By GERALDINE FABRIKANT JUNE 29, 2016

A 1,109-carat uncut diamond offered in an unusual public auction is still waiting for a buyer.

Offered for sale at a public auction on Wednesday evening at Sotheby’s in London, the stone — believed to be the largest still-uncut diamond in the world — failed to sell when it did not meet the minimum reserve, a price that was not specified.

The bidding stopped at $61 million. A fee of about 12 percent, known as the buyer’s premium, would have been added to that price, which would have brought the total cost to about $68 million.

“If you divide it by 1,109 carats, it is about $62,000 a carat,” said Henri Barguirdjian, president and chief executive of Graff Diamonds. “That is a very high price for a rough diamond, so obviously the reserve was too high.”

The stone was discovered last fall in the Lucara mine in Botswana. Selling it at auction was an uncommon move; such stones are normally offered to a handful of sophisticated dealers.

The auction was a gamble for both Lucara and Sotheby’s on the desire among the ultra-wealthy for such a totem of luxury. Britain’s vote last week to leave the European Union may have affected the bidding interest.

Potential bidders had a chance to examine the stone in advance. Evidently they did not think that the diamond, which would probably have been cut into smaller stones, justified a higher price.

The record price for a rough stone was set in May, when Lucara sold an 813-carat diamond at a private auction for $63 million, or about $77,500 a carat.

A version of this article appears in print on June 30, 2016, on page B2 of the New York edition with the headline: 1,109-Carat Diamond Fails to Sell at Auction.