Sulphides and oxides (part 2) Ch- 18

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kevindevriendt
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178771
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Sulphides and oxides (part 2) Ch- 18
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2012-10-21 16:28:06
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Sulphides oxides part nCh 18
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Sulphides and oxides (part 2) Ch- 18
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  1. what are several exmaples of sulphide minerals?
    • pyrite
    • pyrrhotite
    • galenca
    • sphalerite
    • cahlcopyrite
    • chalcocite
  2. which species of pyrrhotite is magnetic?
    Fe7S8 

    Fe23+Fe52+S82-

  3. pyrite

    Sulphur forms ____bonded S2 pairs (S22-) or _____ centered at the cl position in the halite structure - the dimers are orientated parallel to the {_ _ _}
    Covalently

    dimers

    {111}
  4. Pyrite

    Each Fe coordinates with ___ S atoms and each S atoms bonds with __ __ Atoms
    • 6
    • 3 Fe atoms
  5. Which other minerals have similar covalent bonds with anions like in pyrite?
    • Marcasite  (orthorhombic)
    • Cobaltite
    • arsenopyrite
  6. X2O3 oxides 

    what are they also known as?
    what similarities do they have between one another?
    Rhombohedral oxides

    • They share a common structure:
    • -HCP packing (oxygen anions, with metal cations)
    • -Layers of octahedra parallel to {001}

    Within each layer only 2/3 of the octahedral sites contain cations and the occupied octahedra share two oxygen anions (share edges)
  7. Hematite

    Formula:
    crystal system:
    Hardness:
    Form:
    Specularite:
    USe:
  8. Corundum 

    Formula
    Crytal system
    Form
    Use
  9. Ilmenite

    Formula
    Crystal system
    properties
    form
    use
  10. XO2 Oxides

    What are the two structural types?
    • Rutile group: cations in 6 -fold coordination with oxygen
    • Rc/Ra= 0.414 ~ 0.732

    Oxides with "fluorite structure"uranite (UO2) and thorianite( ThO2)
  11. name three polymorphs of TiO2  (rutile group)

    what is the crystal structure of each?
    • Rutile:
    • tetragonal

    • Brookite:
    • orthorhombic

    • Anatase:
    • tetragonal
  12. What is the spinel structure?

    what defines the spinal structure?
    XY2O4

    • oxygen anions form and approximately CCP arrangement with layers parallel to {111}
    • within each unit cell, cations occupy 8 tetrahedral and 16 octahefral sites between the oxygen layers.


  13. What group is magnetite in?
    give its formula
    crystal system?
    form?
    properties
    use?
    • Spinel group
    • Fe3O4
    • isometric
    • octahedral crystals
    • magnetic
    • iron
  14. Spinel

    formula
    crystal systems
    form
    use?
  15. Chromite

    What group?

    Formula
    crystal system
    form 
    use
  16. Spinels consist of?
    Stacked octahedral layers and mixed tetrahedra-octahedral layers
  17. Hematite group or rhombohedral oxides consist of?
    Stacked octahedral layers
  18. pyrrhottite can be either magnetic or non magnetic depending on extent of ___ _______ in it's formula
    Non stoichiometry
  19. Why is pyrite an exception in the sulphide mineral class
    Sulphide mineral class is defined by S2- anion. pyrite however has covelently bonded S22- pairs
  20. What bond dominates oxides?
    dominantly ionic

    high symmetry
  21. Hematite vs Ilmenite?
    • Hematite
    • platy crystals with hexagonal outline

    • Ilmenite
    • tabular parallel to {001} with hexagonal cross section
  22. Which TiO2 polymorph is most common
    Rutile
  23. why do spinels show such extensive substitution solid solution?
  24. Why is structure of spinels different to that of rhombohedral oxides?
    Hexgaonally closed packed  and parallel to {001) (rhombo)

     cubic closed packed parallel to {111} (spinel)

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