An extremely rare blue diamond sold for £6.2 million ($9.5 million) at a London auction on Wednesday, setting a new world record for price per carat.

The fancy deep-blue diamond weighing 5.30 carats sold at Bonhams Fine Jewellery sale in central London for a record $1.8 million per carat, beating the previous record of $1.68 million.

The diamond, which was bought by international diamond house Graff Diamonds, is set in a ‘Trombino’ ring made by Italian jeweller Bulgari around 1965.

“We are delighted with the price it has made,” said Jean Ghika, Director of Bonhams Jewellery. “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.”

The term “fancy” is used to describe a diamond of intense colour. The blue is derived from small amounts of boron impurities within the diamond.