With color ranging from shades of yellow and brown through blue-green to olive, and with a hardness of 8½, chrysoberyl has most of the characteristics necessary for a fine gem. Rare stones of high-quality chrysoberyl demand fairly high prices, and they are sought eagerly by the connoisseur of gemstones. Chrysoberyl is beryllium aluminate, and thus is closely related to the gemstone spinel, which is magnesium aluminate. When pure, chrysoberyl is colorless and relatively uninteresting as a gemstone because of its lack of color dispersion and its moderate refractive index of 1.75. However, few pure samples are known, as chrysoberyl normally contains some iron or chromium in place of aluminum and some iron in place of beryllium. As a result of such impurities, the color of chrysoberyl my be yellowish, greenish, or brownish. Chrysoberyl and beryl are the only important gemstones containing the element beryllium. The minerals beryllonite, euclase, hambergite, and phenakite also contain this element, but they are rare and seldom are seen as cut gems. [Illustration: One of the finest chrysoberyl cat’s-eyes in existence is the 58-carat Maharani from Ceylon. (Actual size.)] The _alexandrite_ variety of chrysoberyl has two colors in delicate balance, and it changes from a columbine red to an emerald green when viewed under different light. When viewed in daylight, which is richer in green, the color balance shifts toward green, and that hue is seen by the observer. Under artificial light, normally richer in red, the color balance shifts toward red, and the stone seems to have changed to that color. This extremely rare stone, named after Czar Alexander II of Russia, is found only occasionally, in Russia and Ceylon. The Russian stones, found with emerald in mica schist, tend to be smaller than the Ceylon stones and have a color change going from emerald green to violet-red. The Ceylon stones, found as pebbles in gem gravels, have a color change going from a less-emerald green to a browner red. The 66-carat, record-size alexandrite in the National Collection shows the color change typical of Ceylon stones. A synthetic stone is commonly marketed as synthetic alexandrite, but this substitute not only is man-made but is actually synthetic corundum instead of synthetic chrysoberyl. [Illustration: In addition to its fine cat’s-eyes and its color-changing alexandrite varieties, chrysoberyl occurs in handsome stones that vary in depth of color. Shown here with an uncut twinned crystal of gem quality from Brazil are a 46-carat stone from Brazil (left) and a 121-carat stone from Ceylon. The uncut crystal is a gift of Bernard T. Rocca, Sr. (Two-thirds actual size.)] _Cat’s-eye_ chrysoberyl contains myriads of tiny fiberlike channels arranged in parallel position. When the stone is cut as a cabochon, a band of light is reflected from the curved top of the stone, producing an effect that resembles the slit pupil of a cat’s eye.