Dolomite (/ ˈ d ɒ l. ə ˌ m aɪ t, ˈ d oʊ. l ə-/) is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally CaMg(CO 3) 2. The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dolomitic rock type is dolostone