Crystals and the Mohs Scale

Jimble Stevens

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, Alexandrite.
7.5 Garnet, Goshenite, Cats Eye Aquamarine, Morganite, Beryl, Aquamarine, Emerald.
7 Clear Quartz,Tigers Eye, Amethyst, Citrine, Agate, Rose Quartz, Jasper, Citrine, Agate, Garnet, Mookite, Smoky Quartz, Tourmaline, Danburite, Ametrine, Aventurine, Rutile Quartz, Kunzite.
Moonstone, Labradorite, Spectrolite, Carnelian, Opalite, Peridot, Fire Opal, Star Moonstone, Jadite, Star Sunstone, Prehnite, Kyanite, Amazonite, Chrysoprase, Chalcedony, Zircon, Bloodstone.
5 Apatite, Apophyllite, Haematite, Obsidian, Cats Eye Apatite, Star Diopside, Turquoise, Lapis Lazuli, Snowflake Obsidian, Sodalite, Opal, Rhodonite.
4 Fluorite, Rhodocrosite, Ammolite, Larimar, Charoite.
3 Calcite, Celestite, Cerussite, Coral, Azurite, Malachite.
2 Selenite (Gypsum), Chrysocolla, Amber, Lepidolite, Pearl.
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 hardly any day to day objects that are more than a 7.