---ADDS BROKER COMMENT AND SHARE PRICE---
Shares in Petra Diamonds (LON:PDL) were lifted after it uncovered an exceptional blue diamond - at a whopping 122.52 carats - from the famous Cullinan mine in South Africa.
It is the latest big find by Petra from the celebrated mine which lies in the foothills of the Magaliesberg mountain range - 37km north-east of Pretoria.
In February, a 29.6 carat diamond was sold for US$25.6 million, while a 25.5 carat diamond sold for US$16.9 million last year.
Petra said this latest stone will require further analysis to assess its potential value and will not be sold before the end of the firs's s current financial year, which ends June 30.
Broker RBC Capital said that with upward momentum behind the sector and the company, it had increased its price target to £2 (from £1.80) for Petra shares with an unchanged 'outperform' recommendation.
It expects the latest find to add to the firm's cash flow in 2015 estimates
"We believe the diamond sector has good long-term fundamentals, and Petra offers a growing production profile," said analyst Des Kilalea.
"We believe the company is well managed, though short-term risks in the South African labour situation are an issue.
"The company has restructured its balance sheet and appears on track to deliver expansion at its four major mines."
It was from Cullinan that the largest rough gem diamond ever found at 3,106 carats was uncovered in 1905.
The stone was cut into the two most important diamonds, which today form part of the Crown Jewels in the Tower of London.
The First Star of Africa is mounted at the top of the Sovereign's Sceptre and which at 530 carats is the largest flawless cut diamond in the world, and the Second Star of Africa, a 317 carat polished diamond which forms the centrepiece of the Imperial State Crown.
Blue diamonds are one of nature's most special treasures. They are so rare that there are no official statistics on their recovery.
Shares added 6.52% to stand at 178p each.