Three Big Rock Groups

As you learned in our last lesson, most rocks are made up of two or more different minerals. There are three basic types of rocks. To understand how these rock groups are different, it is important to understand the nature of magma. Magma is molten rock that is present in the earth's crust. Sometimes magma erupts through cracks in the earth's crust. We call such eruptions volcanoes. At the surface, the magma turns into lava.

The three rock groups are:

• Igneous rocks
• Sedimentary rocks
• Metamorphic rocks

We'll tell you about each of them as we talk about the rock cycle.