The coordination number of a face-centered cubic, or FCC, is 12. This represents the number of other atoms that an atom touches within the crystal lattice structure.
Atoms generally self-organize into a crystalline lattice. Common examples of materials with a crystalline structure include metals, diamonds and other precious stones, and ice. A unit cell is the smallest structure that repeats itself through the lattice. For a face-centered cubic, the unit cell contains four atoms. The FCC also has an atomic packing factor of 0.74, which means the atoms are more tightly packed together than most other atomic arrangements. Other possible structures include body-centric cubic and hexagonal close-packed.