Mining the hardy, much-desired diamond

From Rudi Bakhtiar
CNN NEWSROOM

KIMBERLEY, South Africa (CNN) -- Durable and dazzling, diamonds are a precious accident of nature. The nearly colorless gem is so coveted by people around the globe, that nations lucky enough to discover and mine large diamond deposits can gain tremendous economic benefits.

While diamonds are a global natural resource, it is an intriguing act of nature that most diamond deposits occur in some of the remotest regions of the world.

Five of the seven diamond mining nations are located in Africa, including South Africa, where the first diamond was found on the continent in 1866. Discovery of the highly valued stone helped usher in modern industrial times in South Africa.

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Russia and Australia also harbor great reserves of the sparkling gems.

What is a diamond, and how is it extracted from the ground?

Non-renewable, natural resource

Diamonds are made up almost entirely of carbon, but have traces of impurities like Boron and Nitrogen. The stones are formed deep below the Earth's surface by tremendous heat and high pressure.

"Diamonds, we believe, are formed… in the upper-most part of the mantle, at depths of about 300 kilometers," says Jock Robey, a research geologist for diamond manufacturer De Beers. "They have to be deeper than 150 kilometers, otherwise the carbon will not crystallize as diamonds."

Like crude oil, diamonds are a non-renewable natural resource. Once mined, the brilliant baubles will never grow back. Scientists estimate that the heat and pressure process necessary to transform carbon into diamonds began about three and a half billion years ago.

According to legend, the term "carat" is derived from an ancient measuring unit -- the carob fruit seed.

Carbon deposits far belowground are slowly heated and pressured. The deposits are embedded in crumbly, black volcanic rock called kimberlite, and move closer to the Earth's surface as the tension from a forming volcano forces the soft rock up through the Earth's face.

Kimberlite "is essentially a volcanic rock made up of a variety of distinctive minerals," says Robey. "It has a peculiar color and texture… It's difficult to describe, but it has got different chemistries from other well-known volcanic rocks."

Digging for diamond deposits

So how do diamond experts find the precious stones that are mixed in the black, crumbly kimberlite?

The key to isolating diamond deposits is locating concentrations of four indicator minerals: garnet, ilmenite, chromite and chrome diopside.

"We call them indicators because, together with diamonds, they… are quite heavy, and they get trapped in rivers and in between rocks and the base of the river where you could look for them the same way someone would pan for gold," says Robey.

Diamonds can be mined in two ways: By extracting diamonds from volcanic rock below the earth's surface or by sifting stones from ancient riverbeds.

Diamonds can be mined in two ways. Alluvial mining, or the sifting of stones from ancient river beds or seashores, is one way. But the easiest method is kimberlite mining, or the heavy-duty extraction of diamonds from cone shaped pipes of volcanic rock.

In the mines of South Africa, kimberlite is drilled and blasted on an almost continual basis.

"The diamond recovery process is a very simple process of breaking down that ore initially by crushing, then by adding water and simply churning the material around," says Brian Roodt, De Beers' corporate affairs manager.

Unlike other forms of mining, which can be very detrimental to the landscape, diamond mining uses no chemicals, just rushing water, to extract diamonds from the kimberlite.

"One of the really exciting things, in environmental terms, about diamond mining is that it is a very benign process," Roodt says. "It's simply an addition of water and then a subtraction, and just sort of concentrating the material to get the diamond."