The Oppenheimer Diamond, a nearly perfectly formed 253.7 carats (50.74 g) yellow diamond crystal, is one of the largest uncut diamonds in the world, and measures approximately 20 mm × 20 mm. It was discovered in the Dutoitspan Mine, Kimberley, South Africa, in 1964. Harry Winston acquired the stone and presented it to the Smithsonian Institution in memory of Sir Ernest Oppenheimer.