What is "orthosilicate"

n. 1 (context chemistry English) any salt or ester of orthosilicic acid, (M⁺)₄siliconoxygen₄⁴⁻ or Si(OR)₄ 2 (context mineralogy English) any silicate mineral, such as garnet or olivine, in which the SiO₄ tetrahedra do not share oxygen atoms with each other

The orthosilicate ion, or silicon tetroxide anion, is . The name of the ion is frequently simplified to silicate, as it forms the basis of most mineral-forming silicate oxoanions. An orthosilicate compound is a compound that contains this group.

In its ionic form, orthosilicate is difficult to study. It is an extremely strong base and does not persist in solution, tending to be consumed by water to form extremely weak silicic acid (HSiO; pK = 13.2 at 25 °C), a very difficult-to-control reaction that typically leaves only minuscule amounts of the ion and large amounts of hydrated silica condensate. Its salts, however, are extremely abundant in the form of nesosilicate minerals. Olivine, which may be referred to as magnesium or iron(II) (ortho-)silicate, is the most abundant mineral in the earth's mantle.

The ion has a classic tetrahedral shape, with one silicon surrounded by four oxygen centres. The Si–O bond is 162 pm long.