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Minerals and Igneous Rocks

Minerals and Igneous Rocks. Objectives. Understand the properties and major groups of minerals Briefly outline the three types of rocks and the processes that produce them Discuss some important aspects of igneous rocks and their influence on landscape forms. Minerals. Minerals vs. Rocks

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Minerals and Igneous Rocks

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  1. Minerals and Igneous Rocks

  2. Objectives • Understand the properties and major groups of minerals • Briefly outline the three types of rocks and the processes that produce them • Discuss some important aspects of igneous rocks and their influence on landscape forms

  3. Minerals • Minerals vs. Rocks • Minerals • Naturally-occurring, inorganic solid with a definite chemical composition • Rocks • Made up of one or more minerals Granite rock make up of variety minerals. http://geomaps.wr.usgs.gov/parks/rxmin/rock.html

  4. Mineral Properties • Chemical Composition • Elements that make up a mineral Graphite carbon sheet structure; very soft lead. Source: http://eetd.lbl.gov/newsletter/nl40/images/graphite.gif

  5. Mineral Properties • Hardness • Measures how hard or easily a mineral can be scratched • Most reliable test for mineral identification • Moh’s hardness scale • 1 – softest (talc) • 10 – hardest (diamond) The Mohs’ Hardness Scale MineralHardness Diamond 10 Corundum 9 Topaz 8 Quartz 7 Potassium feldspar 6 Apatite 5 Fluorite 4 Calcite 3 Gypsum 2 Talc 1

  6. Mineral Properties • Cleavage/Fracture • Tendency of minerals to break along weak bonds • Cleavage • Produce flat, shiny surface • Fracture • Uneven surface (fracture)

  7. Mineral Properties • Color • Most noticeable property • Most unreliable in identifying minerals • Streak • Color of a mineral in its powdered form • Does not change

  8. Mineral Properties • Luster • A mineral’s appearance when reflected in light • Two categories • Metallic • Nonmetallic • Pearly, vitreous, dull, etc. Pyrite with a metallic luster. Source: http://www.research.gov/common/images/PublicAffairs/Pyrite-246459--rgov-800width.jpg

  9. Mineral Types • Silicates (SiO4) • Silicon & Oxygen • Most abundant elements in earth’s crust Composition of Earth’s Crust Element Oxygen (O) Silicon (Si) Aluminum (Al) Iron (Fe) Calcium (Ca) Sodium (Na) Potassium (K) Magnesium (Mg) Total Percentage (by Weight) 46.6 27.7 8.1 5.0 3.6 2.8 2.6 2.1 98.5 Quartz composed of SiO2. Source: http://www.nsf.gov/news/news_summ.jsp?cntn_id=118951

  10. Mineral Types • Non-silicates • Carbonates (CO3) • Limestone (CaCO3) • Dolomite (CaMgCO3) • Sulfates (SO4) • Gypsum (CaSO4) • Sulfides • Pyrite (FeS2) • Halides (Cl, Fl, I) • Halite (NaCl) • Oxides (metal + O) • Hematitie (Fe2O3) • Magnetite (Fe3O4)

  11. Classification of Rock Types • Igneous Rocks • Forms from cooling of magma • Sedimentary Rocks • Forms from lithification of rock fragments • Metamorphic Rocks • Forms from rocks change by heat and/or pressure

  12. Igneous Rocks • Intrusive vs. Extrusive (texture) • Intrusive • Cooled beneath the surface • Cooled slowly; Coarse (large) grained • Extrusive • Cooled above the surface • Cooled quickly; Fine grained • Felsic vs. Mafic (composition) • Felsic • Light-colored rocks • Rich in feldspar & silica • Mafic • Dark-colored rocks • Rich in magnesium and iron

  13. Igneous Rocks • Intrusive Forms • Batholith • Massive intrusive body • Stock • Smaller intrusive body • Sill • Intrusive layer concordant to strata • Dike • Discordant intrusive layer that cuts through strata • Laccolith • Intrusive layer that pushes overlying strata forming a dome Insert Fig. 28.5 - intrusions

  14. Igneous Rocks • Jointing • Fractures in bedrock without apparent movement • Exfoliation • Outer layers peel away releasing confining pressure [Insert Fig. 28.8 - exfoliation]

  15. Igneous Rocks in the Landscape • Igneous rocks tend to be more resistant to weathering and erosion

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