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Mineral group Major anion groups Mineral group Major anion groups Native elements None Nitrates 3 Halides F⁻¹, Cl⁻¹, Br⁻¹ Borates 34 Sulfides S⁻², S⁻⁴ Sulfates 4 Arsenides As⁻², As⁻³ Phosphates 4 Sulfarsendies As^{−2 or} As⁻³ and S^{−2 or} S⁻⁴ Chromates (CrO4)⁻⁵ Selenides Se⁻² Arsenates 4 Tellurides Te⁻² Vanadates 4 Oxides O⁻² Molybdates 4 Hydroxides (OH)⁻¹ Tungstates 4 Carbonates 3 Silicates 4

Silicate minerals

Silica tetrahedra are composed of a single, small, tetravalent silicon ion (Si⁺⁴) in fourfold, tetrahedral coordination with four larger, divalent oxygen ions (O⁻²).These silica tetrahedra may be thought of as the basic building blocks, the LEGO®, of silicate minerals. Because the electrostatic valency of each of the four Si–O bonds in the tetrahedron is one (EV = 1), the +4 charge of the silicon ion is effectively neutralized. However, the −2 charges on the oxygen (O⁻²) ions are not neutralized. Each oxygen ion possesses an unsatisfied charge of −1 which it can only neutralize by bonding with one or more additional cations in the mineral structure. Essentially, as a crystal forms, oxygen anions can bond to another silicon (Si⁺⁴) ion to form a second bond with an electrostatic valency of 1 or it can bond to some other combination of cations (e.g., Al⁺³, Mg⁺², Fe⁺², Ca⁺², K⁺¹, Na⁺¹) with a total electrostatic valency of 1.