An igneous rock is hot lava or magma that has cooled. The process of the creation is called Lithification. When you look at the word igneous, you might notice that it sounds familiar to ignite. Igneous rocks are split into two categories, Intrusive and Extrusive. Looking at the word intrusive and extrusive, you should see that extrusive is similar exterior meaning outside. Extrusive means that the lava has cooled outside on the Earth's surface to form an Igneous Rock.