So-called blood diamonds often steal the show, but many other, less glamorous minerals are sold to the United States by violent militias that aren't recognized by the United Nations. Now, one team of scientists thinks a laser-based analysis can fingerprint one mineral common in electronics, to check where it was mined. For the past year, a team led by chemist Richard Hark of Juniata College in Pennsylvania has been working on testing their idea and building a portable laser people can use for on-the-spot analysis. In March, they presented their latest results at the American Chemical Society's annual meeting in San Diego, Calif.
When mineral ores form in the hot magma that moves through the Earth's crust, the ores pick up tiny amounts of different rare Earth elements. Later, when people mine those ores, even ores of the same type should carry different ratios of these elements if they come from different regions. Hark thinks those different rare elements can act as mineral-ore birth certificates, declaring where the ore comes from.
To detect those different elements, Hark wants to pulse a high-energy laser at samples of ore. The laser vaporizes the samples, breaking them down into atoms that then emit up to thousands of different wavelengths of light. Scientists can analyze those wavelengths, which show up on printouts as a row of very narrow, pointed peaks. NASA plans to use the same technique, called laser-induced breakdown spectroscopy, to analyze rocks and soil on Mars.
Hark's team uses a computer program to distinguish between the slightly different wavelength signatures of mineral ores mined from different regions. At the American Chemical Society meeting, team members reported their method helped them identify the origin of 37 samples of columbite-tantalite from around the world. Columbite-tantalite, commonly known as coltan, is found in almost all cell phones, laptops and other electronics. A United Nations report found rebels in the Democratic Republic of Congo have funded their violence with coltan sales over the past decade, during which a series of wars killed 3.1 million people, Bloomberg reported.
Hark is also working with a company that makes large laser-induced breakdown spectroscopy machines for labs, to create a small machine inspectors can carry with them. Hark and his colleagues successfully analyzed a subset of their original 37 coltan samples using the portable analyzer, they reported during the March meeting. Now they're working on making the small machine rugged enough for field use, according to the American Chemical Society's magazine, Chemical & Engineering News.
The magazine also reported on experts who were both skeptical and enthusiastic about Hark's method for ferreting out unethically sold coltan. Frank Melcher of the Federal Institute for Geosciences & Natural Resources in Germany said the lasering technique could aim at the wrong grains of ore and compare grains that shouldn't be compared. On the other hand, Nancy McMillan of New Mexico State University said, "The [laser-induced breakdown spectroscopy] spectrum contains an enormous amount of information and provides a detailed geochemical fingerprint of the material analyzed."
Perhaps the most important next step is making database of the wavelength signatures of coltan from all around the world. After all, once scientists find a mineral ore's signature, they still need to match that signature with a place. That may mean getting dozens of samples of coltan from every deposit around the world. McMillan's work has shown that even 30 samples from a deposit may not be enough, she said.
A database would presumably need samples from the controversial deposits in the Democratic Republic of Congo. Considering the United Nations has imposed sanctions against Congolese coltan since 2003, that may be a tall and dangerous order.
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