How are diamonds formed? Here are 5 Ways

A long time ago, around the 4^th century BC in India, the first diamonds were discovered by people and they quickly started to spread around. As beautiful gemstones as they are, they become highly valued very soon, and also gain symbolic weight in our culture.

In the past, ancient civilizations thought that diamonds were presents from the Gods and believed that they bring wealth, health, and strength. While the symbolism remained and slightly transformed over the years, we have actually managed to find out what process took place in order for diamonds to be formed.

Have you ever wondered how exactly diamonds were formed and what geological factors were involved?

Before we go into how diamonds are formed, let’s first state how diamonds are definitely not formed.

A widespread notion is that diamonds come from coal, or as the quote goes “A diamond is a chunk of coal that did well under pressure”.

Although funny, it is inaccurate, as diamonds are not made of coal, however similar in composition they may be.

Both substances are actually formed from carbon, but this happened in a different place in the earth, with the coal being formed considerably closer to the earth’s surface. While diamonds consist purely of carbon minerals, the coal is a combination of carbon and organic plant matter.

The diamond itself is actually crystallized carbon.

This crystallization occurs deep in the earth’s mantle under conditions of intense heat and pressure. Due to the extremely high temperature and pressure, carbon atoms bond densely to each other in carbon chains where each carbon atom is attached to four other carbon atoms.

These strong covalent bonds that are created between carbon atoms bring about the diamond’s unique hardness.

Speaking of hardness, on the scale that is used to measure the hardness of minerals, ranging from one to ten, a diamond will rate ten. Also, these strong bonds which connect the carbon atoms prevent any other elements to become part of the stone, leaving the diamond pure.

Having defined what diamond is actually made of, we can go more into the 5 different ways in which diamonds are formed.

The first and the main way in which diamonds are formed is quite lengthy and happens deep in the earth’s mantle and is assisted by deep volcanic eruptions. The earth’s upper mantle is a layer 100 miles (160 km) deep in the Earth, which separates the surface from the molten core.

In order for a diamond to form, certain specific conditions need to be met, such as high temperature and pressure. The diamonds form under temperature of around 2000 degrees Fahrenheit (1050 degrees Celsius) and at a pressure of 45 to 60 kilobars (for comparison: that is 50,000 more than the atmospheric pressure at the Earth’s surface).

The perfect conditions are not met everywhere in the earth’s mantle, as the mantle continuously moves the heat and the covering rocks that cause the pressure very often vary in thickness and density.

The diamonds usually form beneath the interior region of the continental crust, which weighs more and is not prone to much movement from tectonic activity. Also, the carbon that is turned into diamond has been actually trapped in the earth’s mantle during the formation of the planet.

So, under the right conditions, the pressure makes the flowing substances which move through the mantle erupt, while forging the trapped carbon into diamonds and moving it towards the surface. Scientists believe that this process occurred quite quickly (relatively speaking, of course), probably in the matter of hours and the travelling rates are thought to be 20 – 30 miles per hour. If it hadn’t happened at this rate, the result would be formation of graphite instead of diamond. Lucky chance, isn’t it?

The cracks where the magma moves are known as kimberlite pipes. Kimberlte is a type of igneous rock which was formed over thousands of years during the formation of the earth’s crust. It is found in vertical holes that extend deep inside the earth in places that had volcanic activity in the past. In some of the kimberlite there are deposits of diamonds and some other minerals such as mica, garnet, and zircon. However, it is estimated that gem-quality diamonds can be found in 1 out of 20 kimberlite pipes. The name actually comes from a South African town Kimberley, where the famous Star of South Africa was found.

These deep volcanic eruptions are the most common way in which diamonds are formed, and yet, they are quite rare and haven’t been noted in the past 400 years.

Overall, this whole process of formation and moving the diamonds cannot be quite pinpointed in terms of duration, but scientists have dated the minerals surrounding the diamond formation and believe that it took between hundreds of millions of years and 1-3 billion years.

Another way of diamond formation that also happens underground is the formation in subduction zones.

Subduction zones are areas in the earth’s mantle that have been created when tectonic plates of different composition and density collided, and one plate was forced beneath the other one. This process has put such areas under great pressure and temperature. If the plates contain materials rich in carbon content, all of the requirements for the formation of diamonds are met.

However, the diamonds that are created in subduction zones require less heat and pressure than the ones formed deep in the mantle. With this method, they can form only 50 miles (80 km) below the earth’s surface and at temperatures reaching around 390 Fº (200 Cº).

As it has been noted, the process of subduction occurs more often in oceanic plates, due to their high density and it is the oceanic plates that are usually subducted into continent plates.

Also, these plates carry the types of rocks that provide the carbon needed for the creation of diamonds. The source of carbon in oceanic plates would most likely be the leftovers of decaying plant life or the calcium carbonate shells of dead marine organisms, along with rocks such as limestone and dolomite that are often part of oceanic crust.

When it comes to collisions that are purely of continent plates, the source of carbon here are some carbon rocks or mantle carbon that has been pushed upwards. This has been the way in which a great number of Indian diamonds were created and such collision still pushes the Himalayas higher even in present day.

It is important to note that the diamonds which are formed in these subduction zones are quite small in size and very few of them manage to actually come out to the surface, which makes them no good for commercial use and there is no search for such deposits. Majority of them will just lie in place millions of years waiting for a volcanic eruption to bring them to the surface.

Another interesting fact to be added is a recent study on blue, boron-containing diamonds. These diamonds are thought to have formed 400 miles (650 km) deep in the ground, and contain inclusions which show that these diamonds are most likely derived from subducted oceanic crust. To find out more, read the latest research about the origin of blue diamonds.

Although it may sound unusual, there are diamonds which have been found inside meteorites.

Here’s a little more on how this process occurred.

During the years, the Earth has been hit by large asteroids on many occasions. The moment when an asteroid strikes the earth, the collision produces high temperature and pressure. As mentioned before, these are the basic prerequisites in diamond formation.

So, upon the impact, the carbon based deposits which are found in the crater turn into diamonds. Still, don’t run immediately if you happen to know some crater around, you won’t find your engagement ring there. The diamonds which form in this way are quite tiny, usually around a couple of nanometers in diameter and are not of gemstone quality.

Such diamonds are likely to be used in industrial purposes because of their strength. Popular impact sites where such diamonds have been found are the Popigai Crater in northern Siberia, Russia (diamonds up to 13 millimeters in size), and Meteor Crater in Arizona (sub-millimeter diamonds).

Although precious and rare, diamonds are not exclusive to Earth.

Considering the fact that carbon is the fourth most abundant element in the universe, it becomes clear that there will be some sort of place where the perfect conditions for the formation of diamond will be created. A great number of nanodiamonds have been detected in meteorites and are believed to have formed when other meteors collided, in the same way that they form when asteroids strike the earth.

Such diamonds have been found by Sminthsonian researchers while cutting a sample from the Allen Hills meteorite. Even though these diamonds are so small that cannot be used in either industrial or commercial purposes, they still represent a source of diamond material.

On the other hand, there are some diamonds of a considerable size that are believed to have originated in and come from space. Such diamond, and actually the largest diamond that has ever been found is “Sergio’”, a 3.167-carat black diamond.

Scientists suppose that this diamond is actually a fragment from an ancient meteor. What’s more, all black diamonds are thought to have formed in space and have come to Earth thorough the debris falling through the atmosphere.

Another quite interesting fact worth mentioning is a former star, Lucy, which has become crystallized carbon after it burned out into a white dwarf and it is supposed to be 10 billion trillion carats! Amazing, right?

Apart from under the earth and in space, diamonds can also be formed on the Earth’s surface. Having learned the conditions needed for diamonds to form, scientists successfully managed to replicate them in a lab in the 1950s, which is when the synthetic diamonds started being produced.

There are two different methods which are used to create synthetic diamonds.

The first method is known as HPTP, or high pressure, high temperature. In this process, a piece of graphite is put in a machine where it undergoes treatments of intense heat and pressure. The whole process of forming can take up to several days before the diamond is created. However, as a metal solution must be added to the graphite, the result is a diamond which has not the same purity of a naturally formed one. So, majority of the diamonds formed with this technique serve for industrial purposes.

The second method includes chemical vapor deposition. It starts with diamond seeds, which would be small silvers of a natural diamond, being placed in a vacuum chamber. Then, with the heating of methane and hydrogen gas the ideal temperature is achieved, whereas the vacuum chamber applies the needed pressure. The result is a cube-shaped diamond that can be seen after 28 days.

It certainly seems that the formation of the diamond can be a quite complex and lengthy process and there are specific conditions that need to be met.

Were you aware of these processes and does it somehow affect your opinion of diamonds?

Mimoza Celevska is a language enthusiast who turned her interests and passion into profession. Customer support professional and freelance content writer. Enjoys carefully crafting unique and research-driven content suited to the particular context. Doesn’t listen to music only when sleeping. If not responding to messages, it can be safely presumed that she’s found a cat somewhere.