Metamorphic Rocks

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Metamorphic Rocks

• Intense Heat and/or Pressure, Yo!

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AIM What are the characteristics of metamorphic
rocks?

• Metamorphic rocks are formed from existing
  bedrock by the action of heat, pressure, and
  chemical action within the Earths crust.

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Meta Rox

• Pressure (Regional/Dynamic Metamorphism)
• At 6 miles beneath the surface, The downward
  pressure 20 tons/in2
• Horizontal pressure is present during mountain
  building

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The REALLY smart version.

• College Definition Metamorphic rock is created
  when heat and pressure break the bonds between
  some of the ions in a mineral, allowing them to
  migrate to other sites in the rock and re-bond.
  Such migration of ions, usually through fluids
  circulating through the rock, results in
  recrystallization of the mineral. Metamorphism
  occurs when heat and pressure exceed certain
  threshold levels, destabilizing the minerals in
  rocks, but do not become high enough to cause
  melting.

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Meta Rox

• Heat and Chemical Action (Thermal or Contact
  Metamorphism)
• High temps may cause partial melting and
  re-crystallization
• A baked zone is present along the edge of an
  igneous intrusion. This will contain contact
  metamorphosed rocks

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Rock Metamorphism

• Rock Transformations (Original ? Morphed)
• Limestone ?Marble (acid test reveals carbonate)
• Sandstone ?Quartzite (harder and denser)
• Shale?Slate?Phyllite?Schist?Gneiss
• Conglomerate?Meta-conglomerate (pebbles stretched
  and squished)

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NOTE!!

• Quartzite and Marble may result from regional /
  dynamic metamorphism but they do not show
  foliation (see ESRT)

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What is Foliation?

• Foliation under intense pressure and heat, some
  minerals may partially melt and re-crystallize as
  new minerals or larger crystals. They may also
  align themselves in sheets or plates (distorted
  layers)of mineral crystals (Schist)

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Foliation

• or they may arrange into bands of alternating
  light and dark minerals (Gneiss)

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Foliation

• High-grade metamorphism will also
• show distorted layering and banding

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Meta Rox

• Foliation