Lecture 18 (11/29/2006)Lecture 18 (11/29/2006)

Systematic Description of MineralsSystematic Description of Minerals

Part 2:Part 2: Oxides, Hydroxides Halides, Oxides, Hydroxides Halides, Carbonates, Sulfates, and Carbonates, Sulfates, and

PhosphatesPhosphates

OxidesOxidesThree main groups based on metal cation/oxygen ratiosThree main groups based on metal cation/oxygen ratios

Hematite GroupHematite Group (X (X22OO33) ) Corundum X=AlCorundum X=Al+3+3

most phases hexagonal most phases hexagonal Hematite X=FeHematite X=Fe+3+3

Ilmenite X=1FeIlmenite X=1Fe+2+2+1Ti+1Ti+4+4

Rutile GroupRutile Group (XO (XO22)) Rutile X=TiRutile X=Tix- +4 cationx- +4 cation Pyrolusite X=MnPyrolusite X=Mn

most phases tetragonalmost phases tetragonal Cassiterite X=SnCassiterite X=Sn

Uraninite X=UUraninite X=U

Spinel GroupSpinel Group (XY (XY22OO44)) Spinel X=Mg, Y=AlSpinel X=Mg, Y=Al

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

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

or orthorhombicor orthorhombic Chrysoberyl X=Be, Y=AlChrysoberyl X=Be, Y=Al

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

Fe-Ti oxidesFe-Ti oxides

FeFe+2+2FeFe+3+3

Spinel Group Spinel Group (XY(XY22OO44))

Gem-quality Gem-quality SpinelsSpinels

Other Common OxidesOther Common Oxides

Rutile (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

HydroxidesHydroxides(OH)(OH)- - main anionic group forming octahedrally main anionic group forming octahedrally

coordinated sheets with weak bonds betweencoordinated sheets with weak bonds between

Two structural types: 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 HydroxidesCommon 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))

HalidesHalides

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

Typically isometricTypically isometric Dominantly ionic bondingDominantly ionic bonding Properties – low hardness, high Properties – low hardness, high

melting points, poor conductors melting points, poor conductors (except at high temperatures)(except at high temperatures)

Common Halides Common Halides

Halite (NaCl)Halite (NaCl)

Sylvite (KCl)Sylvite (KCl)

Flourite (CaFFlourite (CaF22))

Mineral Mineral Groups Groups

formed with formed with Anionic Anionic

ComplexesComplexes

CarbonatesCarbonates

SulfatesSulfates

PhosphatesPhosphates

SilicatesSilicates

Amount of residual chargeAmount of residual chargeindicates relative strength indicates relative strength bonds with cations, which bonds with cations, which reflected in the hardness reflected in the hardness of the mineralof the mineral

CarbonatesCarbonates

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

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

Most are Hexagonal Most are Hexagonal

Other CarbonatesOther Carbonates

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

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

Rhodochrosite – MnCORhodochrosite – MnCO33

BoratesBorates

Kernite – NaKernite – Na22BB44OO66(OH)(OH)22·3H·3H22OO

Borax - NaBorax - Na22BB44OO55(OH)(OH)44·8H·8H22OO

Ulexite – NaCaBUlexite – NaCaB55OO66(OH)(OH)66·5H·5H22OO

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”

SulfatesSulfatesHYDROUS HYDROUS ANHYDROUSANHYDROUS

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 & MolybdatesTungstates & 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

PhosphatesPhosphates

Apatite – CaApatite – Ca55(PO(PO44))33(F,Cl,OH)(F,Cl,OH)– prismatic hexagonal crystalsprismatic hexagonal crystals– common in igneous rocks and common in igneous rocks and

hydrothermal depositshydrothermal deposits

- variable colors- variable colors

Other Common PhosphatesOther Common Phosphates

Monazite – (Ce,La,Y,Th)POMonazite – (Ce,La,Y,Th)PO44

Ore mineral for Rare Earth ElementsOre mineral for Rare Earth Elements

Useful mineral in U-Pb and Th age datingUseful 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

Next Lecture 11/29/06Next Lecture 11/29/06

Systematic Description of MineralsSystematic Description of Minerals

Part 3: Silicates Part 3: Silicates

Read: Klein Chap. 11Read: Klein Chap. 11