A rare blue diamond has been unearthed at a South African mine famed for being the source of some of the most valuable gems ever found.

Reuters reported that the 29.6-carat acorn-sized stone was discovered earlier this month at the Cullinan Diamond Mine near Pretoria. The mine, owned by the Jersey-based firm Petra Diamonds since 2008, is most famous for being the place where the 3,106-carat Cullinan diamond was discovered in 1905. Still the largest rough gem diamond ever found, the Cullinan diamond was eventually cut into nine pieces, the largest two of which -- the Great Star of Africa and the Second Star of Africa -- are among the Crown Jewels of the United Kingdom, held in the Tower of London.

More recently, the mine was also where a 25.5 carat blue diamond was found last year and sold for $16.9 million. In 2008, a diamond known as the Star of Josephine was also found at the mine and sold for $9.49 million.

Petra Diamonds chief executive Johan Dippenaar told Reuters that the latest discovery could be worth even more.

"By some margin ... this is probably the most significant stone we've ever, in terms of blue stones, recovered," Dippenaar said. "The stones in the last year or so are selling well above $2 million per carat. That's not my quote, that's updates in the market." Dippenaar said that the company would decide what to do with the diamond within the next week.

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