DEFINITION OF DOLOMITE

A common carbonate mineral with the formula

(Ca,Mg)CO3, and the word is commonly applied to a rock

made of more than 50 percent of the mineral dolomite, even

though this rock type should technically be termed dolostone.

The rock and the Dolomite Mountains of northern Italy are

both named after Deodat de Dolomieu, who identified them

in 1791. Dolomites are more common in Precambrian carbonate

rocks than in younger sequence, perhaps related to

higher concentrations of CO2 in the atmosphere then, as

compared to younger times.

Dolomite is often found interbedded with or replacing

calcite, reflecting different modes of formation. It may be precipitated

directly from lake or shallow marine lagoonal water

and may also precipitate as a primary cement in pores

between grains in deep marine water. Most dolomite (dolostone)

is probably a replacement of earlier precipitated limestone

aided by magnesium-rich fluids. Conditions favorable

for the replacement of calcium carbonate by dolostone are

found in brackish water where fresh and saltwater mix, and

in brines (salty water) where organisms remove the calcium

carbonate leaving a magnesium-rich fluid behind to crystallize

the dolomite. Magnesium-rich waters can also be

expelled from a sedimentary sequence during burial, and

these fluids can alter a limestone sequence to dolostone.

See also SEDIMENTARY ROCKS.

dolostone See DOLOMITE.

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