Igneous rock



  • Igneous rock is formed when magma cools and solidifies, it may do this above or below the Earth's surface.

  • Magma can be forced into rocks, blown out in volcanic explosions or forced to the surface as lava.

  • The atoms and molecules of melted minerals are what make up magma.

  • These atoms and molecule rearrange themselves into mineral grains as the magma cools, forming rock as the mineral grains grow together.

  • There are over 700 different types of igneous rocks.

  • Examples of igneous rocks include basalt, granite, pumice, obsidian, tuff, diorite, gabbro and andesite.

  • Basalt forms the metamorphic rock granulite when subjected to extreme heat and pressure over time (metamorphism).

  • Granite is a common rock that contains at least 25% quartz and is sometimes used in construction because of its strength.

  • Pumice is an unusual, lightweight rock formed when molten rock is rapidly blown out of a volcano, forming bubbles as it quickly loses pressure and cools at the same time.

  • Obsidian is a volcanic glass that forms quickly without crystal growth, it can have very sharp edges making it useful as a cutting tool or arrowhead.

  • Tuff is a rock formed from volcanic ash.

  • The upper section of the Earth's crust is made up of around 95% igneous rock.


  • Make a fossil cast or check out our rock sorting lesson plan.