World's biggest diamond unearthed

Mystery and tentative excitement surrounded reports yesterday that by far the world's biggest diamond has been unearthed by a small mining company in South Africa.

Experts said that the find - twice the size of the Cullinan, or "Great Star of Africa", discovered near Pretoria in 1905 - was still in need of verification last night. As security was being tightened around the stone, Brett Jolly, a spokesman for the mining firm Two Point Five Construction, said it was being transported to a bank vault in Johannesburg, where it would stay, "until we calm down and decide what we are going to do".

However, neither the South Africa Diamond Board, nor the Diamond and Jewellery Federation, the trade body, confirmed its authenticity as a diamond.

A mobile-phone photograph of the stone - the only one released of it yesterday - shows it to be smooth with a rare green tinge. The first people to inspect the find reportedly viewed it to be industrial grade. A consensus is emerging that it will indeed be cut into a piece of spectacular jewellery. It has been described as being around the size of two fists.