Chrysoberyl

Chrysoberyl is a beryllium aluminum oxide and the third-hardest commonly faceted gemstone after diamond and corundum, registering 8.5 on the Mohs scale. Despite the name, it is not a beryl; the resemblance lies only in its frequent yellow-green color.

The species includes three desirable forms: ordinary transparent chrysoberyl in golden-yellow to green tones, cymophane (chatoyant cat's-eye chrysoberyl) showing a sharp band of light, and alexandrite, the famous color-change variety that shifts from green in daylight to red under incandescent light.

Its durability and brilliance, combined with relative obscurity compared to diamond or sapphire, make it a connoisseur's stone valued by collectors and antique-jewelry enthusiasts alike.

Chrysoberyl crystallizes in beryllium-rich, aluminum-rich environments, most commonly in granitic pegmatites and the metamorphic mica schists adjacent to them. It also forms in contact-metamorphic zones where beryllium-bearing fluids interact with aluminous host rocks.

Because the mineral is hard, dense, and chemically resistant, weathered crystals survive transport and concentrate in alluvial gem gravels. Most gem-quality material, including cat's-eye and alexandrite, is recovered from such secondary placer deposits.

Major sources include Brazil, Sri Lanka, Madagascar, Myanmar, Tanzania, and the Ural Mountains of Russia, the historic origin of fine alexandrite. India and Zimbabwe also produce notable material.

Look for a hard (8.5), transparent to translucent stone with high luster and yellow, greenish-yellow, or honey-brown color. Crystals are often tabular and commonly twinned into pseudohexagonal trillings with a characteristic V-shaped striation.

Cat's-eye chrysoberyl (cymophane) shows a single sharp, silvery-white chatoyant band over a honey body; the 'milk and honey' effect (one side light, one side dark) is diagnostic. Alexandrite shows true daylight-to-incandescent color change.

Look-alikes include cat's-eye quartz and beryl, but both are softer (7-8). Yellow chrysoberyl can resemble citrine, topaz, or yellow sapphire; its 8.5 hardness, lack of cleavage planes typical of topaz, and refractive index distinguish it. Streak is white.

Chrysoberyl is almost exclusively a gemstone. Its hardness and toughness make it excellent for rings and daily-wear jewelry. Faceted golden and green stones are set as durable alternatives to softer yellow gems.

Cat's-eye chrysoberyl is the benchmark for chatoyancy; the term 'cat's eye' used alone in gemology refers specifically to this stone. Fine examples command high prices, especially with sharp, centered eyes and warm honey color.

Alexandrite is among the most valuable colored gems, with strong color change commanding premiums rivaling fine ruby or emerald. Metaphysically, chrysoberyl is associated with discipline, prosperity, and protection, though these claims are not scientific.