The Oppenheimer Blue, the largest and finest fancy vivid blue diamond ever offered at auction, sold for a world record 56.837 million Swiss francs (NZ$85.20 million) after dramatic see-saw bidding, Christie's says.
"It's the most expensive jewel ever sold at auction," Christie's spokeswoman Alexandra Kindermann told Reuters.
The rare rectangular-cut stone, which weighs 14.62 carats, previously belonged to Sir Philip Oppenheimer, who controlled the Diamond Syndicate in London.
It had a pre-sale estimate of between US$38 million and US$45 million (NZ$56.19 million to NZ$66.54 million).
The packed Geneva saleroom broke into applause as Rahul Kadakia, Christie's international head of jewellery, brought down the hammer after two phone bidders ended a 20-minute battle for the gem. The buyer's identity was not immediately known.