GENEVA (Reuters) - An extremely rare, purple-pink diamond mined in Russia, which Sotheby’s described as “a true wonder of nature”, sold for $26.6 million Swiss francs on Wednesday, the auction house said.Sotheby’s had estimated that the flawless oval gem, “The Spirit of the Rose,” could fetch $23 millon-$38 million at the Geneva sale. Bidding opened at $16 million and climbed to the final hammer price of $21 million, plus commission. It was bought by a telephone bidder who chose to remain anonymous, Sotheby’s said. Jewellery expert Benoit Repellin, who led the sale, said it set a record for a diamond graded fancy vivid purple pink sold at auction. The stone weighing 14.83 carats was the largest pink diamond with that colour grading to go on the block.