Rock

In geology, rock is a naturally occurring solid aggregate of one or more minerals or mineraloids. For example, the common Terran rock granite is a combination of the quartz, feldspar and biotite minerals. Terra's outer solid layer, the lithosphere, is made of rock.

Rocks have been used by humans throughout history. From Terra's Stone Age rocks have been used for tools. The minerals and metals found in rocks have been essential to human civilization.

Three major groups of rocks are defined: igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is an essential component of geology.