Abstract
Thermomagnetic analysis along with conventional reflection microscopy and magnetic powder analysis can be used to evaluate the alteration state of the magnetic fraction in a rock. The alteration state is positive or negative depending on the sense of change in a magnetic parameter (±ΔM) observed during thermomagnetic analysis. Grain size, sample preparation, experimental atmosphere, and heating rate are factors which must be considered in interpreting the results of thermomagnetic analysis. The effects of the experimental factors are more pronounced in basic than in acidic rocks because of the greater amount of titanium and other cations in the iron oxides. The effects of experimental factors are likewise more pronounced in extrusive than in intrusive basic rocks because of the more variable cooling conditions and the smaller more chemically heterogeneous iron oxides.
