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Organic matter (OM) entrapped in calcite is regularly used for environmental studies; however, insertion mechanisms and types of interaction remain poorly understood. The present study used a new methodology to investigate interactions between OM and the calcite matrix during crystallization processes with humic acid (HA) entrapment. A multimethod approach confirmed that HA is both adsorbed onto the calcite surface and incorporated into the calcite lattice during crystallization. Our results also confirm the log-linear correlation between fluorescence intensity and calcite matrix HA concentration. Fourier transform infrared spectroscopy showed that HA in colloidal conformation is adsorbed onto the calcite surface as a result of the structure of the OH stretching band. We also developed a new method based on synchrotron analysis that uses sulfur as a tracer element for entrapped HA and that localizes the OM electrostatically adsorbed onto the calcite surface. Changes in the sulfur environment, determined using X-ray absorption near-edge structure spectroscopy, indicated more complex insertion mechanisms than simple adsorption of HA during calcite crystallization. Desorption experiments revealed the stability of the OM atomic structure and its layered nature. These results allowed us to draw up a general model of OM insertion in calcite.

abst R a C t Results of the investigation of paleontological blue and gray bone fragments of small vertebrates coming from stratigraphic layer 770 at San Josecito Cave (Nuevo Leon, Mexico, dating between 28 000 and 19 000 years BP), are presented. Structural and elemental analyses combining X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and particle-induced X-ray and γ-ray emission (micro-PIXE/PIGE), as well as spectroscopic investigations [i.e., UV/visible/near-IR reflectance spectroscopy and X-ray absorption near-edge structure (XANES) spectroscopy] were performed to identify precisely the origin of the blue stain. Prior research has shown that Mn 5+ in tetrahedral coordination could be responsible for the turquoise blue color in mastodon ivory some tens of million years old that was modified by a heat process. Manganese is present in the anionic form of (MnO4) 3– and partially substitute for (PO4) 3– in the hydroxyapatite matrix. The spectroscopic data of the present study have revealed a heat-induced modification, revealed traces of Mn among the typical bone constituents (Ca, P, Sr, Zn), and provided insights into the color origin of the blue paleontological bones from San Josecito Cave. Cations of Mn 5+ in a tetrahedral environment of four O 2– ions in the apatite structure are found in these bones, the same color origin as in the blue mastodon ivory. As indicated by XANES, Mn 4+ ions in octahedral coordination as in pyrolusite are found in gray bones. The presence of submicroscopic Mn oxide inclusions might explain the color of the San Josecito gray bones. The formation of Mn 5+ very likely is induced by heat treatment of the bones under oxidizing conditions. The heat-induced modification of both types of paleontological bones also is indicated by the direct observation of apatite crystals using TEM. The question remains, however, how the heat originated inside the cave.

The formation of subsequent layers of calcium carbonate (CaCO3) in karst caves is a well-known phenomenon observed especially on the prehistoric paintings in the Large Cave (Grande Grotte) of Arcy-sur-Cure, in France. About 40 natural samples coming from the Large Cave were already investigated in a previous work and classified as a function of their crystal morphology, texture, composition and appearance. The presence of at least two calcite types was revealed on the walls: translucent and opaque white or grey calcites. The latter opaque calcites completely obstruct the paintings. The formation of these different calcites depends on various geochemical and geophysical parameters and could also be influenced by biotic processes. Questions remain about formation mechanisms leading to different calcite types and, in particular, about the role of micro-organisms as well as interactions between prehistoric paint layers and calcite layers. Additional natural calcites were studied in order to confirm the first classification. Various syntheses of abiotic calcite were performed to study the influence of environmental parameters on calcite growth. Moreover, several series of biotic calcite were synthesised in a specific medium with two bacteria isolated from the cave in order to test their calcifying properties. All natural and synthetic samples were analysed using complementary microanalytical laboratory techniques. Micro-x-ray fluorescence analysis (micro-XRF) and x-ray absorption near-edge structure spectroscopy (XANES) based on synchrotron radiation also enabled a more detailed distinguishing of different minerals within the complex biotic and abiotic mixtures and layered synthetic samples at microscopic scale. Comparison of natural and synthetic samples gives more detailed insights into the formation mechanisms of the different calcite types found in the Grande Grotte and allows proposing an adapted conservation strategy of its prehistoric paintings. Copyright © 2008 John Wiley & Sons, Ltd.

Manganese oxihydroxide behaviour has been studied under heat treatment to understand the transformation mechanisms and subsequently to gain insights into the preparation procedures of black painting materials during the Palaeolithic period. These manganese oxihydroxides have been studied as a function of heat treatment by TEM, XRD, DTA and FTIR and XANES (Mn K-edge) spectroscopies. These materials have been used as black pigments during the Palaeolithic period to realise rock art paintings such as in Lascaux (Dordogne, France) and Gargas (Midi-Pyre´ne´ es, France). Specific morphological, chemical and structural criteria were determined to distinguish between natural and heat-treated pigments.

Analysis of archeological materials aims to rediscover the know-how of prehistoric men by determining the nature of the painting matter, its preparation mode, and the geographic origin of its raw materials. The preparation mode of the painting matter of the paleolithic rock art apparently consisted of mixing, grinding, and also heat-treatment.

Analyses of archaeological materials attempt to rediscover the know-how of Prehistoric men by determining the nature of the matter, its preparation mode, and its geographic origin. The preparation mode of painting matter of Palaeolithic rock art consisted not only in mixing and grinding but also in heat-treatment. Palaeolithic painters used two main colors: red (iron oxide, hematite) and black (charcoal or manganese oxide). The different phases of manganese oxides can be distinguished using their elemental composition, their structure and the oxidation state of the Mn ion (II, III, IV). Their transformation during heat-treatment has been studied on mineralogical reference samples by means of transmission electron microscopy (TEM) either coupled or not with a heating stage (in situ). These studies have enabled us to understand the transformation mechanisms of manganese oxides and also to gain insights into the preparation procedures of painting materials during the Palaeolithic period. The painting samples studied in this paper come from the cave of Lascaux (Dordogne, France). These studies allow us to distinguish between natural or heat-treated manganese oxides.

International audience; Archaeologists have attempted the interpretation of rock art, but have often disregarded the technical aspects of paints. Analysing paint samples for preparation techniques and studying the various compounds used, allows us to determine the technology of early painters. Palaeolithic artists used two main colours: red (iron oxide: natural hematite or heated goethite) and black (charcoal or manganese oxides). These pigments could be prepared in different ways (grinding, mixing with extender and/or binder or by heating) in order to enhance the properties of the paints. Analyses attempt to determine the physicochemical nature of the matter and its preparation mode, and to get an idea of its geographic origin. This paper presents techniques and methods used in the C2RMF laboratory for manganese oxide pigments. Distinction between manganese oxides with or without other cations is made and heat treatment of manganese oxide minerals is described. Results obtained for black pigment in Lascaux and Ekain caves are presented and discussed. From paint analyses, several conclusions are drawn concerning the technical level of Palaeolithic artists.

International audience; Sulfur compounds are often present in petrochemical wastewater and can be detected by UV spectrophotometry. This technique allows to point out specific absorptions of mineral sulfide and mercaptans and can be used for the determination of acidity constants. From a quantitative point of view, using a spectral deconvolution method, a specific determination of some mercaptans is obtained. Detection limits for ethanethiol and thiophenol are 0.7 and 2.5 mg l−1, respectively.

High-resolution manganese and iron K-edges XANES spectra were collected on several samples of archeological interest: prehistorical paintings and medieval glasses. XANES spectra were collected at the ID21 facility (ESRF, Grenoble, France) using a micro-beam device and at the 11-2 beamline (SSRL, Stanford, USA) using a submillimetric beam. The medieval glasses studied are from gothic glass windows from Normandy (XIVth century). The aim of this study is to help understand the chemical durability of these materials, exposed to weathering since the XIVth century. They are used as analogues of weathered glasses used to dump metallic wastes. These glasses show surficial enrichment in manganese, due to its oxidation from II (glass) to III/IV (surface), which precipitates as amorphous oxy-hydroxides. Similarly, iron is oxidized on the surface and forms ferrihydrite-type aggregates. The prehistorical paintings are from Lascaux and Ekain (Basque country). We choose in that study the black ones, rich in manganese to search for potential evidences of some 'savoir-faire' that the Paleolithic men could have used to realize their paint in rock art, as shown earlier for Fe-bearing pigments. A large number of highly valuable samples, micrometric scaled, were extracted from these frescoes and show large variation in the mineralogical nature ofmore » the black pigments used, from an amorphous psilomelane-type to a well-crystallized pyrolusite. Correlation with the crystals morphology helps understanding the know-how of these early artists.« less

Biosynthetic calcite samples were investigated using combined synchrotron X-ray microspectroscopy mapping. These samples were prepared with bacteria isolated from the Large cave of Arcy-sur-Cure in which prehistoric figures are masked by an opaque calcite layer. The biotic or abiotic origin of this layer is the issue of the present work. As previously known, a large community of bacteria may be involved in the CaCO3 formation in caves. A mixture of calcite/vaterite was obtained from bacteria isolated from the cave. Therefore, we can offer conclusions on their calcifying capability. The rare presence of vaterite in cave environments may be treated as a marker of biotic carbonate formations. Moreover, an amorphous calcium phosphate phase was present in the form of a calcite/vaterite mixture in the biotic model samples. This mixture of phases could be used as a tracer of the biotic process of CaCO3 formation. These biotic tracer phases were not identified using the applied analytical methods in the natural samples taken from the opaque calcite layers that covered the prehistoric figures of the Large cave. In this case, based on the obtained results, the biotic calcite formation process is likely to be considered as an undetectable effect at minimum.

Reaction between dissolved water and sulphide was experimentally investigated in soda-lime-silicate (NCS) and sodium trisilicate (NS3) melts at temperatures from 1000 to 1200 °C and pressures of 100 or 200 MPa in internally heated gas pressure vessels. Diffusion couple experiments were conducted at water-undersaturated conditions with one half of the couple being doped with sulphide (added as FeS or Na 2 S; 1500–2000 ppm S by weight) and the other with H 2 O (∼3.0 wt.%). Additionally, two experiments were performed using a dry NCS glass cylinder and a free H 2 O fluid. Here, the melt was water-saturated at least at the melt/fluid interface. Profiling by electron microprobe (sulphur) and infrared microscopy (H 2 O) demonstrate that H 2 O diffusion in the melts is faster by 1.5–2.3 orders of magnitude than sulphur diffusion and, hence, H 2 O can be considered as a rapidly diffusing oxidant while sulphur is quasi immobile in these experiments. In Raman spectra a band at 2576 cm −1 appears in the sulphide – H 2 O transition zone which is attributed to fundamental S–H stretching vibrations. Formation of new IR absorption bands at 5025 cm −1 (on expense of the combination band of molecular H 2 O at 5225 cm −1 ) and at 3400 cm −1 was observed at the front of the in-diffusing water in the sulphide bearing melt. The appearance and intensity of these two IR bands is correlated with systematic changes in S K-edge XANES spectra. A pre-edge excitation at 2466.5 eV grows with increasing H 2 O concentration while the sulphide peak at 2474.0 eV decreases in intensity relative to the peak at 2477.0 eV and the feature at 2472.3 eV becomes more pronounced (all energies are relative to the sulphate excitation, calibrated to 2482.5 eV). The observations by Raman, IR and XANES spectroscopy indicate a well coordinated S 2− – H 2 O complex which was probably formed in the glasses during cooling at the glass transition. No oxidation of sulphide was observed in any of the diffusion couple experiments. On the contrary, XANES spectra from experiments conducted with a free H 2 O fluid show complete transformation of sulphide to sulphate near the melt surface and coexistence of sulphate and sulphide in the center of the melt. This can be explained by a lower H 2 O activity in the diffusion couple experiments or by the need of a sink for hydrogen (e.g., a fluid which can dissolve high concentration of hydrogen) to promote oxidation of sulphide by H 2 O via the reaction S 2− + 4H 2 O = SO 4 2− + 4H 2 . Sulphite could not be detected in any of the XANES spectra implying that this species, if it exists in the melt, it is a subordinate or transient species only.

Journal of physics / Conference Series 186, 012084 (2009). doi:10.1088/1742-6596/186/1/012084, Iron mineral containing sensory dendrites in the inner lining of the upper beak of homing pigeons [1] and various bird species [2] are the first candidate structures for an avian magnetic field receptor. A new concept of magnetoreception [3, 4] is based on detailed ultra-structural optical and electron microscopy analyses in combination with synchrotron radiation microscopic X-ray fluorescence analysis (micro-XRF) and microscopic X-ray absorption near edge structures (micro-XANES). Several behavioral experiments [5, 6] and first mathematical simulations [6] affirm our avian magnetoreceptor model. The iron minerals inside the dendrites are housed in three different subcellular compartments (bullets, platelets, vesicles), which could be clearly resolved and identified by electron microscopy on ultrathin sections [1, 3]. Micro-XRF and micro-XANES data obtained at HASYLAB beamline L added information about the elemental distribution and Fe speciation [3], but are averaged over the complete dendrite due to limited spatial resolution. Here we present recently performed micro-XRF maps with sub-micrometer resolution (ESRF ID21), which reveal for the first time subcellular structural information from almost bulk-like dendrite sample material. Due to the thickness of 30 μm the microarchitecture of the dendrites can be considered as undisturbed and artefacts introduced by sectioning might be widely reduced., Published by IOP Publ., Bristol

International audience; High-resolution manganese K-edge XANES spectra were collected on a set of 40 Mn-bearing minerals. The pre-edge feature information (position, area) was investigated to extract as much as possible quantitative valence and symmetry information for manganese in various "test" and "unknown" minerals and glasses. The samples present a range of manganese symmetry environments (tetrahedral, square planar, octahedral and cubic) and valences (II to VII). The extraction of the pre-edge information is based on a previous multiple scattering and multiplet calculations for model compounds. Using the method described in this study, a robust estimation of the manganese valence could be obtained from the pre-edge region at 5% accuracy level. This method applied to twenty "test" compounds (such as hausmannite and rancieite) and to fifteen "unknown" compounds (such as axinite and birnessite) provides a quantitative estimate of the average valence of manganese in complex minerals and silicate glasses.

Analyses of archaeological materials aim to rediscover the know‐how of Prehistoric people by determining the nature of the painting matter, its preparation mode, and the geographic origin of its raw materials. This study deals with identification of manganese oxides in black pigments by micro‐XANES (X‐ray absorption near‐edge structure) based on previous TEM (transmission electron microscopy) studies. Complex mixtures of the manganese oxides studied are present in some of mankind’s oldest known paintings, namely those from the caves of Lascaux (Dordogne, France) and Ekain (Basque country, Spain). Scarce manganese oxide minerals, including groutite, hausmannite, and manganite, were found for the first time in Paleolithic art at these archaeological sites. Because there are no known deposits of such minerals in these areas, more distant origins and trade routes are inferred. The closest known Mn‐rich geological province for Lascaux is the central Pyrenees, which is ≈ 250 km from the Dordogne area.

International audience; The ‘Grande Grotte' cave at Arcy-sur-Cure (Yonne, France) with its prehistoric paintings shows important calcite concretions. Two types of calcite have been observed on the wall: translucent yellowish layers and opaque white or grey layers that completely obstruct the paintings. Other calcite types are present in the lakes of the cave (floating calcite rafts at the surface of the lake and soft calcite at the bottom of the lake). The morphology of the different calcites was observed at different scales by optical microscopy with normal and polarized light, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The elemental composition was measured by using particle-induced X-ray emission (micro-PIXE) and the structure by X-ray diffraction (XRD), infrared (FT-IR) and Raman spectroscopy. The bacterial diversity and its role in calcite formation were assessed by culture and 16S-SSCP in order to distinguish and to assess various abiotic and biotic formation mechanisms. The investigation of calcite characteristics enables conclusions on the formation mechanism and on a biotic or abiotic origin of the calcites. The change of calcite types on the walls reveals changes of the environmental cave parameters. In addition, interactions of calcites with the prehistoric paint layer could be evaluated.