An 11.15 carat pink diamond expected to be auctioned off for over $21 million

A dazzling pink diamond described as the second largest internally flawless diamond to ever appear, could fetch more than $21 million when it goes under the hammer in Hong Kong in October, auction house Sotheby's has said. The auction house believes that it has the potential to set a new per carat price record for a fancy vivid pink diamond.

The 11.15 carat cushion-shaped gem is called "Williamson Pink Star" in tribute to two other pink diamonds and was unveiled by the auction house on Wednesday.

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One is the "CTF Pink Star" which sold for a record $71.2 million at auction in 2017. The other is "Williamson" stone, a 23.60 carat diamond given to Britain's Queen Elizabeth as a wedding gift by Canadian geologist John Thorburn Williamson. The monarch wears it in a Cartier brooch and was discovered in his mine in Mwadui, Tanzania. The "Williamson Pink Star" also originates from that mine.

"(Pink diamonds) are exceptionally rare in nature...," Kristian Spofforth, Sotheby’s head of jewellery, told Reuters at a press preview.

"You then add in the extra factors like it being over 10 carats, internally flawless and Type IIA, and you get right down to the pinnacle," he added referring to a subgroup of the most chemically pure diamonds.

Spofforth expects several bids for the gem when it is offered for sale in a standalone auction on October 5.

"There is always going to be a demand for rarity," he said.

“This diamond is a work of art from mother earth and a wonder of nature. It’s comparable to a Monet or a Picasso and is even more rare," Wenhao Yu, chairman of Jewellery and Watches at Sotheby’s Asia, told Forbes.

Before it goes on auction, the "Williamson Pink Star" will go on a tour to Dubai, Singapore and Taipei.

(With inputs from agencies)