An introduction similar to this related to the same subject with is the crystalline structures, if you can paraphrase it in a way that does not make it plagiarized then that's fine too
2 Crystalline structures based on packing of hard spheres
2.1 Introduction
The bonding energy between pairs of atoms is minimized at a xed equilibrium distance r0, because of this most solid materials spontaneously adopt a crystalline arrangement in which atoms or ions are positioned along an ordered periodic array called the crystalline lattice. All metals, and most covalent and ionic solids, form crystalline structures under normal solidi cation conditions. Many properties of crystalline solids depend on the crystal structure, being the manner in which atoms or ions are spatially arranged. When the atoms favor no particular bonding orientations, the crystalline structure can be conveniently described using the hard sphere model. As metallic bonding is nondirectional in nature, the structure of most elemental metals is accurately described by the dense packing of hard spheres. In this model, hard spheres representing nearest neighboring atoms touch one another and form a densely packed structure. In case of elemental metals, all the atoms are identical. Three relatively simple crystal structures are found for most metals: face-centered cubic (FCC), hexagonal close-packed (HCP) and body centered cubic (BCC). FCC and HCP correspond to very dense atomic arrangements called closed packed structure, while BCC is a less dense structure.
Crystal structures determine most of the properties of a material. It can be witnessed in the beautiful natural formations of minerals, or in a more indirect way in industry. For example, turbine blades for ghter jets are grown such that only one crystal orientation is possible within the whole blade. Because of that speci c structure, the blade will not deform when exposed to extreme heat. This is only one of the many consequences of the study of crystallography.