hardness

the property of being rigid and resistant to pressure; not easily scratched; measured on Mohs scale

a quality of water that contains dissolved mineral salts that prevent soap from lathering; "the costs of reducing hardness depend on the relative amounts of calcium and magnesium compounds that are present"

devoid of passion or feeling; hardheartedness

the quality of being difficult to do; "he assigned a series of problems of increasing hardness"; "the ruggedness of his exams caused half the class to fail"

excessive sternness; "severity of character"; "the harshness of his punishment was inhuman"; "the rigors of boot camp"