Cubic Closest-Packed

Way in which atoms (considered as hard spheres) pack together to fill space. In cubic closest-packing, there are three alternating hexagonal layers, a, b, and c, offset from one another so that the spheres in one layer sit in the small triangular depressions of neighboring layers. Each sphere is touched by 12 neighbors, 6 in the same layer, 3 in the layer above, and 3 in the layer below.

Some or all content above used with permission from J. H. Wittke.