'Once in a blue moon diamond' could fetch over $70 million

A Sotheby's employee displays the rare Blue Moon Diamond.
A Sotheby's employee displays the rare Blue Moon Diamond.EPA

GENEVA (REUTERS) - A large blue diamond, one of the world's rarest, could fetch US$35-55 million (S$49-77 million) at auction next week, Sotheby's said on Wednesday, as an industry group reported strong prices for colour diamonds ahead of the holiday season.

The Nov 11 sale also features a Cartier pearl and diamond tiara - estimated at up to US$450,000 - that survived the sinking of the Lusitania cruise liner 100 years ago, and a 15.20 carat fancy orange-pink diamond pendant owned by former James Bond actor Sir Sean Connery, estimated at US$1.2-US$2.4 million.

The flawless "Blue Moon Diamond", which weighs 12.03 carats and is mounted on a ring, is the star lot of more than 500 on offer at Sotheby's semi-annual jewellery sale in Geneva.

"The market for vivid blue diamonds of this level, it's so rare. Each stone is individual, in a sense," David Bennett, worldwide chairman of Sotheby's international jewellery division, told Reuters.

"The GIA (Gemological Institute of America) graded 400 blue diamonds and only four of the 400 were graded (fancy) vivid blue. So even amongst this extremely rare class of blue diamonds, to get one vivid blue, 12 carats, internally flawless, is once in a blue moon," he said.

The stone was discovered in South Africa's famed Cullinan mine in January 2014 and cut into a cushion shape from a 29.62 carat rough crystal.

Its current owner, New York-based jeweller Cora International, bought it from Petra Diamonds, the mine's owner, according to Sotheby's.

"You're looking at something that, by a freak of nature, has been brought up by a volcano. It's just so extraordinary that this diamond would have stayed forever, miles under the earth's surface... It's like the most secret part of the earth has just been shown to us," Bennett said.

In the third quarter of 2015, the best performing fancy colour diamonds were vivid blues, whose price rose up to 6 per cent over the previous quarter, while prices for white diamonds showed declines of 6 to 10 per cent, the Fancy Colour Diamond Index said in an overnight statement.

The index is published by the Fancy Colour Research Foundation, a non-profit industry-backed group based in Israel that tracks wholesale pricing data for yellow, pink and blue fancy colour diamonds in Hong Kong, New York and Tel Aviv.

A 8.48-carat "pigeon's blood" ruby ring that was given to the last Queen of Italy, Maria-Jose, for her wedding to Crown Prince Umberto in 1930 is estimated at US$6 million-US$9 million, Sotheby's said.

At rival Christie's sale on Nov 10, the largest cushion-shaped fancy vivid pink diamond ever to come to auction is estimated at 22-to-27 million Swiss francs (S$31-38 million).