“Every aspect of this auction is unprecedented. Not only is the rough superlative in size and quality, but no rough even remotely of this scale has ever been offered before at public auction,”said David Bennett, worldwide chairman of Sotheby’s Jewellery Division. The gem was uncovered by Lucara Diamond Corp at its Karowe mine in Botswana. In terms of its size, the ‘rough’ is exceeded only by the 3016.75-carat Cullinan Diamond, which was mined in South Africa in 1905. Sotheby’s auction house said it has the potential to be “the largest top-quality polished diamond in existence.” It took experts months to appraise the stone because it is too large to measure with conventional equipment.