GeoRaman

The first edition of GeoRaman conference was organized in Paris (France) in 1986 by Prof. D. C. Smith. The following editions have been held all over the world: Valladolid (Spain) in 1999; Prague (Czech Republic) in 2002; Hawaii (USA) in 2004; Almunecar (Spain) in 2006; Gent (Belgium) in 2008; Sydney (Australia) in 2010; Nancy (France) in 2012; St. Louis (USA) in 2014; Novosibirsk (Russian Federation) in 2016; Catania (Italy) in 2018. GeoRaman 2020 was the 14th edition of the international biennial meeting devoted to the application of Raman spectroscopy to mineralogy, geology and earth sciences in broad sense. However, this edition was marked by the COVID19 pandemic. Initially, it should have been held in spring in Weihai (China), but the circumstances, with a worldwide confinement and strong travel restrictions, in what was the first wave of the pandemic focused on Asia, led to the hard decision to be made to move the meeting to Bilbao (Spain) and hold the conference in the fall. Unfortunately, the successive waves of the pandemic and the global uncertainty prevented the formal celebration of said meeting. Since the beginning of human history, man has been fascinated by looking at the sky and trying to understand its mysteries. Among all the celestial bodies that were admired in ancient times, Mars has always been among the most important, due to its observable size from Earth and to its characteristic reddish colour. Throughout its history, Mars has undergone very distinct chemical and geological processes, resulting in a notable diversity and variety in both physiography and mineralogical composition. Besides, the study of Mars is of special interest for the search of the existence of life on Mars due to its similarities with ancient Earth. In previous editions of GeoRaman, several research works were presented regarding the study of terrestrial analogues, minerals relevant to Mars and even biomolecules that could be present on its surface. The interest on Mars, from the Raman spectroscopy point of view, has been increasing since it was announced that for the first time in history, this technique was going to be included in the payloads of NASA's Mars2020 mission (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals, SHERLOC and SuperCam) and in ESA's EXOMARS mission (RLS instrument). The Perseverance rover is already conducting analysis on Mars, and the Rosalind Franklin rover is scheduled to do so shortly, as well as the JAXA's Raman spectrometer (RAX) on board of the Martian Moons eXploration (MMX) mission for in situ exploration of the Mars' moon Phobos. In the present edition, Xin et al.[1] highlighted the presence of manganese rich minerals that Curiosity and Opportunity rovers have found in sedimentary and basaltic outcrops at Gale and Endeavour craters on Mars, though the exact Mn-bearing mineral species and the related geologic processes still need to be confirmed and elucidated. However, the content of manganese seems to indicate the existence of Mn oxides rather than evaporites or other salts. Furthermore, hydrated manganese oxides were also observed in Martian breccia meteorites Northwest Africa 7034 and 7533. Nevertheless, due to the chemical complexities and often poor crystallinity of Mn-oxide group, there are still difficulties for the quick and accurate phase identification by any single spectroscopic method. In this work, they focus on the Raman analysis of several pure manganese oxides (α-MnO2, β-MnO2, γ-MnO2, δ-MnO2, α-Mn2O3, α-Mn3O4, γ-MnOOH) synthesized in laboratory. These analyses were complemented by scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDS), laser-induced breakdown spectroscopy, X-ray diffraction, mid-infrared spectroscopy and visible near-infrared spectroscopy. The produced dataset will facilitate the phase identifications of Mn-bearing minerals for future applications in Mars explorations missions (e.g., Tianwen-1 orbiter and Zhurong rover and Perseverance rover) as well as terrestrial and other planetary explorations. Ye et al.[2] presented an interesting work on the determination of the features of H2O2 as well as on the detection limits for them. Authors highlight that H2O2 has been detected in the Martian atmosphere and is supported even below the Martian surface. Thus, H2O2 is an important target that can be used to better understand the Martian surface environment and explore extraterrestrial life. They propose an accurate detection and analyses under Martian-relevant temperature conditions for aqueous solutions and mud mixtures. The low-temperature spectral features and ultraviolet (UV) decomposition characteristics of H2O2 are also investigated because low temperatures and UV radiation are key environmental factors that can affect the existence of H2O2 on the Martian surface. Veneranda et al.[3] presented a paper on the Analytical Database of Martian Minerals (ADaMM) project, an extended multianalytical database of mineral phases that have been detected on Mars or are expected to be found at the landing sites where the Mars2020/Perseverance rover is already operating, and ExoMars/Rosalind Franklin rover will do. The most valuable scientific contribution of this work is the use of laboratory prototypes simulating the analytical performances of the spectroscopic systems onboard the Mars 2020 and ExoMars rovers, that is, the Raman Laser Spectrometer (RLS) and SuperCam systems. The proposed dataset will be key in order to optimize the rover's scientific outcome, data treatment and interpretation. According to the authors, ADaMM will also provide access to data treatment and visualization tools developed in the framework of the mentioned space exploration missions. As such, the present work seeks to provide an overview of the ADaMM online platform, spectral tools and mineral collection. Linked to ADaMM online platform, López-Reyes et al.[4] provided a description of the ExoMars Simulator (RLS Sim), a flexible model of RLS instrument, onboard the Rosalind Franklin rover, that operates similarly to the actual instrument, both in laboratory and field conditions, while also emulating the rover operational constraints in terms of sample distribution that are relevant to the Raman analysis. This system can operate autonomously to perform RLS-representative analysis in one or several samples, making it very useful to perform heavy experimental tasks that would otherwise be impossible using a flight-representative model of the instrument. To evaluate the scientific capability of the RLS Sim, authors have compared it with a replica model of RLS, the RLS Flight Spare (FS). Several acquisition aspects, such as spectral range and resolution, the signal-to-noise ratio (SNR), have been evaluated. RLS Sim will be a key model to perform support science for the ExoMars mission and the RLS instrument on the Rosalind Franklin rover. In addition, Canora et al.[5] presented a work on a comparative overview of the performance of a set of Raman instruments, the RLS micro-Raman Laboratory Equipment, the RLS ExoMars Simulator and the RLS Engineering and Qualification Model (EQM) using Martian representative crushed samples, along with an evaluation of instrument performance as a function of the operational scenario. ExoMars 2022 rover will collect samples from different sites on the Oxia Planum plain, using a drill capable of penetrating the near subsurface and rocky outcrops to a depth of 2 m. Then samples are passed to the Analytical Laboratory Drawer (ALD), where the Sample Preparation and Distribution System (SPDS) processes and transports the crushed material into a refillable container, which is then presented to the analytical instruments for sample analysis. According to authors, the final sample grain distribution of the powder sample following the crushing and flattening processes is a critical aspect of the RLS instrument that has a direct impact on its overall performance, related to its mineral identification and operational capabilities. In this work, the RLS team confirms the capability of the RLS instrument performances, by acquiring good-quality spectra from crushed samples provided by the SPDS, whose science return can be further optimized when improving the RLS instrument operation sequence. As it has been mentioned before, the development of the science for the preparation of the mentioned missions is a hard but very important task. In this sense, Weber et al.[6] emphasized that missions to planetary bodies require innovative techniques for the in situ investigation of their surfaces, especially when landings are planned, and state that Raman spectroscopy as an excellent laboratory tool for rapid mineralogical analysis of both terrestrial and extraterrestrial rocks. However, when preparing such space missions, it is essential to be prepared for all possible outcomes, such as samples exhibiting space weathering (SW). In this work, authors study the influence of micrometeorite bombardment on bodies without atmosphere as one trigger of SW. This type of SW effect is simulated with an excimer laser irradiating the investigated samples. They focused the research on olivine, as possible components on Phobos, on pyroxene and their mixtures, analysed by Raman spectroscopy before and after laser irradiation. The characteristic Raman bands of the individual minerals in the spectra are not influenced by this kind of SW. Moreover, the fluorescence-dominated background signal induced by laser irradiation is reduced, facilitating a better interpretation of the individual mineral peaks. Moreover, another way to study our solar system and other planets is through the study of the meteorites that come from the space and fall to Earth's surface through its atmosphere. In the present edition of GeoRaman, several research works were presented on this topic. Cao et al.[7] presented a petrological and mineralogical analyses of Northwest Africa (NWA) 10720 meteorite, a Martian nakhlite with an unbrecciated augitic igneous cumulate texture, consisting of clinopyroxene and olivine set in a fine-grained intercumulus matrix. The results indicate that NWA 10720 has experienced at least two-stage magmatic activity before the eruption. Taking into account the minerals found in the meteorite, and how they are distributed, authors propose the mechanism of formation and the environmental conditions in which it occurred. Prieto-delaVega et al[8] also studied a NWA meteorite, in this case the Northwest Africa 10628 (NWA 10628), which is a shergottite found in Tindouf (Algeria) in 2014. As little was known on this meteorite, they performed a deep Raman characterization complemented by Micro-energy dispersive X-ray fluorescence imaging (μ-ED-XRF). The matrix of the meteorite is dominated by high-Ca pyroxenes, augite and diopside. Olivine and feldspars appeared as small crystals all along the matrix, while Merrillite was found as big crystals in inclusions. As whitlockite can be transformed into merrillite at high temperature and pressure, they suggest that merrillite in the meteorite was originally whitlockite, before its ejection from Mars. They also found minerals related to terrestrial weathering, as well as small anhydrite crystals in the bulk together with gypsum, probably from the partial dehydration of original Martian gypsum by the high-pressure/temperature of ejection. The mineral composition also suggests that ulvospinel could have been the Martian precursor of some of the minerals found. Huidobro et al.[9] proposed the characterization of the Roberts Massif (RBT) 04262 Martian meteorite. It was confirmed that the meteorite matrix is composed of pyroxene and plagioclase (converted to maskelynite due to the shock pressure). Olivine-coarse grains embedded in the matrix were also observed. These grains were coated by hydrated magnesium and calcium sulfates, which would belong to the Mars sulfate deposits or to the terrestrial weathering. Although the sulfates could be formed on Mars due to the oxidation of sulfides or elemental sulfur along the sulfur Mars cycle, their distribution along cracks and fractures confirm that are weathering products. However, other S-bearing compounds that belong to Mars were found, such as elemental sulfur and a thermally transformed iron sulfide. Merrillite and titanomagnetite were also detected. Voropaev et al.[10] presented a Raman spectroscopy and SEM study of a fragment of the Markovka (H4 chondrite) meteorite. Authors described a characteristic set of olivine and pyroxene, oxides such as maghemite and goethite, troilite and carbonates (aragonite). The structural features revealed by Raman spectroscopy allow to draw important conclusions on thermal history of the parent body including both the temperature experienced by the rock on the parent body and their cooling rate as well as the constraints on the size of the parent body and the Mg composition of the assumed fluid. Begunova et al.[11] presented an innovative study of multiwalled carbon nanotubes (MWCNTs) and haematite nanowires that can grow on Iron meteorites and pallasites, which contain a set of Fe–Ni alloys with various structural and elemental compositions. Authors use two meteorites: Chinga ataxite and the metal part of Seymchan (pallasite of the main group [PMG]). Alloys in meteorites are located close to each other; therefore, the influence of the regions bordering between the alloys on the synthesis of nanomaterials was observed. Authors got both MWCNTs and haematite nanowires on the surface of the submicron structure of the Chinga meteorite. They obtained a straight array of haematite nanowires on the surface of a γ-(Fe, Ni) alloy. As we have seen, the study of the solar system through Raman spectroscopy is an area of knowledge that has become very important in recent years. However, all the science that surrounds this subject would not have been possible without the application of this technique to the study of minerals and terrestrial rocks, since they have laid the methodological bases that are now applied in the study of minerals from other planets. In the present GeoRaman edition, several research works were presented regarding the analysis of minerals and ore deposits. For example, Zhukova et al.[12] pointed out the importance of rare-earth elements (REEs) and REE deposits due to their role in the high-tech industry. The REE deposits commonly host REEs in fine-grained mixtures of phosphate minerals characterized by the variable content of volatile components. Authors used Raman spectroscopy, due to the advantages that present over other techniques, to study laterite and carbonatite samples from the Mount Weld deposit, one of the major REE deposits in Western Australia. The hydrous REE phosphate, rhabdophane, could be distinguished from monazite by the presence of peaks in the region 2800–3600 cm−1. Hydroxyfluorapatite was found in carbonatite. The Raman spectra and composition of silcrete and carbonatite apatite were similar; thus, silcrete apatite was identified as hydroxyfluorapatite as well. In addition, the aluminophosphate florencite was characterized and together with rhabdophane was identified in fine-grained mineral mixtures. Authors demonstrated that combining Raman spectroscopy with compositional data, it is possible to characterize phosphate minerals in REE deposits. Grishina et al.[13] reported the new occurrence of cesanite in quite different geological site within sulfate-rich melt inclusions in chloride segregations from kimberlites of Udachnaya-East pipe (Siberia). Cesanite (Ca2Na3(OH)(SO4)3) is a rare mineral found in a few places restricted to a geothermal field and caves. Micro-Raman spectroscopy and SEM-EDS studies distinguished two halite generations: сesanite free and сesanite-bearing, in concentrically zonal segregations according to the results of the mineral and sulfate melt inclusion. Authors applied the Raman spectroscopy and first principles calculations to understand structural and vibrational properties of cesanite daughter mineral in polyphase sulfate inclusions, and they report OH stretching vibrations for the first time. The study aims to clarify the source of the Na-S-Cl-enrichment in the Udachnaya-East pipe, which is highly discussed. Petrology, field and experimental volcanology was also an important field of knowledge present in GeoRaman conference. Sharygin et al.[14] stated that identifying the composition of primary/primitive mantle melts is crucial for understanding the mantle's evolution and mantle-derived magmatism. In this sense, melt inclusions in mantle xenoliths provide key information about such melts. Authors used confocal Raman spectroscopy to characterize mineral assemblage of unexposed crystallized secondary melt inclusions in the olivine from the xenoliths of the sheared garnet peridotites from the Bultfontein kimberlite pipe (Kimberley cluster, Kaapvaal Craton, South Africa). The studied peridotites originated from 112- to 146-km mantle depths. Even though 16 minerals were identified among daughter crystals, several more daughter minerals gave distinct Raman spectra, but they were not determined due to the lack of similar spectra in the databases. This fact, unfortunately, points out that there is much work to be done regarding the development of Raman spectra databases. The results showed that carbonates were predominant among the daughter minerals in the melt inclusions, with two possible models for the origin of these melt inclusions. This melt is genetically related to the kimberlite magmatism that formed the Bultfontein pipe and points at the alkali-rich carbonate composition of primary kimberlite melt. Finocchiaro et al.[15] analysed a group of zeolites coming from areas of the Ionian coast and Palagonia village (Eastern Sicily) by means of in situ Raman spectroscopy as well as by using laboratory micro-Raman to compare the results. Zeolites are present in numerous outcrops of volcanites of different ages in Sicily (Italy). Some of these outcrops are important because they constitute the ideal genesis conditions of some of these minerals, which represent geological indicators of chemical and geothermal gradients involved during their formation. In the geological record, these areas have been influenced by intense volcanic events that produced mineralization of hydrothermal origin. Satisfying results were obtained with portable devices, whose identifications were confirmed by micro-Raman measurements, discerning zeolites of different groups, such as analcime, chabazite, natrolite and phillipsite. In the work by Cassetta et al.,[16] a Raman study of a set of synthetic-basalt glasses was presented, in which the occurrence of small chemical variations appreciably affects their glass transition temperature. Basalts are among the most abundant igneous rocks on Earth, and they are increasingly used as raw materials in glass and ceramic technology due to their unique physicochemical properties. The characteristics of basalts, like the glass transition temperature, are strongly controlled by their structure, which is a function of composition. Therefore, the investigation of the interplay between the intimate structure and the mechanical and physical properties of basalt glasses is of paramount importance in view of their industrial exploitation. Authors showed the existence of a scaling law for the so-called boson peak of four synthetic-basalt glasses, and they infer from its breakdown the occurrence of a deep reorganization of the glass structure resulting from the Na–K replacement in the network, despite small variations of the other major elements. Gemology is another important field of application of Raman spectroscopy. In this sense, in the work by Coccato et al.,[17] a Raman study of Tanzanite was presented. Tanzanite is the blue to violet-blue variety of the sorosilicate zoisite. Its colour makes it a highly appreciated gemstone. In this work, zoisite samples and cut tanzanite gemstones were considered because zoisite Raman spectra are rarely reported in literature and never with a systematic approach. Orientational effects were observed in the spectra, and the photoluminescence bands were differentiated from the Raman signals using different excitation wavelengths. Both portable and laboratory Raman instruments showed comparable performances, opening the way to an effective identification of mounted tanzanite gemstones in jewels. Gemology is sometimes linked to the analysis of artworks and samples of high value. Karampelas et al.[18] analysed 19 green-coloured gems adorning a cross-shaped pendant from the end of 19th century belonging to Einsiedeln Abbey (Switzerland). Using a combination of spectroscopic and microscopic methods, the samples were adequately identified as natural emeralds, with Colombia as their most probable source. In fact, Raman band characteristics of beryl were observed in all samples with a 532-nm laser excitation. In adition, Raman spectra of the samples with a 785-nm laser at higher wavenumber found to be similar to emeralds containing low concentration of alkali elements. The application of Raman spectroscopy in art, archaeology and restoration/conservation works is still a prominent field of knowledge in which Raman analysis plays an important role and whose results are the keys. Rousaki et al.[19] used micro-Raman spectroscopy for the analysis of samples collected from the shelters Campo Cerda 1, Angostura Blanca and Campo Moncada 1 located in Piedra Parada valley, Chubut province, Argentinian Patagonia. Different coloured layers, degradation products and rock supports were analysed. According to the results, authors stated that haematite, goethite, green earth and gypsum were responsible for the main colouration of the pigmented layers together with other components. Gypsum, calcium oxalates and calcite were the major degradation materials affecting the rock paintings and the rock support. Wang et al.[20] studied by micro-Raman spectroscopy the nature of the rusty oil spot pattern of a bowl fragment from Linfen kilns, famous for its oil spotted glazed ware production. The distribution in the glaze of haematite crystals of polygonal shape found in the spots at the glaze surface and around bubbles in the cross section of the glaze suggests that nucleation seeds and small crystals are carried towards the surface by the rise of bubbles during the heating step of the firing. Besides, the degree of the glaze polymerization indicates a firing temperature lower than 1300°C, consistent with the archaeological data. However, Raman spectroscopy is not only suitable for the analysis of inorganic samples but is also very useful in the analysis of organic samples. For example, Quintero Balbas et al.[21] used Raman spectroscopy combined with multivariate analysis to study noninvasively naturally and artificially aged samples of silk and wool fibres dyed with turmeric and saffron dyes, following historical recipes, as well as a historical wool sample coming from a 19th-century Persian carpet. The Raman spectra (at 785 and 1064 nm) obtained from all the samples showed the characteristic peaks of each dye and fibre. The 1064-nm macro FT-Raman offered more information regarding the degradation of the fibre substrate, whereas the μ-Raman at 785-nm spectra proved more suitable in the identification of dye characteristic peaks. The results suggest saffron has a higher light fastness than turmeric and that silk fibres suffer higher fading and more evident degradation than wool. Beyond the characterization of materials that can be found in works of art, Raman spectroscopy has turned out to be very useful in monitoring restoration works and how it affects the application of new materials. On the one hand, Costantini et al.[22] applied Raman spectroscopy for the diagnostic study of some commercial mortars applied to the outside of Punta Begoña Galleries, a historical building located in a coastal environment (Basque Country, Northern Spain) with industrial activities. The obtained results were very useful to understand the deterioration processes in order to study the atmospheric impact that aggressive environments have on modern material in a relatively short period after their application. Among the decay products, gypsum was identified together with sodium nitrate in a minor amount. The presence of magnesium-based secondary products, nitromagnesite and dypingite, was also found formed by the degradation of original magnesium compounds of the mortars. The presence of the degradation compounds was studied considering the orientation of the walls where the commercial mortars were placed. Besides, Raman analyses showed the presence of astaxanthin, which is a bioindicator of pollution level because it appears as the first xanthophyll in highly contaminated areas. On the other hand, Caggiani et al.[23] applied Raman spectroscopy to the study of alkali-activated materials (AAMs) and ‘geopolymers’, which have emerged as a greener alternative to traditional concrete, for large-scale as well as for niche applications such as conservation and restoration of built heritage. In this work, authors apply Raman spectroscopy both to aluminosilicate precursors (metakaolin, pumice, volcanic ash, volcanic soils, clayey sediments, ceramic waste) and to the respective AAMs. The results, differentiated according to the employed precursors, exhibit spectra relative to crystalline and amorphous phases that can give an indication about the newly formed aluminosilicate gel. In recent years, the study of the biocolonization of minerals and rocky areas has taken on great importance, both in the area of art and archaeology, as well as in issues related to the possible presence of life on other planets. For example, Němečková et al.[24] investigated microbial colonizations of gypsum from different sites from Southern Sicily and Eastern Poland using laboratory-based Raman micro-spectrometers and portable Raman spectrometric devices. Authors describe selected zones of microbial colonizations of few types of gypsum from the point of view of the presence of algae and cyanobacteria. Common microbial pigments were detected, such as carotenoids (common Raman bands at around 1525, 1157 and 1004 cm−1). Raman spectra of other pigments were recorded in several zones using near infrared excitation (785 nm) such as chlorophyll (1326, 1285, 1188 and 745 cm−1), scytonemin (1593, 1552, 1438 and 1173 cm−1) and phycobiliproteins (1275 cm−1). Raman microspectrometric investigations of colonizations allow to gather detailed information about pigment distribution in micrometric zones of gypsum samples. In the field of carbon capture and storage (CCS), the role of impurities likely injected with CO2 has to be tackled in order to assess the long-term behaviour of the storage. Sterpenich et al.[25] pointed out that unfortunately, the thermodynamic properties of sulfur and nitrogen oxides gases (SOx and NOx), which would be possibly injected with CO2 depending on the origin of CO2, in saline aquifer are poorly known. In fact, solubility is one of the key parameter to be implemented in geochemical codes modelling long-term evolution of the aquifer after injection. As the solubility of NO is known only at atmospheric pressure, authors proposed a study of the solubility of NO in water and NaCl solutions measured by Raman spectroscopy in the ranges 295–373 K and 2–60 MPa using a high pressure optical cell and after calibration on a few data from molecular simulations. The results showed a decrease of solubility when temperature increases and when salinity increases. Besides, no modification of NO speciation was observed. Following with the application of Raman spectroscopy in the analysis of gases, Tanichev and Petrov[26] highlighted the usefulness of this kind of studies in the in situ analysis of natural gas. They presented two methods for simulating the ν2 Raman band of methane at any spectral resolution and pressure. The first method is based on the use of the spectroscopic parameters of each single line (position, intensity, broadening and shift coefficient), while the second one was based on the use of the spectral profiles, each of which replaces a group of lines. It is necessary to take into account the pressure effect on the spectrum of methane to improve the accuracy of the technique. A comparison of the calculated and measured spectra with a resolution of 0.5 and 7 cm−1 was performed. It was shown that the differences do not exceed 5% for each method in the range of 1–60 atm. Other aspects more related to the singularities of the Raman technique and practical aspects of the analysis are also of interest to GeoRaman. Foucher[27] pointed out that, since micro-Raman spectrometer systems use microscope objectives to focus the laser onto the sample to be analysed, although this method drastically increases the spatial resolution, this focused laser beam may heat and alter the studied material. Author describes the different parameters that influence thermal increase induced by the laser and proposes easy to make experiments to measure them. Author demonstrated that, except for very thin samples or powdered materials, the relevant parameters to consider are the laser power at the sample surface and the duration of exposure to the laser beam, whatever the objective used. In contrast, whereas the risk of sample alteration is almost non-existent for thick transparent materials, for semi-transparent materials, alteration may occur at lower laser power for low magnification objectives than for high magnification objectives. These results are explained by the high aperture angle of microscope objectives which induces high dispersion of the laser within the sample. We would like to thank all the participants (providing great help in the back-ground), the local organizing committees, members of GeoRaman international science advisory committee, University of the Basque Country (UPV/EHU) and Shandong University for their support. We would like to thank all our sponsors: BWTek and Renishaw. We are grateful to the Editor-in-Chief of the Journal of Raman Spectroscopy Prof. Laurence Nafie for approving this special issue and to Wiley for their support. We truly thank all the authors and reviewers of the manuscripts for their invaluable contributions. We are looking forward to see you at the next GeoRaman conference in 2022 in Prague.