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Silicate Mineralogy

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Silicate mineralogy
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Earth Materials Earth Materials Earth Materials 625-102 GEOLOGY 625-102 GEOLOGY Silicate Mineralogy Silicate Mineralogy Lecture 3 Lecture 3 Melbourne Earth Sciences Melbourne Earth Sciences Melbourne Earth Sciences
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  • Earth MaterialsEarth MaterialsEarth Materials

    625-102 GEOLOGY625-102 GEOLOGY

    Silicate MineralogySilicate Mineralogy

    Lecture 3Lecture 3

    Melbourne Earth SciencesMelbourne Earth SciencesMelbourne Earth Sciences

  • Earth MaterialsEarth MaterialsEarth Materials

    Anion groupingsAnion groupings

    l

    l Minerals are Minerals are classified according toclassified according to their their chemistrychemistry

    ((ieie not symmetry, hardness or any other physical property) not symmetry, hardness or any other physical property)

    l

    l They are They are grouped according togrouped according to theirtheir anionsanions

    l

    l Why?Why?

    because minerals rarely contain more than one of these,because minerals rarely contain more than one of these,whereas they often contain several different whereas they often contain several different cationscations

    l

    l Minerals are Minerals are classified into 8 major groupsclassified into 8 major groups

  • Earth MaterialsEarth MaterialsEarth Materials

    Classification of MineralsClassification of Minerals

    l

    l Native elementsNative elements - no anions- no anions

    l

    l SulphidesSulphides - S- S2-2- anions, with variations anions, with variations

    l

    l HalidesHalides - halogens (- halogens (ClCl, F; rarely Br, I), F; rarely Br, I)

    l

    l OxidesOxides - O- O2-2- anions (& hydroxides) anions (& hydroxides)

    l

    l CarbonatesCarbonates - CO- CO332-2- etc. etc. polyanionic gpspolyanionic gps

    l

    l SulfatesSulfates - SO- SO442- 2- groups with variationsgroups with variations

    l

    l PhosphatesPhosphates - PO- PO443-3- with variations with variations

    l

    l SilicatesSilicates -SiO-SiO444-4- with structural variations with structural variations

  • Earth MaterialsEarth MaterialsEarth Materials

    Native ElementsNative Elements

    Native Sulphur, Italy Native Silver, Germany

  • Earth MaterialsEarth MaterialsEarth Materials

    SulphidesSulphides

    Galena, PbS Marcasite, FeS2

  • Earth MaterialsEarth MaterialsEarth Materials

    Halides and OxidesHalides and Oxides

    Fluorite, CaF2 Magnetite, Fe3O4

  • Earth MaterialsEarth MaterialsEarth Materials

    CarbonatesCarbonates

    Malachite, Cu2[(OH)2/CO3])Calcite, CaCO3

  • Earth MaterialsEarth MaterialsEarth Materials

    Sulphates, PhosphatesSulphates, Phosphates

    Gypsum, CaSO4.2H2O Apatite, CaPO4

  • Earth MaterialsEarth MaterialsEarth Materials

    SilicatesSilicates

    Olivine, (Fe,Mg)2SiO4 Quartz, SiO2

  • Earth MaterialsEarth MaterialsEarth Materials

    Silicate MineralsSilicate Minerals

    l

    l Most abundant mineralsMost abundant minerals in the Earth's crust in the Earth's crust

    l

    l Make up Make up 95% of95% of the the EarthEarths crusts crust

    l

    l Made up of Made up of tetrahedral SiOtetrahedral SiO44 anion groups anion groups

    l

    l PolymerisedPolymerised into into compound groupscompound groups by by

    sharing adjacent oxygensharing adjacent oxygen ions ions

    l

    l Linked byLinked by various various cationscations, , espesp..

    FeFe2+2+, Mg, Mg2+2+, Ca, Ca2+2+, K, K++, Na, Na++

    l

    l Aluminium (AlAluminium (Al3+3+ ) ) can can substitute for silicon ionssubstitute for silicon ions

    l

    l Result in Result in complex chemical compositionscomplex chemical compositions

  • Earth MaterialsEarth MaterialsEarth Materials

    The Basic Silicate UnitThe Basic Silicate Unit

    l

    l Unit behaves as a Unit behaves as a compound anioncompound anion

    l

    l Cation radius = 0.41 Cation radius = 0.41 , Anion Radius = 1.40, Anion Radius = 1.40

    l

    l Radius ratio = 0.29Radius ratio = 0.29, therefore , therefore 4-fold Coordination4-fold Coordination

    l

    l Overall Overall charge of - 4charge of - 4

    l

    l one negative charge for each oxygenone negative charge for each oxygen

    SiOSiO44 Tetrahedra Tetrahedra

    --

    ----

    --

  • Earth MaterialsEarth MaterialsEarth Materials

    Arrangements of silicate groupsArrangements of silicate groups

    l

    l Silicate groups may exist as Silicate groups may exist as isolated tetrahedraisolated tetrahedrajoined by cationsjoined by cations eg Olivine eg Olivine

    l

    l or or joined injoined in more complex more complex polymerised groupspolymerised groups

    l

    l Tetrahedra may be Tetrahedra may be arranged asarranged as

    Simple groupsSimple groups

    RingsRings

    Single chainsSingle chains

    Double chainsDouble chains

    SheetsSheets

    FrameworksFrameworks

    3-01

  • Earth MaterialsEarth MaterialsEarth Materials

    Simple SiOSimple SiO44 groups groups

    l

    l Silicate groupsSilicate groups are are isolatedisolated from each other from each other

    l

    l May be May be individualindividual or or simple polymerised groupssimple polymerised groups

    l

    l Individual SiOIndividual SiO44 tetrahedratetrahedra are are linked by cationslinked by cations

    l

    l Closely packed, Closely packed, high densityhigh density structuresstructures

    l

    l eg eg OlivineOlivine (Mg,Fe) (Mg,Fe)22SiOSiO4 4 andand ZirconZircon ZrSiO ZrSiO44, Beryl, Beryl

    3-02

  • Earth MaterialsEarth MaterialsEarth Materials

    Single Chain StructuresSingle Chain Structures

    l

    l Each silicate tetrahedron Each silicate tetrahedron shares twoshares two oxygens oxygens

    l

    l Tetrahedra Tetrahedra joined intojoined into a a continuous chaincontinuous chain

    l

    l ChainsChains are are linkedlinked with each other with each other by cationsby cations

    l

    l e.g. the e.g. the Pyroxene groupPyroxene group of minerals of minerals

    Diopside:Diopside: CaMgCaMg(Si(Si22OO66))

    Augite: Augite: Ca(Mg,Fe)SiCa(Mg,Fe)Si22OO66Hypersthene:Hypersthene: MgFeMgFe(Si(Si22OO66))

    3-03

  • Earth MaterialsEarth MaterialsEarth Materials

    Double Chain StructuresDouble Chain Structures

    l

    l TetrahedraTetrahedra linkedlinked into a into a double chaindouble chain

    l

    l Each SiOEach SiO44 tetrahedron tetrahedron shares 2 or 3 shares 2 or 3 oxygensoxygens

    l

    l Chains are linkedChains are linked with each other with each other by cationsby cations

    l

    l e.g. the e.g. the AmphiboleAmphibole groupgroup of minerals of minerals

    3-04

  • Earth MaterialsEarth MaterialsEarth Materials

    Sheet SilicatesSheet Silicates

    l

    l Continuous Continuous layer of linked SiOlayer of linked SiO44 groups groups

    l

    l Each SiOEach SiO44 tetrahedron tetrahedron shares threeshares three oxygens oxygens

    l

    l LayersLayers are are stacked and linkedstacked and linked together together by cationsby cations

    l

    l Have Have strong cleavage, generally soft mineralsstrong cleavage, generally soft minerals

    l

    l e.g. the e.g. the Mica Mica andand Clay Clay minerals etc.minerals etc.

    3-05

  • Earth MaterialsEarth MaterialsEarth Materials

    Stacking Silicate SheetsStacking Silicate Sheets

    l

    l The tetrahedral The tetrahedral layers can be stacked togetherlayers can be stacked together in inseveral several different waysdifferent ways, e.g.:, e.g.:

    ClaysClays MicasMicas

  • Earth MaterialsEarth MaterialsEarth Materials

    Framework SilicatesFramework Silicates

    l

    l Interlocking frameworkInterlocking framework of SiO of SiO44 tetrahedra tetrahedra

    l

    l Each SiOEach SiO44 tetrahedron tetrahedron shares all shares all fourfour oxygens oxygens

    l

    l Basic formula unit is Basic formula unit is SiOSiO22

    l

    l e.g.: e.g.: QuartzQuartz SiO SiO22

    l

    l FeldsparsFeldspars (note role of Al substitution): (note role of Al substitution): OrthoclaseOrthoclase:: KAlSiKAlSi 33OO88 AlbiteAlbite:: NaAlSiNaAlSi33OO88 AnorthiteAnorthite:: CaAlCaAl22SiSi22OO88

    3-05

  • Earth MaterialsEarth MaterialsEarth Materials

    Feldspar CompositionsFeldspar Compositions

    KK

    NaNa CaCa

    Potassium FeldsparsPotassium Feldspars

    Plagioclase FeldsparsPlagioclase Feldspars

    No Feldspars occurNo Feldspars occur

  • Earth MaterialsEarth MaterialsEarth Materials

    REFERENCESREFERENCES

    l

    l HamblinHamblin & Christiansen, Chapter 3, p.64-72 & Christiansen, Chapter 3, p.64-72

    l

    l Skinner and Porter, Chapter 3, p. 53-59Skinner and Porter, Chapter 3, p. 53-59

    l

    l Clark and Cook, Chapter 6b, p. 116-122Clark and Cook, Chapter 6b, p. 116-122


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