Petra Diamonds, which is emerging from a difficult year for the diamond industry that plunged the company into annual loss, has announced the discovery of a 507-carat white diamond that could singlehandedly improve its finances.

In the year to June 30, Petra, one of a new breed of independent diamond producers, increased production due to its strategy of buying old African diamond mines from De Beers, the industry leader, in an effort to extend their life on a lower cost base.