Yes, we do think these gems are remarkable, but the designation “phenomenal” actually refers to gems that display certain optical phenomena. Cat’s eye and star gemstones fall into this category, and it’s easy to see why. If you’ve ever seen a star sapphire or cat’s eye chrysoberyl in person, you’ve likely been hypnotized by a reflected ray of light that seemed to dance across the stone, moving as if the light were trapped in the stone itself. What’s the science behind the magic? Read on to learn all about cat’s eye and star gemstones.
Chatoyancy is the technical term for the thin bar of reflected light on certain gemstones, which we commonly refer to as cat’s eye. Fittingly, the word chatoyancy derives from the French phrase for “eye of cat”, or “oeil de chat”. The cat’s eye effect occurs when fibrous or needle-like inclusions form in a parallel direction. The gemstone usually needs to be cut en cabochon (a flat back with a domed top) for the effect to be seen to its best advantage. When the gem is turned back and forth, the light reflects along the parallel “lines” and displays a thin bar of light that appears to move across the stone.
One of the fascinating things about the cat’s eye and star effects is that they are found in a wide variety of gemstones. Cat’s eye effects can be found in stones such as chrysoberyl, spectrolite, quartz, tourmaline, moonstone, kornerupine, and apatite, and more rarely, in emerald, iolite, aquamarine, andalusite, scapolite, and tanzanite. Cat’s eye chrysoberyl is the most popular variety for use in fine jewelry, and is a chartreuse shade of green. If you come across a gemstone labeled “cat’s eye” with no other qualifier, it is likely a chrysoberyl. Another popular variety that you’ve likely heard of is tiger’s eye, a brown quartz variety with rich golden hues. Tiger’s eye generally has a striped effect, hence its name.
Asterism is the technical term for when light is reflected in a star shape on a gemstone. This star may have four, six, or more rarely, twelve rays. Generally, the more rays the star has, the more valuable the stone. Asterism occurs when rutile (a kind of mineral) needles are included in the gemstone in multiple parallel directions. This causes the reflected beams of light to crisscross in a star shape. Like chatoyant gems, the gemstone needs to be cut en cabochon for the star to be clearly visible. Gemstones that can have asterism include sapphire, ruby, garnet, moonstone, sunstone, rose quartz, spinel, citrine, diopside, chrysoberyl, and emerald.
This stunning star sapphire is one of our favorites, set into an elaborate cocktail ring worthy of its beauty!
In both cat’s eye and star gemstones, a higher value is placed on effects with a greater clarity or precision. When you shine a beam of light on to the stone, such as from a pen light, the chatoyancy or asterism should be sharp, rather than fuzzy and hard to see. Along with the number of rays, star gemstones are also valued on how closely their body color is to their non-star counterparts. Rutile inclusions dilute the color of the stone, so star gemstones that have retained their natural color while also exhibiting a clear asterism are highly desirable.
We highly recommend you see these remarkable gems in person to fully appreciate their unique qualities! As beautiful as they are in photographs, there is nothing like seeing them in person, where you can move them around and watch the light dance across their surface. If you are in the New England area, stop by any of our store locations to view the different antique and vintage cat's eye and star gemstone jewelry pieces we carry. We also have an excellent selection online for you to peruse!