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.
For more photos see the Sedimentary Rocks Gallery.