326 



MINERALOGY 



FIG. 406. Stephanite. Freiberg, 

 Saxony. 



repeated, yielding a pseudo-hexagonal symmetry. The polar nature 

 of the crystals is shown by the diagonal striations on the prism 



faces; also granular or mas- 

 sive. 



Fine crystals are obtained at 

 Freiberg, Saxony, and in the 

 Ophir mine, Nevada. 



It is an important ore of sil- 

 ver and is found at all the 

 noted silver localities of Europe, 

 as in the Harz ; Pribram, Bo- 

 hemia ; Kremnitz, Hungary ; 

 Kongsberg, Norway. In the 

 United States it is the princi- 

 pal ore of silver in the noted 

 Comstock lode in Nevada; 

 also occurs at other points in 

 Nevada and Idaho. 

 Polybasite, 9 Ag 2 S, Sb 2 S 3 , and Polyargyrite, 12 Ag 2 S, Sb 2 S 3 , 

 are two sulphantimonides in the same series as stephanite, but 

 higher in their silver content. The former usually contains some 

 copper and has a good basal cleavage. The latter is isometric, 

 crystallizes in cubo-octahedrons with a cubic cleavage. 



ENARGITE 



Enargite. 3 Cu 2 S, As 2 S 5 ; Sulpharsenate of copper ; Cu = 

 48.3, As = 19.1, S = 32.6; Orthorhombic ; Type, Didigonal Equa- 

 torial; a:b:c = .8711:1 :.8248; 100 A 110 = 41 3'; 001 A 101 

 = 43 26'; 001 A Oil = 39 31'; Forms, a (100), b (010), c (001), 

 m (110), d (Oil) ; Twinning plane, x (320) ; Cleavage, m perfect, a 

 and b distinct ; Brittle, fracture uneven ; H. = 3 ; G. = 4.4 ; 

 Color and streak, grayish to iron-black ; Luster, metallic; Opaque. 



B.B. Fuses easily in R. F. on coal and yields an arsenic odor. 

 In the 0. F. a sulphur dioxide odor. Roasted and reduced with 

 soda yields malleable copper buttons. It may also contain anti- 

 mony, zinc, or iron. 



General Description. Crystals are small, prismatic, and 

 striated lengthwise ; it usually occurs massive or disseminated. 

 Not a common mineral, but at Butte, Montana, it is an important 

 copper ore. Found also in several localities in Colorado, Utah, 

 and in the Brewster gold mine, South Carolina. 



