The Uncle Sam diamond is the largest diamond ever discovered in the United States. It was first discovered in 1924 in Murfreesboro, Arkansas. This site would eventually become the Crater of Diamond State Park in Arkansas.
The Uncle Sam Diamond was named after the man who discovered it. His name was Wesley Basham but he was nicknamed "Uncle Sam."
The rough diamond weighed in at 40.23 carats but it had to be cut twice. It was a white diamond with a pink cast. Its final form was an emerald-cut diamond weighing 12.42 carats. Its color grade is rated "M" or faint yellow.
Jewelers have described the Uncle Sam diamond as a Type 1a diamond with a light pink tone that is caused by plastic distortion. There are also detectable quantities of nitrogen in the diamond.
The diamond is also classified as an Arkansas diamond. These diamonds are harder than diamonds from other sources. The hardness of the diamond may explain why it was cut in an emerald shape. The hardness would also explain why it had to be cut twice.
The clarity of the stone was assessed as VVS1 (very very slightly included) to indicate that there were very minute non-diamond inclusions.
As for the ownership of the stone, it was first owned by Peikin Jewelers of Fifth Avenue in New York. It was then given to the American Museum of Natural History for display and storage. In 1971, a Boston dealer acquired the diamond and subsequently sold it to an anonymous private collector for $150,000.