UNITED STATES MINERAL RESOURCES 



KYANITE AND RELATED MINERALS 



By Gilbert H. Espenshade 



CONTENTS 



Page 



Abstract of conclusions 307 



Introduction 307 



Exploitation 308 



Geologic environment 308 



Resources 309 



United States resources of kyanite-group min- 

 erals 309 



Deposits of micaceous schist and gneiss 309 



Quartzose deposits 310 



Byproduct sources of kyanite-group minerals 310 



Foreign resources of kyanite-group minerals 310 



Speculative resources 310 



Problems for research 311 



References cited 311 



TABLES 



61. 



62. 



Estimated United States demand for kyanite 

 and synthetic mullite 



United States resources of kyanite and related 

 minerals 



Page 



308 

 309 



ABSTRACT OF CONCLUSIONS 



Kyanite and related minerals are high-alumina silicates 

 used mainly in the manufacture of refractory linings for 

 metallurgical and other types of furnaces. Domestic produc- 

 tion currently exceeds consumption, and considerable ton- 

 nages are exported. Enormous resources of these minerals 

 exist in the United States; this should permit the increase 

 in production that will be needed to meet the demand ex- 

 pected during the next 25 years. Production now comes large- 

 ly from kyanite-quartz deposits in the Southeastern States; 

 kyanite and sillimanite are also recovered as a byproduct 

 from Florida ilmenite sands. Resources of deposits of these 

 two types are very large but make up no more than 5 per- 

 cent of our total resources. The remaining 95 percent or 

 more is in deposits of micaceous schist and gneiss, mostly 

 in the Appalachian Mountain system and in Idaho. None of 

 these deposits is now being mined, but profitable mining of 

 some may eventually be possible. More detailed geologic 



studies and sampling of deposits of the kyanite-group min- 

 erals are needed in order to appraise their economic poten- 

 tial. 



INTRODUCTION 



Kyanite and related minerals (known as the 

 kyanite or sillimanite group) are high-alumina min- 

 erals used in the manufacture of high-quality re- 

 fractory materials and other ceramic products. The 

 most abundant are kyanite, sillimanite, and andalu- 

 site, all having the same chemical composition, 

 Al.SiOs (also written AlaOs-SiOs), but different 

 physical properties. Dumortierite (containing boron) 

 and topaz (containing fluorine) have similar compo- 

 sition but are much scarcer. Each of these minerals 

 has been produced in the United States, but since 

 1950, production has been mostly of kyanite, ac- 

 companied by small amounts of andalusite and silli- 

 manite. An excellent comprehensive review of the 

 properties, treatment, and industrial uses of these 

 minerals and the geology of the deposits has been 

 given by Varley (1965). 



When these minerals are heated to very high tem- 

 peratures, the new compounds mullite (SA^Os 

 ■2Si02) and silica glass are formed. Mullite can also 

 be made from various materials that contain alumina 

 (AloO.O and silica (SiOa), such as mixtures of alu- 

 mina, kaolin, and kyanite, alumina and kaolin, 

 bauxite and kaolin, or alumina and silica sand; this 

 product is known as synthetic mullite (Cooper, 1970,r 

 1060-1061). Mullite retains its strength and stability 

 at high temperatures for long periods of time and 

 has become very widely used as a refractory ma- 

 terial in the metallurgical industry (Foster, 1960; 

 Klinefelter and Cooper, 1961, p. 3-6 ; Varley, 1965) . 

 The refractory properties are improved as the mul- 

 lite content of the material is increased. 



The United States is now the largest producer 

 and consumer of kyanite and synthetic mullite. Do- 

 mestic demand for kyanite and synthetic mullite in 



U.S. GEOL. SURVEY PROF. PAPER 820 



307 



