1. General Structure

A silicate mineral is generally an ionic compound whose anions consist predominantly of silicon and oxygen 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 covalently 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 cations. For example, in the mineral orthoclase [KAlSi₃O₈]_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 [SiO₂]_n. Replacement of one in every four silicon atoms by an aluminum atom results in the anion [AlSi₃O−8]_n, whose charge is neutralized by the potassium cations K⁺.

2. Main Groups

In mineralogy, silicate minerals are classified into seven major groups according to the structure of their silicate anion:^[1][2]

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.

3. Nesosilicates or Orthosilicates

Orthosilicate anion SiO4−4. The grey ball represents the silicon atom, and the red balls are the oxygen atoms. https://handwiki.org/wiki/index.php?curid=1256484

Nesosilicate specimens at the Museum of Geology in South Dakota. https://handwiki.org/wiki/index.php?curid=1124555

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. The Nickel–Strunz classification is 09.A –examples include:

• Phenakite group
  • Phenakite – Be₂SiO₄
  • Willemite – Zn₂SiO₄
• Olivine group
  • Forsterite – Mg₂SiO₄
  • Fayalite – Fe₂SiO₄
  • Tephroite – Mn₂SiO₄
• Garnet group
  • Pyrope – Mg₃Al₂(SiO₄)₃
  • Almandine – Fe₃Al₂(SiO₄)₃
  • Spessartine – Mn₃Al₂(SiO₄)₃
  • Grossular – Ca₃Al₂(SiO₄)₃
  • Andradite – Ca₃Fe₂(SiO₄)₃
  • Uvarovite – Ca₃Cr₂(SiO₄)₃
  • Hydrogrossular – Ca₃Al₂Si₂O₈(SiO₄)_3−m(OH)_4m
• Zircon group
  • Zircon – ZrSiO₄
  • Thorite – (Th,U)SiO₄
  • Hafnon – (Hf,Zr)SiO₄

Kyanite crystals (unknown scale). https://handwiki.org/wiki/index.php?curid=1076808

• Al₂SiO₅ group
  • Andalusite – Al₂SiO₅
  • Kyanite – Al₂SiO₅
  • Sillimanite – Al₂SiO₅
  • Dumortierite – Al_6.5–7BO₃(SiO₄)₃(O,OH)₃
  • Topaz – Al₂SiO₄(F,OH)₂
  • Staurolite – Fe₂Al₉(SiO₄)₄(O,OH)₂
• Humite group – (Mg,Fe)₇(SiO₄)₃(F,OH)₂
  • Norbergite – Mg₃(SiO₄)(F,OH)₂
  • Chondrodite – Mg₅(SiO₄)₂(F,OH)₂
  • Humite – Mg₇(SiO₄)₃(F,OH)₂
  • Clinohumite – Mg₉(SiO₄)₄(F,OH)₂
• Datolite – CaBSiO₄(OH)
• Titanite – CaTiSiO₅
• Chloritoid – (Fe,Mg,Mn)₂Al₄Si₂O₁₀(OH)₄
• Mullite (aka Porcelainite) – Al₆Si₂O₁₃

4. Sorosilicates

Pyrosilicate anion Si₂O6−7. https://handwiki.org/wiki/index.php?curid=1467276

Sorosilicate exhibit at Museum of Geology in South Dakota. https://handwiki.org/wiki/index.php?curid=1971698

Sorosilicates (from Greek σωρός sōros, heap, mound) have isolated pyrosilicate anions Si₂O6−7, 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:

• Hemimorphite (calamine) – Zn₄(Si₂O₇)(OH)₂·H₂O
• Lawsonite – CaAl₂(Si₂O₇)(OH)₂·H₂O
• Axinite – (Ca,Fe,Mn)₃Al₂(BO₃)(Si₄O₁₂)(OH)
• Ilvaite – CaFe^II₂Fe^IIIO(Si₂O₇)(OH)
• Epidote group (has both (SiO₄)⁴⁻ and (Si₂O₇)⁶⁻ groups)
  • Epidote – Ca₂(Al,Fe)₃O(SiO₄)(Si₂O₇)(OH)
  • Zoisite – Ca₂Al₃O(SiO₄)(Si₂O₇)(OH)
    • Tanzanite – Ca₂Al₃O(SiO₄)(Si₂O₇)(OH)
  • Clinozoisite – Ca₂Al₃O(SiO₄)(Si₂O₇)(OH)
  • Allanite – Ca(Ce,La,Y,Ca)Al₂(Fe^II,Fe^III)O(SiO₄)(Si₂O₇)(OH)
  • Dollaseite-(Ce) – CaCeMg₂AlSi₃O₁₁F(OH)
• Vesuvianite (idocrase) – Ca₁₀(Mg,Fe)₂Al₄(SiO₄)₅(Si₂O₇)₂(OH)₄

5. Cyclosilicates

Cyclosilicate specimens at the Museum of Geology, South Dakota. https://handwiki.org/wiki/index.php?curid=1361484

Pezzottaite. https://handwiki.org/wiki/index.php?curid=1453920

Bazzite. https://handwiki.org/wiki/index.php?curid=1872869

Cyclosilicates (from Greek κύκλος kuklos, circle), or ring silicates, have three or more tetrahedra linked in a ring. The general formula is (Si_xO_3x)^2x−, where one or more silicon atoms can be replaced by other 4-coordinated atom. The silicon:oxygen ratio is 1:3. Double rings have the formula (Si_2xO_6x)^2x−. The Nickel–Strunz classification is 09.C. Possible ring sizes include:

• 

  6 units [Si₆O₁₈], beryl (red: Si, blue: O). https://handwiki.org/wiki/index.php?curid=1485628

• 

  3 units [Si₃O₉], benitoite. https://handwiki.org/wiki/index.php?curid=1415149

• 

  4 units [Si₄O₁₂], papagoite. https://handwiki.org/wiki/index.php?curid=1256622

• 

  9 units [Si₉O₂₇], eudialyte. https://handwiki.org/wiki/index.php?curid=1594971

• 

  6 units, double ring [Si₆O₁₈], milarite. https://handwiki.org/wiki/index.php?curid=1104046

Some example minerals are:

• 3-member single ring
  • Benitoite – BaTi(Si₃O₉)
• 4-member single ring
  • Papagoite – CaCuAlSi₂O₆(OH)₃.
• 6-member single ring
  • Beryl – Be₃Al₂(Si₆O₁₈)
  • Bazzite – Be₃Sc₂(Si₆O₁₈)
  • Sugilite – KNa₂(Fe,Mn,Al)₂Li₃Si₁₂O₃₀
  • Tourmaline – (Na,Ca)(Al,Li,Mg)₃₋(Al,Fe,Mn)₆(Si₆O₁₈)(BO₃)₃(OH)₄
  • Pezzottaite – Cs(Be₂Li)Al₂Si₆O₁₈
  • Osumilite – (K,Na)(Fe,Mg)₂(Al,Fe)₃(Si,Al)₁₂O₃₀
  • Cordierite – (Mg, Fe)₂Al₄Si₅O₁₈
  • Sekaninaite – (Fe⁺², Mg)₂Al₄Si₅O₁₈
• 9-member single ring
  • Eudialyte – Na₁₅Ca₆(Fe,Mn)₃Zr₃SiO(O,OH,H₂O)₃(Si₃O₉)₂(Si₉O₂₇)₂(OH,Cl)₂
• 6-member double ring
  • Milarite – K₂Ca₄Al₂Be₄(Si₂₄O₆₀)H₂O

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.

6. 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. The Nickel–Strunz classification is 09.D – examples include:

6.1. Single Chain Inosilicates

• Pyroxene group
  • Enstatite – orthoferrosilite series
    • Enstatite – MgSiO₃
    • Ferrosilite – FeSiO₃
  • Pigeonite – Ca_0.25(Mg,Fe)_1.75Si₂O₆
  • Diopside – hedenbergite series
    • Diopside – CaMgSi₂O₆
    • Hedenbergite – CaFeSi₂O₆
    • Augite – (Ca,Na)(Mg,Fe,Al)(Si,Al)₂O₆
  • Sodium pyroxene series
    • Jadeite – NaAlSi₂O₆
    • Aegirine (or acmite) – NaFe^IIISi₂O₆
  • Spodumene – LiAlSi₂O₆
  • Pyroxferroite - (Fe,Ca)SiO₃
• Pyroxenoid group
  • Wollastonite – CaSiO₃
  • Rhodonite – MnSiO₃
  • Pectolite – NaCa₂(Si₃O₈)(OH)

6.2. Double Chain Inosilicates

• Amphibole group
  • Anthophyllite – (Mg,Fe)₇Si₈O₂₂(OH)₂
  • Cummingtonite series
    • Cummingtonite – Fe₂Mg₅Si₈O₂₂(OH)₂
    • Grunerite – Fe₇Si₈O₂₂(OH)₂
  • Tremolite series
    • Tremolite – Ca₂Mg₅Si₈O₂₂(OH)₂
    • Actinolite – Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂
  • Hornblende – (Ca,Na)_2–3(Mg,Fe,Al)₅Si₆(Al,Si)₂O₂₂(OH)₂
  • Sodium amphibole group
    • Glaucophane – Na₂Mg₃Al₂Si₈O₂₂(OH)₂
    • Riebeckite (asbestos) – Na₂Fe^II₃Fe^III₂Si₈O₂₂(OH)₂
    • Arfvedsonite – Na₃(Fe,Mg)₄FeSi₈O₂₂(OH)₂

• Inosilicate, pyroxene family, with 2-periodic single chain (Si₂O₆), diopside. https://handwiki.org/wiki/index.php?curid=1932185

• 

  Inosilicate with 5-periodic single chain, rhodonite. https://handwiki.org/wiki/index.php?curid=1388024

• 

  Inosilicate with cyclic branched 8-periodic chain, pellyite. https://handwiki.org/wiki/index.php?curid=1839329

7. Phyllosilicates

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 hydrated, with either water or hydroxyl groups attached.

Kaolinite. https://handwiki.org/wiki/index.php?curid=1714717

Examples include:

• Serpentine subgroup
  • Antigorite – Mg₃Si₂O₅(OH)₄
  • Chrysotile – Mg₃Si₂O₅(OH)₄
  • Lizardite – Mg₃Si₂O₅(OH)₄
• Clay minerals group
  • Halloysite – Al₂Si₂O₅(OH)₄
  • Kaolinite – Al₂Si₂O₅(OH)₄
  • Illite – (K,H₃O)(Al,Mg,Fe)₂(Si,Al)₄O₁₀[(OH)₂,(H₂O)]
  • Montmorillonite – (Na,Ca)_0.33(Al,Mg)₂Si₄O₁₀(OH)₂·nH₂O
  • Vermiculite – (MgFe,Al)₃(Al,Si)₄O₁₀(OH)₂·4H₂O
  • Talc – Mg₃Si₄O₁₀(OH)₂
  • Sepiolite – Mg₄Si₆O₁₅(OH)₂·6H₂O
  • Palygorskite (or attapulgite) – (Mg,Al)₂Si₄O₁₀(OH)·4(H₂O)
  • Pyrophyllite – Al₂Si₄O₁₀(OH)₂
• Mica group
  • Biotite – K(Mg,Fe)₃(AlSi₃)O₁₀(OH)₂
  • Fuchsite – K(Al,Cr)₂(AlSi₃O₁₀)(OH)₂
  • Muscovite – KAl₂(AlSi₃)O₁₀(OH)₂
  • Phlogopite – KMg₃(AlSi₃)O₁₀(OH)₂
  • Lepidolite – K(Li,Al)_2–3(AlSi₃)O₁₀(OH)₂
  • Margarite – CaAl₂(Al₂Si₂)O₁₀(OH)₂
  • Glauconite – (K,Na)(Al,Mg,Fe)₂(Si,Al)₄O₁₀(OH)₂
• Chlorite group
  • Chlorite – (Mg,Fe)₃(Si,Al)₄O₁₀(OH)₂·(Mg,Fe)₃(OH)₆

• 

  Phyllosilicate, mica group, muscovite (red: Si, blue: O). https://handwiki.org/wiki/index.php?curid=1536194

• 

  Phyllosilicate, single net of tetrahedra with 4-membered rings, apophyllite-(KF)-apophyllite-(KOH) series. https://handwiki.org/wiki/index.php?curid=1496820

• 

  Phyllosilicate, single tetrahedral nets of 6-membered rings, pyrosmalite-(Fe)-pyrosmalite-(Mn) series. https://handwiki.org/wiki/index.php?curid=1244572

• 

  Phyllosilicate, single tetrahedral nets of 6-membered rings, zeophyllite. https://handwiki.org/wiki/index.php?curid=1289382

• 

  Phyllosilicate, double nets with 4- and 6-membered rings, carletonite. https://handwiki.org/wiki/index.php?curid=1890660

8. Tectosilicates

Silica family (SiO₂ 3D network), β-quartz. https://handwiki.org/wiki/index.php?curid=1851778

The 3D aluminosilicate anion of synthetic zeolite ZSM-5. https://handwiki.org/wiki/index.php?curid=1983394

Quartz. https://handwiki.org/wiki/index.php?curid=1811157

Lunar ferroan anorthosite (plagioclase feldspar) collected by Apollo 16 astronauts from the Lunar Highlands near Descartes Crater. https://handwiki.org/wiki/index.php?curid=1971457

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.^[3] 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 – SiO₂
  • Tridymite – SiO₂
  • Cristobalite – SiO₂
  • Coesite – SiO₂
  • Stishovite – SiO₂
  • Moganite – SiO₂
  • Chalcedony – SiO₂
• Tectosilicates, feldspar group
  • Alkali feldspars (potassium feldspars)
    • Microcline – KAlSi₃O₈
    • Orthoclase – KAlSi₃O₈
    • Anorthoclase – (Na,K)AlSi₃O₈
    • Sanidine – KAlSi₃O₈
  • Plagioclase feldspars
    • Albite – NaAlSi₃O₈
    • Oligoclase – (Na,Ca)(Si,Al)₄O₈     (Na:Ca 4:1)
    • Andesine – (Na,Ca)(Si,Al)₄O₈     (Na:Ca 3:2)
    • Labradorite – (Ca,Na)(Si,Al)₄O₈     (Na:Ca 2:3)
    • Bytownite – (Ca,Na)(Si,Al)₄O₈     (Na:Ca 1:4)
    • Anorthite – CaAl₂Si₂O₈
• Tectosilicates, feldspathoid family
  • Nosean – Na₈Al₆Si₆O₂₄(SO₄)
  • Cancrinite – Na₆Ca₂(CO₃,Al₆Si₆O₂₄) • 2H₂O
  • Leucite – KAlSi₂O₆
  • Nepheline – (Na,K)AlSiO₄
  • Sodalite – Na₈(AlSiO₄)₆Cl₂
  • Hauyne – (Na,Ca)_4–8Al₆Si₆(O,S)24(SO₄,Cl)_1–2
    • Lazurite – (Na,Ca)₈(AlSiO₄)₆(SO₄,S,Cl)₂
• Tectosilicates, scapolite group
  • Marialite – Na₄(AlSi₃O₈)₃(Cl₂,CO₃,SO₄)
  • Meionite – Ca₄(Al₂Si₂O₈)₃(Cl₂CO₃,SO₄)
• Tectosilicates, zeolite family
  • Natrolite – Na₂Al₂Si₃O₁₀·2H₂O
  • Erionite – (Na₂,K₂,Ca)₂Al₄Si₁₄O₃₆·15H₂O
  • Chabazite – CaAl₂Si₄O₁₂·6H₂O
  • Heulandite – CaAl₂Si₇O₁₈·6H₂O
  • Stilbite – NaCa₂Al₅Si₁₃O₃₆·17H₂O
  • Scolecite – CaAl₂Si₃O₁₀·3H₂O
  • Mordenite – (Ca,Na₂,K₂)Al₂Si₁₀O₂₄·7H₂O
  • Analcime – NaAlSi₂O₆·H₂O

The content is sourced from: https://handwiki.org/wiki/Chemistry:Silicate_minerals