Dolomite, common mineral with the formula CaMg (CO₃)₂, found chiefly in rock masses as dolomitic limestone, but occurring sometimes in veins. It has a hardness of 3.5 to 4 and a specific gravity of 2.85. Dolomite crystallizes in the hexagonal system (see Crystal). It is usually colorless, white, or pink, but may be brown, black, or green, depending on the impurities present. In the United States it is found in many localities in Vermont, Rhode Island, New York, and New Jersey. Good crystals of dolomite have been obtained from deposits at Joplin, Missouri. When treated with sulfuric acid, dolomite yields calcium sulfate (gypsum) and magnesium sulfate (Epsom salts). Calcined (heated) dolomite is extensively employed as a lining for Bessemer converters in the production of steel from pig iron.

Some varieties of dolomite are called bitter spar or pearlspar. The name dolomite is sometimes given to any rock composed mainly of massive dolomite, or of any combination of magnesium and calcium carbonates. See also Calcite; Limestone; Magnesite.