Answer:
To be exact: there are no three stages of crystal formation. This is an oversimplification using ill defined terms. The answer depends on the context and on what the one who asked it is interested in. Nucleation Growth and Equilibrium could be called 3 stages, as well as Adsorption Reorientation and Incorporation of new members of the lattice. For experimentalists it could be supersaturation, nucleation and separation as well. Crystallization from solution or even of pure substances is so complex that exact theoretical descriptions virtually do not exist up to date.