3D electron diffraction study of terrestrial iron oxide alteration in the Mineo pallasite

Abstract

The Mineo pallasite is a relatively poorly known meteorite, which shows interesting features that are not fully understood, like the occurrence of iron oxide regions bordering both the olivine grain boundaries and the (Fe,Ni) metal. In this study, the Fe oxides have been characterized by Raman spectroscopy, Electron Microprobe Analysis, Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy (TEM), Energy Dispersive Spectroscopy (EDS) and 3DElectron Diffraction (3D ED). The combination of TEM-EDS and 3D ED yields a reliable identification of the chemical and crystallographic features of the cryptocrystalline portion of the sample. Thus, the Fe-oxides regions were definitely identified as goethite FeO(OH).The occurrence of goethite was unambiguously associated with terrestrial alteration, also confirmed by the presence of calcite, detected by TEM-EDS and 3D ED. Goethite contains minor elements such as Na, Si and Ca likely coming from allumino-silicates in terrestrial environment, and Ni associated with the (Fe, Ni) metal. The observation of goethite along olivine grain boundaries, as alteration product of the (Fe,Ni) metal diagenesis, is also very intriguing as it might be related to the (Fe,Ni) metal intruded into the sub-micrometric olivine fragments during pallasite formation. Further work is needed in order to extensively analyze the texture and composition of olivine/metal boundaries.

Electron crystallography and dedicated electron-diffraction instrumentation

“…His current research is focused on analysing beamsensitive materials such as organics, hybrid crystals and proteins using low-dose 3D ED techniques, one goal being to show that ED can be effectively used across a spectrum of research fields in crystallography for organic and inorganic materials. Most recently, this has included nanocrystals in the pharmaceutical industry , mineralogical applications (Mugnaioli et al, 2022;Toso et al, 2022), medical research (Del Turco et al, 2022) and material science (Kleain et al, 2020;Hamon et al, 2022).…”