LIBRARY 
 
 UNIVERSITY OF 
 ^CALIFORNIA 
 
 EARTH 
 
 SCIENCES 
 LIBRARY 
 
DESCRIPTIVE MINERALOGY 
 
 WITH ESPECIAL REFERENCE TO THE 
 
 OCCURRENCES AND USES OF MINERALS 
 
 BY 
 
 EDWARD HENRY KRAUS, PH.D. 
 
 PROFESSOR OF MINERALOGY AND PETROGRAPHY, AND DIRECTOR OF THE 
 MINERALOGICAL LABORATORY IN THE UNIVERSITY OF MICHIGAN 
 
 GEORGE WAHR, PUBLISHER 
 
 ANN ARBOR, MICH. 
 I9II 
 
r "5O C!?r'D 
 
 iis S rlwu 
 
 Copj-right, 1907, 
 
 KY 
 EDWARD H. KRAUS. 
 
 Copyright, 1911, 
 
 BY 
 EDWARD H. KRAUS. 
 
 EARTH 
 SCIEK 
 LIBR/ 
 
 ANN ARBOR. MICHIGAN 
 
PREFACE 
 
 This text is based to a large extent upon lectures delivered for a number 
 of years by the author at the University of Michigan. It does not attempt 
 to cover the entire field of Mineralogy, but is to aid the student attending the 
 lectures on Descriptive Mineralogy. Blank pages have been bound into the 
 text so that supplementary notes may be easily added. 
 
 The classification followed is essentially the one suggested by Groth 
 according to which the simplest minerals are discussed first and the more 
 complex, especially the silicates and allied compounds, last. Especial empha- 
 sis has been placed upon the association, occurrences, and uses of minerals. 
 Where possible, statistics relating to the production in the United States in 
 recent years have been added. 
 
 As the text is designed primarily for the student of General Mineralogy 
 very little reference has been made to the miscroscopic optical properties. 
 Those desiring such data would naturally refer to some of the excellent texts 
 on Optical Mineralogy and Rock Minerals which have been recently pub- 
 lished in this country. 
 
 Although all possible sources have been drawn upon, no attempt was 
 made to acknowledge the same systematically. A bibliography of the most 
 important and more frequently consulted publications will, however, be 
 found on page vn. For many valuable suggestions and aid in the reading 
 of proof I am indebted to Mr. W. F. Hunt, Instructor in Mineralogy in the 
 University of Michigan ; and also to the Ward's Natural Science Establish- 
 ment, Rochester, N. Y., and the Sullivan Machinery Company, Chicago, 111., 
 for the loan of several cuts. 
 
 Mineralogical Laboratory, 
 
 University of Michigan, EDWARD H. KRAUS. 
 
 September, 1910. 
 
 217049 
 
TABLE OF CONTENTS 
 
 PAGE 
 
 Bibliography . . . . . . . . . . vn 
 
 Introduction ..... . - . . . . . . . i 
 
 Elements . . . . . . . . . . . 3 
 
 Sulphides and analogous selenium, tellurium, arsenic, antimony, and 
 
 bismuth compounds '. . . . . . . 29 
 
 Oxides, hydroxides, and oxysulphides ...... 67 
 
 Haloids . 98 
 
 Nitrates, carbonates, manganites, and plumbites .... 109 
 
 Sulphates, chromates, molybdates, tungstates, and uranates . . 131 
 
 Aluminates, ferrites, borates, and so forth . . . . 155 
 
 Phosphates, arsenates, antimonates, vanadates, niobates, and tantalates 165 
 
 Silicates, including titanates, zirconates, and thorates . . . 183 
 
 Organic compounds . . . .. . . . . . 288 
 
 Classification of minerals according to elements . . . . 293 
 
 Index ,' . . . . . . . . . 319 
 
BIBLIOGRAPHY 
 
 BAUER, M. Edelsteinskunde. 2d edition, Leipzig, 1909. 
 
 Lehrbuch der Mineralogie. 2d edition, Stuttgart, 1904. 
 
 BAUMHAUER, H. Kurzes Lehrbuch der Mineralogie. 3d edition, Frei- 
 burg, 1906. 
 
 BECK, R. Lehre von der Erzlagerstatten. 3d edition, Berlin, 1909. 
 
 Also English translation by W. H. Weed, New York, 1905. 
 
 BEYSCHLAG, F., KRUSCH, P., and VOGT, J. H. L. Die Lagerstatten der Nutz- 
 baren Mineralien und Gesteine. Part i, Stuttgart, 1909. 
 
 BRANNER, J. C. and NEWSON, J. F. Syllabus of Economic Geology, 2d edi- 
 dition, Palo Alto, 1900. 
 
 BRAUNS, R. Chemische Mineralogie. Leipzig, 1896. 
 Das Mineralreich. Stuttgart, 1903. 
 
 BEUHNS, W. Die Nutzbaren Mineralien und Gebirgsarten im Deutschen 
 Reiche. Berlin, 1906. 
 
 CLARKE, F. W. Data of Geochemistry, Bulletin 330, United States Geolog- 
 ical Survey, Washington, 1908. 
 
 BRUSH, G. J. and PENFIEED, S. L. Manual of Determinative Mineralogy. 
 1 6th edition, New York, 1903. 
 
 DANA, E. S. Text-Book of Mineralogy. New edition, New York, 1898. 
 
 DANA, J. D., DANA, E. S., and FORD, W. E. System of Mineralogy. 6th 
 edition 1892, ist Appendix 1899, 2d Appendix 1909. 
 
 DoELTER, C. Physkalisch-Chemische Mineralogie. Leipzig, 1905. 
 
 EAKLE, A. S., Mineral Tables, ist edition, New York, 1904. 
 
 ERNI, H. and BROWN, A. P. Mineralogy Simplified. 3d edition, Phila- 
 delphia, 1901. 
 
 FARRINGTON, O. C. Gems and Minerals. Chicago, 1903. 
 
 FUCHS, E. and DELAUNAY, L. Traite des Cites Mineraux et Metalliferes. 
 2 volumes, Paris, 1893. 
 
 GROTH, P. Chemische Krystallographie. Volumes I and II, Leipzig, 1906 
 
 and 1908. 
 
 Einleitung in die Chemische Krystallographie. Leipzig, 1904. 
 Fuhrer durch die Mineraliensammlung in Miinchen. Munich, 1891. 
 Tabellarische Uebersicht der Mineralien. 4th edition, Braun- 
 schweig, 1898. Also French edition by Joukowsky and 
 Pearce, Geneva, 1904. 
 
 GUERICH, G. Das Mineralreich. Neudamm, 1899. 
 
 HINTZE, C. Lehrbuch der Mineralogie. Volume I, pages i to 1920 (still in 
 press), Volume II, 1897, Leipzig. 
 
VIII DESCRIPTIVE MINERALOGY 
 
 IDDINGS, J. P. Rock Minerals. New York, 1906. 
 
 JOHANNSEN, A. Determination of Rock-Forming Minerals, New York, 1909. 
 
 KEMP, J. F. Handbook of Rocks. 3d edition, New York, 1906. 
 
 Ore Deposits of the United States and Canada, New York. 
 
 3d edition, 1906. 
 
 KLOCKMANN, F. Lehrbuch der Mineralogie. 4th edition, Stuttgart, 1907. 
 KRUSCH, P. Die Untersuchung und Bewertung von Erzlagerstatten. 
 
 Stuttgart, 1907. 
 
 KUNZ, G. F. Gems and Precious Stones of North America. New York, 1890. 
 MERRILL, G. P. Rocks, Rock- Weathering, and Soils. New York, 1906. 
 
 Non-Metallic Minerals. New York, 1904. 
 MIERS, H. A. Mineralogy. London and New York, 1902. 
 Mineral Industry. Published annually, New York. 
 Mineral Resources of the United States. Published annually by the United 
 
 States Geological Survey, Washington. 
 MOSES, A. J., and PARSONS, C. L. Elements of Mineralogy, Crystallography, 
 
 and Blowpipe Analysis. 4th edition, New York, 1909. 
 NAUMANN, C. F., and ZIRKEL, F. Elemente der Mineralogie. I4th edition, 
 
 Leipzig, 1901. 
 
 PENFIELD, S. L. Tables of Minerals. 2d edition, New York, 1907. 
 PHILLIPS, J. A., and Louis, L. Treatise of Ore Deposits. 2d edition, 
 
 London, 1896. 
 
 PIRSSON, L. V. Rocks and Rock Minerals. New York, 1906. 
 RAU, W. Edelsteinskunde. Leipzig, 1907. 
 
 RINNE, F. Praktische Gesteinskunde. 2d edition, Hanover, 1905. 
 RiES, H. Economic Geology of the United States. New and revised edition, 
 
 New York, 1910. 
 ROSENBUSCH, H., and .WUELFING, E. A. Mikroskopische Physiographic 
 
 der Mineralien ' und Gesteine. Volume I, part 2, 
 
 Stuttgart, 1905. 
 
 SAUER, A. Mineralkunde. Stuttgart, 1907. 
 STELZNER, A. W., and BEKGEAT,, A. Die Erzlagerstatten. 2 volumes, 
 
 Leipzig, 1905 and 1906. 
 
 TSCHERMAK, G. Lehrbuch der Mineralogie. 6th edition, Vienna, 1905. 
 VAN HORN, F. R. Lecture Notes on General and Special Mineralogy. 
 
 Cleveland, 1903. 
 
 VON KOBELL, F. Lehrbuch der Mineralogie. 6th edition, Leipzig, 1899. 
 WEINSCHENK, E. Die Gesteinbildenden Mineralien. 2d edition, Frei- 
 burg, 1907. 
 
 WILLIAMS, G. F. Diamond Mines of South Africa. New York, 1902. 
 WINCHF,LL, N. H., and WINCHELL, A. H. Elements of Optical Mineralogy. 
 
 New York, 1909. 
 
INTRODUCTION 
 
 Descriptive mineralogy includes a detailed discussion in some system- 
 atic order of the crystallographic, physical, and chemical properties as also 
 the associations, distribution, and uses of minerals. In general there are 
 two schemes of classification of minerals. In the one all minerals possessing 
 some element as an important constituent are grouped and described together. 
 Thus all important compounds of iron, hematite Fe 2 O 3 , magnetite Fe 3 O 4 . 
 limonite Fe. t O 3 (OH) 6 , pyrite FeS 2 , siderite FeCO 3 and so forth, would 
 be placed in one group and each described regardless of their chemical 
 and crystallographic relationships. This method is, however, not to be 
 considered as truly scientific. The second method, and the one adopted 
 in this text, groups minerals according- to their chemical composition and 
 the important principle of isomorphism. In this way ten classes are easily 
 obtained. 
 
 i. Elements.* 
 
 2.. Sulphides and analogous compounds of selenium, tellurium, arsenic, 
 antimony, and bismuth. 
 
 3. Oxides, hydroxides, etc. 
 
 4. Haloids. 
 
 5. Nitrates, carbonates, etc. 
 
 6. Sulphates, chromates, molydates, tungstates, and uranates. 
 
 7. Borates, aluminates, etc. 
 
 8. Phosphates, arsenates, etc. 
 
 9. Silicates, titanates, etc. 
 10. Organic compounds. 
 
 Within each of the above classes the various species are arranged as 
 far as possible in isomorphous series, thus, bringing together those minerals 
 which possess a similarity in chemical composition and crystal form. All 
 minerals which are considered common are printed in large, heavy type, 
 for example, PYRITE. Minerals which are not common but yet important 
 are indicated with smaller type, thus, Calomel ; while with those which 
 are less important still smaller type is used, for example, DIOPTASE. 
 
 * This classification is essentially that given by von Groth (see Tabellarische 
 Uebersicht der Mineralien, 4th edition, 1898; also French edition of 1904). It does 
 not differ materially from that of Dana (System of Mineralogy, 6th edition, 1892). 
 
I. ELEMENTS 
 
 The elements may be divided into three groups known as the non- 
 metals, semi-metals, and metals. The non-metals include such elements 
 as sulphur, carbon, etc., the specific gravities of which are comparatively 
 low. The semi-metals comprise such elements as arsenic, antimony, bis- 
 muth and so forth and possess a specific gravity ranging from 5.7 to 10. 
 These elements are not ductile. The metals include gold, silver, platinum 
 and so forth. They are usually quite heavy, the specific gravity varying 
 from 7.2 up to 23. These elements are ductile. 
 
 There is a pronounced tendency noticeable among the elements to crys- 
 tallize in the cubic system, especially in the form of the cube, or the closely 
 related form* the rhombohedron of the ditrigonal scalenohedral class of 
 the hexagonal system. The following table showing the number of elements 
 native and artificial crystallizing in the different systems is instructive. 
 
 Cubic system 12 
 
 Hexagonal system 7 
 
 Tetragonal system 2 
 
 Orthorhombic system 2 
 
 Monoclinic system 2 
 
 Triclinic system 
 
 CARBON GROUP 
 
 The members of this group are all infusible and comparatively light 
 in weight. 
 
 DIAMOND ) 
 GRAPHITE V Carbon. 
 
 SCHUNGITE ) 
 
 DIAMOND, Pure Carbon, C. 
 
 Cubic, hextetrahedral class. Observed in crystals which may be micro- 
 scopically small or weigh rnore than 3,000 carats. f Most commonly observed 
 forms are the octahedron, rhombic dodecahedron, and hexoctahedron ; rarer 
 
 * Compare, Kraus, Essentials of Crystallography, 1906, page 60. 
 t The standard of weight for the diamond is the carat which according to locality 
 possesses a different value. Some of these are as follows : 
 
4 DESCRIPTIVE MINERALOGY 
 
 are the cube, tetrahexahedron, and the .tetragonal and trigonal trisoctahe- 
 drons. All of the above forms with the exception of the tetragonal trisocta- 
 hedron may occur either as independent or predominating forms. Develop- 
 ment apparently holohedral. The symmetry of the hextetrahedral class is 
 revealed principally by the etchings and striations observed on the crystal 
 faces. Crystals possessing a distinct tetrahedral habit have, however, been 
 observed. Positive and negative forms are not to be distinguished. Crys- 
 tals are often rounded and distorted. Twins are common. Two twinning 
 laws have been distinguished, (i) Supplementary twins, twinning plane 
 parallel to a face of the cube. Here two tetrahedrons interpenetrate and 
 give rise to a form simulating the octahedron. The characterizing features 
 of such twins are the furrows parallel to the edges of the octahedrons. 
 (2) Contact twins according to the Spinel law, the twinning plane being 
 parallel to a face of the octahedron. Polysynthetic twinning according to 
 this law is also to be observed. 
 
 Highly perfect cleavage parallel to a face of the octahedron. This is 
 of great value in the cutting of the diamond. The fracture is conchoidal 
 and the hardness the greatest of any known mineral being rated as 10 in 
 Mohs's scale. The hardness, however, varies with the crystal faces. It is 
 greater on the faces of the cube than on those of the octahedron. Also 
 according to Bauer the powder from the surface is harder than that 
 obtained from fragments. Australian diamonds and especially the black 
 diamonds from Borneo are said to be harder than those from South Africa. 
 
 Adamantine luster, however, sometimes more or less greasy. Usually 
 
 Florence o. 197200 grams 
 
 Borneo 0.205000 grams 
 
 Leipzig 0.205000 grams 
 
 Batavia 0.205000 grams 
 
 Spain 0.205393 grams 
 
 London 0.205904 grams 
 
 Berlin 0.205440 grams 
 
 Paris 0.205500 grams 
 
 Amsterdam 0.205570 grams 
 
 Lisbon 0.205750 grams 
 
 Frankfurt a/M. .0.205770 grams 
 
 Vienna 0.206160 grams 
 
 Livorno 0.215990 grams 
 
 The diamond carat as defined by Webster's International Dictionary is 3 1/5 
 troy grains or 0.20736 grams. The Century Dictionary places it equal to 3 1/6 troy 
 grains or 0.2052 grams. The South African diamond carat according to Gardner 
 Williams equals 3-174 grains or 0.20567 grams. In 1877 a syndicate of London, 
 Paris, and Amsterdam jewelers fixed the weight of the carat equal to 3.163 troy 
 grains or 0.205 grams. 
 
ELEMENTS 5 
 
 transparent, colorless, and water white (stones of the first water) ; yellow, 
 red, gray, brown, green, bluish rarely blue or black. Doelter thinks that 
 the colors may be caused by small amounts of the oxides of iron, chromium, 
 manganese, or titanium. The streak is ashen gray. 
 
 Specific gravity, 3.50 to 3.53. This is similar to that of topaz, 3.4 
 to 3.6, but differs materially from beryl, 2.7, and quartz, 2.65. 
 
 High refractive powers and strong dispersion. ^14= 2. 40735, 
 7i Na =2.41734, n 7-1 = 2.46476. The play of colors (fire) so characteristic 
 of the diamond is due to the strong dispersion. Owing to inclusions and 
 internal strains and stresses anomalous double refraction is often observed. 
 On account of internal strains the smoky stones from Kimberley often 
 explode. Excellent conductor of heat, hence, cold to the touch. Poor con- 
 ductor of electricity. When rubbed becomes positively electrified. Many 
 diamonds when exposed to light or an electric discharge phosphoresce. 
 Transparent to the X rays. This can be made use of in the detection of 
 imitations of lead glass which are opaque to the X rays. 
 
 Colorless diamonds are pure carbon for on combustion in oxygen -only 
 CO 2 is obtained. Colored stones yield small residues. Dumas and Stass 
 found the residue to be from 1/2000 to 1/500, Erdmann and Marchand 
 i/iooo of the original weight of the stone. Moissan showed that the residue 
 consists principally of iron, silicon, and calcium. According to Doelter some 
 diamonds may be heated to a comparatively high temperature without 
 injury. Unaffected by acids. Diamond powder is oxidized when heated 
 with potassium bichromate and sulphuric acid. Resorbed by molten "blue 
 ground" of South Africa. 
 
 There are three varieties of the diamond, (i) Diamond proper, (2) 
 Bort, (3) Carbonado. ' 
 
 (i) Diamond. Known from time immemorial. Often referred to 
 in the writings of the ancients under the name "adamas." These older 
 stones were obtained from secondary deposits in Eastern India, especially 
 on the east side of Deccan. Here the diamond is associated with corundum, 
 beryl, topaz, etc. Borneo also furnished many diamonds. These were the 
 only known localities up to the discovery of the diamond in 1725 in the 
 gold placers in the province of Minas-Geraes, Brazil. A number of prov- 
 inces of Brazil have yielded diamonds in varying quantities but at present 
 the provinces of Bahia and Minas-Geraes are the most important. Here 
 the diamonds occur in secondary deposits associated with gold, cassiterite, 
 ilmenite, tourmaline, magnetite, pyrope, rutile and so forth. At one time 
 it 'was thought that the flexible sandstone itacolumite was the parent rock 
 of the diamond. Bahia is also important for the occurrence of carbonado. 
 
6 DESCRIPTIVE MINERALOGY 
 
 The most important locality, now yielding most of the world's produc- 
 tion, is South Africa. There are several stories relating to the dis- 
 covery of the diamonds in this section. According to one of these, an 
 ostrich hunter and peddler named O'Reilly, while traveling in 1867 along 
 the south shore of the Orange river near Hopetown, called at the home of 
 the Boer peasant Schalk van Niekerk. O'Reilly's attention was attracted 
 to several stones with which van Niekerk's children were playing. By 
 agreement O'Reilly took the stones with him for identification. Both 
 were pronounced by Dr. Atherstone of Grahamstown to be diamonds. One 
 weighed 8 7/8 carats and sold for about $1,000, whereas the other, being 
 much heavier 21 7/8 carats brought $2,500. It is also stated that van 
 Niekerk in 1869 brought the now famous "Star of South Africa" upon 
 the market which weighed, uncut, 83 1/2 carats. 
 
 Diamonds in South Africa were first found in secondary deposits, that 
 is, in the sands and gravels of the stream beds. These were called "river 
 diggings." Later in 1870 diamonds were discovered in primary deposits 
 upon the plateau between the Vaal and Modder rivers at the place now 
 known as Kimberley. It was soon observed here that the occurrence of 
 the diamond is restricted to limited areas somewhat elliptical or circular 
 in outline. These areas differ in size and are from 20 to 685 meters in 
 diameter. The usual diameter is about 200 to 300 meters. In these areas 
 the diamonds were found on the surface in a soft yellow ground and being 
 away from the river the occurrence was spoken of as the "dry diggings." 
 Below the yellow ground a rusty colored earth is encountered which in 
 turn is underlain by a hard bluish serpentinous breccia. This bluish ser- 
 pentinous rock is called the "blue ground." According to Maskelyne the 
 blue ground of .the Kimberley mine consists of 
 
 SiO 2 39-73% 
 
 A1 2 3 2.31 
 
 FeO 9 . 69 
 
 MgO 24.42 
 
 CaO 10.16 
 
 H,0 7-55 
 
 CO 2 6.56 
 
 Total 
 
 100.42 
 
 The areas or openings in which the diamonds are found constrict 
 below the surface as indicated in the accompanying cross-section through 
 the Kimberley mine, Figure I. These openings are often referred to as 
 volcanic pipes or more simply the "pipes." According to Sir William 
 Crookes the diamond in these pipes is associated with no less than eighty 
 
minerals among which pyrope, magnetite, ilmenite, enstatite, diallage, 
 cyanite, augite, pyrite, zircon, chromite, rutile, corundum, olivine, perov- 
 skite, and calcite are most important. Pyrope is considered the especially 
 characteristic associate of the diamond. The removal of the diamond from 
 the yellow or rusty ground is readily accomplished by washing. To extract 
 the same from the hard serpentinous breccia it is first necessary to expose 
 the rock to weathering upon the open fields known as "depositing floors." 
 
 
 p IG j. Section through the Kimberley Mine. 
 
 Here the rock lumps, six to ten inches in diameter, are often sprayed and 
 broken so as to hasten the weathering. From these "floors" the weathered 
 rock is taken to the crushers and washers. At first the concentrates from 
 the washers were sorted by hand but since 1897 they are placed upon an 
 oscillating plate covered with grease, called the "pulsator." Of all the 
 minerals occurring in the pipes the diamond is the only one which sticks, to 
 grease. At intervals the grease is removed from the pulsator and the 
 diamonds easily recovered. 
 
 The following table, giving the yield in carats per load of rock of 
 
8 DESCRIPTIVE MINERALOGY 
 
 about 730 kilograms, shows that even in the pipes the diamond is not verv 
 abundant. 
 
 Yield per load at the Kimberley and DeBeers Mines: 
 
 1889 . 1.28 carats 
 
 1890 1. 15 carats 
 
 1891 -99 carats 
 
 1892 0.92 carats 
 
 1893 1.05 carats 
 
 1894 0.89 carats 
 
 1895 0.85 carats 
 
 1896 0.91 carats 
 
 1897 0.92 carats 
 
 1898 0.80 carats 
 
 1899 0.71 carats 
 
 1900 0.67 carats 
 
 1901 0.76 carats 
 
 1902 0.76 carats 
 
 1903 0.61 carats 
 
 1904 o. 54 carats 
 
 Pipes have been located in several sections of South Africa. Among 
 the most important producing localities the Kimberley, Koffyfontein, Jagers- 
 fontein, and the Transvaal Premier districts may be mentioned. Some 
 "pipes" are entirely barren of diamonds, while others contain them but 
 not in sufficient quantities to warrant exploitation. . 
 
 Among the other localities for the occurrence of the diamond mention 
 may be made of Australia, Ural Mountains, British Guiana, Columbia, and 
 Mexico. In the United States isolated diamonds have been found in sev- 
 eral states especially in Wisconsin, Indiana, California, Georgia, North 
 Carolina, Kentucky and Michigan. On August I, 1906, the most remarka- 
 ble discovery of diamonds in the United States was made near Murfreesboro, 
 Pike County, about 100 miles south of Little Rock, Arkansas. Here in several 
 months 140 diamonds ranging from 1/16 to 6 1/2 carats in weight were 
 found. They are of various forms and colors. At least one stone was 
 found in a serpentinous matrix, the others in the decomposed rock on the 
 surface. The occurrence being somewhat similar to that of South Africa 
 has attracted wide attention. The region is being thoroughly prospected. 
 
 Many theories for the origin of the diamond have been advanced, 
 none of which is, however, wholly adequate. Some of the following are 
 nevertheless of great interest. 
 
 Cohen believed that the diamonds were disseminated in the lower crys- 
 talline schists and afterwards ejected through the pipes. Later H. Carvill 
 Lewis suggested that the diamonds were formed within the pipes by the 
 action of heat and pressure on hydrocarbons derived from the carbonaceous 
 
shales through which the pipes pass. Giirich, however, suggests that the 
 diamonds did not crystallize in the bine ground but in a rock at lower 
 depths. Hatch and Corstorphine hold that the diamond is an original con- 
 stituent of a highly basic rock from which the serpentinous breccia was 
 subsequently formed. A. W. Rogers advances a similar view. T. G. 
 Bonney found diamonds in an eclogite rock and hence supposes the same 
 to be the source. Others believe that the diamonds are the result of 
 crystallization from metallic carbides in a basic magma. Even solidification 
 from an aqueous solution on account of the rounded character of the stones 
 and the intimate association with the hydrated silicates, known as the zeo- 
 lites, has been suggested. 
 
 B, bizet; 
 
 C 
 
 FIG. 3. FIG. 4. 
 
 G, girdle ; P, pavilion ; C, collet. 
 
 The diamond has long been used for many purposes. The ancients 
 satisfied themselves by polishing the natural crystal faces. In 1456 L,ud- 
 wig van Berquem invented the art of cutting facets on the diamond by 
 means of which the brilliancy or "fire" is greatly increased. Many different 
 styles of cutting have been used. At present but two the brilliant and 
 rosette are employed. The brilliant is most common. Natural octahe- 
 drons, rhombic dodecahedrons and hexoctahedrons are most easily cut into 
 this form. Figure 2 shows the general method employed in giving the 
 octahedron a brilliant cutting. Figures 3 and 4 show the side and top views 
 of the cut stone. Depending upon the character of the uncut stone from 
 1/3 to 1/2 of its weight is lost in cutting. The important diamond cutting 
 centers at present are Amsterdam, Antwerp, St. Claude, New York, Paris 
 and Hanau. 
 
 In 1906 the output of diamonds of the De Beers Consolidated Mines 
 Company and the Premier Diamond Mining Company of South Africa, the 
 world's greatest producers, was about 3,000,000 carats, valued at $33,247,- 
 076. Since 1906. the output has fallen off. 
 
10 DESCRIPTIVE MINERALOGY 
 
 Some famous cut diamonds and their weights are given in the fol- 
 lowing list : 
 
 Dresden 76. 5 carats 
 
 Dresden, green . 40.0 carats 
 
 Empress Eugenia 51 .o carats 
 
 Florentine 133 . 2 carats 
 
 Great Mogul 280.0 carats 
 
 Hope 44-5 carats 
 
 Jubilee 239 . o carats 
 
 Kohinoor, old cutting 186.0625 carats 
 
 Kohinoor, new cutting 106.0625 carats 
 
 Nassac 89 . 5 carats 
 
 Orloff 194 . 75 carats 
 
 Pascha of Egypt 40.0 carats 
 
 Pigott 81.5 carats 
 
 Polar Star 40 . o carats 
 
 Regent 136.875 carats 
 
 Sancy 53-75 carats 
 
 Shah 88.0 carats 
 
 Star of South Africa 46.5 carats 
 
 Star of the East 25.8125 carats 
 
 Star of the South 125.5 carats 
 
 Stewart 120.0 carats 
 
 Tiffany 125 . 5 carats 
 
 The Cullinan diamond was discovered January 25, 1905, in the Trans- 
 vaal Premier mine about 24 miles northeast of Pretoria.* This diamond 
 is the largest ever found and weighs 3,024.75 carats. It is about 10 x 6 1/2 
 x 5 centimeters in size and is a distinct cleavage fragment of a larger stone. 
 It is quite colorless, perfectly transparent, free from twinning and contains 
 but few flaws. It is by far the largest diamond ever found. The assembly 
 of Transvaal voted $1,000,000 for the purchase of the stone in order to 
 present it to Edward VII., King of England. 
 
 (2) Bort. Also called boart or bortz. This is a semi-crystalline, trans- 
 lucent variety, which is dark in color and usually possesses a radial, fibrous 
 structure. The term is also used to designate stones or fragments which 
 are of an inferior quality and, hence, unfit for gem purposes. 
 
 (3) Carbonado. This is often called "black diamond" or simply "car- 
 bon." This variety is compact, opaque and usually black to gray in color 
 a dull brown being the prevailing tone. Broken surfaces show a steel 
 gray, brown, greenish gray, and in some cases, a pinkish tinge. The specific 
 
 * A description of this mine is given by R. A. E. Penrose, Jr., in Economic 
 Geology, 1907, II, 275 to 284. 
 
II 
 
 gravity is 3.15 to 3 . 29. Carbonado is found only in th'e placer deposits 
 
 of the La Chapada and Lavres districts of the Province of Bahia, Brazil. 
 
 Figure 5 shows a cut of the largest carbon ever 
 
 found, weight 3,078 carats. Carbonado is used 
 
 largely in diamond drills and on account of its 
 
 meager occurrence is of great value, being worth 
 
 at present, 1907, $85.00 per carat. 
 
 As already indicated the crystallized variety of 
 the diamond is used for gem purposes and glass cut- 
 ters. The powder, obtained from fragments and 
 stones, is employed for grinding and cutting. Re- |J| 
 cently the diamond, and also bort, have been used 
 in wire-drawing. ^ IG - 5- 
 
 Carbonado is used chiefly in the manufacture of diamond core drills, 
 which consist of a line of hollow rods screwed together in sections of 
 varying lengths and rotated by suitable machinery. The lower end of 
 the rods is provided with a bit in which fragments of carbonado are set. 
 
 Figure 6 shows such a bit. The diamond 
 core drill is of great value in mine prospect- 
 ing because the core reveals the exact nature 
 of the rocks penetrated. Such test holes have 
 been sunk to great depths by the diamond 
 drill. In 1900 in Rybnik, Upper Silesia, a 
 depth of 6,700 feet was reached, while in 
 South Africa several holes over a mile in 
 depth have been drilled. One of these, 
 drilled in 1905, reached a depth of 6,340 feet. 
 Bort is also used for grinding and cut- 
 ting purposes. It has likewise been used in drills but experience shows 
 that carbonado, although much more expensive, gives better results. 
 
 GRAPHITE, Plumbago, Black Lead. C. 
 
 Hexagonal, ditrigonal scalenohedral class, a : c = I : 1 . 3859. Small, 
 tabular, hexagonal crystals showing basal pinacoid, prism of the first order, 
 bipyramids of the second order and rhombohedrons. Crystals are not 
 common. Usually in foliated, compact, scaly, granular or earthy masses. 
 The earthy or shaly, more or less impure, varieties are commonly termed 
 amorphous, the others crystalline graphite. 
 
 Perfect basal cleavage, giving rise to thin flexible laminae. Greasy 
 feel. Hardness i to 2. Specific gravity 1.9 to 2.3. Iron-black to dark 
 steel gray in color with a shiny black streak. Marks paper. Opaque. 
 
12 DESCRIPTIVE MINERALOGY 
 
 Metallic luster, sometimes, however, dull or earthy. Good conductor of 
 electricity. Transparent to the X rays. 
 
 Is essentially pure carbon but not as pure as the diamond. Yields 
 sometimes on combustion as high as 20% ash consisting of Fe 2 O 3 , SiCX, 
 clay and so forth. Not attacked by acids. Infusible. 
 
 Occurs in several ways: large masses and disseminated scales, also 
 in dikes and veins in granites, gneisses, mica schists, and crystalline lime- 
 stones. 
 
 In the United States, Ticonderoga, N. Y., furnishes most of the do- 
 mestic graphite. Here it occurs as disseminated flakes in crystalline lime- 
 stone, quartzite, or silicious schist. Graphite also occurs at Byers, Chester 
 Co., Pa., in a decomposed mica schist. Likewise in Alabama, Georgia, North 
 Carolina, New Hampshire and Montana. The earthy, amorphous variety 
 occurs in Rhode Island in metamorphic carboniferous rocks. 
 
 The largest percentage of the world's supply of graphite is obtained 
 at present from Ceylon. Here it occurs in veins in a garnetiferous granu- 
 lite and is associated with feldspar, rutile, pyrite, biotite, and calcite. Other 
 important localities are Passau, Bavaria ; Steiermark, Austria ; Borrowdale, 
 Cumberland ; Alibert near Irkutsk, Siberia, formerly a great producer ; Par- 
 gas, Finland; Misak, Ural Mountains; St. Johns, New Brunswick, and 
 various other localities. Also found in meteorites, for example, the Toluca, 
 Mexico, meteorite. 
 
 Graphite is thought in some cases to be the result of metamorphic 
 action upon carbonaceous matter. For the Ceylon deposits the reduction 
 of carburetted vapors, while for the Ticonderoga, N. Y., occurrence forma- 
 tion from volatile or liquid hydrocarbons has been suggested. 
 
 Graphite finds extensive application in the manufacture of crucibles, 
 stove polish, paint, lead pencils, lubricants, electrotyping, foundry facings, 
 steam-piping, to color fertilizers, also to color and glaze tea leaves and 
 coffee beans. In 1906 Ceylon exported 40,320 tons valued at $3,406,550. 
 The production of the United States for the same time was 19,797 tons 
 valued at $340,239. In 1908 the output was only about 50% as great as in 
 1906. 
 
 Artificial graphite is manufactured by the Acheson Graphite Company 
 at Niagara Falls, N. Y., and is expected to become a successful competitor 
 of the natural product. 
 
 SCHUNGITE, C. 
 
 Amorphous, black in color with a luster reminding one of anthracite coal. 
 Hardness 3.5 to 4. Specific gravity 1.84 to 1.98. It is hygroscopic and occurs in 
 small quantities in the Huronian schists near Schunga, Government Olonezo, Russia. 
 It is intermediate between anthracite coal and graphite. 
 
13 
 
 SULPHUR, Brimstone, S. 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.8130 : I '. 1.9037. 
 Crystals quite common. Mostly showing pyramidal habit ; sometimes tab- 
 ular due to preponderance of the basal pinacoid. Bisphenoidal habit also 
 to be observed especially on crystals from Ciancina, Sicily. Common forms 
 are the basal pinacoid c, unit bipyramid p, modified bipyramid (1/3 c} s 
 and the unit brachydome n, Figure 7. Four types of 
 twins have been observed with twinning planes parallel to 
 (i) unit macrodome; (2) unit brachydome; (3) unit 
 prism ; and (4) unit bipyramid. Also massive, stalactitic, 
 and in crusts. The massive occurrences may be granular, 
 fibrous, earthy or powdery. 
 
 Imperfect cleavages parallel to the unit prism, basal 
 pinacoid, and unit bipyramid. Conchoidal to uneven frac- 
 ture is quite characteristic. Hardness 1.5 to 2.5. Specific 
 gravity 1.9 to 2.1. On crystal faces adamantine luster, otherwise resinous 
 to greasy. Transparent to translucent. White to yellow streak. Usually sul- 
 phur-yellow in color, may, however, be straw to honey-yellow, yellow-brown, 
 and due to impurities even reddish, greenish or gray. On rubbing becomes 
 negatively electrified. Non-conductor of electricity and heat. On account 
 of the low conductivity and unequal distribution of heat, crystals often 
 crack when held in the hand. If held near to the ear a crackling sound 
 may be heard. 
 
 Usually quite pure. Sometimes contains bitumen, arsenic, selenium 
 and more rarely tellurium. Often contaminated with clay. Heated to 
 108 C. it melts, at 270 C. it burns with a bluish flame giving rise to SO 2 . 
 Insoluble in water and acids. Easily dissolved by CS 2 . 
 
 Sulphur is in general the result of the oxidation of hydrogen sulphide, 
 which may have been formed in several ways. Two types of occurrences 
 of sulphur are usually differentiated depending upon the method of the 
 formation of the hydrogen sulphide, viz: (ij Solfatara type and (2) 
 Sulphate type. 
 
 The Solfatara type is of limited importance commercially. Here sul- 
 phur is the result of volcanic exhalations, principally H 2 S and SO 2 which 
 interact as follows: 2H 2 S -f- SO 2 = 2H 2 O -j- 38. In this way the occur- 
 rences of sulphur at Naples, Vesuvius, and Aetna in Italy, Iceland, Japan, 
 and the Rabbit Hole district, Nevada, are explained. 
 
 The Sulphate type is of quite widespread occurrence and furnishes the 
 world's supply. Here, the common sulphates, gypsum Ca SO 4 , 2H 2 O and 
 celestite SrSO 4 , are reduced by organic matter to the form of the soluble 
 and easily decomposable sulphides which readily yield H 2 S. The H,,S on 
 
14 DESCRIPTIVE MINERALOGY 
 
 oxidation then gives rise to native sulphur, as follows: H 2 S-(-O=H,,O-)-S. 
 Sulphur of this type is associated with celestite, gypsum, aragonite, calcite, 
 etc. The most important deposits are at Girgenti, Sicily, and near Lake 
 Charles about 230 miles west of New Orleans, La. Sicily has for many 
 years supplied the world's market almost exclusively but at present Louis- 
 iana sulphur is an important competitor. Other localities are Gunnison Co., 
 Colo., Sulphurdale, near Beaver, Utah ; Cody, Wyo. ; Concil, Spain ; Bex, 
 Switzerland ; Cracow, Poland ; in the salt deposits at Stassfurt, Germany ; 
 Sechura, Peru ; Rybnick, Silesia ; also various places in Japan, Mexico, and 
 Chile. At Maybee, Mich., sulphur is the result of the reduction of celestite. 
 Also as a deposition from hot springs in the Yellowstone Park. Some- 
 times due to the decomposition of pyrite and other sulphides. 
 
 Sulphur is used chiefly in the preparation of the wood pulp for the 
 manufacture of paper. Small quantities are also used in the manufacture 
 of- matches, gunpowder, medicines, vulcanized rubber, insecticides, bleaching 
 of silk, straw and woolen materials, etc. On account of the present high 
 price of sulphur, $19 to $22 per ton, it is not used as extensively as formerly 
 in the manufacture of sulphuric acid by the chamber process. 
 
 Sulphur is polymorphous but the orthorhombic modification is the only one of 
 importance to the mineralogist. 
 
 SELENSULPHUR. Volcanite, (S, Se). 
 
 Volcanic sulphur containing selenium. Rare. Massive, earthy and fibrous ; 
 orange-red or reddish brown crusts associated with sal ammoniac and alum on the 
 islands of Volcano and Lipari. Also on Kilauea, Hawaii. 
 
 SELENIUM. 
 
 Reported to occur at Culebras, Mexico. Occurrence is doubtful. 
 
 ARSENIC GROUP 
 
 The members of this series crystallize in the ditrigonal scalenohedral 
 class in pseudo-cubical rhombohedrons. They are brittle and non-malleable. 
 
 . ' SPECIFIC RHOMBOHE- 
 
 : c HARDNESS GRAVITY DRAL ANGLE 
 
 Arsenic, As. i : 1.4025 34 5.68 85 4' 
 
 Antimony, Sb. i : 1.3236 34 6.66.8 8.78' 
 
 IELLURIUM, Te. i : 1.3298 2.5 6.16.3 86 57' 
 
 Bismuth, Bi. i : 1.3035 23 9.69.8 8;4o' 
 
ELEMENTS 1 5 
 
 Arsenic, Native Arsenic, As. 
 
 Hexagonal, ditrigonal scalenohedral class. Natural crystals rare and 
 poorly developed showing a cubic or acicular habit. Commonly found in 
 compact, scaly, granular, and fine grained masses with reniform and bot- 
 ryoidal structures. Breaks often into concentric layers. 
 
 Perfect basal cleavage. Uneven and fine grained fracture. Brittle. 
 Hardness 3 to 4 and specific gravity 5.6 to 5.8. Metallic luster. Opaque 
 Color on fresh fracture surface is a tin-white ; tarnishes readily to dark 
 gray or black. Streak tin-white. 
 
 Arsenic, often contains silver, iron, antimony, bismuth, cobalt, nickel 
 and gold. Volatilizes easily forming arsenic trioxide and yielding the char- 
 acteristic garlic odor. 
 
 Commonly observed associated with silver, cobalt, and nickel ores ; 
 thus in the Freiberg, Saxony and the Hartz Mountains districts of Ger- 
 many ; Pribram and Joachimsthal, Bohemia ; Kongsberg, Norway ; in rhom- 
 bohedral crystals Akadanimura, Japan ; various places in Chile. 
 
 Native arsenic furnishes but a small portion of the arsenic used in 
 commerce. Metallic arsenic is a constituent of shot metal. The trioxide 
 is used in dyeing, medicine, calico printing, rodent poisons, glass manu- 
 facture, etc. 
 
 Antimony. Native Antimony. Sb. 
 
 Hexagonal, ditrigonal scalenohedral class. Like arsenic, crystals of 
 antimony are rare. Usually found as compact, granular or lamellar masses. 
 Sometimes radiated and reniform. Perfect basal cleavage. Uneven frac- 
 ture. Brittle. Hardness 3 to 4. Specific gravity 6.6 to 6.7. Metallic lus- 
 ter. Opaque. Tin-white in color, rarely shows yellow, brown or grayish 
 tarnish colors. Streak tin-white. 
 
 Antimony frequently contains silver, arsenic or iron. Easily fusible 
 and volatile. 
 
 Native antimony is not common. Sometimes occurs as incrustations, 
 especially on arsenic. Is usually associated with silver and arsenic min- 
 erals. The chief localities are St. Andreasberg in the Hartz Mountains ; 
 Pribram, Bohemia ; Sala, Sweden ; Sarawak, Borneo. In comparatively 
 large quantities at Prince William Parish, York Co., New Brunswick. 
 
 Native antimony is of no importance commerically. Metallic anti- 
 mony, obtained from the various compounds of the element, is used in 
 the manufacture of type metal, various alloys, pewter, and anti-friction 
 metals. 
 
 TELLURIUM, Native Tellurium, Te. 
 
 Hexagonal, ditrigonal scalenohedral class. Prismatic crystals, rare. Usually 
 compact, fine grained or granular masses. Perfect basal cleavage. Brittle but sectile. 
 Hardness 2 to 3. Specific gravity 6.1 to 6.3. Metallic luster and tin-white in color 
 and streak. 
 
 Tellurium often contains selenium, gold, and silver. 
 
 Of rare occurrence. Usually associated with gold ores. Transylvania; Cripple 
 Creek District, Colo. ; Calaveras Co., Cal. 
 
!6 DESCRIPTIVE MINERALOGY 
 
 Bismuth. Native Bismuth, Bi. 
 
 Hexagonal, ditrigonal scalenohedral class. Psteudo-cubical crystals. 
 Rhombohedral angle 874o'. Crystals rare. Reticulated, arborescent, in 
 plates, also foliated and compact masses. 
 
 Perfect basal cleavage. Brittle, easily pulverized with the hammer. 
 Sectile, somewhat malleable when heated. Hardness 2 to 2>4. Specific 
 gravity 9.7 to 9.8. Metallic luster. Opaque. Reddish silver white in 
 color, often shows brassy yellow tarnish color. Shiny metallic lead gray 
 
 streak. 
 
 Bismuth with traces of arsenic, sulphur, tellurium, etc. 
 
 Not especially abundant but is always associated with silver, cobalt, 
 and nickel ore deposits, also with lead, zinc, and tin ores. Important occur- 
 rences at Schneeberg, Hartz Mountains ; Annaberg, Saxony ; Joachimsthal, 
 Bohemia; Cornwall, and Devonshire, England; Modum, Norway; Bisperg 
 and Broddbo, Sweden ; various places in Chile, Bolivia, New South Wales 
 and New Zealand. Native bismuth also occurs in association with the 
 silver-cobalt-nickel deposits of the Cobalt district, Ontario. 
 
 Native bismuth is the source of the metal and its compounds. It is 
 of considerable importance in the manufacture of easy fusible alloys, rifle 
 bullets, and thermo-piles. The compounds are used in medicine. Bismuth 
 is worth about $1.25 per pound. 
 
 ALLEMONTITE, Arsenical Antimony, (As, Sb). 
 
 This is an isomorphous mixture of arsenic and antimony in which either element 
 may predominate. Reniform masses usually with irregular lamellar or fine-grained 
 structure. Physical properties similar to those of antimony. Hardness 3 to 4. 
 Specific gravity 6.2. Allemont, France; Pnbram, Bohemia; Washoe Co., Nevada: 
 Salpo, Peru. 
 
 TIN, Native Tin, Sn. 
 
 Reported to occur in the gold placers of Miask, Ural Mountains, and in Guiana, 
 South America. Also in Mexico and in the Clarence River, New South Wales. 
 Very rare. Tin is apparently dimorphous. Artificial crystals belonging to the tet- 
 ragonal and orthorhombic systems have been observed. 
 
 PLATINUM GROUP 
 
 The metals of this group form an isodimorphous series. However, 
 only one element, palladium, occurs in both forms. The members of the 
 cubic series are all malleable and possess a hackly fracture while the hex- 
 agonal members are brittle and show distinct cleavages. Platinum is the 
 only member of this group which occurs in comparatively large quantities, 
 the annual production being about 6,500 kilograms. 
 
ELEMENTS 17 
 
 CUBIC SERIES HEXAGONAL SERIES 
 
 (Hc.roctahedral Class} (Ditrigonal Scalenohedral Class) 
 
 Platinum, Pt. IRIDOSMIUM, (Os, Ir.) 
 
 IRIDIUM, Ir. OSMIRIDIUM, (Ir, Os.) 
 
 PLATINIRIDIUM, (Pt, Ir.) PALLADIUM, Pd. 
 
 PALLADIUM, Pd. (Allo palladium.} 
 
 Platinum. Native Platinum, Pt. 
 
 Cubic, hexoctahedral class. Small crystals, usually cubes ; also octa- 
 hedrons and rhombic dodecahedrons. Usual occurrence is in scales, grains 
 or nuggets. When found near parent rock these are angular, otherwise 
 rounded. Sometimes the nuggets are of considerable size, two of the 
 largest weighing 8.33 and 9.62 kilograms, respectively. 
 
 Metallic luster, opaque. No cleavage. Hackly fracture. Hardness 4 
 to 6. Malleable, ductile, and sectile. Specific gravity 14 to 19. The pres- 
 ence of varying amounts of iron (specific gravity 7.3 to 7.8) causes the 
 large variation in the specific gravity. Molten platinum has a specific grav- 
 ity of 19.7, that of hammered platinum is 21.23. The color is silvery- 
 white to dark gray or almost black. May be magnetic, especially if con- 
 siderable iron is present. 
 
 Platinum, but usually containing iron (4 to 19.5%), also iridium, rho- 
 dium, palladium, osmium, copper, and at times gold. Platinum with a spe- 
 cific gravity below 16 contains much iron and is termed iron-platinum. In 
 normal native platinum the amount of iridium present is usually not over 
 5% but in platiniridium it may be as high as 75%. Infusible at ordinary 
 temperatures, according to Violle not under I775C. May be fused and 
 welded in the oxyhydrogen blowpipe. Soluble in hot aqua regia. 
 
 Platinum was first discovered in 1735 in the gold placers of the Pinto 
 river, Columbia. Here it is associated with gold, zircon, magnetite, chrom- 
 ite, etc. In 1822 it was discovered in the alluvial deposits of Nijni-Tagilak 
 in the Ural Mountains. Here it occurs sparsely disseminated as scales and 
 grains in an altered and serpentinized peridotite rock. Platinum is also 
 known to occur in the black sands of California, Oregon, Idaho, Colorado, 
 Wyoming, Utah, and North Carolina. Other localities are British Columbia, 
 Ontario, Brazil, New South Wales, San Domingo, and Borneo. It is always 
 associated with chromite. 
 
 According to Kemp* native platinum may occur in three ways, viz : 
 
 1 i ) Placers. Here the platinum may have been derived from perido- 
 tites. also from pyroxenites, gabbros, metamorphosed gabbros, and syenites. 
 It is associated with chromite, magnetite, garnet, menaccanite, zircon, rutile, 
 topaz, small diamonds, quartz, cassiterite, pyrite, gold, copper, iridosmine, 
 and other members of the platinum group. 
 
 (2) Veins. Platinum has been observed in veins with gold at Til- 
 kerode, Hartz Mountains ; Brazil ; Columbia ; Beresovsk, Russia ; and per- 
 haps Broken Hill, New South Wales. 
 
 * Bulletin 193, U. S. Geological Survey, 1902. 
 
1 8 DESCRIPTIVE MINERALOGY 
 
 (3) Disseminated in eruptive rocks. Platinum, intimately associated 
 with chromite, is found sparingly in basic eruptive rocks, especially, periclo- 
 tites, as for example, at Nijni-Tagilak, Ural Mountains. 
 
 Platinum is used extensively in the manufacture of physical, chemical, 
 and electrical apparatus, photography, dentistry, jewelry, pyrography, non- 
 magnetic watches, and surgical instruments. In Russia from 1826 to 1844 
 it was used for coinage purposes. Most of the annual world's supply 
 (about 6,500 kilograms) comes from the Ural Mountains. In 1906 the 
 United States produced about 46,048 grams valued at $45,189, obtained prin- 
 cipally from the black sands of the Pacific slope. In 1908 the output was 
 23,325 grams, valued at $14,250. At present, 1910, refined platinum is worth 
 about $1.00 per gram. 
 
 IRIDIUM, Native Iridium, Ir. 
 
 Cubic, hexoctahedral class. Small cubical crystals, rare. Usually as grains or 
 scales. Trace of cubical cleavage. Hackly fracture. Metallic luster. Silvery white 
 in color. Hardness 6 to /. Specific gravity 22.6 to 22.8. 
 
 Iridium, with platinum, palladium, or copper. Soluble in cold aqua regia. More 
 infusible than platinum, according to Violle not under I9SOC. 
 
 Occurs in platinum placers in the Ural Mountains; Ava, Burma; and Brazil. 
 It is the rarest of the platinum minerals. 
 
 Tridium, being the hardest known metal, is often used in small percentages as 
 an alloy to harden platinum and other metals of the platinum group. In this way it 
 is used for standards of weight and measure, wire in standard resistance coils, 
 knife edges for delicate balances, points of gold pens, and bearings in watches and 
 compasses. 
 
 Iridium is worth about $1.00 per gram. 
 
 PALLADIUM, Native Palladium, Pd. 
 
 Cubic, hexoctahedral class. Small octahedral crystals. Usually in grains, some- 
 times with radial fibrous structure. Light steel gray color. Hackly fracture. Malle- 
 able and ductile. Hardness 4 to 5. Specific gravity 11.3 to n.8. 
 
 Palladium, with platinum and iridium. Most easily fusible of the platinum group 
 of metals. Fuses according to Becquerel between i36oC. and i38oC. Soluble in 
 cold aqua regia. 
 
 Occurs in Minas-Geraes, Brazil; San Domingo; North Carolina; and in the 
 Ural Mountains. 
 
 Metallic palladium is used in the manufacture of delicate scientific instruments, 
 chronometers, watches, and with platinum in photography. 
 
 IRIDOSMIUM, Iridosmine, Siserskite, (Os, Ir.) 
 
 Hexagonal, ditrigonal scalenohedral class. Small steel to lead gray plates of 
 hexagonal outline. Hardness about 7. Specific gravity 20 to 21.2. 
 
 Isomorphous mixture of osmium and iridium with 20 to 30% of iridium cor- 
 responding to the formulae IrOs 3 to IrOs 4 . Also contains other metals of the plati- 
 num group. When heated loses osmium and affords the characteristic osmium odor 
 Becomes black when heated in alcohol flame. Heated on platinum foil assumes bril- 
 liant colors. 
 
 Occurs in small quantities in the platinum placers of the Ural Mountains and 
 California. 
 
ELEMENTS 19 
 
 OSMIRIDIUM. Hevyanskite, (Ir, Os.) 
 
 Hexagonal, ditrigonal scalenohedral class. In -tabular hexagonal crystals similar 
 to iridosmium. Tin-white. Hardness 7. Specific gravity 18.8 to 19.5. 
 
 Isomorphous mixture of osmium and iridium with 40 to 70% of iridium, cor- 
 responding to IrOs to Ir 4 Os. Unchanged before the blowpipe. Attacked by fused 
 potassium nitrate. 
 
 Found with platinum in the Ural Mountains ; also in Brazil. 
 
 Osmiridium is more abundant and lighter in color than iridosmium. 
 
 . -,&&*&& 
 
 FIG. 8. Section of Franceville Meteorite, one-half Natural Size. 
 
 ALI.OPALLADIUM, Native Palladium, Pd. 
 
 Hexagonal, ditrigonal scalenohedral class. Small six-sided tabular crystals. 
 Metallic luster . Silver white. Basal cleavage. Brittle. Difficult to file. Occurs in 
 diabase at Tilkerode, Hartz Mountains. 
 
 Iron, Native Iron, Fe. 
 
 Cubic, hexoctahedral class. Natural crystals unknown. Crystal form 
 shown by artificial and meteoric iron. Usually observed in disseminated 
 grains, scales, plates, or lumps. Perfect cubical cleavage with hackly frac- 
 ture. Malleable. Hardness 4.5 to 6. Pure iron has a specific gravity of 
 7.88. Steel gray to iron-black in color. Metallic luster. Shiny streak. 
 Magnetic. 
 
 Iron, with varying percentages of carbon, copper, lead, nickel, cobalt 
 and so forth. Infusible before the blowpipe. Soluble in common acids. 
 
 Two types of native iron may be distinguished, viz: (a) terrestrial, 
 and (b) meteoric. 
 
 (a) Terrestrial iron is of very limited occurrence and may be the 
 result of (i) the action of reducing agents upon iron sulphides or oxides. 
 
2O DESCRIPTIVE MINERALOGY 
 
 or (2) it occurs disseminated in eruptive rocks, doubtless the result of 
 magmatic segregation. 
 
 Terrestrial iron of the first type is always free from nickel and occurs 
 at Miihlhausen, Thuringia, also at Planer near Chotzen, Bohemia. The 
 second type usually contains from 2 to 4% of nickel. The most important 
 occurrence of this character is at Blaafjeld, Ovifak, Disco Island, off the 
 coast of Greenland. Here the terrestrial iron is found in small grains, oc- 
 casionally in masses of great size, disseminated in basalt. The iron at this 
 locality was formerly thought to be of meteoric origin. 
 
 (b) Meteoric iron. Many meteorites consist largely of iron, contain, 
 however, varying amounts, 3 to 10%, rarely 20%, of nickel. Small amounts 
 of cobalt are also present. Sections of meteorites, when polished and etched 
 by dilute acid, show several series of parallel lines or bands crossing each 
 other at angles of 60 to 90. These lines or bands are called the Wid~ 
 manstatten figures. They are shown in Figure 8 on a section of the Fran- 
 ceville meteorite. The Widmanstatten figures are intimately associated with 
 the crystalline structure of the meteorite in that they represent the more 
 nickeliferous portions which are but slightly attacked by acid. 
 
 The metallic iron used so extensively in commerce is derived from the 
 various compounds of iron, principally, hematite, Fe 2 O 3 ; magnetite, Fe 3 O 4 ; 
 siderite, FeCO 3 , etc. 
 
 AWARUITE. 
 
 Awaruite is a nickeliferous metallic iron occurring in the sands of the Gorge 
 river, New Zealand. 
 
 JOSEPHINITE. 
 
 Josephinite is also a nickeliferous iron (Fe, Ni 5 ) found in Oregon. 
 
 ZINC. 
 
 It is rather doubtful whether zinc occurs native. Reported to have been found 
 in Victoria, New South Wales, and New Zealand. Artificial crystals belong to the 
 hexagonal system. 
 
 COPPER GROUP 
 
 This group contains the so-called precious metals. They are all rather 
 heavy, soft, and malleable, and crystallize in the hexoctahedral class of the 
 cubic system. 
 
 LEAD, Pb. Amalgam, (Ag, Hg.) 
 
 COPPER, Cu. Mercury, Hg. 
 
 SILVER, Ag. GOLD, Au. 
 
 Goto AMALGAM, (Au, Hg.) 
 LEAD, Native Lead, Pb. 
 
 Cubic, hexoctahedral class. Crystals are rarely found. Usually in plates and 
 thin sheets, also in disseminated and lose grains, sometimes filiform. Malleable and 
 ductile. Hardness 1.5. Specific gravity 11.4. Lead gray in color with metallic 
 luster. Opaque. Tarnishes dark. 
 
21 
 
 Practically pure lead, contains sometimes silver and antimony in small quantities. 
 
 Of very rare occurrence. Has been found in plates which may be ^ c.m. in 
 thickness in the iron deposits of Pajsberg and Nordmarken, Sweden. As loose grains 
 in the gold placers of Transylvania; Ural Mountains; also reported at Breckenridge 
 and Gunnison, Colorado, and the Wood River District, Idaho. 
 
 The metallic lead of commerce is obtained chiefly from galena, PbS ; cerussite, 
 PbCO 3 ; and anglesite, PbSCX. 
 
 COPPER, Native Copper, Cu. 
 
 Cubic, hexoctahedral class. Crystals rather common. The cube, octa- 
 hedron, rhombic dodecahedron, and tetrahexahedrons (especially m = 4) 
 are the most common forms. These occur either independently or in com- 
 bination. A combination of the cube and the tetrahexahedron is quite 
 characteristic of Lake Superior copper, Figure 9. Other combinations are 
 
 $3 HE: 
 
 
 \ 
 
 r 
 
 
 ! K 
 
 e 
 
 k--*' -> 
 
 
 '-- -J--m 
 
 
 
 ^A 
 
 h 
 
 d 
 
 
 { 1 
 
 
 
 
 
 ^^ 
 
 FIG. 9. 
 
 FIG. 10. 
 
 FIG. ii. 
 
 shown in Figures 10 and u. Crystals are often distorted and also show 
 parallel grouping. Twins according to Spinel law. Most commonly ob- 
 served as scales, plates, and lumps, oftentimes weighing many tons.* Also 
 arborescent and filiform. 
 
 Copper has no cleavage but a hackly fracture. Ductile and malleable. 
 Hardness 2.5 3. Specific gravity 8.5 to 9 cast copper 8.83, rolled cop- 
 per 8.95. Metallic luster. Copper red in color, often with tarnish .colors. 
 Red (cuprite, Cu 2 O), blue (azurite, 2Cu CO 3 . Cu (OH) 2 ), green (mal- 
 achite Cu CO 3 . Cu (OH) 2 ), and black (tenorite, Cu O) colors, as a result 
 of decomposition, are often to be observed on the surface of masses of 
 native copper. Streak copper red, metallic and shiny. Good conductor of 
 heat and electricity. Fuses at I33OC. (V. Riemsdyk.) 
 
 Nearly pure copper, but often contains small amounts of silver, bis- 
 muth, mercury, arsenic, etc. Easily soluble in nitric acid, the solution 
 turns azure blue upon the addition of ammonia. 
 
 * In 1857 a mass of copper 45' x 22'* 8' weighing 420 tons was encountered in 
 Ontonagon County, Mich., in the mine now known as the Minnesota. 
 
22 DESCRIPTIVE MINERALOGY 
 
 The most important locality for the occurrence of native copper is the 
 bake Superior region in Northern Michigan. Copper occurs here in three 
 ways, viz : ( I ) as a cement in a reddish quartz porphyry conglomerate. 
 Here the copper is mostly in the form of scales and grains. (2) Filling the 
 cavities of a dark colored igneous rock known as the melaphyr amygdaloid. 
 In many instances the copper of this type is more or less spherical in form 
 and is then called "shot copper." (3) In masses associated with veins of 
 calcite and the zeolites.* Among the common associates of native copper 
 in this region prehnite, datolite, analcite, quartz, epidote, laumontite, calcite. 
 and native silver may be mentioned. 
 
 Inasmuch as the copper of the Lake Superior region is the result of 
 deposition from solution it is thought that the igneous rocks must be con- 
 sidered as the source of the metal. These rocks contain minerals which 
 often show small amounts of copper and by their decomposition and inter- 
 action with a solution of ferrous salts the deposition of metallic copper may 
 have resulted. Recently Fernekesf has shown experimentally that three 
 factors may have been important in the deposition of native copper, namely, 
 the presence of ( i ) copper chloride or some copper silicate and hydrochloric 
 acid, and (2) calcium and sodium silicates, and (3) minerals containing 
 ferrous iron. 
 
 In 1908 the Lake Superior region produced 222,289,584 pounds of cop- 
 per. This was about 2.2% of the total output of the United States or 13% 
 of the world's production for that year. Among the largest mines of this 
 section the following with the production for 1908 may be mentioned. 
 
 POUNDS 
 
 Calumet and Hecla 88,124,007 
 
 Osceola 21,250,794 
 
 Quincy 20,600,361 
 
 Champion 17,786,763 
 
 Baltic 17,724,854 
 
 Tamarack .' 12,806,127 
 
 Mohawk 10,295,881 
 
 Wolverine 9>555> 2 33 
 
 Trimountain 6,034,908 
 
 The ores of the Lake Superior region contain about one per cent of 
 copper and are easy to treat. By means of crushing, washing, and concen- 
 trating with jigs and tables the metallic copper is readily extracted. It is 
 
 * A group of silicate minerals containing water of crystallization. 
 
 f A. C. Lane. The Formation of Lake Superior Copper. Science, 1907. N. S. 
 XXV, 589. Also G. Fernekes, Precipitation of Copper, etc. Economic Geology, 1907, 
 II, 580. 
 
23 
 
 then melted, refined, and cast into ingots. A small amount of "lake" copper 
 is also refined electrolytically. 
 
 Copper also occurs in veins and deposits associated with the various 
 copper minerals, azurite, malachite, cuprite, chalcopyrite, bornite, chalcocite, 
 etc. Some of the other localities for the occurrence of native copper are the 
 Ural Mountains, Siberia ; Nassau, Germany ; Cornwall, England ; Chile ; Bo- 
 livia ; Peru ; Brazil, and Australia. In small quantities in various places in 
 Massachusetts, Connecticut, New Jersey, California; more abundantly in 
 Arizona and New Mexico. 
 
 Metallic copper, as is well known, is used very extensively in commerce. 
 It is worth, April 1910, about 13 cents per pound. Large amounts are 
 used in the manufacture of copper wire, nails and sheets, various alloys, 
 electrical apparatus, also for coinage purposes and chemical reagents. 
 
 SILVER, Native Silver, Ag. 
 
 Cubic, hexoctahedral class. Cube, octahedron, rhombic dodecahedron 
 and tetrahexahedron (m = 2) are most commonly observed as inde- 
 pendent or predominating forms. Crystals are very small and often dis- 
 torted. Twins according to the Spinel law. Also acicular, reticulated or 
 arborescent. Often fine threads or wires, sometimes matted resembling tufts 
 or wads of hair or moss. Masses, plates, and scales. 
 
 No cleavage but malleable and ductile. Hardness 2.5 to 3 and specific 
 gravity 10 to 12; pure 10.52. Metallic luster. Color silver white, usually 
 with yellow brown, gray or black tarnish colors. Thin sheets appear blue 
 in transmitted light. Streak metallic silvery white. Excellent conductor 
 of heat and electricity. 
 
 Silver, usually with varying amounts of gold, as high as 28%, further- 
 more copper, arsenic, antimony, mercury, iron, platinum, etc. Easily fusible, 
 also soluble in nitric acid. 
 
 Occurs commonly with ores of silver, lead, arsenic, cobalt, and nickel. 
 The usual gangue minerals are calcite, quartz, barite, and fluorite. In 
 many cases silver is the result of the reduction of argentite Ag 2 S, cerargy- 
 rite Ag Cl, pyrargyrite Ag 3 SbS 3 , proustite Ag 3 AsS 3 and so forth. Kongs- 
 berg, Norway, has furnished a great deal of silver in the form of crystals 
 and large masses up to 750 pounds. The Saxon mines at Freiberg, Marien- 
 berg, and Annaberg have long been heavy producers. Also Joachimsthal. 
 Bohemia; Ural Mountains; Mexico, especially Sonora, Durango, and Sin- 
 aloa ; Chile ; Peru ; and Bolivia. 
 
 In the United States native silver is found rather extensively in Colo- 
 rado, Montana, Utah, Idaho, Arizona, Nevada, and California. In the Lake 
 
24 DESCRIPTIVE MINERALOGY 
 
 Superior Copper region it occurs in masses with copper forming the so- 
 called "half-breeds." 
 
 At Cobalt, Ontario, large deposits of native silver associated with cobalt 
 and nickel ores were discovered in 1903. Here the deposits occur in narrow 
 veins in slightly inclined metamorphosed fragmental rocks and diabase 
 of Huronian and Keewatin ages. Many large lumps of silver, about 
 95% pure, have been found. Some of these masses weighed from 600 to 
 1000 pounds. The chief associates of silver in this district are niccolite, 
 chloanthite. smaltite, cobaltite, erythrite, annabergite, native bismuth, and 
 so forth. The output for 1909 was 26,364,703 ounces, valued at $12,941,978. 
 
 Rarely found in placer deposits. It is too easily acted upon by circu- 
 lating water. Nevertheless, nuggets valued at over $150,000 have been 
 recovered from the bottom of Cobalt Lake, Ontario. 
 
 Native silver is used for coinage, jewelry, photography, ornamental pur- 
 poses, also in chemical, physical, and surgical apparatus. Silver is worth 
 about 52 cents per ounce. 
 
 Amalgam, Native Amalgam. Silver Amalgam, (Ag, Hg.) 
 
 Cubic, hexoctahedral class. Rhombic dodecahedron and tetragonal tris- 
 octahedron (w 2) are usually the predominating forms; other observed 
 forms are the cube, octahedron, tetrahexahedrons, and hexoctahedron 
 (n='3/2, w 3). Also as disseminated grains; plates, and coatings. 
 
 Brittle, metallic luster. Silver white in color. Hardness 3 to 3.5. 
 Specific gravity 13.7 to 14.1. Streak silvery white. Conchoidal or uneven 
 fracture. Opaque. 
 
 Isomorphous mixture of silver and mercury in varying proportions. 
 The following formulae indicate the great variation in composition Ag 2 Hg ;i 
 to Ag 36 Hg. Heated on charcoal or plaster tablet the mercury volatilizes 
 leaving a globule of silver. 
 
 Not very common. Found principally in association with native mer- 
 cury and cinnabar, thus at Moschellandsberg, Bavaria ; Almaden, Spain ; 
 Kongsberg, Norway ; Chanarilla, Chile ; Sala, Sweden, and so forth. 
 
 Does not occur abundantly enough to be important commercially. 
 
 Mercury, Native Mercury, Quicksilver, Hg. 
 
 Cubic, hexoctahedral class. At ordinary temperature mercury is a 
 liquid, at 38.5C. to 39.44^ it solidifies and crystallizes in the form of 
 the octahedron with a specific gravity of 15.19 (Joule). Usually found as 
 small drops or globules associated with the various mercury minerals, espec- 
 ially cinnabar and calomel. 
 
 Brilliant metallic luster. Tin white in color. Opaque. Very heavy, 
 specific gravity 13.5 to 13.6. Boils at 357 C. 
 
 Nearly pure, may contain a little silver. Easily volatile. 
 
 Native mercury does not occur commonly. The most, important local- 
 ities are Almaden, Spain ; Idria, Austria ; Moschellandsberg, Bavaria ; Avala, 
 Siberia ; New Almaden, and San Jose, California ; and Terlinqua, Texas. 
 
ELEMENTS 25 
 
 Mercury is sometimes deposited by hot springs ; thus in New Zealand, Cali- 
 fornia, and Nevada. 
 
 Most of the mercury of commerce is obtained from cinnabar, HgS. In 
 1906 the United States produced 28,293 flasks of 76^ pounds each valued 
 at $1,157,184. Metallic mercury is used extensively in the amalgamation 
 of silver and gold ores, also in industrial chemistry, medicine, electrical 
 apparatus, dentistry, scientific apparatus of various types, mercury vapor 
 lamps and so forth. 
 
 GOLD, Native Gold, Au. 
 
 Cubic, hexoctahedral class. Crystals are usually small, more or less 
 distorted, and possess dull faces. The most common forms are the octa- 
 hedron, cube, and rhombic dodecahedron. These may occur independently 
 or in combination with one another. Other forms are the tetragonal tris- 
 octahedrons (m = 2, m = 3), and the tetrahexahedron (w = 2). Skele- 
 tal development common. Twins according to the Spinel law. Most com- 
 mon occurrence is as disseminated scales or grains. Also filiform, reticu- 
 lated, and in large lumps or nuggets. Several nuggets weighing as much 
 as 190, 210, 237, and 248 pounds have been reported from the Donolly dis- 
 trict in Australia. 
 
 Malleable and ductile metal. No cleavage, hackly fracture. Hardness 
 2.5 to 3 and specific gravity 15.6 to 19.3. Metallic luster. Golden, brassy 
 to light yellow in color and streak. Opaque. 
 
 Gold, usually contains varying amounts, up to 40%, of silver; also 
 iron, copper, bismuth, palladium, rhodium and so forth. Readily fusible 
 and soluble in aqua regia. Readily acted upon by nascent chlorine forming 
 the soluble chloride. Also rendered soluble by the action of potassium 
 cyanide and oxygen. Forms an amalgam with mercury. 
 
 Gold is widely distributed but in only a comparatively few places in 
 sufficient quantities to be of economic importance. There are two general 
 types of occurrence, viz: (i) In situ, and (2) in secondary deposits called 
 placers. 
 
 Gold occurring in situ is usually found in connection with quartz veins 
 or deposits of irregular shape in igneous and metamorphic rocks of varying 
 ages. Among these rocks mention may be made of talcose, chloritic, argil- 
 laceous, mica, and hornblende schists, gneiss, diorite, porphyry, granites, 
 trachytes and andesites. In some cases the gold occurs as small but dis- 
 tinctly visible particles and is then termed free milling, or it may be invisible 
 and its presence revealed only by assaying. The common associates of gold 
 in quartz veins are pyrite, galena, sphalerite, chalcopyrite, arsenopyrite, tel- 
 lurides, arsenic, bismuth, tetraheclrite, stibnite, magnetite, hematite, barite, 
 fluorite, siderite, and so forth. Of these associates pyrite, chalcopyrite, 
 
?6 DESCRIPTIVE MINERALOGY 
 
 galena, tetrahedrite, sphalerite and arsenopyrite are often auriferous. Ow- 
 ing to the decomposition of the various associated sulphide minerals, espec- 
 ially pyrite, the quartz, where exposed to the surface and the action of 
 percolating waters zone of oxidation is usually more or less cellular and 
 of a rusty appearance. Such quartz is often called "porous" or "rusty" 
 quartz and in it the gold is usually of the free-milling type. 
 
 Free milling gold is easily extracted from the gangue by means of 
 crushing and washing in a stamp mill and subsequent amalgamation with 
 mercury. The low grade ores and also the auriferous sulphides are usually 
 roasted and then treated by either the chlorination or cyanide processes. In 
 the chlorination process the auriferous ores are subjected to the action of 
 nascent chlorine, which may be prepared in various ways. This gives rise 
 to a solution containing gold chloride, AuCl 3 , from which the gold is then 
 easily precipitated either as the metal or sulphide by ferrous sulphate or 
 hydrogen sulphide, respectively. The cyanide process makes use of a weak 
 solution of potassium cyanide and atmospheric oxygen. The finely crushed 
 and roasted ore is placed in large receptacles through which a weak solution 
 of potassium cyanide flows. In time the gold passes into solution as the 
 double cyanide, KAu Cy 2 , and is then readily precipitated by either metallic 
 zinc or electrolysis. 
 
 Placer gold is the result of the disintegration of the rocks containing 
 gold in situ, that is, disseminated or in veins. The rocks, owing to the 
 action of the atmospheric agencies heat, cold, rain, etc. and erosion, are 
 reduced to sand and gravel. The gold on account of its high specific grav- 
 ity becomes concentrated in the stream beds in auriferous regions and is 
 found as scales, grains, and nuggets. Many such occurrences of great 
 value are known. Placers may be ancient, recent, or present, depending 
 upon the geological period in which they were formed. The older placers 
 are often more or less consolidated or protected by means of overlying 
 igneous rocks. Ancient placers occur in California, Australia, New South 
 Wales, South Africa, and in the Black Hills of South Dakota. Recent 
 placers are found in the Klondike district, Alaska ; Colorado ; California : 
 Australia ; Siberia ; and so forth. Present placers are those being formed 
 at the present time and occur along the seacoast at Cape Nome, Alaska, and 
 elsewhere. In nearly all noteworthy gold producing districts, gold has 
 usually been found first in placer deposits and subsequent exploration re- 
 vealed the primary occurrences in situ. 
 
 Placer gold is readily obtained by washing. Usually the sand and 
 gravel is thrown into long wooden troughs called sluices. Through these 
 sluices water flows at a rather rapid rate in order to carry away the lighter 
 rock material. At definite intervals cross-bars, called riffles, are placed in 
 
ELEMENTS 27 
 
 the trough so as to check to some extent the velocity of the water and there- 
 by the transporting power also. This causes the heavy particles to fall to 
 the bottom of the sluices and since mercury is added from time to time 
 and is also caught by the riffles, an amalgam of gold is formed. From this 
 amalgam the gold is easily obtained by volatizing the mercury. 
 
 In some localities hydraulic mining is employed in working placer 
 deposits. This does not differ essentially from the above method and con- 
 sists in directing a large stream of water under high pressure against a 
 bank of the placer in order to loosen the same and wash the sand and gravel 
 down into the sluices. 
 
 At present, 1907, the most important gold producing localities are 
 ( i ) the South African, which includes Transvaal, Rhodesia, and the West 
 Coast. Here the gold occurs in both veins and secondary deposits. (2) 
 The United States, with Colorado, Alaska, California, Nevada, S. Dakota, 
 Utah, and Montana as the largest producers in the order named. The 
 Cripple Creek district of Colorado; the Black Hills of South Dakota; Gold- 
 field and Tonapah, Nevada, and Klondike, Alaska, are all well known gold 
 fields. (3) Australia and New Zealand. Here Victoria is the largest pro- 
 ducer. The occurrences are both in situ and in placers. (4) Russia, prin- 
 cipally in the Ural Mountains, Canada, Mexico, Hungary, Brazil, British 
 India, and Chile also have important deposits. 
 
 In 1908 the world's production of gold amounted to 21,529,300 ounces 
 or 669,651 kilograms,* valued at $444,382,312. The ten largest producers 
 were: 
 
 OUNCES VALUE 
 
 South Africa 7,928,348 $163,869,954 
 
 United States 4,659,360 96,313,256 
 
 Australasia 3>5577O5 72,509,200 
 
 Russia 1,497,076 30,944,561 
 
 Mexico 1,187,445 24,518,548 
 
 British India 504,309 10,424,067 
 
 Canada 462,467 9,559,274 
 
 China 250,000 5,165,000 
 
 Japan I55> 3,203,85 
 
 Columbia 170,000 3,514,073 
 
 Gold occurs in small quantities in ocean water. According to Sonstadt 
 and Liversidge a ton of ocean water near Sidney, Australia, contains 0.032 
 to 0.064 grams of gold. Repeated attempts have been made to extract gold 
 from the ocean. 
 
 Gold is used chiefly for coinage and jewelry, also to some extent in 
 
 * Gold is worth $20.67 per troy ounce or $664.55 per kilogram. 
 
28 DESCRIPTIVE MINERALOGY 
 
 photography. Gold coins of the United States consist of nine parts of 
 gold and one of copper. For jewelry purposes copper and silver are alloyed 
 with gold. The gold content of such alloys is expressed in carats, thus 14 
 carat gold consists of i4/24ths gold and io/24ths other metals. 
 
 GOLD AMALGAM, (Au, Hg, Ag.) 
 
 Contains aside from small percentages of silver (about 5%) as high as 41.63% 
 of gold. It is white in color and has a metallic luster. Occurs usually in friable 
 grains, sometimes in globules, rarely crystallized. Specific gravity about 15.5 Not 
 common. Reported only from Mariposa, California ; platinum placers of Columbia : 
 and Victoria, Australia. 
 
II. SULPHIDES 
 
 AND ANALOGOUS SELENIUM, TELLURIUM, ARSENIC, ANTI- 
 MONY, AND BISMUTH COMPOUNDS 
 
 I. SULPHIDES, ETC., OF THE METALLOIDS 
 
 Here are placed all metallic compounds without oxygen of sulphur, 
 antimony, bismuth, selenium, tellurium, and arsenic. They are usually 
 rather heavy, possess a metallic luster and are opaque. Some of the mineral? 
 of this class are of great importance as ores. 
 
 REALGAR, AsS. 
 
 Monoclinic, prismatic class, a : b : c 1.4403 : I : 0.9729. {$ = 
 II 355 / - Crystals are usually short prismatic; also in coarse or fine granu- 
 lar and compact masses. As an incrustation or coating on various minerals. 
 
 Hardness 1.5 to 2. Specific gravity 3.4 to 3.6. Perfect cleavages 
 parallel to the clinopinacoid and orthoprism. Fracture is conchoidal. Res- 
 inous or greasy luster with an aurora-red or orange-yellow color. Trans- 
 parent to translucent. 
 
 AsS, or sometimes written As 2 S 2 , assuming the constitution to be 
 S = As As = S. Very easily fusible before the blowpipe. Yields a 
 blue flame and dense white fumes with the odor of garlic and sulphur diox- 
 ide. Yields a red sublimate in closed tube. Partially soluble in potassium 
 
 hydroxide. 
 
 Realgar is usually associated with orpiment ; occurs, however, also with 
 ores of silver, lead, and antimony. Sometimes found as a sublimation pro- 
 duct on Vesuvius and Solfatara. In the Yellowstone Park as a deposit from 
 hot springs. Some notable localities are Nagyag and Joachimsthal, Bohe- 
 mia ; Kapnik and Felsobanya, Hungary ; Binnenthal, Switzerland. Various 
 places in Utah and California. Formed in various metallurgical processes. 
 
 The artificial compound finds application in the manufacture of fire- 
 works and pigments. 
 
3O DESCRIPTIVE MINERALOGY 
 
 ORPIMENT, Auripigment, Arsenical Gold Ore, As 2 S 3 . 
 
 Monoclinic, prismatic class, a : b : c = 0.5962 : I : 0.665, |8 = QO4i'. 
 Crystals are short prismatic, but not common. Usually in foliated or gran- 
 ular masses. Sometimes as reniform crusts. 
 
 Hardness iV 2 to 2. Specific gravity 3.4 to 3.5. Perfect cleavage 
 parallel to clinopinacoid. Flexible. Resinous to pearly luster. Lemon yellow 
 in color and streak. Translucent to opaque. Very much like realgar but 
 differs in color. 
 
 As 2 S 3 . When heated becomes red, otherwise like realgar. 
 
 Occurs with realgar from which it has often been formed. Results 
 from the decomposition of arsenic- compounds such as proustite, tennan- 
 tite, or enargite. Principal localities are Tajowa, Hungary ; in large masses 
 at Allchar, Macedonia ; Julamerk, Kurdistan. Also at Mercer, Iron Co., 
 Utah ; San Bernardino Co., California ; Douglas Co., Oregon. As a de- 
 posit from hot springs at Steamboat Springs, Nevada, and in small quan- 
 tities with realgar in the Yellowstone Park. 
 
 The artificial compound is used as a pigment, also in dyeing and tanning 
 processes. Mixed with potassium hydroxide and quicklime it forms a 
 paste for the removal of hair from the skins. 
 
 STIBNITE GROUP 
 
 This group contains the sulphides and selenides of antimony and bis- 
 muth which conform to the general formula M"" 2 R 3 . The members of this 
 group crystallize in the orthorhombic bipyramidal class. 
 
 a : b : c 
 
 STIBNITE, Sb 2 S 3 0.9926 : i : i .0179 
 
 BISMUTHINITE, Bi 2 S 3 0.9680 : i : 0.9850 
 
 GUANAJUATITE, Bi 2 (Se,S) 3 approx. i : i : ? 
 
 STIBNITE, Antimonite, Gray Antimony, Antimony Glance, Sb.S^ 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.9926 : i : 1.0179. 
 Crystals common, prismatic and highly modified. Over 90 forms have been 
 noted. Crystals often show vertical striations ; also may be twisted or bent. 
 In needle-like crystals arranged radially. Bladed and columnar. Occurs 
 in coarse and fine grained masses. Compact. 
 
 Perfect cleavage parallel to brachypinacoid. Slightly sectile. Metallic 
 luster. Hardness 2. Specific gravity 4.6 to 4.7. Lead gray in color and 
 streak. Often tarnishes black. 
 
SULPHIDES 31 
 
 Sb,S ;i . Fuses easily in candle flame. Sometimes auriferous or argen- 
 tiferous. Colors flame greenish blue and yields dense fumes of antimony 
 trioxide. 
 
 Found in veins, with quartz and various antimony minerals which re- 
 sult from the decomposition of stibnite. Also with galena, lead and silver 
 ores, barite, cinnabar, sphalerite, gold. etc. Important localities are Wolfs- 
 berg, Hartz Mountains ; Mileschau, Bohemia ; Arnsberg, Westphalia ; Ma- 
 gurka in granite, Kremnitz and Felsobanya in andesite, Hungary ; Kos- 
 tainik, Siberia ; also in Algeria, Asia Minor, Borneo, Mexico. Excellent 
 crystals from Shikoku, Japan. 
 
 In the United States in 1906 ores were shipped from Shoshone Co., 
 Idaho ; Austin and Battle Mt, Nevada ; Garfield Co., Utah ; and Okanogan 
 Co., Washington. Other deposits occur in Sevier Co., Arkansas ; Kern and 
 Benito Counties, California; Iron Co., Utah. Most of the world's supplv 
 is obtained from France, Algeria, and Italy. 
 
 Stibnite is the chief source of metallic antimony and its compounds. 
 It is used in pyrotechny, safety matches, rubber goods, and percussion caps. 
 
 BISMUTHINITE, Bismuth Glance, Bi 2 S 3 . 
 
 Orthorhombic, bipyramidal ' class, a : b : c = 0.968 : i : 0.985. Very much like 
 stibnite. Well developed crystals are rare. More commonly in bunches of acicular 
 crystals ; also in foliated, radial and granular masses. 
 
 Perfect cleavage parallel to brachypinacoid. Color lead gray to tin white, 
 usually lighter than stibnite. Yellow or iridescent tarnish often to be observed. Metal- 
 lic luster. Hardness 2 and specific gravity 6.4 to 6.6. Lead gray streak. 
 
 BisSs. Fuses easily. Gives with various reagents characteristic bismuth reac- 
 tions. Sometimes copper, iron, or selenium are present. 
 
 Not nearly as common as stibnite. Usually with tin ore deposits ; also in silver- 
 cobalt veins. Schneeberg, and Altenberg, Saxony; Joachimsthal, Bohemia; Corn- 
 wall, England ; New South Wales ; Queensland. With silver-tin-bismuth deposits 
 in Bolivia; Sinaloa, and Guanajuato, Mexico. 
 
 In the United States with gold at Rowan, North Carolina ; with garnet and barite 
 in Beaver Co., Utah : also in Mono and Fresno Counties, California. 
 
 GUANA JUATITE, Frenzelite, Bi,(Se, S) 3 . 
 
 Needle-like crystals ; also granular, fibrous, foliated, or massive. Looks like 
 bismuthinite. Hardness 2.5 to 3.5. Specific gravity 6.25 to 6.62. Color bluish gray. 
 Distinct brachypinacoidal cleavage. Occurs at Guanajuato, Mexico. 
 
 TETRADYMITE, Bi 2 Te,S. 
 
 Hexagonal, ditrigonal scalenohedral class, a : c = i : 1.587. Small crystals. 
 Those from Shubkau near Schemnitz, Hungary, show cyclic fourlings ; twinning 
 plane parallel to V 2 R. Usually in foliated or granular masses. Perfect basal 
 cleavage. Hardness 1.5 to 2. Marks paper. Specific gravity 7.2 to 7.9. Light lead 
 gray color; upon fracture surface a strong metallic luster, otherwise dull. 
 
32 DESCRIPTIVE MINERALOGY 
 
 Bi 2 Te 2 S. Sometimes contains selenium. Composition may vary but in general 
 indicated by the formula given. Fuses readily and reacts for bismuth, tellurium, and 
 sulphur. 
 
 Of rare occurrence. With gold, Schubkau near Schemnitz, Hungary; also other 
 localities in Hungary. In the United States in Spottsylvania Co., Virginia; David- 
 son, Burke, and McDowell Counties, North Carolina ; also in Montana, Colorado, 
 and Georgia. 
 
 Molybdenite, MoS 2 . 
 
 Hexagonal, dihexagonal bipyramidal class, a : c = i : 1.908. Well 
 developed crystals very rare, on account of softness faces are easily des- 
 troyed. Usually in disseminated scales or grains ; sometimes in foliated or 
 granular masses. 
 
 Excellent basal cleavage. Flexible, greasy. Marks paper. Blue gray 
 in color (graphite is black). Hardness I to 1.5. Specific gravity 4.7 to 
 4.8 (graphite 1.9 to 2.3). Gray streak on paper, on glazed porcelain green- 
 ish (graphite shiny black). 
 
 MoS L> . Sometimes auriferous or argentiferous. Reacts for molyb- 
 denum and sulphur. 
 
 Most important molybdenum mineral. Generally disseminated in 
 granites, especially those associated with tin ore deposits, also in syenites, 
 gneisses, and crystalline limestones. 
 
 Large crystals in Renfrew Co., Canada ; Cornwall, England ; Alten- 
 berg, Saxony ; Scandinavia ; Finland ; Ural Mountains. In the United 
 States in many localities along Appalachain, Rocky, and Sierra Nevada 
 Mountains. At present but two localities in the United States have been 
 exploited, namely, Crown Point, Chelan Co., Washington, and Cooper. 
 Washington Co., Maine. 
 
 Chief source of molybdenum and its compounds. Used in the manu- 
 facture of molybdenum steels. 
 
 2. SULPHIDES, ETC., OF THE METALS 
 
 SPHALERITE WURTZITE GROUPS 
 
 The bivalent metals calcium, zinc, cadmium, manganese, iron, and 
 nickel form with one atom of sulphur an isodimorphous series. The one 
 group of this series crystallizes in the cubic system and has as its most im- 
 portant representative sphalerite, ZnS. The other group crystallizes in the 
 hexagonal system. 
 
 The isodimorphous series is as follows: 
 
SULPHIDES 
 
 33 
 
 SPHALERITE GROUP 
 
 (Cubic System ) 
 OLDHAMITE, CaS. 
 
 SPHALERITE, ZnS. Hextetrahedral Class 
 
 Alabandite, MnS. Hextetrahedral Class 
 
 TROILITE., FeS. 
 Pentlandite, (Fe, Ni)S. 
 
 WURTZITE GROUP 
 (Hexagonal System ) 
 
 WURTZITE, ZnS. 
 ERYTHROZINCITE, (Zn,Mn)S. 
 Greenockite, CdS. 
 PYRRHOTITE, FeS.? 
 
 Millerite, NiS. 
 Niccolite, NiAs. 
 
 ARITE, Ni(As,Sb). 
 BREITHAUPTTTE, NiSb. 
 
 OLDHAMITE, CaS, is a rare mineral, 
 in several meteorites. 
 
 SPHALERITE, Blende, Zinc Blende, Black Jack, ZnS. 
 
 Cubic, hextetrahedral class. Crystals are common. Often distorted. 
 The tetrahedrons, rhombic dodecahedron, and the trigonal tristetrahedron 
 (7/2=3) are the most commonly observed forms, Figures 12, 13, and 14. 
 
 " 
 
 / 
 
 
 a 
 
 C 
 
 Ditrigonal 
 
 Pyramidal 
 
 Class 
 
 i 
 
 0-9353 
 
 Ditrigonal 
 
 Pyramidal 
 
 Class 
 
 
 ? 
 
 Ditrigonal 
 
 Pyramidal 
 
 Class 
 
 i 
 
 0.9364 
 
 Ditrigonal 
 
 Pyramidal 
 
 Class 
 
 i 
 
 0.9528 
 
 Ditrigonal 
 
 Pyramidal 
 
 Class 
 
 i 
 
 0.9886 
 
 Ditrigonal 
 
 Pyramidal 
 
 Class 
 
 i 
 
 o . 9462 
 
 Ditrigonal 
 
 Pyramidal 
 
 Class 
 
 
 .. ? 
 
 Ditrigonal 
 
 Pyramidal 
 
 Class 
 
 i 
 
 o . 9962 
 
 ineral. It has been observed in 
 
 small quantities 
 
 FIG. 12. 
 
 FIG. 13. 
 
 FIG. i. 
 
 Crystals are often highly modified. Twins are very common. The twin- 
 ning plane is parallel to a face of the octahedron. Polysynthetic twinning 
 is also to be observed. Also occurs in cleavable, fine and coarse grained 
 masses ; compact, foliated, fibroirs, and more rarely in radiated and botry- 
 oidal masses. 
 
34 DESCRIPTIVE MINERALOGY 
 
 Very perfect rhombic dodecahedral cleavage. Conchoidal fracture. 
 Brittle. Resinous to adamantine luster. High index of refraction, n Na = 
 2.3692. Hardness 3.5 to 4. Specific gravity 3.9 to 4.2. Color varies 
 greatly. When pure it is white. Depending upon impurities it may be 
 brown, red, green, yellow, black, and so forth. Transparent to translucent. 
 Sometimes phosphoresces when broken or rubbed. Streak brown, light yel- 
 low or white. 
 
 ZnS, but may contain varying amounts of iron, manganese, cadmium, 
 lead, tin, mercury, gold, silver, indium, gallium, or thallium. The amount 
 of iron present may be as high as 18%. The other elements are usually 
 present in comparatively small amounts. Fuses with difficulty. On charcoal 
 gives a zinc coating. Soluble in nitric acid with the separation of sulphur; 
 in hydrochloric acid with the evolution of hydrogen sulphide. 
 
 Occurs extensively in dolomitic limestones and other sedimentary rocks, 
 also in crystalline rocks. Usually associated with galena, chalcopyrite, cal- 
 cite, dolomite, barite, fluorite, marcasite, siderite, rhodochrosite, and quartz. 
 Common in silver and lead localities. Sphalerite has doubtlessly been de- 
 posited in many instances by precipitation from aqueous solutions. Hence 
 it is found in veins, cavities, and sometimes in extensive deposits. 
 
 Commonly observed in Freiberg, Saxony ; in dolomite at Binnenthal. 
 Switzerland ; Kapnik, Hungary ; Cornwall, England ; Pribram, Bohemia ; 
 etc., etc. 
 
 In the United States it is especially common in the limestones of Mis- 
 souri, Wisconsin, Iowa, and Illinois, usually associated with galena and 
 calcite. Beautiful crystals at Mineral Point, Wis., and Joplin, Mo. At 
 Franklin Furnace, N. J., a more or less colorless variety cleiophane 
 occurs. Sphalerite is also found in many other localities. 
 
 Sphalerite is used as an ore of zinc. Most of the cadmium, used in 
 commerce, is obtained from sphalerite. It is also used to some extent in 
 the manufacture of zinc sulphate. 
 
 Alabandite, Manganblende, MnS. 
 
 Cubic, hextetrahedral class. Crystals are rare. The cube, rhombic do- 
 decahedron, tetrahedrons, and trigonal tristetrahedron (m=2) are the com- 
 monly observed forms. Usually in granular masses. Perfect cubical cleav- 
 age. Hardness 3.5 to 4. Specific gravity 3.9 to 4. Opaque. When fresh 
 alabandite possesses a submetallic luster ; usually, however, due to tarnish 
 it is more or less dull. Gray black in color, tarnishes to a brown black. 
 Dirty green streak. 
 
 MnS. Fuses with difficulty. Reacts f6r manganese and sulphur. With 
 hydrochloric acid evolves hydrogen sulphide. 
 
SULPHIDES 35 
 
 Not very abundant. With rhodochrosite at Kapnik, Hungary ; Nagyag, 
 Transylvania ; Mexico ; Peru ; and Brazil. 
 
 In the United States in Summit County, Colorado ; . also at Tombstone, 
 Arizona. 
 
 TROII.ITE, FeS, occurs in brownish masses in meteorites. 
 
 Pentlandite, Eisennickelkies, (Fe,Ni)S. 
 
 Cubic. Grains and granular masses. Octahedral cleavage. Hardness 
 3.5 to 4 and specific gravity 4.6 to 5.1. Metallic luster and usually light 
 bronze-yellow in color. Streak black. Non-magnetic. Brittle and opaque. 
 
 (Fe,Ni)S. Yields easily on fusing a magnetic globule. 
 
 Occurs in large quantities at Sudbury, Ontario, in association with 
 chalcopyrite and pyrrhotite. This is the source of most of the nickel used 
 in the United States. Also in various localities in Norway, Sweden, Scot- 
 land, Australia, etc. There are no deposits of economic importance in the 
 United States. 
 
 An important source of nickel. The output of the Sudbury, Ontario, 
 region for 1906 was 21,490,000 pounds valued at $8,948,834. 
 
 WURTZITE, Schalenblende, ZnS. 
 
 Hexagonal, ditrigonal pyramidal class, a : c=i : 0.9353. Crystals rare. Formed 
 artificially. Consist of hexagonal prism with pyramid and basal pinacoid. Mostly 
 as radial fibrous masses associated with sphalerite. Also compact massive. Prismatic 
 and basal cleavages. Hardness 3.5 to 4. Specific gravity 3.98 to 4.07. Color dark 
 brown. Streak light brown. Resinous luster. 
 
 ZnS, same as for sphalerite. Usually contains iron (up to 8%), also cadmium, 
 sometimes as much as 3.66% (Mies, Bohemia). Easily soluble in cold concentrated 
 hydrochloric acid while sphalerite is not. 
 
 Occurs generally in association with sphalerite. Not as common as sphalerite. 
 Some of the important localities are Oruro, Bolivia ; Pribram, Bohemia ; Butte, 
 Montana. 
 
 ERYTHROZINCITE, (Zn,Mn)S, is a wurtzite containing manganese. Occurs at 
 thick transparent plates in Siberian lapis lazuli. 
 
 Greenockite, CdS. 
 
 Hexagonal, ditrigonal pyramidal class, a : c=i : 0.9364. Natural 
 crystals exceedingly small and rare. Usually show hexagonal prisms ter- 
 minated on the one end with an hexagonal pyramid and on the other with 
 a basal pinacoid. Pyramidal and tabular habits. Is usually found as an 
 earthy coating. 
 
 Prismatic and basal cleavages. Hardness 3 to 3.5. Specific gravity 
 4.9 to 5. Honey, lemon, or orange yellow, also brown and brick red. Streak 
 yellow. Resinous adamantine luster. Translucent. 
 
 CdS. Yields on charcoal or plaster tablet characteristic cadmium 
 coating. 
 
36 DESCRIPTIVE MINERALOGY 
 
 Not common. Usually with sphalerite and smithsonite. With* sphaler- 
 ite at Pribram, Bohemia, and many other European localities. 
 
 In the United States with the zinc ores in Missouri and Arkansas. 
 Sometimes colors smithsonite a bright yellow. 
 
 Common as a furnace product. 
 
 PYRRHOTITE, Magnetic Pyrite, FeS. 
 
 Hexagonal, ditrigonal pyramidal class, a : c=i : 0.9528. Well de- 
 veloped- crystals are not common. They usually show tabular development. 
 Common type of occurrence is massive, often granular. 
 
 Basal cleavage but not usually observable. Brittle. Hardness 3.5 to 
 4. Specific gravity 4.54 to 4.64. Metallic luster. Opaque. Bronze-yellow 
 to bronze-red in color. Tarnishes easily to a dark brown. Streak grayish 
 black. Magnetic, sometimes only slightly. 
 
 Groth gives FeS as the probable composition of pyrrhotite. Analyses, 
 always show an excess of I to 2 and even more percent of sulphur, so that 
 various formulae, varying from Fe 5 S 6 to Fe 16 S 17 , are commonly given as 
 indicating the composition of pyrrhotite. Fe 7 S 8 and Fe 1:l S 12 are given most 
 commonly. Rammelsberg suggested Fe n S n + i- Pyrrhotite sometimes con- 
 tains small amounts of cobalt and nickel. Pyrrhotite containing much 
 nickel is usually but slightly magnetic. Fuses on charcoal to a black mag- 
 netic mass. Decomposed by hydrochloric acid yielding hydrogen sulphide. 
 Decomposes easily to pyrite, limonite, siderite, and arsenopyrite. Pseudo- 
 morphs of pyrite and arsenopyrite after pyrrhotite are rather common. 
 
 Usually found as a magmatic segregation in basic plutonic rocks such 
 as gabbros, norites, and peridotites. Found also in schists and older erup- 
 tive rocks. It is commonly associated with pyrite, chalcopyrite, pentlandite, 
 and galena. Occurs at Kongsberg, Norway ; Falum, Sweden ; Bodenmais, 
 Bavaria ; Andreasberg, Hartz Mountains ; Joachimsthal, Bohemia, etc. 
 
 The most important localities in the United States are the Gap Mine, 
 Lancaster Co., Pa., and Ducktown, Tenn. 
 
 Large deposits are found at Sudbury, Canada. Here pyrrhotite is asso- 
 ciated with pyrite and chalcopyrite, and is nickeliferous. 
 
 Also found in meteorites in small quantities. 
 
 Pyrrhotite is an important source of nickel and cobalt. 
 
 Millerite, Capillary Pyrites, NiS. 
 
 Hexagonal, ditrigonal pyramidal class, a : c=i : 0.9886. Very fine, 
 
 slender crystals. Often in radiated groups. Sometimes extremely fine and 
 
 matted together like a wad or tuft of hair. Crystals are rarely doubly ter- 
 minated. Also as a coating. 
 
SULPHIDES 37 
 
 Basal and pyramidal cleavages. Hardness 3 to 3.5. Specific gravity 
 5.3 to 5.9. Metallic luster. Brass to bronze yellow in color. Sometimes 
 shows a gray iridescent tarnish. Greenish black streak. Crystals are 
 elastic. 
 
 NiS. Fuses to magnetic globule. Reacts for nickel and sulphur. 
 
 Never found in large quantities. Usually associated with nickel and 
 cobalt minerals, also with hematite, calcite, dolomite, flourite, pyrrhotite. 
 chalcopyrite, etc. A few European localities are Joachimsthal, Bohemia, 
 Pribram, Hungary ; Freiberg district, Saxony, and Cornwall, England. 
 
 At Antwerp, N. Y., millerite occurs with hematite ; at the Gap Mine, 
 Lancaster Co., Pa., with pyrrhotite and chalcopyrite ; at St. Louis, Mo., in 
 limestone geodes with calcite, dolomite, and sphalerite. 
 
 Used to some extent as an ore of nickel. 
 
 Niccolite, Copper Nickel, Rothkupferkies, NiAs. 
 
 Hexagonal, ditrigonal pyramidal class, a : c=-\ : 0.9462. Crystals 
 are rare. Usually massive and disseminated. Occasionally botryoidal and 
 reniform. 
 
 Imperfect prismatic cleavage. Conchoidal to uneven fracture. Brittle. 
 Hardness 5.5. Specific gravity 7.3 to 7.7. Metallic luster. Light copper 
 red in color, tarnishes brown or grayish. As a result of decomposition 
 niccolite is often coated with a green crust of annabergite, Ni 3 As 2 O 8 , 8H,O. 
 Streak brownish black. 
 
 NiAs, with small amounts of iron and cobalt. The arsenic is often 
 replaced by varying percentages of antimony (up to 28%) and sulphur. 
 Reacts for nickel and arsenic. 
 
 Commonly associated with nickel, cobalt, and silver ores, thus in the 
 Freiberg district of Saxony ; Joachimsthal, Bohemia ; and the Cobalt dis- 
 trict, Ontario. In the last named district niccolite occurs in large quanti- 
 ties, often in veins of considerable width. In smaller quantities at Chat- 
 ham, Conn. ; Franklin Furnace, N. J., Silver Cliff, Colo. ; Thunder Bay, 
 Lake Superior district ; and Tilt Cove, New Foundland. 
 
 An important nickel ore. 
 
 ARITE is a niccolite containing a considerable amount of antimony and conforms 
 to the formula Ni(Sb,As). Not common. 
 
 BREITHAUPTITE, Antimonnickel, NiSb. 
 
 Hexagonal, ditrigonal pyramidal, a : c=i : 0.9962. Crystals are rare. Usually 
 massive and disseminated. Basal cleavage. Uneven fracture. Brittle. Hardness 
 5. Specific gravity 7.5 to 7.6. Light copper red in color, on tarnishing shows a deli- 
 cate violet shimmer. Reddish brown streak. 
 
 NiSb, with small percentages of iron. Fuses with difficulty. 
 
 Occurs with nickel ores, galena, and calcite at St. Andreasberg, Hartz Mountains ; 
 also at Sarrabus, Sardinia. 
 
38 DESCRIPTIVE MINERALOGY 
 
 PYRITE MARCASITE GROUPS 
 
 The metals iron, manganese, nickel, and cobalt form with two atoms 
 of sulphur an interesting isodimorphous series of which the pyrite group 
 crystallizes in the dyakisdodecahedral class of the cubic system, while the 
 members of the marcasite group possess the symmetry of the orthorhombic 
 bipyramidal class. The two groups of this series are : 
 
 PYRITE GROUP 
 
 (Cubic System ) 
 
 HAUERITE, MnS 2 . Dyakisdodecahedral Class* 
 
 PYRITE, FeS 2 . Dyakisdodecahedral Class 
 
 Cobaltite, CoAsS. Dyakisdodecahedral Class 
 
 GERSDORF^ITE, NiAsS. Dyakisdodecahedral Class 
 
 UUvMANNiTE, NiSbS. Dyakisdodecahedral Class 
 
 Smaltite, CoAs 2 . Dyakisdodecahedral Class 
 
 Chloanthite, NiAs 2 . Dyakisdodecahedral Class 
 
 SPERRYIJTE. PtAs 2 . Dyakisdodecahedral Class 
 
 MARCASITE, GROUP 
 (Orthorhombic System ) 
 
 MARCASITE, FeS 2 . Bipyramidal Class 0.7662 : i : 1.2347 
 
 ARSENOPYRITE, FeAsS. Bipyramidal Class 0.6775 : l ' 1.1882 
 
 LoijjNGiTE, FeAs 2 . Bipyramidal Class 0.6689 : I : 1:2331 
 
 GLAUCODOTE, (Co,Fe)AsS. Bipyramidal Class 0.6942 : i : 1.1925 
 
 , CoAs 2 . Bipyramidal Class 0.6773 : l ' 1-1882 
 
 , Ni(As, S, Sb) 2 . Bipyramidal Class ? 
 
 RAMMELSBERGITE, NiAs 2 . Bipyramidal Class ? 
 
 On account of the different chemical behavior of pyrite and marcasite 
 there has been much speculation as to their chemical constitution. The fol- 
 lowing graphical formulae are often used to represent their respective con- 
 stitutions. 
 
 /S S\ /S S\ 
 
 Fet-S Fe S-rFe Fc^ )Fe 
 
 ^S S 7 X S S 7 
 
 Pyrite Marcasite 
 
 The members of this series are comparatively hard, 5 to 6, and vary in 
 color from brass yellow to tin white. 
 
 * Groth and others refer the members of this group to the tetrahedral pentagonal 
 dodecahedral class. 
 
SULPHIDES 
 
 39 
 
 iv, Mangankies, MnS 2 . 
 
 Cubic, dyakisdodecahedral class. Crystals show the octahedron, hexahedron, 
 rhombic dodecahedron, pyritohedron (w=2), and dyakisdodecahedron (n=3/2, w=3). 
 Octahedral and pyritohedral habits most common. Massive. Perfect cubical cleav- 
 age. Hardness 4. Specific gravity 3.4 to 3.5. When fresh, hauerite possesses metallic 
 adamantine luster and brownish red color. But usually is dull, opaque, and brownish 
 black. Reddish brown streak. 
 
 MnSa, sometimes contains iron. Reacts for manganese and sulphur. Decomposed 
 by warm hydrochloric acid with an evolution of hydrogen sulphide and separation 
 of sulphur. 
 
 Occurs in excellent isolated crystals in clay and gypsum at Kalinka, Hungary, and 
 Raddusa, Sicily. 
 
 FIG. 15. 
 
 FIG. 16. 
 
 FIG. 17. 
 
 FIG. 18. 
 
 FIG. 19. 
 
 FIG. 20. 
 
 FIG. 21. 
 
 PYRITE, Fool's Gold, Iron Pyrites, FeS 2 . 
 
 Cubic, dyakisilodecahedral class. Crystals common and often very 
 large. Over 100 forms have been observed. Among these the cube, octa- 
 hedron, and pyritohedron (m=2) occur commonly as independent or pre- 
 dominating forms. Some of the common combinations are the cube and 
 pyritohedron (111=2) Figure 15; octahedron and pyritohedron (111=2) Fig- 
 ures 16 and 17; cube, octahedron, and pyritohedron (m=2) Figure 18; 
 also pyritohedron (m=2), octahedron, and dyakisdodecahedron (^=3/2, 
 7tt = 3) Figure 19. The crystal faces often show striations conforming to 
 the symmetry of the dyakisdodecahedral class as shown by Figure 20. In- 
 terpenetration twins of pyritohedrons with the twinning plane parallel to 
 a face of the rhombic dodecahedron, Figure 21, are sometimes called crys- 
 
40 DESCRIPTIVE MINERALOGY 
 
 tals of the "iron cross." Crystals may be ideally developed but are often 
 greatly distorted. Also massive and disseminated. Fine grained, granular, 
 reniform, globular, stalactitic, also radiated. 
 
 Imperfect cubical cleavage. Conchoidal fracture. Hardness 6 to 6.5. 
 Specific gravity 4.9 to 5.2, pure 5.18. Brittle. Metallic luster. Opaque. 
 Pale brassy to 'golden yellow in color, sometimes with brown or variegated 
 tarnish colors. Greenish to brownish black streak. 
 
 FeS 2 ,with nickel, cobalt, copper, zinc, arsenic, gold, and silver in vary- 
 ing amounts. On charcoal yields sulphur dioxide and magnetic globule. 
 Etched by aqua regia and potassium hydroxide. Insoluble in hydrochloric 
 acid. 
 
 Decomposes readily, especially in a moist atmosphere. Limonite and 
 goethite are the usual decomposition products, although various sulphates 
 and sulphuric acid sometimes result. Pseudomorphs of limonite after pyrite 
 are quite common. 
 
 Pyrite is the most common sulphide mineral and, hence, is found very 
 widely distributed. It occurs in rocks of all ages. Its mode of occurrence 
 varies greatly. Is usually associated with other sulphide minerals, such 
 as galena, sphalerite, chalcopyrite, arsenopyrite, and the like. Also with 
 calcite, siderite, hematite, magnetite, and so forth. Commonly found in 
 quartz, often in association with native gold, see page 25. As nodules and 
 concretions in many slates, sandstones, and coals. 
 
 Excellent crystals of pyrite are found in the Freiberg district, Saxony ; 
 Pribram, Bohemia ; Schemnitz, Hungary, and elsewhere. Enormous quan- 
 tities of massive gold and silver bearing pyrite occur at Rio Tinto, Spain. 
 
 In the United States especially fine crystals occur at Franklin Furnace, 
 N. J. ; Central City Mine, Gilpin Co., "and elsewhere in Colorado; also French 
 Creek, Pa. Large quantities of massive pyrite are annually obtained from 
 Virginia, California, Massachusetts, New York, Alabama, Georgia, Ohio, 
 Indiana, and South Dakota. 
 
 Pyrite is used principally as a source for sulphur dioxide in the man- 
 ufacture of sulphuric acid by the chamber process, and also for sulphate of 
 iron. Small quantities are also used as a mineral paint. 
 
 Cobaltite, Cobalt Glance, CoAsS. 
 
 Cubic,, dyakisdodecahedral class. Usually as small, well developed, 
 crystals showing either the cube or the pyritohedron (m=2). Sometimes 
 both in combination. The cube faces are often striated as shown in Figure 
 20, page 39. More rarely in compact 'and granular masses. 
 
 Perfect cubic cleavage. Conchoidal to. uneven fracture. Brittle. Hard- 
 ness 5.5. Specific gravity 6 to 6.4. Fresh crystals show metallic luster. 
 Opaque. Reddish silver white color. If cobaltite contains much iron the 
 

SULPHIDES 41 
 
 color is apt to be gray. Often with a pinkish coating of erythrite, Co 3 As 2 - 
 O 8 , 8H 2 O. Grayish black streak. 
 
 CoAsS, usually with iron up to 12%. For the ferruginous variety the 
 term ferrocobaltite is often used. Heated on charcoal cobaltite yields a 
 garlic odor and a black magnetic globule. After roasting it gives a dark 
 blue borax bead. Soluble in hot nitric acid. 
 
 An important cobalt mineral. Usually found in small quantities with 
 Other cobalt minerals, also with pyrrhotite, chalcopyrite, pyrite, galena, mag- 
 nite, and so forth. Occurs at Tunaberg and Hakansbo, Sweden ; Skutterud 
 and Nordmark, Norway; Westphalia, Germany; Cornwall, England; and 
 the Cobalt district, Ontario. 
 
 GERSDORFFITE;, Nickel Glance, NiAsS. 
 
 Cubic, dyakisdodecahedral class. Usually octahedral crystals. Other forms are 
 the cube, dodecahedron, and pyritohedron (m=2). Crystals are rare. Compact and 
 disseminated. 
 
 Rather perfect cubical cleavage. Uneven fracture. Brittle. Hardness 5.5. 
 Specific gravity 5.2 to 6.2. Metallic luster. Opaque. Crystals are silver white to 
 steel gray in color but on exposure tarnish dull dark gray. Sometimes coated green 
 with annabergite, Ni 3 As 2 O 8 , 8H 2 O. 
 
 NiAsS, usually with 2 to 6% of iron. Cobalt may also be present. Garlic odor 
 when heated on charcoal, also magnetic globule. Partially soluble in nitric acid 
 yielding a green solution. 
 
 Not a common mineral. Usually alone or with ullmannite. In the Hartz Moun- 
 tains ; Sweden ; Styria ; Scotland ; Ontario, Canada ; British Columbia ; and Phoenix- 
 ville, Pa. 
 
 ULLMANNITE, Antimony Nickel Glance, NiSbS. 
 
 Cubic, dyakisdodecahedral class. Sometimes referred to the tetrahedral penta- 
 gonal dodecahedral (tetartohedral) class. Most common forms are the cube, octa- 
 hedron, and rhombic dodecahedron. Crystals are rare. Habit always cubic. Some- 
 times with pyritohedral and octahedral striations. Crystals from Lolling, Carinthia, 
 show the tetartohedral development. Usually as compact, granular, disseminated 
 masses. 
 
 Perfect cubic cleavage. Uneven fracture. Brittle. Hardness 5 to 5.5. Specific 
 gravity 6.7 to 6.73. Opaque with metallic luster. Lead to steel gray, also dark gray 
 color. Crystals are lighter in color than massive specimens. Does not decompose 
 as readily as gersdorffite. 
 
 NiSbS, with iron an'd arsenic. On charcoal yields antimony coating and a met- 
 allic globule. Soluble in aqua regia yielding a green solution. 
 
 A rare mineral but more common than gersdorffite. Difficult to distinguish 
 from gersdorffite by means of the physical properties only. Found at Lolling, Carin- 
 thia; Siegen, Westphalia; Hartz Mountains; and Montemarba near Sarrubus, Sar- 
 dinia. 
 
 Smaltite, CoAs 2 . 
 
 Cubic, dyakisdodecahedral class. Crystals generally show a cubic habit 
 but are not common. Usually observed in compact, granular, lamellar, or 
 fibrous masses. Also reniform and reticulated. 
 
42 DESCRIPTIVE MINERALOGY 
 
 No distinct cleavage. Uneven fracture. Brittle. Hardness 5.5. Spe- 
 cific gravity 6.4 to 6.6. Metallic luster and opaque. Crystals are tin white 
 to light steel gray in color. Massive specimens are gray to dark gray. 
 Tarnishes dull and is often coated with erythrite (pink) or pharmacolite 
 (white). Streak grayish black. When struck with a hammer yields garlic 
 odor. Difficult to distinguish from chloanthite by means of the physical 
 properties only. 
 
 CoAs 2 , usually with varying amounts of nickel, iron, and sulphur. 
 The. iron content sometimes amounts to 18% which causes an increase in 
 the specific gravity. On charcoal smaltite yields a garlic odor and grayish 
 black magnetic globule. Easily soluble in nitric acid yielding a green so- 
 lution. 
 
 The most common cobalt mineral. Always with cobalt, nickel, and sil- 
 ver ores, also with native bismuth, barite, siderite, quartz, arsenopyrite and 
 so forth. Thus in the Freiberg district, Saxony ; Cornwall, England ; Joa- 
 chimsthal, Bohemia ; Dobschau, Hungary ; Tunaberg, Sweden ; La Motte 
 Mine, Mo. ; and Cobalt district, Ontario. 
 
 Smaltite is an important ore of cobalt. 
 
 Chloanthite, NiAs 2 . 
 
 This mineral is very similar to smaltite in all its crystallographic, phys- 
 ical, and chemical properties. Contains, however, more nickel than smaltite 
 and, hence, is often covered with a green coating of annabergite. A variety 
 from Chatham, Conn., containing 12% of iron and 5% of sulphur, is known 
 as chathamite. 
 
 Occurrence same as for smaltite from which it sometimes cannot be 
 distinguished without a chemical analysis. -ji-iv 
 
 Important nickel ore. 
 
 SPERRYLITE, PtAs 2 . 
 
 Cubic, dyakisdodecahedral class. Small cubic crystals. The cube, octahedron, 
 and pyritohedron (m=2) are the common forms. Hardness 6 to 7. Specific gravity 
 10.6. Looks like platinum. Metallic luster. Streak black. 
 
 PtAs 2 , but contains small amounts of rhodium, iron, and antimony. 
 
 Occurs in the Sudbury district, Ontario; Rambler Mine, Wyoming; also in the 
 stream beds of Macon Co., North Carolina. 
 
 The only compound of platinum occurring in nature. 
 
 MARCASITE, White Iron Pyrites, Spear Pyrites, FeS 2 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.7662 : I : 1.2347. 
 Crystals are usually tabular or short columnar. The commonly observed 
 forms are the basal pinacoid, unit prism, the unit and modified (m=i/T > c) 
 brachydomes. Twins are very common. Two twinning laws \re to be 
 noted with the twinning planes parallel to the unit prism and m 'crodome. 
 Cyclic and polysynthetic twins according to the first law are rathei common. 
 
SULPHIDES 43 
 
 Also massive, stalactitic, reniform, and globular. Often with radial struc- 
 ture. 
 
 Indistinct prismatic cleavage. Uneven fracture. Brittle. Opaque. 
 Metallic luster. Hardness 6 to 6.5. Specific gravity 4.65 to 4.88 (pyrite 
 4.9 to 5.2}. Pale brass yellow or steel gray in color; darker after exposure. 
 Usually lighter in color than pyrite. Streak greenish gray. 
 
 FeS 2 , contains at times copper and arsenic. Chemical properties as 
 for pyrite. However, marcasite decomposes more readily than pyrite. Mar- 
 casite dissolves in concentrated nitric acid with separation of sulphur while 
 pyrite does not. 
 
 Very abundant but not so much so as pyrite. When massive, difficult 
 to distinguish from pyrite. Occurs often with pyrite, galena, fluorite, and 
 sphalerite. Common as concretions in marls, clays, limestones, and coals. 
 In lignite at Littnitz and Altsattel, Bohemia; in marl at Folkestone, Eng- 
 land ; in limestone at Limmer near Hannover, Germany ; with galena and 
 fluorite Derbyshire, England. 
 
 In the United States at Galena, 111., in stalactites ; with sphalerite and 
 galena, Mineral Point, Wis. ; with sphalerite, calcite, etc., at Joplin, Mo. 
 Abundant in many sedimentary rocks especially those containing organic 
 matter ; also common in coal. 
 
 Uses same as for pyrite. 
 
 ARSENOPYRITE, Mispickel, FeAsS. 
 
 Orthorhombic, bipyramidal class, a :b : c = 0.6775 : x : 1.1882. The 
 axial ratio varies with the chemical composition. Often in disseminated 
 crystals which may be long or short prismatic. The usual combination 
 consists of the unit prism and a modified brachydome (m=i/4 c) which 
 are often so developed as to simulate an octahedron. The unit brachy and 
 macrodomes are also frequently observed. The brachydomes are often 
 striated parallel to the a axis. Also often as twins. Most commonly as 
 penetration twins with the unit macrodome as the twinning plane. A sec- 
 ond twinning law, with a face of the unit prism as the twinning plane, is 
 less common. Twins according to second law may be either contact or 
 penetration twins. Arsenopyrite also occurs in columnar, radial, or gran- 
 ular masses ; compact and disseminated ; reticulated. 
 
 Distinct prismatic cleavage. Uneven fracture. Brittle. Hardness 5.5 
 to 6. Specific gravity 5.9 to 6.2. Color is silver white to a light steel gray, 
 tarnishing to brass yellow or gray. Streak black. Opaque. Metallic luster. 
 
 FeAsS, often containing cobalt, antimony, bismuth, silver, and gold. 
 The amount of arsenic varies considerably so that analyses do not always 
 conform to the composition given. Arsenopyrite is sometimes considered 
 
44 DESCRIPTIVE MINERALOGY 
 
 as an isomorphous mixture of marcasite FeS 2 and lollingite FeAs 2 in vary- 
 ing proportions. The variety containing 3 to 9% of cobalt replacing iron 
 is called danaite. On charcoal gives garlic odor and black magnetic globule. 
 Soluble in nitric acid with separation of sulphur. 
 
 Commonly associated with the ores of tin, nickel, cobalt, silver, gold, 
 and lead, also with pyrite, chalcopyrite, and sphalerite. Found in the Frei- 
 berg district, Saxony ; in serpentine at Reichenstein, Silesia ; Cornwall, Eng- 
 land ; Tunaberg, Sweden ; Skutterud, Norway ; in dolomite in Binnenthal, 
 Switzerland, and elsewhere. 
 
 In the United States at Franconia, N. H. ; Chatham, Conn. ; Nevada 
 Co., California; Floyd and Montgomery counties, Virginia; various places 
 in Washington. Also at Deloro, Ontario, in gold bearing quartz veins. 
 
 Arsenopyrite is used principally for the manufacture of arsenic tri- 
 oxide, the arsenic of commerce. If present in sufficient quantities, gold, 
 silver, and cobalt are extracted. Arsenopyrite is mined in Washington and 
 in Floyd and Montgomery counties, Virginia. 
 
 LOLLINGITE, Leucopyrite, FeAs 2 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.6689 : I : 1-2331. Crystals are 
 rare and small. Usual combination consists of the unit prism and the unit macro- 
 dome. Mostly compact and in disseminated granular and acicular aggregates. 
 
 Distinct basal cleavage. Uneven fracture. Brittle. Hardness 5 to 5.5. Specific 
 gravity 7.1 to 7.4. Opaque. Metallic luster. Silver white in color, tarnishes gray. 
 Gray black streak. 
 
 FeAs 2 , always contains sulphur up to 6%. Cobalt, nickel, gold, bismuth, and 
 antimony may also be present. The arsenic content varies considerably. When the 
 composition approaches Fe 2 As 3 , the term leucopyrite is often used. Yields on char- 
 coal the garlic odor of arsenic and fuses with difficulty to a black non-magnetic 
 globule. 
 
 Not a common mineral. In serpentine, sometimes auriferous, at Reichenstein, 
 Silesia ; with siderite at Lolling near Hiittenberg, Carinthia ; Andreasberg, Hartz 
 Mountains ; Roxbury, Conn. ; Brush Creek, Gunnison 'Co., Colorado. 
 
 GLAUCODOTE, (Co,Fe)AsS. 
 
 Orthorhombic, bipyramidal class. Occurs in tin white crystals of a prismatic 
 habit showing a basal cleavage. Also massive. Hardness 5. Specific gravity 5.9 to 
 6.01. Metallic luster. Contains 16 to 25% of cobalt and 12 to 19% of iron. Hintze 
 considers danaite, page 44, as a variety of glaucodote. Is found in crystals of con- 
 siderable size in the chlorite schists of Hakansbo, Sweden, and Huasco, Chile. 
 
 SAFFLORITE, Spathiopyrite, CoAs 2 . 
 
 Orthorhombic, bipyramidal class. This is the Orthorhombic modification of 
 CoAs 2 . Small crystals similar to those of arsenopyrite. Also compact, radial, and 
 fibrous masses. Tin white in color but tarnishes rapidly to gray. Hardness 4 to 5. 
 Specific gravity 6.9 to 7.3. Opaque. Streak gray black. Schneeberg, Saxony; Bieber, 
 Hesse; Wittichen, Baden; Tunaberg and Nordmarken, Sweden; Badeni-Ungureni, 
 Roumania. 
 
SULPHIDES 45 
 
 WOU-ACHITE, Ni(As, S, Sb) 2 . 
 
 Orthorhombic. Very small crystals similar to arsenopyrite, also in radial aggre- 
 gates. Opaque. Metallic luster. Silver white to tin white in color. Streak black. 
 Brittle. Hardness 4 to 5. Specific gravity 6.372. Occurs as a crystallized coating on 
 niccolite associated with calcite, galena, and dyscrasite at Wolfsbach, Baden. 
 
 RAMMELSBERGITE, NiAs 2 . 
 
 Orthorhombic modification of NiAs 2 . Small crystals similar to arsenopyrite. 
 Also compact, granular to fine columnar and fibrous masses. Metallic luster. Opaque. 
 On fresh fracture surface color is tin white with tinge of red. Streak gray black. 
 Prismatic cleavage. Hardness 5 to 6. Specific gravity 7.1 to 7.19. Occurs in limited 
 quantities associated with chloanthite at Schneeberg, Saxony ; Reichelsdorf, Hesse ; 
 Lolling-Hiittenberg, Carinthia. 
 
 SKUTTERUDITE, CoAs 3 . 
 
 Cubic, dyakisdodecahedral class. Crystals show the octahedron, tetragonal tris- 
 octahedron (m=2), rhombic dodecahedron, pyritohedron (m=3), and dyakisdodeca- 
 hedron (^=3/2, w 3). Also massive. Distinct cubical cleavage. Conchoidal to 
 uneven fracture. Brittle. Hardness 6. Specific gravity 6.48 to 6.86. Metallic luster. 
 Light steel gray to tin or greenish white. Tarnishes somewhat reddish. Black 
 streak. Contains small amounts of iron. Found associated with cobaltite in mica 
 schists at Skutterud, Norway. 
 
 WHITNEYITE, Cu 9 As. 
 
 Crystal form unknown. Fine grained ; reddish white in color with brownish 
 and black tarnish colors. Specific gravity 8.47. Hardness 3. Malleable. Metallic 
 luster. Houghton Co., Mich. ; Sonora, Mexico. 
 
 ALGODONITE, Cu 6 As. 
 
 Crystal form unknown. Massive. Silver white to steel gray. Hardness 4. 
 Specific gravity 6.9 to 7.6. Resembles domeykite. Occurs at Algodona, near Co- 
 quimbo, Chile ; Lake Superior Copper district. 
 
 DYSCRASITE GROUP 
 
 The basic arsenides and antimonides of copper and silver apparently 
 form an isomorphous group, as shown by a comparison of their ratios. 
 
 a : b : c 
 
 DOMEYKITE, Cu 3 As. Orthorhombic Bipyramidal Class 0.5771 : I : 0.6802 
 Dyscrasite, Ag s Sb. Orthorhombic Bipyramidal Class 0.5775 : I ' 0.6718 
 
 The elements of crystallization given for domeykite are for artificial 
 crystals. 
 
46 DESCRIPTIVE MINERALOGY 
 
 DOMEYKITE, Cu 3 As. 
 
 Natural crystals unknown. Compact, reniform, botryoidal, and disseminated 
 masses. Tin white in color with yellow and variegated tarnish colors. Hardness 3.5. 
 Specific gravity 7.2 to 7.5. Brittle. Easily fusible. Occurs in Chile; Mexico; with 
 niccolite on Michipicoten Island, Lake Superior ; and in the Lake Superior Copper 
 district. 
 
 A variety of domeykite containing about 10% of nickel and cobalt occurs at the 
 Mohawk Copper mine, Lake Superior district, and is termed mohaivkite. 
 
 Dyscrasite, Ag s Sb. (?) 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.5775 : i : 0.6718. 
 Crystals rarely well developed. Usually columnar, pyramidal, or tabular in 
 habit. Unit prism, brachy and basal pinacoids, unit and modified bipyra- 
 mids are among the forms observed. Striations parallel to the a axis on 
 the basal pinacoid. Repeated twinning parallel to the unit prism, hence 
 often pseudohexagonal. Also compact, granular, nodular, and as a coating. 
 
 Perfect brachydomatic cleavage. Brittle. Uneven fracture. Hardness 
 3.5. Specific gravity 9.4 to 10. Silver white, tarnishes gray, black, or yel- 
 low brown. 
 
 Ag 3 Sb ; composition varies greatly, so that formulae ranging from 
 Ag 18 Sb to Ag 2 Sb have been assigned to dyscrasite. Easily fusible on char- 
 coal yielding the antimony coating and a globule of silver. 
 
 Occurs associated with silver, antimony, arsenic, and cobalt minerals. 
 Thus, at Andreasberg, Hartz Mountains ; Allemont, France ; Spain ; Peru ; 
 Chile ; Cobalt district, Ontario. 
 
 Valuable silver ore. 
 
 GALENA CHALCOCITE GROUPS 
 
 The monosulphides and so forth of lead, silver, and copper form an 
 isodimorphous series which embraces the cubic galena and orthorhombic 
 chalcocite groups. Silver sulphide is the only compound occurring in 
 both groups. 
 
 GALENA GROUP 
 
 (Cubic System ) 
 
 GALENA, PbS. Hexoctahedral Class 
 
 CLAUSTHAUTE, PbSe. Hexoctahedral Class 
 
 ALTAITE, PbTe. Hexoctahedral Class 
 
 Argentite, Ag 2 S. Hexoctahedral Class 
 
 JALPAITE, (Ag,Cu) 2 S. Hexoctahedral Class 
 
 AcuiivARiTE, Ag 2 (S, Se). Hexoctahedral Class 
 
 NAUMANNITE, (Ag 2 , Pb)Se. Hexoctahedral Class 
 
 EUCAIRITE, (Ag, Cu) 2 Se. Hexoctahedral Class 
 
 HESSITE, Ag 2 Te. Hexoctahedral Class 
 
SULPHIDES 
 
 CHALCOCITB GROUP 
 (Orthorhombic System ) 
 
 CHALCOCITE, Cu 2 S. Bipyramidal Class 
 Stromeyerite, (Cu, Ag) 2 S. Bipyramidal Class 
 ACANTHITE, Ag 2 S. Bipyramidal Class 
 PETZITE, (Ag, Au) 2 Te. Bipyramidal Class 
 
 47 
 
 a : b : c 
 
 0.5882 : i : 0.9702 
 
 0.5822 : i : 0.9668 
 
 0.6886 : i : 0.9945 
 
 The members of the chalcocite group crystallize in forms with a prism 
 angle of approximately 120 and, hence, are more or less pseudohexagonal. 
 
 GALENA, Galenite, Lead Glance, PbS. 
 
 Cubic, hexoctahedral class. Well developed crystals are rather com- 
 mon. Cube and octahedron, either independently or in combination, Fig- 
 ures 22 and 23 ; also the rhombic dodecahedron, Figures 24 and 25 ; and the 
 
 FIG. 22. 
 
 FIG. 23. 
 
 FIG. 24. 
 
 FIG. 25. 
 
 tetragonal (m=3, m=2) and trigonal (w=2) trisoctahedrons are the forms 
 most commonly observed. Penetration twins with twinning plane parallel 
 to a face of the octahedron. Also skeletal crystals ; reticulated, and tabular. 
 Mostly in cleavable masses. Compact, granular, fine grained ; rarely stal- 
 actitic and fibrous. 
 
 Very perfect cubical cleavage. Hardness 2.5. Specific gravity 7.3 
 to 7.6. Metallic luster, especially on cleavage surfaces ; otherwise rather 
 dull. Lead gray in color. Grayish black streak. 
 
 PbS, often with small amounts of silver, antimony, iron, zinc, gold, 
 or bismuth. The amount of silver present is generally rather low, 0.05 to 
 0.3%, sometimes, however, i% or more. On this account galena is an 
 important silver ore. The silver content can be detected only by assay. 
 Reacts for lead and sulphur. Soluble in nitric acid with separation of 
 sulphur and lead sulphate. 
 
 Very abundant. Usual associates are sphalerite, chalcopyrite. quartz, 
 
48 DESCRIPTIVE MINERALOGY 
 
 pyrite, calcite, barite, fluorite, marcasite, arsenopyrite, anglesite, cerussite, 
 pyromorphite, etc. 
 
 Galena may occur in general in two ways : ( I ) In veins with pyrite, 
 chalcopyrite, sphalerite, barite, calcite, quartz or fluorite, and (2) in cavi- 
 ties in dolomitic limestones associated with calcite, sphalerite, smithsonite, 
 etc. Galena of the first type of occurrence is usually argentiferous. 
 
 Only a few of the most important localities will be indicated, namely, 
 Freiberg district, Saxony ; Clausthal, Hartz Mountains ; Pribram and Joa- 
 chimsthal, Bohemia ; Derbyshire, Cumberland ; Mexico ; Chile ; Bolivia ; 
 Australia. 
 
 In the United States extensive deposits are found in the limestones of 
 Wisconsin, Illinois, Missouri, Iowa, and Kansas. Excellent crystals occur 
 at Mineral Point, Wis. ; Joplin, Mo., and elsewhere. The argentiferous 
 variety is common in the Leadville, Aspen, Silverton, and other districts 
 of Colorado; also in Utah, Montana, Idaho, etc. 
 
 A valuable lead and silver ore. In 1908 the United States produced 
 310,762 tons of lead, obtained mostly from galena. 
 
 ClvAUSTHAUTE, PbSe. 
 
 Cubic, hexoctahedral class. Rarely in cubes. Commonly in fine grained masses. 
 Sometimes foliated. Looks like galena. Hardness 2.5 to 3. Specific gravity 7.6 to 
 8.8. May contain silver or cobalt in small amounts. Occurs at Clausthal, Lerbach, 
 Zorge, and Tilkerode in the Hartz Mountains; Cacheuta, Argentine Republic. 
 
 Al/TAlTE, PbTe. 
 
 Cubic, hexoctahedral class. Sometimes in cubes, usually in fine grained masses. 
 Metallic luster. Color tin white to yellow, tarnishes bronze' yellow. Indistinct cubical 
 cleavage. Uneven to conchoidal fracture. Hardness 3 to 3.5. Specific gravity 8.1 
 to 8.2. May contain a little silver. With hessite at Altai; Coquimbo, Chile; Red 
 Cloud Mine, Colorado; Calaveras Co., California. 
 
 Argentite, Silver Glance, Ag 2 S. 
 
 Cubic, hexoctahedral class. Crystals may be cubical, octahedral, or 
 rhombic dodecahedral in habit. All forms of the hexoctahedral class have 
 been observed. Penetration twins with the twinning plane parallel to a 
 face of the octahedron. Parallel grouping. Massive and disseminated. Fil- 
 iform and as a coating. 
 
 Indistinct cubical and rhombic dodecahedral cleavages, rarely observed. 
 Small conchoidal fracture, not very distinct. Malleable, sectile; takes im- 
 pression. Hardness 2 to 2.5. Specific gravity 7.2 to 7.4. On fresh sur- 
 face high metallic luster, but on exposure soon becomes dull and black. 
 Dark lead gray in color. Shiny streak. 
 
SULPHIDES 49 
 
 Ag,S. On charcoal fuses with intumescence yielding fumes of sulphur 
 dioxide and a globule of silver. 
 
 Commonly associated with silver, cobalt, and nickel minerals. Occurs 
 at Freiberg, Saxony; Joachimsthal, Bohemia; Schemnitz, Hungary; Kongs- 
 berg, Norway; Cornwall, England; Guanajuata, Mexico; Peru; Chile; 
 etc. Also at "the Comstock Lode, Nevada; with silver and copper in the 
 Lake Superior Copper district ; in comparatively large amounts in the Co- 
 balt district, Ontario. 
 
 An important ore of silver. 
 
 JALPAITE, (Ag,Cu) 2 S, is a cupriferous argentite. Sectile. Dark lead gray in 
 color. Occurs at Jalpa, Mexico ; also in Chile. 
 
 AGUILARITE, Ag 2 (S, Se). An argenite containing selenium. Black skeletal rhom- 
 bic dodecahedrons. Also as fine needles. Sectile. Specific gravity 7.59. Occurs at 
 Guanajuata, Mexico. .:/J 
 
 NAUMANNITE, (Ag 2 ,Pb)Se. Cubic crystals. Usually compact with cubical cleav- 
 age. Sectile. Metallic luster. Hardness 2.5. Specific gravity 8. Iron black in 
 color and streak. With clausthalite at Tilkerode, Hartz Mountains. 
 
 EUCAIRITE, (Ag, Cu) 2 Se. Fine grained and massive. Indistinct cubical cleav- 
 age. Hardness 2 to 3. Specific gravity 7.67. Metallic luster. Tin white to gray. 
 In serpentine at the Skrikerum Copper mine, Sweden; Copiapo, Chile; Sierra de 
 Umango, Argentine Republic. f,j-< ., ; 
 
 HESSITE, Ag 2 Te. 
 
 Cubic, hexoctahedral class. Cubical .crystals, often greatly distorted and highly 
 modified. Coarse and fine grained, compact masses. Sectile. Hardness 2.5 . Specific 
 gravity 8.3 to 9. Lead gray. At times contains gold and lead. Transylvania ; Altai ; 
 Hungary ; Chile ; Calaveras Co., California ; Boulder Co., Colorado ; Utah ; Arizona. 
 
 CHALCOCITE, Copper Glance, Cu 2 S. 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.5882 : I : 0.9702. 
 Crystals are usually thick tabular or short prismatic. Pseudohexagonal on 
 account of prism angle being H935 / . A common combination consists of 
 the basal pinacoid c, the brachydome (m=2/s)e, and the modified bipyra- 
 mid (7/1=1/3)5:, Figure 26. A comparatively large number of forms has 
 been observed. Basal pinacoid is often striated par- 
 allel to the a axis. Several twinning laws. Twinning 
 plane parallel to unit prism most common. Trillings 
 according to this law are psetidohexagonal in form. 
 Also star-shaped forms. Usually compact and dis- 
 seminated masses ; granular. 
 
 Indistinct prismatic cleavage. Conchoidal to uneven fracture. Hard- 
 ness 2.5 to 3. Specific gravity 5.5 to 5.8. High metallic luster on fresh 
 surface which soon becomes dull and black. Color dark lead gray, often 
 tarnished blue or greenish. Streak shiny lead gray. 
 
5O DESCRIPTIVE MINERALOGY 
 
 Cu 2 S, usually with iron, also gold and silver. Soluble in nitric acid 
 with separation -of sulphur and formation of green solution. Decomposes 
 readily to chalcopyrite, bornite, covellite, malachite, and azurite. 
 
 Usual associates are chalcopyrite, bornite, tetrahedrite, siderite, cas- 
 siterite, malachite, and azurite. Chalcocite may occur, first, in veins and 
 second, as an impregnation, especially in bituminous sedimentary rocks. 
 Occurs in veins at Cornwall, England, (excellent crystals) ; Freiberg, Sax- 
 ony ; Joachimsthal, Bohemia ; Kapnik, Transylvania ; Bristol, Conn. ; Butte 
 Copper district, Montana ; Nevada ; Arizona ; Sonora, Mexico ; Province of 
 Quebec. As an impregnation at Mansfield, Germany. 
 
 Chalcocite is an important ore of copper. 
 
 Stromeyerite, Copper Silver Glance, (Cu, Ag) 2 S. 
 
 Orthorhombic, bipyramidal class. Crystals like chalcocite. Usually 
 massive and disseminated. Hardness 2.5 to 3. Specific gravity 6.2 to 6.3. 
 Conchoidal fracture. Metallic luster. Dark lead gray in color and streak. 
 Difficult to distinguish from chalcocite. Reacts for copper, silver, and 
 sulphur. 
 
 Not abundant. Associated with copper and silver minerals. Thus at 
 various places in Siberia, Argentine Republic, Chile, Mexico, Arizona, and 
 Colorado. In considerable quantities in the Cobalt district, Ontario. 
 
 A valuable silver ore. 
 
 ACANTHITE, AgzS. Orthorhombic modification of AgS. Peculiarly twisted, bent, 
 and distorted crystals. Physical and chemical properties like argentite. Found at 
 Joachimsthal, Bohemia; Freiberg, Saxony; etc. According to Krenner acanthite is 
 argentite occurring in misshapen crystals. 
 
 PETZITE, (Ag, Au) 2 Te. Usually massive, granular to compact. Lead gray to 
 iron black color. Black streak. Brittle. Much like hessite, page 49. Hardness 2.5 
 to 3. Specific gravity 8.7 to 9.4. Nagyag, Transylvania; Calaveras and Tuolumne 
 Counties, California; Red Cloud Mine, Colorado, etc. 
 
 CINNABAR GROUP 
 
 This is an isodimorphous group and embraces the sulphides and sele- 
 nides of copper and mercury. One series crystallizes in the cubic, the other 
 in the hexagonal system. 
 
 MHTACINNABAR SERIES 
 
 (Cubic System ) 
 
 METACINNABARITE, HgS. Hextetrahedral Class 
 
 ONOFRITE, Hg(S, Se). Hextetrahedral Class 
 
 TIEMANNITE, HgSe. Hextetrahedral Class 
 
SULPHIDES 51 
 
 CINNABAR SERIES 
 
 (Hexagonal System ) 
 
 a : c 
 
 Covellite, CuS. Trigonal Trapezohedral Class i : 1.1455 
 
 CINNABAR, HgS. Trigonal Trapezohedral Class I : 1.1453 
 
 The members of the metacinnabar series are of little economic impor- 
 tance. 
 
 METACINNABARITE, HgS. Cubic, hextetrahedral class. Small crystals with positive 
 and negative tetrahedrons about equally developed. Rare. Usually massive, also 
 as an apparently amorphous powder and coating. Hardness 3. Specific gravity 7.7 
 to 7.8. Iron black with black streak. Chemical composition like cinnabar. Occurs 
 with cinnabar at various places, especially at Reddington Mine, Lake Co., California. 
 
 ONOFRITE, Hg(S,Se). Massive, fine grained Conchoidal fracture. Hardness 
 2 to 3. Specific gravity 7.6 to 8.1. Color and streak gray black. According to Brush 
 and Penfield onofrite is an isomorphous mixture of metacinnabar and tiemannite. 
 Occurs at San Onofre, Mexico; in considerable quantities at Marysville, Utah. 
 
 TIEMANNITE, HgSe. Cubic, hextetrahedral class. Crystals usually with tetra- 
 hedral habit. Sometimes highly modified. Usually massive, granular to compact. 
 Metallic luster. Steel gray to black lead gray color. Streak nearly black. Hardness 
 2 to 3. Specific gravity 7.1 to 8.5. In closed tube yields a black sublimate, at a 
 distance it appears brown. Soluble only in aqua regia. With hematite at Clausthal, 
 Tilkerode, and Zorge in the Hartz Mountains; Clear Lake, Cal. ; Marysvale, Piute 
 Co., Utah. 
 
 Covellite, CuS. 
 
 Hexagonal, trigonal trapezohedral class, a : c^i : 1.1455. Crystals 
 thin tabular, rare. Usually in compact, fine grained masses. Also as a coat- 
 ing and crust ; in veinlets, reniform, and powdery. 
 
 Perfect basal cleavage. Compact specimens possess an even fracture. 
 Thin plates are flexible. Hardness I to 2. Specific gravity 4.59 to 4.64. 
 Blue black color, when rubbed, indigo blue. Streak black. Dull luster, 
 when rubbed, submetallic and resinous. 
 
 CuS, may contain lead and iron. Easily fusible. Colors flame blue. 
 Soluble in nitric acid with separation of sulphur. 
 
 Usually with chalcopyrite, bornite, or chalcocite from the decomposi- 
 tion of which it has resulted. Occurs in Chile ; Bolivia ; especially in the 
 Butte Copper district, Montana; Rambler Mine, Wyoming; in veins on 
 Kawan Island near New Zealand ; as a sublimation product on Mount Ve- 
 suvius. 
 
 Of minor importance, commercially, as an ore of copper. 
 
52 DESCRIPTIVE MINERALOGY 
 
 CINNABAR, Natural Vermilion, HgS. 
 
 Hexagonal, trigonal trapezohedral class, a : c = I : i . 1453 . Ex- 
 tremely small but highly complex crystals. Over 100 forms have been ob- 
 served. Crystals are usually rhombohedral or 
 thick tabular in habit, Figure 27. The trigonal 
 trapezohedrons are rarely observed. Two twin- 
 ning laws are common ; first, vertical axis is the 
 twinning axis and, second, hexagonal' prism of 
 the second order acts as twinning plane. Usually 
 in fine grained, granular masses ; also as crystal- 
 line crusts or powdery coating. 
 
 Perfect prismatic cleavage. Uneven, splintery, or subconchoidal frac- 
 ture. Hardness 2 to 2.5. Specific gravity 8 to 8.2. Adamantine luster. In 
 thin plates transparent, otherwise opaque. Color and streak cochineal red. 
 The color may, however, on account of impurities and structural differences 
 be scarlet or brownish red, also brown, black, or lead gray. Slightly sec- 
 tile. Positive double refraction. High indices of refraction, w r =2.854, 
 ,.=3.201. Strong circular polarization, fifteen times that of quartz. 
 
 HgS, may contain bitumen, clay, ferric oxide, and so forth as impur- 
 ities. Easily volatile. Soluble only in aqua regia. 
 
 Cinnabar is found in veins, disseminated or irregular masses, in sedi- 
 mentary rocks of various ages as also- in trachytes, quartz porphyries, and 
 serpentine. The common associates are native mercury, pyrite, marcasite, 
 chalcopyrite, stibnite, bitumen, realgar, gold, calcite, barite, fluorite, quartz, 
 and opal. 
 
 Occurs in silurian sandstone at Almaden, Spain ; in triassic shales and 
 dolomite at Idria, Carniola; Moschellandsberg and elsewhere in the Palatin- 
 ate, west of the Rhine ; also in Chile, Peru, Mexico, Japan, and China. 
 
 In the United States the principal deposits are at New Almaden, Santa 
 Clara Co., also Altoona; Trinity Co., and New Idria, San Benito Co., Cal- 
 ifornia. These deposits are mostly associated with serpentine. The Ter- 
 linqua district, Texas, is also a producing locality. Here cinnabar is found 
 in rocks of cretaceous age and is associated with native mercury, calcite, 
 hematite, limonite, and sometimes pyrite. 
 
 At the Steamboat Springs, Nevada, cinnabar is still being deposited, as 
 is also the case at the Sulphur Bank Mine, California. 
 
 According to G. F. Becker cinnabar has been precipitated principally 
 from ascending waters. The mercury is supposed to have been in solution 
 as a double sulphide and then deposited as cinnabar by the action of bitum- 
 inous matter. 
 
SULPHIDES 53 
 
 Cinnabar is the chief source of metallic mercury which is used exten- 
 sively in commerce, see page 24. In 1906 the United States produced 28,- 
 293 flasks of mercury, each weighing- 76^2 Ibs. Of this production,. 22,500 
 flasks were from California and 4,517 flasks from Texas. The remainder 
 was obtained from Arizona, Oregon, Utah, and Washington. In 1906 mer- 
 cury sold at about $39.00 per flask. 
 
 SYLVANITE GROUP 
 
 Here are placed four tellurides of gold and silver. Nothing definite 
 can be said as yet with respect to their chemical or crystallographic rela- 
 tionships. 
 
 a : b : c 
 Sylvanite, (Au,Ag)Te,. Monoclinic Prismatic Class 
 
 1.6339 : i : 1-1265, /2=9025' 
 Calaverite, AuTe,. Monoclinic Prismatic Class 
 
 1.6313 : i : 1.1449, =90I3' 
 KRENNERITE, (Au,Ag)Te 2 . Orthorhombic Bipyramidal Class 
 
 0.9389 : i : 0.5059 
 NAGYAGITE, Au 2 Sb 2 Pb 10 Te 6 S 15 . Orthorhombic Bipyramidal Class 
 
 0.2807 : i : 0.2761 
 
 Although of not very common occurrence, they are, especially sylvan- 
 ite and calaverite, of great importance as gold ores. 
 
 Sylvanite, Graphic Tellurium, (Au,Ag)Te 2 . 
 
 Monoclinic, prismatic class, a : b : c = i .6339 : i : i . 1265, ft =9O25'. 
 Crystals are very small but at times highly complex. Sometimes tabular, 
 prismatic, or pseudo-orthorhombic in habit. Occurs also in branching ar- 
 borescent forms simulating written characters. Twinning is common par- 
 allel to the orthodome. Skeletal development of crystals. Bladed, and 
 imperfect columnar to granular aggregates. Compact granular aggregates 
 are rare. 
 
 Perfect clinopinacoidal cleavage. Hardness 1.5 to 2. Specific gravity 
 7.99 to 8.33. Metallic luster. Steel gray to silver white, also light yellow 
 in color. Streak same as color. 
 
 (Au, Ag)Te 2 , containing also antimony, lead and copper. The gold 
 and silver are usually present in the following proportion: Au : Ag = 
 i : i. Easily fusible. On charcoal yields a white coating. With soda gives 
 a metallic silver-gold globule. 
 
 An important ore of gold. Occurs at Offenbanya and Nagyag, Tran- 
 sylvania; Calaveras Co., Cal. ; Red Cloud Mine, and the Cripple Creek dis- 
 trict, Colorado. 
 
54 DESCRIPTIVE MINERALOGY 
 
 Calaverite, AuTe 2 . 
 
 Monoclinic, prismatic class, a : b : c= 1.6313 : i : i.i449> /3=9 0l 3'- 
 Not well crystallized. Has been considered triclinic. Angles similar to 
 those of sylvanite. Crystals are rare. Usually compact. Conchoidal frac- 
 ture. No cleavage. Hardness 2.5. Specific gravity 9. Metallic luster. 
 Bronze yellow in color. 
 
 AuTe 2 . Essentially a telluride of gold with varying amounts, up to 
 about 4%, of silver. 
 
 Found at Stanislaus Mine, Calaveras Co., California; Red Cloud Mine 
 and Cripple Creek district, Colorado ; Western Australia. 
 
 An ore of gold. 
 
 KRENNERITE, (Au, Ag)Te 2 . Orthorhombic, bipyramidal class, a : b : c = 0.9389 
 : I : 0.5059. Crystals are small, columnar, and vertically striated. Hardness 2 to 3. 
 Specific gravity 8.35. Metallic luster. Silver white to light brassy yellow in color. 
 Like sylvanite in composition. Occurs in quartz at Nagyag, Transylvania ; Cripple 
 Creek district, Colorado ; and Western Australia. Not as abundant as sylvanite or 
 calaverite. 
 
 NAGYAGITE, Au 2 Sb 2 Pb 10 Te 6 S 15 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.2807 : I : 0.2761. Tabular crys- 
 tals, with brachypinacoid predominating. Granular massive and foliated. Excellent 
 clinopinacoidal cleavage. Flexible. Hardness i to 1.5. Specific gravity 6.7 to 7.2. 
 Metallic luster. Dark lead gray in color. Gray black streak inclining to brown. 
 
 AuzSbsPbifeTeoSiB, may contain copper. Composition is not constant. 
 
 Occurs at Nagyag and Offenbanya in Transylvania; also in various places in 
 Colorado associated with sylvanite. 
 
 An ore of gold. 
 
 3. SULPHO-SALTS 
 
 Here are placed those minerals which can be referred to the sulpho 
 acids H 3 FeS 3 , H 3 AsS 3 , H 3 SbS 3 and the like, or to acids derived from them. 
 
 CHALCOPYRITE GROUP 
 
 This group contains the copper salts of the following sulpho acids of 
 iron: H 3 FeS 3 , HFeS,, and H 4 Fe 2 S 5 . The meta acid, HFeS 2 ,can be con- 
 ceived as being derived 'from one molecule of the ortho acid, H 3 FeS 3 , by 
 the elimination of a molecule of H,S. Two molecules of H 3 FeS 3 with the 
 elimination of a molecule of H 2 S would yield the pyro acid, H 4 Fe 2 S 5 . 
 
 The group consists of: 
 
 BORNITE, Cu 3 FeS n . Cubic, Hexoctahedral Class 
 
 CHALCOPYRITE, CuFeS 2 . Tetragonal, Scalenohedral Class 
 BARNHARDTITE, Cu 4 Fe 2 S 5 . ? 
 
 Barnhardtite is an exceedingly rare mineral and is only of scientific 
 interest. 
 
SULPHIDES 55 
 
 BORNITE, Purple Copper Ore, Variegated Copper Ore, Horse Flesh Ore, 
 Cu 3 FeS 3 . 
 
 Cubic, hexoctahedral class. Crystals not common. Cube, either alone 
 or in combination with the octahedron, is the usual form. The rhombic 
 dodecahedron and tetragonal trisoctahedron (w = 2) are also observed. 
 Twins parallel to the octahedron. Usually occurs as compact, granular 
 masses. 
 
 Conchoidal to uneven fracture. Hardness 3. Specific gravity 4.9 to 
 5.1. Metallic luster. Color on fresh fracture surface is between bronze 
 brown and copper red. Tarnishes readily to deep blue purple tints. Streak 
 gray black. 
 
 CiuFeSg, the composition often varies, due to admixture of Cu 2 S. May 
 also contain silver and gold in small amounts. Fuses to gray metallic glob- 
 ule. Soluble in nitric and concentrated hydrochloric acids with a separation 
 of sulphur. 
 
 Occurs with chalcopyrite, chalcocite, and other copper minerals, also 
 with cassiterite and siderite. Is not very common in Europe. Found at 
 Cornwall, England ; Freiberg district, Saxony ; Mansfield, Germany ; Hartz 
 Mountains ; Tuscany ; Siberia ; Norway ; Sweden ; Chile ; Bolivia ; Peru ; 
 South Africa ; Tasmania ; Australia ; Acton, Canada. 
 
 In the United States in considerable quantities associated with allied 
 sulphides of copper in the Butte, Montana, district. In smaller quantities 
 at Bristol, Conn. ; Chesterfield, Mass., etc. 
 
 An important ore of copper. 
 
 FIG. 29. 
 
 CHALCOPYRITE, Copper Pyrites, Yellow Copper Ore, CuFeS 2 . 
 
 Tetragonal, scalenohedral class, a : c=i : 0.98525. Crystals are 
 often greatly distorted and, hence, difficult to interpret. Bisphenoidal and 
 ,-. rramidal habits are common, Figures 28 and 29. Faces of large crystals 
 :ire often dull, striated, and furrowed. The positive unit bispherroid faces 
 
56 DESCRIPTIVE MINERALOGY 
 
 p are commonly dull while those of the negative form r are smooth and 
 brilliant. Contact and penetration twins according to several laws. Re- 
 peated, supplementary, and cyclic twins. Most commonly found in com- 
 pact masses. 
 
 Conchoidal to uneven fracture. Pyramidal cleavage is rarely observed. 
 Hardness 3.5 to 4. Specific gravity 4.1 to 4.3. Brittle. Brass to gold 
 yellow in color. Tarnishes to various blue, purple, and black tints. Irides- 
 cent. Greenish black streak. 
 
 CuFeS 2 , contains at times small but valuable amounts of gold and sil- 
 ver; also selenium, thallium, and arsenic. Fusible to a grayish black mag- 
 netic globule. Soluble in nitric acid with separation of sulphur. 
 
 Most common copper mineral. Usually found with pyrite, sphalerite, 
 bornite, pyrrhotite, cobalt and nickel minerals, siderite, tetrahedrite, malach- 
 its, azurite, galena, cassiterite, and chalcocite. 
 
 Chalcopyrite is found extensively in gneiss at Falum, Sweden ; Mans- 
 field, Germany; Rio Tinto, Spain; Hartz Mountains; Freiberg district, 
 Saxony ; in tin ore deposits Cornwall, England ; Bohemia ; Tuscany ; Chile ; 
 New South Wales ; Japan ; Sudbury district, Canada. 
 
 In the United States chalcopyrite occurs widespread. Especially so in 
 Bingham, Utah ; Bisbee, Arizona ; Butte district, Montana ; Ducktown, Ten- 
 nessee ; Colorado; Pennsylvania, etc. 
 
 An important ore of copper. 
 
 Linnaeite, Cobalt Pyrites, (Ni,Co) 3 S 4 . 
 
 Cubic, hexoctahedral class. Well developed octahedral crystals, some- 
 times showing the cube in combination. Twins according to the Spinel law. 
 Compact and disseminated ; in granular aggregates. 
 
 Imperfect cubical cleavage. Uneven fracture. Brittle. Hardness 5.5. 
 Specific gravity 4.8 to 5.8. Metallic luster. Reddish steel gray in color. 
 Tarnishes copper red and yellow. Grayish black streak. 
 
 (Ni,Co) 3 S 4 , often with iron and copper. The chemical composition 
 varies considerably. Sometimes supposed to be (Co, Ni) 4 S 5 or Co 3 S 4 . On 
 charcoal yields fumes of sulphur dioxide and a magnetic globule. Soluble 
 in nitric acid to a red solution with separation of sulphur. 
 
 Does not occur extensively. Is usually associated with chalcopyrite, 
 pyrrhotite, hematite, bornite, and the cobalt and nickel minerals. Found 
 at Bastnaes, Sweden; Miisen, Prussia; Mine La Motte, Missouri; Mineral 
 Hill, Maryland ; Lovelock's Station, Nevada ; and elsewhere. 
 
 Used- as a source of nickel and cobalt. 
 
SULPHIDES 57 
 
 MIARGYRITE-ZINKENITE GROUPS 
 
 Here are placed metasulph-arsenites and antimonites, etc., of thallium, 
 silver, copper, and lead. These minerals conform to the general formulae, 
 M'R"'S 2 or M"R"' 2 S 4 . 
 
 Two series, depending upon crystallization, may be differentiated. 
 
 MIARGYRITB GROUP 
 (Monoclinic Prismatic Class ) 
 
 a : b : c 
 
 LORANDITE, TlAsS 2 . 0.6827 : i : 0.6650, =90 17'. 
 
 MIARGYRITE, AgSbS 2 . -7479 : J : 0.6432, 
 
 ZINKHNITH GROUP 
 (Orthorhombic Bipyramidal Class ) 
 
 a 
 
 EMPLECTITE, Cu 2 Bi 2 S 4 . 0.5430 
 
 SCLEROCI.ASE, PbAs 2 S 4 . 0.5389 
 
 ZlNKENlTE, PbSb 2 S 4 . 0.5575 
 
 b : c 
 
 i : 0.6256 
 
 i : 0.6188 
 
 i : 0.6353 
 
 None of the minerals of these groups are of economic importance. 
 
 LOKANDITE, TIAsS:. Occurs as tabular, monoclinic crystals. Usually small. 
 Flexible. Good cleavage in three directions. Hardness 2 to 2.5. Specific gravity 5.53. 
 Adamantine luster. Cochineal to carmine red in color. Dark cherry red streak. 
 Found only on realgar at Allchar, Macedonia. 
 
 MIARGYRITE, AgSbSz. Small, monoclinic crystals; acicular or tabular. Also 
 compact and disseminated. Conchoidal fracture. Hardness 2 to 2.5. Specific gravity 
 5.18 to 5.3. Metallic luster. Steel or lead gray to black in color. Deep blood red 
 in thin splinters. Streak cherry red. Found in silver ore deposits, Freiberg, Saxony; 
 Pribram, and Felsobanya, Bohemia ; Hartz Mountains ; Spain ; Mexico. 
 
 EMPI,ECTITE, Cu 2 Bi 2 S4. Orthorhombic. Long' needle-like crystals. Striated. Often 
 poorly developed. Finacoidal cleavage. Compact and disseminated. Uneven fracture. 
 Hardness 2. Specific gravity 6.23 to 6.38. Tin white to steel gray in color. Tar- 
 nishes darker. Black streak. In quartz at Schwarzenberg, Saxony; Wittichen, Black 
 Forest, Baden. 
 
 SCLEROCLASE, Sartorite, PbAs 2 S-i. Small, thin, needle-like crystals belonging to 
 the orthorhombic system. Often striated. Basal cleavage. Very brittle. Hardness 3. 
 Specific gravity 5.4. Light lead gray with red brown streak. Occurs with dufrenoy- 
 site in the dolomite of the Binnenthal, Switzerland. 
 
 ZINKENITE, Zinckenite, PbSbsS^ Orthorhombic, radial, acicular crystals, usually 
 showing .a combination of the unit prism and macrodome. Pseudohexagonal due to 
 twinning. Fibrous, columnar, and massive. Easily broken. Hardness 3 to 3.5. Spe- 
 cific gravity 5.3 to 5.35. Dark to lead gray. Tarnishes. Black streak. With stibnite 
 at Wolfsberg, Hartz Mountains; Hausach, Switzerland; Sevier Co., Arkansas; San 
 Juan Co., Colorado; Eureka, Nevada. 
 
58 DESCRIPTIVE MINERALOGY 
 
 PLAGIONITK, PboSbsSw. Monoclinic, prismatic class, a : b : c = 1.1331 : I : 
 0.4228, /3=zio7io'. Small thick tabular crystals consisting of basal and orthopina- 
 coids with several hemipyramids. Basal pinacoid is usually smooth, other faces 
 striated. Hardness 2.5. Specific gravity 5.4 to 5.6. Dark lead gray to iron black. 
 Black streak. Occurs at Wolfsberg, Hartz Mountains ; Goldkronack, Bavaria. 
 
 JAMESONITE GROUP 
 
 The members of this group can be referred to the general formula 
 M" 2 R'" 2 S 5 . R'" may be arsenic, antimony, or bismuth. 
 
 DUFRENOYSITE, Pb 2 As 2 S 5 . Monoclinic System 
 
 JAMESONITE, Pb 2 Sb 2 S 5 . Orthorhombic System 
 
 COSAUTE, Pb 2 Bi 2 S 5 . Orthorhombic System 
 
 The minerals of this group occur very sparingly. 
 
 DUERENOYSITE, PbiiAssSs. Monoclinic, prismatic class, a : b : c = 0.6510 : I : 
 0.6126, /3=9O33^'. Sometimes considered Orthorhombic. Crystals usually large, 
 thick tabular or columnar, highly modified, but rare. Striated. Compact, massive. 
 Basal cleavage. Brittle. Hardness 3. Specific gravity 3.5 to 3.6. Dark lead gray 
 color. Red brown streak. With scleroclase in the dolomite of the Binnenthal, Swit- 
 zerland. 
 
 JAMESONITE, Pb 2 Sb 2 Ss. Orthorhombic, bipyramidal class, a : b : =0.8195 : I : ? 
 Long, acicular crystals. Usually without good terminations. Commonly in parallel 
 or divergent crystal aggregates. Easily broken. Compact, massive. Basal cleavage. 
 Hardness 2 to 2.5. Specific gravity 5.52 to 5.8. Steel gray to dark lead gray. Streak 
 gray to black. Pb 2 Sb 2 Ss, with iron, silver, copper, or zinc. Occurs at Cornwall, England; 
 Spain; Sevier Co., Arkansas. 
 
 COSALITE, PbaBizSs. Orthorhombic. Striated, prismatic crystals. Also massive, 
 fibrous, or radiated. Lead to blue gray in color. Specific gravity 6.39 to 6.75. Usually 
 contains silver. Cosala, Province SJnaloa, Mexico; Sweden; Mexico; Comstock 
 mine, La Plata Co., and Alaska mine, Ouray Co., Colorado. 
 
 BOULANGERITE GROUP 
 
 The members of this group conform to the general formula M'^R'^Sn. 
 
 BOULANGERITE, Pb 3 Sb 4 S 11 . Orthorhombic System 
 
 DIAPHORITE, { / PK A \ O K o ) Orthorhombic System 
 
 FREIESLEBENITE, f r? Ag^SQ^. j Monoclinic System 
 
 The compound (Pb, Ag^gSb^n is dimorphous. Its monoclinic mod- 
 ification, freieslebenite, is the more important mineral. 
 
SULPHIDES 59 
 
 BOULANGERITE, PbsSbjSu. Orthorhombic, bipyramidal class, a : b : =0.5527 
 : i : 0.7478. Prismatic crystals . Very rare . In crystalline, granular masses. Hard- 
 ness 2.5 to 3. Specific gravity 5.8 to 6.2. Dull metallic luster. Dark lead gray color. 
 Satin-like shimmer. Black streak. Often with yellow spots of Sb 2 O 3 . Occurs usually 
 with stibnite. Not common. Wolfsberg, Hartz Mountains ; Pribram, Bohemia ; Tus- 
 cany; Tyrol; Sweden; Ural Mountains; Nevada. 
 
 FREIESLEBENITE, (Pb, Ag^sSbiSn. Monoclinic, prismatic class, a : b : =0.5872 
 : i : 0.9278, /3=p2i4'. Prismatic crystals. Often striated. Twins. Compact and 
 disseminated. Conchoidal fracture. Hardness 2 to 2.5. Specific gravity 6.2 to 6.4. 
 Lead to light steel gray, tarnishes black. Gray streak. Found at Freiberg, Saxony; 
 Hungary; Spain; Augusta Mountain, Gunnison Co., Colorado. 
 
 PYRARGYRITE GROUP 
 
 This group consists of the orthosulph-arsenite and antimonite of silver. 
 
 Hexagonal System a : c 
 
 Proustite, Ag,AsS,. Ditrigonal Pyramidal Class i : 0.8038 
 Pyrargyrite, Ag 3 SbS 3 . Ditrig-onal Pyramidal Class i : 0.7892 
 
 Although these two minerals differ materially in color, it is not always 
 easy to distinguish them. This can be done, however, by means of the 
 streak, specific gravity, goniometric measurements, as also by the blowpipe. 
 
 Proustite, Light Ruby Silver Ore, Light Red Silver Ore, Ag 3 AsS 3 . 
 
 Hexagonal, ditrigonal pyramidal class. a : c=\ : 0.8038. Commonly 
 prismatic, trigonal or ditrigonal pyramidal in habit. Hemimorphic develop- 
 ment sometimes distinct. Crystals highly modified, distorted, and often 
 difficult to interpret. Twins according to several laws. Massive, dissem- 
 inated, as a coating or dendritic. 
 
 Imperfect pyramidal cleavage. Conchoidal fracture. Brittle. Hard- 
 ness 2.5. Specific gravity 5.58 to 5.64. Brilliant adamantine luster. Trans- 
 lucent to transparent. Color and streak scarlet to vermilion. 
 
 Ag 3 AsS 3 , at .times contains some antimony. On charcoal yields fumes 
 of As 2 O 3 , garlic and sulphurous odors, and a globule of silver. 
 
 Occurs with pyrargyrite in veins with other silver minerals and galena. 
 Calcite is commonly the gangue mineral. Occurs at Freiberg, Saxony ; Joa- 
 chimsthal, Bohemia; Chalanches, Dauphine; Chanarcillo, Chile; Mexico; 
 Spain ; Peru ; Cobalt district, Canada. 
 
 In the United States in the Ruby Silver district, Gunnison Co., also in 
 San Miguel Co., Summit Co., and Ouray Co., Colorado ; Comstock lode and 
 Daney mine, Nevada ; Poor Man's lode, Idaho ; Arizona. 
 
 An important ore of silver. 
 
 Pyrargyrite, Dark Red Silver Ore, Dark Ruby Silver Ore, Ag 3 SbS 3 . 
 
 Hexagonal, ditrigonal pyramidal class, a : c=i : 0.7892. Highly 
 modified and complex crystals. Difficult to interpret, being often greatly 
 distorted. Hemimorphic. Usually prismatic, trigonal and ditrigonal prya- 
 
60 DESCRIPTIVE MINERALOGY 
 
 midal in habit. Many forms have been observed. Twins according to sev- 
 eral laws. Also compact, disseminated, as a coating and dendritic. 
 
 Imperfect pyramidal cleavage. Conchoidal to splintery fracture. Some- 
 what brittle. Hardness 2.5 to 3. Specific gravity 5.85, less if arsenic is 
 present, 5.77 to 5.85. Metallic adamantine luster. In reflected light, dark 
 red to lead gray in color ; in transmitted light, deep red. Transparent only 
 in thin splinters. Purple or cherry red streak. 
 
 Ag 3 SbS 3 , usually with a little arsenic. Easily fusible; yields on char- 
 coal a coating of Sb 2 O 3 and a globule of silver. Occurs as a pseudomorph 
 after argentite. 
 
 Occurrence similar to that of proustite. Found in veins with other 
 silver ores, calcite, galena, etc. Thus in the Freiberg district, Saxony ; Gon- 
 derbach, Westphalia; Pribram, etc., Bohemia; Spain; Mexico; Chile; Colo- 
 rado; Nevada; Arizona; Cobalt district, Canada, etc. 
 
 An important ore of silver. 
 
 BOURNONITE GROUP 
 
 This group embraces two minerals conforming to the general formula 
 M" 3 R'" 2 S G , in which R'" may be antimony or bismuth, and M" lead or 
 copper. 
 
 Bournonite, Pb 2 Cu 2 Sb 2 S 6 . Orthorhombic System 
 
 AIKINITE, PboCu 2 Bi 2 S 6 . Orthorhombic System 
 
 Seligmannite, the corresponding arsenic compound PbzCiizAszSe, is sometimes 
 added to the above group. Its composition is, however, still in doubt. Seligmannitri 
 is a very rare mineral. 
 
 Bournonite, Wheel Ore, Pb 2 Cu 2 Sb,S 6 . 
 
 Orthorhombic, bipyramidal class, a : b : ^=0.9379 : i : 0.8968. 
 Thick tabular crystals of a tetragonal habit ; also prismatic. Vertical stria- 
 tions. Common forms are unit prism, basal, macro- and brachypinacoids, 
 brachydomes, and various bipyramids. Basal pinacoid usually predominates. 
 Twins common, twinning plane parallel to unit prism. Contact and inter- 
 penetration twins giving rise to cross and cog-wheel crystals. Also com- 
 pact, granular, and disseminated masses. 
 
 Imperfect brachypinacoidal cleavage. Conchoidal fracture. Brittle. 
 Hardness 2.5 to 3. Specific gravity 5.7 to 5.9. On fresh fracture surface 
 greasy metallic luster. Crystals often dull. Steel to lead gray, also iron 
 black in color. Gray to black streak. 
 
 Pb 2 Cu 2 Sb 2 S , usually contains arsenic, but never silver. Easily fusi- 
 ble, yields metallic globule, also antimony and lead coatings. Globule colors 
 flame green. 
 
SULPHIDES 
 
 61 
 
 Occurs with galena, sphalerite, stibnite, tetrahedrite, chalcocite, etc., 
 in the Hartz Mountains ; Freiberg, Saxony ; Pribram, Bohemia ; Kapnik, 
 Hungary ; Mexico ; Chile ; Peru ; Bolivia ; Arizona ; Arkansas ; Colorado ; 
 Ontario ; Siberia. 
 
 Important ore of lead and copper. 
 
 AIKINITF;, Patrinite, Pb 2 Cu 2 Bi 2 S 6 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.9719 : I : ? Striated, acicular 
 crystals. Oftentimes bent and twisted. No distinct terminations. Conchoidal frac- 
 ture. Brittle. Hardness 2.5. Specific gravity 6.757. Metallic luster. Lead to steel 
 gray; various tarnish colors, usually brown or black. Easily fusible. With gold 
 in quartz veins at Beresowsk, Ural Mountains ; also in Georgia. 
 
 Gold sometimes occurs as a pseudomorph after aikinite. 
 
 TETRAHEDRITE GROUP 
 
 The tetrahedrites possess the general formulae M" 4 R'" 2 S 7 or M' 4 M" 2 
 R"' 2 S 7 , in which M' indicates copper, mercury or silver; M" either iron 
 or zinc, and R"' arsenic or antimony. Several varieties may be differen- 
 tiated. All crystallize in the hextetrahedral class of the cubic system. 
 
 TETRAHEDRITE, Gray Copper Ore, M" 4 R'" 2 S 7 or M' 4 M" 2 R"',S T . 
 
 Cubic, hextetrahedral class. Excellent crystals showing tetrahedral de- 
 velopment. Often highly modified. Many forms have been observed. Fig- 
 
 FIG. 30. 
 
 FIG. 31. 
 
 FIG. 32. 
 
 ures 30, 31, and 32 show some of the more common combinations, /z=cube, 
 o=positive tetrahedron, d==rhombic dodecahedron, ?i=trigonal tristetrahe- 
 dron (m=2), and r=tetragonal tristetrahedron (w=3/2). The faces of the 
 tetrahedron are often smooth and brilliant, but sometimes may show trian- 
 gular striations. Penetration twins according to the Spinel law. Supple- 
 mentary twins not very common, face of the cube acts as twinning plane. 
 Massive, granular, disseminated, and compact. 
 
 No distinct cleavage. Conchoidal to uneven fracture. Brittle. Hard- 
 
62 DESCRIPTIVE MINERALOGY 
 
 ness 3 to 4. Specific gravity 4.36 to 5.6. Metallic luster, sometimes rather 
 dull. Opaque. Steel gray to iron black, often with brilliant tarnish colors. 
 Sometimes covered with a fine crystalline coating of chalcopyrite or sphaler- 
 ite. Streak black, also reddish brown. 
 
 According to the chemical composition many varieties may be differ- 
 entiated. A few of the more important varieties are the following: 
 
 Cupriferous tetrahedrite. This variety contains, aside from copper, 
 iron, zinc, and small amounts of silver, also antimony with a little arsenic. 
 Specific gravity 4.5 to 5. Hardness 3 to 4. A common variety. 
 
 Argentiferous tetrahedrite, (Freibergite}. Contains as high as 31% 
 of silver. Usually free from arsenic. Specific gravity 4.83 to 5. 
 
 Mercurial tetrahedrite, (Schwatsite}. Contains as much as 18% of 
 mercury ; also antimony and arsenic. Specific gravity 5 to 5.6. 
 
 Arsenical tetrahedrite, (Tennantite) . Contains no silver or mercury 
 and very little antimony. Its composition may in general be expressed by 
 the formula (Cu 2 , Fe, Zn) 4 As 2 S 7 . Specific gravity 4.4 to 4.9. 
 
 The different varieties fuse easily to a gray globule and are soluble in 
 aqua regia. Tetrahedrites on decomposing form malachite, azurite, bour- 
 nonite, cinnabar, chalcopyrite, and so forth. 
 
 Tetrahedrite occurs associated with the various sulphide minerals of 
 copper, silver, lead, and so forth ; especially, chalcopyrite, sphalerite, galena, 
 bournonite, and pyrite. Also quartz, siderite, and barite are common asso- 
 ciates. Found at Freiberg, Saxony; Clausthal, Hartz Mountains; Black 
 Forest, Baden; Pribram, Bohemia; Kapnik, Hungary; Mexico; Bolivia; 
 Chile, and Tuscany. 
 
 In the United States at Butte, Montana ; in many places in Colorado ; 
 Nevada; and Arizona. 
 
 An important copper and silver ore. 
 
 JORDANITE GROUP 
 
 This group contains two minerals which possess the general composition 
 Pb 4 R'".,S T where R'" indicates arsenic or antimony. 
 
 JORDANITE, Pb 4 As 2 S 7 . Monoclinic Prismatic Class 
 
 MENEGHINITE, Pb 4 Sb 2 S 7 . Orthorhombic Bipyramidal Class 
 
 JORDANITE, Pb4As 2 Sr. Monoclinic, prismatic class, a : b : c = 0.4945 : I : 0.2655, 
 /3 = 9o33^'. Pseudohexagonal due to twinning parallel to the unit prism. Crystals 
 highly modified. Perfect clinopinacoidal cleavage. Dark lead gray in color, often 
 tarnished. Hardness 3. Specific gravity 6.4. Streak black. Rare mineral. Found 
 with dufrenoysite in the dolomite of the Binnenthal; Nagyag, Transylvania. 
 
SULPHIDES 63 
 
 MENEGHINITE, Pb 4 Sb 2 S-. Orthorhombic, biypramidal class, a : b : =0.4747 ' J 
 : 0.3428. Although orthorhombic it is considered isomorphous with jordanite. Slen- 
 der prismatic crystals. Usually striated. Fibrous and compact masses. Is similar to 
 stibnite in appearance. Metallic luster. Hardness 2.5. Specific gravity 6.34 to 6.43. 
 Brittle. Blackish lead gray color. With emery at Schwarzenberg, Saxony; Tuscany; 
 Marble Lake, Ontario. 
 
 STEPHANITE GROUP 
 
 Here are placed the sulphantimonates of silver and lead which possess 
 the general formula M" 5 Sb 2 S 8 . 
 
 Stephanite, Ag 10 Sb 2 S 8 . Orthorhombic System 
 
 GEOCRONITE, Pb 3 Sb 2 S 8 . Orthorhombic System 
 
 Stephanite, Brittle Silver Ore, Ag 10 Sb 2 S 8 . 
 
 Orthorhombic, bipyramidal class, a : b : c=o.62()i : i : 0.6851. 
 Thick tabular or prismatic crystals. Rosette and step-like groups Highly 
 modified. Pseudohexagonal in simple as well as twinned crystals. Twin- 
 ning plane parallel to unit prism. Repeated twins, also trillings. Compact, 
 disseminated, and as a coating. 
 
 Brachypinacoidal cleavage. Conchoidal to uneven fracture. Soft but 
 brittle. Hardness 2 to 2.5. Specific gravity 6.2 to 6.3. Metallic luster. 
 Lead gray to iron black. Black streak. 
 
 Ag 10 Sb 2 S s , contains arsenic, iron, and copper. Fuses easily and yields 
 on charcoal a white coating and dark gray globule of silver. 
 
 Occurs with other silver ores at Joachimsthal, Bohemia ; Freiberg, Sax- 
 ony ; Andreasberg, Hartz Mountains ; Sardinia ; Peru ; Comstock lode, and 
 elsewhere, Nevada ; various places in Idaho. 
 
 An important ore of silver. 
 
 GEOCRONITE, PboSb 2 S 8 . Crystals are very rare. Supposed to be orthorhombic 
 and isomorphous with Stephanite. Usually compact. Conchoidal fracture. Hardness 
 2 to 3. Specific gravity 6.4 to 6.54. Light lead gray color, tarnishes black. Occurs 
 in Sweden, Spain, and Tuscany. 
 
 POLYBASITE GROUP 
 
 The members of this group have the general formula M^R"^, where 
 M indicates silver or copper, and R either arsenic or antimony. 
 
 PEARCEITE, (Ag,Cu) 9 AsS 6 . Monoclinic System 
 
 Polybasite, (Ag,Cu) 9 SbS 6 . Monoclinic System 
 
 PEARCEITE, (Ag, Cu)AsS6. Monoclinic, prismatic class, a : b : c = 1.7309 : i : 
 1.6199, /3=909'. Crystals are rhombohedral in development. Brittle. Hardness 3. 
 
64 DESCRIPTIVE; MINERALOGY 
 
 Specific gravity 6.13 to 6.17. Black in color and streak. Found at Aspen, Colorado; 
 Marysville, Montana ; Chile. 
 
 Polybasite, (Ag,Cu) 9 SbS G . 
 
 Monoclinic, prismatic class, a : b : ^=1.7309 : i : 1.5796, /8=9O. 
 Pseudohexagonal. Prism angle H958'. Six-sided thick tabular crystals 
 consisting of a combination of the basal pinacoid with pyramids. Compact 
 and disseminated. Triangular striations on basal pinacoid. 
 
 Perfect basal cleavage. Uneven fracture. Hardness 2 to 2.5. Spe- 
 cific gravity 6 to 6.25. Metallic luster. Iron black. Thin splinters in trans- 
 mitted light are cherry red. Black streak. 
 
 (Ag, Cu) 9 SbS 6 , may contain arsenic, iron, and zinc. Easily fusible. 
 Yields on charcoal white fumes of antimony trioxide and odor of sulphur 
 dioxide. The residue reacts for copper and silver. 
 
 Occurs with other silver minerals at Freiberg, Saxony ; Andreasberg, 
 Hartz Mountains ; Pribram, Bohemia. ; Hungary ; Comstock lode and else- 
 where, Nevada; Colorado; Arizona; Cobalt district, Ontario. 
 
 An ore of silver. 
 
 POLYARGYRITE, AgiSb 2 Si5. Cubic, hexoctahedral class. Very small, distorted 
 crystals. Octahedron, cube, and rhombic dodecahedron are usually in combination. 
 Cubical cleavage. Hardness 2.5. Specific gravity 6.974. Malleable. Dark lead gray 
 to iron black in color . Occurs at Wolfach in the Black Forest, Baden. 
 
 ENARGITE GROUP 
 
 The members of this group are orthosulpho-salts of copper and con- 
 form to the general formula Cu ;! RS 4 , where R is pentavalent arsenic or 
 antimony. 
 
 Enargite, Cu 3 AsS 4 . Orthorhombic System 
 
 (Luzonite) 
 
 FAMATINITE, Cu 3 SbS 4 . ? 
 
 Until recently Cu 3 AsS 4 was supposed to be dimorphous. Moses. has, 
 however, shown that the luzonite, which was formerly considered as the 
 second modification, conforms in every respect, crystallographically, to en- 
 argite. Luzonite is, hence, only a variety of enargite. 
 
 Enargite, Cu,AsS 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c 0.8694 : i : 0.8308. Small 
 prismatic crystals with vertical striations. The usual combination consists 
 of the unit prism, the three pinacoids, and unit brachydome. Penetration 
 
SULPHIDES 65 
 
 twins and star-shaped trillings ; twinning plane parallel to the marcoprism 
 (w=3/2). Usually found in compact, fine or coarse grained masses. 
 
 Perfect prismatic cleavages ; distinct cleavages parallel to the three 
 pinacoids also to be observed. Uneven fracture. Hardness 3. Specific 
 gravity 4.33 to 4.47. Brittle. Submetallic luster. Steel gray to iron black. 
 In artificial light resembles sphalerite. Streak black. Opaque. 
 
 Cu 3 AsS 4 , may contain small amounts of iron and zinc replacing the 
 copper, and some antimony in place of arsenic. Fuses on charcoal and 
 yields garlic odor of arsenic. With soda gives a copper globule. Soluble in 
 nitric acid with separation of sulphur. 
 
 In veins with other copper minerals. Not very common in Europe. 
 Found at Pardid, Hungary, and Brixlegg, Tyrol. More extensive in Peru, 
 Chile, Argentine Republic, Bolivia, Mexico, and the Island of Luzon in 
 the Philippines. 
 
 In remarkably large deposits in the copper mines of the Butte district, 
 Montana ; also in Colorado ; Tintic district, Utah, etc. 
 
 A very important ore of copper. 
 
 FAMATINITE, CusSbS^ Practically nothing is known of the crystallography of 
 this mineral but on account of its chemical composition it is considered isomorphous 
 with enargite. May contain as high as 9% of arsenic. Massive. Fracture uneven. 
 Brittle. Hardness 3.5. Specific gravity 4.57. No cleavage. Reddish steel gray in 
 color. 
 
 A rare mineral. Found with other copper minerals and pyrite in Serra de 
 Famatina, Argentine Republic; also in Cerro de Pasca, Peru. 
 
 Stannite, Tin Pyrites, Bell-Metal Ore, Cu 2 FeSnS 4 . 
 
 Tetragonal, scalenohedral class, a : c=i : 0.986. Exceedingly small 
 bisphenoidal crystals. Very rare. Usually compact, granular, or dissem- 
 inated masses. Uneven fracture. Brittle. Hardness 4, Specific gravity 
 4.3 to 4.52. Metallic luster. Steel gray to iron black in color. Tarnishes, 
 blue. Streak black. 
 
 Cu.,FeSnS 4 , often contains admixture of finely divided chalcopyrite.. 
 Fuses with difficulty ; yields a white coating on charcoal, also metallic glob- 
 ule. Soluble in nitric acid, yielding a green solution with the separation 
 of tin dioxide and sulphur. 
 
 Rare mineral. Usually found with cassiterite, and so forth, in tin ore- 
 deposits. Thus at Cornwall, England; Guanuni and Potosi, Bolivia; Black. 
 Hills, South Dakota. 
 
66 
 
 This group includes but two members, sulpho-germanates of silver, 
 which conform to the general formula Ag 8 GeS 6 . Germanium may be par- 
 tially replaced by tin. 
 
 CANFIELDITE, Ag s (Sn,Ge)S 6 . Hexoctahedral Class 
 
 ARGYRODITE, Ag 8 GeS . Hexoctahedral Class 
 
 CANFIELDITE, Ag 8 (Sn,Ge)So. Cubic, hexoctahedral class. Crystals indistinct. 
 Compact and massive. Specific gravity 6.28. Black in color. Very much like argy- 
 rodite. Found at La Paz, Bolivia. 
 
 ARGYRODITE, AgsGeSe. Cubic, hexoctahedral class. Crystals are exceedingly 
 small. Octahedrons alone or in combination with the rhombic dodecahedron. Com- 
 pact and massive. No cleavage. Hardness 2.5. Specific gravity 6.26. Metallic luster. 
 On fresh fracture reddish steel gray, elsewhere steel gray. Yields black sublimate in 
 closed tube . Fuses on charcoal and yields a white sublimate which later turns yellow. 
 
 Rare. Occurs with marcasite in the Himmelsfiirst mine, Freiberg, Saxony; 
 also in Guanuni and Potosi, Bolivia. 
 
 The element germaniun} was discovered in argyrodite in 1886 by the late Pro- 
 fessor Clements Winkler of the Freiberg School of Mines, Saxony. 
 
 FRANCKEITE, Pb 5 Sn 2 Sb 2 Si2. Crystal form unknown. Occurs in small tabular 
 01 radial fibrous masses of a blackish lead gray color. Rare. Specific gravity 5.55 
 Occurs at Chocaya and Aullagas, Bolivia. 
 
 CYLINDRITE, Pb 6 Sn 6 Sb 2 S2i. Crystal form unknown. Occurs in cylindrical ag- 
 gregates with a dark lead gray color and metallic luster in the Province of Poopa. 
 Bolivia. Hardness 2.5 to 3. Specific gravity 5.42. Very rare. 
 
III. OXIDES, HYDROXIDES, ETC. 
 1. OXIDES 
 
 WATER, H 2 O. 
 
 Above oC. water is a liquid, hence, amorphous. Almost colorless. 
 In large quantities and when pure, it has a bluish tinge. Specific gravity, 
 when pure, at 4C. and 760 mm. barometric pressure is i. That of ocean 
 water may be as high as 1.028. Transparent and singly refractive, Na 
 = 1.3336. When pure it is without odor or taste. 
 
 Water occurs very widely distributed in nature and is an important 
 agency in the disintegration, decomposition, transportation, and formation 
 of minerals. Nearly all minerals are more or less soluble in water, espec- 
 ially if it contain such substances as carbon dioxide, humus acid, hydro- 
 chloric acid, oxygen, etc., in solution. The ocean water contains about 
 3.44% of solid mineral matter in solution. The following 31 elements are 
 found in solution in the ocean, some to be sure only in very small amounts : 
 Iodine, fluorine, phosphorous, silicon, boron, bromine, silver, lead, copper, 
 zinc, cobalt, arsenic, nickel, iron, manganese, aluminium, barium, strontium, 
 lithium, caesium, rubidium, gold, sulphur, nitrogen, carbon, oxygen, cal- 
 cium, magnesium, potassium, sodium, and chlorine. Hence, water is often 
 called the universal solvent. When water freezes it expands. This in- 
 crease in volume is estimated at 9 to 10% and the pressure exerted at 138 
 tons per square foot. Due to this enormous pressure, freezing water is an 
 important geological agency, causing the widening of cracks and crevices 
 thereby extending the zone of activity of water and oxygen and hastening 
 weathering and decomposition. 
 
 ICE, Snow, H 2 O. 
 
 Hexagonal, ditrigonal pyramidal class, a : c=i : 1.617. Water on 
 freezing crystallizes, forming snow or ice. Snow crystals are often very 
 beautiful. They are tabular, and hexagonal in outline, and show a great 
 
68 
 
 DESCRIPTIVE MINERALOGY 
 
 diversity in development. Figure 
 33 represents a magnified snow 
 crystal. Measurements of ice or 
 snow crystals are obviously not 
 very accurate. Lake or stream ice 
 consists of crystals arranged in a 
 definite manner. The c axes of the 
 various crystal particles are all per- 
 pendicular to the extent of the sheet 
 of ice, that is, they are vertical. 
 This uniform crystallographic ar- 
 rangement allows such ice to be 
 easily split along definite planes. 
 The definite orientation is shown 
 by the columnar or prismatic struc- 
 ture, easily observed when lake or 
 stream ice is subjected to partial 
 melting. Glacier ice differs from lake or stream ice in that the crystal 
 particles do not possess a definite orientation. Ice also occurs stalactitic, 
 as icicles. 
 
 Ice is usually colorless, in large masses greenish or bluish. Transpar- 
 ent. Weak double refraction, w Na =1.309, e Na =1.333 at 8C. 
 
 Generally quite pure, but may contain impurities, principally as inclu- 
 sions. This is especially the case of ice formed in disturbed water cr near 
 the shore. 
 
 FIG. 33- 
 
 (Photograph by W. A. Bentley.) 
 
 TELLURITE., TeO 2 . Orthorhombic, a : b : c = 0.4596 : i : 0.4650. Thin tabular 
 crystals. Striated. Often arranged in hemispherical masses. Adamantine luster. 
 Transparent to translucent. White to honey yellow in color. Hardness 2. Specific 
 gravity 5.9. Basal cleavage. Rare. With native tellurium at Zalathna, Transylvania ; 
 Boulder Co., Colorado; also South Dakota. 
 
 TUNGSTITE, WOa.HaO. Orthorhombic, a : b : c = 0.6966 : I : 0.4026 (artificial 
 crystals). Occurs in nature only as powdery and earthy masses. Artificial crystals 
 are transparent. Powdery masses are dull with yellow or greenish yellow color. 
 Soft. Specific gravity 6.5 to 7.2. Rare. With wolframite and other tungsten min- 
 erals at Cornwall, England; Monroe, Conn.; Cabarrus Co., N. C. ; with hiibnerite 
 at Osceola, Nevada. 
 
OXIDES 69 
 
 SENARMONTITE GROUP 
 
 Here are placed the oxides of arsenic, antimony, and bismuth which 
 possess the general formula M'^Og. One compound, Sb 2 O 3 , is dimor- 
 phous. 
 
 CUBIC SERIES 
 
 ARSENOUTE, As 2 O 3 . Hexoctahedral Class 
 
 Senarmontite, Sb,O 3 . Hexoctahedral Class 
 
 ORTHORHOMBIC SERIES 
 
 a : b 
 
 VALENTINITE, Sb 2 O 3 . Bipyramidal Class 0.3914 : i 
 
 BISMITE, Bi 2 O 3 . Bipyramidal Class 0.8166 : I 
 
 c 
 
 0.3367 
 i . 0640 
 
 The axial ratio given for bismite is for artificial crystals, natural crys- 
 tals not being known. The isomorphism between valentinite and bismite 
 is by no means fully established. 
 
 ARSENOUTE, Arsenite, As,O 3 . 
 
 Cubic, hexoctahedral class. Artificial crystals are octahedral. In nature only 
 as white or colorless crusts or coatings on arsenic minerals. 
 
 Conchoidal fracture. Octahedral cleavage. Hardness 1.5. Specific gravity 3.7. 
 Dull to silky luster. Streak white. Astringent taste. Translucent. Yields on char- 
 coal coating and odor of arsenic. Soluble in hydrochloric acid, also in hot water. 
 
 Arsenolite is a decomposition product of minerals containing arsenic. Occurs 
 in small quantities at Andreasberg, Hartz Mountains; Joachimsthal, Bohemia; Kap- 
 nik, Hungary; Cornwall, England; Chile; Peru; California; Nevada. 
 
 Senarmontite, Sb 2 O 3 . 
 
 Cubic, hexoctahedral class. Octahedral crystals. Also granular and 
 compact masses. Octahedral cleavage. Conchoidal to uneven fracture. 
 Hardness 2 to 2.5. Specific gravity 5.22 to 5.3. Greasy luster. Colorless, 
 white and gray. Transparent to translucent. Sublimes. Soluble in hydro- 
 chloric acid. 
 
 Occurs with the decomposition products of minerals containing anti- 
 mony. Found at Constantine, Algeria ; Pernek, Hungary ; Burke Co., N. C. ; 
 South Ham, Quebec ; Sardinia. 
 
 VALENTINITE, Sb 2 O 3 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.3914 : i : 0.3367. Prismatic 
 crystals, sometimes highly modified. Often in radiating groups. Also compact, col- 
 umnar, fibrous, and granular aggregates. Perfect brachypinacoidal cleavage. Hard- 
 ness 2.5. Specific gravity 5.6 to 5.8. Adamantine luster. White, gray to pale red. 
 Translucent. Melts easily and sublimes. Soluble in hydrochloric acid. 
 
 A decomposition product of antimony minerals, especially stibnite. Valentinite 
 is more abundant than Senarmontite. Occurs at Wolfsberg, Hartz Mountains; Pri- 
 bram, Bohemia ; Constantine, Algeria ; Sardinia ; Burke Co., N. C. ; and South Ham, 
 Quebec. 
 
yo DESCRIPTIVE; MINERALOGY 
 
 BISMITE, Bismuth Ocher, Bi 2 O 3 . 
 
 Orthorhombic, a : b : c = 0.8166 : i : 1.0649 (artificial crystals). In nature 
 only as compact, disseminated, and earthy masses. Adamantine to dull luster. Trans- 
 lucent to opaque. Green and straw yellow, also grayish white in color. Soft. Spe- 
 cific gravity 4.36 (the artificial compound is much heavier, 8.07 to 8.86). Rare. 
 Occurs at Schneeberg, Saxony; Joachimsthal, Bohemia; Hungary; Pala, California; 
 Utah; Gaston Co., N. C. 
 
 QUARTZ GROUP 
 
 This is a very important group. It contains those minerals which pos- 
 sess the general formula MO 2 , where M is .tetravalent and may be silicon, 
 titanium, or zirconium. Depending upon the crystallization, four series 
 may be differentiated. 
 
 HEXAGONAL SERIES 
 
 a : c 
 QUARTZ, SiO 2 . Trigonal Trapezohedral Class i : 1.0999 
 
 ORTHORHOMBIC SERIES 
 
 a : b 
 
 TRIDYMITE, SiO 2 . Bipyramidal Class 0.5774 : i 
 
 Brookite, TiO 2 . Bipyramidal Class 0.5941 : i 
 
 0.9544 
 
 I . 1222 
 
 TETRAGONAL SERIES 
 
 a : c 
 Anatase, TiO 2 . Ditetragonal Bipyramidal Class i : i . 7844 
 
 CRISTOBAUTE, SiO 2 . ? ? 
 
 MONOCLINIC SERIES 
 
 a : b : c 
 BADDELEYITE, ZrO 2 . Prismatic Class 0.9768 : i : 1.0475, (3 = 98 40' 
 
 From the foregoing classification it is seen that SiO 2 and TiO 2 , includ- 
 ing rutile page 77, are trimorphous. Quartz is by far the most important 
 mineral of this group. 
 
 QUARTZ, Chalcedony, Agate, Jasper, etc. SiO,. 
 
 Hexagonal, trigonal trapezohedral class, a : c=i : 1.0999. Crystals 
 are very common. Usually prismatic in habit, more rarely pyramidal. Of- 
 ten apparently holohedral, Figure 34. Over 140 forms have been observed 
 of which the following are the most common : Prism of the first order a ; 
 
OXIDES 
 
 positive and negative unit rhombohedrons r and z, respectively ; the positive 
 modified rhombohedrons where m equals 3 or 4; negative modified rhom- 
 bohedron with m = 7; the unit (s} and modified (m = 2) trigonal bipyra- 
 mids of the second order; and the three trigonal trapezohedrons where n 
 equals 6/5, 5/4, 4/3, and m is 6, 5, or 4, respectively. The most common 
 of the three trigonal trapezohedrons is x with the coefficients n and m equal- 
 
 FIG. 34- 
 
 FIG. 35. 
 
 FIG. 36. 
 
 FIG. 37- 
 
 FIG. 
 
 ing 6/5 and 6. Figures 34, 35, 37 and 38 show some of the more common 
 combinations. The basal pinacoid is very rarely observed. Crystals are 
 often arranged in parallel groups, as shown in Figure 36 (after Tschermak) ; 
 sometimes also grouped radially. It is not always possible to distinguish 
 between the positive and negative unit rhombohedrons r and j. The prism 
 faces are often striated horizontally. This is of use in the proper orienta- 
 tion of distorted crystals, which are rather common, Figure 35. Crystals 
 are sometimes bent or twisted. 
 
 The presence of a trigonal trapezohedron, for example .r in Figures 
 37 and 38, allows such crystals to be designated as right- or left-handed 
 crystals. On left-handed crystals a face of the trigonal trapezohedron (.r) 
 lies in the upper left hand corner of the prism face a, Figure 37. In the 
 case of right-handed crystals it is in the upper right hand corner, Figure 38. 
 
7,2 
 
 DESCRIPTIVE MINERALOGY 
 
 Twins are very common. In many cases it is difficult to positively 
 recognize the twinning. This can, however, be done by means of the opti- 
 cal or pyro-electric properties, as also by the etch-figures. Four of the 
 more important twinning laws may be referred to. (i) Common or Dau- 
 phine law, sometimes also called the Swiss law. Here two right- or left- 
 handed crystals so interpenetrate that the positive rhombohedron of the one 
 individual coincides with the negative of the other. This interpenetration 
 causes a face of the trigonal trapezohedrons to appear, in the case of two 
 right-handed crystals, in the upper right hand corner of each one of the prism 
 faces (a). When two left-handed crystals interpenetrate the trigonal trap- 
 ezohedron face (.r) is to be observed in the upper left hand corner, Figure 
 39. This can be explained by the rotation of either one of the indi- 
 
 FIG. 39. 
 
 FIG. 40. 
 
 viduals through 180 about the c axis. Such twinned crystals are not 
 symmetrical to a twinning plane but rather to a twinning axis, which in 
 this case is the crystallographic c axis. (2) Brazilian law. A right- and a 
 left-hand crystal of the same sign interpenetrate so that the twinned crys- 
 tal is symmetrical to a plane parallel to a face of the prism of the second 
 order, Figure 40. Such twins are in reality supplementary twins for they 
 possess the symmetry of the ditrigonal scalenohedral class. This law is 
 often observed on amethyst crystals from Brazil, hence, the name, Brazilian 
 law. (3) Prism of the first order acts as the twinning plane. Here, right- 
 and left-hand crystals interpenetrate. The twinned crystal is symmetrical, 
 not only to the prism of the first order, but also to the basal pinacoid. 
 (4) Japan law. These are contact twins with a face of the unit trigonal 
 bipyramid acting as the twinning plane. The principal axes of the two 
 individuals intersect at an angle of 8435 / . Excellent crystals showing this 
 law are found in Japan. 
 
 Quartz crystals often contain inclusions which may be liquids, gases, 
 or solids. Rutile, chlorite, hematite, organic matter, asbestos, epidote, and 
 
OXIDES 73 
 
 hornblende are among the solids found as inclusions in quartz. Carbou 
 dioxide, either liquid or gaseous, is also noted as an inclusion. Sometimes 
 scales of mica or hematite are distributed in a regular manner, so that such 
 crystals may be separated into layers. Such crystals are called cap quarts. 
 
 Rhombohedral cleavages, generally indistinct and not commonly ob- 
 served. These cleavages are made more pronounced by heating and rapid 
 cooling. Conchoidal fracture is highly characteristic. Brittle. Hardness 7. 
 Specific gravity ranges from 2.5 to 2.8 ; pure quartz 2.653 to 2.66. Vitreous 
 luster, sometimes slightly 'greasy on fracture surfaces. Transparent to 
 opaque. When pure, quartz is colorless. Various shades of gray, yellow, 
 red, blue, green, brown, and black are commonly noted. Many colors dis- 
 appear when heated, thus, the violet color of the amethyst changes first to 
 a yellow, then to a greenish tint, and when a temperature of 25oC. is 
 reached, the crystal is colorless. Brown and smoky crystals usually become 
 colorless when heated to 200 C. It is thought that the various colors may 
 be due to the presence of organic matter or to small amounts of the oxides 
 of some of the rarer elements. Streak white. Positive double refraction, 
 0,= 1.5442, Na = 1-5533- Circular polarization. Often shows natural 
 etch figures. Pyro-electric. Phosphoresces when rubbed. 
 
 SiO 2 . May contain hematite, rutile, hornblende, chlorite, organic mat- 
 ter, and clay as impurities. Not attacked by the common acids. Easily acted 
 upon by hydrofluoric acid ; only slightly by potassium hydroxide. Infusible 
 before the blowpipe. Common as a pseudomorph after many minerals, viz: 
 Calcite, fluorite, siderite, etc. ; also after wood, silicified wood. Only one min- 
 eral occurs as a pseudomorph after quartz, namely, talc. 
 
 The different varieties of quartz may be divided into three large groups, 
 as follows: (a) Phanero crystalline, (b) Cryptocrystalline, and (c) Clas- 
 tic varieties. 
 
 (a) Phanerocrystalline varieties are vitreous, either crystallized or 
 crystalline, and but slightly acted upon by potassium hydroxide. They in- 
 clude the following: 
 
 (1) ROCK CRYSTAL. This is ordinary crystallized quartz. Generally 
 colorless. 
 
 (2) AMETHYST. This variety is purple to violet in color. Color 
 may be due to manganese. Becomes colorless when heated, see above. 
 Generally in crystals. 
 
 (3) ROSE QUARTZ. Usually massive. Pink to rose-red in color, be- 
 coming paler on exposure. 
 
 (4). SMOKY QUARTZ. Smoky yellow to dark brown or black. Often: 
 termed cairngorm stone. When black it is called morion. Becomes color- 
 less when heated, see above. 
 
74 DESCRIPTIVE MINERALOGY 
 
 (5) MILKY QUARTZ. Milk-white in color. Translucent or nearh 
 opaque. Sometimes with a greasy luster. 
 
 (6) YELLOW QUARTZ. Light yellow in color. Often called false 
 topaz or citrine. Citrine is sometimes produced by heating amethyst, see 
 page 73. 
 
 (7) AVENTURINE. Quartz containing scales of mica, hematite, or 
 goethite. 
 
 (8) FERRUGINOUS QUARTZ. Is colored brown or red, due to the pres- 
 ence of either limonite or hematite. 
 
 (9) CHLORITIC QUARTZ. Usually green. Contains chlorite as an 
 inclusion. 
 
 (10) RUTILATED QUARTZ. Usually the rock crystal variety containing 
 fine needles of rutile. 
 
 (n) TIGER'S EYE. Pseudomorph after crocidolite. Chatoyant luster. 
 
 (12) CAT'S EYE, Opalescent, due to inclusions of parallel fibers of 
 asbestos. Grayish brown or green in color. 
 
 (&) Cryptocrystalline varieties are compact and homogeneous. Un- 
 der the microscope they show a crystalline structure. More readily acted 
 upon by potassium hydroxide than the crystalline varieties. 
 
 (1) CHALCEDONY. A transparent to translucent variety having a 
 waxy luster. May be stalactitic, botryoidal, concretionary, and often lines 
 cavities. Is white, grayish, pale to dark brown, blue, or black. 
 
 (2) CARNELIAN OR SARD. A red variety of chalcedony. Sometimes 
 deep clear red, pale red, brownish red, or brown in color. 
 
 (3) CHRYSOPRASE. Apple green chalcedony. 
 
 (4) PRASE. Dull leek-green. Translucent. 
 
 (5) PLASMA. Bright to leek-green, sometimes emerald green. 
 
 (6) HELIOTROPE OR BLOODSTONE. Bright or dark green chalcedony 
 with small spots of red jasper, irregularly distributed. The red spots re- 
 semble drops of blood. 
 
 (7) AGATE. This is chalcedony made up of strata or bands indicating 
 various stages of deposition. The layers may be differently colored or 
 clouded. This gives rise to several varieties of agate, namely, banded, moss, 
 clouded, or fortification agates. In agates the banding is usually in par- 
 allel, but more or less wavy or irregular lines. Agates may be white, pale 
 and dark brown, bluish, etc. 
 
 (8) ONYX AND SARDONYX. These are agates with the banding in 
 parallel straight lines, corresponding to layers in even planes. In ony.v the 
 colors are generally white and black. In sardonyx red layers (carnelian) 
 are also present. 
 
 (9) JASPER. Opaque, red, yellow, dark green, and grayish blue varie- 
 
OXIDES 75 
 
 ties. When the colors are in broad bands or stripes, it is called riband or 
 striped jasper. 
 
 ( 10) FUNT. Gray, smoky, brown, or brownish black, nodular variety, 
 closely related to chalcedony. Usually found in chalk beds and limestones. 
 Translucent. Possesses an excellent conchoidal fracture. Generally cov- 
 ered with a white coating. 
 
 (n) HORNSTONE. Is more brittle than flint. Has a splintery fracture. 
 
 (12) CHERT. A more or less general term applied to hornstone, im- 
 pure flints or jaspers. 
 
 (13) BASANITE. A velvet-black variety used for the streaking of al- 
 loys of precious metals. Also called touch-stone or Lydian stone. 
 
 (c*) Clastic varieties of quartz include many of the silicious f rag- 
 mental rocks. In some cases the individual particles are no longer distinct. 
 
 (1) SAND. In general, loose, unconsolidated grains or fragments of 
 quartz. 
 
 (2) SANDSTONE. Consolidated sand. The cementing material may be 
 silica, iron oxide, calcium carbonate, etc. 
 
 (3) ITACOLUMITE. A flexible sandstone. Contains some mica. 
 
 (4) QUARTZITE OR GRANULAR QUARTZ. Metamorphosed sandstone. 
 The quartz particles are usually not recognizable by the naked eye. 
 
 Quartz is, next to water, the most common of all minerals. It is a 
 very important rock-forming mineral, being a primary constituent of many 
 igneous and sedimentary rocks. It may be formed from fusion, solution, 
 or by sublimation. Quartz occurs in rocks of all ages and in many ore 
 deposits. It is also found abundantly as sand and gravel. 
 
 Rock crystal, amethyst, smoky quartz, cat's eye, tiger's eye, rose quartz, 
 chalcedony, agate, and jasper are used in jewelry and for ornamental pur- 
 poses ; agate and chaledony for mortars and pestles ; rock crystal for dishes, 
 vases, optical instruments, and spectacles ; sand for mortar and plaster, 
 glass, and sandpaper ; sandstone for building and paving purposes, and 
 grindstones ; and ground or crushed quartz and flint in wood fillers, pottery, 
 scouring and polishing soaps, and as an abrasive. 
 
 TRIDYMITE, SiO 2 . _, 
 
 Occurs in two modifications. One is hexagonal, a : c = I : 1.629, and is formed 
 at high temperatures. Below I3OC. tridymite is orthorhombic, a : b : c = 0.5774 : I 
 : 0.9544. These crystals are generally trillings with an hexagonal development. 
 Crystals are usually small and thin tabular. Cyclic twins according to several laws 
 are quite common. Crystals are sometimes arranged in spherical or fan-shaped groups. 
 
 Basal parting. Hardness 6.5 to 7. Specific gravity 2.28 to 2.34 (quartz 2.65). 
 Vitreous luster. White, colorless, yellow, or brown. Transparent to translucent. 
 
 SiO=, usually quite pure. Infusible before the blowpipe. Soluble in a hot, con- 
 
76 DESCRIPTIVE MINERALOGY 
 
 centrated solution of sodium carbonate. Yields a skeleton of silica in salt of phos- 
 phorous bead. 
 
 First found in the trachyte of Mt. San Cristobal, near Pachuca, Mexico. Occurs 
 also in other acid igneous rocks, such as andesite, liparite, etc. ; occasionally in basalt. 
 Found in the trachyte of Siebengebirge, near Bonn, Germany; Transylvania; Italy; 
 France ; Mt. Rainier, Washington ; Yellowstone Park, etc. Not a common mineral 
 
 Brookite, Ti<X 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.5941 : i : 1.1222. Us- 
 ually as pyramidal or prismatic crystals. Figure 41 shows a crystal of the 
 
 pyramidal habit, which consists of a combination 
 of the unit prism (/>) and the brachy bipyramid 
 (c). The prismatic type is rarer. It is sometimes 
 termed arkansite. Many forms have been observed 
 on brook ite. 
 
 Indistinct brachypinacoidal cleavage. Brittle. 
 Hardness 5.5 to 6. Specific gravity 3.8 to 4.1. On 
 heating the specific gravity increases to that of ru- 
 tile, page 78. Metallic-adamantine luster. Trans- 
 lucent to opaque. Red brown, reddish black, or 
 iron black (arkansite) in color. Yellow white to 
 brown streak. 
 
 TiO 2 , may contain ferric oxide. Reactions same as for rutile, page 
 78. Alters by paramorphism to rutile. 
 
 Occurs in various crystalline schists and silicate rocks, also in gold 
 placers. Found at Tremaddoc, Wales ; St. Gotthard, Switzerland ; Miask, 
 Ural Mountains; Magnet Cove, Arkansas, (arkansite); in the placers of 
 North Carolina, etc. 
 
 CRISTOBAUTE., SiO 2 . 
 
 Tetragonal. Octahedral crystals with skeletal development. Spinel-like twins. 
 
 At and above i7SC. cristobalite is cubic. White in color. Translucent. Dull luster. 
 
 Hardness 6 to 7. Specific gravity 2.3. Rare. First found with tridymite at Mt. San 
 Cristobal, Mexico. 
 
 FIG. 41. 
 
 Anatase, Octahedrite, TiO 2 . 
 
 Tetragonal, ditetragonal bipyramidal class, a : ci : 1.7844. Occurs 
 only in small crystals with pyramidal, tabular, or prismatic habit. Figure 
 42 shows a crystal of the pyramidal type and con- 
 sists of the modified bipyramids s (7^ = 1/3), and 
 v (m= 1/7), unit prism m, prism of the second or- 
 der a, and the unit bipyramid of the second order e. 
 Over 75 forms have been observed. 
 
 Perfect pyramidal and basal cleavages. Hard- 
 ness 5.5 to 6. Specific gravity 3.81 to 3.95, when 
 heated increases to that of rutile, page 78. Metal- 
 lic to greasy adamantine luster. Translucent to semi-opaque. Brown, yel- 
 
OXIDES 77 
 
 low, hyacinth red, indigo blue to black; rarely colorless. Streak white. 
 High indices of refraction, w Na = 2.56, e Na = 2.49. 
 
 TiCX, may contain some ferric oxide. Reactions same as for rutile, 
 page 78. Occurs as a pseudomorph after titanite and ilmenite. Alters by 
 paramorphism to rutile. 
 
 Occurs in cracks and cavities in various silicate rocks, also in gold 
 placers. Found at Tavetsch and St. Gotthard, Switzerland ; Fichtelgebirge, 
 Germany , Miask, Ural Mountains ; Norway ; France ; Smithfield, R. I. ; 
 and the gold placers of Burke Co., North Carolina. 
 
 BADDELEYITE, Brazilite, ZrO 2 . 
 
 Monoclinic, prismatic class, a : b : c = 0.9768 : i : 1.0475, P = Q84o'- Small, 
 tabular crystals. Colorless, yellow, brown, or black. Hardness 6.5. Specific gravity 
 5.5 to 5.6. Occurs at Jacupiranga, Brazil ; also in the precious stone placers of 
 Rakwana, Ceylon. 
 
 RUTILE GROUP 
 
 If the formulae of the dioxides of titanium, tin, lead, and manganese are 
 doubled the analogy between their chemical composition and that of zircon 
 and thorite becomes more apparent. This is clearly seen in the following 
 tabulation : 
 
 a 
 
 RUTILE, TiTiO 4 . Ditetragonal Bipyramidal Class - I 
 
 ZIRCON, ZrSiO 4 . Ditetragonal Bipyramidal Class i 
 
 Thorite, ThSiO 4 . Ditetragonal Bipyramidal Class i 
 
 CASSITERITE, SnSnO 4 . Ditetragonal Bipyramidal Class i 
 
 PLATTNERITE, PbPbO 4 . Ditetragonal Bipyramidal Class i 
 
 POUANITE, MnMnO 4 . Ditetragonal Bipyramidal Class i 
 
 c 
 
 0.6439 
 o . 6404 
 o . 6402 
 0.6723 
 
 o . 6764 
 o . 6647 
 
 According to von Groth the structural formula of zircon may be 
 written : 
 
 
 By making the proper substitutions in the above, the structural formulae of 
 the various members of this group are easily obtained. 
 
 RUTILE, TiTiO 4 . 
 
 Tetragonal, ditetragonal bipyramidal class, a : c = i : 0.6439. Crys- 
 tals are common. Usually prismatic or thick columnar, showing vertical 
 striations. The forms commonly observed are the prisms of the first and 
 second orders, unit bipyramid of the first order, and several ditetragonal 
 prisms, especially those where n equals 3/2, 2, and 3, respectively. A com- 
 
78 DESCRIPTIVE MINERALOGY 
 
 bination, frequently observed, consists of the prisms of the first 
 and second orders, and the unit bipyramid of the first order. Twins 
 occur according to two laws, (i) Twinning plane parallel to the unit bi- 
 pyramid of the second order. Here simple contact 
 twins, the so-called "knee-shaped" crystals, are com 
 mon. Also polysynthetic twins, cyclic trillings (Fig- 
 ure 43) and so forth. Sixlings according to this law 
 form a closed ring. The various individuals of the 
 sixling lie in one plane. When adjacent faces of the 
 bipyramid of the second order alternate as twinning 
 plane cyclic eightlings result. Such crystals also 
 FIG. 43^ form a closed ring but the various individuals do 
 
 not lie in the same plane. These eightlings are often called rutile rosettes. 
 (2) The second twinning law is not common. The twinning plane is par- 
 allel to a face of the bipyramid of the second order where tn equals 3. 
 Also as needle-like crystals, often as inclusions. Compact, disseminated, 
 granular, and as rounded pebbles. 
 
 Distinct prismatic and pyramidal cleavages. Conchoidal to uneven 
 fracture. Brittle. Hardness 6 to 6.5. Specific gravity 4.2 to 4.3, ferrugin- 
 ous varieties as high as 5.13. Metallic adamantine luster. Opaque to trans- 
 parent. Red brown, blood red, cochineal red, black (nigrine), and more 
 rarely, yellow, or yellowish brown. Streak yellow or pale brown. Op- 
 tically positive. Very high indices of refraction: w Na =2.616, N a = 2.903. 
 Ti,,O 4 or TiO 2 . Usually contains from 1.5% to 14% of ferric oxide. 
 Infusible. When fused with sodium carbonate and treated with hydro- 
 chloric acid and tin-foil the solution turns violet. Insoluble in acids. Found 
 as a pseudomorph after hematite, and as a paramorph after brookite and 
 anatase, pages 76 and 77. 
 
 Most common titanium mineral. Occurs widely distributed. Is found 
 in gneisses, mica schists, syenites, and diorites. To a small extent in gran- 
 ite, granular limestone, and dolomite. The common associates are quartz, 
 feldspar, hematite, and so forth. 
 
 Occurs in Norway at Arendal and Kragero ; Sweden ; Ural Mountains ; 
 Tyrol ; St. Gotthard and Binnenthal, Switzerland ; Perthshire, Scotland. 
 
 The only producing locality in the United States is in Nelson County. 
 Virginia. Rutile also occurs at Graves Mt, Georgia ; and Magnet Cove, 
 Arkansas. It is also found in secondary deposits with quartz, tourmaline, 
 gold, diamond, etc. 
 
 Used in coloring porcelain yellow and imparting a bluish white tint 
 to artificial teeth. To some extent in special grades of steels and as a mor- 
 dant in dyeing leather. 
 
OXIDES 
 
 79 
 
 ZIRCON, ZrSi0 4 . 
 
 Tetragonal, ditetragonal bipyramidal class, a : c = I : 0.6404. Us- 
 ually in well developed crystals of a prismatic or pyramidal habit. Common 
 forms are the prisms of the first (w) and second (a) orders, the unit (/>) 
 and various modified bipyramids of the first order, and also the ditetragonal 
 
 FIG. 44. 
 
 FIG. 45. 
 
 FIG. 46. 
 
 bipyramid (.r) with the value of n and m equal to 3. Figures 44, 45, and 46 
 show several common combinations. Twins are rare. Twinning plane 
 parallel to the unit bipyramid of the second order. Also as rounded or 
 angular lumps and grains. Never compact. 
 
 Imperfect prismatic and pyramidal cleavages. Conchoidal to uneven 
 fracture. Hardness 7.5. Specific gravity 4.4 to 4.8. Adamantine luster. 
 The commonly observed colors are brown, brownish red, gray, more rarely 
 yellow, green, and colorless. Transparent to opaque. The clear, transpar- 
 ent yellow, red, and brown varieties are hyacinth. The term jargon is ap- 
 plied to such as are colorless or smoky. Strong double refraction, positive. 
 WLI 1.92, e L i 1.97. Colorless Streak. 
 
 ZrSiO 4 . Usually a small amount of ferric oxide is present. Infusible. 
 Decomposed by continued action of hot concentrated sulphuric acid. Not 
 acted upon by hydrofluoric acid. Malacon is an altered variety of zircon. 
 
 A common constituent of the more acid igneous rocks, especially gran- 
 ites and syenites. Also found in crystalline schists, gneisses, and more 
 rarely in granular limestones. Also in secondary deposits with gold, spinel, 
 corundum, etc., thus, on the island of Ceylon ; in the auriferous sands of 
 Transylvania ; with pyrope in Bohemia and Saxony. Occurs at various 
 places in southeastern Norway, usually in a zircon syenite ; Miask, Ural 
 Mountains ; Transylvania ; etc. 
 
 In the United States it is found at various places along the Appa- 
 lachian Mountains, especially at Litchfield, Me. ; Henderson, Iredell, and 
 Buncombe counties, N. C. The occurrence at Zirconia, Henderson Co., N. 
 
8o 
 
 DESCRIPTIVE MINERALOGY 
 
 C., is the only one of commercial importance in the United States. In 
 1903 this locality produced 3,000 pounds of zircon valued at $570. 
 
 Zircon is used principally as a source of zirconia, ZrO 2 , which finds 
 limited use in the manufacture of the Nernst lamp glowers. The hyacinth 
 varieties are cut for gem purposes. Zircon is also used in the manufacture 
 of extremely delicate and sensitive balances and physical apparatus. 
 
 Thorite, Orangite, ThSiO 4 . 
 
 Tetragonal, ditetragonal bipyramidal class, a : c = i : 0.6402. Crys- 
 tals are similar to those of zircon. Usually compact and disseminated. 
 Conchoidal fracture. Vitreous luster. The term thorite is applied to the 
 more or less opaque, dark brown, or black varieties, while the transparent 
 or translucent yellow or orange variety is called orangite. The specific 
 gravity of thorite is 4.4 to 4.7 while that of orangite is 5.19 to 5.40. 
 
 ThSiO 4 . Usually more or less impure. Often contains 7 to 10% of 
 water and small amounts of the oxides of calcium, iron, manganese, uran- 
 ium, and the rare earths. Thorite is believed to be decomposed orangite. 
 Some thorites show a nucleus of fresh orangite. 
 
 Occurs in the pegmatites at Brevik, also at Arendal, Norway. 
 
 A source of thorium compounds. 
 
 CASSITERITE, Tin Stone, Stream Tin, Tin Ore, SnSnO 4 . 
 
 Tetragonal, ditetragonal bipyramidal class, a : c = I : 0.6723. Usually 
 short, thick prismatic crystals, showing the prisms (m and 01) and the unit 
 bipyramids (s and e) of the first and second orders in combination, Figure 
 
 FIG. 47. 
 
 FIG. 48. 
 
 47. Sometimes pyramidal habit. Contact and penetration twins very com- 
 mon. Twinning plane parallel to a face of the unit bipyramid of the second 
 order (e). Figure 48 shows a "knee-shaped" contact twin according to 
 
OXIDES 8 1 
 
 the above law. Also compact and disseminated, reniform, granular, mas- 
 sive, and in rounded grains and pebbles. Concentric and fibrous radial 
 structure is commonly observed. 
 
 Imperfect prismatic cleavages. Brittle. Hardness 6 to 7. Specific 
 gravity 6.8 to 7. Adamantine luster, on fracture surface greasy to resinous. 
 Transparent to translucent. Commonly reddish brown, brownish black or 
 pitch black ; sometimes red, gray, white or yellow, and rarely colorless. 
 Streak is white to pale brown. Optically positive. High indices of refrac- 
 tion : o Na = i .9966, e Na = 2.0934. 
 
 Several varieties of cassiterite may be distinguished, as follows : 
 
 (1) Ordinary cassiterite or tin stone. Crystals and compact masses. 
 
 (2) Wood tin. Botryoidal and reniform masses of varying colors, 
 showing an internal radial fibrous structure. 
 
 (3) Stream tin. Angular and rounded grains or pebbles in secondary 
 deposits. 
 
 Sn 2 O 4 , sometimes written SnO 2 . Usually contains a little iron, man- 
 ganese, silica, and tantalum. Infusible. Yields with difficulty on charcoal 
 a tin coating. Insoluble in acids. 
 
 Cassiterite is commonly associated with wolframite, native bismuth, 
 arsenopyrite, molybdenite, scheelite, stannite, chalcopyrite, hematite, chal- 
 cocite, magnetite, etc. The minerals found in the gangue include tourmaline, 
 topaz, fluorite, apatite, quartz, and zinnwaldite. 
 
 Cassiterite generally occurs in veins cutting granites and eruptive rocks, 
 such as liparites and trachytes. The country rocks adjoining such veins 
 are usually greatly altered and generally show impregnation's of cassiterite 
 Granitic rocks altered in this way are termed greisen, while non-granitic 
 rocks are called zuntter. Deposits of cassiterite are usually considered to 
 be the result of pneumatolytic action. This involves the escape of gases 
 and volatile substances (boron, chlorine, and fluorine), and subsequent action 
 on the country rocks. On account of its great resistance to weathering, cas- 
 siterite is also found extensively in secondary deposits. 
 
 Occurs in Cornwall, England ; Altenberg, Saxony ; Joachimsthal, Bo- 
 hemia ; Sweden ; Malay Peninsula of Malacca ; the islands of Banca and 
 Billiton near Borneo ; Tasmania ; Bolivia ; Mexico ; Australia, and China. 
 
 The deposits in the Black Hills of South Dakota and the Harney Peak 
 and Nigger Hill districts of Wyoming are the most important in the United 
 States. Other occurrences are at Gaffney, S. C. ; Kings Mountains, N. C. : 
 
82 DESCRIPTIVE MINERALOGY 
 
 San Bernardino Co., Cal. ; Rockbridge, Va. ; Coosa Co., Ala. ; El Paso, Texas ; 
 Dillon, Montana; and Buck Creek, Alaska. 
 
 The most important tin ore. There is practically no cassiterite mined 
 in the United States. The world's supply is obtained principally from the 
 East Indies, Australia, Bolivia, and Cornwall, England. 
 
 PLATTNERITE, PbPbCX Tetragonal, ditetragonal bipyramidal class, a : c = i : 
 0.6764. Usually massive. Crystals are very rare. Hardness 5 to 5.5. Specific gravity 
 8.5 to 9.4. Uneven fracture. Iron black in color. Soluble in acids. Streak brown. 
 Opaque. Submetallic luster. Fuses easily, yielding a globule of lead. Occurs at 
 Leadhills, Scotland; Mullan, Idaho. 
 
 POLIANITE, MnMnO 4 . Tetragonal, ditetragonal bipyramidal class, a : c = i : 
 0.6647. Short thick quadratic crystals. Apparently orthorhombic. Crystals are 
 often very small and poorly developed. Usually in compact, granular and fibrous 
 masses. Sometimes reniform. Steel gray in color. Streak grayish black. Hardness 
 6 to 6.5. Specific gravity 4.8 to 5. Occurs with manganite and pyrolusite. Often 
 as a pseudomorph after manganite. Changes to pyrolusite. Found at Flatten and 
 Schneeberg, Saxony; Johanngeorgenstadt, Bohemia; Cornwall, England. 
 
 PYROLUSITE, Black Oxide of Manganese, MnO 2 . 
 
 Pseudomorphous after various manganese minerals, hence, often has 
 the crystal form of manganite. It is commonly found compact, fibrous, 
 massive, stalactitic, dendritic, etc. 
 
 Hardness i to 2.5, soils the fingers. Specific gravity 4.7 to 4.86. Black 
 or bluish black. streak. Black, dark steel gray, or bluish in color. Opaque. 
 
 MnO 2 . Usually with small percentages of water and silica. Py- 
 rolusite is not considered an independent species. Infusible, turns 
 brown when heated. Heated in a closed tube, yields oxygen and water. 
 Reacts for manganese in borax bead. Acted upon by hydrochloric acid 
 evolving chlorine. Is formed from manganite, alabandite, rhodocrosite, 
 manganiferous siderite and limonite, etc. Excellent pseudomorphs after 
 manganite, and calcite are sometimes observed. Is commonly found with 
 manganite, psilomelane, hematite, or limonite. 
 
 Occurs extensively in Thuringia and the Hartz Mountains, Germany; 
 Bohemia ; France ; Hungary ; Brazil ; Russia. 
 
 The principal localities in the United States are Crimora district, Au- 
 gusta Co., Va. ; Cave Spring and Cartersville, Ga. ; Batesville, Ark. ; and 
 Livermore, Alameda Co., Cal. ; Brandon, Vt. 
 
OXIDES 83 
 
 In 1905 Virginia produced 3,947 long tons which was practically all of 
 the output of the United States for that year. Considerable quantities are 
 imported annually from Brazil, Russia, Cuba, and Germany. 
 
 Pyrolusite is used in the manufacture of chlorine, bromine, oxygen, and 
 spiegeleisen ; as a coloring agent in calico-printing and dyeing, glass, pot- 
 tery, "brick, and paints, and as a decolorizer of green glass. 
 
 ZINCITE GROUP 
 
 This group includes the oxides of cadmium, zinc, manganese, mag- 
 nesium, and nickel. There are two series, one of which is cubic and the 
 other hexagonal. The most important member of the cubic series is periclase, 
 
 CUBIC SERIES 
 
 PERICLASE, MgO. Hexoctahedral Class 
 
 MANGANOSITE, MnO. Hexoctahedral Class 
 
 BUNSENITE, NiO. Hexoctahedral Class 
 
 OXIDE of CADMIUM, CdO. Hexoctahedral Class 
 
 HEXAGONAL SERIES 
 
 a : c 
 Zincite, ZnO. Dihexagonal Pyramidal Class i : 1.6219 
 
 This group is similar to the sphalerite-wurztite group of the sulphides, 
 see page 32. 
 
 PERICLASE, MgO. Cubic. Very small cubical and octahedral crystals. Also 
 in grains. Perfect cubical cleavage. Hardness 6. Specific gravity 3.67 to 3.9. Trans- 
 parent. Greenish gray to dark green in color. Vitreous luster. Infusible. Powder 
 soluble in acid. Occurs at Mt. Somma, Vesuvius ; Nordmark, Sweden. 
 
 MANGANOSITE, MnO. Cubic. Extremely small octahedral crystals and compact 
 masses with cubical cleavage. On fresh fracture surface the color is emerald green, 
 which on exposure turns black. Hardness 5 to 6. Specific gravity 5.2. Occurs with 
 periclase at Nordmark, Sweden. 
 
 BUNSENITE, NiO. Cubic. Very small octahedral crystals possessing a hardness 
 of 5.5 and a specific gravity of 6.4. Translucent. Green in color. Vitreous luster. 
 Slightly acted upon by acids. Found with annabergite and native bismuth at Johann- 
 geqrgenstadt, Bohemia. 
 
 CADMIUM OXIDE, CdO. Cubic. Usually occurs as a shiny, black coating con- 
 sisting of octahedrons on hemimorphite at Iglesias, Sardinia. 
 
8 4 
 
 DESCRIPTIVE MINERALOGY 
 
 Zincite, Red Zinc Ore, Red Oxide of Zinc, ZnO. 
 
 Hexagonal, dihexagonal pyramidal class, a : c I : 1.6219. Nat- 
 ural crystals are rare. Frequently, however, formed in metallurgical pro- 
 cesses. Such crystals consist of a pyramid, prism, 
 and basal pinacoid, see Figure 49. Usually as com- 
 pact, granular or foliated masses. 
 
 Perfect basal cleavage. Brittle. Conchoidal 
 fracture. Hardness 4 to 4.5. Specific gravity 5.4 
 to 5.7. Subadamantine luster. Blood to hyacinth 
 red in color, also orange, or yellow. Streak red- 
 dish yellow. Translucent. 
 
 ZnO, may contain as high as 4% of mangan- 
 ese, also small amounts of iron. Infusible. Yields 
 on charcoal a zinc coating and imparts an ame- 
 
 FIG. 49. 
 
 thystine color to the borax bead. Soluble in acids. 
 
 Occurs extensively in Sussex County, New Jersey, in metamorphic 
 limestones of precambrian age associated with franklinite, rhodonite, spha- 
 lerite, rhodocrosite, calcite, hemimorphite, etc. It is an important ore of 
 zinc. 
 
 HEMATITE GROUP 
 
 This group includes the two very important economic minerals, corun- 
 dum and hematite. These are the sesquioxides of aluminium and iron, 
 respectively. They crystallize in the hexagonal system. 
 
 a : c 
 
 CORUNDUM, A1 2 O 3 . Ditrigonal Scalenohedral Class i : 1.364 
 
 HEMATITE, Fe 2 O 3 . Ditrigonal Scalenohedral Class i : 1.359 
 
 Of these minerals hematite is by far the more important, commercially. 
 
 FIG. 50. 
 
 FIG. 51. 
 
 CORUNDUM, Sapphire, Ruby, Emery, A1 2 O 3 . 
 
 Hexagonal, ditrigonal Scalenohedral class, a : c=i : 1.364. Well 
 developed crystals, often rather large, are common. The habit may be pyra- 
 midal, rhombohedral (Figure 50), prismatic (Figure 51), or tabular. 
 The common forms are the prism of the second order (/), unit rhombohe- 
 dron (r), bipyramid of the second order (n) with in equal to 4/3, and 
 
OXIDES 85 
 
 the basal pinacoid (d). Often several modified bipyramids of the second 
 order are present and then the crystals assume a more or less barrel shape. 
 Large crystals are sometimes rough and rounded. Penetration and poly- 
 synthetic twins with the twinning plane parallel to the unit rhombohedron. 
 The basal pinacoid often shows triangular striations. Also occurs massive 
 with, a nearly rectangular parting or pseudo-cleavage. 
 
 Conchoidal fracture. Rhombohedral and basal partings. The hard- 
 ness is 9. Specific gravity 3.9 to 4.1. Colorless, blue, red, brown, yellow, 
 violet, et,c. Sometimes multicolored. Transparent to translucent, or vitreous 
 luster. Optically negative, OJ L . 1.769, ^ u = 1.760. 
 
 ALO.j. Crystals are usually quite pure. Small amounts of ferric oxide 
 may be present as a pigment. Emery generally contains considerable mag- 
 netite, Fe^. 
 
 Three varieties may be distinguished, as follows : 
 
 (1) Sapphire and ruby: This is the gem variety and includes the 
 beautifully colored, transparent stones. If blue it is the sapphire; red, the 
 ruby; green, the oriental emerald; yellow, the oriental topaz; and violet, 
 the oriental amethyst. 
 
 (2) Corundum or adamantine spar. Here are placed crystals and 
 masses with dull colors, usually blue, gray, red, brown, or black. 
 
 (3) Emery. This is a mixture of corundum, magnetite, hematite, and 
 quartz. It was first considered an iron ore. The admixture may be as high 
 as 40%. The hardness is, hence, considerably lower than that of the other 
 varieties. Dark gray to black in color. 
 
 Corundum occurs usually disseminated in crystalline limestone and 
 dolomite, gneiss, mica schist, chlorite schist, peridotite, granite, nepheline 
 syenite, gabbro, norite, etc. 
 
 The gem varieties are found principally in placer deposits in Ceylon, 
 Burma, Hindustan, Siam, China, Ural Mountains; also near Helena, Mon- 
 tana, and in North Carolina. Rubies of a fine and clear quality are very 
 expensive, being worth as much as $1,500 per carat. Sapphires are less 
 expensive, a one carat stone costing anywhere from $6 to $125, depending 
 upon the quality. 
 
 Corundum proper is found in extensive deposits associated with perido- 
 tite in North and South Carolina, and Georgia ; at Raglan and elsewhere in 
 Renfrew county, Ontario, in nepheline syenite ; also in Westchester county, 
 New York ; Chester county, Pennsylvania ; and Chester, Massachusetts. 
 
 Most of the world's supply of emery is obtained from the islands of 
 Naxos and Samos in the Grecian archipelago and from Asia Minor. On 
 Naxos and Samos it occurs in crystalline limestones and schists. It is also 
 found in the Ural Mountains and Saxony. 
 
86 
 
 DESCRIPTIVE MINERALOGY 
 
 In the United States, Chester, Mass., and Peekskill, N. Y., are the 
 only localities producing emery. At Chester, Mass., the emery occurs in 
 amphibolite schists associated with chlorite and margarite ; at Peekskill, 
 N. Y., in peridotite. 
 
 Sapphire and ruby are used extensively for gem purposes and as watch 
 jewels ; massive corundum and emery as abrasives. 
 
 HEMATITE, Specularite, Specular Iron Ore, Red Iron Ore, Fe 2 O 3 . 
 
 Hexagonal, ditrigonal scalenohedral class, a : c=i : 1.359. Crys- 
 tals are rather common, either pyramidal, thin or thick tabular, rhombo- 
 
 hedral, or more rarely prismatic in development. 
 Figure 52 shows a combination in which (r) is 
 the unit rhombohedron, (r') the modified rhom- 
 bohedron with the coefficient m equal to 1/4, 
 and (/>) the hexagonal bipyramid of the second 
 order with m equal to 4/3. A comparatively 
 large number of forms has been observed on 
 . hematite. Tabular crystals are often arranged 
 parallel or in rosettes and are then called "iron 
 roses." Two twinning laws have been noted, (i) Twinning plane parallel 
 to the basal pinacoid. (2) The unit rhombohedron acts as the twinning 
 plane. This law is not common. The basal pinacoid is sometimes striated, 
 due to polysynthetic twinning according to the second law. Occurs more 
 abundantly in compact, granular, micaceous, earthy, columnar, fibrous, bot- 
 ryoidal, reniform, and stalactitic masses. 
 
 No cleavage. Owing to polysynthetic twinning some crystals show 
 a perfect parting parallel to the unit rhombohedron. Conchoidal to uneven 
 fracture. Hardness 5.5 to 6.5, earthy varieties are very soft. Specific 
 gravity 4.9 to 5.3, crystals usually about 5.25. The luster is metallic, splen- 
 dent, or dull. Opaque, except in very thin scales. Steel gray to iron black 
 in color, sometimes with beautiful tarnish colors. Thin scales are blood 
 red to yellow red in transmitted light. The earthy variety is red in color. 
 The streak is cherry red or reddish brown. Sometimes slightly magnetic 
 owing to the presence of a small amount of magnetite, Fe 3 O 4 . 
 
 Fe 2 O 3 . May contain as high as 7% of titanium dioxide, also ferrous 
 oxide, magnesium oxide, phosphoric acid, silica, clay, etc. Infusible. 
 Heated on charcoal it becomes magnetic. Powder is slowly soluble in acids. 
 Occurs as a pseudomorph after calcite, siderite, pyrite, and magnetite. 
 There are several varieties of hematite: 
 (i) Specularite or specular iron ore. This includes crystals, mica- 
 
OXIDES 87 
 
 ceous, and granular masses with a metallic or splendent luster. Usually 
 dark steel gray or black in color. 
 
 (2) Compact or red hematite. Massive. Submetallic to dull luster 
 Iron black or brownish red in color. Often shows radial fibrous structure. 
 Also reniform. 
 
 (3) Red ochcr, reddle, or red clay. A red earthy variety. Very 
 soft. Dull luster. Usually contains considerable clay. 
 
 (4) Argillaceous hematite, red clay ironstone. Hard, and compact. 
 Brownish black, reddish brown, or deep red in color. Contains much clay, 
 sand, jasper, etc. 
 
 (5) Oolitic iron ore. Hematite with oolitic structure. Often fossil- 
 iferous. 
 
 (6) Martitc. Hematite occurring in octahedrons as a pseudomorph 
 after magnetite. 
 
 Hematite is the most important iron ore. It occurs ( I ) as independent 
 deposits, sometimes of great thickness and extent, in rocks of varying ages. 
 (2) As an accessory mineral in many of the igneous rocks such as gran- 
 ites, syenites, etc. (3) In cracks and crevices, usually with quartz. 
 (4) As an inclusion in many minerals, for example, feldspar, heulandite, 
 and carnallite. (5) As a sublimation product in lavas. Thus on Vesuvius, 
 Aetna, etc. (6) Sometimes the result of contact metamorphism. 
 
 Excellent crystals occur on the island of Elba in the Mediterranean 
 Sea; Binnenthal, Tavetsch, and St. Gotthard (iron roses), Switzerland; 
 Arendal, Norway ; Langban and Nordmark, Sweden. 
 
 Enormous deposits of hematite occur in the rocks, chiefly of Huronian 
 and Archean age, in the Lake Superior region of Northern Michigan, Wis- 
 consin, Minnesota, and Canada. Six ranges or districts may be mentioned, 
 viz : Marquettc in Michigan, Mcnomince and Gogcbic in Michigan and 
 Wisconsin, Mesabi and Vermilion in Minnesota, and the Michipicoten in 
 Ontario, Canada. In 1907 this region* produced 41,638,744 long tons of 
 hematite ore which contained from about 45 to 60% of iron and 9 to 13% 
 moisture. Oolitic hematite is found in beds of considerable thickness in 
 the Clinton formation of Lower Silurian age. At Clinton, N. Y., and Bir- 
 mingham and vicinity in Alabama large quantities of this variety of hematite 
 are mined annually. Oolitic hematite is also found in Pennsylvania, Wis- 
 consin, and Canada. Martite occurs in Saxony, Brazil, and in the Ural 
 Mountains; also in the Marquette iron district, Michigan; Millard Co., 
 Utah; Monroe Co., N. Y. ; Chittenden, Digby Co., Nova Scotia; and Mexico. 
 
 * Not including the Michipicoten district. 
 
88 DESCRIPTIVE MINERALOGY 
 
 Hematite is mined in a comparatively large number of states as is 
 shown by the following table giving the production for 1907 : 
 
 Minnesota 28,969,658 long tons 
 
 Michigan 1 1,830,342 long tons 
 
 Alabama 3,144,01 1 long tons 
 
 Wisconsin 804,454 long tons 
 
 Montana, Nevada, New Mexico, 
 
 Utah, and Wyoming 608,056 long tons 
 
 Tennessee 269,182 long tons 
 
 New York 140,101 long tons 
 
 Georgia 106,885 lon g tons 
 
 Virginia 89,867 long tons 
 
 Missouri 4 2 5 2 7 l n g tons 
 
 Kentucky, Maryland, West Virginia 36,000 long tons 
 Pennsylvania 19,403 long tons 
 
 Total 46,060,486 long tons 
 
 Hematite is the chief source of the iron of commerce. About 90% of 
 the iron ore mined annually is hematite. 
 
 CUPRITE GROUP 
 
 The oxides of lead and copper are placed here. No definite relation- 
 ship between the members of this group has, as yet, been pointed out. 
 
 a : b : c 
 
 MASSICOT, PbO. Orthorhombic, Bipyramidal Class 0.6706 : i : 0.9764 
 CUPRITE, Cu 2 O. Cubic, Pentagonal Icositetrahedral Class. 
 
 a : c 
 PARAMEI.ACONITE, CuO. Tetragonal, Bipyramidal Class I : 1.6534 
 
 a : b : c 
 
 MELACONITE, CuO. Monoclinic, Prismatic Class i : 0.6711 : 0.9129, 
 ( Tenorite} ft = 99 32'. 
 
 Cuprite is the most important mineral of this group. 
 
 MASSICOT, PbO. Natural crystals have not been observed. Found as scaly 
 earthy, and compact masses. Artificial crystals are orthorhombic. Yellowish or red- 
 dish in color. Greasy luster. Occurs in Mexico. Rare. 
 
 CUPRITE, Ruby Copper Ore, Red Oxide of Copper, Cu 2 O. 
 
 Cubic, pentagonal icositetrahedral class. Crystals are common. The 
 octahedron and rhombic dodecahedron are the most common forms. They 
 occur either independently or in combination. Other forms are the cube, 
 
OXIDES 89 
 
 trigonal and tetragonal tristoctahedrons (m = 2). The pentagonal icosi- 
 tetrahedron is sometimes observed. Also compact, granular, earthy, and 
 in fine, slender crystal-aggregates (chalcotrichite}. 
 
 Octahedral cleavage, not very pronounced. Conchoidal to uneven frac- 
 ture. Brittle. Hardness 3.5 to 4. Specific gravity 5.7 to 6.15. Metallic 
 adamantine luster on crystal and fresh fracture surfaces, also submetallic 
 or earthy. Cochineal red to almost black. A brick red, earthy variety which 
 is sometimes mixed with hematite or limonite, is called tile ore. Semi- 
 transparent to almost opaque. Streak brownish red to dirty brown, shiny. 
 The streak of chalcotrichite is carmine red. High index of refraction : 
 
 Cu 2 O. Usually quite pure. Colors flame green. Heated on charcoal 
 turns black and yields easily a globule of copper. Soluble in acids and am- 
 monium hydroxide. Alters readily to malachite, azurite, tenorite, or cop- 
 per. Pseudomorphs of malachite after cuprite are quite common. 
 
 Cuprite is usually the result of the oxidation of copper minerals. It 
 occurs at Chessy, France, in large crystals sometimes partially or completely 
 altered to malachite ; also at Cornwall, England ; Dobschau, Hungary ; Chile : 
 Peru ; Bolilia ; Southern Australia ; Ural Mountains ; etc. 
 
 In the United States it is found with other copper minerals at Bisbee, 
 Clifton, and elsewhere in Arizona; Sommerville, N. J. ; Lebanon Co., Pa.; 
 Lake Superior Copper district. 
 
 An important ore of copper. 
 
 PARAMELACONITE, CuO. Tetragonal. Occurs in horizontally striated pyramidal 
 crystals. No cleavage. Hardness 5. Specific gravity 5.83. Brilliant luster. On 
 crystal faces is purplish black in color, on fracture surfaces pitch black. Found at 
 the Copper Queen mine, Arizona. 
 
 u, Tenorite, CuO. 
 
 Monoclinic. Small, scaly crystals of apparently hexagonal outline occur on 
 Vesuvius. Commonly found as a coating on copper minerals. Also massive. Steel 
 gray to black in color. The crystals are termed tenorite, the earthy masses melaconite. 
 Specific gravity of the crystals is 5.82, of the masses 6.25. Hardness 3 to 4. Occurs 
 with native copper in the Lake Superior Copper district ; Ducktown, Tenn. ; and ia 
 various copper mines in Arizona. 
 
 2. HYDROXIDES 
 
 OPAL, SiCX, x H 2 O. 
 
 Amorphous. Usually occurs compact, in veins or masses of irregular- 
 outline. Sometimes stalactitic or reniform. Also loose and more or less, 
 earthy. 
 
QO DESCRIPTIVE MINERALOGY 
 
 Conchoidal fracture is very characteristic. Hardness 5.5 to 6.5, but 
 in earthy varieties may be as low as I. Specific gravity 2.1 to 2.3, when 
 pure 2.15 to 2.2. Vitreous, dull, or greasy luster. Transparent to opaque. 
 Streak white. The color varies greatly, may be white, yellow, brown, red, 
 green, gray, etc. Often a play of colors is to be observed. This is due to 
 fine cracks filled with material possessing a slightly different index of re- 
 fraction than the original substance, and perhaps also to an unequal distri- 
 bution of the water content. Low index of refraction, n u = 1.4347 to 
 1.4555. Sometimes shows anomalous double refraction. 
 
 SiO.,.x H 2 O. The amount of water may vary from i to 21%, is, how- 
 ever, usually between 3 and 13%. May also contain small amounts of the 
 oxides of calcium, iron, magnesium, aluminium, and sodium, as well as 
 bitumen, etc. Many opals are to be considered as dried and hardened gel- 
 atinous silica. Yields water when heated in a closed tube. Infusible. Sol- 
 uble in hot caustic potash or soda. 
 
 There are several varieties of opal : 
 
 - : . c 
 
 (1) Precious opal. Usually bluish or yellowish white in color with 
 excellent play of colors. Used as a gem. 
 
 (2) Fire opal. Yellow to red in color. Semi-transparent. 
 
 (3) Common opal. Translucent to opaque. Shows many colors 
 When milk-white, yellowish, bluish, or greenish it is called milk opal ; with 
 a resinous luster and either wax, honey, or ocher yellow in color, it is 
 resin opal. Wood petrified by opaline material is called wood opal. Prec- 
 ious opal which has become cloudy and white by the loss of water is 
 termed hydrophane. 
 
 (4) Opal jasper is red, reddish brown, or brownish yellow. It pos- 
 sesses a resinous luster. Resembles jasper. 
 
 (5) Hyalite. Colorless and transparent masses of irregular outline. 
 Looks like drops of molten glass. 
 
 (6) Silicious sinter, Geyserite, Fiorite. These include the opaline 
 material deposited from the waters of hot springs. May be porous, com- 
 pact, fibrous, stalactitic, botryoidal, etc. Transparent to opaque. Grayish, 
 whitish, or brown in color. Sometimes has a pearly luster. 
 
 (7) Tripolitc, Diatomaceous or infusorial earth. Consists of the sil- 
 icious remains of diatoms, radiolaria, etc. Is usually porous, earthy, and 
 chalk-like in appearance. Light in weight. 
 
 Opal may result (i) from the decomposition of silicate minerals and is 
 then found in cracks and cavities in such igneous rocks as trachytes, por- 
 phyries, etc. (2) As a deposit from hot springs. (3) By the accumulation 
 of hard, silicious remains of various microscopic organisms. (4) By the 
 
OXIDES 91 
 
 accumulation, partial solution and subsequent sodification of silicious matter 
 derived from radiolaria, infusoria, sponge spicules, etc. 
 
 Precious opal occurs in decomposed trachyte at Czerwenitza, Hungary ; 
 Queretaro and Zimapan, Mexico ; Gem City, and Morrow Co., Washington ; 
 .Opaline, and Latah Co., Utah, etc. Hyalite occurs at Schemnitz, Hun- 
 gary; Bohemia; Mexico; also in New Jersey, and Connecticut. Common 
 opal is rather abundant in Pennsylvania, Idaho, Colorado, California, etc. 
 Geyserite is found in the Yellowstone Park and silicious sinter at the Steam- 
 boat Springs, Nevada. Infusorial earth occurs in considerable deposits at 
 Dunkirk, Md. ; Richmond, Va. ; Drakesville, N. J. ; Socorro, N. M. ; also 
 in California, Missouri, New York, Georgia, Connecticut, etc., etc. In 
 1907 the production of infusorial earth in the United States was valued at 
 $104,406. 
 
 Precious and fire opals are used for gem purposes ; wood opal for orna- 
 mental purposes. Infusorial earth is used largely in polishing powders, 
 scouring soaps, as an absorbent of nitroglycerine, a non-conductor of heat, 
 in fire-proof cement, soluble glass, water filters, and as an adulterant of 
 flour. 
 
 SASSOLITE GROUP 
 
 On account of their striking chemical similarity sassolite and gibbsite 
 are sometimes considered isomorphous even though they do not crystallize 
 in the same system. 
 
 SASSOLITE, B(OH) 3 . Triclinic, Pinacoidal Class 
 
 a : b : c a. /8 y 
 
 1.7329 : i : 0.9228 923o' IO425' 8949' 
 Gibbsite, A1(OH) 3 . Monoclinic, Prismatic Class 
 
 1.7089 : i : 1.9184 943i' 
 
 SASSOLITE, Boric Acid, B(OH) 3 . 
 
 Triclinic, pinacoidal class. Usually in fine scaly or fibrous, crytsals having a 
 prism angle of n89'. Sometimes stalactitic. May be colorless, white, or yellow. 
 Pearly luster. Greasy feel. Hardness i. Specific gravity 1.45. Sour taste. Reacts 
 for boron. Soluble in water. 
 
 Occurs as a sublimation product on the island of Vulcano in the Mediterranean 
 Sea; in the vapors escaping from the hot springs in Tuscany; also at Clear Lake, 
 California. 
 
 A source of boric acid and borax. Large quantities are obtained from the hot 
 springs' of Tuscany. The escaping vapors are conducted into water. The boric acid 
 is absorbed and sassolite deposited. Boric acid is used as an antiseptic, preservative 
 of food, in the manufacture of enamels and glazes for pottery, etc. 
 
92 DESCRIPTIVE MINERALOGY 
 
 Gibbsite, Hydrargillite, A1(OH) 3 . 
 
 Monoclinic, prismatic class. Rarely in tabular crystals with an hexa- 
 gonal outline. Usually stalactitic and mammillary. Surface is generally 
 smooth. Internal structure usually fibrous. Basal cleavage. White, gray- 
 ish, greenish, or reddish in color. Hardness 2.5. Specific gravity 2.3 to 1 
 2.4. Pearly to vitreous luster. Translucent, crystals are sometimes trans- 
 parent. Streak white. Argillaceous odor when breathed upon. 
 
 Infusible. Reacts for aluminium with cobalt solution. Soluble in hy- 
 drochloric or sulphuric acids. Yields water in a closed tube. 
 
 Gibbsite is of limited occurrence. It is usually found with bauxite, 
 thus in Saline and Pulaski counties, Arkansas ; also in Floyd, Bartow, and 
 Walker counties, Georgia. With limonite in Dutchess and Orange coun- 
 ties, New York. 
 
 MANGANITE GROUP 
 
 The hydroxides of aluminium, iron, and manganese, which conform 
 to the general formula M'"O.OH, are placed here. These minerals crys- 
 tallize in the orthorhombic bipyramidal class. 
 
 a : b : c 
 
 Diaspora, A1O.OH. 0.9372 : i : 0.6038 
 
 MANGANITE, MnO.OH. 0.8439 : i : 0.5447 
 
 GOETHITE, FeO.OH. 0.9163 : i : 0.6008 
 
 A comparison of the ordinary axial ratios of these minerals shows con- 
 siderable variation. However, on account of the similarity of form, cleav- 
 age, etc., diaspore, manganite, and goethite are to be considered isomorph- 
 ous. The topical axes show a much closer agreement than is noted above.* 
 
 Diaspore, A1O.OH. 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.9372 : i : 0.6038. Broad 
 columnar and tabular crystals. Flattened parallel to the brachypinacoid. 
 Vertically striated. Crystals not common. Usually in thin scaly and broad 
 fibrous aggregates. 
 
 Perfect brachypinacoidal cleavage. Brittle. Hardness 6 to 7. Specific 
 gravity 3.3 to 3.5. Colorless, pale yellow, violet blue, and brown. Pearly 
 luster on cleavage surfaces, otherwise vitreous. Transparent to translucent. 
 Excellent trichroism. 
 
 A1O.OH. In closed tube yields water. Gives a blue color when heated 
 with cobalt solution. Infusible. After strong ignition it is rendered solu- 
 ble in sulphuric acid. 
 
 * Kraus and Mez, Ueber Topischen Axenverhaltnisse, Zeitschrift fur Krystal- 
 lographie, etc., 1901, 34, 389 to 396. 
 
OXIDES 93 
 
 Commonly found with corundum or emery, dolomite, cyanite. mar- 
 garite, etc. Occurs at Schemnitz, Hungary ; Ural Mountains ; various 
 places in Tyrol ; on the island of Naxos, Grecian archipelago ; Chester, Mass. ; 
 Unionville, Pa. ; Franklin, Macon Co., N. C., etc. Not very common. 
 
 MANGANITE, MnO.OH. 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.8439 : l ' -5447- Com- 
 monly as long or short prismatic crystals. Often with deep vertical stria- 
 tions. Sometimes arranged in groups or bundles. The forms usually ob- 
 served are the unit prism, unil macrodome, and the basal pinacoid. A com- 
 paratively large number of forms has been observed. Also radiated and 
 columnar. Rarely granular or stalactitic. 
 
 Perfect brachypinacoidal cleavage. Uneven fracture. Brittle. Hard- 
 ness 3.5 to 4. Specific gravity 4.2 to 4.4. When fresh, manganite possesses 
 a submetallic luster, an iron black color, and reddish brown to brown black 
 streak. If more or less decomposed, it is steel gray in color with a black 
 streak and metallic luster. 
 
 MnO.OH. Yields water when heated above 200 C. * Reacts for man- 
 ganese with borax bead. Soluble in concentrated hydrochloric acid with an 
 evolution of chlorine. Occurs as a pseudomorph after calcite. 
 
 Alters easily to pyrolusite and, hence, is not often found fresh. Com- 
 monly associated with barite, calcite, siderite, pyrolusite and other man- 
 ganese minerals. Excellent crystals at Ilfeld, Hartz Mountains ; Ilmenau, 
 Thuringia ; Wittichen in the Black Forest, Baden ; Jackson mine, Marquette 
 Co., Mich. ; Douglas Co., Colo. ; various places in Nova Scotia and New 
 Brunswick. 
 
 With pyrolusite it is used in the preparation of oxygen and chlorine, 
 
 GOETHITE, FeO.OH. 
 
 Orthorhombic, bipyramidal class, a : b : c 0.9163 : i : 0.6008. Crys- 
 tals are generally small. May be prismatic, needle-like, tabular, or scaly. 
 The most commonly observed forms are the unit and macro- (n = 2) prisms, 
 brachy, macro and basal pinacoids, macrodome (w = 4), and the unit and 
 macro (w = 2) bipyramids. Also occurs in scaly, fibrous and velvety crusts. 
 Massive and stalactitic. Perfect brachypinacoidal cleavage. Hardness 5 
 to 5.5. Specific gravity 4 to 4.4. Subadamantine luster. Color yellow, red, 
 dark brown, or nearly black. Streak yellow or yellow brown. 
 
 FeO.OH. Usually contains some silica and manganese. On heating 
 yields water. Soluble in hydrochloric acid. Thin splinters fuse to a black 
 magnetic mass. Pseudomorphs after pyrite. Alters to limonite or hema- 
 tite. Generally found with hematite or limonite. Commercially, it is classed 
 with limonite under the heading of brown hematite. It is of comparatively 
 limited occurrence. Found at Pribram, Hungary ; Siegen, Nassau, Ger- 
 many ; Cornwall, England ; Negaunee, Mich. ; Easton, Pa. ; Pike's Peak 
 district, Colo. ; various places in Minnesota. 
 
 Used as an ore of iron. 
 
94 DESCRIPTIVE MINERALOGY 
 
 BAUXITE GROUP 
 
 Here are placed the hydroxides conforming to the formula 
 M /r/ 2 O(OH) 4 in which the metal may be aluminium, iron, cobalt, or nickel. 
 The members of this group do not occur crystallized. 
 
 BAUXITE, A1 2 O(OH) 4 . 
 
 XANTHOSIDERITE, Fe 2 O(OH) 4 . 
 
 WlNKLERITE, (Co,Ni) 2 O(OH) 4 . . . 
 
 BAUXITE, Beauxite, A1 2 O(OH) 4 . 
 
 Crystallization unknown. Usually massive, pisolitic or oolitic, also 
 earthy resembling clay. Sometimes disseminated in concretionary grains. 
 
 May be white, brown, yellow, or reddish. The color is often irregu- 
 larly distributed. Hardness I to 3. Specific gravity 2.55. Argillaceous 
 odor. Variable s'treak. 
 
 A1,,O(OH) 4 . In general the composition varies greatly, showing about 
 50 to 70% of aluminium oxide, 3 to 35% ferric oxide, 12 to 40% water, 2 
 to 30% silica, 3% titanium oxide, also carbon dioxide, phosphoric acid, 
 manganese, etc. Infusible. Yields water in a closed tube. Heated with 
 cobalt solution it turns blue. Soluble with difficulty in hydrochloric acid. 
 
 Bauxite has resulted from the decomposition of feldspathic rocks, such 
 as granites, gneisses, diorites, basalts, etc. It is the principal constituent of 
 laterite, which is quite abundant in tropical regions. Also found in nodules, 
 grains, and in pockets of irregular shape in limestones and dolomites. Such 
 occurrences are thought to be the result of deposition, perhaps from hot 
 solutions. 
 
 Important deposits occur at Baux, near Aries, France ; Vogelsberg, 
 Nassau, Germany; also in Carniola and Ireland. In the United States large 
 deposits are found in a belt extending from Jacksonville, Alabama to Car- 
 tersville, Georgia ; Pulaski and Saline counties, Arkansas ; and near Silver 
 City, New Mexico. In 1907 the United States produced 97,776 long tons 
 of bauxite valued at $480,330. 
 
 Bauxite is used in the manufacture of aluminium, alum, and various 
 refractory products. 
 
 XANTHOSIDERITE, FeO(OH) 4 . Occurs in radial fibrous aggregates of a golden 
 yellow to brownish red color. Found with manganese minerals at Ilmenau, Thuringia 
 
 WINKLERITE, (Co, Ni) 2 O(OH)4, is compact and possesses a bluish or violet 
 color. Found in Spain. Rare. 
 
OXIDES 95 
 
 LIMONITE, Brown Hematite, Bog Iron Ore, Fe 4 O,(OH) 6 . 
 
 Crystallization is supposed to be orthorhombic. Nearly always in com- 
 pact, porous, or earthy masses. Often stalactitic, botryoidal, or mammil- 
 lary. Radial fibrous structure and black varnish-like surfaces are charac- 
 teristic features. Also concretionary. 
 
 Physical properties vary greatly with the variety. Conchoidal or earthy 
 fracture. Hardness I to 5.5. Specific gravity 3.4 to 4. May be brown, 
 yellow brown, brown black, or black. Streak is always yellow brown. 
 
 Fe 4 O 3 (OH) G . Often more or less impure. May contain silica, clay, 
 manganese, phosphorous, and organic matter. Yields water in a closed 
 tube. Thin splinters fuse to a magnetic globule. Soluble in hydrochloric 
 acid, often yielding a gelatinous residue. Common as a pseudomorph after 
 iron minerals, especially pyrite, marcasite, siderite, etc. 
 
 Several varieties of limonite have been distinguished, as follows : 
 
 (1) Compact limonite. This includes the compact massive, stalac- 
 titic, botryoidal, and other varieties which often possesses a radial fibrous 
 structure and smooth varnish-like surfaces. 
 
 (2) Ochreous limonite. Here are placed the earthy, yellow or brown- 
 ish varieties which may be quite impure, on account of an admixture of 
 clay and sand. 
 
 (3) Bog iron ore. Found in marshy and swampy places. More or 
 less loose and porous in texture and may contain organic remains. 
 
 (4) Brown clay ironstone. Usually in compact masses. Often im- 
 pure, may contain clay or sand. Also concretionary and nodular, pisolitic 
 or oolitic. 
 
 Limonite is the usual decomposition product of iron minerals, result- 
 ing through the action of water, carbon dioxide, humus acid, oxygen, etc. 
 Hence it is found very extensively and usually in association with such 
 minerals as pyrite, hematite, magnetite, siderite, etc. ; also wit hmany of the 
 rock-forming minerals which contain iron in small quantities as the am- 
 phiboles, pyroxenes, etc. The so-called residual limonite may be the result 
 of (i) the decomposition of veins containing iron disulphide, or (2) from 
 the weathering of ferruginous rocks. Residual limonite is usually associated 
 with slates, schists, or limestones. . It occurs rather extensively in the 
 United States in a belt extending from Vermont to Alabama. Limonite is 
 also found in considerable quantities in Texas, Iowa, Wisconsin, Minnesota, 
 and Oregon. Likewise in Bavaria, Hartz Mountains, Scotland, Sweden, etc. 
 
 An iron ore ; used also as yellow ocher, burnt umber, burnt sienna, etc., 
 in paint. Jn 1908 the output of limonite* in the United States was 2,620,390 
 
 * This also includes goethite, see page 93. 
 
9o DESCRIPTIVE MINERALOGY 
 
 long tons. This was about J% of the iron ore mined that year. This sup- 
 ply was obtained principally from Alabama, Virginia, West Virginia, Ten- 
 nessee, etc. 
 
 BRUCITE GROUP 
 
 This group embraces the hydroxides of magnesium, manganese, and 
 iron which conform to the formula M"(OH) 2 . The members of this group 
 crystallize in the hexagonal system. 
 
 a : c 
 
 Brucite, Mg(OH) 2 . Ditrigonal Scalenohedral Class i : 1.5208 
 
 MANGANOBRUCITE, (Mg,Mn) (OH) 2 . Ditrigonal Scalenohedral Class ? 
 FERROBRUCITE, (Mg,Fe)(OH) 2 . Ditrigonal Scalenohedral Class ? 
 PYROCHROITE, Mn(OH) 2 . Ditrigonal Scalenohedral Class i : 1.4002 
 
 Of these minerals brucite is the most important. 
 
 Brucite, Mg(OH) 2 . 
 
 Hexagonal, ditrigonal Scalenohedral class, a : c=i : 1.5208. Crys- 
 tals are generally broad tabular. Commonly found in foliated masses ; some- 
 times fibrous and scaly. Fibers are elastic. 
 
 Perfect basal cleavage. Hardness 2 to 2.5. Specific gravity 2.3 to 
 2.4. Thin plates or scales are flexible. Pearly to vitreous luster. Trans- 
 parent to translucent. Color is white, gray, blue, or green. White streak. 
 Looks like gypsum and talc. 
 
 Mg(OH) 2 . If manganese or iron replace a portion of the magnesium 
 manganobrucite and ferrobrucite result. Infusible. Heated with cobalt so- 
 lution it turns pink. Soluble in hydrochloric acid. Decomposes to hydro- 
 magnesite. 
 
 Found with serpentine and other magnesium minerals, also in lime- 
 stones. Occurs at Hobokeh, N. J. ; Brewster, N. Y. ; Texas, Pa. ; Predazzo, 
 Tyrol, etc. 
 
 PYROCHROITE, Mn(OH)2, is isomorphous with brucite. Usually in granular or 
 foliated masses. Pearly luster. When fresh is white but darkens on exposure. Thin 
 scales are translucent. Occurs with magnetite at Pjasberg, Sweden; also at Franklin 
 Furnace, N. J. 
 
 MOLYBDITE, Molybdic Ocher, Mo 3 Fe 2 O 12 . 
 
 Molybdite was formerly considered MoOs. Schaller has, however, shown that 
 its composition may be expressed by the formula Fe 2 O 3 , 3MoO 3 , 7/^H 2 O. 
 
 Fibrous structure, often arranged in radial aggregates. Yellow in color. Silky 
 luster. Yields water in a closed tube and turns dark olive green. Becomes paler 
 on continued heating. Soluble in hydrochloric acid, with difficulty in ammonium 
 hydroxide. 
 
 Occurs at Westmoreland, N. H. ; Telluride, Colo.; Renfrew Co., Ontario; and 
 in California. 
 
OXIDES 97 
 
 OXYSULPHIDES 
 
 There are only two oxysulphides which occur in nature, kermesite 
 Sb 2 SoO, and voltzite, Zn 5 S 4 O. Only kermesite will be described. 
 
 KERMESITE, Pyrostibite, Red Antimony, Sb 2 S 2 O. 
 
 Monoclinic, prismatic class, a : b : c = 3.9650 : i : 0.8535, is approximately 
 90. Acicular crystals, also hair-like fibers, radial fibrous aggregates, and dissemi- 
 nated. Color is cherry red. Adamantine luster. Translucent, almost opaque. Brown- 
 ish red streak. Hardness I to 1.5. Specific gravity 4.5 to 4.6. Blowpipe reactions 
 same as for stibnite. Usually with stibnite and native antimony. Some localities 
 are Pribram, Bohemia ; Braunsdorf, Saxony ; Allemont, Dauphine ; in large quantities 
 at Pereta, Tuscany; South Ham, Quebec, Canada; also York Co., New Brunswick. 
 
IV. HALOIDS 
 
 1. SIMPLE HALOIDS 
 
 Here are placed the simple compounds of the halogen elements, chlor- 
 ine, bromine, fluorine, and iodine, with the various metals. A few of the 
 compounds contain water of crystallization. 
 
 HALITE GROUP 
 
 This group embraces the haloids of potassium, sodium, silver, and 
 ammonium. They all crystallize in the cubic system. There is, however, 
 considerable difference in symmetry to be observed between the various 
 members of the group. 
 
 Sylvite, KC1. Pentagonal Icositetrahedral Class 
 
 SAL AMMONIAC, NH 4 C1. Pentagonal Icositetrahedral Class 
 
 HALITE, NaCl. Hexoctahedral Class 
 
 Cerargyrite, AgCl. Hexoctahedral Class 
 
 EMBOLITE, Ag(Cl,Br). Hexoctahedral Class 
 
 BROMYRITE, AgBr. Hexoctahedral Class 
 
 IODOBROMITE, Ag(Cl,Br,I). Hexoctahedral Class 
 
 MIERSITE, Agl. Hextetrahedral Class 
 
 The compound Agl is dimorphous. The second modification is iody- 
 rite which crystallizes in the dihexagonal pyramidal class, a : c= i : 0.8196 
 Halite is, by far, the most important mineral in this group. 
 
 Sylvite, KC1. 
 
 Cubic, pentagonal icositetrahedral class. Crystals generally show a 
 combination of the cube and octahedron. Gyroidal hemihedrism is revealed 
 by etch figures. Usually in granular and compact masses. 
 
 Perfect cubical cleavage. Conchoidal fracture. Hardness 2 to 2.5. 
 Specific gravity 1.9 to 2. Colorless; due to inclusions may be bluish, yel- 
 lowish or red. Transparent to translucent. Colorless and transparent crys- 
 tals from Stassfurt,' Germany, are termed hovcllite. Due to the presence 
 of magnesium chloride, it may be deliquescent. Disagreeable bitter taste. 
 
 KC1. Sometimes almost pure, but may contain chlorides of sodium 
 and magnesium. Colors flame violet. Easily soluble in water. Fuses and 
 volatilizes easily. 
 
HALOIDS 99 
 
 Mixed with halite and kainite, it occurs in large quantities in the salt 
 deposits of Stassfurt, Germany. Also at Kalusz, Galicia, Austria ; Berchtes- 
 gaden, Bavaria ; Mayo mine in the Salt Range in India ; and on Mt. Ve- 
 suvius. 
 
 Sylvite is of importance in the conversion of Chile saltpeter, NaNO n , 
 into the more valuable potassium nitrate according to the following reac- 
 tion : KC1 -f NaNO 3 = KNO 3 + NaCl. It is also used as a fertilizer. 
 
 SAL AMMONIAC, NH 4 C1. 
 
 Cubic, pentagonal icositetrahedral class. Crystals are rare. Often greatly mis- 
 shapen. Artificial crystals sometimes show a pentagonal icositetrahedron. Usually 
 as fibrous, powdery, or stalactitic masses, also in crusts. 
 
 Imperfect octahedral cleavage. Conchoidal fracture. Hardness 1.5 to 2. Spe- 
 cific gravity 1.5 to 1.6. Colorless, yellow, or brown. Pungent taste. Transparent to 
 translucent. Vitreous luster. 
 
 NH 4 C1, may contain small amounts of ferric chloride. Easily soluble in water. 
 Volatilizes readily and completely. Boiled with potassium hydroxide, it evolves am- 
 monia fumes. 
 
 Occurs as a sublimation product about various volcanoes, thus at Aetna, Vesu- 
 vius, Kilauea, etc. Also near burning coal-beds and in guano deposits. The natitral 
 compound does not occur abundantly enough to be of commercial importance. 
 
 HALITE, Common Salt, Rock Salt, NaCl. 
 
 Cubic, hexoctahedral class. Crystals are generally cubes, rarely in 
 combination with the octahedron, tetragonal trisoctahedron, or the tetra- 
 hexahedron. Crystals are sometimes skeletal or hopper-shaped. Usually 
 as compact, fibrous, or granular aggregates. Also as a fibrous efflorescence, 
 especially in arid regions ; stalactitic. 
 
 Excellent cubical cleavage. Conchoidal fracture. Brittle. Hardness 
 2 to 2.5. Specific gravity 2.1 to 2.3. When pure colorless, due to impuri- 
 ties reddish, blue, gray, greenish, or black. The admixtures may be ferric 
 oxide, hydrocarbons, bitumen, anhydrite, or clay. Easily soluble in water 
 ( i part in 2.8 parts of water). Saline taste. Vitreous luster. Na .= 1.5442. 
 Transparent to translucent. 
 
 NaCl. Sometimes very pure, (Petite Anse, La., 98.88% and Holston 
 Valley, Va., 99.55% NaCl). May contain varying percentages of calcium 
 and magnesium chlorides, also admixtures of gypsum, anhydrite, organic 
 matter, clay, occluded liquids and gases, etc. Colors flame yellow. Vola- 
 tilizes easily before the blowpipe. 
 
 Salt occurs widely distributed. There are four methods of occurrence : 
 (i) Deposits, often of great thickness and extent; (2) Efflorescence; (3) 
 Sublimation product; (4) In solution. 
 
 (i) Deposits. Here the salt is generally associated with gypsum or 
 anhydrite, and is found in sedimentary rocks of all ages. Many deposits 
 
IOO DESCRIPTIVE MINERALOGY 
 
 are very extensive and of great thickness, thus, the thickness in various 
 places in Central New York is 350 feet; in Michigan 400 feet; Stassfurt, 
 Germany, 1,200 feet; Petite Anse, La., 1,756 feet; and Sperenberg, Ger- 
 many, 4,200 feet. 
 
 Some of the more noted salt deposits are at Wieliczka, Galicia; Parajd, 
 Transylvania; Bochnia and Kalusz, Galicia; Berchtesgaden, Bavaria; Hall, 
 Austria ; Stassfurt and Sperenberg, North Germany ; Vic and Dieuze, 
 Western Germany ; Bex, Switzerland ; Northwitch, England ; also various 
 places in Spain, India, China, Peru, Algeria, etc. 
 
 In the United States, New York, Michigan, Ohio, Kansas, Louisiana, 
 California, West Virginia, Texas, and Utah possess large deposits and pro- 
 duce enormous quantities annually. In 1907 the production of the United 
 States was 29,704,128 barrels of 280 pounds each, valued at $7,439*55 T - The 
 five districts producing the largest quantities were : 
 
 Michigan 10,786,630 barrels 
 
 New York 9,642,178 barrels 
 
 Ohio 3,851,243 barrels 
 
 Kansas 2,667,459 barrels 
 
 Louisiana : 1,157,621 barrels 
 
 These districts produced about 95% of the output for 1907. The world's 
 production is obtained principally, in the order named, from the United 
 States, United Kingdom, Germany, Hungary, France, Spain, and Italy. 
 
 There are many explanations for the formation of salt deposits of 
 such great thickness as indicated above. Of these the bar theory of 
 Ochsenius is perhaps the most satisfactory. Ochsenius assumes that a 
 portion of the ocean has been shut off from the main body of water by 
 means of a bar, which rises almost to the surface. Evaporation within the 
 bay would, on account of the shallowness of the water, be greatest on or 
 near the bar. This would cause the water to become more dense and a 
 portion would settle to the bottom behind the bar. In time the saturation 
 of the water in the bay would be such as to cause the deposition of gypsum 
 and rock salt. As the evaporation and concentration of the water continued, 
 more would flow into the bay from the open ocean so that the supply would 
 remain constant. If the bar emerges and entirely cuts off the bay continued 
 evaporation would cause the deposition of not only calcium sulphate and 
 rock salt, but also of the very soluble magnesium and potassium compounds. 
 Owing to the very concentrated nature of the brine in the final stages of 
 deposition many complex double salts result. The deposits at Stassfurt, 
 Germany, cover an area of about 100 square miles and are an excellent 
 illustration of the order in which the various compounds are deposited. In 
 
HALOIDS 10 1 
 
 these deposits four beds or "regions" are easily distinguished. Beginning 
 with the lowest, they are : 
 
 (a) Anhydrite region. This bed is about 330 meters thick and in the 
 upper portion consists of 96% rock salt and 4% anhydrite (CaSO 4 ), in 
 the lower portions as much as 9%' of anhydrite may be present. This re- 
 gion is underlain by gypsum (CaSO 4 . 2H 2 O) and clay. 
 
 (b) Polyhalite region. This section is composed of 91.2% rock salt, 
 6.2% polyhalite (2CaSO 4 . MgSO 4 . K,SO 4 . 2H 2 O), 1.5% tachydrite (CaCl,. 
 2MgCl,. I2EUO), and 0.7% anhydrite. It has a thickness of about 62 
 meters. 
 
 (c) Kieserite region. This is about 56 meters thick and consists of 
 6$% rock salt, 17^0 kieserite (MgSO 4 .H 2 O), 13% carnallite (KCLMgCU. 
 6H 2 O), 3% tachydrite, and 2% anhydrite. 
 
 (d) Carnallite region. This zone consists of 55% carnallite, 25% 
 rock salt, 16% kieserite, and 4% tachydrite. It is about 42 meters thick. 
 Aside from the above, many other minerals, mostly salts of magnesium, 
 calcium, and potassium, are found in this region. 
 
 (e) Kainite region. At Leopoldshall a deposit of considerable thick- 
 ness of kainite (MgSO 4 . KC1. 3H 2 O) is found above the carnallite region. 
 It is thought that the kainite has resulted from the action of limited amounts 
 of water on kieserite and carnallite. 
 
 The whole deposit is overlain by layers of saliferous clay, anhydrite, 
 gypsum, and rock salt. Over thirty different minerals have been observed 
 in the Stassfurt deposits of which halite, anhydrite, polyhalite, kieserite, 
 carnallite, and a portion of the sylvite (KC1), bischofite (MgCl 2 . 6H 2 O), 
 and boracite (2Mg 3 B 8 O 15 . MgCl 2 ) are considered primary minerals. 
 
 (2) As an efflorescence, halite is found in the steppes, near the Cas- 
 pian sea ; in Africa and Chile. 
 
 (3) Near volcanoes it is found in small quantities as a sublimation 
 product. 
 
 (4) Common salt also occurs abundantly in solution in the ocean, 
 salt lakes, salt wells, etc., see page 67. 
 
 Salt is used extensively for household and dairying purposes, meat- 
 and fish-packing, in the manufacture of sodium and its compounds, to glaze 
 pottery, and in various metallurgical processes. Sodium carbonate is used 
 in large quantities in glass and soap making, the bicarbonate for cooking 
 and baking, also in medicine. 
 
 Cerargyrite, Horn Silver, AgCl. 
 
 Cubic, hexoctahedral class. Crystals are rare and poorly developed. 
 The cube, octahedron, and rhombic dodecahedron are common forms 
 
102 DESCRIPTIVE; MINERALOGY 
 
 Twins according to the Spinel law. Usually massive and disseminated, as 
 a crust or coating, stalactitie, dendritic. 
 
 No cleavage. Conchoidal fracture. Highly sectile, waxy. Very soft, 
 hardness I to 1.5. Specific gravity 5.5 to 5.6. Pearly gray, yellowish, 
 greenish, or white in color; on exposure to light turns violet, brown, or 
 black. Resinous adamantine luster. Transparent to translucent. When 
 rubbed becomes shiny. Streak shiny white. 
 
 AgCl, may contain mercury, ferric oxide, or other impurities. Fuses 
 easily and yields a globule of silver. Not acted upon by acids. Slowlv 
 soluble in ammonium hydroxide. 
 
 Found as an alteration product in the upper levels of silver deposits. 
 The usual associates are the various silver minerals, limonite, calcite, bar- 
 ite, etc. Occurs in considerable quantities at Johanngeorgenstadt and Frei- 
 berg, Saxony ; Kongsberg, Norway ; Peru ; Chile ; Mexico ; Broken Hill, 
 New South Wales ; near Leadville, Colo.' ; Comstock Lode, Nev. ; Poor Man's 
 Lode, Idaho ; various places in Utah ; Cobalt district, Ontario. 
 
 Important ore of silver. 
 
 EMBOUTE, Ag(Cl,Br). 
 
 Cubic, hexoctahedral class. Crystals resemble those of cerargyrite. Usually 
 massive. Sectile. Hardness I to 1.5. Specific gravity 5.31 to 5.81. Yellow, grayish 
 green, or yellowish green in color. The percentages of chlorine and bromine vary 
 considerably. Considered an isomorphous mixture in varying proportions of cerargy- 
 rite and bromyrite. Occurs rather abundantly in Chile, Mexico, and Australia. 
 
 BROMYKITE, Bromargyrite, AgBr. 
 
 Cubic, hexoctahedral class. Crystals and aggregates are similar to those of 
 cerargyrite. Usually in small concretions. Malleable. Hardness i to 2. Specific 
 gravity 5.8 to 6. Olive to yellow green in color. Often resembles amber in luster 
 and color. Luster greasy and shiny. Siskin-green streak. 
 
 AgBr, generally contains some chlorine. Occurs in association with other silver 
 minerals in the Plateros district of Mexico, and at Chanarcillo, Chile. 
 
 lODOBROMTTE, Ag(Cl, Br, I). 
 
 Cubic, hexoctahedral class. Small crystals, usually the octahedron in combina- 
 tion with the cube. Soft. Specific gravity 5.7. Sulphur yellow to olive green in 
 color. Resinous luster. Considered an isomorphous mixture of the chloride, brom- 
 ide, and iodide of silver. Occurs in cavities of a ferruginous quartz near Dernbach, 
 Nassau, Germany. 
 
 MIERSITE, Agl, usually contains some copper. Pale to bright yellow in color. 
 Rhombic dodecahedral cleavage. Occurs at Broken Hill, New South Wales. 
 
 IODYRITE, lodargyrite, Agl. 
 
 Hexagonal, dihexagonal pyramidal class, a : c = i : 0.8204. Pronounced hemi- 
 morphic development. Basal pinacoid usually predominates. Generally in thin plates, 
 also compact and disseminated. Distinct basal cleavage. Hardness i to 1.5. Spe- 
 cific gravity 5.7. Pearly gray, yellow, lemon yellow, or green in color. Greasy 
 luster. Shiny streak. Occurs with silver minerals near Dernbach, Nassau; Mazapil, 
 Mexico; Chile; Spain; Lake Valley, Sierra Co., N. M. ; Tonopah, Nevada, and Broken 
 Hill, New South Wales. 
 
HALOIDS 
 
 FLUORITE GROUP 
 
 103 
 
 Here are placed the halogen compounds of bivalent metals which con- 
 form to the general formula M"R' 2 . There are two series, one of which 
 crystallizes in the cubic system, the other in the tetragonal. 
 
 CUBIC SERIES 
 
 HYDROPHILITE, CaCl 2 . 
 FLUORITE, CaF 2 . 
 
 Hexoctahedral Class 
 Hexoctahedral Class 
 
 TETRAGONAL SERIES 
 
 a : c 
 
 SELLAITE, MgF 2 . Ditetragonal Bipyramidal Class i : 0.6596 
 SCACCHITE, MnCl,. ? ? 
 
 LAWRENCITE, (Fe.Ni)Cl 2 . ? ? 
 
 Scacchite and lawrencite are very rare minerals. 
 
 HYDROPHILITE, Chlorocalcite, CaCl 2 . Occurs as crusts or cubic crystals, often 
 coated with hematite, on Mt. Vesuvius. 
 
 FLUORITE, Fluor Spar, CaF 2 . 
 
 Cubic, hexoctahedral class. Excellent crystals are common. The us- 
 ual form is the cube, either alone or in combination with the octahedron, 
 rhombic dodecahedron, tetragonal trisoctahedrons (m = 2 or 3), tetrahex- 
 
 ,J. .* 
 
 FIG. 54. 
 
 FIG. 55. 
 
 ahedrons (m = 2 or 3), and hexoctahedron (n = 2, m = 4~). The habit 
 is generally cubic, although octahedral or rhombic dodecahedral crystals 
 are sometimes observed. Figures 53 and 54 show some common combina- 
 tions. The cube faces are usually smooth and brilliant, those of the octa- 
 hedron rough and dull. Octahedral crystals are sometimes built up by par- 
 allel grouping of small cubes. Penetration twins, with the twinning plane 
 parallel to a face of the octahedron, are rather common, Figure 55. Also 
 
104 DESCRIPTIVE MINERALOGY 
 
 massive, granular, fine or coarse grained ; rarely earthy, columnar, or com- 
 pact. 
 
 Excellent octahedral cleavage. Brittle. Hardness 4. Specific gravity 
 3.1 to 3.2. Usually yellowish, greenish, or blue in color; also various shades 
 of red, brown, white, and colorless. Some of the colors are supposed to be 
 due to hydrocarbons, for many varieties become colorless when heated. 
 Crystals are often multicolored. Transparent to subtranslucent. Vitreous 
 luster. n Na = 1.4339. Phosphoresces when heated. A bluish fluorescence 
 is to be noted on many blue crystals from Cumberland, England. 
 
 CaF 2 . Usually very pure, sometimes contains small amounts of cal- 
 cium Chloride, calcium phosphate, etc. Heated in a closed tube, it decrepi- 
 tates and phosphoresces. Fuses to a white enamel and colors flame ml. 
 Treated with sulphuric acid yields hydrofluoric acid. 
 
 Fluorite occurs in veins in gneiss, schists, limestones, and sandstones. 
 It is also a common gangue mineral and is, hence, found with ores of lead, 
 silver, copper, and especially tin. It is one of the characteristic associates 
 of the "tin ore" deposits, see page 81. Calcite, quartz, barite, pyrite, galena. 
 marcascite, chalcopyrite, and sphalerite are some of the very common asso- 
 ciates of fluorite. Excellent crystals occur at Cornwall, Cumberland, Derby- 
 shire, etc., England ; also found in the Freiberg district, Saxony ; Harz 
 Mts. ; Kongsberg, Norway ; St. Gotthard, Switzerland ; etc. 
 
 In the United States fluorite occurs in considerable quantities in Hardin 
 and Pope counties, Illinois ; Smith, Trousdale, and Wilson counties, Tenne- 
 see; Crittenden, Livingston, Lyon, Caldwell, and Trigg counties, Ken- 
 tucky ; at Jamestown, Boulder Co., Colarado ; various places in New York, 
 Virginia, California, etc. 
 
 In 1907 the production of the United States was 49,486 tons. This 
 was obtained from Illinois, Kentucky, Colorado and Tennessee in the order 
 named. 
 
 Fluorite is used in the manufacture of open-hearth steel, cast iron, 
 opalescent glass, hydrofluoric acid, enamels, glazes, and "agate" ware. 
 
 Fluorite is worth about $9 per ton, when ground $10 to $14. 
 
 SELLAITE, MgF 2 . Tetragonal. Crystals are prismatic. Colorless. Vitreous 
 luster. Translucent. Hardness 5. Specific gravity 2.97 to 3.15. Occurs in anhydrite 
 at Gerbulaz, near Moutiers, Savoy, France. 
 
HALOIDS 105 
 
 TYSONITE GROUP 
 
 This includes minerals with the general formula M'"R' 3 , where R" is 
 an element of the halogen series. 
 
 a : c 
 
 MOLYSITE. FeCl 3 . Hexagonal System i : 1.2350 
 
 TYSONITE, (Ce.La.Di)F 3 . Hexagonal System i : 1.3736 
 
 The class of symmetry in which these minerals crystallize has not yet 
 been determined. 
 
 MOLYSITE, FeCls. Usually as yellowish, brownish, or brownish red crusts on 
 the lavas of Mt. Vesuvius. 
 
 TYSONITE, (Ce.La.Di)F 3 . Hexagonal. Generally in prismatic or thick tabular 
 crystals. Excellent basal cleavage. Hardness 4.5 to 5. Specific gravity 6.13. Light 
 waxy yellow to reddish brown in color. Vitreous to resinous luster, on cleavage 
 surface somewhat pearly. Aside from the rare earths indicated in the formula, 
 yttrium and erbium may be present. Occurs in granite in the Pike's Peak district, 
 Colorado. 
 
 CALOMEL GROUP 
 
 Here are placed minerals possessing the formula M' 2 R' 2 , where M' 
 may be copper, mercury, or lead, and R' any element of the halogen group. 
 
 NANTOKITE, Cu 2 Cl 2 . Cubic, Hextetrahedral Class 
 
 MARSIIITK, Cu,I 2 . Cubic, Hextetrahedral Class 
 
 Calomel, Hg 2 Cl 2 . Tetragonal, Ditetragonal Bipyramidal Class 
 
 COTUNNITE, PbCl 2 . Orthorhombic, Bipyramidal Class 
 
 NANTOKITE, Cu 2 Cl 2 . Cubic, artificial crystals belong to the hextetrahedral class. 
 In nature only massive and granular. Hardness 2. to 2.5. Specific gravity 3.93. Color- 
 less to white. Adamantine luster. Transparent to translucent. Occurs with hematite, 
 cuprite, native copper, and other copper minerals at Nantoko, Chile ; also at Broken 
 Hill, New South Wales. 
 
 MARSHITE, Cu 2 J 2 . Cubic, small tetrahedral crystals of an oily brown color. 
 Translucent. Occurs in cerussite or anglesite at Broken Hill, New South Wales. 
 
 Calomel, Horn Mercury, Hg 2 Cl 2 . 
 
 Tetragonal, ditetragonal class, a : c = i : 1.7229 In small, tabular, 
 or pyramidal crystals. Contact and penetration twins. Crystals are often, 
 very complex. 
 
 Basal and pyramidal cleavages. Hardness i to 2. Specific gravity 
 6.4 to 6.5. Grayish and yellowish white in color, also yellow gray. Ada- 
 mantine luster. Translucent to subtranslucent 
 
I06 . DESCRIPTIVE MINERALOGY 
 
 Hg^Clo. Volatilizes, without fusion, in a closed tube ; also on charcoal, 
 yielding white coating. . Insoluble in water, soluble in aqua regia. Turns 
 black when treated with alkalies. 
 
 Occurs with cinnabar at Moschellandsberg, Bavaria ; Almaden, Spain ; 
 Idria, Carniola ; Horzwitz, Bohemia ; El Doctor, Mexico. 
 
 COTUNNITE, PbCU. Orthorhombic. Small white, acicular crystals. Prism angle 
 is about 62. Also in irregular grains. Adamantine luster. Prismatic cleavage. 
 Hardness 2. Specific gravity 5.23. Easily fusible. Occurs as a sublimation product 
 in the lavas of Mt. Vesuvius. 
 
 BISCHOFITE, MgCU. 6H 2 O. Probably monoclinic. Natural crystals are rare. 
 
 Usually granluar, foliated, or fibrous. White. Very deliquescent. Occurs in the 
 
 carnallite region, see page 101, of the salt deposits at Stassfurt, Germany. Formed 
 by the solution of carnallite. 
 
 A1F 3 .H 2 O. Orthorhombic, a : b : c 0.770 : i : 1.874. Small, 
 steep pyramidal crystals. White. Hardness 3. Specific gravity 2.17. Transparent 
 to translucent. Found with cassiterite at Cornwall, England. Very rare. 
 
 2. DOUBLE CHLORIDES AND FLUORIDES 
 
 CARNALLITE GROUP 
 
 Here belong double chlorides, with varying amounts of water of crys- 
 tallization, of magnesium, calcium, iron, and potassium. 
 
 Carnallite, MgCl,. KC1. 6H 2 O. Orthorhombic, Biypramidal Class 
 DOUGLASITE, Fed,. 2KC1. 2H 2 O. ? 
 
 TACHYDRITE, 2MgCl 2 . CaCl,. i2H 2 O. 
 
 Hexagonal, Ditrigonal Scalenohedral Class 
 ERYTHROSIDERITE, FeCl 3 . 2KC1. H 2 O. ? 
 
 KREMERSITE, FeCl 3 .2(K.NHjCl.H 2 O. ? 
 
 Erythrosiderite and kremersite are very rare minerals. They have been 
 found on Mt. Vesuvius. 
 
 Carnallite, MgCl 2 . KC1. 6H 2 O. 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.5968 : I : 1.3891. 
 Crystals possess hexagonal outline ; rare. Usually massive and granular. 
 
 Conchoidal fracture. Hardness i to 2. Specific gravity 1.6. May be 
 colorless, usually grayish, yellow, and due to admixtures of hematite or 
 
HALOIDS 107 
 
 goethite, often red. Vitreous luster. Deliquescent. Transparent to trans- 
 lucent. Bitter taste. 
 
 MgCL> . KC1 . 6H 2 O. May contain some sodium. Easily fusible. When 
 dissolved in water it yields the chlorides of magnesium and potassium. 
 
 Occurs associated with rock salt and anhydrite in the salt deposits at 
 Stassfurt, Germany, see page 100. 
 
 It is used in large quantities as a fertilizer, also as a source of potas- 
 sium compounds. Mined extensively at Stassfurt, Germany. 
 
 DOUGLASITK, FeCl2.2KC1.2H 2 O. Occurs in limited quantities in the salt deposits 
 at Stassfurt, Germany. 
 
 TACHYDRITE, Tachyhydrite, 2MgCl 2 .CaCl 2 .i2H 2 O. 
 
 Hexagonal, ditrigonal scalenohedral class, a : c i : 1.90. Wax to honey 
 yellow masses. Rhombohedral cleavage. Deliquesces rapidly. A secondary mineral 
 in the salt deposits at Stassfurt, Germany. 
 
 CRYOLITE, Eisstein, A1F 3 . 3 NaF. 
 
 Monoclinic, prismatic class, a : b : c 0.9662 : i : 1.3882, /? = 
 90 n'. Crystals are cubic in habit; were formerly considered orthorhom- 
 bic and triclinia Common forms are the unit prism, basal pinacoid, clino- 
 and orthodomes. Prism angle is 88 2' '. Contact and polysynthetic twins, 
 twinning plane is parallel to a face of the unit prism. Usually in cleavable 
 masses. 
 
 Basal and prismatic cleavages, three directions almost at right angles. 
 Uneven fracture. Brittle. Hardness 2.5 to 3. Specific gravity 2.95 to 3.0. 
 Colorless to snow white; more rarely reddish, brownish, or black. Pearly 
 luster on the basal pinacoid, elsewhere vitreous to greasy. Transparent to 
 translucent. 
 
 A1F 3 . 3NaF. Usually quite pure. Sometimes contains a small amount 
 of ferric oxide as an Impurity. Fuses easily. Imparts a yellow color to 
 the flame. Heated in open tube, it yields hydrofluoric acid which etches the 
 tube. 
 
 Occurs in large quantities in veins in granite containing cassiterite at 
 Ivigtut, Arksukfiord, Western Greenland, and is associated with siderite, 
 quartz, chalcopyrite, pyrite, galena, sphalerite, fluorite, and columbite. This 
 is the only important occurrence of cryolite. Is found in small quantities 
 at Miask, Ural Mts., and in the Pike's Peak district, Colorado. 
 
 Cryolite is used in the manufacture of sodium salts, porcelain, milk 
 glass, and as a bath in the manufacture of aluminium by the electrolytic 
 process, especially at Niagara Falls, N. Y. Calcium fluoride is an important 
 by-product in the manufacture of sodium salts from cryolite and substituted 
 for fluorite (see page 104) as a flux in the open-hearth process of steel 
 
108 DESCRIPTIVE MINERALOGY 
 
 manufacture. In 1907 about 1,438 long tons of cryolite, valued at $28,902, 
 were imported into the United States from Greenland. 
 
 PACHNOLITE, "1 A1F 3 . NaCaF 3 . H 2 O. Monoclinic Prismatic Class 
 THOMSENOLITE,] 
 
 These minerals possess the same chemical composition and crystallize with the 
 same symmetry. Their elements of crystallization are also very similar, as is shown by 
 the following comparison : 
 
 Pachnolite, a : b : c 1.1626 : i : 1.5320, /3 90 20'. 
 Thomsenolite, a : b : c = 0.9973 : i : 1.0333, /3 93 12'. 
 
 They occur as prismatic crystals, or in coarse to fine crystalline, colorless crusts, 
 resembling chalcedony. Alteration products of cryolite. Occur with cryolite in West- 
 ern Greenland and Pike's Peak, Colorado. 
 
 3. OXYCHLORIDES AND OXYFLUORIDES 
 
 MATLOCKITE, Pb 2 OCl 2 . Tetragonal, a : c = i : 1.7627. Small, thin tabular 
 crystals. Uneven to conchoidal fracture. Hardness 2.5. Specific gravity 7.2. Ada- 
 mantine to pearly luster. Yellowish or greenish in color. Transparent to translucent. 
 Alteration product of galena. Occurs at Cromford, near Matlock, Derbyshire, England. 
 
 PERCYUTE, Pb(OH)Cl.Cu(OH)Cl. Tetragonal, also considered cubic. Small 
 azure-blue crystals. Vitreous luster. Occurs with gold at Sonora, Mexico ; with 
 galena in Chile. Boleite from Boleo, California, and Broken Hill, New South Wales, 
 is an argentiferous percylite. 
 
 Atacamite, Cu(OH)Cl. Cu(OH) 2 . 
 
 Orthorhombic, bipyramidal class, a : b : c =F 0.6613 : i : 0.7529. 
 Usually in slender prismatic crystals, consisting of the unit prism, unit 
 brachydome, and brachypinacoid. Prisms are striated vertically. Also 
 massive, reniform ; radial, foliated, granular, and compact aggregates ; 
 sometimes as a sand or crust. 
 
 Perfect brachypinacoidal cleavage. Conchoidal fracture. Hardness 3 
 to 3.5. Specific gravity 3.76. Color various shades of green. Apple green 
 streak. Vitreous luster. Subtransparent to translucent. 
 
 Cu(OH)Cl.Cu(OH) 2 . Yields water at 200 C. Fuses on charcoal, 
 colors flame azure-blue, and yields a globule of copper. Easily soluble in 
 acids .and ammonium hydroxide. 
 
 Usually associated with various copper minerals. Occurs in consider- 
 able quantities in the provinces of Atacama and Tarapaca, Chile ; Bolivia ; 
 Southern Australia; India; Arizona; as a sublimation product on Mt. 
 Vesuvius. 
 
 In Chile atacamite is an important ore of copper. 
 
V. NITRATES, CARBONATES, MANG AN- 
 ITES, AND PLUMBITES 
 
 1. NITRATES 
 
 Here are placed the nitrates of sodium and potassium. Owing to their 
 great solubility, these compounds do not occur in extensive deposits, except 
 under the most favorable conditions. 
 
 SODA NITER, NaNO 3 . Hexagonal, Ditrigonal Scaleno- 
 
 (Chile Saltpeter] hedral Class a : c 
 
 i : o . 8276 
 
 Niter, KNO 3 . Orthorhombic Bipyramidal Class 
 (Saltpeter} a : b : c 
 
 0.5843 : i : 0.7028 
 
 Chile saltpeter is of great importance, commercially. 
 
 SODA NITER, Chile Saltpeter, NaNO 3 . 
 
 Hexagonal, ditrigonal scalenohedral class, a : c == i : 0.8276. Rarely 
 found in crystals. They resemble those of calcite. Generally in crystalline 
 aggregates or grains, also in crusts or deposits of great extent. 
 
 Perfect rhombohedral cleavage. Conchoidal fracture. Brittle. Hard- 
 ness 1.5 to 2. Specific gravity 2.1 to 2.3. Vitreous luster. Colorless, white, 
 yellowish, or reddish brown. Transparent. Cooling and saline taste. 
 Strong double refraction, w Na = 1.5874, e Na = 1.3361. 
 
 NaNO 3 , usually contains some sodium chloride and sulphate. Easily 
 soluble in water, one part in three of water at 15 C. Deliquesces. Colors 
 flame an intense yellow. 
 
 Occurs in large deposits, 6 to 12 feet thick, in the province of Tarapaca, 
 Chile, and at Arane, Bolivia. It is mixed with rock salt, guano, and other 
 minerals in small quantities, among them lautarite, Ca(IO 3 ) 2 . The beds 
 of Chile saltpeter alternate with layers of gypsum, "sand and clay. The raw 
 material is called caliche. These deposits are supposed to have resulted 
 from the oxidation of nitrogenous organic matter, especially guano, in 
 the presence of soda ; perhaps nitrifying bacteria assist in this reaction. In 
 smaller quantities soda niter occurs in San Bernadino and Inyo counties, 
 California; also in Nevada and New Mexico. 
 
 Soda niter is of great value, commercially. It is used extensively as 
 
110 DESCRIPTIVE MINERALOGY 
 
 a fertilizer, in the manufacture of nitric acid and potassium nitrate. Owing 
 to its tendency to deliquesce it cannot be used in gunpowder except in 
 very dry places, for example, in salt mines. Hence, it is converted into 
 the non-hygroscopic potassium nitrate by treating it with a solution of 
 potassium chloride, which occurs in large quantities as sylvite, page 98. 
 or is easily obtained from carnallite, page 106. Chile saltpeter is also the 
 chief source of the iodine of commerce. In 1906 Chile exported 1,719,000 
 long tons of soda niter, 372,222 tons coming to the United States. The 
 remainder was sent to Europe, principally to Germany. It is thought that 
 at the present rate of consumption the Chilean deposits will last about 
 fifty years. 
 
 Niter, Saltpeter, KNO 3 . 
 
 Orthorhombic, bipyramidal class, a : b : c -- 0.5843 : I : 0.7028. 
 Artificial crystals are pseudohexagorial, the prism angle being 118 50'. 
 In nature only as crusts, fine, slender, acicular crystal aggregates ; also as 
 a powdery efflorescence. 
 
 Crystals possess indistinct prismatic and brachypinacoidal cleavages. 
 Conchoidal fracture. Brittle. Hardness 2. Specific gravity 1.9 to 2.1. 
 Vitreous luster. Colorless, white, or gray. 
 
 KNO 3 . Easily soluble in water. Non-hygroscopic. Colors flame violet. 
 
 Occurs as an efflorescence in dry regions, thus in northern Africa, 
 Hungary, India, and in many of the western states ; also in limestone caves 
 at Leonhardshohle, near Homburg, Germany ; Calabria ; Ceylon ; Brazil ; 
 Kentucky ; Missouri ; and in small quantities in the deposits of Chile salt- 
 peter in Chile. It is usually the result of the oxidation of nitrogenous mat- 
 ter in the presence of potash. It is thought that nitrifying bacteria aid in 
 this change. 
 
 The mineral is not used to any extent. The artificial compound, 
 obtained principally by the interaction of sodium nitrate and potassium 
 chloride, pages 98 and 109, is used in large quantities in gunpowder, fire- 
 works, matches, as a flux, and as a mordant in dyeing and printing. 
 
 2. CARBONATES 
 
 A. NORMAL AND ACID CARBONATES 
 
 CALCITE-ARAGONITE GROUPS 
 
 These groups form an isodimorphous series and embrace those min- 
 erals which possess the general formula M"CO 3 . The metal may be cal- 
 cium, magnesium, zinc, iron, manganese, barium, strontium, or lead. The 
 members of the calcite group crystallize in the ditrigonal scalenohedral class 
 of the hexagonal system, those of the aragonite group in the orthorhombic 
 bipyramidal class. Dolomite, CaMg(CO 3 ) 2 , possesses a lower grade of 
 
CARBONATES 
 
 III 
 
 symmetry than the members of the calcite group but on account of the 
 similarity of chemical composition and physical properties it is added to 
 the group. 
 
 CALCITE GROUP 
 (HEXAGONAL SYSTEM) 
 
 CALCITE, CaCO 3 . Ditrigonal Scalenohedral Class 
 
 DOLOMITE, CaMg(CO,),. Trigonal Rhombohedral Class 
 
 * r 
 
 Ditrigonal Scalenohedral ClassJ 
 
 Ditrigonal Scalenohedral Class 
 
 Ditrigonal Scalenohedral Class 
 
 Ditrigonal Scalenohedral Class 
 
 Ditrigonal Scalenohedral Class 
 
 ANKERITE, ( Ca,Mg,Fe) CO 3 
 
 Ditrigonal Scalenohedral 
 Class 
 
 a 
 i 
 i 
 
 c 
 0.8543 
 0.8322 
 0.8100 
 
 i 
 
 i 
 i 
 
 o . 8300 
 0.8104 
 
 0.8129 
 
 i 
 
 o . 8062 
 
 i 
 'i 
 
 0.8170 
 
 0.8183 
 
 
 to 
 
 i 
 
 0.8218 
 
 i : 
 
 i 
 
 0.8175 
 0.8184 
 
 MAGNESITE, MgCO,. 
 BREUNNERTTE, ^Mg,Fe)CO 3 
 SMITHSONITE, ZnCO 3 . 
 MONHEIMTTE. (Zn,Fe s )CO 3 . 
 RHODOCHROSITE, MnCO 
 
 MANGANOCALCITE, 
 
 (Mn,Ca)CO 8 . 
 
 MANGANOSIDERITE, 
 
 (Mn,Fe)CO 3 . 
 
 OUGONITE, (Fe,Mn)CO 3 . Ditrigonal Scalenohedral Class 
 
 SIDERITE, FeCO 3 . Ditrigonal Scalenohedral Class 
 
 SPHAEROCOBAT.TITE, CoCO 3 . Ditrigonal Scalenohedral Class 
 
 ARAGONITE GROUP 
 
 (ORTHORHOMBIC SYSTEM) 
 
 ARAGONITE, CaCO :; . 
 STRONTIANITE, SrCO 3 . 
 
 BROMUTE, (Ca,Ba)CO 3 . 
 WITHERITE, BaCO 3 . 
 TARNOWITZLTE, (Ca,Pb)CO 3 . 
 CERUSSITE, PbCO :! . 
 
 The members of the calcite group possess, when crystallized, a perfect 
 rhombohedral cleavage, the angle varying from 105 to 107. The prism 
 angle of the aragonite group of minerals is approximately 120, varying 
 between n 6 12" and ii748'. 
 
 CALCITE, Calcspar, Iceland Spar, etc., CaCO 3 . 
 
 Hexagonal, ditrigonal Scalenohedral class, a : c = i : 0.8543. Com- 
 monly in well developed crystals, often very complex, Figure 59. The 
 habit varies greatly, may be obtuse or acute rhombohedral, thin tabular, 
 long prismatic, or Scalenohedral. Over 200 forms have been observed. The 
 
 
 a 
 
 b 
 
 : c 
 
 Bipyramidal Class 
 
 o . 6228 
 
 i 
 
 o . 7204 
 
 Bipyramidal Class 
 
 o . 6089 
 
 i 
 
 0.7237 
 
 Bipyramidal Class 
 
 0.5871 
 
 i 
 
 0.7390 
 
 Bipyramidal Class 
 
 0.5949 
 
 i 
 
 0.7413 
 
 Bipyramidal Class 
 
 o . 6220 
 
 i 
 
 0.7168 
 
 Bipyramidal Class 
 
 0.6101 
 
 i 
 
 o . 7229 
 
112 
 
 DESCRIPTIVE MINERALOGY 
 
 unit rhombohedron occurs rarely as an independent form. No less than 
 750 different combinations have been noted. Figures 56 to 59 show several 
 common types of development and combinations. 
 
 Twins are relatively common. Four laws may be referred to. (i') 
 Basal pinacoid acts as the twinning plane. Such twins are rather common. 
 Figure 60. (2) The rhombohedron, ^R, is the twinning plane. Con- 
 
 FIG. 57- 
 
 FIG. 58 
 
 FIG. 59. FIG. 60. FIG. 61. 
 
 tact and poly synthetic twins according to this law are exceedingly common. 
 Figure 6 1 shows a contact twin with y 2 R as the twinning plane. (3) 
 The unit rhombohedron is the twinning plane. The vertical axes are in- 
 clined at angles of go4.6' and 89 14'. This is not a common law. (4) The 
 rhombohedron, 2 R, acts as twinning plane. The vertical axes intersect at 
 angles of 5346' and 126 14'. Crystals twjnned according to this law are 
 sometimes heart-shaped. 
 
 Also in granular, lamellar, fibrous, compact, or earthy masses ; oolitic 
 or pisolitic, stalactitic, nodular, etc. 
 
 Highly, per feet rhombohedral cleavage (io55'). Conchoidal fracture, 
 very rarely observed. Hardness 3. Specific gravity 2.6 to 2.8, when pure 
 2.72. Vitreous to subvitreous luster, also earthy. Colorless, white, gray, 
 yellow, various shades of red, green, blue, etc. Streak white. Transparent 
 to opaque. Strong double refraction, w Na = 1.6585, e Na = 1.4863. 
 
CARBONATES 113 
 
 CaCO 3 . Sometimes very pure. May contain varying amounts of mag- 
 nesium, iron, manganese, zinc, lead, cobalt, barium,' or strontium replacing 
 the calcium. Often mixed with limonite, hematite, organic matter, sand, 
 or brucite. Infusible before the blowpipe, glows, and becomes alkaline. 
 Imparts a red color to the flame. Easily soluble with brisk effervescence 
 in cold dilute acids. Mei gen's test is useful to distinguish compact calcite 
 from aragonite : calcite powder, when boiled for several minutes with co- 
 balt solution either remains white or turns a pale yellow, aragonite, however, 
 assumes a lilac-red color. Occurs as a pseudomorph after aragonite, barite, 
 fluorite, anhydrite, and gypsum. Calcite alters to gypsum and dolomite. 
 Is sometimes replaced by quartz or chalcedony. Pseudomorphs of siderite, 
 smithsonite, cerussite, and malachite after calcite are not uncommon. 
 
 The different varieties of calcite may be grouped as follows: (a) Or- 
 dinary, (b) Limestones, (c} Marbles, (d) Chalk and Marl, and (e) Spnng, 
 Stream, and Cave Deposits. 
 
 (a) Ordinary calcite. Here are placed the crystallized, fibrous, and 
 lamellar varieties. 
 
 ( T ) Dog-tooth spar. Scalenohedral crystals. 
 
 (2) Nail-head spar. Crystals resembling the head of a nail. 
 
 (3) Iceland spar. Colorless and transparent varieties, especially from 
 Eskifiord, Iceland. 
 
 (4) Fontaincblean limestone. Crystals of calcite from Fontainebleau 
 and Nemours, France, and elsewhere, containing as much as 50 to 63% 
 of sand. 
 
 (5) Satin spar. Fibrous variety, with silky luster. White, grayish, 
 or yellow in color. 
 
 (6) Argentine. .Lamellar calcite with a pearly luster. 
 
 (7) Anthraconite, stinkstone. A bituminous calcite. When struck, 
 yields a fetid odor. 
 
 (b) Limestones. This includes many massive varieties, which (i) 
 may be dull and compact, (2) coarse or fine granular, and (3) composed 
 of fragmental material. 
 
 (1) Compact limestones. These may be nearly white, yellow, bluish 
 gray, reddish or black in color. 
 
 (2) Magnesian or dolomitic limestones. These are limestones con- 
 taining varying percentages of magnesium carbonate. 
 
 (3) Lithographic limestone. An even-grained, compact limestone, 
 suitable for lithographic purposes. That from Solenhofen, Bavaria, is buff 
 or drab in color. 
 
 (4) Hydraulic limestone. An impure limestone, containing varying 
 amounts of magnesia, silica, and alumina. After ignition will set under 
 water. 
 
Ji4 
 
 DESCRIPTIVE MINERALOGY 
 
 (5) Bituminous limestone. Contains considerable organic matter 
 When struck yields characteristic odor of bitumen. 
 
 (6) Granular limestone. Compact, but consists of glistening grains 
 of calcite, see Figure 62. Metamorphosed limestone. Sometimes termed 
 crystalline limestone. 
 
 (7) Coquina. Consists of shell remains. 
 
 (8) Oolitic limestone. This consists of small, spherical concretions, 
 resembling fish-roe. 
 
 (9) Pisolitic limestone. The concretions are the size of a small pea. 
 (c} Marbles. Limestones, capable of taking a polish and suitable for 
 
 ornamental and structural purposes, are 
 termed marble. They are usually crys- 
 talline, Figure 62 ( after Weinschenk), 
 and fine to coarse granular. 
 
 (d) Chalk and marl. Very soft, 
 earthy varieties. 
 
 (1) Chalk. Soft, white, earthy 
 masses, consisting of organic remains, 
 especially foraminifera, inoceramus, 
 pecten, ostrea, etc. 
 
 (2) Marl. Soft, earthy calcar- 
 eous deposit, mixed with clay. May 
 contain shell or other organic remains. 
 
 (e) Spring, stream, and cave de- 
 posits. These are largely due to the 
 
 escape of carbon dioxide, which causes the very soluble calcium bicarbon- 
 ate, CaH 2 (CO 3 ) 2 , to pass over to the more insoluble normal carbonate, 
 CaCO 3 , and be deposited. It is thought that certain algae aid in this process. 
 
 (1) Travertine, calcareous sinter, calc tufa, etc. Deposits formed 
 around springs and in stream beds. They are usually porous and often 
 contain twigs, leaves, and other organic remains. Sometimes they are 
 compact and banded, and then termed onyx, onyx marble, or Mexican onyx. 
 
 (2) Stalactites. Icicle-like forms suspended from the roofs of caves. 
 
 (3) Stalagmites. Deposits on the floors of caves, usually conical in 
 form. 
 
 (4) Stagmites. Cave deposits, either stalactites or stalagmites. The 
 term onyx marble is also applied to these deposits. 
 
 (5) Thinolite. Here may be added a tufa-like deposit of a gray or 
 brownish color, occurring in large quantities in many lakes of Nevada and 
 California. 
 
 Calcite occurs very widely distributed. It is a common associate of 
 metalliferous ore deposits ; as limestone, marble, chalk, and marl it occurs 
 
CARBONATES 115 
 
 in large deposits, often of great thickness and extending over wide areas ; 
 common in cracks and cavities in igneous and sedimentary rocks ; and abun- 
 dant as spring, stream, and cave deposits. Excellent crystals are very 
 common. A few of the noted localities are : Eskifiord, Iceland ; Matlock 
 and Eyam, Derbyshire ; Egremont and Alston, Cumberland ; Weardale, Dur- 
 ham ; Furness, Lancashire ; Andreasberg, Hartz Mountains ; Kapnik, Hun- 
 gary ; Joplin, Missouri ; Rossie, St. Lawrence Co., New York, and the Lake 
 Superior Copper district. In the United States large deposits of marble 
 occur in Vermont, New York, Georgia, Tennessee, Massachusetts, Mary- 
 land, Pennsylvania, and California. 
 
 The different varieties of calcite are of great value, commercially. 
 Iceland spar is used in optical instruments ; limestone for building purposes, 
 quicklime, cement, flux in various metallurgical processes, railroad ballast, 
 macadam, in lithography, concrete, etc. ; marble for building, ornamental, 
 monumental and statuary purposes, and as a source of carbon dioxide; 
 chalk for whiting, crayon, scouring and polishing preparations, also as an 
 adulterant; marl for cement. 
 
 DOLOMITE, Pearl Spar, CaMg(CO 3 ) 2 . 
 
 Hexagonal, trigonal rhombohedral class, a : c=i : 0.8322. Rhom- 
 bohedral crystals are common. The faces are often curved, forming sad- 
 dle-shaped crystals. The unit rhombohedron is very common ; also more 
 acute modified rhombohedrons of the first order, especially those with the 
 coefficient m = 2 or 4 ; now and then rhombohedrons of the second order, 
 the characterizing forms of the trigonal rhombohedral class, are observed. 
 The symmetry of this class is also revealed by the etch 
 figures. Figure 63 shows a combination of the basal pina- 
 coid c, unit and modified rhombohedrons of the first order 
 r and m, and the rhombohedron of the second order n 
 with the coefficient m equal to 16/3. Some crystals are 
 rather complex. Twins, with the twinning plane parallel 
 to the basal pinacoid, are not uncommon. The modified 
 rhombohedron of the first order, 2 R, also acts as a 
 twinning plane. This is not a common law. Commonly 
 in coarse to fine grained masses. 
 
 Perfect rhombohedral cleavage. Conchoidal to sub- 
 conchoidal fracture. Brittle. . Hardness 3.5 to 4. Specific 
 gravity 2.80 to 2.95. Vitreous to pearly luster. White, 
 reddish, yellow, brown, or black. Transparent to translucent. 
 
 CaMg(CO 3 ) 2 . Sometimes with small amounts of iron and manganese. 
 According to Bauer the composition of almost all crystals is CaCO 3 : 
 
Il6 DESCRIPTIVE MINERALOGY 
 
 MgCO. 3 =i : i, normal dolomite. However, the ratio of the two carbon- 
 ates varies greatly, usually CaCO 3 predominates. Infusible before the 
 blowpipe, becomes alkaline. Fragments are but slightly acted upon by cold 
 dilute acid. The powder effervesces briskly with hot dilute acid. Occurs 
 as a pseudomorph after calcite, anhydrite, fluorite, barite, and cerussite. 
 Two general varieties of dolomite may be distinguished : (i) crys- 
 tallized and (2) crystalline. 
 
 (1) Crystallized dolomite occurs abundantly in many ore deposits, 
 and in cavities of various igneous and sedimentary rocks. Some important 
 localities are : Hall, Austria ; St. Gotthard, Bex, and elsewhere, Switzer- 
 land ; Kapnik, Hungary ; Clausthal, Hartz Mountains ; Freiberg, Saxony ; 
 Lockport and vicinity, N. Y. ; Joplin, Mo. ; Stony Point, N. C. ; and Rox- 
 bury, Vt. 
 
 (2) Crystalline dolomite. This is a compact, granular variety and 
 often occurs in enormous deposits of great thickness and extent. Many 
 mountain ranges in central Europe are principally dolomite. Crystalline 
 dolomite grades into dolomitic or magnesian limestone, see page 113. Crys- 
 talline dolomites are thought to have resulted in several ways, as follows : 
 (i) As a deposit from lagoons or salt lakes, due to the action of concentrated 
 magnesian brines upon organically formed aragonite. Such dolomites are 
 generally associated with gypsum and rock salt. (2) By the action of 
 solutions containing magnesian salts, such as MgCl 2 or MgSO 4 , upon lime- 
 stones, especially coral reefs. (3) By the leaching of the more soluble 
 calcium carbonate from magnesian limestones. This would tend to increase 
 the percentage of magnesium carbonate. Certain organisms, among them 
 lithothamnia, contain as much as 13% MgCO 3 , the remainder being essen- 
 tially CaCO a . 
 
 Dolomite is used extensively for building, statuary, monumental, and 
 ornamental purposes ; as a source of magnesium compounds ; and as a 
 refractory material. 
 
 ANKERITE, (Ca,Mg,Fe)CO 3 . 
 
 Hexagonal, ditrigonal scalenohedral class, a : c varies from i : 0.8 1 to i : 0.83. 
 Rhombohedral crystals. Usually in compact or granular masses. Rhombohedral 
 cleavage. Gray, white, reddish, or brown in color. Vitreous to pearly luster. 
 
 Ankerite is a ferruginous or manganiferous dolomite, containing about 50% of 
 CaCOs, 25 to 30% MgCOa, 5 to 20% FeCO, and at times 2 to 3% MnCO 3 . It is 
 generally found in metalliferous veins. Siderite is a common associate. 
 
 MAGNESITE, MgCO 3 . 
 
 Hexagonal, ditrigonal scalenohedral class, a : c = i : 0.8104. Not 
 often in rhombohedral crystals. Usually in granular, compact, or earthy 
 masses, resembling unglazed porcelain. 
 
 Crystals have a perfect rhombohedral cleavage. Conchoidal fracture. 
 
CARBONATES II? 
 
 Brittle. Hardness 3.5 to 4.5. Specific gravity 2.9 to 3.1. Transparent to 
 translucent. Colorless, white, yellow, brown, or blackish. 
 
 MgCCX. May contain some iron, manganese, or calcium. Infusible, 
 if ferruginous becomes magnetic. Powder is soluble in hot dilute acids. 
 
 Magnesite is commonly an alteration product of magnesium rocks, due 
 to hydration and carbonization. Thus, olivine, (Mg,Fe),SiO 4 , may alter 
 to serpentine, magnesite, limonite, and opal. Hence, it is usually found in 
 veins in talcose and chloritic schists, serpentine, and other magnesian rocks. 
 It occurs in Moravia and Styria, Austria ; Silesia ; Zillerthal, Tyrol ; Snarum, 
 Norway ; Greece ; Bolton and Roxbury, Mass. ; Lancaster and Chester coun- 
 ties, Pa. ; Tulare, Stanislaus, Santa Clara, Contra Costa, Napa, and Sonoma 
 counties, California. 
 
 Magnesite is used extensively as a source of carbon dioxide and mag- 
 nesium compounds. Calcined magnesite is used in refractory bricks for 
 basic linings in converters, as an adulterant of paint, and in medicine. Most 
 of the magnesite of commerce is obtained from Austria-Hungary, Germany, 
 Greece, California, and India. 
 
 BEEUNNERITE, (Mg,Fe)CO 3 . 
 
 This includes various varieties of ferruginous magnesite which *are intermediate 
 between magnesite and siderite, such as, mesitite and pistomesite. White, yellowish, 
 brown, rarely black, in color. Sometimes turns black on exposure. Specific gravity 
 3 to 3.4. Found at Traversella, Piedmont; Salzburg, Austria. 
 
 SMITHSONITE, Calamine, Dry Bone, ZnCO 3 . 
 
 Hexagonal, ditrigonal scalenohedral class, a : c = i : 0.8062. Crystals 
 are small, usually rough and curved. They often occur in groups on the 
 surface of compact crusts and stalactites. Generally reniform, botryoidal, 
 or stalactitic ; also in cellular crusts with a granular, fibrous, or compact 
 structure. The cellular or porous varieties are sometimes called dry bone. 
 
 Perfect rhombohedral cleavage. Uneven to splintery fracture. Brit- 
 tle. Hardness 5. Specific gravity 4.1 to 4.5. Vitreous to pearly luster. 
 Translucent to opaque. Colorless, yellow, brown, gray, blue, green, or 
 orange yellow. Streak white. 
 
 ZnCO 3 . Usually with some iron, manganese, cobalt, calcium, mag- 
 nesium, and at times considerable cadmium. The smithsonite from Wies- 
 loch, Germany, contains about 3% CdCO 3 . Turkey fat is a term often ap- 
 plied to yellow smithsonite containing greenockite, CdS. A variety from 
 Boleo, California, contains 10.27% cobalt oxide. Is often mixed with sand, 
 clay, ferric oxide, limestone, and dolomite. Infusible before the blowpipe. 
 Gives zinc, and often cadmium, reactions. Easily soluble in hot acids. Com- 
 mon as a pseudomorph after calcite, especially at Mineral Point, Wis. 
 
I I 8 DESCRIPTIVE MINERALOGY 
 
 Usually associated with zinc minerals, especially sphalerite and hemi- 
 morphite, also galena and limonite. It is a secondary mineral and occurs 
 extensively in the upper levels in limestones and dolomites. It is often the 
 result of the action of carbonated waters on other zinc minerals. Occurs 
 at Aachen, in Westphalia, Wiesloeh in Baden, and elsewhere in Germany ; 
 Bleiberg and Raibl, Carinthia ; Chessy, France ; Hungary ; Algeria ; Mat- 
 lock and Mendip Hills near Bristol, England. 
 
 In the United States it is found at Lancaster, Pa. ; Mineral Point, Wis. ; 
 many places in Missouri, Arkansas, Iowa, and Virginia. 
 
 It is an important zinc ore. The term calamine is sometimes applied 
 to smithsonite, but it refers more properly to hemimorphite, HoZnSiCX,. 
 
 MoNHEiMiTEj (Zn,Fe)CO3, is a ferruginous smithsonite, and may contain as 
 high as 50% FeCCX 
 
 RHODOCHROSITE, MnCO :r 
 
 Hexagonal, ditrigonal scalenohedral class, a : c = i : 0.8183. Crys- 
 tals usually show the unit rhombohedron ; sometimes rather small and 
 drusy. Generally in compact or granular masses, also globular, reniform, 
 botryoidal, and in crusts. 
 
 Perfect rhombohedral cleavage. Conchoidal to uneven fracture. Brit- 
 tle. Hardness 3.5 to 4.5. Specific gravity 3.3 to 3.6. Rarely colorless, 
 most generally rose red, also gray., yellow, brown, green ; and due to alter- 
 ation, black. Vitreous to pearly luster. Streak white. Translucent. 
 
 MnCO 3 . May contain as much as 25% CaCO 3 (manganocalcite}, 40% 
 FeCO 3 (manganosiderite'), 4% MgCO 3 ; also small amounts of zinc and 
 cobalt. Infusible before the blowpipe, turns greenish or black. Reacts for 
 manganese. Easily soluble in warm dilute acids. Occurs as a pseudomorph 
 after calcite and fluorite. 
 
 Commonly found with deposits of iron, lead, gold, silver, copper, and 
 manganese minerals, thus at Freiberg, Saxony ; Kapnik, Hungary ; Nagyag, 
 Transylvania ; Hambach near Diez, Nassau ; Mine Hill, Franklin Furnace, 
 N. J. ; Alicante, Lake Co., Colo. ; Butte, Mont. ; Austin, Nevada. 
 
 MANGANOCALCITE, (Mn,Ca)CO 3 , is a rhodocrosite containing as much as 25% 
 calcium carbonate. 
 
 OUGONITE, (Fe, Mn)CO 3 , is a manganiferous siderile. 
 
 SIDERITE, Spathic Iron, Chalybite, FeCO.,. 
 
 Hexagonal, ditrigonal scalenohedral class, a : c = i : 0.8184. Rhom- 
 bohedral crystals are rather common, often distorted and with curved faces. 
 Crystals usually show the unit rhombohedron alone, or in combination 
 with the modified rhombohedrons y 2 R, 2R, and 4R, the prisms of the 
 
CARBONATES IIQ 
 
 first and second orders, various scalenohedrons, and the basal pinacoid. 
 Commonly in coarse to fine granular masses, also botryoidal, globular, or 
 concretionary. 
 
 Perfect rhombohedral cleavage. Conchoidal to splintery fracture. 
 Brittle. Hardness 3.5 to 4.5. Specific gravity 3.7 to 3.9. Vitreous to 
 pearly luster. Usually brownish to brownish red in color ; also ashen gray, 
 yellowish gray, greenish gray, green, and white. Fresh varieties have a 
 white streak. 
 
 FeCCX. Usually contains some CaCO 3 and MnCO 3 . The mangan- 
 iferous varieties are termed oligonitc. Mixed with clay, sand, and organic 
 matter, it is called clay ironstone or blackband. Infusible before the blow- 
 pipe, turns black. Becomes magnetic. Reacts for iron. Effervesces with 
 acids. Occurs as a pseudomorph after fluorite, aragonite, calcite, dolomite, 
 barite, pyrite, and galena. It alters to limonite, hematite, and sometimes 
 to magnetite. 
 
 Siderite occurs commonly with sulphide ore deposits, also in beds and 
 concretions in limestones and shales. The common associates of siderite 
 are pyrite, galena, chalcopyrite, cryolite, tetrahedrite, etc. It occurs with 
 ore deposits in the Hartz Mts. ; Pribram, Bohemia ; Cornwall, England ; 
 Freiberg, Saxony, etc. With cryolite and chalcopyrite in western Green- 
 land. In beds and as concretions in Westphalia; southern Wales; Silesia, 
 etc. In the United States it is found in eastern Ohio, Kentucky, and west- 
 ern Pennsylvania, principally in beds in the Lower Coal measures. 
 
 It is sometimes used as an ore of iron. In 1906 the United' States 
 produced 17,996 tons of siderite. This was only a fraction of one percent 
 of the iron ore mined that year. 
 
 SPHAEROCOBALTITE, CoCO 3 . Hexagonal, ditrigonal scalenoheciral class. Rarely in 
 crystals. Usually in coarse, radial, spherical masses. Velvet black on the surface, rose 
 red in the interior. Reddish streak. Hardness 4. Specific gravity 4 to 4.13. Found 
 at Schneeberg, Saxony. 
 
 ARAGONITE, Flos Ferri, CaCO :i . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.6228 : I : 0.7204. 
 Crystals are rather common and show great diversity in development. 
 They may be domatic (chisel-like), acute pyramidal (spear-shaped), and 
 prismatic (often pseuclohexagonal). Many forms have been observed. 
 Figure 64 shows a common combination which consists of m the unit prism, 
 b brachypinacoid, and k unit brachydome. The prism angle is 116 12', 
 hence, often hexagonal in outline. This pseudohexagonal symmetry is 
 accentuated by twinning. Twins are more common than simple crystals. 
 Usually the unit prism acts as the twining plane. Contact (Figure 65), 
 
DESCRIPTIVE MINERALOGY 
 
 polysynthetic (Figure 66), cyclic, and penetration (Figure 67) twins are 
 commonly observed. Figure 68 shows clearly the pseudohexagonal sym- 
 metry of penetration trillings. Also in radial, columnar and fibrous aggre- 
 gates, stalactitic, branching forms, crusts, reniform, and globular. 
 
 Brachypinacoidal and prismatic cleavages, rather imperfect. Con- 
 choidal fracture. Brittle. Hardness 3.5 to 4. Specific gravity 2.9 to 3. 
 Colorless, white, gray, yellow, relish, green, bluish, and black. Streak 
 
 m 
 
 FIG. 64. 
 
 FIG. 65. 
 
 FIG. 66. 
 
 FIG. 67. 
 
 white. On fracture surfaces greasy luster, elsewhere vitreous. Trans- 
 parent to translucent. 
 
 CaCO 3 . May contain strontium, iron, manganese, lead, or zinc. Effer- 
 vesces easily in acids, but not as readily as calcite. Meigen's test is th( 
 best chemical reaction to differentiate definitely massive aragonite from 
 calcite, see page 113. Aragonite occurs as a pseudomorph after gypsum 
 and calcite. More abundant are, however, calcite pseudomorphs after ara- 
 gonite. At about 600 C., aragonite is changed to calcite. 
 
 Aragonite is usually deposited from aqueous solutions with a tempera- 
 ture over 30 C., at a lower temperature calcite is formed. Aragonite is 
 found ( i ) in cracks and cavities in various kinds of rocks and is usually 
 associated with the zeolites. (2) In ore deposits, especially iron ore. The 
 coralloidal variety occurring with siderite at Hitttenberg, Carinthia, is 
 termed flos ferri. (3) Disseminated in clay. Here aragonite is generally 
 
CARBONATES I 2 1 
 
 associated with gypsum, sulphur, and celestite. (4) As a deposit from hot 
 springs and geysers, sometimes pisolitic and in crusts. (5) Aragonite 
 constitutes the pearly layer of many shells and pearls. Aragonite is not 
 nearly as common as calcite. Some noted localities are: Herrengrund, 
 Hungary ; Bilin, Karlsbad, and Horschenz, Bohemia ; Molina, Aragon, 
 Spain ; Girgenti, Sicily ; Alston Moor, England ; Hoboken, N. J. ; Lock- 
 port, N. Y. ; Warsaw, 111. ; Haddam, Conn., etc. 
 Aragonite is of no importance, commercially. 
 
 STRONTIANITE, SrCO,. 
 
 Orthorhombic, bipyramidal class, a : b : c -- 0.6089 : I : 0.7237 
 Crystals are usually spear-shaped or acicular. They are often arranged in 
 radial aggregates. Forms and twins similar to aragonite, page 119. Pseudo- 
 hexagonal symmetry, prism angle is 117 19'. Also granular and compact, 
 sometimes with a radial, fibrous structure. 
 
 Imperfect prismatic cleavage. Conchpidal fracture. Brittle. Hard- 
 ness 3.5 to 4. Specific gravity 3.6 to 3.8. Vitreous luster, greasy on frac- 
 ture surfaces. Colorless, gray, yellow, yellowish brown, and green. Streak 
 white. Transparent to translucent. 
 
 SrCO :; . Usually contains some calcium and barium. Emmonite, 01 
 calcio Strontianite, from Brixlegg, Tyrol, contains as much as 13% of CaCO 3 . 
 Fuses on the edges, imparts a crimson color to the flame, and becomes 
 alkaline. Easily soluble with effervescence in cold dilute acids. Occurs 
 as a pseudomorph after celestite. 
 
 Occurs in ore deposits, commonly with barite and galena. Thus, at 
 Clausthal, Hartz Mts. ; Freiberg, Saxony ; Hamm in Westphalia, Germany ; 
 Strontian in Argyll shire, Scotland ; Schoharie and Clinton, also various places 
 in Jefferson county, N. Y. ; Ida, Monroe Co., Mich. ; Mount Bonnell and 
 Mount Baker, near Austin, Texas. 
 
 Strontianite is the chief source of strontium compounds, many of which 
 are used extensively in the chemical laboratory. The oxide and hydroxide 
 are of importance in the precipitation of sugar from molasses ; the nitrate, 
 carbonate, and oxalate are used for red fire ; the iodide, bromide, and lactate 
 in medicine. Most of the Strontianite used in the United States is imported 
 from Westphalia, where it occurs in veins in rocks of cretaceous age. 
 
 BROMUTE, Alstonite, (Ca,Ba)CO 3 . 
 
 Orthorhomhic, bipyramidal class, a : b : c 0.5871 : I : 0.7390. An iso- 
 morphous mixture of CaCOj and BaCOs. Crystals are usually acute pyramidal, pseudo- 
 hexagonal. Hardness 4 to 4.5. Specific gravity 3.65 to 3.76. Colorless to grayish 
 white. Luster is slightly greasy. Translucent. Occurs at Fallowfield, near Hexham, 
 Northumberland ; also at Bromley Hill, near Alston, Cumberland. 
 
122 DESCRIPTIVE MINERALOGY 
 
 WITHERITE, BaCO 3 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.5949 : I : 0.7413. 
 Usually in pseudohexagonal bipyramids, resembling quartz. These are 
 penetration trillings with the twinning plane parallel to the unit prism. 
 The prism angle is ii748'. Also compact, in botryoidal, reniform, and 
 globular masses, often showing a lamellar or 'radial fibrous structure. 
 
 Imperfect prismatic cleavage. Uneven fracture. Brittle. Hardness 
 3.5 to 4. Specific gravity 4.2 to 4.35. Colorless, white, gray, or yellow 
 white. Streak white. Vitreous luster, on fracture surfaces somewhat greasy. 
 Translucent. 
 
 BaCO 3 . Easily fusible, imparts a green color to the flame. Readily 
 soluble in dilute hydrochloric acid. Precipitated from solution by sulphuric 
 acid. 
 
 Occurs in large quantities with deposits of galena in northwestern 
 England, thus, at Fallow r field, near Hexham, Northumberland ; Dufton, 
 Westmoreland ; Alston Moor, Cumberland. Otherwise, witherite is not 
 very common. With barite at Freiberg, Saxony ; Lexington, Kentucky ; 
 also in the Thunder Bay district, Lake Superior. 
 
 Witherite is used to adulterate white lead and in the extracting of 
 sugar from sugar-beets. In 1908 the importation of witherite into the 
 United States was valued at $22,159. 
 
 TARNOWITZITE, (Ca,Pb)CO 8 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.6220 : i : 0.7168. This is an 
 isomorphous mixture of CaCOs and PbCOs. The amount of PbCOa present may be 
 as high as g%. Crystals are sometimes rather complicated ; generally pyramidal in 
 habit. Often twins, trillings, and even cyclic twelvelings. White or green in color. 
 Specific gravity 2.99. Occurs in the Friedrich mine, near Tarnowitz, Silesia. 
 
 CERUSSITE, Cerusite, White Lead Ore, PbCO 3 . 
 
 Orthorhombic, bipyramidal class, a : b ': c = 0.6101 : i : 0.7229. 
 Crystals are generally tabular, prismatic, or pyramidal in habit. Often 
 arranged in clusters or star-shaped groups. Many forms have been observed 
 and the crystals are sometimes rather complex. Pseudohexagonal symmetry 
 due to a prismatic angle of 117 14'. Twins are very common and similar 
 to those of aragonite, page 119. The twinning plane is usually a plane 
 parallel to the unit prism. Penetration trillings according to this law form 
 stellate groups. A second twinning law with the twinning plane parallel 
 to the brachyprism, n = 3, is not very common. Also compact, in granular 
 and, more rarely, fibrous masses; reniform, stalactitic, in crusts, and earthy. 
 
 Distinct prismatic and brachydomatic cleavages. Conchoidal fracture. 
 Brittle. Hardness 3 to 3.5. Specific gravity 6.4 to 6.6. Colorless, white, 
 
CARBONATES 1^3 
 
 gray, yellow, brown, blue, green, and black. Streak white. Greasy or 
 resinous luster. Transparent to translucent. 
 
 PbCO 3 . At times contains silver and zinc. A variety from Mt. Poni, 
 Iglesias, Sardinia, containing J% ZnCO 3 , is termed iglesiasite. May con- 
 tain admixtures of galena and organic matter. Fuses easily, decrepitates, 
 and yields a lead coating ; also a globule of lead. Is soluble in nitric acid 
 with effervescence, in hydrochloric and sulphuric acids with a white residue 
 Occurs as a pseudomorph after galena and anglesite. 
 
 Occurs commonly in the upper levels of galena deposits, from which 
 it has resulted by the action of carbonated waters. Anglesite, PbSO 4 , is 
 often an intermediate product. Found at Clausthal, Hartz Mts. ; Johann- 
 georgenstadt, Saxony ; Mies and Pribram, Bohemia ; Friedrichssegen and 
 Ems, Nassau ; Broken Hill, New South Wales, with ores of copper and 
 silver ; L,eadhills, Scotland ; Leadville, Colorado, formerly in great quan- 
 tities ; Pima and Yuma counties, Arizona ; Park City, Utah. 
 
 Cerussite is an important ore of lead and silver. 
 
 BARYTOCALCITK, BaCO ;i . CaCO 3 . 
 
 Monoclinic, prismatic class, a : b : c = 1.1201 : i : 0.8476, /3 102 26'. 
 Small prismatic crystals, also in granular aggregates. Prismatic and basal pinacoidal 
 cleavages. Hardness 4. Specific gravity 3.65. Yellow white in color. Vitreous luster. 
 Translucent. 
 
 BaCO 3 .CaCO 3 . Considered a double salt. The two carbonates are always pres- 
 ent in the same ratio, namely, i : i. Occurs with alstonite, barite, and fluorite at 
 Alston Moor, Cumberland; also Langban, Sweden. 
 
 B. BASIC CARBONATES 
 
 MALACHITE GROUP 
 
 This group includes the basic carbonates of copper, zinc, and lead, 
 
 MALACHITE, CuCO,. Cu(OH) 2 . Monoclinic Prismatic Class 
 
 AZURITE, 2CuCO :1 . Cu(OH)o. Monoclinic Prismatic Class 
 
 HYDROCTJRUSSITE, 2PbCO 3 . Pb(OH) 2 . Dihexagonal Bipyramidal Class 
 
 HYDROZINCITE, ZnCO 3 .2Zn(OH) 2 . ? 
 
 AURLCHALCITU, 2 (Zn.Cu) CO 3 . 3 (Zn.Cu) (OH) 2 . 
 
 Monoclinic Prismatic Class 
 
 The chemical and crystallographical properties of the members of this 
 group vary so greatly that no definite relationship can be pointed out. 
 
124 DESCRIPTIVE MINERALOGY 
 
 MALACHITE, Green Carbonate of Copper, CuCO 3 . Cu(OH) 2 . 
 
 Monoclinic, prismatic class, a : b : c = 0.7823 : I : 0.4036, ft 
 90 3". Crystals are usually acicular, very slender, and without good 
 terminations. Often arranged in groups and tuffs. Vertically striated. 
 The unit prism and the three pinacoids are the forms commonly observed. 
 Twins are rather common, the twinning plane being parallel to the ortho- 
 pinacoid. Commonly in reniform, botryoidal, and stalactitic aggregates 
 with smooth surfaces and banded or radial fibrous structure. Also earthv 
 and in crusts. 
 
 Perfect basal and clinopinacoidal cleavages. Conchoidal fracture. Brit- 
 tle. Hardness 3.5 to 4. Specific gravity 3.7 to 4.1. Bright emerald green, 
 grass green to nearly black in color. Light green streak. Translucent to 
 opaque. Adamantine, silky, or dull luster. 
 
 CuCO 3 .Cu(OH) 2 . Crystals are usually quite pure. Compact masses 
 may be mixed with clay, the oxides of iron and manganese, silica, etc. 
 Fuses easily, colors the flame green, and yields a globule of copper. Yields 
 water and carbon dioxide in a closed tube. Effervesces with acids. Occurs 
 commonly as a pseudomorph, especially after cuprite, atacamite, azurite, 
 tetrahedrite, chalcopyrite, calcite, cerussite, etc. 
 
 Malachite is a common alteration product of copper minerals, usually 
 the result of the action of carbonated waters. Hence, it is found in 
 smaller or greater quantities in the upper levels of all copper mines. In 
 the Ural Mts. it occurs in large quantities ; Chessy, France, pseudomorphs 
 after cuprite ; Cornwall, England ; various places in the Hartz Mts. ; Chile ; 
 Australia. Formerly in magnificent specimens in the Bisbee and Clifton 
 Copper districts of Arizona, especially the Detroit and Manganese Blue 
 mines ; Park City, Utah ; as a coating on native copper in the Lake Superior 
 Copper region ; also in Amelia Co., Virginia, etc. 
 
 Malachite is used as an ore of copper. Also in jewelry and for orna- 
 mental purposes, such as table tops, vases, etc. 
 
 AZURITE, Chessylite, Blue Carbonate of Copper, 2CuCO :! . Cu(OH),. 
 
 Monoclinic, prismatic class, a : b : c = 0.8501 : i : 1.7611, ft = 
 92 24'. Crystals are generally short prismatic or thick tabular, and 
 arranged in spherical aggregates. Often very complex. Common forms 
 are the unit prism, unit negative pyramid, basal pinacoid, and the clinodome 
 with m equal to 1/3. Twins are not common, the twinning plane is parallel 
 to the orthodome with the coefficient m equal to ^. Usually compact ; in 
 reniform and botryoidal masses, often with a velvety, radial fibrous struc- 
 ture ; also earthy and in crusts. 
 
CARBONATES 125 
 
 Distinct clinodomatic cleavage. Conchoidal to uneven fracture. Brit- 
 tle. Hardness 3.5 to 4. Specific gravity 3.7 to 3.83. Vitreous to adaman- 
 tine luster. Light azure to deep blue in color. Streak light blue. Translu- 
 cent to opaque. 
 
 2CuCO ;i .Cu(OH) 2 . Chemical reactions same as for malachite, page 
 124. Occurs as a pseudomorph after cuprite, tetrahedrite, and dolomite. 
 Alters to malachite according to the following reaction : 
 
 2[2CuCO 3 . Cu(OH) 2 ] -|- H 2 O -f CO 2 = 3[CuCO 8 . Cu(OH),]. 
 
 Formation and occurrences same as for malachite. Excellent crystals 
 occur at Chessy, France ; Cornwall, England ; Ural Mts. ; Chile ; Australia ; 
 Bisbee and Clifton Copper districts, Arizona ; also in Utah, California, etc. 
 
 An ore of copper. Paint made from azurite turns green in time, due 
 to an alteration to malachite, see above. 
 
 HYDROCERUSSITE, 2.PbCO 3 . Pb(OH) 2 . 
 
 Hexagonal, dihexagonal bipyramidal class, a : c = i : 1.4187. Occurs as color- 
 less plates on native lead at Langban, Sweden ; with galena at Wanlockhead, Scotland. 
 
 HYDROZINCITIV, Zinc Bloom, ZnCO 3 . 2Zn(OH) 2 . 
 
 Crystal form is unknown. Only in compact, earthy, or fibrous masses ; some- 
 times reniform, stalactitic, or in crusts. Somewhat brittle. Hardness 2 to 2.5. Spe- 
 cific gravity 3.25 to 3.8. Color is snow white to yellowish. Vitreous luster. 
 
 ZnCOs.2Zn(OH) 2 . Composition is not constant. Hydrozincite is an alteration 
 product of rdnc minerals. Hence, is found with hemimorphite, smithsonite, sphalerite, 
 etc. Occurs at Bleiberg and Raibl, Carinthia ; various places in the province of San- 
 tander, Spain ; Sardinia ; Algeria ; Friedensville, Penna ; Linden, Wis. 
 
 AURICHALCITE, 2(Zn.Cu)CO 3 -3(Zn.Cu) (OH) 2 . 
 
 Monoclinic, prismatic class, a : b : c = ? : i : 1:657, = 84 15'. Acicular 
 crystals, also rosette aggregates. Hardness 2. Pale green to sky-blue in color. 
 Pearly luster. Translucent. May contain as, much as 8% CaCOs, and is then known 
 as buratite. Occurs with limonite and calcite at Loktewsk, Altai, Siberia; Chessy, 
 France; Lancaster, Penna.; Santa Caterina Mts., Arizona; Beaver Co., Utah. 
 
 DAWSONITE, Na.Al(OH) 2 CO 3 . Occurs in thin lamellar, and fibrous aggregates. 
 White in color. Vitreous luster. Specific gravity 2.40. Found in a feldspathic dike 
 at Montreal, Canada; also in a cinnabar-bearing dolomite in Tuscany. 
 
 BISMUTITE, probably Bi 2 CO 5 .H 2 O. Occurs in crusts; earthy; amorphous. Dirty 
 green or yellow in color. Found at Schneeberg and Johanngeorgenstadt, Saxony; 
 Gaston Co., N. C.; Brewer's Mine, S. C. 
 
126" DESCRIPTIVE MINERALOGY 
 
 PHOSGENITE, Corneous Lead, (PbCl) 2 CO 3 . 
 
 Tetragonal, a : c i : 1.0876. Short prismatic or acute pyramidal crystals. 
 Common forms are the prisms of the first and second orders, unit and modified 
 (w = 3/2 and 8) bipyramids, and the basal pinacoid. Prismatic cleavages. Con- 
 choidal fracture. Somewhat sectile. Hardness 2.5 to 3. Specific gravity 6 to 6.3. 
 Greasy adamantine luster. Color white, gray, or yellow. White streak. Transparent 
 to translucent. 
 
 (PbCl) 2 CO 3 . This is a chlorocarbonate of lead. Easily fusible. Yields on 
 charcoal a globule of lead. Soluble with effervescence in dilute nitric acid. 
 
 Commonly associated with galena. Has resulted from the alteration of galena. 
 Occurs at. Mt. Poni and Gibbas, Sardinia; Matlock, Derbyshire; with cerussite at 
 Tarnowitz, Silesia ; on ancient lead slags at Laurium, Greece. 
 
 NORTHUPITE, MgCO 3 .Na 2 COs.NaCl. White, yellow, or gray octahedrons. Hard- 
 ness 3.5 to 4. Specific gravity 2.4. Very brittle. Decomposed by hot water with 
 a separation of magnesium carbonate. Occurs sparingly in clay at Borax Lake, San 
 Bernardino Co., Cailfornia. 
 
 C. HYDRATED CARBONATES 
 
 No isomorphous groups have as yet been noted among the hydrated 
 carbonates. 
 
 THERMONATRITE, Na 2 CO 3 . H 2 O. 
 
 Orthorhombic, bipyramidal class, a : b : c 0.3644 : i : 1.2254. Rectangular 
 plates. Generally as a fibrous or earthy efflorescence. Brachypinacoidal cleavage. 
 Hardness 1.5. Specific gravity 1.5 to 1.6. Colorless. Occurs in the soda lakes of 
 Egypt and East India ; also as an efflorescence in arid regions. 
 
 Natron, Soda, Na 2 CO 3 . ioH 2 O. 
 
 Monoclinic, prismatic class, a : b : c = 1.4186 : i : 1.4828, (3 = 
 122 20'. Artificial crystals are usually tabular, somewhat similar to those 
 of gypsum, page ??. They consist of the unit prism, clinopinacoid, and 
 the negative unit pyramid. In nature natron occurs only in crystalline 
 crusts or as an earthy efflorescence. Clino- and orthopinacoidal cleavages. 
 Conchoidal fracture. Hardness i to 1.5. Specific gravity 1.4 to 1.5. Color- 
 less, gray or yellow white. Vitreous luster. Transparent to translucent. 
 
 Na 2 CO 3 . ioH 2 O. When heated, it melts in its water of crystallization. 
 Easily soluble in water. On exposure to air loses water of crystallization 
 and alters to thermonatrite, Na 2 CO 3 .H 2 O. 
 
 Occurs in the soda lakes of Egypt, and North and South America. 
 
CARBONATES 1 27 
 
 Also as an efflorescence in arid regions, and in small quantities on the 
 lavas of Aetna, Vesuvius, etc. 
 
 The artificial compound is used extensively in glass and soap manufac- 
 ture, washing powders, etc. 
 
 Trona, Urao, Na 2 CO ;r NaHCO :! . 2H 2 O. 
 
 Monoclinic, prismatic class, a : b : c == 2.8459 : : : 2.9696, = 
 102 37'. Tabular, fibrous, or columnar crystals. The common forms are 
 the basal and orthopinacoids, and the positive unit pyramid. Generally 
 in crystalline crusts. Perfect orthopinacoidal cleavage. Hardness 2.5 to 3. 
 Streak white. Specific gravity 2.1 to 2.2. Colorless, gray or yellow white. 
 Translucent. Vitreous luster. Alkaline taste. 
 
 Na 2 CO 3 .NaHCO 3 .2H,O. Usually mixed with some NaCl and Na 2 SO 4 . 
 Easily soluble in water. Does not effloresce. Yields much water in a closed 
 tube. Effervesces with acids. Colors flame an intense yellow. 
 
 Occurs in the province of Fezzan, Africa, where it is used to some 
 extent for building purposes ; in the soda lakes of Egypt, East Indies, and 
 Venezuela. Also in Churchill Co., Nevada ; Borax Lake, San Bernardino 
 Co., and Owen's Lake, Inyo Co., California. 
 
 PIRSSONITE, Na 2 CO 3 . CaCO 3 . 2H 2 O. 
 
 Orthorhombic, pyramidal class, a : b : c = 0.5662 : I : 0.3019. Hemimorphic 
 crystals. Colorless to cloudy white. Vitreous luster. Brittle. Hardness 3 to 3.5. 
 Specific gravity 2.35. Soluble with effervescence in cold dilute acids. Occurs in clay 
 in Borax Lake, San Bernardino Co., California. 
 
 GAY-LUSSTTE, Na 2 CO 3 . CaCO 3 . 5H 2 O. 
 
 Monoclinic, prismatic class, a : b : c = 1.4897 : i : 1.4442, /3 = ioi33'. 
 Columnar or wedge-shaped crystals. Colorless, white, gray, or yellow. Prismatic 
 cleavage. Conchoidal fracture. Hardness 2 to 3. Specific gravity 1.9 to 1.95. Trans- 
 parent to translucent. Streak .white or grayish. Vitreous luster. 
 
 NaaCOj.CaCOs.sHaO. Soluble with effervescence in acids. Partially soluble in 
 water, Na 2 CO 3 may be thus readily extracted. Fuses to a white enamel. Colors flame 
 yellow. Occurs at Lagunilla, Venezuela ; Soda Lake, near Ragtown, Nevada. The 
 artificial compound is produced on a large scale in the Leblanc process for the manu- 
 facture of sodium carbonate. 
 
 HYDROMAGNESITE, 3MgCO3.Mg(OH).3H 2 O. Monoclinic, prismatic class, a : b : 
 c = 1.03/9 : i : 0.4652, /8 = 90 (approximately). Has been considered orthorhom- 
 b:c. Small, indistinct acicular crystals. Sometimes arranged in radial groups; also 
 m crusts. Snow-white in color. Earthy to imperfect conchoidal fracture. Hardness 
 
128 DESCRIPTIVE MINERALOGY 
 
 1.5 to 2. Specific gravity 2.15.' Is an alteration product of serpentine. Occurs at 
 Hoboken, N. J. ; Texas, Penna.; Hrubschitz, Moravia; Kraubat, Styria. Predazziie 
 and pencatite are crystalline limestones, mixed with hydromagnesite and periclase, 
 and occur at Predazzo, Tyrol. 
 
 ZARATITE, Emerald Nickel, Texasite, NiCO 3 .2Ni(OH) 2 .4H 2 O. Crystallization 
 is unknown. Usually in fine crystalline, warty crusts. Sometimes, compact and mas- 
 sive. Hardness 3. Specific gravity 2.57 to 2.69. Translucent. Subvitreous luster. 
 Occurs on chromite at Texas, Lancaster Co., Penna.; Island of Unst, Scotland; Tas- 
 mania; Spain. 
 
 3. MANGANITES AND PLUMBITES 
 
 The two acids of manganese, H 2 MnO 3 and H 4 MnO 4 , and the ortho- 
 plumbous acid, H 4 PbO 4 , form compounds which are of considerable import- 
 ance as minerals. 
 
 BRAUNITE GROUP 
 
 This group includes the manganese and iron salts of the manganous 
 acid H 2 MnO s . 
 
 a : c 
 
 BRAUNITE, MnMnO 3 . Ditetragonal Bipyramidal Class i : 0.9922 
 BIXBYITE, FeMnO 3 . Cubic, Hexoctahedral Class 
 
 BRAUNITE, MnMnO 3 . 
 
 Tetragonal, ditetragonal bipyramidal class, a : c = i : 0.9922. Tetragonal 
 bipyramids simulating the octahedron of the cubic system. Crystals are usually very 
 small and arranged in drusy crusts. Commonly the unit tetragonal bipyramid occurs 
 alone, sometimes with the basal pinacoid and the ditetragonal bipyramid with co- 
 efficients n and m equal to 2 and 4, respectively. Twins are not common. Twinning 
 plane is parallel to the prism of the second order. Also in granular aggregates. 
 
 Perfect pyramidal cleavage. Uneven fracture. Brittle. Hardness 6 to 6.5. 
 Specific gravity 4.75 to 4.9. Greasy metallic luster. Opaque. Brown to iron black 
 in color. Brownish black streak. 
 
 MnMnOs. Usually contains some silica and barium oxide. Marc dine is a variety 
 with from 7 to 15% of silica. Infusible. Evolves chlorine when treated with hydro- 
 chloric acid. Imparts an amethystine color to the borax bead. 
 
 Occurs with other ores of manganese, magnetite, and hematite at Ilmenau, Thu- 
 ringia; Ilfeld, Hartz Mts. ; St. Marcel, Piedmont; in large quantities at Jakobsberg 
 and elsewhere in Sweden; India; near Batesville, Arkansas. 
 
 An ore of manganese. 
 
 BIXBYITE, FeMnOs. Cubic. Occurs in small cubes. Black in color. A portion 
 of the iron may be replaced by magnesium and manganese, the manganese by titanium. 
 Occurs with topaz and decomposed manganese garnets (spessartite) in rhyolite in 
 Utah. 
 
MANGAN1TES AND PI/UMBITES I2Q 
 
 HAUSMANNITE GROUP 
 
 Here are placed the manganese and lead salts of the ortho acid having 
 the general formula H 4 RO 4 , where R may be either manganese or lead. 
 
 a : c 
 
 HAUSMANNITE, Mn 2 MnO 4 . Tetragonal Scalenohedral Class i : 1.1573 
 MINIUM, Pb 2 PbO 4 . ? 
 
 HAUSMANNITE, Mr^MnCV Tetragonal, scalenohedral class, a : c = i : I.I573- 
 Crystals are apparently holohedral and possess a bipyramidal habit. The bipyramids 
 are more acute than those of braunite. Crystal faces are often striated horizontally. 
 The common form is the unit bipyramid of the first order; more rarely the modified 
 bipyramid with the coefficient m equal to 1/3, and the prism of the second order. 
 Twins are common. Twinning plane is parallel to the prism of the second order. 
 Cyclic fivelings according to this law are not uncommon. They resemble large bipyra- 
 mids with furrowed edges. Also in granular masses. 
 
 Perfect basal cleavage. Uneven fracture. Hardness 5 to 5.5. Specific gravity 
 4.7 to 4.8. Greasy metallic luster. Brownish black in color. Brown streak. 
 
 Mn 2 MnO 4 . Infusible. Soluble in hydrochloric acid with an evolution of chlorine. 
 
 Usually associated with braunite and other manganese minerals. Occurs at Ilfeld, 
 Hartz Mts. ; Ilmenau, Thuringia; Pajsberg, Nordmarken, Langban, and elsewhere in 
 Sweden. 
 
 MINIUM, Pb 2 PbO 4 . Crystalline form unknown. Occurs only in powdery or 
 crystalline scales or masses. Hardness 2 to 3. Specific gravity 4.6. Opaque. Dull 
 or faint greasy luster. Bright red in color. Streak orange yellow. On charcoal 
 yields globule and characteristic coating of lead. Occurrences in nature are doubtful. 
 Minium is formed when lead ores are roasted, and, hence, is sometimes observed as 
 a pseudomorph after galena and cerussite. Found at Bleialf in the Eifel, Prussia ; 
 Badenweiler, Baden ; Austin, Wythe Co., Va. ; Leadville, Colo. 
 
 CHALCOPHANITE, (Zn,Mn)Mn 2 O 5 .2H 2 O. Hexagonal, ditrigonal scalenohedral 
 class, a : c i : 3.527. Small tabular crystals; also foliated aggregates and stalac- 
 titic. Hardness 2.5. Specific gravity 3.9. Bluish to iron black in color. Chocolate 
 brown streak. Metallic luster. An alteration product of franklinite. Occurs with 
 franklinite at Sterling Hill, Sussex Co., N. J. In hydrofranklinitc iron replaces a 
 portion of the manganese. 
 
 Psilomelane, Black Hematite. 
 
 Occurs only in botryoidal, reniform, or stalactitic masses, usually with 
 a smooth .surface and at times with an apparently fine fibrous structure. 
 Dark gray to iron black in color. Brownish black streak. Dull or sub- 
 metallic luster. Hardness 5 to 6. Specific gravity 3.7 to 4.7. Brittle. 
 Opaque. 
 
 It is doubtful whether psilomelane is an independent mineral or not. 
 It is often considered a manganite of manganese with considerable barium 
 replacing manganese. Usually contains 6 to 17% of barium oxide, i to 6% 
 
130 DESCRIPTIVE MINERALOGY 
 
 water, and varying* amounts of the oxides of potassium, calcium, cobalt, 
 copper, aluminium, silicon, etc. Infusible. Evolves chlorine when treated 
 with hydrochloric acid. Reacts for manganese and barium. 
 
 Occurs with other manganese ores, limonite, barite, etc. Found at 
 Ilfeld, Hartz Mts. ; Ilmenau, Thuringia ; Devonshire, and Cornwall, Eng- 
 land ; Brandon and elsewhere, Vermont; Virginia; Independence Co., 
 Arkansas. 
 
 One of the most common ores of manganese. Uses are the same as 
 for pyrolusite, page 821 
 
 WAD. Compact, earthy masses of a dark brown or black color. Often soils the 
 fingers, may, however, possess the hardness 6. Specific gravity 3 to 4.3. When soft, 
 it is usually loosely compact. Brown streak. Composition varies greatly. Is a 
 mixture of the various manganese minerals. Contains 5 to 14% of water and, in 
 general, the same impurities as psilomelane. The amount of manganese varies from 
 15 to 40%. Wad is used as an ore of manganese, and in the manufacture of chlorine 
 and paint. 
 
VI. SULPHATES, CHROMATES, MOLYB- 
 
 DATES, TUNG STATES, AND 
 
 URANATES 
 
 1. NORMAL SULPHATES AND CHROMATES 
 
 The minerals of this section are normal anhydrous salts of sulphuric 
 and chromic acids, and may be readily divided into several isomorphous 
 groups. 
 
 GLASERITE GROUP 
 
 This group includes the normal anhydrous sulphates of potassium, 
 sodium, and ammonium. The sulphate of potassium and sodium is di- 
 morphous. The group may, hence, be divided into two series, as follows : 
 
 HEXAGONAL SERIES 
 
 a : c 
 GLASERITE, (K,Na),SO 4 . Ditrigonal Scalenohedral Class i : 1.2879 
 
 ORTHORHOMBIC SERIES 
 
 a : b : c 
 
 ARCANITE, (K,Na) 2 SO 4 . Bipyramidal Class 1.7462 : i : 1.3033 
 
 MASCAGNITE, (NH 4 ),SO 4 . Bipyramidal Class 1.7722 : i : 1.2954 
 
 THENARDITE, Na 2 SO 4 . Bipyramidal Class 1.7910 : i : 1.2541 
 
 The elements of crystallization given for arcanite and mascagnite are 
 for artificial crystals. 
 
 GLASERITE, (K,Na),SO 4 . 
 
 Hexagonal, ditrigonal scalenohedral class, a : c = i : 1.2879. Colorless, tabular 
 crystals. Unit prism predominates. Crystals are often arranged in groups resembling 
 aragonite trillings. Vitreous luster. Transparent to translucent. Bitter saline taste. 
 May contain as high as 40% of NasSCh. Occurs with halite at Stassfurt, Germany, and 
 Racalmuto, near Girgenti, Sicily; also in the lavas of Vesuvius. 
 
 ARCANITE, (K, Na^SCX. Orthorhombic, bipyramidal class, a : b : c = 1.7462 
 : i : 1.3033. This modification has not as yet been observed in nature. The artificial 
 crystals show a pseudohexagonal development. 
 
 MASCAGNITE, (NH 4 ) 2 SO 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 1.7722 : i : 1.2954. In nature it 
 occurs only as crusts and stalactites. Colorless, white, or yellow. Pungent taste, 
 slightly bitter. Hardness 2 to 2.5. Specific gravity 1.7 to 1.8. Occurs in the lavas 
 of Aetna, Vesuvius, etc. 
 
132 DESCRIPTIVE MINERALOGY 
 
 THENARDITE, Na 2 SO 4 . 
 
 Orthorhombic, bipyratnidal class, a : b : c = 1.7910 : i : 1.2541. Acute pyra- 
 midal, short prismatic, or tabular crystals. Also in twinned crystals, the twinning 
 plane is parallel to the unit prism. Most commonly in crystal aggregates and crystal- 
 line crusts. 
 
 Brachypinacoidal cleavage. Uneven fracture. Hardness 2.5. Specific gravity 2.68. 
 Colorless to brown. Transparent. When exposed to air it becomes covered with 
 a white crust. Easily soluble in water. . 
 
 Usually found in salt and borax lakes, thus, in the deserts of Chile, Peru, and 
 Bolivia; Lake Balkasch, Central Asia; Borax Lake, San Bernardino Co., California; 
 Rio Verde, Yavapai Co., Arizona. 
 
 APHTHITAUTE is according to von Groth a mixture of glaserite and arcanite. 
 
 GLAUBERITE GROUP 
 
 This group includes three double sulphates of sodium, potassium, cal- 
 cium, and magnesium. 
 
 Glauberite, Na 2 SO 4 .CaSO 4 . Monoclinic Prismatic Class 
 
 VAN'T HOFEITE, 3Na 2 SO 4 .MgSO 4 . ? 
 
 LANGBEINITE, K 2 SO 4 . 2MgSO 4 . 
 
 Tetrahedral Pentagonal Dodecaheclral Class 
 These double sulphates are very unstable compounds. 
 
 Glauberite, Na 2 SO 4 . CaSO 4 . 
 
 Monoclinic, prismatic class, a : b : c= 1.2209 : l ' 1-0270, /3 = ii2 
 n'. Crystals are generally thick tabular, the basal pinacoid predominating. 
 The common forms are the basal and orthopinacoids, unit prism, and the 
 negative unit hemi-pyramid. Occurs also in reniform and lamellar masses. 
 
 Perfect basal cleavage. Conchoidal fracture. Hardness 2.5 to 3. 
 Specific gravity 2.7 to 2.85. Brittle. Vitreous to greasy luster. Colorless, 
 white, gray, yellow, also flesh to brick red. White streak. Bitter saline 
 taste. 
 
 Na 2 SO 4 .CaSO 4 . Fuses easily. When dissolved in water, gypsum, 
 CaSO 4 .2H 2 O, is precipitated. Exposed to moist air the surface becomes 
 coated with a crust of mirabilite, Na 2 SO 4 . ioH 2 O. 
 
 Glauberite is commonly associated with thenardite, mirabilite, halite, etc. 
 It occurs at Villar Rubia, Spain ; Vic, Lorraine, Western Germany ; Ber- 
 chtesgaden, Bavaria ; Stassfurt, Germany ; Austria ; Sicily ; Peru ; Chile. In 
 the United States glauberite is found in the Rio Verde Valley, Arizona; 
 Borax Lake, San Bernardino Co., California. 
 
 VAN'T HOETITE, 3Na;SO 4 .MgSO4. Crystallization unknown. Colorless. Pearly 
 luster. Uneven fracture. Saline taste. Occurs with langbeinite in the salt deposits 
 of the Stassfurt district, Germany. 
 
SULPHATES 
 
 133 
 
 LANGBEINITE, KsSO^MgSCX. Cubic, tetrahedral pentagonal dodecahedral class. 
 Crystals are usually tetrahedral in habit, sometimes very complex. Generally in 
 granular aggregates. Colorless. Greasy luster. Hardness 3 to 4. Specific gravity 
 2.83. Exposed to moist air it becomes cloudy, due to the absorption of water. Easily 
 soluble in hydrochloric acid, less so in water. Occurs in the salt deposits of the 
 Stassfurt district of Germany. 
 
 BARITE GROUP 
 
 The normal anhydrous sulphates and chromates of calcium, strontium, 
 
 barium, and lead are placed in this group. The group consists of two 
 series. 
 
 ORTHORHOMBIC SERIES 
 
 a b c 
 
 Bipyramidal Class 0.8932 i 1.0008 
 
 Bipyramidal Class 0.7809 i 1.2832 
 
 Bipyramidal Class 0.7666 i 1.2534 
 
 Bipyramidal Class 0.8146 i 1.3119 
 
 Bipyramidal Class '0.7852 i 1.2894 
 
 ANHYDRITE, CaSO t . 
 CELESTITE, SrSO 4 . 
 
 BARTOCEI.ESTITE, ( Sr,Ba) SO 4 
 BARITE, BaSO 4 . 
 ANGLESITE, PbSO 4 . 
 
 MONOCLINIC SERIES 
 
 Crocoite, PbCrO 4 . Prismatic Class 0.9603 : i : 0.9171, /? = 102 33'. 
 Anhydrite is sometimes considered as not being strictly isomorphous 
 with celestite. barite, and anglesite. However, on account of its related 
 form and chemical composition it has been included in the orthorhombic 
 series. 
 
 ANHYDRITE, CaSO,. 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.8932 : i : 1.0008. 
 Crystals, which are not very common, are usually prismatic (Figure 69) 
 or thick tabular in habit. The forms generally ob- 
 served are the unit macro- and brachydomes (r and 
 s), and the brachypinacoid (b). The three pinacoids 
 predominate on thick tabular crystals. Polysynthetic 
 twins are rather common, the twinning plane is par- FIG. 69. 
 
 allel to the unit macrodome. Occurs most commonly in cleavable masses ; 
 also fibrous, granular, lamellar, compact, and reniform. 
 
 Cleavage in three directions at right angles. Very perfect cleavage 
 and pearly luster parallel to the basal pinacoid ; perfect cleavage and vit- 
 reous luster parallel to the brachypinacoid, and distinct cleavage with a 
 .greasy vitreous luster parallel to the macropinacoid. Conchoidal fracture. 
 
134 
 
 DESCRIPTIVE; MINERALOGY 
 
 Brittle. Hardness 3 to 3.5. Specific gravity 2.8 to 3. Transparent to 
 translucent. Luster on massive varieties is vitreous to pearly. Color may 
 be white, grayish, bluish, reddish, or black. Streak white. Massive varie- 
 ties resemble marble or lumps of sugar. 
 
 CaSO 4 . Often mixed with bituminous matter. Fuses to a white enamel. 
 Imparts a reddish color to the flame. Fine powder is soluble in concen- 
 trated sulphuric acid. Absorbs water and alters to gypsum, CaSO 4 .2H 2 O, 
 causing a large increase in volume. This increase is estimated to be from 
 33 to 62% of the original volume. This hydration is, no doubt, the cause 
 of the many local disturbances in the rock strata commonly noticed in re- 
 gions where gypsum occurs. Sometimes anhydrite occurs as a pseudo- 
 mo rph after gypsum. 
 
 Occurs commonly in limestones and shales associated with halite and 
 gypsum. Some of the principal localities are the Stassfurt district of Ger- 
 many, page 100 ; Hall, Tyrol ; Bex, Switzerland ; Kapnik, Hungary ; Wie- 
 liczka, Galicia ; Berchtesgaden, Bavaria ; Lockport, N. Y. ; near Philadelphia, 
 Pa. ; Nashville, Tenn. ; Detroit, Mich. ; also in large deposits in Nova Scotia 
 and New Brunswick. 
 
 Anhydrite is of little use commercially. A silicious variety is sometimes 
 cut and polished for ornamental purposes. 
 
 CELESTITE, SrSO 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.7809 : i : 1.2832. 
 Crystals are common, either prismatic (Figure 70), or tabular (Figure 71), 
 
 FIG. 70. 
 
 FIG. 71. 
 
 in habit; rarely pyramidal (Figure 72). The common forms are the unit 
 prism m, unit brachydome o, basal pinacoid c, and the modified macrodome 
 d with the coefficient m equal to l / 2 . Occurs also in fibrous and cleavable 
 masses; more rarely granular, concretionary, globular, or earthy. 
 
 Perfect basal and good prismatic cleavages. The prism angle is 104 
 10'. Uneven fracture. Hardness 3 to 3.5. Specific gravity 3.9 to 4. 
 Vitreous to pearly luster, on fracture surfaces somewhat greasy. White. 
 
SULPHATES 135 
 
 streak. Generally possesses a faint blue tinge, may be white, yellow, more 
 rarely green or reddish. 
 
 SrSO.^. Sometimes very pure, but may contain small percentages of 
 calcium and barium. Fuses to a white enamel. Imparts a crimson color 
 to the flame. Insoluble in acids. More soluble in water than barite. 
 
 Celestite is usually associated with sulphur, gypsum, halite, and occas- 
 ionally galena and sphalerite. There are two principal types of occurrences. 
 
 (i) Disseminated in shales, limestones, and dolomites. The dissem- 
 ination may be in the form of well developed crystals or as irregular parti- 
 cles of varying sizes. When such celestite-bearing rocks are acted upon by 
 circulating water the celestite is dissolved and the so-called gashed, acicular, 
 and vermicular limestones and dolomites of New York and Michigan re- 
 sult. These rocks, as the terms imply, are more or less porous. This 
 method of occurrence of celestite is doubtless more widespread than has 
 hitherto been supposed. 
 
 (2} In cracks and cainties in rocks of varying ages but principally of 
 sedimentary origin. Here celestite is a secondary formation, having been 
 derived from the overlying and adjoining celestite-bearing rocks by the 
 action of circulating water. Most of the best known localities for the occur- 
 rence of celestite are of this type. Celestite is found in association with 
 sulphur and gypsum in the Girgenti Sulphur district of Sicily, also at May- 
 bee: Monroe Co., and elsewhere in Southern Michigan, see page 14. With 
 halite it occurs at Stassfurt, Germany ; Bex, Switzerland, etc. In excellent 
 crystals, some of which are 18 inches in length, in the Crystal Cave on the 
 Island of Put-In-Bay, in Lake Erie ; also on Drummond Island in Lake 
 Huron ; in Jefferson, Schoharie, and Oneida Counties, New York ; at Cedar 
 Cliff, Mineral Co., West Virginia ; Burnet, Burnet Co., Texas ; Larimer 
 Co., Colorado ; Kingston, Canada ; and San Bernardino Co., California. 
 Fibrous varieties occur at Dornburg, near Jena, Germany ; Bell's Mills, 
 Blair Co., Pa. ; and near Montreal, Canada. A red variety is found in 
 Brown Co., Kansas. 
 
 Celestite is used to a small extent in the manufacture of strontium 
 compounds. Strontianite is, however, preferred, see page 121. 
 
 BARTOCELESTITE, (Sr, Ba) SO 4 , is an isomorphous mixture of the sulphates of 
 strontium and barium. Crystals are rare. Usually occurs in radial fibrous aggregates 
 or earthy masses in limestone and marl. Hardness 2.5. Specific gravity 4.1 to 4.2. 
 Found at Greiner and in the Binnenthal, Tyrol ; Drummond Island, Lake Huron, etc. 
 
 BARITE, Heavy Spar, Barytes, BaSO 4 . 
 
 Orthorhombic, bipyramidal class, a : b : = 0.8146 : i : 1.3119. 
 Crystals are common and usually well developed. Over 120 forms have 
 
136 
 
 DESCRIPTIVE MINERALOGY 
 
 been observed. Tabular (Figures 73 and 74), and prismatic (Figures 75 
 and 76), habits are very common. The forms usually observed are 
 the unit prism m, modified (w = l / 2 ) macrodome d, unit brachydome o, and 
 the basal pinacoid c. Tabular crystals are often arranged in crested diver- 
 gent groups. Also in lamellar, fibrous, globular, granular, earthy, stalac- 
 titic, and nodular masses. 
 
 FIG. 73- 
 
 FIG. 74. 
 
 FIG. 75. 
 
 FIG. 76. 
 
 Perfect basal and prismatic cleavages. The prism angle is io 
 Uneven fracture. Brittle. Vitreous to pearly luster, somewhat greasy on 
 fracture surfaces. Transparent to opaque. Colorless, white, yellow, gray, 
 blue, brown, or red. White streak. Hardness 2.5 to 3.5. Specific gravity 
 4-3 to 4.7. 
 
 BaSO 4 . May contain varying amounts of the oxides of strontium and 
 calcium, also silica, clay, or bituminous matter. Occasionally the amount 
 of strontium oxide present may be as high as 12%. Fuses with difficulty. 
 The fused mass reacts alkaline. Reacts easily for sulphur with soda on 
 charcoal. Insoluble in hydrochloric acid. Powdered barite is soluble in 
 warm concentrated sulphuric acid. Imparts a green color to the flame. 
 
 In general barite occurs in two ways, viz: (i) With metalliferous 
 veins, usually associated with galena, sphalerite, fluorite, chalcopyrite, co- 
 balt and nickel minerals, manganese ores, etc. Most of the finest crystals 
 are in ore deposits of this character. This type of occurrence of barite 
 is very widespread but of no commercial importance. (2) In pockets and 
 lenticular deposits, principally in limestones. The pockets may vary from 
 100 to 200 or more feet in width and in some instances have been traced 
 for several miles. This type of occurrence furnishes practically all the 
 barite of commerce. The principal producing localities in the United States 
 are in Washington, Miller, and Cole Counties, Missouri ; Bradley, Mon- 
 roe, London, Cooke, and Greene Counties, Tennessee ; Bedford, Pittsyl- 
 vania, Campbell, and Tazewell Counties, Virginia ; Madison and Gaston 
 Counties, North Carolina. In 1907 the United States produced 89,621 tons 
 of barite. valued at $291,777. This production was obtained, in the order 
 given, from the states named above. Some barite is imported from Germany 
 and New Foundland. Cleaned, bleached, and ground barite is worth from 
 $7.00 to $12.00 per ton. Crude barite averaged $3.26 per ton in 1907. 
 
 Barite is used extensively in the manufacture of paper, rubber, paints, 
 
SULPHATES 
 
 137 
 
 pottery glazes, barium hydroxide, also to coat canvas ham sacks, and as 
 an adulterant of white lead. Some varieties are used for ornamental pur- 
 poses. 
 
 ANGLESITE, PbSO 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c = o . 7852 : I : i . 2894. 
 Crystals are sometimes highly modified and may be short prismatic (Figure 
 77), tabular, or pyramidal (Figure 78), in habit. The forms, commonly 
 observed, are the unit prism m, basal pinacoid c, unit bipyramid s, the 
 brachybipyramid y with the coefficient n equal to 2, unit brachydome o, and 
 the modified macrodome d with the coefficient m equal to y 2 . These are 
 similar to those noted on celestite and barite, pages 134 and 135. Also 
 occurs in granular, compact, stalactitic, and nodular masses. 
 
 FIG. 77. 
 
 FIG. 78. 
 
 Distinct basal and prismatic cleavages. The prism angle is IO343'. 
 Conchoidal fracture. Brittle. Hardness 3. Specific gravity 6.1 to 6.4. 
 High adamantine luster, sometimes is resinous or greasy. Transparent to 
 opaque. Colorless, white, yellow, brown, green, or blue. White streak. 
 
 PbSO 4 . Usually quite pure. Fuses easily in the candle flame. Re- 
 acts for lead and sulphur. Slightly soluble in nitric acid. Powdered an- 
 glesite is soluble in warm concentrated sulphuric acid. Is sometimes found 
 as a pseudomorph after galena. Alters to cerussite. 
 
 Anglesite is a common oxidation product of lead minerals, especially 
 galena. Hence, is usually found in cracks and cavities in galena. Excellent 
 crystals are found at Mt. Poni, Sardinia ; Badenweiler, Black Forest ; Claus- 
 thal, Hartz Mountains ; Felsobanya, Hungary ; Anglesea, England ; Lead- 
 hills, Scotland ; Beresowsk, Ural Mountains ; Phoenixville, Pa. ; various 
 places in Missouri, Wisconsin, Colorado, Utah, Arizona, California, etc. ; in 
 large deposits in Mexico and Australia. 
 
 Anglesite is an ore of lead. 
 
138 DESCRIPTIVE MINERALOGY 
 
 Crocoite, PbCrO 4 . 
 
 Monoclinic, prismatic class, a : b : c = 0.9603 : I : 0.9171, f3 = 102 
 33'. Prismatic or acicular crystals are rather common. Many forms have 
 been noted. Crystals are often highly modified. Prism faces are usually 
 striated vertically. Occurs also in columnar and granular masses, some- 
 times in crusts. 
 
 Distinct basal and prismatic cleavages. Conchoidal to uneven fracture. 
 Sectile. Hardness 2.5 to 3. Specific gravity 5.9 to 6.1. Translucent. 
 Greasy adamantine luster. Various shades of hyacinth red, resembles po- 
 tassium bichromate in color. Orange yellow streak. 
 
 PbCrO 4 . Fuses easily and on charcoal yields with deflagration metallic 
 lead and a yellow coating. Imparts an emerald green color to the salt of 
 phosphorous bead. 
 
 Crocoite is an alteration product of galena. It is usually associated 
 with galena, pyrite, quartz, vanadinite, and wulfenite. Occurs at Beres- 
 owk, Murinski, and Nijni-Tagilak, Ural Mountains; Congonhas do Campo, 
 Brazil ; Island of Luzon in the Philippines ; Dundas, Tasmania ; Vulture 
 district, Maricopa Co., Arizona. 
 
 Crocoite does not occur abundantly enough to be of commercial im- 
 portance. 
 
 2. ANHYDROUS MOLYBDATES, TUNGSTATES, 
 AND URANATES 
 
 WOLFRAMITE GROUP 
 
 This group embraces the anhydrous molybdates and tungstates of cal- 
 cium, lead, iron, and manganese. Depending upon crystallization two ser- 
 ies tetragonal and monoclinic may be differentiated. 
 
 TETRAGONAL SERIES 
 
 a : c 
 
 POWELUTE, CaMoO 4 . Tetragonal Bipyramidal Class i : i . 5445 
 
 Wulfenite, PbMoO 4 . Tetragonal Pyramidal Class i : i . 5777 
 
 Scheelite, CaWO 4 . Tetragonal Bipyramidal Class i : 1.5315 
 
 STOI,ZITE, PbWO 4 . Tetragonal Bipyramidal Class i : i . 5670 
 
 MONOCLINIC SERIES 
 
 a : b : c ft 
 
 Huebnerite, MnWO 4 . Prismatic Class 0.8362 : i : 0.8668, 90 52' 
 
 WOLFRAMITE, (Fe,Mn)WO 4 . 
 
 Prismatic Class 0.8300 : i : 0.8678, 90^38' 
 
 FERBERITE, FeWO 4 . Prismatic Class 0.8229 : i : 0.8463, 90 20' 
 
 The elements of crystallization of ferberite are for artificial crystals. 
 Wolframite, hubnerite, and scheelite are of considerable importance com- 
 mercially. 
 
SULPHATES 
 
 139 
 
 POWEU.ITE, CaMoO 4 . 
 
 Tetragonal system, tetragonal bipyramidal class, a : c ' = I : 1.5445. Small, 
 acute pyramidal crystals and platy masses. Greenish yellow in color. Specific gravity 
 4.25. Sometimes is mixed with scheelite. Occurs in the Peacock mine, Western 
 Idaho ; Houghton Co., Mich. ; as a pseudomorph after molybdenite at Barringer Hill, 
 Llano Co., Texas ; Nye Co., Nevada. 
 
 Wulfenite, PbMoO 4 . 
 
 Tetragonal system, tetragonal pyramidal class, a : c = i : i . 5777. 
 Crystals are most commonly square and thin tabular in habit, also pyra- 
 midal (Figure 79), or short columnar. Tabular crystals 
 are often arranged in groups. Hemimorphic develop- 
 ment is not often observed. The common forms are the 
 upper and lower tetragonal pyramids o and o' ' , the tetra- 
 gonal prism of the third order p with the coefficient n 
 equal to 4/3, and the lower basal pinacoid c. Also occurs 
 in coarse or fine granular masses. 
 
 Fairly perfect pyramidal cleavage. Conchoidal to 
 uneven fracture. Brittle. Hardness 3. Specific gravity 
 6.3 to 7. Resinous or adamantine luster. Transparent 
 to translucent. The color may be various shades of yel- 
 low, green, gray, or red. Yellowish white streak. 
 
 PbMoO 4 . Lead may be partially replaced by calcium, molybdenum 
 by chromium or vanadium. Decrepitates and fuses easily. Yields on char- 
 coal a globule of metallic lead. Decomposed by acids. Gives a blue solu- 
 tion with sulphuric acid and alcohol. Sometimes occurs as a pseudomorph 
 after galena. 
 
 Wulfenite is a secondary mineral, the result of the decomposition of 
 various lead ores. It is commonly associated with galena, pyromorphite, 
 and vanadinite. Occurs at Bleiberg, Carinthia ; Pribram and Rezbanya. 
 Hungary; Freiberg district, Saxony; Phoenixville, Pa.; Tecomah mine, 
 Utah ; various places in Yuma, Maricopa, and Pinal Counties, Arizona ; also 
 in Wisconsin. Missouri and California. 
 
 Scheelite, CaWO 4 . 
 
 Tetragonal system, tetragonal bipyramidal class, a : c = i : 1.5315. 
 
 Crystals are generally small, well developed, and pyramidal (Figure 80) 
 in habit ; rarely tabular. The common forms are the unit 
 tetragonal bipyramids of the first and second orders p 
 and e, and the tetragonal bipyramids of the third order 
 h and s. On h the coefficient n is equal to 3, on s the 
 values of n and m are both equal to 3. Contact and pen- 
 etration twins with the twinning plane parallel to the 
 prism of the second order are not uncommon. Occurs 
 often as crystalline crusts on quartz ; also in reniform, 
 disseminated, or granular masses. 
 
 p IG g Distinct cleavage parallel to the unit bipyramid of the 
 
 first order, less so parallel to the one of the second order. 
 
 Conchoidal to uneven fracture. Hardness 4.5 to 5. Specific gravity 5.9 to 
 
140 DESCRIPTIVE MINERALOGY 
 
 6.2. Greasy to adamantine luster. White streak. Transparent to opaque. 
 Color white, yellow, gray, brown, green, or reddish. 
 
 CaWO 4 . Usually contains some molybdenum. In cuproschcclite cop- 
 per replaces some of the calcium. Fuses with difficulty to a semi-trans- 
 parent glass. Imparts to the salt of phosphorus bead in the reducing 
 flame a green or yellow color when hot, blue when cold. Yields when 
 treated by hydrochloric acid and metallic tin a deep blue precipitate. De- 
 composed by hydrochloric acid yielding a yellow precipitate of WO 3 , which 
 is soluble in ammonium hydroxide. Occurs as a pseudomorph after wolf- 
 ramite. 
 
 Scheelite is a common alteration product of wolframite. It is usually 
 found with the common associates of the tin ore deposits, page 81, namely, 
 cassiterite, fluorite, topaz, apatite, molybdenite, wolframite, bismuth, and 
 quartz. It. occurs in Cornwall and Cumberland, England ; Schlaggenwald 
 and Zinnwald, Bohemia ; Tyrol ; Adelong, New South Wales ; New Zea- 
 land; Tasmania; Beauce Co., Quebec. 
 
 In the United States scheelite occurs at Monroe and Trumbull, Conn. ; 
 Mecklenburg Co., N. C. ; Jardine, Arizona; various places in Idaho and 
 Colorado. 
 
 Scheelite is a source of tungsten and its compounds. 
 
 STOLZITE, PbW r O 4 . 
 
 Tetragonal system, tetragonal bipyramidal class, a : c = i : 1.567. Very small, 
 acute pyramidal "crystals consisting usually of the modified bipyramid with m equal 
 to 2. Also short columnar, and arranged in spherical groups. 
 
 Hardness 3. Specific gravity 7.8 to 8.2. Conchoidal fracture. Color gray, brown, 
 yellow, green, or red. Greasy luster. Translucent. Easily fusible. Reacts for lead 
 and tungsten. Occurs with quartz and mica at Zinnwald, Saxony; Coquimbo, Chile; 
 Broken Hill, New South Wales. 
 
 Huebnerite, MnWO 4 . 
 
 Monoclinic, prismatic class, a : b : c = 0.8362 : i : 0.8668, /? =90 
 52'. Generally in long fibrous, bladed, or stalky crystals without good ter- 
 minations. Brownish red, brownish black, pale yellow, or nearly black in 
 color, in transmitted light ruby red to yellow. Streak yellowish brown to 
 greenish gray. Vitreous to resinous luster. Hardness 4.5 to 5.5. Specific 
 gravity 6.7 to 7.3. Perfect clinopinacoidal cleavage. Often translucent. 
 Occurs with quartz in Ouray and San Juan Counties, Colorado; Dragoon, 
 Arizona ; Black Hills, S. Dakota ; Mammoth district, Nevada ; Inverness 
 Co., Nova Scotia ; Adverville, Pyrenees Mountains ; Peru. 
 
 Hubnerite is an important ore of tungsten. 
 
SULPHATES 
 
 141 
 
 FIG. 81. 
 
 WOLFRAMITE, Wolfram, (Fe,Mn)WO 4 . 
 
 Monoclinic, prismatic class, a : b : c = 0.8300 : i : 0.8678, /3 = 
 90 38'. Formerly considered ortho rhombic. Crystals are generally large, 
 thick tabular (Fig. 81), or short columnar; more rare- 
 ly fibrous. The common forms are the unit prism m, 
 orthopinacoid a, modified orthodomes t and y with the 
 coefficient m equal to V 2 , and the unit clinodome f. 
 Vertical striations are characteristic of the faces in 
 the prism zone. Contact twins with the twinning plane 
 parallel to the orthopinacoid are rather common. 
 Occurs also in bladed, curved lamellar, columnar, or 
 granular masses. 
 
 Perfect orthopinacoidal cleavage. Uneven fracture. Brittle. Hard- 
 ness 5 to 5.5. Specific gravity 7.1 to 7.5. Greasy submetallic luster. Color 
 dark gray, reddish brown, brownish black, and iron black. Streak varies 
 from dark red brown for manganiferous varieties to black for those con- 
 taining much iron. Opaque. Sometimes slightly magnetic. 
 
 (Fe, Mn)WO 4 . An isomorphous mixture of FeWO 4 and MnWO 4 in 
 varying proportions. The p*ercentage of FeO varies from 2 to K)%, MnO 
 from 6 to 22%, while WO B averages about 75%. May contain small amounts 
 of the oxides of calcium, magnesium, columbium, and tantalum. Fuses 
 with difficulty to a magnetic globule. Fused with sodium carbonate and 
 potassium nitrate on charcoal or platinum foil the mass turns green. Treated 
 with sulphuric or hydrochloric acids and metallic tin the solution assumes 
 a deep blue color. Occurs at times as a pseudomorph after scheelite. 
 
 Usually found with tin ore deposits, of which it is a typical associate, 
 see page 81. Sometimes with other ore deposits, such as galena, etc. Some 
 localites are Cornwall, England ; various places in Saxony ; Nertschinsk, 
 Siberia ; Bolivia ; New South Wales ; Felsobanya, Hungary ; Monroe and 
 Trumbull, Conn. ; Black Hills, S. Dakota ; Mecklenburg Co., N. C. ; Mine 
 La Motte, Mo. ; Okanogan and Stevens Counties, Wash. ; in considerable 
 quantities in Boulder Co., Colorado. In 1907 the United States produced 
 1,640 tons valued at $890,048. The supply was obtained chiefly from Colo- 
 rado. 
 
 Wolframite is the chief source of tungsten and its compounds. Tung- 
 sten is used in the manufacture of "high-speed" steels and in electric incan- 
 descent lamps ; sodium tungstate as a mordant and to render fabric non- 
 inflammable ; tungstic oxide to color glass ; and calcium tungstate, on ac- 
 count of its phosphorescent properties, in X-ray apparatus. 
 
142 DESCRIPTIVE MINERALOGY 
 
 FERBEKJTE, FeW(X Monoclinic, prismatic class. Artificial crystals have the fol- 
 lowing elements of crystallization, a : b : c = 0.8229 : i : 0.8463, /3 = 902o'. Occurs 
 in compact, granular aggregates, resembling wolframite. Black in color. Streak 
 brownish black to black. Vitreous luster. Sierra Almagrera, Spain; South Dakota. 
 
 Uraninite, Pitchblende. 
 
 Cubic, hexoctahedral class. Crystals generally show the octahedron and 
 rhombic dodecahedron. Crystals are rare, more commonly in compact, botry- 
 oidal. reniform, columnar, and curved lamellar masses. Often apparently 
 amorphous. 
 
 Conchoidal to uneven fracture. Brittle. Hardness 3 to 6. Specific 
 gravity 4.8 to 9.7, crystals 9 to 9.7. Pitchy or greasy luster on fresh frac- 
 ture surfaces, otherwise dull luster. Pitch black, brownish, greenish, or 
 gray in color. Non-magnetic. Streak dark green, brown to gray black. 
 
 Composition is uncertain. Is considered an uranate of uranyl and lead 
 with varying percentages of the rare earths thorium, cerium, yttrium, 
 lanthanum, erbium, etc., and the gases nitrogen, argon, and helium. Very 
 small amounts of radium, polonium, and actinium are present in some varie- 
 ties. As the result of alteration and admixture varying percentages of water, 
 silica, ferrous oxide, calcium oxide, bismuth, arsenic, and sulphur are some- 
 times noted. Rarely do the oxides of uranium exceed 80 to 85%. Clcveite 
 is a variety from Garta, near Arendal, Norway, and aside from thorium 
 also contains argon and helium. Nivenite is characterized by about 10% 
 of the earths of the yttrium group. It occurs *n Llano Co., Texas. Brbg- 
 gerite is a variety from the Island of Moss near Christiania, containing con- 
 siderable thorium. 
 
 Uraninite is infusible. Easily soluble in warm nitric or sulphuric acids, 
 the solution yields a sulphur yellow precipitate upon the addition of ammo- 
 nium hydroxide. In the oxidizing flame it imparts a yellow green color 
 to the salt of phosphorus bead. The color turns green in the reducing 
 flame. With soda gives a lead coating on charcoal. 
 
 Uraninite occurs in two ways, (i) As a primary constituent of peg- 
 matites and granites. Here uraninite is associated with orthite, thorite, fer- 
 gusonite, etc., and is found in the Arendal and Moss districts, Norway ; 
 Oeregrund, Sweden ; Branchville, Conn. ; Mitchell Co., N. C. ; Marietta, S. 
 C. ; Llano Co., Texas; and the Black Hills, S. Dakota. (2) With metal- 
 liferous ore deposits of lead, silver, and bismuth minerals. Thus, at 
 Joachimsthal and Pribram, Bohemia; Johanngeorgenstadt, Schneeberg, etc., 
 Saxony ; Rezbanya, Hungary ; Cornwall, England ; in considerable quantities 
 associated with auriferous sulphide minerals in the Black Hawk, Kirk, and 
 Wood mines, Gilpin Co., Colorado. The variety from Joachimsthal is very 
 strongly radio-active. 
 
 Uraninite is the principal source of uranium and its compounds. Uran- 
 ium is used in the manufacture of special grades of steel, the compounds for 
 coloring glass and in the preparation of pigments for porcelain painting. 
 As indicated above, uraninite is also important as the source of some of 
 the rare elements, such as radium, polonium, actinium, argon, and helium. 
 Uraninite containing about 50% of uranium oxide is worth about $1,500.00 
 per ton. 
 
SULPHATES M3 
 
 3. BASIC SULPHATES AND CHROMATES 
 
 ALUNITE GROUP 
 
 This group embraces the basic sulphates of aluminium, sodium, potas- 
 sium, iron, and lead. These minerals crystallize in the hexagonal system. 
 
 a : c 
 
 Alunite, K 2 (A1.2OH), ; (SO 4 ) 4 . Ditrigonal Scalenohedral Class i : 1.2520 
 
 JAROSITE, K 2 (Fe.2OH),, (SO 4 ) 4 . 
 
 Ditrigonal Scalenohedral Class I : 1.2492 
 NATROJAROSITE, Na,(Fe.OH) ( . (SO 4 ) 4 . 
 
 Ditrigonal Scalenohedral Class I : 1.1040 
 PI.UMBOJAROSTTK, Pb ( Fe . OH ) ( SO 4 ) 4 . 
 
 Ditrigonal Scalenohedral Class I : 1.2160 
 
 Natrojarosite and plurnbojarosite are very rare minerals. 
 Alunite, Alum Stone, K,(A1.2OH) 6 (SO 4 ) 4 . 
 
 Hexagonal, ditrigonal Scalenohedral class, a : c = i : 1.2520. Small, 
 rhombohedral crystals resembling cubes. Rhombohedral angle is 90 50'. 
 Crystal faces are often curved. Tabular crystals are rare. Also in fibrous, 
 granular, and earthy masses. 
 
 Perfect basal cleavage. Conchoidal, splintery, or earthy fracture. 
 Hardness 3.5 to 4, sometimes harder due to admixtures of quartz, feldspar, 
 etc. Specific gravity 2.58 to 2.8. Colorless, white, yellowish, or reddish. 
 White streak. Pearly luster on cleavage surfaces, otherwise vitreous. Trans- 
 parent to subtranslucent. 
 
 K, (A1.2OH) 6 (SO 4 ) 4 sometimes written K 2 SO 4 . Al 2 (SO 4 ) a .2Al, 
 (OH),,. Water is liberated only at a comparatively high temperature. In 
 natroahmitc some of the potassium is replaced by sodium. Decrepitates and 
 is infusible. Heated with cobalt nitrate it turns blue. Reacts for sulphur 
 when fused on charcoal with soda. Soluble in potassium hydroxide and hot 
 sulphuric acid. Insoluble in hydrochloric acid and water. 
 
 Alunite occurs in irregular deposits and veins in altered feldspathic 
 rocks, such as rhyolites, dacites, trachytes, and andesites. The common 
 associates of alunite are kaolin, pyrite, opal, and quartz. It occurs at 
 Tolfa, near Rome, Italy ; Santorin and elsewhere in the Grecian Archipelago ; 
 near Muszay, Hungary ; Mount Dore, France ; Queretaro, Mexico. In the 
 United States alunite is found in the Rosita Hills, Calico Peak near Rico, 
 National mine near Silverton, and Cripple Creek, Colorado ; Tres Cerritos, 
 Mariposa Co., California ; Ryerson mine near Morenci, Arizona ; and in 
 large quantities associated with gold in the Goldfield district, Nevada. It 
 was formerly thought that alunite is the result of the action of sulphurous 
 vapors on feldspathic rocks. However, Ransome has shown very recently 
 that the alunite of the Goldfield district, Nevada, is due to the action of per- 
 colating water charged with sulphuric acid, resulting from the oxidation 
 of pyrite, upon feldspathic rocks, especially trachytes. 
 
144 DESCRIPTIVE MINERALOGY 
 
 By roasting, lixiviating, and evaporating 60 to 80% of alum may be 
 obtained. Some of the Hungarian varieties are so hard and tough as to be 
 suitable for millstones. 
 
 JAROSITE, K 2 (Fe.2OH) (SO 4 ) 4 . 
 
 Hexagonal, ditrigonal scalenohedral class, a : c - i : 1.2492. Usually in small, 
 tabular crystals consisting of the unit, rhombohedron and the basal pinacoid. The 
 rhombohedral angle is 9O45'. Crystals occur often in druses or crusts. Also in 
 fibrous, granular, and nodular masses. 
 
 Distinct basal cleavage. Brittle. Hardness 2.5 to 4. Specific gravity 3.15 to 
 3.26. Vitreous to subadamantine luster, also dull. Ocher yellow, yellowish brown, 
 or clove brown in color. Shiny yellow streak. Translucent to opaque. 
 
 The formula may be written KsSCh.FeaCSOOs^FezCOH^. Occurs at Barranco 
 Jaroso in Sierra Almagrera, Spain ; Schwarzenberg, Saxony ; Beresowsk, Ural Mts. ; 
 Vulture mine, Arizona ; Tintic district, Utah ; Chaffee Co., Colorado. 
 
 NATROJAROSITE contains sodium replacing some of the potassium. It has been 
 found in Nevada. 
 
 PLUMBOJAROSITE is a variety containing lead replacing potassium. It has been 
 noted on Cook's Peak, Colorado. 
 
 BROCHANTITE GROUP 
 
 This group embraces basic sulphates of copper and lead. 
 
 LINARITE.. (Pb,Cu)SO 4 .(Pb,Cu)(OH) 2 . Monoclinic, Prismatic Class 
 
 STELZNERITE, CuSO 4 .2Cu(OH) 2 . Ortho rhombic, ?- 
 
 Brochantite, CuSO 4 .3Cu(OH) 2 . Orthorhombic, Bipyramidal Class 
 
 Each mineral differs in composition from the preceding by Cu(OH) 2 . 
 
 LINARITE, (Pb, Cu) Sd. (Pb, Cu) (OH) 2 . Monoclinic, prismatic class, a : b : 
 c = 1.7186 : i : 0.8272, ft = IO233'. Small, highly modified crystals with perfect 
 orthopinacoidal cleavage. Conchoidal fracture. Hardness 2.5 to 3. Specific gravity 
 5.3 to 5.45. Azure blue in color. Light blue streak. Adamantine luster. Transparent 
 to translucent. Occurs at Linares, Spain ; Leadhills, Scotland ; Beresowsk, Ural Mts. ; 
 Inyo Co., California. Rare. 
 
 STEI.ZNERITE, CuSO4.2Cu(OH) 2 . Orthorhombic system, class undetermined, a : 
 b : c = 0.5037 : . i : 0.7059. Small, prismatic crystals. Green in color. Vitreous 
 luster. Resembles brochantite. Occurs at Remolinos, Chile. 
 
 Brochantite, CuSO 4 .sCu(OH) 2 . 
 
 Orthorhombic. bipyramidal class, a : b : c = 0.7803 : i : 0.4838. 
 Small, short prismatic crystals with vertical striations. Also reniform 
 with fibrous structure and as drusy crusts. 
 
SULPHATES 145 
 
 Perfect brachypinacoidal cleavage. Hardness 3.5 to 4. Specific grav- 
 ity 3.78 to 3.0. Emerald to blackish green in color. Vitreous to pearly 
 luster. Light green streak. Transparent to translucent. 
 
 CuSCV3Cu(OH) 2 . Loses water at 3ooC. leaving a residue consist- 
 ing of a mixture of copper sulphate and oxide. Fuses on charcoal and 
 yields a globule of metallic copper. Reacts for sulphur with soda on char- 
 coal. 
 
 Occurs with other copper minerals malachite, azurite, and cuprite 
 in the zone of oxidation of copper ore deposits. Thus at Rezbanya, Hun- 
 gary ; Nijni-Tagilak, Ural Mountains; Chile; Copper districts of Arizona; 
 Sonora, Mexico ; Monarch mine, Chaffee Co., Colorado. 
 
 4. ANHYDROUS SULPHATES WITH HALOIDS 
 AND CARBONATES 
 
 Here may be placed several minerals which are combinations of sul- 
 phates with chlorides or fluorides, and carbonates. No definite chemical 
 or crystallographic relationships exist between them. 
 
 SUI.PHOHAUTE, 3Na 2 SO 4 . NaCl . NaF. 
 
 Cubic, probably hextetrahedral class. Occurs as small, brilliant rhombic dodeca- 
 hedrons. Pale greenish yellow in color. Transparent. Slowly soluble in water. 
 Found on hanksite at Borax Lake, San Bernardino Co., California. 
 
 HANKSITE, 9Na 2 SO 4 .2Na 2 CO 3 .KCl. 
 
 Hexagonal, a : c = i : 1.0056. Short prismatic or tabular crystals, some- 
 times resembling quartz. Colorless to yellow. Transparent to translucent. Easily 
 soluble in water. Occurs with halite, glauberite, thenardite, or sulphohalite at Borax 
 Lake, San Bernardino Co., and Death Valley, Inyo Co., California. 
 
 Leadhillite, PbSO, . 2PbCCX . Pb(OH) 2 . 
 
 Monoclinic, prismatic class, a : b : c= 1.7515 : I : 2.2261, j8=o,o28'. 
 Tabular crystals with an apparently hexagonal outline. Crystals usually 
 consist of the unit prism, and the basal and orthopinacoids. The angle 
 between the orthopinacoid and unit prism is I2O27 / . Twins and trillings 
 resembling those of aragonite. The twinning plane is parallel to the unit 
 prism. Also in compact lamellar masses. 
 
 Very perfect basal cleavage. Hardness 2.5. Specific gravity 6.26 to 
 6.55. Rather sectile. Pearly luster on the basal pinacoid, elsewhere resin- 
 ous adamantine. Generally yellow, gray, greenish, or brown in color, rare- 
 ly colorless. White streak. Transparent to translucent. 
 
 PbSO 4 .2PbCO 3 .Pb(OH) 2 . Fuses easily with intumescence, turns yel- 
 low, and when cold is white. Is easily reduced on charcoal to metallic lead. 
 With soda on charcoal reacts for sulphur. Yields water in closed tube. 
 
146 
 
 DESCRIPTIVE MINERALOGY 
 
 Soluble in nitric acid with effervescence leaving a white residue of lead 
 sulphate. Occurs as a pseudomorph after galena and calcite. 
 
 Is usually associated with lead minerals. Found sparingly at Lead- 
 hills, Scotland ; Red Gill, Cumberland ; Matlock, Derbyshire ; Iglesias, Sar- 
 dinia ; also in Missouri, Montana, and Arizona. 
 
 5. HYDRATED SULPHATES 
 
 Mirabilite, Glauber Salt, Exanthalite, Na,SO 4 . ioH,O. 
 
 Monoclinic, prismatic class, a : b : c= i . 1161 : i : i .2383, /?= 107^ 
 45'. Crystals resemble those of pyroxene in form and angle. Usually as 
 a mealy efflorescence or in crusts, sometimes with a fibrous structure. 
 
 Perfect orthopinacoidal cleavage. Hardness 1.5 to 2. Specific gravity 
 1.4 to 1.5. Vitreous luster. Colorless and transparent. On exposure loses 
 water, turns white, and falls to powder. Cooling, salty, bitter taste. 
 
 Na 2 SO 4 . ioH 2 O. When exposed to air loses 8 molecules of water and 
 becomes covered with a white crust. Easily soluble in water. Imparts 
 a yellow color to the flame. Dissolves in its water of crystallization. 
 
 Occurs as a secondary mineral in the halite deposits at Hallstatt, Hun- 
 gary, and Berchtesgaden, Bavaria. Is often deposited from hot springs 
 and salt lakes, thus at Karlsbad, Bohemia ; Great Salt Lake, Utah ; Bay of 
 Kara, Caspian Sea. Near Laramie, Wyoming, it occurs in considerable 
 quantities mixed with mud. 
 
 GYPSUM, Selenite, Satin Spar, Alabaster, CaSO 4 .2H,O. 
 
 Monoclinic, prismatic class, a : b : c = 0.6896 : i : 0.4133. .(3 =98 
 58'. Crystals are usually rather simple and either tabular (Figure 82) or 
 prismatic (Figure 83) in habit. The common forms are the unit prism /;/, 
 clinopinacoid b, negative unit hemi-pyramid p, and the modified positive 
 hemi-orthodome e with the coefficient m equal to 1/3. The prism angle is 
 
SULPHATES 147 
 
 in3o / . Often lenticular due to the rounding of the faces of p and e. 
 Twins according to two laws : ( I ) The orthopinacoid, which is . rarely ob- 
 served on gypsum, is the twinning plane. Contact (Figure 84) and pene- 
 tration (Figure 85) twins according to this law are commonly noted. The 
 contact twins (Figure 84) are often termed swallow-tail twins. (2) The 
 negative unit orthodome is the twinning plane. Twins according to this 
 law are common at Montmartre near Paris and are sometimes called Parisan 
 twins. Crystals are sometimes bent and twisted, and arranged in groups. 
 Also massive, coarse and fine granular, fibrous, foliated, earthy, and as sand. 
 
 Three easily obtainable cleavages are to be noted: (i) Highly per- 
 fect, parallel to the clinopinacoid ; (2) fibrous, parallel to the positive unit 
 hemi-pyramid ; and (3) conchoidal, parallel to the orthopinacoid. Hardness 
 1.5 to 2. Specific gravity 2.2 to 2.4. Pearly luster on the clinopinacoid, 
 elsewhere vitreous ; massive varieties are often dull earthy. Transparent 
 to opaque. Colorless, white, gray, yellow, brown, reddish, or black. White 
 streak. 
 
 CaSO.^H^O. Often mixed with organic matter or clay. Yields water 
 when heated in a closed tube, becomes white and opaque. Imparts a yellow 
 red color to the flame and fuses to an alkaline globule. Soluble in 380 to 
 460 parts of water, with difficulty in acids, and completely in hot potassium 
 hydroxide. Treated with a cold solution of sodium carbonate it yields cal- 
 cite, with a hot solution aragonite. It is converted to anhydrite in a hot 
 solution of halite. 
 
 There are five varieties of gypsum. 
 
 (1) Sclenite. This variety includes crystals and cleavable masses. 
 Usually colorless and transparent. 
 
 (2) Satin Spar. Fine fibrous variety with silky luster. Compare 
 page 113. 
 
 (3) Alabaster. A massive, fine-grained variety. Sometimes used 
 for statuary purposes. 
 
 (4) Rock Gypsum. A compact, scaly or granular variety. Often 
 very impure. Is commonly ground and used as a fertilizer under the name 
 of land plaster. 
 
 (5) Gypsitc. An impure, earthy or sandy variety occurring abundant- 
 ly in Kansas, Arizona, New Mexico, Oklahoma, and other western states. 
 
 Gypsum occurs in large deposits in limestones and shales commonly 
 associated with halite, celestite, sulphur, aragonite, and anhydrite. It also 
 occurs in smaller quantities with metalliferous ore deposits, especially those 
 containing sulphide minerals. Gypsum may be formed in several ways. 
 
 (i) Deposition from solution. The extensive deposits of rock gyp- 
 sum, which are of great commercial importance, have been formed by the 
 
148 DESCRIPTIVE 
 
 gradual evaporation of water in lakes or shallow arms of the sea. At first 
 the calcium sulphate in solution will be deposited as gypsum but, as the 
 brine becomes more concentrated and the percentage of sodium chloride 
 greatly increased, it is precipitated as anhydrite, see page 101. In many 
 cases the evaporation was sufficient to cause only gypsum to be deposited 
 when an influx of water, containing much earthy matter in suspension, 
 greatly diluted the solution. As a result of such disturbances during evap- 
 oration, and of the subsequent deposition of the suspended matter, layers 
 of gypsum and shale commonly alternate. Deposits of gypsum formed in 
 this way are very extensive and occur in New York, Michigan, Kansas, 
 Iowa, Texas, Oklahoma, Wyoming, Oregon, Utah, California, New Mex- 
 ico, South Dakota and Montana. Some of the best known and most ex- 
 tensively worked localities are in Central and Western New York, Alabas- 
 ter and Grand Rapids, Michigan ; Fort Dodge, Iowa ; Blue Rapids, Gyp- 
 sum City, and Medicine Lodge, Kansas ; etc. Large deposits occur also at 
 Hillsboro, Albert Co., New Brunswick; and in Nova Scotia. Excellent, 
 transparent crystals are found at Ellsworth and Canfield in Trumbull Co., 
 also in Mahoning Co., Ohio ; very large crystals in Wayne Co., Utah. 
 
 Gypsite is thought to have been deposited from springs. These spring 
 waters carry much calcium sulphate in solution, having derived the same 
 by leaching deposits of gypsum of the character just described. Some of the 
 deposits in Oklahoma may be the result of erosion and concentration by 
 water of disintegrated rock gypsum. 
 
 (2) Hydration of anhydrite. Gypsum may also be formed by the 
 hydration of anhydrite, see page 133. This change causes the associated 
 rocks to be locally disturbed. Gypsum formed in this way occurs in Cen- 
 tral New York, Northern Ohio, and elsewhere. 
 
 (3) Fwnarolc action. Sulphurous vapors react with limestone or the 
 calcium oxide of decomposing lavas and form gypsum. Gypsum formed 
 in this way occurs only in volcanic regions. 
 
 (4) Decomposition of sulphide minerals. Much of the gypsum found 
 with metalliferous ore deposits has been formed in this way. The oxida- 
 tion of the sulphides yields sulphuric acid which reacts with the limestones 
 of the region and forms gypsum. Gypsum formed by the third and fourth 
 methods is of rather limited occurrence. 
 
 Ground rock gypsum is used extensively as a fertilizer and is com- 
 monly called land plaster. It is also used as a disinfectant, flux in r,lass 
 and porcelain manufacture, in cement, and to weight fertilizers. Alabaster 
 is used for statuary and decorative purposes. Satin spar and a small 
 amount of selenite are used in cheap jewelry and microscopy, respectively. 
 
SULPHATES 149 
 
 Ground gypsum, or terra alba, is used as an adulterant of food, medicine, 
 and paint. 
 
 Gypsum, when calcined so as to drive off i l / 2 molecules of water, is 
 called plaster of paris. Calcined gypsum has the property of "setting," or 
 becoming hard, after being mixed with water. It is used in large quanti- 
 ties in patent wall plasters, stucco, white wash, dentistry, crayons, moulds, 
 casts, etc.; etc. 
 
 In 1908 the production of gypsum in the United States amounted to 
 1,721,829 tons, valued at $4,138,560. Michigan and New York .are the 
 largest producers. The price of rock gypsum varies between 45 cents to 
 $3.50 per ton, ground gypsum is worth about $2.00 per ton, while plaster 
 of paris. is valued at about $3.50 per ton. 
 
 Kieserite, MgSO 4 .H,O. 
 
 Monoclinic, prismatic class, a : b : = 0.9046 : i : 1.7739, ^8 = 91 
 7'. Sometimes in large, pyramidal crystals, but more commonly in coarse 
 or fine granular aggregates or masses. Colorless, white, gray, or yellow. 
 Transparent to translucent. Hardness 3. Specific gravity 2.5 to 2.57. 
 
 MgSO 4 .H 2 O. Absorbs moisture and becomes covered with a white 
 coating of epsomite, Mg$O 4 .7H 2 O. Heated in a closed tube yields water 
 at 200 C. Powdered kieserite, when mixed with water, hardens like plas- 
 ter of paris. Slowly soluble in water. 
 
 Occurs in large quantities in the salt deposits in the Stassfurt district, 
 Germany, see page 101 ; also at Kalusz, Galicia; Hallstatt, Austria; and in 
 the Salt Range, British India. 
 
 Kieserite is a source of potassium compounds. 
 
 EPSOMITE MELANTERITE GROUPS 
 
 These groups include the normal sulphates of magnesium, zinc, nickel, 
 iron, cobalt, manganese, and copper which crystallize with seven molecules 
 of water. There are two orthorhombic and monoclinic-^series. 
 
 EPSOMITE GROUP 
 
 (ORTHORHOMBIC SYSTEM} 
 
 a : b : c 
 
 Epsomite, MgSO 4 .7H.,O. Bisphenoidal Class 0.9901 : i 
 
 GOSLARITE, ZnSO 4 .7H 2 O. Bisphenoidal Class 0.9804 : i 
 
 MORENOSITE, NiSO 4 -7H 2 O. Bisphenoidal Class 0.9815 : i 
 
 0.5709 
 0.5631 
 0.5656 
 
150 DESCRIPTIVE MINERALOGY 
 
 MELANTERITE GROUP 
 
 (MON O CLINIC SYS TEM ) 
 
 a : b : c ft 
 
 Melanterite, FeSO 4 .7H 2 O. Prismatic Class 1.1828 : i : 1.5427, 104 16' 
 MALLARDITE, MnSO 4 .7H 2 O. Prismatic Class ? 
 
 LUCKITE, (Fe,Mn)SO 4 .7H 2 O. Prismatic Class ? ^ 
 
 PISANITE, (Fe,Cii)SO 4 .7H 2 O. 
 
 Prismatic Class 1.1609 : I : 1.5110, 105 22' 
 CUPROMAGNESITE, (Cu,Mg) SO 4 . 7H 2 O. Prismatic Class ? 
 
 BIEBERITE, CoSO 4 .7H 2 O. Prismatic Class 1.1835 : i : 1-4973, IO 4 J 55' 
 
 The elements of crystallization given for the members of the rnelanterite 
 group are for artificial crystals. 
 
 Epsomite, Epsom Salt, MgSO 4 .7H,O. 
 
 Orthorhombic, bisphenoidal class, a : b : c = 0.9901 : i : 0.5709. 
 Crystals show a combination of the unit prism /;/, and the right and left 
 unit bisphenoids z and /, Figure 86. The prism angle 
 is 9O38', crystals are, hence, nearly quadratic in cross- 
 section. In nature usually in granular, fibrous, or earthy 
 aggregates ; as an efflorescence, crust, and stalactitic. 
 
 Perfect brachypinacoidal cleavage. Hardness 2 to 
 2.5. Specific gravity 1.7 to 1.8. Colorless or white. 
 Transparent to translucent. Streak white. Bitter, saline 
 taste. 
 
 MgSO 4 -7H 2 O. Soluble in water. Yields water 
 when heated in a .closed tube. Heated with cobalt nitrate 
 solution it turns pink. Is non-hygroscopic. 
 Epsomite is a common constituent of ocean -and spring water. Thus, 
 it occurs in the spring water at Epsom, England ; Sedlitz, Saidschiitz, and 
 Pullna, Bohemia ; Ofen, Hungary. As an alteration product of kieserite 
 it occurs in the Stassfnrt Salt district, Germany. In some cases may be 
 formed by the action of sulphuric acid on serpentine, talc, magnesite, or 
 other magnesian rocks. At Montmartre. near Paris, epsomite occurs with 
 gypsum. It is also found in the limestone caves of Kentucky, Tennessee, 
 and Indiana. 
 
 Epsomite is used in the manufacture of sodium and potassium com- 
 pounds, in medicine, as a fertilizer in place of gypsum, and as a coating 
 for cotton cloth. 
 
 GOSLARITE, ZnSO-i^HsO. Orthorhombic, bisphenoidal class, a : b : r = 0.9804 
 : i : 0.5631. Long, columnar crystals. Prism angle is 9i7'. Usually as acicular 
 crystals or earthy aggregates, crusts, or stalactitic. Perfect brachypinacoidal cleavage. 
 Hardness 2 to 2.5. Specific gravity 2 to 2.1. Colorless, white, yellowish, or gray. 
 Astringent taste. Is an alteration product of zinc minerals, especially sphalerite. 
 Occurs with rnelanterite and copiapite. Some localities are Rammelisberg near 
 
SULPHATES 151 
 
 Goslar in the Hartz Mountains ; Schemnitz, Hungary ; Falun, Sweden ; Gagnon. 
 Montana. 
 
 Ferrogoslarite is a variety containing about 5% of ferrous sulphate. It occurs 
 at Webb City, Jasper Co., Missouri. 
 
 MORENOSITE, NiSO 4 .7H 2 O. Orthorhombic, bisphenoidal class, a : b : c = 0.9815 
 : i : 0.5656. Generally as emerald green or greenish white acicular crystals or 
 fibrous efflorescence. It is an alteration product of nickel minerals. Occurs at 
 Riechelsdorf, Hesse; Cape Ortegal, Spain; Wallace Mine on Lake Huron. 
 
 Melanterite, Copperas, FeSO 4 .7H,O. 
 
 Monoclinic. prismatic class, a : b : c= i . 1828 : I : 1 . 5427, ft = 104 
 16' '. These values are for artificial crystals. Natural crystals are rare. 
 Usually as capillary, fibrous, or stalactitic crusts or efflorescences. 
 
 Crystals possess basal and prismatic cleavages. Conchoidal fracture. 
 Hardness 2. Specific gravity 1.8 to 1.9. Color, various shades of green. 
 White streak. On exposure loses 6 molecules of water and crumbles to a 
 yellowish green powder. Vitreous to dull luster. Transparent to translu- 
 cent. Sweet, astringent taste, somewhat metallic. 
 
 FeSO 4 .7H.,O. Sometimes contains small amounts of manganese, mag- 
 nesium, or zinc. Easily soluble in water. Yields water when heated in a 
 closed tube. Reacts for ferrous iron. Luckite is a manganiferous variety 
 from Butterfield Canyon, Utah. 
 
 Melanterite is the result of the decomposition of various minerals con- 
 taining sulphide of iron, especially pyrite, marcasite, pyrrhotite, and chal- 
 copyrite. Some localities are Goslar, Hartz Mountains ; Bodenmais , Ba- 
 varia ; Falun, Sweden ; Rio Tinto, Spain ; Herrengrund, Hungary ; etc. 
 In the United States it is generally found as an efflorescence associated with 
 the sulphides of iron. 
 
 Melanterite does not occur abundantly enough in nature to be of com- 
 mercial importance. The artificial compound is used extensively as a mor- 
 dant in dyeing, as a disinfectant, and in the manufacture of ink, bluing, and 
 pigments. 
 
 MALI.ARDITE, MnSO-i^HzO, occurs in colorless, fibrous aggregates in the Lucky 
 Boy mine, Butterfield Canyon, Utah. It is easily soluble in water. 
 
 PISANITE., (Fe,Cu)SO.i.7H 2 O. This is a cupriferous melanterite occurring in 
 blue crystalline aggregates in Turkey. Salvadorite is a variety similar to pisanite. 
 It occurs in the Salvador mine, Quetena, Chile. 
 
 CUPROMAGNESITE, (Cu,Mg) SO 4 . 7H 2 O, occurs as green crusts on Mt. Vesuvius 
 in the lava flows of 1872. 
 
 BIEBERITE, CoSO4.7H 2 O, occurs as light red coatings, crusts, or stalactites at 
 Bieber, Hesse. 
 
 Chalcanthite, Blue Vitriol, Blue-Stone, CuSO 4 .sH,O. 
 
 Triclinic, pinacoidal class, a : b : c = 0.5656 : i : 0.5499, a = 97 
 39', (3 = io649', 7 =7737'- Rarely as small, flat crystals. Occurs gen- 
 erally in crusts with reniform, stalactitic, or fibrous structure. 
 
152 DESCRIPTIVE MINERALOGY 
 
 Crystals possess imperfect basal and prismatic cleavages. Conchoidal 
 'fracture. Hardness 2.5. Specific gravity 2.1 to 2.3. Brittle. Vitreous 
 luster. Color varies from deep to sky or greenish blue. Translucent. Dis- 
 agreeable metallic taste. 
 
 CuSO 4 .5H 2 O. May contain some iron. Fuses and imparts a green 
 color to the flame. Easily reduced to metallic copper with soda on char- 
 coal. Readily soluble in water yielding a blue solution, especially if annnoni- 
 cal. 
 
 Chalcanthite is an alteration product of various copper minerals es- 
 pecially chalcopyrite, bornite, etc. Occurs in the mines at Goslar, Hartz 
 Mountains ; Herrengrund, Hungary ; Falun, Sweden ; Rio Tinto, Spain ; 
 Chessy, France, and Cornwall, England. It was formerly found in con- 
 siderable quantities in the Bluestone mine near Reno, Nevada, and at Cop- 
 iapo. Chile. Occurs also in the mines near Clifton and Jerome, Arizona ; 
 Polk Co., Tennessee ; in stalactites in the Butte Copper district, Montana. 
 Copper is easily extracted from mine waters containing much chalcanthite 
 by precipitation with scrap iron. 
 
 Occurs only rarely in sufficient quantities to be of commercial impor- 
 tance. The artificial compound is used extensively in copper-plating, in 
 batteries, as a mordant, preservative of timber, for spraying plants, etc. 
 
 COQUIMP.ITE, Fe,(SO 4 ) 3 .9H 2 O. 
 
 'Hexagonal, ditrigonal scalenohedral class, a : c = i : 1.5645. Small rhombo- 
 hedral crystals, either thick tabular or short columnar. A combination of a rhombo- 
 hedron and the basal pinacoid often simulates the octahedron. Generally in fine 
 granular aggregates. Hardness 2 to 2.5. Specific gravity 2 to 2.1. May be colorless, 
 yellowish, greenish, or blue. Usually contains a little A1 2 O 3 . Soluble in cold water. 
 Occurs as a decomposition product in the trachyte of Tierra Amarilla near Copiapo, 
 Province of Atacama, Chile. 
 
 AI,UMINITE, A1 2 (OH) 4 SO 4 .;H 2 O. 
 
 Exact crystallization is unknown, perhaps orthorhombic. Generally in warty, 
 botryoidal or reniform masses consisting of very small tabular or prismatic crystals. 
 The masses are earthy and friable. Hardness i. Specific gravity 1.8. White in 
 color. Opaque. Easily soluble in hydrochloric acid, but not in water. Occurs in 
 clay at Halle, Saxony; Kochendorf, Wiirtemberg; Miihlhausen, Bohemia; Sussex 
 Co., England ; etc. 
 
 Copiapite,, Misy, Yellow Copperas, Fe,(Fe.OH),(SO 4 )-,. i8H 2 O. 
 
 Monoclinic, prismatic class, a : b : c = 0.4791 : i : 0.9759, /? = 108 
 4'. Crystals are six-sided and tabular. Usually in granular masses or 
 loosely compact aggregates of crystalline scales. 
 
 Crystals have a basal cleavage. Hardness 1.5. Specific gravity 2.1. 
 Pearly luster. Yellow to yellowish green in color. Transparent to trans- 
 lucent. Disagreeable metallic taste. 
 
SULPHATES 153 
 
 Fe 2 (Fe.OH) 2 (SO 4 ) 5 .i8H 2 O. May contain varying amounts of the 
 oxides of aluminium and magnesium. Easily soluble in dilute acid. Reacts 
 for f erirc iron. Fuses and yields a magnetic globule on charcoal. Gives 
 sulphur reaction with soda. 
 
 Is the result of the alteration of sulphide minerals of iron especially 
 marcasite, pyrite, and pyrrhotite. Occurs at Copiapo, Chile ; Falun, Sweden, 
 and Wherschau, Bohemia. 
 
 The term misy is sometimes used for copiapite, but it often includes 
 other closely related sulphates. 
 
 BLODITK, Na.,Mg(SO 4 ) 2 .4H 2 O. 
 
 Monoclinic, prismatic class a : b : c =11.3492 : i : 0.6717, /3 = ioo49'. Some- 
 times as excellent, highly modified, prismatic crystals. Usually in compact, granular, 
 or fibrous masses. Hardness 2.5 to 3.5. Specific gravity 2.22 to 2.28. Colorless, 
 pale yellow, reddish, or bluish green. Easily soluble in water. On account of 
 impurities often loses water of crystallization on exposure and crumbles. Occurs 
 associated with salt deposits at Stassfurt, Germany ; Hallstatt, Austria, (simonyite) ; 
 Salt Range, British India, (warthite) ; Astrakhan, Asia, (astrakhanite*) ; Argentine 
 Republic, and Chile. 
 
 PICROMERITE, Schonite, K,Mg(SO 4 ) 2 .6H 2 O. 
 
 Monoclinic, prismatic class, a : b : = 0.7438 : i : 0.4861, /3 = io8io' Occurs 
 as thin crusts associated with kainite in the salt deposits of the Stassfurt district, 
 Germany; also at Kalusz, Galicia. Color is generally white. Formed also by fum- 
 arolic action on Mt. Vesuvius. Picromerite is used as a source of potassium salts. 
 
 Polyhalite, K,MgCa,(SO 4 ) 4 .2H,O. 
 
 Distinct crystals are unknown. Crystallization is probably monoclinic. 
 Usually in compact fibrous or lamellar masses. Hardness 3 to 3.5. Specific 
 gravity 2.7 to 2.8. Flesh to brick red in color, sometimes white, yellow, or 
 gray. The red color is probably due to the presence of small amounts of 
 ferric oxide. Translucent. Greasy to pearly luster. 
 
 K,SO 4 .MgSO 4 .2CaSO 4 .2H 2 O. Partially soluble in water, yielding 
 gypsum. Easily fusible. Is an important mineral in the salt deposits of 
 the Stassfurt district, Germany, see page 101. Occurs also at Ischl, Hall- 
 statt. etc., Austria; Vic, Western Germany; Berechtesgaden, Bavaria, and 
 various places in the Alps. 
 
154 DESCRIPTIVE MINERALOGY 
 
 ALUM GROUP 
 
 This group includes minerals which are double salts consisting of the 
 sulphates of aluminium and an alkali metal with 24 molecules of water of 
 crystallization. These minerals occur very sparingly in nature, but some 
 of the artificial compounds are well known and used extensively in the 
 laboratory. The artificial compounds crystallize in the dyakisdodecaheclral 
 class of the cubic system, the predominating form being the octahedron. 
 Several of the minerals possess but 22 molecules of water of crystallization 
 and are doubly refractive, being perhaps monoclinic. 
 
 KAUNITE, Potash Alum, K 2 A1 2 (SO 4 ) 4 .24H 2 O. 
 
 TSCHERMTGITE, Ammonia Alum, (NH 4 ) 2 A1 2 (SO 4 ) 4 .24H 2 O. 
 
 MENDOZITE, Soda Alum, Na 2 Al 2 (SO 4 ) 4 .24H 2 O. 
 
 BOSJEMANITE, Magnesium Alum, MgAl,(SO 4 ) 4 .24H,O. 
 
 APJOHNITE, Manganese Alum, MnAl 2 (SO 4 ) 4 .24H~O. 
 
 HALOTRICHITE, Iron Alum, FeAl 2 (SO 4 ) 4 .24H,O. 
 
 All of the above minerals are secondary formations and very soluble 
 in water. They are of little importance to the mineralogist and hence 
 will not be described. 
 
 Kainite, MgSO 4 .KCl. 3 H 2 O. 
 
 Monoclinic, prismatic class, a : b : c = 1.2186 : I : 0.5863, ^ = 94 
 54'. Crystals are generally tabular in habit, but very rare. Usually in 
 fine grained aggregates and masses. 
 
 Crystals possess orthopinacoidal and prismatic cleavages.' Hardness 
 2. Specific gravity 2.5 to 3. Colorless, yellow, gray, or red. Translucent. 
 Does not deliquesce. 
 
 MgSO 4 .KC1.3H 2 O. Some of the potassium may be replaced by so- 
 dium. Easily soluble in water, on evaporating the solution, picromerite, 
 K,SO 4 .MgSO 4 .6H 2 O, crystallizes out. 
 
 Occurs in the uppermost zone of the salt deposits in the Stassfurt dis- 
 trict, Germany, and at Kalusz, Galicia, see pages 100 and 101. Kainite is 
 a secondary mineral and resulted from the decomposition of carnallite. 
 
 Kainite is important as a fertilizer and as a source of potassium com- 
 pounds. 
 
VIII. ALUMINATES, FERRITES, BOR- 
 ATES, ETC. 
 
 1. ANHYDROUS COMPONDS 
 
 SPINEL GROUP 
 
 This group consists of the metaluminates and ferrites of magnesium, 
 manganese, iron, zinc, chromium, and beryllium which can be referred to 
 the general formula 
 
 O = R O. 
 
 )M. 
 O = R CT 
 
 In this formula R may be replaced by the trivalent elements aluminium, 
 iron, or chromium, and M by the bivalent metals named above. The group 
 is generally divided into a cubic and an orthorhombic series. The mem- 
 bers of the cubic series all crystallize in the hexoctahedral class, the octa- 
 hedron being the predominating form. Chrysoberyl, Be(AlO 2 ) 2 , is the 
 only member of the orthorhombic series. 
 
 CUBIC SERIES 
 
 SPINEL, Mg(AlO 2 ) 2 . Hexoctahedral Class 
 
 PLEONASTE, (Mg,Fe) [(Al,Fe)O 2 ] 2 . Hexoctahedral Class 
 
 HERCYNITE, (Fe,Mg) (A1O 2 ) 2 . Hexoctahedral Class 
 
 PICOTITE, (Fe,Mg) [(Al,Cr,Fe)O 2 ] 2 . Hexoctahedral Class 
 
 Gahnite, Zn[(Al,Fe)O 2 ] 2 . Hexoctahedral Class 
 
 DYSLUITE, (Zn,Mn) [(Al,Fe)O 2 ] 2 . Hexoctahedral Class 
 
 FRANKLINITE, (Fe,Mn,Zn)(FeO 2 ) 2 . Hexoctahedral Class 
 
 CHROMITE, (Fe,Cr) [(Cr,Fe)O 2 ] 2 . Hexoctahedral Class 
 
 JACOESITE, Mn[(Fe,Mn)O 2 ] 2 . Hexoctahedral Class 
 
 MAGNESIOFERRITE, Mg(FeO 2 ) 2 . Hexoctahedral Class 
 
 MAGNETITE, Fe(FeO 2 ) 2 . Hexoctahedral Class 
 
 ORTHORHOMBIC SERIES 
 
 a : b : c 
 Chrysoberyl, Be(AlO 2 ) 2 . Bipyramidal Class 0.4707 : I : 0.5823 
 
 These minerals are all hard, 5.5 to 8.5. Those with metallic luster 
 are the softer, varying from 5.5 to 6.5. 
 
156 
 
 DESCRIPTIVE; MINERALOGY 
 
 SPINEL, Mg(AlO 2 ) 2 . 
 
 Cubic, hexoctahedral class. Generally octahedral in habit. Usual com- 
 binations consist of the octahedron o and rhombic dodecahedron d, Figure 
 87, and, more rarely, the tetragonal trisoctahedron i with the coefficient m 
 equal to 3, Figure 88. ' Contact twins with a face of the octahedron acting 
 as the twinning plane, the so-called Spinel law, are common, Figure 89. 
 
 FIG. 87. 
 
 FIG. 
 
 FIG. 89. 
 
 Also repeated and polysynthetic twinning according to this law. Occurs 
 usually in disseminated or lose crystals, or rounded grains. 
 
 Imperfect octahedral cleavage. Conchoidal fracture. Brittle. Hard- 
 ness 8. Specific gravity 3.5 to 4.1. Vitreous, splendent, or nearly dull 
 luster. Transparent to translucent. White streak. All colors, but espec- 
 ially various shades of red. n = 1.72. 
 
 Mg(AlO 2 ) 2 . May contain small amounts of chromium, iron, and silica. 
 Infusible. Soluble with difficulty in the borax bead. Only slightly acted 
 upon by acids, more readily by potassium bisulphate. Powdered spinel 
 turns blue when heated with cobalt nitrate solution. 
 
 Several varieties of spinel may be distinguished, as follows: 
 
 (1) Balas spinel. Rose red in color. 
 
 (2) Ruby spinel. Deep red variety. 
 
 (3) Rubicelle. Yellow or orange red in color. 
 
 (4) Almandine spinel. Bluish red in color. 
 
 (5) Blue spinel. Light blue in color. Contains about 3.6% of fer- 
 rous oxide. 
 
 (6) Chlorospinel. Emerald to grass green in color. Contains from 
 9 to 15% Fe 2 O 3 and small amounts of CuO. 
 
 Spinel is commonly the result of contact metamorphism, hence, occurs 
 usually in granular limestone, serpentine, or gneiss. The usual associates 
 are chondrodite, corundum, and brucite. Some localities are Aker, Sweden : 
 Amity and Andover districts near the boundary of New York and New 
 
ACUMINATES 157 
 
 Jersey ; various places in St. Lawrence Co., N. Y. ; Bolton, Mass. ; Franklin 
 Furnace, N. J. ; and Macon Co., N. C. 
 
 Transparent varieties of good color are used as gems. 
 
 PLEONASTE, Ceylonite, Black Spinel, (Mg,Fe) [(Al,Fe)O 2 ] 2 . 
 
 Cubic, hexoctahedral class. Crystals are similar to those of spinel proper, but 
 sometimes more highly modified. Hardness 7.5. Specific gravity 3.65 or over. Dark 
 green, brown, or black in color. Usually opaque or nearly so. Uncolored streak. Con- 
 tains iron replacing both magnesium and aluminium. Pleonaste is a typical contact 
 mineral. It occurs with augite in the Monzoni district, Tyrol; in limestone at War- 
 wick and Amity, N. Y. ; Wakefield, Ontario ; etc. Also in the placer deposits of 
 Ceylon. 
 
 HERCYNITE, Iron Spinel, (Fe,Mg) (A1O 2 ) 2 . 
 
 Cubic, hexoctahedral class. Usually as compact, fine granular aggregates, poorly 
 crystallized. Hardness 7.5 to 8. Specific gravity 3.9 to 3.95. Black in color. Gray 
 green streak. Vitreous luster on the conchoidal fracture surface, otherwise dull. 
 Contains iron replacing much of the magnesium. Occurs associated with magnetite 
 and corundum in an hornblende-garnet-gabbro at Ronsberg, Bohemia. 
 
 PICOTITE, Chrome Spinel, (Fe,Mg) [(Al,Cr,Fe)O,] 2 . 
 
 Cubic, hexoctahedral class. Small, octahedral crystals or irregular grains. Black, 
 yellow or greenish brown in color. Dark brown in transmitted light. Streak pale 
 brown. Translucent to nearly opaque. Hardness 8. Specific graviy 4.08. Picotite 
 is essentially a' chrome ceylonite containing over 24%FeO and about 8% Cr 2 O 3 . Oc- 
 curs in olivine rocks such as serpentine, Iherzolite, and basalt. Thus at Lherz, Pyre- 
 nees Mts., and Scottie Creek, Lillooet district, British Columbia. 
 
 Gahnite, Zinc Spinel, Automolite, Zn[(Al,Fe)O 2 ] 2 . 
 
 Cubic, hexoctahedral class. Commonly in octahedral crystals, consist- 
 ing of the octahedron alone, or in combination with the rhombic dodeca- 
 hedron. The hexahedron is sometimes observed. Twins according to the 
 spinel law. Also in granular aggregates. 
 
 Indistinct octahedral cleavage. Conchoidal fracture. Brittle. Hard- 
 ness 7.5 to 8. Specific gravity is usually 4.33 to 4.35, may, however, vary 
 from 4.0 to 4.9. Gray streak. Various shades of green, brown, or black 
 in color. Greasy vitreous luster. Translucent to opaque. 
 
 Zn[(Al,Fe)CX] 2 . Some of the zinc is usually replaced by iron, man- 
 ganese, or magnesium. Infusible. Gives zinc coating on charcoal.. Not 
 attacked by acids or alkalies. 
 
 Occurs in talc schist at Falun, Sweden ; with sulphides of arsenic at 
 Querbach, Schlesia ; in granular limestone at Franklin Furnace, N. J. ; in 
 granite at Haddam, Conn. ; Rowe, Mass. ; Delaware Co., Pa. ; Mitchell Co., 
 N. C. ; Chaffee Co., Colo. ; also in the Brazilian diamonds placers of Minas 
 Geraes. 
 
 DYSLUITE, (Zn,Mn) [(Al,Fe)O 2 ] 2 . This is a brown, manganiferous gahnite 
 from Sterling Hill, N. J. Specific gravity 4 to 4.6. 
 
158 DESCRIPTIVE MINERALOGY 
 
 FRANKLINITE, (Fe,Mn,Zn)(FeO 2 ) 2 . 
 
 Cubic, hexoctahedral class. Crystals are usually octahedral in habit. 
 Common forms are the octahedron and rhombic dodecahedron, Figure 87, 
 page 156. The edges are often rounded. Occurs also in compact, granu- 
 lar masses, and rounded grains. 
 
 Imperfect octahedral cleavage. Conchoidal fracture. Hardness 5.5 to 
 6.5. Specific gravity 5 to 5.22. Metallic or dull luster. Iron black in 
 color. Brown, reddish brown, or black streak. Slightly magnetic. 
 
 (Fe,Mn,Zn) (FeO 2 ) 2 . Composition varies greatly, ZnO from 17 to 
 25%, MnO 10 to 12%, and Fe 2 O 3 about 60%. Infusible. When heated 
 becomes more strongly magnetic. With soda on charcoal yields a bluish 
 green color characteristic of manganese and a white coating of zinc oxide. 
 Reacts for manganese with borax bead. Soluble in hot hydrochloric acid 
 with an evolution of chlorine. 
 
 Franklinite is commonly associated with willemite, zincite, rhodonite, 
 and calcite, and occurs rather extensively at Franklin Furnace and Sterling 
 Hill, Sussex County, N. J. Also found in cubical crystals at Eibach, Nassau. 
 
 Franklinite is a source of zinc, which is easily obtained by heating. 
 The residue contains about 12% of manganese and is used for spiegeleisen 
 in steel manufacture. 
 
 CHROMITE, Chrome Iron, Chromic Iron Ore, (Fe,Cr) ['(Cr,Fe)O 2 ] 2 . 
 
 Cubic, hexoctahedral class. Rarely in octahedral crystals. Usually in 
 compact, fine granular masses, often as disseminated grains. 
 
 Indistinct octahedral cleavage. Uneven to conchoidal fracture. Hard- 
 ness 5.5. Specific gravity 4.3 to 4.6. Pitchy, submetallic to metallic luster. 
 Opaque. Iron to brownish black in color. Dark brown streak. Sometimes 
 slightly magnetic. 
 
 (Fe,Cr) [(Cr,Fe)O 2 ] 2 . May also contain MgO and A1 2 O 3 . The com- 
 position varies considerably. Infusible, sometimes becomes magnetic. When 
 hot the borax bead gives the iron reaction, when cold the chromium. Heated 
 on charcoal or platinum foil with soda and potassium nitrate, the mass turns 
 chrome yellow. Insoluble in acids, but decomposed by fusion with potassium 
 acid sulphate. 
 
 Chromite occurs usually in veins and irregular masses in basic mag- 
 nesium rocks, especially serpentine. It is doubtless the result of magmatic 
 separation. It occurs at Frankenstein, Silesia ; Ural Mountains ; Roeros, 
 Norway ; Island of Unst ; New Zealand ; New Caledonia ; and in Asiatic 
 Turkey. 
 
 In the United States chromite is found in Chester and Delaware Coun- 
 ties, Pa. ; Baltimore Co., Md. ; San Luis Co., Cal. ; and Burnsville, Yancev 
 
ALUMINATES 
 
 159 
 
 Co., N. C. It is often associated with chrome garnet and zaratite. Chromite 
 is also found in platinum placers and the so-called black sands. 
 
 Chromite is the source of metallic chromium and its compounds, which 
 are used in the manufacture of special grades of steels and the chrome 
 colors. Chromite is also used in the manufacture of refractory bricks. The 
 production of chromite in the United States is very small. Most of the 
 chromite is imported from New Foundland and Australia. 
 
 JACOBSITE, Mn[(Fe,Mn)O 2 ] 2 . 
 
 Cubic, hexoctahedral class. Occurs in octahedral crystals, also in rounded dis- 
 seminated grains and granular aggregates. Iron black in color. Metallic luster. 
 Hardness 6. Specific gravity 4.75. Reddish black streak. Opaque. Strongly mag- 
 netic. Chemically jacobsite might be considered as a manganiferous magnetite. 
 Occurs in granular limestone at Jakobsberg, Wermland, Sweden. 
 
 MAGNESIOFERRITE, Magnoferrite, Mg(FeO 2 ) 2 . 
 
 Cubic, hexoctahedral class. Black, octahedral crystals with a dark red streak. 
 Specific gravity 4.65. Strongly magnetic. Occurs with hematite on the lavas of 
 Vesuvius. Aetna, and Stromboli. It is a sublimation product. 
 
 MAGNETITE, Magnetic Iron Ore, Lodestone, Fe(FeO 2 ),. 
 
 Cubic, hexoctahedral class. Octahedral and rhombic dodecahedral crys- 
 tals are very common. Most abundant is the simple octahedron, Figure 90. 
 
 FIG. go. 
 
 FIG. 91. 
 
 FIG. 92. 
 
 The faces of the rhombic dodecahedron are often striated parallel to the 
 long diagonal, Figure 91. Crystals are sometimes highly modified. Over 
 30 forms have been observed. Contact, Figure 89, page 156, and polysyn- 
 thetic twins according to the spinel law are rather common. Crystals are 
 often greatly distorted, Figure 92. Occurs also as disseminated grains, 
 lamellar and compact aggregates, coarse and fine grained masses, loose 
 grains or sand, and dendritic, especially in mica. 
 
160 DESCRIPTIVE; MINERALOGY 
 
 No distinct cleavage. Excellent octahedral parting, due to polysyn- 
 thetic twinning, is often observed. Conchoidal to uneven fracture. Brittle. 
 Hardness 5.5 to 6.5. Specific gravity 4.9 to 5.2. Metallic, submetallic, 
 splendent, or dull luster. Iron black in color. Black streak. Opaque, but 
 very thin lamella, especially dentrites in mica, are pale brown to black in 
 transmitted light. Strongly magnetic. A very strongly magnetic variety 
 occurs at Magnet Cove, Arkansas. More or less decomposed varieties some- 
 times show polarity. 
 
 Fe(FeO 2 ) 2 . Commonly written Fe 3 O 4 . Sometimes contains magnes- 
 ium, nickel, manganese, phosphorus, and titanium. Fuses with difficulty. 
 The powder is easily soluble in hydrochloric acid, and slowly soluble in 
 hydrofluoric acid. Alters to limonite and hematite (martite), page 87. 
 Magnetite occurs as a pseudomorph after pyrite, hematite, and siderite. 
 
 Magnetite occurs in several different ways : 
 
 (1) As a primary constituent of many basic igneous rocks, such as, 
 diabase, gabbro, nepheline syenite, and basalt. It usually occurs as 
 fine, disseminated particles or crystals ; also found in lenticular bodies 
 of considerable size, the result of local concentration. Magnetite of this 
 type of occurrence is often titaniferous and may be associated with pyroxene, 
 brown hornblende, olivine, apatite, spinel, garnet, and plagioclase. At pres- 
 ent it is of little importance, commercially. Some localities are Taberg, 
 Southern Sweden ; Finland ; Ural Mountains ; Unkel on the Rhine ; and 
 various places in New York, New Jersey, Colorado, and Minnesota. 
 
 (2) The result of regional metamorphism. Here, magnetite is gen- 
 erally found as large deposits, fahlbands, or disseminated, in gneiss, schists, 
 granular limestone, and other metamorphic rocks. The common associates 
 are feldspar, hornblende, quartz, apatite, fluorite, pyrite, and hematite. It 
 is thought that deposits of this character may have been formed ( i ) by the 
 metamorphism of limonite, hematite, or pyritiferous rocks ; (2) by depo- 
 sition from iron-bearing magmatic waters; and (3) that in some cases they 
 are probably replacement deposits. Magnetite of this type of occurrence is 
 usually non-titaniferous and of great importance, commercially. Large de- 
 posits occur in the Arendal district, Norway ; Dannemora and Falun, Central 
 Sweden ; Southern Russia ; Algeria ; Brazil ; and in the United States at 
 Mineville, N. Y. ; Cornwall, Pa. ; various place's in New Jersey, Virginia, 
 North Carolina, Colorado, Wyoming, Utah, New Mexico, and Michigan, 
 In 1908 the United States produced- 1,547,797 long tons* of magnetite of 
 this type of occurrence, obtained principally from New York, New Jersey, 
 and Pennsylvania. This was about 5% of the iron ore mined that year. 
 
 * Includes some martite, see page 87. 
 
ACUMINATES l6l 
 
 (3) The result of contact mctamorphism. Here, magnetite occurs 
 along the contact of plutonic rocks, such as granites, with limestones and 
 schists. This is a rather common method of occurrence. Some deposits 
 of this type may prove to be of commercial importance. 
 
 (4) Black Sands. Magnetite occurs extensively as a constituent of 
 river, lake, and sea sands, especially in regions of metamorphic and igneous 
 rocks. It is an important constituent of the black sands, which occur 
 rather widespread in Alaska, California, Idaho, Montana, Colorado, Ore- 
 gon, Washington, and New York. It is associated with chromite, ilmenite, 
 garnet, hematite, olivine, monazite, limonite, zircon, quartz, gold, and the 
 platinum minerals. These sands are of importance as a source of platinum, 
 see page 18. At present, experiments are being made to smelt these sands 
 electrolytically with a view to use them as a source of iron. 
 
 Magnetite is an important ore of iron. 
 
 Chrysoberyl, Be(AlO 2 ) 2 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.4707 : i : 0.5823, 
 Occurs generally in disseminated, tabular crystals. The macropinacoid pre- 
 dominates and is usually vertically striated. Contact twins (Figure 94) and 
 pentration trillings (Figure 95) are very common. Such crystals often show 
 feather-like striations. The twinning plane is the modified brachydome with 
 the coefficient m equal to 3. Penetration trillings (Figure 95) have a 
 pseudohexagonal outline and consist, apparently, of an hexagonal bipyra- 
 mid and basal pinacoid. Occurs also as crystal fragments, and loose or 
 rounded grains. 
 
 FIG. 94. FIG. 95. 
 
 Distinct brachypinacoidal cleavage. Conchoidal fracture. Brittle. 
 Hardness 8.5. Specific gravity 3.65 to 3.84. Greasy luster on fracture 
 surfaces, elsewhere vitreous. White streak. Transparent to translucent. 
 Greenish white, greenish yellow, asparagus to emerald green in color; often 
 columbine red in transmitted light. Sometimes pleochroic. Some varieties 
 show a bluish opalescence or chatoyancy. 
 
 Be(AlO,,)o. May contain some iron. Infusible. Insoluble in acids. 
 The powder turns blue when heated with cobalt nitrate solution. 
 
 There are three varieties : 
 
162 
 
 DESCRIPTIVE MINERALOGY 
 
 (1) Ordinary. Pale green and yellow varieties. When transparent 
 are often used for gem purposes. 
 
 (2) Alexandrite. Emerald green variety, which is columbine red in 
 transmitted light. 
 
 (3) Cat's Eye or Cymophane. An opalescent, yellow green variety 
 from Ceylon. 
 
 Chrysoberyl is usually found in gneiss, mica schist, or granite. It is 
 commonly associated with beryl, tourmaline, garnet, apatite, or sillimanite. 
 It occurs in the Ural Mountains ; Ireland ; Haddam, Conn. ; Norway and 
 Stoneham, Me. ; and Greenfield, N. Y. As rounded pebbles it is found 
 in the gem placers of Ceylon and Brazil. 
 
 Alexandrite and cat's eye are often used as gems. 
 
 SUSSEXITE, [(Mn,Mg)OH]BO 2 . 
 
 Crystallization unknown. Occurs in asbestos-like fibres in seams and veins in 
 calcite, associated with franklinite, willemite, and zincite in Sussex County, N. J. 
 It is white, pink, or yellowish in color. Translucent. Hardness 3. Specific gravity 
 3.42. Pearly to silky luster. 
 
 Boracite, Mg 7 Cl 2 B 16 O 30 . 
 
 Dimorphous, orthorhombic and cubic. At ordinary temperatures bor- 
 acite is orthorhombic but, owing to twinning, crystals are pseudocubic in 
 development. When heated to 265C., crystals become isotorpic and, hence, 
 cubic. Tetrahedral, cubical (Figures 96 to 98), and dodecahedral habits are 
 common. The forms commonly observed are the tetrahedron o, cube h, and 
 rhombic dodecahedron d. Crystals are usually disseminated and small, but 
 well developed. 
 
 FIG. 96. 
 
 FIG. 97. 
 
 FIG. 98. 
 
 No distinct celavage. Conchoidal fracture. Brittle. Hardness 7. 
 Specific gravity 2.9 to 3. Vitreous luster. Transparent to translucent. 
 White, pale green or blue, gray, and yellow in color. White streak. Strong- 
 ly pyroelectric. 
 
 Mg 7 Cl 2 B 10 O 30 . Sometimes contains calcium, iron, and water. Fuses 
 
BORATES 163 
 
 with intumescence to a white glass and imparts a greenish color to the 
 flame. Turns pink when heated with cobalt nitrate solution. Slowly solu- 
 ble in hydrochloric acid. 
 
 Boracite occurs disseminated in gypsum, anhydrite, and carnallite in 
 the salt deposits of the Stassfurt district, Germany. 
 
 2. HYDRATED COMPOUNDS 
 
 BORAX, Tinkal, Na 2 B 4 O 7 . ioH 2 O. 
 
 Monoclinic, prismatic class, a : b : c= 1.0995 : I ' 
 io635'. Short, thick prismatic crystals, resembling augite in habit and 
 angles, page ???. The prism angle is 87. The common forms are the 
 unit prism ; basal, ortho-, and clinopinacoids ; and the positive unit hemi- 
 pyramid. Twins are rare,- the orthopinacoid acts as twinning plane. 
 
 Orthopinacoidal and prismatic cleavages. Rather brittle. Conchoidal 
 fracture. Hardness 2. to 2.5. Specific gravity 1.7 to 1.8. Greasy, vitreous, 
 or earthy luster. Color white, sometimes grayish, bluish, or greenish. Is 
 often covered with a clouded crust. White streak. Alkaline taste. Trans- 
 lucent to opaque. 
 
 Na 2 B 4 O 7 . ioH 2 O. Swells up and fuses to a clear, transparent glass, 
 coloring the flame yellow. Heated with a paste of powdered fluorite and 
 potassium bisulphate it colors the flame yellow and then light green. The 
 green flame may be also obtained by igniting a mixture of borax, alcohol, 
 and a few drops of concentrated sulphuric acid. Soluble in 14 parts of cold 
 water. 
 
 Occurs on the shores and in the muds of the so-called borax lakes in 
 Thibet, California, Nevada, and Oregon. It is usually associated with 
 halite and soda. Most of the borax used in the United States is prepared 
 from colemanite, Ca.,B 6 O 11 .5H 2 O, which occurs extensively in San Ber- 
 nardino, Inyo, Los Angeles, and Ventura Counties, California. 
 
 Borax is used in large quantities in the manufacture of soap, enamels, 
 glass, washing powders, ointments, and lotions ; also in welding, soldering, 
 assaying, blowpiping, and calico printing. It is an antiseptic and is often 
 employed in the preservation of meat and fish. 
 
 Ulexite, Boronatrocalcite, Natronborocalcite, NaCaB 5 O .6H 2 O. 
 
 Monoclinic, prismatic class. The elements of crystallization are un- 
 known. Found generally in white, rounded, fine fibrous masses. Very 
 soft. Specific gravity 1.65 to 1.8. Silky luster. White streak. Translu- 
 cent. Tasteless. 
 
164 DESCRIPTIVE MINERALOGY 
 
 NaCaB 5 O u .6H 2 O. Sometimes it is mixed superficially with halite, 
 gypsum, glauberite, and borax. Easily fusible with intumescence to a 
 clear glass. Imparts a yellow color to the flame. Reacts for boron, see 
 borax, page 163. Soluble with difficulty in hot water. Easily soluble in 
 acids. 
 
 Occurs associated with halite, gypsum, glauberite, and borax in arid 
 regions, especially in Nevada, California, Chile, and in Nova Scotia. 
 
 It is used to some extent in the manufacture of borax and boracic acid. 
 
 PANDERMITE, Priceite, CaoBaOn.sHzO. Monoclinic, prismatic class. Occurs in 
 large quantities in white, chalky or marble-like masses in Panderma, Asiatic Turkey. 
 It is also found in Curry County, Oregon, and San Bernardino County, California. 
 
 COLEMANITE, Ca 2 B G O 13 .5H 2 O. 
 
 Monoclinic, prismatic class, a : b : c = 0.7769 : i : 0.5416, /? = ncr 
 17'. Crystals are usually short prismatic and resemble datolite. Often 
 highly modified. Occurs also in compact, granula*r masses resembling chalk 
 or porcelain. 
 
 Highly perfect clinopinacoidal cleavage. Brittle. Uneven to subcon- 
 choidal fracture. Hardness 3.5 to 4.5. Specific gravity 2.42. Vitreous 
 to dull luster. Milky white, white, gray, or yellowish white in color. White 
 streak. Transparent to opaque. 
 
 Ca 2 B 6 O 11 .5H 2 O. Imparts a yellowish green color to the flame. De- 
 crepitates, exfoliates, and fuses imperfectly. Easily soluble in hot hydro- 
 chloric acid, boracic acid separates on cooling. Insoluble in water. Treated 
 with sodium carbonate it yields borax, Na,B 4 O 7 . ioH 2 O. 
 
 Colemanite is the chief source of borax in the United States, see page 
 163. 
 
 SULFOBORITE, 4MgHBO 3 .2MgSO4.7H 2 O. Orthorhombic, bipyramidal class, a : b 
 : c = 0.6168 : I : 0.8100. Small transparent, prismatic crystals. Colorless or slightlv 
 reddish. Hardness 4 to 4.5. Specific gravity 2.44. Occurs disseminated in carnallite 
 ta Wester-Egeln, Germany. 
 
VIII. PHOSPHATES. ARSENATES, ANTI- 
 
 MONATES. VANADATES. NIOBATES, 
 
 AND TANTALATES 
 
 This class embraces a very large number of minerals of which but 
 comparatively few are of much importance. 
 
 1. NORMAL ANHYDROUS COMPOUND 
 
 These compounds are salts of the ortho, meta, and pyro acids. Several 
 groups may be differentiated. 
 
 TRIPHYLITE GROUP 
 
 This group includes the orthophosphates of sodium, lithium, iron, beryl- 
 lium, and manganese. It consists of four members which crystallize in the 
 orthorhombic system. 
 
 a : b : c 
 
 BERYLLONITE, NaBePO 4 . Bipyramidal Class 0.5724 : i : 0.5490 
 
 NATROPHILITE, NaMnPO 4 . Bipyramidal Class 0.4720 : i : 0.5550 
 
 TRIPHYLITE, Li(Fe,Mn)PO 4 . Bipyramidal Class 0.4348 : i : 0.5266 
 
 LITHIOPHILITE, LiMnPO 4 . Bipyramidal Class 0.4450 : i : 0.5550 
 
 The elements of crystallization given for natrophilite and lithiophilite 
 are only approximate. Triphylite is the most important member of the 
 group. 
 
 BERYLLONITE, NaBePO 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c 0.5724 : i : 0.549. Occurs in 
 short prismatic or tabular crystals. Often highly modified. Perfect basal cleavage. 
 Vitreous luster. Colorless, white, or pale yellow. Hardness 5.5 to 6. Specific 
 gravity 2.85. Found in decomposed granite at Stoneham, Me. 
 
 NATROPHIUTE, NaMnPO4, is a very rare mineral. Deep wine yellow in color. 
 Hardness 4.5 to 5. Specific gravity 3.4. Occurs in cleavable masses at Branchville, 
 Conn. 
 
 TRIPHYLITE, Li(Fe,Mn)PO 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c 0.4348 : i : 0.5266. Crystals are 
 rare. Occurs usually in compact, cleavable masses. Perfect basal cleavage. Un- 
 
1 66 DESCRIPTIVE MINERALOGY 
 
 even to subconchoidal fracture. Greasy luster. Translucent. Hardness 4 to 5. 
 Specific gravity 3.4 to 3.6. Greenish gray to blue in color. Streak grayish white. 
 
 Li(Fe,Mn)PC>4. Easily fusible. Soluble in hydrochloric acid. 
 
 Common associates are spodumene and beryl. OccVirs at Rabenstein, Bavaria; 
 Ketyo, Finland; Grafton, N. H. ; Norwich, Conn.; and Peru, Me. 
 
 LITHIOPHIIJTE, LiMnPO 4 , differs essentially from triphylite in that it possesses 
 a larger percentage of manganese. Lithiophilite and triphylite grade into one an- 
 other. Lithiophilite is pale pink to yellow and clove brown in color. It has been 
 found at Branchville, Conn., and Norway, Me. 
 
 MONAZITE GROUP 
 
 The members of this group are orthophosphates and niobates of the 
 rare earths. They show no definite crystallographic relationship. 
 
 Xenotime YPO 4 . Ditetragonal Bipyramidal Class i 
 
 FERGUSONITE, Y(Nb,Ta)O 4 . Tetragonal Pyramidal Class i 
 
 o . 6208 
 i . 4640 
 
 Monazite, (Ce,La,Di)PO 4 . Monoclinic Prismatic Class 
 
 a : b : c 
 0.9742 : i : 0.9227, /3=io346' 
 
 On account of a very valuable content of thorium dioxide, monazite 
 is, commercially, the most important member of the group. 
 
 Xenotime, YPO 4 . 
 
 Tetragonal, ditetragonal bipyramidal class, a : c= i : 0.6208. Crys- 
 tals are either pyramidal or prismatic in habit, resembling zircon, page 79. 
 They occur either disseminated, attached, or as rolled grains in secondary 
 deposits. 
 
 Perfect prismatic cleavage. Uneven to splintery fracture. Hardness 
 4 to 5. Specific gravity 4.45 to 4.56. Greasy to vitreous luster. Various 
 shades of yellow and brown, also flesh red, and pale gray in color. Streak 
 yellowish white, pale brown, or flesh red. Transparent to opaque. 
 
 YPO 4 . May contain some erbium and gadolinium. Infusible. In- 
 soluble in hot acids. Colors flame green after being moistened with sul- 
 phuric acid. 
 
 Occurs in granites and gneisses, often associated with zircon. Thus 
 at Hittero, Moss, and Arendal, Norway ; Ytterby, Sweden ; St. Gotthard 
 and Binnenthal, Switzerland ; Minas Geraes and Bahia, Brazil ; Clarksville, 
 Ga. ; Alexander, Burke, Henderson, and Mitchell Counties, N. C. ; and 
 Pike's Peak, Colo. 
 
 Xenotime is a source of the yttrium group of elements. 
 
PHOSPHATES 1 67 
 
 FERCUSONITE, Tyrite, Bragite, Y(Nb,Ta)O 4 . 
 
 Tetragonal, pyramidal class, a : c = i : 1.4643. Crystals are pyramidal or 
 prismatic in habit, and usually poorly developed. 
 
 Conchoidal to uneven fracture. Hardness 5.5 to 6. Specific gravity 5.8 to 5.9. 
 Dull luster, on fresh fracture surfaces greasy to submetallic. Brown to pitch black 
 in color. Pale brown streak. Translucent to opaque. 
 
 Y(Nb,Ta)O4. May also contain cerium, erbium, yttrium, and uranium. Sipylite 
 is a variety containing considerable erbium. Becomes luminous when heated to 
 500 or 6ooC. and evolves a small amount of helium. 
 
 Occurs at Cape Farewell, Greenland; Ytterby, Sweden; Arendal, Norway; and 
 in a considerable quantities in Llano County, Texas. 
 
 Monazite, Turnerite, (Ce,La,Di)PO 4 . 
 
 Monoclinic, prismatic class, a : b : c = 0.9742 : i : 0.9227, ft = 103 
 46'. Crystals are generally thick tabular or square prismatic in habit. The 
 prism angle is 8634". Often highly modified. Disseminated or attached. 
 Sometimes twinned, the orthopinacoicl acts as the twinning plane. Occurs 
 also in angular masses, but most commonly in rolled grains as monazite 
 sand. 
 
 Perfect basal cleavage. Conchoidal fracture. Brittle. Hardness 5 
 to 5.5. Specific gravity 4.9 to 5.3. Resinous luster. Transparent to opaque. 
 Red, reddish or yellowish brown, and brownish gray in color. 
 
 (Ce.La,Di)PO 4 . May contain from l / 2 to 19% of thorium dioxide, due 
 doubtless to an admixture of thorite, ThSiO 4 , page 80. This content of 
 ThO r ,, which is usually about 5% in monazite sands, is of great commercial 
 importance. Infusible. Moistened with sulphuric acid it imparts a green- 
 ish color to the flame. Decomposed by hydrochloric acid. 
 
 Occurs disseminated as macroscopic or microscopic crystals in granitic 
 rocks. It has been found at Schiittenhofen, Bohemia ; Arendal, Norway : 
 Miask, Ural Mountains ; Dauphine, France ; Binnenthal, Switzerland ; and 
 in large masses at Amelia Court House, Va. 
 
 The irost important occurrence of monazite is as sand. Extensive 
 deposits of such sands occur in the western part of North and South 
 Carolina, and Georgia ; in the provinces of Amazonas, Bahia, and Minas 
 Geraes, Brazil ; also in the Ural Mountains. The monazite belt of the 
 southern states is over 3,000 square miles in area. 
 
 Aside from quartz -and magnetite, monazite sands usually contain gar- 
 net, zircon, thorite, gold, chromite, and sometimes the diamond. 
 
 Monazite is the source of thorium dioxide which is used extensively in 
 the manufacture of incandescent mantles. Brazil, North and South Caro- 
 lina, and Georgia furnish most of the world's supply. In 1908 the United 
 States produced 422,646 pounds of monazite valued at $50,718. 
 
 YTTRGTANTAUTE is essentially a pyrotantalite of yttrium, Y 4 (Ta 2 O 7 )3. It usually 
 contains some erbium, calcium, uranium, and niobium pentoxide, Nb 2 O 5 . Crystals 
 are orthorhombic and usually poorly developed. Also occurs massive. Black or 
 yellow in color. Submetallic luster. Hardness 5 to 5.5. Specific gravity 5.2 to 5.9. 
 Conchoidal to uneven fracture. Streak grey. Yttrotantalite is a very rare mineral. It 
 has been found at Ytterby and Falun, Sweden. 
 
1 68 DESCRIPTIVE MINERALOGY 
 
 SAMARSKITE, Yttroilmenite, Uranotantalite. 
 
 Orthorhombic, prismatic class, a : b : c = 0.8803 : i : 0.4777. Crystals are 
 not common. Usually in compact masses or grains. 
 
 Conchoidal fracture. Submetallic to greasy luster. Brittle. Hardness 5 to 6. 
 Specific gravity 5.6 to 5.8. Velvet black in color. Dark reddish brown streak. Opaque. 
 Compact masses possess a glassy, amorphous appearance. 
 
 Samarskite is a -niobate of iron, yttrium, cerium, erbium, and uranium. Tan- 
 talum may replace some of the niobium. No definite formula can be assigned to 
 samarskite. Fuses with difficulty. Becomes luminous when heated. Decomposed 
 by concentrated sulphuric acid, yielding a blue solution when boiled with metallic zinc 
 or tin. Gives with salt of phosphorous in both flames an emerald green bead. 
 
 Associated with columbite, it occurs in granite at Miask, Ural Mts. ; also in 
 Mitchell County, N. C., sometimes in masses weighing as much as 20 pounds. 
 
 A source of some of the rarer elements. 
 
 COLUMBITE GROUP 
 
 The metatantalates and niobates of iron and manganese are dimor- 
 phorous. One series is tetragonal and the other orthorhombic. 
 
 TETRAGONAL SERIES 
 
 (Ditetrago-nal Bipyramidal Class} 
 
 a : c 
 
 TAPIOUTE, (Fe,Mn) [(Ta,Nb)O 8 ] 2 . i : 0.6522 
 
 MOSSITE, (Fe,Mn) [(Nb,Ta)O 8 ] 2 . i : 0.6438 
 
 ORTHORHOMBIC SERIES 
 (Orthorhombic Biypramidal Class) 
 
 a 
 
 Tantalite, (Fe,Mn) [ (Ta,Nb)O 3 ] 2 . 0.8304 
 
 COLUMBITE, (Fe,Mn) [(Nb,Ta)O 3 ] 2 . 0.8285 
 
 b : c 
 i : 0.8732 
 
 i : 0.8898 
 
 The members of the tetragonal series are of minor importance and 
 will not be described. 
 
 Tantalite, (Fe,Mn) [(Ta,Nb)O 3 ] 2 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.8304 : i : 0.8732. 
 Habit and development much like columbite. Compact and disseminated. 
 
 Conchoidal to uneven fracture. Brachypinacoidal cleavage scarcely 
 perceptible. Hardness 6 to 6.5. Specific gravity 6.3 to 9. Greasy, subme- 
 tallic luster. Iron black in color. Brownish black streak. Opaque. 
 
 (Fe,Mn) [(Ta,Nb)O 3 ] 2 . According to Naumann-Zirkel tantalite is 
 an isomorphous mixture of ;Fe(TaO 3 ) 2 and Fe(NbO 3 ) 2 , where ;// is 
 
PHOSPHATES 169 
 
 larger than, or at least equal to, n. Infusible. Not attacked by acids. 
 Manganese may replace iron and in manganotantalite nearly all the iron 
 has been thus replaced. May also contain tin and titanium. 
 
 Occurs in granite at Skogbole and Harkasaari, Finland ; Broddbo and 
 Finbo, Sweden, and Paris, Me. 
 
 It is a source of tantalum, which is now of importance in the manu- 
 facture of the tantalum incandescent electric lamps. 
 
 COLUMBITE, (Fe,Mn) [(Nb,Ta)O 3 ] 2 . 
 
 Orthorhombic, bipyramidal class, a : b : = 0.8285 : I : 0.8898. 
 Short prismatic or thick tabular crystals, resembling those of wolframite. 
 The three pinacoids, brachyprism (^ = 3), and the macrodome (m = 2), 
 are the most common forms. Heart-shaped twins with the macrodome, 
 m = 2, acting as the twinning plane are common. Columbite also occurs 
 massive and disseminated. 
 
 Distinct brachypinacoidal cleavage. Conchoidal to uneven fracture. 
 Hardness 6. The specific gravity increases with the amount of Ta,O 5 pres- 
 ent and varies from 5.4 to 6.4. Fracture surfaces show a greasy, submetallic 
 luster. Brown to iron black in color. Streak is brownish, reddish, or black. 
 
 (Fe,Mn) [ (Nb,Ta)O 3 ] 2 . According to Naumann-Zirkel columbite is 
 a mixture of wFe(NbO 3 ) 2 and Fe(TaO 3 ) 2 , where m is larger than, or 
 at least equal to, n. Manganese may replace iron and in manganocolnmbite 
 it is present in considerable quantities. Columbite and tantalite grade into 
 one another. Infusible. Not attacked by acids. Decomposed by potassium 
 bisulphate. Fused with sodium carbonate and then treated with hydrochloric 
 acid and metallic tin, the solution assumes a light blue color. 
 
 Columbite is more abundant than tantalite. It is found with cryolite 
 at Ivigtut, Western Greenland ; also at Bodenmais, Bavaria ; Tammela, 
 Finland; Miask, Ural Mountains; Woodgina Tin district, Pilbara, Western 
 Australia ; Haddam and Branchville, Conn. ; Black Hills, S. Dak. ; and 
 Pike's Peak, Colo. 
 
 Columbite is an important source of niobium and tantalum. 
 
170 DESCRIPTIVE MINERALOGY 
 
 2. BASIC ANHYDROUS COMPOUNDS CON- 
 TAINING CHLORINE AND 
 FLUORINE 
 
 Some of the most important minerals of this class belong to this sec- 
 tion. They are generally salts of the ortho acids and may contain chlorine, 
 fluorine, or an hydroxyl group. 
 
 APATITE GROUP 
 
 This group includes the orthophosphates, arsenates, and vanadates of 
 calcium and lead. All members of the group crystallize in the hexagonal 
 bipyramidal class of the hexagonal system. 
 
 a : c 
 
 APATITE, Ca 5 F(PO 4 ) s . Hexagonal Bipyramidal Class i : 0.7346 
 PYROMORPHITE, Pb 5 Cl(PO 4 ) 3 . 
 
 Hexagonal Bipyramidal Class i : 0.7362 
 
 Mimetite, Pb 5 Cl(AsO 4 ) 3 . Hexagonal Bipyramidal Class i : 0.7276 
 
 ENDUCHITE, Pb 5 Cl[(As,V) O 4 ] 3 . Hexagonal Bipyramidal Class i : 0.7495 
 
 Vanadinite, Pb 5 Cl(VO 4 ) 3 . Hexagonal Bipyramidal Class i : 0.7122 
 
 The axial ratio for endlichite is only approximate. 
 
 APATITE, Ca 5 F(PO 4 ) 3 to Ca 3 Cl(PO 4 ) 3 . 
 
 Hexagonal system, hexagonal bipyramidal class. The axial ratio, a : c, 
 varies from i : 0.7313 to i : 0.7346. Crystals are well developed and 
 often very large. Prismatic (Figures 99 and 100) and thick tabular (Figure 
 101) crystals are common. The latter are often highly modified. Some of 
 the common forms are the unit prism m and bipyramid x of the first order, 
 the basal pinacoid c, the bipyramid of the second order s (20 : 2a : a : 2c) , 
 and the bipyramid of the third order u (3/20 : 30 : a : $c). The sym- 
 metry of the hexagonal bipyramidal class is readily shown by etch figures. 
 Crystals are often vertically striated. The edges are sometimes rounded 
 and appear fused. Also occurs in compact, fibrous, nodular, reniform, bot- 
 ryoidal. or earthy masses. 
 
 Imperfect basal and prismatic cleavages. Conchoidal fracture. Brittle. 
 Hardness 5, massive varieties sometimes 4.5. Specific gravity 3.16 to 3.23. 
 Vitreous luster, on fracture surfaces more or less greasy. Sometimes 
 colorless and transparent, but usually opaque and colored brown, green, 
 gray, yellow, violet red, or white. Streak white. ' May phosphoresce when 
 heated. 
 
PHOSPHATES 171 
 
 The chemical composition varies greatly. Apatite is essentially an 
 orthophosphate . of calcium containing fluorine, chlorine, or hydroxyl, so 
 that the following formulas have been assigned to it: Ca 5 F(PO 4 ) 3 , Ca 5 Cl- 
 (PO 4 ) 3 , and Ca 5 (Cl,F,OH) (PO 4 ) 3 . Fluorine usually predominates, hence, 
 fluor-apatite is more common than chl or o -apatite. Varying amounts of 
 magnesium, manganese, and iron may be present. Fusible with difficulty. 
 Moistened with sulphuric acid, it imparts a green color to the flame. Easily 
 soluble in acids. The nitric acid solution of apatite yields a heavy yellow 
 precipitate with ammonium molybdate. 
 
 FIG. 99. 
 
 FIG. 100. 
 
 FIG. 101. 
 
 There are several varieties of apatite: 
 
 (1) Ordinary Apatite. This includes the crystallized, cleavable, and 
 granular varieties. 
 
 (2) Asparagus Stone. A yellowish green variety occurring in Spain. 
 
 (3) Phosphorite. Fibrous, scaly, or concretionary masses, often with 
 a concentric structure. 
 
 (4) Osteolite. This a earthy, more or less altered apatite. 
 
 (5) Guano. Animal excrement, chiefly of birds, rich in phosphoric 
 acid. Gray to brown in color and porous, granular, or compact in structure. 
 
 (6) Phosphate Rock. This is an impure, massive variety containing 
 about 15 to 40% of P 2 O 5 . It is gray, white, brown, or black in color and 
 may occur in beds, nodules, or as concretions. Hardness varies from 2 to 5. 
 
 Apatite is a common, accessory constituent of many of the igneous rocks. 
 It is also an associate of metalliferous ore deposits, especially those of mag- 
 netite and cassiterite, page 81. Apatite is also found in granular limestones. 
 It is present in small quantities, from 0.02% up, in nearly all types of rocks. 
 
 Some important localities are Ehrenfriedersdorf, Saxony ; Schlaggen- 
 
1 72 DESCRIPTIVE; MINERALOGY 
 
 wald, Bohemia ; St. Gotthard, Switzerland ; Arendal, Norway ; Knappen- 
 wand, Tyrol ; Jumilla, Spain ; Luxullian, Cornwald, England. Large de- 
 posits occur in Lanark, Leeds, Renfrew, and Frontenac Counties, Ontario, 
 and in Ottawa County, Quebec, Canada. 
 
 In the United States apatite is found at Norwich and Bolton, Mass. ; 
 St. Lawrence and Jefferson Counties, N. Y. ; Chester Co., Pa. ; and Alex- 
 ander County, N. C. 
 
 Extensive deposits of phosphate rock or bone phosphate occur in Flor- 
 ida, South Carolina, Tennessee, Pennsylvania, Arkansas, and Alabama. In 
 1908 the United States produced 2,386,138 long tons of phosphate rock 
 valued at $11,399,124. This was obtained principally from Florida, South 
 Carolina, and Tennessee. 
 
 Phosphate rock is used in large quantities in the manufacture of fer- 
 tilizers. Its phosphoric acid content is rendered available by treatment with 
 sulphuric acid. Apatite is also used to some extent in fertilizers and as a 
 source of phosphorous. 
 
 PYROMORPHITE, Pb n Cl(PO 4 ) 3 . 
 
 Hexagonal system, hexagonal bipyramidal class, a : c=i : 0.7362. 
 Small crystals resembling those of apatite (Figures 99 and 100). The 
 common forms are the unit prism m and bipyramid x of the first order, 
 and the basal pinacoid c. The prism faces are sometimes striated horizon- 
 tally. The symmetry of the hexagonal bipyramidal class has been proven 
 by means of etch figures only. Crystals are sometimes rounded and barrel- 
 shaped. Occurs also in botryoidal and reniform aggregates, disseminated, 
 and in crusts. 
 
 Conchoidal to uneven fracture. Brittle. Hardness 3.5 to 4. Specific 
 gravity 6.9 to 7.1, if much calcium is present it may be as low as 5.9. Greasy, 
 adamantine luster. Translucent to opaque. White to pale yellow streak. 
 Usually some shade of green in color, but may be yellow, gray, brown, 
 orange, or white. 
 
 Pb 5 Cl(PO 4 ) 3 . May contain calcium, fluorine, or arsenic. On charcoal 
 it fuses to a globule which on cooling assumes a polyhedral form with a 
 crystalline structure. Yields in the reducing flame a coating and globule 
 of lead. Soluble in nitric acid. Occurs as a pseudomorph after galena and 
 cerussite. 
 
 Pyromorphite is generally a secondary mineral formed from the de- 
 composition of lead ores with which it is commonly associated. It occurs 
 in the Freiberg district of Saxony ; Clausthal, 'Hartz Mts. ; Cornwall and 
 Cumberland, England ; Phoenixville, Pa. ; Lubec and Lenox, Me. ; and Sing 
 Sing, N. Y. 
 
PHOSPHATES 173 
 
 Mimetite, Pb 5 Cl(AsO 4 ) 3 . 
 
 Hexagonal system, hexagonal bipyramidal class, a : c = I : 0.7276. 
 Crystals resemble those of pyromorphite. Occurs also in globular, reni- 
 form. and earthy masses. 
 
 Imperfect pyramidal cleavage. Conchoidal to uneven fracture. Brit- 
 tle. Hardness 3.5 to 4. Specific gravity 7 to 7.3. Greasy, adamantine lus- 
 ter. White streak. Yellow, brown, or white in color. Translucent. 
 
 Pb 3 Cl(AsO 4 ) 3 . Campylite contans 3 to 4% of P 2 O 5 . Hedyphane is a 
 variety with 10 to 14% of CaO. Yields fumes of arsenic trioxide and a 
 globule of lead when heated on charcoal. Soluble in nitric acid and potas- 
 sium hydroxide. 
 
 Like pyromorphite it is a secondary mineral and is always associated 
 with lead ores. It is not as common as pyromorphite. Occurs in Cornwall, 
 and Cumberland, England ; Johanngeorgenstadt, Saxony ; Pribram, Bo- 
 hemia ; Zacatecas, Mexico ; and Phoenixville, Pa. 
 
 ENDLICHITE, Pb 5 Cl[(As,V)O4]3, is an isomorphous mixture of mimetite and 
 vanadinite. It occurs at Hillsboro, Sierra County, New Mexico. 
 
 Vanadinite, Pb 5 Cl(VO 4 ) 3 . 
 
 Hexagonal system, hexagonal bipyramidal class, a : c=i : 0.7122. 
 Crystals are usually prismatic, resembling those of pyromorphite. Often 
 show skeletal development. Occurs also in compact, fibrous aggregates 
 with botryoidal or reniform surfaces. 
 
 Uneven to conchoidal fracture. Brittle. Hardness 2.75 to 3. Specific 
 gravity .6.7 to 7.2. Yellow, brown, or red in color. White to pale yellow 
 streak. Translucent to opaque. Resinous luster on fracture surfaces. 
 
 Pb 5 Cl(VO 4 ) 3 . May contain phosphorous or arsenic. Fuses easily. 
 Reacts for lead and vanadinum. Decrepitates when heated in a closed tube. 
 Easily soluble in nitric acid. 
 
 Occurs associated with lead minerals, but never in large quantities ; 
 thus at Zimapan, Mexico ; Ural Mountains ; Wanlockhead, Scotland ; Sing 
 Sing, N. Y. ; various places in Yuma, Maricopa, Pinal, and Yavapai Coun- 
 ties, Arizona. 
 
 It is a source of vanadinum and its compounds. 
 
 Amblygonite, Li(AlF)PO 4 . 
 
 Triclinic, pinacoidal class, a : b : c = 0.2454 : i : 0.4605, a = 6847 / , 
 /? = 9844', ? =8552 / . Crystals are not common. Occur usually in 
 cleavable, columnar, and compact masses. Polysynthetic twinning is com- 
 mon. 
 
 Basal, prismatic, and domatic cleavages inclined at angles of 7o3o', 
 744o', and 922o'. Conchoidal fracture. Brittle. Hardness 6. Specific 
 gravity 3 to 3.11. Pearly to vitreous luster. White, green, blue, gray, yel- 
 low, or brownish in color. White streak. Translucent. 
 
 Li(AlF)PO 4 . A portion of the fluorine may be replaced by hydroxyl, 
 and the lithium by sodium. Fuses easily with intumescence and colors the 
 
174 DESCRIPTIVE MINERALOGY 
 
 flame carmine red. When powdered it is soluble in sulphuric or hydro- 
 chloric acids. Moistened with sulphuric acid it colors the flame momentarily 
 bluish green. 
 
 Occurs at Penig, Saxony ; Arendal, Norway ; Hebron and Paris, Me. ; 
 Branchville, Conn. ; and in large quantities at Pala, San Diego County, 
 Cal. It is usually associated with lepidolite, petalite, or rubellite. 
 
 Amblygonite is a source of lithium. 
 
 OLIVENITE-WAGNERITE GROUPS 
 
 The members of these groups are basic fluorophosphates and the like, 
 or isomorphous mixtures of them. The minerals of the olivenite group are 
 orthorhombic, while those of the wagnerite group crystallize in the mono- 
 clinic system. 
 
 OLIVENITE GROUP 
 
 ( Orthorhom bic System ) 
 
 a : b : c 
 
 LJBETHENITE, Cu(Cu.OH)PO 4 . Bipyramidal Class 0.7019 : i : 0.9601 
 
 ADAMITE, Zn(Zn.OH)AsO 4 . Bipyramidal Class 0.7158 : i : 0.9733 
 
 OUVENITE, Cu(Cu.OH)AsO 4 . Bipyramidal Class 0.6726 : i : 0.9396 
 DESCUHZITE, (Pb,Zn) (Pb.OH)VO 4 . 
 
 Bipyramidal Class 0.6367 : i : 0.8046 
 
 WAGNERITE GROUP 
 
 (Mono clinic System} 
 
 a : b : c (3 
 HERDERITE, Ca(Be.OH)PO 4 . 
 
 Prismatic Class 0.6307 : i : 0.4274, 90 6' 
 WAGNERITE, Mg(Mg.F)PO 4 . 
 
 Prismatic Class 1.9138 : i : 1.5054, 108 7' 
 TRIPUTE, Fe(Fe.F)PO 4 . . ? 
 
 TRIPLOIDITE, Mn(Mn.OH)PO 4 . 
 
 Prismatic Class 1.8571 : i : 1.4944, io8 c i4' 
 ADEUTE, Ca(Mg.OH)AsO 4 . 
 
 Prismatic Class 2.1978 : i : 1.5642, io645' 
 TILASITE, Ca(Mg.F)AsO 4 . ? 
 
 SARKINITE, Mn(Mn.OH)AsO 4 . 
 
 Prismatic Class 2.0013 : i : 1.5880, ii746' 
 
 Adelite, tilasite, and sarkinite are very rare. 
 
PHOSPHATES 175 
 
 LlBETHENlTE, Cu(Cu . OH) PO 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.7019 : i : 0.9601. Small crys- 
 tals, approximately octahedral in habit and well developed. Often in druses. Also 
 reniform, globular, and compact. 
 
 Very indistinct, brachy and macropinacoidal cleavages. Conchoidal to uneven 
 fracture. Brittle. Hardness 4. Specific gravity 3.6 to 3.8. Resinous luster. Trans- 
 lucent. Dark olive green in color. Streak olive green. 
 
 Cu(Cu.OH)PO 4 . May contain some arsenic. Occurs at Libethen, Hungary; 
 Nijni-Tagilak, Ural Mts. ; Cornwall, England; Bolivia; Chile. 
 
 ADAMITE, Zn(Zn.OH)AsO.i. Occurs in very small, orthorhombic crystals. Hard- 
 ness 3.5. Specific gravity 4.35. Transparent. Vitreous luster. Yellow, violet, or 
 colorless. Varieties containing cobalt are usually rose red, those with copper green. 
 Found at Chanarcillo, Chile ; Cap Garonne, France ; Laurium, Greece. 
 
 OLIVENITE, Cu(Cu.OH)AsO 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.6726 : i : 0.9396. Prismatic 
 and acicular crystals. The prism angle 874o'. Occurs also in reniform and botryoidal 
 masses with a fibrous or earthy structure, and often with a velvety surface. 
 
 No pronounced cleavage. Conchoidal to uneven fracture. Brittle. Hardness 3. 
 Specific gravity 4.1 to 4.6. Adamantine, vitreous, or pearly luster. Subtransparent to 
 translucent. Streak olive green to brown. Various shades of green in color, may 
 also be brown, yellow, or grayish white. 
 
 Occurs in Cornwall and Cumberland, England; Nijni-Tagilak, Ural Mts.; 
 Libethen, Hungary; Tintic district, Utah. 
 
 DESCLOIZITE, (Pb, Zn) (Pb.OH)VO.4, occurs in very small, orthorhombic crystals 
 which usually possess drusy or warty surfaces ; also massive. Hardness 3.5. Specific 
 gravity 5.9 to 6.2. Orange, brownish red, or grayish streak. Cherry to brownish red, 
 light or dark brown, cr black in color. Found in the Argentine Republic; Lake Val- 
 ley, Sierra County, New Mexico; Tombstone and other places in Arizona. Not a 
 common mineral. 
 
 HERDEKITE, Ca ( Be . OH ) PO 4 . 
 
 Monoclinic, prismatic class, a : b : c = 0.6307 : i : 0.4274, p = go6'. Occurs 
 in prismatic crystals, often highly modified. The prism angle is 6339'. Pseudo-ortho- 
 rhombic on account of complex twinning. 
 
 Conchoidal fracture. Brittle. Hardness 5. Specific gravity 3. Vitreous luster. 
 Colorless or pale yellow. Transparent. 
 
 Ca(Be.OH) POi. The hydroxyl may be replaced by fluorine. Liberates aaid water 
 when heated to a high temperature in a closed tube. Phosphoresces with . an orange 
 yellow color. Turns blue when treated with cobalt nitrate solution. Soluble in acids. 
 
 Occurs in Stoneham, Auburji, and Hebron, Maine. 
 
 WAGNERITE, Mg(Mg.F)PO 4 . 
 
 Moncclinic, prismatic class, a : b : c = 1.9138 : i : 1.5054. P io87'. Short 
 and long columnar crystals with vertical striations. Often highly modified. Also 
 massive. 
 
 Imperfect prismatic, orthopinacoidal, and basal cleavages. Conchoidal fracture. 
 
176 DESCRIPTIVE MINERALOGY 
 
 Hardness 5 to 5.5. Specific gravity 3 to 3.15. Greasy, vitreous luster. Translucent. 
 Various shades of yellow, gray, flesh red, and green in color. White streak. 
 
 Mg(Mg.F)PC>4 May contain small amounts of iron and calcium replacing mag- 
 nesium. Fuses with difficulty to a grayish green enamel. Moistened with sulphuric 
 acid it imparts a bluish green color to the flame. The powder is slowly soluble in 
 nitric acids with an evolution of hydrofluoric acid. 
 
 Found sparingly at Werfen, Salzburg, Austria. 
 
 TRIPLITE, Fe(Fe.F)PO 4 . Probably monoclinic and isomorphous with wagnerite. 
 Occurs only in imperfect, crystalline masses with two cleavages at right angles to 
 each other. Conchoidal to uneven fracture. Hardness 4 to 5.5. Specific gravity 3-5 
 to 3.8. Greasy luster. Chestnut brown to black in color. Streak yellow gray to brown. 
 Translucent. Found at Limoges, France ; Helsingfors, Finland ; Stoneham, Me. ; 
 Branchville, Conn. 
 
 Triploidite, (Mn,Fe) [(Mn,Fe)OH]PO4, may be considered a triplite in which 
 manganese predominates and fluorine has been replaced by hydroxyl. Prismatic crys- 
 tals are rare; usually found in crystalline aggregates. Hardness 4.5 to 5. Specific 
 gravity 3.7. Vitreous to greasy adamantine luster. Transparent to translucent. Yellow 
 or reddish brown in color. Occurs at Branchville, Conn. 
 
 CLINOCLASITE, APHANESE, (Cu.OH) 3 AsO 4 . Monoclinic, prismatic class, a : b : 
 c 1.9069 : i : 3.8507, /3 =z 993o'. Small, prismatic crystals. The prism angle 
 is 124. Often arranged in spherical groups. Also hemispherical or reniform masses 
 with a radial fibrous structure. Very perfect basal cleavage. Brittle. Hardness 2.5 
 to 3. Specific gravity 4.2 to 4.4. Pearly luster on cleavage surfaces, otherwise vitreous. 
 Translucent. Externally black blue-green in color, internally verdigris-green. Bluish 
 green streak. Occurs with copper minerals in Cornwall and Devonshire, England ; 
 Sayda, Saxony; and Tintic district, Utah. 
 
 DUKRENITE, Kraurite, Fe 2 (OH) 3 PO,. Orthorhombic, a : b : c = 0.8734 : i 
 0.4260. Crystals are small, rare, and apparently cubical in habit. The surfaces are 
 usually rounded. Occurs also in spherical and reniform aggregates with a radial 
 fibrous structure. 
 
 Distinct macropinacoidal cleavage. Very brittle. Hardness 3.5 to 4. Specific 
 gravity 3.3 to 3.5. Slightly greasy luster. Various shades of green in color, on 
 exposure turns yellow or brown. Yellowish green streak. Translucent to nearly 
 opaque. * Occurs with iron minreals at Limoges, France ; Hirschberg, Westphalia ; 
 Allentown, N. J. ; Rockbridge, Va. 
 
 Lazulite, Mg(Al.OH) 2 (PO,) 2 . 
 
 Monoclinic, prismatic class, a : b : c = 0.9747 : i : 1.6940, (3 = ()i ^8 f . 
 Well developed crystals are not common. They are usually acute pyramidal 
 in habit, sometimes tabular or domatic. Also granular to compact masses. 
 
 Indistinct prismatic cleavage. Uneven fracture. Brittle. Hardness 5 
 
PHOSPHATES 177 
 
 to 6. Specific gravity 3 to 3.12. Vitreous luster. Translucent to opaque. 
 Various shades of blue in color, usually azure blue. White streak. 
 
 Mg(Al.OH) 2 (PO 4 ) 2 . Magnesium may be replaced by iron and cal- 
 cium. Yields water in closed tube and turns white. The blue color may be 
 restored by treatment with cobalt nitrate solution. Moistened with sulphuric 
 acid it imparts a bluish green color to the flame. Not attacked by acid?. 
 
 Occurs at Werfen, Salzburg, Austria ; various places in Styria ; Horrs- 
 joberg, Sweden; Crowders Mt., Gaston County, N. C. ; and Graves Mt., 
 Lincoln County, Ga. 
 
 3. HYDRATED COMPOUNDS 
 
 The hydrated compounds include normal, acid, and basic salts. Very 
 few of these minerals occur in large quantities. 
 
 Struvite, NH 4 MgPO 4 .6H 2 O. 
 
 Orthorhombic, pyramidal class, a : b : c = 0.5667 : I : 0.9121. Ex- 
 cellent example of hemimorphism. Perfect basal cleavage. Translucent 
 to opaque. Vitreous luster. Colorless, but often yellow or pale brown. 
 Hardness 1.5 to 2. Specific gravity 1.66 to 1.75. Found in sewers and 
 guano deposits. 
 
 VIVIANITE GROUP 
 
 This group embraces the ortho salts of magnesium, iron, cobalt, nickel, 
 and zinc containing eight molecules of water. Chemically they are iso- 
 morphous, but only on three of them have -crystallographic investigations 
 been made. These have been referred to the monoclinic prismatic class. 
 
 a : b : c ft 
 
 BOBIERRITE,, Mg. 5 (PO 4 ) 2 .8H 2 O. 103 Approx. 
 
 Vivianite, Fe,,(PO 4 ) 2 .8H 2 O. 0.7498 : i : 0.7017, io426' 
 
 HOERNESITE, Mg 3 ( AsO 4 ) 2 .8H 2 O. ? 
 
 SYMPI.ESITE, Fe :! (AsO 4 ) 2 .8H 2 O. 0.7806 : i : 0.6812, 107 13' 
 
 Erythrite, Co,(AsO 4 ) 2 .8H 2 6. 0.7937 : i : 0.7356, 105 9' 
 
 Annabergite, NL(AsO 4 ) 2 .8H 2 O. ? 
 
 CABRERITE, (Ni,Mg) 3 (AsO 4 ) 2 .8H 2 O. ? 
 
 KOTTIGITE, (Zn,Co) 3 (AsO 4 ) 2 .8H 2 O. ? 
 
 These minerals are all secondary formations and do not occur very 
 abundantly. 
 
 BOBIERRITE. Mg 3 (PO4) 2 .8H 2 O, occurs in aggregates of very small, white monc 
 clinic crystals and in reniform masses in guano at Mejillones, Chile. 
 
17^ DESCRIPTIVE MINERALOGY 
 
 Vivianite, Blue Iron-earth, Fe 3 (PO 4 ) 2 .8H 2 O. 
 
 Monoclinic, prismatic class, a : b : c = 0.7498 : i : 0.7017, (3= 104 
 26'. Crystals are usually thin prismatic. Occurs also in reniform and 
 globular aggregates with a radial, fibrous structure ; often earthy and may 
 then be known as blue iron-earth. 
 
 Clinopinacoidal cleavage. Sectile. Thin laminae are flexible. Hard- 
 ness 1.5 to 2. Specific gravity 2.6 to 2.7. Translucent. On cleavage sur- 
 faces pearly or metallic pearly luster, elsewhere vitreous. When fresh white 
 or colorless ; on exposure, clue to the formation of a basic ferric phosphate, 
 it gradually turns blue. Colorless or bluish white streak, which deepens 
 rapidly to indigo blue. Transparent to translucent, opaque after exposure. 
 Strongly pleochroic. 
 
 Fe a (PO 4 ).,.8H 2 O. Fuses easily and colors the flame bluish green. 
 Yields on charcoal a magnetic globule. Soluble in hydrochloric acid. 
 
 Occurs as a secondary mineral in association with iron compounds. 
 which have been acted upon by circulating waters containing phosphoric 
 acid. It is sometimes found in bones, shells, and roots of trees. Some im- 
 portant localities are Cornwall and Devonshire, England ; Bodenmais, Ba- 
 varia ; Anglars and elsewhere, France: Middletown, Del.; Allentown, N. J : 
 Eddyville, Ky. 
 
 HOERNESITE, Mga(AsO4)2.8H 2 O. Occurs in good sized crystals, often arranged 
 in stellate groups. Perfect clinopinacoidal cleavage. Very soft, 0.5 to i. Specific 
 gravity 2.47. Flexible, resembles talc or gypsum. Snow-white to pale rose red in 
 color. Pearly luster. Occurs at P>anat and Nagyag, Hungary. 
 
 SYMIU.ESITK, FesCAsO^Os.SHnO, occurs in extremely small, acicular crystals which 
 are usually arranged in spherical groups. Very perfect clinopinacoidal cleavage. Brit- 
 tle. Hardness 2.5. Specific gravity 2.96. Pale blue or greenish in color. Found at 
 Lobenstein, Voigtland. and Fclsobanya, Hungary. 
 
 Erythrite, Cobalt lUoom, Co..(AsO 4 ),.8H 2 O. 
 
 Monoclinic, prismatic class, a : b : c = 0.7937 : i : 0.7356, ($= 105 
 9'. Crystals are generally very small, acicular, and vertically striated. 
 Sometimes arranged in spherical and stellate groups. Occurs often in glob- 
 ular, reniform, and earthy masses ; also as a coating. 
 
 Very perfect clinopinacoidal cleavage. Sectile and flexible, especially 
 in thin laminae. Hardness 1.5 to 2.5. Specific gravity 2.95. Crystals 
 possess a pearly luster on the cleavage surfaces, otherwise adamantine to 
 vitreous. Transparent to subtranslucent. Crimson to peach red in color, 
 due to decomposition pearly to greenish gray. Pale red streak. 
 
 Co 3 (AsO 4 )., .8H 2 O. Yields water in a closed tube and turns blue. 
 Acid solutions are red. 
 
 Erythrite is a decomposition product of the arsenides of cobalt. It is 
 commonly found in association with cobaltite, smaltite, and chloanthite in 
 the Freiberg district, Saxony, and rather abundantly in the Cobalt Silver 
 district of ( Ontario. 
 
I'HOSI'IIATKS 179 
 
 Annabergite, Nickel Bloom, Nio(AsO 4 )o.8H.,O. 
 
 Monoclinic. Occurs only in earthy, somewhat crystalline crusts and 
 masses. Very soft. Specific gravity 3 to 3.1. Apple green in color. It is 
 a decomposition product of minerals containing nickel and arsenic, such 
 as niccolite and chloanthite. Found in the Freiberg district, Saxony, and 
 the Cobalt district, Ontario. 
 
 CABRERITE, (Ni,Mg) a (AsO4)-.8HO, is a variety of annabergite containing con- 
 siderable magnesium. 
 
 KoTTiciTK, (Zn,Co) 3 (AsO4) 2 .8HO, is a zinciferous variety of erythrite. 
 
 SCORODITE GROUP 
 
 This group embraces the orthophosphates and arsenates of aluminium 
 and trivalent iron containing two molecules of water of crystallization. 
 These minerals crystallize in the orthorhombic bipyramidal class. 
 
 a : b : c 
 
 VAKISCJTK, A1PO 4 .2H 2 O. 0.8648 : i : ? 
 
 STRUNGITE, FePO 4 .2H 2 O. 0.8652 : i : 0.9827 
 
 Scorodite, FeAsO 4 .2H 2 O. 0.8687 : l ' -953 6 
 
 VARISCITE, A1PO4.2H^O. Orthorhombic. Occurs in reniform crusts with a fine 
 crystalline structure. Sometimes apparently amorphous. Conchoidal fracture. Greasy 
 feel. Hardness 4 to 5. Apple green to colorless. Translucent. Dull waxy luster. 
 Found in Montgomery County, Ark., and in nodular masses in Utah. 
 
 STRENGITE, FePO4.2H 2 O. Orthorhombic, bipyramidal class, a : b : c = 0.8652 
 : i : 0.9827. Usually found in spherical and botryoidal forms with a radial fibrous 
 structure. Crystals are rare. Hardness 3 to 4. Specific gravity 2.87. Vitreous lus- 
 ter. Pale red to almost colorless. Occurs near Giessen, Germany, and in Rockbridgc 
 County, Va. 
 
 BARRANDITE, (Fe, A1)PO4.2H 2 O, is a variety of strengite containing aluminium. 
 
 Scorodite, FeAsO 4 .2H,O. 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.8687 : i : 0.9536. 
 Small, pyramidal or prismatic crystals, often in druses. Also botryoidal and 
 reniform masses with a fibrous structure, or as earthy crusts. 
 
 Crystals possess an important prismatic cleavage. Conchoidal to un- 
 even fracture. Hardness 3.5 to 4. Specific gravity 3.1 to 3.3. Greasy 
 luster on cleavage surfaces, elsewhere vitreous. Grayish white streak. 
 Translucent. Pale green to black or blue green in color ; more rarely blue, 
 red, or brown. 
 
 FeAsO 4 .2H 2 O. Yields water in a closed tube and turns yellow. Easily 
 fusible and colors flame blue. Soluble in hydrochloric acid. 
 
 Occurs commonly with limonite or arsenopyrite. Found at Johann- 
 georgenstadt, Schneeberg, and Schwarzenberg, Saxony; Cornwall, Eng- 
 land ; Nerchinsk, Siberia ; Brazil. 
 
l8o DESCRIPTIVE MINKRAI.OGY 
 
 Pharmacolite, CaHAsO^.aKLO. 
 
 Monoclinic, prismatic class, a : b : c = 0.6137 : i : 0.3622, = 96 
 47'. Crystals are not common. Usually in spherical masses and crusts 
 with a fine fibrous structure. Crystals possess a perfect clinopinacoidal 
 cleavage. Uneven fracture. Thin laminae are flexible. Hardness 2 to 
 2.5. Specific gravity 2.64 to 2.73. Vitreous luster, pearly on cleavage 
 surfaces. Color white to grayish, sometimes reddish or green, due to 
 admixture of erythrite or annabergite. White streak. Translucent to 
 opaque. 
 
 Occurs commonly as a coating on arsenical minerals at St. Andreas- 
 berg, Hartz Mountains ; Joachimsthal, Bohemia. 
 
 EUCHKOIXK, Cu(Cu.OH)AsO4.3HO. Orthorhombic. bipyramidal class, a : b 
 : c =0.6088 : i : 1.0379. Short columnar crystals, often vertically striated and ar- 
 ranged in druses or crusts. The prism angle is 624o'. Crystals are comparatively 
 large. 
 
 Indistinct prismatic cleavage. Conchoidal fracture. Brittle. Hardness 3.5 to 
 4. Specific gravity 3.3 to 3.4. Vitreous luster. Transparent to translucent. Emerald 
 green in color, resembles dioptase, page 211. Pale green streak. Found in mica 
 schist at Libethen, Hungary. 
 
 CHALCOPHYLUTE, (Cu.OH^AsO^CuCOH^.j^HsO. Hexagonal, ditrigonal 
 scalenohedral class, a : c I : 2.5536. Crystals are tabular, parallel to the basal 
 pinacoid. Occurs also massive and in druses. 
 
 Perfect basal cleavage. Hardness 2. Specific gravity 2.4 to 2.66. Transparent 
 to translucent. Pearly luster on cleavage surfaces, otherwise vitreous to subada- 
 mantine. Blue, emerald, or verdigris-green in color. Pale green streak. May con- 
 tain Al-OsyPzO:,, and FeO. Found, at Redruth, Cornwall, England; Saycla, Saxony: 
 Nijni-Tagilak, Ural Mountains. 
 
 PH ARM AcosiDERi'1% Fe ( Fe . OH ) 3 ( AsO 4 ) 3 . 6H,O. 
 
 Cubic, hextetrahedral class. Small crystals consisting commonly of a combina- 
 tion of the cube, rhombic dodecahedron, and the positive and negative tetrahedrons. 
 The crystals faces arc often somewhat rounded. Also granular and massive. 
 
 Imperfect cubical cleavage. Conchoidal to uneven fracture. Hardness 2.5. 
 Specific gravity 2.9 to 3. Adamantine vitreous luster, on fracture surfaces greasy. 
 Transparent to translucent. Various shades of green, brown, and yellow in color. 
 Light yellowish green streak. Usually occurs with limonite and ores of copper. 
 Found in Cornwall and Cumberland, England; Victoria, Australia; Schneeberg. 
 Saxony ; Tintic district, Utah. 
 
 Wavellite, (A1.OH) 3 (PO 4 ) U .5H 2 O. 
 
 Orthorhombic, bipyrainidal class, a : b : c = 0.5573 : i : 0.4084. 
 Well developed crystals are very rare. Commonly in hemispherical or 
 globular masses made up of concentric layers and possessing a radial fib- 
 rous structure. 
 
PHOSPHATES l8l 
 
 Crystals possess fairly good brachypinacoidal and domatic cleavages. 
 Conchoidal to uneven fracture. Brittle. Hardness 3.5 to 4. Specific grav- 
 ity 2.3 to 2.4. Vitreous luster, on fracture surfaces more or less pearly or 
 resinous. Translucent. May be colorless, but is usually gray, yellow, 
 green, brown, blue, or black. White streak. 
 
 fAl.OH) 3 (PO 4 ) 2 .sH 2 O. May also be written 3A1 2 O 3 .2P 2 O 5 . 13H,O. 
 There may be some variations in the amount of water of crystallization 
 present. Fluorine may replace some of the hydroxyl. Infusible. Im- 
 parts a green color to the flame. Turns blue when treated with cobalt ni- 
 trate solution. Soluble in hydrochloric acid or potassium hydroxide. 
 
 Wavellite is a secondary mineral formed by the action of circulating 
 waters containing phosphoric acid upon rocks and minerals rich in alumina. 
 It is found on the surfaces of such rocks, or lining the cracks or cavities 
 in the same. Some localities are Devonshire and Cornwall, England ; Frei- 
 berg district, Saxony ; Bohemia ; York County, Pa. ; Montgomery County. 
 Ark. ; Silver Hill, N. C. 
 
 Turquois, Turquoise, AL(OH),PO 4 .H,O. 
 
 Apparently amorphous. Never crystallized, generally in reniform, bot- 
 ryoidal, or stalactitic masses ; sometimes in veins, crusts or coatings, dis- 
 seminated grains, or rolled and rounded pebbles. 
 
 No cleavage. Conchoidal fracture. Brittle. Hardness 6. Specific 
 gravity 2.6 to 2.8. Generally opaque. Slightly waxy luster. Various 
 shades of blue or green in color. White or slightly greenish streak. 
 
 Al 2 (OH) 8 PO 4 .H a O. Copper and iron may be preesnt in small 
 amounts. Analyses vary considerably. According to Penfield the formula 
 should be written: [Al(OH) 2 ,Fe(OH) 2 ,Cu(OH),H] 3 PO 4 . That is, tur- 
 quois is referred to the orthophosphoric acid, H 3 PO 4 , in which hydrogen 
 has been almost entirely replaced by the monovalent groups Al(OH) 2 ,Fe- 
 (OH) 2 , and Cu.OH. When heated in a closed tube it yields water and at 
 first turns black, afterward brown. Infusible. Colors the flame green. 
 Soluble in acids. 
 
 Turquois is a secondary mineral and is often associated with limonite. 
 It occurs in trachyte near Nischapur, Khodrassan, Persia ; Los Cerillos, also 
 in the Burro Mountains, Gaston County, N. M. ; Turquois Mt., Arizona. 
 
 Used for gem purposes. 
 
 CHILDRENITK, ( Fe,Mn ) Al ( OH ) 2 PO 4 . H 2 O. 
 
 Orthorhombic, bipyramidal class, a : b : 0.7776 : i : 0.5254. Small, tab- 
 ular or bipyramidal crystals; often in druses or crusts. 
 
 Imperfect macropinacoidal cleavage. Uneven fracture. Hardness 4.5 to 5. 
 Specific gravity 3.18 to 3.24. Greasy, vitreous luster. Translucent. Yellowish white 
 to brownish black in color. Occurs at Tavistock, Devonshire, and St. Austle, Corn- 
 wall, England; Hebron, Me. 
 
1 82 DESCRIPTIVE MINERALOGY 
 
 TORBERNITE GROUP 
 
 The minerals of this group are phosphates and arsenates of uranyl. 
 UOo, and the bivalent elements, calcium, barium, and copper. They con- 
 tain eight molecules of water of crystallization. Although they do not all 
 crystallize in the same system, their elements of crystallization are very 
 similar. 
 
 a : b : c 
 
 AUTUNITE, Ca(UO 2 ) 2 (PO 4 ) 2 .8H 2 O. Orthorhqmbic 0.9876 :i '.2.8530 
 URANOSPINITE, Ca(ub 2 ) 2 (AsO 4 ) 2 .8H 2 O. 
 
 Orthorhombic i ( ?) : i : 2.9123 
 
 URANOCIRCITK, Ba(UO 2 ) 2 (PO 4 ) 2 .8H 2 O. ? 
 
 TORBERNITK, Cu(UO 2 ) 2 (PO 4 ) 2 .8H 2 O. Tetragonal i.oooo : i : 2.9382 
 ZKUNERITE, Cu(UO 2 ) 2 (AsO 4 ) i .8H 2 O. Tetragonal i.oooo : i : 2.9123 
 
 These minerals are alteration products of uraninite or pitch-blende, 
 page 142. Uranospinite, uranocircite, and zeunerite are very rare. 
 
 AUTUNITE, Lime Uranite, Ca(UO 2 ) 2 (PO 4 ) 2 .8H 2 O. 
 
 Orthorhombic. Crystals are tabular and quadratic in outline. Also foliated and 
 micaceous. 
 
 Perfect basal cleavage. Hardness i to 2.5. Specific gravity 3 to 3.2. Pearh 
 luster on cleavage surfaces, otherwise subadamantine. Translucent. Lemon to sul- 
 phur yellow in color, resembling orpiment. Pale yellow streak. Brittle. 
 
 Occurs with uraninite at Johanngeorgenstadt and Schneeberg, Saxony ; Limoges. 
 France; Cornwall, England; Middletown and Branchville, Conn.; Mitchell County. 
 N. C. : Black Hill?.. S. Dak. ; Chesterfield, Mass. 
 
 Atitunite is not as common as torbernitc. 
 
 ToKiiERNiTK, Copper Uranite, Cu(UO 2 ) 2 (PO 4 ) : ,.8H 2 O. 
 
 Tetragonal. Crystals possess a quadratic outline, and may be tabular or acute 
 bipyramidal in habit. Also micaceous, foliated, or in crusts. 
 
 Perfect basal cleavage. Hardness 2 to 2.5. Specific gravity 3.5 to 3.6. Vitreous 
 luster, pearly on cleavage surfaces. Translucent. -Green to emerald green in color. 
 Pale green streak. Brittle. 
 
 Contains when fresh twelve molecules of water of crystallization. 
 
 Commonly associated with limonite. Occurs at Johanngeorgenstadt and Schnee- 
 berg, Saxony; Cornwall, England; Limoges, France; Joachims-thai, Bohemia. 
 
IX. SILICATES 
 
 INCLUDING TITANATES, ZIRCONATES, AND 
 
 THORATES 
 
 The silicates are by far the most abundant and important minerals of 
 this division. Many of them pyroxenes, amphiboles, micas, and feldspars 
 are of very great importance as rock minerals. The few titanates, zircon- 
 ates, and thorates, which have thus far been observed in nature, are included 
 here because of the close chemical relationship existing between them and 
 the silicates. For the most part, the composition of all the members of this 
 division is rather complex. 
 
 The orthosilicic acid H 4 SiO 4 may be considered the basis for the deriva- 
 tion of the other silicic acids of the group. By the loss of a molecule of 
 water, it passes over to the mctasilicic add H 2 SiO 3 , and by the loss of water 
 from several molecules, the more complex acids mav be derived. These may 
 be arranged as follows : 
 
 Orthosilicic acid, H 4 SiO 4 . 
 
 Diorthosilicic acid, H Sio(X, (2H 4 SiO 4 - H 2 O). 
 
 Trisilicic acid, H 4 Si-A, (3H 4 SiO 4 4HX>). 
 
 Tetrasilicic acid, H 4 Si 4 O 10 , (4H 4 SiO 4 6H.O). 
 
 Pentasilicic acid, H 4 Si 5 O 12 , ( 5H 4 SiO 4 8H 2 O) . 
 
 Polysilicic acids are those which are still more complex. By eliminating 
 water from two molecules of the metasilicic acid, the important dimetasilicic 
 acid H 2 Si 2 O- may be obtained. 
 
 In many cases it is difficult to interpret a chemical analysis of a sili- 
 cate correctly, because the substance may be considered as a salt of several 
 silicic acids. 
 
 Formerly, silicates were classified according to the ratio existing between 
 the number of oxygen atoms held by the basic and acid elements, thus : 
 
 RATIO 
 
 Unisilicates, 
 
 i 
 
 : i, 2MgO, 
 
 SiOo, 
 
 Olivine. 
 
 Bisilicates, 
 
 i 
 
 : 2. MgO, 
 
 SiO 2 , 
 
 Enstatite. 
 
 Trisilicates, 
 
 i 
 
 . , i KA 
 
 Si "i \ 1 f~~\ 
 
 6SiO 8 , 
 
 Orthoclase. 
 
 
 
 1 A1.,U>. 
 
 
 
 Tetrasilicates, 
 
 i 
 
 1 Li 3 O ; 
 ' 4 ''l A1,O :!5 
 
 SSiO,, 
 
 Petalite. 
 
184 
 
 DESCRIPTIVE MINERALOGY 
 
 Silicates are in general easily distinguished from many of the other min- 
 erals by their hardness, lack of characterizing colors, transparency, non-me- 
 tallic luster, and uncolored streak. They will be considered in the following 
 order given by Groth : 
 
 (1) Basic silicates. 
 
 (2) Orthosilicates. 
 
 (3) Intermediate silicates. 
 
 (4) Metasilicates. 
 
 (5) Polysilicates. 
 
 (6) Zeolites. 
 
 (7) Amorphous silicates containing water. 
 
 STAUROLITE, HFeALSi.O, r! . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.4803 : i : 0.6761. Gen- 
 erally in well developed prismatic crystals, sometimes rather large. Simple 
 crystals usually show a combination of the unit prism ;//, the basal and 
 brachypinacoids c and b, and the macrodome q. Figure 102. Penetration 
 twins according to two laws are very common, (i) The twinning plane is 
 parallel to a face of the brachydome, m = 3/2. The individual crystals in- 
 terpenetrate at an angle of about 90, forming cross- or plus-shaped fains, 
 Figure 103. (2) The modified brachybipyramid (// and 77; =3/2) acts as 
 
 m 
 
 mi 
 
 FIG. 102 FIG. 103 . FIG. 104 
 
 the twinning plane. The crystals intersect at an angle of about 6o\ and 
 such twins are sometimes termed X-shafcd fains, Figure 104. Fresh crys- 
 tals usually possess bright and smooth -faces. 
 
 Distinct brachypinacoidal cleavage. Conchoidal to uneven fracture. 
 Brittle. Hardness 7 to 7.5. Specific gravity 3.4 to 3.8. Vitreous luster, 
 dull when crystals are somewhat altered. Greasy luster on fracture surfaces. 
 Translucent to opaque. Usually reddish brown in color, but may be brown- 
 ish black, yellowish brown, or gray. Colorless streak when fresh. 
 
 P\'('AlO).(Al.OH)(SiC) ( ) 1 ,. Composition varies greatly SiO, from 
 
SILICATES 185 
 
 2 7-9% to 5 l -3%- May contain ferrous iron, magnesium, manganese, and 
 zinc. Nordmarkite is a manganiferous variety from Nordmarken, Sweden. 
 Infusible. Fuses with difficulty with borax or salt of phosphorus. Varieties 
 containing manganese fuse readily to a black magnetic glass. Not attacked 
 by acids, not even cold hydrofluoric acid. 
 
 Occurs generally in metamorphic rocks, especially gneiss, mica schist, 
 and slates. The common associates are cyanite, garnet, tourmaline, and silli- 
 manite. At Mt. Campione in the St. Gotthard district of Switzerland it oc- 
 curs with cyanite in paragonite schist ; also in various places in Tyrol ; 
 Stryia ; Bavaria ; and in Brittany, France. 
 
 Some of the principal localities in the United States are Fannin Co., 
 Ga. ; Cherokee Co., N. C. ; Chesterfield, Mass. ; Franconia, N. H. ; Wind- 
 ham. Me. ; also in New York, Connecticut, and Pennsylvania. 
 
 Clear and transparent crystals are sometimes used for gem purposes. 
 
 DUMORTIERITE, HBAl 8 Si 3 O 20 - 
 
 Orthorhombic, bipyramidal class, a : l> : (- = 0.532 : i : ?. Occurs in thin 
 fibrous or columnar aggregates. The prism angle is 56. Distinct macropinacoidal 
 cleavage. Hardness 7. Specific gravity 3.3. Large specimens are opaque, isolated 
 fibres transparent. Vitreous to silky luster. Deep blue, lavender blue, greenish blue 
 to black in color. Bluish white streak. Strong pleochroism. 
 
 Al(AlO) 7 (BO)H(SiO4) 3 . Infusible, but loses its color and turns white. Re- 
 assumes its blue color when treated with cobalt nitrate solution. Mixed with potas- 
 sium bisulphate and fluorite it imparts momentarily a green color to the flame. This 
 reaction is difficult of execution. 
 
 Occurs disseminated in pegmatite veins. It is commonly associated with feld- 
 spar, quartz, muscovite, and cyanite. It is found at Wolfshau, Silesia; Beaumon, 
 France ; Harlem, N. Y. ; Skamania County, Wash. ; San Diego County, Cal. ; and 
 Clip, Yuma County, Arizona. 
 
 This group embraces the two minerals hemimorphite and clinohedrite 
 with the general formula, 
 
 /0-M-OH 
 1 \0-M-OH, 
 
 in which M indicates zinc and calcium. In hemimorphite only zinc is pres- 
 ent while in clinohedrite both zinc and calcium enter into the composition. 
 Although the minerals do not crystallize in the same systems, their elements 
 of crystallization show some similarity. 
 
1 86 DESCRIPTIVE MINERALOGY 
 
 a : b : c 
 
 HEMIMORPHITE, (Zn.OH),SiO 3 , Orthorhombic, 0.7835 : i : 0.4778 
 
 /?=io3 56'. 
 CLINOHEDRITE, (Zn.OH) (Ca.OH)SiO 3 , 
 
 Monoclinic, 0.6826 : i : 0.3226 
 Both minerals show hemimorphic development. 
 
 HEMIMORPHITE, Calamine, H 2 Zri 2 SiO s . 
 
 Orthorhombic, pryamidal class, a : b : c 0.7835 : i : 0.4778. Us- 
 ually in small, tabular or pyramidal crystals possessing a pronounced hemi- 
 morphic development, Figure 105. Over 45 forms have been observed on 
 hemimorphite. The common forms are the basal, bracliy-, 
 and macropinacoids c, b and a, unit prism g, the modified 
 brachy- and macrodomes m and p (both having the co- 
 efficient m equal to 3), the unit brachy- and macrodomes 
 r and o, and the lower brachypyramid ^ with coefficients 
 n and m equal to 2. On tabular crystals the brachypin- 
 acoid b predominates. Vertical striations are often ob- 
 served on the brachypinacoid. Supplementary twins with 
 the basal pinacoid acting as the twinning plane are some- 
 FIG. 105 times to be noted. Crystals are often arranged in sheaf- 
 
 like groups ; also as druses, especially in cavities. May be fibrous, globular, 
 botryoidal, stalactitic, granular, compact, or earthy. 
 
 Perfect prismatic cleavage. Uneven to conchoidal fracture. Brittle. 
 Hardness 4 to 5. Specific gravity 3.3 to 3.5. Vitreous luster, sometimes ada- 
 mantine. Translucent to transparent. Colorless, white, gray, brown, or 
 blue. Streak white. Strongly pyroelectric. 
 
 (Zn.OH) 2 SiO,. Almost infusible. Fusible with borax to a clear bead, 
 which becomes cloudy on cooling. Yields water when heated in a closed 
 tube. Gelatinizes with acids, even acetic acid. Soluble in concentrated po- 
 tassium hydroxide. Occurs as a pseudomorph after calcite, galena, dolo- 
 mite, fluorite, and pyromorphite. 
 
 It is usually found in limestones associated with sphalerite, smithsonite, 
 galena, and the like. Although it is a common mineral, it is not as abundant 
 as sphalerite. Some important localities are Aachen, Germany ; Raibel and 
 Bleiberg, Carinthia; Silesia; Cumberland and Derbyshire, England; Bo- 
 hemia; Sardinia. 
 
 In the United States it occurs in fine crystalline masses in Sussex 
 County, N. J. ; Phoenixville and Friedensville, Pa. ; Granby, Mo. ; and Pu- 
 laski and Wythe counties, Va. 
 
 Hemimorphite is an important ore of zinc. 
 
SILICATES 
 
 i8 7 
 
 CUNOHEDRITE, (Zn.OH) (Ca.OH)SiO 3 . 
 
 Monoclinic, domatic class, a : b : 0.6826 : i : 0.3226, = 103 56'. Crystals 
 are rather complex and show hemimorphic development. Hardness 5.5. Specific 
 gravity 3.33. Colorless, white, or amethystine. Fuses with intumescence to a white 
 enamel. Easily soluble in hydrochloric acid. Occurs with willemite, phlogopite, gar- 
 net, and axinite in the Tather Mine, near Franklin Furnace, N. J. 
 
 ANDALUS1TE GROUP 
 
 The compound ALSiO 5 is trimorphous, and occurs as the minerals an- 
 dalusite, sillimanite, and cyanite. The first two minerals crystallize in the 
 orthorhombic system, while the third is triclinic. Andalusite and silliman- 
 ite are very closely related in many respects. They are considered salts of 
 orthosilicic acid, whereas cyanite is thought to be derived from metasilicic 
 acid. 
 
 ANDALUSITE, Al,SiO D . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.9856 : I : 0.7020. Oc- 
 curs usually in large, rough, columnar crystals. Often disseminated and, 
 due to superficial alteration, covered with scales of mica or sericite. Figure 
 106 sho\vs the common type of development. The combination consists of 
 the unit prism m, basal pinacoid c, and the unit brachydome d. The prism 
 angle is 89 12', which gives the crystals a tetragonal habit. 
 
 FIG. 106 
 
 FIG. io7a 
 
 FIG. lo/b 
 
 Chiastolitc or Made is a variety occurring in rounded prisms with a 
 regular internal arrangement of carbonaceous impurities as shown in Figures 
 I07a and io7b. 
 
 Distinct prismatic cleavage. Uneven fracture. Brittle. Hardness 7 
 to 7.5, somewhat softer on the surface. Specific gravity 3.1 to 3.2. Usually 
 
1 88 DESCRIPTIVE MINERALOGY 
 
 dull and opaque, rarely with a vitreous luster and transparent. May be 
 greenish, reddish gray, pearl gray, rose red, flesh red, or violet in color. 
 Sometimes strongly pleochoic. White streak. 
 
 Al 2 SiO 5 . The rational formula is often written Al(AlO)SiO 4 . Man- 
 ganandalusite is a variety containing some Mn 2 O 3 . 
 
 Infusible. Turns blue when treated with cobalt nitrate solution. Not 
 acted upon by acids. Alters to cyanite, mica, kaolinite, or dense talcose 
 minerals resembling steatite. Changes to sillimanite when heated to a tem- 
 perature of 1350. 
 
 Occurs essentially in metamorphic rocks. It is commonly found in the 
 contact zones of such igneous rocks as granites, syenites, nepheline syenites, 
 and diorites, being the result of the alteration of clay slates and shales. It 
 is often associated with sillimanite. 
 
 It is found in Andalusia, Spain ; Tyrol ; Braunsdorf, Saxony ; Wunsiedel, 
 Bavaria ; and in transparent crystals in Minas Geraes, Brazil. 
 
 In the United States, Westford, Lancaster, and Sterling, Mass., are im- 
 portant localities ; also Litchfield and Washington, Conn. ; Standish, Me., and 
 elsewhere in the New England States ; to some extent also in Pennsylvania 
 and California. 
 
 Sillimanite, Fibrolite, Al 2 SiO 5 . 
 
 Orthorhombic. a : b : c = 0.970 : I : ?. Usually in long, thin, needle- 
 like crystals ; or in fibrous or columnar masses with a radial structure. 
 Crystals are not distinctly terminated. The prism angle is 69. The prism 
 faces are generally striated vertically and often more or less rounded. 
 
 Perfect macropinacoidal cleavage. Uneven fracture. Hardness 6 to 7. 
 Specific gravity 3.2 to 3.25. Greasy vitreous luster; aggregates somewhat 
 silky. Transparent to translucent. Yellowish gray, grayish white, grayish 
 green, or brown in color. 
 
 Chemical composition and behavior are the same as for andalusite. Mi- 
 croscopic crystals are formed artificially in the manufacture of chinaware. 
 
 Occurs as an accessory constituent of gneisses, quartzites, mica schists, 
 and other metamorphic rocks. It is sometimes associated with andalusite, 
 iolite, zircon, or corundum. Some localities are Bodenmais, Bavaria; Frei- 
 berg, Saxony ; various places in Tyrol ; in secondary deposits in Minas 
 Geraes, Brazil. In the United States sillimanite occurs at Worcester, Mass. ; 
 Norwich and Willimantic, Conn.; Westchester and Monroe counties, N. Y. ; 
 and Chester, Pa. 
 
SI U GATES 189 
 
 CYANITE, Disthene, Kyanite, ALSiO-. 
 
 Triclinic, pinacoidal class, a : b : c = 0.8994 : i : 0.7090, a = 90 
 $ l /2 f , P= 101 2', y= 105 441/2'. Generally in long, broad crystals with- 
 out distinct terminations ; or in coarsely bladed, columnar or fibrous masses. 
 Crystals are sometimes curved and arranged radially. The common forms 
 are the three pinacoids, and the right and left unit hemiprisms. Twins occur 
 according to several laws. Of these laws the one in which the macropinacoid 
 acts as the twinning plane is the most common. Polysynthetic twinning 
 parallel to the basal pinacoid often causes the faces in the prism zone to be 
 striated horizontally. Cyanite is sometimes found in sands and gravels, es- 
 pecially in Russia, India, and Brazil. 
 
 Very perfect macro- and perfect brachypinacoidal cleavages. Brittle. 
 The hardness varies greatly with face and direction. On the macropinacoid, 
 which is usually very large, it is least, 4 to 4.5, parallel to the length of the 
 blades or crystals, and greatest, 6 to 7, in a direction perpendicular to the 
 above. Specific gravity 3.5 to 3.7. Vitreous luster. Transparent to trans- 
 lucent. Generally blue, especially sky blue, in color; also grayish, white, 
 yellow, green, brownish, or colorless. Often multicolored. Rhatzite is a 
 fine fibrous, graish to black variety. 
 
 Al.,SiO-. Chemical composition and behavior similar to that of anda- 
 lusite and sillimanite. Cyanite is, however, more resistive to the action of 
 chemical agents. Hence, Groth considers it a basic metasilicate, (AlO) 2 SiO 3 , 
 while andalusite and sillimanite are interpreted as being basic orthosilicates 
 with the general formula Al(AlO)SiO. t . 
 
 Cyanite is a characteristic mineral of rocks which have been subjected 
 to intense regional metamorphism. Hence, it is found commonly in gneisses 
 and mica schists, especially paragonite schist. It never occurs in eruptive 
 rocks and only rarely in those which are the result of contact metamorphism. 
 The usual associates are garnet, staurolite, corundum, rutile, and lazulite. 
 
 The principal localities are Monte Campione, St. Gothard district, Switz- 
 erland; various places in Tyrol, Sweden, and Brazil. In the United States 
 it is found at Chesterfield, Mass. ; Litchfield and Washington, Conn. ; Thet- 
 ford, Vt. ; Chester and Delaware counties, Pa. ; Buckingham, Va. ; Gaston, 
 Rutherford, and Yancey counties, N. C. 
 
 It is sometimes used as a gem. 
 
DESCRIPTIVE MINERALOGY 
 
 TOPAZ, Al 2 (F,OH) 2 SiO 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.5281 : i : 0.47697. 
 Generally in highly modified, prismatic crystals. Over 140 different forms 
 have been observed. Figures io8a, io8b, and io8c show common combina- 
 tions consisting of the unit and brachyprisms m and I, unit and modified 
 bipyramids u, o, and i, basal pinacoid c, brachypinacoid b, macrodome d, and 
 the modified brachydomes / and y. The prism faces are often striated 
 vertically. Crystals usually have but one end well developed. Sometimes 
 massive, also coarse or fine granular. 
 
 FIG. io8a 
 
 Very perfect basal cleavage, often indicated by well defined cracks. 
 Conchoidal to uneven fracture. Hardness 8. Specific gravity 3.4 to 3.6. 
 Vitreous luster. Usually transparent, but may be translucent or opaque. 
 Colorless, wine yellow, grayish, violet, reddish, or bluish. Some of the col- 
 ored varieties fade on exposure to daylight. The yellow color of many of 
 the topaz crystals from Brazil changes to pale rose-pink when subject to a 
 low, red heat. The biaxial interference figure can be seen in cleavage frag- 
 ments. 
 
 Al 2 (F,OH) 2 SiO 4 . The percentages of fluorine and hydroxyl vary great- 
 ly. Fluorine usually predominates and in the varieties containing a small 
 amount the following approximate proportion generally obtains, F : OH 
 = 3 : i ; the composition of the varieties containing the highest percentage 
 may be expressed approximately by Al 2 F 2 SiO 4 . With an increase of the 
 hydroxyl the a axis increases, while the c axis decreases in length. Often 
 contains considerable amounts of microscopic, liquid and gaseous inclusions, 
 especially liquid carbon dioxide. Infusible and, as indicated above, the colors 
 may change. Treated with cobalt nitrate solution it turns blue. Slightly 
 acted upon by sulphuric acid. Yields hydrofluoric acid when fused with salt 
 
SIUCATES 191 
 
 of phosphorous. Although it resists the action of weathering agencies to a 
 high degree, it sometimes alters to talc and kaolinite. 
 
 Topaz is a characteristic mineral of the pneumatolytic process of for- 
 mation and, hence, is generally associated with cassiterite, tourmaline, quartz, 
 fluorite, apatite, beryl, mica, scheelite, wolframite, and zircon. It occurs in 
 veins, crevices, and pegmatite dikes in highly acid igneous rocks such as gran- 
 ites, rhyolites, gneisses, and mica schists. 
 
 Excellent crystals are found at Schneckenstein, Zinnwald, and Altenberg, 
 Saxony; various places in the Ural Mts., Siberia, Scotland, Ireland, Sweden, 
 Japan, Australia, Mexico, and in Minas Geraes, Brazil. It is often found 
 in the sands and gravels of the streams of Ceylon, Brazil, and the Ural Mts. 
 
 In the United States fine specimens are found in the Thomas Range, 
 Utah, about 40 miles north of Sevier Lake ; also at Nathrop, Colo. ; Ramona 
 district, San Diego County, Cal. ; Trumbull, Conn. ; Huntington and Middle- 
 town, Conn. ; North Chatham, N. H. ; Stoneham, Me. 
 
 Clear and transparent crystals are used as gems. 
 
 DATOLITE GROUP 
 
 This group embraces basic orthosilicates containing calcium, iron, beryl- 
 lium, aluminium, boron, and the elements of the yttrium group. All members 
 of the group crystallize in the monoclinic system. 
 
 a : b : c /3 
 
 Datolite, Ca(B.OH)SiO 4 , 0.6348 : i : 1.2657, 9 9'- 
 
 EUCLASE, Be(Al.OH)SiO 4 , 0.6474 : i : 1.3330, iooi6'. 
 
 HOMILITE, Fe[Ca(B.O)SiO 4 ],, 0.6249 : i : 1.2824, 9O39'. 
 
 Gadolinite, Fe[Be(Y.O)SiO 4 ] 2 , 0.6273 : i : 1.3215, 9 
 
 If the formulas are written as suggested by Bauer, the similarity in 
 comparison is more apparent. 
 
 Datolite, H 2 Ca,B,Si,O 10 , 
 
 EUCLASE, H 2 Be 2 Al 2 Si 2 O 10 , 
 HOMIUTE, FeCa 2 B 2 Si 2 O 10 , 
 Gadolinite, FeBe,Y 2 Si 2 O 10 . 
 
 It will be observed that the formulas given for datolite and euclase in 
 the first table have been doubled. 
 
192 DESCRIPTIVE MINERALOGY 
 
 Datolite, Datholite, Datolithe, Ca(B.OH)SiO 4 . 
 
 Monoclinic, prismatic class, a : b : c = 0.6348 : I : 1.2657, /2 = 9 9'- 
 Usually in excellent, highly modified crystals. Over 100 different forms 
 have been observed. Prismatic and pyramidal, Figures 109 and no, as well 
 as tabular habits are rather common. Botryolite is a compact, fine fibrous 
 variety with globular or botryoidal surfaces. In the Lake Superior copper 
 district it occurs in compact, dull, granular masses, resembling wedgewood 
 ware or unglazed porcelain. 
 
 No cleavage. Conchoidal to uneven fracture. Brittle. White streak. 
 Hardness 5 to 5.5. Specific gravity 2.9 to 3. Vitreous to dull luster, some- 
 times 'resinous on fracture surfaces. Transparent to translucent, rarely 
 opaque. Colorless, white, greenish, yellowish, various shades of red, violet, 
 and brown. 
 
 Ca(B.OH)SiO 4 . Crystals are usually very pure. Colors the flame 
 green and fuses with intumescence to a clear glass. Yields water in a closed 
 tube. Gelatinizes when treated with hydrochloric acid. 
 
 Datolite is a secondary mineral and its occurrences are very similar to 
 those of the zeolites. It is generally found in cracks and cavities in basic 
 igneous rocks, such as diorite, diabase, melaphyre, gabbro, and serpentine. 
 The common associates are calcite, prehnite, native copper, magnetite, and 
 the zeolites. 
 
 Some localities are the Kilpatrick Hills, Scotland ; Arendal and Uto, 
 Norway ; Andreasberg, Hartz Mts., Tyrol ; Bergen Hill, N. J. ; Westfield and 
 Deerfield, Mass. ; Hartford, Conn. ; and in the Lake Superior copper district 
 in excellent crystals and porcelain-like masses. 
 
 Recently the massive, compact varieties of the copper district of North- 
 ern Michigan have been cut and polished for gem purposes. 
 
 EUCLASE, Be(Al.OH)SiO 4 . 
 
 Monoclinic. prismatic class, a : b : c = 0.6474 ' J : I -333> J 8 = I0 J 6'. Occurs 
 only in prismatic crystals, generally very complex. The prism faces are striated ver- 
 tically. Excellent clinopinacoidal cleavage. Conchoidal fracture. High vitreous lus- 
 tre. Transparent, rarely translucent. Hardness 7 to 8. Specific gravity 3.05 to 3.11. 
 
SIUCATES 193 
 
 Colorless to blue or green. Barely fuses before the blowpipe. Not acted upon by 
 acids. Occurs associated with chrysoberyl and topaz in the gold-bearing sands of the 
 Sanarka river, Ural Mts. ; and in quartz veins in chlorite schists at Boa Vista, Minas 
 Geraes, Brazil. 
 
 Euclase is cut for gems. 
 
 HOMILITE, Fe[Ca( 3.0)8104],. 
 
 Monoclinic, prismatic class, a : b : c = 0.6249 : i : 1.2824, 18 = 90 39'. Crystals 
 usually possess an octahedral habit. No distinct cleavage. Subconchoidal fracture. 
 Brownish black to black in color. Grayish white streak. Generally opaque, in thin 
 fragments translucent. Greasy vitreous luster. Hardness 5 to 5.5. Specific gravity 
 3.28 to 3.4. Fuses to a black glass. Easily and completely soluble in hydrochloric 
 acid. Occurs disseminated in the nepheline syenite of the Island of Stoko and vicinity, 
 Norway. 
 
 Gadolinite, Fe[Be(Y.O)SiOJ,. 
 
 Monoclinic, prismatic class, a : b : = 0.6273 : i : 1.3215, ft = ^o 
 33/^>'. Crystals, which are very rare, are usually rough and of a prismatic 
 habit. 7 he common forms are the unit prism, basal pinacoid, unit clino- 
 dome, and the positive and negative hemipyramids. Occurs more commonly 
 in masses. 
 
 No cleavage. Conchoidal fracture. Pitch to greenish black or brown 
 in color. Opaque, thin fragments are translucent and appear green to brown 
 in transmitted light. Greenish gray streak. Hardness 6 to 7. Specific grav- 
 ity 4 to 4.5. Vitreous to greasy luster. 
 
 Fe[Be(Y.O)SiO 4 ] 2 . Contains as high as 16% of the oxide of cerium 
 and from 23 to 51% of the oxides of the yttrium group; also small amounts 
 of other elements not indicated in the formula. Analyses are rather complex. 
 When heated, it glows without fusing. Gelatinizes with hydrochloric acid. 
 
 Gadolinite is not a common mineral. It has been found at Hittero, 
 Norway ; Falun and Ytterby, Sweden ; and in large nodular masses and crys- 
 tals, associated with allanite, fergusonite, fluorite, molybdenite, and other 
 rare minerals, in a pegmatite vein at Barringer Hill, Llano County, Texas. 
 
 It is a source of the oxides of some of the rare earths. 
 
 TOURMALINE, M' AL(B.OH) 2 Si 4 O 19 . 
 
 Hexagonal, ditrigonal pyramidal class, a : c=i : 0.4474. Often in 
 large prismatic crystals with vertical striations. Short, thick crystals are 
 also common. Hemimorphic development is usually very pronounced. The 
 
194 
 
 DESCRIPTIVE MINERALOGY 
 
 blunter pole is the analogue, the more acute the antilogue. Figures in and 
 112 show a characteristic combination consisting of the negative trigonal 
 prism I, the hexagonal prism of the second order s, the unit trigonal prya- 
 mids p and P, the upper negative trigonal pyramid o, the modified pos- 
 itive upper ditrigonal pyramid t, and the lower positive modified trigonal 
 pyramid n. On account of the occurrence of the trigonal prism, cross-sec- 
 
 \ 
 
 FIG. in FIG. 112 FIG. 113 
 
 tions of tourmaline generally show a spherical triangular outline. This is 
 shown by figure 113. When the lateral development of the crystal has been 
 ideal the cross-section is equilateral, otherwise the spherical triangle may be 
 isosceles or scalene. Twins are very rare. Occurs also in compact, dissem- 
 inated masses, and in radially divergent aggregates the so-called tourma- 
 line suns. Also in loose crystals in secondary deposits. 
 
 No well defined cleavage. Subconchoidal to uneven fracture. Hard- 
 ness 7 to 7.5. Specific gravity 2.94 to 3.24. Vitreous luster, on fracture 
 surfaces somewhat resinous. Usually pitch black, brown, gray, yellow, green, 
 or red in color. More rarely colorless or white. Zonal distribution of color 
 is often very marked. Transparent to opaque. The pitch black varieties are 
 commonly opaque. Strong negative double refraction. r = 1 .643, e r = 1.623. 
 Strongly dichroic. The absorption of the ordinary ray vibrating perpendicular 
 to the vertical axis is much stronger than that of the extraordinary. Often 
 used in the production of polarized light, for example, in tourmaline tongs. 
 The red, green, or brown varieties are more strongly pyro-electric than the 
 black. 
 
 M't,Al 3 (B.OH) 2 Si 4 O 10 . On account of the very complex chemical com- 
 position, many formulas have been assigned to tourmaline. The formula 
 given above is the one suggested by Penfield and Foote. M indicates the 
 alkali metals sodium, potassium, or lithium, magnesium, or iron. The 
 hydroxyl is often replaced by fluorine. Some tourmalines contain small 
 amounts of titanium or chromium. Four varieties, based upon the chemical 
 composition, may be differentiated, namely, (i) Lithium, (2) Iron, (3) Iron- 
 magnesium, and (4) Magnesium tourmalines. Powdered tourmaline, when 
 
SIUCATES 195 
 
 fused with a paste of potassium bisulphate and fluorite, imparts a momentary 
 green color to the flame indicating the presence of boric acid. Fusibility 
 varies greatly. Insoluble in acids. Gelatinizes after fusion or strong igni- 
 tion. Although rather resistive to weathering agencies, it frequently alters 
 to muscovite, biotite, or chlorite. 
 
 According to color and occurrences several varieties are commonly dif- 
 ferentiated. 
 
 (1) Ordinary. Crystals of various colors. Black is the most common 
 variety. 
 
 (2) Rnbcllitc. Red, rose red, and ruby red varieties. Sometimes 
 often called siberitc. 
 
 (3) Indicolitc or Indigolite. Bluish varieties. 
 
 (4) Achroite. Colorless variety from the Island of Elba. 
 
 (5) Schorl. This includes the common black varieties. 
 Tourmaline is a very characteristic mineral of pegmatite dikes associated 
 
 with intrusions of granite. It is the result of the pneumatolytic process of 
 formation, as is evidenced by the presence of fluorine, hydroxyl, and boron. 
 It is rather common in contact metamorphic rocks, such as gneisses, schists, 
 and crystalline limestones and dolomites. Its occurrence is usually indicative 
 of nearness to the contact. Some of the common associates are quartz, cas- 
 siterite, fluorite, apatite, topaz, and various copper and iron ores. 
 
 Occurs in Cornwall, England ; Arendal, Norway ; Ural Mts. ; Island of 
 Elba ; Minas Geraes, Brazil ; Burma. 
 
 Excellent crystals are found at Paris, Auburn, and Rumford, Me. ; Had- 
 dam Neck, Conn. ; Goshen, Mass. ; Gouverneur, DeKalb, and Pierrepont, 
 N. Y. ; Grafton, N. H. ; San Diego County, Cal. ; also in various places in 
 Canada. 
 
 Stones of good colors are cut for gem purposes. On account of its 
 strong absorption it is used in making tourmaline tongs, a simple instrument 
 for producing polarized light. 
 
 LAWSONITE GROUP 
 
 The two minerals, lawsonite and carpholite, are placed here. Although 
 their chemical composition is very similar, their crystallographic properties 
 vary greatly. 
 
 a : b : c 
 
 Lawsonite, Ca(A1.2OH) 2 (SiO 3 ) 2 . Orthorhombic, 0.6652 : I : 0.7385 
 CARPHOUTU, Mn(A1.2OH) 2 (SiO 3 ) 2 . Monoclinic, ? 
 
 Lawsonite is sometimes considered an orthosilicate. 
 
196 DESCRIPTIVE MINERALOGY 
 
 Lawsonite, Ca(Al.aOH) 2 (SiO 8 ) 2 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.6652 : i : 0.7385. 
 Thick, tabular and prismatic crystals. Prism angle is 112 44'. Six sided 
 cross section. Perfect basal and brachypinacoidal cleavages. Hardness 8 
 to 8.5. Specific gravity 3.1. Vitreous to greasy luster. Colorless, pale or 
 grayish blue. Often multi-colored. Fuses easily to a black enamel, which 
 gelatinizes readily with hydrochloric acid. 
 
 Occurs in crystals in schists in Martin County, Cal. ; also on the Island 
 of Corsica and in New Caledonia. 
 
 CARPHOUTE, Mn ( A1.2OH ) 2 ( SiO 3 ) 2 . 
 
 Monoclinic. Occurs only in fine hair-like crystals, often in radial aggregates. 
 Vitreous to silky luster. Translucent. Straw, wax, or greenish yellow in color. Color- 
 less streak. Hardness 5 to 5.5. Specific gravity 2.9. Fuses with intumescence. Only 
 slightly acted upon by acids. Occurs with blue fluorite in the tin ore deposits of 
 Schlaggenwald, Bohemia; also at Wippia, Hartz Mts. 
 
 Ilvaite, Lievrite, CaFe 2 (Fe.OH)(SiO 4 ) 2 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.6665 : l ' 0.4427. 
 Columnar to needle-like crystals with vertical striations on the prism faces. 
 The prism angle is 112 38 . Occurs also in compact masses with a radial 
 fibrous structure, and in granular aggregates. 
 
 Distinct basal and brachypinacoidal cleavages. Uneven to subconchoidal 
 fracture. Vitreous luster when fresh, otherwise usualy submetallic. Opaque 
 to slightly translucent. Hardness 5 to 6. Specific gravity 3.9 to 4.1. Black 
 greenish, or brownish in color and streak. The surface is often covered 
 with an ocher-yellow alteration product. 
 
 CaFe 2 (Fe.OH) (SiO 4 ).,. Manganese may replace some of the bivalent 
 iron. Fuses easily and yields a magnetic globule. Gelatinizes with hydro- 
 chloric acid. Usualy the result of contact metamorphism. Occurs gener- 
 ally with iron ore deposits, thus, on the Island of Elba ; Nassau, Germany ; 
 Silesia; Cumberland, R. I.; Somerville, Mass.; also in Greenland and Ice- 
 land. 
 
 HUMITE GROUP 
 
 Chemically and crystallographically this is a most interesting group of 
 minerals, there being uniforrn chemical and crystallographic differences be- 
 tween the successive members of the series. Prolectite possesses the simplest 
 chemical composition. The addition of one molecule of Mg 2 SiO 4 gives the 
 composition of chondrodite, the addition of two molecules that of humite, 
 while the addition of three molecules yields the composition of clinohumite. 
 
SILICATES 197 
 
 PROLECTITE, [Hg(F,QH)] a Mg(SiO 4 ), 
 
 Monoclinic, 1.0803 : i : 3X0.6287, 90 
 Chondrodite, [Mg(F,OH)] 2 Mg 3 (SiO 4 ) 2 , 
 
 Monoclinic, 1 . 0863 : I : 5 X o . 6289, 90 
 HUMITE, [Mg(F,OH)] 2 Mg 5 (Si0 4 ) 3 . 
 
 Orthorhombic, 1.0802 : I : 7X0.6291, 
 CUNOHUMITE, [Mg(F,OH)] 2 Mg 7 (SiO 4 ) 4 , 
 
 Monoclinic, 1.0803 : l ' 9X0.6288, 90 
 
 Although all of the members do not crystallize in the monoclinic system, 
 the elements of crystallization show an interesting relationship. While the 
 a and b axes are practically of the same length, it will be observed that the c 
 axis increases uniformly and in fact in a definite ratio. This ratio, 3:5:7 
 : 9, also holds good for the number of atoms of magnesium in the successive 
 members of the series. The value of the angle /? is in all cases practically 
 90. Only chondrodite is of sufficient importance to warrant a detailed de- 
 scription. 
 
 PROUCCTITE, [Mg(F,OH)] 2 MgSiO 4 . 
 
 Monoclinic, prismatic class. The elements of crystallization, given above, seem 
 to indicate that prolectite is the first member of the humite group. The mineral is 
 extremely rare and has not as yet been analyzed. Has been found in the Ko mine, 
 Nordmarken, Sweden. 
 
 Chondrodite, [Mg(F,OH)] 2 M g: ,(SiO 4 ),, 
 
 Monoclinic, prismatic class, a : b : c= 1.0863 : l ' 3- I 447> j8 = 9O. 
 Occurs in small, highly modified, pseudo-orthorhombic crystals, also in round 
 grains or lumps, and granular aggregates. 
 
 Distinct basal cleavage. Uneven to conchoidal fracture. Vitreous to 
 resinous luster. Translucent to opaque. Brittle. White streak. Brown, 
 light to dark yellow, and hyacinth to garnet red in color. Hardness 6 to 
 6.5. Specific gravity 3.1 to 3.25. 
 
 [Mg(F.OH)] 2 Mg 8 (SiO 4 ) a . Some of the magnesium may be replaced 
 by bivalent iron. Infusible. Reacts for fluorine. 
 
 Chondrodite is a typical contact metamorphic mineral. It occurs com- 
 monly in crystalline limestones and dolomites, associated with spinel, vestt- 
 vianite, magnetite, pyroxene, and phlogopite. Alters to serpentine. Some 
 important localities are Pargas, Finland; Aeker and Gulsjoe, Sweden; Spar- 
 ta, N. J. ; Monroe, and Tilly Foster mine, near Brewster, N. Y. ; also in 
 Burma and on Mt. Vesuvius. 
 
 HUMITE, [Mg(F.OH)] 2 Mg B (SiO 4 ),. 
 
 Orthorhombic.. bipyramidal class. Highly complex crystals, often twinned. Yel- 
 low, reddish, and brownish in color. Vitreous luster. Hardness 6. Specific gravity 
 3.1 to 3.2. Transparent to translucent. Occurs in Sweden; Andalusia, Spain; Mt. 
 Vesuvius ; Tilley Foster mine, N. Y. 
 
198 DESCRIPTIVE MINERALOGY 
 
 CUNOHUMITE, [Mg(F.OH)] 2 Mg 7 (SiO 4 ) 4 . 
 
 Monoclinic, prismatic class. Highly complex crystals. Very similar to and more 
 common than humite. Found on Mt. Vesuvius ; Andalusia, Spain ; Tilley Foster mine, 
 
 N. Y. 
 
 HELVITE GROUP 
 
 The members of this group are orthosilicates containing sulphur, which 
 may be easily liberated as hydrogen sulphide by the action of hydrochloric 
 acid. The two members of the group crystallize in the cubic system. 
 
 HKLVITE, (Mn,Be,Fe) 7 S(SiO 4 ) 3 . Hextetrahedral Class 
 
 DANAUTE, (Fe,Zn,Be,Mn) 7 S(SiO 4 ) 3 . Hextetrahedral Class 
 
 Danalite is sometimes considered a zinciferous variety of helvite. 
 
 HEI,VITE, (Mn,Be ; Fe) 7 S(SiO 4 ) 3 . 
 
 Cubic, hextetrahedral class. Small tetrahedral crystals, oftentimes disseminated. 
 Occurs also in spherical aggregates. 
 
 Indistinct octahedral cleavage. Uneven fracture. Brittle. Hardness 6 to 6.5. 
 Specific gravity 3.1 to 3.3. Resinous to vitreous luster. Translucent. Sulphur, honey, 
 or brownish yellow in color; also siskin green and reddish brown. Colorless streak. 
 Pyroelectric. 
 
 (Mn,Be,Fe)7S(SiOj)3. Somewhat similar in composition to the garnet group of 
 minerals, page 208. Fuses with intumescence to a yellowish brown opaque bead. Yields 
 hydrogen sulphide and gelatinizes when treated with hydrochloric acid. Reacts for 
 manganese. 
 
 Helvite is often associated with iron, zinc, and lead ores. Occurs at Schwarzen- 
 berg and Breitenbrunn, Saxony; Kapnik, Hungary; Ilmen Mts., Russia; Amelia Court 
 House, Amelia County, Va. 
 
 DANALITE, ( Fe,Zn,Be,Mn) 7 S ( SiO 4 ) 3 . 
 
 Cubic, hextetrahedral class. Crystals are apparently holohedral and usually con- 
 sist of a combination of the octahedron and the rhombic dodecahedron. Occurs most- 
 ly massive and disseminated. No distinct cleavage. Subconchoidal to uneven fracture. 
 Brittle. Hardness 5.5 to 6. Specific gravity 3.43. Resinous vitreous luster. Translu- 
 cent. Flesh red to gray in color. Edges fuse easily. Reacts for zinc. Yields hydro- 
 gen sulphide when treated with hydrochloric acid. Occurs in granite at Cape Ann 
 and Gloucester, Mass.; with iron ores at Bartlett, N. H. ; El'Paso County, Colo. 
 
SILICATES 199 
 
 EPIDOTE GROUP 
 
 This group embraces minerals of the following general composition 
 
 Al, = SiO 4 = Al.OH 
 ^ SiO 4 =Ca 
 
 in which a portion of the aluminium may be replaced by iron, manganese, 
 or cerium. The group is dimorphous. 
 
 ORTHORHOMBIC SERIES 
 
 a : b : c 
 Zoisite, CaoAl.,(Al.OH)(SiO 4 ) 3 , Bipyramidal Class 2.9158 : i : 1.7900 
 
 MONOCLINIC SERIES 
 
 a : b : c ft 
 
 CUNOZOISITE, Ca 2 Al 2 ( Al.OH) (SiO 4 ) 3 . 
 
 Prismatic Class 2.8914 : i : 1.8057, 9 8 57 / 
 EPIDOTE, Ca 2 (Al,Fe) 2 (Al.OH) (SiO 4 ) 3 , 
 
 Prismatic Class 2.8914 : i : 1.8057, 9&57' 
 PIEMONTITE, Ca, (Mn,Al) 2 ( Al.OH) (SiO 4 ) 3 . 
 
 Prismatic Class 2.9451 : i : 1.8362, 98 52' 
 Orthite, Ca a (Al,Ce,Fe), (Al.OH) (SiO 4 ) 3 , 
 
 Prismatic Class 2.8473 : l ' I -7^>4, 99 14' 
 
 Although the elements of crystallization given in the tabulation show the 
 close similarity of the members of the group, they are not used in the sub- 
 sequent descriptions of the minerals. The chemical and crystallographic 
 properties of zoisite and epidote are very much alike. In clinozoisite a small 
 amount of aluminium has been replaced by iron, its properties being almost 
 identical with those of epidote, and it will therefore not be described. 
 
 Zoisite, CaJU 2 (Al.OH)(SiO 4 ) 3 . 
 
 Orthorhombic, bipyramidal class, a : b : c=- 0.6196 : i : 0.3429. Pris- 
 matic crystals, often disseminated. Deep vertical striations on the faces of 
 the unit prism, horizontal striations on the brachypinacoid. Crystals are gen- 
 erally bent and without good terminations. Columnar, broad bladed, or fib- 
 rous aggregates are more common than isolated crystals. 
 
 Perfect brachypinacoidal cleavage. Uneven to subconchoidal fracture. 
 Hardness 6 to 6.5. Specific gravity 3.25 to 3.37. Brittle. Vitreous luster, 
 more or less pearly on cleavage surfaces. Commonly ash gray in color, also 
 yellow, greenish gray, brownish, or apple green ; more rarely rose red. Thu- 
 lite is a rose red variety occurring in Tellemarken and at Arendal, Norway, 
 
20O DESCRIPTIVE MINERALOGY 
 
 and at Travesella, Piedmont. Uncolored streak. Transparent to subtrans- 
 lucent. Strongly pleochroic. Zoisite resulting from the alteration of feld- 
 spar is termed saussurite. It is sometimes mixed with actinolite, chlorite, 
 and feldspar. 
 
 Ca 2 Al 2 (Al.OH) (SiO 4 ) ;i . Some ferric oxide may replace A1 2 O 3 . Fuses 
 with intumescence to a transparent bead. Not attacked by acids, but after 
 ignition, gelatinizes with hydrochloric acid. 
 
 Occurs principally in crystalline schists, such as eclogites, amphibolites, 
 glaucophane schists, and metamorphosed gabbros. Zoisite is often the result 
 of metamorphism. The principal localities are Rauris, Salzburg; Saualpe, 
 Carthinia ; Tyrol ; Fichtelgebirge ; Marschendorf , Moravia ; Island of Syra ; 
 the Coast Range, California ; Ducktown, Tenn. ; Chesterfield, Mass. ; and 
 Uniontown, Pa. 
 
 EPIDOTE, Pistacite, Ca 2 (Al,Fe) 2 (Al.OH) (SiO 4 ) 8 . 
 
 Monoclinic, prismatic class, a : b : c= 1.5787 : i : 1.8036, ^ = 64 
 37'. Excellent, highly modified crystals. Over 200 forms have been ob- 
 served. Usually prismatic and deeply striated parallel to the b axis. The 
 
 common forms are the basal and orthopinacoids c 
 and a, hemiorthodome r, unit prism m, and the unit 
 hemipy ramid ' o, figure 114. Polysynthetic twins 
 with the twinning plane parallel to the orthopinacoid 
 are rather common ; more rarely the basal pina- 
 FlG - I: 4 coid acts as twinning plane. Aside from crystals, 
 
 divergent or parallel fibrous and columnar aggregates, and coarse or fine 
 grained masses are common ; sometimes also in spherical or angular grains. 
 Perfect basal and imperfect orthopinacoidal cleavages. Splintery, un- 
 even, or subconchoidal fracture. Brittle. Hardness 6 to 7. Specific grav- 
 ity 3.25 to 3.5. Vitreous to resinous luster. Rarely transparent, usually 
 translucent to opaque. Crystals are generally dark green, bluish green, or 
 blackish green ; aggregates are lighter in color pistachio-green, yellowish 
 green, and more rarely red or colorless. Uncolored to grayish streak. 
 Strongly pleochroic. 
 
 Ca,(Al,Fe) 2 (Al.OH)(SiO 4 ) 3 . The percentages of the oxides of cal- 
 cium, aluminium, iron, and silicon vary considerably as follows, CaO 23 to 
 24%, A1 2 O 3 20 to 30%, Fe 2 O 3 8 to 16%, and SiO, 35 to 37%. As indicated 
 above, clinoscisite is a variety containing little or no iron. Loses water when 
 strongly ignited. Fuses with intumescence to a magnetic slag. After igni- 
 tion gelatinizes with hydrochloric acid. 
 
 Epidote is a very common mineral and occurs in four ways. ( I ) It is 
 a typical metamorphic mineral and is generally associated with garnet, 
 vesuvianite, fassaite, hornblende, hematite, and magnetite. Sometimes it 
 
SIUCATES 201 
 
 occurs very extensively, forming epidote rocks and schists. (2) It is also 
 a common decomposition product of minerals and igneous rocks containing 
 a considerable amount of the oxides of aluminium and calcium, such as 
 feldspar, hornblende, scapolite, pyroxenes, biotite, and the like. (3) Epi- 
 dote is often found as sandy grains in secondary deposits. (4) As a pseu- 
 domorph after scapolite, garnet, augite, and hornblende. 
 
 Beautiful crystals are found in many localities, some of the more im- 
 portant of which are the following: Zillerthal, Fassathal, and Untersulz- 
 bachthal, Tyrol ; Travesella, Piedmont ; Island of Elba ; Dauphine, France ; 
 Arendal, Norway ; Ural Mts. ; also various places in New Hampshire, New 
 York, Massachusetts, Connecticut, New Jersey, Colorado, and Virginia. It 
 is a very common associate of native copper in the Lake Superior copper 
 district. 
 
 Clear, transparent, dark green varieties are sometimes used for gem 
 purposes. 
 
 Manganiferous Epidote, Ca 2 (Mn,Al) 2 (Al.OH) (SiO 4 ),. 
 
 Monoclinic, prismatic class, a : b : c= 1.61 : I : 1.833, P = 11 5 2l ' 
 Crystallographically very similar to epidote. Commonly in crystalline, col- 
 umnar and radial aggregates, more or less indistinct. Perfect basal cleav- 
 age. Hardness 6.5. Specific gravity 3.4. Vitreous luster, especially good 
 on the basal pinacoid. Transparent only in thin sections or fragments. Red- 
 dish brown or black in color. Cherry red streak. Strongly pleochroic. 
 
 May be considered a manganiferous variety of epidote, containing from 
 6 to 19% of MnO. After ignition gelatinizes with hydrochloric acid. 
 
 Occurs at St. Marcel, Piedmont, Italy ; Isle de Groix, Brittany ; Japan ; 
 England ; South Mountain, Pa. 
 
 Orthite, Allanite, Ca 2 (Al,Ce,Re) 2 (Al.OH)(SiO 4 ) 3 . 
 
 Monoclinic, prismatic class, a : b : c= 1.5507 : i : 1.7684, (3= 115 
 i'. Crystals, which are not very common, are either tabular parallel to the 
 orthopinacoid or long prismatic parallel to the b axis. Usually in massive, 
 granular, or bladed aggregates ; also as disseminated grains. 
 
 Distinct basal and orthopinacoidal cleavages, rarely observed. Uneven 
 to conchoidal fracture. Hardness 5.5 to 6. Specific gravity 3 to 4. Greasy,. 
 submetallic luster. Opaque, translucent in thin splinters. Pitch black in 
 color, sometimes brownish or grayish. The black varieties are often coated 
 with a rusty alteration crust. Greenish gray or brown streak. 
 
 Ca,(Al,Ce,Fe),(Al.OH)(SiO 4 ).,. The composition varies greatly. 
 More or less decomposed varieties also contain didymium, lanthanum, yttri- 
 um, magnesium, and water. Those with much water contain less CaO. The 
 amount of Ce.,O : ; varies between i and 28 per cent. Fuses readily with in- 
 tumescence to a black magnetic glass. Gelatinizes with hydrochloric acid, 
 not, however, if previously ignited. 
 
 Orthite occurs in small quantities in all kinds of igneous rocks, especially 
 in granites and pegmatites ; also in gneiss, mica schist, and amphibolite. 
 Sometimes also in crystalline limestone. 
 
2O2 
 
 DESCRIPTIVE MINERALOGY 
 
 CERITE, H (i (Ca,Fe) 2 Ce 6 Si c O 2 
 
 i : 0.8127. Crystals are 
 
 Orthorhombic, bipyramidal class, a : b : c = 
 rare, prismatic. Usually compact and granular. 
 
 Brittle. Splintery fracture. Hardness 5.5. Specific gravity 4.95. Clove-brown, 
 reddish gray to cherry red in color. Translucent to opaque. Grayish white streak. 
 
 Ho(Ca,Fe)2Ce c SioO 2 o. Infusible. Decomposed by hydrochloric acid. Hisinger 
 and Berzelius discovered cerium in this mineral in 1803. 
 
 Occurs in gneiss, associated with bictite, hornblende, chalcocite, orthite, and bis- 
 muthinite in the Bastnaes mine, Ridclaryttan, Sweden. 
 
 FIG. 115 
 
 VESUVIANITE, Idocrase, CaJAl(OH,F)] Al 2 (SiO 4 ) B . 
 
 Tetragonal, ditetragonal bipyramidal class, a : b : c=i : 0.5372. 
 Crystals are generally short and prismatic, rarely pyramidal or acicular. A 
 usual combination consists of the unit prism m predominating, the prism of 
 the second order a, the corresponding bipyramids o and p, and the basal pin- 
 acoid c, figure 115. Over 60 forms have been observed. 
 No twin crystals have been recorded. Occurs also 
 compact and granular, in aggregates with parallel and 
 divergent striations, also in cryptocrystalline masses. 
 Imperfect basal and prismatic cleavages. Uneven 
 and subconchoidal fractures. Hardness 6.5. Specific 
 gravity 3.34 to 3.45. Vitreous luster, greasy on frac- 
 ture surfaces. Occurs in many shades of yellow, 
 green, and brown ; sometimes almost black ; rarely blue. 
 Sometimes transparent, usually translucent. Some- 
 what pleochroic. 
 
 Ca 6 [Al(OH,F)]Al 2 (SiO 4 ) 5 . The composition is very complex and 
 varies somewhat. Titanium may replace the silicon, boron the aluminium, and 
 ferric oxide the aluminium oxide, and calcium may be replaced by varying 
 amounts of magnesium, iron, manganese, sodium, potassium, or lithium. 
 Fuses with intumescence to a greenish or brownish glass. After ignition, 
 it decomposes easily with acids. 
 
 Vesuvianite is a mineral typical of contact metamorphism. It is found 
 commonly in crystalline limestones, associated with garnet, pyroxene, tour- 
 maline, chondrodite, wollastonite, epidote, and the like. It may also occur 
 in gneiss and other crystalline schists. Some of the more important locali- 
 ties are : Monzoni, Fassathal, Tyrol ; Ala Valley, Piedmont ; Eger, Hun- 
 gary ; Morelos, Mexico ; Warren, N. H. ; Newton, N. J. ; Amity, N, Y. ; 
 Rumford, Me. ; various places in Canada. 
 
 Clear and transparent, brown and green varieties are used for gem 
 purposes. 
 
SILICATES 
 
 203 
 
 OLIVINE-WILLEMITE GROUPS 
 
 The members of these groups are normal orthosilicates and conform to 
 the general formula M^SiO^. M may be magnesium, iron, manganese, 
 zinc, or beryllium. The olivine group crystallizes in the orthorhombic sys- 
 tem, the members of the willemite group, with the exception of trimerite, be- 
 long to the hexagonal system. 
 
 OLIVINE GROUP 
 
 (ORTHORHOMBIC SYSTEM} 
 
 ;, CaMgSiO 4 . 
 GLAUCOCHROITE, CaMnSiO 4 . 
 
 FORSTERITE, Mg.,SiO 4 . 
 
 OLIVINE, (Mg,Fe) 2 SiO 4 . 
 HORTONOLITE.. (Fe,Mg,Mn) 2 SiO 4 . 
 FAYAUTE, Fe.,SiO 4 . 
 KNEBEUTE, (Mn,Fe) 2 SiO 4 . 
 TEPHROITE, Mn,SiO 4 . 
 
 Bipyramidal Class o 
 Bipyramidal Class o 
 Bipyramidal Class o 
 Bipyramidal Class o 
 Bipyramidal Class o 
 Bipyramidal Class o 
 Bipyramidal Class o 
 Bipyramidal Class o 
 
 a 
 
 b 
 
 c 
 
 4337 
 
 i 
 
 0-5757 
 
 4400 
 
 i 
 
 o . 5660 
 
 4666 
 
 i 
 
 0.5868 
 
 4657 
 
 i 
 
 0.5865 
 
 4660 
 
 i 
 
 0.5800 
 
 4580 
 
 i 
 
 0.5793 
 
 4670 
 
 i 
 
 ? 
 
 4621 
 
 i 
 
 0.5914 
 
 WILLEMITE GROUP 
 
 (HEXAGONAL SYSTEM) 
 
 TRIMERITE, MnBeSiO 4 
 Phenacite, Be,SiO 4 . 
 Willemite, Zn,SiO 4 . 
 
 Triclinic (Pseudo-hexagonal) 
 Trigonal Rhombohedral Class 
 Trigonal Rhombohedral Class 
 
 a : c 
 
 i : 0.7233 
 
 i : 0.6611 
 
 i : 0.6695 
 
 Of the above minerals, olivine and willemite are by far the most impor- 
 
 tant. 
 
 MONTICELUTE, CaMgSiO t . 
 
 Orthorhombic, bipyramidal class, a : b : f 0.4337 : i : 0.5757. Occurs in 
 small crystals, also in grains and masses. Colorless, white, and yellowish white. 
 Transparent to opaque. No cleavage. Hardness 5 to 6. Specific gravity 3.12 to 3.28. 
 Fuses with difficulty. Soluble in hydrochloric acid, gelatinizes on evaporation. Alters 
 to serpentine or fassite, a variety of augite. Occurs in limestone, the result of contact 
 metamorphism. Thus, on Mt. Somma, Vesuvius; Monzoni district, Tyrol; Magnet 
 Cove, Arkansas. 
 
 GLAUCOCHROITE, CaMnSiO-i, is a rare bluish green mineral occurring with garnet 
 and axinite in the Franklin Furnace district, N. J. 
 
204 
 
 DESCRIPTIVE MINERALOGY 
 
 , Mg 2 SiO 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.4666 : i : 0.5868. Small crystals, 
 often highly complex. Sometimes as irregular, disseminated grains. Brachypinacoidal 
 cleavage. Hardness 6 to 7. Specific gravity 3.19 to 3.33. Transparent to translucent. 
 Colorless, white, gray, yellowish, or greenish. May alter to serpentine. Sometimes 
 contains as much as 5% of Fe 2 O 3 . 
 
 Occurs associated with spinel, augite, and serpentine. It is the result of contact 
 metamorphism on limestone or dolomite. Has been found in the Ural Mts. ; Snarum, 
 Norway; Bolton, Mass. 
 
 OLIVINE, Chrysolite, Peridot, (Mg,Fe),SiO 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.4657 : i : 0.5865. 
 Crystals are prismatic or thick tabular. Not very common. They are 
 usually comparatively simple. A usual combination consists of the unit and 
 brachyprisms in and s, unit bipyramid o, brachy- and 
 macro-domes d and q, and the brachypinacoid b, figure 
 116. Such crystals are somewhat chisel-like in devel- 
 opment. There are three twinning laws, ( i ) unit 
 brachyprisms m and s, unit bipyramid o, brachy- and 
 and (3) brachyprism (2a : b : coc). Occurs also in 
 lose, ^rounded, and disseminated grains and granular 
 aggregates. 
 
 Distinct brachy-, and rather poor macropinacoidal 
 cleavages. Brittle. Hardness 6.5 to 7. Specific gravity 
 3.2 to 3.6, the varieties containing much iron approach 
 4. Vitreous luster, greasy on fracture surfaces. Trans- 
 parent to translucent. Various shades of green, usually olive green, yellow- 
 ish, brown, reddish, grayish, or colorless. Uncolored or slightly yellowish 
 streak. 
 
 (Mg,Fe) 2 SiO 4 . The composition varies greatly. According to Nau- 
 mann-Ziikel olivine may be considered an isomorphous mixture of forster- 
 ite and fayalite, thus, (Mg 2 SiO 4 )-|- Fe 2 SiO 4 . Titanium may replace some 
 of the silicon. Nickel and calcium may also be present in small amounts. 
 The ferruginous varieties are fusible with difficulty, the others infusible. 
 Easily decomposed by acids, even acetic acid, forming gelatinous silica. 
 Olivine weathers easily forming serpentine, limonite, hematite, magnesite, 
 opal, and garnierite. 
 
 Olivine is an essential constituent of many basic igneous rocks. The 
 associates are augite, hypersthene, spinel, plagioclase, feldspar, chromite, 
 pyrope, and magnetite. It is also found in crystalline limestone, the result of 
 metamorphism. The amphiboles, pyroxenes, and talc are typical associates 
 of such occurrences. 
 
SILICATES 205 
 
 Occurs on Mt. Vesuvius; Eifel, Auvergne; Norway; Sweden; Thet- 
 ford, Vt. ; Webster, N. C. ; White Mountains, N. H. ; Lancaster County, Pa. ; 
 New Mexico ; Arizona ; Canada ; Brazil. Has been found in meteorites. 
 
 Transparent varieties are often used for gem purposes. 
 
 HORTONOLITE, (Fe,Mg,Mn) 2 SiCXi, yellowish green, or greenish or brownish black 
 crystals and masses. Hardness 6 to 7. Specific gravity 3.91. Vitreous luster. Asso- 
 ciated with magnetite and calcite, it occurs in the O'Niel mine, Orange county, N. Y. 
 
 ;, Fe 2 SiO 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.458 : i : 0.5793. Crystals are 
 generally tabular and when fresh possess a vitreous luster and a wine-yellow or olive- 
 green color; when altered, the color is reddish with a metallic luster. If much mag- 
 netite is present the color may be black. Hardness 6 to 7. Specific gravity about 4. 
 Usually contains manganese and magnesium. It is found on the Island of Fayal, 
 Azores ; Yellowstone Park ; Rockport, Mass. 
 
 KNEBEUTE, (Mn,Fe):SiO,, occurs in broad columnar aggregates or cleavage 
 masses. Brachypinacoidal and prismatic cleavages. Greasy vitreous luster. Hard- 
 ness 6 to 7. Specific gravity 3.93 to 4.17. Translucent. Grayish to black in color. In- 
 fusible. Ocurs in the magnetite deposits of Dannemora, Sweden. 
 
 TEPHROITE, Mn,SiO 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.4621 : I : 0.5914. Crystals are 
 very rare. Usually in crystalline masses with cleavages in three perpendicular directions. 
 Conchoidal to splintery fracture. Vitreous luster, greasy on fracture surfaces. Trans- 
 lucent to transparent. Gray, brown, reddish, or rose-red in color. Hardness about 6. 
 Specific gravity 3.95 to 4.12. Fuses with difficulty. Decomposed by hydrochloric acid. 
 
 A variety of tephorite from Sterling Hill, N. J., containing zinc, is called roep- 
 perite. 
 
 Occurs with zincite, willemite, and franklinite at Franklin Furnace and Sparta, 
 Sussex County, N. J. ; Pajsberg and Langban, Sweden. 
 
 TRIMEKITE, MnBeSiO.j, 
 
 Triclinic, but on account of twinning, pseudo-hexagonal in development. Angles 
 are very similar to those of phenacite. Crystals are usually thick tabular and pris- 
 matic. Distinct basal cleavage. Brittle. Hardness 6 to 7. Specific gravity 3.48. Vit- 
 reous luster. Transparent to translucent. Salmon pink to nearly colorless. Rare. 
 Occurs with calcite in the Harstig mine, Wermland, Sweden. 
 
 Phenacite, Be,SiO 4 . 
 
 Hexagonal, trigonal rhombohedral class, a : c=i : 0.6611. Crystals 
 may be rhombohedral, prismatic, pyramidal, or lenticular in habit. Often 
 highly modified, showing rhombohedrons of the third order. Supplementary 
 twins are common. 
 
206 DESCRIPTIVE MINERALOGY 
 
 Vitreous luster. Transparent to translucent. Indistinct cleavage paral- 
 lel to the prism of the second order. Conchoidal fracture. Hardness 7 to 8. 
 Specific gravity 2.97 to 3. Colorless, yellowish white, wine yellow, or pale 
 rose red. 
 
 Be 2 SiO 4 . Infusible and not attacked by acids. With borax, the pow- 
 dered mineral fuses quite readily to a clear glass. 
 
 Occurs in pegmatites and some metamorphic rocks. It is commonly 
 associated with emerald, chrysoberyl, apatite, quartz, beryl, amazonstone, 
 and topaz. Very similar to quartz and topaz in appearance. 
 
 Phenacite is found in the Ural Mountains ; Southern Norway ; Brazil ; 
 Durango, Mexico ; Stoneham, Me. ; Pike's Peak, Topaz Butte, and Mount 
 Antero, Colo. 
 
 Some varieties are used for gem purposes. 
 
 Willemite, Zn 2 SiO 4 . 
 
 Hexagonal, trigonal rhombohedral class, a : c == i 10.6695. Crystals 
 are usually very small, although those containing manganese may be of con- 
 siderable size. Long slender or thick prismatic habits are usual. Occurs 
 also in compact, granular masses and in disseminated grains. 
 
 Distinct basal cleavage. Subconchoidal to uneven fracture. Hardness 
 5 to 6. Specific gravity 3.89 to 4.29. Greasy vitreous luster. Transparent 
 to opaque. Colorless, yellowish, brown, reddish, green, yellowish green ; 
 rarely, blue or black. Uncolored streak. 
 
 Zn 2 SiO 4 . Manganese and iron may replace some of the zinc. Troostite 
 is a manganiferous variety from the Franklin Furnace district, N. J. Fuses 
 with difficulty. Reacts for zinc, often also for manganese. Gelatinizes with 
 hydrochloric acid. Sometimes occurs pseudomorphous after calamine. 
 
 The usual associates are franklinitc, zincite, rhodonite, and calcite. 
 The most important locality is Franklin Furnace and vicinity, Sussex Coun- 
 ty, N. J., where it occurs in large quantities. It is found also at Altenberg, 
 near Aachen, Germany ; Musartut, Greenland ; Merritt Mine, Socorro Coun- 
 ty, N. M. 
 
 It is an important ore of zinc. 
 
 DANBURITE GROUP 
 
 This group contains orthosilicates of the following general composition : 
 R"'=(SiO4)-R" (SiO4)=R"' 
 
 The bivalent metal is calcium, while the trivalent element is either boron 01 
 aluminium. They crystallize in the orthorhombic system. 
 
 a : b : c 
 
 Danburite, CaB,(SiO 4 ) 2 . Bipyramidal Class 0.5445 : i : 0.4808 
 
 BARSOWITE, CaAl 2 (SiO 4 ) 2 . Bipyramidal Class ? 
 
 These minerals are not very common. 
 
SILICATES 207 
 
 Danburite, CaB 2 (SiOJ 2 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.5445 : I : 0.4808. 
 Crystals are usually prismatic in habit, resembling topaz. The development 
 varies greatly with the locality. Sometimes rather complex. Over 35 forms 
 have been observed. Occurs also in indistinct crystals and disseminated 
 masses. 
 
 Indistinct basal cleavage. Uneven to conchoidal fracture. Vitreous lus- 
 ter, at times somewhat greasy. Hardness 7 to 7.5. Specific gravity 2.95 to 
 3.02. When fresh and pure, it is transparent, colorless or pale wine yellow; 
 otherwise yellowish white to honey yellow and dark brown. White streak. 
 Transparent to translucent. 
 
 CaB 2 (SiO 4 ) 2 . Fuses easily to a colorless glass, imparting a green color 
 to the flame. After ignition, it gelatinizes with hydrochloric acid ; otherwise, 
 only slightly acted upon by acid. 
 
 Occurs in dolomite at Danbury, Conn. ; also at Russell, St. Lawrence 
 County, N. Y. 
 
 Danburite is not a common mineral. 
 
 BARSOWITE, CaAl 2 ( SiO.i)2, is, according to Groth, isomorphous with danburite. 
 It is sometimes considered a variety of anorthite. Has not been observed in crystals. 
 
 PSEUDOBROOKITE, Fe 4 (TiO 4 ) a . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.9922 : i : 1.1304. Small, rec- 
 tangular, tabular crystals, resembling brookite. Dark brown to black in color. Hard- 
 ness 6. Specific gravity 4.4 to 4.98. Streak ocher yellow. Submetallic luster. Ap- 
 pears red in transmitted light. Occurs in hypersthene andesite in Transylvania ; in 
 the lavas on Mt. Vesuvius ; also in Norway. 
 
 EULYTITE GROUP 
 
 The compound Bi 4 (SiO 4 ) 3 is dimorphous. It occurs as eulytite, cubic, 
 and agricolite, monoclinic. Both of the minerals are quite rare. 
 
 EULYTITE, Bi 4 (SiO 4 ) 3 . 
 
 Cubic, hextetrahedral class. Crystals are generally trigonal tristetrahedrons ; 
 sometimes in combination with the tetrahedron and cube. Supplementary twins are 
 common ; also spherical groups. 
 
 Adamantine luster, inclining to greasy. Subtranslucent to opaque. Hardness 
 5 to 6. Specific gravity 6.1. No cleavage. Conchoidal fracture. Dark or reddish 
 brown, grayish, straw yellow, colorless ; rarely black. Colorless to yellow gray 
 streak. May resemble sphalerite. 
 
 Bu(SiO 4 ) s . Easily fusible. Readily decomposed by acids. 
 
 Occurs with quartz, bismite, native bismuth, chloanthite, and erythrite at Schnee- 
 berg and Johanngeorgenstadt, Saxony. 
 
208 
 
 DESCRIPTIVE MINERALOGY 
 
 AGRICOUTE is the monoclinic modification of BuSisO^. It occurs in radial, spher- 
 ical aggregates. Wine yellow, oily green, brown, or colorless. Physical properties like 
 those of eulytite. Optically monoclinic. It occurs in very small quantities at Schnee- 
 berg and Johanngeorgenstadt, Saxony. 
 
 GARNET GROUP 
 
 This group embraces minerals which possess the general formula, 
 R // 3 R /// 2 (SiO 4 ) 3 , in which R" may be calcium, magnesium, managanese, or 
 ferrous iron, and R"' aluminium, ferric iron, or chromium. In the titanifer- 
 ous varieties, some of the silicon may be replaced by titanium. 
 
 The members of the group crystallize in the hexoctahedral class of the 
 cubic system. 
 
 GROSSULARITE, Ca 8 Al 2 (SiO 4 )o. 
 
 PYROPE, Mg 3 Al 2 (Si0 4 ) 3 . 
 
 SPESSARTITE, Mn,AL,(SiO 4 ) 3 . 
 
 ALMANDITE, Fe 3 Ai 2 (SiO 4 ) 3 . 
 
 Uvarovite, Ca,Cr (SiO 4 ) 3 . 
 
 ANDRADITE, Ca 3 Fe,(SiO 4 ) 3 . 
 
 Garnets are usually isomorphous mixtures of the above, hence, their 
 chemical composition is rather complex. With the exception of pyrope, they 
 are generally well crystallized. The forms and many of the physical prop- 
 erties of the different varieties are similar and will, therefore, be discussed 
 together. 
 
 tic. 116 
 
 FIG. 117 
 
 FIG. 118 
 
 Cubic, hexoctahedral class. Crystals may be either isolated or dissemin- 
 ated. The rhombic dodecahedron d and tetragonal trisoctahedron i (111 = 2), 
 either alone or in combination, are the most common forms. The hexocta- 
 hedron 5 (w = 3, n = 3/2) is also frequently observed, very rarely, how- 
 
SIUCATES 209 
 
 ever, the octahedron or cube. Thirty-five forms have been noted, including 
 representatives of the various forms of the hexoctahedral class. Some crys- 
 tals are highly modified, figures 116, 117 and 118, but when not well devel- 
 oped, they are more or less spherical in outline. Diagonal striations are 
 sometimes observed on the rhombic dodecahedron. Crystals may show a 
 zonal development. Occurs in compact granular masses, and as sand and 
 gravel. 
 
 Imperfect rhombic dodecahedral cleavage. Conchoidal to uneven frac- 
 ture. Brittle. Hardness 6.5 to 7.5. Specific gravity 3.4 to 4.6, depending 
 upon the composition. The precious varieties are transparent, the others 
 commonly translucent to opaque. Vitreous to resinous luster. White streak. 
 Sometimes colorless, but usually colored, commonly, red, brown, yellow, 
 green, and black. All colors, except blue, are to be observed. Light colored 
 garnets are generally transparent to translucent, dark colored varieties, trans- 
 lucent to opaque. Isotropic, sometimes shows anomalous double refraction, 
 especially those varieties containing calcium. 
 
 R" 3 R"' 2 (SiO 4 ) 3 . Depending upon the chemical composition six prin- 
 cipal varieties may be differentiated. These varieties are, however, not often 
 pure ; most garnets are isomorphous mixtures of them. They generally fuse 
 easily to a brownish or black glass, which is sometimes magnetic. Partially 
 decomposed by acids. With the exception of uvarowite, all varieties gelatin- 
 ize with acids after fusion. Garnets alter readily. Epidote, mica, chlorite, 
 serpentine, hornblende, scapolite, orthoclase, oligoclase, calcite, hematite, and 
 limonite have been observed occurring as pseudomorphs after garnets. 
 
 The garnet is a very common mineral. It occurs (i) in crystalline 
 schists, (2) as a contact metamorphic mineral, (3) as a constituent of many 
 eruptive rocks, (4) with various ore deposits, and (5) in secondary deposits. 
 
 The principal varieties are : 
 
 GROSSULARITE, Calcium-aluminium Garnet, Ca 3 Al,(SiO 4 ) 3 . 
 
 Calcium may be partially replaced by ferrous iron, and aluminium by 
 ferric iron. The specific gravity varies from 3.4 to 3.7. Colorless, white, 
 pale emerald green, various shades of yellow, cinnamon brown, and rose red. 
 Cinnamon-stone, hessonite, or essonite include the cinnamon colored, some 
 yellowish, and yellowish red varieties. Grossularite is characteristic of meta- 
 morphosed impure calcareous rocks, and is thus commonly observed in the 
 contact zone of intrusive igneous rocks and in crystalline schists associated 
 with vesuvianite, wollastonite, diopside, scapolite, and other calcium silicates. 
 Some localities are: Ceylon; Mussa Alp, Piedmont; Island of Elba; More- 
 
210 DESCRIPTIVE MINERALOGY 
 
 los, Mexico; (colorless) Tellemark, Norway; Jordansmuehl, Silesia; Hun- 
 gary; Monzoni district, Tyrol; Spain; Parsonsfield, Phippsburg, and Rum- 
 ford, Me. ; Warren, N. H. 
 
 PYROPE, Magnesium-aluminium Garnet, Mg 3 Al 2 (SiO 4 ) 3 . 
 
 May contain calcium and bivalent iron replacing some of the magnesium. 
 Specific gravity 3.7 to 3.75. Deep red to black in color. Often clear and 
 transparent. Commonly used for gem purposes. The pyrope of South Af- 
 rica is sometimes called cape ruby. Pyrope is found chiefly in basic igneous 
 rocks such as peridotites and the serpentine derived from them. It is rarely 
 observed in well developed crystals. Often surrounded by a shell of other 
 minerals to which the term kclyphite has been given. Pyrope is often con- 
 sidered an important associate of the diamond. It is common in Hungary, 
 especially at Meronitz, Triblitz, and Krems ; Zoblitz and Greifendorf, Sax- 
 ony; Kimberley and other diamondiferous localities in South Africa; Cey- 
 lon ; Syracuse, N. Y. ; Murf reesboro, Pike County, Ark. ; Elliott County, Ky. 
 
 SPESSARTITE, Manganese-aluminium Garnet, Mn 3 Al 2 (SiO 4 ) 3 . 
 
 Manganese and aluminium may be replaced by bivalent and trivalent 
 iron, respectively. Specific gravity 4 to 4.3. Brownish to hyacinth red in 
 color. Spessartite occurs in granite, quartzite, and with topaz in rhyolite. 
 When crystallized, usually as tetragonal trisoctahedrons. The principal lo- 
 calities are Aschaffenburg, Bavaria ; Ilfeld, Hartz Mts. ; Pfitschthal, Tyrol ; 
 St. Marcel, Piedmont ; Island of Elba ; Arendal, Norway ; Haddam, Conn. ; 
 Amelia Court House, Amelia County, Va. ; Nathrop, Colo. 
 
 ALMANDITE, Iron-aluminium Garnet, Carbuncle, Fe 3 Al,(SiO 4 ) 3 . 
 
 May contain magnesium and trivalent iron. Specific gravity 3.9 to 4.2 
 Deep red to brownish red or black in color. The transparent red varieties, 
 known as precious garnets, are used for gem purposes ; translucent varieties 
 are called common garnets. Almandite occurs commonly in gneiss, crystal- 
 line mica, talc, chlorite, and hornblende schists, granulite, granite, eclo- 
 gite, and some andesites. The common associates are staurolite, cyanite, an- 
 dalusite, tourmaline, and cordierite. Often well crystallized, but occurs also 
 as rounded grains and pebbles. Some localities are Falun, Sweden ; various 
 places in Saxony and Silesia ; Zillerthal, Tyrol ; Eppenruth, Bavaria ; Saint 
 Gotthard district, Switzerland ; Ceylon ; Finland ; Brazil ; Windham, Me. ; 
 Hanover, N. H, ; Brookfield and Brimfield, Mass. ; Delaware County, Pa. ; 
 
SILICATES 211 
 
 Chaffee County, Colo. ; at the Spurr Mountain Iron Mine, Lake Superior 
 region, altered to a chloritic decomposition product. In Warren and Essex 
 counties, N. Y., it is mined for abrasive purposes. 
 
 Uvarovite, Calcium-chromium Garnet, Ouvarovite, Uwarowite, Ca 3 Cr 2 
 
 May contain some aluminium. Emerald green in color. Vitreous lus- 
 ter. When somewhat decomposed is dull and dirty green. Hardness 7.5. 
 Specific gravity 3.4 to 3.52. Crystals are usually small. It is not a common 
 variety. Found with chromite in serpentine, also in gneiss and crystalline 
 limestone. Occurs in various places in the Ural Mountains ; Texas, Lancas- 
 ter County, Pa. ; New Idria, Cal. ; Orford, Canada. 
 
 ANDRADITE, Calcium-iron Garnet, Black Garnet, Common Garnet, 
 Ca 3 Fe,(SiO 4 ) 3 . 
 
 The composition varies considerably. May contain manganese, ferrous 
 and ferric iron, titanium, or yttrium. The color may be brownish red, brown, 
 grayish black, black, also various shades of yellow or green. Topazolite is a 
 variety resembling topaz in color and transparency. May be also green. 
 Demantoid is a grass green variety. It is found in serpentine and is used 
 as a gem. Schorlomite and melanite are black varieties containing much 
 titanium. Aplome is a common variety of andradite, usually green, yellow, 
 or brown. These garnets occur in nepheline syenite, phonolite, serpentine, 
 chloritic schists, and crystalline limestones. Some localities are: Kaiser- 
 stuhl, Baden ; Schwarzenberg and Breitenbrunn, Saxony ; Moravicza, Dog- 
 nacska, Dobschau, Hungary ; Pfitschthal and Zillerthal, Tyrol ; Zermatt, 
 Switzerland ; Island of Elba ; Arendal, Norway ; Sala, Langbanshytta and 
 Stalmalms mines, Sweden ; Pitkaeranta, Finland ; various places in the Ural 
 Mountains ; New Haven, Conn. ; Franconia, N. H. ; Franklin, N. J. ; Mag- 
 net Cove, Ark. 
 
 The various transparent varieties are often used for gem purposes. 
 About 7,000 tons of compact, massive garnet are mined annually for abrasive 
 purposes. Small garnets are sometimes used as jewels in watches of a 
 cheaper grade. 
 
 Dioptase, H,CuSiO 4 . 
 
 Hexagonal, trigonal rhombohedral class, a : c=i : 0.5281. Found 
 commonly in small, prismatic crystals. The unit prism of the second order 
 in usually predominates and is in combination with a negative rhombohedron 
 
212 
 
 DESCRIPTIVE MINERALOGY 
 
 of the first order r and the rhombohedron of the third order s (p = 18/17, 
 m = g/4), figure 119. The latter form is often indicated by a very narrow 
 face. Twins are very rare. Occurs also in druses and mas- 
 sive. Crystals are often rather complex. 
 
 Perfect rhombohedral cleavage. Brittle. Conchoidal 
 to uneven fracture. Hardness 5. Specific gravity 3.3. 
 Emerald to dark green in color. Green streak. Vitreous 
 luster. Transparent to opaque. 
 
 H 2 CuSiO 4 . Infusible. Turns black. Colors the flame 
 green. Gelatinizes with acids. Forms a blue solution with 
 a separation of silica when acted upon by ammonia and am- 
 monium carbonate. 
 
 It occurs with calcite in limestone on the hill of Altyn- 
 Tuebe in the Kirghiz Steppe, Russia ; Rezbanya, Hungary ; 
 Copiapo, Chili ; Peru ; Clifton, Graham County, and River- 
 side, Pinal County, Ariz. 
 
 Dioptase is sometimes used as a gem. 
 
 FIG. 
 
 Chrysocolla, H 2 CuSiO 4 -f H 2 O. 
 
 Apparently amorphous. Never found in crystals. Occurs in earthy 
 masses, incrustations, and seams. Sometimes reniform, botryoidal, and stal- 
 actitic. Often has an opal-like appearance. 
 
 Conchoidal fracture. Hardness 2 to 4. Specific gravity 2 to 2.2. Shin- 
 ing greasy, vitreous luster. Translucent to opaque. Various shades of green 
 and blue, when impure brown to black. Pure varieties possess a greenish 
 white streak. 
 
 H 2 CuSiO 4 + H 2 O. Pure and fresh varieties appear to possess the com- 
 position given. The presence of varying amounts of opaline material, alum- 
 inium silicates, limonite, and the oxides of copper and manganese cause the 
 chemical and physical properties of chrysocolla to vary greatly. Blackens 
 and yields water when heated in a closed tube. Infusible, but colors the 
 flame green. Decomposed by acids but does not gelatinize. 
 
 Chrysocolla is a secondary mineral, formed by the decomposition of 
 various copper ores, such as, chalcopyrite, tetrahedrite, cuprite, and so forth. 
 It is usually found in the zone of oxidation of copper deposits. The com- 
 mon associates are malachite, azurite, and limonite. It occurs pseudo- 
 morphous after atacamite, azurite, cerussite, and labradorite. Some localities 
 are Cornwall, Eng. ; Ober-Rochlitz, Bohemia ; Kupferberg, Bavaria ; Silesia ; 
 various places in Hungary ; Ural Mountains ; Clifton and Bisbee copper dis- 
 tricts, Arizona ; Lake Superior copper district ; in fact in all important cop- 
 per localities. 
 
 It is an ore of copper and sometimes may be substituted for turquois. 
 
SILICATES 213 
 
 Prehnite, H 2 Ca,Al 2 (SiO 4 ) 3 . 
 
 Orthorhombic, pyramidal class, a : b : c = 0.8401 : i : 1.1097. Crys- 
 tals are usually tabular or prismatic, more or less curved and arranged in 
 sheaf-like groups. Distinct individual crystals are very rare. Also botry- 
 oidal, globular, and stalactitic, often with a radial fibrous structure. The 
 common forms are the basal pinacoid, unit prism with an angle of 80 12', 
 and the macro- and brachypinacoids. 
 
 Distinct basal and indistinct prismatic cleavages. Uneven fracture. 
 Hardness 6 to 7. Specific gravity 2.8 to 3. Waxy vitreous luster, somewhat 
 pearly on the basal pinacoid. Transparent to translucent. Colorless or 
 white, but usually light green, apple green, oil green, also yellow green. 
 Colorless streak. Hemimorphism is revealed by the pyroelectric properties. 
 
 H 2 Ca 2 Al 2 (SiO 4 ) 3 . May contain as much as 7%Fe 2 O 3 . Yields water 
 upon ignition at a comparatively high temperature in a closed tube. Fuses 
 easily with intumescence to white yellow glass. Decomposed by acids after 
 ignition. Prehnite alters to chlorite. It occurs as a pseudomorph after anal- 
 cite, laumontite, and natrolite. 
 
 Prehnite is a secondary mineral and, hence, occurs in fissures and cav- 
 ities in diorite, basalt, diabase, melaphyre, gabbro, and the like. It is usually 
 associated with pectolite, datolite, epidote, calcite, and the various zeolites. 
 In the Lake Superior copper district it occurs with native copper. Other 
 localities are : Bourg d'Oisans, Dauphine, France ; Weilburg and Dillen- 
 burg, Nassau ; Fassathal, Tyrol ; various places in Switzerland and Italy ; 
 Kongsberg, Norway ; Peru ; Chile ; South Africa ; Farmington, Conn. ; Essex 
 County, N. Y. ; Bergen Hill, N. J. ; Cornwall, Pa. 
 
 Prehnite is sometimes used for gem purposes. 
 
 CHLORASTROUTE, a greenish, fibrous mineral occurring in small spherical aggre- 
 gates in the melaphyre amygdaloid of Isle Royale, Lake Superior, is often considered 
 an impure prehnite. It is sometimes also thought to be closely related to thomsonite 
 in composition. Subtransparent. Possesses a beautiful chatoyancy. Hardness 5 to 6. 
 Specific gravity 3.18. Chlorastrolite is cut as a gem. 
 
 Axinite, R" T R'" 4 B 2 (SiO 4 ) s . 
 
 Triclinic, pinacoidal class, a : b : (7 = 0.4927 : I :o.45H,a = 82 54', 
 /3 = 88 9', y = 131 33'. Crystals are generally broad 
 and tabular with sharp edges. Figure 120 consists of 
 the unit tetra-pyramids x and r, hemiprisms M and m, 
 macrodome s, and the macropinacoid a. The prism 
 faces are often striated vertically. The habit varies 
 considerably. Crystals may be very complex. Over 
 40 forms have been observed. Occurs also in lamellar 
 and granular masses. 
 
 Several cleavages are observable. Conchoidal 
 FIG. 120 fracture. Brittle. Hardness 6 to 7. Special gravity 3.3 
 
 Vitreous luster. Transparent to translucent. Uncolored streak. Clove 
 
214 DESCRIPTIVE: MINERALOGY 
 
 brown, pearl gray, plum blue,, honey yellow and greenish yellow in color. 
 Often coated and intergrown with chlorite. 
 
 R // 7 R /// 4 B 2 (SiO 4 ) s . R" is chiefly calcium, but may be also iron, man- 
 ganese, magnesium, and hydrogen, while R'" is trivalent iron and alumin- 
 ium. The average content of B 2 O 3 is about 6%. Fuses easily with intum- 
 escence to a dark green glass, coloring the flame a pale green. Gelatinizes 
 with acid after ignition. 
 
 Axinite occurs in fissures and cavities in the older silicate rocks espec- 
 ially diabase, hornblende schist, and more rarely in granites, usually the re- 
 sult of pneumatolytic action. Also found sparingly in ore deposits. Some 
 localities are : Bourg d'Oisans, Dauphine, France ; on Mount Skopi and 
 Saint Gotthard, Switzerland ; Island of Elba ; Andreasberg, Saxony ; Mon- 
 zoni, Tyrol ; Cornwall, England ; Kongsberg, Norway ; Nordmarken and 
 Dannemora, Sweden ; also in Hungary, Ural Mountains, Japan, Peru, and 
 Chile ; Wales and Phippsburg, Me. ; Cold Spring, N. Y. ; Bethlehem, Pa. ; 
 and Franklin Furnace, N. J. ; Bonsall, and Consumers Mine, Cal. 
 
 Sometimes used as a gem. 
 
 MICA GROUP 
 
 The members of the mica group have a great many characteristics in 
 common. While crystals are often apparently hexagonal or orthorhombic 
 in development, they all, nevertheless, belong to the monoclinic system and 
 possess practically the same elements of crystallization. The prism angle 
 usually approximates 120. Twin crystals are not uncommon. The twin- 
 ning plane is perpendicular to the basal pinacoid and nearly parallel to a 
 face of the unit prism. In some cases the basal pinacoid is the composition 
 plane, in others the unit prism. Polysynthetic twins according to this com- 
 mon law, the mica law, are also to be observed. Now and then the gliding 
 planes, 30: : b : c and 2a : cob : c, act as twinning planes. These are inclined 
 at an angle of about 67 to the basal pinacoid and the resulting twins are 
 somewhat step-like in their development. 
 
 The micas possess an excellent basal cleavage. This cleavage is some- 
 times referred to as the most perfect to be observed on minerals. The cleav- 
 age laminae are more or less elastic. By pressing upon or striking a cleav- 
 age surface a blow with a dull conical point, pressure and percussion figures 
 are produced. These figures possess three or six rays, more commonly six, 
 and have a definite orientation. One of the rays in the pressure figures is per- 
 pendicular to the edges formed by the basal and clinopinacoids, while in the 
 percussion figures the rays extend nearly parallel to them and the prismatic 
 edges, see figures 121 and 122. Natural pressure figures are sometimes 
 observed. 
 
SILICATES 
 
 215 
 
 The optical properties of the micas can be easily studied in cleavage 
 fragments, for these show interference figures, inasmuch as the acute bisec- 
 trix is almost normal to the basal pinacoid. The angle of the optic axes, 
 varies greatly. In biotite the angle may be almost zero, hence, the figure is 
 
 sometimes apparently uniaxial. In 
 phlogopite the angle is commonly 
 about 15, while in the other micas it 
 varies from 50 to 75. In micas of 
 the first class the plane of the optic 
 axes is normal to the plane of symmet- 
 ry. When the optical plane is parallel 
 to the plane of symmetry the micas are 
 said to belong to the second class. 
 From the chemical standpoint, the micas are silicates of varying compo- 
 sition of aluminium and potassium, containing hydrogen, magnesium, iron 
 (ferrous and ferric), sodium, lithium, and fluorine. The content of silica 
 varies between 33% and 55%. Several theories have been advanced to ex- 
 plain the rather complex composition of the members of the group. Ac- 
 cording to Clarke, the micas are derived from the hypothetical orthosilicate 
 Al 4 (SiO 4 ) 3 , while Tschermak considers them as mixtures in varying pro- 
 portions of H 3 Al 3 (SiOJ 3 and (Mg,Fe) {SiO 4 ) 3 . 
 Six varieties are commonly differentiated : 
 
 FIG. 121 
 
 FIG. 122 
 
 BIOTITE, (K,H) 2 (Mg,Fe) 2 (Al,Fe) 2 (Si0 4 ) ; 
 PHLOGOPITE, (K,H) s Mg 3 Al(SiO 4 ) 3 . 
 MUSCOVITE, H 2 KAl 3 (SiO 4 ) 3 . 
 
 PARAGONITE;, H 2 NaAl 3 (SiO 4 ) 3 . 
 Lepidolite, (Li,K) 2 (F,OH),Al 2 Si 3 O 9 , 
 
 ZINNWAUDITS, (Li,K) 3 (F,OH) 2 Al 3 FeSi 5 O 1G . 
 
 0.5777 : i : 2.1932 
 
 /?=952' 
 
 (Tschermak) 
 
 All the micas yield water when heated to a high temperature in a closed 
 tube. They fuse with difficulty. 
 
 The micas are important rock forming minerals and occur extensively 
 in igneous and metamorphic rocks. Some sedimentary rocks also contain 
 considerable quantities of mica. 
 
 BIOTITE, Magnesium-iron Mica, Black Mica, (K,H) (Mg,Fe) 2 (Al,Fe), 
 (Si0 4 ),. 
 
 Monoclinic, prismatic class, a : b : c = 0.5777 : I ' 2 - l 93 2 > /? 95 
 2'. Crystals are usually tabular with an hexagonal or rhombohedral habit. 
 This habit in connection with the very small angle of the optic axes caused 
 
2l6 DESCRIPTIVE MINERALOGY 
 
 biotite to be considered for a long time as rhombohedral and uniaxial. Ac- 
 cording to Hintze about forty crystallographic forms have been observed. 
 The usual combination consists of the basal pinacoid c, clinipinacoid b, and 
 
 the positive and negative hemipyramids m and o, 
 see figure 123. Crystals are often striated horizon- 
 tally, due to the alternation of m and o. Good crys- 
 tals are rarely found. Twins are observed with the 
 FIG. 123. basal- pinacoid as the composition plane, also with 
 
 the twinning plane parallel to either 30 : b : c or 2a : oob :c, see page 214. 
 Generally occurs in disseminated scales. 
 
 Highly perfect basal cleavage, laminae are more or less elastic and may 
 be extremely thin; sometimes given as o.ooi of an inch in thickness. Splen- 
 dent, pearly, and submetallic luster. Hardness 2.5 to 3. Specific gravity 
 2.7 to 3.2. Transparent to opaque. Dark in color, dark brown, black ; more 
 rarely, light brown or greenish. Strong pleochroism. Double refraction 
 strong and negative. Asterism is sometimes to be noted. 
 
 There are two varieties of biotite: (i) Anomite, having the plane of 
 the optic axes perpendicular to the plane of symmetry, and (2) Meroxene 
 in which the optical plane extends parallel to the plane of symmetry. These 
 varieties may be designated as micas of the first and second classes, respec- 
 tively, see page 215. Meroxene is by far the more common variety. 
 
 (K,H) 2 (Mg,Fe) 2 (Al,Fe) 2 (SiO 4 ) 3 . The composition varies greatly. 
 Thus, SiO 2 from 35% to 45%, some of which may be replaced by TiO 2 ; 
 MgO from 10% to 30%, which may be replaced partially or almost entirely 
 by FeO ; A1 2 O 3 from 11% to 20%, replaced to some extent by Fe 2 O 3 ; K 2 O, 
 replaced by some Na 2 O, from 5% to 11% ; fluorine may replace some of the 
 hydrogen. Lepidomelane contains a high percentage of FeO and Fe 2 O 3 , 
 and but little MgO. Meroxene contains only a very small amount of 
 iron, while anomite is characterized by a high percentage of bivalent ele- 
 ments. Some biotite contains small amounts of chromium, barium, and man- 
 ganese. Only slightly attacked by hydrochloric acid ; completely, however, 
 by hot concentrated* sulphuric. Fusible on the thin edges. The darker varie- 
 ties fuse more readily. Biotite alters to chlorite, or to epidote, quartz, and 
 iron oxide. 
 
 Biotite is often considered the most common of all micas. It is an im- 
 portant constituent of many igneous and metamorphic rocks, such as, gran- 
 ites, diorites, gabbros, syenites, prophyries, gneisses, and mica schists. It is 
 often developed by contact metamorphism. On account of its tendency to 
 decompose it is not important in sedimentary rocks. 
 
 The various varieties of biotite are of little or no use, commercially. 
 
SILICATES tI7 
 
 PHLOGOPITE, Amber Mica, Bronze Mica, Magnesium Mica, (K,H) a 
 Mg a Al(Si0 4 ).. 
 
 Monoclinic, prismatic class. The elements of crystallization are the 
 same as given for biotite. Crystals usually resemble those of biotite in form 
 and habit ; large, coarse crystals are sometimes observed. They may possess 
 a pseudo-orthorhombic or trigonal development. Twinned according to the 
 laws described under biotite. Occurs commonly in disseminated scales, 
 plates, and aggregates. 
 
 Highly perfect basal cleavage. Thin laminae are tough and elastic. 
 Specific gravity 2.75 to 2.97. Hardness 2.5 to 3. Pearly to submetallic lus- 
 ter. The color may be silvery gray, yellow, brown, greenish, or copper red. 
 Cleavage laminae are transparent. Phlogopite is a mica of the second class, 
 see page 215. The optic angle is about 15, although it may be smaller. 
 Often shows distinct asterism. 
 
 (K,H) 3 Mg 3 Al(SiO 4 ) 3 . Usually contains a small amount of FeO, I to 
 2% ; potassium may be replaced by sodium and fluorine. The amount of 
 MgO varies between 27 and 29%, the SiO 2 between 41 and 44%. Whitens 
 and fuses on thin edges. Hydrochloric acid acts but slightly upon phlogo- 
 pite, while hot concentrated sulphuric acid decomposes it readily. 
 
 Phlogopite occurs in crystalline limestones, dolomites, schists and in ser- 
 pentine. Important localities : Pargas in Finland ; Aeker, Sweden ; Fassa- 
 thal, Tyrol : St. Lawrence and Jefferson counties, N. Y. Extensive deposits 
 of economic importance occur in Canada. According to Cirkel, the Canadian 
 phlogopite occurs in dikes penetrating gneiss or limestone, or in contact and 
 pocket deposits. It is commonly associated with pyroxene, apatite, and cal- 
 cite. Sydenham and Burgess, Ontario, furnish large quantities of phlogo- 
 pite. Some of the crystals from the Lacey mine, near Sydenham, measured 
 seven feet across the cleavage planes. 
 
 It is used chiefly as an insulator in electrical work. 
 
 MUSCOVITE, White Mica, Potash Mica, Isinglass, H 2 KAl 3 (SiO 4 ) 3 . 
 
 Monoclinic, prismatic class. For elements of crystallization, see biotite, 
 page 215. Crystals are usually tabular with an orthorhombic or hexagonal 
 outline. Sometimes tapering, pyramidal habits are also noted. The forms 
 observed most frequently are the basal pinacoid, unit prism, clinopinacoid, 
 and the clinodome, co a : b : c. Crystals are often large and rough, 
 measuring at times several feet in diameter, and are called blocks or 
 books. Due to partings in several directions at about right angles to the 
 basal pinacoid, which interrupt the true cleavage, these crystals are often 
 
2i8 DESCRIPTIVE; MINERALOGY 
 
 called ribbon, ruled, or A mica. In wedge mica the crystals are thicker at 
 one end than at the other. Twins are common, the basal pinacoid being the 
 composition plane. Occurs also in scaly, foliated, and plumose aggregates ; 
 sometimes compact and cryptocrystalline. 
 
 Highly perfect cleavage parallel to the basal pinacoid, permitting very 
 thin, elastic leaves to be split. Hardness 2 to 3. Specific gravity 2.75 to 
 3.1. Transparent to translucent. Pearly to metallic luster. Colorless, when 
 pure, but usually yellowish, brownish, greenish, or reddish. Some shades 
 of brown and reddish muscovite are termed rum or ruby mica. Uncol- 
 ored streak. Strong double refraction. Negative. The plane of the optic 
 axes is perpendicular to the plane of symmetry. Muscovite is, hence, a 
 mica of the first class. Sometimes shows asterism. 
 
 H 2 KAl 3 (SiO 4 ) 3 . Muscovite proper contains about 45% of SiO 2 . The 
 variety with about 52% of SiO 2 is called phengite. From 8 to 10% of the 
 potassium is generally replaced by sodium. Small amounts of magnesium, 
 calcium, iron, and fluorine are also commonly noted. Fuchsite contains 
 small amounts of chromium while roscoelite has considerable vanadium re- 
 placing the aluminium. Fuses with some difficulty to a grayish or yellowish 
 glass. Not attacked by the common acids. Sericite and damouriie are more 
 or less altered varieties of muscovite. The term sericite is sometimes applied 
 to unaltered muscovite occurring in aggregates of fine scales with a silky 
 luster but without distinct cleavage. 
 
 Muscovite is generally considered the most common mica. It occurs 
 in granites and syenites, especially in pegmatite veins where pneumatolytic 
 action has been effective. It is also common in metamorphic rocks, such as 
 gneisses and schists. Occurs furthermore in some limestones and fragmental 
 rocks. The usual associates of muscovite are feldspar, quartz, tourmaline, 
 beryl, spodumene, sarnarskite, and garnet. Deposits of muscovite of commer- 
 cial value occur in North Carolina, South Dakota, Alabama, South Carolina, 
 Colorado, New Hampshire, Idaho, Georgia, Virginia, New Mexico, and 
 Maine. Some of the principal producing localities are in Mitchell, Yancey, 
 Macon, Jackson, Haywood, and Ashe counties, North Carolina ; Custer Coun- 
 ty, South Dakota; Grafton and Cheshire counties, New Hampshire. Depos- 
 its of excellent muscovite also occur in Ottawa and Berthier counties, Que- 
 bec, Canada. The muscovite mined in the United States during 1908 was 
 valued at $267,925. 
 
 The principal use of muscovite is in the manufacture of windows Tor 
 coal, gas, and oil stoves, gas-lamp chimneys, lamp shades, and so forth. 
 Scrap and waste mica, that is, material too small to be cut into sheets, is 
 ground in large quantities for the manufacture of wall paper, lubricants, 
 fancy paints, and for electrical insulators. Very large amounts of muscovite 
 
SIUCATES 219 
 
 and phlogopite are used for insulating purposes in electrical apparatus and 
 machinery, such as, dynamos, motors, high voltage induction apparatus, 
 switchboards, lamp sockets and the like. Much of the sheet mica used for 
 this purpose is made by cementing small pieces of scrap or waste mica to- 
 gether and is commonly known by the trade name micanite. 
 
 In 1908 the prices per pound of selected sizes of muscovite were as fol- 
 lows : 2 by 2 inches $0.87, 3 by 3 inches $2.75, 3 by 4 inches $3.25, 6 by 8 
 inches $6.75. 
 
 PARAGONITE, Sodium Mica, H 2 NaAl 3 (SiO 4 ) 3 . 
 
 Monoclinic, prismatic class. The elements of crystallization are the same as for 
 biotite. Occurs in compact and fine scaly aggregates, which often resemble sericite. 
 Massive and laminated. 
 
 Perfect basal cleavage. Hardness 2 to 3. Specific gravity 2.8 to 2.9. White, gray- 
 ish, greenish white, or yellow in color. Pearly luster. Large optical angle. Very 
 strong double refraction. 
 
 HsNaAlafSiOOa. Fuses with great difficulty; some varieties exfoliate. Not at- 
 tacked by acids. 
 
 Paragonite is not a common mica. Its common associates are cyanite, staurolite, 
 garnet, and tourmaline. It is generally found in metamorphic rocks. At Monte Cam- 
 pione in the St. Gotthard Alps, Switzerland, it forms a schist and contains the min- 
 erals, referred to, as associates. It is also found in Pfitschthal and Zillerthal, Tyrol; 
 Unionville, Pa. 
 
 Lepidolite, Lithium Mica, (Li,K) 2 (F,OH) 2 Al 2 Si 3 O 9 . 
 
 Monoclinic. The elements of crystallization are unknown as measur- 
 able crystals have never been found. According to Tschermak, they are un- 
 doubtedly very similar to those of muscovite. Twins and trillings according 
 to the mica law are sometimes observed. Usually occurs in scaly, granular 
 masses ; often looks like granular limestone. Also as tabular, cleavable 
 plates. 
 
 Perfect basal cleavage. Hardness 2 to 4. Specific gravity 2.8 to 2.9. 
 Pearly luster. Rose-red or lilac in color, also white, gray, greenish, or 
 brown. White streak. Translucent. Plane of the optic axes is perpendic- 
 ular to the plane of symmetry, that is, it is a mica of the first class. Angle 
 of the optic axes varies from 50 to 80. 
 
 (Li J K) a (F,OH) a Al s Si,O,; Fluorine varies from about 3.5 to 10.5%; 
 Li 2 O 1.25 to 5.9% ; SiO 2 from 49 to 52%. Some varieties from Maine con- 
 tain considerable amounts of rubidium and caesium. Colors the flame red 
 and fuses easily to a white glass. After fusion is easily acted upon by acids. 
 
 Occurs in pegmatite veins, in granites and gneisses, the result of pneu- 
 matolytic action. The common associates are tourmaline, amblygonite, spo- 
 dumene, cassiterite, and topaz. Sometimes intergrown with muscovite. 
 Some localities are : Rozena, Moravia ; Penig, Saxony ; Uto, Sweden ; 
 Island of Elba; Paris, Hebron, Auburn, and Rumford, Maine; Chesterfield, 
 
220 DESCRIPTIVE MINERALOGY 
 
 Mass. ; San Diego County, Cal. Rubbelite, the red lithium variety of tour- 
 maline, is often found embedded in granular lepidolite. 
 It is an important source of lithium compounds. 
 
 COOKEITE, Li(A1.2OH) 3 (SiO3) 2 , is probably an alteration product of 
 lepidolite or tourmaline with which it occurs at Hebron, Me. 
 
 ZINNWAUHTE, Lithium-iron Mica, (Li,K) 3 (F,OH) 2 Al 3 FeSi 5 O 16 . 
 
 Monoclinic, prismatic class. The elements of crystallization are similar to those 
 of biotite. Distinct tabular crystals with a pseudo-hexagonal outline are usually pene- 
 tration trillings. The basal pinacoid generally shows a complex system of striations. 
 Occurs also in fan shaped and rosette groups and in isolated aggregates. Sometimes 
 coarse granular and cleavable. 
 
 Perfect basal cleavage. Hardness 2 to 3. Specific gravity 2.8 to 3.1. Pearly to 
 metallic luster. Pale violet, gray, yellowish, various shades of brown, and more rarely 
 dark green in color. It is a mica of the first class, see page 215. The angle of the optic 
 axes varies from almost o to about 50. 
 
 (Li,K)3(F.OH) 2 Al 3 FeSi5Oie. Composition varies greatly; SiO 2 44 to 47%; F, 
 2 to 8% ; Li*O, i to 5% ; FeO, 10 to 12% ; KsO, 5 to 13%. Some sodium may be pres- 
 ent and a portion of the fluorine may be replaced by the hydroxyl. Fuses easily to a 
 dark colored glass, coloring the flame reddish. Attacked by acids, especially when 
 finely powdered. 
 
 Associated with topaz, scheelite, fluorite, quartz, cassiterite, and so forth, it occurs 
 in cassiterite bearing granites and gneisses. It is the result of pneumatolytic action 
 and is not a very common mineral. The principal localities are Zinnwald, Bohemia; 
 Altenberg, Saxony; Cornwall, England; Nararsuk, Greenland; York region, Alaska. 
 
 GLAUCONITE, Fe"'KSi 2 O 6 -j-H 2 O ? 
 
 Probably monoclinic, analogous to the micas. Never in crystals, but as granular 
 grains or sand resembling gunpowder, or disseminated in sandstone or marl. Some- 
 times in fragile aggregates. Specific gravity 2.3. Composition varies. Clarke suggests 
 the formula given. Found as green sand in rocks of all ages, especially cretaceous and 
 tertiary. Large quantities of this sand, containing from 75 to 90% of glauconite, occur 
 in Northern Prussia along the south shore of the Baltic Sea and contains amber. 
 Also found in southern New Jersey and Texas. On account of the content of potas- 
 sium, it is used as a fertilizer. 
 
 CELADONITE, also written seladonite, is very similar to glauconite. Clarke be- 
 lieves that they may be identical. Usually earthy. Very soft. Specific gravity 2.8 
 to 2.9. Apple to dark green in color. Is a decomposition product of hornblende and 
 augite. Occurs in the Fassathal, Tyrol, and in the Lake Superior district. 
 
a : b : c 
 0.577 = i : -577 
 
 SILICATES 221 
 
 CLINTONITE GROUP 
 
 The members of this group resemble the micas in form and cleavage 
 but are harder and brittle. They are often termed the brittle micas. Chem- 
 ically, they are basic silicates of calcium, magnesium, and aluminium, and are 
 differentiated from the micas by the absence of the alkalies. 
 
 The important members are : 
 
 Margarita, H 2 CaAl 4 Si ii O 12 . 
 
 XANTHOPHYLLITE, H 8 ( Mg,Ca) 14 Al 16 Si 6 O 62 . 
 BRANDISITE, H 8 (Mg,Ca) 12 Al 12 Si 5 O 44 . 
 CLINTONITE, H s ( Mg,Ca) 10 Al 10 Si 4 O 36 . 
 OTTRELITE, H 2 FeAl 2 Si 2 O 9 . 
 CHLORITOID, H 2 FeAl 2 SiO 7 . 
 
 They have been referred to the prismatic class of the monoclinic system. 
 A rhombohedral habit is characteristic. The elements of crystallization, giv- 
 en above, are for waluewite, a variety of xanthophyllite. The other members 
 of the group do not occur in measurable crystals. 
 
 Margarita, Pearl Mica, H,,CaAl 4 Si 2 O 12 . 
 
 Monoclinic. Well developed crystals are rare. The elements are thought 
 to be very similar to those of biotite. Usually in thin six sided plates or 
 lamellar aggregates ; also in granular, scaly masses. 
 
 Perfect basal cleavage, but not as easy as on the micas proper. Lam- 
 inae are brittle and inelastic. Hardness 3 to 4.5. Specific gravity 3. Pearly 
 luster on the basal pinacoid, vitreous on the lateral faces. Translucent. 
 White, reddish white, pink, yellow, and pearly gray in color. It is a mica of 
 the first class, see page 215. Large angle of the optic axes, about 120. 
 
 H 2 CaAl 4 Si.,O 12 . The composition varies somewhat. Magnesium, so- 
 dium, and fluorine may be present. Exfoliates and fuses with difficulty on 
 the edges. Slightly attacked by acids. Dudleyite is brownish yellow alter- 
 ation product. 
 
 Occurs in altered and metamorphosed rocks. ,As an alteration product, 
 it is commonly associated with corundum and emery. Some localities are 
 the island of Naxos and other places in the Grecian archipelago and Asia 
 Minor ; Greiner, Tyrol ; Chester, Mass. ; Peekskill, N. Y. ; Gainesville, Ga. ; 
 Unionville, Pa. ; Dudleyville, Ala. 
 
 XANTHOPHYLLITE, H 8 (Mg,Ca) 14 Al 16 Si 5 O 52 . 
 
 Monoclinic. The variety known as waluewite occurs in distinct crystals with 
 the ratio: a : b : c = 0.5774 : i 0.5773, J 3 109 35^'. They are usually tabular 
 parallel to the basal pinacoid. Crystals sometimes appear to be a combination of the 
 basal pinacoid with a rhombohedron, but are in reality monoclinic. Interpenetration 
 twins and trillings commonly appear to be simple crystals. The basal pinacoid is gen- 
 erally smooth and shiny, the lateral faces rough and rounded. Xanthophyllite is gen- 
 erally found in aggregates and crusts. 
 
222 DESCRIPTIVE; MINERALOGY 
 
 Perfect basal cleavage. Hardness 4 to 5 on the basal pinacoid, 5 to 6 on the 
 lateral faces. Specific gravity 3 to 3.1. Vitreous luster, on cleavage surfaces pearly. 
 Aggregates are wax yellow, crystals leek to bottle green. Transparent to translucent. 
 Infusible, but becomes cloudy. Decomposed with difficulty by hot hydrochloric acid. 
 Associated with magnetite, spinel, and garnet it occurs in talc and chloritic schists in 
 the Ural Mountains. 
 
 BRANDISITE, Disterrite, H 8 (Mg,Ca) 12 Al 12 Si 5 O 44 . 
 
 Monoclinic. Usually in thin tabular plates which appear to be repeated twins ac- 
 cording to the mica law. Perfect basal cleavage. Hardness 5 on the basal pinacoid, 
 otherwise 6 or more. Specific gravity 3 to 3.1. Rather brittle. Vitreous luster. Sub- 
 transparent. Leek to dark green, rarely reddish gray, in color. Infusible, but turns 
 white. Not easily acted upon by acids. Occurs as a contact mineral associated with 
 fassaite and spinel in the Monzoni district, Tyrol. 
 
 CUNTONITE, Seybertite, H 6 (Mg,Ca) 10 Al 10 Si 4 O 36 . 
 
 Monoclinic. Crystals resemble those of brandisite. Usually thick, apparently 
 hexagonal, plates with rough lateral faces. Also in foliated masses. Perfect basal 
 cleavage. Very brittle. Hardness 4 to 5. Specific gravity 3.1. Submetallic luster on 
 the basal pinacoid, resinous on cleavage surfaces, otherwise vitreous. Transparent to 
 translucent. Yellowish, reddish brown, or copper red in color. Infusible, but becomes 
 white and opaque. Easily and completely decomposed by concentrated hydrochloric 
 acid. Associated with amphibole, pyroxene, chondrodite, spinel, and graphite, it oc- 
 curs in serpentine with granular limestone at Amity and Warwick, Orange County, 
 N. Y. 
 
 CHRYSOPHANE, HOLMITE, and HOLMESITE are synonyms for clintonite. 
 
 OTTREUTE, H 2 FeAl 2 Si 2 O 9 . 
 
 Monoclinic. Occurs in small, elongated plates or scales with an hexagonal out- 
 line. Gray, greenish gray, or greenish black in color. Ottrelite is usually considered 
 a variety of chloritoid, although it differs somewhat chemically. It is characterized 
 by a large percentage of MnO. It ocurs in argillaceous schists near Ottrez, Belgium; 
 Northern Michigan, Vermont, and other places. 
 
 CHLORITOID, H 2 FeAl.,SiQ T . 
 
 Monoclinic. Crystals with distinct outlines are rare. Usually in plates which 
 may be hexagonal, also in disk, spindel, or lenticular shaped grains, and foliated, 
 curved scaly, fan and sheaf like masses or aggregates. 
 
 Perfect basal cleavage. Brittle. Hardness 5 to 7. Specific gravity 3.4 to 3.6. 
 Vitreous to pearly luster on the cleavages, on the lateral surfaces resinous. Almost 
 opaque. Gray, greenish gray, greenish black, grass green, or black in color. Uncolored, 
 grayish, or greenish gray streak. Plane of the optic axes is parallel to the plane of 
 symmetry. Large optic angle. Strongly pleochroic. 
 
 H 2 FeAl 2 SiOT. Some of the iron may be replaced by magnesium or manganese. 
 Exfoliates slightly and fuses with difficulty to a black magnetic mass. The fine powder 
 is decomposed by sulphuric acid. Alters to muscovite and penninite. 
 
 Chlorotoid occurs in phyllite, quartzite, mica schist, and metamorphosed sedimen- 
 tary rocks. Often associated with glaucophane. Some localities are St. Marcel, Pied- 
 
SILICATES 223 
 
 mont, Italy; Kossoibrod, Ural Mountains; Zerraatt, Switzerland; Natick, R. L; Sterl- 
 ing, Mass. 
 
 MASONITE, NEWPORTITE, PHYLUTE, SALMITE, SISMONDINE, and BARYTOPHYLLITE 
 are more or less synonymous with chlorkoid. 
 
 CHLORITE GROUP 
 
 This group contains a considerable number of minerals which are close- 
 ly related to the micas, especially with regard to crystal form, scaly or foliated 
 habit, and cleavage. Cleavage laminae are, however, tough and compara- 
 tively inelastic. These minerals are silicates of aluminium or trivalent iron, 
 with magnesium, bivalent iron, or manganese, but are much more basic than 
 the micas. They are also free from alkalies and calcium, and yield water 
 when heated in a closed tube. Characteristic is the green color commonly 
 observed in silicates containing ferrous iron. 
 
 According to Tschermak, the members of this group form a series of 
 isomorphous mixtures of the two silicates : 
 
 Amesite, H 4 Mg 2 AlAlSiO 9 , = At, 
 
 Serpentine, H 4 Mg 2 MgSiSiO 9 , = Sp. 
 
 The A1 2 group in amesite is considered as being replaced by MgSi in 
 serpentine. Such replacements are, according to Groth, rather common. 
 If the amesite molecule be represented by At, and that of serpentine by Sp, 
 then the general composition of these minerals may be expressed as follows : 
 
 AMESITE, At At 4 Sp 
 
 CORUNDOPHILITE, At 4 Sp ...... At 7 Sp 3 
 
 Prochlorite, At 7 Sp 3 At 3 Sp 2 
 
 a : b : c = 0.5774 : 
 i .-0.8531, 0= 117 9'- 
 
 Clinochlore, At 3 Sp 2 AtSp 
 
 PENNINITE, AtSp At 2 Sp 3 
 
 These minerals crystallize in the monoclinic system but clinochlore and 
 penninite are the only ones occurring in well developed crystals. A rhombo- 
 hedral habit is not uncommon. The elements of crystallization given above 
 are for clinochlore. 
 
 AMESITE, H 4 Mg 2 Al 2 SiO 9 . 
 
 The composition may vary from that given to that of the mixture At*Sp. . Six 
 sided plates and foliated aggregates. Resembles green talc. Apple green in color. 
 Hardness 2.5 to 3. Specific gravity 2.7. Pearly luster on cleavage surface. Occurs 
 with rose red diaspore at Chester, Mass. 
 
 CORUNDOPHIUTE, At 4 Sp At 7 Sp 3 . 
 
 Green, more or less six sided plates. -Resembles clinochlore. Occurs with cor- 
 undum at Chester, Mass., and Asheville, N. C. 
 
224 DESCRIPTIVE MINERALOGY 
 
 Prochlorite, (Chlorite and ripidolite in part), At T Sp 3 . . . . At 3 Sp 2 . 
 
 Monoclinic, prismatic class. Crystals are not well developed. Usually 
 as six sided plates and scales, often arranged in divergent, fan shaped, or 
 spheroidal groups. Occurs also massive, foliated, or granular. Sometimes 
 as a scaly or dusty coating on, or disseminated through, quartz, titanite, per- 
 icline, adularia, and so forth. 
 
 Perfect basal cleavage. Laminae are flexible and inelastic. Hardness 
 1. Specific gravity 2.8 to 2.95. Translucent to opaque. Very thin laminae 
 may be transparent. Pearly luster on cleavage surfaces. Various shades 
 of green in color. Slightly pleochroic. 
 
 Chemically, prochlorite is considered a mixture of the amesite and ser- 
 pentine molecules, as indicated above. Usually contains about 27% of Si(X. 
 Almost infusible, yields a black glass. Decomposed by concentrated acids. 
 
 Prochlorite is a very essentail constituent of many chlorite schists, espe- 
 cially those containing magnetite. Occurs in serpentine, granite, gneiss, and 
 so forth. It is a common alteration product of augite, hornblende, garnet, 
 calcite, and also perhaps quartz and feldspar. 
 
 Clinochlore, ripidolite in part, At 3 Sp 2 .... AtSp. 
 
 Monoclinic, prismatic class. Usually in hexagonal pyramidal, tabular 
 rhombohedral, or distinct monoclinic crystals. Sometimes bent and twisted. 
 Twins according to the mica and penninite laws. In the latter case the basal 
 pinacoid acts as the twinning plane. Coarse scaly granular, fine granular, 
 and earthy. Massive. 
 
 Perfect basal cleavage. Laminae are tough, flexible, and but slightly 
 elastic. Hardness 2. Specific gravity 2.55 to 2.8. Translucent to transpar- 
 ent. Pearly luster on the basal pinacoid, elsewhere vitreous to resinous. 
 Various shades of green in color, usually bluish to blackish green. 
 
 Chemical composition as indicated. Contains about 30% of SiO 2 . Fuses 
 with difficulty to a grayish yellow glass. Decomposed by sulphuric acid. 
 
 An important constituent of chlorite schists. Occurs also in talcose 
 schists and rocks, and in serpentine. Often associated with garnet, diopside, 
 magnesite, and apatite. Some localities are : Achmotovsk, Ural Mountains ; 
 Zillerthal, Pfitschthal, and Pfunders, Tyrol ; Zermatt, Switzerland ; Marien- 
 berg, Saxony ; Westchester and Unionville, Pa. ; Brewster, N. Y. 
 
 Penninite, AtSp .... At,Sp 3 . 
 
 Monoclinic, prismatic class, a : b : c = 0.5774 : 1 : 0.8531, = 117 
 9'. Crystals have a distinctly rhombohedral habit. The pyramidal faces are 
 often striated horizontally and appear as steep rhombohedrons, truncated by 
 the basal pinacoid. These crystals are usually trillings according to the 
 mica law. Massive, consisting of an aggregate of scales ; cryptocrystalline. 
 
 Perfect basal cleavage. Flexible. Hardness 2.5. Specific gravity 2.6 
 to 2.85. Transparent to translucent. Pearly luster on cleavage surfaces, 
 elsewhere vitreous. Various shades of green, violet, red, pink, rose red, 
 grayish red, yellowish, and silver white in color. 
 
SILICATES 225 
 
 Chemical composition as indicated above. Contains about 33 % of SiCX. 
 Exfoliates and fuses with difficulty to a yellowish glass. Decomposed by 
 acids. 
 
 Is not as common as clinochlore. Commonly an alteration product of 
 biotite, amphibole, garnet, and feldspar. It is fo.und in veins and cavities in 
 various types of rocks, especially chlorite schists. Some localities are : Bin- 
 nenthal, Pfitschthal, Zermatt, and elsewhere, Switzerland ; Magnet Cove, Ark. 
 
 ORTHOCHLORITES AND LEPTOCHLORITES. 
 
 Chloritic minerals are sometimes divided into two groups, orthochlorites 
 and leptochlorites. The minerals, just described, are classified as orthochlor- 
 ites. They occur usually in crystals or comparatively large lamella. The 
 leptochlorites include closely related substances, occurring in aggregates or 
 microscopic scaly masses. Their chemical composition is more or less doubt- 
 ful. Orthochlorites are not easily decomposed by hydrochloric acid and do 
 not yield much water below 500 ; leptochlorites on the other hand are read- 
 ily decomposed and yield much water. 
 
 The leptochlorites include daphanite, chamosite, metachlorite, clemen- 
 tite, thuringite, cronstedite, euralite, strigovite, diabantite, aphrosiderite, del- 
 essite, and rumpfite. These are known too imperfectly to warrant detailed 
 descriptions. 
 
 SERPENTINE AND TALC GROUP 
 
 Here are placed certain basic magnesium silicates which are somewhat 
 closely related to the chlorites. They may contain either iron or nickel, and 
 yield water on ignition. They differ from the chlorites in that they do not 
 contain aluminium. All are secondary minerals resulting from the decompo- 
 sition of magnesium silicates containing little or no aluminium. Since they 
 never occur in crystals but always in scaly and fibrous aggregates or com- 
 pact, apparently amorphous, masses, their crystallographic nature and chem- 
 ical composition are somewhat uncertain. This is not an isomorphous group. 
 
 SERPENTINE, 
 
 TALC, H 2 Mg 3 Si 4 O 12 . 
 
 Sepiolite, H 4 Mg,Si 3 O 10 . 
 
 Garnierite, H 2 (Ni,Mg)SiO 4 . 
 
 DEWEYUTE, H 12 Mg 4 SLO 1(i . 
 
 GENTHITE, H 12 Mg,Ni 2 Si 3 O i6 . 
 
 Saponite, a silicate of magnesium and aluminium with a variable com- 
 position, is also placed in this group. 
 
226 DESCRIPTIVE MINERALOGY 
 
 SERPENTINE, H 4 Mg 3 Si 2 O 9 . 
 
 Orthorhombic or monoclinic. Never in crystals. Usually compact and 
 massive with a microscopically fine fibrous or foliated structure. Some- 
 times more or less columnar or fibrous, or lamellar and foliated. 
 
 Conchoidal to splintery fracture. Smooth to greasy feel. Dull resinous, 
 greasy, or waxy luster. Takes an excellent polish. Translucent to opaque. 
 Hardness 2.5 to 4. Specific gravity 2.5 to 2.8. Various shades of green in 
 color, also yellowish, grayish, reddish, brownish, or black. Specimens are 
 often multi-colored. White streak. 
 
 According to Weinschenk, there are two distinct modifications of ser- 
 pentine, chrysotile and antigorite. Groth considers antigorite and chrysotile 
 as isomeric modifications. Antigorite is closely related to the chlorites. 
 
 Chrysotile. This is the more common modification and is characterized 
 by its fibrous structure. It occurs in several varieties. 
 
 (1) Common serpentine. Compact, massive. Generally dark in color. 
 Often multi-colored. Sometimes impure. Very abundant. 
 
 (2) Precious serpentine. Massive, more or less homogeneous. Var- 
 ious shades of green in color, sometimes yellowish. Translucent. 
 
 (3) Fibrous serpentine, asbestos. Consists of delicate, fine, parallel 
 fibers, which can be easily separated. Fibers are flexible and adapted for 
 spinning. Silky to silky metallic luster. Various shades of green in color, 
 also yellowish and brownish. Usually found in narrow veins. The fibers 
 extend across the veins. Sometimes called short nbered asbestos. 
 
 (4) V erd-antique , ophicalite. Massive green serpentine mixed irreg- 
 ularly with white calcite, dolomite, or magnesite. Takes an excellent polish 
 and is used extensively for ornamental purposes. Polished serpentine is 
 often termed serpentine marble. 
 
 Antigorite. A lamellar or foliated structure is characteristic for this 
 modification. Generally in scaly or foliated aggregates. Dark green in color. 
 Translucent. Contains a small amount of A1 2 O 3 . 
 
 H 4 Mg 3 Si 2 O 9 . Usually contains some FeO, sometimes also NiO. Yields 
 about 13% of water upon ignition. Splinters fuse with great difficulty. 
 Slightly colored varieties turn pale red when treated with cobalt nitrate so- 
 lution. Decomposed by acids with a separation of silica. May alter to 
 brucite, magnesite, hydromagnesite, and webskyite (H 6 Mg 4 Si 3 O 13 .6H 2 O). 
 
 Serpentine is a secondary mineral resulting from the decomposition of 
 magnesium minerals and rocks, such as, olivine, enstatite, hornblende, aug- 
 ite, chondrodite, peridotite, and Iherzolite. Olivine is the most common 
 source of serpentine, the scales or fibers of serpentine coating the exterior 
 
SIIJCATES 227 
 
 and extending along cracks into the interior of the crystal. The common 
 associates are garnierite, chromite, pyrope, magnesite, platinum, and talc. 
 
 Serpentine occurs in many localities. In the United States it is mined 
 in Chester County, Pa., and also at Easton, Pa. It is found at Hoboken and 
 Montville, N. J. ; Syracuse, N. Y. ; Stevens County, Wash. ; Milford, Conn. 
 Asbestos is not found to any extent in the United States. Most of the as- 
 bestos of commerce is obtained from the mines in the Thetford-Black Lake 
 district, Quebec, Canada. 
 
 Polished massive serpentine and verd-antique are used for ornamental 
 and interior decorative purposes. Asbestos is used extensively in the manu- 
 facture of non-conductors of heat and incombustible materials such as, cloth, 
 boards, felt, rope, paper, paint, cement, and theater curtains. 
 
 TALC, Soapstone, Steatite, H 2 Mg 3 Si 4 O 12 . 
 
 Monoclinic, on account of striking resemblances to the micas and chlor- 
 ites. Distinct crystals have not been observed. Individual scales sometimes 
 have an hexagonal or orthorhombic outline. Usually as foliated masses, 
 globular and stellate groups, and sometimes fibrous, granular, and compact. 
 
 Perfect basal cleavage. Laminae are flexible but inelastic, and possess 
 a pearly luster. Compact talc has an uneven to splintery fracture. Greasy 
 feel. Hardness 1 to 2.5. Specific gravity 2.6 to 2.8. Translucent to trans- 
 parent. White to green, gray, yellowish, reddish, and brown. Percussion 
 figures are similar in outline and orientation to those of mica. 
 
 There are several varieties of talc : 
 
 (1) Foliated talc. Consists of small, easily separable folia. Soapy, 
 greasy feel. Hardness 1, easily impressed by the finger nail. Light green 
 to white in color. 
 
 (2) Steatite or soapstone. Massive. More or less impure. Coarse to 
 fine granular, also schistose. Gray to greenish in color. Hardness 1.5 to 
 2.5. Occurs in large deposits. 
 
 (3) French chalk. Soft, compact, whitish masses. Marks cloth. 
 
 (4) Rensselaerite. Pseudomorphous. Altered from pyroxene. Wax- 
 like masses. Hardness 3 to 4. 
 
 HgMggSi.tOio. Magnesium oxide may be replaced by 1 to 5% of FeO. 
 Small amounts of nickel and aluminium may be present also. When strongly 
 ignited, yields water, hardens, and becomes susceptible to polish. Practically 
 infusible, fuses with great difficulty on very thin edges. Turns white. Soap- 
 stone is but slightly decomposed by salt of phosphorous, while foliated talc 
 becomes pink when treated with cobalt nitrate solution. 
 
 Talc is generally considered an alteration product of non-aluminous mag- 
 nesium minerals, such as the pyroxenes and amphiboles, and olivine. It is 
 
228 DESCRIPTIVE MINERALOGY 
 
 doubtful whether talc is ever a primary mineral. It occurs pseudomorphous 
 after many minerals, for example, after pyroxene, hornblende, enstatite, 
 tremolite, spinel, mica, scapolite, quartz, dolomite, topaz, staurolite, cyanite, 
 garnet, vesuvianite, and chrysolite. Commonly found in metamorphic rocks, 
 such as chloritic schists ; also with serpentine and dolomite. Frequently occurs 
 as talcose schist containing doubly terminated crystals of magnetite, dol- 
 omite, breunnerite, apatite, tourmaline, pyrite, and actinolite. 
 
 Foliated talc occurs at Greiner in the Zillerthal, Tyrol ; various places in 
 Switzerland, Italy, France, and Germany ; at Grafton, and elsewhere, N. H. ; 
 Smithfield, R. I. ; various places in St. Lawrence County, N. Y. The most 
 important producing locality in the United States for talc and soapstone is 
 Gouverneur, St. Lawrence County, N. Y., where talc occurs in connection 
 with limestone, and has been derived from tremolite and enstatite. The Al- 
 bemarle-Nelson County belt in Virginia, Montgomery and Northampton 
 counties, Pa., and Phillipsburg, N. J., also produce large quantities of talc 
 and soapstone annually. Other producing states are North Carolina, Geor- 
 gia, Maryland, Rhode Island, and Massachusetts. In 1908 there were mined 
 117,354 tons, valued at $1,401,222. 
 
 Talc and soapstone are used, when cut into slabs and other shapes, for 
 washtubs, sanitary appliances, laboratory tables and tanks, electrical switch- 
 boards, mantels, hearthstones, fire-brick, kiln linings, foot warmers, slate 
 pencils, crayon for marking iron, glass, and fabrics ; when ground, in the 
 manufacture of paper and dynamite, as pigment in paint, non-conductor of 
 heat, lubricant, also for polishing glass, and for dressing skins and leather. 
 It also enters into the composition of some soaps and toilet powders. Has 
 been used to a small extent as an adulterant of sugar, baking powder, and 
 flour. 
 
 
 
 Sepiolite, Meerschaum, H 4 Mg 2 Si 3 O 10 . 
 
 Crystallization unknown, sometimes thought to be monoclinic. Com- 
 pact, earthy or clayey masses. Rarely fibrous. Smooth feel. Impressed by 
 the finger nail. Hardness 2 to 2.5. Specific gravity I to 2. On account of 
 its porosity, floats on water. Adheres to the tongue. Dull luster. Shiny 
 streak. Conchoidal to uneven fracture. Opaque. White to yellowish, gray- 
 ish, reddish, or greenish in color. When moist, grayish, soapy, and quite 
 soft. 
 
 H 4 Mg,Si 3 O 10 . A variety from Utah contains 6.82% of CuO. Yields 
 much water when strongly ignited. Due to the presence of hygroscopic 
 water, more may be obtained than indicated in the formula. Fuses with dif- 
 ficulty on the thin edges to a white glass, some varieties first turn black. 
 Turns pink when treated with cobalt nitrate solution. Gelatinizes with hy- 
 drochloric acid. 
 
 Usually considered an alteration product of serpentine, or possibly of 
 
SILICATES 229 
 
 magnesite or of an impure opal containing considerable magnesium. It is 
 found principally in nodular masses in serpentine or secondary deposits at the 
 plains of Eskishehr, Asia Minor. Occurs in smaller quantities on some of 
 the islands of the Grecian Archipelago, in Morocco, Moravia, and Utah. 
 
 Meerschaum is easily carved and worked on the lathe, takes an excel- 
 lent polish, and is used extensively for pipe bowls and cigar tips. Asia Min- 
 or furnishes practically all of the meerschaum of commerce. 
 
 Garnierite, Noumeite, H,(Ni,Mg)SiO 4 . 
 
 Doubly refractive, but crystal system undetermined. Generally as com- 
 pact, earthy masses ; apparently amorphous. Easily broken. Also stalactitic 
 and reniform. Apple to emerald green in color. Dull to greasy luster. 
 Sometimes with varnish-like surfaces. Greasy feel. White to greenish 
 streak. Opaque. Conchoidal fracture. Hardness 2 to 3. Specific gravity 
 2.3 to 2.8. 
 
 The composition varies greatly, contains from 35 to 4.7% of NiO. In- 
 fusible, decrepitates, and becomes magnetic. Yields water on ignition. At- 
 tacked by acids. Reacts for nickel. 
 
 An alteration product of olivine and serpentine rocks. Associated with 
 chromite and talc, it occurs in large quantities in serpentine at Noumea, 
 New Caledonia. Is also found at Frankenstein, Silesia ; Webster, N. C. ; 
 Riddles, Douglas County, Oregon. 
 
 It is a valuable ore of nickel. 
 
 , Gymnite, H 12 Mg. t Si 3 O 16 . 
 
 Apparently amorphous masses, resembling resin or gum arabic. Contains many 
 cracks. Greasy luster. Imperfect conchoidal fracture. Translucent to transparent. 
 White to yellow, also reddish, greenish, and rarely scarlet red. Hardness 2 to 3. Spe- 
 cific gravity 2 to 2.3. 
 
 When ignited yields much water. Formula is often written Mg4Si 3 Oio+6H 2 O. 
 Decrepitates, becomes opaque, and fuses with difficulty on thin edges. Slowly decom- 
 posed by hydrochloric acid. 
 
 Occurs in serpentine at Bare Hills, Md. ; Texas, Lancaster County, Pa. ; Fleims- 
 thal, Tyrol ; Passau, Bavaria. 
 
 GENTHITE, Nickel gymnite, H 12 Mg 2 Ni 2 Si 3 O 16 . 
 
 Very similar to deweyite but contains about 30% of NiO. Compact, minutely 
 globular, reniform, or stalactitic ; also as earthy masses. Green to yellow in color. 
 Resinous luster. Conchoidal fracture. Hardness 3 to 4; may be softer. Specific 
 gravity 2.4. Translucent to opaque. Infusible. Decomposed by hydrochloric acid 
 without gelatinizing. Has been termed nickel-scpiolite. Is an alteration product of 
 serpentine. Occurs on chromite at Texas, Lancaster County, Pa., and Alt-Orsova, 
 Hungary; with serpentine at Webster, Jackson County, N. C. 
 
 SAPONITE is a silicate of magnesium and aluminium, yielding water on ignition. 
 Composition is not constant. Nodular and massive. White, gray, yellowish, reddish, 
 brown, and also greenish. Greasy luster and feel. Does not adhere to the tongue. 
 Soft, can be cut with a knife. Hardness about i. Becomes brittle when dry. Specific 
 gravity 2.7. Blackens and fuses with difficulty on thin edges. Decomposed by sul- 
 phuric acid. Occurs in serpentine at Lizard Point, Cornwall, England ; in dolerite 
 near Dunbarton and Glasgow, Scotland ; various places in Sweden. 
 
230 DESCRIPTIVE MINERALOGY 
 
 KAOLINITE GROUP 
 
 The members of this group are silicates of aluminium yielding water on 
 ignition. They correspond to the magnesian minerals, antigorite (serpen- 
 tine) and talc in chemical composition and, like them, show some resem- 
 blances to the micas. 
 
 ANTIGORITE, H 4 Mg 3 Si 2 O 9 . KAOLINITE, H 4 Al 2 Si 2 O 9 . 
 
 ( Serpentine) NONTRONITE, H 4 Fe 2 Si 2 O 9 . 
 
 TALC, H 2 Mg 3 Si 4 O 12 . PYROPHYUJTE, H 2 Al 2 Si 4 O 12 . 
 
 The three atoms of magnesium in antigorite and talc are replaced by 
 two of, aluminium having the same valency. Kaolinite is the most impor- 
 tant member of this group. 
 
 KAOLINITE, Kaolin, China Clay, H 4 Al,Si 2 O 9 . 
 
 Monoclinic, prismatic class, a : b : c = 0.5748 : I : 1-5997, P == 96 
 49'. Generally as compact, friable, or mealy clay-like masses. Rarely in 
 small scales with an hexagonal or orthorhombic outline. 
 
 Scales possess a perfect basal cleavage. Laminae are flexible but not 
 elastic. Subconchoidal to earthy fracture. Hardness i or higher. Specific 
 'gravity 2.2 to 2.6. Scales possess a pearly luster, compact masses are dull. 
 White, yellowish, reddish, bluish, greenish, or brownish in color. Scales 
 may be translucent, masses opaque. Greasy feel. White to yellowish streak. 
 Usually adheres to the tongue and becomes plastic when moistened with 
 water. Argillaceous odor. The older terms nacrite and pholerite refer to 
 certain crystalline and compact varieties. The compact variety of great com- 
 mercial importance is called kaolin or china clay. 
 
 H 4 Al 2 Si 2 O 9 . Yields water on ignition. Infusible. Partially decom- 
 posed by hydrochloric acid, completely by concentrated sulphuric acid. Turns 
 blue when treated with cobalt nitrate solution. 
 
 Kaolinite is always a secondary mineral, the result of the action of post- 
 volcanic, pneumatolytic and hydrothermal processes upon rocks containing 
 feldspar, nephelite, topaz, beryl, augite, scapolite, and other aluminium min- 
 erals. It is sometimes considered as being formed by ordinary weathering. 
 Occurs often as a pseudomorph after these minerals. May be found in ir- 
 regular beds in kaolinised granites, porphyries, and gneisses, and is then 
 mixed with quartz. Also in secondary deposits, the results of transportation 
 and deposition under water. Occurrences of the second type may be very 
 impure. Commonly noted also with ore deposits, especially those of tin, 
 lead, and zinc. Some localities are : St. Yrieix, near Limoges, France ; Corn- 
 
SIUCATES 231 
 
 wall and Devonshire, England; Meissen, Saxony. In the United States 
 kaolin is mined in Chester and Delaware counties, Pa. ; also at various places 
 in North Carolina, Connecticut, Maryland, Virginia, Ohio, and New Jer- 
 sey. North Carolina and Pennsylvania are the largest producers. 
 
 Kaolin is used in large quantities in the manufacture of china-ware, 
 porcelain, tiles, and other refractory materials. 28,649 tons of kaolin, val- 
 ued at $216,243, were mined in 1908. 
 
 NONTRONITE, H 4 Fe 2 Si 2 O 9 . 
 
 Monoclinic. Compact massive, earthy, and apparently amorphous. Soft. Spe- 
 cific gravity 2. Often with a greasy feel. Yellowish green to green in color. Dull 
 luster. Uneven fracture. Opaque. Infusible, changes color, and becomes magnetic. 
 Completely decomposed by acids and potassium hydroxide. Occurs with limonite at 
 Nontron, France; St. Andreasberg and Tirschenreuth, Saxony. Choropal is green 
 nontronite mixed with opal. 
 
 , Pencil Stone, H 2 Al 2 Si 4 O 12 . 
 
 Orthorhombic, but may be monoclinic. Columnar, radial, or stellate aggregates 
 of foliae or fibres; also granular to compact or cryptocrystalline. A compact variety 
 is called agalmatolite or pencil stone. 
 
 Perfect cleavage parallel to the length of the fibers. Laminae flexible, but not 
 elastic. Greasy feel. Hardness i. Specific gravity 2.8 to 2.9. Pearly luster. Trans- 
 lucent. Apple green, white, brownish, or yellowish in color. Looks like talc. 
 
 H 2 Al 2 Si4Oi2. Exfoliates and yields water at a high temperature. Turns white 
 and fuses on the edges. Turns blue when treated with cobalt nitrate solution. Par- 
 tially decomposed by sulphuric acid. Alters to kaolinite. 
 
 Occurs in schistose rocks in the Ural mountains, Sweden, and Brazil. In the 
 United States pyrophyllite occurs at Graves Mountain, Ga. ; Deep River, N. C. ; Ches- 
 terfield, S. C. ; Mahanoy City, Schuylkill County, Pa. 
 
 Compact pyrophyllite is used for slate pencils, agalmatolite for ornamental carv- 
 ings. 
 
 NEPHELITE GROUP 
 
 The members of this group are rather complex silicates of aluminium 
 and the alkalies, and although they are not isomorphous, their chemical com- 
 position is similar. 
 
 NEPHELITE, (Na,K) 8 Al 8 Si 9 O G4 . 
 
 Cancrinite, H,, ( Na,,Ca ) 4 ( NaCO 3 ) , Al 8 Si 9 O 30 . 
 
 DAVYNE, ( Na 2 ,Ca,K 2 ) 16 ( NaCO 3 ,NaSO 4 ,Cl) ^Al^Si^O^. 
 
 Nephelite is the most common mineral of the group. It crystallizes in 
 the hexagonal pyramidal class, while cancrinite and davyne have both been 
 referred to the dihexagonal bipyramidal class. 
 
232 DESCRIPTIVE; MINERALOGY 
 
 NEPHELITE, Nepheline, Elaeolite, (Na,K) 8 Al 8 Si 9 O 34 . 
 
 Hexagonal, pyramidal class, a : c=i : 0.8383. Crystals are short 
 prismatic or tabular, and apparently holohedral. Hemimorphism is revealed 
 by etch figures. The forms generally observed are the prisms of the first 
 and second orders, the corresponding, apparently holohedral, bipyramids, 
 and the basal pinacoids. Occurs also compact, massive, and as disseminated 
 grains. 
 
 Imperfect prismatic and basal cleavages. Conchoidal to uneven frac- 
 tures. Brittle. Characteristic greasy luster on cleavages, elsewhere vitreous. 
 Hardness 5 to 6. Specific gravity 2.55 to 2.65. Colorless, white, yellowish, 
 greenish, gray, brownish red, or red in color. Uncolored streak. 
 
 There are two varieties : 
 
 Nephelite proper. Colorless, white, or gray, glassy occurrences, show- 
 ing in many instances definite crystal outline. Common in the more recent 
 eruptive rocks. Transparent to translucent. 
 
 . Elaeolite. Massive and granular, rarely with a definite outline. More 
 highly colored, green, red, gray, brown, or blue. Cloudy or opaque. 
 Greasy luster. Contains many microscopic, needle-like inclusions. Common 
 and present often in considerable quantities in the older plutonic rocks, such 
 as syenites, phonolites, and basalts. Nepheline-syenite contains a compara- 
 tively large amount of elaeolite. 
 
 (Na,K) 8 Al 8 Si O 34 . The composition varies greatly. The best analyses 
 point to the formula given, although it is often thought that the composition 
 ought to be expressed by the simple formula NaAlSiO 4 , the composition of 
 synthetic soda-nephelite. Potassium is always present as follows : 
 Na : K= (3 to 5) : i. Traces of chlorine are always noted. Hucryptite 
 is lithium-nephelite, while kaliophilite or phacelite are terms applied to po- 
 tassium-nephelite. Gelatinizes easily and rapidly with hydrochloric acid ; on 
 evaporation to dryness cubes of NaCl form. Fuses quite easily to a color- 
 less glass. Alters easily and forms hydronephelite, sodalite, muscovite, can- 
 crinite, analcite, kaolinite, or garnet. 
 
 Nephelite is commonly associated with feldspar, cancrinite, biotite, so- 
 dalite, and zircon. May occur pseudomorphous after leucite. Some localities 
 are: Mount Vesuvius; Katzenbuckel, Baden; Laacher See, Rhenish Prussia; 
 Sweden ; Portugal ; Ural Mountains ; Brazil ; Montreal, and Dungannon 
 township, Ontario, Canada. In the United States at Litchfield, Me. ; Salem, 
 Mass. ; Beemersville, N. J. ; Austin, Tex. ; Magnet Cove, Ark. 
 
SILICATES 233 
 
 Cancrinite, H. ( Na 2 ,Ca ) 4 ( NaCO 3 ) 2 Al 8 Si 9 O 36 . 
 
 Hexagonal, dihexagonal bipyramidal class (?). a : c=i : 0.4409. 
 Crystals are columnar, but rare. Usually in compact, lamellar or columnar 
 masses. 
 
 Perfect prismatic leavage. Uneven fracture. Pearly luster on cleav- 
 ages, elsewhere vitreous to greasy. Transparent to translucent. Usually 
 colored, lemon to brownish yellow, reddish, gray, green, or white; more 
 rarely blue or colorless. Uncolored streak. Hardness 5 to 6. Specific grav- 
 ity 2.45. Fuses easily with intumescence and loss of color to a white blebby 
 glass. Upon ignition turns white and yields water. Effervesces with hydro- 
 chloric acid, and gelatinizes on heating. 
 
 Cancrinite may be a primary constituent of igneous rocks, although in 
 most cases it is a secondary formation, the result of the alteration of nephel- 
 ite. It occurs in nephelite-syenites at Barkevik, Norway ; Miask, Ural Moun- 
 tains ; Finland ; Sarna, Sweden ; Ditro, Hungary ; Montreal and Beloeil, 
 Province of Quebec, Canada; Litchfield and Gardiner, Me. It is usually as- 
 sociated with elaeolite, sodalite, feldspar, titanite, and apatite. 
 
 DAVYNE, Microsomite, (Na 2 ,Ca,K 2 ) lc (NaCO 3 ,NaSO 4 ,Cl) 11 Al 25 Si 24 O 96 . 
 
 Hexagonal, dihexagonal bipyramidal class, a : c = i : 0.4183. Slender columnar 
 to needle-like crystals. Milky vitreous to pearly luster. Transparent to opaque. Col- 
 orless, white, or wine yellow. Perfect prismatic cleavage. Conchoidal to uneven frac- 
 ture. Hardness 5 to 6. Specific gravity 2.4. Easily fusible with intumescence to a 
 white blebby glass. Fresh crystals do not yield water on ignition. Easily soluble in 
 acids with a faint, but distinct odor of hydrogen sulphide. Occurs in the cavities of 
 the lavas and as a sublimation product on Mount Vesuvius. 
 
 SODALITE GROUP 
 
 The members of this group crystallize in the cubic system, and undoubt- 
 edly in the hextetrahedral class, based upon observations on sodalite. Chem- 
 ically, they are acid orthosilicates of sodium, aluminium, and calcium, and 
 contain radicals with chlorine and sulphur, which are not often present in 
 silicates. 
 
 Sodalite, Na,Al 2 (AlCl) (SiO 4 ) 3 . 
 
 NOSEUTE, Na..Al 2 [Al(NaS0 4 )] (SiO 4 ) 3 . 
 
 HAUYNITE, Na CaAl [Al(NaSO 4 )] (SiO 4 ) 8 . 
 
 Lazurite, (Na 2 ,Ca),Al 2 [Al(NaSO 4 ,NaS 3 ,Cl)] (SiO 4 ) 3 . 
 
 These are closely related in many ways to those of the nephelite group. 
 Brogger has shown that there is also a similarity to the garnets, see page 
 208. 
 
 Sodalite, Na 4 Al 2 (AlCl) (SiO 4 ) 8 . 
 
 Cubic, hextetrahedral class. Rhombic dodecahedral habit is common. 
 The forms generally observed are the rhombic dodecahedron, cube, octahe- 
 dron, and the tetragonal trisoctahedron (m = 2). Crystals are apparently 
 
234 DESCRIPTIVE MINERALOGY 
 
 holohedral in development, but the lower symmetry is revealed by etch fig- 
 ures. Twins, according to the spinel law, are generally elongated parallel 
 to a trigonal axis of symmetry. Occurs for the most part massive, in grains, 
 cleavable aggregates, and concentric nodules. 
 
 Distinct dodecahedral cleavage. Uneven to conchoidal fracture. Brit- 
 tle. Hardness 5 to 6. Specific gravity 2.2 to 2.4. Vitreous luster on crystal 
 faces, greasy on cleavages. Generally translucent, but may be transparent 
 to opaque. Colorless, white, gray, light to dark blue, greenish, or reddish. 
 White streak. 
 
 Na 4 Al 2 (AlCl) (SiO 4 ) 3 . The formula is sometimes written 3 Na 2 Al 2 Si 2 O 8 
 -f- 2 NaCl. Colored varieties turn white when heated. Fuses with intum- 
 escence to a colorless glass. NaCl may be extracted by digesting the finely 
 powdered mineral with water. Gelatinizes with hydrochloric acid. May con- 
 tain many microscopic inclusions. Is sometimes an alteration product of 
 nephelite. 
 
 Occurs commonly associated with elaeolite and cancrinite. Some local- 
 ities are : Ditro, Transylvania ; Miask, Ural Mountains ; Mount Vesuvius ; 
 Serra de Monchique, Portugal ; Langesundfiord, Norway ; Montreal and 
 Beloeil, Quebec, and Dungannon, Ontario, Canada ; Litchfield, Me. ; Salem, 
 Mass. ; Crazy Mountains and elsewhere, Mont. 
 
 NOSEUTE, Nosean, Na 4 Al 2 [Al(NaSO 4 )] (SiO 4 ) 3 . 
 
 Cubic. Dodecahedral crystals and irregular grains. Very similar to haiiynite, 
 differing from it principally by the absence of calcium. Gray, bluish, or red. Vitreous 
 luster. Hardness 5 to 6. Specific gravity 2.25. Occurs only in volcanic rocks, espec- 
 ially phonolites. Thus, in the Laacher See district, near the Rhine, Germany; and 
 Hohentwiel, Baden; Canary and Cape Verde Islands. 
 
 HAUYNITE, Haiiyne, Na 2 CaAl 2 [Ai(NaSO 4 )] (SiO 4 ) 3 . 
 
 Cubic. Sometimes in dodecahedral or octahedral crystals. The faces may ap- 
 pear to be more or less fused. Penetration and polysynthetic twins according to the 
 spinel law. Commonly in rounded grains. 
 
 Distinct dodecahedral cleavage. Conchoidal to uneven fracture. Hardness 5 to 
 6. Specific gravity 2.3 to 2.5. Vitreous to greasy luster. Translucent to opaque. 
 Mostly blue in color; also green, red, or black; rarely colorless. Bluish to colorless 
 streak. 
 
 Na 2 CaAl 2 [Al(NaSO4)](SiO 4 ) 3 . The formula is also written 3(Na 2 Ca)Al 2 Si 2 O 8 
 -(-2(Na 2 ,Ca)SO4. Fuses with difficulty to a white glass. Reacts for sulphur. De- 
 composed by hydrochloric acid, yielding gelatinous silica. 
 
 Nephelite and leucite are common associates. It ocurs only in volcanic rocks, 
 especially phonolites and related rocks. Some localities are : the lavas of Mount 
 Vesuvius and vicinity; in the phonolite of the Hohentwiel, Baden; in the Eifel, west 
 of the Rhine, Germany. 
 
 Lazurite, Lasurite, Lapis-Lazuli, Native Ultramarine, 
 
 (Na 2 ,Ca) 2 AlJAl(NaS0 4 ,NaS 3 ,Cl)](Si0 4 ) 3 . 
 
 Cubic. Dodecahedral or octahedral crystals are rare. Usually as irreg- 
 ular grains, or massive containing disseminated pyrite. 
 
 Imperfect dodecahedral cleavage. Uneven fracture. Hardness 5 to 
 
SIUCATES 235 
 
 5.5. Specific gravity 2.4. Vitreous to greasy luster. Deep to azure blue in 
 color, sometimes violet to greenish blue. White streak. Opaque to trans- 
 lucent. 
 
 The mineral is essentially an isomorphous mixture, consisting of about 
 75% of haiiynite, 9% of sodalite, and 16% of natural ultramarine with the 
 composition 3Na 2 Al 2 Si 2 O s -}- 2Na 2 S 3 . Fuses easily to a white blebby glass. 
 Gelatinizes with HC1, loses color, and evolves an odor of hydrogen sulphide. 
 
 Lazulite is a contact mineral and occurs .in crystalline limestones. The 
 principal localities are in central Asia at Badakschau and the southern end 
 of Lake Baikal; occurs also in Chile and in the ejected masses on Mount 
 Vesuvius. 
 
 Highly valued for ornaments, mosaics, and vases. Formerly, it was used 
 as a pigment in oil painting. 
 
 Several comparatively rare silicates of lead, barium, and yttrium may be 
 placed here. 
 
 GANOM ALITE, Pb 4 (PbOH ) ,Ca 4 ( Si,O 7 ) 3 . 
 
 Tetragonal, a : c = i : 0.35, approximately. Long, prismatic crystals; but us- 
 ually massive and granular, resembling granular tephorite. Distinct basal and pris- 
 matic cleavages. Greasy vitreous luster. Colorless to gray, oxidizes on exposure and 
 turns white and dull. Very brittle. Hardness 3 to 4. Specific gravity 5.74. Reddish 
 streak. Fuses in the candle flame. Soluble in nitric acid. Found at Langban and 
 Jakobsberg, Sweden. 
 
 NASONITE, PbiCPbCl^Ca^SiaO?^. Very similar to ganomalite. Contains about 
 3.5% of chlorine replacing the hydroxyl. Compact. White. Greasy luster. Hard- 
 ness 4. Specific gravity 5.425. Occurs at Franklin Furnace, N. J. 
 
 E, Pb 3 Si 2 O T . 
 
 Hexagonal, a : c = I : 0.4863. Crystals are rhombohedral and tabular in habit; 
 also in curved foliated masses. Distinct basal cleavage. Silver white color, often 
 tarnished. Fuses in the flame of a candle. Easily decomposed by acids. Hardness 3. 
 Specific gravity 6.72. Found in the Hartsig mine, Pajsberg, Sweden. 
 
 HARDYSTONITE, Ca 2 ZnSi 2 O 7 . 
 
 Tetragonal. Granular masses with basal and prismatic cleavages. Hardness 3 
 to 4. Specific gravity 3.4. Color white. Vitreous luster. Fuses with difficulty to a 
 cloudy glass, coloring the flame red. Reacts for zinc. Gelatinizes with hydrochloric 
 acid. Occurs with willemite, rhodonite, and franklinite in the North Hill mine, Frank- 
 lin Furnace, N. J. 
 
 BARYUTE, Ba 4 Al 4 Si 7 O 24 . 
 
 Orthorhombic (?). Compact aggregates; prismatic crystals are rare. Hardness 7. 
 Specific gravity 4. Greasy luster. Colorless. Semi-transparent. Infusible. Not 
 acted upon by acids. Occurs as a metamorphic mineral in crystalline limestone at 
 Langban, Sweden. 
 
236 DESCRIPTIVE; MINERALOGY 
 
 lolite, Cordierite, Dichroite, (Mg,Fe) 4 Al 8 (OH) 2 (Si 2 O 7 ) 5 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.5870 : i : 0.5585. 
 Crystals are usually short prismatic with six or twelve sides, hence, pseudo- 
 hexagonal. The prism angle is 119 10'. The faces are often dull and the 
 edges rounded. The common forms are the unit prism, brachyprism (n= 3). 
 and the three pinacoids. Penetration trillings and sixlings with the twinning 
 plane parallel to the unit prism are sometimes observed. Occurs generally 
 in irregular and rounded masses, resembling quartz. 
 
 Distinct brachypinacoidal cleavage, indistinct parallel to the other pin- 
 acoids. Conchoidal to uneven fracture. Hardness 7 to 7.5. Specific gravity 
 2.6 to 2.7. Vitreous to greasy luster. Transparent to subtransparent. Light 
 to dark smoky blue ; also gray, colorless, yellowish, green, brown, or violet. 
 White streak. Very strong pleochroism which is sometimes easily noted, 
 violet blue for vigrations parallel to the b axis, yellowish parallel to c, and 
 grayish blue parallel to a. 
 
 (Mg,Fe) 4 Al s (OH) 2 (Si 2 O 7 ) 5 . The iron is trivalent Some calcium re- 
 places magnesium. Fresh material yields water on ignition. Fuses with 
 difficulty on the thin edges. Slightly acted on by acids. lolite alters easily, 
 taking up water and the alkalies, and losing SiO 2 and MgO. The end pro- 
 ducts are the micas and chlorites. Many of the intermediate substances 
 formed have received such distinctive names as: chlorophyllite, praseolite, 
 aspasiolite, gigantolite, . fahlunite, pinite, pyrargillite, bonsdorffite, and es- 
 markite. 
 
 lolite is found chiefly in gneiss and other crystalline schists and in con- 
 tact metamorphic zones. Occurs also in granite, andesite, and dacite ; also 
 in rounded particles in secondary deposits. The common associates are 
 quartz, orthoclase, albite, tourmaline, pyrrhotite, chalcopyrite, hornblende, 
 andalusite, sillimanite, staurolite, spinel, garnet, zircon, and beryl. Some of 
 the principal localities are : Bodenmais, Bavaria ; Falun, Sweden ; Krageroe, 
 Tvedestrand, and Bamle, Norway ; Island of Elba ; Laacher See, Rhenish 
 Prussia ; Cabo de Gato, Spain ; Ceylon ; Haddam, Conn. ; Brimfield, Mass. ; 
 Richmond, N. H. 
 
 Transparent varieties from Ceylon are sometimes used for gem pur- 
 pose. 
 
 MELILITE GROUP 
 
 According to Vogt, melilite is an isomorphous mixture of the two sili- 
 cates akermanite, which does not occur in nature but is found practically pure 
 in basic calcereous slags, and gehlenite. The latter occurs as a mineral. The 
 composition of these silicates is as follows : 
 
 AKERMANITE, Ca 3 CaSiSi 2 O 10 . 
 
 GEHLENITE, Ca 3 AlAlSi 2 O 10 . 
 
 In melilite these two silicates occur in about equal proportions, so that 
 the composition may be expressed by merging the two formulas. 
 
SILICATES 237 
 
 
 
 E;, Humboldtilite, Sommervillite, Ca 7 Al 2 Si 4 O 20 . 
 
 Tetragonal, ditetragonal bipyramidal class, a : c = i : 0.4548. Small tabular, 
 short prismatic, and rarely long columnar or needle-like crystals. The very common 
 forms are the basal pinacoid, and the prism of the second order. The prism and bi- 
 pyramid of the first order, and the ditetragonal prism, n = 3, are also observed. Oc- 
 curs also in radial aggregates. 
 
 Distinct basal cleavage. Hardness 5 to 5.5. Specific gravity 2.9 to 3.1. Con- 
 choidal to uneven fracture. Greasy luster on fracture surfaces, elsewhere vitreous. 
 Yellow, brown, greenish, gray, and white in color. Translucent. 
 
 Is an isomorphous mixture, see introductory statement to this group. Some of 
 the calcium may be replaced by magnesium and sodium, the aluminium by trivalent 
 iron. Fuses to a yellowish or greenish glass. Gelatinizes with hydrochloric acid. 
 
 Occurs in basic eruptive rocks, especially those containing augite, nephelite, and 
 leucite. Occurs in the lavas of Mount Vesuvius; Herchenberg, Rhenish Prussia; 
 Lobau, Saxony; Finland; Mannheim and Syracuse, N. Y. ; Uvalde County, Texas. 
 
 GEHLENITE, Ca 3 Al 2 Si 2 O 10 . 
 
 Tetragonal, ditetragonal bipyramidal class, a : c = I : 0.4006. Small, dissem- 
 inated, short prismatic, or thick tabular crystals ; also in loose aggregates. Distinct 
 basal cleavage. Hardness 5.5 to 6. Specific gravity 3. Greasy luster. Translucent 
 to opaque. Greenish gray to green or brown. Calcium and aluminium may be par- 
 tially replaced by magnesium, and by ferrous and ferric iron. Fuses with difficulty. Gel- 
 atinizes easily with acids. Occurs in the contact zone in limestone at Monzoni and 
 Predazzo, Tyrol, and artificially in slags. 
 
 ASTROPHYUWTE, (K,Na,H) 4 (Fe,Mn),(Si,Ti) 5 O 16 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 1.0098 : I : 4.7566. Crystals 
 often show apparently monoclinic or triclinic habits. Tabular, long radial, or bladed 
 crystals; also in stellate groups. Basal cleavage. Brittle. Hardness 3 to 3.5. Specific 
 gravity 3.3 to 3.4. Translucent. Distinct pleochroism. Vitreous to metallic luster. 
 Bronze to gold yellow in color. 
 
 May contain small amounts of ZrO, CaO, or MgO. Fuses easily to a black glass. 
 Is oftentimes placed with the pyroxenes or chlorites. Occurs in elaeolite syenite in 
 the Langesund fiord, near Brevik, Norway; Kangerdluarsuk and Narsarsuk, Green- 
 land; Pike's Peak district, Colo. 
 
 PEROVSKITE-ILMENITE GROUP 
 
 The members of this group are metatitanates of calcium, magnesium, 
 manganese, and iron. From the chemical standpoint they are very similar, 
 but they do not all crystallize in the same system. 
 
238 DESCRIPTIVE MINERALOGY 
 
 Perovskite, CaTiO 3 . Pseudo-cubic, probably orthorhombic. 
 
 a- : c 
 
 GEIKIELITE, MgTiO 3 . Hexagonal, i : ? 
 
 PYROPHANITE, MnTiO 3 . Hexagonal, i : 1.369 
 
 Ilmenite, FeTiO 3 , Hexagonal, i : 1.385 
 
 Ilmenite is the most important member of the group and, on account 
 of its similarity, chemically and crystallographically, with hematite, it is 
 sometimes regarded as an oxide. 
 
 Hematite, Fe = Os ^= Fe, Ditrigonal Scalenohedal Class 
 Ilmenite, Fe = Os ^ Ti, Trigonal Rhombohedal Class 
 
 Penfield and Foote have, however, shown that ilmenite is to be consid- 
 ered a metatitanate. The difference in the symmetry of the two formulas 
 finds expression also in the crystals, those of ilmenite being of a lower 
 grade. 
 
 Perovskite, Perowskite, CaTiO 3 . 
 
 Crystals are pseudo-cubical in habit, but are made up of polysynthetic 
 twin lamellae. These are biaxial and probably orthorhombic. The relation 
 between the external form and internal structure is somewhat similar to that 
 of boracite and leucite, with the exception, however, that the lamellae do not 
 disappear on heating. The forms commonly observed are the cube, octahe- 
 dron, and rhombic dodecahedron ; more rarely various tetragonal trisoctahe- 
 drons, tetrahexahedrons, and hexoctahedrons. The cube faces are often 
 striated parallel to the edges, as in the case of pyrite, see page 39. Crystals 
 are often highly modified. F,tch figures indicate a lower grade of symmetry 
 than that of the cubic system. Also in reniform masses or rounded grains. 
 
 Fairly distinct cubical cleavage. Uneven to subconchoidal fracture. 
 Brittle. Hardness 5 to 6. Specific gravity 3.95 to 4.1. Adamantine to me- 
 tallic luster. Transparent to opaque. Color black, grayish black, brownish 
 black, reddish brown, or various shades of yellow. Colorless to gray streak. 
 
 CaTiO 3 . From 2 to 6% of FeO may replace CaO. Knopite is a variety 
 from Alno, Sweden, and contains from 6 to 7% of the cerium earths. In- 
 fusible. Scarcely attacked by hydrochloric acid ; decomposed by hot sul- 
 phuric acid. Alters to ilmenite and magnetite. 
 
 Microscopic crystals occur in metamorphic rocks, such as talc and chlor- 
 ite schists, but are not common. Rather common as a microscopic accessory 
 mineral in young basic eruptive rocks, especially those containing melilite, 
 leucite, and nephelite. Some localities are Achmatow mine, Zlatoust, Ural 
 Mountains ; Zermatt, Switzerland ; Val Malenco, Italy ; Pfitsch, Tyrol ; near 
 Montreal, Canada ; Syracuse, N. Y. ; Magnet Cove,' Ark. ; Elliott County, 
 Kentucky. 
 
 GEIKIEUTE, MgTiO 3 . 
 
 Hexagonal, perhaps trigonal rhombohedral class. Very rarely in small rhombo- 
 hedral crystals, more commonly as rounded or irregular grains. Basal and rhombo- 
 hedral cleavages. Bluish to brownish black in color, in transmitted light red. Metallic 
 
SILICATES 239 
 
 luster. Black streak. Hardness 6. Specific gravity 4. Generally contains iron re- 
 placing some of the magnesium. Occurs in the precious stone placers of Rakwana, 
 Ceylon. 
 
 PYROPHANITE, MnTiO 3 . 
 
 Hexagonal, probably trigonal rhombohedral class. Occurs in small tabular crys- 
 tals with a blood red color and vitreous to submetallic luster in the Harstig mine, 
 Sweden. Hardness 5. Specific gravity 4.5. 
 
 Ilmenite, Menaccanite, Titanic Iron Ore, Titaniferous Iron, FeTiO 3 . 
 
 Hexagonal, trigonal rhombohedral class, a : c = I : 1 . 3846. Crystals 
 are tabular or rhombohedral in habit, and resemble those of hematite, page 
 86, but show rhombohedrons of the second and third orders. Crystals may 
 be highly modified. Thirty-two forms have been recorded. There are two 
 twinning laws, parallel to the basal pinacoid and the unit rhombohedron of 
 the first order. Polysynthetic twinning is rather common parallel to the 
 rhombohedron. Occurs also in thin plates, granular and compact masses, 
 and as disseminated grains and sand. 
 
 No cleavage. Basal and rhombohedral partings. Conchoidal to uneven 
 fracture. Submetallic to metallic luster, especially on fracture surfaces ; 
 otherwise dull. Opaque, thin plates are brown in transmitted light. 
 Iron black to brownish black in color. Black to brownish red streak. Slight- 
 ly magnetic, greatly increased by heating. Hardness 5 to 6. Specific grav- 
 ity 4.3 to 5.5, increasing with the percentage of Fe 2 O 3 present. 
 
 FeTiO 3 . Magnesium may replace some of the iron. Picrotitanite, or 
 better termed picroilmenite, is a variety containing as high as 16% of MgO. 
 Considerable Fe 2 O 3 is sometimes present and such varieties, zuashingtomte 
 and hystatite, pass gradually with an increase in trivalent iron into hematite. 
 The proportion of Fe 2 O 3 to FeTiO 3 may be expressed by the ratio, Fe 2 O 3 : 
 FeTiO 3 = (i to 3) : (10 to i). Thin edges are slightly fused in the reduc- 
 ing flame, infusible in the oxidizing flame. Fused with sodium carbonate and 
 treated with hydrochloric acid and tin foil, it reacts for titanium, the solution 
 turning blue or violet. Decomposed by fusing with potassium bisulphate. 
 Alters to a white, opaque titanite, called leucoxene or better titanomorplwte, 
 or to anatase, perovskite, rutile, limonite, or ferruginous carbonates. 
 
 Occurs widely distributed as an associate of hematite and magnetite. 
 As an accessory mineral it is common in many igneous and metamorphic 
 rocks, such as, granite, syenite, diorite, diabase, gneiss, mica schist, and so 
 forth. In the fissures in these rocks, it is often found in large mases. As a 
 coloring material it is sometimes present in microscopic particles, especially 
 in labradorite and hypersthene. Also found in considerable quantities in 
 black sands. 
 
 Some localities are : Ekersund, Snarum, Kragero, Tvedestrand, and 
 Hittero, Norway ; various places in Sweden ; St. Gotthard district and Bin- 
 nenthal, Switzerland ; Zillerthal and elsewhere, Tyrol ; Charlevoix, Montmo- 
 rency, Beauce, and Montcalm counties, Quebec, Canada ; various places in 
 Orange County, especially Warwick, Amity, and Monroe, Conn. ; South Roy- 
 
240 DESCRIPTIVE MINERALOGY 
 
 alston and Chester, Mass. ; Adamstown, Pa. ; Magnet Cove, Ark. ; Troy, Vt. 
 It is used in the preparation of linings for puddling furnaces. On ac- 
 count of the difficulty in reducing it, ilmenite is not used to any extent as an 
 ore of iron. 
 
 PYROXENE GROUP 
 
 This group consists of metasilicates of calcium, magnesium, iron, alumin- 
 ium, sodium, lithium, manganese, and zinc, corresponding to the general 
 formula M" 2 (SiO 3 ) 2 . Although these minerals crystallize in three different 
 systems orthorhombic, monoclinic, and triclinic, they form a well defined 
 isomorphous group. Their elements of crystallization are very similar. All 
 members are characterized by prism angles and cleavages of about 87 and 
 93. Orthorhombic pyroxenes generally contain no calcium and little or no 
 aluminium. The monoclinic members usually have considerable calcium 
 and may, or may not, contain aluminium and the alkalies. In the triclinic 
 series, manganese is an important constituent. 
 
 i. ORTHORHOMBIC SERIES 
 (Bipyramidal Class} 
 
 a : b : c 
 Enstatite, Mg 2 (SiO 3 ),. 
 Bronzite, (Mg,Fe) 2 (SiO 3 ) 2 . 
 Hypersthene, (Fe,Mg) 2 (SiO 3 ) 2 . 1-0295 : J ' 0.5868 
 
 2. MONOCLINIC SERIES 
 (Prismatic Class) 
 
 (a) Non-aluminous varieties: 
 
 a : b : c 
 
 DIOPSIDE, CaMg(SiO 3 ) 2 . 1.0913 :i =0.5895, 105 51' 
 
 (Malacolite, salite, diallage, etc.) 
 
 HEDENBERGITE,. CaFe(SiO 3 ) 2 . 1.0912 : i 10.5843, 105 25' 
 
 , (Ca,Mg) (Fe,Mn) (SiO 3 ) 2 . 
 
 1.0988 : i : 0.5953, 105 25' 
 , (Ca,Mn) (Mg,Fe,Zn) (SiO 3 ) 2 . ? 
 
 Wollastonite, Ca 2 (SiO 3 ) 2 . J-OSS 1 i : 0.9676, 95 30' 
 
 (b) Aluminous varieties: 
 
 r(Mg,Fe)Ca(Si0 3 )(Si0 3 ). 
 
 AUGITE, J (Mg,Fe)Al(AlO 3 )(SiO 3 ). 1.0921 : i : 0.5893, 105 40' 
 [(Mg,Fe)Fe(Fe0 3 )(Si0 3 ). 
 
 (Fassaite, leucaugite, etc.) 
 
SIUCATES 241 
 
 (c) Varieties containing alkalies: 
 
 a : b : c 
 
 Pectolite, (Ca,Na 2 ) 2 (SiO 3 ) 2 . 1.1140 : i : 0.9864, 95 20' 
 
 JADEITE, NaAl(SiO 3 ) 2 . ? 
 
 Spodumene, LiAl(SiO 3 ) 2 . 1.1238 : i : 0.6355, 110 20' 
 
 ACMITE, NaFe(SiO 3 ) 2 . 1.0996 : i : 0.6012, 106 49' 
 (Aegirite) 
 
 3. TRICLINIC SERIES 
 (Pinacoidal Class) 
 
 a : b : c 
 Rhodonite, Mn 2 (SiO 3 ) 2 . 1.0728 : i : 0.6213 
 
 a =103 18', /? = 108 44', 7 = 81 39' 
 
 FOWT.ERITIV, (Mn,Fe,Ca,Zn,Mg) 2 (SiO 3 ) 2 . 1.0780 : i : 0.6263 
 
 a=io 3 39', = I0 8 4 8.5', 7 = 81 55' 
 
 ( (Ca,Fe,Mn) 2 (Si0 3 ) 2 . 
 BABINGTONITE, Ji f csr\\ 1.0691 : i 10.6308 
 
 J 2 . 
 
 a =I0 4 21^', =108 31', y = 8334 / 
 
 The members of the pyroxene group are important rock minerals. They 
 are rather closely related, chemically and crystallographically, to the miner- 
 als of the amphibole group, page 250. This relationship will be discussed 
 under the amphiboles. 
 
 ORTHORHOMBIC PYROXENES 
 Enstatite, Mg 2 (SiO 3 ) 2 . 
 
 Orthorhombic, bipyramidal class, a : b : c= 1.0308 : i : 0.5885. 
 Distinct crystals are rare. They are prismatic in habit and usually consist 
 of a combination of the unit prism, brachy- and macropinacoids, and brachy- 
 domes. Prism angle is about 92. Generally found in fibrous, lamellar, or 
 compact masses. 
 
 Distinct prismatic and indistinct brachy-* and macropinacoidal cleavages. 
 Brittle. Hardness 5.5. Specific gravity 3.1 10-3.3. Translucent to opaque. 
 Silky or metallic luster, pearly on cleavages. Grayish white, yellowish, light 
 to olive green, and brownish in color. Grayish or uncolored streak. 
 
 Mg 2 (SiO 3 ) 2 . May contain a small amount of iron, usually not over 
 5% of FeO. Slightly fusible on thin edges. Insoluble in acids. Alters to 
 bastite a fibrous aggregate with the composition of serpentine, talc, and 
 serpentine. 
 
 Enstatite is an essential constituent of certain pyroxenites, peridotites, 
 norites, and the serpentines derived from them. Occurs in large crystals in 
 an apatite vein at Kjorrestad, near Bamle, Norway; Aloysthal, Moravia; 
 Kupferberg, Bavaria ; in the diamondiferous blue ground of South Africa ; 
 Tilly Foster mine, Putnam County, and at Edwards, N. Y. ; in the meteor- 
 ite from Bishopville, S. C. 
 
242 DESCRIPTIVE MINERALOGY 
 
 Bronzite, (Mg,Fe) 2 (SiO 3 ) 2 . 
 
 Orthorhombic, bipyramidal class. Same elements of crystallization as 
 for enstatite. Distinct crystals have been observed only in the meteorite 
 from Breitenbach, Bohemia. Prism angle is 91 44'. Occurs in compact, 
 crystalline, fibrous, or granular masses. 
 
 Distinct prismatic cleavage. Pronounced parting parallel to the macro- 
 pinacoid producing fibrous or irregular wavy surfaces with a chatoyant 
 bronzy luster. Hardness 5 to 6. Specific gravity 3.2 to 3.5. Translucent 
 to opaque. Silky metallic, bronzy luster. Darker in color than enstatite, 
 usually brown, green, or yellowish. Uncolored streak. 
 
 (Mg,Fe) 2 (SiO 3 ) 2 . May be interpreted as an isomorphous mixture of 
 MgSiO 3 and FeSiO 3 . FeO varies between 5 and 16%. May contain some 
 A1 O 3 and Fe 2 O 3 . Sometimes considered a ferruginous enstatite. Fuses 
 with great difficulty. Insoluble in acids, except hydrofluoric. 
 
 Occurrences the same as for enstatite. 
 
 Hypersthene, (Fe,Mg) 2 (SiO 3 ) 2 . 
 
 Orthorhombic, bipyramidal class, a : b : c= 1.0295 : I : 0.5868. Oc- 
 curs rarely in small, well developed, or in large indistinct crystals. Usually 
 in granular and foliated aggregates, or in cleavage masses. 
 
 Perfect brachypinacoidal, and indistinct prismatic and macropinacoidal 
 cleavages. Uneven fracture. Brittle. Hardness 5 to 6. Specific gravity 
 3-3 to 3.5. Translucent to opaque. Color black, brownish black, or green. 
 Pearly to metalloidal luster. A copper red iridescence is often to be noted 
 on the macropinacoid, due to the occurrence of microscopic, tabular inclu- 
 sions. These inclusions may be ilmenite, brookite, goethite, or hematite. 
 
 (Fe,Mg) 2 (SiO 3 ) 2 . Similar to bronzite in composition, but contains 
 more iron than magnesium; 15 to 34% FeO, n to 22% MgO. As much 
 as 10% A1 2 O 3 may be present, also varying amounts of Fe 2 O 3 , CaO, or 
 MnO. Fuses more readily than bronzite, and forms a black magnetic mass. 
 Slightly acted upon by acids. 
 
 Hypersthene occurs in many igneous rocks, such as gabbros, norites, 
 andesites, and peridotites. It is. found also in some meteorites. It is com- 
 monly associated with a plagioclase feldspar, especially labradorite. Occurs 
 on St. Paul's Island off the coast of Labrador ; Laacher See, Rhenish Prus- 
 sia ; Farsund, Norway ; Greenland ; Isle of Skye, Scotland ; Mount Shasta, 
 Cal. ; Buffalo Peaks, Colo. ; along the Hudson River and in the Adirondack 
 Mountains, N. Y. 
 
 On account of the metalloidal iridescence or schiller, hypersthene is 
 smoetimes used in jewelry. 
 
SILICATES 
 
 243 
 
 MONOCLINIC PYROXENES 
 (a) Non-aluminous varieties. 
 
 DIOPSIDE, CaMg(SiO 3 ) 2 . 
 
 Monoclinic, prismatic class, a : b : c= 1.0913 : I : 0.5895, (3= 105 
 51'. Crystals are generally short and thick, and nearly square or octagonal 
 in outline. Striations parallel to the basal pinacoid occur commonly on the 
 faces of the vertical zone. Figures 1233 and 123!) show the following forms : 
 
 FIG. 
 
 FIG. 
 
 the three pinacoids, a, b, and c ; unit prism m ; positive unit hemipyramid o ; 
 negative unit hemipyramid u\ positive modified hemipyramid s, (m = 2), 
 and the positive unit hemiorthodome d. The ortho- and clinopinacoids are 
 generally larger than the faces of the unit prism. Contact and polysynthetic 
 twins parallel to the basal pinacoid. Partings parallel to these pinacoids are 
 often observed. Occurs also in compact, broad columnar, granular, lamellar, 
 or rarely fibrous masses. 
 
 Distinct prismatic cleavage. Brittle. Hardness 5 to 6. Specific grav- 
 ity 3.2 to 3.3. Uneven to conchoidal fracture. Transparent to opaque. Vit- 
 reous, resinous, or dull luster ; sometimes inclining to pearly on the partings 
 parallel to the basal pinacoid; Generally light to dark green in color; also 
 colorless, gray, yellow, and rarely blue. Zonal distribution of color is not 
 uncommon. The dark green varieties contain much FeO. White to green- 
 ish streak. Diallage is a thin, foliated, or lamellar variety, green or brown 
 in color, having a hardness of 4 to 6, and a specific gravity of 3.2 to 3.5. 
 Diallage is in part also closely related to augite. Ompliacite is a green 
 variety of diallage. 
 
 CaMg(SiO 3 ).>. Usually contains as much as 5% of FeO; in diallage, 
 however, as high as 8 to 16%. Small amounts of A1 2 O 3 and MnO may also 
 be present; in diallage A1 2 O 3 varies between I and 4%. Chrome-diopside 
 
244 DESCRIPTIVE MINERALOGY 
 
 contains from i to 3% Cr 2 O.j. More or less fusible to a dark, colored or 
 green glass. Not acted upon by common acids. Alters to serpentine, talc, 
 chlorite, and limonite. 
 
 Occurs in granite, gabbro, basalt, pyroxenite, peridotite, and leucite lava ; 
 also in crystalline schists, limestones, and dolomites. Commonly associated 
 with vesuvianite, scapolite, garnet, amphibole, orthoclase, titanite, apatite, 
 tourmaline, spinel, rutile, and so forth. Found at Mussa Alp, Piedmont; 
 Zermatt, Switzerland ; various places in the Tyrol ; Pargas, Finland ; Nord- 
 mark, Sweden ; Laveline, Vosges ; Leucite Hills, Wyo. 
 
 HEDENBERGITE, Calcium-iron Pyroxene, CaFe(SiO 3 ) 2 . 
 
 Monbclinic, prismatic class, a : b : c= 1.0912 : I : 0.5843, /3 = 105 25'. Crystals 
 are rare; usually as dark, greenish black, compact lamellar masses. Light greenish 
 streak. Specific gravity 3.2 to 3.6, increasing with the percentage of iron. Contains 
 about 30% of FeO and 22% of CaO. Sometimes as much as 6.5% of MnO may be 
 present in manganhedenbergite from Vester Silfberg, Lalarne, Sweden. Occurs with 
 magnetite in crystalline limestone at Tunaberg and Nordmark, Sweden; also at Aren- 
 dal, Norway. 
 
 SCHEFFERITE, Manganese Pyroxene, (Ca,Mg) (Fe,Mn) (SiO 3 ) 2 . 
 
 Monoclinic, prismatic class. Tabular and prismatic crystals, also in crystalline 
 masses. Distinct prismatic cleavage. Yellowish to reddish brown or black in color. 
 Contains from 8 to 10% of MnO, 9 to 15% of MgO. Iron-schefferite contains as much 
 as 15% of FeO. Occurs in limestone at Langban, Sweden ; in the Caucasus Moun- 
 tains; containing zinc at Franklin Furnace, N. J. 
 
 JEFFERSON ITE, Manganese-zinc Pyroxene, (Ca,Mn) (Mg,Fe,Zn) (SiO 3 ) 2 . 
 
 Monoclinic, prismatic class. Dark green to brownish black in color. Distinct 
 prismatic and orthopinacoidal cleavages. Submetallic luster, resinous on cleavage sur- 
 faces. Translucent to opaque. Occurs as large, coarse crystals with rounded edges, 
 and as compact masses in crystalline limestone at Franklin Furnace, N. J. Contains 
 about 10% of MnO and 4 to 10% of ZnO. 
 
 Wollastonite, Tabular Spar, Ca 2 (SiO 3 ) 2 . 
 
 Monoclinic, prismatic class, a : b : (7=1.0531 : I : 0.9676, (3 = 95 
 30'. Crystals are usually elongated parallel to the b axis and tabular in 
 habit. The orthopinacoid predominates oftener than the basal pinacoid. 
 Rarely prismatic in development. Crystals are highly modified. Prism angle 
 is 92 40'. Twins parallel to the orthopinacoid. Usually occurs in cleava- 
 ble, fibrous, granular, and compact masses. The broad or slender fibres may 
 have a parallel or divergent structure. 
 
 Perfect basal and orthopinacoidal cleavages ; distinct parallel to the pos- 
 itive unit hemi-orthodome. Hardness 4 to 5. Specific gravity 2.8 to 2.9. 
 Vitreous to silky luster, pearly on cleavage surfaces. Uneven fracture. 
 
SILICATES 
 
 245 
 
 Brittle. Transparent to translucent. White streak. Usually white in color, 
 also colorless, grayish, yellowish, reddish, or brownish. 
 
 Ca a (SiO :! ).,. Generally intermixed with calcite, hence, may effervesce 
 with acids. Fuses on thin edges. Decomposes and gelatinizes with hydro- 
 chloric acid. 
 
 Wollastonite is a typical contact metamorphic mineral and is generally 
 associated with garnet, diopside, vesuvianite, augite, epidote, and calcite. It 
 is found in granular limestone, granite, basalt, and lava. Some localities are 
 Auerbach, Hessen, Germany : Island of Elba ; Cziklova, Hungary ; Mount 
 Vesuvius ; Island of Santorin ; Grenville and elsewhere, Quebec, North Bur- 
 gess and Bastard, Ontario, Canada ; Diana, Lewis County, N. Y. ; Attleboro, 
 Bucks County, Pa. 
 
 (b) Aluminous varieties. 
 
 AUGITE. 
 
 Monoclinic, prismatic class, a : b : c= 1.0921 : I : 0.5893, (3= 105 
 40'. Short columnar crystals with a prism angle of 92 54'. Figures 124 
 and 125 show combinations of the two pinacoids, a and b; unit prism m\ 
 negative hemi-orthodome t, (w = 2); positive unit hemi-pyramid o. The 
 faces of the prism are usually as large or larger than those of the pinacoids. 
 Crystals are generally well developed and in some cases highly modified. 
 Contact twins parallel to the orthopinacoid, figure 126, and penetration twins 
 parallel to the brachy hemipyramid (n = 2,~) are common, figure I26a. Oc- 
 curs also in compact and disseminated grains and granular aggregates, rare- 
 lv fibrous. 
 
 
 m 
 
 m 
 
 FIG. 125 
 
 FIG. 126 
 
 FIG. i26a 
 
 Fairly distinct prismatic cleavage. Conchoidal to uneven fracture. Brit- 
 tle. Hardness 5 to 6. Specific gravity 3.2 to 3. 6, varying with the composi- 
 tion. Usually opaque, may be translucent. Commonly black or greenish 
 black in color, also leek green. Grayish green streak. 
 
 Four varieties may be distinguished: 
 
 Fassadte. Brownish and green crystals, often resembling diopside and 
 epidote. Typical contact metamorphic mineral. Occurs in the Fassathal 
 Tyrol ; Mount Vesuvius ; Traversella, Piedmont. 
 
246 DESCRIPTIVE; MINERALOGY 
 
 Leucaugite. Contains magnesium, calcium, and aluminium, but little or 
 no iron. Light colored, white or gray. Specific gravity 3.2. 
 
 Common augite. Contains considerable iron. Dark green to black in 
 color. As an essential constituent, it occurs disseminated and in well devel- 
 oped crystals in the older basic rocks ; in acid rocks it is generally an acces- 
 sory mineral. When it occurs in basic rocks it is more generally brownish, 
 in acid rocks green. Also found in metamorphic ore deposits, for example, 
 the magnetite deposits of Arendal, Norway ; also in crystalline limestone at 
 Pargas, Finland. 
 
 Basaltic augite. Characteristic of volcanic rocks, such as andesite, pho- 
 nolite, basalt, melaphyre, tuff, lava, and volcanic sand and ashes. Crystals 
 are very simple, usually pitch black in color, and at times with rounded sur- 
 faces. Conchoidal fracture. Translucent to opaque. In thin section dis- 
 tinctly pleochroic. May contain several percent of TiO 2 or Na 2 O. Occurs 
 on the Kaiserstuhl, Baden ; Boreslaw, Bohemia ; Laacher See, Rhenish Prus- 
 sia; Mount Vesuvius; Mount Aetna; the Azores and Cape Verde Islands; 
 Fassathal, Tyrol ; Thetford, Vt. 
 
 Groth interprets augite as being an isomorphous mixture of three mole- 
 cules : (Mg,Fe)Ca(SiO,)(SiO 3 ), (Mg,Fe)Al(AlO 3 ) (SiO 3 ), and (Mg,Fe) 
 Fe(FeO 3 ) (SiO 3 ). The amount of FeO present is usually about 10%. So- 
 dium is not uncommonly present. Fuses and often forms a magnetic glass. 
 Slightly acted upon by acids. Alters to a fibrous hornblende having the form 
 of augite, which is termed iiralitc, also to serpentine. The end alteration 
 products are limonite, quartz, and calcite. 
 
 A common rock mineral, being an essential or accessory constituent of 
 basalt, melaphyre, diabase, tuff, and volcanic sand and ashes. Occurs also in 
 crystalline schists and is commonly the result of contact metamorphism. 
 Found in meteorites and is formed in many furnace slags. 
 
 (c) Varieties containing alkalies. 
 Pectolite, (Ca,Na 2 ) 2 (SiO 3 ) 2 . 
 
 Monoclinic, prismatic class, a : b : c 1.1140 : i : 0.9864, /? = 95 
 20'. Commonly consists of aggregates of divergent fibres or acicular crys- 
 tals, sometimes of considerable length. The ends of the individual fibres or 
 crystals are often very sharp. Occurs also in compact, radial masses. Well 
 developed crystals are commonly tabular parallel to the orthopinacoid, but 
 rare. 
 
 Basal and orthopinacoidal cleavages. Uneven fracture. Brittle. Hard- 
 ness 4 to 5.^ Specific gravity 2.7 to 2.8. White streak. Colorless, white, or 
 grayish white. Translucent to opaque. Vitreous pearly luster, on cleavages 
 silky. 
 
SIUCATES 247 
 
 (Ca,Na 2 ) 2 (SiO 3 ) 2 . Very similar to wollastonite in composition. Con- 
 tains about 10% of Na 2 O. Manganopectolite contains about 4% of MnO. 
 Fuses easily to a white glass. Yields water in a closed tube. Decomposed 
 with hydrochloric acid with the separation of silica. Phosphoresces when 
 crushed in the dark. 
 
 Occurs in fissures and cavities in basic eruptive and metamorphic rocks. 
 Commonly associated with the zeolites, prehnite, and so forth. Some locali- 
 ties are Monte Baldo, Fassathal, and Monzoni, Tyrol ; Ayrshire and Edin- 
 burghshire, Scottland ; Thunder Bay, Ontario, Canada ; Bergen Hill, N. J. ; 
 Isle Royale, Mich. ; Magnet Cove, Ark. 
 
 JADEITE, NaAl(SiO 3 ) 2 . 
 
 Monoclinic, has been considered triclinic, but microscopic examination shows that 
 it is monoclinic with the general properties of the pyroxenes. Never in crystals, al- 
 ways as compact, microcrystalline, granular, foliated, or fibrous aggregates. 
 
 Fibres have cleavages at angles of about 93 and 87. Tough. Splintery fracture. 
 Hardness 6 to 7. Specific gravity 3.3 to 3.5. Subvitreous luster, pearly on cleavages. 
 Translucent. Usually green in color, apple to emerald green, bluish, green, leek green, 
 greenish or yellowish white, white with green spots, or colorless. Uncolored streak. 
 NaAl(SiOs)2. Fuses easily to a transparent blebby glass. Colors the flame yel- 
 low. Insoluble in or only slightly attacked by hydrochloric acid, after fusion readily 
 decomposed. Chloromelanite is dark green to almost black in color and contains con- 
 siderable FeO, CaO, and MgO. 
 
 Occurs embedded in crystalline schists and in rounded masses in secondary de- 
 posits in Burma, Thibet, and southern China. The European and American localities 
 are uncertain. 
 
 Highly prized in China. It is used for the manufacture of ornaments and utensils 
 of various kinds. Often found with relics of prehistoric man. Jadeite is one of the 
 tough, white to greenish minerals included in the' general term jade, page 252. 
 
 Spodumene, Triphane, LiAl(SiO 3 ) 2 . 
 
 Monoclinic, prismatic class, a : b : c= 1.1238 : i : 0.6355, P = IIO 
 20'. Long, columnar crystals, the unit prism predominating; also tabular 
 parallel to the orthopinacoid. Vertical striations and furrows. Prism angle 
 about 93. Twins parallel to the orthopinacoid. Crystals are often very 
 large. Crystals from the Etta mine, near Keystone, Pennington County, S. 
 Dak., measured 30 feet in length and about 2. l /2 feet in diameter. More com- 
 monly in cleavable masses and broad columnar aggregates. 
 
 Perfect prismatic cleavage. Very easy parting parallel to the orthopin- 
 acoid. Uneven to subconchoidal fracture. Brittle. Transparent to opaque. 
 Vitreous luster, pearly on cleavages. White, greenish and grayish white, 
 yellowish green, apple to emerald green, lilac pink, and purple in color. 
 Hardness 6 to 7. Specific gravity 3.1 to 3.2. Hiddenite is a yellow to emer- 
 ald green variety from Stony Point, Alexander County, N. C. A transpar- 
 ent, lilac pink variety from Pala, San Diego County, Cal., which phosphor- 
 esces with an orange pink light when exposed to oscillating electric dis- 
 
248 DESCRIPTIVE MINERALOGY 
 
 charges, the X-rays, ultra-violet light, or to radium emanations, is called 
 kunzite. 
 
 LiAl(SiO 3 ) 2 . Usually contains sodium replacing some of the lithium; 
 FeO and CaO may also be present. In hiddenite there is a small percentage 
 of Cr 2 O 3 , and in kunzite small amounts of the oxides of zinc, nickel, and 
 manganese. Fuses easily, turns white, intumesces, and colors the flame pur- 
 ple red, indicating lithium. Insoluble in acids. Of its many alteration pro- 
 ducts mention will be made only of albite, muscovite, eucryptite, cymatolite 
 (a mixture of albite and muscovite), and quartz. 
 
 Occurs in pegmatite veins with tourmaline, beryl, garnet, lepidolite, 
 feldspar, mica> and quartz as the principal associates. Some localities are 
 Island of Uto, Sweden ; Killiney, Dublin County, Ireland ; Sterzing, Tyrol 
 Sterling and Goshen, Mass. ; Branchville, Conn. ; Windham and Peru, Me. 
 Stony Point, Alexander County, N. C. ; Pennington County, S. Dak. ; Pala, 
 San Diego County, Cal. 
 
 Kunzite and hiddenite are used for gem purposes. The output of the 
 Etta mine, Pennington County, S. Dak., is used as an important source of 
 lithium compounds, especially the carbonate. Lithium salts are used in the 
 manufacture of red fire and for medicinal purposes. 
 
 ACMITE, Aegirite, NaFe(SiO 3 ) 2 . 
 
 Monoclinic, prismatic class, a : b : c= 1.996 : I : 0.6012, p = 106 49'. Long 
 prismatic crystals, more or less tabular parallel to the orthopinacoid, with vertical 
 striations or furrows. The terminal faces are very acute on acmite, on aegirite more 
 obtuse. Prism angle 92 49'. Twins parallel to the orthopinacoid are rather common. 
 Also in very slender hair-like crystals and fine fibrous aggregates. 
 
 Distinct prismatic and indistinct clinopinacoidal cleavages. Perfect parting par- 
 allel to the orthopinacoid. Uneven to subconchoidal fracture. Brittle. Hardness 6 
 to 6. 5. Specific gravity 3.4 to 3.55. Vitreous luster, inclining to resinous. Subtrans- 
 parent to opaque. Reddish brown, brownish black, greenish, or greenish black in color. 
 Yellowish gray to dark green streak. 
 
 NaFe(SiO 3 ) 2 . Usually contains A1 2 O 3 , FeO, MnO, CaO, MgO, and Na 2 O; rarely 
 TiO 2 . The composition of acmite and aegirite is practically the same. Acmite crystals 
 usually have the more acute terminal faces and are brown in thin section ; aegirite 
 green. Aegirite-augite is a green, rock-making augite containing some of the aegirite 
 molecule. They fuse rather easily to a magnetic glass, coloring the flame an intense 
 yellow. Slightly acted upon by acids. 
 
 Occurs in alkali rocks, such as, soda and nepheline syenite, soda granite, and 
 phonolite. Some localities are: Aeker and Langesundfiords, Norway; Kola penin- 
 sula, Russia; Ditro, Hungary; the Azores; Montreal and Beloeil, Canada; Kanger- 
 dluarsuk, Greenland; Magnet Cove, Ark.; Custer County, Colo.; Libertyville, N. J. ; 
 Black Hills, S. Dak. 
 
SILICATES 249 
 
 TRICLINIC PYROXENES 
 Rhodonite, Mn 2 (SiO 3 ) 2 . 
 
 Triclinic, pinacoidal class, a : b : c= 1.0728 : i : 0.6213, 0=103 
 18', /3=io844', 7 = 81 39'. Tabular and prismatic crystals, compara- 
 tively large and with rounded edges, but not very common. Usually in fine- 
 grained, cleavable, or compact masses, also in disseminated grains. 
 
 Prismatic and basal cleavages. Prism angle 92 28'. Compact masses 
 are very tough, crystals brittle. Conchoidal to uneven fracture. Hardness 
 5 to 6. Specific gravity 3.4 to 3.7. Vitreous luster, pearly on cleavages. 
 Crystals are often transparent, masses translucent to opaque. Rose red in 
 color, masses are yellowish, greenish, or brownish ; often black externally, 
 due to the oxidation of MnO on exposure. White streak. 
 
 Mn 2 (SiO 3 ) 2 . Calcium and iron often replace some of the manganese. 
 Bustamite is a radial fibrous, grayish red variety from Mexico, containing 
 from 9 to 20% of CaO. Compact masses are sometimes mixed with varying 
 amounts of CaCO 3 and SiO 2 . Turns black and fuses easily with slight in- 
 tumescence to a brownish glass. Slightly acted upon by acids. Varieties 
 containing an admixture of CaCO 3 effervesce with acids. Hydrorhodonite 
 is an alteration product containing water. 
 
 Occurs with rhodochrosite, calcite, quartz, iron ores, franklinite, and 
 tetrahedrite. Some localities are Elbingerode, Hartz Mountains ; Kapnik 
 and Rezbanya, Hungary; St. Marcel, Italy; Langban and Pajsberg, Sweden: 
 Ekaterinburg, Ural Mountains ; Peru ; Cummington, Mass. ; Cumberland, 
 R. I. ; Franklin Furnace district, N. ]., see fozderite. 
 
 Fowlerite, (Mn,Fe,Ca,Zn,Mg) 2 (SiO 3 ) 2 . 
 
 Occurs in large reddish crystals and compact masses in calcite in the 
 Franklin " Furnace district, N. J. It is a variety of rhodonite, containing 
 from 5 to 8% of ZnO, 3 to g% of FeO, and 6 to 7% of CaO. 
 
 RAI r-roNiTE I (Ca,Fe,Mn) 2 (SiO 3 ) 2 . 
 BABINGTONIT MFe 2 (Si0 3 ) 2 . 
 
 Triclinic, pinacoidal class, a : b : c = 1 .0691 : i : 0.6308, a = 104 2i I / 2 ', P = 108 
 31', 7 = 83 34'. Small six or eight sided, tabular or prismatic crystals, resembling 
 augite somewhat in form. Faces often striated. Occurs also in radial fibrous and 
 fine granular aggregates. Distinct prismatic cleavages with an angle of 92 37'. Brittle. 
 Hardness 5 to 6. Specific gravity 3.35 to 3.4. Vitreous luster. Subtransparent to 
 opaque. Greenish to brownish black, or black in color. Greenish gray streak. 
 
 An isomorphous mixture in varying proportions of (Ca,Fe,Mn) (SiO 3 )2 and 
 Fe(SiO 3 )2. According to Palache and Fraprie, the molecules are present in the pro- 
 portion of about 5^4 parts of the first to i of the second in the babingtonite from 
 Somerville, Mass. Aluminium and titanium may also be present. Fuses easily to a 
 black, magnetic globule. Not acted upon by acids. Alters to limonite. 
 
 Commonly associated with prehnite, quartz, epidote, pyrite, garnet, hornblende, 
 chlorite, feldspar, and calcite. Found at Arendal, Norway; Herbornseelbach, Nassau; 
 Baveno, Italy; Somerville and Athol, Mass. 
 
250 
 
 DESCRIPTIVE MINERALOGY 
 
 AMPHIBOLE GROUP 
 
 This group of minerals is closely related to the pyroxenes and consists 
 of metasilicates of magnesium, aluminium, iron, calcium, sodium, and po- 
 tassium, corresponding to the general formula M" 4 (SiO 3 ) 4 . Like the pyrox- 
 enes, these minerals crystallize in the orthorhombic, monoclinic, and triclinic 
 systems. The monoclinic representatives are the most important. The 
 amphiboles are not as fully developed as the pyroxenes, there being fewer 
 members. They are also simpler crystallographically. The prism angles are 
 about 56 and 124. The prismatic cleavages are more prominent on the 
 amphiboles than on the pyroxenes. 
 
 In order to show the striking crystallographic similarity of the pyrox- 
 enes and amphiboles, the elements of crystallization of two corresponding 
 representatives of the monoclinic system may be written as follows : 
 
 Diopside (Pyroxene) 
 Tiemolite (Amphibole) 
 
 a 
 
 i . 0522 
 1.0598 
 
 c 
 
 0.2959, 
 0.2938, 
 
 ft 
 
 90 22' 
 
 90 34' 
 
 The principal differences between the pyroxene and amphibole groups 
 may be tabulated in a general way, as follows : 
 
 Crystals, 
 
 Prism angles, 
 
 Cleavages, 
 
 Masses, 
 
 Specific gravity, 
 
 Chemical composition, 
 
 Pyroxenes 
 
 Short prismatic, com- 
 plex. 
 
 Pseudo-tetragonal. 
 87 and 93. 
 Prismatic. 
 
 Lamellar or granular. 
 Higher. 
 Alter to amphibole. 
 
 Amphiboles 
 Long prismatic, simple. 
 
 Pseudo-hexagonal. 
 56 and 124. 
 Prismatic, more distinct. 
 Columnar or fibrous. 
 
 Magnesium and the al- 
 kalies are more prom- 
 inent. 
 
 i. ORTHORHOMBIC SERIES 
 
 (Bi pyramidal Class) 
 
 ANTHOPHYUJTE, (Mg,Fe) 4 (SiO 3 ) 4 . 
 
 GEDRITE (Mg,Fe) 4 (SiO 8 ) 2 (SiO,) 2 . 
 
 **' (Mg,Fe) 2 Al 2 (A10 3 ) 2 (Si0 3 ) 2 . f. 
 
 a : b 
 0.5137 : i 
 
 0.5229 : i : 0.217 
 
SIUCATES 251 
 
 2. MONOCLINIC SERIES 
 (Prismatic Class}. 
 
 (a) Non-aluminous varieties: 
 
 a : b : c (3 
 
 Tremolite, CaMg,(SiO) 4 . ) 00/ - T/ , 
 
 Actinolite, Ca(Mg,Fe),(SiO,) 4 . [ '54i5 : i : 0.2886, 105 ii& 
 RICHTERITE, ( Mg,Ca,Mn,K 2 ,Na 2 ) 4 ( SiO 3 ) 4 . 
 
 0.5499 : i : 0.2854, 104 14' 
 
 (b) Aluminous varieties: 
 HORNBLENDE, 
 
 Ca(Mg,Fe),(Si0 3 ) 2 (SiO,),. ) 
 
 Al a (Mg,Fe) s (AlO g ),(SiO,) a . 0.5318 : i : 0.2936, 104 58' 
 
 Fe 2 (Mg,Fe) 2 (Fe0 3 ) 2 (Si0 3 ) 2 . ) 
 
 (c) Varieties containing alkalies: 
 
 ARFVEDSONITE, 
 
 (Fe,Mg,Na 2 ,Ca) 4 (Si0 3 ) 2 (Si0 3 ) 2 . ) 0.5496 : i : 0.2975, 
 (Ca ) Mg,Fe) 2 (ALFe) 2 (A10 3 ) 2 (Si0 3 ) 2 . f 104 15^' 
 
 GlvAUCOPHANE, 
 
 Al,Na,(SiO 8 ) 4 . ) 
 
 (Mg,Fe,Ca),(Si0 3 ) 4 . [ '53 = ' = -^9, 105' 
 
 RlEBECKlTE, 
 
 Fe 2 Na 2 (SiO 3 ) 4 . \ . . c / 
 
 Fe,(SiO 3 ) 4 . j 95 ' 
 
 3. TRICLINIC SERIES 
 
 (Pinacoidal Class}. 
 AENIGMATITE, 
 
 (Na 2 ,K 2 ,Fe) 4 [(Si,Ti)0 3 ] 4 . ) a : b : c 
 
 ALNa 9 (SiO 3 ) 4 . 0.6627 : i : 0.3^05 
 
 (Fe,Mn,Mg.) 3 Ca(Si0 3 ) 4 . ) a = 9 o 6', p= 102 13', 7 = 89 54' 
 
 The amphiboles and pyroxenes are important rock minerals. According 
 to Clarke, about 17% of the igneous rocks consist of the minerals of these 
 groups. 
 
 ORTHORHOMBIC AMPHIBOLES 
 ANTHOPHYLUTE, (Mg,Fe) 4 (SiO 3 ) 4 . 
 
 Orthorhombic, bipyramidal class, a : b : c 1=0.5137 : i : ?. Crystals are rare, 
 never with terminal planes. Generally in lamellar or fibrous masses or aggregates ; 
 also asbestiform. Perfect prismatic cleavage, angle 54 33'; distinct macro- and brachy- 
 pinacoidal cleavages. Hardness 5 to 6. Specific gravity 3.1 to 3.2. Vitreous luster, 
 pearly on cleavages; metallic schiller on the brachypinacoid. Translucent to subtrans- 
 parent. 
 
252 DESCRIPTIVE MINERALOGY 
 
 (Mg,Fe)i(SiO 3 )4- May contain some AUOa. Fuses with difficulty. Not acted 
 upon by acids. Alters to talc. 
 
 Usually found in crystalline schists, especially those containing hornblende. Oc- 
 curs at Kongsberg, Modum, and elsewhere in Norway ; Stansvik, Finland ; Hermann- 
 schlag, Moravia; jenks corundum mine, Franklin, Macon County, N. C. ; Rockport, 
 Mass. Anthophyllite is not common mineral. 
 
 GEDRITE is similar to anthophyllite in its general physical properties, but contains 
 more A1 2 O 3 . For formula, see page 250. Occurs at Gedres, France ; Bamle and else- 
 where, Norway ; Fiskernaes, Greenland. 
 
 These minerals correspond in a general way to enstatite, bronzite, and hypers- 
 thene of the pyroxene group. 
 
 MONOCLINIC AMPHIBOLOUS 
 
 (a) Non-aluminous varieties. 
 Tremolite, CaMg 3 (SiO 3 ) 4 . 
 
 Monoclinic, prismatic class, a : b : ^ = 0.5415 : I : 0.2886, ^ = 105 
 Iiy 2 '. Long or short bladed crystals, generally without distinct terminal 
 faces ; also as fibrous and asbestiform aggregates, and in compact granular 
 masses. 
 
 Perfect prismatic cleavage, angle 124 n'. Very brittle. Hardness 
 5 to 6. Specific gravity 2.9 to 3.1. White to gray or yellow in color. Trans- 
 parent to opaque. Vitreous to silky luster. 
 
 CaMg 3 (SiO 3 ) 4 . Contains little or no FeO, not over 3%. He.vagonite 
 is an amethystine to lavender variety from Edwards, St. Lawrence County, 
 N. Y., containing about 2% of MnO with small amounts of sodium and 
 fluorine. Fuses with difficulty. Not acted upon by acids. Alters to talc. 
 
 Tremolite is a contact metamorphic mineral, occurring in granular 
 limestones and dolomites, and talc schists. Found at Campolongo, St. Gott- 
 hard district, Switzerland ; various places in Sweden and Hungary ; Lee, 
 Mass. ; Canaan, Conn. ; Bryam, N. J. ; Easton, Pa. ; Edenville, Orange Coun- 
 ty, and GouVerneur and Edwards, St. Lawrence County, N. Y. ; Litchfield, 
 Pontiac County, Quebec, and Renfrew and Lanark counties, Ontario, Canada. 
 
 Actinolite, Ca(Mg,Fe) 3 (SiO 3 ) 4 . 
 
 Monoclinic, prismatic class, a : b : c 0.5415 : I : 0.2886, /?=IO5 
 n.y 2 f . Long or short bladed crystals, generally without terminal faces ; more 
 usually as divergent or irregular, columnar, fibrous, or asbestiform aggre- 
 gates ; also in granular masses: Nephrite is a compact variety of tremolite 
 or actmolite, and is included in the general term jade, see page 247. 
 
 Perfect prismatic cleavage. Basal parting. Vitreous luster. Hardness 
 5.5 to 6. Specific gravity 2.9 to 3.2. Usually green in color, also white, 
 gray, or colorless. The green color is due to the presence of ferrous iron. 
 Strongly pleochroic. 
 
 Ca(Mg,Fe) 3 (SiO,) 4 . Often considered an isomorphous mixture of 
 CaMg 3 (SiO 3 ) 4 and CaFe 3 (SiO 3 ) 4 . Contains from 6 to 13% of FeO, also 
 
SILICATES 253 
 
 small amounts of A1 2 O 3 and Na 2 O. Fuses to a gray enamel. But slightly 
 acted upon by acids. Alters to talc, chlorite, epidote, or to an aggregate of 
 serpentine and calcite. 
 
 Actinolite occurs in crystalline schists ; sometimes in such quantities that 
 the rock may be termed actinolite schist. Often formed by contact meta- 
 morphism. Some localities are Greiner, Zillerthal, Tyrol ; Arendal, Nor- 
 way ; Zoblitz, Saxony ; Bolton, Brome County, Quebec, Canada ; Willis's 
 Mountain, Buckingham County, Va. ; Bare Hills, Md. ; Franklin Furnace, 
 N. J. ; Providence, Delaware County, and Kennett, Chester County, Pa. ; 
 Lee and elsewhere, Mass. ; Windham and elsewhere, Vt. 
 
 Asbestos. 
 
 Under this term are included fibrous varieties of tremolite, actinolite, 
 and other non-aluminous amphiboles. The fibres are sometimes long, par- 
 allel, flexible, and easily separated by the fingers. The very fine fibrous and 
 more or less silky varieties are called amianthus; those which are stiff or 
 felt-like, byssolitc. Mountain leather, mountain cork, and mountain wood 
 are compact, irregularly matted, and only slightly flexible varieties. 
 
 Amphibole asbestos is generally termed long fibered asbestos, while the 
 serpentine asbestos, see page 226, is called short fibered. The heat resist- 
 ing property of the amphibole asbestos is about the same as that of the 
 chrysotile asbestos, but the non-conductivity of heat and strength of fibre 
 is less. Chrysotile asbestos gives more satisfactory results. The only 
 producing locality in the United States for amphibole asbestos is Sail Moun- 
 tain, Georgia. Before the increased output of the better chrysotile asbestos 
 by the Canadian mines, there were a number of small mines of the amphi- 
 bole variety in Massachusetts, Connecticut, Virginia, North Carolina, South 
 Carolina, and Georgia. 
 
 For the uses of asbestos, see page 227. 
 
 RICHTERITE, (Mg,Ca,Mn,K 2 ,Na 2 )4(SiO3)4. Monoclinic. Occurs in elongated 
 crystals, usually without distinct terminations. Yellow, red, or brown in color. Spe- 
 cific gravity 2.8 to 3.1. Transparent to translucent. Contains up to 9% of the alkalies. 
 Found in the manganese deposits of Langban and Pajsberg, Sweden. Cummingtonite 
 resembles anthophyllite in composition but is monoclinic. Occurs at Cummington, 
 Mass. ; Kongsberg, Norway ; Greenland. Griinerite is an iron amphibole with the 
 formula Fe 4 (SiOs)4, occurring usually in fibrous or lamellar masses with a brown 
 color and silky luster. Contains but small amounts of MgO and AkOs. Specific grav- 
 ity 3-7- Found at Colobrieres, France, and in the Lake Superior iron district. 
 
 (b*) Aluminous varieties. 
 HORNBLENDE. 
 
 Monoclinic, prismatic class, a : b : c = 0.5318 : I : 0.2936, /3= 104 
 58'. Short, prismatic crystals with a pseudo-hexagonal development, being 
 six-sided and frequently terminated by faces which simulate a rhombohe- 
 dron. Prism angle is 55 49', but varies with the composition. Crystals 
 are usually very simple, consisting of combinations of the unit prism m, pos- 
 
254 
 
 itive unit hemipyramid o, basal pinacoid c, clinopinacoid b, orthopinacoid a, 
 unit clinodome d, and the clinoprism e (w 3), see figures 127, 128, 129 
 and 130. Twinning parallel to the orthopinacoid, figure 131,, Parallel 
 grouping with augite and diallage is sometimes observed. Occurs also in 
 coarse or fine, columnar, bladed, or fibrous aggregates ; further in lamellar 
 or granular masses. 
 
 m 
 
 FIG. 127 
 
 m 
 
 4 
 
 / Ch 
 
 i 
 
 
 1 
 
 a 
 
 m' e 
 ^ 
 
 m 
 
 FIG. 129 
 
 m 
 
 rn 
 
 FIG. 130 
 
 FIG. 131 
 
 FIG. 128 
 
 Perfect prismatic cleavage. Hardness 5 to 6. Specific gravity 2.9 to 
 3.3. Vitreous to silky luster. Usually dark in color, green, brown, to black ; 
 more rarely bluish or dark blue. Grayish green to grayish brown streak. 
 Strongly pleochroic. May be transparent, but generally only translucent to 
 opaque. 
 
 The more important varieties of hornblende are : 
 
 (1) Common hornblende. Generally black, dark green, or leek green 
 in color. Simple crystals. More usually in compact, cleavable grains and 
 masses, or fibrous aggregates. Contains considerable FeO. 
 
 (2) Basaltic hornblende. Brownish black to pitch black in color. Con- 
 tains much iron, TiO 2 , Na 2 O, and K 2 O. Occurs in disseminated crystals and 
 irregular grains in basic igneous rocks. 
 
 (3) Edenite. Light colored, white, gray, or pale green. Contains but 
 little iron. Occurs in crystalline limestone at Edenville, N. Y. 
 
 (4) Pargasite. This variety is rather closely related to edenite. Light 
 bluish green to grayish black, more or less rounded crystals. Occurs as a 
 contact metamorphic mineral in gneisses and crystalline limestone. Found 
 at Pargas, Finland; Grenville, Quebec, Canada; Phippsburg, Me. 
 
 In .chemical composition hornblende is similar to augite of the pyroxene 
 group, see page 245. It may be considered as an isomorphous mixture of 
 
SILICATES 255 
 
 Ca(MgFe) a (SiO,) 2 (SiO,) a , Al 2 (Mg,Fe) 2 (AlO 3 ) 2 (SiO 3 ) 2 , and Fe,(Mg, 
 Fe) 2 (FeO 3 ) 2 (SiO 3 ) 2 . There may be as much as 23% of FeO, 7% of 
 FeoCX;, iS% of A1 2 O 3 , 14% of MgO, and 12% of CaO present, also small 
 amounts of Na 2 O and K 2 O, and up to 7% of T1O 2 . A very small per cent 
 of H 2 O is usually present, which tends to distinguish hornblende from augite. 
 Fuses to a dark colored magnetic glass, the ease of fusibility increases with 
 the percentage of iron and the alkalies. Acted upon by acids after fusion. 
 Alters to chlorite, epidote, calcite, siderite, biotite, limonite, and quartz. 
 Uralite is pyroxene altered to amphibole, with the form of the original min- 
 eral but the cleavage of amphibole. Pyroxenes commonly alter in this way 
 and the process is termed uralitisation. 
 
 Hornblende is an essential or accessory constituent of many plutonic 
 igneous rocks, especially granite, syenite, and diorite ; also of hornblende 
 schist, andesite, phonolite, basalt, and crystalline limestone. There are many 
 localities, but only a few will be given : Arendal and Kongsberg, Norway ; 
 various places in Sweden and Finland ;' Mount Vesuvius ; Aussig and Teplitz, 
 Bohemia ; Thomaston, Me. ; Russell, Pierrepont, and DeKalb, St. Lawrence 
 County, N. Y. ; Silver Cliff, Colo. 
 
 (c~) Varieties containing alkalies. 
 ARFVEDSONITE. 
 
 Monoclinic, prismatic class, a : b : c = 0.5496 : I : 0.2975, /3=io4i5^'. 
 Crystals may be large and prismatic, or small and tabular; not common. Usually in 
 columnar aggregates, or in grains. Twins parallel to the orthopinacoid. Very per- 
 fect prismatic cleavage with an angle of 56 5'. Uneven fracture. Brittle. Hardness 
 5.5 to 6. Specific gravity 3.45. Vitreous luster. Dark bluish black to black in color. 
 Dark bluish gray streak, which distinguishes it from aegirite having a yellowish gray 
 to greenish gray streak. Opaque, transparent in thin sections. 
 
 Chemically it may be considered as an isomorphous mixture of (Fe,Mg,Na 2 Ca)4 
 (SiOs)* and (Ca.Mg.FeMALFeMAlOsMSiOs)* Fuses easily with intumescence and 
 yields a black magnetic globule, coloring the flame yellow. Not acted upon by acids. 
 Barkevikile is intermediate between arfvedsonite and basaltic hornblende. 
 
 Occurs in igneous rocks containing much sodium, especially in nepheline syenites 
 and phonolites. Found at Kangerdluarsuk, Greenland; Aeker, Langesundfiord, and 
 Klein-Aro, Norway; Kola peninsula, Russia. 
 
 KATOFORITE is an amphibole containing considerable sodium and iron and is close- 
 ly related to hornblende. Occurs in syenite at Langesundfiord, Norway. 
 
 Gl,AUCOPHANE. 
 
 Monoclinic, prismatic class, a : b : ^ = 0.53 : i : 0.29, /3 105, approximately. 
 Indistinctly terminated columnar crystals, but usually in broad columnar, fibrous, or 
 granular aggregates and masses. 
 
256 DESCRIPTIVE MINERALOGY 
 
 Perfect prismatic cleavage. Uneven to conchoidal fracture. Brittle. Hardness 
 6 to 6.5. Specific gravity 3 to 3.15. Vitreous luster, inclining to pearly. Translucent 
 to opaque. Blue, lavender, blue, bluish gray, or bluish black in color. Grayish blue 
 streak. Strongly pleochroic. 
 
 May be considered an isomorphous mixture in varying proportions of Na 2 Al 2 
 (SiO 3 )4 and (Mg.Fe.CaMSiO.)^ Fuses easily. 
 
 Occurs in metamorphic rocks only, such as mica schist, eclogite, and crystalline 
 limestone. Found on the islands of Syra and Thermia ; Zermatt, Switzerland ; St. 
 Marcel, Piedmont; islands of Corsia and Groix; New Caledonia; Quincy, Mass.; 
 Coast Range, Cal. 
 
 RIEBECKITE. 
 
 Monoclinic, prismatic class, a : b : c 0.5475 : I : 0.2295, P 103 50'. Crys- 
 tals are long columnar without end faces, the only observed forms being the prism 
 and brachypinacpid. Longitudinally striated. The prism angle is about 56. Occurs 
 also in parallel or divergent fibrous or columnar aggregates. 
 
 Perfect prismatic cleavage. Vitreous luster. Specific gravity 3.3. Hardness 4. 
 Black in reflected light, deep blue or green in transmitted. 
 
 Chemically, riebeckite is an isomorphous mixture of Fe 2 Na 2 (SiO3)4 and Fei 
 (SiO.i)i. Fuses easily, coloring the flame an intense yellow. Crocidolite is a fibrous 
 variety of riebeckite from Griqualand-West, South Africa, containing more iron and 
 possessing a silky luster or chatoyancy. Tiger's eye contains limonite and infiltered 
 quartz, giving it a yellow brown color. Crocidolite and tiger's eye are secondary for- 
 mations of reibeckite. 
 
 Riebeckite occurs in alkali granites and syenites. Found on the island of Cor- 
 sica ; island of Socotra, in the Indian Ocean ; Myndd Mawr, Carnarvonshire, Wales ; 
 Roumania; Narsarsuk, Greenland; El Paso County, Colo.; Lake Superior district. 
 
 Crocidolite and tiger's eye are used for ornamental purposes and in cheap jew- 
 elry. 
 
 TRICLINIC AMPHIBOLHS 
 
 AENIGMATITE. 
 
 Triclinic, pinachoidal class, a : b : = 0.6627 : i : 0.3505, a = 90 6', /3 102 
 13', V = 89 54'- Crystals may be large but indistinct, resembling common hornblende. 
 Twins parallel to the brachypinacoid. 
 
 Distinct prismatic cleavages. Uneven fracture. Brittle. Hardness 5 to 5.5. 
 Specific gravity 3.7 to 3.8. Vitreous luster. Translucent to opaque. Black to brown- 
 ish black in color. Reddish brown streak. 
 
 Groth considers aenigmatite as consisting of a mixture of the three molecules : 
 (Na 2 ,K 2 ,Fe)4[(Si,Ti)O 3 ]4, Al 2 Na 2 (SiO 3 )4, and (Fe,Mn,Mg)Ca(SiO). Contains 
 about 7*A% of TiO 2 . Easily fusible to a brownish black glass. Partially decomposed 
 by acids. Cossyrite is a variety occurring in small black crystals on the island of 
 Pantellaria, and contains perhaps little or no TiO 2 . 
 
 Found in nepheline syenites at Tunugdliarfik and Kangerdluarsuk, southern 
 Greenland; Kola peninsula, Russia. 
 
SILICATES 257 
 
 LEUCITE, Amphigene, K 2 Al 2 Si 4 O 12 . 
 
 Dimorphous, orthorhombic and cubic. At ordinary temperatures crys- 
 tals are pseudocubic, in that they show what is apparently a tetragonal tris- 
 octahedron, and at times also the cube and rhombic dodecahedron. Their 
 interfacial angles, however, differ slightly from those required in the cubic 
 system. Optically, the crystals are shown to consist of a system of ortho- 
 rhombic twin lamellae, which can sometimes be recognized by the striations 
 on the faces. Heated to a temperature of about 500 and over, the lamellae 
 disappear and the crystals become isotropic and truly cubic. Thus, it is evi- 
 dent that leucite was formed at a temperature of about 500 and crystallized 
 in the cubic system, but on cooling it became doubly refractive and ortho- 
 rhombic, the external form being pseudocubic. Generally found in well de- 
 veloped, disseminated crystals, more rarely massive in granular aggregates. 
 
 Very imperfect cleavage parallel to what appears to be the rhombic do- 
 decahedron. Conchoidal fracture. Brittle. Hardness 5.5 to 6. Specific 
 gravity 2.45 to 2.5. Vitreous luster, inclining to greasy on fracture surfaces. 
 Translucent, very rarely transparent. White, gray, yellowish, or reddish 
 in color. White streak. 
 
 K 2 Al 2 Si 4 O 12 . Groth assumes that leucite is composed of a mixture of 
 salts of the trisilicate and orthosilicic acids, because orthoclase and nephelin- 
 ite are alteration products. Some potassium is usually replaced by sodium. 
 Infusible. Turns blue when treated with cobalt nitrate solution. Often 
 contains inclusions which are sometimes arranged in some regular manner. 
 Alters to anacite, or to a mixture of feldspar and nephelinite or muscovite, 
 and finally to kaolin. Pseudoleudte is a pseudomorphous mixture of feld- 
 spar and nephelite from Magnet Cove, Ark. 
 
 Leucite occurs only in igneous rocks, especially young eruptives. Also 
 in leucities, leucite basalts, tephrites, and phonolites. Found in the lavas and 
 ejected masses of Mount Vesuvius; Laacher See, Rhenish Prussia; Kaiser- 
 stuhl, Baden ; Wiesenthal, Saxony ; Brazil ; Leucite Hills and elsewhere, Wyo. 
 
 BERYL, Be,Al 2 Si 6 O ]S . 
 
 Hexagonal, dihexagonal bipyramidal class, a : c=i : 0.4989. Crys- 
 tals are usually long prismatic and very simple, consisting of the prism of the 
 first order and the basal pinacoid. Rarely tabular. Sometimes highly modi- 
 fied. Figure 132 shows a combination of the prism of the first order m, 
 unit and modified (111 = 2) bipyramids of the first order p and u, modified 
 bipyramid of the second order ^ (w = 2), dihexagonal bipyramid v 
 (n = 3/2, m = 2~), and the basal pinacoid c. About fifty forms have been 
 
258 DESCRIPTIVE MINERALOGY 
 
 noted. Crystals are straited vertically and the edges more 
 or less rounded. Occurs also in columnar or granular 
 aggregates, and in rounded grains and masses in secondary 
 leposits. 
 
 Distinct basal cleavage. Conchoidal to uneven fracture. 
 Brittle. Hardness 7.5 to 8 ; is sometimes substituted 
 :or topaz in the Mohs scale of hardness. Specific 
 gravity 2.6 to 2.8. Vitreous luster, inclining to pearly 
 on the basal pinacoid. Transparent to translucent. 
 Streak white. Various shades of green, blue, yellow, and 
 reddish in color. 
 There are three important varieties of beryl : 
 
 (1) Emerald. Emerald green in color. Transparent. Highly prized 
 as a precious stone. The color is probably due to a small amount of Cr 2 O 3 . 
 
 (2) Aquamarine. Usually blue to sea green in color, more rarely yel- 
 low, yellowish green, rose red, and even colorless (goshenite) and water 
 white. Transparent. Also used as a gem, but is not as valuable as the emer- 
 ald. 
 
 (3) Common beryl. Generally green or yellowish to grayish white. 
 Crystals are sometimes extremely large, being measured in feet and weighing 
 as much as 1,500 kilograms (Grafton, N. H.). Sometimes also massive. 
 Cloudy and translucent. 
 
 Be 3 Al 2 (SiO 3 ) 6 . A1 2 O 3 may be partially replaced by Fe 2 O 3 or Cr 2 O 3 . 
 The oxides of calcium, bivalent iron, potassium, sodium, and caesium may 
 be present in amounts up to about 5%. There is also at times a small per- 
 centage of water. Fuses with great difficulty, becoming white and cloudy. 
 Insoluble in acids. Alters to mica or kaolin, the removed beryllium going 
 to form such secondary minerals as bertrandite, herderite, or beryllonite. 
 
 Commonly found in pegmatite veins, gneiss, mica schist, clay slate, or 
 in secondary deposits. The common associates are mica, feldspar, quartz, 
 chrysoberyl, apatite, phenacite, cassiterite, garnet, zircon, and corundum. 
 
 Emeralds of a good quality occur near Musa, Colombia; Tokovoja and 
 Mursinka, district of Ekaterinburg, Ural Mountains; Habachthal, Tyrol; 
 Kosseir on the Red Sea, Egypt ; Alexander County, N. C. ; Mount Antero, 
 Chaffee County, Colo. Aquamarine and other gem beryls are found on the 
 Island of Elba; Mourne Mountains, Ireland; Mursinka and Schaitanka, 
 Ural Mountains ; Goshen, Mass. ; in secondary deposits in Brazil, India, and 
 elsewhere. Common beryl occurs at Bodenmais, Bavaria ; Limoges, France ; 
 Cornwall, Eng. ; Ehrenfriedersdorf, Saxony ; Schaggenwald, Bohemia ; very 
 large crystals at Grafton and Acworth, N. H., and at Royalston, Mass.; 
 Paris, Stoneham, elsewhere, Me. ; Haddam and Litchfield, Conn. ; Chester 
 and Delaware counties, Pa. ; Black Hills, S. Dak. 
 
 Used for gem purposes and as a source of beryllium and its compounds. 
 
SILICATES 259 
 
 FELDSPAR GROUP 
 
 The feldspars constitute the most abundant group of minerals. They 
 are very important rock minerals and, according to the estimates of Clarke, 
 
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260 DESCRIPTIVE MINERALOGY 
 
 make up about 60% of the igneous rocks. Their chemical composition is 
 very similar and may be expressed in general by the formulas M / AlSi 3 O s 
 or M"Al 2 Si 2 O s , in which the metal may be potassium, sodium, calcium, or 
 more rarely barium. Isomorphous mixtures of the fundamental compounds 
 containing essentially but one of these metals are very common. 
 
 Although the feldspars crystallize in the monoclinic and triclinic sys- 
 tems, many of their physical properties are very similar. The prism angles 
 are about 120. Hardness 6 to 6.5. Specific gravity 2.55 to 2.75. The color 
 varies from white, gray, or colorless to the lighter shades of red, yellow, or 
 green; more rarely dark colored. 
 
 All feldspars possess good cleavages in two directions. These cleav- 
 ages make an angle of 90 on monoclinic feldspars, which are, therefore, 
 called orthoclases. In the case of the triclinic feldspars the cleavage angle 
 differs slightly from 90, and these are generally termed the plagiodases. 
 The term plagioclase is, however, often restricted by petrographers to the 
 members of the albite-anorthite series of the triclinic group. 
 
 Most classifications of the igneous rocks are based upon the kind of 
 feldspar they contain. 
 
 MONOCLINIC FELDSPARS 
 
 ORTHOCLASE, Potash Feldspar, Felspar, KAlSi 3 O 8 . 
 
 Monoclinic, prismatic class, a : b : c = 0.6585 : I : 0.5554, /J=n6 
 3'. Commonly in well developed crystals, sometimes measuring a foot or 
 more in length. Figures 133 and 134 show some of the common forms : 
 basal and clinopinacoids c and b, unit prism m, unit and modified positive 
 hemi-orthodomes x and y (m = 2), unit hemipyramid o, and the clinodome 
 n (m = 2}. Crystals are often highly modified, a total of about 80 forms 
 having been observed. The habit may be prismatic parallel to the c axis, 
 tabular parallel to the clinopinacoid b, or as square columns elongated par- 
 allel to the a axis, the basal and clinopinacoids being developed about equally. 
 
 There are three very important twinning laws, the first and second be- 
 ing comparatively common. 
 
 (1) Karlsbad law. The orthopinacoid a acts as the twinning plane, 
 the crystallographic c axis is the twinning axis. Irregular penetration twins 
 are common. Figure 135 shows a twin crystal according to this law. It is 
 designated as a right twin, because the basal pinacoid c lies to the right of 
 the hemiorthodome y. The reverse relationship exists in left twins. Con- 
 tact twins are more rarely observed. 
 
 (2) Baveno Law. The twinning plane is the clinodome n (m = 2). 
 
SILICATES 
 
 26l 
 
 Nearly square, columnar, contact twins, Figure 136. Trillings and four- 
 lings according to this law are also noted. 
 
 (3) Manebach Law. The basal pinacoid c acts as the twinning and 
 composition plane. Contact twins, Figure 137. This law is not as common 
 as the first two. 
 
 Other very rare laws involve twinning planes parallel to either the unit 
 prism, a clinoprism with m equal to 3, the unit positive hemipyramid, or 
 to the positive hemi-orthodome y (m = 2). Occasionally double twinning 
 may be observed, in that crystals according to the Karlsbad law may be 
 further twinned according to the Baveno law. 
 
 FIG. 134 FIG. 135 FIG. 136 
 
 Aside from occurring in crystals, orthoclase is also found in cleavable 
 masses ; further in compact and granular masses, and in irregular grains. 
 Sometimes in masses resembling jasper or flint. 
 
 Perfect basal and slightly inferior clinopinacoidal cleavages, making 
 an angle of 90 ; rarely indistinct prismatic cleavage. Parting sometimes 
 distinct parallel to the orthopinacoid. Pearly luster and iridescence on the 
 basal pinacoid, otherwise vitreous luster. Brittle. Conchoidal, uneven to 
 splintery fracture. Hardness 6. Specific gravity 2.5 to 2.58. Transparent 
 and colorless, or opaque and cloudy, and colored. White, gray, yellowish, 
 reddish, brownish, and rarely greenish in color. White streak. 
 
 The following varieties may be differentiated : 
 
 (1) Adularia. Usually in white to colorless crystals. Transparent 
 or slightly cloudy. Often possesses an excellent opalescence, and is termed 
 moonstone and used for gem purposes. Crystals may be simple, single in- 
 dividuals or complex twins, trillings, or fourlings according to the' Baveno 
 law. Usually found in cracks and veins in gneiss and mica schist. 
 
 (2) Sanidine. Occurs in glassy, transparent or translucent crystals. 
 Sometimes termed glassy feldspar. Generally colorless, white, or gray. Tab- 
 ular and square habits, and Karlsbad twins are most common. May contain 
 considerable sodium. Characteristic of such eruptive rocks as rhyolites, 
 trachytes, and phonolites. Rhyacolitc is a variety occurring in the eject- 
 jnenta of Mount Vesuvius and elsewhere. 
 
262 
 
 DESCRIPTIVE MINERALOGY 
 
 (3) Ordinary orthoclase. Well developed crystals, both as single in- 
 dividuals and twins according to the Karlsbad, Baveno, and other laws ; also 
 in cleavable masses. Generally more or less dull colored, yellowish, bluish, 
 flesh red, dark red, or greenish. Translucent to opaque. Common in gran- 
 ites, syenites, gneisses, and pegmatites. Loxoclase contains 7 to 9% of Na 2 O 
 and 2, to 3% of ICO, and resembles adularia. Graphic granites are inter- 
 growths of orthoclase, or other feldspars, and quartz resembling cuneiform 
 inscriptions, see Figure 138. 
 
 (4) Felsite. White, brown, or reddish, jasper- or flint-like, crypto- 
 crystalline masses of orthoclase containing quartz. 
 
 (5) Perthite. Orthoclase interlaminated with albite, although the 
 term is also used for intergrowths of other feldspars. Perthitic and micro- 
 perthitic structures refer to the character of scuh intergrowths. Figure I38a 
 shows a perthitic interlamination of microcline and albite. 
 
 FIG. 138 (Bastin). 
 
 FiG. 138 a (Bastin). 
 
 KAlSi 3 O 8 . Generally contains from I to 6% of Na,O, also smaller 
 amounts of CaO, MgO, BaO, and Fe 2 O 3 . Fuses with difficulty, coloring 
 the flame violet. Only slightly acted upon by acids. Alters easily by the 
 action of water alone, more rapidly when water contains carbon dioxide or 
 acids. These tend to remove the alkalies and a portion of the SiO 2 , yielding 
 kaolinite and quartz as the end alteration products. Alters also to mus- 
 covite. epidote, zoisite, tourmaline, topaz, alunite, or cassiterite, some of 
 which occur pseudomorphous after orthoclase. At times orthoclase is ob- 
 served pseudomorphous after analcite, laumontite, prehnite, or leucite. 
 
 Orthoclase is especially characteristic of acid plutonic rocks, but occurs 
 also in some eruptive and metamorphic rocks, thus, in granites, syenites, 
 trachytes, phonolites, porphyries, and gneisses. May be of aqueous origin 
 when it occurs as a gangue mineral in metalliferous fissure veins. Some of 
 
SILICATES 263 
 
 the common associates are muscovite, biotite, quartz, tourmaline, the other 
 feldspars, hornblende, apatite, titanite, zircon, beryl, and so forth. Occurs 
 very widely distributed and is often considered the most abundant silicate. 
 A few of the more important localities for crystallized orthoclase are : St. 
 Gotthard district, Switzerland ; Mount Vesuvius ; Baveno, Piedmont ; Laa- 
 cher See and Drachenfels, Rhenish Prussia ; Karlsbad, Bohemia ; Striegau, 
 Silesia ; Manebach, Thuringia ; Arendal, Norway ; Mourne Mountains, Ire- 
 land ; Cornwall, England ; Island of Ceylon ; Perth, Quebec, and Bedford, 
 Ontario, Canada. In the United States at Paris, Me. ; Acworth, Me. ; Had- 
 dam and elsewhere, Conn. ; Rossie and Hammond, St. Lawrence County, 
 and elsewhere, N. Y. ; Mount Antero, Chaffee County, Kokoma, Summit 
 County, and elsewhere in Colorado ; etc., etc. 
 
 The feldspar of commerce is principally orthoclase or microcline, or an 
 intergrowth of both. It is used chiefly as a constituent of the glaze of porce- 
 lain, china, or enamel wares, and as a flux in the manufacture of emery and 
 carborundum wheels. Small quantities are also used in opalescent glasses, 
 artificial teeth, scouring soaps, window washes, fillers for paints, poultry grit, 
 and so forth.* The principal producing localities are Georgetown and 
 Brunswick, Me. ; Glastonbury, Chatham, Haddam, and elsewhere, Conn. ; 
 Bedford, Batcherville, Crown Point, and Ticonderoga, N. Y. ; also various 
 places in Pennsylvania, Maryland, Virginia, Minnesota, and Massachusetts. 
 The production in the United States for 1908 was 70,474 tons, valued at 
 $428,553. A considerable amount of feldspar is mined annually at Bedford, 
 Ontario, Canada. 
 
 SODA-ORTHOCLASE, (Na,K)AlSi 3 O 8 . 
 
 Includes monoclinic feldspars containing considerable Na 2 O, sometimes more than 
 K 2 O, but not showing interlamination with albite. 
 
 HYALOPHANH;, Barium Feldspar, KAlSi 3 O 8 4-BaAl 2 Si 2 O 8 . 
 
 Monoclinic, prismatic class, a : b : c = 0.6584 : I : 0.5512, /3=ii5 35'. Color- 
 less, yellowish, or reddish crystals, often resembling adularia. Hardness 6 to 6.5. . 
 Specific gravity 2.8. Vitreous luster. Transparent or translucent, cloudy. Conchoidal 
 fracture. Contains from 9 to 20% of BaO and 7 to g% of K 2 O. Some sodium is us- 
 ually present. Sometimes considered an isomorphcys mixture of orthoclase and cel- 
 sian. Occurs in the Binnenthal, Switzerland ; Jakobsberg, Sweden ; Waldgu, Bavaria. 
 
 *For a full descripton of the uses and economic occurrences of feldspar in the 
 United States, see Bastin, Bulletin 420, United States Geological Survey. 
 
264 DESCRIPTIVE MINERALOGY 
 
 TRICLINIC FELDSPARS 
 
 MICROCLINE, KAlSi 3 8 . 
 
 Triclinic, pinacoidal class, a : b : c = 0.65 : I : 0.55, a = 90 30', 
 /?=n6, 7 = 90 (approximately). Crystals resemble those of ortho- 
 clase in habit, angles, and crystal form. The angle between the basal 
 and brachypinacoids varies from 90 15' to 90 35', usually about 90 30'. 
 Crystals are generally large and only apparently simple individuals, being 
 in reality polysnthetic twins according to the albite and pericline laws. In 
 the first law the brachypinacoid acts as the twinning plane, in the second the 
 crystallographic b axis is thje twinning axis. Basal sections of polysynthetic 
 twins according to these two laws show under the microscope a characteristic 
 grating-like structure.* This structure is not observed on the other feldspars 
 and is, hence, very charcteristic of microcline. These polysynthetic twins 
 are sometimes further twinned according to the Karlsbad, Baveno, and Mane- 
 bach laws, so common on orthoclase. Occurs also in cleavable and compact 
 granular masses. 
 
 Basal and brachypinacoidal cleavages at an angle of about 90 30', also 
 indistinct prismatic cleavages. Uneven fracture. Hardness 6 to 6.5. Spe- 
 cific gravity 2.54 to 2.57. Vitreous luster, inclining to pearly on the basal 
 pinacoid. White, cream yellow, yellowish gray, red, and green in color. 
 Green varieties, often bright verdigris green, are called amazonite or atnason- 
 stone. Transparent to translucent. 
 
 KAlSi 3 O 8 . Usually contains some Na,O. Chemical composition and 
 behavior are in general the same as for orthoclase. 
 
 Occurrence similar to that of orthoclase, but not common in eruptive 
 rocks. Smoky quartz, topaz, and phenacite are typical associates. Com- 
 monly in regular intergrowths with orthoclase, albite, and other feldspars. 
 Some localities are Striegau, Silesia ; Arendal, Norway ; Magnet Cove, Ark. 
 Amazonstone ocurs in excellent crystals in the Ural Mountains, Green- 
 land, and in the Pike's Peak district, Colo. 
 
 ANORTHOCivASE. Soda Microcline, (Na,K)AlSi 3 O 8 . 
 
 Triclinic, pinacoidal class, o : b : c = 0.6466 : i : 0.5522, a = 90 30', P = 116 
 18', 7 = 90. Crystals are similar to those of the ordinary, feldspars. Twins accord- 
 ing to the common laws of orthoclase, also polysynthetic twinning according to the 
 albite and pericline laws. General physical properties like those of orthoclase. Some- 
 times shows a blue opalescence. 
 
 (Na,K)AlSi 3 O 8 . Often considered an isomorphous mixture of albite and ortho- 
 
 * This can be seen in Figure 1383. 
 
SIUCATES 
 
 265 
 
 clase material in the proportion of 2 to 4.5 parts of albite to one of orthoclase. Some 
 CaO is always present. 
 
 Occurs in the lavas of the Island of Pantelleria, south of Sicily; in the augite 
 syenites and "Rhomben-porphyr" of southern Norway; in the rhyolite of Obsidian 
 Cliff, Yellow Stone Park. 
 
 ALBITE-ANORTHITE SERIES 
 (Plagioclase Feldspars) 
 
 These feldspars are sometimes called the soda-lime feldspars, and also, 
 as already indicated on page 260, the typical plagioclases in the narrower 
 sense. They are regarded as constituting a continuous isomorphous series 
 with albite and anorthite as the end members. According to Tschermak, the 
 chemical composition of the various members of the series may be indicated 
 as follows : 
 
 Albite, NaAlSi 3 O 8 , (Ab), 
 
 Oligoclase, Ab AbgAn^ 
 
 Andesine, AbgA^ .... A^An^ 
 
 Labradorite, At^Ar^ .... A^An^ 
 
 Bytownite, A^Ang An, 
 
 Anorthite, CaAl 2 Si 2 O 8 (An). 
 
 The following table, based upon the calculations of Tschermak and 
 adapted from Klockmann, shows clearly the progressive changes in chemical 
 composition, specific gravity, and certain extinction angles. 
 
 Name 
 
 Composi- 
 tion 
 
 C! fo of An- 
 orthite 
 
 SiO 2 
 
 A1 2 3 
 
 CaO 
 
 Na 2 O 
 
 Specific 
 Gravity 
 
 Extinction Angles 
 
 Basal 
 Pinacoid 
 
 Brachy 
 Pinacoid 
 
 Albite 
 
 
 
 
 68.6 
 
 19.6 
 
 
 ii. 8 
 
 2.605 
 
 + 430' 
 
 + 19 
 
 
 . Ab 
 
 
 
 
 
 
 
 
 
 Oligoclase 
 
 J 
 
 26 
 
 61.9 
 
 24.2 
 
 5.2 
 
 8.7 
 
 2.659 
 
 + i4' 
 
 + 436' 
 
 Andesine 
 
 | J ** Ani 
 
 51-5 
 
 55-4 
 
 28.5 
 
 10.4 
 
 5-7 
 
 2.694 
 
 - 5 io' 
 
 16 
 
 1/abradorite 
 
 j 
 
 76.1 
 
 49-1 
 
 32.8 
 
 i5.3 
 
 2.8 
 
 2.728 
 
 17040' 
 
 2928' 
 
 Bytownite 
 
 , AbjAn-j 
 
 96 
 
 46.6 
 
 34.4 
 
 17-4 
 
 1.6 
 
 2.742 
 
 2733' 
 
 3329' 
 
 
 * An 
 
 
 
 
 
 
 
 
 
 Anorthite 
 
 
 TOO 
 
 43-0 
 
 36.9 
 
 20. i 
 
 
 
 2 . 765 
 
 -37 
 
 -36 
 
 The intermediate members are important constituents of many igneous 
 rocks and more common than albite or anorthite. They are rarely well crys- 
 tallized, but can usually be recognized by the striations on the basal pinacoid, 
 due to multiple twinning according to the albite law. The various members 
 of the series are not easily differentiated macroscopically. 
 
266 
 
 DESCRIPTIVE; MINERALOGY 
 
 ALBITE, Soda Feldspar, NaAlSi 3 O 8 . 
 
 Triclinic, pinacoidal class, a : b : c = 0.6330 : I : 0.5573, 94 5' ', 
 (3=n6 27' ', y = 88 7'. Crystals are usually not large and often similar 
 in development to those of orthoclase, figure 139, or tabular and elongated 
 parallel to the b axis, figure 140. These are called the albite and pericline 
 habits, respectively. Twins are very common, single individuals being rare. 
 The twinning laws are: (i) Albite law, the brachypinacoid is the twinning 
 plane. Simple contact and repeated twins, figures 141 and 142. Polysyn- 
 thetic twins show striations on the basal pinacoid, which extend parallel to 
 the edge between the basal and brachypinacoids. (2) Pericline law, the b 
 axis is the twinning axis. Figure 143 shows a simple contact twin accord- 
 ing to this law, showing the characteristic rhombic cross-section. Polysyn- 
 thetic twins have fine striations on the brachypinacoid. The three twinning 
 laws of orthoclase, page 260, are also occasionally observed. Albite also 
 occurs in lamellar and granular masses, the laminae being often curved and 
 divergent. 
 
 FIG. 139 
 
 FIG. 140 
 
 FIG. 141 
 
 FIG. 142 
 
 Perfect basal and brachypinacoidal cleavages, imperfect parallel to the 
 prism faces. The angle between the basal and brachypinacoids is 86 24'. 
 Brittle. Hardness 6 to 6.5. Specific gravity 2.6 to 2.65, pure albite 2.605. 
 Vitreous luster, inclining to pearly on the cleavages. The basal pinacoid 
 often shows a bluish opalescence, especially on the varieties called peristerite 
 and moonstone. Transparent to translucent. Usually colorless ; rarely col- 
 ored, gray, bluish, reddish, and greenish. 
 
 NaAlSigOg. Sodium is generally replaced by some potassium and cal- 
 cium. Rarely free from calcium. Albite contains more SiO 2 than any of 
 the feldspars, namely 68.6%, see table on page 265. Fuses to a colorless or 
 white glass. Colors the flame yellow. Not acted upon by acids. 
 
 As a rock mineral, albite is not as abundant as the other plagioclases, 
 
SILICATES 267 
 
 but occurs, nevertheless, in many gneisses and other crystalline schists, in 
 granites, diorites, trachytes, and other eruptive rocks. Crystals are found 
 in the cracks and crevices of silicate rocks, and. more rarely in limestones 
 and dolomites. Some of the associates of albite are chlorite, titanite, adularia, 
 axinite, beryl, tourmaline, quartz, chrysoberyl, columbite, and apatite. Found 
 often in regular intergrowth with orthoclase, as perthite, page 262. 
 
 Some important localities are : the St. Gotthard district, Switzerland ; 
 Zillerthal, Pfitsch, and Schmirn, Tyrol; Rauris, Salzburg; Baveno, Italy; 
 Hirschberg and Striegau, Silesia; Roc Tourne, Savoy, and Dauphine, 
 France ; Arendal and Snarum, Norway ; Cornwall, England ; Mursinka, Ural 
 Mountains ; Pike's Peak, Colo. ; Amelia Court House, Va. ; Unionville, Ches- 
 ter County, Pa. ; Haddam, Middletown, and Branchville, Conn. ; Chesterfield, 
 Mass. ; Paris, Me. ; various places in New York, New Hampshire, North 
 Carolina, and elsewhere. 
 
 Moonstone is often used for gem purposes. 
 
 Oligoclase, Soda-lime Feldspar. 
 
 Triclinic, pinacoidal class. For elements of crystallization, see page 
 259. Crystals are columnar parallel to the c axis, or tabular parallel to the 
 basal or brachypinacoids. Twins according to the Karlsbad, albite, or peri- 
 cline laws. Crystals are, however, not very common. Usually observed in 
 compact, cleavable, or granular masses. 
 
 Basal and brachypinacoid cleavages making an angle of 86 32'. Con- 
 choidal to uneven fracture. Brittle. Hardness 6 to 6.5. Specific gravity 
 2.65 to 2.67. Vitreous, pearly, or waxy to greasy luster. Transparent to 
 subtranslucent. White or colorless,, also grayish or reddish white, gray 
 green, or green. Aventurine oligoclase or suns tone is a variety containing 
 disseminated scales of probably hematite or goethite, giving rise to yellow- 
 ish or reddish reflections. 
 
 Ab. . . .AbgAn^ for the percentage composition see the table on page 
 259. Fuses to a clear or blebby glass. Only slightly acted upon by acids. 
 
 Occurs as a rock mineral in some of the acid silicate rocks, such as gran- 
 ites, gneisses, syenites, diorites, prophyries, andesites, and trachytes. Some 
 associates are orthoclase, quartz, tourmaline, epidote, garnet, pyrrhotite, cor- 
 undum, augite, and calcite. Found at Arendal and, as sunstone at Tvedstrand, 
 Norway; Bodenmais, Bavaria; Mount Vesuvius; Lake Baikal; Pargas, Fin- 
 land ; Ural Mountains ; Bakersville, N. C. ; Danbury and Haddam, Conn. ; 
 Fine and Macomb, St. Lawrence County, N. Y. ; Mineral Hill and Unionville, 
 Pa. ; Chester, Mass. 
 
 Aventurine or sunstone is used for gem purposes. 
 
 ANDESINJS. 
 
 Triclinic, pinacoidal class. For the elements of crystallization, see page 259. 
 Generally in cleavable and granular masses, crystals which are similar to those of 
 oligoclase being very rare. 
 
2 68 DESCRIPTIVE MINERALOGY 
 
 Perfect basal and brachypinacoidal cleavages, making an angle of 86 14'. Hard- 
 ness 6. Specific gravity 2.69. Vitreous luster, inclining to pearly. Colorless, white, 
 greenish, gray, yellowish, to flesh red. 
 
 AbsAni AbiAm. Fuses more easily than albite. Occurs especially in andesites, 
 
 diorites, and dacites. Found in the Andes Mountains, South America; Bodenmais, 
 Bavaria; Ekaluit, Greenland; Island of Sardinia; Finland; L'Esterel, France; Toluca, 
 Mexico; Chateau Richer, Montmorency County, Quebec, Canada; Sanford, Me.; Tel- 
 ham, Mass.; Clay County, N. C. Not so abundant as oligoclase. 
 
 Labradorite, Lime-soda Feldspar. 
 
 Triclinic, pinacoidal class. For the elements of crystallization see page 
 259. Well developed crystals are rare, their habit is usually tabular parallel 
 to the brachypinacoid. Twins according to the various laws given for albite. 
 Generally observed in cleavable, granular, or cryptocrystalline masses. 
 
 Perfect basal and brachypinacoid cleavages, making an angle of 86 4'. 
 Hardness 5 to 6. Specific gravity 2.7 to 2.74. Translucent to subtranslu- 
 cent. Gray, brown, or greenish in color, often showing a beautiful play of 
 colors, yellowish, bluish, greenish, or reddish on the brachypinacoid. This 
 labradoresccncc is due to the fine lamellar structure or to microscopic inclu- 
 sions, or to both. Uncolored streak. 
 
 AbjAtti .... Ab An 3 . Fuses to a colorless or white glass, coloring the 
 flame yellow. Decomposed with difficulty by hydrochloric acid. 
 
 Occurs in basic igneous rocks, such as gabbro, norite, basalt, diabase, 
 and andesite. Found on Mount Aetna ; Transylvania ; Finland ; Sweden ; 
 Greenland ; varieties showing an excellent labradorescence are common at 
 various places on the coast of Labrador, also on the Isle of St. Paul ; Adiron- 
 dack Mountains, N. Y. ; Wichita Mountains, Ark. ; various places in Mary- 
 land, North Carolina, and British Columbia. 
 
 Varieties showing the play of colors are used for ornamental purposes 
 and are sometimes termed labrador spar, 
 
 BYTOWNITE. 
 
 Triclinic, pinacoidal class. For the elements of crystallization see page 259. 
 Very similar to labradorite in properties and occurrence, and includes certain feld- 
 spars formerly described as anorthite. Some localities are Bytown, Canada; Neurode, 
 Silesia; Iceland; Hartz Mountains; Island of Corsica. Is not as abundant as labra- 
 dorite. 
 
 Anorthite. Lime Feldspar, CaAl 2 Si 2 O 8 . 
 
 Triclinic, pinacoidal class, a : b : (7 = 0.6347 : I : 0.5501, = 93 13', 
 (3= 115 55', y = 88 48'. Crystals are prismatic and elongated parallel to 
 either the c or b axes, tabular parallel to the' basal pinacoid. Crystals are 
 often very complex. Twins according to the several laws indicated for al- 
 bite. Occurs also in cleavable, granular, or lamellar masses. 
 
 Perfect basal and brachypinacoidal cleavages making an angle of 85 
 
SILICATES 269 
 
 50'. Conchoidal to uneven fracture. Brittle. Hardness 6 to 6.5. Specific 
 gravity 2.7 to 2.8. Transparent to translucent. Uncolored streak. Colorless, 
 white, bluish, yellowish, reddish, or rose red. Vitreous luster, inclining to 
 pearly on the cleavages. 
 
 CaAl 2 Si 2 O 8 . Generally contains small amounts of Na 2 O, K 2 O, MgO, 
 and Fe 2 O 3 . The presence of H 2 O is indicative of some alteration. Fuses 
 with difficulty to a colorless glass. Decomposed by hydrochloric acid with a 
 separation of gelatinous silica. 
 
 Anorthite occurs as an important constituent of basic silicate rocks, 
 such as gabbros, diorites, and basalts ; also as a contact mineral and in me- 
 teorites. Excellent crystals have been observed in the ejectmenta of Mount 
 Vesuvius ; Island of Miyake, Japan ; Iceland ; Monzoni district, Tyrol ; Trans- 
 ylvania; Ural Mountains; Pikesville, Md. ; Franklin Furnace, N. J. 
 
 CSLSIAN, BaAl 2 Si 2 O 8 . 
 
 Triclinic, pinacoidal class. For the elements of crystallization see page 259. 
 Found in compact masses with basal and brachypinacoidal cleavages at an angle of 
 89 36'. Hardness 6 to 6.5. Specific gravity 3.37. Contains about 39% BaO. Color- 
 less. Occurs associated with schefferite and other manganese minerals at Jakobsberg, 
 Sweden. 
 
 SCAPOLITE GROUP 
 
 The members of this group are similar to the triclinic feldspars in chem- 
 ical composition, being aluminium silicates containing either Na 2 O or CaO. 
 Tschermak believes that the composition of the group can best be explained 
 by assuming the isomorphous mixing of two end members, which are 
 analogous to albite and anorthite of the plagioclase group. These compounds 
 are 
 
 Meionite, Na 4 Al 3 Si 9 O 24 Cl(Ma). 
 
 Marialite, Ca 4 Al 6 Si 6 O 25 (Me). 
 
 The composition of the intermediate members may be expressed by the. 
 general formula mMe -\- nMa. It must be pointed out, however, that aside 
 from the constituents indicated in the formulas given above, small amounts 
 of K 2 O, CO 2 , SO 3 , MgO, and H 2 O are usually present. The role these con- 
 stituents play is not clearly understood. The soda varieties contain the larg- 
 est percentages of SiO 2 and chlorine. They also have the lowest specific 
 gravity, refringence and birefringence, and are least soluble in acids. 
 
 The names scapolite and wernerite have been applied quite generally to 
 many members of the group and, hence, the general properties of the group 
 will be given under that caption. 
 
270 DESCRIPTIVE MINERALOGY 
 
 SCAPOLITE, Wernerite, nNa 4 Al 3 Si 9 O 24 Cl -f mCa 4 Al 6 Si 6 O 25 . 
 
 Tetragonal bipyramidal class. The axial ratio varies between i : o . 4393 
 for meionite and i : 0.4425 for marialite. Thick, coarse, prismatic crystals, 
 often large with dull and uneven faces. The common forms are the prisms 
 of the first and second orders m and ,a, unit bipyramids of the same orders 
 o and d, and the bipyramid of the third order s, see figures 144 and 145. 
 Occurs also in fibrous, coarse to fine granular, and compact masses. 
 
 FIG. 144 
 
 Perfect prismatic cleavages. Conchoidal fracture. Brittle. Hardness 
 5 to 6. Specific gravity 2.566 for marialite and 2.764 for meionite. Vitreous 
 luster, inclining to pearly and greasy. Colorless, white, gray, greenish, blu- 
 ish, or reddish. Colorless streak. 
 
 The chemical composition is variable, as explained above. The amount 
 of SiO 2 commonly present varies between 40.45 and 64%. In some cases as 
 much as 4.2% of chlorine has been noted. Some of the scapolites are read- 
 ily decomposed by hydrochloric acid, others not. All are quite easily fusible 
 with intumescence. The scapolites alter to kaolin, epidote, muscovite, bio- 
 tite, albite, and various zeolites. 
 
 Three varieties are commonly differentiated : 
 
 (1) Marialite, Na 4 Al 3 Si O 24 Cl. Always contains some CaO and is 
 not decomposed by acids. Usually as small, clear, and colorless crystals. 
 The common scapolites are cloudy or dull, and more or less colored; some- 
 times rather large. 
 
 (2) Mizzonite, Dipyre, MeMa i to Me^a^ Partially decomposed by 
 acids. Small, prismatic, whitish crystals, often clear. 
 
 (3) Meionite, Ca 4 Al 6 Si 6 O 25 . Completely soluble in hydrochloric acid. 
 Small, colorless and glassy, or milky white crystals, often without distinct 
 terminal faces. 
 
 The scapolite minerals are generally the result of metamorphism. Com- 
 
SII4 GATES 271 
 
 mon in granular limestones near the contact with igneous rocks, also in crys- 
 talline schists and volcanic ejectamenta. May also occur independently. The 
 characteristic associates are the pyroxenes, apatite, garnet, titanite, zircon, 
 biotite, and hornblende. Some localities are Arendal, Norway ; Pargas, Fin- 
 land; Hafnerzell, near Passau, Bavaria; Laacher See, Rhenish Prussia; 
 Mount Vesuvius ; Ripon and Grenville, Quebec, and various places in On- 
 tario, Canada ; Bolton, Mass. ; various places in Northern New York ; Frank- 
 lin and Newton, N. J. 
 
 SARCOUTE, NazCasAUSioOse, is somewhat related to the scapolites. Tetragonal 
 bipyramidal class, a : c = I : 0.4183. Occurs in small reddish white or flesh red, 
 transparent to translucent crystals in the ejectamenta of Mount Vesuvius. Hardness 
 5.5 to 6. Specific gravity 2.54 to 2.93. Resembles analcite. 
 
 EUDIDYMITE GROUP 
 
 The group consists of the two minerals eudidymite and epididymite, 
 having the same chemical composition HNaBeSi 3 O 8 . 
 
 EUDIDYMITE, HNaBeSisOs, monoclinic prismatic class, a : b : c= 1.7107 : I : 
 1.1071, /3 = 9345^'. Occurs in simple and twinned, tabular crystals. Colorless, trans- 
 parent to translucent. Vitreous to pearly or silky luster. Basal cleavage. Hardness 
 6. Specific gravity 2.553. Easily fusible to a colorless or white glass. Partially de- 
 composed by acids. Occurs sparingly in nepheline syenite on the island of Ovre Aro, 
 Norway. 
 
 EPIDIDYMITE, HNaBeSisOs. Orthorhombic bipyramidal class, a : b : c~ 1.7274 
 : i : 1. 068. Simple crystals are usually elongated parallel to the a axis; often as pene- 
 tration twins. Properties are similar to those of eudidymite. Found in southern 
 Greenland associated with eudialyte, arfvedsonite, neptunite, albite, and zircon. A 
 rare mineral. 
 
 TITANITE GROUP 
 
 Here a number of silicates containing titanium or zirconium will be de- 
 scribed of which titanite is the most important. There are no close crystal- 
 lographic or chemical relationships to be noted between them. 
 
 TITANITE, Sphene, Grothite, CaTiSiO 5 . 
 
 Monoclinic, prismatic class, a : b : = 0.4272 : I : 0.6575, 94 
 38'. The habit varies greatly. Disseminated crystals are generally wedge 
 or envelope shaped, while attached crystals are apt to be tabular or prismatic, 
 
272 
 
 DESCRIPTIVE MINERALOGY 
 
 see figures 146 and 147. The common forms are the basal pinacoid c, unit 
 prism m, unit and modified (w 1/2) negative hemiorthodomes 3; and x, 
 clinodome r, and the hemipyramid 11(2.0, : b : 2/3^). In figure 147 the crys- 
 tal has been placed so that the hemipyramid n is vertical, emphasizing the 
 prismatic development parallel to these faces. Contact (Figure 148) and 
 penetration twins (sometimes cruciform) with the basal pinacoid as the 
 twinning plane are rather common. Occurs sometimes compact and massive, 
 more rarely lamellar. 
 
 FIG. 147 
 
 FIG. 148 
 
 Distinct prismatic and domatic cleavages. Conchoidal fracture. Brittle. 
 Hardness 5 to 5.5. Specific gravity 3.4 to 3.6. Transparent or translucent to 
 opaque. Vitreous luster, inclining to adamantine or greasy. Yellow, green, 
 brown, reddish brown, red, and black in color. The transparent or translu- 
 cent yellow, greenish, and other light colored varieties are called sphene, the 
 brown varieties grot kite. 
 
 CaTiSiO 5 . Commonly considered the calcium salt of the dimetasilicate 
 acid H 2 Si 2 O 5 , in which one atom of silicon has been replaced by titanium. 
 May also contain some FeO or MnO. Yttro titanite contains aluminium, 
 iron, and the elements of the yttrium group. Fuses with intumescence on 
 the edges to a dark colored glass. Only partially decomposed by hydrochloric 
 acid, completely by sulphuric and hydrofluoric acids. Titanite alters to rutile, 
 octahedrite, brookite, perovskite, magnetite, or ilmenite. Lcuco.vene and 
 titanomorphite are fine granular or fibrous aggregates of titanite, alteration 
 products of various titanium minerals. 
 
 Titanite occurs disseminated as an important accessory constituent of 
 many igneous rocks, especially hornblende granites, syenites, nepheline syen- 
 ites, trachytes, phonolites, and diorites ; also in crystalline schists and gran- 
 ular limestones. It is found attached in the cracks and cavities in granite, 
 gneiss, and various schists. The common associates are the amphiboles, py- 
 roxenes, apatite, zircon, scapolite, chlorite, and iron minerals. Some locali- 
 ties are Laacher See, Rhenish Prussia; many places in Switzerland and Ty- 
 
SILICATES 273 
 
 rol, especially in the St. Gotthard district, Tavetsch, Zillerthal, and Pfitsch- 
 thal ; Arendal, Norway ; Nordmark, Sweden ; Ural Mountains ; Tremadoc, 
 North Wales ; Grenville, Quebec, and Eganville, Renfrew County, Ontario, 
 Canada ; Sanford, Me. ; Bolton and Lee, Mass. ; Diana, Lewis County, Mon- 
 roe, Orange County, and elsewhere in New York ; Franklin Furnace, N. J. ; 
 Bucks County, Pa. ; Magnet Cove, Ark. 
 Titanite is sometimes used as a gem. 
 
 ZIRKELITE, Ca(Zr,Ti) 2 O 5 , is similar to titanite in general composition but contains 
 zirconium in place of silicon. Occurs in small black crystals belonging to the cubic 
 system in the pyroxenites of Jacupiranga, Province of Sao Paulo, Brazil. Hardness 
 5.5. Specific gravity 4.74. Resinous luster. 
 
 TSCHEFEKINITE is an alteration product of more or less uncertain composition. 
 Is essentially a titano-silicate of aluminium, cerium elements, iron, and beryllium. 
 Amorphous. Black. Vitreous luster. Hardness 5 to 5.5. Specific gravity 4.5 to 4.55. 
 Occurs in the Ural Mountains; southern India; Nelson and Bedford counties, Virginia. 
 
 , H 4 Na 2 ZrSi 3 O 11 . 
 
 Monoclinic at ordinary temperatures but at 140 it passes over into an hexagonal 
 modification. Its behavior is similar to that of tridymite. Hardness 6. Specific grav- 
 ity 2.8. Light yellow to yellowish brown in color, also blue, gray, reddish, and white. 
 Transparent to opaque. May contain calcium replacing some sodium. Found in Nor- 
 way and Greenland. 
 
 ELPIDITE, H 6 Na 2 ZrSisOi8. Orthorhombic. Columnar and felty fibrous masses. 
 White to brick red in color. Pearly luster. Occurs at Igaliko, southern Greenland. 
 
 , Na 18 ( Ca,Fe) 6 ( Si,Zr) 20 O 52 C1. 
 
 Hexagonal, ditrigonal scalenohedral class, a : c = i : 2.1116. Columnar or 
 tabular crystals, sometimes rather large. Also in granular or reniform masses. Red 
 to brown in color. Uncolored streak. Basal cleavage. Translucent. Conchoidal to 
 splintery fracture. Hardness 5 to 6. Specific gravity 2.9 to 3.1. Fuses easily with 
 intumescence to dark green blebby mass, coloring the flame yellow. Decomposed by 
 acids. with separation of silica, the solution reacts for zirconia. Occurs in nepheline 
 syenites at Kangerdluarsuk, Greenland; Kola peninsula, Russian Lapland; Magnet 
 Cove, Ark. Eucolite is a brownish variety occurring at Langesund fiord, Norway. 
 
 STEENSTRUPINE, a thoro-silicate of La, Di, Y, Na, Be, Pb, Nb, and Ce. Occurs 
 at Kangerdluarsuk, Greenland. 
 
 DYSANALYTE, may be considered as having the general formula 6RTiO 3 .RNb 2 O 5 , 
 where R is Ca, Fe, Mn, Ce, and Na 2 . Occurs 'in small, black crystals in granular lime- 
 stone at Voigtsburg, Kaiserstuhl, Baden. Formerly called perovskite. Found also on 
 Mount Vesuvius, Italy. 
 
 PYROCHLORE is similar to dysanalyte, the niobate predominating however. Occurs 
 in small octahedral crystals and in grains. Octahedral cleavage. Conchoidal fracture. 
 Hardness 5 to 5.5. Specific gravity 4.2 to 4.36. Brown, reddish, or blackish brown in 
 
274 DESCRIPTIVE MINERALOGY 
 
 color. Vitreous to resinous luster. Occurs in nepheline syenite at Laurvik, Norway; 
 Miask, Ural Mountains. 
 
 PYRRHITE is closely related to pyrochlore and is found in small, yellow red octa- 
 hedrons at San Miguel, the Azores, and in the Laacher See district, Rhenish Prussia. 
 
 POLYMIGNITE, Ca 3 (CeO)4(Ti 2 O5)5.Ca(NbO 3 )2. Titanium may be replaced by con- 
 siderable zirconium, cerium by yttrium, and calcium by small amounts of iron, man- 
 ganese, potassium, and sodium. Orthorhombic. Long columnar crystals, striated ver- 
 tically. Conchoidal fracture. Hardness 6 to 6.5. Specific gravity 4.75 to 4.85. Black 
 in color. Occurs in zircon syenite at Fredriksvarn, Norway. 
 
 AESCHYNITE is similar to polymignite in composition, but contains thorium and 
 at times helium. Orthorhombic. Columnar and tabular, but imperfectly developed, 
 crystals ; also massive. Iron black to brown in color. Yellow brown streak. Hard- 
 ness 5 to 6. Specific gravity 4.93 to 5.17. Occurs at Miask, Ural Mountains; Hittero, 
 Norway; Konigshain, Silesia. 
 
 POLYCRASE is essentially (Ca,Fe)4Y4(UO 2 )Ti 12 O35.2Y(NbO 3 )3. Orthorhombic. 
 Six-sided, thin tabular crystals, sometimes rather large. Striated vertically. Color 
 black. Streak grayish brown. Opaque, translucent in thin splinters. Hardness 5 to 6. 
 Specific gravity 4.7 to 5.1. Vitreous to resinous luster. Found at Hittero, Norway; 
 North and South Carolina. 
 
 EUXENITE is essentially a titanate and niobate of yttrium, erbium, and cerium, 
 containing uranium, iron, and helium. Orthorhombic, but crystals are rare. Com- 
 monly found massive. Hardness 6.5. Specific gravity 4.6 to 5. Color pitch black. 
 Reddish brown streak. Opaque. Submetallic to greasy vitreous luster. Occurs at 
 Arendal and Hittero, Norway. 
 
 BENITOITE, BaTiSi 3 O 9 . 
 
 Hexagonal, ditrigonal bipyramidal class, a : c = I : 0.7344. Crystals are ditri- 
 gonal bipyramidal and thick tabular in habit. Pale to deep blue in color, rarely color- 
 less. Transparent. Hardness 6.5. Specific gravity 3.65. Conchoidal fracture. Very 
 imperfect pyramidal cleavage. 
 
 BaTiSiaOo. Although commonly interpreted as a titano-silicate, it may be con- 
 sidered, .however, as a metasilicate of barium and titanium. Fuses easily to a trans- 
 parent glass. Practically insoluble in hydrochloric acid. Attacked by hydrofluoric acid 
 and readily dissolved by fused sodium carbonate. 
 
 Occurs associated with natrolite and neptunite in San Benito county, Cal. 
 
 Benitoite is used for gem purposes. 
 
 LORENZENITE, Na 2 Sio(Ti,Zr) 2 O 9 . 
 
 Orthorhombic, bipyramidal class, a : b : c = 0.6042 : i : 0.3592. Small, acicu- 
 lar crystals with distinct brachyprismatic cleavage. Britle. Hardness 6 to 6.25. Spe- 
 cific gravity 3.42. Brilliant adamantine luster. Colorless, inclining to violet or brown. 
 Transparent to translucent. Fuses easily to a black globule. Not attacked by acids. 
 It occurs, associated with aegirite, microcline, albite, and arfvedsonite in pegmatite at 
 Narsarsuk, southern Greenland. 
 
SILICATES .275 
 
 PETAUTE, Castorite, LiAl(Si 2 O 5 ) 2 . 
 
 Monoclinic, prismatic class, a : b : (7=1.1535 ' J : 0.7441, P = H226'. Col- 
 umnar or tabular crystals. Usually compact, fine granular, or foliated masses. 
 
 Perfect basal and imperfect domatic cleavages. Imperfect conchoidal fracture. 
 Brittle. Specific gravity 2.4 to 2.5. Hardness 6 to 6.5. Vitreous luster, inclining to 
 pearly. Transparent to translucent. Colorless, white, gray, reddish or greenish white. 
 Colorless streak. 
 
 LiAl(Si2Os)2. Sodium and potassium may replace some of the lithium. Phos- 
 phoresces when heated. Fuses on the edges and colors the flame red. Soluble in 
 hydrofluoric acid but not in the other common acids. 
 
 The common associates are spodumene, tourmaline, scapolite, lepidolite, and 
 quartz. It is found in the magnetite deposits of Uto, Sweden; Island of Elba; Bolton, 
 Mass.; Peru, Me. 
 
 NEPTUNITE, (Na,K) 2 (Fe,Mn) (Si,Ti) 5 O 12 . 
 
 Monoclinic, prismatic class, a : b : c = 1.3164 : I : 0.8075, = 113 38'. Pris- 
 matic crystals with vertical striations. Vitreous luster, inclining to metallic ; on cleav- 
 ages somewhat greasy. Black in color. Cinnamon brown streak. Distinct prismatic 
 cleavage. Hardness 5 to 6. Specific gravity 3.234. Fuses quite easily to a black glob- 
 ule. Not attacked by the common acids. Easily decomposed by fusion with the alkali 
 carbonates. Occurs with aegirite in the syenite of Igaliko, southern Greenland, and 
 with natrolite and benitoite in San Benito County, Cal. 
 
 MILARITE, HKCa 2 Al 2 (Si 2 O 5 ) 6 . 
 
 Pseudo-hexagonal, a : c =i : 0.6620. At ordinary temperatures biaxial and ap- 
 parently made up of orthorhombic trillings, becomes uniaxial on heating. Specific 
 gravity 2.5 to 2.6. Hardness 5 to 6. Vitreous luster. Colorless to pale green. Con- 
 choidal fracture. Transparent. Fuses easily and is partially decomposed by acids. 
 Occurs with smoky quartz, adularia, apatite, chabasite, titanite, and chlorite in granite 
 at Gletsch and Val Giuf, Switzerland. 
 
 ZEOLITES 
 
 The general term zeolite includes a number of important, hydrated sili- 
 cates, which usually crystallize exceedingly well and are closely related to 
 each other in general chemical composition, in many physical and chemical 
 properties, and also in methods of formation and occurrence. Crystailo- 
 graphically and optically, they are commonly very complex. 
 
 The zeolites are for the most part either hydrated ortho-, meta-, or poly- 
 silicates of aluminium, bearing striking resemblances to the minerals of the 
 nephelite, leucite, and feldspar groups. In many cases part of the aluminium 
 may be replaced by Na,O, CaO, or K,O, also by BaO, SrO, or MgO, but 
 never by the heavier metals. In one case, that of apophyllite, aluminium does 
 not enter at all into the chemical composition. 
 
276 DESCRIPTIVE MINERALOGY 
 
 All the zeolites are quite readily decomposed by hydrochloric acid, many 
 gelatinizing. They fuse easily with a characteristic intumescence. The 
 water may be driven off at different temperatures. In some cases it is so 
 loosely held that it escapes in a dry atmosphere, in others comparatively 
 high temperatures, even ignition, are necessary to remove all traces. Some 
 dehydrated zeolites take up water again when exposed to moisture. The 
 loss of water causes important changes in the optical properties. 
 
 The specific gravity of the various members of the group is relatively 
 low and varies from 2.0 to 2.4. The zeolites are all what may be called com- 
 paratively soft minerals, the hardness varying from 3.5 to 5.5. All are gen- 
 erally colorless, transparent to translucent, and highly vitreous ; sometimes 
 however, more or less colored, due to the presence of various pigments. 
 
 The zeolites are secondary minerals, the result of the decomposition of 
 the chemically related, primary minerals, such as nephelite, leucite, sodalite, 
 and the feldspars, especially the plagioclases. They are never found dis- 
 seminated, but almost always in cracks, crevices, and cavities in basic erup- 
 tive, igneous rocks, such as basalt, diabase, and phonolite ; more rarely in 
 granite and crystalline schists, and sometimes with ore deposits. Zeolites 
 are also sometimes deposited from hot springs, although high temperatures 
 are not essential to their formation. All zeolites decompose rather easily 
 and tend to form calcium carbonate and kaolin. Their common associates 
 are calcite, datolite, prehnite, and pectolite. 
 
 ORTHOSILICATES 
 
 Thomsonite, Comptonite, 2(Ca,Na,)AL(SiO 4 ) 2 .5H 2 O. 
 
 Orthorhombic, bipyramidal class, a : b : c 0.9932 : I : 1.0066. Ver- 
 tically striated prismatic crystals, generally arranged in sheaf- or fan-like 
 groups. The prism angle is 90 26' '. At times as heart-shaped twins, with 
 the unit prism as the twinning plane. Also compact and in spherical con- 
 cretions. 
 
 Perfect brachy- and imperfect macropinacoidal cleavages. Uneven frac- 
 ture. Brittle. Vitreous luster, inclining to pearly on the cleavages. Trans- 
 parent to translucent. Colorless to white, grayish, yellowish, brownish, and 
 reddish. A greenish variety is called lintonite. The colors are often banded 
 resembling agate. Uncolored streak. Hardness 5 to 5.5. Specific gravity 
 2.3 to 2.4. Gelatinizes with acids. Intumesces briskly, fusing to a white 
 enamel. 
 
 Occurs with other zeolites and prehnite in amygdaloidal and other ig- 
 neous rocks. Some localities are Kaaden, Hauenstein, and elsewhere, Bo- 
 hemia; Pflasterkaute, near Eisenach, Thiiringia ; Brevik, Norway; Seisser 
 Alp and in the Fassa valley, Tyrol ; Kilpatrick, Scotland ; Mount Vesuvius ; 
 
SILICATES 277 
 
 Faro island, Sweden ; Cyclopean islands, near Sicily ; Iceland ; Port George 
 and Peter's Point, Nova Scotia ; Table Mountain, Colo. ; rather commonly 
 in the amygdaloidal rocks of the Lake Superior district. 
 
 Sometimes cut and polished for gem and ornamental purposes. 
 
 HYDRONEPHEUTE, HNa 2 Al 3 ( SiO 4 ) 3 . 3H 2 O. 
 
 Probably hexagonal. Massive and radial fibrous aggregates. White, gray, or 
 grayish black. Uneven fracture. Vitreous luster, sometimes dull. Hardness 4 to 6. 
 Specific gravity 2.3 to 2.5. Fuses easily and gelatinizes with acids. Occurs in nephe- 
 line syenite at Litchfield, Me. ; also found on the various islands in the Langesund 
 fiord, Norway. Ranite is closely related to hydronephelite. 
 
 BASIC METASILICATES 
 
 A number of zeolites may be interpreted as being basic metasilicates, of 
 which the members of the natrolite group are the most important. 
 
 NATROLITE GROUP 
 
 The minerals of this group are aluminium silicates containing either 
 calcium, sodium, or barium, and two molecules of water. They crystallize 
 in the monoclinic and orthorhombic systems. Mesolite and scolecite are 
 monoclinic, edingtonite orthorhombic, while natrolite occurs in orthorhombic 
 and monoclinic modifications. The chemical formulas and axial ratios of 
 these minerals may be written as follows : 
 
 a 
 
 Natrolite, Na,Al(AlO) (SiO 3 ) 3 .2H 2 O. 
 
 1.0165 
 0.9786 
 
 c 
 
 0-3599, 90 5' 
 0.3536 
 
 MESOUTE, 
 
 Na 2 Al(AlO)(SiO 3 ) 3 .2H 2 O. ) 
 
 O Q777 ' I O 7226 O2 6' 
 
 CaAl(A1.2OH)(SiO 3 ) 3 .2H 2 O. i ' 9777 
 
 SCOLECITE, CaAl(A1.2OH)(SiO 3 ) 3 .2H 2 O. 0.9763 :i 10.3433, 90 42' 
 EDINGTONITE, 
 
 BaAl(A1.2OH)(SiO 3 ) 3 .2H 2 O. 0.9872 :i 10.3367 
 
 Mesolite is considered an isomorphous mixture of natrolite and scole- 
 cite. The most abundant and important member of the group is natrolite. 
 
 Natrolite, Needle Zeolite, Na 2 Al(AlO) (SiO 3 ) 3 .2H 2 O. 
 
 Dimorphous. Usually orthorhombic, bipyramidal class, a : b : c = 
 0.9786 : i.: 0.3536. Varieties containing small amounts of potassium are 
 monoclinic, prismatic class, a : b : c= 1.0165 : i : 0.3599, ^=-90 5'. 
 
278 DESCRIPTIVE MINERALOGY 
 
 Orthorhombic crystals are long prismatic, nearly square (the prism angle is 
 91 15'), or acicular, often radial, stellate, or interlacing groups or clusters. 
 The monoclinic crystals are very similar to the orthorhombic and are quite 
 rare. Occurs also in fibrous, granular, or compact masses. 
 
 Perfect prismatic cleavage. Brittle. Hardness 5 to 5.5. Specific grav- 
 ity 2.2 to 2.3. Vitreous luster, inclining to pearly. Fracture uneven. Trans- 
 parent to translucent. Colorless, white, flesh red, grayish, greenish, or yel- 
 lowish. 
 
 Na 2 Al(AlO)(SiO 3 ) s .2H 2 O. Some Na 2 O may be replaced by CaO or 
 K 2 O. Loses all of the water at 300, which is absorbed again in a moist 
 atmosphere. Fuses easily forming a colorless glass. Gelatinizes with acids. 
 
 Occurs in cracks and cavities in basic igneous rocks ; also in granite, 
 gneiss, and syenite. It is often an alteration product of lime-soda feldspars, 
 nephelite, sodalite, cancrinite, and noselite. Some localities are Teplitz and 
 Aussig, Bohemia ; Fassathal and elsewhere, Tyrol ; Faro island, Sweden ; 
 Hohentwiel and Kaiserstuhl, Baden ; Auvergne, France ; various places in 
 Norway, Ireland, and Scotland ; Bergen Hill, N. J. ; also in the Lake Superior 
 district, and in the trap of Nova Scotia. Natrolite is found with other zeo- 
 lites, with prehnite, and datolite. 
 
 Galactite, bergmannite, spreu-stein, brevicitc, crocalite, fargite, and meso- 
 type are all varieties of natrolite. 
 
 MESOUTE. 
 
 An isomorphous mixture of the natrolite and scolecite molecules, usually in the 
 ratio of I : 2. Monoclinic, prismatic class. For the elements of crystallization see 
 page 277. Crystals are similar to those of scolecite in habit. Hardness 5. Specific 
 gravity 2.2 to 2.4. White, porcelain-like, yellowish, or grayish. Occurs generally in 
 very slender, acicular crystals, often arranged in tufts. 
 
 SCOLECITE, CaAl(A1.2OH) (SiO 3 ) 3 .2H 2 O. 
 
 Monoclinic, domatic class, a : b : c = 0.9763 : I : 0.3433, P. = 90 42'. Nearly 
 square, slender prismatic crystals, very similar to those of natrolite; often acicular 
 and in divergent groups. Generally twinned parallel to the orthopinacoid, causing ver- 
 tical striations on the clinopinacoid. Also in compact, or radial fibrous or columnar 
 masses. 
 
 Fairly perfect prismatic cleavage. Brittle. Conchoidal to uneven fracture. Vit- 
 reous luster, fibrous varieties are silky. Colorless, white, yellowish, or reddish. Trans- 
 parent to translucent. Hardness 5 to 5.5. Specific gravity 2.2 to 2.4. 
 
 CaAl(A1.2OH)(SiO 3 )s.2H 2 O. About one-third of the water is held more firm- 
 ly than the other, ignition being necessary to drive off the last traces. The chemical 
 behavior ie similar to that of natrolite. 
 
 Not nearly as common as natrolite. Occurs in the Maderanerthal and elsewhere, 
 Switzerland; Iceland; Punah, East India; Black Lake, Megantic County, Quebec, 
 Canada; Table Mountain, Colo. 
 
SIIJCATES 
 
 279 
 
 EDINGTONITE, BaAl(A1.2OH) (SiO 3 ) 3 .2H 2 O. 
 
 Orthorhombic, bisphenoidal class, a : b : c = 0.9872 : I : 0.3367. Has been 
 considered tetragonal. Small pyramidal crystals, also massive. Vitreous luster. Trans- 
 lucent to opaque. White, grayish white, reddish, or brown. White streak. Hardness 
 4 to 4.5. Specific gravity 2.7. Fuses with difficulty to a colorless glass. Occurs asso- 
 ciated with harmotome in the Kilpatrick Hills, Scotland. 
 
 GANOPHYLLITE, Mn 7 (AlO)2(SiO 5 )8.6H 2 O, is also to be considered as a basic 
 metasilicate. Monoclinic, prismatic class, a : b : c = 0.413 : i : 1.831, /3 = 93 21'. 
 Occurs in flat prismatic crystals, also in foliated masses. Hardness 4. Specific grav- 
 ity 2.84. Vitreous luster- Brown in color. Reacts for manganese. Occurs in Harstig 
 mine, Pajsberg, Sweden. 
 
 NORMAL METASILICATES 
 
 The most important normal metasilicate among the zeolites is analcite. 
 
 ANALCITE, Na,Al 2 (SiO 3 ) 4 .2H 2 O. 
 
 Cubic, hexoctahedral class. Generally in well developed tetragonal tris- 
 octahedrons (w = 2), figure 149, or sometimes in combination with the cube, 
 figure 150. The other forms of this class are rarely observed. Crystals are 
 usually quite small, but may be in some cases a foot in diameter. Also com- 
 pact, granular, and earthy. 
 
 FIG. 149 
 
 FIG. 150 
 
 No prominent cleavage. Uneven to conchoidal fracture. Brittle. Hard- 
 ness 5 to 5.5. Specific gravity 2.2 to 2.4. Vitreous luster, sometimes dull. 
 Transparent to nearly opaque. Colorless, white, greenish, grayish, yellow- 
 ish, or reddish. White streak. 
 
280 
 
 DESCRIPTIVE MINERALOGY 
 
 Na,Al 2 (Si 3 O 8 ) (SiO 4 ) .2H 2 O. This formula shows its chemical rela- 
 tionship to soda leucite. Fuses to a colorless, clear glass. Gelatinizes with 
 acids. 
 
 Analcite is commonly a secondary mineral occurring with the other zeo- 
 lites, calcite, datolite, native copper, magnetite, and prehnite in basalt, dia- 
 base, amygdaloids, granite, gneiss, and related rocks. In some cases it is 
 thought to be primary, especially in analcite-basalts and analcite-phonolites. 
 Some localities are the Cyclopean Islands, near Sicily ; Seisser Alp and Fas- 
 sathal, Tyrol ; Aussig and Jabuken, Bohemia ; Arendal, Norway ; Brevik, 
 Sweden ; Andreasbe.rg, Hartz Mountains ; Faro Island ; Iceland ; Kilpatrick 
 Hills, Scotland ; various places in Nova Scotia ; Bergen Hill, N. J. ; Lake 
 Superior district; Table Mountain, Colo. 
 
 ACID METASILICATES 
 
 The following zeolites are to be interpreted as acid metasilicates because 
 some of the water can only be driven off upon ignition. A portion of the 
 water is, therefore, considered as being held by the silicon in the form of 
 hydroxyl groups. 
 
 APOPHYLLITE, H 14 K 2 Ca s ( SiO 3 ) 16 . gH 2 O. 
 
 Ditetragonal bipyramidal class, a : c=i: 1.2515. Four distinct habits 
 are common! (i) Long, square prisms, figure 151; (2) Pseudocubical, fig- 
 ure 152; (3) Pyramidal, figure 153; (4) Flat tabular, figure 154. The com- 
 
 0*7 
 
 FIG. 152 
 
 FIG. 151 
 
 FIG. 154 
 
 FIG. 153 
 
 mon forms are the prism of the second order a, unit .bipyramid of the first 
 order o, and the basal pinacoid c. The prism faces are often brilliant but 
 striated vertically, those of the basal pinacoid dull or rough, while the bipy- 
 
SII,I GATES 28l 
 
 ramid faces may be uneven. About sixty crystallbgraphic forms have been 
 recorded. Also occurs massive, and in granular and concentric aggregates. 
 
 Highly perfect basal, and imperfect prismatic cleavages. Uneven frac- 
 ture. Brittle. Hardness 4.5 to 5. Specific gravity 2.3 to 2.4. Vitreous to 
 pearly luster with a fish eye opalescence on the basal pinacoid. Usually trans- 
 parent, rarely nearly opaque. Often shows anomalous optical properties. 
 
 H 14 K,Ca8(SiO 3 ) 16 .9H 2 O. The composition is more or less uncertain. 
 Usually contains about 5% of K,O and up to 1.5% of fluorine. Some varie- 
 ties evolve small amounts of ammonia when ignited. Only a small part of 
 the water is given off at 100, about one half between 240 and 260, the 
 remainder being liberated upon ignition. Exfoliates and fuses easily to a 
 white enamel, coloring the flame violet. Decomposed by hydrochloric acid 
 with a separation of silica. Alters to calcite, pectolite, and perhaps also kao- 
 lin. 
 
 Occurs with the other zeolites, and datolite, pectolite, native copper, 
 magnetite, and calcite, as a secondary mineral in cracks and cavities in basalt 
 and basic igneous rocks, also in granite, gneiss, etc. Found at St. An- 
 dreasberg, Hartz Mountains ; Freiberg, Saxony ; Seisser Alp and Fassathal, 
 Tyrol ; Faro island, Sweden ; Iceland ; Greenland ; Nova Scotia ; Bergen Hill, 
 N. J. ; Table Mountain, Colo. ; Lake Superior copper district. 
 
 FAUJASITE, H 2 (Na 2 ,Ca) Al 2 (SiO 3 ) 5 .9H 2 O. 
 
 Cubic. Occurs in small octahedrons, sometimes twinned according to the spinel 
 law. Vitreous to adamantine luster. Transparent to translucent. Colorless, white, 
 or brown. Octahedral cleavage. Uneven fracture. Hardness 5.5 to 6. Specific grav- 
 ity 1.9. Decomposed by hydrochloric acid. Fuses with intumescence. Becomes doubly 
 refractive when a part of the water is driven off. Found on the Kaiserstuhl, Baden; 
 Annerod and Grossenbuseck, Hessen ; Daisy mica mine, Ottawa County, Quebec. 
 
 Heulandite, Stilbite in part, H 4 CaAl 2 (SiO 3 ) 6 .3H 2 O. 
 
 Monoclinic, prismatic class, a : b : c = 0.4035 : i : 0.4293, ^ = 91 
 25". Usually more or less tabular parallel to the clinopinacoid. Since many 
 crystals show striations similar to those on plagioclase, heulandite is some- 
 times considered triclinic and the crystals as polysynthetic twins. Occurs 
 also in foliated and granular masses, and in globular forms. 
 
 Perfect clinopinacoidal cleavage. Uneven fracture. Brittle. Vitreous 
 luster, pearly on the clinopinacoid . Transparent to translucent. Color 
 white, gray, brown, and red. White streak. Hardness 3 to 4. Specific 
 gravity 2.1 to 2.2. 
 
 H t CaAl 2 (SiO 3 ) c .3H 2 O. Some of the calcium is usually replaced by 
 strontium, also by potassium, sodium, and more rarely barium. Some of the 
 water is driven off only when ignited. Exfoliates and fuses to a white glass. 
 Decomposed by hydrochloric acid, but does not gelatinize. 
 
 Occurs with other zeolites in cavities in basalts, melaphyres, granites, 
 gneisses, and in ore deposits. Found at Berufiord, Iceland ; Faro island, 
 
282 DESCRIPTIVE MINERALOGY 
 
 Sweden : Arendal and Kongsberg, Norway ; Fassathal, Tyrol ; Kilpatrick 
 Hills, Scotland ; Nova Scotia ; Bergen Hill, N. J. ; north shore of Lake Su- 
 perior. 
 
 BREWSTERITE, H 4 ( Sr,Ba) A1 2 ( SiO 3 ) e . 3H 2 O. 
 
 Monoclinic, prismatic class, a : b : c =10.4046 : I : 0.4203, = 93 4'. A 
 variety of heulandite containing about 9% of SrO and 6.5% of BaO. Tabular or pris- 
 matic crystals. White, yellowish, brownish, greenish, or grayish. Hardness 5. Spe- 
 cific gravity 2.1 to 2.5. Occurs at Strontian in Argylesshire, and Kilpatrick Hills, Scot- 
 land; Giant's Causeway, Ireland; France; Baden. 
 
 EPISTILBITE, H 6 Ca,Al 4 ( SiO 3 ) 1X . 7H 2 O. 
 
 Monoclinic, prismatic class, a : b : c = 0.4194 : i : 0.2881, 18 = 90 40'. Similar 
 in form to heulandite, but differs from it chemically. Occurs at Berufiord, Iceland; 
 Scotland; Margaretville, Nova Scotia. 
 
 MORDENITK, (K 2 ,Na 2 ,Ca) Al 2 SiioO24.7H 2 O. Monoclinic. Very similar to heuland- 
 ite in crystal form. Occurs also in hemi-spherical, reniform, or cylindrical masses, often 
 with a fibrous structure. Clinopinacoidal cleavage. Uneven fracture. Hardness 3 to 
 5. Specific gravity 2.1 to 2.2. Vitreous luster, inclining to pearly. Translucent. 
 White, yellowish, or reddish. Found at Morden, Nova Scotia, and in the Hoodoo 
 Mountains, Wyo. 
 
 INESITE, Rhodotilite, (Mn,Ca) (Mn.OH) 2 SisO8.H 2 O. Triclinic, pinacoidal class. 
 a : b : c 0.9753 : i : 1.3208, a = 92 18', j3 = 132 56', 7 = 93 51'. Crystals are not 
 common, usually in fibrous and radiated aggregates and masses. Rose to flesh red in 
 color. Hardness 6. Specific gravity 3. Vitreous luster. White streak. Occurs with 
 manganese minerals in the Harstig mine, near Pajsberg, also at Jakobsberg, Sweden, 
 and at Dillenburg, Nassau, Germany; Durango, Mexico. 
 
 NEUTRAL POLYSILICATES 
 
 The harmotome and chabazite groups consist of minerals which may be 
 interpreted as being hydrated neutral polysilkates. 
 
 HARMOTOME GROUP 
 
 The members of this group crystallize in the monoclinic system, but ow- 
 ing to very complicated twinning are often pseudo-orthorhombic, pseudo- 
 tetragonal, or even pseudo-cubical in development. Chemically, they are 
 analogous to the plagioclases of the feldspar group, in that their fundamental 
 composition may be interpreted as being due to an isomorphous mixture of 
 two molecules somewhat similar to those of albite and anorthite. 
 
SIUCATES 283 
 
 a : b : c ft 
 
 STILBITE, (Ca,Na 2 )Al 2 Si 6 O 16 .6H,O. 0.7624 : i : 1.1939, 129 n' 
 Phillipsite, 
 
 mCaAl.Si.O^.GHoO. 1 
 
 nCa 2 Ai; S i 4 16 .6H 2 0.i ^S : i : 1.2563, 
 
 Harmotome, 
 
 mBaAl,Si O ia .6HoO. ) 
 
 5 
 
 I26 33 
 The first three members of the group are the most important. 
 
 STILBITE, Desmine. 
 
 Monoclinic, prismatic class, a : b : c =0.7624 : i : 1.1939, ^=129 
 n' '. Simple crystals are unknown, usually as tabular or penetration twins 
 with a pseudo-orthorhombic symmetry. The common forms are the basal 
 and clinopinacoids and the unit prism. The basal pinacoid is the twinning 
 plane. Very commonly several twin crystals are arranged in nearly parallel, 
 or what is sometimes called hypoparallel position, forming a sheaf-like 
 aggregate. 
 
 Perfect clinopinacoidal cleavage. Uneven fracture. Brittle. Hardness 
 3 to 4. Specific gravity 2.1 to 2.2. Vitreous luster, pearly on cleavages. 
 Transparent to translucent. Colorless to white, also brown, yellow, reddish 
 white, or brick red. White streak. 
 
 (Ca,Na 2 )Al 2 Si 6 O 16 .6H 2 O. Potassium may also be present. On heat- 
 ing water is liberated and the optical properties change forming metastilbite ; 
 when but two molecules of water are present the substance is orthorhombic, 
 while in the anhydrous condition it is amorphous. Exfoliates and swells up, 
 and fuses to a white glass. Decomposed by hydrochloric acid with a separa- 
 tion of SiO 2 . 
 
 Stilbite occurs with other zeolites in cavities in amygdaloidal basalts and 
 related rocks, also in granites and crystalline schists, and in ore deposits. 
 Occasionally it is deposited by hot springs, as at Olette in the Pyrenees 
 mountains. Some localities are Arendal and Kongsberg, Norway; Boden- 
 mais, Bavaria ; Faro Island, Sweden ; Island of Disco, Greenland ; Seisser 
 Alp, Fassathal, and elsewhere, Tyrol ; various places in Switzerland ; Dun- 
 bastonshire, Scotland ; Partridge Island and elsewhere, Nova Scotia ; Bergen 
 Hill, N. J. ; Lake Superior district ; Phillipstown, N. J. ; Table Mountain, 
 Colo. 
 
284 DESCRIPTIVE MINERALOGY 
 
 Phillipsite, Christianite. 
 
 Monoclinic, prismatic class, a : b : c = 0.7095 : I : 1.2563. /3 = 124 
 23'. Crystals are never simple but always twinned parallel to the basal pin- 
 acoid. The simplest twins are pseudo-orthorhombic or pseudo-tetragonal in 
 development. These crystals are often cruciform. Occasionally three of 
 the crossed twins are in three rectangular directions. These structures simu- 
 late the symmetry of the cubic system, especially when the reentrant angles 
 are filled, forming an apparent rhombic dodecahedron with characteristic 
 striations. Occurs also in spherical, radial fibrous aggregates. 
 
 Distinct basal and clinopinacoidal cleavages. Uneven fracture. Brittle. 
 Hardness 4 to 4.5. Specific gravity 2.2. Vitreous luster. Translucent to 
 opaque. Colorless, white, yellowish, grayish, reddish, or bluish. White 
 streak. 
 
 The composition of phillipsite may be expressed by the following formu- 
 la: wCaAl 2 Si y O 1G .6H 2 O -f- nCa 2 Al 4 Si 4 O 16 .6H 2 O. Calcium may be replaced 
 in part by potassium or sodium, but never by barium. Fuses easily to a white 
 glass. Gelatinizes with hydrochloric acid. 
 
 Occurs in cavities and fissures in basalt and related rocks. Found in 
 Germany at Stempel near Marburg, on the Kaiserstuhl, Annerod near Gies- 
 sen, and Asbach ; Lauban and Sirgwitz, Bohemia ; Giant's Causeway, Ireland ; 
 Mount Vesuvius ; Island of Sicily. 
 
 Harmotome. 
 
 Monoclinic, prismatic class, a : b : c 0.7031 : I : 1.2310, /3 = 124 
 50'. Crystals are similar to those of phillipsite. Crystals are generally larger 
 than those of phillipsite. The common forms are the three pinacoids 
 and the unit prism. 
 
 Fairly distinct basal and clinopinacoidal cleavages. Uneven fracture. 
 Brittle. Hardness 4 to 5. Specific gravity 2.45 to 2.5. Vitreous luster. Gen- 
 erally translucent, sometimes milky and cloudy. White, gray, yellow, red, or 
 brown in color. White streak. 
 
 Is an isomorphous mixture of wBaA! 2 Si 6 O 16 .6H 2 O and wBa 2 A! 4 Si 4 O 16 . 
 6H 2 O. Contains about 20% of BaO and i% of each of the oxides of po- 
 tassium and sodium. Fuses with difficulty and without intumescence to a 
 white glass. Sometimes phosphoresces when heated. Decomposed by hy- 
 drochloric acid, but does not gelatinize. 
 
 Occurs in amygdaloidal basalts and melaphyres, also in phonolite, tra- 
 chytes, and gneisses, and further with ore deposits. Found at Andreasberg, 
 Hartz Mountains ; Bodenmais, Bavaria ; Pribram, Bohemia ; Zillerthal. Ty- 
 rol; Strontian, Scotland; Christiania, Norway; Rabbit Mountain, Ontario, 
 Canada; New York City. 
 
 Monoclinic, prismatic class, a : b : c = 0.768 : i : 1.245, = 126 33'. Small, 
 complex twins similar to those of phillipsite and harmotome. Brittle. Hardness 4 
 to 4.5. Specific gravity 2.28 to 2.37. Vitreous luster. Colorless to white. 
 
 Is an isomorphous mixture w(Ca,Ba)Al 2 Si6Oi 8 .6H 2 O and nCCa.Ba^AUSuOw 
 6H 2 O. Also contains potassium, sodium, and strontium. Occurs with hornblende, feld- 
 spar, corundum, and chabazite in the Buck Creek corundum mine, Clay County, N. C. 
 
SILICATES 
 
 285 
 
 CHABAZITE GROUP 
 
 This group consists of two members which are interpreted as being iso- 
 morphous mixtures of calcium and sodium silicates containing eight mole- 
 cules of water of crystallization. They crystallize in the ditrigonal scalen- 
 ohedral class of the hexagonal system, cube-like rhombohedrons being rather 
 common forms. 
 
 a : c 
 
 Hexagonal, 
 .8H.O. 
 
 CHABAZITE, | m ^ a *! 2 5! i0 ' 
 ( nCa 2 Al 4 Si 4 O 1G 
 
 1.0860 
 
 wNa 9 Al Si 6 O 1 
 
 
 Hexagonal, 
 
 1.1017 
 
 Of these minerals, chabazite is by far the more common and important. 
 
 CHABAZITE. 
 
 Hexagonal, ditrigonal scalenohedral class, a : c=i : 1.0860. Gen- 
 erally in cube-like rhombohedrons, the pole angle being 94 46', Figure 155. 
 Crystals are sometimes more complex, Figure 156. Penetration twins hav- 
 ing parallel c axes, the twinning plane being the basal pinacoid, are quite 
 
 FIG. 155 
 
 FIG. 156 
 
 FIG. 157 
 
 common ; rarer are contact twins in which the unit rhombohedron is the 
 twinning plane. Phacolite is a variety occurring in twins with a lenticular, 
 hexagonal outline, Figure 157. Occurs also in compact masses. 
 
 Fairly distinct rhombohedral cleavage. Uneven fracture. Brittle. Hard- 
 ness 4 to 5. Specific gravity 2.1 to 2.2. Vitreous luster. Transparent to 
 translucent. Colorless, white, reddish, yellowish, or brown. White streak. 
 
 An isomorphous mixture of wCaAl 2 Si 6 O 16 .8H 2 O and Ca 2 Al 4 Si 4 O ]6 . 
 8H 2 O. Contents vary considerably, SiO 2 from 44 to $0%. Also contains 
 potassium and sodium replacing some of the calcium. Fuses with intumes- 
 cence to a nearly opaque, blebby glass. Decomposed by hydrochloric acid 
 with a separation of silica. 
 
286 DESCRIPTIVE; MINERALOGY 
 
 Associated with heulandite, stilbite, laumontite, and harmotome, it occurs 
 frequently in cavities in basalts, phonolites, and related rocks. Also ob- 
 served in granite, syenite, gneiss, mica and hornblende schists, and as a de- 
 posit of hot springs. Some localities are Oberstein and Annerod, Germany ; 
 Giant's Causeway, Ireland ; Aussig, Bohemia ; Faro Island, Sweden ; Green- 
 land ; Iceland : various places in Nova Scotia ; Richmond, Victoria ; near Bal- 
 timore, Md. ; Bergen Hill, N. J. ; Somerville, Mass. ; Table Mountain, Colo, 
 
 Hexagonal, ditrigonal scalenohedral class, a : c = i : i . 1017. Crystals have 
 generally an hexagonal habit, more rarely rhombohedral. Twins are not common. 
 Distinct prismatic cleavage. Uneven fracture. Brittle. Hardness 4 to 5. Specific 
 gravity 2.0 to 2.2. Vitreous luster. Transparent to translucent, generally translucent. 
 Yellowish or reddish white, flesh red in color, rarely colorless. 
 
 An isomorphous mixture of wNazAUSieOie.SHaO and Na2AUSi4Oi6.8H 2 O. Also 
 contains some calcium and potassium. Fuses easily to a white enamel. Decomposed 
 by hydrochloric acid with a separation of silica. 
 
 Occurs in the basalt of Montecchio Maggiore, northern Italy; Antrim, Ireland; 
 Isle of Skye, Scotland; Andreasberg, Saxony; Transylvania; Phillip Island, Victoria; 
 Nova Scotia; Bergen Hill, N. J. 
 
 Laumontite, Ca(A1.2OH) 2 (Si 2 O 5 ) 2 .2H 2 O. 
 
 Monoclinic, prismatic class, a : b : c= 1.1451 : i : 0.5906, /?= 111 
 14'. Occurs in long columnar crystals, and in radiating and divergent ag- 
 gregates ; also earthy. 
 
 Clinopinacoidal and prismatic cleavages. Hardness 3 to 4. Specific 
 gravity 2.25 to 2.35. Uneven fracture. Not very brittle, but very friable 
 when more or less weathered. Vitreous luster, inclining to pearly on cleav- 
 ages. White, yellowish, grayish, and reddish. Uncolored. 
 
 Ca(A1.2OH) 2 (Si 2 O 5 ) 2 .2H 2 O. Loses one molecule of water in a dry 
 atmosphere, the crystals becoming dull and cloudy, crumbling readily. The 
 other molecule escapes only when ignited. Dehydrated varieties absorb 
 water in a moist atmosphere. Fuses easily with intumescence to a white 
 glass. Gelatinizes with hydrochloric acid. 
 
 Found in cavities and fissures in syenite, basalt, melaphyre, and slates, 
 also with ore deposits. Occurs at Zillerthal, Tyrol ; various places in Switzer- 
 land; Faro Island, Sweden; Greenland; Transylvania; Port George and 
 Peter's Point, Nova Scotia ; Phippsburg, Me. ; Bergen Hill, N. J. ;' Table 
 Mountain, Colo. ; Lake Superior copper district. 
 
SILICATES 287 
 
 HYDRATED SILICATES CONTAINING CAR- 
 BONATES, SULPHATES, AND URANATES 
 
 Several rare minerals, which are hydrated -silicates containing carbon- 
 ates, sulphates, and uranates are placed here. Their composition is rather 
 complex. 
 
 THAUM ASITE, CaSiO 3 . CaSO 4 . CaCO 3 . i sH 2 O. 
 
 Hexagonal. Usually massive, compact, or fibrous. There are traces of a cleav- 
 age. White in color. Somewhat greasy luster. Hardness about 3.5, becomes harder 
 on exposure. Specific gravity 1.877. Infusible, but swells and colors the flame red. 
 Occurs in Sweden and at Paterson, N. J. 
 
 URANOTILE, Uranophane, CaU 2 Si 2 O 1;l .5H 2 O. 
 
 Triclinic, pinacoidal class, a : b : = 0.6257 : i : 0.5943, a 87 41', /3 = 85 18', 
 7 = 96 31'. Small, acicular crystals, often arranged radially; also fibrous and massive. 
 Uneven to conchoidal fracture. Hardness 2.5. Specific gravity 3.8 to 3.9. Honey 
 yellow, siskin green, or greenish black in color. May contain radium. Occurs at Kup- 
 ferberg, Silesia; Wolsendorf, Bavaria; Joachimsthal, Bohemia; Villeneuve, Ottawa 
 County, Quebec; Mitchell County, N. C. ; Stone Mountain, Ga. 
 
 GUMMITE, (Pb,Ca,Ba)U 3 SiO :2 .5H 2 O. 
 
 Cryptocrystalline, apparently amorphous. Occurs compact and disseminated ; 
 sometimes reniform. Conchoidal fracture. Slightly translucent to opaque. Greasy 
 luster. Reddish yellow, orange red, or reddish brown in color. Hardness 2.5 to 3. 
 Specific gravity 3.9 to 4.5. Composition varies a great deal. May contain radium. 
 Is an alteration product of uraninite. Found at Joachimsthal, Bohemia; Schneeberg 
 and Johanngeorgenstadt, Saxony; Flat Rock mine, Mitchell County, N. C. 
 
 AMORPHOUS HYDRATED SILICATES 
 
 A number of minerals are placed here, but only one, allophane, is of 
 sufficient importance to warrant a description. 
 
 Allophane, Al 2 SiO r ,.sH,O. 
 
 Amorphous. Reniform, botryoidal, stalactitic masses ; also as an in- 
 crustation. Resembles opal, especially hyalite. Uneven to conchoidal frac- 
 ture. Very brittle. Vitreous to resinous luster, internally bright and waxy. 
 Usually colored green or blue by copper compounds ; also colorless, yellow, 
 brown, and red. Uncolored streak. Translucent. Infusible. Gelatinizes 
 with hydrochloric acid. Occurs as an alteration product of aluminium sili- 
 cates and is commonly associated with copper compounds. Hardness 3. 
 
X. ORGANIC COMPOUNDS 
 
 SALTS OF ORGANIC ACIDS 
 
 Several compounds, which are salts of oxalic and mellitic acid, will be 
 described briefly. They do not occur to any extent as minerals. 
 
 WHEWELUTE, Calcium Oxalate, CaC 2 O 4 .H 2 O. 
 
 Monoclinic, prismatic class, a : b : c = 0.8628 : i : 1.3677, jS=i07o'. Tabu- 
 lar, prismatic, and pseudo-cubical crystals. Sometimes very large and highly modi- 
 fit 1 More than 50 forms have been recorded. Heart-shaped twins are common ; or- 
 thopinacoid is the twinning plane. Basal cleavage. Specific gravity 2.225 to 2.5. 
 Hardness 2.5. White to colorless. Vitreous to pearly luster. Occurs in coal mines 
 in Saxony and Bohemia. 
 
 OXAUTE, Humboldtine, 2FeC 2 O 4 .3H 2 O. 
 
 Acicular crystals, system undetermined. Usually in fibrous or granular aggre- 
 gates; also earthy, reniform, palty masses and as incrustations. Uneven to earthy 
 fracture Hardness 2. Specific gravity 2.13 to 2.5. Yellow color and streak. Opaque. 
 Easily soluble in acids. Found near Bilin, Bohemia; Gross-Almeorde, Hessen, Ger- 
 many; Kettle Point, Canada. 
 
 MEUJTE, ALC 12 O 12 .i8H 2 O. 
 
 Tetragonal, a : c=i : 0.7454. Simple, pyramidal crystals. Massive and gran- 
 ular. Conchoidal fracture. Brittle. Hardness 2 to 2.5. Specific gravity 1.6. Trans- 
 parent to translucent. Resinous to vitreous luster. Honey, straw, or reddish yellow 
 in color. White streak. Soluble in nitric acid Occurs with coal in Thuringia, Bo- 
 hemia, Moravia, and Russia. 
 
 HYDROCARBONS. 
 
 Petroleum and several closely allied mixtures of various hydrocarbons 
 will be described here. 
 
 Petroleum, Mineral Oil, Crude Oil. 
 
 A thin to thick viscious liquid with a brown, greenish brown, yellow or 
 black color and disagreeable odor. Rarely colorless and transparent. Pos- 
 sesses a characteristic greenish fluorescence. Specific gravity varies from 
 0.6 to 0.9. 
 
 Consists generally of a mixture of various members of the paraffin 
 series C n H, n .,. 2 , but may contain smaller amounts of the representatives of 
 the naphthene C n H, n and benzene C n H 2n _ 6 series. This is especially the 
 case with Russian petroleum. 
 
 Petroleum occurs in sandstones, shales, and limestones of different 
 geological ages. It is generally thought to be organic origin, although it 
 
ORGANIC COMPOUNDS 289 
 
 has been suggested that some petroleum may have been formed from inor- 
 ganic substances. In the United States there were produced in 1908 about 
 180,000,000 barrels of petroleum, Oklahoma, California, Illinois, Texas, 
 Ohio, West Virginia, Louisiana, and Pennsylvania being the largest pro- 
 ducers. The world's production for the same year was 250,000,000 barrels, 
 Russia, Galicia, India, Roumania, Japan, Mexico, Java, and Borneo ranking 
 next to the United States in importance. 
 
 Petroleum, either crude or refined, finds extended use as a fuel, for 
 lubricating and illuminating purposes, and as a source of a very large number 
 of important chemical preparations. 
 
 Ozocerite, Ozokerite, Mineral Wax, Native Paraffin. 
 
 Compact, fibrous, or lamellar masses, sometimes streaked or spotted, 
 consisting of microscopic, doubly refractivje fibres, which are probably 
 orthorhombic. Looks like wax or spermaceti, but is stickier. When pure is 
 colorless to white, generally greenish to yellow brown. If bitumen is present, 
 the color is apt to be black. Thin layers are brownish to reddish brown in 
 transmitted light. Soft, easily indented by the finger nail. Specific gravity 
 0.9 to 0.97. Greasy feel. 
 
 It is essentially native paraffin. Fuses at 70 to 83 C. Becomes plastic 
 between the fingers. Easily soluble in terpentirie and benzol, with difficulty 
 in alcohol and ether. 
 
 Occurs generally with petroleum as an impregnation in sandstones and 
 shales, but is sometimes associated with coal. The principal localities are 
 Boryslaw, Galicia ; Slanik, Roumania ; Baku, Russia ; Emery and Uinta 
 counties, Utah. 
 
 Refined ozocerite is termed ceresin, which is used in the manufacture 
 of candles, ointments, pomades, hydrofluoric acid bottles, leather polishes, 
 pencils, and sealing wax, and as an adulterant of or substitute for beeswax. 
 Okonite, a mixture of a residual product obtained in the process of purifi- 
 cation with resin, caoutchouc, and sulphur, is used extensively for insulating 
 electrical apparatus. 
 
 Hatchettite, urpethitc, zietrisikite, and chrismatite are very similar to 
 ozocerite. 
 
 Asphalt, Asphaltum, Mineral Pitch. 
 
 Amorphous, either as a solid or thick liquid. Brownish to pitch black 
 in color. Pitchy luster. When solid, it has a conchoidal fracture. Not very 
 brittle. Hardness I to 2. Specific gravity i.i to 1.8. Has a bituminous odor. 
 Melts at 90 to 100 and is easily inflammable. Completely or partially soluble 
 in alcohol, ether, petroleum, or terpentine. 
 
 Asphalt is an oxidation product of petroleum and varies greatly in 
 chemical composition. It is not confined to the rocks of any definite geolog- 
 ical age. Occurs sometimes in large pools or lakes and in veins, more com- 
 monly, however, as impregnations in sand, shale, sandstone, and limestone. 
 The principal localities for occurrences of the first kind are Trinidad, Bar- 
 badoes ; in Venezuela, and near the Dead Sea. Utah, Oklahoma, Texas, 
 Kentucky, Wyoming, and Arkansas have important deposits of rocks impreg- 
 nated with asphalt. 
 
2QO DESCRIPTIVE MINERALOGY 
 
 Gilsonite or uintahite is a variety occurring near Fort Duchesne, Utah. 
 Elaterite is an elastic asphalt from Derbyshire, England. Albertite occurs in 
 veins at Hilsborough, Albert County, New Bruswick, and is only partially 
 soluble in terpentine. Grahamite resembles albertite and is found in fissures 
 in West Virginia. 
 
 Asphalt and allied substances are used for paving purposes, road dres- 
 sing, in water-proofing metals, wood, papers, and fabrics, in electrical insula- 
 tions, adulteration of rubber, briquetting of coals, and so forth. 
 
 IDRIALITE. Probably C4oH 2 sO. Occurs with cinnabar and other inorganic ma- 
 terial. Foliated structure. Hardness I to 1.5. Specfic gravity 1.4 to 1.6. Dull to 
 greasy luster. Greenish, gary, or brownish black in color. Yields an indigo blue 
 color when dissolved in hot concentrated sulphuric acid. Found at Idria. 
 
 FlCHTEUTE, C 1S H 32 . 
 
 Monoclinic. a : 'b : c== 1.415 : i : 1.734, P=i2?. Small, tabular crystals and 
 aggregates. White. Pearly luster. Fuses at 46. Occurs as an incrustation on wood 
 in peat beds near Redwitz, Fichtelgebirge, Bavaria. 
 
 HARTITE, C 12 H 20 . 
 
 Probably monoclinic, although sometimes considered triclinic. Columnar or 
 tabular crystals. White, gray, or yellow in color. Hardness I to 1.5. Specific grav- 
 ity 1.05. Fuses at 74. Very soluble in ether. Occurs with coal at Oberhart, Aus- 
 tria, and at Rosenthal and Oberdorf, Styria. 
 
 PYROPISSITE. 
 
 Compact and earthy. Yellow to brown in color. Shiny streak. Dull luster. 
 Specific gravity 0.9. Easily fusible and inflammable. Occurs near Weisenfels, Sax- 
 ony, and at Eisleben and Eger, Bohemia. 
 
 RESINS. 
 Amber, Succinite. 
 
 Amorphous. Irregular, stalactitic, and disseminated masses, varying 
 in size from small grains to lumps weighing about 20 pounds. Large masses 
 are, however, very rare. Conchoidal fracture. Brittle, but easily worked 
 on the lathe. Hardness 2 to 2.5. Specific gravity i.o to i.i. Clear and trans- 
 parent to cloudy and translucent. Often opalescent and fluorescent. Greasy 
 luster. Generally yellow in color, also reddish, brownish, and whitish. 
 
 Amber consists of a mixture of an amorphous insoluble substance, 
 succinic acid, two soluble resins, and a volatile oil. Its chemical composition 
 is generally expressed by the formula C 40 H 64 O 4 . When heated, amber 
 softens, intumesces, and yields a characteristic aromatic odor. Melts, de- 
 composes, and evolves white fumes at 280 to 290. (Copal, which is very 
 similar in many respects to amber, melts at 200 to 220). Insoluble in 
 water. Abour 20 to 25% is soluble in warm alcohol, ether, chloroform, and 
 terpentine. Often contains many inclusions, among them various insects, 
 vegetable remains, liquids, and some minerals. 
 
ORGANIC COMPOUNDS 291 
 
 Amber is a fossil resin obtained from pre-historic conifers. It occurs: 
 principally in a glauconite sand, called blue earth, along the southern coast 
 of the Baltic Sea. Eastern Prussia, especially near the east of Konigsberg, 
 has been the chief source for hundreds of years of the amber of commerce. 
 It is also found various places along the coast of the North Sea in Courland 
 and Livonia, Russia ; Pomerania, Germany. It is reported as occurring also 
 in Roumania ; Spain ; at Lemberg, Galicia ; Catania, Sicily ; Santa Domingo ; 
 Kreischerville, Staten Island, N. Y. ; Eagle Pass and on the Terlingua Creek, 
 Texas ; near Trenton and Camden, N. J. 
 
 Amber is used in the manufacture of stems for pipes and cigar holders, 
 small jewelry, various ornaments, varnish, and as a source of succinic acid. 
 Chips are often pressed together and sold under the name of ambroid. 
 
 BURMITE is very similar to amber but does not contain succinic acid. It occurs 
 in considerabel quantities in Burma. 
 
 A comparatively large number of fossil resins are in many respects similar to 
 amber, but differ from it principally by the entire absence or the presence of but ver> 
 small amounts of succinic acid. They occur generally in coal or lignite, more rarely 
 in sandstone, shale, or clay. The following are only a few of such substances. Co- 
 palite occurs in the blue clay of High Gate, near London ; Retinite at Halle, Ger- 
 many, and Bovey Trace}, Dovenshire, England; Tasmanite in Tasmania; Waldiowite 
 in Moravia; Cedarite in Canada; and Gedanite in the vicinity of Konigsberg, Germany. 
 
 COALS. 
 
 Although the coals are strictly speaking rocks, a brief description of the 
 different varieties is usually given in Descriptive Mineralogy.* Coals are 
 the accumulated remains of vegetable life, which have been more or less 
 altered under the influence of geological processes. In some varieties the 
 plant remains are well preserved, in others entirely obliterated. They consist 
 principally of carbon, hydrogen, and oxygen, although small amounts of 
 nitrogen are generally present. The percentage of carbon is usually lowest 
 in varieties showing a distinct organic structure. The coals are found in 
 various geological formations, from some of the oldest to those which are 
 most recent. 
 
 Four varieties are generally differentiated: (i) Anthracite coal. 
 (2) Bituminous coal. (3) Lignite, and (4) Peat. According to Ries these 
 varieties have a general composition which may be expressed by the follow- 
 ing table : 
 
 C H O N S Ash Moisture 
 
 Anthracite Coal 90.45 2.43 2.45 4.67 
 
 Bituminous Coal 82.70 4.77 9.39 1.62 0.45 1.07 
 73.80 5.79 16.58 1.52 0.41 1.90 
 68.13 6.49 5.83 2.27 2.48 12.30 
 Lignite 58.44 4.97 16.42 1.30 
 
 Peat 59.47 6.52 31.51 2.51 0.22 
 
 * For detailed description, see Ries, Economic Geology of the United States, pp. I 
 to 38. 
 
292 DESCRIPTIVE MINERALOGY 
 
 Anthracite Coal, Hard Coal. 
 
 Contains the highest" percentage of fixed carbon and the lowest of 
 volatile hydrocarbons. Carbon varies between So% and 96%, in the anthra- 
 cites of Pennsylvania between 8$% and 93%. Black to iron gray in color. 
 Black streak. ' Opaque. Hardness 2 to 2.5. Specific gravity 1.3 to 1.7. 
 Vitreous luster, often including metallic. A brilliant iridescence is some- 
 times observed. Amorphous and compact. Conchoidal fracture. Brittle. 
 Does not show the organic structure. Ignites with difficulty, but gives 
 much heat. Does not impart a color to a solution of potassium hydroxide. 
 It occurs interbedded, principally in regions of folded strata. 
 
 Bituminous Coal, Soft Coal. 
 
 This variety ranks next to anthracite coal in the percentage of fixed 
 carbon present, which varies from 75% to 90%. Distinct organic structure 
 is not usually visible to the naked eye, but is easily recognized in thin sections 
 under the microscope. Amorphous and compact, generally showing stratifi- 
 cation ; occasionally fibrous. Brittle. Brown to black in color. Brown to 
 grayish brown streak. Vitreous, pitchy, or greasy luster. Conchoidal to 
 cubical fracture. Hardness 2 to 2.5. Specific gravity 1.15 to 1.5. May 
 contain as high as 30% of ash. Imparts no or only a very slight color to a 
 solution of potassium hydroxide. Burns with a yellow, smoky flame. Coking 
 coals are varieties of bituminous coal which yield coke, while non-coking 
 coals do not. Cannel coal is a compact, coking or non-coking, bituminous 
 coal containing a large amount of volatile constituents. It possesses a con- 
 choidal fracture, dull lustre, ignites easily, and burns with a yellow flame. 
 
 Lignite, Brown Coal. 
 
 Usually contains from 55% to 75% of carbon. Plant remains are gen- 
 erally easily detected by the naked eye. Brown to black in color. Brown 
 streak. Conchoidal fracture. Soft. Specific gravity 1.12 to 1.4. Burns 
 easily with a long, smoky flame. The heating power is lower than for 
 bituminous or anthracite coals. May contain much moisture, and then dis- 
 integrates easily on exposure to the air. Imparts a dark brown color to a 
 solution of potassium hydroxide. Jet is a compact, resinous, coal-black 
 variety of lignite, which takes a good polish and is used for small ornaments 
 and cheap jewelry. 
 
 Peat. 
 
 This variety consists of accumulations of more or less decomposed plant 
 remains. The carbon content varies between 50 and 60%. It is the first 
 product in the formation of coal. Brownish, yellowish, or black in color. 
 Loose and porous, often stratified. Occurs in swamps, marshes, and bogs. 
 When dried, it serves as a fuel. 
 
CLASSIFICATION OF MINERALS AC- 
 CORDING TO ELEMENTS 
 
 It is often desirable to know the minerals in which certain elements 
 occur and the following tables have been arranged to meet this need. In 
 most cases only the more important minerals are included in the classifica- 
 tion. The minerals are given under each element in the order in which they 
 have been described in the text. Page references to the detailed descriptions 
 are given after the formulas. 
 
 ACTINIUM 
 
 See uraninite, page 142. 
 
 ALUMINIUM 
 
 CORUNDUM, 
 
 Gibbsite, 
 
 Diaspora, 
 
 BAUXITE, 
 
 Fluellite, 
 
 Cryolite, 
 
 Alunite, 
 
 Aluminite, 
 
 Kalinite, 
 
 SPINELS, 
 
 Chrysoberyl, 
 
 Amblygonite, 
 
 Lazulite, 
 
 Variscite, 
 
 Wavellite, 
 
 Turquois, 
 
 STAUROLITE, 
 
 ANDALUSITE, 
 
 Sillimanite, 
 
 CYANITE, 
 
 TOPAZ, 
 
 TOURMALINE, 
 
 Zoisite, 
 
 EPIDOTE, 
 
 Hexagonal, 
 
 Monoclinic, 
 
 Orthorhombic, 
 
 Unknown, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Hexagonal, 
 
 Orthorhombic ? 
 
 Cubic, 
 
 Cubic, 
 
 Orthorhombic, 
 
 Triclinic, 
 
 Monoclinic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Amorphous, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Triclinic, 
 
 Orthorhombic, 
 
 Hexagonal, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 A1,O 3 , 84 
 Af(OH) 3 92 
 AIO(OH), 92 
 Al 2 0(OH) 4 ,- 9 4 
 A1F 3 . 3 H,O 106 
 Na 3 AlF 6 107 
 K 2 (A1.20H) 6 (S0 4 ) 4 ,-i 43 
 A1,(OH) 4 SO 4 .7H 2 O, 152 
 
 K 2 Al 2 (S0 4 ) 4 .2 4 H 2 0,-i 5 4 
 Mg(AlO 2 ) 2 , etc. 156 
 
 Be(AKX)o 161 
 Li(Al.F)P0 4 173 
 Mg(A1.0H) 2 (P0 4 ) 2 , 176 
 A1PO 4 .2H,O 179 
 
 (A1.0H),(P0 4 ),.5H 2 O 180 
 A1 (OH),PO 4 .H O 181 
 HFeAl 5 Si 2 O 18 ,i84 
 
 Al,SiO,, 187 
 
 Al,SiO 5> 1 88 
 
 AUSiO,, 189 
 
 Al 2 (F,OH) SiO 4 190 
 
 M' 9 Al 3 (B.OH) 2 Si 4 19 -i93 
 
 Ca AL(Al.OH) (SiO 4 ), 199 
 
 Ca 2 (Al,Fe) 2 (A1.0H)(Si0 4 ) 3 , 
 
 200 
 
294 
 
 DESCRIPTIv'E MINERALOGY 
 
 VESUVIANITE, 
 
 GARNETS, 
 
 Prehnite, 
 
 MICAS, 
 
 Chlorites, 
 
 KAOLINITE, 
 
 Pyrophyllite, 
 
 Nephelite, 
 Sodalite, 
 Spodumene, 
 AMPHIBOLES, 
 
 Leucite, 
 
 BERYL, 
 FELDSPARS, 
 
 ZEOLITES, 
 
 SCAPOLITE, 
 
 Allophane, 
 
 Tetragonal, 
 
 Cubic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Orthorhombic 
 
 or Monoclinic, 
 
 Hexagonal, 
 
 Cubic, 
 
 Monoclinic, 
 
 Orthorhombic 
 
 and Monoclinic, 
 
 Orthorhombic 
 
 and Cubic, 
 
 Hexagonal, 
 
 Monoclinic 
 
 and Triclinic, 
 
 Various systems 
 
 Tetragonal, 
 
 Amorphous, 
 
 CaJAl(OH,F)]Al,(SiO 4 ) 5 , 202 
 R'" 2 Al 2 (SiO 4 ) 3 , etc. 208 
 H,Ca,Al,(SiO 4 ) 3 , 213 
 H 2 KAl(SiO 4 ) 3 ,etc. 214 
 H 4 Mg 2 Al 2 SiO 9 , etc., 223 
 H 4 Al 2 SioO 9 230 
 H 2 Al 2 Si 4 O 12) 231 
 
 (Na,K) 8 Al 8 Si 9 O 84 232 
 
 Na 4 Al 2 (Al.Cl)(Si0 4 ) 3 ,-2 33 
 
 LiAl(SiO 3 ) 2 247 
 
 Silicates of Al, Ca, Mg, Fe 250 
 
 K 2 Al 2 Si 4 12 257 
 
 Be 3 Al 2 Si 6 O 18 258 
 KAlSi 3 O 8 , etc., 259 
 
 Hydrated silicates, 275 
 Ca 4 Al e Si 6 Oo 5 , etc., 270 
 Al 2 SiO 5 .5H 2 O 287 
 
 ANTIMONY 
 
 Native Antimony, 
 
 Allemontite, 
 
 STIBNITE, 
 
 Breithauptite, 
 
 Ullmannite, 
 
 Dyscrasite, 
 
 Nagyagite, 
 
 Miargyrite, 
 
 Zinkenite, 
 
 Plagionite, 
 
 Jamesonite, 
 
 Boulangerite, 
 
 Freieslebenite, 
 
 Pyrargyrite, 
 
 Bournonite, 
 
 TETRAHEDRITE, 
 
 Stephanite, 
 
 Polybasite, 
 
 Senarmontite, 
 
 Valentinite, 
 
 Kermesite, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Orthorhombic, 
 
 Hexagonal, 
 
 Cubic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Hexagonal, 
 
 Orthorhombic, 
 
 Cubic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Cubic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Sb 15 
 (As.Sb), 16 
 Sb 2 S 3 , 30 
 NiSb 37 
 NiSbS 41 
 Ag,Sb, 46 
 Au 2 Sb 2 Pb 10 Te 6 S 15 54 
 AgSbS 2 57 
 PbSb 2 S 4 57 
 Pb 5 Sb 8 S 17 58 
 Pb,SboS B 58 
 Pb 5 Sb 4 S lt -59 
 (Pb,Ag) 2 Sb 4 S 11 ,-59 
 Ag 8 SbS 3 59 
 Pb,Cu 2 Sb,S 6 60 
 M^SbsSr, 61 
 Ag 10 Sb 2 S 8 , 63 
 (Ag,Cu) 9 SbS 6 64 
 SboOo 69 
 Sb,O 3 69 
 Sb S,,O 97 
 
 ARGON 
 
 See uraninite, page 142. 
 
CLASSIFICATION ACCORDING TO ELEMENTS 
 
 295 
 
 Native Arsenic, 
 
 Allemontite, 
 
 REALGAR, 
 
 ORPIMENT, 
 
 Niccolite, 
 
 Cobaltite, 
 
 Gersdorffite, 
 
 Smaltite, 
 
 Chloanthite, 
 
 Sperrylite, 
 
 ARSENOPYRITE, 
 
 Lollingite, 
 
 Glaucodote, 
 
 Safflorite, 
 
 Rammelsbergite, 
 
 Skutterudite, 
 
 Whitneyite, 
 
 Algodonite, 
 
 Domeykite, 
 
 Lorandite, 
 
 Proustite, 
 
 TETRAHEDRITE, 
 
 Tordanite, 
 
 Enargite, 
 
 Arsenolite, 
 
 Mimetite, 
 
 Adamite, 
 
 Olivenite, 
 
 Erythrite, 
 
 Annabergerite, 
 
 Scorodite, 
 
 Pharmacolite, 
 
 Pharmacosiderite. 
 
 ARSENIC 
 
 Hexagonal, As, 15 
 
 Hexagonal, (As,Sb), 16 
 
 Monoclinic, AsS, 29 
 
 Monoclinic, As 2 S 3 , 30 
 
 Hexagonal, NiAs, 37 
 
 Cubic, CoAsS, 40 
 
 Cubic, NiAsS, 41 
 
 Cubic, CoAs 2 , 41 
 
 Cubic, NiAs 2 , 42 
 
 Cubic, PtAs 2 , 42 
 
 Orthorhombic, FeAsS, 43 
 
 Orthorhombic, FeAs,, 44 
 
 Orthorhombic, (Co,Fe)AsS, 44 
 
 Orthorhombic, CoAs 2 , 44 
 
 Orthorhombic, NiAs 2 , 45 
 
 Cubic, CoAs 3 , 45 
 
 Unknown, Cu 9 As, 45 
 
 Unknown, Cu 6 As, 45 
 
 Orthorhombic, Cu 3 As, 46 
 
 Monoclinic, TlAsS 2 , 57 
 
 Hexagonal, Ag 3 As~S 3 , 59 
 
 Cubic, M' ; 4 As 2 S T 6 1 
 
 Monoclinic, Pb 4 As 2 S 7 , 62 
 
 Orthorhombic, Cu 3 AsS 4 , 64 
 
 Cubic, As 2 O 3 , 69 
 
 Hexagonal, Pb r) Cl(AsO 4 ) 3 , 173 
 
 Orthorhombic, Zn(Zn.OH)AsO 4 175 
 
 Orthorhombic, Cu ( Cu.OH ) A sO 4 1 75 
 
 Monoclinic, Co 3 (AsO 4 ) 3 .8H 2 O, 178 
 
 Monoclinic, Ni 3 (AsO 4 ) 3 .8H 2 O. 179 
 
 Orthorhombic, FeAsO 4 .2H 2 O, 179 
 
 Monoclinic, CaHAsO 4 .2H O,- 180 
 
 Cubic, l^e(Fe.OH) 3 ("AsO 4 ) 3 .6H 2 O, 180 
 
 BARIUM 
 
 Bromlite, 
 WITHERITE, 
 
 Barytocalcite, 
 
 Bartocelestite, 
 
 BARITE, 
 
 Barylite, 
 
 Hyalophane, 
 
 Celsian, 
 
 Benitoite, 
 
 Edingtonite, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Orthorhombic ? 
 
 Monoclinic, 
 
 Triclinic, 
 
 Hexagonal, 
 
 Orthorhombic 
 
 and Monoclinic 
 
 (Ca,Ba)CO 3 121 
 BaCO 3 , 122 
 BaCO 3 .CaCO 3 123 
 
 (Sr,Ba)S0 4 ,-i 35 
 BaS0 4 135 
 Ba 4 Al 4 Si 7 O 24 235 
 KAlSi 3 O 8 -fBaAl 2 Si 2 O 8 263 
 BaAl,Si,O 8) 269" 
 BaTiSi 3 6 () , 274 
 BaAl( A1.2OH) (SiO 3 ) 3 .2H 2 O, 
 
 279 
 
296 
 
 DESCRIPTIVE MINERALOGY 
 
 Brewsterite, 
 
 Monoclinic, H 4 ( Sr,Ba) A1 2 ( SiO 3 ) 6 .3H 2 O 2: 
 
 Harmotome, 
 
 Monoclinic, BaAl,Si 6 O 10 .6H 2 O, etc., 284 
 
 Wellsite, 
 
 Monoclinic, (Ca,Ba)Al 2 Si 6 O 16 .6H 2 O, etc., 2 
 
 See also 
 
 psilomelane, 129. 
 
 
 BERYLLIUM 
 
 Chrysoberyl, 
 
 Orthorhombic, Be(AlO 2 ) 2 161 
 
 Beryllonite, 
 
 Ortho rhombic, NaBePO 4 , 165 
 
 Herderite, 
 
 Monoclinic, Ca(Be.OH)PO 4 175 
 
 Euclase, 
 
 Monoclinic, Be(Al.OH)SiO 4 , 192 
 
 Gadolinite, 
 
 Monoclinic, Fe[Be(Y.O)SiO 4 ~|o, 193 
 
 Helvite, 
 
 Cubic, ( Mn,Be,Fe) 7 S ( Si6 4 ) 198 
 
 Danalite, 
 
 Cubic, ( Fe,Zn,Be,Mn) 7 S ( Si6 4 ) 3198 
 
 Phenacite, 
 
 Hexagonal, Be 2 SiO 4 , 205 
 
 BERYL, 
 
 Hexagonal, Be 3 Al,(SiO 3 ) c , 2 57 
 
 Eudidymite, 
 
 Monoclinic, HNaBeSi 3 O 8 , 271 
 
 Epididymite, 
 
 Orthorhombic, HNaBeSi 3 O 8 , 271 
 
 See also 
 
 tscheffkinite, 273, and steenstrupine, 273. 
 
 
 BISMUTH 
 
 Native Bismuth, Hexagonal, Bi, 16 
 
 Bismuthinite, 
 
 Orthorhombic, Bi 2 S s , 31 
 
 Guana juatite, 
 
 Orthorhombic, Bi 2 (Se,S) 3 , 31 
 
 Tetradymite, 
 
 Hexagonal, Bi 2 Te 2 S, 31 
 
 Emplectite, 
 
 Orthorhombic, CiuBi S 4 , 57 
 
 Cosalite, 
 
 Orthorhombic, Pb 2 Bi~S,, 58 
 
 Aikinite, 
 
 Orthorhombic, Pb 2 Cu 2 Bi 2 S , 61 
 
 Bismite, 
 
 Orthorhombic, Bi 2 O 3 , 70 
 
 Bismutite, 
 
 Amorphous, Bi CO-.H 2 O, 125 
 
 Eulytite, 
 
 Cubic, Bi 4 (SiOJ 8 , 207 
 
 Agricolite, 
 
 Monoclinic, Bi 4 (SiO 4 ) 3 , 208 
 
 
 BORON 
 
 Sassolite, 
 
 Triclinic, B(OH) 3 91 
 
 Sussexite, 
 
 Unknown, [ (Mn,Mg)OH]BO 2 162 
 
 Boracite, 
 
 Orthorhombic Mg 7 Cl 2 B 10 O 30 , 162 
 
 
 and Cubic, 
 
 BORAX, 
 
 Monoclinic, Na,B 4 O 7 .ioH,O, 163 
 
 Ulexite, 
 
 Monoclinic, NaCaB B O .6H 2 O, 163 
 
 Pandermite, 
 
 Monoclinic, ' Ca.jBgOu.3HjO, 164 
 
 Colemanite, 
 
 Monoclinic, Ca B O lt .5H~O, 164 
 
 Sulfoborite, 
 Dumortierite, 
 
 Orthorhombic, 4M~srHBO,.2MgSO 4 7H,O, 164 
 Orthorhombic, HBAl 8 Si 3 6, , 185 
 
CLASSIFICATION ACCORDING TO ELEMENTS 
 
 Datolite, 
 
 Homilite, 
 TOURMALINE, 
 
 Danburite, 
 Axinite, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Hexagonal, 
 
 Orthorhombic, 
 
 Triclinic, 
 
 Ca(B.OH)SiO 4 192 
 Fe[Ca(B.6)SiO 4 ],, 193 
 M%Al 3 (B.OH) 2 Si;0 19 -i 93 
 CaB 9 (SiO 4 ) 2207 
 
 ., 213 
 
 BROMINE 
 
 Only a few minerals contain bromine. 
 
 E^nbolite, 
 
 Bromyrite, 
 
 lodobromite, 
 
 Cubic, 
 Cubic, 
 Cubic, 
 
 Ag(Cl,Br), 102 
 AgBr, 102 
 Ag(Cl,Br,I),-io2 
 
 CADMIUM 
 
 There are only two minerals containing cadmium in sufficiently large 
 quantities to find expression in the formulas. 
 
 Greenockite, Hexagonal, CdS, 35 
 
 Oxide of Cadmium, Cubic, CdO, 83 
 
 Not infrequently present in small quantities in sphalerite, 33, wurtzite, 
 35, and smithsonite, 117. 
 
 CAESIUM 
 
 There is only one caesium mineral. 
 Pollucite, Cubic, H 2 Cs 4 Al 4 (SiO 3 ) 9 
 
 Caesium is often present in small quantities in lepiclolite, 219, and 
 beryl, 257. 
 
 CALCIUM 
 
 Oldhamite, 
 
 Hyclrophilite, 
 
 FLUORITE, 
 
 Tachydrite, 
 
 CALCITE, 
 
 DOLOMITE, 
 
 Ankerite, 
 
 Manganocalcite, 
 
 ARAGONITE, 
 
 Bromlite, 
 
 Tarnowitzite, 
 
 Bartyocalcite, 
 
 Pirssonite, 
 
 Gay-Lussite, 
 
 Glauberite, 
 
 Cubic, 
 
 Cubic, 
 
 Cubic, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 107 
 
 CaS,-33 
 CaCL,, 103 
 CaF 2 , 103 
 2MgCl 2 .CaCl,.i2H 2 O, 
 CaCO 3 , in 
 CaMg(C0 3 ) 2 115 
 (Ca,Mg,Fe)CO, 116 
 (Mn,Ca)CO 3 118 
 CaCO 3 . 119 
 (Ca,Ba)CO 3 , 121 
 (Ca,Pb)CO, 122 
 BaCO,.CaCO, 123 
 Xa.,CO 3 .CaC6 3 .2H.,O 127 
 Na CO n .CaCO a .5H "O, 127 
 Na,SO 4 .CaSO 4 132 
 
DESCRIPTIVE MINERALOGY 
 
 'ANHYDRITE, 
 
 Powellite, 
 
 Scheelite, 
 
 GYPSUM, 
 
 Ulexite, 
 
 Pandermite, 
 
 COLEMANITE, 
 
 APATITE, 
 
 Autunite, 
 
 Clinohedrite, 
 
 Datolite, 
 
 Homilite, 
 
 Lawsonite, 
 
 Ilvaite, 
 
 Zoisite, 
 
 Clinozoisite, 
 
 EPIDOTE, 
 
 Piemontite, 
 Orthite, 
 
 VESUVIANITE, 
 
 Monticellite, 
 
 GARNET, 
 
 Prehnite, 
 
 Hardystonite, 
 
 Perovskite, 
 
 PYROXENES, 
 
 AMPHIBOLES, 
 
 Orthorhombic, 
 
 Tetragonal, 
 
 Tetragonal, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Hexagonal, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Monoclinic, 
 Monoclinic, 
 
 Tetragonal, 
 
 Orthorhombic, 
 
 Cubic, 
 
 Orthorhombic, 
 
 Tetragonal, 
 
 Pseudo-cubic, 
 
 Orthorhombic, 
 
 Monoclinic, and 
 
 Triclinic, 
 
 Orthorhombic, 
 
 Monoclinic, and 
 
 Triclinic, 
 
 Triclinic, 
 
 ANORTHITE 
 and PLAGIOCLASES, 
 SCAPOI>ITE, Tetragonal, 
 
 TITANITE, Monoclinic, 
 
 ZEOLITES, Various systems, 
 
 Whewellite, Monoclinic, 
 
 CaS0 4 133 
 CaMoO 4 139 
 
 CaW0 4 139 
 CaSO 4 .2H 2 O 146 
 NaCaB B O 9 .6H,O, 163 
 Ca,P> 6 O 11 .3H 6, 164 
 Ca 2 B 6 lv 5HA 164 
 Ca 5 F(P0 4 ) 3 ,-i 7 o 
 Ca (UO 2 ) o ( PO 4 ) 2 .8H,O 182 
 (Zn.OH ) ( Ca.OH ) Si6 3 187 
 Ca(B.OH)SiO 4 192 
 Fe[Ca(B.O)SiOJ,, 193 
 Ca(A1.2OH),(SiO 3 ),, 196 
 CaFe 2 (Fe.OH) (SiO 4 ) 2 196 
 Ca,Al,(Al.OH) (SiO 4 ) 3 199 
 Ca 2 Al,(Al.OH) (SiO 4 ) 3 199 
 Ca 2 (A"l,Fe) 2 (Al.OH) (SiOJ 3 , 
 
 200 
 Ca 2 (Mn,Al) 2 (Al.OH) (SiO 4 ) 3 , 
 
 2OI 
 
 Ca 2 (Al,Ce,Fe) 2 (Al.OH) (SiO 4 ) 3 , 
 
 2OI 
 
 Ca 6 [ Al ( OH,F) ] A1 2 ( SiO 4 ) 202 
 CaMgSiO 4 203 
 Ca 3 Al 2 (SiO 4 ) 3 , etc., 208 
 H,Ca 2 Al 2 (SiO 4 ) 3 ,2i 3 
 Ca ZnSi 2 O 7 , 235 
 CaTiO,, 238 
 CaMg(Si0 3 ) 2 ,etc. 240 
 
 CaMg 3 (SiO 3 ) 4 ,etc., 251 
 
 CaAl 2 Si 2 O 8 , etc., 268 
 
 Ca 4 Al Si G O 2 ,,, etc., 270 
 CaTiSiO,, 271 
 Hydrated silicates, 275 
 CaC,O 4 .H 2 O 288 
 
 DIAMOND, 
 GRAPHITE, 
 
 Schungite, 
 
 CARBON 
 
 Cubic, C 3 
 
 Hexagonal, C, n 
 
 Amorphous, C, 12 
 
 Carbon is also an essential constituent of the carbonates, pages no to 
 128. and of the organic substances described on pages 288 to 292. See the 
 lists of the various elements. 
 
CLASSIFICATION ACCORDING TO ELEMENTS 299 
 
 CERIUM 
 
 Tysonite, Hexagonal, (Ce,La,Di)F,5, 105 
 
 Monazite, Monoclinic, (Ce,L,a,Di)PO 4 , 167 
 
 Orthite, Monoclinic, Ca 2 (Al,Ce,Fe) 2 (Al.OH) (SiO 4 ) 3 , 
 
 2OI 
 
 Cerite, Orthorhombic, H 6 (Ca,Fe) 2 Ce 6 Si 6 O 26 , 202 
 
 See also thorite, 80, uraninite, 142, gadolinite, 193, tscheffkinite, 273, 
 steenstrupine, 273, polymignite, 274, aeschynite, 274, and euxenite, 274. 
 
 CHLORINE 
 
 Chlorine is an essential constituent of the chlorides, pages 98 to 108. 
 Also consult the lists of the various elements. It is present in small amounts 
 in sulphohalite, 145, hanksite, 145, kainite, 154, apatite and related minerals, 
 170 to 173, davyne, 233, sodalite, 233, and lazurite, 234. 
 
 CHROMIUM 
 
 Crocoite, Monoclinic, PbCrO 4 , 138 
 
 Chromite, Cubic, (Fe,Cr) [(Cr,Fe)O 2 ] 2 158 
 
 Uvarovite, Cubic, Ca 3 (Al,Cr) 2 (SiO 4 ) 3 , 211 
 
 COBALT 
 
 Cobaltite, Cubic, CoAsS 2 40 
 
 Smaltite, Cubic, CoAs 2 , 41 
 
 Glaucodote, Orthorhombic, (Co,Fe)AsS, 44 
 
 Safflorite, Orthorhombic, CoAs 2 , 44 
 
 Skutterudite, Cubic, CoAs 3 , 45 
 
 Linnaeite, Cubic, (Ni,Co) 3 S 4 56 
 
 Winklerite, Unknown, (Co,Ni) 2 O(OH) 4 94 
 
 Sphaerocobaltite, Hexagonal, CoCO 3 , 119 
 
 Bieberite, Monoclinic, CoSO^H.O, 151 
 
 Erythrite, Monoclinic, Co 3 (AsOj 2 .8H 2 O 178 
 
 Kottigite, Monoclinic, (Zn,Co) 3 (AsO 4 ) 2 .8H 2 O, 179 
 
 COLUMBIUM 
 
 See niobium, page 309. 
 
 COPPER 
 
 NATIVE COPPER,Cubic, Cu 21 
 
 Whitneyite, Unknown, Cu 9 As, 45 
 
 Algodonite, Unknown, Cu 6 As, 45 
 
300 
 
 DESCRIPTIVE MINERALOGY 
 
 Domeykite, 
 
 CHALCOCITE, 
 
 Stromeyerite, 
 
 Covellite, 
 
 Barnhardtite, 
 
 BORNITE, 
 
 CHALCOPYRITE, 
 
 Emplectite, 
 
 Bournonite, 
 
 Aikinite, 
 
 TETRAHEDRITE, 
 
 Pearceite, 
 
 Polybasite, 
 
 Enargite, 
 
 Stannite, 
 
 CUPRITE, 
 
 Melaconite, 
 
 (Tenorite) 
 Nantokite, 
 Marshite, 
 Atacamite, 
 MALACHITE, 
 AZURITE, 
 Aurichalcite, 
 
 Linarite, 
 
 Stelznerite, 
 
 Brochantite, 
 
 Cupromagnesite, 
 
 Chalcanthite, 
 
 Libethenite, 
 
 Olivenite, 
 
 Clinoclasite, 
 
 Euchroite, 
 
 Chalcophyllite, 
 
 Torbernite, 
 Zeunerite, 
 Dioptase, 
 Chrysocolla, 
 
 Orthorhombic, Cu 3 As, 46 
 
 Orthorhombic, Cu 2 S, 49 
 
 Orthorhombic, (Cu,Ag) 2 S, 50 
 
 Hexagonal, CuS, 51 
 
 Unknown, Cu 4 Fe 2 S 5 , 54 
 
 Cubic, Cu 3 FeS 3 , 55 
 
 Tetragonal, CuFeS 2 , 55 
 
 Orthorhombic, Cu 2 Bi 2 S 4 , 57 
 
 Orthorhombic, Pb 2 Cu 2 Sb 2 S 6 , 60 
 
 Orthorhombic, Pb.,Cu 9 Bi.,S 6 , 61 
 
 Cubic, M" 4 R'~" 2 S 7 61 
 
 Monoclinic, (Ag,Cu) 9 AsS 6 , 63 
 
 Monoclinic, (Ag,Cu) SbS 6 , 64 
 
 Orthorhombic, Cu 3 AsS 4 , 64 
 
 Tetragonal, Cu 2 FeSnS 4 65 
 
 Cubic, Cu 2 O 88 
 
 Monoclinic, Cub, 89 
 
 Cubic, Cu 2 Cl 2 , 105 
 
 Cubic, Cu 2 L, 105 
 
 Orthorhombic, Cti ( OH ) Cl.Ca ( OH ) 1 08 
 
 Monoclinic, CuCO 3 .Cu(OH) 2 , 124 
 
 Monoclinic, 2CuCO 3 .Cu(OH) 2 , 124 
 
 Monoclinic, 2(Zn,Cu)CO a .3(Zn,Cti) (OH) 2 , 
 
 -125 
 
 Monoclinic, (Pb,Cu)SO 4 (Pb,Cu) (OH) .,,144 
 
 Orthorhombic, Cu SO 4 .2Cu ( OH ) , 144 
 
 Orthorhombic, CuSO 4 .3Cti(OH) a , 144 
 
 Monoclinic, (Cu,Mg)SO 4 .7H 8 O 151 
 
 Triclinic, CuSO 4 .5H O, 151 
 
 Orthorhombic, Cu (Cu.OH) PO 4 , 175 
 
 Orthorhombic, Cu(Cu.OH)AsO 4 , 175 
 
 Monoclinic, ( Cu.OH ) 3 AsO 4 , 176 
 
 Orthorhombic, Cu ( Cu.OH) AsO 4 .3H,O, i8q 
 
 Hexagonal, (Cu.OH) 3 AsO 4 .Cu(O"H) 2 . 3 ^H 2 O, 
 
 i 80 
 
 Tetragonal, Cu (UO 2 ) 2 ( PO 4 ) ,.8H O , 182 
 
 Tetragonal, Cu(UO 2 ) 2 (AsO 4 ) 2 .8H 2 O 182 
 
 Hexagonal, H 2 CuSiO 4 , 211 
 
 Amorphous, *H 2 CuSiO 4 .H 2 O, 212 
 
 DIDYMIUM 
 
 See the cerium, thorium, and yttrium minerals, pages 299, 315, and 317. 
 
 ERBIUM 
 
 Same as for cerium. 
 
CLASSIFICATION ACCORDING TO ELEMENTS 
 
 301 
 
 FLUORINE 
 
 FLUORITE, 
 
 Sellaite, 
 
 Tysonite, 
 
 CRYOLITE, 
 
 Pachnolite, 
 
 Thomsenolite, 
 
 Sulphohalite, 
 
 APATITE, 
 
 Amblygonite, 
 
 Tilasite, 
 
 Wagnerite, 
 
 Triplite, 
 
 TOPAZ, 
 
 Chondrodite, 
 
 Humite, 
 
 Clinohumite, 
 
 VESUVIANITE, 
 
 Lepidolite, 
 
 Zinnwaldite, 
 
 Cubic, 
 
 Tetragonal, 
 
 Hexagonal, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Cubic, 
 
 Hexagonal, 
 
 Triclinic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Tetragonal, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 See also tourmaline, page 193. 
 
 CaF 2 , 103 
 MgF 2 , 104 
 
 (Ce,La,Di)F 3 , 105 
 Na.,AlF 107 
 AlF 8 .NaCaF 3 .H O, 108 
 AlF 3 .NaCaF 3 .H,O 108 
 3Na,SO 4 .NaCl.NaF 145 
 Ca,F(P0 4 ) 3 ,-i 7 o 
 Li(Al.F)PO 4 173 
 Ca(Mg.F)As0 4 174 
 Mg(Mg.F)P0 4 175 
 Fe(Fe.F)PO 4 , 176 
 AL(F,OH) SiO 4 190 
 [Mg(F,OH)] 2 Mg 3 (Si0 4 ) 2 ,-i 9 7 
 [Mg(F,OH)] 2 Mg n (Si0 4 ) 3 ,-i 97 
 [Mg(F,OH)],Mg T (Si0 4 ) 4> 198 
 Ca [ Al ( OH,F) ] Al, ( SiO 4 ) ,,202 
 (Li,K),(F,OH) 9 AL ) Si 3 O, ) 219 
 (Li,K) 3 (F,OH):Al 3 "FeSi 5 10 -22o 
 
 G ALL IUM 
 
 See sphalerite, page 34. 
 
 GERMANIUM 
 
 Onl two minerals contain ermanium. 
 
 Canfieldite, 
 Argyrodite, 
 
 Cubic, 
 Cubic, 
 
 Ag s (Sn,Ge)S c 66 
 Ag 8 GeS G 66 
 
 GLUCINUM 
 
 See beryllium, page 296. 
 
 GOLD 
 
 NATIVE GOLD, 
 
 Gold Amalgam, 
 
 Petzite, 
 
 Sylvanite, 
 
 Calaverite, 
 
 Krennerite, 
 
 Nagyargite, 
 
 Cubic, 
 
 Cubic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 An 25 
 
 (Au,Hg,Ag), 28 
 (Ag,Au) 2 Te 50 
 
 (Au,Ag)Te 2 53 
 AuTe.,, 54 
 (Au,Ag)Te 2 54 
 Au 2 Sb 2 Pb 10 Te 6 S 15 , 54 
 
302 
 
 DESCRIPTIVE MINERALOGY 
 HELIUM 
 
 See uraninite, page 142. 
 
 HYDROGEN 
 
 Hydrogen, combined with oxygen either as water or the hydroxyl.. is 
 present- in many minerals, especially the oxides, hydroxides, and those con- 
 taining water of crystallization. It is also present in the hydrocarbons. See 
 the lists of the various elements. 
 
 INDIUM 
 
 See sphalerite, page 34. 
 
 Todobromite, 
 
 Miersite, 
 
 lodyrite, 
 
 Marshite, 
 
 Lautarite, 
 
 IODINE 
 
 Cubic, 
 
 Cubic, 
 
 Hexagonal, 
 
 Cubic, 
 
 Monoclinic, 
 
 Ag(Cl,Br,I), 102 
 
 Agl, 102 
 
 Agl, 102 
 
 Ctlolo, 105 
 
 Ca(IO,) 2 109 
 
 IRIDIUM 
 
 Platiniridium, 
 Native Iridium, 
 Iridosmium, 
 Osmiridium, 
 
 Cubic, 
 Cubic, 
 Hexagonal, 
 Hexagonal, 
 
 (Pt,Ir)-i 7 
 Ir 18 
 (Os,Ir), 18 
 (Ir,0s),-i 9 
 
 IRON 
 
 Native Iron, 
 
 Troilite, 
 
 Pentlandite, 
 
 PYRRHOTITE, 
 
 PYRITE, 
 
 MARCASITE, 
 
 ARSENOPYRITE, 
 
 Lollingite, 
 
 Glaucodote, 
 
 BORNITE, 
 
 CHALCOPYRITE, 
 
 TETRAHEDRITE, 
 
 Stannite, 
 
 HEMATITE, 
 
 Cubic, 
 
 Cubic, 
 
 Cubic, 
 
 Hexagonal, 
 
 Cubic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Cubic, 
 
 Tetragonal, 
 
 Cubic, 
 
 Tetragonal, 
 
 Hexagonal, 
 
 Fe 19 
 FeS 35 
 (Fe,Ni)S 35 
 FeS 36 
 FeS 2 39 
 FeSo, 42 
 FeAsS 43 
 FeAs,,, 44 
 (Co,Fe)AsS 44 
 Cu 3 FeS s , 55 
 
 CuFeS 2 55 
 M^R^^S,, 61 
 Cu,FeSnS 4J 65 
 Fe 2 O 3 86 
 
CLASSIFICATION ACCORDING TO ELEMENTS 
 
 303 
 
 GOETHITE, 
 
 Xarithosiderite, 
 
 LIMONITE, 
 
 Molysite, 
 
 Douglas'ite, 
 
 Ankerite, 
 
 Breunnerite, 
 
 Monheimite, 
 
 Manganosiderite, 
 
 Oligonite, 
 
 SIDERITE, 
 
 Bixbyite, 
 
 WOLFRAMITE, 
 
 Ferberite, 
 
 Jarosite, 
 
 Natrojarosite, 
 
 Plumbo jarosite, 
 
 Melanterite, 
 
 Pisanite, 
 
 Coquimbite, 
 
 Copiapite, 
 
 Halotrichite, 
 
 Spinels, 
 
 FRANKLINITE, 
 
 CHROMITE, 
 
 Jacobsite, 
 
 Magnesioferrite, 
 
 MAGNETITE, 
 
 Triphylite, 
 
 Tantalite, 
 
 COLUMBITE, 
 
 Triplite, 
 
 Dufrenite, 
 
 Vivianite, 
 
 Symplesite, 
 
 Strengite, 
 
 Scorodite, 
 
 Pharmacosiderite, 
 
 Chiklrenite, 
 
 STAUROLITE, 
 
 Homilite, 
 
 Gadolinite, 
 
 Ilvaite, 
 
 Helvite, 
 
 Danalite, 
 
 EPIDOTE, 
 
 Orthite, 
 
 Ortho rhombic, FeO.OH, 93 
 
 Unknown, Fe,O(OH) 4 94 
 
 Orthorhombic? Fe 4 O 3 (OH) 6J 95 
 
 Hexagonal, FeCl 3 , 105 
 
 Unknown, FeCl,.2KC1.2H,O , 107 
 
 Hexagonal, (Ca,Mg,Fe)CO 3 , 116 
 
 Hexagonal, (Mg,Fe)CO 3 , 117 
 
 Hexagonal, (Zn,Fe)CO 3 , 118 
 
 Hexagonal, (Mn^Fe)CO 3 , 118 
 
 Hexagonal, (Fe,Mn)CO 3 , 118 
 
 Hexagonal, FeCO 3 , 118 
 
 Cubic, FeMnO 3 , 128 
 
 Monoclinic, (Fe,Mn)WO 4 , 141 
 
 Monoclinic, FeWO 4 , 142 
 
 Hexagonal, K 2 ( Fe. 2 OH ) 6 ( SO 4 ) 4 , 144 
 
 Hexagonal, Na 2 (Fe.2OH) 6 (SO 4 ) 4 144 
 
 Hexagonal, Pb ( Fe.2OH ) 6 ( SO 4 ) 4 1 45 
 
 Monoclinic, FeSO 4 -7H 2 O, 151 
 
 Monoclinic, (Fe,Cu) SO 4 .7H 2 O, 151 
 
 Hexagonal, Fe 2 (SO 4 ) 3 .9H O, 152 
 
 Monoclinic, FeI(Fe.OH) ("SO 4 ),.i8H 2 O, 152 
 
 Cubic, FeAl 3 (SO 4 ) 4 "2H O 154" 
 
 Cubic, (Fe,Mg) (A1O,) 2 , etc., 155 
 
 Cubic, (Fe,Mn,Zn)(F~e6 2 ) 2 158 
 
 Cubic, (Fe,Cr) [(Cr,Fe)O 2 ]o 158 
 
 Cubic, Mn[(Fe,Mn)O 2 ] 2 159 
 
 Cubic, Mg(FeCX)o 159 
 
 Cubic, Fe(FeO.,),, 159 
 
 Orthorhombic, U (Fe,Mn) PO 4 , 165 
 
 Orthorhombic, (Fe,Mn) [(Ta,Nb)O 3 J,, 168 
 
 Orthorhombic, (Fe,Mnj f(Nb,Ta)O 3 ] 2 , 169 
 
 Monoclinic? Fe(Fe,F)PO 4 , 176 
 
 Orthorhombic, Fe, ( OH ) 8 PO 4 1 76 
 
 Monoclinic, Fe 3 (PO 4 ),.8H 9 O 178 
 
 Monoclinic, Fe 8 (AsO 4 ) 8 .8H 2 O, 178 
 
 Orthorhombic, FePO 4 .2H 2 O, 1 79 
 
 Orthorhombic, FeAsO 4 .2H O, 179 
 
 Cubic, Fe(Fe.OH)" 3 (AsO 4 ) 3 .6H O 180 
 
 Orthorhombic, (Fe,Mn)Al(OH) 2 PO 4 .H 2 O 181 
 
 Orthorhombic, HFeAl,,SioO 13 , 184 
 
 Monoclinic, Fe[Ca(B.O)SiO 4 ], 193 
 
 Monoclinic, Fe|Be(Y.O)SiO 4 ]o 193 
 
 Orthorhombic, CaFe,(Fe.OH) (SiO 4 )o , 196 
 
 Cubic, (Mn,Be,Fe),S(SiO 4 ) 3 , 198 
 
 Cubic, ( Fe,Zn,Be,M:n) 7 S ( Si6 4 ) 198 
 
 Monoclinic, Ca 2 (Al,Fe) 2 (Al.OH) (SiO 4 ) 3 , 
 
 200 
 
 Monoclinic, Ca 2 (Al,Ce,Fe) 2 (Al.OH) (SiO 4 ) 3 , 
 
 2OI 
 
34 
 
 DESCRIPTIVE MINERALOGY 
 
 OLIVINE, 
 
 Orthorhombic, 
 
 (Mg,Fe),SiO 4 , 204 
 
 Hortonolite, 
 
 Orthorhombic, 
 
 ( Fe,Mg,Mn) 2 ( SiOJ , 205 
 
 Fayalite, 
 
 Orthorhombic, 
 
 Fe 2 SiO 4 205 
 
 Pseudobrookite, 
 
 Orthorhombic, 
 
 Fe 4 (Ti0 4 ) 3 207 
 
 GARNET, 
 
 Cubic, 
 
 Fe,Al 2 (SiO 4 ),, etc., 208 
 
 BIOTITE, 
 
 Monoclinic, 
 
 (K,H) 2 (Mg,Fe) 2 (Al,Fe) 2 (Si0 4 ) 3 , 
 
 
 
 215 
 
 Chloritoid, 
 
 Monoclinic, 
 
 H,FeAloSiO 7J 222 
 
 Nontronite, 
 
 Monoclinic, 
 
 H~Fe 2 Si~,O , 231 
 
 lolite, 
 
 Orthorhombic, 
 
 (Mg,Fe) 4 Al s (OH) 2 (Si 2 T )5 236 
 
 Astrophyllite, 
 
 Orthorhombic, 
 
 (K,Na,H) 4 (Fe,Mn) 4 (Si,Ti) 5 16 , 
 
 
 
 237 
 
 Ilmenite, 
 
 Hexagonal, 
 
 FeTiO,, 239 
 
 PYROXENES, 
 
 Orthorhombic, 
 
 (Mg,Fe) 2 (SiO 3 ) 2 , etc. 240 
 
 
 Monoclinic, 
 
 
 
 and Triclinic, 
 
 
 AMPHIBOLES, 
 
 Orthorhombic, 
 
 Ca(Mg,Fe) 3 (Si0 3 ) 4 ,etc. 250 
 
 
 Monoclinic, 
 
 
 
 and Triclinic, 
 
 
 Neptunite, 
 
 Monoclinic, 
 
 (Na,K),(Fe,Mn)(Si,Ti) 5 O ia , 
 
 
 
 275 
 
 Oxalite, 
 
 Unknown, 
 
 2FeC 2 O 4 .3H 2 O 288 
 
 LATHANUM 
 
 See the cerium, 
 
 thorium, and yttrium minerals pages 299, 315, and 317. 
 
 LEAD 
 
 Native Lead, 
 
 Cubic, 
 
 Pb 20 
 
 GALENA, 
 
 Cubic, 
 
 PbS-47 
 
 Clausthalite, 
 
 Cubic, 
 
 PbSe 48 
 
 Altaite, 
 
 Cubic, 
 
 PbTe 48 
 
 Naumannite, 
 
 Cubic, 
 
 (Ag 2 ,Pb)Se 49 
 
 Nagyagite, 
 
 Orthorhombic, 
 
 Au 2 Sb 2 Pb 10 Te S 15 54 
 
 Scleroclase, 
 
 Orthorhombic, 
 
 PbAsoS 4 57 
 
 Zinkenite, 
 
 Orthorhombic, 
 
 PbSb.,S 4 , 57 
 
 Dufrenoysite, 
 
 Monoclinic, 
 
 PboAsoS,, 58 
 
 Jamesonite, 
 
 Orthorhombic, 
 
 PboSboS,, 58 
 
 Cosalite, 
 
 Orthorhombic, 
 
 Pb,Bi,S,, 58 
 
 Boulangerite, 
 
 Orthorhombic, 
 
 Pb B Sb 4 S 11 ,-r-59 
 
 Freieslebenite, 
 
 Monoclinic, 
 
 (Pb,Ag,) i Sb 4 S 11 r-S9 
 
 Bournonite, 
 
 Orthorhombic, 
 
 PboCu,Sb,S 6 , 60 
 
 Aikinite, 
 
 Orthorhombic, 
 
 PKGtuBi,S fl , 61 
 
 Jordanite, 
 
 Monoclinic, 
 
 Pb>s S T 62 
 
 Meneghinite, 
 
 Orthorhombic, 
 
 Pb 4 Sb,S 7 63 
 
 Geocronite, 
 
 Orthorhombic, 
 
 Pb,Sb,S 8 63 
 
 Franckeite, 
 
 Cubic, 
 
 H) 8 Sn a Sb 2 S 12 , 66 
 
CLASSIFICATION ACCORDING TO 
 
 305 
 
 Cylindrite, 
 
 Platternite, 
 
 Massicot, 
 
 Cotunnite, 
 
 Matlockite, 
 
 Percylite, 
 
 Tarnowitzite, 
 
 CERUSSITE, 
 
 Hydrocerussite, 
 
 Phosgenite, 
 
 Minium, 
 
 ANGLESITE, 
 
 Crocoite, 
 
 Wulfenite, 
 
 Stolzite, 
 
 Plumbojarosite, 
 
 Linarite, 
 
 Leadhillite, 
 
 PYROMORPHITE 
 
 Mimetite, 
 
 Endlichite, 
 
 Vanadinite, 
 
 Descloizite, 
 
 Ganomalite, 
 
 Nasonite, 
 
 Barysilite, 
 
 Cubic, 
 Tetragonal, 
 Orthorhombic, 
 -Orthorhombic, 
 Tetragonal, 
 Tetragonal 
 or Cubic, 
 Orthorhombic, 
 Orthorhombic, 
 Hexagonal, 
 Tetragonal, 
 Tetragonal ? 
 Orthorhombic, 
 Monoclinic, 
 Tetragonal, 
 Tetragonal, 
 Hexagonal, 
 Monoclinic, 
 Monoclinic, 
 .Hexagonal, 
 Hexagonal, 
 Hexagonal, 
 Hexagonal, 
 Ortho rhombic, 
 Tetragonal, 
 Tetragonal, 
 Hexagonal, 
 
 Pb 6 Sn 6 Sb 2 S 21 , 66 
 PbPbO 4 , 82 
 PbO 88 
 PbCl,, 106 
 PboOClo 108 
 Pb(OH)Cl.Cu(OH)Cl,- 
 
 -108 
 
 (Ca,Pb)CO 3 122 
 PbCO,, 122 
 2PbCO 3 .Pb(OH) 2 , 125 
 (PbCl) 2 CO 3 126 
 Pb 2 PbO 4 129 
 
 PbS0 4 -i 3 7 
 PbCr0 4 138 
 PbMoO 4 139 
 PbWO 4 140 
 Pb(Fe.20H) 6 (S0 4 ) 4 144 
 (Pb,Cu)SO 4 .(Pb,Cu)(OH) 2 , 144 
 PbSO 4 .2PbCO 3 .Pb(OH) 2 145 
 
 Pb 5 Cl(P0 4 ) 3 ,-I 7 2 
 
 Pb Cl(As0 4 ) 3 -i 7 3 
 Pb 5 Cl[(As,V)0 4 ] 3 ,-i 73 
 Pb,Cl(V0 4 ) 3 ,-i 73 
 (Pb,Zn) (Pb.OH)VO 4 , 175 
 Pb 4 Ca 4 ( PbOH ) 2 ( Si 2 7 ) 3-235 
 
 Pb 4 Ca 4 (PbCl) 2 (Si 2 7 ) 3 ,-2 35 
 Pb 3 Si 2 7 235. 
 
 Triphylite, 
 
 Lithiophilite, 
 
 Arnblygonite, 
 
 TOURMALINE, 
 
 Lepidolite, 
 
 Zinnwaldite, 
 
 SPODUMENE, 
 
 Petalite, 
 
 LITHIUM 
 
 Orthorhombic, Li(Fe,Mn)PO 4> 165 
 
 Orthorhombic, LiMnPO 4 , 166 
 
 Triclinic, Li(AlF)PO 4< 173 
 
 Hexagonal, M'.Al,(B.OH) 2 Si 4 O 1 o *93 
 
 Monoclinic, (Li,K),(F,OH),Al,Si,O 0> 219 
 
 Monoclinic, (Li,Na) 3 (F,OH) 2 A~l 3 FeSi 5 O 1G , 
 
 220 
 
 Monoclinic, Li Al ( SiO 3 ) 2 , 247 
 
 Monoclinic, LiAl(SioO 5 ) 2 , 275 
 
 Periclase, 
 Brucite, 
 
 Manganobrucite, 
 Ferrobrucite, 
 
 Sellaite, 
 Bischofite, 
 
 MAGNESIUM 
 
 Cubic, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Tetragonal, 
 
 Monoclinic ? 
 
 MgO 83 
 Mg(OH), 96 
 (Mg,Mn)(OH),, 96 
 (Mg,Fe)(OH.) 2 ,- 9 6 
 MgF 2 , 104 
 MgCl" 2 .6H 2 O 106 
 
306 
 
 DESCRIPTIVE MINERALOGY 
 
 Carnallite, 
 
 Orthorhombic, 
 
 Tachydrite, 
 
 Hexagonal, 
 
 DOLOMITE, 
 
 Hexagonal, 
 
 Ankerite, 
 
 Hexagonal, 
 
 MAGNESITE, 
 
 Hexagonal, 
 
 Breunnerite, 
 
 Hexagonal, 
 
 Hydromagnesite, 
 
 Monoclinic, 
 
 Van't Hoffite, 
 
 Unknown, 
 
 Langbeinite, 
 
 Cubic, 
 
 Kieserite, 
 
 Monoclinic, 
 
 Epsomite, 
 
 Orthorhombic, 
 
 Cupromagnesite, 
 
 Monoclinic, 
 
 Blodite, 
 
 Monoclinic, 
 
 Picromerite, 
 
 Monoclinic, 
 
 SPINELS, 
 
 Cubic, 
 
 Magnesioferrite, 
 
 Cubic, 
 
 Sussexite, 
 
 Unknown, 
 
 BORACITE, 
 
 Orthorhombic 
 
 
 and Cubic, 
 
 Sulfoborite, 
 
 Orthorhombic, 
 
 Adelite, 
 
 Monoclinic, 
 
 Tilasite, 
 
 Monoclinic? 
 
 Wagnerite, 
 
 Monoclinic, 
 
 Lazulite, 
 
 Monoclinic, 
 
 Struvite, 
 
 Orthorhombic, 
 
 Bobierrite, 
 
 Monoclinic, 
 
 Hoernesite, , 
 
 Monoclinic ? 
 
 Cabrerite, 
 
 Monoclinic ? 
 
 TOURMALINE, 
 
 Hexagonal, 
 
 Prolectite, 
 
 Monoclinic, 
 
 Chondrodite, 
 
 Monoclinic, 
 
 Humite, 
 
 Orthorhombic, 
 
 Clinohumite, 
 
 Monoclinic, 
 
 Monticellite, 
 
 Orthorhombic, 
 
 Forsterite, 
 
 Orthorhombic, 
 
 OLIVINE, 
 
 Orthorhombic, 
 
 Hortonolite, 
 
 Orthorhombic, 
 
 PYROPE, 
 
 Cubic, . 
 
 BIOTITE, 
 
 Monoclinic, 
 
 PHLOGOPITE, 
 
 Monoclinic, 
 
 Xanthophyllite, 
 
 Monoclinic, 
 
 Brandisite, 
 
 Monoclinic, 
 
 Clintonite, 
 
 Monoclinic, 
 
 Chlorites, 
 
 Monoclinic, 
 
 SERPENTINE, 
 
 Orthorhombic 
 
 
 or Mcnoclinic 
 
 TALC, 
 
 Monoclinic ? 
 
 Sepiolite, 
 
 Monoclinic ? 
 
 MgCU.KC1.6H 2 O 106 
 
 2MgCi 2 .CaCl,.i2H,O 107 
 CaMg(CO 3 ) 0115 
 (Ca,Mg,Fe)C0 3 ,-n6 
 MgCO, 116 
 (Mg,Fe)C0 3 117 
 3 MgC0 3 .Mg(OH) 2 . 3 H 2 0,-i2 7 
 3 Na 2 SO 4 .MgSO 4 132 
 
 K 2 S0 4 .2MgS0 4 133 
 MgS0 4 .H 2 149 
 MgS0 4 . 7 H 2 0-i 5 o 
 (Cu,Mg)S0 4 .7H 2 0, 151 
 Na 2 M g (S0 4 ) 2 . 4 H 2 0-i 5 3 
 K 2 MgCa 2 (S0 4 ) 4 .2H 2 153 
 Mg(AlO 2 ) 2 , etc. 156 
 
 Mg(Fe0 2 ) 2 159 
 |(Mn,Mg)OH]BO 9 162 
 Mg 7 Cl 2 B 16 30 162 
 
 4MgHBO 8 .2MgSO 4 .7H 2 O, 164 
 Ca(Mg.OH)As0 4 -i 7 4 
 Ca(Mg.F)As0 4 ,-i 74 
 Mg(Mg.F)P0 4 ,-i 75 
 Mg(Al.OH) (PO 4 ),, 176 
 NH 4 MgPO 4 .6H,0, 177 
 Mg 3 (P0 4 ) 2 .8H b 177 
 Mo-,(As0 4 ) .8H 2 178 
 (Ni,Mg) a (AsO 4 ) 2 .8H 3 O, 179 
 
 M' 9 Al 3 (B.OH) 2 Si 4 O i ;,-i 93 
 [Mg(F,OH)] 2 MgSiO 4 , 197 
 [Mg(F,OH)i 2 Mg,(Si0 4 ) 8 ,~i97 
 
 [Mg(F,OH)] 2 Mg 5 (Si0 4 ) 3 ,-i 9 7 
 ].Mo;rF,OH)J 2 Mg T (Si0 4 ) 4 -i 9 8 
 CaMgSiO 4 , 203 
 Mg.,SiO 4 , 204 
 (Mg,Fe)jSiO 4 r-fl04 
 (Fe,Mg ! Mn) SiO 4 205 
 Mg 3 AU(SiO 4 ') 3 , 210 
 (K,H);(Mg,Fe) 2 (Al,Fe) 2 (Si0 4 ) 3 , 
 
 -215 
 
 (K,H),Msr,Al(SiO 4 ),, 217 
 H 8 ( Mg,Caj 14 Al 10 Si,O,, , 221 
 H 8 ( Mg,Ca) 10 Al 10 Si,O 44 222 
 H ( Mg,Ca) 10 Al 10 Si 4 30 222 
 H 4 ]\JgoAl,SiO 223 
 H 4 Mg 3 Si 2 9 226 
 
 H 2 Mg 3 Si 4 O 12 227 
 H 4 Mg 2 Si 3 10 , 228 
 
CLASSIFICATION ACCORDING TO 
 
 307 
 
 Garnierite, 
 
 Deweylite, 
 
 Genthite, 
 
 lolite, 
 
 Geikielite, 
 
 PYROXENES, 
 
 AMPHIBOLES, 
 
 Unknown, 
 Amorphous ? 
 Amorphous ? 
 Orthorhombic, 
 Hexagonal, 
 Orthorhombic 
 and Monoclinic 
 Orthorhombic 
 and Monoclinic, 
 
 H 2 (Ni,Mg)Si0 4 ,- 229 
 
 H 12 Mg 4 Si 3 1G 229 
 
 H 12 Mg 2 Ni 2 Si s O 16 , 229 
 
 ( Mg,Fe ) 4 A1 8 ( OH ) 2 ( Si 2 7 ) 5 -236 
 
 MgTiO 3 238 
 
 Mg 2 (SiO 3 ) 2 , etc. 240 
 
 (Mg,Fe) 4 (Si0 3 ) 4 ,etc., 250 
 
 MANGANESE 
 
 Alabandite, 
 
 Erythrozincite, 
 
 Hauerite, 
 
 Polianite, 
 
 PYROLUSITE, 
 
 Manganosite, 
 
 MANGANITE, 
 
 Manganobrucite, 
 
 Pyrochroite, 
 
 Scacchite, 
 
 RHODOCHRO- 
 
 SITE, 
 
 Manganocalcite, 
 Manganosiderite, 
 Oligonite, 
 Braunite, 
 Bixbyite, ' 
 Hausmannite, 
 Chalcophanite, 
 Psilomelane 
 and Wad, 
 Huebnerite, 
 WOLFRAMITE, 
 Mallardite, 
 Luckite, 
 Apjohnite, 
 Dysluite, 
 
 FRANKLINITE, 
 Jacobsite, 
 Sussexite, 
 Natrophilite, 
 Triphylite, 
 Lithiophilite, 
 Tapiolite, 
 Mossite, 
 Tantalite, 
 
 Cubic, 
 
 Hexagonal, 
 
 Cubic, 
 
 Tetragonal, 
 
 Orthorhombic? 
 
 Cubic, 
 
 Orthorhombic, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Tetragonal ? 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Tetragonal, 
 
 Cubic, 
 
 Tetragonal, 
 
 Hexagonal, 
 
 Unknown, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Cubic, 
 
 Cubic, 
 
 Cubic, 
 
 Cubic, 
 
 Unknown, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Tetragonal, 
 
 Tetragonal, 
 
 Orthorhombic, 
 
 MnS 34 
 (Zn,Mn)S 35 
 MnS 2 39 
 MnMnO 4 82 
 MnO,, 82 
 MnO 83 
 MnO.OH 92 
 (Mg,Mn)(OH) 2 96 
 Mn(OH) 2 96 
 MnCl 2 , 103 
 MnCO 3 118 
 
 (Mn,Ca)CO 3 118 
 (Mn,Fe)CO 3 118 
 (Fe,Mn)CO 3 118 
 MnMnO 8 , 128 
 FeMnO 8J 128 
 Mn 8 MnO 4 , 129 
 (Zn,Mn) Mn 2 O 5 .2H 2 O, 129 
 MnO,BaO,H 2 O, etc.", 129 
 
 MnWO 4 , 140 
 (Fe,Mn)WO 4 141 
 MnSO 4 .7H 2 O 151 
 (Fe,Mn)S0 4 .7H 2 O 151 
 Mn A1 2 ( SiO 4 ) 4 .2 4 H 2 O , 1 54 
 
 (Zn,Mn)[(Al,Fe)0,] 2 157 
 (Fe,Mn,Zn) (FeO 2 ) 2 , 158 
 Mn[(Fe,Mn)O 2 ],, 159 
 [(Mn,Mg)OH]BO 2 162 
 NaMnPO 4l 165 
 Li(Fe,Mn)PO 4 165 
 LiMnPO 4 166 
 (Fe,Mn)[(Ta,Nb)O 3 ],, 168 
 (Fe,Mn)[(Nb,Ta)O 3 ] 2 168 
 (Fe,Mn)[(Ta,Nb)0 3 ] 2 ,-i68 
 
3 o8 
 
 DESCRIPTIVE MINERALOGY 
 
 COLUMBITE, 
 
 Ortho rhombic, 
 
 ( Fe,Mn) [ ( Nb,Ta) O 3 ] , 169 
 
 Sarkinite, 
 
 Monoclinic, 
 
 Mn(Mn.OH)AsO 4 174 
 
 Triploidite, 
 
 Monoclinic? 
 
 Mn(Mn.OH)PO 4 176 
 
 Childrenite, 
 
 Urthorhombic, 
 
 ( F e,Mn) Al ( OH) ,PO 4 .H,O 181 
 
 Carpholite, 
 
 Monoclinic, 
 
 Mn(A1.2OH) 2 (Sib s )o, 196 
 
 Helvite, 
 
 Cubic, 
 
 (Mn,Be,Fe) 7 S(SiO 4 ),, 198 *t. 
 
 Danalite, 
 
 Cubic, 
 
 (Fe,Zn,Be,Mn) 7 S(Si6 4 ) 3198 
 
 Piemontite, 
 
 Monoclinic, 
 
 Ca 2 (Mn,Al) 2 (Al.OH)(Si0 4 ) 3 , 
 
 
 
 2OI 
 
 Glaucochroite, 
 
 Orthorhombic, 
 
 CaMnSiO 4 , 203 
 
 Hortonolite, 
 
 Orthorhombic, 
 
 (Fe,Mg,Mn) SiO 4 , 205 
 
 Knebelite, 
 
 Orthorhombic, 
 
 (Mn,Fe) 2 SiO~ 4 205 
 
 Tephroite, 
 
 Orthorhombic, 
 
 Mn SiO 4 205 
 
 Trimerite, 
 
 Triclinic, 
 
 MnBeSiO 4 205 
 
 
 ( Pseudo-hex- 
 
 
 
 agonal), 
 
 
 SPESSARTITE, 
 
 Cubic, 
 
 Mn.,Al (SiO 4 ), 210 
 
 Astrophyllite, 
 
 Orthorhombic, 
 
 (K;Na;H) 4 (Fe,Mn) 4 (Si,Ti) 5 1(i 
 
 
 
 237 
 
 Pyrophanite, 
 
 Hexagonal, 
 
 MnTiO 3 239 
 
 Schefferite, 
 
 Monoclinic, 
 
 (Ca,Mg) (Fe,Mn) (SiO,)* 244 
 
 Jeffersonite, 
 
 Monoclinic, 
 
 (Ca,Mn) (Mg,Fe,Zn) (SiO 3 ) 2 , 
 
 
 
 244 
 
 Rhodonite, 
 
 Triclinic, 
 
 ' Mn, (SiO,) ,249 
 
 Fowlerite, 
 
 Triclinic, 
 
 ( Mn,Fe,Ca,Zn,Mg) ( SiO 3 ) ,, 249 
 
 Babingtonite, 
 
 Triclinic, 
 
 (Ca,Fe,Mn) ( SiO,)o, etc., 249 
 
 Neptunite, 
 
 Monoclinic, 
 
 (Na,K) 2 (Fe,Mn) (Si,Ti) B O 12 , 
 
 
 
 275 
 
 Ganophyllite, 
 
 Monoclinic, 
 
 Mn 7 ( A1O) 2 ( SiO 3 ) 8 .6H 2 O 279 
 
 See also axinite, 
 
 213, aenigmatite, 
 
 256, and dysanalyte, 273. 
 
 MERCURY 
 
 Amalgam, 
 
 Cubic, 
 
 (Ag,Hg), 24 
 
 Native Mercury, 
 
 Cubic, 
 
 Hg, 24 
 
 Gold Amalgam, 
 
 Cubic, 
 
 (Au,Hg,Ag), 28 
 
 Metacinnabarite, 
 
 Cubic, 
 
 HgS,- 5 i 
 
 Onofrite, 
 
 Cubic, 
 
 Hg(S,Se)- 5 i 
 
 Tiemannite, 
 
 Cubic, 
 
 HgSe, 51 
 
 CINNABAR, 
 
 Hexagonal, 
 
 HgS, 52 
 
 TETRAHEDRITE 
 
 , Cubic, 
 
 M" 4 R'",S 7 61 
 
 Calomel, 
 
 Tetragonal, 
 
 Hg.,Cl., 105 
 
 MOLYBDENUM 
 
 Molybdenite, 
 
 Hexagonal, 
 
 MoS.,, 32 
 
 Molybdite, 
 
 Orthorhombic ? 
 
 Mo 3 Fe 2 O 12 7^H 2 O, 96 
 
 Powellite, 
 
 tetragonal, 
 
 CaMo6 4 , 139 
 
 Wulfenite, 
 
 Tetragonal, 
 
 PbMoO 4 139 
 
CLASSIFICATION* ACCORDING TO 
 
 39 
 
 NEODYMIUM 
 
 See didymium, page 300. 
 
 NICKEL 
 
 Josephinite, 
 
 Pentlandite, 
 
 Millerite, 
 
 Niccolite, 
 
 Arite, 
 
 Breithauptite, 
 
 Gersdorffite, 
 
 Ullmannite, 
 
 Chloanthite, 
 
 Wolfachite, 
 
 Rammelsbergite, 
 
 Linnaeite, 
 
 Bnnsenite, 
 
 Winklerite, 
 
 Zaratite, 
 
 Morenosite, 
 
 Annabergite, 
 
 Garnierite, 
 
 Unknown, (Fe,]^), 20 
 
 Cubic, (Fe,Ni)'S 35 
 
 Hexagonal, NiS, 36 
 
 Hexagonal, NiAs, 37 
 
 Hexagonal, Ni(As,Sb), 37 
 
 Hexagonal, NiSb, 37 
 
 Cubic, NiAsS, 41 
 
 Cubic, NiSbS 41 
 
 Cubic, NiAso, 42 
 
 Orthorhombic, Ni(As,S,Sb) 2 , 45 
 
 Orthorhombic, NiAs,, 45 
 
 Cubic, (Ni,Co) 3 S 4 ,56 
 
 Cubic, NiO 83 
 
 Unknown, (Co,Ni) 2 O(OH) 4 , 94 
 
 Unknown, NiCO 3 .2Ni(OH) 2 4H,O, 128 
 
 Orthorhombic, NiSO 4 .7H,O, 151 
 
 Monoclinic, Ni 3 ( AsO 4 ) 2 .8H 2 O, 1 79 
 
 Unknown, H 2 (Ni,Mg)SiO 4 , 229 
 
 See also native iron, page 19, awaruite, page 20, and pyrrhotite, page 36. 
 
 NIOBIUM 
 
 Fergusonite, 
 
 Samarskite, 
 
 Tapiolite, 
 
 Mossite, 
 
 Tantalite, 
 
 COLUMBITE, 
 
 Polymignite, 
 
 Tetragonal, Y(Nb,Ta)O 4 , 167 
 
 Orthorhombic, R" 3 R'" 2 ( Nb,Ta) 6 O,, 168 
 Tetragonal, (Fe.Mn) [(Ta,Nb)6 3 ]o, 168 
 
 Tetragonal, (Fe,Mn) [ (Nb,Ta)O 3 ]o, 168 
 
 Orthorhombic, (Fe,Mn) [ (Ta,Nb)O 3 ]~ 168 
 Orthorhombic, (Fe,Mn) [(Nb,Ta)O 8 ] 2> 169 
 Orthorhombic, Ca 3 ( CeO ) 4 ( Ti 2 O 5 ) 5 .Ca"( NbO 3 ) 2 , 
 
 274 
 
 Se also yttrotantalite, 167, steenstrnpine, 273, dysanalyte, 273, poly- 
 erase, 274, and euxenite, 274. 
 
 NITROGEN 
 
 The following minerals contain nitrogen, which occurs as an essential 
 constituent only in the nitrates and the various ammonium compounds. 
 
 Sal Ammoniac, 
 S9DA NITER, 
 
 Niter, 
 Mascagnite, 
 Tschermigite, 
 Struvite, 
 
 Cubic, 
 
 Hexagonal, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Cubic, 
 
 Orthorhombic, 
 
 See also uraninite, 142. 
 
 NH 4 Cl,- 99 
 
 NaNO 3 , 109 
 
 KNO,, no 
 
 (NH;) 2 S0 4 ,-i 3 i 
 
 (NH 4 ) 2 Al 2 (S0 4 ) 4 .2 4 H 2 0-i54 
 
 NH 4 MgP0 4 .6H 2 177 
 
31O- DESCRIPTIVE MINERALOGY 
 
 OSMIUM 
 
 Iridosmium, Hexagonal, (Os,Ir), 18 
 
 Osmiridium, Hexagonal, (Ir,Os), 19 
 
 See also the other members of the platinum group, page 17. 
 
 OXYGEN 
 
 Oxygen is an important constituent of many classes o-f minerals, see 
 page i. It is therefore present in the vast majority of minerals. The ele- 
 ments, sulphides and analogous compounds, and the haloids do not contain 
 oxygen. 
 
 Native Palladium, Cubic, Pd, 18 
 
 Allopalladium, Hexagonal, Pd, 19 
 
 See also the other members of the platinum group, page 17. 
 
 PHOSPHOROUS 
 
 Phosphorous is contained in the phosphates, described on pages 165 to 
 182. See also the lists of the various elements. 
 
 PLATINUM 
 
 Native Platinum, Cubic, Pt, 17 
 
 Sperrylite, Cubic, PtAs 2 , 42 
 
 See the other members of the platinum group, page 17. 
 
 POLONIUM 
 
 See uraninite, page 142. 
 
 POTASSIUM 
 
 Sylvite, Cubic, KC1 98 
 
 Carnallite, Orthorhombic, MgCl 2 .KC1.6H 2 O 106 
 
 Erythrosiderite, Hexagonal? FeCl 3 .2KCl.H.,O, 106 
 
 Kremersite, Hexagonal? FeCl 3 .2(K,NH 4 )Cl.H 2 O , 106 
 
 Douglasite, Orthorhombic? FeCl 2 .2KC1.2H 2 O, 107 
 
 Niter, Orthorhombic, KNO 3 , no 
 
 Glaserite, Hexagonal, (K,Na) 2 SO 4 , 131 
 
 Arcanite, Orthorhombic, (K,Na) 2 SO 4 , 131 
 
 Langbeinite, Cubic, K 2 SO 4 .2MgSO 4 , 133 
 
CLASSIFICATION ACCORDING TO 
 
 Alunite, 
 
 Jarosite, 
 
 Hank site, 
 
 Picromerite, 
 
 Polyhalite, 
 
 Kalinite, 
 
 Kainite, 
 
 MICAS, 
 
 NEPHELITE, 
 
 Astrophyllite, 
 
 LEUCITE, 
 
 ORTHOCLASE, 
 MICROCLINE, 
 
 Neptunite, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Monoclinic, 
 
 Monoclinic ? 
 
 Cubic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Hexagonal, 
 Orthorhombic, 
 
 Orthorhombic 
 and Cubic, 
 Monoclinic, 
 Triclinic, 
 Monoclinic, 
 
 Milarite, Orthorhombic ? 
 
 APOPHYLLITE, Tetragonal, 
 
 K 2 (A1.20H) 6 (S0 4 ) 4 143 
 K 2 (Fe.20H) 6 (S0 4 ) 4 -i 4 4 
 9Na,S0 4 .2Na CO 3 .KCl, 145 
 K,Mg(S0 4 ) ,.6H 2 153 
 K,,MgCa 2 (S0 4 ) 4 .2H 2 153 
 K 2 Al 2 (S0 4 ) 4 .2 4 H 2 0-i 5 4 
 
 MgS0 4 .KCl. 3 H 2 0-i 5 4 
 (K,H) 2 (Mg,Fe) 2 (Al,Fe) 2 (Si0 4 ) 3 , 
 
 etc., 214 
 
 ( Na,K) 8 Al 8 Si 9 O 34 , 232 
 (K,Na,H) 4 (Fe,Mn) 4 (Si,Ti) 5 1 o, 
 
 237 
 K 2 Al 2 Si 4 O 12 257 
 
 KAlSi 3 O 8 259 
 KAlSi 3 O 8J 264 
 (Na,K) 2 (Fe,Mn)(Si,Ti) 5 12 , 
 
 275 
 
 HKCa,Al,(Si 2 B ) 275 
 H 14 K 2 Ca 8 ( SiO 3 ) 10 .9H 2 O, 280 
 
 See also tourmaline, 193, davyne, 233, and aenigmatite, 256. 
 
 PRASEODYMIUM 
 
 Same as for didymium, page 300. 
 
 RHODIUM 
 
 See the minerals of the platinum group, page 17. 
 
 RUBIDIUM 
 
 Small amounts of rubidium are often observed in the minerals contain- 
 ing caesium, page 297. 
 
 RUTHENIUM 
 
 Occurs in small quantities in the minerals of the platinum group, page 17. 
 
 SAMARIUM 
 
 See the minerals containing cerium, thorium, and yttrium, pages 299, 
 315, and 317, respectively. 
 
312 DESCRIPTIVE MINERALOGY 
 
 SCANDIUM 
 
 Same as for samarium. 
 
 SELENIUM 
 
 Selensulphur, Unknown, (S,Se), 14 
 
 Selenium, Monoclinic, Se, 14 
 
 Guanajuatite, Orthorhombic, Bi (Se,S) 3 , 31 
 
 Clausthalite, Cubic, PbSe 48 
 
 Aguilarite, Cubic, Ag 2 (S,Se), 49 
 
 Naumannite, Cubic, (Ag 2 ,Pb)Se, 49 
 
 Eucairite, Cubic, (Ag,Cu) 2 Se, 49 
 
 Onofrite, Cubic, Hg(S,Se), 51 
 
 Tiemannite, Cubic, HgSe, 51 
 
 SILICON 
 
 Silicon is an essential constituent of the silicates, see pages 183 to 287, 
 
 and also under the various elements. It occurs furthermore in the following 
 oxides : 
 
 QUARTZ, 
 
 Hexagonal, 
 
 SiCX 70 
 
 Tridymite, 
 
 Orthorhombic, 
 
 Si0 2 ,- 75 
 
 Cristobalite, 
 
 Tetragonal, 
 
 SiO 2 76 
 
 Thorite, 
 
 Tetragonal, 
 
 ThSiO 4 80 
 
 OPAL, 
 
 Amorphous, 
 
 SiO 2 .xH 2 O 89 
 
 SILVER 
 
 NATIVE SILVER, 
 
 Cubic, 
 
 Ag, 23 
 
 Amalgam, 
 
 Cubic, 
 
 (Ag,Hg), 24 
 
 Gold Amalgam, 
 
 Cubic, 
 
 (Au,Hg,Ag)-28 
 
 Dyscrasite, 
 
 Orthorhombic, 
 
 Ag 3 Sb 46 
 
 Argentite, 
 
 Cubic, 
 
 Ag,S 48 
 
 Jalpaite, 
 
 Cubic, 
 
 (Ag,Cu) 2 S 49 
 
 Aguilarite, 
 
 Cubic, 
 
 Ag 2 (S,Se)- 49 
 
 Naumannite, 
 
 Cubic, 
 
 (Ag 2 ,Pb)Se 49 
 
 Eucairite, 
 
 Cubic, 
 
 (Ag,Cu) 2 Se 49 
 
 Hessite, 
 
 Cubic, 
 
 Ag 2 Te 49 
 
 Stromeyerite, 
 
 Orthorhombic, 
 
 (Cu,Ag) 2 S- 5 Q 
 
 Acanthite, 
 
 Orthorhombic, 
 
 Ag 2 S 50 
 
 Petzite, 
 
 Orthorhombic, 
 
 (Ag,Au),Te, 50 
 
 Sylvanite, 
 
 Monoclinic, 
 
 (An,Ag)Te 2 53 
 
 Krennerite, 
 
 Orthorhombic, 
 
 (Au,Ag)Te 2 54 
 
 Miargyrite, 
 
 Monoclinic, 
 
 AgSbS 2 57 
 
 Freieslebenite, 
 
 Monoclinic, 
 
 (Pb,Ag 2 ) 5 Sb 4 S 113 - 
 
 -59 
 
CLASSIFICATION ACCORDING TO ELEMENTS 
 
 313 
 
 Proustite, 
 Pyrargyrite, 
 TETRAHEDRITE, 
 Stephanite, 
 
 Pearceite, 
 Polybasite, 
 
 Polyargyrite, 
 
 Canfieldite, 
 
 Argyrodite, 
 
 Cerargyrite, 
 
 Embolite', 
 
 Bromyrite, 
 
 lodobromite, 
 
 Miersite, 
 
 lodyrite, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Cubic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Cubic, 
 
 Cubic, 
 
 Cubic, 
 
 Cubic, 
 
 Cubic, 
 
 Cubic, 
 
 Cubic, 
 
 Cubic, 
 
 Hexagonal, 
 
 Ag.,AsS 3 59 
 Ag.,SbS 3 59 
 M" 4 R'" 2 S 7 61 
 Ag 10 Sb 2 S 8 , 63 
 (Ag,Cu) 9 AsS c 63 
 (Ag,Cu) SbS 6 64 
 Ag 24 Sb 2 S 15 64 
 Ag 8 (Sn,Ge)S 66 
 Ag 8 GeS 6 66 
 AgCl 101 
 Ag(Cl,Br), 102 
 AgBr, 102 
 Ag(Cl,Br,I), 102 
 Agl, 102 
 Agl, 102 
 
 HALITE, 
 CRYOLITE, 
 
 Pachnolite, 
 SODA NITER, 
 
 Dawsonite, 
 
 Northupite, 
 
 Thermonatrite, 
 
 Natron, 
 
 Trona, 
 
 Pirssonite, 
 
 Gay-Lussite, 
 
 Glaserite, 
 
 Arcanite, 
 
 Thenardite, 
 
 Glauberite, 
 
 Van't Hoffite, 
 
 Natrojarosite, 
 
 Sulpbohalite, 
 
 Hanskite, 
 
 Mirabilite, 
 
 Blodite, 
 
 Mendozite, 
 
 BORAX, 
 
 Ulexite, 
 
 Beryllonite, 
 
 Natropbilite, 
 
 Paragonite, 
 
 NEPHELITE, 
 
 Cancrinite, 
 
 SODIUM 
 
 Cubic, NaCl, 99 
 
 Monoclinic, AlFj^NaF, 107 
 
 Monoclinic, AlF 3 .NaCaF 3 .H 2 O, 108 
 
 Hexagonal, NaNO 3 , 109 
 
 Monoclinic? NaAl(OH),CO 3 125 
 
 Cubic, MgCO 3 .Na 2 CO 3 .NaCl, 126 
 
 Orthorhombic, Na 2 CO 3 .H 2 O, 126 
 
 Monoclinic, Na CO 3 .ioH O, 126 
 
 Monoclinic, NaoCO 3 .NaHCO 3 .2H O, 127 
 
 Orthorhombic, Na^CO 3 .CaCO 3 .2H O, 127 
 
 Monoclinic, Na CO 3 .CaCO 3 .5H n "O 127 
 
 Hexagonal, (K> T aj,SO 4 , 131" 
 
 Orthorhombic, (K,Na) 2 SO 4 , 131 
 
 Orthorhombic, Na.,SO 4 , 132 
 
 Monoclinic, Na 2 SO 4 .CaSO 4 132 
 
 Unknown, 3Na.,SO 4 .MgSO 4 , 132 
 
 Hexagonal, Na,(Fe.2OH) 6 (SO 4 ) 4 , 143 
 
 Cubic, 3Na,SO 4 .NaCl.NaF 145 
 
 Hexagonal, 9Na,SO 4 .2Na CO 3 .KCl 145 
 
 Monoclinic, Na SO 4 .ToH.,6, 146 
 
 Monoclinic, Na^Mg(SO 4 ) .4H O, 153 
 
 Cubic, Na 2 Al 2 (SO 4 ) 4 ".24H 2 O 154 
 
 Monoclinic, Na,B 4 O..ioH,O, 163 
 
 Monoelinic, NaCaB,O 9 .6H 2 O, 163 
 
 Orthorhombic, NaBePO 4 , 16*5 
 
 Orthorhombic, NaMnPO 4 , 165 
 
 Monoclinic, H 2 Na A1 3 ( SiO 4 ) 3 , 2 1 9 
 
 Hexagonal, (Na,K) 8 Al 8 Si 9 O 34 , 232 
 
 Hexagonal, H ( Na 2 ,Ca) 4 ( NaCO 3 ) 2 Al 8 Si 9 O 36 , 
 
 233 
 
DESCRIPTIVE MINERALOGY 
 
 Davyne, 
 
 Sodalite , 
 
 Noselite, 
 Haiiynite, 
 
 Lazurite, 
 
 Astrophyllite, 
 
 Pectolite, 
 Jadeite, 
 Acmite, 
 
 Soda-Orthoclase, 
 ALBITE and 
 PLAGIOCLASES, 
 
 Hexagonal, 
 
 Cubic, 
 Cubic, 
 Cubic, 
 
 Cubic, 
 Orthorhombic, 
 
 Monoclinic, 
 Monoclinic, 
 Monoclinic, 
 Monoclinic, 
 Triclinic, 
 
 SCAPOLITE, 
 
 Eudidymite, 
 Epididymite, 
 Catapleiite, 
 
 Elpidite, 
 Eudialyte, 
 Lorenzenite, 
 Neptunite, 
 
 Thomsonite, 
 
 Hydronephelite, 
 Natrolite, 
 
 Mesolite, 
 
 ANACLITE, 
 
 Mordenite, 
 STILBITE, 
 
 Gmelinite, . 
 
 Tetragonal, 
 
 Monoclinic, 
 
 Orthorhombic, 
 
 Monoclinic 
 
 and Hexagonal 
 
 Orthorhombic, 
 
 Hexagonal, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Orthorhombic, 
 Hexagonal ? 
 Orthorhombic 
 and Monoclinic, 
 Monoclinic, 
 
 Cubic, 
 Monoclinic, 
 Monoclinic, 
 Hexagonal, 
 
 ( Na 2 ,Ca.K 2 ) 16 ( NaCO 3 ,NaSO 4 , 
 
 O) u Al a5 Si 84 O M ,-~a33 
 
 Na 4 Al 2 (AlCl)(Si0 4 ) 3 ,-2 33 
 
 Na 4 Al 2 [Al(NaS0 4 )](Si0 4 ) 3) 234 
 Na 2 CaAl 2 [Al(NaSO 4 )](SiO 4 ) 3 , 
 
 234 
 ( Na 2 ,Ca) 2 A1, [ Al ( NaSO 4 ,NaS 3 , 
 
 Cl)](Si0 4 ) 3 ,-2 34 
 (K,Na,H) 4 (Fe,Mn) 4 (Si,Ti) 5 16) 
 
 237 
 
 (Ca,Na 2 ) 2 (SiO 3 ),, 246 
 NaAl(SiO 3 ) 2 247 
 NaFe(SiO 3 ) 2 , 248 
 .(Na,K)AlSi 3 O s 263 
 NaAlSi 3 O 8 , etc., 266 
 
 Ca 4 Al Si e O 23 , etc, 269 
 HNaBeSi 3 O s 271 
 HNaBeSi 3 O 8 271 
 H 4 Na 2 ZrSi 3 11 273 
 
 H a Na 2 ZrSi e O 18 273 
 Na 18 ( Ca,Fe) e ( Si,Zr) 20 O 5 ,C1, 273 
 Na 2 Si 2 (Ti,Zr) 2 O , 2*74 
 (Na,K) 2 (Fe,Mnj (Si,Ti) 5 O 12 , 
 
 275 
 
 2(Ca,Na,)Al 2 (SiO 4 ) 2 .5H O 276 
 HNa 2 Ai;(Si0 4 ) 3 .3H 2 b,-2 77 
 Na 2 Al(AlO) (SiO 3 ) 3 .2H,O , 277 
 
 Na 2 Al(AlO) (SiO 3 ),.2H 2 O, etc., 
 
 278 
 
 NaoAl,(SiO 8 ) 4 .2H 2 O 279 
 (K,,Na,,Ca)Al Si 10 O, 4 .7H,O 282 
 (Ca,Na,)Al 2 Si 8 O in .6H,O, 283 
 Na Al 9 Si O 16 .8H O, etc., 286 
 
 See also tourmaline, 193, steenstrnpine, 273, and dysanalyte, 273. 
 
 STRONTIUM 
 
 STRONTIANITE, Orthorhombic, 
 
 CELESTITE, Orthorhombic, 
 
 Bartocelestite, Orthorhombic, 
 
 Brewsterite, Monoclinic, 
 
 SrCO 3 , 121 
 SrSO 4 134 
 
 (Sr,Ba)SO 4 135 
 
 H 4 ( Sr,Ba) A1 2 ( SiO 3 ) . 3 H 2 O,-282 
 
CLASSIFICATION ACCORDING TO ELEMENTS 
 
 3.15 
 
 SULPHUR 
 
 Sulphur is an essential constituent of the sulphides, sulphates, and allied 
 compounds, see pages 29 to 66, 133 to 154, and under the various elements. 
 It occurs also in the following: 
 
 NATIVE 
 
 SULPHUR, 
 
 Selensulphur, 
 
 Kermesite, 
 
 Helvite, 
 
 Danalite, 
 
 Davyne, 
 
 Noselite, 
 Haiiynite, 
 
 Lazurite, 
 
 Thaumasite, 
 
 Orthorhombic, $,13 
 
 Unknown, (S,Se), 14 
 
 Monoclinic, Sb 2 S O, 97 
 
 Cubic, (Mn~Be,Fe) 7 S(SiO 4 ) a 198 
 
 Cubic, ( Fe,Zn,Be,Mn) 7 S ( Si6 4 ) 3198 
 
 Hexagonal, ( Na 2 ,Ca,K 2 ) 18 ( NaCO 3 ,NaSO 4 , 
 
 Cl) 11 Al 2r ,Si 24 O 96 , 233 
 
 Cubic, Na 4 Al 2 [Al(NaSO 4 )] (SiO 4 ) 3 234 
 
 Cubic, Na 2 CaAl 2 [Al(NaSO 4 )](SiO5) 8 , 
 
 234 
 
 Cubic, ( Na,,Ca) A1 2 [ Al ( NaSO 4 ,NaS 3 , 
 
 Cl](Si0 4 ) 3 ,-2 34 
 Hexagonal, Ca,SCSiO 10 .i5H 2 O, 287 
 
 TANTALUM 
 
 The tantalum minerals usually contain niobium, which see, page 309. 
 
 TELLURIUM 
 
 Native Tellurium, 
 
 Tetradymite, 
 
 Altaite", 
 
 Hessite, 
 
 Petzite, 
 
 Sylvanite, 
 
 Calaverite, 
 
 Krennerite, 
 
 Nagyagite, 
 
 Tellurite, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Cubic, 
 
 Cubic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Te 15 
 BioTcoS 31 
 PbTe 48 
 
 Ag 2 Te 49 
 (Ag,Au),Te 50 
 
 (Au,Ag)Te 2 53 
 Au Te , 54 
 (Au,Ag)Te 2 54 
 Au Sb 2 Pb 10 Te 6 S 1 -, 54 
 TeO,, 68 
 
 THALLIUM 
 
 Lorandite, TlAsS 2 , 57 ; see also sphalerite, page 33. 
 
 THORIUM 
 
 Thorite, Tetragonal, ThSiO 4 80 
 
 See also uraninite, 142, monazite, 167, and aeschynite, 274. 
 
DESCRIPTIVE; MINERALOGY 
 
 TIN 
 
 Native Tin, 
 
 Stannite, 
 
 Canfieldite, 
 
 Franckeite, 
 
 Cylindrite, 
 
 CASSITERITE, 
 
 Hexagonal, 
 
 Tetragonal, 
 
 Cubic, 
 
 Unknown, 
 
 Unknown, 
 
 Tetragonal, 
 
 Sn 16 
 
 CiuFeSnS 4 65 
 Ag 8 (Sn,Ge)S 66 
 Pb,Sn,SboS 12 66 
 PboSrioSboS,!, 66 
 SnCX or Sn~SnO 4 80 
 
 TITANIUM 
 
 TiOo 76 
 
 TiO 2 76 
 
 TiO, or TiTi0 4 77 
 
 Fe(tiO 4 ),, 207 
 
 (K,Na,H) 4 (Fe,Mn) 4 (Si,Ti) 5 16 , 
 
 237 
 
 CaTiO,, 238 
 MgTi6 3 238 
 MnTiOa 239 
 FeTiO,, 239 
 CaSiTiO,, 271 
 Ca(Zr,Ti) O, 273 
 BaTiSi n O OJ 274 
 Na n Si,(Ti,Zr),O q , 274 
 (Na,K) 2 (Fe,Mn)(Si,Ti) 5 12 , 
 
 275 
 
 See also schorlomite and melanite, 215, hornblende, 253, tscheffkinite, 
 273, dysanalyte, 273, polymignite, 274, aeschynite, 274, polycrase, 274, and 
 euxenite, 274. 
 
 Brookite, 
 
 Orthorhombic, 
 
 Anatase, 
 
 Tetragonal, 
 
 RUTILE, 
 
 Tetragonal, 
 
 Pseudohrookite, 
 
 Orthorhombic, 
 
 Astrophyllite, 
 
 Orthorhombic, 
 
 Perovskite, 
 
 Pseudo-cubic, 
 
 Geikielite, 
 
 Hexagonal, 
 
 Pyrophanite, 
 
 Hexagonal, 
 
 Ilmenite, 
 
 Hexagonal, 
 
 TITANITE, 
 
 Monoclinic, 
 
 Zirkelite, 
 
 Monoclinic, 
 
 Benitoite, 
 
 Hexagonal, 
 
 Lorenzenite, 
 
 Orthorhombic, 
 
 Neptunite, 
 
 Monoclinic, 
 
 TUNGSTEN 
 
 Tungstite, 
 
 Scheelite, 
 
 Stolzite, 
 
 Huebnerite, 
 
 WOLFRAMITE, 
 
 Ferberite, 
 
 Orthorhombic, 
 
 Tetragonal, 
 
 Tetragonal, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 Monoclinic, 
 
 WO 3 .H,O, 68 
 CaW0 4 139 
 PbWO 4 140 
 MnWO 4 , 140 
 (Fe,Mn)WO t 141 
 FeWOp 142 
 
 URANIUM 
 
 Uraninite, Cubic, UO,,UO.,,PbO, etc., 142 
 
 Autunite, Orthorhombic, Ca(UO., J (PO 4 ) .8H O 182 
 
 Uranospinite, Orthorhombic, Ca(UO ) (AsO 4 ),.8H O, 182 
 
 Torbnerite, Tetragonal, Cu(UO~)o(PO 4 ).~.8HX> 182 
 
 Zeunerite, Tetragonal, Cu(UO ) 2 (AsO 4 )o.8H,O, 182 
 
CLASSIFICATION ACCORDING TO 
 
 317 
 
 Uranotile, 
 Gummite, 
 
 Triclinic, 
 Amorphous? 
 
 CaU 2 $i 2 O 11 .$H 2 O,2S'j 
 (Pb,Ca~Ba)U 8 SiO 12 .5H 2 O, 287 
 
 See also yttrotantalite , 167, samarskite, 168, polycrase, 274, and 
 euxenite, 274. 
 
 VANADIUM 
 
 Endlichite, 
 
 Vanadinite, 
 
 Descloizite, 
 
 Hexagonal, 
 Hexagonal, 
 Ortho rhombic, 
 
 Pb s Cl[(As,V)0 4 ],,-i 7 3 
 Pb B Cl(V0 4 ),, 173 
 
 (Pb,Zn)(Pb.OH)V0 4 , 175 
 
 See also roscoelite, 218. 
 
 YTTRIUM 
 
 Xenotime, 
 
 Fergusonite, 
 Yttrotantalite, 
 Samarskite, 
 Gadolinite, 
 
 Tetragonal, 
 
 Tetragonal, 
 
 Orthorhombic, 
 
 Orthorhombic, 
 
 Monoclinic, 
 
 YP0 4 166 
 Y(Nb,Ta)PO 4 167 
 Y 4 (Ta 2 7 ) 3 167 
 R",R'",(Nb,Ta) e O M , 168 
 
 Fe[Be(Y.O)Si0 4 ] 2 ,-i 93 
 
 See also yttrotitanite, 272, steenstrupine, 273, polymignite, 274, poly 
 crase,274, euxenite, 274, and the lists under the other rare earths. 
 
 ZINC 
 
 Native Zinc. 
 SPHALERITE, 
 
 Wurtzite, 
 
 Erythrozincite, 
 
 TETRAHEDRITE, 
 
 Zincite, 
 
 SMITHSONITE, 
 
 Monheimite, 
 
 Hydrozincite, 
 
 Aurichalcite, 
 
 Hexagonal, 
 
 Cubic, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Cubic, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Hexagonal, 
 
 Unknown, 
 
 Monoclinic, 
 
 Chalcophanite, Hexagonal, 
 
 Goslarite, Orthorhombic, 
 
 Gahnite, Cubic, 
 
 Dysluite, Cubic, 
 
 FRANKLINITE, Cubic, 
 
 Adamite, Orthorhombic, 
 
 Descloizite, Orthorhombic, 
 
 Kottigite, Monoclinic ? 
 HEMIMORPHITE,Orthorhombic, 
 
 Clinohedrite, Monoclinic, 
 
 Zn, 20 
 ZnS, 33 
 ZnS, 35 
 
 (Zn,Mn)S,-35 
 M'^R'"^,, 61 
 
 ZnO, 84 
 ZnCO 3 , 117 
 (Zn,Fe)CO, 118 
 ZnCO 3 .2Zn(OH) , 125 
 2(Zn,Cu t )C0 3 . 3 (Zn,Cu)(OH) 2 , 
 
 -125 
 
 (Zn,Mn) Mn O 5 .2H O, 129 
 ZnSO 4 .;H O 150 
 Zn[(Al,Fe)O,]o 157 
 
 (Zn,Mn)[(Al,Fe)0 2 ] 2 ,-i 5 7 
 (Fe,Mn,Zn) (FeO ) 2 , 158 
 Zn(Zn.OH)AsO 4 , 175 
 (Pb,Zn) (Pb.OH)VO 4 175 
 (Zn,Co),(AsO 4 ) 2 .8H O 179 
 HoZn.SiO,, 1 86 
 HoZnCaSiO 3 , 187 
 
318 DESCRIPTIVE MINERALOGY 
 
 Danalite, 
 
 Cubic, 
 
 ( Fe,Zn,Be,Mn) 7 S ( SiO 4 ) , 198 
 
 Willemite, 
 
 Hexagonal, 
 
 Zn 2 SiO 4 , 206 
 
 Hardystonite, 
 
 Tetragonal, 
 
 Ca ZnSi,O 7 , 235 
 
 Fowlerite, 
 
 Triclinic, 
 
 ( Mn,Fe,Ca,Zn,Mg) 2 ( SiO 3 ) 2 249 
 
 ZIRCONIUM 
 
 Baddeleyite, 
 
 Monoclinic, 
 
 Zr0 2 77 
 
 ZIRCON, 
 
 Tetragonal, 
 
 ZrSiO 4J 79 
 
 Zirkelite, 
 
 Monoclinic, 
 
 Ca(Zr,Ti) 2 5 273 
 
 Catapleiite, 
 
 Monoclinic 
 
 H^Na-jZrSigOn, 273 
 
 
 and Hexagonal. 
 
 
 Elpidite, 
 
 Orthorhombic, 
 
 H 8 Na 2 ZrSi e O 18 , 273 
 
 Eudialyte, 
 
 Hexagonal, 
 
 Na 13 ( Ca,Fe ) a ( Si,Zr) 20 O 52 C1,, 273 
 
 Lorenzenite, 
 
 Orthorhombic, 
 
 Na,Si,(Ti,Zr) 2 O , 274 
 
 See also astrophyllite, 237, polymignite, 274, and aeschynite, 274. 
 
INDEX 
 
 Figures in heavy type are page references to descriptions. 
 
 Acanthite, 47, 50, 312 
 Achroite, 195 
 Acmite, 241, 248, 314 
 Actinium, 293 
 Actinolite, 251, 252 
 
 schist, 253 
 
 Adamantine spar, 85 
 Adamas, 5 
 
 Adamite, 174, 175, 295, 317 
 Adelite, 174, 306 
 Adularia, 261 
 Aegirite, 241, 248 
 
 -augite, 248 
 Aenigmatite, 251, 256 
 Aeschynite, 274, 299 
 Agalmatolite, 231 
 Agate, 70, 74 
 
 varieties, 74 
 
 Agricolite, 207, 208, 296 
 Aguilarite, 46, 49, 312 
 Aikinite, 60, 61, 296, 300, 304 
 Akermanite, 236 
 Alabandite, 33, 34, 307 
 Alabaster, 146, 147 
 Albertite, 290 
 Albite, 259, 265, 266, 314 
 Alexandrite, 162 
 Algodonite, 45, 295, 299 
 Allanite, 201 
 Allemontite, 16, 294, 295 
 Allopalladium, 17, 19, 310 
 Allophane, 287, 294 
 Almandine spinel, 156 
 Almandite, 208, 210 
 Alstonite, 121 
 Altaite, 46, 48, 304, 315 
 
 Alum group, 154 
 
 stone, 143 
 Aluminates, 155 
 Aluminite, 152, 293 
 Aluminium, 293 
 Alunite, 143, 293, 311 
 Amalgam, 24, 308, 312 
 
 gold, 28, 301, 312 
 
 native, 24 
 
 silver, 24 
 Amazonite, 264 
 Amazonstone, 264 
 Amber, 290 
 
 Amblygonite, 173, 293, 301, 305 
 Ambroid, 291 
 Amesite, 223 
 Amethyst, 73 
 
 oriental, 85 
 Amianthus, 253 
 Ammonium alum, 154 
 Amphibole group, 250, 294, 298, 
 
 304, 307 
 Amphigene, 257 
 Anaclite, 279, 314 
 Anatase, 70, 76, 316 
 Andalusite, 187, 293 
 Andesine, 259, 265, 267 
 Andradite, 208, 211 
 Anglesite, 133, 137, 305 
 Anhydrite, 133, 298 
 
 region, 101 
 
 Ankerite, in, 116, 297, 303, 306 
 Annabergite, 177, 179, 295, 309 
 Anomite, 216 
 
 Anorthite, 259, 265, 268, 208 
 Anorthoclase, 259, 264 
 Anthophyllite, 250, 251 
 Anthracite coal, 291, 292 
 
320 
 
 INDEX 
 
 Anthraconite, 113 
 Antigorite, 226, 230 
 Antimonite, 30 
 Antimonnickel, 37 
 Antimony, 14, 15, 294 
 
 arsenical, 16 
 
 glance, 30 
 
 gray, 30 
 
 native, 15, 294 
 
 nickel glance, 41 
 Apatite, 170, 298, 301 
 Aphanese, 176 
 Aphrosiderite, 225 
 Aphthitalite, 132 
 Apjohnite, 154, 307 
 Aplome, 211 
 Apophyllite, 280, 311 
 Aquamarine, 258 
 Aragonite, no, in, 119, 297 
 Arcanite, 131, 310, 313 
 Arfvedsonite, 251, 255 
 Argentine, 113 
 Argentite, 46, 48, 312 
 Argillaceous hematite, 87 
 Argon, 294 
 
 Argyrodite, 66, 301, 313 
 Arite, 33, 37, 309 
 Arkansite, 76 
 Arsenic, 14, 15, 295 
 
 native, 15, 295 
 Arsenical gold ore, 30 
 
 antimony, 16 
 Arsenite, 69 
 Arsenolite, 69, 295 
 Arsenopyrite, 38, 43, 295, 302 
 Asbestos, amphibole, 253 
 
 long fibered, 253 
 
 serpentine, 226 
 
 short fibered, 226 
 Asparagus stone, 171 
 Asphalt, 289 
 Asphaltum, 289 
 Astrakanite, 153 
 Astrophyllite, 237, 304, 308, 311, 
 
 Atacamite, 108, 300 
 Augite, 240, 245 
 basaltic, 246 
 common, 246 
 
 Aurichalcite, 123, 125, 300, 317 
 Auripigment, 30 
 Automolite, 157 
 Autunite, 182, 298, 316 
 Aventurine, 74 
 
 oligoclase, 267 
 Awaruite, 20 
 Axinite, 213, 297 
 Azurite, 123, 124, 300 
 
 Babingtonite, 241, 249, 308 
 
 Baddeleyite, 70, 77, 318 
 
 Balas spinel, 156 
 
 Banded agate, 74 
 
 Barium, 295 
 
 Barkevikite, 255 
 
 Barnhardtite, 54, 300 
 
 Barite, 133, 135, 295 
 
 Barium feldspar, 263 
 
 Barandite, 179 
 
 Barsowite, 206, 207 
 
 Bartocelestite, 133, 135, 295, 314 
 
 Barylite, 235, 295 
 
 Barysilite, 235, 305 
 
 Barytes, 135 
 
 Barytocalcite, 123, 295, 297 
 
 Barytophyllite, 223 
 
 Basanite, 75 
 
 Bastite, 241 
 
 Bauxite, 94, 293 
 
 Beauxite, 94 
 
 Bell-metal ore, 65 
 
 Benitoite, 274, 295, 316 
 
 Bergmannite, 278 
 
 Beryl, 257, 294, 296, 297 
 
 common, 258 
 Beryllium, 296 
 Beryllonite, 165, 296, 313 
 Bieberite, 150, 151, 299 
 Biotite, 215, 304, 306 
 Bischofite, 106, 305 
 Bisilicates, 183 
 Bismite, 69, 70, 296 
 Bismuth, 14, 16, 296 
 
 glance, 31 
 
 native, 16, 296 
 
 ocher, 70 
 
INDEX 
 
 321 
 
 Bismuthinite, 20, 31, 296 
 Bismutite, 125, 296 
 Bituminous coal, 291, 292 
 
 limestone, 114 
 Bixbyite, 128, 303, 307 
 Blackband, 119 
 
 hematite, 129 
 
 jack, 33 
 
 lead, ii 
 
 oxide of manganese, 82 
 
 sand, 159, 161 
 
 spinel, 157 
 Blende, 33 
 
 Blodite, 153, 306, 313 
 Blood-stone, 74 
 Blue carbonate of copper, 124 
 
 earth, 291 
 
 iron-earth, 177 
 
 spinel, 156 
 
 stone, 151 
 
 vitriol, 151 
 Boart, 10 
 
 Bobierrite, 177, 306 
 Bog iron ore, 95 
 Boleite, 108 
 Bonephosphate, 172 
 Boracite, 162, 296, 306 
 Borates, 155 
 Borax, 163, 296, 313 
 Boric acid, 91 
 Bornite, 54, 55, 300, 302 
 Boron, 296 
 Boronatrocalcite, 163 
 Bort, 5, 10 
 Bortz, 10 
 Bosjemanite, 154 
 Botryolite, 192 
 
 Boulangerite, 58, 59, 294, 304 
 Bournonite, 60, 294, 300, 304 
 Bragite, 167 
 
 Brandisite, 221, 222, 306 
 Braunite, 128, 307 
 Brazilite, 77 
 
 Breithauptite, 33, 37, 294, 309 
 Breunnerite, in, 117, 303, 306 
 Brevicite, 278 
 Brewsterite, 282, 296, 314 
 Brimstone, 13 
 Brittle silver ore, 63 
 
 Brochantite, 144, 300 
 Broggerite, 142 
 Bromargyrite, 102 
 Bromine, 297 
 
 Bromlite, in, 121, 295, 297 
 Bromyrite, 98, 102, 297, 313 
 Bronzite, 240, 242 
 Brookite, 70, 76, 316 
 Brown clay iron stone, 95 
 
 hematite, 95 
 Brucite, 96, 305 
 Bunsenite, 83, 309 
 Buratite, 125 
 Burmite, 290 
 Bustamite, 249 
 Byssolite, 253 
 Bytownite, 259, 265, 268 
 
 Cabrerite, 177, 179, 306 
 Cadmium, 297 
 
 oxide, 83, 297 
 Caesium, 297 
 Cairngorm stone, 73 
 Calamine, 117, 118, 186 
 Calaverite, 53, 54, 301, 315 
 Calc tufa, 114 
 Calcareous sinter, 114 
 Calciostrontianite, 121 
 Calcite, no, in, 297 
 
 varieties, 113 
 Calcium, 297 
 
 oxalate, 288 
 Calcspar, in 
 Caliche, 109 
 Calomel, 105, 308 
 Campylite, 173 
 Cancrinite, 231, 233, 313 
 Canfieldite, 66, 301, 313, 316 
 Cannel coal, 292 
 Cap quartz, 73 
 Cape ruby, 210 
 Carbon, 3, 10, 298 
 Carbonado, 10 
 Carbonates, no 
 Carbuncle, 210 
 Carnallite, 106, 306, 310 
 
 region, 101 
 
322 
 
 INDEX 
 
 Carnelian, 74 
 Carpholite, 195, 196, 308 
 Cassiterite, 77, 80, 316 
 
 ordinary, 81 
 Castorite, 274 
 Catapleiite, 273, 314, 318 
 Cat's eye, 74, 162 
 Cedarite, 291 
 Celandonite, 220 
 Celestite, 133, 134, 314 
 Celsian, 259, 269, 295 
 Cerargyrite, 98, 101, 313 
 Ceresin, 289 
 Cerite, 202, 299 
 Cerium, 299 
 Cerussite, in, 122, 305 
 Cerusite, 122 
 Ceylonite,- 1^7 
 Chabazite, 285 
 Chalcanthite, 151, 300 
 Chalcedony, 70, 74 
 Chalcocite, 46, 47, 49, 300 
 Chalcophanite, 129, 307, 317 
 Chalcophyllite, 180, 300 
 Chalcopyrite, 54, 55, 300, 302 
 Chalcotrichite, 89 
 Chalk, 113, 114 
 
 French, 227 
 Chalybite, 118 
 Chamosite, 225 
 Chathamite, 42 
 Chert, 75 
 Chessylite, 124 
 Chiastolite, 187 
 Childrenite, 181, 303, 308 
 Chile saltpeter, 109 
 China clay, 230 
 Chloanthite, 38, 42, 295, 309 
 Chlorastrolite, 213 
 Chlorine, 299 
 
 Chlorite, 223, 224, 294, 306 
 Chloritic quartz, 74 
 Chloritoid, 221, 222, 304 
 Chlormelanite, 247 
 Chloro-apatite, 171 
 Chlorcalcite, 103 
 Chloropal, 231 
 Chlorspinel, 156 
 Chondrodite, 197, 301, 306 
 
 Chrismatite, 289 
 Christianite, 284 
 Chromates, 131 
 Chrome diopside, 243 
 
 iron, 158 
 
 spinel, 157 
 
 Chromic iron ore, 158 
 Chromium, 299 
 Chromite, 155, 158, 299, 303 
 Chrysoberyl, 166, 161, 293, 296 
 Chrysocolla, 212, 300 
 Chrysolite, 204 
 Chrysophane, 222 
 Chrysoprase, 74 
 Chrysotile, 226 
 
 asbestos, 253 
 Cinnabar, 50, 51,52,308 
 Cinnamon stone, 209 
 Citrine, 74 
 
 Clausthalite, 46, 48, 304, 312 
 Clay, china, 230 
 
 iron stone, 119 
 Cleiophane, 34 
 Clementite, 225 
 Cleveite, 142 
 Clinochlore, 223, 224 
 Clinoclasite, 176, 300 
 Clinohedrite, 186, 187, 298, 317 
 Clinohumite, 197, 198, 301, 306 
 Clinozoisite, 199, 200, 298 
 Clintonite, 221 222, 306 
 Clouded agate, 74 
 Coals, 291, 292 
 Cobalt, 299 
 
 bloom, 178 
 
 glance, 40 
 
 pyrites, 56 
 
 Cobaltite, 38, 40, 295, 299 
 Colemanite, 164, 296, 298 . 
 Columbite, 168, 169, 303, 308, 309 
 Columbium, 299 
 Common opal, 90 
 
 salt, 99 
 Compact hematite, 87 
 
 limestones, 113 
 
 limonite, 95 
 Comptonite, 276 
 Cookeite, 220 
 Copalite, 291 
 
INDEX 
 
 323 
 
 Copiapite, 152, 303 
 Copper, 20, 21, 299 
 
 glance, 49 
 
 gray ore, 61 
 
 native, 21, 299 
 
 n : ckel, 37 
 
 pyrites, 55 
 
 shot, 22 
 
 silver glance, 50 
 
 uranite, 182 
 Copperas, 151 
 Coquimbite, 152, 303 
 Coquina, 114 
 Cordierite, 236 
 Corneous lead, 126 
 Corundophillite, 223 
 Corundum, 84, 293 
 Cosalite, 58, 296, 304 
 Cossyrite, 256 
 Cotunnite, 105, 106, 305 
 Covellite, 51, 300 
 Cristobaltite, 70, 76, 312 
 Crocalite, 278 
 Crocidolite, 256 
 Crocoite, 133, 138, 299, 305 
 Cronstedite, 225 
 Crude oil, 288 
 Cryolite, 107, 293, 301, 313 
 Crystalline dolomite, 116 
 
 limestone, 114 
 Cummingtonite, 253 
 Cuprite, 88, 300 
 
 Cupromagnesite, 150, 151, 300, 306 
 Cuproscheelite, 140 
 Cyanite, 189, 293 
 Cylindrite, 66, 305, 316 
 Cymophane, 162 
 
 D 
 
 Damourite, 218 
 
 Danaite, 44 
 
 Danalite, 198, 296, 303, 308, 315. 
 
 Danburite, 206, 207, 297 
 Daphanite, 225 
 Datholite, 192 
 
 Datolite, 191, 192, 297, 298 
 Datolithe, 192 
 
 Dyvane, 232, 233, 314, 315 
 Dawsonite, 125, 313 
 Delessite, 225 
 Demantoid, 211 
 Descloizite, 174, 175, 305, 317 
 Desmine, 283 
 Deweylite, 225, 229, 307 
 Diabantite, 225 
 Diallage, 240, 243 
 Diamond, 3, 298 
 
 black, 10 
 
 carat, 3 
 
 cut, 10 
 
 drill, ii 
 Diaphorite, 58 
 Diaspore, 92, 293 
 Diatomaceous earth, 90 
 Dichroite, 236 
 Didymium, 300 
 Diopside, 240, 243 
 
 chrome, 243 
 Dioptase, 211, 300 
 Diorthosilicic acid, 183 
 Dipyre, 270 
 Disterrite, 222 
 Disthene, 189 
 Dog-tooth spar, 113 
 Dolomite, in, 115, 297, 306 
 Dolomitic limestones, 113 
 Domeykite, 45, 46, 295, 300 
 Douglasite, 106, 107, 303, 310 
 Dry bone, 117 
 Dudley ite, 221 
 Dufrenite, 176, 303 
 Dufrenoysite, 58, 301 
 Dumortierite, 185, 296 
 Dysanalyte, 273 
 Dyscrasite, 45, 46, 294, 312 
 Dysluite, 155, 157, 307, 317 
 
 E 
 
 Edenite, 254 
 
 Edingtonite, > 277, 279, 295 
 Eisennickelkies, 35 
 Eisstein, 107 
 Elaeolite, 232 
 Elaterite, 290 
 Elements, 3 
 
3 2 4 
 
 INDEX 
 
 Elpiclite, 273, 314, 318 
 Embolite, 98, 102, 297, 313 
 Emerald, 258 
 
 nickel, 128 
 
 oriental, 85 
 Emery, 84, 85 
 Emmonite, 121 
 Emplectite, 57, 296, 300 
 Enargite, 64, 295, 300 
 Endlichite, 170, 173, 305, 317 
 Enstatite, 240, 241 
 Epidote, 199, 200, 293, 298, 303 
 Epididymite, 271, 296, 314 
 Epistilbite, 282 
 Epsomite, 149, 150, 306 
 Epsom salt, 150 
 Erbium, 300 
 
 Erythrite, 177, 178, 295, 299 
 Erythrosiderite, 106, 310 
 Erythrozincite, 33, 35, 307, 317 
 Essonite, 209 
 Eucairite, 46, 49, 312 
 Euchroite, 180, 300 
 Euclase, 191, 192, 296 
 Eucolite, 273 
 Eucryptite, 232 
 Eudialyte, 273, 314, 318 
 Eudidymite, 271, 296, 314 
 Eulytite, 207, 296 
 Euralite, 225 
 Euxenite, 274 
 Exanthalite, 146 
 
 False topaz, 74 
 Famatinite, 64, 65 
 Fargite, 278 
 Fassaite, 240, 245 
 Faujasite, 281 
 Fayalite, 203, 205, 304 
 Feldspar, 259 
 
 barium, 263 
 
 glassy, 261 
 
 group, 259 
 
 lime, 268 
 
 soda, 268 
 
 ordinary, 262 
 
 potash, 260 
 
 soda, 266 
 
 lime, 267 
 Feldspars, 259, 294 
 
 monoclinic, 259, 260 
 
 triclinic, 259, 264 
 Felsite, 262 
 Felspar, 260 
 
 Ferberite, 138, 142, 303, 316 
 Fergusonite, 166, 167, 309, 317 
 Ferrobrucite, 96, 305 
 Ferrocobaltite, 41 
 Ferrogoslarite, 151 
 Ferruginous quartz, 74 . 
 Fibrolite, 188 
 Fichtelite, 290 
 Fiorite, 90 
 Fire opal, 90 
 Flint, 75 
 
 Flos ferri, 119, 120 
 Fluellite, 1 06, 293 
 Fluor-apatite, 171 
 Fluorine, 301 
 Fluorite, 103, 297, 301 
 Fluor spar, 103 
 Fontainebleau limestone, 113 
 Fool's gold, 39 
 Forsterite, 203, 204, 306 
 Fortification agate, 74 
 Fowlerite, 241, 249, 308, 318 
 Franckeite, 66, 304, 316 
 Franklinite, 155, 158, 303, 307, 317 
 Freibergite, 62 
 
 Freieslebenite, 58, 59, 294, 304, 312 
 French chalk, 227 
 Frenzelite, 31 
 Fuchsite, 260 
 
 Gadolinite, 191, 193, 296, 303, 317 
 Gahnite, 155, 157, 317 
 Galactite, 278 
 Galena, 46, 47, 304 
 Galenite, 47 
 Gallium, 301 
 Ganomalite, 235, 305 
 Ganophyllite, 279, 308 
 
225 
 
 Garnet, 208, 294, 298, 304 
 
 black, 211 
 
 calcium-aluminium, 209 
 -iron, 211 
 
 common, 211 
 
 chromium-calcium, 211 
 
 group, 208 
 
 iron-aluminium, 210 
 
 magnesium-aluminium, 210 
 
 manganese-aluminium, 210 
 Garnierite, 225, 229, 307, 309 
 Gay-Lussite, 127, 297, 313 
 Gedanite, 291 
 Gedrite, 250, 252 
 Gehlenite, 236, 237 
 Geikielite, 238, 307, 316 
 Genthite, 225, 229, 307 
 Geocronite, 63, 304 
 Germanium, 301 
 Gersdorffite, 38, 41, 295, 309 
 Geyserite, 90 
 Gibbsite, 91, 92, 293 
 Gilsonite, 290 
 Glaserite, 131, 310, 313 
 Glauberite, 132, 297, 313 
 Glauber salt, 146 
 Glaucochroite, 203, 308 
 Glaucodote, 38, 44, 295, 299, 302 
 Glauconite, 220 
 Glaucophane, 251, 255 
 Glucinum, 301 
 Gmelinite, 285, 286, 314 
 Goethite, 92, 93, 303 
 Gold, 20, 25, 301 
 
 amalgam, 28, 301, 308 
 carat, 28 
 
 fool's, 39 
 
 free milling, 25 
 native, 25, 301 
 Goshenite, 258 
 Goslarite, 149, 150, 317 
 Grahamite, 290 
 Granular limestone, 114 
 
 quartz, 75 
 Graphite. 3, n, 298 
 Graphic tellurium, 53 
 
 granites, 262 
 
 Green carbonate of copper, 124 
 sand, 220 
 
 Greenockite, 33, 35, 297 
 Greisen, 81 
 
 Grossularite, 208, 209 
 Grothite, 271, 272 
 Griinerite, 253 
 
 Guana juatite, 30, 31, 296, 312 
 Guano, 171 
 Gummite, 287, 317 
 Gymmite, 229 
 
 nickel, 229 
 Gypsite, 147 
 Gypsum, 146, 298 
 
 H 
 
 Halite, 98, 99, 313 
 Haloids, 98 
 Halotrichite, 154, 303 
 Hanksite, 154, 311, 313 
 Hardystonite, 235, 298, 318 
 Harmotome, 282, 283, 284, 296 
 Hartite, 290 
 Hatchettite, 289 
 Hauerite, 38, 39, 307 
 Hausmannite, 129, 307 
 Hauy ne, 234 
 
 Hauynite, 233, 234, 314, 315 
 Heavy spar, 135 
 Hedenbergite, 240, 244 
 Hedyphane, 173 
 Helium, 302 
 Heliotrope, 74 
 
 Helvite, 198, 296, 303, 308, 315 
 Hematite, 84, 86, 302 
 Hemimorphite, 185, 186, 317 
 Hercynite, 155, 157 
 Herderite, 174, 175, 296 
 Hessite, 46, 49, 312, 315 
 Hessonite, 209 
 Heulandite, 281 
 Hexagonite, 252 
 Hiddenite, 247 
 Hoernesite, 177, 178 
 Holmesite, 222, 306 
 Holmite, 222 
 
 Homilite, 191, 193, 297, 298, 303 
 Horn mercury, 105 
 silver, 101 
 
326 INDEX 
 
 Hornblende, 251, 253 
 
 basaltic, 254 
 
 common, 254 
 Hornstone, 75 
 Horse flesh ore, 55 
 Hortonolite, 203, 205, 306, 308 
 Hovellite, 98 
 
 Huebernite, 138, 140, 307, 316 
 Humboldtilite, 237 
 Humboldtine, 288 
 Humite, 196, 197, 301, 306 
 Hyacinth, 79, 80 
 Hyalite, 90 
 
 Hyalophane, 259, 263, 295 
 Hydrargillite, 92 
 Hydraulic limestone, 113 
 Hydrocerussite, 123, 125, 305 
 Hydrofranklinite, 129 
 Hydrogen, 302 
 Hydromagnesite, 127, 306 
 Hydronephelite, 277, 314 
 Hydrophane, 90 
 Hydrophilite, 103, 297 
 Hydrorhodonite, 249 
 Hydroxides, 89 
 Hypersthene, 240, 242 
 . Hydrozincite, 12, 125, 317 
 Hystatite, 239 
 
 Ice, 67 
 
 Iceland spar, in, 113 
 Idrialite, 290 
 Idocras", 202 
 IgL./ ite, 123 
 
 Ilmemte, 237, 238, 239, 304, 316 
 Ilvaite, 196, 298, 303 
 Indicolite, 195 
 Indigolite, 195 
 Indium, 302 
 Inesite, 282 
 Infusorial earth, 90 
 lodargyrite, 102 
 Iodine, 302 
 
 lodobromite, 98, 102, 297, 302, 313 
 lodyrite, 98, 102, 302, 313 
 lolite, 236, 304, 307 
 Iridium, 17, 18, 302 
 native, 18, 302 
 
 Iridosmine, 18 
 
 Iridosmium, 17, 18, 302, 310 
 
 Iron, 19, 302 
 
 alum, 154 
 
 cross, 40 
 
 meteoric, 19 
 
 native, 19, 302 
 
 roses, 86 
 
 schefferite, 244 
 
 spinel, 157 
 
 terrestrial, 19 
 
 titaniferous, 239 
 Isinglass, 217 
 Itacolumite, 75 
 
 Jacobsite, 155, 159, 303, 307 
 Jade, 247, 252 
 Jadeite, 241, 247, 314 
 Jalpaite, 46, 49, 312 
 Jamesonite, 58, 294, 304 
 Jargon, 79 
 
 Jarosite, 143, 144, 303, 311 
 Jasper, 70, 74 
 Jeffersonite, 240, 244, 308 
 Jet, 292 
 
 Jordanite, 62, 295, 304 
 Josephinite, 20, 309 
 
 K 
 
 Kainite, 154, 311 
 
 region, 101 
 
 Kalinite, 154, 293, 311 
 Kaliophilite, 232 
 Kaolin, 230 
 Kaolinite, 230, 294 
 Katoforite, 255 
 Kelyphite, 210 
 Kermesite, 97, 294, 315 
 Kieserite, 149, 306 
 
 region, 101 
 
 Knebelite, 203, 205, 308 
 Knopite, 238 
 
 Kottigite, 177, I 79> 299, 317 
 Kraurite, 176 
 Kremersite, 106, 310 
 Krennerite, 53, 54, 301, 312, 315 
 Kunzite, 248 
 Kyanite, 189 
 
INDEX 
 
 327 
 
 Labradorescence, 268 
 Labradorite, 259, 265, 268 
 Labrador spar, 268 
 Land plaster, 147 
 Langbeinite, 132, 133, 306, 310 
 Lanthanum, 304 
 Lapis-lazuli, 234 
 Lasurite, 234 
 Laterite, 94 
 Laumontite, 286 
 Lautarite, 109, 302 
 Lawrencite, 103 
 Lawsonite, 195, 196, 298 
 Lazulite, 176, 293, 306 
 Lazurite, 233, 234, 314, 315 
 -Le-at!7~20, 304 
 
 black, ii 
 
 glance, 47 
 
 native, 20, 304 
 Leadhillite, 145, 305 
 Lepidolite, 215, 219, 297, 301, 305 
 Lepidomelane, 216 
 Leptochlorites, 225 
 Leucaugite, 240, 246 
 Leucite, 257, 294, 311 - 
 Leucopyrite, 44 
 Leucoxene, 239, 272 
 Libethenite, 174, 175, 300 
 Lievrite, 196 
 Lignite, 291, 292 
 Limestone, 113 
 
 varieties, 113 
 Lime uranite, 182 
 Limonite, 95, 303 
 
 varieties, 95 
 Linarite, 144, 300, 305 
 Linnaeite, 56, 299, 309 
 Lintonite, 276 
 
 Lithographic limestone, 113 
 Lithiophilite, 165, 166, 305, 307 
 Lithium, 305 
 Lodestone, 159 
 Lollingite, 38, 44, 295, 302 
 Lorandite, 57, 295, 315 
 Lorenzenite, 274, 314, 316, 318 
 Loxoclase, 262 
 Luzonite, 64 
 
 Luckite, 150, 151, 317 
 Lydian stone, 75 
 
 M 
 
 Made, 187 
 
 Magnesian limestone, 113 
 
 Magnesioferrite, 155, 159, 303, 306 
 
 Magnesite, in, 116, 306 
 
 Magnesium alum, 154 
 
 Magnetic iron ore, 159 
 
 Magnetite, 155, 159, 303 
 
 Magnoferrite, 159 
 
 Malachite, 123, 124, 300 
 
 Malacolite, 240 
 
 Malacon, 79 
 
 Mallardite, 150, 151, 307 
 
 Manganandalusite, 188 
 
 Manganblende, 34 
 
 Manganese alum, 154 
 
 black oxide, 82 
 Magnesium, 305 
 Manganhedenbergite, 244 
 Manganiferous epidote, 201 
 Manganite, 92, 93, 307 
 Manganites, 128 
 Mangankies, 39 
 Manganobrucite, 96, 305, 307 
 Manganocalcite, no, 118, 297, 307 
 Manganocolumbite, 169 
 Manganopectolite, 247 
 Manganosiderite, in, 118, 303, 307 
 Manganosite, 83, 307 
 Manganotantalite, 169 , 
 Marble, 113, 114 '-.r,i a * ' 
 
 serpentine, 226 
 Marcasite, 38, 42, 302 
 Marceline, 128 
 Margarite, 221 
 Marialite, 269, 270 
 Marl, 113, 114 
 Marshite, 105, 300, 302 
 Martite, 87 
 Mascagnite, 131, 309 
 Masonite, 223 
 Massicot, 88, 305 
 Matlockite, 108, 305 
 Meerschaum, 228 
 Meigen's test, 113, 120 
 
328 
 
 INDEX 
 
 Meionite, 269, 270 
 Melaconite, 88, 89, 300 
 Melanite, 211 
 Melanterite, 150, 151, 303 
 Melilite, 236, 237 
 Mellite, 288 
 Menaccanite, 239 
 Mendozite, 154, 313 
 Meneghinite, 62, 63, 304 
 Mercury, 20, 24, 308 
 
 native, 24, 308 
 Meroxene, 216 
 Mesitite, 117 
 Mesolite, 277, 278, 314 
 Mesotype, 278 
 Metachlorite, 225 
 Metacinnabarite, 50, 51, 308 
 Metamorphosed limestone, 114 
 Metasilicic acid, 183 
 Metastilbite, 283 
 Mexican onyx, 114 
 Miargyrite, 57, 294, 312 
 Mica, 214, 294, 311 
 
 A, 218 
 
 amber, 217 
 
 black, 215 
 
 brittle, 221 
 
 bronze, 217 
 
 group, 214 
 
 lithium, 219 
 -iron, 220 
 
 magnesium, 217 
 -iron, 215 
 
 pearl, 221 
 
 potash, 217 
 
 ribbon, 218 
 
 ruby, 218 
 
 ruled, 218 
 
 rum, 218 
 
 sheet, 219 
 
 sodium, 219 
 
 wedge, 218 
 
 white, 217 
 Micanite, 219 
 Microcline, 259, 264, 311 
 
 soda, 264 
 'Microsomite, 233 
 Miersite, 98, 102, 302, 313 
 Milarite, 275, 311 
 
 Milk opal, 90 
 Milky quartz, 74 
 Millerite, 33, 36, 309 
 Mimetite, 170, 173, 295, 305 
 Mineral oil, 288 
 
 pitch, 289 
 
 wax, 289 
 Minium, 129, 305 
 Mirabilite, 146, 313 
 Mispickel, 43 
 Misy, 152, 153 
 Mizzonite, 270 
 Mohawkite, 46 
 Molydbates, 138 
 Molybdenite, 32, 308 
 Molybdic ocher, 96 
 Molybdite, 96, 308 
 Molysite, 105, 303 
 Monazite, 166, 167, 299 
 Monheimite, HI, 118, 303, 317 
 Monticellite, 203, 298, 306 
 Moonstone, 261, 266 
 Mordenite, 282, 314 
 Morenosite, 149, 151, 309 
 Morion, 73 
 Moss agate, 74 
 Mossite, 168, 307, 309 
 Mountain cork, 253 
 
 leather, 253 
 
 wood, 253 
 Muscovite, 215, 217 
 
 N 
 
 Nacrite, 230 
 
 Nagyagite, 53, 54, 294, 301, 304, 315 
 
 Nail-head spar, 113 
 
 Nantokite, 105, 300 
 
 Nasonite, 233, 305 
 
 Natroalunite, 143 
 
 Natrojarosite, 143, 144, 303, 313 
 
 Natrolite, 277, 314 
 
 Natron, 126, 313 
 
 Natronborocalcite, 163 
 
 Natrophylite, 165, 307, 313 
 
 Naumannite, 46, 49, 304, 312 
 
 Needle zeolite, 277 
 
 Neodymium, 309 
 
 Nepheline, 232 
 
INDEX 
 
 329 
 
 Nephelite, 231, 232, 294, 311, 313 
 Nephrite, 252 [316 
 
 Neptunite, 275, 304, 308, 311, 314, 
 Nevyanskite, 19 
 Newportite. 223 
 Niccolite, 33, 37, 295, 309 
 Nickel, 309 
 
 bloom, 178 
 
 glance, 41 
 
 sepiolite, 229 
 gymmite, 229 
 Nigrine, 78 
 Niobium, 309 
 Niter, 109, no, 309, 310 
 Nitrates, 109 
 Nitrogen, 309 
 Nivenite, 142 
 Nontronite, 230, 231, 304 
 Nordmarkite, 185 
 Normal dolomite, 116 
 Northupite, 126, 313 
 Nosean, 234 
 
 Noselite, 233, 234, 314, 315 
 Noumeite, 229 
 
 O 
 
 Ocherons limonite, 95 
 Octahedrite, 76 
 Oldhamite, 33, 297 
 Oligoclase, 259, 265, 267 
 Oligonite, in, 118, 119, 303, 307 
 Olivenite, 174, 174, 295, 300 
 Olivine, 203, 204, 304, 306 
 Omphacite, 243 
 Onofrite, 50, 51, 308, 312 
 Onyx, 74, 114 
 
 marble, 114 
 
 Mexican, 114 
 Oolitic iron ore, 87 
 
 limestone, 114 
 Opal, 89, 312 
 
 varieties, 90 
 Ophicalcite, 226 
 Orangite, 80 
 
 Organic compounds, 288 
 Orpiment, 30, 295 
 Orthite, 199, 201, 298, 299, 303 
 Orthochlorites, 225 
 
 Orthoclase, .259, 260, 311 
 
 ordinary, 262 
 
 soda, 259, 263 
 Orthosilicic acid, 183 
 Osmium, 310 
 
 Osmiridium, 17, 19, 302, 310 
 Osteolite, 171 
 Ottrelite, 221, 222 
 Ouvarovite, 211 
 Oxalite, 288, 304 
 Oxide of cadmium, 83 
 Oxides, 67 
 Oxychlorides, 108 
 
 -fluorides, 108 
 
 -sulphides, 97 
 Ozocerite, 289 
 Ozokerite, 289 
 Oxygen, 310 
 
 Pachnolite, 108, 301, 313 
 Palladium, 17, 18, 19 310 
 
 native, 18, 19, 310 
 Pandermite, 164, 296, 298 
 Paraffin, 289 
 Paragonite, 215, 219, 313 
 Paramelaconite, 89, 90 
 Pargasite, 254 
 Patrinite, 61 
 Pearceite, 63, 300, 313 
 Pearl spar, 115 
 Peat, 291, 292 
 Pectolite, 241, 246, 314 
 Pencatite, 128 
 Pencil stone, 231 
 Penninite, 223, 224 
 Pentasilicic acid, 183 
 Pentlandite, 33, 35, 302, 309 
 Percylite, 108, 305 
 Periclase, 83, 305 
 Peridot, 204 
 Peristerite, 266 
 Perovskite, 237, 238, 298, 316 
 Perowskite, 238 
 Perthite, 262 
 Petalite, 274, 305 
 Petroleum, 288 
 Petzite, 47, 50, 301, 312, 315 
 
330 
 
 INDEX 
 
 Phacelite, 232 
 Phacolite, 285 
 Pharmacolite, 180, 295 
 Pharmacosiderite, 180, 295, 303 
 Phenacite, 203, 205, 296 
 Phengite, 218 
 Phillipsite, 283, 284 
 Phlogopite, 215, 217, 306 
 Pholerite, 230 
 Phosgenite, 126, 305 
 Phosphate rock, 171 
 Phosphates, 165 
 Phosphorite, 171 
 Phosphorous, 310 
 Phyllite, 223 
 Picroilmenite, 239 
 Picrotitanite, 239 
 Picotite, 155, 157 
 .Picromerite, 153, 306, 311 
 Picmontite, 199, 201, 298, 308 
 Pirssonite, 127, 297, 313 
 Pisanite, 150, 151, 303 
 Pisolitic limestone, 114 
 Pistacite, 200 
 Pistomesite, 117 
 Pitchblende, 142 
 
 Plagioclases, 259, 260, 265, 298, 314 
 Plagionite, 58, 294 
 Plasma, 74 
 Plaster of Paris, 149 
 Platiniridium, 17, 302 
 Platinum, 17, 310 
 
 iron, 17 
 
 native, 17, 310 
 Platternite, 77, 82, 305 
 Pleonaste, 155, 157 
 Plumbago, II 
 Plumbites, 128 
 
 Plumbojarosite, 143, 144, 303, 305 
 Polianite, 77, 82, 307 
 Pollucite, 297 
 Polonium, 310 
 Polyargyrite, 64, 313 
 Polybasite, 63, 64, 294, 300, 313 
 Polycrase, 274 
 Polyhalite, 153, 311 
 
 region, IOT 
 Polymignite, 274, 309 
 
 Polysilicic acid, 183 
 Potash alum, 154 
 
 feldspar, 260 
 Potassium, 310 
 Powellite, 138, 139, 298, 308 
 Prase, 74 
 
 Praseodymium, 311 
 Precious opal, 90 * 
 
 serpentine, 226 
 Predazzite, 128 
 Prehnite, 213, 294, 298 
 Prochlorite, 223, 224 
 Prolectite, 197, 306 
 Proustite, 59 2 95> 3 T 3 
 Pseudobrookite, 207, 304, 316 
 Pseudoleucite, 257 
 Psilomelante, 129, 296, 307 
 Purple copper ore, 55 
 Pyrargyrite, 59, 294, 313 
 Pyrite, 38, 39, 302 
 Pyrites, 39 . 
 
 capillary, 36 
 
 cobalt, 56 
 
 copper, 55 
 
 iron, 39 
 
 magnetic, 36 
 
 spear, 42 
 
 tin, 65 
 
 white iron, 42 
 Pyrochlore, 273 
 Pyrochroite, 96, 307 
 Pyrolusite, 82, 307 
 Pyromorphite. 170, 172, 305 
 Pyrope, 208, 210, 306 
 Pyrophanite, 238, 239, 308, 316 
 Pyrophyllite, 230, 231, 294 
 Pyropissite, 290 
 Pyrostibite, 97 
 Pyrrhotite, 33, 36, 302 
 Pyroxenes, 240, 250, 298, 304, 307 
 Pyrrhite, 274 
 
 Quartz, 70, 312 
 varieties, 73 
 Ouartzite, 75 
 Quicksilver, 24 
 
INDEX 
 
 331 
 
 R 
 
 Rammelsbergite, 38, 45, 295, 309 
 Ranite, 277 
 Realgar, 29, 295 
 Red antimony, 97 
 
 clay, 87 
 
 clay ironstone, 87 
 
 copper ore, 88 
 
 hematite, 87 
 
 iron ore, 86 
 
 ocher, 87 
 
 oxide of copper, 88 
 zinc, 84 
 
 silver ore, 59 
 
 zinc ore, 84 
 Reddle, 87 
 Rensselaerite, 227 
 Residual limonite, 95 
 Resin opal, 90 
 Retinite, 291 
 Rhatzite, 189 
 Rhodium, 311 
 
 Rhodochrosite, HI, 118, 307 
 Rhodonite, 241, 249, 308 
 Rhodotilite, 282 . 
 Rhyacolite, 261 
 Riband jasper, 75 
 Richterite, 251, 253 
 Riebeckite, 251, 256 
 Ripidolite, 224 
 Rock crystal, 73 
 
 gypsum, 147 
 
 salt, 99 
 
 Roepperite, 205 
 Roscoelite, 218 
 Rose quartz, 73 
 Rothkupferkies, 37 
 Rubellite, 195 
 Rubicelle, 156 
 Rubidium, 311 
 Ruby, 84, 85 
 
 cape, 210 
 
 copper ore, 88 
 
 silver ore, 59 
 
 spinel, 156 
 Rumpfite, 225 
 Ruthenium, 311 
 Rutilated quartz, 74 
 Rutile, 77, 316 
 
 Safflorite, 38, 44, 295, 299 
 Sal ammoniac, 98, 99, 309 
 Salite, 240 
 Salmite, 223 
 Salt, common, 99 
 
 regions, 101 
 
 rock, 99 
 Saltpeter, 109, no 
 
 Chile, 109 
 Salvadorite, 151 
 Samarium, 311 
 Samarskite, 168, 309, 317 
 Sand, 75 
 
 black, 159, 161 
 
 green, 220 
 Sandstone, 75 
 Sanidine, 261 
 Saponite, 225, 229 
 Sapphire, 84, 85 
 Sarcolite, 271 
 Sard, 74 
 Sardonyx, 74 
 Sarkinite, 174, 308 
 vSartorite, 57 
 Sassolite, 91, 296 - 
 Satin spar, 113, 146, 147 
 Scacchite, 103, 307 
 Saussurite, 200 
 Scandium, 312 
 
 vScapolite, 269, 270, 294, 298, 314 
 Schalenblende, 35 
 Scheelite, 138, 139, 298, 316 
 Schefferite, 240, 244, 308 
 Schonite, 153 
 Schorl, 195 
 Schorlomite, 211 
 Schungite, 3, 12, 298 
 Schwatzite, 62 
 Scleroclase, 57, 304 
 Scolecite, 277, 278 
 Scorodite, 179, 295, 303 
 Seladonite, 220 
 Selenite, 146, 147 
 Selenium, 14, 312 
 Selensulphur, 14, 312, 315 
 Seligmannite, 60 
 Sellaite, 10^, 104, 301, 305 
 vSenarmontite, 69, 294 
 
332 
 
 INDEX 
 
 vSepiolite, 225, 228, 306 
 
 nickel, 229 
 Sericite, 218 
 Serpentine, 225, 226, 306 
 
 common, 226 
 
 fibrous, 226 
 
 marble, 226 
 
 precious, 226 
 Seybertite, 222 
 Siberite, 195 
 Siderite, HI, 118, 303 
 Silicates, 183 
 Silicified wood, 73 
 Silicious sinter, 90 
 Silicon, 312 
 Sillimantite, 188, 293 
 Silver, 20, 23, 312 
 
 glance, 48 
 
 native, 23, 312 
 Simonyite, 153 
 Sipyllte, 167 
 Siserskite, 18 
 Sismondine, 223 
 Skutterudite, 45, 295, 299 
 Smaltite, 36, 41, 295, 299 
 Smithsonite, HI, 117, 297, 317 
 Smoky quartz, 73 
 Snow, 67 
 Soapstone, 227 
 Soda, 126 
 
 alum, 154 
 
 niter, 109, 309, 313 
 Sodalite, 233, 294, 314 
 Soda-orthoclase, 259, 263, 314 
 Sodium, 313 
 Sommervillite, 237 
 Spatbic iron, 118 
 Spathiopyrite, 44 
 Specular iron ore, 86 
 Specularite, 86 
 Sperrylite, 38, 42, 295, 310 
 Spessartite, 208, 210, 308 
 vSphaerocobaltite, in, 119, 299 
 Sphalerite, 32, 33, 297, 317 
 Sphene, 271, 272 
 Spinel, 155, 156, 293, 303, 306 
 
 varieties, 156 
 
 Spodumene, 241, 247, 294, 305 
 Spreustein, 278 
 
 Stagmites, 114 
 Stalactites, 114 
 Stalagmites, 114 
 Stannite, 65, 300, 302, 316 
 Staurolite, 184, 293, 303 
 Steatite, 227 
 Steenstrupine, 273, 296 
 Stelznerite, 144, 300 
 Stephanite, 63, 294, 313 
 Stibnite, 30, 294 
 Stilbite, 281, 283, 314 
 Stinkstone, 113 
 Stolzite, 138, 140, 305, 316 
 Stream tin, 81 
 Strengite, 179, 303 
 Strigovite, 225 
 Striped jasper, 75 
 Stromeyerite, 47, 50, 300, 312 
 Strontianite, HI, 121, 314 
 Struvite, 177, 306, 309 
 Succinite, 290 
 Sulfoborite, 164, 296, 316 
 Sulphates, 131 
 Sulphides, 29 
 Sulphohalite, 145, 301, 313 
 Sulphur, 13, 315 
 
 native, 13, 315 
 Sunstone, 267 
 
 Sussexite, 162, 296, 306, 307 
 Sylvanite, 53, 301, 312, 315 
 Sylvite, 98, 310 
 Symplesite, 177, 178, 303 
 
 Tabular spar, 244 
 Tachydrite, 106, 107, 297, 306 
 Tachyhydrite, 107 
 Talc, 225, 227, 230, 306 
 Tantalite, 168, 303, 307, 309 
 Tantalum, 315 
 Tapiolite, 168, 307, 309 
 Tarnowitzite, in, 122, 297, 305 
 Tasmanite, 291' 
 Tellurite, 68, 315 
 Tellurium, 14, 15, 315 
 
 grpahic, 53 
 
 native, 15, 315 
 Tennantite, 62 
 
INDEX 
 
 333 
 
 Tenorite, 89, 300 
 Tephroite, 203, 205, 308 
 Terra alba, 149 
 Tetradymite, 31, 296, 315 
 Tetrahedrite, 61, 294, 295, 300, 
 
 302, 308, 313, 317 
 Tetrasilicates, 183 
 Tetrasilicic acid, 183 
 Texasite, 128 
 Thallium, 315 
 Thaumansite, 287, 315 
 Thenardite, 131, 132, 313 
 Thermonatrite, 126, 313 
 Thinolite, 114 
 Thomsenolite, 108, 301 
 Thomsonite, 276, 314 
 Thorates, 183 
 Thorite, 77, 80, 312, 316 
 Thorium, 316 
 
 Thulite, 199 , 
 
 Thuringite, 225 
 Tiemannite, 50, 51, 308, 312 
 Tiger's eye, 74, 256 
 Tilasite, 174, 401, 306 
 Tile ore, 89 
 Tin, 16, 316 
 
 native, 16, 316 
 
 ore, 80 
 
 ore deposits, 81, 140, 141 
 
 pyrites, 65 
 
 stone, 80, 8 1 
 
 stream, 80, 81 
 
 wood, 8 1 
 Tinkal, 163 
 Titanates, 183 
 Titanic iron ore, 239 
 Titaniferous iron, 230 
 Titanite, 271, 298, 316 
 Titanium, 316 
 Titancmorphite, 239, 272 
 Topaz, 190, 293, 301 
 
 false, 74 
 
 oriental, 85 
 Topazolite, 211 
 Torbernite, 182, 300, 316 
 Touchstone, 75 
 Tourmaline, 193, 293, 297, 305, 306 
 
 tongs, 194, 195 
 Travertine, 114 
 
 Tremolite, 251, 252 
 Tridymite, 75, 312 
 Trimerite, 203, 205, 308 
 Triphane, 247 
 
 Triphylite, 165, 303, 305, 307 
 Triplite, 174, 176, 301, 303 
 Triploidite, 174, 176, 308 
 Tripolite, 90 
 Trisilicates, 183 
 Trisilicic acid, 183 
 Troilite, 33, 35, 302 
 Trona, 127, 313 
 Troostite, 206 
 Tscheffkinite, 273, 296 
 Tschermigite, 154, 309 
 Tungstates, 138 
 Tungsten, 316 
 Tungstite, 68, 316 
 Turkey fat, 117 
 Turnerite, 167 
 Turquois, 181, 293 
 Turquoise, 181 
 Tyrite, 167 
 Tysonite, 105, 299, 301 
 
 U 
 
 Uintahite, 290 
 Ulexite, 163, 296, 298, 313 
 Ultramarine, 234 
 Ullmannite, 38, 41, 294, 309 
 Unisilicates, 183 
 Uralite, 246, 255 
 Uralitization, 255 
 Uraninite, 142, 293, 294, 316 
 Uranium, 316 
 Uranocircite, 182 
 Uranophane, 287 
 Uranospinite, 182, 316 
 Uranotantalite, 168 
 Uranotile, 287, 317 
 Urao, 127 
 Urpethite, 289 
 Uvarovite, 208, 211, 299 
 Uwarowite, 211 
 
 V 
 
 Valentinite, 69, 294 
 Vanadinite, 170, 173, 305, 317 
 Vanadium, 317 
 
334 
 
 INDEX 
 
 Van't Hoffite, 132, 306, 313 
 Variegated copper ore, 55 
 Variscite, 179, 293 
 Verd-antique, 226 
 Vermilion, natural, 52 
 Vesuvianite, 202, 294, 298, 301 
 Vivianite, 178, 303 
 Volcanite, 14 
 Voltzite, 97 
 
 W 
 
 Wad, 130, 307 
 
 Wagnerite, 174, 175, 301, 306 
 
 Walchowite, 291 
 
 Waluewite, 221 
 
 Warthite, 153 
 
 Washingtonite, 239 
 
 Water, 67 
 
 Wavellite, 180, 293 
 
 Wellsite, 283, 284, 296 
 
 Wernerite, 269, 270 
 
 Wheel ore, 60 
 
 Whewellite, 288, 298 
 
 White lead ore, 122 
 
 Whiteneyite, 45, 295, 299 
 
 Willemite, 203, 206, 318 
 
 Winklerite, 94, 299, 309 
 
 Witherite, in, 122, 295 
 
 Wolfachtite, 38, 45, 309 
 
 Wolfram, 141 
 
 Wolframite, 138, 141, 303, 307, 316 
 
 Wollastonite, 240, 244 
 
 Wood opal, 90 
 
 tin, 86 
 
 Wulfenite, 138, 139, 305, 308 
 Wurtzite, 32, 33, 35, 297, 316 
 
 Xanthophyllite, 221, 306 
 Xanthosiderite, 94, 303 
 Xenotime, 166, 317 
 
 Yellow copperas, 152 
 copper ore, 55 
 quartz, 74 
 Yttrium, 317 
 Yttroilmenite, 168 
 Yttrotantalite, 167, 317 
 Yttrotitanite, 272 
 
 Zaratite, 128, 309 
 Zeolites, 276, 294, 298 
 Zeunerite, 182, 300, 316 
 Zietrisikite, 289 
 Zinc, 20, 317 
 
 blende, 33 
 
 bloom, 125 
 
 native, 20, 317 
 
 spinel, 157 
 Zinckenite, 57 ^ 
 Zincite, 83, 48, 317 
 Zinkenite, 57, 294, 304 
 Zircon, 77, 79, 318 
 Zirconium, 318 
 
 Zinnwaldite, 215, 220, 301, 305 
 Zirconates, 183 
 Zirkelite, 273, 316, 318 
 Zoisite, 199, 293, 298 
 Zwitter, 81 
 
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