Top 10 Hardest Minerals on the Earth according to Mohs Scale of Hardness

Hardness is a measure of how easily a mineral can be scratched. In 1822, Friedrich Mohs, an Austrian mineralogist, developed a scale of hardness based on one mineral's ability to scratch another. The Mohs scale ranks minerals from 1 (softest) to 10 (hardest).

 

Each mineral in the scale can scratch the mineral below it, but not the mineral above it. For example, talc (1) can be scratched by gypsum (2), but gypsum cannot be scratched by talc. Mohs' scale is still one of the best ways to estimate a mineral's hardness. Here is the Mohs scale of hardness, with common objects of equivalent hardness:

Table: Mohs Hardness Scale

Hardness	10	9	8	7	6	5	4	3	2	1
Mineral	Diamond	Corundum	Topaz	Quartz	Orthoclase	Apatite	Fluorite	Calcite	Gypsum	Talc

 

The Top 10 hardest minerals on Earth according to Mohs' scale of hardness are:

        (1)        Diamond (10)

        (2)        Boron carbide (9.5)

        (3)        Stishovite (9.5)

        (4)        Moissanite (9.25)

        (5)        Titanium carbide (9-9.5)

        (6)        Chromium carbide (9-9.5)

        (7)        Tantalum carbide (9)

        (8)        Zirconium carbide (9)

        (9)        Beryllium carbide (9)

      (10)      Aluminium boride (8.5)

 

Here is a detailed explanation of each mineral with its characteristics and uses.

 

(1) Diamond

 

Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. It is the hardest naturally occurring substance known, and it is also the most popular gemstone. Because of their extreme hardness, diamonds have a number of important industrial applications.

Diamond Cut – The Shape That Makes Your Diamonds Special (Source: All Diamond)

 

Formation of Diamond:

 

Diamonds are formed deep within the Earth's mantle, under high pressure and temperature conditions. They are created from carbon atoms arranged in a crystal lattice structure, which gives diamond its remarkable hardness. Carbon-bearing materials, primarily in the form of carbonaceous minerals, are subjected to extreme heat and pressure at depths of around 100 to 200 kilometers (about 62 to 124 miles) below the Earth's surface. Over millions of years, these conditions lead to the formation of diamonds.

 

Characteristics of Diamond:

 

❖           Hardness: Diamond is the hardest known naturally occurring material on Earth. It ranks as a 10 on the Mohs scale of mineral hardness.

❖           Transparency: Diamonds are typically transparent or translucent and are prized for their ability to refract light and create dazzling displays of color and brilliance.

❖           Color: While diamonds are often thought of as colorless, they can come in various colors, including white, yellow, brown, and rare fancy colors like blue, pink, and green.

❖           Luster: Diamonds have a high luster or "sparkle" due to their excellent light dispersion properties.

❖           Cleavage: Unlike many other minerals, diamonds do not exhibit cleavage, which means they don't break along specific planes when subjected to pressure. Instead, they can be cut and polished into various shapes and facets.

 

Uses of Diamond:

 

µ           Jewellery: Diamonds are the most popular gemstone in the world, and they are used to create a wide variety of jewellery, including engagement rings, necklaces, earrings, and bracelets.

µ           Industrial Applications: Diamonds are also used in a variety of industrial applications, including cutting tools, abrasives, and heat sinks.

µ           Scientific Applications: Diamonds are also used in a variety of scientific applications, including diamond anvil cells, which can be used to create extremely high pressures.

 

(2) Boron Carbide

 

Boron carbide is a ceramic material with the chemical formula B4C. It is an exceptionally hard substance and is known for its extreme hardness, low density, and high melting point. Here are some key characteristics and uses of boron carbide:

 

Characteristics:

 

❖           Hardness: Boron carbide is one of the hardest known materials. Its hardness falls just below that of diamond on the Mohs scale, making it extremely resistant to abrasion and wear.

❖            Low Density: Despite its hardness, boron carbide has a relatively low density, which makes it attractive for applications where lightweight yet hard materials are required.

❖           High Melting Point: Boron carbide has a very high melting point, exceeding 2,700 degrees Celsius (4,892 degrees Fahrenheit). This property makes it suitable for high-temperature applications.

❖           Chemical Stability: It is chemically inert and resistant to most acids, making it suitable for use in harsh environments.

❖           Electrical Conductivity: Boron carbide is a semiconductor and has applications in electronics.

 

Uses of Boron Carbide:

 

µ           Armour and Ballistic Protection: Boron carbide is widely used in the manufacture of body armour and ballistic protection materials. Its combination of high hardness and low density makes it effective in stopping high-velocity projectiles.

µ           Abrasive Materials: Due to its extreme hardness, boron carbide is used in the production of abrasive materials, such as grinding wheels and cutting tools, for precision machining and material removal.

µ           Nuclear Applications: Boron carbide is used in nuclear applications, including as a neutron-absorbing material in control rods for nuclear reactors and as shielding material in nuclear radiation research.

µ           Nozzles and Abrasive Blasting: It is used in the manufacture of abrasive blasting nozzles for sandblasting and water jet cutting applications.

µ           Ceramic Armour Plates: Boron carbide is incorporated into ceramic armor plates used by the military and law enforcement to protect personnel from high-velocity threats.

µ           Aerospace and Space Industry: It is used in the aerospace and space industries for its high-temperature resistance and lightweight properties.

µ           Scientific Research: Boron carbide is used in various scientific experiments and high-pressure studies due to its exceptional hardness.

 

It's important to note that while boron carbide has many valuable properties, it is also a challenging material to process and manufacture due to its extreme hardness. Despite this, its unique combination of characteristics makes it indispensable in a variety of specialized applications.

 

(3) Stishovite

 

Stishovite is a rare mineral and a polymorph of silicon dioxide (SiO2), commonly known as silica. It is characterized by its high-pressure crystal structure, which forms under extreme pressure conditions. Here are some key points about stishovite:

 

Characteristics:

 

❖          High-Pressure Phase: Stishovite is a high-pressure phase of silica, meaning it forms under extreme pressures typically found deep within the Earth's mantle, at depths of over 300 kilometers (about 186 miles) and pressures exceeding 10 gigapascals (GPa).

❖          Crystal Structure: Stishovite has a distinct crystal structure that differs from the more common minerals of silica, such as quartz or cristobalite. It has a denser and more compact arrangement of silicon and oxygen atoms due to the extreme pressure conditions under which it forms.

❖          Hardness: Stishovite is one of the hardest known minerals and ranks high on the Mohs scale of mineral hardness, approaching the hardness of diamond.

 

Uses of Stishovite:

 

Stishovite is not commonly used in industrial or commercial applications due to its rarity and the extreme conditions required for its formation. However, it does have some scientific and industrial significance:

 

µ         Scientific Research: Stishovite is valuable in scientific research, especially in the study of the Earth's mantle and the behavior of materials under extreme pressure and temperature conditions. Researchers use stishovite to understand the Earth's interior and the properties of minerals at great depths.

µ          High-Pressure Experiments: Stishovite is used as a marker or pressure gauge in high-pressure experiments. By studying stishovite and its transformations under high-pressure conditions, scientists can gain insights into the properties of other minerals and materials subjected to similar extreme conditions.

µ          Geological Research: Stishovite can provide valuable information about geological processes and the history of impact events on Earth and other celestial bodies. It is found in meteorite impact sites and can be used to identify and study impact-related minerals and structures.

 

In summary, stishovite is a rare and exceptionally hard mineral that forms under extreme pressure conditions deep within the Earth's mantle or as a result of meteorite impacts. Its primary significance lies in scientific research, particularly in the study of high-pressure and high-temperature phenomena, the Earth's geology, and the properties of minerals under extreme conditions.

 

(4) Moissanite

 

Moissanite is a naturally occurring silicon carbide (SiC) mineral that is often synthesized for use as a gemstone. It is known for its remarkable brilliance and hardness. Here are some key points about moissanite:

 

Characteristics:

 

❖          Brilliance: Moissanite exhibits exceptional brilliance and fire, which means it disperses light and creates colourful flashes or "fire" similar to, and sometimes even greater than, that of a diamond.

❖          Hardness: Moissanite is one of the hardest known naturally occurring minerals, ranking just below diamond on the Mohs scale of mineral hardness. This makes it highly resistant to scratching, making it suitable for everyday wear in jewellery.

❖          Color: Moissanite is typically near-colourless, and some specimens may have a slight yellow or greenish tint. High-quality moissanite gemstones are often colourless or nearly so.

❖          Durability: It is a durable gemstone that is less prone to chipping, breaking, or scratching compared to other gemstones like sapphires or emeralds.

❖          Origin: While moissanite was originally discovered in a meteorite crater, the moissanite used in jewellery is typically lab-created through a process called the high-temperature, high-pressure (HTHP) method.

 

Uses of Moissanite:

 

The primary uses of moissanite are in the jewellery industry:

 

µ          Gemstone: Moissanite is a popular and affordable alternative to traditional gemstones like diamonds. It is used in various types of jewellery, including engagement rings, earrings, necklaces, and bracelets. Its brilliance and hardness make it a favoured choice for those seeking a sparkling, durable, and ethical gemstone option.

µ          Diamond Alternative: Moissanite's optical properties, particularly its fiery brilliance, have led to it being used as a diamond alternative or a "diamond simulant." It is often difficult to distinguish moissanite from diamonds without specialized testing equipment.

µ          Ethical and Sustainable: Lab-created moissanite is considered an ethical and sustainable gemstone option because it is not associated with many of the environmental and ethical concerns often associated with diamond mining.

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In summary, moissanite is a gemstone known for its brilliance, hardness, and durability. It is used primarily in the jewellery industry as a diamond alternative or a cost-effective, ethical, and sustainable gemstone choice. Lab-created moissanite has gained popularity for its exceptional optical properties and affordability.

 

(5) Titanium Carbide

 

Titanium carbide (TiC) is a compound composed of titanium and carbon. It is classified as a ceramic material and is known for its remarkable hardness and high melting point. Here are some key characteristics and uses of titanium carbide:

 

Characteristics:

 

❖          Hardness: Titanium carbide is extremely hard, often ranking just below diamond and boron carbide on the Mohs scale of mineral hardness. This makes it highly resistant to wear, abrasion, and scratching.

❖          High Melting Point: It has a very high melting point, exceeding 3,000 degrees Celsius (about 5,432 degrees Fahrenheit). This property makes it suitable for applications involving high temperatures.

❖          Chemical Inertness: Titanium carbide is chemically inert and does not react easily with most chemicals, making it corrosion-resistant.

❖          Electrically Conductive: It exhibits good electrical conductivity, particularly when compared to other ceramics, which makes it useful in certain electronic and semiconductor applications.

 

Uses of Titanium Carbide:

 

µ          Cutting Tools: Titanium carbide is commonly used as a hard coating material for cutting tools, such as drills, end mills, and inserts. When applied as a coating, it enhances the wear resistance and longevity of the tools, allowing them to cut or machine materials like steel more efficiently.

µ          Abrasive Materials: Due to its exceptional hardness, titanium carbide is used in the production of abrasive materials, grinding wheels, and sandpaper for precision machining and material removal.

µ           Wear Parts: It is employed in the manufacture of wear-resistant components, such as nozzles, bearings, and seals, used in industrial equipment subjected to high wear and friction.

µ          High-Temperature Applications: Its high melting point and resistance to thermal shock make titanium carbide suitable for high-temperature applications, including in the aerospace and defence industries for components exposed to extreme heat.

µ          Ceramic Armour: Titanium carbide is used in the development of advanced ceramic armour materials due to its high hardness and resistance to penetration. It can be used in body armour and vehicle armour to protect against projectiles.

µ          Electrodes: Its electrical conductivity makes it valuable for certain electrical and electronic applications, including as an electrode material in some electrochemical processes.

µ          Semiconductor Industry: In the semiconductor industry, titanium carbide can be used in the production of thin films and coatings for integrated circuits and other electronic devices.

µ          Research and Development: Titanium carbide is also used in scientific research, particularly in materials science and engineering, where its unique properties are of interest for various experiments and applications.

 

In summary, titanium carbide is a high-performance ceramic material known for its hardness, resistance to wear, high melting point, and chemical inertness. It is used in a variety of industrial applications, particularly in cutting tools, abrasives, wear-resistant parts, and high-temperature environments, as well as in some electronic and semiconductor applications.

 

(6) Chromium Carbide

 

Chromium carbide (Cr₃C₂) is a compound composed of chromium and carbon. It is a hard and corrosion-resistant ceramic material. Here are some key characteristics and uses of chromium carbide:

 

Characteristics:

 

❖          Hardness: Chromium carbide is a hard material, similar to other carbides, and is often used for its wear-resistant properties.

❖          Corrosion Resistance: It exhibits good resistance to corrosion, making it suitable for use in environments where materials are exposed to chemicals and oxidation.

❖          High Melting Point: Chromium carbide has a high melting point, which makes it useful in high-temperature applications.

 

Uses of Chromium Carbide:

 

µ          Wear-resistant Coatings: Chromium carbide is commonly used as a coating material to improve the wear resistance of various surfaces. It is applied through processes like thermal spraying or chemical vapour deposition to extend the lifespan of parts and equipment subjected to abrasive wear and corrosion.

µ          Cutting Tools: It is used in the manufacture of cutting tools, such as drills, milling cutters, and inserts, to enhance their hardness and wear resistance.

µ          Industrial Equipment: Chromium carbide is employed in the production of wear-resistant components for various industrial equipment, including pumps, valves, and conveyors.

µ          Thermal Spray Applications: It is used in thermal spray applications for rebuilding and protecting equipment components in industries like mining, steel production, and oil and gas.

µ          Ceramic Armour: In some cases, chromium carbide is utilized in the development of ceramic armour materials for personal and vehicle protection against projectiles.

µ          High-Temperature Environments: Due to its high melting point and resistance to oxidation, it finds use in high-temperature applications such as furnace components and in the aerospace industry.

 

In summary, chromium carbide is a hard and corrosion-resistant ceramic material often used as a coating to enhance the wear resistance of surfaces and as a component in various industrial applications, particularly where hardness and resistance to wear and corrosion are required.

 

(7) Tantalum Carbide

 

Tantalum carbide (TaC) is a ceramic compound composed of tantalum (Ta) and carbon (C). It is known for its exceptional hardness and high melting point. Here are some key characteristics and uses of tantalum carbide:

 

Characteristics:

 

❖          Hardness: Tantalum carbide is extremely hard, often ranking among the hardest known materials. It has hardness comparable to that of tungsten carbide and can resist wear, abrasion, and scratching.

❖          High Melting Point: It has an exceptionally high melting point, surpassing 3,700 degrees Celsius (about 6,692 degrees Fahrenheit). This property makes it suitable for use in high-temperature applications.

❖          Chemical Inertness: Tantalum carbide is chemically inert and resistant to most chemical reactions and corrosion. This makes it suitable for use in harsh chemical environments.

❖          Electrical Conductivity: It is a good conductor of electricity, which is advantageous in certain electronic and semiconductor applications.

 

Uses of Tantalum Carbide:

 

µ          Cutting Tools: Tantalum carbide is utilized in the manufacture of cutting tools, such as drills, milling cutters, and inserts. It enhances the wear resistance and lifespan of these tools, making them suitable for machining hard materials.

µ          Abrasive Materials: Due to its extreme hardness, tantalum carbide is used in the production of abrasive materials, grinding wheels, and cutting tools for precision machining and material removal.

µ          High-Temperature Applications: Its high melting point and resistance to thermal shock make tantalum carbide suitable for high-temperature applications, including in aerospace and defense industries for components exposed to extreme heat.

µ           Industrial Equipment: Tantalum carbide is employed in the production of wear-resistant components, such as nozzles, bearings, and seals, used in industrial equipment subjected to high wear and friction.

µ          Ceramic Armour: In some cases, tantalum carbide is used in the development of advanced ceramic armour materials for personal and vehicle protection against projectiles.

µ          Electronics and Semiconductors: Its electrical conductivity makes tantalum carbide valuable in certain electronic and semiconductor applications, such as integrated circuits and other electronic devices.

µ          Scientific Research: Tantalum carbide is also used in scientific research, particularly in materials science and engineering, where its unique properties are of interest for various experiments and applications.

 

In summary, tantalum carbide is a high-performance ceramic material known for its hardness, resistance to wear, high melting point, and chemical inertness. It finds applications in cutting tools, abrasive materials, high-temperature environments, electronics, industrial equipment, and scientific research.

 

(8) Zirconium Carbide

 

Zirconium carbide (ZrC) is a ceramic compound composed of zirconium (Zr) and carbon (C). It is known for its exceptional hardness, high melting point, and resistance to wear. Here are some key characteristics and uses of zirconium carbide:

 

Characteristics:

 

❖          Hardness: Zirconium carbide is extremely hard and ranks among the hardest known materials. It has a high hardness, similar to that of tungsten carbide, making it highly resistant to wear, abrasion, and scratching.

❖          High Melting Point: It has a very high melting point, exceeding 3,200 degrees Celsius (about 5,792 degrees Fahrenheit). This property makes it suitable for use in high-temperature applications.

❖          Chemical Inertness: Zirconium carbide is chemically inert and resistant to most chemical reactions and corrosion. It remains stable in harsh chemical environments.

❖          Electrical Conductivity: It is a good conductor of electricity, which is advantageous in certain electronic and semiconductor applications.

 

Uses of Zirconium Carbide:

 

µ           Cutting Tools: Zirconium carbide is employed in the manufacture of cutting tools, such as drills, milling cutters, and inserts. It enhances the wear resistance and lifespan of these tools, making them suitable for machining hard materials.

µ           Abrasive Materials: Due to its extreme hardness, zirconium carbide is used in the production of abrasive materials, grinding wheels, and cutting tools for precision machining and material removal.

µ           High-Temperature Applications: Its high melting point and resistance to thermal shock make zirconium carbide suitable for high-temperature applications, including in aerospace and defense industries for components exposed to extreme heat.

µ           Industrial Equipment: Zirconium carbide is employed in the production of wear-resistant components, such as nozzles, bearings, and seals, used in industrial equipment subjected to high wear and friction.

µ          Ceramic Armour: In some cases, zirconium carbide is used in the development of advanced ceramic armour materials for personal and vehicle protection against projectiles.

µ           Electronics and Semiconductors: Its electrical conductivity makes zirconium carbide valuable in certain electronic and semiconductor applications, such as integrated circuits and other electronic devices.

µ           Scientific Research: Zirconium carbide is also used in scientific research, particularly in materials science and engineering, where its unique properties are of interest for various experiments and applications.

 

In summary, zirconium carbide is a high-performance ceramic material known for its hardness, resistance to wear, high melting point, and chemical inertness. It finds applications in cutting tools, abrasive materials, high-temperature environments, electronics, industrial equipment, and scientific research.

 

(9) Beryllium Carbide

 

Beryllium carbide (Be₂C) is a compound composed of beryllium (Be) and carbon (C). It is a ceramic material with distinct characteristics and applications. Here are some key characteristics and uses of beryllium carbide:

 

Characteristics:

 

❖          Hardness: Beryllium carbide is a hard material with a high level of hardness, although it is not as hard as some other carbide like tungsten carbide or boron carbide.

❖          Chemical Stability: It is chemically stable and resistant to most acids and chemicals, making it suitable for use in harsh environments.

 

Uses of Beryllium Carbide:

 

µ          Nuclear Industry: Beryllium carbide has historically been used as a neutron moderator in nuclear reactors. It helps control the speed of neutrons and contributes to the overall efficiency of the nuclear reaction.

µ           Semiconductor Industry: Beryllium carbide is used in the semiconductor industry for its unique properties, including its electrical conductivity. It can be used in certain specialized electronic applications.

µ          Ceramic Manufacturing: In some cases, beryllium carbide is used in the production of ceramics and as a component in advanced ceramic materials. Its properties make it suitable for specific applications within the ceramics industry.

µ           Scientific Research: Beryllium carbide may be used in scientific research and experimental studies, particularly in fields where its properties are of interest.

 

It's important to note that beryllium is a toxic element, and compounds containing beryllium, including beryllium carbide, require careful handling and safety precautions due to the potential health risks associated with beryllium exposure. As such, its use is regulated and controlled in many industries, and alternatives are sought when possible.

 

(10) Aluminium Boride

 

Aluminum boride (AlB2) is a chemical compound composed of aluminum (Al) and boron (B). It is a ceramic material known for its unique properties. Here are some key characteristics and uses of aluminum boride:

 

Characteristics:

 

❖          Hardness: Aluminum boride is a very hard material, making it suitable for applications requiring resistance to wear and abrasion. It is not as hard as some other ceramics like boron carbide or diamond, but it is still harder than most common engineering materials.

❖          High Melting Point: It has a high melting point, which makes it suitable for use in high-temperature applications.

❖          Electrical Conductivity: Aluminum boride is an electrical conductor, and this property is useful in some specialized electronic and semiconductor applications.

 

Uses of Aluminium Boride:

 

µ          Ceramics: Aluminum boride is sometimes used as a component in advanced ceramic materials. Its hardness and high melting point make it suitable for specific applications within the ceramics industry.

µ          Cutting Tools: While not as common as other ceramic materials like tungsten carbide, aluminum boride has been considered for use in cutting tools and wear-resistant coatings due to its hardness and wear resistance.

µ           Semiconductor Industry: It is used in some specialized electronic and semiconductor applications due to its electrical conductivity and high-temperature stability.

µ           Thermocouples: Aluminum boride can be used in thermocouples, which are devices that measure temperature based on the electrical conductivity of materials at different temperatures.

µ           Scientific Research: Aluminum boride may be used in scientific research and experimental studies, particularly in fields where its unique properties are of interest.

 

It's important to note that while aluminum boride has certain advantageous characteristics; it is not as widely used as some other ceramics like alumina or silicon carbide. Its application is generally limited to specialized industries and specific use cases where its unique properties are required.