How Many Different Types of Rock Are in the Earth's Surface?

There are three types of rock on the Earth's surface: metamorphic, sedimentary and igneous. Metamorphic rocks are rocks that have changed from one form to the other. Sedimentary rocks are formed from compressed layers of organic and inorganic matter, while igneous rocks are formed from cooled and hardened magma.

Metaphoric rocks typically change due to pressure, heat or chemical processes underneath the Earth's surface. These changes result in two types of metamorphic rock: foliated and non-foliated. Foliated rocks, such as slate, has a layered appearance, while non-foliated rocks, such as marble and quartzite do not. Metamophoric rock can be found on large mountain ranges, such as the Rocky Mountains and Appalachian Mountains.

There are three types of sedimentary rocks: clastic, chemical and organic. Clastic sedimentary rocks, such as sandstone, are formed form weathering rocks. Chemical sedimentary rocks, such as rock salt, are formed from precipitation of dissolved minerals in water. Organic sedimentary rocks, such as coal, are formed from plant or animal debris.

The two types of igneous rocks are intrusive and extrusive. Intrusive rocks are formed from magma that solidifies below the Earth's surface, such as granite, gabbro and diorite. Extrusive rocks, such as pmic and basalt, are created by magma that solidifies on or above the Earth's surface.