The hardness of any mineral is defined by their Mohs scale number: harder the mineral, higher its Mohs number. The Mohs scale was devised by a German geologist and mineralogist Friedrich Mohs in 1812. This method is based on the ability of one mineral to visibly scratch the other(s).
Although the Mohs scale is not precise and strictly ordinal, it has a relevant use in geology, mostly to identify various minerals. To perform the scratch test, metallurgist uses sclerometer or Turner–sclerometer.
Below you will find the list of 12 hardest minerals in the world, ranked according to the Mohs hardness.
Mohs hardness: 1
Chemical formula: MgSi4O10(OH)2
Absolute hardness: 1
Talc is a mineral composed of hydrated magnesium silicate. Cesium and rubidium (with 0.2-0.3 hardness) lithium, sodium and potassium (with 0.5-0.6 hardness) are all softer than Talc. It is a common metamorphic mineral in metamorphic belts of the western United States, Western Alps and in the Himalayan region.
Mohs hardness: 2
Chemical formula: CaSo4 2H2O
Absolute hardness: 3
Gypsum is a sulfate mineral composed of calcium sulfate dihydrate. It is can be used as a fertilizer. Different forms of Gypsum are founded in ancient sculptures of Mesopotamia, Ancient Rome, and the Byzantine empire.
Orbital pictures from the Mars Reconnaissance Orbiter (MRO) indicated the existence of Gypsum dunes in the extreme northern region of Mars. United States, Brazil, and India are among the top 3 countries with the largest Gypsum reserves in the world. It is widely used in soil conditioner and tofu (soybean curd).
Mohs hardness: 3
Chemical formula: CaCO3
Absolute hardness: 9
Calcite belongs to a carbonate group of minerals and it is the most stable polymorph of calcium carbonate. Calcite is a common constituent of sedimentary rocks, most of which is formed from the dead marine organisms.
It has a Mohs hardness scale of 3 and a specific gravity of 2.71. One of the remarkable natural made Calcite structure is found in the Snowy river cave in Lincoln County, New Mexico.
Mohs hardness: 4
Chemical formula: CaF2
Absolute hardness: 21
Fluorite or fluorspar is a colorful mineral and because of its moderate hardness, it is used for making ornaments and other artistry works. Fluorite is also a frequently occurring mineral. China, Mexico, and South Africa are amongst the largest fluorite producing countries in the world.
It is primarily used in optics, where it is used as a window material. Optical lenses are also made up of Fluorite because of its low dispersion causing no or less chromatic aberration.
Mohs hardness: 5
Chemical formula: Ca5(PO4)3(OH-,CI-,F-)
Absolute hardness: 48
Apatite is a group of phosphate minerals, which is generally known as hydroxylapatite, fluorapatite and chlorapatite. The primary use of the Apatite is in fertilizer manufacturing as it is a good source of phosphorus.
It is one of the few minerals, which is produced and used by biological micro-environmental systems. Furthermore, the rock samples collected by the astronauts during the Apollo program contained traces of apatite.
5. Orthoclase Feldspar
Mohs hardness: 6
Chemical formula: KAISi3O8
Absolute hardness: 72
Orthoclase Feldspar is an important mineral that forms igneous rocks. Orthoclase is a common constituent of most granites and other igneous rocks. It is mostly used in the manufacturing process of glasses and some ceramics such as porcelain. It is also a constituent of scouring powder.
Mohs hardness: 7
Chemical formula: SiO2
Absolute hardness: 100
Quartz is the second most abundant mineral in the earth’s crust after feldspar. There are many different varieties of Quartz found in Europe. It is an essential constituent of sedimentary and metamorphic rocks. Quartz crystal has piezoelectric properties and widely used as the crystal oscillator. The Quartz clock is a familiar device made up of this mineral.
Mohs hardness: 8
Chemical formula: AI2SiO4(OH-,F-)2
Absolute hardness: 200
Topaz is a silicate mineral of aluminum and fluorine and its crystal are mostly pyramid in shape. Pure topaz is colorless and transparent but it is usually tinted by impurities. A typical topaz is yellow, pale gray, reddish-gray or blue-brown in color. A large amount of topaz is found in Sri Lanka, Germany, Norway, Nigeria, Australia, Japan, Brazil, Mexico, and the United States.
Mohs hardness: 9
Chemical formula: AI2O3
Absolute hardness: 400
Corundum is the second hardest mineral on the Mohs scale. It is a crystalline form of aluminum oxide with traces of iron, chromium, vanadium, and titanium. Pure corundum is transparent, however, it can have different colors when impurities are present.
Different colored corundum has different names, the red colored corundum is known as ruby, while pink-orange is called padparadscha, and all others are called sapphire.
Mohs hardness: 10
Chemical formula: C
Absolute hardness: 1600
Diamond is the hardest known natural mineral according to the Mohs scale. Diamond hardness depends on its purity and the hardest diamond can only be scratched by other diamonds. Some blue color diamonds are natural semiconductors, some are electrical insulators and the rest are electric conductors.
Approximately 26,000 kg of diamonds are mined annually, out of which 50% of diamonds originate from Central and Southern Africa. Many recent studies show that the Diamond is no more the hardest mineral found on the earth and is replaced by the following.
Wurtzite boron nitride
A very small amount of Wurtzite boron nitride exists on Earth. They are either naturally found or manually synthesized. Various simulations showed that Wurtzite boron nitride can withstand 18 percent more stress than diamond. Naturally, these are produced during volcanic eruptions due to very high temperatures and pressure.
Lonsdaleite, also known as the hexagonal diamond, was named in honor of Kathleen Lonsdale, a famous Irish crystallographer. It is believed that lonsdaleite is 58 percent harder than diamond.
Lonsdaleite is a naturally occurring mineral. It forms when meteorites containing graphite strike the Earth. The heat and stress resulting from the strike transform the graphite into lonsdaleite, which is similar to a diamond but arranged in a different shape.