Scratch hardness

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Scratch hardness tests are used to determine the hardness of a material to scratches and abrasion. The earliest test was developed by mineralogist Friedrich Mohs in 1820 (see Mohs scale). It is based on relative scratch hardness, with talc assigned a value of 1 and diamond assigned a value of 10. Mohs' scale had two limitations; it was not linear, and most modern abrasives fall between 9 and 10.

Ridgeway[1] modified the Moh's scale by giving garnet a hardness of 10 and diamond a hardness of 15. Woodell[2] extended the scale further by using resistance to abrasion, where diamond equals 42.5. Resistance to abrasion is less affected by surface variations than other methods of indentations.

There is a linear relationship between cohesive energy density (lattice energy per volume) and Woodwell wear resistance, occurring between corundum (H=9) and diamond (H=42.5).[3]

Material Mohs' scale Ridgeway's scale Woodell's scale
talc 1
gypsum 2
calcite 3
fluorite 4
apatite 5
orthoclase 6 6
vitreous silica 7
quartz 7 8 7
topaz 8 9
garnet 10
corundum 9 9
fused ZrO2 11
fused ZrO2/Al2O3
fused Al2O3 12
SiC 13 14
boron carbide 14
cubic boron nitride
diamond 10 15 42.5


  1. ^ Ridgeway, R. R; Ballard, A. H. and Bailey, B. L. (1933). "A revised Mohs hardness scale". Trans Electrochem Soc 63: 369. 
  2. ^ Woodell, C.E (1935). "Method of Comparing the Hardness of Electric Furnace Products and Natural Abrasives". Trans. Electrochem. Soc. 68: 111–130. doi:10.1149/1.3493860. 
  3. ^ Plendl, J.N. (1962). "Hardness of Nonmetallic Solids on an Atomic Basis". Phys. Rev. 125 (3): 828–832. doi:10.1103/PhysRev.125.828.