MICA 



417 



p. 90), but modern mica-mining began in New 

 Hampshire in 1803 and in North Carolina in 1867. 

 The grinding of scrap mica began in a small way in 

 North Carolina about 1870 (Broadhurst and Hash, 

 1953, p. 13) and grew rapidly after 1890. 



In the United States, mica has been produced 

 mostly in the Blue Ridge Mountains of North Caro- 

 lina and in the Piedmont from Virginia to Alabama. 

 Next in importance have been the New England 

 States of New Hampshire, Maine, and Connecticut, 

 and then the Black Hills of South Dakota. Smaller 

 amounts have been produced in Colorado, Idaho, and 

 New Mexico, and minor production is reported from 

 Arizona, California, Montana, Nevada, and Wyo- 

 ming. A few deposits are known in Maryland, Mas- 

 sachusetts, Minnesota, New Jersey, New York, 

 Pennsylvania, Texas, Utah, Vermont, and Wash- 

 ington. North Carolina has been the principal pro- 

 ducer of sheet mica and produces yearly 50-60 

 percent of the domestic scrap mica. 



Because of the high cost of hand labor, the 

 United States produces only a small amount of its 

 domestic needs for sheet mica and relies on imports 

 from India, Brazil, and Malagasy Republic for its 

 principal requirements (fig. 50). In 1970, no pro- 

 duction of sheet mica was reported in the United 

 States for the first time in over 100 years, and it is 

 unlikely that there will be much future production. 

 U.S. imports of sheet mica have declined since 1950 

 because of the impact of improved technology and 

 the availability of substitutes. In 1971, the Indian 

 Government announced its decision to take over 

 mica exports as of January 1972 ; the effects of this 

 decision on the industry are not known. 



The United States is the major producer (fig. 51) 

 and consumer of scrap mica, including flake mica. 

 Increased use of scrap probably depends on in- 

 creased needs in housing for rolled roofing, joint 

 cement, and paint. 



North Carolina is the principal producer of scrap 

 mica. Other States producing scrap in 1970 included 

 Alabama, Arizona, Colorado, Connecticut, Georgia, 

 New Hampshire, New Mexico, South Carolina, and 

 South Dakota. Production for the rest of the world 

 is mostly waste from the mining of sheet mica in 

 India, Brazil, and Malagasy Republic. 



MINING AND PREPARATION 



Sheet-mica mining methods are simple and some- 

 times primitive. Most of the mines are small and 

 shallow and require a minimum of equipment. Open- 

 pit methods are used where possible, but most de- 

 posits are mined to some extent in underground 

 workings that are generally irregular and follow 



100,000,000 



No production in 1£ 



I I I I 



1900 1910 1920 1930 1940 1950 1960 1970 



Figure 50. — Production of sheet mica in the United States 

 compared with imports of sheet mica, 1900-70. Data from 

 U.S. Geological Survey and U.S. Bureau of Mines, Mineral 

 Resources of the United States and Minerals Yearbook, 

 1900-70. 



the mica in rich shoots or from one rich pocket to 

 another. Drilling and blasting must be done care- 

 fully to avoid damage to the mica. After a blast, 

 crystals of mica are handpicked from broken rock. 

 Large rocks are broken with sledges, and both 

 waste and mica are usually hoisted to the surface. 

 Because of the handwork involved, mining costs are 

 high in relation to the average amount of sheet mica 

 found in most deposits. IneflSciency and waste are 

 common in mica mining. Handcobbed feldspar is 

 sometimes recovered as a byproduct. 



Processing of sheet mica requires extensive hand 

 labor in cobbing or removing dirt or rock from the 

 books, in rifting or splitting the books into thin 

 sheets, and in trimming broken edges and imper- 

 fections from the sheets. Complete quantitative data 

 are not available, but recovery of good trimmed mica 

 from crude mica ranges from 2 to 8 percent for the 

 average mine and is as much as 19 percent from 

 good-quality crude mica in a few mines (Urban, 

 1932; Amos, 1959, table 1, p. 33). 



