Gem Diamonds has estimated that the 478ct rough white diamond it discovered at the Terai Mine in Lesotho in September could yield a 150ct flawless D-grade round brilliant-cut diamond, making it the largest diamond of its kind in history.

The giant diamond was unveiled at the Middle East-China Diamond and Jewellery Summit (MECDJS) in Dubai on Saturday for the first time, where it was subjected to initial testing by expert diamantaires using diamond analysis and mapping technology owned by Gem Diamonds Technology DMCC. The diamond was named Leseli La Letšeng at the summit, which translates as Light of Letšeng.

Using alternative cuts, initial analysis has revealed that the rough diamond could also create a 300ct flawless D-grade cushion-cut diamond, which would be the largest polished diamond of its type since the production of the British Crown Jewels.

Gem Diamonds chief executive Clifford Elphick said: “It is very seldom that such an extraordinary diamond presents itself and now with the technology that we have to hand, the truly historic potential of the diamond can be determined before it is crafted into its polished form and I am extremely excited to see this potential reached.”

The Leseli La Letšeng diamond is a type II D-coloured diamond, which is the highest grading available for a white diamond. It is the world’s 20th largest rough diamond.

The rough diamond was farmed by Letšeng Diamonds, which is 70 per cent owned by Gem Diamonds and 30 per cent owned by the Kingdom of Letšeng. With the addition of Leseli La Letšeng, Letšeng Diamonds has now produced three of the world’s top 20 diamonds in the past two years.