THE MINERALS OF IDAHO 271 



tetrahedrite, and rarely chalcopyrite may be recognized under the 

 microscope, but the predominant material shows as blue-black 

 specks too small to be identified. These all yield definite reactions for 

 selenium. The calcite occurs in part as lamellar crystals, commonly 

 replaced by quartz and much of the quartz has this lamellar form 

 showing it to be pseudomorphous after calcite. The adularia is 

 recognized in thin sections intergrown with or embedded in the 

 quartz. 83 



LEMHI COUNTY 



Adularia has been noted in the ores of the Gravel Range district. 

 The veins here consist of fillings of fissures in rhyolite, the filling 

 being principally Trustified quartz in wavy bands parallel to the wall 

 or concentrically arranged surrounding an inclusion or filling a former 

 cavity. In the richer parts of the veins thin crimpy layers of dark 

 color and dull to submetallic luster occur parallel to the crustification. 

 These are rich in contained gold and silver and react for selenium. 

 The quartz is hard and flinty and instead of having the usual vitreous 

 luster tends to a dull white. Examined microscopically it is fine 

 grained and occurs in bands composed of grains of slightly different 

 sizes. Adularia, commonty occurring in beautiful rhombic micro- 

 scopic crystals, is intergrown with the quartz or included in it. 



The ore deposits of the Parker Mountain district are in every way 

 similar to those of the Gravel Range district and, although adularia 

 has not, as yet, been recognized in them it very probably occurs. 84 



OWYHEE COUNTY 



Although the preceding occurrences of adularia in Idaho are of 

 importance and interest, especially to the economic geologist, those 

 of Owyhee County are more important to the mineralogist, since in 

 the Silver City district in this county the mineral occurs as large 

 crystals lining cavities in the veins which furnish fine specimens for 

 collections. The mineral has been fully described by Lindgren, 85 

 who found it in the Booneville, Black Jack, and Trade Dollar mines, 

 and the Cumberland vein on War Eagle Mountain. In the vein on 

 which the Booneville, Black Jack, and Trade Dollar mines are 

 opened, valencianite occurs as large milk-white grains with typical 

 cleavage whether the vein is in rhyolite, granite, or bajealt. The 

 valencianite contains inclusions of chalcopyrite and argentite, some- 

 times with fillings of chalcopyrite in cleavage cracks. Crusts of pro- 

 jecting crystals of the valencianite, with more or less curved faces, 

 often coat the walls of open spaces in the vein (pi. 6) and small clear 

 crystals 1 to 3 mm. in diameter may also be found coating cracks 

 and crevices in the granite adjoining the veins. In the Booneville 



« J. B. Umpleby. U. S. Geological Survey. Hull. 539, pp. 46-47, 1913. 



"J. B. Umpleby. U. S. Oeol. Survey, Hull. 528, pp. 172-178, etc., 1913. 



»i Waklemar Lindgren. U. S. Geol. Survey, 20th Ann. Rept., pt. 3, pp. 106-168, etc., 1900. 



