Past exam of the materials science course of the University of Cambridge / 2017 / Paper 1 / 4 / a

The close-packed planes of a cubic close-packed structure are $\{111\}$, with $ABCABC\dots$ stacking. Each layer is a triangular array; the third layer occupies the remaining set of hollows rather than returning above the first.

The basal close-packed planes of a hexagonal close-packed structure are $\{0001\}$ in four-index Miller-Bravais index, or $\{001\}$ with three hexagonal indices. Their stacking is $ABAB\dots$: alternate layers return above the same lateral positions.