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Lecture 18 (11/29/2006)

Systematic Description of Minerals

Part 2: Oxides, Hydroxides Halides,

Carbonates, Sulfates, andPhosphates

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OxidesThree main groups based on metal cation/oxygen ratios

Hematite Group (X2O3) Corundum X=Al+3 

most phases hexagonal Hematite X=Fe+3

Ilmenite X=1Fe+2+1Ti+4 

Rutile Group (XO2) Rutile X=Tix- +4 cation Pyrolusite X=Mn

most phases tetragonal Cassiterite X=Sn

Uraninite X=U

Spinel Group (XY2O4) Spinel X=Mg, Y=Al

X- +2 ; Y- +3 cation  Magnetite X=Fe+2, Y=Fe+3

most phases isometric  Chromite X=Fe+2, Y=Cr

or orthorhombic Chrysoberyl X=Be, Y=Al

Ulvospinel X=Ti+4, Y=Fe+2

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Fe-Ti oxides

Fe+2Fe+3

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Spinel Group (XY2O4) 

Gem-qualitySpinels

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Other Common Oxides

Rutile (TiO2)

Rutile needles inQuartz

Pyrolusite dendriteson fracture faces

Pyrolusite (MnO2)

Mass of botryoidalPyrolusite

Corundum (Al2O3)

Hardness=9

Red = Ruby

Blue = Sapphire

Chrysoberyl (BeAl2O4)

Cyclic twinningin Chrysoberyl

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Hydroxides

(OH)-

main anionic group forming octahedrallycoordinated sheets with weak bonds between

Two structural types:

Brucite-type – trioctahedralsheets (all octahedral cationsites are filled)

Gibbsite-type – dioctahedralsheets (only two of threeoctahedral sites are filled)

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Common Types of HydroxidesBrucite 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))

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Halides

Simple compounds composed oflarge halogen anions (Cl, Br, F, I)

Typically isometric

Dominantly ionic bonding

Properties – low hardness, high

melting points, poor conductors(except at high temperatures)

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Common Halides

Halite (NaCl)

Sylvite (KCl)

Flourite (CaF2)

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Mineral

Groups

formed with Anionic

Complexes

Carbonates

Sulfates

Phosphates

Silicates

Amount of residual chargeindicates relative strengthbonds with cations, which

reflected in the hardnessof the mineral

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Carbonates

Aragonite(High-P) Orthorhombic

Calcite(Low-P - Hexagonal)

Most are Hexa onal

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Other Carbonates

Azurite - Cu3(CO3)2(OH)2 (Blue)

Malachite – Cu2CO3(OH)2 (Green)

Rhodochrosite – MnCO3

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Borates

Kernite – Na2B4O6(OH)2·3H2O

Borax - Na2B4O5(OH)4·8H2O

Ulexite – NaCaB5O6(OH)6·5H2O

H – 2-2.5; SG – 1.7

H – 3; SG – 1.95

H – 1-2.5; SG – 1.96

 “Television Rock”  

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Sulfates

HYDROUS ANHYDROUS

Gypsum – CaSO4·2H2O

Alunite – KAl3(SO4)2(OH)6  Barite – BaSO4 

Anhydrite – CaSO4 

H: 3-3.5SG: 4.5

H: 3-3.5SG: 2.9

H: 2SG: 2.32

H: 4SG: ~2.7

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Tungstates & Molybdates

Woframite – (Fe,Mn)WO4

Scheelite – CaWO4

Wulfenite – PbMoO4

SG: 7-7.5

SG: ~6

SG: 6.8

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Phosphates

 Apatite – Ca5(PO4)3(F,Cl,OH)

–prismatic hexagonal crystals

– common in igneous rocks andhydrothermal deposits

- variable colors

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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 – Al3(PO4)2(OH)3·5H2ORadiating globular aggregates

Turquoise – CuAl6(PO4)4(OH)8·5H2O

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Next Lecture 11/29/06

Systematic Description of Minerals

Part 3: Silicates

Read: Klein Chap. 11