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Articles from GEMSTONES - LOOSE (254 Articles)











Colour-change diaspore: a Turkish treasure

From the land of exotic spice markets, grand bazaars and ancient ruins comes a beautiful, rare and unusual colour-changing gemstone. Megan Austin investigates Turkish diaspore and the trademarked names that honour its country’s heritage.

Nicknamed “a true Turkish delight” by the International Coloured Gemstone Association (ICA), colour-change diaspore is natural and untreated.

Derived from the Greek word ”diaspheirin”, the name diaspore means “to scatter and make a crackling sound when heated,” referring to its tendency to be damaged by heat.

Various trade names for high-quality colour-change diaspore have emerged within the last decade, all referencing the sultans, tsars and ottomans of Turkey. These include zultanite, csarite and ottomanite. Diaspore’s first patented trade name zultanite was registered in 2005 by Turkish jeweller Murat Akgun in honour of the 36 sultans who ruled the Ottoman empire from 1299 to 1923.

Stephen Webster Turkisk diaspore cocktail ring
Stephen Webster Turkisk diaspore cocktail ring

Regal associations are certainly befitting this exotic, pastel-toned gemstone coloured by manganese. Traces of chromium in the presence of iron cause colour changes depending on the light. What appears as kiwi green with flashes of yellow in sunlight might seem raspberry or brownish pink under candlelight, champagne in incandescent light, and something else entirely in other light sources.

Another feather in diaspore’s cap is a property known as trichroism, where three different colours are seen from different directions. These colours – brownish pink, yellowish green and sometimes violet blue – are distinct and contribute towards its colour-change effect.

Common variety diaspore is a bauxite mineral discovered in the Ural Mountains in Russia in 1801 and used as a component for cement. Gemstone-quality diaspore was discovered in the Turkish Anatolian Mountains in the 1970s at heights of more than 4,000 feet.

Gemstone quality colour-change diaspore registers 6.5–7 on Mohs scale. It’s softer than quartz so it requires some care when worn. It has a high lustre and an incredible dispersion, even exceeding diamond, which contributes towards its bright sparkling appearance when cut.

Diaspore has one direction of perfect cleavage that means a single blow can cause it to fracture. Its tendency to cleave presents a challenge for the cutter and yield rates are notoriously low and can be as little as 2 per cent for eye-clean material and 10 per cent for larger sizes. Consequently, large, clean and well-cut gemstones are extremely rare and expensive.

Rare, colour-change diaspore can also exhibit another optical effect known as “chatoyancy” or “cat’s eye.” This occurs when light reflects from inclusions that are laid parallel to the base of a cabochon, resulting in a single band of light moving across the stone when rotated, simulating a cat’s eye.

Common imitations of diaspore including alexite and zandrite are often sold at tourist destinations. Alexite, a cheap glass manufactured in India, uses vanadium, chromium, manganese and iron in varying quantities to mimic the colour-change properties of diaspore. Both alexite and zandrite are easily distinguished from colour-change diaspore using standard gemmological instruments. Currently, there are no known synthetics in production, contributing to its desirability. 


Turkish diaspore on Jeweller's  Facebook

 











ABOUT THE AUTHOR
Megan Austin

Megan Austin FGAA FGA Dip DT BA, is a gemmologist and registered valuer. She operates Megan Austin Valuations.
Visit: meganaustinvaluations.com.au.

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Wednesday, 19 June, 2019 08:39am
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