oxides and hydroxidesruby.colorado.edu/~smyth/g3010/18oxides.pdf · • geikielite mgtio 3 •...
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Descriptive Mineralogy
Oxides and Hydroxides
Classification of the Minerals• Non-Silicates
– Native Elements
– Halides– Sulfides– Oxides– Hydroxides– Carbonates– Sulfates– Phosphates
• Silicates– Orthosilicates– Sorosilicates– Cyclosilicates– Chain Silicates– Layer Silicates– Tektosilicates
Simple Oxides• Hemioxides
– Cuprite (Cu2O)– Ice (H2O)
• Monoxides– Periclase (MgO)– Wüstite (FeO)– Manganosite (MnO)– Lime (CaO)– Zincite (ZnO)– Bromellite (BeO)– Tenorite (CuO)
• Sesquioxides– Corundum (Al2O3)– Hematite (Fe2O3)– Bixbyite (Mn2O3)
• Dioxides– Rutile (TiO2)– Anatase (TiO2)– Brookite (TiO2)– Cassiterite(SnO2)– Pyrolusite(MnO2)
Simple Oxides
Hemi-Oxides (M2O)
• Ice (H2O) Hexagonal• Cuprite (Cu2O)• Why not Na2O?
– (Na radius too large)
Cuprite Cu2O
• Occurrence: Low Temp Hydrothermal (Supergene)
• Use: Minor ore of Cu
Ice H2O
Crystal System Hexagonal
Point Group 6/mmm
Space Group P63/mmc
Optical Uniaxial
Color Colorless
Luster Vitreous
Hardness 1.5
Density 0.95
Ice H2O
Ice H2O
Ice H2O
High Pressure
Phase Diagram
Monoxides (MO)• Rocksalt oxides
– Periclase MgO - Wüstite FeO– Manganosite MnO– Lime CaO– Bunsenite NiO
• Zincite oxides: – Zincite ZnO, – Bromellite BeO
• Other monoxides: – TenoriteCuO, Montroydite HgO
Rocksalt OxidesMgO - FeO - MnO - CaO
Crystal System Cubic
Point Group 4/m-32/m
Space Group Fm3m
Optical Isotropic
Periclase - WüstiteMgO - FeO
Lower mantle phase
Mg2SiO4 = MgSiO3 + MgO
Ringwoodite = Perovskite + periclase
Periclase MgO
Sesquioxides (M2O3)
• Corundum Group– Corundum Al2O3
– Hematite Fe2O3
– Karelianite V2O3 and Eskolaite Cr2O3
• Other Sesquioxides– Bixbyite Mn2O3
Corundum Al2O3
Crystal System Trigonal
Point Group -32/m
Space Group R-3c
Optical Uniaxial
Color Colorless
Luster Vitreous
Hardness 9
Density 4.02
Corundum Al2O3
Corundum Al2O3
Hematite Fe2O3
Crystal System Trigonal
Point Group -32/m
Space Group R-3c
Optical Nearly opaque
Color Red/Metallic
Luster Earthy/metallic
Hardness 6
Density 5.26
Hematite Fe2O3
Bixbyite Mn2O3
Crystal System Cubic
Point Group 4/m-32/m
Space Group Ia3
Optical Nearly opaque
Color Red/Metallic
Luster Earthy/metallic
Hardness 6
Density 4.95
Dioxides• Rutile Group
– Rutile TiO2; Anatase; Brookite– Cassiterite SnO2
– Pyrolusite MnO2
– Stishovite SiO2
• Uraninite (UO2) and Thorianite (ThO2)
• Baddeleyite ZrO2
Rutile TiO2Pyrolusite MnO2Cassiterite SnO2Stishovite SiO2
Rutile TiO2
Crystal System Tetragonal
Point Group 4/mmm
Space Group P42/mnm
Optical Nearly opaque
Color Red
Luster Adamantine
Hardness 6
Density 4.23
Anatase and Brookite TiO2
Cassiterite SnO2
Uraninite UO2Crystal System Cubic
Point Group 4/m-32/m
Space Group Fm-3m
Optical Nearly opaque
Color Black
Luster Submetallic
Hardness 5.5
Density 7-9
Occurrence Lo T HydRoll-front
Use: Major Ore of U
Simple Oxides
Complex Oxides
• Two or more different cations– Spinel Group: M2TO4
– Ilmenite Group : FeTiO3
– Pseudobrookite Group : A2BO5
– Perovskite Group : CaTiO3
• High Pressure silicate analogues
Spinel Group• Spinel MgAl2O4
• Hercynite FeAl2O4
• Chromite FeCr2O4
• Magnesiochromite MgCr2O4
• Magnetite Fe2+Fe3+2O4
• Magnesioferrite MgFe2O4
• Gahnite ZnAl2O4
• Ulvospinel TiFe2O4
• Ringwoodite Mg2SiO4
Spinel Structure
Space Group Fd3m
Edge sharing octahedra
Cell edge ~8.5Å
Two octahedra per
Tetrahedron
MgAl2O4 (Normal) or
Al (MgAl) O4(Inverse)
Ilmenite Group
• Ilmenite FeTiO3
• Geikielite MgTiO3
• Akimotoite MgSiO3
Ilmenite Structure FeTiO3
• Corundum Structure
• Space Group R-3• Alternating
layers of Fe and Ti Octahedra
• Face-sharing Octahedra
• Dense
Pseudobrookite Group
• Pseudobrookite Fe2+Ti2O5
• Ferro-pseudobrookite TiFe3+2O5
• Armalcolite (Mg,Fe2+)Ti2O5
Pseudobrookite Structure
• Space Group Bbmm
• M1 dark • M2 lighter• Open
Structure
Accessory Oxides
Accessory Oxides
Perovskite
• Perovskite CaTiO3
• MgSiO3 (Lower mantle phase)
Perovskite Structure
• Pseudo-cubic• Orthorhombic• Space Group
Pbnm
Hydroxides
• Brucite Mg(OH)2
• Gibbsite Al(OH)3
• Boehmite and Diaspore AlO(OH)• Bauxite (Mixed Al hydroxides)• Goethite FeO(OH)
(+Lepidochrosite)• Limonite Fe(OH)3
Gibbsite Al(OH)3 Di-octahedral
• Two out of three possible octahedral sites occupied
• Tri-valentcations
Brucite Mg(OH)2 Tri-octahedral
• All three possible octahedral sites occupied
• Divalent cations