Tana Clymer from Oklahoma City was touring Arkansas' Crater of Diamonds State Park on Saturday with her family when she found the teardrop-shaped gem which is about the size of a jellybean.
The park is an eroded ancient volcanic crater which is described as the only "diamond-bearing site" that is open to the public.
It also has a "finders keepers" policy. Clymer spied the diamond in the dirt after two hours of sifting and searching through the park's volcanic soil.
"I thought it was a piece of paper or foil from a candy wrapper. Then, when I touched it, I thought it was a marble," she told park officials.
The diamond's appraisal value wasn't immediately known, but it could be worth around USD 50,000 to USD 60,000, 'New York Daily News' reported. Park officials also said it could be worth tens of thousands of dollars if it's legit.
The sparkling souvenir that Clymer found is similar to a 4.21-carat rock discovered in 2006. That one was appraised for about USD 50,000 to USD 60,000, said Bill Henderson, assistant park superintendent. "It appears to be of the same quality.
This particular yellow canary will knock your eyes out. The colour is so brilliant," Henderson told the Daily News. He added that Clymer had tears in her eyes when they told her the diamond's potential value.
She said she may turn the diamond into a ring or use it to help pay for college. Nearly 400 diamonds have been dug up at the 37-acre Arkansas state park this year.