Mineralogy of Cyclosilicates and Inosilicates

Crystal Chemistry of Cyclosilicates and Inosilicates

This article delves deeper into the more complex combination of tetrahedrons found in cyclosilicates and inosilicates.

Cyclosilicate and inosilicate subclasses comprise numerous mineral groups and important mineral species. Cyclosilicates’ most familiar representatives are beryl and the tourmaline supergroup. Inosilicates are subdivided into single-chain silicates with pyroxene supergroup and double-chain amphibole minerals.

Introduction to Cyclosilicates

Cyclosilicate units form by joining three, four, or six SiO₄ tetrahedrons closed into a ring. So sometimes you can run into ring silicates synonym names of this group. By joining three tetrahedrons, a three-membered ring is created, so there is a [Si₃O₉]^6- structural unit, a 4-membered ring will logically have [Si₄O₁₂]^8-, and the most common 6-membered ring – [Si₆O₁₈]^12-.

An example of a three-membered cyclosilicate with [Si₃O₉]^6- unit is a rare California state gem benitoite, BaTi[Si₃O₉].