Asterism is a type of chatoyancy in which the viewer sees the intersection of multiple cat’s-eyes, or a “star,” rather than a single cat’s-eye. Tightly packed, parallel inclusions that are oriented in two different directions will cause a star with four rays. If there are three sets of inclusions, the viewer will see a star…

If you like cat’s-eye gems and want to shop for them, they are very easy to find on websites and in stores that specialize in loose gems. The customers who shop at these stores are usually jewelry designers and gemstone collectors. Cat’s-eye gems are rarely seen in the mass-production jewelry typically sold in department stores…

Rare chatoyant specimens will have a coarse silk with just the right spacing to serve as a diffraction grating. These specimens will produce not only a cat’s-eye, but also a display of spectral colors caused by light passing through the coarse silk and being diffracted into the colors of the spectrum. More familiar examples of…

The best cat’s-eye gems have an eye that meets the following criteria:  it is clearly visible it symmetrically bisects the cabochon it contrasts sharply with the stone’s bodycolor it moves smoothly as the stone is turned If a stone features all of the above criteria and has an exceptional bodycolor, then you have a fantastic cat’s-eye gem. The…

Anyone who cuts cabochons with the intent of producing a cat’s-eye stone must first find a material with a silk of inclusions that is capable of producing an eye. Then the cutter must examine the rough and orient the stone so that the silk will be parallel to the bottom of the stone within the…

Some gems with a highly developed chatoyance can appear to be made of two different materials when illuminated from the proper direction with respect to the observer’s eye. In these stones, the cat’s-eye will appear to divide the stone into a zone of light-colored material on one side of the eye and dark-colored material on…

Many types of gems exhibit chatoyance; however, it is not present in every specimen of those gems and is usually only seen in a minority of specimens. Gems with well-known chatoyance include the following: chrysoberyl, tiger’s-eye, actinolite, apatite, beryl (aquamarine, heliodor, emerald), beryllonite, cerussite, danburite, diaspore, diopside, enstatite, garnet, iolite, kyanite, moonstone, opal, peridot, pezzottaite, prehnite, quartz, rutile, sillimanite, scapolite, spinel, topaz, tourmaline, and zircon.

A good analogy for the chatoyance effect is how light reflects to form a line across the surface of a spool of silk thread. Viewing and moving a spool of silk thread under a beam of incident light can be a useful way to develop an understanding of how parallel inclusions produce an “eye” within…

The name “chatoyance” originates from the French word “chatoyer,” which means “to shine like a cat’s eye.” The analogy also matches the way a cat’s pupils will narrow to a thin slit under bright light. Cat’s Eye with a Slit Pupil: This cat’s eyes have responded to bright light by closing their pupils to a narrow…

Chatoyance is an optical phenomenon in which a band of reflected light, known as a “cat’s-eye,” moves just beneath the surface of a cabochon-cut gemstone. Chrysoberyl and tiger’s-eye are two of the best-known gem materials that exhibit this phenomenon. Excellent specimens of chrysoberyl exhibit the finest chatoyance, and tiger’s-eye is the chatoyant gem most widely used in jewelry. Chatoyance occurs…