Petra sells 122.5-carat blue diamond for $28m

African diamond miner Petra Diamonds has announced it has raised $27.6m through the sale of a rare 122.52-carat blue diamond found at its Cullinana mine in South African in June.

The diamond, which Petra labelled as a "truly significant find", was sold for $225,269 per carat to a beneficiation partnership comprising Petra (15%) and its unnamed polishing partner (85%).

Petra said that the polishing partner will settle its 85% of the agreed value, being $23.5m, immediately and the miner will record this sum as revenue in its first-quarter results (year-end June 2015).

"We are pleased to have concluded this arrangement which records an excellent sales value for the rough stone, and also gives Petra exposure to the uplift in value post beneficiation," said chief executive Johan Dippenaar.

"We look forward to providing the market with further information on the stone's journey at the appropriate time in the future."

Cullinan, located in the foothills of the Magaliesberg mountain range near Pretoria, is said to be one of the world's most important sources of blue diamonds.

The mine, bought by Petra in 2008, is well known for the discovery of the Cullinan diamond in 1905, the largest rough gem diamond ever found at 3,106 carats, which forms part of the Crown Jewels in the Tower of London.