Canadian mining company Lucara Diamon has found the second largest diamond ever seen in the world in the Karowe mine. The 2,492-carat stone is valued at more than 40 million US dollars.

The Tsuana diamond loses out to the Cullinan diamond, discovered over a century ago, which was cut and incorporated into the British Crown Jewels.

"This is a once in hundreds of years event, and an absolute geological phenomenon," said Clifford Elphick, a former executive of the world's largest diamond company, De Beers, which now runs its own mining companies in southern Africa.

He added that the discovery was "the most significant of this century".

Diamonds have formed the basis of the country's prosperity, with gemstone mining making up around a quarter of its GDP, according to the IMF.

The stone, which is two-thirds the size of a drink can, came from Lucara's Karowe mine, which has been the source of several other major discoveries, including the 1,758-carat Sewelô and the 1,109-carat Lesedi La Rona. It was found using X-ray transmission technology installed eight years ago, after the Lesedi La Rona was damaged in the mill when it was found. (Source and image: FT)