Rock (geology)

A rock is a naturally occurring solid. Rocks are made of collections of mineral grains that are held together in a firm, solid mass. They are made of minerals (which are crystalline), or other mineral-like substances.

The Earth's outer solid layer, the lithosphere, is made of rock. That means the Earth's crust is made of rock. The different minerals in the rocks make different kinds of rock.

Rock is often covered by soil or water. It is beneath the oceans, lakes, and rivers of the earth, and under the polar icecaps. Petrology is the scientific study of rocks.