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Dolomite - CaMg(CO3)2


T he Dolomite is a common rock-forming mineral. It is a calcium magnesium carbonate with a chemical composition of CaMg(CO3)2. It is the primary component of the sedimentary rock known asdolostone and the metamorphic rock known as dolomitic marble. Limestone that contains some dolomite is known as dolomitic limestone. Dolomite is rarely found in modern sedimentary environments but dolostones are very common in the rock record. They can be geographically extensive and hundreds to thousands of feet thick. Most rocks that are rich in dolomite were originally deposited as calcium carbonate muds that were postdepositionally altered by magnesium-rich pore water to form dolomite Dolomite occurs in a solid solution series with ankerite (CaFe(CO3)2). When small amounts of iron are present the dolomite has a yellowish to brownish color. Dolomite and ankerite are isostructural.

Properties Of Dolomite

The mineral dolomite crystallizes in the trigonal-rhombohedral system. It forms white, gray to pink, crystals. Dolomite is a double carbonate, having a different structural arrangement, and it does not rapidly dissolve or effervesce (fizz) in dilute hydrochloric acid. Crystal twinning is common. A solid solution series exists between dolomite andiron rich ankerite. Small amounts of iron in the structure give the crystals a yellow to brown tint. Manganese substitutes in the structure also up to about three percent MnO. A high manganese content gives the crystals a rosy pink color noted in the image above. A series with the manganese rich kutnohorite may exist. Lead and zinc also substitute in the structure for magnesium. The mineral dolomite is closely related to huntiteMg3Ca(CO3)4. Because dolomite can be dissolved by slightly acidic water, areas of dolomite are important as aquifers and contribute to karst terrain formation.
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