Minerals usually occur naturally in the ground and are made of non-organic substances. However, sometimes minerals contain organic substances such as coal. There are approximately 2000 minerals with new ones still being discovered. The rocks present in the earth's crust are classified as igneous, sedimentary and metamorphic. Each of the three kinds of rocks is related to the other two.
Igneous rocks compose the majority of the rock in the earth's crust.
They are formed from hardened liquid rock called magma. The magma may move upward because of great pressure, or it may flow out onto the surface of the earth. The texture of igneous rocks is determined by the size of the grains. If the magma solidifies deep within the earth, the size of the crystals in the rock will be large due to slow cooling. These igneous rocks are classified as intrusives .