Classification of Minerals by Anionic Species (Anions are negative ions) Chemical Classification of Minerals Learning goals: How are minerals classified by chemistry? Why is this useful? Anions are Negative Ions May be single species O 2-, F -, Cl -, S 2- May be anionic group (polyanion): CO 3 2-, SO 4 2-, PO 4 3- Silicates are classified by polymerization of the silicate polyanion. Isolated tetrahedra Chains Sheets Frameworks Periodic Table Native Elements (no anions) Native Elements Pure elements that occur as minerals Graphite, diamond (C) Sulfur (S) Gold (Au), Silver (Ag), Copper (Cu) Iron (kamacite) Nickel (taenite) As, Te, Se, Pt, Ir, Os, Pd, Ru, Rh 1
Halides: anion is F, Cl, Br or I Halogens are the elements F, Cl, Br, I Halogens are monovalent anions Halite (NaCl), Sylvite (KCl) Fluorite (CaF 2) Cryolite Na 3 AlF 6 Sulfides: anion is S Sulfur is anion, but is more covalent than ionic Pyrite, marcasite (FeS 2), Chalcopyrite (CuFeS 2) Sphalerite ZnS, Galena (PbS) Chalcocite Cu 2S, Covellite (CuS), Bornite (Cu 5 5FeS 4 4) Realgar (AsS), Orpiment (As 2S 3), Cinnabar (HgS) Stibnite (Sb 2S 3), Molybdenite (MoS 2) Sulfide minerals typically have metallic luster, covalent bonding, and occur in hydrothermal veins. Only rarely do they occur at the surface. Elements in Sulfide Minerals Oxides (Single): anion is O (no polyanion) Hemi-oxide Cuprite (Cu 2O), Ice (H 2 O) Monoxides Periclase group MgO, FeO, CaO, MnO Zincite ZnO, Bromellite BeO Sesquioxides Corundum Al 2O 3, Hematite Fe 2O 3 Dioxides Rutile TiO 2, Cassiterite SnO 2, Pyrolusite MnO 2 Oxides (Complex): anion is O Hydroxides: anion is (OH) - Ilmenite FeTiO 3 Spinel Group Spinel MgAl 2O 4, Magnetite Fe 3O 4 Perovskite CaTiO 3 2
Hydroxides: anion is OH Carbonates anion is (CO 3 ) 2- Brucite Mg(OH) 2 Gibbsite Al(OH) 3 Diaspore AlOOH(Bauxite) Goethite FeOOH Carbonates Anion is (CO 3 ) 2- Calcite CaCO 3, Rhodochrosite MnCO 3 Siderite FeCO 3, Smithsonite ZnCO 3 Dolomite CaMg(CO 3) 2 Aragonite CaCO 3, Witherite BaCO 3 Strontianite SrCO 3,Cerussite PbCO 3 Malachite and Azurite Sulfates and Phosphates: (SO 4 ) 2- and (PO 4 ) 3- Sulfates and Phosphates: (SO 4 ) 2- and (PO 4 ) 3- Barite (BaSO 4), Celestine (SrSO 4) Gypsum CaSO 4.2H 2O Anhydrite CaSO 4 Apatite Ca 5(PO 4) 3OH Turquoise CuAl 6 (PO 4 ) 4 (OH) 8 4H 2 O 3
Silicates are classified by polymerization Orthosilicates (SiO 4 ) 4- : Isolated tetrahedra Sorosilicates (Si 6-2 O 7 ) Bow-Ties Chain silicates (SiO 3) 2- : Infinite single chains (Si 4O 11) 6- : Double Chains Sheet Silicates (Si 4 O 10 ) 4- sheets Framework Silicates (SiO 2 ) framework Orthosilicates: (SiO 4 ) 4- Orthosilicates: Isolated Tetrahedra Isolated SiO 4 tetrahedra Olivine Group (Mg 2SiO 4) Garnet Group (Mg 3Al 2Si 3O 12) Aluminosilicate Group (Al 2SiO 5) Staurolite, Zircon, Titanite Sorosilicates and Cyclosilicates Chain Silicates Epidote Group Ca 2 Al 2 FeSi 3 O 12 (OH) Tourmaline NaMg 3 Al 5 B 3 Si 6 O 27 (OH) 4 Beryl Be 3 Al 2 Si 6 O 18 Cordierite (Mg,Fe) 2 Al(AlSi 5 )O 18 nh 2 O Single Chains Orthopyroxenes Mg 2 Si 2 O 6 Clinopyroxenes CaMgSi 2 O 6 Pyroxenoids Ca 3 Si 3 O 9 Double Chains Amphiboles (Mg,Fe) 7 Si 8 O 22 (OH) 2 4
Chain Silicates Layer Silicates Antigorite Mg 3 Si 2 O 5 (OH) 4 Talc Mg 3 Si 4 O 10 (OH) 2 Kaolinite Al 2 Si 2 O 5 (OH) 4 Pyrophyllite Al 2 Si 4 O 10 (OH) 2 Biotite K(Mg,Fe) 3 AlSi 3 O 10 (OH) 2 Muscovite KAl 2 AlSi 3 O 10 (OH) 2 Chlorite (Mg,Fe) 6 AlSi 3 O 10 (OH) 2 Layer Silicates Framework Silicates (Tektosilicates) Silica Group SiO 2 Alkali Feldspar (Na,K)AlSi 3O 8 Plagioclase NaAlSi 3O 8-CaAl 2Si 2O 8 Feldspathoids (Leucite, Kalsilite, etc) Zeolites (open hydrous frameworks) Tektosilicates (Framework Silicates) Chemical Classification of Minerals Learning goals: How (why) are minerals classified by chemistry? Why is this useful? Why not by cations? How else might you classify minerals? Hardness? Color? Occurrence? Abundance? 5
Give Chemcal Classification of Kamacite (Fe) C. Metal D. Extra-terrestrial Give Class of Troilite (FeS) C. Sulfate D. Phosphate Give Class of Pyrite (FeS 2 ) C. Sulfate D. Phosphate Give Chemical Classification of Barite (BaSO 4 ) C. Sulfate D. Phosphate Chemical Classification of Minerals Learning goals: How (why) are minerals classified by chemistry? Why is this useful? Why not by cations? How else might you classify minerals? Hardness? Color? Occurrence? Abundance? Geochemical Classification of the Elements Lithophile - Ionic Siderophile - Metallic Chalcophile - Covalent Atmophile - Van der Waals 6
Geochemical Classification of the Elements How do the elements partition between coexisting fluid (melt) phases? Gas Phase : Atmophile : Van der Waals Oxide phase: Lithophile : Ionic Sulfide Phase: Chalcophile: Covalent Metal Phase: Siderophile: Metallic 7