Magnetite and Titanomagnetite exhibit magnetic properties which are attributable to the micro-structures developed during oxidation and exsolution: All magnetite iron ores which are lodestones contain maghemite. These lodestones have Hc between 10 and 30 mT, SIRM between 8 and 18 Am2 kg1, and RI between 0.10 and 0.26. Magnetite, titanomagnetite and metals have REM values (ratio of NRM to SIRM) <0.05. Samples (called fulgarites) obtained from the Smithsonian Institution have REM values ranging from 0.45 to 0.92. The REM value serves as a witness parameter to the magnetic fields associated with the lightning bolt. If a high REM value (say≫0.1) can be verified as not to be due to contamination by man and does not contain MD hematite then the rock has LRM (lightning remanent magnetization). The magnetic field associated with lightning can be revealed from an isothermal remanent acquisition (RA) curve. ¿ 1999 American Geophysical Union