The ten reference minerals that define the Mohs hardness scale, from diamond at 10 down to talc at 1.
Diamond is the hardest of the ten Mohs scale reference minerals, with a Mohs hardness of 10. Corundum is second at 9 and Topaz third at 8. The ranking uses each mineral's Mohs number, an ordinal scratch-hardness value, per Wikipedia's Mohs scale article and Encyclopaedia Britannica, as of October 2026.
The Mohs scale of mineral hardness, introduced by German mineralogist Friedrich Mohs in 1812, ranks minerals by whether one can visibly scratch another. Each of its ten steps is defined by a reference mineral, and it is an ordinal scale: a higher number scratches a lower one, but the steps are not equal in size. This list ranks those ten reference minerals from hardest to softest. It is not a ranking of every hard mineral: many other minerals fall between the reference points (for example, a mineral scratched by topaz but not by quartz sits between 7 and 8).
Diamond, a crystalline form of carbon, defines the top of the Mohs scale at 10. On the absolute hardness scale it rates 1,500, nearly four times corundum.
Corundum is crystalline aluminium oxide; its gem varieties are ruby and sapphire. It defines Mohs 9 and, on the absolute scale, rates about twice as hard as topaz (400 vs 200).
Topaz, an aluminium fluorosilicate, defines Mohs 8 and is a widely used gemstone.
Quartz (silicon dioxide) defines Mohs 7. Its piezoelectric properties make it the timing element in quartz watches and electronic oscillators.
Orthoclase, a potassium feldspar common in granite, defines Mohs 6.
Apatite, a group of calcium phosphate minerals and the main natural source of phosphate for fertiliser, defines Mohs 5.
Fluorite (calcium fluoride) defines Mohs 4. It is used as a flux in steelmaking, and the word 'fluorescence' was coined from its glow under ultraviolet light.
Calcite, the calcium carbonate of limestone and marble, defines Mohs 3. Clear crystals show strong double refraction.
Gypsum, a hydrated calcium sulfate used for plaster and drywall, defines Mohs 2.
Talc, a hydrated magnesium silicate, is the softest reference mineral and defines Mohs 1. It is ground into talcum powder.
| # | Name | Chemical Formula | Crystal System | Common Uses | Absolute Hardness |
|---|---|---|---|---|---|
| 1 | Diamond | C | Cubic | Gemstones, cutting tools, abrasives | 1,500 |
| 2 | Corundum | Al₂O₃ | Trigonal | Abrasives, gemstones, watch crystals | 400 |
| 3 | Topaz | Al₂SiO₄(F,OH)₂ | Orthorhombic | Gemstones | 200 |
| 4 | Quartz | SiO₂ | Trigonal | Electronics, glassmaking, gemstones | 100 |
| 5 | Orthoclase | KAlSi₃O₈ | Monoclinic | Ceramics, glass | 72 |
| 6 | Apatite | Ca₅(PO₄)₃(F,Cl,OH) | Hexagonal | Fertiliser, phosphoric acid | 48 |
| 7 | Fluorite | CaF₂ | Cubic | Flux in steelmaking, optics | 21 |
| 8 | Calcite | CaCO₃ | Trigonal | Construction, cement, neutraliser | 14 |
| 9 | Gypsum | CaSO₄·2H₂O | Monoclinic | Drywall, plaster, fertiliser | 2 |
| 10 | Talc | Mg₃Si₄O₁₀(OH)₂ | Monoclinic | Talcum powder, ceramics, paper | 1 |
The ten minerals are the reference minerals of the Mohs scale, ranked by their Mohs number (10 = hardest). Mohs numbers are ordinal: they give the order, not how much harder one mineral is than the next. Each mineral has a different Mohs number, so there are no ties. The 'Absolute hardness' column is the sclerometer-based absolute hardness of each reference mineral as tabulated in Mukherjee, Applied Mineralogy (Springer, 2012), via Wikipedia's Mohs scale article; it is shown for context and does not affect the ranking.
No. It lists the ten reference minerals that define the Mohs scale. Other minerals fall between them; for example, emerald is rated about 7.5 to 8 and moissanite about 9 to 9.5.
Diamond, which defines the top of the Mohs scale at 10.
Diamond (10), corundum (9), topaz (8), quartz (7), orthoclase (6), apatite (5), fluorite (4), calcite (3), gypsum (2) and talc (1).
The Mohs scale is ordinal: it shows which mineral scratches which, not by how much. On the absolute hardness scale, corundum (400) is twice as hard as topaz (200) and four times as hard as quartz (100), while diamond (1,500) is nearly four times as hard as corundum.
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