lecture 18.06.ppt
TRANSCRIPT
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Lecture 18 (11/29/2006)
Systematic Description of Minerals
Part 2: Oxides, Hydroxides Halides,
Carbonates, Sulfates, andPhosphates
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OxidesThree main groups based on metal cation/oxygen ratios
Hematite Group (X2O3) Corundum X=Al+3
most phases hexagonal Hematite X=Fe+3
Ilmenite X=1Fe+2+1Ti+4
Rutile Group (XO2) Rutile X=Tix- +4 cation Pyrolusite X=Mn
most phases tetragonal Cassiterite X=Sn
Uraninite X=U
Spinel Group (XY2O4) Spinel X=Mg, Y=Al
X- +2 ; Y- +3 cation Magnetite X=Fe+2, Y=Fe+3
most phases isometric Chromite X=Fe+2, Y=Cr
or orthorhombic Chrysoberyl X=Be, Y=Al
Ulvospinel X=Ti+4, Y=Fe+2
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Fe-Ti oxides
Fe+2Fe+3
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Spinel Group (XY2O4)
Gem-qualitySpinels
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Other Common Oxides
Rutile (TiO2)
Rutile needles inQuartz
Pyrolusite dendriteson fracture faces
Pyrolusite (MnO2)
Mass of botryoidalPyrolusite
Corundum (Al2O3)
Hardness=9
Red = Ruby
Blue = Sapphire
Chrysoberyl (BeAl2O4)
Cyclic twinningin Chrysoberyl
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Hydroxides
(OH)-
main anionic group forming octahedrallycoordinated sheets with weak bonds between
Two structural types:
Brucite-type – trioctahedralsheets (all octahedral cationsites are filled)
Gibbsite-type – dioctahedralsheets (only two of threeoctahedral sites are filled)
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Common Types of HydroxidesBrucite Mg(OH)2 Gibbsite Al(OH)3
Manganite MnO(OH) Diaspore AlO(OH)
Goethite FeO(OH) Bauxite Al-hydroxide*
*hybrid mix of diaspore, gibbsite, and boehmite (AlO(OH))
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Halides
Simple compounds composed oflarge halogen anions (Cl, Br, F, I)
Typically isometric
Dominantly ionic bonding
Properties – low hardness, high
melting points, poor conductors(except at high temperatures)
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Common Halides
Halite (NaCl)
Sylvite (KCl)
Flourite (CaF2)
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Mineral
Groups
formed with Anionic
Complexes
Carbonates
Sulfates
Phosphates
Silicates
Amount of residual chargeindicates relative strengthbonds with cations, which
reflected in the hardnessof the mineral
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Carbonates
Aragonite(High-P) Orthorhombic
Calcite(Low-P - Hexagonal)
Most are Hexa onal
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Other Carbonates
Azurite - Cu3(CO3)2(OH)2 (Blue)
Malachite – Cu2CO3(OH)2 (Green)
Rhodochrosite – MnCO3
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Borates
Kernite – Na2B4O6(OH)2·3H2O
Borax - Na2B4O5(OH)4·8H2O
Ulexite – NaCaB5O6(OH)6·5H2O
H – 2-2.5; SG – 1.7
H – 3; SG – 1.95
H – 1-2.5; SG – 1.96
“Television Rock”
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Sulfates
HYDROUS ANHYDROUS
Gypsum – CaSO4·2H2O
Alunite – KAl3(SO4)2(OH)6 Barite – BaSO4
Anhydrite – CaSO4
H: 3-3.5SG: 4.5
H: 3-3.5SG: 2.9
H: 2SG: 2.32
H: 4SG: ~2.7
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Tungstates & Molybdates
Woframite – (Fe,Mn)WO4
Scheelite – CaWO4
Wulfenite – PbMoO4
SG: 7-7.5
SG: ~6
SG: 6.8
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Phosphates
Apatite – Ca5(PO4)3(F,Cl,OH)
–prismatic hexagonal crystals
– common in igneous rocks andhydrothermal deposits
- variable colors
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Other Common Phosphates
Monazite – (Ce,La,Y,Th)PO4
Ore mineral for Rare Earth Elements
Useful mineral in U-Pb and Th age
dating
Wavellite – Al3(PO4)2(OH)3·5H2ORadiating globular aggregates
Turquoise – CuAl6(PO4)4(OH)8·5H2O