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Smithsonian National Museum of Natural History

Cat's Eyes

Photograph of a group of chatoyant stones, including elbaites, scapolites, and beryls, from the National Gem Collection.
Photo by Chip Clark. Click to zoom.
SpecimenCatalog NumberLocalityWeight
ScapoliteNMNH G2161-00Myanmar [Burma]3.29 ct
ChrysoberylNMNH G3924-00Sri Lanka171.5 ct
ElbaiteNMNH G5700-00Minas Gerais, Brazil65.5 ct
BerylNMNH G3248-00Madagascar43.51 ct
ElbaiteNMNH G3119-00Minas Gerais, Brazil53.2 ct
ScapoliteNMNH G3301-00Myanmar [Burma]29.9 ct
Elbaite (var. rubellite)NMNH G3786-00California, United States17.5 ct

Gems exhibiting a single bright band are called cat’s eyes. This optical phenomenon, called chatoyancy, is caused by light reflecting off of parallel bundles of tiny hollow tubes or fibrous crystals of another mineral inside the gemstone. When a stone is cut into a cabochon (domed top, flat bottom) the reflected light is focused into bright bands on the surface that are perpendicular to each set of fibers or hollow tubes.Many minerals can sometimes be cut as cat’s eye gems. Clockwise from top: 171.6ct cat’s eye chrysoberyl from Sri Lanka is one of the largest of its kind; a green elbaite gem (53.2ct) from Brazil; a pink elbaite gem (17.5ct) from California; a spectacular teal-colored elbaite gem (65.5ct) from Brazil that forms its cat’s eye as light reflects off of parallel grooves, or striations, on the back side of the stone that were on the original crystal surface: two scapolite gems from Burma, one a white stone (29.9ct) and the other purple (3.3ct); and a stunning golden beryl (43.5ct) from Madagascar.



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