Ferrous metals are (somewhat) unique because they can spontaneously polarize and display a permanent magnetic moment.
But of course all materials interact with magnetic fields.
It is bizarre to think that ``fluid dark matter'' acts only on liquids, because:
- Dark matter interacts via gravity, that is the entire point of dark matter. In regular matter, the gravitational interaction is dictated only by that matter's density.
- The phase (gas, liquid, solid) of regular matter is dictated only by the electromagnetic interactions between the atoms that constitute that matter. Dark matter can't interact electromagnetically, otherwise it wouldn't be dark.