Formation & Sources of Chrysoberyl


Chrysoberyl is another of the numerous minerals that, in gem quality, is usually formed in pegmatite dikes; however, it is also formed in gneiss, mica-schist and granite. Associated with chrysoberyl in pegmatite dikes are such minerals as beryl, tourmaline and apatite, as well as the usual pegmatite assemblage of minerals. In gneiss or schist, it may be found with sillimanite, garnet or beryl.

In the various rocks in which it occurs, chrysoberyl is usually the result of the action of volatile constituents of a molten rock mass. The volatiles that were concentrated by crystallization of the least soluble minerals may bring about the formation of a pegmatite dike, or they may penetrate surrounding rocks along fractures or faults. In the latter instance, veins may be formed or isolated crystals of chrysoberyl and other minerals may form in the rocks that existed earlier as they are metamorphosed to gneisses or schist's.

Since chrysoberyl is a very hard and tough gemstone, it is a natural constituent of alluvial, deposits in areas in which pegmatite dikes are found.

Sources and Recovery Methods

 Despite the fact that chrysoberyl is a comparatively rare mineral, it is found in a number of places in the world, in two or three of which fine gem qualities are mined. Gem material is almost invariably recovered from alluvial gravels, rather than being mined from primary deposits.

The most important source of both fine alexandrites and cat's-eyes is Ceylon. It is the only producer of alexandrite cats-eyes, although, of course, these are of minor importance because of their great rarity. At the present time, a significant producer of both cat's-eye and transparent chrysoberyl is Brazil, especially in the State of Minas Geraes. Other nearby gem-rich states are also producers. Russia produces both clear chrysoberyl and alexandrite from the area around Ekaterinburg (sverdlovsk), the daylight color of which tends slightly toward bluish green, rather than the yellowish green of the Ceylon type. Russian material is usually lower in quality, being not only less transparent but usually smaller in size. Gem chrysoberyl is also mined with other alluvial gem materials in Madagascar. It is one of the many minerals that occurs in and around Mogok, Burma; but, compared with most of the other production of that gem-rich area, it is rarely of the highest quality. Most of the Burma material tends towards very pale colors and to transparency, rather than toward cat's-eye material.

 

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