Dolomite

Dolomite is both a mineral and a rock. The mineral dolomite is calcium magnesium carbonate, CaMg(CO3)2, a rhombohedral carbonate mineral closely related to calcite. The term dolostone or dolomite rock refers to sedimentary rocks composed chiefly of the mineral dolomite. Dolomite occurs in a variety of forms, from crystals to massive, granular aggregates.

Physical properties of dolomite include a color spectrum from colorless to white, often with pink or gray impurities, a Mohs hardness of 3.5 to 4, and a specific gravity around 2.87 to 2.97. It typically forms rhombohedra or tabular crystals and may occur as fine-grained to coarser, devotional masses. Like other carbonates, dolomite reacts with acids, but dolomite generally dissolves more slowly than calcite at room temperature; powdered samples or warmer acids increase the reaction rate.

Dolomite forms through two main processes. Primary dolomite precipitates from magnesium-rich seawater in certain sedimentary environments, especially evaporitic settings. More commonly, limestone is altered diagenetically in the subsurface by magnesium-rich fluids in a process called dolomitization, converting calcite to dolomite and producing dolostone.

Dolostone is widespread in the geological record and plays a significant role as a reservoir rock in oil and gas due to varied porosity and permeability patterns. Dolomite can also metamorphose into dolomite marble under higher temperatures and pressures. Industrial uses include magnesium extraction, refractory applications, cement additives, and decorative stone.

The mineral and rock are named after the French geologist Déodat Gratet de Dolomieu, with the name first applied in the Dolomites of Italy.