The process of turning a liquid material into a highly structured solid whose atoms or molecules are arranged in a well defined three-dimensional crystal lattice is known as crystallisation.
A unit cell is a crystal's tiniest discrete component.
There are millions of these unit cells throughout the crystal.
Ice:
Crystalline structures are created when water molecules are organised in an ordered, cage-like form.
Crystalline compounds, such as ice particles or water molecules, are composed of particles or molecules that are arranged in a certain sequence to produce an ordered structure known as a crystalline compound.