  We have studied the shock-induced phase transition from fullerite to a dense
amorphous carbon phase by tight-binding molecular dynamics. For increasing
hydrostatic pressures P, the C60-cages are found to polymerise at P<10 GPa, to
break at P~40 GPa and to slowly collapse further at P>60 GPa. By contrast, in
the presence of additional shear stresses, the cages are destroyed at much
lower pressures (P<30 GPa). We explain this fact in terms of a continuum model,
the snap-through instability of a spherical shell. Surprisingly, the relaxed
high-density structures display no intermediate-range order.
