Moh’s Scale of Hardness
MINERALS IN MOHS SCALE OF HARDNESS with DIAMOND
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This is a scale used by the Gemologist or Lapidary to determine the degree of hardness of a gemstone or mineral. It has been formulated by giving talc, the softest stone, a value of 1 and the hardest stone, diamond, a value of 10. See table below for more information.
Moh's Hardness Scale
Moh's Hardness Scale
- Calcite, Amber
- Fluorite , Jet
- Apatite, Turquoise, Glass
- Feldspar, Moonstone, Sodalite, Jade
- Quartz , ie Amethyst, Agates, Garnet
- Topaz, Spinel
- Corundum ie Ruby, Sapphire
With regards to Rock Tumbling, there are two important things to understand about the hardness of stones.
1) It is important that you only polish stones of the same level of hardness together in one batch. This is because having a mixture of hardnesses of stones will cause the softer stones to reduce in size very quickly and the harder ones not to polish so well.
2) Stones of between 6 and 8 on the Moh’s hardness scale will polish the best in a Rock Tumbler. Luckily many of the most attractive stones in our gardens and on the beach are from the quartz / agate family which are hardness 7 on the Moh scale so will polish very well. See this page for more details
How to identify the hardness of your stones
Your finger nail has a hardness 2.5 this will scratch gypsum and talc. A copper coin is graded as 4 on the Moh’s hardness scale and will scratch calcite and softer stones and a steel pen knife file at 6.5 will scratch feldspar but not quartz. So it is a good idea to carry a pen knife with you when you are hunting for stones and reject any stones which can be scratched by the knife
You can also carry a Quartz Crystal and use this as a guide to testing the hardness of your stones. If the quartz crystal can scratch the surface of the stone, then the stone is below a hardness of 7 on Moh’s scale and is not suitable for polishing with other quartz based pebbles.
Check that you can identify the difference between a metallic mark left on your stones as opposed to a real scratch into the surface.
Categories: Semi Precious Stones Information