Ordered clusters and dynamical states of particles in a vibrated fluid
  Fluid-mediated interactions between particles in a vibrating fluid lead to both long range attraction and short range repulsion. The resulting patterns include hexagonally ordered micro-crystallites, time-periodic structures, and chaotic fluctuating patterns with complex dynamics. A model based on streaming flow gives a good quantitative account of the attractive part of the interaction. 
Greg A. Voth, B. Bigger, M.R. Buckley, W. Losert, M.P. Brenner, H.A.   Stone, and J.P. Gollub