DOLOMITE

DOLOMITE

Dolomite is the name of a sedimentary carbonate rock and a mineral, both composed of calcium magnesium carbonate CaMg(CO₃)₂ found in crystals.

Dolomite rock is composed predominantly of the mineral dolomite. Limestone that is partially replaced by dolomite is referred to as dolomitic limestone. Dolomite was first described in 1791 as the rock by the French naturalist and geologist, Déodat Gratet de Dolomieu (1750–1801) for exposures in the Dolomite Alps of northern Italy.

The mineral dolomite crystallizes in the trigonal-rhombohedral system. It forms white, gray to pink, commonly curved crystals, although it is usually massive. It has physical properties similar to those of the mineral calcite, but does not rapidly dissolve or effervesce (fizz) in dilute hydrochloric acid unless it is scratched or in powdered form. The Mohs hardness is 3.5 to 4 and the specific gravity is 2.85. Refractive index values are nω = 1.679 - 1.681 and nε = 1.500. Crystal twinning is common. Lead and zinc also substitute in the structure for magnesium.

Recent research has found modern dolomite formation under anaerobic conditions in supersaturated saline lagoons along the Rio de Janeiro coast of Brazil, namely, Lagoa Vermelha and Brejo do Espinho. One interesting reported case was the formation of dolomite in the kidneys of a Dalmatian dog. This was believed to be due to chemical processes triggered by bacteria. Dolomite has been speculated to develop under these conditions with the help of sulfate-reducing bacteria. This joins other research in pointing out many new interesting links between large-scale geology and small-scale microbiology (see geomicrobiology).

Dolomite is used as an ornamental stone, a concrete aggregate, a source of magnesium oxide and in the Pidgeon process for the production of magnesium. In horticulture, dolomite and dolomitic limestone are added to soils and soilless potting mixes to lower their acidity. In nutrition, dolomite is sold sometimes as a dietary supplement on the assumption that it should make a good simultaneous source of the two important elemental nutrients calcium and magnesium.