Geneva Rocks! 2 Nights, 2 Diamonds, 2 Auction Houses and 2 World Records Broken

On Tuesday night, Christie's Geneva rocked the auction world when the fabled 76.02-carat internally flawless Archduke Joseph Diamond fetched $21.48 million – a per-carat world record for a colorless diamond. On the next night, rival Sotheby's Geneva set its own world record when an unnamed 10.48-carat flawless deep-blue diamond sold for $10.86 million, the highest per-carat price ever paid for a blue diamond.

A product of the legendary Golconda mine in India, the cushion-cut Archduke Joseph Diamond shares its lineage with some of the largest and most spectacular diamonds ever discovered, including the 105.6-carat Koh-i-Noor, the 45.52-carat Hope, and the 140.64-carat Regent.

The stone, which is roughly the size of a large strawberry, was named for Archduke Joseph August of Austria (1872-1962), who passed the gem on to his son, Archduke Joseph Francis (1895-1957) in the early 1930s. The most recent owner was luxury jeweler Black, Starr & Frost.

The selling price exceeded pre-auction estimates by more than $6 million. "It is a world record for a Golconda diamond and a world record price per carat for a colorless diamond," Francois Curiel, director of the international jewelry department at Christie's, told reporters. The buyer wished to remain anonymous.

"My understanding is that this stone is going to a museum and it will probably be the centerpiece," said Black, Starr & Frost chairman Alfredo Molina.

At Sotheby's Geneva on Wednesday night, an exceptionally rare deep blue briolette diamond took center stage. Originally expected to fetch up to $4.5 million, the actual selling price of $10.86 million more than doubled the pre-auction estimates.

Reuters reported that London luxury jeweler Laurence Graff bought the drop-shaped stone after a lengthy and heated bidding war. About the size of an almond, the diamond weighs 10.48 carats and is the product of the famous Cullinan mine in South Africa.

"It is certainly a world record price per carat for a deep blue diamond," David Bennett, head of Sotheby's international jewelry department, told reporters after the sale. "It is an extraordinary stone, a very, very mystical deep blue."

Diamond experts speculated that the 10-carat briolette would be recut into a 7-carat vivid blue.