Petra digs up rare blue diamond

Miner Petra Diamonds yesterday revealed that it has recovered a rare blue diamond. The precious stone is 29.6 carats, and was found at its Cullinan mine in South Africa. The company says the stone is “one of the most exceptional” it has ever recovered at the mine, which is an important source of blue diamonds and has been owned by Petra since 2008. The rock could end up with a value in the tens of millions of dollars.