308 



UNITED STATES MINERAL RESOURCES 



1968 was estimated at about 120,000 short tons, and 

 exports were about 20,000 tons; total value of the 

 production was about $10.7 million. The demand in 

 1968 by different industries and the possible demand 

 in the year 2000 (table 61) were estimated by 



Table 61. — Estimated United States demand for kyanite and 

 synthetic mullite 



Cooper (1970, p. 1066-1069). 



According to Cooper, the major trend in the use 

 of these materials as refractories in the next 25 

 years probably will be to replace other types of 

 refractories in metallurgical, glass, and boiler fur- 

 naces. Important nonrefractory uses may also be 

 developed, such as the manufacture of aluminum- 

 silicon alloys, floor and wall tile, spinnable mullite 

 fibers, and blown-wool refractory insulations. 



Before 1951, the United States imported more 

 kyanite than it produced because the massive ore 

 ("strategic kyanite") from India and Kenya was 

 required as an essential component in making the 

 best high-alumina refractory bricks. The fine-grained 

 kyanite concentrate produced from domestic dis- 

 seminated ore is more suitable for other purposes. 

 Manufacture of synthetic mullite began in 1951, and 

 its use has practically eliminated the need for im- 

 ported massive kyanite. 



The increased demand expected in the United 

 States for kyanite-group minerals during the next 

 25 years can be supplied from our very large domes- 

 tic resources. All domestic production for many years 

 has come from mines in the Southeastern States; 

 production from these mines can be increased, and 

 probably several new mines can be opened at other 

 deposits in the region. The increased demand for 

 kyanite expected in the Western States could prob- 

 ably be met by mining some of the deposits in 

 Idaho, California, or New Mexico. Expansion of syn- 

 thetic mullite production might require increased 

 imports of bauxite or alumina, but this need would 

 be very small in comparison to the large quantities 

 of bauxite and alumina imported by the aluminum 

 industry. The trend of exports of kyanite and syn- 

 thetic mullite from the United States over the next 

 25 years is difficult to forecast because foreign pro- 



duction will doubtless increase, and trade patterns 

 may change considerably. 



EXPLOITATION 



Domestic mining of the kyanite-group minerals 

 began in the 1920's when kyanite was mined at 

 Baker Mountain, Va., Ogilby, Calif., and Petaca, N. 

 Mex.; andalusite at White Mountain, Calif.; and 

 dumortierite at Oreana, Nev. Other deposits of 

 various types were mined or prospected between 

 1930 and 1950. Since 1950, nearly all production has 

 come from kyanite-quartz deposits at Baker Moun- 

 tain and Willis Mountain, Va., Graves Mountain, 

 Ga., and Henry Knob, S.C. ; mining at Henry Knob 

 ceased in 1969. Byproduct recovery of kyanite and 

 sillimanite began in 1968 from Florida sands proc- 

 essed for ilmenite and other heavy minerals. Various 

 aspects of domestic mining operations have been 

 discussed by Espenshade and Potter (1960), Foster 

 (1960), Klinefelter and Cooper (1961), and Cooper 

 (1970). 



United States production of kyanite has increased 

 steadily since 1940 when it was 4,241 short tons. 

 By 1950, it was about 15,400 short tons, and in 

 1960, about 33,000 short tons (Varley, 1965, p. 30). 

 Cooper (1970, p. 1066) stated that it was about 

 100,000 short tons in 1968. 



GEOLOGIC ENVIRONMENT 



Kyanite, sillimanite, and andalusite are very com- 

 mon in many parts of the world in aluminous meta- 

 morphic rocks which have undergone the deforma- 

 tion and increased temperatures that accompany 

 mountain building. Each of the AUSiOs minerals 

 forms under certain distinctive ranges of tempera- 

 ture and pressure. Kyanite typically forms in schists 

 and gneisses at fairly high temperatures and pres- 

 sures, under conditions of strong regional or dy- 

 namic metamorphism. Andalusite forms at lower 

 pressure and is very common in the hot zones of con- 

 tact (or thermal) metamorphism surrounding large 

 intrusions of granite or gabbro. Sillimanite forms 

 at higher temperatures during both regional and 

 contact metamorphism. Mullite is a very rare min- 

 eral formed naturally at temperatures even higher 

 than sillimanite. Topaz and dumortierite are much 

 less common than the ALSiOs minerals. They are 

 most abundant in quartzose deposits, some of which 

 appear to be hydrothermally altered volcanic rock. 



The AlzSiOs minerals are principally contained in 

 micaceous schists and gneisses which underlie many 

 square miles in some regions. Kyanite and sillimanite 

 are more abundant than andalusite in these deposits. 

 The content of these minerals may be as much as 



