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, sedimentary rocks by deposition and compression of particulate matter and chemical precipitates, and metamorphic rocks by subjecting other rock types to extreme temperature and pressure. The Earth's lithosphere and mantle are formed of rock.