Africa-focused diamond miner Petra Diamonds said it was upbeat about market conditions as it recorded 'solid prices' in its December tender of stones.The company had reported in November that it had recovered "two exceptional white stones" at 126.4 carats and 91.5 carats.It confirmed on Friday that they were sold at $8.52m and $3.78m, respectively."These solid prices achieved for the two special Cullinan stones as well as for the balance of Petra's recent tender are very encouraging and reaffirm Petra's view that firmer market conditions will continue into the second half of the 2014 full-year," said Chief Executive Johan Dippenaar.The stock was 0.38% higher at 113.53p in early trading.BC