How does carbon turn into diamond?

Who in childhood did not dream of going on a trip to look for diamond placers or find a diamond vein? To look for stones, you need to understand how they are formed in the bowels of the earth and what processes contribute to bringing diamonds to the surface. In ancient times, people believed that diamonds were fragments of the firmament or the walls of heaven. Among Indian beliefs there was also one that stones are capable of reproducing by division, the main thing is that there is a suitable place for them around. When scientists found out that diamond’s composition is related to coal and graphite, people began to think more about the processes, the combination of which does not lead to the appearance of coal, but forms a unique gemstone from carbon molecules.

Mantle-magmatic theory

• diamond veins are formed in geologically stable areas;
• burial depth – from 100 to 200 km;
• pressure – 35-50 kilobar;
• homogeneous environment;
• lack of temperature gradient;
• temperature – from 1100 o C to 1300 o C.

These conditions contribute to the compaction of the structure of the graphite crystal lattice and the transition to a denser cubic form, characteristic of diamonds. Scientists believe that the most suitable conditions for the formation of minerals were between 100 million and 2,5 billion years ago.

Diamonds appear on the surface due to volcanic activity – they are carried out by flows of kimberlite magma. Such a place of volcanic explosion forms a kimberlite pipe – a primary diamond deposit. There is another version according to which graphite turns into diamond not so much under the influence of the temperature and pressure of magma in the depths, but directly upon contact with it, when it is released to the surface.

Synthetic minerals

Modern technologies for synthesizing diamonds make it possible to obtain stones that are not inferior in quality, transparency and hardness to the natural original. There are several ways to obtain an artificial analogue. Diamond production is an expensive and labor-intensive process, so such stones are also not cheap.

• HPHT diamonds. It is obtained through a device resembling an autoclave, which maintains a temperature and pressure similar to that found in the depths of the earth’s bowels. The technology involves the presence of graphite, seed diamonds, and a catalytic metal alloy. Inside the device, the covalent pi bonds of graphite are converted into sigma bonds of diamond. This technique allows you to obtain a gem-quality diamond in 4-10 days.
• CVD diamonds. This option is obtained by film synthesis. It is through this technology that industrial stones are produced. The diamond seed is placed in an airless environment and then filled with methane and hydrogen gases. Microwave rays heat the carbon in methane to 3000 o C, which settles on the base, which, according to the technological process, remains cold. The peculiarity of this technique is the ability to obtain cleaner stones without nitrogen impurities.
• Explosive fusion is the third option for producing artificial diamonds. Artificial stones are formed during the detonation of an explosive base followed by cooling. It is believed that this method also recreates one of the options for the natural formation of diamonds (for example, due to an explosion from an impact when a meteorite falls.

Synthesized stones are not only used in medicine and electronics, they can also be cut as inserts for jewelry. At the same time, it is impossible to distinguish natural diamonds from synthetic ones without special equipment.

Deposits and production

Based on the specifics of primary diamond deposits, the extraction of precious stones is carried out by developing a kimberlite or lamproite tube, which is first mined in an open way – the ore is taken out of the quarry, and then, when the working depth approaches 600 meters, the quarry is closed, and mining is carried out by building a mine. Diamond placers are called secondary deposits. They are formed during the erosion of soil on slopes formed at the site of magma release. The soil is washed away to the foot of the hill, bringing diamonds to the surface. This is one of the options for how precious stones end up in rivers or coastal ocean waters.

How to distinguish from quartz

Natural quartz is very similar in appearance to rough diamond. If quartz is transparent, then an uninitiated person can easily confuse it with a gemstone. Quartz is also used to make jewelry, but its cost and physical properties differ significantly from diamonds.

The hardness of quartz is inferior to diamond. Its limit is 7 units on the Mohs scale. With some effort, you can leave scratches on the surface of the quartz. For the experiment, it is recommended to hold the stone between two coins.

It is quartz, not diamond, that will become invisible when immersed in water. But, this is provided that the gem is completely transparent. Inclusions and impurities will remain noticeable.

Quartz will become covered with condensation if you breathe on it, but diamond will remain clean. Also, when exposed to heat, the quartz stone will quickly heat up, but the diamond will remain cold.

There is a so-called Herkimer diamond – a two-vertex quartz crystal of rock crystal with an indefinite number of facets. It is very similar to a diamond, but has a beautiful natural shape and is valued by collectors. The number of angles can range from 4 to 20. Natural diamonds have the shape of a regular octahedron or cubic. Quartz has hexagonal pseudohexagonal prisms.

How to distinguish from fakes

• The most effective method used in industry is the use of fat. A diamond, if its edge is coated with oil, will stick to the glass surface and hold on, but the quartz crystals will fall off and go into screenings.
• Quartz stone does not have such sharp edges and allows light to pass through, while a cut diamond has sharp edges and will not allow text or objects to be seen through.
• Quartz dissolves in hydrofluoric acid and molten alkalis, diamond is resistant to both environments.

Before conducting an experiment with aggressive media, make sure that you are really ready to harm the stone. If your plans do not include parting with your jewelry, you should use the help of a jeweler.

Chemists joke: if you press coal very hard, you get a diamond. This idea has been exploited at different times by authors of science fiction stories, film directors, animators and computer game developers, thanks to which many people believe that a piece of coal can really be turned into a precious diamond. Superman alone convinced more than one generation of his fans of this.

In principle, it is clear where this idea came from. Coal, at its core, and diamond are forms of the same chemical element – carbon. Indeed, high pressure is a key factor in both the process of turning decaying carbon-based life forms (such as plants) into coal and the process of forming diamonds. But in reality everything is much more complicated.

The chemical composition of coal is very different from diamond.

Diamond is pure carbon in a well-defined crystalline form. It is a transparent and most often colorless crystal, although there are also colored diamonds: yellow, blue, pink and even black. This color deviation from the rule is due to the peculiarities of the natural conditions of crystal formation and the presence of impurities in it. For example, the presence of boron atoms in the structure of diamond gives the crystal a yellow tint, and nitrogen gives it a blue tint. It is worth noting that we are talking about a very small amount of impurities – on the order of one atom per million.

The basis of coal is carbon, however, it cannot be called pure. Coal contains many impurities, including hydrogen, nitrogen, oxygen, sulfur, arsenic, selenium and mercury. In addition, coal, depending on its origin and age, contains various organic compounds.

Carbon does not need high pressure to become a diamond. The process also requires very high temperatures (thousands of degrees). Only under such conditions can a special diamond crystal lattice be formed. When carbon is simultaneously exposed to temperature and pressure, each of its atoms bonds with four neighboring atoms, forming a very strong structure. It is the structure of the crystal lattice that diamond owes its hardness. Each carbon atom in the diamond structure is located in the center of a tetrahedron, the vertices of which are the four nearest atoms. If the composition contained impurities, as in coal, such a bond could not form.

People have finally learned to create artificial diamonds. They are made from graphite.

Graphite, like diamond, is an allotrope of carbon. In appearance it resembles coal, but differs from it in properties, color and the presence of a crystal lattice. Coal does not have any crystalline structure.

The structure of graphite is not at all similar to the structure of diamond. Graphite is formed by parallel layers of carbon atoms arranged at the corners of regular hexagons. The layers are located at a considerable distance from each other and are also shifted relative to each other. This structure explains the property of graphite to exfoliate into flakes, due to which it is used for making pencils and as a lubricant.

Long attempts to obtain an artificial (synthetic) diamond were crowned with success in the mid-twentieth century. At the current level of development of chemistry and technology, obtaining artificial diamonds from graphite is no longer a problem, but requires expensive equipment.

What nature does over millions of years, man can now do in a much shorter period of time. The main thing is to reproduce the conditions under which in nature one form of pure carbon transformed into another, that is, to create high temperature and very high pressure. There are several ways to do this. True, artificial diamonds are quite small, and their production volume is relatively small. For example, a Moscow laboratory can grow up to 1 kilogram of diamonds per year.

By the way, there is also artificial graphite. Unlike diamond, it is produced and used on an industrial scale. And they get artificial graphite from coal.