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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