Crystals and the Mohs Scale

Mohs scale is a scale of the scratchability of stones when they are scratched by another substance.

1 is very soft e.g. Talc, and 10 is very hard e.g. Diamond.

It is a good guide to the general toughness of the stone and it’s ability to withstand impact or pressure..and whether you should  have it in a pouch in your pocket or if it’s fine rolling about next to your keys.

Generally, any crystal that has a Mohs rating of 6 or higher can safely be cleaned in water.

Mohs Scale of Mineral Hardness

Hardness Example
10 Diamond.
9 Corundum, Ruby, Sapphire, Star Ruby, Star Sappire, Star Ruby.
8 Beryl, Emerald, Topaz, Rutile Topaz, Imperial Topaz, Mystic Topaz, Chrysoberyl(8.5), Alexandrite(8.5).
7.5 Garnet, Goshenite(7.5), Cats Eye Aquamarine, Morganite, Beryl, Aquamarine, Emerald(7.5).
7 Clear Quartz,Tigers Eye, Amethyst, Citrine, Agate, Rose Quartz, Jasper, Citrine, Agate, Garnet, Mookite, Smoky Quartz, Tourmaline, Danburite(7-7.5), Ametrine, Aventurine, Rutile Quartz, Kunzite.
6 Feldspar, (Spectrolite), Carnelian (6.5), Opalite, Peridot (6.5), Fire Opal, Star Moonstone, Jadite, Star Sunstone, Prehnite, Kyanite(6-7), Moonstone(6.5), Labradorite(6-6.5), Amazonite(6.5), Chrysoprase(6.5), Chalcedony(6.5), Zircon(6.5-7.5), Bloodstone(6.5).
5 Apatite, Apophyllite, Haemetite (5.5-6.5), Obsidian(5.5), Cats Eye Apatite, Star Diopside(5-6), Turquoise(5-6), Lapis Lazuli(5-6), Snowflake Obsidian(5.5), Sodalite(5.5), Opal(5.5), Rhodonite(5.5).
4 Fluorite, Rhodocrosite, Ammolite, Larimar(4.5-5), Charoite(4.5).
3 Calcite, Celestite, Cerussite, Coral(3.5), Azurite(3.5), Malachite(3.5).
2 Gypsum, Chrysocolla (2-4), Amber (2-2.5), Lepidolite(2.5), Pearl(2.5-4.5).
1 Talc.

To give an idea of day to day items a few handy objects that also fit in the Mohs scale are:

  • A fingernail is 2½,
  • a penny  is just under 3,
  • a knife blade is 5½,
  • glass is 5½,
  • a good steel file is 6½.

There are few day to day objects that are more than a 7.


Article by Jem on 10 October 2013

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