The process through which crystals form, resulting in the change from a liquid or vapor to a solid. Crystallization can happen in two basic ways: 1. By lowering the temperature of a melted material like magma or water, atoms and ions start to aggregate into crystals, forming solid rock or ice. This can also happen from a vapor, as is the case with the formation of snowflakes, but it is much less common. 2. By evaporating water from a solution, the saturation point of the water is reached and a solid begins to precipitate out as crystals (for example, salt flats in the desert have been precipitated out of lakes that dried up).