The Smithsonian Museum in Washington D.C. is now the home of a rare Arkansas diamond that hasn't been seen since 1974 in the United States.

The "Uncle Sam Diamond" is said to be the largest ever found in the U.S. was at Arkansas' Crater of Diamonds State Park in Murfreesboro. The diamond was discovered in 1924 in the park, according to Glen Worthington, the author of several books on diamonds in Arkansas.

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The "Uncle Sam," 40.23-carat diamond has been in custody at the Smithsonian for 3 years under secrecy until now. The rare diamond is a Type II diamond found deep below the ground's surface up to 497 miles. Only one to two diamonds are classified as Type II and they are the most chemically pure diamond having the highest thermal conductivity.

If you're looking for a vacation destination in Arkansas this summer, visit the Crater of Diamonds State Park where more than 33,100 diamonds have been found since 1972. Everything you find in this 37-acre field included a variety of rocks, minerals, and gemstones you can take home for free. Besides the largest "Uncle Sam" diamond ever found, other large diamonds include the 16.37-carat Amarillo Starlight; the 15.33-carat Star of Arkansas; and the 8.52-carat Esperanza.

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