WASHINGTON, DC.- The Smithsonian’s National Museum of Natural History is extending its exhibit of one of the most rarely seen gems in the world, the Wittelsbach-Graff Diamond, to Sept. 1. Before the diamond was exhibited beginning Jan. 28, it had been out of view from the public eye for more than 50 years. It had previously been on public display at the Brussels World’s Fair in 1958. The Wittelsbach-Graff Diamond is in the Harry Winston Gallery in the museum, adjacent to the renowned Hope Diamond, in the Hall of Geology, Gems and Minerals. As a rare blue diamond from the 17th century, the Wittelsbach-Graff Diamond’s properties once suggested a possible link to the same mines in India that produced the 45.52-carat Hope Diamond, the near-perfect example of a deep-blue diamond. However, this has been dispelled by Jeffrey Post, the museum’s curator of gems and minerals. “There is an uncanny resemblance, but t