dolomite. 1 Mineral, calcium magnesium carbonate, CaMg (CO₃)₂. It is commonly crystalline and is white, gray, brown, or reddish in color with a vitreous to pearly luster. The magnesium is sometimes replaced in part by iron or manganese. 2 Carbonate rock composed chiefly of the mineral dolomite, similar to limestone but somewhat harder and heavier. The rock may be metamorphosed into dolomitic marble. Most dolomites probably originated from the partial replacement of the calcium in limestone by magnesium. Its chief uses are as a building stone, for the manufacture of refractory furnace linings, and as basic magnesium carbonate for pipe coverings. Formations of dolomite are very widespread (occurring in Europe, the United States, Africa, Brazil, and Mexico) and notably in the region of the Alps now called the Dolomites, where the rock was first studied by Dolomieu.