The name "Alexandrite" comes from the stones' ostensible discovery on April 23, 1830, the day that young Russian Czar Alexander Nicolajevitch II (reigned 1855 to 1881) had his "comming of age" birthday. Alexandrite was discovered along the banks of the Tokovaya River in the Ural Mountains of Russia. This ultra-rare gemstone discovered in the Tokovaya River's mica schists (igneous rock) and alluvial deposits has a unique ability to change color (pleochroism) due to pseudochromatic coloration caused by changes in ambient light.
Alexandrite (aka Tsarstone) is a variety of the mineral chrysoberyl which is an aluminate of beryllium. Chrysoberyl is usually transparent to translucent and sometimes chatoyant. The most widely used variety of chrysoberyl is an alexandrite. Because of alexandrite's unique ability to absorb certain elements of the color spectrum, it can look greenish-bluish-grey in daylight and reddish-purple (raspberry red) under artificial light. Natural alexandrite is very rare. The finest alexandrite crystals ever found came from the Tokovaya river deposit, and the greatest alexandrite specimen ever found is housed in Moscow's Fersman Mineralogical Museum.
Alexandrite has a hardness of 8.5 on the Mohs scale. The Toughness of Alexandrite is Good. Alexandrite (chrysoberyl) crystalizes in the orthorhombic crystal system, with an "tabular", striated, and/or prismatic Crystal Habit, forming pseudo-hexagonal or cyclic ("iron cross" and "cog wheel") twinning. Alexandrite has a refractive index of 1.745.
Brazilian & Indian Alexandrite
Brazilian Alexandrite occurs in pegmatites surrounding the mining towns of Novo Cruzeiro and Nova Era region of Minas Gerais, Brazil. The color of most Brazilian alexandrite does not shift to the green end of the spectrum as much as Russian alexandrite, although there have been recent discoveries at Nova Era that produce a more pronounced color-shift. These Nova Era stones tend to be small specimens that can be heavily occluded.
Other sources have been the Narsipatnam and Vishakhapatnam mines (Vishnakahaputnam), within the Vishakhapatnam District of the Andhra Pradesh state in central-eastern India. The Vishakhapatmam mines were closed after the 2004 tsunami. There are also alexandrite mines in the Deobhog region (Samunda) in the state of Chhattisgarh (Chattisgarh), north of Andhra Pradesh. Madagascar and Tanzania are also sources for Alexandrite. Due to its extreme rarity, quality specimens of Indian or Brazilian Alexandrite can sell for several thousand dollars per carat.
Alexandrite is a form of chrysoberyl (a cyclosilicate), which is an aluminate of beryllium. Chrysoberyl is transparent to translucent and sometimes chatoyant. Alexandrite's characteristic green to red color change results from small scale replacement of aluminium by chromium oxide.
Chemical composition: BeAl2O4
Natural Alexandrite is very rare. Most alexandrine found on the market today is synthetic. From the late 1800s, synthetic alexandrine was made using corundum which had been treated with vanadium to give it the characteristic color-change effect. Since the early 1970s, true synthetic alexandrite has been produced by using the "flux-melt", "floating point", "floating zone", and "pulled crystal" methods. There are characteristic "rain-like" inclusions in synthetic alexandrite that help with its identification. Most synthetic alexandrite is produced in Japan and Russia.
