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   » Wiki: Silicate Mineral
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Silicate minerals are rock-forming made up of groups. They are the largest and most important class of minerals and make up approximately 90 percent of the Earth's crust.

(1992). 9780582300941, Longman.
(1985). 9780471805809, Wiley. .

In , (silicon dioxide) SiO2 is usually considered a silicate mineral. Silica is found in nature as the mineral , and its polymorphs.

On Earth, a wide variety of silicate minerals occur in an even wider range of combinations as a result of the processes that have been forming and re-working the crust for billions of years. These processes include partial , , , , , and .

Living organisms also contribute to this geologic cycle. For example, a type of known as construct their ("frustules") from silica extracted from . The frustules of dead diatoms are a major constituent of , and of diatomaceous earth.

General structure
A silicate mineral is generally an whose consist predominantly of and atoms.

In most minerals in the Earth's crust, each silicon atom is the center of an ideal tetrahedron, whose corners are four oxygen atoms bound to it. Two adjacent tetrahedra may share a vertex, meaning that the oxygen atom is a bridge connecting the two silicon atoms. An unpaired vertex represents an ionized oxygen atom, covalently bound to a single silicon atom, that contributes one unit of negative charge to the anion.

Some silicon centers may be replaced by atoms of other elements, still bound to the four corner oxygen corners. If the substituted atom is not normally tetravalent, it usually contributes extra charge to the anion, which then requires extra . For example, in the mineral , the anion is a tridimensional network of tetrahedra in which all oxygen corners are shared. If all tetrahedra had silicon centers, the anion would be just neutral silica . Replacement of one in every four silicon atoms by an atom results in the anion , whose charge is neutralized by the cations .

Main groups
In , silicate minerals are classified into seven major groups according to the structure of their silicate anion:Deer, W.A.; Howie, R.A., & Zussman, J. (1992). An introduction to the rock forming minerals (2nd edition ed.). London: Longman Hurlbut, Cornelius S.; Klein, Cornelis ||1985). Manual of Mineralogy, Wiley, (20th edition ed.).
, group
, ,
Note that tectosilicates can only have additional cations if some of the silicon is replaced by an atom of lower valence such as aluminium. Al for Si substitution is common.

Nesosilicates or orthosilicates
Nesosilicates (from Greek νῆσος nēsos, island), or orthosilicates, have the orthosilicate ion, which constitute isolated (insular) SiO44− tetrahedra that are connected only by interstitial . The Nickel–Strunz classification is 09.A –examples include:

Sorosilicates (from Greek σωρός sōros, heap, mound) have isolated anions , consisting of double tetrahedra with a shared oxygen vertex—a silicon:oxygen ratio of 2:7. The Nickel–Strunz classification is 09.B. Examples include:

  • (calamine) – Zn4(Si2O7)(OH)2·H2O
  • – CaAl2(Si2O7)(OH)2·H2O
  • – (Ca,Fe,Mn)3Al2(BO3)(Si4O12)(OH)
  • – CaFeII2FeIIIO(Si2O7)(OH)
  • Epidote group (has both (SiO4)4− and (Si2O7)6− groups)
    • – Ca2(Al,Fe)3O(SiO4)(Si2O7)(OH)
    • – Ca2Al3O(SiO4)(Si2O7)(OH)
    • – Ca2Al3O(SiO4)(Si2O7)(OH)
    • – Ca(Ce,La,Y,Ca)Al2(FeII,FeIII)O(SiO4)(Si2O7)(OH)
    • Dollaseite-(Ce) – CaCeMg2AlSi3O11F(OH)
  • () – Ca10(Mg,Fe)2Al4(SiO4)5(Si2O7)2(OH)4

Cyclosilicates (from Greek κύκλος kuklos, circle), or ring silicates, have three or more tetrahedra linked in a ring. The general formula is (Si xO3 x)2 x, where one or more silicon atoms can be replaced by other 4-coordinated atom(s). The silicon:oxygen ratio is 1:3. Double rings have the formula (Si2 xO5 x)2 x or a 2:5 ratio. The Nickel–Strunz classification is 09.C. Possible ring sizes include:
[File:Beryll.ring.combined.png|6, (red: Si, blue: O)]]
[File:Benitoid.2200.png|3, ]]
[File:Papagoite.2200.png|4, ]]
[File:Eudialyte.2200.png|9, ]]
[File:Milarite.png|6, ]]

Some example minerals are:

Note that the ring in contains two B and four Si tetrahedra and is highly distorted compared to the other 6-member ring cyclosilicates.

Inosilicates (from Greek ἴς is genitive:, fibre), or chain silicates, have interlocking chains of with either SiO3, 1:3 ratio, for single chains or Si4O11, 4:11 ratio, for double chains. The Nickel–Strunz classification is 09.D – examples include:

Single chain inosilicates

Double chain inosilicates

Phyllosilicates (from Greek φύλλον phyllon, leaf), or sheet silicates, form parallel sheets of silicate tetrahedra with Si2O5 or a 2:5 ratio. The Nickel–Strunz classification is 09.E. All phyllosilicate minerals are , with either or groups attached. Examples include:
(red: Si, blue: O)]]
-(KF)-apophyllite-(KOH) series]]
-(Fe)-pyrosmalite-(Mn) series]]

Tectosilicates, or "framework silicates," have a three-dimensional framework of silicate with SiO2 in a 1:2 ratio. This group comprises nearly 75% of the crust of the . Tectosilicates, with the exception of the quartz group, are . The Nickel–Strunz classifications are 09.F and 09.G, 04.DA (Quartz/ silica family). Examples include:

See also

External links
Classification of the silicates (6 classes)

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