Crystallization
Crystallization occurs in two major steps. The first is nucleation. This is the appearance of a crystalline phase from a super-cooled liquid or a supersaturated solvent. The second step is crystal growth, where more atoms link up with the crystal structure. This means the (crystal) particles get bigger; this leads to a crystal state. Loose particles form layers at the crystal's surface and lodge themselves into open pores, cracks, etc.