  We explore the effect of shape -- jagged vs. regular -- in the jamming limit
of very gently shaken packings. Our measure of shape $\eps$ is the void space
occupied by a disordered grain; we show that depending on its number-theoretic
nature, two generic behaviours are obtained. Thus, regularly shaped grains
(rational $\eps$) have ground states of perfect packing, which are
irretrievably lost under zero-temperature shaking; the reverse is the case for
jagged grains (irrational $\eps$), where the ground state is only optimally
packed, but entirely retrievable. At low temperatures, we find intermittency at
the surface, which has recently been seen experimentally.
