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Camosun College GEOS 250

Introduction to Mineralogy Dr. Tark Hamilton Chapter 18: Crystal Chemistry of Rock Forming Silicates. Camosun College GEOS 250. 92% of Continental & Ocean Crust is made of silicate minerals. >95% of the Upper Mantle is Olivine, Pyroxenes Plagioclase and Garnet with traces of Spinel.

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Camosun College GEOS 250

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  1. Introduction to MineralogyDr. Tark HamiltonChapter 18: Crystal Chemistry of Rock Forming Silicates Camosun College GEOS 250

  2. 92% of Continental & Ocean Crust is made of silicate minerals • >95% of the Upper Mantle is Olivine, Pyroxenes Plagioclase and Garnet with traces of Spinel

  3. Close Packing (Electron Cloud) Model of Silica Tetrahedron

  4. Silicate Anion Structural Typesn.b. Cyclo includes 3, 4 & 6 member rings

  5. Silicate Anion Structural TypesAmphiboles Micas and Frameworks

  6. General Silicate Formula • XmYn (Zp Oq) Wr • Where: • X = Large, +1 to +2, weak ≥ 8 fold cations • Y = Medium, +2 to +4, 6 fold cations • Z = Small, ≥ +3, strong 4 fold cations • W = Other anions: (OH)-, F-, Cl-,(SO4)-2,(CO 3)-2 • p/q depends on polyhedral polymerization • m, n & r depend on valence & neutrality

  7. Nesosilicates: Olivine Group • Ordinary Olivine series: Orthorhombic • Forsterite: Mg2SiO4 • Fayalite: Fe2SiO4 • Liebenbergite: (Ni,Mg)2SiO4 • Tephroite: Mn2SiO4 • Monticellite: CaMgSiO4 • Kirschsteinite: CaFeSiO4 • Glaucochroite: CaMnSiO4

  8. ForsteriteFayaliteMonticelliteGlaucochroite

  9. Olivine Structure projected on (100)Octahedra: M2 is ~regular M1 distorted (Mg,Fe,Ni)2SiO4 M1 vs M2 Thermometer M1 distortion = F (Temperature)

  10. Nesosilicates: Garnet Group • Pyralspite series: • Pyrope:Mg3 Al2Si3 O12 • Almandine:Fe3 Al2Si3 O12 • Spessartine: Mn3Al2Si3 O12 • Ugrandite series: • Uvarovite:Ca3Cr2 Si3 O12 • Grossularite:Ca3Al2Si3 O12 • Andradite:Ca3 Fe+32 Si3 O12

  11. Almandine-Australia Spessartine-Australia Uvarovite-Finland Andradite-Afghanistan

  12. Garnet Structure on [001]Lone Tetrahedra, Octahedra & Distorted Cubes

  13. Aluminosilicate Group • Al2SiO5 (mostly orthorhombic) PT indicators • Andalusite: moderate P/T meta-rocks • ½ Al in octahedral chains, ½ as Al-5fold/Si-4 chains • Kyanite (Triclinic): Hi P/T meta-rocks • All Al is octahedral in chains || to C or lone octahedra • Sillimanite: Hi T/P meta-rocks • Octahedral Al chains & || tetrahedral chains Al/Si/Al/Si.. • Mullite: Very High T contact meta • Al8 ((Si,Al)O4) 4 (O,OH,F)

  14. Kyanite on [001]edge sharing octahedra II to c

  15. Andalusite var. ChiastoliteKyanite (below)Sillimanite var. Fibrolite

  16. Sillimanite (left) & Andalusite (right)[Al]VI & [Al-Si]IV chains II to c

  17. Mullite: Isle of MullEifel (S.Wolfsreid), Rotorua (M.leGras)

  18. Sorosilicate “anion-dimer”

  19. Sorosilicate Group • Ions in Ca site Ions in Al site (non-chain) • Epidote Ca Al • Clinozoisite Ca Fe+3 , Al • Piedmontite Ca Mn+3, Fe+3, Al • Allanite: Na, Ca, Ce, La Mg Fe+2 Fe+3 Al • Zoisite Ca Fe+3 , Al

  20. Epidote unit cell on [010]

  21. Epidote versus Zoisite(Monoclinic vs Orthorhombic)

  22. Allanite-BlackZoisitevarThulite-pinkEpidote-GreenTanzanite-3chroicAllanite-BlackZoisitevarThulite-pinkEpidote-GreenTanzanite-3chroic

  23. Cyclosilicates Benitoite Beryl & Tourmaline Papagoite

  24. 6 member Cyclosilicate Group • Beryl: • Borosilicate with up to 7 different ions or vacancies! • Tourmaline: • Borosilicate with up to 7 different ions or vacancies! • Cordierite

  25. Beryl (a) on (0001) w/ unit cell & (b) parallel to C axis vertical Emerald & Aquamarine

  26. Beryl: Aquamarine, Emerald, Morganite

  27. Low Cordierite’s Al-Si backboneOrthorhombic, pseudo-hexagonal High Cordierite: Indialite Is Hexagonal

  28. CordieriteRed Trilings & Blue on Quartz

  29. Tourmaline End Members & Substitutions-Site Occupancies

  30. Tourmaline a (0001) & b C vertical

  31. Tourmaline: ElbaiteDravite

  32. PyroxeneWollastoniteRhodonitePyroxmangite

  33. Pyroxene Ca-Mg-Fe Classification Triangles

  34. Chain Silicates:Cation Sites & Substitutions

  35. (SiO3)-2 Single Chain Polymer

  36. Jadeite NaAl(SiO3)2 Structure on [100]

  37. Jadeite

  38. Monoclinic Pyroxeneprojected onto [001]

  39. Unit Cells of Enstatite & Diopsideprojected on [010] Orthorhombic Monoclinic Who has the larger unit cell & mirror plane? Could pyroxenes exhibit exsolution? Why or not?

  40. Amphibole Compositions in the Ca-Mg-Fe Triangle Hypothetical End member Monoclinic Orthorhombic

  41. Actinolite Orthorhombic Ferro-Actinolite Anthophyllite Grunerite Var. Amosite

  42. C2/m Amphibole on [100]2 anion sites, 7 cation sites!

  43. Chain Silicates:Cation Sites & Substitutions

  44. C2/m Amphibole on [001]T-O-T strips: prismatic habit and cleavage

  45. Intergrowth of 2 polymorphs of:Na0.1Fe2.2Mg4.5Al0.1Si8O22(OH)2 Monoclinic Tremolite Orthorhombic Who has the larger unit cell & mirror plane? What site is Na+ in? What site is Al+3 in? Could amphiboles exhibit exsolution? Why or not?

  46. “Biopyriboles” Mixing single, double and triple chain repeats Single - Enstatite: MgSiO3 Double - Anthophyllite: Mg7Si8O22(OH)2 Quadruple-singles – Aenigmatite: Na2Fe5TiSi6O20 Triple - Jimtompsonite: (Mg,Fe)10Si12O32(OH)4 Double/Triple Pairs- Chesterite: (Mg,Fe)17Si20O54(OH)6

  47. “Biopyriboles” Mixing single, double and triple chain repeats Aenigmatite Repeats groups of 4 single chains

  48. Aenigmatite: Na2Fe5TiSi6O18O2TriclinicStriated blades: Grey, Black, BronzeG. FrettiSan Miguel Azores

  49. Phyllosilicates (Micas & Clays) Undistorted Hexagonal Ring in an Si2O5 sheet (Triangles in tetrahedra = triangles in octahedra)

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