Crystallization mediated by a metastable phase
Almost any solution can undergo a non-trivial crystal growth process given a sufficiently deep quench. For instance, the quench shown in the phase diagram in Fig. 1, from temperature TA, into the fluid-crystal miscibility gap at temperature TB, results in a non-equilibrium uniform solution at point i. When a crystal is introduced (or nucleated) at point v, the bulk fluid (at i) cannot locally coexist with it, as its chemical potential and osmotic pressure do not match the crystal's. Instead the fluid near the cystal surface is depleted to concentration ii at which it forms a sharp interface with a very rarefied solution iii which has a concentration gradient down to iv, the concentration that locally coexists with the crystal.