Marble is a metamorphic rock that forms when limestone is subjected to the heat (temperatures greater than 150 to 200 °C) and pressure (150 megapascals (1,500 bar) of metamorphism causing profound physical or chemical change. It is composed primarily of the mineral calcite (CaCO3) and usually contains other minerals, such as clay minerals, micas, quartz, pyrite, iron oxides, and graphite. Under the conditions of metamorphism, the calcite in the limestone recrystallizes to form a rock that is a mass of interlocking calcite crystals. The protolith may be a sedimentary, igneous, or existing metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble may be foliated. In geology the term “marble” refers to metamorphosed limestone, but its use in stonemasonry more broadly encompasses unmetamorphosed limestone. Marble is commonly used for sculpture and as a building material.