(IDEX Online) - Two more diamonds from the De Beers Exceptional Blue Collection have failed to sell at auction.A 3.24-carat cushion brilliant-cut internally flawless fancy vivid blue, with a $5m to $8m estimate, was withdrawn before the sale at Sotheby's New York last week.And a 2.08-carat cushion-cut fancy intense blue, with a $1.2m to $1.5m estimate failed to find a buyer at the same auction.Last month the first of eight stones in the collection - a 5.53-carat cushion brilliant-cut fancy vivid blue with an estimate of $11m to $15m failed to sell at at Sotheby's Geneva.The stones, weighing a total of just over 32 carats, had a combined value, based on Sotheby's high estimates, of over $85m.They were all recovered from Petra's historic Cullinan mine, in South Africa - and are being sold in Geneva, New York and Hong Kong.So far, the first three stones have not sold. Sotheby's say it still plans to offer the remaining five for sale.Pic courtesy Sotheby's