The oldest type of all rocks is the igneous rock (IG nee us). The word "igneous" comes from a Greek word for fire. Deep inside the earth, the temperature is very high and the minerals there are in liquid form called magma. As the magma pushes towards the earth's surface, it starts to cool and turns into solid igneous rock.

All igneous rocks do not cool the same way. That is why they do not look all the same. Some cool slowly, deep under the earth's surface. These are called intrusive igneous rocks. The slow cooling formed rocks with large crystals. Granite is an example of a rock that cooled slowly and has large crystals.