10 questions · about 2 min · free
Mohs Hardness Scale Quiz
Ten head-to-head pairs. Pick the harder mineral and learn the scratch test that proves it.
10 questions · about 3 minutes
Questions are drawn from a pool of 44, so every attempt is different.
The Mohs scale ranks minerals from 1 (talc, scratched by a fingernail) to 10 (diamond, scratched by nothing). It is the single most useful identification test you can do at home, because a fingernail, a copper coin, a steel knife and a piece of glass give you fixed reference points at roughly 2.5, 3.5, 5.5 and 5.5–6.
This quiz gives you ten pairs of minerals and asks which is harder. Each answer shows both hardness values and the household test that separates them, so by the end you will have the scale memorized without trying.
The Mohs hardness scale
The ten reference minerals and the everyday objects that scratch them.
- 1 Talc — scratched easily by a fingernail
- 2 Gypsum (selenite) — scratched by a fingernail
- 3 Calcite — scratched by a copper coin
- 4 Fluorite — scratched easily by a knife
- 5 Apatite — scratched by a knife with effort
- 6 Orthoclase feldspar — scratches glass with effort
- 7 Quartz — scratches glass and steel easily
- 8 Topaz — scratches quartz
- 9 Corundum (ruby, sapphire) — scratches topaz
- 10 Diamond — scratches everything
How to do a scratch test
Find a fresh, unweathered surface. Try to scratch it with your fingernail, then a copper coin, then a steel blade, then test whether it scratches glass. Wipe the mark: a real scratch stays, a streak of powder from the tester rubs off. The hardness is between the last thing that failed and the first thing that worked. Every mineral page in the StoneSnap wiki lists its Mohs hardness, and the browse-by-hardness pages group the whole catalog by number.
Frequently asked questions
What is the Mohs hardness scale?
A 1–10 ranking of mineral scratch resistance created by Friedrich Mohs in 1812. Each mineral scratches those below it. The scale is ordinal: diamond (10) is about four times harder than corundum (9) in absolute terms.
What hardness is glass?
Ordinary window glass is about 5.5. Anything that scratches glass is harder than 5.5, which rules out calcite, fluorite and most fakes.
What hardness is a fingernail, a coin and a knife?
Fingernail about 2.5, copper coin about 3.5, steel knife or nail about 5.5, hardened steel file about 6.5.
