18 BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



(3) An imperfect crystal, iu quartz, with other sulphides. Crowu Point Mine, Com- 

 etock lode, Storey County, Nevada. (15446.) 



(4) Crystalline aggregate, with ([uartz and other sulphides. Crown Point Mine, 

 Comstock lode, Storey County, Nevada. (65368.) 



(5) Crystallized, iu quartz, with other sulphides. Ophir Mine, Comstock lode. 

 Storey County, Nevada. (15192.) 



STEPHANITE. (BRITTLE SILVER ORE.) 



Compositiou: Ag5SbS4 or 5Ag2S+ 8^383. Sulpb-antimonide of silver, 

 coiitaiuing silver 68.5 j)er ceut., antimony 15.3 per cent., and sulphur 

 16.2 per cent. 



It crystallizes in the orthorhombic system, showing especially the 

 basal, unit prism, and octahedron, brachy plnacoid, and brachy dome 2 

 planes. It also occurs more or less massive and disseminated through 

 other material. It varies in hardness from 2 to 2.5, and its specific 

 gravity is 6.269. It is iron-black iu color and has a metallic luster. It 

 is quite brittle, whence its name, brittle silver ore. 



Stephanite is quite an important source of silver, being found iu 

 many mines, but the extraction of its silver is difiQcult, and the total 

 yield from the mineral has not been large. To illustrate the occurrence 

 of stephanite one specimen is shown. 



(1) Crystallized, iu quartz. Chollar Potosi Mine, Comstock lode. Storey County, 

 Nevada. (15183.) 



PYRARGYRITE, (RUBY SILVER, DARK-RED SILVER ORE.) 



Composition, Ag3SbS3 or 3Ag2S+ 8^283. Sulph-antimonide of silver, 

 containing silver 59.8 per cent., antimony 22.5 per cent., and sulphur 

 17.7 per cent. 



It crystallizes in the rhombohedral system, crystals being somewhat 

 complex and frequently twinned. It also occurs in granular masses 

 and sometimes as impalpable powder. It varies in hardness from 2 to 

 2.5 and in specific gravity from 5.7 to 5.9 ; is black to dark red in color 

 and opaque to translucent and has a bright metallic luster. 



Pyrargyrite is a valuable source of silver and has yielded a consid- 

 erable amount of the metal, but the extraction of the metal is some- 

 what difficult, and ores in which it is the chief mineral, as at Reese 

 River, Nevada, must be very rich in order to pay the expense of work- 

 ing. When it is exposed to decomposing intiuences, as iu the portions 

 of a vein above water level, it is prone to change, argentite, cerargy- 

 rite, and silver being, at times, the result of its decomposition. To 

 illustrate the occurrence of pyrargyrite, six specimens are shown: 



(1) Crystallized, in quartz, with other sulphides. Little Emma Mine, Lump Gulch 

 district, Jefferson County, Montana. (11151.) 



(2) "Well crystallized, in quartz, showing also a few small crystals of stephanite. 

 North Star Mine, Reese River district, Lander County, Nevada. (15133.) 



(3) Well crystallized, in ([uartz, showing also a few small crystals of stephanite. 

 North Star Mine, Reese River district, Lander County, Nevada. (65361?.) 



