Semi-Precious Gemstones: Chrysoberyl
Chrysoberyl used in Jewelry
Source: Brazil, India, Myanmar, Tanzania, Zimbabwe, Sri Lanka, USA (Colorado)
Chrysoberyl is a yellow to greenish-yellow, transparent to translucent, semi-precious version of Alexandrite. Chrysoberyl, like Alexandrite, is a beryllium-aluminum oxide. Chrysoberyl is one of the hardest minerals, falling just below corundum (ruby or sapphire), and diamond.
Chrysoberyl commonly occurs in granites and granite pegmatites while alexandrite occurs in mica schists. Chrysoberyl occurs in yellow, greenish-yellow, green, and brown. Most chrysoberyl is found as an alluvial deposit in river sands and gravels, but can also be found in metamorphic deposits of marble and corundum.
Chrysoberyl crystallizes in the orthorohombic crystal system, forming in slender prisms and usually has a "tabular" crystal habit. Crystal twinning is common, forming platy and tabular 'Brazil-law' twins (above, right).
Cymophane Cat's Eye Chrysoberyl
A chatoyant variety of chrysoberyl is called "cymophane" or "Cat's eye," and is usually a translucent yellow. The name "cymophane" is derived from the Greek words "wave" and "appearance" (wavy appearance). The term "cat's eye" usually refers to chrysoberyl although there are chatoyant varieties of quartz that are mistakenly referred to as cat's eye.
Chrysoberyl Crystallography, Chemistry, Physical Properties
Chrysoberyl Optical Properties
When cutting a cabochon, gem cutters will center the cat's eye slit so that it bisects the stone. The primary source for cat's eye chrysoberyl is the Ural Mountains of Russia, Sri Lanka (Ceylon), Tanzania and the Marambaia valley mines near Teófilo Otoni in Minas Gerais, Brazil.
Pale greenish-yellow chrysoberyl |
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Smoky-brown chrysoberyl |
The chatoyant effect is produced from microscopic needlelike inclusions of rutile. Chrysoberyl can be facet cut, but the cat's eye variety is usually cut into a cabochon. The largest faceted chrysoberyl crystal in the world is from Russia, weighing 66 carats. Chrysoberyl has been mined for thousands of years in Asia where the stone is believed to ward off the evil eye.
Bibliography and Reference on Chrysoberyl
1. Paul R. Shaffer, Rocks, Gems and Minerals  . Martin's Press
2. Renee Newman, Gemstone Buying Guide . International Jewelry Publications; 2nd edition
3. Antoinette L . Matlins, Antonio C. Bonanno, Gem Identification Made Easy . Gemstone Press
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