[Crw-talk] Chatoyancy

[wisawdust at charter.net]

I was asked at the meeting (by our president) to spell and define 
chatoyancy.

ChatoyancyFrom Wikipedia, the free encyclopediaJump to: navigation, 
search Cat's eye effect redirects here. For other senses, see Cat's eye.

Tiger eye
Tiger's eyeIn gemology, chatoyancy ( /ʃəˈtɔɪ.ənsi/ shə-TOY-ən-see), or 
chatoyance or cat's eye effect,[1] is an optical reflectance effect seen 
in certain gemstones. Coined from the French "œil 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.[2][3] Marder and Mitchell 
demonstrated that the precipitates that cause chatoyance in chrysoberyl 
are rutile, titanium dioxide. There was no evidence of tubes or fibers 
in the samples examined. The rutile precipitates were all aligned 
perpendicularly with respect to cat's eye effect. It is reasoned that 
the lattice parameter of the rutile matches only one of the three 
orthorhombic crystal axes of the chrysoberyl, resulting in preferred 
alignment along that direction. 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.

The term Cat's Eye, when used by itself as the name of a gemstone, can 
only be used to refer to a Cat's Eye Chrysoberyl. Any other stone 
exhibiting this phenomenon must have the stone's name after the Cat's 
Eye identifier, e.g., Cat's Eye Aquamarine.

Chatoyancy can also be used to refer to a similar effect in woodworking, 
where certain finishes will cause the wood grain to achieve a striking 
three-dimensional appearance; this can also be called pop-the-grain, 
wood iridescence, moire, vibrancy, shimmer or glow.[4] This effect is 
often highly sought after, and is sometimes referred to as "wet look", 
since wetting wood with water often displays the chatoyancy, albeit only 
until the wood dries. Oil finishes and shellac can bring out the effect 
strongly.

Duane
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