A 232-carat white diamond that experts said is worth £10 million (around $20 million) was unearthed at the Cullinan mine, east of Pretoria and birthplace of the largest known diamond in history almost a century ago.

The new discovery was made by Petra Diamonds, owner of the famous mine. It's the same mine that has supplied the British crown jewels as a part of the world's greatest rough stone, the Cullinan Diamond, found in 1905 with 3,106 carats; later on, these were cut into the smaller stones now seen in the famous royal jewelry.

In a statement released to the press after the unearthing of the diamond, a spokesperson for Petra Diamonds said: "The stone is ... of exceptional size and clarity, and is a magnificent example of the large, high quality diamonds for which the mine is known."

Besides its size, the stone sets itself apart for being a D color Type II diamond; these rough minerals are formed in extreme pressures over very long periods of time and they have no discernible visible absorption spectrum and no measurable nitrogen impurities, which means they are often top quality and highly valued in the precious stones market.

The last time the company sold a white diamond of this sort, in 2010, the 507.3-carat stone went up for $35.3 million in auction, the highest paid price for a diamond in history. Analysts have suggested the newly unearthed stone, which Petra Diamonds announced would be going up for auction in the third trimester of the year, could be sold at any price between $10 and $20 million.

Besides being the home of the biggest diamond in history and a variety of stones over 10 carats, the Cullinan mine is also famous for its rare blue diamonds; last June, Petra Diamonds extracted a 122.5-carat blue stone from the South African excavation.