  We consider the model of composite dark matter assuming stable particles of
charge $-2$ bound with primordial helium nuclei by Coulomb force in $O$He
atoms. We study capture of such dark atoms in matter and propose a possibility
of existence of stable $O$-enriched superheavy nuclei and $O$-nuclearites, in
which heavy $O$-dark matter fermions are bound by electromagnetic forces with
ordinary nuclear matter. $O$He atoms accumulation in stars and its possible
effect in stellar evolution is also considered, extending the set of indirect
probes for composite dark matter.
