The color of this exceptionally rare stone (certain specimens of which can be more valuable than a diamond) changes with the light. Russian alexandrite is bottle green in daylight but a purple-red in artificial light. It was first discovered on the slopes of the Ural Mountains in 1831 on the birthday of Czar Alexander II, whose name it bears. Its colors, red and green, are that of Holy Russia, and it is the Russian national gem. Beryllium aluminate (chromiferous chrysoberyl). Hardness: 8.5. Brazil, Zimbabwe, Sri Lanka.