One of the largest diamonds on record has been unearthed by miners in Lesotho.

The colourless gemstone is around the size of two golf balls and clocks in at 910 carats (182g), about the weight of a snooker ball.

Even more impressive than its size is the stone’s quality. The new find is classified as a Type IIa diamond, which puts it in the top 1% of the world’s finds. With almost no impurities, it ranks alongside famous gems like the Koh-i-Noor. The absence of colour pigmentation further adds to its value.

The diamond was uncovered at the Letseng mine in the mountainous north-east of the landlocked African nation.

Clifford Elphick, chief executive of the mine’s London-based owners Gem Diamonds, called the find a “landmark discovery”.

In a statement, the firm said it believed the stone was the fifth-largest quality diamond ever found.

The Letseng mine “is famous for the size and quality of the diamonds it produces and has the highest average selling price in the world”, says Fortune. The value of the latest find will depend on a variety of factors, but diamonds of a similar weight have sold for sums between £38m and £46m in recent years.

“Assuming that there are no large inclusions running through the diamond, we initially estimate a sale of $40m [£29m],” Richard Knights of London broker Liberum told the Financial Times.

By contrast, 40% of Lesotho's two million residents live below the poverty line of $1.25 per day, Deutsche Welle reports.