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This scale ranks your stone's hardness in relation to other stones. It will help you determine how to take care of your crystals and gemstone jewelry.
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Mohs Scale of Hardness is something we use often when discussing crystals. It tells you how easily your crystal will get scratched by other stones and materials.
Mohs Scale of Hardness is defined by how hard a stone is to scratch. However, it does not take into consideration a stone's durability, brittleness, and cleavage. It is not an end-all-be-all for determining the strength of your crystal. It measures only scratchability.
Austrian mineralogist Friedrich Mohs created the Mohs Scale of Hardness in 1812. It has been the most popular scale used in mainstream mineralogy today.
Friedrich Mohs ranked ten crystals in order of hardness. Here is an example in each level of mineral ranking:
10 - Diamond
9 - Corundum (Ruby, Sapphire)
8 - Topaz
7 - Quartz
6 - Feldspar (Moonstone, Labradorite, Amazonite, etc)
5 - Apatite
4 - Fluorite
3 - Calcite
2 - Gypsum
1 - Talc
The hardest stone on the Mohs Scale is a Diamond at a 10. This means no other stones can scratch a Diamond. The softest is Talc, a powdery stone, at a 1. It will be scratched by every other stone that is harder than a 1.
In simple terms, all materials that are higher on the scale will scratch your stone. All materials that are lower on the scale will not scratch your stone. All materials with the same hardness will not scratch each other or may have tiny scratches.
Keep in mind that the ranking is relative and not linear. That means that the ten stone examples on the scale are not evenly distributed in how hard they are. Diamond (10) is four times as hard as Corundum (9) which is only twice as hard as Topaz (8).
Here are examples of household items you could use to test the hardness of your rocks and minerals.
8.5 - Masonry Drill Bit
8 - Hardened Steel
6.5 - Steel (Nail)
5.5 - Glass, Knife
4.5 - Platinum, Iron
3 - Copper (newer pennies are made of Zinc)
2.5 - Fingernail
For more reliable testing, buy a Mohs Scale of Hardness test kit with hardness picks. These brass alloys are pointed at the tips and drag across your crystals like pencils. They have accurate hardness numbers and can be resharpened when dull.
When testing your crystals with the Mohs Scale of Hardness, make sure you have a sturdy surface. You may want to cover your surface so you don't scratch it instead!
Hold your stone firmly in one hand and create a slow and deliberate scratch over the other stone. Be careful not to let the stones slip and cause injury to your fingers.
Check for scratches in the stone. If there is powder residue, blow or wipe the streaks away. You may want to use a magnifying glass and feel the stone with your finger for actual scratches.
The basic Mohs Scale of Hardness includes 10 minerals as a simple reference guide that has been used popularly for hundreds of years.
Here is a list of additional crystals and their hardness ranking:
9 Corundum (Ruby, Sapphire)
7.5-8 Aqumarine, Beryl
7-7.5 Spessartine Garnet, Staurolite, Tourmaline
7 Agate, Carnelian, Granite, Quartz (Amethyst, Aventurine, Citrine, Rose Quartz, Smoky Quartz)
6.5-7 Jadeite, Jasper, Kunzite, Onyx, Peridot, Tigers Eye
6-7 Bloodstone, Epidote, Tanzanite, Unakite, Zoisite
6-6.5 Chalcedony, Nephrite Jade, Prehnite, Pyrite, Sugilite
6 Feldspar (Moonstone, Labradorite, Amazonite, Sunstone)
5.5-6.5 Diopside, Rhodonite
5.5 Bronzite, Moldavite
5-6.5 Hematite, Magnetite, Opal
5-6 Arfvedsonite, Lapis, Turquoise
5-5.5 Obsidian, Scolecite
5 Apatite, Dioptase
4 Ammonite, Fluorite
3.5-4 Aragonite, Azurite, Chalcopyrite, Cuprite, Dolomite, Malachite, Rhodochrosite, Shungite
3-3.5 Angelite, Bornite, Celestite, Cerrusite, Howlite
2.5-3 Chalcocite, Copper, Galena, Gold, Lepidolite, Silver
2-2.5 Amber, Halite, Ulexite
2 Gypsum, Stibnite
Sometimes you may find your stone scratching a stone that is supposed to be ranked harder on the Mohs Scale of Hardness. There may be a couple of explanations:
1. You may actually be seeing powder remnants from your stone on the harder stone. It may look like a scratch, but in actuality, it streaked from the softer stone.
2. Your stone may have a wide range of hardness. For example, Kyanite can range from 4 to 7.5 depending on how the piece was formed when it crystallized. This could vary your results widely.
3. The harder stone may be more brittle than yours, making it crumble if you put pressure on it. So it's not actually a surface scratch but an internal crack you are seeing.
Mohs Scale of hardness strictly refers to the scratchability of your stone. It does not indicate how brittle it is. Scratching happens on the surface of your stone whereas breakability depends on the structure of your whole stone.
For example, Diamond is the hardest stone on the Mohs Scale of Hardness, but it is also very brittle, making it shatter into tiny pieces when you hit it with a hammer. Jadeite Jade is a 6.5-7 on the Mohs Scale of hardness, but it is very tough, making it ring like a bell when you hit it with a hammer.
Diamond is the hardest stone on the Mohs Scale of Hardness but it is not the hardest stone in the world. There are other stones that are rarer to find, which is why they were not included in the original scale.
Now that you know about the hardness of crystals, shop with confidence. Experiment with raw stones, choose your favorites right here:
If you have any questions about the Mohs Scale of Hardness or crystals, feel free to post them below. We would also love to hear any stories you may have when using this scale with your crystals.
Here are additional resources for you to check out: