/hahrd"nis/, n.1. the state or quality of being hard: the hardness of ice.2. a relative degree or extent of this quality: wood of a desirable hardness.3. that quality in water that is imparted by the presence of dissolved salts, esp. calcium sulfate or bicarbonate.4. unfeelingness or jadedness; callousness.5. harshness or austerity, as of a difficult existence.6. South Midland U.S. ill will; bad feelings: There's a lot of hardness between those two boys.7. Mineral. the comparative ability of a substance to scratch or be scratched by another. Cf. Mohs scale.8. Metall. the measured resistance of a metal to indention, abrasion, deformation, or machining.[bef. 900; ME hardnes, OE heardnes. See HARD, -NESS]
* * *Resistance of a mineral to scratching, described relative to a standard scale of 10 minerals known as the Mohs hardness scale.Hardness is an important diagnostic property in mineral identification. There is a general link between hardness and chemical composition (via crystal structure); thus, most hydrous minerals, halides, carbonates, sulfates, and phosphates are relatively soft; most sulfides are relatively soft (two exceptions being marcasite and pyrite); and most anhydrous oxides and silicates are hard. See also hardening.
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