HOW IS A DIAMOND FORMED?

How is a diamond formed?

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

The earth formation of the natural diamond

Diamonds are highly sought after natural elements. The most common mode of formation is deep beneath the Earth's surface from pure carbon, where it is present in a liquid state. The production time for diamonds is extremely long. Indeed, the creation process occurs over millions (even billions) of years. Diamonds form from carbon under extreme conditions. Indeed, 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 surface of the Earth to then be extracted by men in mines to be used for the creation of precious jewellery. To be able to reach the surface of the Earth, volcanic eruptions because the

arrive at the surface of the Earth at an extremely fast speed.

In other words, the history of diamond formation begins more than three billion years ago at depths between 150 and 200 kilometers from the surface of the Earth (what geologists call "the upper mantle of the Earth") within which reigns an extremely high temperature of up to 1500 degrees. 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 with a microscope or magnifying glass.

How diamonds form in meteorites

If the formation of diamonds were not limited only to their journey through the upper mantle of the Earth, meteorites would have brought us samples of diamonds. Indeed, coming from the interstellar medium, certain 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 strikes 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 mode of diamond formation is found 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 in the rear of the area. 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 the earth thanks to eruptions of volcanic rocks: kimberlites and lamproites. These rocks are rich in magnesium and were used to transport diamonds and various materials from the mantle. These two volcanic rocks are therefore not the sources of the diamonds but rather ensured a role of "elevator" to bring these diamonds up to the surface of the Earth. There are many large diamond deposits all over the world.

Today, it is clear that the world's diamond production is mainly in Africa, where this resource is much more abundant than in the rest of the world. Indeed, about 60% of the world's diamond production is located in Africa with large deposits such as the Democratic Republic of Congo, Botswana, South Africa, Angola and Namibia. The other diamond-producing countries are Russia, but also Australia and 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 buying a diamond, a certificate of authenticity is given to the buyer. This stone identity card is essential because it gathers all the technical and physical characteristics of your diamond according to the Kimberley process.

Primary deposits

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

Extracting diamonds in mines is the most famous 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. The extraction can be done in underground mines, at least one kilometer below the ground, or in the open with the help of earthmoving machines or explosives to extract a good quantity of diamonds.

Secondary and alluvial deposits

These deposits result from the erosion of the rocks of the 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 weathering of the primary deposits. In these deposits, diamonds are transported by rivers. Secondary alluvial deposits consist of processing 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 to the Atlantic Ocean, not far from the mouth of the Orange River, at the edge of which sit many diamond mines. This deposit, which concerns the coasts and the seabed, uses earthmoving equipment or explosives to fetch diamonds from 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 into the world jewelry market for several years. Natural diamonds come from volcanic phenomena on the Earth, while synthetic diamonds are produced in the laboratory under 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.

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

The other method of diamond production is "Chemical Gas Deposition". In other words, this method produces defects with even fewer defects than those found by humans 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 that they do not come from nature and cannot run out because they can be reproduced indefinitely. by the man.