Any rock that forms from the cooling of magma is an igneous rock. Magma that cools quickly forms one kind of igneous rock, and magma that cools slowly forms another kind. When magma rises from deep within the earth and explodes out of a volcano, it is called lava, and it cools quickly on the surface. Igneous rocks are formed from cooling magma deep in Earth's crust or mantle. This cooling magma crystallizes to form rocks like the granite in your house. A rock that cools within Earth's crust will cool very slowly and form larger crystals and is called an intrusive igneous rock.