A stone is a naturally occurring aggregate of minerals and/or mineraloids. The Earth's crust (including the lithosphere) and mantle are formed of rock.Petrology is the study of rocks.
Rocks are classified by mineral and chemical composition, by the texture of the constituent particles and by the processes that formed them. These indicators separate rocks into igneous, sedimentary and metamorphic. They may also be classified according to grain size, in the case of conglomerates and breccias or in the case of individual stones. The transformation of one rock type to another is described by the geological model called the rock cycle.
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