Petra said the diamond, unearthed at its South African Cullinan mine, was “high quality” and of “top colour”.
Blue diamonds are extremely rare and highly coveted.
A similar 26.6 carat stone, also found at the Cullinan mine, was auctioned at Sotheby’s in 2009 for $9.49m. Last year, a 10.48 carat blue diamond, also from the Cullinan mine, sold for $10.8m.
“If [the 2009 sale] is anything to go by, a similar number may be expected to go straight to the bottom line. A nice result and potential to increase our 2013 earnings per share to five cents, from three cents,” Numis Securities said.
Petra Diamond’s shares closed up one per cent at 108.8p yesterday.