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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– Na has no covalent orbitals available

Hemi-Oxides (M2O)

• Na2O occurs as a mineral

– A. True– B. False

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Cuprite Cu2O

• Occurrence: Low Temp Hydrothermal (Supergene)

• Use: Minor ore of Cu

Cuprite Cu2O

• Occurrence: Low Temp Hydrothermal (Supergene)

• 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

Ice H2O snow morphology

Ice H2O

High Pressure

Phase Diagram

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Ice H2O What’s Wrong Here?

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

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Zincite GroupZnO – Zincite,

BeO BromelliteCrystal System Hexagonal Point Group 6mm

Space Group P63mc Optical Uniaxial

Extreme Piezoelectric

Uses: Transducers

Other MonoxidesCuO – Tenorite

HgO MontroyditeOxidized hydrothermal deposits

Covalent Bonding

Irregular coordination

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

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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

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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 Hyd Roll-front

Use: Major Ore of U

Uraninite UO2The Major ore of U

U4+ or U6+?

Same structure as fluorite

U6+ is soluble U4+ is insoluble

U is mobilized by oxidation; immobilized by reduction

Roll-front deposits.

Natural reactors

Simple OxidesComplex 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 MgAl2O4

• Hercynite FeAl2O4

• Chromite FeCr2O4

• Magnesiochromite MgCr2O4

• Magnetite Fe2+Fe3+2O4

• Magnesioferrite MgFe2O4

• Gahnite ZnAl2O4

• Ulvospinel TiFe2O4

• Ringwoodite Mg2SiO4

Spinel Structure

Space Group Fd3mEdge sharing octahedra

Cell edge ~8.5Å

Two octahedra per

Tetrahedron

MgAl2O4 (Normal) or

Al (MgAl) O4(Inverse)

Ringwoodite (spinel) γ-(MgFe)2SiO4

• Dark blue color

• 525 –660km

• ~5% Earth

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

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Pseudobrookite Structure

• Space Group Bbmm

• M1 dark • M2 lighter• Open

Structure

Accessory Oxides

Accessory OxidesPerovskite

• 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

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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