The company said that the optimal route to market for the stone will be identified following an analysis to evaluate its potential value.
The diamond will not be sold before the end of the company’s current fiscal ending 30 June 2014.
Petra said in a statement, "The rarity of a blue diamond of this magnitude sets it apart as a truly significant find."
The latest diamond discovered comes after the company sold a 29.62ct blue diamond from the same mine for over $25m.
Petra Diamonds initially bought a 37% stake in the Cullinan mine from De Beers in 2008 and increased its interest to 74% in late 2009 with the acquisition of Al Rajhi’s holding in the mine.
The company continues to mine the underground resource using block cave mining methods.
Since 2008, Petra has recovered various diamonds, including a 39ct blue diamond sold for $8.8m, a 26ct blue diamond sold for $9.4m in 2009, a 507ct white diamond sold in 2010 for $35.3m and a 25.5ct blue diamond sold for $16.9m in 2013.
Image: The 122.52 carat blue diamond recovered at the Cullinan mine. Photo: courtesy of Petra Diamonds Limited.
