Dolomite is, after calcite, the second most important and abundant of the carbonate minerals. Chemically and structurally, it may be regarded as calcite with half the calcium ions replaced by magnesium. Iron or manganese may substitute for magnesium in dolomite, forming isostructural series with ankerite and kutnohorite. The crystal structure, hexagonal-rhombohedral, is similar to that of calcite, with alternate layers of calcium ions totally replaced by magnesium. This ordered arrangement of cations slightly impairs the overall symmetry of the structure but is essential to the stability of the mineral. specific gravity 2.85, luster vitreous to pearly, color ranges from colorless to white with green, brown, or pink tints, and cleavage is perfect in three directions.

Like calcite, dolomite occurs in virtually all geologic settings in igneous rocks as carbonatite, in metamorphic rocks as marble, and in hydrothermal deposits. Also like calcite, the most abundant occurrences are in sedimentary rocks; rocks composed primarily of dolomite are sometimes referred to as dolostone. Such rocks form vast deposits; in Italy, the Alpine range known as the Dolomites is almost entirely composed of dolomite. However, unlike calcite, dolomite's sedimentary origin is enigmatic. Although it is the most stable carbonate mineral where magnesium is abundant in the marine environment, it is unknown as a primary mineral. The vast, ancient deposits apparently formed from primary calcite or aragonite by diagnosis, yet this process is not observed in modern marine environments.

Dolomite is quarried for building and ornamental stone, road stone, and the production of refractory brick. It is the principal ore of magnesium metal and the source of the magnesium used by the chemical industry. It is also used as flux and in preparing mag. salts. Brazil up to 35 cts. or more @ 100.00 per ct.