The Mohs Hardness Scale, Gemstones & Jewellery

A group of uncut and unpolished gemstones

What is the Mohs Hardness Scale and why is it important for your jewellery?

The Mohs Scale of Hardness was a system devised by German chemist Fredrich Mohs, in 1812, to test the relative hardness of minerals. The Scale consists of a list of ten minerals which are arranged in order of hardness compared to each other and runs from Talc being very soft at number 1, to Diamond which is the hardest mineral at number 10.

The ten minerals, in order, on Mohs Hardness Scale are:

  1. 1. Talc
  2. 2. Gypsum
  3. 3. Calcite
  4. 4. Flourite
  5. 5. Apatite
  6. 6. Orthoclase
  7. 7. Quartz
  8. 8. Topaz
  9. 9. Corundum
  10. 10. Diamond

How the Mohs Scale is Used

To use the scale a mineral is compared to the minerals on the scale by scratching it with the mineral. If the mineral being tested is harder than the mineral it is being compared to, it will leave a scratch on the surface of the other mineral.

The relative hardness of a mineral is determined by the highest number mineral on the scale that it can scratch. For example, if a mineral can scratch a piece of quartz (which has a hardness of 7 on the scale) but not a piece of topaz (which has a hardness of 8 on the scale), its hardness would be assigned a value of 7 on the scale.

The Mohs hardness scale is widely used in mineralogy and materials science as a simple and convenient way to determine the relative hardness of a mineral. The Scale is in widespread use all over the world, even today – you will notice that in every article we write on gemstones we will tell you its hardness according to the Mohs Hardness Scale.

The scale has helped jewellery makers and designers in the past to know what minerals were suitable for different projects, for instance how a gemstone can be shaped and cut.

It is also a very useful thing to know when it comes to your gemstone jewellery as it helps you to know how to store, even how to wear your jewellery pieces.

Why is the Mohs Scale Helpful?

It is extremely useful to know how hard a mineral is. From this we know, without having to experience the damaging results, that a diamond stored loosely next to a pearl could possibly scratch it and damage it. 

A diamond is so strong that the only thing that will cut a diamond is another diamond. For this reason, diamonds are often used to cut glass or engrave on glass.

We have compiled a table below of some Precious and Semi-Precious Stones and Their Hardness (with links to relevant articles on each gemstone).

Gemstones & Mohs Hardness Score

Gemstone (Alphabetically Arranged)Mohs Hardness Scale ScoreGemstone (In Order of Hardness)Mohs Hardness Score
Agate7Amber2 – 2 ½
Alexandrite8 ½Copper2 ½
Amber2 – 2 ½Gold2 ½
Amethyst7Mother of Pearl2 ½
Aventurine7Silver2 ½
Aquamarine7 ½ – 8Copper2 ½ – 3
Calcite3Jet2 ½ – 4
Carnelian7 ½ – 8Pearl2 ½ – 4 ½
Chalcedony6 ½ – 7Calcite3
Citrine7Coral3
Copper2 ½ – 3Malachite3 ½ – 4
Coral3 – 4Steel4 – 4 ½
Corundum9Flourite4
Cubic Zirconia (CZ)9Turquoise4 – 6
Diamond10Lapis Lazuli5 – 6
Emerald7 ½ – 8Opal5 – 6 ½
Fire Opal6 – 6 ½Hematite5 ½ – 6 ½
Flourite4Fire Opal5 ½ – 6 ½
Garnet6 ½ – 7 ½Chelcedony6 ½ – 7
Gold2 ½Onyx6 ½ – 7
Hematite5 ½ – 6 ½Peridot6 ½ – 7
Jadeite6 ½ – 7 ½Agate7
Jet2 ½ – 4Amethyst7
Labadorite6 ½ -7 ½Aventurine7
Quartz7Citrine7
Lapis Lazuli7 or 5 – 5 ½Quartz7
Malachite3 ½ – 4Rock Crystal7
Moissonite9 ½Tigers Eye7
Moonstone6 ½ – 7 ½Garnet6 ½ – 7 ½
Mother of Pearl2 ½Jadeite6 ½ – 7 ½
Rock Crystal7Labradorite6 ½ – 7 ½
Ruby9Moonstone6 ½ – 7 ½
Sapphire9Zircon6 ½ – 7 ½
Onyx6 ½ – 7Aquamarine7 ½ – 8
Opal6 – 7 or 5 ½ – 6 ½Carnelian7 ½ – 8
Pearl2 ½ – 4 ½Emerald7 ½ – 8
Peridot6 ½ – 7Tourmaline7 ½ – 8
Silver2 ½Spinel8
Spinel8Topaz8
Steel4 – 4 ½Alexandrite8 ½
Talc1Corundum9
Tigers Eye7Cubic Zirconia (CZ)9
Titanium Carbide9 – 9 ½Ruby9
Topaz8Sapphire9
Tourmaline7 ½ – 8Tungsten Carbide9
Tungsten Carbide9Titanium Carbide9 – 9 ½
Turquoise5 – 6Moissonite9 ½
Zircon6 ½ – 7 ½Diamond10
Gemstones and their Mohs Hardness Score ©Carathea

The Mohs Scale Used on Everyday Materials

For most people it will help to reference the actual hardness of the gemstones they love and know so well by comparing them to everyday objects.

Material Scale of Hardness
Finger Nail2 ½
Copper Penny2 ½
Tooth5
Pocket Knife Blade5.1
Steel Blade6 ½
Porcelain7 ½
Sandpaper (covered in corundum)9

To Sum Up …

We hope this has explained what the Mohs Hardness Scale is and allows you to relate to it more when we talk about the hardness of different precious and semi-precious stones in our articles. We hope we’ve also highlighted what a valuable contribution this brilliant little Scale was to science, created way back in 1812 by Friedrich Mohs.

Sources

https://gizmodo.com/the-mohs-scale-covers-everything-from-diamonds-to-doubl-1688506986

https://www.gemsociety.org/article/select-gems-ordered-mohs-hardness/

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