National Minerals Information Center

Kyanite and Related Minerals Statistics and Information

Kyanite, andalusite, and sillimanite are anhydrous aluminosilicate minerals that have the same chemical formula, Al2SiO5, but differ in crystal structure and physical properties.  When calcined at high temperatures (around 1,350° C to 1,380° C for kyanite and slightly higher for andalusite and sillimanite), these minerals are converted to mullite, 3Al2O3·2SiO2, and silica, SiO2, which are refractory materials.  In the conversion to mullite, 1 metric ton (t) of mineral concentrate yields about 0.88 t of mullite.  Synthetic mullite is made by heating mixtures of alumina and silica or bauxite and kaolin at around 1,550° C to 2,000° C.  Refractories are heat-resistant materials used in high-temperature applications such as furnaces, boilers, ladles, and kilns, in the metallurgical, glass, chemical, cement, and other industries.

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Joyce Ober

Supv. Physical Scientist
Phone: 703-648-7717