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Transcript of Introduction to Mineralogy, Second edition William D. Nesse Copyright © 2012, by Oxford University...
Introduction to Mineralogy, Second edition
William D. Nesse Copyright © 2012, by Oxford University Press, Inc.
CHAPTER 18
Oxides, Hydroxides,and Halides
Oxides, Hydroxides Halides, Carbonates, Sulfates, and
Phosphates
• Oxides: simple structure like Halite (NaCl)• One or more metals join with oxygen: • Isodesmic, ionic bonding (except Ice)• Cubic or hexagonal close packing• Most are highly symmetrical and belong to
isometric system• Ice is a molecular crystal• Widely distributed, can be mined for metal if in
geologic concentrations
Introduction to Mineralogy, Second edition
William D. Nesse Copyright © 2012, by Oxford University Press, Inc.
Cuprite (cubic) and Ice (hexagonal) structure
Oxide Minerals(note the z:o ratio)
Group Mineral CompositionX2O Cuprite
IceCu2OH2O
XO PericlaseZincite
MgOZnO
X2O3 HematiteCorundumIlmenite
Fe2O3
Al2O3
FeTiO3
XY2O4 MagnetiteChromiteSpinelChrysoberyl
FeFe2O4
FeCr2O4
MgAl2O4
BeAl2O4
XO2 RutileCassiteritePyrolusiteUraninite
TiO2
SnO2
MnO2
UO2
Fe-Ti oxides
FeFe+2+2 FeFe+3+3
Introduction to Mineralogy, Second edition
William D. Nesse Copyright © 2012, by Oxford University Press, Inc.
Spinel Group (XY2O4)
Gem-quality Gem-quality SpinelsSpinels
Other Common OxidesRutile (TiORutile (TiO22))
Rutile needles in Rutile needles in QuartzQuartz
Pyrolusite dendritesPyrolusite dendriteson fracture faceson fracture faces
Pyrolusite (MnOPyrolusite (MnO22))
Mass of botryoidal Mass of botryoidal PyrolusitePyrolusite
Corundum (AlCorundum (Al22OO33))
Hardness=9Hardness=9
Red = RubyRed = RubyBlue = SapphireBlue = Sapphire
Chrysoberyl (BeAlChrysoberyl (BeAl22OO44))
Cyclic twinningCyclic twinningin Chrysoberylin Chrysoberyl
Introduction to Mineralogy, Second edition
William D. Nesse Copyright © 2012, by Oxford University Press, Inc.
Figure 18.9 Brucite and gibbsite structure.
Hydroxides(OH)- main anionic group forming octahedrally
coordinated sheets with weak bonds between
Two structural types:
Brucite-typeBrucite-type – trioctahedral – trioctahedral sheets (all octahedral cation sheets (all octahedral cation sites are filled)sites are filled)
Gibbsite-typeGibbsite-type – dioctahedral – dioctahedral sheets (only two of three sheets (only two of three octahedral sites are filled)octahedral sites are filled)
Common Types of HydroxidesBrucite Brucite Mg(OH)Mg(OH)22 Gibbsite Gibbsite Al(OH)Al(OH)33
Manganite Manganite MnO(OH)MnO(OH) DiasporeDiaspore AlO(OH)AlO(OH)
GoethiteGoethite FeO(OH)FeO(OH) Bauxite Bauxite Al-hydroxide* Al-hydroxide*
*hybrid mix of diaspore, gibbsite, and boehmite (*hybrid mix of diaspore, gibbsite, and boehmite (AlO(OH))AlO(OH))
Halides
• Simple compounds composed of large halogen anions (Cl, Br, F, I)
• Typically isometric• Dominantly ionic bonding• Properties – low hardness, high melting
points, poor conductors (except at high temperatures)
Introduction to Mineralogy, Second edition
William D. Nesse Copyright © 2012, by Oxford University Press, Inc.
Figure 18.11 Halite structure. Each Na+ coordinates with six Cl−.
Common Halides
Halite (NaCl)
Sylvite (KCl)
Flourite (CaF2)
Mineral Groups
formed with Anionic
Complexes
CarbonatesCarbonates
SulfatesSulfates
PhosphatesPhosphates
SilicatesSilicates
Amount of residual chargeindicates relative strength bonds with cations, which reflected in the hardness of the mineral
Recall: Anisodesmic and Mesodesmic bonds
Introduction to Mineralogy, Second edition
William D. Nesse Copyright © 2012, by Oxford University Press, Inc.
Figure 17.1 CO3 2− anionic groups. A carbon cation is situated at the center of three oxygen anions.
Sheets of Oxygen, alternating with divalent cations in octahedral coordination. In calcite all cation layers contain Ca. In Dolomite, alternately Ca and Mg. Other ions can be Fe (siderite), Mn (Rhodochrosite)Complete solid solution between Mg (0.86A) and Fe3+ (0.92A)Limited solid solution between Mg (0.86A) and Mn (0.96A)Ca (1.14A) has only limited solid solution with Mg, Mn and FeCalcite and Aragonite (stable at higher pressure, denser) are polymorphs.
Carbonates
AragoniteAragonite(High-P) Orthorhombic(High-P) Orthorhombic
CalciteCalcite(Low-P - Hexagonal)(Low-P - Hexagonal)
Most are Hexagonal Most are Hexagonal
Other Carbonates
OH bearing carbonates:OH bearing carbonates:
Azurite - CuAzurite - Cu33(CO(CO33))22(OH)(OH)2 2 (Blue)(Blue)
Malachite – CuMalachite – Cu22COCO33(OH)(OH)22 (Green) (Green)
Found in the oxidized zone of Found in the oxidized zone of
hydrothermal depositshydrothermal depositsRhodochrosite – MnCORhodochrosite – MnCO33
Introduction to Mineralogy, Second edition
William D. Nesse Copyright © 2012, by Oxford University Press, Inc.
Figure 17.5 Index of refraction nω in the rhombohedral carbonates. After Kennedy (1947).
Borates
Kernite – Na2B4O6(OH)2·3H2O
Borax - Na2B4O5(OH)4·8H2O
Ulexite – NaCaB5O6(OH)6·5H2O
H – 2-2.5; SG – 1.7H – 2-2.5; SG – 1.7
H – 3; SG – 1.95H – 3; SG – 1.95
H – 1-2.5; SG – 1.96H – 1-2.5; SG – 1.96
““Television Rock”Television Rock”
Sulfates(see Table 17.4)
HYDROUS (stable phase) ANHYDROUS (high salinity)
Gypsum – CaSOGypsum – CaSO44·2H·2H22OO
Alunite – KAlAlunite – KAl33(SO(SO44))22(OH)(OH)66 Barite – BaSOBarite – BaSO44
Anhydrite – CaSOAnhydrite – CaSO44
H: 3-3.5H: 3-3.5SG: 4.5SG: 4.5
H: 3-3.5H: 3-3.5SG: 2.9SG: 2.9
H: 2H: 2SG: 2.32SG: 2.32
H: 4H: 4SG: ~2.7SG: ~2.7
Tungstates & Molybdates
Woframite – (Fe,Mn)WOWoframite – (Fe,Mn)WO44
Scheelite – CaWOScheelite – CaWO44
Wulfenite – PbMoOWulfenite – PbMoO44
SG: 7-7.5SG: 7-7.5
SG: ~6SG: ~6
SG: 6.8SG: 6.8
Phosphates• Apatite – Ca5(PO4)3(F,Cl,OH)
– Fluroapatite, chlorapatite, hydroxy apatite– prismatic hexagonal crystals– common in igneous rocks and hydrothermal
deposits- variable colors
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 – AlWavellite – Al33(PO(PO44))22(OH)(OH)33·5H·5H22OORadiating globular aggregatesRadiating globular aggregates
Turquoise – Turquoise – CuAlCuAl66(PO(PO44))44(OH)(OH)88·5H·5H22OO