite is from the Sjo mine, Grythytte parish, Sweden. Atelestite. Basic bismuth arsenate, H 2 Bi 3 AsO 8 . In minute tabular crystals G = 6'4. Color sulphur-yellow. From Schneeberg, Saxony. C. Normal Hydrous Phosphates, etc. The only important group among the normal hydrous phosphates is the monoclinic VIVIANITE GROUP. Struvite. Hydrous ammonium-magnesium phosphate. In orthorhombic-hemimorphic Sanod P ' 6 r yeUowish; sli 8 htl y soluble. Index, 1'502. From Collophanite. Ca 3 P 2 O 8 .H 2 O. In layers resembling gymnite or opal. Colorless or r*k i' A L59 ' From the island of So mbrero, West Indies. Monile is similar, Mona and Mon eta in the West Indies, where it is associated with monetite, 4 occurring in yellowish white triclinic crystals. PHOSPHATES, ARSENATES, ETC. 607 Hopeite. Hydrous zinc phosphate, Zn 3 P 2 O8.4H 2 O. Orthorhombic. In minute pris- matic crystals. Also in reniform masses. Three cleavages: a (100), perfect; 6 (010), good; c (001), poor. Crystals from Broken Hill show interbanding of two modifications, a- and /3-hopeite which have the same composition but differ in their optical characters. H. = 3'2. G. = 3-0-3' 1. Color grayish white. Optically-, ft = 1'59. Found in cavities in calamine at the zinc mines of Moresnet, Belgium; at the Broken Hill mines, Rhodesia. Parahopeite. Zn 3 P 2 O 8 .4H 2 O. Same as for hopeite. Triclinic. In tabular crystals with deep striations. Good cleavage. H. = 37. G. = 3'3. Colorless. Found at Broken Hill, Rhodesia. Dickinsonite. 3R 3 P 2 O 8 .H 2 O with R = Mn, Fe, Na 2 chiefly, also Ca, K 2 , Li 2 . In tabular, pseudo-rhombohedral crystals; commonly foliated to micaceous. G. = 3 '338- 3-343. Color olive- to oil-green, grass-green. ft = 1-662. From Branchville, Fairneld Co., Conn. Fillowite. Formula as for dickinsonite and also from Branchville, Conn., but differing in angle. In granular crystalline masses. G. = 3'43. Color wax-yellow, yellowish to reddish brown, colorless. ft = T672. The three following triclinic species are related in composition and may be in crystalline form. Roselite. (Ca,Co,Mg) 3 As 2 O 8 .2H 2 O. In small crystals; often in druses and spherical aggregates. G. = 3'5-3*6. Color light to dark rose-red. From Schneeberg, Saxony. Brandtite. Ca 2 MnAs 2 Os.2H 2 O. In prismatic crystals; crystals often united in radi- ated groups. G. = 3'671-3'672. Colorless to white. From the Harstig mine, near Pajs- berg, Sweden. Fairfieldite. A hydrous phosphate of calcium and manganese, Ca2MnP 2 O 8 .2H 2 O. Triclinic. In prismatic crystals; usually in foliated or fibrous crystalline aggregates. G. = 3'07-3'15. Color white or greenish white to pale straw-yellow, ft = T644. From Branchville, Fairfield Co., Conn.; Rabenstein, Bavaria (leucomanganite) . Messelite. (Ca,Fe) 3 P 2 O 8 .2^H 2 O. In minute tabular crystals. Colorless to brownish. ft = 1'653. From near.Messel in Hesse, Germany. Perhaps an alteration of Anapaite through loss of water. Anapaite. Tamanite. (Ca,Fe) 3 P 2 O 8 .4H 2 O. Triclinic. In tabular crystals. One per- fect cleavage. H. = 3 '5. G. = 2 '8. Color greenish white. From the limonite mines near Anapa on the Taman peninsula, Russia. Reddingite. Mn 3 P 2 O 8 .3H 2 O. In orthorhombic crystals near scorodite in angle; also granular. G. = 3'102. Color pinkish white to yellowish white. Optically +. ft = 1'656 . From Branchville, Conn. Palaite. Hydrous manganese phosphate, 5MnO.2P 2 O 6 .4H 2 O. Monoclinic? In crys- talline masses. G. = 3'2. Color, flesh-pink. Indices 1 '65-1 "66. From Pala, San Diego Co., Cal. Derived by alteration from lithiophilite and alters into hureaulite. Stewartite. Hydrous manganese phosphate, 3MnO.P 2 O 5 .4H 2 O. Triclinic? In fibers or minute crystals. G. = 2 '94. Indices, 1 '63-1 '69. Pleochroic, colorless to yellow. Found as an alteration product of lithiophilite from Pala, Cal. Picropharmaoolite. R 3 As 2 O 8 .6H 2 O, with R = Ca : Mg = 5 : 1. In small spherical forms. Color white. From Riechelsdorf and Freiberg, Germany; Joplin, Mo. Trichalcite. CusAs^s.SH^O. In radiated groups, columnar; dendritic. Color verdi- gris-green. From the Turginsk copper mine near Bogoslovsk, Ural Mts. Vivianite Group. Monoclinic Vivianite Fe 3 P 2 O8.8H 2 O a : b : c = 0-7498 : 1 : 0-7015 ft = 75 34' Symplesite Fe 3 As 2 8 .8H 2 O 0-7806 : 1 : 0-6812 72 43' Bobierrite Mg 3 P 2 O 8 .8H 2 Hoernesite Mg 3 As 2 O 8 .8H 2 O Erythrite Co 3 As 2 O 8 .8H 2 O 0-75 : 1 : 0-70 75 Annabergite Ni 3 As 2 O 8 .8H 2 O Cabrerite (Ni,Mg) 3 As 2 O 8 .8H 2 O Kbttigite Zn 3 As 2 O 8 .8H 2 608 DESCRIPTIVE MINERALOGY The VIVIANITE GROUP includes hydrous phosphates of iron, magnesium, cobalt, nickel and zinc, all with eight molecules of water. The crystallization is monoclinic, and the angles, so far as known, correspond closely. VIVIANITE. Monoclinic. Crystals prismatic (mm'" 110 A 110 = 71 58'); often in stellate groups. Also reniform and globular; structure divergent, fibrous, or earthy; also incrusting. Cleavage: b (010) highly perfect; a (100) in traces; also fracture fibrous nearly _L c axis. Flexible in thin laminae; sectile. H. = 1'5 2. G = 2'58 - 2*68. Luster, b (010) pearly or metallic pearly; other faces vitreous. Colorless when unaltered, blue to green, deepening on exposure. Streak colorless to bluish white, changing to indigo-blue and to liver-brown. Transparent to translucent; opaque after exposure. Pleochroism strong; X = cobalt-blue, Y and Z = pale greenish yellow. Optically -f. a = 1*581. ft = 1'604. 7 = 1-636. Comp. Hydrous ferrous phosphate, Fe3P 2 08.8H 2 = Phosphorus pent- oxide 28'3, iron protoxide 43'0, water 287 = 100. Many analyses show the presence of iron sesquioxide due to alteration. Pyr., etc. In the closed tube yields neutral water, whitens, and exfoliates. B.B. fuses at 1 "5, . coloring the flame bluish green, to a grayish black magnetic globule. With the fluxes reacts for iron. Soluble in hydrochloric acid. Obs. Occurs associated with pyrrhotite and pyrite in copper and tin veins; some- times in narrow veins with gold, traversing graywacke; both friable and crystallized in beds of clay, and sometimes associated with limonite, or bog iron ore; often in cavities of fossils or buried bones. Occurs at St. Agnes and elsewhere in Cornwall, England; at Bodenmais, Germany; the gold mines of Verespatak in Transylvania. From Ashio, Shimotsuke, Japan. A variety from the Kertsch and Taman peninsulas, South Russia, that contains small quantities of manganese and magnesium has been called paravivianite. The earthy variety, sometimes called blue iron-earth or native Prussian blue (Fer azure), occurs in Greenland, Carinthia, Guatemala, Bolivia, Victoria, Australia, etc. In North America, in N. J., at Allentown, Monmouth Co., both crystallized, in nodules, and earthy; at Mullica Hill, Gloucester Co. (mullicite}, in cylindrical masses. In Va., in Stafford Co. In Ky., near Eddyville. In Col. at Leadville; in Idaho, at Silver City. In Canada, with limonite at Vaudreuil. Symplesite. Probably Fe 3 As 2 O 8 .8H 2 O. In small prismatic crystals and in radiated spherical aggregates. G. = 2 '957. Color pale indigo, inclined to celandine-green. From Lobenstein, Germany; Hiittenberg, Carinthia. Bobierrite. Mg3P 2 O 8 .8H 2 O. In aggregates of minute crystals; also massive. Color- less to white. From the guano of Mexillones, on the Chilian coast. Hautefeuillite is like bobierrite, but contains calcium. Monoclinic. Index 1*52. From Bamle, Norway. Hoernesite. Mg 3 As2p8.8H 2 O. In crystals resembling gypsum; also columnar; stellar- foliated. Color snow-white. From the Banat, Hungary. ERYTHRITE. Cobalt bloom. Monoclinic. Crystals prismatic and vertically striated. Also in globular and reniform shapes, having a drusy surface and a columnar structure; some- times stellate. Also pulverulent and earthy, incrusting. Cleavage: b (010) highly perfect. Sectile. H. = T5-2'5; least on b. G. = 2'948. Luster of 6 pearly; other faces adamantine to vitreous; also dull, earthy. Color crimson- and peach-red, sometimes gray. Streak a little paler than the color. Transparent to subtranslucent. Strongly pleochroic. Optically -. a = 1'626. ft = 1'661. 7 = 1'699. PHOSPHATES, ARSENATES, ETC. 609 Comp. Hydrous cobalt arsenate, Co 3 As208.8H 2 O = Arsenic pentoxide 38*4, cobalt protoxide 37'5, water 24' 1 = 100. The cobalt is sometimes re- placed by nickel, iron, and calcium. Pyr., etc. In the closed tube yields water at a gentle heat and turns bluish; at a higher heat gives off arsenic trioxide which condenses in crystals on the cool glass, and the residue has a dark gray or black color. B.B. in the forceps fuses at 2 to a gray bead, and colors the flame light blue (arsenic). B.B. on charcoal gives an arsenical odor, and fuses to a dark gray arsenide, which with borax gives the deep blue color characteristic of cobalt. Soluble in hydrochloric acid, giving a rose-red solution. Obs. Occurs at Schneeberg in Saxony, in micaceous scales; Wolfach in Baden; Modum in Norway. From the Veta Rica mine, Sierra Mojada, Coahuila, Mexico; Chile. In the United States, in Pa., sparingly near Philadelphia; in Nev., at Lovelock's station. In Cal. In crystals from Cobalt, Canada. Named from epi>0p6s, red. Annabergite. NiaAsaOs.SH^O. Monoclinic. In capillary crystals; also massive and disseminated. Color fine apple-green. Optically . Mean index, 1'68. From Alle- mont in Dauphine, France; Annaberg, Schneeberg and Riechelsdorf, Germany; in Col.; Nev.; Cobalt, Ontario, Canada. Cabrerite. (Ni,Mg) 3 As2O 8 .8H 2 O. Like erythrite in habit. Also fibrous, radiated; reniform, granular. Color apple-green. From the Sierra Cabrera, Spain; at Laurion, Greece. Kottigite. Hydrous zinc arsenate, ZnsAs2O8.8H2O. Massive, or in crusts. Color light carmine- and peach-blossom-red. Occurs with smaltite at the cobalt mine Daniel, near Schneeberg, Germany. Rhabdophanite. Scovillite. A hydrous phosphate of the cerium and yttrium metals. Massive, small mamillaryj as an incrustation. G. = 3'94-4'OL Color brown, pinkish or yellowish white. Rhabdophanite is from Cornwall; Scovillite is from the Scoville (limonite) ore bed in Salisbury, Conn. Churchite. A hydrous phosphate of cerium and calcium. As a thin coating of minute crystals. G. = 3'14. Color pale smoke-gray tinged with flesh-red. From Cornwall, Eng- land. Uvanite. 2UO3.3V 2 O 6 .15H 2 O. Orthorhombic. Fine granular. Two pinacoidal cleav- ages. Color brownish yellow. Indices, 1 '82-2 '06. Found disseminated in rocks near Temple Rock, 45 miles southwest of Greenriver, Utah. Ferganite. U3(VO 4 )2.6H 2 O. In scales. Color sulphur-yellow. From province of Fergana, Russian Turkestan. Fernandinite. CaO.V^O^SVaOe.MHaO. Massive. Color dull green. Readily soluble in acids, partly soluble in water. Found at Minasragra, Peru. Pascoite. Hydrous calcium vanadate, possibly 2CaO.3V 2 O6.11H 2 O. Monoclinic. In grains. H. = 2'5. G. = 2'46. Color orange. Streak yellow. Indices, 177-1 '83. Easily fusible. Soluble in water. Found at Minasragra, Province of Pasco, Peru. Pintadoite. Hydrous calcium vanadate, 2CaO.V 2 O 6 .9H 2 O. As an efflorescence. Color green. Found coating surfaces of sandstone in Canyon Pintado, Utah. SCORODITE. 987 Orthorhombic. Axes a : b : c = 0*8658 : 1 : 0-9541. dd', 120 A 120 = 60 1'. . pp", 111 A 111 = 111 6'. pp', 111 A 111 = 77 8'. pp'", 111 A 111 = 65 20'. Habit octahedral, also prismatic. Also earthy, amorphous. Cleavage: d (120) imperfect; a (100), 6(010) in traces. Frac- ture uneven. Brittle. H. = 3'5-4. G. = 3'l-3'3. Luster vit- reous to subadamantine and subresinous. Color pale leek-green or liver-brown. Streak white. Subtransparent to translucent. Mean index, 1'84. Comp. Hydrous ferric arsenate, FeAsO 4 .2H 2 = Arsenic pentoxide 49'8, iron sesquioxide 34'6, water 15'6 = 100. 610 DESCRIPTIVE MINERALOGY Pyr., etc. In the closed tube yields neutral water and turns yellow. B.B. fuses easily, coloring the flame blue. B.B. on charcoal gives arsenical fumes, and with soda a black magnetic scoria. Wit^h the fluxes reacts for iron. Soluble in hydrochloric acid. Obs. Often associated with arsenopyrite. From Schwarzenberg, Saxony; Dern- bach, Nassau, Germany; Lolling, Carinthia; Schlaggenwald, Bohemia; Nerchinsk, Siberia, in fine crystals; leek-green, in the Cornish mines. From Congo Free State. From Obira, Japan. Occurs near Edenville, N. Y., with arsenopyrite; in Utah, Tintic district,, at the Mam- moth mine on enargite. As an incrustation on siliceous sinter of the Yellowstone geysers. From Cobalt, Ontario, Canada. Named from anopodov, garlic, alluding to the odor before the blowpipe. Vilateite. Hydrous iron phosphate with a little manganese. Monoclinic. H. = 3-4. G. = 275. Color violet. Index, 174. Found in pegmatite at La Vilate near Chante- loube, Haute Vienne, France. Purpurite. 2(Fe,Mn)PO 4 .H 2 O. Orthorhombic(?). In small irregular masses. Two cleavages at right angles. H. = 4-4*5. G. = 3 '4. Color deep red or reddish purple Refractive index, 1*66-1*65, Fusible. Found at Kings Mt., Gaston Co., N. C., sparingly from Pala, San Diego Co., Cal., Hill City, S. D., and Branchville, Conn. Strengite. FePO4.2H 2 O. Crystals rare; in habit and angle near scorodite; generally in spherical and botryoidal forms. G. = 2 '87. Color pale red. Optically +. = 172'. From iron mines near Giessen, Germany; also in Rockbridge Co., Va., with dufrenite; irom Pala, Cal. Phosphosiderite. 2FePO 4 .3H 2 O. An iron phosphate near strengite, but with 3|H 2 O. Color red. Index 173. From the Siegen mining district, Germany; from Sardinia. Barrandite. (Al,Fe)PO 4 .2H 2 O. In spheroidal concretions, color pale shades of gray. Index, 1-57. From Bohemia. Variscite. A1PO 4 .2H 2 O. Orthorhombic. Commonly in crystalline aggregates and incrustations with reniform surface. Color green. Optically -. = 1'556. Strongly pleochroic. From Messbach in Saxon Voigtland; Montgomery Co., Ark., on quartz in nodular masses from Tooele Co., Utah (Utahlite); crystalized from Lucin, Utah. Lucinite. Comp. same as for varisdte, A1PO 4 .2H 2 O. Orthorhombic. Octahedral habit. Also compact, massive. H. = 5. G. = 2*52. Color green. Indices, 1 -56-1 '59 Found with varisdte at Utahlite Hill, near Lucin, Boxelder Co., Utah. Callainite. A1PO 4 .2H 2 O. Massive; wax-like. Color apple- to emerald-green From a Celtic grave in Lockmariaquer, Brittany. Zepharovichite. A1PO 4 .3H 2 O. Crystalline to compact. Color yellowish or grayish white. From Trenic in Bohemia. Palmerite. HK 2 A1 2 (PO 4 ) 3 .7H 2 O. Amorphous, pulverulent. Color white. Occurs as a stratum in a guano deposit on Mte. Alburno, Salerno, Italy. Rosieresite. A hydrous phosphate of aluminium with lead and copper. In stalao- u 68 ^ G J = 2 ' 2 ' C .olor yellow to brown. Index, 1*5. Isotropic. Infusible. Found in abandoned copper mine at Rosieres, Tarn, France. yelbwm R^Su ^ ^^ ******* f ^^ needles ' Color >rr 5 w^A rite ; ^ hydrous iron-manganese phosphate with lithia, Fe 2 O 3 .6MnO.4P 2 O 6 3 Li,H) 2 0. In cleavable masses. G. = 3*45. Color dark brown. Indices, 171-175 flamf Trom piTaCai ange " red ' ^ perpendicular to cleava S e - Fusibl e> giving lithium SaLmonsite. A hydrous iron-manganese phosphate, Fe 2 O 3 .9MnO.4P 2 O 5 14H,O Cleav- COl0rbUff ' ^4,1-65-1.67. Fou^d Acid Hydrous Phosphates, etc. PHARMACOLITE. " C mmonly in delicate si Cleavage: 6 (010) perfect. Fracture uneven. Flexible in thin laminse. PHOSPHATES, ARSENATES, ETC. 611 H. = 2-2;5. G. = 2'64-273. Luster vitreous; on 6 (010) inclining to pearly. Color white or grayish; frequently tinged red. Streak white. Translucent to opaque. Optically -. a = 1'583. = 1'589. 7 = 1'594. Comp. Probably HCaAsO 4 .2H 2 O = Arsenic pentoxide 53*3, lime 25'9, water 20'8 = 100. Obs. Found with arsenical ores of cobalt and silver, also with arsenopyrite; at Andreasberg in the Harz Mts., Germany; Riechelsdorf in Hesse, Germany; Joachimstal in Bohemia, Markirch, Alsace, etc. Named from ^ap/za/cop, poison. Haidingerite. HCaAsO 4 .H 2 O. In minute crystal aggregates, botryoidal and drusy. G. = 2 -848. Color white. Index, 1 '67. From Joachimstal, Bohemia, with pharmacolite. Wapplerite. HCaAsO 4 .3H 2 O. In minute crystals; also in incrustations. Colorless to white. Found with pharmacolite at Joachimstal, Bohemia. Brushite. HCaPO 4 .2H 2 O. In small slender monoclinic prisms: concretionary massive. Colorless to pale yellowish. = 1*545. Occurs in guano. Metabrushite, similarly asso- ciated, is 2HCaPO4.3H 2 O. Stoffertite is a mineral similar to brushite but said to contain a little more water. From guano deposits on the island of Mona, West Indies. Martinite. H 2 Ca5(PO4)4.|H 2 O. From phosphorite deposits (from guano) in the island of Curacoa, West Indies. Hewettite. CaO.3V 2 O 5 .9H 2 O. In microscopic needles. G. = 2'5-2'6. Color deep red. Pleochroic, light orange-yellow to red. On heating loses water changing color through shades of brown to a bronze. Easily fusible. Found as an alteration of patronite at Minas- ragra, Peru. Also observed from Paradox Valley, Col. Metahewettite. Comp. same as for hewetlite. In minute tabular orthorhombic crys- tals. On heating loses water changing from dark red to yellow-brown. From Paradox Valley, Col., and at Thompson's, Utah. Newberyite. HMgPO4.3H 2 O. In white orthorhombic crystals. Index, 1'52. From guano of Skipton Caves, Victoria. Hannayite, from same locality, is a hydrous phosphate of ammonium and magnesium. Schertelite, Mg(NH 4 ) 2 H 2 (PO 4 ) 2 .4H 2 O. Occurs in small tabular crystals in hot guano deposits near Skipton, southwest of Ballarat, Australia. Stercorite. Microcosmic salt. HNa(NH 4 )PO 4 .4H 2 O. In white crystalline masses and nodules in guano. Hureaulite. H 2 Mn6(PO 4 ) 4 .4H 2 O. In short prismatic crystals (monoclinic). Also massive, compact, or imperfectly fibrous. Color yellowish, orange-red, rose, grayish. Optically . (3 = T654. From Limoges, commune of Bureaux, France. In the United States, at Branchville, Conn.; Pala, Cal. Forbesite. H 2 (Ni,Co) 2 As 2 O 8 .SH 2 O. Structure fibro-crystalline. Color grayish white. From Atacama, Chile. FERRAZITE. 3(Ba,Pb)O.2P 2 O 6 .8H 2 O. A "fava" found in the diamond sands of Brazil. Color dark yellowish white. G. = 3 '0-3 '3. Basic Hydrous Phosphates, etc. Isoclasite. Ca 3 P 2 O 8 .Ca(OH) 2 .4H 2 O. In minute white crystals; also columnar. From Joachimstal, Bohemia. Hemafibrite. Mn 3 As 2 O8.3Mn(OH) 2 .2H 2 O. Commonly in spherical radiated groups. Color brownish red to garnet-red, becoming black. From the Moss mine, Nordmark, Sweden. EUCHROITE. Orthorhombic. Habit prismatic mm'" 110 A 110 = 62 40'. Cleavage: m (110), n (Oil) in traces. Fracture small conchoidal to uneven. Rather brittle. H. = 3 -5-4. G. = 3-389. Luster vitreous. Color bright emerald- or leek-green. Transparent to translucent. Mean index, 1-70. Comp. Cu 3 As2Os.Cu(OH)2.6H 2 O = Arsenic pentoxide 34'2, cupric oxide 47-1, water 187 = 100. Obs. Occurs in quartzose mica slate at Libethen in Hungary, in crystals of consider- able size, having much resemblance to dioptase. Named from evxpoa, beautiful color. 612 DESCRIPTIVE MINERALOGY Conichalcite. Perhaps (Cu,Ca) 3 As 2 O8.(Cu,Ca)(OH)2.|H 2 O. Orthorhombic. Usually reniform and massive, resembling malachite. Color pistachio-green to emerald-green From Andalusia, Spain; Maya-Tass, Akmolinsk, Siberia (crystals); Tintic district, Utah. Bayldonite. (Pb,Cu)3As2O8.(Pb,Cu)(OH)2.H 2 O. In mamillary concretions, drusy. Color green. From Cornwall, England. Tagilite. Cu 3 P2O8.Cu(OH)2.2H 2 .O. In reniform or spheroidal concretions; earthy. Color verdigris- to emerald-green. From the Ural Mts. Leucochalcite. Probably Cu3As 2 O 8 .Cu(OH)2.2H 2 O. In white, silky acicular crystals. From the Wilhelmine mine in the Spessart, Germany. Barthite. 3ZnO.CuO.3As 2 O 6 .2H 2 O. In small monoclinic (?) crystals. H. = 3. G. = 419. Color grass-green. Found in druses of a dolomite at Guchab, Otavi, German Southwest Africa. Volbprthite. A hydrous vanadate of copper, barium, and calcium. In small six-sided tables; in globular forms. . Color olive-green, citron-yellow. Index, 1 '90. From the Ural Mts. Hiigelite. A hydrous lead-zinc vanadate. Monoclinic. In microscopic hair-like crystals. Color orange-yellow to yellow-brown. From Reichenbach near Lahr, Baden, Germany. Cornwallite. Cu 3 As2O8.2Cu(OH)2.H 2 O. Massive, resembling malachite. Color emer- ald-green. From Cornwall; England. Tyrolite. Tirolit. Perhaps Cu 3 As 2 O 8 .2Cu(OH) 2 .7H 2 O. Usually in fan-shaped crystal- line groups; in foliated aggregates; also massive. Cleavage perfect, yielding soft thin flexible laminae. Color pale green inclining to sky-blue. Index, T70. From Libethen, Hungary; Nerchinsk, Siberia; Falkenstein, Tyrol; etc. In the United States, in the Tin- tic district, "Utah. Some analyses yield CaCO 3 , usually regarded as an impurity, but it may be essential. Spencerite. Zn 3 (PO 4 )2.Zn(OH) 2 .3H 2 p. Monoclinic. In radiating and reticulated crystals. Cleavages parallel to three pinacoids. Color white. G. = 3*12. H. = 2*7. = 1-61. Optically -. From Hudson Bay Mine, Salmo, B. C. Hibbenite. 2Zn 3 (PO 4 ) 2 .Zn(OH) 2 .6fH 2 O. Orthorhombic. Tabular parallel to a (100). Cleavages parallel to three pinacoids. Color white. G. = 3 '21. H. = 3 7. Optically . From Hudson Bay Mine, Salmo, British Columbia. CHALCOPHYLLITE. Rhombohedral. Axis c = 2761. cr 0001 A 1011 = 72 2'. In tabular crystals; also foliated massive; in druses. Cleavage: c (0001) highly perfect; r (lOll) in traces. H. = 2. G. = 2'4-2'66. Luster of c pearly; ______^__ of other faces vitreous or subadamantine. Color emerald- or grass-green to verdigris-green. Streak somewhat paler than the color. Transparent to translucent. Opticallv - 1-632. = 1-575. ( ?? I ! lp " 7" A highly basic arsenate of copper; formula uncertain, perhaps uO. As2O5. 14H20. Pyr., etc. - In the closed tube decrepitates, yields much water, and gives a residue of olive-green scales. In other respects like olivenite. Soluble in nitric acid, and in ammonia. Ubs. *rom the copper mines near Redruth in Cornwall; at Sayda, Saxony; Moldawa Bisbi Ariz gary; from ChUe - In the Unite d States, in the Tintic district, Utah; Veszelyite. A hydrous phospho-arsenate of copper and zinc, formula uncertain. a greenish blue crystalline incrustation at Morawitza, in the Banat, Hungary. WAVELLITE. Orthorhombic. Axes a : b : c = 0*5049 : 1 : 0-3751. Crystals rare Usu- hemispherical or S lobul ar with crystalline surface, and PHOSPHATES, ARSENATES, ETC. 613 Cleavage: p (101) and b (010) rather perfect. Fracture uneven to sub- conchoidal. Brittle. H. = 3-25-4. G. = 2-316-2-337. Luster vitreous, inclining to pearly and resinous. Color white, passing into yellow, green' gray, brown, and black. Streak white. Translucent. Mean index, T526 Comp. 4A1PO 4 .2A1(OH) 3 .9H 2 O = Phosphorus pentoxide 35'2, alu- mina 38'0, water 26-8 = 100. Fluorine is sometimes present, up to 2 p. c. Pyr., etc. In the closed tube gives off much water, the last portions of which may react acid (fluorine). B.B. in the forceps swells up and splits into fine infusible particles coloring the flame pale green. Gives a blue on ignition with cobalt solution. Soluble in hydrochloric acid, and also in caustic potash. Obs. From Barnstaple in Devonshire, England; at Zbirow in Bohemia: at Franken- berg, Saxony; Arbrefontaine, Belgium; Montebras, France; Minas Geraes, Brazil, etc. In the United States at the slate quarries of York Co., Pa.; White Horse Station Ches- ter Valley R. R., Pa.; Magnet Cove, Ark. Fischerite. AlPO 4 .Al(OH) 3 .2^H 2 p. In small prismatic crystals and in drusy crusts. Color green. Index, 1'55. From Nizhni Tagilsk in the Ural Mts. Peganite. A1(PO 4 ).A1(OH)3.UH 2 O. Occurs in green crusts, of small prismatic crys- tals, at Striegis, near Freiberg, Saxony. TURQUOIS. Turquoise. Triclinic. Crystals minute and in angle near those of chakosiderite with which it may be isomorphous. Usually massive; amorphous or cryptocrystal- line. Reniform, stalactitic, or incrusting. In thin seams and disseminated grains. Also in rolled masses. Cleavage in two directions in crystals ; none in massive material. Fracture small conchoidal. Rather brittle. H. = 5-6. G. = 2-6-2-83. Luster some- what waxy, feeble. Color sky-blue, bluish green to apple-green, and greenish gray. Streak white or greenish. Feebly subtranslucent to opaque. Opti- cally + . a = 1-61. j8 = 1-62. 7 = 1-65. Comp. A hydrous phosphate of aluminium and copper CuO.3Al 2 3 . 2P 2 5 .9H 2 O or perhaps H 6 (CuOH)[Al(OH) 2 ] 6 (PO 4 )4 = Phosphorus pentox- ide 34-12, alumina 36-84, cupric oxide 9-57, water 19-47 = 100. Penfield considers that the H,(CuOH) and A1(OH) 2 mutually replace each other in the orthophosphoric molecule. Pyr., etc. In the closed tube decrepitates, yields water, and turns brown or black. B.B. in the forceps becomes brown and assumes a glassy appearance, but does not fuse; colors the flame green; moistened with hydrochloric acid the color' is at first blue (copper chloride). With the fluxes reacts for copper. Soluble in hydrochloric acid. Obs. The highly prized oriental turquois occurs in narrow seams (2 to 4 or even 6 mm. in thickness) or in irregular patches in the brecciated portions of a porphyritic trachyte and the surrounding clay slate in Persia, not far from Nishapur, Khorassan; in the Megara Valley, Sinai; in the Kara-Tube Mts. in Turkestan, 50 versts from Samarkand. In the United States, occurs in the Los Cerillos Mts., 20 m. S.E. of Santa Fe, New Mexico, in a trachytic rock, a locality long mined by the Mexicans and in recent years re- opened and extensively worked; in the Burro Mts., Grant Co., N. M.; pale green variety near Columbus, and in Lincoln Co., Nevada. In crystals near Lynch Station, Campbell Co., Va. Natural turquois of inferior color is often artificially treated to give it the tint desired. Mor-ovrr, many ctcncs vrhich are of a fine blue when first found retain the color only so long as they arc kept moist, and when dry they fade, become a dirty green, and are of littlo value. Much of the turquois (not artificial) used in jewelry in former centuries, as well as the present, and that described in the early works on minerals, was bone-turquois (called also odontolite, from o*oy~, tooth), which is fossil bone, or tooth, colored by a phosphate of iron. Its organic origin becomes manifest under a microscope. Moreover, true turquois. when decomposed by hydrochloric acid, gives a fine blue color with ammonia, which is not true of the odontolite. Use. As an ornamental material. 614 DESCRIPTIVE MINERALOGY Wardite. 2A1 2 O3.P 2 O6.4H 2 O. Forms light green or bluish green concretionary incrus- tations in cavities of nodular masses of variscite from Cedar Valley, Utah. H. = 5. G. = 277. Sphserite. Perhaps 4A1PO 4 .6A1(OH) 3 . In globular drusy concretions. Color light gray, bluish. From near St. Benigna, Bohemia. Liskeardite. (Al,Fe)AsO4.2(Al,Fe)(OH)3.5H 2 O. In thin incrusting layers, white or bluish. From Liskeard, Cornwall, England. Evansite. 2A1PO 4 .4A1(OH) 3 .12H 2 O. Massive; reniform or botryoidal. Colorless, or milk-white, n - 1'485. From Zsetcznik, Hungary; Gross-Tresny, Moravia; Tasmania; Coosa coalfield, Ala.; Goldburg, Idaho. CCERULEOLACTITE. Perhaps 3A1 2 O 3 .2P 2 O 6 .10H 2 O. Crypto-crystalline; milk-white to light copper-blue. From near Katzenellnbogen, Nassau, Germany; also East Whiteland Township, Chester Co., Pa. Augelite. 2A1 2 O3.P 2 O 5 .3H 2 O. In tabular monoclinic crystals and massive. G. = 27. Colorless to white. Optically +. = T576. From Bolivia; from the iron mine of Westana, Sweden. The same locality has also yielded the three following aluminium phosphates. BERLINITE. 2A1 2 O 3 .2P 2 O 5 .H 2 0. Compact, massive. G. = 2 '64. Colorless to grayish or rose-red. TROLLEITE. 4Al2O3.3P 2 06.3H 2 O. Compact, indistinctly cleavable. G. = 310. Color pale green. ATTACOLITE. P 2 O 5 ,Al 2 3 ,MnO,CaO,H2O, etc.; formula doubtful. Massive. G.=3'09. Color salmon-red. MINASITE. An aluminium phosphate. In rolled pebbles from Brazil. VASHEGYITE. 4A1 2 3 .3P 2 6 .30H 2 0. Massive. H.= 2-3. G. = 1'96. Color white or yellow to rust-brown when colored by iron oxide. From iron mine at Vashegy in Comi- tat Gomor, Hungary. Soumansite. A fluo-phosphate of aluminium and sodium with water. Tetragonal. Pyramidal habit. H. = 4'5. G. = 287. Colorless. Indices, 1 '55-1 '56. Optically +. Fusible with intumescence. From Montebras in Soumans, Creuse, France. PHARMACOSIDERITE. Isometric-tetrahedral. Commonly in cubes; also tetrahedral. Rarely granular. Cleavage: a (100) imperfect. Fracture uneven. Rather sectile. H. = 989 2 -5. G. = 2*9-3. Luster adamantine to greasy, not very distinct. Color olive-, grass- or emerald-green, yellowish brown, honey-yellow. Streak green to brown, yellow, pale. Subtransparent to subtranslu- cent. n = 1-676. Pyroelectric. Comp. Perhaps 6FeAs0 4 .2Fe(OH) 3 .12H 2 O = Arsenic pent oxide 43% iron sesquioxide 40 '0, water 16 -9 = 100. Some varieties contain K2O. Pyr., etc. Same as for scorodite. Obs. Obtained at the mines in Cornwall. England, with v .. . , . ores of copper; at Schneeberg and Schwarzenberg, Saxony; at Konigsberg, near Schemmtz, Hungary. In Utah, at the Mammoth mine, Tintic district, from QapucxKov, poison, and aidrjpos, iron. * 2F ^ p A.Fe(OH) 2 .8H 2 O. Occurs in small green tabular crystals (mono- Iruro, Cornwall, England. .- In radiated tufts of a y ellow or brownish color. From near St. Benigna in Bohemia; Lancaster Co Pa rnnnl ii with FeO, MnO, CaO, MgO, A1 2 O 3 . Mono- stem Bavaria P W ' Pleochroic - G - = 2 '^- From Hiihnerkobel, Raben- PHOSPHATES, ARSENATES, ETC. 615 Beraunite. Perhaps 2FePO 4 .Fe(OH) 3 .2H 2 O. Commonly in druses and in radiated globules and crusts. Color reddish brown to dark hyacinth-red. From St. Benigna near Beraun, in Bohemia. From Hellertown, Pa. Eleonorite, in tabular crystals, is the' same mineral. From the Eleonore mine near Giessen, Germany. GLOBOSITE, PICITE, DELVAUXITE, KERTSCHENITE, OXYKERTSCHENITE, are other hydrated ferric phosphates. CHILDRENITE. Orthorhombic. Axes a : b : c = 07780 : 1 : 0-52575. mm'", 110 A 110 = 75 46'. rr'", 131 A 131 = 105 9' rr', 131 A 131 = 39 47'. ss', 121 A 121 = 49 56'. Only known in crystals. Cleavage: a (100) imperfect. Fracture uneven. H. = 4-5-5. G. = 3-18-3-24. Luster vitreous to resinous. Color yellowish white, pale yellowish brown, brownish black. Streak white to yellowish. Translucent. 2E = 74. Optically -. a = 1-631. ft = 1-660. 7 = 1*664! Comp. In general 2AlPO 4 .2Fe(OH) 2 .2H 2 O. Phosphorus pentoxide 30'9, alumina 22-2, iron protoxide 31-3, water 15-6 = 100. Manganese replaces part of the iron and it hence graduates into eosphorite. Pyr., etc. In the closed tube gives off neutral water. B.B. swells up into ramifica- tions, and fuses on the edges 'to a black mass, coloring the flame pale green. Heated on charcoal turns black and becomes magnetic. With soda gives a reaction for manganese. With borax and salt of phosphorus reacts for iron and manganese. Soluble in hydro- chloric acid. Obs. From Tavistock, Devonshire, England; from Greifenstein, Germany. In United States, at Hebron, Me. KREUZBERGITE. Aluminium phosphate with Fe,Mn,H 2 O. Orthorhombic. White to yellow. From the Kreuzberg, Pleystein, Bavaria. Eosphorite. Form and composition as for childrenite, but containing chiefly man- ganese instead of iron. In prismatic crystals; also massive. Color rose-pink, yellowish, etc. |8 = 1*65. From Branchvi lie, Conn. Mazapilite. Ca3Fe 2 (AsO 4 )4.2FeO(OH).5H 2 O. In slender prismatic crystals. G. = 3-567-3-582. Color black. From Mazapil, Mexico. YUKONITE. (Ca 3 ,Fe 2 '")(AsO4)2.2Fe(OH) 3 .5H 2 O. Amorphous. In irregular concre- tions. H. 2-3. G. = 2*8. Color nearly black with brown tinge. Decrepitates at low heat, also when immersed in water. Easily fusible with intumescence. From Tagish Lake, Yukon Territory. Calcioferrite. Ca 3 Fe 2 (PO 4 ) 4 .Fe(OH) 3 .8H 2 O. Occurs in yellow to green nodules in clay at Battenberg, Rhenish Bavaria, Germany. Borickite. Perhaps Ca 3 Fe 2 (PO 4 )4.12Fe(OH) 3 .6H 2 O. Reniform massive; compact. Color reddish brown. From Leoben in Styria; Bohemia. Foucherite, possibly same as borichite from Foucheres, Aube, France. Egueiite. A hydrous basic phosphate of ferric iron with calcium and aluminium. Amorphous. In small nodules with fibrous-lamellar structure. Index, 1 '65. Fusibility 1. Easily soluble in hydrochloric acid. Found embedded in clay from Egue'i, Sudan. RICHELLITE. Perhaps 4FeP 2 O 8 .Fe 2 OF 2 (OH) 2 .36H 2 O. Massive, compact or foliated. Color yellow. From Richelle, Belgium. 990 LIROCONITE. Monoclinic. Axes a : b : c = 1-3191 : 1 : 1-6808; ft = 88 33'. mm"' 110 A 110 = 105 39'. me, 110 A Oil = 46 10'. ee', Oil A Oil = 118 29'. m'e, IlO A Oil = 47 24'. Crystals resembling rhombic octahedrons. Rarely granular. Cleavage: m (1 10), e (Oil) indistinct. Frac- ture subconchoidal to uneven. Imperfectly sectile. H. = 2-2-5. G. = 2-882-2-985. Luster vitreous, inclining to resinous. Color and streak sky-blue to verdigris-green. 615 DESCRIPTIVE MINERALOGY Tomn - - A hvdrous arsenate of aluminium and copper, formula uncertain; analysS P 'correspond nearly to CueAl(As0 4 ) 5 3CuAl(OH),20H 2 O = Arsenic pentoxide 28-9, alumina 10-3, cupric oxide 35-9, water 24-9 = 100. Phos- phorus replaces part of the arsenic. Pvr etc In the closed tube gives much water and turns olive-green. B.B cracks open but does not decrepitate; fuses less readily than olivenite to a dark gray slag; on charcoal cracks open, deflagrates, and gives reactions like olivenite. Soluble in nitric acid. Obs. From Cornwall; Herrengrund m Hungary. Chenevixite. Perhaps Cu 2 (FeO) 2 As 2 O8.3H 2 O. Massive to compact. Color dark green to greenish yellow. From Cornwall; Utah. HENWOODITE. A hydrated phosphate of aluminium and copper. In botryoidal globu- lar masses. Color turquois-blue. From Cornwall. Ceruleite. CuO.2Al 2 O 3 .As 2 O5.8H 2 O. Compact, made up of very minute crystals. G. = 2-8. Color, turquois-blue. Soluble in acids. From Huanaco, Taltal province, Chile. Chalcosiderite. CuO.3Fe 2 O 3 .2P 2 O5.8H 2 O. Probably isomorphous with turquois and should have 9H 2 O. In sheaf-Jike crystalline groups, as incrustations. Color light siskin- green. Indices, 1 '83-1 '93. From Cornwall. ANDREWSITE, also from Cornwall, is near chalcosiderite. Kehoeite. A hydrated phosphate of aluminium, zinc, etc. Massive. G. = 2'34. From Galena, S. D. Goyazite. Perhaps Ca 3 AljoP 2 O 2 3.9H 2 O. Strontia has been found in the mineral and it is possible that it is identical with hamlinite. In small rounded grains. Color yellowish white. From Minas Geraes, Brazil. Roscherite. (Mn,Fe,Ca) 2 Al(OH)(PO 4 ) 2 .2H 2 O. Monoclinic. From Ehrensfriedersdorf , Saxony. Uranite Group ^ TORBERNITE. Copper Uranite. Tetragonal. Axis c 2*9361. Crystals usually square tables, sometimes very thin, again thick; less often pyramidal. Also foliated, micaceous. Cleavage: c (001) perfect, micaceous. Laminae brittle. H. = 2-2-5. G. = ! 3'4-3'6. Luster of c pearly, other faces subadamantine. Color emerald- and grass-green, and sometimes leek-, apple-, and siskin-green. Streak paler than the color. Transparent to subtranslucent. Optically uniaxial; negative, w = 1-61. Comp. A hydrous phosphate of uranium and copper, Cu(UO 2 )2P2O 8 . 12H 2 O = Phosphorus pentoxide 14-1, uranium trioxide 56*6, copper 7'9, water 21*4 = 100. Arsenic may replace part' of the phosphorus. Pyr., etc. In the closed tube yields water. Fuses at 2*5 to a blackish mass, and colors the flame green. With salt of phosphorus gives a green bead, which with tin on char- coal becomes on cooling opaque red (copper). With soda on charcoal gives a globule of copper. .Soluble in nitric acid. Obs. From Germany at Schneeberg, etc., Saxony; Reichenbach, Baden; at Joachimstal, Bohemia; Ambert, Puy-de-D6me ; France. From Mt. Painter, South Australia. The material from Gunnis Lake, Cornwall corresponds to Cu(UO 2 ) 2 P 2 O 8 .8H 2 O and is the same as the first dehydration product of torbernite, which has been called meta-torbernite I. G. = 3'68. o> = T623. e=l'625. Zeimerite. Cu(UO>) ; A>,O 8 .SH 2 O. In tabular crystals resembling torbernite in form and color. G. = 3'2. co = 1-64. From Schneeberg, Saxony; near Joachimstal, Bohemia; Cornwall. AUTUNITE. Lime Uranite. Orthorhombic. In thin tabular crystals, nearly tetragonal in form and deviating but slightly from torbernite in angle; also foliated, micaceous. PHOSPHATES, ARSENATES, ETC. 617 Cleavage: basal, eminent. Laminae brittle. H. = 2-2'5. G. = 3-05- 3*19. Luster of c (001) pearly, elsewhere subadamantine. Color lemon- to sulphur-yellow. Streak yellowish. Transparent to translucent. Optically -. Ax. pi. || 6 (010). Bx _L c (001). a = 1-553. = 1-575. 7 = 1-577. Comp. A hydrous phosphate of uranium and calcium, probably analo- gous to torbernite, Ca(UO 2 ) 2 P 2 O 8 .8H 2 O or CaO.2UO 3 .P 2 O 5 .8H 2 O = Phos- phorus pentoxide 15*5, uranium trioxide 62-7, lime 6-1, water 15-7 = 100. Some analyses give 10 and others 12 molecules of water, but it is not certain that the additional amount is essential. Pyr., etc. Same as for torbernite, but no reaction for copper. Obs. With uraninite, as in Germany at Johanngeorgenstadt and Falkenstein; in Italy at Lurisia, Cuneo; in Madagascar; at Tinh-Tuc, Tongking, China; from Mt. Painter, South Australia. In the United States, at Middletown and Branchville, Conn. In N. C., at mica mines in Mitchell Co.; in Alexander Co.; Black Hills, S. D. Bassetite. Composition probably the same as autunite. Monoclinic. /3 = 89 17'. Twinned; tw. pi. 6 (010). Cleavage parallel to three pinacoids. G. = 3'10. Color yel- low. Transparent. Indices, 1 '57-1 '58. From the Basset mines, Cornwall. Previously considered to be autunite. Uranospinite. Probably Ca(UO 2 )2As2O 8 .8H 2 O. In thin tabular orthorhombic crystals rectangular in outline. Color siskin-green. /3 = T63. From near Schneeberg, Saxony. Uranocircite. Ba(UO 2 ) 2 P 2 O 8 .8H2O. In crystals similar to autunite. Color yellow- green. j8-= 1'62. From Falkenstein, Saxon Voigtland, Germany. Carnotite. Approximately, K 2 O.2U 2 O 3 .V 2 O 6 .3H 2 O. Orthorhombic. In the form of powder, sometimes in crystalline plates | j c (001) . Basal cleavage. Color yellow. /3 = 1 '86. Occurs as a yellow crystalline powder, or in loosely cohering masses, intimately mixed with quartzose material. It is found in large quantities in western Colorado and eastern Utah. Is mined there not only for its uranium and vanadium content but also for the small amount of radium it contains. Noted also from Radium Hill, near Olary, South Australia, and from near Mauch Chunk, Pa. TYUYAMUNITE. CaO.2UO 3 .y 2 O 5 .4H 2 O. Perhaps a calcium carnotite. Found at Tyuya-Muyun, Fergana, Russian Central Asia. Uranospathite. A hydrated uranyl phosphate. Orthorhombic, pseudo- tetragonal. In elongated tabular crystals. Cleavages parallel to the three pinacoids. Color yellow to pale green. From Redruth, Cornwall. Previously considered to be autunite. Phosphuranylite. (yO-2)3P 2 O 8 .6H 2 O. As a pulverulent incrustation. Color deep 4emon-yellow. From Mitchell Co., N. C. Trogerite. (UO 2 ) 3 As 2 O 8 .12H 2 O. In thin druses of tabular crystals. Probably tetrago- nal. Color lemon-yellow. From near Schneeberg, Saxony. Walpurgite. Probably Biio(UO 2 ) 3 (OH)24(AsO 4 )4. In thin yellow crystals resembling gypsum. G. = 5'76. Color yellow. Index, 2 '00. From near Schneeberg, Saxony. Rhagite. Perhaps 2BiAsO 4 .3Bi(OH) 3 . In crystalline aggregates. Color yellowish green, wax-yellow. From near Schneeberg, Saxony. ARSENO-BISMITE. A hydrous bismuth arsenate. In cryptocrystalline aggregates. Color yellowish green with tinge of brown. G. = 5'7. Index, 1-6. Found at Mammoth mine, Tintic district, Utah. Mixite. A hydrated basic arsenate of copper and bismuth, formula doubtful. In acicular crystals; as an incrustation. Color green to whitish. From Joachimstal, Bo- hemia; Wittichen, Baden; Tintic district, Utah. Antimonates ; also Antimonites, Arsenites. A number of antimonates have been included in the preceding pages among the phosphates, arsenates, etc. Bindheimite. A hydrous antimonate of lead. Amorphous, reniform; also earthy or incrusting. Color gray, brownish, yellowish. Index, 2'0. A result of the decomposition 518 DESCRIPTIVE MINERALOGY of other antimonial ores; thus at Horhausen, Germany; in Cornwall, England; Sevier meite.' An antimonite of calcium, perhaps CaSb 2 O 4 In groups of minute square octahedrons H. above 5'5. G. = 4713.' Color hyacinth- or honey-yellow, n = 183- 1 87 From St. Marcel, Piedmont; Miguel Burnier, Mmas Geraes. Atopite from Lang- ban, Sweden, is probably the same species. Nadorite PbClSbO 2 . In orthorhombic crystals. H. = 3'5-4. G. = 7'02. Color brownish yellow. = 2 '35. From Djebel-Nador, Constantme. Algeria. Ecdemite. Heliophyllite. Perhaps Pb 4 As 2 O 7 .2PbCl2. In crystals, massive, and as an incrustation. G. = 6'89-7'14. Color bright yellow to green. From Langban, Sweden; also Pajsberg (heliophyllite) . Ochrolite. Probably Pb 4 Sb 2 O 7 .2PbCl 2 . In small crystals, united in diverging groups. Color sulphur-yellow. From Pajsberg, Sweden. Trippkeite. nCuO.As 2 O 3 . In small bluish green, tetragonal crystals. From Copiapo, Chile. Schafarzikite is described as isomorphous with trippkeite with the formula, nFeO.P 2 O 3 . From Pernek, Comitat Pozsony, Hungary. Tripuhyite. An iron antimonate. 2FeO.Sb 2 O 5 . In microcrystalline aggregates of a dull greenish yellow color. From Tripuhy, Brazil. Flajolotite. 4FeSbO 4 .3H 2 O. Compact or earthy. Color lemon-yellow. In nodular masses. From Hammam N'Bail, Constantine, Algiers. Catoptrite. 14(Mn,Fe)O.2(Al,Fe) 2 O 3 .2SiO 2 .Sb 2 O 5 . Monoclinic. Crystals minute tab- ular parallel to 6 (010). Perfect basal cleavage. H. = 5 '5. G. = 4 '5. Color black. In thin splinters, red. Pleochroic, red-brown to red-yellow. From Brattsfor mine, Nord- marken, Sweden. Derbylite. An antimo-titanate of iron. In prismatic, orthorhombic crystals. H. = 5. G. = 4-53. Color black. Tripuhy, Brazil. Lewisite. 5CaO.2TiO 2 .3Sb 2 O 6 . In minute yellow to brown isometric octahedrons. Tripuhy, Brazil. Mauzeliite. A titano-antimonate of lead and calcium, related to lewisite. In dark brown isometric octahedrons. Jakobsberg, Sweden. AMMIOLITE. A doubtful antimonite of mercury; forming a scarlet earthy mass. Chile. Phosphates or Arsenates with Carbonates, Sulphates, Borates Podolite. 3Ca 3 (PO 4 ) 2 .CaCO 3 . Hexagonal. In microscopic prismatic crystals, also in spherulites. G. = 3'1. Color yellow, ft = 1'64. Occurs in cavities in the phosphorite nodules from near the Uschitza River, Podolien, southern Russia. See also staff elite and dahllite, p. 597. Diadochite. A hydrated phosphate and sulphate of ferric iron. Index, 1*606. From Thuringia. Destinezite is similar; from Belgium. Pitticite. A hydrated arsenate and sulphate of ferric iron. Reniform and massive. Yellowish and reddish brown. Index, 1 -63. From Saxony, Cornwall, etc. Svanbergite. A hydrated phosphate and sulphate of aluminium and calcium. In rhombohedral crystals. Color yellow to yellowish brown, rose-red, co = T64. From Horrsjoberg, Sweden. Beudantite. A phosphate or arsenate with sulphate of ferric iron and lead; formula perhaps, 3Fe 2 O 3 .2PbO.2SO 3 .As 2 O 5 .6H 2 O. In rhombohedral crystals. Color green to brown and black. Indices, 175-1 '94. From Dernbach and Horhausen, Nassau. Corkite is same mineral from Cork, Ireland; Beaver Co., Utah. Phosphophyllite. 3Fe 3 P 2 O 8 .2Al(OH)SO 4 .9H 2 O, with Ca,Ba,Mg,Mn,K 2 Monoclinic. Colorless to pale blue-green. 3 pinacoidal cleavages. H. = 3-4. G. = 3 '08. n = T65. From Habendorf, Bavaria. Hinsdalite. 2PbO.3Fe 2 O 3 .2SO 3 .P 2 O 5 .6H 2 O. Pseudo-rhombohedral. In coarse, dull crystals. Cleavage, basal perfect. H. = 4'5. G. = 4'65. Colorless with greenish tone. Indices 1 -67-1 -69. Found at Golden Fleece mine, Hinsdale Co., Col. Lindackerite. Perhaps 3NiO.6CuO.SO 3 .2As 2 O 5 .7H 2 O. In rosettes, and in reniform masses. Color verdigris- to apple-green. From Joachimstal, Bohemia. BO RATES 619 Liineburgite. 3MgO.B 2 O 3 .P2O5.8H 2 O. Monoclinic? In flattened masses, fibrous to earthy structure. Biaxial, . Index, T53. From Ltineburg, Hannover. Lossenite. A hydrous iron arsenate and lead sulphate from Laurion, Greece. Nitrates The Nitrates being largely soluble in water play but an unimportant role in Mineralogy. SODA NITER. Rhombohedral. Axis c = 0-8276; rr" 1011 A 1101 = 73 30'. Homceo- morphous with calcite. Usually massive form, as an incrustation or in beds. Cleavage: r (1011) perfect. Fracture conchoidal, seldom observable. Rather sectile. H. = T5-2. G. = 2'24-2'29. Luster vitreous. Color white; also reddish brown, gray and lemon-yellow. Transparent. Taste cooling. Optically -. co = T5874, e = 1'3361. Comp. Sodium nitrate, NaNO 3 = Nitrogen pentoxide 63'5, soda 36'5 = 100. Pyr., etc. Deflagrates on charcoal with less violence than niter, causing a yellow light, and also deliquesces. Colors the flame intensely yellow. Dissolves in three parts of water at 60 F. Obs. From Tarapaca, northern Chile, and also the neighboring parts of Bolivia; also in Humboldt Co., Nev.; near Calico, San Bernardino Co., Cal. Use. A source of nitrates. The deposits in Chile are of great importance. Niter. Potassium nitrate, KNO 3 . Orthorhombic. = T505. In thin white crusts and silky tufts. Nitrocalcite. Hydrous calcium nitrate, Ca(NO 3 ) 2 .nH 2 O. In efflorescent silky tufts and masses. In many limestone caverns, as those of Kentucky. Nitromagnesite. Mg(NO 3 )2.nH 2 O. In efflorescences in limestone caves. Nitrobarite. Barium nitrate, Ba(NO 3 ) 2 . Isometric-tetartohedral. n = 1'57. From Chile. Gerhardtite. Basic cupric nitrate, Cu(NO 3 )2.3Cu(OH) 2 . In pyramidal orthorhombic crystals. G. = 3 '426. Color emerald-green. /3 = 1713. From the copper mines at Jerome, Ariz. Darapskite. NaNOs.Na2SO4.H2O. Monoclinic. In square tabular crystals. Color- less. From Atacama, Chile. Nitroglauberite. 6NaNO 3 .2Na2SO 4 .3H 2 O. From Atacama, Chile. Lautarite. Calcium iodate, Ca(IO3) 2 . In prismatic, monoclinic crystals, colorless to yellowish. From the sodium nitrate deposits of Atacama, Chile. Dietzeite. -A calcium iodo-chromate. Monoclinic; commonly fibrous or columnar. H. = 3-4. G. = 370. Color dark gold-yellow. From the same region as lautarite. Oxygen Salts 5. BORAXES The aluminates, ferrates, etc., allied chemically to the borates, have been already intro- duced among the oxides. They include the species of the Spinel Group, pp. 418-423, also Chrysoberyl, p. 423, etc. SUSSEXITE. In fibrous seams or veins. H. = 3. G. = 3 -42. Luster silky to pearly. Color white with a tinge of pink or yellow. Translucent. Index, T59. 620 DESCRIPTIVE MINERALOGY Comp. HRB0 3 , where R = Mn, Zn and Mg = Boron trioxide 34 1, manganese protoxide, 41 '5, magnesia 15'6, water 8'8 = 100. Here Mn (+ Zn) : Mg = 3 : 2. Pyr., etc. In the closed tube darkens in color and yields neutral water. If turmeric paper is moistened with this water, and then with dilute hydrochloric acid, it assumes a red color (boric acid). In the forceps fuses in the flame of a candle (F. = 2), and B.B. in O F. yields a black crystalline mass, coloring the flame intensely yellowish green. With the fluxes reacts for manganese. Soluble in hydrochloric acid. Obs. Found on Mine Hill, Franklin Furnace, Sussex Co., N. J., with franklinite, zincite willemite, etc. An intimate mixture of zincite and calcite, not uncommon at Min? Hill, is often mistaken for sussexite, but the ready fusibility of the genuine mineral is dis- tinctive. Ludwigite. Perhaps 3MgO.B 2 O 3 .FeO.Fe 2 O 3 . Orthorhombic. In finely fibrous masses. G. = 3-91-4-02. Color blackish green to nearly black. Index, T86. Strongly pleochroic. From Morawitza, Hungary. Collbranite from Korea is ludwigite. VONSENITE. 3(Fe,Mg)O.B 2 O3.FeO.Fe 2 O3. Similar to ludwigite with more ferrous iron. Riverside ; Cal. Magnesioludwigite. 3MgO.B 2 O3.MgO.Fe 2 O 3 . From Mountain Lake mine, south of Brighton, Utah. Pinakiolite. 3MgO.B 2 O 3 .MnO.Mn 2 O 3 . In small rectangular crystals. H. = 6. G.= 3-881. Luster metallic. Color black. From Langban, Sweden. Nordenskioldine. A calcium-tin borate, CaSn(BOi) 2 . In tabular rhombohedral crystals. H. = 5*5-6. G. = 4'20. Color sulphur-yellow. From the Langesund fiord, Norway. Jeremejevite. Eichwaldite. Aluminium borate, A1BO 3 . In prismatic hexagonal crystals. H. = 6'5. G. = 3/28. Colorless to pale yellow. Index, 1'64. From Mt. Soktuj, Adun-Chalon range in Eastern Siberia. Hambergite. Be 2 (OH)BO 3 . In grayish white orthorhombic prismatic crystals. H. = 7-5. G. = 2-347. Optically +. = 1'588. From Langesund fiord, southern Nor- way; various localities in Madagascar. Szaibelyite. 2Mg5B 4 Ou.3H 2 O. In small nodules; white outside, yellow within. From Rezbdnya, Hungary. BORACITE. Isometric and retrahedral in external form under ordinary conditions, but in molecular structure orthorhombic and pseudo-isometric; the structure becomes isotropic, as required by the form, only when heated to 265. (See Art. 429.) 991 \7 993 Habit cubic and tetrahedral or octahedral; also dodecahedral. Crystals usually isolated, embedded; less often in groups. Faces o (111) bright and smooth, o, (111) dull or uneven. Cleavage: o,o y in traces. Fracture conchoidal, uneven. Brittle H =7 in crystals. G. = 2-9-3. Luster vitreous, inclining to adamantine. Color white, inclining to gray, yellow and green. Streak white. Subtransparent to BORATES 621 translucent. Commonly shows double refraction, which, however, disappears upon heating to 265, when a section becomes isotropic. Refractive index, n = 1-667; 7 - a = 0-0107. Strongly pyroelectric, the opposite polarity corresponding to the position of the + and - tetrahedral faces (see pp. 306, 307). The faces of the dull tetrahedron o / (111) form the analogous pole, those of the polished form o (111) the antilogous pole. Comp. Mg7Cl 2 B 16 O 3 o or 6MgO.MgCl 2 .8B 2 O 3 = Boron trioxide 62*5, magnesia 31'4, chlorine 7'9 = 101'8, deduct (O= Cl) 1'8 = 100. Var. 1. Ordinary. In crystals of varied habit. 2. Massive, with sometimes a sub- columnar structure; stassfurtite of Rose. It resembles a fine-grained white marble or granular limestone. Parasite of Volger is the plumose interior of some crystals of boracite. 3. Eisenstassfurtite contains some Fe. Pyr., etc. The massive variety gives water in the closed tube. B.B. both varieties fuse at 2 with intumescence to a white crystalline pearl, coloring the flame green; heated after moistening with cobalt solution assumes a deep pink color. Mixed with oxide of copper and heated on charcoal colors the flame deep azure-blue (copper chloride). Soluble in hydrochloric acid. Alters very slowly on exposure, owing to the magnesium chloride present, which takes up water. It is the frequent presence of this deliquescent chloride in the massive mineral, thus originating, that led to the view that there was a hydrous boracite (stassfurtite). Parasite of Volger is a result of the same kind of alteration in the interior of crystals of boracite; this alteration giving it its somewhat plumose character, and introducing water. Obs. Observed in beds of anhydrite, gypsum or salt. In crystals in Germany at Kalkberg and Schildstein in Llineburg, Hannover; at Segeberg, near Kiel, in Holstein; massive, or as part of the rock, also in crystals, at Stassfurt, Prussia; at Luneville, La Meurthe, France. Ascharite. A hydrous magnesium borate. In white lumps with boracite. G. = 2'7. Index, 1*54. From Aschersleben and Neustassfurt, Germany. Paternoite. A similar mineral from Sicily. Rhodizite. A borate of aluminium and potassium, with caesium and rubidium. Iso- metric-tetrahedral; in white, translucent dodecahedrons. H. = 8. G. = 3 '41. n = T69. Found on red tourmaline from near Ekaterinburg, Ural Mts.; from Madagascar. Warwickite. (Mg, Fe) 3 TiB 2 O 8 . In elongated prismatic crystals. G. = 3'36. Color dark brown to dull black. From Edenville, N. Y. Howlite. A silico-borate of calcium, H 5 Ca 2 B 6 SiOi 4 . In small white rounded nodules; also earthy. From Nova Scotia; Lang, Los Angeles Co., and in San Bernardino Co., Cal. Lagonite. Fe 2 O3.3B2O3.3H 2 O. An incrustation at the Tuscan lagoons, Italy. Larderellite. (NH 4 ) 2 Bi O 16 .5H 2 O. From the Tuscan lagoons, Italy. COLEMANITE. Monoclinic. Axes a : b : c = 07748 : 1 : 0'5410;j3 = 69 51'. Crystals usually short prismatic (mm'" 110 A 110 = 72 4'). Massive cleavable to granular and compact. Cleavable: b (010) highly perfect; c (001) distinct. Fracture uneven to subconchoidal. H. = 4-4'5. G. = 2*42. Luster vitreous to adamantine, brilliant. Colorless to milky white, yellowish white, gray. Transparent to translucent. Optically + . a = 1'586. = 1'592. 7 = 1'614. Comp. Ca 2 B 6 On.5H 2 O, perhaps HCa(BO 2 ) 3 .2H 2 = Boron trioxide 50'9, lime 27*2, water 21*9 = 100. Pyr. B.B. decrepitates, exfoliates, sinters, and fuses imperfectly, coloring the flame yellowish green. Soluble in hot hydrochloric acid with separation of boric acid on cooling. Obs. First discovered in Death Valley, Inyo Co., Cal.; later in Calico district, San Bernardino Co. Neocolemanite from Lang, Los Angeles Co., Cal., is identical with cole- manite. PRICEITE. Near colemanite. Massive, friable and chalky. Color snow-white. From Curry Co., Oregon. Pandermite is similar; in compact nodules from Asia Minor; Argentina. 622 DESCRIPTIVE MINERALOGY Inyoite. 2CaO.3B 2 O 3 .13H 2 O. Monoclinic. In large tabular crystals. Cleavage, c (001). H. =2. G. = 1-87. Indices, 1 '49-1*52. Decrepitates and fuses with intu- mescence, giving green flame. Largely altered into meyerhofferite. From Mt. Blanco dis- trict, on Furnace Creek, near Death Valley, Inyo Co., Cal. Associated with colemanite. Meyerhofferite. 2CaO.3B 2 O 3 .7H 2 O. Triclinic crystals prismatic, often tabular parallel to a (100). Fibrous. Cleavage, b (010). H. = 2. G. = 2*12. Colorless to white. In- dices, 1 '50-1 '56. Fuses without decrepitation but with intumescence. Found with inyoite (which see) as an alteration product. Pinnoite. MgB 2 O 4 .3H 2 O. Tetragonal-pyramidal. Usually in nodules, radiated fibrous. G. = 2 '29. Color sulphur- or straw-yellow, co = 1'56. From Stassfurt, Germany. Heintzite. Hintzeite. Kaliborite. A hydrous borate of magnesium and potassium. In small monoclinic crystals, sometimes aggregated together. H. = 4-5. G. = 2*13. Colorless to white, ft = T525. From Leopoldshall, Stassfurt, Germany. Hulsite. 12(Fe,Mg)O.2Fe 2 O 3 .lSnO 2 .3B 2 O.2H 2 O. Orthorhombic (?) as small crystals or tabular masses. H. = 3. G. = 4 '3. Color and streak black. Fusible. Found in metamorphosed limestone at a granite contact at Brooks mountain, Seward Peninsula, Alaska. Paigeile is a similar mineral from the same locality with the composition 30FeO.5Fe 2 O 3 .lSnO 2 .6B 2 O 3 .5H 2 O. BORAX. Monoclinic. 994 Axes a : b : c = 1-0995 : 1 : 0-5632; = 73 25'. ca, 001 A 100 = 73 25'. cz, 001 A 221 = 64 8'. mm'", 110 A 110 = 93 0'. oo', III A Til = 57 27'. co, 001 A 111 = 40 31'. zz', 221 A 221 = 83 28'. Crystals prismatic, sometimes large; resembling pyroxene in habit and angles. Cleavage: a (100) perfect; m (110) less so; 6](010) in traces. Fracture conchoidal. Rather brittle. H. = 2-2*5. G. = T69-172. Luster vitreous to resinous; sometimes earthy. Color white; sometimes grayish, bluish or green- ish. Streak white. Translucent to opaque. Taste sweet- ish alkaline, feeble. Optically - . Ax. pi. b (010). Bx a _L 6 (010). Bxo. r A c axis = - 56 50'. 2V = 39. T470. 7 = 1-472. Comp. Na 2 B 4 O 7 .10H 2 O or Na2O.2B 2 O 3 .10H 2 O soda 16-2, water 47-2 = 100. a = 1-447. = Boron trioxide 36'6. of bomx F,~^ ? ' B: fE U fl S Up . and afterward fuses to a transparent globule, called the glass and Pt*?*um bisulphate, it colors the flame around the a alkaline soMon - Boi ^g water the i f Tibet; the crude mineral is called . two small alkaline lakes in t inolderin^ gold Co - ; at , which included also the niter (sodium carbonate) Called <= h ^ o -- by Agricola a sclent t^^^^^^^^^^ ^ preservative; tJLEXITE. Boronatrocalcite. Natronborocalcite. are acTcu& r ,Tn ed mass f ', Ioos e m texture, consisting of fine fibers, which Color S ^ "f^ycrystas. H. = 1. G. - 1'65. Luster silky within. r white. Tasteless. H. = Ophcally +. 1. G. - 1'65. = 1'500. (3 1-508. 7 = T520. BORATES, URANATES 623 Comp. A hydrous borate of sodium and calcium, probably NaCaB 5 O 9 . 8H 2 O = Boron trioxide 43'0, lime 13'8, soda 77, water 35'5 = 100. Pyr., etc. Yields water. B.B. fuses at 1 with intumescence to a clear blebby glass, coloring the flame deep yellow. Moistened with sulphuric acid the color of the flame is momentarily changed to deep green. Not soluble in cold water, and but little so in hot; the solution alkaline in its reactions. Obs. From the dry plains of Iquique, Chile. In Nev., in large quantities in the salt marshes of the Columbus Mining District, Esmeralda Co. Named after the German chemist, G. L. Ulex. Bechilite. CaB 4 O 7 .4H 2 O. In crusts, as a deposit from springs in Tuscany, Italy. Hydroboracite. CaMgB 6 On.6H 2 O. Resembles fibrous and foliated gypsum; color white. /3 = T587. From the Caucasus Mts. Sulphoborite. 2MgSO 4 .4MgHBO 3 .7H 2 O. In colorless prismatic orthorhombic crys- tals. H. = 4. G. = 2-38-2-45. Optically -. ft = 1'540. From Westeregeln, and Wittmar, Germany. Uranates URANINITE. Cleveite. Broggerite. Nivenite. Pitchblende. Isometric. In octahedrons (o), also with dodecahedral faces (d) ; less often in cubes with o and d. Crystals rare. Usually massive and botryoidal; also in grains; structure sometimes columnar, or curved lamellar. Fracture conchoidal to uneven. Brittle. H. = 5'5. G. = 9'0 to 97 of crystals; of massive altered forms from 6*4 upwards. Luster submetallic, to greasy or pitch-like, and dull. Color grayish, greenish, brownish, velvet- black. Streak brownish black, grayish, olive-green, a little shining. Opaque. Comp. A uranate of uranyl, lead, usually thorium (or zirconium), often the metals of the lanthanum and yttrium groups; also containing the gases nitrogen, helium and argon, in varying amounts up to 2'6 p. c. Calcium and water (essential?) are present in small quantities; iron also, but only as an impurity. The relation between the bases varies widely and no definite for- mula can be given. Radium was first discovered in this mineral and it has been shown that it and the helium present are products of the breaking down of the uranium. Var. The minerals provisionally included under the name uraninite are as follows: 1. Crystallized. Uranniobite from Norway. In crystals, usually octahedral, with G. varying for the most part from 9'0 to 9 '7; occurs as an original constituent of coarse granites. The variety from Branchville, Conn., which is as free from alteration as any yet examined, contains chiefly UO 2 with a relatively small amount of UO 3 . Thoria is prominent, while the earths of the lanthanum and yttrium groups are only sparingly represented. Broggerite, as analyzed by Hillebrand, gives the oxygen ratio of tlOs to other bases of about 1:1; it occurs in octahedral crystals, also with d (110) and a (100). G. = 9'03. Cleveite and nivenite contain UO 3 in larger amount than the other varieties mentioned, and are characterized by containing about 10 p. c. of the yttrium earths. Cleveite is a variety from the Arendal, Norway, region occurring in cubic crystals modified by the dodeca- hedron and octahedron. G. = 7'49. It is particularly rich in the gas helium. Nivenite occurs massive, with indistinct crystallization. Color velvet-black. H. = 5'5. G. = 8'01. It is more soluble than other kinds of uraninite, being completely decomposed by the action for one hour of very dilute sulphuric acid at 100. 2. Massive, probably amorphous. Pitchblende. Contains no thoria; the rare earths also absent. Water is prominent and the specific gravity is much lower, in some cases not above 6'5; these last differences are doubtless largely due to alteration. Here belong the kinds of pitchblende which occur in metalliferous veins, with sulphides of silver, lead, cobalt, nickel, iron, zinc, copper, as that from Johanngeorgenstadt, Germany; Pfibram, Bohemia, etc.; probably also that from Black Hawk, Col. 624 DESCRIPTIVE MINERALOGY Pyr., etc. B.B. infusible, or only slightly rounded on the edges, sometimes coloring the outer flame green (copper). With borax and salt of phosphorus gives a yellow bead in O.F., becoming green in R.F. (uranium). With soda on charcoal gives a coating of lead oxide, and frequently the odor of arsenic. Many specimens give reactions for sulphur and arsenic in the open tube. Soluble in nitric and sulphuric acids; the solubility differs widely in different varieties, being greater in those kinds containing the rare earths. Not attract- able by the magnet. Strongly radioactive. Obs. As noted above, uraninite occurs either as a primary constituent of granitic rocks or as a secondary mineral with ores of silver, lead, copper, etc. Under the latter condition it is found in Germany at Johanngeorgenstadt, Marienberg, and Schneeberg in Saxony; in Bohemia at Joachimstal and Pfibram; in Hungary at Rezbanya. Occurs in Norway in pegmatitic veins at several points near Moss, viz.: Annerod (broggerite), Elvestad, etc., also near Arendal at the Garta feldspar quarry (deveite), associated with orthite, fergusonite, thorite, etc. In the United States, at the Middletown feldspar quarry, Conn., in large octahedrons, rare; at Hale's quarry in Glastonbury, a few miles N.E. of Middletown. At Branchville, Conn., in a pegmatite vein, as small octahedral crystals, embedded in albite. In N. C., at the Flat Rock mine and other mica mines in Mitchell Co., rather abundant, but usually altered, in part or entirely, to gummite and uranophane; the crystals are sometimes an inch or more across and cubic in habit. In S. C., at Marietta. In Texas, at the gadolinite locality in Llano Co. (nivenite). In large quantities at Black Hawk, near Central City, Col. Rather abundant in the Bald Mountain district, Black Hills, S. D. Also with monazite, etc., at the Villeneuye mica veins, Ottawa Co., Quebec, Canada. Use. As a source of uranium and of radium salts. Gummite. An alteration-product of uraninite of doubtful composition. In rounded or flattened pieces, looking much like gum. G. = 3'9-4'20. Luster greasy. Color red- dish yellow to orange-red, reddish brown, n = 1'61. From Johanngeorgenstadt, Ger- many, also Mitchell Co., N. C. YTTROGUMMITE. Occurs with cleveite as a decomposition-product. THOROGUMMITE. Occurs with fergusonite, cyrtolite, and other species at the gadolinite locality in Llano Co., Texas. Thorianite. Chiefly thorium and uranium oxides. Isometric, cubic habit. G. = 9'3. Color black. Radioactive. Obtained from gem gravels of Balangoda, Ceylon. Also noted from Province of Betroka, Madagascar. Uranosphaerite. (BiO) 2 U 2 O 7 .3H 2 O. In half-globular aggregated forms. Color orange- yellow, brick-red. From near Schneeberg, Saxony. Oxygen Salts 6. SULPHATES, CHROMATES, TELLURATES A. Anhydrous Sulphates, etc. The important BARITE GROUP is the only one among the anhydrous sul- phates and chromates. ip g ite * A mo sulphate, (NH 4 ) 2 SO 4 . Orthorhombic. Usually in crusts and forms, ft = 1'523. Occurs about volcanoes, as at Etna, Vesuvius, etc. 0r 80 *' ^ ^ C m dal hTrf nr^m ^^T* s ? diu sulphate, Na 2 S0 4 . In orthorhombic crystals, pyrami- Opticanv T i/77 ^ti^ aS twlnS (Fig> 384 ' p - 160) ' White to brownish. n thp vT /V , Sol b f m water " Often ob ^rved in connection with salt AnSfof ?n T a n reS nJf ke T Balk , hash > Central Asia; similarly elsewhere; also in South vSde An" Ta T r n aP rT' ^ Ir ? t , he y nited States > f rms extensive deposits on the Rio erae Ariz. In Cal., at Borax Lake, San Bernardino Co. cruste Co^wh^^ 6 - laSerite " ( K ' Na )^O 4 . Rhombohedral; also massive, in many 3 ,' in' k U SULPHATES, CHROMATES, ETC. 625 67 49'. 995 GLAUBERITE. Monoclinic. Axes a : b c = i'2200 : 1 : T0275; /3 ca, 001 A 100 = 67 49'. cs, 001 A 111 = 43 2' mm'", 110 A 110 = 96 58'. cm, 001 A 110 = 75 30f. In crystals tabular || c (001); also prismatic. Cleavage: c perfect. Fracture conchoidal. Brittle. H. = 2-5-3. G. = 2-7-2-85. Luster vitreous. Color pale yellow or gray; sometimes brick-red. Streak white. Taste slightly saline. Optically. 2V = 7. a = 1-515. j8 = 1-532. y = 1'536. Optical characters change on heating, see p. 297. Comp. Na 2 SO 4 .CaSO 4 = Sulphur trioxide 57'6, lime 20'1, soda 22'3 = 100; or, Sodium sulphate 51'1, calcium sulphate 48 "9 = 100. Pyr., etc. B.B. decrepitates, turns white, and fuses at 1'5 to a white enamel, coloring the flame intensely yellow. On charcoal fuses in O.F. to a clear bead; in R.F. a portion is absorbed by the charcoal, leaving an infusible hepatic residue. Soluble in hydrochloric acid. In water it loses its transparency, is partially dissolved, leaving a residue of calcium sulphate, and in a large excess this is completely dissolved. Obs. In crystals in rock salt at Villa Rubia, in New Castile, Spain; also at Aussee and Hallstatt, Upper Austria; in Germany at Berchtesgaden, Bavaria; Westeregeln; Stassfurt. In crystals in the Rio Verde Valley, Ariz., with thenardite, mirabilite, etc.; Borax lake, San Bernardino Co., Cal. Langbeinite. K 2 Mg 2 (SO 4 )3. Isometric-tetartohedral. In highly modified colorless crystals. G. = 2'83. n = 1'533. From Westeregeln and Stassfurt, Germany; Hall, Tyrol; Punjab, India. Vanthoffite. 3Na 2 SO 4 .MgSO 4 . Almost colorless crystalline material found at Wil- helmshall, near Stassfurt, Prussia. Barite Group. RS0 4 . Orthorhombic m A m'" dd'_ 110 A 110 102 A 102 77 43' 78 49' 78 47' (58 31') Barite BaSO 4 Celestite SrSO 4 Anglesite PbSO 4 Anhydrite CaS0 4 78 22J' 75 50' 76 16J' (83 33') 00' Oil A .011 a b : c 105 26' 0-8152 1 1-3136 104 0' 0-7790 1 1-2801 104 24i' 0-7852 1 1-2894 (90 3') 0-8933 1 1-0008 The BARITE GROUP includes the sulphates of barium, strontium, and lead, three species which are closely isomorphous, agreeing not only in axial ratio but also in crystalline habit and cleavage. With these is also included cal- cium sulphate, anhydrite, which has a related but not closely similar form; it differs from the others conspicuously in cleavage. It is to be noted that the carbonates of the same metals form the isomorphous ARAGONITE GROUP, p. 437. BARITE. Heavy Spar. Barytes. Orthorhombic. Axes a : b : c mm'", 110 A 110 = 78 22|'. cd, 001 A 102 = 38 51 i'. co, 001 A Oil = 52 43'. Crystals commonly tabular G'8152 : 1 : 1-3136. dd" f , 102 A 102 = 102 17'. oo'", Oil A Oil = 74 34'. cz, 001 A 111 = 64 19'. c (001), and united in diverging groups having the axis b in common; also prismatic, most frequently || axis b, d (102) predomi- nating; also || axis c, m (110) prominent; again || axis a, with o (Oil) promi- nent. Also in globular forms, fibrous or lamellar, crested; coarsely laminated, 626 DESCRIPTIVE MINERALOGY laminae convergent and often curved; granular, resembling white marble, and earthy; colors sometimes banded as in stalagmite. Cleavage: c (001) perfect; m (110) also perfect, Fig. 996 the form yielded 996 997 998 999 1000 1001 1002 1003 1004 37 30'. a = 1.636. by cleavage; also 6 (010) imperfect. Fracture un- even. Brittle. H. = 2'5-3;5. G. = 4'3-4'6. Lus- ter vitreous, inclining to resinous; sometimes pearly on c (001), less often on m (110). Streak white. Color white; also inclining to yellow, gray, blue, red, or brown, dark brown. Transparent to translucent to opaque. Sometimes fetid, when rubbed. Opti- cally +. Ax. pi. || 6(010). Bx J_ a (100). 2V = = 1-637. 7 = 1-648. Var. Ordinary, (a) Crystals usually broad or stout; sometimes very large; again in slender needles. (6) Crested; massive aggregations of tabular crystals, the crystals project- ing at surface into crest-like forms, (c) Columnar; the columns often coarse and loosely aggregated, and either radiated or parallel; rarely fine fibrous, (d) In globular or nodular concretions, subfibrous or columnar within. Bologna Stone (from near Bologna) is here included; it was early a source of wonder because of the phosphorescence it exhibited after heating with charcoal. "Bologna phosphorus" was made from it. (e) Lamellar, either straight or curved; the latter sometimes as aggregations of curved scale-like plates. (/) Granular, (g) Compact or cryptocrystalline. (h) Earthy, (i) Stalactitic and stalag- mitic; similar in structure and origin to calcareous stalactites and stalagmites and of much beauty when polished, (h) Fetid; so called from the odor given off when struck or when two pieces are rubbed together, which odor may be due to carbonaceous matters present. The barite of Muzsaj and of Betler, near Rosenau, Hungary, was early called Wolnyn. Cawk is the ordinary barite of the Derbyshire lead mines. Dreelite, supposed to be rhom- bohedral, is simply barite. Michel-levyte from Perkin's Mill, Templeton, Quebec (described as monoclinic), is peculiar in its pearly luster on m, twinning striations, etc. Comp. Barium sulphate, BaSO 4 = Sulphur trioxide 34'3, baryta 657 = 100. Strontium sulphate is often present, also calcium sulphate; further, as impurities, silica, clay, bituminous or carbonaceous substances. Pyr, etc. B.B. decrepitates and fuses at 3, coloring the flame yellowish green; the, fused mass reacts alkaline with test paper. On charcoal- reduced to a sulphide. With soda gives at first a clear pearl, but on continued blowing yields a hepatic mass, which spreads out and soaks into the coal. This reacts for sulphur (p. 340). Insoluble in acids. DifE. Characterized by high specific gravity (higher than celestite, aragonite, albite, calcite, gypsum, etc.); cleavage; insolubility; green coloration of the blowpipe flame. Albite is harder and calcite effervesces with acid. Obs. Occurs commonly in connection with beds or veins of metallic ores, especially of lead, also copper, silver, cobalt, manganese, as part of the gangue of the ore; also often accompanies stibmte. Sometimes present in massive forms with hematite deposits. It is met with m secondary limestones and sandstones, sometimes forming distinct veins, and in SULPHATES, CHROMATES, ETC. 627 the former often in crystals along with calcite and celestite; in the latter often with coooer ores. Sometimes occupies the cavities of amygdaloidal basalt, porphyry, etc forms earthv masses in beds of marl. Occurs as the petrifying material of fossils and occupying cavities in them. Fine crystals are obtained in England at the Dufton lead mines, Westmoreland- also in Cumberland and Lancashire; in Derbyshire, Staffordshire, etc.; Cleator Moor-' Alston Moor. In Scotland, in Argyleshire, at Strontian, Some of the most important of the many European localities are Felsobanya, Nagybanya. Schemnitz, and Kremnitz in Hungary, and Jlef eld, often with stibnite; Huttenberg, Carinthia; Freiberg, Marienberg in Saxony; Claustal in the Harz Mts.; Pribram, Bohemia; Auvergne, France. In the United States, formerly in Conn., at Cheshire^intersecting the red sandstone in veins with chalcocite and malachite. In N. Y., at Pillar Point, opposite Sackett's Harbor massive; at Scoharie, fibrous; in St. Lawrence Co., crystals at DeKalb; the crested variety at Hammond. In Pa., in crystals at Perkiomen lea^mine. In Va., at Eldridge's gold mine in Buckingham Co. In N. C., white ma^sw^aTCrowders Mt., Gaston Co., etc In Tenn., on Brown's Creek; at Haysboro' near Nashville; in large veins in sandstone on the west end of Isle Roy ale, Lake Superior, and on Spar Island, north shore. In Mo. not uncommon with the lead ores; in concretionary forms at Salina, Saline Co., Kan In Col., at Sterling, Weld Co.; Apishapa Creek; also in El Paso and Fremont Cos. In fine crystals, near Fort Wallace, N. M. Crystals enclosing quartz sand, "sand barite," from Norman, Oklahoma. In distorted crystals from the Bad Islands, S. D. In Ontario, in Bathurst, and North Burgess, Lanark Co.; Malway, Peterborough Co.' as large veins on Jarvis, McKellars, and Pie islands, in Lake Superior, and near Fort William' Thunder Bay. In Nova Scotia, in veins in the slates of East River of the Five Islands) Colchester Co. Named from papvs, heavy. Use. Source of barium hydroxide used in the refining of sugar; ground and used as a pigment, to give weight to paper, cloth, etc. CELESTITE. Coelestine. Orthorhombic. Axes a : b : c = 07790 : 1 : 1-2800. 1005 1006 mm"', 110 A 110 = 75 50'. cd, 001 A 102 = 39 24'. d, 001 A 104 = 22 20'. co, 001 A Oil = 52 0'. Crystals resembling those of barite in habit; commonly tabular 1 1 c (001) or prismatic || axis a or 6; also more rarely pyramidal by the prominence of the forms \j/ (133) or x (144). Also fibrous and radiated; sometimes globular; occasionally granular. Cleavage: c (001) perfect; ra (110) nearly perfect; b (010) less distinct. Fracture uneven. H. = 3-3'5. G. = 3'95-3'97. Luster vitreous, sometimes inclining to pearly. Streak white. Color white, often faint bluish, and some- times reddish. Transparent to subtranslucent. Optically +. Ax. pi. || b (010). Bx _L a (100). 2V = 51. a = 1'622. ft = 1'624. 7 = 1'631. Var. 1. Ordinary, (a) In crystals of varied habit as noted above; a tinge of a deli- cate blue is very common and sometimes belongs to only a part of a crystal. The variety from Montmartre, near Paris, France, called apotome, is prismatic by extension of o (Oil) and doubly terminated by the pyramid ^ (133). (6) Fibrous, either parallel or radiated. (c) Lamellar; of rare occurrence, (d) Granular, (e) Concretionary. (/) Earthy; impure usually with carbonate of lime or clay. 628 DESCRIPTIVE MINERALOGY Comp. Strontium sulphate, SrSO 4 = Sulphur trioxide 43'6, stron- tia 56'4 = 100. Calcium and barium are sometimes present. Pyr.j e tc. B.B. frequently decrepitates, fuses at 3 to a white pearl, coloring the flame strontia-red; the fused mass reacts alkaline. On charcoal fuses, and in R.F. is converted into a difficultly fusible hepatic mass; this treated with hydrochloric acid and alcohol gives an intensely red flame. With soda on charcoal reacts like barite. Insoluble in acids. Diff. Characterized by form,' cleavage, high specific gravity, red coloration of the blowpipe flame. Does not effervesce with acids like the carbonates (e.g.,- strontianite); specific gravity lower than that of barite. Obs. Usually associated with limestone, or sandstone of various ages; occasionally with metalliferous ores, as with galena and sphalerite at Condorcet, France; at Rezbanya, Hungary; also in beds of gypsum, rock salt, as at Bex, Switzerland; Ischl, Austria; Liine- berg, Hannover; sometimes fills cavities in fossils, e.g., ammonites; with sulphur in some volcanic regions as at Girgenti, Sicily. From Yate, Gloucester, England. Specimens, finely crystallized, of a bluish tint, are found in limestone about Lake Huron, particularly on Drummond Island, also on Strontian Island, Put-in-Bay, Lake Erie, and at Kingston in Ontario, Canada; Chaumont Bay, Lake Ontario, Schoharie, and Lockport, N. Y. From near Syracuse, N. Y. A blue fibrous celestite occurs at Bell's Mills, Blair Co., Pa. From near Cumberland, Md. In Mineral Co., W. Va., a few miles south of Cum- berland, Md., in pyramidal blue crystals. At Tifflin, Ohio. In Texas, at Lampasas, large crystals. With colemanite at Death Valley, San Bernardino Co., Cal. In Canada, in crystalline masses at Kingston, Frontenac Co.; Lansdowne, Leeds Co.; in radiating fibrous masses in the Laurentian of Renfrew Co. Named from ccelestis, celestial, in allusion to the faint shades of blue often present. Use. Used in the preparation of strontium nitrate for fireworks; other salts used in the refining of sugar, ANGLESITE. Orthorhombic. Axes a : b : c = 07852 : 1 : 1*2894. 1007 1008 1009 d, 110 A 110 = 76 001 A 104 = 22 16*'. 19'. cd, 001 A 102 = 39 23'. co, 001 A Oil = 52 12'. n Some 1 times tabular 1 1 c (001) ; more often prismatic in habit, and in all the three axial directions, m (110), d (102), o (Oil), predominating in the ifferent cases; pyramidal of varied types. Also massive, granular to com- pact; stalactitic; nodular. di.1 C1 vJr age h - C tt ^\ m (1 , 1 Sl o isti ?, ct ' but interrupted. Fracture conchoi- & in tn y 6; H ' = ^t 8 - - G ;- = 6 ' 3 ~ 6 ' 39 - Luster WBUy adaman - tme : in some specimens, m others inclining to resinous and vitreous. Color white, tinged yellow, gray, green, and sometimes blue. Streak uncolored Transparent to opaque. Optically +. Ax. pi. || 6 (010) Bx T 100) B^persion strong, P <. 2V = 60-75. a = 1-877, > -1-882 L T= SULPHATES, CHROMATES, ETC. 629 Comp. Lead sulphate, PbSO 4 = Sulphur trioxide 26*4, lead oxide 73*6 = 100. Pyr., etc. B.B. decrepitates, fuses in the flame of a candle (F. = 1*5). On charcoal in O.F. fuses to a clear pearl, which on cooling becomes milk-white; in R.F. is reduced with effervescence to metallic lead. With soda on charcoal in R.F. gives metallic lead, and the soda is absorbed by the coal. Difficultly soluble in nitric acid. Diff. Characterized by high specific gravity; adamantine luster; cleavage; and by yielding lead B.B. Cerussite effervesces in nitric acid. Obs. A result of the decomposition of galena, and often found in its cavities; also surrounds a nucleus of galena in concentric layers. First found in England at Pary's mine in Anglesea; in Derbyshire and in Cumberland in crystals; at Leadhill, Scotland; in Ger- many at Claustal, in the Harz Mts.; near Siegen in Prussia; Schapbach and Badenweiler in Baden; in Hungary at Felsobanya and elsewhere; Nerchinsk, Siberia; and at Monte Poni, Sardinia; Granada and Andalusia, Spain; massive in Siberia; in Australia, whence it is exported to England. At Broken Hill, New South Wales. In the Sierra Mojada, Mexico, in immense quantities, mostly massive. In the United States in crystals at Wheatley's mine, Phenixville, Pa. ; in Missouri lead mines; in crystals of varied habit at the Mountain View mine, Carroll Co., Md. In Col. at various points, but less common than cerussite. At the Cerro Gordo mines of Cal. (argen- tiferous galena), with other lead minerals. In Ariz., in the mines of the Castle'Dome dis- trict, Yuma Co., and elsewhere. In fine crystals from Kingston and Wardner, Idaho; Eureka, Utah. Named from the locality, Anglesea, where it was first found. Use. An ore of lead. ANHYDRITE. Orthorhombic. Axes a : b : c = 0'8933 : 1 : 1'OOOS. mm'", 110 A 1TO = 83 33' ss', Oil A Oil = 90 3' rr\ 101 A TOl = 96 30' bo, 010 A 111 = 56 19' Twins: 1, tw. pi. d (012); 2, r (101) occasionally as tw. lamellae. Crystals not common, thick tabular, also prismatic || axis 6. Usually massive, cleavable, fibrous, lamellar, granular, and some- times impalpable. Cleavage : in the three pinac- oidal directions yielding rec- tangular fragments but with varying ease, thus, c (001) very perfect; b (010) also perfect; a (100) somewhat less so. Fracture uneven, sometimes splintery. Brittle. H. = 3-3' 5. 1010 1012 1010, 1011, 'Stassfurt 1012, Aussee Luster: c pearly, _ G. = 2-899-2-985. especially after heating in a closed tube; a somewhat greasy; 6 vitreous; in massive varieties, vitreous inclining to pearly. Color white, sometimes a grayish, bluish, or reddish tinge; also brick-red. Streak grayish white. Optically + . Ax. pi. || b (010). Bx J_ a (100). 2V = 42. a = 1-571. (3 = 1-576. 7 = 1'614. Var. 1. Ordinary, (a) Crystallized; crystals rare, more commonly massive and cleavable in its three rectangular directions. (6) Fibrous; either parallel, radiated or plumose, (c) Fine granular, (d) Scaly granular. Vulpinite is a scaly granular kind from Vulpino in Lombardy, Italy; it is cut and polished for ornamental purposes. A kind in contorted concretionary forms is the tripestone. 2. Pseudomorphous; in cubes after rock-salt. Comp. Anhydrous calcium sulphate, CaS0 4 = Sulphur trioxide, 58'8, lime 41-2 = 100. 630 DESCRIPTIVE MINERALOGY Pyr., etc. B.B. fuses at 3, coloring the flame reddish yellow, and yielding an enamel- like bead which reacts alkaline. On charcoal in R.F. reduced to a sulphide; with soda does not fuse to a clear globule, and is not absorbed by the coal like barite; is, however, decomposed, and yields a mass which blackens silver. Soluble in hydrochloric acid. Diff. Characterized by its cleavage in three rectangular directions (pseudo-cubic in aspect); harder than gypsum; does not effervesce with acids like the carbonates. Obs. Occurs in rocks of various ages, especially in limestone strata, and often the same that contain ordinary gypsum, and also very commonly in beds of rock-salt; at the salt mine near Hall in Tyrol, Austria; of Bex, Switzerland; at Aussee, upper Austria, crystal- lized and massive; Liineburg, Hannover, Germany; Kapnik in Hungary; Wieliczka in Poland; Ischl in Upper Austria; Berchtesgaden in Bavaria; Stassfurt, Germany, in fine crystals, embedded in kieserite; in cavities in lava at Santorin Island. " In the United States, at Meriden, Conn.; at Lockport, N. Y., fine blue, in geodes of black limestone, with calcite and gypsum; at West Paterson, N. J.; in limestone at Nash- ville, Tenn., etc. In the salt beds of central Kansas. In Nova Scotia it forms extensive beds. Anhydrite by absorption of moisture changes to gypsum. Extensive beds are some- times thus altered in part or throughout, as at Bex, in Switzerland, where, by digging down 60 to 100 ft., the unaltered anhydrite may be found. Sometimes specimens of anhydrite are altered between the folia or over the exterior. Bassanite. CaSO4. In white opaque crystals having form of gypsum but. composed of slender needles in parallel arrangement. These show parallel extinction and positive elongation. G. = 2 '69-2 76. Transformed into anhydrite at red heat. Found in blocks ejected from Vesuvius. Zinkosite. ZnSO 4 . Reported as occurring at a mine in the Sierra Almagrera, Spain. Hydrocyanite. CuSO 4 . Found at Vesuvius as a pale green to blue incrustation after the eruption of 1868. HOKUTOLITE. A mixture in variable proportions of lead and barium sulphates. A radioactive crystalline crust deposited by hot springs at Hokuto, Formosa. Millosevichite. Normal ferric and aluminium sulphate. As a violet incrustation, Alum Grotto, Island of Vulcano, Lipari Islands. CROCOITE. Monoclinic. Axes a : b : c = 0*9603 : 1 : 0*9159; = 77 33'. 1n1Q mm'", 110 A 1TO = 86 19'. ', 111 A 111 = 60 50'. ck, 001 A 101 = 49 32'. ct, 001 A 111 = 46 58'. Crystals usually prismatic, habit varied. Also imperfectly columnar and granular. Cleavage: m (110) rather distinct; c (001), a (100) less so. Fracture small conchoidal to uneven. Sectile. H. = 2*5-3. G. = 5*9-6*1. Luster adamantine to vitreous. Color various shades Of bright hyacinth-red. Streak orange-yellow. Translucent. p 4<. Comp. Lead chromate, PbCrO 4 = Chromium trioxide 3rl, lead protoxide 68*9 = 100. With _ and nea'r NiT.rfH,*' rTi ^ ^ tS V n cr y stals in I** veins ; ali at Mursinka Tn HuSLrv Molrf^ TT Ura ' Mt ?' ; m BraZl1 ' at Con S^^ do Campo; at Rezbanya infineCryStal8fr0m ^i^ SULPHATES, CHROMATES, ETC. 631 Bellite. Lead chromate containing arsenious oxide. Hexagonal. In aggregates of delicate tuffs. H. = 2' 5. G. = 5'5. Color crimson red, yellow to orange. Fusible. From Magnet, Tasmania. Sulphates with Chlorides, Carbonates, etc. In part hydrous LEADHILLITE. Monoclinic. Axes a : b : c = 17476 : 1 : 2'2154; = 89 48'. mm'", 110 A 110 = 120 27'. ex, 001 A 111 = 68 31'. cw, 001 A 101 = 51 36'. cm, 001 A 110 = 89 54'. Twins: tw. pi. m (110), analogous to aragonite. Crystals commonly tabu- lar || c (001). Cleavage: c (001) very perfect; a (100) in traces. Fracture conchoidal, scarcely observable. Rather sectile. H. = 2'5. G. = 6'26-6'44. Luster of c pearly, other parts resinous, somewhat adamantine. Color white, passing into yellow, green, or gray. Streak uncolored. Transparent to translucent. Optically -. = 1*93. Comp. Sulphato-carbonate of lead, 4PbO.S0 3 .2C0 2 .H 2 or PbSO 4 . 2PbCO 3 .Pb(OH) 2 = Sulphur trioxide 7'4, carbon dioxide 8'2, lead oxide 827, water 17 = 100. Pyr., etc. B.B. intumesces, fuses at 1'5, and turns yellow; but becomes white on cooling. Easily reduced on charcoal. With soda affords the reaction for sulphuric acid. Effervesces briskly in nitric acid, and leaves white lead sulphate undissolved. Yields water in the closed tube. Obs. Found at Leadhill, Scotland, with other ores of lead; in England at Red Gill, Cumberland, and at Matlock, Derbyshire. -From the Mala-Calzetta lead mine near Iglesias, Sardinia (maxite). Observed from Arizona, at the Schulz gold mine with wul- fenite, yanadinite, cerussite; partly altered to cerussite. From Tintic district, Utah; from Searchlight, Nev., from Granby, Mo. SUSANNITE. Regarded at one time as rhombohedral and dimorphous with leadhillite, but probably only a modification of that species. From the Susanna mine, Leadhill, in Scotland. Sulphohalite. 3Na 2 SO 4 NaCl.NaF. In pale greenish yellow octahedrons and dodeca- hedrons, n = T455. From Borax lake, and Searles lake, San Bernardino Co., Cal. Caracolite. Perhaps Pb(OH)Cl.Na 2 SO 4 . As a crystalline incrustation. Colorless. From Atacama, Chile. Kainite. MgSO 4 .KC1.3H 2 O. Usually granular massive and in crusts. Color white to dark flesh-red. Optically . = 1'509. From Stassfurt, Germany, and Wolfenbrittel, Brunswick; Kalusz, Galicia. Connellite. Probably CuSO 4 .2CuCl 2 .19Cu(OH) 2 .H 2 O. Crystals slender, hexagonal prisms. Color fine blue. Optically +. co = 1724. From Cornwall, England; from Eureka, Utah; Bisbee, Ariz. Footeite, originally described as a hydrous oxy chloride of copper from Bisbee, Ariz., is identical with connellite. Spangolite. A highly basic sulphate of aluminium and copper, Cu 6 AlClSOio.9H 2 p. In dark green hexagonal crystals (hemimorphic), tabular or short prismatic. Usually in very small crystals. From the neighborhood of Tombstone, Ariz.; Clifton and Bisbee, Ariz.; Tintic district; Utah; from Cornwall, England; Sardinia. Hanksite. 9Na 2 SO 4 .2Na2CO 3 .KCl. In hexagonal prisms, short prismatic to tabular; also in quartzoids. Color white to yellow. Optically. o> = T481. From Borax Lake, San Bernardino Co., Cal.; also from Death Valley, Inyo Co B. Acid and Basic Sulphates Misenite. Probably acid potassium sulphate, HKSO 4 . In silky fibers of a white color. From Cape Misene, near Naples, Italy. DESCRIPTIVE MINERALOGY BROCHANTITE. Orthorhombic. Axes a : b : c = 07739 : 1 : 0'4871. _ In groups of prismatic acicular crystals (mm"' 110 A 110 = 75 28') and drusy crusts; massive with reniform structure. Cleavage: 6(010) very perfect ; m (110) in traces. Fracture uneven. H.= 3'5-4. G. = 3'907. Luster vitreous; a little pearly on the cleavage-face 6(101). Color emerald-green, blackish green. Streak paler green. Trans- parent to translucent. Comp. A basic sulphate of. copper, CuSO 4 .3Cu(OH) 2 or 4CuO.S0 3 . 3H 2 O = Sulphur trioxide 17'7, cupric oxide 70'3, water 12'0 = 100. Pyr., etc. Yields water, and at a higher temperature sulphuric acid, in the closed tube, and becomes black. B.B. fuses, and on charcoal affords metallic copper. With soda gives the reaction for sulphuric acid. Obs. Occurs in the Ural Mts. ; the konigme (or komgite) was from Gumeshevsk, Ural Mts.; in England near Roughten Gill, in Cumberland and in Cornwall (in part waring- tonite); at Rezbanya, Hungary; in small beds at Krisuvig in Iceland (krisuvigite) ; in Mexico (brongnartine); Atacama and Tarapaca, Chile. In the United States, at Monarch mine, Chaffee Co., Col.; in Utah, at Frisco, in Tintic district, at the Mammoth mine; in Ch'fton-Morenci district, and Bisbee, Ariz. Lanarkite. Basic lead sulphate, Pb 2 SO 6 . In monoclinic crystals. Color greenish white, pale yellow or gray. From Leadhill, Scotland; Siberia; the Harz Mts., Germany. Dolerophanite. A basic cupric sulphate, Cu 2 SOs(?). In small brown monoclinic crystals. From Vesuvius (eruption of 1868). Caledonite. A basic sulphate of lead and copper, perhaps 2(Pb,Cu)O.SO 3 .H 2 O. Said at times to contain CO 2 . In small prismatic orthorhombic crystals. Color deep verdigris- green or bluish green. Index, 1'85. From Leadhill, Scotland; Red Gill, Cumberland, etc., England; Inyo Co., Cal.; Organ Mts., N. M.; Butte, Mon.; Atacama, Chile; New Caledonia. Linarite. A basic sulphate of lead and copper, (Pb,Cu)SO 4 .(Pb,Cu)(OH) 2 . In deep blue monoclinic crystals. Optically . = T838. From Leadhill, Scotland; Cumber- land, England; the Ural Mts.; Broken Hill, New South Wales; Sardinia. Also Inyo Co., Cal.; Eureka, Utah; Schiilz, Ariz.; Slocan, British Columbia. Antlerite. Perhaps CuSO 4 .2Cu(OH) 2 . In light green soft lumps. From the Antler mine, Mohave Co., Ariz. Stelznerite from Remolinos, Vallinar, Chile, is probably the same as antlerite. In prismatic crystals. G. = 3 '9. Alumian. Perhaps A1 2 O 3 .2SO 3 . White crystalline or massive. Sierra Almagrera, C. Normal Hydrous Sulphates Three well-characterized groups are included here. Two of these, the EPSOMITE GROUP and the MELANTERITE GROUP, have the same general formula, RS0 4 .7H 2 0, but in the first the crystallization is orthorhombic, in the second monoclinic. The species are best known from the artificial crystals of the laboratory; the native minerals are rarely crystallized. There is also the isometric ALUM GROUP, to which the same remark is applicable. Lecontite. (Na,NH 4 ,K) 2 SO4.2H 2 O. From bat guano in the cave of Las Piedras, near Comayagua, Central America. MIRABILITE. Glauber Salt. Monoclinic. Crystals like pyroxene in habit and angle. Usually in efflorescent crusts. Cleavage: a (100), perfect; e (001), b (010) in traces. H. = I' 5-2. G. = 1*481. Luster vitreous. Color white. Transparent to opaque. Taste cool, SULPHATES, CHROMATES, ETC. 633 then feebly saline and bitter. Optically . 2V = 76. a = 1-396 6 = T410. 7 = 1-419. Comp. Hydrous sodium sulphate, Na 2 SO 4 .10H 2 O = Sulphur trioxide 24'8, soda 19'3, water 55'9 = 100. Very Pyr., etc. In the closed tube much water; gives an intense yellow to the flame, soluble in water. Loses its water on exposure to dry air and falls to powder. Obs. Occurs at Ischl, Hallstadt, and Aussee in Upper Austria; also in Hungary, Switzerland, Italy; at the hot springs at Carlsbad, Bohemia, etc. Large quantities of this sodium sulphate are obtained from the waters of Great Salt Lake, Utah. Kieserite. MgSO 4 .H 2 O. Monoclinic. Usually massive, granular to compact. Color white, grayish, yellowish. Optically +. ft = 1'535. From Stassfurt, Germany; Hall- stadt, Austria; India. Szomolnokite. FeSO 4 .H 2 O. Monoclinic. Isomorphous with kieserite. In pyramids. G. = 3 '08. Color yellow or brown. Found with other iron sulphates from Szomolnok, Hungary. Apparently identical with ferropallidite from near Copiapo, Chile. Szmikite. MnSO 4 .H 2 O. Stalactitic. Whitish, reddish. From Felsobdnya, Hungary. GYPSUM. Monoclinic. mm' cd, ct, ce, vv', 1014 Axes a : b : c = 0'6899 110 A 110 = 68 30'. 001 A 101 = 28 17'. 001 A 101 = 33 8*'. 001 A 103 = 11 29'. Oil A Oil = 44 17|'. 0-4124; = _80 42'. ', 111 A 111 = 36 12'. nn', 111 A Til = 41 20'. ml, 110 A 111 = 49 9'. mn, 110 A 111 = 59 15'. 1015 1016 1017 1018 Crystals usually simple in habit, common form flattened || 6 (010) or pris- matic to acicular 1 1 c axis; again prismatic by extension o{l (111). Also lentic- ular by rounding of I (111) and e (103). The form e (103), whose faces are usually rough and convex, is nearly at right angles to the vertical axis (edge m (110)/w'" (110), hence the apparent hemimorphic character of the twin (Fig. 1018). Simple crystals often with warped as well as curved surfaces. Also foliated massive; lamellar-stellate; often granular massive; and some- times nearly impalpable. Twins: tw. pi. a (100), very common, often the familiar swallow-tail twins. Cleavage: 6(010) eminent, yielding easily thin polished folia; a (100), giving a surface with conchoidal fracture; n(lll), with a fibrous fracture || (101); a cleavage fragment has the rhombic form of Fig. 1019, with plane angles of 66 and 114. H. = l'5-2. G. = 2*3 14-2'328, when in pure crystals. Luster of b (010) pearly and shining, other faces sub vitreous. Massive varieties often glistening, sometimes dull earthy. Color usually white; some- times gray, flesh-red, honey-yellow, ocher-yellow, blue; impure varieties often black, brown, red, or reddish brown. Streak white. Transparent to opaque. 634 DESCRIPTIVE MINERALOGY Optically + . Ax. pi. || 6 (010), and Bx A c axis = 4 (cf. Fig. 1019). Dispersion p > v; also inclined strong. 30'. 2V = 58. < 1019 52i (at 9*4 C.), Bx r A Bxw = Q 1-520. |8 = 1 ? 523. 7 = 1-530. On the effect of heat on the optical properties, see p. 297. Var. 1. Crystallized, or Selenite; colorless, transpar- ent; in distinct crystals, or broad folia, often large. Us- ually flexible and yielding a fibrous fracture || t (101), but the variety from Montmartre near Paris, France, rather brittle. 2. Fibrous; coarse or fine. Called Satin spar, when fine-fibrous, with pearly opalescence. 3. Massive; Alabaster, a fine-grained variety, white or delicately shaded; earthy or rock-gypsum, a dull-colored rock, often impure with clay, calcium carbonate or silica. Also, in caves, curious curved forms, often grouped in rosettes and other shapes. Comp. Hydrous calcium sulphate, CaS0 4 .2H 2 O = Sulphur trioxide 46-6, lime 32-5, water 20'9 = 100. Pyr., etc. In the closed tube gives off water and becomes opaque. Fuses at 2 '5-3, coloring the flame reddish yellow. For other reactions see ANHYDRITE, p. 629. Ignited at a temperature not exceeding 260 C., it again combines with water when moistened, and becomes firmly solid. Soluble in hydrochloric acid, and also in 400 to 500 parts of water. Diff. Characterized by its softness in all varieties, and by cleavages in crystallized kinds; it does not effervesce with acids like calcite, nor gelatinize like the zeolites; harder than talc and yields much water in the closed tube. Obs. Gypsum often forms extensive beds in connection with various stratified rocks, especially limestones, and marlites or clay beds. It occurs occasionally in crystalline rocks. It is also a product of volcanoes, occurring about fumaroles, or where sulphur gases are escaping, being formed from the sulphuric acid generated, and the lime afforded by the decomposing lavas. It is also produced by the decomposition of pyrite when lime is present. Gypsum is also deposited on the evaporation of sea-water and brines, in which it exists in solution. Fine specimens are found in the salt mines of Bex in Switzerland; Hall in Tyrol, Austria; the sulphur mines of Sicily; in the clay of Shotover Hill, near Oxford, England; and large lenticular crystals at Montmartre, near Paris, France. A noted locality of alabaster occurs at Castelino, 35 m. from Leghorn, Italy, whence it is taken to Florence for the manufacture of vases, figures, etc. Occurs in extensive beds in several of the United States, and more particularly N. Y., Iowa, Mich., Okla., Texas, Ohio, and Ark., and is usually associated with salt springs, also with rock salt. Also on a large scale in Nova Scotia, etc. Handsome selenite and snowy gypsum occur in N. Y., near Lockport in limestone. In Md., large grouped crystals on the St. Mary's in clay. In Ohio, large transparent crystals have been found at Ellsworth and Canfield, Trumbull Co. In Tenn., selenite and alabaster in Davidson Co. In Ky., in Mammoth Cave, it has the forms of rosettes, or flowers, vines, and shrubbery. Also common in isolated crystals and masses, in the Cre- taceous clays in the western United States. In enormous crystals, several feet in length, in Wayne Co., Utah. In Nova Scotia, in Sussex, Kings Co., large single and grouped crystals, which mostly contain much symmetrically disseminated sand. Named from yy^os, the Greek for the mineral, but more especially for the calcined mineral. The derivation' ordinarily suggested, from 777, earth, and tyeiv, to cook, corre- sponds with this, the most common use of the word among the Greeks. Burnt gypsum is called Plaster-of-Paris, because the Montmartre gypsum quarries, near Pans, are, and have long been, famous for affording it. Use. In the manufacture of plaster-of-Paris used for molds and casts and as "staff " in erection of temporary buildings; in making adamant plaster for interior use; as land plaster for fertilizer; as alabaster for ornamental purposes. Hesite. (Mn,Zn,Fe)SO 4 .4H 2 O. In loosely adherent aggregates. Color clear green, from Colorado. SULPHATES, CHROMATES, ETC. 635 Epsomite Group. RS0 4 .7H 2 0. Orthorhombic Epsomite MgS0 4 .7H 2 O a : b : c = 0-9902 : 1 : 0-5709 (Fe,Mg)S0 4 .7H 2 Goslarite ZnSO 4 .7H 2 O 0-9807 : 1 : 0-5631 Ferro-goslarite (Zn,Fe)SO 4 .7H 2 O Morenosite NiSO 4 .7H 2 O 0-9816 : 1 : 0-5655 EPSOMITE. Epsom Salt. Orthorhombic. Usually in botryoidal masses and delicately fibrous crusts. Cleavage: 6 (010) very perfect. Fracture conchoidal. H. = 2-0-2-5. G. = = 1*751. Luster vitreous to earthy. Streak and color white. Transparent to translucent. Taste bitter and saline. Optically . 2V = 52. a = 1-433. ft = 1-455. T = 1-461. Comp. Hydrous magnesium sulphate, MgSO 4 .7H 2 O = Sulphur triox- ide 32-5, magnesia 16-3, water 51-2 = 100. Obs. Common in mineral waters, and as a delicate fibrous or capillary efflorescence on rocks, in the galleries of mines, and elsewhere. In the former state it exists at Epsom, England, and at Sedlitz and Saidschitz (or Saidschiitz) in Bohemia. At Idria in Carniola, Austria, it occurs in silky fibers, and is hence called hair salt by the workmen. Also ob- tained at the gypsum quarries of Montmartre, near Paris. Also found at Vesuvius, at the eruptions of 1850 and 1855. The floors of the limestone caves of Kentucky, Tennessee, and Indiana, are in many instances covered with epsomite, in minute crystals, mingled with the earth. In the Mammoth Cave, Ky., it adheres to the roof in loose masses like snowballs. From Laramie Basin, Wy.; near Leona Heights, Alameda Co., Cal.; Cripple Creek, Col. Goslarite. ZnSO 4 .7H 2 O. Commonly massive. Color white, reddish, yellowish. Optically . = 1'480. Formed by the decomposition of sphalerite, and found in the passages of mines, as at the Rammelsberg mine near Goslar, in the Harz Mts., Germany, etc. In Mon. at the Gagnon mine, Butte. Ferro-goslarite (4*9 p. c. FeSO 4 ) occurs with sphalerite at Webb City, Jasper Co., Mo. Cuprogoslarite (13 '4 p. c. CuSO-j) occurs as a light greenish blue incrustation on the wall of an abandoned zinc mine at Galena, Kan. Morenosite. NiSO4.7H 2 O. In acicular crystals; also fibrous, as an efflorescence. Color apple-green to greenish white. = 1 '489. A result of the alteration of nickel ores, as near Cape Hortegal, in Galicia; Riechelsdorf, in Hesse, Germany; Zermatt, Switzerland, containing magnesium. Melanterite Group. RS0 4 .7H 2 O. Monoclinic a : b : c Melanterite FeSO 4 .7H 2 1 -1828 : 1 : 1 -5427 ft = 75 44' Luckite (Fe,Mn)SO 4 .7H 2 O Mallardite MnSO 4 .7H 2 O Pisanite (Fe,Cu)SO 4 .7H 2 O 1-1609 : 1 : 1-5110 74 38' Bieberite CoSO 4 .7H 2 1-1815 : 1 : 1-5325 75 20' Cupromagnesite (Cu,Mg)SO 4 .7H 2 O Boothite CuSO 4 .7H 2 O 1-1622 : 1 ; 1-500 74 24' Chalcanthite CuSO 4 .5H 2 O Triclinic a : b : c = 0-5656 : 1 : 0-5507; a = 82 21', ft = 73 11', 7 = 77 37'. The species here included are the ordinary vitriols. They are identical in general formula with the species of the Epsomite group, and are regarded as the same compound essentially under oblique crystallization. The copper sulphate, chalcanthite, diverges from the others in crystallization, and con- tains but 5 molecules of water. 636 DESCRIPTIVE MINERALOGY MELANTERITE. Copperas. Monoclinic. Usually capillary, fibrous, stalactitic, and concretionary; also massive, pulverulent. Cleavage: c (001) perfect; m (110) less so. Frao- turernchoidal. Brittle. H. = 2. G. = 1-89-1-90. Luster vitreous. Color, various shades of -green, passing into white; becoming yellowish on exposure. Streak uncolored. Subtransparent to translucent. Taste sweetish astrin- gent, and metallic. Optically + . 2V = 86. a = 1-471. ft = 1-478. 7 = 1 *486 Comp Hydrous ferrous sulphate, FeSO 4 .7H 2 O = Sulphur trioxide 28-8, iron protoxide 25-9, water 45*3 = 100. Manganese and magnesium sometimes replace part of the iron. Obs Proceeds from the decomposition of pyrite or marcasite; thus near Goslar in the Harz Mts Germany; Bodenmais in Bavaria; Falun, Sweden, and e sewhere. Usually accompanies pyrite in the United States, as an efflorescence. In crystals from near Leona Heights, Alameda Co., Cal. Luckite (1'9 p. c. MnO) is from the "Lucky Boy mine, Butterfield Canon, Utah. Mallardite. MnSO 4 .7H 2 O. Fibrous, massive; colorless. From the mine Lucky Boy," south of Salt Lake, Utah. Pisanite. (Fe,Cu)SO 4 .7H 2 O. CuO 10 to 15 p. c. In concretionary and stalactitic forms. Color blue. From Turkey. From Bingham, Utah; Ducktown, Tenn. near Leona Heights, Cal. SALVADORITE. A copper-iron vitriol near pisanite. From the Salvador mine Quetena, Chile. Bieberite. CoSO 4 .7H 2 O. Usually in stalactites and crusts. Color flesh- and rose-red. From Bieber, in Hesse, Germany, etc. Boothite. CuSO 4 .7H 2 O. Usually massive. H. = 2-2'5. G. = 1'94. Color blue, paler than chalcanthite. Found at Alma pyrite mine, near Leona Heights, Alameda Co., and at a copper mine near Campo Seco, Calaveras Co., Cal. CUPROMAGNESITE. (Cu,Mg)SO 4 .7H 2 O. From Vesuvius. CHALCANTHITE. Blue Vitriol. Triclinic. Crystals commonly flattened || p (111). Occurs also massive, stalactitic, reniform,_sometimes with fibrous structure. Cleavage: M (110), m (110), p (111) imperfect. Fracture conchoidal. Brittle. H. = 2-5. G. = 212-2 -30. Luster vitreous. Color Berlin-blue to sky-blue, of different shades ; sometimes a little greenish. Streak uncolored. Subtransparent to translucent. Taste metallic and nauseous. Optically . 2V = 56. a = 1-516. ft = 1-539. 7 = 1'546. Comp. Hydrous cupric sulphate, CuSO 4 .5H 2 = Sulphur trioxide 32-1, cupric oxide 31-8, water 361 = 100. Pyr., etc. In the closed tube yields water, and at a higher temperature sulphur tri- oxide. B.B. with soda on charcoal yields metallic copper. With the fluxes reacts for copper. Soluble in water; a drop of the solution placed on a surface of iron coats it with metallic copper. Obs. Found in waters issuing from mines and in connection with rocks containing chalcopyrite, by the alteration of which it is formed; thus at the Rammelsberg mine near Goslar in the Harz Mts., Germany; Falun in Sweden; Parys mine, Anglesea, England; at various mines in County Wicklow, Ireland; Rio Tinto mine, Spain; Zajecar, Servia. From the Hiwassee copper mine, also in large quantities at other mines, in Polk Co., Tenn. In Ariz., near Clifton, Graham Co., and Jerome, Yavapai Co.; in Cal. near Leona Heights, Alameda Co.; from Ely and Reno, Nev. Syngenite. Kaluzite. CaSO 4 .K 2 SO 4 .H 2 O. In prismatic (monoclinic) crystals. Color- less or milky-white. = 1 '517. From Kalusz, Galicia. SULPHATES. CHROMATES, ETC. 637 Loweite. MgSO 4 .Na 2 SO 4 .2|H 2 O. Tetragonal. Massive, cleavable. Color pale yel- low. Index, 1'49. From Ischl, Austria. Blodite. MgSO4.Na 2 SO4.4H 2 O. Crystals short prismatic, monoclinic; also massive granular or compact. Colorless to greenish, yellowish, red. Optically . ft = 1/488. From the salt mines of Ischl and at Hallstadt (simonyite), Austria; at Stassfurt, Germany; the salt lakes of Astrakhan (astrakanite), Asia; India; Chile, etc. From Soda Lake, San Luis Obispo Co., Cal Leonite. MgSO 4 .K 2 SO 4 .4H 2 O. In monoclinic crystals from Westeregeln and Leo- poldshall, Germany. = 1-487. Boussingaultite. (NH 4 ) 2 SO 4 .MgSO 4 .6H 2 O. From the boric acid lagoons, Tuscany. Italy. Index, 1-474. Picromerite. MgSO 4 .K 2 SO 4 .6H 2 .O. As a white crystalline incrustation. Monoclinic. Optically +. /3 = 1'463. From Vesuvius with cyanochroite, an isomorphous species in which copper replaces the magnesium. Also at Stassfurt (schoenite) and Aschersleben, Germany; Galusz in East Galicia. Polyhalite. 2CaSO 4 .MgSO 4 .K 2 SO 4 .2H 2 O. Triclinic. Usually in compact fibrous or lamellar masses. Color flesh- or brick-red. Optically . ft = 1'562. Occurs at the mines of Ischl, Hallstadt, etc., in Austria; in Germany at Berchtesgaden, Bavaria; Stassfurt, Prussia. Hexahydrite. MgSO 4 .6H 2 O. Columnar to fibrous structure. Cleavage prismatic. G. = 1"76. Color, white with light green tone. Pearly luster. Opaque. Salty, bitter taste. B.B. exfoliates and yields water but does not fuse. Found in Lillooet district, British Columbia. Alum Group. Isometric RA1(SO 4 ) 2 .12H 2 O or R 2 SO 4 .A1 2 (SO 4 ) 3 .24H 2 O. Kalinite Potash Alum KA1(SO 4 ) 2 .12H 2 Tschermigite Ammonia Alum (NH 4 )A1(S0 4 ) 2 .12H 2 O Mendozite Soda Alum NaAl(SO 4 ) 2 .12H 2 O The ALUMS proper are isometric in crystallization and, chemically, are hydrous sulphates of aluminium with an alkali metal and 12 (i.e., if the for- mula is doubled, 24) molecules of water. The species listed above occur very sparingly in nature, and are best known in artificial form in the laboratory. The HALOTRICHITES are oblique in crystallization, very commonly fibrous in structure, and are hydrous sulphates of aluminium with magnesium, man- ganese, etc. ; the amount of water in some cases is given as 22 molecules, and in others 24, but it is not always easy to decide between the two. Here belong: Pickeringit. Magnesia Alum. MgSO 4 .Al 2 (SO 4 )3.22H 2 O. In long fibrous masses; and in efflorescences. Halotrichite. Iron Alum. FeSO 4 .Al 2 (SO 4 )3.24H 2 O. In yellowish silky fibrous forms. Index, 1.48. Bilinite. FeSO 4 .Fe 2 (SO 4 ) 3 .24H 2 O. Radiating fibrous. Color white to yellow. From Schwaz, near Bilin, Bohemia. Apjohnite. Manganese Alum. MnSO 4 .Al 2 (SO 4 ) 3 .24H 2 O. Bushmanite contains MgO. In fibrous or asbestiform masses; also as crusts and efflorescences. Dietrichite. (Zn,Fe,Mn)SO 4 .Al 2 (SO 4 ) 3 .22H 2 O. Coquimbite. Fe 2 (SO 4 ) 3 .9H 2 O. Rhombohedral. Granular massive. Color white, yel- lowish, brownish. Optically +. = 1-550. From the Tierra Amarilla near Copiapo, Chile (not from Coquimbo). Quenstedtite. Fe 2 (SO 4 ) 3 .10H 2 O. In reddish tabular crystals. With coquimbite, Chile. 638 DESCRIPTIVE MINERALOGY Ihleite. Fe 2 (SO 4 ) 3 .12H 2 O? An orange yellow efflorescence on graphite. From Mu- grau, Bohemia. Perhaps identical with copiapite. Alunogen. A1 2 (SO 4 ) 3 .18H 2 O. Usually in delicate fibrous masses or crusts; massive. Color white, or tinged with yellow or red. From near Bilm, Bohemia; Bodenmais, Ger- many; Pusterthal, Tyrol, Austria; from Vesuvius; Elba. Fjom Cripple Creek, Doughty Springs, and Alum Gulch, Col. DOUGHTYITE. A hydrated aluminium sulphate deposited by the alkaline waters of the Doughty Springs in Col. Krohnkite. CuSO 4 .Na 2 SO 4 .2H 2 O. Monoclinic crystalline; massive, coarsely fibrous. Color azure-blue. Optically . /3 = 1'577. From Calama, Atacama, Chuquicamata, Autofagasta, and Collahurasi, Tarapaca, Chile. Natrochalcite. Cu 4 (OH) 2 (SO 4 )2.Na 2 SO4.2H 2 O. Monoclinic. Habit pyramidal. Per- fect basal cleavage. H. = 4 -5. G. = 2 '3. Color bright emerald-green. = 1-65. Found at Chuquicamata, Autofagasta, Chile. PHILLIPITE. Perhaps CuSO 4 .Fe 2 (SO 4 ) 3 .nH 2 O. In blue fibrous masses. Found at the copper mines in the Cordilleras of Condes, province of Santiago, Chile. Ferronatrite. 3Na 2 SO 4 .Fe 2 (SO 4 ) 3 .6H 2 O. Rhombohedral. Rarely in acicular crystals; usually in spherical forms. Color greenish or gray to white. Optically + eo = 1-558. From Sierra Gorda near Caracoles, Chile. Romerite. FeSO 4 .Fe 2 (SO 4 ) 3 .14H 2 O. In tabular triclinic crystals; granular, massive. Color chesnut-brown. From Goslar in the Harz Mts., Germany; Persia; Chile. Basic Hydrous Sulphates Langite. Near brochantite. CuSO 4 .3Cu(OH) 2 .H 2 O. Usually in fibre-lamellar, con- cretionary crusts. Color blue to greenish blue. From Cornwall. Herrengrundite. 2(CuOH) 2 SO 4 .Cu(OH) 2 .3H 2 O with one-fifth of the copper replaced by calcium. In thin tabular monoclinic crystals; usually in spherical groups. Color emerald-green, bluish green. From Herrengrund, Hungary. Vernadskite. 3CuSO 4 .Cu(OH) 2 .4H 2 O. In aggregates of minute crystals. H. = 3'5. Occurs as an alteration of dolerophanite at Vesuvius. Kamarezite. A hydrous basic copper sulphate from Laurion, Greece. Cyanotrichite. Lettsomite. Perhaps 4CuO.Al 2 O 3 .SO 3 .8H 2 O. In velvet-like druses; in spherical forms. Color bright blue. From Moldawa in the Banat, Hungary; Cap Ga- ronne, France. In Utah and Arizona. Serpierite. A basic sulphate of copper and zinc. In minute crystals, tabular, in tufts. Color bluish green. From Laurion, Greece. Beaverite. CuO.PbO.Fe 2 O 3 .2SO 3 .4H 2 O. Hexagonal ? In microscopic plates Color canary-yellow. Refractive index > 174. From Horn Silver mine, Frisco, Beaver Co Utah. Vegasite. PbO.3Fe 2 O 3 .3SO 3 .6H 2 O. Hexagonal. In microscopic fibrous crystals some- times showing hexagonal plates. Optically - . Indices, 1 75-1 '82. Found in Yellow Pine district, near Las Vegas, Nev. COPIAPITE. Monoclinic. Usually in loose aggregations of crystalline scales, or granular massive; mcrusting. Cleavage: b (010).. H. = 2-5. G. = 2-103. Luster pearly. Color sul- phur-yellow, citron-yellow. Translucent. Optically -. a = 1-527. =' l'O4/. y = 1'572. Comp.A basic ferric sulphate, perhaps 2Fe 2 O 3 .5SO 3 .18H 2 O = Sul- phur tnoxide 38 -3, iron sesquioxide 30-6, water 31-1 = 100. arSe^nrl fnl^l Wh / Ch !l? S been . 8 3 mew ^t vaguely applied. It seems to belong in t here and in part also to other related species. Janosite is identical with copiapit?. SULPHATES, CHROMATES, ETC. 639 Pyr., etc. Yields water, and at a higher temperature sulphuric acid. On charcoal becomes magnetic, and with soda affords the reaction for sulphuric acid. With the fluxes reacts for iron. Soluble in water, and decomposed by boiling water. Obs. The original copiapite was from Copiapo, Chile. Also from Elba and from near Leona Heights, Alameda Co., Cal. Other hydrated ferric sulphates: Castanite.- Fe 2 O 3 .2SO 3 .8H 2 O. Color chestnut-brown. From Sierra Gorda, Chile. Utahite. 3Fe 2 O3.2SO 3 .7H 2 O. In aggregates of fine scales. Color orange-yellow From the Tintic district, Utah; Guanaco, ' Taltal, Chile. Perhaps identical with carpho- siderite. Amarantite. Fe 2 O 3 .2SO 3 .7H 2 O. Triclinic. Usually in columnar or bladed masses, also radiated. Color amaranth-red. From near Caracoles, Chile. Hohmannite is the same partially altered; this is probably also true of paposite. Fibroferrite. Fe^Os^SO-j-lOHaO. Orthorhombic. In delicately fibrous aggregates. Color pale yellow, nearly white. From the Tierra Amarilla near Copiapo, Chile. Raimondite. 2Fe 2 O 3 .3SO 3 .7H 2 O. In thin six-sided tables. Color between honey- arid ocher-yellow. From the tin mines of Ehrenfriedersdorf ; mines of Bolivia. Perhaps iden- tical with carphosiderite. Carphosiderite. 3Fe 2 O 3 .4SO 3 .7H 2 O. In reniform masses, and incrustations; also in micaceous lamellae. Color straw-yellow. From Greenland. Utahite, apatelite, raimon- dite and cyprusite are probably identical with carphosiderite. Planoferrite. Fe 2 O 3 .SO 3 .15H 2 O. Orthorhombic? In rhombic or hexagonal plates. Yellowish green to brown. From near Morro Moreno, Autofagasta, Chile. Glockerite. 2Fe 2 O 3 .SO 3 .6H 2 O. Massive, sparry or earthy; stalactitic. Color brown to ocher-yellow to pitch-black; dull green. From Goslar, Harz Mts., Germany. Knoxvillite. A hydrous basic sulphate of chromium, ferric iron, and aluminium. In rhombic plates. Color greenish yellow. From the Redington mercury mine, Knoxville, Cal. REDINGTONITE. A hydrous chromium sulphate, in finely fibrous masses of a pale purple color. From Redington mercury mine, Knoxville, Cal. Cyprusite. Perhaps 7Fe 2 O 3 .Al 2 O 3 .10SO 3 .14H 2 O. An aggregation of microscopic crystals. Color yellowish. From the island of Cyprus. Perhaps identical with carpho- siderite. Aluminite ( Websterite) . A1 2 O 3 .SO 3 .9H 2 O. Usually in white earthy reniform masses, compact. Index, 1'48. From near Halle, Germany, in clay; also at Newhaven, Sussex, England, and elsewhere. Paraluminite. Near aluminite, but supposed to be 2A1 2 O 3 .SO 3 .15H 2 O. Felsobanyite. 2A1 2 O 3 .SO 3 .10H 2 O. Massive; in scaly concretions. Color snow-white. From near Felsobanya, Hungary. Botryogen. Perhaps MgO.FeO.Fe 2 O 3 .4SO 3 .18H 2 O. Monoclinic. Usually in reniform and botryoidal shapes. Color deep hyacinth-red, ocher-yellow. 13 = 1*548. From Falun, Sweden; also from Persia; from Lake and Napa Cos., Cal. Sideronatrite. 2Na 2 O.Fe 2 O 3 .4SO 3 .7H 2 O. Fibrous, massive. Color yellow. From the province of Tarapaca, Chile. Also on the Urus plateau, near Sarakaya, on the island, Cheleken, in the Caspian Sea (urusite). Voltaite. Perhaps 3(K 2 ,Fe)O.2(Al,Fe) 2 O 3 .6SO 3 .9H 2 O. In octahedrons, etc. Color dull oil-green to brown or black. From the solfatara near Naples; Schmolnitz, Hungary; also Persia. Metavoltine. Perhaps 5(K 2 ,Na 2 ,Fe)O.3Fe 2 O 3 .12SO 3 .18H 2 O. In aggregates of minute yellow scales. Occurs with voltaite in Persia. From Vesuvius; found in fumeroles on islands of Milo and Vulcano; from Miseno, Italy. ALUNITE. Alumstone. Rhombohedral. Axis c = 1-2520. In rhombohedrons, resembling cubes (rr' 1011 A 1101 = 90 50'). Also massive, having a fibrous, granular, or impalpable texture. 640 DESCRIPTIVE MINERALOGY Cleavage: c (0001) distinct; r (lOll) in traces. Fracture flat conchoidal, uneven; of massive varieties splintery; and sometimes earthy. Brittle. H. = 3-5-4. G. = 2-58-2:752. Luster of r vitreous, basal plane somewhat pearly. Color white, sometimes grayish or reddish. Streak white. Transparent to subtranslucent. Optically + . co = 1-572. e = 1'592. Comp. Basic hydrous sulphate of aluminium and potassium, K 2 A1 6 (OH)i 2 (SO 4 ) 4 = Sulphur trioxide 38'6, alumina 37'0, potash 11-4, water 13 -0 = 100. Sometimes contains considerable soda, natroalunite. Pyr., etc. B.B. decrepitates, and is infusible. In the closed tube yields water, some- times also ammonium sulphate, and at a higher temperature sulphurous and sulphuric oxides. Heated with cobalt solution affords a fine blue color. With soda and charcoal infusible, but yields a hepatic mass. Soluble in sulphuric acid. Obs. Forms seams in trachytic and allied rocks, where it has been formed as a result of the alteration of the rock by means of sulphurous vapors; as at Tolfa, near Civitavecchia, Italy; in Hungary; on Milo, Grecian Archipelago; at Mt. Dore, France; Kinkwaseki, Formosa. In the United States, associated with diaspore, in rhombohedral crystals, tabu- lar through the presence of c (0001) at the Rosita Hills, Custer Co., and from Red Mt., Col.; Marysvale, Utah; Goldfield and near Sulphur, Nev. JAROSITE. _Rhombohedral. Axis c = 1-2492; rr' lOll A TlOl = 90 45', cr 0001 A 1011 = 55 16'. Often in druses of minute crystals; also fibrous, granular massive; in nodules, or as an incrustation. Cleavage: c (0001) distinct. Fracture uneven. Brittle. H. = 2-5-3-5. G. = 3-15-3-26. Luster vitreous to subadamantine : brilliant, also dull. Color ocher-yellow, yellowish brown, clove-brown. Streak yellow, shining. Optically +. co = 1-74. e = 177. Comp. K 2 Fe 6 (OH)i 2 (SO 4 ) 4 = Sulphur trioxide 31*9, iron sesquixoide 47-9, potash 9-4, water 10'8 = 100. Obs. The original Gelbeisenerz was from Luschitz, between Kolosoruk and Bilin, Bohemia, in brown coal; and later from Modum, Norway, in alum slate. The jarosite was from Barranco Jaroso, in the Sierra Almagrera, Spain; Schlaggenwald, Bohemia; Elba; Chocaya, Potosi, Bolivia. In the United States on quartz in the Vulture mine, Ariz.; in Chaffee County, Col.; Tintic district, Utah; Lawrence Co., S. D.; Dona Ana Co. N. M Bisbee, Ariz.; Brewster Co., Texas. ^ Natrojarosite. Na*Fe 6 (OH) 12 (SO 4 ) 4 . Rhombohedral. In minute tabular crvstals. Color yellow-brown. From Soda Springs Valley, Esmeralda Co., Nev. Plumbojarosite. PbFe 6 (OH) 12 (SO 4 ) 4 . Rhombohedral. In minute tabular crystals. Color dark brown. From Cook's Peak, N. M., and in Beaver County, Utah. Palmierite. 3(K,Na) 2 SO 4 .4PbSO 4 ? In microscopic plates, often hexagonal in outline. Colorless. Fusible. Found in fumerole deposits at Vesuvius. K 2 0.3A1 2 3 .4SO 9H 2 0. In rounded masses, similar to compact N ^ S 4 - Al2 ( S 4 ) 3 - 5A1 (OH) 3 .H 2 0. Compact. White. From Almeria, From^m^ 6 * ? er i hapS 6 ? a 9- A1 ^3.3S0 3 .33H 2 0. In minute colorless acicular crystals. From limestone-inclusions m lava, near Mayen, Rhenish Prussia; Tombstone, An/ of TUNGSTATES, MOLYBDATES 641 canary-yellow. H. =2. G. > 3 '3. Indices, 1 '57-1 -61. Infusible. Readily soluble in acids. From Gilpin Co., Col. Uranopilite. Perhaps CaUgSaOai^SH^O. In velvety incrustations; yellow. From Johanngeorgenstadt, Germany. Zippeite, voglianite, uraconite are uncertain uranium sulphates, from Joachimstal, Bohemia. Minasragrite. An acid hydrous vanadyl sulphate (V 2 O2)H 2 (SO4).15HjO. Probably monoclinic. In granular aggregates, small mammillary masses, or in spherulites. Two cleavages. Color blue. Indices 1-5 1-1 '54. Strongly pleochroic, deep blue to colorless. Easily fusible. Soluble in cold water. Found as an efflorescence on patronite from Minas- ragra, Peru. Rhomboclase. A hydrated acid ferric sulphate. Fe 2 O 3 .4SO3.9H 2 O. In rhombic plates. Basal cleavage. Colorless. Occurs at Szomolnok, Hungary. Tellurates; also Tellurites, Selenites In earthy incrustations; yellowish to white. From Montanite. Highland, Mon., with tetradymite. Emmonsite. Probably a hydrated ferric tellurite. In thin yellow-green scales. From near Tombstone, Ariz. Durdenite. Hydrous ferric tellurite, Fe2(TeOs)3.4H2O. In small mammillary forms; greenish yellow. Honduras. Chalcomenite. Hydrous cupric selenite, CuSeO 3 .2H 2 O. In small blue monoclinic crystals. From the Cerro de Cacheuta, Argentina, with silver, copper selenides. MOLYBDOMENITE is lead selenite and COBALTOMENITE probably cobalt selenite, from the same locality as chalcomenite. Oxygen Salts 7. TUNGSTATES, MOLYBDATES The monoclinic Wolframite Group and the tetragonal Scheelite Group are included here. Wolframite Group Wolframite (Fe,Mn)WO 4 a : b : c = 0-8300 : 1 : 0-8678 Hiibnerite MnWO 4 0-8362 : 1 : 0-8668 89 89 22' WOLFRAMITE. Monoclimc. Axes a : mm'", 110 A 110 = 79 23'. at, 100 A 102 = 61 54'. c = 0-8300 : 1 : 0-8678; ay', 100 A 102 = 62 54' ff', Oil A Oil = 81 54'. 89 22' 1020 Twins: (1) tw. axis c with a (100) as comp.-face; (2) tw. pi. k (023), Fig. 449, p. 171. Crystals commonly tabular || a (100); also prismatic. Faces in prismatic zone vertically striated. Often bladed, lamellar, coarse divergent columnar, granular. Cleavage: b (010) very perfect; also parting || a (100), and || t (102). Fracture uneven. Brittle. H. = 5-5-5. G. = 7-2-7-5. Luster submetallic. Color dark grayish or brownish black. Streak nearly black. Opaque, magnetic. = 1*93. Sometimes weakly 642 DESCRIPTIVE MINERALOGY Comp. Tungstate of iron and manganese (Fe,Mn)W0 4 . Fe : Mn = chiefly 4 : 1 (FeO 18-9, MnO 47 p. c.) and 2 : 3 (FeO 9'5, MnO 14-0). Pyr., etc. Fuses B.B. easily (F. = 2-5-3) to a globule, which has a crystalline surface and is magnetic. With salt of phosphorus gives a clear reddish yellow glass while hot which is paler on cooling; in R.F. becomes dark red; on charcoal with tin, if not too satu- rated, the bead assumes on cooling a green color, which continued treatment in R.F. changes to reddish yellow. With soda and niter on platinum foil fuses to a bluish green manganate. Decomposed by aqua regia with separation of tungstic acid as a yellow powder. Suffi- ciently decomposed by concentrated sulphuric acid, or even hydrochloric acid, to give a colorless solution, which, treated with metallic zinc, becomes intensely blue, but soon bleaches on dilution. Obs. Wolframite is often associated with tin ores; also in quartz, with native bismuth, scheelite, pyrite, galena, sphalerite, etc. In Bohemia in fine crystals at Schlackenwald, Zinnwald, Bohemia; in Germany at Schneeberg, Freiberg, Altenberg, Neudorf; at Ner- chinsk, Siberia; Chanteloup, near Limoges, France; near Redruth and elsewhere in Corn- wall with tin ores. From Sardinia; Greenland; Central Provinces, India. In South America, at Oruro in Bolivia. With tin stone at various points in New South Wales. In the United States at Lane's mine, Monroe, Conn.; Flowe mine, Mecklenburg Co., N. C., with scheelite; in Mo., near Mine la Motte; Laurence Co., S. D.; Boulder Co.] Col.; Ariz. Use. An ore of tungsten. Hiibnerite. Near wolframite, but containing 20 to 25 p. c. MnO. Usually in bladed forms, rarely in distinct terminated crystals. Color brownish red to hair-brown to nearly black. Streak yellowish brown, greenish gray. Often translucent, ft = 2 '24. Mammoth district, Nev.; Ouray County, Col., and near Silyerton, San Juan Co.; Black Hills, S. D.; Dragoon, Ariz. Also in Peru, and in rhodochrosite at Adervielle in the Pyrenees. Scheelite Cuprotungstite Cuproscheelite Powellite Stolzite Wulfenite Scheelite Group. Tetragonal-pyramidal CaW0 4 pp' (111 A 111) = 79 55J' c = 1-5360 CuWO 4 (Ca,Cu)W0 4 Ca(Mo,W)0 4 80 1' c = 1-5445 PbW0 4 80 15' c = T5667 PbMo0 4 80 22' c = 1-5771 The SCHEELITE GROUP includes the tungstates and molybdates of calcium and lead; also copper. In crystallization they belong to the Pyramidal class of the Tetragonal System. Wulfenite is probably hemimorphic. SCHEELITE. Tetragonal-pyramidal. Axis c = 1-5356. ee', 101 A Oil = 72 40*'. pp', 111 A ill = 79 55*' cp, 001 A 111 = 65 16|'. ce, 001 A 101 = 56 56'. 1021 1022 1023 1024 Forms: (102), e (101). ft (113), p (111), k (515), ft (313), ,,(131) TUNGSTATES, MOLYBDATES 643 Twins: (1) tw. pi. a (100), both contact- and penetration-twins (Fig. 416, p. 167). Habit octahedral, also tabular. Symmetry shown by faces k, h, s (Fig. 1023). Also reniform with columnar structure; massive granular. Cleavage: p (111) most distinct; e (101) interrupted. Fracture uneven. Brittle. H. = 4-5-5. G. = 5-9-6-1. Luster vitreous, inclining to adaman- tine. Color white, yellowish white, pale yellow, brownish, greenish, reddish. Streak white. Transparent to translucent. Optically -f. Indices: w = 1-918. e = 1-934. Comp. Calcium tungstate, CaWO 4 = Tungsten trioxide 80-6, lime 19-4 = 100. Molybdenum is usually present (to 8 p. c.). Copper may replace calcium, see cupro- scheelite. Pyr., etc. B.B. in the forceps fuses at 5 to a semi-transparent glass. Soluble with borax to a transparent glass, which afterward becomes opaque and crystalline. With salt of phosphorus forms a glass, colorless in outer flame, in inner green when hot, and fine blue when cold; varieties containing iron require to be treated on charcoal with tin before the blue color appears. In hydrochloric or nitric acid decomposed, leaving a yellow powder soluble in ammonia. The hydrochloric acid solution treated with tin and boiled assumes a blue color, later changing to brown. Obs. Scheelite is usually associated with crystalline rocks, and is commonly found in connection with cassiterite, topaz, fluorite, apatite, molybdenite, or wolframite, in quartz; also associated with gold. Thus at Schlackenwald and Zinnwald, Bohemia; Altenberg, Saxony; Riesengrund in the Riesengebirge, Germany; the Knappenwand in the Unter- sulzbachtal, Tyrol, Austria; Carrock Fells in Cumberland, England; Traversella in Pied- mont, Italy; Meymac, Correze, France (containing Ta 2 O 5 ); Sweden; Pitkaranta in Fin- land. In New South Wales, at Adelong, from a gold mine; New Zealand, massive; Mt. Ramsay, Tasmania, with cassiterite. From Sonora, Mexico. In the United States, at Lane's Mine, Monroe, and at Trumbull, Conn.; Flowe mine, Mecklenburg Co., N. C.; the Mammoth mining district, Nev.; with gold at the Charity mine, Warren's, Idaho; Lake Co., Col.; Atolia mining field, Cal.; White Pine Co., Nev.; Dragoon, Ariz. In quartz veins in Risborough and Marlow, Beauce county, Quebec. Use. An ore of tungsten. Cuprotungstite. Cupric tungstate, CuWO 4 . From the copper mines of Llamuco, near Santiago, Chile. CUPROSCHEELITE, from the vicinity of La Paz, Lower California, is (Ca,Cu)WO 4 , with 6'8 p. c. CuO; color green. From Montoro, Spain; from Yeoral, New South Wales. Powellite. Calciuni molybdate with calcium tungstate (10 p. c. WO 3 ), Ca(Mo,W)O 4 . In minute yellow tetragonal pyramids. G. = 4'349. w = 2 '00. From western Idaho; Houghton Co., Mich.; from Llano Co., Texas, and Nye Co., Nev. Stolzite. Lead tungstate, PbWO 4 . In pyramidal tetragonal crystals. H. = 2-75-3. G. = 7-87-8-13. Color green to gray or brown. Optically -. and p angles quoted abov. The point p which is 54 37' back from the pole to 010 or b marks _the place where the normal to the prism face 230 would ejnerge from the sphere. The normal to 232, which is the twinning axis will emerge on the meridian that runs through the point p and at such a distance below it that it will make the angle 60 31' with the negative end of the c axis. Chords are drawn to p from the points where the a and b axes meet the equator of the sphere and then chords parallel to these are drawn from the points x, y and z which are in each case 60 31' from the point where the negative end of the c axis cuts the spherical surface. The common meeting point of these chords T marks the place where the twinning axis pierces the spherical surface. The next step is to determine the point t at which the twinning axis cuts the twinning plane. The line OPp is by construction at right angles to the line connecting -3/2a and 16. Therefore a vertical plane which is normal to the twinning plane would intersect that plane in the line connecting 3 /2c and P. The twinning axis OT would He in this plane also. Consequently the point t, where OT and -3/2c-P intersect would Ke both on the twinning axis and in the twinning plane. In order to make the method of construction clearer Fig. 1042 is given. Here the twinning axis is repeated from Fig. 1041. The twin posi- tion of the crystal is to be found by revolving it from its normal position through an arc of 180, using the twinning axis as the axis of revolution. This will turn the twinning plane about upon the point t as a pivot and so transpos3 the points -3/2a, 6 and -3/2c to points equidistant from it in an opposite position. By drawing lines through t and laying off equal distances beyond that point the new points -3/2 A, B and -3/2C will be obtained. These points lie upon the three axes in their twin position and so determine their directions. The plotting of the twin axes in the top view follows similar methods. In order to make the construction learer a separate figure. Fig. 1043, is given. The line 0-t is laid off at an angle of 4 37' to the 6 axis. Upon this it h * th^ 1S foun l b y Projection upward from the clinographic view below. This meS 6 "? 1 a , r U u d which the axes are ^olved 180 to their twin Y methods of construction and the directions of APPENDIX A 657 1043 Upon the twin axes found in this way the portion of the crystal in twin position is drawn in exactly the same manner as if it was in the normal position. (2). To plot the axes for the calcite twin shown in Fig. 1044. In this case it was desired to represent a scalenohedron twinned upon the rhombohedron / (0221) and so drawn that the twinning plane should be vertical and have the position of 6 (010) of an orthorhombic crystal. The angle from c (001) to / (0221) equals 63 7'. In order to make \ the face / vertical, the vertical axis \ must be inclined at an angle of 26 53', or the angle between the c axes of the two individuals com- posing the twin would be double this or 53 46'. These relations are shown in Fig 1045. As indicated in Fig. 1046 the position of these axes, c and C in the figure, are easily obtained at inclinations of 26 53* by use of the graduation of the vertical ellipse that passes through B and -B. The points X,X' and Y, Y' indicate the intersections with this same eclipse of the two planes containing the a\, a- 2 and a 3 axes in their respective inclined positions, the angles -BX, BX', and BY and -BY' being in each case equal to 26 53'. In order to have the twinning plane occupy a posi- tion parallel to the 010 plane of an orthorhombic crystal it is necessary to revolve the axes so 1044 1045 1045 that one of the a hexagonal axes shall coincide with the position of the a axis of the orthor- hombic system, as -a 3 , a 3 in Fig. 1046. The two other hexagonal axes corresponding to the axis c must therefore lie in a plane which includes -a 3 , a s and the points X and X' and have such positions that they will make angles of 60 with -o 3 , a 3 . The construction necessary APPENDIX A to determine the ends of these axes is as follows: Draw the two chords lettered x-x' SrouKh^Snte that are 60 from -a s and a 3 and parallel to the direction of a chord that would ^Hhrough -B and X. In a similar way draw the two chords y-y through the second r of Sts that are 60 from -a, and a,, parallel to the direction of a chord that wou?d pis through the points B and X. The intersections of these two sets of chords determfnTthe points * and -a* which are the ends of these respective axes. The hexagon shown in the figure connects the ends of the fll , 2 and a s axes that lie in a plane perpendicular to the axis c. The set of axes that belong to the axis C are to be found m a similar way. The length of the vertical axis is to be obtained by multiplying that of calcite c = 0'854 by three and laying off on the vertical line the length obtained or 2'562 This is transferred to the twin axis c by drawing the line p'-p' parallel to the line p-p. The desired figure of the calcite twin is to be drawn upon these two sets of inclined axes. DRAWING CRYSTALS BY USE OF THE STEREOGRAPHIC AND GNOMONIC PROJECTIONS The following explanation of the methods of drawing crystals from the projections of their forms has been taken with only minor modifications from Penfield's description.* 1. USE OF THE STEREOGRAPHIC PROJECTION In explaining the method, a general example has been chosen; the construction of a drawing of a crystal of axinite, of the triclinic system. Figure 1047A represents a steno- graphic projection of the ordinary forms of axinite, m (110), a (100), M (110), p (111), r (111) and s (201). As shown by the figure, theirs* meridian, locating the position of 010, has been chosen at 20 from the horizontal direction SS'. Figure 1047B is a plan, or an orthographic projection of an axinite crystal, as it appears when looked at in the direction of the vertical axis. It may be derived from the stereo- graphic projection in a simple manner, as follows: The direction of the parallel edges made by the intersections of the faces in the zone m, s, r, m', A, is parallel to a tangent at either m or m', and this direction may be had most easily by laying a straight edge from m to m' and, by means of a 90 triangle, transposing the direction to B, as shown by the construction. The construction of C, which may be called a parallel-perspective view, may next be explained: It is not a clinographic projection like the usual crystal drawings from axes, but an orthographic projection, made on a plane intersecting the sphere, represented by the stereographic projection, A, along the great circle SES'; the distance EC being 10. The plane on which a drawing is to be made may, of course, have any desired inclination or position, but by making the distance CE equal 10 and taking the first meridian at 20 from S, almost the same effects of plan and parallel perspective are produced as in the conventional method of drawing from axes^ where the eye is raised 9 28' and the crystal turned 18 26'. The easiest way to explain the construction of C from A is to imagine the sphere, repre- sented by the stereographic projection, as revolved 80 about an axis joining S and S', or until the great circle SES' becomes horizontal. After such a revolution, the stereographic projection shown in A would appear as in D, and the parallel-perspective drawing, E, could then be derived from D in exactly the same manner as B was derived from A. This is, for example, because the great circle through m, s and r, D, intersects the graduated circle at x, where the pole of a vertical plane in the same zone would fall, provided one were present; hence the intersection of such a surface with the horizontal plane, and, con- sequently, the direction of the edges of the zone, would be parallel to a tangent at z: In other words, E is a plan of a crystal in the position represented by the stereographic pro- jection, D. Although not a difficult matter to transpose the poles of a stereographic projection so as to derive D from A, it takes both time and skill to do the work with ac- curacy, and it is not at all necessary to go through the operation. To find the direction of the edges of any zone in C, for example m s r, note first in A the point x, where the great circles m s r and SES' cross. During the supposed revolution of 80 about the axis SS', the pole x follows the arc of a small circle and falls finally at x' (the same position as x of D) and a line at right angles to a diameter through x', as shown by the construction, is the desired direction for C. Similarly for the zones pr, MrM' and MspM', their inter- sections with SES' at w, y and z are transposed by the revolution of 80 to w', y' and z'. The transposition of the poles w, x, y and z, A, to w', x', y' and z' may easily be accomplished * Am. J. Sc., 21, 206, 1906. APPENDIX A 659 in the following ways: (1) By means of the Penfield transparent, small-circle pro- tractor (*ig- 68, p. 39) the distances of w, x, y and z from either S or S' may be deter- mined and the corresponding number of degrees counted off on the graduated circle. (2) 1047 Development of a plan and parallel-perspective figure of axinite, triclinic system from a stereographic projection (after Penfield) Find first the pole P of the great circle SES', where P is 90 from E or 80 from C, and is located by means of a stereographic scale or protractor (Fig. 62, p. 35) : A straight line drawn through P and x will so intersect the graduated circle at x', that S'x and S'x' are equal in degrees. The reason for this is not easily comprehended from A, but if it is im- agined that the projection is revolved 90 about an axis A A', so as to bring S' at the center, the important poles and great circles to be considered will appear as in figure 1048, where P and C' are the poles, respectively, of the great circles ES'E' and AS' A', and x is 41 from S' as in figure 1047 A. It is evident from the symmetry of figure 1048 that a plane surface touching at C', P and x will so intersect the great circle AS' A' that the distances S'x and S'x' are equal. Now a plane passing through C", P, x and x', if extended, would intersect the sphere as a small circle, shown in the figure, but since this circle passes through C', which in figure 1047A is the pole of the stereographic projection (antipodal to C), it will be projected in figure A as a straight line, drawn through P and x, since the intersec- tions upon the plane of projection of all planes that pass through the point of vision of the projection will appear as straight lines. (3) In figure 1048 B is located midway between E 660 APPENDIX A and A' BS'B' is a great circle, and W, 40 from C, is its pole: It is now evident from the symmetry of the figure that a great circle through W and x so intersects the great circle A&A' that the distances S'x and S'x' are equal. Transferring the foregoing relations to figure 1047A, W, 40 from C, is the pole of the great circle SBS', and a great circle drawn through W and x falls at x'. However, it is not necessary to draw the great circle through W and x to locate the point x' on the graduated circle: By centering the Penfield transparent great circle protractor, (Fig. 67, p. 39) at C, and turning it so that W and x fall on the same great circle, the point x may be transposed to x', and other points, w f , y' and z', would be found in like manner. The three foregoing methods of transposing x tox',z to z', etc., are about equally simple, and it may be pointed out that, supplied with transparent stereographic protractors, and having the poles of a crystal plotted in stereo- graphic projection, it is only necessary to draw the great circle SES' and to locate one point, either W or P, in order to find the directions needed for a parallel-perspective drawing, cor- responding to figure 1047C. Thus, with only a great circle protractor, the great circle through the poles of any zone may be traced, and its intersection with SES' noted and spaced off with dividers from either S or S'; then the great circle through the intersection just found and W is determined, and where it falls on the divided circle noted, when the desired direction may be had by means of a straight edge and 90 triangle, as already explained. 2. DRAWING OF TWIN CRYSTALS BY USE OF THE STEREOGRAPHIC PROJECTION In the great majority of cases the drawing of twin crystals can be most advantageously accomplished by the use of a stereographic projection of their forms. It is only necessary first to prepare a projection showing the poles of the faces in the normal and twin po- sitions and then follow the methods outlined above. The preparation of the desired pro- jection may, however, need some explanation. An illustrative example is given below taken from an article by Ford and Tillotson on some Bavenno twins of orthoclase.* According to the Baveno law of twinning the n (021) face becomes the twinning plane and as the angle c A n = 44 56 1/2' the angle between c and c' (twin position) becomes 89 53'. For the purposes of drawing it is quite accurate enough to assume that this angle is exactly 90 and that accordingly the r. face of the twin will occupy a position paral- lel to that of the b face of the normal individual. Fig. 1049 shows the forms observed of the crystals both in normal and in twin positions, the faces in twin position being indicated by open circles and a prime mark (') after their respective letters, while the zones in twin position are drawn in dashed lines. Starting out with the forms in normal position, the first face to transp9se is the base c. This form, from the law of the twinning, will be transposed to c' where it occupies the same position as 6 of the normal individual, and it necessarily follows that 6 itself in being transposed will come to b' at the point where the normal c is located. In turning therefore the crystal to the left from normal to twin position, the fades c and 6 travel along the great circle I through an arc of 90 until they reach their respective twin positions. We have, in other words, revolved the crystal 90 to the left about an axis which is parallel to the faces of the zone I. The pole of this axis is located on the stereo- graphic projection at 90 from the great circle I and falls on the straight line II, another great circle which intersects zone I at right angles. This pole P is readily located by the stereographic protractor on the great circle II at 90 from c. The problem then is to re- volve the poles of the faces from their normal positions about the point P to the left and through an arc of 90 in each case. During the revolution the poles of the n faces remain on the great circle I and as the angle n A n = K) , the location of their poles when in twin position is identical with that of Am. J. Sc., 26, 149, 1908. APPENDIX A 661 the normal position and n' falls on top of n. We can now transpose the great circle II from its normal to its twin position, since P remains stationary during the revolution and we have determined the twin position of c. The dashed arc II' gives the twin position of the 1049 great circle II. The twin position of y must lie on arc II' and can be readily located at y', the intersection of arc II' with a small circle about P having the radius P Ay. It is now possible to construct the arc of the zone III in its transposed position III', for we have two of the points, y' and n' of the latter, already located. By the aid of the Penfield transparent great circle protractor the position of the arc of the great circle on which these two points lie can be determined. On this arc, III', o' and m' must also lie. Their positions are most easily determined by drawing arcs of small circles about b' with the required radii, 6 A o = 63 8', b A //* = 59 22 1/2' and the points at which they intersect arc III' locate the position of the poles o' and m f . At the same time the corresponding points on IV may be Jocated, it being noted that IV and III are the same arc. But one other form remains to be transposed, the prism z. We have already 6' and m' located and it is a simple matter with the aid of the great circle protractor to determine the position of the great circle upon which they lie. Then a small circle about 6' with the proper radius, b/\z = 29 24', determines at once by its intersections with this arc the position of the poles of the z faces. It may be pointed out that if it should be desired to make use of the methods of the gnonomic projection for the drawing of the figures as described below, the stereographic projection of the forms may be readily transformed into a gnomonic projection by doubling the angular distance from the center of the projection to each pole by the use of the stereo- graphic protractor, Fig. 62, p. 35. 3. USE OF THE GNOMONIC PROJECTION As an illustration, the method of drawing a simple combination of barite has been chosen. The forms shown in figure 1050 are c (001), m (110), o (Oil) and d (102). The location of the poles in the gnomonic projection is shown in A, where, as in figure 1047A. the first 662 APPENDIX A meridian is taken at 20 from the horizontal direction SS . The poles of the prism m and locations of S and S' (compare figure 1047A) fall in the gnomonic projection at infinity. In any plan such as figure 1050B, the direction of an edge made by the meeting of two faces 1050 A at oo tfatoo y at oo is at right angles to a line joining the poles of the faces, shown in figures A and B by the di- rection at 90 to the line joining m" and c. The parallel-perspective view, 1050C, is an orthographic projection (compare figures 1047 A and C) drawn on a plane passing through S and S', and intersecting the sphere on which the gnomonic projection is based as a great circle passing through E, figure 1050A, and drawn parallel to SS', the distance cE being 10: This great circle is called by Gold- schmidt the Leitlinie. To find such intersections as between m"' and c, and m and d, figure C, note, as in figure 1047A, where the great circles through the poles of the faces intersect the Leitlinie; thus, the one through m'" and c at x, and that through m and d (through d parallel to m m", since m and m" are at infinity) at y. Next imagine the points x and y transposed as in figure 1047 A to x' and y', which latter pomts, however, are located at infinity: This transposition is done by locating first the so-called Winkelpunkt, W, of Goldschmidt, 40 from c in figure 1050A, and as in figure 1047A, 90 from a point B, which is an equal number of degrees from E and A' (compare figure 1048). Of the three methods given above for transposing x and y to x' and y', the third may be easily applied in the gnom- onic projection. Great circles, or straight lines, through W and x and W and y, figure 1050A, if continued to infinity, would determine x' and y', which is accomplished by draw- ing lines parallel to Wx and Wy through the center. It is not necessary, however, to draw the lines Wx and Wy, nor the parallel lines through the center; all that is needed to find the directions of the edges m'" A c and m A d is to lay a straight edge from W to x, re- spectively W to y, and with a 90 triangle transpose the directions to C, as indicated in the drawings. The principles are exactly the same as worked put for the interrelations of figures 1047A and C. As in the case of the stereographic projection, it is evident that, given the poles of a crystal plotted in the gnomonic projection, it would be necessary to draw only one line, the Leitlinie, and to locate one point, the Winkelpunkt, W, in order to find all possible directions for a plan and parallel-perspective views, corresponding to figures 1050B and C. APPENDIX B TABLES USEFUL IN THE DETERMINATION OF MINERALS THIS Appendix contains a series of tables, more or less complete, of minerals arranged according to chemical composition or to certain prominent crystallographic or physical characters. These, it is believed, will be of service not only to the student, but also to the skilled mineralogist. The type used in the printing of the mineral names indicates their relative importance. Table I is a complete list of the species named in this book arranged first according to the prominent basic elements which they contain and secondly according to their acid radicals. Table II is of Minerals arranged according to their System of Crystallization. The other tables make no claim to completeness, being limited often to common and important species. For an exhaustive system of Determinative Tables based particularly upon blowpipe and chemical characters, the student is referred to the work of Professors Brush and Pen- field, mentioned on p. 330. TABLE I. MINERALS ARRANGED ACCORDING TO CHEMICAL COMPOSITION The following lists include all definitely described mineral species arranged first according to their important basic elements and secondly according to their acid radicals. If a given mineral contains two or more prominent bases its name is repeated in all the ap- propriate sections. ALUMINIUM NOTE : Aluminium is of such common occurrence among the silicate minerals tnat it is impracticable to list all of these minerals that contain it. Therefore only those sili- cates which are essentially aluminium minerals are included in the following list. Chloralluminit , A1C1 3 .6H 2 O. GIBBSITE, A1 2 O 3 .3H 2 O. CRYOLITE, Na 3 AlF 6 . Hydrotalcite, Al(OH) 3 .3Mg(OH) 2 .3H 2 O. Koenenite, Al,Mg, oxy chloride. Shanyavskite, A1 2 O 3 .4H 2 O. Fluellite, A1F 3 .H 2 O. Dundasite, Pb(AlO) 2 (CO 3 ) 2 . Prosopite, CaF 2 .2Al(F,OH) 3 . Dawsonite, Na 3 Al(CO 3 ) 3 .2Al(OH) 3 . Pachnolite, Thomsenolite, NaF.CaF 2 .AlF 3 . Zunyite, (Al(OH,F,Cl) 2 )6Al 2 Si 3 Oi 2 . H 2 O. Topaz, [Al(F,OH)] 2 SiO 4 . Gearksutite, CaF 2 .Al(F,OH) 3 .H 2 O. ANDALUSITE, Al 2 SiO 5 . Ralstonite, (Na 2 ,Mg)F 2 .3Al(F,OH) 3 .2H 2 O. SILLIMANITE, Al 2 SiO 6 . Creedite, 2CaF 2 .2Al(F,OH) 3 .CaSO 4 .2H 2 O. Cyanite, Al 2 SiO 5 . Corundum, A1 2 O 3 . Dumortierite, 8Al 2 O 3 .B 2 O 8 .6SiO 2 .H 2 O. Spinel, MgO.Al 2 O 3 . Staurolite, (AlO) 4 (AlOH)Fe(SiO 4 ) 2 . Hercynite, FeO.Al 2 O 3 . Kaolinite, H 4 Al 2 Si 2 O 9 . Gahnite, ZnO.Al 2 O 3 . Faratsihite, (Al,Fe) 2 O 3 .2SiO 2 .2H 2 O. Chrysoberyl, BeO.Al 2 O 3 . Halloysite, H 4 Al 2 Si 2 O 9 .H 2 O. Uhligite, Ca(Ti,Zr)O 6 .Al (Ti,Al)O 6 . Newtonite, H 8 Al 2 Si 2 On.H 2 O. DIASPORE, A1 2 O 3 .H 2 O. Cimolite, 2Al 2 O 3 .9SiO 2 .6H 2 O. Bauxite, A1 2 O 3 .2H 2 O. Montmorillonite, H 2 Al 2 Si 4 Oi 2 .nH 2 O. 663 664 APPENDIX B PYROPHYLLITE, H 2 Al 2 (Si0 3 ) 4 . Allophane, Al 2 Si06.5H 2 0. Melite, 2(Al,Fe) 2 3 .S10 2 .8H 2 0. Collyrite, 2Al 2 O 3 .SiO 2 .9H 2 O. Schrotterite, 8Al 2 O 3 .3SiO 2 .30H 2 O. Hamlinite, Al,Sr, phosphate Plumbogummite, Pb,Al, phosphate. Florencite, Al,Ce, phosphate. Georceixite, BaO.2Al 2 O 3 .P 2 O 6 .5H 2 O. Crandallite, 2CaO.4 A1 2 O 3 .2P 2 O 5 . 10H 2 O. Harttite, (Sr,Ca)O.2Al 2 O 3 .P 2 O 6 .SO 3 .5H 2 O. Durangite, Na(AlF)AsO 4 . Amblygonite, Li(AlF)PO 4 Fremontite, (Na,Li)Al(OH,F)PO 4 . Lazulite, 2AlPO 4 .(Fe,Mg)(OH) 2 . Tavistockite, Ca 3 P 2 O 3 .2Al(OH) 2 . Cirrolite, Ca 3 Al(PO 4 ) 3 .Al(OH) 3 . Synadelphite, 2(Al,Mn)AsO 4 .5Mn(OH) 2 . Hematolite, (Al,Mn)AsO 4 .4Mn(OH) 2 . Barrandite, (Al,Fe)PO 4 .2H 2 O. Variscite, A1PO 4 .2H 2 O. Lucinite, A1PO 4 .2H 2 O. Callainite, A1PO 4 .2H 2 O. Zepharovichite, A1PO 4 .3H 2 O. Palmerite, HK 2 A1 2 (PO 4 ) 3 .7H 2 O. Rosier6site, Hydrous, Al,Pb,Cu, phosphate. WAVELLITE, 4A1PO 4 .2A1(OH) 3 .9H 2 O. Fischerite, AlPO 4 .Al(OH) 3 .2iH 2 O. Peganite, A1PO 4 .A1(OH) 3 .HH 2 O. TURQUOIS, CuO.3Al 2 O 3 .2P 2 O 5 .9H 2 O. Wardite, 2A1 2 O 3 .P 2 O 6 .4H 2 O. Sphserite, 4A1PO 4 .6A1(OH) 3 . Liskeardite, (Al,Fe)AsO 4 .2(Al,Fe) (OH). 5H 2 O. Evansite, 2A1PO 4 .4A1(OH) 3 .12H 2 O. ' Coeruleolactite, 3 A1 2 O 3 .2P 2 O 5 . 10H 2 O. Angelite, 2Al 2 O 3 .P 2 O 6 .3H 2 q. Berlinite,Trolleite, Attacolite 1 Hydrous Minasite, Vashegyite j Alphosphates Soumansite, Hydrous, Al,Na, fluo-phosphate. Childrenite,2AlPO 4 .2Fe(OH) 3 .2H 2 O. Eosphorite, 2AlPO 4 .2(Mn,Fe) (OH) 3 .2H 2 O. Egueiite, Hydrous, Fe,Al,Ca, phosphate. Liroconite, Cu 6 Al(AsO 4 ) 5 .3CuAl(OH) 6 . 20H 2 O. Henwoodite, Al,Cu, hydrous phosphate. Ceruleite, CuO.2Al 2 O 3 .As 2 O 5 .8H 2 O. Kehoite, Hydrous, Al,Zn, phosphate. Goyazite, Ca 3 Al 10 P 2 O 23 .9H 2 O. Rosch6rite, (Mn,Fe,Ca) 2 Al(OH) (PO 4 ) 2 .2H 2 O. Svanbergite, Hydrous Al, Ca, phosphate and sulphate. Teremejevite, A1BO 3 . Rhodizite, A1,K, borate. Millosevichite, (Fe,Al) 2 (SO 4 ) 3 . Spangolite, Cu6AlClSO 10 .9H 2 O. Alumian, A1 2 O 3 .2SO 3 . KaUnite, KA1(SO 4 ) 2 .12H 2 O. Tschermigite, (NH 4 )A1(SO 4 ) 2 .12H 2 O. Mendozite, NaAl(SO 4 ) 2 .12H 2 O. Pickeringite, MgSO 4 .Al 2 (SO 4 ) 3 .22H 2 O. Halotrichite, FeSO 4 .Al 2 (SO 4 ) 3 .24H 2 O. Apjohnite, MnSO 4 .Al 2 (S0 4 ) 3 .24H 2 O. Dietrichite,(Zn,Fe,Mn)SO 4 .Al 2 (SO 4 )H 3 .22 2 O. Alunogen, A1 2 (SO 4 ) 3 .18H 2 O. Cyanotrichite, 4CuO.Al 2 O 3 .SO 3 .8H 2 O. Knoxvillite, Hydrous, Fe,Al,Cr, sulphate. Cyprusite, 7Fe 2 O 3 . A1 2 O 3 . 10SO 3 . 14H 2 O. Aluminite, A1 2 O 3 .SO 3 .9H 2 O. Paraluminite, 2A1 2 O 3 .SO 3 .10H 2 O. Felsobanyite. 2A1 2 O 3 .SO 3 .10H 2 O. Voltaite, 3(K 2 ,Fe)O.2(Al,Fe) 2 O 3 .6SO 3 .9H 2 O. ALUNITE, K 2 A1 6 (OH) 12 .(SO 4 ) 4 . Lowigite, K 2 O.3A1 2 O 3 .4SO 3 .9H 2 O. Almeriite,Na 2 SO 4 .Al 2 (SO 4 ) 3 .5Al(OH) 3 .H 2 O. Ettringite,6CaO.Al 2 O 3 .3SO 3 .33H 2 O. Zincaluminite, 2ZnSO 4 .4Zn(OH) 2 .6Al(OH) 3 . 5H 2 O. Mellite, A1 2 C 12 O 12 .18H 2 O. ANTIMONY NOTE : The antimonates are not in- cluded in this list. Allemontite, SbAs 3 . NATIVE ANTIMONY, Sb. Stibnite, Sb 2 S 3 . Kermesite, Sb 2 S 2 O. Senarmontite, Valentinite, Sb 2 O 3 . Cervantite, Sb 2 O 3 .Sb 2 O 6 . Stibiconite, H 2 Sb 2 O 5 . Stibiotantalite, (SbO) 2 (Ta,Nb) 2 O 6 . ARSENIC NOTE : The arsenates are not included in this Ust. NATIVE ARSENIC, As. Allemontite, SbAs 3 . REALGAR, AsS. ORPIMENT, As 2 S 3 . Arsenopyrite, FeAsS. Arsenolite, Claudetite, As 2 O 3 . BARIUM Witherite, BaCO 3 . Bromlite, (Ba,Ca)CO 3 . Barytocalcite, BaCO 3 .CaCO 3 . Hyalophane, (K 2 ,Ba)Al 2 (SiO 3 ) 4 . Celsian, BaAl 2 Si 2 O 8 . Cappelenite, Y,Ba, boro-silicate. Hyalotekite, (Pb,Ba,Ca)B 2 (SiO 3 ) 12 . Barylite, Ba 4 Al 4 Si 7 O 24 . Taramellite, Ba^e'' Fe 4 '" SiidO M . Brewsterite, H 4 (Sr,Ba,Ca)Al 2 (SiO 3 ) 6 .3H 2 O. Wellsite, (Ba,Ca,K 2 )Al 2 Si 3 Oi .3H 2 O. Harmotone, (K 2 ,Ba)Al 2 Si 5 Oi 4 .5H 2 O. Edingtonite, BaAl 2 Si 3 Oi .3H 2 O. Benitoite, BaTiSi 3 O 9 . Leucosphenite, Na 4 Ba(TiO) 2 (Si 2 O 5 ) 5 . Georceixite, BaO.2Al 2 O 3 .P 2 O 5 .5H 2 O. Ferrazite, 3(Ba,Pb)O.2P 2 O 5 .8H 2 O. Volborthite, Cu,Ba,Ca, vanadate. Uranocircite, Ba(UO 2 ) 2 P 2 O 8 .8H 2 O. Nitrobarite, Ba(NO 3 ) 2 . Barite, BaS0 4 . APPENDIX B 665 BERYLLIUM Chrysoberyl, BeAl 2 O 4 . Eudidymite, Epididymite, HNaBeS.\ 3 O 8 . Beryl, Be 3 Al 2 (SiO 3 ) 6 . Helvite, (Be,Mn,Fe) 7 Si 3 Oi 2 S. Danalite, (Be,Fe,Zn,Mn) 7 Si 3 Oi 2 S. Phenacite, Be 2 SiO 4 . Trimerite, (Mn,Ca) 2 SiO 4 .Be 2 SiO 4 . Euclase, HBeAlSiO 5 . Gadolinite, Be 2 FeY 2 Si 2 O 10 . Bertrandite, H 2 Be 4 Si 2 O 9 . Beryllonite, NaBePO 4 . Herderite, Ca[Be(F,OH)]PO 4 . Hambergite, Be 2 (OH)BO 3 . BISMUTH NATIVE BISMUTH, Bi. BlSMUTHINITE, Bl 2 S 3 . Guanajuatite, Bi 2 Se 3 . Tetradymite, Bi 2 (Te,S) 3 . Grunlingite, Bi 4 TeS 3 . Joseite, Wehrlite, bismuth tellurides. Daubreete, Bi, oxychloride. Bismite, Bi 2 O 3 . Bismutosparite, Bi 2 (CO 3 ) 3 .2Bi 2 O 3 . Bismutite, Bi 2 O 3 .CO 2 .H 2 q. Eulytite, Agricolite, Bi 4 Si 3 Oi 2 . Pucherite, BiVO 4 . Atelestite, H 2 Bi 3 AsO 8 . Walpurgite, Bi 10 (UO 2 ) 3 (OH) 24 (AsO 4 ) 4 . Rhagite, 2BiAsO 4 .3Bi(OH) 3 . Arseno-bismite, hydrous Bi arsenate. Mixite, Hydrous Cu, Bi, arsenate. Uranosphaerite, (BiO) 2 U 2 O 7 .3H 2 O. Montanite, Bi 2 p 3 .Te0 3 .2H 2 O. Koechlinite, Bi 2 O 3 .MoO 3 . BORON NOTE : The borates are not included in this list. Sassolite, B(OH) 3 . Cappelenite, Y,Ba, boro-silicate. Hy alotekite, (Pb . Ba, Ca) B 2 (SiO 3 ) . DANBURITE, CaB 2 (SiO 4 ) 2 . Datolite, HCaBSiO 5 . Homilite, Ca 2 FeB 2 Si 2 Oi . Axinite, Ca,Al, boro-silicate. Tourmaline, complex boro-silicate. Dumortierite, 8AL>O 3 .B,O 3 .6SiO 2 .H 2 O. Serendibite, 10(Ca,Mg)O.5Al 2 O 3 .B 2 O 3 .6SiO 2 . Manandonite, H 4 4Li 4 Ali 4 B 4 .Si6O 53 . Bakerite, Hydrous Ca, boro-silicate. Searlesite, NaB(SiO 3 ) 2 .H 2 O. Luneburgite, 3MgO.B 2 O 3 .P 2 O 5 .8H 2 O. CADMIUM Greenockite, CdS. Cadmiumoxide, CdO. Otavite, Cd carbonate. CESIUM Pollucite, 2Cs 2 O.2Al 2 O 3 .9SiO 2 .H 2 O. Rhodizite, Al,K,Cs, borate. CALCIUM Oldhamite, CaS. Fluorite, CaF 2 . Hydrophilite, CaCl 2 . Yttrofluorite, (Ca 3 ,Y 2 )F 6 . Nocerite, 2(Ca,Mg)F 2 .(Ca.Mg)O. Tachhydrite, CaCl 2 .2MgCl 2 .12H 2 O. Prosopite, CaF 2 .2Al(F.OH) 3 . Pachnolite, Thomsenolite, NaF.CaF 2 .AlF 3 . H 2 O. Gearksutite. CaF 2 .Al(F,OH) 3 .H 2 O. Creedite, 2CaF 2 .2Al(F,OH) 3 .CaSO 4 .2H 2 O. Yttrocerite, (Y,Er,Ce)F 3 .5CaF 2 .H 2 O. UhUgite, Ca(Ti,Zr)O 5 .Al(Ti,Al)O 5 . Calcite, CaCO 3 . Dolomite, CaCO 3 .MgCO 3 . Ankerite, CaCO 3 .(Mg,Fe,Mn)CO 3 . Aragonite, CaCO 3 . Bromlite, (Ba,Ca)CO 3 . Barytocalcite, BaCO 3 .CaCO 3 Parisite, [(Ce,La,Di)F] 2 Ca(CO 3 ) 2 . Pirssonite, CaCO 3 .Na 2 CO 3 .2H 2 O. Gay-Lussite, CaCO 3 .Na 2 CO 3 .5H 2 O. Gajite, basic, hydrous, Ca, Mg, carbonate. Uranothallite, 2CaCO 3 .U(CO 3 ) 2 . 10H 2 O. Liebigite, Hydrous Ca,U, carbonate. Voglite, Hydrous U,Ca,Cu, carbonate. Milarite, HKCa 2 Al 2 (Si 2 O 5 ) 6 . Rivaite, (Ca,Na 2 )Si 2 O 6 . A^desinT Mixtures of NaAlSi 3 8 and Labradorite CaAl 2 Si 2 O 8 . Anorthite, CaAl 2 Si 2 O 8 . Anemousite, Na 2 O.2CaO.3Al 2 O 3 .9SiO 2 . Pyroxene, Ca,Mg, etc., silicate. Wollastonite, CaSiO 3 . PECTOLITE, HNaCa 2 (SiO 3 ) 3 . Schizoh'te, HNa(Ca,Mn) 2 (SiO 3 ) 3 . Rosenbuschite, near pectolite with Zr. Wohlerite, Zr-silicate and niobate of Ca,Na. Lavenite, Zr-silicate of Mn,Ca. Babingtonite, (Ca,Fe,Mn)SiO 3 with Fe 2 (SiO 3 ) 3 . Hiortdahlite, (Na 2 ,Ca)(Si,Zr)O 3 . Amphibole, Ca, Mg, etc., silicate. Arfvedsonite, Na,Ca,Fe, silicate. Leucophanite i AT T> n a -i- Meliphanite I ***&,<& fluo-sihcate. Custerite, Ca 2 (OH,F)SiO 3 . Didymolite, 2CaO.3Al 2 O 3 .9SiO 2 . Ganomalite, Pb 4 (PbOH) 2 Ca 4 (Si 2 O 7 ) 3 . Nasonite, Pb 4 (PbCl) 2 Ca 4 (Si 2 O 7 ) 3 . Margarosanite, Pb(Ca,Mn) 2 (SiO 3 ) 3 . Hardystonite, Ca 2 ZnSi 2 O 7 . Rocblingite, 5(H 2 CaSiO 4 ).2(CaPbSO 4 ). Haiiynite, Na 2 Ca(NaSO 4 .Al)Al 2 (SiO 4 ) 3 . Grossularite, Ca 3 Al 2 (SiO 4 ) 3 . Andradite, Ca 3 Fe 2 (SiO 4 ) 3 . 566 APPENDIX B UVAROVITE, Ca 3 Cr 2 (SiO 4 )3. Schorlomite, Ca 3 (Fe,Ti 2 ) [(Si,Ti)O]. MonticeUite, CaMgSiO 4 . Glaucochroite, CaMnSiO 4 . Trimerite, (Mn,Ca) 2 SiO 4 .Be2SiO 4 . SCAPOLITE GROUP, Mixtures of Ca 4 Al 6 Si 6 O25 and Na 4 Al 3 Si 9 O 24 Cl. Sarcolite, (Ca,Na 2 )3Al 2 (SiO 4 ) 3 . Melilite, Na 2 (Ca,Mg) n (Al,Fe) 4 (SiO 4 ) 9 . Cebollite, Gehlenite, Vesuvianite,Ca 6 [Al(OH,F)]Al 2 (Si0 4 ) 6 . DANBURITE, CaB 2 (SiO 4 ) 2 . Guarinite, 2(K,Na) 2 O.8CaO.5(Al,Fe,Ce) 2 O 3 . 10SiO 2 . Datolite, HCaBSiO 5 . Homilite, CazFeB^iAo. ZOISITE, Ca2(AlOH)Al 2 (SiO 4 ) 3 . Epidote, Ca 2 [(Al,Fe)OH](Al,Fe) 2 (SiO 4 ) 3 . Piedmontite, Ca 2 (AlOH) (Al,Mn) 2 (SiO 4 ) 3 . Allanite, (Ca,Fe) 2 (AlOH) (Al,Ce,Fe) 2 (SiO 4 ) 3 . AXINITE, Ca,Al, boro-silicate. PREHNITE, HzCa^SiO^. Harstigite, Mn,Ca, silicate Cuspidine, Ca 2 Si(O,F 2 ) 4 . ILVAITE, CaFe 3 (FeOH)(SiO 4 ) 2 . Clinohedrite, H 2 CaZnSiO 6 . Stokesite, H4CaSnSi 3 Oii. Lawsonite, Hibschite, H 4 CaAl 2 Si 2 Oi . Beckelite, Ca 3 (Ce,La,Di) 4 Si 3 O 15 . Angaralite,2(Ca,Mg)0.5(Al.Fe) 2 O 3 .6SiO 2 . Serendibite, 10(Ca,Mg)O.5Al 2 O 3 .B 2 O 3 .6SiO 2 . Silicomagnesiofluorite, H 2 Ca 4 Mg 3 Si 2 O 7 Fi . Gro thine, Ca,Al, silicate. , Aloisite, Fe,Ca,Mg,Na, silicate. Inesite, H 2 (Mn,Ca) 6 Si 6 Oi 9 .3H 2 O. Hillebrandite, Ca2SiO 4 .H 2 O. Crestmoreite, 4H 2 CaSiO 4 .3H 2 O. Riversideite, -2CaSiO 5 .H 2 O. Lotrite,3(Ca,Mg)0.2(Al,Fe) 2 3 .4Si0 2 .2H 2 Okenite, H 2 CaSi 2 O 5 .H 2 O. Gyre-lite, H 2 Ca 2 Si 3 O 9 .H 2 O. APOPHYLLITE, H 7 KCa 4 (SiO 3 ) 8 .4H 2 O. Ptilolite. (Ca,K 2 ,Na,)Al 2 Si 10 O 24 .5H 2 O. Mordemte, (Ca,K 2 ,Na2)Al 2 Sii O 24 .20H 2 O. HEULANDITE, H 4 CaAl 2 (SiO 3 )6.3H 2 O. Brewsterite, H 4 (Sr,Ba,Ca)Al 2 (SiO 3 ) 6 .3H 2 O. Epistilbite, H 4 CaAl 2 (SiO 3 ) 6 .3H 2 O. Wellsite, (Ba,Ca,K 2 )Al 2 Si 3 O 10 .3H 2 O. Phillipsite, (K 2 ,Ca)Al 2 Si 4 Oi 2 .4iH 2 O. StUbite, (Na 2 ,Ca)Al 2 Si 6 Oi 6 .6H 2 O. Flokite, H 8 (Ca,Na 2 )Al 2 Si 9 O 26 .2H 2 O. Gismondite, CaAl 2 Si 2 O 8 .4H 2 O. Laumontite, H 4 CaAl 2 Si 4 Oi 4 .2H 2 O. Laubanite, Ca2Al 2 Si 5 Oi 5 .6H 2 O. CHABAZITE, (Ca,Na 2 )Al 2 Si 4 Oi 2 .6H 2 O. Gmelinite, (Na 2 ,Ca)Al 2 Si 4 Oi 2 .6H 2 O. Levynite, CaAl 2 Si 3 O 10 .5H 2 O. Faujasite, H 4 Na 2 CaAl 4 Si, O 38 . 18H 2 O. Scolecite, Ca(AlOH) 3 (SiO 3 ) 3 .2H n O. M S5% N^^SiaOio^HaO +2[CaAl 2 Si 3 O 10 3H 2 OJ. Gonnardite, (Ca,Na 2 ) 2 Al 2 Si 6 O 15 .5^H 2 O. Thomsonite, (Na 2 ,Ca)Al 2 Si 2 O 8 .2H 2 O. Hydrpthomsonite ; (H 2 ,Na 2 ,Ca)Ali phosphate. Fernandinite, CaO.V 2 O4.5V 2 O5.14H 2 O. Pascoite, 2CaO.3V 2 O 5 .llH 2 O. Pintadoite, 2CaO.V 2 O 5 .9H 2 O. Pharmacolite, HCaAsO 4 .2H 2 O. Haidingerite, HCaAsO 4 .H 2 O. Wapplerite, HCaAsO 4 .3H 2 O. Brushite, HCaPO 4 .2H 2 O. Martinite, H 2 Ca 5 (PO 4 ) 4 4H 2 O. Hewettite \p a o W O QTT O Metahewettite }<-aO.3V 2 O 5 .9H 2 O. Isoclasite, Ca 3 P 2 O 8 .Ca(OH) 2 .4H 2 O. Conichalcite, (Cu,Ca) 3 As 2 O 8 . (Cu,Ca) (OH) 2 . - ^H 2 0. Volborthite, Cu,Ba,Ca, vanadate. Mazapilite, Ca 3 Fe 2 (AsO 4 ) 4 .2FeO(OH).5H 2 O. Yukonite, (Ca 3 ,Fe 2 '")(AsO 4 ) 2 .2Fe(OH) 3 . 5H 2 O. Calcioferrite,Ca 3 Fe 2 (PO 4 ) 4 .Fe(OH) 3 .8H 2 O. Borickite, Ca 3 Fe 2 (PO 4 ) 4 .12Fe(OH) 3 .6H 2 O. Egueiite, Hydrous Fe,Al,Ca, phosphate. Goyazite, Ca 3 Ali P 2 O 23 .9H 2 O. Roscherite, (Mn,Fe,Ca) 2 Al(OH) (PO 4 ) 2 . 2H 2 O. Ca(UO 2 ) 2 P 2 O,8H 2 O. Uranospinite, Ca(UO 2 ) 2 As 2 O 8 .8H 2 O. Tyuyamunite, CaO.2UO 3 .V 2 O 5 .4H 2 O. Romeite, CaSb 2 O 4 . Lewisite, 5CaO.2TiO 2 .3Sb 2 O 5 . Mauzeliite, Pb,Ca, titano-antimonate. Podolite, 3Ca 3 (PO 4 ) 2 .CaCO 3 . Svanbergite, Hydrous Al,Ca, phosphate and sulphate. Nitrocalcite, Ca(NO 3 ) 2 .rcH 2 O. Lautarite, Ca(IO 3 ) 2 . Dietzeite, Ca iodo-chroniate. Nordenskioldine, CaSn(BO 3 ) 2 . Howlite, H 5 Ca 2 B 5 SiOi 4 . COLEMANITE, Ca 2 B 6 On.5H 2 O. Inyoite, 2CaO.3B 2 O 3 .13H 2 O. Meyerhofferite, 2CaO.3B 2 O 3 .7H 2 O. Ulexite, NaCaB 5 O 9 .8H 2 O. Bechilite, CaB 4 O 7 .4H 2 O. Hydroboracite, CaMgB 6 On.6H 2 O. GLAUBERITE, Na 2 SO 4 .CaSO 4 . Anhydrite \rO 8 .8H 2 O. Scorodite, FeAsO 4 .2H 2 O. Vilateite, Hydrous Fe, Mn, phosphate. Purpurite, 2(Fe,Mn)PO 4 .H 2 O. Strengite, FePO 4 .2H 2 O. Phosphosiderite, 2FePO 4 .3^H 2 O. Barrandite, (Al,Fe)PO 4 .2H 2 O. Koninckite, FePO 4 .3H 2 O. Sicklerite, Fe 2 O 3 .6MnO.4P 2 O 5 .3(Li,H) 2 O. Salmonsite, Fe 2 O 3 .9MnO.4P 2 O 5 . 14H,O. Liskeardite, (Al,Fe) AsO 4 .2(Al,Fe) (OH) 3 . 5H 2 O. Pharmacosiderite,6FeAs0 4 .2Fe(OH) 3 . 12H 2 0. Ludlamite, 2Fe 3 P 2 O 8 .Fe(OH) 2 .8H 2 O. Cacoxenite, FePO 4 .Fe(OH) 3 .4^H 2 O. Beraunite, 2FePO 4 .Fe(OH) 3 .2|H 2 O. Childrenite, 2AlPO 4 .2Fe(OH) 2 .2H 2 O. Mazapilite, Ca 3 Fe 2 (AsO 4 ) 4 .2FeO(OH).5H 2 O. Yukonite, (Ca 3 ,Fe 2 ' / ') (AsO 4 ) 2 .2Fe(OH) 3 . 5H 2 O. Calciof errite, Ca 3 Fe 2 (PO 4 ) 4 . Fe (OH ) 3 . 8H 2 O. Borickite, Ca 3 Fe 2 (PO 4 ) 4 . 12Fe(OH) 3 .6H 2 O. Egueiite, Hydrous Fe,Al,Ca, phosphate. Richelite, 4FeP 2 O 8 .Fe 2 OF 2 (OH) 2 .36H 2 O. Chenevixite, Cu 2 (FeO) 2 As 2 O 8 .3H 2 O. Chalcosiderite, CuO.3Fe 2 O 3 .2P 2 O 5 .8H 2 O. Roscherite, (Mn,Fe,Ca) 2 Al(OH) (PO 4 ) 2 . 2H 2 0. Tripuhyite, 2FeO.Sb 2 O 5 . Flajolotite, 4FeSbO 4 .3H 2 O. Catoptrite, 14(Mn,Fe)O.2(Al,Fe) 2 O 3 .2SiO 2 . Derbylite, Fe antimo-titanate. Diadochite, Hydrous Fe phosphate and sulphate. Pitticite, Hydrous Fe arsenate and sul- phate. Beudantite, 3Fe 2 O 3 .2PbO.2SO 3 .As 2 O 8 .6H 2 O. Hinsdalite, 3Fe 2 O 3 .2PbO.2SO 3 .P 2 O 5 .6H 2 O. Lossenite, Hydrous Fe,Pb, arsenate and sulphate. Ludwigite, 3MgO.B 2 O 3 .FeO.Fe 2 O 3 . Vonsenite, 3(Fe,Mg)O.B 2 O 3 .FeO.Fe 2 O 3 . Magnesioludwigite, 3MgO.B 2 O 3 .MgO.Fe 2 O 3 . Warwickite, (Mg,Fe) 3 TiB 2 O 8 . Lagonite, Fe 2 O 3 .3B 2 O 3 .3H 2 O. Hulsite, 12(Fe,Mg)O.2Fe 2 O 3 .lSnO 2 .3B 2 O 3 . Millosevichite, (Fe,Al) 2 (SO 4 ) 3 . Szomolnokite, FeSO 4 .H 2 O. Ilesite, (Mn,Zn,Fe)SO 4 .4H 2 O. Melanterite, FeSO 4 .7H 2 O. Pisanite; (Fe,Cu)SO 4 .7H 2 O. Halotrichite, FeSO 4 .Al 2 (SO 4 ) 3 .24H 2 O. Bilinite, FeSO 4 .Fe 2 (SO 4 ) 3 .24H 2 O. Dietrichite, (Zn,Fe,Mn)SO 4 .Al 2 (SO 4 ) 3 . 22H 2 O. Coquimbite, Fe 2 (SO 4 ) 3 .9H 2 O. Quenstedtite, Fe 2 (SO 4 ) 8 .10H 2 O. Ihleite, Fe 2 (SO 4 ) 3 .12H 2 O. Phillipite, CuSO 4 .Fe 2 (SO 4 ) 3 .nH 2 O. Ferronatrite,3Na 2 SO 4 .Fe 2 (SO 4 ) 3 .6H 2 O. Romerite, FeSO 4 .Fe 2 (SO 4 ) 3 .14H 2 O. Beaverite, CuO.PbO.Fe 2 O 3 .2SO 3 .4H 2 O. Vegasite, PbO.3Fe 2 O 3 .3SO 3 .6H 2 O. Copiapite, 2Fe 2 O 3 .5SO 3 .18H 2 O. Castanite, Fe 2 O 3 .2SO 3 .8H 2 O. Utahite, 3Fe 2 O 3 .2SO 3 .7H 2 O. Amaranthite, Fe 2 O 3 .2SO 3 .7H 2 O. Fibrof errite, Fe 2 O 3 .2SO 3 .10H 2 O. Raimondite, 2Fe 2 O 3 .3SO 3 .7H 2 O. Carphosiderite, 3Fe 2 O 3 .4SO 3 .7H 2 O. Planoferrite, Fe 2 O 3 .SO 3 .15H 2 O. Glockerite, 2Fe 2 O 3 .SO 3 .6H 2 O. Knoxvillite, Hydrous Fe,Al,Cr, sulphate. APPENDIX B 671 Cyprusite, 7Fe 2 O 3 . A1 2 O 3 . 10SO 3 . 14H 2 O. Botryogen, MgO.FeO.Fe 2 O 3 .4SO 3 . 18H 2 O. Sideronatrite, 2Na 2 O.Fe 2 O 3 .4SO 3 .7H 2 O. Voltaite, 3(K 2 ,Fe)O.2(Al,Fe) 2 O 3 .6SO 3 .9H 2 O. Metavoltine, 5(K 2 ,Na 2 ,Fe)O.3Fe 2 O 3 .12SO 3 . 18H 2 O. Jarosite, K 2 Fe 6 (OH) 2 (SO 4 ) 4 . Natrojarosite, Na 2 Fe 6 (OH) 12 (SO 4 )4. Plumbo jarosite, PbFe(OH)ij(SO 4 ) 4 . Quetenite, MgO.FeoO 3 .3SO 3 .13H 2 O. Rhomboclase, Fe 2 O 3 .4SO 3 .9H 2 O. Emmonsite, Hydrous Fe tellurate. Durdenite, Fe 2 (TeO 3 ) 3 .4H 2 O. WOLFRAMITE, (Fe,Mn)WO 4 . Reinite, FeWO 4 . Ferritungstite, Fe 2 O 3 .WO 3 .6H 2 O. Humboltine, FeC 2 4 .2H 2 0. LEAD Native Lead, Pb Galena, PbS. Altaite, Pb,Te. Clausthalite, PbSe. Naumannite, (Ag 2 ,Pb)Se. Zorgite, Pb,Cu, selenide. Chiviatite, 2PbS.3Bi 2 S 3 . Rezbanyite, 4PbS.5Bi 2 S 3 . Zinkenite, PbS.Sb 2 S 3 . Andorite, Ag 2 S.2PbS.3Sb 2 S 3 . Sartorite, PbS.As 2 S 3 . Platynite, PbS.Bi 2 Se 3 . Galenobismutite, PbS.Bi 2 S 3 . Hutchinsonite, (Tl,Ag,Cu) 2 S.As2S 3 + PbS. As 2 S 3 ? Baumhauerite, 4PbS.3As 2 S 3 . Schirmerite, 3(Ag 2 ,Pb)S.2Bi 2 S 3 . Rathite, 3PbS.2As 2 S 3 . Jamesonite, 2PbS.Sb 2 S 3 . Dufrenoysite, 2PbS.As 2 S 3 . Cosalite, 2PbS.Bi 2 S 3 . Kobellite, 2PbS.(Bi,Sb) 2 S 3 . Plagionite, Heteromorphite, Semseyite, Pb, Sb, sulphides. Freieslebenite, 5(Pb,Ag 2 )S.2Sb 2 S 3 . Diaphorite, 5(Pb,Ag 2 )S.2Sb 2 S 3 . Boulangerite 5PbS.2Sb 2 S 3 . Mullanite, 5PbS.2Sb 2 S 3 . Bournonite, 3(Pb,Cu 2 )S.Sb 2 S 3 . Seligmanite, 3(Pb,Cu 2 )S.As 2 S 3 . Aikinite, 2PbS.Cu 2 S.Bi 2 S 3 . Lillianite, 3PbS.(Bi,Sb) 2 S 3 . Guitermanite, 3PbS.As 2 S 3 . Lengenbachite, 7[Pb, (Ag,Cu) 2 ]S.2As 2 S 3 . Jordanite, 4PbS.As 2 S 3 . Meneghinite, 4PbS.Sb 2 S 3 Geocronite, 5PbS.Sb 2 S 3 . Beegerite, 6PbS.Bi 2 S 3 . Epiboulangerite, 3PbS.Sb 2 S 3 . Teallite, PbSnS 2 . Franckeite, Pb 5 Sn 3 FeSb 2 Su. Cylindrite, Pb 3 Sn 4 FeSb 2 Si 4 . Cotunnite, PbCl 2 . Percylite, PbCl 2 .CuO.H 2 O. Boleite, 9PbCl 2 .8CuO.3AgC1.9HoO. Pseudo-boleite, 5PbCl 2 .4CuO.6H 2 O. Cumengite, 4PbCl 2 .4CuO.5H 2 O. Matlockite, PbCl 2 .PbO. Mendipite, PbCl 2 .2PbO. Lorettoite, PbCl 2 .6PbO. Laurionite, PbCl 2 .Pb(OH) 2 . Penfieldite, 2PbCl 2 .PbO. Daviesite, Pb oxychloride. Schwartzenbergite, Pb(I,Cl) 2 .2PbO. Massicot, PbO. Senaite, (Fe,Mn,Pb)O.TiO 2 . Qoronadite, (Mn,Pb)Mn 3 O 7 . Minium, 2PbO.PbO 2 . Plattnerite, PbO 2 . Cerussite, PbCO 3 . PHOSGENITE, PbCO 3 .PbCl 2 . Hydrocerussite, 2PbCO 3 .Pb(OH) 2 . Dundasite, Pb(AlO) 2 (CO 3 ) 2 . Alamosite, PbSiO 3 . Barysilite, Pb 3 Si 2 O 7 . Molybdophyllite, (Pb,Mg)SiO 4 .H 2 O. Ganomalite, Pb 4 (PbOH) 2 Ca 4 (Si 2 O 7 ) 3 . Nasonite, Pb 4 (PbCl) 2 Ca 4 (Si 2 O 7 ) 3 . Margarosanite, Pb(Ca,Mn) 2 (SiO 3 ) 3 . Hy alotekite, (Pb, Ba, Ca) B 2 (SiO 3 ) , 2 . Roeblingite, 5(H 2 CaSiO 4 ).2(CaPbSO 4 ) Hancockite, Pb,Mn,Ca,Al, etc., silicate. Kentrolite, 3PbO.2Mn 2 O 3 .3SiO 2 . Melanotekite, 3PbO.2Fe 2 O 3 .3SiO 2 . Plumboniobite, Y,U,Pb,Fe, niobate Monimolite, Pb,Fe, antimonate. Carminite, Pb 3 As 2 O 8 .10FeAsO 4 . Georgiadesite, Pb 3 (AsO 4 ) 2 .3PbCl 2 . PYROMORPHITE, Pb 4 (PbCl)(PO 4 ) 3 . Mimetite, Pb 4 (PbCl)(AsO 4 ) 3 . Vanadinite, Pb 4 (PbCl)(VO 4 ) 3 . Trigonite, Pb 3 MnH(AsO 3 ) 3 . Plumbogummite, Pb,Al, phosphate. Descloizite, (Pb,Zn) 2 (OH)VO 4 . Pyrobelonite, 4PbO.7MnO.2V 2 O 5 .3H 2 O. Dechenite, PbV 2 O 6 . Psittacinite \ T^I ^ , !, Mottramite ) Pb,Cu, vanadates. Furnacite, Pb,Cu, chrom-arsenate. Tsumebite, Pb,Cu, phosphate. Rosiere"site, Hydrous Al,Pb,Cu, phosphate. Ferrazite, 3(Ba,Pb)O.2P 2 O 5 .8H 2 O. Bayldonite, (Pb,Cu) 3 As 2 O 8 . (Pb,Cu) (OH) 2 . Hiigelite, Hydrous Pb,Zn, vanadate. Bindheimite, Hydrous Pb antimonate. Nadorite, PbClSbO 2 . Ecdemite, Pb 4 As 2 O 7 .2PbCl 2 . OchroUte, Pb 4 Sb 2 O 7 .2PbCl 2 . Mauzeliite, Pb,Ca,titano-antimonate. Beudantite, 3Fe 2 O 3 .2PbO.2SO 3 .As 2 O 6 .6H 2 O. Hinsdalite, 3Fe 2 O 3 .2PbO.2SO 3 .P 2 O 6 .6H 2 O. Lossenite, Hyclrous Fe, Pb, arsenate and sulphate. Anglesite, PbSO 4 . CROCOITE, PbCrO 4 672 APPENDIX B Phcenicochroite, 3PbO.2Cr0 3 . Vauquelinite, 2(Pb,Cu)CrO 4 . (Pb,Cu) 3 P 2 O s Bellite, Pb arseno-chromate. Leadhillite, PbSO 4 .2PbCO 3 .Pb(OH) 2 . Caracolite, Pb(OH)Cl.Na 2 SO 4 . Lanarkite, Pb 2 SO 6 . Caledonite, (Pb,Cu)S0 4 . (Pb,Cu) (OH) 2 . Linarite, (Pb,Cu)SO 4 . (Pb,Cu) (OH) 2 . Beaverite, CuO.PbO.Fe 2 O 3 .2SO3.4H 2 O. Vegasite, PbO.3Fe 2 O 3 .3SO 3 .6H 2 O. Plumbojarosite, PbFe 6 (OH)i 2 (SO 4 ) 4 . Palmierite, 3(K,Na) 2 SO 4 .4PbSO 4 . Chillagite, 3PbW0 4 .PbMo0 4 . WULFENITE, PbMoO 4 . LITHIUM Petalite, LiAl(Si 2 O 5 ) 2 . Spodumene, LiAl(SiO 3 ) 2 . Eucryptite, LiAlSiO 4 . LEPIDOLITE, Lithium mica. Zinnwaldite, Lithium-iron mica. Manandonite, H 24 Li 4 Ali 4 B 4 Si6()5 3 . TRIPHYLITE, Li(Fe,Mn)PO 4 . Lithiophilite, Li(Mn,Fe)PO. AMBLYGGNITE, Li(AlF)PO 4 . Fremontite, (Na,Li)Al(OH,F)PO 4 . Sicklerite, Fe 2 O 3 .6MnO.4P 2 O 5 .3(Li,H) 2 O. MAGNESIUM Chloromagnesite, MgCl 2 . Sellaite, MgF 2 . Nocerite, 2(Ca,Mg)F 2 (Ca,Mg)O. Koenenite, Al,Mg, oxy chloride. Carnallite, KCl.MgCl 2 .6H 2 O. Bischofite, Mi " , _.- Jl 2 .6H 2 0. Tachhydrite, CaCl 2 .2MgCl 2 .12HoO Ralstonite, (Na 2 ,Mg)F 2 .3Al(F.OH) 3 .2H 2 O. Periclase, MgO. Spinel, MgO.Al 2 O 3 . Magnesioferrite, MgO.Fe 2 O 3 . Jacobsite, (Mn,Mg)O.(Fe,Mn) 2 O 3 . BRUCITE, Mg(OH) 2 . Hydrotalcite, Al(OH) 3 .3Mg(OH) 2 .3H 2 O. Pyroaurite, Fe(OH) 3 .3Mg(OH) 2 .3H 2 0. Dolomite, CaCO 3 .MgCO 3 . Ankerite, CaCO 3 .(Mg,Fe,Mn)CO 3 . Magnesite, MgCO 3 . Mesitite, 2MgCO 3 .FeCO 3 . Pistomesite, MgCO 3 .FeCO 3 . Northupite, MgCO 3 .Na 2 CO 3 .NaCl. Tychite, 2MgCO 3 .2Na 2 CO 3 .Na 2 SO 4 . Nesquehonite, MgCO 3 .3H 2 O. Hydromagnesite, 3MgCO 3 .Mg(OH) 2 .3H 2 O. Hydrogiobertite,MgC0 3 .Mg(OH) 2 .2H 2 0. Artimte, MgCO 3 .Mg(OH) 2 .3H 2 O. Lansfordite, 3MgC0 3 .Mg(OH) 2 .21H 2 0. Brugnatelhte, MgCO 3 .5Mg(OH) 2 .Fe(OH) 3 . 4ji2v-J Gajite basic, hydrous Ca,Mg, carbonate. Stichtite,2MgC0 3 .5Mg(OH) 2 .2Cr(OH) 3 . ENSTATITE, MgSiOs. HYPERSTHENE, (Fe,Mg)Si0 3 . Pyroxene, Ca,Mg, etc., silicate. ANTHOPHYLLITE, (Mg,Fe)SiO 3 . Amphibole, Ca,Mg, etc., silicate. GLAUCOPHANE, NaAl (SiO 3 ) 2 . (Fe,Mg)SiO 8 , IOLITE, H 2 (Mg,Fe) 4 Al 8 SiioO 3 7. Molybdophyllite, (Pb,Mg)SiO 4 .H 2 O. Pyrope, Mg 3 Al 2 (SiO 4 ) 3 . Chrysolite, (Mg,Fe) 2 SiO 4 . Monticellite, CaMgSiO 4 . Fosterite, Mg 2 SiO 4 . Hortonolite, (Fe,Mg,Mn) 2 SiO 4 . CHONDRODITE, [Mg(F,OH)] 2 Mg 3 (SiO 4 ) 2 . Humite, [Mg(F,OH)] 2 Mg 5 (Si0 4 ) 3 . Clinohumite, [Mg(F,OH)] 2 Mg 7 (SiO 4 ) 4 . Kornerupine, MgAl 2 SiO 6 . Sapphirine, Mg 5 Ali 2 Si 2 O 2 7. Serendibite, 10(Ca,Mg)O.5Al 2 O 3 .B 2 O 3 .6SiO 2 . Silicomagnesiofluorite, H 2 Ca 4 Mg 3 Si 2 O 7 Fi Lptrite,3(Ca,Mg)O.2(Al,Fe) 2 O 3 .4SiO 2 .2H 2 O. Biotite, Magnesium-iron mica. Phlogopite, Magnesium mica. Ta3niolite, K, Mg, silicate. Seybertite, H 3 (Mg,Ca) 6 Al 5 Si 2 Oi 8 . Xanthophyllite, H 8 (Mg,Ca) 14 Al 16 Si 6 O 52 . Chloritoid, H 2 (Fe,Mg)Al 2 SiO 7 . Clinochlore, Penninite, H 8 Mg 5 Al,Si 3 O 18 . Prochlorite, Fe,Mg, chlorite. Brunsvigite, 9(Fe,Mg)O.2Al 2 O 3 .6SiO 2 .8H 2 O. Griffithite, 4(Mg,Fe,Ca)O. (Al,Fe) 2 O 3 .5SiO 2 . 7H 2 O. Spodiophyllite, (Na 2 ,K 2 ) 2 (Mg,Fe) 3 (Fe,Al) 2 . Serpentine, H 4 Mg 3 Si 2 O 9 . Deweylite, 4MgO.3SiO 2 .6H 2 O. Genthite, 2NiO.2MgO.3SiO 2 .6H 2 O. Nepouite, 3(Ni,Mg)O.2SiO 2 .2H 2 O. Garnierite, H 2 (Ni,Mg)SiO 4 + water. Talc, H 2 M g3 (Si0 3 ) 4 . SEPIOLITE, H 4 Mg 2 Si 3 Oi . Spadaite, 5MgO.6SiO 2 .4H 2 O. Saponite, Hydrous Mg,Al, silicate. Celadonite, Fe,Mg,K, silicate. Pholidolite, K 2 0. 12(Fe,Mg)0. A1 2 3 . 13SiO 2 5H 2 O. Colerainite, 4MgO.Al 2 O 3 .2SiO 2 .5H 2 O. Tartarkaite, Al,Mg, hydrous silicate. Geikielite, (Mg,Fe)TiO 3 . Berzeliite, (Ca,Mg,Mn,Na 2 ) 3 As 2 O 8 . Wagnerite, (MgF)MgPO 4 . Adelite, (MgOH)CaAsO 4 . Tilasite, (MgF)CaAs0 4 . Lazulite, 2AlPO 4 .(Fe,Mg)(OH) 2 Struvite, Hydrous, NH 4 ,Mg, phosphate. Pyrophosphorite, Mg 2 P 2 O 7 .4(Ca 3 P 2 O 8 . Ca 2 P 2 O 7 ). Roselite, (Ca,Co,Mg) 3 As 2 O 8 .2H 2 O. Bobierrite, Mg 3 P 2 O 8 .8H 2 O. Hcernesite, Mg 3 As 2 O 8 .8H 2 O. Cabrerite, (Ni,Mg) 3 As 2 O 8 .8H 2 O. Newberyite, HMgPO 4 .3H 2 O. Hannayite i Hydrous, NH 4 ,Mg, Schertelite / phosphates. APPENDIX B 673 Liineburgite, 3MgO.B 2 O 3 .P 2 O 6 .8H 2 O. Nitromagnesite, Mg(NO 3 ) 2 .nH 2 O. Sussexite, H(Mn,Zn,Mg)BO 3 . Ludwigite. 3MgO.B 2 O 3 .FeO.Fe 2 O 3 . Vonsenite, 3(Fe,Mg)O.B 2 O 3 .FeO.Fe 2 O 3 . Magnesioludwigite, 3MgO.B 2 O 3 .MgO.Fe 2 O 3 . Pinakiolite, 3MgO.B 2 O 3 .MnO.Mn 2 O 3 . Szaibelyite, 2Mg 5 B4Oi,.3H 2 O. BORACITE, Mg 7 Cl 2 Bi 6 O 30 . Ascharite, Hydrous Mg, borate. Warwickite, (Mg,Fe) 3 TiB 2 O 8 . Pinnoite, MgB 2 O 4 .3H 2 O. Heintzite, Hydrous Mg,K, borate. Hulsite, 12(Fe,Mg)O.2Fe 2 O 3 . !SnO 2 .3B 2 O 3 . 2H 2 O. Hydroboracite, CaMgB 6 On.6H 2 O. Sulphoborite, 2MgSO4.4MgHBO 3 .7H 2 O. Langbeinite, K 2 Mg 2 (SO4) 3 . Vanthoffite, 3Na 2 SQ4.MgSO 4 . Kainite, MgSO 4 .KC1.3H 2 O. Kieserite, MgSO 4 .H 2 O. Epsomite, MgSO 4 .7H 2 O. Cupromagnesite, (Cu,Mg)SO 4 .7H 2 O. Loweite, MgSO 4 .Na 2 SO 4 .2H 2 O. Blodite, MgSO 4 .Na 2 SO 4 .4H 2 O. Leonite, MgSO 4 .K 2 SO 4 .4H 2 O. Boussingaulite, (NH 4 ) 2 SO 4 .MgSO 4 .6H 2 O. Picromerite, MgSO 4 .K 2 SO 4 .6H 2 O. Polyhalite, 2CaSO 4 .MgSO 4 .K 2 SO 4 .2H 2 O. Hexahydrite, MgSO 4 .6H 2 O. Pickeringite, MgSO 4 .Al 2 (SO 4 ) 3 .22H 2 O. Botryogen, MgO.FeO.Fe 2 O 3 .4SO 3 . 18H,O. Quetenite, MgO.Fe 2 O 3 .3SO 3 .13H 2 O. . MANGANESE Alabandite, MnS. Hauerite, MnS 2 . Samsonite, 2Ag 2 S.MnS.Sb 2 S 3 . Sacchite, MnCl 2 . Chlormanganokalite, 4KCl.MnCl 2 . Manganosite, MnO. Senaite, (Fe,Mn,Pb)O.TiO 2 . Pyrophanite, MhTiO 3 . Sitaparite, 9Mn 2 O 3 .4Fe 2 O 3 .MnO 2 .3CaO. Vredenburgite, 3Mn 3 O 4 .2Fe 2 O 3 . FRANKLINITE, (Fe,Zn,Mn)O. (Fe,Mn) 2 O 3 . Jacobsite, (Mn,Mg)O.(Fe, Mn) 2 O 3 . Hausmannite, MnO.Mn2O 3 . Coronadite, (Mn,Pb)Mn 3 O 7 . Crednerite, 3CuO.2Mn 2 O 3 . BRAUNITE, 3Mn 2 O 3 .MnSiO 3 . Bixbyite, FeO.MnO 2 . Polianite, MnO 2 . Pyrolusite, MnO 2 . Manganite, Mn 2 O 3 .H 2 O. Pyrochroite, Mn(OH) 2 . Backstromite, Mn(OH) 2 . Chalcophanite, (Mn,Zn)O.2MnO 2 .2H 2 O Heta3roHte, 2ZnO.2Mn 2 O 3 .lH 2 O. Psilomelane, Hydrous Mn manganate. Wad, Mn oxides. Skemmatite, 3MnO 2 .2Fe 2 O 3 .6H 2 O. Beldongrite, 6Mn 3 O5.Fe 2 O 8 .8H 2 O. Rhodochrosite, MnCO 3 . Schizolite, HNa(Ca,Mn) 2 (SiO 3 ) 3 Lavenite, Zr-silicate of Mn, Ca. Rhodonite, MnSiO 3 . Pyroxmangite, Mn,Fe pyroxene. Babingtonite, (Ca,Fe,Mn)SiO 3 with Fe 2 (SiO 3 ) 3 . Margarosanite, Pb(Ca,Mn) 2 (SiO 3 ) 3 . Helvite, (Be,Mn,Fe) 7 Si 3 O 12 S. Danalite, (Be,Fe,Zn,Mn) 7 Si 3 O 12 S. Spessartite, Mn 3 Al 2 (SiO 4 ) 3 . Partschinite, (Mn,Fe) 3 Al 2 Si 3 Oi 2 . Glaucochroite, CaMnSiO 4 . Knebelite, (Fe,Mn) 2 SiO 4 . Tephrdite, Mn 2 SiO 4 . Trimerite, (Mn,Ca) 2 SiO 4 .Be 2 SiO 4 . Friedelite, H 7 (MnCl)Mn 4 Si 4 Oi 6 . Pyrosmahte, H 7 ((Fe,Mn)Cl)(Fe,Mn) 4 Si 4 Oi 6 Piedmontite, Mn epidote. Hancockite, Pb,Mn,Ca,Al, etc., silicate. Harstigite, Mn,Ca, silicate. Leucophoenicite, Mn 5 (MnOH) 2 (SiO 4 ) 3 . Ardennite, Al,Mn,V, silicate. Langbanite, Mn silicate with Fe antimon- ate. Kentrolite, 3PbO.2Mn 2 O 3 .3SiO 2 . Carpholite, H 4 MnAl 2 Si 2 O 10 . Pochite, Hi6Fe 8 Mn 2 Si 3 O 2 9. Inesite, H 2 (Mn,Ca) 6 Si 6 Oi9.3H 2 O. Ganophyllite, 7MnO.Al 2 O 3 .8SiO 2 .6H 2 O. Alurgite, Manganese mica. Dixenite, MnSiO 3 .2Mn 2 (OH)AsO 3 . Bementite, H 6 Mn 5 (SiO 4 ) 4 . Ectropite, Mn 2 Si 8 O 28 .7H 2 O. Agnolite, H 2 Mn 3 (SiO 3 ) 4 .H 2 O. Hodgkinsonite, 3(Zn,Mn)O.SiO 2 .H 2 O. Gageite, Hydrous, Mn,Mg,Zn, silicate. Caryopilite, 4MnO.3SiO 2 .3H 2 O. Neotocite, Hydrous, Mn, Fe, silicate. Astrophyllite, Na,K,Fe,Mn,Ti-silicate. Neptunite, Fe,Mn,K,Na, titano-silicate. COLUMBITE-TANTALITE, (Fe,Mn) (Nb,Ta) 2 O 6 . Hielmite, Y,Fe,Mn,Ca, stanno-tantalate. Berzeliite, (Ca,Mg,Mn,Na 2 ) 3 As 2 O 8 . Lithiophilite, Li(Mn,Fe)PO 4 . Natrophilite, NaMnPO 4 . Graftonite, (Fe,Mn,Ca) 3 P 2 O 8 . Triplite, (RF)RPO 4 ; R = Fe,Mn. Triploidite (ROH)RPO 4 ; R = Mn.Fe. Sarkinite, (MnOH)MnAsO 4 . Trigonite, Pb 3 MnH(AsO 3 ) 3 . Lacroixite, Na 4 (Ca,Mn) 4 Al3(F,OH) 4 P 3 Oi . 2H 2 0. Pyrobelonite, 4PbO.7MnO.2V 2 O 6 .3H 2 O. Allactite, Mn 3 As 2 O 8 .4Mn(OH) 2 . Synadelphite, 2(Al,Mn)AsO 4 .5Mn(OH) 2 . Flinkite, MnAsO 4 .2Mn(OH) 2 . HematoHte, (Al,Mn)AsO 4 .4Mn(OH) 2 . Retzian, Y,Mn,Ca, phosphate. Arseniopleite, (Mn,Ca) 9 (Mn,Fe) 2 (OH) (AsO 4 ) 6 . Manganostibiite, Mn antimonate. 674 APPENDIX B Dickinsonite l Hydrous Mn,Fe,Na, Fillowite I phosphates. Brandite, Ca 2 MnAs 2 O 8 .2H 2 O. Fairfieldite, Ca 3 MnP 2 O 8 .2H 2 O. Reddingite, Mn 3 P 2 O 8 .3H 2 O. Palaite, 5MnO.2P 2 O 6 .4H 2 O. Stewartite, 3MnO.P 2 O 5 .4H 2 O. Purpurite, 2(Fe,Mn)PO 4 .H 2 O. Sicklerite, Fe 2 O 3 .6MnO.4P 2 O 5 .3(Li,H) 2 O. Salmonsite, Fe 2 O 3 .9MnO.4P 2 O 6 . 14H 2 O. Hureaulite, H 2 Mn 6 (PO 4 ) 4 .4H 2 O. Hemafibrite, Mn 3 As 2 O 8 .3Mn (OH) 2 .2H 2 O. Eosphorite, 2AlPO 4 .2(Mn,Fe) (OH) 2 .2H 2 O. Rosche-rite, (Mn,Fe,Ca) 2 Al(OH) (PO 4 )o.2H,O Catoptrite, 14(Mn,Fe)O.2(Al,Fe) 2 O 3 .2SiO 2 . Sussexite, H(Mn,Zn,Mg)BO 3 . Pinakiolite, 3MgO.B 2 O 3 .MnO.Mn 2 O 3 . Szmikite, MnSO 4 .H 2 O. Ilesite, (Mn,Zn,Fe)SOi.4H 2 O. Mallardite, MnSO 4 .7H 2 O. Apjohnite, MnSO 4 .Al 2 (SO 4 ) 3 .24H 2 O. Dietrichite, (Zn,Fe,Mn)S0 4 .Al 2 (SO 4 ) 3 . 22H.O. Hiibnerite, MnWO 4 . MERCURY Native Mercury, Hg. Amalgam, (Ag,Hg). Metacinnabarite, HgS. Tiemannite, HgSe. Onofrite, Hg(S,Se). Cotoradoite, HgTe. Cinnabar, HgS. Livingstonite, HgS.2Sb 2 S 3 . Calomel, HgCl. Kleinite, Hg,NH 4 , chloride. Eglestonite, Hg 4 Cl 2 O. Terlinguaite, HgClO. Mosesite, Hydrous Hg,NH 4 , chloride. Montroydite, HgO. Ammiolite, Hg antimonite. MOLYBDENUM Molybdenite, MoS 2 . Molybdite, MoO 3 . Powellite, Ca(Mo,W)O 4 . Chillagite, 3PbWO 4 .PbMoO 4 . WULFENITE, PbMoO 4 . Koechlinite, Bi 2 O 3 .Mo0 3 . NICKEL Awaruite, FeNi 2 . Jbsephinite, FeNi 3 . Maucherite, Ni 3 As 2 . PENTLANDITE, (Fe,Ni)S. Millerite,NiS Beyrichite, NiS. Hauchecornite, Ni(Bi,Sb,S)? Niccolite, NiAs. Breithauptite, NiSb Polydymite, Ni 4 S 6 . Badenite, (Co,Ni,Fe) 2 (As,Bi) 8 . Bravoite, (Fe,Ni)S 2 . Cobaltnickelpyrite, (Co,Ni,Fe)S 2 . CHLOANTHITE, NiAs 2 . Gersdorffite, NiAsS. Willyamite, CoS 2 .NiS 2 .CoSb 2 .NiSb 2 . Villamaninite, Cu,Ni,Co,Fe, sulphide. Ullmanite, NiSbS. Kallilite, Ni(Sb,Bi)S. Rammelsbergite, NiAs 2 . Wolfachite, Ni(As,Sb)S. Melonite, NiTe 2 . Bunsenite, NiO. Zaratite, NiCO 3 .2Ni(OH) 2 .4H 2 O. Genthite, 2NiO.2MgO.3SiO 2 .6H 2 O. Nepouite, 3(Ni,Mg)O.2SiO 2 .2H 2 O. Garnierite, H 2 (Ni,Mg)SiO 4 + water. Connarite, H 4 Ni 2 Si 3 Oi . Annabergite, Ni 3 As 2 O 8 .8H 2 O. Cabrerite, (Ni,Mg) 3 As 2 O 8 .8H 2 O. Forbesite, H 2 (Ni,Co) 2 As 2 O 8 .8H 2 O. Lindackerite, 3NiO.6CuO.SO 3 .2As 2 O 6 . 7H 2 0. Morenosite, NiSO 4 .7H 2 O. PLATINUM Native Platinum, Pt. Sperrylite, PtAs 2 . POTASSIUM SYLVITE, KC1. Chlormanganokalite, 4KCl.MnCl 2 . Rinneite, FeCl 2 .3KCl.NaCl. Hieratite, K,Si, fluoride. CARNALLITE, KCl.MgCl 2 .6HoO. Kremersite, KCl,NH 4 Cl.FeCl 2 .H 2 O. Erythrosiderite, 2KCl.FeCl 3 .H 2 O. Milarite, HKCa 2 Al 2 (Si 2 O 5 ) 6 . Orthoclase, Microcline, KAlSi 3 O 8 . Hyalophane, (K 2 ,Ba)Al 2 (SiO 3 ) 4 . Anorthoclase, (Na,K)AlSi 3 O 8 . Leucite, KAl(SiO 3 ) 2 . Kaliophilite, KAlSiO 4 . ApophylUte, H 7 KCa 4 (SiO 3 ) 8 .4|H 2 O. PtiloHte, (Ca,K 2 ,Na 2 )Al 2 Si 10 O 24 .5H 2 O. Mordenite, (Ca,K 2 ,Na 2 )Al 2 SiioO 24 .20H 2 0. - Wellsite, (Ba,Ca,K 2 )Al 2 Si 3 O 10 .3H 2 0. Phillipsite, (K 2 ,Ca)Al 2 Si 4 O, 2 .4iH 2 O. Harmotone, (K 2 , Ba) Al 2 Si 6 Oi 4 . 5H 2 O . Offretite, Potash zeolite. Muscovite, H 2 KAl 3 (SiO 4 ) 3 . TaBniolite, K,Mg, silicate. Sppdiophyllite, (Na 2 K 2 ) 2 (Mg,Fe) 3 (Fe,Al) 2 (SiO 3 ) 8 . Celadonite, Fe,Mg,K, silicate. Glauconite, Hydrous Fe, K, silicate. Astrophyllite, Na,K,Mn,Fe, titano-sih'cate. Palmerite, HK 2 Al 2 (PO 4 ) 3 .7HoO. Carnotite, K 2 O.2U 2 O 3 .V 2 O 5 .3H 2 O. Niter, KNOs. Rhpdizite, A1,K, borate. Heintzite, Hydrous Mg,K, borate. Taylorite, 5K 2 SO 4 . (NH 4 ) 2 S0 4 . Aphthitalite, (K,Na) 2 SO 4 . Langbeinite, K 2 Mg 2 (SO 4 ) 3 . APPENDIX B 675 Kainite, MgSO 4 .KC1.3H 2 O. Hanksite, 9Na 2 SO4.2Na 2 CO 3 .KCl. Misenite, HKSO 4 . Lecontite, (Na,NH 4 ,K)SO 4 .2H 2 O. Syngenite, CaSO 4 .K 2 SO 4 .H 2 O. Leonite, MgSO 4 .K 2 SO 4 .4H 2 O. Picromerite, MgSO 4 .K 2 SO 4 .6H 2 O. Polyhalite, 2CaSO 4 .MgSO 4 .K 2 SO 4 .2H 2 O. Kalinite, KA1(SO 4 ) 2 .12H 2 O. Voltaite, 3(K 2 ,Fe)O.2(Al,Fe) 2 O 3 .6SO 3 .9H 2 O. Metavoltine, 5(K 2 ,Na 2 ,Fe)O.3Fe 2 O 3 .12SO 8 . 18H 2 O. ALUNITE, K 2 A1 6 (OH) 12 (SO 4 ) 4 . Jarosite, K 2 Fe 6 (OH) 12 (SO 4 ) 4 . Palmierite, 3(K,Na) 2 SO 4 .4PbSO 4 , Lowigite, K 2 O.3A1 2 O 3 .4SO 3 .9H 2 O. SILVER Native Silver, Ag. Amalgam, (Ag,Hg). Dyscrasite, Ag 3 Sb. Chilenite, Ag 6 Bi. Cocinerite, Cu 4 AgS. Stutzite, Ag 4 Te. Naumannite, (Ag 2 ,Pb)Se Argentite, Ag 2 S. Hessite, Ag 2 Te. , Petzite, (Ag,Au) 2 Te. Aquilarite, Ag 2 (S,Se). Eucairite, Cu 2 Se.AgSe. Crookesite, (Cu,Tl,Ag) 2 Se. : Stromeyrite, (Ag,Cu) 2 S. Acanthite, Ag 2 S. Sternbergite, Ag 2 S.Fe 4 S 5 . Sylvanite, (Au,Ag)Te 2 . Krennerite, (Au,Ag)Te 2 . Muthmannite, (Ag,Au)Te. Andorite, Ag 2 S.2PbS.3Sb 2 S 3 . Matildite, Ag 2 S.Bi 2 S 3 . Miargyrite, Ag 2 S.Sb 2 S 3 . Smithite, Ag 2 S.Sb 2 S 3 . Trechmanite, Ag 2 S.As 2 S 3 . Hutchinsonite, (Tl,Ag,Cu) 2 S.As 2 S 3 + PbS. As 2 S 3 (?). Schirmerite, 3(Ag 2 .Pb)S.2Bi 2 S 3 . Freieslebenite, 5(Pb,Ag 2 )S.2Sb 2 S 3 . Diaphorite, 5(Pb,Ag 2 )S.2Sb 2 S 3 . Stylotypite, 3(Cu 2 ,Ag 2 ,Fe)S.Sb 2 S 3 . Lengenbachite, 7[Pb, (Ag,Cu) 2 ]S.2As 2 S 8 . PYRARGYRITE, 3Ag 2 S.Sb 2 S 3 . PROUSTITE, 3Ag 2 S.As 2 S 3 . Pyrostilpnite, 3Ag 2 S.Sb 2 S 3 . Samsonite, 2Ag 2 S.MnS.Sb 2 S 3 . STEPHANITE, 5Ag 2 S.Sb 2 S 3 . POLYBASITE, 9Ag 2 S.Sb 2 S 3 . Pearceite, 9Ag 2 S.As 2 S 3 . Polyargyrite, 12Ag 2 S.Sb 2 S 3 . Xanthoconite, 3Ag 2 S.As 2 Ss. Argyrodite, 4Ag 2 S.GeS 2 . Canfieldite, 4Ag 2 S.SnS 2 . Cerargyrite, AgCl. Embolite, Ag(Br,Cl). Bromyrite, AgBr. lodobromite, 2AgCl.2AgBr.AgI. Miersite, 4AgI.CuI. lodyrite, Agl. SODIUM Halite, NaCl. Villiaumite, NaF. Huantajayite, 20NaCl.AgCl. Rinneite, FeCl 3 .3KCl.NaCl. CRYOLITE, Na 3 AlF 6 . ChioUte, 5NaF.3AlF 3 . Ralstonite, (Na 2 ,Mg)F 2 .3Al(F,OH) 3 .2H 2 O. Northupite, MgCO 3 .Na 2 CO 3 .NaCl. Tychite, 2MgCO 3 .2Na 2 CO 3 .Na 2 SO 4 . Dawsonite, Na 3 Al(CO 3 ) 3 .2Al(OH) 3 . Thermonatrite, Na 2 CO 3 .H 2 O. Natron, Na 2 CO 3 . 10H 2 O. Pirssonite, CaCO 3 .Na 2 CO 3 .2H 2 O. Gay-Lussite, CaCO 3 .Na 2 CO 3 .5H 2 O. Trona, Na 2 CO 3 .HNaCO 3 .2H 2 O. Eudidymite, Epididymite, HNaBeSi 3 O 8 . Rivaite, (Ca,Na 2 )Si 2 O 6 . Anorthoclase, (Na,K)AlSi 3 O 8 . Albite, NaAlSi 3 O 8 . Oligoclase Mixtures of CaAl 2 Si 2 O 8 , and Andesine Labradorite Anemousite, NaO.2CaO.3Al 2 O 3 .9SiO 2 . Ussingite, HNa 2 Al'(SiO 3 ) 3 . ACMITE, NaFe(SiO 3 ) 2 . JADEITE, NaAl(SiO 3 ) 2 . PECTOLITE, HNaCa 2 (SiO 3 ) 3 . Schizolite, HNa(Ca,Mn) 2 (SiO 3 ) 3 . Rosenbuschite, near pectolite with Zr. Wohlerite, Zr-silicate and niobate of Ca,Na. Hiortdahlite, (Na 2 .Ca) (Si,Zr)O 3 . GLAUCOPHANE, NaAl(SiO 3 ) 2 .(Fe,Mg) Si0 3 . RIEBECKITE, 2NaFe(SiO 3 )o.FeSiO 3 . CROCIDOLITE, NaFe(SiO 3 ) 2 .FeSiO 3 . Arfyedsonite, Na^a^e" silicate. jiEnigmatite, Fe,Na,Ti-silicate. Weinbergerite, NaAlSiO 4 .3FeSiO 3 . Elpidite, Na 2 O.ZrO 2 .6SiO 2 .3H 2 O. Catapleiite, H 4 (Na 2 , Ca) ZrSi 3 On . Nephelite, NaAlSiO 4 . CANCRINITE, H 6 Na6Ca(NaCO 3 ) 2 Al 8 (Si0 4 ) 9 . Microsommite, Davyne, near cancrimte. SODALITE, Na 4 (AlCl)Al 2 (SiO 4 ) 3 Hackmanite, near sodalite. HAITTNITE, (Na 2 ,Ca) 2 (NaSO 4 .Al)Al 2 (SiO 4 ) 3 . Noselite, Na 4 (NaSO 4 .Al)Al 2 (SiO 4 ) 3 . LAZURITE, Na 4 (NaS 3 .Al)Al 2 (SiO 4 ) 3 . SCAPOLITE GROUP, Mixtures of Ca 4 Al 6 Si 6 O 26 and Na 4 Al 3 Si 9 O 24 Cl. Sarcolite, (Ca,Na 2 ) 3 Al 2 (SiO 4 ) 3 . Melilite, Na 2 (Ca,Mg) n (Al,Fe) 4 (SiO 4 ) 9 . Mordenite, (Ca,K 2 ,Na 2 )Al 2 Si, O 24 .20H 2 O. Stilbite, (Na 2 ,Ca)Al 2 Si 6 Oi 6 .6H 2 O. 676 APPENDIX B Flokite, H 8 (Ca,Na2)Al 2 Si 9 O 26 .2H 2 O. CHABAZITE, (Ca,Na 2 )Al 2 Si 4 Oi 2 .6H 2 O. Gmelinite, (Na 2 Ca)Al 2 Si 4 O I2 .6H 2 O. Analcite, NaAlSi 2 O 6 .H 2 O. Faujasite, H4Na 2 CaAl4Si 10 O3 8 . Natrolite, Na 2 Al 2 Si 3 Oi .2H 2 O. Mesolite, Na 2 Al 2 Si 3 Oi .2H 2 O + 2[CaAl 2 Si 3 Oi .3H 2 O]. Gonnardite, (Ca,Na 2 ) 2 Al 2 Si 6 O, 5 .5|H 2 O. Thomsomte, (Na 2 ,Ca)Al 2 Si 2 O 8 .2H 2 O. Hydrothomsonite, (H 2 ,Na 2 ,Ca)Al 2 Si 2 O 8 . 5H 2 q. Arduinite, Ca,Na, zeolite. Echellite, (Ca,Na 2 )O.2Al 2 O 3 .3SiO 2 .4H 2 O. Epidesmine, (Na 2 ,Ca)Al 2 Si 6 Oi 6 .6H 2 O. Erionite, H 2 CaK 2 Na 2 Al 2 Si6O 17 .5H 2 O. Hydronephelite, HNa 2 Al 3 Si 3 Oi 2 .3H 2 O. Paragonite, H 2 NaAl 3 (SiO 4 ) 3 . Spodiophyllite, (Na 2 ,K 2 ) 2 (Mg,Fe) 3 (Fe,Al) 2 (Si0 3 ) 8 . Searlesite, NaB(SiO 3 ) 2 .H 2 O. Molengraafite, Ca,Na, titano-silicate. Astrophyllite, Na,K,Mn,Fe,titano-silicate. Narsarsukite, Fe,Na, titano-silicate. Leucosphenite, Na 4 Ba(TiO) 2 (Si 2 O 5 ) 5 . Lorenzenite, Na 2 (TiO) 2 Si 2 O 7 . Epistolite, Ti,Na,etc., niobate. Berzeliite, (Ca,Mg,Mn,Na 2 ) 3 As 2 O 8 . Natrophilite, NaMnPO 4 . Beryllonite, NaBePO 4 . Jezekite, Na 4 CaAl(AlO) (F,OH) 4 (PO 4 ) 2 . Lacroixite, Na 4 (Ca,Mn) 4 Al 3 (F,OH) 4 P 3 O 16 . 2H 2 O. Durangite, Na(AlF)AsO 4 . Fremontite, (Na,Li)Al(OH,F)PO 4 . raiowite 11 ^ }3(Mn,Fe,Na 2 ) 3 P 2 8 .H 2 0. Stercorite, HNa(NH 4 )PO 4 .4H 2 O. Soumansite, Hydrous Al,Na, fluophosphate. SODA NITER, NaNO 3 . Darapskite, NaNO 3 .Na 2 SO 4 .H 2 O. Nitroglauberite, 6NaNO 3 .2Na 2 SO 4 .3H 2 O Borax, Na 2 B 4 O 7 .10H 2 O. Ulexite, NaCaB 5 O 9 .8H 2 O. Thenardite, Na 2 SO 4 . Aphthitalite, (K,Na) 2 SO 4 . GLAUBERITE, Na 2 SO 4 .CaSO 4 . Vanthoffite, 3Na 2 SO 4 .MgSO 4 . Sulphohalite, 3Na 2 SO 4 .NaCl.NaF. Caracolite, Pb(OH)Cl.Na 2 SO 4 . Hanksite, 9Na 2 SO 4 .2Na 2 CO 3 .KCl Lecontite, (Na,NH 4 ,K) 2 SO 4 .2H 2 O. Mirabikte, Na 2 SO 4 . 10H 2 O. Loweite, MgSO 4 .Na 2 SO 4 .2iH 2 O. Blodite, MgSO 4 .Na 2 SO 4 .4H 2 O. Mendozite, NaAI(SO 4 ) 2 .12H 2 O. Krohnkite, CuSO 4 .Na 2 SO 4 .2H 2 O. NatrochalciteCu 4 (OH) 2 (S0 4 ) 2 .Na 2 S0 4 .2H 2 0. Ferronatnte, 3Na 2 S0 4 .Fe 2 (S0 4 ) 3 .6H 2 6 Sideronatrite, 2Na20.Fe203.4S03.7H20 3 . 12S0 3 . Palmierite, 3(K,Na) 2 SO 4 .4PbSO 4 . Almeriite, Na 2 SO 4 .Al 2 (SO 4 ) 3 .5Al(OH) 3 .H 2 O. STRONTIUM Strontianite, SrCO 3 . Ancylite, 4Ce(OH)CO 3 .3SrCO 3 .3H 2 O. Ambatoarinite. Rare earths, Sr, carbonate. Brewsterite, H 4 (Sr,Ba,Ca)Al 2 (SiO 3 ) 6 .3H 2 O. Fermorite, (Ca,Sr) 4 [Ca(OH,F)][(P,As)O 4 ] 3 . Hamlinite, Sr,Al, phosphate. Harttite, Sr.Al. phosphate and sulphate. Celestite, SrSO 4 . THORIUM Trftomfte & /Ca,Ce,Y,Th, fluo-silicates. Thorite, ThSiO 4 . Auerlite, Th silico-phosphate. Yttrialite, Th,Y, silicate. Mackintoshite, U,Th,Ce, silicate. Yttrocrasite, Hydrous Y,Th, titanate. Pyrochlore, RNb 2 O 6 .R(Ti,Th)O 3 . MONAZITE, (Ce,La,Di)PO 4 with ThO 2 . Thorianite, Th and U oxides. TIN Stannite, Cu 2 S.FeS.SnS 2 . Canfieldite, 4Ag 2 "S.SnS 2 . Teallite, PbSnS 2 . Franckeite, Pb 5 Sn 3 FeSb 2 S 14 . Cylindrite, Pb 3 Sn 4 FeSb 2 Si 4 . Cassiterite, SnO 2 . Stokesite, H.CaSnSisOu. Hielmite, Y,Fe,Mn,Ca, stanno-niobate. Nordenskioldine, CaSn(BO 3 ) 2 . Hulsite, 12(Fe,Mg)0.2Fe 2 3 . !SnO 2 .3B 2 O 3 . 2H 2 O. TITANIUM ILMENITE, FeTiO 3 . Senaite, (Fe,Mn,Pb)O.TiO 2 . Arizonite, Fe 2 O 3 .3TiO 2 . Pyrophanite, MnTiO 3 . Pseudobrookite, Fe 4 (TiO 4 ) 3 . Rutite, Ti0 2 . Octahedrite, Brookite, TiO 2 . Uhligite, Ca(Ti,Zr)O 5 .Al(Ti,Al)O 6 . Natrojarosite, Na 2 Fe 6 (OH) 12 (S0 4 ) 4 Molengraafite, Ca,Na, titano-silicate. Keilhauite, Ca,Al,Fe,Y, titano-silicate. Ischeffkmite, Ce, etc., titano-silicate Astrophyllite, Na,K,Fe,Mn, titano-silicate. Johnstrupite Mosandrite Ce, etc., titano-silicates Rmkite Narsarsukite, Fe,Na, titano-silicate. Neptunite, Fe,Mn,Na,K, titano-silicate. Benitoite, BaTiSi 3 O 9 . Leucosphenite, Na 4 Ba(TiO) 2 (Si 2 O 6 ) 6 . Lorenzenite, Na 2 (TiO) 2 Si 2 O 7 . Joaquinite, Ca,Fe, titano-sih'cate. PEROVSKITE, CaTiO 3 . Knopite, Ca,Ce, titanate. APPENDIX B 677 Dysanalyte, Ca,Fe, titano-silicate. Geikielite, Mg,Fe, titanate. Delorenzite, Fe,U,Y, titanate. Yttrocrasite, Hydrous Y, Th, titanate. Brannerite, (UO,TiO,UO 2 )TiO 3 . Pyrochlore, RNb 2 p 6 .R(Ti,Th)O 3 . Aeschynite, Ce, niobate-titanate. Polymignite, Ce,Fe,Ca, niobate-titanate. Euxenite 1 ^ r ^ TT i_ j Polvcrase Y Ce,U mobate- Blomstrandine-Priorite j tltanates - Betafite, U, etc., niobate-titanate. Epistolite, Na,Ti, etc., mobate. Lewisite, 5CaO.2Tiq 2 .3Sb 2 O 5 . Mauzeliite, Pb,Ca, titano-antimonate. Warwickite, (Mg,Fe) 3 TiB 2 O 8 . TUNGSTEN Tungstenite, WS 2 . Tungstite, WO 3 . WOLFRAMITE, (Fe,Mn)WO 4 . Hubnerite, MnWO 4 . SCHEELITE, CaWO 4 . Cuprotungstite, CuWO 4 . Powellite, Ca(Mo,W)O 4 . Chillagite, 3PbWO 4 .PbMoO 4 . Reinite, FeWO 4 . Ferritungstite, Fe 2 O 3 .WO 3 .6H 2 O. URANIUM Rutherfordine, UO 2 CO 3 . Uranothallite, 2CaCO 3 .U(CO 3 ) 2 .10H 2 O. Liebigite, Hydrous, U,Ca, carbonate. Voglite, Hydrous, U, Ca, Cu, carbonate. Mackintoshite, U,Th,Ce, silicate. Uranophane, CaO.2UO 3 .2SiO 2 .6H 2 O. Delorenzite, Fe,U,Y, titanate. Brannerite, (UO,TiO,UO 2 )TiO 3 . Hatchettolite, U, tantalo-niobate. Samiresite, U, etc., niobate. Fergusonite, Y,Er ; U, niobate. Samarskite, Fe,Ca,U,Ce,Y, niobate. Ampangabeite, U, etc., niobate. Annerodite, U,Y, niobate. Euxenite 1 v n^ TT u ^ Polvcrase \ Y > Ce > U ' mobate- Blomstrandine-Priorite j tltanates - Betafite, U, niobate-titanate. Plumboniobite, Y,U,Pb, niobate. Uvanite, 2UO 3 .3V 2 O 6 .15H 2 O. Ferganite, U 3 (VO 4 ) 2 .6H 2 O. Torbernite, Cu(UO 2 ) 2 P 2 O 8 .8H 3 O. Zeunerite, Cu(UO 2 ) 2 As 2 O 8 .8H 2 O. Bas'sTtfte }Ca(UO 2 ) 2 P 2 O 8 .8H 2 O. Uranospinite, Ca(UO 2 ) 2 As 2 O 8 .8H 2 O. Uranocircite, Ba(UO 2 ) 2 P 2 O 8 .8H 2 O. CARNOTITE, K 2 O.2U 2 O.V 2 O 6 .3H 2 O. Tyuyamunite, CaO.2UO 3 .V 2 O 5 .4H 2 O. Uranospathite, Hydrous uranyl phosphate. Phosphuranylite, (UO 2 ) 3 P 2 O 8 .6H 2 O. Trogerite, (UO 2 ) 3 As 2 O 8 .12H 2 O. Walpurgite, Bi 10 (UO 2 ) 3 (OH) 24 (AsO 4 ) 4 . .URANINITE, Uranyl, etc., uranate. Gummite, alteration of uraninite. Thorianite, Th and U oxides. Uranosphaerite, (BiO) 2 U 2 O 7 .3H 2 O. Johannite, Hydrous Cu,U, sulphate. Gilpinite, (Cu,Fe,Na 2 )O.UO 3 .SO 3 .4H 2 O. Uranopilite, CaU 8 S 2 O 3 i.25H 2 O. VANADIUM fcS PATRONITE, VS 4 . Sulvanite, 3Cu 2 S.V 2 S 5 . Alaite, V 2 O 5 .H 2 O. Ardennite, Al,Mn,V, silicate. Roscoelite, Vanadium mica. Pucherite, BiVO 4 . Vanadinite, Pb 4 (PbCl)(VO 4 ) 3 . Descloizite, (Pb,Zn) 2 (OH)VO 4 . Pyrobelonite, 4PbO.7MnO.2V 2 O 5 .3H 2 O. Dechenite, PbV 2 O 6 . Calciovolborthite, (Cu,Ca) 3 V 2 O 8 . (Cu,Ca) (OH) 2 . Turanite, 5CuO.V 2 O 5 .2HoO. }Pb,Cu,nadates. Uvanite, 2UO 3 .3V 2 O 5 .15H 2 O. Ferganite, U 3 (VO 4 ) 2 .6H 2 O. Fernandinite, CaO. V 2 O 4 .5V 2 O 5 . 14H 2 O. Pascoite, 2CaO.3V 2 O 5 .llH 2 O. Pintadoite, 2CaO.V 2 O 6 .9H 2 O. MeUhewettite } CaO.3V !O ,9H 2 O. Volborthite, Hydrous, Cu,Ba,Ca, vanadate. Hiigelite, Hydrous, Pb,Zn, vanadate. CARNOTITE, K 2 O.2U 2 O 3 .V 2 O 5 .3H 2 O. Tyuyamunite, CaO.2UO 3 .V 2 O 5 .4H 2 O. Minasragrite, (V 2 O 2 )H 2 (SO 4 ) 3 . 15H 2 O. YTTRIUM, Etc. Yttrofluorite, (Ca 3 ,Y 2 )F 6 . Yttrocerite, (Y,Er,Ce)F 3 .5CaF 2 .H 2 O. Tengerite, Y carbonate. Cappelenite, Y,Ba, boro-silicate. Melanocerite \ Caryocerite [Ca,Y,Ce, fluo-silicates. Steenstrupine J Tritomite, Th,Ce,Y,Ca, fluo-silicate. Gadolinite, Be 2 FeY 2 Si 2 Oi . Yttriah'te, Th,Y, silicate. Rowlandite, Y sih'cate. . Thalenite, Y silicate Thortveitite, (Sc,Y) 2 Si 2 O 7 . Cenosite, H 4 Ca 2 (Y,Er) 2 CSiOi 7 . Keilhauite, Ca,Al,Fe,Y, titano-silicate. Delorenzite, Fe,U,Y, titanate. Yttrocrasite, Hydrous Y,Th, titanate. Risorite, Y niobate. Fergusonite, Y,Er r niobate. Sipylite, Er niobate. Yttrotantalite, Y, etc., tantalate-niobate. 678 APPENDIX B Samarskite, Fe,Ca,U,Ce,Y, niobate-tanta- late. Annerodite, U,Y, niobate. Hielmite, Y,Fe,Mn,Ca, stanno-tantalate. Euxenite ! Y ,Ce,U, niobate- Plumboniobite, Y,U,Pb,Fe, niobate. XENOTIME, YPO 4 . Retzian, Y,Mn,Ca, arsenate. Rhabdophanite, Hydrous Ce,Y, phosphate. ZINC Sphalerite, ZnS. Wurtzite, ZnS. Voltzite, Zn^O. ZINCITE, ZnO. Gahnite, ZnO.A] 2 O 3 . FRANKLINITE, (Fe,Zn,Mn)O. (Fe,Mn) 2 3 . Chalcophanite, (Mn,Zn)O.2MnO 2 .2H 2 O. Hetserolite, 2ZnO.2Mn 2 O 3 .lH 2 O. Smithsonite, ZnCO 3 . Rosasite, 2CuO.CuCO 3 .5ZnCO 3 ? Aurichalcite, 2(Zn,Cu)CO 3 ,3(Zn,Cu)(OH) 2 . Hydrozincite, ZnCO 3 .2Zn(OH) 2 . Hardystonite, Ca 2 ZnSi 2 O 7 . Danalite, (Be,Fe,Zn,Mn) 7 Si 3 Oi 2 S. Willemite, Zn 2 SiO 4 . Calamine, H 2 ZnSiO 5 . Clinohedrite, H 2 CaZnSiO 5 . Hodgkinsonite, 3(Zn,Mn)O.SiO 2 .H 2 0. Gageite, Hydrous, Mn, MR, Zn, silicate. Tarbuttite, Zn 3 P 2 O 8 .Zn(OH) 2 . Adamite, Zn 2 (OH)AsO 4 . Descloizite, (Pb,Zn) 2 (OH)VO 4 . Par^peite } ^P 2 O 8 .4H !O . Kottigite, Zn 3 As 2 O 8 .8H 2 O. Barthite, 3ZnO.CuO.3As 2 O 5 .2H 2 O. Hugelite, Hydrous, Pb, Zn, vanadate Spencerite, Zn 3 (PO 4 ) 2 .Zn (OH) 2 .3H 2 O. Hibbenite, 2Zn 3 (PO 4 ) 2 .Zn(OH) 2 .6iH 2 O. Veszelyite, Hydrous, Cu, Zn, phospho- arsenate. Kehoeite, Hydrous, Al, Zn, phosphate. Sussexite, H(Mn,Zn,Mg)BO 3 . Zinkosite, ZnSO 4 . Ilesite, (Mn,Zn,Fe)SO 4 .4H 2 O. Goslarite, ZnSO 4 .7H 2 O. Dietrichite, (Zn,Fe,Mn)SO 4 .Al 2 (SO 4 ) 3 . 22H 2 O. Serpierite, Hydrous, Cu, Zn, sulphate. Zincaluminite, 2ZnSO 4 .4Zn(OH) 2 .6Al(OH) 3 . 5H 2 O. ZIRCONIUM Baddeleyite, ZrO 2 . Uhligite, Ca(Ti,Zr)O 6 .Al(Ti,Al)O 6 . Rosenbuschite, Na,Ca,Zr, silicate. Wohlerite, Na,Ca,Zr, silicate and niobate. Lavenite, Mn,Ca,Zr, silicate. Hiortdahlite, (Na 2 , Ca) (Si, Zr) O 3 . Eudialyte, Zr,Fe,Ca,Na, silicate. Elpidite, Na 2 O.ZrO 2 .6SiO 2 .3H 2 O. Catapleiite, H 4 (Na 2 ,Ca)ZrSi3O n . Zircon, Zr SiO 4 . Chalcolamprite, R ' 'Nb .O 6 . R ' 'SiO 3 . APPENDIX B 679 TABLE II. MINERALS ARRANGED ACCORDING TO THEIR SYSTEM OF CRYSTALLIZATION. The following lists are intended to include all well-recognized species, whose crystalliz- ation is known, arranged according to the system to which they belong, and further classi- fied by their luster and specific gravity; the hardness is also given in each case. I. CRYSTALLIZATION ISOMETRIC.* A. LUSTER NONMETALLIC. Specific Gravity. Hard- ness. Specific Gravity. Hard- ness. Sal Ammoniac (p. 397) . Kalinite (p. 637) Faujasite (p. 555) Sylvite (p. 396) 1-53 175 1-92 1-98 1-5-2 2-2-5 5 2 Arsenolite (p. 409) Schorlomite (p. 510) . . . Betafite (p. 591) Hercynite (p. 420). 3-7 3-81-3-88 3-75-4-17 3-9-3-95 1-5 7-7-5 7-5-8 Halite (p. 395) 2-14 2-5 Sphalerite (p 367) 3-9-4-1 3'5-4 Hydrophilite (p. 399) . . Sodalite (p. 502) Analcite (p. 554) Noselite (p. 503) Northupite (p. 450) Haiiynite (p. 503) 2-2 2-14-2-30 2-2-2-3 2-25-2-4 2-38 2-4-2-5 5-5-6 5-5-5 5-5 3-5-4 5-5-6 Nantokite (p. 395) Marshite (p. 395) Alabandite (p. 369) Perovskite (p. 586) .... Berzeliite (p. 593) Gahnite (p. 420) 3-93 5-6? 3-95-4-04 4-03 4-08 4-0-4-6 2-2-5 3-5-4 5-5 5 7-5-8 Leucite (p. 469) 2-45-2-50 5-5-6 Pyrochlore (p 587) 4-2-4-36 5-5-5 Lazurite (p. 503) Sulphohalite (p. 631)... Tychite (p. 450) Ralstonite (p. 402) .... 2-38-2-45 2-49 2-5 2-58 5-5-5 3-5 3-5 4-5 Koppite (p. 587) Zirkelite (p. 428) Hatchettolite (p. 587).. Lewisite (p. 618) 4-45-4-56 471 4-8-4-9 4-95 5-5 5 5-5 Voltaite (p. 639) 2-79 3^ Atopite (p. 618) . 5-03 5-5-6 Villiaumite (p. 396) Langbeinite (p. 625) 2-81 2-83 Percylite, Boleite (p. 401). 5-08 2-5 Zunyite (p. 505) ... Pollucite (p. 470) Boracite (p. 620) 2-87 2-90 2-9-3 7 6-5 7 Mauzeliite (p. 618) Manganosite (p. 411) . . Neotantalite (p. 587) 5-11 5-18 5-2 6-6-5 5-6 3-8 Pharmacosiderite, (p. 614) . . 2-9-3 2-5 lenarmontite (p. 409) . . Samiresite (p. 587) 5-2-5-3 5-24 2-2-5 Plazolite (p. 580) . 3-13 6-5 Embolite (p. 397) 5-3-54 1-1-5 Nitrobarite (p 619) .... Fluorite (p. 398) Helvite (p. 504) Garnet (p. 505) 3-2 3-2 3-16-3-36 3-3-4-3 4 6-6-5 6-5-7-5 Cerargyrite (p. 397).... Miersite (p. 598) Vlicrolite (p. 587) lodobromite (p. 397) 5-55 5-6 5-5-6-1 571 1-1-5 5-5 1-1-5 Rhodizite (p. 621) 3-4 8 Bromyrite (p. 397) 5-8-6 2-3 Danalite (p. 504) . . 3-43 5'5-6 Cuprite (p. 410) . 5-85-6-15 3-5-4 Hauerite (p. 378) Diamond (p. 345) Yttrofluorite (p. 399) . . Spinel (p. 419) Periclase CD. 411) .. 3-46 3-52 3-55 3-5-4-1 3-67 4 10 4-5 8 6 Eulytite (p. 504) Bunsenite (p. 411) Monimolite (p. 593) . . . Sglestonite (p. 401) Mosesite CD. 402) . . 6-11 64 6-58;7'29 8-3 4-5 5-5 5-6 2-3 3 * Some pseudo-isometric species are here included, some species are included in both lists. Species with submetallic luster are placed under B, but 680 APPENDIX B B. LUSTER METALLIC (AND SUBMETALLIC) . Specific Gravity. Hard- ness. Specific Gravity. Hard- ness. Hauerite (p. 378) 3-46 4 Canfieldite (p. 394) 6-28 2-5-3 Sphalerite (p. 367) Alabandite (p. 369) Cubanite (p. 374) 3-9-4-1 3-95-4-04 4-0-4-1 3-5-4 3-5-4 4 Ullmannite (p. 379) Smaltite, Chloanthite (p. 378) 6-2-6-7 6-4-6-6 5-5-5 5 '5-6 Dysanaly te (p. 586) .... Chromite (p. 423) Villamaninite (p. 379) . . Tennantite (p. 391) 4-13 4-3^-57 4-4 44^-49 5-6 5-5 4-5 3-4 Skutterudite(p.380)... Willyamite (p. 379) Polyargyrite (p. 562) . . . Laurite (p. 379) 6-7-6-86 6-87 6-97 7-0 6 5-5 2-5 7-5 Tetrahedrite (p. 390) . . . Magnesioferrite (p. 420) 4-4-5-1 4-57-4-65 3-4 6-6-5 Argentite (p. 364) IRON (p. 356) 7-2-7-36 7-3-7-8 2-2-5 4-5 Polydymite (p. 373) . . . 4-5-4-8 4-5 Galena (p. 363) 7-4-7-6 2-5-3 Cobaltnickelpyrite (p. 378) 4-71 5 Eucairite (p. 365) Vletacinnabarite (p 369) 7-5 7-8 2-5- Q Jacobsite (p. 421) . . . 475 6 Clausthalite (p 364) 7'6 8"8 2 >p > *3 Sychnodymite (p. 373) . LlNN^EITE (p. 374) 4-76 4-8-5 5-5 S"aumannite (p. 364) . . . Altaite (p. 364) 8-0 8-16 2-5 3 Carrollite (p. 374) Bixbyite (p. 425) 4-85 4-95 5-5 6-6-5 Tiemannite (p. 369) Hp??itp (n 36^ 8-2-8-5 0.0 Q.K 2-5 O.C PENTLANDITE (p. 369) 5-0 3-5-4 Copper (p. 353) Uraninitf* fr> fi^ 8-8-8-9 Q Q-7 2-5-3 5.K Pyrite (p. 377) .... Franklinite (p. 420) . . 4-95-5-10 5-07-5-22 6-6-5 6-6-5 Thorianite (p. 624). Silver (p. 352) 9-3 10-1-11-1 2-5-3 Magnetite (p. 420) Bornite (p. 374) . Gersdorffite (p. 379) Cuprite (p. 410) Brongniardite (p. 387) . . ' 5-18 4-9-5-4 5-6-6-2 5-85-6-15 5-95 6-6-5 3 5-5 3-5^ 3-5 Sperrylite (p. 379) Lead (p. 354) Palladium (p. 355) .... AMALGAM (p. 354) Platinum (p. 355) 10-6 11-4 11-3-11-8 137-14-1 14-19 6-7 1-5 4-5-5 3-3-5 4-4-5 Corymte (p. 379) Argyrodite (p. 391). . . 5-95-6-03 6-1-3-2 4-5-5 2-5 Gold (p. 350) Iridium (p. 355) .... 15-6-19-3 22-6-22-8 2-5-3 6-7 Cobaltite (p. 379) 6-6-3 5-5 APPENDIX B 681 II. CRYSTALLIZATION TETRAGONAL. A. LUSTER NONMETALLIC. Specific Gravity. Hard- ness. Specific Gravity. Hard- ness. Mellite (p. 645) Darapskite (p. 619) Pinnoite (p. 622) Apophyllite (p. 546) Loweite (p. 637) 1-64 2-29 2-3-2-4 2-38 2-2-5 4-5-5 2-5-3 Hardystonite (p. 498).. Torbernite (p. 648) Trippkeite (p. 618) Octahedrite (p. 428) ... Rutile (p. 427) 3-4 3-4-3-6 3-8-3-95 4-18-4-25 3-4 2-2-5 5-5-6 6-6-5 Ecdemite (p. 618) 6-9-7-1 2-5-3 Xenotime (p. 592) 445-4-56 4-5 Sarcolite (p. 518) Marialite (p. 518) 2-54-2-93 2-57 6 5-5-6 Powellite (p. 643) Thorite (p. 522) 4-53 4-4-54 3-5 4-5-5 Mizzonite (Dipyre), (p. 517) 2-62 5-5-6 Fergusonite (p. 588) Zircon (p. 520) 4-4-5-8 4-68^-7 5-5-6 7-5 Wernerite (Scapolite), (p. 516) 2-66-2-73 5-5-6 Romeite (p. 618) Sipylite (p. 588) 471 4-89 5-5-6 6 Meionite (p. 516) 2-70-2-74 5-5-6 Nasonite (p. 498) 54 4 Edingtonite (p. 555) .... Narsarsukite (p. 585) . . . Chiolite (p. 400) Soumansite (p. 614). . . . 270 2-7 2-84-2-99 2-87 4-4-5 7-0 3-5-4 4-5 Ganomalite (p. 498) Scheelite (p. 642) Phosgenite (p. 450) Calomel (p. 395) 5-74 5-9-6-1 6-6-09 6-48 3 4-5-5 2-75-3 1-2 Melilite (p 518) 2-9-3-1 5 Wulfenite (p. 643) 67-7-0 275-3 Gehlenite (p. 518) Meliphanite (p. 496) . . . Sellaite (p 399) 2-9-3-1 3-01 2'97-3'15 5-5-6 5-5-5 5 Cassiterite (p. 425) Matlockite (p. 401) .... Tapiolite (p. 590) 6-8-7-1 7-2 7-36-7-5 6-7 2-5-3 6 Zeunerite (p. 616) 3-2 2-2-5 Larettoite (p. 401) 7-6 3 Pinnoite (p 622) 3-27-3-37 3-4 Stolzite (p. 643) 7*87-8-13 2-75-3 Vesuvianite(p.519).... 3-35-3-45 6-5 B. LUSTER METALLIC (AND SUBMETALLIC). Chalcopyrite (p 374) 4-1-4-3 3-5-4 Polianite (p. 427) 4-84-5-0 6-6-5 STANNITE (p. 394) 4-3-4-5 4 Reinite (p. 644) 6-64 4 Rutile (p 427) 4-18-4-25-5-2 6-6-5 Hauchecornite (p. 372) . 64 5 Fergusonite (p. 588) Hausmannite (p, 424) . . 4-4-5-8 47^-86 5-5-6 5-5-5 Tapiolite (p. 590) Maucherite (p. 362) 7-36-7-5 7-83 6 5 Braunite (p. 425)1 4-75-4-82 6-6-5 Plattnerite (p. 428) 8-5 5-5-5 682 APPENDIX B III. CRYSTALLIZATION HEXAGONAL.* Rhombohedral species are distinguished by a letter R. A. LUSTER NONMETALLIC. Specific Hard- Specific Hard- Gravity. ness. Gravity. ness. Ice (p 411) 0-9 1-5 Hamlinite (p. 601) R. . 3-23 4-5 Cyprusite?(p.639)... Ettringite (p. 640) . . . Thaumasite (p. 581) . Koenenite (p. 401)R . Gmelinite (p. 554) R. Pyroaurite (p. 455) R Coquimbite (p. 637) R. 1-75 1-75 1-88 2-0 2-04-2-17 2-07 2-09 2 2-2-5 3-5 2-0 4-5 2-3 2-2-5 Pyrochroite (p. 435) R. Jeremejevite (p. 620) . . Dioptase (p. 515) R Svanbergite (p. 618) R. Cronstedtite (p. 571) R Hematolite (p. 606) R. Connellite (p. 631) 3-26 3-28 3-28-3-35 3-30 3-35 3-35 3-36 2-5 6-5 5 5 3-5 3-5 3 Utahite (p. 639) R Mesitite (p. 443) R. . . . 3-33-3-42 3-5-4 Chabazite(p.552)R... 2-08-2-16 2-09-2'16 4-5 4-4-5 Rhodochrosite (444) R. Svabite (p. 598) 3-45-3-60 3-52 3-5-4-5 5 Hydronephelite? (p. 558) 2-26 4-5-6 Fermorite (p. 597) 3-52 5 Soda niter (p. 619) R .. 2-26 1-5-2 Florencite (p. 601) R. . . 3-58 5 TriHvmitp (rt 4-07} 2-28-2-33 7 Benitoite (p. 585) 3-6 6-2-6-5 _L riLiy 1111 tt? \p A^' / . > Rinneite (p. 399) R. . 2-3 3 Siderite (p. 443) R 3-83-3-88 3-5-4 Brucite (p. 434) R 2-38-2-4 2-5 Rhabdophanite (p. 609) Cancrinite (p. 501) 2-42-2-5 5-6 R 3-94-4-01 3-5 Microsommite (p. 501) 2-44 6 Wurtzite (p. 371). ... 3-98 3-5-4 Kaliophilite (p. 501).... 2-49 6 Corundum (p. 413) R.. 3-95-4-10 9 Carphosiderite? Willemite(p.513)R.... 3-94-4-19 5-5 (p. 539) R. 2-50 4-4-5 Geikielite (p. 586) R. . . . 4-0 6-0 Colerainite (p. 583) .... 2-51 2-5-3 Sphserocobaltite (446) R 4-02-4-13 4 Metavoltine (p. 639) . . . 2-53 2-5 Melanocerite (p. 406) R. 413 5-6 Chalcophyllite(p.612)R 2-44-2-66 2 Tritomite (p. 496) R 4-20 5-5 Nephelite (p. 499) 2-55-2-65 5-5-6 Nordenskioldine (620) R 4-20 5-5-6 Hanksite(p. 631) Ferronatrite (p. 638) R. Milarite (p. 455) 2-56 2-56 2-57 3-3-5 2 5-5-6 Caryocerite (p. 496) R. Parisite (p. 621) Smithsonite(p.445)R.. 4-29 4-36 4-30-4-45 5-6 4-5 5 Spodiophyllite (p. 572) . 2-6 3-3-2 Beudantite (p. 618) R. . 4-4-3 3-5-4-5 Aphthitalite (p. 624) R. 2-64 3-3-5 Plumbogummite? Quartz (p. 403) R. . . . 2-65 7 (p. 601). 4^-9 4-5 Beryl (p. 495) 2' 64-2' 7 ;2' 80 7-5-8 Britholite (p. 580) .... 4-4 5-5 Eucryptite (p. 500) 2-67 Cappelenite (p. 496) . . . 4-41 6-6-5 Alunite (p. 639) R 2-67 3-5^ Pyrophanite (p. 418) . . . 4-5 5 Penninite (pseu.) Hinsdalite (p. 618) 4-65 4-5 (p. 570) R. 2-6-2-85 2-71 2-25 3 Molybdophyllite (p.498) Bastnasite (p. 449) 47 4-9 3-4 . 4-5 Calcite (p. 438) R Nepouite (p. 515) 2-5-3-2 2-2-5 GrREENOCKITE (p. 371) . 4-9-5-0 3-3-5 Alumian (p. 632) 2-74 2-3 Hematite (p. 415) R 4-9-5-3 5-5-6-5 Catapleiite(p.496).... 2-8 6 Xanthoconite (p. 393) R 5-5-2 2 Dolomite (p. 442) R. . . . 2-8-2-9 3-5-4 Zincite (p. 411) . 5-4-5-7 4-4-5 Martinite (p. 611) R. 2-89 Bellite (p. 631) 5-5 2-5 Eudialyte(p.496)R... 2.91-2-93 5-5-5 PROUSTITE, (p. 389) R 5-6 2-2-5 Ankerite (p. 443) R 2-95-3-1 3-5-4 lodyrite (p. 397) 5-6-57 1-1-5 Phenacite (p. 514) R. 2-97-3-0 7-5-8 Fluocerite (p. 399) 5-7-5-9 4 Tourmaline (p. 540) R. 2-98-3-20 7-7-5 PYRARGYRITE (p. 389) R 5-85 2-5 Bityite (p. 558) Magnesite (p. 443) R. . . Pyrosmalite (p. 515)R . Friedelite (p. 515) R. Podolite (p. 618) Spangolite (p. 631)R. . 3-0 3-0-3-12 3-06-3-19 3-07 3-1 3-14 5-5 3-5-4-5 4-4-5 4-5 2 Penfieldite (p. 401) Barysilite (p. 498) Tysonite (p. 399) Pyromorphite (p. 597) . . Vanadinite (p. 598) Mimetite (p. 598) 6-11 6-13 6-5-7-1 6-66-6-86 7-0-7-25 3 4-5-5 3-5-4 3 3'5 Apatite (p. 595) Harttite (p. 601) Jarosite(p. 640) R...!! 3-17-3-23 3-2 3-20 5 4-5-5 Kleinite (p. 395) . . 8-0 8-08-8-2 3-5 2-2-5 Cinnabar (p. 370) R. . . . Raimondite (p. 639) . . . 3-20 3 Wilkeite (p. 597) . 3-23 5 Some pseudo-hexagonal species are included. APPENDIX B B. LUSTER METALLIC (AND SUB METALLIC). 683 Specific Gravity. Hard- ness. Specific Gravity. Hard- ness. Graphite (p. 347) R Chalcophanite 'p. 435) R Ilmenite (p 417) R. 2-1-2-2 3-91 4-5-5 1-1-5 2-5 5-6 Pyrargyrite (p. 389) R. . Tellurium (p. 349) R.... Allemontite (p 349) R 5-85 6-1-6-3 6'2 2-5 2-2-5 3'5 COVELLITE (p. 371) Pyrrhotite (p. 373) Molybdenite (p. 360) . . . Langbanite (p. 539) . . . Xanthoconite (p. 393) . . Hematite (p. 415) R. ... Senaite (p. 418) R Millerite (p. 372) R. 4-6 4-6 47-4-8 4-92 5 5-2-5-3 5-3 5-3-5-65 1-5-2 3-5^-5 1-1-5 6-5 5-5-6-5 6 3-3-5 ANTIMONY (p. 349) R . . Tetradymite (p. 360) R. Niccolite (p. 372) Breithauptite (p. 372) .. Platynite (p. 385) R. . . . Cinnabar (p. 370) R. . . . BISMUTH (p. 349) R. . . . Iridosmine (p 355) R 67 7-2-7-6 7-3-7-67 7-54 8 8-0-8-2 9-7-9-8 19-3-21-1 3-3-5 1-5-2 5-5-5 5-5 2-3 2-2-5 2-2-5 6-7 ARSENIC (p. 348) R 56^57 3-5 IV. CRYSTALLIZATION ORTHORHOMBIC. A. LUSTER NONMETALLIC. Teschemacherite (p.450) Thermonatrite (p. 452) . Carnallite (p. 401) Struvite (p. 606) Epsomite (p. 635) . . 1-45 1-5-1-6 1-6 1-65-17 175 1-5 1-1-5 1-1-5 2 2-2-5 Edingtonite (p. 555) . . . Hillebrandite (p. 546) Hopeite (p. 607) Phosphosiderite (p.610) Talc (p. 575) 2-69 27 276 276 2-7-2-8 4-4-5 5-5 2-5-3 375 1-1-5 Mascagnite (p. 624) .... Nesquehonite (p. 452) . . Goslarite (p. 635) 177 1-84 2'0 2-2-5 2-5 2-2-25 Beryllonite (p. 595) .... Haidingerite (p. 610) . . . Strengite (p. 610) 2-84 2-85 2-87 5-5-S 1-5-2-5 3-4 Erionite (p. 558) 1-99 Prehnite (p. 534) 2-8-2-95 6-6-5 Morenosite (p. 635) .... Sulphur (p. 347) 1-9-2-1 2-07 2-2-5 1-5-2-5 Guarinite (p. 525) Anhydrite (p. 629) 2-9-3-3 2-90-2-98 6-5 3-3-5 Lindackerite (p. 618). . . Newberyite (p. 611).... Stellerite (p. 558) Niter (p. 619) 2-0-2-5 2-10 2-12 2-09-2-14 2-2-5 3-3-5 3-5-4 2 Aragonite (p. 446) Spodiosite? (p. 600) Leucophanite (p. 496) . . Cebollite (p. 518) 2-94 2-94 2-96 2-96 3-5-4 4 5 5-0 Sideronatrite (p. 639) . . Epidesmine (p. 558) .... Fluellite (p. 402) 2-15 2-16 2-17 2-2-5 3 Danburite (p. 522) Bementite (p. 582) Hopeite (p. 607) 2-97-3-02 2-98 3-0-3-1 7-7-25 3-2 Natrolite (p. 556) Okenite? (p. 546) Fels6banyiteQ..639).. . Thomsonite (p. 557) .... Wavellite (p. 612) 2-20-2-25 2-28 2-33 2-3-2-4 2-33 5-5-5 4-5-5 1-5 5-5-5 3-5-4 Tyrolite (p. 612) Harstigite (p. 535) Reddingite (p. 607) .... Lawsonite (p. 540) Grothine (p. 545) 3-0-31 3-05 3-10 3-08 3-09 1-5 5-5 3-3-5 7-5-8 Hambergite (p 620) 2-35 7-5 Humite (p. 536) 3-1-3-2 6-6-5 Pirssonite (p. 452) . . . . : Sulfoborite (p. 623) Dawsonite (p 452) 2-35 2-38-2-45 2-40 3-35 4 Anthophyllite (p. 486) . . Andalusite (p. 524) Enstatite (p. 472) 3-1-3-2 3-16-3-2 3-15-3-3 5-5-6 7-5 5-5 Fischerite (p. 613) 2-46 5 Autunite (p. 616) 3-05-3-19 2-2-5 Peganite (p. 613) Variscite (p. 610) Lucinite (p. 610) Elpidite (p. 496) Howlite? (p. 621) Bertrandite (p. 539) Lanthanite (p. 453) .... lolite (p. 497) Thenardite (p. 624) .... 2-50 2-52 2-52-2-59 2-55 2-6 2-6 2-6-2-66 2-68-2-69 3-3-5 4 5 6-5-7 3-5 6-7 2-5-3 7-7-5 2-3 Monticellite (p. 513) . . . Eosphorite (p. 615) Childrenite (p. 615) Sillimanite (p. 526) .... Scorodite (p. 609) Lossenite (p. 619) ?orsterite (p. 513) Dumortierite (p. 543) . . Kornerupine (p. 544) . . . 3-03-3-25 3-11-3-15 3-18-3-24 3-24 3-1-3-3 3-2-3-33 3-26 3-27 5-5-5 5 4-5-5 6-7 3-5-4 6-7 7' 6-5 684 APPENDIX B A. LUSTER NONMETALLIC Specific Gravity. Hard- ness. Specific Gravity. Hard- ness. Zoisite (p. 530) 3-25-3-37 6-6-5 Barylite (p. 498) 4-03 7 Dufrenite (p 605) 3-23-3-4 3-5-4 Tephroite (p. 513) 4-4-12 5-5-6 Chrysolite (p. 511) Warwickite (p. 621)... Euchroite (p 611) 3-27-3-37 3-35 3-39 6-5-7 3-4 3-5-4 Carminite (p. 594) .... Ampangabeite (p. 591) Fayalite (p. 513) 4-105 3-97-4-29 4-4-14 2-5 4-0 6-5 Astrophyllite (p. 585) . Diaspore(p.431) Lorenzenite (p. 586) . . . Purpurite (p. 610) Natrophilite (p. 594) . . Cenosite (p. 580) 3-3-3-4 3-3-3-5 3-4 3-4 3-41 3-41 3 6-5-7 6-0 4-4-5 4-5-5 5-5 Retzian (p. 606) Olivenite (p. 603) Hulsite (p. 622) Witherite (p. 447) Adamite (p. 604) Pseudobrookite (p 424) 4-15 4-1-44 4-3 4-3-4-35 4-34-4-35 44-5 4 3 3 3-3-75 3-5 Gerhardtite (p. 619) . 3-43 2 Barite (p. 625) 4-5 2-5-3-5 Hypersthene(p.473).. Uranospinite (p. 617) . Guarinite (p. 525) .... Calamine (p. 539) 3-4-3-5 3-45 3-49 3-4-3-5 5-5 2-3 6 4-5-5 Derbylite (p. 618) Euxenite (p. 591) Yttrocrasite (p. 586) .. Cerite(p. 540). 4-53 4-6-5 4-8 4'86 5 6-5 5-5-6 5-5 Lithiophilite (p. 594).. Topaz (p. 523) 3-42-3-56 3-4-3-65 4-5-5 8 Blomstrandine (p. 591) . iEschynite (p 591) 4-8-4-9 4-QQ.C.17 r; fi Langite (p. 638) 3-49 2-5-3 Poly erase (p 591) 4'97 5 -04 K. a Erikite (p. 580) Uranocircite (p. 617) Triphylite (p. 594) Epididymite (p. 455) . . . Mazapilite (p. 615). 3-5 3-53 3-52-3-55 3-55 3-57 5-5 4-5-5 5-5 4-5 Cotunnite (p. 399) ..... Pyrobelonite (p. 604) . . . Valentinite (p. 410) ... Samarskite (p. 59$ .... Yttrotantalite (p 590) 5-24-5-8 5-38 5-57 5-6-5-8 ^^ 'vQ 2 3-5 2-5-3 5-6 K K..K. Thortveite (p. 529).. Hemafibrite (p. 611) . . Chrysoberyl (p. 423) . . . Aurichalcite (p. 451) 3-57 3-50-3-65 3-5-3-8 3-54-3-64 6-7 3 8-5 Melanotekite (p. 539). . '. Annerodite (p. 591) .. . Phcenicochroite? (p. 630) 5-7 5-7 5-75 6-5 6 3-3-5 Ardenmte (p. 539) .. . Libethenite (p. 603).... Staurolite (p. 543) 3-62 3-6-3-8 3-65-3-75 6-7 4 7-7-5 Tellurite (p. 410) Descloizite (p. 604) .... Tsumebite (p 604) 5-9 5-9-6-2 A.I 2 3-5 Q.C Strontianite (p. 447) 3-68-3-71 3-5-4 Kentrolite (p. 539)... 6-19 5 Bromlite (p. 447) 3-72 4-4-5 Anglesite (p 628) 6'12-fV3Q 2-7^ ^ ATACAMITE (p. 400) .... Uranophane (p. 581) Flinkite (p. 606) '. Serpierite (p. 638).... Brochantite (p. 632) Brookite (p. 429) 376 3-81-3-9 3-87 3-91 3-87-4-07 3-3-5 2-3 4-4-5 3-5-4 5-5-6 Pucherite (p. 594) Saledonite (p. 632) Daviesite (p. 401) Laurionite (p. 401) Cerussite (p. 448) Nadorite (p 618) 6-25 6'4 6-46-6-57 7-09 4 2-5-3 3-3-5 3-3-5 Q.C_4 Pmakiolite (p. 620) 3-88 6 Ochrolite (p. 618) Ancylite (p. 449) 3-9 4-5 Vlendipite (p. 401) 7-7-1 2-5-3 Celestite (p. 627) . . . Ludwigite (p. 620) . . Knebelite(p.513). 3-95-3-97 3-91^-02 3-9-4-1 3-3-5 5 6-5 Georgiadesite (p. 594) . Stibiotantalite (p. 590) Montroydite (p. 412) . . . 7-1 6-0-74 3-5 5-5 1-5-2 Brookite (p. 429) . IlvaiteKp. 538) . . Gothite (p. 431) ... Sternbergite (p. 367) Manganite (p. 432) Enargite(p.393)...: Wittichenite (p. 388) B. LUSTER METALLIC (AND SUBMETALLIC). Stibnite (p. 358) . . Famatinite (p. 393) . . . Klaprotholite (p. 386) . Hutchinsonite (p. 386) Euxenite (p. 591) Chalmersite (p. 366) Chalcostibite (p. 386) . 3-87-4-07 4-0-4-05 4-0-44 4-1-4-2 4-2-44 4-43-4-45 4-5 5-5-6 5-5-6 5-5-5 1-1-5 4 3 4-5^-6 4-57 4-6 4-6 4-6-5 47 4-75-5 2 3-5 2-5 1-5-2 6-5 3-5 3-4 APPENDIX B B. LUSTER METALLIC (AND SUBMETALLIC) . 685 Specific Hard- Specific Hard- Gravity. ness. Gravity. ness. Pyrolusite (p. 430) 473-4-86 2-2-5 Kentrolite (p. 539) . 6'19 5 Polymignite (p. 591) . . . Stylotypite (p. 388) Marcasite (p. 380) ^Eschynite (p. 591) Urbanite (p. 477) ZlNKENITE (p. 385) .... Andorite (p. 385) 4-77-4-85 4-8 4-85-4-9 4-93; 5-17 5-3 5-3-5-35 5-34 6-5 3 6-6-5 5-6 3-5 3-3-5 Aikinite (p. 388) Stromeyerite (p. 366) . . . STEPHANITE (p. 392) Guanajuatite (p. 359) . . Mullanite (p. 388) Geocronite (p. 392) . . Wolfachite (p. 382) . . . 6-1-6-8 6-15-6-3 6-2-6-3 6-25-6-6 6-3 6-3-6-45 6-37 2-2-5 2-5-3 2-2-5 2-5-3-5 3-5 2-5 4-5-5 Sartonte (p. 385) 5-39 3 Emplectite (p. 386) 6-3-6-5 2 Columbite (p. 588) Rathite (p. 386) DUFRENOYSITE 5-36-6-0 5-4 i 6 3 Teallite (p. 394) . . .- Meneghinite (p. 391). .. BlSMUTHINITE 6-4 6-4 1-2 2-5 (p. 387) 5-55 3 (p 359) 6-4-fi-^ 2 Chalcocite (p. 366) Yttrotantalite (p. 590) . 5-5-5-8 5.5-5-9 2-5-3 5-5-5 Schapbachite (p. 387) . . Alloclasite (p. 382) . . 6-43 6-6 3-5 4-5 Annerodite (p. 591).. . . 57 6 Cosalite (p. 387) 6-4-6-75 2-5-3 Melanotekite (p. 539).. . Bournonite (p. 388) .... 5-7 5-7-5-9 6-5 2-5-3 Nagyagite (p. 383) Rammelsbergite 6-85-7-2 1-1-5 Seligmanite (p. 388)... . 3 (p. 382) 6-9-7-2 5-5-6 BOULANGERITE Safflorite (p. 382) . 6-9-7-3 4'5-5 (p. 387) 575-6-0 2-5-3 Tantalite (r> ttR} 7 7-^i Hielmite (p. 591) 5-82 5 Lolling! te (p 381) 7-0-7-4 K K.C Diaphorite (p. 387) 5-9 2-5-3 Acanthite (p. 367) 7-2-7-3 2-2-5 Glaucodot (p. 382) 5-9-6-0 5 Krennerite (p 383) Q.OC Arsenopyrite (p. 381) . . 5-9-6-2 5-5-6 Dyscrasite (p. 361) 9-4-9-8 3-5-4 \ Natron (p. 452) r . CRYST, A. 1-44 1-48 1-615 1-66 1-6-1-8 1-69-1-72 1-70 1-78 1-84 1-87 1-90 1-9-2-0 1-9-2-0 1-94 1-98 2 : 2-035 2-04-2-14 2-08 2-07-2-19 2-08-2-14 2-10 2-10 \LLIZA1 LUSTER . 1-1-5 1-5-2 2-5 2 1-2 1-5-2 2-2-5 1-5 2-2-5 2-0 2 2 2-3 2-5 2-0 3 2-2-5 3-4 2-5-3 3 2-5 5 TON MONOCLINIC. SONMETALLIC. Trona (p 453) 2-12 2-1-2-2 2-12 2-12 2-13 2-16 2-16-2-20 2-16-24 2-21 2-18-2-22 2-20 2-2 2-2-2-4 2-25 2-25 2-26 2-25-2-36 2-29 2-28-2-37 2-3 2-31 2-31-2-33 2-3-2-4 2-39-2-46 242 2-5-3 3 2-5 4-5 3-5 3-5-4 5-5-5 2-2-5 3-5-4 2-3 4^-5 5 2-5 4-4-5 4-5 3-5-4 2-5-3 4^-5 4-5 1-0 1-5-2 2-5-3-5 6-6-5 4-4-5 Mirabilite (p. 632) Whewellite (p. 641) Stercorite (p. 611) Aluminite (p. 639) Alunogen (p. 638) Borax (p. 622) Boussingaultite (p. 637) . Apjohnite? (p. 637) Fibroferrite? (p. 639). . . Inyoite (p. 622) Picromerite (p. 637) Castanite (p. 639) Quenstedtite (p. 637) . . . Heintzite (p. 622) Hydromagnesite (p. 452) Stilbite (p. 551) Scolecite (p. 557) Brushite (p. 611) Heulandite (p. 548) Darapskite (p. 619) Phillipsite (p. 550) Mesolite (p. 557) Blodite (p. 637) Melanterite (p. 636) . . . Halotrichite? (p. 637) . . Pickeringite (p. 637) . . Hydroboracite (p. 623) . Gay-Lussite (p. 452) . . . Krohnkite (p. 638) Epistilbite (p. 549) Gismondite (p. 552) .... Laumontite (p. 552) .... Metabrushite (p. 611) . . Wellsite (p. 549) Natrochalcite (p. 638) . . Griffithite (p. 572) Artinite (p. 453) Diadochite (p. 618). . . . Botryogen (p. 639) Mordenite (p. 548) Kainite (p. 631) 8uetenite?.(p. 640) opiapite (p. 638) Flokite (p. 552) . Gypsum (p. 633). Gibbsite (p. 435) Petalite (p. 455) Colemanite (p. 621). . . . 686 APPENDIX B A. LUSTER NONMETALLIC. Specific Gravity Hard- ness. Specific Gravity Hard- ness. Hautefeuillite (p. 608) . Brewsterite (p. 549) . . . Harmotome (p. 550) . . Pascoite (p. 609) Ectropite (p. 582) Hoernesite (p. 608).... Wapplerite? (p. 611) . . Serpentine (p. 573) . . . Calcioferrite (p. 615) . . Eudidymite(p.455)... Orthoclase (p. 457) . . . Kieserite (p. 633) Vivianite (p. 608) Syngenite (p. 636) Kaolinite (p. 578) Pharmacolite (p. 610) Clinochlore (p. 569) . . . Pectolite (p. 483) Augelite (p. 614) Bavenite (p. 558) 2435 245 2-44-2 246 246 247 248 2-50-2-6 2-52-2-5 2-55 2-57 2-57 2-58-2-6 2-60 2-6-2-6 2-64-2-7 2-65-2-7 2-68-2-7 2-7 27 2-71 273 2-7-2-8 2-75 2-77 2-76-3 2-8-2-9 27-3-1 2-78-2-85 2-78-2-96 2-805 2-84 2-82-3-20 2-86 2-86 2-88 2-8-2-9 2-8-2-9 2-89 2-9 2-90 2-77-2:96 2-9 2-91 2-92 2-92-2-94 2-93 2-9-3-0 2-93-3 2-93-3 2-95-3 2-93-3 2-94 2-95 2-96 2-5 5 4-5 2-5 4 1 2-2-5 2-5-4 2-5 6 6 3-3-5 1-5-2 2-5 2-2-5 2-2-5 2-2-5 5 4-5-5 5-5 4-5 3-5 2-5-3 3-4 2-5-3 2-2-5 2-5-4 2-5-3 1-2 6-6-5 4-4-5 2-5-3 5-6 2-2-5 4-5-5 1-2 4-5 1-1-5 2-5 34 2-5-3 5-0 1-5 5-5-5 5-5-5 3 2-3 2-5 4 4-5 1-5-2-5 2-5 Cabrerite (p. 609) Beraunite (p. 615) .... Herderite (p. 601) Margarite (p. 566) Amphibole (p. 487) .... Leucosphenite (p. 585) Fremontite (p. 602) . . . Lazulite (p. 605) Wagnerite(p. 600).... Szomolnokite (p. 633) . Xanthophyllite (p. 567) Seybertite (p. 566) Lepidomelane (p. 565). Bassetite(p. 617) Kottigite (p. 609) Euclase (p. 529) Glaucophane (p. 492) . . Ludlamite (p. 614) Spencerite (p. 612) Lacroixite (p. 601) Herrengrundite (p. 638) Churchite? (p. 609) Chondrodite (p. 536) . . . Clinohumite (p. 536) . . . Prolectite (p. 538) 2-96 2-98. 2-99-3-0 2-99-3-0 2-9-34 3-0 3-04 3-06 3-07 3-08 3-09 3-3-1 3-0-3-2 3-10 3-1 3-10 3-10-3-1 3-12 3-12 3-13 3-13 3-14 3-1-3-2 3-1-3-2 3-13-3-2 3-185 3-199 3-2 3-21 3-3-3-6 3-23 3-29 3-25-3-5 3-3 3-3 3-3 73-3 3-33 33-3-35 3-37 3-38 3-34 340 41-344 42-3-48 343 343 344-3-8 34-3-5 346 44-3-45 45-3-50 34-3-65 5-3-55 2 5 3-5-4-5 5-6 6-5 5-5 5-6 5-5-5 4-6 4-5 3 2-5-3 7-5 6-6-5 3-4 27 4-1 2-5 o o *o 6-6-5 6-6-5 6-5-7 5 3-7 5-6 5-6 6-7 5-6 6-7 2 5-5 6-5-7 6-6-5 5 3-5-4 6-5 5-5-6 7-5 4-5 4-5-5 1-5-2 5 6 4-5 5-5-5 6-6-5 Didymolite (p. 497) Creedite (p. 402) Glauberite (p. 625).... Vilateite (p. 610) Polyhalite? (p. 637) Muscovite (p. 560) . . . Lepidolite (p. 562) Biotite (p. 563) . . . Spodumene (p. 480) .... Eureaulite (p. 611) 3 alaite(p. 607). / Hibbenite (p. 612) Pyroxene (p. 474) . . Phlogopite (p. 565).... Prochlorite (p. 571) Hyalophane (p. 460) . . Ganophyllite (p. 546) . . Zinnwaldite (p. 563) .... Cuspidine (p. 535) . . . Neptunite (p. 585) Johnstrupite (p. 585) . . . Epidote (p 531) Mmguetite (p. 572) Liroconite (p. 615) Wollastonite (p. 482) Pyrophyllite (p. 579) . . . Prosopite (p. 402) Rosenbuschite (p. 483) . Trogerite (p. 617) Ottrelite? (p. 567) ailpinite (p. 640) Clinohedrite (p. 540) Jadeite (p. 479) ! Celsian (p. 460) . . . Epistolite(p.592). Corundophilite (p. 571) Stilpnomelane (p. 572) Tamiolite (p. 565) Custerite (p. 497) . . . lomilite (p. 529) Dickinsonite (p. 607) Piedmontite (p. 532) . . Wohlerite (p. 484) apphirine (p. 544) .... liebeckite (p. 493) Fillowite (p. 607) Isoclasite? (p. 611) Roscoelite (p. 565) ..... Carpholite (p. 540)... Datolite(p.527).... Pachnolite (p. 402) Thomsenolite (p. 402) Cryolite (p. 399) .' Mosandrite (p. 585) Jezekite (p. 601) Erythrite(p.608).. Yiplite (p. 600) . ORPIMENT (p. 357) Rinkite (p. 585) ... Arfvedsonite (p. 494) . . . j ynadelphite (p. 606) itanite (p. 583) . j Symplesite (p. 608) cmite(p. 479).. . ! APPENDIX B 687 A. LUSTER NONMETALLIC. Specific Gravity. Hard- ness. Specific Gravity. Hard- ness. Veszelyite (p. 612) Lavenite (p. 484) Chloritoid? (p. 567) Keilhauite (p. 585) Graf tonite (p. 594) 3-53 3-51-3-55 3-52-3-57 3-52-3-77 37 3-5-4 6 6-5 6-5 5 Dihydrite (p. 605) Sarkinite (p. 601) Pyrostilpnite (p. 390) . . Thalenite (p. 529) Clinoclasite (p. 604) . 4-4-4 4-18 4-2 4-2 4-19-4-36 4-5-5 4-5 2 6-5 2-5-3 Dietzeite (p. 619) 3-70 3-4 Kermesite (p. 383) 4-5-4-6 1-1-5 Triploidite (p. 601) REALGAR (p. 357) 37 3-6 4-5-5 1-5-2 Catoptrite (p. 618) Lautarite (p. 619) 4-5 4-59 5-5 Barytocalcite (p. 449) . . Adelite, Tilasite (p. 601) 3-65 3-74 4 5 Monazite (p. 593) Linarite (p. 632) 4-9-5-3 5-3-545 5-5-5 2-5 Chalcomenite (p. 641) . . 3-76 Lorandite (p. 386) 5-53 2-2-5 Azurite (p. 451) 3-77-3-83- 3-5-4 Baddeleyite (p. 428) .... 5-5;6-025 6-5 Leucophoenicite (p. 538) Allactite (p 606) 3-8 3-83-3-85 5-5-6 4-5 Vauquelinite (p. 630) . . . Crocoite (p. 630) 5-8-6-1 5-9-6-1 2-5-3 2-5-3 Allanite (p. 533) 3 -5-1 -2 5-5-6 Agricolite (p. 510) 6-0? Claudetite (p. 409) Hodgkinsonite (p. 582) 3-85HL-15 3-91 2-5 4-5-5 Tenorite (p. 412) Leadhillite (p. 631) 5-8-6-25 6-26-6-44 3-4 2-5 Malachite (p. 450) 3-9-4-03 3-5-4 Lanarkite (p. 632) 6-3-64 2-2-5 Durangite (p. 601) 3-94-4-07 5 A.telestite (p. 606) 6-4 3-1-5 Hancockite (p. 533) Partschinite (p. 510) . . . Gadolinite (p 529) 4-0 4-0 4-0-4-5 6-7 6-5-7 6-5-7 Alamosite (p. 483) Fiedlerite (p. 401) Hiibnerite (p. 642) 6-5 7-2-7-5 4-5 5-5-5 Barylite (p. 498) Tagilite (p. 612) 4-03 4-08 7 3-4 Raspite (p. 643) Terlinguaite (p. 401) . . . 8-7 2-3 Barthite (p. 612) 4-19 3 B. LUSTER METALLIC (AND SUBMETALLIC). YVmrnHmioritp fn ^Sfi^l 3'3 3 Semseyite (p. 387) 5-95 2-3 Allanite (p. 533) Arizonite (p. 418) Crednerite (p. 424) ^mitViitfk (n ^Sfi^ 3-5-4-2 4-25 4-9-5-1 4*9 5-5-6 5-5 4-5 T5-2 POLYBASITE (p. 392). . . . Pearceite (p. 393) FREIESLEBENITE (p 387) 6-0-6-2 6-15 6-2-6-4 2-3 3 2-2-5 MlARGYRITE (p. 386) . . PLAGIONITE (p. 387) . . . JAMESONITE (p. 386) . . . Rittingerite(p.393).... 5-1-5-3 54 5-5-6-0 5-63 2-2-5 2-5 2-3 2-2-5 Jordanite (p. 391) Wolframite (p. 641).... SYLVANITE (p. 382) CALAVERITE (p. 383)... 6-39 7-2-7-5 7-9-8-3 9 3 5-5-5 1-5-2 2-5 688 APPENDIX B VI. CRYSTALLIZATION TRICLINIC. A. LUSTER NONMETALLIC. Specific Gravity. Hard- ness. Specific Gravity. Hard- ness. Sassolite (p. 435) 1-48 1-54 1-89 2-11 2-12 2-12-2-30 2-17 2-5 2-54-2-57 2-57-2-60 2-62-2-65 2-65-2-67 2-68 2-68-2-69 2-70-2-72 2-74-2-76 2-6-2-83 275 2-8 2-94 3-0-31 1 2-5 2-5 2 2-5 3-3-5 6-7 6-6-5 6 6-6-5 6-6-5 6-6-5 6-6-5 6-6-5 5-6 3-5 3-5 5-5-5 Inesite (p. 546) Amblygonite (p. 602) . . . Fairfieldite (p. 607) Messelite (p. 607) Chalcosiderite (p. 616) . Axinite (p. 534) 3-03 3-01-3-09 3-10 3-11 3-27 3-27 3-3 3-35-3-37 3-37 3-4-3-68 3-47 3-52-3-57 3-5-3-6 3-56-3-67 3-67 . 3-8 3-85 3-99 4-1 576 6 6 3-5 3-5 4-5 6-5-7 5-5-6 37 5-5-6 6-6-5 5-5-6-5 6-7 6-5 3-5 5-7-25 5-5-5 5-5-6 2-5-3 37 3-5 Lansfordite(P-453).... Hannavite (p. 611) Amarantite (p. 639) (I Meyerhofferite (p. 622) . Ml Chalcanthite(p.636)... 1 Romerite (p. 638) Ussingite (p. 470) Hiortdahlite (p. 485) . . . Parahopeite (p. 607) . . . Babingtonite (p. 485) . . Celsian (p. 460) Rhodonite (p. 484) Trimerite (p. 515) Microcline (p. 460) Anorthoclase (p. 461) . . _^-Albite (p. 464) .Oligoclase (p. 466) Anemousite (p. 468) Andesine (p. 466) .^Jabradorite (p. 466) .. Anorthite (p. 467) ^ Turquois (p. 613) Chloritoid? (p. 567) Roselite (p. 607) Cyanite (p. 526) Brandtite (p. 607) Pyroxmangite (p. 485) . . ^Enigmatite (p. 494) Margarosanite (p. 498) . Tarbuttite (p. 604) Walpurgite? (p. 617) ... Monetite (p. 606) Anapaite (p. 607) Stewartite (p. 607) Schizolite (p. 483) APPENDIX B 689 TABLE III. CRYSTALLINE HABIT. I. ISOMETRIC SYSTEM. In the following lists some species are enumerated whose crystalline habit is often so marked as to be a distinctive character. Cubes. METALLIC LUSTER: Galem^ ! Pyrite. NONMETALLIC LUSTER: FluonTe : Cuprite (at times elongated into capillary forms) Cerargyrite; Halitej Sylvite; Boracite; Pharmacosiderite. Also Percy lite; Perovskite. Cube-like forms occur with the following: Apophyllite (tetragonal); Cryolite (mono- clinic). Also with the rhombohedral species: Chabazite: Alunite; Calcite; rarely Quartz and Hematite. Octahedrons. METALLIC AND SUBMETALLIC LUSTER: Magnetite: Franklinite; Chro- mite; Uraninite. Also sometimes, Galena; Pvrite; Linnaeite; Dysanalyte. NONMETALLIC LUSTER: Spinel (incl."Hercynite and Gahnite) ; Cuprite; Diamond; Pyro- chlore and Microlite; Ralstonite; Periclase; Alum. Forms somewhat resembling regular octahedrons occur with some tetragonal species, as Braunite; Hausmannite; Chalcopyrite; Zircon,- etc.; also with some rhombohedral species, as Dolomite. Dodecahedrons. METALLIC LUSTER: Magnetite; Amslgam. NONMETALLIC LUSTER: Garnet; Cuprite; SoH^lif^ Tetrahexahedrons. Native Copper; Fluorite. Trapezohedrons. NONMETALLIC LUSTER: Garnet; Leucite; Analcite. Also Gersd Pyritohedrons. METALLIC LUSTER: JPyrite^ (Jobaltite. Also Gersdorffite; Hauerite (submetallic). Tetrahedrons. METALLIC LUSTER: Tetrahedrite. NONMETALLIC LUSTER: Sphalerite; Boracite; Helvite; Eulytite; Diamond; Zunyite. The tetragonal sphenoids of Chalcopyrite sometimes closely resemble tetrahedrons. II. TETRAGONAL SYSTEM. Square Pyramids. SUBMETALLIC LUSTER: Braunite; Hausmannite. NONMETALLIC LUSTER: Zircon; Wulfenite; Vesuvianite; Octahedrite; Xenotime. Square Prisms. NONMETALLIC LUSTER: zircon: vesuvianite.: Scapolites; Apophyllite; Phosgenite. """" Square tabular crystals occur with Apophyllite; Wulfenite; Torbernite. Prisms nearly square are noted with a itiuritDer of orthorhombic species, e.g., Topaz; Andalusite; Danburite: also with the monoclinic Pyroxene (100 A 010 = 90, 110 A 110 = 87) III. HEXAGONAL SYSTEM. Hexagonal Prisms. NONMETALLIC LUSTER: Bervl: Apatite: Pyromprphite; Vanadi- nite; Mimetite (usually indistinct rounded forms). Also Nephelite; Milarite: Tysonite, and others. Hexagonal prisms are also common with the rhombohedral species: Quartz; Calcitej the Micas, efc. Numef^ Tourmaline L Willemite; Phenacite; Dioptass, etc. Again, with ous rare specit could be included here. - Many orthorhombic (or monoclinic) species having a prismatic angle of about 60 (and 120) simulate this form both in simple crystals and still more as the result of twinning. Thus, Aragonite; Strontianite; Leadhillite; lolite. It is also to be noted that the isometric dodecahedron, e.g., of Garnet, has often the form of a hexagonal pyramid with trihedral terminations (cf. Fig. 470, p. 175). Tabular hexagonal prisms are noted with various species. Thus, METALLIC LUSTER: Graphite; Molybdenite; Hematite; Ilmenjte; Pyrrhotite. NONMETALLIC LUSTER: Tri^ Hexagonal Pyramids. Apatite: Corundum, (rhombohedral); Quartz (rhombohedral- trapezohedral) : Hanksite. This form is often simulated by various orthorhombic species, in part as the result of twinning. For example, METALLIC LUSTER: Chalcocite; Stephanite; Polybasite; Jor- danite; etc. Also Brookite. NONMETALLIC LUSTER: Witherite; Bromlite; Cerussite; lolite. Trigonal Prisms. Tourmaline. Rhombohedrons. Angle ?5 u (and 105): Calcite ; : JDolomitej. Siderite : PJiodochrosite. Angle not far from 90: Chabazite; Alunite ; Talciter'also Quartz ; Hematite. Scalenohedrons. Calcite and allied Carbonates^ ProustifE7~~ 690 APPENDIX B IV. ORTHORHOMBIC, MONOCLINIC AND TRICLINIC SYSTEMS. Prismatic Crystals. METALLIC LUSTER: Stibnite; Arsenopyrite; Bournonite; Manga- m NONMETALLIC LUSTER: (orthorhombic) Tojmz; Sj^ijrolite; Andalusite; arite: Celes- tite; Danburite. Also (monoclinic) Pyroxene; Amphibole; Qrthoclase, and many others. Epidote crystals are often prismatic in aspect (Fig. 894, p. 531JT Tabular Crystals. Barite; Cerussite; Calamine; Diasppre; Wollastonite; 4 lhl 'te, Acicular Crystals. METALLIC LUSTER: Stibnite; BismutEimtej Miflente; Jame- sonite; Aikinite, and other species. NONMETALLIC LUSTER: gectolite; Natrolite: Scolecite; Thomsonite, and other Zeolites. Also Aragonjie; Strontianite; lesd ' 6f ten Calcite. Also many other species. TwinTrystals. The habit of the twins occurring with many species is very character- istic. Reference is made to pp. 165 to 172 and the accompanying figures for a presentation of this subject. TABLE IV. STRUCTURE OF MASSIVE MINERALS Fibrous. Fibers separable: Asbestus (amphibole); also the similar asbestiform va- riety of serpentine (chrysotile) ; Crocidolite (color blue). Fibers not separable, chiefly straight: Anthophyllite; Calcite; Gypsum. Also Aragonite; Barite; Celestite; Anhydrite; Brucite; Enstatite; Wollastonite; Dufrenite; Vivianite. See also Columnar below. Fibrous-Radiated. Wavellite; Pectolite; Thomsonite; Natrolite; Stilbite, Scolecite; and other Zeolites; Gothite; Malachit . Columnar. METALLIC LUSTER: Stibnite; Hematite; Jamesonite; Zinkenite, etc. NONMETALLIC LUSTER: Limonite; Gothite; Aragonite; Amphibole (tremolite, actino- lite, etc.); Epidote; Zoisite; Tourmaline; Sillimanite; Natrolite and other Zeolites: Stron- tianite; Witherite; Topaz. Cyanite has often a bladed , tructure. Fibrous and columnar varieties pass into one another. Lamellar-Stellate. Gypsum; Pyrophyllite; Talc. Foliated. METALLIC LUSTER: Graphite; Molybdenite; Tetradymite; Sternbergite- Nagyagite. NONMETALLIC LUSTER: Talc; Orpiment; Gypsum; Pyrophyllite; Serpentine; Gypsum Micaceous. The Micas, p. 559: also the Brittle Micas, p. 566, and the Chlorites, p. 568 Also Brucite; Orpiment; Talc; Torber^ite; Autunite. Granular. METALLIC LUSTER: Galena; Hematite; Magnetite. Many sulphides, sulpharsemtes; etc., have varieties which are fine-granular to compact and impalpable NONMETALLIC LUSTER: Pyroxene (coccolite); Garnet; Calcite; Barite, etc Botryoidal, Mammillary, Reniform, etc. METALLIC LUSTER: Hematite; Arsenic- Allemontite. Malachite; Prehnite; Smithsonite; Calamine; Chalcedony; Stalactitic. METALLIC LUSTER: Limonite; Psilomelane; Marcasite. NONMETALLIC LUSTER: Calcite; Aragonite; Gibbsite; Chalcedony. Granular Cleavable. METALLIC LUSTER: Galena. NONMETALLIC LUSTER: Calcite; Dolomite; Sphalerite; Fluorite. Oolitic. Calcite; Aragonite; Hematite. fcartny. NONMETALLIC LUSTER: Magnesite; piolite TABLE V. PHYSICAL CHARACTERS. I. CLEAVAGE. Cubic. METALLIC LUSTER: Galena. STER: Halite: Sylvite. The cleavage of Anhydrite (also of Cyro- Ui. also Corundum, p. 413. Diamond. Magnetite (also Franklinite) has often distinct l ^ Sodalite; Hauynite. 75 105! > dral '~ alcite and other s P ecies of th ^ wine group (pp. 437-445) angles Square Prismatic (90). - Scapolite; Rutile; Xenotime. APPENDIX B 691 Prismatic. Barite (78 i, 101^); Celestite; Amphibole (54 and 126), etc. Basal. METALLIC LUSTER: Graphite; Molybdenite. NONMETALLIC LUSTER: Apophyllitej Topaz; Talc; the Micas and Chlorites; Chalco- phyllite, etc. Pyroxene often shows marked basal parting. Pinacoidal. METALLIC LUSTER: Stibnite. NONMETALLIC LUSTER: Gypsum; Orpiment; Euclase; Diaspore; Sillimanite; Cyanite; Feldspars. II. HARDNESS. 1. Soft Minerals. The following minerals are conspicuously Soft, that is, H = 2 or less; they hence have a greasy feel. (See further the Tables, pp. 679 to 688.) METALLIC LUSTER: Graphite; Molybdenite; Tetradymite; Sternbergite; Argentite; Nagyagite; some of the Native Metals (Lead, etc.). NONMETALLIC LUSTER: Talc; Pyrophyllite; Brucite; Tyrolite; Orpiment; Cerargyrite; Cinnabar; Sulphur; Gypsum. Also Calomel, Arsenolite, and many hydrous sulphates, phosphats, etc. 2. Hard Minerals. Minerals whose hardness is equal to or greater than 7 (Quartz = 7). The following minerals are here included: LUSTER NONMETALLIC QUARTZ (p. 403) 7 Tridymite (p. 407) 7 Barylite (p. 498).- 7 Dumortierite (p. 543) 7 Danburite (p. 522) 7-7'25 BORACITE (p. 620) 7 Zunyite (p. 505) 7 CYANITE (p. 526) 5-7'25 TOURMALINE (p. 540) 7-7*5 GARNET (p. 505) 6'5-7'5 IOLITE (p. 497) 7-7-5 STAUROLITE (p. 543) 7-7 "5 Schorlpmite (p. 510) 7-7*5 Sapphirine (p. 544) 7'5 Euclase (p. 529) 7'5 Hambergite (p. 620) 7'5 ZIRCON (p. 520) 7'5 ANDALUSITE (p. 524) 7'5 BERYL (p. 495) 7'5-8 Lawsonite (p. 540) 7'5-8 Phenacite (p. 514) 7'5-8 Gahnite (p. 420) 7'5-8 Hercynite (p. 420) 7 '5-8 SPINEL (p. 419) 8 TOPAZ (p. 523) 8 Rhodizite (p. 621) 8 CHRYSOBERYL (p. 423) 8'5 CORUNDUM (p. 413) 9 DIAMOND (p. 345) 10 The following minerals have hardness equal to 6 to 7, or 6 '5 7. LUSTER METALLIC: Iridosmine (p. 355); Iridium (p. 355); Sperrylite (p. 379). LUSTER NONMETALLIC: Ardennite (p. 539); Axinite (p. 534); Bertrandite (p. 539); Cassiterite (p. 425); Chrysolite (p. 511); Diaspore (p. 431); Elpidite (p. 496); Epidote (p. 531); Forsterite (p. 513); Gadolinite (p. 529); Jadeite (p. 479); Partschinite (p. 510); Sillimanite (p. 526); Spodumene (p. 480); Trimerite (p. 515). III. SPECIFIC GRAVITY. Attention is called to the remarks in Art. 302 (p. 199), on the relation of specific gravity to chemical composition. Also to the statements in Art. 303 as to the average specific gravity among minerals of metallic and norimetallic luster respectively. The species in each of the separate lists of Table II of minerals classified with reference to crystallization are arranged according to ascending specific gravities. Hence the lists give at a glance minerals dis- tinguished by both low and high density. IV. LUSTER. (See Art. 364, p. 249) Metallic. Native metals; most Sulphides; some Oxides, those containing iron, man- ganese, lead, etc. Submetallic. Here belong chiefly certain iron and manganese compounds, as Ilmenite; Ilvaite; Columbite; Tantalite (and allied species); Wolframite; Braunite; Hausmannite. Also Brookite; Uraninite, etc. Adamantine. Here belong minerals of high refractive index: (a) Some hard minerals: Diamond; Corundum; Cassiterite; Zircon; Rutile. (6) Many species of high density, as compounds of lead, also of silver, copper, mercury. Thus, Cerussite, Anglesite, Phos- genite, etc.; Cerargyrite; Cuprite; some Cinnabar, etc. (c) Also certain varieties of Sphal- erite, Tjtanite and Octahedrite. (592 APPENDIX B Metallic-Adamantine. Pyrargyrite; some varieties of the following: Cuprite, Cerus- site, Octahedrite, Rutile, Brookite. Resinous or Waxy. Sphalerite; Sulphur; Elseohte; Serpentine; many Phosphates. Vitreous. Quartz and many Silicates, as Garnet, Beryl, etc. Pearly The foliated species: Talc, Brucite, Pyrpphylhte. Also (on cleavage sur- faces) conspicuously the following: Apophyllite, Stilbite, Heulandite. Also, less promi- nent: Barite; Celestite; Diaspore; some Feldspar, and others. Silky. Some fibrous minerals, as Gypsum, Calcite; also Asbestus; Malachite. V. COLOR. The following lists may be of some use in the way of suggestion. It is to be noted, how- ever, that especially in the case of metallic minerals a slight surface change may alter the effect of color. Further, among minerals of nonmetallic luster particularly, no sharp line can be drawn between colors slightly different, and many variations of shade occur in the case of a single species. For these reasons no lists, unless inconveniently extended, could make any claim to completeness. (a) METALLIC LUSTER. Silver-white, Tin-white. Native silver; Native Antimony, Arsenic and Tellurium; Amalgam; Arsenopyrite and Lollingite; several sulphides, arsenides, etc., of cobalt or nickel, as Cobaltite (reddish); some Tellurides; (Bismuth (reddish).) No sharp line can be drawn between these and the following group. Steel-gray. Platinum; Manganite; Chalcocite; Sylvanite; Bournonite. Blue-gray. Molybdenite; Galena. Lead-gray. Many sulphides, as Galena (bluish); Stibnite; many Sulpharsenites, etc., as Jamesonite, Dufrenoysite, etc. Iron-black. Graphite; Tetrahedrite; Polybasite; Stephanite; Enargite; Pyrolusite; Magnetite; Hematite; Franklinite. Black (with submetallic luster). Ilmenite; Limonite; Columbite; Tantalite, etc.; Wolframite; Ilvaite; Uraninite, etc. The following are usually brownish black: Braunite; Hausmannite. Copper-red. Native copper. Bronze-red. Bornite (quickly tarnished giving purplish tints) ; Niccolite. Bronze-yellow. Pyrrhotite; Pentlandite; Breithauptite. Brass-yellow. Chalcopyrite; Millerite (bronze). Pale brass-yellow: Pyrite; Mar- casite (whiter than Pyrite). Gold-yellow. Native gold; chalcopyrite and pyrite sometimes are mistaken for gold. Streak. The following minerals of metallic luster are notable for the color of their streak: Cochineal-red: Pyrargyrite. Cherry-red: Miargyrite. Dull Red: Hematite; Cuprite; some cinnabar. Scarlet: Cinnabar (usually nonmetallic). Dark Brown: Manganite; Franklinite; Chromite. Yellow: Limonite. Tarnish. The following are conspicuous for their bright or variegated tarnish: Chal- copyrite; Bornite (purplish tints); Tetrahedrite; some Limonite. (6) NONMETALLIC LUSTER. Colorless. IN CRYSTALS: Quartz; Calcite; Aragonite; Gypsum; Cerussite; Angles- ite; Albite; Barite; Adulana; Topaz; Apophyllite; Natrolite and other Zeolites; Ce- lestite; Diaspore; Nephelite; Meionite; Calamine; Cryolite; Phenacite, etc MASSIVE: Quartz; Calcite; Gypsum; Hyalite (botryoidal) White. - CRYSTALS: Amphibole (tremolite); Pyroxene (diopside, usually greenish). lit^T l IVE iCr i^ ; Ml l k 7 Q uartz 5 Felspars, especially Albite; Barite; Cerussite, Scapo- lite; Talc; Meerschaum; Magnesite; Kaolinite; Amblygonite, etc. Blue. BLACKISH BLUE: Azurite; Crocidolite. INDIGO-BLUE: Indicolite (Tourmaline); Vivianite. AZURE-BLUE: Lazulite; Azurite; Lapis Lazuli; Turquois m IN " BLUE: Sapphire; C y anite ; Mite; Azurite; Chalcanthite and many copper APPENDIX 693 SKY-BLUE, MOUNTAIN-BLUE: Beryl; Celestite. VIOLET-BLUE: Amethyst; Fluorite. GREENISH BLUE: Amazon-stone; Chrysocolla; Calamine; Smithsonite; some Turquois; Beryl. Green. BLACKISH GREEN: Epidote; Serpentine; Pyroxene; Amphibole. EMERALD-GREEN: Beryl (Emerald); Malachite; Dioptase; Atacamite; and many other copper compounds; Spodumene (hiddenite); Pyroxene (rare); Gahnite; Jadeite and Jade. BLUISH GREEN: Beryl; Apatite; Fluorite; Amazon-stone; Prehnite; Calamine; Smith- sonite; Chrysocolla; Chlorite; some Turquois. MOUNTAIN GREEN: Beryl (aquamarine); Euclase. APPLE-GREEN: Talc; Garnet; Chrysoprase; Willemite; Garnierite; Pyrophyllite: some Muscovite; Jadeite and Jade, Pyrophyllite. PISTACHIO-GREEN: Epidote. GRASS-GREEN: Pyromorphite; Wavellite; Variscite; Chrysoberyl. GRAYISH GREEN: Amphibole and Pyroxene, many common kinds; Jasper; Jade. YELLOW-GREEN to OLIVE-GREEN: Beryl; Apatite; Chrysoberyl; Chrysolite (olive- green); Chlorite; Serpentine; Titanite Datolite; Olivenite; Vesuvianite. Yellow. SULPHUR-YELLOW: Sulphur; some Vesuvianite. ORANGE-YELLOW: Orpiment; Wulfenite; Mimetite. STRAW-YELLOW, also WINE-YELLOW, WAX- YELLOW: Topaz; Sulphur; Fluorite; Can- crinite; Wulfenite; Vanadinite; Willemite; Calcite; Barite; Chrysolite; Chondrodite; Titanite; Datolite, etc. BROWNISH YELLOW: Much Sphalerite; Siderite; Gothite. OCHER- YELLOW: Gothite: Yellow ocher (limonite). Red. RUBY-RED: Ruby (corundum); Ruby spinel; much Garnet; Proustite; Vana- dinite; Sphalerite; Chondrodite. COCHINEAL-RED: Cuprite; Cinnabar. HYACINTH-RED. Zircon; Crocoite. ORANGE-RED. Zincite; Realgar; Wulfenite. CRIMSON-RED: Tourmaline (rubellite); Spinel, Fluorite. SCARLET-RED: Cinnabar. BRICK-RED: Some Hematite (red ocher). ROSE-RED to PINK: Rose quartz; Rhodonite; Rhodochrosite; Erythrite; some Scapo- lite. Apophyllite and Zoisite; Eudialyte; Petalite; Margarite. PEACH-BLOSSOM RED to LILAC: Lepidolite; Rubellite. FLESH-RED: Some Orthoclase; Willemite (the variety troostite); some Chabazite; Stilbite and Heulandite; Apatite; rarely Calcite; Polyhalite.. BROWNISH RED: Jasper; Limonite; Garnet; Sphalerite; Siderite; Rutile. Brown. REDDISH BROWN: Some Garnet; some Sphalerite; S aurolite; Cassiterite; Rutile. CLOVE-BROWN: Axinite; Zircon; Pyromorphite. YELLOWISH BROWN: Siderite and related carbonates; Sphalerite; Jasper; Limonite; Gothite; Tourmaline; Vesuvianite; Chrondrodite; Staurolite. BLACKISH BROWN: Titanite; some Siderite; Sphalerite. SMOKY BROWN: Quartz. Black: Tourmaline; black Garnet (melanite); some Mica (especially biotite): also some Amphibole, Pyroxene and Epidote (these are mos'ly greenish or brownish back); further, some Sphalerite and some kinds of Quartz (varying from smoky brown to black); also Allanite; Samarskite. Some black minerals with submetalhc luster are mentioned on p. 692. Streak. The streak is to be noted in the case of some minerals with nonmetallic luster. By far the majority have, even when deeply colored in the mass (e.g. Tourmaline), a streak differing but little from white. The following may be mentioned: ORANGE-YELLOW: Zincite, Crocoite. COCHINEAL-RED: Pyrargyrite and Proustite. SCARLET RED: Cinnabar. BROWNISH RED: Cuprite; Hematite. BROWN: Limonite. ,. , , ., A The streak of the various copper, green and blue minerals, as Malachite, Azunte, etc., is about the same as the color of the mineral itself, though often a little paler. GENERAL INDEX Abbreviations, 5 Absorption of light, 222 biaxial crystals, 287 uniaxial crystals, 268 Acicular structure, 183 Acid salts, 319 Acids, 318 Adamantine luster, 209 Aggregate polarization, 300 Aggregates, crystalline, 182 optical properties, 300 Airy's spirals, 270 Albite law (twinning), 172 Alkalies, test for, 319 Alkaline taste, 310 Alliaceous odor, 310 Aluminium (aluminum), tests for, 338 Amorphous structure, 8, 183 Amplitude of vibration, 203 Amygdaloidal structure, 183 Analyzer, 229 Analysis, blowpipe, 331 chemical, 326 microchemical, 326 Angle, critical, 210 of extinction, 278 Angles, measurement of, 152 of isometric forms, 63, 66, 70 Anisometric crystals, 252 Anisotropic crystals, 252 Anomalies, optical, 301 Anorthic system, 143 Antimony, test.- for, 338 Aborescent structure, see Dendritic, 183 Argillaceous odor, 310 Arsenic, tests for, 338 Artificial minerals, 1, 326 Asterism, 250 Astringent taste, 310 Asymmetric class, 147 Atom, 311 Atomic weight, 311 Axes, crystallographic, 15 of symmetry, 11 optic, 276, 285 dispersion of, 289, 292 Axial angle, optic, 277 \ measurement of, 284 plane, 26 ratio, 26 B Barium, tests for, 338 Basal pinacbid, 78, 95, 122, 134 Bases, chemical, 318 Basic salts, 319 Baveno twins, 171 Becke test, 216 Belonite, 180 Betrand ocular, 279 Berylloid, 98 Bevel, Bevelment, 57 Biaxial crystals, behavior of light in, 270 positive and negative, 277 Biaxial indicatrix, 274 interference figure, 281 optic axes, 281 Binary symmetry, 11 Bi-quartz wedge plate, 280 Birefringence, determination of, 237 Bisectrix, acute, 277 obtuse, 277 Bismuth, tests for, 338 Bitter taste, 310 Bituminous odor, 310 Bivalent element, 317 Bladed structure, 182 Blebby bead, 332 Blowpipe, 330 flame, 331 Borax bead tests, 336 Boron, tests for, 338 Botryoidal structure, 183 Brachy-axis, 121 Brachydome, 123 Brachypinacoid, 122 Brachyprism, 123 Brachypyramid, 124 Brazil law (twin). 168, 404 Brewster's law, 227 Bri; Cadmium 7, 73, 91, 116, 130, s formula, 321 >r, 338 696 GENERAL INDEX Carlsbad twin, 170 Center of symmetry, 12 Charcoal tests, 334 Chemical compound, 318 composition and optical char- acters, 298 elements, 311, 312 formula, 312 mineralogy, 311 radicals, 317 reactions, 317 symbol, 312 tests, 328, 338 Chlorides, tests for, 338 Chromium, tests for, 339 . Circular polarization, 240, 270 imitated by mica sec- tions, 300 Classification of minerals, 343 Cleavage, 186 basal, 187 cubic, 187 dodecahedral, 187 octahedral, 187 prismatic, 187 rhombohedral, 187 Clino-axis, 133 Clinodome, 135 Clinohedral class, 138 Clinopinacoid, 134 Clinoprism, 135 Clinopyramid, 135 Closed tube tests, 333 Cobalt, tests for, 339 nitrate, use of, 332 Cohesion, 186 Colloid structure, 183 Colloidal minerals, 324 Color, 204, 247, 248 complementary, 205 Columnar structure, 182 Complementary colors, 205 Composition-plane, 161 Compound crystals, 160 Concentric structure, 182 Conchoidal fracture, 191 Conductivity, for electricity, 306 for heat, 304 Conical refraction, 276 Conoscope, 243 ,, - Contact goniometer Contact-twin, 162 Cooling taste, 310 Copper, tests for, 389^ Coralloidal struetur Corrosion forms, 191^. Cotangent relation,; Jlffi Critical angle, 210 h Crossed dispersion, Crypto-crystalline, H Crystal, definition, H distorted form, 30 Crystalline aggregate, 8, 182 structure, 8 Crystallites, 180 Crystallization, systems of, 15 Crystallography, 7 literature of, 2 Cube, 54 Cubic system, 52 Curved crystals and faces, 177 D Decrepitation, 332, 333 Deltoid dodecahedron, 69 Dendritic structure, 173, 183 Density, 195 Description of species, 343 Determination of minerals, 341 Diamagnetic minerals, 309 Diamagnetism, 309 Diametral prism, monoclinic system, 134 orthorhombic system, 122 Diaphaneity, 247 Diathermancy, 305 Dibasic acid, 318 Dichroism, 247, 268 Dichroscope, 269 Diffration, 223 Dihexagonal bipyramidal class, 95 Dihexagonal pyrism, 96 Dihexagonal pyramid, 98 Dihexagonal pyramidal class, 98 Dimorphism, 325 Diploid, 65 Dispersion, 221 crossed, 294 horizontal, 293 inclined, 292 of bisectrices, 293, 294 of optic axes, 289 Distorted crystals, 13, 174 Ditetragonal bipyramidal class, 77 Ditetragonal prism, 79 pyramid, 82 Ditetragonal pyramidal class, 84 Ditrigonal bipyramidal class, 103 Ditrigonal prism, 103 pyramid, 103 Ditrigonal pyramidal class, 109 Ditrigonal scalenohedral class, 104 J. Divergent structure, 182 Dodecahedron, 54 deltoid, 69 dyakis, 65 pentagonal, 64 tetrahedral, 72 rhombic, 54 Domatic class, 138 Domes, 31, 123, 135, 145 Double refraction, 223 Drusy, 183 Dyakis-dodecahedron, 65 Dyakisdodecahedral class, 63 GENERAL INDEX 697 E Earthy fracture, 191 Effervescence, 328 Eightling, 164 Elasticity, 186, 194 Elastic minerals, 194 Electrical conductivity in minerals, 306 Electro-negative elements, 313 -positive elements, 313 Elements, angular, 128, 139, 148 axial, 128, 139, 148 chemical, 312 Elliptically polarized light, 240 Elongation, negative or positive, 280 Enantimorphous forms, 71, 113 Epoptic figures, 288 Etching figures, 189 Exfoliation, 332 Expansion by heat, 304 Exterior conical refraction, 276 Extinction, 230 directions, character of, 239 inclined, 260, 278 parallel, 260, 278 Extinction-angle, 278 Extraordinary ray, 254 Feel, 310 Fetid odor, 310 Fibrous structure, 182 Filiform, 183 First order prisms, 79, 95 pyramids, 80, 97 Fiveling, 164 Flame coloration, 332 oxidizing, 331 reducing, 331 Flexible, 194 Fluorescence, 251 Fluorides, test for, 339 Fluxes, 336 Foliated structure, 182 Forceps, 330 Form, 30 Formula, chemical, 312, 320 calculation of, 321 Fracture, 191 Frictional electricity in minerals, 306 Fundamental form, 30 Fusibility, 304, 332 scale of, 332 Gels, 324 General mineralogy, literature of, 3 Gladstone law, 210 Glass, optical characters of, 252, 300 Glass tubes, 331, use of, 333 Gliding planes, 187 Glimmering luster, 250 Glistening luster, 250 Globular structure, 183 Globulites, 180 Glowing, 332, 333 Gnomonic projection, 40 Gnomonic projection of isometric forms, 62 hexagonal forms, 99, 109 tetragonal forms, 84 triclinic forms, 147 monoclinic forms, 137 orthorhombic forms, 127 Goniometer, contact or hand, 152 horizontal, 155 reflecting, 154 theodolite, 157 two-circle, 157 Granular structure, 182 Greasy luster, 249 Grouping, molecular, 22 parallel, 172, 173 Gyroidal forms, 71 H Habit, crystal, 10 Hackly fracture, 191 Hand goniometer, 152 Hard minerals, 193 Hardness, 191 Heat, 303 effect on optical properties, 296 Heavy solutions, 198 Hemihedral forms, 21 Hemimorphic class, hexagonal system, 98 monoclinic system, 138 orthorhombic system, 126 tetragonal system, 84 Hexagonal axes, 94 bipyramidal class, 100 prisms, 95, 96 prism of third order, 111 pyramidal class, 101 pyramids, 97, 98 symmetry, 11 system, 17, 94 trapezohedral class, 102 trapezohedron, 102 Hexakistetrahedron, 70 Hexoctahedral class, 52 Hexoctahedron, 59 Hextetrahedral class, 66 Hextetrahedron, 70 Holohedral forms, 21 Horizontal dispersion, 292 goniometer, 155 Horse-radish odor, 310, 334 Houppes, 288 Hour-glass structure, 478 Hydroxides, 318 698 GENERAL INDEX Icosahedron, 65, 67 Icositetrahedron, 58 Impalpable structure, 182 Indicatrix, biaxial, 274 uniaxial, 257 Indices, crystallographic, Dana, 29 Goldschmidt, 29 Naumann, 29 Weiss, 29 rational, 29 refractive, 207 determination of, 280, 213, 216 Incidence, angle of, 206 Inclined dispersion, 292 hemihedrons, 67 Inclusions, 179 Inelastic minerals, 194 Insoluble minerals, 329 Interference of light, 224, 230 colors, 236 biaxial crystals, 260 uniaxial crystals, 278 figures, biaxial, 281 inclined, 267, 283 uniaxial, 260 Interior conical refraction, 276 Intumescence, 332 Iridescence, 250 Iron, test for, 339 Iron cross, 166 Isodiametric crystals, 252 Isodimorphism, 325 Isometric crystals, optical properties 252 system, 16, 52 Isomorphism, 322 Isomorphous group, 322 mixtures, 323 Isotropic crystals, 252 Jolly balance, 196 Klein solution, 198 K Lamellar polarization, 302 . structure, 182 Lamp for blowpipe, 330 Law of rational indices, 29 Lead, test for, 339 Left-handed crystal, 114, 403 polarization, 241 Light, nature of, 200 Light-ray, 204 Light velocity, relation to refractive index, Light-waves, 202 Liquids with high refractive indices, 213 Lithium, test for, 339 Lorentz law, 210 Lorenz law, 210 Luster, 249 M Macro-axis, 121, 144 Macrodome, 123, 145 Macropinacoid, 122, 145 Macroprism, 123 Macropyramid, 124 Magnesium, test for, 339 Magnetic minerals, 308 Magnetism, 308 Magnets, natural, 308 Malleable minerals, 193 Mammillary structure, 183 Manganese, test for, 339 Manebach twin, 171, 457 Margarites, 180 Measurement of crystal angles, 152 Mercury, test for, 339 Meta-colloids, 325 Metagenetic twins, 163 Metallic-adamantine luster, 249 Metallic luster, 249 Metallic pearly luster, 249 Metals, 313 Mica plate, use of, 264 Mica sections superposed, 300 Micaceous structure, 182 Microchemical analysis, 326 Microcosmic salt, v. Salt of Phosporus, 336 Microlites, 180 Microscope, 245 Miller hexagonal axes, 117 indices, 117 indices, 28 Mimetic crystals, 14 Mineral, artificial, 326 literature of, 4 definition of, 1 synthesis, 326 Mineral kingdom, 1 Mineralogical journals, 4 Mineralogy, chemical and determinative, literature of, 4 science of, 1, 2 Models of crystals, 21 Mohs scale of hardness, 191 Molecular networks, 22, 25 structure, 7 weight, 316 Molecule, 311 Molybdenum, test for, 339 Monobasic acid, 318 Monoclinic axes, 133 crystals, 134 optical characters, 291 system, 17, 133 Mossy structure, 183 GENERAL INDEX 699 N Natural magnets, 308 Naumann's indices, 29 Negative crystal, biaxial, 277, 286 uniaxial, 254, 258, 264 element, 313 elongation, 280 Network, molecular, 22 Neutral salt, 319 Newton's rings, 225 Nickel, test for, 339 Nicol prism, 228 Niobium, test for, 339 Nitrates, test for, 339 Nodular structure, 183 Non-metallic luster, 249 Non-metals, 313 Normal angles, 44 class, isometric system, 52 hexagonal system, 95 monoclinic system, 133 orthorhombic system, 121 tetragonal system, 77 triclinic system, 144 salt, 319 Oblique system, 133 Octahedron, 54 Ocular, Bertrand, 279 Odor, 310 Opalescence, 250 Opaque, 247 Open tube tests, 334 form, 30 Optic axes, 273, 276 axial angle, 277 axis, 254 Optical anomalies, 301 characters of crystalline aggregates, 300 twin crystals, 298 effect of heat upon, 296 pressure on, 300 relation to chemical composition, 298 tests, methods and order of, 295 Ordinary ray, 254 Ortho-axis, 133 Orthodome, 135 Orthopinacoid, 134 Orthoprism, 135 Orthopyramid, 135 Orthorhombi ombic axes, 121 bipyramidal class, 121 bisphenoidal class, 128 crystals, 121 optical characters, 288 dispersion, 289 pyramidal class, 126 system, 17, 121 Oscillatory combination, 176 Oxides, 318 Oxidizing flame, 331 Paragenetic twins, 163 Parallel extinction, 260, 278 grouping, 172 hemihedrons, 64 Paramagnetic minerals, 309 Paramagnetism, 309 Parameter, 27 Paramorph, 27' Paramorphism, 27 Parting, 188 Pearly luster, 249 Penetration-twin, 162 Penfield beam balance, 197 Pentagonal dodecahedron, 64 tetrahedral, 72 hemihedral class, 63 icositetrahedral class, 71 icositetrahedron, 71 Pentavalent element, 317 Percussion figure, 188 Pericline law (twinning), 172, 462 Periodic law, 314, 315 Phanero-crystaUine, 182 Phosphates, test for, 339 Phosphorescence, 251 Phosphoric acid, test for, 339 Photo-electricity, 307 Physical characters, 185 mineralogy, literature of, 2 Piezo-electricity, 307 Pinacoid, 31 Pinacoidal class, 144 Plagiohedral class, 71 Plagiohedral hemihedral class, 71 Plane-polarized light, 226 Plane of polarization, 226 Planes of symmetry, 10 Platinum wire, 330, 336 Play of colors, 250 Pleochroic halos, 288 Pleochroism, 247, 287 Pleomorphism, 325 Point system, 23 Polariscope, 229, 243 Polarization, 226 Polarization-brushes, 288 -microscope, 245 Polarized light, 226 Polarizer, 229 Polysynthetic twinning, 163 Positive crvstal, biaxial, 277, 286 uniaxial, 254, 258, 264 element, 313 elongation, 280 Potassium, test for, 340 Pressure, effect upon optical characters, 300 figures, 189 700 GENERAL INDEX Primary optic axes, 276 Prism, 30 hexagonal system, dihexagonal, 96 first order, 95 second order, 96 third order, 100 monoclinic system, 135 orthorhombic system, 123 tetragonal system, ditetragonal, 79 first order, 79 second order, 79 third order, 85 triclinic system, 145 Prismatic class, 133 Projection, gnomonic, 40 literature of, 44 horizontal, 31 spherical, 31 stereographic, 32 literature of, 44 Pseudo-hexagonal crystals, 14, 169, 437 -isometric crystals, 301 Pseudomorph, 183, 326 Pseudomorphism, 326 Pseudosymmetry, 14, 60, 164, 174, 297 Pycnometer, 197 Pyramid, 31 hexagonal system, dihexagonal, 98 first order, 97 second order, 97 third order, 100 monoclinic system, 135 orthorhombic system, 124 tetragonal system, ditetragonal, 79 first order, 79 second order, 79 third order, 85 triclinic system, 145 Pyramidal hemihedral hemimorphic class, 101 Pyramidal-hemimorphic class, hexagonal system, 101 tetragonal system, 86 Pyritohedral class, 63 Pyritohedron, 64 Pyro-electricity, 306 Pyrognostics, 338 Q Quarter-undulation mica plate, 264 Quartz wedge, 231 use of, 286 Radiated structure, 182 Radical, chemical, 317 Rational indices, law of, 29 Reaction, chemical, 317 Reagents, chemical, 328 Reducing flame, 331 Reduction of metals, 334 Reflecting goniometer, 154 Reflection of light, 205 angle of, 205 Refraction, 206 double, 223 strength of, 224 Refractive index, 207 determination of, 213. 216, 180 relation to light velocitv, 208 indices, principal, 209 Refractometer, 241 Regular system, 52 Relief, high or low, 212 Reniform structure, 183 Resinous luster, 249 Reticulated structure, 182 Rhombic section, 462 sphenoid, 128 Rhombohedral class, 104, 110 Rhombohedral division, 103 Rhombohedral hemihedral class, 104 hemimorphic class, 109 tetartohedral class, 110 Rhombohedron, positive and negative, 104, 105 second order, 110 third order, 110 Right-handed crystal, 114, 403 polarization, 241 Roasting, 334 Rontgen rays, 25 Saccharoidal structure, 182 Saline taste, 310 Salt of phosporus, 337 Salts, 319 Scalenohedron, 106 tetragonal, 88 Scalenohedral class, 87 Scale of fusibility, 332 Scale of hardness, 191 Schiller, 251 Schillerization, 251 Sclerometer, 192 Second order prism, hexagonal system, 96 tetragonal system, 79 pyramid, hexagonal system, 97 tetragonal system, 79- rhombohedron, 110 Secondary optic axes, 276 twinning, 165, 188 Sectile, 193 Selenite-plate, 236, 266 Selenium, test for, 340 Semi-metals, 313 Semi-transparent, 247 Sensitive tint, 236 use of, 266 GENERAL INDEX 701 Separable, 182 Shining luster, 250 Silica, test for, 340 Silky luster, 249 Silver, test for, 340 Soda, use of, 330, 336 Sodium, test for, 340 Soft minerals, 193 Solid solution, 323 Solubility in minerals, 328 Solution planes, 189 Sonstadt solution, 198 Sound waves, 201 Specific gravity, 195 determination of, 196 Spectroscope, 221 Sphenoid, 87 rhombic, 128 Sphenoidal class, monoclinic system, 138 orthorhombic system, 128 tetragonal system, 87 hemihedral class, 87 tetartohedraj class, 89 Spherical projections, 31 Spherulites, 300, 459 Splendent luster, 250 Splintery fracture, 191 Stalactitic structure, 183 Stellated structure, 182 Stereographic circles and scales, 36 projection, 32 literature of, 44 hexagonal forms, 99, 108 isometric forms, 61 tetragonal forms, 83 triclinic forms, 146 monoclinic forms, 137 orthorhombic forms, 126 protractor, 35, 39 Streak, 247 Strength of double refraction, 224 Striations, 176 Strike-figure, v. Percussion-figure, 188 Strontium, test for, 340 Structure of minerals, 182 Sublimate, 333, 334 Subtranslucent, 247 Subtransparent, 247 Subvitreous, 249 Sulphates, test for, 340 Sulphides, test for, 340 Sulpho-salts, 320 Sulphur, test for, 340 Sulphurous odor, 310 Swelling up, 332 Symbol, chemical, 312 crystallographic, 27 Symmetry, 10 axis of, 11 center of, 12 classes, 15 exhibited by Stereographic pro- jection, 45 of systems, 18, 19 planes of, 10 Synthesis, mineral, 326 System, hexagonal, 94 isometric, 52 monoclinic, 133 . orthorhombic, 121 tetragonal, 77 triclinic, 143 Systems of crystallization, 15 Tangent relation , 49 Tarnish, 250 Taste, 310 Tautozonal faces, 45 Tellurium, test for, 340 Tenacity, 193 Test paper, 330 Tetartohedral class, isometric system, 72 tetragonal system, 89 forms, 22 Tetragonal bipyramidal class, 85 bisphenoidal class, 89 crystals, 77 pyramidal class, 86 scalenohedron, 88 sphenoidal class, 87 symmetry, 11 system, 16, 77 trapezohedral class, 89 trapezohedron, 89 trisoctahedron, 58 tristetrahedron, 69 Tetrahedral class, 66 hemihedral class, 66 pentagonal dodecahedral class, 72 s/ pentagonal dodecahedron, 72 Tetrahedron, 67 Tetrahexahedron, 56 Tetravalent element, 317 Theodolite goniometer, 157 Thermo-electricity, 307 Third-order prism, hexagonal system, 100 tetragonal system, 85 pyramid, hexagonal system, TOO tetragonal system 85 rhombohedron, 110 Thoulet solution, 198 Tin, test for, 340 Titanium, test for, 340 Total reflection, 210 refractometer, 219, 241 Tourmaline tongs, 243 Translucent, 247 Transparency, 247 702 GENERAL INDEX Transparent, 247 Trapezohedral class, hexagonal system, 102, 112 tetragonal system, 89 hemihedral class, 102 tetratohedral class, 112 Trapezohedron, 58 hexagonal, 102 tetragonal, 89 trigonal, 113 Tribasic acid, 318 Trichite, 180 Triclinic axes, 143 crystals, 143 optical characters of, 295 system, 17, 143 symmetry, 115 Trigonal bipyramidal class, 114 class, 103 division, 103 hemihedral class, 103 hemimorphic class, 109 prism, 103 pyramid, 103 pyramidal class, 114 symmetry, 11 system, 103 tetartohedral class, 114 hemimorphic class, 114 trapezohedral class, 112 trapezohedron, 113 trisoctahedron, 57 trictetrahedron, 69 Trigondodecahedron, 69 Trigonotype class, 103 Trilling, 164 Trimorphous, 325 Tripyramidal class, hexagonal system, 100 tetragonal system, 85 Trisoctahedron, 57 Trirhombohedral class, 110 Tristetrahedrons, 69 Trivalent element, 317 Truncate, truncation, 56 Tungsten, test for, 340 Twin crystals, 160 optical characters of, 298 Twinning, artificial, 188 axis, 161 plane, 161 polysynthetic, 163 repeated, 163 secondary, 165 symmetrical, 163 Twins, isometric, 165 hexagonal, 167 monoclinic, 170 orthorhombic, 169 spinel, 419 tetragonal, 166 ' triclinic, 172 Two-circle goniometer, 157 U Ultra-blue, 521 Uneven fracture, 191 Uniaxial crystals, 253 behavior of light in, 253 determination of refrac- tive indices, 254 examination in conver- gent polarized light, examination in polarized light, 259 interference colors, 260 optical characters, 270 positive and negative, 254 indicatrix, 257 wave surface, 255 Unit form, 30 Univalent element, 317 Uranium, test for, 340 Uralitization, 490 Valence, 317 Vanadium, test for, 340 Velocity of light, 203 relation to refractive in- dex, 208 Vicinal forms, 24 Vitreous luster, 209 W Water of crystallization, 320 Water-waves, 201 Wave-front, 203 Wave-length, 204 Wave-motion, 201 Wave-surface, biaxial crystals, 273 uniaxial crystals, 255 Waxy luster, 249 Westphal balance, 199 White light, 204 Widmanstatten lines, 356 X-rays and crystal structure, 25 Zinc, test for, 340 Zirconium, test for, 341 Zirconoid, 82 Zonal equations, 46 Zone, 31 Zone-axis, 31 INDEX TO SPECIES Aarite, v. Arite, 372 Abriachanite, 493 Acadialite, 552 Acanthite, 367 Acerdese, v. Manganite Achmatite, 532 Achroite, 542 Acmite, 479 Actinolite, Actinote, 489 Adamantine spar, 413 Adamine, 604 Adamite, 604 Adelite, 601 Adipocire, v. Hatchettite Adular, Adularia, 458 ^Edelite, 535 ^Egirine, 419 ^girite, 479 ^Egirite-augite, 477 jEnigmatite, 494 JEschynite, 591 Agalite, 576 Agalmatolite, 562 Agaric mineral, 440 Agate, 405 Agate-jasper, 406 Agnolite, 582 Agricolite, 510 Aguilarite, 365 Aikinite, 388 Akermanite, 519 Alabandin, 369 Alabandite, 369 Alabaster, 634 Oriental, 440 Alaite, 436 Alalite, 476 Alamosite, 483 Alaskaite, 386 Alaun, v. Alum, Alaunstein, v. Alunite Albertite, 647 Albite, 464 Alexandrite, 424 Algodonite, 362 Alisonite, 364 Allactite, Allaktit, 606 Allagite, 485 Allanite, 533 Allemontite, 349 Allochroite, 508 Alloclasite, Alloklas, 382 Allopalladium, 356 Allophane, 580 Almandine, Almandite, 507, 419 Almeriite, 640 Aloisiite, 545 Alpha-quartz, 403 Alshedite, 584 Alstonite, v. Bromlite, 447 Altaite, 364 Alum, 637 Alumian, 632 Alumina, 413, 418 ACUMINATES, 418 et seq. Aluminite, 639 Aluminium borate, 620 carbonate, 452 chloride, 399 fluorides, 399, 400 hydrates, 431, 435 mellate, 645 oxide, 413, 431, 435 phosphates, 605, 610, etc. silicates, 523, 524, 5?6, 578, 579, 580, etc. sulphates, 632, 637, 639 Aluminium ore, 433 Alumstone, 639 Alundum, 414 Alunite, 639 Alunogel, 434 Alunogen, 638 Alurgite, 565 Amalgam, 354 Amarantite, 639 Amazonite, 461 Amazonstone, 461 Ambatoarinite, 449 Amber, 276, 645 Amblygonite, 602 Amblystegite, 473 Amesite, 571 Amethyst, 405 Oriental, 410 Amianthus, 490. 573 Ammiolite, 618 Ammonium, carbonate, 450 chloride, 397 oxalate, 644 phosphates, 610, etc. 703 Ammonium, sulphates, 624, etc. Ampangabeite, 591 Amphibole, 487 AMPHIBOLE Group, 485 Amphibole-anthophyllite, 489 Amphigene, 469 Amphodelite, 468 Analcime, 554 Analcite, 554 Anapaite, 607 Anatase, 428 Ancylite, 449 Andalusite, 524 Andesine, 466 Andorite, 385 Andradite, 507 Andrewsite, 616 Anemousite, 468 Angaralite, 540 Anglesite, 628 Anhydrite, 629 Animikite, 362 Ankerite, 443 Annabergite, 609 Annerodite, 591 . Annite, 565 Anomite, 564 Anorthite, 467 Anorthoclase, 461 Anthophyllite, 486 Hydrous, 487 Anthracite, 648 Antigorite, 573 Antimonarsen, v. Allemontite ANTIMONATES, 618 Antimonblende, v. Kermes- ite Antimonglanz, v. Stibnite ANTIMONIDES, 372, etc. Antimonite, 358 ANTIMONITES, 618 Antimonnickel, v. Breithaup- tite Antimonsilber. v. Dyscras- ite Antimonsilberblende, v. Py- rargyrite Antimony, 349 Gray, 358 Native, 349 704 INDEX TO SPECIES Antimony, Red, v. Kermesite White, 409 Antimony oxides, 409 oxysulphide, 383 sulphide, 358 Antimony glance, 358 Antlerite, 632 Apatite, 595 Aphanese, Aphanesite, 604 Aphrite, 440 Aphrizite, 542 Aphrosiderite, 571 Aphthalose, 624 Aphthitalite, 624 Apjohnite, 637 Aplome, 508 Apophyllite, 546 Apotome, 627 Aquamarine, 495 Araeoxene, 604 Aragonite, 446 Arcanite, 624 Ardennite, 539 Arduinite, 558 Arendalite, 531 Arfvedsonite, 494 Argentine, 440 Argentite, 364 Argentobismutite, v. Matil- dite Argyrodite, 394 Arite, 372 Arizonite, 418 Arkansite, 430 Arquerite, 354 Armangite, 594 Arragonite, v. Aragonite, 44 O ARSENATES, 592 Arsenic, 348 White, 409 Arsenical antimony, 349 Arsenic oxide, 409" sulphide, 357 ARSENIDES, 361 Arsenikalkies, v. Arsenopy- nte Arsenikkies, y. Arsenopy- rite Arseniopleite, 606 Arseniosiderite, 606 Arsenkies, v. Arsenopyrite Arsenobismite, 617 Arsenoferrite, 378 Arsenolite, 409 Arsenopyrite, 381 Arsensilberblende, v. Prous- tite Artinite, 453 Asbestos, Asbestus, 489, 573 , Blue, 493 Asbolan, 436 Asbolite, 436 Ascharite, 621 Asmanite, 408 Asparagus-stone, 596 Aspasiolite, 498 Asphaltum, 647 Asteria, 413 Asteriated quartz, 405 sapphire, 413 Astrakanite, 637 Astrolite, 496 Astrophyllite, 585 Atacamite, 400 Atelestite, 606 Atopite, 618 Attacolite, 614 Auerlite, 522 Augelite, 614 Augite, 477 Auralite, 498 Aurichalcite, 451 Auripigmentum, 357 Automolite, 420 Autunite, 616 Aventurine feldspar, 465 quartz. 405 Ax-stone, 482 Axinite, 534 Awaruite, 356 Azurite, 451 B Bababudanite, 493 Babingtonite, 485 Backstromite, 435 Saddeckite, 562 Jaddeleyite, 428 Jadenite, 374 Sagrationite, 533 Saikalite, 477 Jakerite, 581 Salas ruby, 419 Saltimorite, 573 Samlite, 526 Sarbierite, 458 3aricalcite, 440 iarite, 625 Barium carbonate, 447, 449 nitrate, 619 silicate, 460, 498, 549, 550, 555, etc. sulphate, 625 ariumuranit, 617 arkevikite, 494 Barrandite, 610 Barsowite, 523 Barthite, 612 Barylite, 498 Barysilite, 498 Baryt, Barytes, 625 Baryta, v. Barium Baryta-feldspar, 460 Baryta-orthoclase, 460 I Barytocalcite, 449 1 Baryturanit, 617 Basanite, 406 Bassanite, 630 1 Bassetite, 617 Bastite, 474, 573 Bastnasite, 449 I Batchelorite, 579 Bathvillite, 646 Batrachite, 512 Baumhauerite, 386 Bauxite, 433 Bavenite, 558 Bayldonite, 612 Bazzite, 540 Beaumontite, 549 Beauxite, 433 Beaverite, 638 Bechilite, 623 Beckelite, 540 Beegerite, 392 | Beilstein, v. Nephrite Beldongrite, 436 Bellite, 631 | Bell-metal ore, 394 Belonesite, 399 Bementite, 582 I Benitoite, 585 Beraunite, 615 Bergamaskite, 491 Bergblau, v. Azurite Bergkrystall, v. Quartz Bergmannite, 556 Bergsalz, v. Halite Bergseife, 579 Bergtheer, v. Pittasphalt | Berlinite, 614 Bernstein, v. Amber Berthierite, 386 Bertrandite, 539 Beryl, 495 Beryllium aluminate, 423 borate, 620 phosphate, 601 silicate, 495, 496, 514, 529, 539 Beryllonite, 595 Berzelianite, 365 Berzeliite, 593 Betafite, 591 Beta-quartz, 403 Beudantite, 618 ' Beyrichite, 372 Bieberite, 636 Bildstein, v. Agalmatolite Bilinite, 637 Bindheimite, 617 Binnite, 391 Biotina, Biotine, 468 Biotite, 563 Bisbeeite, 581 Bischofite, 402 Bismite, 410 I Bismuth, 349 INDEX TO SPECIES 705 Bismuth arsenate, 606 carbonate, 449, 454 oxide, 410 oxychloride, 401 selenide, 359 silicate, 504 sulphide, 359 tellurate, 641 telluride, 360 uranate, 617 vanadate, 594 Bismuth glance, 359 Bismuth gold, 350 Bismuth ocher, 410 Bismuthinite, 359 Bismutite, 454 Bismutoplagionite, 387 Bismutosmaltite, 380 Bismutosphaerite, 449 Bittersalz, v. Epsomite Bitter spar, Bitterspath, v. Dolomite Bitumen, 646, 647 Bituminous coal, 648 Bityite, 558 Bixbyite, 425 Bjelkite, 387 Black jack, 367 Black lead, 347 Blanfordite, 477 Blatter tellur, v. Nagyagite Blaueisenerde, v. Vivianite Bleiantimonglanz, v. Zinken- ite Bleiglanz, v. Galena Bleiniere, Bleinierite, v. Bind- heimite Bleischweif, 363 Bleivitrol, v. Anglesite Blende, 367 Blodite, 637 Bloedite, Bloedite, 637 Blomstrandine, 591 Bloodstone, 405 Blue asbestus. 493 iron earth, 608 John, 398 malachite, v. Azurite vitriol, 636 Bobierrite, 608 Bccumlerite, 399 Boghead cannel, 648 Bog-iron ore, 433 manganese, 436 Bole, 579 Boleite, 401 Bologna stone, 626 Boltonite, 513 Bone-phosphate, 597 turquoise, 613 Bonsdorffite, 498 Boort, 345 Boothite, 636 Boracite, 620 BORATES, 619 Borax, 622 Borickite, 615 Boric acid, 435 Bomite, 374 Boron hydrate, 435 silicate, 522, 527 Boronatrocalcite, 622 Bort, 345 Bostonite, 575 Botryogen, 639 Botryolite, 528 Boulangerite, 387 Bournonite, 388 Boussingaultite, 637 Bowenite, 572 Bowmannite, 601 Brackebuschite, 604 Bragite, 588 Brandisite, 566 Brandtite, 607 Brannerite, 586 Brauneisenstein, v. Limon- ite Braunile, 425 Braunstein, Grauer, v. Pyro- lusite Bravoite, 378 Brazilian pebble, 325 emerald, 542 sapphire, 542 Brazilite, 428 ' Bredbergite, 508 Breislakite, 490 Breithauptite, 372 Breunerite, 443 Breunnerite, 443 Brevicite, 556 Brewsterite, 549 Britholite, 580 Brittle silver ore, 392 Brochantite, 632 Broggerite, 623 Bromargyrite, 397 BROMIDES, 397 Bromlite, 447 Bromyrite, 397 Brongnartine, 632 Brongniardite, 387 Bronzite, 472 Brookite, 429 Brown coal, 648 iron ore, 432 iron stone, 432 hematite, 432 ocher, 432 spar, 443 Brucite, 434 Brugnatellite, 453 Brunsvigite, 572 Brushite, 611 Bucholzitef526 Bucklandite, 532, 533 Buhrstone, 406 Bunsenite, 411 Buntkupfererz, v. Bornite Burrstone, 406 Bushmanite, 637 Bustamite, 484 Buttermilcherz, v. Cerargy- rite Byssolite, 490 Bytownite, 467 Cabrerite, 609 Cacholong, 408 Cacoxenite, 614 Cadmia, 540 Cadmium sulphide, 371 Cadmium blende, v. Green- ockite, 371 Cadmium oxide, 411 Caesium silicate, 470 Cainosite, v. Cenosite, 580 Cairngorm stone, 405 Caking coal, 648 Calamine, 539, 445 Calaverite, 383 Calc sinter, 440 spar, 438 tufa, 440 Calcioferrite, 615 Calciostrontianite, 448 Calciovolborthite, 604 Calcite, 438 Calcium arsenate, 610, etc. antimonate, 618 borate, 620, 621, etc. carbonate, 438, 446 chloride, 399 flouride, 398 iodate, 619 molybdate, 643 niobate, 587, etc. nitrate, 619 oxalate, 644 oxyfluoride, 401 phosphate, 595, 606, 611, etc. silicate, 483, 467, etc. sulphate, 629, 633, etc. sulphide, 369 Calcium tantalate, 587 titanate, 583, 586 tungstate, 642 Caledonite, 632 Californite, 520 Callainite, 610 Calomel, 395 Campylite, 598 Canaanite, 476 Cancrinite, 501 sulphatic, 501 Canfieldite, 394 Cannel coal, 648 Caoutchouc, Mineral, 647 706 Capillary pyrites, 372 Caporcianite, 552 Cappelenite, 496 Caracolite, 631 Carbon, 345 Carbonado, 345 CARBONATES, 436 Carlosite, 585 Carminite, 594 Carnallite, 401 Carnegieite, 468 Carnelian, 405 Carneol, v. Carhelian Caraotite, 617 Carpholite, 540 Carphosiderite, 639 Carrollite, 374 Caryinite, 593 Caryocerite, 496 Caryopilite, 582 Cassiterite, 425 Castanite, 639 Castor, CastorHe, 455 Caswellite, 565 Catapleiite, 496 Cataspilite, 498 Catlinite, 580 Catoptrite, 618 Cat's eye, 405, 424 Cauk, Cawk, 626 Cebollite, 518 Celadonite, 577 Celestine, 627 Celestite, 627 Celsian, 460 Cenosite, 580 Cerargyrite, 397 Cerite, 540 Cerium carbonate, 449 fluoride, 399 niobates, 587 phosphates, 593, 609, etc. silicates, 533, 540, 585, etc. Ceruleite, 616 Cerussite, 448 Cervantite, 410 Cesarolite, 424 Ceylanite, Ceylonite, 410 Chabazite, 552 Chalcanthite, 636 Chalcedony, 405 Chalcocite, 366 Chalcodite, 572 Chalcolamprite, 587 Chalcomenite, 641 Chalcophanite, 435 Chalcophyllite, 612 Chalcopyrite, 374 Chalcosiderite, 616 Chalcosine, 366 Chalcostibite, 386 Chalcotrichite, 411 Cfcalk, 440 French, 575 INDEX TO SPECIES Chalmersite, 366 Chalybite, 443 Chamoisite, Chamosite, 572 Chathamite, 378 Chemawinite, 645 Chenevixite, 616 Chert, 406 Chessy copper, 451 Chessylite, 451 Chesterlite, 461 Chiastolite, 525 Childrenite, 615 Chilenite, 362 Chillagite, 643 Chiolite, 400 Chiviatite, 385 Chladnite, 472 Chloanthite, 378 Chloralluminite, 399 Chlor-apatite, 595 Chlorargyrite, 397 Chlorblei, v. Cotunnite CHLORIDES, 395 Chlorite, 568 CHLORITE Group, 568 Chloritoid, 567 Chloritspath, v. Chloritoid Chlormanganokalite, 399 Chlorocalcite, 399 Chloromagnesite, 399 Chloromelanite, 482 Chloropal, 582 ' Chlorophseite, 571 Chlorophane, 398 Chlorophyllite, 498 Chlorquecksilber, v Calo- mel Chlorospinel, 419 Chlorsilber v. Cerargyrite Chondrarsenite, 601 Chondrodite, 536 Chrismatine, Chrismatite, 645 Christianite, 468 Christobalite, 408 Christophite, 368 CHROMATES, 630, etc. Chrome diopside, 476 Chrome spinel, 419 Chromeisenstein, v. Chrom- ite Chromic iron, 423 Chromite, 423 Chromitite, 423 Chromium oxide, 423 sulphate, 639 sulphide, 374 Chrysoberyl, 423 Chrysocolla, 581 Chrysolite, 511 CHRYSOLITE Group, 510 Chrysoprase, 405 Chrysotile, 573 Churchite, 609 Cimolite, 579 Cinnabar, 370 Inflammable, 646 Cinnamon-stone, 507 Cirrolite, 606 Citrine, 405 Clarite, 393 Claudetite, 409 Clausthalite, 364 Clay, et seq. 578 Clay iron-stone, 416 Brown, 433 Cleavlandite, 465 Cleiophane, 368 Cleveite, 623 Cliachite, 434 Cliftonite, 347 Clinochlore, 569 Ch'noclase, 604 Clinoclasite, 604 Clinoenstatite, 477 Clinohedrite, 540 Clinohumite, 536 Clinozoisite, 532 Clintonite, 566 CLINTONITE Group, 566 Coal, Mineral, 647, 648 Cobalt arsenate, 607, 608 carbonate, 446, 453 arsenide, 378, 379, 380, 381 selenite, 641 sulph-arsenide, 378 sulphate, 636 sulphide, 378 Cobalt bloom, 608 Cobalt glance, v. Cobaltite Cobaltine, 379 Cobaltite, 379 Cobaltnickelpyrite, 378 Cobaltoadamite, 604 Cobaltocalcite, 441 Cobaltomenite, 641 Coccolite, 477 Cocinerite, 362 Cockscomb Pyrite, 380 Crelestine, 627 Coeruleolactite, 614 Cohenite, 356 Coke, 648 Colemanite, 621 Colerainite, 583 Cb'lestine, v. Celestite Collbranite, 620 Collophanite, 606 Collyrite, 580 Colophonite, 508, 520 Coloradoite, 369 COLUMBATES V. NlOBATES. 587 Columbite, 588 Comptonite, 558 Confolensite, 579 Conichalcite, 612 INDEX TO SPECIES 707 Connarite, 577 Connellite, 631 Cookeite, 563 Copal, Fossil, 645 Copaline, Copalite, 645 Copiapite, 638 Copper, 353 Emerald, v. Dioptase 515 Gray, 390 Indigo, v. Covellite, 371 Native, 353 Red, v. Cuprite, 410 Copper, Vitreous, v. Chalco- cite, 366 Yellow, 374 Copper arsenate, 603, 604, 612, etc. arsenide, 362 carbonate, 450, 451 chloride, 395, 400 manganate, 424 iodide, 395 nitrate, 619 oxides, 410, 412 oxychlorides, 400 phosphates, 603, 612, etc. selenides, 365 selenite, 641 silicates, 515, 581 sulphantimonate, 393 sulphantimonites, 386 et seq. sulpharsenates, 393 sulpharsemte, 386 sulphates, 630, 632; hy- drous, 636 et seq. sulphides, 366, 371, 374 et seq. sulpho-bismuthites, 386 tungstate, 643 vanadates, 604 Copper glance, 366 Copper mica, 616 Copper nickel, 372 Copper pyrites, 374 Copper uranite, 616 Copper vitriol, 636 Copperas, 636 Coprolites, 597 Coquimbite, 637 Cordierite, 497 Cordylite, 449 Gorki te, 618 Cornwallite, 612 Coronadite, 424 Corundophilite, 571 Corundum, 413 Corynite, 379 Cosalite, 387 Cossyri'te, 494 Cotunnite, 399 Couseranite, 517 Covellite, 371 Crandallite, 601 Creedite, 402 Crednerite, 424 Crestmoreite, 546 Crichtonite, 417 Cristobalite, 408 Crocalite, 556 Crocidolite, 493 Crocoite, 630 Cromfordite, v. Phosgenite Cronstedtite, 571 Crookesite, 365 Crossite, 493 Cryolite, 399 Cryolithionite, 400 Cryophyllite, 363 Cryptolite, 593 Cryptoperthite, 460 Cuban, 374 Cubanite, 374 Cube ore, v. Pharmacosider- ite Cube spar, v. Anhydrite Culsageeite, 572 Cumengite, 401 Cummingtonite, 489 Cuprite, 410 Cuproadamite, 604 Cuprobismutite, 385 Cuprodescloizite, 604 Cuprogoslarite, 635 Cupromagnesite, 636 Cuproplumbite, 364 Cuproscheelite, 643 Cuprotungstite, 643 Cuspidine, 535 Custerite, 497 Cyanite, 526 Cyanochroite, 637 Cyanotrichite, 638 Cyclopite, 468 Cylindrite, 394 Cymatolite, 481 Cymophane, 423 Cyprine, 519 Cyprusite, 639 Cyrtolite, 522 D Dahllite, 597 Damourite, 561 Danaite, 382 Danalite, 504 Danburite, 522 Dannemorite, 489 Darapskite, 619 Datholite, 527 Datolite, 527 Daubreeite, Daubreite, 401 Daubreelite, 374 Davidsonite, 496 Lake Daviesite, 401 Davyne, 501 Dawsonite, 452 Dechenite, 604 Deeckeite, 518 Delessite, 571 Delatynite, 645 Delorenzite, 586 Delphinite, 531 Delvauxite, 615 Demant, v. Diamond, 345 Demantoid, 508 Derbylite, 618 Derbyshire spar, 398 Descioizite, 604 Desmine, 551 Destinezite, 618 Dewalquite, 539 Deweylite, 575 Diabantite, 571 Diadochite, 618 Diallage, 477 Dialogite, 444 Diamant, 345 Diamond, 345 Diamond, Bristol, George, 405 Dianite, 589 Diaphorite, 387 Diaspore, 431 Diasporogelite, 434 Diatomite, 409 Dichroite,.497 Dickinsonite, 607 Didymolite, 497 Dietrichite, 637 Dietzeite, 619 Dihydrite, 605 Diopside, 476 Dioptase, 515 Dipyre, 517 Disterrite, 566 Disthene, 526 Dixenite, 581 Dog-tooth spar, 439 Dolerophanite, 632 Dolomite, 442 Domeykite, 362 Domingite, 387 Doppelspath, v. Calcite Dopplerite, 646 Double-refracting spar, Doughtyite, 638 Douglasite, 402 Dreelite, 626 Dry-bone, 445 Dudleyite, 572 Dufreniberaunite, 605 Dufrenite, 605 Dufrenoysite, 387 Dumortierite, 543 Dundasite, 452 Durangite, 601 Durdenite, 641 708 Dysanalyte, 586 Dyscrasite, 361 Dysluite, 420 Dysodile, 646 Dyssnite, 485 Dysyntribite, 500, 562 E Ecdemite, 618 Echellite, 558 Ectropite, 582 ficume de Mer, 576 Edelite, 535 Edenite, 490 Edingtonite, 555 Egeran, 520 Eglestonite, 401 Egueiite, 615 Ehrenwerthite, 432 Ehlite, 605 Eichbergite, 385 Eichwaldite, 620 Eisen, v. Iron Eisenblau, v. Vivianite Eisenbliithe, v. Flos ferri Eiaenglanz, v. Hematite Eisenglimmer, v. Hematite Eisenkies, v. Pyrite Eisenniekelkies, v. Pentland- ite Eisenrahm, v. Hematite Eisenrosen, v. Hematite Eisenspath, v. Siderite Eisenstassfurtite, 621 Eisspath, v. Rhyacolite Eisstein. v. Cryolite Ekdemite, 618 Elseolite, 499 Elaterite, 647 Electrum, 350 Elements, 344 et seq. Eleolite, 499 Eleonorite, 615 Elpidite, 496 Embolite, 397 Embrithite, 387 Emerald, 495 Oriental, 413 Uralian, 508 Emerald copper, v. Dioptase, 515 Emerald nickel, 453 Emery, 410 Emmonsite, 641 Emplectite, 386 Empressite, 383 Enargite, 393 Endeiolite, 587 Endellionite, v. Bournonite 388 Endlichite, 598 Enstatite, 472 Eosphorite, 615 INDEX TO SPECIES Epiboulangerite, 394 Epichlorite, 571 Epidesmine, 558 Epididymite, 455 EPIDOTE Group, 530 Epidote, 531 Epigenite, 394 Epistilbite, 549 Epistolite, 592 Epsom salt, 635 Epsomite, 635 Erbium niobate,, 588, 591 Erbsenstein, v. Pisolite Erdkobalt, v. Asbolite Erikite, 580 Erinite, 605 Erionite, 558 Erubescite, 374 Erythrite, 608 Erythrosiderite, 402 Esmarkite, 498 Esmeraldaite, 433 Essonite, 507 Ettringite, 640 Eucairite, 365 Euchroite, 611 Euclase, 529 Eucolite, 496 Eucolite-titanite, 584 Eucryptite, 500 Eudialyte, 496 Eudidymite, 455 Eudyalite, 496 Eugenglanz, v. Polvbasite Eukairite, 365 Euklas, 529 Eulytine, 504 Eulytite, 504 Eupyrchroite, 596 Euralite, 571 Eusynchite, 604 Euxenite, 591 Evansite, 614 Facellite, 501 Fahlerz, 390 Fahlunite, 498 Fairfieldite, 607 Palkenhaynite, 390 False Galena. 367 Famatinite, 393 Faratsihite, 578 ?argite, 556 ?aserkiesel, v. Fibrolite ?aserzeolith, v. Natrolite ?assaite, 477 Faujasite, 555 "ava, 428 Fayalite, 513 ^eather-alum, v. Halotrich- ite feather-ore, 387 ^edererz, v. Jamesonite FELDSPAR Group, 456 Feldspar, Baryta, 460 Blue v. Lazulite Common, 457 Glassy, 458 Labrador, 466 Lime, 467 Potash, 457, 460 Soda, 464 Felsobanyite, 639 Felspar, v. Feldspar Ferganite, 609 Fergusonite, 588 Fermorite, 597 Fernandinite, 609 FERRATES, 418 Ferrazite, 611 Ferritungstite, 644 Ferroanthophyllite, 487 Ferrobrucite, 434 Ferrocalcite, 441 Ferrocobaltite, 379 Ferrogoslarite, 635 Ferronatrite, 638 Ferropallidite, 633 Feuerblende v. Pyrostilpnite, Fibroferrite, 639 Fibrolite, 526 Fichtelite, 645 Fiedlerite, 401 Fillowite, 607 Fiorite, 409 Fire opal, 408 marble, 356 Fireblende, v. Pyrostilpnite, 390 Fischerite, 613 Flagstaffite, 646 Flajolotite, 618 Fleches d' amour, 427 Flinkite, 606 Flint, 406 Float-stone, 409 Flokite, 552 Florencite, 601 Flos ferri, 446 Fluellite, 402 Fluocerite, 399 Fluor v. Fluorite, Fluor-apatite, 595 Fluor spar, 398 FLUORIDES, 398 et seq. Fluorite, 398 Flusspath, v. Fluorite Foliated tellurium v. Nag- yagite, 383 Pontainebleau limestone, 439 Footeite, 631 ?orbesite, 611 ?orstereite, 513 Fossil copal, 645 wood, 405, 408 ^oucherite, 615 Fouqueite. 532 INDEX TO SPECIES 709 Fowlerite, 484 Franckeite, 394 Francolite, 596 Franklinite, 420 Fraueneis, v. Selenite Frauenglas, v. Mica Fredricite, 391 Freibergite, 390 Freieslebenite, 387 Fremontite, 602 French chalk, 576 Frenzelite, 359 Friedelite, 515 Frieseite, 367 Fuchsite, 561 Fuggerite, 518 Furaacite, 604 Gadolinite, 529 Gageite, 582 Gahnite, 420 Gajite, 453 Galactite, 556 Galapectite, 579 Galena, Galenite, 363 Galena, False, 367 Galenobismutite, 386 Galmei, v. Calamine Ganomalite, 498 Ganophyllite, 546 Garnet, 505 Cinnamon, 507 Chrome, 417 Grossalur, 507 Oriental, 507 Precious, 507 Tetrahedral, v. Helvite White, v. Leucite Garni erite, 575 Gastaldite, 493 Gavite, 576 Gay-Lussite, 452 Gearksutite, 402 Gedanite, 645 Gedrite, 487 Gehlenite, 518 Geikielite, 586 Gekrosstein, v. Tripe stone Gelbbleierz, v. Wulfenite Gelbeisenerz, v. Jarosite Gelbeisenstein, v. Xantho- siderite Genthite, 575 Geocerellite, 646 Geocerite, 646 Georceixite, 601 Geocronite, 392 Geomyricite, 646 Georgiadesite, 594 Geraesite, 601 Gerhardtite, 619** GERMANATES, 394 Gersdorffite, 379 Geyerite, 381 Geyserite, 409 Gibbsite, 435 Gieseckite, 500, 562 Gigantolite, 498, 562 Gilbertite, 561 Gilpinite, 640 Gilsonite, 647 Giorgiosite," 453 Gips, v. Gypsum Girasol, 408 Gismondine, 552 Gismondite, 552 Glance coal, 648 Cobalt, v. Colbaltite Copper, v. Chalcocite Glanzeisenerz, v. Hematite Glaserite, v. Aphthitalite Glaskopf, Brauner, v. Limon- ite Rother, v. Hematite Glassy Feldspar, 458 Glauber salt, 632 Glauberite, 625 Glaucochroite, 513 Glaucodot, 382 Glaucolite, 517 Glauconite, 577 Glaucophane, 492 Glaukodot, 382 Glessite, 645 Glimmer, v. Mica Globosite, 615 Glockerite, 639 Glucinum, v. Beryllium Gmelinite, 554 Goethite, 431 Gold, 350 Goldfieldite, 391 Gold tellurides, 382, 383 Gonnardite, 557 Goshenite, 496 Goslarite, 635 Gothite, 431 Goyazite, 616 Graftonite, 594 Grahamite, 647 Gramenite, Graminite, 582 Grammatite, 489 Granat, v. Garnet Grandiderite, 544 Graphic tellurium. 382 Graphite, 347 Gray antimony, 358 copper, 390 Greenalite, 577 Green lead ore, 597 Greenockite, 371 Greenovite, 584 Grenat, v. Garnet Griffithite, 572 Griphite, 500 Grossular, Grossularite, 507 Grothine, 545 Grothite, 584 Griinbleierz, v. Pyromor- phite Griineisenerde, v, Dufrenite Griinerite, 490 Griinlingite, 360 Guadalcazarite, 369 Guanajuatite, 359 Guano, 597 Guarinite, 525 Guejarite, 386 Guitermanite, 388 Gummierz, v. Gummite Gummite, 624 Gymnite, 575 Gypsum, 633 Gyrolite, 546 Haarkies, v. Millerite Haarsalz, v. Epsomite Hackmanite, 502 Hematite, v. Hematite Haidingerite, 610 Hair salt, 635 Halite, 395 Hallerite, 562 Hallite, 572 Halloysite, 578 Halotrichite, 637 Hamartite, 449 Hambergite, 620 Hamlinite, 601 Hancockite, 533 Hanks! Hannaite, 611 HaMfouite, 498 Harl. Harmotomc Harstigite, 535 Hartite, 645 Harttite, 601 Hastingsite, 491 Hatchettine, Hatchettite, 645 Hatchettolite, 587 Hauchecornite, 372 Hauerite, 378 Haughtonite, 564 Hausmannite, 424 Hautefeuillite, 608 Hauyne, 503 Haiiynite, 503 Haydenite, 552 Heavy spar, 625 Hebronite, 602 Hedenbergite, 476 Hedyphane, 598 Heiiitzite, 622 Heliodor, 495 710 Heliophyllite, 618 Heliotrope, 405 Hellandite, 540 Helvite, Helvine, 504 Hemafibrite, 611 Hematite, 415 Brown, 432 Hematogel, 434 Hematolite, 606 Hematostibiite, 606 Hemimorphite, 539 Henwoodite, 616 Hepatic cinnabar, 370 Hercynite, 420 Herderite, 601 Herrengrundite, 638 Herschelite, 552 Hessite, 365 Hessonite, 507 Hetaerolite, 435 Heterocline, 425 Heteromorphite, 387 Heulandite, 548 Hewattite, 611 Hexahydrite, 637 Hibbenite, 612 Hibschite, 540 Hielmite, Hjelmit, 591 Hieratite, 400 Hiddenite, 481 Highgate resin, 645 Hipgensite, 604 Hillebrandite, 546 Himbeerspath, v. Rhodochro- site Hinsdalite, 618 ^jabzeitc, 622 Hiortdah'.u Hoernesite, 608 Hohmannite, 639 Hokutolite, 630 Hollandite, 424 Holmquistite, 493 Holzopal, v. Wood-opal Holzzinnerz, v. Wood- tin Homilite, 529 Honey-stone, Honigstein, v. Mellite Hopeite, 607 Horn quicksilver, 395 Horn silver, 397 Hornblei, v. Phosgenite Hornblende, 490 Hornesit, Hornsilber, 397 Hornstone, 406 Horse-flesh ore, 374 Horsfordite, 362 Hortonolite, 513 Howlite, 621 INDEX TO SPECIES Huantajayite, 396 Hiibnerite, 642 Hiigelite, 612 Hudsonite, 492 Hullite, 571 ' Hulsite, 622 Humboltine, 645 Humboldtilite, 518 Humboldtite, 528 Humite, 536 Huntilite, 362 Hutchinsonite, 386 Hureaulite, 611 Hussakite, 592 Hyacinth,- 521, 507 Hyalite, 409 Hyalophane, 460 Hyalosiderite, 511 Hyalotekite, 498 Hydrargillite, 435 Hydraulic limestone, 440 Hydroboracite, 623 HYDROCARBONS, 645 Hydrocerussite, 452 Hydroclinohumite, 538 Hydrocyanite, 630 Hydrofranklinite, 435 Hydrogothite, 433 Hydrogiobertite, 453 Hydrohematite, 433 Hydromagnesite, 452 Hydromica, 561 Hydromuscovite, 561 Hydronephelite, 558 ' Hydrophane, 408 Hydrophilite, 399 Hydrotalcite, 435 Hydrothomsonite, 558 Hydroxyapatite, 596 Hydrozincite, 451 Hypersthene, 473 Hypostiibite, 551 Iberite, 498 Ice, 411 Ice spar, v. Rhyacolite Iceland spar, 439 Iddingsite, 512 Idocrase, 519 Idrialite, 646 Igelstromite, 435 Ihleite, 638 Ilesite, 634 Illmenite, 417 Ilmenorutile, 427 Hvaite, 538 Imerinite, 490 Impsonite, 647 Indianaite, 579 Indianite. 467 Indicolite, 542 Indigolite. .542 Inesite, 546 Inflammable cinnabar, 646 Infusorial earth, 409 Inyoite, 622 lodate of calcium, 619 lodembolite, 397 IODIDES, 397 lodobromite, 397 lodyrite, 397 lolite, 497 Hydrous, 498 Iridium, 355 Iridosmine, 355 Iron, Chromic, v. Chromite Magnetic, 420 Meteoric, 356 Native, 356 Oligist, v. Hematite Iron aluminate, 420 arsenates, 608, 609, etc. arsenides, 381 carbide, 356 carbonate, 443 chlorides, 399 chromate, 423 columbate, 588 ferrate, 420 hydrates, 431, 432 niobate, 588 oxalate, 528 oxide, 415, 420; hy- drated, 431, 432 phosphates, 605, 608, 610 etc. silicates, 513, 538, 571, 572 sulphantimonite, 386 sulpharsenide, 381 sulphates, 636, 637, 638, etc. sulphides, 369, 373, 377, 381 magnetic, 373 tantalates, 588 tellurite,.641 titanates, 417, 424 tungstates, 641, 644 Iron alum, 637 Iron natrolite, 556 Iron pyrites, 377 Magnetic, 373 White, 380 Irvingite, 563 Iserine, 427 Isoclasite, 611 Isothose, 458 Itabirite, 417 Itacolumite, 406 Ixiolitc J Jacobsite, Jade, 482 : 489 B INDEX TO SPECIES 711 Jade tenace, 482 Jadeite, 479-^-7 Jalpaite, 365 Jamesonite, 386 Janosite, 638 Jargon, 521 Jarosite, 640 Jasper, 406 Jaspopal, 409 Jefferisite, 572 Jeffersonite, 477 Jeremejevite, 620 Jet, 648 Jezekite, 601 Joaquinite, 586 Johannite, 640 Johnstrupite, 585 Jordanite, 391 Joseite, 360 Josephinite, 356 Jurupaite, 498 K Kaersutite, 491 Kainite, 631 Kakoxen, 614 Kaliborite, 622 Kalifeldspath, v. Orthoclase Kaligliinmer, v. Muscovite Kalinite, 637 Kaliophilite, 501 Kalisalpeter, v. Niter Kalgoorlite, 369 Kalkglimmer, 470 Kalkspath, v. Calcite Kalkuranit, v. Autunite Kallait, v. Turquois Kallfflte, 379 Kalomei, 395 Kaluszite, 636 Kamacite, 356 Kammererite, 570 Kamarezite, 638 Kammkies, v. Marcasite Kampylite, 598 Kaolin, 578 Kaolinite, 578 Karminspath, v. Carminite Karneol, v. Carnelian Karstenite, v. Anhydrite Karyinite, 593 Kataforite, 491 Katzenauge, v. Cat's-eye Kehoeite, 616 Keilhauite, 585 Kelyphite, 509 Kentrolite, 539 Kermes, 383 Kermesite, 383 Kerosene, 646 Kerrite, 572 Kertschinite, 615 Kibdelophan, 418 Kidney ore, 416 stone, 489 Kieselwismuth, v. Euytite Kieselzinkerz, v. Calamine Kieserite, 633 Kilbrickenite, 392 Killinite, 562 . Kjerulfine, 600 Klaprotholite, 386 Kleinite, 395 Klinoklas, 604 Klinozoisit, 532 Knebelite, 513 Knopite, 586 Knoxvillite, 639 Kobaltbliithe, v. Erythrite Kobaltglanz, v. Cobaltite Kobaltkies, v. Linnaeite Kobaltspath, v. Sphaerocobal- tite Kobellite, 387 Kochsalz, v. Halite Koechlinite, 644 Koenenite, 401 Kohlenspath, v. Whewellite Koksharovite, 491 Kongsbergite, 354 Konigite, 632 Koninckite, 610 Koppite, 587 Kornerupine, 544 Korund, v. Corundum Kotschubeite, 569 Kottigite, 609 Krantzite, 645 Kraurite, 605 Kreittonite, 420 Kremersite, 402 Krennerite, 383 Kreuzbergite, 615 Krisuvigite, 632 Krohnkite, 638 Kronkite, Kronnkite, 638 Kryptoperthit, 460 Ktypeite, 447 Kunzite, 481 Kupfer, v. Copper Kupferantimonglanz, v. Chal- costibite Kupferblende, v. Sandberger- ite Kupferglanz, v. Chalcocite Kupferglimmer, v. Chalco- phyllite Kupferindig, v. Covellite Kupferkies, v. Chalcopyrite Kupferlasur, v. Azurite Kupfernickel, v. Niccolite Kupferschaum, v. Tyrolite Kupferuranit, v. Torbernite Kupfervitriol, v. Chalcan- thite Kupfferite, 491 Kyanite, 526 Kylindrite, 394 Labrador feldspar, 466 Labradorite, 466 Lacroixite, 601 Lagonite, 621 Lampadite, 436 Lanarkite, 632 Landerite, 509 Langbanite, 539 Langbeinite, 625 Langite, 638 Lansfordite, 453 . Lanthanite, 453 Lanthanum carbonate, 453 Lapis-lazuli, 503 Larderellite, 621 Lassalite, 577 Lasurapatite, 596 Lasurite, 503 Latrobite, 468 Laubanite, 552 Laumonite, 552 Laumontite, 552 Laurionite, 401 Laurite, 380 Lautarite, 619 Lavenite, 484 Lavrovite, 476 Lawrencite, 399 Lawsonite, 540 Lazulite, 605 Lazurite, 503 Lead, 354 Black, 347 Native, 354 White, v. Cerussite Lead antimonate, 617 arsenates, 598 carbonates, 448, 452 chloride, 399, 401 chloro-carbonates, 450 chromates, 630 dioxide, 428 molybdate, 643 oxides, 412, '424, 428 oxychlorides, 401 phosphate, 597 selenides, 364, 365 silicates, 498, 539 sulphantimonate, 394 sulphantimonites, 385, etc. sulpharsenites, 385 etc. sulphates, 628 etc. sulphate-carbonate, 631 sulphide, 363 sulphobismuthites, 386 etc. telluride, 364 712 INDEX TO SPECIES Lead tungstate, 643 vanadates, 598, 604 Lead glance, 363 Lead vitriol, v. Anglesite Leadhillite, 631 Lecontite, 632 Ledererite, 554 Lederite, 584 Ledouxite, 362 Lehrbachite, 365 Lengenbachite, 388 Lennilite, 572 Leonhardite, 552 Leonite, 637 Leopoldite, 397 Lepidocrocite, 432 Lepidolite,.562 Lepidomelane, 565 Lepolite, 468 Lettsomite,, 638 Leucaugite, 477 Leuchtenbergite, 569 Leucite, 469 Leucochalcite, 612 Leucomanganite, 607 Leucopetrite, 646 Leucophanite, 496 Leucophoenicite, 538 Leucopyrite, 381 Leucosphenite, 585 Leucoxene, 418 Levynite, 554 Lewisite, 618 Libethenite, 603 Liebenerite, 500, 562 Liebigite, 454 Lievrite, 538 Lignite, 648 Ligurite, 584 Lillianite, 388 Lime, v. Calcium Lime-mesotype, 557 Lime uranite, 515 Limestone, 440 Hydraulic, 440 Magnesian, 442 Limonite, 432 Linarite, 632 Lindackerite, 618 Linnaeite, 374 Linsenkupfer, v. Liroconite Lintonite, 557 Liroconite, 615 Liskeardite, 614 Lithia mica, 562 Lithionglimmer, v. Lepido- lite Lithiophilite, 594 Lithium phosphates, 594. 602 silicates 480, 500, 562 Lithographic stone, 440 Lithomarge, 578 Liveingite, 387 Livingstonite, 385 Lodestone, 421 Loeweite, 637 Loewigite, 640 Lollingite, 381 Lorandite, 386 Loranskite, 591 Lorenzenite, 586 Lorettoite, 401 Lossenite, 619 Lotrite, 546 Loweite, 637 Lowigite, 640 Loxoclase, 458 Lublinite, 439 Lucinite, 610 Luckite, 636 Ludlamite, 614 Ludwigite, 620 Luigite, 545 Lumachelle, 440 Liineburgite, 619 Lussatite, 405 Lutecite, 407 Luzonite, 393 Lydian stone, 406 M Mackintoshite, 529 Made, 525 Maconite, 572 Magnesioferrite, 420 Magnesioludwigite, 620 Magnesite, 443 Magnesium aluminate, 419 arsenate, 608 borate, 621, 622 carbonates, 443, 452, 453 ferrate, 420 fluoride, 399 hydrate, 434 oxides, 411, 434 phosphates, 600, 608, 611 silicates, 472, 473, etc.; 513, 536, 573, 576 sulphates, 633, 635 titanate, 586 Magnetic iron ore, 420 Magnetic pyrites, 373 Magnetite, 420 Magnetkies, v. Pyrrhotite Magnoferrite, 420 Malachite, 450 Blue, v. Azurite Green, 450 Malacolite, 476 Malacon, 522 Maldonite, 350 Malinowskite, 391 Mallardite, 636 Maltha, 646 Manandonite, 563 MANGANATES, 418 Manganandalusite, 524 Manganapatite, 596 Manganblende, v. Alabandite Manganbrucite, 434 Manganchlorite, 569 Manganepidote, v. Piedmon- tite Manganese antimonate, 606 arsenates, 601, 606 carbonate, 444 disulphide, 378 hydrates, 432, 435 niobate, 588 oxides, 411, 424, 425, v 427, 430, 432, 435 phosphates, 594, 600, silicates, 484, 513, 582, etc. sulphates, 633, 636 sulphide, 369, 378 tantalate, 588 titanate, 418 tungstate, 642 Manganfayalite, 513 Manganglanz v. Alabandite Mangangranat, v. Spessar- tite Manganhedenbergite, 476 Manganite, 432 Manganmagnetite, 420 Manganocalcite, 441, 444 Manganocolumbite, 589 Manganophyllite, 564 Manganosiderite, 444 Manganosite, 411 Manganospherite, 444 Manganostibiite, 606 Manganotantalite, 589 Manganpectolite, 483 Manganspath) v. Rhodochrc site Mangantantalite, 588 Mangan-vesuvianite, 520 Marble, 440 Verd-antique, 573 Marcasite, 380' Marceline, 425, 485 Margarite, 566 Margarodite, 561 Margarosanite, 498 Marialite, 518 Marignacite, 587 Mariposite, 565 Marmatite, 368 Marmolite, 573 Marshite, 395 Marsjakskite, 577 Martinite, 611 Martite, 417 Mascagnite, 624 Maskelynite, 467 INDEX TO SPECIES 713 Masonite, 567 Massicot, 412 Matildite, 386 Matlockite, 401 Maucherite, 362 Mauzeliite, 618 Maxite, 631 Mazapilite, 615. Meerschaum, 576 Meionite, 516 Melaconite, 412 Melanglanz, v. Stephanite Melanite, 508 Melanocerite, 496 Melanophlogite, 408 Melanotekite, 539 Melanterite, 636 Melilite, 518 Melinophane, v. Meliphan- ite Meliphanite, 496 Melite, 580 Mellate of aluminium, 645 Mellite, 645 Meionite, 382 Menaccanite, 417 Mendipite, 401 Mendozite, 637 Meneghinite, 391 Menilite, 408 Mennige, v. Minium Mercurammonite, 395 Mercury, 354 Horn, 395 Native, 354 Mercury antimonite, 618 chloride, 3Q5 selenides, 369 sulphides, 369, 370 sulpho-selenide, 369 telluride, 369 Mercury amalgam, 354 Meroxene, 564 Mesitite, 443 Mesitinspath, v. Mesitite Mesole, v. Thorn sonite Mesolite, 557 Mesotype, 556 Messelite, 607 Metabrushite, 611 Metachinabarite, 369 Metahewettite, 611 Metastibnite, 359 Meta-torbernite I, 616 Metavoltine, 639 Metaxite, 575 Meteoric iron, 356 Mexican onyx, 440 Meyerhofferite, 622 Miargyrite, 386 MICA Group, 559 Mica, Iron, 563, 565 Lime, 566 Lithia, 562 Mica, Magnesia, 563, 565 Potash, 560 Soda, 562 Vanadium, 565 Micaceous iron ore, 415 Michei-levyte, 626 Microcline, 460 Microcosmic salt, 611 Microlite, 587 Microsonunite, 501 Microperthite, 460 Microphyllite, 467 Microplakite, 467 Miersite, 397 Miesite, 598 Mikroklin, 460 Milarite, 455 Milky quartz, 405 Millerite, 372 Millosevichite, 630 Mimetene, Mimetesite, 598 Mimetite, 598 Minasite, 614 Minasragrite, 641 Mineral caoutchouc, 647 Mineral coal, 647 oil, 646 pitch, 647- resin, 645 tallow, 645 tar, v. Pittasphalt wax, 645 Minguetite, 572 Minium, 424 Mirabilite, 632 Misenite, 631 Mispickel, 381 Misy, 638 Mitchellite, 423 Mixite, 617 Mizzonite, 517 Mocha stone, v. Moss agate Mock lead, 291 Moissanite, 356 Mohawkite, 362 Molengraaffite, 585 Molybdanbleispath, v, Wul- fenite Molybdanglanz, v. Molyb- denite MOLYBDATES, 641 Molybdenum sulphide, 360 trioxide, 410 Molybdenite, 360 Molybdic ocher, 410 Molybdite, 410 Molybdomenite, 641 Molybdophyllite, 498 Molybdosodalite, 502 Molysite, 399 Monazite, 593 Monetite, 606 Monheimite, 445 Monimolite, 593 Monite, 606 Monrolite, 526 Montanite, 641 Monticellite, 513 Montmorillonite, 579 Montroydite, 412 Moonstone, 458, 465 Moravite, 571 Mordenite, 548 Morencite, 582 Morenosite, 635 Morganite, 495 Morion, 405 Moroxite, 596 Mosandrite, 585 Mosesite, 402 Moss agate, 405 Mossite, 590 Mottramite, 604 Mountain cork, 490 leather, 490 soap, 578 tallow, 645 wood, 490 Miillerite, 582 Mullanite, 388 Muller's glass, 409 Mullicite, 608 Mundic, v. Pyrite Murchisonite, 458 Muscovite, 560 Muscovy glass, 562 Mussite, 478 Muthmannite, 383 N Nadeleisenerz, v. Gothite Nadelerz, v. Aikinite Nadelzeolith, v. Natrolite Nadorite, 618 Naegite, 522 Nagyagite, 383 Nailhead spar, 439 Nantokite, 395 Napalite, 645 Naphtha, 646 Narsarsukite, 585 Nasonite, 498 NATIVE ELEMENTS, 344 Natramblygonite, 602 Natrium, v. Sodium Natroborocalcite, 622 Natrochalcite, 638 Natrolite, 556 Natrojarosite, 640 Natromontebrasite, 602 Natron, 452 Natrophilite, 594 Naumannite, 364 Needle ironstone, 432 Needle ore, v. Aikinite Needle zeolite, v. Natrolite, 556 714 INDEX TO SPECIES Nemalite, 434 Neocolemanite, 621 Neotantalite, 587 Neotocite, 485, 582 Nepheline, 499 Nephelite, 499 Nephrite, 489 Nepouite, 575 Neptunite, 585 Nesquehonite, 452 Nevyanskite, 355 Newberyite, 611 Newtonite, 579 Niccolite, 372 Nicholsonite, 446 Nickel antimonide, 372 arsenates, 609 arsenides, 372, 378, 382 carbonate, 453 oxides, 411 silicate, 575 sulphantimonide, 379 sulpharsenide, 379, 382 sulphate, 635 sulphides, 369, 372, 373 telluride, 382 Nickelantimonglanz, v. Ull- maimite Nickelarsenikglanz, v. Gers- dorffite Nickel-gymnite, 575 Nickel-skutterudite, 380 Nigrine, 427 Nigrite, 647 NIOBATES, 587 Niter, 619 Niter, Soda, 619 NITRATES, 619 Nitrobarite, 619 Nitrocalcite, 619 Nitroglauberite, 619 Nitromagnesite, 619 Nivenite, 623 Nocerite, 401 Nontronite, 582 Nordenskipldine, 620 Nordmarkite, 544 Northupite, 450 Nosean,' 503 Noselite, 503 Noumeite, 575 Nussierite, 598 Ocher, Brown, 432 Red, 415 Ochrolite, 618 Octahedrite, 428 Odontolite 613 (Eil de chat, 424 (Ellacherite, 561 Offretite, 554 Oil, Mineral 646 Oisanite, 532 Okenite, 546 Oldhamite, 369 Oligist iron v. Hematite Oligoclase, 466 Oligonite, 444 Olivenerz, v. Olivenite Olivenite, 603 Olivine, 511 Omphacite, 477 Oncosin, 561 Onofrite, 369 Onyx, 406 Mexican, 440 Onyx marble, 440 Oolite, 440 Opal, 408 Opal jasper, 409 Ophicalcite, 573 Ophiolite, 573 Ophite, 575 Orangite, 522 Oriental alabaster, 440 amethyst, 413 emerald, 413 ruby, 413 topaz, 413 Orientite, 582 Orpiment, 357 Orthite, 533 Orthoclase, 457 Orthose, v. Orthoclase Oruetite, 360 Osannite, 494 Osmelite, 483 Osmiridium, 355 Osmium sulphide, 379 Osteolite, 596 Otavite, 452 Ottrelite, 567 Ouvarovite, 508 Owenite, 572 3XALATES, 644 Oxammite, 644 3xiDEs, 402 3XYCHLORJDES, 400 3XYFLUORIDES, 400 Dxykertschenite, 61 DXYSULPHIDES, 383 3zarkite, 557 Ozocerite, 645 Pachnolite, 402 Pagodite, 562 Paigeite, 622 Paisbergite, 484 Palaite, 607 Palladium, 355 Palmerite, 610 Palmierite, 640 Panabase, v. Tetrahedrite Pandermite, 621 Paposite, 639 Paracelsian, 460 Paraffin, 645 Paragonite, 562 Parahopeite, 607 Paralaurionite, 401 Paraluminite, 639 Paramelaconite, 412 Parasite, 621 Paravivianite, 608 Paredrite, 428 Pargasite, 490 Parisite, 449 Parophite, 562 Parrot coal, 648 Partschinite, 510 Pascoite, 609 Passauite, 517 Paternoite. 621 Patronite, 361 Peacock Ore, 374 Pearceite, 393 Pearl sinter, 409 Pearl-spar, 441 Peat, 648 Pebble, Brazilian, 405 Pechblende, Percherz, v. Uraninite Peckhamite, 474 Pectolite, 483 Peganite, 613 Pencil-stone, 579 Penfieldite, 401 Pennine, 570 Penninite, 570 Pentlandite, 369 Peplolite, 498 Percylite, 401 Periclase, 411 Pericline, 465 Peridot, 511 Peristerite, 465 Perthite, 460 Perofskite, 586 Perovskite, 586 Perowskit, 586 Petalite, 455 Petrified wood, 406 Petroleum, 646 Petzite, 365 Phacelite, Phacellite, 501 hacolite, 553 Pharmacolite, 610 Pharmacosiderite, 614 Phenacite, 514 Phengite, 561 Philadelphite, 572 Philipstadite, 491 Phillipite, 638 Phillipsite, 550 Phlogopite, 565 3 hoenicite, 630 Phcenicochroite, 630 Pholerite, 578 INDEX TO SPECIES 715 Pholidolite 577 Phosgenite, 450 PHOSPHATES, 592 Phosphoferrite, 601 Phosphorite, 596 Phosphophyllite, 618 Phosphorsalz, v. Stercorite Phosphosiderite, 610 Phosphuranylite, 617 Photicite, 485 Phyllite, 567 Physalite, 523 Picite, 615 Pickeringite, 637 Picotite, 419 Picroepidote, 532 Picrolite, 573 Picromerite, 637 Picropharmacolite, 607 Picrotitanite, 417 Piedmontite, 532 Pigeonite, 479 Pinakiolite, 620 Pinguite, 582 Pinite, 562, 498 Pinnoite, 622 Pintadoite, 609 Piotine, 576 Pirssonite, 452 Pisanite, 636 Pisolite, 440 Pistacite, 531 Pistomesite, 443 Pitchblende, 623 Pittasphalt, 646 Pitticite, 618 Placodine, 3 r >2 Plagioclase, 374 Plagionite, 38T 7 Plancheite, 515 Planoferrite, 639 Plasma, 405 Plaster of Paris, 634 Platina, 355 Platiniridium, 355 Platinum, 35 r Platinum, arsenide, 379 Plattnerite, 428 Platynite, 385 Plazolite, 580 Plenargyrite, 386 Pleonaste, 419 Plessite, 356 Plumbago, 347 Plumbogummite, 601 Plombocalcite, 441 Plumbojarosite, 640 Plumboniobite, 592 Plumbostib, 387 Plumosite, 387 Podolite, 618 Pochite, 545 Polianite, 427 Pollucite, 470 Polyadelphite, 508 Polyargite, 562 Polyargyrite, 393 Polyarsenite, 601 Polybasite, 392 Polycrase, 591 Polychroilite, 498 Polydymite, 373 Polyhalite, 637 Polylithionite, 563 Polymignite, 591 Polysphaerite, 598 Ponite, 445 Poonahlite, v. Scolecite Porpezite, 350 Posepnyte, 646 Potash alum, 637 Potassium borate, 622 chloride, 396 nitrate, 619 silicate, 457, 460, 469, 560, etc. sulphate, 624 Potstone, 576 Powellite, 643 Prase, 405 Praseolite, 498 Prehnite, 534 Preslite, 604 Pfibramite, 368 Priceite, 621 Priorite, 591 Prismatine, 544 Przibramite, 368 Prochlorite, 571 Prolectite, 538 Prosopite, 402 Protobastite, 473 Proustite, 389 Prussian blue, Native, 608 Przibramite, 432 Pseudoboleite, 401 Pseudobrookite, 424 Pseudocampylite, 598 Pseudoleucite, 470 Pseudomalachite, 605 Pseudomeionite, 516 Pseudomesqlite, 557 Pseudophillipsite, 550 Pseudophite, 570 Pseudosteatite, 579 Pseudowollastonite, 483 Psilomelane, 436 Psittacimite, 604 Ptilolite, 548 Pucherite, 594 Puflerite, 551 Punamu, 482 Purple copper ore, 374 Purpurite, 610 Puschkinite, 532 Pycnite, 523 Pycnochlorite, 571 Pyrargillite, 498 Pyrargyrite, 389 Pyreneite, 508 Pyrgom, 477 Pyrite, 377 .Pyrites, Arsenical, v. Arseno- pyrite, 381 Capillary, 372 Cockscomb, 380 Copper, 374 Iron, 377 Magnetic, 373 Radiated, 380 Spear, 380 Tin, 394 White iron, 380 Pyroaurite, 435 Pyrobelonite, 604 Pyrochlore, 587 Pyrochroite, 435 Pyrolusite, 430 Pyromorphite, 597 Pyrope, 507 Pyrophanite, 418 Pyrophosphorite, 606 Pyrophyllite, 579 Pyrophysalite, 523 Pyroretinite, 646 Pyrosclerite, 572 Pyrosmalite, 515 Pyrostilpnite, 390 Pyroxene, 474 PYROXENE Group, 470 Pyroxmangite, 485 Pyrrharsenite, 593 Pyrrhite, 588 Pyrrhotine, 373 Pyrrhotite, 373 Q Quartz, 403 Quartzine, 407 Quartzite, 406 Quecksilber, Gediegen, v. Cinnabar Quecksilberhornerz, v. Calo- mel (uenstedtite, 637 luetenite, 640 uicksilver, 354 uisqueite, 347 R Radelerz, v. Bournonite Radiated pyrite, 380 Radiotine, 573 Rafaelite, 401 Raimondite, 639 Ralstonite, 402 Ramirite, 604 Rammelsbergite, 382 Ranite, 558 Raspite, 643 716 INDEX TO SPECIES Rathite, 386 Rauchquarz, v. Smoky Quartz Raumite, 498 Realgar, 357 Red antimony, v. Kermesite chalk, 416 copper ore, 410 hematite, 415 iron ore, 416 lead ore, 630 ocher, 416 silver ore, 389 zinc ore, 411 Reddingite, 607 Reddle, 416 Redingtonite, 639 Redruthite, 366 Reinite, 644 Reissite, 549 Remingtonite, 453 Rensselaerite, 576 Resin, Mineral, 645 Retinalite, 573 Retinite, 645 Retzbanyite, 385 Retzian, 606 Rezbanyite, 385 Rhabdophanite, 609 Rhaetizite, 527 Rhagite, 617 Rhodalose, v. Bieberite Rhodizite, 621 Rhodochrome, 570 Rhodochrosite, 444 Rhodolite, 507 Rhodonite, 484 Rhodophyllite, 570 Rhodotilite, 546 Rhodusite, 493 Rhonite, 494 Rhomboclase, 641 Rhyacolite, 458 Riband jasper, 406 Richellite, 615 Richterite, 489 Rickardite, 362 Ricolite, 573 Riebeckite, 493 Rinkite, 585 Rinneite, 399 Ripidolite, 569 Risorite, 588 Rittingerite, 393 Rivaite, 455 Riversideite, 546 Rizopatronite, 361 Rock crystal, 405 meal, 440 milk, 440 salt, 395 Roeblingite, 498 Romerite, 638 Roepperite, 513 Romanzovite, 507 Romeite, 618 Romerite, 638 Rosasite, 449 Roscherite, 616 Roscoelite, 565 Rose quartz, 405 Roselite, 607 Rosenbuschite, 483 Rosieresite, 610 Rosite, 562 Rosolite, 509 Rothbleierz, v. Crocoite Rotheisenerz, Rotheisenstein, v. Hematite Rothgiiltigerz, v. Pyrargy- rite Rothkupfererz, v. Cuprite Rothnickelkies, v. Niccolite Rothoffite, 508 Rothspiessglanzerz, v. Ker- mesite Rothzinkerz, v. Zincite Rowlandite, 529 Rubellite, 542 Rubicelle, 419 Rubin, 419 Ruby, Almandine, 419 Balas, 419 Oriental, 413 Spinel, 419 Ruby blende, 368 Ruby copper, 410 Ruby silver, 389 Ruby zinc, 368 Ruin marble, 440 Rumanite, 645 Rumpfite, 572 Ruthenium sulphide, 302 Rutherfordine, 449 Rutile, 427 Safflorite, 382 Sagenite, 405, 427 Sahlite, 477 Sal Ammoniac, 397 Salite, 477 Salmiak, 397 Salmite, 567 Salmonsite, 610 Salt, Rock, 395 Saltpeter, v. Niter Salvadorite, 636 Samarskite, 590 Samiresite, 587 Sammetblende, 432 Samsonite, 390 Sandbergerite, 391 Sanguinite, 390 Sanidine, 458 Saphir d'eau, 498 Saponite, 576, 579 Sapphire, 413 Sapphirine, 544 Sarcolite, 518 Sard, 405 Sardonyx, 406 Sarkinite, 601 Sartorite, 385 Sassolite, 435 Satin spar, 439, 634 Saualpite, 530 Saussurite, 350 Scacchite, 399 Scapolite, 516 SCAPOLITE Group, 515 Schafarzikite, 618 Schalenblende, 368 Schapbachite, 387 Schaumerde, v. Aphrite Schaumopal, 409 Schaumspath, v. Aphrite Scheelbleispath, v. Stolzite Scheelite, 642 Scheelspath, v. Scheelite Scheererite, 645 Schefferite, 477 Schertelite, 611 Schiller-spar, 474 Schirmerite, 386 Schizolite, 483 Schlangenalabaster, v. Tripe- stone Schmirgel, v. Emery Schneiderite, 552 Schoenite, 637 Schorlomite, 510 Schorza, 531 Schreibersite, 356 Schrifterz, Schrifttellur, v. Sylvanite Schrotterite, 580 Schuppenstein, v. Lepidolite Schwartzembergite, 401 Schwatzite, 391 Schwefel v. Sulphur Schwefelkies, v. Pyrite Schwefelquecksilber, v. Cin- nabar Schwerbleierz, v. Plattnerite Jchwerspath, v. Barite Scleroclase, v. Sartorite Scolecite, Scolezite, 557 Scorodite, 609 Scorza, 531 Scovillite, 609 Searlesite, 583 Seebachite, 552 SELENIDES, 364, 365 Selenite, 634 SELENITES, 641 Selenium, 344 Selenquecksilber, v. Tieman- nite Selensulphur, 348 INDEX TO SPECIES 717 Selenwismuthglanz, v. Guan- juatite Seligmannite, 388 Sellaite, 399 Semeline, 584 Semi-opal, 408 Semseyite, 387 Senaite, 418 Senarmontite, 409 Sepiolite, 576 Serendibite, 545 Sericite, 561 Serpentine, 573 Serpeirite, 638 Seybertite, 566 Shanyavskite, 436 Shattuckite, 581 Shepardite, 472 Sheridanite, 571 Shell marble, 440 Siberite, 542 Sicklerite, 610 Siderite, 443 Sideronatrite, 639 Siderophyllite, 564 Siegenite, 374 Silber, v. Silver Silberamalgam, v. Amalgam Silberglanz, v. Argentite Silber hornerz, v. Cerargy- rite Silex, Silica, 403 SILICATES, 454 Siliceous sinter, 409 Silicified wood, 404 Silicomagnesiofluorite, 545 Silicon oxido, 403, 407, 408 Sillimanite, 526 Silver, 352 Silver antimonide, 361 arsenide, 362 bismuthide, 362 bromide, 397 chlorides, 397 iodide, 397 selenide, 364 . sulphantimonites, 386, 389 sulpharsenite, 389 sulphide, 364, 367 sulpho-bismuthite, 386 sulpho-germanate, 394 telluride, 362, 365, 382 Silver glance, 364 Simetite, 645 Simonyite, 637 Sinopite, 580 Sinter, Siliceous, 409 Sipylite, 588 Siserskite, 355 Sismondine, Sismondite, 567 Sisserskite, 355 Sitaparite, 418 Skapolith, 516 Skemmatite, 436 Skleroklas, v. Sartorite Skogbolite, 590 Skutterudite, 380 Smaltite, 378. Smaragd, v. Emerald Smaragdite, 490 Smectite, 579, 580 Smegmatite, 579 Smirgel, v. Emery Smithite, 386 Smithsonite, 445, 539 Smoky quartz, 405 Soapstone, 576 Sobralite, 485 Soda alum, 637 Soda-mesotype, 557 Soda microcline, 461 Soda niter, 619 Soda orthoclase, 458 Soda-sarcolite, 518 Sodalite, 502 Sodium borate, 622 carbonate, 452, 453 hloride, 395 fluoride, 399, etc. nitrate, 619 phosphate, 594, etc. silicate, 464, 502, 554, 556 sulphate, 625: hydrous 632, etc. Somervillite, 518 Sonnenstein, v. Sunstone Soretite, 491 Souesite, 356 Soumansite, 614 Spadaite, 577 Spaerocobaltite, 446 Spangolite, 631 Spargelstein, v. Asparagus stone Spathic iron, 443 Spatheisenstein, v. Siderite Spear pyrites, 380 Speckstein, v. Steatite Specular iron, 415 Speerkies, v. Marcasite Speiskobalt, v. Smaltite Spencerite, 612 Spessartine, Spessartite, 507 Speziaite, 491 Sperrylite, 379 . Sphaerite, 614 Sphaerocobaltite, 446 Sphalerite, 367 Sphene, 583 Sphenomanganite, 432 Spiauterite, v. Wurtzite Spinel, 419 Spinel ruby, 419 Spinthere, 584 Spodiophyllite, 572 Spodiosite, 600 Spodumene, 480 Sporogelite, 434 Spreustein, 556 Sprodglanzerz, v. Polybasite Sprodglaserz, v. Polybasite Sprudelstein, 446 Spurrite, 581 Staffelite, 596, 597 Stalactite, 440 Stalagmite, 440 Stannite, 394 Stassfurtite, 621 Star-quartz, 405 sapphire, 410 Staurolite, 543 Staurotide, 543 Steatite, 576 Steenstrupine, 496 Steinheilite, 498 Steinmannite, 363 Steinmark, v. Lithomarge Steinsalz, v. Halite Stellerite, 558 Stelznerite, 632 Stephanite, 392 Stercorite, 611 Sternbergite, 367 Stewartite, 607 Stibiconite, 410 Stibiotantalite, 590 Stibnite, 358 Stichtite, 453 Stilbite, 551, 548 Stilpnochloran, 572 Stilpnomelane, 572 Stoffertite, 611 Stokesite, 540 Stolpenite, 579 Stolzite, 643 Strahlerz, v. Clinoclasite Strahlkies, v. Marcasite Strahlstein, 489 Stratopeite, 485 Stream tin, 426 Strengite, 610 Strigovite, 572 Stromeyerite, 366 Strontianite, 447 Strontianocalcite, 440 Strontium carbonate, 447 silicate, 549 sulphate, 627 Struvite, 606 Striiverite, 427 Stiitzite, 362 Stylotypite, 388 Succinic acid, 645 Succinite, 645, 507 Sulfoborite, 623 SULPHANTIMONATES, 393 SULPHANTIMONITES, 383 SULPHARSENATES, 393 SULPHARSENITES, 383 SULPHATES, 624 718 INDEX TO SPECIES SULPHIDES, 357 SULPHOBISMUTHITES, 383 Sulphoborite, 623 Sulphohalite, 631 SULPHOSTANNATES, 315 Sulphur, 347 Sulvanite, 393 Sundtite, 385 Sunstone, 466 Susannite, 631 Sussexite, 619 Svabite, 598 Svanbergite, 618 Sychnodymite, 373 Sylvanite, 382 Sylvite, 396 Symplesite, 608 Synadelphite, 606 Synchisite, 449 Syngenite, 636 Syntagmatite, 489 Szaboite, 474 Szaibelyite, 620 Szechenyiite, 489 Szmikite, 633 Szomolnokite, 633 T Tabular spar, 482 Tachhydrite, 402 Tachyhydrite, Tachydrite, 402 Taeniolite, 565 Taenite, 356 Tafelspath, v. Wollastonite Tagilite, 612 Talc, 575 Talkeisenerz, v. Magnetite Talktriplite, 600 Tallingite, 402 Tallow, Mineral, 645 Tamanite, 607 TANTALATES, 587 Tantalite, 588 Tantalum, 349 Tapalpite, 389 Tapiolite, 590 Taramellite, 498 Tarbuttite, 604 Tarnowitzite, 446 Tartarkaite, 583 Tasmanite, 646 Tavistockite, 606 Tawmanite, 532 Taylorite, 624 Teallite, 394 Tellur, v. Tellurium TELLURATES, 641 Tellurbismuth, 360 Tellurblei, v. Altaite TELLURIDES, 364 et sea Tellurite, 410 TELLURITES, 641 Tellurium, 349 Tellurium oxide, 410 Tellurnickel, v. Melonite Tellursilber, v. Hessite Tellurwismuth, v. Tetrady mite Temiskamite, 372 Tengerite, 454 Tennantite, 391 Tenorite, 412 Tephroite, 513 Terlinguaite, 401 Termierite, 579 Teschemacherite, 450 Tesseralkies, v. Skutterudite Tetradymite, 360 Tetrahedrite, 390 Thalenite, 529 Thallite, 531 Thallium selenide, 365 Thaumasite, 581 Thenardite, 624 Thennonatrite, 452 ThermophyUite, 575 Thinolite, 441 Thiorsauite, 468 Thomsenplite, 402 Thomsonite, 557 Thonerde, v. Aluminium Thorianite, 624 Thorite, 522 Thorium silicate, 522, 540 Thortveitite, 529 Thorogummite, 624 Thulite, 530 Thuringite, 571 Tiemannite, 369 Tiger-eye, 405 Tilasite, 601 Tile ore, 410 Tilkerodite, 364 Tin, Native, 354 Tin borate, 620 oxide, 425 sulphide, 394 Tin ore, Tin stone, 425 Tin pyrites, 394 Tincal, 622 Tinkal, 622 Tirolite, 612 TlTANATES, 583 Titaneisen, v. Ilmenite Titanic iron ore, 417 Titanite, 583 Titaniumoxide, 427, 428, 429 ritanomorphite, 584 Toernebohnite, 540 Topaz, 523 False, 405 Oriental, 413 Topazolite, 508 Porbanite, 648 Torberaite, 616 Touchstone, 406 Tourmaline. 540 Traversellite, 476 Travertine, 440 Trechmanite, 386 Tremolite, 489 Trichalcite, 607 Tridymite, 407 Trigonite, 601 Trimerite, 515 Tripestone, 629 Triphane, 480 Triphyline, 594 Triphylite, 594 Triplite, 600 Triploidite, 601 Triploite, 409 Trippkeite, 618 Tripuhyite, 618 Tritochorite, 604 Tritomite, 496 Trogerite, 617 Troilite, 373 Trolleite, 614 Trona, 453 Troostite, 514 Tscheffkinite, Tschewkinit, 585 Tschermigite, 637 Tsumebite, 604 Tufa, Calcareous, 440 Tungsten trioxide, 410 Tungstenite, 361 Tungstite, 410 Turanite, 604 Turgite, 433 Tiirkis, 613 Turmalin, 540 Turnerite, 593 Turquois, Turquoise, 613 Tychite, 450 Tyrite, 588 Tyrolite, 612 Tysonite, 399 Tyuyamunite, 617 U Uhligite, 428 Uintahite, Uintaite, 647 Ulexite, 622 Ullmannite, 379 Jltrabasite, 392 Jltramarine, 503 Umangite, 365 Jnionite, 530 Jraconite, 641 Jralite, 490 JRANATES, 623 Jraninite, 623 Jranite, 616 Jranium arsenate, 617 carbonates, 454 niobates, 590, 591 phosphates, 616 silicates, 581 sulphate, 641 INDEX TO SPECIES 719 Uranmica, 616 Uranocircite, 617 Uranniobite, 623 Uranophane, 581 Uranopilite, 641 Uranosphaerite, 624 Uranospathite, 617 Uranospinite, 617 Uranothallite, 454 Uranotil, 581 Uranpecherz, v. Uraninite Urao, 453 Urbanite, 477 Urpethite, 645 Urusite, 639 Ussingite, 470 Utahite, 639 Utahlite, 610 Uvanite, 609 Uvarovite, Uwarowit, 508 Vaalite, 487, 572 Valencianite, 458 Valentinite, 410 Vanadinbleirerz, v. Vanadin- ite Vanadinite, 598 Vanadium silicate, 565 Vanthoffite, 625 Variegated copper ore, 374 Variscite, 610 Vashegyite, 614 Vauquelinite, 630 Vegasite, 638 Velardenite, 518 Velvet copper ore, v. Lett- somite Venasquite, 568 Venus-hairstone, 427 Verd-antique, 573 VERMICULITES, 572 Vermilion, v. Cinnabar Vernadskite, 638. Vesuvianite, 51i> Veszelyite, 612 Victorite, 472 Vilateite, 610 Villamaninite, 379 Villiaumite, 396 Viluite, 519 Violan, 476 Viridine, 525 Vitreous copper, v. Chalcocite silver, v. Argentite Vitriol, Blue, 636 Vitriolbleierz, v. Anglesite Vivianite, 608 Voelckerite, 596 Voglianite, 641 Voglite, 454 Volborthite, 612 Voltaite, 639 Voltzite, Voltzine, 383 Vonsenite, 620 . Vorobyevite, 495 Vrbaite, 386 Vredenburgite, 418 Vulpinite, 629 W Wad, 436 Wagnerite, 600 Walkerite, 483 Walpurgite, 617 Waluewite, 567 Wapplerite, 611 Wardite, 614 Waringtonite, 632 Warrenite, 387 Warwickite, 621 Washingtonite, 418 Wassersapphir, v. lolite Wavellite, 612 Webnerite, 385 Websterite, 639 Wehrlite, 360 Weibullite, 386 Weibyeite, 449 Weinbergerite, 494 Weissbleierz, v. Cerussite Weissgiiltigerz, v. Freibergite Wellsite, 549 Wernerite, 516 Wheel ore, 388 Whewellite, 644 White antimony, 409 White arsenic, 409 garnet, v. Leucite iron pyrites, 380 lead ore, 448 Whitneyite, 362 Wiikite, 591 Wilkeite, 597 Willemite, 513 Williamsite, 575 Willyamite, 379 Wilsonite, 562 Wiltshireite, 386 Wiluite, 507, 520 Winchite, 489 Wiserine, 428 Wismuth, v. Bismuth Wismuthantimonnickel- glanz, v. Kallilite Wismuthblende, v. Eulytite Wismuthglanz, v. Bismuthin- ite Wismuthspath, v. Bismutite Withamite, 532 . Witherite, 447 Wittichenite, 388 Wocheinite, 434 Wohlerite, 484 Wolfachite, 382 Wolframite, 641 Wolfsbergite, 386 Wolftonite, 435 Wollastonite, 482 Wolnyn, 626 Wood, Fossil, Petrified, 406 Wood copper, 603 Wood opal, 409 Wood tin, 426 Worthite, 526 Wulfenite, 643 Wiirfelerz, v. Pharmacosider- ite Wurtzite, 371 Xalostocite, 509 Xantharsenite, 601 Xanthoconite, 393 Xanthophyllite, 567 Xanthosiderite, 433 Xanthoxenite, 614 Xenolite, 526 Xenotime, 592 Yellow copper ore, 374 lead ore, 643 Yenite, 538 Yttergranat, 508 Yttrialite, 529 Yttrium carbonate, 454 Yttrium niobates, 588, etc. phosphates, 592, 601 silicates, 529 Yttrocerite, 402 Yttrocolumbite, v. Yttrotan- talite, 590 Yttrocrasite, 586 Yttrofluorite, 399 Yttrogummite, 624 Yttrotantalite, 590 Yukonite, 615 Zamboninite, 582 Zaratite, 453 ZEOLITES, 547 Zepharovichite, 610 Zeunerite, 616 Zeigelerz, v. Tile ore Zeophyllite, 546 Zeyringite, 446 Zietrisikite, 645 Zinc, 349 Red Oxide of, 411 Zinc aluminate, 420 arsenates, 604, 609 carbonates, 445 oxide, 411, 420 oxysulphide, 383 phosphate, 607 silicates, 513, 539, 540 720 Zinc, sulphates, 630, 635 sulphides, 367, 371 vanadate, 604 Zinc blende, 367 Zinc ore, Red, 441 Zincorodochrosite, 445 Zincaluminite, 640 Zincite, 411 Zinckenite, 385 Zincocalcite, 441 INDEX TO SPECIES Zinkblende, v. Sphalerite Zinkenite, 385. Zinkosite, 630 Zinkspath, v. Smithsonite Zinnerz, 425 Zinnkies, v, Stannite Zinnober, v. Cinnabar Zinnstein, 425 Zinnwaldite, 563 Zippeite, 641 Zircon, 520 Zirconium dioxide, 428 silicate, 520, 484 Zirkelite, 428 Zoisite, 530 Zorgite, 365 Zunyite, 505 Zurlite, 518 Zwieselite, 500 c 14 DAY USE RETURN TO DESK FROM WHICH BORROWED ^ARTH SCIENC This book is due on the last on the date to which renewed. Renewed books are subject to immediate recall. LD 21-50m-6,'60 (B1321slO)476 General Library University of California Berkeley