Orthosilicate

Silicate minerals
Copper silicate mineral chrysocolla
Category	Mineral

Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of rock-forming minerals and make up approximately 90 percent of the Earth's crust. They are classified based on the structure of their silicate groups, which contain different ratios of silicon and oxygen.

Nesosilicates (from Greek νῆσος nēsos, island), or orthosilicates, have the orthosilicate ion, which constitute isolated (insular) [SiO₄]⁴⁻tetrahedra that are connected only by interstitial cations. Nickel–Strunz classification: 09.A

Sorosilicates (from Greek σωρός sōros, heap, mound) have isolated double tetrahedra groups with (Si₂O₇)⁶⁻ or a ratio of 2:7. Nickel–Strunz classification: 09.B

Cyclosilicates (from Greek κύκλος kuklos, circle), or ring silicates, have linked tetrahedra with (T_xO_3x)^2x− or a ratio of 1:3. These exist as 3-member (T₃O₉)⁶⁻ and 6-member (T₆O₁₈)¹²⁻ rings, where T stands for a tetrahedrally coordinated cation. Nickel–Strunz classification: 09.C

Note that the ring in axinite contains two B and four Si tetrahedra and is highly distorted compared to the other 6-member ring cyclosilicates.

Cyclosilicate, [Si₆O₁₈] – 6-membered single rings, beryl (red: Si, blue: O)

Cyclosilicate, [Si₃O₉] – 3-membered single ring, benitoite

Cyclosilicate, [Si₄O₁₂] – 4-membered single ring, papagoite

Cyclosilicate, [Si₉O₂₇] – 9-membered ring, eudialyte

Cyclosilicate, [Si₆O₁₈] – 6-membered double ring, milarite