A 50-carat white diamond has fetched 6.5 million Swiss francs (dollars) at a Christie's auction of jewelry, with the auctioneer saying an anonymous trader snapped up the rare stone.

The Harry Winston-crafted diamond ring was the top lot Wednesday among hundreds of items at Christie's spring auction in Geneva. A fancy vivid yellow diamond ring of 20.49 carats brought about $5.5 million — achieving a near-record price per carat, the auction house said.

The price for the yellow diamond ring, which included the buyer's premium, easily eclipsed the expected range for a hammer price of up to $4.5 million.

Rahul Kadakia, head of international jewelry at Christie's, trumpeted a "monster price" per carat for the yellow diamond.

Overall, Christie's auction collected nearly $82 million.