World's biggest diamond ?

A small South African mining company has claimed to have discovered the world's biggest-ever diamond. 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' (seen next to a mobile phone) 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.