Silicates are the most abundant class of minerals. It has been estimated that up to 90% of the Earth's crust is composed of silicate minerals. All igneous rocks, most metamorphic rocks, and many sedimentary rocks are composed of silicates.
The basic chemical unit of silicate minerals is `~SiO_4^4^-` . Each `~SiO_4` unit is called a tetrahedron. The tetrahedrons can combine in a variety of interesting ways. Silicates are divided into subclasses based on the way their tetrahedrons are arranged:
Nesosilicates: contain single unbonded tetrahedrons - example: fosterite
Sorosilicates: contain two tetrahedrons linked by an oxygen ion - example: lawsonite
Inosilicates: contain single chain and double chain tetrahedrons - example: diopside
Cyclosilicates: contain rings of tetrahedrons - example: beryl
Phyllosilicates: contain sheets of tetrahedrons linked by shared oxygens - example: talc
Tectosilicates: contain interconnected tetrahedrons going out in all directions - example: quartz
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