CO2 production by impact in carbonates? An ATEM and stable isotope (C,O) study

Carbonates may have been a common target for large impacts on the Earth and possible related CO2 outgassing would have important consequences for the composition of the atmosphere. To estimate volatile release during such impacts, isotopic ratios (C-13/C-12 and O-18/O-16) were determined on highly shocked carbonate samples in combination with SEM and analytical transmission electron microscopy (ATEM) investigations. The study was performed on both naturally and experimentally shocked rocks, i.e. 50-60 GPa shocked limestone-dolomite fragments from the Haughton impact crater (Canada), and carbonates shocked in shock recovery experiments. For the experiments, unshocked carbonates consisting of mixture of dolomite and calcite from the Haughton area were used. Naturally shocked samples were collected in the polymict breccia near the center of the Haughton crater

Structural Studies of Hydroxy-Ga Pillared Clays by Ga K-Edge X-Ray Absorption

A natural montmorillonite clay was intercalated by hydroxy-Ga polycations (Ga13), obtained by basis hydrolysis of metal salts. These species are structural analogues of Al13. The clay interlayer cations were exchanged in Ga13 solutions containing various amounts of organic polymer. The synthesized materials were aged and/or calcined to 150 and 500°C. In a first approach, Ga-K edge experiments were carried out to investigate the local environment of Ga atoms intercalated into the interlayer space. The study of the first nearest neighbours, oxygen atoms, revealed a decrease in the average bond distance after calcination, which traduced dehydroxylation of the Gal3 pillas. By studying the second nearest neighbours, gallium atoms, the Fourier transforms indicate the presence of the central tetrahedrally coordinated gallium of the Ga13 polycations whose contribution disappears upon ageing or calcination

Assessment of archaeological bone and dentine preservation from Lazaret Cave (Middle Pleistocene) in France

Chemical and structural changes in bones and dentine from Cervus elaphus jaws during fossilization were studied by chemical analysis, infrared spectroscopy (IR) and X-ray diffraction (XRD). Data were used to discuss the modifications of bones and dentine from the Lazaret prehistoric cave (Nice, France) which is an important archeologic site of Middle Pleistocene age. Fossil bones and dentine mainly consisted of hydroxy-carbonate apatite as the primary phase and of calcite as a secondary phase. Carbonation, fluorination and recrystallization processes are shown as more important in bone and dentine than in tooth enamel. A good correlation was found between the a cell parameter of apatite and its CO3 and fluorine contents in the bones studied. Fluorine enrichment seems to be related to the permeability of the upper sedimentary levels. Lazaret fossil bones and dentine are less stable than enamels and their use for dating has to be taken with caution

Determination of Mg Site Geometry in Pyroxenes by Full Multiple Scattering Calculations

We present a comparison between experiment and Full Multiple Scattering calculations at the magnesium K-edge for two pyroxenes: diopside where magnesium atoms are in M1 site and enstatite where magnesium atoms are in two distinct sites M1 and M2. The purpose of this work is to determine how the number of octahedral sites on the one hand and the site distortion on the other hand affect the magnesium K-edge XANES spectra

A1K-XANES Formation in Some Tetrahedral and Octahedral Compounds

Experimental and theoretical study of Al K-XANES in AlPO4 (berlinite) and in KAl(S04)212H2O(K-alum) with different types of Al environment is performed. Calculations proved that the experimental XANES are well reproduced within EXAFS-like approach to electron scattering description i.e. considering the single-, double- and triple-scattering processes on two and approximately linear three-atoms chains originated at Al-absorbing atom and consisting mainly of O-atoms chosen under the same for both compounds empirical "selection rule"

Gallium Crystal Chemistry in Synthetic Goethites

The distribution of Ga and Al atoms within the octahedral sheets of synthetic goethites has been investigated by XRD and Ga K-edge XANES and EXAFS spectroscopies. XRD results indicate a solid solution between goethite (α-FeOOH) and GaGoe4 (40 mol% of Ga). The XANES data indicate the presence of 6Ga in the solid solution. The fitting procedures for EXAFS spectra show no evidence of preferential octahedral site substitutions for Ga