MOHS HARDNESS SCALE
HARDNESS
REPRESENTATIVE MINERAL
10
 Diamond, C
9
 Corundum (Ruby, Sapphire), Al2O3
8
 Topaz, Al2SiO4(OH,F)2
7
 Quartz, SiO2
6
 Feldspar, e.g., KAlSi3O8
5
 Apatite, Ca5(PO4)3(OH,F)
4
 Fluorite, CaF2
3
 Calcite, CaCO3
2
 Gypsum, CaSO4-2H2O
1
 Talc, Mg3Si4O10(OH)2
 
HARDNESS
 FAMILIAR OBJECT
5.5
 Glass plate, knife blade
3
 Copper penny
2.5
 Fingernail

You will be using a glass plate (H=5.5) most of the time.  There are two ways to apply the test:

  1. Try to scratch a fresh surface of the mineral with a corner of the glass plate.  If the glass plate scratches the mineral, the glass plate is harder than the mineral.  Hence, the hardness of the mineral is less than 5.5 (H<5.5).
  2. Try to scratch the surface of the glass plate with a fresh corner of the mineral.  If the glass plate is not marked by the mineral, then the hardness of the mineral is less than 5.5 (H<5.5).
Sometimes it is important to do the test both ways, especially if the mineral has hardness that is the same as the hardness of the glass plate (5.5).  In this case, the mineral and the glass plate will scratch each other but only a little.

You can use a copper penny and your fingernail in the same way to determine the hardness of a mineral relative to H=3 and H=2.5 respectively.

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