Figure 1
Illustration: (Top) Reprinted from [12]; (Bottom) Alan Stonebraker, adapted from [11]

Figure 1: Tetrahedral objects have been found to pack with high density, even denser than other non-spherical objects that have been designed to pack densely. “Egg cokes” produced from compressed coal powder (top) have a roughly biaxial, ellipsoidal shape. The aspect ratio of these coal briquettes coincides remarkably closely with that of biaxial ellipsoids that, according to the study of Donev et al. [11] have the highest density of RCP of all possible biaxial ellipsoids (red line in bottom panel).