  The nonbaryonic dark matter of the Universe can consist of new stable double
charged particles $O^{--}$, bound with primordial helium in heavy neutral
O-helium (OHe)"atoms" by ordinary Coulomb interaction. O-helium dark atoms can
play the role of specific nuclear interacting dark matter and provide solution
for the puzzles of dark matter searches. The successful development of
composite dark matter scenarios appeals to experimental search for the charged
constituents of dark atoms. If $O^{--}$ is a "heavy quark cluster" $\bar U \bar
U \bar U$, its production at accelerators is virtually impossible and the
strategy of heavy quark search is reduced to search for heavy stable hadrons,
containing only single heavy quark (or antiquark). Estimates of production
cross section of such particles at LHC are presented and the experimental
signatures for new stable quarks are outlined.
