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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
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
*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
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