UC-NRLF 302 , BERKELEY I .RY UNIVERSITY OF CALIFORNIA SCIENCES ELEMENTS OF MINERALOGY, CRYSTALLOGRAPHY - AND BLOWPIPE ANALYSIS- FROM A PRACTICAL STANDPOINT INCLUDING A DESCRIPTION OF ALL COMMON OR USEFUL MINERALS, THEIR FORMATION AND OCCURRENCE, THE TESTS NECESSARY FOR THEIR IDENTIFICATION, THE RECOGNITION AND MEAS- UREMENT OF THEIR CRYSTALS, AND THEIR ECONOMIC IMPORTANCE AND USES IN THE ARTS BY ALFRED J. I^OSES, E.M., PH.D. Professor of Mineralogy, Columbia University, New York City AND CHARLES LATHROP PARSONS, D.Sc., D.CHEM, Chief Chemist United States Bureau of Mines FIFTH EDITION ENLARGED ANJD IN LARGE PART REWRITTEN ' 'NEW YORK D. VAN NOSTRAND COMPANY 25 PARK PLACE 1916 Ft I JCIENCES Entered according to the Act of Congress in the year 1916, by A. J. MOSES AND C. L. PARSONS In the Office of the Librarian of Congress. All rights reserved. PRESS OF THE NEW ERA PRINTING COMPANY LANCASTER. PA PREFACE. In this, the fifth edition of our textbook, the "practical stand- point" of the former editions is maintained and skill in "Sight Recognition and Rapid Determination of Common and Econom- ically Important Minerals" is still the chief objective. About two hundred additional pages have been needed and the changes, while distributed, are principally: (a) Descriptions of new economic groups and species consequent on the great development in industrial applications. (b) Discussions of formations and occurrences, in recognition of the growing interest in mineral genesis and of its value both in diagnosis and in connecting more closely geology and mineralogy. (c) An enlarged section on crystallo-optics, schemes for crushed fragments and grouped optical distinctions consequent upon the proved value of the polarizing microscope in rapid mineral determinations. (d) New tables for determination. Two other new features may be mentioned : 1. In the introductory chapter, as a substitute for the usual crystallo graphic course involving symbols and axes, we have given a simplified method of classifying and identifying real crystals by partial symmetry and angles which enables the student after two or three lessons to recognize the crystalline system of real crystals and often to identify the species by simple measurements. 2. The gem minerals have been assembled and described in a separate chapter. 3G0415 TABLE OF CONTENTS. PREFACE iii BIBLIOGRAPHY xi PART I. CRYSTALLOGRAPHY. CHAPTERS I. TO X., PAGES i TO 156. CHAPTER I. Introductory i to 27 Crystals and Their Angles I Contact Goniometers .,.. 3 Approximate Measurements . . 5 Symmetry and Classification 6 Determination of Crystals by Partial Sym- metry and Approximate Angles 12 By Crystal Axes and Symbols 20 Crystal Structure 26 II to VII. The "Systems," Their Classes, Forms and Symbols 28 to 66 The Triclinic System 28 The Monoclinic System 32 The Orthorhombic System 36 The Tetragonal System 42 The Hexagonal System 48 The Isometric System 58 VIII. The Grouping of Crystals and Their Imperfec- tions 68 to 81 Twin Crystals 68 Crystal Aggregates 70 Terms of Growth and Habit 74 Irregularities of Faces 77 Internal Peculiarities 79 Intergrowths and Parallel Growths 81 IX. The Determination of the Geometrical Constants of a Crystal 82 to 95 Measurement of Interfacial Angles 82 Stereographic Projections 84 V vi TABLE OF CONTENTS. Symmetry and Elemental Faces 87 Zonal and Graphic Determination of Indices 88 Calculation of Axial Elements 91 Crystal Drawing 92 X. Crystals-Optics 96 to 155 Light and Its Fundamental Phenomena. ... 96 Optically Isotropic and Anisotropic Crystals 99 Double Refraction and Polarization in Cal- cite 100 Optically Uniaxial Crystals 102 Optically Biaxial Crystals 105 Production of Plane Polarized Light 107 The Polarizing Microscope and Its Ad- justments 117 Preparation of Material for Optical Testing 125 Determining Isotropic or Anisotropic 127 Determining Indices of Refraction 127 Determining Sign of Elongation 134 Determining Birefringence 135 Determining Isotropic Uniaxial or Biaxial . 140 Determining the Character of Double Re- fraction 145 Determining Angle between Optic Axes . . . 147 Determining the Crystalline System by Optical Tests 150 Absorption, Color and Pleochroism 151 Determining Pleochroism 153 PART II. BLOWPIPE ANALYSIS. CHAPTERS XL TO XIV. Pages 156 to 207. XL Apparatus Blast, Flame, Etc 156 to 163 XII. Operations of Blowpipe Analysis 164 to 181 XIII. Summary of Useful Tests with the Blowpipe 182 to 196 XIV. Schemes for Qualitative Blowpipe An- alysis 197 to 200 PART III. MINERALOGY. CHAPTERS XV to XXI Pages 208 to 549. XV. Definition and Physical Characters. . . 208 to 230 TABLE OF CONTENTS. vii XVI. The Chemical Characters of Minerals. . 231 to 238 XVII. Formation and Occurrence 239 to 260 XVIII. The Minerals of the Metalliferous Ore Deposits 261 to 416 The Iron Minerals 261 The Manganese Minerals 277 The Cobalt and Nickel Minerals 286 The Zinc and Cadmium Minerals 295 The Tin Minerals : 304 The Titanium Minerals 308 The Zirconium, Thorium, Cerium and Yttrium Minerals 310 The Lead Minerals 316 The Bismuth Minerals 324 The Arsenic Minerals , 327 The Antimony Minerals 332 The Vanadium Minerals 336 The Uranium and Radium Minerals. ..... 341 The Chromium Minerals 345 The Molybdenum Minerals 348 The Tungsten Minerals 350 The Columbium and Tantalum Minerals. . 354 The Copper Minerals 357 The Mercury Minerals 373 The Silver Minerals 37& The Gold Minerals. 392 The Platinum Group Minerals 401 The Aluminum Minerals 406 XIX. Minerals Important in the Industries and Not Already Described 417 to 478 The Potassium Minerals 417 The Sodium Minerals 421 The Lithium Minerals 4 28 The Ammonium Minerals 430 The Barium Minerals 431 The Strontium Minerals 434 The Calcium Minerals 437 The Magnesium Minerals 450 viii TABLE OF CONTENTS. The Boron Minerals 454 The Minerals of Chlorine, Bromine, Iodine and Fluorine 459 The Sulphur Minerals 460 The Selenium and Tellurium Minerals 464 The Hydrogen Minerals 465 The Nitrogen Minerals 466 The Phosphorus Minerals 467 The Carbon Minerals 472 XX. Silica and the Rock- Forming Silicates . 479 to 549 Silica 482 The Feldspars 488 The Feldspathoids 497 The Pyroxene and Amphibole Groups 500 Garnet 509 Vesuvianite 511 The Olivine Group 512 The Scapolite Group 515 The Andalusite Group 517 Staurolite 520 Beryl, Topaz and Tourmaline 521 Titanite , 525 The Epidote Group 526 The Zeolite Group 529 The Mica Group 537 The Chlorite Group 541 The Hydrous Silicates of Magnesium 543 The Hydrous Silicates of Aluminum 547 XXI. Minerals Used as Precious and Orna- mental Stones 550 to 579 Transparent Stones 550 Translucent to Opaque Stones 570 PART IV. DETERMINATIVE MINERALOGY. XXII. Tables for the Rapid Determination of the Common Minerals 580 to 614 Explanatory 580 Key '. 585 TABLE OF CONTENTS. ix Minerals of Metallic or Submetallic Lustre . 586 Minerals of Non-metallic Lustre. 594 A. By Blowpipe and Physical Characters B. By Aid of Polarizing Microscope Table of Atomic Weights 614 General Index 6l 5 Index to Minerals 62 5 BIBLIOGRAPHY. It is not proposed to offer a complete bibliography but simply to name a few standard and usually recent works in each division of the subject. Treatises, Mineralogy. Dana, J. D. System of Mineralogy, 6th edition, with three appendices (1899, 1909 and 1915). John Wiley & Sons, N. Y., 1892. Hintze, Carl. Handbuch der Mineralogie. Bd. i, 1904; Bd. 2, 1897. vonVeit & Co., Leipzig. (Still incomplete.) Text Books, Mineralogy. Bauer, M. Lehrbuch der Mineralogie. 2d ed. 1904. E. Schweizbart., Stuttgart. Dana-Ford. Manual of Mineralogy. i3th edition. John Wiley & Sons, N. Y., 1912. Miers, H. A. Mineralogy. An Introduction to the Scientific Study of Minerals. Macmillan & Co., London, 1902. Naumann-Zirkel. Elemente der Mineralogie. I3thed. 1898. W. Engelmann, Leipzig. Phillips, A. H. Mineralogy. The Macmillan Co., New York, 1912. Rogers, A. F. Introduction to the Study of Minerals. McGraw-Hill Book Co., N. Y., 1912. Tschermak, G. Lehrbuch der Mineralogie. 6th ed. 1905. A. Holder, Wien. Determinative Mineralogy and Blowpipe Analysis. Brush-Penfield. Manual of Determinative Mineralogy. i6th edition. John Wiley & Sons, N. Y., 1906. Eakle, A. S. Mineral Tables. John Wiley & Sons, N. Y., 1904. Fuchs-Brauns. Anleitung zum Bestimmen der Mineralien. 6th ed. A. Topelmann, Giessen, 1913. Frazer-Brown. Tables for the Determination of Minerals. 6th edition. J. B. Lippincott Co., Philadelphia, 1910. Kraus-Hunt. Tables for the Determination of Minerals. McGraw-Hill Book Co., N. Y., 1911. Lewis, J. V. Determinative Mineralogy. 2d ed. John Wiley & Sons, N. Y., Plattner- Kolbeck. Probierkunst mit der Lotrohre. 7th edition. Johann Earth Leipzig, 1907. Chemical Mineralogy. Brauns, R. Chemische Mineralogie. Tauchnitz, Leipzig, 1896. Doelter, C. Physikalische-Chemische Mineralogie. J. A. Earth, Leipzig, 1905, Doelter, C. Handbuch der Mineral Chemie, Bd. I, II, III. T. Sternkopf. Dresden, 1912-1913. Microchemical Analysis. Chamot, E. M. Elementary Chemical Microscopy. John Wiley & Sons, N. Y., 1916. xii BIBLIOGRAPHY. Occurrence, Association and Origin of Minerals. Beyschlag-Krusch-Vogt. (Translated by S. J. Truscott.) The Deposits of the Useful Minerals and Rocks, Vol. i, 1914; Vol. 2, 1916; Vol. 3, . Mac- millan & Co., London. Clarke, F. W. The Data of Geochemistry. Bulletin No. 660, U. S. Geol. Surv., 1915. Leith and Meade. Metamorphic Geology. Henry Holt & Co., 1915. Lindgren, W. Mineral Deposits. McGraw-Hill Book Co., 1913. Van Hise, C. R. A Treatise on Metamorphism. Monograph 47, U. S. Geol. Surv., 1904. Weinschenck, E. Grundziige der Gesteinskiinde, Herder. Freiburg im Bries- gau, 1905. Rock Minerals and Their Microscopic Examination. Iddings, J. P. Rock Minerals. 2d edition. John Wiley & Sons, N. Y., 1912. Johannsen, A. Determination of Rock Forming Minerals. John Wiley & Sons, N. Y., 1908. Johannsen, A. Manual of Petrographic Methods. McGraw-Hill Book Co., 1914. Luquer, L. Mel. Minerals in Rock Sections. 4th edition. D. Van Nostrand Co., 1913. Weinschenck-Clark. Petrographic Methods. McGraw-Hill Book Co., N. Y., 1912. Wright, F. E. The Methods of Petrographic-Microscopic Research. Carnegie Institution, 1911. Microscopic Study of Minerals. Murdoch, J. Microscopical Determination of the Opaque Minerals. John Wiley & Sons, N. Y., 1916. Schroeder van der Kolk, J. L. C. Tabellen zur mikroskopischen Bestimmung der mineralien nach ihren Brechnungsexponenten. 2d edition. C. W. Kreidel, Wiesbaden, 1906. Seeman, F. Leitfaden der Mineralogischen Bodenanalyse. W. Braunmiiller, 1914. Winchell-Winchell. Elements of Optical Mineralogy. D. Van Nostrand Co., N. Y., 1908. Rare Minerals. Cahen and Wootton. The Mineralogy of the Rarer Metals. J. B. Lippincott Co., Philadelphia, 1912. Gems and Precious Stones. Bauer, Max. Edelsteinkunde. 2d edition. Tauchnitz, Leipzig. Cattelle, W. R. Precious Stones. J. B. Lippincott Co., Philadelphia, 1903. Crookes, Sir Wm. Diamonds. Harper Bros., N. Y., 1909. Escard, J. Les Pierres Prccieuses. Dunod et Pinat, Paris, 1914. Farrington, O. C. Gems and Gem Minerals. A..W. Mumford, Chicago, 1903. Eppler, A. Die Schmuck und Edelsteine. Felix Krais, Stuttgart, 1912. Smitn, G. F. II. Gem Stones. James Pott & Co., N. Y., 1912. Crystallography (Geometrical). Bayley, W. S. Elementary Crystallography. McGraw-Hill Book Co., N. Y., 1910. Hilton, H. Mathematical Crystallography. Clarendon Press, Oxford, 1903. BIBLIOGRAPHY. xiii Lewis, W. J. A. A Treatise on Crystallography. University Press, Cambridge, Eng., 1899. Linck, G. Grundriss der Kristallographie, 3d ed. G. Fischer, Jena, 1913. Tutton, A. E. H. Crystallography and Practical Crystal Measurement. Macmillan & Co., London, 1911. Viola, C. M. Grundziige der Kristallographie. W. Engelmann, Leipzig, 1906- Walker, T. L. Crystallography. McGraw-Hill Book Co., N. Y., 1914. Crystallography (Physical and Chemical). Becker, A. Krystalloptik. F. Erike, Stuttgart, 1903. Fletcher, L. The Optical Indicatrix. H. Frowde, London, 1892. v. Groth, P. Chemische Krystallographie. 3 vols. W. Engelmann, Leipzig, 1910. v. Groth, P. Physikalische Krystallographie. W. Engelmann, Leipzig, also translation of part by Jackson. John Wiley & Sons, N. Y., 1910. Groth-Marshall. Introduction to Chemical Crystallography. John Wiley & Sons, N. Y., 1906. Tamman, G. Kristallisiren und Schmelzen. J. A. Earth, Leipzig, 1903. Voigt, W. Elemente der Krystallphysik. von Veit & Co., Leipzig, 1898. Crystal Structure. Bragg, W. H. & W. L. X-Rays and Crystal Structure. G. Bell and Sons, London, 1915. Pope, W. J. Annual Report Chemical Society London, p. 258. London, 1908. Schonflies, A. Krystallsysteme und Krystallstructur. B. G. Teubner, Leipzig, 1891. Sohnke, L. Entwickelung einer Theorie der Krystallstructur. B. G. Teubner, Leipzig, 1879. Story-Maskelyne and Others. Report Committee of British Association for Advancement Science, 1901. Tutton, A. E. H. Crystalline Structure and Chemical Constitution. Mac- millan & Co., London, 1910. Liquid Crystals. Lehmann, O. Fliissige Kristalle. W. Engelmann, Leipzig, 1904. Schenck, R. Kristallinische Fliissigkeiten und Fliissige Kristalle. W. Engel- mann, 1905. The Uses of Minerals. Dammer und Tietze. Die Nutzbaren Mineralien. 2 vols. F. Enke, Stuttgart, Mineral Resources of the United States. Annually since 1883. U. S. Geol. Survey. The Mineral Industry. Annually since 1892. McGraw-Hill Book Co., N. Y. Engineering and Mining Journal, especially Annual Review number. History of Mineralogy. Fletcher, L. Guide to Mineral Collection of British Museum. v. Kobell, F. Geschichte der Mineralogie. J. G. Cotta, Miinchen, 1864. Mineral Synonyms'. Chester, A. H. Dictionary of the names of Minerals. John Wiley & Sons, N. Y., 1896. Egleston, T. Catalogue of Minerals and Synonyms. Washington, Govt. Printing Office, 1887. PART I. CRYSTALLOGRAPHY. CHAPTER I. INTRODUCTORY. The meaning of the word crystal in ancient times, and even in the English of the Middle Ages, was ice. Transparent, colorless quartz was called crystal because it was supposed to be ice in permanent form, the solids obtained on the evaporation of water were crystal, because like ice, they were solids formed from water. The Common Limited Meaning of Crystal. Both the quartz and the solid salts from solutions occurred in shapes bounded by plane surfaces, and as other substances both opaque and transparent possessed such shapes, by an extension of meaning crystal came to signify a shape bounded by plane faces, and more exactly, crystals, in this limited sense, are solids, formed only when a chemical element or a chemical compound solidifies, and bounded by plane faces at definite angles to each other which are characteristic of the substance. The Broader Meaning of Crystal, It is known now that this "polyhedral" shape is due to definite internal structure and that this structure is of such a nature that a "crystal" always shows the same physical characters* in all parallel directions and, generally speaking, different characters in different directions. * For instance, crystals will often break in directions parallel to planes yielding solids absolutely constant in angles, they will transmit light or conduct heat or elec- tricity with the same velocity along all parallel lines, but with different velocity along lines not parallel. 2 C7? YSTALLOGRAPHY. But solidified chemical substances consist, for the most part, of crowded aggregations of individuals with little or no trace of plane-faced boundaries. Every grain, nevertheless, possesses the perfect regular internal structure with the physical characters constant in parallel directions and varying in directions not parallel, and often in earlier stages of growth did possess the polyhedral shape until crowding obliterated it. The broad definition of crystal must therefore include these individuals. That is, crystals are distinct individual solids resulting from the solidification of a chemical substance and showing constancy of properties in parallel directions and varying properties in direc- tions not parallel. Under favorable conditions of free space, time and surroundings crystals will be bounded by plane surfaces at definite angles to each other and characteristic of the substance. Crystallization. Crystallization is therefore that solidification of a chemical element or compound which results in individuals possessing a crystal structure. These individuals may be completely bounded by plane surfaces or partially bounded by plane surfaces, or may lack all plane boundaries. They are identical in essentials and there is no line of division in the non-essentials. GEOMETRICAL CRYSTALLOGRAPHY.* Crystallography is broadly divided into: Geometrical or Morphological Crystallography. Physical Crystallography. Chemical Crystallography. Of these this book considers only those portions of the first two which experience has proved to be most useful in the identification and description of minerals. Geometrical crystallography considers the relations between the bounding faces. In elementary work the principal tasks are determinations of "system," recognition of type symbols, approximate angle meas- * Geometrical Crystallography often receives an unmerited proportion of the time devoted to the study of crystals as a natural result of the fact that the geometrical relations were first studied. INTR OD UCTOR Y. 3. urements, and, perhaps most important, interpretation of crystal descriptions. In more advanced work the tasks are exact measurements of angles, projection and delineation, determination of indices and elements (axial angles and parameters) and calculation of the- oretical angles from elements and indices. The Angles' of Crystals. In any crystal three sorts of angles exist: 1. Plane angles between "edges" (intersections of faces). 2. Dihedral or interfacial angles. 3. Polyhedral angles between three or more planes. While all of these are characteristic the interfacial angles are most conveniently used. Single crystals show only salient angles, re-entrant angles are common on twinned crystals. Law of Constancy of Interfacial Angles. The angles of crystals of any one substance conform to the following law: In all crystals of the same substance the angles between corresponding faces are constant. This law, the first to be announced, was gradually developed; for instance, Steno in 1669 announced that in rock crystal there was no variation of angle in spite of the variation in relative size of the faces. In 1704 Guglielmini stated that every salt had its peculiar crystals, the angles of which were constant Rome Delisle in 1783 measured and described over four hundred crystal forms and announced that in each species "the respective inclination of the faces to each other never varies." Aside from the crystals of the isometric system it is now held to be true that the crystals of each chemical substance have a separate and definite set of angles, certain so-called isomorphous substances crystallizing however with very nearly the same angles. Contact Goniometers. Measurements within one or two degrees may be made with Contact goniometers, the most simple type of which consist of an arm pivoted upon a protractor. Fig. I shows Penfield Goniometer Model B, consisting of a cardboard on which is printed a semicircle graduated from o to 180 in both directions. 4 CRYSTALLOGRAPHY. An arm of transparent celluloid is swivelled by means of an eyelet exactly in the center of the semicircle tightly enough to turn with some difficulty. FIG. i. FIG. 2. In measuring, the crystal or model is placed as shown so that the card edge and swinging arm are each perpendicular to the edge of -intersection of the two faces, and in such close contact that no light passes between these and the faces. To facilitate this one part of the swinging arm and the base edge of the card are blackened. A more expensive instru- ment, Fig. 2, consists of a brass protractor with detach- able arms which can be slid upon the pivot until of the most convenient length for the particular crystal, In measuring the arms are detached and set at an angle a little less than the angle to be measured, clamped loosely and one of the arms placed in perfect contact with one crystal face. The other arm then nearly touches the second face and, while holding between the eye and the light, is brought into perfect INTR OD UCTOR Y. 5 parallelism with the second face by a gentle pressure with the forefinger. The arms are then replaced on the arc, as in the figure, and the angle is read. THE APPROXIMATE MEASUREMENT OF INTERFACIAL ANGLES. Determinations of symmetry, system, type symbols, and ap- proximate angles, of sufficient accuracy to greatly help in the recognition of mineral species, can be made with very simple apparatus and even without apparatus. In many cases the task is not so much to ascertain the value of the angles as to estimate the equality or inequality of different angles and the parallelism of faces to each other or to certain lines. By Inspection Alone. Estimates are best made by placing the two crystal faces con- cerned at right angles to a horizontal surface and tracing their intersections with the surface. The eye recognizes 90 with close approximation and fractional parts of 90 such as 45, 30, 60 with fair accuracy. Parallelism of faces is judged by placing one of the faces in contact with a horizontal surface and noting the position taken by the other face. Parallelism between a face and a line is judged by placing a straight edge in different positions of contact with the face. If in any of the positions the straight edge and the line are parallel, the face and the line are also parallel. Paral- lelism of three or more faces to a common line is judged by the parallelism of the edges between the faces. The Measuring. A convenient order of measuring and recording is as follows: A zone, or series of planes parallel to the same line, is selected which shows numerous or very well developed faces. This zone is placed with the faces vertical and a sketch made by tracing (or following approximately) these faces on the paper, giving for instance the outline a, b, c, d, e^f, g, h, Fig. 3. The edges between the oblique planes are then roughly sketched in and letters or numbers assigned to each oblique face. Each angle of the vertical zone is then measured two or three 6 CRYSTALLOGRAPHY. times, taking care to reset the goniometer after each reading. The average for each angle is then recorded. Usually the supple- ment angle, which can be read directly on Penfield Model B, is read and recorded, partly because the sum of all the supplement angles of a zone is 360, partly because other angles are more simply checked or calculated and largely because crystallographic descriptions almost invariably record the supplement angles. FIG. 4. Any angle is conveniently designated by the symbols of the two faces, for instance, the angle between a and b by a A b, the angle between / and x by t A x and so on. If the crystal is many-faced it may be convenient to also draw a circle and letting some point as c, Fig. 4, represent the face c, Fig. 3, layoff the supplement angles of that zone as arcs and draw the corresponding radii. By methods described later, p. 84, this drawing may be made to include the oblique faces. One advantage is that the unequal development of corresponding faces of a zone makes no change in the position of the "poles" a, b, c, etc., of Fig. 4. The "ideal" and the actual yield the same "poles." The angles between oblique faces or oblique and vertical faces are then measured. All essentially equal angles are assembled and considered. Necessarily such an assemblage groups together angles between "equivalent" faces it may also include angles between non- equivalent faces. Usually other facts will quickly separate these. THE SYMMETRY OF CRYSTALS. Although the angles between corresponding faces of all crystals of the same substance are equal, different crystals of the same INTR OD UCTOR Y. 7 substance often show unequal numbers of faces, different angles and notably different shapes. The property which such very different crystals of the same substance have in common is expressed by the following law: The Law of Symmetry. All crystals of any one substance are of the same grade of symmetry. Symmetry is fundamentally repetition. The sphere has in- finite geometric symmetry. Every plane through the center divides it into symmetrical halves. Every diameter is an axis of infinite symmetry. True geometric symmetry to lines and planes is rarely shown in the shapes of crystals. The actual symmetry is a symmetry in molecular structure (see page 26), a repetition in different directions of exactly the same arrangement. This shows in the crystal shape but as symmetry of direction with repetition of equal angles and not often as symmetry of position with repetition of equal-sized faces. That is, there is in practically every crystal some repetition or recurrence of equal angles or similarly grouped faces, and two faces symmetrical in this sense may be unequally distant from the center, unequal in size and different in shape.* The " Elements " of Symmetry. It is customary to consider the symmetry of a crystal with reference to the center, axes, and planes, these being collectively known as "Elements of Symmetry." Symmetry to the Center. Each face of the crystal has an opposite parallel face. Thus Fig. 5 represents a crystal of axinite with opposite parallel faces. Symmetry to an Axis. When the crystal is revolved about some line through the center each group of faces is repeated 2, 3, 4, or 6 times during the revolution. * They will, however, be alike in lustre, markings and angles they make with planes or axes of symmetry. CR YSTALLOGRAPHY. Thus in each of the orthographic projections, Figs. 6, 7, 8, 9, 10, there is an axis of symmetry perpendicular to the plane of the paper. "Axes" of symmetry in crystals are rather directions than lines through specific points. Thus while in the topaz crystal of ideal FIG. 5 . FIG. 6. FIG. 7. shape shown* in Fig. 6 there is an axis of two-fold geometric symmetry perpendicular to the plane of the page and through the center of the drawing, the topaz crystal of Fig. 7 showing the same number of faces at the same angles has only symmetry of direction to an axis perpendicular to the page. Whether the axis is consid- ered to be central or not is of no consequence. Figs. 8, 9, 10 show respectively projections of calcite with a three-fold axis, zircon with a four-fold axis and beryl with a two- fold axis. The axis in each case is perpendicular to the plane of the page. Finding an Axis of Symmetry. Try any evidently prominent direction, place it in a vertical position. Note first whether there are any recurrent angles in the group of faces (if any) which are parallel to it; if not it cannot be an axis of symmetry. If there are recurrent angles in the zone of faces parallel to the direction note next the oblique faces and revolve, or imagine a revolution of, the entire crystal about the direction. Note the grouping of faces at any initial position. If during the revolution new groups of faces appear to * These drawings 6-10 are orthographic projections on a horizontal plane with one zone vertical. Parallel edges appear as parallel lines. INTR OD UCTOR Y. 9 take positions parallel to the initial positions of all the faces the direction of rotation is a probable axis of symmetry. If, by measurement, the angles for one position correspond in value and order with those for the other position the existence of the sym- metry axis is confirmed. According to the number of times corresponding groups or faces recur during a complete revolution about a symmetry axis, the axis is known as two-fold, three-fold, four-fold, or six-fold. No other varieties exist. FIG. 8. FIG. 9. FIG. 10. Symmetry to a Plane. A plane of symmetry holds a definite angular relation to a crystal rather than a fixed position in the crystal. So regarded it may be said that with respect to any plane of symmetry the crystal faces are in pairs and that the angle between each pair is bisected by the plane of symmetry, or that a plane of symmetry is so related to a crystal that on each side of that plane there will be grouped the same number of faces at the same angles to it and to each other and in the same order. Thus, not only in the model illustrated, Fig. 6, but in the crystals shown in Figs. 7, 8, 9, 10 there are planes of symmetry parallel to each of the dot and dash lines and each perpendicular to the plane of the paper. The Law of Symmetry therefore means : That while the crystals of any one substance will not all be alike in shape even when the variations due to size and to unequal development of faces have been eliminated, there will be, in every crystal of the substance, wherever found or under whatever con- ditions formed, the same "Elements" of symmetry. 10 CR YSTALLOGRAPHY. Crystal Models and their Geometric Symmetry. Models in which all equivalent faces are the same distance from the center, and therefore of equal size and the same shape, are much used in crystallography. It is desirable to restrict this use as the skill acquired in the study of models is of little use in the recognition of crystals.* Fundamentally the problem is to recog- nize directions of equivalent structure. In the crystal such direc- tions are indicated by faces symmetrical in direction, alike in markings, luster and relation to cleavage but of any size or shape, while in the model such directions are indicated by faces sym- metrical in position and alike in size and shape. A model is symmetrical to the center when every straight line through the center encounters at equal distances on each side of the center two corresponding points. A model is symmetrical to an axis when if revolved about this axis the model reoccupies the same position in space, two, three, four, or six times during one complete revolution. That is, corresponding groups of glanes exchange positions after revolutions of 180, 120, 90 or 60. FIG. ii. FIG. 12. FIG. 13. FIG. 14. The line CC in the zircon crystal, Fig. n, is an axis of four-fold or tetragonal symmetry, for, as shown in the horizontal projection, Fig. 12, the crystal occupies the same position in space when by rotation about CC any point a has moved to b, c, d or again to a, and does not for any other position. * Crystals are often spoken of in terms of models and said to be "distorted" when conforming perfectly to all known crystal laws but not resembling the model. INTRODICTORY. II The line CC in the apatite crystal, Fig. 13, is an axis of six-fold or hexagonal symmetry, because, as shown in horizontal projection, Fig. 14, the crystal occupies the same position in space when by rotation about CC any point a has moved to b, c, d, e, f or again to a. A model is symmetrical to a plane when the plane so divides it that either half is the mirrored reflection of the other, and every line perpendicular to the plane connects corresponding parts and is bisected by the plane of symmetry. FIG. 15. FIG. 16. For example, in Fig. 15, the shaded plane so divides the model that a line from an angle b perpendicular to the plane passes through a corresponding angle a, or a perpendicular from c, the center of an edge, passes through d, the center of a similar edge. ab, cd and all similar lines are bisected by the shaded plane. In Fig. 1 6 both of the shaded planes are planes of geometric symmetry for the model. Classification of Crystals. The basis of classification is always, directly or indirectly, symmetry and profound investigations have proved that the crystal structure as limited by the law of simple mathematical ratio is of 32 types or classes. Nearly all the important minerals crystallize in ten or eleven of the thirty-two classes. The six crystal *' systems" constitute a more convenient classifi- cation. Each system includes two or more classes. Two methods of determining system will be described. 12 CRYSTALLOGRAPHY. 1. A method based on partial symmetry, which is very quickly and easily used for determining the systems of actual crystals and which supplemented by angle measurements will often deter- mine the mineral. 2. A method based on crystal axes, but indirectly upon sym- metry in the choice of crystal axes. This is indispensable in a mathematical consideration of the relations between faces and in the understanding of a crystal description. CONSIDERATION OF CRYSTALS BY PARTIAL SYMMETRY AND APPROXIMATE ANGLES, WITHOUT SYMBOLS. Rapid Method for Finding the System of a Crystal. The following rules quickly determine the "system" of a crystal, without the need of a complete determination of symmetry or any consideration of "crystal" axes. They apply to all 32 classes except one.* Approximate measurements, as described p. 5, are usually needed. Essential Condition. System. More than one axis of three-fold sym- Isometric. metry. One axis of four-fold symmetry, and one Tetragonal. only. One axis of three-fold symmetry, and one Hexagonal. only. Rhombohedral division. One axis of six-fold symmetry. Hexagonal division. More than one axis of two-fold symmetry Orthorhombic. but no axis of higher symmetry (or one axis and two planes of symmetry). One axis of two-fold symmetry only, or Monoclinic. one plane of symmetry only, or both. Without axes or plane of symmetry. Triclinic. DISTINGUISHING SPECIES BY APPROXIMATE ANGLES. Because the angles between corresponding^ faces are constant and characteristic, the measuring of a few selected angles will often serve to determine the mineral. Certain angles are char- * The scalenohedral class of the tetragonal system by these rules would be ortho- rhombic. t Corresponding faces on the same crystal, or on different crystals of the same substance, occupy corresponding or symmetrical positions with reference to the symmetry axes and usually correspond in lustre and markings. They frequently do not correspond in shape. INTR OD UCTOR Y. acteristic, others are common to many crystals, for instance, the angles between faces parallel to the four-fold axis in the tetragonal are possible angles for any substance crystallizing in the tetragonal system. The "cleavage" directions are of great service in orienting the crystal. These and the angles between them are used in the lists which follow each system. ISOMETRIC SYSTEM. Principal Characteristic. If a crystal has more than one axis of three-fold symmetry it is an isometric crystal and not otherwise. It may or may not have three four-fold axes. Prominent Features. The bounding planes are often squares and equilateral triangles or these with their corners cut off. Corresponding faces and equal angles are more frequent than in other systems. Often the dimen- sions are closely equal in three or more directions. Angles. These are of the same "series" whatever the species. They are therefore classed by their "habit," that is, dominant "forms" on the crystals. Tetrahedral, Fig. 17. (Four faces at 70 31'.) Sphalerite, tetrahedrite. FIG. 17. FIG 18. FIG. 19. Cubic, Fig. 1 8. (Six faces at 90.) Argentite, cuprite, fluorite, galenite, halite, pyrite, smaltite. Octahedral, Fig. 19. (Eight faces at 109 29'.) Chromite, cuprite, fluorite, frank- linite, galenite, linnaeite, magnetite, pyrite, spinel. CR YSTALLOGRAPHY. Dodecahedral, Fig. 20. (Twelve faces at 120.) Cuprite, garnet, magnetite, sphaler- ite. Pyritohedral, Fig. 21. (Twelve faces often at 126 53' and 113 35'.) Cobaltite, pyrite, smaltite. Trapezohedral , Fig. 22. (Twenty-four faces often at 131 19' and 146 27'.) Analcite, garnet, leucite. Fie. 20. FIG. 21. FIG. 22. The following show notably good cleavages: Cubic. Galenite, halite. Octahedral. Fluorite. Dodecahedral. Sphalerite. TETRAGONAL SYSTEM. Principal Characteristic.* If the crystal shows one axis of four-fold symmetry and only one it is a tetragonal crystal. Prominent Features. A section taken at right angles to the four-fold axis is usually square or octagonal, that is with angles of 90 or 135 between adjacent faces. The dimension in direction of the four-fold axis is usually notably greater or less than in directions at right angles thereto. Angles. In the zone of the four-fold axis (faces a, m, Fig. 23) there are no variations in angle dependent on the species. All show the same series of angles and between corresponding faces these are principally 90, more rarely 143 8'. INTRODUCTORY. In all other zones the angles vary with the species. Those important tetragonal minerals which often show macro- scopic crystals may be classified by angles and cleavage as follows : ANGLES BETWEEN CORRESPONDING FACES OBLIQUE TO THE FOUR-FOLD Axis. 71 20' chalcopyrite. 121 41' cassiterite. 99 38' wulfenite. 123 8' rutile (p A p, Fig. 23). 100 5' scheelite. 123 19' zircon. 105 apophyllite. 129 21' vesuvianite. 109 53' braunite. 136 15' wernerite. Braunite, scheelite and wulfenite cleave at the angles mentioned. Wernerite and rutile cleave parallel the four-fold axis giving angles of 90 and 135. Apophyllite cleaves to cubic forms, but in one direction much more easily than in the other two. FIG. 23. FIG. 24. FIG. 25. HEXAGONAL CRYSTALS. Principal Characteristic. If the crystal shows one and only one axis of three- fold sym- metry it is a hexagonal crystal, rhombohedral division. If the crystal shows one and only one axis of six- fold symmetry it is a hexagonal crystal, hexagonal division. Prominent Features. A section taken at right angles to the axis of three-fold or six- fold symmetry is usually a hexagon or twelve-sided, that is with angles of 120 or 150 or in some minerals an equilateral triangle with the corners "modified." The dimension parallel this axis is usually notably greater 1 6 , CRYSTALLOGRAPHY. (prismatic crystals) or less (tabular crystals) than the dimensions at right angles thereto. Angles. In the zone of the three-fold axis, Fig. 24, or six-fold axis, Fig. 25, there are no variations in angle dependent on the species. All show the same series of angles and between corresponding faces these are principally 120 or larger such as 141 47' the occur- rence of which tends to produce a nearly circular cross section. In all other zones the angles vary with the species. The important hexagonal minerals, which occur frequently in macroscopic crystals, may be classified by angles and cleavage as follows: I. WITH Axis OF THREE-FOLD SYMMETRY (USUALLY RHOMBOHEDRAL HABIT). (a) Angles are both interfacial and cleavage: (b) Angles interfacial only: 85 14' chabazite. 107 rhodochrosite. 85 31' ilmenite. 86 hematite. 107 siderite. 90 50' alunite. 105 5' calcite. 107 24' magnesite. 92 37' willemite. 106 15' dolomite. 107 40' smithsonite. 116 36' phenacite. 107 58' proustite. 133 8' or 103 tourmaline. II. WITH APPARENT Axis OF SIX-FOLD SYMMETRY (USUALLY PRISMATIC HABIT). (c) Often capped by horizontal plane: (d) Often capped by oblique planes: Beryl nephelite. 86 4' or 128 2 ' corundum. lodyrite pyrargyrite. 94 14' or 133 44' quartz. Mimetite pyromorphite. 142 15' apatite. Vanadinite. (e) Tabular: graphite, molybdenite, iridosmine. ORTHORHOMBIC CRYSTALS. Principal Characteristic. If a crystal shows either more than one axis of two-fold sym- metry (or one axis with more than one plane of symmetry) and nothing of higher symmetry it belongs to the orthorhombic system. Prominent Features. Cross sections taken at right angles to the axes of symmetry are unlike in angles and tend to rectangles and rhombs or these combined. Angles. There is no zone which has a constant series of angles for all species. The interfacial angles in the zones parallel to the axes of symmetry are unlike except when 90 and vary with the species. INTRODUCTORY. Because the three axes of symmetry are all two-fold no prac- ticable method exists for distinguishing between them. If, how- ever, in any crystal angles are found that correspond to important angles in the zones of at least two such axes, for any species, the crystal is probably of that species. In the table the columns A, B, C give prominent angles in zones parallel to the three symmetry axes. Other prominent angles are assembled in D. Thus in Fig. 26, the symmetry axes being shown by dotted lines, in the zone of the vertical axis the angle m A m is 129 31', in the zone of the axis from front to back d A d is 119 46'. No angles occur in the zone of the axis from left to right, and finally such an angle as p A p = 139 53' is evidently prominent. These are found in the columns C, A and D respectively under chrysoberyl. The important orthorhombic minerals which frequently occur in macroscopic crystals may be classified as follows: bisected by cleavage. t = parallel cleavage. C B A D Stibnite QO 26' * 108 36' Andalusite go 48' t 190 50' Natrolite ... ... pz 75' rare rare 142 23' Sillimanite gi 45' * none none none Goethite Enargite Manganite Brookite 94 52' * 97 53' t QQ 40' * ' 00 ^0' 113 6' 114 19' rare 117*30' 122 50' rare 101 31' Columbite 100 43' 140 37' 06 ?i' 90 f Barite . 101 38' t 102 17' 74 34' 90 t Sulphur 101 46' 46 i 6' 55 26' 1 06 26' Anglesite Calamine Celestite Marcasite 103 44' t 103 51' t 104 10' t I0q q't 101 13' 101 II' 6^ AO' 75 36' 76 78 2' 90 90 t Arsenopyrite 112 27' t :c', {ooi}. Two faces, each parallel to both basal axes. The faces c of Fig. 49 and subsequent figures. 6. CLINO PINACOID. oo:^:oor; {oio}. Two faces, each parallel to the clino and vertical axes. The faces b of Fig. 49 and subsequent figures. 7. ORTHO PINACOID. a : co~b : oo c ; {100}. Two faces, each parallel to the ortho and vertical axes. The faces a of Fig. 49 and subsequent figures. Combinations in the Prismatic Class. Pyroxene.- Axes a : ~b : c == 1.092 : I : 0.589; $ 74 10' 9". Fig. 50 shows the three pinacoids, a, b and c, the unit prism m, the negative unit hemi-pyramid p and the positive hemi-pyramid v = (a : 1 : 2r); {22?}. Fig. 52 is the same without v and Fig. 51 omits also the basal pinacoid 56' ORTHOCLASE. Axes a: b: c = 0.658 : 1:0.555; /3 = 46". Fig. 57 shows the unit prism m, clino and basal pinacoids fr and <:, and positive hemi orthodome y = (a : co : 2^:); {20!}. In Fig- 58 y is replaced by o = (a : oo ^ : c) ; { iol} and in Fig. 60 the clino pinacoid is omitted. Fig. 59 includes the forms of 57 and also a clino prism 2 ($a :~b: coc) ; {130} and the unit pyramid p. Other Classes in the Monoclinic System. Two other classes are known : 3. CLASS OF THE MONOCLINIC SPHENOID. With one axis of 2-fold symmetry. Example : Fichtelite, C 18 H 32 . Examples in salts are tartaric acid and cane-sugar, C 12 H 22 O U . 4. CLASS OF THE MONOCLINIC DOME. With one plane of symmetry. Examples : The rare minerals clinohedrite and scolecite. CHAPTER IV. ORTHORHOMBIC SYSTEM. THE orthorhombic * system includes three classes of symmetry, in all of which the crystallographic axes may be chosen at right angles to each other, but are not interchangeable. In this system of moderate symmetry certain facts common to all crystals can be better illustrated and understood than in the other systems. Two of these are discussed under the headings " Series " and " Symbols for Individual Faces." Series. All forms which ever appear upon crystals of the same sub- stance belong to one series. That is, their faces occur at such angles that if one of the faces is taken as the unit and its intercepts expressed by d : b : c all other faces may be simply expressed in terms of this face. For instance in the crystals of topaz, Figs. 78 to 80, the calculated intercepts for certain faces and their symbols, when / is taken as the unit face, are as follows : FACE. P m I f h CALCULATED INTERCEPTS. SYMBOLS IN TERMS OF /. 0.528 0.528 0.528 0.528 1.056 00 10.477 10.318 : 0.954 ; 03 : co : 0.954 0.528 :co : 0318 a 1 (T {in} a ~b ^3:mc [okl] 3. MACRO DOME. 4 a: cob -.me {hoi} 4. RHOMBIC PRISM. 4 nd:~b:cDC {hko} CR YSTALLOGRAPHY. NAME. FACES. WEISS. MILLER, Each face parallel to two axes : 5. BASAL PINACOID. 2 md-.aib-.c {001} 6. BRACHY PINACOID. 2 ma:~b:cQC {010} 7. MACRO PINACOID. 2 a: ml: me {100} Description of the Type Forms. I. RHOMBIC PYRAMID. na \b : mc\ {hkl}. Eight faces, each of which cuts file three axes in the same relative distances, which are never simple multiples of each other. In the ideal forms the faces are equal scalene triangles. A pyramid may be composed either of faces with the unit inter- cepts, or the faces may be at other angles, with any one or two of the intercepts simple multiples of the unit intercepts. For instance if in the series of figures 63 to 67 the faces / con- stitute the unit pyramid d : b : c ; { 1 1 1 } ; then a series of pyramids which might occur with this would have different symbols and names. The pyramid s, shown in Fig. 63 enclosing p and in Fig. FIG. 63. FIG. 64. FIG. 65. FIG. 66. FIG. 67. 64 combined with p ; would be called a brachy pyramid, its symbol being za : ~b : \c ; {364}. ORTHORHOMBIC SYSTEM. 39 The pyramid w shown in Fig. 65 enclosing / and in Fig. 66 combined with / would be called a macro pyramid, its symbol be- ing d : | : |<; ; {322} ; and the pyramid r shown in Fig. 67 com- bined with p would be called a unit series pyramid, its symbol be- ing d : b : 2c ; {221}. 2. BRACHY DOME. &>a\b\mc\ {okl}. Four faces, each parallel to the brachy axis but cutting the macro axis and vertical axis in distances not simply proportionate. The faces d in Fig. 68. 3. MACRO DOME. a\!)\mc\ {hoi}. Four faces, each parallel to the macro axis but cutting the brachy axis and the vertical axis in distances not simply propor- tionate. The faces o in Fig. 69. FIG. 68. FIG. 69. 4. RHOMBIC PRISM. na\b\zac \ {hko} . Four faces, each parallel to the vertical axis and cutting the basal axes in distances not simply proportionate. The intercepts on the basal axes may be in the unit ratio or FIG. 70. FIG. 71. one of the intercepts may be relatively lengthened just as in the pyramids. The faces m in Fig. 68. In Fig. 70 if / is the unit pyramid then, relatively, m is the unit prism d\b\v>c\ {no}; and / is a brachy prism 2d : b : oo c ; { 1 20} . CR YSTALLOGRAPHY. 5. BASAL PINACOID. oo<#:co:r; {001}. Two faces, each parallel to the basal axes. The faces c in Figs. 71-80. 6. BRACHY PINACOID. oo:^:co = (a : oo a : a : r); { 101 1); and/ = (a : oo a : a : 2c)\ { 202 1 } ; but at the lower end the trigonal pyramid p only. Fig, 130 shows m t p and a, but does not so evidently reveal the hemi- morphic symmetry. Fig. 1 3 1 again shows m and a central, with at one end / and at the other/. FIG. 129. FIG. 130. FIG. 131. \ OTHER CLASSES OF SYMMETRY IN THE RHOMBOHEDRAL DIVISION. In each there is an axis of three-fold symmetry. 1 6. CLASS OF HEMIMORPH. TRIGONAL PYRAMID 3 ORDER. The three -fold axis. No planes or center of symmetry. Example sodium periodate, NaIO 4 '3H 2 O. 17. CLASS OF RHOMBOHEDRON 3 ORDER. The three-fold axis and center of symmetry. Examples Dolo- mite, ilmenite, willemite, phenacite, dioptase. HEXAGONAL SYSTEM. 55 1 8. CLASS OF TRIGONAL TRAPEZOHEDRON. The three-fold axis and three two -fold axes of symmetry at 90 thereto. Examples Quartz, cinnabar. 19. CLASS OF TRIGONAL PYRAMID 3 ORDER. The three-fold axis and one plane of symmetry at 90 thereto. No examples known. 22. CLASS OF DlTRIGONAL PYRAMID. The three-fold axis, three planes at 60 and one at 90 to the three. No examples known. HEXAGONAL DIVISION. CLASS OF DIHEXAGONAL PYRAMID. 27. No. 6. Holohedral, Liebisch. No. 13. Normal Group, Dana. A few minerals, notably beryl, crystallize in forms symmetrical to one horizontal plane and to six vertical planes at thirty degrees to each other and to one six-fold and six two-fold axes which are the lines of intersection of these planes, Fig. 132. Choosing Crystallographic Axes. The six-fold axis is chosen as the vertical r, the two-fold axes as the horizontal axes a, one of which is conventionally placed from left to right. Tabulation of the Seven Type Forms. NAME. FACES. WEISS. MILLER. Each face oblique to c. 1. DIHEXAGONAL PYRAMID. 24 a : na \pa : me {hkll} 2. HEXAG. PYRAMID 2 ORDER. 12 2a \2a\a\mc {h-h.2h-l} 3. HEXAG. PYRAMID i ORDER. 12 a : co a :a : me {kohl} Each face perpendicular to c. 4. BASAL PINACOID. 2 co a : co a : co a :c {0001} Each face parallel to c. 5. DIHEXAGONAL PRISM. 12 a \na\pa : me {hklo\ 6. HEXAG. PRISM 2 ORDER. 6 2a : 2a : a : co c {1120} 7. HEXAG. PRISM i ORDER. 6 a : as a : a : co c {ioTo} Description of the Type Forms. i. DIHEXAGONAL PYRAMID. a : na \pa : me ; {hkll}. Twenty -four faces, Fig. 133, each of which cuts the three hori- zontal axes at unequal distances, simple multiples of each other ; and the vertical axis at some distance not simply related to the others. In the ideal form the faces are scalene triangles. CR YSTALLOGRAPHY. 2. HEXAGONAL PYRAMID OF SECOND ORDER. See Fig. 104. 3. HEXAGONAL PYRAMID OF FIRST ORDER. a : oo a : a : mc\ {hohl}. Twelve faces, Fig. 1 34, each parallel to one horizontal axis, cutting the others at equal distances, and the vertical axis at some distance not simple proportionate. In ideal forms the faces are isosceles triangles. 4. BASAL PINACOID, The faces c of Figs. 135 to 137. . 5. DIHEXAGONAL PRISM. See Fig. 1 06. FIG. 132. FIG. 133. FIG. 134. 6. HEXAGONAL PRISM OF SECOND ORDER. See Fig. 107. 7. HEXAGONAL PRISM OF FIRST ORDER. See Fig. 108 or the faces m of Figs. 135 to 137. Combinations in the Class of Dihexagonal Pyramid. Beryl. Axes a : c = I : 0.499. FIG. 135. FIG. 136. FIG. 137. Fig. 135 shows the prism of first order m and basal pinacoid c ; in Fig. 136 the second order pyramid*? = (2 a : 2a : a : 2c] ;{ 1 121}; occurs and in Fig. 137 the unit pyramid p is also present HEXAGONAL SYSTEM. 57 OTHER CLASSES IN THE HEXAGONAL DIVISION. Each with an axis of six-fold symmetry. 23. CLASS OF THIRD ORDER HEMIMORPHIC PYRAMID. The six- fold axis only. Example nephelite. 24. CLASS OF HEXAGONAL TRAPEZOHEDRON. The six-fold axis and six 2-fold axes of symmetry at 90 thereto. Example Barium-antimonyl dextro-tartrate potassium nitrate, Ba(SbO) 2 - (C 4 H 4 6 ) 2 .KN0 3 . 25. CLASS OF THIRD ORDER HEXAGONAL PYRAMID. The six- fold axis and a plane of symmetry at 90 thereto. Examples Apatite, pyromorphite, mimetite, vanadinite. 26. CLASS OF HEMIMORPHIC DIHEXAGONAL PYRAMID. The six- fold axis and six planes of symmetry at 30 to each other inter- secting therein. Example lodyrite. CHAPTER VII. ISOMETRIC SYSTEM. THE Isometric * system includes all crystal forms which can be referred to three interchangeable axes at right angles to each other, that is axes about which there are equal numbers of faces grouped with corresponding faces at the same angles. Five classes are distinguished, of which three include nearly all known isometric minerals. HEXOCTAHEDRAL CLASS. 32. No. I. Holohedral, Liebisch. No. I. Normal Group, Dana. Symmetry of the Class. There are three planes of symmetry, Fig. 138, parallel to cube iaces, and six planes through diagonally opposite cube edges. There are also, Fig. 139, three four-fold, four three-fold and six two-fold axes of symmetry. Choosing Crystallographic Axes. The three axes of four-fold symmetry are chosen as the crystal- lographic axes. Usually one is assumed to be vertical and one to extend from left to right. Tabulation of the Seven Type Forms. NAME. FACES. WEISS. MILLER. Each face intersects all axes. 1. HEXOCTAHEDRON. 48 2. TRAPEZOHEDRON. 24 3. TRISOCTAHEDRON. 24 4. OCTAHEDRON. 8 Each face parallel to one axis. 5. DODECAHEDRON. 12 6. TETRAHEXAHEDRON. 24 a na : co a Each face parallel to two axes. 7. CUBE. 6 a CD a: co a Description of the Type Forms. i. HEXOCTAHEDRON. a : na : ma ; {hkl}. * Also called Tesseral, Tessular, Regular, Cubic and Monometric. 5 8 {hkl} {hkk} [hhl] {ill} {no} [hko] ISOMETRIC SYSTEM. 59 Forty-eight faces each cutting the three axes in three different, but simply proportionate distances. In the ideal forms the faces are scalene triangles. Fig. 140 shows a : %a : 3*2 ; {321}. FIG. 138. FIG. 139. mi/.^ SX\ K/& i-^f^f* The small black squares and triangles indicate axes of four-fold and three-fold sym- metry respectively. 2. TRAPEZOHEDRON. a : ma : ma ; {hkk}. Twenty-four faces, each cutting two axes equally and the third in some shorter distance bearing a simple ratio to the others. In FIG. 140. FIG. 141. FIG. 142. FIG. 143. the ideal form the faces are trapeziums. Fig. 141 shows a : 2a : 2a ; {211}. 3. TRISOCTAHEDRON. a : a : ma\ {hhl}. Twenty -four faces, each cutting two axes at equal distances, the third axes at some longer distance a simple multiple of the others. In the ideal forms the faces are isosceles triangles. Fig. 142 shows r = (a : a : 20) ; {221}. 4. THE OCTAHEDRQN. a : a : a\ {m}. Eight faces, Fig. 143, each cutting the three axes at equal distances. In the ideal form the faces are equilateral triangles. 5. TETRAHEXAHEDRON. a : na : coa ; {hko}. Twenty -four faces, Fig. 144, each parallel to one axis and cut- 6o CR YSTALL O GRAPHY. ting the other two unequally in distances bearing a simple ratio to each other. In the ideal forms the faces are equal isosceles tri- angles. Fig. 144 shows a : 20, :coa; {210}. FIG. 144. FIG. 145. FIG. 146. 6. THE DODECAHEDRON. a : a : CD a: (no). ' c ) Twelve faces, Fig. 145, each parallel to one axis and cutting the others at equal distances. In the ideal form each face is a rhombus. 7. THE CUBE. a : oo a : oo a ; {100}. FIG. 147. FIG. 148. FIG. 149. f ox*' \) r a- 4 Six faces, Fig. 146, each parallel to two axes. In the ideal forms the faces are squares. Combinations in the Hexoctahedral Class. The most frequently occurring forms are the cube a, the octahe- FIG. 150. FIG. 151. FIG. 152. dron/, the dodecahedron graphic axes. Tabulation of the Seven Type Forms. FACES. WEISS. NAME. Each face intersects all axes. 1. HEXTETRAHEDRON. 24 2. TRISTETRAHEDRON. 12 3. DELTOHEDRON. 12 4. TETRAHEDRON. 4 Each face parallel to one axis. 5. TETRAHEXAHEDRON. 24 6. DODECAHEDRON. 12 Each face parallel to two axes. 7. CUBE. 6 na : ma ma : ma a : ma a : a net : oo a a : co a co a '. co a MILLER. {hkl} {hkk} [hhl] {III} {no} {100} Descriptions of the Type Forms. i . HEXTETRAHEDRON. a\na\ ma ; {hkl}. Twenty-four faces each cutting the three axes in three different, rSOMETRIC SYSTEM. but simply proportionate, distances. In the ideal forms the faces are scalene triangles. Fig. 166. 2. TRISTETRAHEDRON. a : ma : ma ; [hkk] . Twelve faces, Fig. 167, each cutting two axes equally and the FIG. 166. FIG. 167. third in some shorter distance bearing a simple ratio to the others. In the ideal form the faces are isosceles triangles. 3. DELTOHEDRON. a:a:ma\ {hhl}. Twelve faces, each cutting two axes equally and the third in some longer distance a simple multiple of the others. In the ideal form the faces are trapeziums. Fig. 1 68 shows r = (a : a : 20) ; 221}. FIG. 168. FIG. 169. 4. THE TETRAHEDRON. a : a : a; {m}. Four faces, Fig. 169, each cutting the three axes at equal dis- tances. In the ideal form the faces are equilateral triangles. 5. TETRAHEXAHEDRON. Fig. 144. 6. THE DODECAHEDRON. Fig. 145. 7. THE CUBE. Fig. 146. Combinations in the Hextetrahedral Class. The characteristics of the crystals of this group are best shown in combinations of forms, since the simple forms are comparatively rare and the predominating form is frequently the cube. The combination of the positive and negative tetrahedrons, Fig. 170 occurs in crystals of sphalerite and tetrahedrite. The combi- 6 4 CR YSTALLOGRAPHY. nation of the tetrahedron and cube a, Figs. 171 and 172, is com- mon in boracite and pharmacosiderite. The tetrahedron with the dodecahedron d, Fig. 173, occurs in tetrahedrite, and with both cube and dodecahedron, Fig. 174, in boracite. FIG. 170. FIG. 171. FIG. 172. Figs. 175 and 176 are crystals of tetrahedrite. In Fig. 175 the negative form of n (a : 2a : 20) ; {211}; occurs and in Fig. 176 the positive form of n with the dodecahedron d. FIG. 173. FIG. 174. FIG. 175. Fig. 177 includes the dodecahedron d, the deltohedron r (a : a : 20) ; {221}; and the tristetrahedrons o = (a : ^a : 30) ; {311}; and n = (a : 2a : 20) ; {211} ; Fig. 178 shows the hextetrahedron s FIG. 176. FIG. 177. FIG. 178. = (a : | a : 3^) ; {321}; combined with the cube and tetrahexa- hedron g .-= (a : \a : oo a) ; (3 20} . ISOMETRIC SYSTEM. CLASS OF THE DIPLOID. 30. No. 4. Pentagonal Hemihedry, Liebisch. No. 2. Pyritohedral Group, Dana. Symmetry of the Class. Crystals of the common mineral pyrite FIG. 179. and of the minerals cobaltite and smaltite are symmetrical to three planes at right angles and to three axes of two-fold and four axes of three-fold symmetry, as shown in Fig. 179. Choosing Crystallographic Axes. The three axes of two-fold, symmetry are chosen as the crystallographic axes. Tabulation of the Seven Type Forms. FACES. WEISS. NAME. Each face intersects all the axes. 1. DIPLOID. 24 2. TRAPEZOHEDRON. 24 3. TRISOCTAHEDRON. 24 4. OCTAHEDRON. 8 Each face parallel to one axis. 5. PYRITOHEDRON. 12 6. DODECAHEDRON. 12 Each face parallel to two axes. 7. CUBE. 6 na : ma nia : nia a : ma a : a co a : oo a MILLER. {hkl} {hkk} {hhl} {in} {110} {100} Description of the Type Forms. i. DIPLOID. a : na : ma ; {hkl}. Twenty-four faces each cutting the three axes in three different, but simply proportionate, distances. In the ideal form the faces are trapeziums. Fig. 180 shows a positive form. FIG. 1 80. FIG. 181. 2. TRAPEZOHEDRON, Fig. 141. 3. TRISOCTAHEDRON, Fig. 142. 4. THE OCTAHEDRON, Fig. 143. 6 66 CR YSTALLOGRAPHY. 5. PYRITOHEDRON. a : na : coa; {.hko}. Twelve faces, Fig. 1 8 1 , each parallel to one axis and cutting the other two unequally in distances bearing a simple ratio to each other. In the ideal forms the faces are pentagons. 6. THE DODECAHEDRON, Fig. 145. 7. THE CUBE, Fig. 146. Combinations in the Class of the Diploid. FIG. 182. ' FIG. 183. FIG. 184. Fig. 182 shows the pyritohedron e = (a : 2a : coo) ; {210}; with the cube a. Figs. 183 and 184 show the same form with the octahedron /. FIG. 185. FIG. 186, FIG. 187. Fig. 185 shows the three forms combined. Fig. 186 shows the same pyritohedron e and octahedron / combined with the diploid s = (a : \a : $a) ; {321}; and Fig. 187 shows this diploid with the cube and octahedron. OTHER CLASSES IN THE ISOMETRIC SYSTEM. 28. CLASS OF THE TETARTOID. Three axes of two-fold sym- metry at 90 to cube faces and four of three-fold through opposite corners of the cube. Example Ullmannite. 29. CLASS OF THE GYROID. Three axes of four-fold symmetry, at 90 to cube faces, four of three-fold through opposite corners of cube, six of two-fold through diagonally opposite edges, amples Sylvite, sal-ammoniac. Ex- ISOMETRIC SYSTEM. 6? IMPORTANT SUPPLEMENT ANGLES BETWEEN ADJACENT FACES IN ISOMETRIC CRYSTALS. CUBE 90 OCTAHEDRON 70 31' DODECAHEDRON 60 CUBE TO OCTAHEDRON 54 44' CUBE TO DODECAHEDRON 45 OCTAHEDRON TO DODECAHEDRON 35 i^ Polar Edge. Other Edges. Tetrahexahedra 320 46 n' 22 37' 210 36 52 36 52 3io 25 50 53 17 Pyritohedra 320 67 22 62 30 210 53 7 66 25 310 36 52 72 32 Edge in Axial Plane. Trapezohedra 311 35 5' 50 28 211 48 ii 33 33 322 58 2 19 45 Edge in Diagonal. Edge in Axial Plane. Other Edges. Hexoctahedra 321 21 47' 31 o' 21 47 421 17 45 25 12 35 57 CHAPTER VIII. THE GROUPING OF CRYSTALS AND THEIR IMPERFECTIONS. Crystals are more frequently grouped than isolated and with respect to their grouping may be divided into symmetrically grouped or "twin" crystals and unsymmetrically grouped crystals, usually known as crystal aggregates. TWIN CRYSTALS. Crystals frequently form which consist of two individuals, one of which is reversed with respect to the other. In such crystals re-entrant angles are common. FIG. 188. FIG. 189. Such growths are called twin crystals. If the individuals inter- penetrate they constitute a penetration twin. If simply in contact along a certain plane they constitute a contact twin. Fig. 188 shows a contact twin octahedron very frequent in the spinel group. Fig. 189 shows the corresponding penetration twin. Symmetry of Twin Crystals. The crystal may be (a) symmetrical only to a line called a "twin axis," always parallel to a possible edge of the crystal but never an axis of two-, four- or six-fold symmetry. Fig. 190 shows pyroxene with the twin axis parallel to a prism edge. Fig. 191 shows the "Iron Cross" of pyrite, a twin pyritehedron with the twin axis a cubic edge. Fig. 192 shows quartz with the twin axis parallel a prism edge; these frequently penetrate and as the positive 68 THE GROUPING OF CRYSTALS. 69 rhombohedron of one coincides with the negative of the other, the twin structure is then only recognized by etching. FIG. 190. FIG. 191. FIG. 192. (b) Symmetrical to a twin axis and also to a "twin plane" at right angles to the axis. The plane is always parallel to a possible face of the crystal but never a plane of symmetry for either individual. Fig. 193 shows an aragonite twin, the twin plane a prism face. Fig. 194 shows a twin cube, the twin plane being an octahedral FIG. 193. FIG. 194. FIG. 195. face. Fig. 195 shows a twin of albite, the brachy pinacoid being the twin plane. Repeated Twinning. Frequently there is a repetition of the twinning, a third indi- vidual occurring reversed upon the second, a fourth upon the third, and so on. If the successive twin planes are parallel the phenomenon is called "poly synthetic twinning" the individuals may be thin lamellae and the re-entrant angles striae. Fig. 196 shows the polysynthetic twinning of albite. CR YSTALLOGRAPHY. If the successive twin planes are oblique to each other repetition may lead to " circular forms" as in orthorhombic marcasite with the prism face the twin plane, Fig. 197, because the prism angle 74 55' is approximately one fifth of 360. FIG. 196. FIG. 197. FIG. 198. Sometimes the "circular form" is pseudosymmetrical and ap- proximates a higher class of symmetry; for instance, repetition of Fig. 193 leads to pseudohexagonal forms, Fig. 198, the prism angle being 63 48'. CRYSTAL AGGREGATES. Crystals of any substance even when not grouped symmetrically may be grouped with a degree of regularity characteristic of that particular occurrence of the substance and sometimes character- istic of many occurrences. The Individual Crystals of an Aggregate. Unless formed while floating, like snow crystals in air, or gypsum crystals in clay, or leucite in a molten magma, the individual crystal will not be completely bounded by plane faces. If formed in a cavity attached to and projecting from the rock the opposite ends will be plane faced and so much of the rest as is free. As compactness increases the plane faces diminish in number and may entirely disappear, although the individual may still be evident. Finally, the individuals may be microscopic and the mass dense. Terms Dependent on the Shape and Grouping of the Individual Crystals of an Aggregate. Whether showing plane faces or not the individuals may be distinguished as to their shape by such terms as : THE GROUPING OF CRYSTALS. 71 Columnar when the individual crystals are relatively long in one direction, Fig. 199. Bladed a variety of columnar in which the columns are flattened like a knife blade. Fibrous a variety of columnar in which the columns are slender threads or filaments, Fig. 200. Lamellar when the individual crystals appear as layers or plates, either straight or curved. Foliated a variety of lamellar in which the plates separate easily. FIG. 199. FIG. 200. Columnar Beryl. Fibrous Serpentine. Micaceous a variety of lamellar in which the leaves can be obtained extremely thin. Granular when the individual crystals are angular grains, either coarse or fine. Impalpable or dense a variety of granular in which the grains are invisible to the naked eye. With respect to the grouping, the individual crystals may be: Parallel in crystals with plane faces this may extend to all cor- responding faces and edges, Fig. 201, and may be recognized by the simultaneous reflection of light from parallel faces, or it may be partial with respect to an edge or a face. 7 2 CR YSTALLOGRAPHY. In crystals lacking plane faces there result parallel fibers, blades, columns, lamellae, etc. FIG. 201. Parallel Copper Crystals. Radiating diverging from a common center. Reticulated crossing like the meshes of a net, Fig. 202. Resetted overlapping like the petals of a rose. Drusy minute crystals resting close together on a common underlayer, giving a rough sand-paper like surface. FIG. 202. Reticulated Stibnitc. THE GROUPING OF CRYSTALS FIG. 203. 73 Reniform Hematite. FIG. 204. Botryoidal Prehnite. FIG. 205. Stalactitic Gibbsite. 74 CR YSTALLOGRAPHY. Terms Describing the External Shape of Aggregates. Many terms are used. The more important of these are: Reniform with the shape of a kidney, Fig. 203. Botryoidal resembling a bunch of grapes, Fig. 204. Mammillary natter but rounded shapes. Pisolitic small rounded particles the size of a pea. Oolitic similar but smaller like fish roe. Nodular occurring in separate rounded lumps or nodules. Stalactitic in* hanging cones like icicles, Fig. 205, 206. FIG. 206. Stalactite of Limonite. Cockscomb the free ends of radiating crystals forming a ridge. Plumose like a feather. Sheaf -like resembling a sheaf of wheat. Arborescent or Dendritic branching like a tree, Fig. 207. Mossy similar to dendritic but a more minute structure. Coralloidal like coral in form. Amygdaloidal almond-shaped. Wire-like as in silver. Geode a hollow nodule lined with crystals. TERMS OF GROWTH AND "HABIT." Dependent upon the conditions of growth crystals may be " Embedded" in a groundmass, Fig. 208, or "Attached" by one end to the rock and extending into free space. The former has a chance for complete plane faced boundaries, the latter necessarily lacks some of the faces. THE GROUPING OF CRYSTALS. FIG. 207. 75 Arborescent Copper. Habit. The term habit is used to express the usual or prevailing shape of the crystals of a substance. The habit under one set of condi- tions at formation is fairly constant, both as to occurring forms and their relative development. The habit for another set of FIG. 208. 7 6 CR YSTALL OGRAPHY. conditions (another locality) may involve just the same forms with a different relative development or the forms themselves may be different. The principal terms of habit are: Prismatic Habit. Notably elongated in one direction, which is liable to be the direction of the optic axis or of an axis of symmetry or of the intersection of cleavages. Tabular Habit. Notably extended parallel some prominent plane, either a cleavage or, if uniaxial, at right angles to the optic axis. Other terms, as cubic, octahedral, pyramidal, with the prefix habit, imply that the usually dominant form is the cube, octahedron and pyramid respectively. Figs. 209 and 210 represent quartz crystals composed of the same common forms m { lolo j , p { ioli } , p {oiTi } , in Fig. 209 the FIG. 209. FIG. 210. FIG. 211. equivalent faces are equal sized, in Fig. 210 they are not, but in each case equivalent faces are directions of equivalent structure, and the crystal symmetry and interfacial angles are the same in both. Sometimes the forms appear to be of higher or lower symmetry than that proper to the substance, for instance, the not unusual combination in zircon of the forms p {in} and a = {100} may develop as in Fig. 211 suggesting the isometric dodecahedron, although the supplement angles p : p and p : a instead of being 60 are respectively 56 40' and 61 40'. Conversely, the isometric dodecahedron sometimes develops so as to closely imitate the prism fiooj and pyramid {in} of zircon. THE GROUPING OF CRYSTALS. 77 Skeleton Crystals. If the material comes faster to the edges than elsewhere the faces become relatively depressed or hopper-shaped as in cuprite, Fig. 212, or if the dominant accretion is at the solid angles com- posite patterns like those of snow crystals or gold may result. FIG. 212. FIG. 213. FIG. 214. Sometimes the faces build up most quickly, leaving the edges relatively depressed, as in quartz. (d) Microlites* Microscopic, not easily identified rods and needles frequently rounded or frayed at the ends, Fig. 213. IRREGULARITIES OF FACES OF CRYSTALS. The perfectly smooth and plane crystal is difficult to find, except in very minute crystals. Striated Faces. Crystal faces are frequently marked by parallel lines or fine "grooves" called "striations" each of which is bounded by two definite planes. That is, they are parallel to edges. Usually they line a face in one direction only, sometimes in two, or more often three, and frequently not intersecting but branching feather-like from a common line. They may occur on simple crystals as in chabazite, but often are due to repeated or polysynthetic twinning, Fig. 196. If the indi- viduals are thin the reentrant angles become grooves or striations. Fig. 215 shows twinning striations on a magnetite crystal from Port Henry, N. Y.* At other times striations result from an oscillation or contest between two crystal forms. This is true of the striations on the * Crystallites, a name applied to minute forms not crystalline in shape, are now held to be molecular mixtures of different substances. CR YSTALLOGRAPHY. prism faces of quartz, which are due to an alternate formation of prism and rhombohedron ; or the striations on pyrite due to an oscillation between the cube and the pyritohedron, Fig. 215. FIG. 215. Striated Pyrite, Aspen, Colo. After S. Smillie. False or Apparent Faces. Oscillatory stria may be so frequent as to give rise to an apparent plane made up of these edges. It will not reflect a signal. Ap- parent faces may also result from the contact of the crystal during growth with an already formed crystal. Vicinal Faces. Prominent faces with simple indices are sometimes replaced wholly or in part by flattened pyramids, the faces of which are in definite zones but with complicated indices. Concentration currents which are too feeble to completely cover the larger faces are a possible explanation. Like etch figures, they usually belong to forms which prove the true symmetry of the crystal. Roughened or Coated Faces. The faces of crystals may be coated with minute crystals of the same or some other substance. Sometimes only particular faces are so covered. Secondary growths and natural etchings may also roughen faces. Curved Faces. Curved faces are not frequent and are nearly always convex. They may be due to strains after formation which exceeded the elastic limit as in stibnite, gypsum, galenite. THE GROUPING OF CRYSTALS. 79 Sometimes the edges appear to have been melted as in many apatites, augites and hornblendes. Apparently Curved Faces. A rounded effect may be produced by many true faces in one zone, as in beryl, or by a series of vicinal faces each nearly parallel to the preceding as in diamond. Crystals also appear curved because composed of individual smaller crystals only approximately parallel as in dolomite or siderite. INTERNAL PECULIARITIES. Zonal Structures. The deposition of layer after layer on the growing crystal is not usually observable unless there has been an intermittent growth or some change in the composition of the material de- posited. Intermittent growth permits between layers the de- positing of dust or fine lamellae of a foreign substance and this may be repeated several times. Such may be the explanation of "phantoms" in which an earlier stage of growth is delicately outlined as in quartz, gypsum and fluorite. There may also result parallel planes of easy separation, e. g. t capped quartz. Often the inner kernel is like the outer hull in shape but it may be a different form, e. g., calcite kernel (0112) hull (ion). Change of composition tends to layers of different colors or transparency, any of which reveal the zonal structure. California tourmalines are good examples. The partial decomposition of a crystal may also develop or make visible the zonal structure. Hour- Glass Structure. This is essentially a variety of zonal structure with the revealing of the "growth pyramids" upon each face of the nucleus, the total shape suggesting an hour glass as in many augites. Inclusions. Foreign substances shut in a crystal during rapid solidification may be solid, liquid or gaseous. Solid inclusions may be separa- tions from enclosed magma or aqueous solution, or due to altera- tion or be mechanically retained during crystallization of an impure mixture. Such solids are: 8o CR YSTALLOGRAPHY. (a) Glass, from enclosed magma. (b) Crystals from magma or solutions, often microlites or long prismatic like rutile (Fig. 216), actinolite or tourmaline in quartz, or plate-like, as in the minute scales of iron oxide in hypersthene, sunstone or carnallite. FIG. 216. Rutile in Quartz, N. C- (c) Sand or other associated material as in the crystals of calcite called Fontainebleau limestone, which contains sometimes as much as sixty percent of silica. These solids may show no evidence of arrangement or may be definitely arranged as in the case of the magnetite in mica or the carbonaceous material in chiastolite as shown in successive sections of a crystal in Fig. 217. FIG. 217. Liquid Inclusions. Chalcedony, quartz, topaz, halite, and other species frequently contain microscopic cavities partially filled with water, brine, liquid carbonic acid and other liquids. Gaseous Inclusions. Occur in round and simple cavities or negative crystals.* Usually the gas is under high pressure and may be water vapor, hydrocarbons such as marsh gas, nitrogen and carbonic oxide. THE GROUPING OF CRYSTAL. 8 1 INTERGROWTHS AND PARALLEL GROWTHS OF TWO DIFFERENT MINERALS. Crystals of two minerals forming at the same time may : (a) Mutually penetrate each other, for example, quartz and orthoclase in graphic granite. (b) Arrange themselves with a certain face or edge of one parallel to a corresponding part of another; for example, staurolite and cyanite with brachy pinacoids parallel. (c) The larger mass may orient the smaller; for example, prisms of rutile on hematite with the prism edge of rutile perpen- dicular to an edge of hematite and the prism face of rutile in contact with basal plane of hematite. Form of Amorphous Minerals (Colloids and Glasses). Natural minerals of colloidal origin (see p. 235) are frequently reniform (kidney-shaped), botryoidal (grape-shaped), stalactitic, and in other rounded shapes. With lack of space they may be dendritic. Often cracked as result of drying. Natural glasses often show fluidal texture. * Supposed to form when the shut in liquid contains more molecules of the same material as the host. Their separation against the walls of cavities give the faces CHAPTER IX. THE DETERMINATION OF THE GEOMETRICAL CONSTANTS OF A CRYSTAL. This chapter outlines* a simple method in crystal examination with a one circle goniometer, stereographic projection and graph- ical or zonal solutions, under the principal divisions of: I. Measurement of the Interfacial Angles. II. Stereographic Projection. III. Determination of Symmetry and Selection of Elemental Faces. IV. Zonal and Graphic Determination of Indices. V. Calculation of Axial Elements. To this is added: VI. Crystal Drawing. I. MEASUREMENT OF INTERFACIAL ANGLES. The angles between smooth bright faces can be measured to half minutes or even closer on a one circle reflecting goniometer as follows: The available crystals are carefully examined. Good crystals with bright smooth faces are more apt to be found among little crystals than large ones. During examination they are handled by either a pencil of wax or by the forceps, never by the fingers. Each selected crystal is studied with a hand-glass and a sketch is made, usually a horizontal projection of the crystal with some selected zone vertical such as is described p. 6. The Goniometer. Among "one-circle" goniometers one of the best and simplest is the Fuessf (4, A) shown* in Fig. 218. * For a more complete description of the same course see A. J. Moses, in the School of Mines Quarterly, Vol. XXVII, July, 1906, p. 432. f R. Fuess, Steglitz, near Berlin, marks 260, or about 65 dollars. 82 GEOMETRICAL CONSTANTS OF A CRYSTAL. 83 The axes of the two telescopes, C and T, are in the same hori- zontal plane and intersect in the axis of rotation. Before the objective of the observation telescope T is an extra lens which brings the crystal into focus. When it is raised the telescope is focused through the collimator, upon the light. The crystal carrier, shown between the telescopes, includes three motions in straight lines at right angles to each other (by the axis and the slides n and 0) and two tipping motions on circular arcs at right angles. The crystal is attached by wax at p and the desired edge* made coincident with the axis of rotation. FIG. 218. The Measuring. The telescope T is set at 100 to 120 degrees to the collimator C, the graduated circle and crystal are turned together by the wheel/, Fig. 218, until the reflected signal, Fig. 219, is seen through the telescope, the screw a is tightened, the fine adjustment made by the tangent screw F, and the vernier read. The screw a is again loosened and the rotation continued until the signal, Fig. 219, is received from a second face; this is centered * With small ciystals all the angles of a zone may be measured with one adjust- ment. 84 CRYSTALLOGRAPHY. by F and a and recorded as before. The difference between the two readings is the supplement angle* between the faces. The best order of measurement, methods of recording, averaging of corresponding angles, adjustments of apparatus, and other details are given in the more complete descriptions. FIG. 219. FIG. 220. ^ \ x-/*TN I * ^' .' **. II. THE STEREOGRAPHIC PROJECTIONf OR STEREOGRAM. That is {he projection of an imaginary surrounding sphere upon its equatorial plane by lines drawn to its south pole. The crystal is assumed to be surrounded by a sphere, the centers of the sphere and the crystal coinciding, and radii to be drawn from the center perpendicular to each face of the crystal. From the point P where any such radius cuts the surface of the sphere (called the pole of the corresponding face) a line, Fig. 221, is supposed to be drawn to the south pole S, and the point P' where this line pierces the equatorial plane is the stereographic projection of the face. The method of projection varies with the face. A very brief outline would be as follows: Select the plane of projection, usually perpendicular to a zone of prominent or numerous faces, or to an apparent axis. Draw a circle of any convenient diameter, and let the point B, Fig. 222, be taken as the pole of a chosen vertical face. * Because under the conditions stated both telescopes are fixed in directions, say OC and TO, Fig. 220. If ON and ON' are the normals to the two crystal faces NON' will be the supple- ment angle between the faces. The two reflections will occur when ON and ON' respectively bisect COT. The difference in rotation to these positions being NON r . t By this method vertical zone-circles project as diameters, oblique zone circles as circles, each passing through both ends of a diameter and face-poles project as points Small circles also project as circles. The entire projection is called a "stereogram." The zonal relations and the spherical triangles are therefore all represented; and can be graphically solved or calculated. GEOMETRICAL CONSTANTS OF A CRYSTAL. 85 FIG. 221. Perspective of a Stereographic Projection. Projecting the Vertical Faces. Measure the supplement angles between this face and any other vertical face L and lay off the corresponding arc BL upon the circumference, thus determining the projection of L. Projecting Oblique Faces on Known Diameters. If any oblique face lies in a zone with a horizontal and a vertical face its projection is on the diameter through the vertical face. If the face makes equal angles with any two vertical faces, its projection is on the diameter midway between the diameters through the projections of the two vertical faces. In either case the distance of the desired projection from the center may be found by laying off CD, Fig. 222, equal to the angle with the horizontal face (or BD equal the angle with the vertical face of the same zone) and drawing DS. Then is OR the desired distance,* and is laid off upon the proper diameter (in this case on BB). * The distance may be laid off by a protractor, devised by Professor Penfield, in which the values of the stereographically projected degrees have been determined for a circle of convenient size. 86 CR YSTALLOGRAPHY. Projecting Oblique Faces on Known Oblique Zones. If during measurement an oblique face is found to lie in an oblique zone with three (or even two)* already projected faces, the circle drawn through these three points is the zone circle upon which the desired projection lies.f FlG. 222. In Fig. 222 let BPB be such a circle and Q a face in the same zone, then to project Q. Draw the diameter CS at 90 to BB, draw BZ through X the intersection of CS with the_zone circle. Find Y a quadrant's distance from Z and draw YB, its inter- section with CS is F the projection of the "pole of the zone." Then 'measure the angle between the oblique face Q and any known face P of the zone. Draw a line from F through the known face (P), prolong it, cutting the circumference at 7, lay off JK equal to the supplement angle between the faces P and Q and draw KF, intersecting the zone in the desired projection of Q. Projecting an Oblique Face not in a Known Zone. This involves angles between the unknown face and two (or three) known faces. Preferably these are vertical faces or the * Problem 4, p. 23, Characters of Crystals, by A. J. Moses. t The Penfield stereographic protractors include a protractor of celluloid with projected semicircles for each degree by which the corresponding radius may be determined and another protractor by which any angle may be laid off on any oblique zone. GEOMETRICAL CONSTANTS OF A CRYSTAL. 87 horizontal face. The projection then' involves the drawing of projected small vertical and horizontal circles. Failing these oblique small circles must be drawn.* in. DETERMINATION OF THE SYMMETRY AND THE ELEMENTAL FACES. Determining the Symmetry.f This can usually be determined by two tests directly from the stereographic projection. 1. If by revolving a tracing of the projection on the projection itself about the coincident centers, all the poles of the tracing coincide with those of the projection more than once in a complete revolution, then an axis of two-fold, three-fold, four-fold or six- fold symmetry exists in the crystal perpendicular to the plane of projection. 2. If by folding the paper tracing on any diameter, all the poles of the one half cover those of the other, then this diameter is the trace of a plane of symmetry perpendicular to the plane of projection. The following table will identify the "system" unless a very unimportant zone has been chosen as the vertical zone. Symmetry Diameters of Center. of Symmetry. System. Six-fold Six or none Hexagonal Four-fold Four, two or more Isometric or Tetragonal Three-fold Three or none Hexagonal or Isometric Two-fold Two or none Isometric or Orthorhombic Two-fold None Monoclinic None One Monoclinic None None Triclinic The isometric crystal will always yield the same projection for some other position, also in projections of isometric crystals there are three points 90 apart which are surrounded by the same group- ing of planes. In tetragonal projections there are two such points. * Explained in detail in School of Mines Quarterly, Vol. 27, p. 441. t This is tentative, other crystals of the same substance may reveal faces which lower the symmetry. Indeed the true symmetry of a crystal is known only when all the characters have been considered. Structurally equivalent directions not only imply similar groupings of bounding faces but physical identity in all respects. 88 CR YSTALLOGRAPHY. Choosing Elementary Faces. The three axial planes (100), (oio) and (ooi) and the "para- metral" plane (in) are essential to the determination of axes, parameters and indices. The axial planes are each parallel to two crystal axes (or con- versely the crystal axes are parallel to their intersection), their choice therefore is dependent on the symmetry. If any (hkl) face occurs it may be chosen as (in) or lacking such a face any two of (okl), (hoi), (hko) may be chosen as (on), (101) or (no) and from these the position of (in) be found. IV. ZONAL AND GRAPHIC DETERMINATION" OF INDICES. Zonal " Indices." All edges of a zone are parallel. Their common direction is called the zone^xis. There must be a radius in a spherical pro- jection parallel to each zone axis, and this radius is known if the indices of the point at which it cuts the sphere are known. These three numbers are called zone indices and may be derived from the indices of any two faces of the zone* by cross mul- 905 tiplication and subtraction of f the twice written indices (strik- ing off end terms and reading down alternately from left to 100 right and from right to left). For instance, in Fig. 223, a zone with i = (133) and g = (311), the values of the zone indices [uvw] are obtained as follows: FIG. 223. 010 30 3313 XXX 1131 u = 3 - 3 = o v = 9 i =8 or [uvw] = [088] = [on] w = i 9 = 8 Face in Two Zones. The indices of a face in two zones result from a similar cross multiplication of the two sets of zone indices. For instance, if a face h, Fig. 223, lie in the zone of i = (133) and g = (311) for * Miller's Treatise on Crystallography, 1839, pp. 7. 8 and 10. GEOMETRICAL CONSTANTS OF A CRYSTAL. 89 which the zone indices are [oil] and also in the zone of b = (335) and c = (395) for which similarly the zone indices are [503], the values of (hkl) the indices of the face h are (355) for XXX 1 3 5 < h = 3 o k = 5 ~ o or (hkl) = (355) I =o +5 Various special and more rapid methods of utilizing zone indices exist, for instance, In any zone passing through two of (ooi), (oio), (100). Every face in the zone will have that index zero which is zero in both. That is: For zone (ooi), (oio) the type symbol is (okl), " " (ooi), (100) " " " " (hoi), 11 " (oio), (100) " " " " (hko). Even more useful is the determination of symbols by zones through one of (ooi), (oio) or (100). The ratio of the two indices, which are zero for (ooi), (oio), or (100), is constant for all faces of the zone. Hence: Zones through (ooi) h/k constant, " (oio) A// " , (100) k/l " . If then an unknown face lie at the intersection of two such zones and the indices of one face in each zone are known the indices of the unknown face become known. For instance, Fig. 223, the same unknown face h lies in a zone with (oio) and (305) and also in a zone with (100) and (in). To substitute in hkl we have therefore From first zone, 3, -, 5, From second zone, , I, i. Remembering these are ratios and combining by inspection, the indices of the face h must be (355). Similarly the indices of the face b must be (335) and of k must be (on) and e (131), ^tc. Graphical Determinations of Indices. It will usually happen that only the indices of a few faces can be obtained directly by zonal equations, certain factors being CR YSTALLOGRAPHY. lacking. Simple graphical constructions can be made which will give a fresh start. The devices are numerous and one such is briefly described.* To Find the Indices of P = hkl. The methods vary a little with the system. Two of the three relations-, 7 and 7 need to be determined, for instance: K I I (a) Finding - from (no) and the corresponding (hko) . Find T, Fig. 224, the intersection of the radius through no and the tangent at 100. Take RT parallel to CA as unity. FIG. 224. OKI Oil R 010 FIG. 225. Then the radius through (hko) will cut this line RT at a point T such that h ( \ first index 3 . RT = 7 or RT' = ^~T~ = in Fig. 224. k \ ) second index 2 (b) Finding -j from on and the corresponding okl. Graphically or from the records of measurements determine the angle (ooi) A (on). For convenience lay this off in the fourth quadrant as A'E, Fig. 225, and find T the inter- * These graphic solutions were described by A. J. Moses and A. F. Rogers in School of Mines Quarterly, Vol. 24, pp. 11-22. GEOMETRICAL CONSTANTS OF A CRYSTAL. 91 section of the corresponding radius with the tangent at B. Take RT parallel CB as unity. Similarly measure the angle ooi A okl, lay this off from A' as A'D and find the intersection T', Fig. 225, of the corresponding radius with RT, then k I RT = -j = -in Fig. 225. The same angles are used in Fig. 225 as in Fig. 224; hence com- bining by inspection with - = T we have rf- /V -, I, 2, that is 324 satisfies both, hence P = (hkl) = (324). V. THE CALCULATION OF AXIAL ELEMENTS. Simple formulae in terms of the indices and interfacial angles are most used. For the fairest average every available measured angle should have due weight. Considering the systems in order: The Isometric System. In this system the parameters are equal and the angles between the axes are right angles. The Tetragonal System. Taking the parameter a = I the only axial element is c. The formulae of the orthorhombic apply if a is made equal unity (a = i). The Orthorhombic System. Taking the parameter 6 = I the axial elements are a and c. The simplest formulae are: a = - tan (100) A (hko)', c = - tan (ooi) A (ofe/). K K Similar but somewhat more complex formulae exist for the (hkl) angles. The Hexagonal System. Taking the parameter a = I the only axial element is c. 92 CRYSTALLOGRAPHY. The simplest formulae for this are c = T cos 30 tan (oooi) A (kohl) = tan (oooi) A (hh2hl). The Monoclinic System. Taking the parameter b as unity the axial elements are the values of a and c and of the acute angle (3 between the vertical and clino axes. = (100) A (ooi), cos (ooi) A (hko) )S * = cos (oio) A (hko) ' The simplest formulae for d and c are h cot (oio) A (hko) = k~ sin ft ~ ' I tan (ooi) A (okl) = k~ sin ft The Triclinic System. The axial elements are the parameters &, b and c, in which b is taken as unity and the angles between the axes a = b A c, ft = a A c and 7 = 6 A d. The formulae are much more complex; for instance the simplest is a _ \sm (S - AC) sin (S - AS) 1 2 ~ M sin 5 sin (5 - BC) in which ^1 = (100), C = (ooi), 5 = oio and 5 = $(AB + B.C + ^C). VI. CRYSTAL DRAWING. Clinographic and orthographic projections of crystals are much used in illustration. Clinographic Projections. In clinographic drawings the crystal is projected upon a vertical plane by parallel rays oblique to the plane of projection. The eye is assumed at an infinite distance a little to the right and above the center of the crystal. GEOMETRICAL CONSTANTS OF A CRYSTAL. 93 The figures obtained in this way have an appearance of solidity, all parallel edges are parallel and all points in a given line remain the same proportionate distances apart. The drawing consists chiefly of two stages, first finding the "axial cross" of the crystal, that is the true projection of the crystal axes cut off at the parameter lengths; second, finding the direction of the projection of any edges from the indices of the intersecting planes. Construction of " Axial Cross." All axial crosses are derived from the projection of three equal lines at right angles, that is, from the isometric axial cross* for constructing which formulae exist dependent on the direction of the line of sight. For other systems the necessary changes! are made in the directions of these isometric axes and then each is changed in length to fit the parameters of the species. Thus in a monoclinic species the an- FlG. 226. gle between the clino and vertical axes being known the projection of the front to back isometric axis is replaced by the projection of a line equal in length to an isometric axis but in the direction^ of the desired clino axis. These three lines, Fig. 226, are then lengthened or shortened in the propor- tions given by the parameters of the species. If a : b : c = 0.73 : 1 : 1.23, the left to right axis is not changed, the vertical is made 1.23 times its isometric length and the front to back axis 0.73 its isometric length DD. * For the drawings of this book the projected isometric "axial cross" consists of three lines. OA : OB : OC = 37 : 100 : 104, in lengths intersecting at a common center and with BOC = 93 8', AOC = 116 17'. See Fig. 226. t See A. J. Moses, Characters of Crystals, pp. 79-84. t To obtain this direction in perspective proceed as follows: Upon the isometric "cross" layoff Or = OC^cos ft and On = OA sin ft, Fig. 226. Complete the parallelo- gram OrDn\ then is DD the projection of a line equal in length to an isometric axis but in the direction of the desired clino axis. 94 CR YSTALL O GRAPHY. Determination of the Direction of Edges.* The unit form is obtained by joining the extremities of the axial cross by straight lines, and other simple forms are easily drawn by methods which suggest themselves. The projection of the edge between any two planes may be derived from the re- ciprocals of the Miller indices or the Weiss coefficients as follows: For instance in Fig. 227 let OA, OB, OC be one half of any projected axial A y .-'** cross and the problem be to find the pro- jection of the edge between two planes for which the symbols are: The dome oo a : b : \c or (041), _ The prism a : b : ooc or (no). The respective Weiss coefficients or reciprocal Miller indices are oo : i : 4, and I : I : oo . Dividing each by the third term, which is equivalent to moving each face parallel to itself until it cuts c at its parametral value OC, The dome oo : J4 : i ; The prism o : o : I . The traces of these planes on AOB are respectively YY and OS. These traces intersect at 5. The two planes have therefore one point in common at S and one at C, hence the desired projected edge* is parallel SC. All other intersections may be obtained in the same manner on the axial cross. Construction of the Figure. Generally the principal forms are drawn first and the minor modifying planes later, either in ideal symmetry or so as to indicate the relative development of faces and forms. A second axial cross may be drawn parallel to that used in determining the edge directions and these may be transferred by triangles. * Prismatic traces, such as OS for (no), involve considering the trace of the corresponding pyramid, that is, o : o : i means a line OS through the centre parallel to AB (not drawn), the trace of the pyramid (in). GEOMETRICAL CONSTANTS OF A CRYSTAL. 95 Orthographic Projections. (See Figs. 6 to 10.) The projection upon a plane by lines perpendicular to that plane. Usually a prominent zone is placed perpendicular to the plane of projection and its faces appear as lines inclined to each other at their true values. The Projection of Oblique Edges is very much as in clino- graphic projection. If, as is usual, the plane of projection is the plane of two crystal axes then the projection of any oblique edge is obtained by drawing the axes, and finding the traces of each plane by laying off on these axes the proper intercepts.* The inter- section of any two traces is a point of the edge, the intersection of the two axes is another. If a stereographic projection upon the same plane has been made the tangent to the outer circle at the point where it is cut by the zone of the two planes is the direction of their edge. * As in clinographic projection, the intercepts are reduced so that the third term is unity. CHAPTER X. CRYSTALLO-OPTICS. Light, the agent which by its action on the retina produces the sensation of vision, is transmitted in any homogeneous medium in straight lines which may be called light rays. There is a vibration, or a waxing and waning of force, at right angles to the direction of transmission which may be designated in direction and intensity by a straight line at right angles to the direction of advance and may for convenience be called a vibration. In common light these "vibrations" may be thought of as constantly altering in direction though always in the same plane and changing so rapidly that the effect during the period of a distinct impression upon the retina is an average of many. It is possible, however, by certain methods later to be explained to reduce these vibrations of many orientations to one direction, that is, to "polarize" com- mon light. Reflection. Rays of light falling on a polished surface are reflected and follow two laws. 1. The angle of incidence is equal to the angle of re- flection. 2. Both rays are in the same plane perpendicular to the re- flecting surface. Let MM', Fig. 228, be a section of a mirror. The hand at O appears to be seen at 0' by the eye at , the line 00' being perpendicular to the mirror and bisected by it. The an- gles i and i f are equal. 96 CRYSTALLO-OPTICS. 97 Refraction. Rays of light in passing obliquely from one medium to another in which the velocity of transmission is different are bent or refracted. If the velocity is lessened the bending is towards the perpendicular to the surface of contact, if the velocity is increased the bending is away from the perpendicular. Thus in Fig. 229 let AB represent the surface of contact and let the light velocity be slower in the lower medium. Any ray of light CO on entering this medium is bent towards the perpendicular ON and follows a path such as OD, similarly C'O follows OD> '. Conversely if the light travels in the opposite direction, on reaching AB the rays would be bent from the perpendicular ON. Index of Refraction. It has been proved that whatever the angle of incidence, the ratio of the sines of the angles of incidence and the angle of refrac- tion is constant for the same two media and equal to the ratio of the velocities of the incident and the refracted ray. That is, sin i Vi n = ~. = "TT . sin r V 2 sin i ab , Thus in Fig. 230 the ratio -7 or is equal to the ratio sin r cd sin V a'V ~ / or "717 This constant ratio for any two media is called sin r' c'd' the index of refraction of the second medium with respect to the first. Unless otherwise specified a stated index of refraction assumes the first medium to be air.* There is no refraction with normal incidence. With a plane- parallel plate the ray emerging at the second surface is parallel to the ray entering at the first surface. If the indices of refraction of two media with respect to air are known the direction of any ray after bending may be found by drawing concentric circles as in Fig. 230 with radii correspond- ing to these indices. In the circle corresponding to the first medium a diameter is drawn parallel to the incident ray. From its end T (or T'), Fig. 230, a line perpendicular to the surface is * The absolute index of refraction assumes Vi to be the velocity of light in a vacuum. 9 8 CR YSTALLOGRAPHY. drawn, the point c (or c') where it cuts the second circle is a point of the refracted ray OD (or OD'). Total Reflection. If the angle of refraction is greater than the angle of incidence, as is the case when light travels faster in the second medium, FIG. 229. FIG. 230. V V there is a so-called "critical" angle of incidence for which the angle of refraction is 90; that is, the refracted ray travels along the border surface. For any angle of incidence greater than this the light is totally reflected. In Fig. 231 constructed on the same values as Figs. 229 and 230 rays like DO and D'O follow paths OC and OC' in the second medium, but some ray 10 at the critical angle Z follows the path OB. All rays incident at greater angles than Z, such as MO, fail utterly to penetrate the second medium and are totally reflected as along OP. The value of the critical angle is easily found from the indices of refraction of the two media, let n be that of the first, and n' that of the second, then n sin i = n' sin r, but if r is 90 sin r = I, that is, n sin i = n' or sin i = . If the second medium is air n n' = i and the index of refraction of the first medium is n = - sin ^ Dispersion. When white light passes obliquely from oae medium into an- * The ray at the critical angle is found graphically by drawing a tangent at x, Fig. 230, thus finding y a point of the desired diameter. CR YSTALL O- OPTICS. 99 other, it is decomposed into a spectrum consisting of many kinds of light which are differently colored.* These component so-called monochromatic lights have each a different wave-length! which can be closely calculated. For in- stance, in million ths of a millimeter some prominent colors are: Violet Hj 393.3, Blue FI 486, Green E 526.9, Yellow D x 589.5, Red C 656.2, Red A 760.4. With nearly all substances the shorter the wave-length the greater the refraction of the light, that is, the violet is most bent, the red least. It follows therefore that indices of refraction differ with the light used and should be obtained with monochromatic light. OPTICAL GROUPS. According to their optical symmetry crystals may be classified as: I so tropic. Isometric. Anisotropic, Uniaxial. Hexagonal and tetragonal. Anisotropic, Biaxial. Orthrohombic, monoclinic, and triclinic. THE OPTICALLY ISOTROPIC CRYSTALS. Any normal isometric crystal shows the same optical properties in all directions, and is therefore optically isotropic. J Ignoring a few salts which crystallize in class 28, p. 66, and are circularly polarizing in all directions the following statements, hold: The Index of Refraction of any isometric crystal is a constant for all directions of transmission. Absorption increases with the thickness and may be selective, giving color, but in any one crystal equal thicknesses in different directions give equal absorption and the same color tint. That is, the optical tests on isotropic crystals are limited to color, index of refraction and absence of double refraction. * With plane parallel plates the light emerging from the second surface is parallel to the entering light and the color is not noticed. With a prism of proper angles the divergence is increased at the second surface of contact and a spectrum obtained. t The distance light advances during a complete vibration is called its wave-length. t Isotropic media behave alike in all directions with regard to light phenomena. Most liquids and glasses are isotropic. 100 CR YSTALLOGRAPHY. THE GENERAL PROPERTIES OF ANISOTROPIC CRYSTALS. Ahisotropic media do not behave alike in all directions. As all crystals except those of the isometric system show different optical behavior in directions not parallel they are said to be optically anisotropic. All anisotropic minerals are doubly refracting in most directions but possess either one or two directions of single refraction known as optic axes. DOUBLE REFRACTION AND POLARIZATION IN CALCITE. That a ray of ordinary light entering calcite emerges as two rays of polarized light may be demonstrated as follows : A moderately thick calcite* cleavage, Fig. 232, is mounted with a rhombic face vertical and so that it can be revolved about a horizontal axis perpendicular to this face, Fig. 233. A horizontal ray of light, IT, Fig. 234, is allowed to fall upon the vertical face. It passes through. the calcite and emerges as two rays, one, TO, undiverted from its course, as would happen with ordinary refraction and perpendicular incidence, while the other, TE, has undergone some "extraordinary" refraction. On FIG. 232. FIG. 233. FIG. 234. revolution of the calcite the diverted or extraordinary ray, TE, appears to revolve around the ordinary ray, TO, at a fixed distance * Double refraction in calcite was described in 1670 by Erasmus Bartholin, of Copenhagen, one year after Steno's announcement of the constancy of corresponding angles in quartz. That all its optical behavior corresponded to a double shelled ray surface was discovered by Huyghens in 1678. CR YSTALL O- OPTICS. I o I from it and both evidently remain in a plane parallel to the plane abed through the short-diagonal, Fig. 232. The two rays also appear to be of approximately equal bright- ness and not to change during the revolution of the calcite. Proof that the Rays are not Common Light. If the two rays TO and TE are common light then by shutting off one and allowing the other to go through a second calcite rhomb mounted like the first there should again result two rays of essentially equal brightness for all stages of rotation of the calcite rhomb. This however is not the case. If TO, the ordinary ray, is used as a source, then, when the short diagonals of the vertical faces of the two calcite rhombs are parallel only an ordinary ray is seen, when they are crossed only an extraordinary, between these positions there are always two rays which alternately wax and wane and are only equal when the short diagonals are at 45 to each other. Also if TE, the extraordinary ray, is used as a source there is a similar series of results, but the relative positions of the two calcites for any particular result have changed by 90. That is, an ordinary ray is seen when the short diagonals are crossed, and an extraordinary ray when they are parallel and for any inter- mediate position, the intensities of the two rays have been reversed. The rays TO and TE therefore differ from common light and differ from each other by some 90 relation. Transmission in other directions in calcite gives similar results, but with this difference, that for the same thickness the divergence of 10 and IE differs from a maximum for transmission at right angles to the three-fold symmetry axis to zero for transmission parallel to it. Theory to Explain Double Refraction of Calcite. The few facts stated show that the results depend upon the crystal structure of the calcite. If it is assumed that this structure is such that the vibrations of any entering ray* are converted * The different effects of the same structure on common light and on a ray from the first calcite fit in with this theory. For the rapidly changing orientation of the vibrations in common light yield rapidly changing components and an average essentially equal "brightness" for the two rays for all positions, whereas the fixed vibration direction of the "polarized ray" yields varying components as the relative positions of the calcites change. 1 02 CR YSTALL O GRAPHY. into two sets of straight-lined vibrations, one parallel to abed, Fig. 232, one at right angles thereto, all the results of the experi- ment may be graphically shown for different relative positions of the two calcites by representing these directions of vibration by straight lines and the intensities by the lengths of these lines. Assuming that the vibrations of the extraordinary ray are parallel abed and that of the ordinary at right angles thereto, the problem is simply to resolve the initial ray, represented by a line definite in length and parallel (or at right angles) to the short diagonal of the first calcite, into components parallel and at right angles to the short diagonal of the second calcite. Double Refraction not Limited to Calcite. By other methods later to be elaborated it may be shown that double refraction is a common property of all crystals except the isometric and that the vibrations of any entering ray are converted by any crystal (not isometric) into two sets of straight- lined vibrations in planes at right angles to each other, the direc- tions of these planes being dependent on the crystal. THE OPTICALLY UNIAXIAL CRYSTALS. Optic Axis. In every crystal of the hexagonal or tetragonal system the direction of the principal crystallographic axis (c) is a direction either of single refraction or of circular polarization and the directions equally inclined to the crystallographic axis are optically equivalent. The crystallographic axis c is therefore an Optic Axis. Ray Surface. The optical properties of a uniaxial crystal are best understood by considering the shape of the Ray Surface,* which consists of two shells with a common center. One is a sphere, the other an ellipsoid of revolution, the axis of revolution being either the major or minor axis of the ellipse but always a diameter of the sphere. It is also the optic axis. Evidently for every direction except that of the optic axis two rays are transmitted, an ordinary with a velocity indicated by * Assume one vibration of monochromatic light within a homogeneous medium and the transmission of this vibration in all directions along rays. At the end of any period the motion will have reached some definite point on each ray. The closed surface through these points is the ray surface of the substance. CR YSTALL O- OPTICS. 103 the sphere radius and an extraordinary with a velocity indicated by the corresponding radius vector of the ellipsoid, and the greatest difference of velocity exists for the direction of transmission at right angles to the optic axis. Positive and Negative Character of Ray Surface. The spherical shell may surround the ellipsoid shell or vice versa. The former combination is called a positive ray surface, the latter a negative. In the positive ray surface, Fig. 235, the constant ordinary ray is evidently faster for any directions of transmission than the extraordinary and the slowest ray is evidently the extraordinary transmitted at right angles to the axis of rotation or optic axis. In the negative ray surface, Fig. 236, this is reversed and the Section of Positive Ray Surface. Section of Negative Ray Surface. fastest ray is the extraordinary ray transmitted at right angles to the optic axis. If the direction of vibration of the fastest and slowest rays be denoted respectively by X and Z then, as indicated in the ray surfaces, Z is the axis of rotation or optic axis in a positive ray surface and X in a negative. Or since the optic axis is the crystallographic axis c we may summarize : + when Z parallel c, - " X " c. Indices of Refraction. From what has just been said it follows that for any direction of transmission there is one constant index of refraction and for 104 CR YSTALL OGRAPHY- any direction but the optic axis there is a second index varying with the direction. Finally that the indices of refraction obtained for a direction at right angles to the optic axis are the largest and smallest obtainable and are called the principal indices. The principal indices are most conveniently, and in conformity with the usage in biaxial crystals, denoted by 7 and a, y, the largest index, is the index of the 'slowest transmitted ray, with vibration direction parallel Z; a, the smallest index, is the index of the fastest transmitted ray with vibration direction parallel X. Hence the relations may also be stated: Positive when vibration of 7 = c, Negative when vibration a. = c. " Birefringence " and Phase Difference. The difference between the principal indices is called the birefringence or strength of double refraction. In different crystals of the same species it is more constant than the indices themselves. For any direction except that of the optic axis, both rays are retarded but one more than the other. There must therefore develop a phase difference increasing with the thickness. If the direction is at right angles to the optic axes Phase difference = thickness X birefringence or A = t(y a). Vibration Directions. For any direction of transmission the two rays will possess definite directions of vibration at 90 to each. When these can be compared with a crystallographic direction they are useful. One will always be in the plane through the optic axis. Circular Polarization. In quartz and cinnabar crystals the light transmitted in the direction of the optic axis is "circularly polarized." That is ordinary polarized rays with vibration in straight lines in a known plane emerge with their vibrations in a different plane. The angle of rotation is dependent on the thickness and for quartz amounts to 24 per millimeter for sodium light. A thin section or fragment of basal quai tz of say .03 to .04 mm. thickness would therefore develope less than one degree of rotation. In other directions these minerals behave nearly, though not exactly, like ordinary uniaxial minerals. Absorption and Pleochroism. In symmetry if not in degree the absorption phenomena corre- spond to the transmission. The absorption of the ordinary ray CR YSTALL O- OPTICS. 105 \ being independent of the direction of transmission, while that of the extraordinary varies with the inclination to the optic axis, but is constant for the same angle and differs most from that of the ordinary for transmission normal to the optic axis. THE OPTICALLY BIAXIAL CRYSTALS. Optic Axis. In orthorhombic, monoclinic and triclinic crystals, no true optic axes exist because there is no direction of optical isotropy. There are, for monochromatic light* and constant temperature, two directions of single refraction, and as in most cases the uniaxial optic axis is a direction of single refraction these by a strained analogy are called optic axes, for light of that wave-length. They are determinable directions and therefore useful and their very variations for temperature and wave-length constitute tests. The Biaxial Ray Surface. For a given temperature a monochromatic light motion starting from a point within a biaxial crystal reaches at any moment a very complicated double ray surface which is symmetrical only to three lines at right angles called principal vibration directions, and three planes, each through two of these lines, called optical principal sections. Two of the three lines are always the vibration directions of the fastest and slowest rays, the third is at right angles to these and is the vibration direction corresponding to some ray of intermediate velocity. It may be noted that the planes and axes of geometric symmetry are alwaysf optical principal sections or principal vibration directions. In conformity with the convention of the uniaxial crystals let the vibration directions of the fastest and slowest rays be * The directions of single refraction or so-called optic axes depend upon the principal indices of refraction, hence change both with wave-length and temperature, the amount of change varying from a few minutes to many degrees. t Thus in Orthorhombic Crystals the principal vibration directions and optical principal sections are constant for all colors, in Monoclinic Crystals one principal vibration direction and one optical principal section are fixed for ail colors, the others vary with the wave-length; in Triclimc Crystals there are no principal vibration directions or principal sections which are constant for all cclors. io6 CR YSTALLOGRAPHY. denoted by X and Z respectively and let F represent a direction at right angles to X and Z. The shape of the ray surface may be judged from the shape of the optical principal sections X Y, XZ, and YZ. Section XY. Section XZ. Section YZ. Optical Principal Section XY, Fig. 237, cuts the two shells of the ray surface as a circle within an ellipse with radius, major and minor axes respectively slowest, fastest and intermediate veloci- ties.* Optical Principal Section YZ, Fig. 238, cuts the two shells of the ray surface as an ellipse within a circle with radius, major and minor axes respectively fastest, intermediate and slowest veloci- ties. The Optical Principal Section XZ. This is the most important section because it is the plane of the optic axes. It cuts from the ray surface an ellipse and a circle which intersects the ellipse in four symmetrically placed points, , Fig. 239. The radius, major and minor axes are respectively the intermediate, fastest and slowest velocities.! Near but not at the points E ; common tangent planes can be drawn to each shell. The directions, A A , normal to these common tangent planes are directions of single refraction, that is, are the * These velocities are proportionate to the reciprocals of a, /9, y, the indices of refraction for rays with vibrations parallel X, F and Z. t The light emerging on the direction AA is not simply the singly refracted ray which has travelled in the crystal in the direction A A but all that diverging cone of rays with as a point and the circle of contact of the tangent plane as a base. Each ray has its own direction of vibration. CR YSTALL O- OPTICS. 1 07 so-called optic axes and the rays travelling in these directions have the intermediate velocity (or index of refraction /3). Positive and Negative Character of Ray Surface.* In XZ, the plane of the optic axes, X and Z bisect the angles between these axes. If the acute bisectrix is Z (Bx a = Z), the ray surface is said to be positive.^ If the acute bisectrix is X (Bx a = X), the ray surface is said to be negative. OPTICAL PROPERTIES AND CONSTANTS OF BIAXIAL CRYSTALS. These can most simply be stated by reference to the uniaxial crystals. Indices of Refraction. The principal indices are for rays with vibration directions parallel the three axes of symmetry; one will be 7 the largest index anywhere obtainable, one will be a, the smallest, the third will be ]8, that of a ray with vibration directions at right angles to these. For other directions intermediate values are obtained. There is no constant index. Birefringence. The difference between the largest and smallest index (7 a) is the birefringence of the crystal. Optic Axial Angle. The angles between the optic axes can be measured the acute angle is designated by 2 V. Vibration Directions. As with the uniaxial these lead to a knowledge of the symmetry. PRODUCTION OF PLANE POLARIZED LIGHT. Plane polarized light may be produced from common light: * This conforms strictly to the usage in the uniaxial which is a special case of biaxial with the angle between the optic axes zero, the acute bisectrix being in the direction c- t In terms of principal indices these might be written Positive, vibration of y =Bx a , Negative, vibration of a=Bx a - 108 CR YSTALLOGRAPHY. 1. By reflection from a non-metallic surface.* 2. By double refraction and absorption. f 3. By double refraction and total reflection. NicoPs Prisms. The third method is most used and while many polarizing prisms exist all are based on the prism described by William Nicolt in 1828. It may be briefly described as consisting of a cleavage of iceland spar (calcite) with a length about three times its breadth. Let aBdC, Fig. 240, be a principal section through the optic axis XY and the short diagonals aB and Cd of opposite small cleavage faces. To secure the needed directions these small faces, at 70 52' and 109 8' to the edge BD, are ground away and replaced by faces, indicated by AB and CD at 68 and 112, to the edge. The prism is then cut through by a plane through AD at right angles both to the new terminal faces and to the principal section. The parts are carefully polished and cemented by Canada balsam, the index of refraction of which is about 1 .54. The index of refraction of the ordinary ray is 1.658, that of the extraordinary ray varies with the direction of transmission be- tween 1.486 and 1.658. For instance, the ray transmitted parallel to DB has an index 1.516. The general effect therefore of such a construction is that any incident ray IE, Fig. 240, on entering is split into two rays. The ordinary ray, with an index of refraction of 1.658, if incident at * The reflected ray is perfectly polarized only when it is at right angles to the refracted ray. For this particular angle of incidence (tan i = n}. The vibrations are at right angles to the plane through incident and reflected ray. With glass a series of parallel plates are used each plate increasing the proportion of polarized light. The device is inexpensive but it is difficult to obtain enough perfectly polarized light because of the small angle to which the incident rays must be limited. t Double refraction and absorption. Certain substances, such as tourmaline, absorb one ray much more rapidly than the other, and a thickness can be chosen for which one ray is totally absorbed, the other being partially transmitted with vibrations all in one plane. The very simple polariscope called the tourmaline pincers depends on this prin- ciple but the light is colored. t Edinb. New Phil. Jour., VI, 83-94. CR YSTALL O- OPTICS. 109 the balsam at an angle greater than its critical angle, follows some path EJ and is totally reflected at the balsam along JH and absorbed by the blackened walls about the nicol. The extraordinary ray, however, follows some path EF and if its index is less than 1 .54, is simply diverted a little by the balsam, say, along FS, and thereafter following the path SG parallel EF emerges travelling parallel the incident ray IE but plane polarized and, according to the assumption made on describing double refraction FIG. 240. FIG. 241. Jo /. in calcite, with its vibration direction in the plane of AB the short diagonal of the face of the nicol. Fig. 240 shows the nicol section with light incident in the direction IE parallel the length of the nicol. In Fig. 241 the construction considers light incident at any angle and shows that only the rays between J and I e will yield pure extraordinary rays, since these are furnished only by light rays incident at the balsam between the critical angles of the ordinary and HO CRYSTALLOGRAPHY. extraordinary ray.* This so-called "opening angle" of the nicol is about 25. The critical angle of the ordinary ray is EKV = 68 13', Fig. 241, corresponding to an incident ray J at 37 59' to EZ. Both components of any ray incident at an angle greater than 37 59' would be transmitted. The critical angle of the varying extraordinary ray is ENW = 81 34', corresponding to an incident ray I e at 13 12' to EZ. Neither component of any ray incident at an angle less than 13 12' would be transmitted. That is, the useful or opening angle of the nicol is I EI e = 37 59' 13 12' = 24 47'. This opening angle may be increased considerably by different constructions. For instance, the Hartnack-Prazmowsky prism is calcite with the end faces at right angles to the others and with linseed oil instead of balsam. In others the material is different. Sodium nitrate prisms have been made, but while optically good were hygroscopic. Combinations of glass and calcite are successful as polarizers but not as analyzers because they are not achromatic. In some devices the ordinary ray is transmitted instead of the extraordinary. THE FUNDAMENTAL PHENOMENA BETWEEN CROSSED NICOLS. Crossed Nicols. The term nicol is hereafter used to designate any form of polarizer. If two nicols are placed so that the light from one reaches the other, the light will go through the second unchanged if the faces of the nicol are parallel, but if one is rotated the light emerging from the second nicol will vary in intensity with their relative position. Let PP r Fig. 242 be the direction of vibration of light from the first nicol and CP its amplitude, then if A A' is the direction of vibration of the extraordinary ray in the second nicol and BB r that of the ordinary ray the components of CP in these direc- tions will be Ca and Cb, of which the former will be transmitted, the latter totally reflected at the balsam. * For elaborate discussion see Johannsen's "Manual of Petrographic Methods," pp. 158-175. CR YSTALL O- OPTICS. Ill If the rotation is clockwise Ca will decrease and at 90 of rota- tion, with crossed nicols, it will be zero, that is, none of the light from the first nicol will emerge from the second nicol and the field will be dark. As the rotation is continued Ca will increase until at 180 it again equals CP and so on. The first nicol is often called the Polarizer, the second the Analyzer. FIG. 243. / / The fundamental phenomena between crossed nicols upon which all optical tests rest may be described under the headings Depolar- ization, Extinction and Interference and they may be illustrated by any simple combination of polarizer and analyzer as tourmaline pincers or two nicols prisms set in a hole bored in a block of wood and a slit crossing the hole at right angles for the insertion of the crystal plate. Depolarization. If a plate of glass or a section of an isometric crystal is placed between crossed nicols, the dark field remains dark. But if a section of a doubly refracting crystal is so inserted, the field is in general illuminated because any ray of light from the first nicol emerges from the section as two parallel rays with vibrations at right angles to each other, each of which would furnish a com- ponent in the direction of vibration of the second nicol. In other words, the dark field would be illuminated, although the nicols remain crossed. Extinction. If any doubly refracting crystal section is revolved between the nicols in its own plane until its vibration directions are parallel 112 CR YSTALLOGRAPHY. to the vibration direction of the nicols the light from the first nicol will be transmitted without change through the section but on reaching the second nicol will be stopped because its vibration direction is at right angles to the vibration direction of the second nicol. That is, the light, which in general passes through the described combination of crossed nicols and crystal section, will be shut out or extinguished every 90 or four times during a revolution of the section in its own plane. Interference of Monochromatic Polarized Light Between Crossed Nicols. Two rays of polarized light of the same wave-length, following the same path and with vibrations in the same plane will combine FIG. 244. or "interfere," their vibrations either supplementing or opposing each other according to the so-called phase difference of the rays. For instance, if the light incident at the lower surface of a section of a doubly refracting plate shown in Fig. 244 is polarized, monochromatic and parallel, interference will take place between crossed nicols as follows: The less refracted ray FD from the incident ray EF and the more refracted ray BD from the parallel incident ray AB will, after emergence, follow the same path DC (parallel to the incident rays) but their vibrations will take place in planes at right angles to each other. There will in general be a phase difference between FD and BD because they are unequal in length, different in vibration direction, CR YSTALL O- OPTICS. 1 1 3 and, having encountered different structures, have been retarded unequally. Reaching the analyzer the vibrations of FD and BD will be brought into the same plane, each furnishing a component in the direction of the vibration plane of this second nicol, and therefore, they will combine or "interfere." Similarly from each point of the upper surfaces of the crystal section there will emerge two rays with the same phase difference as BD and FD which will be brought by the analyzer to the same "interference." For the understanding of interference between crossed nicols two important limit cases must be considered. Denote the difference in retardation of the two rays by A and the wave-length of light by X then : 1. If A = X, 2X, 3X, -, n\ the two components following the same path will oppose and exactly neutralize each other, the light will be stopped and darkness will result for all positions of the crystal section. 2. If A = I/2X, 3/2X, 5/2X (or any odd multiple of i/2\), the two components following the same path will supplement each other and the field be most strongly illuminated for all positions of the crystal section. The proof for the first statement is as follows: Let PP', Fig. 245, represent the direction of vibration and OP the intensity of the light from the first nicol. Let RR' and SS' represent the vibration (or extinction) directions of the doubly refracting plate and AA f the direction of vibration direction of the second nicol. Then at the instant of entering the plate OP is resolved into components OM and ON. OP, OM and ON will be the same* phase and evidently also when one of the two has gained relatively, just a wave-length (or 2 or 3, etc., wave-lengths) their phases will still be alike, that is, the components of OM and ON in the vibration direction A A' are OX and OY equal\ and in opposite directions. Practical Confirmation. A wedge of doubly refracting substance, for instance, a little wedge of gypsum made by shaving down a cleavage with a sharp knife or better by rubbing it down will show, in monochromatic light under low magnification, dark bands at regular intervals, which vary in distance apart with the color of the light used and correspond to differences between the emerg- ing rays of one, two, three, etc., wave-lengths. * If OP at end of its vibration then so are OM and ON, if in middle so are they, t Because they are horizontal projections of equal parallel lines OM and PN. 9 114 CRYSTALLOGRAPHY. INTERFERENCE COLORS WITH WHITE LIGHT. The "retardation" A has a definite numerical value dependent on thickness, direction and material. For a given section it differs only slightly for different wave-lengths of light. If there- fore white light, which is composed of many rays of different wave- lengths, is used as a source of light, the retardation A may be at the same time: (a) approximately a multiple of the wave-length of light of one or more colors, which would therefore be shut out; (b) closely an odd multiple of the half wave-lengths of other colors leaving these at nearly their full intensity, and (c) intermediate, with still other colors. The resultant so-called interference color shown by the section of a doubly refracting substance between crossed nicols would be the combination of what is left of the different monochromatic colors. The Interference Color Corresponding to a Given Value of A. If A be divided successively by the wave-lengths of the different colors and the quotients considered, those colors will be wholly or nearly shut out for which the quotients are closely i, 2, 3, 4, etc., and those colors will be nearest their full values for which the quotients approach 1/2, 3/2, 5/2, etc. For quotients of inter- mediate values the colors will be partially shut out. If then due allowance is made for the relative intensities of the spectrum colors the interference color will be evident. Using five prominent colors only an approximate determination may be made either graphically or by direct calculation. Graphically. In Fig. 246 the construction is as follows: The first vertical line is the A scale divided into spaces representing 100 /z/z (millionths of a millimeter). The remaining five vertical lines are divided respectively into spaces proportionate to the half wave-lengths (in millionths of a millimeter) for Hi (violet), 393.3; Fi (blue), 486.0; E (green), 526.9; Di (yellow), 589.5; C (red), 656.2; A (red) 760.4. Taking any length as indicating maximum light draw lines of this length opposite I, 2, 3, 4, wave-lengths. Draw parallel lines regularly diminishing to the length zero opposite 1/2, 3/2, 5/2, etc., wave-lengths. The lines represent the proportion of the violet, yellow, etc., present. They do not show the coloring intensities which in the order of colors stated are roughly O, I, 2, 3, 6, 2. CR YSTALL O- OPTICS. A fair approximation therefore to the interference color corre- ponding to any value of A will result bv following a horizontal I / 1 ?v i F 7 1 IG. 246. >/ < nr f I . Tron Gray. ^^ ^= =^ JEEE Pale Gray. I ' Pure White. ' Pale Yelloxr. Bright Yellcw. - * i __ _= ^zi ...^^ 7 Orange Red. Red. ^^ jn: J 5 ( .' z::=:: "^Z 1 Blue. Jjj Bluish Green. ; - o- Yellowish Green. S, Yellow. - - Orange Red. ^ , " - Red. Violet (sensitive tint No. 2). - -Blue. Bluish Green., j ' Green. ~ ~ "= o Yellowish Green. 3, Yellow. * - r< .-Rose Red- Reddish Carmine. - Purplish Carmine. I Violet Gray (sensitive tint - . ~ -= ( Bluish Gray No - 3 > - - j - % Pale Green. 1 J o a - ' " ; r White of high o order. straight edge across from this value and noting the relative lengths of the horizontal lines. 116 CRYSTALLOGRAPHY. By Calculation. For instance let A = 900 MM (millionth of a millimeter). QOO HI Violet = 2.29 over 1/2 present. O z^O FI Blue = 1.85 about 3/10 present. 400 E Green - - = 1.70 about 1/2 present. 527 QOO DI Yellow = 1.52 almost all present. 59 QOO C Red = 1.37 about 3/4 present. That is, the color is made up of almost all the yellow, 3/4 of the red, about 1/2 of the violet and green and 3/10 of the blue. Multiplying by the relative intensities for each color, as stated in graphical method, the following proportions result: Violet o, blue 3/10, green I, yellow 6, red 3/2. That is, yellow greatly pre- dominates. The red more than balances the green and the blue and the remaining red tints the dominant yellow, forming orange. The Interference Color Scale. The interference colors grade from black for A = o, to colors not clearly distinguishable from white with A beyond 2,000 MM- Because the colors repeat to some extent periodically they are divided into so-called "Orders,"* the convenient transition color between orders being a so-called sensitive violet because very minute changes in A result in decided changes to blue or red. Order. Last Color. Value. First Sensitive violet, No. i 575 pp. Second Sensitive violet, No. 2 1,130 IJL/J. Third Sensitive violet, No. 3 (violet gray) 1,652 /JL/J, In Fig. 246 the names of the principal colors of the color scale are approximately opposite the corresponding values of A. The first order colors start with black and pass through shades * These are not quite Newton's orders, which end respectively at A = 551, 1101, and 1652. This division gives no sensitive violet in the first order, one in the second, and two in the third. CR YS TA LL O- OPTICS. 117 of gray to nearly pure white* at A = 250 /zju. Beyond this the shorter waves are more completely shut out and the yellow orange and red reach a maximum. The second order colors are in general bright spectrum colors Indigo, blue, green, yellow, orange, red. The third order colors are paler and more complex because with increasing values A becomes an approximately perfect multiple of i/2\ for an increasing number of wave-lengths. For example: A = 1500 is 5/2\ for orange red, 7/2\ for indigo, 3\ for green, 2\ for red, 4\ for violet. The resultant total effect is between car- mine and purple. The higher orders. With the still higher values for A the pale- ness and indefiniteness of the colors are still more noticeable and beyond the fourth order the colors are usually grouped as " high order whites." The Polarizing Microscope and Its Adjustment. The modern polariscope for the study of crystals is the polarizing microscope. With the proper attachments it yields all the desired tests either with relatively large or microscopic quantities of material. The simplest polarizing microscope necessarily includes the essentials of an ordinary microscope (a stand supporting a tube carrying objective and ocular, a platform or stage and means of focusing and illuminating), and in addition a nicol, "the polar- izer," below the object, to polarize the incident light, and another above the objective, "the analyzer" arranged to be thrown in or out and " crossed " with respect to the polarizer. To these essentials may be added many devices and attachments for special purposes resulting in a highly complex piece of mechan- ism. For general work something between the two extremes is most satisfactory. The Illuminating System. This consists of the mirror, and the condensing lens and some- times a diaphragm. The mirror has one plane face and the other concave. It may * For this value the diminished intensities of the colors are relatively nearly as in white light. Il8 CRYSTALLOGRAPHY. be tipped in any direction and usually has a limited up-and-down motion. Its purpose is to reflect light from the source to the object. The plane mirror should be used for sunlight or for low magnifica- tions, the concave for high magnifications without the condenser, for very high magnifications and interference phenomena the plane mirror and condensing lens. The condenser or condensing lens illuminates the object with a cone of light. In some instruments it rests on the top of the polarizer, in others it is swung into position by a lever, being attached to the same system it is raised with the polarizer and at its highest point is practically level with the upper surface of the stage. The principal use is in obtaining the so-called convergent light effects. The best effects are obtained when the condenser* is in focus; this often is at the highest point. The Polarizer and Analyzer. The nicols prism has been described in detail, p. 109. Two polarizing prisms called nicols are needed in the polarizing microscope. The lower, called "the polarizer" can be raised or lowered by lever or screw and swung or drawn aside. Usually it can be adjusted so that its plane of vibration is either parallel or diagonal to the cross hairs as in Fig. 247. The analyzer is usually a flat-ended prism such as the Glan- Thompson placed above the objective and arranged to slide in and out of the microscope tube. It frequently can be rotated through 90, as in Fig. 248, so that the plane of vibration may be placed cross or parallel to that of the polarizer. In certain microscopes such as Fig. 248 both nicols can be rotated together instead of rotating the stage. The Objectives and Oculars. Different objectives and oculars are used in crystal work, never of very high power, the most used combinations varying in magnification from 50 to 400 diameters. * Focus on a section with a low power objective, turn plane mirror until some object, tree, window bar, etc., is in field. Raise and lower condenser until this image is sharp, then slightly rotate mirror. CR YSTALL O- OPTICS. 119 The objective receives the light from the object, focuses it and produces a real image. Its magnifying power increases with the tube length of the microscope and its resolving power or power to make details visible increases with the number of rays coming FIG. 247. Leitz Microscope No. 30. from the object and on its relative freedom from spherical* and chromaticf aberration. * Unequal magnification in different parts of the field and haziness due to different focal lengths. t Different focal lengths of light of different colors. 120 CR YSTALL OGRAPHY. FIG. 248. Fuess Microscope No. VI. Objectives are usually numbered and sometimes marked in terms of the focal length ranging from low powers of 3 inch to high powers of 1/12 inch or less. CR YSTALL O- OPTICS. 1 2 1 \ Oculars. The ocular or eye piece most used is the Huyghens* ocular made of two plano-convex lenses with their plane surfaces towards the eye, the lower or field lens collects the rays and lessens the spherical and chromatic aberration. The upper or eye lens connects the rays into parallel rays and gives an enlarged inverted image of the object. "Cross hairs" or micrometers are placed at the focal plane of the field lens. The cross hairs usually intersect in the line of sight at right angles and parallel to the vibration plane of the nicols. To obtain high magnification it is generally better to use a high power objective and low or medium power eye piece as the higher power oculars cause indistinctness. The Field of View with Huyghen's ocular is roughly in fractions of an inch five times the reciprocal of the magnifying power in diameters, e. g., 50 diameters of the field is i/io inch. The Path of the Light and Formation of the Image. The object Oi, Fig. 249, receives rays from a mirror, these pass through the diaphragm CD and condenser system, then through the objective and cross at FI and enter the lower or field lens of the eye piece giving a real\ inverted image at 2 , which is enlarged by the upper or eye lens to the virtual and still inverted image at 4 . The optical tube length of the microscope is A, Fig. 249, the distance between the two foci FI of the objective and F% of the eye lens. The magnifying power of an objective increases with the tube length. L is the mechanical tube length usually 160 mm. and EP the eye point. The Mechanical Parts of a Polarizing Microscope. The Stand. The support to which the other parts are attached. Usually with a heavy horse-shoe base. The Stage. The simple stage is a circular disc, Fig. 247, with a central hole. It can be rotated about an axis coincident with * In the Ramsden ocular the convex sides of the two lenses face each other and the image is not inverted. t The real image results when the object is further from the lens than the focal length. It is on the opposite side of the lens and can be projected. The virtual image results when the object is nearer the lens than the focal length. It can not be projected. 122 CR YSTALLOGRAPHY. the line of sight. In some instruments it is permanently centered, in some adjustable. It should be graduated so that angular rotations can be read to fractions of a degree. In more elaborate instruments it has sliding screws ss' Fig. 248, and other acces- sories. FIG. 249. After Bausch and Lomb. Body Tube and Draw Tube. These carry most of the optical parts, the draw tube sliding in the body tube. In both 247 and 248 the draw tube is graduated to show the "optical tube length," A. Coarse and Fine Adjustment. The coarse adjustment is usually a rack and pinion motion of the drawing tube with respect to the stand while the fine adjustment CRYSTALLO-OPTICS. 123 is by a micrometer screw with a graduated milled head, n, Fig. 248, the value of one division usually being .01 mm. Centering Screws. Two screws producing motion at right angles and attached either to the objective holder, as in Fig. 247, or to the stage. Objective Holder. This is usually a clutch or clasp, k, Fig. 248, which is really a pair of steel tongs which grips a collar on the objective between its jaws. It is always advisable to give the objective a slight twist after inserting it. Slots for Accessories. A slot is always provided just above the objective for the inser- tion of the so-called test plates (quarter undulation mica plate, gypsum red of first order, quartz wedge, etc.). The better instruments have a second slot in the telescope above the analyzer for the introduction of a Bertrand lens, /, Fig. 248, by which the interference figures are made visible. ADJUSTMENTS OF THE MICROSCOPE. The resolving power, definition and freedom from much aberra- tion are judged by means of selected slides, such as those of diatoms, using a weak ocular and the light from a white, thinly clouded sky. Focusing. This should be tried first with a medium power objective, the focal length of which may be 1/4 inch or more. Set the objective lower than this and focus upward. In using a high power "place the eye on a level with the stage" and looking toward a window lower the objective until only a thin film of light remains between the cover glass and the lens and then focus upward. When prac- ticable, use a low power as a finder. Centering. Focus on a minute grain and move the glass until the grain coincides with A, Fig. 250, the intersection of the cross hairs. Revolve the stage 360 and note the orbit of the grain. The center (C) of the orbit is the center of rotation. When the grain is at B, 124 CR YSTALLOGRAPHY. that is, after 180 rotation, move it half-way to A by the two FIG. 250. adjustment screws and the other half by moving the object glass, operation. Repeat the Determining Vibration Direction of Lower Nicol. In the original nicols prism the vibra- tion direction is that of the short diag- onal. In other forms this direction needs to be determined because known dis- tinctions can then be made between the indices of refraction, the absorption directions, etc. With the upper nicol out rotate a section of biotite showing the cleavage cracks until the position of maximum darkness is reached. The plane of vibration of the lower nicol will then be parallel to the cleavage cracks. Or use a thin dark-colored tourmaline which is darkest when the vibration plane of the nicol is perpendicular to its optic or c f axis. Or, removing the polarizer, view the light reflected from a plane polished surface the surface will appear darkest when the vibration plane of the nicol is perpendicular to it. Determining Magnification. The magnifying power of any combination of lenses is the pro- duct of the magnifying power of the objective and eye piece used. A table giving the magnification for each combination should accompany each microscope. It is usually stated in diameters and can be obtained approxi- mately by placing on the stage a cover glass with lines ruled a known distance apart, focusing on this and obtaining its image on a ground glass 10 inches above the eye-point. Then the magnification in diameters is equal to the distance apart of two lines of the image divided by the distance apart of the same two lines on the cover glass. If an Abbe drawing apparatus is avail- able the lines may be projected by this and sketched and their distance apart measured. Using a Microscope. The student should sit upright with the microscope directly CR YSTALL O- OPTICS. 1 25 in front and both hands free for manipulation. Either eye may be used, the other being kept open. A glare should be avoided and that amount of light used which shows the structure. Dust should be removed from lenses and nicols by a soft brush or by blowing and wiping with clean lens paper. Sudden changes of temperature and direct sunlight are to be avoided. Lubricate only with clock oil. Cleanse working parts if necessary with benzene. One of the most satisfactory polarizing microscopes is the Leitz* No. 30, sometimes known as the Berkey Model No. I, shown in Fig. 247. The adjustable polarizer and analyzer are Glan-Thompson prisms and the condensing lens is inserted or thrown aside by rotating the milled head beneath the stage. The stage is permanently centered. The graduation can be read to i/io of a degree. The upper plate is traversed by lines of orientation. The graduated drawing tube has an inside diameter of 24 mm. The Bertrand lens is of 6 mm. diameter, can be centered to the microscope, also focused with the draw-tube. The Fuess microscope, f Model VI, Fig. 248, is planned to fit a large number of accessory devices and is especially characterized by the arrangement for simultaneous rotation of polarizer and cap analyzer, by the cogs rZ, r' Z' , the object remaining at rest, but the same relative change taking place as if the stage were revolyed and the nicols at rest. There is an elaborate mechanical stage, the rotation of which can be read to minutes and has quick rotation by hand, slow rota- tion by ratchet, and sliding motions in two directions. Preparation of Material for Optical Testing. As most observations are made by transmitted light it is neces- sary to prepare the objects so that they will transmit light and not overlap. Sections in Crystallographic Directions. The tests unless otherwise specified require what is known as ''plane parallel" plates, that is, that the light shall enter and * E. Leitz, Wetzlar, Germany, and N. Y. t R. FueSvS, Steglitz, Germany. 126 CRYSTALLOGRAPHY. emerge from essentially parallel surfaces. Such parallel surfaces may be opposite faces of a crystal or cleavage, or a face may be cemented to glass and an opposite artificial face ground on or a section not parallel to any known face may be made at any angle and ground, and verified goniometrically with reference to other faces. Rock Sections. A fragment may be chipped from the mass or a thin slice cut from it with an endless wire fed with carborundum or by a circular metal disc charged with diamond dust. One side is ground smooth and polished and cemented to glass and this ground down usually to a thickness of .03 to .04 mm. on a rotating disc fed with carborundum or emery. After cleaning the thin fragment is cemented to glass by Canada balsam, and covered with a cover glass of .10 to .15 mm. thickness, using the same cement. Good sections require* very careful lapidary work and satis- factory tools and are to a great extent made by skilled workmen. Crushed Fragments. In mineral testing much more rapid work can be done with the so-called "crushed fragment" sized by screens to an average thickness of .03 to .04 mm. The method of preparing suggested is as follows: A small fragment is crushed by pressure in a small agate mortar (or by pounding on a steel plate with a hammer). Grinding is avoided. The crushed material is then sieved through a small loo-mesh screen f upon a I2o-mesh screen, the finer portion pene- trating that. The particles remaining on the i2O-mesh screen are 'shaken out on a clean paper and a few fragments are placed on an object glass by a flattened wire or knife point. A drop of a monobromnaphthalin or other liquid is placed to one side and the powder is drawn into it by a tilted cover slip which is then placed in position. * The process of preparation is described in detail in Chapter V of Luquer's "Minerals in Rock Sections," and in pp. 190-195, Iddings' "Rock Minerals" and other similar works. f Easily made by boring a one inch hole through two square pieces of soft wood, say 2 in. x 2 in. x ^ in., inserting the wire gauze between and driving a pin-like brad near each corner. CR YSTALLO-OPTICS. 127 a monobromnaphthalin has an index of refraction of about 1.655. It forms a plane parallel sheet between the object glass and cover glass, and eliminates the effects due to irregular surfaces of the enclosed particles more or less perfectly as its indices approximate or differ from those of the liquid. THE OPTICAL TESTS WITH THE POLARIZING MICROSCOPE. Determining Isotropic or Anisotropic. (Singly refracting vs. Doubly refracting.) (See Depolarization, p. in.) With crossed nicols and (usually) white light and the condensing lens removed or lowered. Using moderate power, focus with upper nicol out, then push in the nicol and rotate the stage. Isotropic. If the field is dark throughout rotation the substance is singly refractive in this direction. If powder is being used the grain may be made to turn in the liquid by pressure with a point on the cover glass and other directions tried or a convergent light test may be made. Anisotropic. The field is dark at intervals of 90 and elsewhere illuminated, and often colored. It is to be noted that "local" double refraction, varying in different places, may occur as a result of strain in singly refracting substances. DETERMINING INDICES OF REFRACTION. While the methods of determining indices of refraction, p. 97, are essentially the same for all substances, it is only optically isotropic substances, p. 99, such as liquids, glasses and isometric crystals which with monochromatic light and constant tempera- ture have each one index of refraction whatever direction of trans- mission is used. In any doubly refracting substance the refractive indices vary with the direction of vibration of the light rays and if the problem is determining the principal indices of refraction certain definite directions of transmission must be secured. When this is not done the indices obtained are only intermediate indices. Uniaxial crystals, p. 102, although singly refracting in one 128 CRYSTALLOGRAPHY. direction, give two indices of refraction for any other direction of transmission; one of these is constant whatever the direction, the other varies between limits, the limiting values being the principal indices. Biaxial crystals, p. 105, have two directions of single refraction and two indices for each other direction of transmission and there is no constant index. METHODS WITH LIQUIDS OF KNOWN INDICES. In these methods involving a comparison with the known indices of liquids, a series of liquids which are transparent, stable and without action on instrument or substance are required. The number needed will depend upon the purpose, whether simply to classify in groups or to obtain as closely as possible the true indices. Simple liquids or mixtures may be used. Johannsen gives a list of about seventy, ranging from water, 1.33, to molten- selenium,* 2.92. Van der Kolkf particularly recommends about fifty, ranging from 1.33 to 1.93, and Wright, % from mixtures of a comparatively small number of liquids obtains any desired value between 1.45 and 1.96. The liquids should be kept in small stoppered and capped bottles, preferably blackened and in systematic order. The deter- mination of the index of any liquid at ordinary room temperature may be made quickly with a simple total refractometer, p. 133. If a piece of ground glass is placed on the drop of liquid the limit line of the liquid alone appears. Determining the Index of Refraction by the Becke Line. This test is based upon the occurrence of total reflection at a vertical boundary between two substances of different indices and a consequent concentration of light on the side of the substance with the higher index (denser substance). In Fig. 251 let BL be the vertical boundary between the denser * "Manual of Petrogra] >hic Methods," p. 260. t"Tabellen zur mikroskopischen Bestimmung der Mineralien," von J. L. C. Schroeder van der Kolk, 2d ed., Wiesbaden, 1906. t " Methods ot Petrographic Microscopic Research," F. E Wright, Carnegie Inst., 1911, p 98. See also Menvin, Jour Wash. Acad. Set., 3, 35. CR YSTALL O- OPTICS. 129 FIG. 251. (shaded) and less dense substances and let the microscope be focused at O. Then as explained, p. 98, all the oblique rays in the less dense medium incident at the contact plane will pass into the more dense, for instance, AO will continue as Oa, whereas of the rays in the denser medium all incident at the contact plane at more than the crit- ical angle NOT will be totally re- flected, for instance, CO will continue as Oc, and only the remaining rays pass into the less dense medium. Evidently, therefore, if the light is narrowed by a light stop or iris or by lowering the polarizer, there will be a strong concentra- tion of the light on the side of the denser medium. On slightly raising the objective the focal plane, for instance PP, cuts the series of concentrated rays in a broadening band giving the effect of a bright band moving into the denser substance. This test is made with a high power objective and a light stop below the stage upon a fragment or grain with an approximately vertical boundary or edge and surrounded by a liquid of known index. If singly refracting any position of the fragment will give the same result, if doubly refracting the positions of extinction will give the greatest and least values. With both nicols in, the stage is revolved until the grain is black. The upper nicol is then drawn out, the condensing lens and lower nicol lowered or a light stop used to prevent the entrance of divergent rays, and the microscope sharply focused on the vertical boundary. If the objective is now raised slightly, a line of light, parallel to the boundary, will appear to move into the substance which has the higher index. By lowering the objective the white line is moved in the opposite direction. The method will detect differences of .001, therefore with a sufficient number of liquids will determine the true indices to this degree of accuracy. Indices of Refraction by Oblique Illumination. Van der Kolk Test. If any fragment with tapering edges is immersed in a liquid it will act like a lens, and either concentrate 10 130 CR YSTALLOGRAPHY. or disperse the light as the surrounding liquid is of lower or higher index. When viewed with ordinary central illumination the effect in either case is a dark border, indicating merely a difference in indices. FIG. 252. FIG. 253. "7 If, however, by tipping the mirror, or, better, using the con- denser and interposing a card or other obstruction to the light rays on one side the illumination is made inclined, different effects will be obtained, as shown, Fig. 252, in which the fragment F is the denser and the bright side is towards the card C and Fig. 253, in which the liquid L has the higher index and the bright side of the fragment F is away from the card C. is the objective. To obtain the results* stated hereafter this test requires a medium power objective and condensing lens. With both nicols in, revolve the stage until the grain is dark. Then, with the upper nicol out and the grain in focus, slide a sharp-edged card below the lower nicol, drop the condenser until the edge of the card is sharply focused, then drop a little further. Move the card slowly toward the grain and notice which side of the grain becomes the brighter. Bright side of grain toward card Index grain greater than index liquid. Bright side of grain away from card Index grain less than index liquid. If the index of the grain is just that of the liquid for yellow *As explained by Wright, Am. Jour. Sci., 21, 362, 1906, these phenomena can be reversed by raising or lowering the condenser. For the position of the card chosen (below the focus of the condenser) the results appear as stated below. CRYSTALLO-OPTICS. 131 light, the grain will be bordered by red on the side near the card and blue on the opposite side. METHODS AVAILABLE WITH GREATER THICKNESSES. Due de Chaulnes Method. This method depends on the fact that if an image 0, Fig. 254, is accurately focused and then a transparent plane parallel plate interposed between it and the objective the image is blurred and only becomes clear again when the objective is raised a distance 00'. The rays OA and OB are refracted on emergence and ap- pears to be at O'. It may be shown* that the displace- ment 00' or Ms a function of the thick- ness T and the index of refraction of the substance. The particular applicability of the method is for cut stones and crystals of high indices. It requires opposite parallel faces.f The manipulation is as follows: Set the fine adjustment screw of the microscope near the upper part of its motion, and place a minute spot of ink on the object glass. Center this spot, cover it with the crystal plate and focus upon the ink spot through the plate as sharply as possible. Remove the plate without disturb- ing the object glass; then, using the fine adjustment only, and keeping count of the number of rotations, lower the objective until the spot of ink is again in focus. Measure the thickness of the plate with a micrometer gauge and denote this thickness by r, and the displacement or change in focal length by t. n = T- t' Simple Refractometers. Refractometers based upon the principle of total reflection, in which the indices of refraction can be rapidly determined upon polished or natural surfaces from a millimeter in diameter up are * If one good face exists a second parallel may be imitated by a drop of liquid and a bit of cover glass. t Iddings, "Rock Minerals," p. 120. 1 32 CR YSTALLOGRAPHY. now considerably used in testing gems and could well be used more in determining minerals. The surface of contact is the diametral plane of a glass hemi- sphere of very high index of refraction. There are two methods of admitting the diffused incident light: 1. From above the plane of contact. The method of grazing incidence, Fig. 255, all incident rays bent towards the normal, the last ray iO to enter being that parallel to the contact plane, which emerges along Or, hence the field of a telescope in the direction rO would only have its lower half illuminated or allowing for the lens it would appear as shown. 2. From below the plane of contact. The method of total reflec- tion proper, Fig. 256, all rays incident at more than the critical FIG. 255. FIG. 256. angle Noi are totally reflected while those incident at smaller angles are largely transmitted through the crystal. The field of a telescope in the direction rO therefore receives more light in the upper half than in the lower and, allowing for the lens, it appears as shown. Obviously light admitted both above and below produce counter- acting effects. The manipulation is as follows: Place a drop of liquid of known index of refraction on the center of the glass of the instrument; on this place the crystal face. Admit light from below or from above but not both, as counter- acting effects are obtained, and use the sodium flame. If only the limit line for the liquid is found, repeat with a liquid of higher index of refraction. Carefully revolve the crystal, keeping the same face in contact with the glass. If the revolution produces no movement in the CR YSTALL O- OPTICS. 133 FIG. 257. limit line or lines, the value is read and the note made that the substance is probably either amorphous or isometric. If the rev- olution produces obvious movement, and two lines are obtained, both are read when at their greatest distance apart. It should be noted whether one (uniaxial) or both lines (bi- axial) move during the revo- lution. In the simpler instruments such as the Fuess Simple Refractometer Model 4, shown in Fig. 257, in section, 1/2 scale, or the Herbert Smith refractometer shown in outline; full scale, in Fig. 258, the resulting sharply divided light and shade are viewed through the eye piece on a scale 5, Fig. 257. FIG. 258. The glass of the hemisphere in both instruments has an index of refraction a little over 1.8. The scales read to 1.8. Fig. 259 shows the appearance of the scale with a singly refracting sub- stance of index 1.49, Fig. 260 shows the scale with a doubly refract- ing substance with indices I 66 and 1.70. 134 CR YSTALLOGRAPHY. FIG. 259. FIG. 260. Determining the Sign of Elongation. The direction in which a crystal or a crystal section is longest is called its elongation (or sometimes its principal zone). This direction in uniaxial crystals is often the direction of the axis c and in the needles, fibers, etc., obtained by crushing it is connected with the structure, especially the cleavage. If the elongation is parallel or approximately parallel to one of the vibration (extinction) directions of the fragment or section a useful subdivision results by determining whether this vibration direction corresponds to the faster or to the slower ray. The vibration (extinction) directions in the section are found and the stage is revolved 45 from that extinction position which is nearest the "elongation" and the interference color is noted. A test plate of known retardation A and on which the directions* of vibration X and Z (or a and c) of its fastest and slowest rays are marked is then inserted in the slot above the ocular. The changes in color and the moving in or out of the color bands along the periphery of the section or fragments are noted. If the new color on comparison with the color chart is higher by A of the test plate and the color bands move out, then corre- sponding vibration directions of substance and the test plate are parallel if, on the contrary, the new color is lower by A and the color bands move in the corresponding vibration directions are crossed. * Strictly X and Z are the principal vibration directions of the crystal. CR YSTALL O- OPTICS. 1 35 The directions of X and Z therefore being now known the follow- ing convention exists. The sign of elongation is plus (+) when the elongation is parallel Z, and minus ( ) when the elongation is parallel X. The test plate most used is the Quarter Undulation Mica Plate, a sheet of mica of thickness corresponding to a blue gray interference color or say 140 MM which is i/4\ for a medium inter-yellow. A very gradual tapering wedge is even better as the succession of colors prevents mistake. The slot above the objective may be parallel to a cross hair in which case the vibration directions of the test plate must be diagonal, or the slot may be diagonally placed and the test plate made with its length parallel X or F. The former method is more convenient as the simple turning of the test plate upside down reverses its relation to the crystal under examination. DETERMINING BIREFRINGENCE. The birefringence or strength of double refraction of any doubly refracting substance is the difference between its maximum and minimum indices of refraction. If these indices can be deter- mined to the third decimal their difference may be taken as the birefringence. In practice the birefringence is usually determined from the retardation and consequent interference color and the thickness of the section. This gives the true birefringence of the substance only in exceptional cases.* The relation between retardation A, thickness t and refractive indices n\ and n for any section are : A = t(ni - n). The retardation and the thickness must of course be expressed in the same unit. The retardation can be measured with considerable accuracy by compensators. The thickness determination is less accurate. * In uniaxial crystals only when the section is parallel the optic axis and in biaxial crystals only when the section is parallel to the plane of the optic axis. 1 36 CR YSTALL OGRAPHY. Determining the Retardation by a Compensating Wedge. The process is closely that for determining the sign of elongation. The section or grain is focused, the upper nicol pushed in, an extinction position is found, and the stage revolved 45 to the position of brightest illumination. The interference color is care- fully observed and then a wedge of some mineral is inserted in the slot above the objective and the interference color of the combina- tion noticed, if this is higher than before the conditions are reversed so that the corresponding vibration directions are crossed and the wedge gradually pushed in until the interference color is run down to black.* The value of A for the thickness of wedge interposed is the desired value and this may be approximated by counting the number of times during the insertion of the wedge the original color reappears, if n times, then the color is a red, blue, green, etc., of the n + i order, for which the value may be looked up in a color chart. If at the position of compensation the mineral is removed the color given by the wedge alone should be that shown by the mineral alone and the wedge may be gradually withdrawn and the color repetition used as a check. The wedges most used are : The Quartz Wedge. A thin wedge-shaped plate of quartz mounted between glasses and usually showing four orders. The values of A for different places may be shown on a scale. The von Federow Mica Wedge. Composed of fifteen quarter undulation mica plates superposed in equivalent position, but each about 2 mm. shorter than the one beneath it. Each plate compensates by 140 /JL/JL. If n plates are needed to render the field dark then* A = n X 140. Many more elaborate compensators exist such as the Babinet compensator, the Michel Levy comparator, the Wright combination wedge, with which A may be determined within a few ///*. Usually they cannot be attached to the simple micro- scope. Bands of interference colors on wedge-shaped outer portions of fragments may be counted, giving thus approximately the color order. * Weinschenck recommends running down to sensitive violet No. I, A = 5 75 MM- This value would then be added to the value of A interposed. f That is, if one step is dark and the two adjacent steps equally bright, A = n X 140, but if no step is dark and two adjacent are equally bright the value is intermediate. CR Y STALL O- OPTICS. 1 37 Very low values of A (low order whites, grays, etc.) may be approximately determined by use of test plates, giving the sensi- tive violet No. I, A = 575 such as: The Gypsum test plate. A value as small as lo/z^t added or subtracted notably changes the color. The Bravais double plate, consisting of two halves of a sensitive violet set in opposite direction, is even more delicate. Originally made of mica ^ mm - thick. It is said to react for the double refraction produced by finger pressure on a cube of glass. Measuring the Thickness of the Crystal or Fragment. If the refractive index of the substance is known the simplest plan is to focus successively on its upper and lower surface, using the fine adjustment screw. The distance corresponding to the movement of the screw multiplied by the average index of refrac- tion of the substance is the thickness.* This is the de Chaulnes method, p. 131. If the section is loose a mark may be made on an object glass and focused, then the section slid on and the fine adjustment turned until some point on the surface is in focus. This is inde- pendent of the index of refraction. The error diminishes with increasing thickness; with thin sec- tions it will probably be ten per cent. Determining the " Birefringence." The quotient obtained by dividing the retardation by the thickness t is the strength of the double refraction of that section. It is only that of the crystal when the section, as before stated, is parallel to the optic axis (uniaxial) or plane of the optic axes (biaxial) . Approximate Determinations of Birefringence in Terms of Color. It is sometimes convenient to classify fragments or sections of approximately constant thickness by their birefringence ex- pressed in terms of color. For instance, for crushed fragments or sections five color terms can easily be used. The terms of color, and the equivalent birefringences for a thickness 0.035 mm., and the detail, or effect, of the test-plates may be stated as follows: * If small basal cleavages of barite are placed at the corners of the slide and ground down with it, their interference colors can be used to determine the thickness for n\ n = .01, hence t = A/.oi = looA. 138 CRYSTALLOGRAPHY. Equivalent Terra of color. Detail. Birefringence. BLACK Unchanged by rotation o GRAY OR WHITE ... By gypsum plate made yellow for crossed position, blue or purple for parallel position < 0.008 BRIGHT A By gypsum plate made white or gray or black for crossed position 0.008 to 0.024 BRIGHT B By gypsum plate bright colors for both positions. By mica plate notably dif- ferent tints for crossed and parallel positions 0.024 to 0.06 HIGH ORDER Not describably affected by mica plate in either position > 0.06 The term ''Bright" signifies definite, brilliant colors. "High order" signifies faint varied tints not easily distinguished, and grading into white. Bright A are the lower-order bright colors reducible to whites, etc., by the gypsum plate. Abnormal Interference Colors. Strictly the birefringence of a doubly refracting substance, while often more constant than the indices of refraction, is not the same for all colors. In some minerals it is zero for certain wave-lengths. If, as with vesuvianite and chlorite, for instance, it is near zero for yellow, a deep blue appears no matter what the thickness of the slide. Other minerals show other abnormal colors. The color of the mineral itself may modify the interference color and in some monoclinic or triclinic crystals a modification results because the colors have no constant positions of darkness. DETERMINING EXTINCTION ANGLES BETWEEN CROSSED NICOLS. As explained, p. I n, when either of the two rays emerging from a crystal section is parallel to the vibration direction of the lower nicol the field is dark. The angle between this direction and some recognizable crys- talline direction, cleavage, crack, face, twin plane, etc., is called the extinction angle of the section. General Method. Place the section on the stage of the microscope, focus with the upper nicol out, make some characteristic crystalline direction CR YSTALL O- OPTICS. 1 39 coincide with a cross hair, read the vernier, push in the upper nicol and rotate the stage of the microscope until the field is at its maximum darkness. Again read the vernier. The difference between the two readings is the extinction angle of the section with the chosen direction. Because of the gradual change from light to darkness the recog- nition of maximum darkness is difficult and if a closer determina- tion is desired, the average of a number of measurements taken as follows may be used. After carefully determining the position of the crystalline direc- tion rotate the stage clockwise until the field is dark at some reading a. Continue the rotation until the field is light, then turn back counter clockwise to some reading of. The reading halfway between is near maximum darkness. With colorless crystals the determination may be verified by slightly rotating the upper nicol. If the installation is accurate the field and the crystal will brighten simultaneously, retaining the same tone. Sensitive Tint Plates. If the gypsum test plate, p. 137, or a quartz plate yielding sensitive violet No. I is inserted in the slot above the objective and the grain or section adjusted to only partly cover the field, the entire field will be violet for the extinction positions but the slight- est rotation will change the color of the mineral to purple or indigo. The Bravais double plate, p. 137, will do this with even greater delicacy one half becoming purple, the other indigo. Many other devices exist also involving color contrasts de- veloped when the vibration directions of the fragment and the nicols are nearly but not quite parallel. To all of these are two strong objections. 1. They are not available for monochromatic light. 2. They transmit only a small percentage of the light and are effective only for crystal sections which are light in color and which themselves yield the low colors of the first order. Special Points Extinction. In tetragonal, hexagonal and orthorhombic crystals, the vibra- tion directions coincide with the crystal axes for light of any wave- 140 CR YS TALL O GRA PHY. length. Hence white light is used and in general the extinction direction will be parallel or symmetrical to observed crystalline directions. In monoclinic crystals the maximum and characterizing extinc- tion angles are obtained in sections parallel to the plane of sym- metry.* Moreover, because the vibration directions are different for light of different wave-length monochromatic light should be used. DETERMINING UNIAXIAL OR BIAXIAL BY INTERFERENCE FIGURES. The optical properties of a crystal may be studied, not only in one direction but simultaneously in a great number of different directions, by use of convergent polarized light. With the polarizing microscope select by parallel light a suitable grain or section, either one that shows darkness between crossed nicols for a complete rotation or one that retains a uniform illumi- nation throughout or failing these a grain which for a given thick- ness shows the lowest interference color (that is, is nearest normal to an optic axis). This grain is then carefully focused, using a high power objective and the condensing lens directly under, the stage. The upper nicol is pushed in, the eye piece removed, and the interference figure viewed by looking down the tube. The interference figure thus seen is made by the objective ajone, these images are small but often sharply defined, the removal of the eye piece, however, makes it impossible to measure the distance between the axial points in any biaxial figure. A magnified imagef can be ob- tained if the eye piece is retained and the Bert- rand lens inserted in the microscope tube as de- scribed, p. 123. What has happened may be briefly explained as follows: In Fig. 261 the foci of the objective and * This plane being always parallel or perpendicular to the plane of the optic axes can be found by convergent light tests. t The image can also be seen through the eye piece by means of a hand glass held a little above it. FIG. 261. ' ~m t i**"** L & CR Y STALL O- OPTICS. 141 the condensing lens L coincide at /. Every point, p, q or r, in the focal plane F is the vertex of a cone of rays which is made parallel by L, traverses the crystal as a parallel bundle and is by 0' again brought to focus at points p'q'r' of the focal plane F f . Each di- rection in the crystal plate therefore is traversed by a minute bundle of parallel rays, which undergo the same extinction and interference phenomena as were described for parallel light, and record them at some point in the focal plane F f . Every point of the image formed in the focal plane F' therefore corresponds to a direction in the crystal and is dark four times in a revolution and of a specific color at all other times. The image is known as the "interference figure," the shape, brightness and tints of which depend upon the structure of the plate for all the directions traversed by the rays. The results obtained differ as the crystal is isotropic, uniaxial or biaxial. Isotropic. The section which remained dark throughout rota- tion in parallel polarized light between crossed nicols still remains dark. UNIAXIAL INTERFERENCE FIGURES. The section which remained dark throughout rotation in paral- lel polarized light between crossed nicols is at right angles to the FIG. 262. FIG. 263. optic axis. It does not remain dark in convergent light but develops the characteristic interference figure, Fig. 262, which consists of 142 CRYSTALLOGRAPHY. 1. A dark cross, tne arms of which intersect in the center of the field, and remain parallel to the vibration directions of the nicols during rotation of the fragments. This cross, sometimes called the isogyres, corresponds to the emerging rays which for any one position of the stage have their vibration planes parallel to the nicols. As the stage is rotated suc- cessive rays come into these positions, maintaining the same effect. 2. With monochromatic light the field will be of the color used, but if the section is not too thin,* the center of the black cross will be surrounded by concentric dark circles. Suppose a cone of polarized monochromatic light passed through the plate with its axis, parallel to the optic axis. The ray in the direction of the axis will pass through unchanged and be stopped by the analyzer. All oblique rays at some particular angle will have a phase difference equal one wave-length and therefore will yield a circle of darkness. The rays at some larger angle will have a phase difference equal two wave-lengths and yield a second concentric circle of darkness and so on. With white light the concentric circles will be color rings, arranged strictly in the order of the interference colors. Oblique Sections. From sections which in parallel light were not black but showed the lowest obtainable interference color, an eccentric interference figure may be obtained, Fig. 263. The center of the figure revolves as the stage is rotated but the arms of the black cross remain parallel to the vibration planes of the nicols, unless the obliquity is great when they may be curved. If the Birefringence is Weak. There may appear only the black cross and no rings which may be so hazy that the existence of a figure is best proved by using the gypsum test plate in which case two opposite quadrants will be colored blue and two orange. * In uniaxial crystals in which the optic axis is a direction of circular polarization the interference figures from thin sections are essentially as described but in thicker sections the bars do not reach the center and the inner circle has that color tint which the entire section would have with parallel light. On turning the analyzer this color will change in an order dependent on the direction of rotation produced by the sub- stance. CR YSTALL O- OPTICS. BIAXIAL INTERFERENCE FIGURES. Sections Perpendicular to Acute Bisectrix.* When obtainable a section equally inclined to both optic axes, that is, normal to the acute bisectrix yields the following very characteristic figure : i. Whatever the position of the plate the "isogyres" ap- pear as two dark bars or brushes which correspond to the emergence of rays with their vibration planes parallel to those of the nicols. They are not constant in shape. For the so-called normal position one connects the points of emergence of the optic axes, the other is a thicker, lighter band at right angles to the first and midway between the axes. FIG. 264. FIG. 265. If the stage is rotated, other rays vibrate parallel to the nicols and the straight dark lines seem to dissolve into an hyperbola the poles of which are the loci of the optic axes and, Fig. 266, the branches of which rotate in the opposite direction to the rota ton of the stage. The convex side of each is always toward the other branch. The Isogyres can always be graphically found as follows: The directions of vibration of any pair of emerging rays can be found by bisecting the angles between the two lines formed by connecting the point with the loci of the optic axis. The isogyres result by connecting those points, the vibrations at which are parallel to the vibrations of the nicols. * To determine the acute bisectrix it may be necessary to first measure the axial angle. Ordinarily the interference figure in a section normal to the obtuse bisectrix will resemble the figure parallel to plane of optic axes, Fig. 267, and the axial loci will not be visible. 1 44 CRYS TALL O GRAFHY. Thus in Fig. 264, let L and L f be the points of emergence of the optic axes. PP f and A A' the vibration directions of polarizer and analyzer respectively, then the hyperbolae through L and U are the isogyres because connecting any point as a, c, d or e with L and L' the bisectors are parallel PP' on A A' whereas for other points of the field such as b the bisectors are not parallel these directions. Many points near the hyperbola give bisectors nearly parallel PP' and A A', therefore at these there is approximate extinction resulting in a broad brush rather than a sharp line. 2. With convergent monochromatic light there will be, in a field of the color used, black closed curves around the loci of the optic axes corresponding to retardations of one, two, three, etc., wave-lengths. These curves will not be circles but ovals which corresponding to bases of cones until some pair unite at or near the center to a cross loop or figure eight around both axes and subsequent rings form lemniscates around this as in Fig. 265. The shapes of these curves do not change on rotation of the plate. FIG. 266. FIG. 267. If white light is used the superimposed interference figures may be much more complex as neither the axial loci nor the isogyres nor the cones of equal retardation coincide, and upon the changes in the isochromatic curves during the rotation rest important distinctions between crystalline systems. Sections Perpendicular to an Optic Axis. Sections which remain uniformly illuminated with parallel polarized light between crossed nicols are at right angles to an optic axis and yield an interference figure somewhat like the uniaxial figure. The black cross, however, is replaced by a single CR YSTALL O- OPTICS. black bar, essentially straight, Fig. 268, whenever the trace of the plane of the optic axes coincides with the vibration direction of other nicols. For all other angles of rotation it is curved and resembles one arm of an hyperbola through the axis, Fig. 269, the convex side toward the other axis. This arm rotates in the opposite direction to the rotation of the stage. FIG. 268. FIG. 269. Oblique Sections. The sections which in parallel light between crossed nicols yield the lowest interference colors show figures something like those just described. The single black bar which rotates in the opposite direction to the stage proves the biaxial character. Sections Parallel to the Plane of the Optic Axes. Such sections yield in monochromatic light an interference figure, Fig. 267, not easily distinguishable from that given by a uniaxial plate cut parallel to the optic axis. DETERMINING THE CHARACTER OF THE DOUBLE REFRACTION. Optical Character of Uniaxial Crystals in Parallel Light. If the direction of the optic axis is known from the shape of the crystal or otherwise, the ray vibrating parallel to it is the extra- ordinary. Or if determinations on several fragments yield one constant index of refraction (ordinary) and one varying (extra- ordinary), then the character results by (+). The ordinary or constant index is less than the extraordinary or varying index. ( ). The constant index is greater than the varying index. No corresponding test exists for biaxial crystals, ii 146 CR YSTALLOGRAPHY. Uniaxial Crystals with Convergent Light. The interference figure, Fig. 262, is changed characteristically by test plates inserted in the slot above the objective. The Quarter Undulation Mica Plate inserted with its vibration directions diagonal to those of the nicols breaks the color rings into quadrants, and breaks the cross at the center developing two FIG. 270. FIG. 271. black spots. The relative effects in positive and negative crystals are shown in Figs. 270, 271, the arrow being the vibration direc- tion Z of the slower ray of the mica plate. The corresponding signs -f- and are suggested by the relative position of these dark spots and the direction Z. If the Gypsum Test Plate is similarly inserted the black cross becomes reddish violet and near the center two opposite quadrants become blue, the other two yellow. If a line be assumed to join the blue quadrants this line in positive crystals crosses the direction of vibration X and in negative crystals is parallel to it, again suggesting the correspond- ing + and signs. Uniaxial Oblique Sections. Rotate the plate until only one quadrant of the figure is in the field, judge the position of the center of the cross by the arms or curvature of the color rings, insert the mica and note the position of the shifting color arcs or of any developed dark spot with reference to Z of the mica plate. Biaxial Sections Normal Acute Bisectrix. In sections normal the acute bisectrix, the quarter undulation mica plate may be used as described above, for uniaxial crystals CR YSTALL O- OPTICS. when the distance between the points of emergence of the axes is small. The compensating quartz wedge may be inserted successively with Z and X parallel to the diagonal line connecting the axial points. In one of these insertions the rings around each axis will expand, moving toward the center and corresponding rings will merge in one curve. When this direction is Z the character is plus (+), when the direction is X the character is minus ( ). Biaxial Sections Showing the Optic Axis. Sections perpendicular, or nearly, to an optic axis show the dark bar which is noticeably convex* towards the acute bisectrix. If rotated into the position of Fig. 269 and the gypsum test plate inserted the bar becomes violet red but is differently bordered in positive and negative crystals. Positive crystals concave side yellow, convex side blue. Negative crystals, concave side blue, convex side yellow. Determining the Angle between the Optic Axis. As stated p. 105 the so-called optic axes of biaxial crystals are determinable directions for monochromatic light and constant FIG. 272. temperature. The angle between them can therefore be measured.* The optic axes lie in the plane of X and Z and these directions bisect the angles between the axes. Either however may be the acute bisectrix Bx a , Fig. 272. Usually a plane parallel plate is cut normal to the acute*bisectrix. The rays travelling parallel to the optic axis are obliquely incident at the air and are refracted, the apparent angle, Fig. 272, denoted by 2E, being larger than the true angle, denoted by 2V. \ Although^ a definite character for a crystal of definite com- * Unless the axial angle is very close to 90. f In Fig. 272, for instance, 2V = 56, 2E = 98. t In orthorhombic crystals the same plate will be normal for all colors, but in the other systems this is not so, but if the plate be cut normal for a middle color, say yellow, the results for all colors will be approximately accurate. 148 CR YSTALLOGRAPHY. position 2 V varies widely in the great minerals which are isomor- phous mixtures and is therefore less used than the other optical characters. Determining the Apparent Angle with the Microscope. The apparent axial angle* 2E may be determined in such a plate as Fig. 272 in any suitably equipped microscope, by measuring the distance, 2d, between the points of emergence of the optic axes. Usually the interference figure is placed in its diagonal position, Fig. 266, and the distance 2d measured between the foci of the hyperbola by some form of micrometer eye piece. FIG. 273. Then sin E = d/C, in which C is a constant for the same system of lenses and is determined once for all by means of crystals of known axial angles. * The axial angle can also be determined in sections showing the emergence of only one optic axis by means of the curvature of the isogyres (p. 143). (See Johann- sen, " Petrographic Methods," p. 480.) CR YSTALL O- OPTICS. 149 For instance, if in a mica 2E = 91 50' and d = 41.5 divisions on the scale, then C = d/sin E = 57.78 for that combination of lenses. Determination of the Axial Angle by Rotation. A more exact measurement may be made by actual rotation of the plate about Y as an axis. The microscope, with some form of rotation apparatus, Fig. 274, attached, may be used or a polariscope, Fig. 273. The microscope or polariscope is usually FIG. 274. v. Federow Universal Stage. horizontal and the nicols are crossed at 45 to the horizon, sor that when the line connecting the axial points is horizontal the interference figure shows the hyperbola. The section is adjusted so that the axial points of the interference figure remain on the horizontal cross hair during revolution. The crystal is then revolved and the arms of the hyperbola are successively made tangent to the vertical cross hair. The difference between the two readings is the apparent angle 2E. Determining the True Angle. A second measurement may be made of the apparent angle in a plate normal to the obtuse bisectrix. Denoting this by 2E' the sinE relation is tan V = - ^ . sin E If the middle index /3 is known sinE smF If the section is immersed in a liquid of index or even the mean index found by Becke test, then E = V. 150 CRYSTALLOGRAPHY. DETERMINING THE CRYSTALLINE SYSTEM BY OPTICAL TESTS. The crystalline system can usually be identified as follows: If each grain or section tested is Homogeneous, that is, shows in all parts the same optical behavior. Determine by test page 127 whether isotropic or anisotropic. Anisotropic. Confirm by the fact that no interference figure is produced by convergent light. (a) Amorphous. Absence of crystalline form or cleavage. (b) Isometric. Presence of crystalline form or cleavage. B. Anisotropic. By test page 140 seek out suitable fragment or section* and determine whether uniaxial or biaxial. (a) Uniaxial. Confirm by fact that in other grains or sections extinction always takes place for directions parallel or symmetrical to crystal outlines, cleavage cracks, etc., p. 139. No purely "optical" distinction exists between the tetragonal and hexagonal crystals. The section or fragment which yielded the interference figure may show outlines or cleavages character- istic of the system. Tetragonal Angles of 90 or 135. Hexagonal Angles of 60 or 120. (b) Biaxial, i. Orthorhombic. In the interference figure ob- tained in grain or section normal to a bisectrix with white light the shape of the isochromatic curves will be symmetrical to the line joining the optic axes, to the line through the center at right angles thereto and to the central point. In all sections or grains parallel to any one of the three crystallo- graphic axes a, b, and c, the extinction will take place with parallel light in directions parallel or symmetrical to cleavage cracks and crystal outlines. There may be two cases dependent on the different axial angles for light of different wave-length, and as the colors fringing the hyperbola will be in inverse position to the axial * Much can be done with forms of rotation apparatus. Fig. 274 shows the v. Federow Universal Stage with three axes of rotation. The stand IV carrying the stage can be placed on the stage of the microscope. By k the stage is rotated about a horizontal axes, the amount of rotation being shown on T. The stage K is rotated about a second axis perpendicular to the first, the amount being read on the vernier m;"it also carries a third axis, Hd (a diameter in its plane). Finally the glass plate, S, carrying the object can be rotated in its plane. CRYSTALLO-OPTICS. 151 points. For red less than violet, the red is further from the center than the blue. For red greater than violet, the red is nearer the center than the blue. 2. Monoclinic. In the interference figure obtained described above with white light the shape of the isochromatic curves will be symmetrical to one line or the central point. The line of sym- metry may join the axial points (Inclined Dispersion) or (6) be at right angles to this (Horizontal Dispersion) or there may "be symmetry to the center (Crossed Dispersion). In all grains or sections parallel to the axes of geometric sym- metry extinction will take place in directions parallel or symmetrical to crystal outline or cleavage cracks. In all other grains or sections the directions will be oblique and unsymmetrical. (c) Tridinic. In the interference figure with white light the isochromatic curves are not symmetrical to line or center. The directions in which extinction takes place are always oblique and unsymmetrical to crystal outlines or cleavages. ABSORPTION, COLOR AND PLEOCHROISM. Absorption. When monochromatic light is either reflected from or trans- mitted through a crystal it undergoes partial absorption, the amount absorbed increasing with the thickness. If the crystal is doubly refracting the rate of absorption will probably be different for the two rays transmitted in any direction and also different in different directions. If white light, composed of a multitude of lights of different color and different wave-lengths, is used each component light is affected as described, but the percentages absorbed may be either alike or different (Selective Absorption). Color. If the absorption of all the colors has been essentially in the same ratio the body appears colorless or white. If not in the same ratio, then it appears that tint which results from the combined effect of the unabsorbed portions of the component lights. 152 CRYSTALLO GRA PHY. The color depends also on the proportions* of the different monochromatic colors in the light used as a source, for instance, alexandrite is red by candle light, green by sunlight and of an intermediate tint by a tungsten light. The substance simply possesses the power to absorb certain tints, that is, light of certain wave-lengths more rapidly than others. The "color" is what is left. Transparency vs. Opacity. If the non-absorbed rays penetrate the substance it appears transparent and colored or colorless, if they are all reflected it appears opaque, colored or white. If all are absorbed it appears black. Pleochroism in General. In doubly refracting crystals the color in different directions may be noticeably different as in epidote and iolite. The two rays transmitted in any one direction may also be differently colored. Usually the eye observes a mixed resultant color. This variation in color is called pleochroism or dichroism. It is impossible in singly refracting material and in colorless doubly refracting material. In colored doubly refracting material it is a common but not necessary phenomenon, and when present is best displayed by the deeper colored crystals. Pleochroism in Uniaxial Crystals. The optic axis is a direction of single refraction for white light and pleochroism does not occur in this direction, that is, in sections normal to the optic axis the color is constant, but in any other section the two rays are differently absorbed and may be differently colored. The color of one of these rays is constant for a given thickness whatever the direction of the section. The color of the other varies with the section and differs most from the constant (ordi- nary) ray in the section cut parallel to the optic axis and in all other sections the ordinary will be found to approach the constant * The proportions of the different monochromatic colors varies even in sunlight, and the differences between even the best artificial light and sunlight are very great, the former usually containing far greater proportions of yellow and red. CR YSTALL O- OPTICS. 1 53 tint of the ordinary as the sections become more nearly per- pendicular to the optic axis. The relation of absorption to transmission varies: the directions of principal ab- sorption (maximum and minimum) coincide for all colors with the principal vibration directions A' and Z. There is no necessary relation between degree of absorption and indices of refrac- tion and two classes may be made. 1. Absorption of ordinary ray greater than that of extraordinary ray. 2. Absorption of ordinary ray less than that of extraordinary ray. Pleochroism in Biaxial Crystals. A pleochroic biaxial crystal shows pleochroism in all directions. It is true there are for any one temperature and light of any one wave-length two directions of single refraction. But when white light is used each color has its slightly different direction of single refraction and moreover the light which emerges travelling in one of these directions is merged with the doubly refracted light from an inner cone of rays which after emergence travel in the direction of the optic axis, therefore any such composite bundle will show dichroic effects and will not give darkness between crossed nicols. It is customary to record the colors obtained for rays vibrating parallel X, Y and Z and where possible to record also the relative degrees of absorption in these directions. The directions of principal absorption (maximum and minimum) coincide with X, Y, Z for all colors in orthorhombic crystals. They do not so coincide in triclinic crystals nor completely coincide in monoclinic crystals. There is no relation between the degree of absorption and the indices of refraction. Maximum absorption may be in the plane of the optic axes or perpendicular thereto. Determining Pleochroism with the Microscope. Minute grains and fragments as well as larger sections may be examined as follows: Focus with the upper nicol out; push in upper nicol and rotate the stage until the field is dark; push out the upper nicol and note the color of stone. Rotate the stage 90 and again note the color. These positions usually give the maxi- mum difference in color for the direction of transmission. The pleochroism may appear as a change in color or a change in the shade of the same color. In intermediate positions of rotation the color is due to com- ponents of each of the extreme colors, in the diagonal position these components are equal. There emerge from the stone two rays vibrating at right angles but differently absorbed and possibly colored, but not sufficiently divergent to be seen separately and yield a combination color. 154 CR YSTALLOGRAPHY. If one can be held back the other can be seen or vice versa. When the lower nicol of a microscope is parallel an extinction direction one of the two rays that gets through and its color is seen. When the stage has been revolved 90 the other ray gets through and its color is seen. In intermediate positions the color is due to both. If it is desired to show the colors side by side a dichroscopic ocular may be used, Fig. 275. The action is like that of the dichroscope described below. It is especially applicable to the grains in thin sections. Determining Pleochroism with Dichroscope. The colors of the ordinary and extraordinary rays may be con- trasted side by side by means of a "dichroscope," Fig. 276, which FIG. 275. FIG. 276. 1 G / / / s / i is in its essentials a cylindrical casing with a rectangular hole, H, at one end and a lens, L, at the other and between a rhomb of calcite S of such a length that the two images of the hole are just in contact. In some instruments the terminal faces of the rhomb are ground at right angles to its length, but usually wedges of glass G are attached. The section or stone to be tested may be directly attached to a movable cap C by means of some kind of wax or cement so that the light which has traversed it passes into the window, H. The instrument shown, Fig. 277, has convenient devices by which the crystal, or section, or cut stone may be held and turned about two axes, one at right angles to the length of the tube, the CR YSTALL O- OPTICS. 1 55 other parallel to the length of the tube, and thus examined in different directions. FIG. 277. >< The method of using is as follows: Hold the stone close to the square orifice and rotate the instrument until the two images are of the same color. Midway between two such positions the colors differ most. Whether pleochroism is shown for this position or not, place the stone in a second notably different position and again try for the limit colors. In examining a cut stone revolve the dichroscope rather than the stone so as to avoid different light effects from different positions of facets, and verify the fact that the differences are due to pleochroism by noting that the two images of any face interchange colors for 90 of rotation of the dichroscope. The dichroscope does not produce the colored rays, they emerge from the crystal and the calcite simply renders them more diver- gent so they can be seen at the same time. As the dichroscope is turned each ray from the crystal is de- composed in the calcite and contributes a portion of its intensity to each of the two images, but at the positions of maximum difference of color the vibration directions of the two rays from the crystal and the vibration directions of the calcite coincide. PART II. BLOWPIPE ANALYSIS CHAPTER XI. APPARATUS, BLAST, FLAME, ETC. Qualitative determination of component elements and tests of fusibility and solubility are very important aids in the identi- fication of mineral species, and together with a limited number tests with wet reagents are here discussed under the title of Blowpipe Analysis. Bartholin, the describer of double refraction, appears to have been the first to utilize the blowpipe in mineral testing, for in 1670 he states that iceland spar before the blowpipe was burned to lime. Kunckel nine years later recommended its use in chemical testing. Its more systematic use in mineral testing dates from Anton Swab in 1733 and was developed at first in Sweden by Gahn, Cronstedt, Berzelius and others and later in Germany by Plattner, Richter, von Kobell and Bunsen. The Advantage of " Blowpipe Tests." Minerals are in general insoluble in water and many of them insoluble in acids. Their examination by wet methods would usually require a previous fusion and solution. With the blowpipe the tests are made directly upon the mineral, and are rapidly obtained, with very little material and with very simple, easily portable apparatus and reagents. Although group separations, except for instance into volatile and non-volatile, are not practicable the order of testing is not indifferent as it is often desirable that certain elements be detected and largely removed before making the tests for the others. 156 APPARATUS, BLAST, FLAME. 157 The set of apparatus which has been found best in the work at Columbia University consists of the following articles : 1 Streak plate (fine grained) E & A 5310, size 2 1/8" x 3 3/8". 2 Ft. rubber tubing, 1/8" I D, pure gum, E & A 6052. i Dropping tube, pipette, small, E & A 5224, 6 Reagent bottles in wood block, with i Gas blowpipe, Plattner's, E & A No 794, modified, i Forceps, platinum tipped, French style, E & A 3206. i Cupel holder, 2 moulds, i stamp, E & A 829, made more convex by Columbia, i Steel hammer, Colton's, wire handled, E & A 3820. i Leed's Diamond mortar, E & A 4628, in wooden box. i Chisel and borer (combined) not magnetized, E & A 817. i Bar magnet in iron case, one end bevelled, Columbia make, i Coal tray, E & A 853, but size 5^" x 4 1 A". 6 Watch glasses, 2" E & A 7832. 12 Closed tubes sublimation, closed at one end, O D 8 mm., I D 6 mm., length TOO mm. J. Kavalier's hard Bohemian combustion tubing. The Blowpipe special short corks in bottles. 3 Pieces charcoal, willow, close grained, best grade. i Holder for platinum wire, E & A 831. i Platinum wire (6 inches) B & S No. 28. i Outfit box, for carrying apparatus. 6 Inch white rubber tubing, 3/16" I D. i Box for hardness scale New England Box Co. i Merwin's flame color screen G. M. Flint, Cambridge, Mass, i Penfield contact goniometer, model B, Sheffield Scientific School, i Coddington lens, loX, Bausch & Lomb No. 162. i File, i/8"x3"xi/8". The best form of blowpipe (Fig. 278) consists of: 1. A tapering tube of brass or German silver (B), of a length proportionate to the eyesight of the user. 2. A horn or hard rubber mouthpiece (C) at the larger end of the tube. This should be of trumpet-shape to fit against the lips. 3. A moisture chamber (A) at the smaller end of the tube connected by ground joints to : 4. A tapering jet () at right angles to the moisture chamber. 5. A tip of platinum or brass (c\ shown enlarged, which should be bored from a solid piece, and with an orifice of o. 5 millimeter diameter. The tip is by far the most important part of the blowpipe, and, if correctly made, the flame produced will be perfectly regular and will not flutter. When not in use the blowpipe should be so placed that the tip is supported free from con- tact. If the tip is clogged by smoke or other- wise is should be burned out or cleaned with the greatest care so as not to injure the regu- ular form of the orifice. 158 BLOWPIPE ANALYSIS. Gas Blowpipe. For most purposes the gas blowpipe, Fig. 279, is a convenient form and is extensively used. The flame is not quite so hot as that from rape-seed oil, but is sufficient to round the edges of a calamine splinter. Oxidation and reduction are easily obtained and the cleanliness and ease of control cause it to be preferred by FIG. 279. many. The ordinary blowpipe can be made into a gas blowpipe by means of an attachment to connect to the moisture chamber. Blowpipe Lamps. Bunsen Burner. The simplest form of lamp for laboratory pur- FIG. 280. FIG. 281. poses is the ordinary Bunsen burner, Fig. 280, using gas and fur- nished with a special top (), or an inner tube shaped to spread APPARATUS, BLAST, FLAME. 159 the flame. When used with the blowpipe the orifices (&) at the bottom of the burner should be closed, so that no air enters with the gas. A flame about 4 cm. high gives the best results. The hottest flame and greatest variations in quantity and quality of flame are obtained from oils rich in carbon, such as refined rape- seed, or olive or lard oil, or from mixtures of turpentine and alco- hol. These can be used in the field and where gas is not available. In some kinds of blowpipe work they are to be preferred to gas, but will not serve for bending glass or for heating without the blowpipe. Berzelius Lamp. A lamp with two openings, Fig. 281, is gen- erally used for oil. The wick should be soft, close-woven and cylindrical, such as is used with Argand lamps. It should be folded and inserted with the opening toward the lower side of the brass holder. To fill the lamp both caps are removed and the oil poured in through the smaller orifice. During work, the smaller cap is hung on the vertical rod ; the larger is placed over the smaller orifice loosely, keeping out the dust, but admitting the needed air. The lamp is lighted by blowing a flame up and across the wick. When well charred, the wick is carefully trimmed parallel to the brass holder. Fletcher Lamp. The Fletcher blow- pipe lamp, Fig. 282, gives good satisfac- tion, and a modified form, burning solid fats, tallow or paraffine, is especially adapted for field work. Supports of Charcoal, Plaster, Etc. Charcoal. Charcoal made from soft woods, such as willow or pine, is used to support the substance and receive any coats or sublimates that may form, and, in a measure, is a reducing agent. A convenient size is 4 inches long, I inch broad, and ^ inch thick. Plaster. Plaster tablets are used for the same purpose. These are prepared by making a paste of plaster of Paris and water, just thick enough to run, which is spread out upon a sheet of oiled glass and smoothed to a uniform thickness ( V^" to %") by another smaller sheet of glass, which may be conveniently handled by gum- ming a large cork to one side and using it as a plasterer's trowel. FIG. 282. 160 BLOWPIPE ANALYSIS. While still soft, the paste is cut with a knife into uniform slabs, 4" by \y 2 ". It is then dried, after which the tablets are easily detached. FORCEPS, with platinum tips for fusion tests. The most con- FIG. 283. venient form is shown, Fig. 283, the platinum ends projecting at least three fourths of an inch. PLATINUM WIRE AND HOLDER. Wire of the thickness of about one quarter millimeter and a holder in which the wires can be changed and with a receptacle for a stock of wires. CLOSED AND OPEN TUBES. See Figs. 296 and 297. CUPEL HOLDER AND CUPELS, for silver determination. See Figs. 403 and 404. Miscellaneous Apparatus : REAGENT BOTTLES. Eight 2-oz. wide-mouthed bottles; for borax, soda, salt of phosphorus, and bismuth flux will be needed at all times in a convenient stand. ANVIL. Slab of polished steel, about \\" by i\" by J", or better a Leeds diamond mortar, Fig. 284. HAMMER. Steel, with square face, -|" or i"; the most satisfac- tory being the Colton with wire handles, Fig. 285. FIG. 284. FIG. 285. Other important pieces of apparatus are : bar magnet, with chisel edge ; trays, for dirt and for charcoal ; lens and watch glasses ; cutting pliers ; small porcelain dishes, ivory spoon and dropping tube. Very useful accessories are the Merwin Color Scale, p. 165 ; a Hardness Scale, p. 217, and a Penfield Goniometer, Fig. I. APPARATUS, BLAST, FLAME. 161 BLAST AND FLAME. The Blast. The blast is produced by the muscles of the distended cheeks, and not by the lungs. It is best to sit erect, with the blowpipe held lightly but firmly in the right hand, and with the elbows against the sides. Then, with the cheeks distended and the mouth closed, place the mouth- piece against the lips, breathe regularly through the nose, and allow air to pass into the pipe through the lips. From time to time, as needed, admit air to the mouth from the throat. In this manner, after learning to breathe through the nose while keeping the cheeks distended, a continuous blast can be blown without fatigue. The Flame. A LUMINOUS FLAME (Fig. 286) usually shows three distinct por- tions. 1. A very hot non-luminous veil, a, of carbon dioxide and free oxygen. 2. A yellow luminous mantle, b, of burning gases and incandescent carbon. 3. An interior dark cone, c, of unburned gases, not always visible. Oxidation and Oxidizing Flame. The oxidizing flame is non-luminous, for lumi- nosity indicates unconsumed carbon, and hence a reducing action. To produce such a flame, place the tip of the blowpipe almost touching the top of the burner, or the wick, and extending in % the breadth of the flame ; blow parallel to the burner top or wick until there is produced a clear blue flame nearly an inch long. This blue flame is weakly reducing, but just beyond the blue at a (Fig. 287) is an intensely hot, nearly colorless zone, which is strongly oxidizing, and the bead is held in this usually as far from the tip of the blue flame as the bead can be kept fluid. If the substance to be oxi- dized is supported on charcoal, a weak blast must be used. 12 162 BLOWPIPE ANALYSIS. With the gas blowpipe all that is necessary is to avoid an excess of gas. The blue flame is, as before, surrounded by the oxidizing colorless mantle. Purity of Oxidizing Flame by Action on Mo0 3 . Regulate the supply of gas until the blowing produces a clear blue flame nearly an inch long. This blue flame itself is weakly reducing, but is surrounded by an intensely hot, nearly colorless zone, which is strongly oxidizing. The bead is held in the latter, Fig. 287, as far out from the tip as it will keep fluid. Make a loop in platinum wire by bending it around a pencil point so that the end meets but does not cross the straight part, FIG. 287. FIG. 288. Fig. 288. Heat the loop, dip it into borax and fuse the portion that adheres to a clear bead. Add more borax until the bead is of full rounded shape. Dip the hot bead into the MoO 3 , dissolve the adhering material at the tip of the blue flame and make the bead alternately brown or black from MoO 2 and colorless from MoO 3 by varying the posi- tion of the bead in the flame. Purity of Reducing Flame by Action on Mn0 2 . Regulate the gas to produce a larger flame than for the pre- ceding test. This may be so done that during the blast there is still a distinctly yellow part near the end of the flame. The bead should be kept covered by this yellow portion, Fig. 289. The blast must be continuous ; too strong to produce a sooty flame, and not strong enough to oxidize by excess of air. The blue flame also is reducing because of the carbon monoxide it contains, but it is not as effective. APPARATUS, BLAST, FLAME. Make a borax* bead as in the preceding test. Dip it while hot into the MnO 2 and heat in the oxidizing flame ; if only a little MnO 2 is used the bead will become violet-red when cold. It can be made colorless in the reducing flame by steady blowing. If FIG. 289. more is used the bead will be nearly black when cold before reduc- tion and amethystine after reduction. Or cupric oxide or oxide of nickel may be dissolved in a borax bead until the bead is opaque, and then reduced on charcoal to a clear bead and a metallic button. * When the flux is salt of phosphorus, the wire should be held over the flame so that the ascending hot gases will help to retain the flux upon the wire. CHAPTER XII. OPERATIONS OF BLOWPIPE ANALYSIS. Fusion. The degree of fusibility and manner of fusion of a min- eral are of great assistance in its determination. The degree of fusibility is stated in terms of a scale of fusibility as suggested by von Kobell or sometimes in terms such as easily fusible, difficultly fusible. The scale somewhat modernized is : Easily Fusible. 1. Stibnite or Sulphur. Fuse in closed tube below red heat Coarse splinters fuse in a candle or gas flame. 2. Chalcopyrite or Galenite. Fuse in closed tube at red heat. Standard splinters fuse in luminous flame. 3. Garnet (Almandite) or Stilbite. Standard splinters easily fuse before the blowpipe to a globule. 4. ActinoUU or Barite. Standard splinters are easily rounded before the blowpipe. Fine splinters fuse easily to a globule. Difficultly Fusible 5. Orthoclase or Sphalerite. Standard splinter rounded on thin edges before the blowpipe. Only finest splinters fused to a globule. 6. Calamine or Enstatite. Finest edges only rounded before blowpipe. Infusible. j. Quartz or Topaz. Retaining edges in all their sharpness after treatment. The Test. The substance should be tried on coal to see if vola- tile or reducible. If not then as shown in Fig. 290, sharp edged thin splinters of some approximately constant size (say 1^x4 mm.) are held in the platinum forceps just beyond the tip of the blue flame. 164 OPERATIONS OF BLOWPIPE ANALYSIS. I6 S FIG. 290. If easily fused or reduced on coal, the platinum forceps must be avoided and the closed tube used (for I and 2). If in powder, or with a tendency to crumble, grind and mix with water to fine paste, spread thin on coal and dry, and, if co- herent, hold in the forceps. The fragment should project beyond the platinum as in Fig. 290, so that heat may not be drawn. off by the platinum, and the flame directed especially upon the point. It is always well to examine the splinter with a mag- nifying glass, before and after heating. The manner of fusion may be such as to result in a glass or slag which is clear and transparent, or white and opaque, or of some color, or filled with bubbles. There may be a frothing or intumescence, or a swelling and split- ting (exfoliation). In certain instances the color and form may change without fusion, etc. Flame Coloration. A number of minerals when heated color the flame, some at a gentle heat, some only at the highest heat attainable. Repeated dipping of the mineral in hydrochloric acid usually assists by forming volatile chlorides. A good method to cover all cases is as follows: Arrange a black background, such as a piece of charcoal, powder the substance finely, flatten the end of a clean platinum wire and dip it in dilute acid, then in the powder, and hold it first just touching the flame near the blowpipe and then at the tip of the blue flame. Merwin's Color Scale * consisting of three colored strips of celluloid : No. I, blue ; No. 2, overlapping blue and violet ; No. 3, violet, which absorb different portions of the spectrum is most satisfactory for distinguishing the red flames of calcium, strontium, lithium, and the violet flames of potassium in the presence of sodium. The sodium coloration is absorbed in all three, the observed colors for the rest in I, 2, 3 order are Potassium Blue-violet Violet and violet-red Violet and violet-red Calcium Greenish yellow Absorbed Faint crimson Strontium or lithium Absorbed Absorbed Crimson * Science, Vol. 30, p. 571. 1 66 BLOWPIPE ANALYSIS. The important flame colorations are : Yellows. YELLOW. Sodium and all its salts. Invisible with blue glass. Reds. CARMINE. Lithium compounds. Masked by soda flame. Violet through blue glass. Invisible through green glass. SCARLET. Strontium compounds. Masked by barium flame. Violet red through blue glass. Yellowish through green glass. YELLOWISH. Calcium compounds. Masked by barium flame. Greenish gray through blue glass. Green through green glass. Greens, YELLOWISH. Barium compounds, molybdenum sulphide and oxide ; borates especially with sulphuric acid or boracic acid flux. PURE GREEN. Compounds of tellurium or thallium. EMERALD. Most copper compounds without hydrochloric acid. BLUISH. Phosphoric acid and phosphates with sulphuric acid. FEEBLE. Antimony compounds. Ammonium compounds. WHITISH. Zinc. Blues. LIGHT. Arsenic, lead and selenium. AZURE. Copper chloride. WITH GREEN, Copper bromide and other copper compounds with hydrochloric acid. Violet. Potassium compounds. Obscured by soda flame. Purple red through blue glass. Bluish green through green glass. In sili- cates improved by mixing the powdered substance with an equal volume of powdered gypsum. USE OF THE SPECTROSCOPE. When salts of the same metal are volatilized in the non-lumi- nous flame of a Bunsen burner the spectra produced, on de- composing the resultant light by a prism, will show lines identical in color, number and relative position. Salts of different metals will yield different lines. Although, with pure salts, the already described flame color- ations are generally distinct and conclusive, it will frequently hap- pen that in silicates or minerals containing two or more reacting OPERATIONS OF BLOWPIPE ANALYSIS. I6 7 FIG. 291. substances the eye alone will fail to identify the flame coloration. It is well therefore to supplement the ordinary flame tests by spectroscopic observation. In the blowpipe laboratory the chief use of the spectroscope will be to identify the metals of the potas- sium and calcium families singly or in mixtures. For this purpose the direct vision spectroscope of Hoff- man, Fig 291, is the most con- venient. The substance under examination should be moistened with hydro- chloric acid and brought on a plati- num wire into the non-luminous flame of the Bunsen burner as in the ordinary flame test. In viewing the flame through the properly adjusted spectroscope certain bright lines will be seen, and by comparing these with the chart, Fig. 294, or with substances of known com- position, the nature of the substance may be determined. The sodium line will almost invariably be present and the position of the other lines will be best fixed by their situation relative to this bright yellow line. The more ordinary form of spectroscope, Fig. 292, has special FIG. 292. advantages in allowing an easy comparison of flames. A is the observation telescope, B the collimator through which the light from the flames J/and M' is sent as parallel rays through the prism i68 BLOWPIPE ANALYSIS. FIG. 293. collimator and its the flame G. P to the telescope A. The third telescope C sends the image of a micrometer scale to A by which the relative distance apart of the lines is judged. Fig. 293 shows an enlarged view of the collimator B. By means of the little rect- angular prism i the light from a second flame H, placed at one side, is sent through the spectrum obtained side by side with that from FIG. 294. Ca HHWWB Ted org. yellow The chart (Fig. 294) and brief description of spectra of substances giving distinct lines with the Bunsen flame will be of service. POTASSIUM two red lines and one violet line. SODIUM a single bright yellow line, which with higher dispersion is resolved into two lines. Almost always present from the small amounts of sodium in dust. LITHIUM one very bright deep red line and a faint line in the orange. STRONTIUM a number of characteristic red lines and one blue line. CALCIUM a bright red, and a bright green line, with fainter red to yellow lines and a line in the violet. BARIUM a number of yellow and green lines. OPERATIONS OF BLOWPIPE ANALYSIS. 169 Absorption Spectra. The spectroscopic examination of the light reflected by or trans- mitted through colored minerals is likely to become of value in their identification. The apparatus used may be a separate instrument such as the "Pocket Spectroscope" with absorption spectrum and normal spectrum side by side, and electrically illuminated wave-length scale or a spectroscope ocular for the microscope, and it must be possible to determine the position of the bands with accuracy. The spectra obtained show often wide somewhat hazy black bands the position of which can be stated between limits and in other instances the series of very characteristic sharp bands which some can be closely placed. In certain instances the bands are due to the presence of known coloring elements, uranium, the rare earths, chromium, vanadium, etc. In other instances the elements causing the colors are not known. In certain species such as almandine garnet and zircon very char- acteristic lines are obtained, others like diamond sometimes give lines, sometimes do not. VOLATILIZATION. In blowpipe analysis, antimony, arsenic, cadmium, zinc, tin, lead, mercury and bismuth are always determined by securing sublimates of either the metals themselves or of some volatile oxide, iodide, etc. Other elements and compounds, such as sulphur, selenium, tel- lurium, osmium, molybdenum, ammonia, etc., are also volatilized and in part determined during volatilization as odors or by sub- limates. Certain other compounds, particularly chlorides of sodium and potassium and of some other metals, such as copper, tin and lead, yield sublimates ordinarily disregarded. Volatilization tests are commonly obtained on charcoal, or plaster or in open and closed tubes. Treatment on Charcoal. A shallow cavity, just sufficient to prevent the substance slip- ping, is bored at one end of the charcoal and a small fragment or a very little of the powdered substance is placed in it. The charcoal I/O BLOWPIPE ANALYSIS. is held in the left hand, so that the surface is at right angles to the lamp but tipped vertically at about 120 to the direction in which the flame is blown. A gentle oxidizing flame is blown, the blue flame not touching the substance, but being just behind and in a line with it. After a FIG. 295. few moments the test is examined and all changes are noted, such as position and color of sublimates, color changes, odors, decrepi- tation, deflagration, formation of metal globules or magnetic parti- cles. The heat is then increased and continued as long as the same reactions occur, but if, for instance, a sublimate of new color or position is obtained, it is often well to remove the first sublimate either by transferring the substance to another piece of charcoal or by brushing away the first formed sublimate after its satisfac- tory identification. The same steps should then be followed using the reducing flame. The sublimates differ in color and position on the charcoal ; some are easily removed by heating with the oxidizing flame, some by the reducing flame, some are almost non-volatile, and some impart colors to the flame. Treatment on Plaster Tablets. Experience has shown that the sublimates obtained on charcoal and plaster supplement each other. The method of using is pre- cisely the same and white sublimates are easily examined by first smoking the plaster surface by holding it in the lamp flame. The coatings differ in position, and to some extent in color. OPERATIONS OF BLOWPIPE ANALYSIS. 17 1 Plaster is the better conductor, condenses the oxides closer to the assay, and therefore, the more volatile coatings are thicker and more noticeable on plaster, while the less volatile coatings are more noticeable when spread out on charcoal. Charcoal supplements the reducing action of the flame, and therefore is the better sup- port where strong reduction is desired. Comparison of Important Sublimates on Charcoal and Plaster.* I. Without Fluxes. Treated First in 0. F., then in R. F. ARSENIC. White volatile coat. On smoked plaster it is crys- talline and prominent ; on charcoal it is fainter and less distinct, but the odor of garlic is more marked. Deposits at some distance from assay. Fumes invisible close to assay. ANTIMONY. White pulverulent volatile coat, more prominent on charcoal. Is deposited near assay and the fumes are visible close to assay after removal of flame. SELENIUM. On Charcoal. Horse-radish odor and a steel-gray coat. On Plaster. Horse-radish odor, brick-red to crimson coat. TELLURIUM. On Charcoal. White coat with red or yellow border. On Plaster. Deep brown coat. CADMIUM. On Charcoal. Brown coat surrounded by peacock tarnish. On Plaster. Dark brown coat shading to greenish-yellow and again to dark brown. MOLYBDENUM. Crystalline yellow and white coat with an outer circle of ultramarine blue. Most satisfactory on plaster. LEAD. ) Yellow sublimate with outer fringe of white. More BISMUTH. ) noticeable on charcoal than on plaster. ZINC. White, not easily volatile coat, yellow while hot. Best on charcoal. TIN. White non-volatile coat close to assay, yellowish while hot. Best on charcoal. * Certain compounds give a white coating before the blowpipe which at times cause confusion. Among these are many chlorides and 'the sulphate of lead. Galena and lead sulphides also give white sublimates which must not be confused with the arsenic or antimony coats. BLOWPIPE ANALYSIS. II. With Bismuth Flux.* LEAD. On Plaster. Chrome yellow coat. On Charcoal. Greenish-yellow, equally voluminous coat. BISMUTH. On Plaster. Chocolate-brown coat, with an underlying scar- let; with ammonia it becomes orange-yellow, and later cherry-red. On Charcoal. Bright red band with a fringe of yellow. MERCURY. On Plaster. Scarlet coat with yellow, but if quickly heated is dull yellow and black. On Charcoal. Faint yellow coat. ANTIMONY. On Plaster. Orange coat stippled with peach-red. On Charcoal. Faint yellow coat. ARSENIC. On Plaster. Yellow and orange coat, and not usually satis- factory. On Charcoal. Faint yellow coat. TIN. On Plaster. Brownish-orange coat. On Charcoal. White coat. The following tests show only on the plaster : SELENIUM. Reddish-brown, nearly scarlet. TELLURIUM. Purplish-brown with darker border. MOLYBDENUM. Deep ultramarine blue. III. With Soda (Sodium Carbonate or Bicarbonate). Soda on charcoal exerts a reducing action partly by the forma- tion of sodium cyanide, partly because the salts sink into the char- coal and yield gaseous sodium and carbon monoxide. The most satisfactory method is to mix the substance with three parts of the moistened reagent and a little borax ; then spread on the char- coal and treat with a good reducing flame until everything that can be absorbed has disappeared. Moisten the charcoal with water, break out and grind the portion containing the charge. Wash away the lighter part and examine the residue for scales and magnetic particles. * Two parts of sulphur, one part of potassium iodide, one part of acid potassium sulphate. OPERATIONS OF BLOWPIPE ANALYSIS. 1/3 The reduction may result in : 1 . Coating, but no reduced metal. Volatile white coating and garlic odor, . . . As. Reddish-brown and orange coating with characteristic variegated border, Cd. Non-volatile coating, yellow hot and white cold, . . Zn. Volatile steel-gray coating and horseradish odor, . Se. Volatile white coating with reddish border, . . Te. 2. Coating with reduced metal. Volatile thick white coating and gray brittle button, . Sb, Lemon-yellow coating and reddish-white brittle button, Bi. Sulphur-yellow coating and gray malleable button, . Pb. Non-volatile white coating, yellow hot, and malleable white button, . Sn. White coating, made blue by touch of R. R, and gray infusible particles, Mo. 3. Reduced metal only \ Malleable buttons, Cu, Ag, Au. Gray magnetic particles, .... Fe, Co, Ni. Gray non-magnetic infusible particles, W, Pt, Pd, Ir, Rh. The carbonate combines with many substances forming both fusible and infusible compounds. Many silicates dissolve with a little of the reagent, but with more are infusible ; a few elements form colored beads with the reagent, especially on platinum. The residue left after heating may contain malleable metallic beads of copper, lead, silver, tin or gold. It may consist of a brittle easily fusible button of bismuth, antimony, or the sulphide f arsenide or antimonide of some metal. It may be magnetic from the presence of iron, cobalt or nickel or it may show an alkaline reaction, when touched to moistened red litmus or tumeric paper, indicating the presence of some member of the potassium or cal- cium group of metals. Infusible Compounds. Mg, Al, Zr, Th, Y, Gl. Fusible Compounds. SiO 2 effervesces and forms a clear bead that remains clear on cooling if the reagent is not in excess. TiO 2 effervesces and forms a clear yellow bead crystalline and opaque on cooling,- WO 3 and MoO 3 effervesce but sink in the charcoal. Ba, Sr, Ta, V, Nb sink into the charcoal. Ca fuses, then decomposes, and the soda sinks into the charcoal. 1/4 BLOWPIPE ANALYSIS. Colored Beads. Mn forms a turquois or blue-green opaque bead with soda on platinum wire in the oxidizing flame. Cr forms a chrome-yellow opaque bead with soda on platinum wire in the oxidizing flame, which becomes green in reducing flame. Sulphur Reaction. If a little of the residue, with some of the charcoal beneath, is taken up upon the point of a knife and placed upon a wet silver coin, the coin will be blackened if sulphur was present as a sulphide. Sulphates and other sulphur compounds will also give the same reaction after thorough fusion. The test should always be made on a fresh piece of charcoal. IV. With Metallic Sodium. Reducing effects which are obtained with soda only by hard blowing may be accomplished by the use of metallic sodium im- mediately and with the greatest ease. The metal should be handled carefully and not allowed to come in contact with water. It should be kept in small tightly closed bottles, and if kept cov- ered with naphtha, which is not necessary, care should be taken that the naphtha is not exposed to fire. A cube of sodium about a quarter-inch in diameter is cut off with a knife and hammered out flat. The powdered substance is placed upon the sodium, pressed into it and the whole moulded into a little ball with a knife blade. This sodium ball should not be touched with the fingers, for if some oxides are present, such as lead oxide, spontaneous combustion may take place. After plac- ing the sodium ball on the charcoal it should be touched care- fully with a match or with the Bunsen flame. A little flash ensues and the reduction is accomplished. The residue can now be safely heated with the reducing flame of the blowpipe, any reduced metal collected together and the sodium compounds volatilized or ab- sorbed by the charcoal. When present in sufficient quantity, beads of the malleable metals can be obtained immediately from almost any of their mineral compounds ; metals, like zinc and tin, which require reduction before volatilization yield their sublimates with comparative ease ; and if a little of the charcoal beneath the assay is placed on a wet silver coin the sulphur reaction will be obtained if sulphur was present. In general the results are the same as outlined for soda but are much more easily secured. Even silica, silicates, borates, etc., are reduced but are generally identified by other means. OPERATIONS OF BLOWPIPE ANALYSIS. 175 These reactions are not successful on plaster tablets on account of their non-absorbent character. inch and closed FIG. 296. Tests in Closed Tubes. A plain narrow glass tube about 4 inches by at one end is best. The usual purposes are to note the effects of heat without oxidation, and to effect fusions with such reagents as KHSO 4 or KC1O 3 . Enough of the substance is slid down a narrow strip of paper, previously in- serted in the tube, to fill it to the height of about one half inch ; the paper is withdrawn and the slightly inclined tube, Fig. 296, heated at the lower end grad- ually to a red heat. The results may be : evolution of water, odorous and non-odorous vapors, sublimates of vari- ous colors, decrepitation, phosphores- cence, fusion, charring, change of color, and magnetization. Acid or alkaline moisture in the upper part of tube, Odorless gas that assists combustion (nitrates, chlorates and per oxides),. ....... Pungent gas that whitens lime water, . Odors. Odor of prussic acid, Odor of putrid eggs, Odor that suffocates, fumes colorless, bleaching action, H 2 O. O. CO 2 . Odor that suffocates, fumes violet, . . . . I.* fumes brown, .... Br. fumes greenish yellow, . . Cl, fumes etch the glass, . . F. Odor of nitric peroxide, fumes reddish-brown, . NO 2 . Odor of ammonia, fumes colorless or white, . . NH 3 .f CN. H 2 S. SO 2 . *I, Br, Cl, F and N 2 O 5 are assisted by mixing substance with acid potassium sulphate. f NH 3 , Hg, As, Cd are assisted by mixing with soda. BLOWPIPE ANALYSIS. Sublimates. Sublimate white, fusing yellow, .... PbCl 2 . fusing to drops, disagreeable odor, Os. and volatile, NH 4 (salts). yellow hot, infusible, . . . HgCl. yellow hot, fusible, . . . HgCl 2 . fusible, needle crystals, . . Sb 2 O 3 . volatile, octahedral crystals, . . As 2 O 3 . fusible, amorphous powder, . . TeO 2 . Sublimate mirror-like, collects in globules, . . Hg. does not collect in globules, . As, Cd, Te. Sublimate red when hot, yellow cold, . . . S. Sublimate dark red when hot, reddish-yellow cold, . As 2 S 3 . Sublimate black when hot, reddish-brown cold, . Sb 2 S 3 . Sublimate black, but becomes red when rubbed, . HgS. Sublimate red to black, but becomes red when rubbed, Se. Color of substances changes from white to yellow, cools yellow, . . . PbO. from white to yellow, cools white, . . . ZnO. from white to dark yellow^ cools light yellow, . Bi 2 O 3 . from white to brown, cools yellow, . . . SnO 2 . from white to brown, cools brown, . . . CdO. from yellow or red to darker, after strong heat, cools green, Cr 2 O 3 . from red to black, cools red,. .... Fe 2 O 8 . from blue or green to black, cools black, . CuO. Tests in Open Glass Tubes. By using a somewhat longer tube, open at both ends and held in an inclined position, a current of air is made to pass over the heated substance, and thus many substances not vola- tile in themselves absorb oxy- gen and release volatile oxides. The substance should be in state of powder. Place the assay near the lower OPERATIONS OF BLOWPIPE ANALYSIS. 177 end of the tube, Fig. 297, and heat gently, creasing the air current by holding the nearly vertical. Odor that suffocates, bleaching action, Odor of rotten horseradish, Odor of garlic, . . . Sublimate white volatile octahedral crystals, Sublimate white partially volatile, fusible to yellow drops, pearl gray cold, Sublimate white non-volatile powder, dense fumes, Sublimate white non-volatile powder, fu- sible to colorless drops, Sublimate white non-volatile powder, fusi- ble to yellow drops, white when cold, Sublimate white non-volatile fusible powder, Sublimate gray, red at distance, Sublimate yellow hot, white cold, crystal- line near the assay, blue in reducing flame, Sublimate brown hot, yellow cold, fusible, Sublimate metallic mirror, and then strongly, in- tube more and more SO 2 , indicating S. Se0 2 , ' As 2 3 , ' As 2 3 , < PbOCl, ' Sb 2 o 3 , Te0 2 , " PbS0 4 , BiS0 4 , " Se0 2 , Se. As. As. PbCl,. Sb. Te. PbS. BiS. Se. Mo0 3 , Bi 2 3 , Mo. Bi. Hg. Bead Tests with Borax and with Salt of Phosphorus. Preliminary to bead tests, many compounds, sulphides, arsenides, arsenates, etc., may be converted into oxides by roasting as follows : Treat in a shallow cavity on charcoal at a dull red heat, never allowing the substance to fuse or even sinter. Use a feeble oxidiz- ing flame to drive off sulphur, then a feeble reducing flame to reduce arsenical compounds, then reheat in an oxidizing flame. Turn, crush, and reroast until no sulphurous or garlic odor is noticeable. Sodium tetraborate or borax may be considered as made up of sodium metaborate and boron trioxide. The boron trioxide at a high temperature combines with metallic oxides, driving out volatile acids, and by the aid of the oxidizing flame the resulting borates fuse with the sodium metaborate to form double borates which are often of a characteristic color. The color may differ when hot and cold and according to the degree of oxidation and reduction. 13 178 BLOWPIPE ANALYSIS. Sodium ammonium phosphate, or salt of phosphorus, by fusion loses water and ammonia and becomes sodium metaphosphate. The sodium metaphosphate at high temperatures combines with metallic oxides to form double phosphates and pyrophosphates, which like the double borates are frequently colored, although the colors often differ from those obtained with borax. A bead of either flux is made on platinum wire as described on page 162, and the substance is added gradually to the warm bead and fused with it in the oxidizing flame. The ease of dissolving, effervescence, color, change of color, etc., should be noted. We may greatly simplify the tabulation of results by the follow- ing division : 1. Oxides which Color neither Borax or Salt of Phosphorus, or at Most Impart a Pale Yellow to the Hot Bead when Added in Large Amounts. OXIDES OF NOTICEABLE DISTINCTIONS. ALUMINUM. Cannot be flamed opaque. ANTIMONY. Yellow hot in oxidizing flame, flamed opaque gray in reducing flame, on charcoal with tin black. Expelled by reducing flame in time. BARIUM. Flamed opaque white. BISMUTH. Like antimony. CADMIUM. Like antimony, but not made black by fusion with tin. CALCIUM. Like barium. LEAD. Like antimony, but not made black by fusion with tin. MAGNESIUM. Like barium. SILICON. Only partially dissolved in salt of phosphorus. STRONTIUM. Like barium. TIN. Like aluminum. ZINC. Like antimony, but not made black by fusion with tin. I 2. Oxides which Impart Decided Colors to the Beads. The colors in hot and cold beads of both fluxes and under both oxidation and reduction are shown in the following table. The abbreviations are : sat = saturated ; fl = flamed ; op = opaque. OPERATIONS OF BLOWPIPE ANALYSIS. 179 Hot and cold relate to same bead ; hot and cold to larger amounts of the oxide. OXIDES OF VIOLET. BLUE. GREEN. RED. BROWN. YELLOW. COL'L'SS Chromium, O.F. R.F cold hot, cold hot hot Cobalt, O.F. R.F. hot, cold hot, cold Copper, O.F. R.F. cold hot cold (op.) cold hot Iron, O.F. R.F. hot, cold hot hot, cold cold c 4 . Ca. A white precipitate. Residue b. Moisten with concentrated HC1 and try coloration of flame. Ba. Yellowish-green flame. Sr. Scarlet flame. CONFIRMATION Ba and Sr. Fuse residue b with two to three pts. of soda in a pla- tinum capsule : treat fusion with boiling water, filter, reject filtrate, dissolve residue in acetic acid, add a few drops of H 2 S water, if it gives any precipitate, saturate with H 2 S and filter, and to filtrate add K 2 Cr 2 O 7 . Ba = yellow precipate. Filter, and to nitrate add CaSO^ warm and let stand. Sr = white precipitate. PART III. MINERALOGY. CHAPTER XV. DEFINITION AND PHYSICAL CHARACTERS OF MINERALS. Definition of a Mineral. The solid crust of the earth is composed principally of " min- erals " each of which may be broadly defined as a homogeneous substance of definite chemical composition, found ready-made in na- ture, and not directly a product of the life or the decay of an organ- ism. Usually also it will possess a definite and characteristic crys- talline structure. The definition excludes laboratory products and natural sub- stances of organic origin. Laboratory products and natural products may differ only in origin ; for example, ice of the pond and the factory, natural and synthetic ruby. The line is arbitrarily drawn. Natural Substances of Organic Origin. Materials which have formed part of living organisms, coal, chalk, pearls, coral, shells, etc., are not minerals. If by natural agencies their organic structure is lost and a crystalline structure obtained or if their com- ponents recombine or combine with other elements, the new substances are minerals. The Definite Chemical Composition. The composition of a homogeneous mineral may vary by a series of replacements as explained under Isomorphism, p. 232, or in the case of " Gel Minerals," p. 235, may vary from taking up (adsorb- ing) other substances. In the former case a formula can be figured from the analysis, in the latter it is difficult or impossible. The Characteristic Crystalline Structure. This is a less constant attribute than was believed. While it is true that most minerals occur usually in the crystalline condi- 208 PHYSICAL CHARACTERS. 209 tion, it is a recognized fact that under proper conditions they occur in the amorphous condition either glassy or as a " gel mineral." The Crystalline Condition. A mineral is sometimes defined as a natural crystal, that is, possessing a crystalline structure and occurring either in crystals of characteristic shapes or in masses made up of many little crystals so crowded together that the shapes are not evident. In the crystal and in each grain of the aggregation the crystalline structure will be shown by the constancy of the properties in parallel directions and their variation in directions not parallel. The Amorphous Condition. It has become recognized that quite a number of minerals have never been found in crystals and in the mass fail to show any regular crystalline structure. Such minerals are said to be amorphous. Usually they are "Gel minerals," products of weathering or hot springs action, which by their lack of uniform composition, generally amorphous structure and external appearance, suggest that they are products of colloidal origin. Opal is the best example. The obsidians and the glassy inclusions in volcanic rocks are quickly cooled magma, that is, they are essentially minerals in solution. The Study of Minerals or " Mineralogy." Mineralogy considers the one thousand or so definite minerals and the many thousands of varieties and doubtful species which constitute the solid crust of the earth. Its purpose is the study of all the qualities of these minerals ; their chemical composition as revealed by analyses ; their molecular structure as revealed by crystalline form and by physical tests, and their origin and mode of formation as revealed by associated minerals, the alterations which they undergo and their synthetic production. In elementary work in mineralogy, especially in a technical course, the principal object is the acquisition of an " eye knowledge " of the common and commercially important minerals so that they may be recognized at sight or determined rapidly by a few simple tests. This knowledge can be acquired only by handling and test- ing many labelled and unlabelled specimens, and is best preceded by a thorough drill in the use of the blowpipe and a 'study of models and natural crystals. With this there should be gained a knowledge of their characters, economic uses and occurrence. THE PHYSICAL CHARACTERS OF MINERALS. Minerals being for the most part in the crystalline condition, the geometric and optical characters described, pages I to 155, constitute their most important physical characters. The term is, however, very commonly used for the temaining physical charac- ters described in the following pages and often subdivided into 15 210 MINERALOGY. groups, such as characters dependent on light, or cohesion or general characters, etc. LUSTRE. THE lustre of a mineral is dependent upon its refractive power, its transparency and its structure. It may be called the kind of brilliancy or shine of the mineral. METALLIC lustre is the lustre of metals. It is exhibited only by opaque minerals, and these, with the exception of the native metals, have a black or nearly black streak. Some authorities* make this very important, using the streak to confirm the lustre. It can, however, be used safely only in one direction. If the streak is essentially black the lustre is metallic, but the green streak of alabandite, the brownish red of specular hematite, the copper red of native copper, the pale greenish gray of molybdenite, do not prevent their lustre being metallic. NON-METALLIC lustre is exhibited by all transparent or trans- lucent minerals. It may be vitreous, adamantine, resinous, pearly, silky, greasy or waxy. Vitreous. The lustre of a fracture surface of glass or of a quartz crystal. Index of refraction n = 1.3 to 1.8. Adamantine. The almost metallic lustre of the uncut diamond, zircon or cerussite, exhibited by minerals of high index of refrac- tion, n 1.9 to 2.5. Resinous. The lustre of resin or sphalerite. Greasy. The lustre of oiled glass or elaeolite. n = 1.7 to 1.9. Pearly. The lustre of the mother of pearl or of foliated talc. Common parallel to a very perfect cleavage. Silky. The lustre of silk or of satin spar, due to a fibrous structure. Dull. Without lustre or shine of any kind. Kaolin or chalk are good examples. The prefix sub, as sub-metallic, sub-vitreous, is used to express an imperfect lustre of the kind. The words splendent, shining, glistening, glimmering and dull are terms of intensity dependent on the quantity of light reflected. Lustre should, when possible, be determined by a comparison with minerals of known lustre, and should always be observed on a fresh or unaltered surface. The degree and kind of lustre are always the same on like faces * Brush-Penfield, Determinative Mineralogy, p. 226 ; Dana-Ford, p. 66. PHYSICAL CHARACTERS. 211 of the crystal, but may be different on unlike faces, as in apophyllite, which has pearly basal pinacoid and vitreous prism faces. COLOR. The surface colors are of two classes. 1. Colors dependent on the chemical constituents. 2. Colors dependent on physical causes. Color Dependent on Chemical Composition. Color is one of the least constant mineral characters, and varies with different specimens of the same species. It is frequently changed by a few hundredths of one per cent, of some organic or inorganic substance dissolved in the mineral, or by larger amounts of mechanically included foreign material. In describing color the terms white, gray, brown, black, blue, green, yellow and red are used, with prefixes, which suggest the shade by the color of some familiar object. These need no expla- nation. Color Due to Physical Causes. If the observed surface color changes with the direction in which it is viewed it is due to interference of light. Play or Change of Colors. A succession of colors, varying with the direction the mineral is viewed, as in opal, labradorite, or diamond. Iridescence. Bands of prismatic colors, either from the interior of a mineral, as from a thin film of air between cleavages ; or ex- ternal and due to a thin coating or alteration. Tarnish. A surface which has been exposed to the air or to moisture is often of different color from the fresh fracture. Opalescence. A milky or pearly reflection, sometimes an effect of crystalline structure, at other times due to fibrous inclusions. Asterism. A star effect by reflected light, as in the ruby, or by transmitted light, as in some micas, and due to structure planes or symmetrically arranged inclusions. PHOSPHORESCENCE. Many minerals, after being subjected to various outside influ- ences, emit light which often persists for some time after removal of the exciting cause. Such emission of light is known as phosphorescence. 212 MINERALOGY. Phosphorescence may be induced by ordinary light, heat, fric- tion, mechanical force or electrical stress but especially by the action of radium, polonium and actinium emanations, by X-rays and by ultra-violet light. In a particular specimen it may be induced by only one or by several of the agencies named. Phosphorescence is not always a characteristic of species but rather of the particular specimen or of species from a certain locality. On the other hand certain species are nearly always phosphorescent. Diamonds are generally strongly phosphorescent under radium emanations, but the degree of reaction varies with the individual specimen. They also phosphoresce under the influence of polonium, actinium, X-rays, ultra-violet rays and some rare specimens will glow in the dark even after exposure to sunlight or the light of the electric arc. WilK mite from Franklin, New Jersey, and kunzite are strongly phosphor- escent under the influence of radium, polonium, actinium and X-rays. Chlorophane, a variety of fluorite, phosphoresces at times by the simple heat of the hand, while fluorite itself may phosphoresce, fluoresce or do neither according to the specimen. All minerals from Borax Lake, California, phosphoresce under the influence of ultra- violet rays, which would seem to indicate some common phosphor- escent constituent. FLUORESCENCE. Fluorescence is induced by much the same agencies as phos- phorescence, but the emitted light, which may be white or colored, persists only during the action of the exciting agent. Colorless fluorite fluoresces under the influence of sunlight, autunite from Mitchell county, N. C., and hyalite from San Luis Potosi, Mexico, fluoresce wonderfully under the influence of ultra- violet light. STREAK. The streak of a mineral is the color of its fine powder. It is usually obtained by rubbing the mineral on a piece of hard, white material, such as unglazed porcelain, and brushing off the excess, or it may be obtained less perfectly by scratching the mineral with a knife or file, or by finely pulverizing a fragment of the specimen. The streak often varies widely from the color of the mass and is nearly constant for any species. When not white it is a character- istic very useful in determination. PHYSICAL CHARACTERS. 21$ TRANSLUCENCY. The translucency of a mineral is its capacity to transmit light. A mineral is said to be : Transparent. When objects can be seen through it with clear- ness. Subtransparent. When objects can be more or less indistinctly seen through it. Translucent. When light passes through, as through thin por- celain, but not enough to distinguish objects. Subtranslucent. When only the thin edges show that any light passes. Opaque. When no light appears to pass even through the thin edges. CLEAVAGE AND PARTING. Many crystallized substances when sharply struck or when pressed with a knife edge split into fragments bounded by smooth plane surfaces which are always parallel to faces of simple forms* in which the substance can crystallize. These surfaces are more splintery than the true crystal faces but the angles between them are just as exact as the interfacial angles. When the separation can be obtained with equal ease in any part of the crystal and there is only a mechanical limit to the thinness of the resulting plates, the character is called cleavage. When, however, the separation can be obtained only at irregular intervals the character is called parting. Furthermore, all crystals of the same substance show the same cleavage, whereas parting may be obtained in one crystal and not in another. When cleavage or parting is obtained parallel to one face of a crystal form it will be obtained with equal ease parallel to all faces of the form. For instance, galenite cleaves parallel to all planes of the cube, Fig. 275 ; calcite, Fig. 276, in three directions parallel to all the faces of a rhombohedron with diedral angles of 105 5' ; and some crystals of hematite show parting planes parallel to all the faces of the rhombohedron. Cleavage may be obtained parallel to the faces of two or more crystal forms, for instance gypsum splits easily into plates parallel to the clino-pinacoid, these plates again break parallel to the ortho- 214 MINERALOGY. pinacoid and to the dome { i o I } and the final shape is a rhombic plate with angles of 66. Terms of Cleavage. Cleavage is said to be perfect or eminent when obtained easily, giving smooth, lustrous surfaces. Inferior FIG. 298. Galenite Cleavage, Pyrenees, alter Lacroix. degrees of ease of cleavage are called distinct, indistinct or imper- fect, interrupted, in traces, difficult. Manipulation. Directions of cleavage are often indicated by a pearly lustre on faces parallel to the cleavage direction, the lustre being due to repeated light reflections from cleavage rifts, or FIG. 299. Calcite Cleavage. cracks may be visible. The absence of indications is not proof that cleavage cannot be obtained, but only that previous pressure or shock have not started the separation. PHYSICAL CHARACTERS. 215 Cleavage is usually obtained by placing the edge of a knife or small chisel upon the mineral parallel to the supposed direction of cleavage and striking a quick, sharp blow upon it with a hammer. In some instances the cleavage is produced by heating and sud- denly plunging the mineral in cold water. Sudden heat alone will often produce decrepitation and with easily cleavable minerals the fragments will be cleavage forms. Frequently the cleavage is made apparent during the grinding of a thin section. Parting is a secondary character produced in some instances and not in others as a result of pressure after solidification. It takes place along a so-called glide plane.* PERCUSSION FIGURES. If a rod with a slightly rounded point is pressed against a firmly supported plate of mica and tapped with a light hammer, three little cracks will form, radiating f from the point, Fig. 301. The most distinct of these is always FIG. 301. parallel to the clino-pinacoid, the others at an angle ;r thereto which is 53 to 56 in muscovite, 59 in lepidolite, 60 in biotite, 61 to 63 for phlogopite. In the same way on cube faces of halite a cross is developed with arms parallel to the diag- onals of the face. On an octahedral face a three-rayed star is developed. ELASTICITY. Elasticity is capable of exact measurement, but is of little value in determination of minerals. The following terms are used : Elastic. A thin plate will bend and then spring back to its original position when the bending force is removed, as in mica. Flexible or Pliable. A thin plate will bend without breaking, as in foliated talc. *The artificial development of a glide plane fgbm in calcite is shown in Fig. 300. If the edge ad of the larger angle is rested upon a steady support and the blade of a knife pressed steadily at some point i of the opposite edge, the portion of the crystal between i and c will be slowly pushed into a new position of equilibrium as if by rota- tion about fgbm until the new face gc f b and the old face gcb make equal angles with fgbm. f By pressure alone, three cracks diagonal to these are developed. 2l6 MINERALOGY. TENACITY. The following terms are used : Brittle. Breaks to powder before a knife or hammer and can- not be shaved off in slices. Sectile. Small slices can be shaved off which, however, crumble when hammered. Malleable. Slices can be shaved off which will flatten under the hammer. Tough. The resistance to tearing apart under a strain or a blow is great. Ductile. Can be drawn into wire. Every ductile mineral is malleable and both are sectile. The sectile minerals are: graphite, bismuth, copper, silver, gold, platinum, chalcocite, agentite, molybdenite, orpiment, tetra- dymite, senarmontite, arsenolite, cerargyrite. FRACTURE. When the surface obtained by breaking is not a plane or a step- like aggregation of planes it is called a fracture and described as : Conchoidal, rounded and curved like a "pip 302 1 11 T~> * shell, rig. 302. Even, approximately plane. Uneven, rough and irregular. Hackly, with jagged sharp joints and depressions as with metals. Splintery, with partially separated splin- ters or fibers. HARDNESS. The resistance of a smooth plane surface to abrasion is called its hardness, and is commonly recorded* in terms of a scale of ten common minerals selected by Mohs: * In more exact testing the crystal may be moved on a little carriage under a fixed vertical cutting point and the pressure determined, which is necessary to produce a vis- ible scratch. Other methods are planing or boring with a diamond splinter under con- stant pressure, and comparing the loss in weight for a given penetration or given num- ber of movements. The loss of weight during grinding and the pressure necessary to produce a permanent indentation or a crack have also been used as determinants of hardness.' PHYSICAL CHARACTERS. 21 7 1. Talc, laminated. 6. Orthoclase, white cleavable. 2. Gypsum, crystallized. 7. Quartz, transparent. 3. Calcite, transparent. 8. Topaz, transparent. 4. Fluorite, crystalline. 9. Sapphire, cleavable. 5. Apatite, transparent. 10. Diamond. Intermediate values are: Window glass 5.5, Jewelers file 6.5, Zircon 7.5, Chrysoberyl 8.5, Carborundum 9.5. These numbers have no quantitative relation there is no com- mon difference. The diamond is much further from sapphire than this is from talc.* In testing, some inconspicuous but smooth surface of the mineral is selected and a sharp point of known hardness is pressed upon the surface and moved back and forth several times on the same line a short distance (y& inch}. If the mineral is not scratched it is harder than the standard used, and the next higher on the scale is tried in the same way. A good method is to try the hardness of the mineral first with the finger nail (2.5), then with a pocket knife (about 6). (a) If the finger nail cuts then 2 and I are tried. (ft) If the finger nail makes no scratch but the knife does 3,4, 5, and 6 are tried. (c) If the knife does not scratch the specimen the harder mem- bers, 6 to 10, are used successively until one is found which scratches the mineral. The jewelers file and conical pencils made of the upper members of the scale are much used. For cut stones and other valuable specimens it is often wise to use dully polished slabs of the test minerals and determine the power of an edge of the cut stone to scratch the polished test piece. Care must be taken to distinguish between a true scratch and the production of a " chalk " mark which rubs off. Altered or rough surfaces must be avoided. Pulverulent fibrous or splintery minerals are " broken down " or their particles pushed aside by the test and yield an "apparent" hardness often much lower than the true hardness. * The average of five attempted comparisons from 9 down give roughly sapphire 100, topaz 30, quartz 18, orthoclase 12, apatite 7, fluorite 3^, calcite 2^, gypsum %. 218 MINERALOGY. ETCHING FIGURES . When a crystal or cleavage is attacked by any solvent the action proceeds with different velocities in crystallographically different directions, and if stopped before the solution has proceeded far, the crystal faces are often pitted with little cavities of definite shape. The absolute shape varies with many conditions ; time, tempera- ture, solvent, crystallographic orientation and chemical composition. The figures, whatever their shape, conform in symmetry to the class to which the crystal belongs, and are rarely forms common to several classes. They are alike on faces of the same crystal form and generally unlike on faces of different forms, and serve, therefore, as an important means (perhaps the most important) for determining the true grade of symmetry of a crystal and also for recognizing and distinguishing faces. Fig. 303 shows the shape and direction of the etchings upon a cube of pyrite. These conform to the symmetiy of the group 01 FIG. 303. FIG. 304. * the diploid, p. 65. On the other hand the etchings upon a cube of fluorite, Fig. 304, show a higher symmetry corresponding to that of the hexoctahedral group, p. 58. SPECIFIC GRAVITY. . The specific gravity of a substance is equal to its weight divided by the weight of an equal volume of distilled water. The character is an unusually constant one, the variations in varieties of the same species not being great and even these being due usually to actual differences in composition. Strictly the temperature of the water should be 4 C., or if not the result should be multiplied by a factor which is the specific gravity of the water used. Generally the water is used at the ordinary room temperature without correction. PHYSICAL CHARACTERS. 2I 9 Pure material must be selected free from cavities, and air bubbles clinging to the surface must be brushed off while the fragment is in the water. Substances soluble in water must be determined in alcohol, benzine or other liquids in which they are insoluble, and the result multiplied by the specific gravity of the liquid used. The specific gravities of the minerals considered in this book range from water (ice) 0.92, to iridosmine 19 to 21. Minerals of metallic and submetallic luster are heavy, rarely as low as 4. The great group of silicates range chiefly between 2 and 3.5, zircon reaching 4.7. Direct Weighing in a Delicate Balance. Except for very small material the most accurate results are obtained with a delicate balance such as an assay balance or a dia- mond balance, Fig. 305, within at least one tenth milligram. The FIG. 305. result should be correct to the third decimal. A small wooden bench, Fig. 306, is used to hold a beaker of distilled water above the scale pan, and a platinum spiral, Fig. 307, to hold the stone. Three weighings are needed : W= weight of the stone. S= weight of the spiral when suspended from the end of the 22O MINERALOGY. determined balance frame and immersed in the distilled water as in Fig. 307. (This weight may be made once for all.) W = weight of the stone and the spiral suspended in distilled water. W Then, Sp. Gr. = 5+ w _ w - Usually no correction need be made for temperature.* The Jolly Balance. This instrument gives the relative weights in terms of the stretching of a spiral spring. In the older form, Fig. 308, two scale pans c and d are attached, one below the other, to a spiral spring parallel to which is a mirror with a graduated scale. FIG. 308. FIG. 307. FIG. 306. The lower pan d is kept submerged in distilled water. Three readings are made by noting the heights at which the white bead b on the wire and its image in the graduated mirror coincide when the spiral comes to rest. * Greater speed and, if proper corrections for temperature are made, equal or greater accuracy are obtained by substituting for distilled water benzol or toluol, which have less surface tension than water. The result obtained by the above formula must then be multiplied by the specific gravity of the benzol or toluol for the temperature at which the weighing was made. PHYSICAL CHARACTERS. 221 A. Instrument reading with nothing in either scale pan. B. Reading with mineral in upper scale pan. C. Reading with same fragment transferred to lower scale pan. B-A Sp. Gr. = w - c The result is quickly attained and unless the fragment is small is accurate to the second decimal. The Kraus Recording Jolly Balance. Professor Kraus described* an improved Jolly balance, Fig. FIG. 309. FIG. 310. W 20- Z2- 309, requiring only two readings, which may be verified at the end of the operation. * Described in Am. Jour Sci., XXXI, 561, 1911 Made by Eberbach & Son Com- pany, Ann Arbor, Mich. 222 MINERALOGY. The parts are : (The scale and verniers are shown enlarged, Fig. 310). (a) An outer rectangular tube with a fixed vernier, W. (ft) An inner round tube movable by a milled head and carrying with it a second vernier, L. (c) An adjustable rod within the round tube, carrying the spring and scale pans and a pointer which swings in front of a small cir- cular mirror. (d*) A graduated scale which may be clamped, or if undamped moves with the inner tube. The operation is as follows : 1. The graduated scale, the two verniers and the pointer are all placed at zero, the lower scale pan being immersed in water. 2. The fragment is placed in the upper scale pan, the scale un- damped and the milled head turned, driving the round tube and its attachments upward until the pointer is again at zero. The reading of W corresponds to the weight in air. 3. The fragment is transferred to the lower scale pan, the scale clamped, the milled head turned till the pointer is again at zero. The reading of L corresponds to the loss of weight in water. Hence, c r W Sp. Gr. = -j- . A minor advantage is that both weighings remain recorded until the end of the operation and may be checked. Method for Small Fragments. The difficulty of determining small grains by the chemical bal- ance lies in the weighing in water rather' than the weighing in air. The following simple method * has been used: Substitute for the spiral a small vessel containing vaseline. Weigh this in air and water, denoting these weights by w and w r . Place several of the little crystals or grains on the vaseline and weigh in air, denoting this by W, then warm the vaseline and let them sink into it and weigh in water, denoting this by W y then q W-w ~ R. Smeeth, Sci. Proc. Roy. Dublin Soc., 6, 1888, 61. PHYSICAL CHARACTERS. 223 Using the Pycnometer or Specific Gravity Flask. Very porous minerals and powders are determined by weighing in a little glass bottle the stopper of which ends in a fine tube. In a later form there are two openings, one, the neck, is closed by a ground stopper carrying a thermometer, the other ends in a capil- lary tube. In ordinary use the mineral is weighed (A) and the bottle full of water is also weighed {B\ The mineral is then inserted in the bottle and displaces its bulk of water, and the difference between this weight ( C) and the sum of the other two weights is the weight of the displaced water. c r A Sp.Gr. = + A _ c . If special precautions * are used this apparatus may be relied upon to the third decimal with one gram of substance. Complete removal of air bubbles is secured by placing the pycnometer under an air pump after the fragments are covered with the liquid. Using Heavy Liquids. If a fragment of a mineral, which may be very minute, is dropped into a test-tube containing a liquid of higher specific gravity it will float. If the liquid is diluted, the diluent being stirred in drop by drop, there will be one stage at which the fragment if pushed down will neither sink nor rise but stay where pushed. The specific gravity of the liquid is then determined either roughly by dropping in fragments of material of known specific gravity until one is found which just sinks and another which floats, the liquid being of a specific gravity between these ; or for more accurate determination the most convenient balance is that of Westphal, Fig. 285. The beam is graduated in tenths and the weights A, B and C are respectively unit, -^ and -j-J-^. This balance is so constructed that when the thermometer float is suspended in distilled water at 15 C. a unit weight must be hung at the hook to obtain equilibrium. If then the test-tube is nearly filled with the heavy liquid and weights added until equilibrium is secured the specific gravity is known. * See Mier's Mineralogy, p. 191. f For the use of heavy liquids in preparation of material for Chemical Analyses see Iddings, Rock Minerals, p. 25. 22 4 MINERALOGY. For instance in the figure the weights employed are : Unit weight at hook, value i.ooo Unit weight at sixth division, value 0.600 JQ weight at sixth division, value 0.060 weight at ninth division, value 0.009 Specific gravity . . 1.669 The Westphal Balance. The principal heavy liquids are : * Thoulet Solution. Mercuric iodide and potassium iodide, in the ratio of five parts to four by weight, are heated with a little water until a crystalline scum forms, then filtered. The maximum spe- cific gravity is nearly 3.1 and may be lowered by the addition of water to any desired value. Klein Solution. Cadmium borotungstate with a maximum spe- cific gravity of 3.6 if fused, 3.3 if dissolved. Brauris Solution. Methylene iodide, CH 2 T 2 , with a maximum specific gravity of 3.32 which can be lowered by the addition of benzol. It darkens from exposure to light but may be clarified by shaking with a little mercury or copper. By addition of iodoform and iodine it may be raised to a specific gravity of 3.65. *See Neues Jahrb. f. Min., 1889, II., 185, for list of solids which when melted have specific gravity up to 5. PHYSICAL CHARACTERS. 225 Retger's Solution. Silver thallium nitrate which is liquid at 75 C, has a maximum specific gravity of over 4.5 which can be low- ered by the addition of hot water. Specific Gravity Tubes. In gem testing, a series of tubes, usually three, fitted with glass stoppers or corks and containing liquids of different densities are sometimes used and by diluting and using " indicators," that is, fragments of a known specific gravity, the gravity of a liquid which just floats a specimen may be tested. Diffusion Columns. By pouring into a test tube a heavy liquid and on top of this a lighter liquid and allowing these to stand several hours a diffusion takes place so that the density increases regularly with the depth. By use of "indicators" the Sp. Gr. for the level to which the stone sinks may be determined.* TASTE. Minerals soluble in water often have a decided taste : Astringent. The taste of alum. Saline or Salty. The taste of common salt. Bitter. The taste of epsom salts. Alkaline. The taste of soda. Acid. The taste of sulphuric acid. Cooling. The taste of nitre. Pungent. The taste of sal-ammoniac. ODOR. Odors are rarely obtained from minerals, except by setting free some volatile constituent. The terms most used are : Garlic. The odor of garlic obtained by heating minerals con- taining arsenic. Horseradish. The odor of decayed horseradish obtained from minerals containing selenium. Sulphurous. The odor obtained by heating sulphur or suL phides. Fetid. The odor obtained by dissolving sulphides in acid. Bituminous. The odor of bitumen. *See Mier's Mineralogy, p. 192. 16 226 MINERALOG Y. Argillaceous. Obtained from serpentine and some allied min- erals, after moistening with the breath. FEEL. Terms indicating the sense of touch are sometimes used : Smooth. Like celadonite or sepiolite. Soapy. Like talc. Harsh or Meager. Like aluminite. Cold. Distinguishes gems from glass. THE THERMAL CHARACTERS. Transmission of Heat Rays. HEAT rays may be reflected, refracted, doubly refracted, polar- ized and absorbed, and it is possible, though difficult, to determine a series of thermal constants for crystals. Conductivity. The rapidity with which heat is conducted in different directions in a crystal is in accordance with its symmetry. This may be shown on any face or cleavage surface as follows: (a) The surface is breathed upon, quickly touched by a very hot wire, dusted with lycopodium powder, turned upside down and tapped carefully. The powder falls from where the moisture film has evaporated, but adheres elsewhere, giving a sharply out- lined figure. The entire operation should take less than three seconds. (<5) The surface is coated with a mixture of three parts elaidic acid and one part wax, brought into contact with a hot wire, and the temperature maintained until the wax has meked around the wire. The boundary of the melted patch is visible, after cool- ing, as a ridge. A circle indicates either an isometric crystal or a basal section of a hexagonal or tetragonal crystal. All other sections yield ellipses varying in eccentricity and in position of axes. Expansion. When a crystal is uniformly heated, directions crystallographic- ally alike expand in the same proportion, but directions unlike do not The expansion may be accurately measured for any direction but the methods involve apparatus of great precision and cost. Change of Crystal Angles Produced by Expansion. An isometric crystal uniformly heated expands without change of angles. In all other systems the expansion varies with the direction and certain angles are changed PHYSICAL CHARACTERS. 227 THE MAGNETIC CHARACTERS. Magnetism. A few iron-bearing minerals attract the magnetic needle or are attracted by a steel magnet. Of these minerals, magnetite, pyrrhotite and platinum will themselves occasionally act as magnets. Para- and Diamagnetism. Any substances will be either attracted or repelled in some degree in the field of a strong electromagnet. If a rod of the substance is suspended by a fiber so as to swing horizontally between the poles of an electromagnet, the rod is paramagnetic, if pulled into "axial" posi- tion with its ends as near the poles of the magnet as possible, and, is diamagnetic, if pushed into an "equatorial" position with its ends as far from the magnetic poles as possible. Crystals are more strongly magnetized in certain directions than in others. Action on a Magnetic Needle. Haiiy's Method of Double Magnetism. A delicate magnetic needle, or as Hau'y showed, a needle made by a bar magnet to take an east and west position, may be attracted by stones containing iron, such as garnet, chrysolite, tourmaline. ELECTRICAL CHARACTERS. Heat, friction and pressure often develop electric charges in minerals. The charges are, however, weak and the chief differ- ences lie in the length of time the electricity is retained. In the testing the drier the atmosphere, the better. If humidity is great no results may be obtained. The best results are obtained from polished surfaces. In handling the material an insulated pincers would be better than the fingers. Frictional Electricity. All minerals are electrified by friction but the -f or character may vary in varieties of a species and even in the same specimen. The electricity is developed by brushing or striking several with a woolen cloth. Its presence is recognized by taking a stone by an insulated holder near some form of electrometer. The duration of the charge is determined by placing the min- eral stone in contact with a metal plate which is itself in contact with surrounding bodies, and in a dry room. From time to time the mineral is again tried with the electrometer. 228 MINERALOGY, Although Haliy devoted considerable space * to these properties they have not been developed much since his day. Haiiy used a light brass rod with brass spheres on both ends, balanced like a magnetic needle on a fine point. This being electrified, either positively by bringing near a rod of electrified sealing wax, or negatively by touching with the rod, an elec- trified mineral will attract or repel the needle according as it has opposite or similar electricity. Similarly a pith ball suspended by a silk thread may be charged and used or cat's hair may be positively electrified by rubbing between the fingers. The Bohnenberger-Fechner Electrometer is a more elaborate device consisting of a single gold leaf, hanging between poles of a Zamboni dry battery The stone is ap preached to the knob on the conductor. If the stone was electrified, the gold leaf becomes charged and clings to the opposite pole of the battery. The following examples illustrate the property : Electrified Positively by Friction. Topaz, 24 hours duration. Rock crystal, J^ hour. Corundum, several hours duration. lolite, ^ hour. Odontolite, several hours duration. Diamond, y 2 hour. Also spinel, tourmaline, garnet, chrysolite, beryl, spodumene, zir- con, moonstone, axinite, titanite, phenacite, diopside, epidote. Sulphur and amber are examples of minerals which develop negative electricity. Electrical Conductivity. All minerals conduct, but practically, conductivity is limited to the metals, some metalloids, most sulphides, tellurides, selenides, bismuthides, arsenides and antimonides, some of the oxides, and, at higher temperature, a few haloids. If a rod is introduced into a weak current, the strength of which is varied by resist- ances and the deviation observed in a galvanometer, the results will vary for different minerals between very wide limits dependent upon the constitution of the chemical molecule more than upon the crystalline structure. Practical applications of this property are the electrostatic con- centrators in which the mixture falling on a moving surface is electrified more or less rapidly according to its conductivity and thereby (repelled) different distances. Similarly a flat stick of sealing wax made electric by rubbing and held over a fine sand-like mixture will attract the better con- ductors ; for example, will take cassiterite from zircon. * Traite des caracteres physiques des Pierres Precieuses, Paris, 1817, pp. 113-185. PHYSICAL CHARACTERS. 229 These changes may be measured with accurate goniometers and the relative expansions calculated. Change of Optical Characters Produced by Expansion. The expansion of a crystal changes the indices of refraction for different directions. With isometric crystals the index may become either larger or smaller. With tetragonal and hexagonal crystals the principal indices of refraction may alter unequally. The inter- ference figure will also alter and for a particular temperature will disappear. In orthorhombic, monoclinic and triclinic crystals the interference figure may undergo even more striking changes. For instance, in gypsum with yellow light at 20 C. the axial angle is 92, at 100 C. it is reduced to 51, at 134 C. it is zero, and for still higher temperatures the optic axes pass into a plane at right angles to their former position. Melting and Inversion Points. Fusibility in terms of a rough scale as a blowpipe test has been described, p. 164, and changes of color and other phenomena by moderate heat on p. 1 76. Recent improvements in the thermoelectric couple and the electric resistance furnace have made possible laboratory deter- minations of the changes which minerals undergo with increased temperatures and the consequent changes in volume, etc., are 01 great geological importance. Both the melting point, that is " the temperature at which the crystalline and the liquid substance can remain side by side in equilibrium " and the inversion point, that is " the temperature at which two different crystalline forms of the same substance can so remain are determined." For instance a quartz changes to /3 quartz at 575 C. and to christobaltite at about 800, and the latter melts at about 1600 C. Similarly anorthite melts at 1552, albite below 1200, and their isomorphous mixtures at intermediate values. The presence of other minerals lowers the melting point and pure types, usually synthetic, are used. Natural minerals usually show a " melting interval " of 40 or 50 degrees.* *See publications of Dolter, Neues Jahrb. f. Min., u, 60, 1903. Tschermak, Min. Mitt., 21, 211, 307. Also Joly, Trans. Roy. Dublin Soc., 6, 283, and the more recent work of Day, White, Sosman and others, in the Geophysical Laboratory publications. 230 MINERALOGY. Pyroelectricity and Piezoelectricity. Poorly conducting crystals which have not a center of symmetry if altered in volume either by a temperature change or by pressure will frequently accumulate positive and negative charges of elec- tricity at different points. PYROELECTRICITY. Usually the crystal is heated in an air- bath to a uniform temperature, then drawn quickly once or twice through an alcohol flame and allowed to cool. During the cooling of the crystal positive charges collect at the so-called antilogue poles, and the negative charges at the analogue poles. In PIEZOELECTRICITY the charges are developed by pressure, for instance, calcite pressed between the fingers becomes positively electrified, tourmaline compressed in the direction of the vertical axis develops a positive charge at the antilogue end and a negative charge at the analogue end or precisely the charges which would result from cooling a heated crystal. The charges are detected by such methods as are described under frictional electricity. In Kundfs Method the positive and negative poles may be distinguished by blow- ing upon the cooling crystal a fine well dried mixture of equal parts of powdered sulphur and red oxide of lead; The nozzle of the bellows is covered by a fine muslin net. In passing through the sieve, the sulphur is negatively electrified and is attracted by the antilogue poles, coloring them yellow, while the minimum is positively electri- fied and is caught by the analogue poles, coloring them red. CHAPTER XVI. i CHEMICAL CHARACTERS OF MINERALS. Minerals are either elements or are formed by the uniting of atoms of different elements in definite proportions in accord- ance with the laws of chemistry and for either identification or classification their chemical composition is their most important characteristic. Empirical Formulas. The chemical composition of a mineral is determined by exact quantitative analysis and from this a formula is calculated which shows which elements and how many atoms of each occur therein. Such formulas are called empirical and do not of necessity express the structure of the molecule,* but only the composition ratio. In fact, the symbols adopted are always the simplest which can express the proportions shown by analysis to exist between the atoms and which satisfy their valences. Calculation of Formulas. A very pure specimen of beryl gave the following results on analysis: Per cent BeO, 14.01 A1 2 3 , 19.26 Si0 2 , 66.3; The sum of the atomic weights for each group is : BeO = 25. A1 2 O 3 = 1 02. SiO 3 = 60. The results of analysis represent the proportion in which the groups are present in the molecule. Consequently, the relation between the number of groups must be : * True molecular formulas can not be given to minerals, for they are volatile or soluble only in rare instances, and are probably always some unknown multiple of the empirical. 231 232 MINER A LOGY. Percentage Atomic Proportionate Composition. Weights. Number of Groups. 14.01 ~ 25 = .56 19.26 -f 102 = .189 66.37 -f 60 = 1.106 Now, as fractional atoms cannot exist, our problem is simply to find the smallest number of whole groups which stand to each other in this relation, and, as .56 : .189 : 1.106 = 3 : I : 6, very nearly, therefore, the composition is represented by 3BeO -f A1 2 O 3 -f- 6SiO 2 , which may be better written Be^A^SigO^, or, as it at once becomes evident that the proportion between silicon and oxygen is that of a metasilicate, Be 3 Al 2 (SiO 3 ) 6 . It will now be found, on calculating the theoretical percentage composition of Be 3 Al 2 (SiO 3 ) 6 , that it agrees within the limits of error with that found by analysis, and as the twelve affinities of the six SiO 3 radicals are satisfied by those of Be and Al atoms, the formula probably represents the composition of the compound. The true molecular formula is, however, ?/Be 3 Al 2 (SiO 3 ) 6 wherein n represents some whole number. In this way the formulas of many minerals have been settled beyond question, while for others this success has not been reached. ISOMORPHISM.* Frequently the results of analyses show that the minerals con- tain elements foreign to their true composition. These may be present as impurities but if the mineral is homogeneous it is usually found that these unexpected elements replace analogous elements of the true molecule. Many beryls, for instance, contain Cs, H 2 , Na 2 , Ca, or Mg replacing Be; and Fe or Cr replacing Al. This replacement is explained by the principle of isomorphism. Isomorphous Substances. Substances are said to be isomorphous if they fulfill the following conditions: (a) Show distinct similarity in their molecules and a close re- semblance in their reactions. * Absolute isomorphism does not exist except in the isometric substances. The replacement of one element for another in either all or part of the molecules pro- duces some change in the angles. CHEMICAL CHARACTERS OF MINERALS, 233 (b) Crystallize in forms which in the regular system are identical, and in the other systems are so closely related as to require, at times, special care in angle measurement to recognize any differ- ence. (c) Are capable of mixing in varying proportions to form homo- geneous crystals. The third condition is the most important.* The others have no recognized limit. For instance the orthorhombic sulphates form an isomorphous series. Species. Type Formula. Axial Ratio. a:b:c. Prism Angle, no: iio. Dome Angle, IO2 : IO2. Barite BaSO 4 .815 : i : 1.313 78 22' 77 43' Celestite Anglesite Anhydrite SrSO4 PbSO 4 CuS0 4 .779 : i : 1.280 .785: i : 1.289 .893: i :i.oo8 75 50' 76 1 6' 83 33' 78 49' 78 47' These not only occur as the type minerals but as mixed crystals known as calcio- celestite, barylocelestite, leedsite, etc. The carbonates form two characteristic isomorphous groups, the first orthorhombic and the second rhombohedral. Axial Ratio, d : b : c. Aragonite, CaCOs 622 : i : .720 Strontianite, SrCOs 609 : i : .724 Witherite, BaCOs 603 : i : .730 Cerussite, PbCOs 610 : i : .723 Prism Angle, 119 A iTo. 6 3 48' 62 41' 62 12' 62 46' Bromlite, (Ba.Ca)CO 3 , Emmonite, (Sr.Ca)COs, are instances of mixed crystals with extensive replacement. Many occurrences show smaller replacement. Axial Ratio - . Rhombohedron. a Calcite, CaCOs 854 74 55' Siderite, FeCO 3 818 73 o Smithsonite, ZnCOs 806 72 20' Magnesite, MgCO 3 811 72 36' Rhodochrosite, MnCOs 818 73 o In this group the mixed crystals are exceedingly common and many variety names exist usually involving the name of the principal replacing element such as manganocalcite, ferriferous rhodochrosite, calciferous siderite, etc. In addition there are double salts such as dolomite, CaMg(CO 3 ) 2 , and subspecies ankerite, (CaCOs) (Mg.Fe.Mn)CO 8 . * Retger's rule is: "Two substances are truly isomorphous if the physical proper- ties of their mixed crystals are continued functions of their chemical composition." 234 MINERALOGY. Isomorphous Mixtures or Homogeneous Mixed Crystals. When two or more isomorphous substances mix to form homo- geneous crystals the resulting solids are variously called "homo- geneous mixed crystals," "isomorphous mixtures" and "solid solutions."* Most mineral species are isomorphous mixtures and their color, specific gravity, fusibility and other qualities may vary widely in consequence. Although it is generally held that mixed crystals consist of isomorphic molecules united "like stones in a building" it is convenient to regard them as formed by the replacement of one element or radical by another isomorphous with it, rather than as a mixture of different individual molecules. The principle of isomorphic replacement is well illustrated in the garnets which have the class formula R3 // R2 // '(SiO4)3 in which R" stands for any combination of the isomorphous divalent atoms Ca, Mg, Fe", Mn taken three at a time and R'" denotes any combination of the isomorphous trivalent atoms Al, Cr or Fe'". Therefore while the typical species Grossularite, CasAMSiO^s Spessartite, Pyrope, Mg3Al 2 (SiO 4 )3 Andradite, Almandite, FesA^CSiO-Os Uvarovite, have the formulas assigned to them; when pure they are in fact seldom found on analysis to more than approach these formulas. For instance: Si0 2 . A1 2 O 3 . CaO. MnO. FeO. MgO Fe 2 8 . Grossularite: Vesuvius 39.8 20.16 35.42 0.46 1. 21 0.97 1.03 Jordansmiihl .... 37.8 21.13 31.28 0.45 4.19 2.88 Spessartite: Theoretical 36.4 20.60 43.0 Glen Skiag 35-99 16.22 O.4O 15.24 23.27 0.47 8.64 Accordingly garnets vary through all combinations of color, with wide divergence of composition. Still their crystalline forms are identical and their composition can be expressed as of a definite type. Formulas of Isomorphous Mixtures. The formulas are calculated from the analyses as before by dividing the percentage composition by the molecular weight of the radical (or atomic weight of the element). * The term solid solution includes also non-isomorphous combinations. Any solution of a solid in a solid. CHEMICAL CHARACTERS OF MINERALS. 235 For instance, the spessartite from Glen Skiag. Molecular Number Percentage. Weight. Ratio. of Groups. MnO 15-24 -7-71 = .2146"! FeO 23.27 -r 71.9 = .3236 I MgO 0.47 -T- 40.36 = .0116 f CaO 0.40 -5- 56.10 = .oo7oJ AbOs. . . 16.22 -f- 102.2 = .1587") }- .2128 1.14 Fe 2 O 3 8.64 -f- 159.8 = .0541 J SiO 2 35-99 ^60 = .5998 .5998 3-23 This only approximates a garnet formula, giving 3 R"0, i.i 4 R2'"0 3 , 3.2 3 Si0 2 and probably indicates some loss of divalent elements by weathering, or some inter- mixed impurities. A black sphalerite from Felsobanya, Hungary, gave: Percentage. Atomic Weight. Ratio. Number of Groups. S 33-25 Zn 50.02 Fe 15.44 > 1.040 Cd 30 Pb i. 01 In expressing the composition of an isomorphous mixture by formulas the letter R is used to represent a varying group of isomorphic or equivalent elements, and it may have the valency of these elements designated by dots above and to the right of the letter. When elements are placed in a parenthesis with a period between, as (Zn.Fe)S, it means, that the zinc and iron taken together are equivalent to one atom of sulphur. GEL MINERALS AND ADSORPTION. There are a series of mineral products, all results of weathering or hot springs action, which by their lack of uniform composition, generally amorphous structure and external appearance suggest that they are "hydrogels," that is, products of the colloidal condition. In common with artificial "hydrogels" they take up or "adsorb" foreign material from solution in proportions inde- pendent of molecular weights and independent of crystalline similarity. Although such "hydrogels" are homogeneous and not mechanical mixtures, they are like solutions rather than definite chemical compounds and no way is known by which to 236 MINERAL OGY. tell which constituents are united and which adsorbed. No con- stancy in analysis is to be expected and no good formulas will result. CHEMICAL ALTERATIONS. The results of alteration through atmospheric agencies, infiltra- tion of water, etc., tend at times to so alter the individual that its composition varies widely from the type. New species may form and frequently the original mineral and its alteration product may both be present in the same fragment or crystal. In general the new material is softer and less coherent than the original and the microscope quickly proves the lack of homo- geneity. CHEMICAL TYPES. Minerals like other definite chemical compounds are either elements, oxides, acids,* bases or salts, the last being by far the most numerous. 1. The Elements, as Au, Ag, Cu, Sb, C, S. These are frequently alloyed with other elements as copper with silver, sulphur with selenium, etc. Only about one fifth of the known elements occur "native," that is as minerals. 2. Oxides. Elements in combination with oxygen, such as cuprite, Cu 2 O, cassiterite, SnO 2 , hematite, Fe 2 O 3 . Only about a dozen are sufficiently common to be described in this book. 3. Hydroxides. (Bases.) Containing hydroxyl (OH) as an important radical, as ^brucite, Mg(OH) 2 , limonite, Fe 4 O 3 (OH) 6 . Very few of these are described. 4. Acids. The only example described is sassolite, H 3 BO 3 . 5. Salts. Most minerals can be considered as derived from known or hypothetical inorganic acids, and in many instances they have been artificially produced in the laboratory as normal, acid or basicf salts of these acids. * As defined under the ionic theory: Acids are compounds, the dilute water solutions of which contain hydrogen ions. Bases or hydroxides are compounds, the dilute water solutions of which contain hydroxyl "(OH) ions. Salts are formed by union of base with acid, water also forming. t In normal salts all of the hydrogen of the acid or hydroxyl of the base have been replaced by metallic elements or acid radicals respectively. In acid salts only part of the hydrogen has been replaced. In basic salts only part of the hydroxyl has been replaced. CHEMICAL CHARACTERS OF MINERALS. 237 The most important groups of salts are : The Sulphides, derivatives of H 2 S and to a less extent their analogues the selenides, tellurides, arsenides and antimonides, as galenite, PbS, clausthalite, PbSe, hessite, Ag 2 Te, niccolite, NiAs. The Chlorides, derivatives of HC1, and to a less extent their analogues the fluorides, bromides and iodides as halite, NaCl, fluorite, CaF 2 , bromyrite, AgBr, iodyrite, Agl. The Carbonates, derivatives of H 2 CO 3 , as calcite, CaCO 3 ; basic salts of carbonic acid also occur, as malachite, Cu 2 (OH) 2 CO3. The Sulphates, derivatives of H 2 SO 4 , as barite, BaSO 4 . The Phosphates, derivatives of H 3 PO 4 , as vivianite, Fe 3 (PO 4 ) 2 + 8H 2 O. The Silicates. By far the largest subdivision. They may generally be considered as derivatives of orthosilicic acid, H 4 SiO 4 , as chrysolite (Mg.Fe) 2 SiO 4 , metasilicic acid, H 2 SiO 3 , as rhodonite, MnSiO 3 , or some hypothetical polysilicic acid, as H 4 Si 3 Og, repre- sented by orthoclase, KAlSi 3 O 8 . Less common are: nitrates, derivatives of HNOs, chromates, derivatives of HhCKX and of HCrC>2, molybdates, derivatives of H2MoO4; tungstates, derivatives of H2\VO4; borates, derivatives of HBO2, HsBOs or of H2B4O; aluminates, deriva- tives of HA1O2; arsenates, derivatives of HsAsC^; vanadinates, derivatives of HsVCX; columbates, derivatives of HCbOs; sulpharsenites, derivatives of HsAsSa and their analogues the sulphantimonides. Water of Crystallization. The water given off when hydroxides or acid or basic salts are heated is usually expelled only under a temperature approaching a red heat. Such water is not reassumed in the presence of mois- ture, and is not considered to be present in the mineral as water but to be in intimate combination. Its loss destroys the original mineral. In other minerals water is given off at relatively low tempera- tures, sometimes at common temperatures (laumontite) , some- times by a slight increase (gypsum) or below 300, natrolite. Such water is frequently reassumed by the mineral in the presence of moisture and the physical properties may remain unaltered. That is the release of the water has not destroyed the original substance, and it is assumed to be present in the minerals as water (called water of crystallization) and is expressed in the formula as molecules of H 2 O, thus gypsum, CaSO 4 + 2H 2 O. 238 MINERALOGY. MICROCHEMICAL METHODS. "The application of chemical operations to the examination and study of very small quantities of material." The tests are either tests for elements or tests which by color changes, etchings, etc., of polished surfaces give clues to species. Both require much practice and are as yet largely reserved for special investigation and little used in general mineralogical testing. The recent works of Chamot* and Murdoch! should be consulted. In the study of the rock-forming silicates, especially in their more minutely crystallized varieties, tests for certain great ele- ments such as Al, Ca, Mg, K, Na are desirable and the crystallized fluo-silicates obtained by the Boricky method by treatment of the silicates with hydrofluoric acid as well as the series of crystals obtained by the Behren's method by treatment with hydrofluoric and sulphuric acids and subsequent addition of different reagents to the resulting sulphate solutions are used to some extent. Both are described in Luquer's "Minerals in Rock Sections," pp. 136- 139- A few microchemical tests and re-crystallizations are described in parts of the book. It has not seemed necessary to tabulate them. * "Elementary Chemical Microscopy," John Wiley & Sons, 1915. f "Microscopical Determination of Opaque Minerals," John Wiley & Sons, 1916. CHAPTER XVII. THE FORMATION AND OCCURRENCE OF MINERALS. The solid crust of the earth consists almost entirely of minerals, of which about a thousand species have been identified, which involve in their composition practically all of the known elements. But the vast mass of the crust consists of aggregations* of a few great silicates composed almost entirely of nine elements themselves calculatedf to constitute over 98 per cent, of the crust in the following proportions : 49.85 Fe 4.12 Na 2.33 Si 26.03 Ca 3.18 K 2.33 Al 7.28 Mg 2. ii H 0.97 The remaining species involving the eighty elements are in part disseminated in these aggregations or rocksf in minute amounts but are largely concentrated in special deposits, pegmatite veins, ore veins, contacts, saline residues, etc. The history of a mineral, the r61e it has played, is largely told by the occurrence and associates and alternations but these must be considered according to certain fundamental principles of mineral formation which have been revealed by consideration of formations still going on and laboratory experiments. Associates (Paragenesis). This association may be accidental, as in a conglomerate, but the association in the rock in which they were formed may reveal much as to the order of formation, the processes which were active, and the temperature and pressure during formation. Alteration and Pseudomorphs. The alterations show whether the changes are essentially struc- tural, involving a molecular rebuilding or essentially chemical * F. W. Clarke, U. S. Geol. Survey, Bull. 491, p. 33. fOf the remaining 1.8 per cent, ten other elements in order, Ti, Cl, C, P, S, Fl, Ba, Mn, Sr, N, are estimated to total 1.33 per cent, leaving 0.47 for the remaining sixty-odd elements. J Aggregations of minerals large enough to be of geological significance and constant enough in characters to be identified are called rocks. 239 240 MINERAL OGY. with oxidation, reduction, partial solution, or the entire removal of one subvStance and its replacement by another. Frequently minerals are found as "pseudomorphs," that is, in crystalloids, the shapes of which belong to some other mineral. In many instances these are merely casts or incrustations which prove little as to the process, but in other instances they are evi- dently the result of the gradual and often incomplete alteration of the original mineral and give important clues to the process of alteration and add weight to synthetic experiments by showing that in nature similar changes actually occur. Petrifactions differ from pseudomorphs principally in that they are alterations or replacement of organic remains by mineral sub- stances. Physical and Chemical Characters. Any conclusion as to the origin or mode of formation of a min- eral must be in conformity with its observed physical and chemical characters. For instance, the solubility is a most important factor in determining the order of separation whether from aqueous or fusion solutions. Leucite crystals are isometric in shape, but their optical characters indicate a system of lower symmetry unless the material is heated to 433 C, the conclusion is that these isometric crystals formed above 433. Cyanite at about the melting point of copper assumes the characters of sillimanite, hence, ignoring the effect of pressure, it formed below that temperature. Synthetic Production of Species and of Alterations. The successful reproduction of a mineral by a method which does not conflict with the known natural conditions is an important clue as to its probable origin,* but is not conclusive, for the same species is often made in several ways. For instance : ortho- clase has been formed from fused magma, from sublimation and in the wet way and by action of solutions on leu cite, and galenite has * The production of species synthetically has several other purposes, such as settling the composition : (a] By producing crystals identical in characters with those of some natural sub- stance but avoiding the frequent natural inclusions, weathering, etc., which lead to varying analyses. () Obtaining crystals of massive or poorly crystallized minerals. (c) Obtaining simple types which are rare in nature and rinding new members of series. FORMATION AND OCCURRENCE OF MINERALS. 241 been formed by sublimation, by electrochemical reactions and by superheated water in a sealed tube. On the other hand, probable theories which have not been synthe- tically checked are not necessarily wrong. The processes of nature are not all to be reproduced, especially the geologic periods of time. So also the alteration of a mineral in the laboratory or even the production of pseudomorphs by possible natural methods may be of value as indicating what would happen under similar condi- tions maintained longer periods. The method of synthesis chosen must conform as far as possible with the observed conditions, must employ reagents that occur in nature and are thought to have taken part in the making. Geo- logic time may be in part compensated for by increased pressure and a temperature of 1 00 to 300; microscopic crystalline crusts must often be accepted as the equivalent of larger natural crystals. THE PROCESSES OF MINERAL FORMATION. The processes of mineral formation may be broadly grouped under the headings: 1. Crystallization from molten silicate magmas. 2. Formation by pneumatolysis, that is, processes in which gases and vapors play a prominent part. 3. Crystallization or precipitation from aqueous solutions. CRYSTALLIZATION FROM MOLTEN SILICATE MAGMAS. Below the present crust of the earth the regularly increasing temperature and pressure indicate that at some depth everything must be a fluid mass. This fluid mass or magma by volcanic forces penetrates any crack or crevice in the crust above, some- times reaching and overflowing at the surface (volcanic rocks) at other times being forced between strata far below the surface (plutonic rocks). The Nature of a Magma. The fluid magma consists chiefly of silicates but partly of oxides, sulphides, fluorides and ferrates mutually dissolved in each other with certain volatile constituents, chiefly water. As it cools the various minerals separate partly as type species, partly as mixed crystals. 17 242 MINERAL OG Y. The order of separation rests more on solubility than fusibility* and much upon eutectic ratios, for in a cooling mass if more than the proportion of one constituent is present than is necessary to form the "eutecticum" or mixture with lowest melting point that constituent would separate first.t Other factors such as supersaturation exist, the number of components is considerable, the composition of the magma is constantly changing and the problem is very complex. FORMATION BY PNEUMATOLYSIS. Pneumatolysis is Bunsen's name for those processes in which gases and vapors play an important part. Aqueous solutions may contribute to the reaction. % Usually, the term is limited to the action of gases and vapors on preexisting minerals, but is here allowed to include certain minor processes. The Gases and Vapors. Volcanoes emit much steam and relatively small amounts of other vapors, often at first O and N, mixed about as in air, and a little H, and later, probably by the action of the steam and the high temperature in decomposing existing compounds, there arise vapors of HC1, SO 3 , SO 2 , H 2 S, CO 2 , CO, Cl, CH 4 , HF, SiF 2 , B 2 O 3 . Similar gases and vapors are released from slowly cooling magma which force themselves into the already solidified magma and the neighboring rocks and produce new minerals and recrystallizations. The gases and vapors act as solvents and also as "mineralizers" much as in the many experiments with sealed tubes and frequently the action is catalytic as in many such experiments. Pneumatolytic action has occurred : * Quartz fusible at 1625 often begins to crystallize at noo to 1200. Vesuvius lavas are still molten at 1100. The nearly infusible leucite, for instance, in a leucite-tephrite magma goes into a solution at a little above red heat and separates at a red heat. t For instance, the eutecticum of chrysolite MgzSiO4 and diopside CaMaSi2O6 is 32 per cent, chrysolite, 68 per cent, diopside. In a cooling mass if more than 32 per cent, chrysolite were present chrysolite would separate first, with less chrysolite diopside would separate first. J Above the critical temperature, which for water is 375 C., physical differ- ences between the gaseous and liquid conditions cease. One minor cone of Etna is estimated to have discharged vapor at rate of 4,620,000 gallons per day. FORMATION AND OCCURRENCE OF MINERALS. 243 (a) Around volcanoes by action of vapors and gases on country rock and on minerals already formed from exhalations. (b) In pegmatite veins. (c) In contacts. (d) In and near tin lodes. (e) In some apatite veins. (/) In silver and gold veins near younger* eruptives. Minor Processes Involving Gases and Vapors. In certain instances the formation does not involve preexisting solids but is either (a) Due to the mixing of two gases or vapors. (b) Due to the decomposition of gases or vapors by heat. In other instances "sublimates" form at cooling which may be true sublimates, involving no change of chemical composi- tion or may be of more complicated origin. CRYSTALLIZATION OR PRECIPITATION FROM WATERY SOLUTIONS. Water is the chief agent in the alteration and concentration of minerals. Distilled water at ordinary temperatures and pressures will dissolve large amounts of the soluble salts and small amounts of almost all other substances, for instance, in per cents, gypsum 0.25, calcite 0.0025, barite 0.0002; anhydrous silicates very slightly and quartz so slightly that no numbers have yet been found to express it. Increased temperature and pressure in general increase solubility. Rain Water. Rain water is the principal cause of the decay or weathering of rocks. In passing through the atmosphere it absorbs about 0.65. per cent, oxygen and 0.03 per cent, carbon dioxide. This charged water possesses greatly increased solvent power and an oxidizing action. For instance, water saturated with COz dissolved o.io to 0.12 per cent, of calcite or forty times as much as pure water. More important, however, as bearing upon the alteration of silicates, is that water containing carbonic acid or alkaline carbonates in solution will decompose: many silicates. Free oxygen may oxidize sulphides and arsenides and further oxidize oxides or even drive out COz, for instance forming hematite from siderite, 4FeCOs + 2O + 3H 2 = 2 Fe 2 O 3 * Called propylization and consisting in the change of the original minerals of the eruptive to chlorite, clay, calcite, pyrite, etc. 244 MINERAL OG Y. Rain water also mechanically sorts and transports the less soluble portions and by streams carries the soluble portions to marshes, lakes and seas, where ultimately by evaporation new mineral deposits develop. The minerals are not attacked with the same rapidity, the presence of certain elements seeming to be the principal determin- ing factor: Calcium bearing minerals are most readily attacked and the CaO is largely carried away. The alkalis, soda and potash, also form soluble salts but the Na2O is principally carried off in solution, while the K2O, to a great extent, recombines to new species. Magnesium is slightly carried off but for the most part forms hydrous magnesia minerals. Ferric oxide is not much attacked. Ferrous oxide largely combines with oxygen and water to form limonite. Most of the alumina and silica remain but with some formation of colloidal aluminous silicates and silicic acid. The leached products possess a certain power to reabsorb lost substances, clays and soils take up potash, hydroxides of iron also absorb. Underground Water. The rain water in part sinks through the soil, penetrating by pores and fissures to considerable depths,* and with infiltra- tions from lakes, ocean and water courses and smaller amounts of water from ancient sediments or released by cooling magmas, f forms the so-called "underground or ground water." In the upper portions there is free circulation, the action is essentially that of rain water, solution and oxidation and much of the water returns to the surface by springs. Lower there is less circulation, the water is poorer in oxygen than rain water, but contains in solution such salts as carbonates of calcium, magnesium, potassium and sodium, or locally chlorides and sulphates. The action is more varied than at or near the surface. Organic materials may cause reduction to lower oxides or native metals, and of alkaline sulphates to sulphides, which then are able to. precipitate sulphides from silicates, carbonates and sulphates of the metals. Under the increased pressure the water tends to enter into combination. *Said in extreme cases to be 10,000 feet. t Cooling igneous rocks and late phases of an intrusion may release water often carrying in solution metallic ores, sulphur, boron, fluorine, etc. FORMATION AND OCCURRENCE OF MINERALS. 245 THE SEPARATION OF SOLID COMPOUNDS FROM WATERY SOLUTIONS. The principal methods by which the constituents of a watery solution are separated from the solution as solids are : I. Decreased Solvent Power by : (a) Decreased pressure or temperature, as in the case of solutions rising from below. (b) Evaporation. This is practically restricted to the seas and lakes at the surface, as in the interior the hollows are soon filled with water vapor. (c) Loss of a Constituent. A loss of CO 2 takes place in mov- ing water in contact with air, as at outlets of springs or rivers. (d) Solution of Another Substance. Solutions saturated with one substance can dissolve another, but a saturated complex solu- tion contains less of either salt than when saturated by it alone. Hence a saturated solution coming in contact with a new sub- stance may dissolve some of it, but if so will deposit some of the 'substance previously in solution. II. Precipitation. The precipitation of a mineral may take place as follows: (a) As the result of the meeting of two solutions. (b) By the action of gases upon a solution. (c) By electrolytic action, probably. (d) By the action of a solid upon a solution. Very dilute solutions and slow action are favorable to well- developed crystalline material. The law of mass action rules, that is, each material exerts chemical action pro- portionate to its mass. Exactly opposite results are obtainable; for instance, BaCOs with sufficient sulphate solution is all changed to BaSC>4 and BaSO4 with sufficient carbonate solution is all changed to BaCOs. If the quantity of solution is not sufficient, a stage is reached in which both salts are simultaneously in solution. III. Metasomatic Replacement. Replacement, or metasomatic replacement, while often involving a complicated series of chemical reactions, implies always the action of a solution on an existing mineral in such a way that as each particle of the mineral is dissolved it is immediately replaced by a particle of another mineral of different chemical composition. MINERAL OCCURRENCES. The occurrence of minerals may be discussed under the following headings: 246 MINERAL OG Y. A. The Great Mineral Aggregates or Rocks. B. The Minerals Produced During the Cooling of a Magma. 1. The Minerals which Crystallize from Molten Silicate Magmas. 2. Pegmatite Veins and their Minerals. 3. Magma tic Segregations and their Minerals. 4. Zeolites. 5. The Minerals Formed near Volcanoes. C. The Minerals Produced by Weathering and the Weathering Solutions. 6. The Minerals of the Mechanical Sediments. 7. The Minerals of the Chemical Sediments. 8. The Minerals of the Sediments due to Organisms. D. Metamorphic Minerals and Vein Minerals. 9. The Minerals of Contacts. 10. The Minerals of Regional Metamorphism. 11. The Minerals of Veins and Replacements. A. THE GREAT MINERAL AGGREGATES OR ROCKS. Practically all minerals are constituents of igneous, sedimentary, or metamorphic rocks. Igneous or Eruptive Rocks. About ninety-five per cent, of the crust of the earth consists of rocks which come from the interior of the earth as molten silicate magmas. See page 241. These molten magmas were forced up into crevices in the crust above, sometimes reaching and overflowing at the surface (volcanic rocks*), at other times formed deep within the earth (plu tonic rocksf). Evidently the same magma may form both plutonic and volcanic rocks containing essentially the same mineral species. The great plutonic and volcanic rocks and their dominant minerals are: * The volcanic rocks having cooled rapidly are often glassy, or fine-grained with constituent minerals unrecognizable to the eye alone or with flow structures and steam cavities. Below the surface they show less glass and more and larger crystals often with glassy inclusions. f The plutonic rocks having cooled slowly at great depths are solid and coarsely crystalline with recognizable constituent minerals and do not often contain glassy inclusions. Liquid inclusions are frequent. FORMATION AND OCCURRENCE OF MINERALS. 247 Plutonic. Volcanic. Dominant Minerals. Granite Rhyolite Quartz and orthoclase. Syenite Trachyte Orthoclase with mica or hornblende. Diorite Andesite Plagioclase with hornblende or biotite. Gabbro Basalt Plagioclase with pyroxene or chrysolite. Peridotite Chrysolite pyroxene, hornblende. The Sedimentary Rocks. The volcanic rocks and the plutonic rocks which by erosion or upheaval reach the surface undergo a process of breaking down partly chemical, partly mechanical, by the combined action of rainwater with its contained oxygen and carbonic acid, unequal expansion due to varying temperatures, the action of glaciers, living and decaying organic matter and other factors. The residual solid material and the weathering solutions form new so-called sedimentary rocks, which in general are stratified and less firm and coherent than igneous rocks. The Mechanical Sediments. The residual solid material is to some degree mechanically sorted by water, wind or glaciers into the coarser grains containing more unaltered material and finer grains containing more colloidal and hydrated material. By pressure and the cementing action of materials deposited from percolating waters these deposits of gravel, sand and clay are reconsolidated into conglom- erates, sandstones and shales,* the shales being by far the most abundant. * Average compositions are : Sandstones (Clarke). Shales (Leith and Meade). Quartz 66.8 3I-9I Feldspars 11.5 17.60 Clay 6.6 10.00 Iron hydroxides 1.8 4.75 Carbonates n.i 7.90 Sericite 18.40 Other minerals 2.2 9-44 The sandstones and conglomerates consist for the most part of visible fragments of the minerals of the igneous rocks, cemented by calcium carbonate, silica, clay, ferric hydroxide, calcium and barium sulphates. The shales form from finer particles with much colloidal material (silicic acid, clay, etc.) and adsorbed alkalis and alkaline earths. In drying the colloidal material almost disappears, fine-grained quartz and white mica (sericite) develop and much of th*e hydrous iron oxide is reduced and combined to chlorite, siderite or pyrite. 248 MINERALOGY. The Chemical Sediment. The solutions consequent upon the breaking down or weathering of rocks are in part redeposited in the mechanical sediments as cements in part precipitated in other rocks, but much of it is carried away to rivers, lakes or oceans, and there may form deposits. If these form without the assistance of organisms, vegetable or animal, they are known as chemical sediments.* The "rocks" which are chemical sediments are chiefly anhydrite, gypsum and halite or rock salt; locally there are other deposits such as the potassium deposits of Stassfurt, the soda nitre of Chili and various borates which have geological sig- nificance. Sediments Due to Organisms. These include: 1. The inorganic portion of skeletons of animals and plants consist mostly of carbonate of lime, some of phosphate of lime, some of silica. 2. The organic substance usually of plants, partly of animals, such as coal or petroleum. 3. Living and dead organisms may act to precipitate sediments, as when plants expel CO 2 and become coated with CaCO 3 or albumen generates ammonium carbonate, precipitating CaCO 3 . The "rocks" belonging to this division are the limestones and dolomites, the phosphate rock, coal and some silica deposits such as diatomaceous earth. Metamorphic* Rocks. Both igneous and sedimentary rocks are greatly altered by the intense horizontal pressures which cause rock folding or mountain making. Not only is a lamellar structure developed but under the pressure and resultant heat the circulating waters effect recrystallizations and molecular rearrangements "in place" usually with decrease of volume, that is, denser minerals. Often water is introduced as in amphibole, chlorite and mica. The resultant rocks are essentially alike whether formed from igneous or sedimentary rocks. Quartzites form from sandstone and from silica precipitated by organisms. Slates form from shales. Mica schists form from shales, sandstones and igneous rocks. * While strictly any change in composition or structure is metamorphism the term is generally reserved for strongly marked changes such as clay shale to mica schist. FORMATION AND OCCURRENCE OF MINERALS. 249 Hornblende schists or amphibolites form from basic igneous rocks rich in pyroxene; chlorite schists form from rocks rich in iron and alumina silicates. Gneisses form from different igneous and sedimentary rocks. B. THE MINERALS FORMED DURING THE COOLING OF A MAGMA. 1. The Minerals which Separate from the Liquid Magma. The average composition* of igneous rocks is not greatly dif- ferent from that already given p. 239 for the average composition of the crust of the earth. In any given magma many possible combinations exist, and the same magma, solidifying under different conditions, may yield different minerals. In general all the K, Na and Ca and most of the Mg, Al and Fe unite with oxygen and silicon to form silicates. Excess of Si separates as SiOz and relatively small amounts of Fe and Al form oxides, ferrates and aluminates and Mg may combine as an aluminate. Experience shows that the number of minerals which actually form is greater in the medium basic magmas than in the highly siliceous or very basic magmas. Taking an average of some 700 described igneous rocks, Clarke estimates that a few great groups constitute an overwhelming proportion, although in particular instances other groups may dominate. He gives as the proportions: 1. The feldspars 59.5 per cent. 2. The pyroxenes and amphiboles 16.8 ' 3. Quartz 12.0 " 4. The micas 3.8 " " 5. Accessory minerals 7.9 " " 100.0 " " In addition to the great groups mentioned other important primary minerals in certain igneous rocks are: The Feldspathoids, nephelite, leucite, sodalite, haiiynite, noselite. The Chrysolite Group. Chrysolite, fayalite, etc. Tourmaline and topaz in regions near pneumatolytic action. Garnet in its varieties pyrope, andradite, almandite and spessar- tite. Corundum and spinel in rocks rich in alumina. * On basis of 1,000 to 1,500 analyses O 47.05, Si 28.26, Al 7.98, Fe 4.47, Ca 3.43, Mg 2.34, Na 2.54, K 2.50. Of the remaining 1.43 per cent. Ti 0.45, H 0.16, C 0.13, P o.ii, S o.n, Ba .097. Clarke, Bulletin 491, U. S. Geol. Survey, p. 27. t Ibid., p. 31. 250 MINERAL OGY. The Accessory or Minor Primary Minerals. Certain minerals are sometimes present in igneous rocks in small amounts among which are: Elements, graphite, diamond, iron, copper, gold, platinum. Sulphides, pyrrhotite, pyrite, pentlandite, molybdenite, millerite. Oxides* magnetite, hematite, ilmenite, chromite, rutile, brookite, hausmannite, cassiterite. Silicates, allanite, analcite, iolite, sillimanite, titanite, zircon. Sundries, apatite, calcite, fluorite, monazite. 2. Pegmatite Veins and their Minerals. Igneous rocks are often cut by dikes or veins consisting chiefly of coarse and even gigantic crystals of the common minerals of the igneous rock, and usually a large number of other minerals which are in part the accessory minerals of the igneous rock, in part minerals containing the same elements combined with water, fluorine, chlorine, boron and in part combinations of elements not observed in the igneous rock. Crystal druses are frequent. These veins are believed to represent a late stage of solidification in which the magma, thinned both by the loss of the already solidified minerals and by the release of the volatile substances dissolved therein under pressure, penetrates cracks both in the solidified portion and in the surrounding rock. The Minerals of Pegmatites. While there are pegmatites of most of the plutonic rocks the granitic pegmatites and the elaeolite-syenite pegmatites are most important and contain the greatest variety in minerals. In granitic pegmatites the typical species which often develop as large or giant crystals are feldspars (chiefly orthoclase and microcline, often intergrown with albite), quartz, mica (chiefly muscovite or lepidolite, less biotite) , tourmaline (dark in compact rock often colored in the druses), spodumene, and beryl. Very widely distributed species are apatite, zircon, titanite, fluorite, topaz, rutile, monazite, columbite. Where the vein penetrates other rock it may take up con- stituents therefrom and develop such minerals as garnet, andalu- * Ferrates, chromates, etc., included. t In certain localities Weinschenck describes pegmatites due to rock pressure, these lack the crystal druses and may be dense mica-like masses with enclosed large crystals such as the Lisens andalusite and the enormous 25 m. long quartz of Zillerthal. FORMATION AND OCCURRENCE OF MINERALS. 251 site, zoisite, phlogopite, sillimanite, cyanite, staurolite, iolite, spinel, corundum, possibly diamond. Minor minerals in granite pegmatites are allanite, amblygonite, brookite, cassiterite, chrysoberyl, euclase, fergusonite, gadolinite, graphite, ilmenite, magnetite, molybdenite, petalite, phenacite, samarskite, triphyllite, uraninite. In Nepheline-Syenitic Pegmatites the great minerals are the soda feldspars, albite and anorthoclase, the soda pyroxenes, acmite and segirite, the soda amphiboles barkivikite and arfvedsonite, nephelite, sodalite, concrinite, zircon. In addition there are a host of rare silicates, titanites, zirconates, columbates, tantalates and other compounds of both common and rare elements. A few of these species are astrophyllite, eudialyte, euxenite, lavenite, mosandrite, polycrase, pyrochlore, rinkite, thorite, wohlerite. In still other varieties of pegmatites there may be developed large crystals of apatite, wernerite, labradorite, hypersthene, green hornblende, pyroxene, rutile. The economically important minerals of the pegmatites are numerous and include not only quartz, feldspar and mica but cassiterite, wolframite, the minerals of yttrium and thorium, zircon, apatite, and the lithium minerals. 3. Magmatic Segregations and their Minerals. The eruptive rocks of a district may have such chemical char- acters in common and such gradations into one another as to indicate that they are due to splitting up or "differentiation" of one homogeneous rock magma into several by the segregation of certain constituents. It is believed that the changes take place chiefly before the magma is forced up.* The Minerals of Magmatic Segregations. The minerals which segregate are the minerals which first crystallize, that is: Oxides, magnetite, ilmenite, chromite, corundum, rutile, cas- siterite. Sulphides, pyrrhotite, pentlandite, chalcopyrite, pyrite, molyb- denite. Elements, iron, platinum, copper, gold. The rocks involved are chiefly basic gabbro, peridotite, norite, occasionally acidic granite. * The high specific gravity 5.6 of the earth as a whole in comparison to 2.7 to 2.8 for its crust suggests an interior segregation of the heavier materials near the center. 252 MINERALOGY. 4. Zeolites. The formation of zeolites, in the cavities in basic lavas, peg- matite dikes and ore veins is probably the last phase of con- solidation of a magma. Their rarity in veins suggests the need of stagnant waters. The process is not well understood and is intimately connected with the method of formation of metallic copper. The best known zeolites are: heulandite, stilbite, laumontite, chabazite, analcite, natrolite, thomsonite. 5. The Minerals formed near Volcanoes. These rising vapors act on the sides of the crevices and react upon each other, producing many minerals in small amounts, the principal groups being: Sulphur by the reaction SO 2 + 2H 2 S = 38 + 2H 2 O. Oxides* by the decomposition of chlorides at high temperature. Carbonates by the action of CO 2 on the oxides. If the flowing lava passes over vegetable matter sal-ammoniac (NH 4 C1) is formed. Chlorides and sulphates may form by action of the vapors on the adjacent rocks. A. Scacchi gives a large list but those in quantity at Vesuvius are chiefly al unite and gypsum. Other minerals are, amphibole, tourmaline, topaz, phlogopite, chondrodite, vesuvianite, epidote, fluorite. The hot solutions near extinct volcanoes often produce at and near the surface potash minerals, sericite, adularia, alunite and other species such as gypsum, jarosite, fluorite, barite, calcite, chlorite, epidote. C. THE MINERALS PRODUCED BY WEATHERING AND THE WEATHERING SOLUTIONS. These may be considered as constituting the following "Occur- rences''^ .6. The Mechanical Sediments. 7. The Chemical Sediments. * A crack in lava at Vesuvius in 1817 was filled in 10 days with a 3-ft. thick deposit of hematite. t The gossans or oxidized portions of ore deposits are due to the weathering solu- tions but are considered later. FORMATION AND OCCURRENCE OF MINERALS. 253 8. The Sediments of Organic Origin. As previously stated, p. 244, part of the weathering solutions penetrate and join the underground water. 6. The Minerals of the Mechanical Sediments. The minerals will be either (a) Minerals in fragments of the original rock. (&) New minerals. The minerals from the original rock need not be listed except to say that a few species dominate such as quartz, feldspars and micas. The accessory minerals, magnetite, zircon, corundum, ilmenite, chromite, tend to accumulate. The New Minerals. Comparatively few form, the principal ones being Hydrous aluminum silicates of the kaolin group often colloidal. Colloidal silicic acid yielding opal, chalcedony or chert. Iron hydroxides probably in colloidal condition. Sericite (white muscovite) from feldspar. Rutile, possibly from titanic acid in colloids. // the decomposition is partial there will be intermediate products. Albite and anorthoclase from more basic feldspars. Chlorite from hornblende, biotite, pyroxene. Epidote from feldspar. Serpentine from chrysolite, enstatite, pyroxene, hornblende. Talc from pyroxene, amphibole, enstatite. Magnetite from chrysolite, biotite. Amphiboie from pyroxene. Under peculiarly favorable circumstances the silica may be carried away, leaving bauxite, gibbsite, limonite or other hydroxides. 7. The Minerals of the Chemical Sediments. The deposition of minerals from weathering solutions may take place from springs or running streams or in marshes, lakes, seas or ocean. The Minerals Deposited by Springs.* Although all springs contain mineral matter the water is often merely rain water which has followed a comparatively short * Clarke classifies them as chloride waters, sulphate waters, carbonate waters, silicious waters, nitrate, phosphate and borate waters, acid waters. Bulletin 491, U. S. Geol. Survey, p. 190. 2 54 MINERAL OGY. course through the soil and emerged at a lower elevation. It con- tains little more than the dissolved gases from the atmosphere. Other springs, particularly thermal springs and geysers with tem- peratures independent of the season of the year, may contain sufficient dissolved material to deposit solids on emergence or during their passa'ge underground. The principal deposits ob- tained are: Carbonates, calcite, aragonite, siderite, hydrozincite, hydro- dolomite (stalactites, calc sinter, tufa, and flos ferri are of this type). Silica, opal, quartz, chalcedony. Sulphides and Sulphur, cinnabar, realgar, orpiment, stibnite, galenite, sulphur. Other Deposits. Sassolite, scorodite, fluorite, celestite, the alums, halloysite, siderite, and limonite. The Minerals Deposited by Running Streams. The dissolved material of rivers and streams consists essentially of carbonates, sulphates and chlorides of calcium, sodium, mag- nesium and potassium and considerable silica. Before reaching the ocean most of the silica, carbonic acid and calcium, and about half of the potassium disappear.* Definite mineral deposits are rare; the mud at the bottom is clay like. Sometimes there are deposits of travertine. The Minerals formed in Oceans. Some deposits of calcium carbonate and of dolomite are believed to be chemical sediments. Glauconite forms just beyond the wave * For comparison of mineral components the general average for river and lake waters and the mean of 77 analyses of ocean water collected by Challenger expedition are here given: Bull. U. S. Geol. Surv., 491, p. 106. River and Lake. Ocean. COs 35-15 2.07 SO4 12.14 7-6p Cl 5-68 55.29 Br .18 NO 3 90 Ca 20.39 i. 20 Mg 3-41 3-72 Na 5.79 30.59 K 2.12 i. ii (FeAl) 2 3 2.75 11.67 FORMATION AND OCCURRENCE OF MINERALS. 255 action and the other important iron silicates, greenalite, chamosite and thuringite, are supposed to have a similar origin. The proportion of dissolved solids in the ocean is only 33 to 37 in the 1,000. Deep sea dredgings bring to light principally a red clay containing minute crystals of a rare zeolite called phillipsite, nodules of hydrated oxide of manganese and iron and some enstatite, all apparently resulting from the decomposition of a lava. For the dissolved constituents to separate there is needed a concentration of the solution, usually a land-locked basin with a shallow bar between it and the sea. The usual formation consists of beds of anhydrite, gypsum and halite. After their separation the mother liquor contains chiefly sulphates and chlorides of potassium and magnesium. These usually escape; in fact, only one great deposit is known, that of Stassfurt and Leopoldshalle, south of Magdeburg, Prussia. It has been theorized that the raising of the bar converted the basin into a salt lake from which further evaporation occurred, giving successively kieserite, carnallite and by secondary reactions kainite, sylvite, boracite and a series of other species. Minerals formed in Lakes. In some lakes calcium minerals are rare and the deposits are chiefly halite and other soda minerals such as mirabilite, natron and trona. In others which have probably received boric acid from hot springs the boron minerals are prominent especially borax and ulexite. Other carbonates, sulphates and chlorides are also present. 8. The Minerals of the Sediments due to Organisms. Aragonite and Calcite. By Action of Animals. Where marine life is abundant CC2 is the principal gas in the sea water; similarly when organic decay is in progress ammonium carbonate is formed. The shells and frameworks are in part aragonite, in part calcite. By Action of Plants. Algae chara, mosses and many aquatic plants absorb the CO2 and thus become coated with CaCOs, forming sinter or travertine, which may later be compacted by further deposition of CaCOs. Fresh water marls also are in part due to action of plants. Dolomite. In marine sediments magnesium carbonate tends to accumulate, while the more soluble calcium carbonate is dissolved. Coral in the living animal is aragonite. Coral rock may be essentially dolomite, the lime being removed and replaced by magnesia from the sea. Magnesite. 256 MINERAL OGY. i Ltmonite (bog ore) is in part due to one of the algae. Silica taken from ocean water by sponges, radiolaria, etc., forms banks of horn- stone. Diatoms in marshes yield great beds of soluble silica. Algae in hot springs precipitate geyserite. Sulphur is separated from sulphates by certain algae and bacteria, and by de- composing organic matter. Pyrite, marcasite and some other sulphides are precipitated from solutions by decomposing organic matter. Phosphates. The marine deposits of bone shell and animal matter by relatively more rapid solution of the carbonates form phosphate nodules and by later changes form the large deposits of phosphate. Soda Nitre and Nitre may be regarded as due to nitrifying organisms. D. METAMORPHIC MINERALS AND VEIN MINERALS. 9. The Minerals of Contacts. Contact metamorphism occurs when an igneous rock penetrates another rock and is a pneumatolytic process involving heat, pressure, and the mineralizing vapors given off by the intrusive rock, chiefly steam and often fluorine, boric acid, etc. The text- ures of both rocks change and new minerals form, at the contact and for some distance from it. The action is largely a rearrangement of the same material into new compounds with little total chemical change. This is most marked in the country rock. In the igneous rock the attempt of the vapors to escape may form the minerals of the pegmatites such as tourmaline. The zone of contact will vary from a few inches to a mile in width. Granite Contact with Limestone. An impure siliceous limestone in contact with an eruptive granite would probably be converted into a granular marble* containing crystals of silicates, chiefly calcium-bearing but varying with the impurities in the limestone. Very characteristic species are garnet (chiefly grossularite), vesuvianite, amphibole (especially tremolite, also actinolite, horn- blende, pargasite), pyroxenes (especially diopside, also fassaite), wollastonite, wernerite, epidote, biotite, and tourmaline (especially brown varieties). Tf magnesia is plentiful there may form: spinel, brucite, and * The more silica present the more CO 2 will be displaced. FORMATION AND OCCURRENCE OF MINERALS. 257 the silicates, forsterite, chrysolite, enstatite, hypersthene, and their alterations, talc and serpentine. Carbonaceous material forms graphite. Minor minerals are rutile, fluorite, zircon, monazite, lapis lazuli. Contacts with Argillaceous Rocks. (Clays, shales and slates.) Near the contact the rocks are baked to a dense hornfels which under the microscope may show many minerals; further out this grades into schists. The most characteristic species are: Micas especially biotite. Andalusite (chiastolite), frequently sillimanite and sometimes cyanite, staurolite, tourmaline and iolite. Amphibole (hornblende). Feldspars anorthite, albite, etc. Quartz. Accessories are rutile, graphite, spinel, corundum. Contact metamorphism will effect similar changes in other mineral deposits, sandstones, beds of anhydrite, gypsum or siderite or even basic eruptive rocks. There may be almost fusion near the intrusive mass and in such a case the metamorphic minerals may pass back to igneous minerals, for instance, amphibole to chrysolite and pyroxene. 10. The Minerals Formed in Regional Metamorphism. The chemical changes due to intense pressure from rock folding, circulating waters often hot and charged with many constituents including the so-called mineralizing agents are very complex,* many new minerals form often denserf than the originals and many with constitutional water, J basic feldspars tend to form more acid varieties, pyroxene to change to amphibole and amphibole to chlorite or conversely micas and chlorite may form feldspars and hornblende. After the crushing has ceased, as shown by the fact that they are not crushed, porphyritic crystals of anhydrous minerals develop * Clarke sums up the reactions producing chemical changes in metamorphism as molecular rearrangement, hydration, dehydration, oxidation, reduction; other changes by percolating solutions, and by gases and vapors, changes by igneous intrusives. t Largely molecular rearrangements giving decreased volume, e. g., plagioclase and orthoclase to albite, zoisite, muscovite, quartz with loss of 15 per cent, volume. | Micas, chlorites, epidotes, etc. 18 258 MINERALOGY. of higher density than the average of the rock. No simple list can be made, the material and the reactions being too varied. Minerals often developed porphyritically are garnet, staurolite, andalusite, iolite, albite, rutile, tourmaline, pyroxene, amphibole, ilmenite, apatite, magnetite, topaz, biotite, titanite. Other common or locally very prominent species are : sillimanite, cyanite, the micas (phlogopite, biotite, muscovite), other feldspars, the chlorites, epidote, zoisite, and piedmontite, serpentine and talc, wollastonite, wernerite, corundum, beryl and chrysoberyl, graphite. Important ore bodies, especially* in iron, manganese and zinc may be products of metamorphic action. Minor species are vesuvianite, prehnite, zircon, hematite, monazite, gibbsite, pyrophyllite, spinel. ii. The Minerals of Veins and Replacements. In all classes of rocks there are numerous fissures and cavities into which the underground water can penetrate. Many of these have been rilled by minerals deposited from these waters. Veins strictly are tabular or sheet-like masses rilling crevices or fissures. Technically they are called "mineral veins" only when they contain ores. More irregular bodies called stocks, beds, lenses, occur which may sometimes owe their shape to the filling of irregular cavities but more often to a solution and replacement of the original minerals of the country rock (see p. 246). Fre- quently also deposits occur which are not so definitely! connected .with veins arid yet evidently are complete or partial replacements .of a rock such as limestone by a new mineral. i . For instance, the Cleveland oolitic iron, ore is oolitic carbonate of ,iron which has replaced oolitic limestone; and the manganese deposits of the Thuringer Wald are manganese ores which have replaced everything but the quartz of a porphyry. * For instance, Weinschenk gives as accessories in the crystalline schists: Oxide ore bodies, magnetites like Oravitza, manganese oxides like Langban, 'manganese zinc deposits, like Franklin, magmatic concentrations in gneiss or erup- tives. Sulphide ore bodies pyrrhotite, pyrite, chalcopyrite, sphalerite, galenite. Carbonate ore bodies siderite usually in limestone. Emery in granular limestone, Naxos, and in mica schist, Chester, Mass. t Replacements are usually connected with some channel or fissure through which the aqueous, or gaseous solutions may have entered. , . . , FORMATION AND OCCURRENCE OF MINERALS. 259 The minerals of veins by their composition and arrangement are shown to be deposits from solution, but in most cases not simply solutions of the neighboring rocks in the underground water but also solutions in the vapors of deep-seated magmas. Veins with metallic contents being usually connected with some intrusion of igneous rock. As the vapors rise into regions of lower pressure and tempera- ture condensation takes place, fluid solutions form, various species separate and are deposited on the walls and may ultimately fill the fissure, forming a vein. The minerals formed in this way are usually divided into ores* and gangue minerals and a complete list would include most of the species described in this book. The following lists give some idea of relative frequency. Primary Ores. The great ores are pyrite, galenite, sphalerite, and chalcopyrite. These frequently carry valuable amounts of silver, gold, copper, nickel. Common in veins also are arsenopyrite, stibnite, tetrahedrite, chalcocite, native gold, gold tellurides (calaverite, sylvanite, pet- zite, etc.). Rich silver minerals argentite, polybasite, proustite, pyrargyrite, stephanite. Others are, smaltite, cobaltite, niccolite, millerite, braunite, hausmannite, rhodo- chrosite, bornite, enargite, etc. Gangue Minerals. The great gangue mineral is quartz (or sometimes the silica is chalcedony or opal or both) and following this are calcite, dolomite, siderite and other carbonates, fluorite, barite. Locally common fare rhodonite, rhodochrosite and orthoclase (valencianite) , roscoelite. Others are zeolites, chlorite, axinite,{ celestite. High Temperature Veins. Certain deposits appear from their minerals and the' changes in the country rock to have formed at higher temperatures and * Ores are minerals containing desired elements. Gangue minerals are all other minerals in the deposit. The minerals formed from the ascending waters may be called primary, those formed later secondary. t Tonopah, Nev , Pachuca, Mex., Butte, Mont., Silverton, CbL - ' J Kongsberg, Norway. 260 MINERAL OGY. pressures and with so decided pneumatolytic action that their minerals suggest those of a pegmatite. The most important group of these are the tin veins which grade into wolframite or molybdenite veins and with them Lind- gren classes* certain veins of gold quartz and gold telluride (Australia) and certain veins of copper, lead and cobalt character- ized by association with tourmaline. The characterizing gangue minerals of such deposits are : Tourmaline, biotite, garnet, fluorite, topaz, pyroxene, amphi- bole, apatite, ilmenite, magnetite, mica, spinel, feldspar (usually albite), lithia mica. The ore minerals of tin veins are fairly constant and include cassiterite, molybdenite, wolframite, scheelite, bismuth, bismuthinite, arsenopyrite and minor amounts of the common sulphides, pyrite, pyrrhotite, chalcopyrite, galenite, sphalerite. Secondary Vein Minerals. Veins, like the rock in which they occur, undergo changes. Near the surface there is oxidation and solution, lower the solu- tions may yield up their contents, forming an economically very important "zone of secondary enrichment," below this again will be the unaltered ore, often very much poorer in the desired constituent than the enriched zone above it. Important secondary ores are: Iron. Limonite (often forming the principal metallic mineral in the upper part of a vein), hematite, vivianite. Silver. Rich silver minerals as secondary enrichments and native silver, cerargyrite, bromyrite, embolite, iodyrite in the upper portions. Copper. Chalcocite, covellite, cuprite and bornite as secondary enrichments, malachite, azurite, copper, chrysocolla, chalcanthite, brochantite in upper portions, Gold. Native gold both as secondary enrichment and in upper portions. Lead. Cerussite, anglesite, pyromorphite, mimetite, crocoite, vanadinite, wulfenite. Zinc. Smithsonite, calamine. * "Mineral Deposits," 611. CHAPTER XVIII. THE MINERALS OF METALLIFEROUS ORE DEPOSITS. The order* in which the minerals are described is chiefly based on their economic uses as in the former editions but more groups have been made, each group consisting of the chief minerals containing some economically important element, its ores and possible ores, and the more common alteration products. To place each group in its right perspective its economic and genetic relations are discussed under the headings Economic Importance and Formation and Occurrence. These group dis- cussions are followed by the descriptions of species. In discussing formation and occurrence four great groups* of deposit are usually made. I. Magmatic segregations, p. 251. II. Contact deposits, p. 256. III. Veins and replacements, p. 258. IV. Sedimentary deposits, p. 252, including placers, residual de- posits, chemical sediments and some deposits of doubtful genesis. In descriptions where possible details previously given under the descriptions of these occurrences will be omitted. THE IRON MINERALS. The minerals described are: Metal Iron Fe Sulphides Pyrrhotite FCnSn+l Hexagonal Pyrite FeS 2 Isometric Marcasite FeS 2 Orthorhombic Oxides Magnetite Fe 3 4 Isometric Hematite Fe 2 3 Hexagonal Ilmenite FeTiOs Hydroxides Turgite Fe 4 05(OH) 2 Goethite FeO(OH) Orthorhombic Limonite Fe 2 (OH) 6 .Fe 2 O3 Sulphates Copiapite Fe 2 (FeOH) 2 (S04) 5 + i8H 2 O Monoclinic Melanterite FeS0 4 + 7H 2 * " Beyschlag Vogt and Krusch." Truscott's translation, Vol. i, p. 240. 261 262 MINERALOG Y. Phosphate Vivianite Fe3(PO 4 )2 +~8H 2 O Monoclinic Carbonate Siderite FeCOs Hexagonal Silicates Chamosite Hydrous iron aluminum silicate Thuringite " Other iron minerals elsewhere described are arsenopyrite, frank- linite, chromite, columbite, wolframite, fayalite, as well as -many iron-rich varieties of pyroxene, amphibole, garnet, mica, etc. ECONOMIC IMPORTANCE. The iron minerals have important and varied uses, which may briefly be described under the following heads: I. In natural state. II. As ores of iron. III. As ores of sulphur and iron. I. Uses in Natural State. In 1914 the production of ocher, umber and sienna and natural oxide paints was 51,495 short tons.* Limonite and hematite are the principal natural oxides ground for paint. II. Minerals Used as Ores of Iron. In the United States the minerals smelted for iron are, in order of quantity used,f hematite, limonite, magnetite, and siderite. Goethite and turgite are commercially included with limonite under the name brown hematite, and some ilmenite is smelted with other ores. The residues from the roasting of pyrites are sometimes used as a source of iron. In 1915 the United States produced 58,843,804! long tons of iron ore, about four fifths of which came from the Lake Superior region of Michigan, Wisconsin and Minnesota, and about one eighth came from the Southern States. The greater portion of the iron ore mined in the world each year is converted into pig iron. That is, the ore is deprived of its oxy- gen by the action of incandescent carbon and the hot reducing * Mineral Resources U. S. t Ernest F. Burchard, in Mineral Resources of United States, 1914, gives as amounts mined for 1914: Hematite, 38,286,670 long tons; limonite' and goethite, 1,537,750 long tons; magnetite, 1,610,203 long tons; siderite, 5,138- long' tons. The total production for 1914 being one-third less than either 1913 or 1915. { Engineering and Mining Journal, 1916. MINERALS OF METALLIFEROUS ORE DEPOSITS. 263 gases resulting from its combustion, and becomes a liquid mass of metallic iron, combined and mixed with a little carbon, silicon, phosphorus, sulphur and other impurities. The furnace used is a vertical shaft, everywhere circular in horizontal section, but usually widening from the top downwards to a certain level, and then again narrowing to the hearth. Hot air is forced into the furnace through nozzles called tuyeres, entering just above the hearth. The ore and fuel are analyzed and some flux is added, which, when combined with the ash of the fuel and the foreign ingredi- ents of the ore, forms a definite silicate of known fusibility, called the slag. The temperature of the furnace differs at different levels, but is practically the same at all times at any one level. The ore, charged at the top, in alternate layers with fuel and flux, passes through zones of different temperature as it descends, and is reduced, carburized, fused, and flows into the hearth. The slag forms in a definite zone after the complete reduction of the iron, and falls also to the hearth, but, being lighter, floats on the melted iron until drawn off. From time to time the metal is run out into sand moulds, forming the pigs or pig iron, of which 29,- 971,191* long tons were produced in the United States in 1915. This pig iron, by various processes, is converted into wrought iron, cast iron and steel. III. Minerals Used as Ores of Sulphur and Iron. Pyrite, and, to a less extent, marcasite and pyrrhotite, are very extensively used in the manufacture of sulphuric acid. In 1914, f 1,363,279 tons were so used in the United States, of which 336,662 were domestic, 1,026,617 imported. The sulphides are burned in furnaces with grates, and the gases are converted into sulphuric acid. The residues, in addition to iron, frequently contain copper,) nickel or gold, which are extracted later. FORMATION AND OCCURRENCE OF THE MINERALS OF IRON. The iron minerals occur in all four classes of deposit. Magrnatic Segregation. Titaniferous magrietite% and ilmenite, in basic rocks. * Loc. cit. f Mineral Industry, 1914, p. 692. J In. many cases this is a microscopic mixture of pure magnetite and ilmenite which may be separated by magnetic concentration. Beyschlag Vogt and Krusch, p. 254. 264 MINERAL OGY. As at Ekersund-Soggendal, Norway; Taberg, Sweden ; Saguenay River and St. Paul's Bay, Canada; and Elizabeth town and Sand- ford Lake, Adirondacks, N. Y. Magnetite from acid magmas with some hematite, both free from titanium. This includes the enormous Swedish magnetite deposits such as Kiirunavaara, Gellivare, etc., and others in Norway. Pyrrhotite in the nickel-pyrrhotite deposits of Canada, Norway, Sweden and Piedmont pyrite sometimes being prominent. Pyrite in the great intrusive pyritic deposits, such as Rio Tinto, Spain; Agordo, Italy; Bodenmais, Bavaria; Sain Bel, France. Possibly Fahlun, Sweden. Some authorities* regard the great- est of these to be magmatic segregations. Contact Deposits. Hematite of Elba and the magnetite and hematite of Christiania, Sweden; Banat, Hungary; and "practically every known iron deposit along the Pacific coast from Alaska to southern Chili. "f Pyrrhotite and pyrite as at Traversella, Piedmont; Ducktown, Tenn.J Veins. Pyrite, marcasite, pyrrhotite and siderite all occur as vein min- erals, pyrite much more frequently than the others. Replacements. Limonite replacing limestone is common along the Appalachian Mountains and extensively mined in the Southern States. Hematite is often a replacement of limestone as at the great deposit of Ulverstone, Lancashire. The most important ex- amples, are the great Lake Superior deposits which consist chiefly of hematite but also goethite and turgite and are be- * Beyschlag, Vogt and Krusch. Truscott translation, p. 301, f Eckel, "Iron Ores," p. 87. J Lindgren, "Mineral Deposits," p. 598. " As first deposited the iron formation consisted of iron carbonate or ferrous silicate (grenalite) with some ferric oxide all minutely interlayered with chert form- ing the ferruginous chert. When these were exposed to weathering the ferrous compounds, the siderite and greenalite, oxidized to hematite and limonite essentially in siiu, although some of it was simultaneously carried away and redeposited. The result was ferruginous chert or jasper, averaging less than 30 per cent, of iron. MINERALS OF METALLIFEROUS ORE DEPOSITS. 265 lieved to have formed by weathering of lean silicates and carbonates of sedimentary origin and subsequent replacement of silica. Siderite deposits formed by replacement of limestone exist in Cornwall, the Alps and Bohemia. Sediments. Magnetite (black sands) , or ilmenite (iserite) . Transported con- centrates. Limonite or siderite. Bog deposits largely precipitated by iron bacteria. If much carbonic acid or decaying organic matter is present the bog ore formed is siderite. If air has free access the bog ore is limonite. Hematite, limonite, siderite and the silicates chamosite and thur- ingite. " Marine Basin Ores" as deposited in sea basins, usually oolitic. The Clinton oolitic ores are typical. Pyrite, pyrrhotite and marcasite disseminated or in concretions in limestone, clay, marl and coal as at Meggen and Rammelsberg, Germany. Residual. Limonite, goethite, etc., left after weathering, p. 247, sometimes hematite and colloidal mixtures. The Appalachian ores and the ores of Cuba are types. Limonite, formed chiefly by alteration of pyrite and pyrrhotite. The most important Gossan deposits are in Ducktown District, Tenn., and Great Gossan Lead, Va. IRON. COMPOSITION. Fe with some Ni, Cr, Co, Mn. GENERAL DESCRIPTION. Masses and imbedded particles of white to gray metal, resembling manufactured iron. CRYSTALLIZATION. Isometric, several meteoric irons showing minute cubes and cubes modified by {m} and {no}. Some meteorites, especially the Braunau, are single crystals the same cubic cleavage planes extending through the entire lump. Etching frequently develops the crystalline structure as lines or bands at 60 or 90 which are in part due to plates of varying composition and in part to parting planes parallel to {211}. PHYSICAL CHARACTERS. Opaque. Lustre, metallic. Color, steel-gray to iron- The concentration of the iron to 50 per cent, and over has been accomplished essentially by the leaching of the silica bands from the chert and jasper." C. K. Leith, Economic Geology, Vol. 3, p. 276. 266 MINER A LOGY. black. Streak, metallic gray. H., 4 to 5. Sp. gr., 7.3 to 7.8. Strongly attracted by the magnet. Tough and malleable. Fracture, hackly. BEFORE BLOWPIPE, ETC. Infusible. Soluble in acids. In borax or salt of phos- phorus, reacts only for iron. REMARKS. Iron is found sparingly in eruptive rocks, especially basalts, usually in minute grains as at Antrim, Ireland, and in the trap rocks of New Jersey and the dolerite of Mt. Washington, N. H. Masses up to the size of a walnut are found in the basalt of Aschenhiibel, Saxony, and masses, one of which weighed fifty thousand pounds, have weathered, from the basalt of Ovifak, Disco Island, Greenland. Iron occurs at Chotzen, Bohemia, apparently as the result of the reduction of limonite, and most meteorites are either alloys of iron and nickel or contain such alloys. PYRRHOTITE. Magnetic Pyrites, Mundic. COMPOSITION. Fe n S n + x . Fe 6 S 7 to Fe n S 12 , with frequently small percentages of cobalt or nickel. GENERAL DESCRIPTION. Usually a massive bronze metallic min- eral, which is attracted by the magnet and can be scratched with a knife. Sometimes occurs in tabular hexagonal crystals. Physical Characters. H., 3.5 to 4.5. Sp. gr., 4.5 to 4.6. LUSTRE, metallic. OPAQUE. STREAK, grayish-black. TENACITY, brittle. COLOR, bronze-yellow to bronze-red, but subject to tarnish. Attracted by the magnet. BEFORE BLOWPIPE, ETC. Fuses readily on charcoal to a black magnetic mass, evolves fumes of sulphur dioxide, but does not take fire. In closed tube, yields a little sulphur. In open tube, gives fumes of sulphur dioxide. Soluble in hydrochloric acid, with evolution of hydrogen sulphide and residue of sulphur. SIMILAR SPECIES. Pyrrhotite resembles pyrite, bornite and nic- colite at times, but differs in being attracted by the magnet and by its bronze color on fresh fracture. REMARKS. The most important deposit is that at Sudbury, Canada. Others are Kongsberg, Norway; Andreasberg, Harz; Ducktown, Tenn., Piilaski, Va.; Straff ord and Ely, Vt.; Lancaster Gap"; 'Pa. Smaller beds "are common. PYRITE. Iron Pyrites, Fool's Gold. COMPOSITION. FeS 2 (Fe 46.7, S 53.3 per cent.), often contain- ing small amounts of Cu, As, Ni, Co, Au. v GENERAL DESCRIPTION. A brass -colored, metallic mineral, frequently in cubic, or .other isometric, crystals. or in crystalline masses, which may be any shape, as botryoidal, globular, .stalac- titic, etc. Less frequently in non-crystalline masses. MINERALS OF METALLIFEROUS ORE DEPOSITS. 267 FIG. 312. FIG. 313. FIG. 314. FIG. 316. FIG. 317. FIG. 318. FIG. 319. FIG. 320. CRYSTALLIZATION. Isometric, class of diploid, p. 65. Most common forms are cube a, Fig. 312, and pyritohedron ^, Fig. 313, a : 2a : co a ; { 2 10} or combinations of these, Fig. 315. The octa- hedron also occurs alone, Fig. 314, or in combination with a and , Figs. 316, 317, 318, and the diploid 5 = (a : fa : 30); {321} is not rare in combinations, Fig. 319^ 320. The faces of the cube and pyritohedron are frequently striated in one direction parallel to intersections of these two forms. Physical Characters. H., 6 to 6.5. Sp. gr., 4.9^0 5.2. LUSTER, metallic. OPAQUE. STREAK, greenish-black. TENACITY, brittle. COLOR, pale to full brass-yellow and brown from tarnish. BEFORE BLOWPIPE, ETC. On charcoal, takes fire and burns with a blue flame, giving off fumes of sulphur dioxide, and leaving a 268 MINERAL OGY. magnetic residue which, like pyrrhotite, dissolves in hydrochloric acid with evolution of hydrogen sulphide. In closed tube, gives a sulphur deposit. Insoluble in hydrochloric acid, but soluble in nitric acid with separation of sulphur. SIMILAR SPECIES. Pyrite is harder than chalcopyrite, pyrrho- tite, or gold. It differs from gold, also, in color, streak, and brit- tleness. It differs from marcasite . chiefly in the fact that its sulphur is more oxidized by the same treatment; for instance, pyrite in very fine powder is completely dissolved in about its own bulk of strong nitric acid whereas marcasite leaves some separated sulphur; or if boiled with a solution of ferric sulphate about 52 per cent, of the sulphur of pyrite is dissolved and about 12 per cent, of the sulphur of marcasite. REMARKS. The uses and occurrence are described p. 263. The most cele- brated locality is the Rio Tinto region, in Spain, from which immense quantities of a gold- and copper-bearing pyrite are annually procured. Norway and Ger- many are large producers. The largest deposits worked in the United States are in Virginia, New York and California. In compact specimens it is not easily altered, but granular masses readily oxidize and are decomposed, forming sulphate of iron and sulphuric acid, thus acting as a vigorous agent in the decomposition of rocks. The final results are usually limonite and sulphates of calcium, sodium, magnesium, etc. MARCASITE White Iron Pyrites. COMPOSITION. FeS 2 , as in pyrite. GENERAL DESCRIPTION. Ferric sulphide is dimorphous. Mar- casite differs from pyrite in crystalline form, and in little else. It occurs in orthorhombic forms, and in crystalline masses. The compound crystals have given rise to such names as cockscomb FIG. 321. FIG. 323. FIG. 322. pyrites, spear pyrites, etc., from their resemblance to these objects. Often, with radiated structure. Color on fresh fracture is usually whiter than in pyrite. MINERALS OF METALLIFEROUS ORE DEPOSITS. 269 FIG. 324. Marcasite Twin Crystal. After Lacroix. 0.7662: i : 1.2342. CRYSTALLIZATION. Orthorhombic, a : 1 : c Crystals usually tabular parallel to base. Simple forms show unit prism m, basal pinacoid c and often one or more brachy domes as g= (oo^ : b\ \c) ; {013}. Compound "fivelings" with twin plane m, Figs. 323 and 324, are frequent. Supplement angles are mm = 74 55', cg= 22 21 ', Physical Characters. H., 6 to 6.5. Sp. gr., 4.6 to 4.9. LUSTRE, metallic. OPAQUE. STREAK, nearly black. TENACITY, brittle. COLOR, pale brass-yellow, darker after exposure. BEFORE BLOWPIPE, ETC. As for pyrite. SIMILAR SPECIES. As for pyrite, from which it is only dis- tinguishable by crystalline form, cleavage, and by the slighter effect of oxidizing agents (see pyrite) . REMARKS. Marcasite is more readily decomposed than pyrite, and is, therefore, an even less desirable constituent in building material, etc. It is found at Cumming- ton, Mass.; Warwick, N. Y.; Joplin, Mo.; Haverhill, N. H.; and in many other localities and is usually mistaken for pyrite. Well-known foreign localities are the chalk marls near Dover, England, the clay beds near Carlsbad. The Wilkinson Mine of Wisconsin yields it in commercial quantities. 270 MINERALOGY. THE SULPHATES OF IRON. Decomposing sulphides form sulphates which in dry regions may persist but oftener are dissolved and lost. There are a large series of these of which the best known are MELANTERITE. Copperas, FeSO 4 + yH 2 O. A pale green fibrous efflorescence on pyrite or marcasite, or stalactite massive or pulverulent. It has a sweet astringent taste and on exposure it becomes dull yellowish-white. Found at Copperas Mt., Ohio; Goslar, Hartz; and many other localities. COQUIMBITE. Fe 2 (SO4)3 + 9H 2 O. Violet to white or greenish-glassy material often with hexagonal crystals with an astringent taste, often coated with copiapite. Found as a large bed in trachyte rock at Tierra Amarilla, Atacama, Chili. COPIAPITE. Misy, Fe 2 (FeOH) 2 (SO 4 )5 + i8H 2 O, often with some A1 2 O 3 or MgO. Brownish-yellow to sulphur-yellow, granular, or in loosely compacted crystalline scales, with a disagreeable metallic taste. Found with coquimbite, also in New Mexico, California, and elsewhere. For all three the tests are essentially alike. H., 2 to 3, sp. gr., 1.8 to 2.1. Tastes as stated. On charcoal, fuse and become magnetic. Yield water inclosed tube and some sulphuric acid. Soluble in water, giving the solution a reaction for sulphuric acid. MAGNETITE. Lodestone, Magnetic Iron Ore. COMPOSITION. Fe 3 O 4 (Fe, 72.4 per cent.) often contains Ti, Mg. GENERAL DESCRIPTION. A black mineral with black streak and metallic lustre, strongly attracted by the magnet and occurring in all conditions from loose sand to compact coarse or fine grained masses. CRYSTALLISATION. Isometric, usually octahedra, Fig. 325, or loosely coherent masses of imperfect crystals. Sometimes the FIG. 325. FIG. 326. FIG. 327. dodecahedron d, Fig. 326, or a combination of these, Fig. 152, or more rarely with the angles modified by the trapezohedron o = (a :T>a : 30) ; {311}. Fig. 327. Twinning parallel to an octahedral face occurs, sometimes shown by striations upon the octahedral faces. MINERALS OF METALLIFEROUS ORE DEPOSITS. 271 Physical Characters. H., 5.5 to 6.5. Sp. gr., 4.9 to 5.2. LUSTRE, metallic to submetallic. f OPAQUE. COLOR and STREAK, black. TENACITY, brittle. Strongly attracted by magnet and sometimes itself a magnet (lodestone). Breaks parallel to octahedron. BEFORE BLOWPIPE, ETC. Fusible with difficulty in the reduc- ing flame. Soluble in powder in hydrochloric but not in nitric acid. SIMILAR SPECIES': No other black mineral is strongly attracted by the magnet. REMARKS. The occurrences are described,' p. 263. In this country it is obtained from Pennsylvania, New York, New Jersey and Michigan. Lodestones are obtained mainly from Magnet Cove, Ark. HEMATITE. Specular Iron, Red Iron Ore. COMPOSITION. Fe 2 O 3 , (Fe 70 per cent.), often with SiO 2 , MgO, etc., as impurities. GENERAL DESCRIPTION. Occurs in masses varying from bril- liant black metallic to blackish red and brick red with little luster. The black is frequently crystallized, usually in thin tabular crys- tals set on edge in parallel position, less frequently in larger highly modified forms and finally in scale-like to micaceous masses. The red varieties vary from compact columnar, radiated and kidney- shaped masses to loose earthy red material. In all varieties the streak is red. CRYSTALLIZATION. Hexagonal, scalenohedral class, p. 48. Axis c = 1.365. The most common forms on the Elba crystals are the unit rhombohedron / and the scalenohedron n s= (20. : 2a : a : ^c) ; {2243}. The rhombohedron g = (a : co a : a : \c ; { io?4} also FIG. 328. FIG. 329. FIG. 330. 272 MINERALOGY. occurs. Thin plate-like crystals are the rule at other localities. Sometimes grouped in rosettes, as in the " Eisenrosen," Fig. 331 Supplement angles, pp = 94 ; nn = 5 1 59' ; cp = 57 37' ; gg 37 2' en 61 13'. FIG. 331- FIG. 332. Eisenrosen, Fibia Switz. Radiated r en i form, Geikie. Physical Characters. H., 5.5 to 6.5. Sp. gr., 4.9 to 5.3. LUSTRE, metallic to dull. OPAQUE. STREAK, brownish red to cherry red. TENACITY, brittle un- COLOR, iron black, blackish red to cherry red. less micaceous. Sometimes slightly magnetic. BEFORE BLOWPIPE, ETC. Infusible. Becomes magnetic in re- ducing flame. Soluble in hot hydrochloric acid. In borax reacts for iron. VARIETIES. Specular Iron. Brilliant micaceous or in crystals. Black in color. Red Hematite. Submetallic to dull, massive, blackish red to brownish red in color. Red Ochre. Earthy impure hematite usually with clay. Often pulverulent. Clay Ironstone. Hard compact red material mixed with much clay or sand. Martite. Octahedral crystals, probably pseudomorphs. SIMILAR SPECIES. Resembles at times the other iron-ores and massive cuprite. It is distinguished by its streak and strong mag- netism after heating in reducing flame. REMARKS. As described on p. 264, the greatest hematite deposit is due to con- centration and replacement and other great deposits to contact deposits and marine oolitic ores while relatively small amounts are due to magmatic segregation. By far the larger part is obtained from the Marquette and Gobegic ranges of Michigan MINERALS OF METALLIFEROUS ORE DEPOSITS. 273 and from the Mesabi range in Minnesota. Smaller but by no means inconsiderable amounts are mined in Alabama and other states. ILMENITE. Menaccanite, Titanic Iron-Ore. COMPOSITION. FeTiO 3 , sometimes containing small amounts of Mg or Mn. FIG. 333. FIG. 334. GENERAL DESCRIPTION. An iron-black mineral, usually mas- sive or in thin plates or imbedded grains or as sand. Also, in crystals closely like those of hematite in angle. CRYSTALLIZATION. Hexagonal. Class of third order rhom- bohedron, p. 54. Axis c = 1.385. Usually thick plates showing basal pinacoid c, unit prism m and unit rhombohedron p, Fig. 334, or without the prism, Fig. 333. Supplement angles pp = 94 29'; ^=57 58'. Physical Characters. H,, 5 to 6. Sp. gr., 4.5 to 5. LUSTRE, submetallic. OPAQUE. STREAK, black to brownish-red. TENACITY, brittle. COLOR, iron-black, Slightly magnetic. BEFORE BLOWPIPE, ETC. Infusible in oxidizing flame ; slightly fusible in reducing flame. In salt of phosphorus gives a red bead which, on treatment in reducing flame becomes violet, slowly soluble in hydrochloric acid and the solution boiled with tin is violet and on evaporation becomes rose-red. SIMILAR SPECIES. Differs from magnetite and hematite in the titanium reactions. REMARKS. As described on p. 263, it occurs as magmatic segregations from basic rocks, also as crystals and grains in igneous rocks and schists and as sand. USES. It has been used as a constituent of the lining of puddling furnaces and in the making of ferrotitanum. GOETHITE. COMPOSITION. FeO(OH). Fe, 62.9 per cent. GENERAL DESCRIPTION. A yellow, red or brown mineral, occurring in small, dis- tinct, prismatic crystals (orthorhombic), often flattened like scales, or needle-like, or 19 274 MINERALOGY. grouped in parallel position. These shade into feather-like and velvety crusts. Oc- curs also massive like yellow ochre. PHYSICAL CHARACTERS. Opaque to translucent. Lustre, adamantine to dull. Color, yellow, reddish, dark-brown and nearly black. Streak, yellow or brownish- yellow. H., 5 to 5.5. Sp. gr., 4 to 4.4. BEFORE BLOWPIPE, ETC. Fuses in thin splinters to a black magnetic slag. In closed tube yields water. Frequently reacts for manganese. Soluble in hydrochloric acid. USES. Goethite is an ore of iron, but is commercially classed with limonite under the name of brown hematite. Large ocherous deposits in Minnesota. TURGITE. Hydrohematite. COMPOSITION. Fe4O 5 (OH) 2 , Fe = 66.2 per cent. GENERAL DESCRIPTION. Nearly black, botryoidal masses and crusts resembling limonite but with a red streak and often with a fibrous and satin-like appearance on fracture. Also bright red earthy masses. Usually associated with limonite or hematite. PHYSICAL CHARACTERS. Opaque. Lustre, submetallic to dull. Color, dark red- dish-black in compact form, to bright red in ocherous variety. Streak, brownish red. H., 5.5-6. Sp. Or., 4.29-4.68. BEFORE BLOWPIPE, ETC. Decrepitates violently, turns black and becomes mag- netic. Yields water in closed tube with violent decrepitation. SIMILAR SPECIES. Is distinguished from limonite and hematite by its violent de- crepitation when heated, its red streak, and its water test. REMARKS. Like goethite it is frequently mistaken for and classed with limonite. It occurs with limonite at Salisbury, Conn., and in various localities in Prussia and Siberia. USES. It is an ore of iron but commercially is classed with limonite. LIMONITE. Bog-Ore, Brown Hematite. Co. IPOSITION. Fe 2 (OH) 6 Fe 2 O 3 , (Fe, 59.8 per cent). Fre- quently quite impure, from sand, clay, manganese, phosphorus, etc. GENERAL DESCRIPTION. Never crystallized, but grading from FIG. 335. Stalactite of Limonite, Hungary. Columbia University. MINERALS OF METALLIFEROUS ORE DEPOSITS. 275 the loose, porous bog-ore and earthy ochre of brown to yellow color and dull lustre ; to compact varieties, often with smooth, black, varnish-like surface, but on fracture frequently showing a somewhat silky lustre and a fibrous radiated structure. Sometimes stalactitic, Fig. 335, and often with smooth rounded surfaces and is pseudomorphs. It is frequently found pseudomorphous. Physical Characters. H., 5 to 5.5. Sp. gr., 3.6 to 4. LUSTRE, varnish-like, silky, dull. OPAQUE. STREAK, yellowish-brown, TENACITY, brittle, eartny. COLOR, brown, nearly black, yellow like iron rust. BEFORE BLOWPIPE, ETC. In closed tube yields water, and be- comes red. Fuses in thin splinters to a dark magnetic slag. Usu- ally reacts for silica and manganese. Soluble in hydrochloric acid, and may leave a gelatinous residue. VARIETIES. Bog-Iron, loosely aggregated ore from marshy ground, often intermixed with and replacing leaves, twigs, etc. Yellow ochre, umber, etc., earthy material, intermixed with clay. Brown clay ironstone, compact, often nodular masses, impure from clay. SIMILAR SPECIES. Distinguished from other iron-ores, except goethite, by its streak, and from the latter by lack of crystalliza- tion. REMARKS. The occurrences are described, p. 264. The largest deposits which are regularly mined exist in the States of Alabama, Michigan and Tennessee. SIDERITE. Spathic Ore. COMPOSITION. FeCO 3 , (FeO 62.1, CO 2 37.9 per cent.) usually with some Ca, Mg or Mn. GENERAL DESCRIPTION. Occurs in FlG 336 granular masses of a gray or brown color and also in masses with rhombohedral cleavage and in curved rhombohedral crystals, Fig. 336. At times it is quite black from included carbonaceous matter. CRYSTALLIZATION. Hexagonal. Sca- lenohedral class, p. 48. Axisr = 0.8184. Usually rhombohedrons of 73, often with curved (composite) faces; like those of dolomite. 2 7 6 MINERALOGY. Physical Characters. H., 3.5 to 4. Sp. gr., 3.83 to 3.88. LUSTRE, vitreous to pearly. OPAQUE to translucent. STREAK, white or pale yellow. TENACITY, brittle. COLOR, gray, yellow, brown or black. CLEAVAGE, rhombohedron of 107. VARIETIES : Clay Ironstone, earthy or stony mixtures, with silica, clay, limonite, hematite. Blackband, mixtures with clay and carbon. Spherosiderite, secondary siderite in cavities of basalt usually botryoidal. BEFORE BLOWPIPE, ETC. Decrepitates, becomes black and mag- netic and fuses with difficulty. Soluble in warm acids with effer- vescence. Slowly soluble in cold acids. May react for man- ganese. SIMILAR SPECIES. It is heavier than dolomite and becomes mag- netic on heating. Some stony varieties resemble varieties of spha- lerite. REMARKS. As described, p. 265, siderite deposits of economic value occur as replacements of limestone and as sedimentary deposits. Stony, impure "clay iron- stone" and bituminous "black band" occur as immense strata in England and Wales and this country in Pennsylvania, Ohio, Virginia and Tennessee, always in connection with the Coal Measures. Siderite is common in metallic veins, usually being considered gangue. Sometimes, as at Roxbury, Conn., it has been the ore. USES. It is used as an ore of iron and when high in manganese it is used for the manufacture of spiegeleisen. THE SILICATE IRON ORES* (Chamosite, Thuringite, Greenalite, Berthierine). In various parts of Europe iron ores have been found which are partly silicates. Some have been worked on an extensive scale. In this country the Lake Superior ores are believed to be formed in considerable part by the alteration of such a silicate greenalite. COMPOSITION. Definite formulae are difficult, chamosite, thuringite and greenalite are hydrous silicates of iron and aluminum (berthierine is believed to be a mixture of chamosite and magnetite). By averaging analyses the following percentages resulted. SiO 2 . Fe 2 3 . AloOa. FeO. MgO. H 2 0. Greenalite Thuringite Chamosite 32.86 22.8 26.04 22.26 13-5 i-3 17.2 18.6 36.40 36.3 39-74 2.17 8.48 IO.O2 12.41 * The "green earths," glauconite, now forming in the marine muds and found in Cretaceous sediments and celadonite are similar in composition. MINERALS OF METALLIFEROUS ORE DEPOSITS. 277 GENERAL DESCRIPTION. Chamosite is usually oolite or compact, thuringite foliated, greenalite in granules, the colors range from gray through green to black. BLOWPIPE CHARACTERS. Chamosite is said to fuse easily, thuringite less easily, and both to gelatinize with acids. REMARKS. A bed 60 ft. thick of chamosite and thuringite at Schmiedefeld, Thuringia, yielded 140,000 tons in 1899. Berthierine at Hayanges, near Metz, is a valuable ore. Other deposits exist in Switzerland, France and Bohemia. Greenalite is abundant in the Mesabi in the ferruginous cherts. THE MANGANESE MINERALS. The minerals described are: Isometric Tetragonal Tetragonal Orthorhombic Hexagonal Triclinic Orthorhombic Other silicates containing manganese and elsewhere described are spessartite and piedmontite, and there are manganiferous amphiboles, pyroxenes, axinites and other species. Manganese is also an important constituent of franklinite, wolframite, huebnerite, and columbite. ECONOMIC IMPORTANCE. The principal economic uses of manganese minerals are in the production of the alloys with iron, spiegeleisen and ferromanganese f used in the manufacture of steel, and in the making of manganese steels to resist abrasion and shock, such as car wheels, gears, crushing machinery. The method of smelting is very like that used in the manufacture of pig-iron. Manganese is also an im- portant constituent of other alloys, especially manganese bronze and so-called silver bronze. Minor uses are in the manufacture of chlorine, bromine, oxygen, disinfectants, driers for varnishes; as a decolorizer to remove the iron green color from glass and also, when added in larger quantity, to give an amethystine color to glass and pottery; in the ordinary Sulphide Alabandite MnS Oxides Braunite Mn 2 O 3 Hausmannite Mn3O 4 Pyrolusite MnO 2 Polianite MnO 2 Psilomelane MnO 2 + (H 2 O. ,K 2 O.BaO) Wad Mixture of oxides Hydroxide Manganite MnO(OH) Carbonate Rhodochrosite MnC0 3 Silicates Rhodonite MnSiOs Tephroite Mn 2 SiO 4 278 MINERALOGY. dry battery; in calico printing, making green and violet paints, etc. Certain iron ores are very rich in manganese and are valuable in making spiegeleisen. In 1914,* 445,827 long tons of mangan- iferous iron ores were mined in the United States. Also a large amount of franklinite was used for the production of zinc oxide and 100,198 tons* of a highly manganiferous by-product obtained. In the West, especially in Colorado and Arizona, manganese ores often carry silver, and several thousand tons are smelted each year with other silver-bearing minerals, the manganese acting as a flux. Much of the Arkansas material is also used as flux. In 1914, 39,881 tons were thus used. The manganese minerals important as ores are the oxides pyrolusite, psilomelane (including wad), braunite and manganite, and sometimes rhodochrosite. In 1914! 2,635 tons were produced mainly in Virginia, Arkansas and Georgia. Owing chiefly to the fact that "most of the known manganese ore deposits of the United States yield material that must be washed or concentrated to obtain a marketable product"* this country imports most of its material from Russia, India and Brazil. In 1914 the comparison in long tons was: Production. Imports. Manganese Ore 2,635 283,294 Ferromanganese 100,731 82,997 Spiegeleisen 76,625 2,870 THE FORMATION AND OCCURRENCE OF MANGANESE ORES. The Primary Sources. The igneous rocks contain a small percentage of manganese (Mn 0.77 per cent., Clarke), syenites, porphyries, and basalts are said to contain about 0.36 per cent. (Lindgren). The schists also contain small percentages of manganese and certain^ schists carry manganese silicates, rhodonite and tephroite or one or more of spessartite (manganese garnet), piedmontite (manganese epidote). or manganese varieties of pyroxene or amphi- bole. * Mineral Resources of Ihe U. S., 1914, t D. F. Hewett in Mineral Resources of the U. S., 1914, Ft. i, p. 166. t See under residual deposits, next page. MINERALS . OF METALLIFEROUS ORE DEPOSITS. 279 The sedimentary rocks contain manganese as oxides or rhodonite or rhodochrosite. The ores are secondary and are the result usually of weathering and concentration in some instances combined with contact action. The resulting deposits are chiefly oxides and sometimes carbonates and classify as : Contact Deposits containing hausmannite, braunite, franklinite, rhodonite, tephroite, etc., as at Langban and other Wermland deposits of Sweden and at Franklin Furnace, N. J. Veins (lateral secretions) containing pyrolusite, psilomelane, manganite, poliantite, as at Schwarzenberg, Saxony; Ihlefeld, Harz; and Thuringer Wald; and at Veitsch, Styria; chiefly rho- dochrosite. Replacements, consisting of rhodochrosite or the oxides, lime- stones by rhodochrosite, Las Cabesses, French Pyrenees; porphyry with exception of quartz by oxides, Thuringer Wald. Sedimentaryf deposits. Consisting of pyrolusite, psilomelane, manganite and earthy mixtures called wad. As Bog Ores, usually with bog iron and often by aid of organisms. Wickes, Mont.; Hillsborough, New Brunswick; Norway, Sweden. ^4 s Lake or Sea Beds. The enormous deposit of Kutais, Trans- Caucasus are oolitic pyrolusite cemented by earthy manganese. Residual Deposits, chiefly pyrolusits, psilomelane and wad, sometimes braunite. India from decomposing archaean rocks carrying spessartite and rhodonite. Often with enormous masses of psilomelane, pyrolusite or braunite. Brazil (Minas Geraes) from decomposing schists carrying rhodonite, tephroite and spessartite. Texas from decomposing schists carrying spessartite, piedmontite and tephroite. Cremora, Va. in concentric layers of pyrolusite and psilomelane forming lumps and larger bodies in clay. * "The lode-like manganese deposits on the north side of the Thuringer Wald exhibit a transformation so complete that only the quartz of the original rock remains unaffected." Beyschlag, Vogt and Krusch, Truscott, 142. t They are frequently near similar deposits of iron but on account of the relatively easier solubility of the manganese carbonate the deposits usually separate. The manganese oxides are probably precipitated in the colloidal condition, with a tendency to absorb certain oxides especially of barium and potassium but in time crystallize. 280 MINERALOGY. MANGANIFEROUS IRON OR SILVER OR ZINC ORES. By far the larger portion of the manganese mined in the United States is in the form of mixtures of iron oxides, with relatively small proportions of manganese oxides, these are obtained chiefly from the Lake Superior region and also from Colorado and Arkansas. Manganese residues are obtained from the zinc ores of Franklin Furnace, N. J. Manganiferous silver ores consisting of psilomelane and probably other oxides with small quantities of silver and lead minerals are found near the ore bodies at Leadville and elsewhere and used as fluxes, silver being recovered. ALABANDITE. Manganblende. COMPOSITION. MnS, (Mn 63.1, S 36.9 per cent.). GENERAL DESCRIPTION. A dark iron-black metallic mineral with an olive green streak. Usually massive, with easy cubic cleavage and occasionally in cubic or other isometric crystals. Also massive granular PHYSICAL CHARACTERS. Opaque. Lustre, metallic. Color, deep black with brown tarnish. Streak, olive green. H., 3.5 to 4. Sp. gr., 3.95 to 4.04. Brittle. BEFORE BLOWPIPE, ETC. Turns brown, evolves sulphur dioxide and fuses. Gives sulphur reactions with soda. Soluble in dilute hydrochloric acid with rapid evolution of hydrogen sulphide. SIMILAR SPECIES It is distinguished from all similar species by its streak. REMARKS. The other manganese minerals are derived in part from the alteration of this species. It occurs with other metallic sulphides. BRAUNITE. COMPOSITION. Mn 2 O 3 , but usually containing MnSiO 3 . GENERAL DESCRIPTION. Brownish black granular masses and occasional minute tetragonal pyramids almost isometric, t 0.985. Physical Characters. H,, 6 to 6.5. Sp. gr., 4.75 to 4.82. LUSTRE, submetallic. OPAQUE. STREAK, brownish black. TENACITY, brittle. COLOR, brownish black to steel gray. BEFORE BLOWPIPE, ETC. Infusible. With borax an amethys- tine bead. Soluble in hydrochloric acid, evolving chlorine and generally leaving gelatinous silica. SIMILAR SPECIES. Resembles hausmannite, but has a darker streak and is harder. MINERALS OF METALLIFEROUS ORE DEPOSITS. 281 FIG. 337. FIG. 338. FIG. 339. Braunite, pp = 70 7'. Hausmannite, pp = 74 34'. REMARKS. As stated on p. 279, it occurs as important ore in the contact deposits of Langban, etc., Sweden, and as large masses in the residual deposits of Vizianagram, India. In the veins at Ilmenau, Thuringia, and Ihlfeld Hartz it occurs crystallized and massive, and it forms part of the Batesville, Arkansas, residual deposit. HAUSMANNITE. COMPOSITION. MngO^. (Mri,O s 69.0, MnO 31.0 per cent.). GENERAL DESCRIPTION. Black granular strongly coherent masses occasionally in simple and twinned tetragonal pyramids which are more acute than those of braunite, c= 1-174. PHYSICAL CHARACTERS. -Opaque. Lustre, submetallic. Color, brownish black. Streak, chestnut brown. H., 5 to 5.5. Sp. gr., 4.72 to 4.85. Strongly coherent. BEFORE BLOWPIPE, ETC. Infusible. Colors borax bead amethystine. Soluble in hydrochloric acid with evolution of chlorine. SIMILAR SPECIES. Differs from braunite in hardness, streak and absence of silica. PYROLUSITE. Black Oxide of Manganese. COMPOSITION. MnO 2 , (Mn 63.2 per cent.). GENERAL DESCRIPTION. A soft black mineral of metallic lustre. Frequently composed of short indistinct crystals or radiated needles, but also found compact, massive, stalactitic, and as velvety crusts. Usually soils the fingers. Frequently in alternate layers with psilomelane. Physical Characters. H., i to 2.5. LUSTRE, metallic or dull. STREAK, black. COLOR, black to steel gray. Sp. gr., 4.7 to 4.86. OPAQUE. TENACITY, rather brittle. BEFORE BLOWPIPE, ETC. Infusible, becomes brown. Usually yields oxygen and a little water in closed tube. Colors borax bead amethystine. Soluble in hydrochloric acid with evolution of chlorine. 282 - MINERALOGY, SIMILAR Species. Distinguished by its softness and black streak from other manganese minerals. REMARKS. As described on p. 279, occurs in the vein, replacement, sedimentary and residual deposits and usually associated with psilomelane. The great sedimentary deposit at Kutais, Transcaucasia, is compact pyrolusite separated by mixed ores and has a thickness of six to sixteen feet. Another enormous deposit exists at Nicopol. In this country the residual deposits at Crimera, Va., Carters ville, Ga., and Batesville, Ark., and the streaks and pockets in certain hematites of Lake Superior are the important deposits. Other deposits exist in California, Vermont and North Carolina. The purest material for use in glass making is obtained near Sussex, N. B. f and from the Tenny Cape district, Nova Scotia. POLIANITE. COMPOSITION. MnC>2 (Mn 63.1 per cent.). GENERAL DESCRIPTION. A hard, dark gray, submetallic substance occurring in composite groups of minute crystals or as an outer coating on manganite. CRYSTALLIZATION. Tetragonal c = .6646. Small crystals on pyrolusite or parallel groupings of pseudorhombic shape. PHYSICAL CHARACTERS. Opaque. Lustre, submetallic. Color, steel to iron gray. Streak, black. H., 6 -6.5. Sp. gr., 4.83-5.02. BEFORE BLOWPIPE, ETC. Like pyrolusite. REMARKS. Occurs at Flatten, Bohemia, in the typical crystal groups. In other localities is often entirely or partly changed to pyrolusite. MANGANITE. COMPOSITION. MnO(OH), (Mn 62.4,0 27.3, H 2 O 10.3 per cent). GENERAL DESCRIPTION. Occurs in long and short prismatic FIG. 340. Manganite, Ilefeld, Hartz. N. Y. State Museum. MINERALS OF METALLIFEROUS ORE DEPOSITS. 283 (orthorhombic) crystals often grouped in bundles with fluted or rounded cross-section and undulating terminal surface, rarely mass- ive, granular or stalactitic. Physical Characters, H., 4. Sp. gr., 4.2 to 4.4. LUSTRE, submetallic. OPAQUE. STREAK, reddish brown to black. TENACITY, brittle. COLOR, steel gray to iron black. BEFORE BLOWPIPE, ETC. Like pyrolusite, but yields decidedtesk for water and very little oxygen. REMARKS. Formed in the same deposits as pyrolusite and frequently altered to pyrolusite. PSILOMELANE. Black Hematite. COMPOSITION. Perhaps MnO 2 + (H 2 O, K 2 O or BaO) or H 4 MnO 6 , with replacement by Ba or K. GENERAL DESCRIPTION. A smooth black massive mineral com- monly botryoidal, stalactitic or in layers with pyrolusite. Never crystallized. Physical Characters. H., 5 to 6. Sp. gr., 3.7 to 4.7. LUSTRE, submetallic or dull. OPAQUE. STREAK, brownish black. TENACITY, brittle. COLOR, iron black to dark gray. BEFORE BLOWPIPE, ETC. Infusible. In closed tube yields oxygen and usually water. Soluble in hydrochloric acid, with evolution of chlorine. A drop of sulphuric acid added to the solu- tion will usually produce a white precipitate of barium sulphate. SIMILAR SPECIES. Distinguished from pyrolusite by its hard- ness, and from limonite by its streak. REMARKS. Its localities are the same as for pyrolusite, and the two minerals are usually mined together. WAD. Bog Manganese. COMPOSITION. Mixture of manganese oxides, with often oxides of metals other than manganese such as cobalt, copper and lead. GENERAL DESCRIPTION. Earthy to compact indefinite mixtures of different metallic oxides, in which those of manganese predominate. Dark brown or black ' in color; often soft and loose, but sometimes hard and compact. PHYSICAL CHARACTERS. Opaque. Lustre dull. Color brown to black. Streak brown. H., 1/2 to 6. Sp. gr., 3 to 4.26. Often soils the fingers. BEFORE BLOWPIPE, ETC. As for psilomelane, but often with strong cobalt or copper reactions. 284 MINERALOGY. USES. Wad is used as a paint and in the manufacture of chlorine. REMARKS. Large deposits exist at Wickes, Montana; Hillsborough, New Bruns- wick; and Norway. RHODOCHROSITE. COMPOSITION. MnCO 3 , (MnO 61.7, CO 2 38.3 per cent.) with partial replacement by Ca, Mg or Fe. GENERAL DESCRIPTION. Rose pink to brownish red rhombo- hedral crystals, usually small and curved like dolomite. Fre- quently massive cleavable, or granular or compact. Less fre- quently botryoidal or incrusting. CRYSTALLIZATION. Hexagonal. Scalen- FIG. 341. ohedral class, p. 48. Axis ^=.8184. An- gles as in siderite. Usual form a rhombo- hedron of 7 3 . Optically . Physical Characters. H . , 3 . 5 to 4. 5 . gr., 3.3 to 3.6. LUSTRE, vitreous to pearly. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle. COLOR, light pink, rose red, brownish red and brown. CLEAVAGE, parallel to rhombohedron. BEFORE BLOWPIPE, ETC. Infusible, but decrepitates violently and becomes dark colored.* In borax yields amethystine bead. Soluble in warm hydrochloric acid, with effervescence, slowly sol- uble in the cold acid. SIMILAR SPECIES. Distinguished from rhodonite by form, cleavage, effervescence and infusibility. REMARKS. The great manganese deposits of Huelva, Spain, are chiefly rhodo- chrosite, containing rhodonite, and this is being mined in enormous quantities. In the Quelez District, Brazil, rhodochrosite with tephroite forms large lenses which by alteration have yielded psilomelane. Other producing localities are Merioneth- shire, Wales, and Chevron, Belgium. It is also found in ore-veins, as a gangue mineral in the silver veins of Butte, Montana, Austin, Nev., and elsewhere. It is not mined, in this country. RHODONITE. COMPOSITION. MnSiO 3 , with replacement by Fe, Zn or Ca. GENERAL DESCRIPTION. Brownish red to bright red, fine * May become magnetic from impurities. MINERALS OF METALLIFEROUS ORE DEPOSITS. 285 grained or cleavable masses and dissemi- FIG. 342. nated grains, often coated with a black oxide. Sometimes in triclinic crystals either tabular parallel to c or like the forms of pyroxene. CRYSTALLIZATION. Fig. 342 shows three pinacoids a, b and c y the hemi-unit prisms m and M t and two quarter pyramids v t and t v of & : b : 2c. The supplement angles are Franklin Furnace. mM= 92 28' ; cm=* 68 45' ; cM= 86 23'. Physical Characters. H.,5.$ to 6.5. Sp. Gr., 3.4 to 3.68. LUSTRE, vitreous. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle. COLOR, brownish-red to flesh-red, bright-red, greenish, yellowish. BEFORE BLOWPIPE, ETC. Blackens and fuses easily with slight intumescence. With fluxes reacts for manganese and zinc. In powder is partially dissolved by hydrochloric acid, leaving a white residue. If altered may effervesce slightly during solution. REMARKS. In the gneisses and crystalline schists rhodonite occurs as a primary alteration product as interbedded layers, lenses and beds often of considerable extent as near Ekaterinenberg, Urals, Langban, Sweden (with iron ore beds) Bukowina, Russia. Near Rosenau, Hungary, the deposit is over forty feet thick. Many other localities exist. In the United States it occurs at Blue Hill, Maine, Cummington, Mass., Franklin, N. J., in the ore veins of Butte, Montana, and elsewhere. USES. Probably to some extent as an ore and a small amount is polished as an ornamental stone. Chiefly important as a source of the oxides. TEPHROITE. COMPOSITION. Mn 2 SiO 4 (MnO.7o.2, SiO 2 29.8 per cent.). Usually with some MgO, sometimes with ZnO. GENERAL DESCRIPTION. As gray to flesh red masses which cleave (?) in direc- tions at right angles. CRYSTALLIZATION. Orthorhombic; crystals rare, a : ~b : I = .4621 : i : .5914. PHYSICAL CHARACTERS. Translucent to transparent. Lustre, vitreous to greasy. Color, ash gray, flesh red, brown. Streak, gray. H., 5.5 to 6. Sp. gr., 4 to 4.1. BEFORE BLOWPIPE, ETC. Fusible with some difficulty. Soluble in hydrochloric acid with gelatinous residue. REMARKS. Common in certain rocks which by their alteration have yielded manganese deposits as in central Texas and in the Lafayette District, Brazil. First discovered among the Franklin Furnace minerals and later in the Langban and Paisberg, Sweden, deposits in small crystals. Millerite NiS Hexagonal Pentlandite (Fe.Ni)S Isometric Niccolite NiAs Hexagonal Annabergite Ni3(AsO 4 )2.8H 2 O Monoclinic Garnierite H 2 (Ni.Mg)SiO 4 .H 2 O MINERAL OGY. THE NICKEL AND COBALT MINERALS. The cobalt minerals described are: Sulphide Linnaeite (Co.Ni)sS4 Isometric Sulpharsenide Cobaltite CoAsS Isometric Arsenide Smaltite (Co.Ni)As 2 Isometric Arsenate Erythrite Co 3 (AsO4)2.8H 2 O Monoclinic Cobaltiferous arsenopyrite, pyrite and pyrrhotite occur. The nickel minerals described are : Sulphides Arsenide Arsenate Silicates Chloanthite, or highly nickeliferous smaltite; and nickeliferous pyrrhotite and pyrite in which the nickel is supposed to be present as pentlandite are important ores. ECONOMIC IMPORTANCE. Cobalt. The metal cobalt has, as yet, no important use ; the oxide is used to impart a blue color to glass and pottery. The chief com- mercial compound is SMALT, a cobalt glass, the cobalt replacing the calcium of ordinary glass. This is ground and used as a fine blue pigment, which is unaltered by exposure. Cobalt blue and Rinmann's green are compounds of cobalt with alumina and zinc oxide respectively. The extraction of cobalt from a nickeliferous matte is an elabor- ate chemical operation involving- solution in hydrochloric acid, pre- cipitation of manganese and iron as basic carbonates, and of other metals as sulphides, leaving a solution of chloride of nickel and cobalt. From these the cobalt is precipitated with great care, by means of calcium hypochlorite, as cobaltic hydroxide, after which the nickel is precipitated as hydroxide by lime-water. By using selected ores, mattes especially rich in cobalt may be obtained and for ordinary purposes the small nickel contents are neglected. The amount of available cobalt ore has been greatly increased of late due to the silver-bearing cobalt ores of Cobalt, Ont., but the amount used is small, approximating 20 tons of the oxide each year in this country. MINERALS OF METALLIFEROUS ORE DEPOSITS. 287 No production of cobalt ores is reported for 1914* in this country, but Ontario produced 97 tons of ore and New Caledonia exported 920 tons of ore and 25 tons of matte. Germany elec- trolytically separates cobalt from copper of Belgian Congo. Metallic nickel is extensively used in different alloys, and, in- deed, was first obtained as a residual alloy with copper, iron and arsenic, in the manufacture of smalt. This alloy was called Ger- man silver or nickel silver and largely used in plated silverware. Later, a large use for nickel was found in coins, the United States Mint alone using nearly one million pounds between 1857 and 1884. In this alloy copper is in large proportion, the present five cent piece being 25 per cent, nickel, 75 per cent, copper, and in other coins the percentage of copper being still greater. The most extensive application of nickel at present is in the manufac- ture of nickel steel for armor plates and other purposes. The uses of nickel steel are continually increasing, as the metal has some excellent properties possessed by no other alloy. To a limited extent nickel is used in a nickel-copper alloy for casing rifle bullets. An alloy of iron and nickel containing 30 per cent, of nickel is non-magnetic and is used in electric heaters and in parts of other electrical apparatus. "Monel metal" an alloy of 68 per cent, nickel, 1.5 per cent, iron and 30.5 per cent, copper made by extracting the nickel and copper from the ore without separating them, is said to be stronger than nickel steel, unaffected by sulphuric acid and silver white in color. A sulphate of nickel and ammonium is also manufactured in large amounts for use in nickel plating. The nickel of commerce is nearly all obtained either from the garnierite of New Caledonia or from the deposit of nickel-bear- ing sulphides of Ontario. The garnierite is smelted in a low blast furnace, with coke and gypsum, and the matte of nickel, iron and sulphur thus produced is alternately roasted and fused with sand, in a reverberatory furnace, until nearly all the iron has been re- moved. The nickel sulphide, by oxidation, is converted into oxide. Nickel oxide is obtained from 'the pyrrhotite and chalcopyrite of Sudbury, Canada. The ore is first roasted to remove much of the sulphur, and is then smelted, together with nickel-bear- ing slags of previous operations. A nickel matte carrying much * Mineral Industry, 1914, p. 548. 288 MINERALOGY. copper and some iron is produced through which air is blown in a silica -lined Bessemer converter and most of the iron is carried into the slag. A matte, rich in nickel and copper, results. This may be directly roasted and reduced by carbon to produce nickel-copper alloys for the manufacture of German silver. In order to separate the nickel the concentrated matte is fused with sodium sulphate and coke, after which the melted sulphides are allowed to settle. Under these conditions the copper and iron sulphides form a very fluid mass with the soda, and, with some nickel, rise to the top while the lower portions of the mass are highly nickeliferous. The two layers are separated and each is re-treated in much the same manner. The nickel sulphide result- ing is partially roasted and is fused with sand, by means of which most of the iron is removed as a silicate in the slag. The nickel sulphide remaining is by oxidation converted into the oxide. The oxide is sold directly to steel makers or may be reduced to metal by mixing with charcoal and heating, white hot, in a graphite crucible. No nickel ore is reported as produced in this country in 1914. Canada produced* ore containing 12,937 short tons of nickel in addition to about 200 tons of nickel oxide. New Caledonia exported 94,154 tons of ore and 5,287 tons of matte. Norway and Germany were also producers. Nickel is now successfully refined by electrolysis, but the de- tails of the process are jealously guarded. It is doubtful, however, if nickel can be separated from cobalt in this manner, although most other impurities are removed. The Mond process for the extraction of nickel from its ore and for its separation from cobalt promises to become important. The process is based on the discovery that when carbon monoxide is passed over heated nickel, volatile nickel carbonyl, Ni(CO) 4 is formed. As cobalt does not react in this way, the separation of nickel from cobalt is easily accomplished. The reconversion of the nickel carbonyl into nickel and carbon monoxide is a simple operation. THE FORMATION AND OCCURRENCE OF COBALT AND NICKEL ORES Nickel and cobalt occur usually together and are present in * Mineral Industry, 1914. MINERALS OF METALLIFEROUS ORE DEPOSITS. 289 the earth's crust in minute percentages. Nickel less than .01 (Clarke), cobalt between .001 and .0001 (Vogt). The peridotites and pyroxenic rocks and the serpentines derived from them contain most of these elements. The occurrences of importance are principally: Magmatic Segregations. (a) Of nickeliferous pyrrhotite and pyrite and various nickel and cobalt minerals, especially pentlandite or millerite, as at Sudbury, Ontario; Gap Mine, Pennsylvania; and many small deposits in Norway, (b) Of iron nickel alloys see Iron, p. 266. Normal Veins. Containing sulphides and arsenides (smaltite, chloanthite, nic- colite, linnceite, cobaltite and rarer species). In schists and gneiss and conglomerates near basic intrusive dikes and in the dikes themselves, as at the Cobalt, Ontario, district and Annaberg and Schneeberg, Saxony; and Dobschau, Hungary. Veins in Serpentine (Lateral Secretion) containing hydrous silicates or oxides, garnierite, genthite, pimelite or asbolane. Due to a weathering of the peridotite to serpentine with a concentra- tion of the nickel or cobalt in the cracks and fissures as in the garnierite and asbolane deposits of New Caledonia and the pimelite of Frankenstein, Silesia. LINN^ITE. Cobalt Pyrites. COMPOSITION. (Co.Ni) 3 S 4 , often with some Fe or Cu replacing. GENERAL DESCRIPTION. A steel-gray metallic mineral usually in granular or compact masses intermixed frequently with chal- copyrite ; also in small isometric crystals, usually the octahedron p, Fig. 343, or this with the cube a, Fig. 344. FIG. 343. FIG. 344. 20 290 MINERALOGY. Physical Characters. H., 5.5. Sp. gr., 4.8 to 5. LUSTRE, metallic. OPAQUE. STREAK, nearly black. TENACITY, brittle. COLOR, steel-gray, with reddish-tarnish. CLEAVAGE, cubic imperfect. BEFORE BLOWPIPE, ETC. On charcoal fuses to a magnetic glob- ule, and gives off fumes of sulphur dioxide. In borax bead gives a deep blue color, and with frequent replacement of borax the red bead of nickel may be obtained. Soluble in nitric acid to a red solution and with separation of sulphur. REMARKS. Occurs in veins at Miisen and Siegen, Prussia, and Mineral Hill, Maryland. It occurs mostly massive with other cobalt and nickel minerals and with chalcopyrite, pyrrhotite, bornite, at Mine La Motte, Mo., Lovelock's Station, Nev., and in a few other American localities. USES. Does not occur in large amounts, but is used as a source of both cobalt and nickel. COBALTITE. Cobalt Glance. COMPOSITION. CoAsS, (Co 35.5, As 45.2, S 19.3 per cent.) GENERAL DESCRIPTION. A silver white to gray metallic min- eral resembling linnaeite in massive state but in crystals differing in that the forms are the pyritohedron e, and cube #, and these com- bined, Fig. 347. Physical Characters. H., 5.5. Sp. gr., 6 to 6.1. LUSTRE, metallic. OPAQUE. STREAK, black. TENACITY, brittle. COLOR, silver white to gray. CLEAVAGE, cubic. BEFORE BLOWPIPE, ETC. On charcoal fuses to a magnetic globule and evolves white fumes with garlic odor. Unaltered in closed tube. Soluble in warm nitric acid to rose-red solution, with residue of sulphur and arsenous oxide. FIG 345. FIG. 346. FIG. 347. MINERALS OF METALLIFEROUS ORE DEPOSITS. 291 REMARKS. Cobaltite occurs in large quantities as an independent stratum 2 feet thick, near Daschkessan, Caucasus, underlying magnetite. At Skutterud, Norway, it occurs free from nickel massive and disseminated in mica schist. In Saxony in veins with barite. At the Cobalt region, Ontario, and in Grant Co., Oregon, in small amounts. SMALTITE. CHLOANTHITE.* COMPOSITION. (Co.Ni)As 2 , varying widely in proportion of cobalt and nickel, and usually containing some iron also. GENERAL DESCRIPTION. A tin-white to steel-gray metallic min- eral resembling linnaeite and cobaltite. Usually occurs granular massive, but also in isometric crystals, especially modified cubes with curved faces. Physical Characters. H., 5.5 to 6. Sp. gr., 6.4 to 6.6. LUSTRE, metallic. OPAQUE. STREAK, black. TENACITY, brittle. COLOR, tin-white to steel-gray. CLEAVAGE, octahedral. BEFORE BLOWPIPE, ETC. On charcoal fuses, yields white fumes with garlic odor and leaves a magnetic residue, which, when oxi- dized in contact with frequently replaced borax, yields successively slags colored by iron, cobalt, nickel and possibly by copper. In closed tube yields arsenical mirror. (If sulphur is present also yields a red sublimate.) Soluble in nitric acid to a red to green solution according to proportion of cobalt and nickel. Partially soluble in hydrochloric acid, especially so after fusion, but yields no voluminous precipitate of yellow arsenic sulphide, as does arsenopyrite when similarly treated. SIMILAR SPECIES. Differs from linnaeite and cobaltite in cleav- age, specific gravity and blowpipe reactions. Differs from most arsenopyrite and tetrahedrite in the cobalt blue slags which it yields. It can best be distinguished from cobaltiferous arseno- pyrite by the reaction in acids after fusion. REMARKS. Occurs in veins as stated on p. 289. It was the original mineral deposited in the veins at the Cobalt district, Ontario. It occurs also in veins at Annaberg and Schneeberg, Saxony, Reichelsdorf, Hesse, Gunnison Co., Colorado, and in small amounts at Franklin, N. J., Mine La Motte, Mo., and elsewhere. A ferriferous variety occurs in gneiss at Chatham, Conn. * There is no line between chloanthite NiAs2 and smaltite CoAs2, the usual specimen is an isomorphous mixture. The Cobalt district mineral is such a mixture. 292 MINERALOGY. ERYTHRITE. COMPOSITION. Co3(AsO4)2.8H 2 O, (CoO 37.5, As2O 5 38.4, H 2 O 24.1 per cent.). GENERAL DESCRIPTION. Groups of minute peach red or crimson crystals forming a drusy or velvety surface. Also in small globular forms or radiated or as an earthy incrustation of pink color. PHYSICAL CHARACTERS. Translucent. Lustre, adamantine or pearly. Color, crimson, peach red, pink and pearl gray. Streak, paler than color. H., 1.5. to 2.5. Sp. gr., 2.91 to 2.95. Flexible in laminae. BEFORE BLOWPIPE, ETC. On charcoal fuses easily, evolves white fumes with garlic odor, and leaves a magnetic residue, which imparts the characteristic blue to borax bead. Soluble in hydrochloric acid to a light red solution. Asbolane or asbolite is essentially a mixture of oxides of manganese and cobalt and is grouped under wad, p. 283. The asbolane from the lateral secretion veins in serpentine in New Caledonia has been an important source of cobalt. MILLERITE. Capillary Pyrites. COMPOSITION. NiS, (Ni 64.4 per cent.). GENERAL DESCRIPTION. A brass-colored mineral with metallic lustre, especially characterized by its occurrence in hair-like or needle crystals, often interwoven or in crusts made up of radiating needles. Physical Characters. H., 3 to 3.5. Sp. gr., 5.3 to 5.65. LUSTRE, metallic. OPAQUE. STREAK, greenish-black. TENACITY, crystals elastic. COLOR, brass or bronze yellow. BEFORE BLOWPIPE, ETC.^-On charcoal spirts and fuses to a brittle magnetic globule, which will color borax red. Soluble in aqua regia to a green solution, yielding with dimethy'glyoxime the characteristic crimson precipitate. REMARKS. Millerite occurs as a magmatic segregation with nickeliferous pyrrho- tite at Gap Mines, Pa., as needle crystals in cavities of other minerals such as hema- tite (Antwerp, N. Y.), dolomite (near St. Louis, Mo.), chalcopyrite (Baden), or in ore veins, especially with iron, cobalt, nickel and bismuth minerals. PENTLANDITE. COMPOSITION. (Fe.Ni)S. Sudbury average of five analyses Ni 35-57 Co 0.83, Fe 29.06, S 33.25 per cent. GENERAL DESCRIPTION. Light bronze-yellow, granular masses of metallic lustre. Octahedral cleavage. Color of fresh fracture that of pyrrhotite but tarnishes to more brassy yellow. MINERALS OF METALLIFEROUS ORE DEPOSITS. 293 Physical Characters. H., 3.5 to 4. Sp. gr., 4.6 to 5. LUSTRE, metallic. OPAQUE. STREAK, black. TENACITY, brittle. COLOR, light bronze yellow. NOT MAGNETIC. BEFORE BLOWPIPE, ETC. Fuses readily to a magnetic globule which gives bead tests for nickel. Soluble in nitric acid, the solution yielding with dimethyl-glyoxime the characteristic crim- son precipitate. REMARKS. Occurs as the important nickel mineral in the nickel-pyrrhotite magmatic segregation at Sudbury, Ontario. It occurs also at Lillehammer, Nor- way, with chalcopyrite. NICCOLITE. Copper Nickel. COMPOSITION. NiAs, (Ni 43.9 per cent.). As is replaced to some extent by Sb or S, and Ni by Fe or Co. GENERAL DESCRIPTION. A massive mineral of metallic lustre, characteristic pale copper red color and smooth impalpable struct- ure. Sometimes the copper-red kernel has a white metallic crust. Occasionally occurs in small indistinct hexagonal crystals. Physical Characters. H., 5 to 5.5. Sp. gr., 7.3 to 7.67. LUSTRE, metallic. OPAQUE. STREAK, brownish-black. TENACITY, brittle. COLOR, pale copper red with dark tarnish. BEFORE BLOWPIPE, ETC. On charcoal fuses easily, giving off white fumes with garlic odor and leaving a magnetic residue, which will color borax bead red and sometimes blue, in which case the borax must be renewed until the cobalt is all removed. In open tube yields a white sublimate and a yellowish-green pul- verulent residue. Soluble in concentrated nitric acid to a green solution, which may be tested as under millerite. SIMILAR SPECIES. Differs from copper in hardness, black streak and brittleness. REMARKS. Occurs principally in ore veins in the crystalline schists, often with silver ores as in the Saxon mines and many other European localities. Occurs in considerable quantity at la Rioja, Argentina, and Albergera Velha, Portugal. The principal American locality is at Cobalt, Ont. It is also found at Lovelock's, Nevada; Tilt Cove, Newfoundland; Chatham, Conn.; and Thunder Bay, Lake Superior. 294 MINERALOGY. ANNABERGITE. Nickel Bloom. COMPOSITION. Ni3(AsO 4 )2.8H 2 O, (NiO 37.4 As 2 O 5 38.5, H 2 O 24.1 per cent.). GENERAL DESCRIPTION. Pale apple-green crusts, and occasionally very small hair-like crystals. Usually occurs on niccolite or smaltite. PHYSICAL CHARACTERS. Dull. Color, apple-green. Streak, greenish-white. H., i. BEFORE BLOWPIPE, ETC. On charcoal, fuses easily to a magnetic button, and be- comes dull and yellow during fusion, evolving garlic odor. In closed tube, yields water and darkens. With borax, gives red bead. Soluble in nitric acid. REMARKS. Results from the weathering of niccolite or smaltite and is usually found incrusting these minerals though sometimes massive as at Churchill Co., Nevada; and Reichelsdorf, Silesia. GARNIERITE. Noumeite. COMPOSITION. H 2 (Ni.Mg)SiO 4 + H 2 O? very variable. GENERAL DESCRIPTION. Loosely compacted masses of brilliant dark-green to pale-green mineral, somewhat unctuous. Structure often small mammelonated, with dark-green, varnish-like surfaces, enclosing dull green to yellowish ochreous material. Easily broken and earthy. Physical Characters. H., 2 to 3. Sp. gr., 2.27 to 2.8. LUSTRE, varnish-like, to dull. OPAQUE. STREAK, light green to white. TENACITY, fr'able. COLOR, deep green to pale greenish-white. UNCTUOUS, adheres to the tongue. BEFORE BLOWPIPE, ETC. Infusible, decrepitates and becomes magnetic. In closed tube yields water. Borax bead gives nickel reaction. Partially soluble in hydrochloric and nitric acids. SIMILAR SPECIES. Differs from malachite and chrysocolla in structure and unctuous feeling. Differs from serpentine in deep color and nickel reaction. REMARKS. Occurs as described on p. 289, in lateral secretion veins in serpentine* in Noumea, New Caledonia, derived from a peridotite. Also from similar weathering of a peridotite at Riddles, Oregon. A similar large deposit is reported in Malaga, Spain. USES. Next to the nickel-pyrrhotites it is now the most im- portant source of nickel. * At Locris, near Athens, a dull brown 7 per cent. NiO ore occurs and in eastern Cuba there are vast deposits of limonite carrying 0.8 per cent, of nickel and cobalt, both deposits apparently due to decay of peridotites. MINERALS OF METALLIFEROUS ORE DEPOSITS. 295 Sphalerite Wurtzite Goslarite Zincite Smithsonite Hydrozincite Aurichalcite Willemite Calamine Franklinite Gahnite ZnS ZnS ZnSO 4 .7H 2 O ZnO ZnCO 3 ZnCO 3 .2Zn(OH) 2 (Zn, Cu) 6 (C03) 2 (OH) Zn 2 Si0 4 (ZnOH) 2 Si0 3 (Zn, Mn)Fe 2 O 4 ZnAl 2 O 4 Isometric Hexagonal Orthorhombic Hexagonal Hexagonal Hexagonal Orthorhombic Isometric Isometric The name GENTHITE has been used for green nickeliferous magnesium silicates of very varying composition which occur coating chromite at Lancaster Co., Pa., and forming a layer in sandstone in Webster Co., N. C., and the name PIMELITE for a similar material with more alumina from Frankenstein, Silesia. THE ZINC AND CADMIUM MINERALS. The zinc minerals described are: Sulphides Sulphate Oxide Carbonates Silicates Aluminates and Ferrates The cadmium mineral described is: Sulphide Greenockite CdS. Hexagonal ECONOMIC IMPORTANCE. The important ores of zinc are sphalerite, smithsonite, and cala- mine; and, in New Jersey, willemite, zincite and franklinite. Cadmium is not obtained directly from greenockite but from zinc ores. In this country, Missouri and New Jersey have for years yielded most of the zinc ore but the development of the "flotation" processes has made new centers of zinc production, such as Mon- tana and Idaho, and the ores of Colorado and Oklahoma have come into the market.* In all, in 1915, this country produced 492,495 tons of metallic zinc. More complete statistics for 1914, exclusive of secondary zinc, recovered from old brass and zinc articles, give in short tons: Manufactured. Imported. Exported. Metallic Zincf 353,049 860 64,802 Zinc in Zinc Pigments 70,619 2,629$ 15, Zinc Dust 1,003 2,004 * By states in 1914 the yield in tons of contained zinc was in the order: Missouri 105,994 New Jersey 74,253 Montana 55.79O Colorado 48,387 Wisconsin 31,113 Idaho 21,106 Oklahoma 13,992 Kansas 11,284 Mineral Resources of U. S., 1914, Vol. 2, p. 877. f Of this, 9,631 from foreign ores. J Oxide. 296 MINERAL OGY. Metallic zinc is obtained by distillation of its roasted ores with carbon. The sulphide and carbonate, by roasting, are converted into oxide, and the silicates are calcined to remove moisture. The impure oxides, or the silicates, are mixed with fine coal and charged in tubes or vessels of clay, closed at one end and connected at the other end with a condenser. These are submitted to a gradually increasing temperature, by which the ore is reduced to metallic zinc, and, being volatile, distills, and is condensed. Apparently successful processes are now in use for the direct deposition of zinc from its ores by electrolysis. The principal uses of metallic zinc are in galvanizing iron wire or sheets and in manufacturing brass. A smaller amount is made into sheet zinc. Zinc oxide, ground in oil, constitutes the paint zinc white. The oxide may be made from the metal by heating it to a temperature at which the zinc takes fire and drawing the fumes into suitable condensers; or, as in this country, it may be made directly from the ore. Other pigments, also in this country made directly from the ore, are "leaded zinc oxide," and zinc lead oxide, the former having more lead oxide. " Ltikophone" an intimate mixture of ZnS and BaSO 4 obtained by chemical precipitation is in this country made chiefly from skimmings and scrap. The world's production of zinc in metric tons for 1913 was estimated:* United States 323,200 Great Britain 59,ooo Germany 285,000 Holland 24,000 Belgium 198,000 Russia 9,000 France 70,000 Norway 8,000 Zinc Dust results if the retorts cool rapidly below the freezing point (about 418 C.); the vapor condenses as a blue powder containing about ten per cent, of ZnO. It is extensively used in the separation of gold from cyanide solutions. Cadmium is obtained almost entirely from the Upper Silesian zinc ores. About 4^ metric tons were so obtained! in 1914 of which this country imported 1,239 pounds. The first fumes are * Mineral Industry, 1914, p. 793. f Mineral Industry, 1914, p. 82. MINERALS OF METALLIFEROUS ORE DEPOSITS. 297 redistilled and finally reduced with carbon. The metal is used in fusible alloys and certain forms of silver plating. The sulphide forms a splendid yellow pigment unaltered by exposure. FORMATION AND OCCURRENCE OF ZINC ORES. There seems to be no proof of any frequent occurrence of zinc in igneous rocks even in minute quantities. A few analyses indi- cate its occasional occurrence and Washington states that there are reasons for thinking it is " more apt to be present in acid rocks." It is reported in traces in the Triassic sediments of Schwarzwald and in sea water. The occurrences are contact deposits, veins, replacements and residual deposits. Contact Deposits.* The celebrated deposit at Franklin Furnace, containing willem- ite, franklinite, zincite, is probably of this type and the deposits at Tres Hermanas, New Mexico, chiefly willemite and the Magda- lena Mines, New Mexico containing much sphalerite, are in con- tact zones. Veins. Sphalerite is one of the common sulphides of the mineral veins. Replacements in Sedimentary Rocks. The most important zinc deposits of the world occur in lime- stone, usually with lead, and possibly concentrated there by circu- lating waters bearing sulphate solutions from which the zinc was precipitated principally as the sulphide, which later formed car- bonate, smiihsonite or silicate calcimine. The latter are usually above the sulphides. At Moresnet the oxidized ores extend from the surface to a depth of 200 to 300 feet, the sulphides underlying. Similar great deposits exist in Silesia; Bleiberg, Carinthia; and the Mississippi Valley, especially near Joplin, Mo. Metasomatic replacement is claimed specifically! for Bleiberg, Carinthia, Upper Silesia, part of Moresnetf and some others. The origin of the zinc solutions is disputed. * Lindgren, " Mineral Deposits," 675 and 694. t Beyschlag, Vogt and Krusch, Truscott's translation, 42 and 183. t Lindgren, "Mineral Deposits," 416. 298 MINERALOGY. Residual Deposits of smithsonite and calamine as at the Bertha Mines, Va. SPHALERITE. Blende, Zinc Blende, Black-jack. COMPOSITION. ZnS (Zn, 67 per cent). Often contains Cd, Mn, Fe. GENERAL DESCRIPTION. A mineral of resinous lustre shading in color from yellow through brown to nearly black and trans- parent to translucent It occurs frequently cleavable massive but also in crystals and in compact fine-grained masses or alternate concentric layers with galenite. FIG. 348. FIG. 349. FIG. 350. CRYSTALLIZATION. Isometric. Hextetrahedral class, p. 62. Usually the dodecahedron d with the tetrahedron p and a modify- ing tristetrahedron o = (a : 30, : 30); {311!. Fig. 349, usually with rounded faces. More rarely the + and tetrahedron, Fig. 348 and sometimes in twin crystals like Fig. 350. Index of refraction for yellow light, 2.3692. Physical Characters. H., 3.5 to 4. Sp, gr., 3.9 to 4.1. LUSTRE, resinous. TRANSPARENT to translucent. STREAK, white to pale brown. TENACITY, brittle. COLOR, yellow, brown, black ; rarely red, green or white. CLEAVAGE, parallel to rhombic dodecahedron (angles 1 20 and 90). BEFORE BLOWPIPE, ETC. On charcoal fuses with difficulty, but readily yields a sublimate, sometimes brown at first from cadmium and later yellow while hot, white when cold and becoming bright green if moistened and ignited with cobalt solution. With soda gives a sulphur reaction. Soluble in hydrochloric acid with effer- vescence of hydrogen sulphide. SIMILAR SPECIES. Smaller crystals sometimes slightly resemble garnet or cassiterite, but are not so hard. MINERALS OF METALLIFEROUS ORE DEPOSITS. 299 REMARKS. The occurrences are as stated on p. 297. It is obtained largely as concentrates in southwest Missouri, Wallace, Idaho; Kansas, Miami, Oklahoma, at Friedensville, Pa., in the southwestern part of Wisconsin, at Pulaski, Va., and at many other places. In small quantities it is of very common occurrence. WURTZITE. ZnS, found in small hexagonal crystals at Joplin, Mo. (prism and base), and Butte, Mont, (pyramidal). Also occurs in concentric layers of radiat- ing fibers (Schalenblende) with sphalerite at Pribram, Bohemia; Pontpeau, France; Liskeard, Cornwall. The Schalenblende of Geroldseck, Baden, is all wurtzite. In physical and blowpipe tests essentially like sphalerite. GOSLARITE. Zinc Vitriol. ZnSO 4 .7H 2 O, is formed by the oxidation of sphalerite in damp locations. It is a white or yellowish earthy mineral with nauseous astringent taste. Usually an incrustation or mass shaped like the original sphalerite or in stalactites. Rarely needle-like orthorhombic crystals. Goslarite is formed by the oxidation of sphalerite, especially in the presence of iron sulphides. Its interesting feature is that many great zinc deposits appear to have been precipitated from sulphate solutions. ZINCITE. Red Zinc Ore. COMPOSITION. ZnO, (Zn 80.3 per cent.) with usually some Mn or Fe. GENERAL DESCRIPTION. A deep red to brick-red adamantine mineral occurring in lamellar or granular masses, either in calcite or interspersed with grains and crystals of black franklinite and yellow to green willemite. A few hexagonal pyramids have been found. Physical Characters. H., 4 to 4.5. Sp. gr., 5.4 to 5.7. LUSTRE, sub-adamantine. TRANSLUCENT. STREAK, orange yellow. TENACITY, brittle. COLOR, deep red to orange red. CLEAVAGE, basal and prismatic yielding hexagonal plates. BEFORE BLOWPIPE, ETC. Infusible. On charcoal gives reactions for zinc as described under sphalerite. In closed tube blackens, but is again red on cooling. With borax usually gives amethystine bead. Soluble in hydrochloric acid without effervescence. SIMILAR SPECIES. Differs from realgar and cinnabar in its asso- ciates, infusibility and slow volatilization. REMARKS. Occurs at Sterling Hill, near Ogdensburgh, and Mine Hill, near Franklin Furnace, N. J., constituting only about one half per cent, of the average ore. Also in small amounts in Schneeberg, Saxony; the lead mines of Tuscany; Olkusz, Poland, and elsewhere. 300 MINERAL OGY. SMITHSONITE. Dry Bone, Calamine. COMPOSITION. ZnCO 3 (ZnO, 64.8 ; CO 2 , 35.2 per cent). GENERAL DESCRIPTION. Essentially a white vitreous mineral but often colored yellowish or brownish by iron. Structure stalactitic or botryoidal, or with drusy crystal surface ; also in porous cavernous masses and granular. Sometimes of decided colors, as deep green or bright yel- low, from copper or cadmium respectively. CRYSTALLIZATION. Hexagonal. Scaleno- hedral class, p. 48. Axis c = 0.8063. Usually small rhombohedrons of 73, Fig. 351, like those of siderite. Optically . Physical Characters. H., 5. Sp. gr., 4.3 to 4.5. LUSTRE, vitreous to dull. TRANSLUCENT to opaque. STREAK, white. TENACITY, brittle. COLOR, shades of white, more rarely yellow, green, blue, etc. CLEAVAGE, parallel to rhombohedron (107). BEFORE BLOWPIPE, ETC. Infusible but readily yields white sublimate on coal, often preceded by brown of cadmium. The sublimate becomes yellow when heated and becomes bright green when moistened with cobalt solution and then heated. Soluble in acids with effervescence. SIMILAR SPECIES. Distinguished from calamine by its efferves- cence and from other carbonates by its hardness. REMARKS. Occurs secondary after sphalerite as a replacement of limestone or dolomite, and as residual material. The many zinc deposits usually consist in their upper portions of smithsonite and calamine; this is the case at Moresnet, Silesia, many of the deposits of the Mississippi Valley, and the Magdalena District, New Mexico. HYDROZINCITE. Zinc Bloom. COMPOSITION. ZnCO 3 '2Zn(OH) 2 , (ZnO 75.3, C0 2 13.6, H 2 O ii.i per cent.). GENERAL DESCRIPTION. Usually a soft white incrustation upon other zinc minerals, or as dazzling white stalactites, or earthy and chalk like. PHYSICAL CHARACTERS. Opaque. Lustre, dull or pearly. Color, pure white to yellowish. Streak shining white. H., 2 to 2.5. Sp. gr., 3.58 to 3.8. BEFORE BLOWPIPE, ETC. Infusible. Coats the coal like smithsonite. Yields water in closed tube. Soluble in cold dilute acids with effervescence. REMARKS. Hydrozincite results from the alteration of other zinc ores and occurs in minor quantities in many zinc deposits. Larger quantities have been found at Santander, Spain; Raibl, Carinthia and Constantine, Algeria. MINERALS OF METALLIFEROUS ORE DEPOSITS. 301 AURICHALCITE, (Zn, Cu) 5 (CO ) 2 (OH) 6 , in pale bluish green and often velvety incrustations often on smithsonite. Sometimes pearly imperfect crystals. H = 2, Sp. gr., 3.54 to 3.64. BEFORE BLOWPIPE, ETC. Infusible, colors flame green and yields white coating made green by moistening with cobalt solution and igniting. Soluble in acids with effervescence. REMARKS. Occurs in Zacatecas, Mexico; Salt Lake Co., Utah; Santa Caterina, Arizona; Laurium, Greece; Rezbanya, Hungary; and many other localities. WILLEMITE. Troostite. COMPOSITION. Zn 2 SiO 4 , (ZnO, 72.9; SiO 2 , 27.1); often with much manganese replacing zinc. GENERAL DESCRIPTION. Compact, translucent, somewhat res- inous material, yellow or greenish or brownish red in color, often mottled; granular mixtures with black frank- FIG. 352. linite; transparent and opaque prismatic crystals often large (Franklin, N. J.), Fig. 352. Brown, granular masses with minute crys- tals (Altenberg, Belgium). Dark gray cellular masses with radial ag- gregates of slender crystals (Tres Hermanas, New Mexico). CRYSTALLIZATION. Hexagonal. Class of third order rhombo- hedron, p. 54. Axis c= 0.6775. p= {ioi~i},e= {oil2},a = {1120}. Supplement angles are pp = 64 30'; ee = 36 47'. Physical Characters. H.,5. Sp. gr. 3.89 to 4.2. LUSTRE, resinous. TRANSPARENT to opaque. STREAK, nearly white. TENACITY, brittle. COLOR, greenish to sulphur yellow, apple green, white, flesh red, gray, brown and blue. REMARKS. Occurs as the result of contact metamorphism (presumably of cala- mine) in its two most important localities, Sussex County, New Jersey, and Tres Hermanas, New Mexico. Also found in Altenberg near Moresnet in a layer with calamine and smithsonite; and in Stolberg in veins. From Greenland blue colored crystals are reported, and it has been recognized at Socorro, New Mexico, and Clifton, Arizona. CALAMINE. Electric Calamine. COMPOSITION. (ZnOH) 2 SiO 3 , (ZnO, 67.5 ; SiO 3 , 25.0; H,O, 7.5 per cent.). 3 02 MINERALOGY. FIG. 353. Altenberg. GENERAL DESCRIPTION A white or brownish white vitreous mineral frequently with a drusy surface or in radiated groups of crystals, the free ends of which form a ridge or cockscomb, also, but more rarely, small distinct trans- parent crystals. It occurs also granular, stalactitic, botryoidal and as a constituent of some clays. CRYSTALLIZATION. Orthorhombic. Hemimorphic class, p. 41. Axes a : & : c 0.783 ; i : 0.478. The crystals are usually tabular, the broad face being the brachypinacoid b, while the prism m is relatively small, v is the pyramid 2d : b : 2c ; {121}. Optically +, with acute bisectrix vertical. 2E for yellow light = 78 39'. Physical Characters. H., 4.5 to 5. Sp. gr., 3.4 to 3.5. LUSTRE, vitreous to pearly. OPAQUE to transparent. STREAK, white. TENACITY, brittle. COLOR, yellow to brown, white, colorless, rarely blue or green. BEFORE BLOWPIPE, ETC. Fusible only in finest splinters. With soda and borax, on charcoal yields a white coating, which is made bright green by heating with cobalt solution. In closed tube, yields water. With acids, dissolves, leaving a gelatinous residue. SIMILAR SPECIES. It is softer than prehnite, harder than cerus- site, and gelatinizes with acids. It differs from willemite in water reaction, and from stilbite in difficulty of fusion. REMARKS. Occurs usually with smithsonite in upper portions of the great zinc replacement deposits, p. 297, or as residual material. Sometimes forms separate deposits as at Herbesthal, Belgium, or may be with hydrozincite as at Cumillas Santander, Spain. In this country it has been mined at Granby, Mo., Sterling Hill, N. J., Bertha, Va., and various localities in Tennessee, Arkansas and Nevada. FRANKLINITE. COMPOSITION. (Fe.Mn.Zn) (Fe.Mn) 2 O 4 . GENERAL DESCRIPTION. A black mineral re- sembling magnetite. Occurs in compact masses, rounded grains and octahedral crystals. Only slightly magnetic and generally with brown streak. The red zincite and yellow to green willemite are frequent associates. The crystals are modified octahedrons rarely sharp cut as in magnetite FIG. 354- MINERALS OF METALLIFEROUS ORE DEPOSITS. 303 Physical Characters. H., 6 to 6.5. Sp. Gr., 5 to 5.2. LUSTRE, metallic or dull. OPAQUE. STREAK, brown to black. TENACITY, brittle. COLOR, black. Breaks parallel to octahedron. Slightly magnetic at times. BEFORE BLOWPIPE, ETC. Infusible. On charcoal with soda gives white coat of zinc oxide. In beads gives manganese reaction. Slowly soluble in hydrochloric acid with evolution of some chlorine. SIMILAR SPECIES. Distinguished from magnetite and chromite by bead tests and associates. REMARKS. The only, noteworthy locality is that in the vicinity of Franklin Fur- nace, New Jersey. Here, however, the deposit is large and has been extensively developed. USES. The zinc is recovered as zinc white and the residue is smelted for spiegeleisen an alloy of iron and manganese used in steel manufacture. Franklinite has also been ground for a dark paint. GAHNITE. Zinc Spinel, ZnAl 2 C4. Octahedral crystals of green to black color. Usually opaque and vitreous and with gray streak. H., 7.5 to 8. Sp. gr., 4 to 4.6. On charcoal infusible but gives the coating of zinc oxide. Occurs in talcose schist at Falun, Sweden, in greenish crystals in Calabria, etc., and in this country especially with franklinite and willemite at Franklin Furnace, N. J., and with pyrite at Rowe, Mass. GREENOCKITE. COMPOSITION. CdS, (Cd, 77.7 per cent.) GENERAL DESCRIPTION. Usually a bright yellow powder upon sphalerite, or a yellow coloration in smithsonite. Very rarely as small hemimorphic hexagonal crys- tals. ^ = 0.81 1 1. PHYSICAL CHARACTERS. Translucent. Lustre earthy 01 adamantine. Color yel- low to orange yellow or bronze yellow. Streak orange yellow. H., 3 to 3.5. Sp. gr., 4.9 to 5.0. BEFORE BIOWPIPE, ETC. Infusible, but is easily volatilized in the reducing flame, coating the coal with a characteristic brown coat and a iridescent tarnish. In closed tube, turns carmine red on heating, but is yellow on cooling. Soluble in strong hydrochloric acid, with effervescence of hydrogen sulphide. REMARKS. Occurs as crystals in igneous rocks with prehnite at Bishopstown, Scotland. In many localities it occurs incrusting sphalerite* as at Friedensville, Pa., and in Missouri. In Marion County, Arkansas, it colors smithsonite, forming the so-called "turkey fat" ore. * In deposits of wurtzite and sphalerite (Schalenblende) the greenockite is princi- pally in the wurtzite. One analysis (Pribram) showing 3.66 per cent. 304 MINER A LOG Y. THE TIN MINERALS. The minerals described are: Sulphide Stannite (Cu.Sn.Fe)S Isometric Oxide Cassiterite SnO 2 Tetragonal Staniferous pyrite occurs in the Bolivian mines and tin is also found as an occasional constituent of tantalite, columbite, and other columbates and tantalates. It is also an essential constituent of a few rare species.* ECONOMIC IMPORTANCE. Cassiterite is the only ore of tin, and while deposits exist in this country (in Virginia, North and South Carolina, Dakota, Alaska and elsewhere, the product for 1914 was only ore from Alaska, equivalent to 104 tons of metallic tin) .f The world's supply of tin, amounting yearly to about 125,000 long tons, comes chiefly from the East India islands and Bolivia. The following figures are given for 1915:^ Long Tons. Straits and Malay Peninsula (exports) 66,760 Banka and Billiton (sales) 15.093 Bolivia (exports) 18,800 China (exports and production) 7,097 Cornwall (production) 4,000 Australia (exports) 2,275 South Africa (production) 2,158 Nigeria 1,899 118,082 The principal use of tin is for the manufacture of tin plate sheet-iron coated with tin which is used for making cans, house- hold utensils, etc. Tin is also largely used in alloys, such as bronze, bell metal, pewter, solder and tin amalgam. Tinfoil is also made from it. Large quantities of sodium stannate are used in calico printing. The ore as mined is first separated from gangue and impurities by washing, jigging, etc., and if necessary, is then calcined or roasted, to remove volatile elements, such as sulphur, arsenic, antimony. * Such as canfieldite, franckeite, kylindrite, nordenskioldine. t Mineral Production U. S., 1914, Summary by H. D. McCaskey. } Engineering and Mining Journal, 1916, p. 67. MINERALS OF METALLIFEROUS ORE DEPOSITS. 305 The concentrated and purified ore may then be smelted with carbon in a shaft furnace. The modern practice is, however, to smelt the ore for several hours in a reverberatory furnace with coal. The liquid tin is drawn off and the slags are resmelted at a higher temperature, frequently requiring the addition of iron or of lime to aid in the separation of the tin, which they still contain. The impure metal obtained is slowly heated to a temperature but little above the melting point of tin ; comparatively pure tin separates and this is further purified by oxidation. This oxidation is accom- plished either by forcing green wood under the liquid metal causing violent agitation or by repeatedly pouring the melted tin in a thin stream from ladles. Tin may also be refined by electrolysis. FORMATION AND OCCURRENCE OF TIN DEPOSITS. Tin oxide occurs in granite* in amounts rarely exceeding 0.05 per cent, and occasionally minute crystals of cassiterite are visible. In granite pegmatites, cassiterite is sometimes more abundant as in the Black Hills, South Dakota. In Durango and Jalisco, Mexico, it occurs in a rhyolitic surface flow.f The primary source of tin therefore is an acid magma and all important deposits are derived from such magmas by pneumatolytic action,* p. 242, in which two great stages are recognized. First, extraction from the acid magma by aid of fluorine and its compounds, the tin in gaseous state exhaling through cracks in the crust from the still molten interior of the magma. Second. The deposition in the fissures and in the country rock and the conversion of the latter into "greisen" by the intro- duction of tin, fluorine, lithium and silica. * Especially in the mica, but also in the feldspar. | Lindgren "Mineral Deposits," p. 632. % " One entire class of deposit, that of the tin lodes, owes its existence entirely to the action of these gases and vapors either between themselves or upon the rocks with which they come in contact." Beyschlag, Vogt and Krusch, "Ore Deposits," P- 174- Coarse-grained rocks consisting of quartz, mica, topaz, or tourmaline and cassiterite. For the Erzgebirge, Lindgren quotes: Quartz 50.28, topaz 12.14, lithia, mica, 36.80, cassiterite 0.43, "Mineral Deposits," p. 620. 21 306 MINERAL OGY. Tin Veins. The great deposits are veins or lodes in or near granite such as the long-worked deposits of the Saxon and Bohemian Erzgebirge and of Cornwall and Devon, England. The great deposits of Mt. Bischof, Tasmania, are in "intensely altered"* porphyritic dikes but derived from the same magma as a distant granite mass. The veins worked in the "straits" are in limestone but sur- rounded by granite hills. The Bolivian veins at Oruro contain silver minerals and much pyrite, but the pneumatolytic action is indicated by the abundant tourmaline in the country rock. Contact Deposits. The contact deposits at Pitkaranta, Finland, include not only copper and iron ores but cassiterite with microscopic topaz and with scheelite and fluorite. Residual Deposits. The erosion and weathering of tin deposits results in the forma- tion of placers or "gravels," some just below the outcrop as at Mt. Bischoff, Tasmania, but usually further from the parent rock. The weathering removes sulphides and the gravels yield the purest tin. About three quarters of the world's supply comes from such deposits, chiefly Malay Peninsula, Banka and Billiton, but also China, Siam, New South Wales and Alaska. STANNITE. Tin Pyrites. COMPOSITION. (Cu.Sn.Fe)S. Uncertain. GENERAL DESCRIPTION. A massive, granular mineral, of metallic lustre and steel- gray color. It is often intermixed with the yellow chalcopyrite. PHYSICAL CHARACTERS. Opaque. Lustre metallic. Color steel gray to nearly black. Streak black. H = 4. Sp gr., 4.5 to 4.52 Brittle. BEFORE BLOWPIPE, ETC. In the reducing flame fuses. In the oxidizing flame yields SO 2 , and is covered by white oxide, which becomes bluish-green when heated with cobalt solution. Soluble in nitric acid to a green solution, with separation of sulphur and oxide of tin. With soda, gives sulphur reaction. REMARKS. Stannite occurs in comparatively small amount in the tin regions of Cornwall, Zinnwald and Bolivia. In this country it has been found at the Peerless Mine, Black Hills, South Dakota. * Roughly 35 per cent, topaz, 65 per cent, quartz, Beyschlag, Vogt and Krusch, P- 445 MINERALS OF METALLIFEROUS ORE DEPOSITS. 307 CASSITERITE. Stream Tin. Tin Stone. COMPOSITION. SnO 2 , (Sn 78.6 per cent.), and usually with some Fe 2 O 3 , and sometimes Ta 2 O 5 , As 2 O 6 , SiO 2 or Mn 2 O 3 . GENERAL DESCRIPTION. A hard and heavy brown to black mineral occurring either in brilliant adamantine crystals or more frequently in dullbotryoidal and kidney-shaped masses and rounded pebbles, often with a concentric or fibrous radiated structure. FIG. 355- FIG. 356. FIG. 357- Stoneham, Me. Cornwall, Eng. Zinnwald. CRYSTALLIZATION. Tetragonal. Axis c = 0.672. Common forms are the unit first and second order pyramids and prisms p, a r m, and d, and the ditetragonal pyramid z = (a : \a : $c) ; {321}. Supplement angles // = 58 19' ; dd= 46 28' ; mz = 24 59'. Frequently twinned parallel to the second order pyramid, Fig. 357- Optically + with high indices of refraction 1.996 and 2.093. Physical Characters. H., 6 to 7. Sp. gr., 6.8 to 7.1. LUSTRE, adamantine to dull. OPAQUE to translucent STREAK, white or pale brown. TENACITY, brittle. COLOR, brown to nearly black, sometimes red, gray, or yellow. CLEAVAGES, indistinct pyramidal and prismatic. BEFORE BLOWPIPE, ETC. Infusible, but in powder becomes yel- low and luminous. On charcoal with soda and strong heat yields white sublimate which is made bluish green by heating with cobalt solution. Insoluble in acids. The uncrushed mineral placed on a piece of zinc in dilute hydro- chloric acid is coated with gray metallic tin. VARIETIES. Tin Stone. Crystals and granular masses. 308 MINERALOGY. Wood Tin. Masses with concentric structure, the zones being of different color and internally fibrous. Stream Tin. Rounded pebbles and grains found in alluvial deposits. SIMILAR SPECIES. The high specific gravity distinguishes it from silicates which it resembles, and the infusibility and insolu- bility distinguish it from wolframite, etc. REMARKS. In America the chief localities are Alaska; Harney Peak, South Dakota; Temescal, California; Gaffney, South Carolina; and Lincolnton, North Carolina; Shenandoah Valley, Virginia; and Durango, Mexico. It has been found also in New Hampshire, Maine, Massachusetts, Alabama, Wyoming and Montana. THE TITANIUM MINERALS. The minerals described are : Oxides Rutile TiO 2 Tetragonal Octahedrite TiO 2 Brookite TiO 2 Orthorhombic Titanium is also a constituent of ilmenite and titanite, and occurs in certain varieties of common silicates, pyroxene, amphi- bole, mica, garnet (schorlomite), chrysolite as well as in a number of titanites and titanosilicates. ECONOMIC IMPORTANCE. Although the ninth in quantity of the elements in the earth's crust, titanium has few uses. The production for 1914 at the Roseland, Va., mines was equivalent to 138 tons of titanic oxide.* Oxide of titanium is used to impart a pinkish color to artificial teeth and an ivory-like appearance to porcelain and from it titan- ium carbide electrodes for arc lights are made. Ferrotitanium alloy is assuming importance as a deoxidizer in casting steel ingots for rolling mills. Also used for incandescent lamp filaments, color- ing material for ceramics and various salts used in dyeing. FORMATION AND OCCURRENCE OF DEPOSITS. Titanium Deposits. The earth's crust contains 0.43 (Clarke) per cent, of titanium, much of which is in the magmatic segregation of ilmenite and titaniferous magnetite already mentioned, p. 263. Rutile in economic quantities is also .the result of magmatic segregation and four important localities exist: * Mineral Resources of the U. S., 1914. MINERALS OF METALLIFEROUS ORE DEPOSITS. 309 In Amhers^ and Nelson counties, Va., in syenite, grading into gabbro and with gabbro dikes. At Kiagero, Norway, "streak-like" in granite with dikes on both sides. At St. Urbain's Bay, St. Paul, Canada, where the ilmenite segregations run high (up to 20 per cent.) in orange red rutile. At Mt. Crawford, So. Australia, where rutile crystals in economic quantity can be washed from a kaolinized dike. RUTILE. Nigrine. COMPOSITION. TiO 2 , (Ti 61 per cent.). GENERAL DESCRIPTION. Brownish red to nearly black pris- matic crystals often included in other minerals in hair-like or needle-like penetrations. Also coarse crystals embedded in quartz, feldspar, etc., or in parallel and crossed and netted needles upon hematite or magnetite. Occasionally massive when black and iron bearing. FIG. 358. FIG. 359. FIG. 360. Magnet Cove, Ark. CRYSTALLIZATION. Tetragonal. Axis c 0.644. Very close to cassiterite in angles and forms. Usual combinations are unit first and second order pyramids, p and d, and first and second order prisms, m and a. Often twinned in knees, Fig. 360, and rosettes, Fig. 359- As fine hair-like inclusions, Fig. 216. Prisms often striated vertically. Supplement angles pp = 56 52'; dd = 45 2'. Optically + with very high indices of refraction 2.616 and 2.902 for yellow light. 310 MINERAL OGY. Physical Characters. H., 6 to 6.5, Sp. gr., 4.15 to 4.25. LUSTRE, adamantine to nearly metallic. OPAQUE to transparent. STREAK, white, pale brown. TENACITY, brittle. COLOR, reddish brown, red, black, deep red when transparent. BEFORE BLOWPIPE, ETC. Infusible. In salt of phosphorus dissolves very slowly in the oxidizing flame to a yellow bead which becomes violet in the reducing flame. Insoluble in acids. SIMILAR SPECIES. It is redder and of lower specific gravity than cassiterite. The nearly metallic lustre, weight and infusi- bility separate it from garnet, tourmaline, vesuvianite, and pyrox- ene. REMARKS. In addition to the magmatic segregations mentioned rutile occurs as an accessory mineral in the igneous rocks, in the sediments, with the hardening shales and the bauxite deposits and in the metamorphic rocks. It is often included in quartz and feldspar. In this country notable localities are Graves Mt., Ga., Magnet Cove, Ark., and Alexander Co., N. C. OCTAHEDRITE. TiO 2 . In small pyramidal tetragonal crystals c = 1.777. Either black opaque and nearly metallic, or brown translucent and adamantine. BROOKITE = TiO2. Orthorhombic. Axes a : 5 : c = 0.842 : i : 0.944. Either brown translucent crystals which are thin and tabular, or black opaque crystals of varied habit. ZIRCONIUM, THORIUM, CERIUM, YTTRIUM MINERALS. The mineral ) described are : Oxide Zirconium oxide ZrOz Phosphates Monazite (Ce, La, Di)PO4 Monoclinic Xenotime Yt PO 4 Tetragonal Silicates Zircon ZrSiO4 Tetragonal Thorite ThSiO 4 Tetragonal Cerite Hydrated cerium silicate Orthorhombic Gadolinite YtzI^FeSiaOio Monoclinic Uranate Thorianite TM^.UsOs Isometric These elements also enter into a large series of silicates, phos- phates and niobates, some of which are mentioned in footnotes of the succeeding pages. Samars&ite, fergusonite, and allanite, are described in this book. ECONOMIC IMPORTANCE. Zirconium. The metal has no uses. The oxide zirconia glows brilliantly when highly heated and is very durable. It is used for coating MINERALS OF METALLIFEROUS ORE DEPOSITS. 311 the cylinders of the Drummond light and the filament of the Nernst light is chiefly zirconia with less yttria and other rare earths. A recent larger use is as the " opacifier " in the white glass used in indirect electric lighting. The chief source is the Brazilian zir- conium oxide. The zircon of Norway and of North and South Carolina were formerly important sources. The zirconia is made from zircon* or altered zircon (zirconium oxide) by fusing with acid potassium fluoride, extracting with hot water, treating with hydrochloric acid and precipitating with ammonia. Thorium. The metal and its alloys have no economic uses. The oxide, thoria, is very important because of its use in different incandescent gas mantles. The mantle of the Welsbach lamp consists of about 99 per cent, of thoria with one per cent, of ceria. Thoria is manufactured by methods which are carefully guarded. In practice monazite as it comes into the markets is separated from other impurities which occur in the sand by means of Wetherill magnetic separators. This monazite is then treated with strong sulfuric acid' and the thorium later precipitated. Both thorite} and ihorianite are used for the manufacture of thoria, but the supply is limited. The chief source is the cerium mineral, monazite, of which it is stated about 3000 tons per year are used. Monazite carries salts of thorium as impurities and in quantities varying from traces to as much as 18.5 per cent, of thorium oxide. Brazil furnishes most of the monazite although Travancore, Madras, in 1912 produced 1,135 tons, containing 14 per cent, thoria and Ceylon 224 Ibs. thorianite in 1910. Cerium. Metallic cerium is an important part of the alloy called "Misch metal" made from residues after removal of thoria. It is used as a reducing agent and is said to be the alloy in patent cigar lighters. The oxide ceria is used in various incandescent mantles and the * A few of the other species containing zirconium are wohlerite, eudialite, naegite, zirkelite and lavenite. t The following minerals also are usually rich in thorium and would be valuable if found in quantity: Thorogummite, mackintoshite, aeschynite, zirkelite, tscheffkinite, yttrialite, caryocerite, euxenite, pyrochlore. 312 MINERALOGY. fluoride in the flaming arc light. Other compounds are used in making and fixing dyes and in color photography. Cerite is made directly into a crude sulphate used as a catalyst in sulphuric acid manufacture. The manufacture of the oxide is incidental to the manufacture of thoria. No mineral is used exclusively for making ceria.* Monazite is the principal source.f Yttrium. The oxide yttria, Y 2 O3, was used in the Nernst lamp filament and in gas mantles. Gadolinite\ is the chief mineral, though yttria may be recovered in any separation of the groups. FORMATION AND OCCURRENCE OF ZIRCONIUM, THORIUM, CERIUM AND YTTRIUM DEPOSITS. These elements occur in the igneous rocksj and certain gneisses. Zirconium is the -most plentiful, but cerium and yttrium are estimated at only o.ooi per cent, and thorium at only o.oooi per cent. The economic deposits are practically limited to pegmatites of granite or syenite, such as those of southern Norway and Sweden or Baringer Hill, Texas and to residual deposits such as the monazite sands of Brazil or the gold washings of Henderson County, N. C., and the " zircon favas" (Favas = rounded pebbles) bearing gravels of Minas Geraes, Brazil. A sandstone carrying 12 to 29 per cent, of zircon occurs near Ashland, Va. ZIRCONIUM OXIDE. Zirconium oxide, ZrO 2 , occurs in negligible quantities as the mineral baddeleyite, of which a crystal fragment (monoclinic) was found in the Ceylon gem gravels at Rakwana, and it has been found at Jacupiranga, Brazil, and Alno, Sweden, in basic (magnetite, pyroxene, chrysolite) rocks. The oxide is, however, found in quantity in the syenite gravels of Serra de Caldas and Rio Verdinho, Minas Geraes, Brazil, as masses of dark, greenish gray color with fibrous concentric "Glaskopf" structure resulting from decomposed zircon and locally known as "Zircon Favas." * A few of the many other species carrying cerium are tysonite, parisite, bast- naesite, mosandrite, tritomite, fluocerite. t Others are yttrfalite, tengerite, xenotime, etc. % Zircon, monazite, allanite and xenotime are most frequently observed. MINERALS OF METALLIFEROUS- ORE DEPOSITS. 313 MONAZITE. COMPOSITION. (Ce.La.Di)PO 4 , but with notable quantities of thorium and silicon and frequently small amounts of erbium and ytterbium. GENERAL DESCRIPTION. Small, brown, resinous crystals, or yellow, translucent grains, disseminated or as sand. Sometimes in angular masses. CRYSTALLIZATION. Monoclinic. Axes 0.926; /9= 76 20'. Crystals are usually small and flat, but sometimes large. Fig. 361 shows the pinacoids a and b, the unit pyramid, prism and dome /, m and o and the prism /= (20, : b : coc) ; { 120}. Sup- plement angles mm = 86 34' ; ad = 39 OPTICALLY -f , with axial plane nearly a and acute bisectrix nearly vertical. Axial angle in red light 2E 29 to 31. Sp. gr., 4.9-5-3. OPAQUE, to translucent. TENACITY, brittle. CLEAVAGE, basal, perfect. Physical Characters. H., 5-5.5. LUSTRE, resinous. STREAK, white. COLOR, clove or reddish brown, yellow. BEFORE BLOWPIPE, ETC. Turns gray when heated, but does not fuse. Is decomposed by hydrochloric acid with a white residue. Solutions added to a nitric acid Solution of ammonium molybdate produce a yellow precipitate. REMARKS. Occurs as crystals in the pegmatites of Norway and Sweden, and in large crystals and masses at Amelia County, Va. Disseminated in gneiss in Brazil and in North Carolina and as needles or minute crystals in apatite of Arendal, Norway Hurdstown, N. J., and elsewhere. Residual deposits occur in Brazil as sea shore sands near Prado, Bahia, and Esperito Santo, and in beds of gravel in Minas Geraes and elsewhere. Also found in the gold and platinum washings of Siberia, Colombia and in North Carolina (formerly important) and the tin deposits of Malay, Nigeria and Nyassaland. XENOTIME. COMPOSITION YtPC"4 (VtzOa 54 to 64, Ce 2 Os o to n, ThOz o to 3, ZrC2 o to 2 per cent.). GENERAL DESCRIPTION. Soft yellow, brown or red crystals, zircon-like in form with easy prismatic cleavage. MINERALOGY. CRYSTALLIZATION. Tetragonal, c = 0.6187. Common forms unit prism m. unit pyramid p, second order prism a. Supplement angle pp = 55 30'. PHYSICAL CHARACTERS Opaque. Lustre, resinous to vitreous. Color, yellows, browns and flesh red. Streak, paler than color. H., 4 to 5. Sp. gr. 4.45 to 4.56. Cleavage, perfect parallel m. BEFORE BLOWPIPE, ETC. Infusible. Bluish green flame with sulphuric acid. Insoluble in acids. REMARKS. Occurrence like monazite in the Swedish pegmatites, and the residual deposits of Brazil and North Carolina. Also in larger crystals at Alexander Co., N. C. ZIRCO N. Hyacinth. COMPOSITION. ZrSiO 4 (ZrO 67.2, SiO 2 32.8 per cent.). GENERAL DESCRIPTION. Small, sharp cut, square prisms and pyramids with adamantine lustre and brown or grayish color. Sometimes in large crystals and in irregular lumps and grains. CRYSTALLIZATION. Tetragonal. Axis c = 0.640. Common forms: unit prism m, unit pyramid p, second order prism a, and pyramids u = (a : a : 3$); {331} and x = (a : $a : 3^); (311). Supplement angles pp = 56 41'; uu = 83 9'; mu = 20 12'; ax = 31 53'; mp = 47 50'; pp over top 84 20'. Optically + with strong refraction and double refraction (a = 1.9239; 7 = 1.9628 for yellow light). FIG. 362. FIG. 363. FIG. 364. FIG. 365. Physical Characters. H., 7.5. Sp. gr., 4.68 to 4.70. LUSTRE, adamantine. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle. COLOR, brown, reddish, gray, colorless, green, yellow. CLEAVAGES, imperfect, parallel to both pyramid and the prism. BEFORE BLOWPIPE, ETC. Infusible, losing color and sometimes becoming white. Insoluble in acids or in soda. MINERALS OF METALLIFEROUS ORE DEPOSITS. 315 REMARKS. Occurs in minute crystals in granite and especially in nephelite or augite syenite, as in the Wichita Mts., Oklahoma. Larger crystals occur in pegma- tites as in Southern Norway, Litchfield, Maine, and Canada. Less common in crystalline schists (Tyrol) and occasionally in beds of iron ore, Mineville, N. Y., and Fredericksvarn, Norway. Residual deposits often contain zircon as in the gold sands of North Carolina and the gem gravels of Ceylon and Expailly, France. THORITE Orangite. COMPOSITION. ThSiO4, carrying some water. GENERAL DESCRIPTION. Black or orange-yellow tetragonal crystals like those of zircon. Also found massive. PHYSICAL CHARACTERS. Translucent to transparent. Lustre resinous. Colo r black, brown and orange. Streak, orange to brown. Brittle. H., 4.5-5. Sp. gr., 4.4-5.2. BEFORE BLOWPIPE, ETC. Infusible. Gelatinizes with hydrochloric acid before being heated by blowpipe but not after. In closed tube yields water and the orange variety becomes nearly black while hot, but changes to orange again on cooling. REMARKS. Thorite occurs in large black crystals in a pegmatite near Arendal, Norway, and as masses and crystals of orange color at Lb'vo and other localities near Brevik, Norway. A mass was found in the Champlain iron region, New York. It occurs in veins in hornblende granite in Sutherland, Scotland, and at the Trotter Mine, New Jersey. CERITE. COMPOSITION. Hydrated cerium silicate with CeaOs 36 to 72, Y 2 Oi o to 7, ZrOt o to 1 1 per cent. GENERAL DESCRIPTION. Granular masses between clove brown and cherry red in color. Rarely crystals. Resembles red granular corundum. CRYSTALLIZATION. Orthorhombic highly modified short prisms. PHYSICAL CHARACTERS. Nearly opaque. Luster, dull to resinous. Color, cherry red, brown, gray. Streak, gray or white. H., 5.5. Sp. gr., 4.86. BEFORE BLOWPIPE, ETC. Infusible.. In closed tube yields water. With soda a yellow slag nearly colorless on cooling. Gelatinizes with hydrochloric acid. REMARKS. Occurs at Bastnas, Sweden, as a bed in gneiss with allanite, chalco- pyrite, and other minerals. GADOLINITE. COMPOSITION. Yt2Be2FeSi2Oio (Yttrium Oxides 51.8, BeO 10.0, FeO 14.3, SiO 2 23.9 per cent.). GENERAL DESCRIPTION. Rounded or nodular masses, internally glassy and nearly black, externally earthy and reddish or yellow. Somewhat resinous in luster. Sometimes in coarse monoclinic crystals. PHYSICAL CHARACTERS. Translucent. Lustre, vitreous to greasy. Color, black or greenish black. Streak, greenish gray. H., 6.5 to 7. Sp. gr., 4.24 to 4.47. BEFORE BLOWPIPE, ETC. Infusible but swells and cracks and if glassy glows brightly. Gelatinizes with hydrochloric acid. REMARKS. Occurs in pegmatite veins. Abundant at Baringer Hill, Llano Co., Texas. Found at Hittero and Riser, Norway, and Kararfvet and Ytterby, Sweden, Lead Pb Isometric Galenite PbS Isometric Bournonite PbCuSbSa Orthorhombic Jamesonite Pb 2 Sb 2 S 5 Orthorhombic Clausthalite PbSe Isometric Minium Pb 3 4 Anglesite PbS0 4 Orthorhombic Pyromorphite Pb 5 Cl(P0 4 )3 Hexagonal Mimetite Pb 6 Cl(AsO4)3 Hexagonal Cerussite PbC0 3 Orthorhombic 316 MINERALOGY. THORIANITE. ThO 2 U3O 8 (ThO 2 70 to 80, Ce 2 O 3 12 to 28, UO 3 12 to 25, ZrO2 up to 3 per cent-), occurring as small black water worn cubic crystals found in the Ceylon gem gravels. Sp. gr., 9.3. THE LEAD MINERALS. The minerals described are: Metal Sulphide Sulphantimonites Selenide Oxide Sulphate Phosphate Ar senate Carbonate Zinkenite, plagionite, boulangerite, geocronite, linarite and phos- genite are briefly mentioned. Other lead minerals described elsewhere are crocoite, vanadinite, descloizite, wulfenite, and lead is found in many other species. ECONOMIC IMPORTANCE. The world uses about 1 ,500,000 tons of lead per year, of which this country, in 1915, produced 565,356 tons from domestic ores.* Of this 221,797 tons was soft lead, mainly produced in Missouri, containing almost no silver and gold. During the same year 317,463 tons of lead was desilverized; indeed, it may be said that by far the most important use of lead ore is to mix and smelt with silver ores, whereby metallic lead containing silver and gold are obtained. The principal use of metallic lead is in the manufacture of white lead and large amounts are used for the preparation of red lead, litharge, shot, lead pipe and sheet lead. A certain amount of lead containing antimony, 24,370 tons in 1915, is produced which is used in type and in alloys for friction-bearings. The argentiferous lead ores of the west, which ordinarily run low in lead are smelted in blast-furnaces. The ore, if it contains much sulphur, is roasted, to remove the sulphur and other volatile constituents, and is then fused, forming a silicate, which is * Engineering and Mining Journal, 1916, p. 56. MINERALS OF METALLIFEROUS ORE DEPOSITS. 317 charged in the furnace with the proper proportions of fuel and flux (limestone, hematite, etc.). The reduction takes place under the action of the blast. Metallic lead, carrying most of the silver, is produced, and if either sulphur or arsenic is present, a sulphide (matte) and an arsenide (speiss) of iron, copper, etc., will form, and above all these will float the slag composed of the gangue and the flux. The furnace is usually oblong in section, and the hearth is con- nected, by a channel from the bottom, with an outer basin or well, so that the metal stands at the same level in each and can easily be ladled out. Above the hearth, and enclosing the smelting zone, are what are called the water jackets, in which cold water circu- lates. The furnace gases pass through a series of condensing chambers. The matte, speiss and the dust collected in the condensing cham- bers are all treated for silver, gold, lead, copper, etc., usually at different works. The metallic lead, or base bullion, is desilverized by remelting in large kettles, raising it to the melting-point of zinc, adding metallic zinc and cooling to a point between the melting- points of zinc and lead. The lighter solidified zinc separates, carry- ing with it the silver and gold, and forms a crust on the surface of the lead, from which it is skimmed. The lead is further purified and the zinc, gold and silver sepa- rated electrolytically or by distillation. FORMATION AND OCCURRENCE OF LEAD DEPOSITS. The evidence as to the presence of lead minerals as primary constituents of igneous rocks is not very conclusive. Minute amounts have been found in a few analyses. Lead forms no important silicates.* The great lead deposits appear to be galenite as a primary mineral deposited with other sulphides especially sphalerite No deposits due to magmatic segregation are known. Vein Deposits. These are estimated to supply one third of all the lead as opposed to one half in metasomatic replacements.* Veins are more or * Rare species barysilite, hyalotekite, ganomalite. t Beyschlag, Vogt & Krusch (Truscott), p. 775. 318 MINERALOGY, less directly connected with intrusions of igneous rock and may be in crystalline schists or igneous rocks or the older sediments and are often rich in silver. At Freiberg, Saxony, they are in gneiss, at Clausthal, Harz; and Przibram, Bohemia; in clay slate and graywacke, at Linares, Spain ; in granite. Other important veins are at Kapnik, Hungary; Shoshone, Idaho; Cornwall, England. Replacements.* Usually in limestone or dolomite as in Missouri, Wisconsin, Illinois and Kentucky; Leadville and Aspen, Colorado; Park City and Tintic, Utah ; Eureka, Nevada; Elkhorn, Mont. ; Derby- shire and Cumberland, England; Raibl and Bleiberg, Carinthia; Iglesias, Sardinia; Sala, Sweden; and Upper Silesia. Contact Deposits. The greatest* lead mine, Broken Hill, New South Wales, was regarded as "saddle lodes, "f p. 328, but is now said to be a contact deposit, the ores intergrown with garnet, rhodonite, etc. Other contact deposits are South Mountain, Idaho, and Magdalen Mines, New Mexico. LEAD. Native Lead. COMPOSITION. Pb, with sometimes a little Sb or Ag. GENERAL DESCRIPTION. Usually small plates or scales or globular masses em- bedded in other minerals. Very rarely in octahedrons or dodecahedrons. PHYSICAL CHARACTERS. Opaque. Lustre metallic. Color and streak lead gray. H., 1.5. Sp. gr., 11.37. 'Malleable. BEFORE BLOWPIPE, ETC. Fuses easily, coating charcoal with yellow oxide, and tinging flame light blue. Soluble in dilute nitric acid. GALENITE. Galena. COMPOSITION. PbS (Pb 86.6 per cent.), usually with some silver and frequently sulphide of antimony, bismuth, cadmium, etc. GENERAL DESCRIPTION. A soft, heavy, lead-gray mineral, with metallic lustre and easy cubical cleavage. Sometimes in crystals. Rarely fine-grained or fibrous. * Deposited as simple sulphides, chiefly galenite and sphalerite, sometimes with pyrite and chalcopyrite. Later oxidation and weathering forms carbonate, sulphate, phosphate, etc. * Said to yield yearly about one ninth of world's production of lead. Beyschlag, Vogt and Krusch, p. 1102. t Ibid., 1173- MINERALS OF METALLIFEROUS ORE DEPOSITS. 319 CRYSTALLIZATION. Isometric. Usually the cube, Fig. 366, or cubo-octahedron, Fig. 367, sometimes octahedral or showing that rare form the trisoctahedron r = (a : a :2a); {221}; Fig. 368. Sometimes twinned or in skeleton crystals or reticulated. FIG. 366. FIG, 367. FIG. 368. Physical Characters. H., 2.5. Sp. gr., 7.4 to 7.6. LUSTRE, metallic OPAQUE. STREAK, lead-gray. TENACITY, brittle. COLOR, lead-gray. CLEAVAGE, cubic, very easy. BEFORE BLOWPIPE, ETC. On charcoal decrepitates and fuses easily, yielding in O. F. a white sulphate coat, and in R. F. a yellow coat and metallic button of lead. With bismuth flux, gives a strong iodide coat, which appears chrome-yellow on plaster and greenish-yellow on charcoal. With soda, yields malleable lead and a sulphur test. Soluble in excess of hot hydrochloric acid, from which white lead chloride separates on cooling. Soluble also in strong nitric acid, with separation of sulphur and lead sulphate. SIMILAR SPECIES. Characterized by its cleavage, weight and appearance, except in some fine-grained varieties. REMARKS. The occurrences have been described, p. 317. The great producing states in 1914 were Missouri, 192,612; Idaho, 174,263; Utah, 85,622; Colorado, 37,106 (short tons of lead). USES. It is the chief ore of lead, and as it usually contains silver, the silver-bearing deposits are more frequently worked than the purer galenite, and both the lead and silver are recovered. BOURNONITE. COMPOSITION. PbCuSbSa, (Pb 42.5, Cu 13.0, Sb 24.7, S 19.8 per cent.). GENERAL DESCRIPTION. A gray metallic mineral, nearer steel-gray than galenite, and occurring fine-grained, massive and in thick tabular crystals, or cross Fig. 370, and "cog-wheel" twins. Supplement angles mm = 86 20', co = 43 43', cu = 33 320 MINERALOGY, FIG. 369. FIG. 370. Harz. Kapnik. PHYSICAL CHARACTERS. Opaque. Lustre, metallic. Color, steel-gray to nearly black. Streak, steel-gray. H., 2.5 to 3. Sp. gr., 5.7 to 5.9. Brittle. Cleavages imperfect. BEFORE BLOWPIPE, ETC. On charcoal, fuses easily, yielding heavy white sub- limate, and later a yellow sublimate. With bismuth flux yields strong greenish- yellow coat on charcoal and a mingling of chrome yellow and peach red on plaster. After sublimates have formed, the residue will color 'the flame deep green, or if mois- tened with a drop of hydrochloric acid, will color the flame bright azure blue. Soluble in nitric acid to a green solution, with formation of a white insoluble residue. REMARKS. Occurs as secondary mineral in veins as at Kapnik, Hungary; Endellion, Cornwall; Reported in Yavapai Co., Arizona. JAMESONITE. Feather Ore. COMPOSITION. Pb 2 Sb 2 S 5 . (Pb 50.8, Sb 29.5, S 19.7 per cent.). GENERAL DESCRIPTION. Steel-gray to dark-gray metallic needle crystals, or hair- like and felted; also compact and fibrous massive. PHYSICAL CHARACTERS. Opaque. Lustre, metallic. Color, steel-gray to dark- lead gray. Streak, grayish-black. H., 2 to 3. Sp. gr., 5.5 to 6. Brittle. BEFORE BLOWPIPE, ETC. Decrepitates and fuses very easily, and is volatilized, coating the charcoal white and yellow as in bournonite. With bismuth flux, reacts like bournonite. In closed tube, yields dark-red sublimate, nearly black while hot. Soluble in hot hydrochloric acid, with effervescence of hydrogen sulphide. REMARKS. Secondary in veins with stibnite as at Freiberg, Saxony, and Sevier Co., Arkansas; or with galenite as at Przibram. In Zimapan, Mexico, occurrs in com- mercial quantity. The following four species are representative of a series of secon- dary minerals formed in lead and antimony veins. In blowpipe characters all are like jamesonite. Hardness, 2.5 to 3.5. The specific gravity, 5.3 to 6.5, increases with the lead. ZINKENITE. PbS.Sb 2 S 3 . Columnar and fibrous steel-gray material from Wolfs- berg, Harz, Sevier Co., Ark., etc. PLAGIONITE. 5PbS.4Sb 2 S 3 . Druses of short thick notably oblique (monoclinic) crystals of dark lead gray color from Wolf ach, Baden; Wolfsberg, Harz, etc. BOULANGERITE. 3PbS.Sb2S 3 . Feathery masses and needle crystals'of bluish lead gray color, often covered with yellow spots due to oxidation. From Echo District, Nevada; Bottino, Tuscany, etc. GEOCRONITE. 5PbS.Sb 2 S 3 . Light lead gray massive granular material from Sala, Sweden and Inyo Co., Calif. MINERALS OF METALLIFEROUS ORE DEPOSITS. 321 CLAUSTHALITE. COMPOSITION. PbSe, (Pb 72.4, Se 27.6 per cent.)- Many contain silver or cobalt GENERAL DESCRIPTION. Bluish gray fine granular masses of metallic lustre. Rarely foliated. Resembles galenite. PHYSICAL CHARACTERS. Opaque. Lustre, metallic. Color, bluish lead gray. Streak, grayish black. H., 2.5 to 3. Sp. gr., 7.6 to 8.8. BEFORE BLOWPIPE, ETC. On charcoal fuses and yields odor like decayed horse- radish, coats the charcoal with a white sublimate with red border, and later a yellow coat forms. In open tube gives a red sublimate. With soda yields a mass which blackens silver. MINIUM. COMPOSITION. Pb O 4 . (Pb 90.6 per cent.). GENERAL DESCRIPTION. A vivid red powder or loosely compacted mass of dull or greasy lustre. Often intermixed with yellow. PHYSICAL CHARACTERS. Opaque. Bright red. Lustre, dull or greasy. Streak, orange yellow. H., 2 to 3. Sp. gr., 4.6. BEFORE BLOWPIPE, ETC. Is reduced to metallic lead, and yields the characteristic lead sublimates. REMARKS. The artificial product is the red lead of commerce. Chiefly an altera- tion of galenite or cerussite, sometimes pseudomorphous after them. Occurs Wythe Co., Virginia; Leadhills, Scotland; Bleialf, Eifel; Brilon, Westphalia, etc. ANGLESITE. COMPOSITION. PbS0 4 , (PbO 73.6, SO 3 264 per cent.). GENERAL DESCRIPTION. Simple crystals, often transparent and colorless, white brittle masses and compact granular masses of gray color from intermixed galenite. Sometimes in concentric layers around a core of unaltered galenite. FIG. 371. FIG. 372. Phoenixville, Pa. CRYSTALLIZATION. Orthorhombic. Axes a : b : c 0.785 : i : 1.289. Crystals vary greatly in type, but are rarely twinned. Unit prism m and domes such as n = (a : oo b : Y^c); {102} ; z = (a : oo b : %c]\ (104) ; and pyramids q = (20, :b : c); {122} are frequent. Supplement angles: mm = 76 17'; en = 33 24'; cz = 22 19'; cq = 56 48'- 322 MINERAL OGY. Physical Characters. H., 3. Sp. gr., 6.12 to 6.39. LUSTRE, adamantine to vitreous. TRANSPARENT to opaque. STREAK, white. TENACITY, very brittle. COLOR, colorless, white, gray; rarely yellow, blue or green. CLEAVAGE, basal and prismatic (90 and 103 43')- BEFORE BLOWPIPE, ETC. On charcoal decrepitates and fuses easily to a glassy globule pearly white on cooling. In R. F. is re- duced and yields metallic lead and the yellow sublimate. With soda yields the sulphar reaction. Insoluble in hydrochloric acid but is converted into chloride. Slowly soluble in nitric acid. SIMILAR SPECIES, It differs from the carbonate, cerussite, in absence of twinned crystals and of effervescence in acids. It is heavier than barite and celestite, and yields lead. REMARKS. Anglesite is formed by the oxidation of galenite and found wherever exposed deposits of galenite occur. Large quantities have been found in Sierra Mojada, Mexico; Leadville, Colorado; Cerro Gordo, California; Yuma Co., Arizona. An earthy variety occurs near Coquimbo, Chili. Famous localities for crystals are Monte Poni Sardinia; Wheatley's Mine, Pennsylvania; Anglesey, England and Felsobanya, Hungary. LINARITE. [(PbCu)OH] 2 SO4. In small, deep blue, monoclinic crystals. PYROMORPHITE. COMPOSITION. Pb 5 Cl(PO 4 ) 3 , (PbO 82.2, P 2 O 5 15.7, Cl 2.6 per cent.) often with some As, Fe or Ca. GENERAL DESCRIPTION. Short hexagonal prisms and branching and tapering groups of prisms in parallel position. The color is most frequently green, brown, or gray. Also in moss-like interlaced fibers and masses of imperfectly developed crystals. Less frequently in globular and reniform masses. CRYSTALLIZATION. Hexagonal, class of third order pyramid, P- 57- Axis c = 0.736. Usual form prism m and base c. Faces m horizontally striated, sometimes tapering. Physical Characters. H., 3.5 to 4. Sp. gr., 5.9 to 7.1. LUSTRE, resinous. TRANSLUCENT to opaque. STREAK, white to pale yellow. TENACITY, brittle. COLOR, green, gray, brown; also yellow, orange, white. BEFORE BLOWPIPE, ETC. On charcoal fuses to a globule which on cooling does not retain its globular form but crystallizes, show- MINERALS OF METALLIFEROUS ORE DEPOSITS. 323 ing plane faces. In reducing flame yields white coat at a distance and yellow coat nearer the assay, and a brittle globule of lead. In closed tube with magnesium ribbon yields a phosphide which, moistened with water, evolves phosphine. With salt of phos- phorus saturated with copper oxide yields an azure blue flame. Soluble in nitric acid, and from the solution ammonium molybdate throws down a yellow precipitate. SIMILAR SPECIES. Differs from other lead minerals in fusing to a crystalline globule without reduction. REMARKS. A decomposition product of galenite and other lead minerals occurring near the outcrop and sometimes in sufficient quantities to be smelted. Found at Phoenixville, Pa., Davidson county, N. C., Lenox, Me., Cour d'AIene, Idaho, and in many foreign localities, notably Huelgoet, Brittany; Ems, Nassau; Berezov, Siberia; Cornwall, Derbyshire and Cumberland, England; Leadhills, Scotland. MIMETITE. 3Pb 3 (AsO 4 )2 + PbChsor Pb 6 Cl(AsO 4 )3, of ten with some replacement by P or Ca. Pale yellow to brown hexagonal prisms or globular groups of crystals. Sometimes incrusting. Streak, white. H., 3.5. Sp. gr., 7.0 to 7.25, lower when Ca is present. On charcoal fuses easily and is reduced to metallic lead, coating the coal with white and yellow sublimates and yielding strong arsenical odor. Found in Cumber- land, England; Cerro Gordo, Calif.; Yuma Co., Arizona, etc. CERUSSITE. White Lead Ore. COMPOSITION. PbCO 3 , (PbO, 83.5 ; CO 2 , 16.5 per cent.). Often carries silver. GENERAL DESCRIPTION. Very brittle, white or colorless ortho- rhombic crystals; silky, milk-white masses of interlaced fibres; granular, translucent, gray masses and compact or earthy, opaque masses of yellow, brown, etc., colors. FIG. 373. FIG. 374. CRYSTALLIZATION. Orthorhombic. Axes a : b : c = 0.610 : i : 0.723. Common forms: unit pyramid p, and prism m and a series of brachy domes such as x = (> a : b : %); {012} ; w = (<*> a : 324 MINERALOGY. b : 2c); {021} andv = (oo a : b : y); {031}. Frequently twinned about m sometimes yielding six-rayed groups as in Fig. 374. Supplement angles are mm = 62 46', pp = 50, ww = 110 40'. Physical Characters. H., 3 to 3.5. Sp. gr., 6.46 to 6.51. LUSTRE, adamantine, silky. TRANSPARENT or translucent. STREAK, white. TENACITY, very brittle. COLOR, white, gray, colorless or colored by impurities. CLEAVAGES, parallel to prism and brachy dome. BEFORE BLOWPIPE, ETC. On charcoal, decrepitates, fuses and gives a yellow coating, and finally a metallic globule. In closed tube, turns yellow, then dark, and on cooling is yellow. Effer- vesces in acids, but with hydrochloric or sulphuric acid leaves a white residue. SIMILAR SPECIES. Distinguished from anglesite by efferves- cence in acids and by frequent occurrence of twinned crystals. Has higher specific gravity than most carbonates. REMARKS. Found in the oxidized zone of lead deposits. Formerly the principal mineral of the Leadville, Colorado deposits and in large masses in Pima Co., Arizona. Now abundant at Cour d'Alene, Idaho; Cerro Gordo, California, and especially Broken Hill, New South Wales. PHOSGENITE. Pb2Cl 2 CO 3 . In transparent, colorless or gray tetragonal crystals. THE BISMUTH MINERALS. The minerals described are: Metal Bismuth Bi Hexagonal Sulphide Bismuthinite Bi 2 S 3 Orthorhombic Tetturide Telradymite Bi 2 (Te.S) 8 Hexagonal Carbonate Bismutite (BiO) 2 CO 3 .H 2 O Oxide Bismite Bi 2 3 Orthorhombic Bismuth is the metallic element in other species such as pucherite, eulytite, cheleutite, and aikinite, and a constituent of a series of so-called sulpho-bismutites.* ECONOMIC IMPORTANCE. The important ores are bismuthinite, bismuth and bismite. The world's supply comes chiefly from Bolivia, the principal company producing 437 tons in 1914 and this country following with no, tons obtained entirely as a by-product in electrolytic lead refining, * Such as chiviatite, cuprobismutite, emplectite, matildite and klaprotholite. MINERALS OF METALLIFEROUS ORE DEPOSITS. 325 largely from unidentified species, and Peru and Australia supplying the rest. The uses of bismuth are chiefly dependent upon its property of forming easily fusible alloys with other metals, especially tin, lead, and cadmium. These alloys expand in cooling, and are therefore used in type metal, in reproducing woodcuts, in making safety plugs for boilers, etc. Also in anti-friction metals and pewter. The salts of bismuth have numerous uses in medicine and in the arts, are used in calico printing, cosmetics, as pigments, in making glass of high refractive po\ver, and to impart lustre to porcelain. In Saxony the ores are first roasted to free them from sulphur r arsenic and other volatile constituents. After roasting they are smelted in crucibles with iron, charcoal and slag, the melted bismuth settling out in the bottom of the crucible ; or the roasted ores may be treated with strong hydrochloric acid (i : i) which dissolves the bismuth and from which it is precipitated as oxychloride by the addition of water. The metal may be further purified electro- lytically. When bismuth is found to be present in the cupellation of lead ore, it is recovered by saving the last products of oxidation. From this by solution in hot hydrochloric acid and precipitation as oxychloride the bismuth may be recovered. More recentlyf the cupellation slag is fused with sodium sulphate and carbon at about 1500 C. giving three layers bismuth, copper matte, and soda slag. FORMATION AND OCCURRENCE OF BISMUTH DEPOSITS. Veins. The usual occurrence is in veins as in the cobalt bismuth veins at Schneeberg, Saxony, the silver cobalt veins of Joachims- thai, Bohemia* the tin silver veins of Bolivia, and various gold veins. Pegmatites. Bismuth in quantity may also occur in pegmatites as in New South Wales. * Eng. & Min. Journ. 1916, p. 82. f Mineral Resources U. S., 1914. % U. S. Patent 1,098,854. 326 MINERALOGY. BISMUTH. Native Bismuth. COMPOSITION. Bi, often alloyed with As or impure from S or Te. GENERAL DESCRIPTION. A brittle silver-white mineral with a reddish tinge, often in branching shapes or in isolated grains or cleavable masses. Physical Characters. H., 2 to 2.5. Sp. gr., 9.7 to 9.83. LUSTRE, metallic. OPAQUE. STREAK, silver white. TENACITY, sectile to brittle. COLOR, reddish silver white. BEFORE BLOWPIPE, ETC. On charcoal fuses easily and vola- tilizes completely, coating the charcoal with a yellow sublimate. With bismuth flux forms a chocolate brown and red coating which is best seen on plaster, and which is changed by action of ammonia fumes to red and orange. Sojuble in strong nitric acid from which solution water will precipitate a white basic salt. SIMILAR SPECIES. Bismuth is characterized by its silver streak, reddish tinge, and arborescent structure. REMARKS. Bismuth in economic quantity is found in the tin silver veins of Tasna .and Chorolque, Bolivia, in a gold-bearing magnetite in Queensland, Australia, in a pegmatite in New England district, New South Wales and in the silver, cobalt and tin veins of Saxony and Bohemia. The metal is not found in any quantity in the United States, although obtained at Monroe, Conn., Colorado, in Inyo Co., California, .and in Chesterfield district, South Carolina. BISMUTHINITE. COMPOSITION. Bi2S 8 , (Bi 81.2, S 18.8 per cent.). May contain Cu or Fe. GENERAL DESCRIPTION. A lead gray mineral of metallic lustre usually occurring in foliated or cleavable masses, or in groups of long needle-like orthorhombic crystals. PHYSICAL CHARACTERS. Opaque. Lustre, metallic. Color, lead gray or lighter, often with yellow tarnish. Streak, lead gray. H., 2. Sp. gr., 6.4 to 6.5. Slightly sectile. BEFORE BLOWPIPE, ETC. On charcoal yields some sulphur, fuses easily with spirting, and coats the coal with white and yellow sublimates. Yfelds the character- istic bismuth reactions with bismuth flux and with nitric acid as described under bismuth. With soda gives sulphur reaction. REMARKS. Bismuthinite occurs in the tin veins of Bolivia and Cornwall, in a pegmatite in New England district, New South Wales, in hornstone at Wolfach, Baden, and in Meymac, France. In this country at Beaver Co., Utah, and Inyo Co., California. TETRADYMITE. COMPOSITION. Bi 2 (Te.S)s or BiTeS. Either an alloy or a telluride of bismuth. GENERAL DESCRIPTION. Very soft, flexible, foliated masses of steel-gray color MINERALS OF METALLIFEROUS ORE DEPOSITS. 327 and bright metallic lustre, or small indistinct rhombohedral crystals. Will mark paper like graphite. PHYSICAL CHARACTERS, ETC. Opaque. Lustre, metallic. Color, pale steel- gray. Streak, gray. H., 1.5 to 2. Sp. gr., 7.2 to 7.6. Flexible in laminae. Cleav- age, basal. BEFORE BLOWPIPE, ETC. On charcoal fuses easily and is completely volatilized, yielding a white fusible sublimate, followed by a yellow sublimate. The flame during fusion is colored blue. The white sublimate if placed on porcelain and moistened with concentrated sulphuric acid becomes rose colored. If dropped into boiling concentrated sulphuric acid a deep violet color is produced. REMARKS. Occurs especially in gold veins or with gold as at Schubkau, Hungary"; Orawitza, Banat; Tellemark, Norway, and in this country in Virginia, North and South Carolina, Georgia and Montana. In quartz with gold in Arizona. BISMUTITE. COMPOSITION. (BiO^COs, HzO, variable. GENERAL DESCRIPTION. A light colored incrustation or earthy mass or powder. PHYSICAL CHARACTERS. Opaque. Lustre, dull or vitreous. Color, white, green and yellow. Streak, colorless to greenish. H., 4-4.5. Sp. gr., 6.9-7.7. Tenacity, brittle. BEFORE BLOWPIPE, ETC. Fuses easily on charcoal, giving a yellow coat and in R. F. a metallic globule which completely volatilizes. With bismuth flux on plaster gives brown and red coat. Yields water in closed tube and decrepitates. Soluble with effervescence in strong HC1, and on dilution with much water the white oxy- chloride of bismuth is precipitated. REMARKS. It is usually associated with metallic bismuth or the sulphide and occurs at Brewer's Mine, S. C., Phcenix, Arizona, Inyo Co., Calif. BISMITE. Bismuth Ochre. COMPOSITION. Bi2Oa, Bi 89.6 per cent, when pure. GENERAL DESCRIPTION. A yellowish or gray powder or earthy mass. PHYSICAL CHARACTERS. Opaque. Color, grayish, greenish or yellowish white. Lustre, dull. BEFORE BLOWPIPE, ETC. As for bismutite but does not effervesce with acids nor yield water in closed tube. REMARKS. The 400 ft thick "gossan" of the Schneeberg mines contains much bismite. It forms part of the bismuth at Bamford, Australia, and several mines in Colorado but in general is only a coating on other bismuth species. THE ARSENIC MINERALS. The minerals described are: Metal Arsenic As Hexagonal Sulphides Orpiment As 2 S 3 Orthorhombic Realgar As 2 S 2 Monoclinic Sulpharsenide Arsenopyrite FeAsS Orthorhombic Arsenide Lollingile FeA S2 ** Other species in which arsenic is an essential constituent are: 328 MINERALOGY. niccolite, mimetite, olivenite, smaltite, enargite, proustite, cobaltite, tennantite, and sperrylite. ECONOMIC IMPORTANCE. A rsenopyrite and lollingite are sometimes mined for their arsenic but to a very great extent arsenic is obtained as a by-product in the roasting of ores of other elements such as the cobalt ores of Ontario and certain copper, silver and tin ores. The world's production of "white arsenic," As 2 O 3 , is possibly 100,000 metric tons,f France being the great producer and Ger- many and this country following. In 1914 this country produced 4,670 short tonsj and imported 1,600. Metallic arsenic is ordinarily produced by sublimation from a mixture of the oxide and charcoal, but may be produced by sub- limation at a high heat directly from arsenopyrite out of contact with air. It is a constituent of some useful alloys, shot metal being the chief. The poisonous oxide commonly known as arsenic or white arsenic, is produced in large quantities by the roasting of arseno- pyrite and other arsenical ores and as a by-product in the prepara- tion of tin, silver, nickel and copper. It is used in dyeing, in medicine, in sheep washing, in calico printing, as a preservative for timber and for natural history specimens, in the manufacture of fly paper, and rat poisons, and in glass manufacture. Many important coloring matters as well as the artificial red and yellow sulphides are commercial products. Paris green is an arsenate of copper extensively used as an insecticide. FORMATION AND OCCURRENCE OF ARSENIC DEPOSITS. There are no known metasomatic replacements of arsenopyrite or other arsenic minerals. Veins. (Arsenopyrite, lollingite orpiment, realgar.} Arsenopyrite as at the Devon Great Consol. Mine, and carrying gold as in the Saddle * Others are gersdorffite, rammelsbergite, skutterudite. t Statistics (incomplete) 1912 gives total of 94,699 metric tons, of which France produced 81,880. Mineral Industry, 1915, p. 50. % Mineral Resources U. S., 1914. Beyschlag, Vogt & Krusch (Truscott), p. 923. MINERALS OF METALLIFEROUS ORE DEPOSITS. 329 lodes of Bendigo, West Australia, and Deloro, Canada. Realgar and orpiment as at Kapnik, Hungary. Contacts. The gold-bearing loltingite and arsenopyrite of Riechenstein, Silesia, occur as irregular lenses in highly altered tourmaline-bear- ing schists, the lollingite intergrown with contact minerals such as diopside, vesuvianite, titanite, fluorite. Orpiment and realgar are also stated* to occur in contacts. ARSENIC. Native Arsenic. COMPOSITION. As, generally with some Sb and sometimes with Bi or a little Co, Ni, Fe, Ag or Au. GENERAL DESCRIPTION. A tin-white metal, tarnishing almost black. Usually granular, massive, with reniform surfaces. Can frequently be separated in concentric layers. Rarely found in needle-like crystals. PHYSICAL CHARACTERS. Opaque. Lustre, nearly metallic. Color, tin white, tarnishing nearly black. Streak, tin white. H., 3.5. Sp. gr., 5.63 to 5.73. Brittle. Granular fracture. BEFORE BLOWPIPE, ETC. On charcoal, volatilizes without fusion, yielding strong garlic odor, white fumes, crystalline white sublimate and pale blue flame. May leave a residue of impurities. REMARKS. Principally as a minor constituent of silver or cobalt-nickel veins as in many mines in Saxony, Bohemia and the Harz, the silver veins of Kongsberg, Norway; Chanarcillo, Chili; and Hidalgo, Mexico. It was found also in pockets in dolomitic limestone in Santa Cruz Co., Arizona; and in a vein in a quarry near Montreal. REALGAR. COMPOSITION. As 2 S 2 , (As, 70.1; S, 29.9 per cent.). GENERAL DESCRIPTION. A soft, orange-red mineral, of resinous lustre, usually occurring in translucent, granular masses, but also compact and in transparent monoclinic crystals. Physical Characters. H., 1.5 to 2. Sp. gr., 3.4 to 3.6. LUSTRE, resinous. TRANSLUCENT to transparent. STREAK, orange red. TENACITY, slightly sectile. COLOR, aarora red, becoming orange yellow on long exposure. BEFORE BLOWPIPE, ETC. On charcoal, fuses easily, barns with a blue flame, yields white fumes, with garlic odor and also odor of sulphur dioxide and is volatilized completely. In closed tube yields red sublimate. Soluble in nitric acid, with separation of sulphur. Soluble also in potassium hydroxide from which hy- drochloric acid precipitates yellow flakes. *'ibid. t in. 330 MINERALOGY. REMARKS. Occurs with orpiment and sometimes with cinnabar as a deposit from hot springs, as in the Yellowstone, also in ore veins as at Kapnik, Hungary, and Schneeberg, Saxony. ORPIMENT. COMPOSITION. As 2 S 3 , (As, 61; S, 39 per cent.). GENERAL DESCRIPTION. Lemon-yellow, foliated masses, which cleave into thin, pearly, flexible scales, and also granular masses like yolk of hard-boiled eggs. Less frequently as reniform crusts and imperfect orthorhombic crystals. Physical Characters. H., 1.5 to 2. Sp. gr., 3.4 to 3.6. LUSTRE, resinous or pearly. TRANSLUCENT to nearly opaque. STREAK, lemon yellow. TENACITY, slightly sectile. COLOR, lemon yellow. CLEAVAGE, in plates or leaves. BEFORE BLOWPIPE, ETC. As for realgar, except that the sub- limate in closed tube is yellow. REMARKS. Often formed by alteration of realgar in air and sunlight and found with it both in ore veins as at Kapnik and Felsobanya, Hungary, and in clay as at Tajowa, Hungary, and Tooele and Iron Counties, Utah. Also a sublimation product near Naples or deposited from hot water as at Steamboat Springs, Nevada. Other occurrences are in brown coal in Styria, in gypsum in Hall, Tyrol. Foliated masses occur at Moldawa, Banat. ARSENOPYRITE. Mispickel. COMPOSITION. FeAsS. (Fe 344, As 46.0, S 19.6 per cent.) sometimes with replacement of iron by cobalt, or arsenic by anti- mony in part. GENERAL DESCRIPTION. Silver white to gray mineral with metallic lustre. Usually compact or in granular masses or dis- seminated grains. Less frequently in orthorhombic crystals or columnar. CRYSTALLIZATION. Orthorhombic a : b : c = 0.677 : J ' 1.188. Common forms, unit prism m combined with a brachy dome either d = (cod: b: c}\ {on} or e = (cod: b: Jc); (014). Crossed twins, Fig. 377, occur and fivelings, as in Fig. 197 of marcasite. Supplement angles mm = 68 13', dd = 99 50', ee = 33 05'. Physical Characters. H., 5.5 to 6. Sp. gr., 6 to 6.2. LUSTRE, metallic. OPAQUE. STREAK, grayish-black. TENACITY, brittle. COLOR, silver white to steel gray. MINERALS OF METALLIFEROUS ORE DEPOSITS. 331 BEFORE BLOWPIPE, ETC. Strikes fire with steel and yields an odor like that of garlic. In closed tube a red sublimate, yellow when cold, on longer treatment a black sublimate. On charcoal yields abundant white fumes and arsenical odor and coating and fuses to a magnetic globule. After short treatment the residue is FIG. 375. FIG. 376. FIG. 377. soluble in hydrochloric acid with evolution of hydrogen sulphide and precipitation of the yellow sulphide of arsenic. The residue may react for cobalt. Insoluble in hydrochloric acid. Soluble in nitric acid with separation of sulphur. SIMILAR SPECIES. Massive varieties of the metallic cobalt min- erals and varieties of leucopyrite resemble arsenopyrite but are safely distinguished by blowpipe tests, especially the closed tube test. REMARKS. Arsenopyrite is found chiefly in crystalline schists and the veins which penetrate them associated with ores of silver, cobalt, tin, zinc, etc. Frequently gold-bearing and worked as gold ore as at Deloro, Canada; Passagem, Brazil; and localities in New South Wales. Sometimes carries cobalt (New England) or nickel (Bolivia) and sometimes is in quantity sufficient to be mined for its arsenic (Great Consols Mine, Devonshire). LOLLINGITE. Leucopyrite. COMPOSITION. Fe 3 As 4 to FeAs 2 sometimes with Co, Ni, Au or S. GENERAL DESCRIPTION. Massive silver-white or gray metallic mineral some- times occurring in orthorhombic crystals, closely agreeing in angles with crystals of arsenopyrite. PHYSICAL CHARACTERS. Opaque. Lustre, metallic. Color, silver-white or gray. Streak, grayish-black. H., 5 to 5.5. Sp gr., 7 to 7.4. Brittle. Cleavage, basal BEFORE BLOWPIPE, ETC. Like arsenopyrite, except that sulphur reactions are less pronounced or do not appear at all. REMARKS. Lollingite is the principal mineral at Reichenstein, Silesia, and is mined for its arsenic. 332 MINERALOG Y. THE ANTIMONY MINERALS. The minerals described are: Metal Antimony Sb Hexagonal Sulphides Stibnite Sb 2 S 3 Orthorhombic Kermesite Sb2S2O Monoclinic Oxides Valentinite SbzOs Orthorhombic Senarmontite SbaOs Isometric Antimony Ochre Sb 2 O 4 + wH 2 O Other species containing antimony are numerous, especially compounds with lead and sulphur. Species described elsewhere* are jamesonite, bournonite, tetrahedrite, livingstonite, pyrargyrite, stephanite, dyscrasite. ECONOMIC IMPORTANCE. The world production of metallic antimony is about 25,000 tons per year, principally f from China and France. In addition to this there is a considerable production of antimonial lead. In 1914 no metallic antimony was produced directly in this country but 2,705 tons either in antimonial lead or as a by- product in refining copper. In 1915! owing to increased demands some smelters were working on ore from Alaska, Mexico and California. The principal use of antimony is in hardening alloys of lead, etc., such as type metal, pewter and babbitt metal. Both the metal and the oxide are used in making flint glass. The sulphide is used in vulcanizing rubber, and in safety matches, percussion caps and fireworks, and there are numerous uses for different salts such as "tartar emetic" in medicine and others in pigments and dyes. In smelting, the ore is heated and the melted sulphide drained off. The sulphide may then be roasted, forming the oxide, which is easily reduced by fusion with charcoal, or more frequently the sulphide is mixed with wrought-iron scraps and salt, placed in a crucible or furnace and fused. The iron combines with the sulphur and the metallic antimony settles to the bottom. In a later method the sulphide ore and oxy sulphide residue * Others are volgerite, guejarite, berthierite, nadorite, etc. t In 1910, 20,536 metric tons of which China produced 13,032, France 6,390, Hungary 1,038. Mineral Industry, 1914, p. 47. t Engineering and Mining Journal, 1916, p. 79. MINERALS OF METALLIFEROUS ORE DEPOSITS. 333 from a former operation are treated by a blast of air in a converter. The sulphide becomes volatile oxysulphide and is carried off and condensed. Some metallic antimony is tapped and the oxysul- phide is subsequently distilled with a reducing agent. THE FORMATION AND OCCURRENCE OF ANTIMONY DEPOSITS. There are no great antimony deposits.* Most frequently the occurrence is in narrow veins of little depth in or near eruptive rocks and there are a few metasomatic replacements and some beds of disputed origin. The usual primary mineral is stibnite which may be auriferous and the usual oxidized product antimony ochre, though in the Algerian deposits senarmontite and valentinite predominate. Veins. In central France are many narrow veins of stibnite which some- times widen into lenses, as at Freycenet, Puy de Dome; La Lin- coulne is a prominent locality. The veins are in granite, gneiss, mica schist, graywacke, etc. The veins of lyo and Sujo, Japan, are in schists and sometimes in sediments near contacts with quartz porphyry. Replacements. At Allkhar, Macedonia, a body of solid stibnite without gangue replaces dolomite. Near the surface it is antimony ochre. The beds of senarmontite with a little stibnite and some zinc and lead minerals at Djebel-Hamimat and Sidi Rgheiss, Algeria; are conformable to the containing beds of limestone and marl and have been called sedimentary but are thought to be replacements. f Ore Beds. Stibnite with jamesonite, zinkenite, etc., occurs in Sevier Co., Arkansas, in lenticular masses in sandstone and marl. ANTIMONY. Native Antimony. COMPOSITION Sb, sometimes with As, Fe or Ag. GENERAL DESCRIPTION. A very brittle, tin-white metal, usually massive, with fine, granular, steel-like texture or lamellar or radiated. Very rarely in rhombohedral crystals or complex groups. PHYSICAL CHARACTERS. Opaque. Lustre, metallic. Color, tin white. Streak tin white. H., 3 to 3.5. Sp. gr., 6.5 to 6.72. Very brittle. * Beyschlag, Vogt and Krusch (Truscott), 777. t Ibid., 1190. 334 MINERAL OGY. BEFORE BLOWPIPE, ETC. Fuses very easily, colors the flame pale green, gives copious white fumes, which continue to form as a thick cloud after cessation of blast, and often yield a crust of needle-like crystals. REMARKS. Antimony to the amount of at least a ton was found in a quartz stibnite vein in argillite slate in Prince William, New Brunswick. Small amounts occur in Kern Co., California, and in Andreasberg, Harz; Allemont, France; Huasco, Chili; Sarawak, Borneo, and other localities. STIBNITE. Gray Antimony. COMPOSITION. Sb 2 S 3 , (Sb 71.8, S 28.2 per cent.). Sometimes contains silver or gold. GENERAL DESCRIPTION. A lead-gray mineral of bright metallic lustre, occurring in imperfectly crystallized masses, with columnar or bladed structure; less frequently in distinct, prismatic, ortho- rhombic crystals or confusedly interlaced bunches of needle-like crystals; also in granular to compact masses. CRYSTALLIZATION. Orthorhombic. Axes a : b : c = 0.993 : i : 1.018. Prismatic forms, often bent and curved or in divergent groups. The vertical planes are striated longitudinally. Common forms: unit prism m, unit pyramid p and pyramid s = (a : b : %c)\ {113}. Supplement angles mm = 89 34'; pp = 70 48'; 55 = 35 36'. Physical Characters. H., 2. Sp. gr., 4.52 to 4.62. LUSTRE, metallic. OPAQUE. STREAK, lead gray. TENACITY, brittle to sectile. COLOR, lead gray, often with black or iridescent tarnish. CLEAVAGE, easy, parallel to brachy pinacoid, yielding slightly flexible, blade-like strips. BEFORE BLOWPIPE, ETC. On charcoal, fuses very easily, yield- ing the same dense sublimate as antimony. The odor of sulphur dioxide may also be noticed. On charcoal, with soda, yields sulphur test. In closed tube fuses easily, yields a little sulphur and a dark sublimate which is brownish red when cold. Soluble completely in strong boiling hydrochloric acid, with evo- lution of H2S, with precipitation of white basic salt on addition of water and after dilution an orange precipitate on addition of H 2 S. Strong nitric acid decomposes stibnite into white Sb 2 O5 and S { Strong hot solution of KOH colors stibnite yellow and partially dissolves it. From the solution hydrochloric acid will throw down an orange precipitate. MINERALS OF METALLIFEROUS ORE DEPOSITS. 335 SIMILAR SPECIES. Differs from galenite in cleavage, and from all sulphides by ease of fusion and cloud-like fumes. REMARKS. Occurs as described p. 333, in narrow veins and as irregular replace- ments in limestone and in beds of disputed origin. The most important localities are Hunan, China, and the central plateau of France. Others are Queratero, Mexico; lyo and Sujo, Japan; Borneo; Pereta, Tuscany. In this country it was mined in Arkansas and is obtained from Alaska and California. KERMESITE. Red Antimony. COMPOSITION. Sb 2 S 2 O or 2Sb 2 S 3 -Sb 2 O 3 , (Sb 75.0, S 20.0, O 5.0 per cent.). GENERAL DESCRIPTION. Fine hair-like tufts of radiating fibers and needle-like crystals, of a deep cherry-red color and almost metallic lustre. PHYSICAL CHARACTERS. Nearly opaque. Lustre, adamantine. Color, dark cherry red. Streak, brownish red. H., I to 1.5. Sp. gr., 4.5 to 4.6. Sectile and in thin leaves slightly flexible. BEFORE BLOWPIPE, ETC. As for stibnite. REMARKS. Kermesite results from partial oxidation of stibnite. Extensive de- posits exist at Pereta, Tuscany. VALENTINITE. COMPOSITION. Sb 2 O 3 , (Sb, 83.3 per cent.). GENERAL DESCRIPTION. Small white flat crystals ( orthorhombic ) or radiating groups of silky lustre and white or gray color. Also in spheroidal masses with radiated lamellar structure. PHYSICAL CHARACTERS. Translucent. Lustre, adamantine or silky. Color, white, gray, pale red. Streak, white. H., 2.5 to 3. Sp. gr., 5.57. BEFORE BLOWPIPE, ETC. Fuses easily, coating the charcoal with white oxide. In R. I. is reduced, but again oxidizes and coats the coal, coloring the flame green. Solu- ble in hydrochloric acid. REMARKS. Occurs in quantity in radiated form at Ain Bebbouch, Algiers; and massive at Kostainik, Servia. In other localities as Rosia, Tuscany; Braunsdorf, Saxony, in crystals. SENARMONTITE. COMPOSITION. Sb 2 O 3 , (Sb, 83.3 per cent.). GENERAL DESCRIPTION. Colorless to gray octahedral crystals and granular masses. PHYSICAL CHARACTERS. Transparent to translucent. Lustre, resinous. Color, colorless or gray. Streak, white. H., 2 to 2.5. Sp. gr., 5.22 to 5.30. BEFORE BLOWPIPE, ETC. Like valentinite. REMARKS. Occurs as large replacement deposit in clay and limestone at Djebel- Hamimat, Algeria. Elsewhere chiefly as small crystals on other antimony minerals as at Kostainik, Servia, and Wolfe Co., Quebec. ANTIMONY OCHRE. Cervantite and Stibiconite. COMPOSITION. Cervantite, Sb 2 O 4 , Stibiconite, Sb 2 O4, H 2 O. GENERAL DESCRIPTION. Pale yellow to reddish white, masses, crusts and powder with greasy lustre or dull. Streak white. H., 4 to 5.5. Sp. gr., 4.08 to 5.28. 336 MINERALOGY. BEFORE BLOWPIPE, ETC. Infusible in forceps. Stibiconite yields water in closed tube, decrepitates and fuses on charcoal. Cervantite yields no water, and on charcoal is easily reduced. REMARKS. These species are the common result of the oxidation of antimony deposits and usually occur together as in Borneo. The extensive deposits in Sonora, Mexico and the upper 60 feet of the Pricov, Bohemia, deposit are called stibiconite while others as at Pereta, Tuscany, are called cervantite. THE VANADIUM MINERALS. The minerals described are: Sulphide Patronite VS 4 (?) Vanadates Vanadinite Pb 5 Cl(VO 4 )3 Hexagonal Descloizite (PbZn) 2 (OH)VO 4 Orthorhombic Hewettite and Metahewettite CaO, 3V 2 O 5 .9H 2 O Silicates Roscoelite Vanadium Mica Other minerals containing vanadium are carnotite, and the briefly described and in part indefinite species mottramite, psitta- cinite, dechenite, volborthite, pucherite, and pascoite. ECONOMIC IMPORTANCE. It was proved* in 1830 that the unusual ductility of the iron made from the Taberg, Sweden, ores was due to the vanadium in the ores. Since that the use of vanadium in iron and steel has slowly increased. Iron castings are made by vanadium finer grained and less porous. It removes oxygen and nitrogen from steel and the combined effect of this and a small amount (0.15 to 0.25 per cent.) retained in the steel enormously increases the tensile strength and thereby the resistance to shock and abrasion. Vanadium steel is increas- ingly used for steel castings for locomotives, automobiles, die blocks, heavy drop forge work, etc. Tough alloys are made with copper, such as vanadium bronze much used for trolley wheels, bronze gearing, etc. The oxide V 2 O5 is used in place of platinum as a catalytic agent in the manufacture of sulphuric acid and other processes and with aniline as a black dye and in making an indelible ink. This country produced in 1914 carnotite and roscoelite ore con- taining 452 tons of vanadium.f The great source, however, is the * Mining World, 1905, p. 659. f Mineral Resources U. S. 1914, p. 14. MINERALS OF METALLIFEROUS ORE DEPOSITS. 337 patronite of Peru, which is oxidized and reduced either with Thermit or in the electric furnace to form ferro-vanadium. Roscoelite is roasted with salt, the sodium vanadate extracted with water, ferrous sulphate added and the precipitated iron vanadate reduced in the electric furnace. The product is a ferro- vanadium containing 25 to 50 per cent, of vanadium. The proc- ess for vanadinite, now of relatively little importance, involved previous extraction of the lead by reduction with carbon and sodium carbonate, the slag being treated as above. In the production of radium from carnotite, the vanadium re- mains in solution as sodium vanadate from which it is precipitated by ferrous sulphate. THE FORMATION AND OCCURRENCE OF VANADIUM DEPOSITS. Vanadium is not a rare element, it occurs in small amounts in many igneous rocks as V 2 O 3 up to .O3-.O5 per cent, replacing Fe 2 O 3 and Al 2 Os in some pyroxenes (up to 2 per cent.) amphiboles and micas and is almost invariably present in magmatic deposits of titaniferous iron.* (5 analyses average 0.27 per cent.) Not- ably the ore of Taberg, Sweden. Sediments. After weathering of the igneous rocks the vanadium is con- centrated in the resulting clays, sandstones (many of the copper- bearing standsones carry vanadium) and beds of iron ore and eco- nomically important deposits have resulted as in the sandstones of Colorado and Utah, Cheshire, England, and Perm, Russia, and the oolitic limonites of Mafenay, France. It is found in the baux- ites and clays near Paris. The ash of lignites from San Rafael, Mendoza, Argentina and Yauli, Peru, contain about 38 per cent, of V 2 O 5 , and the asphalt grahamite of West Virginia and Oklahoma carries vanadium; the great deposit of vanadium sulphide in Cerro de Pasco is in large part an asphalt containing a large amount of sulphur. Veins. Vanadium also occurs in ore veins and ore bodies, notably with gold as the vanadium mica roscoelite as a primary mineral but more frequently as lead or copper vanadates in the oxidized portions. * Clarke, Bull. 491, 673. 23 338 MINERALOGY. PATRONITE. COMPOSITION. VS 4 (?), (58.79 S, 19.53 V, 1.87 Ni, 3.47 C, per cent.). GENERAL DESCRIPTION. Greenish black, resembling slaty coal, consisting of the vanadium sulphide mixed with metallic sulphides chiefly a nickel bearing pyrite (bravoite) and free sulphur. H. 3.5 and 2.5. Sp. gr. 2.5 and 2.71. BEFORE BLOWPIPE, ETC. No record has yet been made of its blowpipe, etc., characters. On roasting it yields the recorded test, p. 196, with hydrochloric acid. REMARKS.* Found only as a lens-shaped mass 28 feet wide by 350 feet long, filling a fault in red shales (Cretaceous) at Minisraga, Cerro de Pasco, Peru. The larger portion of the mass (called quisqueite H. 2.5, sp. gr., 1.75) is a lustrous black asphalt-like material with more sulphur than carbon which blends in a coke-like material 86 per cent, carbon (H. 4.5, sp. gr. 2.2). Below the lode is a blue black shale containing up to 13 per cent, vanadium oxide. The ore is burned and the ashes carrying the vanadium exported. VANADINITE. V VAIN AUJ. mil!*. COMPOSITION. 3Pb 3 (VO 4 )2.PbCl 2 or Pb 5 Cl(VO 4 ) 3 , (PbO, 78.7; 2 O 5 , 194; Cl, 2.5 per cent.), often with P or As replacing V. FIG. 378. FIG. 379. GENERAL DESCRIPTION. Small, sharp, hexagonal prisms, some- times hollow, of bright-red, yellow or brown color. Also parallel groups and globular masses of crystals. CRYSTALLIZATION. Hexagonal. Class third order pyramid, p. 57. Axis c = 0.712. Simple prism m with base c, or more rarely with pyramid p and third order pyramid v = (fa : 2> a : a: 3c); {2131}, Fig. 379. * See Jour. Am. Chem. Soc., 29, 1907, July, Trans. Am. Inst. Min. Eng., 1909, 292. Bulletin 70, Bureau Mines, p. 55. MINERALS OF METALLIFEROUS ORE DEPOSITS. 339 Physical Characters. H., 3. Sp. gr., 6.66 to 7.23. LUSTRE, resinous on fracture. OPAQUE, or translucent. STREAK, white to pale yellow. TENACITY, brittle. COLOR, deep red, bright red, yellow or brown. BEFORE BLOWPIPE, ETC. Fuses easily on charcoal to a black mass, yielding a yellow sublimate in the reducing flame. The residue gives deep-green bead, with salt of phosphorus in the re- ducing flame. With strong nitric acid the substance becomes deep red, then dissolves to a yellow solution. Fused with KHSCX, yields a clear yellow, then a red, and finally yellow when cold. VARIETIES. Endlichite. The V 2 O5 replaced in part by As 2 O5. REMARKS. Vanadinite occurs in the oxidized zone of lead-bearing veins in many localities especially New Mexico and Arizona. Sometimes the quantity is worth concentrating as at the Mammoth Gold Mine, Arizona, and Cutter, Sierra Co., N. M. Descloizite and wulfenite are common associates. Foreign localities are Dumfries- shire, Scotland, on calamine, Berezof Urals with pyromorphite. The variety endlichite is reported* in quantity in Baraga Co., Michigan, the ore showing 21.5 per cent, vanadium. DESCLOIZITE. COMPOSITION. (Pb.Zn)(PbOH), VO 4 , (PbO, 55-4J ZnO, 19.7; V 2 O 6 , 22.7; H 2 0, 2.2). GENERAL DESCRIPTION. Small purplish-red, brown or black crystals, forming a drusy surface of crust. Also fibrous, massive. PHYSICAL CHARACTERS. Transparent to nearly opaque. Luster, greasy. Color, purplish red, brown or black. Streak, orange or brown. H., 3.5. Sp. gr., 5.9 to 6.2. BEFORE BLOWPIPE, ETC. On charcoal, fuses to black mass, enclosing metal. In closed tube yields water. Vanadium reactions as in vanadinite. VARIETIES. Cuprodescloizite in crusts and reniform masses with radiated structure contains 6.5 to 9 per cent, copper. REMARKS. Descloizite is a frequent associate of vanadinite and at the Mammoth Gold Mine, Arizona, and the Mimbres Mine near Georgetown, New Mexico, was more plentiful than the vanadinite. In Sierra de Cordoba, Argentina, occurs with pyromorphite and vanadinite. The variety cuprodescloizite has been found in considerable quantities at Charcas, San Luis Potosi and Zacatecas, Mexico, and near Bisbee, Arizona; also in Otavi, German East Africa. Less important vanadates are: MOTTRAMITE (CuPb) 5 V 2 Oio 2H 2 O). Thin, blackish green incrustations upon the Keuper sandstone at Mottram, St. Andrews, Cheshire, England. Streak yellow, H = 3, G = 5-9- PSITTACINITE. 4(CuPb)O.V 2 O 6 H 2 O, thin greenish incrustations on quartz in Silver Star District, Montana. Also Laurium, Greece. * Mineral Industry, 1914, p. 762. 340 MINERAL OGY. DECHENITE. PbV^Oe. Massive botryoidal red to yellow. Streak orange yellow. H., 3 to 4. Sp. gr. 5.6 to 5.8 from Lauterthal, Prussia. VOLBORTHITE. (Cu.Ca.Ba) 3 (OH) 3 VO 4 in six-sided green to yellow tables. Streak yellowish green. From Urals and Utah. PUCHERITE. BiVO4 in druses of small orthorhombic crystals of reddish brown color. Streak yellow. From Schneeberg, Saxony. HEWETTITE AND METAHEWETTITE. COMPOSITION. CaO.3V 2 O 5 .9H 2 O. (V2O 6 70.01, V2O 3 0.35, CaO 7.25, H 2 O 21.30 per cent.). GENERAL DESCRIPTION. Both occur as reddish earthy powders from mahogany red to brownish red the hewettite being the brighter. Hewettite also occurs in mahogany red needles and metathewettite in aggregates of highly pleochroic scales. Sp. gr., 2.554; hewettite, 2.511 metahewettite. BEFORE BLOWPIPE, ETC. Both darken on heating and as water escapes again grow lighter in color ending bronze (hewettite) or yellow brown (metahewettite). Melt easily to a dark red liquid. Both slightly soluble in water and yield the de- scribed test, p. 196, with hydrochloric acid. REMARKS. Hew.ttite occurs in pockets and fissures of a shale overlying patronite. Metahewettite is the chief constituent of a red vanadium ore from Paradox Valley, Montrose Co., Colorado, and through a wide area to Thompson, Utah. Occurs as an impregnation of sandstone. At Thompson it is associated with a gray vanadium- bearing silicate and with particles of selenium. PASCOITE is 2CaO.3V2Os.nH2O in orange red thin plates (monoclmic) some- what adamantine lustre. An alteration of patronite not observed in the surface .deposit at Minisraga but has formed since on the walls of an exploratory tunnel. ROSCOELITE. Vanadium Mica. COMPOSITION. Doubtful, V 2 O 3 replacing A1 2 O 3 in muscovite formula perhaps. Percentage of V 2 O 3 very variable, sometimes 20-29 per cent. GENERAL DESCRIPTION. Minute scales with micaceous cleav- age dark green to brown in color suggesting a chlorite. Lustre pearly. H., 2. Sp. gr., 2.92 to 2.94. BEFORE BLOWPIPE, ETC. Fuses easily to a black glass. Essen- tially insoluble in acids. Gives emerald green bead in R. F. with salt of phosphorus after fusion with sodium carbonate gives the described test, p. 196, with hydrochloric acid. Remark?. Occurs as primary mineral in gold veins in Granite Creek, California, and with gold telluride at the Magnolia District, Colorado. Near Newmire and Placerville, on both sides of Bear creek in San Miguel Co., Colorado, as an impreg- nation of a fine-grained sandstone showing as a dull green band nearly parallel to the bedding. Although averaging only i}^ P er cent. V2O 5 is mined at a profit. MINERALS OF METALLIFEROUS ORE DEPOSITS. 341 THE URANIUM AND RADIUM MINERALS. The minerals described are : Uranate Uraninite Uranyl uranate 2UO3.UO 2 (?) Isometric Vanadate Carnotite (K 2 Ca)2UO3.V 2 O 5 3H2O(?) Phosphates Autumte Ca(UO 2 ) 2 (PO4)2.8H 2 O Orthorhombic Torbernite Cu(UO 2 ) 2 (PO 4 ) 2 .8H 2 O Tetragonal Coracite, and gummite and uraconite are mentioned briefly after uraninite, uvanite after carnotite. Uranium is also present in the described species thorianite, thorite, fergusonite, samarskite, euxenite, polycrase, and xenotime, and in a large series* of phos- phates, carbonates, arsenates, sulphates and silicates. ECONOMIC IMPORTANCE. The metal uranium has a limited use in uranium steel, as a small percentage of uranium increases the elasticity and hardness of or- dinary steel. A few tons of sodium uranate, commercially known as uranium yellow, are used each year in coloring glass yellow with a greenish reflex, and in coloring porcelain orange or black. A small amount is used in photography and in the manufacture of uranium salts important in the laboratory. Aside from this the importance of uranium lies in its use for the extraction of radium which is always with uranium in amount proportionate to the uranium present. The ratio is constant for old, unaltered minerals and has been calculated as: Ra = 3.4 X io- 7 . That is, from I gm. U there would develop .00000034 gm. radium (or i gm. Ra from 3,000,000 gm. U), thereafter there would be equilibrium. If, however, the mineral is relatively young and secondary or if it has been altered by percolating waters and one or more of products removed equilibrium may not exist and the ratio be different. Many tons of uraninite have been worked over to obtain a few grams of impure radium chloride, the remarkable properties of which are being widely studied. It * See Bulletin 70, Bureau of Mines, p. 92. Some of species are sulphate, johan- nite, arsenate, trogerite, silicate uranophane, phosphate fritzscheite, carbonate, liebigite. 342 MINER ALOG Y. seems probable that there is here the first known instance of the decomposition of the chemical atom, for radium gives off helium apparently as a decomposition product, and with the evolution of an amount of energy far beyond any previous conception. It also is continually throwing off emanations or rays which affect a photographic plate and discharge an electroscope. Some of these too are of a material character. Still years must elapse before any loss of weight can be detected by the most delicate balance. The uses of radium are in scientific research and in medicine, though in the latter the results are still uncertain. Good results are claimed in treatment of lupus, skin diseases, and some forms of cancer and it is said to have favorable results on rheumatism. Baths have been established by the Austrian government at St. Joachimsthal which are recommended for rheumatism, neural- gia, chronic eczema, etc. Radium has been proved in a number of cases to change the color of minerals such as diamond and sapphire. The three minerals which are important commercial sources of uranium and radium are carnotite, uraninite and autunite, and smaller amounts may be credited to uvanite and torbernite. The production* in 1914 in the United States was 4,294 tons of ore, carrying 87.2 tons of U 3 Os and 22.3 grams of metallic radium, chiefly from carnotite from Colorado and Utah but some from uvanite from the Henry Mountains, Utah. Other sources were uraninite from Cornwall, Austria and the mines of Colorado, of carnotite from Olary, Australia, and of autunite from Guarda, Portugal. Uraninite is roasted with sodium carbonate and nitrate, leached with water and the residues treated with sulphuric and nitric acids, giving uranyl sulphate, from which other salts are made. Ores containing both uranium and vanadium (carnotite, uvanite) are usually subjected to wet treatment, boiled with a solution of sodium or potassium carbonate or treated with dilute sulphuric acids. At other times it is roasted with salt or fused with acid potassium sulphate and leached with water. The uranium salts are in the solution and are suitably precipitated, the radiumf is in the residues from which it and barium are obtained together and separated by fractional crystallization based on the difference in solubility of their chlorides. FORMATION AND OCCURRENCE OF URANIUM DEPOSITS. Uranium is found in granitic rocks and their pegmatites usually with tungsten, in small amounts chiefly as crystalline uraninite. * Mineral Resources U. S. 1914, p. 14. t See Bull. 70, Bureau of Mines, 69 to 82. MINERALS OF METALLIFEROUS ORE DEPOSITS. 343 Veins. Important deposits are generally in veins, the primary mineral being usually the amorphous variety of uraninite pitchblende. In Tin Veins. In Cornwall and Devon in several veins, espe- cially one at Grampound.* In Silver Nickel Cobalt Veins. In the Erzgebirge, especially at Joachimsthal, Bohemia, near but not with tin, in slates near granite. In Silver Gold Veins. In Gilpin Co., Col. (Wood mine, Kirk mine, etc.), in gneiss and mica schist with silver- and gold-bearing pyrite and chalcopyrite. Sedimentary. Uranium minerals, especially carnotite, occur concentrated in the Dakota sandstone in Utah and Colorado. In Utah, where it has in part replaced the original calcite cement, at other times appears in fissures or funnel-shaped cavities. Fossil remains are frequent and the carnotite is abundant in and near them. URANINITE. Pitchblende. COMPOSITION. Uranyl uranate and may contain Ca, N, Th, Zr, Fe, Cu, Bi, etc. GENERAL DESCRIPTION. A black massive mineral of botryoidal or granular structure and pitch-like appearance. Rarely in small isometric crystals. Physical Characters. H., 5.5. Sp. gr., 6.5 to 9.7. LUSTRE, pitch-like, submetallic. OPAQUE. STREAK, gray, olive green, dark brown. TENACITY, brittle. COLOR, some shade of black. BEFORE BLOWPIPE, ETC. Infusible or very slightly fused on edges, sometimes coloring the flame green from copper. On char- coal with soda may yield reaction for lead, arsenic and sulphur. In borax yields a green bead made enamel black by flaming. Soluble in nitric acid to a yellow liquid from which ammonia throws down a bright yellow precipitate. See also p. 195. SIMILAR SPECIES. The appearance and streak are frequently sufficient distinctions. The bead tests are characteristic. * Beyschlag, Vogt & Krusch (Truscott), p. 713. 344 MINERAL OG Y. VARIETIES. Crystallized. The crystals of the granites and their pegmatites are complex in composition and often carry rare earths and nitrogen, because of which other names have been given such as cleveite, nivenite, broggerite, uranniobite. Pitchblende. The uraninite of the ore veins appears to be of colloidal origin; it contains no rare earths and little nitrogen, but contains water and is often intermixed with metallic sulphides. Coracite. Partially altered uraninite. REMARKS. The important variety pitchblende occurs in veins as stated p. 343, another important deposit being the Vereinigt Mine at Johanngeorgenstadt, Saxony r Coracite occurs north of Sault Ste. Marie. The crystallized variety occurs in pegmatites as at Branchville, Conn., Annerod, Norway, Mitchell and Yancy Cos., North Carolina. Nodular material occurs in a pegmatite at Abraki Pahai, India. GUMMITE. An alteration of uraninite of doubtful composition but with 61-75 per cent, of UOs occurs in rounded and flattened gum-like masses of reddish yellow to red or brownish color. H., 2.5, sp. gr., 4. Principal locality, the Flat Rock Mine, Mitchell Co., N. C., but also Texas, and Joachimsthal, Bohemia. CARNOTITE. COMPOSITION. (K 2 , Ca)O, 2UO 3 , V 2 O 5 + H 2 O. (?) It is pro- posed to use the name carnotite for the potassium compound and tyuyamunite for the calcium compound. GENERAL DESCRIPTION. Usually a canary yellow or lemon yellow material, but sometimes red or black. Sometimes in loosely cohering masses of minute scales, oftener disseminated, filling interstices in sandstone. Rarely compact and wax-like. CRYSTALLIZATION. Under the microscope shows rhombic plates with basal cleavage and rhombic symmetry. BEFORE BLOWPIPE, ETC. Easily soluble in hydrochloric or nitric acid. REMARKS. Occurs as stated p. 343, in sandstone in Colorado and Utah, notably in Paradox Valley, Colorado, and San Juan Co., Utah. The Utah deposits carry less carnotite and the. ore varies more in color than the deposits of Colorado. Further east, as at Placerville, the carnotite is small in amount and the dominant species is roscoelite. Carnotite in small amounts is found in crevices in a granite, at Olary, South Aus- tralia, and a large deposit is reported under the name ferghanite at Ferghana, Russian Turkestan. UVANITE, 2UO3, 3V 2 O5.i5H 2 O is a recently described brownish-yellow hydrous uranium vanadate resembling carnotite in appearance and occurring in economic quantities at Temple Rock, Emery Co., Utah. MINERALS OF METALLIFEROUS ORE DEPOSITS, 345 AUTUNITE. Lime Uranite. COMPOSITION. Ca(UO 2 )2(PO 4 ) 2 + 8H 2 O, (UO 3 63.7, CaO 6.1, P 2 O 6 15.5, H 2 O 15.7 per cent.). GENERAL DESCRIPTION. Nearly square (90 43') orthorhombic plates of bright yellow color and pearly lustre, or in micaceous aggregates. PHYSICAL CHARACTERS. Translucent. Lustre, pearly on base. Color, lemon to sulphur yellow. Streak, pale yellow. H., 2 to 2.5. Sp. gr., 3.05 to 3.19. Brittle. Cleavage basal. BEFORE BLOWPIPE, ETC. On charcoal fuses with intumescence to a black crystal- line globule. With salt of phosphorus or borax in the reducing flame yields a green bead. Dissolves in nitric acid to a yellow solution. REMARKS. The only deposit of economic importance is in northern Portugal. The veins are in granite and schist and are richest near Guarda in Beira. The vein material is largely quartz and feldspar with clay and the autunite is disseminated. Torbernite is present and in the vicinity are veins carrying tungsten, tin, galena, etc. Occurs in many localities in small amounts. TORBERNITE. Copper Uranite. COMPOSITION. Cu(UO 2 ) 2 (PO 4 ) 2 + 8H 2 O, (UO 3 61.2, CuO 8.4, P 2 O 5 15.1, H 2 O 15.3 per cent.). GENERAL DESCRIPTION. Thin square tetragonal plates of bright green color and pearly lustre. Sometimes in pyramids or micaceous aggregates. PHYSICAL CHARACTERS. Translucent. Lustre, pearly. Color, emerald to grass green. Streak, pale green. H., 2 to 2.5. Sp. gr., 3.4 to 3.6. Brittle. BEFORE BLOWPIPE, ETC. Fuses easily to a black mass and colors the flame green. In borax yields a green glass in O. F., which becomes opaque red in R. F. Soluble in nitric acid to a yellowish-green solution. REMARKS. The deposit of autunite at and near Guarda, Portugal, contains torbernite and a deposit reported near Farina, South Australia, is principally torber- nite. Other localities are Cornwall, England, and Joachimsthal, Bohemia. THE CHROMIUM MINERALS. The minerals described are : Chromite FeCr 2 O4 Isometric Crocoite PbCrO4 Monoclinic Spinel, chrysolite, serpentine, pyroxene, mica, garnet, chlorite, etc., have chromium-bearing varieties, and there are chromium- bearing clays* and a few unimportant chromates.t ECONOMIC IMPORTANCE. The only commercial ore is chromite. This country produced in 1915^ 3,281 long tons, chiefly from Shasta and Fresno counties, % Mineral Resources, U. S., 1915, pt. i, p. 2. * Wolchonskoite, miloschite, chrome ochre. t Phoenicochroite, vauquelinite, tarapacaite. 346 MINERAL OGY. California. In the same period this country imported 76,455 tons as follows : Exported to U. S. Total Output New Caledonia 28,031 67,000 Rhodesia 22,800 57,333 Portugese Africa 11,230 Canada 10,087 Greece 4,305 Turkey, Russ'a, Japan and India are also producers. The most important use is the manufacture of sodium and potassium bichromate and chromate, used in calico printing, electric batteries, the chrome colors and pigments, etc. Chromite is also used in the manufacture of ferrochrome, which in turn is used in making chrome steel, much used for high speed tools, armor plate and projectiles which possesses great hardness and resistance to impact. Mixed with a suitable binder chromite is made into highly refractory bricks for copper and steel furnaces. Ferrochrome is made in the electric furnace. FORMATION AND OCCURRENCE OF CHROMIUM DEPOSITS. The only ore of chromium is chromite and all known deposits of chromite occur in peridotite or the serpentine derived from it,* almost entirely as magmatic segregations, occasionally as secon- dary chromite by alteration of chromium-bearing silicates. Magmatic Segregations. The earth's crust contains, it is estimated, .01 per cent, of chromium but the peridotites contain generally 0.2 to 0.5 per cent, and up to I per cent.f of Cr 2 O 3 and the segregations up to 60 per cent, chiefly as chromite but also as chrome spinel (picotite) and the chromium-bearing silicates mentioned on last page. The deposits may be in essentially unaltered peridotite as at the Island of Hestmando, Norway; Mt. Dun, New Zealand, or Kraubat, Styria; or they may be in serpentine rock as at Feragen, Norway, Tirbaghi Hills and Mt. Dere, New Caledonia; Thetford, Canada; Selukwe and Beira, Rhodesia. * Beyschlag, Vogt & Krusch (Truscott), p. 244. t Beyschlag, Vogt und Krusch (Truscott), p. 244. MINERALS OF METALLIFEROUS ORE DEPOSITS. 347 Secondary Deposits. Secondary deposits of chromite due to the decomposition of chrome-bearing silicates are reported in Bosnia. Residual Deposits. Chromite being very resistant to atmospheric influences is very common in gravels, these forming part of the New Caledonia deposits and at one time utilized from the Ural platinum deposits. CHROMITE. Chromic Iron. COMPOSITION. FeCr 2 O 4 , (FeO 32, Cr 2 O 3 68 per cent), some- times with A1 2 O 3 or MgO as replacing elements. GENERAL DESCRIPTION. Usually a massive black mineral resem- bling magnetite. Occurs either granular or compact or as dissem- inated grains. Rarely in small octahedral crystals. Frequently with more or less serpentine, mechanically intermixed, giving rise to green and yellow spots and streaks. Physical Characters. H., 5.5. Sp. gr., 4.3 to 4.6. LUSTRE, sub- metallic to metallic. OPAQUE. STREAK, dark-brown. TENACITY, brittle. COLOR, black. May be slightly magnetic. BEFORE BLOWPIPE, ETC. Infusible, sometimes slightly fused by reducing flame, and then becomes magnetic. In salt of phos- phorus, in oxidizing flame, gives yellow color hot, but on cooling becomes a fine emerald-green. With soda and nitre on platinum fuses to a mass, which is chrome-yellow when cold. Insoluble iu acids. SIMILAR SPECIES. Chromite is distinguished from other black minerals by the salt of phosphorus reactions, and to a consider- able extent by the serpentine with which it occurs. REMARKS. Occurs as described, p. 346. In this country the Woods Mine, near Baltimore, furnished from 1828 to 1850 most of the ore used by the world, the rest coming from the platinum deposits of the Urals. Later deposits were worked in Lancaster County, Pa., and in California and the latter are still worked. CROCOITE. COMPOSITION. PbCrO 4 , (PbO, 68.9 ; CrO 3 , 31.1 per cent.). GENERAL DESCRIPTION. Bright hyacinth-red mineral, usually in monoclinic pris- matic crystals, but also granular and columnar. The color is like that of potassium dichromate. 348 MINERALOGY. PHYSICAL CHARACTERS. Translucent. Lustre, adamantine. Color, hyacinth red. Jtreak, orange yellow. H., 2.5 to 3. Sp. gr., 5.9 to 6.1. Sectile. Cleavage, prismatic. BEFORE BLOWPIPE, ETC. In closed tube, decrepitates violently, becomes dark, but recovers color on cooling. Fuses very easily, and is reduced to metallic lead with, .deflagration, the coal being coated with a yellow sublimate. With borax or S.Ph., forms yellow glasses, which are bright green when cold. Soluble in nitric acid to a yellow solution. Fused with KHSO 4 in closed tube, yields a dark-violet mass, red on solidifying and greenish-white when cold, which distinguishes it from vanadinite. REMARKS. Chromium was discovered in samples of this mineral by Vauquelin in 1797. It occurs in lead-bearing veins in gneiss and granite in Berezof, Mursinska and Nischni Tagilsk, Urals. Similarly in Hungary and Brazil. Fine crystals come from the Broken Hill Mine, Australia. It is nowhere found in commercial quantities. THE MOLYBDENUM MINERALS. The minerals described are : Sulphide Molybdenite MoS2 Hexagonal Oxide Molybdite MoOs Orthorhombic Wulfenite PbMoO 4 Tetragonal Other molybdates* are powellite, CaMoO 4 , pateraite, CoMoO 4 , and belonesite, MgMoO 4 . ECONOMIC IMPORTANCE. The only ores are molybdenite and, in one or two instances, wulfenite. The production is chiefly from Queensland and New South Wales, Australia, South Norway and Canada. The pro- duction probably is not over 300 tons per year.f None was produced in this country in 1914-1915, though work was com- menced on a deposit near Georgetown, Colo. In general, the ore is less than 3 per cent, and is concentrated by flotation. An alloy with iron or manganese containing 50 to 75 per cent. Mo, is prepared by the alumino-thermic process or by heating the molybdenite in a carbon tube with the electric arc, and is used to toughen and harden steel for wire drawing, tool steel, crank and shaft forgings, etc. Alloys with nickel and chromium are also made. The metal is used in various electrical devices. A considerable quantity is used in the production of molyb- denum salts, such as Ammonium molybdate, used to determine phosphorus in iron * Silicates are unknown, f Australia, 1913, 145 tons. MINERALS OF METALLIFEROUS ORE DEPOSITS. 349 and in Europe as a fireproofing material and as a disinfectant. Sodium molybdate, used to impart a blue color to pottery and in dyeing silks and woolens, and molybdic acid from which useful chemical reagents are prepared. The great demand from France in 1914 is said to be due to a process for the preservation of cordite.* FORMATION AND OCCURRENCE OF MOLYBDENUM DEPOSITS. Molybdenum occurs in igneous, metamorphic and sedimentary rocks, principally as the sulphide molybdenite. The economically important deposits appear to be always con- nected with granites and frequently associated with tungsten. Disseminated or following joints and crevices as at Cooper, Maine. In pegmatites as at Romaine, Quebec. In veins in granite as at Knaben Mine, S. Norway; Chelan county, Washington; and Dillon, Montana. Contacts. Sometimes in contacts of granite with limestone, as at Texeda Island, B. C., where the molybdenite is fine-grained and massive and included in ore bodies of bornite and chalcopyrite. MOLYBDENITE. COMPOSITION. MoS 2 , (Mo 60.0, S 40.0 per cent.). GENERAL DESCRIPTION. Thin graphite-like scales or foliated masses of metallic lustre and bluish gray color, easily separated into flexible non-elastic scales. Sometimes in tabular hexagonal forms and fine granular masses. Soft, unctuous and marks paper. Physical Characters. H., I to 1.5. Sp. gr., 4.6 to 4.9. LUSTRE, metallic. OPAQUE. STREAK, greenish.* TENACITY, sectile to malleable. COLOR, bluish lead gray. CLEAVAGE, basal. BEFORE BLOWPIPE, ETC. In forceps infusible, but at high heat colors the flame yellowish green. On charcoal gives sulphurous odor and slight sublimate, yellow hot, white cold, and deep blue when flashed with the reducing flame. Soluble in strong nitric acid and during solution on platinum it is luminous. With sul- * Mineral Industry, 1914, p. 529. 350 MINERALOGY. phuric acid yields a blue solution. In salt of phosphorous and borax yields characteristic molybdenum reactions. SIMILAR SPECIES. Differs from graphite in streak and blowpipe reactions. May usually be distinguished by its lighter bluish gray color. REMARKS. Economic deposits are as stated, p. 349. Commercially unimportant occurrences are in the tin mines of Bohemia, Saxony, Cornwall and elsewhere and the minute flakes common in California gold quartz and the copper veins of Clifton, Arizona, and Chili. It is found in many American localities, especially, Westmore- land, N. H., Blue Hill Bay, Maine, Okanogan Co., Wash., and Pitkin, Colorado. MOLYBDITE. COMPOSITION. MoOs, (Mo 66.7 per cent.).f GENERAL DESCRIPTION. An earthy yellow powder or, rarely tufts and hair-like crystals of yellowish-white color. PHYSICAL CHARACTERS. Opaque to translucent. Lustre, dull or silky. Color, yellow or yellowish white. Streak, straw yellow. H., i to 2. Sp. gr., 4.49 to 4.5. BEFORE BLOWPIPE, ETC. On charcoal fuses, yielding crystals yellow hot, white cold, and made deep blue by the reducing flame. In borax and salt of phosphorus gives characteristic molybdenum reactions. WULFENITE. COMPOSITION. PbMoO 4 , sometimes containing Ca, Cr. V. GENERAL DESCRIPTION. Usually in thin, square, tetragonal crystals of yellow, orange or bright orange-red color and resinous lustre. Less frequently in granular masses or acute pyramidal crystals. H., 3. Sp. gr., 6.7-7. BEFORE BLOWPIPE, ETC. Fuses easily on charcoal, giving yel- low coat and finally a metallic globule. Tests with sulphuric acid, borax and salt of phosphorus as described, p. 190. REMARKS. Wulfenite occurs with other lead minerals. It is found in many localities in New Mexico and Arizona ;t in the lead regions of Wisconsin and Arizona; at Phcenixville, Pa.; Inyo County, Cal.; Southampton, Mass., and many other places, always associated with other ores of lead. THE TUNGSTEN MINERALS. The minerals described are: Wolframite (FeMn)WO 4 Monoclinic Scheelite CaWO 4 Tetragonal * Best seen on glazed porcelain. t According to Schaller it is molybdate of iron. Zeit. f. Kryst., 43, 331. \ Commercial quantities have been obtained from the Mammoth Mine, Pinal Co. MINERALS OF METALLIFEROUS ORE DEPOSITS. 351 Minor species are tungstite, meymacite, cuprotungstite, cupro- scheelite and stolzite. ECONOMIC IMPORTANCE. The world's total production is about 10,000 tons per year of 60 per cent. WO 3 . In 1915 the United States produced 2,165 tons chiefly from Colorado and California. The great producers in 1913 were:* Burma i,732 Australia 752 United States 1,397 Bolivia 564 Portugal 1,380 Argentina 539 The material is often recovered as a by-product from tin, as at Heberton, Queensland, or in the treatment of gold or silver ores (British Columbia) or with copper ores (Peru) and usually under- goes preliminary concentration (to 60 per cent. WO 3 ). Tungstic oxide, WO 3 , may first be extracted from the ore and this reduced to tungsten in the powder form. In this country the ore is reduced directly in the electric furnace to ferro-tungsten, which, added to steel, gives a product of great toughness, especially valued for high-speed cutting tools, which retain their temper even when red hot and are said to save 20 to 30 per cent, in power alone. The steel is also used for armor plate and projectiles and for permanent magnets. Alloys with Pt, Cr, Co, Al, etc., are made, the tungsten usually giving strength to the alloy. Metallic tungsten is used in place of platinum for winding resis- tance furnaces and in electrical contacts and as a filament in incandescent lamps. Its melting point is 3267 C. Tungstic acid and sodium tungstate are used in dyeing and to render cotton and wood uninflammable. Other uses are in pig- ments. THE FORMATION AND OCCURRENCE OF TUNGSTEN DEPOSITS. Veins. The only important ores are wolframite and scheelite, these occur chiefly in veins in or near granite either with cassiterite or of the cassiterite type, but also in veins with silver, gold, etc. * Mineral Industry, 1914, p. 756. 352 MINERAL OGY. Veins with Cassiterite. Wolframite is the most constant asso- ciate of cassiterite and secondary scheelite is frequent. Examples are: Tavoy District, Lower Burma; tungstite said also to occur. Sierra de Estrella, Portugal; with much arsenopyrite. Heberton, Queensland; Cornwall; Zinnwald and Altenbefg. Veins without Cassiterite. Wolframite occurs at Sierra de Cordoba, Argentina (carries Columbium); Castello Branco, and Beira, Portugal; Boulder county, Colorado, near silver and gold veins. In some of the Queensland and Chilean veins it is intimately associated with bismuth or silver. Scheelite often occurs in gold veins as in Atolia, Kern county, California; Halifax county, Nova Scotia; in veins in slate with gold-bearing arsenopyrite, and Sloan District, British Columbia, in large lenses. Large deposits exist at Scheelite, Nevada. Replacements. The deposits at Trumbull, Conn., are regarded as replacements* of limestone; the scheelite preceded the wolframite, the latter occurring only as pseudomorphs after scheelite. The deposits near Lead and Dead wood, South Dakota, are in dolomite. WOLFRAMITE, Ferberite, Huebnerite. COMPOSITION. (Fe.Mn)WO 4 . (About 76 per cent. WO 3 .) Strictly Fe\VO 4 is ferberite, MnW0 4 is huebnerite. The species, however, replace each other.f GENERAL DESCRIPTION. Heavy dark-gray to black sub- metallic crystals, orthorhombic in appearance, bladed non-termi- nated crystals often reddish brown in color, cleavable and granular masses. CRYSTALLIZATION. Monoclinic. Axes a : b : c = 0.830 : i 0.868, ft = 89 22'. Usual combination shown in Fig. 378 of unit prism m, ortho * Beck and Weed, p. 539. f F. L. Hess proposes the arbitrary distinction into ferberite for iron tungstate with less than 20 per cent, manganese tungstate, huebnerite for manganese tungstate with less than 20 per cent, iron tungstate and wolframite for all intermediate pro- portions. MINERALS OF METALLIFEROUS ORE DEPOSITS. 353 pinacoid a, e = (a = 81 unit clino dome d and + and 102} Supplement angles, mm ae = 62 QO b : Ytf}', ae = 61 ortho domes = 79 23'; dd FIG. 378. Zinnwald. 54; ae = 1 54; ae = 2 54. Physical Characters. H., 5 to 5.5. Sp. gr., 6.8 to 7-55- LUSTRE, resinous to sub-metallic. STREAK, dark-brown, yellowish-brown and gray. COLOR, dark-gray, black, and reddish-brown. OPAQUE to translucent. In one locality transparent. CLEAVAGE very perfect in one direction, joio). BEFORE BLOWPIPE, ETC. Fuses readily to a crystalline globule, which is magnetic. In salt of phosphorus yields a reddish-yellow glass, which in reducing flame becomes green, and if this bead is pulverized and dissolved with tin, in dilute hydrochloric acid, a blue solution results. Partially soluble in hydrochloric acid, the solution becoming blue on addition of tin. SIMILAR SPECIES. Distinguished by its fusibility and specific gravity from similar iron and manganese minerals. REMARKS. The chief occurrences are as stated, p. 352, and other similar deposits in Angaras, Peru; Siam; Salamanca, Spain; St. Leonards, France; Brazil and else- where. Found also in many deposits of stream tin, sometimes in considerable quantities. Occurs in at least twelve of the United States, but is worked chiefly in Colorado, and to a minor extent in Idaho, Nevada, New Mexico and South Dakota. SCHEELITE. COMPOSITION. CaWO 4 , (CaO 19.4, WO 3 80.6 per cent.), some- times with replacement by molybdenum. GENERAL DESCRIPTION. Heavy brownish white or white masses and square pyramids. Also drusy crusts of yellow or brown crystals. CRYSTALLIZATION. Tetragonal. Class of third order pyramid, p. 47. Axisc = 1.536. The unit first order pyramid p and second order d are most common with sometimes a modifying third order pyramid, x = (a : 3 a : 3 C )> !3n)- Supplement angles are pp = 79 55'; ee = 72 40'. 24 354 FIG. 379. MINERALOGY. FIG. 380. FIG. 381. Schlackenwald. Trumbull, Conn. Physical Characters. H., 4.5 to 5. Sp. gr., 54 to 6.1. LUSTRE, adamantine. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle. COLOR, pale yellow, gray, brown, white or green. CLEAVAGE, distinct parallel to first order pyramid, indistinct parallel to second order pyramid. BEFORE BLOWPIPE, ETC. Fusible with difficulty on sharp edges. In salt of phosphorus forms a clear bead which in the reducing flame becomes deep blue, and if the bead is powdered and dis- solved in dilute hydrochloric acid it yields a deep blue solution, especially on addition of metallic tin. Scheelite is soluble in hy- drochloric or nitric acid, leaving a yellow residue. SIMILAR SPECIES. Distinguished among non-metallic minerals by its weight and behavior in salt of phosphorus. REMARKS. The chief occurrences are as stated, p. 352; it is also frequent as a secondary mineral with wolframite. There are many minor occurrences with gold or silver or lead and copper deposits. Examples are with gold at Warren's, Idaho, and Val Toppa, Piedmont, with silver and lead at Oracle, Arizona, and Snake River, Nevada; with copper at Llamuco, Chile. THE COLUMBIUM AND TANTALUM MINERALS. The minerals described are': Columbite 1 Tantalite j Samarskite Fergusonite (Fe.Mn)(CbTa) 2 O 6 Orthorhombic (Fe.Ca.U02) 3 (Y.Er.Ce)2(Cb.Ta) 6 2 i Orthorhombic (YEr.Ce)(Cb.Ta)O 4 Tetragonal Less common are yttrotantalite, pyrochlore, euxenite, skogbolite, stibiotantalite. MINERALS OF METALLIFEROUS ORE DEPOSITS. 355 The wolframites of Rosario, Argentina; and Auvergne, France, contain columbium. ECONOMIC IMPORTANCE. No production is reported for this country, the small amount used, possibly 100 tons, coming from Western Australia. Colum- bium has practically no uses , tantalum, on account of its hardness, toughness, ductility and high fusion point (2,250 to 2,300 C.) is made* into filaments for incandescent lights which are con- siderably used. It is used in dental and surgical steel, watch springs, etc., and is suggested for laboratory crucibles. FORMATION AND OCCURRENCE OF COLUMBIUM AND TANTALUM DEPOSITS. These elements are usually found together and the minerals which they form are found almost entirely in granite pegmatites, as at the Etta Mine, South Dakota, or in the gravels resulting from the decomposition of pegmatites as at Greenbushes,, West Australia, in pebbles 5-6 inches in diameter.f COLUMBITE. TANTALITE. COMPOSITION. (Fe, Mn)(Cb, Ta) 2 O 6 (grading from columbite, FeCb 2 O 6 , to tantalite, FeTa 2 Oe). Usually contains a little tin, often a little tungsten. GENERAL DESCRIPTION. Black, often bright and sometimes iridescent crystals. Also in large dull black masses and in pebbles in tin gravels. CRYSTALLIZATION. Orthorhombic. a : b : c = .828 : I : .889. Common forms a {oioj, b }iooj, m = {no}, d {739}. Supple- ment angle mm = 79 17'. Physical Characters. H.> 6. Sp. gr. 5.4 to 7. LUSTRE, sub-metallic. OPAQUE. STREAK, dark red to black. TENACITY, brittle. COLOR, black. CLEAVAGE in two directions at right angles. * By pressing a mixture of the oxide and paraffine into threads, then reducing them to metal in a vacuum. It is said one pound of tantalum will make 20,000 2o-candle power filaments. t Also small, dull pebbles of stibiotantalite, Sb (CbTa) 2 O 8 . 356 MINERALOGY. BEFORE BLOWPIPE, ETC. Infusible. Fused with potassium hydroxide and boiled with tin gives deep-blue solution on dilution with water the color disappears. Insoluble in hydrochloric acid, partially decomposed by sulphuric acid. SIMILAR SPECIES. By infusibility and lower specific gravity from wolframite, by greater opacity and absence of tin test from cassiterite. REMARKS. Occurs in considerable quantities in large black crystals at the Etta Mine, Black Hills, South Dakota, and as pebbles 5-6 inches in diameter in the tin gravels of Greenbushes, Western Australia. Famous crystal localities are the cryolite of Greenland, the granites of Bodenmais, Bavaria; Miask, Urals; Haddam, Connecticut and Amelia Co., Virginia. It is found in the gold sands of Sanarka Urals. FIG. 384. FIG. 382. FIG. 383. Coiumbite. Samarskite. Fergusonite. SAMARSKITE. COMPOSITION. RsR2(Cb,Ta) 6 O2i. R chiefly FeCaUO 2 . RCe, Yt metals. GENERAL DESCRIPTION. Irregularly shaped masses and rough orthorhombic crystals (Fig. 383) of velvet black color and notable lustre. Streak reddish brown. H., 5 to 6. Sp. gr., 5.6 to 5-8. BEFORE BLOWPIPE, ETC. Fuses with difficulty to black glass; in closed tube glows, cracks and blackens. With salt of phosphorus green uranium bead. De- composed sufficiently by boiling concentrated sulphuric acid to give a blue color on addition of zinc or tin and hydrochloric acid. REMARKS. Found in granite pegmatites at Mitchell and McDowell counties, North Carolina, and near Miask, Urals, in both cases with columbite. Also in Queensland, Australia. FERGUSONITE. COMPOSITION. (Y, Er, Ce)(CbTa)O 4 . GENERAL DESCRIPTION. Brownish black, tetragonal crystals (Fig. 384) and masses with brilliant glassy lustre on fresh fracture. Streak pale brown. H., 5.5 to 6. Sp. gr., 5.8 or less if hydrated. BEFORE BLOWPIPE, ETC. Infusible, becomes pale yellow on charcoal. De- composed by sulphuric acid, the white residue giving a blue color with tin and hydrochloric acid. MINERALS OF METALLIFEROUS ORE DEPOSITS. 357 Copper Cu Isometric Covellite CuS Hexagonal Chalcocite Cu 2 S Orthorhombic Bornite Cu 5 FeS 4 Isometric Chalcopyrite CuFeS 2 Tetragonal Enargite Cu 3 AsS4 Orthorhombic Famatinite Cu 3 SbS 4 Tetrahedrite CusSbizS; Isometric Cuprite Cu 2 Isometric Tenorite CuO Triclinic Atacamite Cu(OH)Cl.Cu(OH) 2 Orthorhombic Chalcanthite CuSO4.5H 2 Triclinic Brochantite Cu 4 SO 4 (OH)6 Orthorhombic Malachite Cu 2 (OH) 2 C0 3 Monoclinic Azurite Cu 3 (OH) 2 (C0 8 ) 2 Monoclinic Chrysocolla uSiO 3 .2H 2 O REMARKS. Occurs in considerable quantity in the granite of Baringer Hill, Llano Co., Texas. Other localities are Cape Farewell, Greenland; Ytterby, Sweden; Arendal, Norway. THE COPPER MINERALS. The minerals described are : Metal Sulphides Sulphoarsenite Sulphoantimonite Oxides Basic chloride Sulphates Carbonates Silicates The great deposits of pyrite and pyrrhotite usually carry copper and both directly because of its extraction and indirectly as the primary ores from which the richer ores largely form are the greatest and most important sources. ECONOMIC IMPORTANCE. The world's production of copper in 1915 was 1,061,283 metric tons, of which this country produced 646,212; Bolivia, 75,000; Canada 47,202; Peru, 47,142; and Mexico, Australia, Germany,, Africa, Spain and Portugal from 25,000 to 35,000 each. The ores which yielded this product probably do not differ greatly in proportions from an earlier estimate, f based on the production of 1909. Sulphide ores 60 to 65 per cent. Oxidized ores 15 to 20 " Native copper 12 " Enargite 5 Tetrahedrite Y^ The production in this country was derived approximately in the following percentages : Arizona, 31; Montana, 18.5; Michigan, * Engineering and Mining Journal, 1916, p. 48. t Beyschlag, Vogt & Krusch (Truscott), 872. 358 MINERALOGY. 17; Utah, 13; New Mexico, 4.5; Nevada, 4; Alaska, 4; the re- maining 8 per cent, chiefly from California, Idaho and Tennessee. The method of extraction of the copper is dependent upon the nature of the ore, and may roughly be classed under three headings : Treatment of native copper. Treatment of oxidized ores. Treatment of sulphides. A great many processes exist or have existed, but these for a general brief discussion may be reduced to a small number of type processes of which the others are variations due to local conditions or constituents of the ore. Treatment of Native Copper. Native copper occurs in enormous quantities in Michigan, and the deposits mined average less than two per cent, of copper, al- though occasionally large masses of the metal are found. The rock is crushed by steam stamps and the copper separated from the rock by the action of water and the use of jigs, tables, and other concentrating apparatus. The concentrated material is then melted in a large reverberatory furnace with limestone and slags from previ- ous operations. The new slag thus formed contains the remain- ing rock and is removed, leaving behind copper, which after a period of reduction by charcoal and stirring is cast into ingots. Treatment of Oxidized Ores. The oxidized ores in Arizona which averaged over ten per cent, of copper, were smelted in blast-furnaces with coke and the neces- sary flux to make a slag with the associated gangue. The result being an impure metal called black copper, which was later refined. The ores are now more often mixed with sulphides. The carbonate and silicate ores at Ajo,f Arizona, carrying 1.5 per cent, copper, are being leached with dilute sulphuric acid and electrolytically precipitated. Treatment of Sulphides. The treatment of sulphides is quite varied, depending chiefly on the precence or absence of arsenic, the richness of the ore and the local conditions. * Engineering and Mining Journal, 1916, p. 48. t Ibid., p. 55- MINERALS OF METALLIFEROUS ORE DEPOSITS. 359 The modern practice involves a concentration by flotation which may bring a 2 per cent, ore up to 25 per cent., but makes necessary, on account of the pulverized condition, either a roasting or smelting in a reverberatory furnace or sintering and then smelting in a blast furnace.* The ores always contain iron, copper and sulphur, and may contain arsenic, antimony, silver, gold, etc. All the smelting processes depend on the facts that at high temperatures copper has a greater affinity for sulphur than iron has, and iron a stronger affinity than copper for oxygen. So that if such an ore is subjected to oxidation by roasting, oxides result; but in the subsequent fusion, if enough sulphur has been left, the copper will form a fusible sulphide, and the oxidized iron will unite with the gangue and the flux to form a slag. By regulating the roasting, the sulphur contents may be brought to any desired percentage. The roasted ore is smelted for copper either in a shaft-furnace, or when silver or gold is present, in a reverberatory furnace. The blast furnaces are rectangular in cross section and may be as large as 25 ft. x 144 ft. and may treat over 3,000 tons per day. The slag and matte flow through a trapped spout to an outer fore hearth where the matte settles and is tapped and the slag flows out at the top. The copper matte is often blown in a converter, by which the sulphur, arsenic and antimony are driven off, the iron oxidized and converted into slag, and black copper obtained. The crude copper is refined either by remelting and oxidation, or more frequently electrolytically. The great uses of copper are in electrical work and in alloys with zinc and tin, such as brass, yellow metal, bronze, bell metal, and German silver. Copper sulphate is also important. THE FORMATION AND OCCURRENCE OF COPPER ORES. Copper is obtained from deposits of all the great classes and it is estimated f that the world's yield is about in the following proportions : Magmatic segregation 10 to n per cent. Contacts and contacts combined with veins 25 to 30 " Veins 40 " Metasomatic replacements 3 Native copper 12 " Ore beds 4 By-products I * Lawrence Addicks in Eng. and Min. Journ., 1916, p. 91. t Beyschlag, Vogt & Krusch (Truscott), p. 944. 360 MINER ALOG Y. Magmatic Segregations. The chalcopyrite in norite at Sudbury, the sulphides in serpen- tine at Mt. Catini, Tuscany, and the bornite at O'kiep Namaqua- land, Cape Colony, in a rock chiefly feldspar, are generally accepted as segregations. Many bedded copper deposits formerly attributed to heated waters are probably magmatic intrusions such as the great copper- bearing pyrite deposits of Rio Tinto, Spain, and Mt. Lyell, Tasmania.* Contacts Usually with Veins. True contacts with garnet, augite, wernerite, wollastonite, vesuvianite, etc., are often associated with ordinary copper veins- The great deposits of this type are: Clifton, Bisbee, and Globe, Arizona; Mednorudiansk, Urals; Bingham Canon, Utah; and Cananea, Mexico. Veins. This most productive class includes the great deposits of chalco- cite, bornite and enargite at Butte, Montana, in granite near rhyolite; Burra Burra, S. Australia, of carbonates and oxides, in a complex of slate, limestone and sandstone; Moonta and Wallaroo, S. Australia, of chalcopyrite and bornite in quartz porphyry but with the carbonates and atacamite in large quantities; Aschio Japan. Sometimes the presence of tourmaline or cassiterite indi- cate high temperatures and cooperation of vapors as at Cactus Mine, Utah; Las Condes, Chili; Dolceath Mine, Cornwall; Heber- ton, Australia. Metasomatic Replacements. The great auriferous pyrite deposits of Rio Tinto and Mt. Lyell mentioned under magmatic segregations are by some regarded as replacements. f The copper-bearing pyrrhotite and pyrite of Ducktown, Tenn., are said to have been formed by replacement of limestone by "igneous emanations. " * Ibid., 943 and 877. t Lindgren, p. 602, 605. t Ibid., p. 709. MINERALS OF METALLIFEROUS ORE DEPOSITS. 361 Other replacements are the important deposits of Bosccheggrano, Tuscany, and Otavi, German S. W. Africa.* Sedimentary. Occurrence in beds in sedimentary rocks does not prove sedi- mentary origin. Throughout Europe and America sandstones are found which contain copper ores, chiefly chalcocite, but of date later than the sediments and probably deposited from solutions of pre-existing ore in the sediments or adjoining rocks. Such deposits occur at Coro Coro, Bolivia; Colorado and New Mexico; the Permian sandstones of Russia, and elsewhere. At Boleo, Lower California, conglomerates and tuffs interstrati- fied with copper minerals occur, the tuffs being regarded as intru- sions of volcanic mud and the concentration of the copper minerals to the action of springs. Nodules of malachite and azurite occur in the Bunter sandstone in many localities, \ some of which are worked, as in Lorraine; Rhenish Prussia; Mottram, St. Andrews, England; etc. Copper is sometimes found in placers and river beds as at Ste. Catalina, Argentina. Native Copper in Basic Lava Flows. The one great occurrence is in the melaphyre of the Lake Superior region, where the copper occurs with zeolites filling the blowholes of the melaphyre and also the interstices in a con- glomerate, chiefly melaphyre. True veins also occur, which are richest where they cross the melaphyre. The intimate association with calcite and the zeolites laumontite, analcite, natrolite, etc., and such species as prehnite, epidote, datolite (carrying boron) and apophyllite (carrying fluorine) indi- cate deposition from water at moderate temperatures. It is a special case of formation of zeolites differing from the ordinary only in the presence of copper in the solutions. * Beyschlag, Vogt & Krusch (Truscott), 916. t Ibid., 1182. J Ibid., 1184. These solutions are considered to be in part of magmatic origin and to have risen at the consolidation of the rocks. Beyschlag, Vogt & Krusch (Truscott), 935. 362 MINERALOGY. Many other relatively unimportant occurrences of native copper are associated with basic eruptive rocks with the same mineral association, calcite, prehnite, epidote and zeolites, such as the Faroe Islands; Oberstein, Germany; Bay of Fundy, N. S. Oxidation and Cementation, or Secondary Enrichment of Copper Ores. In the upper portions of many copper deposits the primary ores, pyrite, pyrrhotite, chalcopyrite, etc., are oxidized. If much pyrite is present soluble sulphates, CuSO 4 and Fe 2 (SO SIMILAR SPECIES. It is more brittle than argentite, and differs from bornite in not becoming magnetic on fusion. REMARKS. Often a cementation species but also primary, as in the deeper levels at Butte, Montana, and Virgilina, Va., and the 25 ft. veins at the Bonanza Mine, Copper River, Alaska. In the numerous copper deposits in sandstone the principal mineral is chalcocite, often replacing wood and plants, as in Texas and New Mexico and the Permian beds of Russia. Famous localities for crystallized chalcocite are Bristol, Conn., and Cornwall' England. BORNITE. Purple Copper Ore. Horse Flesh Ore. COMPOSITION. Cu 5 FeS 4 , (Cu 63.3, Fe 11.2, S 25.5 per cent.), but often contains admixed chalcocite. GENERAL DESCRIPTION. On fresh fracture, bornite is of a pecu- liar red-brown color and metallic lustre. It tarnishes to deep blue and purple tints, often variegated. Usually massive, sometimes small cubes or other isometric forms. Physical Characters. H., 3. Sp. gr., 4.9 to 54. LUSTRE, metallic. OPAQUE. STREAK, grayish black. TENACITY, brittle. COLOR, dark copper red, brownish or violet blue, often varied. BEFORE BLOWPIPE, ETC. Blackens, becomes red on cooling, and finally fuses to a brittle, magnetic globule and evolves sulphur MINERALS OF METALLIFEROUS ORE DEPOSITS. 365 dioxide fumes. In oxidizing flame with borax or salt of phosphate phorus, gives green bead when hot, greenish blue when cold, the bead is opaque red in the reducing flame. Soluble in nitric acid, with separation of sulphur. REMARKS. Bornite is often found with chalcopyrite and is both primary and a cementation product, as at Mt. Lyell, Tasmania, and Butte, Montana. In certain localities it is the principal mineral, as at some Chilian mines and the magmatic segregations at O'kiep, Little Namaqualand, Cape Colony. It occurs also in com- mercial quantities with chalcocite but without chalcopyrite in quartz veins in an altered volcanic rock at Virgilina, Va., and as lenses in limestone with little chalco- pyrite on Texada Island, British Columbia. CHALCOPYRITE. Copper Pyrites. Yellow Copper Ore. COMPOSITION. CuFeS 2 , (Cu 34.5, Fe 30.5, S 35.0 per cent.), with mechanically intermixed pyrite at times. GENERAL DESCRIPTION. A bright brassy yellow mineral of metallic lustre, often with iridescent tarnish resembling that of bornite. Usually massive. Sometimes in crystals. CRYSTALLIZATION. Tetragonal. Scalenohedral class, p. 47. Axis = 0.985. Sphenoids predominate, / = unit sphenoid ; o = (a : a : ^c) ; {772}; t=*(a:a:\c)\ { 1 14} ; v = (a : a : 4*) ; {441}; * = (a\2a\c)\ {212}. Supplement angles (over top) // = 108 40' ; 00= 128 52' ; 38 25' 159 39'- FIG. 388. FIG. 389. FIG. 390. French Creek, Pa. Ellenville, N. Y. Physical Characters. H., 3.5 to 4. Sp. gr., 4.1 to 4.3. LUSTRE, metallic. OPAQUE. STREAK, greenish black. TENACITY, brittle. COLOR, bright brass yellow, often tarnished in blue, purple and black hues. 366 MINER A LOG Y. BEFORE BLOWPIPE, ETC. On charcoal fuses with scintillation to a brittle magnetic globule. With soda yields metallic malleable red button and sulphur test. In closed tube decrepitates, becomes dark and iridescent and may give deposit of sulphur. Flame and bead reaction like bornite. Soluble in nitric acid with separation of sulphur, and from the solution ammonia throws down a brown precipitate, and leaves the liquid deep blue in color. SIMILAR SPECIES. Chalcopyrite is softer and darker in color than pyrite, and differs from gold in black streak and brittleness. REMARKS. Usually primary, often in small amount, cupriferous pyrite and pyr- rhotite. Occurs also as cementation product, p. 362. Occurs in all classes of deposit, as described p. 360, in most of localities mentioned and in many others, being one of the great sulphides of metallic ore deposits. ENARGITE. COMPOSITION. Cu 3 AsS 4 , (Cu 48.3, As 19.1, S 32.6 per cent). Sometimes with Cu replaced in part by Zn or Fe and As by Sb. GENERAL DESCRIPTION. A black brittle min- FIG. 391. era j O f metallic lustre, occurring usually colum- nar or granular but sometimes in orthorhom- bic crystals. CRYSTALLIZATION. Orthorhombic. Axes a: b \ c 0.871 : i : 0.825. m = unit prism, / = (2% \T> \ cor); {120}. Supplement angles are mm = 82 7'; //= 120 7'. Missouia Co., Mont. Physical Characters. H., 3. Sp. gr., 4.43 to 4.45. LUSTRE, metallic. OPAQUE. STREAK, blackish gray. TENACITY, brittle. COLOR, black or blackish gray. BEFORE BLOWPIPE, ETC. On charcoal fuses, yields white fumes with garlic- odor. With soda yields malleable copper and a reaction for sulphur. In closed tube decrepitates, yields sulphur sublimate, then fuses and yields red sublimate of arsenic sulphide. Soluble in nitric acid. REMARKS. As stated, p. 357. enargite is one of the great ores, yielding probably five per cent, of the copper of the world. It is apparently a primary mineral and forms nearly one third of the ore at Butte, Montana.* Other large deposits are Sierra * Beyschlag, Vogt & Krusch (Truscott), p. 871. I I ,-* r MINERALS OF METALLIFEROUS ORE DEPOSITS. 367 Famatina, Argentina; in clay slate; Tinctic, Utah; with rich silver and gold minerals; Mancanyan, Luzon; with tetrahedrite in porphyry; Morococha and Cerro de Pasco, Peru, with tennantite; Hedworda Mine near Coquimbo, Chili, at Bor, Servia and Parad, Hungary, in porphyry. FAMATINITE. CusSbS 4 (Cu 43.3; Sb 27.4; S 29.3, per cent.) is a mineral of metallic lustre and granular structure with a color suggesting that of fresh fractured bornite. Streak black. H., 3 to 4. Sp. gr., 4.5 to 4.6. Before the blowpipe it gives off white fumes of antimony and leaves a brittle black globule. It is found with enargite at Sierra Famatina, Argentina, and Cerro de Pasco, Peru, in considerable quantities. It is associated with the ores of Goldfield, Nevada. TETRAHEDRITE. Gray Copper Ore. COMPOSITION. Cu 8 Sb 2 S 7 . Cu often partially replaced by Fe, Zn, Pb, Hg, Ag, and the Sb by As. FIG. 392. FIG. 393. FIG. 394. GENERAL DESCRIPTION. A fine grained, dark gray mineral of metallic lustre. Characterized especially by the tetrahedral habit of its crystals which are sometimes coated with yellow chalcopyrite. FIG. 395. FIG. 396. CRYSTALLIZATION. Isometric. Hextetrahedral class, p. 62. The tetrahedron p, Fig. 392, usually predominates, often modified by the tristetrahedron n = (a : 2a :2a); {211}; Figs. 395, 396, and less frequently by other forms such as the dodecahedron d t Fig. 393, and the deltohedron r = (a : a : 2a); {221} ; Fig. 394. 368 MINERALOGY. Physical Characters. H., 3 to 4.5. Sp. gr., 4.5 to 5.1. LUSTRE, metallic. OPAQUE. STREAK, black or reddish brown. TENACITY, brittle. COLOR, light steel to dark lead gray or iron black. BEFORE BLOWPIPE, ETC. On charcoal fuses easily to a globule which may be slightly magnetic. Evolves heavy white fumes with sometimes garlic odor. The roasted residue gives bead and flame reactions for copper. Soluble in nitric acid to a green solu- tion with white residue. SIMILAR SPECIES. The crystals are characteristic. The fine grained fracture in conjunction with the color is often sufficient to distinguish it. It is softer than arsenopyrite and the metallic cobalt ores, and does not generally yield a strongly magnetic residue on heating. Bournonite and chalcocite are softer, and finally the blowpipe reactions are distinctive. VARIETIES. Tennanite approximating CusAs 2 S 7 , but grading into ordinary tetrahedrite and undistinguishable by crystal form or general appearance. Freibergite, argentiferous, and schwatzite, "mercurial, are im- portant ores respectively of silver and mercury. Other varieties carry bismuth, zinc or lead. REMARKS. Tetrahedrite is one of the most frequent minerals of the copper deposits, especially in veins in the schists and older eruptives. Widely distributed in the copper veins of the Andes, porphyries of Chili, the Peruvian Cordilleras and Algeria. Occurrences are numerous in Saxony, Harz, Hungary, France, Cornwall and elsewhere. In this country abundant in the mines of Silverton and Aspen, Colorado, and at Park City, Utah. Also is found in the mines of Butte, Montana; and Bingham, Utah. Tennantite occurs in crystals in Cornwall and massive in Mt. Lyell, Tasmania; Morococha, Peru; Teniente, Chile; Gilpin County, Colorado; Laramie County, Wyoming and sparingly in the enargite veins at Butte. CUPRITE. - Red Oxide of Copper, Ruby Copper Ore. COMPOSITION. Cu 2 O (Cu 88.8 per cent). Sometimes inter- mixed with limonite. GENERAL DESCRIPTION. Fine grained masses, dark red, brown- ish-red and earthy brick-red in color ; or deep red to crimson, transparent, isometric crystals, usually octahedrons, or cubes. Also capillary. MINERALS OF METALLIFEROUS ORE DEPOSITS. 369 FIG. 397. FIG. 398. FIG. 399. Sp. gr., 5.85 106.15. TRANSPARENT to opaque. TENACITY, brittle. CRYSTALLIZATION. Isometric. Class of gyroid, p. 66. The octahedron /, cube a and dodecahedron d predominating. Index of refraction for red light 2.849. Physical Characters. H., 3.5 to 4. LUSTRE, adamantine or dull. STREAK, brownish red. COLOR, crimson, scarlet, vermilion, or brownish red. BEFORE BLOWPIPE, ETC. On charcoal blackens and fuses easily to a malleable red button. Flame and bead tests give the color for copper. Soluble in nitric acid to a green solution. Soluble also in strong hydrochloric acid to a brown solution which diluted with water yields a white precipitate. SIMILAR SPECIES. It is softer than hematite and harder than cinnabar or proustite, and differs from them all by yielding an emerald-green flame and a malleable red metal on heating. REMARKS. Chiefly secondary, part in the gossan intermixed with limonite and in part developed lower as in limestones where copper solutions have formed carbon- ates. It has formed the principal or a very important portion of deposits at Cobar, New South Wales; Coro Coro, Bolivia; Chessy, France; IllapeL Chili; many mines in Peru; and Boleo, Lower California. In the United States it is especially abundant in the Bisbee district, Arizona; and an important ore in certain mines in Colorado, New Mexico, Nevada, Wyoming and California. TENORITE. Melaconite, Black Oxide of Copper. COMPOSITION. CuO, (Cu 79.85 per cent.). GENERAL DESCRIPTION. Dull black earthy masses, black powder and shining black scales. PHYSICAL CHARACTERS. Lustre, metallic in scales, dull in masses. Color and streak black. H., 3. Sp. gr., 5.82 to 6.25. BEFORE BLOWPIPE, ETC. Infusible, otherwise like cuprite. REMARKS. Occurs in fissures in the lava of Vesuvius, as a black coat on chalcopy- rite and as dull black masses with chrysocolla. REMARKS. Occurs as a sublimation product at Vesuvius and as an occasional decomposition product in oxidized zone as at Bisbee, Arizona, and Bingham, Utah. 25 370 MINERALOGY. Said to occur in relatively large quantity at the Rambler Mine, Wyoming, and in Waldo district, Oregon, and to be intermixed with the secondary chalcocite of Ducktown, Tenn. BROCHANTITE. CuSO 4 3Cu(OH) 2 . Velvety, emerald-green crusts of fine orthorhombic needle crystals, botryoidal masses and vein-like with fibrous structure. Transparent to translucent. Lustre, vitreous. Streak, pale green. H., 3.5 to 4. Sp. gr., 3-9- BEFORE BLOWPIPE, ETC. On charcoal turns black, colors the flame -emerald green and leaves malleable red button. Insoluble in water, but soluble in acids. In closed tube yields water. REMARKS. A minor ore occurring occasionally in oxidized zone and sometimes in economic quantity, as at Chiquicamata, Chili; Monarch Mine, Chaffee Co., Colorado, and the Clifton-Morenci districts, Arizona, Coro Coro, Bolivia. ATACAMITE. COMPOSITION. Cu(OH)Cl.Cu(OH) 2> (Cu 59-45, Cl 16.64 per cent.). GENERAL DESCRIPTION. Confused aggregates of crystals of bright or dark-green color. Also granular or compact massive, or as a crust. Rarely in slender ortho- rhombic prisms. PHYSICAL CHARACTERS. Translucent to transparent. Lustre, adamantine to vitreous. Color, bright green, emerald green, blackish green. Streak, apple green. H., 3 to 3-5- Sp. gr., 3.75 to 3-77- BEFORE BLOWPIPE, ETC. On charcoal yields white fumes and a coating which is brown near the assay and white at some distance from it, fuses to a copper-red, malle- able button, and colors the flame a beautiful and persistent blue "without the aid of hydrochloric acid. In closed tube yields water and a gray sublimate. Soluble in acids to a green solution. REMARKS. Found in large quantities in Chili in the oxidation zone at Atacama, partly as sand but also in veins, especially at Las Remolinos, Chili, and at Toco- pilla, Bolivia, also very plentiful at Wallaroo, South Australia. Minor localities are Boleo, Lower California; Cornwall, England; Vesuvius and Etna. CHALCANTHITE. Blue Vitriol. COMPOSITION. CuSO 4 -5H 2 O, (CuO 31.8, SO 3 32.1, K 2 O 36.1 per cent.). GENERAL DESCRIPTION. A blue, glassy mineral, with a disagreeable metallic taste. It occurs usually as an incrustation, with fibrous, stalactitic or botryoidal structure; but sometimes in flat triclinic crystals. PHYSICAL CHARACTERS. Translucent. Lustre, vitreous. Color, deep blue to sky blue. Streak, white. H., 2.5. Sp. gr., 2.12 to 2.30. Brittle. Taste, metallic nauseous. CRYSTALLIZATION. Triclinic. Axes a :b~: ^ = 0.566 : I : 0.551. Axial angles = 82 21'; /? = 73 11'; 7 = 77 IG * 4 ' 37'r Prominent forms, right and left unit prisms m and M y unit pyramid /, and the pinacoids a and b. Angles mM= 56 50'. Optically . BEFORE BLOWPIPE, ETC. On charcoal, fuses, coloring flame green and leaving metallic copper. In closed tube yields water and sulphur dioxide and leaves a white powder. Easily soluble in water to a blue solution. MINERALS OF METALLIFEROUS ORE DEPOSITS. 371 REMARKS. Chalcanthite is of great interest as the intermediate stage in the so- called secondary enrichment. Often present in the waters of copper mines, from which large quantities are recovered as at Rio Tinto, Spain, and at Wicklow, Ireland. Occasionally found in quantity and mined, as at Bluestone Mine, Lyon County, Nevada; United Verde Mine, Arizona; Copaquire, Taraposa and Chiquicamata, [ Chili. MALACHITE. Green Carbonate of Copper. COMPOSITION. Cu 2 (OH) 2 CO 3 , (CuO 71.9, CO 2 19.9, H 3 O 8.2 per cent.) GENERAL DESCRIPTION. Bright-green masses and crusts, often with a delicate, silky fibrous structure or banded in lighter and darker shades of green. Sometimes stalactitic. Also in dull- green, earthy masses, and rarely in small, slender, monoclinic crystals. Frequently coating other copper minerals or filling their crevices and seams. Physical Characters. H., 3.5 to 4. Sp. gr., 3.9 to 4.03. LUSTRE, silky, adamantine or dull. TRANSLUCENT to opaque. Streak, pale green. TENACITY, brittle. COLOR, bright emerald to grass green or nearly black. BEFORE BLOWPIPE, ETC. On charcoal, decrepitates, blackens, fuses, and colors the flame green, leaving a globule of metallic copper. In closed tube, blackens and yields water and carbon dioxide. Soluble in acids, with effervescence. SIMILAR SPECIES. Distinguished by color and effervescence with acids. REMARKS. Malachite is the most common oxidation product, and may occur in more important masses in the zone of enrichment by replacement of limestone or dolomite or as a later alteration of other secondary minerals such as chalcocite. The purest and probably largest deposit is in limestone at Mednorudiansk near Nishni Tagilsk, which yields most of the malachite worked into art objects. Other famous localities are Bisbee and Morenci, Arizona; Santa Rita, New Mexico; Cobar, New South Wales; Bura Burra, Australia; many mines in Chili, and in the deposits in sandstone as at Coro Coro, Bolivia, and Perm, Russia. Often it occurs pseudo- morphic after azurite and cuprite as at Chessy, France. AZURITE. Blue Carbonate of Copper. COMPOSITION. Cu 3 (OH) 2 (CO 3 )2, (CuO 69.2, CO 2 25.6, H 2 O 5.2 per cent.). GENERAL DESCRIPTION. A dark-blue mineral occurring in highly modified, glassy, monoclinic crystals and groups. When 372 MINERALOGY. massive, it may be vitreous, velvety, or dull and earthy. It fre- quently occurs incrusting other copper ores, or distributed through their cracks and crevices. CRYSTALLIZATION. Monoclinic. Axes & : b : c = 0.850 : i : 0.881 ; ft = 87 36'. Crystals very varied in habit. Those figured show basal pina- FIG. 401. FIG. 402. Arizona. Chessy, France. coid c, ortho-pinacoid a, unit prism m, unit dome , (A1 2 O 8 65.4, H 2 O 34.6 per cent.). GENERAL DESCRIPTION. Best known as a white or nearly white mineral, usually occurring in small stalactities (Fig. 205) or thin smooth crusts, with fibrous internal structure. Rarely in small monoclinic crystals. The great deposits of "bauxite" in Georgia are, however, chiefly gibbsite. PHYSICAL CHARACTERS. Translucent. Lustre, faint vitreous. Color, white greenish, reddish, yellow. Streak, white. H., 2.5 to 3.5. Sp. gr., 2.38. BEFORE BLOWPIPE, ETC. Infusible, exfoliates, glows and becomes white. With cobalt solution becomes deep blue. In closed tube yields water. Soluble in hydro- chloric or sulphuric acid. REMARKS. Rare as pure material, plentiful in bauxite and laterite. The pure mineral is found with corundum in Asia Minor, in elaeolite syenite in Norway and in small quantity at Richmond and Lenox, Mass., and Dutchess and Orange counties, N. Y. ALUMINITE. COMPOSITION. (AlO^SO^HjO, (A1 2 O 3 29.6, SO 8 23.3, H,O 47.1 per cent). GENERAL DESCRIPTION. Usually found in white rounded or irregular masses of chalk-like texture and peculiar harsh feeling. PHYSICAL CHARACTERS. Opaque. Lustre, dull or earthy. Color and streak, white. H., l to 2. Sp. gr., 1.66. Meagre to the touch and adheres to the tongue. BEFORE BLOWPIPE, ETC. Infusible. In closed tube yields much acid water. With cobalt solution becomes deep blue. Easily soluble in acid. REMARKS. Found in clay beds at Halle, Germany, and at Brighton, England, filling a three-foot cleft in the chalk. Other localities in France and Bohemia. ALUNOGEN. COMPOSITION. A1 2 (S0 4 ) 3 + 18 H 2 O, (A1 2 O 3 15.3, SO 3 36.0, H 2 O 4 8.7 per cent.). GENERAL DESCRIPTION. A delicate fibrous crust of white or yellow color. Some- times massive. Tastes like alum. PHYSICAL CHARACTERS. Translucent. Lustre, vitreous or silky. Color, white yellowish or reddish. Streak, white. H., 1.5 to 2. Sp. gr., 1.6 to 1.8. Taste, like alum. 41 6 MINER ALOG Y. BEFORE BLOWPIPE, ETC. Melts in its own water of crystallization, but becomes infusible. It is colored deep blue by cobalt solution. In closed tube yields much acid water. Easily soluble in water. REMARKS. Formed by action of sulphuric acid of decomposing sulphides upon aluminous shales. Also formed during volcanic action. The large deposit near Silver City, New Mexico, has been mentioned on p. 410. ALUNITE. Alum Stone. COMPOSITION. K(A1OH) 3 (SO 4 ) 2 + 3 H 2 0, (A1 2 8 37.0, K 2 O 11.4, SO 3 38.6, H 2 O 13 per cent). GENERAL DESCRIPTION. Occurs fibrous and in tabular to nearly cubic rhombohedral crystals, or so intermixed with a siliceous material as to form a hard granular and nearly white rock. Physical Characters. H., 3.5 to 4. Sp. gr., 2.58 to 2.75. LUSTRE, vitreous. TRANSPARENT to nearly opaque. STREAK, white. TENACITY, brittle. COLOR, white, grayish or reddish. BEFORE BLOWPIPE, ETC. Infusible and decrepitates. With cobalt solution becomes deep blue. With soda infusible, but the mass will stain silver. In closed tube yields water at a red heat. Im- perfectly soluble in hydrochloric or sulphuric acid. The specimen may be boiled in water or acid to remove soluble sulphates, then heated to redness, again boiled in water, the clear liquid tested by addition of BaCl 2 . REMARKS. The formation and principal occurrences are stated on p. 410, and its uses on p. 418. CHAPTER XIX. MINERALS IMPORTANT IN THE INDUSTRIES AND NOT ALREADY DESCRIBED. In this division the minerals are rather of chemical than of metallurgical importance, although the line is difficult to draw. So far as possible the minerals used as sources of compounds of a particular element are grouped together. It is to be noted that the minerals are for the most part products of weathering of the rocks and deposited from weathering solu- tions, rather than separations from magma or magmatic waters. THE POTASSIUM MINERALS. THE minerals described are : Chlorides Sylvite KC1 Isometric Carnallite KCl.MgCl 2 6H 2 Orthorhombic Kainite KCl.MgSO 4 .3H 2 O Monoclinic Sulphates Ka Unite K Al(SO 4 ) 2 .i2H 2 O Isometric Nitrate Nitre KN0 3 Orthorhombic In addition to these, potassium is a constituent of many silicates, such as orthoclase, muscovite and leucite. It is also found in solution in many brines. ECONOMIC IMPORTANCE. Potash salts to the amount of 306,000 tons were imported in 1913. In 1914 this had diminished to 243,000 and in 1915 to 85,000 tons* valued at $3,765,224. The imports in pounds of different salts were: 1914- 1915. Carbonate of, crude 9,326,899 5.386,719 Caustic, not including refined 7,284,176 2,032,319 Cyanide of 4*7. 139 871,871 Chloride of 371,521,920 2,296,606 Nitrate of, saltpeter, crude 2,230,528 6,855 Sulphate of 80,447,360 25,415,040 All other 14,590,437 7,502,806 Total 485,818,459 170,555.450 * Mineral Industry of U. S., 1915, p. 96. 28 417 41 8 MINERALOGY. As one effect of the European war this country has been forced to search for and utilize other sources for potash than the Stassfurt salts and in 1915 potash salts to the value of $342,000 were obtained* from domestic sources, such as: By-product potash from the cement manufacture. Potassium sulphate from alunite of Maryvale, Utah. Dried kelp. By evaporation of water from Jesse Lake, Nebraska. The usesf of the potassium salts and the quantities used are indicated by the importations for the month of February, 1914: Fertilizer salts: Other potash salts: Long Tons. Pounds. Kainite 72,008 Carbonate of potash. . 1,674,685 Manure salts 12,451 Caustic potash 520,166 Sulphate of potash 5,098 Nitrate of potash. . . . 22,699 Chloride of potash 13,172 Cyanide of potash. ... 5,641 Other potash salts. ... 638,112 The carbonate of potash is used in glass-making, the cyanide in metallurgy, the nitrate in explosives, the sulphate and the chloride in fertilizers. Other large amounts are used in making soap, matches, in photography and pharmacy. While the search for the solid deposits similar to those of Stassfurt and for deposits of nitrate of commercial importance has not been successful other saline lakest rich in potash salts are being equipped for extraction, such as Searles Lake, California; Owens Lake, California; Great Salt Lake, Utah. Alunite, p. 416, has been successfully treated at Marysvale, Utah. It is crushed, roasted, digested with water and potassium sulphate obtained. The filter cake is about 65 per cent. A1 2 O 3 and the K 2 SO 4 over 95 per cent. pure. Methods have been described and patented for production of potassium salts from orthoclase, leucite and sericite or white muscovite. It is said the products are necessarily low grade. j| * Ibid., p. 95. t Ibid., p. 95. t Mineral Resources, U. S., 1915, pp. 101-103. Ibid., p. no. || Ibid., p. 95- MINERALS IMPORTANT IN THE INDUSTRIES. 419 FORMATION AND OCCURRENCE. The crust of the earth contains, it is estimated, 2.33 per cent, of potassium, very largely in the great silicates, orthoclase, muscovite and leucite and in the products resulting from their decomposition. It is necessary to plant life and is present in all soils, being, as stated on p. 244, at the decomposition of the rocks carried off to a much less extent than sodium by the solutions, but adsorbed by colloidal matters 'in clay and soil and often recombined to sericite (white muscovite). The portion that does reach the sea is again lessened by seaweed and even in land-locked basins after the deposition of the less soluble calcium and sodium salts is rarely deposited but remains in the mother liquor or bitterns. Some Michigan brines contain up to 3 to 5 gm. per liter. One at Fair- port Harbor, Ohio, ran 7.4 KC1. Under the Ochsenius "bar" theory, p. 423, the dense solutions before the separation of the potassium and magnesium salts reach the bar level and the "bitterns" escape to the sea. In rare instances, as at Stassfurt, Germany, p. 225, from peculiar geological conditions these residual salts (Abraumsalze) are de- posited principally as carnallite and kainite, sylvite being sub- ordinate. Smaller deposits exist in Upper Alsace, Tyrol, Kalusz, Galicia, and India and valuable deposits have been found in mining salt near Suria, south of Cardona, near Barcelona, in northeastern Spain. Nitre deposits are numerous but not generally large an exten- sive layer exists in the soda nitre region of Tarapaca, Chili, and small deposits in Arizona, Idaho and elsewhere. SYLVITE. COMPOSITION. KC1, (K 52.4 per cent.). GENERAL DESCRIPTION. Colorless, transparent cubes or white masses, which look like common salt and have somewhat similar taste. Absorbs moisture and becomes damp. PHYSICAL CHARACTERS. Transparent when pure. Lustre, vitreous. Color, color- less white, bluish, reddish. Streak, white. H., 2. Sp. gr., 1.97 to 1.99. Taste, like salt. Cleavage in cubes. BEFORE BLOWPIPE, ETC. Fuses very readily, coloring flame violet. If added to a salt of phosphorus and copper oxide bead, the flame is colored azure blue. Soluble in water and acids. 420 MINERALOGY. CARNALLITE. COMPOSITION. KCl.MgCl + 6H.jO (K 14.1 percent.). GENERAL DESCRIPTION. A massive and somewhat granular mineral occurring in beds or strata at the Stassfurt potash salts deposit of Germany. Seldom found in crystals. PHYSICAL CHARACTERS. Translucent to transparent. Lustre, sub- vitreous. Color, white, brownish and reddish. Streak, white. H., i. G=i.62. Taste, salty and bitter. BEFORE BLOWPIPE, ETC. Same as for sylvite. Very deliquescent. USES. Is the chief source of the manufactured potash salts of commerce which are so largely used as fertilizers. It is simply dissolved in water and the potassium chloride crystallized out at the proper temperature. KAINITE. COMPOSITION. MgSO 4 .KCl + 3H 2 O. GENERAL DESCRIPTION. White to dark red granular crusts with salty taste, also tabular and prismatic monoclinic crystals. Physical Characters. H., 2.5-3. Sp. gr., 2.05-2.2. LUSTRE, vitreous. TRANSPARENT to translucent. STREAK, colorless. TASTE, salty and astringent. COLOR, white to reddish white, and colorless. BEFORE BLOWPIPE, ETC. Easily fusible, coloring the flame violet. After fusion on charcoal in reducing flame the moistened mass will stain bright silver. Soluble in water. KALINITE. Potash Alum. COMPOSITION. KAl(SO 4 ) 2 -f i2H 2 O, (K 2 Og.g, Al a O 8 10.8, SO 3 33.8, H 2 O45.5 per cent.). GENERAL DESCRIPTION. Natural alum with the peculiar taste, occurring as a white efflorescence on argillaceous minerals. Usually fibrous, or as mealy crusts, or compact. PHYSICAL CHARACTERS. Transparent or translucent. Color, white. Lustre, vitreous. Streak, white. Taste, astringent. Tenacity, brittle. H., 2.5. Sp. gr., 1.75. BEFORE BLOWPIPE, ETC. On heating, becomes liquid, yields water, and finally swells to a white, spongy, easily-powdered mass, which is infusible, but colors the flame violet. With cobalt solution, becomes deep blue on heating. Soluble in water. REMARKS. A white efflorescence on pyritiferous clays or clay slates arid a sublimation product of burning coal fields and volcanoes. NITRE. Saltpetre. COMPOSITION. KNO 3 , (K 2 O 46.5, N 2 O 5 53.5 per cent). GENERAL DESCRIPTION. White crusts, needle-like, orthorhom- bic crystals and silky tufts, occurring in limestone caverns or as incrustations upon the earth's surface or on walls, rocks, etc. Not altered by exposure. MINERALS IMPORTANT IN THE INDUSTRIES. 421 Physical Characters. H., 2. Sp. gr., 2.09 to 2.14. LUSTRE, vitreous. TRANSLUCENT. STREAK, white. TENACITY, brittle. COLOR, colorless, white, gray. TASTE, salty and cooling. BEFORE BLOWPIPE, ETC. On charcoal fuses easily, deflagrates violently like gunpowder, colors the flame violet. Soluble in water, REMARKS. Occurs as an efflorescence in soils containing excrement as in India, Egypt, Algeria, Persia, Spain. Sometimes occurs lining the walls of caves in lime- stone as in Kentucky, Tennessee, France and Germany. THE SODIUM MINERALS. The minerals described are : Chloride Halite NaCl Isometric Sulphate Mirabilite Na 2 SO 4 .loH 2 O Monoclinic Nitrate Soda Nitre NaNO s Hexagonal Carbonate Trona Na 2 CO 3 .HNaCO 3 .2H 2 O Monoclinic Sodium is an important constituent in plagioclase nephelite, sodalite and other silicates, and in such minerals as cryolite, ulexite and borax. ECONOMIC IMPORTANCE. The only sodium salt produced in quantity in the United States is halite, of which the production in 1915* was 5,352,409 short tons produced by fourteen states, nearly half coming from Michi- gan and New York and about one fifth from Ohio, Kansas, Louisiana and California in the order named. Mirabilite from Wyoming and the Great Salt Lake and trona from Nevada and California in comparatively small amounts are obtained. Soda nitre was importedf in 1914 to the amount of 620,533 tons, as well as many manufactured salts. Those imported in excess of 500 tons in 1914 being: Sulphide 1,265 Nitrite 922 Prussiate 1,147 Phosphate 682 Ash 1,114 Silicate 523 * Mineral Resources U. S., 1915, p. 265. f Mineral Industry, 1914, p. 675. 422 MINERAL OGY. In this country about one fifth of the salt is mined or obtained from deep shaft mines* or open cuts as rock salt, the rest is ob- tained by evaporation of the artificial or natural brines, bitterns, and sea water, using as heat the sun's rays or an artificial source. Probably one half the halite is used for culinary and preservative purposes, over 1,000,000 tons per year are converted into sodium and chlorine compounds, chief among which aref sodium carbonate and bicarbonate, caustic soda and bleaching powder. About 2,000 tons of metallic sodium are made in the United States yearly by the Castner process and until recently 8,000 to 9,000 tons of sodium cyanide for metallurgical purposes. Minor uses are in glazing pottery and in many metallurgical processes and the manufactured carbonate and caustic soda have their large uses in glass and soap making, bleaching, etc. Soda nitre is used in the manufacture of nitre for gunpowder, in the production of nitric acid, but chiefly for fertilizing purposes. FORMATION AND OCCURRENCE OF SODIUM SALTS. The economically important sodium compounds which occur as minerals are all deposits from weathering solutions assisted in the case of soda nitre probably by organic deposits. Halite occurs in beds varying from a few feet to over three thousand feet in thickness, in all geologic agesj except the Archaean, commonly underlain by gypsum and anhydrite, sometimes alter- nating with clay, gypsum, anhydrite, marl and dolomite. It occurs also in nearly all water, from infinitesimal quantities to strong brines, and as incrustations on high planes in dry regions. The solids in seawater average 3.5 per cent. The evaporation of 300 feet would only mean a bed of less than six feet thick. As it is difficult to imagine a steady subsidence sufficient to *Salt mines are worked in Livingston County, New York; near Detroit, Mich- igan; in Ellsworth and Rice Counties, Kansas, and on Weeks and Avery Islands, Louisiana. t Sodium sulphate (salt-cake) is first made and from this caustic soda, carbonate, bicarbonate, etc. tWeinschenk gives Silurian "Pendschab," Carboniferous, England and North America; Dyas, north and middle Germany; Triassic, Wurtemberg and the Alps; Jurassic, Bex, Switzerland; Cretaceous, Algiers; Tertiary, Carpathians, Spain, Sicily; Armenia, Persia. " Grundziige des Gesteinskunde," 243. MINERALS IMPORTANT IN THE INDUSTRIES. 423 explain deposits 1 ,000 to 3,000 ft. thick the Bar theory of Ochsenius* is generally accepted. For the dissolved constituents to separate there is needed a concentration of the solution, usually a land- locked basin with a shallow bar between it and the sea, the surface layers sinking as they become denser. Michigan, New York, Ohio and Pennsylvania produce salt derived from "the evaporation of some great sea." At least six successive periods of evaporation took place and each bed of salt is underlain by one or more of dolomite anhydrite and marl. Enormous dome-shaped deposits of very pure rock salt sur- rounded on all sides by clay occur in Louisiana. On Weeks Island it is at least 4,000 ft. thick and very pure. At Petite Anse there are 2,263 f eet f P ure sa lt> then 7 ^ eet f foreign matter, then more salt to an unknown depth. Curiously, they are overlain by enormous beds 200 to 600 feet thick of gypsum and anhydrite or oil-bearing limestone. The conditions of formation are not understood, f In the drier western states halite is found as at Salton, California, in crusts 10-20 inches thick, then mud, then another salt crust and the whole over hard clay. Similar deposits occur in North Africa. Famous foreign salt deposits are Wieliczka, Poland; Cheshire, England; Salzburg, Tyrol. The Sulphates of Soda. Like halite, the sulphates of soda are derived from the weather- ing solutions but rather in inland "lakes" lacking much calcium or magnesium. Little is formed in marine basins, the sulphuric acid being there deposited as gypsum, anhydrite, kieserite, etc. As with the sulphates of lime, p. 440, strong salt solutions dehydrate therefore the hydrous sulphate mirabilite is deposited from pure solution, while the anhydrous sulphate thenardite deposits in presence of much halite. * "Die Bildung der Steinsalzlager," Halle, 1877. The reason for the non-evaporation of the residual salts is that the dense solu- tions in time reach the level of the bar and the residual bittern escapes. The Gulf of Karaboghaz, east side of Caspian Sea, is instanced by Clarke. "Data Geochemistry," p. 211. Bulletin Geol. Surv. 491. t Lindgren, "Mineral Deposits," 288. 424 MINERALOGY. Near Laramie, Wyoming, are " lake deposits 20-30 feet deep, principally of sodium sulphate, mirabilite, Na 2 SO 4 + ioH 2 O." The upper few inches is nearly pure white below the crystals and intermixed mud containing 36 per cent. Na 2 SO 4 (pure mirabilite containing 44 per cent.). The same mineral separates from the Great Salt Lake, when the temperature is low, and is heaped up by the waves on the beaches where, if not collected, it redissolves as soon as the temperature rises, and a similar winter formation takes place at Lacu Sarat, Roumania. Soda Nitre. Soda nitre forms in small amounts as the result of the action of bacteria on organic matter and the union of the nitric acid with soda, and may accumulate in caves as at Holmdale, Idaho. Somewhat larger deposits of less certain origin occur in Death Valley, Cali- fornia, along the shore line of an ancient sea.* The world's great deposits are in Tarapaca and Antofagasta, Chili, a rainless, desolate region 3,000 feet above the sea between the Andes and the Coast Ranges and near the latter. Often the deposits are only ten miles from the sea. The area is broken by transverse ranges into a series of plateaus or "pampas" which slope from the Andes to the coast ranges, Superficial beds of common salt and soda nitre I to 6 ft. thick occur under a few feet of earth, the nitrate often on somewhat higher ground, but at other times they are mixed indiscriminately, the soda nitre averaging about 25 per cent. The impure soda nitre or "caliche" is hand-picked from the associated chlorides and sulphates and refined. The origin is not certain.! The soil of Venezuela and other parts of South America is unusually rich in nitrates. Mountain floods, which occur at intervals of seven or eight years, may have carried the soluble nitrate to the pampas where it is again de- posited. Other theories are the leaching of bird guano and the mingling with the salt waters of an enclosed basin. * Mineral Industry, 1914, p. 673. t Discussion, Clarke, Bulletin U. S. Geol. Survey, 491, pp. 242-246. MINERALS IMPORTANT IN THE INDUSTRIES. 425 The Carbonates of Sodium. The carbonates of sodium occur in soils and in certain lakes and "playa" lakes (dry in summer, flooded in the wet season). The white efflorescence on the "playas" is a mixture of these with chlorides. Trona is much more common than the laboratory product, natron. The manner of their deposition from weathering solutions is variously attributed to : 1. Direct deposition of the teachings of rocks* poor in lime and rich in soda as in the Lahontan Lakes of Nevada, in which the decomposing rocks are rhyolites and andesites, or Owen's Lake, California, where the waters run through volcanic ash. 2. Reduction from alkaline sulphates by algaef as in part at least explaining the natron lakes of Egypt. 3. Double decomposition between sodium sulphate or chloride and calcium bicarbonate as explaining some Hungarian deposits. Examples of deposits, some of which have been worked are: Searles Lake, California.^. Contains trona in "fish bone" crys- tals which look like flat splinters of wood projecting into the ground like roots for 6-7 inches. Green River, Wyoming, where borings in sandstone yielded at 700 feet an almost concentrated solution of carbonates. Ragtown, Nevada, where analyses showed an average Na 2 COs 47, NaHCO 3 31, H 2 O 16 per cent. Owen's Lake, California. The dissolved salts being one third carbonates of soda. HALITE. Rock Salt, Common Salt. COMPOSITION. NaCl, (Na 60.6 per cent.), usually impure. GENERAL DESCRIPTION. Halite occurs frequently granular, sometimes coarse, often dense and mixed with clay. Colors white, gray, brown or blue and red from uncertain coloring material, green from copper, brown from bituminous substances. In dry countries it occurs as a fibrous efflorescence. It is liable to absorb moisture and becomes damp, especially when containing calcium or magnesium chlorides. It is known by its taste. * Bulletin, U. S. Geol. Survey, 149, 229. t Ibid., 230. ' $ Mineral Industry, 1914, p. 676. 426 MINERALOGY. CRYSTALLIZATION. Isometric in cubes and cavernous crystals and cubic cleavages often with symmetrical etchings, more rarely other forms. FIG. 414. FIG. 415. FIG. 417. Physical Characters. H., 2.5. Sp. gr., 2.4 to 2.6. LUSTRE, vitreous. TRANSLUCENT to transparent STREAK, white. TENACITY, brittle. COLOR, white, colorless, yellow, brown, deep blue. TASTE, salt. CLEAVAGE, cubic. BEFORE BLOWPIPE, ETC. Decrepitates violently, fuses very easily and colors the flame yellow and may be volatilized. Easily soluble in cold water. , SIMILAR SPECIES. The taste distinguishes it from all other minerals. REMARKS. The mode of occurrence, type localities and uses have been described on pp. 422-423. MIRABILITE. Glauber Salt. COMPOSITION. Na 2 SO 4 + ioH 2 O (Na 2 O 19.3, SO 3 24.8, H 2 O 55.9 per cent.). GENERAL DESCRIPTION. Translucent) white, fibrous crusts or monoclinic crystals, closely resembling those of pyroxene in form and angle. On exposure loses water and falls to powder. Physical Characters. H., 1.5 to 2. Sp. gr., 1.48. LUSTRE, vitreous. TRANSPARENT to opaque. STREAK, white. TASTE, salty and bitter. COLOR, white or faintly greenish. BEFORE BLOWPIPE, ETC. On charcoal fuses, colors the flame yellow and leaves a mass which will stain bright silver. In closed tube yields much water. Easily soluble in water. MINERALS IMPORTANT IN THE INDUSTRIES. 427 REMARKS. Type occurrences have been described on p. 423. Others are the bottom of the Bay of Kara Bougas, an inlet of the Caspian Sea, in deposits sometimes a foot in thickness. Massive at Logrdno, Spain; without salt in great layers at Bompensieri, Sicily; Tiflis, Tarapaca, Chile; New Albany, Ind. In gypsum in Westmoreland and as a sublimation product at Vesuvius. THENARDITE. Na2SO4. Twinned tabular orthorhombic crystals and as an efflorescence. Soluble in water. Found at Borax Lake, Cal., and Villa Rubia. Spain, in good crystals, dense material at Stassfurt, Prussia, Rio Verde, Arizona, etc, GLAUBERITE. Na 2 SO4.CaSO 4 . Tabular monoclinic crystals and lamellar masses in rock salt and in the mud of borax lakes. SODA NITRE. Chili Saltpetre. COMPOSITION. NaNO 3 , (Na 2 O 36.5, N 2 O 5 63.5 per cent). GENERAL DESCRIPTION. Rather sectile granular masses or crusts of white color, occurring in enormous beds and as an efflorescence. Rarely found as rhombohedral crystals of the forms of calcite. On exposure crumbles to powder. Physical Characters. H., 1.5 to 2. Sp. gr., 2.24 to 2.29. LUSTRE, vitreous. TRANSPARENT. STREAK, white. TENACITY, brittle. COLOR, colorless, white or yellowish. TASTE, cooling and salty. BEFORE BLOWPIPE, ETC. On charcoal deflagrates less violently than nitre and becomes liquid. Colors the flame yellow. Very easily soluble in water. REMARKS. The occurrence and uses have been described on pp. 422, 424. TRONA. Urao. COMPOSITION. Na 2 CCyNaHCO 3 -f 2H 2 O, (Na 2 O 41.2, CO 2 38.9, H 2 O 19.9.). GENERAL DESCRIPTION. Beds and thin crusts of white glistening material, often fibrous and occasionally in monoclinic crystals. It is not altered in dry air. PHYSICAL CHARACTERS. Translucent. Lustre, vitreous, glistening. Color, white, gray, yellowish. Streak, white. H , 2.5 to 3. Sp. gr., 2.11 to 2.14. Taste, alkaline. BEFORE BLOWPIPE, ETC. Fuses- easily, coloring flame yellow. In closed tube yields water and carbon dioxide. Easily soluble in water. Effervesces vigr/ously in cold dilute acids. REMARKS. The chief occurrences have been described on p. 425; others are Armenia, Venezuela and British East Africa. GAY-LUSSITE. Na 2 CO3.CaCO 3 .5H 2 O. White monoclinic pyramidal crystals at Soda Lake, Nevada; Venezuela, etc. THE LITHIUM MINERALS. The minerals described are : 428 MINERAL OG Y. Phosphate Silicates Amblygonite Spodumene Lepidolite Petalite LiAl(SiO 3 ) 2 , R 3 Al(SiO,) 3 LiAl(Si 2 6 ) 2 Triclinic Monoclinic Monoclinic Monoclinic Lithia is also a constituent of a series of double phosphates such as triphyllite and triplite, of less well-known silicates cookeite, eucryptite and of certain varieties of tourmaline. ECONOMIC IMPORTANCE. About 3,000 tons of the phosphate amblygonite were pro- duced* in the Black Hills deposits near Keystone and shipped to Newark for treatment. The silicates are little if at all used. The chief use now is as lithia hydrate in prolonging the life of a storage battery. There are small uses in photography, medicine and fireworks. The carbonate was formerly extensively used as a remedy for rheumatism. FORMATION AND OCCURRENCE OF LITHIUM MINERALS. Lithia is present in most igneous rocks but chiefly in pegmatites of soda-rich rocks. Examples are: Keystone, South Dakota. Spodumene and amblygonite, the former in enormous crystals, the latter in nodules up to 1,000 Ibs. in weight. Montebras, France: Amblygonite. Pa/a, California: Amblygonite, lepidolite. Branchville, Conn: Amblygonite, triphyllite, spodumene. Chesterfield, Mass.: Spodumene. Paris and Hebron, Maine: Amblygonite, lepidolite. AMBLYGONITE. COMPOSITION. Li (A1.F)PO 4 , (Li 2 O 10.1 percent, generally partly replaced). GENERAL DESCRIPTION. A cleavable compact massive or columnar mineral some- what resembling orthoclase. Sometimes in large "indistinct crystals. PHYSICAL CHARACTERS. H = 6, Sp. 0^=3.01-3.09. Lustre, pearly to vitreous. Streak, white. Brittle. Translucent. Color, usually white, sometimes with green, blue, yellow or brown tints. BEFORE THE BLOWPIPE, ETC, Gives characteristic red lithia flame, fuses with intumescence to an opaque white globule. Soluble in sulphuric acid when powdered. REMARKS. Occurs in quantity at Pala, California. USES. Is an important source of lithium and carries a comparatively high percentage of this element. * Mineral Industry, 1914, p. 500. MINERALS IMPORTANT IN THE INDUSTRIES. 429 SPODUMENE. COMPOSITION. LiAl(SiO 3 ) 2 , Li 2 O 8.4 per cent, with some sodium replacing lithium. GENERAL DESCRIPTION. White or greenish- white monoclinic crystals, sometimes of enormous size, more rarely small emerald-green, and larger lilac colored crystals. Also in masses. Character- ized by an easy parting parallel a in addition to the prismatic cleavage. CRYSTALLIZATION. Monoclinic. Axes a : 1) \ c= 1.124 : I : 0.636; /9 = 69 4 b : fc), {103} ; Figs. 431 and 434. Supplement angles mm = 68 30'; pp = 36 12'; cr = 11 29'. Physical Characters. H., 1.5 to 2. Sp. gr., 2.31 to 2.33. LUSTRE, pearly, silky, vitreous. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle, laminae flexible. COLOR, white, colorless, gray, red, yellow, brown. CLEAVAGE, clino-pinacoid perfect, unit ortho-dome fibrous, and ortho-pinacoid conchoidal. The cleavage fragments are rhombic plates with angles 66 and 114. BEFORE BLOWPIPE, ETC. When heated quickly becomes white and opaque and fuses to an alkaline globule, coloring the flame yellowish-red. In closed tube yields water. Soluble in hydro- chloric acid. The powdered dehydrated mineral when mixed with water will form a compact mass. Gives sulphur reaction. VARIETIES. Selenite. Crystals or transparent cleavable masses. Satin Spar. Fine translucent fibrous varieties with sheen of silk. Alabaster. Compact and fine grained, suitable for carving. Rock Gypsum. Scaly, granular or dull colored and compact. Gypsite. An impure unconsolidated earthy or sandy form of gypsum, which in many places is found to contain a suitable percentage of foreign material so that the addition of a retarder is not necessary to effect a slow set. SIMILAR SPECIES. Talc, brucite, mica, calcite, heulandite, stil- bite. It is softer than all but talc, lacks the greasy feeling of talc and is further characterized by quiet solubility, cleavages and calcium flame. REMARKS. The commonest of sulphates and chiefly a chemical sediment, as described on p. 440, and not usually an original separate but derived from anhydrite, usually in dense masses, which may include large crystals. Famous crystal localities are Montmartre, Paris; Girgenti, Sicily; Wayne Co., Utah; Ellsworth Co., Ohio. In Mammoth Cave, Kentucky, it imitates rosettes, flowers, etc. ARAGONITE. Flos Ferri. COMPOSITION. CaCO 3 , (CaO 56.0, CO 2 44.0 per cent). GENERAL DESCRIPTION. Simple or pseudohexagonal crystals. MINERALS IMPORTANT IN THE INDUSTRIES. 445 Also columnar and needle masses, oolitic, stalactitic and coral-like. The prevailing tint is white, but the color is occasionally violet or pale green. FIG. 435. FIG. 436. FIG. 437. FIG. 438. Bilin, Bohemia. Herrengrund. CRYSTALLIZATION. Orthorhombic. Axes a : b : c = 0.622 : i : 0.721. Occasionally simple crystals, Fig. 435, with acute domes and pyramids such as e = (QO a : b : 6c), {061 } ; and s = (fa : b : 6c), {9.12.2}. These grade into needle-like forms. More fre- quently twinned, with twin plane m, giving prisms with pseudo- hexagonal cross sections, Figs. 437 and 438. Supplement angles are: mm = 63 48'; dd = 71 33'; w = 130 21'; ee = 153 57'. Physical Characters. H., 3.5 to 4. Sp. gr., 2.93 to 2.95. LUSTRE, vitreous. TRANSLUCENT or transparent. STREAK, white. TENACITY, brittle. COLOR, white, violet, yellow, pale green. CLEAVAGE. Parallel to brachy pinacoid, prism, and brachy dome. BEFORE BLOWPIPE, ETC. Infusible, colors flame red. In closed tube decrepitates, loses weight and falls to pieces. With hydro- chloric acid, dissolves with rapid effervescence. Powdered and boiled in a test-tube with dilute cobalt solution aragonite is turned to a lilac color. SIMILAR SPECIES. Natrolite and other zeolites which occur in needle crystals do not effervesce in acids. Strontianite and wither- ite have higher specific gravity and are fusible. Calcite has a lower specific gravity, differs in form, cleaves in three directions with equal ease yielding a rhombohedron of 105 5', and in powder is unaffected when boiled with cobalt solution. 446 MINERALOGY. REMARKS. Occurs as crystals in gypsum and clay, as at Bastennes, France, and Molina, Aragon, and in the sulphur deposits of Sicily and the lead veins of Silesia. Coral like (flos ferri) or fibrous at the Styrian and Carinthian iron mines and the Organ Mts., New Mexico. As needles in hollows of basalt. As the pearly layer of shells and the material of coral. CALCITE. Calcspar, Limestone, Marble, Iceland Spar, Etc. COMPOSITION. CaCOs, (CaO 56.0, CO 2 44.0 per cent.). GENERAL DESCRIPTION. Yellowish white to white or colorless, more or less transparent crystals, of many shapes, all of which FIG. 439. FIG. 440. FIG. 441. will cleave to a rhombohedron of 105. Cleavable, coarse- and fine-grained, fibrous and loosely coherent masses. Crusts, stalac- tites. CRYSTALLIZATION. Hexagonal. Scalenohedral class, p. 48. Axis 2 given off from volcanoes and depositing in fissures and elsewhere in the crater. The most important deposit is at Hokkaido, Japan, in walls and massive heaps in an old crater still yielding fumes. Another not yet worked is at Popocatapetl, Mexico, and a deposit exists on a volcanic island near New Zealand. f Smaller deposits exist in the Yellowstone. Deposits from Hot Springs. Superficial deposits due to oxidation of H 2 S exist near hot springs, J some of which are workable, as at Cody, Wyoming; Cove Creek, Utah; Cuprite, Nevada; and Sulphur Bank, Cali- fornia. In Gypsum of Chemical Sediments. Nearly all great gypsum beds contain sulphur and nearly all great sulphur beds occur with gypsum and limestone associated with hydrocarbons, carbonates and sulphates. It is practically certain the sulphur is due to the reduction of gypsum by organic agencies. The most important deposits are those of Sicily and Louisiana. In Sicily the sulphur-bearing gypsum carrying 8 to 25 per cent. S is with blue gray limestone, clay, sandstone and halite. At Calcasieu, Louisiana, almost 100 feet of pure sulphur underlies clay and limestone. Other localities in which S was derived from beds of gypsum are Texas; Conil near Cadiz, Spain; Bex, Switzerland; Cracow, Poland. * The pyrite in limestone of Lake Champlain sometimes yields crusts of sulphur an inch thick. t Mineral Industry, 1914, p. 689. \ Lindgren, "Mineral Deposits," 338. MINERALS IMPORTANT IN THE INDUSTRIES. 463 SULPHUR. Brimstone. COMPOSITION. S, sometimes with traces of tellurium, selenium, or arsenic. Often mixed with clay or bitumen. GENERAL DESCRIPTION. Translucent or transparent, resinous, crystals of characteristic yellow color. Also in crusts, stalactites, spherical shapes, and powder. Sometimes brown or green. FIG. 458. FIG. 459. CRYSTALLIZATION. Orthorhombic. Axes :<5:r = o. 813:1: 1.903. Usually the pyramid/, sometimes modified by the base c, the pyramid s = (d : b : % r), { 1 1 3 } ; or the dome d = ( oo d : b : c), {on}. Supplement angles // = 73 34' ; ss = 53 9'; cd= 62 if. Optically + . Axial plane, the brachy-pinacoid. Acute bisec- trix vertical. Axial angle with yellow light 2V '= 69 5'. Physical Characters. H., 1,5 to 2.5. Sp. gr., 2.05 to 2.09. LUSTRE, resinous. TRANSPARENT to translucent. STREAK, white or pale yellow. TENACITY, brittle. COLOR, yellow, yellowish-orange, brown, or gray, CLEAVAGE, parallel to base, prism and pyramid, not perfect. BEFORE BLOWPIPE, ETC. Melts easily, then takes fire and burns with a blue flame aud suffocating odor of sulphur dioxide. In closed tube melts and yields a fusible sublimate, brown hot, yellow cold, and if rubbed on a moistened silver coin the coin is blackened. Insoluble in acids. REMARKS. Occurrence and uses, as described on p. 461-462. 464 MINER ALOG Y. THE SELENIUM AND TELLURIUM MINERALS. The mineral described is: Tellurium Te, Hexagonal Native selenium is not proved. Selensulphur is a name given to ' selenium-bearing sulphur from Vulcano, Lipari, Sandwich Islands and Japan. Several selenides* occur including selenides of mercury, tiemanite, and onofrite, and selenide of lead, clausthalite. Selenium. Selenium in minute quantities occurs in the copper ores of Butte, Montana, and other copper regions. 22,867 pounds was recovered in 1914 from their electrolytic refining. f It is also found in the gold bullion from Tonopah, Nevada, and Redjang Lebong, Sumatra. In none of these cases have the selenium minerals been identified. Selenium is used principally to give a red color to the glass used in signal lamps and to color enamels red. According to Roscoe and SchorlemmerJ selenium heated for considerable time to 210 C. attains a granular condition. In this condition if ex- posed to diffused daylight its electric resistance diminishes in- stantly and on shutting off light it slowly regains it. A number of electrical inventions depend on this, such as automatic lighting and extinguishing gas buoys. Selenium cells for measuring the intensity of light have been constructed. Minor uses are in micro- scopic and chemical work. Tellurium. Tellurium occurs plentifully! in combination with gold, silver, mercury, lead and bismuth as the minerals calaverite, sylvanite, krennerite, hessite, petzite, nagyagite, coloradoite, tetradymite. Oxidized products are rare.|| * Rarer species, naumannite, berzelianite, lehrbachite, eucairite, zorgite, crookesite. f Mineral Resources U. S. f 1914, p. 13. % "Chemistry," Vol. I, p. 462. Rarer tellurides are altaite, stutzite, tapalpite. It has been estimated th'^t at the Cripple Creek locality the weight of tellurium exceeds that of the gold approximately in the ratio 7 to 5; that is, with a gold production of up to 1908 of $191,830,000 there has been about 450 tons of tellurium. l| Tellurite, emmonsite, durdenite. MINERALS IMPORTANT IN THE INDUSTRIES. 465 Although found in the slimes of the copper refineries there are no economic uses. TELLURIUM. COMPOSITION. Te with a little Se, S, Au, Ag, etc. GENERAL DESCRIPTION. A soft tin white mineral of metallic lustre occurring fine grained or in minute hexagonal prisms. PHYSICAL CHARACTERS. Opaque. Lustre, metallic. Color and streak, tin-white. H., 2 to 2.5. Sp. gr., 6.1 to 6.3. Rather brittle. BEFORE BLOWPIPE, ETC. On charcoal fuses easily, volatilizes, coloring flame fjreen and forming a white coat, which is made rose color by transferring to porcelain and moistening with sulphuric acid. Soluble in hydrochloric acid. REMARKS. Occurs at Zalathna, Siebenburgen, in sandstone, sprinkled through pyrite or alternating with it in thin layers; at the John Jay mine, Colorado, in pieces up to 25 pounds, and in California. THE HYDROGEN MINERALS. The mineral described is: Water. H 2 O, Hexagonal. HYDROGEN, which forms about one per cent, of the earth's crust, is a constituent of many minerals, being present in combination and as water of crystallization. It is present to a limited extent in natural gas and in volcanic gases; it escapes in combination with sulphur from many sulphur springs and, in combination with car- bon, occurs as marsh gas, petroleum, ozocerite, etc. Its compound water is everywhere in nature and the great part it plays in the formation and decomposition of minerals has been discussed, p. 244. It is a universal solvent when pure. The uses are too well known to need summarizing even if sta- tistics were available. The minor item of mineral waters in 1914 amounted to 54,358,466 gallons and the yearly supply of water for one great city probably exceeds in weight the yearly production of any other mineral product in the entire country. WATER. Ice, Snow. COMPOSITION. H 2 O, (H., n.i, O., 88.9 per cent). GENERAL DESCRIPTION. Ice or snow at or below o C. Water from o to 1 00 C. Steam above 100 C., or aqueous vapor at all ordinary temperatures. CRYSTALLIZATION. Hexagonal. Axis c = 1.403 approximately. As snow, the crystals are principally compound star-like forms branching at 60 and of great diversity. Simple crystals are sometimes found as hail. Optically -f. 466 MINERALOGY. FIG. 460. FIG. 461. FIG. 462. FIG. 463. Magnified Snow Crystals. Physical Characters. H. (ice), 1.5. Sp. gr. (ice), 0.91. LUSTRE, vitreous. TRANSPARENT. STREAK, colorless. TENACITY, brittle. COLOR, white or colorless, pale blue in thick layers. Tasteless if pure. BEFORE BLOWPIPE, ETC. Melts at o C. Under pressure of 760 mm. boils at 100 C. and is converted into steam. THE NITROGEN MINERALS. The two great nitrates, soda nitre and nitre, have been de- scribed and their occurrence and importance discussed. Other minor nitrates exist, one of which, nitrocalcite, Ca(NO 3 )2 + wH 2 O, is not uncommon as an efflorescence in limestone caves and it is stated* that in the war of 1812 the material from Mammoth Cave, Kentucky, was leached and converted into nitre by filtering through wood ashes. Nitrocalcite is also found in the soil of Venezuela. A few still rarer nitrates are known, such as darap- skite and gerhardtite, others have been reported and nitrogen is found in uraninite. The necessity of nitrogenous compounds for plant food and for explosives has resulted in successful attempts to fix atmospheric nitrogen by the arcf calcium cyanamide and Haber methods, and to further utilize the ammonium sulphate produced in coking * Merrill's "Rock-forming Minerals," p. 318. t In the production of calcium cyanamide, coke and lime are fused together to form calcium carbide. This, when heated, is treated with pure nitrogen made at the present time by liquifying air and boiling off the oxygen. In the arc method the nitrogen and oxygen of the air are directly combined under the influence of the electric discharge. In the Haber process nitrogen and hydrogen are made to com- bine under pressure at elevated temperatures in the presence of some catalyzing agent. MINERALS IMPORTANT IN THE INDUSTRIES. 467 and estimated* as about 700,000 tons per year. A process for oxidizing this ammonia to nitric acid is still needed. THE PHOSPHORUS MINERALS. The minerals described are. Apatite Ca 5 (Cl.F)(PO 4 )3 Hexagonal Wagnerite Mg2PO4F Monoclinic Wavellite A1 6 (OH) 6 (PO 4 )4 + pH 2 O Orthorhombic Vivianite Fe 3 (PO 4 )2 8H 2 O Monoclinic Phosphides exist in iron meteorites, but otherwise phosphorus occurs only in the form of phosphates, of which there are known about fifty, including xenotime, monazite, pryomorphite, amblygon- ite, lazulite, variscite, turquois, torbernite, and autunite. ECONOMIC IMPORTANCE. The yield of crystalline apatite is nearly negligible and the phosphorite deposits of Spain are no longer worked. There may be some recovery of such material as a by-product in the concen- tration of the iron ores of New York and Norway. Practically the economic deposits are limited to rock phosphates and guanos. In 1915 this country produced f 1,835,667 long tons of phosphate rock distributed as follows : Florida 1,358,611 Tennessee and Arkansas 3 89, 7 59 South Carolina 83,460 Idaho, Utah and Wyoming 3.83? The world's production in 1913 amounted to over 6,780,000 metric tons. In 1914 there was a heavy decline to less than 4,000,000 tons.J This country produced over one half and the other great producers were Tunis and Algeria both working "bone" phosphates. There is a small use for making phosphorus, but the principal use is as phosphates for fertilizers. A considerable amount is ground raw and used directly, but the greater part is converted into soluble phosphates by treatment with sulphuric acid, in which state it is more readily available as plant food. * Gilbert, Publication 2421 Smithsonian Inst. t Minerals Res. U. S., 1915, advance sheets. J Mineral Industry, 1914, p. 585. 468 MINERAL OG Y. FORMATION AND OCCURRENCE OF PHOSPHATES. Phosphorus is present in the crust of the earth to the amount of about one tenth of one per cent. In the form of apatite and to a much less extent monazite and xenotime it is widely distributed as minute crystals in igneous rocks. The economic deposits may be grouped under several heads. Magmatic Segregations. The great apatite-iron deposits of Gellivare and Kiirunavaara, Norway, are magmatic segregations* consisting of magnetite with considerable fluor --apatite. Veins. Veins the material of which is believed to have been pneuma- tolytically, p. 242, extracted from the neighboring gabbro by hydrochloric acid and deposited there as chlorapatite while at the same time the plagioclase of the country rock has been converted into scapolite, occur at Oeddegadenf Bamle, Norway, and along the coast at Langesund, Snarum, Arendal, etc. Associated are large crystals of wagnerite and enstatite and there is abundant rutile, ilmenite and pyrrhotite. The original gabbro contained 0.65 P 2 O 5 14 to 1.5 HC1. Similar conditions prevailt with the Canada veins which are in close association with a gabbro (pyroxenite). The apatite is fluor apatite with a little chlorine; there is no enstatite but some augite, biotite, scapolite, calcite, titanite, and ilmenite. Apatite is a constant associate of tin veins, as at Ehrenfriedensdorf, Zinnwald, Cornwall, Devonshire, South Dakota, but is practically never in lead, silver, zinc or gold veins. The formerly important deposits of fibrous concretionary apatite or phosphorite of Estramadura, Spain, occur in 16 foot quartz veins in clay slate in and near granite and at Jumilla, Spain, there is a basic eruptive of sanidine and leuctte with a net- work of veins rich in apatite. Secondary Phosphates. Some of the weathering solutions due to the decomposition of apatite react with other decomposition products producing secon- dary phosphates.]] * Beyschlag, Vogt and Krusch (Truscott), 173. t Ibid., 175. 453- t Ibid., 454- Beyschlag, Vogt and Krusch (Truscott), 452. || Especially phosphates of iron and aluminum such as Iron. Vivianite, du- frenite, strengite, etc. Aluminum. Wavellite, turquoise, variscite, etc. Of these vivianite is common in bog-iron ore. MINERALS IMPORTANT IN THE INDUSTRIES. 469 The greater portion of the phosphoric acid in the weathering solutions reaches the soil or the sea and is taken up by plant and animal organisms, from which there result beds of guano, fossil bones and marine deposits of bone, shell and animal matter, all of which may undergo further alterations. Marine Sediments. When the -marine organism dies the remains, shells, fishes bones and teeth, etc., collect in the ooze at the bottom and by relatively more rapid solution of the carbonates may form phos- phate nodules or oolitic beds and if these deposits become land may be still further concentrated by further leaching out of the carbonates as in the pebble rock deposits of the coasts and rivers of North and South Carolina or may be essentially unaltered* as in the great new deposits of Idaho and Utah where the phosphate shales and oolitic beds occur near the center of a great formation in beds 200 feet thick, or may present both stages as in western Tennessee, where there are found both brown residual phosphates due to leaching of phosphatic limestones and blue or black oolitic and shaly beds. Other important marine deposits exist in Tunis and Algeria and the large deposits of phosphate are derived chiefly or entirely from marine deposits and are chiefly Ca 3 (PO 4 )2, but are said to contain more fluorite as the geologic age increases, the purest ap- proaching fluor apatite. Guano Beds. Guano beds are formed by sea birds in rainless regions, as on the islands near Chili and Peru, and are sometimes 100 feet in depth and average over twenty per cent, of phosphate and even more of ammonia salts. By leachingt some deposits have lost their ammonia salts, as at Navassa and Sombrero and others of the West Indies. Christmas Island, Indian Ocean, is a large producer and others are in Polynesia. Replacements. GuanoJ may furnish solutions of phosphates capable of attacking * Lindgren, " Mineral Deposits," p. 260. t Lindgren, "Mineral Deposits," p. 257. % Guano contains many phosphates, some of which are acid. Clarke gives 'Bulletin 491 U. 'S. Geol. Survey, 496, a list of 10 species. 470 MINERALOGY. underlying rocks, forming phosphate of lime with limestone or phosphates of aluminum* from the feldspars of igneous rocks, as in the trachyte of Clipperton Atoll, North Pacific. Similarly the marine sediment phosphates, may be in part dis- solved and replace limestone, as in the "white phosphate" of Tennessee. APATITE. Asparagus Stone. Phosphate Rock. COMPOSITION. Ca 6 (Cl.F)(POJ 3 , GENERAL DESCRIPTION. Large and small hexagonal prisms, usually of green or red color, but sometimes violet, white or yellow. Also in compact varieties which are commonly dull-gray or white, rock-like masses or nodules not unlike common limestone. FIG. 464. FIG. 465. FIG. 466. FIG. 467. Paris, Me. Zillerthal. CRYSTALLIZATION. Hexagonal. Class 3 order pyramid, p. 57. Axis c = 0.735. Usually the unit prism m terminated by the unit pyramid p with or without the base c. More rarely the second order prism a or the flat pyramid o = (a : co a : a : y 2 c\ {ioF2}, Fig. 469 ; and occasionally third order pyramids, as t = ($a : A,a : ::), {3143}, Fig- 469- Supplement angles : pp 37 44'; rr=22 = 40 18' cr= 22 59'. Optically , low refraction, weak double refraction. * A species called minervite, approximating H2KAl2(PO4)s6H2O, has been found in the Minerva Grotto, France, and similar material from Oran Cave, Algeria, Jenolan Cave, New South Wales. Ibid., 497. MINERALS IMPORTANT IN THE INDUSTRIES. 471 Physical Characters. H., 4.5 to 5. 83., gr., 3.17 to 3.23. LUSTRE, vitreous to resinous. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle. COLOR, green, red, brown, yellow, violet, white, colorless. CLEAVAGE, imperfect basal and prismatic. BEFORE BLOWPIPE, ETC. Fuses with difficulty on sharp edges and colors the flame yellowish-red, or, if moistened with concen- trated sulphuric acid, colors the flame momentarily bluish-green. Easily soluble in hydrochloric acid. If to ammonium molybdate in nitric acid solution a few drops of a nitric acid solution of apatite be added, a bright-yellow pre- cipitate will be thrown down on heating. In the chlorine variety silver nitrate will produce a curdy white precipitate in the nitric acid solution. VARIETIES. Certain mineral deposits are essentially of the same composition as crystalline apatite. Phosphorite. Concretionary masses, with fibrous or scaly struc- ture. H = 4.5. Phosphate Rock. Approaches Ca 3 (PO 4 ) 2 ; sometimes is only phosphatized limestone, shale, etc. ; usually marine sediment. Guano. Granular to sponge-like and compact material, of gray to brown color. Sometimes with lamellar structure. SIMILAR SPECIES. Green crystals, differ from beryl in lustre, hardness and solubility. Red crystals differ from willemite in not gelatinizing or yielding zinc. REMARKS. Occurs as described on p. 468. The most famous American localities for the pure mineral are in Ontario and Quebec, Canada. * Others, smaller in extent, occur at Bolton, Mass.; Crown Point, N. Y., and Hurdstown, N. J. WAGNERITE. COMPOSITION. Mg 2 PC>4F, P 2 O 5 43.8, MgO 49.3, F u.8 per cent. GENERAL DESCRIPTION. Cleavable masses and rough monoclinic crystals of yellow to flesh red color. H., 5 to 55. Sp. gr., 2.98. BEFORE BLOWPIPE. Fuses at 4 to greenish gray glass. With sulphuric acid gives bluish flame. In closed tube with phosphorus glass gives fluorine. Soluble in hydrochloric acid. REMARKS. The dominant mineral in some of the phosphate veins of Bamle, Norway. WAVELLITE. COMPOSITION. A1 6 (OH) 6 (PO4)4 + 9H 2 O, (Al 2 Os 38.0, P 2 O 5 35.2, H 2 O 26.8 per cent.). F is sometimes present. GENERAL DESCRIPTION. Hemispherical masses which, when broken, yield com- plete or partial circles with radiating crystals, rarely large enough to be measured. 472 MINERAL OGY. Occasionally stalactitic. Color most frequently white, green or yellow. H., 3.5 to 4. Sp. gr., 2.31 to 2.34. BEFORE BLOWPIPE, ETC. Whitens, swells, and splits, but does not fuse. With cobalt solution becomes deep blue. In closed tube yields acid water. Soluble in hydrochloric acid. Ammonium molybdate produces a yellow precipitate from nitric acid solutions. REMARKS. A secondary mineral chiefly in clays and fractures. In the United States is most abundant at Magnet Cove, Ark., Holly Springs, Pa., where it was used for manufacture of phosphorus, and Silver Hill, N. C. Foreign localities are Barnstaple, Devonshire; Dillenburg, Nassau; Cerhovic, Bohemia. VIVIANITE. Blue Iron Earth. COMPOSITION Fe 3 (PO 4 ) 2 -f 8H 2 O. (FeO 43.0, P 2 O 6 28.3, H 2 O 28.7 per cent.). GENERAL DESCRIPTION. Usually found as a blue to bluish green earthy mineral, often replacing organic material as in bones, shells, horn, tree roots, etc. Also found as glassy crystals (monoclinic), colorless before exposure, but gradually becoming blue. PHYSICAL CHARACTERS. Transparent to opaque. Lustre, vitreous to dull. Color and streak, colorless before exposure, but usually blue to greenish. H=l.5 to 2. Sp. gr., = 2.58 to 2.69. Brittle. BEFORE BLOWPIPE, ETC. Fuses easily to a black magnetic mass and colors flame pale bluish-green, especially after moistening with concentrated sulphuric acid. In closed tube yields water. Soluble in hydrochloric acid. The dried powder is brown. REMARKS. Common with bog iron ore. Occurs earthy in peat moss as in Shet- land or near tree roots, or with horns of the elk, Isle of Man, as crystals with pyrrhotite (Bodenmais) or pyrite (Cornwall), or radiating aggregates often within fossil shells (Crimea and Mullica Hill, N. J.). THE CARBON MINERALS. The more definite minerals described are : Graphite C Hexagonal Ozoceritf C n H 2n +2 In addition to these there are a large number of gaseous, liquid and solid carbon compounds, of economic importance which are on the border line of mineralogy, occurring naturally but being generally without definite composition or crystalline form. Among these the following are briefly described: PETROLEUM, ASPHALT, MINERAL COAL, COPALITE, and AMBRITE. Other carbon minerals elsewhere described are diamond, and amber. Carbon also exists in enormous quantities in the mineral carbonates such as calcite, dolomite, magnesite, cerussite, siderite, and aragonite and in a number of hydro- carbons, chiefly paraffins and resins, some of which are very definite in composition and may even be crystalline, but are economically unimportant such as Scheererite CH 4 Monoclinic Hatchettite C : H = i : i Sometimes crystals Fichtelite C 5 H 8 Monoclinic Hartite Cu-Hia Monoclinic MINERALS IMPORTANT IN THE INDUSTRIES, 473 ECONOMIC IMPORTANCE. From this standpoint the carbon minerals surpass all others both in quantities used and values. Of the $2,114,946,024 valua- tion placed upon the mineral products of the United States, for 1914 $895,615,858 are for coal and petroleum, an amount ex- ceeding the combined value of the production of all the metals. Graphite. In 1915 the output of crystalline graphite in the mines of this* country was 3,537 tons.* Amorphous graphite to the extent of 1,1 8 1 tons-was also produced. The total product of the world is over 100,000 tons annually, obtained mainly from Ceylon and Austria, of which 13,821 tons was imported into the United States in 1915. About one half the graphite is used in the making of crucibles, the dust and the amorphous material are used chiefly for stove polish, foundry facings and paints, and the other large uses are electrical purposes, making lead pencils and lubricants. Minor uses are in electrotyping and in protecting various products against moisture, especially gunpowder, but also tea leaves, coffee beans, and even fertilizers. Ozocerite is mined in Hungary and Utah and in 1914 the United States imported! over 4,000 tons but mined none. In the crude state it serves as an insulator for electric wires. By distilling it yields: a refined product, ceresine, used for candles, waxed paper and hydrofluoric acid bottles; burning oils; parafiine; a product with properties and appearance of vaseline ; and a black residuum which in combination with india rubber constitutes the insulating material called okonite. Petroleum. The production of crude petroleum in the United States in 1914 was 265,762,535^: barrels. The world's production was 400,483,489 barrels. This country therefore producing over 66 per cent, of all while Russia produced less than 17 per cent, and no other country except Mexico (5.29 per cent.) as much as five per cent. * Mineral Resources U. S., 1915, p. 82. t Mineral Resources U. S., 1914, p. 356. % Mineral Industry, 1914, p. 568. 474 MINERALOG Y. Large amounts of petroleum in the crude state and all the distilled heavy oils for which there is no market are used as "fuel oils" and a smaller amount of special oils for lubricating purposes. Its chief value is due to its distillation products, mainly kerosene. Other valuable products arising from distillation of this crude oil are gasoline, naphtha,* benzene. Various products such as lubricating oils, vaseline and paraffine are made from the residuum after the burning oils have been distilled off. Asphalts. This country produced! and manufactured from petroleum in 1915 740,254 tons of asphalt as follows: Bituminous rock 44.329 Gilsonite and Wurtzilite 20,559 Grahamite 10,863 Manufactured asphalt 664,503 In addition to which it imported chiefly from Trinidad and Venezuela, 180,689 tons of asphalt. The world's production is probably about 400,000 tons of asphalt and 600,000 tons of bituminous rock, Trinidad and Venezuela furnishing over one half of the former and France and Italy most of the latter. The principal use is for pavements of streets and roads, mixed with sharp sand, limestone, and a little coal-tar residuum. They are also used as cement, roofing and floor material, as a paint and waterproofing for wood or metal, for insulating electric wires, and as an adulterant and coloring material in rubber goods. Manjak and gilsonite are important constituents of black var- nishes. A product called "ichthyol" is used externally and internally in medicine, derived from a bituminous rock full of fossil fish at Seefeld, Tyrol. Fossil Resins. The fossil resins copalite and ambrite do not occur in the United States. They are oxidized hydrocarbons much resembling ordi- . ' , * Gasoline is also obtained from natural gas. In 1914 to the amount of 42,652,632 gallons with little loss in the value of the gas. The natural gas yield in 1914 was valued at $94,115,524. It consists essentially of marsh gas, but also contains hydrogen, nitrogen and some other gases, and is used in immense quantities as a fuel and, after being enriched, for illuminating purposes, and is also burned to produce lamp black. t Mineral Resources U. S., 1915, p. 140. MINERALS IMPORTANT IN THE INDUSTRIES. 475 nary resin in appearance, and are extensively used in varnishes and japans. Mineral Coal. The world's production of mineral coal in 1914 was 1,226,330,612 metric tons, of which three countries produced 86 per cent, as follows : United States 517,285,050 or 47 per cent. Great Britain 292,047,544 " 24 " Germany 191,511,154 " 15 " The estimated production in the U. S. for 1915 is 518,000,000 tons. FORMATION AND OCCURRENCE OF THE CARBON MINERALS. With the exception of diamond and some varieties of graphite the carbon minerals are of undoubted organic origin, due to former plant and animal life. Graphite is not necessarily so, as is proved by its presence in meteorites and cast iron. Separation from Magma.* Graphite occurs in the Disco Island iron, p. 266, which contains up to four per cent, of carbon, partly as graphite. It occurs also in pegmatites and nepheline syenites. Metamorphosed Sediments. Graphite results from the alteration of the carbonaceous matter in the sediment. Occurrences are numerous both of flake or crystallized graphite as in Alabama and Pennsylvania, and of the so-called amorphous graphite as in California. Considerable graphite is found in the famous Witwatersrand conglomerate and is said to be of later formation, sometimes replacing the quartz. Contacts. GRAPHITE resulting from the intrusion of igneous rocks may be of definitely organic origin as in the case of the altered coal beds, at Raton, New Mexico; Sonora, Mexico, and Styria, in which the intermediate stages from coal to graphite are present. In other instances it is attributed to magmatic exhalations, for instance : * Mineral Industry, 1914, p. 131. t Lindgren, " Mineral Deposits," p. 699. Beyschlag, Vogt and Krusch (Truscott), p. 1161. 476 MINERAL O-G Y. " The graphite gneiss of Passau contains the mineral as a secon- dary impregnation only at the contact with granite"* and speaking of the graphites of Quebec "The conclusion is justified that they were developed by igneous emanations shortly after the close of intrusive activity, "f .Contacts occur also at Ticonderoga. Veins. Graphite occurs in veins in igneous rocks and the surrounding sediments, as at Ceylon, in fine-grained gneiss intruded by granites and pegmatites. Dillon, Montana, along contact of pegmatitic granite with schists and limestone. Near Ticonderoga, New York, in similar contact. The Alibert mines of Irkutsk, Siberia, in nepheline syenite. The Borrowdale, Cumberland, in porphyry. The origin is puzzling and variously ascribed to igneous exhala- tions,! infiltration of liquid hydrocarbons and subsequent meta- morphism and to gaseous compounds derived from the adjoining sediments. It is of interest that graphite occurs in considerable quantity in the silver veins of Silver Islet || and to a less extent in the silver veins of Temiskaming. Sedimentary. Mineral coal, asphaltum, petroleum and ozocerite are all of organic origin. The coals are sediments from wood grown in place or carried there by currents, the petroleum and asphalt are chiefly found in clay shales, sands, sandstones and limestones and the ozocerite is a derivative of petroleum. GRAPHITE. Plumbago, Black Lead. COMPOSITION. C. Sometimes with iron, sand, clay, etc. GENERAL DESCRIPTION. Disseminated flakes or scaly to com- pact masses, and more rarely six-sided plates. Soft, greasy and cold to the touch ; black to very dark gray in color and usually metallic in lustre. When impure it is apt to be slaty or earthy. * Weinschenck, "Grundziige der Gesteinskunde," p. 319. fLindgren, "Mineral Deposits," p. 704. J "Grundziige der Gesteinskunde," p. 319, 320. Lindgren, "Mineral Deposits," p. 700. II Beyschlag, Vogt & Krujch (Truscott), p. 669. MINERALS IMPORTANT IN THE INDUSTRIES. 477 Physical Characters. H., I to 2. Sp. gr., 2.09 to 2.25. LUSTRE, metallic to dull. OPAQUE. STREAK, dark-gray. TENACITY, scales flexible, COLOR, black or dark gray. slightly sectile. CLEAVAGE, basal, cleaves into plates. UNCTUOUS, marks paper. BEFORE BLOWPIPE, ETC. Infusible, but is gradually burned. May react, if impure, for water, iron and sulphur. Insoluble in acids. If a piece of graphite is brought into contact with a piece of zinc in a solution of copper sulphate, it is quickly copper-plated. Molybdenite under the same test is very slowly plated. SIMILAR SPECIES. Differs from molybdenite in darker color, streak, flame test and salt of phosphorus bead, and as above men- tioned. Micaceous hematite is harder and has a red streak. Graphite is distinguished from amorphous carbon by treatment with strong oxidizing agents (KC1O 3 and HNO 3 ), by which it is converted into graphitic acid, Ou^Oi, a yellow transparent substance. REMARRS. The occurrence and uses have been described on pp. 475 and 473. OZOCERITE OR MINERAL WAX. COMPOSITION. Closely C., 85.5, H., 14.5, per cent. Essentially one of the higher members of the paraffin series, C n H2 n +2. GENERAL DESCRIPTION. Resembles wax in appearance and consistency, usually brown to nearly black and foliated, sometimes with greenish opalescence, which it imparts to its solutions. H., about 2. Sp. gr., 0.93 to 0.95. BEFORE BLOWPIPE, ETC. Melts at 51 to 63 C. Soluble in ether, naphtha or turpentine, partially soluble in boiling alcohol. REMARKS. Ozocerite is regarded as a derivative of petroleum. Originally found in.Slanik, Moldavia, then in larger quantities in Boryslaw, Galicia, and Emery and Uinta Counties, Utah; Baku, Persia, and other localities. PETROLEUM. A mixture of liquid hydrocarbons. The American oils consist essentially of hydrocarbons of the paraffine series, C n H2 n +2, with smaller amounts of the series C n H2 n and C n H2 n -e. The Russian oil, obtained mainly from Baku, on the Caspian, and the oils from Rangoon, Galicia, are different in character, consisting mainly of the naphthenes C n H2 n and do not yield as much illuminating oil on distillation. The German petroleum is intermediate and the Canadian is rich in the solid paraffins. GENERAL DESCRIPTION. It varies from a- light easily flowing liquid to a thick viscous oil. Usually dark brown or greenish in color with a distinct fluorescence. Sp. gr., 0.6 to 0.9. REMARKS. Occurs usually in clay, shales, sands, sandstones and limestones and in cavities to which it has penetrated from the adjoining rocks. 478 MINERAL OGY. ASPHALTUM OR MINERAL PITCH. Mixtures of different hydrocarbons and their oxidized products. GENERAL DESCRIPTION. Varying from thick, highly viscous liquids to solids, generally black in color and with a pitch-like luster. Melt usually from 35 to 40 C. and burn easily with a pitchy odor and bright flame. They are slightly heavier than water. Trinidad. Sp. gr., 1.28. REMARKS. Asphaltum includes the true ASPHALT of the famous pitch lakes of Trinidad and of Bermudez, Venezuela and the Dead Sea; the MANJAK of Barbadoes; the elastic ELATERITE, of Derbyshire, England; the ALBERTITE of New Brunswick; the GILSONITE and WURTZILITE of Utah, the GRAHAMITE of Oklahoma. Besides these sandstone and limestone impregnated with asphalt occur. MINERAL COAL. GENERAL DESCRIPTION. Mineral coal is a compact massive material of black or brownish black color and submetallic to earthy lustre. It is without crystalline structure or cleavage and has a conchoidal fracture. H., 0.5 to 2.5. Sp. gr., i. to 1.8. BEFORE BLOWPIPE, ETC. Infusible but burns and may become pasty and in closed tube yield oily and tarry materials. Insoluble in acids, alcohol, ether, etc. VARIETIES. The entire series would range from peat to anthracite. Kemp giving* as typical compositions O N 43 i 33 2 25 0.8 13 0.8 2.5 trace The differences in appearance are great, ranging through the brown spongy peat, the brownish black lignite, the compact brown to black bituminous and the bright submetallic black anthracite. COPALITE or Highgate Resin from the London blue clay and copal found in the soil of the African coast are pale yellow to gray or dirty brown resins. H., about 3. Sp. gr., i.oi. Giving aromatic odor when broken. It is soluble with difficulty in alcohol and turpentine and is very valuable for varnishes. AMBRITE OR DAMMAR. A fossil resin from New Zealand resembling Kauri gum of the same locality and of the East Indies, the Moluccas and from New Zealand. It is not so hard as copal but is harder than resin. It is a valuable basic constituent of varnishes. The New Zealand dammar is almost wholly fossil * "Hand-book of Rocks," p. 104. Woody tissue .... Peat C 50 59 H 6 6 Lignite Bituminous coal . . Anthracite. . 69 82 . OS 5-5 5 2.=; CHAPTER XX. SILICA AND THE ROCK-FORMING SILICATES. The order of discussion is by groups of chemically or genetically related species. The economic discussion begins the chapter but the discussions of Formation and Occurrence and of Optical Determination precede the individual groups. ECONOMIC IMPORTANCE. Aside from the occasional occurrence of certain silicates in specimens suitable for gems, only a few of this greatest group of common minerals are of economic importance as distinct minerals. The Quarry Industry. The great stone or quarry industry* represents in the United States a capital of over $125,000,000, and produced in 1914 material worth in the rough over $77,000,000, and consists in the extraction of blocks of either limestone and marble or of silica and silicates. The values of silicate rocks quarried in this country were : Granite $20,028,910 Basalt and Related Rocks 7.865,998 Sandstone 7,501,808 Bluestone 1,086,699 Slate 5,706,787 GRANITE, commercially speaking, includes a number of hard, durable rocks, such as granite proper, syenite, gneiss, schist, dio- rite, and andesite, which are composed of silicates usually three or more and principally quartz, the feldspars and the micas, pyroxene and amphibole. It is used in enormous quantities in buildings, in paving blocks and in construction of bridges and dams, monumental work, flagstones and curbstones, crushed stone, etc. BASALT and the related rocks include basalt, diabase and other * The facts and figures are taken from Mineral Resources of the U. S., 1914 and 479 480 MINER ALOG Y. dark igneous rocks similar in composition and properties. Their uses are chiefly as crushed stone for roads, railroad ballast and concrete. SANDSTONE is composed of grains, chiefly quartz, with a little feldspar, mica or other minerals, and is classified as siliceous, ferruginous, calcareous or argillaceous, according to the nature of the cement which binds the grains together. Its uses are the same as those of granite, but a larger proportion of the quantity quarried is used in building. BLUESTONE is a very hard, durable, fine-grained sandstone, cemented together with siliceous material. It is used principally for flag and curb stone. SLATE is used chiefly as roofing material and for interior work, such as blackboards, table tops, sinks, etc. Small amounts are ground for mineral paint. The production of silica or other silicates for economic purposes in the United States in 1915 was valued at over $31,000,000 and may be summed up as: Short Tons. Value. Quartz "2,575 #273,553 Infusorial earth and Tripoli 611,021 Feldspars "3. 769 629,356 Micas 4,236 428,769 Garnets 4,3<>i 139-584 Asbestos (amphibole and serpentine) i,73i 76,952 Talc and soapstone 186,891 1,891,582 Clays* (kaolinite, etc.) 2,209,860 3-756,568 Fuller's earth (kaolinite, etc.) 47,901 489,219 Sand (chiefly quartz) 95,46i 386,261 Millstones, Buhrstones, grindstones 816,134 Sand and gravel for building, glass making, molding, paving, grinding, etc 76,603,303 23,121,617 Individual Minerals or Groups. QUARTZ is used in large amounts in the manufacture of sand- paper, porcelain, pottery, glass, honestones, oilstones, and as a flux. Other large uses are as a wood filler and in paints, scouring soaps, the making of carborundum and ferro-silicon. Fused quartz is used for chemical apparatus, and colored and chalce- donic varieties are used as semi-precious or ornamental stones. * 1914. Clay products in 1915 were valued at $37,325,388 of which "white ware products" and "sanitary products" represented about two thirds. SILICA AND THE ROCK-FORMING SILICATES. 481 INFUSORIAL EARTH and TRIPOLI are calcined and made into water filters, polishing powders, soap filling and boiler and steam- pipe covering. FELDSPAR is crushed in large quantities for admixture with kaolin in the manufacture of porcelain and chinaware, chiefly to form the glaze, but partly mixed with the kaolin and quartz in the body of the ware. It is also used in enamel brick and tile, and as binder for emery and corundum wheels. The purest is used in the manufacture of artificial teeth. For AMPHIBOLE see Serpentine. THE MICAS, especially muscovite and phlogopite, have become of great importance as non-conductors in electrical apparatus, and are also used in stove and furnace doors. The larger sheets are cut and split to the desired size; the waste is, to some extent, built up into plates suitable for certain grades of electrical work, and for covering steam boilers and pipes. Large amounts of formerly wasted material are now ground and used for decorative interior work, to ornament porcelain and glassware, to spangle wall paper, in calico printing, as a lubricant and more recently as an absorbent of nitro-glycerine and in the manufacture of certain smokeless powders. BIOTITE bronzed by heating is used for decorative purposes and lepidolite in glass making. GARNET is ground for an abrasive. SERPENTINE is to some extent mined and used as ornamental stone, but is commercially classed with the marbles. The fibrous varieties of both amphibole and serpentine are known commer- cially as asbestos, and are extensively made into yarns, ropes and paper for fire-proof purposes, boiler and steam-pipe cover- ing, piston packing, theatre curtains, firemen's suits. It is also used for fire-proof paints and cements, and for lining safes. Asbestos of long fine fiber is used in the laboratory as a filtering medium. FIBROUS TALC and compact talc, or soapstone, are extensively used, the former for grinding to "mineral pulp," used in paper manufacture, the latter for many purposes, usually because it is refractory, expands and contracts very little, retains heat well and is not attacked by acids. These properties make it valuable in 32 482 MINER ALOG Y. furnaces, crucibles, sinks, baths, hearths, electrical switch boards and cooking utensils. Talc is also used in cosmetics, refractory paints, slate pencils, crayons, gas tips, as a lubricant and in soap making. CHLORITE is ground and us:d in hard rubber, rubber tires, foundry facings, etc. KAOLINITE AND CLAY. Enormous and varied industries use as their raw material the beds of clay which result from the decom- position of the feldspars and other silicates. These beds are composed in part of some hydrous aluminum silicate such as kaolin- ite, but usually with intermixed quartz, mica, undecomposed feldspar, oxides and sulphides of iron. Their properties and uses depend chiefly upon their composition. The clay industries include the manufacture of common brick, paving brick, fire-brick, and hydraulic cement, all varieties of earthenware, stoneware and porcelain, terra cotta, sewer pipes and drain tiles, and are carried on all over the country and the world. FULLERS EARTH, a kind of clay, is used in the refining and clarifying of mineral oils, and for bleaching lard and cottonseed oils. THE OTHER SPECIES AND GROUPS aside from a limited use of transparent or brightly colored material as precious or ornamental stone can not be said to have present economic importance. SILICA. The minerals described are: Quartz SiO 2 Hexagonal Chalcedony SiO 2 Tridymite SiO 2 Hexagonal Opal Si0 2 .wH 2 O Various other names have been given, some based on optical differences as quartzine, hissatite, ps eudo chalcedony , lutecite, some on specific gravity as granulina and jenzschite. Of them all cristobaltite is best characterized and apparently represents the form which silica takes if formed at high temperatures. FORMATION AND OCCURRENCE OF SILICA. According to experiments silica by slowly increasing tempera- tures passes through the various conditions of a quartz, quartz, tridymite and cristobaltite. SILICA AND THE ROCK-FORMING SILICATES. 483 a quartz is ordinary quartz like that of mineral veins at ordinary* temperatures. If heated above 575 C. it develops the characteristic etch figures of /3 quartz (quartz of the granites and porphyries). It is unstable | above 800 C M tending to pass into tridymite above 800 C. and into cristobaltite at 1,470. The occurrences may be grouped as: Crystallization from Magma. Quartz as the youngest constituent of granites, rhyolites and quartz porphyries and as a less important constituent of syenite and some basic igneous rocks. Tridymite chiefly in volcanic rocks trachyte, rhyolite, and ande- site. Pegmatites. Quartz in enormous crystals. Dakota, Maine, Connecticut, Norway, etc. Veins. Quartz both as chief gangue of ore veins and alone. Chalcedony, opal and fine grained mixtures as later constituents. Sediments. Mechanical Sediments. Quartz as chief part of sand and sand- stone and important part of shale. Tripoli results from leaching out of calcareous material from siliceous limestone as in S. E. Missouri. Chemical Sediments. Opal, chalcedony and sometimes quartz by hot springs and from the colloidal silica formed by weathering. Sediments due to Organisms. Diatomaceous Earth. Microscopic water plants, called diatoms, build silica into their cells. Their remains accumulate both in salt and fresh water, forming beds. The Richmond beds from the Chesapeake to Petersburg, Virginia, are in parts 30 feet thick. The Bilin, Bohemia, beds are 14 feet thick. Other large deposits exist near Socorro, New Mexico and Nevada. Metamorphic Rocks. As quartzite, quartz schist and an essential constituent of other rocks partly primary, partly secondary. * Am. Jour. Sci. 48, 28, 293. t Ibid., 22, 276. 4 8 4 MINERALOGY. THE OPTICAL DETERMINATION OF THE SILICAS. QUARTZ Uniaxial + 1-553 1-544 CHALCEDONY Biaxial 1-537 TRIDYMITE Biaxial + 1.47? OPAL Isotropic 1.446 7 a 0.009 0.002 In Thin Sections. Quartz. Usually fresh unweathered and without definite shape. Low relief, smooth surface. Interference colors gray or first order yellow. Basal sections dark between crossed nicols and with convergent light giving uniaxial cross and sometimes one ring red on outer edge, blue on inner. Circularly polarizing. Basal sections i mm. thickness turn the plane of polarization for yellow light 21.7 to right or left. Chalcedony. Between crossed nicols radial and parallel fibres, each of which has parallel extinction, and negative elongation. If spherulitic may show dark cross. Tridymite. Tile-like aggregates with strong relief and rough surface. Hardly noticeable birefringence. With crossed nicols and convergent light distorted biaxial figure. (Uniaxial at 130 C.) Opal. Shapeless with strong relief, rough surface and dark between crossed nicols or may show double refraction and even a negative cross (hyalite) as result of strain. QUARTZ. Rock Crystal, Amethyst. COMPOSITION. SiO 2 , (Si 46.7, O 53.3 per cent.). GENERAL DESCRIPTION. A hard, brittle mineral which is best known in transparent, glassy, hexagonal crystals, colorless, and as FIG. 470. FIG. 471. FIG. 472. SILICA AND THE ROCK-FORMING SILICATES. 485 the somewhat greasy lustred, shapeless, transparent mineral of granite and other igneous rocks. Colorless if pure, but often yellow, violet, or smoky and more rarely other colors. CRYSTALLIZATION. Hexagonal. Class of trigonal trapezohe- dron, p. 55. Axis c = 1.0999. Usually a combination of unit FIG. 473. FIG. 474- FIG. 475. FIG. 476. prism m with one or both unit rhombohedra, / and f, the former often larger and brighter, and the prism faces nearly always hori- zontally striated. The second order pyramid s = (20, : 2a : a : 2c) ; {1121}; frequently occurs and rarely the trapezohedral faces x = (|a : 6a : a : 6c), {5161) ; either right, Fig. 475, or left, Fig. 476. Supplement angles pp = 85 46'; mp = 38 13'; ms = 37 58'; mx = 12 i'. Twinned crystals are not rare. See page 68. Physical Characters. H., 7. Sp. gr., 2.65 to 2.66. LUSTRE, vitreous to greasy. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle to tough. COLOR, colorless and all colors. CLEAVAGE, difficult, parallel to rhombohedron. BEFORE BLOWPIPE, ETC. Infusible. With soda, fuses with marked effervescence to a clear or opaque bead, according to the proportions used. Insoluble in salt of phosphorus and slowly soluble in borax. Insoluble in all acids except hydrofluoric. VARIETIES. Rock-forming quartz is colorless or slightly cloudy or rose tinted, the quartz of ore veins is frequently amethystine. The principal varieties, which are discussed more at length under quartz as a semi-precious stone, p. 567, are 486 MINER ALOG Y. Rock Crystat.-rPme, colorless or nearly colorless quartz. Amethyst. Purple to violet and shading to white. Fracture shows lines like those of the palm of the hand. Color disappears on heating, and is probably due to a little manganese. Rose Quartz. Light-pink or rose-red, becoming paler on long exposure to light. Usually massive. Colored by titanium or. manganese. Yellow Quartz or False Topaz. Light yellow. Smoky Quartz. Dark yellow to black. Smoky tint, due to some carbon compound. Milky Quartz or Greasy Quartz. Translucent. Usually mass- ive. Common as a rock constituent. Ferruginous Quartz. Opaque, brown or red crystals, sometimes small and cemented like a sandstone. Aventurine. Spangled with scales of mica, hematite or goethite. Cat's Rye. Opalescent, grayish-brown or green quartz with in- cluded parallel fibers of asbestus. REMARKS. The formation of quartz is discussed on p. 483, and its uses, p. 480. Localities are infinite in number, a few famous ones being Switzerland; Japan; Carrara, Italy; Herkimer Co., New York; Hot Springs, Arkansas; Alexander Co., North Carolina. CHALCEDONY. COMPOSITION. Silica with occasionally a little water. GENERAL DESCRIPTION. Bluish gray or translucent material in mammillary linings of cavities and concretions. Lustre like wax. Grades into more highly colored and more opaque varieties. H., 6.5 to 7. Sp. gr., 2.62 to 2.64. CRYSTALLIZATION. Never in crystals visible to the naked eye but under the micro- scope with crossed nicols is seen to be composed of minute radiating needle crystals. VARIETIES. Optically distinct from quartz. The color-names such as Agate, Carnelian, Sard, Onyx, Sardonyx, Chrysoprase, Bloodstone, are discussed on p. 572: Other very common materials are essentially chalcedony, such as Flint. Smoky-gray to nearly black, translucent nodules, found in chalk-beds. Jasper. Opaque and containing considerable amounts of iron, and alumina, and often highly col- ored, as red, brown, or yellow. Touchstone. Velvet-black and opaque, on which metal streaks are easily made and compared. TRIDYMITE. FIG. 477. COMPOSITION. SiOa. GENERAL DESCRIPTION. Small, colorless, hexag- onal plates. Often in wedge shaped groups of two or three, Fig. 477. Usually prism and base sometimes pyramidal faces from which c = 1.6304 calculated. SILICA AND THE ROCK-FORMING SILICATES. 487 PHYSICAL CHARACTERS. Transparent. Lustre, vitreous. Color, colorless or white. Streak, white. H., 7. Sp. gr., 2.28 to 2.33. Brittle. BEFORE BLOWPIPE, ETC. Like quartz, but soluble in boiling sodium carbonate. OPAL. COMPOSITION. SiO 2 .wH 2 O, (H 2 O, 5 to 12 per cent.). GENERAL DESCRIPTION. Colorless, white and many colored "veins" and incrustations with internal color reflections. More often without ' ' opalescence " but translucent and with wax-like to porcelain-like lustre. Also free masses of rounded, kidney, stalactitic and other shapes often dull or pumice-like. Color- less masses like drops of melted glass and clay like or chalky beds. CRYSTALLIZATION. No crystalline structure s evident and apparently opal is " amorphous" in the most complete sense. Physical Characters. H., 5.5 to 6.5. Sp. gr., 2.1 to 2.2. LUSTRE, vitreous, pearly, dull. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle. COLOR, colorless and all colors. BEFORE BLOWPIPE, ETC. Infusible. Becomes opaque and yields more or less water. Soluble in hydrofluoric acid more easily than quartz and soluble in caustic alkalies^ VARIETIES. Precious and Fire Opal. With play of colors. Common or Semi-Opal. Translucent to opaque, with greasy lustre and of all colors, but without play of colors. Hyalite. Colorless transparent masses resembling drops of melted glass or of- gum arabic. Geyserite, Siliceous Sinter. Loose, porous opal silica deposited from hot water. Opaque, brittle and often in stalactitic or other imitative shapes. Pearl Sinter. Pearly, translucent material found in volcanic tufa and near hot springs is similar. Diatomaceous or Infusorial Earth. Massive, chalk-like or clay- like material composed of the remains of diatoms. Tripoli. Residue from leached-out siliceous limestone. For opal as a precious stone see p. 571. 4 88 MINERALOGY. THE FELDSPARS. The feldspars here described are : Orthoclase KAlSi 3 O 8 Monoclinic Microcline KAlSi 3 O 8 Triclinic Plagioclase w(NaA!Si 3 O 8 ) + (CaAl 2 Si 2 O8) Triclinic Albite, oligoclase, andesite, labradorite, bytownite and anorthite are included under plagioclase and the barium feldspars hyalophane and celsian are briefly mentioned after orthoclase. This group of silicates constituting nearly sixty per cent, of the crust of the earth is believed to be composed of three fundamental substances, KAlSi 3 O 8 , NaAlSi 3 O 8 and CaAl 2 Si 2 O 8 . The isomorph- ous mixtures of these are given different names, but they all have many points of close resemblance, such as crystal angles, habit, modes of twinning, cleavage angles, hardness and specific gravity. FORMATION AND OCCURRENCE OF FELDSPARS. Their occurrences may be summarized as follows: Crystallization from Magma. Orthoclase. Opaque or nearly in granite, syenite, porphyry and more glassy in trachyte, phonolite, rhyolite, etc. Microcline. In granites. Albite. Not prominent as a primary mineral. On chemical grounds considered to be present in granites, groundmass of porphyry, etc., and acid eruptives. Oligoclase and andesite. More common in granites than albite. Very frequent also in syenite, diorite, trachyte, andesite, diabase, etc. ; and particularly accompanies orthoclase. Labradorite and bytownite are especially in gabbros and norites but also in other basic rocks, diorite, diabase, basalt, andesite, etc. Anorthite. In gabbro and norite, basalt, etc., especially if carrying chrysolite. Much rarer than labradorite. Pegmatites. The feldspars, particularly orthoclase, microcline, albite and oligoclase, are the principal minerals of the pegmatites. Contacts. Anorthite occurs as a contact mineral with limestone at Mon- zoni, Tyrol. SILICA AND THE ROCK-FORMING SILICATES. 489 Veins. Orthoclase. The variety valencianite (essentially adularia), oc- curs in many of the younger ore veins evidently deposited from the ascending currents and often replacing former gangue min- erals.* Examples are Tonopah, Nevada, Gold Road, Arizona, Cripple Creek, Colorado; Valencia, Guanajuato. Sediments. The arkose sandstones of Portland, Conn., are high in feldspars and they are abundant as fragments and in shales and slates. The potash feldspars predominate. In Metamorphic Rocks. The plagioclases are less abundant than orthoclase and micro- cline. The potash feldspar is usually microcline.'f Adularia, however, occurs in clefts in the crystalline schists as in the Alps. Albite is common in gneiss and the schists (chlorite schists of Alps) and in metamorphosed eruptives. Labradorite is found in many amphibolites. THE OPTICAL DETERMINATION OF FELDSPARS. If the mineral is a feldspar sections in balsam will show frequent crystal outlines, low relief like that of quartz, gray to middle first order colors, frequent cleav- j . u- i FlG - 478> age cracks and twinning, biaxial interference figures and very of- ten cloudiness from weathering. Crushed fragments will be lath- like. If orthoclase twinning will be common and sections showing it will be divided into two parts, Fig. 478, which extinguish for dif- ferent positions between crossed nicols (Carlsbad law) or the divi- sion will be diagonal with the two parts exstinguishing at the same Sanidine, Carlsbad twin. (Cohen.) * Lindgren, Mineral Deposits, 434 to 438. f Iddings, "Rock Minerals," 237. 490 MINERALOGY. time but with the X and Z directions crossed (Baveno law) ; the material will rarely be clear and pellucid. If microdine most sections will show between crossed nicols the plaid or grating structure of dark and light bands due to two systems of twinning, as shown in Fig. 479. FIG. 479- Microcline grating structure. (Finlay.) \ If plagiodase there will usually show between crossed nicols parallel dark and light bands due to multiple twinning, with the lamellae parallel to (oio) the brachy pinacoid (Albite law), which may be broad, Fig. 480, or narrow, Fig. 481, or both, or may pinch out. Sometimes a second series crosses these at different angles in different varieties (Pericline law) . The More Exact Optical Determination in Sections of Known Orientation by Extinction Angles. On account of the two easy cleavages (ooi) and (oio) flakes of known orientation are easily obtained and crushed fragments also tend to furnish these though in orthoclase plates parallel (ooi) predominate while in plagioclase plates parallel (oio) are more common because of the lamellar development parallel to it. These cleavage sections are much used, the " Guide" or reference line in each being the trace of the other cleavage. The extinction angles may be positive or negative, the rule being that with the sections in the positions of Figs. 482 and 483, with the cleavage SILICA AND THE ROCK-FORMING SILICATES. 491 FIG. 480. FIG. 481. Plagioclase, showing broad lamellae, in gabbro. (Cohen.) Plagioclase, showing narrow lamellae, in diabase. (Cohen. ) cracks parallel to a cross hair, clockwise rotations are + (positive) and counter clockwise are (negative) . FIG. 482. FIG. 483. Feldspars. Section (oio). Section (ooi). These angles together with other constants are as follows: Species Indices. Birefrin- gence. Extinction Angles. Michel Levy. I i y a on (coi) on (oio) Orthoclase Microcline .526 529 540 545 557 1-563 1.588 519 .522 532 537 549 555 575 O.OO7 O.OO? O.008 O.OO8 0.008 O.O08 O.OI3 +isi + 4 + 2 - ^ - 5 -37 + 5 + 5i + I9^ + 8 - 8 -18 -36 1 8 1 6 5 1 6 27 53 Albite Oligoclase Andesite Labradorite Anorthite 492 MINERALOGY. Extinctions on Sections Perpendicular to (oio). Michel Levy Method. In rock sections (oio) and (ooi) may be difficult to find but any section perpendicular to a twin plane will, when the twin is parallel to one of the nicols, be equally illuminated and the angles of extinction with this line will be equal. But there are many such sections giving different extinction angles and only the maximum extinction angles are characteristic. Hence numerous sections must be tried and only the larger angles considered. The maximum extinction angles are tabulated above. Fouque deter- mined the orientation of sections by convergent light tests in sections perpendicular the acute or obtuse bisectrix. ORTHOCLASE. Feldspar, Potash Feldspar. COMPOSITION. KAlSi 3 O 8 , with some replacement by Na. GENERAL DESCRIPTION. Cleavable masses, showing angle of 90; and monoclinic crystals, of flesh-red, yellow or white color. Also compact, non-cleavable masses, resembling jasper or flint. Some- times colorless grains or crystals. CRYSTALLIZATION. Monoclinic. Axes /? = 63 57'; a :%: c = 0.659 : i 10.555. Most frequent forms: unit prism m t pina- colds b and c and positive orthodomes o = (a : oo b : c); J 101 } ; and y = (a : oo b : 2c); (201). Supplement angles are : mm = 61 13'; cm = 67 47'; co = 50 17'; cy = 80 18'. FIG. 484. FIG. 485. FIG. 486. FIG. 487. - Twin forms of Carlsbad type, Fig. 488, twin plane the ortho- pinacoid, are very common; the Baveno type, Fig. 489, twin plane a clinodome, and Mannebacher type, twin plane the base c, Fig. 490, are less common. SILICA AND THE ROCK-FORMING SILICATES. 493 FIG. 488. FIG. 489. FIG. 490. Physical Characters. H., 6 to 6.5. Sp. gr., 2.44 to 2.62. LUSTRE, vitreous or pearly. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle. COLOR, flesh -red, yellowish, white, CLEAVAGE, parallel to c and colorless, gray, green. b, hence at right angles. BEFORE BLOWPIPE, ETC. Fuses in thin splinters to a semi- transparent glass and colors the flame violet. Insoluble in acids. VARIETIES. Ordinary. Simple or twinned crystals, sometimes of great size, of nearly opaque pale red, pale yellow, white or green color. More frequently imperfectly formed crystals and cleavable masses, in the granitic rocks. Adularia. Colorless to white, transparent, often opalescent. Usually in crystals. Sanidine and Rhyacolite. Glassy, white or colorless crystals in lava, trachyte, etc. Loxoclase. Grayish-white or yellowish crystals, which have a tendency to cleave parallel to the ortho pinacoid. Felsite. Jaspery or flint-like masses of red or brown color. SIMILAR SPECIES. Differs from the other feldspars in the cleav- age at 90, the greater difficulty of fusion, the absence of stria- tions. The very common red or brownish color of orthoclase does not occur in plagioclase. REMARKS. The occurrence and uses are described on p. 488, and 481. It changes to kaolin quartz, opal, epidote and sericite, by the removal of bases through the action of acid waters. Orthoclase is quarried at South Glastonbury and Middletown, Conn.; Edgecomb and Brunswick, Me.; Chester, Mass.; Brandywine Summit, Pa.; Tarrytown and Fort Ann, N. Y., and the Spruce Pine district, N. C. HYALOPHANE. (K 2 , Ba)Al 2 (SiO 3 )4 and CELSIAN. BaAhSizOs, are barium 494 MINER ALOG Y. feldspars, stated by Iddings to be "monoclinic in all discernible physical properties." The former resembles adularia and occurs in dolomite in Binnenthal, Switzerland, and Jakobsberg, Sweden. The latter is massive cleavable from Jakobsberg, Sweden. MICROCLINE. COMPOSITION. KAlSi 3 Os GENERAL DESCRIPTION. Like orthoclase. There is no practicable macroscopic distinction between orthoclase and microcline and it is very probable that they are identical. One theory is that the individuals are triclinic and submicroscopic, but that in orthoclase they alternate in twin position, remaining invisible and giving an "ap- parent monoclinic" structure, whereas in microcline a number of successive indi- viduals are parallel followed by a number in twin position, thereby becoming visible as twin lamellse, but grading into submicroscopic and apparently monoclinic portions. REMARKS. The distinctions are optical (see p. 491 and Fig. 479). PLAGIOCLASE. Albite, Anorthite, and Isomorphous Mixtures. The name " plagioclase" was originally given to minerals closely resembling common feldspar in cleavage, crystal form, mode of occurrence, hardness, specific gravity and other physical charac- ters, but with the angle between the two cleavages about 86 in- stead of 90. The very great variations in composition led to the establishment of several species, in which, however, the variations in composition were still great, and finally to a theory, now gen- erally accepted, which may be expressed as follows : The plagio- clases consist of isomorphous mixtures of two (or three) triclinic com- pounds, NaAlSi z O & and CaAS 2 St 2 8 (and KAlSi^O^. Some specimens approach the end members, and are then called respec- tively albite, anorthite (and microcline), but, in general, distinct species cannot be said to ezist. In accordance with this, the more prominent species names are here given as varieties of the group name PLAGIOCLASE. COMPOSITION. ?^(NaAlSi 3 O 8 ) + ^(CaAl 2 Si 2 O 8 ), with some re- placement by KAlSi 3 O 8 . GENERAL DESCRIPTION. Granular masses or small triclinic crystals, or coarser masses. Each grain or crystal cleaves easily in two directions, which make an angle of about 86 with each other, and shows on one or both surfaces by reflected light the parallel "twin striations." Some varieties show marked play of colors, others the moonstone effect. Usually light colored, and most frequently colorless, white or faintly tinged, sometimes (labradorite) dark gray. Just about the hardness of a good knife. SILICA AND THE ROCK-FORMING SILICATES. 495 CRYSTALLIZATION. Triclinic, usually in crystals resembling that shown in Fig. 491, with supplement angles mM approximately 60, and frequently twinned either by the albite law, twin plane b, Fig. 494, which, if repeated, results in striations on c; or by the pericline law, twin axis the macro axis, Fig. 493, producing stri- ations on b. Albite and anorthite are frequently crystallized, the other varie- ties less frequently. FIG. 491. FIG. 492. FIG. 493. ; COMPOSITION AND SPECIFIC GRAVITY OF TYPES. Denoting NaAlSI 3 O 8 by Ab and CaAl 2 Si 2 O 8 by An the names most used are as follows: ALBITE AbiAn to Ab 6 Ani OLIGOCLASE Ab 6 Ani to Ab 3 Ani ANDESINE Ab 3 Ani to AbiAni LABRADORITE AbiAni to AbiAn 3 BYTOWNITE AbiAn 3 to AbiAn 6 ANORTHITE AbiAn 6 to The percentage composition and specific gravities of types are: Sp. Gr.* SiO 2 . A1 2 3 . Na 2 O. CaO. AbiAno 2.605 68.7 19.5 II. 8 o AbeAni . 64.9 22.1 IO.O 3 AbsAni 2.649 62.0 24.O 8.7 5-3 AbiAm 2.679 55-6 28.3 5-7 10.4 AbiAns 49.3 32.6 2.8 15.3 AbiAne 46.6 34- 1 1.6 17.4 AboAni 2.765 43-2 36.7 20. i * On pure artificial feldspars also Ab2Am 2.660, AbiAn2 2.710, AbiAm 2.733. Natural material is impure and ranges 2.5 to 2.8. 496 MINERALOGY. Physical Characters. H., 5 te 7- Sp. gr.. 2.5-2.8 in minerals. LUSTRE, vitreous or pearly. TRANSLUCENT to opaque. STREAK, white. TENACITY, brittle. COLOR, varies. CLEAVAGES, at 86 approx. Distinguishing the Varieties. Something can be judged by the occurrence, p. 488. The end members, albite and anorthite, are less common than the others and the albite and oligoclase or andesine are to be expected in the more acid igneous rocks such as the granites, while the labradorite, bytownite and anorthite favor the dark-colored basic rocks. In the schists and metamorphic rocks generally albite is common. The optical distinctions as outlined on p. 490 are conclusive if the orientation is known. A few simple macroscopic indications are as follows: Albite. Usually pure white, granular or with curved cleavage surfaces, or in crystals (Figs. 491 to 493) in cavities. Often encloses the rarer minerals, tourmaline, beryl, chrysoberyl, topaz, etc. Not easily altered. American localities are Branchville, Conn.; Paris, Maine; Chesterfield, Mass.; Amelia Co., Virginia; Pikes Peak, Colorado. Oligoclase often accompanies orthoclase as grayish white, translucent masses, with somewhat greasy lustre and marked twin striations. Occurs also as reddish cleavable masses, sunstone, and rarely as crystals. American localities are Fine and McComb, New York; Mineral Hill, Perm.; Bakersville, N. C. Andesine is similar to oligoclase. Observed in the granular and volcanic rocks of the Andes. Also common in the Rocky Mts., Sandford, Maine, etc. Labradorite is usually in dark gray cleavable masses often associated with hypersthene. Commonly iridescent, showing beautiful changing colors, blue, green and red, from inclusions of diallage, ilmenite or goethite. Striated like oligoclase. Is notably absent in localities containing orthoclase and quartz. Found abundantly in the Adirondacks, N. Y., in the Wichita Mountains, Ark., in Quebec and in Labrador. SILICA AND THE ROCK-FORMING SILICATES. 497 Bytownite, originally a greenish white feldspar from By town, Canada, is now simply a name for plagioclase between labradorite and anorthite. Anorthite. Comparatively rare as a pure mineral. Best known in the small glassy crystals of Vesuvius and the white crystals of Miyake, Japan, often covered with a black crust, the massive granular indianite from India, and the contact mineral of Monzoni, Tyrol. THE FELDSPATHOIDS. The minerals described are : Leucite K.Al(SiO 3 ) 2 Isometric Melilitc Cai 2 Al4(SiO 4 )2 Tetragonal Nephelite 7NaAlSiO 4 + NaAl(SiO 3 ) 2 Hexagonal Sodalite Group Isometric The analcite, p. 531, of certain plutonic rocks near Butte, Montana, and Pikes Peak, Colorado, and the dike at Heron Bay, L. S., also belongs here. FORMATION AND OCCURRENCE OF FELDSPATHOIDS. Feldspathoids are* " Silicates of alumina and an alkali or alkaline earth that are practically equivalent to feldspars in their relation to rocks." They form from magmas unusually rich in sodium or potassium and are limited to igneous rocks or rarely to schists resulting from metamorphosis of igneous rocks. Two divisions may be made. In Volcanic Rocks. Leucite. Almost entirely confined to younger eruptive rocks, phonolite, tephrite and other leucite rocks and their tuffs. Melilite. Restricted to younger basic eruptives, such as augite bearing basalts. Nephelite. In glassy crystals in volcanic ejecta, phonolite- tephrite, etc. Noselite and Haiiynite. Almost limited to microscopic material in phonolite, etc., and always associated with nephelite or leucite, Sodalite. In microscopic crystals, trachytes, phonolites and lava. * Kemp, "Handbook of Rocks," p. 186. 33 498 MINERAL OGY. In Plutonic Rocks. Leucite rare but often represented by pseudomorphs. Nephelite as massive and coarsely crystalline elaeolite in elseolite- syenite. Sodalite common in elaeolite-syenite. OPTICAL DETERMINATION OF FELDSPATHOIDS. 7 a 7 a Leucite .' Biaxial + 1.5809 1.5808 o.ooi Melilite Uniaxial 1.631 1.629 0.002 Nephelite Uniaxial 1.542 1.538 0.004 Sodalite Isotropic 1.483 Haiiynite 1 Noselite I IS tr plC "^ In Thin Sections. Leucite. Nearly round cross sections. Isotropic in small crys- tals but showing intersecting twin lamellae and zonal inclusions in larger crystals. No relief, smooth surface. Low bluish-gray interference colors best proved with gypsum red test plate. Melilite. Lath-shaped sections or irregular often with markings parallel the length. Marked relief. Very low interference colors or abnormal, p. 138. Nephelite. Rectangular or hexagonal sections in volcanic rock shapeless in plutonic. No relief, smooth surface, low first order interference colors. Basal sections give broad cross, no rings. Other sections extinguish parallel cleavages. Hauynite, Noselite, Sodalite. Dodecahedral crystals or shape- less. Surface rather rough. Gas and glass inclusions especially near border. Dark between crossed nicols or abnormal. Distinc- tions by microchemical tests. LEUCITE. COMPOSITION. KA1(SIO 3 ) 2 . FlG - 494. GENERAL DESCRIPTION. Gray, translucent to white and opaque, disseminated grains and trap- ezohedral crystals -in volcanic rock. CRYSTALLIZATION. Isometric externally, but with polarized light, showing double refraction at all temperatures below 500 C. SILICA AND THE ROCK-FORMING SILICATES. 499 Physical Characters. H., 5.5 to 6. Sp. gr., 2.45 to 2.50. LUSTRE, vitreous to greasy, TRANSLUCENT to opaque. STREAK, white. TENACITY, brittle. COLOR, white or gray, or with yellowish or red tint. BEFORE BLOWPIPE, ETC. Infusible. With cobalt solution, be- comes blue. Soluble in hydrochloric acid, leaving a fine powder of silica. REMARKS. It is not common in America, but is found in the Leucite Hills. Wyoming, and also in the northwestern part of the same state, and in Montana, It is represented by pseudomorphs at Magnet Cove, Arkansas. Very common in the Vesuvian lavas and in other parts of Italy. MELILITE. Cai2Al 4 (SiO4)2 with Na, Mg and Fe replacing Ca and Al, occurs in short prisms and in tabular tetragonal crystals. Color, honey-yellow to brown. H., 5. Sp. gr., 2.9. Fuses quite easily to a yellowish or green glassy globule. Gelatinizes with hydrochloric acid. It is found in the Vesuvian lavas, certain basalts of Wiirttemberg and the Sandwich Islands and elsewhere. NEPHELITE. Elseolite. COMPOSITION. ;NaAlSiO 4 + NaAl(SiO 3 ) 2 . With partial re- placement of Na by K or Ca. GENERAL DESCRIPTION. Small, glassy, white or colorless grains or hexagonal prisms with nearly flat ends, in lavas and eruptive rocks, or translucent reddish-brown or greenish masses and coarse crystals, with peculiar greasy lustre. Physical Characters. H., 5.5 to 6. Sp. gr., 2.55 to 2.65. LUSTRE, vitreous or greasy. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle. COLOR, white, colorless, reddish, brownish, greenish or gray. CLEAVAGE, prismatic and basal. BEFORE BLOWPIPE, ETC. Fuses to a colorless glass. When heated with cobalt solution, becomes blue. Soluble in hydro- chloric acid, with residue of gelatinous silica. VARIETIES. The usually massive varieties, with greasy lustre, are called elaeolite. REMARKS. Southern Norway; Greenland; Miask, Urals; Austin, Texas; Litch- field, Me.; Salem, Mass.; the Ozark Mountains, Arkansas; Cripple Creek, Col. are important localities of elaeolite. Nephelite is abundant in the lavas of Vesuvius, and in basalts near Heidelberg, Germany, and Aussig, Bohemia. 500 MINERALOGY. THE SODALITE GROUP. A group of silicates containing the unusual radicals Cl, SO 3 and S. The formulae as written and the isometric crystallization suggest a relationship to garnet. SODALITE. Na4(AlCl)Al 2 (SiO4) 3 Is found in bright blue to gray masses, em- bedded grains, concentric nodules resembling chalcedony and rarely dodecahedral crystals sometimes of a pale pink color. It occurs at Litchfield, Me., various localities in Montana, Quebec, and Ontario; also in Vesuvius lavas, at Kaiserstuhl, Baden; and Miask, Urals. HAUYNITE. 2(Na 2 Ca)Al 2 (SiO 4 ) 2 .(Na 2 .Ca)SO4 possibly, but very complex and with varying proportions of Na and Ca. Occurs as glassy blue to green imbedded grains, or rounded isometric crystals in igneous rock. NOSELITE. Na4(NaSO4.Al)Al 2 (SiO 4 ) 3 not distinguishable from haiiynite except by microchemical tests.* Haiiynite is from Mt. Dore, Puy de Dome; Vesuvian lavas, the Eifel and Crazy Mt., Montana. Noselite is from Lake Laach, Cape Verde Islands, etc. THE PYROXENE AND AMPHIBOLE GROUPS. THE PYROXENE GROUP. Enstatite (Mg.Fe)SiO 3 Orthorhombic Hyperslhene (Mg.Fe)SiO 3 Orthorhombic Pyroxene RSiO 3 Monoclinic Acmite NaFe(SiO 3 )2 Monoclinic Wollastonite CaSiO 3 Monoclinic Other described species belonging to this group are spodumene, rhodonite, and jadeite! THE AMPHIBOLE GROUP. The minerals described are: Anthophyllite (Mg.Fe)SiOs Orthorhombic Amphibole RSiO 3 Monoclinic Glaucophane NaAl(SiO 3 ) 2 (Fe.Mg)SiO 3 Monoclinic Crocidolite NaFe (SiO 3 ) 2 FeSiO 3 The compositions of the two groups are related, but while the amphiboles are largely formed from the pyroxenesf corresponding members are lower in calcium and higher in magnesium. There *For instance gypsum crystals obtained by evaporating the hydrochloric acid solution prove haiiynite. f When the amphibole retains the outward form of the pyroxene it is called uralite. The change usually commences on the surface and the uralite does not form a single compact crystal, but consists of numerous slender columns parallel to one another. These little columns or fibers have their I and 5 axes parallel to the positions of these axes in the parent mineral. SILICA AND THE ROCK-FORMING SILICATES. 501 are also close relations in crystalline form, as shown by the follow- ing comparison of constants: Pyroxene a : b : c = 1.0921 : I : 0.5893 = 74 10' Amphibole a : %b : c = 1.1022 : I : 0.5875 = 73 58' The "habit" and cleavage are however always different. FORMATION AND OCCURRENCE OF PYROXENES AND AMPHIBOLES. The occurrences may be classed as Separations from Magma in Plutonic Rocks. PYROXENES. Diopside, and some augites in granites, syenites and diorites. Enstatite, hypersthene, diopside, diallage and darker augites; in more basic rocks, gabbros, norites, pyroxenites, peridotites, etc. Acmite in nephelin syenites, granites, etc. AMPHIBOLES. Common hornblende in granite, syenite, diorite, gabbro. Basaltic hornblende in gabbro. Separations from Magma in Volcanic Rocks. PYROXENES. Augite as important constituent of many volcanic rocks, espe- cially basalt, melaphyre, diabase, andesite, porphyries, and ash and tuff of volcanoes. Enstatite and hypersthene as accessories in small crystals. Acmite in leucite and nephelite rocks. Diopside and sahlite rare. No diallage. AMPHIBOLES. Basaltic hornblende chiefly in basalts, andesites, and volcanic tuffs. Secondary Crystallizations in Igneous Rocks. The amphibole actinolite is common, sometimes formed from pyroxene, sometimes from hornblende. Secondary pyroxene is rare. Contacts. The PYROXENES, fassaite, wollastonite, diopside, sahlite and some- times augite and the AMPHIBOLES, edenite, and common hornblende. 50 2 MINERALOGY. In Metamorphic Rocks. PYROXENES. Diopside and sahlite in clefts in the schists or in granular lime- stone. Augite less frequent. Enstatite and hypersthene in metamorphosed igneous rocks, serpentine and some gneiss. AMPHIBOLES. Tremolite always metamorphic, especially in granular limestone and dolomite in regions of crystalline schists. Actinolite is more widespread, not only as a secondary mineral in igneous rocks resulting from the alteration of pyroxene but forming actinolite schists with chlorite and epidote or magnetite and as crystallizations in talc. Hornblende is common, sometimes forming hornblende schist and hornblende gneiss. Anthophyllile and glaucophane occur in schists, the former often with hornblende or actinolite, the latter sometimes forming inde- pendent glaucophane schists. OPTICAL DETERMINATION OF PYROXENES AND AMPHIBOLES. The characters of use in distinction are: Refractive Indices. Birefrin- gence. Extinct. Pleochroism. y a 7 a On oio. PYROXENES: Enstatite 1.669 1-705 1.702 to 1.727 1.722 1.813 1.635 .657 .636 .636 .653 639 1.665 1.692 1.680 to 1.706 1.697 1.763 1.621 1.633 1.609 1.611 1.629 1.621 O.O09 0.013 O.O22 to O.O2I 0.025 0.050 O.OI4 O.O24 O.027 O.O25 O.024 O-OI8 38 to 45 38 to 54 2 to 5 35 16 15 15 to 25 4 to 6 Weak Strong, red to green None Not intense Strong, yellow to green or brown None Sometimes None Weak Strong yellow to green Strong blue to yellow Hypersthene Diopside Augite Acmite . . Wollastonite AMPHIBOLES: Anthophyllite Tremolite Actinolite Hornblende* Glaucophane The indices indicate marked relief and rough surfaces in balsam. Interference colors in thin sections (due to 7 a) will be rather low in enstatite, hypersthene SILICA AND THE ROCK-FORMING SILICATES. 503 and wollastonite. The other pyroxenes will show very bright colors, more so than the amphiboles because of the strong absorption of the latter in direction of cleavage lines of longitudinal sections. In convergent light. All are biaxial with axial plane (oio). Pyroxenes: Axial angle. Sign. Enstatite ... Large + Hypersthene Large Pyroxene Large + Acmite Small Wollastonite Large or + Amphiboles : Anthophyllite Large + Amphibole Large Glaucophane Medium Acute bisectrix. \\c II a 36 to 54 to c (front) nearly || c +32 to c (back) 70 to 90 to c front 84 to 86 to c front Basal sections show characteristically different outlines and cleavage lines in pyroxene, Fig. 495, and in amphibole, Fig. 496. They yield symmetrical interference figures, Fig. 266, with enstatite, hype*sthene and anthophyllite, and may show the emergence of an optic axis, Fig. 269, with the other pyroxenes and glaucophane. FIG. 495. FIG. 496. Pyroxene. Amphibole. The section (oio) yields the most characteristic tests, giving maximum birefringence (interference colors) pleochroism and ex- tinction angles. It is parallel to the axial plane therefore may give the interference figure of Fig. 267. In finding (oio) in a rock section a partial guide is the one system of parallel cleavage lines (so also on 100) and these maximum interference colors and pleochroic differences. The extinction angle results when the longitudinal section, * In basaltic hornblende the indices are higher and birefringence so high that no bright colors result and the extinction varies from o to + 10. Figs. 497, 498, 499, to the nearest extinction. MINERALOGY. is revolved from the cleavage lines as a reference irrinn . This direction will be X in acmite, and wollastonite and Z in the < may be proved by test, p. 134, for faster and slower ray (elongation). wollastonite and Z in the others and this nH slnwpr rav fplnnpaHnTO Enstatite-Hypersthene. Pyroxene (Diopside). Amphibole (Tremolite). THE ORTHORHOMBIC PYROXENES. Enstatite and Hypersthene. Natural iron free MgSiO 3 is not known. COMPOSITION. (Mg.Fe)SiO 3 . Although these two substances have the same general formula and nearly identical axial ratios, the increase in iron contents not only affects such characters as color fusibility, and specific gravity but the position of the optic axes so that Des Cloizeaux made the distinction,* on the basis of the fact that with about 10 per cent. FeO the optic axial angle was 90, between Enstatite with FeO < 10 per cent, and optically +. Hypersthene with FeO > 10 per cent, and optically . EN STATITE. Bronzite. COMPOSITION. (Mg.Fe) SiO 3 . GENERAL DESCRIPTION. Brown to gray or green, lamellar or fibrous masses, with sometimes a peculiar metalloidal lustre (bronzite). Rarely in columnar orthorhombic crystals. PHYSICAL CHARACTERS. Translucent to opaque. Lustre, pearly, silky or metal- loidal. Color, brown, green, gray, yellow. Streak, white. H., 5.5. Sp. gr., 3.1 to 3.3. Brittle. BEFORE BLOWPIPE, ETC. Fusible on the edges. Almost insoluble in acids. With cobalt solution is turned pink. *As Dana states it, "The essential difference between them, according to Des- Cloizeaux, lies in the axial dispersion which is uniformly p v for hypersthene." SILICA AND THE ROCK-FORMING SILICATES. 505 REMARKS. Occurrences as stated on p. 501 ; also found in meteorites. The largest crystals (pseudomorphs) are from the apatite-iron deposits of Bamle, Norway. The fibrous talc of Edwards, N. Y., is altered enstatite. Other localities are Kupferberg, Bavaria, and Baste, Harz. HYPERSTHENE. COMPOSITION. (Mg.Fe)SiOs, with more iron than enstatite GENERAL DESCRIPTION. Dark-green to black, foliated masses or rare orthorhom- bic crystals, which grade into enstatite. Frequently shows a peculiar iridescence, due to minute interspersed crystals. PHYSICAL CHARACTERS. Translucent to opaque. Lustre, pearly or metalloidal. Color, dark-green to black. Streak, gray. H., 5 to 6 Sp. gr., 3.4 to 3.5. Brittle BEFORE BLOWPIPE, ETC. Fuses on coal to a black, magnetic mass. Partially soluble in hydrochloric acid. REMARKS. It occurs at St. Paul, Labrador, and the Saranac Region, N. Y.; with labradorite; Bodenmais, Bavaria, in the intrusive pyrite deposit; Aranyer Berg, Hungary; Mt. Dore, Auvergne; etc. BASTITE. An alteration product of enstatite near serpentine in composition. It is usually foliated and of a yellowish or greenish color and has a peculiar bronze-like lustre on the cleavage surface. H., 3.5-4. Sp. gr., 2.5-2.7. PYROXENE. Augite. COMPOSITION. RSiO 3 . R = Ca, Mg, Mn, Fe, Al, chiefly. GENERAL DESCRIPTION. Monoclinic crystals. Usually short and thick, with square or nearly square cross-section, or octagonal and with well-developed terminal planes. Granular, foliated and columnar masses and rarely fibrous. Color, white, various shades of green, rarely bright green, and black. CRYSTALLIZATION. Monoclinic. ft = 74 10'. Axes a :1) : c 1.092 : i : 0.589. FIG. 500. Diopside, Pitcairn, N. Y. FIG. 501. Rossie, N. Y FIG. 502. J Diopside, De Kalb, N. Y FIG. 503. Fassaite. Common forms : unit prism m, the pinacoids a, b and c, the negative and, more rarely, the positive unit pyramids p and p t the 506 FIG. 504. MINERALOGY. FIG. 505. ^ A FIG. 506. A Leucaugite, Sing Sing, N Y Augite. Augite twin. negative and positive pyramids v and v = (d : 6 : 20) ; {221} Supplement angles are: mm = 92 50' ; // = 48 29' ; pp = 59 ( 42' z/z/ = 68 42'; -w= 84 = 49 54' ; = 65 21' = 33 49' ; cp Contact twins, twinning plane a, Fig. 521, are common. Also twin lamellae parallel c, shown by striations on the vertical faces and by basal parting. Optically -f . Axial plane b. Strong double refraction. Varying axial angle. Usually not strongly pleochroic. Physical Characters. H., 5 to 6. Sp.gr., 3.2 to 3.6. LUSTRE, vitreous, dull or resinous. OPAQUE to transparent. STREAK, white to greenish. TENACITY, brittle. COLOR, white, green, black, brown. CLEAVAGE, prismatic (angle 87 10'). BEFORE BLOWPIPE, ETC. Variable. Usually fuses easily to dark glass, sometimes to magnetic globule. Not generally solu- ble in acids. VARIETIES. Diopside. CaMg(SiO 3 ) 2 . Usually white or pale-green to nearly black. Common Pyroxene. Ca(Mg.Fe)SiO 3 . Chiefly shades of green and black. Augite. CaMg(SiO 3 ) 2 , with (Mg.Fe)(Al.Fe) 2 SiO 6 . Dark-green to black. In addition there are intermediate members of the isomorphous series such as hedenbergite, (Ca.Fe)(SiO 3 ) 2 , grayish-green. Schef- SILICA AND THE ROCK-FORMING SILICATES. 507 ferite containing up to 8 per cent. MnO, jeffersonite containing ZnO, and diallage, thin foliated pyroxene, green or brown in color. SIMILAR SPECIES. Differs from amphibole, as therein described. ACMITE, COMPOSITION. NaFe (SiO 3 )2. GENERAL DESCRIPTION. Occurs in long, prismatic monoclinic crystals of dark green or dark brown color. Sometimes green on interior and brown on exterior of crystal. In acmite these are acutely terminated and in aegirite, bluntly. Also found needle-like and fibrous. Streak, yellowish gray. H., 6-6.5. Sp. gr., 3.5. BEFORE BLOWPIPE, ETC. Fuses easily to a black, slightly magnetic globule, and colors the flame yellow. Only slightly affected by acids. REMARKS. Found at Magnet Cove, Ark.; Montreal, Canada; Langesund fiord, Norway; West Greenland, etc. WOLLASTONITE. COMPOSITION. CaSiO 3 , SiO2 51.7, CaO 48.3. GENERAL DESCRIPTION. Cleavable to fibrous white or gray masses. Also in monoclinic crystals, near pyroxene in angle. Sometimes compact. Usually inter- mixed with calcite. H., 4.5 to 5. Sp. gr., 2.8 to 2.9. BEFORE BLOWPIPE, ETC. Fuses to a white glass, color- ing the flame red. Soluble in hydrochloric acid, generally effervescing and always gelatinizing. SIMILAR SPECIES. Differs from pectolite and natrolite in red flame, difficulty of fusion, and absence of water. Harrisville, N. Y. Tremolite does not gelatinize. REMARKS. Occurs chiefly in limestone contacts with pyroxene, calcite, garnet, etc Abundant in Lewis and Warren Counties, New York, and at numerous localities in Hungary, Finland, Norway, etc. ANTHOPHYLLITE. COMPOSITION. (Mg.Fe)SiOs, corresponding to enstatite-hypersthene of the pyroxene group. GENERAL DESCRIPTION. Gray, brown or green lamellar and fibrous masses often resembling asbestos. Rarely in orthorhombic crystals. H., 5.5 to 6. Sp. gr., 3 to 3-2. BEFORE BLOWPIPE, ETC. Fuses with difficulty to a black enamel which is attracted by the magnet. Insoluble in acids. REMARKS. Occurs at Franklin, Macon Co., N. C., with corundum, Kongsberg, Norway; Gedres, France, etc. (gedrite is an aluminous variety). AMPHIBOLE. Hornblende. COMPOSITION. RSiO 3 , R being more than one of the elements, Ca, Mg, Fe, Al, Na and K. GENERAL DESCRIPTION. Monoclinic crystals either long with acute rhombic section or shorter with six-sided cross section. 508 MINERALOGY. Often with ends like flat rhombohedron. Also columnar, fibrous and granular masses, rarely lamellar, often radiated. Colors : white, or shades of green, brown or black. FIG. 508. FIG. 509. FIG. 510. Russell, N. Y. CRYSTALLIZATION. Monoclinic. Axes a \ b : c = o. 551:1: 0.294; /9=73 58'. Common forms : unit prism m, pinacoids b y c and sometimes a, unit clino-dome d and unit pyramid /. Supplement angles are : mm= 55 49'; cm *= 75 52'; dd = 31 32'; // = 31 41'. Twinning as in pyroxene. Optically -J-- Axial plane b. Strong double refraction. Often strongly pleochroic. Physical Characters. H., 5 to 6. Sp. gr., 2.9 to 3.4. LUSTRE, vitreous to silky. TRANSPARENT to opaque. STREAK, white or greenish. TENACITY, brittle to tough. COLOR, white, gray, green, black, brown, yellow and red. CLEAVAGE, prismatic, angle of 124 11'. BEFORE BLOWPIPE, ETC. Varies. Usually fuses easily to a colored glass, which may be magnetic. Not affected by acids. VARIETIES: Tremolite. CaMg 3 (SiO 3 ) 4 , white to gray in color. Crystals, long-bladed or short and stout. Fibrous masses, the fibres parallel, radiating or interlaced and compact masses. Originally from Tremola, Switzerland. Sp. gr., 2.9 to 3.1. Actinolite. Ca(Mg.Fe) 3 (SiO 3 )4, bright green or grayish-green crystals and fibrous masses and compact (nephrite) as in tremolite. Sp. gr., 3 to 3.2. Hornblende* Ca(Mg.Fe) 3 (SiO 3 ) 4 , with aluminous compound. * See Bulletin 491, U. S. Geol. Survey, p. 367. SILICA AND THE ROCK-FORMING SILICATES. 509 Sometimes written as (Al.Fe) (F.OH)SiO 3 , sometimes as an ortho- silicate isomeric with garnet or mica.* Crystals and blade-like masses varying from light green (edenite), dark green (pargasite) and black (common hornblende), but also mouse-colored and other shades. Other varieties are cummingtonite (Mg.Fe)SiO3, griinerite (FeSiO 3 ), richterite, containing 5 per cent, of MnO, etc. Nephrite or Jade is compact and extremely tough, microscopi- cally fibrous, may have composition of tremolite or actinolite. Asbestus is in fine, easily separable fibres, white, gray, or greenish. SIMILAR SPECIES. Differs from tourmaline in cleavage, crystal- line form and tendency to separate into fibres, from the fibrous zeolites in not gelatinizing with acids, from epidote in color, fusi- bility and cleavage. The differences between it and pyroxene are : Amphibole, prism angle and cleavage 124; tough, often fibrous, rarely lamellar, often blade-like or pseudo-hexagonal crystals, usually simple. Pyroxene, prism and cleavage angle 87; brittle, rarely fibrous, often lamellar, crystals, square or octagonal and often complex GLAUCOPHANE. A sodium amphibole, NaAl(SiO 3 )2(Fe.Mg)SiO 3 , blue in color and occurring in indistinct monoclinic prisms or in columnar and fibrous masses. Crystals show distinctly different colors when viewed by transmitted light through different faces. Cleavage prismatic. H., 6 to 6 5. Sp gr , 3 to 3.1. It is widely distributed as glaucophane schists in the Coast Ranges of California; Syra, Greece; Zermatt, Switzerland, etc. CROCIDOLITE. Blue Asbestus. NaFe(SiO 3 )2 FeSiO 3 . Long delicate easily separable blue fibers and massive. H., 4. Sp. gr., 3.2 to 3.3. Found in Griqualand, South Africa; Coiling, Tyrol; Cumberland, R. I., and elsewhere. GARNET. COMPOSITION. R" 3 R'" 2 (SiO 4 ) 3 . R" is Ca, Mg, Fe or Mn. R"' is Al, Fe'" or Cr, rarely Ti. GENERAL DESCRIPTION. Imbedded isometric crystals, either complete or in druses and granular, lamellar and compact masses. Usually of some brown, red or black color, but occurring of all colors except blue, and harder than quartz. Also found in alluvial material as rounded grains. *" Common hornblende consists of (Ca.Mg.Fe.Na K H Al.Fe)SiO 3 , in which Ca is about one quarter of all the bases." "So-called basaltic hornblende is richer in ferric iron than common hornblende." Iddings, "Rock Minerals," p. 336. MINERALOGY. CRYSTALLIZATION. Isometric. Usually a combination of the dodecahedron d and the tetragonal trisoctahedron, n=(a\2a\ 20) ; FIG. 511. FIG. 512. FIG. 513. {211 j, Fig. 513, or these as simple forms, Figs. 511, 512, or more rarely with the hexoctahedron, s = (a i fa : 30) ; {321), Fig. 164. Optical Characters. Isotropic but often with local weak double refraction. Index of refraction 1.739 to 1.878, hence in balsam the surface appears very rough. Physical Characters. H., 6.5 to 7.5. Sp. gr.,* 3.15 to 4.38. LUSTRE, vitreous or resinous. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle to tough. COLOR, brown, black, violet, yellow, red, white, green. CLEAVAGE, dodecahedral, imperfect. BEFORE BLOWPIPE, ETC. Fuses rather easily to light brown glass, except in case of infusible chromium and yttrium varieties. Insoluble before fusion, but after fusion will usually gelatinize with hydrochloric acid. Bead reactions vary with composition. VARIETIES. Grossularite. C^K\ 2 (^iO^) y White, pale yellow, pale-green, brown-red rose-red. Pyrope. Mg 3 Al 2 (SiO 4 ) 3 Deep-red to nearly black, often trans- parent. Almandite. Fe 3 Al 2 (SiO 4 ) 3 . Fine deep-red to black. Includes part of precious and of common garnet. Spessdrtite. Mn 3 Al 2 (SiO 4 ) 3 . Brownish-red to purplish hyacinth red. Andradite. Ca 3 Fe 2 (SiO 4 ) 3 . Yellow, green, red, brown, black. Includes many of the common garnets. Uvarovite Ca 3 Cr 2 (SiO 4 ) 3 . Emerald green, small crystals. SILICA AND THE ROCK-FORMING SILICATES. 511 Schorlomite. Ca3(Fe.Ti) 2 (SiTi) 4 Oi2. Black. Common Garnet is a mixture of grossularite, almandite and andradite. FORMATION AND OCCURRENCE OF GARNETS. Widely distributed in all classes of rocks. Some of the occur- rences are: Separations from Magma. Almandite in granite and andesite. Andradite in granite and leucite-nephelite rocks. Spessartite in granite and rhyolite. Pyrope in peridotites and their serpentines. Contacts with Limestone. Grossularite and andradite. Metamorphic Rocks. Grossularite in limestones. Common garnet in schists, eclogites, amphibolites, etc. Almandine in schists and gneisses. Andradite in gneiss and serpentine. Spessartite in gneiss and quartzite. Ouvaromte in serpentines. REMARKS. Important localities for gem garnet are mentioned on p. 567. In Lewis and Warren Counties, N. Y.; Rabun County, Ga., and Burke County, N. C., garnets are mined for use as an abrasive. VESUVIANITE. Idocrase. COMPOSITION. Ca 6 [Al(OH, F)] Al,(SiOJ 6 with replacement of Ca by Mn, and Al by Fe. GENERAL DESCRIPTION. Brown or green, square or octagonal prisms and less frequently in pyramidal forms. Also in columnar masses or granular or compact. CRYSTALLIZATION. Tetragonal. Axis c = o. 5 3 7. Usually the unit prism m with base c and unit pyramid p. Prismatic faces often vertically striated. Supplement angles // = 50 39' ; cp = 37 14'. Optical Characters. Uniaxial (rarely + ) . Indices varying considerably but always over 1.7, hence in balsam marked relief and rough surface. 7 0;, 512 MINERALOGY. o.ooi to 0.006, hence very low interference colors. Basal sections yield faint cross in convergent light. FIG. 514. FIG. 516 Monzoni, Tyrol. Physical Characters. H., 6.5. Sp. gr., 3.35 to 3.45. LUSTRE, vitreous to resinous. TRANSLUCENT to opaque. STREAK, white. TENACITY, brittle. COLOR, brown or green, rarely yellow or blue Dichroic. CLEAVAGE, indistinct, prismatic and basal. BEFORE BLOWPIPE, ETC. Fuses easily with intumescence to a green or brown glass. At high heat yields water in the closed tube. Very slightly affected by hydrochloric acid, but after igni- tion is dissolved leaving a gelatinous residue. SIMILAR SPECIES. The crystals and the columnar structure dis- tinguish it from epidote, tourmaline, or garnet. The colors are not often like those of pyroxene. FORMATION AND OCCURRENCE. Chiefly in contacts as at Mon- zoni, Tyrol; Ala, Piedmont; Morelos, Mexico; Rumford, Maine. Also in blocks of limestone enclosed in igneous rock as at Vesuvius. Rarely in gneiss and schists and in dense aggregates in serpentine. A massive variety of vesuvianite resembling jade has been called californite. THE OLIVINE GROUP. The minerals^described are : Forsterite Chrysolite Fayalite Mg 2 Si0 4 (Mg.Fe) 2 Si04 Fe 2 SiO4 Orthorhombic Orthorhombic Orthorhombic Other members of the group are tephroite, hortonolite, knebelite and roepperite. All are orthosilicates of magnesium, calcium, SILICA AND THE ROCK-FORMING SILICATES. 513 iron and manganese, and all orthorhombic with the prismatic angle about 50, and the unit brachydome about 60. FORMATION AND OCCURRENCE OF OLIVINES. Separations from Magma. Chrysolite especially in the basic rocks. Dunite is nearly pure chrysolite. It is essential in peridotite and norite, common as microscopic crystals in basalt, gabbro and dolerite and as minor accessory in andesite, trachyte, volcanic ash and ejecta. Fayalite in nephelin syenite, rhyolite and granite pegmatites. Contact or Regional Metamorphism. Fosterite in limestone. Chrysolite in limestone, amphibolite, talc schist. In Meteorites. Chrysolite. FORSTERITE. Mg 2 SiO 4 in white crystals or yellowish or greenish imbedded grains. H., 6 to 7. Sp. gr., 3.2. BEFORE BLOWPIPE, ETC. Unaltered. Dissolves in hydrochloric acid with separation of a jelly. REMARKS. Not common as pure material but a component of chrysolite. Occurs in ejected masses of Mt. Somma and in limestone at Kaiserstuhl, Baden, and Rox- bury, Mass. In serpentine at Snarum, Norway. CHRYSOLITE. Olivine, Peridot. COMPOSITION. (Mg.Fe) 2 SiO 4 , GENERAL DESCRIPTION. Transparent to translucent, yellowish- green granular masses, or disseminated glassy grains, or olive- green sand. When containing much iron, the color may be reddish-brown, or even, by alteration, opaque-brown or opaque- green. Rarely in orthorhombic crystals. CRYSTALLIZATION. Orthorhombic. Axes d : "b : c 0.4657 : i : 0.5865. Fig. 517 shows the pinacoids a, b and c, the unit forms of pyramid, prism, macro and brachy dome m, /, o and d y the macro prism /= (a : 2b : co <:); {210} and macro pyramid q = (a : 2b : c}\ {212}. Supplement angles are mm = 49 57'; pp = 40 5'; co = 51 33' 34 MINERALOGY. Optical Characters. Biaxial +. Axial plane (ooi). Acute bisectrix a. y 1.697, a i. 66 1 hence in balsam rough with marked relief. y a = 0.036, hence second or third order colors in thin sections. Extinction usually parallel to cleavage lines. FIG. 517. FIG. 518. In thin rock sections, Fig. 518, the outline, the cleavage cracks, parallel (oio) and (100) and the frequent partial alteration to serpentine assist in its recognition. Physical Characters, H., 6.5 to 7. Sp. gr., 3.27 to 3.57. LUSTRE, vitreous. TRANSPARENT to translucent. STREAK, white or yellowish. TENACITY, brittle. COLOR, yellowish-green to brownish-red. BEFORE BLOWPIPE, ETC. Loses color, whitens, but is infusible unless proportion of iron is large, when it fuses to a magnetic glob- ule. Soluble in hydrochloric acid with gelatinization of silica. SIMILAR SPECIES. Differs by gelatinization from green granular pyroxene. Is harder than apatite and less fusible than tourmaline. VARIETIES : Hyalosiderite. A highly ferruginous variety of chrysolite, con- taining sometimes as high as thirty per cent, of ferrous oxide. Titan-olivine, a deep yellow or red variety from Kaiserstuhl, Baden, in basalt with about five per cent, of TiO 2 ; from Pfunders, Tyrol; and Zermatt, Switzerland; in talcose schist. REMARKS. By alteration forms limonite and serpentine, and the excess of magnesia usually forms magnesite. Further change may alter the serpentine to magnesite, leaving quartz or opal. Found at Thetford, Vt., Webster, N. C., Water- ville, N. H., also in Virginia, Pennsylvania, New Mexico, Oregon. Prominent foreign localities are Vesuvius and Mt. Somma, the Swedish iron deposits, the Sandwich Islands, etc. USES. Transparent varieties are sometimes cut as gems (see page 566). SILICA AND THE ROCK-FORMING SILICATES. 515 FAYALITE. Fe2SiO4. In minute yellow to black crystals and massive. H., 6.5. Sp. gr., 4.32. BEFORE BLOWPIPE, ETC. Fuses easily to black magnetic globule. Gelatinizes with acids. REMARKS. Found in granite pegmatites at Mourne Mts., Ireland, and Rock- port, Mass.; in nepheline syenite in Wisconsin; in volcanic rocks at Fayal, Azores; Yellowstone Park; Lipari and elsewhere. THE SCAPOLITE GROUP. The scapolites are regarded as a series of isomorphous mixtures oimeionite (Me) = Ca 4 Al 6 Si6O25 and marialite (Ma), Na4Al 3 Si 9 O24Cl. These end members are not common, marialite occurring in a volcanic rock near Naples and meionite at Vesuvius and Lake Laach. The species described are : Wernerite Me: Ma from 3 : i to i : 2 Tetragonal Mizzonite Me : Ma from i to 2 to i : 3 Tetragonal FORMATION AND OCCURRENCE. Not known as primary minerals in igneous rocks. Sometimes secondary. Contacts. Common in limestone contacts. Metamorphic Rocks. Common in schists and gneiss containing pyroxene or epidote, also unaltered gabbros by (pneumatolytic?) alteration of lime soda feldspars. Found in limestones. WERNERITE. Scapolite. COMPOSITION. A silicate of calcium, and aluminum, of complex composition. It contains also soda and chlorine. GENERAL DESCRIPTION. Coarse, thick, tetragonal, " club- shaped," crystals, usually quite large and dull and of some gray, green, or white color. Cleavage surfaces have a characteristic fibrous appearance. Also in columnar and granular masses. CRYSTALLIZATION. Tetragonal. Class of third order pyramid, p. 47. Axis c 0.438. Usually prisms of first order m y and second order a, and unit pyramid /. Supplement angle // = 43 45'. MINERALOGY. Optical Characters. Uniaxial, . Indices vary with composition, 7 1.597 to 1.555, a 1.558 to 1.542, hence in balsam colorless grains or laths showing cleavage lines but smooth and without relief, 7 a 0.013, hence FIG. 519. FIG. 520. Usual form. Meionite of Vesuvius. usually somewhat brilliant interference colors in thin sections. Interference figure in basal sections. Distinguished from feldspars by absence of twinning, from quartz by cleavage and from both by higher interference colors. Physical Characters. H., 5 to 6. Sp. gr., 2.66 to 2.73. LUSTRE, vitreous to dull. OPAQUE to translucent STREAK, white. TENACITY, brittle. COLOR, gray, green, white, bluish, reddish. CLEAVAGE., parallel to both prisms. BEFORE BLOWPIPE, ETC. Fuses with intumescence to a white glass containing bubbles. Imperfectly soluble in hydrochloric acid. SIMILAR SPECIES. Crystals often resemble those of pyroxene; the angles of the terminal planes are conclusive. Massive ma- terial resembles feldspar, but has a characteristic fibrous appear- ance on the cleavage and is more fusible. REMARKS. Especially abundant at Bolton and other localities in Mass., and in northern New York and Canada. Other prominent localities are Pargas, Finland; Arendal, Norway; and Lake Baikal. MIZZONITE. Dipyre. With 54 to 57 p. c. SiO 2 , corresponding to Me : Ma = i : 2 to Me : Ma =1:3. In slender square prisms with essentially the characters of wernerite. Found at Vesuvius; in the Pyrenees; at Bamle, Norway; Canaan, Conn.; and Ripon, Quebec SILICA AND THE ROCK-FORMING SILICATES. 517 THE ANDALUSITE GROUP. The minerals described are : Andalusite Sillimanite Cyanite Al(AlO)SiO 4 Al(A10)SiO 4 (A10) 2 SiO 3 Orthorhombic Orthorhombic Triclinic These minerals with identical chemical composition, for which the simplest empirical formula would be A^SiOs, are generally regarded as different in chemical structure and the formulae written as above. Sillimanite is the most stable under the action of heat, the others changing to it. FORMATION AND OCCURRENCE OF ANDALUSITE GROUP. In Igneous Rocks. Sillimanite and andalusite occasionally occur in granite, but according to Iddings* the andalusite is accompanied by inclusions of sedimentary rock. Contacts. Andalusite (chiastolite) usually without sillimanite in contact zone of schists and slates with intrusions. Cyanite occasional. Metamorphic Rocks. Andalusite, sillimanite and cyanite in some gneisses and mica schists. OPTICAL DETERMINATION OF THE ANDALUSITE GROUP. All are biaxial and with high indices showing in balsam high relief and rough surface. Useful characters may tabulate as follows: Elongation . Indices Refraction. Usual Appearance in Sections. Y a y a Andalusite + 1.643 1.676 1.729 1.632 1.656 I.7I7 O.OII O.02I O.OII Short prisms, square sections. Slender needles and aggregates, Bladed crystals, six-sided sec- tions. Sillimanite Cyanite . . . Between each other the appearance, the sign of elongation, the relatively bright interference colors of sillimanite and the large- angled interference figure and oblique (30) extinction on the easy * Rock Minerals, p. 290. MINERALOGY. cleavage (100) of cyanite, generally suffice. The symmetrically arranged carbonaceous inclusions in andalusite, Fig. 217, and the needle aggregates of sillimanite Fig 521 also assist. FIG. 521. Sillimanite needle aggregate. In both andalusite and sillimanite the axial plane is (oio) and the acute bisectrix is c, the former giving a very large angle, the latter a small angle. ANDALUSITE. Chiastolite. COMPOSITION. Al(AlO)SiO 4f (A1 2 O 3 63.2, SiO 2 36.8 per cent.) GENERAL DESCRIPTION. Coarse, nearly square prisms of pearl gray or pale red color, or in very tough, columnar or granular masses. An impure soft variety (chiastolite) occurs in rounded prisms, any cross section of which shows a cross or checkered figure, due to the symmetrical deposition of the impurities, p. 80. FIG. 522. FIG. 523. SILICA AND THE ROCK-FORMING SILICATES 519 CRYSTALLIZATION. Orthorhombic. Axes a : b : c = 0.986 : i : 0.702. Usually either the unit prism m, and base r, or these with the unit brachy dome d. Supplement angles are mm = 89 12' , dd=7o 10'. Physical Characters. H., 7 to 7.5. Sp. gr., 3.16 to 3.20. LUSTRE, vitreous. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle to tough. COLOR, rose-red, flesh-red, violet, pale green, white, pearl-gray. CLEAVAGE, prismatic, imperfect at angle of 90 48' BEFORE BLOWPIPE, ETC. Infusible. In powder becomes blue with cobalt solution. Insoluble in acids. REMARKS. It occurs as stated on p. 517. It alters rather readily to cyanite or kaolin. Found in many localities in the New England States, also in Pennsylvania and California. It has been recognized in granite in Cornwall and Saxony. Large crystals are found at Lisens, Tyrol, and transparent crystals in Minas Geraes, Brazil. SILLIMANITE or FIBROLITE. COMPOSITION. Al(AlO)SiO 4 . GENERAL DESCRIPTION. Long, almost fibrous orthorhombic crystals, and fibrous or columnar masses of brown or gray color. PHYSICAL CHARACTERS. Transparent to translucent. Lustre, vitreous. Color, brown, gray, greenish. Streak, white. H., 6 to 7. Sp. gr., 3.23 to 3.24. Tough. Cleavage, parallel to brachy pinacoid. BEFORE BLOWPIPE, ETC. Infusible, becomes dark blue with cobalt solution. In- soluble in acids. REMARKS. Chiefly found in mica schist, gneiss, etc. Sometimes with andalusite. USES. In the stone age it was used for tools, weapons, etc., being second only to jade in toughness. CYANITE. Kyanite. COMPOSITION. (AlO) 2 SiO 3 , probably a basic me- tasilicate. GENERAL DESCRIPTION. Found in long blade- like triciinic crystals, rarely with terminal planes. The color is a blue, deeper along the center of the blades, and at times passes into green or white. Physical Characters. H., 5 to 7. Sp. gr., 3.56 to 3.67. LUSTRE, vitreous. TRANSLUCENT to transparent. STREAK, white. TENACITY, brittle. COLOR, blue, white, gray, green to nearly black. CLEAVAGE, parallel to the three pinacoids. 520 MINERALOGY. BEFORE BLOWPIPE, ETC Infusible, with cobalt solution be- comes blue. Insoluble in acids. STAUROLITE. COMPOSITION. Fe(AlO) 4 (AlOH)(SiO 4 ) 2 , but varying. May con- tain Mg or Mn. GENERAL DESCRIPTION. Dark brown to nearly black ortho- rhombic prisms often twinned, or in threes, crossing at 90 and I2O. Surfaces bright if unaltered. Very hard. CRYSTALLIZATION. Othorhombic. Axes d : b : c 0.473 : l : 0.683. Usual forms : unit prism m, unit dome o and pinacoids b and c. Frequently in twins crossed nearly at right angles, Fig. 566, or nearly at 60, Fig. 567. Supplement angles are : mm = 50 40' ; co = 55 14'. Optical Characters. Biaxial + , axial plane (100), acute bisectrix c, hence inter- ference figure (large angle) in basal section. Indices of refraction high, y = 1.746, a = 1.736, hence marked relief in balsam. 7 a = o.oio, hence interference colors like quartz. Extinctions parallel or symmetrical to outlines. Elonga- tion -f- . Distinctly pleochroic in shades of brown. FIG. 525. FIG. 526. FIG. 527. Physical Characters. H., 7 to 7.5. Sp. gr., 3.65 to 3.75. LUSTRE, resinous or vitreous. TRANSLUCENT to opaque. STREAK, white. TENACITY, brittle. COLOR, dark brown, blackish-brown, gray when weathered. BEFORE BLOWPIPE, ETC. Infusible, except when manganlfer- ous. Partially soluble in sulphuric acid. REMARKS. Occurs chiefly in gneiss and mica schist; and rarely as a contact mineral in clay slates. Abundant at Claremont, Grantham, and Lisbon, N. H.,. SILICA AND THE ROCK-FORMING SILICATES. 521 at Windham, Me., Chesterfield, Mass., Litchfield, Conn., and several other locali- ties in New England. Also in New York, North Carolina, Georgia, and Pennsyl- vania. Foreign localities are Mt. Campione, Switzerand; Greiner, Tyrol; Brittany; Ireland. BERYL, TOPAZ AND TOURMALINE. Beryl Be 3 Al 2 (SiO 3 )6 Hexagonal Topaz Al(Al(O.F 2 ))SiO4 Orthorhombic Tourmaline Ri8B2(SiO 5 )4 Hexagonal While not a group in any chemical or crystallographic sense, the minerals are conveniently discussed together as to formation and occurrence and optical properties. FORMATION AND OCCURRENCE. Topaz and tourmaline are due to pneumatolytic action; beryl is so in part, perhaps wholly. They occur often associated. The chief occurrences are : Igneous Rocks. Beryl, topaz and tourmaline in granites and especially in pegma- tites. Examples: Mourne Mt., Ireland; Elba, Finbo, Sweden; Black Hills, Dakota; Grafton, N. H. Topaz in Rhyolite, Nathrop, Colorado; Thomas Range, Utah. Contacts. Iron tourmaline between schists and granites. Magnesium tourmaline in limestone contacts. Veins. Topaz and tourmaline almost invariably present in tin veins and common in other high temperature deposits. Beryl (emerald) of Muzo, Colombia, in calcite veins in sediments, probably derived from nearby pegmatites. Replacements. Topaz metasomatically replaces country rock, forming topaz rocks near the tin veins of Schneckenstein, Saxony; and Mount Bischoff, Tasmania. Tourmaline similarly in tin regions, as at Cornwall, replaces mica and feldspar, forming tourmaline granites, luxullianite, etc. Metamorphic Rocks. Beryl and tourmaline occur in mica schists, and gneiss and tourmaline in clay slates. * Beyschlag, Vogt and Krusch (Truscott), p. 415. 5 22 MINERALOGY. OPTICAL CHARACTERS. y a y a Elonga- tion. Beryl Uniaxial ( ) .572 to 1.578 .567 to 1.573 O.OO6 C ) Topaz . . Biaxial (+) .617 to 1.637 .609 to 1.629 O.OO8 (+) Tourmaline: Lithium Magnesium. . . Iron Biaxial ( ) Biaxial ( ) Biaxial ( ) .637 to 1.650 .631 to 1.653 .642 to 1.685 .620 to 1.625 .612 to 1.629 .622 to 1.651 O.OI4 to O.O2I 0.019 to 0.024 0.020 tO O.O34 - (-) (-) (-) For topaz the axial plane is the easy basal cleavage .001 and the acute bisectrix is c. In thin sections in balsam relief is low in beryl, medium in topaz, marked in tourmaline. Interference colors in thin sections are evidently very low in beryl, about like quartz in topaz and while bright in tourmaline may be masked by the strong absorption (greatest at right angles toe). Pleochroism is strong in tourmaline and little noticed in the others. BERYL. Emerald, Aquamarine. COMPOSITION.* Be 3 Al 2 (SiO 3 ) 6 . GENERAL DESCRIPTION. Hexagonal prisms, from mere threads to several feet in length. Usually some shade of green. Some- times in large columnar or granular masses. Harder than quartz. FIG. 528. FIG. 529. FIG. 530. CRYSTALLIZATION. Hexagonal. Axis c = 0.499. Usually prism m with base c, sometimes with unit pyramid / or second order form e=(2a:2a:a: 2r) ; {1121}. Supplement angles cp = 29 56'; ^ = 44 56'. * Sodium, lithium and cesium may replace beryllium. SILICA AND THE ROCK-FORMING SILICATES. 523 Physical Characters. H., 7.5 to 8. Sp. gr., 2.63 to 2.8. LUSTRE, vitreous. TRANSPARENT to nearly opaque. STREAK, white. TENACITY, brittle. COLOR, emerald to pale-green, blue, yellow, white, red, colorless. CLEAVAGE, imperfect basal and prismatic. BEFORE BLOWPIPE, ETC. Fuses on thin edges, often becom. ing white and translucent. Slowly dissolved in salt of phosphorus to an opalescent bead. Insoluble in acids. VARIETIES. Emerald. Bright emerald green, from the presence of a little chromium. Aquamarine. Sky-blue to greenish-blue. Goshenite. Colorless. SIMILAR SPECIES. Harder than apatite, quartz or tourmaline. Differs in terminal planes from quartz and in form from chryso- beryl. Lacks distinct cleavage of topaz. Rarely massive. Usu- ally some shade of green. REMARKS. Beryls are especially abundant at Acworth and Graf ton, * N. H.; Royalston, Mass.; Paris and Stoneham, Me.; Alexander County, N. C.; the Black Hills of South Dakota, and Litchfield, Conn. Famous foreign localities are Muzo, Colombia; the Urals, Brazil, India and Australia. USES. Emerald and aquamarine are cut as gems (see p. 559). TOPAZ. COMPOSITION. Al 12 Si 6 O 25 F 10 or Al(Al(O.F 2 ))SiO 4 . GENERAL DESCRIPTION. Hard, colorless or yellow transparent orthorhombic crystals with easy basal cleavage. Also massive in columnar aggregates, and as rolled fragments and crystals in allu- vial deposits. CRYSTALLIZATION. Orthorhombic. ^1^:^ = 0.529:1: 0.477. Prisms often vertically striated. Crystals rarely doubly termi- nated. The predominating forms are the unit prism m y brachy prism / = (2% : ~b : oo c) ; { 1 20} (with predominance of / the section is often nearly square); base c, unit pyramid / and dome /= (oo d : b\ 2r); {021}. Supplement angles are : mm 55 43'; //= 93 1 1' ; // = 38 ; /"(top) = 87 1 8'. * Those at Acworth and Grafton are sometimes of immense size. One crystal, near the railroad station of Grafton Centre, measures 3 feet 4 inches by 4 feet 3 inches on horizontal section, and is exposed for over 5 feet. 524 FIG. 531- MINERALOGY. FIG. 532. FIG. 533. Omi, Japan. Physical Characters. H., 8. Sp. gr., 3.4 to 3.65. LUSTRE, vitreous. TRANSPARENT to nearly opaque. STREAK, white. TENACITY, brittle. COLOR, colorless, yellow, pale-blue, green, white, pink. CLEAVAGE, basal perfect. BEFORE BLOWPIPE, ETC. Infusible, but yellow varieties may become pink. With cobalt solution the powder becomes blue. Slowly dissolved in borax. If powdered and heated with previ- ously fused salt of phosphorus in open tube the glass will be etched. Insoluble in acids. REMARKS. Fine crystals are obtained in Colorado, Utah, and Maine and well- known foreign localities are Minas Geraes, Brazil; the Urals; Mexico; Japan, and the tin mines of Saxony. For topaz as a gem mineral see page 564. TOURMALINE. Schorl. COMPOSITION. R 18 B 2 (SiO 6 ) 4 . R chiefly Al, K, Mn, Ca, Mg, Li. GENERAL DESCRIPTION. Prismatic crystals, the cross sections of which frequently show very prominently a triangular prism. Color, usually some dark smoky or muddy tint of black, brown or blue, also bright green, red, and blue, or rarely colorless. Some- times the centre and outer shell are different colors, as red and green. Sometimes the color is different at two opposite ends. Occurs also columnar in bunches or radiating aggregates and in compact masses. CRYSTALLIZATION. Hexagonal. Hemimorphic class, p. 52. Axis c = 0.448. Prevailing forms : trigonal prism m, second order prism a, tri- gonal pyramids / (unit) and /= (a : co a : a : 2c\ {2021 }. Sup- plement angles are : pp = 46 52' ;/*= 77 ; mp = 62 40'. SILICA AND THE ROCK-FORMING SILICATES. 525 FIG. 534. FIG. 535. FIG. 536. Physical Characters. H., 7 to 7.5. Sp. gr., 2.98 to 3.20. LUSTRE, vitreous or resinous. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle. COLOR, black, brown, green, blue, red, colorless. CLEAVAGE, difficult, parallel to R and i - 2. BEFORE BLOWPIPE, ETC. Usually fuses, sometimes very easily. With a paste of KHSO 4 ,CaF 2 and water it yields a green flame. Insoluble in acids, but after strong ignition gelatinizes. SIMILAR SPECIES. Differs from hornblende in hardness, crystal- line form and absence of prismatic cleavage. Differs from garnet or vesuvianite in form, difficult fusion, and green flame. REMARKS. The chemical formula is not decided. Others suggested are AlsR'sSieBsOsi. AluR'uSieBsOsi. AlyR'sSieBsOai. Strictly tourmaline represents an isomorphous group with three great types. Iron Tourmaline. The common black variety, which alone is important as a rock-making mineral. Associated commonly with muscovite or biotite. Magnesium Tourmaline. Often found in limestone or dolomite, with phlogopite as the accompanying mica. Alkali Tourmaline. Contains lithium or sodium, sometimes potassium in less amount. Found in pegmatites, with muscovite and lepidolite. Often transparent red, green, blue, etc. Famous localities are Gouverneur and Pierrepont, N. Y.; Paris and Hebron, Maine; Pala, California; foreign localities are Urals, Brazil, Elba and Carinthia. For tourmaline as a gem mineral, see p. 564. TITANITE. Sphene. COMPOSITION. CaSiTiO 5 . GENERAL DESCRIPTION. Brown, green or yellow, wedge-shaped or tabular monoclinic crystals, with adamantine or resinous lustre. 526 MINERALOGY. CRYSTALLIZATION. Monoclinic. ft = 60 FlG - S37 - 17'. Axestf : ~b : c = 0.755 : I : 0.854. Crys- tals very varied. The most common forms are : pinacoids c and a, unit prism m, negative unit pyramid /, domes x = (a : oo "b : y 2 c] ; {102}, and s= (_oo a : 7 : 2r); {021}, and the pyramid / = (a : b : fa) ; {112}. Supplement angles are: mm = 66 29' ; // = 43 49' ; //= 46 f . Optical Characters. Biaxial + . Axial plane (oio). Interference figure character- ized by large differences in axial angle for different colors, and broad rainbows instead of black hyperbola. Indices very high, 7 2.009, 1.887, 7 ~ 0.1214. In sections interference colors usually very high but in some sections grays of i order. Extinction angles not characteristic. Physical Characters. H., 5 to 5.5. Sp. gr., 3.4 to 3.56. LUSTRE, adamantine or resinous. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle. COLOR, brown to black, yellow, green, rarely rose-red. CLEAVAGE, prismatic easily, pyramidal less easily. . BEFORE BLOWPIPE, ETC. Fuses, with intumescence t to a dark glass, sometimes becoming yellow before fusion. In sal of phos- phorus after reduction, the bead is violet. Partly soluble in hydrochloric acid, completely so in sulphuric acid. FORMATION AND OCCURRENCE Crystallizes from magma as ac- cessory mineral chiefly in the plutonic rocks, such as hornblende, granite, syenite, and elaeolite-syenite, but also in trachytes, etc. Secondary in metamorphic rocks, in rocks carrying rutile or ilmenite, in clefts, gneiss, or schists or in granular limestone. REMARKS. Famous localities are Tavetsch, Switzerland; Pfitsch, Tyrol; Renfrew, Ontario, and other Canadian apatite veins; Diana, New York; Brewsters, N. Y.: Bridgewater, Pa., and Magnet Cove, Ark. For titanite as a gem see p. 566. THE EPIDOTE GROUP. The minerals described are : Ca 2 Al 2 (Al.OH)(SiO4) 3 Orthorhombic Ca 2 Al 2 (A1.0H)(Si04) 3 Monoclinic Ca2(Al.Mn) 2 (Al.OH)(SiO4) 3 Monoclinic (Ca.Fe) 2 (Al.Ce.Fe) 2 (Al.OH)(SiO4) 3 Monoclinic Epidote Piedmontite AUanite SILICA AND THE ROCK-FORMING SILICATES. 527 FORMATION AND OCCURRENCE OF EPIDOTE GROUP. Separation from Magma. Allanite is an accessory mineral in granite, pegmatites, and in other igneous rocks in minor amounts. Epidote is rare but sometimes is found intergrown with allan- ite and occasionally alone, as in granite of Ilchester, Md. Secondary in Igneous Rocks. Epidote is widely distributed as an alteration of the feldspars and other minerals rich in calcium, piedmontite is secondary in the original locality, the zoisite in Piedmont granite is probably secondary and it accompanies epidote in altered gabbros (sauss- urite). Contacts. Epidote in contacts with limestone and other rocks high in calcium. Metamorphic Rocks. Zoisite is especially found in metamorphosed igneous rocks high in calcium, as amphibolite or glaucophane schist. Epidote is common in clefts and hollows of gneiss and schists (forms with quartz the rock epidosite). Ore Beds. Zoisite in sulphides, epidote rarely. OPTICAL DETERMINATION OF EPIDOTE GROUP. The ready distinctions between members of the group lie in the color, pleochroism, interference colors and extinctions. Color. Pleochroism. Interference Colors. Extinctions with Cleavages. Zoisite Epidote Piedmontite . Allanite Colorless |' Yellowish to "j j yellow-brown > (. greenish J Red Brown None Strong if colored Red to yellow Strong Very low order Often high orders Medium Parallel Varying angle Varying angle In general high relief and rough surface. All are biaxial. Epidote differs from pyroxene in the fact that the plane of the optic axis is perpendicular to the cleavage cracks. 5 28 MINERALOGY. ZOISITE. Thulite. COMPOSITION. Ca 2 Al 2 ( Al.OH) (SiO 4 ) 3 . GENERAL DESCRIPTION. Gray or green and rose red (thulite) columnar and fibrous aggregates. More rarely, deeply striated orthorhombic prisms with indistinct terminations and perfect cleavage parallel to the brachy-pinacoid. PHYSICAL CHARACTERS. Transparent to opaque. Lustre, vitreous to pearly. Color, white, gray, brown, green, pink and red. Streak, white. H., 6-6.5. Sp. g r -> 3- 2 S-3- 35- Optically -f . BEFORE BLOWPIPE, ETC. Swells up and fuses easily to a glassy mass which does not readily assume globular form. Not affected by HC1 before ignition, but after igni- tion it is decomposed with formation of jelly. REMARKS. Found at Ducktown, Tenn., Chesterfield, Mass., Uniontown, Pa., and many other localities. EPIDOTE. COMPOSITION. Ca 2 Al 2 (AlOH)(SiO 4 ) 3 with some iron replacing aluminum. GENERAL DESCRIPTION. Coarse or fine granular masses of peculiar yellowish-green (pistache green) color, sometimes fibrous- Also in monoclinic crystals and columnar groups, from yellow- green to blackish-green in color. CRYSTALLIZATION. Monoclinic. = FIG. 538. 64 37'. Axes a : b : c = 1.579 : I : 1,804. Common forms : m = unit prism, a and c P mac ids, p unit pyramid and o unit dome. Supplement angles are mm = 109 56'; ca = 64 37'; co = 63 42'. Crys- tals extended in the direction of the ortho-axis, in the zone of which are two cleavages (ooi) and (100) at 64 37' to each other. Physical Characters. H., 6 to 7. Sp. gr., 3.25 to 3.5. LUSTRE, vitreous. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle. COLOR, yellowish-green to nearly black and nearly white, also red and gray. CLEAVAGE, basal, easy. BEFORE BLOWPIPE, ETC. Fuses easily with intumescence to a dark, usually slightly magnetic, globule. At high heat yields water. Slightly soluble in hydrochloric acid, but if previously ignited, it dissolves, leaving gelatinous silica. REMARKS. Famous localities for crystallized epidote are Untersulzbachthal, Tyrol; Bourg d'Oisans, Dauphiny; Warren, N. H.; Alaska. PIEDMONTITE. Similar in angle to epidote, but with 5 to 15 p. c. Color reddish brown and reddish black. H. = 6.5. G. = 3.404. SILICA AND THE ROCK-FORMING SILICATES. 529 Known chiefly in the occurrence with braunite at St. Marcel, Piedmont, and the piedmontite schists of Japan. ALLANITE. COMPOSITION. Analogous to epidote, but a silicate of the cerium and yttrium groups with lime and iron. GENERAL DESCRIPTION. Pitch black or brownish embedded veins and masses and flat tabular or prismatic (like a nail) monoclinic crystals. PHYSICAL CHARACTERS. Opaque. Lustre, submetallic or pitch-like. Color, pitch black or brown. Streak, nearly white. H., 5.5 to 6. Sp. gr., 3.5 to 4.2. Brittle. BEFORE BLOWPIPE, ETC. Fuses very easily, becoming strongly magnetic, and at high temperature yielding water. Usually gelatinizes with hydrochloric acid, but after ignition is insoluble. REMARKS. Found in Sweden, Norway, Greenland and the Urals. In this country at Baringer Hill, Texas; Amherst Co., Virginia; South Mountain, Penn., and many other localities. IOLITE. Dichroite, Cordierite. COMPOSITION. Mg3(Al.Fe) 6 (SiO4)4(SiO 3 )4. GENERAL DESCRIPTION. Short, six- or twelve-sided orthorhombic prisms and massive, glassy, quartz-like material. Usually blue in color. The color is often deep blue in one direction and gray or yellow in a direction at right angles with the first. PHYSICAL CHARACTERS. Transparent or translucent. Lustre, vitreous. Color, light to smoky blue, gray, violet or yellow. Dichroic. Streak, white. H., 7 to 7.5. Sp. gr., 2.6 to 2.66. Brittle. Cleaves parallel to brachy-pinacoid. OPTICAL CHARACTERS. Colorless or bluish with low relief in balsam (7 1.54 to 1.56). If blue is pleochroic. In thicker material pleochroism very marked. Birefringence weak (0.009), hence colors like quartz. Extinction parallel cleavage cracks. BEFORE BLOWPIPE, ETC. Fuses with difficulty, becoming opaque. With cobalt solution becomes blue-gray. Partially soluble in acids. REMARKS. Occurs in gneis^ and sometimes in granite, rarely in volcanic rocks, and is formed by contact with igneous matter. It is easily altered to a soft lamellar or fibrous material of green or yellow color, and is rarely found entirely unaltered. THE ZEOLITE GROUP. The minerals described are: ZEOLITES PROPER.* Analcite NaAl(SiO 3 ) 2 + H 2 O Isometric Natrolite Na 2 Al(AlO)(SiO 3 ) 3 + 2H 2 O Orthorhombic Chabazite (Ca.Na 2 )Al 2 (SiO 3 )4 + 6H 2 O Hexagonal Stilbite H 4 (Na 2 Ca)Al 2 (SiO 3 )6 + 4H 2 O Monoclinic Heulandite H 4 CaAl 2 (SiO 3 ) 6 + 3H 2 O Monoclinic Harmotome BaAbSisO^sH^O Monoclinic Thomsonite (CaNa 2 ) 2 AUSi4Oi 6 5H 2 O Orthorhombic * To these may be added ptilolite, mordenite, brewsterite, epistilbite, phillipsite, gismondite, laubanite, gmelinite, levynite, faujasite, edingtonite, mesolite, erionite, wellsite, and perhaps other species. 35 53 o MINERAL OGY. ZEOLITE ANNEX.* Apophyllite Hi4K 2 Ca 8 (SiO 3 )i6 + 9H2O Tetragonal Pectolite HNaCa 2 (SiO 3 )3 Monoclinic Prehnite H 2 Ca 2 Al2(SiO4)3 Orthorhombic Datolite Ca(B.OH)SiO 4 Monoclinic FORMATION AND OCCURRENCE OF ZEOLITES. The zeolites are of especial interest from their frequent connec- tion with native copper, silver, magnetite, pyrrhotite and other ores. Their presence appears to prove formation at low tempera- tures and it is believedf they may represent a last stage of cooling and a crystallization from residual solutions. The occurrences are of the following types: Separation from Magma in Plutonic Rocks. Analcite is the chief constituent of a dike at Heron Bay, L. S., and occurs in sodalite syenite of Butte, Mont., and certain rocks of Pikes Peak, Col. Filling Blowholes and Crevices in Basic Lava. This is the principal occurrence but whether secondary entirely or largely a last stage of separation is not settled. All the species so occur, pectolite and datolite not so much in the blowholes as in veins and cavities. In Rocks and Ore Deposits Due to Contact.! Somewhat rare but including some important iron deposits, stilbite, analcite and datolite. In Ore Deposits. Not common but including! Andreasberg, Harz; Kongsberg, Norway; Arqueros, Chili; Guanajuato, Mex. ; and Republic, Washington. All but thomsonite and pectolite are stated to so occur. Metamorphic Rocks. Stilbite, chabazite and datolite possibly more frequently than the others in gneiss and schists, rarely in serpentine. * Brought here because their mode of occurrence is like that of the zeolites and because the minerals which they resemble and from which they need to be dis- tinguished are chiefly zeolites. t See Lindgren, Mineral Deposits, pp. 395, 494, 586. \ Ibid., p. 395. Lindgren, 1. c. p. 586. SILICA AND THE ROCK-FORMING SILICATES. 531 Hot Springs. Stilbite, chabazite, and apophyllite. The rare zeolite phillipsite is about the only mineral that has been found in deep-sea dredging. THE OPTICAL DETERMINATION OF ZEOLITES. The zeolites proper show little or no relief in balsam and are usually colorless, often fibrous. Prehnite, pectolite and datolite show decided relief. Optically the minerals described may be separated in two divisions by their birefringence. In thin sections judged by inter- ference colors. BIREFRINGENCE VERY Low. 7 a .001 to .007. 7 a Character. Extinction. 7 a Analcite .OOI Isotropic 1-4 87 Chabazite Harmotome Heulandite Stilbite 003 .005 .OO6 .007 Uniaxial ( ) Biaxial (+) Biaxial (+) Biaxial ( ) || length = Yf varies || length = X 1. 4 1.508 1.505 1.500 85 1-503 1.498 1.494 BIREFRINGENCE MODERATE OR HIGH. (7 0;) .012 to .045. Natrolite .012 Biaxial (+) || length = Z 1.488 1-475 Thomsonite .028 Biaxial (+) || length = X 1-525 1.497 Prehnite 033 Biaxial (+) || cleavage lines 1.649 1.616 Pectolite .038 Biaxial (+) || length = Z 1.61 Datolite 045 Biaxial ( ) |i c (nearly) = Z 1.670 1 1.626 ANALCITE. COMPOSITION. NaAl(SiO 3 ) 2 + H 2 O. GENERAL DESCRIPTION. Small white or colorless trapezohe- FIG. 539. FIG. 540. FIG. 541. Island of Cyclops. drons, Figs. 539, 540, or modified cubes, Fig. 541 ; rarely granular or compact with concentric structure. t Hence may be faster or slower (d=) than the other ray according to section examined. 532 MINERAL OGY. CRYSTALLIZATION. Isometric. The trapezohedron n = (a: 20, : 20) ; (21 1), is most frequent sometimes modified by the cube a or dodecahedron d, and in some crystals the cube predominates. Physical Characters. H,, 5 to 5.5. Sp. gr., 2.2 to 2.29. LUSTRE, vitreous. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle. COLOR, white, colorless, greenish, red. BEFORE BLOWPIPE, ETC. Fuses easily and quietly to a clear, colorless glass. Yields water in closed tube. Gelatinizes with hydrochloric acid. NATROLITE. Needle Zeolite. COMPOSITION. Na 2 Al(AlO) (SiO 3 ) 3 -f 2H 2 O. GENERAL DESCRIPTION. Colorless to white, slender, nearly square prisms, with very flat pyramids. Usually in radiating and interlacing clusters and bunches. Also fibrous granular and compact. CRYSTALLIZATION. Orthorhombic. Axes d : b \ c = 0.979 : I : 0.354* Angle of prism = 88 46'. Physical Characters. H., 5 to 5.5. Sp. gr., 2.2 to 2.25. LUSTRE, vitreous. TRANSPARENT to opaque. STREAK, white. TENACITY, brittle. COLOR, colorless, white, yellow, red. CLEAVAGE, prismatic. BEFORE BLOWPIPE, ETC. Fuses very easily to a colorless glass. In closed tube, yields water. Soluble in hydrochloric acid, with gelatinization. SIMILAR SPECIES. Differs from pectolite in square cross-sec- tion and fusion to a clear, colorless glass. REMARKS. Occurs with other zeolites and with prehnite, calcite and datolite. CHABAZITE. COMPOSITION. (Ca, Na 2 )Al 2 (SiO 3 ) 4 + 6H 2 O. GENERAL DESCRIPTION. Simple rhombohedral crystals, almost cubic, also in modified forms and twins. Faces striated parallel to edges. Color, white, pale-red and yellow. SILICA AND THE ROCK-FORMING SILICATES. 533 Physical Characters. H., 4 to 5. Sp. gr., 2.08 to 2.16. LUSTRE, vitreous. TRANSLUCENT, transparent. STREAK, white. TENACITY, brittle. COLOR, white, red, yellow. CLEAVAGE, parallel to the unit rhombohedron. CRYSTALLIZATION. Hexagonal. Scalenohedral class, p. 48. Axis c = 1 .086. Unit rhombohedron p and negative rhombo- hedra e = (a : co a : a : J^); {1012}, and /== (a : oo a : a : 2c) ; {2021} are most common. Supplement angles //=85 14'; ^=54 47'- Optically usually, sometimes -f ; interference figure confused. FIG. 542. FIG. 543. FIG. 544- FIG. 545- BEFORE BLOWPIPE, ETC. - Intumesces and fuses to a nearly white glass containing bubbles. Yields water in closed tube. Soluble in hydrochloric acid, leaving flakes and lumps of .jelly. STILBITE. Desmine. COMPOSITION. H 4 (Na 2 .Ca) Al 2 (SiO 3 ) 6 + 4H 2 O. GENERAL DESCRIPTION. Tab- ular crystals, of white, brown or red color, pearly in lustre on broad faces and frequently united by these faces in sheaf- like groups. Sometimes globular or radiated. Crystals are ortho- rhombic in appearance, but really complex monoclinic twins. Physical Characters. H., 3.5 to 4. LUSTRE, vitreous or pearly. STREAK, white. COLOR, yellow, brown, white, red. CLEAVAGE, parallel to pearly face. Cape Blomidon, N. S. Sp. gr., 2.09 to 2.2. TRANSLUCENT. TENACITY, brittle. 534 MINERALOGY. BEFORE BLOWPIPE, ETC. Swells and exfoliates in fan shapes, and fuses easily to a white, opaque glass. Yields water in closed tube. Soluble in hydrochloric acid, with a pulverulent residue. HEULANDITE. COMPOSITION. H 4 CaAl a (SiO 3 ) 6 + 3 H 2 O. GENERAL DESCRIPTION. Monoclinic crystals, with very bright, pearly, cleavage surfaces. The face parallel to the cleavage is also bright pearly, and is less symmetri- cal than the corresponding face of stilbite. PHYSICAL CHARACTERS. Transparent to translucent. Lustre, pearly and vitreous. Color, white, red, brown. H., 3.5-4. Sp. gr. 2.18-2.22. Brittle. Cleaves parallel to a pearly face. BEFORE BLOWPIPE, ETC. Exfoliates and fuses easily to a white enamel. In the closed tube yields water. Soluble in hydrochloric acid, with a residue of fine powder. HARMOTOME. H2(K2,Ba)Al2Si 6 Oi5 + 4H 2 O. Occurring in crossed monoclinic twins of usually white color. H., 4.5. Sp. gr., 2.44 to 2.50. BEFORE BLOWPIPE, ETC. Whitens, crumbles, fuses quietly at 3.5 to a white translucent glass. Decomposed by hydrochloric acid without gelatinizing. THOMSONITE. (Ca.Na2)2Al 4 (Si0 4 )4 + 5H 2 O. Usually in radiating fibers or slender prismatic crystals or amygdaloidal with fibrous structure radiating from several centers and of different colors. BEFORE BLOWPIPE, ETC. Fuses with intumescence at 2 to a white enamel. Gelatinizes with hydrochloric acid. APOPHYLLITE. COMPOSITION. H 14 K 2 Ca 8 (SiO 3 ) 16 + 9H 2 O, with replacement by fluorine. GENERAL DESCRIPTION. Colorless and white or pink, square crystals. Sometimes flat, square plates or approximate cubes ; at other times pointed and square to nearly cylindrical in section. Notably pearly on base or may show in vertical direction a peculiar fish eye internal opalescence. Found occasionally in lamellar masses. CRYSTALLIZATION. Tetragonal. Axis ^=1.252. Usually com- binations of unit pyramid /, base c, and second order prism a. Supplement angle pp = 76 ; cp = 60 32'. Prism faces vertically striated. Physical Characters. H., 4.5 to 5. Sp. gr., 2.3 to 2.4. LUSTRE, vitreous or pearly. TRANSPARENT to nearly opaque. STREAK, white. TENACITY, brittle. COLOR, colorless, white, pink or greenish. CLEAVAGE, basal SILICA AND THE ROCK-FORMING SILICATES. 535 BEFORE BLOWPIPE, ETC. Exfoliates and fuses to a white enamel. In closed tube yields water. In hydrochloric acid forms flakes and lumps of jelly. FIG. 546. FIG. 547. FIG. 548. \ FIG. 549. PECTOLITE. COMPOSITION. HNaCa 2 (SiO 3 ) 3 . GENERAL DESCRIPTION. White or gray radiating needles and fibers of all lengths up to one yard. Also in tough compact masses and rarely in monoclinic crystals. PHYSICAL CHARACTERS. Translucent to opaque. Lustre, vitreous or silky. Color, white or gray. Streak, white. H., 5. Sp. gr., 2.68 to 2.78. Brittle. BEFORE BLOWPIPE, ETC. Fuses easily to a white enamel- Yields water in closed tube. Gelatinizes with hydrochloric acid. REMARKS. Occurs with zeolites, prehnite, etc., in cavities and seams of basic eruptive rocks. PREHNITE. COMPOSITION. H 2 Ca 2 Al 2 (SiO 4 ) 3 . GENERAL DESCRIPTION. A green to grayish-white vitreous mineral. Sheaf-like groups of tabular crystals, united by the basal planes. Sometimes barrel -shaped crystals and frequently reniform or botryoidal crusts, Fig.' 270, with crystalline surface. Physical Characters. H., 6 to 6.5. Sp. gr., 2.8 to 2.9$. LUSTRE, vitreous. TRANSLUCENT. STREAK, white. TENACITY, brittle. COLOR, light to dark green or grayish-white. CLEAVAGE, basal. BEFORE BLOWPIPE, ETC. Easily fusible to a whitish glass con- taining bubbles. In closed tube yields a little water. Soluble in hydrochloric acid, and after fusion is soluble with a gelatinous residue. 536 MINERALOGY. SIMILAR SPECIES. Resembles calamine or green smithsonite somewhat, but is more easily fused, and does not gelatinize unless previously ignited. DATOLITE. COMPOSITION. Ca(B.OH)Si0 4 . GENERAL DESCRIPTION. Highly modified, glassy, monoclinic crystals often lining a cavity in a basic rock. Usually colorless, but also white or greenish. Also in compact, dull, white or pink masses, resembling unglazed porcelain. FIG. 550. FIG. 551. FIG. 552. Bergen Hill, N. J. Lake Superior. CRYSTALLIZATION. Monoclinic. /?=89 51'. Axes a\b\ c *=. 0.634 : i : 1.266. Prominent forms are the pinacoids a and c t the unit prism m, negative unit pyramid ]>, unit clino-dome d, clino-prism /= (20, : b : oo^), {120} ; and positive hemi-pyramid r= (a : b : Jr), {112}. Supplement angles are mm = 64 47' ; //=;6 29'; J5J5=5 9 5'; dd= 103 23'. Physical Characters. H., 5 to- 5. 5. Sp. gr., 2.9 to 3. LUSTRE, vitreous. TRANSLUCENT to nearly opaque. STREAK, white. TENACITY, brittle. COLOR, colorless, white, greenish. BEFORE BLOWPIPE, ETC. In forceps or on charcoal fuses easily to a colorless glass, and if mixed with a flux of acid potassium sulphate and calcium fluoride and a little water it will color flame green. In closed tube yields water at a high heat. Soluble in hydrochloric acid, with gelatinization. SIMILAR SPECIES. Differs from the zeolites in crystalline form and flame and from colemanite by gelatinization. SILICA AND THE ROCK-FORMING SILICATES. 537 THE MICA GROUP. The minerals described are: Muscovite H 2 (K.Na)Al 3 (SiO4)3 Monoclinic Biotite (H.K) 2 (Mg.Fe)2Al 2 (SiO4) 3 Monoclinic Phlogopite R 3 Mg 3 Al(SiO4)3 Monoclinic Margarite I^CaAUSiaOw Monoclinic The micas are characterized by the very perfect basal cleavage, the cleavages are usually elastic but in margarite slightly brittle. They occur in lamellar and scaly masses and sometimes in mono- clinic crystals easily mistaken for hexagonal or orthorhombic. FORMATION AND OCCURRENCE OF THE MICAS. Separation from Magma. Biotite very common, disseminated in granite, syenite, diorite, trachyte, andesite, gabbro, peridotite, the best crystals are in volcanic ejecta, large plates sometimes occur in granite. Muscovite. Alone or more frequently with biotite as an im- portant constituent of many granites and some quartz porphyries but not in recent volcanic rocks. Phlogopite. In some peridotites and leucite lavas. In Pegmatites. Muscovite, phlogopite, lepidolite. Contact Metamorphism. Biotite, muscovite common, phlogopite in dolomitic limestone. Margarite in rocks high in alumina as at Crugers Point, N. Y., with staurolite and tourmaline. Metamorphic Rocks. Biotite in gneisses and schists in large amounts. Muscovite is very common in mica schists and gneiss. The secondary variety sericite, formed by the alteration of feld- spars, quartz porphyries, and various silicates carrying aluminum, often forms schists, frequently mistaken for talcose schist. Paragonite, forming schists in Switzerland and Tyrol. Phlogopite in granular limestones and serpentine. Margarite is invariably associated with corundum and emery as if formed from them. 538 MINERALOGY. OPTICAL DETERMINATION OF THE MICAS. The tests are on basal or transverse sections. Transverse Sections. Often lath-like with parallel cleavage cracks. When the plane of the lower nicol is parallel to these cracks there is : With one nicol. Maximum absorption and pleochroism. Indices ranging 1.57 to 1.64, but overlapping so as not to be distinctive. With crossed nicols. Extinction except with margarite and un- usual biotite, which have small extinction angles. Basal Sections. Often scales or hexagonal plates, always approximately per- pendicular to the acute bisectrix X. With convergent light are all biaxial (-). Axial angle varying widely. With conical point. Percussion figure, p. 215, the most promi- nent line parallel (oio). If the line connecting the axes of the interference figure is at right angles to this the mica is said to be of the first order, Fig. 553, if parallel, of the second order Fig. 554. 553 554 First Order. Second Order. The birefringence in the two sections is notably different (see 7 a and 7 j3). Transverse Section. Basal Section. V a Extinction. Pleochroism y ft Order. 2 Et Biotite Muscovite . . Paragonite. . Phlogopite . . Margarite. . . .033 to .060 .033 to .049 Large .044 .009 o (rarely 10) 6 + Strong None None Moderate None o .005 to .008 Small o Small Second* First First Second o to 12 60 to 80 70? o to 30 76 tO 120 * Except anomite. t Exceptional biotites have 2E 60 to 70 and exceptional muscovites have small angles. SILICA AND THE ROCK-FORMING SILICATES. 539 MUSCOVITE. Potash Mica, White Mica, Isinglass. COMPOSITION. H 2 (K.Na)Al 3 (SiO 4 ) 3 ,*with some replacement by Mg or Fe. GENERAL DESCRIPTION. Disseminated six-sided scales and rough crystals, which cleave with great ease into thin, elastic, transparent leaves. Also in masses of coarse or fine scales some- times grouped in globular, stellate and plumose forms. Usually transparent and pale gray in color, and with pearly lustre on the cleavage surfaces. CRYSTALLIZATION. Monoclinic. ft = 89 54'. Prism angle = 59 48'. Crystals usually rhombic or hexagonal in section, with rough faces, and usually tapering. Sometimes very large, several feet across. Cleavage is approximately at right angles to the prism. FIG. 555 FIG. 556 Physical Characters. H., 2 to 2.5. Sp. gr., 2.76 to 3. LUSTRE, vitreous, pearly on cleavage. TRANSPARENT in laminae. STREAK, white. TENACITY, elastic. COLOR, gray, brown, green, yellow, violet, red, black. CLEAVAGE, basal, eminent. BEFORE BLOWPIPE, ETC. Fuses only on thin edges to a yellow- ish glass. Insoluble in acids. SIMILAR SPECIES. Differs from talc or gypsum in being elastic, Is usually lighter colored than biotite. VARIETIES: Fuchsite is a green muscovite containing chromium. Sericite is secondary muscovite formed in the weathering and alteration of feldspars and other silicates as nephelite, scapolite and andalusite. It occurs in fine white scaly or silky aggregates often called talc schist and also often embedded in the cloudy portion of the feldspar. Damourite, margarite, pinite, gieseckite are essentially the same material. REMARKS. The occurrence, p. 537, and uses p. 481 have been described. The most productive mica mines of the United States are in Mitchell, Yancey, Jackson and Macon Counties, S. C., and Groton, N. H. Other large deposits exist at Grafton, N. H.; Las Vegas and Cribbensville, N. M., and Deadwood and the Black Hills, S. 540 MINER A LO G Y. D., many of which are intermittently mined. Also in Nevada, California, Colorado and Pennsylvania in quantity and quality fit for use. Large quantities of mica are annually imported from India. PARAGONITE. H2NaAl2(SiC4)3 or sodium muscovite, occurring in massive scaly aggregates similar to sericite but not known as a primary mineral. It consti- tutes the mass of a rock at Mt. Campione, Switzerland, containing staurolite and cyanite and a soapstone-like mass with actinolite at Pfitschthal and Zillerthal, Tyrol. BIOTITE. Black Mica, Magnesium Mica. COMPOSITION. An orthosilicate approximating (H.K) 2 (Mg.Fe) 2 ~ Al 2 (Si0 4 ) 3 . GENERAL DESCRIPTION. The most common of the micas. Accompanies muscovite in granitic rocks and schists, but is usually dark green to black in color and in comparatively small scales. Also as black, green and red crystals at Vesuvius. It cleaves into thin, elastic leaves. CRYSTALLIZATION. Monoclinic. = 90. a : b : c = 0.577 : i : 3.274. Habit tabular, Fig. 555. mm supplement angle 60. Physical Characters. H., 2.5 to 3 Sp. gr., 2.7 to 3.1. LUSTRE, pearly, vitreous, submetallic. TRANSPARENT to opaque. STREAK, white. TENACITY, tough and elastic. COLOR, commonly black to green. CLEAVAGE, basal, eminent. BEFORE BLOWPIPE, ETC. Whitens and fuses on thin edgos. Decomposed by boiling sulphuric acid, FIG. 557 with separation of scales of silica. REMARKS. Occurs as described on p. 537. It alters much more readily than muscovite, epidote, or hydrous micas. Prominent localities are Vesuvius, Lake Baikal, Greenwood Furnace, N. Y., Pikes Peak. Col., Butte, Mont. PHLOGOPITE. Amber Mica, Bronze Mica. COMPOSITION. R 3 Mg 3 Al(SiO 4 ) 3 , where R = H,K,MgF. GENERAL DESCRIPTION. Large and small, brownish-red to nearly black crystals. Usually rough, tapering, six-sided prisms. Thin plates sometimes show a six-rayed star by transmitted light. Optically . Axial plane parallel to b, that is parallel to the principal line of the percussion figure. Axial angle small, but varying in the same specimen. Pleochroic in colored varieties. SILICA AND THE ROCK-FORMING SILICATES. 541 Physical Characters. H., 2.5 to 3. Sp. gr., 2.78 to 2.85. LUSTRE, pearly or submetallic. TRANSPARENT to translucent. STREAK, white. TENACITY, tough and elastic. COLOR, yellowish-brown, brownish-red, green, colorless. CLEAVAGE, basal eminent. BEFORE BLOWPIPE, ETC. Whitens and fuses on thin edges. In closed tube yields water. Soluble in sulphuric acid with separa- tion of scales of silica. REMARKS. Occurs in enormous crystals in Ontario and Quebec, and in various localities through New York and New Jersey. MARGARITE. COMPOSITION. H 2 CaAl 4 Si2Oi2 = Silica 30.2, alumina 51.3, lime 14.0, water 4.5 = 100. GENERAL DESCRIPTION. Gray to pink micaceous material with pearly lustre, incrusting corundum or associated with it. H., 3.5 to 4.5. Sp gr., 2.99 to 3.08. BEFORE BLOWPIPE, ETC. Whitens and fuses at 4.5. Yields water in closed tube. Slowly decomposed in hydrochloric acid. REMARKS. Found in this country with corundum at Chester, Mass. ; Unionville, Pa.; Crugers Point, N. Y.; Gainesville, Ga.; Dudley ville, Ala. Foreign occurrences are Naxos and Gumuch-Dagh, Asia Minor; Sterzing, Tyrol, etc. THE CHLORITE GROUP. The species described are: Clinochlore \H 8 (Mg,Fe) lAhSbOw Monoclinic Penninite J Prochlorite H4o(Fe,Mo)23AIi4Sii3O2o Monoclinic Species or doubtful species elsewhere described are chamosite, ihuringite and berthierine, p. 276. Many other names have been given, the chlorites being probably isomorphous mixtures of undetermined end members. Tschermak assumed an isomorphous series analogous to the plagioclase series with serpentine (Sp), H4(Mg.Fe)3Si 2 O 9 , at one end and a chlorite from Chester, Mass., Amesite (At), H4(Mg.Fe) 2 Al 2 Si 2 O9, as the other. On this theory the distinctly crystallized species clinochlore and penninite are SpAt, the species prochlorite is SpaAtn and the species corundophilite SpAU. A number of dark green chlorite-like substances occurring in fine scales and fibres and not distinguishable from one another microscopically are given names on the basis of analyses but are in general simply described as chlorites or leptochlorites. Delessite is a type. 542 MINERALOGY. FORMATION AND OCCURRENCE OF CHLORITES. In Igneous Rocks. They are never primary in igneous rock but very common as secondary minerals not only as the green unidentified pigment called viridite but as irregular scaly aggregates and pseudomorphs formed from biotite, amphibole, pyroxene, garnet, or less directly from feldspars and ferromagnesian minerals combined. In Metamorphic Rocks. Very widely distributed and very difficult usually to distinguish from one another. Sometimes dominant forming chlorite schists, or in other schists, sometimes forming veins in serpentine, often with magnetite. OPTICAL DETERMINATION OF CHLORITES. The microscopic varieties are optically indistinguishable, the coarse may in part be distinguished from each other. Characters in Common. In transverse section. Color usually green, occasionally red (Cr). Relief slight in balsam. 7 = i .57 to 1 .59. Pleochroism marked in greens and yellows. In basal section. Pleochroism not observable. Interference colors none or faint. Differential Characters. Extinction with Cleav- age. Z to c Axial A f" Interference Colors (Transverse Section) 7 a. Interference Figure. Clinochlore Penninite Prochlorite 2 to 7 o + 12 tO 90 o + o to 30 .01 like quartz .001 to .003 nearly black or anomalous indigo blue Biaxial (+) Uniaxial (db) Biaxial (+) CLINOCHLORE. COMPOSITION. H8(Mg.Fe) 5 Al 2 Si 3 Oi8. GENERAL DESCRIPTION. Green, white and rose-red crystals with cleavage like mica, the cleavage plates however being only slightly elastic. Also masses made up of coarse or fine scales and earthy. H., 2 to 2.5. Sp. gr., 2.65 to 2.78. CRYSTALLIZATION. Monoclinic. Pseudohexagonal. Crystals usually six-sided plates, or sometimes with rhombohedral habit. SILICA AND THE ROCK-FORMING SILICATES. 543 BEFORE BLOWPIPE, ETC. Whitens and fuses with difficulty to a grayish black glass. In closed tube yields water at a high heat. Soluble in sulphuric acid, only slightly so in hydrochloric acid. REMARKS. Found in green chlorite schist at Achmatowsk, Urals, and Zillerthal, Tyrol. In serpentine at Westchester, Penn. Rose red (kotschubeile) in California and Urals. White (leuchtenbergite) in Traversella, etc. PENNINITE. COMPOSITION. Like clinochlore. GENERAL DESCRIPTION. Like clinochlore but crystals thick pseudorhombodehral or tapering. BEFORE BLOWPIPE. Like clinochlore. REMARKS. The differences are chiefly optical (see p. 542) and in habit of crystals. Found in Zermatt, Switzerland; Zillerthal, Tyrol; Ala, Piedmont; Texas, Penn., as cherry red kammererite. PROCHLORITE. COMPOSITION. H4o(Fe.Mg) 23 Ali4Sii 3 O9o. GENERAL DESCRIPTION. Dark-green masses, composed of coarse to very fine scales. Also tabular and sometimes twisted six-sided crystals, which easily cleave into thin plates which are not elastic. H., i to 2. Sp. gr., 2.78 to 2.96. BEFORE BLOWPIPE, ETC. Whitens and fuses to a nearly black glass. In closed tube yields water. Soluble in sulphuric acid. REMARKS. Found massive in Montgomery Co., N. C., and in the tin veins of Cornwall. Other localities are St. Gothard on adularia; Traversella, Piedmont; Zillerthal, Tyrol; Washington, D. C. DELESSITE, a dark-green massive mineral of scaly or short fibrous appearance. H., 2.5. Sp. gr., 2.9. It yields water in the closed tube and is decomposed by HC1 with separation of silica. Found in cavities of amygdaloidal eruptive rocks. THE HYDROUS SILICATES OF MAGNESIUM. The species described are : Serpentine Talc H 2 Mg 3 (SiO 3 )4 Monoclinic Sepiolite H 4 Mg2Si 3 Oio FORMATION AND OCCURRENCE. Both are secondary minerals chiefly formed, it is believed, by the alteration (possibly by carbonated water) of magnesian silicates such as chrysolite, enstatite, hypersthene, anthophyllite and tremolite, but also by the action of magnesian waters on non magnesian silicates such as feldspar. Secondary in Igneous Rocks. Serpentine forms as a rock from peridotite, according to Wein- schenck,* other rocks such as pyroxenite "never turn to serpen- tine." _ V" * " Petrographic Methods," 315 (Weinschenck-Clark). 544 MINER ALOG Y. Serpentine forms as pseudomorphs in rocks containing chrysolite, etc., sometimes after the parent mineral, sometimes after a mineral which it has displaced. Talc may form as a rock from peridot! te.* Soapstone is probably altered eruptive rock. In Metamorphic Rocks. Serpentine in layers between gneiss, granulite, limestone, talc and chlorite schist. Talc is common in chloritic schists, serpentine, dolomite, etc. The talc beds of St. Lawrence Co., N. Y., are regarded as secondary alterations of tremolite or enstatite in schistose limestone. For instance Clarke gives t 2Mg 2 SiO 4 + 2H 2 O + C0 2 = H 4 Mg3Si 2 O9 + MgCO 3 (Chrysolite) (Serpentine) (Magnesite) CaMg 3 (Si0 3 )4 + H 2 + C0 2 = H 2 Mg 2 (SiO 5 ) 4 + CaCO 3 (Tremolite) (Talc) (Calcite) THE OPTICAL DETERMINATION. Serpentine and talc in thin sections are essentially colorless, non- pleochroic and with little relief (7 1.51 to 1.59). Both are biaxial and the lammellae of antigorite and talc may show interference figures respectively (+) and ( ). The elongation of chrysotile fibres is (+). Antigorite laths show as "lattice structure," chrysotile fibres as "net or mesh structure." The minerals differ optically chiefly in birefringence. 7 a in serpentine is .on to .013, giving colors in thin sections in middle and end of first order. In talc 7 a is .038 to .043, giving bright third order colors like muscovite. Indeed sericite (muscovite) and talc are not dis- tinguishable by optical tests. SERPENTINE. COMPOSITION. H 4 Mg 3 Si 2 O 9 , with replacement by Fe. GENERAL DESCRIPTION. Fine granular masses or microscop- ically fibrous. Also foliated and coarse or fine fibrous. Color, green, yellow or black, and usually of several tints dotted, striped and clouded. Very feeble, somewhat greasy lustre and greasy feel. Crystals unknown. * Ibid., 317, by "intense chemical processes" sometimes near acid eruptives. t Bull. U. S. Geol. Surv. 491, p. 575 and 578. SILICA AND THE ROCK-FORMING SILICATES. 545 Physical Characters. H., 2.5 to 4., Sp. gr., 2.5 to 2.65. LUSTRE, greasy, waxy or silky. TRANSLUCENT to opaque. STREAK, white. TENACITY, brittle. COLOR, green to yellow, brown, red, black, variegated. BEFORE BLOWPIPE, ETC. Fuses on edges. In closed tube, I yields water. In cobalt solution becomes pink. Soluble in hy- I drochloric acid, with a residue. VARIETIES : Serpentine Rock. Containing the three varieties below with unaltered chrysolite, pyroxene, etc., and by-products chromite, magnetite, magnesite, sometimes garnierite. Antigorite. Lamellar or flaky deep green material or lath-like crystals in seams and crevices of serpentine rock. Chrysotile. Seams and crevices in the chrysolite fill with fibres perpendicular to their sides and later the compact serpentine fills in between. Massive or Compact Serpentine. Dense aggregates making up the ground mass of most occurrences. REMARKS. Chrysotile in commercial quantities occurs in Vermont and Arizona; the great source however is the Thetford region, Quebec, Canada. Massive serpen- tine or verd antique marble is obtained at Milford, Conn. Many localities such as Newburyport, Mass.; Montville, N. J.; Texas, and West Chester, Penn., yield serpentine of ornamental quality. Well-known foreign localities are Falun, Sweden; Portsay, Aberdeen; the Lizard Cornwall, New Zealand (Bowenite). TALC. Steatite, Soapstone. COMPOSITION. H 2 M g 3 (SiO 3 ) 4 . GENERAL DESCRIPTION. A soft, soapy material, occurring foli- ated, massive, and fibrous, with somewhat varying hardness. Usu- ally white, greenish or gray in color. Crystals almost un- known. Physical Characters. H., i to 4. Sp. gr., 2.55 to 2.87. LUSTRE, pearly or wax-like. TRANSLUCENT. STREAK, white. TENACITY, sectile. COLOR, white, greenish, gray, brown, red. CLEAVAGE, into non-elastic plates. FEEL, greasy. 36 546 MINERALOGY. BEFORE BLOWPIPE, ETC. Splits and fuses on thin edges to white enamel. With cobalt solution, becomes pale pink. Insoluble in acid. VARIETIES. Foliated Talc. H = I. White or green in color. Cleavable into non-elastic plates. Soapstone or Steatite. Coarse or fine, gray to green, granular masses. H., 1.5 to 2.5. French Chalk. Soft, compact masses, which will mark cloth. Agolite. Fibrous masses of H. 3 to 4. Rensselaerite. Wax-like masses. H., 3 to 4. Pseudomorphous after pyroxene. SIMILAR SPECIES. Softer than micas or brucite or gypsum. Further differentiated by greater infusibility, greasy feel, and the flesh-color obtained with cobalt solution. REMARKS. Much of the so-called talc schist has proved to be sericite (or secon- dary muscovite) in scaly aggregates harder than talc but undistinguishable optically. An immense deposit of fibrous talc at Gouverneur and Edwards, N. Y., is mined, and the total output is ground for use in paper-making, etc. Large soapstone quarries are worked at Francestown, N. H., Chester, Saxon's River, Cambridgeport and Perkinsville, Vt., Cooptown, Md., and Webster, N. C. Massachusetts, New Jersey, Pennsylvania, Virginia and Georgia are also producing states. SEPIOLITE. Meerschaum. COMPOSITION. H 4 Mg 2 Si 3 O 10 . GENERAL DESCRIPTION. Soft compact white, earthy to clay- like masses, of very light weight. Rarely fibrous. Physical Characters. H., 2 to 2.5. Sp. gr., i to 2. LUSTRE, dull. ' OPAQUE. STREAK, white. TENACITY, brittle. COLOR, white, gray, rarely bluish-green. FEEL, smooth. BEFORE BLOWPIPE, ETC. Blackens, yields odor of burning and fuses on thin edges. In closed tube yields water. With cobalt solution becomes pink. In hydrochloric acid gelatinizes. >SIMILAR SPECIES. Resembles chalk, kaolinite, etc., but is characterized by lightness and gelatinization with acids. REMARKS. Possibly formed from Magnesite. The name "meershaum" refers to to the fact that it will float on water when dry. Most of the material used for pipes is SILICA AND THE ROCK-FORMING SILICATES. 547 obtained from Turkey. It occurs in large amount in Spain, and in smaller quantities in Greece, Morocco and Moravia. There are no productive American localities. USES. As material for costly tobacco pipes. In Spain it is a building stone. In Algeria it is used as a soap. THE HYDROUS SILICATES OF ALUMINUM. The species described are : T Kaolinite H 4 Al2Si 2 O9 Well characterized | Pyrophyllite HAl(SiO 3 ) 2 .,, R alloy site H4Al 2 Si 2 O 9 + H 2 O Poorly characterized < Allophane Al 2 SiO 6 + SH 2 O Montmorillonite H 2 Al 2 (SiC>3)4 + nH 2 O FORMATION AND OCCURRENCE. Residual and Sedimentary Clays. The great aluminum silicates, especially the feldspars, nephelite, and wernerite, by weathering, tend to form hydrous silicates of aluminum as residual products. These consist in part probably of the definite silicate kaolinite* chemically equivalent to serpen- tine but largely of colloidal residues, "gels," less definitely recog- nizable and hardly to be called true minerals. The deposits known as CLAYS contain also free quartz and varying amounts of many other species. The clays may be " residual " resulting from decay in place as with the china clays of Meissen, Saxony, and Cornwall, England, or they may have been transported by water, ice or wind and redeposited as " sedimentary " clays. The original rocks from which they formed may be of almost any class, granites syenites, pegmatites and even basic rocks; gneiss, limestones, shales. Plasticity in clays appears to be dependent on the col- loidal matter present whether silicic acid, alumina, iron oxide or organic. f KAOLINITE. Kaolin, China Clay. COMPOSITION. H 4 Al 2 Si2O9. GENERAL DESCRIPTION. Compact and clay-like or loose and mealy masses of pure white, or tinted by impurities composed of * The usual formula given is 2KAlSi 3 8 + 2H 2 O + CO 2 = H 4 Al 2 Si 2 9 + K 2 CO 3 + 4SiO 2 . Orthoclase Kaolinite t See N. B. Davis, Trans. Am. Inst. Min. Engs., Feb., 1915. 548 MINERALOGY. extremely minute scales and plates. Rarely crystallized in small rhombic or six-sided plates optically monoclinic. Physical Characters. H., 2 to 2.5. Sp. gr., 2.6 to 2.63. LUSTRE, dull or pearly. OPAQUE or translucent. STREAK, white or yellowish. TENACITY, brittle. COLOR, white, yellow, brown, red and blue. It is stated that the cloudy effects in feldspars are due to sericite and not kaolin which is rarely observed in thin sections.* Kaolinite should show no relief (index 1 .55) in balsam and low interference colors (7 a = .007). BEFORE BLOWPIPE, ETC. Infusible. Yields water in closed tube. With cobalt solution, becomes deep blue. Decomposed by sulphuric acid, but is insoluble in nitric or hydrochloric acids. REMARKS. Kaolinite in crystalline scales occurs at the National Bell Mine, Silver- ton, Col., and at Tamaqua, Penn. Kaolinite is mined at Okahumka, Lake County, Florida, at Sylva, Dilsboro and Webster, N. C., and at several places in New Castle County, Del., and Chester and Delaware Counties, Pa. Kaolin of poorer quality is obtained in Ohio and New Jersey, and many other deposits are known throughout the Atlantic States. FIG. 558. Pyrophyllite, Lincoln Co., Ga. N. Y. State Museum. FYROPHYLLITE. Pencil Stone. COMPOSITION. HAl(SiO 3 ) 2 . GENERAL DESCRIPTION. Radiated foliae or fibres and compact masses of soapy feeling and soft and smooth like talc. * Weinschenck-Clark, " Petrographic Methods," p. 318. SILICA AND THE ROCK-FORMING SILICATES. 549 white, greenish, brownish or yellow. Streak, white. H., I to 2. Sp. gr., 2.8 to 2.9. Flexible. BEFORE BLOWPIPE, ETC. Whitens and fuses on the edges, and often swells and spreads like a fan. In closed tube yields water. Partially soluble in sulphuric acid. REMARKS. Occurs in beds with schists as compact material at Deep River, N. C.. and as foliated material, often radiated, in Lincoln Co., Ga.; Ouro Preto, Brazil, Often with cyanite. USES. Extensively manufactured into slate pencils, foot warmers and other uses of "soapstone." HALLO YSITE. Probably H 4 Al 2 Si 2 O9 + H 2 O (Le Chatelier). Amorphous clay- like white or yellowish material. H., i to 2. Sp. gr , 2.0 to 2.2. BEFORE BLOWPIPE, ETC. As for kaolinite but yielding more water in closed tube. REMARKS. Includes indianaite, a compact china clay, of Lawrence Co., Indiana, and is considered to be the principal constituent of many clay beds in Alabama, Georgia; Steinbruck, Styria; Elgin, Scotland, and elsewhere. ALLOPHANE. Al 2 SiO 5 + 5H 2 O. A translucent, sometimes wax-like material often found in copper and iron mines, filling crevices and fissures or stalactitic and colored by intermixtures of chrysocolla, malachite or limonite; also in cavities in marls and limestones. H., 3. Sp. gr., 1.85 to 1.89. BEFORE BLOWPIPE, ETC. Crumbles but is infusible. Becomes blue color with cobalt solution. Gelatinizes with hydrochloric acid. REMARKS. Occurs at Richmond, Mass., with gibbsite. In marl at Saalfeld, Thuringia. With copper minerals in Polk Co., Tenn. MO NTMORILLONITE. Probably H 2 Al 2 Si4Oi 2 + n aq. Very soft, often soap-like, white, pinkish or variously colored material, which softens in water and does not adhere to the tongue H., i ?. Sp. gr., 2 to 2.2. BEFORE BLOWPIPE, ETC. Infusible, loses water. REMARKS. Found at Branchville, Conn, (pink) ; Montmorillon, France (rose red) and many clay-like materials of similar properties are grouped under it as a type,, such as stolpenite, saponite, erinite, severite, confolensite, etc. CHAPTER XXI. MINERALS USED AS PRECIOUS AND ORNAMENTAL STONES. No very systematic order is followed; the species are described in two groups: A. The Transparent Stones. B. The Translucent to Opaque Stones. Where the species has been described already the description is not duplicated but the properties* which count most in the dur- ability and beauty of the stone are assembled and detailed, and with these characters something is given as to occurrence. Very little is stated as to the history, methods of cutting, famous stones, superstitions, etc., the descriptions in fact being of the native uncut mineral, not of the cut stone. A. THE TRANSPARENT STONES. DIAMOND. COMPOSITION. C. GENERAL DESCRIPTION. Transparent, isometric crystals with a peculiar adamantine lustre like oiled glass. Usually colorless or slightly tinted. Also translucent, rough, rounded aggregates and opaque or compact masses of gray to black color. Especially characterized by a hardness exceeding that of any other known substance. CRYSTALLIZATION. Isometric. Crystals practically always complete, showing no signs that they were ever attached to any support. Usually in octahedrons, Fig. 560, with smooth faces or with triangular markings, often with edges replaced by smaller faces,* Fig. 559, which frequently results in a rounded many-faced * For instance the DURABILITY is dependent on hardness, density, toughness and absence of too easy cleavages; the beauty upon agreeable color, clearness or trans- parency, brilliancy or lustre (itself dependent both on density and index of refraction) and fire (itself dependent on dispersion). * Hextetrahedral modifying faces are most common, while rounded hexoctahedra and, more rarely, cubes and other forms occur. Frequently twinned parallel to the octahedron. 550 MINERALS USED AS PRECIOUS STONES. 551 crystal. Very perfect cleavage parallel to the octahedron, that is, in four directions at angles of 70 31' and 109 29' to each other. Readily developed by a sharp blow on a knife held in proper posi- tion, this being usually preceded by a scratch. FIG. 559. FIG. 560. FIG. 561. Physical Characters. HARDNESS. It is called 10, but the stones from Borneo and N. S. Wales are much harder than those from other localities and the Cape stones are softer. The hardness may vary in parts of the same stone. SPECIFIC GRAVITY. 3.145 to 3.518 (Crookes.) Bort and Carbonado range 3.47 to 3.50. LUSTRE. When polished peculiarly brilliant, typical adaman- tine. When unpolished like oiled glass. COLOR. Colorless or faintly bluish or less valued " off-colors" tinged with yellow, brown and green. More rarely decided colors red, pink, sapphire blue (a little greenish), canary yellow, decided green. Optical Characters. REFRACTION. Single with index very high and constant. 2.4175. Often local double refraction, due to strain (sometimes from in- cluded liquid carbonic acid). TOTAL REFLECTION. Critical angle very small 24 26', this per- mitting the stone to be cut so as to send back all entering light. COLOR DISPERSION. Very high, .044, exceeded only by titanite, .051, and demantoid, .057. Approached by zircon, .038. ABSORPTION SPECTRUM. Not constant, sometimes a line in the violet. PERMEABILITY TO X-RAYS. Highly transparent. LUMINESCENCE. Excited in some diamonds by ultra-violet light or by radium or X-rays as a clear, luminous blue, a few 552 MINERALOGY. become luminous on mere rubbing and others by exposure to sunlight. BEFORE BLOWPIPE, ETC. In fine powder is slowly burned in presence of air over a bunsen burner or alcohol lamp. In large mass and in absence of air is very little affected even by white heat. Insoluble in acids. VARIETIES : Ordinary. In rounded crystals with distinct cleavage. Bort. Technically any diamond or fragment of diamond not deemed worthy to be cut. Crystallographically, an individual composed of many smaller crystals, sometimes enclosing a simple crystal, oftener not, and having no constant directions of cleavage. Sometimes the little crystals are radially placed and their edges form a rough surfaced sphere. Carbonado. Black massive or granular material from Brazil. Formation and Occurrence. The only chance of studying the genesis of the diamond in place is in South Africa. In this region the diamond-bearing ground consists of comparatively limited areas circular or oval in form, the upper portion pale yellow and crumbly, but lower down firmer and bluish-green. The diamonds are distributed through the mass sometimes 4 to 6 to the cubic yard. The minerals with the diamonds are chiefly broken fragments of serpentine, diallage, garnet, magnetite, etc., and the mass extends downward nearly vertically but narrowing somewhat like large " pipes" or cylinders or funnels for an unknown depth. The older theory was that these funnel-shaped pipes were volcanic like Vesuvius and that the diamonds were formed with considerable heat. There are various objections. Volcanoes would have formed elevations and there would have been over- flows. No indications of this exist and even if present conditions resulted from erosion there would have been as a result of the erosion diamonds and rocks from the pipes in the ravines and water courses in the vicinity, but there never are, the nearest being 20 miles distant. Moreover, the diamonds have retained their form and brilliancy, whereas Herr W. Ludzi, of Leipzig, fused in a crucible at about 2,000 centigrade the "blue ground" containing MINERALS USED AS PRECIOUS STONES. 553 diamonds and half an hour of this resulted in a marked corrosion of the crystals. A theory which seems to have greater probability is that the blue ground was forced up from below under great pressure by steam and other vapors. The diamonds show signs of this great pressure, often containing liquid drops of carbonic acid, and the blue ground being heterogeneous mixed-up or broken material, apparently originally a rock of such material as pyroxene and garnet, some of which is often included boulder-like in the mass. The sides of the contact wall also show smoothed surfaces (slickensides) and scratches, suggesting the up-and-down motion several times of this material. Such a theory would also explain the absence of the rock in the ravine nearby, because the pasty mass of mud by the escape of the vapors would settle down rather than protrude and would be protected from erosion. The Cutting of Diamonds. Until the fifteenth century diamonds were not cut but worn in the natural state or covered with a green varnish. Some little polishing of the natural faces had been done by native lapidaries and to disguise the presence of little flaws or defects. In 1475 Louis de Berquem discovered that, by rubbing one stone with another, diamonds could be cut and is said to have cut three large stones for Charles the Bold of Burgundy. Wheels charged with diamond dust followed but as late as 1562 the only forms were the octahedron and the table, in the latter of which one solid angle of the octahedron had been cut off until the resulting new face was one half the width of the stone. These were followed by the rose cut with a flat base and 24 triangular facets, and the brilliant,* Fig. 561, a modification of the table with more faces, usually 58, 33 above the girdle, 25 below. Its angles are chosen so that the incident light entering falls on the lower faces at angles greater than the critical angle, 24 26', and is totally reflected, preferably through the inclined faces, thus producing extreme brilliancy and dispersion of the light or color. Artificial or Synthetic Diamonds. Diamonds were found by Friedel in the Canon Diablo meteorite. Moissan thereupon experimented by saturating iron with carbon, * Said to have been discovered by Vincenzio Peruzzi in 1 790. 554 MINERALOGY. then fusing the mass and pouring quickly into a vessel containing water and mercury. Minute crystals barely visible to the naked eye were obtained. Majorana heated carbon in the electric arc and while hot blew it by an explosion of gunpowder into a cavity in a steel block. Small diamonds resulted. Pulverized carbon heated on iron, wire in the electric arc in an atmosphere of hydrogen yielded diamond crystals. Silicates like the blue ground fused in a crucible with carbon yielded small diamonds. REMARKS. Diamonds have been known in India for over 3,000 years but do not appear to have reached Europe until about the time of Caesar Augustus. They were not valued for their beauty but for supposed supernatural virtues and worn uncut and unpolished and indeed until the fifteenth century had at most their natural faces polished. India supplied practically all the diamonds until 1725, when the Brazilian deposits were discovered and Brazil in turn supplied the world until 1867, when the River diggings of South Africa and a little later, 1870, the "dry diggings" or Kimberley deposits were discovered. These still are the great source, although diamonds are or have been obtained from New South Wales, Australia, Rhodesia and German South Africa. A few diamonds have been found in British Guiana, in the Shantung Province, China, and in the gold washings in the Ural Mountains, and in four districts in the United States, first along the western base of the Sierra Nevadas; second, along the line of the Terminal Moraine in Wisconsin, Michigan, Indiana, and Ohio, presumably coming from somewhere in Canada; third, in Kentucky and Ten- nessee; fourth, along the eastern base of the Appalachians from Virginia to Alabama. CORUNDUM. Sapphire, Ruby. Described on p. 412. COMPOSITION. AUOs. Transparent varieties of corundum are known as rubies* if red", sapphiresf if blue and fancy J sapphires if other colors, the colorless variety is called white sapphire. The preferred colors are pigeon blood or purplish red and velvety corn flower blue. Optical Characters. UNIAXIAL ( ) 7- 1.766 to 1.744, - 1-757 to 1.765, y-a very constant .0083 to .009. Color dispersion weak .018. Pleochroism * Ruby is from Latin rubere = red. f The sapphire of the ancients was lapis lazuli, but in course of time this became a general designation of blue stone and later of the blue corundum. Plato's adamant was supposed to have been sapphire. Hyacinth was also used for stone apparently sapphire. % Fancy sapphires are sometimes known as " oriental " topaz, amethyst, etc. MINERALS USED AS PRECIOUS STONES. 555 usually distinct, sometimes strong. Twin colors varying with color and locality. LUMINESCENCE. Very varied. Burmese rubies brilliant red with ultra-violet light, Siam rubies no luminescence. Synthetic rubies more brilliant even than Burmese. Ceylon rubies phos- phorescent (yellow) on heating. EFFECTS OF HEAT. Ruby loses color but cools through white and green to the original tint. Sapphire strongly heated is decolor- ized in part and if pale violet or yellow may become white, if deep violet may become rose colored. FIG. 562. Corundum Crystals, Ceylon. U. S. National Museum. BEAD TESTS. Synthetic and natural rubies color salt of phos- phorus beads green in R. F. OCCURRENCE. Very largely from gravels or alluvial deposits sometimes in place as in Yogo Gulch, Montana, and Siam. SAPPHIRES. Ceylon. Chiefly from the gravels in Sahara Gamuwa province with spinel, zircon, beryl, topaz, etc. These gravels extend far below water level, and in one case 120 ft. and underlie swamps and rice fields. The crystals are pyramidal (while the corundum in place is prismatic). Siam. Probably half the sapphires, including the finest corn flower blue stones are from Siam. India. In Kashmir in the Himalayas, 14,000 ft. above sea level, fair quality stones occur in a hard rock (gneiss) and were found in considerable quantities at the foot of a precipice where a landslide had occurred. 556 MINERALOGY. FIG. 563. Australia. Many colors, but none red or fine blue, are found near Anakie, Queensland, in a gravel of decomposed basalt. Montana. At Yogo Gulch in place in a dike which cuts through limestone and in gravels on the Upper Missouri River. The colors are given as deep and light aquamarine, greens, yellows, pinks, amethystine. The lustre is peculiar, almost metallic. RUBIES. Burmah. The most valued rubies come from Mogok north of Mandaly in Upper Burmah, 4,000 ft. above sea. They occur in a sort of clay called " byon," considered to be the result of the decay of a crystalline limestone containing also spinels, sapphires, and tourmalines. Also found in a gravel bed underlying alluvial deposits in Mogok Valley. Siam. Darker colored rubies are found in Siam associated with red spinel and sapphires at the Navony Mine near Bangkok. Some also are found with the sapphires at the Pailinh Sapphire Mine in eastern Siam. Ceylon. Not found in place and only comparatively rarely in the gravels. They are never the true Burmese red, though often more brilliant. Synthetic Rubies and Sapphires. Corundum is synthetically made by the method of Verneuil in pear-shaped drops or "boules," Fig. 564, which are true anhedral crystals, and are character for character, except shape, identical with the natural ruby or sapph- ire.* They bear the same rela- tion to the natural stone that the ice of the pond does to the manufactured ice and while easily distinguished before cutting, are distinguished afterwards only with difficulty by inclusions, mode of distribution of color, etc. The apparatus of Veneuil, Fig. 563, is an inverted oxyhydrogen ^^JKurion ~ blowpipe, in which the raw ma- ll terial, a carefully prepared pow- der, is sifted regularly through a sieve into an enlargement of the oxygen tube, the speed being regulated by a tapping hammer, and is carried with the oxygen * A. J. Moses, Amer. Jour. Sci., XXX, 271, 1910. FIG. 564. MINERALS USED AS PRECIOUS STONES. 557 to the fusion chamber and falls as a melted drop on the sup- port, where it gradually builds up the boule. STONES RESEMBLING THE SAPPHIRE. IOLITE. Water sapphire. Described on p. 529. The stones that are usually cut are light to dark smoky blue. It also occurs violet. Pleochroism very strong. The principal colors smoky blue and yellowish white being visible to the unaided eye. It is therefore cut with the table face perpen- dicular to the direction of deepest blue. Occurrence Cutting Material. Chiefly found in water-worn masses in the river gravels of Ceylon. One piece in the British Museum weighs 177 grams. The Had- dam, Conn., material is sometimes cut. Other localities are Bodenmais, Bavaria, Finland, Sweden. BENITOITE. BaTi(SiOs)3. This stone was discovered in 1906 and at first cut and sold as sapphire. Few stones exceed 2 carats, one was 7 carats. The characters of importance are as follows: H., 6.5. Sp. gr., 3.64 to 3.72. Color. Varies from deep blue with a violet tint to pure blue or a lighter shade, sometimes perfectly colorless. Refraction and Indices of Refraction. Doubly refracting, uniaxial, positive. Ordinary index is 1.757 and the extraordinary 1.804. Birefringence strong, .047 (Eppler says .03). Dispersion strong, producing considerable fire. Pleochroism strong, ordinary ray white extraordinary greenish blue to reddish blue. As light transmitted perpendicularly to the base is practically colorless, the gem should be cut with a table parallel to the principal axis which is contrary to the rule for sapphire. Effects of Heat. Color unchanged until it fuses quietly to a transparent glass at about 3. Salt of phosphorus bead violet in reducing flame. Effects of Acid. Practically insoluble in hydrochloric acid, readily attacked by hydrofluoric acid and dissolves in fused sodium carbonate. Occurrence. Occurs in veins and crusts of natrolite in a hornblende schist of the Coast Range of California. It occurs with the rare mineral neptunite, in Diablo Range, near the headwaters of San Benito River, California. CYANITE. Composition. Al 2 SiO 5 . Described on p. 519. Azure to cornflower blue varieties only are cut. Green and white occur. There are many distinctions from sapphire such as hardness, 5 to 7, numerous striations and cracks, lower indices, 7 1.7280: 1.712, lower specific gravity, 3.56 to 3-67. Occurrence of Cutting Material. The finest sky blue crystals come from Mt. Campione, St. Gothard, Switzerland; Zillerthal and Pfitschthal, Tyrol; India (where it is sorted with sapphire and sold at good prices), near the peak of Yellow Mt., Bakersville, N. C., and Diamantina, Brazil. HAUYNITE. Composition. CaSO 4 2(Na 2 Ca)Al 2 (SiO 4 )2. Described on p. 500. Occurs occasionally as transparent sky-blue grains, and is cut. Its isotropic character and very low index, 1.49, distinguish it. Occurrences Cutting Material. Near Albano, Italy, in Auvergne, France, and at Niedermendig on the Rhine. 558 MINERALOGY. SPINEL.* Balas Ruby. COMPOSITION. Mg(AlO 2 ) 2 , (MgO 28.2, A1 2 O 3 71.8 per cent.) Iron, manganese and chromium are sometimes present. FIG. 569. FIG. 570. FIG. 571. GENERAL DESCRIPTION. Usually in octahedral, simple or twinned crystals, varying in color according to composition, and even in the gravels which round the still harder ruby retaining much of their sharpness. Spinel is not well known as a gem partly because the red varieties were until comparatively recently not distinguished by jewelers from the ruby. Some great historic rubies have proved to be spinels. CRYSTALLIZATION. Isometric, the octahedron p or this modi- fied by the dodecahedron d or the trapezohedron o = (a : $a : 30) ; VARIETIES : The transparent varieties most valued are : Balas Ruby. Rose red or pink. Ruby Spinel. Clear red. These varieties are said always to show a pale yellow reflection from the interior of the stone. Less valued are: Rubicelle, yellow to orange; Sapphirine, steely blue; Almandine, purple to violet. The opaque varieties include: Ceylonite (Iron Magnesia Spinel). Dark-green, brown, black, usually opaque. Picotite (Chrome Spinel). Yellowish to greenish-brown, translucent. Physical Characters. H., 8 to 8.5. Sp. gr., 3.5 to 3.7. (Cey- lonite 4.1.) LUSTRE, vitreous. COLOR, as given and intermediate. STREAK, white. CLEAVAGE, octahedral difficult. * From a word for a "little spark," referring to the fiery red of most prized kind. MINERALS USED AS PRECIOUS STONES. 559 Optical Characters. Singly refracting. Indices of red and blue stones 1.716 to 1.720. Deep violet ones 1.730. Color dispersion weak, .020. Very slightly penetrated by X-rays. REMARKS. The common opaque spinels occur occasionally in igneous rocks, picotite with chromite, ceylonite with magnetite, but are more common in metamor- phosed limestone, both contact and enclosed in schists. The gem varieties are also most frequent in limestones and dolomites. Corundum is a common associate. The principal localities for gem spinel are the ruby-bearing limestones of Burma and Siam, which yield red varieties, and the gem gravels of Ceylon, which yield blue and violet varieties. Other localities are Expailly, France; Badakschan, Tartary; and in this country gem specimens have been obtained at Hamburg, N. J.; San Luis Obispo, Cal., and Orange County, N. Y. The crystals also occur in many localities in North Carolina, Massachusetts and near the New York and New Jersey line. BERYL. Emerald, Aquamarine. Described on p. 552. COMPOSITION. Be 3 Al 2 (SiO 3 )6. This mineral furnishes the gems, emerald, aquamarine, golden beryl, morganite and heliodore. Optical characters needing further detail are : REFRACTION AND INDICES OF REFRACTION. Doubly refracting, uniaxial and optically negative. y a y a Range i 572 to 1.598 1.567 to 1.59 .005 to .008 Colombian emerald 1.584 1.578 .006 Siberian aquamarine 1.582 1.576 .OO6 Morganite 1.598 ? 1-59 .008 BIREFRINGENCE weak .005. DISPERSION small. PLEOCHROISM is usually faint but the South American emerald gives yellowish-green and bluish-green. EMERALD. Grass green, inclining rather to blue than yellow. It has no fire, is only moderately hard, usually flawed ("an emerald without a flaw"), and not as brilliant as some other green stones like hiddenite and demantoid, yet from ancient times its color has given it high rank. The emerald of ancient times came from Upper Egypt. The locality was lost and refound in 1820 in the mountain range to the west of the Red Sea, where both emerald and beryl occur in micaceous and talc schists. The emeralds are inferior to those from Colombia. The three great districts, discovered in Colombia in 1558 by the Spaniards soon after their conquest of Peru, were worked irregularly. That of Muzo, 75 miles north- 560 MINERALOGY. west of Bogota, is still working and is the chief source of the emeralds of the best grade. They are said to be sent chiefly to India to be cut. The localities of the other two were lost and one only was rediscovered in 1896, the other is still "lost." Fine emeralds, but inferior to the Muzo stones, come from the Ural Mts. near Ekakrinenberg and the Salzburg Alps in Austria have yielded emeralds from the time of the Romans down. Other localities are: Arendal, Norway; Topsham, Maine; Alexander Co., N. C. AQUAMARINE. "Green like the sea," that is deep, blue-green and grading from this towards colorless. It is much used for brooches, and pendants, occurs in large quantities and fine grade both at Minas Novas and other parts of Brazil and at Mursinka, Urals, and of fine grade at Adun Tschilon, Siberia. Poorer grades are abundant. GOLDEN BERYL of light and deep golden yellow is found in Macon Co., N. C., Delaware Co., Penn., etc. MORGANITE, from Maharita, Madagascar, is of pure rose pink color. HELIODORE, from German S. W. Africa, golden yellow by daylight, green by artificial light is said to be beryl. CHRYSOBERYL. Alexandrite, Cymophane. COMPOSITION. BeAl 2 O 4 , (BeO 19.8, A1 2 O 3 80.2 per cent.), with oxides of chromium and iron giving the color. GENERAL DESCRIPTION. Pale green or yellowish tabular crys- tals; thicker deep emerald-green crystals, which by transmitted light are a purplish red ; and rolled pebbles sometimes with an internal opalescence. CRYSTALLIZATION. Orthorhombic a : b : c = 0.470 : i : 0.580. Often flat contact twins with feather-like striations, Fig. 573, FIG. 572. FIG. 573- Urals. Haddam, Conn. Alexandrite occurs in simple, Fig. 572, or twinned crystals snowing unit pyramid p and prism m with brachy-pyramid r = (2a : b : 2c), ji2ij; and prism n = (2 a : b : oo c ), {120}. Supplement angles rr = 72 17'. are mm = 50 21'; nn = 86 28'; pp = 40 MINERALS USED AS PRECIOUS STONES. 561 VARIETIES. Alexandrite, the deep green variety, which is so called because it was found in the emerald mines of the Urals on the birthday of the Emperor Alexander II. By daylight it is bluish to olive green in color and by lamp- or gas-light raspberry red, the cause of the change being the strong absorption of yellow and blue rays, the residual product varying with the source of light. For instance, with the tungsten light it is neither red nor green but intermediate. Fine stones are scarce, the best coming from near Ekaterinberg, poorer from Tokowaja. Larger stones of good quality come from Ceylon and others from the Weld River, Tasmania. Cymophane or Cats Eye. Yellowish-green and with minute parallel cavities. If cut cabochon with the rounded surface parallel to these a sharp line of opalescent light appears crossing the stone at right angles to the cavities, which seems to float in the surface as the stone is moved. Principal locality is Ceylon, others come from Brazil. Chrysoberyl or Oriental Chrysolite. Chrysoberyl or Oriental Chrysolite. Color, pale yellowish green. From Minas Novas, Brazil, and some from Rhodesia and Haddam, Conn. It is often confused with the yellow spodumene from Brazil. Physical Characters. H., 8.5. Sp. gr., Alexandrite 3.644. Others 3.68 to 3.78. LUSTRE, vitreous to greasy but less greasy than chrysolite. COLORS. As described under varieties. Optical Characters. Biaxial (+). Axial plane (oio). Acute bisectrix c . 7 = 1.750 to 1.757, <* = I-74 2 to i.749 7 - a = .009. PLEOCHROISM. Very strong in alexandrite in columbine red, orange and emerald green. The cymophane and oriental chryso- lite show less strong pleochroism. ACTION X-RAYS. Rather easily penetrated. BEFORE BLOWPIPE, ETC. Infusible. In powder, is turned blue by cobalt solution. Insoluble in acids. REMARKS. Occurrences as described under varieties. No fine gems have been found in the United States, although the mineral occurs sparingly in Stowe, Peru and Canton, Me., New York City, and Greenfield, N. Y., Haddam, Conn. 37 562 MINERAL OGY. OTHER BERYLLIUM GEMS. Beryllium which has no other economic value is the chief element not only in beryl and chrysoberyl but in the following species cut as precious stones. EUCLASE. Be(AlOH)SiO4. Sea green or pale blue or colorless crystals with vitreous lustre. It takes a brilliant polish and when cut greatly resembles the aqua- marine. It is very seldom cut, both because the crystals are valued by collectors and because of the very easy cleavage to which it owes its name. Found in Brazil at Villa Rica. Minas Geraes in the topaz locality, but never in the same druse. Also in diamond sand at Bahia. In Urals on Sanarka River in the gold washing and associated with topaz. Other localities are Peru and Tasmania. PHENACITE. COMPOSITION. Be 2 SiO 4 (BeO 45.55, SiO 2 54.45 per cent.). GENERAL DESCRIPTION. Colorless, transparent, rhombohedral crystals, usually small, frequently lens-shaped. Sometimes yellowish and sometimes in prismatic forms. Harder than quartz. FIG. 574. FIG. 575. Mt. Antero, Col. Florissant, Col. CRYSTALLIZATION. Hexagonal. Class of third order rhombohedron, p. 54. Axis c== 0.661. Supplement angles xx 75 $7' ; rr = 63 24'. Optically -f- . PHYSICAL CHARACTERS. Transparent to nearly opaque. Lustre, vitreous. Color, colorless, yellow, brown. Streak, white. H. 7.5 to 8. Sp. gr. 2.97 to 3. Brittle. Cleavage, prismatic. BEFORE BLOWPIPE, ETC. Infusible and unaffected by acids. Made dull blue by cobalt solution. The colorless water clear varieties when cut possess considerable brilliancy, about that of a white sapphire. OCCURRENCE. In granite pegmatites, quartz porphyry and mica schist. Cut- able stones are found in the Urals at the emerald mines at Stretinsk and at Miask. In Colorado at Pikes Peak and Topaz Butte and Mount Antero. In Brazil at Minas Geraes. BERYLLONITE. NaBePO 4 . A clear colorless mineral occasionally cut. The transparency and brilliancy of the stone resembles that of topaz, but lack of "fire" and softness are against it. H., 5.5. OCCURRENCE. Found loose among the disintegrated material of a granite vein at Stoneham, Maine. GADOLINITE. Be2FeY2Si2Oio, is occasionally cut as an opaque black stone. MINERALS USED AS PRECIOUS STONES. 563 ZIRCON. Hyacinth. Matura Diamonds. Described on p. 314. COMPOSITION. ZrSiCX Transparent zircons possess the qualities which should make them rank high, namely, brilliancy, strong color dispersion, durability and agreeable colors including the fine golden yellow, aurora red to deep red and leaf green. COLORS AND COLOR NAMES. Zircon, brown, violet, green (leaf- green), blue. Hyacinth* aurora red, sometimes deep red. Jacinth, yellow often golden. Jargon, grayish- white or white, especially if not hard. Matura Diamonds, colorless (usually made so by heating). Notable Characters. The characters following would seem to indicate at least two structurally different substances, one isotropic or nearly so, the other tetragonal. CRYSTALLIZATION. Sharp, tetragonal crystals. The Ceylon pebbles, however, show no crystal faces. REFRACTION AND INDICES OF REFRACTION. Doubly refracting, uniaxial and positive, but with wide differences, some with both indices close together and ranging from 1.79 to 1.84. Others with ordinary ranging from 1 .92 to 1 .93 and extraordinary 1 .96 to 1 .99. BIREFRINGENCE. In some almost zero, in others very strong, as much as .06. Other characters are : LUSTRE. Adamantine approaching that of the diamond. It is increased by heating. COLOR DISPERSION. Very high, .038, diamond being only .044. Hence considerable fire, though inferior to that of the diamond. ABSORPTION SPECTRUM. Often show lines characteristic of uranium, corresponding to wave-lengths 651, 588 and 512. Many zircons do not show the bands. PLEOCHROISM. Exceedingly faint even in most highly colored stones. ACTION X-RAYS. Practically opaque. * Hyacinth, from an old Indian word originally used for sapphire, then especially for yellow sapphire and generally for other yellow stones, then more definitely for yellow zircon and garnet. Now queerly twisted to the more red stones while the yellow are called by another spelling of the same word, Jacinth. MINERALOGY. LUMINESCENCE. Sometimes luminescent during grinding or if heated on Bunsen burner. SPECIAL TEST. Under the microscope many zircons show a "feathery" appearance called "ratine" and described as resem- bling a liqueur poured in water. BEFORE BLOWPIPE, ETC. Infusible but at about 500 C., the color is weakened and may be destroyed. The green may become fine yellow and the pale brown become colorless. Some colorless stones from Tasmania become brown on heating. Insoluble in acids. OCCURRENCE. The finest stones come from Ceylon. Fine red stones are brought from central Queensland and from New South Wales. Small hyacinths and deep red stones are found at Expailly, France. Rounded pebbles in Tasmania. Other localities in Germany and Bohemia. TOPAZ. Precious Topaz. Described on p. 523. COMPOSITION. Al^SieC^Fio. The best known topaz is yellow or sherry to brownish yellow. Decided blues are called Brazil sapphires. Red or pink topaz (usually the result of heating the Brazil yellow stone) are known as Brazil rubies. Much of the so-called topaz is yellow quartz (citrine or burnt amethyst). This though unsatisfactory can claim old usage, for it is generally admitted that topaz first meant a yellow chrysolite from Topazion, an island in the Red Sea, and later the name stood for any yellow gem and in this sense it is still used by the jewelers. Brazil and the Urals are the chief sources of gem topaz. Brazil in decomposed rock and gem gravels at Ouro Preto, Villa Rica and Minas Novas, as wine yellow, blue, pinkish and brownish yellow, light green and colorless. Urals. Fine green and blue from Alabastika, Perm and Miask. Reddish from gold washings at Troisk, pale brown from near Nertschinsk. Other localities are: Cairngorm, Scotland. Sky blue pebbles. Tasmania. Color- less, sea-green and blue. Japan. Colorless and bluish. San Luis Potosi, Mexico and Pike's Peak, Colorado. Colorless. DANBURITE. A borosilicate of lime, occurring in considerable quantity as pale wine colored orthorhombic crystals at Russell, N. Y. Has been found in Japan as colorless transparent crystals greatly resembling topaz which when cut show considerable brilliancy. H., 7.5. Sp. gr., 2.97 to 3.02. TOURMALINE. Rubellite, Etc. Described on p. 524. COMPOSITION. R 18 B 2 (SiO 5 )4. R chiefly Al, K, Mn, Ca, Mg, Li. This mineral yields numerous transparent stones of many colors. MINERALS USED AS PRECIOUS STONES. 565 The green and red and brown are most cut. The variety names* are purely color names and are not much used; more often the name tourmaline with the prefix green, red, etc. Oddities are cats eye tourmaline and green tourmaline, ruby red in artificial light (Ekaterinenberg). The most notable characters are the strong pleochroism and absorption, the development by friction or heat of -f and charges of electricity at opposite ends of the c axis, and the fusi- bility sometimes easy, sometimes difficult. OCCURRENCE. The great localities are Minas Novas and Arrasuhy. Brazil (green and red), Ekaterinenberg and Transbaikal, Russia (pink, blue, green and red); Pala and Mesa Grande, California (pink, green and blue), Ceylon (the yellow "turumali" from which the name tourmaline came). Other localities are Burmah, Madagascar, Mt. Mica and Auburn, Maine. SPODUMENE. Hiddenite, Kunzite. Described on p. 429. COMPOSITION. LiAl(SiO 3 )2, with traces of chromium, or manga- nese in the colored varieties. This species yields stones with beautiful lustre. VARIETIES AND THEIR OCCURRENCE. HIDDENITE. Yellowish to deep emerald green tinged with yellow. Color attributed to chromium. Ends of crystals usually different color. From Stony Point, N. C., at the Emerald Mine. About 200 carats were found. The largest crystal would have yielded a stone of s| carat. KUNZITE. Lilac, pink, colorless. The crystals often pale, observed through the prism and rich amethystine observed transversely. Color attributed to manga- nese. Found near the deposit of colored tourmalines at Pala, California. One crystal, the Pala Princess, weighs 2,444^ carats. SPODUMENE. Yellow to colorless with a touch of green. Found in Brazil, Minas Geraes, with chrysoberyl (often confused with it). Notable Characters. Hiddenite is strongly pleochroic. Kunzite is pleochroic, in violet and yellow, or with paler crystals, pink and nearly white. Kunzite becomes luminescent with X-rays or radium or ultra-violet light * Achroite colorless. Indicolite indigo blue or dark blue. Brazilian Sapphire lighter blue but never sapphire tinted. Rubellite rose red and pink. Siberite violet red. Siberian ruby dark red. Brazilian emerald dark green but never emerald. Ceylon peridot yellow. Brazilian peridot yellowish green. Ceylon chrysolite greenish yellow. Schorl black. 566 MINERAL OGY. CHRYSOLITE. Olivine, Peridot. Described on p. 513. COMPOSITION. (Mg.Fe) 2 SI0 4 . Chrysolite, the golden stone of Pliny, was yellow topaz and topazius was chrysolite. This has gradually been inverted. Peridot is of uncertain origin and is apparently the same as Pliny's callaina. PERIDOT, sometimes called the evening emerald, is deep bottle green 'Mike tourmaline with a dash of yellow" to less attractive olive green. The approved color, "like that seen in looking through a delicate green leaf." CHRYSOLITE is pale greenish yellow. Notable Characters. The stones are too soft for ring stones (H., 6.5) but have a very brilliant somewhat oily lustre when polished. The Birefringence is .036, higher than most gem stones and usually easily recognized in a cut stone by the doubling of edges as seen through the table face. The Pleochroism is faint, one image more yellow than the other, stronger in olive-colored stones Peridot may give straw yellow and green. ACTION OF HEAT. Dark stones are made lighter in the oxidiz- ing flame, becoming more yellowish brown and in the reducing flame more green. OCCURRENCE OF CUTTING MATERIAL. Most of it comes from the Island of St. John in the Red Sea. Crystals yielding stones Up to 80 carats in weight are found. It is believed that this is the long lost source of the fine, large stones so common in European altar decorations. Arizona and New Mexico furnish dark yellowish green peridot without crystal form. Queensland and Upper Burma supply light green stones. STONES RESEMBLING CHRYSOLITE. TITANITE OR SPHENE. CaTiSiOs. This mineral, described p 525, fur- nishes stones of great brilliancy and fire of about the colors of chrysolite and brown topaz. They are, however, too soft for much wear H. = 5.5. COLORS. Yellowish green, suggesting chrysolite or demantoid and brownish yellow resembling topaz. LUSTRE. Very brilliant, almost adamantine. PLEOCHROISM. Vivid with twin tints, green, yellow and reddish. REFRACTION AND INDICES OF REFRACTION. Double refracting, biaxial positive. The smallest index varies from 1.888 to 1.917, the largest from i 914 to 2.053. BIREFRINGENCE. .12. So large that the doubling of the opposite edges when viewed through one of the faces is obvious to the unaided eye, even in a thin stone. MINERALS USED AS PRECIOUS STONES. 567 COLOR DISPERSION. .051. Greater even than that of the diamond and result- ing in a great deal of " fire." OCCURRENCE OF CUTTING MATERIAL. Switzerland, in St. Gothard; Tyrol, Pfitschthal; New York at Tilly Foster in yellow to brown; Pennsylvania, Bridge- water. DIOPSIDE. MgCa(SiO3)2 Iron is usually present in small amounts, described p. 506. This mineral, a member of the group of monoclinic pyroxenes occasionally occurs in transparent specimens worthy of cutting. Light to dark oily leaf green or bottle green. OCCURRENCE OF CUTTING MATERIAL. Light green crystals in Ala Piedmont and DeKalb. N. Y. Dark green crystals from Zillerthal, Tyrol. ENSTATITE. (Mg.Fe)SiOs, described p. 504, is now found as transparent green material accompajiying the diamonds in South Africa and is cut in facetted stones and sold as the Cape green garnet. BPIDOTE. CaaAl(AlOH)(SiO 4 )3, described p. 528, is of a peculiar shade of yel- lowish green, similar. to that of the pistachio-nut By transmitted light in directions at right angles the stone will appear respectively green and brown, by reflected light Is nearly black. Bauer states only one locality furnishes material which is transparent enough to be worth cutting, namely, Knappenwand, Untersulzbachthal, Tyrol. PREHNITE. H 2 CaoAl2(SiO4)3. This mineral described p. 535, occurs in Nama- qua land in beautiful crystals which furnish green stones like chrysolite and others resembling chrysoprase. The material from the many other localities is only trans- lucent and little used. MOLDAVITE. A green glass found in Bohemia and Moravia and resembling green bottle glass, was long suspected to be the product of old and forgotten glass factories. The finding of the same material deep down in the garnet mines of northern Bohemia show that it far antedates man and the present supposition is that the fragments are glassy bombs due to the bursting of a meteorite which fell in near the end of the Tertiary period. GARNET.- -Demantoid, Almandine, Etc. Described on p. 509. COMPOSITION. R" 3 R"'2(SiO4) 3 . R" is Ca, Mg, Fe or Mn. R'" is Al, Fe'" or Cr, rarely Ti. GEM VARIETIES AND THEIR OCCURRENCE. DEMANTOID, so called from its diamond like lustre and fire is the most highly valued garnet. It is also called olivine and uralian emerald, and is a variety of andradite, Ca$Fe2(SiO4)3, of an emerald green to olive green color (more yellow than the true emerald) with brilliant lustre and the greatest color dispersion (fire),. 057, known. Its index is very high, 1.88 to 1.89, but it is soft, 6 to 6.5 It is found in the Sissersk district, western side of the Urals and in Piedmont. ESSONITE or Hessonite, reddish brown to orange, CINNAMON STONE golden yellow to brown, and HYACINTH or false hyacinth, golden yellow, are all essentially alike and are of the general formula CasAhtSiO^s. They are somewhat softer than 568 MINERALOGY. other garnets, 7, but take a good polish and are more brilliant by artificial light. A peculiar granulated appearance under the glass is very characteristic. The best are from the Ceylon gravels, also found at San Diego Co., California, and formerly in Switzerland. ALMANDINE, known also as Syriam garnet, Adelaide ruby, and Siberian garnet, is violet, reddish violet, crimson and brownish red. It loses brilliancy in artificial light and was formerly much used cut "cabochon." It is remarkable for its char- acteristic absorption spectrum and is of the type FesAhCSiO^s. Formerly from Alabanda, Asia Minor, whence the name. Various parts of India and Burmah, Brazil, Uruguay, Australia, U. S. A., German East Africa. RHODOLITE. A rose pink variety from Macon Co.. N. C., equivalent to two molecules pyrope to one of almandine. PYROPE, the most used garnet, is also known by many misleading names, like Cape ruby, Colorado ruby, while not a clear transparent stone often occurs fire red and blood red. Light-colored stones backed by colored glass constitute the fire doublets. It is of the type Mg 3 Al 2 (SiO4)3. Occurs in enormous quantities in Bohemia near Teplitz as small red stones with tinge of yellow. Also in the "blue ground" of the diamond mines at Kimberley, and in Arizona, Colorado, Australia, Rhodesia, etc. SPESSARTITE of the type Mn 3 Al 2 (SiO4) 3 has furnished a few very fine stones; it is more brilliant than hyacinth and of a peculiar brownish red color. Occurs at Spessart, Germany, Ceylon and Amelia Co., Va. PHYSICAL AND OPTICAL CHARACTERS OF GARNETS. SPECIFIC GRAVITY. 3.55 to 4.20 or, by varieties, essonite, 3.6-3.7; pyrope, 3.7- 3.8; rhodolite, 3-79-3-87; almandine, 3.9-4.2; spessartite, 4-4.3; demantoid, 3.85. HARDNESS. A little harder than quartz. Essonite, 7 + ; pyrope, 7 + ; rhodolite, 7 + ; almandine, 7.5; spessartite, 7.5-8; demantoid, 6.-6.5. LUSTRE. Vitreous but takes good polish. The lustre of essonite is more brilliant by artificial light. On the other hand, almandine loses brilliancy. REFRACTION AND INDICES OF REFRACTION. Singly refracting and yet practically always with some local double refraction giving between crossed nicols every 90 gradual transitions from light to darkness. Essonite, 1.75-1.78; pyrope, 1.75-1.78; rhodolite, 1.76; almandine, 1.77-1.81; spessartite, 1.79-1.81; demantoid, 1.88-1.89. COLOR DISPERSION. Essonite, .028; pyrope, .027; almandine, .024; demantoid, 057- ABSORPTION SPECTRUM. Almandine and rhodolite show lines corresponding to wave-lengths 570 to 585 and 510-495. ACTION X-RAYS. Essonite almost unpenetrated. QUARTZ. Amethyst, Citrine, Etc. Described on p. 484. COMPOSITION. SiO 2 . COLOR VARIETIES AND THEIR OCCURRENCE. ROCK CRYSTAL. Colorless and water clear. The crystallus of the ancients, from the idea that it was ice permanently frozen. It was made into drinking cups and solid finger rings for the Romans, and balls of crystal were carried in the hands for coolness and used also as a lens for cauterizing and for kindling fire. MINERALS USED AS PRECIOUS STONES. 569 At present rock crystal is cut into imitation diamonds, such as Lake George, Bristol, Irish, etc., diamonds. The chief localities are Sierra do Cristaes, Brazil, Madagascar and Switzerland, others are France, Hungary AMETHYST, from a Greek word meaning "wineless,"* is purple to violet, often irregularly diffused. "The rosy hue shining out from the purple." It is less bril- liant by candle light. Amethyst invariably shows on fracture curious ripple marks, due to the fact that it is always composed of alternating right- and left-handed crystals. Up to 1600 and even in the nineteenth century it kept a high rank. "Queen Char- lotte's necklace, valued at $10,000, would possibly now be valued at $500.00." Fine amethysts come from Rio Grande do Sul, Brazil, and from Uruguay and Siberia. Other localities are numerous, such as Ceylon, India, N C , Ga., Penn. In preparing for market the poorer colored portions are chipped from the pebbles and crystals and the fine-colored bits selected and sold. CITRINE, from citron, alluding to the brownish-yellow to yellow color, is commonly called by jewelers topaz. Much of the yellow quartz sold is, however, burnt amethyst or burnt smoky quartz. It is chiefly from Brazil. CAIRNGORM, from the locality Cairngorm, in Scotland, is often sold as Scotch topaz. SMOKY QUARTZ. The Spanish variety from Sierra Morena, Spain, turns yellow on heating and is sold as Spanish topaz. "Alengon diamonds" were smoky quartz. ROSE QUARTZ, named from its color, is not found in crystals. The best comes from South Dakota, Paris, Me., Katonah, N. Y. Other localities are Madagascar, Bavaria and Urals. Sometimes called Bohemian ruby. VARIETIES DUE TO INCLUSIONS OR STRUCTURE AND THEIR OCCURRENCE. PRASE OR MOTHER OF EMERALD. Originally a pale green stone, colored by included leek green fibres of actinolite and supposed at one time to be the matrix of the emerald. It was valued because it was supposed to possess the powers of the emerald to a less degree (for instance, to lose its color on contact with poison). Although the ancient locality is unknown it occurs at Halbachtal, Salzburg, Breitenbunn, Saxony, Finland and Scotland. AVENTURINE QUARTZ. The name from "Aventura" an accident was first applied to a glass produced by accidentally spilling copper filings into the melted glass. This material, now sold as goldstone, is somewhat similar to quartz, containing spangles of mica, hematite, etc. The favorite colors are golden brown, reddish and greenish. The green from the Altai Mts. is much valued in China. STAR QUARTZ. Showing a six-rayed star. Usually massive rose or milky quartz. CAT'S EYE. Translucent greenish or greenish gray due to asbestos. Chiefly from Ceylon and India and an inferior grade from Fichtelgebirge, Bavaria. * Pliny states: "The lying Magi hold that these gems are an antidote to drunken- ness and take their name from this property," and then he suggests the name to have been given because the color approximated but did not reach wine color. King suggests the word is a corruption of the Persian word Shimest* 570 MINERALOGY. It is imitated by "bleached " tiger's eye. It was a valued specific for croup, sore eyes, colic, and other troubles. TIGER'S EYE AND FALCON'S EYE. There was found in Griqualand, West South Africa, large quantities of an altered fibrous mineral, crocidolite, consisting chiefly of quartz. While sold originally as crocidolite it is now sold as tiger's eye if tawny yellow in color and as falcon's eye when deep blue in color. A similar but paler blue altered crocidolite from Salzburg, Austria, is called siderite or sapphire quartz. DUMORTIERITE QUARTZ. Is cut from the California and Arizona localities. ANDALUSITE. Composition. AhSiOs. Described p. 518. Transparent var- ieties are remarkable for strong pleochroism and for a red color visible from the in- terior in addition to the brown or green body color. Optical Characters. Biaxial ( ), y, 1.643; a, 1.632; 7 a, .on. Strongly pleochroic. Brown shows reddish brown and greenish yellow. Green shows olive green, yellow and red. Occurrence. Good stones are found at Minas Novas, Minas Geraes, Brazil, and in the gem gravels of Ceylon. AXINITE. A borosilicate of .calcium and aluminum. Triclinic in acute wedge-shaped (axe-shaped) crystals. The triclinic symmetry very evident, Fig. 5. The colors are clove brown to smoky violet, sometimes cherry red, and the lustre a strong vitreous which takes a good polish. OPTICALLY biaxial ( ) with y = 1.68, a = 1.67, y a = .009, and strong pleochroism, giving violet, green and brown. BEFORE BLOWPIPE, ETC. Violet changes to brown, then becomes colorless. Fuses easily. Gives green flame of boron. Insoluble in acid, but gelatinizes after fusion. OCCURRENCE. Violet crystals from Roseberry, Tasmania. Brown to red crystals from Bourg d'Oisans, Dauphiny. Reported from San Diego Co., Cal. Other minerals occasionally cut as transparent stones are staurolite, chondrodite, datolite, various zeolites, fluorite, apatite, piedmontite, cancrinite, willemite, cassiterite. B. THE TRANSLUCENT TO OPAQUE STONES. TURQUOIS. Turkis or Turkish Stone.* COMPOSITION. Al2(OH) 3 PO4.H 2 O and always contains some copper and iron which give it color. GENERAL DESCRIPTION. Sky blue to green opaque nodules or veins, also in rolled masses. In general not crystalline but apparently colloidal and somewhat porous. It is the only opaque stone which ranks as a precious stone, and was the Callais of Pliny which "resembled Lapis Lazuli but whiter and of the hue of the sea where it is shallow." * The gem came from Persia to Europe by way of Turkey. MINERALS USED AS PRECIOUS STONES. 571 It has always been the favorite stone in Persia and in Europe in the middle ages it was most popular, the preference being for the greener shades. Physical Characters. SPECIFIC GRAVITY. 2.75 to 2.89. Los Cerillos, 2.71 to 2.82. Surface stones, 2.42 to 2.65. HARDNESS. Less than 6. LUSTRE. Dull and wax-like but takes a good and fairly durable polish. COLOR. Sky blue to greenish blue or when iron prevails, yellow- ish green to apple green or pea green. The colors are more blue in artificial light than daylight. All fade in time, and the color is injured by perspiration, grease, liquids anu heat. Optical Characters. Index of refraction about 1.6 1. Not penetrated by X-rays. BEFORE BLOWPIPE, ETC. Infusible but colors the flame green. In closed tube cracks, flies to pieces, yields water and becomes brown. Soluble in hydrochloric acid, the solution becoming fine blue with ammonia. REMARKS. A secondary phosphate due to action of phosphate solutions on aluminous material. The best stones still come from eastern Persia near Nishapur in seams in a brecciated trachyte. Inferior specimens come from Asia Minor at Serbal in Sinai Peninsula, Turkestan and Kirghiz. Ancient Aztec workings exist near Los Cerrillos, New Mexico, and good stones were obtained near these at Turquois Hill. Other old workings in San Bernardino Co., Calif., yielded pale colored stones and Nevada, Nye Co., yields a dark sky blue to pale blue. Often mottled or "turtle back" material. Arizona, Colorado, Mexico also have yielded material. IMITATIONS OF TURQUOIS AND SIMILAR STONES. Turquois can be colored by placing in a solution of Berlin blue under an air pump and exhausting the air. Turquois colored by Berlin blue is grayish blue by artificial light and changes color in ammonia. By precipitating the proper proportions of hydrous phosphate of aluminum and copper phosphate and pressing hydraulically while still wet a product can be made equal or superior in color to natural. Slight differences of hardness, specific gravity and indices of refraction exist but the principal distinctions are that if heated real turquois splinters, flies to pieces and turns brown, and synthetic turquois fuses quietly to a black glass. In water synthetic turquois becomes deeper blue and the surface shows many little cracks. ODONTOLITE OR BONE TURQUOIS. In the vicinity of Simor, Lower Languedoc, France, are found numerous (ossil teeth and bones, of the mastodon and dinotherium, which have taken up phosphate of iron and become bluish gray in 572 MINERALOGY. color but on heating become a beautiful blue. Occasionally also they are found colored green by copper salts. Some similar material found in Siberia is also blue colored. The material strongly resembles turquois, but differs from it in that its color by candle light is dull and gray; under the microscope the organic structure is evi- dent; it effervesces when touched with acid, and it yields a bad smell on ignition. CHRYSOCOLLA, p. 372, is rarely cut unless contained in some harder substance like quartz or chalcedony. Occasionally translucent blue and bluish green specimens are cut. It has an enamel-like texture and some blue specimens resemble turquois. VARISCITE. A1PO42H2O in bright green to bluish green, compact, opaque, rounded masses and veins resembling turquois and suitable for cutting. It may be the oldest gem.* It is found in Cedar Valley, Utah and in several parts of Nevada. LAZUXITE. Blue Spar. A complex phosphate of aluminum and other bases. The massive material is sometimes cut and could readily be mistaken for turquois. In Germany it is known as "Blauspat." The principal occurrences are Kriglach, Styria; Werfen, Salzburg; Zermatt. Tyrol; Sinclair Co., N. C., and Graves Mt., Ga. SMITHSONITE. ZnCO 3 described on p. 300. The sacred stone of the Aztecs "Chalchihuitl," long supposed to have been turquois, is now thought to be the beautiful banded azure blue smithsonite of the Ysabelita mine, Mexico. Green smithsonite occurs at the same mine. OPAL. Described on p. 487. COMPOSITION. Si0 2 .wH 2 O, (H 2 O, 5 to 12 per cent.). "Made of the glories of the most precious gems," "fairest and most pleasing of all jewels" is Pliny's description of opal. The beauty is due not to the color of the stone but to varying brilliant inter- ference colors, produced by thin films of air or of other opal in the cracks developed during the drying of the original jelly- like mass. On the basis of color of the stone opals are broadly divided by jewelers into: WHITE OPALS, colorless, milky yellowish and other light tints. BLACK OPALS, dark gray, blue and nearly or quite black. FIRE OPALS, reddish or orange colored. Many names have been used based on the predominance of one or the other inter- ference color; these are little used now. An example is harlequin opal, with the interference colors in small, regular angular patches of every hue. In others some peculiarity in structure is the basis of a name. * There was found in an Old Celtic grave at Mane er Hrock in Brittany a con- siderable number of rounded beads from the size of naxseed to that of a pigeon's egg, from apple to emerald green in color, and often necked with white or blue. The composition is close to variscite. The remarkable thing is that they are more trans- parent, and of more beautiful colors than any specimens found elsewhere. MINERALS USED AS PRECIOUS STONES. 573 HYDROPHANE. The cracks being filled with air fail to give play of color but if filled with a denser medium, by dropping in water the colors appear. CACHOLONG, a milky white almost opaque variety, which adheres to the tongue. GIRASOL. Almost transparent but with a wave of blue light, something as in moonstone. OCCURRENCE. The ancient source of the best is said to have been India. No such gem comes from there now. The mines in Hungary near Czernovitza yielded much slightly yellowish opal and some fine, and were long the only important source. In the early eighties the rich blue opals were discovered in Queensland, Australia, in thin veins through a brown jasper, and a little later bright yellowish opals were found in pipes of jasper in a sandstone rock in West Queensland. In 1889 white opals of fine quality were found at White Cliffs, New South Wales, in Cretaceous rocks replacing other minerals, bones and wood, and filling cavities. In ten years these were exhausted. In 1904 at Lightning Ridge, New South Wales, the dark-colored so-called black opals were found in essentially the same formation as at White Cliffs. These also are practically exhausted. Mexico yields many fire opals and some white opals which are sometimes facetted, sometimes cut with matrix. They are more translucent than other opals and are said to lose their play of colors. In Humboldt County, Nevada, opalized wood, often of dark color but with beautiful play of colors is found. It has a tendency to crack during and after cutting. CHALCEDONY. Carnelian Onyx, Etc. Described on p. 486. COMPOSITION. Silica with occasionally a little water. The earlier gems were engraved rather than cut and no substance has proved as suitable or durable as chalcedony. Before the coming of the sapphires and other transparent gems from India and Ceylon, carnelian and onyx were much used by the Romans and through the Renaissance period for seals and cameos. The beeswax then used did not stick to it. "Signeth very faire without any of the wax sticking to it." A pale blue variety, sapphirine, was used much earlier in Baby- lonian and Persian cylinders and Etruscan scarabs. The best known varieties are: CHALCEDONY or Girasol, white, gray and " tendon " color. CARNELIAN. To the Romans dull brick red and little value, now the name for clear red. SARD. To the Romans the bright clear red now the name for brownish-red. CHRYSOPRASE (golden leek), an apple green variety, colored by nickel. BLUE CHRYSOPRASE. Chalcedony containing chrysocolla. BLOODSTONE OR HELIOTROPE. Deep leek green with spots of red jasper. Said to have been used as a mirror in detecting solar eclipses. Much used in the Byzan- tine period for sacred carvings, the red jasper being said to be the Savior's blood. 574 MINERALOGY. AGATE. Variegated chalcedony in clouds, bands, spots or layers. Named for the river Achates in Sicily. MOSS AGATE AND MOCHA STONE, with moss-like inclusions. ONYX. Originally oriental alabaster, later the tricolored agate used for signet rings. Pliny says "a white mark on sard like the human nail placed upon flesh and both of them transparent." The tricolored agate was cut across parallel layers so as to give two bands of dark brown with a layer of colorless transparent between. This was long the favorite signet stone. Onyx to-day is an agate with regular, even planes of different colors, especially white and black or white, brown and black, and was used much for cameos. SARDONYX. Onyx with one of the layers of sard. Pliny's perfect sardonyx was base black or chocolate; middle opaque, fatty white; surface brown or red. OCCURRENCE. India is noted for its fine carnelians and agates. Brazil furnishes the "carnelian" so-called free from iron, which is colored and polished at Idar* Uruguay furnishes much material and agate and chalcedony are found in a great many localities in America, such as Agate Bay, Lake Superior, Colorado and through the Rocky Mountains. Agatized wood comes from Arizona. Chrysoprase from Venus Hill, California, and Blue Chrysoprase from Globe, Arizona. JADE.f The great " Nephrit-Frage " arose because jade weapons apparently composed of Asiatic jade were found in many parts of Europe, and no localities for raw jade were known. More careful search found raw jade in Silesia, Siberia, Italy, and elsewhere. Possibly only because its toughness made jade suitable for delicate carving and possibly from superstition, China and Japan and to some extent India and ancient Mexico grew to value the jade beyond other stones and to carve from it with im- mense labor vessels, figures, beads and amulets. The plundering of China has brought many of these to Europe and America. In Europe in the early part of the seventeenth century it was enormously valued. Deboot says a piece no larger than a thaler sold for 100 pounds. This seems to have been due to the powerful medicinal properties attributed to it. Both worn as an amulet and administered as a powder, it was held to cure kidney troubles. In 1863 Damour showed that while most of the light-colored jade objects were, as supposed, the variety nephrite of the mineral amphibole, many of the more valued green jades, though much *The white chalcedonies formerly found at Idar and the so-called Brazilian carnelian now worked there are free from iron. They are therefore easily given other colors by different solutions and processes, the colors including black, sard brown, sard onyx, lemon yellow, blue, deep blue, green. t Jade for various reasons has an extensive literature and has been more valued by various races and for more various reasons than perhaps any other stone. In the Stone Age the man with the tough jade weapon was master of the man with weapons of any other material, and jade weapons were valued and sought for with a care not since equaled. MINERALS USED AS PRECIOUS STONES. 575 like nephrite in toughness and translucency, were of a totally different composition and were definitely harder and heavier. To these he gave the name jadeite and a third name chloromelanite, essentially a jadeite rich in iron. In these the constant characters were extreme toughness, lack of brilliancy and in general trans- lucency, and the dominant color was from white to green. Al- though two distinct minerals, it has seemed most convenient to discuss them as if varieties of one substance, broadly called jade. COMPOSITION. Nephrite Ca(MgFe) 3 (SiO 3 ) 4 , Jadeite Na 2 Al white, gray, green, brown or red, often with streaks of emerald green. LUSTRE. Dull, oily, not brilliant, even when polished. CRYSTALLIZATION AND STRUCTURE. Both are monoclinic. In nephrite the microscopic crystals are confusedly interlaced fibres, which in the New Zealand material are sometimes coarser and recognizable. Jadeite occurs in both fine fibrous and granular masses. CLEAVAGE. Not recognizable except in thin sections. In nephrite cleavages of 54 38' have been detected. In jadeite cleavages of about 86 have been detected. REFRACTION AND INDICES OF REFRACTION.- Though both are doubly refracting, this is not determinable in the cut stone. The indices average, nephrite about 1.6 1, jadeite about 1.67. ACTION X-RAYS. Nephrite nearly opaque. BEFORE BLOWPIPE, ETC. Nephrite is unchanged at red heat, but fuses at 4 to a colored glass. Jadeite fuses very easily (2.5) 5 76 MINERAL OGY. with a strong yellow flame to a transparent bubbly glass. Neither is readily attacked by hydrochloric acid. OCCURRENCE. Nephrite occurs in great masses twenty to forty feet thick, in gneiss, in Turkestan, in the valleys of the Karakash, Yarkand and Kashgar rivers. These are the sources of most of the light-colored nephrite with specific gravity 2.9 to 3. It is said to occur in several provinces in China, and it occurs in place, in serpentine on D'Urville Island, New Zealand, and also as numerous boulders" of dark green, light green, and gray color. Other occurrences are : as boulders near Lake Baikal, Siberia; both as boulders and in place in Silesia: in New Guinea and Alaska. Jadeite is found as boulders and with albite forming light colored layers in green serpentine in Mogoung, Upper Burma. The serpentine is in sandstone. It is nearly all sold to China and amounts to about $250,000 per year. Jadeite is said to occur also in China and Thibet and to have been found in place in Italy. JADE-LIKE MINERALS. CALIFORNITE, a compact variety of vesuvianite, described on p. 511, has the appearance of a jade and polishes well. It is found in Siskiyou and Fresno Counties, California. The pieces are in some cases as much as 5 feet square and 2 feet thick, of excellent quality for polishing. The associated rock is precious serpentine. SERPENTINE. H4Mg 3 Si 2 O9, with replacement by Fe. Described, p. 544. Although a soft mineral serpentine takes a good polish and is durable and its frequent occurrence in translucent varieties of bright oil green to paler green resem- bling jade and the ease with which it is worked has resulted in its very extensive use for decorative purposes, art work, cameos, intaglios, etc. At Zoblitz, Saxony, it is the basis of a large industry. Special varieties are: Williamsite, apple green, nearly transparent. Bowenite or Tangiwai, rich to pale green. Satelite, a dull green fibrous variety, mixed with chalcedony and cut as cat's eye. Green stone of South Africa, malachite green. Localities are very numerous. Snarum, Norway; Miask, Urals; Newburyport, Mass.; Milford Sound, New Zealand, and Smithfield, R. I., Texas, Pa.; Venus Hill, Cal. (satelite). LAPIS LAZULI. This stone, the sapphire of the ancients and the only stone of value in Egypt at the time of the early Pharaohs, is not a mineral but a complex of calcite, colored by three blue aluminum silicates. One lazurite, an ultramarine, involving sodium sulphide, one hauynite, and the third sodalite. It is a deep blue, sometimes purplish, and often spangled with little crystals of pyrite. The Chilian variety is a yellower blue and has white or gray flecks. OCCURRENCE. The Egyptians are said to have had mines in Ethiopia. The oldest known mines are in the Kokseha Valley, Badakshan, Afghanistan, and it is also said to occur in India at Sadmoneir and Bijour. Other localities are Lake Baikal, near the source of the Koultouk; the Chilean Andes, and Thibet. MINERALS USED AS PRECIOUS STONES. 577 IMITATIONS OF LAPIS LAZULI AND SIMILAR STONES. IMITATIONS. The best is a jasper from Nunkirk, stained blue. It is called German lapis and perfectly imitates the Chilean, but fades in time. AZURITE, p. 371, is sometimes used as an imitation. It is the same color but softer. OCCURRENCE. Material suitable for cutting is found in many localities: Urals, Australia, Chile, Arizona, California. SODALITE, p. 500, mentioned as forming part of lapis lazuli, occurs also separa- tely and is sometimes cut cabochon and has a limited use. In Bolivia it was used by the aborigines cut pearl shaped. It rarely has the fine blue lapis color. OCCURRENCE. In dense masses at Dungannon, Hastings County, Ont., Canada, and at Litchfield, Maine. In translucent material in Greenland; Siebenburgen and Vesuvius. FELDSPAR. Moonstone, Amazonite, Etc. Described on p. 488. COMPOSITION. The group is considered to consist of three distinct species and a number of intermediate "isomorphous mixtures." Orthoclase KAlSisOs Monoclinic Albite NaAlSiaOs Triclinic Anorthite CaAl 2 Si 2 O 8 Triclinic Although constituting about one half of the known crust of the earth this group of great species only occasionally furnishes material suitable for jewelry. MOONSTONE. "Colorless, diffusing brilliant rays in a circle after the fashion of that luminary." The only variety valued in jewelry. Chiefly a variety of orthoclase, but also of albite or intermediate mixtures. The milky, bluish opalescence from which they take their name is caused by inclusions, which lie about perpendicular to one of the cleavages. They are always cut more or less steeply en cabochon and go well as a border for large colored stones. OCCURRENCE. At the present day practically all the moonstones on the market come from the interior of Ceylon. Formerly many came from the St. Gothard district in Switzerland. Beautiful stones with blue opalescence come from California. Other localities are Amelia Court House, Va., Rio de Janeiro, Brazil, and West Australia. Albite moonstone is found at Media, Penn. Peristerite is a less transparent variety from Macomb, N. Y., and Bathurst, Canada, which shows a pigeon blue opalescence. AMAZONITE OR AMAZON STONE. This is a green opaque variety of the potash feldspar microcline. The most valued variety is apple green in color; the brighter green and the varieties with streaks and flecks of white yellow or red are of little worth. The principal localities are in the Ilmen Mountains, Orenburg, Russia, Virginia, Pikes Peak, Col., and in North Carolina. The name was given by Spaniards to some green mineral found among the Indians dwelling near the Amazon River. No occurrence of Amazon stone there, however, 38 578 MINERALOGY. has been found and there appears to have been some confusion with a jade or similar stone. SUNSTONE OR HELIOLITE. Sunstone is chiefly a variety of oligoclase, but also of albite and contains flakes of hematite or goethite which impart a spangled bronze appearance. The colors vary from grayish white to reddish gray, and the material resembles aventurine quartz and is sometimes called aventurine feldspar. Bauer states that this variety of feldspar around 1800 was very rare and costly. Only a few specimens were known from one locality, Sattel Island in the White Sea. It is now found in East India, Ceylon. The best sunstone is from Christiania fiord, Norway. Sunstone almost equal to the Norwegian is found at Media, Dela- ware County, Penn., and in Amelia Co., Va. LABRADORITE. The body color is usually a dull gray, but the "interference" colors which come and go as the stone is turned from side to side are usually broad flashes of blue and green, but also in yellow, red, pearl gray, orange, puce, amber, and peach-blossom hues. These colors are due both to a regular lamellar structure and to regularly placed microscopic inclusions. The finest specimens are brought from the Isle of St. Paul off the coast of Labrador, but other localities yield beautiful material, Brisbane, Queensland, with a blue schiller; Djamo, Finland, a colorless labradorite, showing the interference colors in concentric circles. MALACHITE. Cu 2 (CO 3 )(OH) 2 . Described on p. 371. The green copper carbonate. Although by the ancient Greeks and Romans the easily worked malachite was used as a gem, it is now only occasionally so used. The fine fibrous and stalactitic varieties are, however, used in large quantities, especially in Russia at Ekaterinenberg and Petrograd for the making of jewel cases, vases and even table tops and large columns. In general, however, the articles are only covered with a thin veneer of the malachite made from comparatively small pieces carefully built together like a mosaic. OCCURRENCE. The finest malachite is found in large masses at the copper mines of Nizhni Tagilsk in the Ural Mountains. It accompanies the copper ores in many parts of the world. CHLORASTROLITE OR ISLE ROYALE GREENSTONE, from chioros (green), aster (star), and lithos (stone). Small rounded pebbles from Isle Royale, Lake Superior, which are opaque, of a mottled green color, somewhat chatoyant on the rounded sides, and take a high polish. AMBER. Succinite Simetite. Amber is a fossil resin, derived from a now extinct variety of pine which lived during the Tertiary period. Its composition is: carbon, 78.96; hydrogen, 10.51 ; oxygen, 10.52. It consists mainly (85 to 90 per cent.) of a resin which resists all solvents. PROPERTIES. H., 2.5. Sp. gr., 1.065 to 1.081. Lustre resinous and very brilliant after polishing. The color is yellow, sometimes reddish, brownish, and whitish, often clouded. The variety from Sicily, simetite, is brownish red MINERALS USED AS PRECIOUS STONES. 579 with a beautiful bluish to greenish fluorescence. Singly refracting, though often locally doubly refracting. Index about 1 .54. Nega- tively electrified by friction. While the Sicilian amber if fluorescent still commands a high price, the Prussian amber is sold by the pound and used for mouthpieces of pipes, cigar and cigarette- holders, umbrella handles and locally cut for cheap jewelry. It formerly ranked very high, the Greeks obtained it from the Teutonic tribes and according to King, is entitled to " the highest antiquity in the list of precious stones used for personal ornament," since Homer mentions no gem except 'the gold necklace hung with bits of amber/" It is obtained now as for over 2,000 years chiefly from lignite-bearing sandstone along the coast of the Baltic from Danzig, West Prussia, to Memel, East Prussia. The most beautiful is obtained off shores of Catania, Sicily. JET. Jet is a compact, soft, light coal of a lustrous velvet black color, suscep- tible of a high polish. The early Britons turned it on the lathe into rings, bracelets, anklets and later made it into scarf pins, bracelets, beads, etc., and in Whitby, Yorkshire, there is still a large industry amounting to about $1,000,000 per year. OCCURRENCE. The finest specimens are now found in detached pieces in a clay near Whitby, Yorkshire, England. It also occurs in Germany, Colorado, South France, and Aragon, Spain. IMITATIONS. In this country it has been displaced by black-colored chalcedony. It is also imitated in gutta percha, glass, and obsidian. ANTHRACITE is turned into compass cases, cups, saucers, vases, candlesticks and paperweights, and is carved by hand into a variety of small ornaments. Most of the anthracite is worked at Mountain Top, near Glen Summit, Lucerne County, Pa. RHODONITE. MnSiOs. Described on p. 271. The fine-grained massive variety is often cut into vases, paper weights, and in rounded stones for brooches, etc. It is very tough, takes a good polish and in color is a fine rose to dark red, often attractively veined with black. The principal localities for cutting material are Cummington, Mass , and Ekateri- nenberg, Urals. THULITE is a beautiful rose to peach-blossom red variety of zoisite, itself an orthorhombic epidote. It owes its color to a little manganese and is essentially opaque. Fine specimens come from Telemark, Norway, and Traversella, Piedmont. HEMATITE. Fe 2 O 3 . Described on p. 271. The compact brilliant black variety of the great iron ore was used as a gem by the Babylonians and Egyptians and to this day it is made into beads, signet stones, bracelets, etc. When cut with a dull polish it is very similar to black pearl. Other translucent or opaque stones occasionally cut are: thom- sonite, lepidolite, fuchsite, hypersthene, lodestone, ilmenite, pyrite and rutile. PART IV. DETERMINATIVE MINERALOGY. CHAPTER XXII. TABLES FOR RAPID DETERMINATION OF THE COM- MON MINERALS. All schemes* for determining minerals utilize essentially the same tests and differ principally in the order in which they are applied, the number of minerals considered and the completeness with which the minor or confirmatory tests are stated in the scheme or covered by a reference to the descriptions of the minerals. The tables which follow are in the main an elaboration of the tables in the former editions, employing essentially the same classi- fying tests but differing in the following points: i. The results of the major tests are summed up in a "KEY" to 59 numbered groups. 2. The number of species has been increased. 3. The groups contain tabulations of confirmatory tests. 4. In the thirty-five groups of minerals of non-metallic lustre alternative tables A and B are given, A the physical and chemical tests, B the tests upon crushed fragments with the polarizing microscope. The latter have proved their value during several years of use as auxiliary tables and are now incorporated. * They may be said to vary between the von Kobell (Brush-Penfield) type in which "the tables have been so developed that tests for characteristic chemical constituents furnish the chief means of identification" (preface 1898 edition Brush- Penfield Determinative Mineralogy}, and in which lustre, fusibility and tests for elements are the classifying tests, and the Weisbach-(Frazer-Brown) type, in which the purpose was "to help the determination of minerals by their physical char- acteristics" (preface Weisbach's Tabellen, first edition, 1866), and in which lustre, streak, color, sectility and hardness are the classifying tests. 580 TABLES FOR RAPID DETERMINATION. 581 In discussing this addition of microscopic tests to the ordinary mineral schemes the writer said,* "schemes by which a student with a few months' experience 'deter- mines' the identity of a larger or smaller series of the more common or important minerals rarely include the exact easily applied distinctions obtainable with the polarizing microscope, although this instrument is now in every mineralogical laboratory and in most well equipped chemical laboratories. " If the polarizing microscope is to be used in such work the tests must be quickly obtainable and accurate. The thin sections of the petrographer will not therefore be available, nor in general can those optical characters be made prominent which are only obtainable for some particular direction of transmission of light. In my opinion also, for this particular kind of scheme, the optical characters should be made subordinate to the very thoroughly worked out so-called 'blowpipe tests' and 'physical tests.' " The Tests Leading to the Key. In the tables which follow, the minerals are divided first into minerals of metallic lustre and minerals of non-metallic lustre (see p. 210). The minerals of metallic lustre are sub-divided into twenty-four groups by the tests (or characters) 1. Color, see p. 211. 2. Streak, see p. 212. 3. Heating on charcoal, see p. 169. The minerals of non-metallic lustre are divided into thirty-five groups by five tests. ' i. "Taste" or Solubility in Water. See p. 180. The test is valuable because the existence of a "taste" is unmistakable, but the recognition of the taste is not easy. 2. Solubility in Dilute Hydrochloric Acid. See p. 180. This test fails only from carelessness. 3. Treatment on Charcoal with Soda. This is Test II of page 197. 4. Treatment in Platinum Forceps. This is the "fusion test." of pp. 164 and 165. The scheme and the safety of the forceps both require that the absence of volatile or easily fusible elements should first be proved on charcoal. 5. Flame Coloration. See p. 165. * Scheme for Utilizing the Polarizing Microscope in the Determination of Minerals of Non-Metallic Lustre, by A. J. Moses. 582 DETERMINATIVE MINERALOGY. The Minor Tests of the Groups 1-24 and 2$A to The species are in order of hardness and characters of deter- minative value are in parallel columns. Following each species is the number of the page on which it is described. The determination must always be confirmed by ref- erence to this description and, when possible, by comparison with known specimens. The Tests* of the Alternative Groups 256 to 296. The tests recorded assume the use of crushed fragments but in the text descriptions of the species, especially in the silicates, special optical distinctions are given for thin sections, cleavages, etc. Crushing and Mounting is described on p. 126. The thickness of the resultant grains is near the 0.03 to 0.04 mm. of well made thin sections. The Classifying Tests are : i . The relative indices of refraction of the grains and of four chosen mounting liquids. 2. The birefringence of the grains expressed in five terms deter- mined by the interference colors. The Relative Indices of Refraction are determined by "The Becke Test," p. 128, and "The van der Kolk Test," p. 129. The scheme considers only the indices of refraction corresponding to the two positions of extinction in the fragment. The liquids used are: Index at 15 C. Xylol ....................................... 1,487 Bromoform .................................. i,59O a Monobrom-napthalin ....................... 1.655 Methylene Iodide ..................... * ...... i74O The Birefringence is approximately determined in terms of interference colors as described on p. 137. Interference Color. Effect of Gypsum Red. Other Tests. BLACK Red except at extinction positions. Unchanged by rotation. GRAY OR WHITE Made yellow for crossed position, blue or purple for parallel posi- tion. BRIGHT A. Made white or gray or black for crossed position. TABLES FOR RAPID DETERMINATION. 583 BRIGHT B. Bright colors for both positions. By mica plate notably dif- ferent tints for crossed and parallel positions. HIGH ORDER. Indefinite colors for both positions. Not noticeably affected by mica plate in either position. Minor Tests. Upper Nicol Out. Shape.* The self-explanatory terms "laths, "needles," "fibres," "triangles," "rhombs," "rectangles," and "irregular" are used. The term "plates" implies flat particles lacking straight edge boundaries. Color by Transmitted Light. If no color is given in the scheme, the fragments are colorless. Pleochroism. See p. 153. Minor Tests with Crossed Nicols. Extinction and Extinction Angles. See p. 138. The method of designating here used is: Ex. 1 1 when the angle turned is zero. Ex., Sym. when the angle turned is one-half the angle between two crystalline directions. Ex., Obi. when the extinction is neither "parallel" nor "symmetrical," or the angle may be stated, e. g., Ex. 27. Elongation. In "laths," "needles," "fibres, "etc., the longer direction or "Elongation" is usually a crystallographic direction. By the method p. 134 its "sign" may be determined as EL, (+) or El., (-). Interference Figure. See pp. 140 to 145. The Optical Sign or Character. See p. 146. Precautions. / 1. The specimen should first be carefully studied with a hand glass. If it is one substance so far as this shows the testing may go on. If not fragments of the different substances must be obtained and separately tested. 2. If fine-grained or dull, crushed particles should be examined with the microscope as to homogeneity. The tests will be un- * Ciushing tends to develop the cleavages, and in a liquid the fragments tend to lie on the broadest cleavage surface, thus giving considerable constancy in shape for fragments of each mineral. 584 DETERMINATIVE MINERALOGY. reliable if the material is impure, unless the effect of the impurity upon the test is known. 3. Lustres and colors should be observed on fresh fractures especially in minerals of metallic lustre. 4. Classifying tests must be decided; not weak, nor indefinite. If undecided, the species on both sides of the dividing line, must be considered. 5. If as may happen the tests fit no species in the scheme or do fit some species the description of which is radically unlike the specimen, then either some error has been made or the specimen belongs to a species not included in the scheme, for which more elaborate tables will be needed. CONVENTIONS AND ABBREVIATIONS. The species in each group are printed in heavy type or ordinary type, according to their importance. The formula following is expected to \uggest confirmatory blow-pipe tests. The page reference to the complete description of the species is also given. H., is hardness. Sp. gr., specific gravity. Systems of Crystallization are indicated by the letters: I (iso- metric), T (tetragonal), O (orthorhombic) , M (monoclinic), Tri (triclinic), H (hexagonal). Terms in Blowpipe Tests. Soda for sodic carbonate, S. Ph. for salt of phosphorus, O. F. and R. F. for oxidizing and reducing flame, Co. Sol. for cobalt solution, coal for charcoal, Bi.Fl for Bismuth flux-, Fl for flame, subl. for sublimate. The numbers under fusibility are the v. Kobell scale, p. 164. The "residue'* means residue after fumes have ceased. Terms in Optical Tests. Ex., ||; Ex., Obi.; Ex., 22; Ex., Sym., denote that the extinc- tion is respectively parallel, oblique, at angle of 22, and sym- metrical. EL, (+); El., (-), denote that the elongation is ( + ) or ( ). I. C. is for interference color, < for less than and > for greater than. TABLES FOR RAPID DETERMINATION. 585 KEY. I. MINERALS OF METALLIC OR SUBMETALLIC LUSTRE. The Color is The Streak is HEATED ON CHARCOAL YIELDS 1< a o a>"3 "0 < White Coating But no Garlic Odor. iASi &5s gg? gll s!*l 8fo bO-3'iS o Us? a ^"3 Is*! fii H Not Previ- ously In- cluded. A. Black or Nearly 1. Black I 2 3 4 5 6 2. Not Black 7 8 9 10 B. Silver-White, Tin White or Gray 1. Black 11 12 13 14 2. Not Black 15 16 17 18 19 20 C. Yellow, Copper, Red, Bronze, or Blue 1. Black 21 22 2. Not Black 23 24 II. MINERALS OF NON-METALLIC LUSTRE. A. Minerals with De- Which Color the Flame. 25 cided Taste Which do not Color the Flame. 26 WITH HYDROCHLORIC ACID : Effer- Forms Dissolves Is In- vesces. Jelly. only. soluble. Arsenical Odor. 27 28 B. Tasteless, but with Soda on Charcoal in the Reducing Flame Viplds Fumes and a Metallic Globule. Fumes but not a Me- tallic Globule 29 32 33 30 34 31 35 No Fumes but Magnetic Residue. 36 37 Fuses Easily to a White Glass or Enamel. 38 39 40 41 Fuses Easily to a Col- orless Glass. 42 43 44 Fuses Easily to Colored Glass or Enamel. 45 46 47 48 C. Neither A nor B but Heated in Pt. Fuses with More Diffi- culty than Common 49 50 51 52 Forceps : Orthoclase. Is Infusible but in Pow- der Made Deep Blue 53 54 55 by Cobalt Solution. Is Infusible, not Made Deep Blue by Cobalt 56 57 58 59 Solution. 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O ^"^ ^- 1 1 O O ^H , Z cu jv * 2 ' -il w "o 3 o >> u i s E co " E G 3 ffi ffi ft E ' ES CO TJ CO CO . . cr 4> . ^ CO ^^ *^ CO ^^ r i r J ^ld i-H r i B S S M C 3 cu jg 3 .2 1|| || 1! 1 |l| II d ac< 1uS "cu > 1 "1 CUO (-< Ctf ^ ^ ^ u ^ ft .9 g: j -2 'S jj x -S -2 ^ "S 2 .S & S3 CO W P4 ** >5 U PQ U J U E fi 10 1 ^ 2 | . r. M N 3 CJ U O oj cd rt QJ QJ QJ ^> S3 fl G 1| 1 1 o S 1 u S S S CO M ^ ^ W sii .ti S ^S "O > T3 1* O IOOO /-? ln 00 I> tO <5 N' "^"^^^gO r^ piO CO O O o o ffi o r ^ Q/J o c3 ^ N CO 10 00 H 6 t^. o t- ^ffi 5 do S ^~ b/j -tN* W t^ B \r> \r> oj ^^ I ^t^c_^o 5 10 -J 3 N ^ (N -Q -g gO J 'S Q 2*o oo C^-Q^JO "t^o2o ^ 2-S - t5 1 S ^ S^2^ "3 O>-" PH M ^fOo^" 10 .S^PP^ O *O Pyrargyrite, p. 2.5 Sp, ^ #. C3 . r r ^0*1** *P5 * . * " * H^K OK HE CD EE OE ^EuElE (XEHE O E E E 587 f 2 , I I *fl 1 I o d d 1 & ? S u A O 03 "" ^ |j ^ >> d 4) ,9 "3 s * *^ *> 3 3p ^ o ^ "o .2 jg T3 O > W C 1 j d ^ f_" JH ^ > 4* i 4> C Q *" W '5 (T CO w toO ' 1 " O i 1 jfjjl Ilia 60 to ^S^^-o H 5 S w '1 rt w 3 13 to Q Pu ^ IO t*- X^ is 1 1 1 ? 1 s 41 C3. d kC fj OJ '3 Ci> 1 1 cS u *O .2*0 4. ^41 III Jo o 41 .J 3 a en isl > C/3 w HH (N M "c TJ- O u-> 1> * ^ 1 O O voQ oo "::> > N .si .-a ^ JiJ i : i ** ^ ^ ^s ^^^ 111 u 4, |g 0) O 2 ^T | Is 1 5*| 3 t-H ffi -J ffihtd Sol. HNOs. low ppt. wi monia radioactivity e 195 -o v ~ tn - * ----2 5^^w ti:= 5 '> V O S b, 2 S 3 10 \r> fO - s CwQ'rjC NO h/i !X 3 OJ M - 'S ft aT l :g o "So ^ M to r~* to 10 w o I ffi I ffidw 588 WffiK ffiffi 1 I No oxygen Much water. A little oxygen Unchanged Unchanged Unchanged Unchanged "o cr. V c J h O i CO "o w | w ffi S g .2 II QJ u u c 2 RM ^OJ 3 3 2 E C/3 ^ ffi ^ S S^s s 3 3 1 w . *-^ T^ 30 1 11 1 1 1 1 C c i. _ . J- c 1 O amids. nutbrov S^ i d ! S I'l 03 ^ -&* I S 1 y ^ O O 09 3 S 8^ 2 u, v/^ jy .d fin Cubic clej streak Twinned Streak cl S'i || Q OH ^ "o ^ o fe ^ 5 & S3.E 8 M d 1 1 C^ "o > rt - - _0 - - t- t^ 1 1 So a I a I g 1 1 ' d d d ^ o o o c C C PQ ^ ^ S ^ 0) rj ^ c c C , 1 ^0 O! 1 0* 00 d rf 00 oq j 0* J w ^ d aJC/2 2- o ^ 2 Uranini 10 2 o uo g 10 g a u |2 vO CQ to jsf 3 3 2 ,_; ffi HE dffi ^ ffi HH'ffi KOffi H ffi rror and black subl nish red Later mirror black O. T. spongy platinum and white ubl. subl. or and B 2 ! Like cobaltite. Often with erythrite After ignition Sol., with odor of H 2 S, and yellow ppt. .a .a A ^ -U 2 ^ igh As - . d Cl t - W5 00 CU C/} *T5 S o -"> w -i-> W IO VH K ) < ffi O ffi hH I 1 ^i i .s "S as - 5 . ? ^ > 8 " to w | to . -* 1 1 h 4 (Closed Tube Unl Specified O. T.J S Jii . "9 53 3 CO * 2 3 *3.3| , 3-0 . M ! ^ OJD ll CO O. T. white cryst Mirror and blacl Decrepitates. B ish red subl. 1 u O 8 ^ 0) a; 3 . >1 f i ! -H C 3 vE 1? - sod. (J ^ J3 d! O O '~ * 3-5 U K % ^ to '^ ^ i_ (U H ^3 5 P E 3 M 2 ' >> '^^'c^' K ^ 3 ffi ffi "S ^J HH Jin ,4 i H O oSljsffi ; a CO w 1 1 ^ o | " U 33 S fe i s i i - g 2 "8 s O -2 ^ ^ a; S^ ^ a ^ ^ ^ s? s, 33 fe C* u ^3 3 >.5S u 8 ^jH ^ -*-> '^ 3 C'^'>'Saj t *^ 3*^^^(j j* PQ M r:! H OJ . [JH '> ^ < O "^.5*:r u 'oaj' Q .2 > w) *o P4 d 3 111 ill s||| C/3 O H P^ C/3 W ^ *O iJ *O 333 o x .__ rt ^ M M P4 1 = 5 N 1 J3 O M ~ M H ^ M OJ H C4 n H 13 H 1 fe " I '. (1) (L) aJ M^cg _g 2c. w j5'.ti ir! o co SaQ^OQ^^ ^ Q J ^ Q ^ U J2 W ^ O ^ G O "" 8 a; ^ 'o ? JU > c "o .5 w s O 3 < g co O O\ 1O ,, M IT) O \O O 10 t> 1> t, M "c 4 00*^4^10^4 1> us O 00 ^ o I ^ aj-';9>ic/)2cLj 60 OQ^roOS M 2 "^ O j2 10 a; -j rj- (g to ^goo ^ f^ r pi, ti CO "^ ^ "* Q Q ^3 Q o to U 4 ^C/] ^C/3 C^^-SC/} o" >-* M'> W %&- - J * ^ M" J C^ M g a n M ^ 05 ^ i> ,_; >t C^ *K ^t ro ^ . a !/3 ^ in :f S d d d c^o oo* d ^^ . d ji co d d co (2 s . d d\ d & d l P d ' .g | o, T 'S 'S *o 10 aj d J 2 a oT - ^.y *2 ^ 1 C3 cJ JH ^'3 I g-g^Sog -M Z * *( - S 8 OT N . H N > ^H ^^ t OK ^ffidffi^ffi^ffi' PH L L 11 S-; A-; d-; ~ K OK S ^ iH % a x^ iH |s|v>|2 .2 ro o as w co CO ro O K^Kffiffi H i: 6 Q ^ ffi 5 s is IE ^ o oo CO t^. 0\ H*2 2 ^ N t^ PQ ^ d^ d CO roCO M pq N niss ft CO OK 591 Offi S I! Magne heating O\ OO o ^ GJ M fc . oco > % ^C D <*H J2 flrj O d i 'Si | I ,3-0 "Ell 13 i 3 3 CO 32 Si S ^ w 2 g M "3 c^ I 11 c o rf . -J "| g sll - s 1; 3~ s S H g fi . So |-a H 1'R^ o S'J ^3 ^0 S to M c Q < cy cu ^ ^7" g 330 5 'So ^2 3 " vc g* l CJ *-< '5i >H j !^ 1 6 s c5 S 6 \ >"a cu 3 2 1 55 fc S 3 5 3 5 ffi 3 -3 E ffl >_ 1 1 I i I 3 -3w -3 3^ scS C/2 C/] C/2 C/3 W K 1 1 , ,r"O ^ ^ c o> i g M> ^Oti^ d" S5 ^g j^^ 3 82| |. 3a ,| |o ^ 5J^a ^f-a^ | -^ 'i^gS - *? S 2 i -ill .^3 ^|"t 5|1i 13-S5 l?lSl l8l-l S ^ $ OQ rt u ^;j j en 05 l _ M _. | 1 1 ? 2 22 ^ t^ t 'U cq e N 10 2 up up ta J O ^ H N M ^d,^-* c/} 1 ^ ^ fe: oj-4 E CJ ^ W? Qj CuO " &C C^ 2 J U M ^ J g J J ^ & fe >^ ^J*-< ^HJH NO*-< (S| -i-t 1 |J S u o 5 ^ *e * ft. S gd ^ W) N . M row) d $ o . o, o\o, da ^ ^a 1 (fl IO d d ^ d ^ ^ E*Q< .S fO aT oT d oT R 1 S * "? (J u"" pis d b 1 2 .tj N > .t: * ^ "2 * '-^ * 1^1 |j |s |a |a 3 1 O?H g *J 2^7 to fe >fl rt 5%* ^ HH ^O O | fc IO O w f^ SfO oro ^fO l^rc ^ . . ? ^^ aJ r ^ _ 0*1 - W - . . P< . . . nJfflEE O ^ S W E K 0) ffiK^K KM HK ^'ffi ffiffi 592 ja.s '53 "5 "55 3 >> 3 to to 4> 32 11 Xylol Gray or White Gray or White Bright A. High Order High Order Spherulitic aggregates Laths. Ex., ||. Blue crystals. Ex. Obi. Laths Ex., || or polygons Ex. Sym. Aggregates Rhombs. Ex. Sym. High I. C. Trona Mirabilite Chalcanthite Nitre Soda Nitre 594 26. A. Crystal System: Name, Composi- tion, Hardness and Specific Gravity. Taste. On Charcoal. Closed Tube. I. Sal Ammoniac, 430, NH 4 C1 Saline White fumes White subl. H., 1.5 to 2 Sp. gr., 1.52 M. Alunogen, p. 4iS, Astringent Fuses, becomes Much water a Al 2 (S0 4 )3i8 H 2 infus. Deep blue S0 2 H., 1.5 to 2 Sp. gr., 1.6 to 1.8 with Co. sol. M. Melanterite, p. 270, Astringent Darkens becomes Like alunogennd FeSO 4 7H 2 O magnetic H., 2 Sp. gr., 1.9 O. Epsomite, P- 453, Bitter F. = i becomes Much acid water MgS0 4 7H 2 infus. Pink with H., 2 to 2. 5 Sp. gr., 1.7 Co. sol. O. Goslarite, p. 299, Astringent White subl. bright Water ZnS0 4 . 7H 2 green with Co. sol. H., 2 to 2.5 Sp. gr., 2.0 M. Copiapite, p. 270, Metallic, F. =4.5105 become Much acid water Fe 3 (OH) 2 (S04)6i8H 2 nauseous magnetic H.,2.5 Sp. gr., 3.1 H. Coquimbite, p. 270, Astringent Fuses becomes Like alunogen Fe 2 (S0 4 )s9H 2 magnetic H., 2 to 2.5 Sp. gr., 2.1 M. Kieserite, p. 453, Fuses Much water MgSO 4 .H 2 O H., 3 to 3-5 Sp. gr., 2.5 26. B. (CRUSHED FRAGMENTS.) Index of Refraction. Interference Color. Recrystallization in a Drop of Water. Name. Gray or White Aggregate Laths. Ex., ||. Spear points Epsomite Ex. Sym. Like epsomite Kieserite Gray or White Branching aggregates. Melanterite < Xylol Rhombic ends Gray or White Feathery. Ex., ||. Alunogen Aggregate Like epsomite Goslarite Black Aggregates Ibranching at 60 Sal Ammoniac and 90. Isotropic > Xylol Bright B. No recrystallization Copiapite Bright A. Precipitate on heating Coquimbite 27. A. Crystal System : Name, Composition, Hardness and Specific Gravity. Fusibility (on Coal). Closed Tube. Other Tests. Usual Color. M. Annabergite, p. 294, 4 Water See p. 191 forNi Pale green Ni 3 (AsO 4 )2+8H 2 O Pale green H., 1.5 to 2. 5 streak M. Erythrite, p. 292, 2 5 Water Borax deep blue. Crimson to pink C0 3 (As0 4 ) 2 .8H 2 0. F. and R. F. H., 1.5 to 2.5 Sp. gr., 2.9 Streak pink O. Olivenite, Cu 2 (OH)AsO 4 2 tO 2-5 Water Emerald green Olive green to H., 3 Sp. gr., 4.4 Fl. blackish H. Mimetite, p. 323, I 5 White Greenish yellow Yellow brown Pb 5 Cl(AsO 4 )s subl. subl. with Bi H.,3-5 Sp. gr., 7 Fl. 595 27. B. (CRUSHED FRAGMENTS.) Name. Index of Refraction. Interference Color. Other Notable Characters. < Methylene Iodide Aggregate Bright B. Greenish hairs or aggregate Laths. Pleochroic pink to red. Ex. about 32 Annabergite Erythrite > Methylene Iodide Gray or White to Bright A. Bright B. Irregular . Colorless, greenish Irregular. Green to yellow Mimetite Olivenite xB. A- Crystal System : Name, Composition, Hardness and Specific Gravity. Fusibil- ity (on Coal). Closed Tube. Other Tests. Usual Color. O. Orpiment, p. 330, As2Ss H., 1.5 to 2 Sp. gr., 3.4 to 3-6 M. Realgar, p. 329, AsS H., 1.5 to 2 Sp. gr., 3.4 to 3.6 H. Proustite, p. 388, Ag 3 AsS 3 H., 2 to 2.5 Sp. gr., 5.6 to 5.7 I I I Boils. Trans- parent yel- low subl. Boils. Subl. black hot, red cold Fuses. Slight red subl. yel- low cold Sol. HNOs resi- due S. Streak lemon yellow Sol. HN0 3 . Streak orange red Sol. HNOs. Streak scarlet Lemon yellow Orange red Ruby red 28. B. (CRUSHED FRAGMENTS.) Name. Index of Refraction. Interference Color. Other Notable Characters. > Methylene Iodide Bright B. or masked Bright B. or masked Masked Micaceous plates or irregular Irregular. Yellow to orange Irregular. Brownish orange Orpiment Realgar Proustite 29. A. Crystal System : Name, Composition, Hardness and Specific Gravity. Fusibil- ity (on Coal). Closed Tube. Other Tests. Usual Color. O. Cerussite, p. 323, PbCOs H., 3 to 3-5 Sp. gr., 6.5 to 6.6 T. Phosgenite, p. 324, (PbCl) 2 C0 3 H., 3 Sp. gr., 6 . Bismutite, p. 327, BiO.Bi(OH) 2 C0 3 H., 4.4 Sp. gr., 6.9 1-5 I. i-S Dark yellow subl. Fusible sublimate Water Greenish yellow with Bi flux Like cerussite Chocolate and red with Bi Flux Colorless to white Colorless to white White to yellow 29. B. (CRUSHED FRAGMENTS.) Name. Index of Refraction. Interference Color. Other Notable Characters. > Methylene Iodide ? . Bright A. to B. High Order ? Rectangular. Ex., ||, El., (+) Irregular or needles with Ex., Phosgenite Cerussite Bismutite 596 30. A. Crystal System: Name, Composition, Hardness and Specific Gravity. Fusibil- ity (on Coal.) Closed Tube. Other Tests. Usual Color. M. Kermesite, p. 335. I Blackens, Vol. white subl. Cherry red Sb 2 S 2 O fuses, dark coal. Brown, H., i to 1.5 red subl. red streak Sp. gr., 4.5 to 4.6 O. Valentinite, p 335. 1.5 Fuses, part- Vol. white subl. White Sb 2 3 1 y s u b - coal. Fibrous H., 2.5 to 3 Sp. gr., 5.6 limes I. Senarmontite, p. 335. 1-5 As above Vol. white subl. White Sb 2 3 Octahedra H., 2.5 to 3 Sp. gr., 5.2 . Bismite, p. 327, Bi 2 O 3 i.S(?) Water Erf n coal White H., Sp. gr., 4.3 M. Crocoite, p. 346, 1.5 KHSO 4 Pb* on coal. Orange red PbCr0 4 dark vio- S. Ph. green. H., 2.5 to 3 let hot, Streak orange Sp. gr., 5.9 to 6.1 green ish cold T. Wulfenite, p. 350. 2 Darkens, Pb* on coal. Yellow red gray PbMo04 decrepi- Mo p. 190 H., 3 Sp. gr , 6.7 to 7 tates H. Vanadinite, p 338, 1.5 Pb* on coal. Red brown yel- PbbCUVOOs V. p. 196 low H., 3 Sp. gr., 6.6 to 7.8 O. Descloizite, p. 339, 3-5 Water Pb* on coal. Black, brown (PbOH)V0 4 (Pb,Zn) V. p. 196 H., 3.5 Sp. gr., 5.9 to 6.2 H. Pyromorphite p. 322, 2 On coal recrys- Green, yellow Pb 5 Cl(P04)3 tallizes, Pb*. gray H., 3.5 to 4 P. p. 204 Sp. gr., 5-9 to 7.1 . Minium, p. 321, Pb 3 O4 1.5 Pb* on coal Red H., 2. to 3 Sp. gr., 4.6 30. B. (CRUSHED FRAGMENTS.) Index of Refraction. Interference Color. Other Notable Characters. Name. Bright B. Needles. Ex., || Valentinite Black Irregular Senarmontite Gray or White Irregular. Colorless to green Pyromorphite to Bright A. Bright B. Irregular or Laths. Yellow Vanadinite > Methylene to orange Iodide Bright B. Irregular. Brown to green- Descloizite ish Bright B. Irregular. Pleochroic, yellow Crocoite to orange High Order Irregular. Yellow Wulfenite Masked Needles. Ex., ||, pleochroic, Kermesite ruby red j> ? Minium ? ? Bismite * On coal with Bi Fl, greenish yellow subl. t On coal with Bi Fl, chocolate and red. 597 31. A. Crystal System: Name, Composition, Hardness and Specific Gravity. Fusibil- ity (on Coal;. Closed Tube and KHSO 4 . Usual Color. Hot. Cold. Sunlight. H. lodyrite, p. 392, Agl H., 1.5 Sp. gr., 5-6 to 5.7 I. Cerargyrite, p. 391, AgCl H., 2 to 3 Sp. gr., 5 to 5.5 I. Bromyrite, p. 392, AgBr H., 2 to 3 Sp. gr., 5.8 to 6 I. Embolite, p. 39 2 , Ag(Cl.Br) H M 2 to 3 Sp. gr., 5.3 to 5.8 H. Pyrargyrite, p. 389, AgsSbSs H., 2.5 Sp. gr., 5.8 M. Linarite, p. 322, [(PbCu)OH] 2 S0 4 H., 2.5 Sp.gr., 5.3 to 5.4 O. Anglesite, p. 321, PbSO4 H., 3 Sp. gr., 6.1 to 6.4 T. Cassiterite, p. 307, SnO 2 H., 6 to 7 Sp. gr., 6.8 to 7.1 I I I I I 1-5 2-5 7 Deep red Yellow Dark red Dark red Yellow Yellow White Violet Yellow Green Yellow Green Lemon yellow Pearl gray to colorless Green or yellow Green or yellow Dark red to black Azure blue Colorless or white Brown to black Closed Tube. On Charcoal. Fuses. Subl. black hot, red cold Whitens yields water Decrepi- tates White and later pink. In R.F. disappears With Bi.Fl yellow subl. and green Fl With Bi. Fl yellow subl. With soda white subl. bluish green with Co. sol. 31. B. (CRUSHED FRAGMENTS.) Name. Index of Refraction. Interference Color. Other Notable Characters. > Methylene Iodide Black Black Black Black Gray or White to Bright A. Bright B. High Masked Irregular Irregular. Greenish Irregular Irregular. Yellowish Irregular Laths. Ex., |[. Blue Irregular. Colorless to pleo- chroic yellow Irregular. Dark red Cerargyrite Embolite Bromyrite lodyrite Anglesite Linarite Cassiterite Pyrargyrite 32. A. Crystal System : Name, Composition, Hardness and Specific Gravity. Fusibil- ity. Closed Tube. The Sublimate on Charcoal. Usual Color. . Hydrozincite, p. 30, Zn 3 CO 3 (OH) 4 H., 2.5 Sp. gr., 3.6 to 3.8 H. Greenockite, p. 303, CdS H., 3 to 3. 5 Sp. gr., 4.9 to 5 I. Sphalerite, p. 298, ZnS H., 3.5 to 4 Sp. gr., 3.9 to 4.1 H. Smithsonite, p. 300, ZnCOs H., 5 Sp. gr., 4.3 to 4.5 7 7 7 7 Yellow hot yields water Carmine hot, yellow cold Yellow hot, if pure White non vol. Bright green with Co. sol. Brown. Often iris tarnish Like hydro- zincite Like hydro- zincite Chalk white Bright yellow Brown to yellow Brown to nearly white 598 32. B. (CRUSHED FRAGMENTS.) Name. Index of Refraction. Interference Color. Other Notable Characters. < a Monobrom- Napthalin Black or Bright A. Irregular or Laths with Ex., ||. El. <+) Hydrozincite > a. Monobrom- Napthalin Black p High Order Triangles and irregular. Yel- low. Cleav. at 60, 90 Yellow Rhombs with Ex., Sym. or Ir- regular Sphalerite Greenockite Smithsonite 33. A. Crystal System: Name, Composition, Hardness and Specific Gravity. Fusi- bility. Closed lube. The Sublimate on Charcoal. Usual Color. O. Calamine, p. 301, (ZnOH) 2 SiO 3 H., 5 Sp. gr., 3.4 to 3.5 H. Willemite, 301, Zn 2 SiO 4 H., 5.5 Sp. gr., 3.9 to 4.2 6 5-5 Water White non vol. bright green with Co. sol. Like calamine White, yellow Yellow, brown, greenish 34. A. O. Molybdite, 350, MoO 3 H., i to 2 Sp. gr., 4.5 H. Zincite, p. 299, ZnO H., 4.5 Sp. gr., 5.4 to 5.7 2(?) 7 Blackens White. Deep blue by R. F. Like calamine Yellow Deep to brick red 35. A. T. Calomel, p. 377, Hg 2 Cl 2 H., i to 2 Sp. gr., 6.5 O. Sulphur, p. 463, S Vol. i Mirror with soda Fusible subl. White volatile None, but White, colorless Yellow brown T. Calomel, p. 377, Hg 2 Cl 2 Vol. Mirror with White volatile White, colorless H., i to 2 Sp. gr., 6.5 soda O. Sulphur, p. 463, S i Fusible subl. None, but Yellow brown H., 1.5 to 2.5 brown hot strong SO 2 Sp. gr., 2.0 to 2.1 yellow cold fumes H. Cinnabar, p. 376, HgS Vol. Mirror with None Vermilion, scar- H., 2 to 2.5 Sp. gr., 8.1 soda let, red I. Gahnite, p. 302, ZnAlOi Unchanged Weak but like Green, brown, H., 7.5 to 8 Sp. gr., 4 to 4 7 calamine black 33. B. (CRUSHED FRAGMENTS.) Index of Refraction. Interference Color. Other Notable Characters. Name. < a Monobrom- Bright B. Laths. Ex., ||. El. (+) Calamine Napthalin > Monobrom- Bright A. to B. Irregular. Colorless to Willemite Napthalin brown 34. B. > Methylene Iodide Masked Laths or irregular. Yellow to orange Minute needles, Ex., I Zincite Molybdite 35. B. > Methylene Iodide Masked High Order Black Hi.eh Order Irregular. Brilliant red Rhombs and rectangles Irregular Cinnabar Calomel Gahnite Sulphur 599 36. A. Crystal System : Name, Composition, Hardness and Specific Gravity. Fusibil- ity. Closed Tube. Streak. Usual Color. H. Siderite, p. 275, FeCO 3 H., 3-5 to 4 Sp. gr., 3.8 to 3.9 5 Black mag- netic Nearly white if pure Light to dark brown. Cleav- able or granular 37. A. M. Vivianite, p. 472, 2 to 2. 5 Water. Blue Bluish green Fe 3 (P04) 2 +8H 2 (Turns earthy to H., 1.5 to 2 brown) blackish blue Sp. gr., 2.6 to 2.7 crystals . Garnierite, p . 294, 7 Water de- Pale green Deep green to H 2 (Ni,Mg)Si04+H 2 crepitates pale green H., 2 to 3 Sp.gr., 2.3 to 2. 8 . Limonite, p. 274. 5 to 5. 5 Much water. Yellowish brown Yellowish brown Fe 2 03.Fe 2 (OH) 6 Reddens to nearly black. H., 5 to 5.5 Sp. gr., 3.6 to 4 i Not crystals O. Goethite, p. 273, 5 to 5.5 Water. Yellowish brown Yellowish brown FeO(OH) Reddens to nearly black. H., 5 to 5. 5 Sp.gr., 4 to 4.4 Often crystals . Turgite, p. 274, StoS-S Flies to Brownish red Red to black Fe 4 6 (OH) 2 pieces. crusts H., 5.5 to 6 Water Sp. gr., 4-3 to 4.7 H. Hematite, p. 271, Fe 2 O 3 7 Brownish red Dull dark red H., 5.5 to 6.5 Sp. gr., 4-9 to 5.3 36. B. (CRUSHED FRAGMENTS.) Index of Interference Name. Refraction. Color. Other Notable Characters. > Methylene Iodide High Order Rhombs. Ex. Sym. Index |j short diag. closely Siderite that of methvlene iodide 37. B. < Methylene Iodide Gray or White. Aggregate Bright B. Irregular. Greenish Laths. Ex., ||. El., (+) or Ex, 30 El., ( -). Pleochroic blues or colorless Garnierite Vivianite > Methylene Iodide Bright B. High Order ? Masked Yellow fibres, Ex., Obi., and irregular, opaque Laths Ex. , 1 1 . Pleochroic yel- low Irregular. Opaque Dark red or opaque Limonite Goethite Turgite Hematite 600 38. A. Crystal System : Name, Composition, Hardness and Specific Gravity. Fusibil- ity. Flame Coloration. Other Tests. Usual Appearance. M. Gaylussite, p. 427, i-5 Yellow Closed tube White crystals CaNa2(C0 3 )25H 2 water H., 2 to 3 Sp. gr., 1.9 O. Witherite, p. 433, 2 Yellowish Solution gives White columnar BaCOa green ppt with H 2 SO 4 and pseudo- H., 3 to 4 Sp. gr., 4.3 hexagonal H. Cancrinite, p. 570, 2 Yellow Jelly on heating Yellow or white R(Na 2 C0 3 )(Si0 4 ) solution massive H., 5 to 6 Sp. gr., 2.4 39. A. O. Thomsonite, p. 534, 2 I n t u mesces. White radiated (Na 2 Ca)Al2Si20 8 +sH 2 Much water or green spher- H., 5 to 5.5 Sp. gr., 2.4 ical M. Pectolite, p. 535, 2 Yellow Water in closed White radiating HNa 2 Ca(SiO 3 )3 tube fibres H., 5 Sp. gr., 2.7 M. Wollastonite, P- 507. 4 Red Often effervesce White semi- CaSiOs from calcite fibrous or gray H., 4.5 to 5 Sp. gr., 2.8 crystals I. Lazurite, p. 576, 3-5 Yellow Blue in fine Deep blue, usu- Na 4 (NaS 3 Al) Al 2 (SiO 4 ) 3 powder. Odor ally spangled H., 5 to 5.5 Sp. gr., 2.4 H 2 S with acid with pyrite H. Chabazite, p. 532, 3 I ntu mesces Nearly cubic; (CaNa2)Al(Si0 4 ) 3 6H 2 Striated. H., 4.5 Sp. gr., 2.O tO 2.1 White and pink T. Apophyllite, p 534. 2 Pale violet One easy cleav- Colorless cubic Hi 4 K 2 Ca 8 (SiO 3 )i69H 2 O (Color age. Exfoliates or pointed H., 4.5 to 5 Screen) during fusion crystals with Sp. gr., 2.3 to 2.4 opalescence in direction c 38. B (CRUSHED FRAGMENTS.) Index of Refraction. Interference Color. Other Notable Characters. Name. < Bromoform Bright A. Plates or Laths. Ex., || Cancrinite > Bromoform High Order Plates or Laths with Ex., ||. Witherite El., (-). 39. B. < Bromoform Black Gray or White Gray or White Gray or White to Bright A. Blue included particles Rectangular. Ex., |j or iso- tropic with uniaxial I. F. Rhombs. Ex. Sym. Laths. Ex., H Lazurite Apophyllite Chabazite Thomsonite > Bromoform Gray or White Bright A. Laths or Needles. Ex. ||. El., (+) Needles. Ex., ||. El., (+) Wollastonite Pectolite 601 40. A. Crystal System: Name, Composition, Hardness and Specific Gravity. Fusi- bility. Flame Coloration. Other Tests. Usual Appearance. M. Gypsum, p. 443. 3 to 3. 5 Yellowish Cleaves to a Colorless "sele- CaS0 4 +2H 2 red rhombic plate nite." White H. f i. 5 to 2 Sp. gr., 2.3 of 66. Solu- or tinted scaly tion recrystal- or fibrous lizes masses M. Cryolite, p. 412, 1-5 Yellow Blue if ignited Translucent re- AlNa 3 F 2 with Co. sol. sembling H., 2.5 Sp. gr., 2.9 to 3 watery snow O. Anhydrite, p. 442, 3 to 3-5 Yellowish Cleaves three Blue and white. CaS0 4 red directions at Cleavable and H., 3 to 3-5 Sp.gr., 2.9 to 3 90 fine-grained M. Heulandite, p. 534. 3 Swells withheat. White or red H 4 CaAl 2 (Si03)6+3H 2 Lozenge shaped crystals H., 3.5 to 4 Sp. gr., 2.2 pearly face M. Stilbite, p. 533, 3 Swells greatly Sheaf -1 i ke H 4 R 2 Al 2 (SiO3)6 +4H 2 O during fusion. groups or many H., 3-5 to 4 Symmetrical small brown or Sp. gr., 2.1 to 2.2 pearly face white crystals I. Fluorite, p. 441, CaF2 3 Red to Phosphorescent. Glassy cubes of H., 4 Sp. gr., 3 to 3.3 orange Cleavages at purple yellow 70 3 1' and green M. Harmotome, p. 534, 3 Whitens before White or color- (BaK 2 )Al 2 Si 5 Oi 4 .5H 2 O fusing less crossed H., 4-5 Sp. gr., 2.5 twins T. Wernerite, group p.5i5, 3 Yellow Bubbles in fused Gray and green- (Silicates of NaCaAl) material. Clea- ishoctagonalor H., 5 to 6 Sp. gr., 2.7 vages at 90 square prisms O. Prehnite, p. 535, 2-5 Intumesces. Green rounded H 2 Ca 2 Al 2 (Si0 4 ) 3 Bubbles in crusts or sheaf- H., 6 to 6.5 Sp.gr., 2. 8 to 2.9 fused material like groups I. Boracite, p. 458, 3 Yellowish Violet if ignited Minute glassy Mg7Cl 2 Bi 6 O 3 o green with Co. sol. crystals H., 7 Sp. gr., 2.9 to 3 40. B* (CRUSHED FRAGMENTS.) Index of Refraction. Interference Color. Other Notable Characters. Name. Black Polygons 3, 4, 5 or 6-sided, Fluorite Xylol Gray or White Laths. Ex., j|. El., (-) Stilbite < Bromoform to Bright A. Bright B. Rectangles. Ex., |[. Diag- Anhydrite onal striations Bright B.or Laths. Ex., ||. El., (-). Wernerite High Order Inclusions Bright A. Laths. Ex., ||. El., (-) Prehnite > Bromoform Bright A. and irregular Irregular Boracite Bright B. See above Anhydrite 602 41. A. Crystal System : Fusibil- Flame Name, Composition, ity. Coloration. Other Tests. Usual Appearance. Hardness and Specific Gravity. M. Lepidolite, p. 429, 2 Crimson Acid water in Lilac or pink (KLi) 3 Al(SiO 3 ) 3 closed tube. scaly masses or H., 2.5 Sp.gr., 2.8 to 3.2 Easy cleavage gray plates O. Barite, p. 432, BaSO 4 4 Yellowish Cleaves to White and and H., 2.5 to 3-5 green rhombic plates tinted crys- Sp. gr., 4.3 to 4.6 of 78. Heavy tals and masses O. Celestite, p. 435, SrSO 4 3-5to4 Crimson Cleaves to Pale blue white H., 3 to 3.5 Sp.'gr., 4 rhombic plates crystals and of 76. Heavy fibrous M. Amphibole, (tremolite), 4 Cleavage and White fibrous p. 508, CaMg 3 (SiO 3 ) 4 prism 124 30' radiating or H.,5to6 Sp.gr., 2.9 to 3.4 prisms M. Pyroxene, (diopside). 4 Cleavage and White or green p. 506, CaMg(SiOs) 2 prism 87 51 inclined 8- H., 5 to 6 Sp.gr., 3. 2 to 3.6 sided prisms O. Zoisite, p. 528, 3 to 3 5 Swells and fuses Gray brown col- Ca 2 (AlOH)Al 2 (SiO 4 ) 3 to bubbly umnar. One H., 6 to 6.5 Sp. gr., 3.3 glass easy cleavage M. Petalite, p. 430, 4 Crimson Phosphorescent Colorless or LiAl(Si 2 5 ) 2 on heating white cleav- H., 6 to 6.5 Sp. gr., 2.4 able Tri. Plagioclase, p. 494, 4 to 4 5 Yellow Cleavage 87 White, gray, See 44-A. approx. red. Striated Tri. Amblygonite, p. 428, 2 Crimson to Momentary White masses Li(AlF)PO 4 yellowish blue-green Fl. with one easy II., 6 Sp. gr., 3 to 3.1 red with H 2 SO 4 cleavage H. Tourmaline, p. 524, 3-5 Green with Electric by heat Brown prisms Ri 8 B 2 (Si0 6 ) 4 KHSO 4 or friction often trigonal H., 6 to 6.5 +CaF 2 and hemimor- Sp. gr., 2.8 to 2.9 phic M. Spodumene, p. 429, 3-5 Crimson Sprouts during White, green and LiAl(Si0 3 ) 2 fusion. Cleav- pink crystals H., 6.5 to 7 age at 87 often lamellar Sp. gr., 3.1 to 3.2 41. B. (CRUSHED FRAGMENTS.) Index of Interference Refraction. Color. Name. Other Notable Characters. Laths and Plates. Twinning Plagioclase Gray or W T hite < Bromoform to Bright A. See p. 491 for varieties Petalite Bright A. to B Plates Amblygonite Rectangular, Ex., || ; or rhom- Barite bic, Ex. Sym.; or irregular > Bromoform G rWhite t^gSStr. to Bright A/ Like barite Plates and Rhombs. Biax. Laths or fibres. Ex. Obi. Celestite Lepidolite Amphibole El. (+). See p. 502 Irregular Tourmaline Gray or White Plates Zoisite >a-Monobrom- ^ \J ite Laths. Ex., 2o-25 El., ( +) Spodumene , T , , ,. to Bright A. Naphthalm Brjght A tQ B Laths and Rhombs. Ex. Pyroxene Obi. see p. 502 603 42. A. Crystal System: Name, Composition, Hardness and Specific Gravity. Fusibil- ity. Flame Coloration. Other Tests. Usual Appearance. H. Nephelite, p. 499. 4 Yellow Blue with Co. Gray or reddish, NaAl8SiOs4 sol. greasy massive. H., 5 5 to 6 Also smal) Sp. gr., 3-2 to 3.6 white prisms - O. Natrolite, p. 532, 2-5 Yellow Quiet fusion White needles Na 2 Al 2 Si3Oio nearly .square H., 5 to 5-5 Sp. gr., 2.2 with flat pyra- midal ends I. Analcite, p. 531, 3 Yellow Becomes opaque White or color- NaAl(SiO 3 )2.H 2 O before fusion less trapezohe- H., 5 to 5-5 dra Sp. gr., 2.2 to 2.3 M. Datolite, p. 536, 2 tO 2. 5 Green Intumesces Bright colorless Ca(BOH)Si0 4 complex crys- H., 5 to 5-5 Sp. gr., 2.9 to 3 tals. Porcelain masses I. Sodalite, p. 500 3-5 to4 Yellow Closed tube Gray, blue, etc. Na.Al.Cl.Si whitens massive and H., 5.5 to 6 Sp gr., 2.2 crystals 43. A, . Ulexite, p. 457, CaNaB 5 O9.8H 2 O H., i Sp. gr., 1.65 M. Colemanite, p. 458, Ca 2 B 6 On.5H 2 O H., 4 to 4.5 Sp. gr., 2.2 to 2.3 Tri. Plagioclase, p. 494, wNaAlSisOs +mCaA! 2 Si 2 8 H., 5 to 6.5 Sp. gr., 2.5 to 2.8 i 5 1-5 4 to 4.5 Reddish yellow Green Yellow Solutions de- posit crystals of sassolite Two easy cleav- ages (86, 87, etc.). Varie- ties by scheme P- 491 White fibres in " Cotton balls" Colorless com- plex crystals. White, chalky or porcelain W T hite, gray, red- dish, cleavable, striated 42. B. (CRUSHED FRAGMENTS.) Name. Index of Refraction. Interference Color. Other Notable Characters. Equal Xylol Black or Gray or White Black Gray or White to Bright A. Irregular glassy Needles and Laths. Ex., ||. El. (+) Analcite Sodalite Natrolite > Xylol < Bromoform Gray or White Irregular or Laths with Ex., ||. El. (-) Nephelite > Bromoform Bright B. Irregular Datolite 43. B. < Bromoform Gray or White Gray or White or Bright A. Fine needles. Ex., ||. (-) Plates and Laths. Ex. see p. El. Obi. Ulexite Plagioclase Equal or > Bromoform Bright A. Plates Colemanite 44. Certain work out here. varieties of Plagioclase, Amphibole, Pyroxene and Spodumene may In this case use 41. A. and B. 604 45. A. Crystal System : Name, Composition, Hardness and Specific Gravity. Fusi- bility. Flame Coloration. Other Tests. Usual Appearance. M. Malachite, p. 37i. 3 Green, blue Closed tube, Bright green Cu 2 (OH) 2 CO 3 with HC1 black much fibrous in- H., 3. 5 to 4 Sp.gr., 3.9 to 4 water crusting or dull M. Azurite, p. 371, 3 Like mala- Like malachite. Dark-blue glassy Cu 3 (OH) 2 (C0 3 ) 2 chite Streak blue crystals, velvety H., 3-5 to 4 Sp. gr., 3.8 or dull crusts 46. A. T. Mellilite, p. 499, 3 Intumesces White or yellow- Complex Silicate ish small H., 5 Sp. gr., 2.9 to 3.1 square prisms M. Allanite, p. 529, 2-5 Swells, becomes Black "nail 1 ' or "Cerium Epidote" magnetic plate crystals H., 5. 5 to 6 Sp.gr., 3-5 to 4 O. Tephroite, p. 285, 3-5 Amethyst borax Ash gray to red- Mn 2 SiO 4 bead dish masses H., 5.5 to 6 Sp. gr., 4.1 45. B. (CRUSHED FRAGMENTS.) Index of Refraction. Interference Color Other Notable Characters. > Methylene Tr>HiHf Masked Masked Irregular. Blue Laths. Ex. Obi. Arrowhead Azurite Malachite twins. Green 46. B. < a-Monobrom- Gray or White Plates Melilite Naphthalin Bright B. Irregular. Brown, pleochroic Allanite > Methylene High Order Plates. Pleochroic Tephroite Iodide 47. A. Crystal System . Name, Composition, Hardness and Specific Gravity. Fusibil- ity. Flame Coloration. Other Tests. Usual Appearance. O. Autunite, p. 345, 3 Yellowish Borax colorless Yellow square Ca(U0 2 ) 2 (P0 4 ) 2 +8H 2 red O. F., green plates scales H., 2 to 2. 5 Sp.gr, 3 to 3. 2 R F. See p. and aggregates T95 T Torbernite, p. 345, 3 Azure blue Borax green O Pearly green Cu(UO 2 ) 2 (PO 4 ) 2 +8H 2 O with HC1 F. red R. F. plates H., 2 to 2.5 Sp. gr., 3.4 to 3.6 t O. Atacamite, p. 370, 3 to 4 Azure blue White and red Emerald-green, Cu 2 (OH) 3 Cl sublimates aggregates and H., 3 to 3-5 prisms Sp. gr., 3.7 to 3-8 O. Brochantite, p. 370, 3-5 Green, blue Fused with soda Emerald-green CuSO 4 .3Cu(OH) 2 with HC1 stains silver needles and H., 3.5 to 4 Sp. gr., 3.9 crusts I. Cuprite, p. 368, Cu 2 O 3 Azure-blue Streak brownish Dark-red H., 3.5 to 4 with HC1 red masses and Sp. gr., 5.8 to 6.1 crystals or hair-like 605 47. B. (CRUSHED FRAGMENTS.) Name. Index of Refraction. Interference Color. Other Notable Characters. < Bromoform Gray or White Plates. Pale yellow Autunite > Bromoform < a-Monobrom- Naphthalin Black Bright A. Rectangles. Uniax. Green Laths. Ex., ||. EL, ( ) or Irregular Torbernite Prehnite > Methylene Iodide Black Bright A. Masked Irregular or Needles- Red Laths. Ex., ||, El., (+). Green Plates or Laths. Ex., ||. Green Cuprite Brochantite Atacamite 48. A. Crystal System : Name, Composition, Hardness and Specific Gravity, Fusibility. Flame Colora- tion. Other Tests. Usual Appearance. M. Roscoelite, p. 340, 3 S. Ph. 0. F yel- Dark green "Vanadium Mica" low R. F. green scales H., 2 ? Sp. gr., 2.9 . Crocidolite,p.509,NaFeSi 3-5 Yellow After fusion is Blue fibres H., 4 Sp. gr., 3.3 magnetic M. Titanite, p. 525, 4 S. Ph. O.F. then Brown or green CaSiTiOs R. F. violet "e n vel o pe" H., 5 to 5-5 Sp.gr., 3.4 to 3.5 Cleavages 113 and wedge shaped crystals M. Pyroxene, p. 505, 4 Cleavage and Green to black RSiOs. Many varieties prism angles inclined prisms H., 5 to 6 Sp. gr., 3.2 to 3.6 87 5' Cross section 8-sided. M. Amphibole, p. 507, 4 Cleavage and Green to black RSiOs. Many varieties prism angles fibrous or pris- H., 5 to 6 Sp. gr., 2.9 to 3.4 124 30' m a c i c with rhombic or six- sided section. O. Hypersthene, p. 505, 5 After fusion is Black foliated (Mg.Fe)SiO 3 magnetic sometimes H., 5 to 6 Sp. gr., 3.4 to 3.5 pearly Tri. Rhodonite, p. 284, 3 to 3.5 Borax, O. F. Red or brown MnSiOs amethystine fine-grained or H., 6 to 6.5 Sp.gr., 3.4103.7 cleavable. M. Epidote, p. 528, 3 to 4 After fusion will Pistache or Ca 2 (Al.Fe) 2 (A1OH) (SiO 4 ) 3 gelatinize blackish green H., 6 to 7 Sp. gr., 3.2 t. 3.5 Water in closed grains or tube needles T. Vesuvianite, p. 511, 3 After fusion will Brown, or green Ca 2 Al 3 (Oh.F) (Si0 4 ) 2 gelatinize. square prisms H., 6.5 Sp. gr., 3.3 to 3.4 Water in closed or columnar or tube compact Tri. Axinite, p. 570, 2 to 3 Green Intumesces Brown or violet. H 2 R 4 (BO)Al 3 (Si04) 5 with "Axe" shaped H., 6.5 to 7 Sp. gr., 3.3 Bo. Fl. I. Garnet, p. 509, 3 to 4 After fusion will Brown or red 12, R3R 2 (Si0 4 ) 3 gelatinize. Often 24 and 36 faced H., 6.5 to 7.5 nearly spherical crystals Sp. gr., 3.1 to 4.3 H. Tourmaline, p. 524, 3 to 5 Green After fusion will Black opaque, RBi(SiO B )< with gelatinize. Often brown, and H., 7 to 7.5 Sp.gr., 3 to 3 2 Bo. Fl. roughly tri- bright colored angular prisms 606 48. B. (CRUSHED FRAGMENTS.) Name. Index of Refraction. Interference Color. Other Notable Characters. < a-Monobrom- Naphthalin Gray or White to Bright A. Bright A. to B. Irregular. Pleochroic black to smoky Laths. Ex., 10 20. El. (+) Pleochroic green to yellow Pleochroic green to yellow Pleochroic green to brown Tourmaline, (Dark Varieties) Amphibole, see p. 502 Actinolite Pargasite Hornblende > a-Monobrom- Naphthalin < Methylene Iodide Gray or White Gray or White Bright A. Bright A. to B. Bright B. Irregular Irregular Laths. Ex., 10, El. (+) Laths and Rhombs. Ex., 30 to 54. Rarely pleochroic Pleochroic. Brown. Ex., o to 10. El. (+) Axinite Vesuvianite Rhodonite Pyroxene, see p. 502 Hedenbergite, Augite Amphibole, Basaltic Horn- blende > Methylene Iodide Black Bright B. High Order Abnormal Apple Green Irregular. Tinted reddish, brownish, etc. Pleochroic green, yellow. Ir- regular Pleochroic brown or colorless. Plates Plates, pleochroic in greens Garnet, most varieties Epidote Titanite Roscoelite 49. A. Crystal System: Flame Name, Composition, Hardness Fusibility. Colora- Other Tests. Usual Appearance. and Specific Gravity. tion. O. Strontianite, p. 436, 5 Crim- Sprouts and White or tinted SrCO 3 son glows intensely columnar or H., 3 to 3-5 Sp. gr., 3.7 during fusion compact M. Barytocalcite, p. 433, 5(?) Yellow- Pale green after White or tinted (Ba.Ca)CO ish fusion masses and H., 4 Sp. gr., 3.6 green crystals 50. A. . Sepiolite, p. 546, 5 Pink ignited White smooth H4Mg 2 Si 3 Oio with Co. Sol. feeling, light H., 2 to 2.5 Sp. gr., i to 2 masses. Rare- ly fibrous M. Wollastonite, p. 507, 4 Yellow- Often efferves- White to gray CaSiOs red ces fibrous to com- H., 4 to 5 Sp. gr., 2.8 to 2.9 pact masses. Rarely crystals Tri. Anorthite, p. 494, 5 Yellow- Cleavage angle Colorless or gray CaAl 2 Si 2 O 8 red 86 crystals and H., 6 to 6.5 Sp. gr., 2.75 compact 607 51. A. Crystal System : Name, Composition, Hardness and Specific Gravity. Fusibility Flame Colora- tion. Other Tests. Usual Appearance. M. Biotite, p. 540, (H.K) 2 (Mg.Fe) 2 Al 2 (SiO 4 )3 H., 2.5 to 3 Sp. gr., 2.7 . Serpentine, p. 544, H 4 Mg3Si2O 9 H., 3 to 4 Sp. gr., 2.5 to 2.6 H. Apatite, p. 470, Ca 6 (Cl.F) (P0 4 ) 3 H., 4.5 to 5 Sp. gr., 3.2 T. Scheelite, p. 353, CaWO 4 H., 4.5 to 5 Sp.gr., 5.9 to 6. i O. lolite, p. 529, H 2 (Mg,Fe) 4 Al 8 Sii 037 H., 7 to 7.5 Sp. gr., 2.6 5 5 to 5.5 5 5 5 to 5-5 Yellow- ish red Pale red Cleaves to thin elastic plates Pink if ignited with Co. Sol. Easy solution P. test p. 191 S. Ph. 0. F. colorless to white. R. F. deep blue A little water in closed tube Black "mica" rarely in large sheets Mottled yellow, green, -feeble lustre or silky Green, red and white prisms. Resinous lustre. White compact Heavy yellowish masses, resin- ous lustre. Square pyra- mids Like blue or purple quartz. Often altered 49. B. (CRUSHED FRAGMENTS.) Name. Index of Refraction. Interference Color. Other Notable Characters. < a-Monobrom- Naphthalin High order Laths. Ex., H. El. ( ) Strontianite > a-Monobrom- Naphthalin High order Laths. Ex. Obi. Barytocalcite 50. B. (CRUSHED FRAGMENTS.) < Bromoform Gray or White Aggregate Gray or White to Bright A. Fibres. Ex., ||. El. (+) or irregular Laths. Ex., 35 40 Sepiolite Anorthite > Bromoform Gray or White Laths or Needles. Ex., ||. El. (+) Wollastonite 51. B. (CRUSHED FRAGMENTS.) < Bromoform Gray or White. Aggregate Gray or White Gray or White to Bright A. Fibres. Ex., |l. El. (+). or irregular Pleochroic if colored Serpentine Chrysotile Antigorite Biotite lolite > Bromoform < Methylene Iodide Gray or White Irregular. Ex., || cleavages Apatite : > Methylene Iodide Bright A. Irregular Scheelite 608 52. A Crystal System: Name, Composition, Hardness and Specific Gravity. Fusibility. Other Tests. Usual Appearance. O. Talc, p. 545. H 2 Mg 3 (SiO3)4 H., i to i. 5 Sp. gr., 2.5 to 2.9 . Pyrophyllite, p. 548, HAl(Si0 3 ) 2 H., i to 2 Sp. gr., 2.8 to 2.9 Chlorite Group, p. 541, H., i to 2. 5 Sp. gr., 2.6 to 2.9 Mica Group, p. 537, H., 2 to 3 Sp. gr., 2.7 to 3 M. Orthoclase, p. 492, (or Microcline), KAlSisOs H., 6 to 6.5 Sp. gr., 2.5 to 2.6 O. Enstatite-Hypersthene, p. 504, (Mg.Fe)SiOs H., 55 Sp. gr., 3.1 to 3-3 O. Anthophyllite, p. 507, (MgFe)SiOs H., 5. 5 to 6 Sp.gr., 3^1 to 3. 2 H. Tourmaline, p. 524, Ri 8 B 2 (Si0 5 )4 H., 7 to 7.5 Sp. gr., 3 to 3.2 H. Beryl, p. 522, BesAUCSiOOe H., 7. 5 to 8 Sp. gr., 2.6 to 2.8 5 to 5.5 5 to 5-5 4 to 5 5 to 6 5 to 6 5 5 to 5-5 Pink with Co. Sol. Soapy feeling Blue with Co. Sol. Much water in closed tube. Cleave to non- elastic plates Water at high heat closed t ube . Cleave to elastic plates Violet flame (color screen). Cleavage 90. Rarely striated After fusion is mag- netic Green Fl. with Bo. Fl. After fusion will gelatinize Often white on fu- sion White greenish or gray foliated com- pact and fibrous Radiated foliae or fibres and compact masses Dark green, rarely red, coarse and fine scales and crystals Black, amber, gray, etc., scales and pseudohexagonal crystals Flesh red, white, gray, etc. Cleav- ages and crystals common Gray, brown, black lamellar to fibrous, pearly metalloidal Gray to green lamel- lar and fibrous Red, blue, colorless, etc., prisms often triangular Green, yellow, blue, hexagonal prisms. Also columnar 52. B. (CRUSHED FRAGMENTS.) Index of Refraction. Interference Color. Other Notable Characters. Name. < Bromoform Abnormal blue or blown or gray Gray or White Gray or White to Bright A. Gray or White to Bright A. Bright A. Gray or White to Bright A. Plates. Biax. I. F. Green. Pleochroic Irregular Laths. Ex., || on ooi, 5 on oio Laths. Ex., 15 on ooi, 5 on oio. Crossed twinning (grating) Irregular, or plates. Biax. I. F. Laths. Ex., ||, El. (+) Chlorite Group See page 542 Beryl Orthoclase Microcline Talc Pyrophyllite > Bromoform < tt-Monobrom- Naphthalin Gray or White or Black Gray or White to Bright A. Plates. Biax. I. F. Distinc- tions p. Irregular. Pleochroic and colorless Mica Group Tourmaline > orMonobrom- Naphthalin Gray or White to Bright A. Bright B. Laths and fibres. Ex., ||. El. (+). Colorless Laths. Ex., H, El. (+). Pleochroic pink to green Fibres. Ex. ||. El. (+) 609 Enstatite Hypersthene Anthophyllite 53. A. . Allophane, 549. Al 2 Si0 6 .5H 2 H., 3 Sp. gr., 1.88 Much water Crumbles when heated Sky blue, green, brown and white crusts 54. A. M. Aluminite, p. 415, Al 2 SOn +pH 2 O H., i to 2 Sp. gr., 1.6 . Bauxite, p. 413, A1 2 O(OH) 4 H., i to 3 Sp. gr., 2.4 to 2.5 I. Leucite, p. 498, KAl(SiO 3 ) 2 H., 5.5 to 6 Sp.gr., 2.4 to 2. 5 O. Wavellite, p. 471, A1(OH) 6 (PO 4 ) 4 +9H 2 O H., 3 to 4 Sp. gr., 2.33 Much water. S0 2 Water at high heat Acid water etches Infusible with soda but mass will stain silver May become mag- netic in R. F. Violet Fl. (Color screen) White chalky with harsh feel Rounded grains or earthy or clay-like Translucent white, nearly spherical Spheres and hemi- spheres of radiat- ing crystals 54. B. (CRUSHED FRAGMENTS.) Name. Index of Refraction. Interference Color. Other Notable Characters. < Xylol Gray or White Fibres. Ex., Obi. Aluminite > Xylol < Bromoform Black aggregate Gray or White or Black. Bright B. Irregular Irregular. Twin lamellae in- clusions Rectangles and needles. Ex., ||. El. (+) Bauxite Leucite Wavellite 55. A. Crystal System: Name, Composition. Hardness and Specific Gravity. Closed Tube. Other Tests. Usual Appearance. M. Kaolin, p. 547, H 4 Al 2 Si 2 O 9 Water Usually plastic Dull white, mealy H., 2 to 2.5 Sp. gr., 2.6 unctuous M. Gibbsite, p. 415, A1(OH) 3 Water Exfoliates Smooth pearly H., 2.5 to 3.5 Sp. gr., 2.4 crusts or fibres H. Alunite, p. 416, Water at Violet Fl. Cub ids or granular K(A10 3 ) (S0 4 ) 2 +3H 2 red heat or fibrous. White H., 3. 5 to 4.5 Sp.gr., 2.6 to 2. 7 or tinted Tri. Cyanite, p. 519, Al 2 SiO 5 Softer parallel Blue blade-like. K.,sto7 Sp. gr., 3-6 to 3.7 length Centre bluest O. Sillimanite, p. 519, Al 2 SiOs Very tough Thin gray or brown H., 6 to 7 Sp. gr., 3.2 crystals or fibrous O. Andalusite, p. 518, Al 2 SiO 5 Inclusions. See p. Gray or pink nearly H., 7 to 7.5 Sp.gr., 3. i to 3. 2 80 square prisms H. Phenacite, p. 567, Be 2 SiO 4 Resembles quartz Colorless rhombo- H., 7.5 to 8 Sp. gr., 2.96 hedral crystals O. Diaspore, p. 415, AIO(OH) Water Pink or brown foli- H., 6.5 ated O. Topaz, p. 523, Ali 2 Si 6 O 2B Fi O. T. F. Easy basal cleav- Colorless, yellow H., 8 Sp. gr., 3.4 to 3.6 with age and bluish crys- S. Ph. tals. Columnar I. Spinel, p. 558, MgAl 2 O4 Completely soluble Red, black, etc., H., 8 Sp. gr., 3.5 to 4.5 S. Ph. octahedra O. Chrysoberyl, 560, BeAl 2 O 4 Tabular and twin- Pale to deep green H., 8.5 Sp. gr., 3.5 to 3..8 ned crystals H. Corundum, p. 412, A1 2 O 3 Nearly cubic part- Gray, blue, red, etc. H-, 9 Sp. gr., 3.9 to 4.1 ing striations crystals 610 55. B. (CRUSHED FRAGMENTS.) Name. Index of Refraction. Interference Color. Other Notable Characters. < Bromoform Gray or White. Aggregate Gray or White. Aggregate Gray or White or Black Irregular and plates. Cloudy Plates Three or six-sided with Uniax. I. F. or irregular Kaolinite Gibbsite Alunite > Bromoform < cc-Monobrom- Naphthalin Gray or White Gray or White to Bright A. Plates with Biax. I. F. and irregular Irregular or laths with Ex. || Topaz Andalusite > a-Monobrom- Naphthalin < Methylene Iodide Black Gray or White to Bright A. Gray or White to Bright A. Bright A. Bright B. Irregular. Tinted green or brown Irregular Laths. Cross cracks. Ex. 30. El. (+) Laths or Needles. Ex. ||. El. (+) Laths. Ex. |1. El. ( ). Spinel Phenacite Cyanite Sillimanite Diaspore > Methylene Iodide Gray or White to Bright A. Gray or White to Bright A. Irregular, green or colorless Irregular Chrysoberyl Corundum 56. A. Crystal System: Name, Composition, Hardness and Specific Gravity. Fragments in HC1. With Cobalt Solution. Usual Appearance. H. Calcite, p. 446, CaCOs Rapid eff . Unchanged on boil- White, yellowish, H., 3 Sp. gr., 2.7 cold ing etc., crystals and granular (marble) O. Aragonite, p. 444, CaCOs Rapid eff. Lilac on boiling White, yellowish, H. f 3.5 to 4 Sp. gr., 2.9 cold prisms, needles, fibres coral-like H. Dolomite, p. 448, Slow eff. Pink on ignition White or pink CaMg(C0 3 )2 cold curved rhombohe- H., 3. 5 to 4 Sp.gr., 2. 8 to 2. 9 drons, granular H. Magnesite, p. 453, MgCOs Very slow Pink on igni f ion White nodules shell- H., 3. 5 to 4.5 Sp.gr., 3 to 3. i eff. cold like fracture also cleavable H. Rhodochrosite, p. 284, Very slow Unaffected Pink to red curved MnCOs eff. cold rhombohedrons or H., 4.5 Sp. gr., 3.5 to 4.5 massive 56. B. (CRUSHED FRAGMENTS.) Index of Refraction.* Interference Color. Other Notable Characters. Name. High Order Plates or laths. Ex. ||. El., Aragonite < a-Monobrom- Naphthalin High Order Rhombs. Striations || long diagonal. Ex. Sym. Calcite > orMonobrom- Naphthalin High Order High Order High Order Rhombs. Ex. Sym. Rhombs. Ex. Sym. Rhombs. Ex. Sym. Dolomite Magnesite Rhodochrosite * All except aragonite cleave to rhombohedrons of 105 to 107. * These are parallel short diagonal. The indices parallel the long diagonal are notably larger by 0.17 to 0.22. 6n 57. A. Crystal System: Name, Composition, Hardness, and Specific Gravity. Closed Tube. Other Tests. Appearance. Cerite, p. 351. Ce., etc., Si. H. f 5.5 Sp. gr., 4.9 T. Thorite, p. 315. ThSiO 4 H., 5 Sp. gr., 4.8 to 5-2 O. Chrysolite, p. 513, (MgFe) 2 Si0 4 H., 6.5 to 7 Sp.gr., 3.3 to 3-6 O. Forsterite, p. 513. Mg 2 SiO 4 H., 6 to 7 Sp. gr., 3.2 to 3.3 Water Water Whitens Whitens In forceps. Yellow In borax dark yel- low O. F. hot High sp. gr. Usu- ally altered In forceps whitens Brown to cherry red massive. Resinous Orange to brown, zircon shaped Olive to gray green glassy grains and masses of grains White or yellow grains or crystals 58. A. Garnierite, p. 294, Blackens. Borax O. F. violet Emerald- and pale- H 2 (Ni.Mg)SiO 4 +H 2 O Yields hot, brown cold green and cellular H., 2 to 3 Sp. gr., 2.3 to 2.8 water masses and crusts. . Chrysocolla, p. 372, Blackens. With soda on coal Enamel -like crusts, CuSiO 3 .2H 2 O Yields a copper button. veins or compact H., 2 to 4 Sp. gr., 2 to 2.3 water Emerald green Fl. H. Brucite, p. 452, Mg(OH) 2 Water Pink with Co. Sol. White foliated or H., 2.5 Sp. gr., 2.4 fibrous. Pearly O. Cervantite, p. 335, Sb 2 O 4 Easily reduced on Yellow to white dull H., 4 to 5 Sp. gr., 4.1 charcoal or pearly M. Monazite, p. 313, Reflected light with spectro- Resinous brown (Ce.La.Di)PO 4 scope gives broad line be- crystals or yellow H., 5 to 5.5 Sp. gr., 4.9 to 5.3 tween the red and yellow and grains narrow line in the green Turquois, p. 570, Blackens. P test see p. 191. Sky-blue to green A1 2 (OH) 3 P0 4 H 2 Yields Blue Fl. with HC1 nearly opaque H., 6 Sp. gr., 2.6 to 2.8 water with lustre of wax M. Gadolinite, p. 315, Unaltered Swells, cracks and Rough green to Yt 2 Be 2 FeSi 2 Oio often glows black prisms H., 6.5 to 7 Sp. gr., 4.3 57. B. (CRUSHED FRAGMENTS.) Name. Index of Refraction. Interference Color. Other Notable Characters. < a-Monobrom- Naphthalin Bright A. Irregular. Colorless or pleo- chroic yellow Chondrodite > a-Monobrom- Naphthalin Bright B. Bright B. Irregular, colorless, yellow Irregular. Colorless Chrysolite Forsterite > Methylene Iodide Black Often isotropic Thorite 58. B. (CRUSHED FRAGMENTS.) < Bromoform Black or Gray or White Black or Ag- gregate Plates, Uniax. I. F. Fibres, Ex. ||. El. ( ) Irregular. Pale blue or green Brucite Chrysocolla = Bromoform Gray or White Aggregate Irregular. Greenish Garnierite > Bromoform Gray or White Aggregate Bright B. Irregular Plates. Faint yellow Turquois Monazite > Methylene Iodide Varies Black to high order Normally anisotropic, often isotropic Gadolinite 612 59. A. Crystal System: Name, Composition, Hardness and Specific Gravity. Other Tests. Usual Appearance. T. Xenotime, p. 313, YPO 4 Test P. p. 191 Zircon-like crystals, brown H., 4 to 5 Sp. gr., 4.5 or yellow in color T. Fergusonite, p. 356, Test Cb p. 1 86 Brownish black resinous Cb, TaYCe, etc. H., 5.5 to 6 Sp. gr., 5.8 . Opal, p. 487, SiO 2 nH 2 O In closed tube. A little No crystals. Translucent. H., 5. 5 to 6.5 Sp.gr., 2. i to 2. 2 water becomes opaque May be any color, opaque Rarely play of colors and dull T. Rutile, p. 309, TiO 2 S. Ph. 0. F. yellow, Brownish red to black H., 6 to 6. 5 Sp.gr., 4.1 to 4.2 made violet R. F. hairs to coarse crystals Chalcedony, p. 486, SiOa No crystals "Tendon" colored, red, blu- H., 6.5 Sp. gr., 2.6 ish, etc. Lustre wax-like H. Quartz, p. 484, SiO 2 Horizontal striations Prisms with rhombohedra. H., 7 Sp. gr., 2.65 on prisms Also massive. Colorless and all colors H. Tridymite, p. 486, SiO 2 Minute tabular and twinned H., 7 Sp. gr., 2.3 crystals I. Garnet, p. 510, Uvarovite, Green bead with S. Ph. Emerald green, dodeca- Ca3Cr 2 (SiO 4 )3 hedrons H., 7.5 Sp. gr., 3.1 to 4.3 T. Zircon, p. 314, ZrSiO4 Glows intensely on Sharp square pyramid and H., 7.5 Sp. gr., 4.7 heating. Adamantine prism brown, gray, red. lustre etc. Also pebbles O. Staurolite, p. 520, Dark brown, usually twin- Fe(A10) 4 (A10H)(Si0 4 ) ned (cross) prisms at 90 H., 7.5 Sp. gr., 3-6 to 3-7 and 120 H. Tourmaline, p. 524, Green flame with Transparent deep red (Rubellite) Ri 3 B 2 (SiO B ) 4 KHSCu CaF 2 prisms H., 7 to 7.5 Sp. gr., 3 to 3.2 I. Diamond, p. 550, C In powder is burned Colorless and tinted octa- H., 10 Sp. gr., 3.51 to CO 2 . Cleavages at hedra with rounded edges. 70 31'. Lustre like oiled glass 59. B. (CRUSHED FRAGMENTS.) Name. Index of Refraction. Interference Color. Other Notable Characters. < Xylol Black Gray or White Irregular Plates. Twinned Opal Tridymite > Xylol < Bromoform Gray or White to Bright A. Gray or White to Bright A. Irregular Irregular. Fibrous with crossed Nicols Quartz Chalcedony > Bromoform < a-Monobrom- Naphthalin Gray or White to Bright A. Irregular. Red, pleochroic Tourmaline, (Rubellite) = Methylene Iodide Gray or White Irregular. Pleochroic. In- clusions Staurolite > Methylene Iodide Black Black Bright B. High Order High Order Irregular. Pink Irregular Irregular Irregular. Yellow to reddish Garnet, (Uvarovite) Diamond Zircon Xenotime Rutile 613 INTERNATIONAL ATOMIC WEIGHTS. = 16. H = l. Aluminium Al 27.1 26.9 Neodymium. . . Ne Antimony Sb 120.2 119.3 Neon Argon A 39.9 39.6 Nickel . . . . Ni Arsenic As 75.0 74.4 Nitrogen . . . N Barium Ba 137.4 136.4 Osmium . . . . Os Beryllium (Glucinum) . Be 9.1 9.03 Oxygen. . . .O Bismuth Bi 208.5 206.9 Palladium. . . Pd Boron B II 10.9 Phosphorus . . P Bromine Br 79-96 79-36 Platinum . . . Pt Cadmium Cd 112.4 ni-6 Potassium . . . K Caesium Cs 133 132 Praseodymium . Pr Calcium Ca 40.1 39.8 Radium. . . . Ra Carbon C 12.00 11.91 Rhodium . . . Rh Cerium Ce 140 139 Rubidium . . . Rb Chlorine Cl 35-45 35- 18 Ruthenium. . . Ru Chromium Cr 52.1 51.7 Samarium . . . Sm Cobalt Co 59.0 58.56 Scandium. . . . Sc Columbium (Niobium). Cb 94 93.3 Selenium. . . . Se Copper ....... Cu 63.6 63.1 Silicon .... Si Erbium E 166 164.8 Silver Ag Fluorine F 19 18.9 Sodium . . . . Na Gadolinium Gd 156 155 Strontium . . . Sr Gallium Ga 70 69.5 Sulphur . . . . S Germanium Ge 72.5 71.9 Tantalum . . . Ta Gold Au 197.2 195.7 Tellurium . . . Te Helium He 4 4 Terbium Tb Hydrogen H 1.008 i.ooo Thallium . . . Tl Indium In 114 113.1 Thorium. . . . Th Iodine I 126.85 125.90 Thulium. . . . Tm Iridium ... . . . . Ir 193.0 191.5 Tin Sn Ir on Fe 55.9 55.5 Titanium. . . . Ti Kr ypton Kr 81.8 81.2 Tungsten . . .W Lanthanum La 138.9 137.9 Uranium. . . . U Lead Pb 206.9 205.35 Vanadium ... V Lithium Li 7.03 6.98 Xenon .... X Magnesium Mg 24.36 24.18 Ytterbium . . . Yb Manganese Mn 55.0 54.6 Yttrium. . . . Yt Mercury Hg 200.0 198.5 Zinc Zn Molybdenum Mo 96.0 95.3 Zirconium. . . Zr 614 = 16. 143.6 20 58.7 14-04 16.00 106.5 31.0 194.8 39-15 140.5 225 103.0 85.4 101.7 150 44.1 79.2 28.4 107.93 23-05 87.6 32.06 183 127.6 1 60 204.1 232-5 171 119.0 48.1 184.0 238.5 51.2 128 173.0 89.0 65.4 90.6 H=l. 142.5 19.9 58.3 189.6 15.80 105.7 30.77 J93-3 38.86 139-4 223.3 102.2 84.8 IOO.9 148.9 43-8 78.6 28.2 IO7. 12 22.88 86.94 31.83 181.6 126.6 158.8 202. 6 230.8 169.7 118.1 47-7 182.6 236.7 50.8 127 171.7 88.3 64.9 89-9 GENERAL INDEX. Abnormal interference colors, 138 Absorption in crystals, 99, 104, 151 spectra, 169 Acids, definition, 236 Acute bisectrix, 107, 143 Adamantine lustre, 210 Adjustment of goniometer, 83 of microscope, 122, 123 Adsorption, 235 Aggregates, crystal, 70 shape and grouping, 70 Alterations, chemical, 236, 239, 240 Aluminum, hydrous silicates, 547 silicates, 517 summary of tests, 182 see also, 173, 202, 206 Aluminum minerals, 406 uses and extraction, 408 Ammonium, test, 182 Ammonium minerals, 430 Amorphous condition, 209 Amygdaloidal, 74 Analyzer of microscope, 118 Angle between optic axes, 107, 147, 149 Angles, 3 apparent with microscope, 148 approximate, 5, 12 changed by expansion, 226 critical, no extinction, 138 measurement of interfacial, 3, 82 of hexagonal crystals, 16 of isometric crystals, 67 of monoclinic crystals, 19 of orthorhombic crystals, 17 of tetragonal crystal?, 15 of triclinic crystals, 20 opening, no Anisotropic crystals, 100, 127 Antimony, summary of tests, 182 see also, 171, 172, 176, 197, 198, 199, 200 Antimony minerals, 332 uses and extraction, 332 formation and occurrence, 333 Anvil, 160 Apparatus, 156 Arborescent, 74 Arsenic, summary of tests, 183 see also, 171, 172, 173, 176, 197, 205 Arsenic minerals, 327 economic importance, 328 Arsenic minerals, formation and occur- rence, 328 Associates, 239 Asterism, 211 Atomic weights, table of, 614 Axes, crystallographic, 20 choosing, 20, 29, 32, 37, 43, 49, 52, 55, 58, 62, 65 interchangeable, 21 of symmetry, 7, 8, 10 of the six systems, 21 optic, 102 Axial angle, optic, 107 measurement, 147, 149 changed by heat, 229 Axial cross, construction, 93 elements, calculation of, 91 Balance, 219 Jolly, 220 Kraus- Jolly, 221 Westphal, 224 Barium, summary of tests, 173 (see also 202, 205, 207) Barium minerals, 431 uses and production of, 431 formation and occurrence, 432 Bar theory, 255, 419 Basal pinacoid, 30, 34, 39, 44, 49, 56 plane, 53 Basalt, 479 Bases, definition, 236 Basic lava flows, copper in r 361 Beads, how to make, 162 Bead tests, 177 table of, 179 Becke line, 128 Beryllium minerals, 562 Berzelius lamp, 157 Biaxial crystals, 105 interference figure, 140, 143, 145 ray surface, 105 Birefringence, 104, 107 determining, 135, 137 Bisectrix, acute and obtuse, 107, 143 Bismuth, summary of tests, 184 see also, 171, 172, 173, 176, 178, 199, 200 Bismuth minerals, 324 formation and occurrence, 325 uses and extraction, 325 Bismuth-flux, 172 615 6i6 GENERAL INDEX. Bladed, 71 Blast, method of blowing, 161 Blowpipe analysis, scheme for, 197 operations of, 154 Blowpipe apparatus, 157 Blowpipe, description of, 157 Blowpipe lamps, 158 Blowpipe tests, summary of, 182 advantages of, 156 Bluestone, 480 Boracic acid flux, 184 Borax, reactions with, 177, 179 how to make bead, 162 Borax lakes, minerals of, 255, 456 Boron, summary of tests, 184 see also, 205, 206 Boron minerals and their uses, 454 formation and occurrence 455 Botryoidal, 74 Brachy dome, 39 pinacoid, 30, 39 pyramid, 38 Brass, 296, 359 Braun's solution, 224 Bravais double plate, 137 Brittle, 216 Bromine, summary of tests, 184 see also, 175, 203, 459 Bronze, 304, 359 Building stones, 479 Bunsen burner, 156 Cadmium borotungstate solution, 224 mineral, 293 source and use, 296 summary of tests, 185 see also, 173, 176, 180, 198 Calcite, double refraction in, 100 Calcium minerals, 437 formation and occurrence, 438 see also, 169, 173, 202, 205, 207 summary of tests, 185 uses and production, 437 Carbonated water, solvent power, 243 Carbonates, 425 , from spring waters, 254 Carbon minerals, 472 economic importance, 473 formation 'and occurrence, 475 Carbon dioxide, summary of tests, 105 see also, 204, 205 Cements, see hydraulic cements, 324 Centering of goniometer, 83 of microscope, 123 Center of symmetry, 7, 10 Cerium minerals, 310 Cerium production and uses, 311 Change of color, 211 Character, optical, 103, 107, 145 Charcoal, method of using, 169 reactions obtained on, 171 Chart, spectroscopic, 168 Chemical alterations, 236, 239 balance for sp. gr., 219 composition, 208, 231 characters, 240 sediments, 248, 253 types, 236 Chlorine, summary of tests, 185 see also, 459 Chromium, minerals, 346 see also 176, 179, 201 uses and production, 346 formation and occurrence, 346 summary of tests, 185 Circular polarization, 104 Characteristics, isometric crystals, 13 hexagonal crystals, 15 orthorhombic crystals, 16 monoclinic crystals, 17 tetragonal crystals, 14 triclinic crystals, 19 Classification of crystals, n Cleavage, 13, 213 Clino dome, 33 pinacoid, 34 Clinographic projection, 92 Closed tubes, reactions in, 175 Coal, 478 Cobalt, 173, 179, 198, 202 summary of tests, 186 Cobalt minerals, 286 uses and production, 286 formation and occurrence, 288 Coefficients of Weiss, 22 Color, causes of, 151, 155 changes in closed tubes, 176 Color screen, Merwin's, 165 scale, interference, 196 terms, 138 Colloids, 81, 209, 235 Coloration of flame, 165 Colors, interference, 114 Columbium minerals, 554 tests, 1 86 Columnar, 71 Compensating wedges, 136 Composition of minerals, 208 Conchoidal, 216 Conductivity of heat, 226 electrical, 229 Conglomerates, 247, 398 Constants of crystals, 82, 91, 107 Contact goniometers, 3 minerals, 256 twins, 68 Convergent polarized light, 140 Copper, in basic lava, 361 summary of tests, 186 see also, 173, 176, 179, 199, 202 Copper minerals, 357 formation and occurrence, 359 GENERAL INDEX. 6l 7 Copper uses, production and extraction, 357 Coralloidal, 74 Corresponding faces, 7, 12, 23 Crossed nicols, no Crystal aggregates, 70 constants, determination, 82 definition, i drawing, 92 systems, 21 condition, 209 structure, 26, 208 Crystallites, 77 Crystallization, 2 from magma, 241 from solution, 243 water of, 237 Crystallographic axes, 20 Crystallo-optics, 96 to 155 Crystals, angles of, 3 biaxial, 105 classification, n curved faces, 78 definition, i, 2 embedded, 74 forms, 23 grouping, 68 growth of, 74 habit, 74, 75 inclusions, 79 irregularities of faces, 77 isotropic, 99 laws of 3,7, 9, 24 measurement of, 5, 82 models, 10 negative, 80 parallel growth, 71, 8 1 positive and negative, 103, 107 sections, 125 skeleton, 77 striations, 77 symmetry of, 6 to II, 87 twin, 68 uniaxial, 102 Cube, 60 Cupel holder, 160, 379 Cupellation, test for silver, 378 Curved faces of crystals, 78 Cutting diamonds, 553 Definite chemical composition, 208 Deltohedron, 63 Dendritic, 74 Depolarization, in Destructive interference, 112 Diamagnetism, 228 Dichroscope, 154 Dichroscopic ocular, 154 Diffusion columns, 225 Dihexagonal pyramid, 55 prism, 50 Diploid, 65 Dispersion of light, 98 Ditetragonal prism, 38, 44 pyramid, 43 Ditrigonal prism, 53 Dodecahedron, 60 Domes, 30, 33, 39 Double magnetism, 228 Double refraction, 102, 107 strength of, 104 Drawing crystals, 92 Drusy, 72 Ductile, 216 Dull in lustre, 210 Earth's crust, 208, 239 Economic importance, see under eacJ group. Edges, direction of, 3, 94 Elastic, 215 Elasticity, 215 Elements, axial, 91 principal, 239 Electrical characters, 228 conductivity, 229 Elongation, sign of, 134 Embedded crystals, 74 Empirical formulas, 231 Equivalent faces, 7, 12, 23 Eruptive rocks, 246 Etched crystals, 78 Etching figures, 28 Eutecticum, 242 Evaporation, 245 Exhalations, minerals due to, 252 Expansion of by heat, 226 change of angle by, 226 change of optical characters by, 227 Extinction between crossed nicols, no, 139 Extinction angles, 138 Faces, corresponding, 7, 12, 23 curved, 78 elemental or parametral, 87, 88 false or apparent, 78 irregularities, 77 roughened, 78 striated, 77 symbols, 21 vicinal, 78 Faster and slower ray, 134 Federow universal stage, 149 Feel, terms used, 226 Ferrochrome, 346 Ferro-manganese, 277 Ferrotitanium, 308 Fibrous, 71 Flame colorations, 165 oxidizing, 161 reducing, 162 6i8 GENERAL INDEX. Flame structure of, 161 Flaming, 180 Fletcher lamp, 159 Flexible, 215 Fluorescence, 212 Fluorine, summary of tests, 187 see also 175, 182, 204, 459, 460 Focusing a microscope, 123 Foliated, 71 Forceps, 160 Form, ideal, 10 Formation of minerals, see mineral forma- tion (and under each group) Forms, combinations of, 23 definition, 23 possible on a crystal, 27 symbols of, 23 Formulas of minerals, determining, 231, 234 empirical, 231 Fracture, 216 Frictional electricity, 228 Fuess goniometer, 82 microscope, 120, 125 refractometer, 131 Fusibility, scale of, 164 Fusion, 165 Fusion-solutions, 242 Gabbro, 251 Gangue minerals, 259 Gases in mineral formation, 242, 243 Gas blowpipe, 158 Gel minerals, 208, 209, 235 Gems, 550 Genesis of minerals, 239-260 Geode, 74 Geometrical constants, 82 crystallography, 2 Geometric symmetry, 10 German silver, 287 Glasses, 81, 209 Gold, tests for, 173 Gold minerals, 392 economic importance, 393 formation and occurrence, 394 Goniometers, contact, 3 Fuess', 82 Gneiss, 249 Granular, 71 Granite, 247, 256, 479 Graphic determination of indices, 89 Greasy lustre, 210 Ground water, see underground water Grouping of crystals, 68, 71 Growth of crystals, 74 Guano beds, 469 Gypsum test plate, 137, 146 Habit of crystals, 74, 75 Hackly fracture, 216 53 Hammer. 160 Hand-goniometers, 3 Hardness, 216 scale of, 217 Heat, conductivity, 226 expansion, 226 Heat rays, transmission, 226 Heating power of flame, 164 Heavy liquids, use of, 223 Hemi prism, etc., 30, 33 Hemimorphic ditrigonal pyramid, etc., Hexagonal crystals, angles, 16 axial elements, 91 characteristics, 15 classes, 48 to 57 forms, 48 to 57 optical tests, 150 Hexahedron, 60 Hextetrahedron, 63 Hexoctahedron, 58 Hollow crystals, 77 Homogeneous mixed crystals, 234 Hot springs, 455, 462 Hour glass structure, 79 Hydrochloric acid, solubility in, 180 Hydrofluoric acid, solubility in, 181 Hydrogen minerals, 465 Hydroxides, 236 Ideal forms, 10 Igneous rocks, 246 minerals in, 305, 309, 312, 348, 439 Illuminating system, 117 Image in microscope, 121 Imitations lapis lazuli, 577 turquois, 571 Imperfections of crystals, 68 Inclusions in crystals, 79 Indices of Miller, 22 graphic determination, 89 Indices of refraction, 97, 99, 103, 104, 107 measurements of, 127 by Becke line, 128 by Due de Chaulnes method, 131 by oblique illumination, 129 by refractometers, 132 by Van der Kolk method, 129 with liquids, 128 Indices zonal, 88 nterchangeable axes, 21 nterfacial angles, measurement, 5, 82, 87 ntergrowths, 81 nterference of monochromatic light be- tween crossed nicols, 112 colors with white light, 114 abnormal, 138 color scale, 116 destructive, 112 figures, 140, 141, 143, 145 ntercepts, 21 GENERAL INDEX. 619 Internal peculiarities, 79 Inversion points, 227 Iodine, summary of tests, 187 see also, 123, 175, 203, 460 Iridescence, definition, 211 Iridium minerals, 401 Iridium, uses* 402 formation and occurrence, 404 Iron, summary of tests, 188 see also, 173, 176, 179, 198, 200,202 Iron minerals, 261 extraction, 262 economic importance, 262 formation and occurrence, 263 Irregularities of crystal faces, 77 Isochromatic curves, 144 Isogyres, 143 Isometric crystals angles, 13, 67 classes and forms, 58 to 66 characteristics, 13 in polarized light, 99, 127 Isomorphism, 232 Isomorphous mixtures, 233, 234 substances, 232 Isotropic crystals, 99, 127, 141 Jolly's balance, use of, 220 Klein's solution, 224 v. Kobell's scale of fusibility, 163 Kraus Jolly balance, 221 Lakes, minerals formed in, 255, 455 Lamellar, 71 Lamps, blowpipe, 158 Law of constancy of interfacial angles, 3 of simple mathematical ratio, 24 of symmetry, 7, 9 Lead, summary of tests, 188 see also, 171, 172, 173, 176, 199, 200 Lead minerals, 316 formation and occurrence, 317 uses, production and extraction, 316, 317 Light, dispersion, 98 monochromatic, 99 plane polarized, 107 transmission, 96 vibrations, 96, 101 Limestone, 248 Liquids for indices of icfraction, 128 Lithium, summary of tests, 189 see also, 169, 205 Lithium minerals, uses and production, 428 formation and occurrence, 428 Lustre, 210 Macro dome, etc., 30, 39 Magma, minerals of, 249 see also silicate groups molten silicate, 241 Magnesium, summary of tests, 189 hydrous silicates, 543 Magnesium, see also, 153, 181, 202, 206 Magnesium minerals, 449 economic importance, 450 formation and occurrence, 451 Magmatic segregations, 251, 263, 289, 308, 346, 360, 404, 410, 468 Magnetic characters, 227 Magnetism, 228 Magnification, 124 Malleable, 216 Mammillary, 74 Manganese, summary of tests, 189 see also, 179, 201 Manganese minerals, 277 uses and production of, 277 formation and occurrence, 277 Manganiferous ores, 280 Marine borates, 456 Marine sediments (phosphates), 469 Marshes, 456 Mathematical ratio, law of, 24 Measurement of interfacial angles, 5, 82 Mechanical sediments, 247, 253 Melting points, 227 Mercury, summary of tests, 190 see also, 172, 176, 200, 205 Mercury minerals, 373 economic importance, 373 formation and occurrence, 374 uses, production and extraction, 373 Merwin's color screen, 165 Metallic lustre, 210 Metasomatic replacement, 245 (see Replacements) Metamorphic rocks, 248 minerals in, 257, and group discus- sions Micaceous, 71 Mica schist, 248 Mica test plate, 135, 146 Microchemical methods, 238 Microlites, 77 Microscope, adjustments, 122, 123 polarizing, 117, 119, 120, 125, 148 testing with, 127 Miller's indices, 22 Mineral formation, 241, 349 chemical sediments, 253 contacts, 256 in magma, 249 magmatic segregations, 251 mechanical sediments, 253 oceans, 254 pegmatites, 250 regional metamorphism, 257 replacements, 256 running streams, 254 springs, 253 veins, 258 620 GENERAL INDEX. Mineral formation, near volcanoes, 252 weathering, 252 Mineral occurrence, (See under each group) synthesis, 240 Mineralizers, 242 Mineralogy, definition, 209 Mineral, definition, 208 Minerals, iron, etc., see Iron minerals, etc. Mixed crystals, 234 Models of crystals, 10 Moh's scale of hardness, 217 Molybdenum summary of tests, 190 see also, 162, 171, 172, 173. i?4. 2O1 ' 205 Molybdenum minerals, 348 formation and occurrence, 349 uses and production, 348 Monel metal, 287 Monochromatic light, 99 interference with, 112 Monoclinic crystals, angles, 19 axial elements, 92 classes and forms, 32 to 35 charaotersitics, 17 in polarized light, 151 type forms, 32 Mortar, Leeds, 160 Negative crystals, 80 ray surfaces, 103, 107 Nickel, extraction of, 287 summary of tests, 191 see also, 173, 179. 198, 201 Nickel minerals, 286 formation and occurrence, 280 uses and production of, 287 Nicol's prism, 108 vibration direction of, 124 Nitric acid, summary of tests, 191 see also, 203 Nitrogen, minerals of, 466 Nodular, 74 Non-metallic lustre, 210 Norite, 251 Objectives of microscope, 118 Oblique illumination, 129 Obtuse bisectrix, 107 Oceans, minerals formed in, 254 Occurrence of minerals, 239, 260 (See also iron, copper, lead, etc.) of faces in series, 24 Ochre, 262 Oculars of microscope, 118 Octahedron, 59 Odors in closed tubes, 175 in open tubes, 177 terms used, 225 Oil and oil-lamps, 159 Old gold veins, 383, 396 Oolitic, 74 Opalescence, 211 Opaque, 213 Open tubes, reactions in, 176 Opening angle, no Optic axes, determination of angle, 147, 149 Dptic axis, uniaxial, 102 biaxial, 105, 106 Optical character, 103, 107, 145, 146, 147 changed by expansion, 227 characters, 96 to 155 (See also under silicate groups.) constants, determining, 127 distinctions between systems, 150 groups, 99 principal sections, 106 tests with microscope, 107 Optically anistropic crystals, 100, 127 biaxial crystals, 105 isotropic crystals, 99, 127 uniaxial crystals, 102 Optic axial angle, 107 Ore beds, 333 Organic sediments, 248, 255 Organisms, minerals formed by, 255 Origin of minerals, 239-260 Orthographic projection, 95 Ortho pinacoid, 34 Orthorhombic crystals, angles, 17 axial elements, 91 characteristics, 16 classes and forms, 37-41 in polarized light, 150 Osmium uses, 403 Oxidation by means of blowpipe, 161 Oxides, 236 Oxidizing flame, 161 Paints, 262, 296 Palladium, uses, 403 Paragenesis, 239 Parallel grouping, 71 growth, 8 1 polarized light, 108 Paramagnetism, 228 Parameters, 22 Parametral face, 88, 22 Paris green, 328 Partial symmetry, 12 Parting, 213 Path of light in microscope, 121 Pearly lustre, 210 Pegmatites, 250, 305, 312, 325, 348, 355, 409, 483, 488 Penetration twins, 68 Penfield's goniometer, 3 protractors, 85, 86 Percussion figures, 215 Peridotite, 251 Pewter, 325 GENERAL INDEX. 621 Phase difference, 104 Phosphorescence, 211 Phosphorus summary of tests, 181 see also, 204 Phosphorus, minerals of, 467 economic importance, 467 formation and occurrence, 468 Physical characters, 209, 240 Piezoelectricity, 230 Pig iron, 262 Pinacoid, see basal,' brachy, clino, macro, and orthopinacoids Pisolitic, 74 Placers and gravels, 399, 404 Plane, basal, 53 of symmetry, 9, 10 of vibration, 102 Plane polarized light, 107 Plaster tablets, preparation, 159 sublimates on, 171 Platinum minerals, 401 formation and occurrence, 404 production and uses, 402 Platinum wire and holder, 160 Play of color, 211 Pleochroism, 104, 152 with microscope, 153 with dichroscope, 154 Plumose, 74 Plutonic rocks, 246 Pneumatolysis, 242 Polariscope, for axial angle, 149 Polarization in calcite, 100 circular, 104 Polarized light, 101, 107 Polarizer of microscope, 118 Polarizing microscope, 117 Polysynthetic twins, 69 Positive uniaxial, 103 biaxal, 107 Possible forms, 27 Potassium, summary of tests, 191 see also, 169, 205, 207 Potassium minerals, 417 formation and occurrence, 419 uses and production, 417 Precious and ornamental stones, 550 to 579 Precipitation from watery solutions, 243 Preparation of material, 125 Primary minerals, 259, 278, 288, 305 Principal indices, 104 optical section, 106 vibration directions, 105 Prism, see brachy, clino, dihexagonal, ditetragonal, ditrigonal, hemi, hexa- gonal, macro, ortho, rhombic, tetra- gonal, trigonal Prismatic habit, 76 Processes of formation, 241 Projection, clinographic, 92 Projection, oblique faces, 85, 86 orthographic, 95 stereographic, 84 vertical faces, 85 Protractors, Penfield's, 85, 86 Pseudomorphs, 239 Pseudo symmetry, 70 Pycnometer, 223 Pyramid, see clino, dihexagonal, ditetra- gonal, hemi, hemimorphic, hexagonal, orthorhombic, tetragonal, trigonal Pyramidal habit, 76 Pyritohedron, 66 Pyroelectricity, 230 Qualitative blowpipe analysis, 197 Quarry industry, 479 Quarter undulation mica plate, 135, 146 Quartz wedge, 136 Quartzite, 248 Quicksilver, see mercury Radiating crystals, 72 Radium minerals, 341 luminescence, 212 tests for, 195 Rain water, 243 Ray surface, biaxial, 105 positive and negative, -103, 106 uniaxial, 132 Reagent bottles, 160 Reducing flame, 162 Reduction by flame, 162 with metallic sodium, 174 with soda, 173 Referring a face to axes, 21 Reflection goniometers, 82 of light, 96 total, 98 Refraction, definition, 97 double, 102, 107 in calcite, 100 index of, 97, 103, 107, 128, 129, 131, 132 Refractometers, 131 Fuess simple, 133 Herbert Smith, 133 Reniform, 74 Repetition, 7 Replacement, metasomatic, 245, 258, 264, 297, 317, 333, 351, 357, 36o, 384, 404, 452, 469, 521 Residual deposits, 265, 279, 298, 306, 312, 347, 355, 399, 404, 432 Resinous lustre, 210 Retardation, determining, 136 Retger's solution, 225 Reticulated, 72 Rhombic prism, 39 pyramid, 38 Rhombohedron of the first order, 49 622 GENERAL INDEX. Rhodium, uses, 403 Roasting, 379 Rocks, definition, 246 eruptive, 246 metamorphic, 248 plutonic, 246 sedimentary, 247 sections of, 126 volcanic, 246 Resetted, 72 Roughened faces of crystals, 78 Running streams, deposition by, 254 Saline residues, 419, 452, 455, 462 Salt of phosphorus, reactions with, 177, 179 bead, how to make, 162 Salts, chemical, 236 Sandstones, 247, 480 Scale of hardness, Moh's, 217 fusibility, i>. Kobell's, 164 Scalenohedron, hexagonal, 49 Schemes for blowpipe analysis, 197-207 for determination of minerals, Scorification, 379 Sectile, 216 Secondary crystallizations, 501 deposits, 347 phosphates, 468 vein minerals, 260 Sections of crystals, 125 or rocks, 126 oblique, 145 perpendicular acute bisectrix, 143 perpendicular optic axis, 141, 144 Sediments, chemical, 248, 253, 483 due to organisms, 248, 255, 483 mechanical, 247, 253, 483, 489 marine, 469 Segregations, see magmatic segregations Selenides, 396, 464 Selenium, summary of tests, 192 see also, 171, 172, 173, 176 Sensitive tint plates, 137, 139 Separation from magma, 241, 249 and silicate groups from watery solutions, 243, 245 Series, 24, 36, 42 Shales, 247 Sheaf like, 74 Sienna, 262 Signal, 84 Sign of elongation, 135 Silica, 482 Silicates, and their uses, 479 Silicates, rock forming, 479 Silicate magma, 241 Silicon, summary of tests, 192 see also, 173, 202, 205 Silky lustre, 210 Silver cupellation test, 378 Silver in manganese ores, 280 in lead ores, 316 see also, 173, 189, 203 summary of tests, 192 Silver minerals, 378 formation and occurrence, 382 uses, production and extraction, 380 Simple mathematical ratio, law of, 24 Skeleton crystals, 77 Slate, 248, 480 Smalt, 286 Smeeth specific gravity method, 222 Smith (Herbert) refractometer, 133 Soda, reactions with, 172 Soda lakes, minerals of, 258 Sodium carbonate, 172, Sodium, reactions with, 174 summary of tests, 193 see also, 169, 205 Sodium minerals, 421 formation and occurrence, 422 production and uses, 421 Solid solutions, 234 Solids in ocean and rivers, 254 Solubility tests, 180 Solvent power of water, 242 Solutions, fusion, 242 solid, 234 watery, 242 Specific gravity, 218 determination, 219 flask, 223 Spectra, absorption, 169 Spectroscope, use of, 166 chart, 168 Splintery fracture, 216 Springs, minerals from, 253 Stalactitic, 74 Stereographic projection, 84 Stfeak, definition and determination, 212 Striations of crystals, 77 Strontium, summar3 r of tests, 193 see also, 173, 202, 205, 207 Strontium minerals and their uses, 434 formation and occurrence, 435 Structure, crystals, 26, 208 hour glass, 79 zonal, 79 Sublimates in closed or open tubes, 176, on charcoal or plaster, 171 Sulphates of soda, 423 Sulphur deposits, 462 Sulphur extraction, 461 from pyrite, etc., 263 summary of tests, 193 see also, 176, 189 Sulphur minerals and their uses, 460 formation and occurrence, 462 from spring water, 254 Sulphuric acid, 460 Supports for blowpiping, 159 GENERAL INDEX. 623 Surface conductivity, 226 Symbols of crystal faces, 21 of forms, 23 of Miller, 22 of Weiss, 22 type, 25 Symmetry of crystals, 6 axes of, 7, 8, 10 centre of, 7, 10 classes, n, 25 determination, 87 geometric, 7, 10 partial, 12 planes of, 9, 10 law of, 7, 9 Synthesis of minerals, 240 Synthetic corundum, 556 diamonds, 553 turquois, 571 Systems, the six crystal, 21 System, determination, by axes, 21 by optical tests, 150 by partial symmetry, 12 Tables, mineral determination, 585-613 atomic weights, 614 Tabular habit, 76 Tantalum minerals, 355 Tarnish, definition, 211 Taste, terms used, 225 Tellurides, 395. 396 Tellurium, summary of tests, 193 see also, 172, i?3. i?6 Tellurium minerals, 464 Tenacity, 216 Tetragonal crystals, angles, 15 axial elements, 91 characteristics, 14 classes and forms, 42 to 47 in polarized light, 150 series, 42, 45 Tetrahedron, 63 Tetrahexahedron, 59 Tetrapyramid, 29 Thermal characters, 226 Thickness determining, 137 Thorium minerals, 310 formation and occurrence, 312 uses and production of, 311 Thoulet solution, 224 Tin, summary of tests, 194 see also, 171, 172, 173, 176, 181, 198, 199, 202 Tin minerals, 304 economic importance, 304 formation and occurrence, 305 Tin plate, 304 Titanium, summary of tests, 194 see also, 179, 181, 200, 202, 206 Titanium minerals, 308 economic importance, 308 Titanium, formation and occurrence, 308 Total reflection, 98 Tough, 216 Translucency, 213 Transparency, 152, 213 Transmission of heat, 226 of light, 96 Trapezohedron, 59 Triclinic crystals, angles, 20 axial elements, 91 characteristics, 19 classes and forms, 29 to 31 in polarized light, 151 Trigonal prism, first order, 53 Trisoctahedron, 59 Tristetrahedron, 63 Tube tests, 175, 176 Tungsten, summary of tests, 194 see also, 173, 179, 200 Tungsten minerals, 350 economic importance, 351 formation and occurrence, 351 Twin crystals, 68 axis, 68 plane, 69 symmetry of, 68 Twinning, polysynthetic, 69 Twins, contact, 68 penetration, 68 Type faces in any class, 25 metal, 332 symbols, 25 Types, 185 chemical, 236 Umber, 262 Underground water, 244 Uniaxial interference figures, 141 oblique sections, 146 optical characters, 103 ray surface, 102 vs. biaxial, 140 Uniaxial crystals, 102 in polarized light, 141 Unit face, 36 Unit prism, 39 pyramid, 38 Universal stage, 149 Uranium, summary of tests, 195 see also, 179, 201 Uranium minerals, 341 formation and occurrence, 342 uses and production, 341 Van der Kolk test, 129 Vanadium, summary of tests, 196 see also 121, 173, 179, 201 formation and occurrence, 337 uses and production, 336 Vein minerals, primary, 259 624 GENERAL INDEX. Vein minerals, secondary, 260 see under groups Veins, high temperature, 259 pegmatite, 250 Verneuil's blowpipe, 556 Vibration direction of lower nicol, 124 in calcite, 101 of faster and slower rays, 134 see also 104, 107, no Vibrations, plane of, 102 Vicinal faces, 25, 78 Vitreous lustre, 210 Volatilization, elements affected, 169 of light, 96, 101 Volcanic exhalations, vapors and acid solutions, 410, 439, 455, 462 rocks, 246 minerals of, 497 Volcanoes, minerals near, 250 Wave length of light, 99 Water of crystallization, 237 rain, 243 solvent power, 243 tests for, 175, 205 underground, 244 Watery solutions, minerals from, 243 solids from, 245 Weathering and weathering solutions, 247 Weathering, minerals produced by, 252 see saline residues, residual deposits and sediments Wedges, compensating, 136 Weiss's parametral symbols, 22 Westphal's balance, 224 White lead, 316 Wire like, 74 X-Rays and phosphorescence, 211 Young gold and silver veins, 382-395 Yttrium, production and uses, 312 Zeolites, 252 Zinc, summary of tests, 196 see also, 118, 171, 173, 176, 181, 198 Zinc minerals, 295 formation and occurrence, 297 uses and production ot, 295 Zinc pigments, 296 Zirconium minerals, 310 formation and occurrence, 312 Zonal determination of indices, 88 structures, 79 Zone relations, 88 Zones, 23 INDEX TO MINERALS. Names of species are in heavier type, varieties and synonyms in lighter type; the black numbers refer to the descriptions, the prefix t. is placed before the number of the group of the tables for determination. Acmite, 507. 251. Actinolite, 508, 256 Adamantine, spar. 413 Adularia, 252, 493 Aegirite, 507 Agate, 574 Agolite, 546 Alabandite, 280, t. 10 Alabaster, 443, 444 Alberdte, 478 Albite, 496, 69, 70, 250, 251, 253, 257, 258, 260, 494 Alexandrite, 561 Allanite, 529, t. 46, 251 Allophane, 549. t. S3 Almandine, 558, 567 Almandite, 510, 249 Aluminite, 415, t. 54 Alum stone, 416 Alunite, 416, t. 55, 252 Alunogen, 415, t. 26 Amalgam, 386, t. 19 Amazonite, 577 Amazonstone, 577 Amber, 578 Amber mica, 540 Amblygonite, 428, t. 41, 251 Ambrite, 478 Amethyst, 569, 484, 486 Amphibole, 507, t. 41, t. 48, 249, 252, 253, 256, 257, 258, 260, 501, 503 Amphibole group, 500 Analcite, 531, t. 42 Andalusite, 518, t. 55, 250, 257, 258, 570 Andalusite group, 517 Andesine, 495, 496 Andradite, 510, 249 Anglesite, 321, t. 31, 260 Anhydrite, 442, t. 40, 248, 254 Ankerite, 448 Annabergite, 294, t. 27 Anorthite, 494, t. 50, 257 Anorthoclase, 251, 253 Anthophyllite, 507, t. 52 Antigorite, 545 Antimony, 333, t. 15 Antimony ochre, 335 Apatite, 470, t. 51, 250, 251, 258, 260, 467 Aphthitalite, t. 25 Apophyllite, 534, t. 39 Aquamarine, 560, 522, 523, Aragonite, 444, t. 56, 69, 70, 254, 255 Argentine, 448 Argentite, 386, t. 5, 259 Arsenic, 329, t. 15 Arsenopyrite, 330, t. n, 259, 260 Asbestus, 509 Asparagus stone, 470 Asphaltum, 478, 474 Atacamite, 370, t. 47 Augite, 505,^506 Aurichalcite, 301, t. 29 Autunite, 345, t. 47 Aventurine, 486, 569 Axinite, 569, 570, t. 48, 259 Azurite, 371, t. 45, 260, 577 Balas ruby, 558 Baddelyite, 312 Barite, 432, t. 41, 252, 259 Barytocalcite, 433, t. 49 Bastite, 505 Bauxite, 413, t. 54, 253 Benitoite, 557 Beryl, 522, t. 52, 71, 250, 258, 559 Beryllonite, 562 Biotite, 540, t. 51, t. 52, 250, 256, 257, 258, 260, 481 Bismite, 327, t. 30 Bismuth, 326, t. 17, 260 Bismuth ochre, 327 Bismuthinite, 326, t. 17, 260 Bismutite, 327, t. 29 Black diamond, 552 hematite, 283 jack, 298 lead, 476 mica, 540 opal, 572 oxide of copper, 369 oxide of manganese, 281 Blende, 298 Bloodstone, 573 Blue carbonate of copper, 371 625 626 INDEX TO MINERALS. Blue iron earth, 472 chrysoprase, 573 spar, 572 vitriol, 370 Bog iron ore, 274, 275 manganese, 283 Bone turquois, 571 t Boracite, 458, t. 40, 255 Borax, 456, t. 25, 255 Bornite, 364, t. 22, 259, 260 Boronatrocalcite, 457 Bort, 552 Boulangerite, 320 Bournonite, 319, t. 17 Braunite, 280, t. 6, 259 Brimstone, 463 Brittle silver ore, 389 Brochantite, 370, t. 47, 260 Bromargyrite, 392 Bromyrite, 392, t. 31, 260 Bronze mica, 540 Bronzite, 504 Brookite, 310, t. 10, 250, 257 Brown clay ironstone, 275 hematite, 274 Brucite, 452, t. 58, 256 Bytownite, 495 Cacholong, 573 Cairngorm, 569 Calamine, 301, t. 33, 260 Calaverite, 400, 259 Calif ornite, 576, 512 Calc spar, 446 Calcite, 446, t. 56, 252, 254, 255, 259, 437 Calomel, 377, t. 35 Cancrinite, t. 38, 251 Capillary pyrites, 292 Carbonado, 552 Carnallite, 420, t. 25, 255, 451 Carnelian, 573 Carnotite, 344 Cassiterite, 307, t. 7, t. 31, 251, 260 Cat's-eye, 486, 561, 569 Celestite, 435, t. 41, 254, 259 Celsian, 493 Cerargyrite, 391, t. 31, 260 Cerite, 315, t. 57 Cerussite, 323, t. 29, 260 Cervantite, 335, t. 58 Ceylonite, 558 Chabazite, 532, t. 39, 77 Chalcanthite, 370, t. 25, 260 Chalcedony, 486, t. 59, 254, 259 484, 573 Chalchihuitl, 572 Chalcocite, 364, t. 5, 259, 260 Chalcopyrite, 365, t. 22, 251 Chalk, 448 Chamosite, 254 Chiastolite, 257, 80, 518 Chili saltpetre, 427 China clay, 547 Chloanthite, 291 Chlorastrolite, 578 Chlorite group, 541, t. 52, 252, 253, 257, 258, 259, 482 Chondrodite, t. 57, 252 Chromic iron, 346 Chromite, 346, t, 10, 250, 251 Chrysoberyl, 560, t. 55, 251, 258 ; Chrysocolla, 372, t. 58, 260, 572 Chrysolite, 513, t. 57, 257, 566 oriental, 561 Chrysoprase, 573 Chrysotile, 545 Cinnabar, 376, t. 35, 254 Cinnamon stone, 567 Citrine, 569 Clausthalite, 321, t. 13 Clay, 482 Clay ironstone, 272 Clinochlore, 542 Coal, mineral, 478 Cobalt glance, 290 pyrites, 289 Cobaltite, 290, t. n, 259 Colemanite, 458, t. 43 Columbite, 355, t. 6. t. 10, 250 Common garnet, 511 opal, 487 pyroxene, 506 Copalite, 478 Copiapite, 270, t. 26 Copper, 362, t. 24, 72, 75, 250, 251, 260 Copper glance, 364 nickel, 293 pyrites, 365 uranite, 345 vitriol, 370 Coquimbite, 270, t. 26 Cordierite, 529 Corundum, 412, t. 55, 249, 251, 258, 554 Crocidolite, 509, t. 48 Crocoite, 347, t. 30, 260 Cryolite, 412, t. 40 Cuprite, 368, t. 47, 77, 260 Cyanite, 519, t. 55, 251, 257, 258, 557 Cymophane, 561 Dammar, 478 Dark ruby silver, 389 Datolite, 536, t. 42 Delessite, 543 Demantoid, 567 Descloizite, 339, t. 30 Desmine, 533 Diallage, 507 Diamond, 550, t. 59, 250, 251 Diaspore, 415, t. 55 Diatomaceous earth, 487 Dichroite, 529 Diopside, 506, t. 41, 256, 567 INDEX TO MINERALS. 627 Dipyre, 516 Dog-tooth spar, 447 Dolomite, 448, t. 56, 248, 255, 259, 451 Dry-bone, 300 Edenite, 509 Eisstein, 412 Elaeolite, 499 Elaterite, 478 Electric calamine, 301 Embolite, 392, t. 31, 260 Emerald, 559, 522, 523, Emery, 412, 413 Enargite, 366, t. i, 259 Enstatite, 504, t. 52, 256, 501, 503, 567 Epidote, 528, t. 48, 252, 253, 256, 258, 567 Epidote group, 526 Epsomite, 453, t. 26, 452 Epsom salt, 453 Erythrite, 292, t. 27 Essonite, 567 Euclase, 562, 251 Falcon's eye, 570 False topaz, 486 Fancy sapphires, 554 Fayalite, 515, 249 Feather ore, 320 Feldspars, 488, 492. 249, 250, 481 Feldspathoids, 497 Ferberite, 352 Fergusonite, 356, t. 59, 251 Ferruginous quartz, 486 Fibrolite, 519 Fire opal, 487, 572 Flint, 486 Flos ferri, 444 Fluorite, 441, t. 40, 250, 252, 254, 257, 259, 260, 438 Fluor spar, 441 Fontainebleau sandstone, 80, 447 Fool's gold, 266 Forsterite, 513, t. 57, 257 Franklinite, 302, t. 7 Freibergite, 367 French chalk, 546 Fullers earth, 482 Gadolinite, 315, t. 58, 251 Gahnite, 302, t. 35 Galena, 318 Galenite, 318, t. 3, t. 13, 259 Garnet, 509, t. 48, t. 59, 249, 250 256, 258, 260, 481, 567 Garnierite, 294, t. 37, 58 Gay-Lussite, 427, t. 38 Geocronite, 320 Geyserite, 487 Gibbsite, 415, t. 55, 73, 253, 258 Gilsonite, 478 Girasol, 573 Glauber salt, 426 Glauberite, 427 Glauconite, 254 Glaucophane, 509 Goethite, 273, t. 9, t. 37 Gold, 399, t. 24, 250, 251, 259, 260 Gold selenides, 396 Gold tellurides, 400, t. 16, t. 23, 259, 260, 395 Golden beryl, 560 Goshenite, 523 Goslarite, 299, t. 26 Graphite, 476, t. 6, 250, 251, 257, 258, 473, 475 Gray antimony, 334 copper ore, 367 Greasy quartz, 486 Greenalite, 254 Greenockite, 303, t. 32 Green carbonate of copper, 371 Grossularite, 510, 256 Griinerite, 509 Guano, 469 Gummite, 344 Gypsite, 444 Gypsum, 443, t. 40, 248, 252, 254, 438 Halite, 425, t. 25, 248, 254, 422 Halloysite, 549, 254 Harmotome, 534, t. 40 Hausmannite, 281, t. 10, 250, 259 Hauynite, 500, 497, 498, 249, 557 Heavy spar, 432 Hedenbergite, 506 Heliodore, 560 Heliolite, 578 Heliotrope, 573 Hematite, 271, t. 9, t. 37. 73, 250, 258, 260, 579 Hessite, 387, t. 16 Heulandite, 534, t. 40 Hewettite, 340 Hiddenite, 565, 429 Hornblende, 508, 507, 251, 256, 257 Horn silver, 391 mercury, 377 Horse flesh ore, 364 Huebnerite, 352 Hyacinth, 563, 567, 314 Hyalite, 487 Hyalophane, 493 Hyalosiderite, 514 Hydrophane, 573 Hydrozincite, 300, t. 32, 254 Hydrohematite, 274 Hypersthene, 505, t. 48, t. 52, 251, 256, 501, 503 Ice, 465 Iceland spar, 446, 447 Idocrase, 511 628 INDEX TO MINERALS. Ilmenite, 273, t. 4. t. 9. 250, 251, 258, 260 Indianite, 497 Indicolite, 565 Indigo copper, 363 Infusorial earth, 481, 487 lodargyrite, 392 lodyrite, 392. t. 31. 260 lolite, 529, t. 51, 251, 257, 258, 557 Indium, 406 Iridosmine, 406, t. 19 Iron, 265, t. 18, 251 Iron pyrites, 266 Isinglass, 539 Jacinth, 563 Jade, 574 Jadeite, 575 Jamesonite, 320, t. 13 Jargon, 563 Jeffersonite, 507 Jasper, 486 Jeffersonite, 507 Jet, 579 Kainite, 420, t. 25, 255 Kalinite, 420, t. 25 Kaolin, 547 Kaolinite, 547, t. 55, 482 Kermesite, 335, t. 30 Kieserite, 453, t. 26, 255, 451 Krennerite, 400 Kunzite, 429, 565 Kyanite, 519 Labradorite, 495, 496, 251, 578 Lapis Lazuli, 257, 576 Laterite, 413 Lazulite, 572 Lazurite, 576, t. 39 Lead, 318 Lepidolite, 429, t. 41, 250, 260 Leucite, 498, t. 54, 249, 497, 498 Leucopyrite, 331 Light ruby silver, 388 Lime uranite, 345 Limestone, 446, 448 Limonite, 274, t. 9, t. 37, 74, 253, 254 256, 260 Linarite, 322, t. 31 Linnaeite, 289, t. 14 Lithia mica, 429 Lodestone, 270 Lollingite, 331, t. n Loxoclase, 493 Magnesian limestone, 448 mica, 540 Magnesite, 453, t. 56, 255, 452 Magnetic iron ore, 270 pyrites, 266 Magnetite, 270, t. 4. 77, 250, 251, 253 258, 260 Malachite, 371, t. 45, 260, 578 Vlanganblende, 280 Manganite, 282, t. 10 Manjak, 478 Marble, 446, 448 Margarite, 541, t. 52 Marialite, 515 Marcasite, 268, t. 22, 70, 256 Marl, 448 Vlartite, 272 Mascagnite, 430 Matura diamonds, 563 VIeerschaum, 546 Meionite, 515 Melaconite, 369 Melanterite, 270, t. 26 Melilite, 499, t. 46, 497, 498 Menaccanite, 273 Mercurial tetrahedrite, 375 Mercury, 375, t. 20 Metacinnabarite, 376, t. 6 Metahewettite, 340 Mica group, 537, t. 52, 249, 260, 481 Microcline, 494, t. 52, 250, 490 Milky quartz, 486 Millerite, 292, t. 22, 250 Mimetite, 323, t. 27, 260 Mineral coal, 478 Minium, 321, t. 30 Mirabilite, 426, t. 25, 255 Mispickel, 330 Misy, 270 Mizzonite, 516 Mocha stone, 574 Moldavite, 567 Molybdenite, 349, t. 16, 250, 251, 260 Molybdite, 350, t. 34 Monazite, 313, t. 58, 250, 257 Montmorillonite, 549 Moonstone, 577 Morganite, 560 Moss agate, 574 Mottramite, 339 Mundic, 266 Muscovite, 539, t. 52, 250, 258 Native antimony, 333 arsenic, 329 boric acid, 456 bismuth, 326 copper, 362 gold, 399 iron, 265 lead, 318 mercury, 375 platinum, 405 silver, 385 sulphur, 463 tellurium, 465 INDEX TO MINERALS. 629 Native vermilion, 376 Natrolite, 532, t. 42 Needle zeolite, 532 Nephelite, 499, t. 42, 249, 251, 497, 498 Nephrite, 575 Niccolite, 293, t. 21, 259 Nickel bloom, 294 Nigrine, 309 Nitre, 420, t. 25, 256 Noselite, 500, 249, 497, 498 Noumeite, 294 Ochre, red, 272 yellow, 275 Octahedrite, 310 Odontolite, 57* Oligoclase, 495, 496 Olivenite, t. 27 Olivine, 5*3 Olivine group, 512 Onofrite, 377, t. 2 Onyx, 574, 448 Opal, 487, t. 59. 253, 254, 256, 259, 572 Orangite. 315 Orpiment, 330, t. 28, 254 Orthoclase, 492, t. 52, 250, 259, 489 Ozocerite, 477, 473 Palladium, 406 Pandermite, 458 Paragonite, 540 Pargasite, 256, 509 Patronite, 338 Pearl spar, 448 Pectolite, 535, t. 39 Pencil-stone, 548 Penninite, 543 Pentlandite, 292, t. 22, 250, 251 Peridot, 513, 566 Peristerite, 577 Petalite, 430, t. 41, 251 Petroleum, 477, 473 Petzite, 400, 259 Phenacite, 562, t. 55, 251 Phlogopite, 540, t. 52, 250, 258 Phosgenite, 324, t. 29 Phosphate rock, 256, 471 Phosphorite, 471 Picotite, 558 Piedmontite, 528, 258 Pitchblende, 343, 344 Plagioclase, 494, t. 41, t. 43, 490 Plagionite, 320 Platiniridium, 406 Platinum, 405, t. 18, t. 19, 250, 251, 402 Plumbago, 476 Plumbocalcite, 448 Polianite, 282, t. 6 Polybasite, 390, t. 2, 259 Potash alum, 420 Potash feldspar, 492 Potash mica, 539 Prase, 569 Precious opal, 487 topaz, 564 Prehnite, 535, t. 40, 73, 258, 567 Priceite, 458 Prochlorite, 543 Proustite, 388, t. 28, 259 Psilomelane, 283, t. 6 Psittacinite, 339 Pucherite, 340 Purple copper ore, 364 Pyrargyrite, 389, t. 7, t. 31, 259 Pyrite, 266, t. 22, 68, 75, 77, 250, 251, 256, 259 Pyrolusite, 281, t. 6 Pyromorphite, 322, t. 30, 260 Pyrope, 568, 570, 249 Pyrophyllite, 548, t. 52, 258 Pyroxene, 505, t. 41, t. 48, 249, 251, 256, 258, 260, 501, 503 Pyroxene group, 500 Pyrrhotite, 266, t. 22, 250, 251 Quartz, 484, t. 59, 68, 76, 249, 250, 254, 257, 259, 480, 484, 568 Realgar, 329, t. 28, 254 Red antimony, 335 hematite, 272 iron ore, 271 ochre, 272 oxide of copper, 368 zinc ore, 299 Rensselaerite, 546 Rhodochrosite, 284, t. 56, 259 Rhodolite, 568 Rhodonite, 284, t. 48, 259, 579 Rhyacolite, 493 Richterite, 509 Rock crystal, 568, 484, 486 gypsum, 444 meal, 448 salt, 248, 425 Roscoelite, 340, t. 48, 259 Rose quartz, 486, 569 Rubellite, 564 Rubicelle, 558 Ruby, 554, 412, 413, 556 copper, 368 spinel, 558 silver, 388, 389 Rutile, 309, t. 10, 59, 80, 250, 251, 253, 257. 258 Sal ammoniac, 430, t. 26 Salt, 425 Saltpetre, 420 Samarskite, 356, 251 Sanidin, 493, 489 Sapphire, 554, 412, 413. 555 630 INDEX TO MINERALS. Sapphire, fancy, 554 synthetic, 556 Sapphirine, 558 Sard, 573 Sardonyx, 574 Sassolite, 456, t. 25, 254 Satin-spar, 447 Scapolite group, 5*5 Scheelite, 353, t. 51. 260 Schefferite, 506 Schorl, 524 Schorlomite, 51 1 Schwatzite, 368 Selenite, 443. 444 Semi opal, 487 Senarmontite, 335, t. 30 Sepiolite, 546, t. 50 Sericite, 539. 252, 253 Serpentine, 544, t. 51, 71, 253, 257, 258, 481, 576 Siderite, 275, t. 36, 254, 258 Siliceous sinter, 487 Sillimanite, 519, t. 55, 251, 257, 258 Silver, 385, t. 19, 260 Silver glance, 386 Simetite, 578 Smaltite, 291, t. n, 259 Smithsonite, 300, t. 32, 260, 572 Smoky quartz, 486, 569 Snow, 465 Soapstone, 545 Soda nitre, 427, t. 25, 256, 424 Sodalite, 500, t. 42, 249, 251, 497, 498, 577 Sodalite group, 500 Spartaite, 448 Spathic ore, 275 Specular iron, 271 Sperrylite, 405, t. n Spessartite, 568, 510, 249 Sphalerite, 298, t. 7, t. 32, 259 Sphene, 525, 566 Spinel, 558, t. 55, 68, 249, 256, 258, 260 Spodumene, 429, t. 41, 250, 565 Stalactite, 448 Stalagmite, 448 Stannite, 306, t. 12 Star quartz, 569 Stassfurtite, 458 Staurolite, 520, t. 59, 251, 257, 258 Steatite, 545 Stephanite, 389, t. 2, 259 Stibiconite, 335 Stibnite, 334, t. 2, t. 12, 72, 254, 259 Stilbite, 533, t. 40 Stream tin, 307, 308 Stromeyerite, 387, t. 19 Strontianite, 436, t. 49 Succinite, 578 Sulphur, 463, t. 35, 254, 256 Sunstone, 578 Sylvanite, 400, 259 Sylvite, 419, t. 25, 255 Talc, 545, t. 52, 253, 257, 258, 481 Tantalite, 355 Tellurium, 465, t. 16 Tennantite, 368, t. i Tenorite, 369, t. 5 Tephroite, 285, t. 46 Terlinguaite, 378 Tetradymite, 326, t. 17 Tetrahedrite, 367, t. 2, t. 12, t. 15, 259, 378 Thenardite, 427 Thomsonite, 534 Thorianite, 316 Thorite, 315, t. 57, 251 Thuringite, 254 Thulite, 528, t. 39, 579 Tigers eye, 5?o Tiemannite, 377, t. 12 Tin stone, 307 Tin pyrites, 306 Tinkal, 456 Titanic iron ore, 273 Titanite, 525, t. 48, 250, 258, 566 Titan olivine, 514 Topaz, 523, t. 55, 249, 250, 258, 260, 564 Torbernite, 345, t. 47 Touchstone, 486 Tourmaline, 524, t. 41, t. 48, t. 52, t. 59, 249, 250, 252, 256, 257, 258, 260, 564 Travertine, 254, 448 Tremolite, 508, t. 41, 256 Tridymite, 486, t. 59, 484 Tripoli, 481, 487 Trona, 427, t. 25, 255 Troostite, 301 Turgite, 274, t. 9, t. 37 Turkis, 570 Turkish stone, 570 Turquois, 570, t. 58 Uintahite, 478 Ulexite, 457, t. 43, 255 Umber, 275 Uralite, 500 Uraninite, 343, t. 8, t. 10, 251 Uvanite, 344 Uvarovite, 510, t. 59 Valencianite, 259, 489 Valentinite, 335, t. 30 Vanadinite, 338, t. 30, 260 Vanadium mica, 340 Variscite, 572 Vesuvianite, 511, t. 48, 252, 256, 258 Vivianite, 472, t. 37, 260 Volborthite, 340 Wad, 283 Wagnerite, 471, t. Water, 465 INDEX TO MINERALS. Water sapphire, 55? Wavellite, 471, t. 54 Wernerite, 515, t. 40, 251, 256, 258 White iron pyrites, 268 lead ore, 323 mica, 539 opal, 572 Willemite, 301, t. 33 Witherite, 433, t. 38 Wolframite, 352, t. 9, 260 Wollastonite, 507, t. 39, 256, 258 Wood tin, 308 Wulfenite, 350, t. 30, 260 Wurtzite, 299, t. 32 Wurtzilite, 478 Xenotime, 313, t. 59 Yellow copper ore, 365 Yellow ochre, 275 quartz, 486 Zeolite group, 529 Zinc blende, 298 vitriol, 299 bloom, 300 Zincite, 299, t. 34 Zinkenite, 320 Zircon, 314, t. 59, 76, 250, 251, 258, 563 Zircon favas, 312 Zirconium oxide, 312 Zoisite, 528, t. 41, 251, 258 RETURN EARTH SCIENCES LIBRARY TO -*> 230 McCone Hall 642-2997 LOAN PERIOD 1 1 MONTH 2 3 4 5 6 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS Books needed for class reserve are subject to immediate recall DUE AS STAMPED BELOW FORM NO. DD8 UNIVERSITY OF CALIFORNIA, BERKELEY BERKELEY, CA 94720