A class of organism, lithotrophs, use minerals (inorganic substrates) for energy conservation/reducing equivalents in biosynthesis.
However such organisms on Earth are limited to single-celled prokaryotes in the Domains Archea or Bacteria.
The question is, are higher organisms, specifically animal-like lithotrophic organisms (as opposed to plant-like or fungi-like) possible?
If yes, what would be the evolutionary justification? (i.e. How would the organism work?)
The main problem with higher organisms of this kind, is the lack of useful inorganic substrates that are also abundant. Let's assume that the lithotroph only uses minerals for energy conservation and not as a reducing equivalent (it either uses organic sources, or CO2 fixation probably the former since its animal-like). Let's also assume relative abundance of the necessary inorganic substrate (but not as much as gaseous substrates like O2), and unavailability of better oxidants (again, O2)