An extremely rare fancy deep-blue diamond weighing 5.30 carats sold at Bonhams Fine Jewellery sale in London for £6.2 million ($9.5 million 7.3 million euros) on April 24th, setting a new record price of $1.8m per carat.

The previous world record price per carat for a blue diamond was $1.68m. This rare gem was bought by Graff Diamonds, the international diamond house headquartered in New Bond Street. London. Bidding came from round the world via 25 telephone lines as well as bidders in the packed saleroom.

The fancy deep-blue diamond is set in a ‘Trombino’ ring made by Bulgari, the renowned Italian jeweller favoured by Hollywood film stars, and the epitome of fashion and innovation during the 1960s. The ring was made circa 1965 and had been estimated to fetch £1,000,000 to £1,500,000 at the Bonhams auction.

Jean Ghika, Director of Bonhams Jewellery Department for Europe commented after the sale: “We are delighted with the price it has made. It was a sensational stone which charmed everyone who viewed it prior to the sale. Blue diamonds, especially those over 5.00 carats, are extremely rare to see on the market and continue to be highly sought-after. We are honoured to have handled the sale of such a unique gem.”

Blue diamonds are very rarely seen on the market and fancy-coloured diamonds are among the most valuable and sought-after in the world. They have delighted royals and celebrities over the centuries, with the most famous blue ‘Hope Diamond’ bought by King Louis XIV of France in the late 17th Century. The stunning 45.52-carat diamond, originating from India was eventually stolen from the Crown Jewels by thieves in the French Revolution and then smuggled to London, finally coming to rest in the Smithsonian Natural History Museum in Washington, D.C.

The Bulgari ring features a cushion-shaped fancy deep-blue diamond, weighing 5.30 carats. It is set horizontally within a mount pavé-set with brilliant-cut diamonds and courses of baguette-cut diamonds.

The term “fancy” is used to describe a diamond of intense colour and the colour “fancy deep-blue” is one of the rarest. The extraordinary colour blue is derived from small atoms of boron mixing with the carbon atoms in a diamond, affecting the absorption of light passing through the stone and lending it a blue appearance. Blue diamonds are structurally very pure and account for less than one per cent of all diamonds mined.