Mineral Quiz 3 results1: Witherite (22%)2: Rhodochrosite (83%)3. Kernite (33%)4: Cerussite (61%)5: Aurichalcite (89%)6: Fluorite (100%)Bonus: Bornite (44%)Average: 79.8% Highest grade: 108%GY 302: Crystallography & MineralogyGY 302: Crystallography & MineralogyUNIVERSITY OF SOUTH ALABAMALecture 18: Class VIII-SilicatesOlivine GroupLecture 18: Class VIII-SilicatesOlivine GroupLast Time: Poster PreparationFirst Draft due: Friday Nov 12 (5:00PM) (small format)First Draft due: Friday Nov 23 (12:00 Noon)(final full size)*You must reserve a time to print the poster wellin advance of the due datePoster PreparationToday’s AgendaClass VIII Minerals1. Basic classification of silicates2. Nesosilicates (Olivine, Garnet Groups, Aluminum Silicates)3. Olivine Group>3000 (i.e., most minerals)SiO44-SilicatesVIIIapatite PO43-PhosphatesVIIgypsum, anhydriteSO42-SulfatesVIcalcite, aragonite, malachiteCO32-CarbonatesVhalite, fluoriteCl-, Fl-HalidesIVLargelyIonichematite, magnetite, limoniteO2-OH-Oxides\hydroxidesIIICovalentPyrite, Chalcopyrite, GalenaS-SulfidesIIMetallicMetals: Gold, Copper, SilverSemi-metals: Arsenic (As)Non-metals: diamond, graphite, sulfurnoneNative ElementsIDominant BondExamplesAnion(s)NameClassMineral ClassesThe basic silicate tetrahedraSilicate ClassificationSiO44-The basic silicate tetrahedraSilicate ClassificationCovalent radius of Si = 1.11 AIonic radius of Si4+= 0.41 ACovalent radius of O = 0.73 AIonic radius of O2-= 1.40 AThe basic silicate tetrahedraSilicate ClassificationCovalent radius of Si = 1.11 AIonic radius of Si4+= 0.41 ACovalent radius of O = 0.73 AIonic radius of O2-= 1.40 ASo what?SiO4tetrahedra is 40% ionic and 60% covalent in character and the bond can be “polymerized”Chalk boardSilicate coordinationA-X ratios (e.g., Si-O or Al-O) = rA rAl3+ = 0.37rX rO2-Magic number for A-X to switch from tetragonal to octahedral coordination is 0.414A-X = 0.732 to 0.414 (octahedral, 6 fold)A-X = 0.225 to 0.414 (tetrahedral, 4 fold)octahedraltetragonalSilicate ClassificationSiO44-The basic silicate tetrahedraSilicate ClassificationSiO44-The basic silicate tetrahedraSilicate ClassificationNesosilicate Structure (plan model)CationsdownupMg2+down (z = -1/2)Mg2+up (z = 0)Nesosilicate Structure (3D model)NesosilicatesMineral Formula SystemNESOSILICATESOlivine Group Forsterite Mg2SiO4Orthorhombic Fayalite Fe2SiO4OrthorhombicGarnet GroupPyrope Mg3Al2(SiO4)3Isometric Almandine Fe3Al2(SiO4)3IsometricSpessartine Mn3Al2(SiO4)3Isometric Grossular Ca3Al2(SiO4)3IsometricUvarovite Ca3Cr2(SiO4)3Isometric Andradite Ca3Fe2(SiO4)3IsometricAluminum Silicates Kyanite Al2SiO5TriclinicSillimanite Al2SiO5OrthorhombicAndalusite Al2SiO5OrthorhombicStaurolite Fe2Al9O6(SiO4)4(O,OH)2MonoclinicTopaz Al2SiO4(F,OH)2OrthorhombicOther NesosilicatesChloritoid (Fe,Mg)2Al4O2(SiO4)2(OH)4Monoclinic Titanite ('Sphene') CaTiSiO5MonoclinicZircon ZrSiO4IsometricWillemite Zn2SIO4TrigonalDatolite CaBSiO4(OH) MonoclinicOlivine Group Fayalite (Fe2SiO4); Forsterite (Mg2SiO4)Crystal: OrthorhombicPt. Group: 2/m 2/m 2/mHabit: prismatic, granularSG: 3.2; H: 6.5L: vitreous; Str: whiteCol: colorless-green (For) yellow (Fay)Clev: good (010), poor (100)Optics: Biaxial +/-nα= 1.651; nβ= 1.670; nγ= 1.689Nesosilicate MineralsFayalite (named after the Fayal Island, Azores)Forsterite (named after Johann Forster, German naturalist )Olivine Group Fayalite (Fe2SiO4); Forsterite (Mg2SiO4)Occurrence: ultramafic and basaltic igneous rocks (peridotite, dunite, komatiite)Associated Mins: pyroxenes, chromiteCan be confused with: when fine grained, quartz, pyroxeneUses:peridot (gemstones)Nesosilicate Mineralshttp://som.web.cmu.edu/structures/S086-forsterite.htmlNesosilicateshttp://www.gly.uga.edu/schroeder/geol3010/olivinephase.gifNesosilicateshttp://www.geoclassroom.com/mineralogy/olivine_melting.gifhttp://gore.ocean.washington.edu/classpages/ocean410_2001/notes/unit09_files/image007.gifNesosilicateshttp://www.geoclassroom.com/mineralogy/olivine_melting.gifNesosilicateshttp://www.geoclassroom.com/mineralogy/olivine_melting.gifNesosilicateshttp://www.geoclassroom.com/mineralogy/olivine_melting.gifNesosilicateshttp://www.geoclassroom.com/mineralogy/olivine_melting.gifNesosilicateshttp://www.geoclassroom.com/mineralogy/olivine_melting.gifToday’s Stuff To Do1. Mineral selection (NOW)2. Ore Assessment Exercise Next Time1. Garnet and other neosilicates2. Lab: Neso and orthosilicates minerals Group VI/VII