SO WHAT ARE DIAMONDS?
What are diamonds? How are diamonds made? Why are natural diamonds so rare? Why do they have such inherent value?
SO WHAT EVEN ARE DIAMONDS?
While you've probably got a basic answer to this question, we wanted to give you more detail since, as professional diamantaires, it’s something we find fascinating. There are even people who, incorrectly, think diamonds are just made from coal.
Diamonds are the most precious of all precious gems and are supremely rare. But why are they so rare? Why do these “Veblen goods” have such inherent value and allure? Let us give you a real deep-dive on the subject…
When it comes to diamond formation we need to talk about the basic geology of the Earth. We of course live on the thin solid crust of our planet. That crust is on average around 40km deep. Actually, it ranges from 5km to 70km deep and sits atop the mantle. The mantle is itself mostly comprised of a super-heated, molten metal soup. With current technology, the crust is basically everything we can observe and study. Relative to the overall scale of our planet, the crusts thickness is roughly equivalent to the skin of an apple.
To give you an idea of just how little humankind has explored depth wise, the deepest hole we’ve ever made on Earth is in the Kola Peninsula in Russia (known as the Kola Well). This well was drilled for research purposes between 1970 and 1975 and it went down 7km (about 23,000ft). While that’s still a remarkable feat, one has to appreciate how the depth of the planets crust averages 40km so we’ve clearly not yet made it anywhere near the Earth’s mantle which sits below the crust. The mantle is precisely where diamonds were formed.
While rubies, emeralds, sapphires and virtually all other precious gems come from the crust of the earth, the home of diamonds is much deeper and much more rarefied. Diamonds are formed in the mantle of the Earth and, in fact, only two gemstones in the world were formed in the molten rock of the Earth's mantle. They are the diamond and the peridot. A peridot is also known as chrysolite and it is a deep yellowish-green transparent variety of olivine (which is itself a magnesium iron silicate and a key mineral of the Earth’s upper mantle).
The mantle of the Earth goes down to a depth of almost 2,900km and is the thickest layer of our planet. It accounts for almost 85% of Earth’s total volume. We know remarkably little about the mantle and most of what we do even know has been derived from seismological research and scientific predictions.
This mantle is sub-divided into different layers. The upper mantle ranges from where the Earth’s crust ends to a depth of around 675 km. Although it’s a viscous, molten, hot soup that's in a state of constant motion thanks to convection currents, it is largely formed from a type of rock called peridotite. This rock is of special interest to us at We Love Diamonds because, as diamantaires, we know that kimberlite is a very rare variant of peridotite. That is formed in volcanic pipes and is the host rock to diamonds. It is these kimberlite diamond pipes that have brought up most diamonds from depths of up to 300km.
The lower mantle of the Earth ranges from around 675km deep to almost 3,000km below the surface (that’s over 1,850 miles). Most diamonds come from the upper mantle but some do come from the lower mantle too and they are commonly known as superdeep diamonds. The Cullinan Diamond, which we talk about in our blog here, is one famous example of a superdeep diamond.
We then move down into the Earth’s core which consists of a solid inner core (with a radius of 1,220km) and a liquid outer core (which extends up to a radius of 3,400km). The depth of the centre of the Earth is 6,378km which is just under 4,000 miles below the surface.
When we experience earthquakes on the planet’s surface, these mostly occur in the crust where the tectonic plates ebb and flow. This creates tension and, in turn, earthquakes. Earthquakes do also happen in the mantle and they do so at unimaginable pressures. Although we don’t fully understand all of the dynamics of this, many scientists believe this could partially be caused by minerals changing from one state to another (which would change their volume and potentially cause earthquakes in the mantle). However, the type of eruptions that delivered the remarkable gift of diamonds to all of us humans living up here on the surface no longer occur because the earth has since cooled significantly over billions of years since then which now makes such eruptions impossible.
So we’ve established that diamonds are formed in a Goldilocks zone within the mantle of the Earth. You’ll probably already know that they are made of carbon (or, more specifically, carbon that has crystallised to form diamonds). To expand a little further, diamonds are made of billions of carbon atoms which all have a highly organised and unique cubic crystal lattice structure where every carbon atom is strongly bonded to four other atoms. That’s why they’re so hard. The formation of these diamonds occurred between 1 and 3 billion years ago under the heat and pressure of the Earth's mantle.
We typically measure pressure in pascals. To give you an idea of the extraordinary level of pressure in the mantle where diamonds are formed, imagine a herd of 80 elephants standing atop each other all on just one of your toes. That’s the equivalent of five to six gigapascals. That is the typical pressure diamonds were formed under.
Temperature-wise, we’re talking about a temperature of between 900°C and 1,300°C and that's almost a quarter of the temperature of the Sun’s surface (which stands at around 5,000°C). The melting point of a diamond is almost 4,000°C and it’s so high because the very strong carbon-carbon covalent bonds of a diamond operate in 3 dimensions and they all have to be broken throughout their structure before any melting can even begin to occur. Diamonds also do not conduct electricity as the electrons are all tightly gripped between the atoms and are thus not free to move.
For all intents and purposes therefore, diamonds are not just timeless and eternal but they are practically indestructible thanks to their unique cubic crystal lattice structure. That’s why you need a diamond to cut another diamond and why any diamonds you buy from us will genuinely last forever.
A VIOLENT JOURNEY...
Practically all of the diamonds we find on or near the surface of Earth were blasted up to the surface during violent volcanic eruptions around 25m years ago inside the mantle of our planet. No such eruptions have occurred in recent times since the earth was much, much hotter then and these eruptions were much more profound than the rare eruptions we experience today. After these eruptions reached the planet’s surface they built up a mound of volcanic material. That material eventually cooled and most diamonds are found within this material. They are known as the Kimberlites because their route to the surface was via “Kimberlite pipes”. These are volcanic pipes which rose from around 300km below the surface in the upper mantle of the Earth via the high-pressure eruption of "kimberlite magma". That magma expanded and blasted through rock as it reached its rapid, violent journey to the crust.
Where diamonds were blasted to stable areas they survived (in others they were eviscerated). Most of these stable areas include what is now Russia, Australia, Africa and the America’s and is precisely why these are the regions where most diamonds are now discovered and mined today having previously lay unnoticed for millions of years. The rarity of diamonds becomes even more telling when you consider that over the last couple of hundred years, only around 7,000 kimberlite pipes have ever been discovered and tested. Less than 1,000 of them contain diamonds and only 5% to 6% of those are economically viable enough for the likes of De Beers, Alrosa and Rio Tinto to mine them.
Modern humans only appeared around 200,00 years ago and dinosaurs between 233 and 243 million years ago. Diamonds were mostly formed between 1 billion years ago and 3 billion years ago so diamonds really are forever when compared to us. The Hope Diamond, for example, was dated as being over 1 billion years old. The earliest recorded piece of surviving diamond jewellery dates back to a ring that was made around 300BC. Since then diamonds have truly emerged as the unrivalled gemstone of choice and a ubiquitous cultural touchstone.
IS GRAPHITE THE SAME AS DIAMONDS?
No. While diamonds and graphite are chemically identical (both are entirely made of carbon) they're physically miles apart in terms of their relative hardness. Using the Mohs Hardness Scale for Minerals, diamonds are the world’s hardest known natural substance with a hardness factor of 10. No other naturally occurring substance has such an incredible hardness factor. The crystal structure of graphite has a hardness factor of less than 1. This is because, in diamonds, the carbon atoms are arranged tetrahedrally and each carbon atom is attached to four other carbon atoms. This gives diamonds an extraordinarily strong, rigid, three-dimensional structure which results in an infinite, super-strong network of atoms. The carbon atoms contained in graphite only bond to 3 other carbon atoms. So while a diamond has a tetrahedral structure, graphite takes the form of layers. The presence of these layers means that the carbon atoms in graphite slide over each other more easily which significantly reduces their strength and hardness.
WHAT ABOUT COAL?
To dispel a common myth, diamonds are not formed from coal and coal plays no role in the formation of a diamond. Most diamonds are far, far older than plants anyway and plant debris is the primary material of coal. Furthermore, coal is a sedimentary rock that is rarely buried deeper than about 3km.
Scientists believe that the carbon source of diamonds was instead derived from carbon that was trapped in the interior of the Earth's during its formation (and/or possibly carbon which was delivered down to great depths by the process of subduction - a geological process where the oceanic lithosphere gets recycled into the Earth's mantle at converging boundaries).
So although coal is carbon-dense like diamonds (and indeed graphite), diamonds are categorically not formed from coal. Instead, coal molecules are randomly stacked which is not just what gives coal its colour but why coal burns so easily and why it can be broken into smaller pieces. Try breaking a diamond into smaller pieces with a piece of coal, you'll make quite the mess!
The phrase “a diamond is a chunk of coal that did well under pressure” is therefore completely false. Diamonds stand alone from practically anything else on Earth. They say diamonds are forever which is not completely true but it's certainly an incontestable fact that, relative to the universe, they technically will last forever and will certainly outlast humankind, our planet and perhaps even most of the universe. Good luck in naming something else that you can ever own with the same timeless and eternal potential...
REAL IS INDEED RARE
As we have hopefully explained - natural, authentic diamonds are absolutely finite and they are only getting rarer and rarer as we mine/discover them. It's a sad fact that nature will not be gifting us anymore diamonds from the planet’s mantle since the level of volcanic activity required to do so ended tens of millions of years ago and will not be occurring ever again.
Despite the extraordinary expanse of time since their formation and the incredible human effort dedicated to finding these eternal items, diamonds are just so, so incredibly rare to find that it’s almost a miracle that they are ever found. To put this exceptional rarity into context then just consider this. If every diamond that has ever been cut from the entirety of human history was collected together, they would just about fill one double-decker bus. In turn, the subset of those diamonds that would meet the stringent diamond quality requirements of We Love Diamonds (in terms of their colour, cut, clarity, carat and certification) are just an even smaller fraction of that again and would probably fit into the drivers glovebox!
Diamonds are natures gift and we love them. However, as we always say, without you they’re just diamonds.