Petra’s sparkling discovery

The South African mine which produced the world's largest diamond, the 3100 carat Cullinan Diamond part of which sits in the Queen's sceptre, has produced another monster.

Petra Diamonds, the Aim-listed miner, said today it has discovered a 507-carat diamond at its Cullinan mine. That will put the new find in the top 20 largest diamonds ever dug out of the ground. Uncut and as yet unnamed, it is reckoned to be of a very high quality.

It is reckoned the stone should fetch more than the Light of Letseng, a 478-carat white diamond found by rival Gem Diamonds which was sold last year for $18.4 million (£11.5 million).

A collapse in the value of rough diamonds left Petra Diamonds nursing a 10% fall in sales to $69 million in the year to the end of June.

Underlying profits dived 80% to $7.8 million while write offs took the bottom line to a $89 million loss.