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January-February 2014

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Color in Natural Diamonds: The Beauty of Defects

IN ITS PURE FORM, DIAMOND IS COLORLESS. However, in nature (or even when made in laboratories), diamonds are never composed of 100 percent carbon atoms. Even colorless diamonds will contain some defects: missing carbon atoms or containing trace amounts of nitrogen or hydrogen, for example. When present in certain atomic arrangements and concentrations, most minor components cause absorption of specific wavelengths of light, giving rise to color. The color in diamond is not source specific, even if some mines are known to produce more of certain colors, such as blue diamonds from the Premiere mine in South Africa, or brown and pink diamonds from the Argyle mine in Australia. Virtually every single diamond mine could produce any kind of colored diamond. At auction, record prices for gems are currently held by pink and blue diamonds: for example, $2,155,332 per carat for a 24.78-carat Fancy vivid pink diamond (sold at Sotheby's in 2010) and $1.8 million per carat for a 5.3-carat Fancy deep blue diamond (sold at Bonhams in London in April 2013).

Dr. Eloïse Gaillou, associate curator of the gem and mineral collection at the Natural History Museum of Los Angeles County, specializes in the physics and geology of diamonds.

Dr. George R. Rossman, the McMillan Professor of Mineralogy at the California Institute of Technology in Pasadena, studies the origin of color in minerals and applications of spectroscopy to mineralogy.

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