Aste, Tomaso2015-12-132015-12-130031-9007http://hdl.handle.net/1885/85018I study the structural organization and correlations in very large packings of equally sized spheres, reconstructed in three dimensions with x-ray computed tomography. I show that the geometrical structure can be conveniently studied as a packing of irregular tetrahedra with volume distribution that must decay exponentially with parameters controlled by the conditions of mechanical stability, nonoverlapping, and space filling. I argue that the system’s structure can be described as constituted of two phases: (1) an “unconstrainedâ€phase which freely shares the volume and (2) a “constrained†phase which assumes configurations accordingly with the geometrical constraints. It results that the granular system exploits heterogeneity maximizing freedom and entropy while constraining mechanical stability.Keywords: Computerized tomography; Entropy; Packing; Stability; X ray analysis; Granular system; Mechanical stability; Parameters control; Granular materials200610.1103/PhysRevLett.96.0180022015-12-12