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Volcanic Rocks
The Latin word igneous means "fire-formed." Igneous rocks are formed when molten rock cools and hardens. There are two classes of igneous rocks - extrusive and intrusive.

Extrusive igneous rocks are created when lava and/or pyroclastic materials cool at or above Earth's surface (Earth's exterior). Extrusive rocks are also called volcanic rocks.

Intrusive igneous rocks are formed when magma cools and solidifies below the surface of Earth (Earth's interior). Intrusive rocks are also called plutons. The majority of Earth's igneous rocks are plutons.

Information on intrusive igneous rocks
Information on extrusive igneous rocks
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