Igneous Rocks

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Igneous Rocks
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Igneous Rocks

• Igneous from fire
• Igneous rock develops when magma cuts its way
  through the crust. The magma will cool and
  harden to form igneous rocks.

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Igneous Rocks 2 Types
a. Intrusive Igneous
Produced by cooling of magma deep below the
crust. We say intrusive because the magma
intrudes, or enter, into other rock masses
beneath surface of earth.

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Grain Size Texture

• Intrusive Rocks magma cools slowly underground
  large crystals form producing course-grained rock
  
• Different mineral crystals are easily seen.
• Example Granite, Diorite

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Igneous Rock Structures

• Magma that cools hardens underground are
  Intrusions.
• Batholiths large masses covering gt 100 sq km
• Laccolith floor of intrusion is parallel to
  underlying rock layer

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Igneous Rock Structures

• Sill Sheet of magma flows between the layers of
  rock and hardens. Lies parallel to rock layer
  surrounding it.
• Dyke Magma forces it way through rock layers by
  following existing vertical fractures
  solidifies.

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Example of a Dyke
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Igneous Rocks 2 Types
b. Extrusive Rock
Produced by the rapid cooling of lava on earths
surface.

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Igneous Rock Structures

• When lava erupts onto earths surface, it often
  forms volcanoes. The masses of rock leftover
  after eruptions are called Extrusions.
• Lava Flows erratically shaped masses of
  extrusive rock it flows.

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Grain Size Texture

• Extrusive Rocks lava cools rapidly very
  small crystals form producing fine-grained rock
• Unable to see grains w/naked eye
• Example Obsidian, Basalt