cat’s-eye

Table of Contents

Introduction References & Edit History Related Topics

Images

cat’s-eye

gemstone

Written and fact-checked by The Editors of Encyclopaedia Britannica

Article History

Related Topics:: corundum; tigereye; crocidolite; cymophane; quartz cat’s-eye

See all related content

cat’s-eye, any of several gemstones that, when cut en cabochon (in convex form, highly polished), display a luminous band reminiscent of the eye of a cat; this particular quality is termed chatoyancy. Precious cat’s-eye, the rarest and most highly prized, is a greenish chatoyant variety of chrysoberyl called cymophane; the chatoyant effect is due to minute parallel cavities. Quartz cat’s-eye, the commonest, owes its chatoyancy and grayish green or greenish colour to parallel fibres of asbestos in the quartz. The two may be distinguished by their specific gravities; chrysoberyl is much denser. Crocidolite cat’s-eye (African cat’s-eye), more commonly known as tigereye (or tiger’s-eye), is quartz that contains oriented fibres of crocidolite that have been replaced by silica. Corundum cat’s-eye is an imperfect star sapphire or ruby in which the star is reduced to a luminous zone.

The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Michael Ray.

chrysoberyl

Table of Contents

Introduction References & Edit History Related Topics

Images

chrysoberyl

gemstone

Written and fact-checked by The Editors of Encyclopaedia Britannica

Article History

Related Topics:: gemstone; cymophane; chrysolite; alexandrite; multiple oxide

See all related content

chrysoberyl, gemstone, beryllium and aluminum oxide (BeAl₂O₄). A variety that is often cloudy, opalescent, and chatoyant is known as cymophane. Some cymophane, when cut en cabochon (in convex form), comprises the most highly prized cat’s-eye.

Alexandrite is a remarkable and valued variety that when viewed along the different crystallographic (optical) axes, changes from columbine red to orange yellow to emerald green. In addition, the stone changes from green in daylight to red in artificial light.

Chrysoberyl occurs in pegmatites, aplites, and mica schists; because of its durability, it often occurs as a detrital mineral in streams and gravel beds. Most chrysoberyl comes from Minas Gerais, Braz.; the variety cymophane is mostly from the gem gravels of Sri Lanka. For detailed physical properties, see oxide mineral (table).

Chrysoberyl is often mistaken for chrysolite, because of their similar colour, and has been called oriental chrysolite. The name chrysolite, however, should properly be restricted to a pale-green olivine, a silicate mineral that is softer and less dense than chrysoberyl.

This article was most recently revised and updated by Richard Pallardy.