If you ask any random person what is the hardest material on Earth, the most likely answer would be diamond. It is fairly common knowledge. But is diamond actually the hardest material or mineral on Earth? We’ll find out in this article.
How is hardness determined?
The hardness of any mineral is defined by its Mohs scale number: the harder the mineral, the higher its Mohs number. The Mohs scale was devised by a German geologist and mineralogist, Friedrich Mohs, in 1812.
This scale is important for mineralogists and geologists because it offers a feasible technique to evaluate the hardness of a mineral by comparing it against a set of standard reference minerals.
Although the Mohs scale is not precise and strictly ordinal, it has a relevant use in geology, mainly to identify the hardness of various minerals. It works by analyzing the ability of a material to scratch the other (softer) material. Electronic manufacturers often use this scale to test the resilience of flat panel display modules.
Modern phone displays, for example, use Gorilla Glass that scratches at level 8 on the Mohs scale of hardness.
Below is our list of the hardest minerals in the world, ranked according to their Mohs hardness. We have also mentioned the absolute hardness of some of the minerals.
Table of Contents
10. Quartz
This fantastic specimen of #amethyst #quartz has a beautifully deep violet colour! Did you know that amethysts are violet due to irradiation and impurities of iron? #MineralMonday #LapworthRocks #HelloBrum #mineral #geology #gems@geology_bham @ace_national @unibirmingham pic.twitter.com/rrZEjzdacn
— Lapworth Museum of Geology (@lapworthmuseum) November 8, 2021
Mohs Hardness: 7
Quartz belongs to the group of silicate minerals. Primarily found in metamorphic, igneous, and sedimentary rocks, it is the second-most abundant mineral in the Earth’s continental crust, behind Feldspar.
It is made of silicon and oxygen atoms that form a three-dimensional framework of tetrahedra. These strong chemical bonds between silicon and oxygen atoms give Quartz its hardness.
Quartz ranks seventh on the Mohs scale of mineral hardness, which makes it quite resistant to scratching and abrasion. It can be opaque, translucent, or transparent, depending on the inclusions and impurities present.
Clear and transparent Quartz minerals are highly valued in gemstone applications. Colored varieties like amethyst and citrine are popular choices in jewelry.
The mineral is also widely used in the electronics industry for its piezoelectric properties. It’s an important component in crystal oscillators and resonators, used in devices like radios, computers, and watches to provide frequency control and precise timekeeping.
9. Topaz
Mohs Hardness: 8
Topaz is a naturally occurring (silicate) mineral made of fluorine and aluminum. In its natural state, topaz is mostly colorless, but it can also be found in golden brown and yellow color. Different impurities can make a topaz crystal appear pink, reddish, or golden-orange, though they are extremely rare.
At Mohs hardness of 8, topaz is harder than some well-known minerals such as quartz, tungsten, and zircon. But much softer than silicon carbide and diamond.
Thanks to its remarkable hardness, diverse range of colors, and typical transparency, quartz is a popular choice for jewelry, often being cut and polished into gemstones.
It is found in several locations worldwide where rocks like rhyolite and pegmatite are formed. Most of the fine-quality imperial topaz is created in the state of Minas Gerais in southeastern Brazil. Significant amounts of topaz are also found in the United States, Sri Lanka, Australia, Mexico, Japan, and Russia.
Other Material with similar hardness – Hardened Steel
A drill bit made of hardened steel | Image Courtesy: Emrys2
Hardened steel is any carbon steel that has gone through a hardening process. In this process, high-carbon steel is first heated until it reaches its critical temperature before being quenched in water (or brine solutions).
The heat treatment and the subsequent quenching allow the steel to reach its maximum hardness but also make it very brittle and susceptible to breaking under stress. However, this issue can be resolved by a process called tempering.
In this process, the alloy is re-heated at much lower temperatures and then allowed to cool down gradually in still air. Tempering removes some of the excess hardness of the alloy but increases its elasticity.
As the name suggests, hardened steel is not only tougher but also considerably more malleable compared to regular steel, which has a Mohs hardness of 4.5.
The Mohs hardness of hardened steel can be used as a reference for harder minerals that we will discuss ahead.
8. Silicon nitride
Silicon nitride ceramic has good properties such as high strength, high hardness, and high temperature resistance, and its hardness can reach HRA91~93; It has good thermal hardness and can withstand high temperatures of 1300~1400℃; It has a smallhttps://t.co/L78ZOzP2xT pic.twitter.com/M8R0RBC920
— INNOVACERA (@Innovacera) May 18, 2021
Mohs Hardness: 8.5
Silicon nitride (Si3N4) is one of the hardest-known ceramic materials on Earth that ranks very high on the Mohs scale of mineral hardness, typically between 8.25 and 8.5.
The mineral is made up of silicon and nitrogen atoms. It can exist in many different crystalline structures, with hexagonal and cubic phases being the most common.
Silicon nitride is known to have many advantageous properties. Its high tensile strength and toughness make it resistant to fracture and able to withstand mechanical stresses.
It also exhibits excellent thermal stability, which means it does not expand or contract significantly with temperature changes. Moreover, it is chemically inert and resistant to numerous corrosive substances, acids, and alkalis.
Did you know?
Silicon nitride ball bearings are harder than metal. The hardness and wear-resistant properties of this mineral make it ideal for cutting and shaping hard materials like steel and alloys.
In the medical field, silicon nitride has been used in artificial hip joints, offering durability and reduced wear compared to conventional materials.
7. Chrysoberyl
Alexandrite under UV light | Image Courtesy: Wikimedia Commons
Mohs Hardness: 8.5
Chrysoberyl (“a gold-white spear”) is an exotic gemstone with the chemical formula BeAl2O4. At 8.5 Mohs hardness, it is one of the hardest minerals on Earth.
Chrysoberyl is often associated with another beryllium gemstone called beryl. The two minerals are composed of nearly similar elements – aluminum and beryllium, but they are present in different compositions (Chrysoberyl has a high ratio of aluminum to beryllium).
The mineral is found in three varieties – ordinary chrysoberyl, alexandrite, and cymophane.
Ordinary chrysoberyl is yellowish-green in color and has no special qualities. On the other hand, alexandrite and cymophane have unique qualities.
Alexandrite shows color changes under sunlight. This is due to the presence of small amounts of chromium ions in its crystal structure. It appears greenish in daylight and turns reddish under low light.
Chrysoberyl is known for its hardness and resistance to chemical weathering. It can be found in river sands and deposits with other minerals such as topaz, corundum, garnet, and diamond.
Other Minerals with Similar Mohs Hardness
- Chromium (8.5)
- Silicon Nitride (8.5)
- Tantalum Carbide (9-9.5)
6. Corundum
Corundum crystals | Image Courtesy: Wikimedia Commons
Mohs Hardness: 9
Absolute Hardness: 400
Corundum is a naturally occurring aluminum oxide that contains traces of titanium, vanadium, iron, and chromium. Pure corundum is transparent and almost colorless; however, it can have different colors when impurities are present.
Different colored corundum crystals have different names: the red-colored corundum is known as ruby, while pinkish-orange is called padparadscha, and all others are called sapphire.
Since corundum is very high up on the Mohs scale, it can scratch almost every other mineral. Due to its hardness and unusually high density, it is widely used as an abrasive.
Crushed corundum granules (of uniform size) are used for polishing compounds, grinding wheels and media, and various cutting applications.
Corundum is also highly valued as a gemstone. Two of its gem varieties, ruby and sapphire, are cardinal gems — they are traditionally considered more precious than other gems.
5. Tungsten carbide
Tungsten carbide ring
Mohs Hardness: 9 – 9.5
Young’s modulus: 530–700 GPa
Tungsten carbide is a versatile compound known for its exceptional hardness, strength, and wear resistance. Its hardness is a standout feature, owing to the robust covalent bonds formed between tungsten (W) and carbon (C) atoms.
This chemical compound forms a very dense and rigid crystalline structure. Its density is close to that of gold, which gives it a substantial weight for its size. It is also significantly stiffer and denser than steel, about twice as stiff and twice as dense as steel.
However, despite its hardness, tungsten carbide is brittle and can fracture under extreme stress or impact.
It is widely used in cutting tools, including milling cutters, drill bits, and turning tools. Its hardness makes it ideal for machining and cutting hard materials like steel and composites.
The mineral finds a crucial role in metal forming and stamping dies, where it can maintain sharp edges for prolonged periods under high-pressure conditions. It is also used in downhole equipment for oil and gas exploration, where it can endure the abrasive conditions encountered in drilling.
4. Titanium carbide
Crystal structure of titanium carbide
Mohs Hardness: 9 – 9.5
Elastic modulus: 400 GPa
Titanium carbide is nearly as hard as diamond and surpasses the hardness of most other natural and synthetic materials. It is the only carbide in the titanium-carbon system. Its exceptional hardness is due to strong covalent bonds between titanium and carbon atoms.
In its natural form, titanium carbide is extremely rare and can be found as a mineral known as khamrabaevite. This natural mineral was first discovered in 1984 on Mount Arashan, located in western Kyrgyzstan.
It is quite heavy for its size due to its high density, which is similar to that of gold. This is why jewelry items made from tungsten carbide have a substantial weight despite their compact size.
Like Tungsten carbide, Tantalum carbide is also used for making machining and cutting tools, such as drill bits and milling cutters.
The nanoparticles of Titanium Carbide have a large surface area and are more effective in terms of properties and applications. For example, their coatings are applied to cutting tools to further enhance their performance and longevity.
Titanium carbide is used in aerospace applications, such as jet engine blades, turbine components, and nozzles. It is also used to manufacture heating elements, high-temperature furnace components, body armor, vehicle armor, and other protective materials.
3. Moissanite (Silicon Carbide)
Moissanite, a crystal form of silicon carbide at 14x magnification
Mohs Hardness: 9.25
Moissanite is an extremely rare mineral and naturally occurring silicon carbide. It was first discovered in 1893 by French chemist and Nobel laureate Henry Moissan, after whom the mineral is named.
At first, he mistakenly identified these newly found moissanite crystals as diamonds due to their remarkably similar physical characteristics. It wasn’t until 1904 that Henry Moissan successfully recognized them as silicon carbide, marking a pivotal moment in mineralogy. Intriguingly, the first-ever artificial silicon carbide had already been synthesized a few years before this pivotal discovery.
The earliest known terrestrial source of Moissanite can be traced to rare C chondrite meteorites. These meteorites are unique for their high carbon and amino acid content, and they are known to carry some of the oldest minerals formed within our solar system, including materials that originated from beyond our solar system.
The discovery of Moissanite in nature’s other sources didn’t occur until the 1960s. One notable location where Moissanite was found is within a diamond mine situated in Russia’s Yakutia region. This finding expanded our understanding of the mineral’s natural occurrence and added to its significance in both geological and gemological studies.
Due to its rarity in nature, the majority of the moissanite used today is produced through artificial processes in laboratories. It has several industrial and commercial uses due to its exceptional hardness and remarkable optical and thermal properties.
Moissanite is commonly utilized as a cost-effective alternative to diamonds in jewelry. Moissanite jewelry offers a more budget-friendly option compared to jewelry featuring genuine diamonds. It can also be used to conduct high-pressure experiments instead of diamonds.
Other Minerals with Similar Mohs Hardness –
- Boron Nitride (9.36)
- Titanium diboride (9.5)
- Rhenium diboride
2. Stishovite
Mohs Hardness: 9.5
Stishovite is one of the rarest and hardest known naturally occurring minerals, discovered in Meteor Crater in 1962. It ranks at about 9.5 on the Mohs scale of mineral hardness, making it even harder than ruby, sapphire, and most other gemstones.
Like Quartz, Stishovite is a mineral form of silicon dioxide. However, it crystallizes in a different and high-pressure form. It has a more open and symmetrical arrangement of silicon and oxygen atoms, which makes its tetragonal crystal structure significantly denser.
With a density of 4.287 grams per cubic centimeter, tungsten carbide is the second densest polymorph of silica, after seifertite.
Although stishovite is not a practical engineering material, its exceptional hardness can be of interest to materials scientists for understanding high-pressure behavior in materials.
It may be found in certain extraterrestrial environments; its discovery in outer space can provide insights into their geological history and impact events.
1. Diamond
The Hope Diamond
Mohs Hardness: 10
Absolute Hardness: 1500
Diamond is considered the hardest natural mineral on Earth, and it is verified by both the Mohs and Vickers scales. It is a crystalline form of carbon characterized by an exceptionally rigid atomic structure.
It has a high refractive index and the highest thermal conductivity of any natural element. The density of diamonds ranges from 3,150 kg/m³ to 3,530 kg/m³.
While diamonds have the highest Mohs hardness, it’s important to note that this doesn’t render them indestructible. In fact, diamonds can be scratched by other diamonds.
Most gem-quality diamonds form at a depth of 100 miles below the Earth’s surface, where temperatures (and pressure) conditions are incredibly high. However, some rare diamonds have been known to come from below depths of 500 miles. These diamonds are even more unusual because they have undergone even more extreme temperature and pressure conditions during their formation.
Diamonds serve numerous purposes beyond their commercial use in jewelry. They are extensively employed in various industrial applications, including grinding, cutting, drilling, and polishing.
Diamonds have been produced synthetically in laboratories ever since their invention in the 1950s. Today, the majority of the synthetic (artificial diamonds) are produced by the HPHT (high-pressure, high-temperature) process.
Similar to natural diamonds, synthetic diamonds can also exhibit a range of colors. These colors are achieved by introducing various impurities, such as nitrogen and boron, into the diamond-making process.
More than 110 million carats of rough diamonds are mined every year.
This diamond holds a never-before-seen mineral that can’t exist on Earth’s surface https://t.co/HxLYyu1rZi
— Popular Science (@PopSci) October 11, 2023
Other Hardest Material
Diamene (Graphene)
Graphene atoms
We all have heard about graphene at least once, but what exactly is it? In simple terms, graphene is a single layer of carbon atoms with a hexagonal lattice. It is perhaps one of the most remarkable materials developed in the 21st century.
Graphene is the base element in carbon nanotubes and has potential applications in multiple industries. Graphene is a perfect conductor of heat and electricity. For its size, it is the strongest known material on Earth.
But here we are talking about the hardest material (as we know that hardest and strongest are two different parameters). In terms of hardness and stiffness, we know that graphene is inferior to diamond. However, researchers have found a method to make graphene as hard as a diamond.
A team of scientists from the Advanced Science Research Center, City University of New York, have combined two layers of graphene sheets to create a new material that transforms into a diamond-like film upon compression, showing both elastic deformation and chemical changes. They named this new material ‘Diamene.’
In simple words, diamene can temporarily become stiffer and harder than diamond when compressed with enough force. It won’t be surprising to see this material in armor and protective clothing due to its flexibility and lightweight.
Interestingly, the research also concluded that adding more than two layers of graphene doesn’t make the material harder. Instead, it might have the opposite effect, potentially reducing its hardness.
Wurtzite Boron Nitride
3D representation of Wurtzite structure
In recent years, Wurtzite Boron Nitride (w-BN) has attracted much attention (from both industrial and academic fields) due to its superior properties and various potential applications. It is a wurtzite form of the boron nitride in which nitrogen and boron atoms crystallize in a six-member ring formation.
Boron Nitride can be in amorphous (non-crystalline), hexagonal (similar to graphite), cubic (similar to diamond, but slightly weaker), and wurtzite form.
According to a study, wurtzite boron nitride can withstand 18 percent more stress than diamond. Wurtzite Boron also remains more stable in higher temperatures than the diamond, making it a better option for use in cutting and drilling tools.
In addition to extreme hardness, w-BN has high thermal conductivity and high thermal expansion. Due to excellent thermal and chemical stability, boron nitride ceramics are used in high-temperature equipment and metal casting.
Different from diamond and other important minerals, researchers still need to fully realize the potential (in terms of strength) of wurtzite boron nitride as it is extremely rare in nature. It is extremely difficult to produce pure w-BN artificially. Only small amounts of w-BN have been synthesized in a lab.
Palladium Microalloy Glass
Palladium is a rare silvery white metal with the lowest melting point of all platinum group metals (which include platinum, osmium, rhodium, ruthenium, and iridium).
While Palladium has a soft appearance and is ductile, its strength and hardness increase substantially under low temperatures.
Most of the world’s supply of palladium is used in the auto industry (catalytic converters) and the electronics sector. It is also used in medicine, water treatment, and printing process. The metal has numerous potential applications but is constrained by its limited availability.
As we know, glasses and other ceramic materials are brittle, meaning they are strong but not so tough. The same can be said about reinforced glasses such as Gorilla Glass.
But in 2011, a team of researchers at Caltech came up with a specially designed metallic glass that is both stronger and tougher than most materials on Earth. The metallic glass is a micro-alloy of phosphorous, palladium, germanium, silicon, and silver.
Palladium allows the micro-alloy metallic glass to form shear bands (a narrow zone of intense strain), making the glass undergo intense plasticity under stress and thus causing it to bend rather than crack.
Palladium Microalloy Glass is much stronger than hardened steel and perhaps one of the hardest materials on this list that does not have carbon.
The material was developed by a collaboration of researchers at Caltech and Lawrence Berkeley National Laboratory under the U.S. Department of Energy.
Buckypaper
Buckypaper | Wikimedia Commons
Imagine a material with one-tenth the weight but at least 250 times stronger than steel and can also conduct electricity. Its potential applications would be endless. The material we are referring to is called ‘Buckypaper,’ which first gained attention from the scientific community in the early 2000s.
Buckypaper is made of carbon nanotubes which are about 50,000 times thinner than our hair ( between 25-µm to 72-µm thick). A carbon nanotube (CNT) is basically a cylindrical tube made up of graphene with a diameter of a nanometer. It is an allotrope of carbon.
There are basically two main variants of nanotubes – Single-wall carbon nanotubes (SWCNTs) and Multi-wall carbon nanotubes (MWCNTs). They are one of the strongest materials ever synthesized.
The powerful atomic bonds of buckypaper make it twice as hard as diamond and 250 times hard than steel (ordinary steel has Mohs hardness between 4-4.5).
Buckypaper has some other intriguing characteristics that separate it from ordinary composite materials. For example, it conducts electricity and disperses heat efficiently, which makes it a feasible material for use in the semiconductor and electronics industry. Buckypaper also has potential biological applications.
Although it may sound like science fiction, this remarkable material is light and stable enough to potentially be used for futuristic structures like a space elevator.
Lonsdaleite
On the left-hand side (a) is the pure diamond, and on the right (b) is a diamond with lonsdaleite impurities. Two diamond samples from the Popigai crater in Siberia. | Image Courtesy: Hiroaki Ohfuji et al./Nature
Lonsdaleite, also known as the hexagonal diamond, is a rare allotrope of carbon (like graphite and diamond) that is only found in meteorite debris in nature.
Lonsdaleite was first discovered in 1967 at the Canyon Diablo meteorite, an asteroid that created the Barringer Crater in Arizona, U.S. It is named after British crystallographer Kathleen Lonsdale widely known for her work in X-ray crystallography.
Lonsdaleite is called a ‘hexagonal diamond‘ due to its hexagonal crystal structure, which is similar to that of wurtzite boron nitride.
Imagine a carbon-rich meteorite containing graphite hurtling down toward the Earth. Upon collision with the Earth’s surface, the meteorite experiences a massive surge in temperature and pressure. This increased pressure and temperature allow the graphite to compress and transform into a diamond.
However, instead of gaining a cubic lattice, which is found in ordinary diamonds, it retains the hexagonal lattice of graphite. In simple terms, lonsdaleite is similar to diamond but with a different crystal structure.
According to computer simulations, lonsdaleite is estimated to be 58 percent harder than diamond and can withstand higher pressures (indentation hardness).
However, most lonsdaleites found in nature exhibit lower hardness than diamonds. This is likely due to the impurities present in the material. Researchers believe that impurity-free lonsdaleite would be much harder than any diamond found on Earth.
More To Know
What is the significance of hardness in mineralogy?
Hardness is a crucial property in mineralogy for several reasons:
- It aids in mineral identification and classification
- It provides insights into a mineral’s formation and geological history
- It helps in assessing the effects of weathering and erosion on landscapes and ecosystems
Moreover, hardness has industrial applications, from construction to manufacturing. Minerals with specific hardness levels are used as cutting tools, abrasive materials, or even in the electronics industry. It is also used in the production of ceramics and glass to ensure that the final products have the desired properties like resistance to wear, heat, or chemical corrosion.
Can minerals change their hardness under different conditions?
Yes, the hardness of some minerals can change under extreme temperature and pressure conditions. For example, stishovite and coesite are polymorphs of quartz formed under ultrahigh-pressure conditions, which is why they are substantially harder.
The presence of impurities or foreign substances in a mineral’s crystal lattice can also affect its hardness. For example, calcite, in its purest form, is relatively soft and has a consistent hardness. However, common impurities in calcite, like magnesium and iron, can influence its physical properties (depending on the type and concentration of impurities).
Can you scratch a diamond with another diamond?
Yes. Scratching a diamond with another diamond is indeed possible. However, it depends on the specific orientation and sharpness of the contact points. Diamond facets and edges can be polished or cut to different shapes and sharpness, affecting their scratching ability.
Is There Any Other Method To Measure the Hardness of Materials?
In material science, there are mainly three ways one can measure the hardness of a mineral/material – scratch, indentation, and rebound.
The scratch hardness, as we talked about earlier, measures how resistant a material is from a fracture due to friction from a harder material. Perhaps the most common scratch hardness test is the Mohs scale. To perform a scratch test, mineralogists often use an instrument called a sclerometer.
Indentation hardness tests determine the hardness of a material by measuring its resistance to deformation from a sharp object (indenter). It is mostly used in mechanical engineering. The two most common indentation hardness test scales are – the Brinell scale and the Vickers hardness test.
Brinell Scale – Established in 1900 by Swedish engineer John Brinell, the Brinell scale was the first-ever standardized test for indentation hardness. It is denoted by BHN or HB.
Typically, a 10 mm diameter steel ball is used as an indenter to perform the test. However, for harder materials, the steel ball is replaced by a tungsten carbide ball. The maximum force used in this test is 3,000 kilograms-force (kgf).
Vickers Hardness Test – An alternative to the Brinell scale, the Vickers hardness test was developed at a British engineering company, Vickers Ltd, in 1921.
Diamond indenter used in a Vickers test | Image Courtesy: R. Tanaka
Vickers test is often considered the ‘easiest’ hardness test to perform since the size and type of the indenter don’t affect the required calculations. An indenter can be used for all materials/metals irrespective of their hardness. It is denoted by Vickers Pyramid Number (HV).
The third type of hardness test is called the rebound hardness test. In this test, a diamond-tipped ball is dropped on the test material from a fixed height to measure its hardness.
Leeb rebound hardness test – One of the commonly used methods for testing metal hardness is the Leeb rebound hardness test, which uses the rebound velocities to determine the hardness.
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How does talc, the softest mineral, make it to the top 10 hardest minerals? Sloppy thinking. This list shows examples of the various levels of hardness, not a top 10 list.
if you will research, these examples are based from mohs scale of hardness. the other minerals are within the between from 1 -10. these are chosen because they based it in their atomic structure difference.
It still isn’t a top ten list. It is a list that shows examples of each point on the mohs scale.
then you shouldn’t have named it the top eleven hardest minerals, you blow right over dozens of hard minerals and include talc and calcite. You title belongs on a totally different article . . . you failed to fulfill the promises of the title
if you will research, Varun Kumar is telling us that talc is the eleventh hardest mineral known to man . . . . LMFAO . . . . in case you’re wondering, it’s absolutely NOT the eleventh hardest mineral, it’s not even in the top 100. How to completely fail to support your title Varun, there has never been a bigger need for a “scrap this and do it over again” plan
atomic structure is never mentioned except ONCE in the after notes about the hexagonal structure of some carbon crystals that aren’t even included in the top eleven hardest minerals. What I’m seeing is Varun Kumar telling us feldspar and calcite are almost as hard as diamonds . . . .
completely agree, his title promises us a top ten hardest minerals and then proceeds starting with the absolute softest mineral, then to the next softest mineral, you don’t even hit the hard minerals until you hit number seven. Well there are more than eleven minerals available to write about. I think the dude should totally scrap this article, keep the headline and try to make a new article that sticks to the headline. Smoking a lot of dope beforehand is not recommended . . .
What about neutronium