What is the hardest mineral?
Quick answer
Diamond is the hardest naturally occurring mineral, scoring 10, the top of the Mohs hardness scale. It’s made of pure carbon atoms locked in an extremely strong 3D structure. Only another diamond can easily scratch a diamond.
The Mohs hardness scale
German geologist Friedrich Mohs created this scale in 1812. Each mineral can scratch the ones below it.
| Hardness | Mineral | Everyday comparison |
|---|---|---|
| 1 | Talc | Scratched by a fingernail |
| 2 | Gypsum | Scratched by a fingernail |
| 3 | Calcite | Scratched by a copper coin |
| 4 | Fluorite | Scratched easily by a knife |
| 5 | Apatite | Scratched by a knife |
| 6 | Orthoclase feldspar | Scratches glass slightly |
| 7 | Quartz | Scratches glass easily |
| 8 | Topaz | |
| 9 | Corundum (ruby, sapphire) | |
| 10 | Diamond | Scratches everything else |
The scale isn’t evenly spaced: diamond is several times harder than corundum, the next step down.
Why diamonds are so hard
Diamond and graphite (pencil “lead”) are both pure carbon. The difference is structure:
- In diamond, each carbon atom bonds tightly to four others in a rigid 3D lattice.
- In graphite, carbon forms flat sheets that slide over each other, making it soft.
Diamonds form about 150–200 km deep in Earth’s mantle under huge heat and pressure, then reach the surface in volcanic eruptions.
Hard isn’t the same as tough
Diamond resists scratching, but it can chip or shatter if struck sharply at the right angle. Toughness and hardness are different properties.
Anything harder?
Scientists have studied rare materials such as lonsdaleite, a form of carbon found in meteorite impacts, and some lab-made materials that may rival or beat diamond in certain tests. But among common natural minerals, diamond is still the champion.
Diamonds are also valued as gemstones; see how to find out how much something is worth. For another element fact, read why gold’s symbol is Au.
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