A five-carat, certified and natural, rectangular step-cut Brazilian Alexandrite (Chrysoberyl) with 90 - 100% color-change. © RAF Jewels
Alexandrite is a variety of Chrysoberyl, a mineral that is chemically Beryllium Aluminate (BeAl2O4). The gemstone is most notable for its distinct and mesmerizing color-change effect — a shift between a green-blue to a purple-red hue under daylight and incandescent light, respectively — and being one of the birthstones for June (along with Moonstone and Pearl). The gemstone was serendipitously discovered when miners were extracting emeralds within Russia's Ural Mountain Range between 1829 and 1833. From excavating hundreds of Russian emerald specimens, they recovered only one color-changing Russian Alexandrite.
Upon the discovery, authorities controlling the mine sent Alexandrite samples to the country's mineralogical department for further study and analysis. Mineralogists studied the gemstone carefully and published numerous accounts of its properties and unique phenomena. They confirmed it as a variety of cymophane, another name for Chrysoberyl. In 1834, the Russian Imperial Mineralogical Society recognized the gemstone's "first-rank" properties and changed its name to Alexandrite in honor of Tsarevich Alexander Nikolaevich (Tsar Alexander II) - the next Tsar of Russia.
While the color-changing gemstone fascinated miners and geologists, it also proved highly durable and resistant – it had no cleavage planes and registered 8.5 on the Mohs Hardness Scale.¹ For perspective, diamonds are 10, rubies and sapphires are 9, and emeralds are 7.5 - 8.
Remarkably, a recent analysis of Alexandrites by SSEF in Basel, Switzerland, uncovered the mystery behind its natural color-changing phenomena. Researchers at SSEF discovered that the color-change in Alexandrites occurs due to Chromium, a trace element, inside the mineral. When two distinct light sources — daylight and incandescent — carrying different spectrum emissions, illuminate the crystal its absorbs different color wavelengths and emits a different color. Notably, the absorption spectrum of Alexandrite was similar to those of emeralds and rubies.
Since the preliminary discovery of Alexandrites in Russia, other geographical regions across the world have become significant sources. These include Brazil, Sri Lanka (Ceylon), India, and East Africa.
¹ Schmetzer, Karl, Bosshart, George, Epelboym, Marina, Kiefert, Lore, & Malsy, Anna-Kathrin. (2020). Russian Alexandrites. Stuttgart: Schweizerbart.