1. n. [Geology]
The most compact arrangement in space of uniform spheres (atoms and molecules in mineral crystals, or grains in sedimentary rocks) that results in a structure having no more than 26% porosity. Rhombohedral packing is more stable mechanically than cubic packing. Cubic packing is the most porous packing arrangement, with about 47% porosity in the ideal situation. Most sediments, however, are not uniform spheres of the same size, nor can they be arranged in a cubic structure naturally, so most sediments have much less than 47% porosity of ideal cubic packing and commonly less than the 26% porosity of ideal rhombohedral packing.