How do you compare the hardness of a gemstone?

How do you compare the hardness of a gemstone?

When we help clients select their jewellery, they often ask how hard the gemstones are.

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.

 

If you'd like to know more, or would like us to help you with an enquiry, do make contact.

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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.