Mining company in South Africa finds rare blue diamond

A rare blue diamond has been unearthed at a mine in South Africa.

The 25.5-carat stone was recovered by Petra Diamonds at its Cullinan mine and is expected to bring large profits.

Experts say it could be worth more than $10m (£6m), and the find gave a boost to Petra's share price.

Similar finds in recent years from the Cullinan mine have commanded high prices and Petra, with operations in Botswana and Tanzania, is expecting a high level of interest from buyers.

"It's very unusual for a diamond of this quality and size to come to market," said company spokeswoman Cathy Malins.

The mine, north-east of Pretoria, has produced hundreds of large stones and is famed for its production of blue diamonds.

A similar 26.6-carat blue rough diamond discovered by the company in May 2009 was cut into a near perfect stone and fetched just under $10m at a Sotheby's auction.

It was named the "Star of Josephine" by its new owner.

Another deep-blue diamond from Cullinan was auctioned for $10.8m last year and set a world record for the value per carat.

The largest ever rough gem diamond was discovered at the Cullinan mine in 1905 and was presented to the British monarch Edward VII.

The 3,106-carat stone was then cut, with two of the principal diamonds forming part of the British crown jewels - the 530-carat First Star of Africa and the Second Star of Africa at 317 carats.