sn.l'lln COMPOUNDS 



I'yrargyritr is an important ore of silver occurring in mo-t sil 

 mines, as at Andreasberf-; and Freiberg, Saxony; at Pribram, 

 Bohemia; Kongsberg, Norway; at various localities in Chili and 

 Mexico. In the Tinted St:ites in the Ruby district, Colorado, 

 associated with tetrahedrite ; in the Poorraan's Lode, Idaho, in 

 large ma e- ; also in Arizona and New Mexico. Artificially formed 

 l>y precipitating a solution of silver with potassium sulph antimo- 

 nate; this precipitate is amorphous, but if mixed with sodium car- 

 bonate and heated in a sealed tube above 80 the product becomes 

 crystalline. 



PROUSTITE 



Proustite. Light ruby silver ; Ag 3 AsS 3 ; Ag = 65.4, As = 

 15.2, S =_ 19.4 ; Hexagonal ; Type, Ditrigonal Polar ; c = .8039, 

 0001 A 1011 = 42 51', e A e' = 42 46', vvv' = 74 _39, r*r[ = 

 72 12'; Forms, a (1120), e(0112), _r (1011), m (1010), (2131); 

 Twinning plane, u (1014) and r (1011) common, e and c rare; 

 Cleavage, r distinct ; Brittle, fracture conchoidal ; H. = 2-2.5 ; 

 G. = 5.57-5.64 ; Color and streak, scarlet ; Transparent to trans- 

 lucent, becoming black 

 on exposure ; <o = 3.087, 

 = 2.792, <o- =0.295; 

 Optically (-). 



B.B. On coal in 

 R. F. fuses easily and 

 yields an arsenic odor 

 and sulphur fumes, may 

 yield a white coat of ar- 

 senic trioxide. Reduced 

 with soda yields a glob- 

 ule of malleable silver. 

 Soluble in nitric acid 

 with the separation of 

 sulphur. 



General Description. 

 Crystals elongated 



and terminated by the scalenohedron v, or the rhombohedron e. 

 Proustite is isomorphous with pyrargyrite and resembles it in 

 every respect except in its light color and in its streak. Fresh 

 specimens are very beautiful, but soon lose their ruby color and 

 become dark and opaque unless protected from the light. 



Fio. 404. Proustite. Freiberg, Saxony. 



