Intrusive and Extrusive Igneous Rocks

At first, many people are puzzled when they learn about magma and lava. They are both exactly the same stuff! The only difference is that it is called magma while it is underground, and lava when it is on the surface. Why do we need two different words for it? As you will see, the rocks formed underground by magma are very different from the rocks that form on the surface from lava. As you see how different those rocks are, you will get a better understanding of why we use "magma" and "lava".