This is starting to become a bit of a habit: Gem Diamonds have unearthed another whopper from their Letšeng mine in the African kingdom of Lesotho.

It was only a few weeks ago that an exceptional 196 carat white diamond was recovered at Letšeng, and they have followed this up by announcing today that a remarkable 185 carat rough white diamond was recovered from the same mine at the end of October. The two exceptional diamonds are pictured together, below.

Early examinations indicate that this latest rough diamond will yield top colour and top clarity polished diamonds.

Diamonds such as this are sold as individual stones rather than in a job lot as a part of a routine sales or tendering process, and a certain amount of marketing and PR will take place to ensure that the right buyer is found and the best price achieved.

A rough diamond such as this could sell for more than $50,000 per carat, which would make this gem worth close to $10 million, and taken together these two recent finds might yield upwards of $20 million for Gem Diamonds – a healthy boost to turnover from just two diamonds for a company with reported half year sales of a little over $100 million.

Buyers in the Far East have recentlybeen paying high prices for exceptional diamonds, but buyers in Hong Kong and China will tend to wait until the diamond is cut & polished before buying the finished article.

It’s more likely that these diamonds will sell to one of the more traditional diamantaires in Antwerp, New York, Israel, or Mumbai, or perhaps to a ‘big name’ jeweller and specialist in large diamonds such as Laurence Graff.

The Letšeng diamond mine is located high up in the mountains of the African kingdom of Lesotho (pictured below), a landlocked country entirely surrounded by South Africa. It is said to be the only independent state in the world that lies entirely above 1,400 metres (4,593 ft) in elevation.

UPDATE 25 November 2010: Gem Diamonds announced this morning that they have successfully sold these two rough diamonds to SAFDICO for US$22.74 million, or $59,833 per carat.

One of the partners of SAFDICO is Laurence Graff, who we predicted (in our piece above) would be a likely buyer of these gems. Note that we also predicted that these two exceptional diamonds would yield ‘upwards of $20 million’, so we’re feeling quite clever right now.

Gem Diamonds also reported today that they sold a 4.68 carat rough blue diamond for US$155,000 per carat, the highest price per carat achieved for a Letšeng rough diamond to date.