International
Tables for Crystallography Volume C Mathematical, physical and chemical tables Edited by E. Prince © International Union of Crystallography 2006 
International Tables for Crystallography (2006). Vol. C, ch. 9.2, p. 752


Figure 9.2.1.2
(a) Symmetry axes of a single closepacked layer of spheres and (b) the minimum symmetry of a threedimensional close packing of spheres. 