Minerals known as Silicates are composed of silicon and oxygen in the form of variously connected tetrahedral SiO44- units. Any member of the silicon-oxygen-based silicate family of anions is referred to as a silicate in chemistry. The silicate family includes the orthosilicate SiO44, the metasilicate SiO32, and the pyrosilicate Si2O76. The word is used to describe such anions as well as their salts, such as sodium metasilicate, and any ester that has the matching chemical group, such as tetramethyl orthosilicate.
Large polymeric Silicates anions frequently take the form of chains and rings (as in polymeric metasilicate [SiO32-]n), double chains (like in [Si2O52-]n), and sheets (as in [Si2O52-]n). Both silicate cations and silicate anions go by this name. In geology and astronomy, the term "silicate" is used to refer to a silicate mineral, an ionic solid having silicate anions, and a form of rock that is predominantly made up of such minerals. Even if they do not follow the standard formula or contain atoms other than oxygen, any anions containing silicon may occasionally be referred to as "silicate," for instance hexafluorosilicate [SiF6].
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