Sotheby's expects over $33 million for world's largest, rarest, flawless round diamond

Sotheby's unveiled Thursday what it calls the "world's largest, rarest and most valuable D-Flawless round white diamond to have ever been offered for private sale, with experts predicting the gem could fetch over $33 million.

The 102.34-carat white diamond, mined by De Beers in Botswana, is the only known round brilliant-cut gem over 100 carats perfect according to every critical criterion, said Sotheby's.

In addition to the high number of carats, the stone is also perfect in colour, clarity and cut ever graded by the Gemological Institute Of America (G.I.A.), the auction house noted.

The stone is also part of an ultra-rare subgroup of gem-quality diamonds known as Type IIA, signalling chemical purity and making it crystal-clear to the eye. (Image courtesy of Sotheby's.)

The stone, which is about the size of a large strawberry, belongs to an ultra-rare subgroup of gem-quality diamonds known as Type IIA, signalling chemical purity and making it crystal-clear to the eye.

To date, only seven D-colour diamonds weighing more than 100 carats have ever been sold at an auction, and none of them have been round brilliant cuts. Diamond cutters usually prefer to maximise the yield from a rough stone by producing a pear or emerald-cut stone.

The diamond, currently on display at Sotheby's London showroom, is about 61 carats smaller than the one which currently holds the title of the world's most expensive D-Flawless diamond - An 163.41-carat emerald-cut part of a De Grisogono necklace that sold for $33.7 million in Geneva last year.

The 163-carat flawless emerald stone part of a De Grisogono necklace that sold for $33.7 million in Geneva last year. (Image: PRNewsfoto | de GRISOGONO.)

But Sotheby's Diamonds believes the rock will "greatly exceed" that price, currently a world-record, due to its exceptional quality and rarity.

The Pink Star holds the world's auction record for any diamond (Photo: Sotheby's.)

The auction record for any diamond is held by the "Pink Star," which sold for $71.2 million at Sotheby's Hong Kong in April last year.