Some igneous rocks form from volcanic lava.
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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 Earth’s 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 it’s 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.
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TES XXVI, 3 fall 2010
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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Basalt is volcanic rock. It is the most common type of rock in the Earth's crust and it makes up most of the ocean floor. It forms when lava reaches the Earth's surface at a volcano or mid ocean ridge.
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