Dynamic patterns of granular solids

With nothing more than beads in a glass box, physicists have revealed yet another mysterious property of granular solids, now recognized by scientists as a unique state of matter, like solids or gases...

But when they filled the box nearly to the top — which, they expected, would cause the beads to clog — the beads instead moved in graceful, swirling currents.

Found at Wired Science, where there is more information and additional links.