Metamorphic Rocks

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Metamorphic Rocks

• c. Classify rocks by their process of formation.
• d. Describe processes that change rocks and the
  surface of the earth.

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Metamorphic Rock

• Meta is ancient Greek for change.
• Morphosis is ancient Greek for form.
• Metamorphic rock then is rock that has changed
  from one form to another.

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Origins of Metamorphic Rock

• Metamorphic rocks are rocks in which the
  structure, texture, or composition of the rock
  have changed. All three types of rock can be
  changed by heat, pressure, or a combination of
  both.
• A rocks texture or mineral composition can
  change when its surroundings change. If the
  temperature of pressure of the new environment is
  different from the one in which the rock formed,
  the rock will undergo metamorphism.

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Contact Metamorphism

• Contact Metamorphism when magma moves through the
  crust, the magma heats the surrounding rock and
  changes it.
• Some minerals in the surrounding rock are changed
  into other minerals by this increase in
  temperature.
• The greatest change occurs where magma comes into
  direct contact with the surrounding rock.

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Regional Metamorphism

• Regional metamorphism occurs when pressure builds
  up in rock that is buried deep below other rock
  formations, or when large pieces of the Earths
  crust collide with each other.
• The increased pressure and temperature causes
  rock to become deformed and chemically changed.

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Metamorphism
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How Metamorphic Rocks Form

• Deep below the Earths surface the intense heat
  and pressure can change rocks.
• Their appearance, texture, crystal structure and
  mineral content can change.
• Fossils will be destroyed.

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Almost Melted!

• Metamorphic rocks are often squished, smeared
  out, and folded.
• Despite these uncomfortable conditions,
  metamorphic rocks do not get hot enough to melt,
  or they would become igneous rocks.

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Classifying

• Classified by the arrangement of the grains.
• Foliated
• Non-foliated
• Usually harder and denser than the rock they come
  from.

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Texture of Metamorphic Rock

• All metamorphic rock has one of two textures.
• Foliated Metamorphic Rock
• Non-foliated Metamorphic Rock

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Foliated Metamorphic Rock

• Grains are in parallel layers of bands.
• Foliated is the Latin word for leaf.
• Describes the thin layering found in many
  metamorphic rocks.
• These rocks will split these bands.

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Slate

• Formed when shale is subjected to pressure.
• Denser, more compacted than shale.
• Produces flat plates when broken.

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Slate to Schist

• If slate is subjected to even greater pressure
  and moderate temperatures, schist is formed.

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Granite to Gneiss

• Granite becomes gneiss when subjected to heat and
  pressure.

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Key Idea!

• Heat Pressure metamorphic rock

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Non-Foliated Rock

• Mineral grains are randomized.
• Amorphous
• Do not split into layers
• Usually smoother and denser than the parent rock.

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Quartzite

• Occurs when sandstone is compressed by pressure.
• Usually very hard.

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Marble

• Formed from metamorphosed limestone
• Much harder and denser