The Beauty of Geological Nature Illinois contains many natural resources, including a large variety of minerals, rocks and fossils. Minerals are crystalline materials made of elements or groups of elements. They have unique structures and occur naturally.
Rocks are natural combinations of one or more minerals.
The three main types of rocks are igneous, metamorphic and sedimentary. Igneous rocks are formed by the cooling of liquid rock on or within the earth. Metamorphic rocks are made as a result fo changes that occur in other rocks from conditions like heat, pressure and chemical reactions. Sedimentary rocks are composed of small pieces of rocks, shells or the remains of living things that build up and are cemented together. Fossils are evidence of prehistoric life that is preserved in rock.