Alexandrite: The Rare Colour-Changing Gemstone

Alexandrite is a variety of chrysoberyl, a mineral composed of aluminium and beryllium oxide (BeAl₂O₄). What sets it apart from all other precious stones is its remarkable colour-change effect, known as the "alexandrite effect".

In natural daylight, it displays hues ranging from green to blue-green, sometimes with teal undertones. Under artificial incandescent light, it transforms, revealing tones of red, red-purple or raspberry.

This phenomenon is explained by the presence of trace amounts of chromium in the crystal structure of chrysoberyl. Chromium selectively absorbs certain wavelengths of light: daylight, rich in blue and green wavelengths, brings out the green hues, while incandescent light, richer in red wavelengths, reveals the stone's purple tones.

The discovery of alexandrite is steeped in legend. According to the most widely told account, it was found in 1830 in the emerald mines of the Urals, in Russia, and named in honour of the future Tsar Alexander II, who came of age on that very day.

The stone's colours — green and red — corresponded to the Russian imperial colours, immediately conferring upon it the status of a national gemstone. The Russian Ural deposits produced some of the finest alexandrites ever discovered, with a particularly pronounced colour change.

These mines are today virtually exhausted, making period Russian alexandrites exceptionally rare and sought after by collectors. Over the decades, further deposits have been discovered around the world, each yielding stones with distinct characteristics.

Each source produces alexandrites with distinct characteristics, and a stone's geographical origin considerably influences its value on the market.

Evaluating an alexandrite rests on specific criteria, quite distinct from those applied to diamonds or other coloured stones. Below are the determining factors, in order of importance.

Alexandrite is one of the most expensive gemstones in the world. Prices vary enormously according to quality, origin and the size of the stone.

By way of comparison, a top-quality alexandrite can cost more than a diamond, a ruby or an emerald of equivalent size. This extreme valuation is explained by the combination of natural rarity and sharply rising global demand, particularly in Asia.

Alexandrite is the birthstone for the month of June (alongside pearl and moonstone) and is traditionally associated with the 55th wedding anniversary.

In crystal-healing traditions, it is associated with balance and harmony between body and mind. Its colour change symbolises adaptability and flexibility, a reminder that change is a constant of life. It is also regarded as a stone of luck and prosperity, inheriting its symbolism from the Russian imperial tradition.

In sentimental jewellery, to give an alexandrite is to celebrate a rich and multifaceted relationship — a person whose personality reveals itself in different lights. It is an ideal choice for those seeking a truly unique engagement ring, far removed from convention.

With a hardness of 8.5 on the Mohs scale (just below sapphire and ruby), alexandrite is perfectly suited to everyday wear. It resists the scratches and knocks of daily life, making it an excellent choice for an engagement ring or an everyday ring.

To best showcase the colour change, a clean solitaire setting or a surround of small white diamonds is often preferred, so as not to compete with the chromatic phenomenon.

At Bonnot Paris, we guide our clients in the search for exceptional alexandrites and the creation of bespoke pieces that bring out the full beauty of this extraordinary stone. Every alexandrite is selected for the intensity of its colour change and the beauty of its hues.

The rarity and high price of natural alexandrite have led to the development of synthetic versions. Synthetic alexandrite, produced in a laboratory using the Czochralski method or flux growth, shares the same chemical composition and physical properties as the natural stone.

Caring for an alexandrite is relatively straightforward, thanks to its excellent hardness. Here are our recommendations for preserving the brilliance of your stone over the years.

For everyday cleaning, use lukewarm soapy water with a mild soap and a soft brush (such as a soft-bristled toothbrush). Rinse thoroughly with clean water and dry with a soft, lint-free cloth. Ultrasonic cleaning is generally safe for alexandrite, unless the stone has fractures or significant inclusions — if in doubt, opt for manual cleaning.

Avoid sudden thermal shocks and prolonged exposure to harsh chemicals (chlorine, household products). Store your alexandrite jewel separately from other pieces, ideally in an individual pouch or a dedicated compartment of your jewellery box.

Choosing an alexandrite for an engagement ring is a deeply personal and distinctive choice. Here is why this stone deserves your attention.