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Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia

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PERICLASE


PERICLASE (Periklas—Périclase—ѕериклаз) (Scacchi, A. 1840), from Gk. “peri” – around and “klasis” – breaking, alluding to its perfect cubic cleavage.

Composition & Properties. Oxide – MgO, cubic system. Hardness 5.5-6. Density 3.7-3.9. Glass luster. Perfect cleavage in one direction. Fragile. Color: yellowish, grayish-green, brownish-yellow, sometimes colorless. It is often represented with transparent to half-transparent isometric grains, more rarely with crystals. Periclase is formed under the conditions of high-temperature contact metamorphism in magnesio-carbonate layers poor with SiO2 and Al2O3; and also under the annealing of serpentinites and in burnt coal dumps. There are no separate deposits of this mineral. In Russia, periclase is found in the form of small crystals in the North Urals, in serpentinites in the Serov. In 1968, it was discovered in Kazakhstan, in the South Urals, in chromites of the Kempirsaiskiy massif. It is often replaced with brucite. In Sweden, periclase is represented in skarn marbles at Långban, Värmland Prov. In the U.S.A., in California, at the Crestmore quarry, Riverside Co., periclase replaced brucite of irregular shaped grains. Its small transparent crystals are faceted for collection purposes from time to time.

Synthesis. As gem-quality rough material synthetic periclase is of obvious interest. In the U.S.A. and Australia, colorless and rose synthetic periclase with the admixtures of nickel (Ni2+) and manganese (Mn4+) are produced from melt with the method by Verneille. Under the trade name lavernite it is used for the imitation of gemstones, for example for the imitation of spinel.

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