Low temperature magnetic transition of chromite in ordinary chondrites

We present low temperature magnetic data (thermal demagnetization, hysteresis) obtained on thirty three ordinary chondrite meteorites. A magnetic transition is observed in the 40–80 K range (average 66 K), and is interpreted as a ferrimagnetic to paramagnetic phase transition. We present quantitative analyses of changes in magnetization across the magnetic phase transition and chemical elemental analyses to argue that chromite, a common accessory mineral in meteorites, is the mineral undergoing the phase transition, and not troilite or tetrataenite as proposed in previous studies. Moreover, we observe a correlation between the measured Curie temperature and chemical composition of chromites in ordinary chondrites. Low temperature magnetic measurement are thus a sensitive indicator of chromite composition in these meteorites, and as such a possible proxy to the understanding of their thermal metamorphism.