Most diamonds are not colorless. In fact, in the formation of most diamonds, a few atoms of nitrogen are substituted for carbon as the crystal grows. These imperfections interact with light to tint the stones yellow or brown. Typically, the more yellow a diamond is, the less it is worth, until the color is intense enough for the stone to be graded a fancy color, such as this intense yellow gem. The 18.30-carat Shepard Diamond from South Africa was acquired in exchange for a small collection of diamonds that had been seized as smuggled goods by the United States Customs Service. The old mine cut diamond is named for the Smithsonian employee who facilitated the exchange, Glen P. Shepard, former Purchasing Officer, in 1958. The Shepard Diamond is on display in the Gem Hall at the Smithsonian’s National Museum of Natural History.
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