Hexagonal Close Packed
There are two lattice parameters in HCP, a and c, representing the
basal and height parameters respectively.
In the ideal case, the c/a ratio is 1.633, however,
deviations do occur.
Coordination number and APF for HCP are exactly the same as those for
FCC: 12 and 0.74 respectively.
This is because they are both considered close packed
structures.