The rough stone, the largest ever discovered in the African country, originally weighed 404 carats and measured over 7 centimetres in length.
A flawless 163-carat clear diamond fetched about $US34 million ($49.4 million) at Christie's in Geneva.
The world's largest colourless diamond to go on auction is unveiled by Christie's auctioneers in Geneva, Switzerland. It has been set in a necklace which has been called The Art of de Grisogono.
The diamond was first taken from a 404-carat stone that was found in the African nation of Angola a year ago.
The auction house said it expected the "masterpiece of unparalleled beauty and exquisite workmanship" to fetch around $25 million (21.2 million euros), with other experts saying it could rake in double that amount.
A team of more than 10 specialists from the Julius Klein Group in NY transformed the rough diamond into the final cut and polished gem.
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"I am disappointed that the Art of De Grisogono didn't sell for a more dazzling price", said Tobias Kormind, head of 77Diamonds.com, a London-based online jeweller.
The left side of the necklace is made up of 18 emerald-cut diamonds and the right side composed of two rows of pear-shaped emeralds. It took more than 1,700 hours to create.
Diamond cleaver Ben Green analysed the gem for months and eventually started working on splitting the rough diamond in two in June past year. This is the first time that the spectacular diamond has been sold at public auction since the famous sale of the French Crown Jewels in 1887.
The gem was named after Cardinal Mazarin, an Italian cardinal and diplomat, as well as a great art collector, who served as a chief minister under Louis XIII and Louis XIV, and who bequeathed it and other diamonds to the Sun King in his will.
The stone was 40% bigger than a diamond Sotheby's sold in 2013 for about $31m, he said.