image: Optical photomicrograph of a sulfide-inclusion-bearing rough diamond from the Orapa kimberlite, Botswana. Below the natural diamond growth surface, at center, are several hexagonal grains of iron sulfide (Fe-S) surrounded by an irregular black rim. This rim is caused by internal fracture of the diamond on its 150-km ascent to the Earth's surface in the explosive volcanism of the kimberlitic magma. Sulfide grains like these are removed for rhenium-osmium isotopic analysis to reveal the age of the diamond and the composition of the sulfide. Diameter of sulfide grains are about 0.25 mm. This image relates to an article that appeared in the July 22, 2011, issue of Science, published by AAAS. The study, by Dr. Steven Shirey of Carnegie Institution of Washington in Washington, D.C., and colleagues was titled, "Start of the Wilson Cycle at 3 Ga Shown by Diamonds from Subcontinental Mantle." view more
Credit: Photo courtesy of Steven B. Shirey, Carnegie Institution of Washington