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Silicates

The silica tetrahedron, [SiO4]4-

Cyclosilicates

The cyclosilicates form rings of linked [SiO4]4- tedrahedra with either [Si3O9]6-, [Si4O12]8-, or [Si6O18]12- configurations. Cordierite with the chemical formula (Mg,Fe)2Al4Si5O18 represents an example of the cyclosilicate group.

Inosilicates

In the inosilicates, [SiO4]4- tedrahedra are linked as chains, which in turn are linked together by cations. Single-chain inosilicates form [Si2O6]4- groups, and double-chain inosilicates form [Si4O11]6- groups. Pyroxenes, e.g. diopside with the chemical formula CaMgSi2O6, are single-chain, and amphiboles, e.g. hornblende (Ca2(Mg,Fe,Al)5(Al,Si)8O22(OH)) or actinolite (Ca2(Fe,Mg)5Si8O22(OH)2) are double-chain inosilicates.

Nesosilicates

In the nesosilicate group, [SiO4]4- tedrahedra are isolated from each other and share their oxygens with octahedral groups, which contain cations, such as Mg2+, Fe2+, or Ca2+. A common rock-forming mineral of the nesosilicate group is olivine with the chemical formula (Mg,Fe)2SiO4.

Phyllosilicates

Phyllosilicates comprise sheets of [SiO4]4- tedrahedra rings, where three of the four oxygens of each tedrahedrons are shared resulting in [Si4O10]4- groups. Biotite with the chemical formula K(Mg,Fe)3(AlSi3O10)(F,OH)2 is a common rock-forming phyllosilicate.

Sorosilicates

Two [SiO4]4- tedrahedra are linked by a shared corner oxygen to form [Si2O7]6- groups. An example for the sorosilicate group is the mineral epidote with the chemical formula Ca2Al2(Fe3+,Al)(SiO4)(Si2O7)O(OH).

Tectosilicates

Complete linkage of [SiO4]4- tedrahedra results in the 3-dimensional framework of the tectosilicates. Quartz (SiO2) and the feldspars (plagioclase, microcline) (e.g. anorthite, CaAl2Si2O8) are tectosilicates.





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