Showing papers on "Hematite published in 1999"
TL;DR: In this article, the authors investigated the kinetic effect of specific adsorption interactions on the chemical reduction of uranyl (UVIO22+) by ferrous iron, and derived a rate law for surface-catalyzed U(VI) reduction by Fe(II), d[U(VI)] dt =−k[≡ Fe III OFe II OH 0 ][U( VI)] ads where the bimolecular rate constant k has a value of 399 ± 25 M−1 min−1 at 25°C.
647 citations
TL;DR: In this paper, the micro-Raman spectra of hematite, magnetite and other iron oxides were compared with literature data and compared with a Stokes-Anti-Stokes procedure was used to control the local temperature during the measurement and also for calibration of the wavenumbers.
Abstract: Films and powders of iron oxide (Fe2O3) prepared by two different sol–gel syntheses, starting from Fe(NO3)3·9H2O or FeCl3·6H2O, were investigated by Raman microscopy. Different phases with different morphology were produced according to the preparation. The spectra obtained in the micro-Raman configuration were compared with the ambiguous data in the literature given by conventional Raman techniques. The principal difficulty in the correct interpretation of the Raman spectrum of the iron oxides is the co-existence of different phases. Contradictory results are also explained by laser–induced thermal effects which easily change the wavenumbers and lineshapes of the phonons. A Stokes–Anti-Stokes procedure was utilized to control the local temperature during the measurement and also for calibration of the wavenumbers. The micro-Raman spectra of hematite, magnetite and other iron oxides are presented and compared with literature data. Copyright © 1999 John Wiley & Sons, Ltd.
471 citations
TL;DR: It is maintained that no intermediate phases were positively identified between mono-, di-, and trimers and a range of solid polynuclear phases, which indicates fast polymerisation as the OH/Fe ratio of the system increases.
427 citations
TL;DR: In this paper, the temperature induced goethite-hematite phase transformation was studied using in situ synchrotron X-ray powder diffraction with a capillary Debye-Scherrer geometry and a translating image plate system (TIPS).
Abstract: The temperature induced goethite-hematite phase transformation that occurs at about 250 °C was studied using in situ synchrotron X-ray powder diffraction with a capillary Debye-Scherrer geometry and a translating image plate system (TIPS). To our knowledge, this is the first time the goethitehematite transformation has been investigated in real time. The sample was a pure, synthetic, stoichiometric goethite with 1 μm long needle-shaped crystals. The microstructural characterization showed that the sample was well crystallized. The Rietveld refinement of 30 powder patterns extracted from the image in the range 25‐800 °C demonstrates that an intermediate phase with nonstoichiometric composition (“protohematite” ) forms after the decomposition of goethite. The cell parameter b of goethite dramatically decreased during the phase transformation while a and c instead continued to increase. Protohematite is iron-deficient and retains residual hydroxyls for charge balance. With temperature protohematite progressively transforms into hematite. Empty layers (pores) are consequently formed about the hematite clusters. The distribution of iron vacancies was modeled in the powder patterns with stacking faults that were simulated using anisotropic broadening coefficients of the pseudo-Voigt profile function. Its disappearance with temperature was effectively followed with a decrease of the density of stacking faults.
295 citations
TL;DR: In this article, the effect of natural organic matter (NOM) on metal ion sorption to mineral surfaces is a complex function of the environment in which the mineral and ions reside, as well as the source, molecular weight distribution and composition of the NOM.
220 citations
TL;DR: In this article, the authors report on the results of a study on the sorption of U(VI) by hematite in the absence and presence of Suwannee river humic acid (HA) and over a range of other system conditions (e.g., pH, I).
219 citations
TL;DR: In this paper, transmission electron microscopy (TEM) with energy dispersive X-ray (EDX) analysis and EFTEM/EELS was used to study bed sediments from two acid mine drainage (AMD) sites in western Montana, USA.
174 citations
TL;DR: In this article, the pH-dependent variation of the interaction forces has been evaluated and the large experimental difference in the pH dependence of interaction force is in accord with the expected proton affinity behavior of both crystal faces, as predicted with the MUSIC model.
Abstract: Charging is a basic property of the solid/solution interface of minerals. The charging at different crystal faces depends on the surface chemical composition, that is, the type and number of proton-reactive surface groups. Atomic force microscopy has provided direct information on the pH-dependent charging properties of individual crystal faces (Eggleston and Jordan, Geochim. Cosmochim. Acta, 1998) of hematite (001 face) and quartz (101 face). This promising scanning force technique may enable the testing of structure−reactivity relations as applied in the MUlti SIte Complexation model (MUSIC). The published pH-dependent variation of the interaction forces has been evaluated. The large experimental difference in the pH dependence of the interaction force is in accord with the expected proton affinity behavior of both crystal faces, as predicted with the MUSIC model. The reactivity of the 001 face of hematite is quite exceptional, because the surface groups only charge at extremely high or low pH values in...
155 citations
TL;DR: In this article, the authors obtained uniform alpha-Fe2O3 particles within the nanometer range (100-300 nm) by precipitation of iron (III) perchlorate in the presence of urea.
146 citations
TL;DR: In this article, the crystallization of ferrihydrite prepared by hydrolysis of Fe(NO3)3 solutions containing phosphate was investigated at different pH (3-9), temperatures (298, 323, and 373 K), and initial P/Fe atomic ratios for periods to 730 d.
Abstract: We investigated the crystallization of ferrihydrite prepared by hydrolysis of Fe(NO3)3 solutions containing phosphate. Crystallization was studied at different pH (3-9), temperatures (298, 323, and 373 K), and initial P/Fe atomic ratios for periods to 730 d. Generally, crystallization was inhibited or only poorly crystallized lepidocrocite was formed at P/Fe > 2.5%. Phosphate favored the formation of hematite over goethite at all temperatures for most of the pH and P/Fe ranges investigated. This result is consistent with a model in which phosphate acts as a template for hematite formation, in analogy with other anions, such as oxalate. However, goethite was preferentially formed at alkaline pH and P/Fe > 1%, probably because high phosphate concentration resulted in a large increase in the negative charge of the ferrihydrite particles. This resulted in turn in less aggregation, a process that is known to precede dehydration to hematite. Phosphate greatly influenced the morphology of hematite and goethite. Hematite was often ellipsoidal or spindle-shaped. Twinned goethite crystals with a hematite core were formed at alkaline pH at P/Fe > 1%. Both hematite and goethite particles incorporated phosphate in an occluded form not desorbable by repeated alkali treatments.
125 citations
TL;DR: In this article, the sorption of dissolved Pu(V) on a natural zeolitic tuff that was equilibrated with synthetic groundwater was examined using synchrotron-based microanalytical techniques.
Abstract: Subsurface transport of groundwater contaminants is greatly influenced by chemical speciation, precipitation, and sorption processes. The transport of Pu potentially released from spent nuclear fuel disposal and storage sites will be dependent on its interaction with mineral surfaces and speciation in the subsurface. The sorption of dissolved Pu(V) on a natural zeolitic tuff that was equilibrated with synthetic groundwater was examined using synchrotron-based microanalytical techniques. The tuff contained trace quantities of smectites and iron and manganese oxides, which are present as fracture fill and pore space materials. Synchrotron-based micro-X-ray fluorescence (SXRF) showed that Pu is predominantly associated with manganese oxides (rancieite) and smectites but not with iron oxides (hematite). In situ micro-X-ray absorption near-edge structure (XANES) spectroscopy measurements on two highly enriched regions of Pu indicated that the average oxidation state of sorbed Pu was (+V) in one region and (+VI) in the other. The observed heterogeneous speciation of the sorbed Pu demonstrates the complex nature of this process. Thermodynamic equilibrium calculations indicated that the solution was dominated by negatively charged Pu species, suggesting that sorption to the negatively charged manganese oxide surfaces would be energetically prohibited. Subsequent speciation changes upon sorption to manganese oxide surfaces are discussed.
TL;DR: This paper showed that the formation of iron ore at one of those deposits, Mount Tom Price, involved initial high temperature crystallisation of magnetite-siderite-iron silicate assemblages.
Abstract: Giant iron-ore deposits, such as those in the Hamersley Province of northwestern Australia, may contain more than a billion tonnes of almost pure iron oxides and are the world's major source of iron. It is generally accepted that these deposits result from supergene oxidation of host banded iron formation (BIF), accompanied by leaching of silicate and carbonate minerals. New textural evidence however, shows that formation of iron ore at one of those deposits, Mount Tom Price, involved initial high temperature crystallisation of magnetite-siderite-iron silicate assemblages. This was followed by development of hematite- and ferroan dolomite-bearing assemblages with subsequent oxidation of magnetite, leaching of carbonates and silicates and crystallisation of further hematite. Preliminary fluid inclusion studies indicate both low and high salinity aqueous fluids as well as complex salt-rich inclusions with the range of fluid types most likely reflecting interaction of hydrothermal brines with descending meteoric fluids. Initial hematite crystallisation occurred at about 250 °C and high fluid pressures and continued as temperatures decreased. Although the largely hydrothermal origin for mineralisation at Mount Tom Price is in conflict with previously proposed supergene models, it remains consistent with interpretations that the biosphere contained significant oxygen at the time of mineralisation.
TL;DR: In this article, the solid-state phase transition of nanocrystalline maghemite to hematite was investigated by energy dispersive x-ray diffraction (EDXRD).
Abstract: Homogeneous maghemite (γ–Fe2O3) nanoparticles with an average crystal size around 5 nm were synthesized by successive hydrolysis, oxidation, and dehydration of tetrapyridino-ferrous chloride. Morphological, thermal, and structural properties were investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and x-ray diffraction (XRD) techniques. Rietveld refinement indicated a cubic cell. The superstructure reflections, related to the ordering of cation lattice vacancies, were not detected in the diffraction pattern. Kinetics of the solid-state phase transition of nanocrystalline maghemite to hematite (α–Fe2O3), investigated by energy dispersive x-ray diffraction (EDXRD), indicates that direct transformation from nanocrystalline maghemite to microcrystalline hematite takes place during isothermal treatment at 385 °C. This temperature is lower than that observed both for microcrystalline maghemite and for nanocrystalline maghemite supported on silica.
TL;DR: In this article, the authors investigated three series of ferrihydrite-rich samples prepared by coprecipitation and found that the highest activity, 100% conversion after 20 min on line, was observed in a dried sample that contained ferri hydrite and a non-crystalline and possibly hydrated gold oxyhydroxide phase, AuOOH·xH2O.
Abstract: In the light of a recent study which identified the beneficial influence of poorly crystallised ferrihydrite Fe5HO8·4H2O on the activity of CO conversion catalysts comprising gold nanoparticles on oxidic iron, we have investigated three series of ferrihydrite-rich samples prepared by coprecipitation. The samples were structurally and chemically characterised using X-ray diffraction and both 57Fe and 197Au Mossbauer spectroscopy, and tested for CO oxidation at room temperature using a microreactor with on-line GC. The highest activity, 100% conversion after 20 min on line, was observed in a dried sample that contained ferrihydrite and a non-crystalline and possibly hydrated gold oxyhydroxide phase, AuOOH·xH2O. The activity of the same materials after calcination, where the gold was transformed to 3–5 nm Au metal particles and the ferrihydrite to hematite, was less than ca. 7%. This is the first report of a synergistic interaction between AuOOH·xH2O and ferrihydrite resulting in an active catalyst for room temperature CO oxidation, and contrasts with previous work which has been interpreted in terms of the requirement for metallic Au nanoparticles.
TL;DR: In this paper, the authors used X-ray diffraction and transmission electron microscopy to distinguish heated goethite from natural hematite using a double signature, namely selective broadening of diffraction reflections and porous nanostructure.
Abstract: Yellow goethite (α-FeOOH) and red hematite (α-Fe 2 O 3 ) were used as pigments by Palaeolithic painters. When heated, goethite dehydrates and transforms to hematite. Archaeologists wonder whether prehistoric people knew of this property and used it. We present a way to distinguish heated goethite from natural hematite. The methods used are X-ray diffraction and transmission electron microscopy. A double 'signature', namely selective broadening of diffraction reflections and porous nanostructure, is evidenced in heated goethite. Coupled with mineralogical associations, this allows us to establish a procedure to investigate the natural or artificial origin of hematite samples. Applied to the Palaeolithic site of Troubat, it reveals no difference between the Magdalenian and Azilian cultures concerning the heat-treatment of pigments; an area specializing in heat-treating pigments may, nevertheless, have existed inside the cave, which would indicate that heating was deliberate.
TL;DR: In this article, the results showed that anatase, brookite and trace of hematite coexisted at lower pH (1.8 and 3.6) and at higher pH (6.0), the uniform solid solution of iron-titanium oxide formed.
Abstract: Fe(III)-doped TiO2 nanoparticles with different Fe(III) content (at %, nominal) have been prepared at different pH using hydrothermal method. The products were characterized by X-ray powder diffraction, transmission electron microscope, electron diffraction, diffuse reflectance spectra, XPS and spot EDX analysis. All the studies showed that anatase, brookite and trace of hematite coexisted at lower pH (1.8 and 3.6) when Fe(III) content was as low as 0.5% and the distribution of iron ions was non-uniform between particles. But at higher pH (6.0), the uniform solid solution of iron-titanium oxide formed. The photoelectrochemical properties were studied by measuring photocurrent at different electrode potentials and the results showed the phenomena of p-n photoresponse existence in samples prepared at pH 1.8–6.0.
TL;DR: In this article, a simple geochemical balance of lateritization processes governing the development of several tens of meters of weathering profiles overlain by ferricretes is estimated on the basis of detailed mineralogical and geochemical data.
TL;DR: In this paper, three different synthetic methods are used to investigate the temperature dependence of the fractionation between water and hematite, akaganeite, and goethite at near-surface temperatures.
TL;DR: In this paper, a cubic zirconia doped with iron oxide has been synthesized by high-energy ball milling from powder mixtures of monoclinic ZrO2 and hematite.
Abstract: Fully stabilized cubic zirconia doped with iron oxide has been synthesized by high-energy ball milling from powder mixtures of monoclinic zirconia and hematite. It is found that the iron ions dissolved in cubic ZrO2 are in substitutional positions with a maximum solubility of approximately 18.5 mol% α–Fe2O3. The unit-cell volume of the cubic ZrO2 phase decreases with increasing iron content. During heating the cubic-to-tetragonal transition occurs at approximately 827 °C and the tetragonal-to-monoclinic transition seems to be absent at temperatures below 950 °C. During cooling the tetragonal-to-monoclinic transition occurs at 900–1100 °C.
TL;DR: In this paper, the authors conclude that the magnetic particles present in the airborne dust particles are most likely Maghemite (γ-Fe2O3) or magnetite (Fe3O4).
Abstract: The Mars Pathfinder lander carried two magnet arrays, each containing five small permanent magnets of varying strength. The magnet arrays were passively exposed to the wind borne dust on Mars. By the end of the Mars Pathfinder mission a bull's-eye pattern was visible on the four strongest magnets of the arrays showing the presence of magnetic dust particles. From the images we conclude that the dust suspended in the atmosphere is not solely single phase particles of hematite (α-Fe2O3) and that single phase particles of the ferrimagnetic minerals maghemite (γ-Fe2O3) or magnetite (Fe3O4) are not present as free particles in any appreciable amount. The material on the strongest magnets seems to be indistinguishable from the bright surface material around the lander. From X-ray fluorescence it is known that the soil consists mainly of silicates. The element iron constitutes about 13% of the soil. The particles in the airborne dust seem to be composite, containing a few percent of a strongly magnetic component. We conclude that the magnetic phase present in the airborne dust particles is most likely maghemite. The particles thus appear to consist of silicate aggregates stained or cemented by ferric oxides, some of the stain and cement being maghemite. These results imply that Fe2+ ions were leached from the bedrock, and after passing through a state as free Fe2+ ions in liquid water, the Fe2+ was oxidized to Fe3+ and then precipitated. It cannot, however, be ruled out that the magnetic particles are titanomagnetite (or titanomaghemite) occurring in palagonite, having been inherited directly from the bedrock.
TL;DR: In this paper, the influence of Ni or Pb sorption on the kinetics of ferrihydrite crystallization to goethite/hematite was examined, and it was shown that metals with a higher stability constant would retard the transformation process to a greater extent.
TL;DR: In this paper, a fly ash from a high-sulfur coal source was wet-sieved at 100, 200, 325, and 500 mesh and each of the five size fractions was then magnetically separated.
TL;DR: In this article, a data set for the Sorption of Np(V) on hematite is provided and the effect of carbonate species on neptunyl (NpOJ) Sorption as a function of partial pressures of COj is investigated.
Abstract: A data set for the Sorption of Np(V) on hematite is provided and the effect of carbonate species on neptunyl (NpOJ) Sorption as a function of partial pressures of COj is investigated. Data for neptunyl Sorption on goethite and quartz are also presented. The Sorption of carbonate species on hematite was investigated and the data are compared to carbonate sorption by goethite as reported by van Geen et al. [1]. Finally, the sorption data are analyzed with nXEQL (v 3.1; [2]) and the Triple Layer Model configuration (TLM: Davis et al. [3]) of the particle/water interface is invoked. Binding constants of postulated surface species are presented. Surface Charge density data from Potentiometrie titrations of the hematite suspension at different ionic strengths (NaC104) were analyzed with FITEQL and TLM parameters were estimated (pK., = 8 . 4 ; pK.2 = 10.4; pK^.^ = 8.55; pKc,04= -10 .33; n, = 1.86 n m ' ^ C, = 1.6 F/m^ C^ = 0.2 F/m'). A pHpzc of 9.4 ± 0 . 1 was determined. Neptunium sorption by hematite is independent of ionic strength (0.005 to 0.1 M NaC104) for the experimental conditions of Np(V)T = 1.2 X 10\"' M and 4.46 X 10\"' M hematite surface sites. Under these conditions, fractional Np sorption was in the pH ränge of 6 to 8. FITEQL analysis of the adsorption data was achieved with an inner-sphere surface complexation reaction
TL;DR: In this article, a combination of selective dissolution, magnetic susceptibility, and X-ray dif- fraction (XRD) techniques was used to quantify or characterize the soil component of fine-grained maghemite.
Abstract: Many soils developed from volcanic rocks in southern Brazil exhibit spontaneous magneti- zation caused by the presence of fine-grained maghemite (3J-Fe203), but few attempts were made to quantify or characterize this important soil component. To that end, clays were separated from freely drained soils derived from acid (>~63% Sit2), intermediate (54-62% SiO~), and basic (--<53% Sit;) igneous rocks produced by the Paranfi flood volcanism. The sample set included soils with a wide range of pedogenic development on different landscape positions. The Fe oxide mineralogy of these samples was examined by using a combination of selective dissolution, magnetic susceptibility, and X-ray dif- fraction (XRD) techniques. Hematite and maghemite were the primary Fe oxides in mature soils (Oxisols, Ultisols, and Alfisols) developed from basic rocks; whereas goethite was dominant in all other soils, especially those formed from acid-intermediate rocks. The association of maghemite with basic rock materials suggests that it was primarily formed by oxidation of lithogenic magnetite. A strong, positive correlation (R 2 = 0.89) was obtained between mass specific magnetic susceptibility (X) of the clay frac- tions and maghemite contents estimated by XRD. Either method could be used for quantitative analyses, but X was more sensitive than XRD at low maghemite concentrations (<2 wt. %). The clay-sized maghem- ites were superparamagnetic with an estimated value for the mass specific magnetic susceptibility (X~f) value of 91,000 10 -8 m 3 kg ~ and frequency dependent variations of 10-15%. The maghemites also had low unit cell constants, which, if attributed entirely to replacement of Fe by AI, would correlate with AI substitutions in the range of 5-16 mole %. Selective dissolution of the soil maghemites was achieved by treatment of Fe oxide concentrates with 1.8 M I-I2SO 4 at 75~ for 2 h.
TL;DR: In this article, the speciation of chromium in overlayers on atomically clean surfaces of single crystal magnetite (Fe 3 O 4 ) and hematite (α-Fe 2 O 3 ) were studied using Cr L-edge, Fe Ledge, and O K-edge X-ray absorption spectra collected with synchrotron radiation.
TL;DR: In this paper, a parameterized classical potential model for the interaction of water and hydroxide with iron oxide was used to calculate the optimal proton arrangement and proton binding energies on the (012) surface of hematite.
TL;DR: In this paper, the recovery of hematite fines from quartz and corundum using selective magnetic coating was studied as a function of pH, particle size, magnetic colloidal concentration, magnetic field strength and ratio of hemetite:quartz Synthetic mixtures assaying around 45-72% Fe2O3 was upgraded to 90-92% with recovery level of 90-96%.
TL;DR: In this paper, the authors demonstrate the ability of Raman spectroscopy to determine the mineralogical character of a rock that originated on Mars using point analyses and multipoint scans using laboratory spectrometers.
Abstract: To demonstrate the ability of Raman spectroscopy to determine the mineralogical character of a rock that originated on Mars, we analyzed a small slab of “normal Zagami” by point analyses and multipoint scans using laboratory spectrometers Spectra of clinopyroxenes were dominant; their compositions were estimated from a calibration of Raman peak positions with Mg/(Mg+Fe) based on lunar pyroxenes of known composition, and these agree with compositions obtained by electron microprobe A few spectra of orthopyroxene were observed The broad spectrum of maskelynite was observed, but not that of plagioclase feldspar Spectra of minor phosphates, magnetite, and pyrrhotite were obtained, as were spectra of an organic contaminant and of hematite, both apparently introduced during sample handling prior to Raman analysis The modal analysis based on the multipoint scans agrees well with published values If the spectra had been obtained on the surface of Mars by Raman spectroscopic analysis as a stand-alone method and no other information about the sample was available (and by ignoring the spurious hematite and organic material), we could rule out sedimentary and plutonic rock types and conclude that the sample was a pyroxene-phyric basalt
TL;DR: It is demonstrated that in situ Mossbauer spectroscopy can help determine whether hydrothermal mineral deposits exist on Mars, which is significant for exobiology because of the issue of whether that world ever had conditions conductive to the origin of life.
Abstract: Hydrothermal spring systems may well have been present on early Mars and could have served as a habitat for primitive life. The integrated instrument suite of the Athena Rover has, as a component on the robotic arm, a Mossbauer spectrometer. In the context of future Mars exploration we present results of Mossbauer analysis of a suite of samples from an iron-rich thermal spring in the Chocolate Pots area of Yellowstone National Park (YNP) and from Obsidian Pool (YNP) and Manitou Springs, Colorado. We have found that Mossbauer spectroscopy can discriminate among the iron-bearing minerals in our samples. Those near the vent and on the surface are identified as ferrihydrite, an amorphous ferric mineraloid. Subsurface samples, collected from cores, which are likely to have undergone inorganic and/or biologically mediated alteration (diagenesis), exhibit spectral signatures that include nontronite (a smectite clay), hematite (alpha-Fe2O3), small-particle/nanophase goethite (alpha-FeOOH), and siderite (FeCO3). We find for iron minerals that Mossbauer spectroscopy is at least as efficient in identification as X-ray diffraction. This observation is important from an exploration standpoint. As a planetary surface instrument, Mossbauer spectroscopy can yield high-quality spectral data without sample preparation (backscatter mode). We have also used field emission scanning electron microscopy (FESEM), in conjunction with energy-dispersive X ray (EDX) fluorescence spectroscopy, to characterize the microbiological component of surface sinters and the relation between the microbiological and the mineralogical framework. Evidence is presented that the minerals found in these deposits can have multi-billion-year residence times and thus may have survived their possible production in a putative early Martian hot spring up to the present day. Examples include the nanophase property and the Mossbauer signature for siderite, which has been identified in a 2.09-billion-year old hematite-rich chert stromatolite. Our research demonstrates that in situ Mossbauer spectroscopy can help determine whether hydrothermal mineral deposits exist on Mars, which is significant for exobiology because of the issue of whether that world ever had conditions conductive to the origin of life. As a useful tool for selection of samples suitable for transport to Earth, Mossbauer spectroscopy will not only serve geological interests but will also have potential for exopaleontology.
TL;DR: In this paper, a study was carried out on synthetic goethite samples using XRD and TEM and the existence of water up to high heating temperatures was found to be coherent with the typical porous microstructure accompanying the phase transformation.
Abstract: Red and black were the two colours around which Palaeolithic art was organised. Manganese oxides and charcoal were the black pigments and hematite (α-Fe 2 O 3 ) the red one. The latter mineral is naturally abundant, but archaeological observations nevertheless suggest that the well-known colour change accompanying the dehydration of yellow goethite (α-FeOOH) to red hematite may have been employed by Prehistoric artists to obtain red pigment. In order to confirm this assumption, a study was carried out on synthetic goethite samples using XRD and TEM. In particular, the goethite-to-hematite transformation was observed in situ and provided useful information about both dehydration and recrystallisation processes. The existence of water up to high heating temperatures was found to be coherent with the typical porous microstructure accompanying the phase transformation. Similar studies were carried out on archaeological hematites coming from Troubat, a French Pyrenean Palaeolithic site. Characteristic features of previous heating were identified, such as pores or small amounts of maghemite (α-Fe 2 O 3 ), which confirms that Prehistorics had acquired this technical know-how.