Sotheby's has announced that, on November 13 in Geneva, it will offer the world's largest internally flawless vivid pink diamond, known as the Pink Star.

The most valuable diamond ever offered at auction, one of 'the earth's greatest natural treasures'

Estimated to realise in excess of $60m, the Pink Star is the most valuable diamond to ever be offered at auction. It is also the largest of its kind ever graded by the Gemological Institute of America.

"I have had the privilege of examining some of the greatest gemstones in the world over the past 35 years, and I can say, without hesitation, that The Pink Star diamond is of immense importance," commented Sotheby's David Bennett, chairman of jewellery.  

"It is difficult to exaggerate the rarity of vivid pink diamonds weighing only five carats, so this 59.60 carat stone is simply off any scale, and passes, I believe, into the ranks of the earth's greatest natural treasures."

The Pink Star is more than double the size of the 24.78 carat Graff Pink diamond that set the world record for any diamond at auction in November 2010, selling for $45.7m with Sotheby's.

The Pink Star was mined by De Beers in Africa in 1999, and it took the esteemed Steinmetz Diamonds two years to cut and polish it from its rough state.

It has previously been sold privately in 2007, but the details of the sale have not been disclosed.

Sotheby's is among the world leaders for jewellery sales, and will host two other important diamond auctions on October 7 in Hong Kong: an 118.2 carat white diamond is expected to see $25m-30m, while the world's largest fancy blue diamond - The Premier Blue - may set a record per-carat price.

Sign up to our free weekly newsletter to stay ahead of the latest jewellery and collecting news.