Silicate

The most abundant group of minerals in Earth’s crust, the structure of silicates are dominated by the silica tetrahedron, SiO44-, with metal ions occurring between tetrahedra). The mesodesmic bonds of the silicon tetrahedron allow extensive polymerization and silicates are classified according to the amount of linking that occurs between the tetrahedra.

Orthosilicates, also called "nesosilicates," have isolated (unlinked) tetrahedra. The charge of isolated tetrahedra is balanced by other cations (Mg2+, Fe2+, Al3+, etc.). Common orthosilicates inlcude olivine and garnet
Disilicates, also called "sorosilicates," have paired tetrahedra. The most common disilicate is epidote.
Ring silicates, also called "cyclosilicates," consist of linked rings of tetrahedra. There are several types of rings
Si3O9 (rare), Si4O12 (also rare), and Si6O18 (common). The most common ring silcates are tourmaline and beryl.
Chain silicates, also called "inosilicates" occur in two forms: single chains of tetrahedra (pyroxenes) and double chains of tetrahedra (amphiboles).
Sheet silicates, also called "phyllosilicates," consist of sheets of tetrahedra. The most common sheet silicates are micas and clay minerals.
Framework silicates, also called "tectosilicates" are networks of tetrahedra. Quartz and feldspars are the most common framework silicates.

Silicate structures

All tetrahedral structures have net negative charge (except for the silica polymorphs) and cations required to balance charges. Cations also serve to bond negatively charged structural elements such as halogens and water. One complicating factor is that Al3+ commonly substitutes for Si4+ in chain, sheet and framework silicates.