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Igneous Rocks

Igneous rocks are formed from cooling magma. They can either be formed inside the Earth’s crust or outside.

Igneous rocks

Igneous rocks

  • Igneous rocks are formed from cooling magma.
  • There are two types of igneous rock: intrusive and extrusive.
Features of igneous rock

Features of igneous rock

  • They are very hard.
  • These rocks contain crystals.
Intrusive igneous rock formation

Intrusive igneous rock formation

  • Intrusive igneous rocks are formed inside the Earth’s crust.
  • They are formed from magma.
  • Because they form underground where it is hotter, they take a long time to cool.
  • This means the crystals that form are larger.
Extrusive igneous rock formation

Extrusive igneous rock formation

  • Extrusive igneous rocks are formed outside the Earth’s crust.
  • They are formed from lava from a volcanic eruption.
  • Because they form on the Earth’s surface where it is cooler, they take a short time to cool.
  • This means the crystals that form are smaller.
Examples and their uses

Examples and their uses

  • Granite – used in building and tiles.
  • Basalt – used in construction and building roads.
  • Pumice – this floats on water because of air that was trapped when it cooled. Some people use this rock to remove the dead skin from their feet.
  • Obsidian – jet black in colour, this rock has been used for making tools and weapons such as arrowheads.
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