Showing papers on "Hematite published in 1978"
TL;DR: The different types of iron oxide phases associated with the surfaces of two suites of kaolins from Georgia, U.S.A., and from the Southwest Peninsula of England, have been identified using electron spin resonance (ESR) spectroscopy combined with magnetic-filtration, thermal, and chemical treatments as discussed by the authors.
Abstract: The different types of iron oxide phases associated with the surfaces of two suites of kaolins from Georgia, U.S.A., and from the Southwest Peninsula of England, have been identified using electron spin resonance (ESR) spectroscopy combined with magnetic-filtration, thermal, and chemical treatments. It has been shown that the English kaolins are coated with a lepidocrocitelike phase, which is readily removed by de Endredy’s method of deferrification, while the Georgia kaolins are coated with a hematite- or goethitelike phase, which is not removed by this treatment. Throughout the course of this study, the effects of the various physical and chemical treatments on the brightness values of the kaolins were examined.
81 citations
TL;DR: A series of mixed iron and titanium oxide coprecipitates ranging in composition between 0 ~ 0.7 with permanent and pH dependent negative charge were identified after aging NH3 coprecipes of Fe and Ti nitrate at 7WC and pH 5.5 for 70 days.
Abstract: A series of mixed iron and titanium oxide coprecipitates ranging in composition between 0 ~ 0.7) with permanent and pH dependent negative charge. Synthetic Ti-ferrihydrite and amorphous TiO2 were completely soluble in acid ammonium oxalate (2 hr extraction in the dark) whereas poorly crystalline anatase (width at half height, WHH > 2.0~ was partly oxalate soluble. NH4-oxalate soluble Ti was particularly high in soils developed under a cool montane climate (afro-alpine) and lower in soils of warmer subtropical climate, which contain anatase and futile. Several mixed Fe-Ti crystalline phases were identified after aging NH3 coprecipitates of Fe and Ti nitrate at 7WC and pH 5.5 for 70 days: (1) goethite and hematite in the composition range 0 < Ti/Ti + Fe ~< 0.20; at low Ti concentrations (<5 mole %) goethite was favored and/or hematite inhibited; (2) microcrystalline pseudorutile in the composition range 0.20 ~ Ti/Ti + Fe ~< 0.70; (3) anatase and ferriferous anatase in the range 0.70 ~< Ti/Ti + Fe < 1.0; with decreasing proportion of Ti the crystal- linity of anatase decreased. The results suggest that secondary or pedogenic Ti-Fe oxides can form by coprecipitation and crystallization in the weathering solution, and emphasize the essential role of water (as opposed to dry oxidation) in the alteration of primary titaniferous minerals.
54 citations
TL;DR: The East Berlin Formation is a 200m fluvial and lacustrine sequence of red and gray sandstone and mudstone that accumulated in a tropical rift valley during Early Jurassic time.
Abstract: The East Berlin Formation is a 200-m fluvial and lacustrine sequence of red and gray sandstone and mudstone that accumulated in a tropical rift valley during Early Jurassic time. The hematite pigment that colors the red beds is authigenic, produced by four post-depositional processes. (1) Brown and yellow-brown limonite that stained the surfaces of the detrital particles of sand and mud converted to hematite by aging. (2) In the sandstone, pervasive intrastratal solution of Fe-silicate grains, especially pyroxene, amphibole, epidote, chlorite, and biotite provided iron for precipitation of hematite, or a red ferric oxide precursor that then aged to hematite. These two processes were volumetrically the most important in generating hematite pigment. (3) In all the red beds, abundant mag etite grains were oxidized to hematite; ilmenite grains were oxidized to hematite-rutile. (4) In the sandstones, replacement of Fe-silicate grains by dolomite cement yielded additional iron for hematite cement. Conversion of limonite stains on clay particles to hematite by aging was the major source of hematite in flood-plain grayish red mudstone, a darker red (lower value and less yellow hue) than the interbedded stream channel sandstone of pale red and pale yellowish brown colors. Intrastratal solution of Fe-silicate grains in the fluvial and lacustrine sandstones produced an average of about 3 percent by volume of hematite cement. Pyroxene, amphibole, epidote, chlorite, and biotite grains were consistently protected from post-depositional solution in the impermeable dolomite concretions and grayish red mudstone of the flood-plain deposits and also in lacustrine gray mudstone. The limonite surface stains on detrital particles in the lakes were removed in the reducing, organic-rich bottom w ter so that the impermeable lacustrine gray mudstone and black shale are not reddened by aging of limonite to hematite nor by intrastratal solution.
34 citations
TL;DR: The red lutites of the Littleham Mudstone Formation of southeast Devon as discussed by the authors have an average total iron content of about 5.5%, with an average ratio of 0.16, while the pale material has a total ratio of 2.7%.
Abstract: The Littleham Mudstone Formation of southeast Devon consists predominantly of red lutites of Late Permian or Early Triassic age. Present within the lutites are spherical pale patches that have sharp boundaries against the red lutite and often contain dark, organic centers rich in uranium and vanadium. Chemical and Mossbauer analysis of the oxidation state of iron in this formation shows that the red lutite contains an average total iron content of about 5.5%, with an Fe2+/Fe3+ ratio of 0.16, while the pale material has a total iron content of 2.7%, with an Fe2+/Fe3+ ratio of 1.2. In the pale material, iron is present only within silicate (clay material) lattice sites, but the red lutite contains hematite as well. The hematite has an important superparamagnetic component and is considered to have a bimodal grain size distribution with two modes of occurrence: as interlayer crystals within clay minerals and as external coatings or grains. The Fe2+/Fe3+ ratios and total iron content show that the red lutite is not merely the pale material with hematite added, but that about 50% of the Fe2+ in the clay mineral lattice in the pale material is oxidized to Fe3+ in the red lutite. This change in oxidation state is not coincident with the pale-red boundary but begins within the pale patches. The mechanism by which this occurred is considered to be an in situ oxidation that produced the red lutite, accompanied by the precipitation of ferric hydroxide from solution. This process is inhibited in the pale patches where Fe2+ ions would be more soluble and readily removed. Geotechnical tests on the lutites show that the spherical patches must have formed after a thickness of 1,000 to 1,300 m of overlying strata had been deposited.
This thickness encompasses the whole of the Triassic beds of southeast Devon and implies that the reddening occurred at the end of Triassic or in early Jurassic time. It is suggested that the reddening was aided by a change from arid to humid climate that occurred in the area at this time.
25 citations
TL;DR: In this paper, annealing at temperatures between 475° and 600° C precipitation of an iron-rich phase occurs and the precipitation sequence involves two transitional stages before the formation of hematite, the equilibrium precipitate.
Abstract: Natural iron-bearing rutile, formed under low temperature hydrothermal conditions, is chemically homogeneous on an electron-microscope scale (at a resolution of about 10 A) On annealing at temperatures between 475° and 600° C precipitation of an iron-rich phase occurs The precipitation sequence involves two transitional stages before the formation of hematite, the equilibrium precipitate The first phase is coherent with the rutile structure and has the general characteristics of Guinier-Preston zones The second transitional phase is a monoclinic variant of the rutile structure and is partially coherent with the matrix Annealing experiments enable a Time-Temperature-Transformation (TTT) plot to be constructed for the exsolution process and the kinetics are interpreted in terms of the structural changes involved at each stage of the process
25 citations
TL;DR: In this paper, the first stage of oxidation leads to the formation of a covering layer constituted of silica plus iron oxide (mainly hematite). Solid state diffusion of oxygen then takes place through this layer, which progressively evolves with the crystallization of the silica and a relaxation of stress due to fracture.
Abstract: The oxidation of fayalite to hematite and silica by oxygen and oxygen-nitrogen or oxygen-water vapour mixtures has been studied by TGA, SEM and X-ray diffraction. In the temperature range 690 to 950° C, the isotherms of oxidation are pseudo-parabolic. The Arrhenius plot shows a break near 840° C, related to the quartz-cristobalite transformation, the activation energy being about 230 kJ mol−1. The first stage of oxidation leads to the formation of a covering layer constituted of silica plus iron oxide (mainly hematite). Solid state diffusion of oxygen then takes place through this layer, which progressively evolves with the crystallization of silica and a relaxation of stress due to fracture. After the fracture of the covering layer, whiskers of hematite grow, usually on a silica substrate, and align themselves along linear defects. Under specific conditions, their growth is periodic.
17 citations
14 citations
Journal Article•
TL;DR: Detrital iron-titanium (Fe--Ti) oxide minerals of the ulvospinel-magnetite (titanomagnetite) and ilmenite-hematite (Titanohematite) solid solution series are common in uranium-bearing sandstones.
Abstract: Detrital iron-titanium (Fe--Ti) oxide minerals of the ulvospinel-magnetite (titanomagnetite) and ilmenite-hematite (titanohematite) solid solution series are common in uranium-bearing sandstones. Alteration of Fe--Ti oxide minerals in oxidizing environments formed secondary products (primarily hematite) that are distinct from those produced under reducing conditions (iron disulfide minerals). Oxidation of sulfidized Fe--Ti oxide minerals, by the processes that formed uranium rolls, produced ferric oxide minerals (limonite) having textures that mimic those of the iron disulfides. Titanomagnetite and titanohematite have been severely depleted in the ore-bearing zones of some uranium deposits. The alteration of detrital Fe--Ti oxide minerals near uranium ore deposits may produce characteristic signatures in the magnetization of the sandstone. Knowledge of the distribution and magnetic properties of these minerals can aid in interpreting data from total magnetic-field and magnetic-susceptibility surveys of uranium deposits.
10 citations
10 citations
TL;DR: Chelatometric titration of iron after solvent extraction with MIBK from solutions prepared by use of CPA is found to be accurate for samples such as pyrite cinder.
10 citations
05 Dec 1978-The Journal of the Japanese Association of Mineralogists,Petrologists and Economic Geologists
TL;DR: In this article, the stability and paragenesis of Fe-Ti oxide and silicate minerals in hematite-bearing basic schists are compared to those in hemetite-free ones.
Abstract: The Sanbagawa basic schists in the Shiragayama area, central Shikoku contain hematite, ilmenite, rutile, sphene and some magnetite. Mineral assemblages of Fe-Ti oxide and silicate minerals in hematite-bearing ones are significantly different from those in hematite-free variety. Excluding albite, quartz, epidote, chlorite and phengite, the mineral assemblages of hematite-bearing ones are hematite+riebeckitic actinolite+sphene or hematite+crossite+sphene in the lower grade zone and hematite+ilmenite+rutile+hornblende±magnetite in the higher grade zone. In the other variety, the mineral assemblages are actinolite+sphene±rutile in the lower grade zone, and ilmenite+hornblende in the higher grade zone. Combining the mode of occurrence and chemistry of Fe-Ti oxides and sphene as well as the Mn-Fe2+ partitioning among magnetite, hematite and ilmenite, stability and paragenesis were determined. Magnetite, ilmenite and rutile in the hematite-bearing basic schists occur in the garnet and biotite zones, whereas, in the hematite-free ones, rutile is restricted to the garnet zone at the prograde stage, and ilmenite occurs in the biotite zone. Sphene is widespread in all the zones, but its occurrence is restricted to the lower grade zone at the prograde stage of metamorphism; its occurrence in the higher grade zone postdates major mineralization. The stable oxide mineral assemblages are magnetite+hematite, hematite+rutile, magnetite+hematite+ilmenite, magnetite+hematite+rutile, hematite+ilmenite+rutile and magnetite+hematite+ilmenite+rutile. Ilmenite and hematite contain significant amounts of MnO; the maximum MnO content of ilmenite and hematite are 24.1 and 2.1 wt. per cent, respectively. Therefore, the paragenesis of Fe-Ti oxide minerals can be determined only in the FeO-Fe203-Ti02-MnO system. The stability of Fe-Ti oxide minerals and sphene is controlled by the bulk-rock chemistry as well as pressure, temperature and oxygen fugacity.
TL;DR: In this article, it is concluded that the change in the oxygen content of the coolant in nuclear power stations will rapidly reflect itself in changes in the stoichiometry of the magnetite-type solids and, if higher levels of oxygen or localized attacks take place, the structure of the particles will suffer more drastic changes to hematite in a short time.
Journal Article•
01 Jan 1978
TL;DR: A review of the works on the hydrothermal synthesis of the crystals of some transition metal oxides is undertaken in this paper, where the process of obtaining the bulk crystals and the crystalline films are discussed.
Abstract: A review of the works on the hydrothermal synthesis of the crystals of some transition metal oxides is undertaken. The data on hydrothermal crystallization of magnetic oxides and the hydroxides of iron (hematite, magnetite, goethite, ferrites, garnets) as well as that of manganese and titanium are described in detail The process of obtaining the bulk crystals and the crystalline films are discussed.
TL;DR: In this article, the Mossbauer spectra of polycrystalline hematite shocked at pressures up to 40 GPa were studied in the temperature range between 100 and 300 K.
Abstract: Mossbauer spectra of polycrystalline hematite shocked at pressures up to 40 GPa are studied in the temperature range between 100 and 300 K. The initial temperatures T0 of the samples before applying pressures are 80 and 300 K. The Morin transition is broadened over a range of 70 K and occurs only for one half of the total number of iron atoms at both the T0. Debye temperatures T are estimated according to the Mossbauer data to be 360 K for raw hematite and 270 or 140 K for shocked one at T0 = 80 and 300 K, respectively. The results are discussed in terms of the formation of point defects located mainly close to the surfaces of grains. The average concentration of point defects is estimated to 1020 to 1021 cm−3. No metastable phases are observed.
[Russian Text Ignored].
TL;DR: The heat of adsorption of water physically adsorbed on these pigments can be calculated from the measured heats of immersion of the samples both activated in vacuum (10 −5 mmHg) for 24 h at room temperature and in equilibrium with water vapour under conditions close to that required in order to obtain the statistical monolayer on the surface.
TL;DR: In this paper, the reduction condition of hematite ore under high pressure (O~100kg/cm2) 1-1,.flow was studied with a d'namic gas low type high pressure DTA equipment.
Abstract: Synopsis The ~fJec t of reduction condition if hematite ore (32 ~60 mesh) under high pressure (O~100kg/cm2) 1-1 , .flow was studied with a d)'namic gas jlow type high pressure DTA equipment. Besides the usual nonisothermal DTA method, new attempt was made 011 the isothermal DTA method with this equipment . The results obtained are summarized as follows .' ( 1) The rate of reduct ioll was increased when the reduction temperature was raised from 500° to 850°C. The lowering of reduction rate at about 700°C, which was already pointed out ill some papers. was tlot observed. (2) The e./fect of increasing H2 pressure on the reductioll rate became very small at pressures above 15 kg /Cln' . The e./fect of H 2 pressure was relatively large whell the temperature and gas pTfssure are low. (3) The rate if reduction became high with increasing .flow rate of H 2 (STP). It wasfolilld that the e./fect of gas jlUdJ rate all the rate of reduction was quite larger thall the e./fect qf gas /Jressllre lIlIder the eX/lel'imentai cOllditions ado/lied.