Dolomite

Dolomite is a common rock-forming mineral. It is a calcium magnesium carbonate with a chemical composition of CaMg (CO3)2. It is the primary component of the sedimentary rock known as dolostone and the metamorphic rock known as dolomitic marble. Limestone that contains some dolomite is known as dolomitic limestone.

Dolomite, type of limestone, the carbonate fraction of which is dominated by the mineral dolomite, calcium magnesium carbonate [CaMg(CO3)2].

Along with calcite and aragonite, dolomite makes up approximately 2 percent of the Earth’s crust. The bulk of the dolomite constitutes dolostone formations that occur as thick units of great areal extent in many sequences of chiefly marine strata. (The rock dolostone is referred to by only the mineral name—i.e., dolomite—by many geologists.) The Dolomite Alps of northern Italy are a well-known example. Other relatively common occurrences of the mineral dolomite are in dolomite marble and dolomite-rich veins. It also occurs in the rare igneous rock known as dolomite carbonatite.

From the standpoint of its origin, the dolomite of dolostones is one of the most interesting of all the major rock-forming minerals. As discussed below, a large percentage of the dolomite in thick marine dolostone units is thought by many geologists and geochemists to have been formed by replacement of CaCO3 sediment rather than by direct precipitation.

Dolomite is used as a source of magnesium metal and of magnesia (MgO), which is a constituent of refractory bricks. Dolostone is often used instead of limestone as an aggregate for both cement and bitumen mixes and also as a flux in blast furnaces. The use of dolostone as a flux has increased, especially since environmental contamination has become a widely heeded consideration, because the resulting slag can be employed for such things as lightweight aggregate, whereas that formed when limestone is used cannot. Such is the case because dolostone-based slag does not slake (disintegrate in water), but limestone-based slag does.