366 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



BOISE COUNTY 



Muscovite occurs in crystals and flakes of moderate size in coarse 

 pegmatitic masses and streaks in the granites of the several gold 

 mining districts of Boise County. 



CASSIA COUNTY 



Mica prospects are reported to exist in Cassia County 30 miles from 

 Albion. No details regarding them have been available. 74 



IDAHO COUNTY 



Prospecting for mica is reported to have been carried on at Pardee 

 in Idaho County. 75 



KOOTENAI COUNTY 



Muscovite is abundant in the schists and gneisses of the area of 

 supposedly Archaen rocks about Lake Coeur d'Alene and occurs 

 occasionally in somewhat coarser crystals in pegmatitic streaks in 

 them but nowhere, so far as known, in crystals of such size or quality 

 as to encourage prospecting for commercial deposits. 



LATAH COUNTY 



The principal deposits of mica in Idaho are in Latah County, where 

 there are a number of mines which have been worked intermittently 

 and which have made an important total production of mica of 

 excellent quality. The deposits lie in a belt about 2 miles wide that 

 extends north and south for several miles in township 41 north, range 

 2 west, from 3 to 6 miles north of Avon. They lie at elevations of 

 3,400 to 4,700 feet above sea level along the top and to the west of 

 a high mountain ridge extending south from the Thatuna Hills. The 

 mica occurs in masses of pegmatite which cut the micaceous-schistose 

 metamorphic rocks of the district. There are many sheets of the 

 pegmatite, some of them outcropping for several hundreds of meters 

 (yards). The distribution of the marketable mica is not uniform in 

 the pegmatites and some bodies very rich in good muscovite are found. 

 In addition to the mica, quartz, and feldspar, the pegmatites contain 

 black tourmaline, garnet, and beryl. The principal mines of the 

 district are the Levi Anderson, Muscovite, Morning Star, Sunshine, 

 Maybe, and Luella. 76 



OWYHEE COUNTY 



Muscovite is occasionally found in small plates and crystals in 

 pegmatitic streaks, segregations or veins in the granite of the Silver 

 City district. 



7 * U. S. Oeol. Survey, Bull. 624, p. 119, 1917. 



75 Idem. 



76 Douglas B. Sterrett. U. S. Grol. Survey, Bull. 740, pp. 86-93, 1923. 



