Diamonds – Purest carbon

By Hu Berry

Its simple chemical formula ‘C’ belies its worth and splendour.

Typically yellow, brown or grey to colourless; less often in blue, green, black, translucent white, pink, violet, orange, purple and red, diamonds glow in ethereal beauty. Women have loved, men have killed, and fortunes have been made or lost through the lure of diamonds.

Namibia’s diamonds lay strewn and undisturbed across the desert for aeons before their unlikely discovery a mere century ago. Rapidly reaching the zenith of Namibia’s export earnings, their decline in sales has recently been as spectacular as their ascent, reminding us that the saying ‘diamonds are forever’ may be as flawed as some of the defects that make them imperfect. When the global money supply runs low, diamonds lose their allure because their absolute exclusivity and value transcends the buying power of paper notes.

De Beers diamonds.

The ancient Greeks knew the diamond as ‘adámas’ (I overpower, I am untamed and unbreakable), acknowledging its high diffusion of light and hardness. This durability was later formalised by a German mineralogist Friederich Mohs, who developed a scale of 10 where hardness is defined as resistance to scratching. A pencil lead (graphite) has a hardness of 1; a fingernail 2.5; a copper coin about 3.5; a knife blade 5.5; window glass 5.5; and a steel file 6.5. Diamonds top the list at 10, with an absolute hardness 1 600 times that of talc, which rates a mere 1.

Recently, science has discovered new minerals found from asteroids or formed during volcanic eruptions that outdo diamonds. But for sheer lustre nothing approaches a gem-quality blue diamond, infused with traces of boron. It is the dispersion of white light into spectral colours that gives the primary gemological characteristic of diamonds.

Only the purest form of carbon possesses a cleavage of 111, meaning to a diamond cutter that it can be shaped perfectly in four directions.

Polished diamonds are commonly judged by the ‘four Cs’: carat, clarity, colour and cut. Their criteria are rigorous. Carat expresses the mass (weight), with one full carat equal to 200 milligrams. Clarity measures a diamond’s flaws, or inclusions. Beginning with Flawless, the levels move down to Very Very Slight (VVS), Very Slight (VS), Slightly Included (SI) and Included (I).

Sperrgebiet.

Colour comes in a scale of transparency running from D to Z, starting with Exceptional White Plus and ending with Light Yellow. Gem-quality diamonds may be colourless or occur in any shade including the non-spectral hues of gray, brown and black. The most common is colourless followed, in order of rarity, by yellow and brown, then by blue, green, black, translucent white, pink, violet, orange, purple, and the rarest, red.

A ‘black’ or Carbonado diamond is not truly black, but contains numerous dark inclusions. Finally, the geometric proportions of the rough diamond and how it has been pre-shaped by the cutter determines a diamond’s cut.

To give birth to these points of perfection, the fertilisation of the Earth requires very specific conditions. Carbon-bearing materials must be exposed to pressures that would flatten a motor car and temperatures that would turn it into molten metal.

Only two places on Earth meet these requirements – beneath stable continental plates at depths of 140 to 190 kilometres and at the site of a meteor strike. Meteor impact events create shock zones of high pressure and temperature suitable for diamond formation. Extra-terrestrial diamonds stretch the mind and imagination. Consider evidence indicating that white dwarf stars have a core of crystallised carbon, which astrophysicists describe as a diamond. The largest discovered yet, is unreachable to humans.

Diamonds

Located 50 light years away in the constellation of Centaurus, it has a diameter of 4 000 kilometres and is estimated to be ten billion trillion trillion carats. This inconceivable ‘gem’ is referred to, tongue in cheek, by astronomers as Lucy, after the Beatles song Lucy in the Sky with Diamonds.

Back on Earth, geologists must identify rare, deep magma eruptions that form volcanic pipes to bring diamonds to the surface. Such occurrences were the kimberlite pipes in Southern Africa that spewed their lode onto the surface, making it possible for diamonds to be transported by powerful water flushes along the Gariep River to the Atlantic Ocean and then thrown onto beaches for prospectors to discover.

In 1908, when a labourer presented his supervisor August Stauch with a rough diamond he had picked up in the desert when working on the Lüderitz-Aus railway line, he unwittingly launched a diamond rush of epic proportions. Little did the men, who subsequently lay literally on their stomachs on moonlit nights to find diamonds sparkling on the desert floor, realise that about one fifth of their bodies contained exactly the same material as the purest form of carbon they were searching for.

This article appeared in the 2009/10 edition of Conservation and the Environment in Namibia.

Hu Berry was a scientist, conservationist and specialist tour guide. He was one of Venture Publications' most valued authors. Sadly he passed away in July 2011. To read more about him click here.