What is a diamond?
Diamond is a naturally occurring mineral which grows in a regular three-dimensional crystalline pattern, composed of pure (or very nearly pure) carbon. Diamond has some unique properties: it is generally accepted as the hardest substance known to man (scoring a maximum 10 on the Mohs scale of mineral hardness), and diamond is also unusual in its ability to conduct heat extremely well (its thermal conductivity is five times that of copper) but to conduct electricity very poorly – a combination which has important applications in industry.
But what makes diamond really special, apart from its astonishing antiquity, is its optical properties, specifically its very high refractive index. This property, along with dispersion and the way in which a diamond is cut, is what gives a diamond its brilliance and its adamantine lustre.
Diamond is also very a stable material, being highly resistant to acids and other chemicals, and also to changes in temperature. This stability explains why diamonds are still being found today despite their great age. We get the word ‘diamond’ from the Greek word adamas, which means invincible or unconquerable.
How old are diamonds?
It’s difficult to be very precise but the simple answer is: very old. The ‘youngest’ diamonds are thought to be at least 990 million years old, and some are believed to be as much as 4.25 billion years old, which is almost as old as the Earth itself (around 4.54 billion years). So diamonds are incredibly old, even on a geological timescale.
Diamonds pre-date the dinosaurs by hundreds of millions of years, and in fact many diamonds actually pre-date all life on earth. Think about that the next time you glance at a diamond in a piece of jewellery: the diamond is probably older than life itself. Truely timeless.
How were diamonds formed?
Rough diamond crystals; photo by DTC
The formation of diamonds requires tremendously high pressure and (to a lesser degree) temperature. Pressures of 45-60 kilobars are necessary, which put another way means 45,000 to 60,000 times atmospheric pressure. The temperature required for diamond formation is rather less extreme at 900–1300 °C.
The correct combination of pressure and temperature only existed in a few places and at depths of around 100 miles below the earth’s surface, or in some cases at depths of 200 miles or even more. But of course diamonds had to make their way to the surface in order to be found and recovered, and they made this journey in violent volcanic eruptions where diamond-bearing rock was thrust upwards by magma from depths of around 100 miles or more. This is about three times deeper than the source of most volcanic eruptions and so it’s a relatively rare occurence.
These relatively small surface volcanic craters are known as volcanic pipes, but not all pipes contain diamonds, and even fewer are economically viable for the recovery of diamonds.
So diamonds were formed at great depths and in only a few places where the correct combination of high pressure and temperature existed. Then in only a few places were diamonds thrust upwards by volcanic eruptions, and in even fewer cases have those diamonds been discovered and susequently recovered. In short, diamonds are a miracle of nature and only a very few diamonds ever leave the place of their birth in order to adorn one of us in a piece of jewellery.
Where are diamonds found?
Diamonds are found in over 20 countries around the world, very often in deserts and frozen tundra. Most of the world’s production (by value) is in central and southern Africa, but diamonds are also found in Russia, Australia, Canada, India and some parts of South America. The world’s biggest producer of diamonds is Botswana, which accounts for about one quarter of all diamond production, with other leading producers being Russia, South Africa, Angola, Democratic Republic of Congo, Canada and Namibia.
How are diamonds discovered and mined?
Diamond mining companies spend a large amount of money and time in various stages of exploration and sampling before a diamond mine is given the go-ahead for full development. Early stage exploration involves searching for various ‘indicator’ minerals that experience has shown are associated with diamond discoveries. Samples of soil and sediment materials are collected and analysed, and drilling is carried out in order to collect sub-surface core samples. Geophysics techniques such as magnetic and electromagnetic analysis are also used to map the Earth’s geology in order to look for diamond deposits.
Once a viable diamond deposit has been found (which is a rare occurence) a diamond mine can be developed. The timeframe from early exploration through to commercial production of a diamond mine can often be 5 to 10 years. Most of the world’s major diamond mines are open pit mines where the diamond deposits are on the surface, but there are also some underground mines where diamond deposits are below the surface.
Another type of diamond deposit is an alluvial deposit, where the diamonds have been scattered away from the original volcanic pipe and they are now lying in sands and gravels along riverbanks and even under the sea: De Beers recovers diamonds from under the Atlantic ocean off Namibia and South Africa using marine mining techniques.
How are diamonds cut and polished?
Once diamonds have been recovered by the diamond mining companies (of which there are dozens, but only a handful of major mining companies such as De Beers, Rio Tinto, BHP Billiton, Alrosa…) then they sorted into categories, valued, and sold to diamond cutting and polishing companies (of which there are hundreds or even thousands, but De Beers for example sells to fewer than 100 clients whilst Rio Tinto sells diamonds to around 25 clients).
These diamond cutting and polishing/processing companies are generally referred to as diamantaires, a word of French origin which is perhaps best translated into English as ‘master diamond cutter’ but also refers to someone who has considerable expertise in diamond valuation, 4Cs gemmology or diamond trading.
Diamantaires look very carefully at a rough diamond before starting to cut it. Every single diamond is unique and so every rough diamond needs to be planned by the diamantaire in order to maximise the outcome: the polished diamond (or diamonds plural: many rough diamonds yield more than one polished stone).
The objective is to maximise the value of the polished diamond(s) that are recovered from the rough stone. Of course value is closely linked to the carat weight of a polished diamond, but the value can also be considerably affected by the cut, clarity and colour. These four characteristics are referred to as the 4Cs of diamonds.
Diamantaires use technology to help them to predict the polished outcome of a rough diamond, but they also use their judgement and experience — in many ways it’s still an art as much as a science.
The cutting process often uses high-tech lasers to ‘prepare’ a diamond: to begin the shaping process so that it starts to resemble one of the familiar polished shapes: round, pear, heart shape etc. The facets of the polished diamond are then polished using various tools and the great skills of an experienced diamond cutter.
Diamond cutting; photo by DTC
The tiny facets on a diamond (57 of them on a conventional ‘brilliant cut’ round polished diamond) are polished to an extremely fine, smooth surface, with very crisp edges where the facets join one another. The polishing process involves using tools to hold the diamond against a metal disc which is rotating at high speed (pictured right), similar to a potter’s wheel. The metal disc is impregnated with oil and diamond grit, and it’s this diamond grit which actually cuts the gem diamond.
During the cutting and polishing process, it is common for more than half of the weight of the original rough diamond to be cut or polished away, so for example a 2 carat rough diamond will typically yield a polished diamond that weighs less than 1 carat.
Much of this process is finished by hand and eye – it’s far from automated – so each and every polished diamond is not only a miracle of nature, it is also finely crafted by a highly skilled artisan, making every diamond both unique and a genuine work of art.
Today, diamonds are cut in a number of countries around the world with India being the main diamond cutting centre (generally in the state of Gujurat in cities such as Surat and Ahmedabad), but other diamond cutting countries include Belgium, Israel, China, Thailand, Russia, Armenia, South Africa, Botswana, Namibia and the USA (some large diamonds are cut in New York).
Sources: Wikipedia, IdexOnline, De Beers, GIA
