THE MINERALS OF IDAHO 131 



In a specimen from the Rabbitfoot mine in the eastern part of the 

 Gravel Range district pyrite appears in an unusual form. Litho- 

 physae-like cavities in silicified rhyolite contain tabular hexagonal 

 crystals up to 2 mm. in diameter, now composed of granular pyrite. 

 These look very much like pseudomorphs after mica crystals, although 

 it is possible that the original crystals were some other mineral, such 

 as polybasite or pyrrhotite. 



OWYHEE COUNTY 



In the Silver City and other silver mining districts of Owyhee 

 County pyrite is not common in the veins, but occurs abundantly 

 in the altered lavas of the wall rocks. In the South Mountain district 

 it is a constituent of heavy masses of intergrown sulphides and 

 contact silicates. 



SHOSHONE COUNTY 



In Shoshone County pyrite is common in all veins and also over 

 wide areas sparsely disseminated in the sedimentary rocks, especially 

 those of the Prichard formation. In places the pyrite in the slates 

 is in the form of isolated cubic crystals which may reach 5 cm. (2 

 inches) in diameter. Minute and deeply striated brilliantly lustrous 

 cubic crystals occur with larger crystals of arsenopyrite replacing 

 sericitic slates in the walls of the Stanley antimony vein at Burke. 

 It is universally present in the lead-silver veins but seldom in large 

 pure masses and not often in well-formed crystals. Certain beds of 

 quartzite in the Wardner mines are largely replaced by pyrite so fine 

 grained as to be difficult of recognition. This pyrite decomposes 

 very readily and specimens, when placed in a dry place become coated 

 with a hairlike growth of crystals of ferrous sulphate. The tem- 

 perature of certain stopes in the Bunker Hill mine is greatly raised 

 by the heat generated by the decomposing pyrite. Fine-grained 

 pyrite occurs abundantly, intergrown with pyrrhotite and some 

 chalcopyrite, in a quartz-ankerite gangue in nonproductive veins of 

 the "Wisconsin t} 7 pe" cast of Kellogg. Beautifully iridescent druses 

 of minute crystals appear in vuggy quartz in the Lombardy vein in 

 Italian Gulch north of Kellogg and druses of brilliant crystals occur 

 in a gouge in a small tunnel overlooking Elk Creek Slough above 

 the mouth of Elk Creek. Pyritohedral crystals 2 cm. (1 inch) or 

 less in diameter have been found in sericitic shale in the Yankee Boy 

 silver mine on Big Creek. Globular and sperical forms of pyrite 

 with internally radiating structure have been obtained from the 

 Greenhill- Cleveland mine at Mace and the Gold Hunter mine at 

 Mull an. Pyrite occurs in intimate intergrowth with galena and 

 sphalerite in many of the mines of the Pine Creek Basin. The pyrite 

 in the Golden Chest and other gold mines of the Murray section is 

 auriferous. 



