Arguably the rarest and most desirable of coloured gemstones (excluding diamonds), Alexandrite is a rich and beautiful blue green colour when viewed in natural sunlight. Viewed in incandescent light, the same stone will show a rich purple red. You’ll love alexandrite, the gem that changes colour!
Alexandrite is a gem variety of the mineral chrysoberyl discovered in 1830 in Czarist Russia. Since the old Russian imperial colours are red and green it was named after Czar Alexander II on the occasion of his coming of age.
So how does the colour change work? Most gems transmit and absorb light throughout the visible spectrum and we interpret the mixture of the transmitted wavelengths as the gem’s colour. Alexandrite transmits light only in the blue-green and red regions of the spectrum whilst the rest of the spectrum is absorbed. When viewed under different light sources you see one of the two colours. In daylight, or in artificial light like fluorescent light, light waves in the green region predominate. In candlelight, or artificial light like tungsten light, light waves in the red region predominate. The gem is displaying changes in the light, not changing itself.
Today, fine alexandrite is most often found in period and estate jewellery since newly-mined gems are extremely rare. The original source in Russia’s Ural Mountains has long since closed after producing for only a few decades and only a few stones can be found on the market today. Material with a certificate of Russian origin is still highly valued by the trade. Some alexandrite is found in Zimbabwe and Brazil but very little shows a dramatic colour change. For many years, alexandrite was almost impossible to find because there was so little available.
Then in 1987, a new find of alexandrite was made in Brazil at a locality called Hematita. The Hematita alexandrite shows a striking and attractive colour change from raspberry red to bluish green. Although alexandrite remains extremely rare and expensive, the production of a limited amount of new material means a new generation of jewelers and collectors have been exposed to this beautiful gemstone, creating an upsurge in popularity and demand.
When evaluating alexandrite, pay the most attention to the colour change: the more dramatic and complete the shift from red to green, without the bleeding through of brown from one colour to the next, the more rare and valuable the stone. The other important value factors are the attractiveness and intensity of the two colours, the clarity, and the cutting quality. Due to rarity, large sizes command very high premiums.