1. 1 Rock Forming Silicate Minerals

2. 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. 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. 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. 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 12- -8 (4 tetrahedra ring), Si 6 O 18 - 12 (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. 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 11 -6 (double chain of tetrahedra) (1:2.75; Si:0) –Phyllo: Si 4 O 10 -4 (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. 7 Silicate Subclasses Neso (a) Soro (b) Cyclo (c, d, e)

8. 8 Silicate Subclasses Ino Phylo

9. 9 Silicate Subclasses Tecto [SiO 2 ]

10. 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. 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 2+ 8-6Cubic to octahedral Mn 2+ 6Octahedral Fe 2+ 6Octahedral Mg 2+ 6Octahedral Fe 3+ 6Octahedral Ti 4+ 6Octahedral Al 3+ 6-4Octahedral to tetrahedral Si 4+ 4Tetrahedral

12. 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. 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. 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

15. 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 6.5- 7 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

16. 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

17. 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

18. 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

19. 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

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