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.