Lattice is close-packed, if its packing factor is greater than that of random close packing, 0.87, and is loosely packed if its packing factor is less than that of random loose packing, 0.75.
Ideally packed (δ=1) structures can be represented by the stacking sequence of close-packed layers:
|stacking||elementary metals||selected alloys|
|AB||h||D6h4||A3 hcp||XY||C6v4||B4 wurtzite|
|ABC||c||Oh5||A1 fcc||XY||Td2||B3 zincblende|
Not ideally packed structures can be obtained by deformations and partitions of the above lattices, here are some examples:
For metal alloys with unequal size ions the diversity of close-packed structures grows. For the case, when the smaller ions fit into the voids of the close-packed lattice formed by the larger ones, see ionic compounds with close-packed sublattice.
ABC notations (see Wikipedia):