Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals. They are classified based on the structure of their silicate ion group.

Subclasses:

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Nesosilicates or Isosilicates

Nesosilicates (or orthosilicates) have isolated [SiO₄]⁴⁻

tetrahedra that are connected only by interstitial cations.

• Phenacite group
  • Phenacite - Be₂SiO₄
  • Willemite - Zn₂SiO₄
• Olivine group
  • Forsterite - Mg₂SiO₄
  • Fayalite - Fe₂SiO₄
• 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)_1-m(OH)_4m
• Zircon group
  • Zircon - Zr₂SiO₄
  • Thorite - (Th,U)₂SiO₄
• 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)(F,OH)₂
  • Humite - Mg₇(SiO₄)(F,OH)₂
  • Clinohumite - Mg₉(SiO₄)(F,OH)₂
• Datolite - CaBSiO₄(OH)
• Titanite - CaTiSiO₅
• Chloritoid - (Fe,Mg,Mn)₂Al₄Si₂O₁₀(OH)₄

Sorosilicates

Sorosilicates have isolated double tetrahedra groups with (Si₂O₇)⁶⁻ or a ratio of 2:7.

• Hemimorphite (calamine) - Zn₄(Si₂O₇)(OH)₂·H₂O
• Lawsonite - CaAl₂(Si₂O₇)(OH)₂·H₂O
• Ilvaite - CaFe²⁺₂Fe³⁺O(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)
  • Clinozoisite - Ca₂Al₃O(SiO₄)(Si₂O₇)(OH)
  • Tanzanite - Ca₂Al₃O(SiO₄)(Si₂O₇)(OH)
  • Allanite - Ca(Ce,La,Y,Ca)Al₂(Fe²⁺,Fe³⁺)O(SiO₄)(Si₂O₇)(OH)
• Vesuvianite (idocrase) - Ca₁₀(Mg,Fe)₂Al₄(SiO₄)₅(Si₂O₇)₂(OH)₄

Cyclosilicates

Cyclosilicates, ring silicates, have linked tetrahedra with (Si_xO_3x)^2x- or a ratio of 1:3. These exists as 3-member (Si₃O₉)^6-, 4-member (Si₄O₁₂)^8- and 6-member (Si₆O₁₈)^12- rings.

• 3-member ring
  • Benitoite - BaTi(Si₃O₉)
• 4-member ring
  • Axinite - (Ca,Fe,Mn)₃Al₂(BO₃)(Si₄O₁₂)(OH)
• 6-member ring
  • Beryl/Emerald - Be₃Al₂(Si₆O₁₈)
  • Cordierite - (Mg,Fe)₂Al₃(Si₅AlO₁₈)
  • Tourmaline - (Na,Ca)(Al,Li,Mg)_3-(Al,Fe,Mn)₆(Si₆O₁₈)(BO₃)₃(OH)₄

Inosilicates

Inosilicates, 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.

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 (Acmite) - NaFe³⁺Si₂O₆
  • Spodumene - LiAlSi₂O₆
• Pyroxenoid group
  • Wollastonite - CaSiO₃
  • Rhodonite - MnSiO₃
  • Pectolite - NaCa₂(Si₃O₈)(OH)

Double chain inosilicates

• Amphibole group
  • Anthophyllite - (Mg,Fe)₇Si₈O₂₂(OH)₂
  • Cumingtonite series
    • Cummingtonite - Fe₂Mg₅Si₈O₂₂(OH)₂
    • Grunerite - Fe₇Si₈O₂₂(OH)₂
  • Tremolite series
    • Tremolite - Ca₂Mg₅Si₈O₂₂(OH)₂
    • ActinoliteCa₂(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)
    • Riebeckite (asbestos) - Na₂Fe²⁺₃Fe³⁺₂Si₈O₂₂(OH)₂
    • Arfvedsonite - Na₃(Fe,Mg)₄FeSi₈O₂₂(OH)₂

Phyllosilicates

Phyllosilicates, sheet silicates (from Greek φύλλον phyllon, leaf), form parallel sheets of silicate tetrahedra with Si₂O₅ or a 2:5 ratio.

• Serpentine group
  • Antigorite - Mg₃Si₂O₅(OH)₄
  • Chrysotile - Mg₃Si₂O₅(OH)₄
  • Lizardite - Mg₃Si₂O₅(OH)₄
• Clay mineral group
  • Kaolinite - Al₂Si₂O₅(OH)₄
  • Illite - (K,H₃O)(Al,Mg,Fe)₂(Si,Al)₄O₁₀[(OH)₂,(H₂O)]
  • Smectite -
  • Montmorillonite - (Na,Ca)_0.33(Al,Mg)₂(Si₄O₁₀)(OH)₂·nH₂O
  • Vermiculite - (MgFe,Al)₃(Al,Si)₄O₁₀(OH)₂·4H₂O
• Talc - Mg₃Si₄O₁₀(OH)₂
• Pyrophyllite - Al₂Si₄O₁₀(OH)₂
• Mica group
  • Biotite - K(Mg,Fe)₃(AlSi₃O₁₀)(OH)₂
  • Muscovite - KAl₂(AlSi₃O₁₀)(OH)₂
  • Phlogopite - KMg₃Si₄O₁₀(OH)₂
  • Lepidolite - K(Li,Al)_2-3(AlSi₃O₁₀)(OH)₂
  • Margarite - CaAl₂(Al₂Si₂O₁₀)(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

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.

• Quartz group
  • Quartz - SiO₂
  • Tridymite - SiO₂
  • Cristobalite - SiO₂
• Feldspar group
  • Alkali-feldspars
    • Potassium-feldspars
      • Microcline - KAlSi₃O₈
      • Orthoclase - KAlSi₃O₈
      • Sanidine - KAlSi₃O₈
    • Anorthoclase - (Na,K)AlSi₃O₈
    • Albite - NaAlSi₃O₈
  • 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 - (Na,Ca)(Si,Al)₄O₈ (Na:Ca 2:3)
      • Bytownite - (Na,Ca)(Si,Al)₄O₈ (Na:Ca 1:4)
    • Anorthite - CaAl₂Si₂O₈
• Feldspathoid group
  • Analcime - NaAlSi₂O₆·H₂O
  • 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
• Petalite - LiAlSi₄O₁₀
• Scapolite group
  • Marialite - Na₄(AlSi₃O₈)₃(Cl₂,CO₃,SO₄)
  • Meionite - Ca₄(Al₂Si₂O₈)₃(Cl₂CO₃,SO₄)
• Analcime - NaAlSi₂O₆•H₂O
• Zeolite group
  • Natrolite - Na₂Al₂Si₃O₁₀•2H₂O
  • Chabazite - CaAl₂Si₄O₁₂•6H₂O
  • Heulandite - CaAl₂Si₇O₁₈•6H₂O
  • Stilbite - NaCa₂Al₅Si₁₃O₃₆•17H₂O

References

• Deer, W.A.; Howie, R.A., & Zussman, J. (1992). An introduction to the rock forming minerals, 2nd edition, London: Longman. 

• 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 edition, London: Geological Society of London, 982 pp. 

• Hurlbut, Cornelius S. (1966). Dana's Manual of Mineralogy, 17th edition. ISBN ISBN 0-471-03288-3. 

• Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy, 20th edition. ISBN ISBN 0-471-80580-7.