Mohs Hardness

Mohs Hardness

Mohs Hardness	Example Mineral	Field Identification
1	Talc	Easily scratched with fingernail
2	Gypsum	Scratched with fingernail
3	Calcite	Scratched with copper coin
4	Fluorite	Scratched with knife
5	Apatite	Scratches glass with effort
6	Orthoclase Feldspar	Easily scratches glass
7	Quartz	Scratches steel and glass easily
8	Topaz	Scratches quartz
9	Corundum	Scratches almost all minerals
10	Diamond	Scratches all known substances

Why does Laubscher still use it?

Because in practice:

Very soft minerals (Mohs < 3, e.g., talc, clay, chlorite) tend to have very low cohesion and very low residual shear strength.

They behave plastically, absorb energy, and facilitate sliding or squeezing.

So in the field, a vein you can scratch with your nail often corresponds to low shear resistance zones (e.g., fault gouge).

🔍 Field proxy: If the material has Mohs ≈ 1–2, you’re probably dealing with something that has c < 50 kPa and φ < 20° — that’s significant geomechanically.