Alexandrita

Alexandrita, also known as alexandrite, is a gemstone variety of chrysoberyl (BeAl2O4) renowned for its color-change properties. It appears green in daylight or fluorescent light and shifts to reddish-purple under incandescent or artificial light. The mineral was first described in the Ural Mountains of Russia in 1834 and was named after Tsar Alexander II.

Chemically, alexandrite is BeAl2O4 with chromium as a trace impurity responsible for the dramatic color change. It exhibits strong pleochroism, and the color-change effect is most noticeable in well-cut stones. The mineral has a hardness of 8.5 on the Mohs scale, refractive indices in the vicinity of 1.74–1.76, and a specific gravity around 3.7. It crystallizes in the orthorhombic system.

Sources of alexandrite include the historical Russian Urals, with significant modern deposits in Sri Lanka, Brazil, Madagascar, Tanzania, India, and Myanmar. High-quality stones showing a vivid green-to-red color change are rare and can be highly valued; the strength and consistency of the color change, along with clarity and cut, influence price.

Gem-quality alexandrite is typically cut as faceted gems to maximize color shift. Heat treatment can affect color distribution and may alter the color-change effect, so cutters balance hue, saturation, and clarity. Natural alexandrite remains relatively rare; synthetic alexandrite has been produced since the 20th century using various methods and is commonly available as a more affordable alternative to natural stones.