Written by Amy Woodyatt, CNN

A gold-hunter claims to have found the UK's largest gold nugget, weighing a hefty 121.3 grams (4.28 ounces), in a Scottish river.

The metal lump, found in two pieces and dubbed "The Reunion Nugget," was discovered by a treasure hunter in May.

If proven to be from Scotland, the precious metal would usurp the "Douglas Nugget," weighing 85.7 grams and found in 2016, as the largest gold nugget found in the UK.

Lee Palmer, who had been writing a book on the origins of gold in the UK, told CNN he was approached by the anonymous gold-hunter, who wanted his find recorded. The prospector discovered the metal using a technique called "sniping," which involves scraping out the crevices at the bottom of a river, Palmer said.

Palmer, author of "Gold Occurrences in the UK: A Gold Prospector's Guide," told CNN that the pieces seemed to come from the same lump of gold. The two pieces, 89.6 grams and 31.7 grams, "fit perfectly like a jigsaw," and could have been broken apart by rock strike or glacial damage, Palmer said.

However, gold expert Neil Clark told CNN that while there are more than 300 locations where gold can be found in Scotland, proving the metal's provenance would be difficult.

"Even if this nugget did come to a museum to be looked at, it's virtually impossible to tell where it had come from because there's only one isotope of gold that's found naturally," Clark, author of "Scottish Gold: Fruit of the Nation" and curator at Glasgow's Hunterian Museum, told CNN.

"So gold is basically gold -- the only way of checking to see where a piece of gold has come from is to locate the impurities in it, and even then, it's very difficult," he added.

Scottish gold ownership laws could also complicate the situation -- the majority of gold falls under the ownership of the Crown, or certain estates in Scotland, Clark added.

Palmer, who is not involved in the sale of gold, told CNN that he hoped the nugget would be exhibited in London's Natural History Museum, or the National Museum of Scotland.

"You could say it's priceless," Palmer told CNN.