The Letšeng mine in the tiny southern African kingdom of Lesotho has produced another colossal gem-quality diamond. The 442-carat, Type IIa stone could be worth as much as $18 million. The still-unnamed rough gem is the fifth-largest gem-quality diamond ever unearthed at Letšeng, a mine that is recognized as the highest dollar-per-carat kimberlite mine in […]