Raman spectroscopy, assisted by X-ray fluorescence and laser-induced breakdown spectroscopy, to characterise original and altered mineral phases in the NWA 2975 Martian shergottite

A fragment of the NWA 2975 Martian meteorite, an enriched basaltic shergottite, was analysed to complete its geochemical characterisation performed 10 years ago. By this means, the feasibility of the employed techniques in a combined way for present and future space exploration missions can be tested. For this aim, Raman spectroscopy was used supported by micro energy dispersive X-ray fluorescence (mu-EDXRF) and laser-induced breakdown spectroscopy (LIBS) for an accurate interpretation of molecular and elemental results. Raman spectroscopy results from two setups, InVia from Renishaw and RLS Simulator, were compared. The major minerals detected by Raman spectroscopy were pyroxenes (mainly augite, pigeonite and enstatite) and plagioclases (mainly shocked maskelynite). Raman spectroscopy allowed defining different metal compositions for these main minerals based on the secondary Raman spectroscopy bands in the 200-500 cm(-1) region. In addition, other minerals were found such as merrillite, as well as pyrrhotite and apatite, in several veins and cracks of the meteorite, in agreement with the initial report by the Meteoritical Bulletin. Moreover, it should be highlighted that coesite was found for the very first time in this meteorite.

Automated summary

The geochemical characterisation of the NWA 2975 Martian meteorite was completed using Raman spectroscopy supported by micro energy dispersive X-ray fluorescence (mu-EDXRF) and laser-induced breakdown spectroscopy (LIBS), which enabled an accurate interpretation of molecular and elemental results. Various major minerals, including pyroxenes and plagioclases, were detected and different metal compositions for these minerals were defined based on secondary Raman spectroscopy bands. Additionally, the presence of coesite, a high-pressure polymorph of silica, was identified in this meteorite for the first time.