The first two layers of atoms in a cubic closest packed structure are identical to the first two layers in a hexagonal closest packed structure. The third layer is different. Atoms in the third layer in a CCP structure sit directly above empty dimples in the first layer giving an ..ABCABC.. arrangement. The atoms in the third layer in a HCP structure sit directly above the atoms in the first layer.

Click on a triangular dimple in the second layer that will hold an atom in a cubic closest packed structure.

For comparison, click on a dimple that will hold an atom in a HCP structure.