Mohs Hardness Scale Explained

Are you using gemstones in your jewellery designs? Whether you’ve been working with diamonds for decades or you’re just starting to learn the stone setting basics, it’s useful to get to know the gemstones you’re working with, in more detail. That’s where Mohs hardness scale comes in.

It may sound strange but Mohs hardness scale is a great asset to have in your back pocket. Or pinned to your jewellery studio wall for that matter! Read our guide below on Mohs hardness scale and learn how to use it to your advantage.

What is Mohs hardness scale?

Mohs hardness scale is a chart that measures how resistant a gemstone or mineral is to being scratched or damaged when exposed to general wear and tear. The higher the number on the scale, the harder the gemstone is.

Mohs hardness scale

 

Mineral Scale of Hardness Common Object Comparison
Diamond 10 (Hardest)
Corundum 9 Masonry drill bit (8.5)
Topaz 8
Quartz 7
Orthoclase 6 Steel tool(6.5)
Apatite 5
Fluorite 4 Copper coin (3.5)
Calcite 3
Gypsum 2 Fingernail (2.5)
Talc 1 ( Softest)

 

What is Mohs hardness scale used for?

Mohs hardness scale was developed by German geologist, Friedrich Mohs, in the 1800s and is used worldwide to quantify the hardness of a mineral. The scale is not exact but is based on the ability of one substance (whose hardness is known) to scratch and damage another. For example, if a newly discovered mineral is scratched and damaged by Aquamarine (7.5 –  8 hardness) but not damaged by Amethyst (7 hardness) then its hardness on Mohs scale would fall somewhere between 7 and 7.5.

How to use Mohs hardness scale to choose gemstones

When it comes to choosing gemstones for your work, there are a couple of things to consider:

  • Are you making jewellery that is meant for everyday wear such as engagement rings?
  • Are you creating something that your customers are likely to wear less often?

These considerations should point you in the direction of a gemstone with a particular hardness and durability. But there are few other things to keep in mind when choosing gemstones too…

Durable gemstones for everyday wear

If you want to specialise in engagement rings and you’re learning your craft in more detail, you’ll need to get to know gemstones that score highly on Mohs hardness scale, and that also have a sturdy internal structure.

Diamonds are traditionally sought after gemstones for engagement rings because of their value but also because of their hardness. What is the hardness of diamond on the Mohs scale? Diamond scores a 10 on Mohs hardness scale – it’s the hardest known mineral. This makes it an excellent choice for engagement rings that will be worn every day and exposed to general wear and tear.

Having said that, diamonds can still be vulnerable to cracks and fractures, if hit at a certain angle. So, if you’re looking for a gemstone that will be durable enough for an engagement ring design and score well on Mohs hardness scale, you should consider using rubies or sapphires. As part of the Corundum family, they’re hard enough for everyday wear (9 hardness, just behind a diamond) and they’re also incredibly tough with a strong internal structure.

Softer gemstones for occasional wear

When you’re choosing gemstones that are a little less expensive to buy wholesale, and for use with earrings or pendants that are less likely to be worn every day, you have a huge variety to pick from. Just check out the A-Z Mohs hardness scale chart below – it’s incredibly varied!

But before you choose, have a think about whether the stone you would like to work with will be heavily exposed to light, heat, or to chemicals that could have an impact on its look and structure. Certain gemstones, when exposed to light for long periods of time will change in colour. Others may also be prone to cracking if exposed to too much heat. So it’s always a good idea to do your research on a particular gemstone before using it in your designs.

Take emerald for example. It’s a tough gemstone at 7.5 – 8 on Mohs hardness scale. But it’s less durable than a sapphire or ruby because it naturally has a weaker structure with more inclusions, so it’s more prone to breakage. Often, emeralds are treated with oils to improve colour. So, it’s important to avoid cleaning them with chemicals and ultrasonic cleaners that will strip the oils and dampen the colour of the stone too.

Whatever route you decide to take with gemstones, weigh up your options before you commit to a wholesale purchase. Ask yourself whether the jewellery you’re making requires a hard, durable stone, how protected the stone will be by your style of setting, and whether it’s likely that your customer will wear it every day.

Your A-Z Mohs scale of hardness chart for gemstones

We thought it may help for you to have a guide to hand on the hardness of each of the gemstones we supply here at Cooksongold. Use this to help inform which gemstones you use for your latest collections.

 

Gemstone Scale of Hardness
Agate 7
Amber 2 – 2.5
Amethyst 7
Aquamarine 7.5 – 8
Carnelian 7
Citrine 7
Cubic Zirconia (CZ) 8 – 8.5
Diamond 10
Emerald 7.5 – 8
Fire Opal 6 – 6.5
Fluorite 4
Garnet 6.5 – 7.5
Hematite 5.5 – 6.5
Jadeite 6.5 – 7
Labradorite 6 – 6.5
Lapis Lazuli 5 – 5.5
Malachite 3.5 – 4
Moissanite 9.5
Moonstone 6 – 6.5
Mother of Pearl 2.5
Onyx 6.5 – 7
Opal 5.5 – 6.5
Pearl 2.5
Peridot 6.5 – 7
Quartz 7
Rhodochrosite 3.5 – 4
Ruby 9
Sapphire 9
Tigers Eye 6
Topaz 8
Tourmaline 7 – 7.5
Turquoise 5 -6
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