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Why must an abrasive be harder than the material being ground or polished?

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Angle grinder — abrasive Worker using an angle grinder to smooth a piece of metal.

An abrasive must be harder than the material it is intended to grind, polish, or remove because its primary function is to wear away the surface of a less resistant substance.12

Hardness, which measures a material's resistance to indentation or scratching, is the fundamental property that allows an abrasive to effectively penetrate and displace the surface of the target material. If an abrasive were softer than or equal in hardness to the target, it would fail to create the necessary mechanical action to remove material, as it would lack the ability to scratch or abrade the surface.23

This relationship is quantified through various testing methods, such as the Mohs hardness scale, which ranks materials based on their ability to scratch one another, and more precise industrial tests like the Knoop and Vickers scales. By ensuring the abrasive is significantly harder, industry can achieve the precise components and smooth finishes required for modern manufacturing.231