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Dolomite

A white or light-colored mineral, essentially CaMg(CO₃)₂, used in fertilizer, as a furnace refractory, and as a construction and ceramic material. An important sedimentary and metamorphic mineral, found as the principal mineral in dolostones and metadolostones, and as an important mineral in limestones and marbles where calcite is the principal mineral present. Also found as a hydrothermal vein mineral, forming crystals in cavities; and found in serpentinites and similar rocks.

The carbonate mineral CaMg(CO₃)2. Often small amounts of iron, manganese, or excess calcium replace some of the magnesium; cobalt, zinc, lead, and barium are more rarely found. Dolomite is normally white or colorless with a specific gravity of 2.9 and a hardness of 3.5–4 on Mohs scale. It can be distinguished from calcite by its extremely slow reaction with cold dilute acid. Dolomite is a very common mineral, occurring in a variety of geologic settings. It is often found in ultrabasic igneous rocks, notably in carbonatites and serpentinites, in metamorphosed carbonate sediments, where it may recrystallize to form dolomite marbles, and in hydrothermal veins. The primary occurrence of dolomite is in sedimentary deposits, where it constitutes the major component of dolomite rock and is often present in limestones.

Material Notes:

Weathering end products: Limestones, dolomites, marbles. Occurrence: Dolomites, marbles.

Very slowly dissolved in cold acids. Powder readily dissolves in warm acids with effervescence. May exhibit triboluminescence.

Dolomite and ferroan dolomite occur frequently as pseudomorphs after calcite and also after aragonite. Rarely pseudomorphic after cerussite, baryte and fluorite.

Several species have been recognized as incrustation or substitution pseudomorphs after dolomite crystals. There is no specific data on health dangers or toxicity for this mineral, however you should always treat mineral samples as potentially toxic/dangerous and use sensible precautions when handling them. A major source of magnesium, particularly for agricultural and pharmaceutical applications.

Dolomite is believed to have formed by replacement of some of the calcium in a calcium carbonate limestone deposit with magnesium, while the sediment was undergoing lithification, being converted from layers of dead clam and other sea animal shells into crystallized calcite or calcium carbonate. The resultant dolomite mineral, CaMg(CO₃)₂ is a true double salt. The calcium and magnesium ions in dolomite exist in separate layers in the crystal matrix. Dolomite has a calcium layer, then a carbonate layer, then a magnesium layer then a carbonate layer, and so on.

Dolomite is harder and denser than the calcite form of calcium carbonate or limestone, and is more chemically inert and more impervious to acid attack.

As an industrial mineral, dolomite's usage is significantly less than calcite's. This is primarily due to the relative lack of high brightness deposits of dolomite. The alteration process that forms dolomite tends to bring in additional impurities that reduce brightness or tint the stone brown or gray. In regions where high brightness dolomites do exist, they share many of the applications of calcium carbonate.

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