The largest rough diamond to be discovered in over a century could sell for more than $70m (£48m) at a Sotheby’s auction.

The 1109-carat ‘Lesedi la Rona’ – the largest gem-quality rough diamond to be discovered in over a century and the largest rough diamond in existence today – will be sold at a standalone auction in London on 29 June. The diamond, which is around the size of a tennis ball, was uncovered by diamond production firm Lucara in November 2015 at its Karowe mine in Botswana. According to a study by the Gemological Institute of America (GIA), the Lesedi La Rona’s “top colour and transparency exemplify the “limpid” appearance commonly associated with type IIa diamonds” – a rare and coveted subgroup which comprises less than 2% of all gem diamonds. The GIA said stones in this group are “the most chemically pure and often show extraordinary optical transparency”. Meanwhile, independent reports suggest the Lesedi La Rona has the potential to yield the largest top-quality diamond that has ever been cut and polished, with the resulting polished diamonds being D-colour – the highest colour classification for white diamonds.

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. 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.” In terms of its size, the Lesedi La Rona is exceeded only by the famous Cullinan Diamond, mined in South Africa in 1905. The 3016.75-carat Cullinan Diamond produced nine major diamonds that are part of the historic Crown Jewels of the United Kingdom, including the Great Star of Africa – currently the largest top-quality polished diamond in existence, weighing 530.20 carats.