Introducing colour change gemstones: the perfect illusionists to take centre stage upon any wrist, finger or neck.
Colour change gemstones are commanding a growing audience, and the price of admission ranges from the surprisingly affordable to the seriously stratospheric.
These rarities are chameleons of the gemstone world, coveted for their ability to change colours in different light.
The human eye perceives light in the visible spectrum, comprised of red, orange, yellow, green, blue and violet wavelengths.
Colour change gemstones have two transmission windows in the visible spectrum of roughly equal size, and the nature of the illumination dictates the perceived colour.
For example, alexandrite is coloured by the trace element chromium that produces transmission windows in red and blue wavelengths.
As candlelight is rich in red wavelengths and daylight is rich in green/blue
wavelengths, alexandrite looks red when viewed in candle light and green when viewed in daylight.
This effect is applied to any gemstone with an ability to transmit two (or more) different ranges of wavelengths and is known as “the alexandrite effect”.
The value of these extraordinary gemstones is primarily based on the strength of the colour change (weak, moderate or strong), followed by the actual colours of the stone.
Factors such as size, cut and clarity are less important due to the rarity of the colour change phenomenon.
Locations like Madagascar, Sri Lanka, Burma, east Africa, Russia and Turkey are rich sources of these gemstones.
Top billing in any colour change performance is alexandrite, a rare variety of chrysoberyl originally found in the Ural Mountains and named after Czar Alexander II of Russia.
The finest specimens display a vivid bluish-green in daylight and a purplish- red in incandescent light. Fine quality Russian alexandrites larger than one carat command a premium.
For an exotic twist on a conventional stone, there is colour change sapphire, a variety of corundum. The most popular type changes from blue or violet in daylight to violetish purple or strong reddish purple in incandescent light.
Another very rare variety changes from green to reddish-brown.
A well-kept secret is Australian colour change sapphires from the central Queensland gemstone fields that display some unusual colour changes – brown to green, yellow to pink, or golden orange to orangey-green.
Another twist on a favourite is colour change garnet, either pyrope type or a mixture of pyrope and spessartite varieties.
These gemstones change from a deep green or blue-green in daylight to red or purple in incandescent light.
Rivalling alexandrite and sapphire for hardness and durability is colour change spinel. This chameleon can change from blue to purple or from light bluish-violet to light pink, resembling colour change sapphire without the hefty price tag.
The captivating magic of colour change gemstones will far outlive any show, and as prices of conventional gemstones in fine qualities are rising, these exotics present alternatives for those who demand unique, collectible gemstones.