In gemology, chatoyancy (or chatoyance) is an optical reflectance effect seen in certain gemstones. Coined from the French "oeil de chat", meaning "cat's eye", chatoyancy arises either from the fibrous structure of a material, as in tiger eye quartz, or from fibrous inclusions or cavities within the stone, as in cat's eye chrysoberyl. The effect can be likened to the sheen off a spool of silk: the luminous streak of reflected light is always perpendicular to the direction of the fibres. For a gemstone to show this effect best it must be cut en cabochon, with the fibers or fibrous structures parallel to the base of the finished stone. Faceted stones are less likely to show the effect well.
Gem species known for this phenomenon include the aforementioned quartz, chrysoberyl, beryl (especially var. aquamarine), tourmaline, apatite, moonstone and scapolite. Glass optical cable can also display chatoyancy if properly cut, and has become a popular decorative material in a variety of vivid colors.
SUBMITTED PHOTO from Left: Baylee Misner, Jace Heath, Jasmine Wheeler, Emma Watts Are Part of Future Rockhounds of America, a Geology Club for Pebble Pups 8 to 12 Years of Age. the Pocatello Chapter Is Supported Locally by the Southeastern Idaho Gem and Mineral Society.[bullet]This Past Year the SEIGMS Poky Rockstars Have Been Learning about Minerals That Have Special Properties or Effects. on April 6 the Rockstars Demonstrated Some of These Phenomena by Hosting an "Amazing Mineral Magic Show" at the Annual SEIGMS Gem and Mineral Show at the Fairgrounds. Youngsters Visiting the Kids' Booth Discovered Rocks That Float, Minerals You Write with, and Minerals That Display Special Effects Such as Magnetism, Double Refraction, Chatoyancy, Natural Fiber Optics, and Fluorescence. Our Young Magicians Provided Educational Handouts That Reveal the Secrets of Our Magical Minerals and Their Strange and Wonderful Forms
Apr 14, 2013; SUBMITTED PHOTOFrom left: Baylee Misner, Jace Heath, Jasmine Wheeler, Emma Watts are part of Future Rockhounds of America, a...