A silicate is a compound containing an anionic silicon compound. The great majority of silicates are oxides, but hexafluorosilicate ([SiF 6 ] 2−) and other anions are also included. Orthosilicate  is the anion SiO 4 4− or its compounds.Related to orthosilicate are families of anions (and their compounds) with the formula [SiO 2+n ] 2n− .ilica, or silicon dioxide, SiO 2, is sometimes considered a silicate, although it is the special case with no negative charge and no need for counter-ions. Silica is found in nature as the mineral quartz, and its polymorphs.