  a silicate is a compound containing an anionic silicon compound. the great majority of silicates are oxides, but hexafluorosilicate ([sif6]2â) and other anions are also included. "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. silicates comprise the majority of 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. 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. ==structural principles== in the vast majority of silicates, including silicate minerals, the si occupies a tetrahedral environment, being surrounded by 4 oxygen centres. in these structures, the chemical bonds to silicon conform to the octet rule. these tetrahedra sometimes occur as isolated sio44- centres, but most commonly, the tetrahedra are joined together in various ways, such as pairs (si2o76-) and rings (si6o1812-). commonly the silicate anions are chains, double chains, sheets, and three-dimensional frameworks. all these such species have negligible solubility in water at normal conditions. ==occurrence in solution==  silicates are well characterized as solids, but are less commonly observed in solution. the anion sio44- is the conjugate base of silicic acid, si(oh)4, and both are elusive as are all of the intermediate species. instead, solutions of silicates are usually observed as mixtures of condensed and partially protonated silicate clusters. the nature of soluble silicates is relevant to understanding biomineralization and the synthesis of aluminosilicates, such as the industrially important catalysts called zeolites.christopher t. g. knight, raymond j. balec, stephen d. kinrade "the structure of silicate anions in aqueous alkaline solutions" angewandte chemie international edition 2007, volume 46, pages 8148 -8152.  ===silicates with non-tetrahedral silicon=== although the tetrahedron is the common coordination geometry for silicon compounds, silicon is well known to also adopt higher coordination numbers. a well-known example of such a hi
Oxoanions Silicates