close packing is one of two crystal structures that derive from stacking
close-packed-planes of hard sphere atoms. In the HCP structure only two
stacking locations are employed in the sequence which can be represented
as .....ABABABABAB....... packing. The lattice of the hexagonal close packed
crystal is hexagonal and a basis of two atoms is placed in the same orientation
on each lattice point. The diagrams below illustrate the geometry and space
filling of this crystal structure.
hcp structure has the same nearest neighbor configuration as the fcc close
packed structure that uses the three possible stacking locations in an
.....ABCABCABCABC..... sequence. The next-nearest-neighbors (nnn) differ
in these two crystals.