Diamond is a gemstone having a crystal structure. It is made of carbon atoms. It actually is the hardest material known. Diamond, one of the two naturally occurring forms of carbon, has this property thanks to its three-dimensional crystal structure where atoms are bonded to each other by strong chemical bonds. Graphite, another naturally occurring form of carbon, is quite soft as opposed to diamonds since there are no strong chemical bonds between the two-dimensional carbon layers.
Diamonds are very hard and have been used for jewelry (25%) and industry (75%) for centuries. A completely pure diamond is colorless. Structural defects and other impurities cause the diamond to appear colored. For example, nitrogen causes the diamond to be yellow or brown, and boron to be gray-blue. Permanent distortions in the shape are the source of pink or red color. The most common diamond in nature is a colorless diamond made of pure carbon. It is followed by yellow, brown and blue diamonds. The red diamond is the rarest type of diamond.
Natural diamonds are formed over the centuries with the addition of atoms to the crystal structure one by one. It is also possible to synthesize diamonds by chemical processes. A chemical vapor deposition technique can produce 400 milligrams of diamond per day.
Most people think that the metamorphosis of coal produces diamonds. This idea is even mentioned in the history of the formation of diamonds in most science classes. However, coal plays a rare role in the formation of diamonds. In fact, most diamonds are much older than the first land plants on the planet. The source material of coal is land plants! Even this is enough to end the idea that the diamond deposits of the world are made of coal. Another problem with this idea is that the coal veins are sedimentary rocks, which are usually horizontal or near-horizontal rock fragments. The source rocks of the diamonds are vertical chimneys filled with blast rocks.
Four different processes are thought to be responsible for the formation of almost all natural diamonds on and around the Earth’s surface. One of these processes explains almost all of the diamonds ever extracted.
Diamond Formation in the World Mantle
Earth scientists think that all of the world’s commercial diamond deposits are formed in the mantle and come to the surface with deep-source volcanic eruptions. These eruptions produce kimberlite and lamproite chimneys, pursued by diamond seekers.
Most of these chimneys do not contain diamonds or contain too few diamonds to attract commercial interest. However, if they contain enough diamonds to make a profit, underground mines are being established on such chimneys. From some of these chimneys, diamonds break off due to weather and abrasion and they can be found in currents and sediment deposits of coastlines.
Natural diamonds require very high temperatures and pressures to form. These conditions are found in limited areas of the world mantle: 150 km or more below the surface, the temperature can be around 1050 ° C. The critical temperature-pressure environment required for diamond formation and stability is not available all over the world. It is originally thought to be found in the mantle beneath the stationary inner parts of the continental shells.
Diamonds that build up and accumulate in these diamond stability zones spill out onto the earth’s surface during deep-source volcanic eruptions. Such eruptions can tear the mantle pieces and quickly throw them onto the surface. This type of volcanic eruption is extremely rare and has never been observed by contemporary people.
Does coal play a role in this process? Coal is a sedimentary rock; is composed of plant residues accumulated on the surface of the world. At a depth of more than 3.2 km, coal is uncommon. It is very unlikely that coal will descend from the earth’s crust down to the depths of a continental crust. The carbon source of mantle diamonds is probably the carbon that is trapped in the earth during the formation of the planet or descends into the depths.
Diamond Formation in Submerged Areas
Small diamonds were found in the rocks which were thought to have sunk deep into the mantle by plate tectonic processes and then have gone back to the surface. The formation of diamonds in a submerged plate can only take place 80 km below the surface and at temperatures as low as 200 ° C. In a study, it was discovered that the diamonds in Brazil contain tiny mineral additives that are compatible with the mineralogy of the oceanic crust. There were also some contributors who pointed out that sunk seawater had played a role in their formation.
In another study, the origin of blue, boron-containing diamonds, which were formed at depths as large as 650 km, were examined. These super-deep diamonds also contained additives indicating that they were derived from submerged oceanic crust.
Is there any share of coal in the process? Coal is not a possible carbon source for this process. The most likely carbon sources of the diamonds formed by the sinking of an oceanic slab may be carbonate rocks such as limestone, marble and dolomite and plant residues in coastal depressions.
Detailed Information about Diamond and Its Formation
Diamond is a metastable carbon allotrope in which carbon atoms are arranged in a front-centered cubic crystal structure called diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is insignificant under standard conditions. It is known as a substance with the highest physical properties based on a strong covalent bond between its atoms. It has the highest hardness and thermal conductivity. Due to these properties, diamond is the first in cutting and polishing tools used in the industry.
Due to its extremely robust structure, it can be affected by very few foreign substances such as boron and nitrogen. One-millionth of the atomic contamination causes diamonds to pick up colors like blue (boron effect), yellow (nitrogen effect), green (radiation effect). The diamond also has optical power to dissipate light. Natural diamonds are formed at high temperatures and pressures, from 140 to 190 kilometers deep. Carbon-containing minerals provided the necessary carbon resources, and the formation of diamonds took place in about 1 billion to 3.3 billion years, equivalent to 25 percent to 75 percent of the world’s age. Diamond is found in rock fragments known as kimberlite and lamproites caused by magma flowing and cooling from volcanic eruptions.
Not all of the diamonds on Earth are made of magma. It was found that meteorites contain carbon in the form of diamonds. The kind of diamond called carbonado, which is found in South America and Africa, came from meteorites about 3 billion years ago. The diamond was also formed under other natural high-pressure conditions. Very small micro-diamonds and nano-diamonds of micrometers and nanometers were formed with the shock of high pressure and temperature suitable for the formation of diamonds in the craters created by meteorites hitting the earth. In Russia, the Popigai crater, created by an asteroid, has the largest diamond deposit in the world, estimated at trillions of carats.
Scientific evidence shows that white dwarf stars have crystallized carbon and oxygen nuclei. For example, the Harvard Astrophysics Center identified the dwarf star, codenamed BPM 37093, 50 light-years away, as a diamond with a diameter of 4,000 km. Diamonds can be produced synthetically with today’s technology. There are also diamond-like stones that contain cubic zirconia and silicon carbide, often called imitation, with their appearance and many other features. Special gemology techniques have been developed to distinguish between natural diamonds, synthetic diamonds, and diamond imitations.
It is thought that the diamond was first found in alluvial deposits along the Penner, Krishna and Godavari rivers in India and has been used for at least 3,000 years, but probably for 6,000 years. Diamonds have been included in the class of precious stones as they are used as religious symbols in Ancient India. Its use in engraving tools is as old as human history. The popularity of diamonds has grown rapidly since the 19th century, with growing supply and demand, advanced cutting and polishing techniques, growth in the world economy, and advertising campaigns.
In 1772, Antoine Lavoisier, a French scientist, used a lens to concentrate the sun’s rays on a diamond and showed that the only product produced by combustion was carbon dioxide, proving that the diamond was made of carbon. In 1797, the British chemist Smithson Tennant repeated this experiment and elaborated. He found the chemical equivalence of these substances by showing that burning diamond and graphite released the same amount of gas.
The most well-known use of diamonds is that it has been used for ornamentation in jewelry since ancient times. It is also used as an industrial abrasive to cut hard materials. In the 20th century, gemologists developed methods of grading diamonds according to their properties. The following four properties are widely used as the basic descriptors of the value of diamonds: 1- Carat (weight), 2- Cut (proportional cut quality, symmetry, and polish), 3- Color (how close or colorless it is white), 4- Clarity (lack of inclusion).
One of the most important points to be considered in the formation of diamonds is that diamond formation can only occur with a certain temperature and pressure. The most appropriate values in this formation are close to the core of the world. Diamonds often crystallize at an incredibly large pressure and only high temperatures in the upper layers of the earth’s surface. Less than 30% of diamonds polished and nailed to jewelry. Today, more than 70% is used for industrial purposes.
Diamonds are extracted from many parts of the earth. Today, 7 producing countries account for 80% of total diamond production, Botswana, Russia, South Africa, Angola, Namibia, Australia, and Zaire. In 2000, the total estimated production of raw diamonds was 120 million carats worldwide, but about 50% loss in the cutting and polishing process. Therefore, when the original 120 million raw diamonds are processed, only 18 million carats come to the open market as a polished gemstone. The diamond formed in nature is at least 990 million years old. The youngest diamond is 1 billion years old, from Botswana and the oldest diamond is 3.3 billion years old, from South Africa. In order to determine the age of the diamond, a different method, radioactive aging test, is applied instead of the carbon test used in many materials.
The main sedimentary species with diamonds are gravelly alluvials, glacial smears, and kimberlite breccias. The diamond is found only in the kimberlite breccias, along with the rock in which it is formed, more than 120 km deeper in the earth’s crust (eg Kimberly, South Africa). The conditions necessary for the synthesis of diamonds support this theory. Diamonds found in alluvial and glacial pebbles are thought to be separated from the kimberlite block as a result of erosion or glacial movements and re-accumulate in rivers or glacial smears.
Diamonds, which can be colorless as well as having various colors ranging from red to black, can be transparent, translucent or non-transparent. Most precious diamonds are transparent and colorless. Colorless or pale blue stones are the most valuable, but very rare. Most of those used as jewelry is slightly yellowish. “Fancy” diamonds are characterized by their distinctive colors; the least common ones are red, blue and green, while orange, violet, yellow and yellowish-green are more common. An important part of industrial diamonds are in colors ranging from gray to brown and are between translucent and opaque. However, it is very difficult to distinguish between a qualified industrial diamond and a low-value gem diamond. The color of the diamond can be changed by bombarding with various types of atomic particles.
The extraordinary brightness of the diamond is due to its high refractive power; a properly cut (shaved) diamond reflects light much more than an unshaved diamond and therefore appears more glazed. The glow of diamond is caused by the high separation power; As white light passes through the stone, it splits into various colors of the spectrum and gives the stone a sparkling appearance.
The hardness of the diamond on the Mohs scale is 10; The hardness of corundum, which is the closest mineral to diamond, is 9. In fact, diamond is much harder than corundum; If the Mohs scale was considered linear, the hardness of the diamond would be 42. The hardness of the diamond varies significantly in different directions so that some surfaces are more easily cut and polished than others.
According to the atomic structure of the diamond, determined by X-rays, each carbon atom is bound to four adjacent atoms equidistantly within the crystal. The crystal structure, densely and strongly bonded by this tight weave, gives very different properties than diamond graphite and other forms of natural carbon.