1 Rock Forming Silicate Minerals

2 Importance of the Silicates Abundance –~25% of all known minerals –Make up ~90% of earth’s crust –Composed of dominant elements in earth’s crust (O, Si, Al, Fe, Mg, Ca, Na, K) –Rock-forming minerals Economic uses –Building construction (brick, stone, morter, glass) –Technology (silicon chips)

3 What Are Silicates? Frameworks based on the linkage of cation centered coordination polyhedron –The silica tetrahedra: the building block of the silicate minerals –SiO 4 -4 is the basic unit Si 2 O 7 SiO 4 Si 4 O 11 SiO 3 Si 2 O 5 SiO 2 Si 2 O 6

4 The Silicates Frameworks based on the linkage of SiO 4 -4 tetrahedra –Results in a structurally stable, anion complex –Suitable for the formation of polymers (two or more shared complex ions of the same type) Charge reaching the cation is exactly 1/2 the charge on the anion –Limited ways in which polymers can form (Pauling’s Rules) –Charge balance in minerals attained by: Sharing oxygen between adjoining tetrahedra Linking tetrahedra with other cations Si 2 O 7 SiO 4 Si 4 O 11 SiO 3 Si 2 O 5 SiO 2

5 Silicates Structure Ratio of Si to O determines structural configuration and is the criteria for silicate classification (subclasses) –Neso: SiO 4 -4, separate tetrahedra (1:4; Si:0) –Soro: Si 2 O 7 -6, double tetrahedra (1:3.5; Si:0) –Cyclo: Si 3 O 9 -6 (3 tetrahedra ring), Si 4 O (4 tetrahedra ring), Si 6 O (6 tetrahedra ring) (1:3; Si:0) SiO 4 Si 2 O 7 SiO 3 Si 4 O 11 Si 2 O 5 SiO 2 Si 2 O 6

6 More Silicates Structure Ratio of Si to O determines structural configuration and is the criteria for silicate classification (subclasses) –Ino: SiO 3 -2 (single chain of tetrahedra) (1:3; Si:0), Si 4 O (double chain of tetrahedra) (1:2.75; Si:0) –Phyllo: Si 4 O (OH) 2, sheets of tetrahedra (1:2.5; Si:0) –Tecto: SiO 2, three dimensional frameworks (1:2; Si:0) SiO 4 Si 2 O 7 SiO 3 Si 4 O 11 Si 2 O 5 SiO 2 Si 2 O 6

7 Silicate Subclasses Neso (a) Soro (b) Cyclo (c, d, e)

8 Silicate Subclasses Ino Phylo

9 Silicate Subclasses Tecto [SiO 2 ]

10 The Silicates Six silicate subclasses Name Structural linkage of SiO 4 -4 Silica Tetrahedra Geometry; Examples Nesosilicates SiO 4 independent silica tetrahedra; olivine, garnet Sorosilicates Si 2 O 7 double silica tetrahedra; epidote Cyclosilicates SiO 3 ring of silica tetrahedra; beryl (emerald), tourmaline Inosilicates Si 2 O 6 Si 4 O 11 chains of silica tetrahedra; pyroxene, amphibole Phyllosilicates Si 2 O 5 sheets of silica tetrahedra; mica, clay Tectosilicates Si0 2 frameworks of silica tetrahedra; quartz, feldspar

11 Structural Formulas and Silicate Group Minerals Where do the other cations fit? Coordination polyhedron with oxygen depends on ionic radius CationC.N.Polyhedron K+K+ 8-12Cubic Na + 8-6Cubic to octahedral Ca Cubic to octahedral Mn 2+ 6Octahedral Fe 2+ 6Octahedral Mg 2+ 6Octahedral Fe 3+ 6Octahedral Ti 4+ 6Octahedral Al Octahedral to tetrahedral Si 4+ 4Tetrahedral

12 Structural Formulas and Silicates Describes the structural and chemical relationship between related minerals (mineral groups) through a generalized description of the chemical formula Symbology –X = large, weakly charged cations, C.N. >6 (with oxygen) Na, K, & Ca (sort of) –Y = medium-sized, 2+ to 4+ cations, C.N. = 6 Mg, Fe +2, Fe +3, Al, Ti, & Ca (sort of) –Z = small cations, C.N. = 4 Mainly Si +4, but also Al +3 –W = additional anionic groups OH -, Cl -, F - Results in generic formula for all silicates: X m Y n (Z p O q )W r

13 T-X Phase Diagrams Diagrams showing the relationship between temperature, composition, and proportion of crystals and liquid in a melt –Liquidus: t-x at which first crystals form from a melt –Solidus: t-x at which the last melt crystallizes

14 The Solvus and Miscibility Gaps Miscibility gap (opposite of solid solution) –Defined by the solvus Outline of the miscibility gap Represents the area of a phase diagram where naturally occurring minerals do not occur

Mineral Families Nesosilicates Nesosilicates Olivine groupOlivine –Forsterite - Mg 2 SiO 4Forsterite –Fayalite - Fe 2 SiO 4Fayalite Garnet groupGarnet –Pyrope- Mg 3 Al 2 (SiO 4 ) 3Pyrope –Almandine - Fe 3 Al 2 (SiO 4 ) 3Almandine –Spessartine - Mn 3 Al 2 (SiO 4 ) 3Spessartine –Grossular - Ca 3 Al 2 (SiO 4 ) 3Grossular –Andradite - Ca 3 Fe 2 (SiO 4 ) 3Andradite –Uvarovite - Ca 3 Cr 2 (SiO 4 ) 3Uvarovite –Hydrogrossular - Ca 3 Al 2 Si 2 O 8 (SiO 4 ) 3-m (OH) 4mHydrogrossular Zircon group –Zircon - ZrSiO 4Zircon –Thorite - (Th,U)SiO 4Thorite Al 2 SiO 5 group –Andalusite - Al 2 SiO 5Andalusite –Kyanite - Al 2 SiO 5Kyanite –Sillimanite - Al 2 SiO 5Sillimanite –Dumortierite - Al BO 3 (SiO 4 ) 3 (O,OH) 3Dumortierite –Topaz - Al 2 SiO 4 (F,OH) 2Topaz –Staurolite - Fe 2 Al 9 (SiO 4 ) 4 (O,OH) 2Staurolite

Sorosilicates Cyclosilicates Epidote group (has both (SiO 4 ) 4− and (Si 2 O 7 ) 6− groups) –Epidote - Ca 2 (Al,Fe) 3 O(SiO 4 )(Si 2 O 7 )(OH)Epidote –Zoisite - Ca 2 Al 3 O(SiO 4 )(Si 2 O 7 )(OH)Zoisite –Clinozoisite - Ca 2 Al 3 O(SiO 4 )(Si 2 O 7 )(OH)Clinozoisite –Tanzanite - Ca 2 Al 3 O(SiO 4 )(Si 2 O 7 )(OH)Tanzanite –Allanite - Ca(Ce,La,Y,Ca)Al 2 (Fe 2+,Fe 3+ )O(Si O 4 )(Si 2 O 7 )(OH)Allanite –Dollaseite-(Ce)- CaCeMg 2 AlSi 3 O 11 F(OH)Dollaseite-(Ce) 3-member ring –Benitoite - BaTi(Si 3 O 9 )Benitoite 6-member ring –Axinite - (Ca,Fe,Mn) 3 Al 2 (BO 3 )(Si 4 O 12 )(OH)Axinite –Beryl/Emerald - Be 3 Al 2 (Si 6 O 18 )BerylEmerald –Cordierite - (Mg,Fe) 2 Al 3 (Si 5 AlO 18 )Cordierite –Tourmaline - (Na,Ca)(Al,Li,Mg) 3- (Al,Fe,Mn) 6 (Si 6 O 18 (BO 3 ) 3 (OH) 4Tourmaline

Inosilicates SiO 3, 1:3, Si 4 O 11, 4:11 ratio Single chain Pyroxene groupPyroxene –Enstatite - orthoferrosilite series Enstatite - MgSiO 3Enstatite Ferrosilite - FeSiO 3Ferrosilite –Pigeonite - Ca 0.25 (Mg,Fe) 1.75 Si 2 O 6Pigeonite –Diopside - hedenbergite series Diopside - CaMgSi 2 O 6Diopside Hedenbergite - CaFeSi 2 O 6Hedenbergite Augite - (Ca,Na)(Mg,Fe,Al)(Si,Al) 2 O 6Augite –Sodium pyroxene series Jadeite - NaAlSi 2 O 6Jadeite Aegirine (Acmite) - NaFe 3+ Si 2 O 6AegirineAcmite –Spodumene - LiAlSi 2 O 6Spodumene Pyroxenoid group –Wollastonite - CaSiO 3Wollastonite –Rhodonite - MnSiO 3Rhodonite –Pectolite - NaCa 2 (Si 3 O 8 )(OH)Pectolite Double chain Amphibole groupAmphibole –Anthophyllite - (Mg,Fe) 7 Si 8 O 22 (OH) 2Anthophyllite –Cumingtonite series Cummingtonite - Fe 2 Mg 5 Si 8 O 22 (OH) 2Cummingtonite Grunerite - Fe 7 Si 8 O 22 (OH) 2Grunerite –Tremolite series Tremolite - Ca 2 Mg 5 Si 8 O 22 (OH) 2Tremolite Actinolite - Ca 2 (Mg,Fe) 5 Si 8 O 22 (OH) 2Actinolite –Hornblende - (Ca,Na) 2- 3 (Mg,Fe,Al) 5 Si 6 (Al,Si) 2 O 22 (OH) 2Hornblende –Sodium amphibole group Glaucophane - Na 2 Mg 3 Al 2 Si 8 O 22 (OH) 2Glaucophane Riebeckite (asbestos) - Na 2 Fe 2+ 3 Fe 3+ 2 Si 8 O 22 (OH) 2Riebeckiteasbestos

Phyllosilicates Si 2 O 5 or a 2:5 ratio Clay mineral groupClay mineral –Halloysite - Al 2 Si 2 O 5 (OH) 4Halloysite –Kaolinite - Al 2 Si 2 O 5 (OH) 4Kaolinite –Illite- (K,H 3 O)(Al,Mg,Fe) 2 (Si,Al) 4 O 10 [(OH ) 2,(H 2 O)]Illite –Montmorillonite- (Na,Ca) 0.33 (Al,Mg) 2 Si 4 O 10 (OH) 2 ·nH 2 OMontmorillonite –Vermiculite - (MgFe,Al) 3 (Al,Si) 4 O 10 (OH) 2 ·4H 2 OVermiculite –Talc - Mg 3 Si 4 O 10 (OH) 2Talc –Palygorskite - (Mg,Al) 2 Si 4 O 10 (OH)·4(H 2 O)Palygorskite –Pyrophyllite - Al 2 Si 4 O 10 (OH) 2Pyrophyllite Mica groupMica –Biotite - K(Mg,Fe) 3 (AlSi 3 )O 10 (OH) 2Biotite –Muscovite - KAl 2 (AlSi 3 )O 10 (OH) 2Muscovite –Phlogopite - KMg 3 (AlSi 3 )O 10 (OH) 2Phlogopite –Lepidolite - K(Li,Al) 2- 3 (AlSi 3 )O 10 (OH) 2Lepidolite –Margarite - CaAl 2 (Al 2 Si 2 )O 10 (OH) 2Margarite –Glauconite - (K,Na)(Al,Mg,Fe) 2 (Si,Al) 4 O 10 (OH) 2Glauconite Chlorite group –Chlorite - (Mg,Fe) 3 (Si,Al) 4 O 10 (OH) 2 (Mg,Fe) 3 (OH) 6

Tectosilicates Quartz group –Quartz - SiO 2Quartz –Tridymite - SiO 2Tridymite –Cristobalite - SiO 2Cristobalite Feldspar familyFeldspar –Alkali-feldspars Potassium-feldspars –Microcline - KAlSi 3 O 8Microcline –Orthoclase - KAlSi 3 O 8Orthoclase –Sanidine - KAlSi 3 O 8Sanidine Anorthoclase - (Na,K)AlSi 3 O 8Anorthoclase –Plagioclase feldsparsPlagioclase Albite - NaAlSi 3 O 8Albite Oligoclase - (Na,Ca)(Si,Al) 4 O 8 (Na:Ca 4:1)Oligoclase Andesine - (Na,Ca)(Si,Al) 4 O 8 (Na:Ca 3:2)Andesine Labradorite - (Na,Ca)(Si,Al) 4 O 8 (Na:Ca 2:3)Labradorite Bytownite - (Na,Ca)(Si,Al) 4 O 8 (Na:Ca 1:4)Bytownite Anorthite - CaAl 2 Si 2 O 8Anorthite Feldspathoid familyFeldspathoid –Nosean - Na 8 Al 6 Si 6 O 24 (SO 4 )Nosean –Cancrinite - Na 6 Ca 2 (CO 3,Al 6 Si 6 O 24 ).2H 2 OCancrinite –Leucite - KAlSi 2 O 6Leucite –Nepheline - (Na,K)AlSiO 4Nepheline –Sodalite - Na 8 (AlSiO 4 ) 6 Cl 2Sodalite Hauyne - (Na,Ca) 4- 8 Al 6 Si 6 (O,S)24(SO 4,Cl) 1-2Hauyne –Lazurite - (Na,Ca) 8 (AlSiO 4 ) 6 (SO 4,S,Cl) 2Lazurite Scapolite groupScapolite –Marialite - Na 4 (AlSi 3 O 8 ) 3 (Cl 2,CO 3,SO 4 )Marialite –Meionite - Ca 4 (Al 2 Si 2 O 8 ) 3 (Cl 2 CO 3,SO 4 )Meionite Zeolite groupZeolite –Natrolite - Na 2 Al 2 Si 3 O 10 2H 2 ONatrolite –Chabazite- CaAl 2 Si 4 O 12 6H 2 OChabazite –Heulandite - CaAl 2 Si 7 O 18 6H 2 OHeulandite –Stilbite - NaCa 2 Al 5 Si 13 O 36 17H 2 OStilbite

Pyroxene Amphibole Biotite Mica Mafic Minerals Igneous Rock-Forming Minerals Felsic Minerals Orthoclase Feldspar Muscovite Mica Quartz Plagioclase Feldspar (Ca/Na) Olivine