chrysoberyl(redirected from Beryllium aluminium oxide)
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chrysoberyl(krĭs`əbĕr'ĭl) [Gr.,=golden beryl], a beryllium aluminate used as a gem. It has a vitreous luster and is transparent to translucent. The more valuable cat's-eyecat's-eye,
gemstone that displays a thin band of reflected light on its surface when cut as a cabochon. Its name is derived from its supposed resemblance to the eye of a cat.
..... Click the link for more information. is a variety of chrysoberyl. Another variety, alexandrite, was first discovered in the Ural Mts. of Russia, on the birthday of Czar Alexander II, for whom it was named. It is remarkable in that it is green by daylight and raspberry red under artificial light. It was popular in imperial Russia, both because of its association with the czar and because red and green were the colors of the empire. It is now found chiefly in Sri Lanka and Brazil.
a mineral of the subclass of multiple oxides, with the composition BeAl2O4. Chrysoberyl crystallizes in the orthorhombic system. Small short-columnar crystals are common, and tabular crystals sometimes occur. Flattened twins and triplets are typical. The color is yellowish or yellowish green. The emerald-green, chromium-containing variety of chrysoberyl that appears red-violet in artificial light is called alexandrite (seeALEXANDRITE); the golden yellow variety exhibiting a bluish chatoyancy is called cymophane, or cat’s-eye. Chrysoberyl has a vitreous luster, a hardness of 8.5 on Mohs’ scale, and a density of 3,500–3,700 kg/m3.
Chrysoberyl is found in the form of large segregations together with muscovite and beryl in granitic pegmatites occurring in rocks with a high aluminum content. It is typical of beryl-bearing magnetite-containing skarns. It is associated with taaffeite and spinel in magnesian skarns. Chrysoberyl is also typical of fluoritic metasomatites. Alluvial deposits are found in Burma and Sri Lanka. Fluoritic metasomatites with chrysoberyl and phenakite that have a high BeO content may serve as beryllium ores. Translucent chrysoberyls with attractive colors, that is, alexandrite and cymophane, are gems of order, or class, I.
REFERENCESMineraly: Spravochnik, vol. 2, fasc. 3. Moscow, 1967.
Geneticheskie tipy gidrotermal’nykh mestorozhdenii berilliia. Moscow, 1975.
A. I. GINZBURG