Traces Of Hematite Research Articles

Raman Investigations on the Frame of the Painting “White Man’s Buffalo” by the Artist Charles M. Russell

The present work was a part of pre conservation treatment investigation. Micro-Raman Spectroscopy has been used for the characterization of a specimen belonging to the frame of the Gilcrease Museum oil painting “White Man’s Buffalo” by the artist Charles M. Russell. The main components of the Van Dyck Brown pigment (VDK) such as hematite (Fe2O3), α-goethite (α-FeOOH), amorphous carbon, and humic substances were identified by using two different excitation sources (514 and 633 nm). Traces of hematite and intercalated barite (BaSO4) were found and could come from the Armenian Bole that is commonly used in the water gilding technique of gold leaf. The use of a protein-organic binding medium such as rabbit-skin glue was indicated.

Scientific study of the pigments and binders used in mural painting from the 16th‐century ce St Mary's Church of Cheriapally, Kottyam, Kerala, and its relevance to conservation

AbstractThe aim of this investigation was to analyze the materials and techniques of the paintings in the 16th‐century ce St Mary's Church, to evaluate deterioration of the paintings, and to propose a suitable conservation treatment for their preservation. The material analysis of ground, pigments, binders, and plasters was undertaken using binocular microscopy, field emission scanning electron microscopy (SEM)–energy dispersive X‐ray spectroscopy, X‐ray fluorescence, Fourier transform infrared spectroscopy in reflectance (KBr) and transmittance mode (attenuated total reflection), thin‐film X‐ray diffraction, and micro‐Raman spectroscopy. Gas chromatography–mass spectrometry (GC‐MS) was used for identifying proteinaceous and lipidic materials extracted from the micro‐samples. The study generated data on two different red and green pigments used as decorative materials. The red pigments were identified as cinnabar along with traces of hematite and clay minerals, and green as malachite and the minor presence of other minerals. SEM analysis identified cotton fiber embedded in the coarse plaster layer that provided better strength to the plaster. Plant oils and proteins found as the binder in the pigment samples suggested that the painting technique was executed as tempera. Lead white and gypsum materials were used in previous restoration works.

A preliminary mineralogical and physicochemical characterization of the Neogene clays from the Timgad Basin (Massif of Aur\xe8s, NE Algeria): potential use in the manufacturing of bricks and ceramic industry

This study aims at the mineralogical and physicochemical characterization of the clay formations of the Miocene age from the Timgad Basin (Massif of Aurès, NE Algeria), in order to evaluate their possible valorization, notably for their potential use in the manufacturing of bricks and ceramic industry. For this purpose, four samples were taken from a clay-dominated formation that outcrops 5 km east of the Timgad city. Each sample was collected, prepared, and analyzed by the appropriate analytical methods of characterization such as X-ray diffraction, X-ray fluorescence, and scanning electron microscopy. Moreover, other complementary analyses are performed in this study such as laser granulometry and geotechnical tests. The results of the different tests revealed that the clay formations of the Timgad Basin are non-refractory clays and characterized by medium plasticity. These clays are constituted of more than 50% of fine fraction, mainly represented by kaolinite in association with non-negligible proportions of illite, chlorite, mixed-layer clay minerals, and traces of smectite. Besides, this clayey assemblage is accompanied by some proportion of quartz and calcite, as well as traces of hematite, feldspar, and gypsum. In the light of these results and in combination with the particle size distribution, as well as the results of geotechnical tests, it is concluded that the Neogene clays of the Timgad Basin present high limits of Atterberg. Consequently, their use in the field of manufacturing of bricks and terra cotta ‘Terre Cuite’ products is subordinated to a preliminary treatment with addition of a degreasing agent, in the form of coarse sand, in order to improve their plasticity.Article HighlightsMineralogical and physicochemical properties of the Neogene clays from the Timgad Basin have been investigated.The studied clays have ideal mineralogical composition and physicochemical properties thus making them applicable in the manufacturing of bricks and ceramic industry.Addition of coarse sand to the Neogene clays will greatly improve the plasticity of these raw materials.

Towards a detailed comprehension of the inertisation processes of amphibole asbestos: in situ high-temperature behaviour of fibrous tremolite

AbstractThermal behaviour of fibrous tremolite from Maryland, USA has been investigated in situ up to breakdown temperature. Tremolite can be found both as primary constituent and as contaminant in Asbestos Containing Materials (ACMs). The products of breakdown are subcalcic diopside and calcium-rich clinoenstatite in a 2:1 ratio, traces of hematite plus minor silica-rich amorphous material. Thermal expansion follows a regular trend up to 723 K before the onset of Fe2+ oxidation/OH– deprotonation which is completed at 1023 K. At 923 K the Fe3+ migration starts towards M(1) and the corresponding counter-migration of Mg to M(2) and M(3). At T close to structure breakdown, M(2) shows a significant site-scattering reduction possibly consistent with the occurrence of minor vacancies. In fully oxidised tremolite, Fe3+ is allocated prevalently at M(1) and subordinately at M(3). As it is well-known that M(1), along with M(2), is the most exposed octahedral site at the surface of amphiboles, most of the Fe3+ is available for participating in the Fenton-like reactivity of oxidised tremolite, potentially making it dangerous for human health. This point should be properly taken into account in the evaluation of the safety of thermally decomposed tremolite-containing ACMs, in particular in the case of accidentally incomplete treatments.

Structural, textural, morphological, magnetic and electromagnetic study of Cu-doped NiZn ferrite synthesized by pilot-scale combustion for RAM application

The synthesis of the Ni0.5-xZn0.5-xCu2xFe2O4 (x = 0; 0.10 and 0.15) ferrite with the differential of pilot-scale production by the combustion reaction method was investigated for RAM application purposes. Combustion temperatures ranging from 682 °C to 738 °C were observed. All ferrites were sintered at 1200 °C for 1 h. A comprehensive study of the influence of substitution with Cu2+ in a partial and proportional way to the Ni2+ and Zn2+ ions, doping mode little reported in the literature, and also of the sintering process over the structural, textural, morphological, magnetic and electromagnetic properties of NiZnCu ferrites was performed. The XRD patterns of the ferrites as synthesized revealed the formation of the cubic structure of the inverse spinel as majoritary phase, and traces of hematite and zinc oxide as segregated phases. After sintering, it was proven the single-phase formation of cubic spinel ferrite structure. The introduction of Cu led to a reduction in the lattice parameter, whose values ranged from 8.337 to 8.385 Å. The EDX results confirm the composition of oxides. The textural and morphological analyses confirmed the densest characteristic, with increase of particle size and reducing of surface area and pore volume after Cu-doping. All ferrites showed characteristics of soft ferrimagnetic material, where the increase in Cu content contributed to a slight reduction in saturation magnetization, whose values were of ~22–29 emu/g for the as synthesized ferrites and ~71–85 emu/g for the sintered ones. The best result of electromagnetic absorption in X-band was presented by the sintered ferrite with 0.3 mol of Cu, reaching an attenuation of 99.8% at 11.5 GHz frequency, thus confirming the efficiency of the pilot-scale combustion synthesis in obtaining a ferrite with great potential for RAM application.

Mineralogical petrographic and geochemical characterization of marmora from the Roman quarries of Cabra (Córdoba) and Antequera (Málaga), External Sector Areas of the Betic Chain, Spain

This paper the results of the mineralogical-petrographic and geochemical characterization of marmora from the quarry sectors of Cabra, Córdoba, and Antequera, Málaga in Spain. They are located in the western area of the Subbetic Zone within the Betic Chain and were exploited as marmora in Roman times. The archaeometric analysis of these quarries has a great importance for archaeological research since the proper characterization of geological outcrops to know the source of a significant number of architectural, epigraphic, sculptural, inscription and decoration elements used in the Roman Baetica province. As it is very difficult to determine the commercialization area or use for each rock type found in these two quarries sectors, the study methodology proposed in this paper is based on the characterization of the rocks sampled from these quarries by using also different analytical techniques, including polarized optical microscopy, X-ray diffraction and X- ray fluorescence. In the Cabra quarries three stone lithotypes have been identified: CW1, C-R1 and C-R2. The C-R1 and C-R2 lithotypes (Red Cabra varieties) show differences from a petrographic-mineralogical and chemical point of view: higher SiO2 and Al2O3 in C-R1 than in C-R2, which is related to a higher content in quartz and phyllosilicates, the C-R2, which also presents calcite-filled veins and traces of hematite. In the Antequera quarries, four stone lithotypes have been identified: A-RS, A-W2, A-R and A-BR lithotypes. The A-R lithotype (Red Antequera variety) is characterized by presence of siderite, iron oxides and pelagic ooids. The breccia (A-BR) show fragments of red micritic and oolitic limestones, a characteristic stone variety of the Penibetic. The A-RS lithotype contains siderite and hematites. Petrographic or mineralogical differences have not been found in the white varieties (CW1 and A-W2), but some geochemical differences related to higher content in P2O3 in CW1 are of particular interest.

Clove and cinnamon: Novel anti–oxidant fuels for preparing magnetic iron oxide particles by the sol–gel auto–ignition method

Magnetic spinel ferrite particles were successfully prepared from only iron (III) nitrate, using clove and cinnamon plant extracts for the first time as eco-fuels for auto–ignition synthesis. Both natural substances were shown to play dual roles in the synthesis of the magnetic particles; i.e. as fuels (agents for biogenic reduction), and as anti–oxidants for preserving the magnetic phases during subsequent heating. In this regard, no special protective environments such as H2/N2 or argon gases were required during the heat stabilisation process, and samples could be stabilised by heating to 550 °C in air. The magnetic crystalline phase is mostly maghemite (γ-Fe2O3) rather than magnetite (Fe3O4), as revealed by Raman, since no Raman active phonon modes were detected for magnetite, and most of the bands were related to maghemite, with traces of hematite. Both fuels produced strongly magnetic soft ferrites, with magnetisation values of 75 A m2 kg−1, around the expected ones for maghemite Moreover, TG curves showed that maghemite degradation only occurs at relatively high temperatures, namely at 550 °C for Clove, and at 744 °C for Cinnamon, confirming the sustainable nature of the as-obtained materials against oxidation.

Palaeo- and rock-magnetic investigations across Jurassic-Cretaceous boundary at St Bertrand’s Spring, Drôme, France: applications to magnetostratigraphy

Palaeo- and rock-magnetic investigations of the St Bertrand’s Spring (Le Ravin de Font de St Bertrand) locality in France were carried out in order to contribute to, and improve, the stratigraphy of the Jurassic-Cretaceous boundary interval. Magnetic susceptibility shows slightly diamagnetic behaviour in the lowermost part of the profile and an increase (paramagnetic) towards its middle and upper parts. Rock-magnetic measurements throughout the section show magnetite as the main magnetic fraction, together with traces of hematite. Additionally, thermal demagnetization indicates the presence of goethite. Our magnetostratigraphy indicates three normal/reversed polarity sequences; possibly encompassing the magnetozones M19r to the M17n. This suggests that the St Bertrand section straddles the Tithonian/Berriasian boundary and reaches the middle Berriasian sensu lato.

Influence of electron-beam irradiation on surface properties of magnetic iron oxide nanoparticles stabilized with citrate

Influence of electron beam (EB) irradiation on surface properties of magnetite was investigated using XRD, TEM, DLS, zeta-potential, FTIR and Raman spectroscopy. Fe3O4 particles were synthesized by alkaline hydrolysis of ferrous ions and stabilized with sodium citrate. Dry samples of bare and citrate- coated Fe3O4 particles were EB-irradiated with doses up to 300 kGy. The crystallite sizes of uncoated and citrate-coated magnetite were found to be in the range of 25–27 nm and 30–32 nm, respectively. EB- irradiation did not result in phase and size change of Fe3O4 nanoparticles. Using DLS and TEM analysis, it has been found, that EB-irradiated bare Fe3O4 nanoparticles have aggregated in aqueous dispersion. Traces of hematite and maghemite were identified on the surface of EB-irradiated bare particles by Raman spectroscopy. Radiation-induced oxidation of magnetite was probably involved to radiolysis of water molecules adsorbed onto particle surface and formation of hydroxyl radicals which are strong oxidize species. Disaggregation of citrate-coated particles in water dispersion after EB irradiation has been assigned to disruption of Fe-citrate bonds.

Thermal properties of some Egyptian kaolin pastes for pelotherapeutic applications: Influence of particle geometry on thermal dosage release

Abstract The present study aims to evaluate the potentiality of 7 selected structural highly ordered kaolinite-rich samples from Egyptian Carboniferous sedimentary deposits (located at Abu Zenima district, west central Sinai peninsula) to use them in medicinal semisolid formulations as peloids. The effect of particle geometry and kaolinite crystallite size are studied to check their influence on thermal dosage performance. The studied samples exhibit a variable mineralogy. Kaolinite is the main constituent (ranging from 81 to 94%), followed by quartz (up to 14%), lesser amounts of anatase and halite, and traces of hematite, magnetite, alunite and gypsum. The kaolinite order “Hinckley Index” varies from 1.28 to 1.50. 1:1 (w/w) kaolin mud pastes were prepared with purified water in Eppendorf tubes using a touch vibration vortex mixer for 2 min. The cooling kinetics of pastes were measured by using a differential scanning calorimetry equipment (Shimadzu DSC-50Q). Specific heats were calculated, following Cara et al. (2000). The granulometry and geometric surface area were measured by laser diffraction (Mastersizer 2000LF, Malvern Instruments) in the range 0.02 and 1500 μm. All analyzed samples showed a clear predominance of particles under 4 μm (ranging from 82 to 94%), with median size (D50) ranging from 0.93 to 1.35 μm. The heat retention time during cooling from 50 °C to 32 °C reached up to 30.82 min, oscillating around an average of 28.72 min, and the temperature corresponding to the minimal dosage time (T20) was not exceed below 34.7 °C. A good correlation (R2 = 0.875) was found between heat retention time and specific heats. There is no correlation between kaolinite content and thermal properties, but R2 values around 0.6 are found with granulometry (finer the particles, greater the heat retention time t32 and the specific heat). Even if sample H5 (Gabal Hazbar deposit) is not the richest in kaolinite, it exhibits the best thermal dosage performance, in accordance with the granulometry (D50 = 0.93 μm), and geometric surface area (3.73 m2/g).

Avaliação microestrutural e magnética de Fe3O4 sintetizada pelo método de reação de combustão

ResumoNanopartículas de magnetita têm sido objeto de inúmeras pesquisas científicas em diversas áreas, como por exemplo na biomedicina, devido à magnetização espontânea, estabilidade química e não toxicidade. Este trabalho tem como objetivo avaliar as propriedades microestruturais e magnéticas de nanopartículas de magnetita (Fe3O4) sintetizadas por reação de combustão induzida em forno de micro-ondas sob atmosfera de nitrogênio. A influência do fluxo de N2 durante a síntese na estrutura, morfologia e característica magnética do produto sintetizado foi investigada. As amostras foram caracterizadas por difração de raios X, microscopia eletrônica de varredura e medidas magnéticas. Os resultados mostram que foi possível obter a fase magnetita com traços de hematita (Fe2O3). O fluxo de N2 e o tempo de exposição interferiram na estrutura e na característica magnética do produto sintetizado. Todas as amostras apresentaram pequenos aglomerados de formas irregulares e tamanhos que variam em aproximadamente 20 μm e magnetização de saturação entre 31 e 70 emu/g, mostrando ser materiais promissores para aplicações na biomedicina.

Magnetic Properties of Mg<sub>0.4</sub>Ca<sub>0.6</sub>Fe<sub>2</sub>O<sub>4</sub> Nanoparticles Synthesized by Sol-Gel Method for Hyperthermia Treatment

Powders of Mg0.4Ca0.6Fe2O4were prepared by sol-gel using ethylene glycol and Mg, Ca and Fe nitrates as starting materials. Those powders were heat treated at different temperatures (300, 400, 500 and 600 °C) for 30 min. The materials obtained were characterized by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). The Ca-Mg ferrite with the most appropriate magnetic properties was further analyzed by transmission electron microscopy (TEM). The heating capability of the nanoferrites was also tested via magnetic induction. The XRD patterns of these Ca-Mg ferrites showed a cubic inverse spinel structure. Furthermore, neither traces of hematite nor orthorhombic Ca ferrite phases were detected. Moreover, all the Ca-Mg ferrites are superparamagnetic and the particle size distribution of these Ca-Mg magnetic nanoparticles exhibits an average diameter within the range of 10-14 nm. The needed temperature for hyperthermia treatment was achieved at around 12 min.

Evaluation of the effectiveness of treatment products in improving the quality of ceramics used in new and historical buildings

Abstract Ceramic samples made with a mixture of 70% ball clay and 30% quartz sand were moulded and then fired at 900 °C in an electric kiln. Samples were then treated with different products and analyses and tests were performed to evaluate the physical changes induced by the application of these products and their effects on the quality of the ceramics. A petrographic study indicated that the ceramics were composed of quartz, small amounts of mullite and sanidine and traces of hematite. Mineral clays (i.e. kaolinite) disappeared during firing. Two consolidating products (Paraloid B72 and Tegovakon V) and one water repellent (Silo 111) were applied to samples by capillarity, and physical changes (colour, water flow, porosity and pore size distribution) were measured. Finally, we carried out salt crystallization tests in order to determine which product improved the quality of the ceramics. Treated samples registered a decrease in porosity and a general increase in pore size. The application of Silo 111 drastically reduced water absorption by immersion and by capillarity. This product was also responsible for a decrease in pore interconnection. Samples treated with Tegovakon V performed better in terms of their overall hydric behaviour. Silo 111 was the only product that did not modify the colour of samples when compared with untreated ones, and after accelerated aging tests, samples treated with this product hindered the absorption of saline solution into ceramic pores and prevented their decay. Paraloid B72 did not improve any of the properties of the ceramics.

Influence of the Ratio between the Amounts of Reagent Total/H<sub>2</sub>O to Obtain Ferrites Mn<sub>0.65</sub>Zn<sub>0.35</sub>Fe<sub>2</sub>O<sub>4</sub> by Combustion Reaction

This work proposes to study the influence of dilution on the synthesis of ferrites Mn0.65Zn0.35Fe2O4 using glycine. It was used the reactants/H2O proportions of 1:0; 1:3.5; 1:7; 1:10, and 1:14 (100 mL of H2O). During the synthesis were measured the time and temperature of combustion. The samples were characterized by X-ray diffraction and X-ray fluorescence. The dilution in the samples increased with the increasing of the reaction time and flame temperature. For samples synthesized with 1:0, 1:3.5; and 1:7 ratio were observed traces of hematite, and to the remaining samples only the single phase of the Mn0.65Zn0.35Fe2O4 spinel. The crystallite sizes ranged from 32 to 42 nm.

Pisolitic flint kaolin from Kalabsha, Egypt: A laterite-derived facies

Nodular, pisolitic, and plastic kaolins from Kalabsha area, Egypt were investigated for their textural, mineralogical, and geochemical compositions to examine their source and origin. The three kaolins are composed of kaolinite, quartz, anatase, and traces of hematite and rutile. Clay fractions have relatively high Nb (56–189 ppm) and Zr (480–1260 ppm) contents. Heavy minerals from the sand fractions are composed of zircon, high Cr rutile, and leucoxene. Detrital quartz occurs as either monocrystalline or polycrystalline grains with worm-like corrosion features. Two types of quartz were distinguished based on their cathodoluminescence (CL) analysis; bright and dark luminescence quartz. Rare earth elements (REEs) patterns show enrichment of light REEs relative to heavy REEs ((La/Yb) N = 1.6–10) and negative Eu anomaly (Eu*/Eu = 0.6–0.7). Nodular and pisolitic kaolins show distinct positive Ce anomaly (Ce*/Ce = 1.2–3.4) and a variable LREE depletion. The pisolitic kaolin is considered here as flint kaolin based on its unique characteristics such as hardness, massiveness, conchoidal fracture, high density, very fine-grained nature, resistance to slacking in water, high crystallinity, and homogeneous compositions. Abundance of high Cr rutile, polycrystalline, and dark luminescent quartz suggest a contribution of medium to high grade metamorphic mafic rocks to the source of Kalabsha kaolins, while presence of zircon, bright luminescence monocrystalline quartz, and REEs pattern indicate a contribution of granitic rocks. The unusual high Nb contents attest to a contribution of alkaline rocks in the source area of the deposits. Lithostratigraphic succession, pisolitic texture, corroded quartz, depletion of many trace elements including LREE, distinct positive Ce anomaly, unusual grain size distribution, and compositional homogeneity suggest a lateritic precursor of the pisolitic flint kaolin. The lateritic precursor sediments have been deferrated and resilicified in the sedimentary basin to form the whitish flint clays with their unique physical and mineralogical characteristics as a result of volume increase associated to the transformation of Al-hydroxide minerals to kaolinite. Textural and geochemical variations unambiguously show that the overlying plastic clays are not derived by reworking from the pisolitic kaolins, but are derived from the saprolites underlying the lateritic crusts in the source region (sequential stripping).

304L stainless steel oxidation in carbon dioxide: An XPS study

From the early beginning of the oxidation of 304L stainless steel in carbon dioxide at 1273 K (1 min, for a weight gain of 0.02 mg cm −2), the surface of the alloy was entirely covered by oxides: magnetite Fe 3O 4, chromia Cr 2O 3 and traces of wüstite Fe 1− x O. Later on, for weight gains approaching 1 mg cm −2, magnetite remained at the outer interface, with traces of hematite (Fe 2O 3), above a thick layer of wüstite Fe 1− x O. Magnetite and wüstite may favour adhesion of thermal plasma protective coatings such as alumina.

Synthesis and characterisation of Fe–V–O thin film photoanodes

FeVO 4 was synthesised using a low temperature, aqueous precipitation reaction. The material prepared directly from this synthesis was found to be predominantly amorphous and required a thermal treatment. The resultant material was characterised using XRD, FT-IR, Raman spectroscopy and magnetic susceptibility measurements. Materials annealed above 600 °C were found to consist mainly of FeVO 4, although traces of hematite were found following annealing at higher temperatures. Diffuse-reflectance UV spectroscopy and subsequent Tauc plots revealed a band gap of ca. 2.00 eV corresponding to an indirect transition. Photocurrent–voltage characteristics recorded under simulated solar illumination indicate that photocurrents are sensitive to annealing temperature and the number of layers deposited on an electrode surface.

Laser ablated Fe 100− xPd x and Fe 100− xMn x thin films ( x=20 and 50)

Thin films (50 nm) of Fe 100− x Pd x and Fe 100− x Mn x ( x=20 and 50) were deposited by laser ablation on a Si wafer and studied by X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS). In all cases, the XRD patterns of the target surface before and after ablation show a congruent transfer of ablated material. For the Fe 80Pd 20 thin film, XRD spectra show the formation of FePd, iron, Pd oxide and traces of hematite in the ablated film. Complementary information obtained by CEMS indicates the presence of an upper 50-nm thick surface layer of hematite in the deposited film. Fe 50Pd 50 phase was observed by CEMS and a Pd oxide component was identified by XRD, along with traces of hematite. In the case of Fe 80Mn 20, the CEMS spectrum is consistent with the occurrence of the antiferromagnetic FeMn phase and the XRD pattern also shows the presence of Fe in the structure. For the system Fe 50Mn 50, we obtain by CEMS an antiferromagnetic phase of FeMn and by XRD we trace the presence of nanohematite and in-depth iron. For x=20 in both iron-rich systems investigated, we observe the segregation of iron with subsequent conversion to hematite. The study shows that the stoichiometry of the compounds plays a decisive role in determining their structural and magnetic properties.

Mössbauer spectroscopic studies on the iron forms of deep-sea sediments

Mossbauer spectroscopy was applied to characterize the valence states Fe(II) and Fe(III) in sedimentary minerals from a core of the Peru Basin. The procedure in unraveling this information includes temperature-dependent measurements from 275 K to very low temperature (300 mK) in zero–field and also at 4.2 K in an applied field (up to 6.2 T) and by mathematical procedures (least-squares fits and spectral simulations) in order to resolve individual spectral components. The depth distribution of the amount of Fe(II) is about 11% of the total Fe to a depth of 19 cm with a subsequent steep increase (within 3 cm) to about 37%, after which it remains constant to the lower end of the sediment core (at about 40 cm). The steep increase of the amount of Fe(II) defines a redox boundary which coincides with the position where the tan/green color transition of the sediment occurs. The isomer shifts and quadrupole splittings of Fe(II) and Fe(III) in the sediment are consistent with hexacoordination by oxygen or hydroxide ligands as in oxide and silicate minerals. Goethite and traces of hematite are observed only above the redox boundary, with a linear gradient extending from about 20% of the total Fe close to the sediment surface to about zero at the redox boundary. The superparamagnetic relaxation behavior allows to estimate the order of magnitude for the size of the largest goethite and hematite particles within the particle-site distribution, e.g. ∼170 A and ∼50 A, respectively. The composition of the sediment spectra recorded at 300 mK in zero-field, apart from the contributions due to goethite and hematite, resembles that of the sheet silicates smectite, illite and chlorite, which have been identified as major constituents of the sediment in the <2 μm fraction by X-ray diffraction. The specific “ferromagnetic” type of magnetic ordering in the sediment, as detected at 4.2 K in an applied field, also resembles that observed in sheet silicates and indicates that both Fe(II) and Fe(III) are involved in magnetic ordering. This “ferromagnetic” behavior is probably due to the double-exchange mechanism known from other mixed-valence Fe(II)–Fe(III) systems. A significant part of the clay-mineral iron is redox sensitive. It is proposed that the color change of the sediment at the redox boundary from tan to green is related to the increase of Fe(II)–Fe(III) pairs in the layer silicates, because of the intervalence electron transfer bands which are caused by such pairs.