The tennis ball sized gem quality diamond named 'Lesedi La Rona', meaning 'Our Light' in Botswana's Tswana language was uncovered by Canadian mining firm Lucara Diamond Corp in November 2015 at their Karow mine in Botswana.
Measuring approximately 66.4 x 55 x 42 mm, the colossal rough diamond, auctioneers said is of exceptional transparency and quality and is around 2.5 to over 3 billion years old.
Auctioneers have estimated the diamond to achieve a sale in excess of USD 70 million.
In terms of size, the rough is exceeded only by the 3016.75 carat Cullinan diamond, mined in South Africa in 1905, and which produced nine major diamonds that are now part of the historic Crown Jewels of the United Kingdom.
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It includes the 530.20 carats Great Star of Africa - currently the largest top-quality polished diamond in existence.
David Bennett, Worldwide Chairman of Sotheby's Jewellery Division, said, "The 'Lesedi la Rona' is simply outstanding and its discovery is the find of a lifetime. It is a huge honour for Sotheby's to have been entrusted with its sale.