Tell which minerals are present in various types of igneous rocks. List and describe the characteristics of intrusive igneous rocks. List and describe the characteristics of extrusive igneous rocks, including textures. Explain the origin of various types of igneous rocks, including cooling history. Explain how igneous rocks are classified.
Igneous rocks form by cooling and crystallizing from hot molten magma or lava.
Igneous rocks that cool and crystallize beneath the Earth's surface are called intrusive igneous rocks . Igneous rocks that cool and crystallize on the Earth's surface are called extrusive igneous rocks . Extrusive igneous rocks tend to be fine grained or glassy . Sometimes they are vesicular with tiny holes formed by the release of trapped gases. Other extrusive igneous rocks have a fragmental or pyroclastic texture composed of pieces of volcanic rock and ash welded together by heat.