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Silicate minerals are rock-forming s made up of groups. They are the largest and most important class of minerals and make up approximately 90 percent of . In , (silicon dioxide) is usually considered a silicate mineral. Silica is found in nature as the mineral , and its . 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 . For example, a type of known as s construct their s ("frustules") from silica extracted from . The frustules of dead diatoms are a major constituent of , and of .


General structure

A silicate mineral is generally an whose s 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 ly 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 s. 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 , are classified into seven major groups according to the structure of their silicate anion:Hurlbut, Cornelius S.; Klein, Cornelis , , 1985). ''Manual of Mineralogy'', Wiley, (20th edition ed.). 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 'island'), or orthosilicates, have the , which constitute isolated (insular) that are connected only by interstitial s. The is 09.A –examples include: *Phenakite group ** – ** – * group ** – ** – ** – * group ** – ** – ** – ** – ** – ** – ** – *Zircon group ** – ** – ** – * group ** – ** – ** – ** – ** – ** – * group – ** – ** – ** – ** – * – * – * – * (aka Porcelainite) –


Sorosilicates

Sorosilicates (from Greek '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: * () – * – * – * – *Epidote group (has both and groups} ** – ** – *** – ** – ** – ** – * () –


Cyclosilicates

Cyclosilicates (from Greek 'circle'), or ring silicates, have three or more tetrahedra linked in a ring. The general formula is (Si''x''O3''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''x''O5''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 units , (red: Si, blue: O) File:Benitoid.2200.png, 3 units , File:Papagoite.2200.png, 4 units , File:Eudialyte.2200.png, 9 units , File:Milarite.png, 6 units, double ring , Some example minerals are: * 3-member single ring ** – * 4-member single ring ** – . * 6-member single ring ** – ** – ** – ** – ** – ** – ** – ** – * 9-member single ring ** – * 6-member double ring ** – 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

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


Single chain inosilicates

* group **Enstatite – orthoferrosilite series *** – *** – ** – **Diopside – hedenbergite series *** – *** – *** – **Sodium pyroxene series *** – *** (or acmite) – ** – ** - *Pyroxenoid group ** – ** – ** –


Double chain inosilicates

* group ** – **Cummingtonite series *** – *** – **Tremolite series *** – *** – ** – **Sodium amphibole group *** – *** () – *** – File:Pyroxen-chain.png, Inosilicate, pyroxene family, with 2-periodic single chain , File:Tremolite-chain.png, Inosilicate, clinoamphibole, with 2-periodic double chains , File:Wollastonite-chain.png, Inosilicate, unbranched 3-periodic single chain of File:Rhodonite-chain.png, Inosilicate with 5-periodic single chain, File:Pellyite-chain.png, Inosilicate with cyclic branched 8-periodic chain,


Phyllosilicates

Phyllosilicates (from Greek 'leaf'), or sheet silicates, form parallel sheets of silicate tetrahedra with or a 2:5 ratio. The Nickel–Strunz classification is 09.E. All phyllosilicate minerals are d, with either or groups attached. Examples include: * ** – ** – ** – * group **1:1 clay minerals (TO) *** – *** – **2:1 clay minerals (TOT) *** – *** – *** – *** (smectite) – *** – *** – **Other clay minerals *** – *** (or attapulgite) – (Mg,Al)2Si4O10(OH)*4(H2O) * group ** – ** – ** – ** – ** – ** – ** – File:Muskovite.sheet.png, Phyllosilicate, mica group, (red: Si, blue: O) File:Apophyllite.sheet.png, Phyllosilicate, single net of tetrahedra with 4-membered rings, -(KF)-apophyllite-(KOH) series File:Pyrosmalite.sheet.png, Phyllosilicate, single tetrahedral nets of 6-membered rings, -(Fe)-pyrosmalite-(Mn) series File:Zeophyllite.sheet.png, Phyllosilicate, single tetrahedral nets of 6-membered rings, File:Carletonite.sheet.png, Phyllosilicate, double nets with 4- and 6-membered rings,


Tectosilicates

Tectosilicates, or "framework silicates," have a three-dimensional framework of silicate with in a 1:2 ratio. This group comprises nearly 75% of the of the . Tectosilicates, with the exception of the quartz group, are s. The Nickel–Strunz classifications are 09.F and 09.G, 04.DA (Quartz/ silica family). Examples include: *3D-Silicates, quartz family ** – ** – ** – ** – ** – ** – ** – *Tectosilicates, group **Alkali feldspars (potassium feldspars) *** – *** – *** – *** – ** feldspars *** – *** –      (Na:Ca 4:1) *** –      (Na:Ca 3:2) *** –      (Na:Ca 2:3) *** –      (Na:Ca 1:4) *** – *Tectosilicates, family ** – ** – ** – ** – ** – ** – *** – *Tectosilicates, group ** – ** – *Tectosilicates, family ** – ** – ** – ** – ** – ** – ** – ** –


See also

* * *


References


External links


Mindat.org, Dana classification

Webmineral : Dana's New Silicate Classification
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