A wide range of natural K-, Na-, Ca- or (K + Li)-micas have been systematically examined by Raman spectrometry. The spectra are interpretable in terms of regular variations in peak positions and chemical parameters. Several vibrations give higher wavenumbers for Na-micas compared to K-micas, in accord with the smaller ionic size of Na+ than K+. The ≈195 cm-1 and ≈270 cm-1 peak wavenumbers and intensities vary as functions of the chemistry of the octahedral sites, i.e. the replacement of Mg2+ by Mn2+, Zn2+, Cr3+, Fe3+, Ti4+, and especially by Al3+, or by a vacancy, and the replacement of (OH)- by F-. The group of ≈700 cm-1 peaks vary in wavenumber and intensity with the replacement of Si by Al in the tetrahedra; distinct Si-O-Si and Si-O-Al vibrations can be recognized. Di- and tri-octahedral micas are distinguished on the basis of certain relative peak intensities which vary considerably with polarization direction, and of trends with increasing Al(iv), Al(vi) or Al(tot.). Calibration of these trends for the chemical analysis of mica microinclusions seems feasible once the uncertainties in the data set are resolved by the determination of further samples selected to highlight the effect of specific elements.

The haüynophyre emitted from a parasitic vent of the Vulture stratovolcano is a S- and Cl-rich, leucitemelilite- bearing lava flow containing an unusually large amount of sodalite-group minerals (>23 vol.%). Mineralogical and chemical study of phenocrysts has led to the identification of black haüynes, blue lazurites and of Cl-rich white or black noseans. X-ray diffraction (XRD) study confirms the occurrence of nosean having a low symmetry (P23). Raman spectra and XRD data show that S is fully oxidized to SO4 in black haüynes and in white noseans, while it is partly reduced to form S3– groups in blue lazurites, which also contain H2O molecules. Structural and chemical data strongly question the validity of the Hogarth and Griffin (1976) method widely used to resolve the ratio S6+/S2– in sodalite-group phases from EMPA data. Among euhedral phenocrysts, large lazurites are only faintly zoned. All other phases show variable core-rim chemical zoning and many phenocrysts are partially resorbed and/or colour-zoned. Black haüynes have highly variable S/Cl and slightly lower SiO2/Al2O3 ratios, larger FeTOT contents and more compatible trace elements than lazurites. Thin opaque noseansodalite rims surrounding all crystals are interpreted as a result of rapid crystallization driven by exsolution of a S-scavenging fluid phase. We suggest that the extreme complexity of the mineralogical assemblage reflects variable aSiO2 and aH2O of the silicate melts.

Raman spectrometry has been established as an instrument of choice for studying the structure and bond type of known molecules, and identifying the composition of unknown substances, whether geological or biological. This versatility has led to its strong consideration for planetary exploration. In the context of the ExoGeoLab and ExoHab pilot projects of ESA-ESTEC & ILEWG (International Lunar Exploration Working Group), we investigated samples of astrobiological interest using a portable Raman spectrometer lasing at 785 nm and discuss implications for planetary exploration. We find that biological samples are typically best observed at wavenumbers >1100 cm−1, but their Raman signals are often affected by fluorescence effects, which lowers their signal-to-noise ratio. Raman signals of minerals are typically found at wavenumbers <1100 cm−1, and tend to be less affected by fluorescence. While higher power and/or longer signal integration time improve Raman signals, such power settings are detrimental to biological samples due to sample thermal degradation. Care must be taken in selecting the laser wavelength, power level and integration time for unknown samples, particularly if Raman signatures of biological components are anticipated. We include in the Appendices tables of Raman signatures for astrobiologically relevant organic compounds and minerals.