Study of thermomagnetic identification of greigite as an indispensable carrier to natural remanent magnetization of sediments

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The main target of the research is to elucidate thermomagnetic property of greigite which is generally found as a minor, but indispensable magnetic mineral in various types of sediments. The Curie temperature of greigite has been reported as 320 degrees C in most of the previous works. However some of the greigite-bearing sediments show stable remanence close to 400 degrees C. To solve this inconsistency, we conducted rock magnetic and X-ray diffraction (XRD) studies using natural greigite sample form Erhjen-chi section, southern Taiwan.XRD results show that greigite has survived by heating up to 340 degrees C, but difficult to detect magnetically above that temperature. We also applied a high-temperature XRD method in helium atmosphere. The existence of greigite was confirmed during the heating up to 380 degrees C. We also found neo-formation of pyrrhotite, pyrite, and marcasite by the heating above 340 degrees C. Hematite was also observed above 380 C. These results are consistent with the fact that some of the greigite-bearing sediments can hold remanent magnetization after the heating up to 400 degrees C. Some of neo-formed minerals could show the magnetization inherited from the original magnetic minerals, however.We are now thinking to continue further investigation on this topic, because we also found that our result was strongly dependent upon the purity of the sample. It is necessary to check reproducibility of the results by using several different samples.