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{{Short description|Rock-forming minerals with predominantly silicate anions}}{{Use dmy dates|date=February 2019}}File:Spodumene-sd305c.jpg|thumb|right|Lithium aluminium silicate mineral spodumenespodumeneSilicate 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.WEB,weblink Mineral - Silicates, britannica.com, 8 May 2018, live,weblink 25 October 2017, BOOK, Deer, W.A., Howie, R.A., Zussman, J., 1992, An introduction to the rock-forming minerals, Longman, London, 2nd, 0-582-30094-0, BOOK, Hurlbut, Cornelius S., Klein, Cornelis, 1985, Manual of Mineralogy, 20th, Wiley, 0-47180580-7,weblink In mineralogy, silica (silicon dioxide, {{chem2|SiO2}}) is usually considered a silicate mineral rather than an oxide mineral. 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.(File:Diatomaceous Earth BrightField.jpg|thumb|right|Diatomaceous earth, a biogenic form of silica as viewed under a microscope. The imaged region measures approximately 1.13 by 0.69 mm.)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.{{Citation needed|date=April 2019}}

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 {{chem|[KAlSi|3|O|8|]|n}}, 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 {{chem|[SiO|2|]|n}}. Replacement of one in every four silicon atoms by an aluminum atom results in the anion {{chem|[AlSi|3|O|8|−|]|n}}, whose charge is neutralized by the potassium cations {{chem|K|+}}.

Main groups

In mineralogy, 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 {{ISBN|0-582-30094-0}}Hurlbut, Cornelius S.; Klein, Cornelis ||1985). Manual of Mineralogy, Wiley, (20th edition ed.). {{ISBN|0-471-80580-7}}{| class=wikitable! Major group !! Structure !! Chemical formula !! Example

Nesosilicates >		| olivine, garnet, zircon...

Sorosilicates >		| epidote, melilite group

Cyclosilicates >		nO3n]2n− >| beryl group, tourmaline group

Inosilicates >		nO3n]2n− >| pyroxene group

Inosilicates >		nO11n]6n− >| amphibole group

Silicate_minerals#Phyllosilicates>Phyllosilicates	sheets	[Si2nO5n]2n−	micas and clays

Tectosilicates >		xSiyO(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

(File:Silicate-tetrahedron-3D-balls.png|thumb|Orthosilicate anion {{chem|SiO|4|4-}}. The grey ball represents the silicon atom, and the red balls are the oxygen atoms.)(File:Nesosilicates exhibit, Museum of Geology, South Dakota.jpg|thumb|Nesosilicate specimens at the Museum of Geology in South Dakota)Nesosilicates (from Greek {{wikt-lang|grc|νῆσος}} {{transl|grc|nēsos}} 'island'), or orthosilicates, have the orthosilicate ion, present as isolated (insular) {{chem2|[SiO4](4−)}} tetrahedra connected only by interstitial cations. The Nickel–Strunz classification is 09.A –examples include:

• Phenakite group
  • Phenakite – {{chem2|Be2SiO4}}
  • Willemite – {{chem2|Zn2SiO4}}
• Olivine group
  • Forsterite – {{chem2|Mg2SiO4}}
  • Fayalite – {{chem2|Fe2SiO4}}
  • Tephroite – {{chem2|Mn2SiO4}}
• Garnet group
  • Pyrope – {{chem2|Mg3Al2(SiO4)3}}
  • Almandine – {{chem2|Fe3Al2(SiO4)3}}
  • Spessartine – {{chem2|Mn3Al2(SiO4)3}}
  • Grossular – {{chem2|Ca3Al2(SiO4)3}}
  • Andradite – {{chem2|Ca3Fe2(SiO4)3}}
  • Uvarovite – {{chem2|Ca3Cr2(SiO4)3}}
  • Hydrogrossular – {{chem|Ca|3|Al|2|Si|2|O|8|(SiO|4|)|3−m|(OH)|4m|}}
• Zircon group
  • Zircon – {{chem2|ZrSiO4}}
  • Thorite – {{chem2|(Th,U)SiO4}}
  • Hafnon – {{chem2|(Hf,Zr)SiO4}}

• {{chem2|Al2SiO5}} group
  • Andalusite – {{chem2|Al2SiO5}}
  • Kyanite – {{chem2|Al2SiO5}}
  • Sillimanite – {{chem2|Al2SiO5}}
  • Dumortierite – {{chem|Al|6.5–7|BO|3|(SiO|4|)|3|(O,OH)|3}}
  • Topaz – {{chem2|Al2SiO4(F,OH)2}}
  • Staurolite – {{chem2|Fe2Al9(SiO4)4(O,OH)2}}
• Humite group – {{chem2|(Mg,Fe)7(SiO4)3(F,OH)2}}
  • Norbergite – {{chem2|Mg3(SiO4)(F,OH)2}}
  • Chondrodite – {{chem2|Mg5(SiO4)2(F,OH)2}}
  • Humite – {{chem2|Mg7(SiO4)3(F,OH)2}}
  • Clinohumite – {{chem2|Mg9(SiO4)4(F,OH)2}}
• Datolite – {{chem2|CaBSiO4(OH)}}
• Titanite – {{chem2|CaTiSiO5}}
• Chloritoid – {{chem2|(Fe,Mg,Mn)2Al4Si2O10(OH)4}}
• Mullite (aka Porcelainite) – {{chem2|Al6Si2O13}}

Sorosilicates

(File:Silicate-double-tetrahedra-3D-balls.png|thumb|Pyrosilicate anion {{chem|Si|2|O|7|6-}})(File:Sorosilicates exhibit, Museum of Geology, South Dakota.jpg|thumb|Sorosilicate exhibit at Museum of Geology in South Dakota)Sorosilicates (from Greek {{wikt-lang|grc|σωρός}} {{transl|grc|sōros}} 'heap, mound') have isolated pyrosilicate anions {{chem|Si|2|O|7|6-}}, 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 – {{chem2|(Sc,Y)2(Si2O7)}}
• Hemimorphite (calamine) – {{chem2|Zn4(Si2O7)(OH)2H2O}}
• Lawsonite – {{chem2|CaAl2(Si2O7)(OH)2H2O}}
• Axinite – {{chem2|(Ca,Fe,Mn)3Al2(BO3)(Si4O12)(OH)}}
• Ilvaite – {{chem2|CaFe^{II}2Fe^{III}O(Si2O7)(OH)}}
• Epidote group (has both {{chem2|(SiO4)(4−)}} and {{chem2|(Si2O7)(6−)}} groups}
  • Epidote – {{chem2|Ca2(Al,Fe)3O(SiO4)(Si2O7)(OH)}}
  • Zoisite – {{chem2|Ca2Al3O(SiO4)(Si2O7)(OH)}}
    • Tanzanite – {{chem2|Ca2Al3O(SiO4)(Si2O7)(OH)}}
  • Clinozoisite – {{chem2|Ca2Al3O(SiO4)(Si2O7)(OH)}}
  • Allanite – {{chem2|Ca(Ce,La,Y,Ca)Al2(Fe^{II},Fe^{III})O(SiO4)(Si2O7)(OH)}}
  • Dollaseite-(Ce) – {{chem2|CaCeMg2AlSi3O11F(OH)}}
• Vesuvianite (idocrase) – {{chem2|Ca10(Mg,Fe)2Al4(SiO4)5(Si2O7)2(OH)4}}

Cyclosilicates

(File:Cyclosilicate exhibit, Museum of Geology, South Dakota.jpg|thumb|Cyclosilicate specimens at the Museum of Geology, South Dakota)File:Pezzottaite-256889.jpg|thumb|PezzottaitePezzottaiteFile:Bazzite - Fibbia Ticino Switzerland.jpg|thumb|BazziteBazziteCyclosilicates (from Greek {{wikt-lang|grc|κύκλος}} {{transl|grc|kýklos}} '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:File:Beryll.ring.combined.png|6 units {{chem2|[Si6O18]}}, beryl (red: Si, blue: O)File:Benitoid.2200.png|3 units {{chem2|[Si3O9]}}, benitoiteFile:Papagoite.2200.png|4 units {{chem2|[Si4O12]}}, papagoiteFile:Eudialyte.2200.png|9 units {{chem2|[Si9O27]}}, eudialyteFile:Milarite.png|12 units, double ring {{chem2|[Si12O30]}}, milariteSome example minerals are:

• 3-member single ring
  • Benitoite – {{chem2|BaTi(Si3O9)}}
• 4-member single ring
  • Papagoite – {{chem|CaCuAlSi|2|O|6|(OH)|3}}.
• 6-member single ring
  • Beryl – {{chem2|Be3Al2(Si6O18)}}
  • Bazzite – {{chem2|Be3Sc2(Si6O18)}}
  • Sugilite – {{chem2|KNa2(Fe,Mn,Al)2Li3Si12O30}}
  • Tourmaline – {{chem|(Na,Ca)(Al,Li,Mg)|3–|(Al,Fe,Mn)|6|(Si|6|O|18|)(BO|3|)|3|(OH)|4|}}
  • Pezzottaite – {{chem2|Cs(Be2Li)Al2Si6O18}}
  • Osumilite – {{chem2|(K,Na)(Fe,Mg)2(Al,Fe)3(Si,Al)12O30}}
  • Cordierite – {{chem2|(Mg,Fe)2Al4Si5O18}}
  • Sekaninaite – {{chem2|(Fe^{+2},Mg)2Al4Si5O18}}
• 9-member single ring
  • Eudialyte – {{chem|Na|15|Ca|6|(Fe,Mn)|3|Zr|3|SiO|(O,OH,H|2|O)|3|(Si|3|O|9|)|2}}{{chem|(Si|9|O|27|)|2|(OH,Cl)|2}}
• 6-member double ring
  • Milarite – {{chem2|K2Ca4Al2Be4(Si24O60)H2O}}

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

Inosilicates

Inosilicates (from Greek {{wikt-lang|grc|ἴς}} {{transl|grc|is}} [genitive: {{wikt-lang|grc|ἰνός}} {{transl|grc|inos}}] 'fibre'), or chain silicates, have interlocking chains of silicate tetrahedra with either {{chem2|SiO3}}, 1:3 ratio, for single chains or {{chem2|Si4O11}}, 4:11 ratio, for double chains. The Nickel–Strunz classification is 09.D – examples include:

Single chain inosilicates

• Pyroxene group
  • Enstatite – orthoferrosilite series
    • Enstatite – {{chem2|MgSiO3}}
    • Ferrosilite – {{chem2|FeSiO3}}
  • Pigeonite – {{chem2|Ca0.25(Mg,Fe)1.75Si2O6}}
  • Diopside – hedenbergite series
    • Diopside – {{chem2|CaMgSi2O6}}
    • Hedenbergite – {{chem2|CaFeSi2O6}}
    • Augite – {{chem2|(Ca,Na)(Mg,Fe,Al)(Si,Al)2O6}}
  • Sodium pyroxene series
    • Jadeite – {{chem2|NaAlSi2O6}}
    • Aegirine (or acmite) – {{chem2|NaFe^{III}Si2O6}}
  • Spodumene – {{chem2|LiAlSi2O6}}
  • Pyroxferroite - {{chem2|(Fe,Ca)SiO3}}
• Pyroxenoid group
  • Wollastonite – {{chem2|CaSiO3}}
  • Rhodonite – {{chem2|MnSiO3}}
  • Pectolite – {{chem2|NaCa2(Si3O8)(OH)}}

Double chain inosilicates

• Amphibole group
  • Anthophyllite – {{chem2|(Mg,Fe)7Si8O22(OH)2}}
  • Cummingtonite series
    • Cummingtonite – {{chem2|Fe2Mg5Si8O22(OH)2}}
    • Grunerite – {{chem2|Fe7Si8O22(OH)2}}
  • Tremolite series
    • Tremolite – {{chem2|Ca2Mg5Si8O22(OH)2}}
    • Actinolite – {{chem2|Ca2(Mg,Fe)5Si8O22(OH)2}}
  • Hornblende – {{chem|(Ca,Na)|2–3|(Mg,Fe,Al)|5|Si|6|(Al,Si)|2|O|22|(OH)|2|}}
  • Sodium amphibole group
    • Glaucophane – {{chem2|Na2Mg3Al2Si8O22(OH)2}}
    • Riebeckite (asbestos) – {{chem2|Na2Fe^{II}3Fe^{III}2Si8O22(OH)2}}
    • Arfvedsonite – {{chem2|Na3(Fe,Mg)4FeSi8O22(OH)2}}

File:Pyroxen-chain.png|Inosilicate, pyroxene family, with 2-periodic single chain {{chem2|(Si2O6)}}, diopsideFile:Tremolite-chain.png|Inosilicate, clinoamphibole, with 2-periodic double chains {{chem2|(Si4O11)}}, tremoliteFile:Wollastonite-chain.png|Inosilicate, unbranched 3-periodic single chain of wollastoniteFile:Rhodonite-chain.png|Inosilicate with 5-periodic single chain, rhodoniteFile:Pellyite-chain.png|Inosilicate with cyclic branched 8-periodic chain, pellyite

Phyllosilicates

Phyllosilicates (from Greek {{wikt-lang|grc|φύλλον}} {{transl|grc|phýllon}} 'leaf'), or sheet silicates, form parallel sheets of silicate tetrahedra with {{chem2|Si2O5}} or a 2:5 ratio. The Nickel–Strunz classification is 09.E. All phyllosilicate minerals are hydrated, with either water or hydroxyl groups attached. Examples include:

• Serpentine subgroup
  • Antigorite – {{chem2|Mg3Si2O5(OH)4}}
  • Chrysotile – {{chem2|Mg3Si2O5(OH)4}}
  • Lizardite – {{chem2|Mg3Si2O5(OH)4}}
• Clay minerals group
  • 1:1 clay minerals (TO)
    • Halloysite – {{chem2|Al2Si2O5(OH)4}}
    • Kaolinite – {{chem2|Al2Si2O5(OH)4}}
  • 2:1 clay minerals (TOT)
    • Pyrophyllite – {{chem2|Al2Si4O10(OH)2}}
    • Talc – {{chem2|Mg3Si4O10(OH)2}}
    • Illite – {{chem2|(K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2,(H2O)]}}
    • Montmorillonite (smectite) – {{chem2|(Na,Ca)0.33(Al,Mg)2Si4O10(OH)2nH2O}}
    • Chlorite – {{chem2|(Mg,Fe)3(Si,Al)4O10(OH)2(Mg,Fe)3(OH)6}}
    • Vermiculite – {{chem2|(Mg,Fe,Al)3(Al,Si)4O10(OH)24H2O}}
  • Other clay minerals
    • Sepiolite – {{chem2|Mg4Si6O15(OH)26H2O}}
    • Palygorskite (or attapulgite) – {{chem2|(Mg,Al)2Si4O10(OH)4(H2O)}}
• Mica group
  • Biotite – {{chem2|K(Mg,Fe)3(AlSi3)O10(OH)2}}
  • Fuchsite – {{chem2|K(Al,Cr)2(AlSi3)O10(OH)2}}
  • Muscovite – {{chem2|KAl2(AlSi3)O10(OH)2}}
  • Phlogopite – {{chem2|KMg3(AlSi3)O10(OH)2}}
  • Lepidolite – {{chem|K(Li,Al)|2–3|(AlSi|3|)O|10|(OH)|2|}}
  • Margarite – {{chem2|CaAl2(Al2Si2)O10(OH)2}}
  • Glauconite – {{chem2|(K,Na)(Al,Mg,Fe)2(Si,Al)4O10(OH)2}}

File:Muskovite.sheet.png|Phyllosilicate, mica group, muscovite (red: Si, blue: O)File:Apophyllite.sheet.png|Phyllosilicate, single net of tetrahedra with 4-membered rings, apophyllite-(KF)-apophyllite-(KOH) seriesFile:Pyrosmalite.sheet.png|Phyllosilicate, single tetrahedral nets of 6-membered rings, pyrosmalite-(Fe)-pyrosmalite-(Mn) seriesFile:Zeophyllite.sheet.png|Phyllosilicate, single tetrahedral nets of 6-membered rings, zeophylliteFile:Carletonite.sheet.png|Phyllosilicate, double nets with 4- and 6-membered rings, carletonite

Tectosilicates

File:Beta-quartz-CM-2D-balls.png|thumb|Silica family {{chem2|(SiO2}} 3D network), β-quartzquartzFile:Zeolite-ZSM-5-vdW.png|thumb|Aluminosilicate family, the 3D model of synthetic zeolitezeolite Tectosilicates, or "framework silicates," have a three-dimensional framework of silicate tetrahedra with {{chem2|SiO2}} in a 1:2 ratio. This group comprises nearly 75% of the crust of the Earth.BOOK, Deer, W.A., Howie, R.A., Wise, W.S., Zussman, J., 2004, Rock-forming minerals. Volume 4B. Framework silicates: silica minerals. Feldspathoids and the zeolites, 2nd, Geological Society of London, London, 982 pp, Tectosilicates, with the exception of the quartz group, are aluminosilicates. The Nickel–Strunz classifications are 09.F and 09.G, 04.DA (Quartz/ silica family). Examples include:

• 3D-Silicates, quartz family
  • Quartz – {{chem2|SiO2}}
  • Tridymite – {{chem2|SiO2}}
  • Cristobalite – {{chem2|SiO2}}
  • Coesite – {{chem2|SiO2}}
  • Stishovite – {{chem2|SiO2}}
  • Moganite – {{chem2|SiO2}}
  • Chalcedony – {{chem2|SiO2}}
• Tectosilicates, feldspar group
  • Alkali feldspars (potassium feldspars)
    • Microcline – {{chem2|KAlSi3O8}}
    • Orthoclase – {{chem2|KAlSi3O8}}
    • Anorthoclase – {{chem2|(Na,K)AlSi3O8}}
    • Sanidine – {{chem2|KAlSi3O8}}
  • Plagioclase feldspars
    • Albite – {{chem2|NaAlSi3O8}}
    • Oligoclase – {{chem2|(Na,Ca)(Si,Al)4O8}}     (Na:Ca 4:1)
    • Andesine – {{chem2|(Na,Ca)(Si,Al)4O8}}     (Na:Ca 3:2)
    • Labradorite – {{chem2|(Ca,Na)(Si,Al)4O8}}     (Na:Ca 2:3)
    • Bytownite – {{chem2|(Ca,Na)(Si,Al)4O8}}     (Na:Ca 1:4)
    • Anorthite – {{chem2|CaAl2Si2O8}}
• Tectosilicates, feldspathoid family
  • Nosean – {{chem2|Na8Al6Si6O24(SO4)}}
  • Cancrinite –{{chem2| Na6Ca2(CO3,Al6Si6O24)}}{{Hydrate|2}}
  • Leucite – {{chem2|KAlSi2O6}}
  • Nepheline – {{chem2|(Na,K)AlSiO4}}
  • Sodalite – {{chem2|Na8(AlSiO4)6Cl2}}
  • Hauyne – {{chem|(Na,Ca)|4–8|Al|6|Si|6|(O,S)24(SO|4|,Cl)|1–2|}}
    • Lazurite – {{chem2|(Na,Ca)8(AlSiO4)6(SO4,S,Cl)2}}
• Tectosilicates, scapolite group
  • Marialite – {{chem2|Na4(AlSi3O8)3(Cl2,CO3,SO4)}}
  • Meionite – {{chem2|Ca4(Al2Si2O8)3(Cl2CO3,SO4)}}
• Tectosilicates, zeolite family
  • Natrolite – {{chem2|Na2Al2Si3O102H2O}}
  • Erionite – {{chem2|(Na2,K2,Ca)2Al4Si14O3615H2O}}
  • Chabazite – {{chem2|CaAl2Si4O126H2O}}
  • Heulandite – {{chem2|CaAl2Si7O186H2O}}
  • Stilbite – {{chem2|NaCa2Al5Si13O3617H2O}}
  • Scolecite – {{chem2|CaAl2Si3O103H2O}}
  • Mordenite – {{chem2|(Ca,Na2,K2)Al2Si10O247H2O}}
  • Analcime – {{chem2|NaAlSi2O6H2O}}

See also

• {{annotated link|Classification of non-silicate minerals}}
• {{annotated link|Classification of silicate minerals}}
• {{annotated link|Silicate mineral paint}}

References

{{reflist}}

External links

• Mindat.org, Dana classification
• Webmineral : Dana's New Silicate Classification

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