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Rocks – Views of Earth’s History

Rocks – Views of Earth’s History. Glacial grooves – Kelly’s Island, Port Clinton. Rock Type Classification Igneous rocks Sedimentary rocks Metamorphic Rocks. Igneous rocks Intrusive extrusive. Magma types. Basaltic-hottest,most fluid, low[gas],lowSiO 2

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Rocks – Views of Earth’s History

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  1. Rocks – Views of Earth’s History Glacial grooves – Kelly’s Island, Port Clinton

  2. Rock Type Classification Igneous rocks Sedimentary rocks Metamorphic Rocks

  3. Igneous rocks Intrusive extrusive

  4. Magma types Basaltic-hottest,most fluid, low[gas],lowSiO2 ……….CALMEST………. Andesitic-over subduction zones;intermediate Rhyolitic-coolest,least fluid,high[gas],highSiO2 ….MOST EXPLOSIVE….

  5. Magma – molten rock that often collection in underground chambers basaltic (50% SiO2) andesitic (60% SiO2) rhyolitic (70% SiO2) Formation Factors: temperature, water content, mineral composition Note Partial Melting, Fractional Crystallization

  6. Igneous rock classification A. By mineral composition Felsic – light color, high[Si], with quartz and feldspar Mafic – dark color, lower [Si), lots of Fe, Mg Intermediate – between Mafic, Felsic extremes FELSIC MAFIC Rhyolite (fine grain) Gabbro (coarse grain) Basalt (fine grain) Granite (coarse grain)

  7. By grain size (cooling rate) • Small/no Crystals Medium/large Crystals Granite Obsidian

  8. By texture (fractional crystallization) • Homogeneous Porphyritic • *CRYSTALS OF UNIFORM SIZE *CRYSTALS OF SAME • MATERIAL, BUT DIFFERENT • SIZES

  9. Igneous resources Ores – contain useful minerals/materials Pegmatites – veins of large-grained minerals Kimberlites – formed deep in crust (diamonds) Tourmaline, 10” x 3” diameter Pegmatite w/blue corundum crystals Olmsteadite crystals, 1.1 cm length

  10. Kimberlite from Murphreesboro, Arkansas

  11. Sedimentary rocks A. Formation Sediments generated by wind/water weathering & erosion, ice breakage, and precipitation “Clastic” sediments = broken rock, mineral fragmts • Deposition/burial • c. Lithification (Compaction/cementation) • Physical, Chemical transformation of sediments into • sedimentary rocks (including precipitation of • minerals and growth of mineral crystals) • Note: Sand resists compaction; spaces remaining • permit collection of groundwater, oil, and • natural gas

  12. Sedimentary rock types A. Clastics course-grained conglomerate breccias medium-grained sandstone fine-grained siltstone shale (mudstone)

  13. Gravel sediment (pebbles, cobbles, boulders) CONGLOMERATE Gravel sediment (rocks, cobbles, boulders) BRECCIA DIFFERENCE? INFERENCES?

  14. Sand sediments SANDSTONE Silt sediments SILTSTONE Clay sediments MUDSTONE (SHALE)

  15. Features of sedimentary rocks 1) Bedding = horizontal layering graded bedding – larger, heavier particles settle to bottom cross-bedding – formed as inclined sedimentary layers move forward across a horizontal surface

  16. Fossil inclusion – burial followed by formation of impressions, • mineralization of body parts

  17. Sedimentary rock types (cont.) • Chemical Sedimentary Rocks • evaporites • calcite(CaCO3), halite(NaCl), gypsum(CaSO4) • organics • limestone(mainly calcite), coal(vegetation remains)

  18. Evaporites *form as dissolved materials precipitate out as water evaporates *formed in arid regions, along oceans and drainage basins Great Salt Lake, UT following 5-year drought period, 2003

  19. Alabaster gypsum

  20. Organic sedimentary rocks *formed from the remains of once-living organisms * e.g., limestone, coal * fossils often occur Life forms compression lithification

  21. Metamorphic rocks *from “meta,” to change, and “morphe,” form * low, intermediate, and high grade metamorphosis Minerals in Metamorphosed Shale low grade inter-grade high grade ++chlorite++ +white mica (most muscovite)+++ +++++++biotite+++++++++ +++++++++++garnet++++++++++ ++++staurolite++++ +++kyanite++++ ++sillimanite++

  22. Metamorphic textures • Foliated – have wavy layers and bands of minerals (mineral grains • with long axes in one direction) schist gneiss slate phyllite

  23. b. non-foliated (made from minerals w/blocky crystal shapes Quartzite (from sandstone) Marble (from limestone)

  24. The Rock Cycle SEDIMENTS Deposition, burial, lithification weathering, erosion SEDIMENTARY ROCKS ---------------------------------------------------------------------------------------------------------------- H E A T A N D P R E S S U R E uplift IGNEOUS ROCKS METAMORPHIC ROCKS cooling, crystallization melting MAGMA

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