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