CAT'S-EYE is a well established term in the trade in precious stones, and more than one mineral which exhibits chatoyancy—a
French word signifying a changeable, undulating lustre, like the eye
of a cat in the dark— is termed, and sold as " cat's-eye."
true cat's-eye is cymophane, a variety of chrysoberyl, a mineral
resembling beryl in containing the element glucinum (beryllium), but
otherwise distinct. Chrysoberyl is devoid of silica, which beryl
possesses, and is, theoretically, composed of glucina, 19.8 and
alumina, 80.2. Jewellers variously call chrysoberyl " cat's-eye," "
Oriental cat's-eye," or " Cey-lonese cat's-eye." Besides its principal
components, chrysoberyl frequently contains impurities such as iron
and chromium oxides. Chrysoberyl is very hard—8.5, being third in
Mohs's scale to the diamond, and when cut is susceptible of a high
polish. Heavier than the