Minor elements in forsterites of Orgueil (C1), Alais (C1) and two interplanetary dust particles compared to C2‐C3‐UOC forsterites

Abstract

Abstract— The rare Mg‐rich silicate fraction of the C1 meteorites, Orgueil and Alais, is dominated by minute (< 30 μm) forsterite. Twenty three forsterite grains of these meteorites as well as large forsterites in two chondritic porous interplanetary dust particles (IDPs) are characterized by levels of MnO generally, but not always, higher than found in forsterites of C2, C3 and unequilibrated ordinary chondrites (UOC). Forsterite in Orgueil contains 900 to 6200 ppmw MnO while Alais forsterite has less than 2000 ppmw MnO suggesting that the forsterites in the two meteorites are chemically distinct. Alais forsterite shows lower Cr and Al relative to Orgueil forsterite. The C1 forsterites do not show Fe‐poor (FeO < 0.3), refractory‐rich (Al, Ca, Ti, V) compositions which are relatively common in the C2‐C3‐UOC meteorites suggesting that the most primitive forsterite compositions are not present in these C1 meteorites. While minor elements in forsterite can not distinguish unambiguously between C1 and C2‐C3‐UOC sources, the high Mn levels in some IDP forsterites are similar to some C1 forsterites suggesting a possible relation between the forsterites of these two extraterrestrial samples.