Cat's eye gems of such minerals as apatite and diopside 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. Chrysoberyls that show a color change are known as alexandrites. All varieties of this gem are prized jewelry stones.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Orthorhombic. Crystals tabular or prismatic, sixling-twins common; also massive and as waterworn pebbles.|
|Colors||Yellowish green, yellow, gray, brown, blue-green, deep green, red, violet. Rarely colorless. Cat's eye is usually dark yellowish brown to pale yellow, honey yellow, greenish.|
|Specific Gravity||3.68-3.80; colorless 3.70; gems usually higher. Australia: 3.72-3.74.|
|Cleavage||Distinct 1 direction, seldom observed, varies to poor.|
|Luminescence||Usually none, pale green chrysoberyl from Connecticut noted yellow-green in SW.|
|Spectral||Yellowish and brown gems have strong band at 4440 due to Fe, especially Sri Lankan gems. Also may be bands visible at 5040 and 4860.|
|Transparency||Transparent to opaque|
|Phenomena||Chatoyancy (“cat's eye")|
|Formula||BeAl2O4 + Fe, Ti|
|Pleochroism||Distinct, in shades of yellow and brown.|
|Optics||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.|
|Etymology||From the Greek chrysos for “golden” and beryllos, a sea-green precious stone, in reference to the typical yellowish-green color of this mineral.|
|Occurrence||Occurs in pegmatites, gneiss, mica schist, dolomitic marbles; also found as stream pebbles and detrital grains.|
|Inclusions||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.
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. This is due to the fine silk inclusions that create the effect. A microscope is needed to resolve these fibers. 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.
The alexandrite variety of chrysoberyl is well known today as a scarce and very expensive gem.
In the 19th century, yellow-green chrysoberyl was commonly known as chrysolite, a term also used to refer to peridot. This name is no longer used. Peridot and chrysoberyl are 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).
All varieties of chrysoberyls have been synthesized. Non-chatoyant chrysoberyl stones have been flux grown since the late 19th century. They have also been created with melt processes as well as hydrothermally. Cat’s eyes have been synthesized since the 1970s and have been available commercially since the 1980s. The synthetic chatoyant stones can be distinguished from their natural counterparts by: 1. their undulating needle inclusions (natural chrysoberyls have parallel needle inclusions), 2. a lack of other typical inclusions, and 3. a weak yellow fluorescence in shortwave ultraviolet light.
See the alexandrite gem listing for more information on its synthesis.
Consult a professional gemological laboratory to distinguish synthetic from natural chrysoberyls.
See the gem listing for alexandrite for more information on that chrysoberyl variety.
- Russia: alexandrite of finest quality in mica schist, near Sverdlovsk.
- Australia (Anakie, Queensland): yellow-green chrysoberyl.
- Brazil (especially Jacuda, Bahia): fine facetable material; also cat’s eyes, alexandrite.
- India: cat’s eyes with sillimanite fibers, from Kerala.
- Myanmar: some alexandrite; rarely colorless facetable chrysoberyl.
- Sri Lanka: all types, some of the world’s finest cat’s eyes, also alexandrite; faceting material all colors, rarely colorless.
- Zimbabwe: fine alexandrite, intense color change.
- USA: Colorado, Connecticut, Maine, New Hampshire. New York, South Dakota.
- Finland; Japan; Madagascar; Zaire.
Facetable chrysoberyl is known up to several hundred carats. Cat’s eyes of similar size have also been found. Star chrysoberyls (displaying asterism) are known but very rare. Faceted gems over 40-50 carats are very rare.
The world’s largest cut cat’s eye is “The Eye of The Lion,” a 465-ct oval cabochon from Sri Lanka. This dark, greenish yellow gem was cut from a piece of rough weighing over 700 carats.
The world’s largest faceted chrysoberyl is a 245-ct flawless oval, slightly yellowish green, 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, D.C): 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).
- Iranian Crown Jewels: 147.7 (Sri Lanka, chartreuse); 25 (gray-green cat’s eye).
- 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. (Care should be taken when faceting the stone, since it’s sensitive to knocks and extreme heat). No special care is required for these gems. 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 information.