The Crater of Diamonds State Park is an 888-acre Arkansas state park situated over an eroded volcanic pipe(鉱脈). The park is the only diamond mine open to the public, and for a small fee, tourists can dig for diamonds and other gemstones(原石). Park visitors find more than 600 diamonds of all colors and grades each year. Visitors may keep any gemstone they find regardless of its value. The largest diamond found at the crater is also the largest ever unearthed(発掘する) in the US.