Apart from being gorgeous gems, diamonds are famously known for their extreme hardness. But with scientific and technological evolution bringing us new materials, one has to wonder:
Are diamonds the hardest substance on Earth?
The answer to this question would be:
No, diamonds aren’t actually the hardest substance on Earth, as there are a few naturally occurring substances that are harder. But more importantly, there are synthetic materials that exhibit extreme hardness, much more than diamonds do.
Are you shocked? Well, we were, too!
In this article, we’ve covered substances that are harder than diamonds and a bit of science behind them, so without further ado, let’s jump right in.
How Hard Is A Diamond?
Carbon is one of the most interesting elements in nature, with physical and chemical properties, unlike any other element. With six protons in its nucleus, it’s the lightest abundant element that is capable of forming a bunch of complex bonds.
All known forms of life are based on carbon, as its atomic properties enable it to connect with up to four other atoms. Geometries of those bonds enable carbon to self-assemble into a stable crystal lattice.
And when the conditions are right, carbon atoms can form a solid, extremely hard structure known as a diamond.
These bonds between carbon atoms – along with their shape – make them the strongest gems.
Diamonds are made from carbon that’s been under extreme heat and pressure, found in the depths of the Earth’s mantle. The creation process lasts between 1.3 and 3 billion years.
The pressure and heat cause the carbon molecules to change so that they can be as close together as possible. The closeness of these molecules forms the rigid bond, which makes the resulting diamond so hard.
When we say “hard,” we mean it:
Diamonds are rated a perfect “10 out of 10” on the Mohs scale of hardness. This scale characterizes the resistance to scratching of various minerals through the ability of a harder material to scratch a softer one.
By the way, the Mohs scale of mineral hardness was created by German geologist and mineralogist called Fridrich Mohs in 1812.
Diamonds are known as the hardest material in the world; we’ve all heard that claim before. Surprisingly enough, there are six materials that are considered to be even harder.
Nonetheless, diamonds are still one of the hardest naturally occurring materials on Earth.
Honorable Mentions Among Minerals
Three terrestrial materials aren’t as hard as diamonds but are still pretty interesting to look at because of their strength. Since we’re already here, we figured that it wouldn’t hurt to look at these honorable mentions.
With the arrival of nanotechnology – alongside the evolution of nanoscale understandings of modern materials – we now acknowledge that there are many different metrics to assess other “extreme” materials and their impressive properties.
On the biological side, spider silk is notoriously tough. With the higher strength-to-weight ratio than most conventional materials like steel and aluminum, it’s also interesting how incredibly thin and sticky it is.
Darwin’s bark spiders have the toughest silk of all spiders, and, get this – it’s ten times stronger than Kevlar.
Silicon carbide is a naturally occurring mineral, also known as moissanite, and it’s only slightly less hard than a diamond. Silicon carbide grains have been produced since 1893. They can be bonded together through a low-temperature and high-pressure process known as sintering to create very hard ceramic materials.
These materials play a role in a wide variety of applications, such as car brakes and clutches, plates in bulletproof vests – and they even boast some useful semiconductor properties in electronics.
Of course, diamonds are harder than these and clock in at 7th place on the list of the hardest materials found – or created – on Earth. Although other rare natural materials – and a few synthetic ones – have surpassed diamonds, they still hold one important record:
Diamonds remain the single most scratch-resistant material known to us.
Metals like titanium are way less scratch-resistant, and even ultra-hard ceramics or tungsten carbide can’t compete with the diamond when it comes to hardness regarding scratch resistance.
Other extremely hard crystals such as sapphires and rubies still fall short of diamonds. But as we already mentioned, six materials have the vaunted diamond beat in terms of hardness.
Let’s take a look at them!
1. Wurtzite Boron Nitride
Instead of carbon, crystals can be made out of a number of other atoms or compounds. One of them is boron nitride. The 5th and the 7th element on the periodic table will come together to form various possibilities.
It can be amorphous, hexagonal, cubic, and wurtzite form. The last one of these forms is extremely rare and extremely hard. Formed during volcanic eruptions, it’s only been discovered in small quantities.
That means that we’ve never tested its hardness experimentally.
However, according to the recent simulations, it forms a different kind of crystal lattice – a tetrahedral one – that is harder than a diamond.
Imagine a meteor full of carbon – therefore containing graphite – hurdles through our atmosphere and crashes into the Earth. You might see a falling meteor as an extremely hot body.
However, only the outer layer of it is hot; the inside remains cool for most of its journey towards Earth.
Upon impact with our planet, the pressure inside becomes more powerful than any other natural process on Earth’s surface, causing the graphite to compress into a crystalline structure. However, it doesn’t possess the cubic lattice of a diamond but rather a hexagonal lattice.
This hexagonal lattice can achieve hardness that is 58% greater than what diamonds achieve.
Even though the actual examples of lonsdaleite contain a certain amount of impurities to make them softer than a diamond, if a graphite meteor without impurities were to strike the Earth, it would produce material harder than any other terrestrial diamond.
Now, this is the point where we leave the realm of naturally occurring substances behind and focus on synthetic materials.
Dyneema, a thermoplastic polyethylene polymer, is peculiar for having high molecular weight.
Most molecules are chains of atoms with several thousand atomic mass units in total. However, ultra-high-molecular-weight polyethylene has very long chains, with molecular mass measuring in the millions of atomic mass units.
With extremely long chains for their polymers, the interactions between molecules are strengthened, creating a pretty tough material. In fact, it’s so tough that it has the highest impact strength compared to any other thermoplastic.
It’s called the strongest fiber in the world – and it outperforms all tow and mooring ropes. Even though it’s lighter than water, it can stop bullets and has 15 times the strength of the same amount of steel.
Isn’t that insane?
The military uses Dyneema to create armor, and the commercial fishing industry uses it for nets and ropes. Additionally, outdoor-gear companies are realizing its potential as they implement it in their products due to its incredible strength.
4. Palladium Micro-Alloy Glass
It’s important to distinguish two crucial properties that all physical materials have:
Strength – which is how much force it can withstand before deforming – and toughness, which refers to how much energy it takes to fracture or break it.
Most ceramics are strong but not tough; they can shatter with vice grips or even when dropped from a modest height. Elastic materials such as rubber can hold a lot of energy but can easily be deformed, thus not strong at all.
Most glassy materials are quite brittle; they’re strong but not very tough. Even reinforced glass such as Pyrex or Gorilla Glass isn’t that tough on the scale of materials.
However, scientists developed a new micro-alloy glass that features five elements:
Palladium provides a pathway for forming strain localization, which allows the glass to deform plastically and not crack. It defeated all types of steel and anything on this list when it comes to both strength and toughness.
By the way, this is the hardest material that doesn’t include carbon.
Unfortunately, the price of palladium – and the complex techniques needed to make palladium glass – prevent mass-production at this time. Otherwise, it could be the best material for fabricating vehicles and aircraft.
On the other hand, smaller applications can still be viable. In particular, scientists who created the glass believe that it may be the perfect material for dental implants.
It’s well known for quite some time that there’s a form of carbon that’s harder than diamond called carbon nanotubes. This material can hold a rigid cylindrical-shaped structure by binding carbon together into a hexagonal shape.
If we take an aggregate of carbon nanotubes and create a macroscopic sheet of them, we can create the so-called buckypaper.
Each nanotube is between 2 and 4 nanometers across, but each one is extremely strong and tough. In fact, it’s only 10% the weight of steel – but has hundreds of times the strength.
Even more so, buckypaper is fireproof, thermally conductive, and possesses electromagnetic shielding properties.
Buckypaper use on the structural base of the vehicles and its body seems like one of the best applications of this material. However, we still need to wait a few years to see real commercial applications due to the complex process and higher production costs.
On the first spot, we have a hexagonal carbon lattice that’s only a single atom thick. That is what a sheet of graphene is – and some would say it’s the most revolutionary material to be developed in this century.
Graphene is the basic structural element of carbon nanotubes, and its applications are expanding continuously. Interestingly enough, graphene is a multimillion-dollar industry, and it’s expected to grow into a multi-billion dollar industry in a few decades.
In proportion to graphene’s thickness, it’s the strongest material ever created. It’s an extraordinary conductor of both electricity and heat and is almost 100% transparent in light.
What’s more, graphene can be used to improve the strength of other materials. Scientists have shown that adding a trace amount of graphene to metals, plastics, or other materials can make these materials much stronger.
Graphene is the most heat-conductive material found to this date. As it’s also light and strong, it means that it’s a perfect material for making heat-spreading solutions. That could be useful in microelectronics as well as in larger applications, such as thermal fouls for mobile devices.
Since graphene is the thinnest material in the world, it has an extremely high surface area to volume ratio. That makes it a very promising material for use in batteries; it could potentially enable batteries to store more energy and charge faster.
Graphene has promise for additional uses such as:
- Anti-corrosion coatings and paints
- Efficient and precise sensors
- Flexible displays
- Faster and efficient electronics
- Efficient solar panels
- Faster DNA sequencing
- Drug delivery
Graphene is such a great building block that it looks like any industry can benefit from it. Only time will tell where graphene will make a huge impact or if other new materials will be even more suitable.
If you’re still asking yourself the question, “Are diamonds the hardest substance on Earth?” let us sum it up for you once and for all.
Even though diamonds are famously known to be the hardest substance on the Earth, there are actually six other materials that are even harder. But nonetheless, diamonds are still extremely hard.
The quest to make materials harder, stronger, lighter, tougher – BETTER – is most likely never going to end. If scientists can push the boundaries of the materials available to us farther than ever before, the limits for what becomes achievable can only expand.
As we advance into the nanotech age, materials like the ones we described here become increasingly critical to our quality of life. As the 21st century unfolds, we’re yet to witness what suddenly becomes feasible with these new materials.