Crowley justknew he was going to make some point about the relative hardness of birds' beaks and granite mountains, and plunged on quickly.

Much of the water from open wells and borewells is not suitable for drinking due to its relative hardness.

It has a relative hardness of 5.5.

If done with care and scrupulously clean glassware, the experiment you describe is at least an indicator of relative hardness.

However, both Theophrastus and Pliny the Elder had compared the relative hardness of minerals known to them in the ancient world, including diamond and quartz.

The work of digging the nest may take up to five hours; the speed with which it is dug seems to be dependent upon the relative hardness of the ground.

The stone, although fine-grained, is siliceous, and partial cementing with silica accounts for its relative hardness.

The two kinds are distinguished from one another readily by differences in their relative hardness.

Stone comes in many varieties and artists have abundant choices in color, quality and relative hardness.

She further sorted the metal by relative hardness and purity according to the qualities the crystals displayed.