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Why can a harder mineral scratch a softer mineral?

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Faux amphibolite — geology A rock formation called “faux amphibolite,” from the Nuvvuagittuq greenstone belt in northern Quebec, dated to 4.28 billion years ago.

In the study of geology, a mineral's hardness is defined as its resistance to being scratched. This physical property is fundamentally determined by the strength of the chemical bonds holding the mineral's atoms, ions, or ionic groups together.12

When a harder mineral comes into contact with a softer one, the stronger electrical forces within the harder mineral's crystal structure allow it to overcome the weaker bonds of the softer mineral. Because the atoms in the harder substance are joined by more powerful forces, they remain intact while the surface of the softer material is disrupted, resulting in a scratch.23

This relationship is the basis for the Mohs hardness scale, which ranks minerals from 1 (talc) to 10 (diamond). By testing which minerals can scratch others, geologists can identify unknown specimens by determining their relative position on this scale.45