Huge Mellon Blue diamond sells for $25.6 million

The huge Mellon Blue - a 9.51-carat blue diamond – went under the hammer on Tuesday and sold for $25.6 million.

It was once owned by US art collector Bunny Mellon.

The diamond was sold by auctioneers Christie's in Geneva as part of its Magnificent Jewels sale in the Swiss city, reports AFP.

The gem sold for 20,525,000 Swiss francs at the Hotel des Bergues.

"The Mellon Blue is an outstanding stone," said Max Fawcett, head of jewellery at Christie's in Geneva.

"More than that, though, it has also become symbolic of a lifestyle of a bygone era -- the type only possible with a Gilded Age fortune."

The giant blue rock, which is set in a serpentine ring, was once the property of Rachel Lambert Mellon (Bunny Mellon), a US horticulturalist, philanthropist and art collector.

The stone is graded as internally flawless, adds AFP.

The diamond was reportedly last seen in 2014, when it was auctioned for more than $32 million, after Bunny’s death.

This time around, the sale price didn’t rise to the point expected, Tobias Kormind, managing director of Europe's largest online diamond jeweller 77 Diamonds, believes. He explained in a statement: "Geopolitical tensions... and a weakened Chinese economy that kept many usual buyers away, left the room distinctly cautious," he said.

"Whether this restraint will ripple through the rest of the Geneva season remains to be seen."

Sotheby's is holding its annual Royal and Noble Jewels sale in Geneva on Wednesday.

Among the artefacts up for auction is a brooch seized from Napoleon Bonaparte as he fled the Battle of Waterloo in 1815, valued at $150,000 to $250,000. And a 10.08-carat The Glowing Rose pink diamond, which is expected to fetch about $20 million.