Why Diamond Is Hard: The Hardness of Materials



Diamond is nature’s hardest substance made of carbon. High temperature and high pressure are required for the carbons to come to the diamond structure. Therefore, the diamond is formed under the ground crust at the upper mantle border. It can be formed with a temperature of about 1200 ℃ in which the magma is received about 150 kilometers below the earth and the pressure of about 60 tons applied by the earth’s crust. The formation age of diamonds is thought to be between one billion and three billion years. So why do you think diamonds are so hard?

Diamond is the hardest known substance. One of the two naturally occurring forms of carbon, diamond is very hard due to its three-dimensional crystal structure in which the atoms bond to each other with strong chemical bonds. Graphite, the other naturally occurring form of carbon, is quite soft, unlike diamond, since there are no strong chemical bonds between two-dimensional carbon layers. Diamonds have been used for centuries in jewelry (25%) and industry (75%) for carving because they are so hard.



A completely pure diamond is colorless. Structural defects and other impurities cause the diamond to appear colored. For example, nitrogen causes diamonds to be yellow or brown and boron to gray-blue. Permanent distortions in the shape are the source of the pink or red color. The most common diamond in nature is a colorless diamond consisting 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 by adding individual atoms to the crystal structure. It is also possible to synthesize diamonds by chemical processes. With the chemical vapor deposition technique, 400 milligrams of diamond can be obtained in a day.

Is Diamond the Hardest Material Known?


Until 2005, the hardest material known was the diamond. But scientists at the University of Bayreuth in Germany succeeded in producing a new substance in 2005 by overheating pure carbon. The resulting substance had a harder structure than diamond. Scientists have called this new material a hyper-diamond, or aggregated carbon nanowire (ADNR *). When viewed from the outside, this material, which has an incredible hardness, resembles a pitch or a bright and black pudding.

So how was this new substance made? In fact, it was known that one type of pure carbon was transformed into another pure carbon by applying heat and pressure. But the Bayreuth team that produced this substance did not use either of these substances. Instead, they opted for a third substance, carbon fullerite. Another name for this substance is buckminsterfullerene or “buckyballs”. The reason it got this name comes from the fact that 60 carbon atoms in this substance come together to form a shape similar to a soccer ball. This shape is named after the architect because it resembles the geodesic domes invented by American architect Richard Buckminister Fuller (1895-1983).



Normally, the carbon atoms in the diamond are stacked in the form of a pyramid, while the new material produced in this new material is in the form of small and intertwined rods. These are so small that they are called “nanorods”. Nanos is a Greek word and is used in our language to mean “dwarf”. Each of the carbon atoms in this new material is one micron (one-millionth of a meter) long and 20 nanometers (twenty billionths of a meter) wide. To give an example from ourselves, it corresponds to approximately one fifty thousandths of a human hair. By subjecting carbon fullerite to extreme heat (2,200 degrees) and extreme pressure (about two hundred thousand times atmospheric pressure), they created the hardest and most durable material known. However, they also created the most durable and dense material known to science to date.

The density of a substance depends on the degree of tightness of its molecules and is only measured using X-rays. The ADNR * material is 0.3% denser than diamond. Durability is defined as a measure of compressibility. It is the name given to the equal amount of power to be applied by each side of the substance to decrease in volume. The basic unit of durability is Pascal. The strength of ADNR * material is 491 gigapascals (GPa), that of the diamond is 442 GPa, and that of iron is 180 GPa. The hardness of a substance is an easier term to determine. If a substance can leave a scratch on another substance, it is harder. The hardness scale of the diamond material is MH 10. ADNR is out of the scale as it can draw diamonds.

How the Hardest Known Substance ADNR Was Created


Until recently, the hardest substance known was undoubtedly diamond. But a substance created by scientists in Germany seized the diamond’s throne. The hardest material in the world is no longer the diamond. Scientists at Germany’s Bayreuth University created a new substance in 2005 by superheating pure carbon. This newly discovered material was called a hyper diamond, or aggregated carbon nanowire (ADNR). From the outside, this incredibly hard substance looks more like a pitch or shiny black pudding. The carbon atoms in a diamond look like stacks of cubes stacked in pyramids. The newly discovered ADNR material, on the other hand, consists of small and nested rods. Because they are so small, these are called ‘nanorods’.



It has long been known that one of the pure carbon types (graphite) can be converted into another type of pure carbon (diamond) by temperature and pressure. But scientists at Germany’s Bayreuth University did not use either substance. They preferred the third type of carbon fullerite (buckyballs). The 60 carbon atoms in this substance come together to form a molecule similar to a soccer ball. Scientists at the University of Bayreuth in Germany have succeeded in making the hardest known material by subjecting the Fullerite substance to extreme temperature (2220 degrees) and extremely high pressure (two hundred thousand times atmospheric pressure).

Durability is a measure of compressibility: In order for the substance to shrink in volume, an equal amount of force must be applied from each side. The basic unit of this power is the pascal. ADNR’s endurance level is 491 gigapascals (GPa). The diamond has a strength of 442 GPa. The strength of iron is 180 GPa. Accordingly, it is three times more difficult to compress ADNR than iron. If one item can leave a scratch on another, that item is harder. German mineralogist Friedrich Mohs invented the Mohs hardness scale in 1812. The scale starts with the softest substance, talcum powder (MH 1). Talcum powder is soft enough to be scratched with a nail. The hardness of the diamond at the top of the scale is MH 10. As a result, we can easily say that. ADNR is harder than diamond.

How to Measure the Hardness of Diamonds and Other Minerals


When it comes to hardness, it is important which substances or which property we are talking about. Otherwise, there is no specific definition we need to understand when it comes to hardness. For example, when talking about water hardness, the word meaning does not mean “hardness”. Likewise, when we talk about the hardness of the elements, the word “hardness” is the true meaning of the word.

When we talk about water is hard, it means that some of the minerals in the water are more than they should be. These minerals are usually calcium and magnesium. As you can guess when we talk about the degree of hardness, we would like to explain how much these minerals that make the water harder are found in water. The “hardness” you are talking about is hardness as we know it. In other words, it is the word that indicates the physical strength and strength of the substance. Hardness is generally closely related to the molecular structures of substances and the geometric arrangement of the elements that make up the substance.



I have never heard of any talk of hardness at the elemental level. But I would say that the hardest substance in the world is diamond, an allotrope of the element carbon. The hardest substance of diamond is related to the geometrical arrangement of the element carbon. Graphite, another allotrope of the element carbon, is a very soft substance compared to diamond. In other words, it would not be correct to say “carbon element is the hardest element”. Substances formed by atoms that make covalent bonds are harder than substances formed by atoms that make ionic bonds.

As for how it is measured, there is a relative way around it. French mineralogist Friedrich Mohs made a classification of hardness about 170 years ago, arguing that “a hard substance scratches or wears off the substance that is softer than itself”. Accordingly, he scaled the hardness between 1 and 10 and gave 1 point to the least hard mineral and 10 points to the hardest substance (ie diamond). According to this scale, the nails have a hardness of 2.5, glass 5.5, and copper coins of 3 degrees. According to more precise measurements, it is not even possible to approach the diamond in hardness. While the hardness of the diamond is 1600, the corundum substance, which comes after the diamond, remains at 400 and rubies only at 200.

Mohs Hardness Scale


The hardness of minerals is measured relatively with the aid of a scale called the Mohs hardness scale, which was introduced by the Austrian mineralogist Friedrich Mohs in 1812. To find the hardness of a mineral according to the Mohs hardness scale, the mineral or minerals whose hardness is known are rubbed against each other and the mineral whose hardness is to be determined is rubbed together and thus it is determined according to which mineral has drawn another. As a result, the hardness of the mineral is found according to this process. For example, a mineral drawn with Apatite and quartz has a hardness of 6 according to the Mohs scale. While doing this, the following issues should be taken care of in order not to cause mistakes. Minerals that are brittle may appear to be lower than their hardness level because they break and crumble when rubbed against other minerals. Since very soft minerals (with less hardness) can leave their dust on the hard mineral during rubbing, it can give an image as if it were scratching the hard mineral.



Minerals’ resistance to scratching is known as hardness. Therefore, the hardness can also be called the scratchability property of the mineral. The hardness of minerals is directly related to their crystal structures and the bond strength between atoms. As the bond strength increases, the hardness of the minerals also increases. Hardness is a relative concept and the determination of the hardness is made by trial using a mineral whose hardness is known or materials such as penknife, needle, etc. The most widely used scale (chart) for this is the chart developed by Mohs. In the Mohs hardness series, the hardness of 10 minerals is ranked from the softest to the hardest. According to this chart, the order from the softest to the hardest is as follows;

1- Talc, Graphite, Kaolin (Mg3 (Si4O10) (OH) 2) can be scratched with a fingernail
2- Gypsum, Anthracite, Rock Salt (Ca SO4 2H2O)
3- Calcite, Dolomite (Ca CO3) can be scratched with a pocket knife or needle.
4- Fluorite (Ca F2)
5- Apatite (Ca5 F (PO4) 3
6- Feldspar (Orthoclase) (K Al Si3O8)
7- Quartz, Agate (SiO2)
8- Topaz (Al2 (SiO4) (OH F) 2 “those who can scratch the glass”
9- Corundum (Al2 O3)
10- Diamond (C)

It is known that the ratios between each hardness grade on the Mohs hardness scale are not equal. For example, the difference in hardness between diamond and corundum is several times that of topaz and corundum.

How Diamond, the Hardest Material, Is Cut?


Until recently, the diamond was known as the hardest material in the world. There are scientific studies showing that Vurtsit boron nitride and lonsdaleite minerals are natural materials harder than diamond. Due to its impressive appearance, the use of diamonds as jewelry is more well known. However, diamond has an important place in industrial applications because it is the hardest material. It seems difficult for these newly discovered minerals, which are quite rare on earth, to replace diamonds.

The shaping of the diamond dates back to the Middle Ages. Before that, it is known to be used in its natural form. However, the hardness of the diamond prevents it from being shaped as desired. In the natural state of the diamond, a flawless crystal structure and the parts where this structure is distorted exist together. Due to these imperfections in its structure, diamond is cut and shaped using various tools, including diamonds. So diamond is cut using diamonds again. The cutter is placed on the flawed areas in the diamond’s structure and the stone is divided with light strokes. Natural diamond pieces are then ground using cast iron discs with diamond dust added. Thus, shiny and symmetrical diamond surfaces are created. However, 60% of the diamond can be lost during these processes.



Diamond cutting techniques are constantly improving. Since diamond is a valuable mineral, studies have been carried out on how it can be cut without damaging it, without decreasing its value and with the least waste. Let’s examine how the diamond is cut from the oldest techniques to the present day. It has been noticed that as the diamond is processed, its luster increases as it reaches smooth surfaces. For this, the diamond was constantly sought to cut the diamond in different styles and to shine even higher. So how can the world’s hardest mine be cut? Yes, we know that only another diamond can cut the diamond, but there is a direction between the carbon that makes up the diamond, which we call cleavage. We can roughly compare this to how it follows a smooth path when tearing papers in one direction but curls up when tearing in a different direction.

But of course, let’s not forget that diamond is very different from paper and it is not that easy to cut. The raw diamond is examined by the master of cutting and he determines how a stone will come out and the direction of its cleavage. After he finishes his examination, he marks the cutting direction he decides and starts the cutting process. A thin-tipped hard cutter is attached to the stone from the marked point and with a small blow, the stone is split in that direction. This process requires serious experience and precision. The cutting is continued so that this cut surface becomes the table of the stone.

Why Diamond Is Harder Than Graphite


What does a sparkling diamond have in common with a pencil tip? Diamond is an extremely hard material, while the graphite that forms the pencil tip is very soft. These two different substances actually meet in miraculous evidence of creation. An uncut diamond is the hardness champion of all minerals and all materials. (L. Vlasanov & D. Trifonov, 107 stories About Chemistry, Mir Publishers, 1977) Therefore, crystal diamond is used as an abrasive in cutting, drilling, and flattening all kinds of materials. Hardness is the resistance of minerals against scratching by external forces. It is easy to recognize the minerals by their hardness. Relative hardness value can be determined by drawing one mineral with another. Having scored all minerals to determine their hardness, scientists have found it appropriate to give diamonds 10 points out of 10. So what makes diamonds so hard?

It is remarkable that the brittle and soft graphite tip we use in pencils and the diamond consists of the same atoms. Graphite is composed of carbon atoms just like diamonds. However, one is very soft while the other is extremely hard. While one is like a piece of black coal, the other can have a shiny surface. While one is extremely abundant in nature, it is very difficult to come across the other. For all these reasons, the diamond has a material value that cannot be compared with graphite. So, how is it possible for a carbon atom to assume two identities so different from each other? Before this difference, let’s talk about the carbon atoms that make up the diamond. The carbon atom is extremely important for living things. British chemist Nevil Sidgwick also emphasizes this in his Chemical Elements and Their Compounds. Carbon has a unique structure that is completely different from other elements in terms of the number and variety of compounds it can make.



So far, over half a million different compounds of carbon have been separated and identified. But even this gives little information about the strengths of carbon because carbon is the basis of all living matter. (Nevil V. Sidgwick, The Chemical Elements and Their Compounds, vol.1, Oxford: Oxford University Press, 1950, p.490) The different bonds of carbon with hydrogen alone form a large family known as “hydrocarbons”. In this family; There are natural gas, liquid petroleum, kerosene, kerosene, and various machine oils. Hydrocarbons known as ethylene and propylene are the foundation of the petrochemical industry. Other hydrocarbons also form compounds such as gasoline, toluene, and turpentine. Naphthalene, which is put in closets to protect our clothes from moths, is another type of hydrocarbon.

Hydrocarbons combined with chlorine or fluorine constitute different substances such as anesthetics, fire extinguishers, and freons used in refrigerators. The carbon that makes diamonds is such an important atom. The crystal structure of diamond is the most perfect example in the crystal world and there is no similar one. Carbon atoms are in an ideal geometric order to give the diamond its hardness in diamond crystals. Graphite also consists of carbon; however, its atoms are not arranged in the same order as in a diamond. This condition is called allotropy by scientists.

The Reason for the Hardness Difference Between Diamond and Graphite


When all known substances are cooled sufficiently, they change their state and turn into a solid-state of the substance. The nature of the solids formed depends on the forces that hold the atoms, ions, or molecules together. Solids can be crystalline or amorphous. In crystal solids, the molecules are in orderly order. Salt and sugar are the best examples of crystalline solids. In amorphous solids, the molecules are arranged in random order. For example, butter is one of the best examples of rubber. The biggest difference between crystalline solids and amorphous solids is that crystal solids melt at a certain temperature, while amorphous solids gradually soften and gain fluidity in a certain temperature range.



Diamond and graphite are in the crystal solids class. The structures and properties of crystals vary according to the types of forces that hold the particles together. At this point, covalent crystals including diamond and graphite should be examined. Covalent crystals have atoms at their lattice points. Covalent crystals are formed by a lattice of covalent bonds formed between atoms dispersed throughout the entire solid. These covalent bonds form a three-dimensional network structure in the crystalline structure. The reason for the strength of this network structure is that covalent crystals are very hard and have a high melting point. Due to the immobile condensation of electrons, crystal structures formed by covalent bonds cannot conduct electricity. Substances such as graphite formed by a different covalent bond of carbon, on the other hand, form a two-dimensional mesh, conducting electricity well.

The most important example of covalent bonding is shown as two allotropes of the carbon atom. These are diamond and graphite. The carbon atom in the diamond is attached to its four neighbors and continues through the tetrahedral skeletal layer. These three-dimensional and robust covalent bonds are the reason why diamond material is the hardest known solid substance with the highest melting point. The graphite material is black shiny and electrically conductive. In graphite, it forms two-dimensional covalent bonds. The weakness of these bonds can be shown as the reason why the graphite material is softer than diamond.

7 Materials Harder Than Diamonds


Although the claim that diamond is the hardest substance in the world is frequently featured on the internet, materials harder than diamonds have also been discovered. Carbon is the element underlying life and organic structures. It has a structure that can be connected to four other atoms at the same time. Thus, it can create extremely complex structures. Both coal and diamond are made up of carbon, but their atomic arrangement is different. (If you can apply enough pressure and heat, you can also make diamonds with some carbon.) Although diamonds are still one of the hardest and strongest materials in the world, they are no longer alone at the top. In fact, there are six substances that are stronger than that.



  • Honor Award: Silicon Carbide

Although Silicon Carbide is generally obtained artificially, it can be found in nature as a form of moissanite. This material, which is slightly weaker than a diamond in its natural state, has been produced since 1893. As a result of the processing of silicon carbide with high pressure and low temperature, a strong material from diamond is obtained, which is reinforced. This durable material is also used in electronics because it is a semiconductor.

  • Wurtzite Boron Nitride

In these structures built using boron nitride instead of carbon, it is possible to obtain various atomic configurations. Especially the hexagonal or cubic version is harder than diamond. Very few of these structures that generally emerged after volcanic eruptions have been found. When they form a pyramid-like structure, these materials are 18% harder than diamonds.

  • Lonsdaleite

Lonsdaleite, the closest thing to being a Moon Stone in Pokemon games, is a very interesting material. When a meteorite filled with carbon passes through the atmosphere, it only gets warmer on the outside. When they hit the Earth, the pressure inside the body becomes more than any other natural process. Therefore, graphite forms a crystalline structure under pressure. This object, which forms a hexagonal structure, can become 58% harder than diamonds.

  • Dyneema

If we were to make Spider-Man’s webs with material from this world, we would probably use Dyneema. This structure, lighter than water, 15 times stronger than steel, draws attention with its incredibly long molecular length. This structure, which is the strongest known thermoplastic, is also called the strongest fiber.



  • Palladium Micro Alloy Glass

Hardness and durability are not the same. Hardness is how much force an object can resist, while strength (or durability) is how much energy the object can resist without breaking and without breaking its structure. There are materials who have high durability or hardness but not both. Ceramics are hard but not durable. Elastic materials are durable but not hard, they are weak structures. A material developed in 2011 attracted attention as a new structure using phosphorus, silicon, germanium, silver, and palladium. This material has managed to be harder than all types of steel. It also stands out as the hardest non-carbon-based structure.

  • Buckypaper

This type of paper, made up of carbon nanotubes, has been known since the late 20th century. Hexagonally bonded carbons form one of the most stable structures known. This structure, which has a weight of 10% of steel, is hundreds of times stronger when it comes to hardness. This material, which is a non-flammable and very good thermal conductor, can be used in fields such as science, electronics, military, and biology.

  • Graphene

Graphene, one of the hexagonal carbon structures, stands out as a two-dimensional material with only 1 atom thickness. Structures made from a single graphene leaf are being used in more and more areas and create a multi-million dollar market. This structure, which is very successful in both conducting electricity and conducting heat, completely transmits light.

Although the search for harder, stronger materials is not a journey that will end easily, scientists seem to be in a not bad spot right now. Nanotechnology and metamaterials will open up a whole new world for us.

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Savaş Ateş

My wife has a huge interest in diamonds. After she asked me a lot of questions about it, I found myself in diamonds. I made a lot of research on it. I read books. I visited manufacturers. I visited the stores. I have made good friends in that field. I want to share my experiences with you.

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