Diamond in the dust

Rough diamonds may sometimes be mistaken for worthless pebbles, 17th-century physician Sir Thomas Browne once said - but not when they are a beautiful and rare 232-carat white diamond such as the one found at Petra Diamonds' Cullinan mine, east of Pretoria, the firm said yesterday.

It is uncertain where exactly the stone was mined, such is the tonnage of ore being pulled from various areas in the mine. It is only later mixed at surface.

In a statement, the company explained that "the stone is a D-colour, Type 2 diamond of exceptional size and clarity, and is a magnificent example of the large, high-quality diamonds for which the mine is known".

Just 1%-2% of natural diamonds are reportedly Type-2 gems, so they are rare. They are also clear and have no impurities.

Petra Diamonds said the market would be updated "when finalised on the expected timing for the sale of this stone, which is expected to be in the second quarter of this financial year".

The largest diamond the company has sold from the Cullinan operations was the 507-carat Cullinan Heritage diamond four years ago. It was bought by Hong Kong jeweller Chow Tai Fook for about R386-million - the highest price on record for a rough diamond.

A Petra Diamonds spokesman explained to The Times the intricate process of securing the precious stone. "The company mines between two and three million tons of ore each year from underground using machinery. The ore is then brought to the surface and moves through the processing plant, which gradually crushes the rock to smaller and smaller pieces, until it goes to the final recovery section. In the recovery section, it is mainly a 'hands-free' automated process which uses X-ray technology to separate the diamonds from other material.

"The final product is then retrieved by the final recovery team, which is in an area of high-level security. Therefore, the diamonds recovered are never attributable to one person or simply picked out of the mine - it is the whole mining team who is responsible."

The stones cut from the famous Cullinan diamond discovered in 1905 are part of the British crown jewels. As one Twitter user said, "don't let the Queen see it".