A silicate in which some of the silicon atoms have been replaced by aluminium atoms. As silicon atoms are tetravalent and aluminium atoms are trivalent, the requirement of overall charge neutrality means that cations such as sodium and potassium ions are required when one silicon atom is replaced and cations such as magnesium and calcium ions when two atoms are replaced. Aluminosilicates are very common in the crust of the earth, with the feldspathoids forming one major class.