SULPHIDES, ARSENIDES, ANTIMONIDl - 



wall iniii.-s. in Bolivia, Zinmvald, and the Black Hills, South 

 Dakota. It is not a common mineral, and, uliile it contains con- 

 siderable tin and copper, owing to its restricted occurrence it is of 

 minor importance as an ore. 



PYRITE 



Pyrite. FeSj ; Bisulphide of iron ; Fe = 46.6, S = 53.4 ; 

 Isometric; Type, Tesseral Central; Common forms, a (100), o 

 (lll),e (120), s (312); Twinning supplementary and interpene- 

 trating; Cleavage, a and o distinct; Brittle, fracture conchoidal 

 to uneven; H. =6-6.5; G. =4.5-5.1; Color, light brass yellow; 

 Streak, greenish to brownish black; Luster, metallic, often 

 brilliant. 



B.B. On coal in O. F., yields a sulphur dioxide odor, darkens, 

 and in R. F. becomes magnetic. With the fluxes reacts for iron. 

 In the closed tube yields a sublimate of sulphur. Soluble in hot 

 nitric acid. 



General description. Crystals are very common of cubic, 

 octahedral, or pentagonal dodecahedral habit, or combinations of 

 these three forms. Numerous other forms, including all seven forms 

 of the type, have been described, as on crystals from Gilpin County, 

 Colorado. The cube and pyritohedral faces are usually striated 

 parallel to their intersection ; on the cube the striations are parallel 

 to the opposite sides and at right angles to the striations on adja- 

 cent faces, indicating the hemihedral symmetry of the pyrite cube. 

 Penetrating supplementary twins of the plus and minus pyritohe- 

 drons are obtained at Minden, Prussia; complex stellate and 

 parallel growths are common in clays, slates, and argillites. A 

 peculiar elongated octahedral form, possibly a tetragonal phase, 

 occurs at French Creek, Pennsylvania. Beautiful crystals are 

 obtained from the Isle of Elba, from Peru, and from French Creek, 

 Pennsylvania. Pyrite also occurs massive, granular, or in nodules. 



Chemically pyrite may contain copper, nickel, and cobalt sul- 

 phides as mixtures, as well as arsenic and metallic gold. It is the 

 most widely distributed of all the sulphides, occurring under the 

 most varied conditions; as primary constituent of igneous rocks 

 and secondary impregnations, in sedimentary rocks, clays, and coal 

 formations, as well as filling veins, fissures, and joints, where it is 

 associated with other sulphides, carbonates, sulphates, and oxides. 

 By oxidation it yields sulphates, acid sulphites, and sulphuric acid, 



