Silicate

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Silicate

A silicate is a compound containing an anion in which one or more central silicon

Silicon

Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. The atomic mass is 28.0855....
atoms are surrounded by electronegative ligand

Ligand

In chemistry, a ligand is either an atom, ion, or molecule that bonds to a central metal, generally involving formal donation of one or more of its electrons....
s. This definition is broad enough to include species such as hexafluorosilicate ("fluorosilicate"), [SiF₆]^2-, but the silicate species that are encountered most often consist of silicon

Silicon

Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. The atomic mass is 28.0855....
with oxygen

Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
as the ligand. Silicate anions, with a negative net electrical charge, must have that charge balanced by other cations to make an electrically neutral compound.

Silica, or silicon dioxide

Silicon dioxide

The chemical compound 'silicon dioxide', also known as 'silica' , is an oxide of silicon with a chemical formula of and has been known for its hardness since antiquity....
, SiO₂, is sometimes considered a silicate, although it is the special case with no negative charge and no need for counter-ions.

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Encyclopedia

A silicate is a compound containing an anion in which one or more central silicon

Silicon

Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. The atomic mass is 28.0855....
atoms are surrounded by electronegative ligand

Ligand

Silicon

Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. The atomic mass is 28.0855....
with oxygen

Oxygen

Silicon dioxide

Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
quartz

Quartz

Quartz is the most abundant mineral in the Earth's continental crust . It is made up of a Crystal structure of silica tetrahedra. Quartz has a hardness of 7 on the Mohs scale and a density of 2.65 g/cm?....
, and its polymorphs

Polymorphism (materials science)

Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements....
.

In the vast majority of silicates, including silicate minerals

Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
, the Si atom shows tetrahedral

Tetrahedron

A tetrahedron is a polyhedron composed of four triangle faces, three of which meet at each vertex . A regular tetrahedron is one in which the four triangles are regular, or "equilateral", and is one of the Platonic solids....
coordination by 4 oxygens. In different mineral

Mineral

Polymer

A polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties....
: they occur singly, joined together in pairs, in larger finite clusters including rings, in chains, double chains, sheets, and three-dimensional frameworks. The minerals are classified into groups based on these anion structures; a list is given below.

Silicon may adopt octahedral

Octahedron

An octahedron is a polyhedron with eight faces. A regular octahedron is a Platonic solid composed of eight equilateral triangles, four of which meet at each wikt:vertex....
coordination by 6 oxygens at very high pressure, as in the dense stishovite

Stishovite

Stishovite is an extremely hard, dense tetragonal form of silicon dioxide. It was traditionally considered the hardest known oxide; however, boron suboxide was recently discovered to be much harder....
polymorph of silica that is found in the lower mantle of the Earth, and which is also formed by shock during meteorite

Meteorite

A meteorite is a natural object originating in outer space that survives an impact with the Earth's surface. While in space it is called a meteoroid....
impacts. Lack of space around the oxygen atoms makes this coordination for Si very rare at normal pressure, but it is known in the hexahydroxysilicate anion, [Si(OH)₆]^2-, as found in the mineral thaumasite

Thaumasite

Thaumasite is a Silicate minerals with chemical formula calcium3silicon6?12. It occurs as colorless to white prismatic Hexagonal crystal system crystals, typically as acicular radiating groups....
.

Silicate rock

In geology

Geology

Geology is the science and study of the solid and liquid matter that constitute the Earth. The field of geology encompasses the study of the composition, structural geology, physical properties, dynamics, and History of the Earth of Earth materials, and the processes by which they are formed, moved, and changed....
and astronomy

Astronomy

Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
, the term silicate is used to denote types of rock

Rock (geology)

In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock....
that consist predominantly of silicate minerals

Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
. Such rocks include a wide range of igneous, metamorphic

Metamorphic rock

Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form"....
and sedimentary types. Most of the Earth's mantle and crust

Crust (geology)

In geology, a crust is the outermost solid shell of a planet or moon, which is chemically distinct from the underlying mantle . Crusts of Earth , our Moon, Mercury , Venus, and Mars have been generated largely by igneous processes, and these crusts are richer in incompatible elements than their respective mantle s....
are made up of silicate rocks. The same is true of the Moon

Moon

The Moon is Earth's only natural satellite and the List of natural satellites by diameter satellite in the Solar System. The average centre-to-centre distance from the Earth to the Moon is km, about thirty times the diameter of the Earth....
and the other rocky planet

Planet

A planet , as 2006 definition of planet by the International Astronomical Union , is a celestial body orbiting a star or Stellar evolution#Stellar remnants that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared the neighbourhood of planetesimals....
s.

On Earth, a wide variety of silicate minerals occur in an even wider range of combinations as a result of the processes that form and re-work the crust. These processes include partial melting

Melting

Melting is a process that results in the phase change of a substance from a solid to a liquid. The internal energy of a solid substance is increased to a specific temperature at which it changes to the liquid phase....
, crystallization

Crystallization

Crystallization is the process of formation of solid crystals Precipitation from a solution, melting or more rarely Deposition directly from a gas....
, fractionation

Fractionation

Fractionation is a separation process in which a certain quantity of a mixture is divided up in a number of smaller quantities in which the wikt:composition changes according to a gradient....
, metamorphism

Metamorphism

Metamorphism is the solid-state Crystallization of pre-existing Rock due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids....
, weathering

Weathering

Weathering is the decomposition of earth Rock , soils and their minerals through direct contact with the planet's atmosphere. Weathering occurs in situ, or "with no movement", and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, wind, and gravity....
and diagenesis

Diagenesis

In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration and metamorphism....
. Living things also contribute to the silicate cycle near the Earth's surface. A type of plankton

Plankton

Plankton consist of any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. Plankton are defined by their ecological niche rather than their Phylogenetics or taxonomy classification....
known as diatom

Diatom

Diatoms are a major group of eukaryote algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as Colony in the shape of filaments or ribbons , fans , zigzags , or stellate colonies ....
s construct their exoskeleton

Exoskeleton

An exoskeleton is an external skeleton that supports and protects an animal's body, in contrast to the internal endoskeleton of, for example, a human skeleton....
s, known as tests, from silica. The tests of dead diatoms are a major constituent of deep ocean sediment

Sediment

Sediment is any particulate matter that can be sediment transport by fluid dynamics, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers....

Silicates have been observed in space, around evolved stars and planetary nebula

Planetary nebula

A planetary nebula is an emission nebula consisting of a glowing shell of gas and Plasma formed by certain types of stars when they die. The name originated in the 18th century because of their similarity in appearance to gas giants when viewed through small optical telescopes, and is unrelated to the planets of the solar system....
e such as NGC 6302

NGC 6302

NGC 6302 , is a bipolar nebula planetary nebula in the constellation Scorpius. It is one of the most interesting and complex planetary nebulae observed....
. They are found in both amorphous form and crystalline form, though the range of types that have been found is far smaller than those found on Earth.

Mineralogy

Mineralogically

Mineralogy

Mineralogy is an Earth Science focused around the chemistry, crystal structure, and physical properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization....
, silicate minerals

Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
are divided according to structure of their silicate anion into the following groups:

Nesosilicate
Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
s (lone tetrahedron) - [SiO₄]^4-, eg olivine
Olivine

The mineral olivine is a magnesium iron Silicate minerals with the formula 2siliconoxygen4. It is one of the most common minerals on Earth, and has also been identified in meteorites and on the Moon, Mars, and comet Wild 2....
.
Sorosilicates (double tetrahedra) - [Si₂O₇]^6-, eg epidote
Epidote

Epidote is a calcium aluminium iron Silicate minerals mineral, Ca2Al2O, crystallizing in the monoclinic system. Well-developed crystals are of frequent occurrence: they are commonly prismatic in habit, the direction of elongation being perpendicular to the single plane of symmetry....
.
Cyclosilicates (rings) - [Si_nO_3n]^2n-, eg tourmaline
Tourmaline

Tourmaline is a crystal silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classed as a semi-precious stone and the gem comes in a wide variety of colors....
group.
Inosilicates (single chain) - [Si_nO_3n]^2n-, eg pyroxene
Pyroxene

The pyroxenes are a group of important rock-forming silicate minerals found in many igneous and metamorphic rock rock . They share a common structure comprised of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems....
group.
Inosilicates(double chain) - [Si_4nO_11n]^6n-, eg amphibole
Amphibole

Amphibole defines an important group of generally dark-colored rock-forming Silicate minerals minerals, composed of double chain SiO4 tetrahedron, linked at the vertices and generally containing ions of iron and/or magnesium in their structures....
group.
Phyllosilicates (sheets) - [Si_2nO_5n]^2n-, eg mica
Mica

The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic with a tendency towards pseudo-hexagonal crystals and are similar in chemical composition....
s and clay
Clay

Clay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired....
s.
Tectosilicates (3D framework) - [Al_xSi_yO_2(x+y)]^x-, eg quartz
Quartz

Quartz is the most abundant mineral in the Earth's continental crust . It is made up of a Crystal structure of silica tetrahedra. Quartz has a hardness of 7 on the Mohs scale and a density of 2.65 g/cm?....
, feldspar
Feldspar

Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's Crust .Feldspars crystallize from magma in both intrusive and extrusive igneous rocks, as veins, and are also present in many types of metamorphic rock....
s, zeolite
Zeolite

Zeolites are Microporous material, aluminosilicate minerals commonly used as commercial absorbents. The term zeolite was originally coined in 1756 by Sweden mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that had been absorbed by the material....
s.

Note that tectosilicates can only have additional cations if some of the silicon is replaced by a lower-charge cation such as aluminium

Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
, to give a negative charge overall. This substitution can also take place in other types of silicate.

Some rare minerals have more than one type of anion coexisting in their crystal structures, or complex-shaped anions that are intermediate between the simple types above.