Weighing an astonishing 1,109 carats, the Lesedi La Rona is the largest gem-quality rough diamond to be discovered in more than a century. Dubbed “the find of a lifetime”, it is expected to fetch more than $70 million at a standalone sale at Sotheby’s London on 29 June.   Weighing 1,109 carats, the Lesedi La Rona rough diamond will be on sale at Sotheby's London on 29 June.Experts believe that once it has been cut and polished, this gigantic gemstone could knock the 530.20ct Great Star of Africa off the top spot as the world’s largest top-quality polished diamond. Despite constant diamond mining in many parts of the world, no other rough gemstone approaching its size has been discovered since the 3,016.75ct Cullinan Diamond was unearthed in 1905. This yielded the pear-shaped Great Star of Africa as well as another eight diamonds, all of which form part of the Crown Jewels housed in...