Article by Sumeet Chordia, G.G.

Alexandrite is a variety of Chrysoberyl, a mineral that is chemically Beryllium Aluminate (BeAl2O4). The gemstone is most notable for its distinct color-change effect – a shift between a green-blue to a purple-red hue under daylight and incandescent light, respectively. The gem was serendipitously discovered when miners extracted emeralds from sites within Russia's Ural Mountain Range between 1829 and 1833. From excavating hundreds of emerald specimens, they recovered only one of these types of color-changing mineral.

Upon its discovery, authorities controlling the mine sent 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 gemstone mesmerized miners and geologists for its color-change phenomena, it also proved highly durable and resistant – the gem 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.