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Metamorphic Rocks

Metamorphic Rocks. Metamorphic Rocks : form when heat and/or pressure change pre-existing rocks. Metamorphism : the process of forming metamorphic rocks. Formation of Metamorphic Rocks.

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Metamorphic Rocks

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  1. Metamorphic Rocks

  2. Metamorphic Rocks: form when heat and/or pressure change pre-existing rocks. • Metamorphism: the process of forming metamorphic rocks.

  3. Formation of Metamorphic Rocks • Recrystallization: the process of increasing the size of the mineral crystals/clasts AND/OR changing the mineral composition WITHOUT MELTING. • HIGH heat and pressure allows atoms to rearrange Animation

  4. Types of Metamorphism • Contact Metamorphism: caused by contact with extreme HEAT (magma/lava OR hot fluids) that will alter the rock. • No foliation

  5. When extreme heat is added to a Quartz sandstone, you get Quartzite. When extreme heat is added to Limestone, you get Marble.

  6. Limestone (sedimentary) Marble (metamorphic) Diorite (igneous) Marble (metamorphic) Limestone (sedimentary) A thick body of diorite was injected between layers of limestone of the Helena Formation in northern Montana. The great heat of the intrusion baked the limestone above and below it into white marble.

  7. Types of Metamorphism • Regional Metamorphism: occurs over wide regions when rocks are exposed to extreme heat AND pressure. • Foliated rocks • Folded rocks • Faulted rocks

  8. Warped, distorted layers

  9. Folded Rock outcrop on I-68, Maryland

  10. Textures of Metamorphic Rocks • Foliated rocks: have layers of mineral crystals • occurs when pressure aligns minerals into layers.

  11. In SLATY FOLIATION, rocks may split into flat, thin layers

  12. In SCHISTOSE foliation, minerals have been squished into flakes of mica

  13. In GNEISSIC foliation, minerals have been squished into bands of color (“zebra stripes”)

  14. Textures of Metamorphic Rocks 2. Nonfoliated Rocks: not layered • rocks were not subjected to a directional pressure and/or • minerals are not flat Quartzite Marble

  15. Key Identifying Features of Metamorphic Rocks • Foliation • Bent/Distorted Layers

  16. Key Identifying Features of Metamorphic Rocks 3. Key Identifier Minerals: • Garnet - Dark Red Color • Mica – Shiny, flaky mineral

  17. FOLIATED NON

  18. Which metamorphic rock is nonfoliated, and composed of calcite?

  19. Which metamorphic rock is foliated, and consists of ONLY mica?

  20. Vocabulary • Recrystallization: changing the size of mineral crystals or mineral composition without melting. • Foliation: Mineral layering or banding

  21. Vocabulary • Slaty Foliation: Fine-grained and breaks into thin, smooth layers. • Schistose Foliation: Medium-grained with high mica content. • Gneissic Texture: Coarse-grained with banded minerals.

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