Lucara Diamond Corp. sold an 813-carat jewel for US$63 million, making it the most expensive rough gem on record and raising the prospects for the sale of the Lesedi la Rona, the world's second-biggest such stone that was unearthed last year.

The 1109 carat "Lesedi La Rona" diamond is displayed in a case at Sotheby's in the Manhattan borough of New York, U.S., May 4, 2016. [Photo/Agencies]

The sale of The Constellation was worth US$77,649 a carat and Lucara will retain a 10 per cent interest in the net profit received in the polished products, the Vancouver-based company said in a statement Monday. The stone was bought by Nemesis International DMCC, a Dubai-based rough-diamond trading company.

Both diamonds were recovered from Lucara’s Karowe mine in Botswana, which is gaining a reputation for producing the world’s biggest and best stones. The 1,109-carat Lesedi la Rona, just smaller than a tennis ball, was the largest diamond discovery for more than 100 years and the stone is second in size only to the Cullinan, cut into the Great Star of Africa gem in the British Crown jewels.

"This is a great result for Lucara and should only add to the fevered expectations around the auction of Lesedi la Rona," said Edward Sterck, a London-based analyst at BMO Capital Markets Ltd. "The US$63 million price achieved is above our expectations."

The record price provides further evidence that the world's biggest and rarest diamonds are more resilient after prices for rough diamonds — what mined gems are called before they're cut and polished — slumped 18 per cent last year, the most since the financial crisis in 2008, amid lower demand and an industrywide credit crunch.

Applying the same dollar per carat implies a so-called floor price of US$86 million for the Lesedi la Rona, according to Sterck.