If you have spent any time researching engagement rings, diamonds, or gemstones, you will almost certainly have come across the Mohs Scale. It gets mentioned a lot and not always with much explanation.
Here is everything you actually need to know about it, what it means for your ring, and why it matters when you are choosing a stone that is going to be worn every day for the rest of your life.
What Is the Mohs Scale?
The Mohs Scale was developed in 1812 by Friedrich Mohs, a German geologist, as a way of measuring and comparing the hardness of minerals. Specifically, it measures how resistant a mineral is to being scratched by another mineral.
The scale runs from 1 to 10. At the bottom sits Talc - so soft that almost anything will scratch it. At the very top sits Diamond - the hardest naturally occurring substance on earth, which can only be scratched by another diamond.
One important thing to understand is that the scale is not linear. Each number does not represent a fixed, equal increment in hardness. Diamond at 10 is not just twice as hard as Corundum at 9 - it is approximately four times harder. The numbers simply tell you which mineral scratches which, not by how much.
A mineral rated 7 on the Mohs scale will scratch anything rated 6 or below. It will be scratched by anything rated 8 or above. That is the essential logic of the whole system.
The Full Scale
|
Mineral |
Mohs Score |
What It Means |
|
Talc |
1 |
The softest mineral — scratched by a fingernail |
|
Gypsum |
2 |
Scratched by a fingernail with effort |
|
Calcite |
3 |
Scratched by a copper coin |
|
Fluorite |
4 |
Scratched by a steel knife |
|
Apatite |
5 |
Scratched by a steel knife with effort |
|
Feldspar |
6 |
Scratched by a steel file |
|
Quartz |
7 |
Scratches glass and most steels |
|
Topaz |
8 |
Scratches quartz and all below |
|
Corundum (Ruby/Sapphire) |
9 |
Scratches everything below — extremely hard |
|
Diamond |
10 |
The hardest natural substance — only scratched by another diamond |
What Does This Mean for Your Engagement Ring?
For a ring you are going to wear every single day - through washing up, gym sessions, gardening, typing, cooking - hardness matters a great deal. Daily life is full of surfaces and materials that can scratch a softer stone.
As a general rule, any stone used in an engagement ring should ideally sit at 7.5 or above on the Mohs scale. Below that and you risk visible scratching over time, particularly from contact with dust and grit - which contains quartz particles that rate at 7.
This is why diamonds and sapphires are so frequently used in engagement rings. They sit at the top of the hardness scale and genuinely stand up to the demands of everyday wear in a way that softer stones simply cannot.
How Do Our Stones Rate?
Diamond - 10
The hardest substance in the world, natural or lab grown. Lab grown diamonds have exactly the same chemical structure as mined diamonds - pure crystallised carbon - which means they share identical hardness. A lab grown diamond from Ethica will not scratch any differently to a mined diamond costing three times as much.
Ruby and Sapphire - 9
Both ruby and sapphire are forms of corundum and sit at 9 on the Mohs scale. This makes them the second hardest gemstone available for jewellery and a genuinely excellent choice for an engagement ring that will be worn daily. Our lab grown sapphires - available in blue, pink, yellow, and padparadscha tones - offer the same hardness as natural sapphires at a fraction of the cost and with full traceability.
Alexandrite - 8.5
A rare and beautiful colour-changing stone that shifts from green in daylight to red in artificial light. At 8.5 on the Mohs scale it is very well suited to daily wear.
Emerald - 7.5 to 8
Emeralds sit at 7.5 to 8 on the Mohs scale which places them solidly in the suitable for rings category, with one caveat. Natural emeralds almost always contain internal fractures, called inclusions, which can make them more susceptible to chipping with impact. Lab grown emeralds have fewer of these inclusions, making them both more durable and more vivid in colour.
Aquamarine and Morganite - 7.5 to 8
Both are forms of beryl and sit at 7.5 to 8 on the Mohs scale. Perfectly suitable for rings but worth being mindful of impact given their typically lighter colours can show chips more visibly than darker stones.
Amethyst and Quartz - 7
At 7 on the Mohs scale, amethyst and quartz are at the lower boundary of what we would recommend for everyday ring wear. They will resist most scratches from daily life but are more vulnerable than stones higher on the scale. They are lovely in earrings, pendants, and occasional-wear pieces - but for an engagement ring worn daily, we would guide you towards something rated 8 and above.
Hardness vs Toughness - an Important Distinction
One thing the Mohs scale does not measure is toughness - a stone's resistance to breaking or chipping under impact. These are different properties.
Diamond is the hardest substance on earth but it is not unbreakable. A sharp impact at the right angle can chip a diamond because diamond has what is called cleavage - directional planes along which it splits more easily. This does not mean you need to treat your diamond ring with excessive caution in daily life. It does mean you should avoid things like dropping it on hard surfaces or knocking it against stone or metal with force.
Moissanite has no cleavage planes, which means it is actually somewhat tougher than diamond even though it sits fractionally lower on the hardness scale.
Hardness tells you how resistant a stone is to scratching. Toughness tells you how resistant it is to breaking. A great everyday ring stone needs to be high in both - which is why diamonds, moissanite, and sapphires are consistently the best choices.
Our Recommendation
For an engagement ring that is going to be worn every day, for years and decades, we always recommend choosing a stone rated 8 or above on the Mohs scale. This gives you the confidence that the stone will look as beautiful in ten years as it does on the day you receive it.
Our collection is built around exactly this principle. Every stone we offer - lab grown diamonds, lab grown sapphires, lab grown rubies, and lab grown emeralds - is selected for its suitability for daily wear as well as its beauty.
If you have any questions about which stone might be right for you, we would love to help. That is exactly what our free consultations are for.
Book a free consultation with Ethica Diamonds →
In person at our Newquay studio or virtually from anywhere in the UK.
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