1. Lecture 18 (11/29/2006) Systematic Description of Minerals Part 2: Oxides, Hydroxides Halides, Carbonates, Sulfates, and Phosphates

2. Oxides Three main groups based on metal cation/oxygen ratios Hematite Group (X 2 O 3 ) Corundum X=Al +3 most phases hexagonal Hematite X=Fe +3 most phases hexagonal Hematite X=Fe +3 Ilmenite X=1Fe +2 +1Ti +4 Rutile Group (XO 2 )Rutile X=Ti x- +4 cationPyrolusite X=Mn most phases tetragonalCassiterite X=Sn Uraninite X=U Spinel Group (XY 2 O 4 )Spinel X=Mg, Y=Al X- +2; Y- +3 cation Magnetite X=Fe +2, Y=Fe +3 most phases isometric Chromite X=Fe +2, Y=Cr or orthorhombicChrysoberyl X=Be, Y=Al Ulvospinel X=Ti +4, Y=Fe +2

3. Fe-Ti oxides Fe +2 Fe +3

4. Spinel Group (XY 2 O 4 ) Gem-qualitySpinels

5. Other Common Oxides Rutile (TiO 2 ) Rutile needles in Quartz Pyrolusite dendrites on fracture faces Pyrolusite (MnO 2 ) Mass of botryoidal Pyrolusite Corundum (Al 2 O 3 ) Hardness=9 Red = Ruby Blue = Sapphire Chrysoberyl (BeAl 2 O 4 ) Cyclic twinning in Chrysoberyl

6. Hydroxides (OH) - main anionic group forming octahedrally coordinated sheets with weak bonds between Two structural types: Brucite-type – trioctahedral sheets (all octahedral cation sites are filled) Gibbsite-type – dioctahedral sheets (only two of three octahedral sites are filled)

7. Common Types of Hydroxides Brucite Mg(OH) 2 Gibbsite Al(OH) 3 Manganite MnO(OH) DiasporeAlO(OH) GoethiteFeO(OH) Bauxite Al-hydroxide* *hybrid mix of diaspore, gibbsite, and boehmite (AlO(OH))

8. Halides  Simple compounds composed of large halogen anions (Cl, Br, F, I)  Typically isometric  Dominantly ionic bonding  Properties – low hardness, high melting points, poor conductors (except at high temperatures)

9. Common Halides Halite (NaCl) Sylvite (KCl) Flourite (CaF 2 )

10. Mineral Groups formed with Anionic Complexes CarbonatesSulfatesPhosphatesSilicates Amount of residual charge indicates relative strength bonds with cations, which reflected in the hardness of the mineral

11. CarbonatesAragonite (High-P) Orthorhombic Calcite (Low-P - Hexagonal) Most are Hexagonal

12. Other Carbonates Azurite - Cu 3 (CO 3 ) 2 (OH) 2 (Blue) Malachite – Cu 2 CO 3 (OH) 2 (Green) Rhodochrosite – MnCO 3

13. Borates Kernite – Na 2 B 4 O 6 (OH) 2 ·3H 2 O Borax - Na 2 B 4 O 5 (OH) 4 ·8H 2 O Ulexite – NaCaB 5 O 6 (OH) 6 ·5H 2 O H – 2-2.5; SG – 1.7 H – 3; SG – 1.95 H – 1-2.5; SG – 1.96 “Television Rock”

14. Sulfates HYDROUS ANHYDROUS Gypsum – CaSO 4 ·2H 2 O Alunite – KAl 3 (SO 4 ) 2 (OH) 6 Barite – BaSO 4 Anhydrite – CaSO 4 H: 3-3.5 SG: 4.5 H: 3-3.5 SG: 2.9 H: 2 SG: 2.32 H: 4 SG: ~2.7

15. Tungstates & Molybdates Woframite – (Fe,Mn)WO 4 Scheelite – CaWO 4 Wulfenite – PbMoO 4 SG: 7-7.5 SG: ~6 SG: 6.8

16. Phosphates  Apatite – Ca 5 (PO 4 ) 3 (F,Cl,OH) –prismatic hexagonal crystals –common in igneous rocks and hydrothermal deposits - variable colors

17. Other Common Phosphates Monazite – (Ce,La,Y,Th)PO 4 Ore mineral for Rare Earth Elements Useful mineral in U-Pb and Th age dating Wavellite – Al 3 (PO 4 ) 2 (OH) 3 ·5H 2 O Radiating globular aggregates Turquoise – CuAl 6 (PO 4 ) 4 (OH) 8 ·5H 2 O

18. Next Lecture 11/29/06 Systematic Description of Minerals Part 3: Silicates Read: Klein Chap. 11