GENEVA - A plum-sized diamond known as the "Pink Star" goes under the hammer Wednesday in Geneva in an auction hoped to rake in US$60 million (S$75 million), the highest price ever for a gemstone.
The Sotheby's auction comes a day after rival house Christie's sold an almond-shaped diamond dubbed "The Orange" for US$35.5 million, also a record in its category.
The world's biggest pink diamond, the "Star" belongs to "the ranks of the Earth's greatest natural treasures," said Sotheby's David Bennett.
"It's really extraordinarily rare," Bennett, the chairman of Sotheby's jewellery division in Europe and the Middle East, told AFP of the gem glimmering inside a well-guarded showcase.
"Very, very few of these stones have ever appeared at auction."
The flawless 59.60-carat pink diamond is the largest in its class ever graded by the Gemological Institute of America (GIA), with the second biggest less than half its size, he said.
The sparkling oval-cut rock, which has received the highest possible GIA colour and clarity rating, will be part of the auction house's Magnificent Jewels auction at a luxury Geneva hotel Wednesday evening.
Set on a ring, it measures 2.69 by 2.06 centimetres (1.06 by 0.81 inches), and weighs 11.92 grammes (0.026 pounds). It would earn Sotheby's around $5.0 million per gramme or $1.0 million per carat if it fetches its asking price.
Bennett described the estimate as "very reasonable".
"The international demand for exceptional diamonds keeps on growing," he said.
Three years ago, Sotheby's set a record when it sold the "Graff Pink" diamond for US$46.2 million dollars. Half the size of the "Pink Star", it came from a private collection and had not been on the market for 60 years.
"That was an unequalled price for any diamond or jewel ever sold at auction," said Bennett.