Mohs' scale of mineral hardness was created by the German mineralogist Friedrich Mohs to measure hardness. He based it on ten readily available minerals. As it is an ordinal scale, you have to compare two minerals to decide which is harder. The scale is neither linear nor logarithmic: for example, corundum is twice as hard as topaz, but diamond is almost four times as hard as corundum.
The absolute hardness of minerals is measured with a sclerometer. One of the measures of hardness, given in the table, is the Vickers number (HV). It is based on the area of the indentation after applying a standard load.
| Hardness | Mineral | Absolute Hardness |
|---|---|---|
| 1 | Talc (Mg3Si4O10(OH)2) | 1 |
| 2 | Gypsum (CaSO4·2H2O) | 3 |
| 3 | Calcite (CaCO3) | 9 |
| 4 | Fluorite (CaF2) | 21 |
| 5 | Apatite (Ca5(PO4)3(OH-,Cl-,F-)) | 48 |
| 6 | Orthoclase (KAlSi3O8) | 72 |
| 7 | Quartz (SiO2) | 100 |
| 8 | Topaz (Al2SiO4(OH-,F-)2) | 200 |
| 9 | Corundum (Al2O3) | 400 |
| 10 | Diamond (C) | 1500 |
The mnemonic traditionally taught to geology students to remember this table is "The Girls Can Flirt And Other Queer Things Can Do." The table has been modified to incorporate additional substances that may fall in between two levels.
| Hardness | Mineral |
|---|---|
| 1 | Liquid |
| 2 | Gypsum |
| 3 | Calcite |
| 4 | Fluorite |
| 5 | Apatite |
| 6 | Orthoclase |
| 7 | Vitreous pure silica |
| 8 | Quartz |
| 9 | Topaz |
| 10 | Garnet |
| 11 | Fused zirconia |
| 12 | Fused alumina |
| 13 | Silicon carbide |
| 14 | Boron carbide |
| 15 | Diamond |