Linked from
The 23 pages that link to Magnetite, each with the reason it gives.
SerpentinizationRelated: Magnetite can form as iron is redistributed during serpentinization.
Iron(II)Related: Its mixed valence shows iron(II) coexisting with iron(III) in one mineral.
RustRelated: It can form in oxygen-poor regions beneath or within corrosion layers.
SerpentiniteRelated: Iron released during serpentinization can form magnetite and generate hydrogen.
HedenbergiteRelated: Magnetite commonly occurs alongside hedenbergite in iron skarns.