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Lecture Notes Oxides and Hydroxides

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Descriptive Mineralogy<br />

<strong>Oxides</strong> <strong>and</strong><br />

<strong>Hydroxides</strong><br />

• Hemioxides<br />

– Cuprite (Cu 2O)<br />

– Ice (H 2O)<br />

• Monoxides<br />

– Periclase (MgO)<br />

– Wüstite (FeO)<br />

– Manganosite (MnO)<br />

– Lime (CaO)<br />

– Zincite (ZnO)<br />

– Bromellite (BeO)<br />

– Tenorite (CuO)<br />

Simple <strong>Oxides</strong><br />

• Sesquioxides<br />

– Corundum (Al 2O 3)<br />

– Hematite (Fe 2O 3)<br />

– Bixbyite (Mn 2O 3)<br />

• Dioxides<br />

– Rutile (TiO 2)<br />

– Anatase (TiO 2)<br />

– Brookite (TiO 2)<br />

– Cassiterite(SnO 2)<br />

– Pyrolusite(MnO 2)<br />

Hemi-<strong>Oxides</strong> (M2O)<br />

• Ice (H2O) Hexagonal<br />

• Cuprite (Cu2O)<br />

• Why not Na2O?<br />

– Na radius too large<br />

– Na has no covalent orbitals available<br />

Classification of the Minerals<br />

• Non-Silicates<br />

– Native Elements<br />

– Halides<br />

– Sulfides<br />

– <strong>Oxides</strong><br />

– <strong>Hydroxides</strong><br />

– Carbonates<br />

– Sulfates<br />

– Phosphates<br />

Simple <strong>Oxides</strong><br />

• Silicates<br />

– Orthosilicates<br />

– Sorosilicates<br />

– Cyclosilicates<br />

– Chain Silicates<br />

– Layer Silicates<br />

– Tektosilicates<br />

Hemi-<strong>Oxides</strong> (M2O)<br />

• Na 2O occurs as a mineral<br />

– A. True<br />

– B. False<br />

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1


Cuprite Cu 2O<br />

• Occurrence: Low Temp<br />

Hydrothermal (Supergene)<br />

• Use: Minor ore of Cu<br />

Ice H 2O<br />

Crystal System Hexagonal<br />

Point Group 6/mmm<br />

Space Group P63/mmc Optical Uniaxial<br />

Color Colorless<br />

Luster Vitreous<br />

Hardness 1.5<br />

Density 0.95<br />

Ice H 2O snow morphology<br />

Cuprite Cu 2O<br />

Ice H 2O<br />

• Occurrence: Low<br />

Temp Hydrothermal<br />

(Supergene)<br />

• Strongly covalent<br />

• O SP 3<br />

• Cu SP<br />

• Use: Minor ore of Cu<br />

Ice H 2O<br />

High<br />

Pressure<br />

Phase<br />

Diagram<br />

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Ice H 2O What’s Wrong Here?<br />

Monoxides (MO)<br />

• Rocksalt oxides<br />

– Periclase MgO - Wüstite FeO<br />

– Manganosite MnO<br />

– Lime CaO<br />

– Bunsenite NiO<br />

• Zincite oxides:<br />

– Zincite ZnO,<br />

– Bromellite BeO<br />

• Other monoxides:<br />

– TenoriteCuO, Montroydite HgO<br />

Periclase - Wüstite<br />

MgO - FeO<br />

Lower mantle phase<br />

Mg2SiO4 = MgSiO3 + MgO<br />

Ringwoodite = Perovskite + periclase<br />

Rocksalt <strong>Oxides</strong><br />

MgO -FeO -MnO -CaO<br />

Crystal System Cubic<br />

Point Group 4/m-32/m<br />

Space Group Fm3m<br />

Optical Isotropic<br />

Periclase<br />

MgO<br />

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Zincite Group<br />

ZnO – Zincite,<br />

BeO Bromellite<br />

Crystal System Hexagonal Point Group 6mm<br />

Space Group P63mc Optical Uniaxial<br />

Extreme Piezoelectric<br />

Uses: Transducers<br />

Sesquioxides (M2O3)<br />

• Corundum Group<br />

– Corundum Al2O3<br />

– Hematite Fe2O3<br />

– Karelianite V2O3 <strong>and</strong> Eskolaite Cr2O3<br />

• Other Sesquioxides<br />

– Bixbyite Mn2O3<br />

Corundum Al 2O 3<br />

Other Monoxides<br />

CuO – Tenorite<br />

HgO Montroydite<br />

Oxidized hydrothermal deposits<br />

Covalent Bonding<br />

Irregular coordination<br />

Corundum Al 2O 3<br />

Crystal System Trigonal<br />

Point Group -32/m<br />

Space Group R-3c<br />

Optical Uniaxial<br />

Color Colorless<br />

Luster Vitreous<br />

Hardness 9<br />

Density 4.02<br />

Corundum Al 2O 3<br />

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Hematite Fe 2O 3<br />

Crystal System Trigonal<br />

Point Group -32/m<br />

Space Group R-3c<br />

Optical Nearly opaque<br />

Color Red/Metallic<br />

Luster Earthy/metallic<br />

Hardness 6<br />

Density 5.26<br />

Bixbyite Mn 2O 3<br />

Crystal System Cubic<br />

Point Group 4/m-32/m<br />

Space Group Ia3<br />

Optical Nearly opaque<br />

Color Red/Metallic<br />

Luster Earthy/metallic<br />

Hardness 6<br />

Density 4.95<br />

Rutile TiO 2<br />

Pyrolusite MnO 2<br />

Cassiterite SnO 2<br />

Stishovite SiO 2<br />

Hematite Fe 2O 3<br />

Dioxides<br />

• Rutile Group<br />

– Rutile TiO2; Anatase; Brookite<br />

– Cassiterite SnO2<br />

– Pyrolusite MnO2<br />

– Stishovite SiO2<br />

• Uraninite (UO2) <strong>and</strong> Thorianite<br />

(ThO2)<br />

• Baddeleyite ZrO2<br />

Rutile TiO 2<br />

Crystal System Tetragonal<br />

Point Group 4/mmm<br />

Space Group P42/mnm Optical Nearly opaque<br />

Color Red<br />

Luster Adamantine<br />

Hardness 6<br />

Density 4.23<br />

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Anatase <strong>and</strong> Brookite TiO 2 Cassiterite SnO2<br />

Uraninite UO2 Crystal System Cubic<br />

Point Group 4/m-32/m<br />

Space Group Fm-3m<br />

Optical Nearly opaque<br />

Color Black<br />

Luster Submetallic<br />

Hardness 5.5<br />

Density 7-9<br />

Occurrence Lo T Hyd<br />

Roll-front<br />

Use: Major Ore of U<br />

Simple <strong>Oxides</strong><br />

Uraninite UO 2<br />

The Major ore of U<br />

U4+ or U6+?<br />

Same structure as fluorite<br />

U6+ is soluble U4+ is insoluble<br />

U is mobilized by oxidation; immobilized by reduction<br />

Roll-front deposits.<br />

Natural reactors<br />

Complex <strong>Oxides</strong><br />

• Two or more different cations<br />

– Spinel Group: M2TO4<br />

– Ilmenite Group : FeTiO3<br />

– Pseudobrookite Group : A2BO5<br />

– Perovskite Group : CaTiO3<br />

• High Pressure silicate analogues<br />

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Spinel Group<br />

• Spinel MgAl2O4<br />

• Hercynite FeAl2O4<br />

• Chromite FeCr2O4<br />

• Magnesiochromite MgCr2O4<br />

• Magnetite Fe 2+ Fe 3+ 2O4<br />

• Magnesioferrite MgFe2O4<br />

• Gahnite ZnAl2O4<br />

• Ulvospinel TiFe2O4<br />

• Ringwoodite Mg2SiO4<br />

Ringwoodite<br />

(spinel) γ-(MgFe) 2SiO 4<br />

• Dark blue<br />

color<br />

• 525 –<br />

660km<br />

• ~5%<br />

Earth<br />

Ilmenite Structure FeTiO 3<br />

• Corundum<br />

Structure<br />

• Space Group R-3<br />

• Alternating<br />

layers of Fe <strong>and</strong><br />

Ti Octahedra<br />

• Face-sharing<br />

Octahedra<br />

• Dense<br />

Space Group Fd3m<br />

Edge sharing<br />

octahedra<br />

Cell edge ~8.5Å<br />

Two octahedra per<br />

Tetrahedron<br />

MgAl2O4 (Normal)<br />

or<br />

Al (MgAl) O4 (Inverse)<br />

Spinel Structure<br />

Ilmenite Group<br />

• Ilmenite FeTiO3 • Geikielite MgTiO3 • Akimotoite MgSiO3 Pseudobrookite Group<br />

• Pseudobrookite Fe 2+ Ti2O5<br />

• Ferro-pseudobrookite TiFe 3+ 2O5<br />

• Armalcolite (Mg,Fe 2+ )Ti2O5<br />

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7


Pseudobrookite Structure<br />

• Space<br />

Group<br />

Bbmm<br />

• M1 dark<br />

• M2 lighter<br />

• Open<br />

Structure<br />

Accessory <strong>Oxides</strong><br />

Perovskite Structure<br />

• Pseudo-cubic<br />

• Orthorhombic<br />

• Space Group<br />

Pbnm<br />

Accessory <strong>Oxides</strong><br />

Perovskite<br />

• Perovskite CaTiO 3<br />

• MgSiO 3 (Lower mantle phase)<br />

<strong>Hydroxides</strong><br />

• Brucite Mg(OH) 2<br />

• Gibbsite Al(OH) 3<br />

• Boehmite <strong>and</strong> Diaspore AlO(OH)<br />

• Bauxite (Mixed Al hydroxides)<br />

• Goethite FeO(OH)<br />

(+Lepidochrosite)<br />

• Limonite Fe(OH) 3<br />

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• Two out of<br />

three<br />

possible<br />

octahedral<br />

sites<br />

occupied<br />

• Tri-valent<br />

cations<br />

Gibbsite Al(OH) 3<br />

Di-octahedral<br />

• All three<br />

possible<br />

octahedral<br />

sites<br />

occupied<br />

• Divalent<br />

cations<br />

Brucite Mg(OH) 2<br />

Tri-octahedral<br />

12/1/2012<br />

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