Argentite, the simple sulphide of silver, is the chief source from which silver is obtained. It looks like galena, and has the same hardness, streak and specific gravity, but can be distinguished by the galena having a very perfect cubic cleavage while the argentite has no cleavage. Argentite is easily cut with a knife (sectile). It is usually found in irregular masses, but sometimes in cubes which make very choice cabinet specimens; and is associated with such other minerals as galena, sphalerite, chalcopyrite, pyrite, fluorite, quartz, and calcite. It occurs in fissures and veins all through the Cordilleran regions, especially in California, Colorado, Nevada (Comstock Lode), Arizona (Silver King Mine) and about the shores of Lake Superior. Pyrargyrite Ag₃SbS₃ Pl. 7 _ruby silver_ or _dark red silver_ Usually occurs in irregular masses; hardness 2.5; specific gravity 5.8; color dark red to black; streak purplish red; luster metallic to adamantine; translucent on thin edges. Pyrargyrite, the sulphide of silver and antimony, is distinguished by its dark red color and the purplish streak. It may look like prousite, but is easily distinguished from the latter which has a scarlet streak. It also at times looks like hematite and cinnabar, but the hematite has a hardness of 6, and the latter has the bright red color throughout, while pyrargyrite turns black when exposed to the light, so that the characteristic red color will be seen only on fresh surfaces. The characteristic red color can only be kept on the mineral if it is constantly protected from the light. Sometimes pyrargyrite occurs in crystals and these belong to the hexagonal system, and are prisms with low faces on the ends, as on plate 7, and the mineral is peculiar in that the faces on the opposite ends are unlike. Pyrargyrite is found mostly in fissures and veins of quartz, fluorite, calcite, etc., and associated with pyrite, chalcopyrite, galena, etc. It is fairly common in Colorado in Gunnison and Ouray counties, in Nevada, New Mexico, Arizona, etc. Prousite Ag₃ AsS₃ Pl. 7 _light red_ _silver_ Usually occurs in irregular masses; hardness 2.5; specific gravity 5.6; color scarlet to vermilion; streak the same; luster adamantine; transparent on thin edges. In general this mineral is very like pyrargyrite, but has the scarlet color and streak which are entirely characteristic. It is likely to have the surface tarnished black, which happens on exposure to light, so that it is essential to be sure that fresh surfaces are being examined. Occasionally it is found in crystals, of the same type as the preceding mineral. It is generally found associated with pyrargyrite. Cerargyrite AgCl _horn silver_ Usually found in irregular masses or incrustations; hardness 1 to 1½; specific gravity 5.5; color pearly gray, grayish green to colorless, but turning violet brown on exposure to light; luster resinous; transparent on thin edges.