Precious gems have long inspired awe and wonder — and it’s no surprise why. Deeply saturated hues, shifting colours, and gleaming luminescence make gemstones seem almost otherworldly. And yet, they couldn’t be more of this world, mined from the depths of the earth. One species of mineral, chrysoberyl, is particularly sought after not only for its beauty, but also due to its rarity.
Chrysoberyl is a lustrous collector gemstone that follows only diamond and corundum in its hardness, making it a very durable candidate for jewellery as it can easily stand up to everyday wear. And yet, chrysoberyl is not often found in jewellery due to its scarcity. Discovering a chrysoberyl of more than one or two carats is considered very rare, and larger stones (and those with few inclusions) are rarer still.
Our Fine Gems, Lapidary Works of Art and Natural History auction taking place on 6 December in Los Angeles offers a variety of chrysoberyl, including alexandrite. Ahead of the sale our Director of Natural History, Claudia Florian, shares 5 things you need to know about this exceptional gemstone.
1.Alexandrite
Like the Wizard of Oz’s “Horse of a Different Colour,” this variety of chrysoberyl is known for its extraordinary ability to change colour. When exposed to sunlight, alexandrite appears green, but when under incandescent light, it appears red — an “emerald” by day and a “ruby” by night! The term “alexandrite effect” is now used to describe the colour-shifting properties of other gemstones as well, like the colour-shift garnet and sapphire.
Alexandrite, with its durability, transparency, and colour shifting hue, is one of the most coveted gems in the world. And yet, it’s not often used in modern jewellery. Historically mined in Russia’s Ural Mountains in the 1800s, alexandrite can sometimes be found in antique Russian jewelry, including Faberge. Tiffany also produced some alexandrite rings and platinum ensembles at the turn of the 20th century, as the firm’s master gemologist, George Frederick Kunz (1856-1932), was particularly fascinated by the gem. Additionally, smaller alexandrites were occasionally used in Victorian jewellery from England.
2.Yellow Chrysoberyl
Commonly known as simply chrysoberyl, this gem is considered a collector’s stone due to its scarcity. It can be transparent or translucent and has either a yellowish-green hue, a brownish-yellow hue, or is colourless. The finest yellow chrysoberyls, however, are transparent with a vivid yellow hue and no hints of brown. A yellow chrysoberyl larger than two carats is considered rare. Chrysoberyl was popular during the Edwardian and Victorian eras, but was often inaccurately named chrysolite.
3.Red Chrysoberyl, A.KA. Red Alexandrite
Only discovered in the mid-1970s, red chrysoberyl is exclusively found in Brazil’s Malacacheta region, making it very unlikely to come across. The gem is ruby red in color, which gemmologists have attributed to the extra trace element chromium present in the stone. Most often with no color change, these stones can sometimes exhibit the “cymophane effect,” which exhibits a floating light reflection that moves as the polished gem is rotated.
4.Phenomenal Gemstones and the Chatoyancy or “Cat’s Eye” Effect
Though one might use the term “phenomenal” to describe any number of beautiful stones, the gemological term “phenomenal” refers only to gems that exhibit an optical phenomenon such as the cat’s eye effect (chatoyancy), stars (asterism), labradorescence (as in labradorite), or adularesence (as in moonstones).
The cat’s eye effect is rare in chrysoberyl and alexandrite, created by the scattering of light that is reflected back to the viewer as a thin line. This line is caused by needle-like inclusions and platelets that run parallel to the c-axis of the stone. The resulting effect is reminiscent of, you guessed it, a cat’s eye with its vertical iris. The color of milk and honey in its most idealized form, the cat’s eye chrysoberyl is most sought-after when its lustrous line is well-centered and distinct at the apex of the dome.
Keep an eye out for cat’s eye chrysoberyl and alexandrite mined from the Barro Preto deposit in Brazil or certain deposits in Sri Lanka, which are known to produce the finest examples. The brighter the color, the more expensive the gem.
5.Countries of Origin
The state of Minas Gerais in Brazil is known for harbouring some of the most valuable stones in the world and has produced some of the best examples of chrysoberyl and alexandrite in recent decades. The Soturno River, a major river in Minas Gerais, was relatively prolific in producing alexandrite occurrences from 1975 through 1987 during a small rush of mining. Since then, only a few carats a year of gem-quality material has been produced.
Brazil isn’t the only place where chrysoberyl can be found, however. The finest alexandrites were originally found in the Ural Mountains, which produced large cut stones up to 30 carats. Sri Lanka has produced up to 65 carats, often with unique colors. Other known sources of desirable chrysoberyl include Myanmar, Tanzania, Madagascar, Orissa in India, and Zimbabwe.
