Thermoremanent magnetization (TRM) in hematite is larger than TRM in magnet
ite for grain sizes greater than or equal to 10 mum. We show that hematite'
s weak spontaneous magnetization M-s causes its strong TRM, since the self-
demagnetizing field H-d opposing large domain wall displacements is proport
ional to M-s. In hematite, H-d is comparable to the Earth's magnetic field
but in magnetite, H-d is 1000 times larger. As a result, Earth's field TRM
of MD hematite (approximate to0.3 Am-2/kg) outweighs TRM and induced magnet
ization of MD magnetite (approximate to0.01-0.02 Am-2/kg) and rivals TRM of
single-domain and PSD magnetite as a source of magnetic anomalies on Earth
and perhaps on Mars.