Rock is a naturally occurring aggregate of minerals and/or mineraloids. Rocks are classified by mineral and chemical composition; the texture of the constituent particles; and also by the processes that formed them. Rocks are thus separated into igneous, sedimentary, and metamorphic rocks.
Igneous rocks are formed from molten magma, and sedimentary rocks by deposition of either detrital or organic matter, or chemical precipitates (evaporites), followed by compression of the particulate matter and cementation.
Metamorphic rocks are formed by subjecting any rock type (including previously formed metamorphic rock) to different temperature and pressure conditions than those in which the original rock was formed. The PT metamorphic-rock-forming conditions are always higher than those at the earth's surface, and are sufficiently high enough to change the original mineralogy to either other minerals or to other forms.
The Earth's crust (including the lithosphere), and the mantle are formed of rock.
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