What is the name for a mineral’s resistance to being scratched?

Hardness is a mineral’s resistance to being scratched.

Mineralogists commonly compare hardness using the Mohs scale, introduced by German geologist Friedrich Mohs in 1812. The original scale contains ten reference minerals arranged from talc at 1 to diamond at 10. A mineral can scratch another mineral only if it is harder than that mineral.

Hardness is different from toughness. Hardness measures resistance to scratching, while toughness describes resistance to breaking, chipping, or deformation. A hard mineral can still be brittle; diamond is extremely hard but can split along certain cleavage directions.

The Mohs scale is ordinal rather than evenly spaced. Diamond is not merely twice as hard as corundum: modern tests show a much larger difference in absolute hardness. Field geologists may also use a fingernail, copper coin, or steel blade as practical scratch tests.