Etienne Balan

Sorbonne Université | UPMC · Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC) - UMR 7590

Density functional theory is used to investigate the vibrational stretching properties of OH groups in ideal and chemically disordered dravite models. Different schemes of cationic occupancy are considered, including the occurrence of vacancies at the X site and Mg–Al inversion between the Y and Z sites. The harmonic coupling between different OH g...

The structure of corundum is not amenable to accommodating beryllium, yet Be is commonly added to corundum for purposes of colour modification. Where the main sites in corundum are octahedrally coordinated, Be is tetrahedrally coordinated in all known Be minerals. To attempt to explain this discrepancy, the configurations of Be in the Be–Al–O±H sys...

The near-infrared (NIR) spectra of hydrous minerals display absorption bands involving multiple excitations of vibrational modes. They usually involve OH stretching modes, but their interpretation is not straightforward due to the combined effects of bond anharmonicity and vibrational coupling. In the present study, the mid-infrared (MIR) and near-...

The OH-stretching infrared absorption spectrum of a tourmaline sample close to the foitite end-member is interpreted in the light of the density functional theory (DFT) modeling of iron-bearing Y3Z6 clusters in tourmaline. The iron-bearing clusters reflect the Al-rich and Na-deficient character of foitite and contain either two Fe2+ and one Al3+ or...

This study presents and discusses infrared spectroscopic data of well characterised, naturally occurring trioctahedral layer silicates of the serpentine (Srp), talc (Tlc), and sepiolite (Sep) mineral groups, which are found in reactivated faults and sequences of white and green clay veins (deweylite and garnierite) of the New Caledonian Ni-silicate...

The theoretical vibrational properties of a series of Fe- and Al-bearing lizardite models have been determined at the density functional theory level. Each periodic model displays a single cationic impurity substituted at an octahedral or tetrahedral site of a supercell of lizardite (Mg3Si2O5(OH)4) containing 162 atoms. The isovalent Fe2+ for Mg2+...

Plain Language Summary Tropical landscapes are often covered by nutrient‐depleted soils overlying lateritic weathering profiles, that result from a complex set of chemical reactions between air, water, rocks, and living organisms. Mineral phases hosted by these deep weathering profiles, such as clays, have formed from reactions between primary mine...

The OH stretching vibrational properties of eight serpentine samples from veins of the New Caledonian ophiolite have been investigated by Fourier-transform infrared spectroscopy (FTIR) in the mid-infrared and near-infrared ranges and by Raman spectroscopy. The samples were selected for their monophasic composition (Lz: lizardite; Ctl: chrysotile; a...

The infrared absorption spectrum of a natural antigorite sample from New Caledonia is compared to its theoretical counterpart computed for the pristine antigorite m=17 polysome within the density functional perturbation theory framework. The theoretical model reproduces most of the bands related to Si-O stretching in the 800–1300 cm−1 range, OH lib...

Although OH overtone bands of 1:1 phyllosilicates are commonly observed in their near-infrared (NIR) spectra, their interpretation in terms of transitions between specific vibrational states is still uncertain. This situation can be traced back to the coupled nature of the fundamental OH-stretching modes involving the interlayer OH groups of 1:1 ph...

Traces of life may have been preserved in ancient martian rocks in the form of molecular fossils. Yet the surface of Mars is continuously exposed to intense UV radiation detrimental to the preservation of organics. Because the payload of the next rovers going to Mars to seek traces of life will comprise Raman spectroscopy tools, laboratory simulati...

Hydrous defects in diopside (CaMgSi2O6) play an important role in the water budget of the Earth's mantle. Related OH-stretching modes lead to a variety of infrared absorption bands observed in natural or experimental samples. In the present study, we report new low-temperature infrared spectra of reference natural diopside samples in the OH-stretch...

The atomic-scale structure, relative stability and infrared spectroscopic properties of OH defects in corundum (α-Al2O3) are theoretically investigated at the density functional theory level. Comparison with experimental data makes it possible to assign most of the narrow bands observed between 3150 and 3400 cm−1 in natural and Ti- or V-doped synth...

Ferralsols and Acrisols are major types of soils of the Amazon basin observed on various landform units comprising plateau surfaces, incised hills at their edges and slopes. The present study focuses on an Acrisol developed on plateaus surfaces from northwest Amazonia and a Ferralsol from the convex hills of the incised plateau edges. Local geomorp...

The infrared spectra of natural quartz, and synthetic quartz produced in conditions relevant to natural environments, generally contain some association of OH-stretching absorption bands at 3596, 3585, 3483, 3431, 3379 and 3313 cm−1, and/or a broad band at ∼ 3400 cm−1. In this study, a series of OH-bearing defects has been theoretically investigate...

The search for the most ancient traces of life on Earth has always been fraught with controversies because of the inevitable degradation undergone by fossilized biomolecules. Laboratory experiments may provide unique clues to achieve a better mechanistic understanding of the key processes involving (biogenic or abiotic) organic carbon during a geol...

The Neogene Içá Formation is a major sedimentary deposit in central Amazonia (Brazil) that is critical to the understanding and modeling of the evolution of the Amazon Basin. However, its chronostratigraphy is poorly defined, mostly because it is not fossiliferous and it does not contain volcanic ash levels. This study is the first attempt at the a...

Clay minerals from the kaolinite group contain impurities (transition ions) and point defects (radicals). Their study by EPR provides information on the physicochemical conditions in which these minerals were formed. In addition, by measuring the intensity of the spectrum for certain defects created by natural irradiation, it is possible to date th...

Forthcoming exploration of Mars aims at identifying fossil biosignatures withinancient clay-rich formations. The subsurface of Mars has mostly acted as a giantfreezer for the last 4 Gyr, thereby preserving potential remains of martian life.Yet, volcanism and impactors have periodically triggered the circulation of hydrothermalfluids, inevitably cau...

First-Principles Modeling of Vibrational Electron Energy Loss Spectra - Volume 25 Supplement - G Radtke, D Taverna, M Lazzeri, E Balan, FS Hage, QM Ramasse, OL Krivanek, TC Lovejoy

Equilibrium ³⁷Cl/³⁵Cl fractionation factors in selected molecules, Cl-bearing crystalline solids, and silicates in which Cl occurs at trace or minor concentration level are determined from first-principles calculations, within the density functional theory (DFT) scheme. Results on benchmarking molecules and crystalline solids are consistent with th...

Secondary minerals in soils can record climatic changes affecting continental surfaces over geological times. Their dating should refine our present knowledge about their potential periods of formation as well as their relations with the ongoing change of climate and erosion/weathering regimes. In the present study, twenty kaolinite samples from tw...

Bone reactivity offers a potential way to record local physical–chemical conditions prevailing in fossilisation environments and archaeological sites. In the present study, a series of fossil bone samples from the karstic environments of the Bolt's Farm cave system (Cradle of Humankind, South Africa) and from fluvio‐lacustrine environments of the T...

The chemical and isotopic compositions of biogenic apatite are important geochemical markers, which can suffer modifications during fossilisation. Compared with modern ones, fossil apatites generally exhibit variations in carbonate content, enrichment in fluorine, incorporation of trace elements and an increase in crystallinity parameters. Detailed...

Although adsorption at the solid surface is the first step controlling boron incorporation in the crystal lattice during the standard growth mechanism of calcite and aragonite, little is known about the identity, structure and isotopic composition of the boron complexes formed at the CaCO3-solution interface. To generate this important information,...

Theoretical mineral-solution equilibrium isotopic fractionation can contribute to the interpretation of Zn isotopic compositions. In this study, we investigate equilibrium isotopic fractionation properties of hexaaquo zinc complex, a major Zn aqueous species, using first-principles molecular dynamics (FPMD) based on density functional theory (DFT)....

Bones mostly consist of composite materials based on almost equivalent volume fractions of mineral (apatite) and organic (collagen) components. Accordingly, their infrared spectroscopic properties should reflect this composite nature. In this letter, we show by theory and experiment that the variability of the strong phosphate bands in the ATR-FTIR...

This study focuses on the dating of millimetric pisoliths from ferruginous duricrusts located in central Amazonia (Brazil), by coupling detailed mineralogy and two relevant dating methods: (i) (U-Th)/He analysis of goethites by mass spectrometry; (ii) analysis of radiation-induced defects of kaolinites embedded in duricrusts by electron paramagneti...

The attenuated total reflectance (ATR) spectra of two calcite samples have been measured using Ge and diamond internal reflection elements. One of the samples was obtained by precipitation from solution and displays sub-micrometer sized particles. The second sample was obtained by grinding a single-crystal of calcite (‘‘Iceland spar’’ variety). The...

The ¹¹B/¹⁰B ratio in calcite and aragonite is an important proxy of oceanic water pH. However, the physico-chemical mechanisms underpinning this approach are still poorly known. In the present study, we theoretically determine the equilibrium isotopic fractionation properties of structural boron species in calcium carbonates, BO3³⁻, BO2(OH)²⁻ and B...

The use of volcanic glass as recorder of paleoenvironmental conditions has existed for 30years. In this paper we investigate the methodological aspects of the determination of water content, isotopic composition, and water speciation in volcanic glass using the High Temperature Conversion/Elemental Analyzer (TCEA) mass spectrometer system on millig...

The stable isotope composition of biogenic apatite is an important geochemical marker that can record environmental parameters and is widely used to infer past climates, biomineralization processes, dietary preferences and habitat of vertebrates. In this study, theoretical equilibrium isotopic fractionation of oxygen, carbon and calcium in hydroxya...

A general approach to model vibrational electron energy loss spectra obtained using an electron beam positioned away from the specimen is presented. The energy-loss probability of the fast electron is evaluated using first-principles quantum mechanical calculations (density functional theory) of the dielectric response of the specimen. The validity...

Many properties of aqueous cations depend on their coordination state. However, the lack of long-range order and the dynamic character of aqueous solutions make it difficult to obtain information beyond average coordination parameters. A thorough understanding of the molecular scale environment of aqueous cations usually requires a combination of e...

Substitutional mechanisms involving hydrogen incorporation at vacant tetrahedral sites play a major role in water incorporation in olivine. Infrared (IR) absorption spectra of hydrous forsterite samples usually display a cluster of narrow and weakly anharmonic OH stretching bands at wavenumbers above 3500 cm⁻¹. A broader absorption band displaying...

The isotopic compositions of natural materials are determined by their parent reservoirs, on the one hand, and by fractionation mechanisms, on the other hand. Under the right conditions, fractionation represents isotope partitioning at thermodynamic equilibrium. In this case, the isotopic equilibrium constant depends on temperature, and reflects th...

We have studied the H2 production under ionizing radiation of water confined in synthetic saponite and montmorillonite as a function of the relative humidity. The H2 radiolytic yields in the dry systems are very similar to that measured in a non-swelling clay mineral. They are 2–3 times higher with one water layer in the interlayer space, evidencin...

This chapter introduces the physical basis of infrared and Raman spectroscopies. Starting from standard harmonic lattice dynamics, a special attention is given to the relationship between the atomic-scale vibrational properties of the clay mineral and the spectroscopic quantities actually measured. The expression of the low-frequency dielectric per...

Attenuated total reflectance (ATR) infrared spectra were measured on a synthetic and a natural fluorapatite sample. A modeling approach based on the computation of the Fresnel reflection coefficient between the ATR crystal and the powder sample was used to analyze the line shape of the spectra. The dielectric properties of the samples were related...

Isotopic composition analysis contributes significantly to the investigation of the biogeochemical cycle of zinc with its economical, environmental and health implications. Interpretation of isotopic measurements is however hindered by the lack of a set of equilibrium isotopic fractionation factors between Zn-bearing minerals. In this study, equili...

Despite the importance of boron as a proxy of past ocean pH, the crystal-chemical factors controlling its incorporation in the structure of calcium carbonates are still poorly understood. This is partly linked to an imperfect knowledge of the coordination, protonation state and local environment of boron species in these minerals. In the present st...

Hydrogen incorporation in olivine involves many OH-defects, which will control the hydrogen solubility at mantle conditions. Several of these OH-defects are identified from the investigation of forsterite (the olivine Mg end-member). We study here the effect of Fe2+, Fe3+, Al3+ and Cr3+ on OH-defects in order to improve our understanding of the hyd...

The reactivity under ionizing radiation of synthetic and natural talc was studied. The two samples were chosen as models of non-swelling clays. H2 production measurements evidenced that the H2 yield in synthetic talc was of the same order of magnitude as in water, implying a very efficient production, and then recombination, of hydrogen atoms arisi...

Progressive biomineralization of a skeleton occurs during ontogeny in most animals. In fishes, larvae are poorly mineralized, whereas juveniles and adults display a progressively more biomineralized skeleton. Fossil remains primarily consist of adult specimens because the fossilization of poorly-mineralized larvae and juveniles necessitates excepti...

The powder infrared spectra of a sulfate-bearing calcitic coral sample are recorded at room temperature in attenuated total reflectance (ATR) geometry and at low temperature in transmission geometry. The comparison of ATR spectra recorded with diamond or Ge crystal confirms that the width and the shape of the prominent absorption bands, related to...

Microbialites are organo-sedimentary rocks found in abundance throughout the geological record back to ~3.5 Ga. Interpretations of the biological and environmental conditions under which they formed rely on comparisons with modern microbialites. Therefore, a better characterization of diverse modern microbialites is crucial to improve such interpre...

Reconstructing the original biogeochemistry of organic microfossils requires quantifying the extent of the chemical transformations they experienced during burial and maturation processes. In the present study, fossilization experiments have been performed using modern sporopollenin chosen as an analogue for the resistant biocompounds possibly cons...

We report a density-functional theory (DFT)-based study of the interface of bulk water with a prototypical oxide surface, MgO(001), and focus our study on the often-overlooked surface electric field, which we find to be significantly stronger than potentially expected for a flat and non-polar surface in the presence of liquid water. In particular,...

The theoretical determination of the isotopic fractionation between an aqueous solution and a mineral is of utmost importance in Earth sciences. While for crystals, it is well established that equilibrium isotopic fractionation factors can be calculated using a statistical thermodynamic approach based on the vibrational properties, several theoreti...

First-principles calculations based on the density functional theory (DFT) with or without the addition of a Hubbard U correction, are performed on goethite in order to determine the iron and oxygen reduced partition function ratios (β-factors). The calculated iron phonon density of states (pDOS), force constant and β-factor are compared with reeva...

Experimental and theoretical evidence for the coupled substitution of B and H in synthetic forsterite and a natural olivine is presented. The intensities of OH bands at 3704 cm−1 (//z), 3598 cm−1 (//x,y), and 3525 cm−1 (//x) in a heterogeneous B-doped synthetic forsterite crystal matches the zoning of B concentration measured by ion probe. The two...

A series of fossil tooth enamel samples was investigated by Fourier transform infrared (FTIR) spectroscopy, C-13 and F-19 magic-angle spinning nuclear magnetic resonance (MAS NMR) and scanning electron microscopy (SEM). Tooth remains were collected in Mio-Pliocene deposits of the Tugen Hills in Kenya. Significant transformations were observed in fo...

Kaolin-group minerals typically form as a result of hydrothermal alteration and/or weathering processes. They occur in environments as diverse as tropical soils, continental sedimentary deposits, and altered crustal rocks. They have also been detected on the surface of Mars. Given their prevalence, they have attracted the attention of researchers i...

The equilibrium fractionation factor between two phases is of importance for the understanding of many planetary and environmental processes. Although thermodynamic equilibrium can be achieved between minerals at high temperature, many natural processes involve reactions between liquids or aqueous solutions and solids. For crystals, the fractionati...

Microbialites are organo-sedimentary structures found in abundance throughout the geological record back to 3.5 Ga. Although they are considered as among the oldest life remains on Earth, the search for fossils of microbial cells remains a challenge due to the difficulty to distinguish biogenic traces from abiotic artefacts. In order to improve our...

The structure and spectroscopic properties of selected models of B-type carbonate defects in apatite locally compensated by fluoride or hydroxyl ions are investigated using first-principles quantum mechanical calculations. Theoretical infrared absorption spectra and 13C, and 19F nuclear magnetic resonance chemical shifts are determined. Among the i...

Incorporation mechanism of sulfate groups in major calcium carbonates (calcite, aragonite and vaterite) is investigated using first-principles quantum-mechanical calculations. For each mineral, the stable structure of the substituted site is determined. In calcite and aragonite, a tilting of the sulfate-group with respect to the orientation of plan...

Hydroxyl defects in pure forsterite are usually ascribed to incorporation of protons fully compensating the electrostatic charge of cationic vacancies. However, partially compensated vacancies have been predicted from theoretical considerations. Here, we theoretically determine the structural, vibrational and infrared spectroscopic properties of pa...

The mechanism and magnitude of fluorine incorporation in H-bearing forsterite were investigated through a combined experimental and theoretical approach. Forsterite samples were synthesized in a piston cylinder press at 2 and 4 GPa, in hydrous conditions, with or without fluorine. High fluorine solubilities of 1715 and 1308 ppm F were measured by p...

A series of fossil tooth enamel samples has been investigated by Fourier-transform infrared spectroscopy (FTIR), (13)C and (19)F magic-angle spinning nuclear magnetic resonance (MAS NMR), and scanning electron microscopy (SEM). Tooth remains were collected in Mio-Pliocene deposits of the Tugen Hills. Significant transformations are observed in foss...

The mechanism and magnitude of fluorine incorporation in H-bearing forsterite were investigated through a combined experimental and theoretical approach. Forsterite samples were synthesized in a piston cylinder press at 2 and 4 GPa, in hydrous conditions, with or without fluorine. High fluorine solubilities of 1715 and 1308 ppm F were measured by p...

The structure and the polarized infrared absorption spectrum of OH-defects in wadsleyite (beta-Mg2SiO4) are studied, at 0 and 15 GPa, by first-principles calculations based on density functional theory (DFT). Four types of OH-defects are considered: fully protonated magnesium vacancies, fully protonated silicon vacancies, silicon vacancies compensa...

Water incorporation in forsterite samples synthesized under low to medium silica-activity conditions mostly occurs via a substitutional mechanism in which a Si vacancy is compensated by four protons. Corresponding IR absorption spectra display a cluster of narrow and weakly anharmonic OH-stretching bands at wavenumbers above 3,500 cm−1. However, th...