The Oppenheimer Diamond, a nearly perfectly-formed 253.7 carat (50.74 g) yellow diamond

Diamond

In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...

 crystal, is one of the largest uncut diamonds in the world. It measures approximately 20 × 20 millimeters. It was discovered in the Dutoitspan Mine, Kimberley, South Africa, in 1964. Harry Winston

Harry Winston

Harry Winston was an American jeweler. He donated the Hope Diamond to the Smithsonian Institution in 1958 after owning it for a decade, and traded the Portuguese Diamond to the Smithsonian in 1963.-History:...

 acquired the stone and presented it to the Smithsonian Institution

Smithsonian Institution

The Smithsonian Institution is an educational and research institute and associated museum complex, administered and funded by the government of the United States and by funds from its endowment, contributions, and profits from its retail operations, concessions, licensing activities, and magazines...

 in memory of the late Sir Ernest Oppenheimer

Ernest Oppenheimer

Sir Ernest Oppenheimer was a diamond and gold mining entrepreneur, financier and philanthropist, who controlled De Beers and founded the Anglo American Corporation of South Africa.-Career:...

.