Crystallization which can be a natural or artificial process is the formation of a solid due to the build up crystals from a homogeneous solution. The word homogeneous comes from Greek and means 'same kind'. A perfect example is water freezing to form ice or snow. All crystals form the same way which is by atoms coming together to form a uniformed cluster.
Materials may also solidify as they precipitate out of a liquid or gas. Precipitation in mineralogy refers to a dissolved mineral that comes out of water, an example could be a teaspoon of salt which has previously been dissolved in a glass of water.
Crystallization can take place in nature very quickly or it can also take place over thousands of years. Natural crystals from deep within the Earth's crust took millions of years to form.
As we go about our daily lives we're surrounded by crystals in the form of salt, sugar and of course minerals and gemstones.