The crystallization process consists of two major events, nucleation and crystal growth. Nucleation is the initial process that forms the site upon which additional particles are deposited during the subsequent crystal growth phase. When solute molecules dispersed in a solvent gather into clusters, they elevate solute concentration in a small region. Normally these clusters redissolve but under the right operating conditions (temperature and supersaturation), they reach a critical size and become stable nuclei. It's this nucleation process that determines the crystal structure, arranging the atoms in a defined and periodic manner. Both nucleation and growth will continue to occur simultaneously while the supersaturation exists.
Enough talk, now watch NurdRage electrically crystallize metal out of a solution down below!
Some more fun with crystals; Crystal Garden Growing Time Lapse - and you might also want to check out Mexico's giant crystal cave; goo.gl/FBFn9
Bonus: Timelapse of Crystals Growing