An unidentified Asian buyer paid a record US$3.07 million ($4.3 million) for a rare 2.52 carat Vivid green diamond at an auction in Geneva, auctioneers Sotheby's said.

Sotheby's said it was the highest price ever paid for a green diamond, which was also the largest of its kind ever to appear at auction.

Green and red diamonds are regarded as the rarest among coloured diamonds, but the Vivid Green nonetheless fell below the auctioneer's estimate of US$3.1 million to US$5.12 million.

However, a set composed of of a ruby and diamond necklace and matching earrings that belonged to a 19th century British duchess fetched US$5.77 million, five times its estimate, during the autumn jewellery sale in Geneva.

"The Roxburghe Rubies, a magnificent suite comprising a ruby and diamond riviere necklace and earrings, the property of Mary, Duchess of Roxburghe, attracted extraordinary pre-sale attention at exhibitions around the world both for the quality of the rubies and the significant historical provenance," said David Bennett, Sotheby's Chairman of Jewellery for Europe and the Middle East.

The necklace, made in 1884, was created with 24 cushion-shaped rubies and 24 similarly cut diamonds, mounted in silver and gold.