Raman spectroscopic properties and Raman identification of CaS‐MgS‐MnS‐FeS‐Cr₂FeS₄ sulfides in meteorites and reduced sulfur‐rich systems

Abstract

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 (Cr 2 FeS 4 ). Natural samples come from three enstatite chondrites, three aubrites, and one anomalous ungrouped enstatite meteorite. Synthetic samples range from pure endmembers (CaS, FeS, MgS) for the Cr-rich sulfides; and at 290 and 335 cm À1 for troilite with, occasionally, an extra peak at 240 cm À1 . A peak at 160 cm À1 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.

Sulfur solubility in reduced mafic silicate melts: Implications for the speciation and distribution of sulfur on Mercury

“…With increasing (Mg+Ca)/Fe ratio, a peak at 210 cm −1 progressively appears. Similar peak positions were identified in oldhamite (CaS) and niningerite ((Mg,Fe)S; Avril et al, 2013). Raman spectra in silicate melts were acquired with a 1 μm spot and care was taken to avoid contamination from micro-nuggets of sulfide and metal melts or crystals.…”

Laser alteration on iron sulfides under various environmental conditions

“…[e.g. , ] For example, they are widely distributed on Mars and Venus . In addition, iron sulfides were identified on the Moon, as well as in meteorites .…”

Identification of inclusions in carbon steels using micro‐Raman spectroscopy

“…Similarly, the bands at 276 and 314 cm −1 in Fig. (d) are possibly related to the Raman modes of (Mn,Fe)S, which are at lower wavenumbers than those of MnS . Theoretically, the vibration frequencies of a diatomic molecule are reduced by increasing the atomic mass .…”

“…The shifts of Raman bands towards lower and higher frequencies due to the substitution of atoms with different mass have been widely reported in the investigation of various systems. In addition, it was believed that pure MnS is not Raman active because of the Fm3m symmetry of the rocksalt structure; therefore, it is reasonable to believe that the bands at 276 and 314 cm −1 are actually from a solid solution of monosulfide, which is most likely (Mn, Fe)S in the comet‐shaped inclusions. The weak shoulder band at approximately 334 cm −1 in Fig.…”