Silicate mineral
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
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
]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
3O−
8]
n, whose charge is neutralized by the potassium
.
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
Nesosilicates (from Greek
- Phenakite group
- 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 – Ca
3Al
2Si
2O
8(SiO
4)
3−m(OH)
4m
- Zircon group
- Al2SiO5 group
- Andalusite – Al2SiO5
- Kyanite – Al2SiO5
- Sillimanite – Al2SiO5
- Dumortierite – Al
6.5–7BO
3(SiO
4)
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
Sorosilicates
Sorosilicates (from Greek σωρός sōros 'heap, mound') have isolated pyrosilicate anions Si
2O6−
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:
- Thortveitite – (Sc,Y)2(Si2O7)
- Hemimorphite (calamine) – Zn4(Si2O7)(OH)2·H2O
- Lawsonite – CaAl2(Si2O7)(OH)2·H2O
- Axinite – (Ca,Fe,Mn)3Al2(BO3)(Si4O12)(OH)
- Ilvaite – CaFeII2FeIIIO(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(FeII,FeIII)O(SiO4)(Si2O7)(OH)
- Dollaseite-(Ce) – CaCeMg2AlSi3O11F(OH)
- Vesuvianite (idocrase) – Ca10(Mg,Fe)2Al4(SiO4)5(Si2O7)2(OH)4
Cyclosilicates
Cyclosilicates (from Greek κύκλος 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:
-
6 units [Si6O18], beryl (red: Si, blue: O)
-
3 units [Si3O9], benitoite
-
4 units [Si4O12], papagoite
-
9 units [Si9O27], eudialyte
-
12 units, double ring [Si12O30], milarite
Some example minerals are:
- 3-member single ring
- Benitoite – BaTi(Si3O9)
- 4-member single ring
- Papagoite – CaCuAlSi
2O
6(OH)
3.
- Papagoite – CaCuAlSi
- 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(Si
6O
18)(BO
3)
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 – Na
15Ca
6(Fe,Mn)
3Zr
3SiO(O,OH,H
2O)
3(Si
3O
9)
2(Si
9O
27)
2(OH,Cl)
2
- Eudialyte – Na
- 6-member double ring
- Milarite – 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
Single chain inosilicates
- Pyroxene group
- Enstatite – orthoferrosilite series
- Enstatite – MgSiO3
- Ferrosilite– FeSiO3
- Pigeonite – Ca0.25(Mg,Fe)1.75Si2O6
- Diopside – hedenbergite series
- Diopside – CaMgSi2O6
- Hedenbergite – CaFeSi2O6
- Augite – (Ca,Na)(Mg,Fe,Al)(Si,Al)2O6
- Sodium pyroxene series
- Spodumene – LiAlSi2O6
- Pyroxferroite - (Fe,Ca)SiO3
- Enstatite – orthoferrosilite series
- Pyroxenoid group
- Wollastonite – CaSiO3
- Rhodonite – MnSiO3
- Pectolite – NaCa2(Si3O8)(OH)
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)
5Si
6(Al,Si)
2O
22(OH)
2 - Sodium amphibole group
- Glaucophane – Na2Mg3Al2Si8O22(OH)2
- Riebeckite (asbestos) – Na2FeII3FeIII2Si8O22(OH)2
- Arfvedsonite – Na3(Fe,Mg)4FeSi8O22(OH)2
-
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
Examples include:
- Serpentine subgroup
- Antigorite – Mg3Si2O5(OH)4
- Chrysotile – Mg3Si2O5(OH)4
- Lizardite – Mg3Si2O5(OH)4
- Clay mineralsgroup
- 1:1 clay minerals (TO)
- Halloysite – Al2Si2O5(OH)4
- Kaolinite – Al2Si2O5(OH)4
- 2:1 clay minerals (TOT)
- Pyrophyllite – Al2Si4O10(OH)2
- Talc – Mg3Si4O10(OH)2
- Illite – (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2,(H2O)]
- Montmorillonite (smectite) – (Na,Ca)0.33(Al,Mg)2Si4O10(OH)2·nH2O
- Chlorite – (Mg,Fe)3(Si,Al)4O10(OH)2·(Mg,Fe)3(OH)6
- Vermiculite – (Mg,Fe,Al)3(Al,Si)4O10(OH)2·4H2O
- Other clay minerals
- Sepiolite – Mg4Si6O15(OH)2·6H2O
- Palygorskite (or attapulgite) – (Mg,Al)2Si4O10(OH)·4(H2O)
- 1:1 clay minerals (TO)
- Mica group
- Biotite – K(Mg,Fe)3(AlSi3)O10(OH)2
- Fuchsite – K(Al,Cr)2(AlSi3)O10(OH)2
- Muscovite – KAl2(AlSi3)O10(OH)2
- Phlogopite – KMg3(AlSi3)O10(OH)2
- Lepidolite – K(Li,Al)
2–3(AlSi
3)O
10(OH)
2 - Margarite – CaAl2(Al2Si2)O10(OH)2
- Glauconite – (K,Na)(Al,Mg,Fe)2(Si,Al)4O10(OH)2
-
Phyllosilicate, mica group, muscovite (red: Si, blue: O)
-
Phyllosilicate, single net of tetrahedra with 4-membered rings, apophyllite-(KF)-apophyllite-(KOH) series
-
Phyllosilicate, single tetrahedral nets of 6-membered rings, pyrosmalite-(Fe)-pyrosmalite-(Mn) series
-
Phyllosilicate, single tetrahedral nets of 6-membered rings, zeophyllite
-
Phyllosilicate, double nets with 4- and 6-membered rings, carletonite
Tectosilicates
Tectosilicates, or "framework silicates," have a three-dimensional framework of silicate
- 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
- Alkali feldspars (potassium feldspars)
- Tectosilicates, feldspathoid family
- Tectosilicates, scapolite group
- Tectosilicates, zeolite family
See also
- Classification of non-silicate minerals – List of IMA recognized minerals and groupings
- Classification of silicate minerals – List of IMA recognized minerals and groupings
- Silicate mineral paint – Paint coats with mineral binding agents
References
- ^ "Mineral - Silicates". britannica.com. Archived from the original on 25 October 2017. Retrieved 8 May 2018.
- ISBN 0-582-30094-0.
- ISBN 0-47180580-7.
- ISBN 0-582-30094-0
- ISBN 0-471-80580-7
- ^ 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.