A rare pink diamond, described as "full of fire and light," and one of the earth's "greatest natural treasures," could fetch a record of more than $60 million at auction in November, Sotheby's said.
The "Pink Star", which weighs a whopping 59.60 carats, is the most valuable diamond offered at auction, said the auction house.
The oval stone with the top grading of vivid pink was put on display amid tight security at a luxury hotel in Geneva, Switzerland on Wednesday.
"It is full of fire and light. If it sells it will be a record price for any gemstone so far at auction," David Bennett, chairman of Sotheby's jewelry division in Europe and the Middle East, told Reuters in Geneva, where it will be the star lot of the Nov. 13 sale.
"The top end in all categories in auction prices are very, very strong. People are seeking the very rare, the exceptional, the outstanding. This stone is," he said.
The current record is held by the "Graff Pink", a 24.78 carat fancy intense pink diamond bought by Laurence Graff, the London-based jeweller known as "The King of Diamonds", at a 2010 auction for 45.44 million Swiss francs ($45.75 million then).
The "Pink Star" was cut and polished from a 132.5 carat rough diamond mined by De Beers somewhere in Africa in 1999, according to Sotheby's, which said it had no information on the exact geographic origin.
The stone, mounted on a ring, was first sold in 2007 and the current owner remains anonymous, a Sotheby's spokeswoman said.
Bennett said the vivid pink diamond is "of immense importance" because of its extraordinary size and exceptionally rich color that surpass all others known to exist in government, royal or private collections.
It is "simply off any scale, and passes, I believe, into the ranks of the earth's greatest natural treasures."
Eric Valdieu, a former Christie's jewel expert now of Valdieu Fine Arts, recalls seeing the "Pink Star" displayed at the Smithsonian Institution in Washington in 2003.
"The buyers of a stone like this are very few, international fortunes in Latin America, Asia or the Middle East," he said.
Rival auction house Christie's is offering three jewels from the collection of Bolivian tycoon Simon Itturi Patino among the pieces going under the hammer at its Geneva sale on Nov. 12.
The pieces, including a 1930s emerald and diamond necklace by French jeweller Cartier estimated at $7 million to $10 million, feature rare gems and embody the taste of "The King of Tin" who founded the family dynasty, the private auction house owned by French billionaire Francois Pinault said in a statement.
"The Patino family had extraordinary things, objects which dealers and private collectors will go after with gusto," Valdieu said.
(The Associated Press contributed to this report)