Formation and Structure
Dolomite is a carbonate mineral composed of calcium magnesium carbonate. Its chemical formula is CaMg(CO3)2. It forms when limestone or other carbonate rocks are subjected to magnesium-rich groundwater and experiences increasing temperatures and pressures over geological time. As a result of these alteration processes, some of the calcium in the original carbonate mineral is replaced by magnesium. Dolomite crystallizes in the trigonal-rhombohedral crystal system and commonly forms crystals with curved, scalenohedral shapes. Its Mohs hardness is 3.5 to 4, and it has a white or grey color. On a microscopic scale, dolomite has been observed to have ordered arrangements of magnesium and calcium carbonate ions.
Applications as an Industrial Mineral
Due to its chemical and physical properties, Dolomite has a variety of industrial uses. One of the most important applications is its use as an flux in iron and steel production. Finely ground dolomite is mixed with sinter plant feed materials to help remove impurities and protect the refractory linings of furnaces from corrosion during smelting. Dolomite is also used as an aggregate in road building, concrete production and railroad ballast. It performs well in these construction applications because it is chemically inert and resistant to weathering. Dolomitic limestone can also undergo calcination to produce dolomitic quicklime and dolomite cement. These products are suitable for use in the construction of sewers and reservoirs due to their high resistance to water penetration.
As a mineral filler and extender, finely ground dolomite powder finds applications in plastics, rubber, paints, paper and pesticide industries. It renders improved strength, flexibility, opacity and other useful properties to end products. Due to its white coloration, dolomite is utilized in ceramic glazes, linoleum flooring, roofing materials and as an agricultural soil conditioner to neutralize acidity. Pharmaceutical companies sometimes harness dolomite as an inexpensive calcium and magnesium dietary supplement, antacid or laxative. Dolostone rock is also suitable for dimension stone, ornamental stonework and monument applications where a creamy white appearance is desirable.
Occurrences and Mining
Commercial dolomite deposits form in a variety of geological settings, primarily from sediments precipitated in shallow marine environments during ancient periods of Earth history. Major world producers of dolomite include the United States, Russia, Ukraine, Germany, Turkey and countries in North Africa and the Middle East. Notable dolomite deposits exist in the Appalachian Mountains, Michigan and Texas in the United States. Russia's Ural Mountains contain extensive resources of the mineral. In Africa, large dolomite reserves are found spread across Morocco, Algeria and Egypt.
Underground mining techniques such as room and pillar, shrinkage stoping and longwall top coal caving are employed when dolomite occurs in thick, tabular beds. Open pit mining is carried out for surface or shallow deposits. Operators drill, blast and load the dolostone rock using large excavating and hauling equipment. Primary crushing and sizing takes place near quarries to produce lump and fine aggregate fractions. Further processing involves washing, screening and sometimes calcination depending on end use requirements. Transportation occurs via conveyors, trucks, barges or rail. Environmental permitting covers issues related to blasting, air quality, dewatering and site rehabilitation.
As a versatile industrial mineral, dolomite plays an important supporting role in modern industries from ironmaking to construction to agriculture. Its widespread natural availability and varied applications ensure dolomite mining and usage will remain economically significant for the foreseeable future. Continuous improvements in processing technology also help maximize recovery and utilization of this industrially valued carbonate resource.
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