What is the Mohs hardness scale?

The Mohs scale, created by Friedrich Mohs in 1812, ranks minerals 1 to 10 by scratch resistance. A mineral can scratch any with a lower or equal number and is scratched by any higher. It is ordinal, not linear, so the gaps between numbers are not equal.

Is the Mohs scale linear?

No. It is a relative ranking, not a measurement of absolute hardness. Diamond at 10 is far more than ten times harder than talc at 1 — its absolute (Vickers) hardness is roughly 1500 times greater. The jump from corundum (9) to diamond (10) is the largest on the scale.

How do I test hardness without lab equipment?

Use common objects of known hardness as references. A fingernail is about 2.5, a copper coin about 3.5, a steel knife or nail about 5.5, and glass about 5.5 to 6. If your fingernail scratches the mineral it is below 2.5; if a knife does not, the mineral is above 5.5.

Which gemstones are hardest?

Diamond tops the scale at 10, followed by corundum (ruby and sapphire) at 9, and topaz at 8. Hardness matters for jewellery durability — softer stones like opal (about 5.5 to 6.5) and pearl scratch easily and need gentler care.

What is the difference between Mohs and Vickers hardness?

Mohs is an ordinal scratch scale from 1 to 10, while Vickers is an absolute measurement of indentation hardness in kgf/mm². The approximate Vickers figures in this table show how non-linear Mohs really is — each step up represents a steeply increasing absolute hardness.

Mohs Hardness Scale Reference

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The Mohs scale ranks minerals from 1 (talc, the softest) to 10 (diamond, the hardest) by their resistance to scratching. This reference gives the defining mineral at each of the ten levels, the approximate absolute (Vickers) hardness, and everyday objects you can use to test an unknown sample in the field.

How it works

The Mohs scale is ordinal: a higher-numbered mineral scratches any lower-numbered one, but the steps are not equal in absolute terms. The rule for comparing two materials is simply:

if A_mohs >  B_mohs  → A scratches B
if A_mohs == B_mohs  → they may just barely scratch each other
if A_mohs <  B_mohs  → B scratches A

The approximate Vickers column shows how non-linear the scale is — the gap from corundum (9) to diamond (10) dwarfs every other step.

Field test objects

You can bracket an unknown mineral’s hardness with common items:

Fingernail — about 2.5
Copper coin — about 3.5
Steel knife / nail — about 5.5
Glass plate — about 5.5 to 6
Steel file — about 6.5

If your fingernail scratches it, it is softer than 2.5. If a steel knife will not scratch it but glass will not scratch the knife, you have narrowed it to around 5.5 to 6.