THE MINERALS OF IDAHO 269 



times other minerals, which are known as pegmatites or giant granites. 

 Commercial mica and feldspar deposits are confined to such pegma- 

 tites. Pegmatites are of rather frequent occurrence in some parts of 

 Idaho and are mined for mica in Latah County, although no com- 

 mercially valuable feldspar deposits have as yet been opened. Such 

 occurrences of orthoclase feldspar as have been noted are mentioned 

 below. The variety of this mineral which is known as adularia of 

 valencianite is considered separately. 



ADAMS COUNTY. 



Peculiar pegmatitic veins carrying flesh-red orthoclase associated 

 with quartz, muscovite, and either chalcopyrite or bornite occur in 

 the Lucky Strike (Walter James) and the Panama-Pacific (Victoria) 

 claims in the Seven Devils Copper mining districts. 81 



BOISE COUNTY 



Orthoclase occurs as a constituent of coarse pegmatitic spots and 

 veins in the granite of Boise County especially near Shafer Creek and 

 Idaho City. 



KOOTENAI COUNTY 



The quartz monzonite of the Chilco Mountain area is described by 

 Calkins 8 - as containing porphyritic orthoclase phenocrysts 1 inch 

 long. A specimen of this rock from the Lieberg trail on the southwest 

 side of Chilco Mountain several miles south of Lake Pend Orielle 

 contains well-formed pinkish orthoclase phenocrysts up to 3 inches 

 in maximum diameter. 



LATAH COUNTY 



Numerous pegmatites which are mined for mica near Avon contain 

 coarse masses of orthoclase. Few specimens of this feldspar have been 

 available for description and no data regarding it have been obtainable. 

 Such specimens as have been seen are dirty white in color and present 

 no unusual features. 



LEMHI COUNTY 



Orthoclase occurs in rounded crystals, carlsbad twins, and nearly 

 spherical masses in granite or granite gneiss in the Blackbird district. 

 These are approximately 3 inches in maximum diameter. They 

 weather free from the rock and strew the ground like pebbles. 



OWYHEE COUNTY 



Orthoclase occurs as a constituent of pegmatites in the granite of 

 the Silver City district. 



" D. C. Livingston and F. B. Lahey. Idaho Bureau of Geology and Mines, Bull. 1, pp. 37-38, 1920. 

 82 F. C. Calkins and D. F. MacDonald. U. S. Oeol. Survey, Bull. 384, p. 44, 1909. 



