Rare Alexandrite Gems

Alexandrite Rough from Tanzania

Alexandrite is one of the rarest of all colored gemstones and is famed for its color change from green in daylight to red under incandescent light. Fine faceted alexandrite over 1 carat is more valuable than sapphire, ruby or emerald.

Alexandrite is a gem known for its strong pleochroism, displaying colors such as emerald green, red, and orange-yellow. It has the unique ability to change colors from one hue in artificial light to another in natural daylight. This color transformation from red to green is caused by the gem's absorption of light in the yellow and blue parts of the spectrum. In general, alexandrite appears emerald green in daylight and takes on a raspberry-red hue under incandescent lighting.

According to a popular but probably apocryphal story, alexandrite was discovered by the Finnish mineralogist Nils Gustaf Nordenskjold, (1792 -1866) on the tsarevitch Alexander's sixteenth birthday on April 17, 1834, and named alexandrite in honor of the future Tsar Alexander II of Russia. It is apparently true that alexandrite was first identified (but not discovered) by Nordenskjold, but likely some years earlier, around 1831. It was Count Lev Alekseevich Perovskii (1792-1856) who named the gem alexandrite.

Tsar Alexander II

Alexandrite is a variety of chrysoberyl, with an excellent hardness of 8.5 on the Mohs scale. Chyrsoberyl has a refractive index of 1.746-1.763 and a density or specific gravity of 3.70-3.78.

Alexandrite is very rare because of its chemical composition. While it is a form of chrysoberyl, it has an extra trace element in addition to iron and titanium. It is the presence of chromium that gives it the emerald-green hue in daylight. Alexandrite exhbiting chatoyancy or the cat's eye effect is known, but very rare.

The original source of alexandrite in the Ural mountains in Russia has been worked out. An important alexandrite deposit was found in 1987 in Minas Gerais in Brazil and other deposits are found in Burma, Madagascar, Sri Lanka and Tanzania.

Alexandrite is rarely found in large sizes. The largest cut alexandrite weighs 66 carats and is in the Smithsonian Institution in Washington, D.C.