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MOST IMPORTANT MINERAL SUITE: The Silicate Minerals

MOST IMPORTANT MINERAL SUITE: The Silicate Minerals . Si + O = 75% of Crust Silicates make up 95% + of all Rocks SiO 4 : -4 charge Link Corner-To-Corner by Sharing Oxygen atoms . Nesosilicates - Isolated Tetrahedra . Representatives: Garnet Kyanite Olivine Zircon Topaz Staurolite

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MOST IMPORTANT MINERAL SUITE: The Silicate Minerals

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  1. MOST IMPORTANT MINERAL SUITE: The Silicate Minerals • Si + O = 75% of Crust • Silicates make up 95% + of all Rocks • SiO4: -4 charge • Link Corner-To-Corner by Sharing Oxygen atoms

  2. Nesosilicates - Isolated Tetrahedra • Representatives: • Garnet • Kyanite • Olivine • Zircon • Topaz • Staurolite • Sphene • SiO4 in Formula

  3. Sorosilicates - Paired Tetrahedra • Epidote is the most common example • Lawsonite • Vesuvianite • Si2O7 in Formula

  4. Cyclosilicates - Rings • Beryl (Emerald) • Cordierite • Tourmaline • SinO3n in Formula

  5. What is a Tetrahedron? • In many silicates, Al, Be and other ions occur in tetrahedral coordination • Substitution of Al for Si maintains charge balance in Feldspars • Some mineralogists count all tetrahedra in classifying structure • By this criterion, Beryl and Cordierite are tectosilicates

  6. Inosilicates - Chains Single Chains (Pyroxenes) SiO3 or Si2O6 in Formula

  7. More Realistic Picture

  8. Major Pyroxenes • Ferromagnesian • Enstatite (MgSiO3) – Hypersthene (Mg,Fe)SiO3 • Calcic • Diopside: CaMgSi2O6 • Pigeonite: Ca0.25(Mg,Fe)1.75Si2O6 • Hedenbergite: CaFeSi2O6 • Augite: XYZ2O6

  9. Other Pyroxenes • Sodic • Jadeite: NaAlSi2O6 • Breakdown of Na-Feldspar • High Pressure Metamorphism • Aegerine (Acmite) NaFe3Si2O6 • Spodumene: LiAlSi2O6 • Pegmatite Mineral

  10. Pyroxenes and Cations

  11. Silica Chains and Octahedra

  12. Silica Chains and Octahedra

  13. Two Sites in Pyroxenes

  14. Pyroxenoids • Have single chains but more complex bends to accommodate cations • Lack pyroxene cleavage • Wollastonite (CaSiO3) • Rhodonite and Pyroxmangite (MnSiO3) • Mn is a good match in size and charge for Fe and Mg • Pure Mn true pyroxenes exist • These have complex chains because of variable compositions

  15. Wollastonite CaSiO3

  16. Wollastonite End-On

  17. Rhodonite

  18. Pyroxmangite

  19. Biopyriboles • Biotite = Silica sheets with (Mg,Fe) Sheets in between • Amphiboles and Pyroxenes are strips of Biotite sheets • Biopyribole = Biotite + Pyroxene + Amphibole

  20. Inosilicates - Chains Double Chains (Amphiboles Si4O11 in Formula)

  21. Major Amphiboles • Anthophyllite (Mg,Fe)7Si8O22(OH)2) • Cummingtonite (Fe2Mg5Si8O22(OH)2) -Grunerite (Fe7Si8O22(OH)2) • Tremolite (Ca2Mg5Si8O22(OH)2) – Actinolite (Ca2(Mg,Fe)5Si8O22(OH)2) • Hornblende (X2-3Y5Z8O22(OH)2) • Glaucophane (Na2Mg3Al2Si8O22(OH)2) and Riebeckite (Na2Fe++3,Fe+++2Si8O22(OH)2)

  22. Beyond Amphiboles • There are a few 3-chain and mixed chain silicates • Discovered only in 1970’s • Occur in asbestos

  23. Phyllosilicates – Sheets (Si2O5 in Formula)

  24. Phyllosilicates - Sheets Si2O5 sheets with layers of Mg(OH)2 or Al(OH)3 • Micas • Clay minerals • Talc • Serpentine (asbestos) minerals

  25. Tectosilicates - Three-Dimensional Networks • Quartz Feldspars

  26. Tectosilicates • Quartz and Polymorphs • Feldspars • K-Feldspars (KAlSi3O8) • Plagioclase (NaAlSi3O8)- (CaAl2Si2O8) • Barium Feldspars (BaAl2Si2O8) • Feldspathoids (Foids) • Scapolites • Zeolites

  27. K-Feldspars and Mixtures • K-Feldspars (KAlSi3O8) • Microcline (Slow cooling) • Orthoclase (Faster cooling) • Sanidine (Fastest cooling, High T) • Anorthoclase: Solid solution of K-Feldspar and Albite (NaAlSi3O8) • Perthite: K-Feldspar with exsolved plagioclase • Antiperthite: Plagioclase with exsolved K-Feldspar

  28. Plagioclase • Solid solution of Albite (NaAlSi3O8) and Anorthite (CaAl2Si2O8) • 0-10% An = Albite: Na-Metasomatism • 10-30% An = Oligoclase: Granites • 30-50% An = Andesine: Andesites and Diorite • 50-70% An = Labradorite: Basalt and Gabbro • 70-90% An = Bytownite: Rarest • 90-100% An = Anorthite: Metamorphic

  29. Feldspathoids (Foids) • Fill “ecological niche” of feldspars in Si-poor rocks • Never occur with quartz • Leucite (KAlSi2O6) • Nepheline ((Na,K)AlSiO4)

  30. Scapolites and Relatives • Sodalite (Na8(AlSiO4)6Cl2) • Lazurite (Na,Ca)8(AlSiO4)6(SO4,S,Cl)2) • Scapolite • Marialite = Albite + NaCl • Meionite = Anorthite + CaSO4 or CaCO3

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