The company that has discovered what could be the world's largest diamond says it will carry out conclusive tests on the stone early next week.
Experts say the find would be the stone of the century, if genuine
The South African company says it has asked the president of the World Federation of Diamond Bourses to carry out the examination.
Experts have been sceptical about the discovery, saying the light-green stone may turn out to be a fluorite crystal.
But the firm insists it could still turn out to be a diamond.
But diamond industry analysts remain sceptical about whether a diamond of such a size is even possible.
The stone was found earlier this week in a small mine in South Africa's north-west province.
A spokesman for De Beers, the world's biggest diamond mining company, said the north-west province was not known for producing gems and greenish stones were even rarer.
The firm also said that if the find were genuine it would be the stone of the century.