  We report a degenerate quasicrystal in Monte Carlo simulations of hard
triangular bipyramids each composed of two regular tetrahedra sharing a single
face. The dodecagonal quasicrystal is similar to that recently reported for
hard tetrahedra [Haji-Akbari et al., Nature (London) 462, 773 (2009)] but
degenerate in the pairing of tetrahedra, and self-assembles at packing
fractions above 54%. This notion of degeneracy differs from the degeneracy of a
quasiperiodic random tiling arising through phason flips. Free energy
calculations show that a triclinic crystal is preferred at high packing
fractions.
