Martin Potts, an analyst at FinnCap, says that this stone may break the record price paid for a rough diamond. The current record holder, a 507 carat white stone, fetched $35.3m in February 2010.
The only bad news for Petra is that they can not sell the stone in the year ending 30 June 2014, as Potts says "it will require considerable analysis before Petra is in a position to sell it".
On the back of the news FinnCap has moved its price target for the company up from 171p to 180p. Shares in the company were up by more than six per cent at pixel time, as traders greeted news of another high value find for the FTSE 250 firm.
Since Petra acquired the mine in 2008, it has produced four high value blue diamonds, fetching a total of just shy of $60m. Cullinan has now produced over 750 stones weighing more than 100 carats, 130 stones weighing more than 200 carats, and around a quarter of all diamonds weighing in excess of 400 carats.
Analysts at Investec suggest that the pictures released by Petra don't "appear to be as vivid" as the last special stone recovered by the company, a 29.6 carat exceptional blue stone which went for $26m.
As a result the stone may not attain the same value per carat, "but even if it's a quarter of the value per carat it could still be worth around $26m" as a result of its much larger mass.