(IDEX Online) - Petra says like-for-like rough diamond prices rose by 46.5 per cent in the six months to December 2021 amid strong demand across all sizes and qualities.The UK-based miner today announced sales of $140.6m at Tender 4, an increase of almost 10 per cent on Tender 3. Last week it announced an interim figure for around 80 per cent of sales as it held Tender 4 in South Africa for the first time since the pandemic.Petra also provided figures showing per carat prices achieved form its three South African mines and one (Williamson) in Tanzania at Tender 4. Koffiefontein $856/ct; Williamson $369/ct; Cullinan $180/ct; Finsch $151/ct.Richard Duffy, chief executive of Petra, said: "Demand spanned the entire spectrum of rough assortments and sizes, with a notable increase in the price of larger stones - particularly the white D-colours, for which Cullinan is renowned, as well as fancy coloured diamonds. "Whilst we believe this market reflects the structural change in underlying supply and demand dynamics, which we expect to continue in the medium term, it is too soon to determine what impact the current conflict in Ukraine will have on the global economy and the diamond market specifically."Further tenders are planned for April and June. Pic courtesy Petra, shows Koffiefontein mine