Mohs Hardness
Also: Mohs scale, Scratch hardness, Mineral hardness
A unitless rating from 1 to 10 that captures how well a mineral withstands being scratched by something harder than itself.
Introduced in 1812 by the German mineralogist Friedrich Mohs, the Mohs hardness — also called the Mohs scale or scratch hardness — is still the go-to qualitative gauge of how resistant minerals and metals are to being scratched. Its logic could hardly be simpler: whichever material has the higher Mohs value can scratch the one below it, but not the reverse. That single property makes the scale a handy shorthand both in coin authenticity testing and across materials science.
Reading the scale
Running from 1 for talc, the softest mineral, up to 10 for diamond, the hardest natural substance, the scale is deliberately ordinal. Crucially it is not linear: the gaps between neighbouring steps are uneven, so you cannot interpolate between them arithmetically.
| Step | Reference mineral | Everyday comparison |
|---|---|---|
| 1 | Talc | Crumbles under a fingernail |
| 2 | Gypsum | Scratchable with a fingernail |
| 3 | Calcite | Scratchable with a copper coin |
| 4 | Fluorite | Scratchable with a knife (easily) |
| 5 | Apatite | Scratchable with a knife (with effort) |
| 6 | Feldspar | Scratchable with a steel file |
| 7 | Quartz | Scratches glass |
| 8 | Topaz | Scratches quartz |
| 9 | Corundum (sapphire/ruby) | Scratches topaz |
| 10 | Diamond | Scratches everything |
Where the precious metals sit
Ranging from 2.5 to 4.75 on the scale, precious metals count as fairly soft — a fact that accounts both for their signature malleability (ductility) and for how readily they mark:
| Metal | Mohs hardness (approx.) |
|---|---|
| Gold (999) | 2.5 |
| Silver (999) | 2.5–3.0 |
| Platinum | 3.5–4.5 |
| Palladium | 4.75 |
| Tungsten | 7.5 |
That softness in fine gold and fine silver is exactly why coins and jewellery blend them with copper or other metals: an alloy lifts the hardness appreciably while leaving the essential precious-metal character largely intact.
What it means for authenticity
Scratch hardness helps, but on its own it will not settle authenticity. Consider tungsten at Mohs 7.5 — far harder than gold, yet it turns up as the core of faked bars precisely because its density of 19.25 g/cm³ almost matches gold's 19.32 g/cm³. So a tungsten forgery will slip past a hardness check and a weighing alike; only pairing density testing with ultrasound and X-ray fluorescence gives you real confidence.
As a rough everyday guide, a real gold coin yields easily to a steel knife blade (Mohs ~5.5) — which, obviously, is the last thing you should ever do to one. The coin authenticity test and the coin weight checker give you safer, non-destructive routes to the same answer.
How the test works
Hardness A > hardness B → A scratches B, B does not scratch A
Hardness A = hardness B → both scratch each other
You run it by hand, pressing the testing material onto the sample and then judging whether an actual groove was cut or whether only the softer tool wore away.
The short version
Mohs hardness sorts materials by scratch resistance on a 1-to-10 scale and is useful for telling precious metals apart from fakes or alloying partners. For a trustworthy gold valuation or authenticity check, though, pair it with further physical clues such as density and melting point.