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The Letseng mine in the small Kingdom of Lesotho, South Africa has just uncovered another massive diamond rough: a 198-carat stone, roughly the size of a large letseng 198 caratstrawberry.

A diamond over 100 carats is rare enough – with only about 10 to 15 found each year worldwide – but a rough that is nearly 200 carats is an exceedingly rare find. A stone of this size is expected to yield a polished diamond around 100 carats, or half the weight of the rough it originated from.

Even though the stone’s size is impressive, it is not even close to being the largest ever uncovered from the Letseng mine. In fact, the Letseng mine is well-known for churning out large, quality rough over the years, and has the highest price per carat production of all the mines in the world. Some of the largest include the Letseng mineLesotho Promise, the 15th largest diamond in the world at 603 carats; the Letseng Legacy at 493 carats, and the Leseli La Letseng at 478 carats which are 18th and 20th largest respectively.

What makes this rough even more valuable is its’ designation of Type IIa, which constitutes less than 2% of all natural diamonds. Type IIa diamonds have no measurable nitrogen impurities, making them chemically pure. This not only gives them exceptional optical transparency, but also a high likelihood of achieving a colorless (D-E-F) grade and a high clarity grade. Officials from Gem Diamonds Ltd, which own the majority stake in the Letseng mine, confirmed this after inspection of the stone noting it as “an exceptional white, high-quality diamond that displays no fluorescence”.

Martin Potts, a London-based mining analyst has estimated the 198 carat stone to fetch somewhere between $12 to $15 million.

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