302-pp19 - Mineralogy Lecture Test Results Average 82.9 Highest grade 98 A 4 B 9 C 6 D 0 F 0 GY 302 Crystallography& Mineralogy GY 302

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Unformatted text preview: Mineralogy Lecture Test Results Average: 82.9% Highest grade: 98% A: 4 B: 9 C: 6 D: 0 F: 0 GY 302: Crystallography & Mineralogy GY 302: Crystallography & Mineralogy UNIVERSITY OF SOUTH ALABAMA Lecture 19: Class VIII-Silicates Neosilicates (orthosilicates) Lecture 19: Class VIII-Silicates Neosilicates (orthosilicates) Last Time Class VIII Minerals 1. Basic classification of silicates 2. Nesosilicate structure Nesosilicates The basic silicate tetrahedra Silicate Classification Covalent radius of Si = 1.11 A Ionic radius of Si 4+ = 0.41 A Covalent radius of O = 0.73 A Ionic radius of O 2- = 1.40 A So what? SiO 4 tetrahedra is 40% ionic and 60% covalent in character and the bond can be “polymerized” Silicate coordination A-X ratios (e.g., Si-O or Al-O) = rA rAl 3+ = 0.37 rX rO 2- Magic number for A-X to switch from tetragonal to octahedral coordination is 0.414 A-X = 0.732 to 0.414 (octahedral, 6 fold) A-X = 0.225 to 0.414 (tetrahedral, 4 fold) octahedral tetragonal Silicate Classification down up Mg 2+ down (z = -1/2) Mg 2+ up (z = 0) Nesosilicate Structure Today’s Agenda Class VIII Minerals 1. Garnet Group 2. Aluminosilicates Nesosilicate Minerals http://webmineral.com/data andradite http://www.wrightsrockshop.com/gallery/garnet/ uvarovite Garnet Group Garnet Group Pyrope (Mg 3 Al 2 (SiO 4 ) 3 ) Almandine (Fe 3 Al 2 (SiO 4 ) 3 ) Grossular (Ca 3 Al 2 (SiO 4 ) 3 ) Crystal: Isometric Pt. Group: 4/m 3 2/m...
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This note was uploaded on 02/05/2012 for the course GLY 302 taught by Professor Staff during the Spring '11 term at S. Alabama.

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302-pp19 - Mineralogy Lecture Test Results Average 82.9 Highest grade 98 A 4 B 9 C 6 D 0 F 0 GY 302 Crystallography& Mineralogy GY 302

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