Raman spectroscopic properties and Raman identification of CaS‐MgS‐MnS‐FeS‐Cr2FeS4 sulfides in meteorites and reduced sulfur‐rich systems |
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Authors: | Caroline Avril Valérie Malavergne Razvan Caracas Brigitte Zanda Bruno Reynard Emeline Charon Ema Bobocioiu Fabrice Brunet Stephan Borensztajn Sylvain Pont Martine Tarrida François Guyot |
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Institution: | 1. Université Paris Est‐Marne La Vallée, Laboratoire des Géomatériaux et Environnement, , 77454 Cedex, France;2. Laboratoire de Géologie, ENS Lyon‐CNRS15 parvis des Italiens, , 69342 Lyon Cedex 07, France;3. Muséum National d'Histoire Naturelle & CNRS UMR7202, , 75005 Paris, France;4. Laboratoire de Géologie, Ecole normale supérieure‐CNRS, , 75005 Paris, France;5. ISTerre‐CNRS, Université de Grenoble 1, , 38041 Grenoble Cedex 9, France;6. Laboratoire d'Interface et Systèmes Electrochimiques, UPR15 CNRS, , 75252 Paris, France;7. IMPMC/IPGP, UMR 7590 CNRS, , 75252 Paris, France |
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Abstract: | Raman spectra were acquired on a series of natural and synthetic sulfide minerals, commonly found in enstatite meteorites: oldhamite (CaS), niningerite or keilite ((Mg,Fe)S), alabandite (MnS), troilite (FeS), and daubreelite (Cr2FeS4). Natural samples come from three enstatite chondrites, three aubrites, and one anomalous ungrouped enstatite meteorite. Synthetic samples range from pure endmembers (CaS, FeS, MgS) to complex solid solutions (Fe, Mg, Ca)S. The main Raman peaks are localized at 225, 285, 360, and 470 cm?1 for the Mg‐rich sulfides; at 185, 205, and 285 cm?1 for the Ca‐rich sulfides; at 250, 370, and 580 cm?1 for the Mn‐rich sulfides; at 255, 290, and 365 cm?1 for the Cr‐rich sulfides; and at 290 and 335 cm?1 for troilite with, occasionally, an extra peak at 240 cm?1. A peak at 160 cm?1 is present in all Raman spectra and cannot be used to discriminate between the different sulfide compositions. According to group theory, none of the cubic monosulfides oldhamite, niningerite, or alabandite should present first‐order Raman spectra because of their ideal rocksalt structure. The occurrence of broad Raman peaks is tentatively explained by local breaking of symmetry rules. Measurements compare well with the infrared frequencies calculated from first‐principles calculations. Raman spectra arise from activation of certain vibrational modes due to clustering in the solid solutions or to coupling with electronic transitions in semiconductor sulfides. |
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