Aluminium silicate
Aluminium silicate (or aluminum silicate) is a name commonly applied to chemical compounds which are derived from aluminium oxide, Al2O3 and silicon dioxide, SiO2 which may be anhydrous or hydrated, naturally occurring as minerals or synthetic. Their chemical formulae are often expressed as xAl2O3.ySiO2.zH2O These include the compounds:-
Al2SiO5, (Al2O3.SiO2), which occurs naturally as the minerals andalusite, kyanite and sillimanite which have different crystal structures.
Al2Si2O5(OH)4, (Al2O3·2SiO2·2H2O), which occurs naturally as the mineral kaolinite and is also called aluminium silicate dihydrate. It is a fine white powder and is used as a filler in paper and rubber and also used in paints.
Al2Si2O7, (Al2O3.2SiO2), called metakaolinite, formed from kaolin by heating at 450 °C (842 °F).
Al6SiO13, (3Al2O3.2SiO2), the mineral mullite, the only thermodynamically stable intermediate phase in the Al2O3-SiO2 system at atmospheric pressure. This also called '3:2 mullite' to distinguish it from 2Al2O3.SiO2, Al4SiO8 '2:1 mullite'.