A model poses with the Pink Star diamond at Sotheby's auction house in central London. "It is difficult to exaggerate how rare this is," said David Bennett, as the largest pink diamond ever graded went on display. Sotheby's estimated the 59.6 carat stone would sell for more than £37 million (HK$464 million). If that happens, it will be an auction record for any jewel, set by the Graff Pink, which was bought for £28.5 million in 2010. "This is a very exciting diamond," said Bennett, chairman of Sotheby's European jewellery division. "Apart from the words about how rare it is, it's just such a beautiful stone. Pink diamonds, in my experience, are the most desired of all the colours." The stone was mined in Africa by De Beers in 1999. It was sold privately in 2007.