  With simulation and experiment we examine the effect of grain anisotropy on
the angle of repose in a two-dimensional geometry. We find that the structure
of the granular packing can be directly controlled by changing the aspect ratio
of the grains, and that the specific type of order strongly affects the angle
of repose and the resulting dynamics. The angle of repose is largest for dimer
grains, and is smaller for both monomer and trimer grains. The motion of a
collapsing grain heap consists of large scale collective shear when monomer
grains are considered, but occurs via tumbling of grains on the surface for
dimers, and via disorderly bulk tumbling for trimer grains.
