Structural and Thermodynamic Explanations of Ostwald's Rule

Ostwald proposed that the solid first formed on crystallisation of a melt or a solution would be the least stable polymorph. It is shown that this can be rationalized on the basis of irreversible thermodynamics, structural relationships, or a combined consideration of statistical thermodynamics and structural variation with temperature. It is concluded that the rule cannot be a universal law but is only in the nature of a possible preferred tendency.