Crystal

The word crystals originates from the Greek word "Krystallos" meaning clear ice, and once referred mainly to quartz, rock crystal.
In general, crystals form when they undergo a process of solidification. Under ideal conditions, the result may be a single crystal, where all of the atoms in the solid fit into the equal crystal structure. However, normally, many crystals form simultaneously during solidification, foremost to a polycrystalline solid. For example, most metals encountered in everyday life are polycrystals. Crystals are often symmetrically intergrown to figure crystal twins.
Which crystal structure the fluid will form depends on the chemistry of the fluid, the conditions in which it is being solidified, and also on the ambient pressure. The process of forming a crystalline formation is often referred to as crystallization.