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Mineralogy

Mineralogy. Minerals – chemical compounds that form naturally as solids with shapes determined by the arrangement of atoms, e.g., quartz (SiO 2 ).

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Mineralogy

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  1. Mineralogy Minerals – chemical compounds that form naturally as solids with shapes determined by the arrangement of atoms, e.g., quartz (SiO2). Crystals – the morphological manifestation of a mineral, e.g., quartz crystals commonly comprise hexagonal prisms topped by hexagonal pyramids and halite (NaCl) crystals commonly occur as cubes.

  2. World’s largest crystals: A cave in the Naica Lead Zinc mine, Mexico

  3. Miners in Cueva de los Crystals: the mineral gypsum Crystals of a variety of gypsum (CaSO4.2H2O) precipitated from hot water at 60 degrees celsius in a limestone cave in the Naica mine

  4. Minerals Tourmaline on Feldspar Beryl (Be3Al2(SiO3)6 Emerald

  5. Pyrite (FeS2) crystals

  6. Feldspars – two of the most important rock-forming minerals Plagioclase Albite – NaAlSi3O8 Anorthite CaAl2Si2O8 K-feldspar Sanidine Orthoclase Microcline KAlSi3O8

  7. Colours and forms of quartz Citrine Amethyst Milky quartz Rose quartz

  8. Quartz crystals displaying prism and pyramid faces

  9. Crystal Shapes Quartz (SiO2) Diamond (C) Halite (NaCl) Calcite (CaCO3) Stibnite (Sb2S3) Garnet (Fe3Al2Si3O12)

  10. Quartz Crystal Pyramid Faces display consistent angular relationships Angles measured with a goniometer Prism

  11. Crystals have ordered arrangements of atoms Order Disorder

  12. X-ray diffraction X-ray beam splits into numerous smaller beams. Interference of waves of different beams produces a diffraction pattern on a screen or film. The pattern indicates the spacing and arrangement of atoms.

  13. Atomic structure of galena (PbS) Surface of galena (PbS) imaged With an atomic force microscope Sulphur Lead

  14. The atomic structure of halite (NaCl) Ionic bonding

  15. Ionic bonding – transfer of electrons Anion - Cation +

  16. Relative sizes of ions Ion co-ordination

  17. The atomic structure of diamond Covalent bonding

  18. The source of Diamonds The ‘Big Hole’ at Kimberly, South Africa Kimberlite containing diamond

  19. Cutting diamonds

  20. Covalent bonding – sharing of electrons

  21. Atomic structure of graphite Covalent bonding within sheet Van der Waal’s bonding between sheets

  22. Ice Crystals Hydrogen bonding

  23. The silicon tetrahedron

  24. Silicate Structures Inosilicate Inosilicate Nesosilicate (Single chain) (Double chain) SiO44 - Si4O116 - SiO32- Sheet silicate Framework silicate Si4O104 - SiO2

  25. Nesosilicate (Fe,Mg)2SiO4 Olivine

  26. Inosilicate (Single Chain) Diopside Pyroxene CaMgSi2O6 Hypersthene (Fe,Mg)SiO3

  27. Inosilicate (Double Chain) Amphibole Tremolite Ca2Mg5Si8O22(OH)2 Riebeckite Na2Fe5Si8O22(OH)2 Tigers Eye

  28. Sheet Silicate Biotite KAl(Fe,Mg)3Si3O10(OH)2 Muscovite KAl3Si3O10(OH)2

  29. Asbestos Chrysotile (Mg3Si2O5(OH)4 Uses and risks (Insulation, heat, fire resistance) Serpentine (Mg3Si2O5(OH)4

  30. Framework Silicate Quartz SiO2 Albite NaAlSi3O8 Plagioclase Anorthite CaAl2Si2O8 Amethyst SiO2 K-feldspar KAlSi3O8

  31. SiO2 + AlO2 + SiO2 + SiO2 = AlSi3O8- SiO2 + AlO2 + AlO2 + SiO2 = Al2Si2O82- Relationship of Quartz structure to Feldspar Structure Imagine four SiO2 molecules 4 x SiO2 = Si4O8 Substitute Al3+ for Si4+ in one of these molecules Add Na+ or K+ to supply missing charge = NaAlSi3O8 or KAlSi3O8 Albite K-Feldspar Add Ca2+ to supply missing charge = CaAl2Si2O8 Anorthite

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