Iron-rich Silicate Research Articles

Cosmic dust impacts on the Hubble Space Telescope.

Exposure of the Hubble Space Telescope to space in low Earth orbit resulted in numerous hypervelocity impacts by cosmic dust (micrometeoroids) and anthropogenic particles (orbital debris) on the solar arrays and the radiator shield of the Wide Field and Planetary Camera 2, both subsequently returned to Earth. Solar cells preserve residues from smaller cosmic dust (and orbital debris) but give less reliable information from larger particles. Here, we present images and analyses from electron, ion and X-ray fluorescence microscopes for larger impact features (millimetre- to centimetre-scale) on the radiator shield. Validated by laboratory experiments, these allow interpretation of composition, probable origin and likely dimensions of the larger impactors. The majority (~90%) of impacts by grains greater than 50 μm in size were made by micrometeoroids, dominated by magnesium- and iron-rich silicates and iron sulfides, metallic iron-nickel and chromium-rich spinel similar to that in ordinary chondrite meteorites of asteroid origin. Our re-evaluation of the largest impact features shows substantially fewer large orbital debris impacts than reported by earlier authors. Mismatch to the NASA ORDEM and ESA MASTER models of particle populations in orbit may be partly due to model overestimation of orbital debris flux and underestimation of larger micrometeoroid numbers. This article is part of the theme issue 'Dust in the Solar System and beyond'.

The rheological response of magma to nanolitisation

Viscosity exerts a fundamental control on magmatic kinetics and dynamics, controlling magma ascent, eruptive style, and the emplacement of lava. Nanolites – crystals smaller than a micron – are thought to affect magma viscosity, but the underlying mechanisms for this remain unclear. Here, we use a cylinder compression creep technique to measure the viscosity of supercooled silicate liquids with different amounts of iron (0–20 wt% FeOtot) as a function of temperature, applied shear stress, and time. Sample viscosity was independent on the applied shear stresses, and as expected, melt viscosity decreases as temperature is increased, but only until a critical temperature where a time-dependent increase in viscosity occurs for samples contaning 6.0 wt% FeOtot or more. The magnitude of this increase is controlled by the melt iron content. At constant temperature, these changes are substantial and can reach up to three orders of magnitude for the sample with the most iron. Using transmission electron microscopy, X-ray diffraction, and viscosity modelling, we conclude that this viscosity increase is caused by the formation of nanolites. By using scaling approaches to test suspension effects with and without crystal aggregation, we conclude that the nanolites have only a minimal direct physical effect on the observed viscosity change. Rather, our models show that it is the chemical shift in the groundmass silicate melt composition associated with non-stoichiometric crystallisation that dominates the observed viscosity increase. These findings suggest that iron-rich silicates may encounter chemical viscosity jumps once certain elements are removed from the melt phase to form nanolites. Our work demonstrates an underlying mechanism for the role played by nanolites in viscosity changes of magmas.

Spatial variability of arsenic fractionation in an abandoned arsenic-containing mine: Insights into soil particle sizes and quantitative mineralogical analysis

Soil particle sizes and mineral phases play a major role in the migration of arsenic (As) in mine. In this study, soil As fractionation and mineralogical composition in different particle sizes soil at naturally mineralized and anthropogenically disturbed zones from an abandoned mine were comprehensively studied. The results showed that soil As contents in anthropogenically disturbed mining zone (MZ), processing zone (PZ), and smelting zone (SZ) were increased with decreasing of soil particle sizes. The contents of As in the fine soil particles (0.45–2 μm) reached to 850–4800 mg·kg−1, which mainly existed at readily soluble, specifically sorbed, and Al-oxide fractions, and contributed to 25.9–62.6 % of the total As contents in soil. Conversely, soil As contents in naturally mineralized zone (NZ) were decreased with decreasing of soil particle sizes and As was mainly accumulated in the coarse fraction of soil (0.075–2 mm). Despite the speciation of As in 0.075–2 mm soil mainly existed as residual fraction, the content of non-residual As fraction reached up to 1636 mg·kg−1, indicating a high potential risk of As in naturally mineralized soil. The utilization of scanning electron microscopy, fourier transform infrared spectroscopy combined with mineral liberation analyzer revealed that soil As in NZ and PZ was mainly retained by iron (hydrogen)oxide, while whereas the dominant host minerals for soil As in MZ and SZ were the surrounding rocks of calcite and the iron-rich silicate mineral biotite. Notably, both of the calcite and biotite exhibited high mineral liberation, which was partly contributed to a significant portion of mobile As fraction in MZ and SZ soil. The results suggested that the potential risks of soil As from SZ and MZ at abandoned mine, particularly in the fine soil particles, should be a prior concern.

Carbon dioxide sequestration by mineral carbonation via iron complexation using bipyridine chelating ligands.

An innovative mineral carbonation method was developed to synthesize iron(II) carbonate (FeCO3) by cation complexation using 2,2'-bipyridine as ligand. First, complexes of iron(II) and different ligands were theoretically analyzed and discounted in terms of their temperature and pH-dependent stabilities, iron-ligand interactions, possible by-products and difficulty of analysis, choosing 2,2'-bipyridine as the most suitable ligand. Then, the Job plot was used to verify the complex formula. The stability of [Fe(bipy)3]2+ at pH 1-12 was further monitored for 7 days using UV-Vis and IR spectroscopy. Good stability was observed between pH 3 and 8, decreasing within pH 9-12 where the carbonation reaction occurs. Finally, the reaction between Na2CO3 and [Fe(bipy)3]2+ was performed at 21, 60, and 80 °C and pH 9-12. The total inorganic carbon measured after 2 h shows that the best carbonate conversion (50%) occurred at 80 °C and pH 11, being the most suitable conditions for carbon sequestration. SEM-EDS and XRD were used to examine the effect of synthesis parameters on the morphology and composition of FeCO3. The FeCO3 particle size increased from 10 μm at 21 °C to 26 and 170 μm at 60 and 80 °C respectively with no pH dependence. In addition, EDS analysis supported the carbonate identity, whose amorphous nature was confirmed by XRD. These results would help prevent the iron hydroxide precipitation problem during mineral carbonation using iron-rich silicates. These results are promising for its application as a carbon sequestration method with a CO2 uptake of around 50% obtaining Fe-rich carbonate.

Exploring the secondary mineral products generated by microbial iron respiration in Archean ocean simulations.

Marine chemical sedimentary deposits known as Banded Iron Formations (BIFs) archive Archean ocean chemistry and, potentially, signs of ancient microbial life. BIFs contain a diversity of iron- and silica-rich minerals in disequilibrium, and thus many interpretations of these phases suggest they formed secondarily during early diagenetic processes. One such hypothesis posits that the early diagenetic microbial respiration of primary iron(III) oxides in BIFs resulted in the formation of other iron phases, including the iron-rich silicates, carbonates, and magnetite common in BIF assemblages. Here, we simulated this proposed pathway in laboratory incubations combining a model dissimilatory iron-reducing (DIR) bacterium, Shewanella putrefaciens CN32, and the ferric oxyhydroxide mineral ferrihydrite under conditions mimicking the predicted Archean seawater geochemistry. We assessed the impact of dissolved silica, calcium, and magnesium on the bioreduced precipitates. After harvesting the solid products from these experiments, we analyzed the reduced mineral phases using Raman spectroscopy, electron microscopy, powder x-ray diffraction, and spectrophotometric techniques to identify mineral precipitates and track the bulk distributions of Fe(II) and Fe(III). These techniques detected a diverse range of calcium carbonate morphologies and polymorphism in incubations with calcium, as well as secondary ferric oxide phases like goethite in silica-free experiments. We also identified aggregates of curling, iron- and silica-rich amorphous precipitates in all incubations amended with silica. Although ferric oxides persist even in our electron acceptor-limited incubations, our observations indicate that microbial iron reduction of ferrihydrite is a viable pathway for the formation of early iron silicate phases. This finding allows us to draw parallels between our experimental proto-silicates and the recently characterized iron silicate nanoinclusions in BIF chert deposits, suggesting that early iron silicates could possibly be signatures of iron-reducing metabolisms on early Earth.

Effects of temperature, CO content, and reduction time on the selective reduction of a limonitic laterite ore

The production of nickel and cobalt from laterite ores has gained increasing attention as their demands continue to rise. This study evaluated the effects of temperature (700–1000 °C), CO content (10–70 vol%), and reduction time (10–90 min) on the selective reduction of a limonitic laterite ore and examined the mechanism of the selective reduction. SEM/EDS observation shows that the ore consists of goethite, hematite and small particles of clinochlore cemented by amorphous iron-rich silicate phase. Nickel and cobalt occur with goethite mineral in this ore. It was observed that fine grains of Fe-Ni-Co alloy dispersed within magnetite phase in reduced samples. XRD and XPS analyses show increased Fe2SiO4 generation with increasing reduction temperature, and elements nickel and cobalt were capatured in Fe2SiO4 according to SEM/EDS observation. Reduction at temperature above 850 °C resulted in a sharp increase in Fe2SiO4 generation and decrease in the specific surface area of the ore. The morphological and compositional observations indicate that CO content over 20 vol% promoted Fe formation from the laterite ore but hardly enhanced the formation of Ni and Co. The difference in equilibrium CO partial pressures for the formation of Fe, Ni, Co accounts for selective reduction. The current study suggests that selective reduction can be achieved by controlling reduction temperature and gas composition. Under the optimum condition of 850 °C, 20 vol% CO-80 vol% CO2 and 60 min, the degrees of metallisation of iron, nickel, and cobalt reduction were 17.5%, 87.3%, and 91.5%, respectively.

Sound velocity and compressibility of melts along the hedenbergite (CaFeSi2O6)-diopside (CaMgSi2O6) join at high pressure: Implications for stability and seismic signature of Fe-rich melts in the mantle

Iron-rich silicate melts play an important role in the magmatic history of the Earth and the Moon. However, their elastic properties at high pressures, especially the sound velocities, are poorly understood. Here we determined the ultrasonic sound velocities of two silicate melts along the hedenbergite (Hd, CaFeSi2O6) – diopside (Di, CaMgSi2O6) join at high pressure and temperature conditions up to 6 GPa and 2329 K, using the high-pressure ultrasonic technique combined with synchrotron radiation in a multi-anvil apparatus. Our results show that Fe can significantly reduce the sound velocity while increasing the density of silicate melts. Comparing the melts of Di, Hd, and a mixture of 50 mol% hedenbergite + 50 mol% diopside (Hd50Di50), we find that although densities of the Hd-Di melts can be well-described by a linear mixing law empirically at high pressures, sound velocities do not vary with composition linearly. Assuming that the low-velocity regions in Earth's upper mantle are mainly due to the presence of partial melt, we applied our results to study the gravitational stability and seismic signature of Fe-rich silicate melts in the mantle, combined with melt geometry and compaction models. For the low-velocity zone (LVZ) in mantle asthenosphere, although the degree of seismic velocity reduction can be explained by the presence of a small amount of partial melt distributed in film/band geometry along grain boundaries, silicate melts formed in this depth range are too light to be gravitationally stable, but may be completely entrained in the convecting mantle due to the small melt fraction and low melt-matrix separation velocity. For the low-velocity layer (LVL) above the mantle transition zone, the presence of Fe-rich melts (with FeO>∼10 wt%) distributed in textural equilibrium with the ambient mantle is a plausible explanation.

Ferric iron triggers greenalite formation in simulated Archean seawater

AbstractSedimentary rock deposits provide the best records of (bio)geochemical cycles in the ancient ocean. Studies of these sedimentary archives show that greenalite, an Fe(II) silicate with low levels of Fe(III), was an early chemical precipitate from the Archean ocean. To better understand the formation of greenalite, we explored controls on iron silicate precipitation through experiments in simulated Archean seawater under exclusively ferrous conditions or supplemented with low Fe(III). Our results confirm a pH-driven process promoting the precipitation of iron-rich silicate phases, and they also reveal an important mechanism in which minor concentrations of Fe(III) promote the precipitation of well-ordered greenalite among other phases. This discovery of an Fe(III)-triggering iron silicate formation process suggests that Archean greenalite could represent signals of iron oxidation reactions, potentially mediated by life, in circumneutral ancient seawater.

The geological setting of arsenic enrichment in groundwater of the shallow aquifers of the Tista Floodplain, Rangpur, Bangladesh

Arsenic is present in water samples within the studied active floodplain areas of the Tista river, Rangpur Division, Bangladesh. All the water samples contain less arsenic than the WHO prescribed limit of 10 μg/L. 93.33% groundwater samples have higher Mn content than the permissible limit of 0.01 mg/L of WHO. The heavy metal concentrations of water can be expressed as Fe>Mn>Zn>As on the basis of their mean content. The heavy metals are negatively correlated with the well depth which is indicative of the influence of the anthropogenic activities on the concentrations of heavy metals. The arsenic concentration in water samples is higher in the central part of the study area. The coarser grain size, dominance of physical weathering, elevated topography and the effective flushing of groundwater resulted low concentration of arsenic in the groundwater. The EDS study reveals that arsenic occurs as coating materials of the silicate minerals. The river waters also have arsenic content lower than WHOs permissible limit. The factor analysis reveals that the iron and arsenic is released by the chemical weathering of arsenic bearing minerals like pyrite and arsenopyrite. The Fe and Mn derived in the groundwater by the chemical weathering of iron and manganese bearing minerals such as iron rich clay, silicate minerals and iron sulfides. Â

Physical state of an early magma ocean constrained by the thermodynamics and viscosity of iron silicate liquid

The initial cooling stage and crystallization of a magma ocean were significantly affected by the thermodynamics and viscosity of iron silicate liquid. Here, we use first-principles molecular dynamics based on density functional theory plus the Hubbard U method to study the structures, thermodynamics and viscosities of Fe2SiO4 liquid at 3000–6000 K under pressure conditions spanning the entire mantle. Our calculations show that the compressibility of Fe2SiO4 liquid is weakened at pressures above 50 GPa. The densification of Fe2SiO4 liquid under compression is mainly manifested by a decrease in the distance among Si–O polyhedra and an increase in the cation-anion coordination number. We find that the viscosity of the Fe2SiO4 liquid has a positive pressure dependence, and the effect of pressure on viscosity decreases with increasing temperature. The predicted behaviour of viscosity coefficients of the Fe2SiO4 liquid at different P-T conditions can be described well as: η(P,T) = exp[−7.89+0.0042P−0.0000632P2+(3800+61.6P+0.18P2)/(T−1000)]. Compared to Mg2SiO4 liquid, the viscosity of Fe2SiO4 liquid is lower under the pressure of the lower mantle along isotherms. We calculate the adiabat of the Fe2SiO4 liquid in a magma ocean, and the results show that the iron content has little effect on the adiabats of (Mg,Fe)2SiO4 liquid in the magma ocean. Combining our calculated thermodynamic properties and viscosities with those of previous studies, the physical properties of an early magma ocean were constrained. The upper bound of the potential temperature for magma ocean crystallization is 3250 K. We constructed the range of the viscosity profile of a magma ocean and found that the lower viscosity of iron-rich silicate liquid would maintain the viscosity of an early magma ocean in the range of several mPas. As the magma ocean starts to crystallize, the lower bound of the viscosity at the surface and the core-mantle boundary are 0.0020 Pas and 0.0068 Pas, respectively. The weakening of the viscosity of the iron silicate liquids would have a significant impact on the evolution of the magma ocean.

Centrilobular nodules in a smoker: Respiratory bronchiolitis or something else?

A 63-year-old male was referred for right upper lobectomy for squamous cell lung cancer. Pre-operative chest computed tomography scan described the biopsy proven subpleural squamous cell carcinoma as well as bilateral diffuse centrilobular micronodules favored to represent respiratory bronchiolitis in the context of significant past smoking history. On histological examination of the resection specimen, these multifocal nodules corresponded to macules of macrophages filled with iron rich pigment and silicate particles, consistent with a histologic diagnosis of siderosilicosis. Upon further questioning, the patient’s occupation of welding was confirmed by his primary care physician. We herein point out key features of this entity.

Observations, Meteorites, and Models: A Preflight Assessment of the Composition and Formation of (16) Psyche.

Some years ago, the consensus was that asteroid (16) Psyche was almost entirely metal. New data on density, radar properties, and spectral signatures indicate that the asteroid is something perhaps even more enigmatic: a mixed metal and silicate world. Here we combine observations of Psyche with data from meteorites and models for planetesimal formation to produce the best current hypotheses for Psyche's properties and provenance. Psyche's bulk density appears to be between 3,400 and 4,100 kg m−3. Psyche is thus predicted to have between ~30 and ~60 vol% metal, with the remainder likely low‐iron silicate rock and not more than ~20% porosity. Though their density is similar, mesosiderites are an unlikely analog to bulk Psyche because mesosiderites have far more iron‐rich silicates than Psyche appears to have. CB chondrites match both Psyche's density and spectral properties, as can some pallasites, although typical pallasitic olivine contains too much iron to be consistent with the reflectance spectra. Final answers, as well as resolution of contradictions in the data set of Psyche physical properties, for example, the thermal inertia measurements, may not be resolved until the NASA Psyche mission arrives in orbit at the asteroid. Despite the range of compositions and formation processes for Psyche allowed by the current data, the science payload of the Psyche mission (magnetometers, multispectral imagers, neutron spectrometer, and a gamma‐ray spectrometer) will produce data sets that distinguish among the models.

Compositional Constraints for Lucy Mission Trojan Asteroids via Near-infrared Spectroscopy

Abstract We report near-infrared (0.7–2.5 μm) reflectance spectra for each of the six target asteroids of the forthcoming NASA Discovery-class mission Lucy. Five Jupiter Trojans (the binary (617) Patroclus system, (3548) Eurybates, (21900) Orus, (11351) Leucus, and (15094) Polymele) are well characterized, with measurable spectral differences. We also report a survey-quality spectrum for main-belt asteroid (52246) Donaldjohanson. We measured a continuum of spectral slopes including “red” (Orus, Leucus), “less red” (Eurybates, Patroclus-Menoetius), and intermediate (Polymele), indicating a range of compositional end-members or geological histories. We perform radiative transfer modeling of several possible surface compositions. We find that the mild-sloped spectra and low albedo of Patroclus and Eurybates imply similar compositions. Eurybates (∼7 wt.% water ice) and Patroclus (∼4 wt.% water ice) are consistent with a hydrated surface. Models for Orus and Leucus are consistent with each other and require a significantly more reddening agent (e.g., iron-rich silicates or tholin-like organics). Polymele has a linear spectrum like Patroclus, but a higher albedo more closely aligned with Orus/Leucus, defying simple grouping. Solar system formation models generally predict that the Jovian Trojans accreted in the outer solar system. Our observations and analysis are generally consistently with this expectation, although not uniquely so.

Structure, crystal chemistry and compressibility of iron-rich silicate perovskite at pressures up to 95 GPa

Structure, crystal chemistry and compressibility of iron-rich silicate perovskite at pressures up to 95 GPa

Depositional model for banded iron formation host to gold in the Archean Rio das Velhas greenstone belt, Brazil, based on geochemistry and LA-ICP-MS magnetite analyses

Petrographic and geochemical data were obtained for selected carbonaceous and siderite-bearing chert and banded iron formation (BIF) from the Archean Rio das Velhas greenstone belt (RVGB), Quadrilátero Ferrífero, including seven orogenic gold deposits (Cuiabá, Lamego, Raposos, Roça Grande, São Bento, Urubu and Ápis) and two barren BIFs (Sumidouro and Campo Grande). The RVGB has Algoma-type BIFs that differ in terms of lithological association, mineralogical assemblage and geochemistry. Trace element geochemistry of the BIFs is used to investigate their depositional environment, and to evaluate if primary geochemical and petrographic features have implications for gold mineralization. The chert layers of the Lamego and Urubu deposits exhibit significant, positive Eu anomalies (Eu/Eu*PAAS = 1.57–4.01) and low contents of immobile elements (Al2O3 = <0.34 wt%, TiO2 = <0.02 wt%), suggesting a high contribution of hydrothermal fluid in their formation, with relatively low detrital input. The carbonate- and the magnetite-rich BIF of the Cuiabá, Roça Grande, Ápis and Raposos deposits display Eu/Eu*PAAS = 1.34–3.25; Al2O3 = 0.04–1.47 wt%, TiO2 = <0.03 wt%, interpreted to represent an intermediate contribution of hydrothermal fluid, as well as limited detrital input. The São Bento, Campo Grande and Sumidouro BIF show a significant mineralogical variability including magnetite, carbonate and iron-rich silicates. Their Eu/Eu*PAAS = 1.1–2.6; Al2O3 = 0.11–6.82 wt%, TiO2 = 0.03–0.33 wt% suggest high detrital input and low hydrothermal fluid influence. Textural relations and mineral assemblages of magnetite-rich samples indicate three main generations of this mineral: (i) diagenetic (very low grade metamorphic), (ii) early and (iii) main-stage hydrothermal. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses show that Ti, V, Ni and Co contents of magnetite systematically fluctuate. Their concentrations of Ti (50–677 ppm), V (11–207 ppm), Ni (8–166 ppm) and Co (3–14 ppm) in magnetite (i) are the highest comparatively to types (ii) and (iii) (Ti = 7–352 ppm; V = 0.2–59 ppm; Ni = 1–22 ppm; Co = 0.1–7 ppm). Even higher trace element content of the Sumidouro (i) is related to important clastic input to seawater during BIF deposition. The composition of magnetite types (ii) and (iii) is dependent on coexisting minerals (sulfides, carbonates and silicates), and on the type of mechanism of their formation (dissolution-reprecipitation, or re-equilibration). The mineralogical, geochemical and geological diversity of the RVGB BIFs, as well as magnetite composition in BIF, point to a depositional model for the RVGB BIF within the Rio das Velhas basin related to both proximity to the hydrothermal vent and of terrigenous sedimentary input.Deposition of chert layers (e.g., Lamego and Urubu deposits) was favored near the hydrothermal vents on the abyssal plain due to high concentration of silica and organic carbon. Away from the hydrothermal source, chert transitioned to carbonate-rich BIF, typical of Cuiabá, Roça Grande and Ápis, which still formed under the influence of organic matter. Magnetite-rich BIF, i.e. Raposos deposit, was deposited further away from the volcanic center, with limited supply of organic carbon and silica. In a submarine environment with greater clastic input, such as continental shelfs and island arcs, BIF composition was influenced by detrital contamination, and iron-rich silicates (i.e., stilpnomelane and chlorite) are common, besides magnetite and carbonate; this is the case for the São Bento, Campo Grande and Sumidouro BIFs. The BIF types with abundant iron-rich carbonate and-or magnetite host gold mineralization more efficiently since they are especially favorable to sulfides replacement accompanied by gold precipitation.

Spectral evidence for amorphous silicates in least-processed CO meteorites and their parent bodies

Least-processed carbonaceous chondrites (carbonaceous chondrites that have experienced minimal aqueous alteration and thermal metamorphism) are characterized by their predominately amorphous iron-rich silicate interchondrule matrices and chondrule rims. This material is highly susceptible to destruction by the parent body processes of thermal metamorphism or aqueous alteration. The presence of abundant amorphous material in a meteorite indicates that the parent body, or at least a region of the parent body, experienced minimal processing since the time of accretion. The CO chemical group of carbonaceous chondrites has a significant number of these least-processed samples. We present visible/near-infrared and mid-infrared spectra of eight least-processed CO meteorites (petrologic type 3.0–3.1). In the visible/near-infrared, these COs are characterized by a broad weak feature that was first observed by Cloutis et al. (2012) to be at 1.3-µm and attributed to iron-rich amorphous silicate matrix materials. This feature is observed to be centered at 1.4-µm for terrestrially unweathered, least-processed CO meteorites. At mid-infrared wavelengths, a 21-µm feature, consistent with Si–O vibrations of amorphous materials and glasses, is also present. The spectral features of iron-rich amorphous silicate matrix are absent in both the near- and mid-infrared spectra of higher metamorphic grade COs because this material has recrystallized as crystalline olivine. Furthermore, spectra of least-processed primitive meteorites from other chemical groups (CRs, MET 00426 and QUE 99177, and C2-ungrouped Acfer 094), also exhibit a 21-µm feature. Thus, we conclude that the 1.4- and 21-µm features are characteristic of primitive least-processed meteorites from all chemical groups of carbonaceous chondrites. Finally, we present an IRTF + SPeX observation of asteroid (93) Minerva that has spectral similarities in the visible/near-infrared to the least-processed CO carbonaceous chondrites. While Minerva is not the only CO-like asteroid (e.g., Burbine et al., 2001), Minerva is likely the least-processed CO-like asteroid observed to date.

Low-temperature MIR to submillimeter mass absorption coefficient of interstellar dust analogues

Context. To model the cold dust emission observed in the diffuse interstellar medium, in dense molecular clouds or in cold clumps that could eventually form new stars, it is mandatory to know the physical and spectroscopic properties of this dust and to understand its emission. Aims. This work is a continuation of previous studies aiming at providing astronomers with spectroscopic data of realistic cosmic dust analogues for the interpretation of observations. The aim of the present work is to extend the range of studied analogues to iron-rich silicate dust analogues. Methods. Ferromagnesium amorphous silicate dust analogues were produced by a sol-gel method with a mean composition close to Mg1−xFexSiO3 with x = 0.1, 0.2, 0.3, 0.4. Part of each sample was annealed at 500 °C for two hours in a reducing atmosphere to modify the oxidation state of iron. We have measured the mass absorption coefficient (MAC) of these eight ferromagnesium amorphous silicate dust analogues in the spectral domain 30−1000 μm for grain temperature in the range 10−300 K and at room temperature in the 5−40 μm range. Results. The MAC of ferromagnesium samples behaves in the same way as the MAC of pure Mg-rich amorphous silicate samples. In the 30−300 K range, the MAC increases with increasing grain temperature whereas in the range 10−30 K, we do not see any change of the MAC. The MAC cannot be described by a single power law in λ− β. The MAC of the samples does not show any clear trend with the iron content. However the annealing process has, on average, an effect on the MAC that we explain by the evolution of the structure of the samples induced by the processing. The MAC of all the samples is much higher than the MAC calculated by dust models. Conclusions. The complex behavior of the MAC of amorphous silicates with wavelength and temperature is observed whatever the exact silicate composition (Mg vs. Fe amount). It is a universal characteristic of amorphous materials, and therefore of amorphous cosmic silicates, that should be taken into account in astronomical modeling. The enhanced MAC of the measured samples compared to the MAC calculated for cosmic dust model implies that dust masses are overestimated by the models.

Light scattering studies of randomly oriented polycrystalline fayalite micro particles as interstellar dust analogues

Fayalite (Fe2Si04), the iron end-member of the olivine group, is found in various extraterrestrial environments including the interstellar medium and meteorite. Since the iron rich silicates, i.e. fayalites, are not abundantly found in earth, there has been lack of sufficient experimentation and modeling leading to the unavailability of sufficient experimental data of fayalite for comparative analyses with computations and astrophysical observations. In this work interstellar fayalite dust analogues were synthesized in the laboratory using simple chemical route. Shape and size dispersed interstellar dust analogue models for laboratory synthesized fayalite particles were developed for performing theoretical computations of light scattering parameters (e.g., angular profiles of intensity and degree of linear polarization, geometric and single-scattering albedo, asymmetry parameter and cross-sections of extinction and absorption) using discrete dipole approximation (DDA). In order to demonstrate the validity of our models, phase function and degree of linear polarization were measured using a laboratory based setup and the results were compared with DDA computed theoretical values at three wavelengths 543.5nm, 594.5nm and 632.5nm respectively.

Pressure-dependent compatibility of iron in garnet: Insights into the origin of ferropicritic melt

Iron-rich silicate melts in the Earth’s deep mantle have been seismologically and geochemically inferred in recent years. The origin of local enrichments in iron and low-velocity seismic anomalies that have been detected in dense mantle domains are critical to understanding the mantle’s evolution, which has been canonically explained by long-term chemical reactions between the Earth’s silicate mantle and its liquid iron outer core. However, the Pleistocene alkaline ferropicrites (∼0.73Ma) from Wudi, North China, show chemical and Sr–Nd–Os isotopic features that suggest derivation from the preferential melting of silica-deficient eclogite, a lithology of delaminated mafic lower continental crust that had stagnated at mid-upper mantle depths during the Mesozoic decratonization of the North China block. These rocks are characterized by substantial enrichment in iron (14.9–15.2wt% Fe2O3), relative depletion in silica (40–41wt% SiO2) and decoupled Y and heavy rare earth element (HREE) compositions. These ferropicrites have particularly higher Y/Yb ratios than the other Cenozoic basalts from North China. The pressure-dependent compatibility of Fe, Y and Yb in eclogitic garnet can adequately explain the Fe-enrichment and Y-HREE decoupling of the Wudi ferropicrites and indicates that the eclogites were melted at pressures of 5–8GPa, as also constrained by previous high-P–T experiments. This melting depth ties together a seismically imaged high-velocity anomaly that extends from 150km to 350km in depth under the study area, which has been commonly interpreted as evidence for the stagnation of the missing, delaminated continental lithosphere. Our findings provide an alternative mechanism to produce an extremely iron-rich mantle reservoir in addition to core–mantle interaction. Iron-rich silicate melts that form by this process are likely to be denser than the ambient mantle peridotite (and therefore drive flow downward) and may play a more significant role in the deep-mantle geophysical and geochemical diversities than previously considered.

Effect of Sodium Sulfate Addition on the Production of Ferronickel from Lateritic Ore

Lateritic nickel ore from Manisa — Caldag region was roasted to form ferronickel at 1200 ◦C for 1 h with additions of metallurgical coke and sodium sulfate varying by weight 5–15% and 0–20%, respectively. Formed metallic part of roasted sample was separated from non-metallic part by magnet and examined by means of X-ray diffraction analysis and scanning electron microscopy. In spite of kamacite α-(Fe,Ni) formation, iron-rich silicate structure that causes iron losses was observed for samples roasted with only coke. Kamacite formation increased with increment of the coke percentage but iron-rich silicate structure remained almost same. With addition of sodium sulfate, elimination of iron-rich silicate phase was achieved and easily magnetizable metallic particles were obtained.