Therapeutic properties

What is the strongest stone on earth?

Diamond still remains the standard of hardness and is used in various methods for measuring the mechanical hardness of materials (Rockwell, Vickers, Mohs methods). But there are materials that are not only comparable in hardness to diamond, but also superior to it in this characteristic. In an article in the journal Popular Mechanics, their Vickers microhardness is given to compare materials. Materials whose hardness exceeds 40 GPa are considered superhard. For a “standard” diamond, this indicator can fluctuate between 70 and 150 GPa, depending on its purity and the method of production (as a rule, the hardness of diamond is given as 115 GPa). The same applies to other materials: their hardness changes depending on the sample synthesis conditions, and sometimes varies depending on the direction of the load applied to it. 1. Fullerite (up to 310 GPa) Polymerized fullerite is the hardest substance currently known to science. It is a molecular crystal – a structure in the nodes of which there are not individual atoms, but entire molecules (fullerenes are one of the allotropic modifications of carbon, shaped like soccer balls). Fullerite leaves scratches on the diamond surface, just like on plastic. 2. Lonsdaleite (before 152 GPa) The prediction of the existence of lonsdaleite practically coincided with its discovery in nature. This allotrope of carbon, much like diamond, was found in a meteorite crater. But natural lonsdaleite, which was probably formed from graphite, which was part of the meteorite, did not have record hardness. It was only in 2009 that scientists proved that in the absence of impurities, lonsdaleite can be harder than diamond. Its high hardness is given by approximately the same mechanism that operates in the case of wurtzite boron nitride. 3. Wurtzite nitride wrinkle (before 114 GPa) Boron nitride with a wurtzite (dense hexagonal) crystal structure is harder than it seems: when a load is applied, it undergoes local structural modifications, interatomic bonds in its lattice are redistributed, and the hardness of the material increases by 78%. 4. Nanostructured cubonite (up to 108 GPa) Cubic boron nitride was first prepared in 1957 Robert Wentorf (Robert H. Wentorf Jr.) for the company General Electric. In 1969, the company registered the trademark “Borazon” for the crystal. In the USSR, cubic boron nitride was first synthesized in Institute of High Pressure Physics of the Academy of Sciences under the direction of Academician L. F. Vereshchagin. Since 1965, elbor has been synthesized on an industrial scale using technology Abrasive plant “Ilyich” (Leningrad). The unique properties of Cubonite (also known as CBN, Borazon and Kingsongite) are widely used in industry. The hardness of cubonite (a cubic modification of boron nitride) is close to diamond and is 80–90 GPa. Due to the Hall-Petch law, a decrease in the size of crystal grains leads to an increase in hardness, and scientists have proven that nanostructuring of cubonite can increase its hardness to 108 GPa. 5. Carbon boron nitride (up to 76 GPa) The atoms of nitrogen, carbon and boron are similar in size. Carbon and boron form similar crystalline structures that are highly hard. Scientists are making attempts to synthesize superhard materials consisting of atoms of all three types – and not without success: for example, the cubic modification of BC2N exhibits a hardness of 76 GPa. 6. Boron carbide (up to 72 GPa) Boron carbide, a material common in modern industry, was obtained back in the century before last. Its microhardness (49 GPa) can be significantly increased by introducing argon ions into the crystal lattice – up to 72 GPa. 7. Boron-carbon-silicon (up to 70 GPa) Alloys based on the boron-carbon-silicon system are extremely resistant to chemical attack and high temperature; they are characterized by high microhardness, reaching 70 GPa (for B4CB4Si) 8. Magnesium aluminum boride (up to 51 GPa) The alloy of boron, magnesium and aluminum is known for its low coefficient of sliding friction (if this material were not so expensive, it could be used to make machines and mechanisms that operate without lubrication) and high hardness. AlMgB thin films14, obtained by pulsed laser deposition, demonstrate microhardness up to 51 GPa. 9. Rhenium diboride (up to 48 GPa) The mechanical properties of the boron and rhenium compound are very unusual: due to the layer-by-layer alternation of different atoms, rhenium diboride is anisotropic, i.e., when measuring hardness along different crystallographic planes, different values ​​are obtained. When tested under low load, rhenium diboride exhibits a hardness of 48 GPa, but as the load increases, the hardness value drops sharply, settling at approximately 22 GPa. Therefore, some researchers doubt whether rhenium diboride should be classified as a superhard material. 10. Monocrystalline boron suboxide (up to 45 GPa) Boron suboxide, containing an “insufficient” amount of oxygen atoms, clearly demonstrates the properties of ceramic materials: high strength, chemical inertness, abrasion resistance at a relatively low density. Boron suboxide is capable of forming grains in the form of icosahedrons, which are neither individual crystals nor quasicrystals – these are twin crystals consisting of 20 “fused” tetrahedral crystals. The hardness of boron suboxide single crystals is 45 GPa. Hard rocks are widely used in the construction industry. They are used for finishing work, in the construction of buildings and monuments, and they are used to produce crushed stone, tiles, paving stones and even works of art. A large number of different types of rocks have been explored on our planet, the properties of which differ from each other. Therefore, in order to choose the right material for solving a specific problem, it is important to know the characteristics of natural stones, including hardness, strength, and other physical and chemical characteristics. Below is what the hardest rocks are like.


Granite is a rock of igneous origin with an average density within the range. The stone has a granular structure, and the grains can be small, medium and large, depending on the grade. Granite is one of the strongest rocks. Fine- and medium-grained stones are considered the most durable—their average compressive strength can reach 3000 kg/cm2. The rock-forming minerals are mica, feldspar and quartz. In addition to them, the rock may contain other inclusions that determine the color of the stone.


Diorite is an igneous rock with granular inclusions of colored minerals, which is very similar to granite. However, there are a number of differences between these stones. In particular, it is much more difficult to split diorite. The mineral composition of the stone is a mixture of plagioclase and multi-colored clastic rocks. For example, it could be apatite, pyroxene, iron compounds, hornblende or quartz. As a rule, the amount of the latter mineral is small. If the quartz content in granite is no less than 1/4, in diorite the number of inclusions of this mineral usually does not exceed 5%. It is customary to distinguish granodiorites into a separate category – such stones can consist of quartz on Another difference between diorite and granite is the level of shine after polishing. Udiorite is dull, with an oily tint, augranite is bright, glassy.


Syenite is also one of the strongest rocks, similar to granite, formed predominantly by potassium feldspar. The content of this mineral can reach 70%, while quartz syenite is absent. Also rock-forming minerals include mica, pyroxene and amphibole. Depending on their relationship, the stone can acquire grayish and pinkish tones. Compared to granite, syenite is less durable and has a lower strength—its compressive strength is only 2000 kg/cm2, its density does not exceed 2213 kg/m3.


  • black, shining with red, dark blue and golden shades;
  • in the form of a rock with snowy blue tints and transitions of all-blue, greenish, dark gray colors.

The average density of labradorite is about 2340 kg/m3, the compressive strength is in the range from 1000 to 2000 kg/cm2. This rock is easier to process than granite. It is most convenient to work with stones where the grain size is


This rock is classified as granite, but in fact gabbro stones are softer and easier to process. The average density of stone is about 2970 kg/m3, but the compressive strength does not exceed 196 MPa.

A distinctive feature of gabbro is its unique dark color, which can vary from gray to charcoal black. Such shades are given to the stone by inclusions of biotite and iodine varieties of amphibole – hornblende.


Basalt is a volcanic rock that is used as a construction, facing, fire- and acid-resistant material. This is the hardest type of stone despite the fact that its mineral composition is very similar to nagabbro. Thus, the compressive strength of ubasalt can reach 490 MPa—most other stones certainly cannot boast of such indicators.


An igneous rock of dense structure, which is sometimes called an analogue of basalt, granite and gabbro.

A separate category is distinguished by Gabbro-Diabase granite, which is mined in Karelia. This rock is in a transitional state between gabbro and diabase, and is distinguished by its high strength and uniform deep black color.

The diabases themselves also have excellent strength characteristics—the hardness of the stone on the Mohs scale is and the compressive strength is within


This metamorphic rock gets its name from its origin—it is formed from recrystallized quartz grains. Quartzite is characterized by a dense granular structure. The stone has high hardness – on the Mohs scale it is equal to 7 points. The density of the rock is about 2700 kg/m3.

This durable mineral has significant compressive strength—in some varieties of quartzite it can reach 450 MPa, which is higher than granite.

The names of the varieties of this stone are given by their mineral composition, for example, magnetite or kyanite quartzite. Depending on the content of impurities, the rock can acquire crimson, gray or soft pink shades, including those merging with each other.


This natural stone is classified as clastic sedimentary rock. It can have a homogeneous or layered structure, in which a mineral substance acts as a connecting element between sand grains. Sandstones are mainly formed from quartz; mica, feldspar, glauconite, and other minerals are also present.

Depending on the structure, sandstone can be:

  • lithographic—has high uniformity and density, lithography is used;
  • oolitic—has an airy structure, consisting of small spherical particles held together by a cementing substance;
  • pisolite – an analogue of oolitic, but with particles of larger diameter;
  • shell rock – has a significant number of inclusions of shells and fragments, due to which a highly porous structure is formed.

The density of sandstone can reach 2670 kg/m3, this figure directly depends on the mineral-forming composition of the rock. The material is easy to process and is used in various fields of construction and arts and crafts.

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