How do you compare the hardness of a gemstone?

How do you compare the hardness of a gemstone?

Relative to each other some gemstones are harder or softer. In order to measure this, the Moh’s scale is used. The scale is from 1-10, 10 being hardest, e.g. a diamond and 1 being softest, e.g. talc. Scratching the surface with a stone of a known hardness, a scelerometer, carries out testing a stone. This is of course damaging.The scale was invented by the German scientist Mohs in 1812 and is as follows: 

Hardness

Mineral

Absolute Hardness

1

Talc(Mg3Si4O10(OH)2)

1

2

Gypsum (CaSO4·2H2O)

2

3

Calcite (CaCO3)

9

4

Fluorite (CaF2)

21

5

Apatite(Ca5(PO4)3(OH-,Cl-,F-))

48

6

Orthoclase Feldspar (KAlSi3O8)

72

7

Quartz (SiO2)

100

8

Topaz (Al2SiO4(OH-,F-)2)

200

9

Corundum (Al2O3)

400

10

Diamond (C)

1500

 

On the scale, fingernail has hardness 2.5; copper penny, about 3.5; a knife blade, 5.5; window glass, 6.5; steel file, 6.5. Using these ordinary materials of known hardness can help approximate the position of a mineral on the scale.

 

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Article by Adam J

Adam J

Adam's been working at Jacobs since 2003, has a professional jewellers diploma and looks after the business as whole.