Semi-Precious Gemstones | Chrysoberyl

Chrysoberyl Gemstones

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 is a very hard material, with a hardness of 8.5 on the Mohs scale. Chrysoberyl crystallizes in the orthorohombic crystal system, forming in slender prisms and usually has a "tabular" crystal habit. Crystal twinning is common. Chrysoberyl has a refractive index of 1.745. Chrysoberyl has distinct cleavage and a vitreous surface luster.

Cymophane Cat's Eye Chrysoberyl

Chatoyant 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.

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.

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.

Chemical composition: BeAl₂O₄

Referance Credits & Suggestions for Further Study on Gemstones

Judith Crowe, The Jeweler's Directory of Gemstones . DK Publishing

Walter Schumann, Gemstones of the World . NAG Press; 2Rev Ed edition

Richard W. Wise, Secrets of the Gem Trade: Connoisseur's Guide to Precious Gemstones . Brunswick House

Renee Newman, Gemstone Buying Guide . International Jewelry Publications; 2nd edition

Smithsonian, Rock and Gem. DK Publishing

Antoinette L . Matlins, Antonio C. Bonanno, Gem Identification Made Easy . Gemstone Press; 3rd edition

Paul R. Shaffer, Herbert S. Zim, Raymond Perlman, Rocks, Gems and Minerals . Martin's Press