Silicate mineral
Template:Short description Template:Use dmy dates
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust.[1][2][3]
In mineralogy, the crystalline forms of silica (Template:Chem2) are usually considered to be tectosilicates, and they are classified as such in the Dana system (75.1). However, the Nickel-Strunz system classifies them as oxide minerals (4.DA). Silica is found in nature as the mineral quartz 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 melting, crystallization, fractionation, metamorphism, weathering, and diagenesis.
Living organisms also contribute to this geologic cycle. For example, a type of plankton known as diatoms construct their exoskeletons ("frustules") from silica extracted from seawater. The frustules of dead diatoms are a major constituent of deep ocean sediment, and of diatomaceous earth.Script error: No such module "Unsubst".
General structure
A silicate mineral is generally an inorganic compound consisting of subunits with the formula [SiO2+n]2n−. Although depicted as such, the description of silicates as anions is a simplification. Balancing the charges of the silicate anions are metal cations, Mx+. Typical cations are Mg2+, Fe2+, and Na+. The Si-O-M linkage between the silicates and the metals are strong, polar-covalent bonds. Silicate anions ([SiO2+n]2n−) are invariably colorless, or when crushed to a fine powder, white. The colors of silicate minerals arise from the metal component, commonly iron.
In most silicate minerals, silicon is tetrahedral, being surrounded by four oxides. The coordination number of the oxides is variable except when it bridges two silicon centers, in which case the oxide has a coordination number of two.
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 cations. For example, in the mineral orthoclase Template:Chem, 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 Template:Chem. Replacement of one in every four silicon atoms by an aluminum atom results in the anion Template:Chem, whose charge is neutralized by the potassium cations Template:Chem.
Main groups
In mineralogy, silicate minerals are classified into seven major groups according to the structure of their silicate anion:[4][5]
| Major group | Structure | Chemical formula | Example |
|---|---|---|---|
| Nesosilicates | isolated silicon tetrahedra | [SiO4]4− | olivine, garnet, zircon... |
| Sorosilicates | double tetrahedra | [Si2O7]6− | epidote, melilite group |
| Cyclosilicates | rings | [SinO3n]2n− | beryl group, tourmaline group |
| Inosilicates | single chain | [SinO3n]2n− | pyroxene group |
| Inosilicates | double chain | [Si4nO11n]6n− | amphibole group |
| Phyllosilicates | sheets | [Si2nO5n]2n− | micas and clays |
| Tectosilicates | 3D framework | [AlxSiyO(2x+2y)]x− | quartz, feldspars, zeolites |
Tectosilicates can only have additional cations if some of the silicon is replaced by an atom of lower valence such as aluminum. Al for Si substitution is common.
Nesosilicates or orthosilicates
Template:Main category Nesosilicates (from Greek Template:Wikt-lang Template:Transliteration 'island'), or orthosilicates, have the orthosilicate ion, present as isolated (insular) Template:Chem2 tetrahedra connected only by interstitial cations. The Nickel–Strunz classification is 09.A –examples include:
- Template:Chem2 group
- Humite group – Template:Chem2
- Datolite – Template:Chem2
- Titanite – Template:Chem2
- Chloritoid – Template:Chem2
- Mullite (aka Porcelainite) – Template:Chem2
Sorosilicates
Template:Main category Sorosilicates (from Greek Template:Wikt-lang Template:Transliteration 'heap, mound') have isolated pyrosilicate anions Template:Chem, 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:
- Thortveitite – Template:Chem2
- Hemimorphite (calamine) – Template:Chem2
- Lawsonite – Template:Chem2
- Axinite – Template:Chem2
- Ilvaite – Template:Chem2
- Epidote group (has both Template:Chem2 and Template:Chem2 groups}
- Vesuvianite (idocrase) – Template:Chem2
Cyclosilicates
Cyclosilicates (from Greek Template:Wikt-lang Template:Transliteration 'circle'), or ring silicates, have three or more tetrahedra linked in a ring. The general formula is (SixO3x)2x−, 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 (Si2xO5x)2x− or a 2:5 ratio. The Nickel–Strunz classification is 09.C. Possible ring sizes include:
-
6 units Template:Chem2, beryl (red: Si, blue: O)
-
3 units Template:Chem2, benitoite
-
4 units Template:Chem2, papagoite
-
9 units Template:Chem2, eudialyte
-
12 units, double ring Template:Chem2, milarite
Some example minerals are:
- 3-member single ring
- 4-member single ring
- 6-member single ring
- 9-member single ring
- 6-member double ring
The ring in axinite contains two B and four Si tetrahedra and is highly distorted compared to the other 6-member ring cyclosilicates.
Inosilicates
Template:Main category Inosilicates (from Greek Template:Wikt-lang Template:Transliteration [genitive: Template:Wikt-lang Template:Transliteration] 'fibre'), or chain silicates, have interlocking chains of silicate tetrahedra with either Template:Chem2, 1:3 ratio, for single chains or Template:Chem2, 4:11 ratio, for double chains. The Nickel–Strunz classification is 09.D – examples include:
Single chain inosilicates
- Pyroxene group
- Enstatite – orthoferrosilite series
- Pigeonite – Template:Chem2
- Diopside – hedenbergite series
- Sodium pyroxene series
- Jadeite – Template:Chem2
- Aegirine (or acmite) – Template:Chem2
- Spodumene – Template:Chem2
- Pyroxferroite - Template:Chem2
- Pyroxenoid group
Double chain inosilicates
- Amphibole group
- Anthophyllite – Template:Chem2
- Cummingtonite series
- Tremolite series
- Hornblende – Template:Chem
- Sodium amphibole group
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Inosilicate, pyroxene family, with 2-periodic single chain Template:Chem2, diopside
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Inosilicate, clinoamphibole, with 2-periodic double chains Template:Chem2, tremolite
-
Inosilicate, unbranched 3-periodic single chain of wollastonite
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Inosilicate with 5-periodic single chain, rhodonite
-
Inosilicate with cyclic branched 8-periodic chain, pellyite
Phyllosilicates
Template:Main category Phyllosilicates (from Greek Template:Wikt-lang Template:Transliteration 'leaf'), or sheet silicates, form parallel sheets of silicate tetrahedra with Template:Chem2 or a 2:5 ratio. The Nickel–Strunz classification is 09.E. All phyllosilicate minerals are hydrated, with either water or hydroxyl groups attached. Many phyllosilicates are clay-forming and may be further classified as 1:1 clay minerals (one tetrahedral sheet and one octahedral sheet) and 2:1 clay minerals (one octahedral sheet between two tetrahedral sheets). Below is a list of phyllosilicate minerals and their chemical formulas, organized by mineralogical group:
- Chlorite group[6] – Template:Chem2Template:Quad(2:1:1 clays)
- Chamosite – Template:Chem2Template:Quad(Fe endmember)
- Clinochlore – Template:Chem2Template:Quad(Mg endmember)
- Cookeite – Template:Chem2
- Kaolinite-Serpentine group[7]
- Kaolinite subgroupTemplate:Quad(1:1 clays)
- Serpentine subgroup
- Amesite – Template:Chem2
- Antigorite – Template:Chem2
- Bowenite – Template:Chem2Template:Quad(yellow-green variety of antigorite)[8]
- Chrysotile – Template:Chem2
- Cronstedtite – Template:Chem2
- Lizardite – Template:Chem2
- Népouite – Template:Chem2
- Pecoraite – Template:Chem2
- Mica group[9]
- Brittle mica group[10]
- Dioctahedral mica group
- Celadonite subgroup
- Glauconite – Template:Chem2
- Muscovite – Template:Chem2[11]
- Fuchsite – Template:Chem2Template:Quad(Cr replaces Al in muscovite)[12]
- Illite – Template:Chem2Template:Quad(K-deficient muscovite)[13]Template:Quad(2:1 clay)
- Mariposite – Template:Chem2Template:Quad(Cr-bearing muscovite)[14]
- Phengite – Template:Chem2Template:Quad(Fe/Mg-bearing muscovite)[15]
- Paragonite – Template:Chem2
- Roscoelite – Template:Chem2
- Trioctahedral mica group
- Aspidolite – Template:Chem2
- Biotite subgroup – Template:Chem2
- Annite – Template:Chem2Template:Quad(Fe endmember)
- Phlogopite – Template:Chem2Template:Quad(Mg endmember)
- Hendricksite – Template:Chem2
- Lepidolite (polylithionite-trilithionite series) – Template:Chem2
- Zinnwaldite series – Template:Chem2
- Sepiolite – Template:Chem2[16]Template:Quad(2:1 clay)
- Smectite group[17]Template:Quad(2:1 clays)
- Palygorskite (or attapulgite) – Template:Chem2[19]Template:Quad(2:1 clay)
- Pyrophyllite-Talc group[20]
- Minnesotaite – Template:Chem2
- Pyrophyllite – Template:Chem2
- Talc – Template:Chem2Template:Quad(2:1 clay)
- Vermiculite – Template:Chem2[21]Template:Quad(2:1 clay)
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Phyllosilicate, mica group, muscovite (red: Si, blue: O)
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Phyllosilicate, single net of tetrahedra with 4-membered rings, apophyllite-(KF)-apophyllite-(KOH) series
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Phyllosilicate, single tetrahedral nets of 6-membered rings, pyrosmalite-(Fe)-pyrosmalite-(Mn) series
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Phyllosilicate, single tetrahedral nets of 6-membered rings, zeophyllite
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Phyllosilicate, double nets with 4- and 6-membered rings, carletonite
Tectosilicates
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Tectosilicates, or "framework silicates," have a three-dimensional framework of silicate tetrahedra with Template:Chem2 in a 1:2 ratio. This group comprises nearly 75% of the crust of the Earth.[22] Tectosilicates, with the exception of the quartz group, are aluminosilicates. The Nickel–Strunz classifications are 9.F (tectosilicates without zeolitic Template:Chem2), 9.G (tectosilicates with zeolitic Template:Chem2), and 4.DA (quartz/silica group). Below is a list of tectosilicate minerals and their chemical formulas, organized by mineralogical group:
- Quartz group (silica) – Template:Chem2
- α-quartz – trigonal, quartz under Template:Convert
- β-quartz – hexagonal, high-temperature quartz
- Coesite – monoclinic polymorph
- Cristobalite – tetragonal polymorph
- Moganite – monoclinic polymorph
- Stishovite – hard and dense tetragonal polymorph
- Tridymite – orthorhombic polymorph
- Feldspar group[23]
- Alkali feldspar series (potassium feldspars or K-spar)
- Plagioclase feldspar series
- Albite – Template:Chem2Template:Quad(Na endmember)
- Oligoclase – Template:Chem2Template:Quad(Na:Ca 90:10 to 70:30)[24]
- Andesine – Template:Chem2Template:Quad(Na:Ca 50:50 to 70:30)[25]
- Labradorite – Template:Chem2Template:Quad(Na:Ca 30:70 to 50:50)[26]
- Bytownite – Template:Chem2Template:Quad(Na:Ca 10:90 to 30:70)[27]
- Anorthite – Template:Chem2Template:Quad(Ca endmember)
- Other feldspars
- Feldspathoid group[30]
- Cancrinite subgroup
- Danalite – Template:Chem2[31]
- Kalsilite – Template:Chem2
- Leucite – Template:Chem2
- Nepheline subgroup
- Sodalite subgroup
- Scapolite group[33]
- Zeolite group[34]
- Amicite – Template:Chem2
- Analcime – Template:Chem2
- Brewsterite subgroup – Template:Chem2
- Chabazite-Lévyne subgroup
- Clinoptilolite subgroup – Template:Chem2
- Cowlesite – Template:Chem2
- Dachiardite-K – Template:Chem2
- Edingtonite – Template:Chem2
- Erionite subgroup – Template:Chem2
- Faujasite subgroup – Template:Chem2
- Ferrierite subgroup – Template:Chem2Template:Quad(Ferrierite-Mg)
- Garronite-Ca – Template:Chem2
- Gismondine – Template:Chem2Template:Quad(Gismondine-Ca)
- Gmelinite subgroup – Template:Chem2Template:Quad(Gmelinite-Na)
- Heulandite subgroup – Template:Chem2
- Hsianghualite – Template:Chem2
- Laumontite – Template:Chem2
- Mordenite – Template:Chem2
- Nabesite – Template:Chem2
- Natrolite subgroup
- Paulingite subgroup – Template:Chem2Template:Quad(Paulingite-K)
- Phillipsite subgroup
- Harmotome – Template:Chem2
- Phillipsite – Template:Chem2Template:Quad(Phillipsite-Ca)
- Pollucite – Template:Chem2
- Stilbite subgroup
- Thomsonite subgroup – Template:Chem2Template:Quad(Thomsonite-Ca)
- Wairakite – Template:Chem2
- Yugawaralite – Template:Chem2
See also
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References
External links
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Template:Strunz Template:Authority control
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- ↑ Deer, W.A.; Howie, R.A., & Zussman, J. (1992). An introduction to the rock forming minerals (2nd edition ed.). London: Longman Template:ISBN
- ↑ Hurlbut, Cornelius S.; Klein, Cornelis ||1985). Manual of Mineralogy, Wiley, (20th edition ed.). Template:ISBN
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