32-2 MINERALOGY 



Occurs at Pribram, Bohemia; in the Harz; and in the Echo 

 district, Nevada. It is an ore of lead, but too rare to be of much 

 importance. 



PYRARGYRITE 



Pyrargyrite. Dark ruby silver ; Sulphantimonide of silver, 

 A g2 Sb 2 S 3 ; Ag = 59.9, Sb = 22.3, S = 17.8 ; Hexagonal ; Type, 

 Ditrigonal Polar; c = 0.7891 ; 0001 A 1011 = 42 2(X, e A e'=_42 

 5', r_ A r' = 71_22', v A v'=74 25'; Forms, a 1120), m_(1010), 

 e (0112), r (1011), v (2131) ; Twinning plane, 1120 also 1014 quite 

 common, lOll or 1012 rare ; Cleavage, r distinct, e less so ; Brittle, 

 fracture conchoidal ; H. = 2.5 ; G. = 5.77-5.86 ; Color, grayish 

 black to black; Streak, purplish red; Luster, adamantine; 

 Nearly opaque, deep red in thin splinters; o> = 3.084, = 2.881, 

 <o- = .203; Optically (-). 



B.B. Fuses easily on coal to a globule and yields a white 

 coat of antimony trioxide. In R. F. or with soda yields a malle- 

 able button of silver. Soluble in nitric acid with the separation of 

 sulphur and insoluble oxide of antimony. In the closed tube 

 yields a red sublimate. 



General description. Crystals usually quite complicated both 

 through twinning and the complexity of the forms. A large num- 

 ber of forms have been described, but as formerly pyrargyrite and 

 proustite were considered one and the same species, their individual 

 forms have not as yet been entirely separated. Doubly terminated 

 crystals are not common, but when they do occur they are generally 

 supplementary twins with the basal plane as the composition face, 

 in which case the two terminations are similar. The polarity of 

 its symmetry is shown by the striations on the prism faces, which 

 are not symmetrical to the basal plane. Also occurs compact, 

 granular, or disseminated. 



Pyrargyrite occurs in veins associated with other silver minerals, 

 as argentite, proustite, or native silver, with sulphides and arsen- 

 ides ; calcite, barite, fluorite, or quartz are the gangue minerals. 

 In such cases it has been produced by the interaction of antimonides 

 on silver, in solution, either by precipitation or replacement at 

 comparatively low temperatures, which also its synthesis in the 

 laboratory would indicate. Often alters to argentite and forms 

 pseudomorphs after native silver. 



