Alexandrite (named after the Russian Tsar Alexander II 1818-1881) is one of the three main varieties of the mineral Chrysoberyl.
Alexandrite will exhibit emerald green, red and orange-yellow colours depending on viewing direction in partially polarised light. However, its most distinctive property is that it changes colour in artificial light compared to daylight. The colour change from red to green is due to strong absorption of light in a narrow yellow portion of the spectrum, while allowing large bands of blue-greener and red wavelengths to be transmitted. Typically, alexandrite has an emerald-green colour in daylight (relatively blue illumination of high colour temperature) but exhibits a raspberry-red colour in incandescent light (relatively yellow illumination). This is typical of the alexandrite found in the Ural Mountains of Russia.
According to a popular but controversial story, alexandrite was discovered by the Finish mineralogist Nils Gustaf Nordenskiöld (1972-1866) and named in honour of the future Tsar Alexander II of Russia. The very first crystals were discovered in April 1834 in the emerald mines near the Tokovaya River in the Urals. It was at first thought to be an emerald. Although alexandrite is a relatively young gemstone, it certainly has a noble history. Since it shows both red and green, the principal colours of old Imperial Russia, it inevitably became the national stone of tsarist Russia.
Top quality alexandrite is rare and rarely used in modern jewellery. In antique Russian jewellery you are more inclined to come across it. Master gemmologist George Frederick Kunz (1856-1932) was also fascinated by this gemstone and the jewellers firm produced some beautiful pieces at the end of the 19th and beginning of the 20th century. Smaller alexandrites were occasionally used in Victorian jewellery in England. Alexandrite up to 5 carats and larger were traditionally thought to be found only in the Ural Mountains, but have since been found in larger sizes in Brazil. Other deposits are located in India, Madagascar and Sri Lanka. Alexandrite in sizes over 3 carats are very rare.