Rock samples containing (ferri) magnetic minerals acquire an isothermal remanent magnetization (IRM) after exposure to a direct magnetic field. Measuring IRM(B) allows to produce IRM acquisition curves which were modelled by cumulative log Gaussian (CLG) functions (Robertson and France, 1994) to discriminate the different magnetic phases. An approach of how to find the best model has been added to this method. From the investigation of a magnetite sample it is inferred that with the method the remanence acquisition coercive force for each magnetic component in a sample can be deduced. The method allows to detect minute concentrations of magnetically hard material in a predominant magnetically soft sample and vice versa. It furthermore allows to extrapolate the IRM behaviour of samples that do not reach saturation IRM in the experiment. The study of a natural hematite renders it possible that even well-defined hematite may be contaminated by (ferri)magnetic impurities biasing the remanence acquisition coercive force of the sample towards lower values. ¿ 1998 American Geophysical Union