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4.16: Metamorphic Rock Classification

  • Page ID
    5376
  • What's the difference in these two rocks?

    The rock on the left was the sedimentary rock shale. Now it's the metamorphic rock slate. Slate looks very similar to shale, but it is harder and more platy. The rock on the right is gneiss. The light and dark minerals have separated into bands. Gneiss is produced by higher temperature metamorphism. The original rock was different in both cases.

    Common Metamorphic Rocks

    Some of the most common metamorphic rocks are listed below (Table below). Their parent rock and the type of metamorphism are also mentioned.

    The table shows some common metamorphic rocks and their original parent rock.

    Picture Rock Name Type of Metamorphic Rock Comments

    alt

    Slate Foliated Metamorphism of shale

    alt

    Phyllite Foliated Metamorphism of slate, but under greater heat and pressure than slate

    alt

    Schist Foliated Often derived from metamorphism of claystone or shale; metamorphosed under more heat and pressure than phyllite

    alt

    Gneiss Foliated Metamorphism of various different rocks, under extreme conditions of heat and pressure

    alt

    Hornfels Non-foliated Contact metamorphism of various different rock types

    alt

    Quartzite Non-foliated Metamorphism of quartz sandstone

    alt

    Marble Non-foliated Metamorphism of limestone

    alt

    Metaconglomerate Non-foliated Metamorphism of conglomerate

    Summary

    • Foliated metamorphic rocks are platy.
    • Non-foliated metamorphic rocks are massive.
    • The more extreme the amount of metamorphism, the more difficult it is to tell what the original rock was.
    • Marble is metamorphosed limestone.

    Review

    1. What does a foliated metamorphic rock look like?
    2. How do slate, phyllite, and schist differ from each other? How are they the same?
    3. What is quartzite?

    Explore More

    Use the resource below to answer the questions that follow.

    1. How are metamorphic rocks classified?
    2. How do metamorphic rocks form?
    3. What is recrystallization?
    4. Why are these rocks the most dense?
    5. Where do metamorphic rocks form?
    6. Where does regional metamorphism occur?
    7. What is a foliated rock?
    8. What does shale become when heated and put under pressure?
    9. What is schist?
    10. Describe gneiss.
    11. What is the evidence for regional metamorphosis?
    12. What is contact metamorphism?
    13. Where does contact metamorphism occur?
    14. Describe non-foliated rocks.
    15. Why is hornfels unique?
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