One of the world's largest uncut diamonds ever discovered has been unveiled to the world after it was mined in Botswana in Southern Africa.

Key points: The 1,758-carat diamond is larger than a tennis ball and is of "variable quality"

The 1,758-carat diamond is larger than a tennis ball and is of "variable quality" The Botswana mine has produced more than 12 diamonds larger than 300 carats

The Botswana mine has produced more than 12 diamonds larger than 300 carats The diamond is still smaller than the 3,016-carat record holder

Canadian company Lucara Diamond Corp owns the Karowe Diamond Mine where the unbroken 1,758-carat diamond — which is bigger than a tennis ball — was discovered.

It is now the world's second-largest mined diamond, although it is significantly smaller than the record-holder, the 3,016.75-carat Cullinan Diamond, which was discovered in South Africa in 1905.

The company has not revealed the price it expects its record find to fetch.

"Weighing close to 352 grams and measuring 83mm x 62mm x 46mm, the diamond has been characterised as near gem of variable quality, including domains of high-quality white gem," the company said in a statement.

The diamond is the largest Lucara has mined from its Botswana operations in recent years, beating its previous discoveries of a 472-carat and a 327-carat diamond recovered in 2018.

Its previous record, the 1,109-carat Lesedi La Rona diamond discovered in November 2015, was sold for $US53 million ($75 million) to British diamond dealer Graff Diamonds in 2017.

The Cullinan Diamond was cut into nine diamonds for the British crown jewels, which includes the Cullinan I, which is inserted in the Queen's Sceptre and the Cullinan II, which is lodged in the crown that the monarch wears to the opening of parliament.

Lucara Diamond Corp has not revealed how much it expects to sell the diamond for. ( Supplied. )

WA's Argyle mine unveils giant white diamond

The news of the Botswana diamond follows the announcement of one of the largest white diamonds ever produced by the Argyle mine in Western Australia on Tuesday.

The octahedral-shaped 28.84-carat stone was recovered in March and will be sent to Belgium to be sold.

"We don't see many this shape, or colour, or that clarity, generally out of the mine," Argyle general manager of operations Andrew Wilson said.

"We've probably seen 20 of those in the last 36 years of operations, of the plus-20-carat size."

The Argyle diamond mine is scheduled to close down in 2020.

The large diamond was unearthed at the Argyle mine in WA's Kimberley. ( Supplied: Rio Tinto )

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