Idealized structure of sodium metasilicate.

Metasilicates are silicates containing ions of empirical formula SiO2− 3. Common stoichiometries include MI 2SiO3 and MIISiO3. Metasilicates can be cyclic, usually the hexamer (SiO3)12−6 or chains (SiO3)2− n.

Common compounds containing metasilicate anion are:

Pyroxene (diopside) is a mineral classified as a metasilicate.