RAPAPORT... Rough prices tumbled at Petra Diamonds' latest tender as geopolitical challenges dented the market.The April sale realized $86.1 million, down from $140.6 million in March, the miner reported Tuesday. Like-for-like prices dropped 24%, but were 3.2% higher than in December. The average price fell 29% month on month to $135 per carat, according to Rapaport calculations, reflecting a weakening of the product mix."As anticipated, these prices were below the significant increase we saw in our March sales, reflecting the seasonally quieter period and the ongoing uncertainty around the impact of the conflict in Ukraine," said Petra CEO Richard Duffy.The company sold 635,806 carats at the tender, compared with 735,222 carats in March. The sale was Petra's fifth of the fiscal year, which runs through June 30. The miner intends to hold another tender in June.During the event, a blue diamond weighing 13.74 carats from the Cullinan mine sold for $5.7 million as part of a partnership between Petra and diamond supplier Stargems, with the miner set to receive 50% of the profits from the resulting polished. This follows similar collaborations between the two companies on a 342.92-carat, white diamond and an 18.30-carat blue.Image: The processing plant at Petra's Williamson mine in South Africa. (Petra Diamonds)