(IDEX Online) - A couple celebrating their 10th wedding anniversary found a 1.9-carat brown diamond.Seth and Jessica Erickson were visiting the Crater of Diamonds State Park, near Murfreesboro, in Arkansas, USA, which charges day trippers $10 a day to sift the soil - and lets them keep any gems they find.They found the diamond after an hour of "wet sifting" - using a pair of meshed screens to check the soil for gems.The couple, from Chatfield, Minnesota, named the stone HIMO, the initials of their children.The park, formerly operated as a commercial mine, is a lamproite, a volcanic rock that together with kimberlites is a common host for diamondsIn 1924 it yielded the USA's biggest ever diamond, a 40.23-ct white diamond with a pink cast which was cut into a 12.42-carat emerald shape and purchased by a private collector for $150,000 in 1971.Pic shows Seth and Jessica Erickson and their diamond.