Distribution Of Ferric Iron Research Articles

Revisiting the nontronite Mössbauer spectra

The distribution of ferric iron (Fe 3+ ) between the octahedral and tetrahedral sheets of smectites is still an active problem due to the difficulty of identifying and quantifying the tetrahedral ferric iron ( [4] Fe 3+ ). Mossbauer spectroscopy has often been used to address this problem, with the spectra being fitted by a sum of doublets, but the empirical attribution of each doublet has failed to yield a uniform interpretation of the spectra of natural reference Fe 3+ -rich smectites, especially with regard to [4] Fe 3+ , because little consensus exists as to the [4] Fe 3+ content of natural samples. In an effort to resolve this problem, the current study was undertaken using a series of synthetic nontronites [Si 4–x [4] Fe x 3+ ] [6] Fe 2 3+ O 10 (OH) 2 Na x with x ranging from 0.51 to 1.3. Mossbauer spectra were obtained at 298, 77, and 4 K. Statistically acceptable deconvolutions of the Mossbauer spectra at 298 and 77 K were used to develop a model of the distribution of tetrahedral substitutions, taking into account: (1) the [4] Fe 3+ content; (2) the three possible tetrahedral cationic environments around [6] Fe 3+ , i.e., [4Si]-(3 [6] Fe 3+ ), [3Si [4] Fe 3+ ]-(3 [6] Fe 3+ ), and [2Si 2 [4] Fe 3+ ]-(3 [6] Fe 3+ ); and (3) the local environment around a [4] Fe 3+ , i.e., [3Si]-(2 [6] Fe 3+ ) respecting Lowenstein’s Rule. This approach allowed the range of Mossbauer parameters for [6] Fe 3+ and [4] Fe 3+ to be determined and then applied to spectra of natural Fe 3+ -rich smectites. Results revealed the necessity of taking into account the distribution of tetrahedral cations ( [4] R 3+ ) around [6] Fe 3+ cations to deconvolute the Mossbauer spectra, and also highlighted the influence of sample crystallinity on Mossbauer parameters.

The stoichiometric effects of ferric iron substitutions in serpentine from microprobe data

ABSTRACTGiven that secondary magnetite is common in serpentinites, it is clear that serpentinites are oxidized rocks. Questions remain, however, concerning the distribution of ferric iron among magnetite and serpentine minerals and the role of ferric iron-rich serpentine in the formation of secondary magnetite. Direct determination of ferric iron in serpentine is not possible using an electron microprobe. We show, however, that the stoichiometic effects of ferric iron substitutions are detectable, although not quantifiable, by microprobe. First, we demonstrate that for studies that provide both microprobe analyses of major elements of serpentine and Mössbauer analysis of ferric iron, substitution effects are obvious. Next, it is equally clear that the early veins forming at the onset of olivine hydration (type 1 veins) show no indication of the presence of ferric serpentine, although a small amount of ferric ‘brucite’ may occur. Finally, we show that secondary (type 2) veins, which form as the system becomes open to fluids in equilibrium with plagioclase or pyroxene, contain, in addition to significant alumina, stoichiometric indications of ferric iron substitution. The serpentine in these veins is magnesian, usually with Mg#s around 96–98. Thus, even if a significant proportion of this iron is ferric, it comprises only a small fraction of the total ferric iron budget of the rock. Given that reduced iron is known to be abundant in early-formed brucite and early-formed serpentine and given that brucite, in particular, is absent from evolved serpentine veins, we propose that most magnetite in serpentinites forms as a tertiary product via oxidation of brucite.

VNIR spectral variability of the igneous stratified Stillwater Complex: A tool to map lunar highlands

Lunar highlands are plagioclase-rich terrains produced by crystal floating in a Magma Ocean system. Lunar samples revealed the presence of anorthositic (plagioclase > 90%) samples from the Highlands, associated to more mafic rocks. Recently, remote sensing data permit mapping those terrains with high spatial and spectral resolution allowing detection of plagioclase and mafic crystal field (C.F.) absorptions. In this paper we have studied bidirectional spectral characteristics in the visible near-infrared (VNIR) of rocks from the Stillwater Complex, a cumulitic igneous stratified complex, with composition varying from mafic to sialic (e.g., pyroxenite, anorthosite). We investigated both slabs and powders of these rocks to give indication of the spectral variability of rock analogs of lunar crust, from a mineralogical point of view. Samples have been spectrally separated in four main groups considering the different C.F. absorption association, reflectance and spectral shape for both slab and powder spectra. More spectral details can be obtained from the analysis of powder spectra than from the slab spectra. The composition of rocks can be addressed by studying spectral parameters, such as the position and the intensity of the absorption (e.g., band center and band depth). The analysis of our plagioclase-pyroxene-bearing samples indicates that mafic composition can be clearly obtained for samples characterized by one pyroxene phase, even for few amounts of pyroxene, from powder spectra. On the other hand, slab spectra show clear pyroxene absorptions only for rocks with mafic abundance at least >20%. The intensity of the mafic absorptions of these samples shows a linear trend with respect to the abundance of pyroxenes (orthopyroxene + clinopyroxene, for samples with ferrosilite amount less than ca. 25%). Considering all pyroxene-bearing samples, the band depth of slab spectra are linearly related to the volumetric distribution of ferrous iron in pyroxenes.

A simple model for the effect of hydration on the distribution of ferrous iron at reduced hematite (0 1 2) surfaces

Using a simple ionic model with polarizable oxygen ions and dissociating water molecules, we have calculated the energetics governing the distribution of Fe(II)/Fe(III) ions at the reduced (2 × 1) surface of α-Fe 2O 3 (hematite) (0 1 2) under dry and hydrated conditions. The results show that systems with Fe(II) ions located in the near-surface region have lower potential energy for both dry and hydrated surfaces. The distribution is governed by coupling of the ferrous iron centers to positive charge associated with missing oxygen atoms on the dry reduced (2 × 1) (0 2 1) surface. As the surface is hydroxylated, the missing oxygen rows are filled and protons from dissociated water molecules become the positive charge centers, which couple more weakly to the ferrous iron centers. At the same time, the first-layer iron centers change from fourfold or fivefold coordination to sixfold coordination lowering the potential energy of ferric iron in the first layer and favoring migration of ferrous iron from the immediate surface sites. This effect can also be understood as reflecting stronger solvation of Fe(III) by the adsorbed water molecules and by hydrolysis reactions favoring Fe(III) ions at the immediate surface. The balance between these two driving forces, which changes as a function of hydration, provides a compelling explanation for the anomalous coverage dependence of water desorption in ultra-high vacuum experiments.

Distribution of divalent metal transporter-1 in the monkey basal ganglia

An accumulation of iron occurs in the brain with age, and it is thought that this may contribute to the pathology of certain neurodegenerative diseases, including Parkinson's disease. In this study, we elucidated the distribution of divalent metal transporter-1 (DMT1) in the monkey basal ganglia by immunocytochemistry, and compared it with the distribution of ferrous iron in these nuclei by Turnbull's Blue histochemical staining. We observed a general correlation between levels of DMT1, and iron staining. Thus, regions such as the caudate nucleus, putamen, and substantia nigra pars reticulata contained dense staining of DMT1 in astrocytic processes, and were also observed to contain large numbers of ferrous iron granules. The exceptions were the globus pallidus externa and interna, which contained light DMT1 staining, but large numbers of ferrous iron granules. The thalamus, subthalamic nucleus, and substantia nigra pars compacta contained neurons that were lightly stained for DMT1, but few or no iron granules. The high levels of DMT1 expression in some of the nuclei of the basal ganglia, particularly the caudate nucleus, putamen, and substantia nigra pars reticulata, may account for the high levels of iron in these regions.

Effect of potassium nutrition of rice on rhizosphere redox status

With four soils differing in K supplying power and with four rice cultivars (Oryza sativa L.) differing in K uptake kinetic parameters, the relationship between K fertilizer application and soil redox status in rhizosphere and; the distribution of ferrous iron and other toxic substances on the root surface and in the rhizosphere; and the effect of K supply on uptake of reduced iron by rice plants have been studied. The results show that K application on K-deficient soils reduced the content of active reducing substances and ferrous iron in the soil, raised the soil redox potential in the rhizosphere, increased the Eh value of rice roots and lowered the content of iron in the rice plants. These effects of K varied with different rice cultivars. When no K fertilizer was applied, active reducing substances and ferrous iron in rhizosphere soils were decreased more by the rice cultivars absorbing K strongly (e.g. Shanyou 64) than by cultivars absorbing K weakly (e.g. Zhongguo 91). Therefore, the diminution of the toxic substances by K application in the weakly K-absorbing cultivars was more significant. The observation of a rhizobox separated by a nylon screen showed that appreciably more iron oxides, compared with the control, were deposited at or adjacent to the root surfaces of the rice plant supplied with K fertilizer, fully demonstrating the relationship between K nutrition and the total oxidizing power of rice plants. According to the distribution of active reducing substances and ferrous iron, the oxidizing range of the rice root extended in K application treatment a few centimeters away from the root plane. K application to rice affected the soil redox status in rhizosphere in many ways. The main effect was an increase of the oxidizing power of the rice root. As a result, the value of soil Eh was increased, the contents of active reducing substances and ferrous iron were lowered, as well as the number of oxygen consuming microorganisms.

Distribution of iron during embryogenesis and early larval life in sea lampreys (Petromyzon marinus)

The distribution of ferric iron was examined in eggs, embryos, and early larvae (up to 77 d post fertilization (PF)) of the sea lamprey, Petromyzon marinus, using the Prussian blue staining technique. Iron was not detected in eggs and embryos but was detected in the lumen of the oesophagus at 17 – 33 days PF, when the newly hatched larvae burrow and commence exogenous feeding. The posterior intestine and hindgut became the primary location of iron absorption by 36 days PF, and subsequent development (36 – 63 days PF) showed an iron distribution suggesting elimination of excess metal through exfoliation of epithelial cells of the posterior intestine. The deposition of iron in macrophages of the intestine and liver (Kupffer cells) by 40 days PF may be related to both erythrophagocytosis and erythropoiesis at this time. Iron deposits in the macrophages of the pronephros and the atrium of the heart at 42 – 44 days PF were likely a consequence of endocytosis/filtration of the metal from circulating plasma. The commencement of iron deposition in specific tissues of larval lampreys seems to be correlated with the time they begin filter-feeding. Macrophages play an important role in iron metabolism in early larval life of lampreys.

Distribution of Ferric Iron in some Upper-Mantle Assemblages

The distribution of ferric iron among the phases of uppermantle rocks, as a function of pressure (¥), temperature (T) and bulk composition, has been studied using Fe Mb'ssbauer spectroscopy to determine the Fe3*/lLFe ratios of mineral separates from 35 peridotite and pyroxenite samples. The whole-rock Ft complement of a peridotite is typically shared approximately evenly among the major anhydrous phases (spinel and/ or garnet, orthopyroxene and clinopyroxene), with the important exception ofolivine, which contains negligible Fe3*. Whole-rock Fe3* contents are independent oftheTand P of equilibration of the rock, but show a well-defined simple inverse correlation with the degree of depletion in a basaltic component. Fe in spinel and in both pyroxenes from the spinel lherzolite fades shows a positive correlation with temperature, presumably owing to the decrease in the modal abundance of spinel In garnet peridotites, the Fe3* in garnet increases markedly with increasing T and P, whereas that in clinopyroxene remains approximately constant. The complex nature of the partitioning of Fe between mantle phases results in complicated patterns of the activities of the Fe3*-bearing components, and thus in calculated equilibrium

Reduced signal intensity on MR images of thalamus and putamen in multiple sclerosis: increased iron content?

High-field-strength (1.5-T) MR imaging was used to evaluate 47 patients with definite multiple sclerosis and 42 neurologically normal control patients. Abnormal, multiple foci of increased signal intensity on T2-weighted images, most prominent in the periventricular white matter, were apparent in 43 of 47 MS patients and in two of 42 control patients. A previously undescribed finding of relatively decreased signal intensity most evident in the putamen and thalamus on T2-weighted images was seen in 25 of 42 MS patients and correlated with the degree of white-matter abnormality. In the normal control patients a prominently decreased signal intensity was noted in the globus pallidus, as compared with the putamen or thalamus, correlating closely with the distribution of ferric iron as determined in normal Perls'-stained autopsy brains. The decreased signal intensity (decreased T2) is due to ferritin, which causes local magnetic field inhomogeneities and is proportional to the square of the field strength. The decreased T2 in the thalamus and striatum in MS may be related to abnormally increased iron accumulation in these locales with the underlying mechanism remaining speculative.

Oxygen in the Precambrian atmosphere: An evaluation of the geological evidence

Geological evidence often presented in favor of an early anoxic atmosphere is both contentious and ambiguous. The features that should be present in the geologic record had there been such an atmosphere seem to be missing. Many of the features advanced in support of an anoxic model can be ascribed to diagenetic alterations, and most diagenetic environments are reducing. Recent biological and interplanetary studies seem to favor an early oxidized atmosphere rich in CO 2 and possibly containing free molecular oxygen. The existence of early red beds, sea and groundwater sulphate, oxidized terrestrial and sea-floor weathering crusts, and the distribution of ferric iron in sedimentary rocks are geological observations and inferences compatible with the biological and planetary predictions. It is suggested that from the time of the earliest dated rocks at 3.7 b.y. ago, Earth had an oxygenic atmosphere.

Another instance of haemoglobin in a flatworm (Phaenocora typhlops Vejdovsky 1880)

Summary(1) The occurrence of haemoglobin in Phaenocora typhlops (Vejdovsky) is reported.(2) Rhabdocoels were examined spectrophotometrically. The distribution of the pigment was studied by a sodium nitroprusside‐benzidine technique, and the distribution of ferric iron with Perl's technique.(3) Characteristic bands of oxyhaemoglobin were observed at 540 and 580 nm. The oxyhaemoglobin was reduced to haemoglobin by the addition of sodium dithionite and an absorption band appeared at about 560 nm.(4) Haematin was found principally around the pharynx, though a little was found in front of the latter and along the length of the gut. Ferric iron was distributed throughout the worm.(5) The occurrence of haemoglobin in P. typhlops and P. unipunctata is compared. It is suggested that less occurs in the former species. Whether or not this is related to the presence of zoochlorellae is considered. Certainly both species burrow actively in mud where reduced oxygen conditions can occur.

Carbonate Identification and Genesis as Revealed by Staining

ABSTRACT Carbonate minerals are stained over a set period of time with alizarin red-S and potassium ferricyanide only if they will react with dilute hydrochloric acid solution, with which the stain is prepared. The rates of solution of carbonates in the acid control the intensity of color development. For calcite, the rate of solution varies with the optic orientation of the section. The speed of carbonate solution is changed if the acid concentration is altered, but only at concentrations of about 0.1 N is the optic orientation of calcite differentiated by the stain. Etching reduces thin section thickness and clarifies rock texture. Staining with alizarin red-S differentiates carbonate minerals into two groups. Aragonite, calcite, witherite, and cerussite, which dissolve rapidly in dilute hydrochloric acid, are stained, while dolomite, siderite, magnesite, and rhodochosite, which react much more slowly with the acid, remain unstained. The distribution of ferrous iron, as distinguished by staining with potassium ferricyanide, has proved to be highly significant in the genesis of cements. Ferrous iron can be introduced at any one stage in cementation, or repeatedly, forming zoned patterns. The paragenesis of zoned ferroan cements can be reconstructed after staining. Solution of the more soluble original constituents can sometimes be dated in relation to cementation. Ferroan calcite can be secondary in origin and is usually associated with replacement minerals.

Metamorphic pyroxenes from the Broken Hill district, New South Wales

SummaryThe Archean rocks of the Barrier Ranges, New South Wales, show zones of progressive regional metamorphism of which the highest is characterized by orthopyroxene-bearing basic granulites. Within this zone, further increase in metamorphic grade results in a detectable change in distribution of ferrous iron and magnesium between coexisting orthopyroxene and clinopyroxene, the latter becoming relatively richer in iron. Mutual solid solution between the two pyroxene phases also appears to increase. The value of coexisting pyroxenes as indicators of metamorphic grade is thus established. There are some points of disagreement between the Broken Hill results and previously advanced theories of cation distribution in pyroxenes.

The Distribution of Ferric Iron between Hydrochloric Acid and Isopropyl Ether Solutions. II. Polymerization of the Iron in the Ether Phase, the Effect of the Acid Concentration on the Distribution, and the Two-Ether-Phase Region

The Distribution of Ferric Iron between Hydrochloric Acid and Isopropyl Ether Solutions. II. Polymerization of the Iron in the Ether Phase, the Effect of the Acid Concentration on the Distribution, and the Two-Ether-Phase Region

The Distribution of Ferric Iron between Hydrochloric Acid and Isopropyl Ether Solutions. III. Spectral, Isopiestic and Magnetic Susceptibility Studies

The Distribution of Ferric Iron between Hydrochloric Acid and Isopropyl Ether Solutions. III. Spectral, Isopiestic and Magnetic Susceptibility Studies