Synthetic powders of pure goethite exhibit an antiferromagnetic behavior and negligible isothermal remanent magnetization up to 4 Tesla. However thermoremanence up to 0.3 Am2kg-1 can be imparted to the samples. High field measurements show median acquisition field of 9--13 T and suggest saturation fields of the order of 102 T. Large increase in remanence at low temperature is an intrinsic feature of goethite. The weak ferromagnetism observed is linked to a bulk origin for spin imbalance rather than to an effect of very fine grain-size or surface defects. The results are compared with properties of rocks bearing goethite and hematite. ¿ American Geophysical Union 1989