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The Science Behind Your Diamond Ring (And Why It's Not Forever!)

In terms of gemstone celebrity status, diamond is on the A-list and boasts an almost unrivalled prestige in the gemstone-world. Not surprisingly, some of the most famous (and infamous) gems in Royal attire are diamond. For example, there’s the massive blue 45.52-carat Hope diamond, on show at the Smithsonian institution (in Washington DC), which used to be the 116 carat Tavernier Blue belonging to Louis XIV of France (it wound up in the US via London following the French Revolution.) And there’s the enormous 3,106 carat Cullinan I, otherwise known as the Great Star of Africa, which is part of the Sovereign's Scepter with Cross of the British Crown Jewels.

Diamond is most commonly considered as a gemstone, but diamond is also an essential material for advancing science. It is the hardest material known, and therefore has unrivalled engineering and manufacturing applications. Diamond is also the best conductor of heat known, for example, if a diamond were 1 km long and a flame were placed on one end of the diamond, with a hand on the other end, the person would feel the heat almost instantly, as if the flame were applied directly to their hand. Furthermore, geologists love diamonds because they provide otherwise inaccessible samples of the deep Earth, and thus provide the best window with which to study the deep carbon cycle.

The origin of the 'Diamonds Are Forever' slogan

So, let’s begin with some historical context. In 1947 a woman you’ve probably never heard of (Ms. Frances Gerety), working at an advertising firm you’ve probably never heard of (N.W. Ayer & Son) commissioned by a company you must have heard of (De Beers) coined the phrase ‘A Diamond Is Forever’, and the rest is history. Ok, so maybe a few other things happened along the way that have culminated in the present day social norm where it is almost totally unacceptable to propose marriage without presenting (or promising) a diamond engagement ring in exchange for a ‘yes’.

The slogan has been ranked the #1 advertising slogan of the 20th century by a magazine called Advertising Age (although their website currently displays the 2.0 plural slogan ‘Diamonds Are Forever’.) And for good reason, it’s simple, catchy, and sounds cool. However, as a statement, it is inaccurate. Diamond is very brittle, and they’re also unstable at the low pressures of Earth’s surface. However, it takes a lot of energy (heat) for diamond to transform into its stable state of graphite at low pressure, so in terms of stability scientists call diamond metastable. Nonetheless, it is not stable, stricto sensu. Also, if one heats up diamond in the presence of oxygen gas, the diamond and oxygen combine to make CO2-gas. I’ve done this to over 100 diamonds in the last five years to measure the fine-detailed chemistry of this gas to understand the geological origin of diamond-forming carbon – but that’s not the point, so let’s continue with the historical context.

It is thought that diamond mining started in India around 500 BC, and the first diamonds found their way to Europe via Alexander the Great (in 327 BC). A few centuries later (in 1772) the great French scientist named Antoine Lavoisier proved that diamond and graphite both have the same chemistry and are almost entirely made of carbon. Lavoisier was the first person to demonstrate the concept of polymorphism, where two totally different physical things can be made of exactly the same chemical stuff; in fact the most common black-spot (inclusion) found in diamond is graphite. The relationship between diamond and graphite is as follows: Diamond is stable at high pressures and graphite is stable at high temperatures. For diamond to form, we need to generate pressures of above about 50000 atmospheres (I’ve done this myself in high-pressure laboratories in London, Long Island, and Washington DC – it’s easy to do.)

How and where you find them

So if such ludicrously high pressures are required, how come we get diamonds at Earth’s surface? The answer is that diamonds form at great depth, in parts of Earth’s interior where the pressures are high enough and the temperatures low enough to stabilise diamond instead of graphite. These conditions are found beneath unusually thick parts of Earth’s crust called cratons. Thus, where there’s a craton, there could be a primary diamond mine. The classic diamond mines of Southern Africa, Siberia, Australia, South America, and Canada are all situated on cratons (note, there’s a craton beneath Antarctica but there is also a moratorium on mining!)
Photo: Getty
A man washing diamonds in a mine in Kono - Sierra Leone.
This still doesn’t answer the question, because we still need to transport diamond from the high-pressure niche where it grew to the very low-pressure environment of Earth’s surface so we can mine it and make pretty things or super hard industrial tools. An enigmatic type of volcanic eruption called kimberlite (named after Kimberley in South Africa where they were discovered) achieves this feat, because they are thought to erupt at super-sonic speed through more than 150 km of the Earth and transport anything in their path to the surface, including diamond. So the hunt becomes easier; now we just need to look for kimberlites on cratons right? Wrong. Diamond is super hard, which means rivers can transport it for hundreds of kilometers without damaging it. This is why movies like Blood Diamond show people sieving diamonds from rivers – but we’ll come to blood diamonds a little later. In fact, in my opinion, the most bizarre diamond mine is located off the Namibian coast in the Atlantic. Here diamonds are sucked up from beneath the waves using massive machines that look like the offspring of vacuum cleaners and oilrigs.

Dirty diamonds vs clean diamonds

Now let me explain why I like dirty diamonds and jewellers like clean diamonds. Gemologists classify diamond using the 4-C’s, a classification protocol established by the Gemological Institute of America (an independent non-profit organisation). The 4-C’s are the [1] Cut, [2] Clarity, [3] Colour, and [4] Carat (where 1 carat = 0.2 gram, but was actually developed using the weight of Carob seeds). Conversely, geologists like me apply the 4-W’s, a classification protocol I made up for a lecture I gave to Gemology students at Kingston University. The 4-W’s are [1] What is this? [2] Where did this come from? [3] When did this form, [4] Why did this happen?

To answer my four questions requires a bit more than pure diamond, because pure diamond is usually comprised of 99.9% carbon and 0.1% nitrogen. Note, add more nitrogen and the diamonds turn yellow, remove the nitrogen and add boron and they turn blue, irradiate diamond and it turns green, and deform diamond to turn it pink/brown.

The real age of a diamond

Carbon and nitrogen are useless for deciphering the age of a diamond, and are only mildly useful at illuminating the chemistry of the environment where they formed. This is why geologists look for dirty spots, or 'inclusions' as they are more commonly termed. These dirty spots are sometimes minerals from the deep Earth, and by looking at their chemistry we can peer into the deep Earth (note, the deepest samples of the Earth ever seen are diamond inclusions.) We can also use radioactive isotopes to determine an age for the inclusion (and then assume that it is the same age as the diamond). By doing this it appears that most natural diamonds are seriously old, I’m talking 3.6-0.9 billion years old! We also know that some of the largest diamonds formed from carbon that used to be in the oceans and was recycled back into Earth’s interior by the processes of plate tectonics – in fact, some of the carbon in these diamonds may have once been ocean dwelling creatures. Another fun fact, at present we don’t really know if gem-quality diamonds are still forming today, so gem-quality diamonds could well be a finite commodity.

Now, if that didn’t impress you, this fact surely will. The oldest pieces of anything we have ever seen are diamonds formed in solar systems that no longer exist. In short, they formed planets that maybe hosted life, they existed for billions of years and then succumb to their inevitable fate – they were destroyed when their central stars exploded (called a super nova) – and this all happened before our solar system existed. That’s right, some diamonds are older than our whole solar system. In fact, if the solar systems that existed before ours were hosts to a planet like Earth with life like us writing articles like this, then all that may be left of them are what scientists who study meteorites (meteoriticists) call pre-solar grains: tiny diamonds around 1 micrometer in size (0.001mm). I don’t know about you, but this concept blows my mind.

Blood Diamonds

Anyhow, an article about diamond wouldn’t be complete without some words on Blood Diamonds, and synthetic diamonds.
Blood Diamond is a term that specifically refers to conflict diamonds. These are diamonds that are sourced and sold illegally, and sometimes used to fund terrorists involved in civil wars, alongside other illicit activities. This practice is obviously brutal, and leads to suffering. To counter this, in the year 2000 several diamond-producing nations established the Kimberley Process (in Kimberly, South Africa.) In short, one now requires a Kimberley Process Certificate to move rough diamonds across any international boundary and to prove the legality of the diamond acquisition; needless to say, the idea is that warlords cannot acquire a Kimberley Process Certificate. These certificates are encoded documents produced by the governments in which the diamonds were mined.

The principal countries of conflict (Angola, Sierra Leone, DRC and Ivory Coast) at the time of initiation of the KPC have now all had some form of democratic elections. Most major rough diamond traders offer full transparency on the origin of their stones, and will provide the paperwork to prove it. Likewise, jewellers should also provide a diamond grading report from a trusted source (like the Gemological Institute of America.) So if a dealer is unwilling to do this, then you should probably reconsider purchasing from that dealer. Note, these reports should also state if the diamond is natural or synthetic, and treated or untreated. Which leads on to the final topic, synthetic- and treated-diamonds.

Can you tell a real diamond from a fake one?

An important point to note is that synthetic and treated diamonds are not the same thing. A synthetic diamond was made in a laboratory, but a treated diamond can be synthetic or natural.

Synthetic diamonds aren’t fake, they’re as much diamond as a natural diamond. Synthetic diamonds are also referred to as artificial, cultured, grown or cultivated diamonds – so be careful when buying on websites, and always seek a diamond grading report from an accredited institution (they are sometimes sold in the same price range as natural diamonds – cheeky, I know.) Synthetic diamonds differ from imitation diamonds, such as silicon carbide (known as moissanite) or cubic zirconia, in that their physical structure and chemistry is the same as a natural diamond. However, they don’t share the same story, they’re not made by Mother Nature, they’re not older than 3 billion years, they’re the product of a machine. As such, to many people, they do not boast the aforementioned unrivalled prestige when compared to natural gemstones.

Treated diamonds (sometimes referred to as enhanced diamonds) are stones which have had undesirable characteristics altered or removed, such as the removal of inclusions (laser drilling), covering of cracks (fracture filling), or colour enhancement/modification (high-temperature and high-pressure treatment.) For example, high-temperature and high-pressure treatment can turn a brown diamond (not so desirable) into a pink diamond (highly desirable).

So can we tell if a diamond is natural or synthetic, treated or un-treated? Well, even people who’ve worked with diamonds for many years cannot just look at them using a hand-lens or microscope and tell the difference. Remember, they’re still just diamond – natural or synthetic, treated or un-treated – diamond is diamond in the physical sense and so they’re identical to our simple human eyes. But there are specialised technologies designed to do just this, and most respectable dealers own these machines (this is not an advert, so no examples will be given!) Furthermore, if the jeweller provides the diamond grading report, this will state if the sample is an untreated natural, a treated natural, an untreated synthetic, or a treated synthetic.

So, in conclusion: diamonds are amazing, beautiful, intriguing, and can be really, really old. They aren't forever – but they’re totally giving forever a run for its money.

Full disclosure, from Jan 2008 to June 2011 my research was, in part, funded by the Diamond Trading Company which is part of the De Beers Group of companies.