Descriptive Mineralogy

Oxides and Hydroxides Classification of the Minerals • Non-Silicates • Silicates – Native Elements – Orthosilicates – Halides – Sorosilicates – Sulfides – Cyclosilicates – Oxides – Chain Silicates – Hydroxides – Layer Silicates – Carbonates – Tektosilicates – Sulfates – Phosphates 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) 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 Oxides MgO-FeO-MnO-CaO

Crystal System Cubic Point Group 4/m-32/m Space Group Fm3m Optical Isotropic Periclase - Wüstite MgO - 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 TiO2 Pyrolusite MnO2 Cassiterite SnO2 Stishovite 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 UO2 Crystal 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 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 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-valent cations Brucite Mg(OH)2 Tri-octahedral

• All three possible octahedral sites occupied • Divalent cations