Formation

Dolomite is a carbonate mineral composed of calcium magnesium carbonate. It forms when limestone or other carbonate sediments are altered by magnesium-rich groundwater or seawater. The chemical reaction involves the replacement of the calcium carbonate in limestone by magnesium carbonate to form its crystals. This process of dolomitization requires favorable conditions of high magnesium concentrations, optimal temperatures and pressures over long periods of time. The exact conditions and timing of dolomitization can vary greatly between different geologic environments.

Physical Properties

It has a distinctive rhombohedral crystal structure that gives it perfect cleavage in three directions. It has a hardness of 3.5–4 on the Mohs hardness scale, placing it between calcite and fluorite. As such, it can be scratched by a knife blade. Its crystals often form as clusters of microcrystals that appear fibrous or stalactitic in form over time. Its color varies from white to brown, gray or pink depending on impurities within the mineral. In composition it may contain minor amounts of iron and aluminum substituting for calcium and magnesium respectively. It is less soluble than limestone in water, making it more resistant to erosion.

Occurrence and Distribution

It occurs in many locations around the world, often forming great masses of rock known as dolomitic limestone or dolostone. Major deposits are found in the United States, Canada, Mexico, Brazil, Russia, India and countries across Europe, Africa and the Middle East. Notable occurrences include the Dolomite Alps mountain range at the border between Italy and Austria. This region gave its name to the entire mineral. Economically important deposits are found in Yorkshire, England and various areas of the United States such as the Ozarks and Midcontinent regions. It frequently forms in older Paleozoic sedimentary basins deposited during the Ordovician and Mississippian periods.

Uses

It has numerous industrial applications stemming from its useful chemical and physical properties. One of the largest uses is as a source of magnesium oxide in iron and steel making as well as in magnesium production. Over 50% of mined dolomite goes to these metallurgical applications. Another major use is as an aggregate in roadbuilding, construction and landscaping works. The crushed mineral is often used as a raw material or pigment filler in making cement, plaster and other building products. Finely ground dolomite is employed as an acid neutralizer, agricultural lime and flux in ceramic and glass production. Additionally, crushed dolomite is utilized for railroad ballast, filter stone and other specialized applications.

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