Gem Diamonds has recovered a 910 carat rough diamond at its Letšeng mine in Lesotho, the fifth largest rough ever found.
The D colour type IIa diamond is the largest to be unearthed at Letšeng, outranking the 603 carat Lesotho Promise recovered in 2006.
That stone was sold for $12.4 million, to Graff Diamonds, which owns a 15% stake in Gem Diamonds.
Last year, Graff bought the 1,109 carat Lesedi la Rona, the second largest rough diamond in history, for $53 million, or $47,790 per carat.
The discovery follows a recent revival of exceptionally large stones recovered at Letšeng, which is known for its high value production.