The State Park called Crater of Diamonds is located near at Murfreesboro in Arkansas.
There are a number of other Kimberley pipes in the area but only the Crater of Diamonds park has diamonds. It seems to not have the best or largest diamonds and never been successful as a commercial diamond mine.
Now the public can visit and you can pay to play or pay to prospect - keeping any diamonds and gemstones you find.
Why is there only 1 diamond mine in Arkansas and the USA?
Why does the only diamond mine in the USA also have a wide variety of gemstones including agate, amethyst, garnet, hematite, jasper and peridot.
UPDATE: There is not just the one diamond mine in the USA.