The diamond was found in Arkansas by Wesley Oley Basham, a worker at the Arkansas Diamond Corporation. The name "Uncle Sam" does not come from the national figure, but was the nickname of Basham.

The diamond was 40.23 carats in raw material, and later fashioned into a 12.42-carat (2.484 g) emerald-cut gem. It was M on the diamond color scale and is of pure IIa diamond type meaning the amount of impurities it has is below a few parts per million. The clarity of the stone was assessed as VVS1, which stands for Very Very Slightly Included and means the stone has minute non-diamond inclusions that are difficult for a skilled grader to see under 10x magnification.

In 1971, it was sold for $150,000.

The diamond saved the Arkansas Diamond Corporation, being months from bankruptcy.

The diamond was found in Crater of Diamonds State Park in Arkansas, the only public diamond mine in the world.

More Info: en.wikipedia.org