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MOHS HARDNESS SCALE
| OLD | NEW | MATERIAL | ABSOLUTE HARDNESS |
| 1 | 1 | talc | 1 |
| 2 | 2 | gypsum | 3 |
| 3 | 3 | calcite | 9 |
| 3.5 | copper penny | ||
| 4 | 4 | florspar (florite) | 21 |
| 5 | 5 | apatite | 48 |
| 5.5 | glass, knife steel | ||
| 6 | 6 | orthoclase, file steel | 72 |
| 6.5 | novaculite (silicon dioxide) red rouge (ferric oxide) |
||
| 7 | vitreous pure silica | ||
| 7 | 8 | quartz | 100 |
| 8 | 9 | topaz | 200 |
| 10 | garnet | ||
| 8.5 | green chromium oxide | ||
| 11 | fused zirconium oxide | ||
| 9 | sapphire or corundum | 400 | |
| 9.2 | 12 | fused alumina | |
| 9.3 | boron | ||
| 9.4-5 | 13 | silicon carbide | |
| 9.5-6 | 14 | boron carbide | |
| 9.7 | stishovite (rare form of silicon dioxide) Norbide (special form of silicon nitride) |
||
| 9.8-9 | cubic boron nitride | ||
| 10 | 15 | diamond | 1500 |
Below is an interesting artifact, sent to me by Dr. Charles J. Di Como of Riverdale, New York.
It is an image of part of a letter from Fredrick Mohs to CE Wilbour in 1852.
