 | Chrysoberyl is an aluminate of beryllium with the formula BeAl2O4. Despite the similarity of their names, chrysoberyl and beryl are two completely different gemstones.
Chrysoberyl is the third-hardest frequently encountered natural gemstone. The three main varieties are ordinary yellow-to-green chrysoberyl, cymophane (cat's eye), and alexandrite. |  |
 | Cymophane exhibits chatoyancy or opalescence that appears very much like an eye of a cat. When cut to cabochon, the mineral forms a silky band of light extending across
the surface of the stone. Microscopic tubelike cavities or needlelike inclusions of rutile are orientated parallel to the c-axis producing the chatoyant effect. | 
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