How is a diamond formed?

HOW IS A DIAMOND FORMED?

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

The Terrestrial Formation of Natural Diamond

Diamonds are highly sought-after natural elements. The most common way they form 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 (or even billions) of years. Diamonds form from carbon under extreme conditions. 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 to then be extracted by humans in mines for use in the creation of precious jewelry. To reach the Earth's surface, volcanic eruptions cause them to

reach the Earth's surface at an extremely rapid speed.

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

Diamonds have many specific characteristics that experts can observe with a microscope or a magnifying loupe.

Diamond formation in subduction zones

Another method of diamond formation is found in subduction zones. Subduction is a geodynamic process during which one tectonic plate sinks beneath another less dense plate (oceanic or continental), thus entering the mantle. This phenomenon can sometimes lead to volcanism in the back-arc region. Thus, high temperatures and pressures are recreated, which represents favorable development conditions for a diamond, as crystallization is promoted in these elements.

How diamonds form in meteorites

If the formation of diamonds were not limited solely to their journey through the Earth's upper mantle, meteorites would have brought us diamond samples. 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 dust of the meteorite. In fact, they were visible with the aid of a microscope: small crystals appeared but were not entirely visible because they were the size of fine particles.

Also, asteroid impacts allow for the formation of diamonds. Indeed, when a large-diameter asteroid 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.

The Different Types of Deposits

This mineral, formed deep within the earth under extreme conditions, reaches the surface through volcanic rock eruptions: kimberlites and lamproites. These rocks are rich in magnesium and have transported diamonds and various mantle materials. These two volcanic rocks are therefore not the sources of diamonds but rather acted as an "elevator" to bring these diamonds to the Earth's surface. There are many large diamond deposits worldwide.

Today, it is clear that global diamond production is mainly in Africa, where this resource is much more abundant than in the rest of the world. Indeed, approximately 60% of the world's diamond production is in Africa, with important deposits in countries such as the Democratic Republic of Congo, Botswana, South Africa, Angola, and Namibia. Other diamond-producing countries include Russia, as well as Australia and Canada.

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

Primary deposits

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

The extraction of rough diamonds from mines is the most well-known method and is not an easy task, requiring 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. Extraction can take place in underground mines, at least one kilometer below the surface, or in open-pit mines 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 liberated diamonds in particular rocks or deposits. These secondary deposits contain minerals and are called "placers" and are diamond-bearing rocks or deposits obtained by the erosion and alteration of primary deposits. In these deposits, diamonds are transported by watercourses. Alluvial secondary deposits involve processing river alluvium to find diamonds. This type of work is often carried out in Brazil through artisanal or industrial production but requires a large production of river water.

Underwater deposits

Finally, there are also diamond deposits on 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, on the banks of which many diamond mines are located. This deposit, which concerns coastal areas and the seabed, uses earthmoving equipment or explosives to extract diamonds tens of meters under the sea.

Synthetic diamonds

While we've discussed the formation of natural diamonds, we can also talk about synthetic diamonds, which have entered the global jewelry market several years ago. Natural diamonds originate from the Earth's volcanic phenomena, whereas synthetic diamonds are produced in laboratories under equally extreme conditions that replicate what happens on Earth and help address the issue of depleting natural resources. Indeed, synthetic diamonds can be reproduced infinitely (see how to identify a diamond).

There are two ways to produce diamonds in laboratories. First, the "HPHT" (High Pressure, High Temperature) method is the one that most closely resembles the natural production method. In this process, graphite (composed of pure carbon) is subjected to high pressures and high temperatures to crystallize into a diamond.

The other method for producing diamonds is "Chemical Vapor Deposition" (CVD). In other words, this method produces defects, even fewer defects than those found by humans in nature. A piece of diamond is placed in a depressurization chamber, then treated with a natural gas and heated.

Synthetic diamonds are thus the fruit of human ingenuity and possess the same characteristics as natural diamonds, with the sole difference being that they do not originate from nature and cannot be depleted, as they can be reproduced indefinitely by humans.

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