Classification Minerals by Anionic Species (Anions are negative ions) How would you organize some 5000 species minerals? Color? Hardness? Occurrence environment? Chemistry? Positive ions? (cations) Negative ions? (anions) Chemical Classification Minerals Learning goals: How are minerals classified by chemistry? Why is this useful? Chemical Classification Minerals Learning goals: How are minerals classified by chemistry? By anionic species. Chemical Classification Minerals Learning goals: 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 the silicate polyanion. Isolated tetrahedra Chains Sheets Frameworks 1
Chemical Classification Native Elements (no anions) Halides (F, Cl, Br, I) (monovalent halogen) Sulfides & arsenides (S, Ar) Oxides (O) Hydroxides (OH) Sulfates & phosphates (SO 4, PO 4 ) Carbonates (CO 3 ) Silicates: orthosilicates, sorosilicates, chain silicates, layer silicates, framework silicates 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 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 2
Sulfides: anion is S Sulfur is anion, but is more covalent than ionic (stoichiometry is less strict) 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 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 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 3
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 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! 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 4
Silicates are classified by polymerization Orthosilicates (SiO 4 ) 4- : Isolated tetrahedral O / Si = 4.0 Sorosilicates (Si 2 O 7 ) 6- Bow-Ties 3.75 Chain silicates (SiO 3) 2- : Infinite single chains 3.0 (Si 4O 11) 6- : Double Chains 2.75 Sheet Silicates (Si 4 O 10 ) 4- sheets 2.5 Framework Silicates (SiO 2 ) framework 2.0 Orthosilicates: (SiO 4 ) 4- Si/O: <~1/4 O / Si = 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 ~ ¼ O / SI = 3 3.5 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 Chain Silicates Single Chains Si/O ~ 1/3 O / Si = 3.0 Orthopyroxenes Mg 2 Si 2 O 6 Clinopyroxenes CaMgSi 2 O 6 Pyroxenoids Ca 3 Si 3 O 9 Double Chains Si/O 4:11 O / (Si+Al) = 2.75 Amphiboles (Mg,Fe) 7 Si 8 O 22 (OH) 2 5
Chain Silicates Layer Silicates O / Si = 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 Layer Silicates Framework Silicates (Tektosilicates) O / Si = 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) O / (Al + Si) IV Framework Silicates = 2.0 Sheet Silicates = 2.5 Amphiboles = 2.75 Chain Silicate = 3.0 Sorosilicates = 3.5 Orthosilicates = 4 Tektosilicates (Framework Silicates) 6
Chemical Classification Native Elements (no anions) Halides (F, Cl, Br, I) Sulfides & arsenides (S, Ar) Oxides (O) Hydroxides (OH) Sulfates & phosphates (SO 4, PO 4 ) Carbonates (CO 3 ) Silicates: orthosilicates, sorosilicates, chain silicates, layer silicates, framework silicates Chemical Classification 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? Kamacite (Fe) C. Metal D. Extra-terrestrial Kamacite (Fe) C. Metal D. Extra-terrestrial Give Classification Troilite (FeS) Give Classification Troilite (FeS) 7
Give Classification Pyrite (FeS 2 ) Give Classification Pyrite (FeS 2 ) Barite (BaSO 4 ) Barite (BaSO 4 ) Fluorite (CaF 2 ) E. Halide Fluorite (CaF 2 ) E. Halide 8
Apatite (Ca 3 (PO 4 ) 3 F) Apatite (Ca 3 (PO 4 ) 3 F) E. Halide E. Halide Homework 1 Due Tuesday Chemical Classification 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 the Elements Lithophile - Ionic Siderophile - Metallic Chalcophile - Covalent Atmophile - Van der Waals Geochemical Classification 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 9
Geochemical Classification 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 Geochemical Classification 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 Geochemical Classification 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 the Elements Atmophile - Van der Waals Lithophile - Ionic Chalcophile - Covalent Siderophile - Metallic 10
Geochemical Classification the Elements Geochemical Classification the Elements Atmophile - Van der Waals Lithophile - Ionic Chalcophile - Covalent Siderophile - Metallic Atmophile - Van der Waals Lithophile - Ionic Siderophile - Metallic Chalcophile - Covalent 11