Chatoyancy

Chatoyancy in the gemstone chrysoberyl is induced by the presence of the mineral rutile, a mineral primarily composed of titanium dioxide. These rutile precipitates align perpendicularly, contributing to the cat's eye effect. This alignment is attributed to the rutile's lattice parameter, which matches only one of the three orthorhombic crystal axes of chrysoberyl, leading to its preferred orientation in that direction. Optimal presentation of effect yellow-green quartz showing the cat's-eye effect. To bring out the chatoyancy effect, gemstones are typically fashioned into a cabochon cut, characterized by a rounded, flat base rather than facets, with the fibrous structures aligned parallel to the base. High-quality specimens display a single, sharply defined band of light that moves across the stone when rotated, while lower-quality stones may show a banded effect similar to cat's-eye quartz. Faceted stones do not showcase the effect well. Varieties of chatoyant materials Gem species known for this phenomenon include quartz, chrysoberyl, beryl (especially aquamarine varieties), charoite, tourmaline, labradorite, selenite, feldspar, apatite, moonstone, thomsonite and scapolite amongst others. Chatoyancy is not limited to gemstones but can also be found in wood and carbon fiber. Synthetically made gemstones with optical fibers can also have chatoyancy. These gemstones are available in a variety of vibrant colors. Cat's eye terminology When the term "cat's eye" is used to describe a gemstone by itself, it typically refers to cat's eye chrysoberyl. It can also be used as an adjective to indicate the chatoyance phenomenon in another stone, for example, cat's eye aquamarine. ==In woodworking==

Chatoyancy in wood occurs in various species – particularly hardwoods and the various types of Nanmu woods of China and South East Asia, particularly where stresses from the weight of the growing tree result in denser patches, or where stresses cause burl or ''bird's eye''. This 'figure', which has a striking three-dimensional appearance, is highly prized by woodworkers and their clients alike, and is featured regularly in furniture, musical instruments, and other decorative wood products. Figuring takes on a variety of forms and is referred to as flame, ribbon, tiger stripe, quilting, among other names. This effect is sometimes called wet look, since wetting wood with water often displays the chatoyancy, albeit only until the wood dries. Certain finishes cause the wood grain to become more pronounced. Oil finishes, epoxy, and shellac can strongly bring out the wet look effect. When the refractive index of the finish nearly matches that of the wood, light scattering no longer occurs at the wood surface, adding the appearance of depth to the wood's figure. Measurement No method to measure wood chatoyance is unanimously accepted by the scientific community. Some methods have been proposed, such as one named PZC after the names of its inventors, Pisani, Zanetta and Codoro. This measure has been used to measure typical values for a number of wood species; some results are reported below: ==See also==