hardness

The quality of being hard.

Who can number the cloudes in wiſedom? or who can ſtay the bottles of heauen, / When the duſt groweeh^([sic – meaning groweth]) into hardneſſe and the clods cleaue faſt together?

An instance of this quality; hardship.

The quantity of calcium carbonate dissolved in water, usually expressed in parts per million (ppm).

The resistance to scratching, cutting, indentation or abrasion of a metal or other solid material.

The penetrating ability of electromagnetic radiation, such as x-rays; generally, the shorter the wavelength, the harder and more penetrating the radiation.