Comparison of the iron-bearing crystals and phases from Tamdakht H5 and Annama H5 ordinary chondrites by X-ray diffraction, magnetization measurements and Mössbauer spectroscopy

Abstract

The iron-bearing phases and crystals within (i) the bulk interior and the fusion crust from Tamdakht H5 and (ii) the bulk interior from Annama H5 ordinary chondrites were studied by optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction (XRD), magnetization measurements, and Mössbauer spectroscopy. The main iron-bearing phases/crystals such as olivine, orthopyroxene, clinopyroxene, troilite, chromite, and hercynite, as well as Fe-Ni-Co alloy with the α₂-Fe(Ni, Co), α-Fe(Ni, Co) and γ-Fe(Ni, Co) phases were identified in both meteorites. XRD and Mössbauer spectroscopy showed high contents of Fe-Ni-Co alloy in the bulk interiors from Tamdakht H5 and Annama H5 ordinary chondrites. The fusion crust from Tamdakht H5 contains a new phase of magnesioferrite. A classification scheme for H, L, and LL ordinary chondrites using the relative areas of Mössbauer spectral components was applied to these meteorites' classification. The ratios of the M1 and M2 site occupations by Fe²⁺ in olivine and orthopyroxene were determined using XRD and Mössbauer spectroscopy, showing consistent results. The equilibrium cation distribution temperatures for olivine and orthopyroxene in Tamdakht H5 and Annama H5 were determined using XRD and Mössbauer spectroscopy.