rock

Constituent of the Earth's crust composed of minerals or materials of organic origin that have consolidated into hard masses. There are three basic types of rock: igneous, sedimentary, and metamorphic. Rocks are composed of a combination (or aggregate) of minerals, and the property of a rock will depend on its components. Where deposits of economically valuable minerals occur they are termed ores. As a result of weathering, rock breaks down into very small particles that combine with organic materials from plants and animals to form soil. In geology the term ‘rock’ can also include unconsolidated materials such as sand, mud, clay, and peat.

The change of one type of rock to another is called the rock cycle.