A flawless 163-carat clear diamond fetched about $US34 million ($44.5 million) at Christie's in Geneva on Tuesday evening.
The diamond, the centrepiece of an asymmetric gem-studded necklace designed by Fawaz Gruosi, founder of Geneva jeweller De Grisogono, exceeded the auction house's expectation of $US25 million. The stone was the largest of its kind ever auctioned.
A team of 10 specialists in New York cut the jewel from a rough 404-carat stone discovered in Angola last year, the biggest diamond ever found in that country.
The necklace is made of 18 diamonds on one side and two rows of pear-shaped emeralds on the other. It took more than 1700 hours to create.
The Geneva autumn auction season concludes on Wednesday, when Sotheby's will auction a pink diamond worth as much as $US30 million.
Sotheby's holds the record for the most expensive diamond ever auctioned, having sold the 59.6-carat Pink Star for $US71 million to Hong Kong-based jewellery retailer Chow Tai Fook.