The most abundant group of minerals in Earth’s Outermost layer of a differentiated planet, asteroid or moon, usually consisting of silicate rock and extending no more than 10s of km from the surface. The term is also applied to icy bodies, in which case it is composed of ices, frozen gases, and accumulated meteoritic material. On Earth, the Click on Term to Read More, the structure of silicates are dominated by the Silicon dioxide, SiO2. tetrahedron, SiO44-, with Element that readily forms cations and has metallic bonds; sometimes said to be similar to a cation in a cloud of electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. A diagonal line drawn Click on Term to Read More ions occurring between tetrahedra). The mesodesmic bonds of the silicon tetrahedron allow extensive Process of reacting molecules together to form three-dimensional networks or chains. Silicon tetrahedra are usually polymerized in silicate minerals and melts. Classification of silicate minerals is based upon their degree of polymerization. Click on Term to Read More 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 Group of silicate minerals, (Mg,Fe)2SiO4, with the compositional endpoints of forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Olivine is commonly found in all chondrites within both the matrix and chondrules, achondrites including most primitive achondrites and some evolved achondrites, in pallasites as large yellow-green crystals (brown when terrestrialized), in the silicate portion Click on Term to Read More and Mineral generally found in terrestrial metamorphic rocks, although igneous examples are not uncommon. Garnet is a significant reservoir of Al in the Earth's upper mantle. The garnet structure consists of isolated SiO4 tetrahedra bound to two cation sites. The A site holds relatively large divalent cations (Ca2+, Mg2+, Fe2+, Mn2+); the Click on Term to Read More
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 "Class of hydroxyl-bearing silicate minerals with a sheet-like structure. They result from aqueous alteration are dominantly serpentine and smectite in meteorites; found in the matrixes of carbonaceous chondrites. Phyllosilicates consist of repeating sequences of sheets of linked tetrahedra (T) and sheets of linked octahedra (O). The T sheet consists of Click on Term to Read More," consist of sheets of tetrahedra. The most common sheet silicates are micas and clay minerals.
Framework silicates, also called "tectosilicates" are networks of tetrahedra. Composed of SiO2, quartz is one of the silica group minerals most common in Earth's crust, but never found in meteorites as inclusions visible to the naked eye. Quartz in meteorites has been found in very small quantities in eucrites, other calcium-rich achondrites, and in the highly reduced E chondrites1. Click on Term to Read More and feldspars are the most common framework silicates.
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.