By Peter Greste
BBC News, Johannesburg
A small South African mining company has claimed to have discovered the world's biggest-ever diamond.
Experts say the find would be the stone of the century, if genuine
A shareholder in the unnamed mine told the BBC the stone had been unearthed at their operation in the north-west province on Monday afternoon.
He said the giant gem was about 7,000 carats - which would be twice the size of the Cullinan Diamond, centre-piece of the British crown jewels.
But industry experts are sceptical about the unconfirmed claim.
Brett Jolly, a shareholder at the mine, said the stone had been taken to a bank vault in Johannesburg.
Mr Jolly said he hoped tests on Tuesday would prove its worth.
In a photograph emailed to the BBC, the 'stone' appears to be about the size of a coconut, and has a greenish tinge.
But 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.