Lucara Diamond Corp sold an 813-carat jewel for $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 unearthed last year. The sale of The Constellation was worth $77,649 a carat and it was bought by Nemesis International DMCC, a Dubai-based 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 1109-carat Lesedi la Rona, just smaller than a tennis ball, was the largest diamond discovery for more than 100 years and it is second in size only to the Cullinan, cut into the Great Star of Africa gem in the British crown jewels.The record price provides evidence the biggest and rarest diamonds are more resilient after prices for rough diamonds slumped 18% last year, amid lower demand and an industry-wide credit crunch. ..