It has been found that the angles between corresponding faces on various crystals of the same substance are constant. However the shapes of crystals may differ because of the fact that the crystal faces are unequally developed. Here we have represented two crystals A and B in two dimensions which have different shapes but the angles between corresponding faces of them are same.

The shape or the external form of a crystal depends upon the rate of deposition of atoms or ions on the different faces. During crystallization of sodium chloride, the crystals obtained by crystallization from aqueous solution are cubic while those obtained by crystallization from urea solution are octahedral.