An "outstanding vivid blue" 29.6 carat blue diamond has been recovered from Petra Diamonds' (LON:PDL) Cullinan mine in South Africa.
"Blue diamonds are among the rarest and most highly coveted of all diamonds and the Cullinan mine is the most important source of blues in the world," the FTSE 250 miner said in a brief statement.
"This stone is one of the most exceptional stones recovered at Cullinan during Petra's operation of the mine."
VSA Capital said there were "bound to be comparisons made in quality with the Cullinan diamond which is a far larger, but blue-white stone, which now resides in the Tower of London mounted to the Queen’s sceptre".
City broker Canaccord noted that last year Petra recovered a 25.5 carat blue diamond from Cullinan that was sold for US$16.9mln.
"In 2009 the company recovered a 26.6 carat from the mine, which yielded an internally flawless 7.03 carat polished stone, named 'Star of Josephine'," said analyst Dmitry Kalachev.
"It was sold for US$9.5mln at a Sotheby’s auction, achieving a record price per carat."
The broker keeps its buy stance and 163 pence a share target.
In the firm's first half results, Canaccord expects production of 1.56mln carats (up from 1.25mln in H1/13FY), revenue of US$173mln and a net debt position of US$135mln.
Petra shares edged up 0.08% on Tuesday to stand at 122.60p each.