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Hardness is a measure of a mineral's resistant to abrasion. This property is easily determined and is used widely for field identification of minerals. More than a century ago. Friedrich Mohs (1773-1839), a German mineralogist, assigned arbitrary relative numbers to ten common minerals in order of their hardness.
Hardness
Mineral
Test
1 Talc Fingernail (2.5)
2 Gypsum
3 Calcite Cooper coin (3)
4 Flourite Knife blade (5.5)
5 Apatite
Glass plate (5.5+)
6 K-feldspar
7 Quartz Streak plate (7)
8 Topaz
9 Corundum
10 Diamond
A simpler version of the Mho's scale can be established using three types of hardness:
SOFT - Minerals that can be scratched with a fingernail
INTERMEDIATE - Minerals that cannot be scratched with a fingernail but can be scratched with a steel nail.
HARD - Minerals that cannot be scratched with a steel nail.
Mineral
Hardness
Calcite
INTERMEDIATE
Mineral cannot be scratched with a fingernail but can be scratched with a steel nail.
Gypsum
SOFT
Mineral can be scratched with a fingernail
Pink Feldspar
HARD
Mineral cannot be scratched with a steel nail.
White Feldspar
HARD
Mineral cannot be scratched with a steel nail.
Gray Feldspar
HARD
Mineral cannot be scratched with a steel nail.
Quartz
HARD
Mineral cannot be scratched with a steel nail.