This is the name given to the yellow, yellow-green or graygreen variety of chrysoberyl, which displays the phenomenon of chatoyancy because of the inclusion of numerous fine, parallel crystal needles.
Appearance The color is greenish yellow or yellowish, sometimes with a rather cold, almost grayish tone. Some fine stones are a honey brown. In the proper light, the near side will appear yellowish white while the brown of the far side will be intensified, creating a milk-and-honey effect. Cat’s-eye is always cut en cabochon, round or oval, to emphasize the cat’s eye effect, and can be fairly transparent. Due to its hardness, it takes and maintains good luster, and the more pronounced and pleasing the cat's-eye effect, the greater is its value.
Distinctive features The most common cat’s-eye stones are the quartzes, which, however, usually have a rather different color from chrysoberyl and are less transparent with brighter, but more superficial, chatoyancy. If there is any doubt, they can immediately be distinguished by their different density, because refractive indices are always hard to establish for curved stones.
Occurrence Cymophanes are mainly found in Sri Lanka and Brazil, although they are not common.
Value Cat's-eye is highly prized by collectors and connoisseurs. its value is accordingly quite high. Very fine examples are less valuable than the principal gemstones, including alexandrite, but more so, for example, than a fine topaz or spinel. Due to its value and hardness, it is also known as “noble cat's-eye."
Simulants and synthetics Various natural stones have been used as substitutes, including fluorite, which, however, is much softer, and kornerupine, a gem still rarer than cymophane, with lower hardness and density. Quartz has also been used, although its color rarely resembles that of cymophane and its density is also much lower. To our knowledge, no attempts have been made to produce this gem synthetically.