Study of Fe2+ -Mg2+ order-disorer in pyroxene from the Cachari meteorite.

ABDU, Y.; SCORZELLI ROSA,; SOUZA AZEVEDO, I.; VARELA, ME

Suiza

Congreso; Meetings of the Meteoritical Society; 2007

The Cachari meteorite, found in 1916 in Argentina, is a monomictic eucrite that belongs to the basaltic achondrites. It is composed mainly of low-Ca pyroxene and plagioclase [1, 2]. Mössbauer spectroscopy indicates that the only Fe-containing mineral present in the Cachari eucrite is pyroxene [3]. The study of intracrystalline distribution of Fe2+ and Mg2+ between the nonequivalent octahedral sites M1 and M2 in pyroxenes is useful in tracing the thermal history of a rock. In unshocked and slowly cooled pyroxenes, Fe2+ orders at the M2 site whereas Mg2+ occurs predominately at the M1 site [4]. Here we study the partitioning of Fe2+ and Mg2+ between the M1 and M2 sites in pyroxene from the Cachari eucrite by Mössbauer spectroscopy in the temperature range (300 K – 80 K) and electron microprobe analysis.