Igneous Rock

    Igneous rock is magma or lava that has been cooled whether in the crust or on the crust of the earth, with or without crystallization.  At the core of the earth, there is a very hot substance called magma, under great pressure. When magma reaches the surface, it becomes lava. The crust of our planet is hardened lava that has come up through weak points in the mantle, and settled on the surface. It is about 5km thick under the ocean floor, and as much as 50km under the five continents. When magma is forced up into hollows in the crust, it is called "intrusive" rock and is only seen when years of erosion has scoured clean the rock or dirt above, creating batholiths, laccoliths, sills and/or dikes. However, magma does not always stop there. Sometimes it will reach the surface, change its name to lava, and then harden as "obtrusive rock". A volcano is a very clear demonstration of this external process. For information on the internal process, scientists might re-create the earth's crust in a laboratory and force magma into weak spots, observing all the while. Granite, basalt, obsidian and andesite are all good examples of igneous rock. Below is an image a volcano spewing lava, and a diagram of the earth's crust, mantle, and core.