(IDEX Online) - Petra Diamonds says revenue increased by a third (33 per cent) in the last quarter to $140.6m, driven by a surge in prices.The UK-based miner said like-for-like prices at its March tender were up 37.6 per cent on December and a 157.88ct Type IIa white stone from its Cullinan mine sold for $5.5m.CEO Richard Duffy spoke of a "positive outlook for the business" in a trading update published yesterday."Although we anticipate some pull back in diamond prices from the elevated March tender levels as a result of the economic impact of the war in Ukraine, the structural shift in the diamond market continues to provide positive momentum," he said.Despite the revenue increase, the number of carats sold was down 31 per cent during the quarter ending 31 March, and down 16 per cent on the YTD.Quarterly production was up 18 per cent to 830,456 carats, largely as a result of operations resuming at its Williamson mine, in Tanzania.Petra also operates the Koffiefontein, Cullinan (pictured) and Finsch mines, in South Africa.