The previous record was held by the "Beau Sancy" (seen here), a pear-shaped diamond of 34.98 carats, sold by rival Sotheby's for 9 million Swiss francs last May.
"The market is not on the best form at the moment. The sale on Tuesday night was almost flabbergasting," Curiel said.
He added that the buyer, who bid by telephone, wished to remain anonymous, but said the last bidder to drop out of the sale was Fred Mouawad, an international dealer with offices in Dubai, the Middle East and Geneva.
The seller was Black, Starr & Frost, an American jeweller founded in 1810 and based in California.
"My understanding is that this stone is going to a museum and it will probably be the centrepiece," Black, Starr & Frost's chairman Alfredo Molina told Reuters in the Geneva saleroom.
Diamonds and gemstones are a safe refuge for investors in difficult economic times, he said. "There is a crisis and people don't trust governments and banks. Paper money is a depreciating asset," he added.
The diamond was the star lot at Christie's semi-annual jewellery sale in Geneva, which fetched 76.6 million francs, with 290 of 348 lots sold.
Image Courtesy: Wikimedia Commons