  We describe a series of experiments involving the creation of cylindrical
packings of star-shaped particles, and an exploration of the stability of these
packings. The stars cover a broad range of arm sizes and frictional properties.
We carried out three different kinds of experiments, all of which involve
columns that are prepared by raining star particles one-by-one into hollow
cylinders. As an additional part of the protocol, we sometimes vibrated the
column before removing the confining cylinder. We rate stability in terms of r,
the ratio of the mass of particles that fall off a pile when it collapsed, to
the total particle mass. The first experiment involved the intrinsic stability
of the pile when the confining cylinder was removed. The second kind of
experiment involved adding a uniform load to the top of the column, and then
determining the collapse properties. A third experiment involved testing
stability to tipping of the piles. We find a stability diagram relating the
pile height, h, vs. pile diameter, delta, where the stable and unstable regimes
are separated by a boundary that is roughly a power-law in h vs. delta with an
exponent that is less than one. Increasing friction and vibration both tend to
stabilize piles, while increasing particle size can destabilize the system
under certain conditions.
