What are diamonds and how are diamonds formed naturally?

Have you ever heard the expression “Diamonds are a girl’s best friend”? Why do you think that might be true? It’s because diamonds are pretty special minerals. In this blog post (and related YouTube video) we're learning what makes diamonds so special. We learn what diamonds are made of, how diamonds are formed naturally, and where diamonds come from.

What are diamonds made of?

Diamond is an allotrope of carbon. Allotropes are different structural forms of a certain element. That means that there are different possible ways to organize the atoms of one single element to create different three-dimensional structural arrangements of that element. For example, some allotropes of carbon include diamond, graphite, fullerenes, and others.

The diamond allotrope has a cubic crystal structure with the carbon atoms in the unit cell forming tetrahedral structures. The unit cell of diamond is the basic unit, which, when translated in all the directions in space, creates the crystals that we know as diamonds. The tight tetrahedral arrangement of the carbon atoms in the diamond structure, together with the very strong bonds between these atoms, makes it extremely difficult to break these bonds. In fact, it’s so difficult that the only material known to be able to cut or scratch a diamond is another diamond. This makes it perfect for the jewelry industry because diamonds will maintain their polish even if they are worn for a very long time. Understanding how diamonds are formed naturally helps us understand why the diamond structure is so difficult to break.

How are diamonds formed naturally?

Here we focus on natural diamonds and how natural diamonds are formed. But there are also synthetic diamonds, which are grown in labs through a process called chemical vapor deposition.

In order to form diamonds naturally, huge pressures and temperatures are needed. We find these kinds of conditions that are perfect for diamond formation in one of the Earth’s inner layers—the mantle. The mantle is the layer between the Earth’s crust and its outer core. The high pressures in the upper mantle compress the carbon atoms together in the closely packed crystal structure that we observe in diamonds. Applying pressures of about 45-60 kilobars under temperature conditions of up to 1300 degrees Celsius is the natural process through which diamonds are formed in the Earth’s mantle.

But if diamonds are formed inside the Earth, how do they get to the Earth’s surface?

Diamonds were carried upwards from the mantle, towards Earth’s surface, by the lava originating in deep volcanic eruptions. These violent volcanic eruptions happened billions of years ago when Earth was much hotter. The magma from these violent eruptions traveled at very high speeds towards the Earth’s surface through vertical structures, breaking the Earth’s crust. This magma brought with it mantle rocks, including the volcanic rock called kimberlite, which then cooled upon reaching the Earth’s surface. The vertical tunnels through which the magma traveled to the Earth’s crust are called kimberlite pipes, and it’s inside these kimberlite rocks that we find the diamonds formed billions of years ago in the Earth’s mantle.

So next time you admire a beautiful diamond jewelry, just remember that it’s a gemstone formed through reactions that took place billions of years ago. That’s a pretty ancient and expensive piece of heritage we have from our planet!

Where do diamonds come from?

Diamonds come from diamond mines established in the locations where the magma containing diamonds broke through the Earth’s crust and created the kimberlite deposits. The countries with the highest diamond production are: Russia, Botswana, The Democratic Republic of Congo, Australia, and Canada. These are only the five biggest diamond production countries, but there are other countries with large diamond production. Here, you can find a list of all the diamond mines in the world.

Colored diamonds: what gives diamonds their color?

Depending on the conditions under which the diamonds were formed, they can have different colors. Diamonds have different colors either because of impurities trapped in the diamond structure, or because of certain defects in the lattice, or because of the effects of radiation on diamonds. In this blog post, I explain which one of these causes is responsible for which diamond color.

Applications of diamonds

Diamonds as gemstones in jewelleries

Besides the all-romantic “will you marry me” overpriced way of showing your love towards someone, we also have some more useful applications of diamonds. In fact, only about 20% of the mined diamonds are used in jewelries as gemstones. The other uses of diamonds (summarized below) are focused on industrial and research applications.

Diamonds for industrial and research applications

Diamonds can be used for cutting, grinding, and polishing materials, including other diamonds. Diamonds can also be used in diamond windows in research equipment, in diamond speaker domes in high-quality speakers, for engraving granite and quartz, and even in medicine for drills in dental tools. And nanodiamonds even have potential uses in cancer research for monitoring how well the cancer medication works in cancer patients.

Diamonds in Nuclear Magnetic Resonance

Diamonds are also being used in Nuclear Magnetic Resonance (NMR). In NMR, researchers use the nitrogen-vacancy (NV) centers in diamonds to increase the sensitivity of NMR experiments to be able to record NMR experiments on much smaller sample volumes than in conventional NMR.

High pressures with diamond anvil cells

My favorite application of diamonds is creating new forms of materials by exposing them to high pressures. In materials research, scientists use what we call diamond anvil cells to induce high pressures in materials. We do this by pressing together two diamonds. The closer together the diamonds get, the higher the pressures in the material that’s in between the diamonds. This helps researchers study the properties of materials, monitor phase transitions in materials, and possibly create new high-pressure phases of materials with improved properties.

Let me know in the comments which one of the diamond applications I mentioned you think it’s most interesting.