ABSTRACT
The pumice volcanic samples could have possible connections to the evolution of life and give us insight about their bio-geochemical processes related. In this regard, the samples from the volcanic eruption from La Restinga (El Hierro, Spain) in 2011 have been mainly studied by means of Raman spectroscopy. The research also includes analysis of XRD, Scanning Electron Microscopy and Optical Microscopy to support the Raman analysis. The results show that the Raman methods and mineral analyses are in strong agreement with the results obtained from other authors and techniques. The internal white foamy core (WFC) of the studied pumice samples shows amorphous silica, Fe-oxides, Ti-oxides, quartz, certain sulfates, carbonates, zeolites and organics. On the other hand, the external part (dark crust - DC) of these samples mainly presents primary-sequence mineralogy combined with some secondary alteration minerals such as olivine, feldspar, pyroxene, amorphous silica, and Fe-oxide. Raman spectroscopy detected other minerals not yet reported on these samples like barite, celestine and lepidocrocite. Also, the different chemometric and calibration methods for Raman spectroscopy in elemental composition, mineral classification and structural characterization has been successfully applied. From the astrobiological perspective, the research was also complemented with comparisons to other similar samples from terrestrial analogs. The main consideration was taking into account the proposed hypothesis regarding the potential behavior of the pumice as a substrate for the evolution of life. Furthermore, the detailed analysis from La Restinga eruption is coherent with the mineral phases and processes discussed from previous literature. The white internal part fulfills the conditions to work as an organic reservoir, confirmed by the detection of organic matter and selected minerals that could be used as energy sources for bacterial communities. The external layers of the samples work as a shielding layer to protect the organics from decay in extreme conditions. Finally, here we have demonstrated that the characteristics and advantages of Raman spectroscopy could help to assess and understand the possible biogenicity and alteration processes of any geological sample to be found on Mars.
Subject(s)
Exobiology , Geologic Sediments/analysis , Minerals/analysis , Spectrum Analysis, Raman/methods , X-Ray DiffractionABSTRACT
The secondary products of an arsenopyrite-bearing mine waste dump were characterized in order to ascertain their mineralogical, chemical and environmental features and to appraise their role in the abatement of As in the environment. To this purpose, representative surface samples of weathered sulfides (including cemented phases) and hardpan samples were collected and studied by X-ray powder diffraction (XRD), polarized light microscopy, electron microprobe analysis (EMPA), micro-Raman spectroscopy and digestion, extraction and leaching methods. Scorodite, amorphous ferric arsenates (AFA), elemental sulfur, hydronium jarosite, goethite, hematite and hydrous ferric oxides were the secondary products identified in the mine wastes. The hardpan was mainly constituted by gangue minerals, including sulfides (arsenopyrite and pyrite/marcasite) with different weathering degrees, cemented by cracked yellow phases corresponding to AFA with Fe/As molar ratios of 1.14-1.85 and elemental sulfur. These cracked compounds were also the binding agent in the other cemented phases. Hydronium jarosite and Fe (oxyhydr)oxides were enriched in As, showing values of 0.19-3.98 and 0.81-7.49 wt.% As2O5, respectively. The As leachability and lability from hardpan and cemented phases were not decreased as compared to those from the other weathered phases not showing cementation in the mine waste dump.
ABSTRACT
We test the capabilities of in situ Raman spectroscopy for non-destructive analysis of degradation processes in invaluable masterpieces, as well as for the characterization of minerals and prehistoric rock-art in caves. To this end, we have studied the mechanism of decay suffered by the 15th-century limestone sculptures that decorate the retro-choir of Burgos Cathedral (N Spain). In situ Raman probe detected hydrated sulfate and nitrate minerals on the sculptures, which are responsible for the decay of the original limestone. In addition, in situ Raman analyses were performed on unique speleothems in El Soplao Cave (Cantabria, N Spain) and in the Gruta de las Maravillas (Aracena, SW Spain). Unusual cave minerals were detected in El Soplao Cave, such as hydromagnesite (Mg5(CO3)4(OH)2·4H2O), as well as ferromanganese oxides in the black biogenic speleothems recently discovered in this cavern. In the Gruta de las Maravillas, gypsum (CaSO4·2H2O) was identified for the first time, as part of the oldest cave materials, so providing additional evidence of hypogenic mechanisms that occurred in this cave during earlier stages of its formation. Finally, we present preliminary analyses of several cave paintings in the renowned "Polychrome Hall" of Altamira Cave (Cantabria, N. Spain). Hematite (Fe2O3) is the most abundant mineral phase, which provides the characteristic ochre-reddish color to the Altamira bison and deer paintings. Thus, portable Raman spectroscopy is demonstrated to be an analytical technique compatible with preserving our cultural and natural heritage, since the analysis does not require physical contact between the Raman head and the analyzed items.
