It’s the diamond. It still holds the rank of the hardest material in nature. The mineral withstands a pressure of up to 97 megapascals (about 9,000 times atmospheric pressure) before breaking up and is only scratched by another diamond. But, incredible as it may seem, the jewel’s reign is threatened by two other minerals: lonsdaleite and boron nitrate with a wurtzite crystalline structure. They would be 58 and 18% harder than diamond, respectively. But, for now, this is only in theory, since the hardness of the two has not yet been physically proven. The problem is that both are extremely rare on the planet. Ionsdaleite comes from meteor impacts on Earth and boron nitrate wurtzite is only found after very violent volcanic eruptions. What is known is that the minerals gained the attention of scientists, since they can be substitutes – cheaper – for diamond and compatible with medical, industrial and space applications.
THE TOUGH
See the ten references on the Mohs scale, which measures the ability of one material to scratch another
BABY POWDER
Hardness grade: 1. It is the softest and can be scratched even by a fingernail.
Where is it found: In mineral deposits formed by rocks that have undergone transformations because of the heat and pressure of the Earth’s interior.
Utility: It serves as a thermal and electrical insulator in buildings and is present in ceramics.
GYPSUM
Hardness grade: 2. It just doesn’t get scratched by the talc.
Where is it found: In deposits of sedimentary rocks (which are formed with the help of water, wind and ice).
Utility: It serves as a thermal and acoustic insulator and as a plaster to immobilize fractures and manufacture statues.
CALCITE
Hardness grade 3. It is crossed out by the seven minerals above it on the scale and even by a small copper penny.
Where is it found: In deposits with limestone sedimentary rocks, found in rivers, lakes and caves.
Utility: Used in optical instruments, in steel industries and in soil acidity correction.
FLUORITE
Hardness grade: 4. It is easily scratched by a kitchen knife.
Where is it found: It is a mineral of hydrothermal origin, formed where hot water circulates.
Utility: It serves as an auxiliary in the smelting and manufacture of hydrofluoric acid. It is also used in the manufacture of glass, enamels and ceramics.
APATITE
Hardness grade: 5. It scratches talc, gypsum, calcite, fluorite and itself.
Where is it found: In organic deposits, in magmatic rocks (formed by the magma of volcanoes) and in deposits.
Utility: It composes the bones of animals and is important for the production of fertilizers.
FELDSPAR
Hardness grade: 6. Crosses himself, but is unable to cross the four others above him on the scale.
Where is it found: Hydrothermal deposits (where there is hot water) of pegmatite (mineral rocks).
Utility: Very common in the production of glass and ceramics.
QUARTZ
Hardness grade: 7 . It is tough and capable of scratching the glass.
Where is it found: Meta-sedimentary deposits (rocks that have undergone changes due to pressure, temperature and time) of quartz.
Utility: Used in the manufacture of glass, ceramics, enamel, soap, fiber optics and electronic products.
TOPAZ
Hardness grade: 8 . It scratches quartz, but is scratched by corundum and diamond.
Where is it found: Hydrothermal deposits (where there is hot water) of pegmatite (mineral rocks).
Utility: Precious stone sold commercially by jewelry stores.
CORUNDUM
Hardness grade: 9. It can scratch topaz, but it’s not harder than diamond.
Where is it found: Primary pegmatite deposits, secondary sedimentation deposits.
Utility: It is considered a gem and is sold commercially in jewelry stores.
DIAMOND
Hardness grade: 10 . It’s the toughest. It can only be scratched by itself.
Where is it found: Kimberlite deposits (rocks formed by volcanic eruptions) and in sedimentary deposits.
Utility: In industry, it serves as a cutting tool and for carving materials, in addition to being an expensive jewel.
RESISTANCE HEROES
These are the new minerals tipped for the title of «world’s toughest»
BORON NITRATE WURTZITE
Position in ranking: Today, it would take the place of corundum. It is as hard as diamond, but when put under pressure it becomes stronger. This happens because the electrons present in its structure begin to repel each other to relieve the tension between them. That is, they are able to disassemble and rearrange, hardening the mineral. Boron nitrate wurtzite would be in second place because it has impurities in its structure and its hardness is momentary, only getting harder under pressure.
Where is it found: Around volcanoes. The mineral is formed after strong eruptions.
Utility: It also doesn’t have a certain function, but it would be a cheaper substitute for diamond in industrial and even space applications.
LONSDALEITE
Position in ranking: Today, the mineral would be between topaz and corundum. All lonsdaleite samples ever found showed structural flaws and impurities, leaving the mineral with a hardness lower than the theoretical value (simulated by computer), in which it would withstand a pressure of 152 megapascals (about 15,000 atmospheres) – 58% more than the diamond. But scientists are working so that, in the future, they can recreate a structure based on this material, forming an ultra-resistant material.
Where is it found:In craters. It is formed under high pressure and temperature by the impact of meteors on the Earth’s surface.
Utility:The use is still undefined, but the mineral could be a substitute for diamond in industrial tools.
SOURCESDouglas do Nascimento Silva, chemical engineer and professor of chemical engineering at the Federal University of São Paulo (Unifesp) in Diadema; Akihisa Motoki, mineralogist and professor at the Faculty of Geology at the State University of Rio de Janeiro (Uerj).