A TECHNIQUE that reveals where an emerald was mined could help bring smuggling of the gems under control. The method could also give teeth to a gem-control initiative in Colombia, where the government is struggling to regulate the country鈥檚 lucrative emerald industry.
Unlike rubies and diamonds, emeralds are not normally considered 鈥渃onflict鈥� gemstones, jewels that help to fund the illegal purchase of weapons. And no country that produces emeralds is under international sanctions on its exports. The emerald trade has, however, been linked to illegal drug trafficking and paramilitary groups in Colombia and other regions where the gems are mined, including Afghanistan.
Emeralds are also mined in Africa, Russia and Brazil, but smuggling is a particular problem in Colombia, partly because its emeralds鈥� reputation for quality ensures they sell for almost twice as much as similar gems mined elsewhere. Buying foreign emeralds and passing them off as Colombian is also thought to be a popular way for local drug barons to launder money.
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When a method of identifying an emerald鈥檚 origin was announced in 2000, it made headlines. Researchers at the National Centre for Scientific Research (CNRS) in Nancy, France, showed that the oxygen isotope ratio in an emerald is characteristic of the region it was mined in (快猫短视频, 6 February 2000, p 14). But measuring the ratios required specialist equipment and vaporising a tiny amount of the gem, which was not popular with either gem dealers or labs.
Now Alain Cheilletz, Philippe de Donato and Odile Barres at the National Polytechnic Institute of Lorraine (INPL) in Nancy and CNRS have unveiled a new method that solves these problems. It is non-destructive and relies on equipment that gem labs use routinely. Traders already scrutinise emeralds鈥� infrared spectra to check whether they have been artificially treated to hide imperfections, but Cheilletz and his colleagues say the spectra can also reveal where the stones were mined. 鈥淚f the claims are true then it is extremely useful,鈥� says Ken Scarratt, director of the testing laboratory at the American Gem Trade Association in New York. 鈥淭he [equipment is] commonplace, so it鈥檚 bringing it home to a useful level.鈥�
The technique looks for lines in emerald spectra that correspond to deuterated water, in which one of the hydrogen atoms of the water molecule is replaced by its isotope deuterium. Atoms of different rare-earth elements that are present strain the water bonds, producing up to five additional bands in the pattern.
The group collected samples from 46 emerald mines worldwide and found that their spectra fell into five different groups that corresponded to geographical regions. Even within a group there were differences between individual mines, the team reports in a paper to be published in Applied Spectroscopy. The researchers have already used the method to show that a supposedly Colombian emerald for sale at a gem fair in Basle, Switzerland, was in fact from Afghanistan.
The team is now discussing the possibility of licensing the technology to the Colombian government, as part of an initiative by the government agency for education and training (SENA) to establish a gemmologists鈥� training centre in Bogot谩. Beatriz Tabourda of SENA says she hopes the centre will be able to use the method to issue internationally recognised certificates of origin to discourage people from buying smuggled goods that lack documentation.
But not everyone is convinced of the merits of a certificate scheme. 鈥淲ith conflict diamonds, there is a specific reason why everyone wanted such an identification to put international pressure on. But I have not seen documentation that smuggling is a serious enough issue,鈥� says Ivette Torres, a Colombian mineral industry analyst for the US Geological Survey in Reston, Virginia. Scarratt argues that could change: 鈥淕iven today鈥檚 politics, the origin can easily become important.鈥�