A variety of chrysoberyl, alexandrite changes color from green during the day to crimson red at night. The color change is also made between yellow/pink during the day and red/pink during the night.
Alexandrite was discovered in 1830 in Russia 30km from Moscow and was given this name in honor of Prince Alexander II who at the time of discovery was of age and because the colors of the Russian empire were red and green...being so rare and obviously valuable , Alexandrite quickly became one of the most expensive semi-precious stones and its main landmark is precisely the way in which the stone changes color depending on the light to which it was exposed. The bigger the difference between the shades, the higher its price will be. Alexandrite is a rare gem, whose price can even exceed that of a diamond. Alexandrite is extremely rare and valuable. The more dramatic the transition from red to green, the more valuable the stone. Genuine alexandrite is one of the most expensive stones in the world.
Alexandrite is nicknamed by crystal admirers "emerald by day and ruby by night". What is absolutely remarkable about this crystal is its surprising ability to change its color: in natural light it is green or blue-green, in artificial light - red, purple-red or raspberry-red. This change in color is due to the content of iron and titanium (elements specific to crystals from the chrysoberyl category), but also to chromium impurities. It is precisely these chromium impurities that cause the color to change. An even rarer variety of Alexandrite, called Cymophan, exhibits strong shimmer and a "cat's eye" effect. Thus, it is not surprising that Alexandrite is considered one of the most expensive in the world, being rarer than ruby, sapphire, diamond and emerald.
Natural alexandrite – The high price of alexandrite is determined both by its rarity and by its extremely unusual color. The stone appears blue or blue-green in daylight, but turns pink to purple in candlelight or exposed to incandescent light. Natural alexandrite first appeared in Russia, where it was named after Tsar Alexander II in the early 1800s. Mines in Tanzania and Brazil then captured the market, after the resources in the Russian mines were exhausted due to massive exploitation. Natural alexandrite rarely costs less than 10,000 dollars per carat (0.2 grams), so 50,000 dollars per gram!