Abstract
The thermal change in susceptibility of ferromagnetic mineral grains separated from igneous rocks was measured by a ballistic method in a weak magnetic field. The thermal change of susceptibility was classified into four types. These types were discussed in connection with the condition under which the original rock was formed. The dependency of the Curie-point and the magnitude of the susceptibility upon the chemical constitution was examined, the content of TiO2 in ferromagnetic mineral being especially taken into account. Besides, the relation between the magnitude of susceptibility and the grain size was obtained from the viewpoint of the magnetic property of small particles.
