<P> Other examples of sorosilicates include lawsonite, a metamorphic mineral forming in the blueschist facies (subduction zone setting with low temperature and high pressure), vesuvianite, which takes up a significant amount of calcium in its chemical structure . </P> <P> Orthosilicates consist of isolated tetrahedra that are charge - balanced by other cations . Also termed nesosilicates, this type of silicate has a silicon: oxygen ratio of 1: 4 (e.g. SiO). Typical orthosilicates tend to form blocky equant crystals, and are fairly hard . Several rock - forming minerals are part of this subclass, such as the aluminosilicates, the olivine group, and the garnet group . </P> <P> The aluminosilicates--bkyanite, andalusite, and sillimanite, all Al SiO--are structurally composed of one (SiO) tetrahedron, and one Al in octahedral coordination . The remaining Al can be in six-fold coordination (kyanite), five-fold (andalusite) or four-fold (sillimanite); which mineral forms in a given environment is depend on pressure and temperature conditions . In the olivine structure, the main olivine series of (Mg, Fe) SiO consist of magnesium - rich forsterite and iron - rich fayalite . Both iron and magnesium are in octahedral by oxygen . Other mineral species having this structure exist, such as tephroite, Mn SiO . The garnet group has a general formula of X Y (SiO), where X is a large eight-fold coordinated cation, and Y is a smaller six-fold coordinated cation . There are six ideal endmembers of garnet, split into two group . The pyralspite garnets have Al in the Y position: pyrope (Mg Al (SiO)), almandine (Fe Al (SiO)), and spessartine (Mn Al (SiO)). The ugrandite garnets have Ca in the X position: uvarovite (Ca Cr (SiO)), grossular (Ca Al (SiO)) and andradite (Ca Fe (SiO)). While there are two subgroups of garnet, solid solutions exist between all six end - members . </P> <P> Other orthosilicates include zircon, staurolite, and topaz . Zircon (ZrSiO) is useful in geochronology as the Zr can be substituted by U; furthermore, because of its very resistant structure, it is difficult to reset it as a chronometer . Staurolite is a common metamorphic intermediate - grade index mineral . It has a particularly complicated crystal structure that was only fully described in 1986 . Topaz (Al SiO (F, OH), often found in granitic pegmatites associated with tourmaline, is a common gemstone mineral . </P>

Minerals are generally derived from materials that are