Carbonates are sedimentary rocks composed primarily of carbonate minerals, including calcite (CaCO3), aragonite (CaCO3), and dolomite (CaMg(CO3)2). The proportion of each mineral in a carbonate rock can be determined by X-Ray Diffractometry. Carbonates more rich in calcite and/or aragonite are called limestone. Carbonate rocks composed mainly of the mineral dolomite are also called dolomite (formerly dolostone). When metamorphosed both rocks become marble.