Figure 1: A granular flock.

A monolayer of millimetre-sized tapered brass rods align spontaneously on a vibrating surface amidst a background of aluminium beads. Bead and rod area fractions are 0.51 and 0.16 respectively.
A monolayer of millimetre-sized tapered brass rods align spontaneously on a vibrating surface amidst a background of aluminium beads. Bead and rod area fractions are 0.51 and 0.16 respectively.