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Glossary:Hardness
- Metal - hardness is the measure of the resistance encountered in pressing a steel ball into the metal.
- Minerals - hardness is the resistance of a mineral to scratching. Determined by the Mohs scale.
- Water - hardness is the ion content of water.
A property of water that causes formation of an insoluble residue when the water is used with soap and a scale in vessels which water has been allowed to evaporate. It is primarily due to the presence of ions of calcium and magnesium, but also to ions of other alkali metals, other metals (such as iron), and even hydrogen. Hardness of water is generally expressed as ppm of CaC03 (40 ppm Ca produces a hardness of 100 ppm as CaC03), also as mg/L, and as the combination of carbonate hardness and noncarbonate hardness.