Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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Mohs' scale

A scale used to determine the hardness of solids, especially minerals. It is named after the German mineralogist Friedrich Mohs. The scale reads as given below:
Hardness    Material
1           Talc—easily scratched by the fingernail
2           Gypsum—just scratched by the fingernail
3           Calcite—scratches and is scratched by a copper coin
4           Fluorite—not scratched by a copper coin and does not scratch glass
5           Apatite—just scratches glass and is easily scratched by a knife
6           Orthoclase— easily scratches glass and is just scratched by a file
7           Quartz—not scratched by a file
8           Topaz
9           Corundum
10          Diamond
The scale has been extended as follows:
Hardness    Material
1           Liquid
2-6         As indicated above on the chart
7           Vitreous pure silica
8           Quartz
9           Topaz
10          Garnet
11          Fuzed zirconia
12          Fuzed alumina
13          Silicon carbide
14          Boron carbide
15          Diamond

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