The sale by Southern African diamond mining company Petra Diamonds of an exceptional blue diamond in its fifth tender cycle lifted the average prices per carat received 22% higher than those of the prior Tender 4 sale. The London Stock Exchange-listed company, headed by CEO Richard Duffy, reported on Tuesday that the price upliftment was the result of a remarkable14.76 ct exceptional clarity diamond, recovered from Cullinan diamond mine in Gauteng, fetching $8.2-million.