(IDEX Online) - Five blue diamonds weighing a total 85.6 carats has been sold to to a partnership between De Beers and Diacore for just over $40m.The Letlapa Tala Collection, from Petra's iconic Cullinan mine, in South Africa, were offered at a competitive tender.The miner said it was the first time five rough blue diamonds of significant size, colour and clarity had been offered for sale at one time.The collection takes its name from the local word for "blue rock" and comprises five Type IIb blue diamonds of 25.75, 21.25, 17.57, 11.42 and 9.61 carats in size.De Beers and the South African wholesaler and manufacturer Diacore agreed to pay of $40.36m in cash prior to delivery of the stones."The result of this special tender affirms the very high value placed on blue diamonds, which are undoubtedly one of nature's rarest treasures," said Richard Duffy, Petra's chief executive.