Jewelry Lovers

Seldom properly valued by laymen, but an inexhaustible source of wonderful delight to collectors, are the chrysoberyls. Little known, jealously hoarded by the earth and only yielded up in parsimonious numbers, they are assured of a prominent place among the gemstones. Their great rarity, combined with their three varieties, completely different from one another, has rendered them prized objects of desire. Alexandrite and cat’s-eye, two varieties as precious as they are strangely attractive, are the basis of the chrysoberyls’ fame.

The simple, transparent chrysoberyl, whose name, derived from the Greek chrysos = gold, indicates that it contains beryllium, but actually consists of equal parts of beryllia and alumina and is thus a beryllium aluminate. This combination crystallizes in well-formed prisms. which evince an irresistible tendency to grow in that form as trillings, which result in a star-shaped figure or crystal with six-sided circumference. Gay, and even a little frivolous, they sparkle in shades of finch yellow to lime green via deep chartreuse and olive green to warm, smoky, golden tobacco tones. In all these alluring colors we have once again an allochromatic or extraneous coloring agent, for the combination of the two molecules of beryllium and aluminium oxides is by itself colorless. As color-producing metals, iron (up to 6 percent) and chromium (only o.6 percent ) have been proved. Titanium is found occasionally in mere traces. Thanks to great hardness (8.5) chrysoberyl takes a good polish, resulting in a strong surface luster which, jointly with high refractive index (1.75), produces a very lively brilliance. The likewise high specific gravity (3.71) favors its concentration in river debris, i.e., in secondary deposits. All these properties place chrysoberyl immediately next to corundum, with whose similarly colored specimens it can easily be confused.

The chatoyant variety of chrysoberyl—the silken-sheened cat’s-eye–is of an unusual nature, for it is characterized by a very striking and at the same time singularly beautiful play of light, which, allied with the rarity of its occurrence, is the reason for its popularity with collectors. Over the surface hovers a silvery band of light, whose apparent detachment from the body of the stone seems mysterious and magical. At the slightest turn of the stone the line of light leaps into surging movement; leaving its static position, flitting swiftly like a lissom cat, it glides—as if divorced from reality—over the domed surface. This wondrous phenomenon is caused by reflection of the incident light from hair-fine parallel fibers in the interior of the stone. The ribbon of reflected light always runs at right angles to the alignment direction of the embedded fibers. Cat’s-eyes are normally cut en cabochon because the bright band of light is best evoked in this way. By means of the convex external shape it is narrowed to a sharp track of light, comparable to the slit-shaped pupils of cats‘ eyes. The narrower and more precise the trace of the line of light, the greater the value. Occasionally other kinds of gemstones show a similar chatoyancy. But of all these varieties, likewise named cat’s-eyes, chrysoberyl is not only the noblest but also the most valuable. Its personal name cymophane (derived from the Greek kyma = wave, and phanein = to appear) differentiates it from its less distinguished cousins. It is strange that the cymophane, despite its ghostly appearance, has never given rise to any myths, for surprisingly no superstitious emotion has been attached to it.

A gemstone so truly unusual and mysterious as alexandrite—the third of the chrysoberyl brothers—which, though unpretentious, appeal’ to the predilection of connoisseurs, well deserves a place in the limelight. Here it may display, with most marvellous magic, its salient property of changing its color chameleonlike between daylight and artificial light. In fact, alexandrite is not only one of the most costly gemstones in the world, but also one of the most remarkable; for daylight discloses its gentle moss green, with a vaguely bluish suffusion, which changes to raspberry red or amethyst purple in or under artificial lighting. Its color is a characteristic chromium pigmentation; however, the cause of the phenomenal day-and-night magic does not lie in the chromium’s changing by different light, but results from the composition of the light. Daylight contains mainly blue rays, artificial light is rich in red.

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