SEE THE WORLD'S MOST EXPENSIVE UNCUT DIAMOND SET TO BE SOLD FOR £52 MILLION AT AN AUCTION

The Lesedi la Rona, almost the size of a tennis ball, was unearthed in Botswana in November.

The rough diamond is 1,109 carats and believed to be more than 2.5 billion years old.

The Mayfair auction, which is the first time a rough diamond of such a size has gone on public sale, takes place at Sotheby's later.

The Lesedi la Rona, which means 'our light' in the Tswana language spoken in Botswana, was discovered by Lucara Diamond Corp's Karowe mine.

David Bennett, worldwide chairman of Sotheby's jewellery division, said the diamond's discovery is "the find of a lifetime". 

"Every aspect of this auction is unprecedented. Not only is the rough superlative in size and quality, but no rough even remotely of this scale has ever been offered before at public auction," he said.

Image copyrightSOTHEBY'S

Image captionThe diamond is thought to be more than 2.5 billion years old

According to a study by the Gemological Institute of America, the rough diamond's colour and transparency "exemplify" type IIA diamonds. 

Stones in this group are "the most chemically pure and often show extraordinary optical transparency".