The rhombic dodecahedron is a convex polyhedron composed by 12 rhombuses (where the long diagonal is √2 times the short one). It is a Catalan solid dual to the cuboctahedron truncated octahedron. Many of them can come together to form a honeycomb as shown here (see also this web of Angel Requena). One can put one ball inside each cell to produce the face-centered cubic packing, the best one as states the famous Kepler conjecture.
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| Source: http://en.wikipedia.org/wiki/File:Bienenwabe_mit_Eiern_und_Brut_5.jpg |
