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,[1] and measures approximately 20 mm × 20 mm (0.79 in × 0.79 in).

It was discovered in the Dutoitspan Mine, Kimberley, South Africa, in 1964.

[1] Harry Winston acquired the stone and presented it to the Smithsonian Institution in memory of Sir Ernest Oppenheimer.

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