Glass Alteration Research Articles

Natural fumarolic alteration of fluorapatite, olivine, and basaltic glass, and implications for habitable environments on Mars.

Fumaroles represent a very important potential habitat on Mars because they contain water and nutrients. Global deposition of volcanic sulfate aerosols may also have been an important soil-forming process affecting large areas of Mars. Here we identify alteration from the Senator fumarole, northwest Nevada, USA, and in low-temperature environments near the fumarole to help interpret fumarolic and acid vapor alteration of rocks and soils on Mars. We analyzed soil samples and fluorapatite, olivine, and basaltic glass placed at and near the fumarole in in situ mineral alteration experiments designed to measure weathering under natural field conditions. Using synchrotron X-ray diffraction, we clearly observe hydroxyl-carbonate-bearing fluorapatite as a fumarolic alteration product of the original material, fluorapatite. The composition of apatites as well as secondary phosphates has been previously used to infer magmatic conditions as well as fumarolic conditions on Mars. To our knowledge, the observations reported here represent the first documented instance of formation of hydroxyl-carbonate-bearing apatite from fluorapatite in a field experiment. Retreat of olivine surfaces, as well as abundant NH4-containing minerals, was also characteristic of fumarolic alteration. In contrast, alteration in the nearby low-temperature environment resulted in formation of large pits on olivine surfaces, which were clearly distinguishable from the fumarolic alteration. Raman signatures of some fumarolically impacted surfaces are consistent with detection of the biological molecules chlorophyll and scytenomin, potentially useful biosignatures. Observations of altered minerals on Mars may therefore help identify the environment of formation and understand the aqueous history and potential habitability of that planet.

The Interaction Between Nuclear Waste Glass and Ordinary Portland Cement

The interaction between simulated reference waste glasses SON68 and SM539, and cement has been studied in suspensions of ordinary Portland cement and synthetic cement water with pH 13.5 at 30°C. The cement appears to trigger glass dissolution by consumption of glass matrix components. This leads to fast glass dissolution at a constant rate with formation of a porous gel layer on the glass. A glass dissolution model has been proposed considering that the silicon coming from the glass reacts with portlandite to form C‐S‐H phases. The transformation of C‐S‐H into C‐A‐S‐H phases is a second parallel driving force especially for the Al‐rich SM539 glass. After consumption of the portlandite, the glass alteration rate is expected to decrease.

99Tc‐ and 239Pu‐Doped Glass Leaching Experiments: Residual Alteration Rate and Radionuclide Behavior

The long‐term behavior of high‐level nuclear glass subjected to alpha/beta radiation by long‐life radionuclides must be investigated with respect to geological disposal. This study focuses on the effects of alpha and beta radiations on the chemical reactivity of R7T7 glass with pure water, mainly on the residual alteration rate regime. Glass specimens doped with 0.85 wt% 239PuO2 (α emitter) and 0.24 wt% 99TcO2 (β emitter) that simulate alpha and beta dose rate corresponding to long‐term disposal conditions are leached under static conditions in argon atmosphere at 90°C, in initially pure water and at a high surface‐area‐to‐volume ratio (S/V = 20/cm). The alteration rate is monitored by the release of glass alteration tracer elements (B, Na, and Li). Radiation effects on the leached glass and its gel network are characterized by SEM and TEM analyses. Plutonium and technetium releases are also measured by radiometry, and their chemical oxidation state is assessed by measuring the pH and reduction–oxidation potential of the leachates. The results do not highlight any significant effect of alpha/beta radiation on the residual alteration of these doped glasses. These observations are consistent with solid characterizations, which show that a protective layer can be formed under such irradiation fields. Under our experimental conditions (Eh~380 mV/SHE, pH90°C = 8–8.6), very low concentrations of soluble plutonium are measured in the leachate, indicating strong plutonium retention, whereas technetium performs as a soluble element and is not retained in the altered layer.

SON68 glass dissolution driven by magnesium silicate precipitation

Abstract Experimental results are reported on the effect of magnesium silicate precipitation on the mechanisms and rate of borosilicate glass dissolution. Leaching experiments with SON68 glass, a borosilicate containing no Mg, were carried out in initially deionized water at 50 °C with a glass-surface-area-to-solution-volume ratio of 20,000 m−1. After 29 days of alteration the experimental conditions were modified by the addition of Mg to trigger the precipitation of Mg-silicate. Additional experiments were conducted to investigate the importance of other parameters such as pH or dissolved silica on the mechanisms of precipitation of Mg-silicates and their consequences on the glass dissolution rate. Mg-silicates precipitate immediately after Mg is added. The amount of altered glass increases with the quantity of added Mg, and is smaller when silicon is added in solution. A time lag is observed between the addition of magnesium and the resumption of glass alteration because silicon is first provided by partial dissolution of the previously formed alteration gel. It is shown that nucleation does not limit Mg-silicate precipitation. A pH above 8 is necessary for the phase to precipitate under the investigated experimental conditions. On the other hand the glass alteration kinetics limits the precipitation if the magnesium is supplied in solution at a non-limiting rate.

HLW glass dissolution in the presence of magnesium carbonate: Diffusion cell experiment and coupled modeling of diffusion and geochemical interactions

The influence of diffusion of reactive species in aqueous solutions on the alteration rate of borosilicate glass of nuclear interest in the presence of magnesium carbonate (hydromagnesite: 4MgCO3·Mg(OH)2·4H2O) is investigated together with the ability of coupled chemistry/transport models to simulate the processes involved. Diffusion cells in which the solids are separated by an inert stainless steel sintered filter were used to establish parameters for direct comparison with batch experiments in which solids are intimately mixed. The chemistry of the solution and solid phases was monitored over time by various analytical techniques including ICP-AES, XRD, and SEM. The primary mechanism controlling the geochemical evolution of the system remains the consumption of silicon from the glass by precipitation of magnesium silicates. The solution chemistry and the dissolution and precipitation of solid phases are correctly described by 2D modeling with the GRAAL model implemented in the HYTEC reactive transport code. The spatial symmetry of the boron concentrations in both compartments of the cells results from dissolution coupled with simple diffusion, whereas the spatial asymmetry of the silicon and magnesium concentrations is due to strong coupling between dissolution, diffusion, and precipitation of secondary phases. A sensitivity analysis on the modeling of glass alteration shows that the choice of these phases and their thermodynamic constants have only a moderate impact whereas the thickness of the filter has a greater barrier effect.

Investigation of local environment around rare earths (La and Eu) by fluorescence line narrowing during borosilicate glass alteration

The local environment of europium in soda-lime borosilicate glasses with a range of La2O3 content was probed by continuous luminescence and Fluorescence Line Narrowing (FLN) to investigate the local environment of rare earth elements in pristine and leached glass. After aqueous leaching at 90°C at pH 7 and 9.5, rare earths were fully retained and homogeneously distributed in the amorphous alteration layer (commonly called gel). Two separate silicate environments were observed in pristine and leached glasses regardless of the lanthanum content and the leaching conditions. A borate environment surrounding europium was not observed in pristine and leached glasses. During glass alteration, OH groups were located around the europium environment, which became more organized (higher symmetry) in the first coordination shell.

Effect of iron metal and siderite on the durability of simulated archeological glassy material

Under anoxic conditions, the presence of iron is expected to enhance the alteration rate of silicate glass. In order to understand the underlying mechanisms, experiments were performed on a synthetic glass simulating archeological artifacts to study the effect of metallic iron and siderite in a clay-type groundwater. Characterization of the altered samples at different durations reveals different impacts of iron on glass alteration. In contact with siderite, the sorption of the released silicon maintains temporarily a high alteration rate which eventually drops. With metallic iron, glass is altered near the maximum dissolution rate throughout the experiment because of Fe-silicate precipitation.

Geochemical characterization of tubular alteration features in subseafloor basalt glass

There are numerous indications that subseafloor basalts may currently host a huge quantity of active microbial cells and contain biosignatures of ancient life in the form of physical and chemical basalt glass alteration. Unfortunately, technological challenges prevent us from observing the formation and mineralization of these alteration features in situ, or reproducing tubular basalt alteration processes in the laboratory. Therefore, comprehensive analysis of the physical and chemical traces retained in mineralized tubules is currently the best approach for deciphering a record of glass alteration. We have used a number of high-resolution spectroscopic and microscopic methods to probe the geochemical and mineralogical characteristics of tubular alteration features in basalt glasses obtained from a suite of subseafloor drill cores that covers a range of different collection locations and ages. By combining three different synchrotron-based X-ray measurements – X-ray fluorescence microprobe mapping, XANES spectroscopy, and μ-XRD – with focused ion beam milling and transmission electron microscopy, we have spatially resolved the major and trace element distributions, as well as the oxidation state of Fe, determined the coordination chemistry of Fe, Mn and Ti at the micron-scale, and constrained the secondary minerals within these features. The tubular alteration features are characterized by strong losses of Fe2+, Mn2+, and Ca2+ compared to fresh glass, oxidation of the residual Fe, and the accumulation of Ti and Cu. The predominant phases infilling the alteration regions are Fe3+-bearing silicates dominated by 2:1 clays, with secondary Fe- and Ti-oxides, and a partially oxidized Mn-silicate phase. These geochemical patterns observed within the tubular alteration features are comparable across a diverse suite of samples formed over the past 5–100Ma, which shows that the microscale mineralization processes are common and consistent throughout the ocean basins and throughout time. The distributions of Ti and Cu are distinct between tubular mineralization and the crack-filling minerals and thus delineate sequential stages of fluid–rock interaction. The preserved chemistry of clay and oxide mineralization in the tubular alteration then represents a common precursor state (e.g. Ti accumulation), that has not yet undergone recrystallization (e.g. titanite formation) as observed in many older, metamorphosed examples of tubular alteration.

Antagonist effects of calcium on borosilicate glass alteration

Numerous studies have been conducted on glass and cement durability in contact with water, but very little work to date has focused directly on interactions between the two materials. These interactions are mostly controlled by silicon–calcium reactivity. However, the physical and chemical processes involved remain insufficiently understood to predict the evolution of coupled glass–cement systems used in several industrial applications. Results are reported from borosilicate glass alteration in calcium-rich solutions. Our data show that four distinct behaviors can be expected according to the relative importance of three key parameters: the pH, the reaction progress (short- or long-term alteration) and the calcium concentration. Glass alteration is thus controlled by specific mechanisms depending on the solution chemistry: calcium complexation at the glass surface, precipitation of calcium silicate hydrates (C–S–H) or calcium incorporation in the altered layer. These findings highlight the impact of silicon–calcium interactions on glass durability and open the way for a better understanding of glass–cement mixing in civil engineering applications as well as in nuclear waste storage.

Can alteration experiments on impact melts from El'gygytgyn and volcanic glasses shed new light on the formation of the Martian surface?

AbstractThis investigation involved three specimens: an altered felsic sample of impactite from the ICDP El'gygytgyn drill core D1c, and two reference volcanics from Iceland, namely a rhyolitic glass and a basaltic glass. The goal of this work was to better understand the alteration of impact melt and volcanic glass, and to apply the results to an investigation of alteration processes below the surface of Mars. Hydrothermal batch alteration experiments with the El'gygytgyn sample showed formation of various silica phases such as cristobalite, opal, and quartz. According to geochemical modeling, zeolites were also expected, but zeolite minerals already present in the impactite prior to the experiment may have masked possible experimental zeolite growth. Basaltic glass was altered to smectite, talc, and opal. The accompanying numerical modeling gave results that were similar or comparable to the laboratory experiments. Rhyolitic glass was kinetically more stable than basaltic glass, and showed only minor formation of calcite and feldspar during the 3‐week experiment. The study showed that closed‐system isochemical alteration of both siliceous and mafic glasses and melts results in the formation of smectites and zeolites. Therefore, to link alteration features on Mars to specific physical conditions, the exact identity of the mineral phases present in surface rocks must be known. Moreover, our simulations on closed‐system isochemical alteration showed that the fraction of zeolites and silica formed relative to smectite depends on the source mineral altered. Therefore, fractions of these mineral groups present in the Martian soil may be used to better predict source rock characteristics.

Alteration of glassy volcanic rocks to Naand Ca-smectites in the Neogene basin of Manisa, western Anatolia, Turkey

AbstractAlkali- and Ca-rich smectites occur in association with Neogene lacustrine sedimentary rocks and high-K calc-alkaline volcanic rocks with compositions ranging from andesite to rhyolite in western Anatolia (Turkey). Major clay occurrences are associated predominantly with the Foça and Akçaköy ignimbrites and with the ignimbrites within the Rahmanlar pyroclastics. Experimental studies indicate that the main clay minerals present are Na- and Ca-smectite and subordinate illite, associated with silica polymorphs, trace clinoptilolite and chlorite. The authigenic minerals formed by weathering and metasomatic reactions between hot volcanic material and lake water. Smectite was produced as a result of argillic alteration of the volcanic glass and feldspars of the ignimbrites, Rahmanlar pyroclastics and reworked volcaniclastic sediments through chemical weathering and dissolution-precipitation processes and formed as authigenic phases both in terrestrial and nearby shallow lacustrine environments under prevalent humid or semi-humid climate during the Neogene.

Pathways of volcanic glass alteration in laboratory experiments through inorganic and microbially-mediated processes

AbstractRhyolitic obsidian was reacted with natural waters to study the effect of water chemistry and biological activity on the composition and formation mechanisms of clay. Two sets of experiments (18 months, 6 years) used fresh, hypersaline water (Mg-Na-SO4-Cl- and NaCl-rich) and seawater. The 6-year experiments produced the transformation of obsidian into quartz, apparently by in situ re-crystallization (Cuadros et al., 2012). The most abundant neoformed clay was dioctahedral (typically montmorillonite), indicating chemical control by the glass (where Al > Mg). Altered glass morphology and chemistry in the 18-months experiments indicated in situ transformation to clay. Magnesium-rich (saponite) clay formed under water-chemistry control in the bulk and within biofilms with elevated Mg concentration (Cuadros et al., 2013). The contact between microbial structures and glass was very intimate. Glass transformation into quartz may be due to some characteristic of the obsidian and/or alteration conditions. Such combination needs not to be uncommon in nature and opens new possibilities of quartz origin.

Hydrothermal and thermal treatment of natural clinoptilolite zeolite from Bigadiç, Turkey: An experimental study

The clinoptilolite rich zeolite from Bigadic which was formed from alteration of volcanic glass were treated with acidic (HCl, H3BO3, H3PO4), alkaline (KOH, NaOH) solutions. Hydrothermally treated and untreated samples were heat treated at 400, 550 and 700°C. XRD, ICP-MS and N2 gas adsorption were used for physicochemical characterization of zeolites. Considering the Si/Al > 4 and Na+K/Ca+Mg H3PO4 > HBO3 > KOH > NaOH. XRD analysis indicated that the structure of zeolite was not altered with acids and alkali treatments. The structure of zeolite treated with HCl and other acids started to deform at 400 and 550°C respectively. In treatment with HCl, Si/Al ratio increases with significant a decrease in K content which resulted in a decrease in the heat stability of zeolite. No change was observed in the structure and thermal stability of clinoptilolite after alkali treatments. The fact that although significant amount of Na is removed with H3BO3 acid and Na is increased with NaOH but the thermal stability remains the same indicates that Na cation is not an important parameter as much as K. HCl and H3PO4 acid treatments increased the surface area depending on the dissolution of amorphous material and H3PO4 was found to be more effective. However, the total pore size decreased due to formation of new micropores.

Contribution of atom-probe tomography to a better understanding of glass alteration mechanisms: Application to a nuclear glass specimen altered 25 years in a granitic environment

We report and discuss results of atom probe tomography (APT) and energy-filtered transmission electron microscopy (EFTEM) applied to a borosilicate glass sample of nuclear interest altered for 25.75years at 90°C in a confined granitic medium in order to better understand the rate-limiting mechanisms under conditions representative of a deep geological repository for vitrified radioactive waste. The APT technique allows the 3D reconstruction of the elemental distribution at the reactive interphase with sub-nanometer precision. Profiles of the B distribution at pristine glass/hydrated glass interface obtained by different techniques are compared to show the challenge of accurate measurements of diffusion profiles at this buried interface on the nanometer length scale. Our results show that 1) Li from the glass and hydrogen from the solution exhibit anti-correlated 15nm wide gradients located between the pristine glass and the hydrated glass layer, and 2) boron exhibits an unexpectedly sharp profile (~3nm width) located just outside of the Li/H interdiffusion layer; this sharp profile is more consistent with a dissolution front than a diffusion-controlled release of boron. The resulting apparent diffusion coefficients derived from the Li and H profiles are DLi=1.5×10−22m2·s−1 and DH=6.8×10−23m2·s−1. These values are around two orders of magnitude lower than those observed at the very beginning of the alteration process, which suggests that interdiffusion is slowed at high reaction progress by local conditions that could be related to the porous structure of the interphase. As a result, the accessibility of water to the pristine glass could be the rate-limiting step in these conditions. More generally, these findings strongly support the importance of interdiffusion coupled with hydrolysis reactions of the silicate network on the long-term dissolution rate, contrary to what has been suggested by recent interfacial dissolution–precipitation models for silicate minerals.

Apparent overconsolidation of mudstones in the Kumano Basin of southwest Japan: Implications for fluid pressure and fluid flow within a forearc setting

AbstractThe Kumano Basin is located in the Nankai Trough subduction zone of southwest Japan. During the past 1.6 million years, approximately 800 meters of sandy turbidites and hemipelagic mud were deposited near the distal edge of the forearc basin, at Site C0002 of the Integrated Ocean Drilling Program. Constant‐rate‐of‐strain consolidation tests yield estimates of in situ permeability that range from 2.6 × 10−17 m2 to 2.5 × 10−18 m2; overconsolidation ratios range from 1.7 to 2.6, and values of the compression index range from 0.39 to 0.78. Several processes contributed to the apparent overconsolidation. Strata dip toward land, and pore fluids probably migrate up‐dip and vent along a bathymetric notch near the seaward edge of the basin. Efficient lateral drainage through sandy turbidites has kept pore pressures within interbeds of mudstone at (or close to) hydrostatic. In addition, alteration of dispersed volcanic glass, precipitation of authigenic clay minerals, and collapse of random grain fabric has probably strengthened the bonding among grains. Cementation is particularly likely within the lower basin (unit III), where values of porosity remain anomalously high. If fluid overpressures (and underconsolidation) exist anywhere within the basin, the most likely loci are where sandy turbidites terminate against impermeable mudstones along landward‐dipping on‐lap surfaces. Those types of on‐lap geometries, in addition to structural closures, might provide promising targets for oil/gas accumulation in other forearc basins, particularly where petroleum source rocks have been buried to the optimal depths of catagenesis.

Dolomite effect on borosilicate glass alteration

Dolomite (CaMg(CO3)2) is one of the common rock-forming minerals in many geological media, in particular in clayey layers that are currently considered as potential host formations for a deep radioactive waste disposal facility. Magnesium in solution is one of the elements known to potentially enhance the alteration of nuclear glasses. The alteration of borosilicate glasses with dolomite as a Mg-bearing mineral source was investigated for 8months in batch tests at 90°C. Glass composition effects were investigated through two compositions (SiBNaAlCaZrO and SiBNaAlZrO) differing in their Ca content. The Ca-rich glass alteration is slightly enhanced in the presence of dolomite compared to the alteration observed in pure water. This greater alteration is explained by the precipitation of Mg silicate phases on the dolomite and glass surfaces. In contrast, the Ca-free glass alteration decreases in the presence of dolomite compared to the alteration observed in pure water. This behavior is explained by Ca incorporation in the amorphous layer (formed during glass alteration) coming from dolomite dissolution. Calcium acts as a layer reorganizer and limits glass alteration by reducing the diffusion of reactive species through the altered layer. Modeling was performed using the GRAAL model implemented within the CHESS/HYTEC geochemical code to discriminate and interpret the mechanisms involved in glass/dolomite interactions. Magnesium released by dolomite dissolution reacts with silica provided by glass alteration to form Mg silicates. This reaction leads to a pH decrease. The main mechanism controlling glass alteration is the ability of dolomite to dissolve. During the experiment the quantities of secondary phases formed were very small, but for longer time scales, this mechanism could supply sufficient Mg in solution to form large amounts of Mg silicates and sustain glass alteration. The ability of the GRAAL model to reproduce the concentrations of elements in solution and solid phases regardless of the amount of dolomite and the glass composition strongly supports the basic modeling hypothesis.

Microbial and inorganic control on the composition of clay from volcanic glass alteration experiments

Biological activity plays a substantial role in the geochemistry of the Earth’s surface. Particularly interesting are effects on clay formation because clays are abundant and have high surface-to-volume ratio, resulting in clays making up a large fraction of the overall mineral-fluid interface and having an effective control of mineral reactions. Thus, biological control on clay composition would affect element budget globally and the mineralogy of subsequent diagenetic processes. Biological acceleration of clay production would result in enhanced clay control of mineral reactions and faster organic C sequestration, by adsorption on clay minerals, with implications for the C and related cycles. We investigated the combined effect of microbial activity and water chemistry on the composition of neoformed clay by reacting volcanic glass with natural waters covering a large composition range (fresh water from a lake and a spring, seawater, and hypersaline water). The microbes (bacteria, fungi, and algae) were totally or partially identified using molecular and microscopy techniques. The solid alteration products were analyzed using cryo-SEM to investigate the mineral-microbe interface and TEM-AEM to study the composition of the neoformed clay. The solution chemistry was also investigated. We found that clay composition was controlled mainly by glass chemistry, rather than biological activity, through a mechanism of in situ transformation. The resulting clay was Al-rich (dioctahedral composition). In one case (inorganic experiment, freshwater lake), the specific inorganic conditions of pH and Mg and Si concentration promoted formation of Mg-rich (trioctahedral clay). Microbes, however, did influence clay composition by confining glass grains in biofilms where water chemistry is significantly different from the bulk solution. Alteration in such conditions generated significant amounts of trioctahedral, Mg-rich clay in the hypersaline water experiment, whereas it favored production of dioctahedral, Al-rich clay in the freshwater lake experiment. It is thus demonstrated that biofilms can exert an effective control on clay mineralogy.

Impact of iron on nuclear glass alteration in geological repository conditions: A multiscale approach

Interactions between nuclear glass and Fe were investigated in a clayey environment to better understand the mechanisms and driving forces controlling the long-term behavior of high-level waste glass in a geological repository. An integrated experiment involving a Glass–Iron–Clay (GIC) stack was run at a laboratory scale in anoxic conditions for 2years and the interfaces were characterized by a multiscale approach using scanning electron microscopy coupled with energy dispersive spectroscopy, transmission electron microscopy, Raman microspectroscopy and scanning transmission X-ray microscopy at the SLS Synchrotron. The characterization of glass alteration patterns on cross sections revealed an increase in glass alteration with the Fe content and the proximity between the glass and Fe. The alteration layers are polyphase and stratified with an inner porous gel layer incorporating Fe and an outer layer composed of nanocrystalline Fe-silicates. Several mechanisms which could affect the glass alteration kinetics and the transport properties of the alteration layer are proposed to explain this pattern: (i) consumption of hydrolyzed silica by precipitation of Fe-silicates; (ii) penetration of Fe within the gel porosity probably as precipitates such as Fe oxyhydroxide or Fe-silicates. These new data may imply some consequences when considering the long-term behavior of glass in geological disposal conditions.

Dynamics of Water Confined in Gel Formed During Glass Alteration at a Picosecond Scale

This paper reports on the characterization at a picosecond scale of water dynamics in gel formed during glass alteration by neutron scattering. The water dynamics in gel are compared with the dynamics of water confined in porous silica-based material (MCM41) having pore wall surfaces with Si-OH, Al-OH, or Zr-OH terminal groups and pore sizes around 2.3nm in the presence of ions existing in a leachate derived from glass alteration. It is shown that the presence of ions does not impact the water mobility in model materials whatever the pore surface composition. In the gel, water is two to three times slower than in the bulk, and the fraction of fixed protons is similar to the model material having an Al-OH surface. Two hypotheses are proposed to explain these results: the ion concentrations in pores of the gel can be higher than in the leachate located outside the gel forming hydration shell around ions, thereby hindering the water motions, and/or the pore wall composition of the gel consisting of elements such Al that can immobilize water molecules. In addition to the Al effect, the presence of Ca can slow down water diffusion due to the binding of H2O molecules in strong complexes with Ca2+.

Glass-Iron-Clay interactions in a radioactive waste geological disposal: a multiscale approach

ABSTRACTIn France, nuclear glass canisters arising from spent fuel reprocessing are expected to be disposed in a deep geological repository using a multi-barrier concept (glass/canister/steel overpack and claystone). In this context, glass - iron or corrosion products interactions were investigated in a clayey environment to better understand the mechanisms and driving forces controlling the glass alteration. Integrated experiments involving glass - metallic iron or magnetite - clay stacks were run at laboratory scale in anoxic conditions for two years. The interfaces were characterized by a multiscale approach using SEM, TEM, EDX and STXM at the SLS Synchrotron. Characterization of glass alteration patterns on cross sections revealed various morphologies or microstructures and an increase of the glass alteration with the proximity between the glass and the source of iron (metallic iron or magnetite) due to the consumption of the silica coming from the glass alteration. In case of magnetite, the silica consumption is mainly driven by a sorption of silica onto the magnetite. For experiments containing metallic iron, the silica consumption seems to be strongly driven by silicates precipitation including Fe and Fe/Mg when the Fe is not enough available. Moreover, in addition to Fe-silicates observed at the surface of the gel layers, iron is incorporated within the gel probably as nanosized precipitates of Fe-silicates which could affect its physical and chemical properties. Those results highlighted the impact of the distance between glass and iron source and the nature of the iron source which drive the process consuming the silica coming from the glass alteration.