(IDEX Online) - A 100.94-carat D-color IF diamond - the largest stone ever cut in Russia - is to be auctioned by Christie's Geneva with a high estimate of $18m.The "Spectacle" (pictured) was cut from a 207.29-carat rough stone unearthed in 2016 at the Zarnitsa kimberlite pipe in the Sakha Republic (Yakutia) - Russia's first ever diamond mine. The Diamonds of Alrosa factory, Moscow, spent a year and eight months preparing and cutting the stone."The emerald shape was chosen as it presented the perfect geometry of the diamond," said Christie's in a statement."Emerald cut is incompatible with any imperfections, as it allows the observer to gaze endlessly into the clear, unobstructed depths of the gem."Viewings take place next month in Taipei and Geneva. The Spectacle will be offered for sale on 12 May at the Geneva Magnificent Jewels auction (estimate $12m to $18m).