The nonmetallic minerals may appear glassy, greasy, silky, or pearly. Cleavage is a test to determine the way a mineral splits in planes. Cleavage is related to the mineral's crystal structure. Mica, for example, splits in thin sheets. Some minerals break into sharp, splintery pieces called fractures.
Every mineral has a particular specific gravity, or density.
It may be determined by weighing the mineral in the air and then suspended in water. The weight in the air, divided by the difference in weight while in water, is the specific gravity. Hardness is still another identification test. The mineral with the higher number can scratch anything beneath it or equal to it in hardness. Thus a diamond can scratch everything.