Silicate

A silicate is a compound containing an anionic silicon compound. The great majority of silicates are oxides, but hexafluorosilicate ([SiF6]2−) and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth’s crust, as well as the other terrestrial planets, rocky moons, and asteroids. Sand, Portland cement, and thousands of minerals are examples of silicates. “Orthosilicate” is the anion SiO44- or its compounds. Related to orthosilicate are families of anions (and their compounds) with the formula [SiO2+n]2n-. Important members are the cyclic and single chain silicates {[SiO3]2-}n and the sheet-forming silicates {[SiO2.5]-}n.
Silicate compounds, including the minerals, consist of silicate anions whose charge is balanced by various cations. Myriad silicate anions can exist, and each can form compounds with many different cations. Hence this class of compounds is very large. Both minerals and synthetic materials fit in this class.