Hematite Content Research Articles

Morphology of Atmospheric Particles over Semi-Arid Region (Jaipur, Rajasthan) of India: Implications for Optical Properties

The regional dust morphology and spectral refractive indices (RIs; governed by hematite, Fe2O3 content at short wavelengths) are key elements for ascertaining direct radiative forcing of mineral dust aerosols. To provide morphological features of background mineral dust from a semi-arid zone in the vicinity of the Thar Desert, we carried out an expedition to the Jaipur city during late winter of 2012. Morphological analysis reveals the predominance of “Layered”, “Angular” and “Flattened” particles, while the frequency distribution of a total of 235 dust particles shows the aspect ratio, AR and circularity parameter, CIR (measures of particle’s non-sphericity) typically ~1.4 and ~0.8, respectively. Sensitivity analysis at 550 nm wavelength reveals the equivalent sphere model may underestimate Single Scattering Albedo, SSA for the dust with low (~1.1%) hematite by ~3.5%. Both underestimation (by ~5.6%) and overestimation (up to 9.1%) are probable in case of dust with high hematite content (~5.68%). In addition, the effect of AR on the dust scattering is significant in case of dust with high hematite content. More such regionally representative dust morphological data are required for better estimation of regional radiative forcing of mineral dust aerosols.

The effects of quartz recrystallization and reaction on weak phase interconnection, strain localization and evolution of microstructure

We conducted axial compression and general shear experiments, at T = 900 °C and P = 1.5 GPa, on samples of banded iron formation (BIF) and synthetic aggregates of quartz, hematite and magnetite to investigate how dynamic recrystallization of quartz promotes strain localization, and the role of weak second phases (oxides) on the rheology and microstructural evolution of the aggregates. Experiments showed strain localization into oxide rich layers, and that the oxide content and oxide distribution are key factors for the strength of the aggregate. Only 2–10 wt.% hematite leads to pronounced weakening and increasing hematite content above ∼10% has only a minor additional effect. Where oxide grains are dispersed, the initial strength contrast with quartz induces stress concentrations at their tips, promoting high stress recrystallization-accommodated dislocation creep of quartz. Fine recrystallized quartz reacts with oxide, forming trails of fine reaction product (ferrosilite/fayalite) leading to the interconnection/percolation of a weaker matrix. The strength contrast between the quartz framework and these fine-grained trails promotes strain localization into micro-shear zones, inducing drastic strain weakening. Thus dynamic recrystallization of quartz promotes syn-deformational reactions leading to a microstructurally-controlled evolution of phase strength contrast. It results in a rheologic transition from load-bearing framework to a matrix-controlled rheology, with transition from S–C′ to S–C fabric with increasing strain.

Soil moisture balance and magnetic enhancement in loess–paleosol sequences from the Tibetan Plateau and Chinese Loess Plateau

We present a first combined environmental magnetic and geochemical investigation of a loess–paleosol sequence (<55 ka) from the Chuanxi Plateau on the eastern margin of the Tibetan Plateau. Detailed comparison between the Ganzi section and the Luochuan section from the Chinese Loess Plateau (CLP) allows quantification of the effects of provenance and climate on pedogenic magnetic enhancement in Chinese loess. Rare earth element patterns and clay mineral compositions indicate that the Ganzi loess originates from the interior of the Tibetan Plateau. The different Ganzi and CLP loess provenances add complexity to interpretation of magnetic parameters in terms of the concentration and grain size of eolian magnetic minerals. Enhanced paleosol magnetism via pedogenic formation of ferrimagnetic nanoparticles is observed in both sections, but weaker ferrimagnetic contributions, finer superparamagnetic (SP) particles and stronger chemical weathering are found in the Ganzi loess, which indicates the action of multiple pedogenic processes that are dominated by the combined effects of mean annual precipitation (MAP), potential evapotranspiration (PET), organic matter and aluminium content. Under relatively high MAP and low PET conditions, high soil moisture favours transformation of ferrimagnetic minerals to hematite, which results in a relatively higher concentration of hematite but weaker ferrimagnetism of Ganzi loess. Initial growth of superparamagnetic (SP) particles is also documented in the incipient loess at Ganzi, which directly reflects the dynamic formation of nano-sized pedogenic ferrimagnets. A humid pedogenic environment with more organic matter and higher Al content also helps to form finer SP particles. We therefore propose that soil water balance, rather than solely rainfall, dominates the type, concentration and grain size of secondary ferrimagnetic minerals produced by pedogenesis.

Thermal magnetic behaviour of Al-substituted haematite mixed with clay minerals and its geological significance

Clay minerals and Al-substituted haematite (Al-hm) usually coexist in soils and sediments. However, effects of clay minerals on Al-hm during thermal magnetic measurements in argon environment have not been well studied. In order to quantify such effects, a series of Al-hm samples were synthesized, and were then mixed with clay minerals (illite, chlorite, kaolinite and Ca-montmorillonite). The temperature dependence of magnetic susceptibility curves in an argon environment showed that Al-substituted magnetite was produced during the thermal treatment via the reduction of Al-hm by the clay mineral, which leads to a significant magnetic enhancement of the thermal products. In addition, the reductive capacity varies among different types of clay minerals, that is, illite > chlorite > kaolinite > Ca-montmorillonite. Furthermore, the iron content in the clay minerals and Al content of Al-hm are two predominant factors controlling the reduced haematite content. The iron is released from the clay minerals and provides the reducing agent, while Al decreases the crystallinity of haematite and thus facilitates the chemical reaction. Therefore, the thermal magnetic measurements can be used to quantify the Al content of Al-hm in natural samples. Our study provides significant information for palaeomagnetism and environmental magnetism studies, such as thermal magnetic analysis and palaeomagnetic intensity reconstruction using ancient pottery and kilns.

Determining hematite content from NUV/Vis/NIR spectra: Limits of detection

Hematite occurs in various geologic settings including igneous, metamorphic, and sedimentary rocks as well as in soils. However, it frequently occurs at low concentrations, especially in soils, where it may be <1% by weight. Because hematite has the potential to be an indicator of oxidizing and climatic conditions in soils and paleosols, it is important to understand its limit of detection. In this paper we examine the limits of detection of hematite visually and with diffuse reflectance spectrophotometry (DRS) and X‑ray diffraction (XRD). To accomplish this we used a sample set consisting of “knowns” or calibration samples. These known samples consisted of 15 different matrices of varying mineral composition into which hematite in 7 different concentrations ranging from 0.01 to 4% by weight were mixed. Including the 0% hematite, our calibration data set consisted of 120 samples. Visually, hematite can be detected at a concentration of 0.01% by weight in a light matrix and 0.5% in the darkest of our matrices. However, because of metamerism, visual techniques cannot specifically identify hematite. We find that for both DRS and XRD the limit of detection is also dependent on the matrix. For XRD the limit of detection for hematite in bulk samples is about 1%. For DRS the limit of detection depends on the data reduction technique used. The commonly used Kubelka‑Munk remission function and its first and second deriva tives can easily identify hematite at the 0.5% level. However, the first derivative of the percent reflectance curve can detect hematite at 0.01% by weight in a light matrix and 0.05% in a dark matrix. We suggest that the first derivative of DRS curves is the best currently available method for qualitatively detecting the mineral hematite at low concentrations found in soils, sediments, and rocks. Work described in this paper may be applied in several situations. Our study of visual limits of hematite detection should aid field geologists in assessing hematite content. Analysis of color wave length bands may also have application in remote sensing by indicating which bands are most sensitive to hematite, reported to be an important constituent of the martian surface. Furthermore, this study could help clarify remotely sensed terrestrial albedo changes, especially the Sahara/Sahel transition where the sediments change from light, quartz-dominated to dark, hematite-dominated. Our study also points out that with laboratory‑based spectra the first derivative of the reflectance curve is the most sensitive transform for processing spectral data for hematite, thereby allowing concentrations as low as 0.01% to be detected.

Geochemical prospecting for rare earth elements using termite mound materials

The Blockspruit fluorite prospect, located in North West State of the Republic of South Africa, occurs within an actinolite rock zone that was emplaced into the Kenkelbos-type granite of Proterozoic age. There are a large number of termite mounds in the prospect. For geochemical prospecting for rare earth elements (REEs), in total, 200 samples of termite mound material were collected from actinolite rock and granite zones in the prospect. Geochemical analyses of these termite mound materials were conducted by two methods: portable X-ray fluorescence (XRF) spectrometry and inductively coupled plasma-mass spectrometry (ICP-MS). Comparison of the two methods broadly indicates positive correlations of REEs (La, Ce, Pr, Nd, and Y), in particular Y and La having a strong correlation. As the result of modal abundance analyses, the actinolite rock at surface mainly consists of ferro-actinolite (89.89 wt%) and includes xenotime (0.26 wt%) and monazite (0.21 wt%) grains as REE minerals. Termite mound materials from actinolite rock also contain xenotime (0.27 wt%) and monazite (0.41 wt%) grains. In addition, termite mound materials from the actinolite rock zone have high hematite and Fe silicate contents compared to those from granite zone. These relationships suggest that REE minerals in termite mound materials originate form actinolite rock. Geochemical anomaly maps of Y, La, and Fe concentrations drawn based on the result of the portable XRF analyses show that high concentrations of these elements trend from SW to NE which broadly correspond to occurrences of actinolite body. These results indicate that termite mounds are an effective tool for REE geochemical prospection in the study area for both light REEs and Y, but a more detailed survey is required to establish the distribution of the actinolite rock body.

Tumoricidal Effect of Hematite (α-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;) and SiO&lt;sub&gt;2&lt;/sub&gt; Nanoparticles in Human Rhabdomyosarcoma Cell Line

Nanotechnology provides the opportunity for the development of new materials in the nanometer size range with many potential applications in biological sciences and clinical medicine. RD (muscle cancer cell line) was seeded out in 25 cm2 plastic tissue culture flasks (NuncWiesbaden Germany) individually, in Minimum Essential Medium (MEM) with Hanks salts, containing 10% fetal bovine serum (FBS) and 2 mM L-Glutamine along with some nonessential amino acids and were incubated for 24 h for proper attachment to the substratum and kept at a 96 wells plate, incubated at 37°C and 5% CO2. SEM was employed to the nanoparticles and size of α-Fe2O3 and SiO2 nanoparticles were about 66 nm and 250 nm. Moreover 10-80μg/mL of Hematite (α-Fe2O3) and SiO2 nanoparticles dispersed solution were labeled for each row of 96 wells plate. The present study evaluates the different parameters, e.g. time of incubation, cytotoxicity and cellular viability of the Human Rhabdomyosarcoma cell line (RD) as an experimental model. The viability of cells was determined by means of neutral red assay (NRA) after the cell-exposition to different concentrations of Hematite (α-Fe2O3) and SiO2 nanoparticles into mentioned tumoricidal cells

Variáveis mineralógicas preditoras de fontes de produção de sedimentos, em uma bacia hidrográfica do Rio Grande do Sul

O uso da mineralogia como ferramenta para a avaliação das propriedades dos minerais que compõem o solo é extremamente importante para o entendimento das diferentes relações químicas e físicas que ocorrem nele. Essas propriedades/variáveis, na identificação das fontes de sedimentos em suspensão, podem ajudar a elucidar os fatores e processos que regem a transferência de sedimentos e poluentes dos sistemas terrestres para os sistemas aquáticos. Os objetivos deste estudo foram caracterizar quantitativamente a mineralogia do solo das fontes e dos sedimentos em suspensão, em uma bacia hidrográfica, e identificar quais variáveis mineralógicas possuem propriedades traçadoras. Para a identificação das fontes, foi utilizado o método fingerprinting, que compara os solos de diferentes fontes e os sedimentos que são encontrados em suspensão no canal de drenagem, usando elementos traçadores. Os principais minerais que compõem o solo das fontes e do sedimento foram caulinita, minerais de camada 2:1 e hematita e goethita. Entre os óxidos, a hematita foi o que predominou entre as amostras. As variáveis mineralógicas, teor de caulinita e de goethita apresentaram capacidade discriminante e puderam ser usados como traçadores na identificação das fontes de produção de sedimentos e na estimativa da contribuição de cada uma das fontes, aumentando assim a capacidade preditiva do modelo. A maior contribuição na produção de sedimentos foi dos canais fluviais, seguidos pela malha e, por último, pelas estradas.

In-situ X-ray diffraction activation study on an Fe/TiO2 pre-catalyst.

This study focuses on the use of in situ powder X-ray diffraction (PXRD) and quantitative phase analysis using the Rietveld method to monitor the structural properties of a titania-supported iron (10% Fe/TiO2) pre-catalyst during calcination (oxidation) and activation (reduction) in the temperature range 25-900°C. The TiO2 oxidation study revealed an increase in anatase particle size before the anatase to rutile phase transformation, lending credibility to the bridging mechanism proposed by Kim et al. [(2007), Mater. Sci. Forum, 534-536, 65-68]. Pre-catalyst oxidation experiments allowed for the determination of a suitable calcination temperature (450°C) of the pre-catalyst in terms of maximum hematite concentration and appropriate particle size. These experiments also confirmed that the anatase to rutile phase transformation occurred at higher temperatures after Fe addition and that anatase was the sole donor of Ti(4+) ions, which are known to migrate into hematite (Gennari et al., 1998), during the formation of pseudobrookite (Fe2TiO5) at temperatures above 690°C. Using the results from the oxidation experiments, two pre-catalyst samples were calcined at different temperatures; one to represent the preferred case and one to represent a case where the pre-catalyst had been excessively heated. Samples of the excessively heated catalysts were exposed to different reducing gas atmospheres (5, 10 and 100% H2/N2) and heated in the in situ PXRD reactor, so that diffraction data could be collected during the activation process. The results show that reduction with gases containing low concentrations of H2 (5 and 10%) led to the formation of ilmenite (FeTiO3) and we were able to show that both anatase and rutile are consumed in the reaction. Higher concentrations of H2 led to the formation of magnetite (Fe3O4) and metallic iron (Fe(0)). We also noted a decrease in the anatase to rutile transformation temperature under reducing atmospheres when compared with the pre-catalyst heat-treatment experiment. A reduced calcination temperature prior to reduction allowed more facile Fe reduction.

α-Fe2O3 /(PVA + PEG) Nanocomposite films; synthesis, optical, and dielectric characterizations

Hematite (α-Fe2O3) nanorods with an average diameter of 40 nm were prepared using a template-free sol–gel method. These nanorods then mixed with polyvinyl alcohol (PVA)/polyethylene glycol (PEG) blend at concentrations of 0.0, 0.5, and 1.0 wt.%. The transmittance percentage (T%) of the films showed a decrease from 80.26 to 33.24 %. The direct optical band gap also decreased from 5.28 to 4.83 eV whereas the refractive index significantly increased with increasing the hematite content. The dielectric measurements were performed in the temperature range 303–413 K and frequency range 30 kHz–3.0 MHz. According to the temperature dependence of the dielectric constant (e’), αa-relaxation peaks observed in all films and assigned to the micro-Brownian motion of the polymer blend chains. The behavior of the ac conductivity, σac (f), of the nanocomposite films indicated that the homogenous distribution of α-Fe2O3 nanorods allows the formation of conductive three-dimensional networks throughout the nanocomposite film. Also, indicated that the correlated barrier hopping is the most suitable conduction mechanism.

Compositional heterogeneity of picroilmenite from the Zarnitsa pipe according to the data of thermomagnetic analysis

Thirty-nine samples of picroilmenites from seven boreholes drilled along the submeridional profile in the Zarnitsa pipe of the Yakut diamondiferous province are examined. Individual microprobe determinations are conducted on two mutually perpendicular profiles of each sample in order to study compositional the heterogeneity of picroilmenite. Besides, the thermomagnetic curves are recorded for each sample. The model for processing the thermomagnetic curves based on the dependence of the parameters of the thermomagnetic curves (the Curie points and specific magnetic moment of picroilmenite) on hematite content in picroilmenite is suggested. The correct description of the experimental curve for each picroilmenite sample requires introducing two distributions of hematite concentration. The mean value of the first distribution coincides with the microprobe determinations, while the second distribution has a higher hematite content than the first one. It is shown that the areas with increased hematite content in the picroilmenite grains gravitate to the edges of the grains. It is hypothesized that the increase in hematite content is caused by epigenetic transformation of primary picroilmenite and it can probably serve as a proxy for the dynamics of picroilmenite formation. The applicability of the data of thermomagnetic analysis for the express determination of picroilmenite composition is assessed; the capabilities and limitations of the suggested procedure are demonstrated.

Color variations of the Quaternary Red Clay in southern China and its paleoclimatic implications

The red clay and red weathering crust are widely distributed in southern China. To study the possible relationship between soil color and paleoclimatic environment, three color parameters, lightness (L⁎), redness (a⁎) and yellowness (b⁎), of twelve Quaternary Red Clay (QRC) profiles in southern China were measured using a colorimeter. Colors of the QRC profiles vary vertically: a⁎ and b⁎ generally increase downward and L⁎ decreases downwards. Colors of the QRC also show spatial variation: a⁎ and b⁎ generally increase towards the equator; whereas L⁎ increases away from it. Both a⁎ and b⁎ are positively significantly correlated with clay (<2μm) content, free Fe (Fed), Fed/Fet ratios and other soil weathering indices of the QRC (ρ<0.05), and the correlations between a⁎ and the weathering indices are much stronger than those between b⁎ and the indices. a⁎ mainly reflects hematite content in soils. Compared with magnetic susceptibility (χ), a⁎ of the QRC is a more promising paleoclimatic indicator, although it is sometimes disturbed by uneven parent materials and dissolution of hematite by water logging. The upward decrease of a⁎ of the QRC profiles reflects a cooling and drying paleoclimate since the end of the Last Interglacial, and the spatial variation of a⁎ coincides with more optimum hydrothermal conditions in lower-latitude areas of southern China.

A new method for separation, characterization, and quantification of natural nanoparticles from soils

Properties and distribution dynamics of nanoparticles are pertinent to ecological and human health. Wide variation in particle density confounds their accurate separation for study. The objective of this study was to develop a fine-particle separation protocol requiring no constant density assumption. Six soils with contrasting properties were chosen for study. Size distributions of suspended particles following centrifugation were assessed using dynamic light scattering. Mineralogy was determined by X-ray diffraction. Particle characteristics were examined using transmission electron microscopy. A significant pooled logarithmic relationship was found between centrifugation speed and particle-size distribution. Nanoparticles (<100 nm) became dominant by fractional volume at widely differing separation energies among the six soils. However, relations were strong between separation energies and fractional volume for individual soils. Bi- and tri-modal-size distributions within suspensions were related to density differences of soil components. Re-aggregation at high separation energy was apparent for the tropical soils. Light-scattering, UV–Visible absorbance, and chemical analyses distinguished samples of high hematite content from those without hematite. These results indicate that dynamic light scattering in conjunction with a standard centrifuge regimen provides a practical means of collecting colloidal particles within a targeted size range, compensating for natural variations among the soil samples.

Induration Process of Pellets Prepared from Mixed Magnetite–35% Hematite Concentrates

To explore the possibility of successfully processing iron ore pellets with a high content of hematite, thermogravimetric tests were performed to study the induration process of pellets composed of a mixture of iron ore concentrates (magnetite and 35% wt of hematite). Thermogravimetric tests were performed nonisothermally from 25°C to 1400°C using two heating rates, 5 and 50°C/min. To identify the reactions involved and to follow the microstructural evolution throughout the induration process, selected tests were arrested at predetermined temperatures, and samples were rapidly cooled to room temperature for later characterization using X-ray diffraction (XRD) and scanning electron microscopy (SEM) along with energy dispersive spectroscopy (EDS). It was found that the formation of phases such as calcium ferrite (CF), magnesium ferrite (MF), silico-ferrites of calcium (SCF) and silico-ferrites of calcium and aluminum (SCFA) are influenced by the heating rate. The microstructure of the fired pellet processed at 50°C/min showed compact small grains of the sintered phase of the secondary hematite (SH), partially surrounded by a slag phase. In contrast, the fired pellet processed at 5°C/min exhibited a microstructure consisting of the SH phase with a faceted morphology surrounded by a relatively large amount of the slag phase. The results suggest that the pellet processed at 50°C/min had a more satisfactory response to the induration process.

Estimation of Oxidized Pellets of a Brazilian Hematite Concentrate by Adding Serpentine

Estimation of Oxidized Pellets of a Brazilian Hematite Concentrate by Adding Serpentine

An Intelligent Switching Control for the Intervals of Concentration and Flow-rate of Underflow Slurry in a Mixed Separation Thickener

The mixed separation thickening process (MSTP) of hematite beneficiation is a strong nonlinear cascade process where the input is the underflow slurry pump speed and the outputs are the inner loop underflow slurry flow-rate (USF) and the outer loop underflow slurry concentration (USC). During its operation, some large random disturbances generated from the flotation middling would cause the underflow slurry flow-rate (USF) to fluctuate frequently, making it outside the technologically specified range. This would decrease the flotation time and cause the unexpected level fluctuations of flotation machines, leading to the deterioration of the concentration grade. In this paper, a cascade control structure based upon the USC and USF intervals is proposed for such an un-modellable nonlinear cascade process, where the fuzzy control, rule-based reasoning, switching control and cascade control are combined together. A novel intelligent switching control method is established that includes a USF presetting unit via system static model, a fuzzy reasoning based USF set-point compensator, a maintainer of USF set-point and a switching mechanism using rule based reasoning. The successful application to a real hematite concentration plant has shown the effectiveness of the proposed method. In particular, the real application has shown that the proposed method can ensure the USC, the USF and the fluctuation of its rate of change within their target ranges when the process is subject to the flotation middling random disturbance. As a result, the concentration grade has been much improved.

Petrology and Genesis of the Bhainskati Iron Ore Deposit of Palpa District, Western Nepal

The Bhainskati Formation of the Tansen Group in Palpa area is known for hematite iron ore deposit for long time. A prominent band of hematite of about 1-2 km thickness extending &gt;5 km was identified in the upper part of the Bhainskati Formation in the present study and the band is repeated three times in the area by folding and faulting. Petrographic study shows that it is oolitic ironstone of sedimentary shallow marine origin. Main minerals in the band are hematite, goethite, quartz, calcite, siderite and albite. Hematite content varies considerably among samples and occurs mainly as oolite and cement. The Bhainskati ironstone with its ferrous mineral assemblage and well-rounded texture of the ooids suggests prodeltaicto estuarine with shallow marine environment reduced clastic input.

Conducting polymers doped with a mineral phase: structural and electrical study

This work reports the results obtained of a series of novel doped conducting polymers (CPs) of polyaniline/hematite (PANI/HEM), which were synthesized in acidic aqueous solution by the in situ chemical oxidative polymerization, using ammonium peroxydisulfate as oxidant reagent. The synthesis was carried out with 20, 40 y 60 % (weight percent) contents of hematite (HEM) at 8 and 14 h of polymerization times (tP). These composites were structurally characterized by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). An electrochemical analysis was made by Electrochemical impedance spectroscopy (EIS). Results of this study allow to evaluate the influence of hematite on the improvement of the structural properties and in the increase of the electric conductivity (sac) of the doped polymers compared to CPs without dopant agents.

Effects of elevated temperatures on mechanical properties of concrete containing haematite evaluated using fuzzy logic model

Concretes containing different proportions of haematite (15, 30, 45 and 60%) were fabricated and subjected to elevated temperatures (25, 200, 400, 600 and 800°C). The cement content and water/cement ratio were 450 kg m−3 and 0·38 respectively. The compressive strength and elasticity modulus of concretes were determined according to ASTM C39 and ASTM C469. A rule based Mamdani type fuzzy logic model for predicting the compressive strengths and elasticity modules of concretes containing haematite has been developed. The inputs were haematite content (%), exposure time (h) and temperature T (°C); the outputs were compressive strength and compressive elasticity modulus. It is shown that all the results of the model for elasticity modulus and compressive strength were in good correlation with the experimental results for all data sets.

Soil discrimination using diffuse reflectance Vis–NIR spectroscopy in a local toposequence

Vis–NIR spectroscopy is nowadays presented as a possible routine method for soil sample analysis. However, there is still no consensus on which is the best multivariate statistical method to use. We propose to use principal component analysis to complete the spectral data treatment. The soil samples came from a pedological cover made up of red–yellow Latosols: 88 samples of 11 soil profiles on four toposequences were collected; clay, organic matter, silica, iron, aluminum and titanium total contents were determined; the contents of goethite, hematite, gibbsite, and kaolinite were calculated. Diffuse reflectance Vis–NIR spectroscopy at wavelengths from 400 to 2400nm combined with principal component analysis (PCA) was sufficiently sensitive to discriminate different Latosols. Wavelengths of 700nm and 2200 to 2300nm were influenced by content ratios of organic matter and iron oxides (700nm), and kaolinite and gibbsite absorption (2200 and 2300nm). The spectral responses were affected not only by the content of these constituents, but also by the composition of the minerals, so that the same class of Latosol may have different or similar spectral responses. The role of microaggregation is discussed.