A rare blue diamond sells for record $48.5 million at auction

Sotheby’s says a rare blue diamond has sold for a record $48.5 million at a Geneva auction, including fees.

The 12.03-carat Blue Moon diamond, set in a ring, is said to be among the largest known fancy vivid blue diamonds and was the showpiece gem at the auction Wednesday in Geneva. The pre-auction estimate was $35 million to $55 million. Applause broke out in the packed auction room after the hammer came down at a price of 43.2 million Swiss francs, excluding fees.

The Blue Moon — so-called in reference to its rarity, playing off the expression “once in a blue moon” — topped the previous record price of $46.2 million set five years ago by the Graff Pink.

On its Twitter account, Sotheby’s said the jewel was purchased by a Hong Kong private collector and promptly renamed the Blue Moon of Josephine,”= similar to the name given to a pink diamond ring that sold for $28.5 million at Christie’s in Geneva a day earlier, Sweet Josephine. That also was bought by a Hong Kong collector who was not publicly identified.

The polished blue gem was cut from a 29.6-carat diamond discovered last year in South Africa’s Cullinan mine, which also yielded the 530-carat Star of Africa blue diamond in the British crown jewels.

Sotheby’s says experts took five months for an “intense study” of the original diamond, and a master cutter took three months to craft, cut and polish the stone. The auction house said in a video that the Cullinan mine was the “only reliable source in the world for blue diamonds,” and only a tiny percentage of those found there contain even a trace of blue.

Blue diamonds are formed when boron is mixed with carbon when the gem is created.