Presentation Information
[R5-P-07]The ferrihydrite/goethite and pyrrhotite contradictions in the NWA11469 meteorite
*Sena Toyonaga1, Balazs Bradak1, Seto Yusuke2, Akos Kereszturi3 (1. Kobe Univ. Marit. Sci., 2. Osaka Met. Univ. Sci., 3. Konkoly Astron. Inst., RCAES, Hungary)
Keywords:
Carbonaceous chondrite,NWA11479,Rock magnetic analysis,Scanning electron microscopy
A combined rock magnetic study and scanning electron microscopy were conducted on the NWA11469 carbonaceous chondrite. The studied meteorite was purchased in 2016 in Mauritania, and no detailed analysis of its magnetic mineralogy has been published yet. The goal of our study is to reveal the basic rock magnetic characteristics and magnetic mineralogy of the meteorite. The preliminary study indicates magnetic contributors such as various iron/nickel alloys (kamacite, taenite), ferrihydrite, goethite, and pyrrhotite. Further magnetic mineral contributors, magnetite, were identified by rock magnetic experiments. The combined rock magnetic study and SEM analysis showed slightly contradictory results, i.e. no magnetite was found during the SEM analysis of the samples, and vice versa, no sign of ferrihydrite/goethite and pyrrhotite was indicated by the rock magnetic experiments. The lack of magnetite contributors during the SEM analysis, may be explained by the similarities between particular magnetic parameters (coercivity) of pyrrhotite and magnetite, which does not allow the clear separation of the two by certain magnetic experiments. In contrast, the lack of marks of magnetic mineral transformation of ferrihydrite/goethite and pyrrhotite during thermomagnetic experiments and the characteristics of the thermomagnetic curves suggest that magnetite may need to exist in the meteorite. As an alternative theory, the expected marks of mineral alteration of the weakly magnetic ferrihydrite/goethite may be hidden behind the magnetic signal of the commonly appearing strongly magnetic components like Fe/Ni alloys. The preliminary results of NWA11469 defined the next step of the research, namely the clarification of the differences between the SEM and rock magnetic results , regarding the identification of ferrihydrite/goethite and pyrrhotite during thermomagnetic experiments.
