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Bureau of Mines / Minerals yearbook: Metals and minerals 1978-79
Year 1978-79, Volume 1 (1978-1979)

Potter, Michael J.
Kyanite and related materials,   pp. 503-506 PDF (439.3 KB)

Page 503

  503Kyanite and Related Materials 
By Michael J. Potter' 
 Kyanite, andalusite, and sillimanite are anhydrous aluminum silicate minerals
that are alike in both composition and use patterns and have the same chemical
formula, A1203*Si02. Related materials include synthetic mullite, dumortierite,
and topaz, also classified as aluminum silicates, although the last two additionally
contain substantial proportions of boron and fluorine, respectively. All
of these kyanite-group substances can serve as raw materials for manufacturing
special high-performance, high-alumina refräctories, but there has
no record in recent years of significant utilization of either dumortierite
or topaz for this purpose in the United States. 
 Although published statistics are incomplete, it appears that the United
States, India, and the Republic of South Africa are the leading world producers
of kyanitegroup minerals. It can be presumed that the U.S.S.R. and perhaps
a few other industrialized nations also produce significant quanti 
ties of these materials. 
 U.S. kyanite estimated production in both 
1978 and 1979 increased slightly in tonnage 
and value. Export and import data since 
1977 for kyanite and mullite-containing materials are no longer collected
as a separate 
category by the Bureau of the Census. 
 NL Industries, Inc., announced in late 1978 the sale of its Taylor Refractories
Division to Didier Werke of Wiesbaden, Federal Republic of Germany. The sale
of the division and related assets amounted to approximately $32 million.
Taylor produces mullite and other special refractories, plus a wide range
of kiln furniture, shapes, bricks, and monolithic refractories, mainly based
on nonbasic materials. 
 Legislation and Government Programs.—The allowable depletion rates
for kyanite, established by the Tax Reform Act of 1969 and unchanged through
1979, were 22% for domestic production and 14% for foreign operations. 
 Kyanite was produced in the United States in 1978 and 1979 at three open
pit mines, two in Virginia and one in Georgia. Kyanite Mining Corp. operated
the Willis Mountain and East Ridge mines in Buckingham County, Va. C-E Minerals,
Inc., operated the' Graves Mountain mine in Lincoln County, Ga. 
 Estimated output of domestic kyanite in both 1978 and 1979 showed slight
increases in tonnage and value. Kyanite production statistics for 1979 (and
for all previous years since 1949) are withheld to avoid disclosing company
proprietary data. 
 There are three types of synthetic mullite. Fused synthetic mullite is made
by melting Bayer process alumina and silica, or bauxite and kaolin, in an
electric furnace at around 3,450'F. High-temperature sin- 
tered synthetic mullite is prepared by sintering mixtures of alumina and
kaolin, bauxite and kaolin, or alumina, kaolin, and kyanite above 3,180*F.
Low-temperature sintered synthetic mullite is made by sintering siliceous
bauxite or mixtures of bauxite and kaolin above 2,820*F. 
 Output of synthetic mullite in 1978 and 1979 was largely of the high-temperature
sintered variety, and the four producers of this material were A. P. Green
Refractories Co. at Philadelphia, Pa.; C-E Minerals, Inc., at Americus, Ga.;
Didier Taylor Refractories Corp. at Greenup, KY.; and HarbisonWalker Refractories
Co. at Eufala, Ala. Electric-furnace-fused mullite was produced by Muscle
Shoals, Electrochemical Div., at Tuscumbia, Ala. (in 1978), and The Carborundum
Co. at Niagara Falls, N.Y. 

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