Oxides and Hydroxides

Home , Cuprite, Manganosite, Periclase, Zincite

12/1/2012

Classification of the Minerals Descriptive Mineralogy • Non-Silicates • Silicates – Native Elements – Orthosilicates – Halides – Sorosilicates – Sulfides – Cyclosilicates Oxides and – Oxides – Chain Silicates – Hydroxides – Layer Silicates Hydroxides – Carbonates – Tektosilicates – Sulfates – Phosphates

Simple Oxides Simple Oxides

• Hemioxides • Sesquioxides – Cuprite (Cu O) 2 – Corundum (Al2O3) – Ice (H O) 2 – Hematite (Fe2O3) • Monoxides – Bixbyite (Mn2O3) – Periclase (MgO) • Dioxides – Wüstite (FeO) – Rutile (TiO2) – Manganosite (MnO) – Anatase (TiO2) – Lime (CaO) – Brookite (TiO2) – Zincite (ZnO) – Cassiterite(SnO2) – Bromellite (BeO) – Pyrolusite(MnO2) – Tenorite (CuO)

Hemi-Oxides (M2O) Hemi-Oxides (M2O)

• Ice (H2O) Hexagonal • Na2O occurs as a mineral • Cuprite (Cu2O) • Why not Na2O? – A. True – Na radius too large – B. False – Na has no covalent orbitals available

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Cuprite Cu2O Cuprite Cu2O • Occurrence: Low • Occurrence: Low Temp Temp Hydrothermal Hydrothermal (Supergene) (Supergene) • Use: Minor ore of Cu • Strongly covalent •O SP3 •Cu SP • 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 snow morphology

Ice H2O

High Pressure Phase Diagram

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Ice H2O What’s Wrong Here?

Monoxides (MO) Rocksalt Oxides • Rocksalt oxides MgO -FeO -MnO -CaO – Periclase MgO - Wüstite FeO – Manganosite MnO Crystal System Cubic – Lime CaO Point Group 4/m-32/m – Bunsenite NiO • Zincite oxides: Space Group Fm3m Optical Isotropic – Zincite ZnO, – Bromellite BeO • Other monoxides: – TenoriteCuO, Montroydite HgO

Periclase - Wüstite MgO - FeO Periclase MgO

Lower mantle phase

Mg2SiO4 = MgSiO3 + MgO Ringwoodite = Perovskite + periclase

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Zincite Group Other Monoxides ZnO – Zincite, CuO – Tenorite BeO Bromellite HgO Montroydite Crystal System Hexagonal Point Group 6mm Oxidized hydrothermal deposits Space Group P63mc Optical Uniaxial Extreme Piezoelectric Covalent Bonding Uses: Transducers Irregular coordination

Corundum Al2O3 Sesquioxides (M2O3) Crystal System Trigonal • Corundum Group Point Group -32/m – Corundum Al2O3 Space Group R-3c – Hematite Fe2O3 Optical Uniaxial – Karelianite V2O3 and Eskolaite Cr2O3 Color Colorless • Other Sesquioxides Luster Vitreous – Bixbyite Mn2O3 Hardness 9 Density 4.02

Corundum Al2O3 Corundum Al2O3

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Hematite Fe2O3 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

Bixbyite Mn2O3 Dioxides

Crystal System Cubic • Rutile Group Point Group 4/m-32/m – Rutile TiO2; Anatase; Brookite Space Group Ia3 – Cassiterite SnO2 Optical Nearly opaque – Pyrolusite MnO2 Color Red/Metallic – Stishovite SiO2 Luster Earthy/metallic • Uraninite (UO2) and Thorianite Hardness 6 (ThO2) Density 4.95 • Baddeleyite ZrO2

Rutile TiO Rutile TiO2 2 Pyrolusite MnO2 Crystal System Tetragonal Cassiterite SnO2 Point Group 4/mmm Stishovite SiO2 Space Group P42/mnm Optical Nearly opaque Color Red Luster Adamantine Hardness 6 Density 4.23

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Anatase and Brookite TiO 2 Cassiterite SnO2

Uraninite UO2 Uraninite UO2 Crystal System Cubic The Major ore of U Point Group 4/m-32/m U4+ or U6+? Space Group Fm-3m Same structure as fluorite Optical Nearly opaque U6+ is soluble U4+ is insoluble Color Black U is mobilized by oxidation; immobilized by reduction Luster Submetallic Roll-front deposits. Hardness 5.5 Natural reactors Density 7-9 Occurrence Lo T Hyd Roll-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

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Spinel Group Spinel Structure

• Spinel MgAl2O4 Space Group Fd3m • Hercynite FeAl2O4 Edge sharing • Chromite FeCr2O4 octahedra • Magnesiochromite MgCr2O4 Cell edge ~8.5Å 2+ 3+ • Magnetite Fe Fe 2O4 Two octahedra per • Magnesioferrite MgFe2O4 Tetrahedron • Gahnite ZnAl2O4 MgAl2O4 (Normal) • Ulvospinel TiFe2O4 or • Ringwoodite Mg2SiO4 Al (MgAl) O4 (Inverse)

Ringwoodite γ (spinel) -(MgFe)2SiO4 Ilmenite Group

• Ilmenite FeTiO3 • Dark blue • Geikielite MgTiO3 color • Akimotoite MgSiO3 • 525 – 660km • ~5% Earth

Ilmenite Structure FeTiO3 Pseudobrookite Group • Corundum Structure • Space Group R-3 • Pseudobrookite Fe2+Ti2O5 • Alternating • Ferro-pseudobrookite TiFe3+2O5 layers of Fe and • Armalcolite (Mg,Fe2+)Ti2O5 Ti Octahedra • Face-sharing Octahedra • Dense

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Accessory Oxides Pseudobrookite Structure

• Space Group Bbmm • M1 dark • M2 lighter • Open Structure

Accessory Oxides Perovskite

• Perovskite CaTiO3

• MgSiO3 (Lower mantle phase)

Perovskite Structure Hydroxides

• Pseudo-cubic • Brucite Mg(OH)2

• Orthorhombic • Gibbsite Al(OH)3 • Space Group • Boehmite and Diaspore AlO(OH) Pbnm • Bauxite (Mixed Al hydroxides) • Goethite FeO(OH) (+Lepidochrosite)

• Limonite Fe(OH)3

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Gibbsite Al(OH)3 Brucite Mg(OH)2 Di-octahedral Tri-octahedral

• Two out of • All three three possible possible octahedral octahedral sites sites occupied occupied • Divalent • Tri-valent cations cations