Igneous Rocks

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Igneous Rocks

• Hot rocks/Fire Rocks
• Igneous comes from Latin and means fire.

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Key Questions

1. What is an Igneous Rock?
2. How are Igneous Rocks classified?
3. What are the two types of Igneous rocks?
4. What are the characteristics of Intrusive Igneous
   Rocks?
5. What are the characteristics of Extrusive Igneous
   Rocks?
6. What is Volcanic Glass?

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Igneous Rock

• Igneous rocks form when molten rock cools and
  solidifies.
• Molten rock is called magma when it is below the
  Earths surface and lava when it is above.

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when molten rock cools and solidifies
Magma (below)
Lava (above)
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Igneous Rock classification

• Igneous rocks are classified two different ways
• Where they were formed
• What they are made from (mineral composition)

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Intrusive Igneous Rocks

• Igneous rocks that form below the Earths surface
  are called intrusive igneous rocks.
• They form when magma enters a pocket or chamber
  underground that is relatively cool and
  solidifies into crystals as it cools very slowly.

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Crystal size
magma
Intrusive
slowly
Magma (below)
when molten rock cools and solidifies
large
Lava (above)
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Intrusive Igneous Rock

• Most intrusive rocks have large, well formed
  crystals. The mineral crystals within them are
  large enough to see without a microscope.
• The more slowly molten rock cools within the
  Earth, the larger the igneous rocks crystals will
  be.
• Examples of intrusive igneous rocks are granite,
  gabbro and diorite

Diorite
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Crystal size
magma
Intrusive
slowly
Magma (below)
when molten rock cools and solidifies
large
Lava (above)
Granite, gabbro, diorite
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Extrusive Igneous Rocks

• Extrusive igneous rocks, or volcanics, form when
  magma makes its way to Earth's surface. The
  molten rock erupts or flows above the surface as
  lava, and then cools forming rock.
• Most extrusive (volcanic) rocks have small
  crystals. Examples include basalt, rhyolite, and
  andesite.

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Lava
Crystal size
Quickly
Small or not visible
Extrusive
Pumice, obsidian, basalt
magma
Intrusive
slowly
Magma (below)
when molten rock cools and solidifies
large
Lava (above)
Granite, gabbro, diorite
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Volcanic Glass

• Pumice, obsidian, and scoria are examples of
  volcanic glass.

• These rocks cooled so quickly that few or no
  mineral grains formed.

• Most of the atoms in these rocks are not arranged
  in orderly patterns, and few crystals are
  present.

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Glassy Igneous Rocks
Glassy Igneous Rocks cool so rapidly, that atoms
dont have enough time to get together, bond and
form crystals. To cool this quickly the rocks
MUST be extrusive.

• Pumice (left)
• Scoria (bottom left)
• Obsidian (bottom)
• Note gasses in the lava can cause fine holes
  called vesicles as seen in the pumice and scoria.

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Classification

• Igneous Rocks are also classified by their
  physical and chemical properties.

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Lava
Crystal size
Quickly
Small or not visible
Physical chemical properties
Pumice, obsidian, basalt
Extrusive
magma
Intrusive
slowly
Magma (below)
when molten rock cools and solidifies
large
Lava (above)
Granite, gabbro, diorite
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