Magnetic properties related to thermal treatment of pyrite

Detailed rock magnetic experiments were conducted on high-purity natural crystalline pyrite and its products of thermal treatments in both argon and air atmospheres. In argon atmosphere (reducing environment), the pyrite is altered by heating to magnetite and pyrrhotite; the latter is stable in argon atmosphere, and has coercive force and coercivity of remanence of similar to 20 and similar to 30 mT, respectively. Whereas in air, the pyrite is ultimately oxidized to hematite. First order reversal curve (FORC) diagram of the end product shows that the remanence coercivity of hematite is up to similar to 1400 mT. The corresponding thermal transformation process of pyrite in air can be simply summarized as pyrite -> pyrrhotite -> magnetite -> hematite. These results are helpful for understanding of sedimentary magnetism, secondary chemical remanence and meteorolite magnetic properties.