Introduction to Mineralogy, Second edition William D. Nesse Copyright © 2012, by Oxford University Press, Inc. CHAPTER 18 Oxides, Hydroxides, and Halides

Oxides, Hydroxides Halides, Carbonates, Sulfates, and Phosphates

Oxides: simple structure like Halite (NaCl) One or more metals join with oxygen: Isodesmic, ionic bonding (except Ice) Cubic or hexagonal close packing Most are highly symmetrical and belong to isometric system Ice is a molecular crystal Widely distributed, can be mined for metal if in geologic concentrations

Introduction to Mineralogy, Second edition William D. Nesse Copyright © 2012, by Oxford University Press, Inc. Cuprite (cubic) and Ice (hexagonal) structure

Oxide Minerals (note the z:o ratio) GroupMineralComposition X2OX2OCuprite Ice Cu 2 O H 2 O XOPericlase Zincite MgO ZnO X2O3X2O3 Hematite Corundum Ilmenite Fe 2 O 3 Al 2 O 3 FeTiO 3 XY 2 O 4 Magnetite Chromite Spinel Chrysoberyl FeFe 2 O 4 FeCr 2 O 4 MgAl 2 O 4 BeAl 2 O 4 XO 2 Rutile Cassiterite Pyrolusite Uraninite TiO 2 SnO 2 MnO 2 UO 2

Fe-Ti oxides Fe +2 Fe +3

Introduction to Mineralogy, Second edition William D. Nesse Copyright © 2012, by Oxford University Press, Inc.

Spinel Group (XY 2 O 4 ) Gem-qualitySpinels

Other Common Oxides Rutile (TiO 2 ) Rutile needles in Quartz Pyrolusite dendrites on fracture faces Pyrolusite (MnO 2 ) Mass of botryoidal Pyrolusite Corundum (Al 2 O 3 ) Hardness=9 Red = Ruby Blue = Sapphire Chrysoberyl (BeAl 2 O 4 ) Cyclic twinning in Chrysoberyl

Introduction to Mineralogy, Second edition William D. Nesse Copyright © 2012, by Oxford University Press, Inc. Figure 18.9 Brucite and gibbsite structure. Hydroxides (OH) - main anionic group forming octahedrally coordinated sheets with weak bonds between Two structural types: Brucite-type – trioctahedral sheets (all octahedral cation sites are filled) Gibbsite-type – dioctahedral sheets (only two of three octahedral sites are filled)

Common Types of Hydroxides Brucite Mg(OH) 2 Gibbsite Al(OH) 3 Manganite MnO(OH) Diaspore  AlO(OH) Goethite  FeO(OH) Bauxite Al-hydroxide* *hybrid mix of diaspore, gibbsite, and boehmite (  AlO(OH))

Halides Simple compounds composed of large halogen anions (Cl, Br, F, I) Typically isometric Dominantly ionic bonding Properties – low hardness, high melting points, poor conductors (except at high temperatures)

Introduction to Mineralogy, Second edition William D. Nesse Copyright © 2012, by Oxford University Press, Inc. Figure Halite structure. Each Na + coordinates with six Cl −.

Common Halides Halite (NaCl) Sylvite (KCl) Flourite (CaF 2 )

Mineral Groups formed with Anionic Complexes CarbonatesSulfatesPhosphatesSilicates Amount of residual charge indicates relative strength bonds with cations, which reflected in the hardness of the mineral Recall: Anisodesmic and Mesodesmic bonds

Introduction to Mineralogy, Second edition William D. Nesse Copyright © 2012, by Oxford University Press, Inc. Figure 17.1 CO 3 2− anionic groups. A carbon cation is situated at the center of three oxygen anions. Sheets of Oxygen, alternating with divalent cations in octahedral coordination. In calcite all cation layers contain Ca. In Dolomite, alternately Ca and Mg. Other ions can be Fe (siderite), Mn (Rhodochrosite) Complete solid solution between Mg (0.86A) and Fe3+ (0.92A) Limited solid solution between Mg (0.86A) and Mn (0.96A) Ca (1.14A) has only limited solid solution with Mg, Mn and Fe Calcite and Aragonite (stable at higher pressure, denser) are polymorphs.

CarbonatesAragonite (High-P) Orthorhombic Calcite (Low-P - Hexagonal) Most are Hexagonal

Other Carbonates OH bearing carbonates: Azurite - Cu 3 (CO 3 ) 2 (OH) 2 (Blue) Malachite – Cu 2 CO 3 (OH) 2 (Green) Found in the oxidized zone of hydrothermal deposits Rhodochrosite – MnCO 3

Introduction to Mineralogy, Second edition William D. Nesse Copyright © 2012, by Oxford University Press, Inc. Figure 17.5 Index of refraction n ω in the rhombohedral carbonates. After Kennedy (1947).

Borates Kernite – Na 2 B 4 O 6 (OH) 2 ·3H 2 O Borax - Na 2 B 4 O 5 (OH) 4 ·8H 2 O Ulexite – NaCaB 5 O 6 (OH) 6 ·5H 2 O H – 2-2.5; SG – 1.7 H – 3; SG – 1.95 H – 1-2.5; SG – 1.96 “Television Rock”

Sulfates (see Table 17.4) HYDROUS (stable phase)ANHYDROUS (high salinity) Gypsum – CaSO 4 ·2H 2 O Alunite – KAl 3 (SO 4 ) 2 (OH) 6 Barite – BaSO 4 Anhydrite – CaSO 4 H: SG: 4.5 H: SG: 2.9 H: 2 SG: 2.32 H: 4 SG: ~2.7

Tungstates & Molybdates Woframite – (Fe,Mn)WO 4 Scheelite – CaWO 4 Wulfenite – PbMoO 4 SG: SG: ~6 SG: 6.8

Phosphates Apatite – Ca 5 (PO 4 ) 3 (F,Cl,OH) –Fluroapatite, chlorapatite, hydroxy apatite –prismatic hexagonal crystals –common in igneous rocks and hydrothermal deposits - variable colors

Other Common Phosphates Monazite – (Ce,La,Y,Th)PO 4 Ore mineral for Rare Earth Elements Useful mineral in U-Pb and Th age dating Wavellite – Al 3 (PO 4 ) 2 (OH) 3 ·5H 2 O Radiating globular aggregates Turquoise – CuAl 6 (PO 4 ) 4 (OH) 8 ·5H 2 O