Lodestone
presence or absence of magnetic minerals does not tell us directly abut the former magnetic field.
it could have been strong, but have had no minerals of the right sort to record it, or it could have been strong, had the right minerals, but they got reformatted by thermal events.
Let's see what we get, then try to make sense of it. Hold the guesses for now. They're guaranteed to be wrong, at least in part, maybe all over...