Aluminium silicate

Aluminium silicate is any chemical compound made from a mixture of alumina (Al2O3) and silica (SiO2), or the hydrate of such a mixture. The chemical formula of an aluminium silicate is x Al2O3·y SiO2, with hydrates adding z H2O. Because aluminium, silicon, and oxygen are the most common elements in Earth's crust, many minerals are aluminium silicates.

Depending on the molar ratio of alumina to silica, different aluminium silicates have different formulas. The most common type is the 1:1 ratio, Al2SiO5, which is found as three minerals: andalusite, kyanite, and sillimanite. Kaolinite is an aluminium silicate hydrate with a 1:2:2 ratio, giving it the formula Al2Si2O5(OH)4.

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