(Corrects currency conversion in six paragraph)
By Stephanie Nebehay
GENEVA A flawless vivid blue diamond weighing 7.03 carats sold on Tuesday for a record 10.5 million Swiss francs (6.2 million pounds), the highest price paid per carat for any gemstone at auction, Sotheby's said.
The rectangular-shaped blue stone, the rarest to enter the international market this year, went to an anonymous buyer bidding by telephone after hectic bidding see-sawed between two callers for 15 minutes.
It was the centrepiece of its semi-annual sale in Geneva, conducted by David Bennett, chairman of Sotheby's jewellery department in Europe and the Middle East, who said the results showed the market's resilience despite the economic downturn.
"This is already a new world record price for a fancy vivid blue diamond and a new world record per carat for any gemstone (at auction)," Bennett told reporters.
"It is fantastic in this market and shows that these rare things are very much in demand," he said.
The final price includes a commission paid by the buyer to the auction house. The stone sets a record price per carat for any gemstone sold at auction of $1,349,752, (890, 275 pounds) Sotheby's said.
The previous record price for a fancy vivid blue diamond was $7.9 million, including commission, for a stone weighing 6.04 carats at sale in Hong Kong in October 2007, also by Sotheby's.
The new owner will have the right to name the stone, which is mounted in a platinum ring. The pre-sale catalogue estimate was 6.8 million to 10 million francs, excluding commission. The hammer price excluding commission was 9.3 million francs.
It was put up for sale by London-listed Petra Diamonds, which extracted it last year from the historic Cullinan mine in South Africa, the world's most regular supplier of blue diamonds of size and quality. Blue are the rarest of the diamond family after reds.
"To have a stone mined last year and cut the early part of this year so it is absolutely virgin coming straight from the mine has never happened before," Bennett said. "This is one of the extremely rare substances in our universe."
The sale fetched a total of 39.5 million swiss francs for 266 lots which found new owners, while another 80 pieces were stranded on the block.
"In this general economic environment to see $35 million worth sold in a session shows a lot about the resilience of fine jewels no matter what the climate," Bennett said.
Fresh stones to the market, including coloured diamonds, fetched good prices, the Briton said.
(Editing by Jonathan Lynn and Jon Boyle)