Gems of war: scientists struggle to identify conflict diamonds

Science News,  August 10, 2002  by John Pickrell

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Most researchers are attempting to find a single method that would identify diamonds from anywhere, says Vicenzi. However, since this seems beyond researchers' grasp at the moment, "we have to come up with alternatives," he says. Finding specific, rare characteristics that tie diamonds to specific sources may provide a partial solution until a more universal method is developed.

Vicenzi reports one type of rare characteristic that appears in some carbonados. Deep within Earth, some diamonds come into contact with radioactive materials, such as thorium or uranium, that can impart a unique signature known as a radiation halo.

To detect this rare damage, Vicenzi and his colleagues bombard the surface of a diamond with electrons, which cause it to throw off a pattern of light influenced by the radiation damage. The areas of damage produce a bull's-eye of light that appears to be consistent among stones to similar types and intensities of radiation.

The team has used this technique to characterize carbonados from the Central African Republic. Although it hasn't yet been tried on gem-grade stones, Vicenzi holds that this technique could be adapted to flag contraband gems from specific regions.

There are some inherent problems with any technique that depends on a single characteristic to link a gem to its source, says geologist Eva Anckar of the University of Cape Town in South Africa. "Any one, single characteristic does not sufficiently discriminate between diamonds from different sources," she says. Also, many methods being tested require partial destruction of the gem. Instead, her team proposes a method that takes into account several variables and leaves gems whole.

The scientists first shine an infrared beam through intact diamonds and measure the wavelengths absorbed. These data reveal impurities, such as nitrogen, hydrogen, and oxygen locked within the diamond, Anckar says. The researchers then combine these data with various measurements of the color and overall shape of rough diamonds.

In a pilot study, the scientists compiled eight measurements on each of 495 diamond specimens that came from three mines. Using multiple characteristics and complex statistical methods, the researchers found that diamonds from each site--two in South Africa and one in Canada--showed unique clusters of characteristics.

"The method shows great promise," says Anckar, though it requires examining whole parcels of gems from any given region, because it's the range of characteristics over a group of gems that gives away the identity.

Anckar is currently compiling those profiles for diamonds in a "global atlas of diamond characteristics," she says.

PIPE DREAM "Strictly analytical methods all suffer from critical weaknesses," says Harris. Practicality is the biggest drawback of stone-by-stone analyses, he says. He has calculated that most methods would be so time consuming as to be impractical. Moreover, complex analytical techniques that require slicing gems will probably never be implemented, Harris says.