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In 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, woods, and carbon fibre. Coined from the French œil de chat, meaning 'cat's eye', chatoyancy arises either from the fibrous structure of a material, as in tiger's eye quartz, or from fibrous inclusions or cavities within the stone, as in cat's eye chrysoberyl.[2][3]


The precipitates that cause chatoyance in chrysoberyl are the mineral rutile, composed mostly of titanium dioxide. Examined samples have yielded no evidence of tubes or fibres.[citation needed] The rutile precipitates all align 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.

A cabochon yellow-green quartz showing the cat's-eye effect.

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 (rounded with a flat base rather than faceted), with the fibres or fibrous structures parallel to the base of the finished gem. The best finished specimens show a single sharply defined band of light that moves across the stone when it is rotated. Chatoyant stones of lesser quality display a banded effect as is typical with cat's-eye varieties of quartz. Faceted stones do not show the effect well.

Gem species known for this phenomenon include the aforementioned quartz, chrysoberyl, beryl (especially var. aquamarine), charoite, tourmaline, labradorite, selenite, feldspar, apatite, moonstone, thomsonite and scapolite amongst others. Glass optical cable can also display chatoyancy if properly cut, and has become a popular decorative material in a variety of vivid colors.[citation needed]

The term "cat's eye", when used by itself as the name of a gemstone, refers to a cat's eye chrysoberyl.[citation needed] It is also used as an adjective which indicates the chatoyance phenomenon in another stone, e.g., cat's eye aquamarine.

In woodworking[edit]

Chatoyancy in wood occurs in various species[4] – 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.[5]

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.


No method to measure wood chatoyance is unanimously accepted by the scientific community. Some methods have been proposed, such as one named PZC,[6] which was used to measure typical values for a number of wood species; some results are reported below:[7]

(common name)
PZC average
Afrormosia 14.2
Afzelia 14.1
Alder 15.0
Alder, Red 16.8
Anigre 14.4
Ash, American White 11.5
Ash, European 12.8
Ash, Olive 14.9
Beech, European 10.6
Birch 18.3
Black Locust 16.4
Bocote 11.5
Bog Oak 11.6
Bubinga 19.2
Cedar, European 7.6
Cedar, Spanish 21.3
Cerejeira 14.1
Cherry, Black 18.0
Cherry, Sweet 15.7
Chestnut, Sweet 14.4
Cypress, Mediterranean 9.3
Ebony, Macassar 11.3
Elm 14.5
Etimoe 22.1
Eucalyptus 13.9
Fir, Douglas 11.1
Fir, European Silver 10.0
Granadillo 14.3
Guarea 17.2
Ipe 11.7
Iroko 21.8
Jatoba 17.5
Khaya 23.0
Koa 26.4
Koto 12.5
Larch, European 10.9
Limba 16.1
Limba, Black 18.7
Lime, European 12.2
Louro Faia 17.4
Louro Preto 11.3
Mahogany, Honduras 21.4
Makore 21.0
Mansonia 18.0
Maple, European 14.2
Maple, Hard 16.1
Movingui 15.3
Mulberry 18.2
Oak, Red 12.2
Oak, Sessile 12.6
Obeche 11.1
Okoume 23.6
Olive 8.3
Osage Orange, Green 17.0
Ovangkol 20.0
Padouk 17.4
Pear 10.5
Pine, Swiss Stone 10.7
Pine, unspecified 13.2
Poplar 14.7
Poplar, Yellow 11.9
Purpleheart 13.7
Red Gum 12.6
Rosewood, Cocobolo 9.5
Rosewood, Indian 11.2
Rosewood, Kingwood 14.3
Rosewood, Madagascar 11.7
Rosewood, Santos 12.5
Sapele 20.7
Satinwood 13.9
Spruce, Fiemme 9.3
Sucupira 9.8
Teak 15.7
Tineo 14.7
Walnut, African 20.2
Walnut, Black 18.6
Walnut, European 17.5
Wenge 8.5
Yew 9.8
Zebrawood 19.1
Ziricote 7.0

See also[edit]

  • Asterism (gemology) – ornamental stones that exhibit a luminous star when cut en cabochon
  • Optical phenomena – Observable events that result from the interaction of light and matter


  1. ^ Reinersmann, Walter Schumann ; [translated by Elizabeth E.; Shea], Daniel (2008). Minerals of the world (2nd ed.). New York, NY.: Sterling Pub. Co. p. 19. ISBN 9781402753398.
  2. ^ Mukherjee, Swapna (2011). Applied mineralogy : applications in industry and environment. Dordrecht: Springer. ISBN 978-9400711617.
  3. ^ Hancock, Paul L.; Skinner, Brian J., eds. (2006). "gemstones". The Oxford companion to the earth (1st ed.). Oxford: Oxford Univ. Press. ISBN 9780198540397.
  4. ^ "Woodworking word of the day: chatoyance | Wood". WOOD Magazine. 2022-05-24. Archived from the original on 24 May 2022. Retrieved 3 August 2022.
  5. ^ "What is Chatoyance? – PZC Chatometry". 2022-01-12. Archived from the original on 12 January 2022. Retrieved 2022-05-24.
  6. ^ Pisani, Paolo; Zanetta, Laura; Codoro, Davide (2021-12-29). "Measuring wood chatoyance". Wood Material Science & Engineering: 1–12. doi:10.1080/17480272.2021.2018625. ISSN 1748-0272. S2CID 245572069.
  7. ^ "PZC Chatometry – A standard system to measure wood chatoyance" (in Italian). Retrieved 2022-01-03.
  • Webster, R., Jobbins, E. A. (Ed.). (1998). Gemmologist's compendium. St Edmundsbury Press Ltd, Bury St Edwards.
  • Mitchell, T. et al. Proceedings of the Electron Microscopy Society of America (EMSA), 1982.