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Dolomite Rock or Dolostone

Pictures of Sedimentary Rock Types

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Dolomite rock, also sometimes called dolostone, is usually a former limestone in which the mineral calcite is altered to dolomite. (more below)
A revamped limestone
Photo (c) 2006 Andrew Alden licensed to About.com
Dolomite was first described by the French mineralogist Déodat de Dolomieu in 1791 from its occurrence in a range of the southern Alps. The rock was given the name dolomite by de Saussure, and today the mountains themselves are called the Dolomites. What Dolomieu noticed was that dolomite looks like limestone, but unlike limestone it does not bubble when treated with weak acid. The mineral responsible is also called dolomite.

Dolomite is very significant in the petroleum business because it forms underground by the alteration of calcite limestone. This chemical change is marked by a reduction in volume and by recrystallization, which combine to produce open space (porosity) in the rock strata. Porosity creates avenues for oil to travel and reservoirs for oil to collect. Naturally, this alteration of limestone is called dolomitization, and the reverse alteration is called dedolomitization. Both are still somewhat mysterious problems in sedimentary geology.

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