MINERALS

Hardness

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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.

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©Guillermo Rocha/Brooklyn College