A Hong Kong billionaire bought a rare, flawless "Blue Moon Diamond"  for a whopping  48.6 million Swiss francs ($48.4 million) on Wednesday in Geneva, setting a world record for an auctioned gemstone, according to Sotheby's auction house.

Billionaire and property tycoon Joseph Lau bought the 12.03 carat blue diamond for his 7-year-old daughter and renamed it "Blue Moon of Josephine" after her daughter.

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The sale comes a day after Lau spent $28.5 million to buy a rare 16.08-carat pink diamond  at Sotheby's rival auction house Christie's.

The Blue Diamond, cushion-shaped and mounted on a ring, has the top grading of fancy vivid blue and weighs 12.03 carats. The pre-sale estimate price of the rock was between $35 million to $55 million.

"It is a new record price for any gemstone and per carat," David Bennett, worldwide chairman of Sotheby's international jewellery division said at a press conference.

At rival auction house Christie's on Tuesday, a rare diamond of pink hue fetched $28.5 million, setting a new record for any pink diamond ever offered in auction.

The same Chinese tycoon bought that diamond and promptly named the stone "Sweet Josephine."

Bennet of Sotheby's called  the' Blue Diamond'' a 'magical stone' with its colour, shape, and purity almost perfect.

He said the sale broke the previous record held by the 24.78-carat  Graff Pink,  which fetched $46.2 million at the Sotheby's auction in November 2010.

Bennet said the blue diamond stone was found in a South African mine and was sold to Sotheby's by New York-based jeweller Cora International last year.

The blue hue of the diamond is due to the amount of the element boron present in its crystal structures.

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