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)

Group Mineral CompositionX2O Cuprite

IceCu2OH2O

XO PericlaseZincite

MgOZnO

X2O3 HematiteCorundumIlmenite

Fe2O3

Al2O3

FeTiO3

XY2O4 MagnetiteChromiteSpinelChrysoberyl

FeFe2O4

FeCr2O4

MgAl2O4

BeAl2O4

XO2 RutileCassiteritePyrolusiteUraninite

TiO2

SnO2

MnO2

UO2

Fe-Ti oxides

FeFe+2+2 FeFe+3+3

Introduction to Mineralogy, Second edition

William D. Nesse Copyright © 2012, by Oxford University Press, Inc.

Spinel Group (XY2O4)

Gem-quality Gem-quality SpinelsSpinels

Other Common OxidesRutile (TiORutile (TiO22))

Rutile needles in Rutile needles in QuartzQuartz

Pyrolusite dendritesPyrolusite dendriteson fracture faceson fracture faces

Pyrolusite (MnOPyrolusite (MnO22))

Mass of botryoidal Mass of botryoidal PyrolusitePyrolusite

Corundum (AlCorundum (Al22OO33))

Hardness=9Hardness=9

Red = RubyRed = RubyBlue = SapphireBlue = Sapphire

Chrysoberyl (BeAlChrysoberyl (BeAl22OO44))

Cyclic twinningCyclic twinningin Chrysoberylin 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-typeBrucite-type – trioctahedral – trioctahedral sheets (all octahedral cation sheets (all octahedral cation sites are filled)sites are filled)

Gibbsite-typeGibbsite-type – dioctahedral – dioctahedral sheets (only two of three sheets (only two of three octahedral sites are filled)octahedral sites are filled)

Common Types of HydroxidesBrucite Brucite Mg(OH)Mg(OH)22 Gibbsite Gibbsite Al(OH)Al(OH)33

Manganite Manganite MnO(OH)MnO(OH) DiasporeDiaspore AlO(OH)AlO(OH)

GoethiteGoethite FeO(OH)FeO(OH) Bauxite Bauxite Al-hydroxide* Al-hydroxide*

*hybrid mix of diaspore, gibbsite, and boehmite (*hybrid mix of diaspore, gibbsite, and boehmite (AlO(OH))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 18.11 Halite structure. Each Na+ coordinates with six Cl−.

Common Halides

Halite (NaCl)

Sylvite (KCl)

Flourite (CaF2)

Mineral Groups

formed with Anionic

Complexes

CarbonatesCarbonates

SulfatesSulfates

PhosphatesPhosphates

SilicatesSilicates

Amount of residual chargeindicates 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 CO3 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 FeCalcite and Aragonite (stable at higher pressure, denser) are polymorphs.

Carbonates

AragoniteAragonite(High-P) Orthorhombic(High-P) Orthorhombic

CalciteCalcite(Low-P - Hexagonal)(Low-P - Hexagonal)

Most are Hexagonal Most are Hexagonal

Other Carbonates

OH bearing carbonates:OH bearing carbonates:

Azurite - CuAzurite - Cu33(CO(CO33))22(OH)(OH)2 2 (Blue)(Blue)

Malachite – CuMalachite – Cu22COCO33(OH)(OH)22 (Green) (Green)

Found in the oxidized zone of Found in the oxidized zone of

hydrothermal depositshydrothermal depositsRhodochrosite – MnCORhodochrosite – MnCO33

Introduction to Mineralogy, Second edition

William D. Nesse Copyright © 2012, by Oxford University Press, Inc.

Figure 17.5 Index of refraction nω in the rhombohedral carbonates. After Kennedy (1947).

Borates

Kernite – Na2B4O6(OH)2·3H2O

Borax - Na2B4O5(OH)4·8H2O

Ulexite – NaCaB5O6(OH)6·5H2O

H – 2-2.5; SG – 1.7H – 2-2.5; SG – 1.7

H – 3; SG – 1.95H – 3; SG – 1.95

H – 1-2.5; SG – 1.96H – 1-2.5; SG – 1.96

““Television Rock”Television Rock”

Sulfates(see Table 17.4)

HYDROUS (stable phase) ANHYDROUS (high salinity)

Gypsum – CaSOGypsum – CaSO44·2H·2H22OO

Alunite – KAlAlunite – KAl33(SO(SO44))22(OH)(OH)66 Barite – BaSOBarite – BaSO44

Anhydrite – CaSOAnhydrite – CaSO44

H: 3-3.5H: 3-3.5SG: 4.5SG: 4.5

H: 3-3.5H: 3-3.5SG: 2.9SG: 2.9

H: 2H: 2SG: 2.32SG: 2.32

H: 4H: 4SG: ~2.7SG: ~2.7

Tungstates & Molybdates

Woframite – (Fe,Mn)WOWoframite – (Fe,Mn)WO44

Scheelite – CaWOScheelite – CaWO44

Wulfenite – PbMoOWulfenite – PbMoO44

SG: 7-7.5SG: 7-7.5

SG: ~6SG: ~6

SG: 6.8SG: 6.8

Phosphates• Apatite – Ca5(PO4)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)PO4

Ore mineral for Rare Earth Elements

Useful mineral in U-Pb and Th age dating

Wavellite – AlWavellite – Al33(PO(PO44))22(OH)(OH)33·5H·5H22OORadiating globular aggregatesRadiating globular aggregates

Turquoise – Turquoise – CuAlCuAl66(PO(PO44))44(OH)(OH)88·5H·5H22OO