JOHANNESBURG, Aug 28: A small South African mining firm has claimed unearthing the world’s largest diamond, but industry insiders are sceptical about the find.

A photo of the diamond has been circulated on the internet, showing a massive green-tinged stone sitting on a desk next to a cell phone to illustrate its size — which is purported to be 7000 carats.

This is double the size of the current holder of the world’s largest title — the Cullinan diamond which was found in South Africa around a century ago.

“If it is what it is, it’s very, very rare,” said leading gemmologist Les Milner from the Jewellery Council Labs. “I tend to be very sceptical about this kind of thing.”

He said it was hard to tell from the picture, but that the stone -- found in the North West province -- was the typical octahedral shape of a diamond.

“Nobody has actually seen it to ascertain whether it is a diamond or not,” he said.

An online mining industry website, Mining Weekly, quoted a spokesman for the company claiming to have found it, as saying the stone was in a Johannesburg bank vault, and the company was consulting with lawyers.—AFP