  The relic abundance of heavy stable particles charged under a confining gauge
group can be depleted by a second stage of annihilations near the deconfinement
temperature. This proceeds via the formation of quarkonia-like states, in which
the heavy pair subsequently annihilates. The size of the quarkonium formation
cross section was the subject of some debate. We estimate this cross section in
a simple toy model. The dominant process can be viewed as a rearrangement of
the heavy and light quarks, leading to a geometric cross section of hadronic
size. In contrast, processes in which only the heavy constituents are involved
lead to mass-suppressed cross sections. These results apply to any scenario
with bound states of sizes much larger than their inverse mass, such as U(1)
models with charged particles of different masses, and can be used to construct
ultra-heavy dark-matter models with masses above the na\"ive unitarity bound.
They are also relevant for the cosmology of any stable colored relic.
