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Metamorphic Rocks

Metamorphic Rocks. “If something is gneiss, don’t take it for granite.”. Metamorphic Agents. Pressure (>1,000 times atmospheric pressure) Temperature (>300 degrees C) Chemical Fluids (mineral saturated hot water). Metamorphic Environments. Contact (thermal) – intrusion by magma

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Metamorphic Rocks

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  1. Metamorphic Rocks “If something is gneiss, don’t take it for granite.”

  2. Metamorphic Agents • Pressure (>1,000 times atmospheric pressure) • Temperature (>300 degrees C) • Chemical Fluids (mineral saturated hot water)

  3. Metamorphic Environments • Contact (thermal) – intrusion by magma • Hydrothermal – ion-rich hot water circulates through cracks • Mountain Building – regional metamorphism

  4. Metamorphic Changes -Rocks adjust to new conditions by: • Changes in texture • Changes in mineralogy

  5. Changes in Texture • Compaction • Recrystallization - may cause • Foliation • Lineation

  6. Changes in Minerology • Recrystallization – small crystals reform into larger crystals of the same mineral • Formation of new minerals – elements recombine to form new minerals • Garnet, Chlorite and others found only (or mostly) in metamorphic rock

  7. Grades of Metamorphosis • Low Grade – Low temperature and pressure results in slate and phyllite • “Rock cleavage” in slate • Foliated • Fine grained • Slate looks dull, phyllite is shiny

  8. Grades of Metamorphosis (cont.) • Intermediate Grade – higher temperatures and pressures than Low Grade • Schist • Foliated • Mica, garnet

  9. Grades of Metamorphosis (cont.) • High temperatures and pressures • Gneiss and Migmatite • Dark & light banding of mica (dark), quartz & feldspar (light)

  10. Slate – parent rock is shale (sedimentary) Phyllite – parent rock is slate Schist – parent rock is phyllite Gneiss – parent rock is schist Migmatite – parent rock is gneiss Foliated Metamorphic Rock Sequence

  11. Non-Foliated Metamorphic Rocks & Their Parent Rocks • Marble – Parent rock is limestone or dolostone (calcite, reacts with acid) • Quartzite – Parent rock is sandstone • Anthacite – Parent rock is bituminous coal • Hornfels – Parent rock is any rock type

  12. Metamorphic Rock Dichotomous Key Proceed to Dichotomous Key Activity

  13. View in slide show, then click to view: Dichotomous Metamorphic Key

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