Brett Jolly, a British developer, told The Guardian that the people who told him of the diamond were trying to convince him to buy the land where they said it was found.
"I think they were salting the mine, that's what I think," he said, referring to a scheme used to interest unwary buyers in played-out mines.
Recently, Jolly had described the diamond as more than twice as big as the fabled Cullinan, which weighed more than 3,100 carats and was found in South Africa in 1905.
Jolly told the newspaper that he first saw his “diamond” on Thursday and described it as an obvious piece of plastic. He said the two miners who showed it to him had a diamond tester and claimed to test it but “the cap was still on the bloody thing.”
Jolly said he plans to report the matter to police.