"Simply put, it has everything you could ever want from a diamond: the classic shape begs to be worn, while the quality puts it in an asset class of its own," said Lisa Hubbard, Chairman of North and South America for Sotheby's International Jewellery Division, in a press release.

The uncut diamond weighed over 200 carats.

The massive gem will lead the house's Magnificent Jewels auction, culminating a six-city exhibition tour that included stops in Dubai, London and Hong Kong. (Other highlights include colored diamonds, a collection of Kashmir sapphire jewelery and several Art Deco pieces from Cartier.)

"People everywhere have been drawn to it from across the room and they are in awe of its size, particularly when they put it on their hand," says Gary Schuler, the head of Sotheby's jewelery department in New York. "They can't believe there's a diamond this pure of such impressive scale."

Diamonds classed as flawless -- free of internal defects under intense magnification -- are extremely rare, especially at larger sizes.

Only five other flawless diamonds over 100 carats have ever been sold at auction, according to Sotheby's, including an 118.28 carat oval diamond that sold for $30.6 million at a Sotheby's Hong Kong auction in 2013.

The rough diamond, which was mined by De Beers in southern Africa, originally weighted over 200 carats, and was carefully refined for more than a year before it got to its current size and cut.

"A classic emerald cut like this one allows for a wide expanse of pure material to be viewed without the distraction of a more complex facet arrangement," Schuler says. "It's almost like looking at the glimmer of a reflecting pool."

Sotheby's estimates that the auction, which features more than 350 other pieces, is estimated to achieve more than $50 million in sales.(CNN)