The Mellon Blue, a 9.51-carat fancy vivid blue diamond formerly owned by the US art collector Bunny Mellon, sold for $25.6 million at auction on Tuesday.

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

The gem sold for 20,525,000 Swiss francs at the Hotel des Bergues, having been estimated to fetch between 16 and 24 million francs.

Rahul Kadakia, who conducted the sale, said the price was evidence of the “elite appetite amongst collectors for extraordinary and storied gems”.

The stone, set in a serpentine ring, once belonged to Rachel Lambert Mellon, better known as Bunny Mellon, a US horticulturalist, philanthropist and art collector.

“The Mellon Blue is an outstanding stone,” said Max Fawcett, head of jewellery at Ch

See Full Page