The rough diamond that could polish off world gemstone record

IT IS a mere speck on the map, but deep beneath its inhospitable plateaux, nature has gifted Lesotho some of the grandest sparklers in the world.

The rich seam of the African enclave's mines became clear yesterday, after the discovery of a huge gem experts believe could yield the largest polished round diamond in history.

It weighs 478 carats and is the 20th largest rough diamond ever recovered. Such is its outstanding clarity and rounded shape, it has set tongues wagging in the upper echelons of the stone trade. Once polished, tentative speculation has it that the white diamond could reach a valuation well into eight figures.

The diamond, which has not yet been named, is the fourth remarkable gem to be unearthed from the Letšeng mine in only two years.

Lesotho, geographically surrounded by South Africa, is an impoverished nation, where shepherds take refuge in crude, thatched huts when they are not crossing mountains by horseback. However, it is also regarded as the most productive region in the world for precious stones.

After initial examinations by gemologists in the Belgian city of Antwerp, it is estimated the rock has a completely flawless centre and might even yield a 150-carat polished gem stone. If so, it would dwarf the likes of the Koh-i-noor diamond, the centrepiece of the Crown Jewels.

The grade-D stone – the highest quality – was unearthed a fortnight ago at Letšeng, in the landlocked country's Maluti mountains. The glittering prize emerged from the hundreds of thousands of tons of kimberlite rock mined every day.

Sculpting it into a marketable asset is an arduous task, involving several months' work.

It is not yet clear exactly what the stone will produce, but, typically, it will take three months to assess any cracks or faults and decide how best to maximise the yield before polishing begins. The danger of the stone shattering during cutting is ever present.

Clifford Elphick, the chief executive of Gem Diamonds, the majority owner of Letšeng, said: "Preliminary examination of this remarkable diamond indicates that it will yield a record-breaking polished stone of the very best colour and clarity."

The mine, has enjoyed great success since reopening four years ago, producing the 603-carat Lesotho Promise, the 493-carat Letšeng Legacy and the 601-carat Lesotho Brown, respectively the 15th, 18th and 16th largest rough diamonds. The Promise, little bigger than a golf ball, sold for £12.4 million two years ago

The Lesotho government also has a stake in Letšeng. Monyane Moleleki, the minister for natural resources, promised yesterday to further develop the mine "for the benefit of the people".

IN NUMBERS

THE record for the largest rough diamond belongs to the Cullinan, discovered near Pretoria in 1905. The size of a bowling ball, it weighed 3,106 carats and yielded nine major stones. The largest, the Star of Africa, held the record for the world's biggest cut diamond at 530.2 carats. It forms part of the Royal sceptre in the British Crown Jewels.

It was superseded by the Golden Jubilee, a 545 carat diamond cut from a 755 carat stone found in South Africa.

However, the largest rock of all is the BPM 37093. Some 2,500 miles in diameter, it is floating 50 light years away in the Centaurus solar system. It weighs a modest 10 billion trillion trillion carats.