COLLECTIONS I\ ECONOMIC GKOLOGY AND METALLURGY. 17 



It varies in harduess from 2.5 to 3, aucl when pure its specific gravity- 

 is 10.5, but impurities may raise it to 11. 1, or lower it to 10.1. It has 

 a beautiful white coloi-, which soon tarnishes on exposure. It has a 

 full metallic luster, and is malleable and ducLik\ 



It is an abuiidatit source of silver, aiul is sometimes the chief prod- 

 uct of a mine; tliis was especially so at the Silver Islet Mine, in Lake 

 ISu))erior. It is not limited to any level iu its occurrences, being found 

 at and near the snrface as well as iu very deep workings. In the former 

 case it is frequently the result of the decomposition of other silver min- 

 erals, while in the latter it is an original silver mineral. To illustrate 

 the occurrence of free silver, twelve specimens are shown. 



(1) Coarse wire, witli quartz ami sulpliides. Silver King Mine, Piiial County, 

 ArizoL'a. (65154.) 



(2) Thick wire or spike, iu calcite with galena andbleudo. Sauta Domingo Mine, 

 Batopilas, Mexico. (64961.) 



(•i) Wire or inoi?s, iu a cavity in (juartz, togetlier with various sulphides. Caribou 

 Mine, Grand Island district, Boulder County, Colorado. (1929:i.) 



(4) Wire, on galena. May Flower Mine, Wood River District, Idaho. (5666.) 



(5) Arborescent plates, in quartz, with sulphides, especially galena. Monitor Mine, 

 Philadelphia district, Nye Connty, Nevada. (15405.) 



(6) Intimately mixed with various sulphides in quartz. Monitor Mine, Philadel- 

 phia district, Nye County, Nevada. (65366.). 



(7) Very thiu plates, on chalcocite. Gagnou Mine, Butte, Silver Bow County, 

 Montana. (33766.) 



(8) A^ery thin plates, on chalcocite. Gagnon Mine, Butte, Silver Bow County 

 Montana. (65367.) 



(9) Plates, filling crevices in decomposed material. American Flag Mine, Ely dis- 

 trict, Pioche, Lincoln County, Nevada. ( 15302. ) 



(10) Plates, on indurated clay, \)sirt of the silver being altered to the chloride, 

 cerargyrite . Two Ikes Mine, Silver City district, New Mexico. (10199.) 



(11) Very thin plates, in decomposed material. Silver Reef district, Washington 

 County, Utah. (55328.) 



(12) Thin flakes, in fossiliferous sandstone, the silver being associated with the 

 fossils. Stormont Mine, Silver Reef district, Washington County, Utah. (5.5331.) 



ARGENTITE. (VITREOUS SILVER, SULPHURET OF SILVER, SILVER 



GLANCE.) 



Composition: Ag2S. Sulphide of silver, coutaiuiug, when pure, silver 

 87.1 per cent, and sulphur 12.9 per cent. 



It crystallizes iu the isometric system, especially in cubes, octahe- 

 drons, and dodecahedrons. It also occurs in reticulated, arborescent, 

 and filiform masses, and occasionally amorphous. It varies iu hardness 

 from 2 to 2.5, and in specific gravity from 7.19 to 7.3G, has a lead gray 

 color, inclining to black, and a full metallic luster. It can be easily cut 

 with a knife into thin shavings. 



Argentite is an abundant source of silver, being found iu many 

 mines, especially below the water level. To illustrate the occurrence 

 of argentite, five specimens are shown. 



(1) A group of branching octahedrons. Batopilas, Mexico. ((54973.) 



(2) An imperfect crystal, in quartz, with other sulphides. Consolidated Virginia 

 Mine, Comstock lode, Storey County, Nevada. (15171.) 



9110— No. 42 2 



