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Some igneous rocks form from volcanic lava.
Click on image for full size
Courtesy of USGS

Igneous Rocks

Igneous rocks form when molten rock cools and becomes solid. Molten rock is called magma when it is below the Earthís surface and lava when it is above.

Sometimes magma pushes up through cracks to the surface of the Earth. It cools and becomes a volcanic rock. Basalt is the most common type of volcanic rock. It makes up most of the rocks on the ocean floor.

Other times, magma cools when itís deep underground. This forms a different type of igneous rock called a plutonic rock. Plutonic rocks usually have large crystals. Granite is a type of plutonic rock that you are likely to find.


Last modified June 17, 2003 by Lisa Gardiner.

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The Fall 2010 issue of The Earth Scientist, focuses on rocks and minerals, including articles on minerals and mining, the use of minerals in society, and rare earth minerals, and includes 3 posters!

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