Article: KYANITE, ANDALUSITE, SILLIMANITE AND MULLITE

Kyanite, andalusite and sillimanite are naturally occurring polymorphic forms of the sillimanite mineral group, sharing the common chemical formula Al^sub 2^SiO^sub 5^. Mullite, having the general chemical formula Al^sub 6^Si^sub 2^O^sub 13^, is a closely associated aluminum silicate mineral that occurs rarely in nature, but can also be produced when sillimanite minerals are calcined at high temperatures.

Together, the sillimanite group minerals and mulHte are valued as raw materials in the manufacturing of refractory and ceramic products because of several key attributes. These include high alumina content and extremely low chemical impurities; the ability to increase the strength of fired ...

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