An extremely rare blue diamond was auctioned in Geneva for $21.5 million, auction house Sotheby's said, AFP reported.

The “Mediterranean Blue,” a fantastic bright blue diamond weighing 10.3 carats and worth an estimated $20 million, drew fierce bidding.

The auction started at $10.8 million and turned into a real battle before the diamond was sold to a private US collector, whose name was not disclosed, for $21.5 million, Sotheby's said.

The “Mediterranean Blue,” which is a brand new blue diamond recently mined from South Africa's legendary Cullinan mines, has caused a huge stir in the diamond industry since it was first announced in March.

Ahead of its final unveiling in Geneva, it was revealed as part of Sotheby's debut exhibition in Abu Dhabi last month, where it was displayed alongside seven other “exceptional” diamonds and gemstones totalling more than $100 million.

“At the top of the pyramid of rarity are the blue diamonds,” said Quig Bruning, Sotheby's head of jewelry for North America, Europe and the Middle East, at the Abu Dhabi show.

Having been an auctioneer at the event, Bruning described the gemstone as “unquestionably the defining stone of the season”. He stressed that the stone “ranks among the best blue diamonds we have sold”.

Tobias Cormind, head of Europe's largest online jeweller 77 Diamonds, was less optimistic, describing the sale as “less glamorous than expected”.

“The diamond surpassed its $20 million estimate, indicating that there was significant interest,” Cormind admitted.

“But broader uncertainties, including ongoing trade tensions between the US and China, may have lowered bidder confidence and dampened what could have been a more fired-up atmosphere,” he added. | BGNES