Mining company in South Africa finds rare blue diamond 18 April 2013 Last updated at 17:09 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. 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.