Dolomite 's the name of a sedimentary carbonate rock and a mineral, both composed of calcium magnesium carbonate CaMg(CO3)2 found in crystals. Dolomite rock (also dolostone)'s composed predominantly of the mineral dolomite. Limestone that's partially replaced by dolomite's referred to as dolomitic limestone, or in old U.S. geologic literature as magnesian limestone. Dolomite was first described in 1791 as the rock by the French naturalist and geologist, Déodat Gratet de Dolomieu (1750R… (More on Dolomite)