Amounts Of Hematite Research Articles

Catalytic Degradation of Methyl Blue in Wastewater by Hematite

In this paper, catalytic degradation of simulated methyl blue in wastewater was investigated using hematite as heterogeneous catalyst in like-Fenton reaction. Through single factor experiments, the effects of the H2O2 dosage, the hematite dosage, initial pH value and reaction time on methyl blue catalytic degradation were studied. The results showed that as the amount of hematite, H2O2 dosage and reaction time increases, the degradation increases, more than a certain degradation value , the trend decreases and tends to stabilize. The optimal operating conditions determined by orthogonal experiments are as following: hematite dosage was 3g/L, H2O2 dosage was 3mL/L, and 4h at pH=9.The Fenton reaction system of hematite as heterogeneous catalyst has a wide range of pH, in the range of 3 to 11 have better removal effect, and generally more than 85%.

Mechanical properties of polymer concretes containing different amount of hematite or colemanite

Polymer concretes (PCs) were created by using varying concentrations of silica sand as aggregate and also hematite, colemanite and a commercial epoxy resin. Hematite is known to exhibit radiation shielding properties. Mechanical performance was evaluated including unit weight, pulse velocity, compressive strength, flexural strength, splitting tensile strength, modulus of elasticity and dynamic elastic modulus. As expected, mechanical properties depend on the resin concentration, the aggregate type and aggregate content in the mixture. Hematite particles have a larger effect than colemanite on mechanical properties of PCs. Inclusion of hematite provides significant improvement of the mechanical properties studied PCs in comparison to PC with silica sand only.

An assessment study of tiles from Topkapı Palace Museum with energy‐dispersive X‐ray and Raman spectrometers

A limited number of studies concerning Ottoman ceramic technology have been performed using the scanning electron microscopy‐energy dispersive X‐ray spectrometry and micro‐Raman spectroscopy techniques. The discovery of the ceramics, which were described as ‘Iznik’, at excavation sites outside of the city of Iznik, caused disagreements over the exact origin of Iznik products. In this study, bodies, glazes, and pigments of 46 tile/ceramic shards of unknown origin, which were supplied from the vaults of Topkapı Palace Museum, and two reference tile fragments, known as Kütahya products, supplied from the demolished Surp Krikor Lusavoriç church and, additionally, two Iznik reference tiles were examined using the scanning electron microscopy‐energy dispersive X‐ray spectrometry and micro‐Raman spectroscopy techniques. Results of both techniques were evaluated together for the first time to determine the power of nondestructive Raman spectroscopy technique in differentiation of Ottoman tiles. In this work, bodies of the Kütahya tiles were found to be different than Iznik and Tekfur stone‐paste bodies, which are rich in clay rather than quartz. Two different lead‐alkali glaze compositions were found for Kütahya tiles; one was rich in PbO (over 35%) and the other one was rich in alkali (PbO less than 25%). Barite inclusions were detected in the bodies and in the glazes of some Ottoman tiles, which could be the fingerprint for the Kütahya products. It was found that the under glaze red decoration is essentially a mixture of hematite and quartz in different proportions. Shades of red decoration mainly depend on the amount of hematite in the mixture. Sixteenth century tomato red decoration contains more quartz compared with 17th century dark red decoration. This study showed that a similar technology was also applied at Kütahya in the 16th century. A linear correlation was found between the position of the Raman intense stretching peak Q3 and lead oxide content of lead‐alkali glazes, which could allow for the differentiation of Ottoman tiles based on the nondestructive Raman analysis. This study provides an important additional reference data and discussion for the Ottoman tiles. Copyright © 2011 John Wiley & Sons, Ltd.

Biological origin of minerals in pisoliths in the Darling Range of Western Australia

Bauxitic pisoliths are widespread and abundant in the Darling Range of Western Australia. They occur as lag and within soil, range in size from a few millimetres to over 10 mm and largely consist of gibbsite with various amounts of hematite, maghemite, goethite, quartz, anatase and corundum. Scanning electron microscopy (SEM) revealed various morphologies throughout the pisoliths resembling fungal hyphae that are composed of gibbsite and Fe oxides. The fungal hyphae exhibit significant differences in size and shape, and they are gibbsitised in different ways and at different stages of development. Our interpretation of these observations led to the conclusion that the pisoliths, in part, are formed by the active precipitation of Al and Fe by fungi, rather than by subsequent replacement of fungi by Al and Fe.

Thermomagnetic Analyses of the Permeability-Controlling Minerals in Red and White Sandstones in Deep Tight Gas Reservoirs: Implications for Downhole Measurements

Summary Our recent work on deep tight gas reservoirs containing red and white sandstones (Potter et al. 2009) has suggested that the presence of small amounts of hematite in reservoir samples can have a dramatic effect on permeability. Such conclusions were made using laboratory-based low- and high-field magnetic-susceptibility measurements on reservoir-rock samples and by comparing these measurements with the permeability data. These rapid, nondestructive magnetic measurements have been applied previously in clastic reservoir samples (Potter 2007; (Ivakhnenko 2006; Ivakhnenko and Potter 2008; Potter and Ivakhnenko 2008) and carbonate reservoir samples (Al-Ghamdi 2006; Potter et al. 2011). However, such laboratory-based analyses are not representative of the downhole in-situ conditions, especially in deep gas reservoirs where the temperature can reach quite high values. Typical tight-gas-reservoir depths can reach approximately 4000 m (Abu-Shanab et al. 2005) and 6000 m (Tang et al. 2008), and the equivalent temperatures would measure 131 and 192°C, respectively, if one assumes the normal geothermal gradient (Mayer-Gurr 1976). This paper investigates the in-situ magnetic properties of deep tight gas reservoir samples (containing permeability-controlling reservoir minerals hematite and illite) by means of laboratory experiments to model downhole temperature conditions. We perform magnetic hysteresis measurements at various temperatures in order to identify and quantify mineralogy and model changes in the magnetic behavior of these minerals at in-situ downhole conditions. From these measurements, we are able to show whether the mineralogy or domain state of the permeability-controlling minerals is likely to change with temperature in deep gas reservoirs. These changes can potentially have a major effect on permeability. We also demonstrate that there are strong correlations between core-permeability and magnetic-susceptibility data in these tight-gas-reservoir samples. The permeability is low in red sections of the core wherever there is hematite.

Kinetic study of the thermal transformation of limonite to hematite by X-ray diffraction, μ-Raman and Mössbauer spectroscopy

A kinetic study about the phase limonite (FeO(OH)-nH2O) was performed through X-ray diffraction, μ-Raman spectroscopy and Mossbauer spectroscopy. The oxide powder sample was extracted from Taraco district, Huancane province of Puno (Peru). X-ray diffraction identified the phase goethite as the main mineralogical component, and then the sample was subjected to in-situ heat treatment in the temperature range: 100 to 500°C in oxidizing (air) and inert (nitrogen) atmospheres. The goethite phase remains stable in this range: room temperature to 200°C. Between 200°C to 250°C there is a phase transition: α-Fe3 + O(OH) → α-Fe2O3, i.e., from goethite to hematite phase, taking as evidence the evolution of the diffraction profiles. At 200°C spectra shows the start of broadened magnetic component and it was adjusted through of a magnetic distribution giving a mean field of 38.6T and a relative area of 52.9%, which is a characteristic of goethite. Also, it is noticed the presence of a small amount of hematite with a mean field of 49.0T linked with a superparamagnetic broadened doublet of relative area of 47.1% where the domains of the particles have sizes smaller than 100 A and it is evidence the superparamagnetic limit; i.e., the superparamagnetic effect tends toward a distribution of magnetic fields. Moreover, the Raman spectra of the in-situ thermal treatment, support the transition at 290°C through the transformation of characteristic bands of goethite to hematite phase at the frequency range from 200 to 1,800 cm − 1.

Improved KNN-SMOreg algorithm and its application in predicting the amount of hematite from uranium

Hematite,as a typical alteration mineral,plays a very important role in uranium exploration.Traditional modeling method usually treats every feature with the same probability.However,this does not hold in many real world applications,which may also cause the reduction of the accuracy of prediction.We propose a novel method called WKNN-SMOreg,which weights the features according to the association of their attributes on the hybrid of KNN and SMOreg.In this way,the error caused by the features with lower association will be reduced.The experiment results show,compared with KNN,SVM and KNN-SMOreg,the novel method improves the accuracy of prediction,and reduces the negative impact of the noise,which also implies that the new method can be well applied in the prediction of alteration minerals.

Research on Process Mineralogy of Potassium-Rich Shale

The process mineralogy of potassium-rich shale from Chaoyang of Liaoning, China, was studied. Research results showed there are much less variety and smaller quantities in mineral compositions. Calculated mineral composition by means of chemical composition analysis combined with XRD, MLA, IR and TG-DSC analyses showed that main minerals with were Potassium-feldspar, muscovite, biotite and illite, and gangue minerals were quartz and small amounts of hematite. Potassium-rich minerals such as potassium-feldspar and muscovite contact smoothly with quartz respectively, and there was the direction arrangement among potassium-feldspar, quartz and muscovite in the shale. And quartz and hematite were main cement in the shale. The influences of the research results on the potassium extraction from potassium-rich shale were distinct.

Controlling Photoactivity in Ultrathin Hematite Films for Solar Water‐Splitting

AbstractA promising route to increase the performance of hematite (α‐Fe2O3) photoelectrodes for solar hydrogen production through water‐splitting is to use an extremely thin layer of this visible light absorber on a nanostructured scaffold. However, the typically poor performance of ultrathin (ca. 20 nm) films of hematite has been the limiting factor in implementing this approach. Here, the surprising effect of a substrate pretreatment using tetraethoxysilicate (TEOS) is reported; it results in drastic improvements in the photoperformance of 12.5 nm thick films of hematite. These films exhibit a water oxidation photocurrent onset potential at 1.1 V versus the reversible hydrogen electrode (vs. RHE) and a plateau current of 0.63 mA cm−2 at 1.5 V vs. RHE under standard illumination conditions, representing the highest reported performance for ultrathin hematite films. In contrast, almost no photoactivity is observed for the photoanode with the same amount of hematite on an untreated substrate. A detailed study of the effects of the TEOS treatment shows that a monolayer of SiOx is formed, which acts to change the hematite nucleation and growth mechanism, increases its crystallinity, reduces the concentration of carrier trapping states of the ultrathin films, and suggests its further application to quantum‐dot and extremely‐thin‐absorber (ETA)‐type solar cells.

Microstructural characterization and influence of manufacturing parameters on technological properties of vitreous ceramic materials

Microstructure of vitreous ceramic samples manufactured from kaolinitic-clay and feldspars raw materials from Cameroon was investigated in the range 1150–1250 °C by X-ray diffraction and scanning electron microscopy and by measuring some technological properties. Moreover, the simultaneous influence of feldspars content, heating temperature and soaking time on water absorption and firing shrinkage was evaluated by adopting the response surface methodology (Doehlert matrix), using the New Efficient Methodology for Research using Optimal Design (NEMROD) software. The results show that a spinel phase, mullite, glassy phase and some amount of hematite were formed. However, the spinel phase and potassic feldspar, as compared to the sodic one, disappeared at moderate firing temperature and soaking time. Apparently, mullite developed from spinel phase, which is formed from the demixion of metakaolin. On the other hand, it is found that the effects of fluxing content and firing temperature on the measured properties were almost similar and more influent than soaking time. Antagonistic and synergetic interactions existed between the considered parameters, and their importance differed for the considered properties. By using this mathematical tool, suitable operating conditions for manufacturing vitreous bodies were determined.

Magnetic nanoparticles based on iron coated carbon produced from the reaction of Fe2O3 with CH4: a Mössbauer study

In this work, it was investigated the production of magnetic nanoparticles encapsulated with carbon by the reaction of hematite and methane by Temperature Programmed Reaction up to 950°C. XRD and Mossbauer analyses showed that the materials prepared at 600°C and 700°C are mainly composed of magnetite and small amounts of hematite α -Fe2O3 with particle size of 30–40 nm. At higher temperatures, the spectra also display two central doublets corresponding to wustite phase (Fe1 − x O). The materials were also characterized by magnetization measurements, BET surface area, thermal analysis (TG) and SEM. These materials can be prepared by a simple and low cost process and show great potential to be used as adsorbents and catalyst support.

WO3−Fe2O3 Photoanodes for Water Splitting: A Host Scaffold, Guest Absorber Approach

Solar hydrogen production via watersplitting with hematite (Fe2O3) has been limited by poor light absorption and a small hole diffusion length. These drawbacks can be overcome by using a high-surface-area host to support a thin layer of hematite—allowing photogenerated holes to be produced in high proximity to the semiconductor-liquid junction. Here we demonstrate the effectiveness of this concept using a nanostructured host scaffold (WO3) prepared by atmospheric pressure CVD to support a thin layer of Fe2O3 nanoparticles deposited by a similar method. A 20% increase in the photocurrent was observed in host−guest electrodes as compared to control films with the same amount of hematite (equivalent to a 60 nm film) deposited without the host scaffold. The improvement is attributed to an increase in the absorbed photon conversion efficiency (APCE), especially for longer wavelengths where the photon penetration depth is large in hematite. For light with a wavelength of 565 nm, the APCE improves to 8.0%, as co...

Investigation of factors affecting pellet strength in straight grate induration machine

During induration in a straight grate machine, the green pellets pass through four different thermal treatments, namely drying, preheating, heating and cooling. The pellet bed is fired with downdraught firing leading to thermal gradients through the bed. Corex sludge, which is used as fuel in the pellet mix, supplies the necessary energy for uniform heating of the pellet. The physicochemical conditions, e.g. the temperature and oxygen partial pressure mainly depend on the amount of fuel incorporated in the pellet mix. As a result the percentage and the distribution of various phases in the pellets vary, leading to deviation in quality. To study the distribution of phases and their impact on cold crushing strength at different carbon levels (1·20 and 1·35%), pellets from different layers of the induration bed in an industrial straight grate were characterised. It was observed that the strength of the pellets varied from 142 to 268 kg/pellet and 128 to 245 kg/pellet across bed, with carbon 1·20 and 1·35% respectively. It was found that middle layer pellets had higher strength compared to top and bottom layers. It was observed that amount of hematite, magnetite, porosity and the pore size plays a significant role on the pellet strength. Pellets with 1·20% carbon showed better physical and microstructural properties across the pellet bed compared to pellets with 1·35% carbon.

Cor de solo, formas do fósforo e adsorção de fosfatos em Latossolos desenvolvidos de basalto do extremo-sul do Brasil

Latossolos Brunos e Vermelhos férricos desenvolvidos de basalto representam parcela expressiva dos solos intensivamente cultivados do Sul do Brasil. Além dos perfis monomatizados típicos, brunos ou vermelhos, incluem-se, atualmente, nestas duas classes perfis polimatizados, que apresentam os horizontes superficiais brunados e os subsuperficiais mais avermelhados, anteriormente individualizados como Latossolo "Bruno/Roxo". Não há, ainda, no Sistema Brasileiro de Classificação de Solos, um consenso quanto aos componentes de cor mais apropriados para separação dos Latossolos Brunos e Vermelhos. Graças à sua textura muito argilosa e ao alto conteúdo de óxidos de ferro, tais solos apresentam elevada capacidade de adsorção de fosfatos, à qual se pressupõe seja diferenciada de acordo com as formas dos óxidos de ferro presentes em cada modalidade. Por outro lado, a matéria orgânica, ao interagir com os óxidos de ferro, pode igualmente mascarar o efeito individual desses óxidos na fixação. Desse modo, o presente trabalho objetivou: (a) testar a utilidade e a eficácia do uso de dados espectrais obtidos por refletância difusa como ferramenta para identificação dos óxidos de ferro goethita (FeOOH) e hematita (Fe2O3); (b) quantificar, por fracionamento químico, as diferentes formas ou compartimentos onde se encontra o fósforo nesses solos, e (c) avaliar o efeito dos diferentes tipos e proporções de hematita e goethita na adsorção de fósforo, bem como o efeito da matéria orgânica na redução dessa capacidade sortiva. Foram selecionados seis perfis de solo em Santa Catarina e Rio Grande do Sul, sendo dois Latossolos Brunos típicos, dois Latossolos Vermelhos férricos e dois Latossolos Brunos, provisoriamente denominados Latossolo Bruno/Vermelho férrico. Os perfis foram caracterizados do ponto de vista físico, químico e mineralógico, sendo as amostras de quatro horizontes de cada perfil selecionadas para análises mais detalhadas. As técnicas de refletância difusa utilizadas mostraram-se altamente promissoras para a identificação e quantificação dos óxidos de ferro presentes. O matiz 4 YR, em amostras naturais úmidas, correspondeu a valores aproximadamente iguais de hematita e de goethita nos solos, sendo esse valor proposto como limite de separação entre Latossolos Brunos e Vermelhos e entre Nitossolos Vermelhos e Háplicos. Para a maioria dos solos, as quantidades totais de fósforo foram superiores a 1.000 mg kg-1, indicando alta reserva potencial desse nutriente. No fracionamento químico seqüencial, evidenciou-se o predomínio das formas "oclusas" de fósforo (Pdcb), seguida das formas orgânicas, P adsorvido a formas cristalinas dos óxidos de ferro e P ligado a compostos de ferro de baixa cristalinidade. O coeficiente A da equação de Freundlich modificada, que estima a quantidade de P necessária para manter 1 mg L-1 P na solução após um dia de equilíbrio, foi menor nos Latossolos Vermelhos em relação aos Brunos. Em todos os solos, entretanto, o valor de A mostrou-se inversamente correlacionado com o conteúdo de matéria orgânica, indicando que, além do efeito individual dos óxidos de ferro na fixação, o aumento no conteúdo de matéria orgânica exerce papel extremamente importante na redução da sorção de fosfatos desses solos.

Selective Dissolution Techniques, X-Ray Diffraction and Mössbauer Spectroscopy Studies of Forms of Fe in Particle-Size Fractions of an Entic Haplustoll

Particle-size fractions (∅ = mean diameter, 5–2 μm, 2–1 μm, and <1 μm) from the Ap horizon of an Entic Haplustoll from Argentina were treated with the selective-dissolution techniques ammonium oxalate (OX), dithionite-citrate-bicarbonate (DCB), NaOH, and Na-pyrophosphate (PY), and studied by X-ray powder diffraction (XRD) and 57Fe Mossbauer spectroscopy (MS). Quartz, feldspar, smectite, illite and interstratified illite-smectite are the dominant minerals whereas Fe oxides and oxy-hydroxides are present in low concentration but increase as particle size decreases. Poorly crystallized oxides (highly Al-substituted hematite and goethite) amounts are lower, comparable to or slightly higher than the hematite amounts in the ∅ = 5–2 μm, 2–1 μm and <1 μm fractions respectively. This hematite is well crystallized but presents some degree of Al-substitution. Magnetite/maghemite was identified in the 2–1 μm fraction. Paramagnetic Fe3+ and Fe2+ are associated to the clay minerals and/or hydroxyl-interlayered 2:1 type material present; part of this Fe3+ is located in the hydroxy-interlayers its amount being higher in the smallest fraction. Any possible changes after the PY and NaOH treatments were not detected by MS.

Types of Magnetic Carriers in Late Cenozoic Sediments, Sanmenxia Basin, Northern‐Central China

AbstractLate Cenozoic sediments in the Sanmenxia Basin, northern‐central China are used for SIRM, remanence coercivity, susceptibility, alternating field and/or thermal demagnetization experiments. It was found that different magnetic carriers occur among loess‐palaeosol, lacustrine‐fluvial gray green deposits and brownish red pluvial‐alluvial sediments. Magnetic carriers of loess‐palaeosol are dominated by magnetite, with only minor amounts of hematite and maghemite. Gray green lacustrine‐fluvial deposits contain less amounts of ferromagnetic minerals that include more magnetite, and less hematite, together with unstable minerals such as goethite and possible siderite. Pluvial‐alluvial sediments also contain magnetite and hematite, but dominant by magnetite.

Multiple Iron-Rich Spinel Phases and Hematite in a Magnetic Soil Developing on Tuffite

A dusky red Latosol developing on tuffite was examined in detail in order to characterize its iron oxide mineralogy. Magnetic separation and selective chemical treatment were employed. The mineralogical analyses were carried out by powder X-ray diffraction and Mossbauer spectroscopy, with the electron microprobe technique being used to assess the chemical composition of selected grains. Results reveal that iron-rich spinel-structure phases from this pedosystem are rather variable in chemical composition and lattice parameters, and can be grouped in at least three major populations: the first group consisting of the iron-richest phase, with very low Ti and Cr and virtually no Mg content and high Al; the second group presenting Ti>Mg>>Al>Mn contents but no Cr and the third group related to the Mg-richest phase with Mg>Ti>>Al>Mn. Two major populations of hematite were also identified: one with ∼15 mol% Al and other practically Al-free. The first group is thought to be a product of neoformation in an Al-rich pedogenic medium whereas the second is likely to be transformed directly from maghemite. Though chemical treatment along with physical techniques provide a powerful way to characterize iron oxides of tropical soils, some methodological difficulties still remain, particularly those concerned with (i) the characterization and quantification of maghemite in presence of relatively large amount of hematite in the soil mixture, particularly by Mossbauer spectroscopy, and (ii) the allocation of the isomorphous substituents for iron in the cation sites of the spinel structure. Possible mechanisms of alteration of iron-rich phases in this pedosystem are discussed.

Record of middle Pleistocene climate change from Buck Lake, Cascade Range, southern Oregon—Evidence from sediment magnetism, trace-element geochemistry, and pollen

Comparison of systematic variations in sediment magnetic properties to changes in pollen assemblages in middle Pleistocene lake sediments from Buck Lake indicates that the magnetic properties are sensitive to changes in climate. Buck Lake is located in southern Oregon just east of the crest of the Cascade Range. Lacustrine sediments, from 5.2 to 19.4 m in depth in core, contain tephra layers with ages of ≈300–400 ka at 9.5 m and ≈400–470 ka at 19.9 m. In these sediments magnetic properties reflect the absolute amount and relative abundances of detrital Fe-oxide minerals, titanomagnetite and hematite. The lacustrine section is divided into four zones on the basis of magnetic properties. Two zones (19.4–17.4 m and 14.5–10.3 m) of high magnetic susceptibility contain abundant Fe oxides and correspond closely to pollen zones that are indicative of cold, dry environments. Two low-susceptibility zones (17.4–14.5 m and 10.3–5.3 m) contain lesser amounts of Fe oxides and largely coincide with zones of warm-climate pollen. Transitions from cold to warm climate based on pollen are preceded by sharp changes in magnetic properties. This relation suggests that land-surface processes responded to these climate changes more rapidly than did changes in vegetation as indicated by pollen frequencies. Magnetic properties have been affected by three factors: (1) dissolution of Fe oxides, (2) variation in heavy-mineral content, and (3) variation in abundance of fresh volcanic rock fragments. Trace-element geochemistry, employing Fe and the immobile elements Ti and Zr, is utilized to detect postdepositional dissolution of magnetic minerals that has affected the magnitude of magnetic properties with little effect on the pattern of magnetic-property variation. Comparison of Ti and Zr values, proxies for heavy-mineral content, to magnetic properties demonstrates that part of the variation in the amount of magnetite and nearly all of the variation in the amount of hematite are due to changes in heavy-mineral content. Variation in the quantity of fresh volcanic rock fragments is the other source of change in magnetite content. Magnetic-property variations probably arise primarily from changes in peak runoff. At low to moderate flows magnetic properties reflect only the quantities of heavy minerals derived from soil and highly weathered rock in the catchment. At high flows, however, fresh volcanic rock fragments may be produced by breaking of pebbles and cobbles, and such fragments greatly increase the magnetite content of the resulting sediment. Climatically controlled factors that would affect peak runoff levels include the accumulation and subsequent melting of winter snow pack, the seasonality of precipitation, and the degree of vegetation cover of the land surface.Our results do not distinguish among the possible contributions of these disparate factors.

Mineralogy of three slightly palagonitized basaltic tephra samples from the summit of Mauna Kea, Hawaii

Certain palagonites from Hawaii are considered to be among the best analogs for Martian fines, based upon similar spectral properties. For this study, three distinctly colored layers were sampled from slightly palagonitized basaltic tephra just below the summit of Mauna Kea at 4145 m elevation. The mineralogy of size fractions of these samples was examined by diffuse reflectance (visible and near‐IR) and far‐IR spectroscopy, optical microscopy, X ray diffraction, Mössbauer spectroscopy, magnetic analysis, electron microprobe analysis (EMPA), and transmission and scanning electron microscopy. For the 20–1000 μm size fraction, sample HWMK11 (red) is essentially completely oxidized and has a hematite (Ti‐hematite) pigment dispersed throughout the silicate matrix. The alteration is present throughout particle volumes, and only a trace amount of glass is present; no palagonitic rinds were detected. In addition to ferric Fe‐Ti oxides, other phases detected were plagioclase feldspar and a trace of olivine. Sample HWMK12 (black) has the lowest proportion of ferric‐bearing phases and is thus least weathered. It consists mostly of unaltered glass with embedded plagioclase and minor amounts of pyroxene, olivine, and Ti‐magnetite. In some grains, a thin palagonitic rind is visible, indicating some surface alteration. The mineralogy for sample HWMK13 (yellow) is the same as that for HWMK12, except that it has distinct, well‐developed palagonitic rinds consisting of erionite and smectite. For all samples, the amount of glass and plagioclase decreases and the amount of smectite increases with decreasing particle size for size fractions &lt;20 μm. For HWMK11, the amount of hematite is essentially constant, and mica is present only in the coarse clay‐sized fraction; smectites are low in structural Fe. For HWMK12 and HWMK13, the zeolite erionite is present along with smectites and nanophase ferric oxides (np‐Ox). Erionite abundance decreases and np‐Ox abundance increases with decreasing particle size. The smectite in both black and yellow samples contains some Fe3+ in octahedral layers. There were only two mineral phases containing iron in the fine clay fraction, namely, smectites and iron oxides. For HWMK11, relatively large iron oxide particles (0.1 to 0.4 μm) were dispersed on clay surfaces; for HWMK12 and HWMK13, much finer np‐Ox particles were present in lesser concentrations. Formation of the zeolite erionite is consistent with the arid climate zone where these samples were collected. However, transient hydrothermal processes that occurred during the eruption of Mauna Kea volcano under its permanent ice cap during the Pleistocene may have resulted in minerals such as zeolites and smectites which may persist as relicts over a long period of time. Most of the iron released during weathering of basaltic tephra precipitated as poorly crystalline iron oxides and some of the Fe has substituted for the octahedral cations in the structure of authigenic smectites. The Ti‐hematite in HWMK11, however, is the result of high‐temperature oxidation of Ti‐magnetite and exsolution from ironbearing silicate phases. Visible and near‐IR reflectivity spectra for the &lt;20 μm size fraction of HWMK11 is dominated by well‐crystalline Ti‐hematite. Corresponding spectra for HWMK12 and HWMK13, whose ferric mineralogy is dominated by np‐Ox particles, are more similar to Martian bright‐region spectra.

Anomalous Magnetization by Chemical and Microbial Processes in Hydrocarbon Seepage Environments

Anomalous magnetization has been reported from several commercial hydrocarbon accumulations. Although the processes responsible for such anomalous magnetization are relatively poorly understood, the formation and destruction of magnetic mineral assemblages can be predicted from thermodynamic criteria and microbiologic activity. Under the influence of hydrocarbons, magnetite and pyrrhotite are the most important magnetic minerals formed, and the most abundant magnetic mineral destroyed is hematite. Hence, the invasion of hydrocarbons may result in anomalous magnetization relative to the total magnetization prior to hydrocarbon invasion, depending on the amounts of authigenic magnetite and pyrrhotite formed relative to the amounts of hematite destroyed. Anomalous magnetization may be present vertically above the location of hydrocarbon seepage or may be laterally displaced where the migration of the escaping hydrocarbons is influenced by forces in addition to buoyancy. This is likely where local or regional groundwater flow has a significant lateral component, or where hydrocarbon seepage is funnelled by inclined beds and faults of high permeability. Magnetism may be generated also by natural and anthropogenic processes that have no relationships to an underlying or adjacent hydrocarbon accumulation. Consequently, anomalous magnetization, even if associated with a hydrocarbon accumulation, may or may not be genetically related to it.