(IDEX Online) - Petra's rough sales tally was down by almost 40 per cent at its latest tender. In March the UK-based miner sold 735,222 carats for $140.6m. In April it sold 635,806 carats for $86.1m, down by 38.8 per cent.Like-for-like rough diamond prices decreased by almost a quarter (23.7 per cent). Like-for-like prices at its March tender were up 37.6 per cent on December 2021.Per-carat prices at Koffiefontein, the loss making South African mine that Petra wants to sell, fell from $856 in March to $431 in April.Richard Duffy, Petra's chief executive, commenting on the company's overall performance, said: "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. Prices nevertheless remain above our December tender levels, providing for some consolidation in a diamond market that continues to be supportive."Highlight of its April tender was a 13.74-ct blue diamond, which sold for $5.7m in a partnership with Stargems.Pic courtesy Petra Diamonds