What Is the Mohs Scale? Gemstone Hardness Explained

Ask a gemmologist whether a stone suits an everyday ring and they will reach for one number first: its Mohs hardness. The Mohs scale is a two-century-old ranking of scratch resistance, and once you understand it, a great deal of buying advice suddenly makes sense. Here is what the scale is, and how to use it.

What the scale measures

The Mohs scale, pronounced moze, rates how well a mineral resists scratching: whether a sharp point or a harder material can mark its surface. In the early 1800s the German mineralogist Friedrich Mohs chose ten reference minerals and ordered them so that each can scratch the ones below it. The system still runs from 1, talc, to 10, diamond, the hardest natural substance known.

The ten reference points

| Mohs | Reference mineral | | --- | --- | | 10 | Diamond | | 9 | Corundum (sapphire, ruby) | | 8 | Topaz | | 7 | Quartz | | 6 | Feldspar | | 5 | Apatite | | 4 | Fluorite | | 3 | Calcite | | 2 | Gypsum | | 1 | Talc |

Familiar gems slot in around these: ruby and sapphire at 9, alexandrite at 8.5, emerald and aquamarine around 7.5 to 8, quartz at 7, moonstone at 6 to 6.5, turquoise at 5 to 6, pearls softer still.

The numbers are not evenly spaced

This is the part most people miss. The scale is ordinal, not linear: each step simply means harder than, not harder by the same amount. Diamond sits only one number above corundum, yet it is many times harder in absolute terms. So treat the numbers as a ranking, not a ruler.

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Hardness is not toughness

Scratch resistance is only one kind of durability. Toughness, the ability to survive a knock without chipping or cracking, is a separate property, and some hard gems are brittle. Emeralds often carry inclusions that weaken them; topaz cleaves cleanly under a sharp blow; a diamond can chip on its girdle. Stability against heat, light and chemicals is a third axis entirely. A jewel's real-world durability is all three together.

Where it came from

Mohs published his system in the early nineteenth century as a field tool: with no instruments, a geologist could carry the ten reference minerals and rank an unknown stone simply by seeing which one scratched which. Two hundred years on, the same idea still anchors gemmology courses, museum labels and buying guides, because a scratch test needs nothing but the stones themselves.

Using it when you buy

For a ring worn daily, such as an engagement ring, aim for 7 or above; quartz-level hardness resists the abrasion of everyday dust, which itself contains quartz. Earrings and pendants live a gentler life, so softer treasures like moonstone, opal and pearl are perfectly at home there. Whatever the stone, store pieces separately so harder gems cannot scratch softer ones.

There is a household angle too. Everyday dust contains quartz particles, which is why softer stones slowly lose their polish with years of wear even when they are never dropped. A gentle wipe with a soft cloth before storage removes the grit that would otherwise sit against the gem.

Built for real life with Shewah

Shewah works in solid gold and certified lab-grown diamonds, a 10 on the Mohs scale and the most durable centre stone there is, made to order in Surat and shipped to the US, UK and Australia. Explore Shewah's jewellery or message us on WhatsApp at +91 96622 66360.

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Sources

• Mohs Scale - Gem and Mineral Hardness - GIA
• The Mohs Hardness Scale and Chart for Select Gems - International Gem Society