(IDEX Online) - Sotheby's is to sell a collection of eight blue diamonds with a combined value, based on its high estimates, of over $85m.The De Beers Exceptional Blue Collection - a total of just over 32 carats recovered from Petra's historic Cullinan mine, in South Africa - will be sold in Geneva, New York and Hong Kong from November 2022 to early 2023.The highlight is the De Beers Exceptional Blue 11.29, a step-cut fancy vivid blue, weighing 11.29 carats, with estimates of $28m to $50m.The collection has been cut from five rough diamonds weighing a total of 85.62 carats (ranging from 9.61 to 25.75 carats) that were jointly bought by De Beers and Diacore in November 2020.Four of the diamonds were GIA-graded as fancy vivid, the highest of all color gradings, and the De Beers Exceptional 3.24 carat diamond is internally flawless.Blue diamonds are a fabulous fluke of nature, produced by the random presence of the atomic lattice-bound trace element boron within the diamond's carbon structure during its formation deep in the earth's core. The full collection is:De Beers Exceptional Blue 11.29: a step-cut Fancy Vivid Blue, weighing 11.29 carats(est. $28/50 million) De Beers Exceptional Blue 5.53: a cushion brilliant-cut Fancy Vivid Blue, weighing 5.53(est. $11/15 million) De Beers Exceptional Blue 4.13: a step-cut Fancy Intense Blue, weighing 4.13 carats(est. 2.5/3.5 million) De Beers Exceptional Blue 3.24: a cushion brilliant-cut Internally Flawless Fancy Vivid Blue, weighing 3.24 carats(est. $5-8 million) De Beers Exceptional Blue 3.10: a cushion brilliant-cut Fancy Vivid Blue, weighing 3.10 carats(est.$4.5/5 million) De Beers Exceptional Blue 2.08: a cushion-cut Fancy Intense Blue, weighing 2.08 carats(est. $1.2/1.5 million) De Beers Exceptional Blue 1.50: a round brilliant-cut Fancy Intense Blue, weighing 1.50 carats(est. $750,000/1 million) De Beers Exceptional Blue 1.22: an oval brilliant-cut Fancy Intense Blue, weighing 1.22 carats(est. $600/800,000)Pic courtesy De Beers