Copy of Lecture_3_Grain_Mineralogy

Copy of Lecture_3_Grain_Mineralogy - Grain Mineralogy...

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Grain Mineralogy Lecture Outline I.Crust composition II.Quartz III.Feldspar IV.Rock fragments V.Other grains VI.Classification Reading Assignment: Boggs, Chapter 5, p. 119-139
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Crust Composition: Elements There are 92 naturally occurring elements, but most are rare.
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Crust Composition: Minerals Silicate Minerals Common Silicate Minerals : Feldspar, Quartz, Olivine, Pyroxene, Amphibole, Mica Common Non-Silicate Minerals : Carbonates, Oxides, Sulfides, Phosphates, Salts There are ~ 3000 minerals, 10 account for 90% of crust!
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Crust Composition: Rock Type Continental Crust : Granite ~ 60% Feldspar, 25% Quartz 10% Mica, Amphibole Sedimentary Rocks : Mudstones , Sandstones, Carbonates
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Net Result: Grain Types Most common grain produced is some type of Feldspar, but Feldspar weathers rapidly Quartz, already abundant, is enhanced on Earth surface because it is resistant to weathering Rock Fragments – mostly sedimentary, but can be metamorphic or volcanic Granite or Gneiss rock fragments are classified with Feldspar
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Breakdown of Primary Grains Types Quartz Plutonic = “common quartz” Volcanic Metamorphic = composite/polycrystalline Vein Feldspar Alkali Feldspar (Mostly K-Feldspar = K-spar) Plagioclase Rock fragments Sedimentary (SRF) Metamorphic (MRF) Volcanic (VRF)
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Quartz Mineral Characteristics Superior hardness (7) Chemically stable SiO 2 tetrahedron Monocrystalline (most stable) to composite grains Most common sedimentary grain (65% of average sandstone) Extinction under polarized light (straight to highly undulatory), first-order birefringence (white-gray) Grain shape (subequant to bipyramidal) Inclusions & vacuoles Clear to wide variety of colors by inclusions
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Range of Extinction Straight Slightly Undulose Strongly Undulose
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Inclusions & Vacuoles
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This note was uploaded on 04/09/2011 for the course GEO 416M taught by Professor Staff during the Spring '08 term at University of Texas at Austin.

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Copy of Lecture_3_Grain_Mineralogy - Grain Mineralogy...

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