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Why Is Diamond So Hard?

Why Is Diamond So Hard?

It’s widely known that diamonds are one of the hardest materials on Earth; we’ve said this more times than we could count. 

But not many people know why this is the case.

So, our mission today is to tell you all about the origins of the hardness of diamonds and some little-known facts about this characteristic of theirs. Here’s one to kick things off: Due to their extreme hardness, diamonds have been assigned some unique jobs and served special purposes over the years, too. 

Here’s what we mean by that: Diamonds have been used for the precise cutting of hard materials for a long time now – and that’s because of their exceptional hardness.

These are all facts that will help you understand why is diamond so hard and how it has been used due to its hardness. Let’s jump straight in and find out why this precious stone is as hard as it is.

How Are Diamonds Made & Where Does The Hardness Come From? 

The process that needs to take place for a diamond to form and grow is one of the key reasons why diamonds are so hard. So, the place where this story begins is deep underground – where diamonds are made. 

What a diamond essentially is can be summed up as hardened and crystallized carbon. Due to the immense pressure and heat that carbon is exposed to underground, it begins to crystallize and slowly becomes a diamond.

That’s the simplified version, anyway.

Diamonds take between 1 and 3.5 billion years to form, which is quite a long time. So, yes, this process can be considered a slow one.

But, even the time that needs to pass in order for a piece of carbon to become a diamond plays a factor in the diamonds’ hardness:

When a process takes as long as one in which diamonds are formed, it means that everything that goes on is happening extra slowly – and, in a sense, that’s what makes it so durable.

We get that this might not make much sense at first, but here’s something to consider: Just look at how much time forming a blade or a sword takes and how many times it needs to be exposed to extreme heat in order to become as durable as it needs to be.

That’s because tempering a material makes it hard. On that note, “tempering” refers to exposing a material to extreme heat and then cooling it off quickly.

Blacksmiths do this by dipping a blade in a special oil – but the diamonds are a bit of a different story.

Diamonds can be damaged by heat, sure, but we’re talking about diamonds that are deliberately exposed after cutting and being polished for the shop window.

While a diamond is in the ground and still not cut or changed in any way, it gradually cools down – and the extreme heat that has turned carbon into a diamond slowly disappears.

That’s one of the main reasons that diamonds get graded with a 10 out of 10 on the Mohs scale of mineral hardness.

Now, what does that mean? Are diamonds virtually indestructible? 

Well, not exactly. Diamonds are hard, but they can be brittle in some scenarios. We’ll take a look at the difference between toughness and hardness soon enough.

For instance, you’ll see examples of machines that use diamonds for cutting simply because of their hardness. But, at the same time, that requires a high level of care – exactly because of the brittleness of the diamonds.

So, the same natural process that’s responsible for turning carbon into diamonds leaves us with a material that’s quite hard – the hardest one on Earth, to be precise. And yet, it can also be very brittle in some conditions. 

Weird, huh?

Related Read: An In-Depth Guide on Diamond Cutting: How Are Diamonds Cut?

The Chemistry Behind It 

All life known to humans is carbon-based, and that makes carbon one of the fascinating elements on Earth. Something so common in our world also has the ability to – under specific conditions – turn into the hardest mineral there is.

The chemistry behind it might seem like something nobody that isn’t a chemist can’t understand, but trust us when we say: There’s nothing too hard to understand behind the process of carbon turning into a diamond.

Let’s take a closer look at some details of the process that needs to take place for a diamond to form. 

Diamonds are formed in the Earth’s mantle – under extreme pressure and heat, might we add. These conditions occur in limited zones of about 100 miles below the Earth’s surface, where temperatures are at least 2000 degrees Fahrenheit and the pressure is 725,000 pounds per square inch – or more.

That is the critical temperature and pressure needed for natural diamond formation and growth. The carbon atoms then bond together in this extreme environment, creating a mineral we call a diamond.

Those are some huge numbers there, huh? It’s perfectly understandable to feel a bit intimidated by them – but here’s the thing: The beauty of maths, physics, and chemistry is that everything is perfectly logical when you are familiar with and understand the laws that surround the question at hand.

All these huge numbers are mere indicators of what carbon must go through to be turned into a diamond and what the chemical reasoning behind the hardness of a diamond is.

There are but a few materials out there that could withstand as much heat and pressure as carbon can in the process of forming a diamond. For this exact reason, diamonds are as hard as they are.

The immense pressure that takes place while a diamond is forming is responsible for the density and the hardness of the resulting gem.

There are materials that are close in hardness to diamonds – but they aren’t as dense and as hard as diamonds are since that amount of stress and pressure are not even close to what is happening during the diamond-forming process.

That should be enough for most of you to understand the chemical aspect behind the process that takes place in order for a diamond to form and grow.

Hardness Vs. Toughness

Some differences between hardness and toughness are quite often neglected but are crucial for people that want to understand the characteristics of diamonds.

Diamonds are famous for their hardness and are even graded as the hardest mineral on the Mohs scale. Famously, this characteristic of diamonds is widely known, but not many people realize what hardness means in this sense.

People also quite often confuse toughness with hardness and therefore think that diamonds are tough instead of hard. Or, worse yet, that just because diamonds are hard that it must mean they’re tough, as well.

Hardness is regarded as a characteristic related to the external hardness of the material and the general scratch-resistant properties of the diamond’s surface.

On the other hand, toughness is an overall ability to withstand pressure and force without suffering critical damage.

These are two different characteristics and should never be mistaken for one another, especially when it comes to diamonds. You see, diamonds can’t easily be scratched – but a moderate hit with a hammer will shatter almost any diamond you can find.

What we’re saying here is that diamonds are easily shattered but aren’t easily scratched or otherwise damaged on the surface. That’s pretty much the whole point of differentiating hardness from toughness.

A good example of a material that possesses a great amount of toughness is steel – or any kind of metal that’s not particularly easy to destroy.

People who often overlook the fact that diamonds aren’t as tough as they think don’t pay close attention to their diamonds. And that often leads to them dropping a necklace, for example, and dealing critical damage to their diamonds as a result of that drop.

That’s just a little heads up – something to keep in mind when handling any diamond that comes in your possession. As hard as it might be, there’s a certain amount of stress that a diamond can’t withstand, so please, be careful.

Learn More:

Things Diamonds Are Used For Because Of Their Hardness

Drilling, cutting, and polishing are all things you probably wouldn’t think a diamond could be used for, huh? But for some credible reasons, they are – maybe even more than some of you might realize.

The tools made from diamonds are extremely durable and can pierce or cut materials that would otherwise be hard or impossible to process.

As we explained already, diamonds are employed in jobs like cutting and drilling because of their hardness. On the flip side, their lack of toughness calls for extreme care and caution when using diamonds as tools.

For example, a drill that uses a diamond or a diamond-plated end might snap easier than you’d think. Just adding a little pressure from a bad angle could be enough to snap the drill in two. 

We’re talking about a drill that pierces one of the hardest materials on Earth. Concrete or different kinds of metals, even bulletproof glass, is cut with a diamond saw or drilled with a diamond drill.

The majority of you probably know how hard concrete is, and some of you might have had a chance or two to see and feel bulletproof glass – which is much thicker and harder than regular glass, by the way.

It’s worth noting that even the diamonds used in the jewelry business are, hands down, some of the most durable and long-lasting jewelry pieces you will ever come across. 

Here’s an interesting fact to prove our point: Diamond watches are some of the least repaired pieces of jewelry out there, and it’s all thanks to the hardness of the diamonds.

See Also:

Common Misconceptions About Diamonds’ Hardness 

People often have tendencies to see something as a proven fact when it’s nothing more than a common misconception that people are used to spreading.

For example, people think that diamonds that have been grown in a lab aren’t as hard as natural diamonds. That’s absolutely not true since even the diamonds made in a lab have a 10 out of 10 grade on the Mohs scale.

Some so-called diamonds that are artificially made aren’t as hard as the natural ones. But these are often stones or rocks that look like diamonds but aren’t diamonds based on their chemical composition.

Don’t get these rocks mistaken with lab-grown diamonds. And more importantly, don’t think that diamonds grown in a lab are softer or less hard just because they’re made artificially and aren’t as expensive as genuine ones.

Learn More:


Knowing that diamonds take billions of years to form, some might think that the hardness of a diamond comes purely from that.

Although that’s generally true, there are some other factors – like chemistry – that need to be taken into consideration when answering the question of why is diamond so hard.

Nothing here is too complex to understand, but the big numbers used to describe the natural process that takes place in order for a diamond to form and grow might seem scary at times.

Don’t worry; if you didn’t get a clear picture about this process, you can always scroll up to the beginning of this article and start reading again. 

We also had to look at these pieces of information multiple times to get a better grasp on what exactly goes on under the ground to ensure diamonds’ hardness. 

Not only do these bits of information give you a clear picture, but they also show you that these natural processes that take place are, in fact, logical. It makes sense once you take some time to understand them.

Anyway, we hope that this has been a helpful article and that it taught you a thing or two about why diamonds are as hard as they are.

Read Also: Can A Diamond Destroy A Diamond?