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4.3: The Chemical Classification of Gems and Minerals

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    The Chemical Classification of Gems and Minerals

    Gems can be organized into classes, based on their chemistry.

    Table \(\PageIndex{1}\): Classes of Gems and Minerals

    Class Description
    Class I: Pure Elements Metals, alloys, semi-metals, and non-metals
    Class II: Sulfides Sulfur is the principal anion: includes tellurides and arenides
    Class III: Halides Halogen elements are anions: F, Cl, Br
    Class IV: Oxides Oxygen is the principal anion, includes hydroxides in which the hydroxyl radical (OH) acts as the anion
    Class V a:Carbonates Carbonate radical (CO3) is the principal anion
    Class V b:Borates Borate radical (BO3) and borate groups are anions
    Class VI a:Tungstates Anions are principally WO4
    Class VI b:Sulphates Sulphate radical (SO4) is the principal anion
    Class VII: Phosphates Anions are principally PO4
    Class VIII: Silicates Silicate groups as anions combining with other elements: includes silica SiO2

    Class I Pure Elements

    Table \(\PageIndex{2}\): Pure Elements

    Class I Pure Elements
    Diamond Carbon (C)

    Class II Sulfides

    Table \(\PageIndex{3}\): Sulfides

    Class II Sulfides
    Marcasite FeS2
    Pyrite FeS2
    Sphalerite ZnS

    Class III Halides

    Table \(\PageIndex{4}\): Halides

    Class III Halides
    Fluorite CaF2

    Class IV Oxides

    Table \(\PageIndex{5}\): Oxides

    Class IV Oxides
    Anatase TiO2
    Brookite TiO2
    Chrysoberyl BeAl2O4
    Corundum Al2O3
    Hematite Fe2O3
    Opal SiO2nH2O
    Quartz SiO2
    Rutile TiO2
    Spinel MgAl2O4

    Class Va Carbonates

    Table \(\PageIndex{6}\): Carbonates

    Class Va Carbonates
    Aragonite CaCO3
    Azurite Cu3(OH/CO3)2
    Calcite CaCO3
    Cerrussite PbCO3
    Malachite Cu2(OH)2CO3
    Rhodochrosite MnCO3
    Smithsonite ZnCO3

    Class Vb Borates

    Table \(\PageIndex{7}\): Borates

    Class Vb Borates
    Hambergite Be2(OH/BO3)
    Sinhalite MgAl(BO4)
    Ulexite NaCaB5O6·5H2O

    Class VIa Tungstates

    Table \(\PageIndex{8}\): Tungstates

    Class VIa Tungstates
    Scheelite Ca(WO4)

    Class VIb Sulphates

    Table \(\PageIndex{9}\): Sulphates

    Class VIb Sulphates
    Barite Ba(SO4)

    Class VII Phosphates

    Table \(\PageIndex{10}\): Phosphates

    Class VII Phosphates
    Amblygonite LiAl(F,OH/PO4)
    Apatite Ca5(F/PO4)2
    Brazilianite NaAl3(OH2/PO4)2
    Turquoise CuAl6((OH)2PO4)4·4H2O

    Class VIII Silicates

    Table \(\PageIndex{11}\): Silicates

    Class VIII Silicates
    Andalusite Al2SiO5
    Beryl Be3Al2(SiO3)6
    Iolite (Cordierite) Mg2Al4Si5O18
    Garnet X3Y2Si3O12 (X = Mg, Fe or Ca) (Y = Al else Fe3+ or Cr)
    Jadeite NaAlSi2O6
    Nephrite Ca2(MgFe)5(Si4O11)2
    Topaz Al2SiO4(FOH)2
    Tourmaline (Na1+, Ca2+)(Li1+, Mg2+, Al3+). (Al3+, Fe3+, Mn3+)6(BO3)3 (Si6O18) (OH)4
    Peridot Mg2SiO4, Fe2SiO4
    Zircon Zr(SiO4)

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