HOW IS A DIAMOND FORMED?

How is a diamond formed?

Diamond is an extremely coveted stone and its price increases over the years. Indeed, a precious gift of nature, natural diamonds are exhaustible resources that see their value increase. This pure carbon crystal has an exceptional composition due to its brilliance and hardness. There are different mechanisms for the formation of natural diamonds that explain the rarity of this most precious and oldest stone that the Earth has ever known.

 

The terrestrial formation of natural diamonds

Diamonds are highly sought-after natural elements. The most common way they are formed is deep below the Earth's surface from pure carbon, where it is present in a liquid state. The production time for diamonds is extremely long. In fact, the creation process occurs over millions (or even billions) of years. Diamonds are formed from carbon under extreme conditions. In fact, the production process requires a sufficient degree of pressure and heat to transform this carbon into a diamond. Once formed, diamonds gradually rise to the Earth's surface and are then extracted by humans in mines to be used to create precious jewelry. In order to reach the Earth's surface, volcanic eruptions, as the

arrive at the Earth's surface at an extremely fast speed.

In other words, the history of diamond formation begins more than three billion years ago at depths of 150 to 200 kilometers from the Earth's surface (what geologists call "the Earth's upper mantle"), within which an extremely high temperature of up to 1500 degrees prevails. In these extreme temperatures, pure carbon will create a diamond by crystallizing. This transparent mineral will rise to the surface of the Earth when the magma of a volcano melts to bring out these diamonds buried more than 150 kilometers below the Earth.

Diamonds have many specific characteristics that experts can observe using a microscope or magnifying glass.

How diamonds form in meteorites

If the formation of diamonds were not limited to their path traveled in the Earth's upper mantle, meteorites would have brought us samples of diamonds. Indeed, coming from the interstellar medium, some grains trapped inside meteorites would have reached us for 4.55 billion years thanks to the absence of chemical interactions with the grains. Thus, the diamonds were located inside the residual powder of the meteorite. Indeed, they were visible using a microscope: small crystals appeared but were not completely visible because they represented the size of fine particles.

Also, asteroid impacts allow the formation of diamonds. Indeed, when an asteroid of a large diameter hits the Earth, the power of the impact is so great that the pressures and temperatures generated during this shock are sufficient to form diamonds.

 

Diamond formation in subduction zones

Another way diamonds form is in subduction zones. Subduction is a geodynamic process during which a tectonic plate sinks under another plate of lower density (oceanic or continental) and thus sinks into the mantle. This phenomenon can sometimes give rise to volcanism behind the zone. Thus, high temperatures and pressures are recreated which represent favorable development conditions for a diamond because crystallization is favored in these elements.

The different types of deposits

This mineral, founded in great depths below the earth and in extreme conditions, arrives on Earth thanks to eruptions of volcanic rocks: kimberlites and lamproites. These rocks are rich in magnesium and have allowed the transport of diamonds and various materials from the mantle. These two volcanic rocks are therefore not the sources of diamonds but rather have ensured an "elevator" role to bring these diamonds back to the surface of the Earth. There are many and important diamond deposits throughout the world.

Today, it is clear that the world production of diamonds is mainly in Africa, where this resource is much more abundant than in the rest of the world. Indeed, approximately 60% of the world production of diamonds is located in Africa with important deposits such as the Democratic Republic of Congo, Botswana, South Africa, Angola or even Namibia. Other diamond producing countries are Russia but also Australia or Canada.

Due to their high value, diamonds sometimes pose a problem and fuel a conflict of illegitimate diamonds on the market (conflict diamonds). Thus, when purchasing a diamond, a certificate of authenticity is given to the buyer. This identity card of the stone is essential because it brings together all the technical and physical characteristics of your diamond in accordance with the Kimberley process.

Primary deposits

The first deposits were mainly kimberlites and lamproites. These deposits are mainly found in ancient continental areas. These "source rocks" are originally the host rocks of diamonds that allowed diamonds to rise to the surface of the earth. However, not all of these rocks contain diamonds. Indeed, the distribution of diamonds would not be homogeneous.

Mining rough diamonds is the most well-known and is not an easy task and requires a lot of time to dig deep into the earth. On average, to obtain one carat of diamond, it is necessary to extract ten tons of rock. Mining can be done in underground mines, at least one kilometer below the ground, or in open pits with the help of earthmoving equipment or explosives to extract a good quantity of diamonds.

Secondary and alluvial deposits

These deposits result from the erosion of rocks from primary deposits and the reconcentration of the released diamonds in rocks or in particular deposits. These secondary deposits contain minerals and are called "placers" and are diamondiferous rocks or deposits obtained by the erosion and alteration of primary deposits. In these deposits, diamonds are transported by rivers. Alluvial secondary deposits consist of treating river alluvium to find diamonds. This type of work is often carried out in Brazil in artisanal or industrial production but requires a large production of river water.

Underwater deposits

Finally, there are also diamond deposits in the seabed. Indeed, the best known are not located far from Africa and are buried in sediments. The diamonds were carried towards the Atlantic Ocean, not far from the mouth of the Orange River, on the banks of which are located many diamond mines. This deposit, which concerns the coastlines and the seabed, uses earthmoving equipment or explosives to fetch diamonds tens of meters under the sea.

Synthetic diamonds

If we have talked about the formation of natural diamonds, we can also talk about synthetic diamonds which have been integrated for several years, the global jewelry market. Natural diamonds come from volcanic phenomena on Earth while synthetic diamonds are produced in the laboratory in extreme conditions which also reflect what is happening on Earth and make it possible to respond to the problem of the depletion of natural resources. Indeed, synthetic diamonds are infinitely reproducible ( see how to recognize a diamond ).

There are two ways to produce diamonds in laboratories. First, the "HPHT" (High Pressure, High Temperature) method is the one that comes closest to the natural production method. Indeed, graphite (made of pure carbon) is subjected to high pressure and high heat to crystallize into a diamond.

The other method of diamond production is "chemical vapor deposition". In other words, this method produces defects with even fewer defects than those found by man in nature. A piece of diamond is placed in a depressurization chamber and then treated with natural gas and heated.

Synthetic diamonds are therefore the fruit of human inventiveness and have the same characteristics as natural diamonds, with the only difference being that they do not come from nature and cannot be exhausted because they can be reproduced indefinitely by man.