In crystallography, crystal structure is a description of the ordered
arrangement of atoms, ions, or molecules in a crystalline material. Ordered
structures occur from the intrinsic nature of the constituent particles to
form symmetric patterns that repeat along the principal directions of three-
dimensional space in matter.
The smallest group of particles in the material that constitutes this
repeating pattern is the unit cell of the structure. The unit cell completely
reflects the symmetry and structure of the entire crystal, which is built up
by repetitive translation of the unit cell along its principal axes. The
translation vectors define the nodes of the Bravais lattice.