Magnesite

magnesite (măg`nəsīt), mineral, magnesium carbonate, MgCO₃, white, yellow, or gray in color. It originates through the alteration of olivine or of serpentine by waters carrying carbon dioxide; through the replacement of calcium by magnesium in calcareous rocks, sometimes limestone but more often dolomite; and through precipitation from waters rich in magnesium that have undergone reaction with sodium carbonate. Caustic magnesite is not thoroughly calcined, 3% to 4% of carbon dioxide being left; mixed with magnesium chloride it makes oxychloride cement, which is extensively used for floorings and as a stucco. Dead-burned magnesite is calcined in kilns until it contains less than 1% of carbon dioxide; it is made into an excellent firebrick. Magnesite is also used in the manufacture of Epsom salts, face powder, boiler wrappings, and disinfectants.

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magnesite [′mag·nə‚sīt]

(mineralogy)

MgCO₃The mineral form of magnesium carbonate, usually massive and white, with hexagonal symmetry; specific gravity is 3, and hardness is 4 on Mohs scale. Also known as giobertite.

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magnesite

A natural magnesium carbonate.

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Magnesite 

a mineral of the calcite group of the carbonate minerals. Its composition is MgCOs, containing 47.82 percent MgO, 52.18 percent CO2, and isomorphic admixtures—often Fe, more rarely Mn and Ca. Magnesite crystallizes in the trigonal system and exhibits perfect rhombohedral cleavage; it has the same structure as calcite. Magnesite occurs in rhombohedral or irregularly elongated crystals; in zones of rock weathering it forms porcelain-like cryptocrystalline masses. A white or yellowish gray mineral, it is brittle and has a hardness of 3.75-4.25 on MohsVscale and a density of 2,900-3,100 kg/m³.

Magnesite deposits are found in salt-bearing sedimentary rocks in association with gypsum and in altered magmatic ultrabasic rocks; when altered by metamorphism, magnesite is found in association with talc; and when altered by weathering, almost without admixtures. The most important industrial deposits of magnesite, however, are associated with metamorphosed dolomites. Such deposits are located in many countries, the largest occurring in the Precambrian strata of the USSR (Satka in the Urals, Talaia and other sites in the Enisei Ridge, Savina in Vostochnyi Saian) and northeastern China, and in the Democratic People’s Republic of Korea and Brazil.

Magnesite loses 92-94 percent of its carbon dioxide content when roasted at 1000°C and is subsequently converted into a chemically active powdery mass known as caustic magnesia. This product is used in magnesia binding cement; in the manufacture of cellulose, thermal insulation, synthetic rubber, plastics, and viscose; in chemical processing; and as a fertilizer. Roasted magnesia with low chemical activity and high (up to 2800°C) refractoriness is obtained by raising the temperature to 1500-1650°C; it is used primarily in metallurgy. The processing of magnesite in electric furnaces yields fused periclase, which is used in ceramics and as a heat-resistant electrical insulating material.

In 1972 the annual world production of magnesite exceeded 12 million tons. Approximately 70 percent of the total was produced in socialist countries: the USSR (approximately 2.5 million tons of MgO), Czechoslovakia, the People’s Republic of China, and the Democratic People’s Republic of Korea.

REFERENCES

Trebovaniia promyshlennosti k kachestvu mineraVnogo syr’ia. Fasc. 40: V. A. Rybnikov and A. A. Veikher, Magnezit, 2nd ed. Moscow-Leningrad, 1961.
Kurs mestorozhdenii nemetallicheskikh poleznykh iskopaemykh. Moscow, 1969.
Smolin, P. P. “Tendentsii ispol’zovaniia magnezial’nogo syr’ia.” In the collection Nemetallicheskie poleznye iskopaemye. Moscow, 1971.

P. P. SMOLIN