David Bennett, chairman of Sotheby's jewellery division in Europe and the Middle East, said the diamond belonged in "the ranks of the earth's greatest natural treasures".
"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," he said in a statement.
The sparkling oval-cut rock, which has received the highest possible colour and clarity rating from the Gemological Institute of America (GIA), was presented to reporters Wednesday and will be part of the auction house's Magnificent Jewels auction in Geneva on November 13.
Set on a ring, the gem measures 2.69 by 2.06 centimetres (1.06 by 0.81 inches), and weighs 11.92 grammes (0.026 pounds). It would rake in around $5.0 million per gramme or $1.0 million per carat if Sotheby's receives its asking price.
At a luxury Geneva hotel, amid tight security, a model gracefully turns her hand to allow the glimmering stone to catch the light.
"It's very flattering, it's very feminin. It's the colour of rose champagne," Bennett told AFP.
Listed as an internally flawless fancy vivid pink diamond, the now plum-sized shimmering gem was 132.5 carats in the rough when it was mined by De Beers in Africa in 1999, Sotheby's said, not specifying which African country it came from.
It was then cut and polished over a period of two years by Steinmetz Diamonds, and was called the "Steinmetz Pink" when it was first unveiled to the public in 2003.
The all-but translucent rock was renamed after it was first sold four years later for an undisclosed sum to an unidentified buyer.
In addition to receiving the highest colour and clarity ratings possible for pink diamonds, the rock falls into a rare subgroup of stones with the chemically purest diamond crystals and often extraordinary optical transparency, comprising less than two percent of all gem diamonds, according to the GIA.
"The occurrence of pink diamonds in nature is extremely rare in any size," GIA senior vice president Tom Moses said in the statement, pointing out that "polished pink diamonds over 10 carats very rarely occur with an intense colour."
The "Pink Star" is the largest in its category to ever be graded by the institute and is more than twice the size of the 24.78-carat "Graff Pink" diamond that set the world auction record for a diamond and any gemstone or jewel when it was sold at Sotheby's in Geneva in 2010 for $46.2 million.
The diamond was among the world's rarest diamonds shown in an exhibit at the Smithsonian Institution in Washington DC in 2003, that also included the De Beers Millennium Star, the Allnatt diamond and the Moussaieff Red.
It was also the star attraction at a London Natural History Museum exhibit of diamonds in 2005 and 2006.
Before going under the hammer in November, the "Pink Star" will go on a worldwide tour of cities including Hong Kong, New York, London, Zurich and Geneva, Sotheby's said.