The mineral chrysoberyl is found in transparent yellow to greenish yellow color, but only two varieties are widely known as gemstones: cat’s eye and alexandrite.
Alexandrite is the extremely rare variety of the mineral chrysoberyl that actually changes color from green, in daylight, to red, in incandescent light.
It was discovered in 1830 in Czarist Russia. Since the old Russian imperial colors are red and green it was named after Czar Alexander II on the occasion of his birthday.
Alexandrite can be found in jewels of this period. Master gemologist George Kunz of Tiffany was a fan of alexandrite and the company produced rings featuring fine alexandrite in the late nineteenth and early twentieth century, including some set in platinum in the twenties. Victorian jewelry from England also features sets of small alexandrites.
Alexandrite alternates with pearl and moonstone as the birthstone for the month of June.