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Sedimentary and Metamorphic Rocks

Sedimentary and Metamorphic Rocks. Sedimentary Rocks. Made from sediment / organic matter Rock goes through weathering and erosion, and is broken down into tiny fragments, some of which may be chemically altered Sediment Sediment is compacted and cemented

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Sedimentary and Metamorphic Rocks

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  1. Sedimentary and Metamorphic Rocks

  2. Sedimentary Rocks • Made from sediment / organic matter • Rock goes through weathering and erosion, and is broken down into tiny fragments, some of which may be chemically altered • Sediment • Sediment is compacted and cemented • Squeezed together; dissolved minerals crystallize and act as “cement” to bond sediment together • COMPACTION AND LITHIFICATION

  3. Classifying Sedimentary Rocks How do sedimentary rocks form? • Clastic • Sediment is compacted and cemented • Further classified by size of sediment grain • Sediment is held together by matrix material (“cement”) • Chemical; biogenic • Dissolved substances precipitate out of solution leaving a solid product OR • Made from organic matter • May CONTAIN FOSSILS! Tells about previous conditions on earth!

  4. Depositional Environment • Sandstone – beaches, desert • Ripples, sand dune patterns in layers to determine which environment • Shale; mudstone – deep, calm water • Water must be deep, calm enough for fine sediment grains to deposit • Lake and ocean bottoms • Limestone – deepest water, coral reefs • Shelled organisms die, CaCO3 accumulates • Conglomerate – rivers; glaciers • Rivers transports differently-sized particles that deposit along shore, riverbed, etc.; cemented together with mud to form stone • Rivers can transport materials long distances • Coal – swamp • Halite – dried up body of salt water

  5. Sedimentary rock samples (left; and sedimentary rocks in outcrop. Note the layers, or strata, that you can see in the sedimentary rock. C. Chesterman, 1979

  6. Metamorphic Rocks Previous existing rocks that go through extreme T and P changes that chemically alters the rock (ROCK DOES NOT MELT) Contact metamorphism -- comes into contact with magma (small scale) Regional metamorphism -- large, extreme changes and deformation

  7. Agents of Metamorphism • Heat • Magma • Change in location (depth) of rock • E.g. - Cookies! • Minerals become unstable and recrystallize • Heat is energy source that drives change • Pressure • Causes mineral grains to compact • Can create a new density or cause minerals to recrystallize • Hydrothermal solution • Hot water / mineral solutions that dissolve some substances in mineral, deposit new ones, causes change in composition

  8. How Metamorphic Rocks are Classified • Degree of foliation • Minerals recrystallize, can be re-oriented • Appears layered / banded • Due to preferred orientation of mineral (stress and strain!)

  9. Classification cont’d • Nonfoliated • Not banded • Usually only one mineral in rock composition

  10. Metamorphism, Environment, and History • Rock type: type of metamorphism • Volcanism, mountain building • Parent rock type -- history • Shale / siltstone - slate -> schist -> gneiss with T or P • Sometimes just burial • Granite, Schist -> Gneiss……with intense T or P • Mountain building • Can determine direction of force from foliation • More T and P -> Melting of Gneiss….back to Granite! • Limestone -> marble • Sandstone -> quartzite • Organic coal -> anthracite coal (just burial…increased P, Low T)

  11. Formation of Coal

  12. Here are a few examples of metamorphic rocks (samples to the right, rock outcrop above). C. Chesterman, 1979

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