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Conflict Diamonds Elude Mass Spectrometry

Scientists conclude that mass spectrometry does not offer a solution for identifying conflict diamonds. Conflict diamonds make up approximately 4% of the world's diamond trade and are used to fund rebels and guerillas and their causes. The United Nations has condemned the sale of conflict diamonds some of which originate from the Congo basin, Sierra Leone and Angola.

Geologist and mineralogists discussed ways to characterize diamonds during two sessions this past week at the Spring meeting of the American Geophysical Union in Washington, D.C.  These sessions were to followup on the request made by President Bill Clinton shortly before he left office to see if scienetists can determine the geographic origin of a diamond.

Typically, all diamonds have impurities, but they are in the range of parts-per-million, parts-per-billion or even smaller.  Just a few hundred parts-per-million of nitrogen make diamonds yellow, while much smaller amounts of boron will make them blue. Carbonados, or black diamonds, are used mostly as an industrial abrasive and contain iron and copper. Except for these slight impurities, diamonds are made up of carbon and are the hardest known natural material on Earth.

The trouble is diamonds all come from deep inside the earth, so any chemical signature will reflect their origin over a hundred kilometers under the surface. And many of the conflict diamonds come from alluvial deposits formed when stones are washed away by water and weather such they could be moved miles from their geological origin.

Peter Heaney, an Associate Professor of Geoscience at Pennsylvania State University, and Dr. Edward Vicenzi of the Smithsonian Institution, tried to see whether a mass spectrometer and a transmission electron microscope could be used to characterize minuscule pieces of diamond removed from gemstones to determine their origin.  "Most crystals have structural mistakes such as missing rows or layers," says Heaney.  "Different locations may have different defect assemblages so that we can associate diamonds with their original locations." The ratios of carbon isotopes in diamonds were also studied.

"It takes very sophisticated equipment to measure these things in diamonds," says Heaney.  "Using current methods, it is not possible to screen out conflict diamonds because it would be very labor-intensive."

"I think the opinion of most people who have been thinking about this today is that practical methods have not been demonstrated for telling where diamonds come from," James Shigley of the Gemological Institute of America told a news conference.

Yet mass spectrometry could play a larger role in characterizing diamond coatings. The diamond industry is looking at the possibility of applying an invisible chemical coating on "honest" diamonds at the source to allow a spectrographic analysis to be made that may show where a diamond originates. But this approach would not allow all the diamonds already in the marketplace to be categorised, so that in the meantime diamonds will continue to conceal their origins.

 

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