Silicate minerals

Last updated on 23 July 2017

Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of rock-forming minerals and make up approximately 90 percent of the Earth's crust.[1] They are classified based on the structure of their silicate groups, which contain different ratios of silicon and oxygen.

Chrysocolla.jpg
Chrysocolla.jpg

Nesosilicates or orthosilicates

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Basic (ortho-)silicate anion structure
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Nesosilicate specimens at the Museum of Geology in South Dakota

Nesosilicates (from Greek νῆσος nēsos, island), or orthosilicates, have the orthosilicate ion, which constitute isolated (insular) [SiO4]4− tetrahedra that are connected only by interstitial cations. Nickel–Strunz classification: 09.A

Examples are:

Kyanite crystals.jpg
Kyanite crystals (unknown scale)

Sorosilicates

Sorosilicates exhibit, Museum of Geology, South Dakota.jpg
Sorosilicate exhibit at Museum of Geology in South Dakota

Sorosilicates (from Greek σωρός sōros, heap, mound) have isolated double tetrahedra groups with (Si2O7)6− or a ratio of 2:7. Nickel–Strunz classification: 09.B

Examples are:

Cyclosilicates

Cyclosilicate exhibit, Museum of Geology, South Dakota.jpg
Cyclosilicate specimens at the Museum of Geology, South Dakota

Cyclosilicates (from Greek κύκλος kuklos, circle), or ring silicates, have linked tetrahedra with (TxO3x)2x or a ratio of 1:3. These exist as 3-member (T3O9)6− and 6-member (T6O18)12− rings, where T stands for a tetrahedrally coordinated cation. Nickel–Strunz classification: 09.C

Examples are:

  • 3-member ring
  • 6-member ring

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

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Cyclosilicate, [Si6O18] – 6-membered single rings, beryl (red: Si, blue: O)

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Cyclosilicate, [Si3O9] – 3-membered single ring, benitoite

Papagoite.2200.png

Cyclosilicate, [Si4O12] – 4-membered single ring, papagoite

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Cyclosilicate, [Si9O27] – 9-membered ring, eudialyte

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Cyclosilicate, [Si6O18] – 6-membered double ring, milarite

Inosilicates

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

Examples are:

Single chain inosilicates

Double chain inosilicates

Inosilicate, pyroxene family, with 2-periodic single chain (Si2O6), diopside

Inosilicate, clinoamphibole, with 2-periodic double chains (Si4O11), tremolite

Inosilicate, unbranched 3-periodic single chain of wollastonite

Inosilicate with 5-periodic single chain, rhodonite

Inosilicate with cyclic branched 8-periodic chain, pellyite

Phyllosilicates

Phyllosilicates (from Greek φύλλον phyllon, leaf), or sheet silicates, form parallel sheets of silicate tetrahedra with Si2O5 or a 2:5 ratio. Nickel–Strunz classification: 09.E. All phyllosilicate minerals are hydrated, with either water or hydroxyl groups attached.

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Kaolinite

Examples are:

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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

Pyrosmalite.sheet.png

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

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

Lunar Ferroan Anorthosite (60025).jpg
Lunar ferroan anorthosite (plagioclase feldspar) collected by Apollo 16 astronauts from the Lunar Highlands near Descartes Crater

Examples are:

Gallery

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Nesosilicate (SiO4)

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Sorosilicate (Si2O7), as in suolunite
[Ca2Si2O5(OH)2·H2O]

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Tectosilicate, aluminosilicate 3D network, zeolite family, synthetic zeolite ZSM-5

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Silica family (SiO2 3D network), β-quartz

See also

Further references

  • 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 ed.). London: Geological Society of London. p. 982 pp.
  • Hurlbut, Cornelius S. (1966). Dana's Manual of Mineralogy (17th ed.). ISBN 0-471-03288-3.
  • Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20th ed.). Wiley. ISBN 0-471-80580-7.

External links

Media related to Silicates at Wikimedia Commons

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