Classification of by Anionic Species (Anions are negative ions) How are minerals classified by chemistry? Why is this useful? How are minerals classified by chemistry? By anionic species. Why is this useful? Because there is very little substitution at anion sites 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 1
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 Halides: anion is F, Cl, Br, or I Periodic Table 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 5FeS 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 2
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 Ilmenite FeTiO 3 Spinel Group Spinel MgAl 2O 4, Magnetite Fe 3O 4 Perovskite CaTiO 3 Hydroxides: anion is (OH) - Hydroxides: anion is OH Brucite Mg(OH) 2 Gibbsite Al(OH) 3 Diaspore AlOOH (Bauxite) Goethite FeOOH Carbonates anion is (CO 3 ) 2- 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 3
Sulfates and Phosphates: (SO 4 ) 2- and (PO 4 ) 3- Sulfates and Phosphates: (SO 4 ) 2- and (PO 4 ) 3- Sulfates and Phosphates: (SO 4 ) 2- and (PO 4 ) 3- Sulfur is 6+ Phosphorus is 5+ Contrast sulfide (S 2- ) and sulfate (S 6+ ). Phosphide (P 3- ) and phosphate (P 5+ ). Sulfates and phosphates are oxidized! 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 Silicates are classified by polymerization Orthosilicates (SiO 4 ) 4- : Isolated tetrahedra Sorosilicates (Si 2 O 7 ) 6- 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 4
Orthosilicates: (SiO 4 ) 4- Si/O: <~1/4 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 Si/O: 1/3 ~ 1/4 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 Si/O ~ 1/3 Orthopyroxenes Mg 2 Si 2 O 6 Clinopyroxenes CaMgSi 2 O 6 Pyroxenoids Ca 3 Si 3 O 9 Double Chains Si/O 8:22 Amphiboles (Mg,Fe) 7 Si 8 O 22 (OH) 2 Chain Silicates Layer Silicates Si/O ~ 2/5 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 5
Layer Silicates Framework Silicates (Tektosilicates) Si/O 1/2 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) 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? Give Chemical Classification of Kamacite (Fe) C. Metal D. Extra-terrestrial E. Oxide Give Classification of Troilite (FeS) E. Oxide 6
Give Classification of Pyrite (FeS 2 ) E. Oxide Give Chemical Classification of Barite (BaSO 4 ) E. Oxide Give Chemical Classification of Fluorite (CaF 2 ) E. Halide Give Chemical Classification of Apatite (Ca 3 (PO 4 ) 3 F) E. Halide 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 7
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 Elements partition among immiscible fluids by bond type (!!) Geochemical Classification of the Elements Lithophile - Ionic Siderophile - Metallic Chalcophile - Covalent Atmophile - Van der Waals 8