Valued for thousands of years, chrysoberyl is a surprising gem that you'll love as much for what it does as for how it looks. Chrysoberyl is an action gem, changing and moving in response to light. In the gem world, special effects are known as phenomena. The gem varieties of chrysoberyl respond to light in surprising ways.

For example, one variety of chrysoberyl is color-changing alexandrite, which is red in lamplight and green in daylight. In the entire gem kingdom, no other gem has a color change so dramatic.

But the best-known special effect of chrysoberyl is an eye, which is displayed when certain specimens of this gem are cut in a dome shape. Cat's-eye chrysoberyl has a pupil-like band of light that sweeps across its dome. The “eye” is caused by fibrous inclusions that reflect the light in a sharply defined pattern. The effect is uncanny and quite cat-like. Although other gem varieties can display this effect, none is as dramatic.

The eye will open and close when you hold the cat's-eye between two light sources and rotate it: it splits into two bands that move apart and back together as if the stone is winking at you.

Fine cat's-eye chrysoberyl often also shows the "milk and honey" effect. When a bright light source is directed at the side of the stone, one side of the eye will be milky white and the other remains gold. When the stone is rotated, the colors switch.

The color of cat's-eye chrysoberyl ranges from a honey-brown to an apple green with rich gold colors generally the most valued. The most important value factor is the strength and sharpness of the eye.

In Sri Lanka, where cat's-eye has been treasured for centuries, it was regarded as a powerful charm protecting against evil spirits. Chrysoberyl has long been considered a good-luck charm in many cultures.

Chrysoberyl can also be found in a faceted variety, which has a honey-gold to green color. It may remind you of yellow sapphire, topaz, tourmaline, or citrine. But next to the other attention-grabbing varieties, plain faceted chrysoberyl is often overlooked. As a result this gem is surprisingly affordable.

Chrysoberyl, no matter its variety, is very durable, with a Mohs hardness of 8.5. It is an excellent gem for everyday wear and perfect for men's rings. Cat's-eyes are especially popular in men's jewelry.