The "sensational" 163.41-carat flawless diamond, suspended from an emerald and diamond necklace called The Art of Grisogono, will be one of the highlights at the Christie's autumn jewel auction.
"To date, this is the largest D flawless diamond ever to appear for sale at auction," Christie's said when it first announced the gem would be part of its annual Magnificent Jewels sale.
The auction house said it expected the "masterpiece of unparallelled beauty and exquisite workmanship" to fetch around USD 25 million (21.2 million euros), with other experts saying it could rake in double that amount.
The rough was analysed in Antwerp and cut in New York, where a team of 10 diamond-cutting specialists were involved in mapping, plotting, cleaving, laser-cutting and polishing the giant rough rock into a polished, flawless diamond.
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A team from Swiss luxury jeweller de Grisogono then created 50 different designs around the 163.41-carat diamond, before opting for an asymmetric necklace with the stone as its centrepiece.
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.
"The Art of de Grisogono is one fabulous Christmas present and wallflowers need not apply," Tobias Kormind, head of the 77 Diamonds firm that tracks the global diamond market, said in a statement.
He pointed out that when rival auction house Sotheby's sold an 118.28-carat flawless D diamond in 2013, it was sold for USD 30.6 million.
Another highlight of today's auction is the "Le Grand Mazarin", a 19.07-carat light pink diamond, which was once set in the crowns of numerous French kings and emperors, including Napolean.
The gem was named after Cardinal Mazarin, an Italian cardinal and diplomat, as well as a great art collector, who served as chief minister under Louis XIII and Louis XIV, and who bequeathed it and other diamonds to the Sun King in his will.