Small Amounts Of Magnetite Research Articles

Mineralogical and Chemical Changes after Reduction Roasting of Xinjiang Iron Ore, China

The mineralogical and chemical changes in Chinese Xinjiang iron ore containing impurities, lead, and zinc as a result of reduction roasting were studied via chemical analysis, optical microscopy, X-ray fluorescence (XRF), electron probe microanalysis (EPMA), and energy-dispersive spectroscopy (EDS). Analysis showed that hematite was the main iron-bearing mineral, with small amounts of magnetite and iron silicate; lead impurities were mainly lead oxide and lead–iron alum, while zinc oxide was the main zinc impurity. X-ray fluorescence analysis for raw samples indicated the presence of quartz, hematite, magnetite, chlorite, calcite, and dolomite. The results of the analysis of roasted samples showed an increase in hematite at temperatures of 750 °C and 950 °C, while the elemental iron increased at a temperature of 1200 °C, along with the conversion of galena to lead oxide and sphalerite to zinc oxide, with a stable quartz ratio. The chemical analysis of the raw sample showed that the TFe grade of the sample was 47.04%, while the contents of harmful Pb and Zn impurities were 0.39% and 0.30%, respectively, both of which exceed the index (less than 0.10%) required by the iron industry for raw materials. The content of harmful sulfur impurities was also high, at 1.19%, which needs to be eliminated or reduced. The results of EPMA and EDS analysis of pre-roasting raw samples showed that chemical compositions vary in different locations in the hematite, magnetite, sphalerite, and galena micro-zones. It has also been observed that quartz is mostly diffused with magnetite and hematite, and sulfur appears in small quantities in most regions. The analysis after roasting showed that the percentages of lead, zinc, and sulfur impurities decreased by a large rate. It is clear that the roasting process plays a major role in removing impurities such as sulfur, which appears in a small percentage after the roasting process, and also helps in oxidizing the impurities of lead and zinc, which helps in removing them.

Preparation and characterization of Martian soil simulant NEU Mars-1

Abstract To develop Martian soil simulant, basalts of the Chahar volcanic group in Wulanchabu, Inner Mongolia, China were selected as the simulant initial materials, which were ground and sorted to a predetermined particle size ratio, and small amounts of magnetite and hematite were added. The main phases of NEU Mars-1 simulant were plagioclase, augite and olivine. The glass transition and crystallization temperatures of NEU Mars-1 were 547.8 and 795.7 °C, respectively. The complex dielectric constant, magnetic conductivity (0.99–1.045), and dielectric loss tangent angles (0.0025–0.030) of NEU Mars-1 were all stable in the frequency range of 2–18 GHz. Mossbauer spectroscopy results showed that the mass ratio of Fe2+ to Fe3+ in the simulant was 77.6:22.4. The NEU Mars-1 Martian soil simulant demonstrated particle size ratio, chemical composition, phase composition, thermal stability, and dielectric property similar to Martian soil, and can be used as the substitute material to extract oxygen and metals with in-situ resource utilization technologies.

Trace element composition of magnetite from the Xinqiao Fe–S(–Cu–Au) deposit, Tongling, Eastern China: constraints on fluid evolution and ore genesis

The Xinqiao deposit is one of several polymetallic deposits in the Tongling ore district. There are two types of mineralization in the Xinqiao: skarn-type and stratiform-type. The skarn-type mineralization is characterized by iron oxides such as magnetite and hematite, whereas stratiform-type mineralization is characterized by massive sulfides with small amounts of magnetite and hematite. We defined three types of ores within the stratiform-type mineralization by the mineral assemblages and ore structures. Type I ore is represented by magnetite crosscut by minor calcite veins. Type II is a network ore composed of magnetite and crosscutting pyrite. Type III is a massive ore containing calcite and hematite. Type I magnetite is characterized by highly variable trace element content, whereas Type II magnetite has consistently higher Si, Ti, V, and Nb. Type III magnetite contains more In, Sn, and As than the other two types. Fluid–rock interaction, oxygen fugacity (fO2), and temperature (T) are the main factors controlling element variation between the different magnetite types. Type I magnetite was formed by more extensive fluid–rock interaction than the other two types at moderate fO2 and T conditions. Type II magnetite is thought to have formed in relatively low fO2 and high-T environments, and Type III in relatively high fO2 and moderate-T environments. Ca + Al + Mn and Ti + V discrimination diagrams show that magnetite in the Xinqiao deposit is hydrothermal in origin and is possibly linked with skarn.

Magnetic analysis of commercial hematite, magnetite, and their mixtures

Magnetic techniques are suitable to detect iron oxides even in trace concentrations. However, since several iron oxides may be simultaneously present in natural and synthetic samples, mixtures of magnetic particles and magnetic interactions between grains can complicate magnetic signatures. Among the iron oxide minerals, hematite (α-Fe2O3) and magnetite (Fe3O4) are the most common. In this work, different commercial hematite powders, normally used as Fe precursor in laboratory synthesis of Fe-containing oxides, were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). The effects of different concentrations of the hematite and magnetite on the magnetic properties of a set of mixtures (from 1 to 10 wt% magnetite) were then investigated by measuring the hysteresis loops, first order reversal curves (FORCs), thermal demagnetization, and isothermal remanent magnetization (IRM) curves. The three commercial hematite powders presented different magnetic behaviors mostly due to the effects of particle size. The magnetic results of mixtures reveal that it is very difficult to identify hematite magnetic signals by means of hysteresis loops, FORCs, or thermal demagnetization when even a small amount of magnetite (>5 wt%) is present due to magnetite’s high specific magnetization. However, IRM was found to be a sensitive method to determine the presence of hematite when magnetite is simultaneously present as high as 10 wt%.

Growth of Hematite Nanostructures in Iron Foil for Environmental Cleaning

Hematite (Fe2O3) nanostructures were successfully grown on the surface of iron foil by simple thermal oxidation in air. The iron foil was heated at 300 – 700 °C for 8 h to produce Fe2O3 nanosheets and nanowires. The oxide layer is primarily composed of Fe2O3 with a small amount of magnetite (Fe3O4) and wustite (FeO). The photocatalytic activity of the Fe2O3 nanowires was investigated by degradation of methyl orange dye under 30 W UV light in the presence of a minute amount of hydrogen peroxide. The Fe2O3 nanowires exhibit excellent photocatalytic activity, wherein 2.5 ppm of the methyl orange was fully decomposed in 30 min.

Enhancement of TiO₂ NPs Activity by Fe₃O₄ Nano-Seeds for Removal of Organic Pollutants in Water.

The enhancement of the photocatalytic activity of TiO2 nanoparticles (NPs), synthesized in the presence of a very small amount of magnetite (Fe3O4) nanoparticles, is here presented and discussed. From X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses, the crystallinity of TiO2 nanoparticles (NPs) seems to be affected by Fe3O4, acting as nano-seeds to improve the tetragonal TiO2 anatase structure with respect to the amorphous one. Photocatalytic activity data, i.e., the degradation of methylene blue and the Ofloxacin fluoroquinolone emerging pollutant, give evidence that the increased crystalline structure of the NPs, even if correlated to a reduced surface to mass ratio (with respect to commercial TiO2 NPs), enhances the performance of this type of catalyst. The achievement of a relatively well-defined crystal structure at low temperatures (Tmax = 150 °C), preventing the sintering of the TiO2 NPs and, thus, preserving the high density of active sites, seems to be the keystone to understand the obtained results.

Magnetite-bearing zones in metasediments at Broken Hill, Australia: signatures of black smokers?

High-quality aeromagnetic data show linear magnetic zones within generally non-magnetic metasediments of the Broken Hill and Sundown Groups in the medium- to high-grade metamorphic Willyama Supergroup at Broken Hill, Australia. On-ground investigations show that these anomalies are generated by small amounts of magnetite within the metasediments. The magnetite concentrations are controlled by bedding and transgressed by schistosity. At the outcrop scale, the bedding-parallel nature of the magnetite concentrations is illustrated by decimetre-scale mapping with a magnetic susceptibility meter. At a 1:25 000 scale, there are areas where the relationship between magnetic anomalies and bedding is either unclear or apparently transgressive. Resolution of such situations requires an order of magnitude more detail in both the magnetic data and the geological mapping. This was provided by ground magnetometer surveying, magnetic susceptibility meter surveying and detailed lithological and structural mapping. In the areas studied, no evidence was found for genuinely transgressive relationships between magnetite concentrations and bedding. On a microscopic scale, the magnetite grains are independent of the other main Fe-bearing minerals with no replacement of garnet or biotite by magnetite. Thus, the magnetite did not result from influx of an oxidising fluid during or after high-grade metamorphism. Given that the magnetite concentrations are bedding-parallel and that the magnetite grains are not the result of replacement of ferrous iron-bearing minerals, it is concluded that the magnetite (or its ferric iron precursor) was an original component of the metasediments in these zones. The magnetite does not form clusters as expected with detrital magnetite. The magnetite-bearing zones can be either pelitic or psammitic, so it appears there was not a porosity/permeability control. The most likely origin for the magnetite or its precursor is a rain of particles onto the seafloor from an overlying oxidised water column. Such particles may have been derived from distal plumes resulting from spent orebody-forming fluids. The close relationship in places, between banded iron formation and magnetite-bearing metasediment zones supports this suggestion. Magnetite in metasediments close to the base of Sundown Group may have resulted from spent fluids related to formation of the Broken Hill orebody. However, there are magnetite-bearing metasediment zones within the Broken Hill Group and also stratigraphically higher in the Sundown Group that may be related to as yet undiscovered orebodies. The detailed lithological and structural mapping resulted in some new insights into the structural behaviour of Willyama Supergroup metasediments. In the Yanco Glen southeast area, the distribution of lithologies is largely controlled by D2 shears, producing a series of slices that resemble bedding on aerial photographs. In the Monuments area, D2 shears also control the distribution of lithologies, but extensive melting of psammites and flow parallel to S2 is an added feature.

Magnetic Mineralogical Characteristics of Hamersley Iron Ores in Western Australia

This paper presents the research outcomes of a magnetic mineralogical study on Hamersley iron ores. Thermal magnetic analysis shows that typical high-grade martite-microplaty hematite or M- (mpl H) and martite-microplaty hematite-goethite or M-(mpl H)-g ores contain a small amount of original magnetite. A small amount of magnetite/maghemite and pyrite/pyrrhotite/siderite may exist in typical martite-goethite (M-G) and martite-ochreous goethite (M-oG) ores. In “the hardcap zone”, M-(H)-g ores contain a small amount of magnetite and maghemite. Compared with XRD, thermal magnetic analysis is not only more sensitive in identifying trace of magnetite contained in high-grade hematite ores, but also more diagnostic in identifying other unstable magnetic minerals like maghemite and pyrite/pyrrhotite/siderite co-existed in the ores.

Augite-anorthite glass-ceramics from residues of basalt quarry and ceramic wastes

Dark brown glasses were prepared from residues of basalt quarries and wastes of ceramic factories. Addition of CaF2, Cr2O3 and their mixture CaF2-Cr2O3 were used as nucleation catalysts. Generally, structures with augite and anorthite as major phases and small amount of magnetite and olivine phases were developed through the crystallization process. In the samples heat treated at 900?C the dominant phase is augite, whereas the content of anorthite usually overcomes the augite at higher temperature (1100?C). Fine to medium homogenous microstructures were detected in the prepared glass-ceramic samples. The coefficient of thermal expansion and microhardnessmeasurements of the glass-ceramic samples were from 6.16?10-6 to 8.96?10-6?C-1 (in the 20-500?C) and 5.58 to 7.16GP, respectively.

Análisis de proveniencia de las arenas del complejo de dunas parabólicas El Socorro, Baja California, México, mediante una caracterización mineralógica y granulométrica

In this study, fourteen superficial sandy sediment samples and fifteen core samples, taken at 2 to 30 m in depth, were analyzed in order to determine the granulometry and mineralogical features of the dune system named duna costera El Socorro (DCES), San Quintin, Baja California, Mexico. In addition, we investigated the sediment provenance by analyzing twelve samples collected from three nearby arroyos and sand bars. The main components of the DCES are plagioclase and quartz (35 - 39 % and 36 - 58 % plagioclase, and 50 - 56 % and 38 - 60 % monocrystalline quartz for core samples and superficial samples, respectively). The remaining components include scarce lithic fragments and abundant heavy minerals, mostly hornblende and traces of pyroxene, but also small amounts of magnetite and ilmenite (> 1 % in volume). The samples from arroyo El Socorro (south of the DCES) and arroyo Santo Domingo (~45 km north of the DCES) contain 69 and 52 % monocrystalline quartz, respectively, while arroyo San Simon, located north of the DCES,

Magnetite in seafloor serpentinite--Some like it hot

Research Article| February 01, 2014 Magnetite in seafloor serpentinite—Some like it hot Frieder Klein; Frieder Klein * 1Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA *E-mail: fklein@whoi.edu. Search for other works by this author on: GSW Google Scholar Wolfgang Bach; Wolfgang Bach 2Geosciences Department, University of Bremen, 28359 Bremen, Germany Search for other works by this author on: GSW Google Scholar Susan E. Humphris; Susan E. Humphris 1Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA Search for other works by this author on: GSW Google Scholar Wolf-Achim Kahl; Wolf-Achim Kahl 2Geosciences Department, University of Bremen, 28359 Bremen, Germany Search for other works by this author on: GSW Google Scholar Niels Jöns; Niels Jöns 2Geosciences Department, University of Bremen, 28359 Bremen, Germany Search for other works by this author on: GSW Google Scholar Bruce Moskowitz; Bruce Moskowitz 3Department of Earth Sciences, and Institute for Rock Magnetism, University of Minnesota, Minneapolis, Minnesota 55455, USA Search for other works by this author on: GSW Google Scholar Thelma S. Berquó Thelma S. Berquó 4Department of Physics, Concordia College, Moorhead, Minnesota 56562, USA Search for other works by this author on: GSW Google Scholar Geology (2014) 42 (2): 135–138. https://doi.org/10.1130/G35068.1 Article history received: 28 Aug 2013 rev-recd: 22 Oct 2013 accepted: 24 Oct 2013 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Frieder Klein, Wolfgang Bach, Susan E. Humphris, Wolf-Achim Kahl, Niels Jöns, Bruce Moskowitz, Thelma S. Berquó; Magnetite in seafloor serpentinite—Some like it hot. Geology 2014;; 42 (2): 135–138. doi: https://doi.org/10.1130/G35068.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Serpentinization of mantle peridotite generates molecular hydrogen that can be exploited by microorganisms to gain metabolic energy; however, the mechanisms that control hydrogen generation and magnetite formation during serpentinization remain poorly understood. We have examined partly to completely serpentinized peridotites recovered during the Ocean Drilling Program and find a remarkable variation in the abundance of magnetite. Some completely serpentinized peridotites have as much as 6.15 wt% magnetite, whereas others are nearly magnetite free (<0.04 wt%). Using isotopic, magnetic, and thermodynamic constraints, our study reveals a simple link between the abundance of magnetite, Fe content of brucite, and serpentinization temperature. Samples with abundant magnetite have Fe-poor brucite and were formed at temperatures of 200–300 °C, whereas magnetite-poor samples are associated with Fe-rich brucite and were formed at temperatures <∼200 °C. We demonstrate that, despite the small amounts of magnetite, abundant hydrogen is generated through Fe(III) hosted in serpentine, lending support to the idea that low- to moderate-temperature serpentinization can generate abundant hydrogen within the temperature limits of life. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

In situ Raman Spectroscopic Study of NaCl Particle-Induced Marine Atmospheric Corrosion of Carbon Steel

The study of NaCl particle-induced atmospheric corrosion is facilitated by in situ Raman spectroscopic analysis through real time identification of corrosion products. Droplet formation on carbon steel by the deliquescence of pre-deposited NaCl particles that were exposed to high relative humidity (RH) (>80%), and corrosion initiation under the droplets were observed using an optical microscope. Pitting initiated within several minutes under the NaCl droplets. In situ and ex situ Raman spectra from the various rust species that formed during the corrosion process show that green rust (GR) formed close to the corrosion pit (i.e., anodic site) while lepidocrocite (γ-FeOOH) clusters precipitated outside of the GR region. A small amount of magnetite (Fe3O4) was also detected, mostly in the transitional region from GR to lepidocrocite. Upon exposure to an ambient atmosphere, GR transformed to lepidocrocite. This study confirms that the initial rust formed in NaCl particle-induced marine atmospheric corrosion of carbon steel is GR and lepidocrocite. While revealing the initiation mechanisms of NaCl particle-induced marine atmospheric corrosion of carbon steel, this study also provides insights for future studies involving wet-dry cycle exposures, which are more akin to the real atmospheric corrosion process.

Characterization and Reduction Behavior of Mill Scale

This paper presents an initial part of a project devoted to the recycling of mill scale in the form of self-reducing briquettes. First chemical and morphological characteristics of mill scale were investigated and next its gaseous reduction behavior was studied by thermogravimetry. The chemical characterization showed that wustite is the major constituent of this waste matter, with small amounts of magnetite, hematite and metallic iron. The microscopic examination of the scale revealed its complex and layered microstructure with three distinct zones. The outer layer is relatively thin and porous. It is mainly composed of hematite and magnetite. The intermediate layer is made of the dense, columnar grains of wustite. The inner layer is a very porous wustite. The gaseous reduction by carbon monoxide has a topochemical character regardless of initial morphology of scale and, depending on temperature and reducing gas composition it produces a porous iron or the iron whiskers. The unreacted shrinking core model with one interface fits quite well the kinetic data and the activation energy of reduction is about 80 kJ/mol.

Raman spectroscopy of hydrous inclusions in olivine and orthopyroxene in ophiolitic harzburgite: Implications for elementary processes in serpentinization

Secondary microinclusions in olivine and orthopyroxene in a harzburgite sample obtained from northern Oman ophiolite were examined by micro-Raman spectroscopy. The microinclusions were a consequence of fluid inclusions trapped by the minerals during the healing of fluid-filled cracks. We can expect an almost closed-system reaction to have occurred between the fluid and minerals. We attempted to distinguish the individual contributions of olivine and orthopyroxene to the serpentinization of peridotite. The inclusions in olivine mainly consist of lizardite and brucite with small amounts of magnetite, H2, and CH4, while those in orthopyroxene mainly consist of talc and chromian spinel with or without CH4 and graphite. The fluid involved was most probably a mixture of H2O and a smaller amount of CO2. We examined whether reduced gases were produced through reactions of the fluid with olivine and orthopyroxene. The role of magnetite (or magnetite component in chromian spinel) is of vital importance in the generation of these gases. Orthopyroxene facilitates the formation of talc in the serpentinization of peridotite.

Characteristics of Magnetic Fabric of Wenquan Granite Pluton in the Western Qinling Mountains and Implications for Emplacement Mechanism

AbstractWenquan pluton is situated in the western Qinling mountains and is adjacent to the south of the Shangdan suture zone. Through analyses of regional tectonics and the anisotropy of low‐field magnetic susceptibility (AMS) together with rock magnetism of 125 oriented samples, the emplacement mechanism of the pluton is studied. The values of most mean susceptibilities (km) show a wide variation range. Thermomagnetic curves demonstrate that the paramagnetic minerals such as biotite, acting as the main magnetic carriers, made dominant contributions to the magnetic susceptibility of the samples with low values, also including a small contribution to remanence from small amount of magnetite. The magnetite, however, acted as the dominant magnetic carrier of the samples with high magnetic susceptibility values. The corrected anisotropy degree (PJ ) less than 1.2 can be regarded as flow magnetic fabrics based on microscopic observations. The shape parameters (T) of most of magnetic susceptibility ellipsoid display that the Wenquan pluton is dominated by oblate compressional fabric, and the magnetic foliations are dominant over magnetic lineations. In addition, it is well marked that most magnetic foliations of the samples on the border seem parallel to the edge of the granite pluton, which have relatively steep inclinations, and interior ones appear relatively disordered besides magnetic lineations. Hence it can be revealed that the magnetic fabrics of the pluton are mainly formed by the lateral compression during the emplacement. Though the magnetic fabrics show N‐NEE and SW directed compression as a whole, the compression caused by the closure of the Shangdan suture zone during the Indo‐China period became much weaker than that in the main orogenic stage. Consequently it can be concluded that the weak compression setting can be reflected by the characteristics of magnetic fabrics when the pluton emplaced, and furthermore the relatively sustained and even extensional environment was probable and understandable, which was consistent with the regional tectonic setting in the extension stage of the emergence of delamination when the Qinling orogenic belt evolved to post‐collision stage.

Structural properties of iron phases formed on low alloy steels immersed in sodium chloride-rich solutions

Products of corrosion were obtained from low alloy steels submitted to total immersion tests in solutions containing sodium chloride at different concentrations, during seven days. In order to properly characterize the adherent (AR) and the non-adherent rusts (NAR), a methodology including room temperature Mossbauer spectrometry, diffuse reflectance infrared Fourier transform spectroscopy, Raman spectroscopy, scanning electron microscopy and X-ray diffraction was addressed. The techniques showed that the AR samples were composed of non-stoichiometric magnetite, goethite, akaganeite and lepidocrocite. The composition of the NAR samples was the same, but with very small amounts of magnetite. Different cell parameters and mean crystallite sizes were found for all phases presented in AR and the NAR samples. The corrosion rates were higher than 580 μm/y. The ratio of the abundances of goethite to the sum of lepidocrocite, akaganeite and magnetite were less than one.

Chemical etching induced shape change of magnetite microcrystals

We observed an interesting chemical etching induced shape change of magnetite microcrystals. Treatment in a NaBH4 aqueous solution was found to be capable of transforming the shape of magnetite microcrystals from octahedra to plates, meanwhile, a small amount of magnetite was reduced to form an Fe–B amorphous alloy. The observed shape change process proceeded massively in ambient conditions and involved no surfactant. The structures of magnetite microcrystals were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy with selected area electron diffraction. The magnetite microplates are single crystals with the flat top surface parallel to the (111) plane of their fcc crystal structure. We observed a similar shape change process for Fe2O3, Co3O4, and Co2O3 microcrystals, but not for Pb3O4 microcrystals. A probable mechanism for the shape change of magnetite microcrystals induced by treatment in NaBH4 aqueous solution was proposed on the basis of the experimental results.

Characterization of rust phases formed on low carbon steel exposed to natural marine environment of Chennai harbour – South India

AbstractThe corrosion behaviour of low carbon steel exposed to marine atmospheric, splash and immersion zones has been systematically studied by exposing steel specimens for a period of 12 months at the boat basin corrosion station of Chennai harbour, Chennai, Tamil Nadu, South India. The literature on similar work has been thoroughly reviewed which led to the initiation of this study for the first time at this harbour. The corrosion product (rust) on the specimens at 1, 2, 3 and 12 months was obtained and characterized by Fourier transform infrared spectroscopy (FT‐IR) and X‐ray diffraction (XRD) analysis. Acaganeite was the rust phase identified in the splash zone as revealed by the FT‐IR and XRD analysis. The other dominant phases were lepidocrocite, goethite and ferroxyhite. Small amounts of magnetite were also found to be present. The transformation of phases was observed in this investigation and discussed. A remarkable difference in the FT‐IR and XRD patterns of the corrosion products at the splash and immersion zones were noticed and the corresponding phases formed were reported in this paper. The rate of corrosion in all the three zones was compared.

Magnetic properties and potential field modeling of the Peculiar Knob metamorphosed iron formation, South Australia: An analog for the source of the intense Martian magnetic anomalies?

Magnetic property measurements show that the strongly metamorphosed Peculiar Knob iron formation (IF), South Australia, is coarse‐grained, high‐grade hematite with variable amounts of magnetite and maghemite. This body exhibits a relatively low magnetic susceptibility (&lt;0.3 SI) that cannot explain the associated intense magnetic anomaly, 30,000 nT, in terms of induced magnetization alone. Peculiar Knob IF possesses an extremely intense (∼120 A m−1) remanence, directed steeply upward. This ancient remanence reinforces the local Earth's field (inclination −63°). A simple geological model, constrained by drilling and physical property measurements, explains both the observed magnetic and gravity anomalies, consistent with the Poisson theorem. Koenigsberger ratios (Qs) of 10 and greater, as found here, are rare in nature. We postulate that acquisition of a thermoremanent magnetization (TRM) by the ore during postmetamorphic cooling from above the Curie/Néel temperature accounts for the intense remanence and high Qs. Although the hematite is in the multidomain size range, the coercivity is higher than expected. Also, the natural remanent magnetization (NRM) values are less than 10% of the expected value for a saturated TRM of hematite. On the basis of reflected light, scanning electron microscope observations, and rock magnetism, we propose that the common fine intergrowths of a very small amount of magnetite and/or maghemite within the hematite host are responsible for the relatively high coercivity and contribute to the NRM. These intergrowths are not normal exsolution lamellae and were likely present at high temperature. This study suggests that coarse‐grained hematite‐rich bodies that carry TRM and have been subjected to high‐grade (&gt;680°C) metamorphism may be possible sources for some of the prominent Martian anomalies.

An In Situ Raman-Electrochemical Investigation of Carbon Steel Corrosion in Na2CO3 ∕ NaHCO3, Na2SO4, and NaCl Solutions

The anoxic corrosion of carbon steel liners inside failed copper nuclear waste containers is dependent on the composition of the groundwater to which it is exposed. The influence of carbonate/bicarbonate, sulfate, and chloride in solutions simulating concentrated groundwaters at pH 8.9 on the composition of the corrosion products formed on A 516 Gr 70 carbon steel has been investigated at room temperature. In situ Raman spectroscopic identification of the corrosion products formed during polarization at constant potential was conducted in a spectroelectrochemical cell. Siderite was established as the main product in sodium carbonate/bicarbonate solutions, and the observance of iron carbide indicates extensive steel dissolution in this environment. In mixed carbonate, sulfate, chloride solutions, compact deposits of carbonate-containing, and to a lesser degree, sulfate-containing green rusts were formed, along with small amounts of magnetite. In chloride-dominated solutions very thin, compact films, undetectable by Raman spectroscopy, were formed. Ex situ Raman analysis suggests this film may be magnetite.