Rare 25.5 carat blue diamond found in South Africa

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 sell for more than $10,000,000.

"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 $10 million at a Sotheby's auction. Another deep-blue diamond from Cullinan was auctioned for $10.8 million last year and set a world record for the value per carat.

In 1905, the renowned Star of Africa blue diamond - the world's second largest cut diamond - was discovered at the Cullinan mine. The pear-shaped 530-carat stone was presented to King Edward VII and became part of the British crown jewels.