76-carat Archduke Joseph Diamond sells for $21.5 million

A massive cushion-shaped diamond, which was owned by the Archduke Joseph August of Austria, Palatine of Hungary (1872-1962), fetched US$21.5 million at Christie's on Tuesday at the Four Seasons Hotel des Bergues, Geneva.

The winner, who asked to remain anonymous, bid over the phone. Auction officials expected the diamond would come in at $15 million.

The stone is from the ancient Golconda mines in India, which have been the source of the world's most coveted historical diamonds, including the Kohinoor, in the Royal Collection at the Tower of London, and the Regent, considered the finest diamond in the French Crown Jewels.

The last time this rock went on sale was in November 1993, reaching $6.5 million in the same city. The diamond has since been sold privately yet Christie's has refused to identify its present owner.

Image of the Four Seasons Hotel Des Bergues Geneva – Switzerland is by Ugg Boy from Flickr Creative Commons