302-pp26 - Peoples Choice Poster Award First Prize Matthew...

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Peoples Choice Poster Award First Prize Matthew Hatch (tourmaline) Honorable Mention Matt Engle (Malachite) GY 302: Crystallography & Mineralogy GY 302: Crystallography & Mineralogy UNIVERSITY OF SOUTH ALABAMA Lecture 26: Class VIII-Silicates Tektosilicates part 2: Feldspars Lecture 26: Class VIII-Silicates Tektosilicates part 2: Feldspars Last Time Class VIII Minerals (Tektosilicates) 1. Quartz Group Tektosilicate Minerals Mineral Formula System Quartz Group Quartz SiO 2 (multiple varieties) Trigonal Cristobalite SiO 2 Tetragonal Coesite SiO 2 Monoclinic Chalcedony SiO 2 “non crystalline” Opal SiO 2 ·nH 2 O “non crystalline” ”Chert” SiO 2 (multiple varieties) “non crystalline” Basic chemical composition: SiO 2 Agate - banded variety of chaledony Amethyst - purple Avanturine - translucent chalcedony Carnelian - flesh red chalcedony Cat's Eye - chatoyant Chalcedony - microcrystalline quartz Chert - cryptocrystalline quartz Chrysoprase - apple green chalcedony Citrine - yellow Flint - microcrystalline quartz Hornstone - flint Jasper - red or brown chalcedony Moss Agate - variety of chaledony Plasma - green chalcedony Prase - leek green chalcedony Rock Crystal Rose Quartz - rose colored Sapphire Quartz - blue colored Smoky Quartz - brown to black Tiger Eye - entombed asbestos ht p:/ webmineral.com Quartz Varieties [SiO 2 ] Six Quartz Polymorphs Displacive polymorphic transformations require relatively minor changes in the crystal lattice (e.g., modification of α , β or γ crystallographic angles). There is generally no change in energy at the transformation threshold so polymorphic transformations are instantaneous and reversible.
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Quartz: Last Words Except for 2 situations : 1) Nephaline*-bearing rocks NaAlSiO 4 + 2SiO 2 NaAlSi 3 O 8 (albite) 2) Corundum-bearing rocks Al 2 O 3 + SiO 2 Al 2 SiO 5 (Sil/And/Ky) * A feldspathoid; you’ll hear about these next time Today’s Agenda Class VIII Minerals (Tektosilicates) 1. Feldspar Group Tektosilicate Minerals (Feldspars) Mineral Formula System
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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-pp26 - Peoples Choice Poster Award First Prize Matthew...

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