Chrysoberyl is a hard, tough, and durable gem. Although it lacks fire, specimens are very valuable. Most chrysoberyl gems are yellow, and some are brown or green. A rare, costly variety, known as alexandrite, exhibits different colors in natural and artificial light. If viewed in sunlight, its color is dark yellow-green to greenish-blue. If viewed in artificial light, its color is strawberry-red. Alexandrite was discovered on the birthday of the Russian Czar Alexander II, and was named in his honor.

Another expensive form of chrysoberyl is the unusual cat's eye variety. When polished as cabochons, these stones exhibit a narrow band of concentrated light along the width of the gem. This effect, known as cat's eye effect, is caused by inclusions of fine, slender parallel fibers in the gem. The cat's eye variety may be called "cat's eye", cat's eye, "precious cat's eye", "oriental cat's eye", "catseye", or "chrysoberyl cat's eye". Many other gems also exhibit a cat's eye effect, but only chrysoberyl's cat's eye enjoys the privilege of having the name "cat's eye". (All other gems that exhibit a cat's eye effect must have the gem name preceding, such as "quartz cat's eye", whereas chrysoberyl's cat's eye is known simply as "cat's eye".)

Facts about Cat's Eye

Mineral information:  Chrysoberyl

Chemical composition: BeAl₂O₄

Color	Yellow, orange-yellow, yellow-green, green, bluish-green, and brown. The variety alexandrite becomes reddish in artificial light.
Hardness	8½
SG	3.5 - 3.8
RI	1.744 - 1.755
DR	.009
Luster	Vitreous