If it come to particles, the surface atoms define the polarity of a particle not the EN difference or anything you would think of for a molecule. Also, the crystal structure is not of any importance.

Given your material is magnetite, then you will have very probably an oxide surface at high pH and this surface will have a negative polarisation. With decreasing pH your surface will be more and more covered with hydroxide instead of oxide and you will go towards a neutral (no polarisation) or even positive polarisation at low pH.

Usually you add surface-stabilising ligands. With them you can easily define the polarity, hydrophilic or hydrophobic character of the particles regardless of the material. Just imagine chemical functionalities on the outer side of the surface ligand pointing towards the solution.

I would guess that a suitable surface ligand might make your magnetite particles soluble in pentanes (in an extreme case).

Absolute "cool" surface ligands for magnetite are o-semiquinones for the anchoring on the particle. They can be chemically easily varied on the outer side.

Prof. Axel Klein

Wow what a great answer thank you so much (this exactly the case of zeta potential of particles too)

So from this point magnetite is always hydrophilic because of the surface oxygen functionalities. That what I though until I read that it is somehow hydrohphobic and needs modification to increase its dispersibility

https://pdfs.semanticscholar.org/bfef/5006d175ecbb25490caf3c7b23c996eb424e.pd

Yes, this is the zeta potential!