Cat’s eye gems of many different mineral species are well known, but when the term “cat’s eye” is used alone it always refers to the rare gemstone chrysoberyl. However, not all chrysoberyls show this chatoyant effect. Transparent to translucent chrysoberyl without a cat’s eye can make a wonderful faceted stone. Chatoyant chrysoberyls are cut into cabochons to best display their spectacular eyes. Some chrysoberyls that show a color change are known as alexandrites. All varieties of this gem are prized jewelry stones.
a = 1.740-1.759; β= 1.747-1.764; γ = 1.745-1.770. Biaxial (+), may also be ( - ), 2V= 70°. Indices vary with Fe content. Colorless (Sri Lanka): a = 1.740; β = 1.745; γ = 1.750. Australia: a = 1.756-1.765; β= 1.761-1.772; γ = 1.768-1.777.
Biaxial +, Biaxial -
From the Greek chrysos for “golden” and beryllos, a sea-green precious stone, in reference to the typical yellowish-green color of this mineral.
Occurs in pegmatites, gneiss, mica schist, dolomitic marbles; also found as stream pebbles and detrital grains.
In cat's eye, there are short needles and tubes parallel to the long axis of the crystal. Liquid-filled cavities with 2-phase inclusions, stepped twin planes.
The transparent variety of chrysoberyl makes a handsome faceted gem. With indistinct cleavage and hardness of 8.5, it’s one of the toughest stones for jewelry purposes. In general, the bright yellow and yellow-green shades are the most desirable, but some of the browns are also striking. Properly cut gems are very brilliant, although they lack fire due to low dispersion. Chrysoberyls from Australia have unusually high refractive indices and could possibly be misidentified as yellow-brown sapphires.
Chatoyant or cat’s eye chrysoberyl is also known as cymophane. That name comes from a Greek word meaning “appearing like a wave,” alluding to the opalescent, hazy appearance of the surface of some crystals. However, the eye of a chatoyant chrysoberyl is the sharpest of any cat’s eye gemstone. Fine silk inclusions create this effect. Resolving these fibers requires a microscope.
The eye in a chrysoberyl cat’s eye often has a shimmering blue tone. The optimum color for these stones is a honey brown. When light obliquely strikes such a stone, it usually creates a shadow effect within the gem. The side away from the light is a rich brown, while the side facing the light is yellowish white. This so-called “milk and honey” look is characteristic of the finest cat’s eyes. This effect in stones over 20 carats can result in very high values.
In the 19th century, yellow-green chrysoberyl was commonly known as chrysolite, a term also used to refer to peridot. The name “chrysolite” has since fallen out of use. Gemologists now recognize peridot and chrysoberyl as distinct gem species. Despite their names, beryl and chrysoberyl are also distinct species (though they do both include in their chemical makeup the rare element beryllium).
Manufacturers have synthesized all varieties of chrysoberyls. Non-chatoyant chrysoberyl stones have been flux grown since the late 19th century. Laboratories have also used melt as well as hydrothermal creation processes.
Cat’s eyes have been synthesized since the 1970s and available commercially since the 1980s. Gemologists can distinguish these synthetic chatoyant stones from their natural counterparts by the following characteristics:
their undulating needle inclusions (natural chrysoberyls have parallel needle inclusions),
Facetable chrysoberyl is known up to several hundred carats, and cat’s eyes of similar size have also been found.
Faceted gems over 40-50 carats are very rare. The world’s largest cut cat’s eye is “The Eye of The Lion,” a dark, greenish yellow 465-ct oval cabochon, cut from a piece of Sri Lankan rough weighing over 700 carats.
The world’s largest faceted chrysoberyl is a flawless 245-ct, slightly yellowish green oval-cut gem from Sri Lanka.
British Museum of Natural History (London): 29.4 (Sri Lanka, yellow-green); 45 (The Hope chrysoberyl, flawless oval cat’s eye).
Royal Ontario Museum (Toronto, Ontario, Canada): 42.72 (Sri Lanka, chartreuse green)
American Museum of Natural History (New York): 74.4 (emerald cut, yellowish green, may be world’s finest of this color).
Smithsonian Institution (Washington, DC): cat’s eyes: 171.5 (Sri Lanka, gray-green); 47.8 (Sri Lanka); 58.2 (The Maharani, Sri Lanka); faceted: 114.3 (Sri Lanka, yellow-green); 120.5 (Sri Lanka, green); 46.3 (Brazil, yellow-green); 31.7 (Sri Lanka, brown); 6.7 (Brazil, dark green star).
Private Collections: Cat’s eyes up to 300 carats are in private collections. Stones reported include a flawed 185-ct yellow Brazilian gem; a superb 120-ct yellow Brazilian gem in a Japanese collection; and a 79.30-ct brown Sri Lankan oval and a 66.98-ct flawless yellow Brazilian stone in a U.S. collection.
Chrysoberyl is a very durable stone suitable for any jewelry setting. However, care should be taken when faceting this material, since it’s sensitive to knocks and extreme heat. Otherwise, these gems require no special care. They can be cleaned mechanically, per the instructions of the machine to be used, or, of course, with warm, soapy water and a brush. Consult our gemstone jewelry cleaning guide for more recommendations.