Once owned by Spain's Infanta Margarita Teresa, the huge, rare, deep-blue Wittelsbach-Graff Diamond will join other gems at Washingon, D.C.'s National Museum of Natural History for seven months next year. Weighing 31.06 carats, the diamond may be from the same mine as the Hope Diamond. Current owner Laurence Graff is lending the brilliant gem not only for exhibition but also research. Graff bought the diamond last December at auction for $24.3 million, a record price for a single stone at the time.