A California couple was in “just the right place” to find a 4.38-carat yellow diamond, the largest one discovered this year at the Arkansas Crater of Diamonds State Park.

Noreen and Michael Wredberg were visiting the Hot Springs National Park, when they decided to take a detour and stop by the Crater of Diamonds park.

They had only been there for an hour, when Ms Wredberg spotted a “sparkling gem on top of the ground” on 23 September, said a press release issued by the park last month about the finding, which was widely reported only in October.

“I didn’t know it was a diamond then, but it was clean and shiny, so I picked it up,” Ms Wredberg was quoted as saying by the release.

The couple then took it to the park’s Diamond Discovery Centre, which confirmed the shiny yellow jelly bean-like object was indeed a diamond.

Park authorities said a bout of rainfall just two days before the Wredbergs visited led to the right conditions for discovering the gemstone.

“The soil had dried a little, and the sun was out when Ms Wredberg visited two days later. She was in just the right place to see her diamond sparkle in the morning sunlight,” said park interpreter Waymon Cox.

Ms Wredberg named the diamond Lucy’s Diamond, after her husband’s pet kitten.

The couple have since returned to California, but have not decided on what they will do with their new gemstone, reported CBS News. They are also yet to get the diamond appraised.

Authorities at the Arkansas park are not trained to appraise or grade diamonds found at the park, but to offer resources to finders, identify discovered gemstones and register them, said Mr Cox.

Valuations of diamonds also depend on whether they are uncut, graded or cut.

The “Strawn-Wagner” diamond, for instance, was found at the park in 1990 and whittled from a 3.03-carat white diamond into a 1.09-carat round gem in 1997.

Graded as “perfect” by the American Gem Society, the Strawn-Wagner was mounted on a gold and platinum ring and purchased by the Arkansas government through private donations for $36,000, according to Mr Cox.

Arkansas is the only state in the US with a public diamond mine. While visitors have to pay an entry fee of $10, there are additional charges for obtaining tools to hunt for diamonds. The park operates on a “finders keepers” policy, under which visitors are allowed to keep the gemstones they find.

Over 75,000 diamonds have been discovered at the park since 1906, according to the press release. Ms Wredberg’s diamond is one of the 258 diamonds found there in the past year.

The largest diamond found in the park was called the “Uncle Sam”. It was estimated to be 40.23 carats and was discovered in 1924.

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