Kokowai Springs, Mount Egmont, New Zealand: Chemistry and mineralogy of the ochre (ferrihydrite) deposit and analysis of the waters

Childs, C. W.; Wells, N.; Downes, Colin J.

doi:10.1080/03036758.1986.10426958

Cited by 28 publications

(32 citation statements)

References 12 publications

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“…Our data are also consistent with previously published d-values between 0.15-0.25 nm for both natural and synthetic ferrihydrite (Carlson and Schwertmann, 1981;Childs et al, 1986;Chukhrov et at., 1973;Eggleton and Fitzpatrick, 1988;Towe and Bradley, 1976;Van der Giessen, 1966).…”

Section: Clays and Clay Mineralssupporting

confidence: 82%

“…Although both natural and synthetic ferrihydrite occur in forms with intermediate numbers of peaks (Carlson and Schwertmann, 1981;Childs et aL, 1986;Brearley, 1997;Lee et al, 1996;Lewis and Cardile, 1989;Li et al, 1999;Schwertmann et al, 1999), only synthetic 2LFh and 6LFh have been widely used for structural and chemical studies. Under appropriate conditions, ferrihydrite can transform to hematite, goethite, lepidocrocite, magnetite, or maghemite (Cornell and Schwertmann, 1996;Campbell et al, 1997).…”

Section: Copyright 9 2000 the Clay Minerals Society 11mentioning

confidence: 99%

“…Fefrihydrite is a common iron oxide mineral in lowtemperature surface environments such as soils, lakebottom sediments, drainage ditches, and hot-and coldspring deposits (e.g., Chukhrov et al, 1973;Schwertmann and Fischer, 1973;Childs et al, 1986;Schwertmann et al,, 1987;Schwertmann, 1988;Schwertmann and Taylor, 1989). Because of its small grain size (<--6 nm) and large surface area (hundreds of square meters per gram), even small amounts of ferrihydrite can have important consequences for many soil properties (Cornell and Schwertmann, 1996;Jambor and Dutrizac, 1998;Childs, 1992).…”

Section: Introductionmentioning

confidence: 99%

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Transmission Electron Microscopy of Synthetic 2- and 6-Line Ferrihydrite

Janney

Cowley

Buseck

2000

Clays and clay miner.

206

161

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Abstraet~High-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), annular dark-field scanning transmission electron microscope (STEM) images, and electron nanodiffraction were used to examine structures of synthetic 2-and 6-line ferrihydrite specimens. 086, 0.093, 0.107, 0.112, 0.119, 0.125, and 0.135 nm are visible in strongly exposed SAED patterns. Small quantities of hematite, magnetite or maghemite, and an acicular material tentatively identified as goethite were observed in the 6-line ferrihydrite, but these quantities do not contribute significantly to the overall diffracted intensity from the sample.

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Section: Clays and Clay Mineralssupporting

confidence: 82%

Section: Copyright 9 2000 the Clay Minerals Society 11mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Transmission Electron Microscopy of Synthetic 2- and 6-Line Ferrihydrite

Janney

Cowley

Buseck

2000

Clays and clay miner.

206

161

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“…For all the samples containing Si, an additional band attributable to Si-O-Fe stretching [16,25,41] occurs. Its shift from 930 up to 1000 cm -1 with increasing Si/Fe molar ratio indicates partial silicate polymerization [25,46]. Similar features were reported previously [18,27,40].…”

Section: Sem Xrd and Ftir Studiessupporting

confidence: 76%

“…Also, synthetic ferrihydrites analyzed so far exhibited usually low Si/Fe molar ratios, and the data for higher Si/Fe ratios are scarce [44]. The reason for this is probably a quite low silica content (up to several mass percent) in most of natural ferrihydrites [1,25,[45][46][47][48], but in some environments, such as modern seafloor hydrothermal vents, higher Si/Fe ratios (up to ca. 3) were reported [15,16,49,50].…”

Section: Introductionmentioning

confidence: 99%

The influence of silicate on transformation pathways of synthetic 2-line ferrihydrite

Rzepa

Pieczara

Gaweł

et al. 2016

J Therm Anal Calorim

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In this study, a series of synthetic ferrihydrite samples of Si/Fe molar ratios ranging from zero to 1.5 were heated up to 1000°C using simultaneous TG-DTA equipment. The XRD, FTIR, SEM-EDS and magnetic susceptibility measurements were carried out prior to and after heating. It has been found that silicate retards ferrihydrite transformation to hematite and affects crystallinity of the product. Low Si admixture in the precursor reduces hematite crystal size severely, but the increase in average crystal dimensions with increasing Si/Fe molar ratio was observed. High Si content results in the formation of hematite which exhibits a wide range of crystal habits. The conversion of pure ferrihydrite to hematite proceeds without any intermediate phase, whereas the increasing silicate content in the pristine oxyhydroxide strongly affects the transformation pathway. During annealing of high-Si ferrihydrites, the presence of two or three intermediate Fe 2 O 3 polymorphs (gamma, epsilon and beta) was demonstrated prior to the crystallization of final a-Fe 2 O 3 . The conditions favoring crystallization of intermediate phases result from progressive silica polymerization which forms separate matrix-type phase and impedes the aggregation of iron oxide nanoparticles.

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Ferrihydrite: A review of structure, properties and occurrence in relation to soils

Childs

1992

J Plant Nutrition & Soil

Self Cite

119

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Ferrihydrite occurs in soils undergoing rapid weathering, and in soils containing soluble silicate or organic anions which inhibit the formation of more crystalline iron oxides. Because of its very high specific surface area and adsorptive capacity (analogous to allophane), ferrihydrite can profoundly influence soil properties, even if present in only low concentrations. Ferrihydrite was recognised as a mineral by the International Mineralogical Association in 1975. Its structure and chemical formula, however, are not yet clearly understood. Most evidence to date indicates hexagonal‐close‐packed layers of O2′, OH, and H2O with Fe(III) occupying octahedral positions and giving a trigonal unit cell (a=0.508 nm; c=0.94 nm). Some samples appear to have only a partially ordered structure and uncertainty exists as to how to name such material. Natural ferrihydrites commonly contain up to about 9% Si and the role and location of silicate are subjects of active research. At concentrations greater than 5‐10%, ferrihydrite in soils can usually be identified by X‐ray diffraction. At lower concentrations, a combination of methods can be indicative. Acid‐oxalate‐extractable iron is a convenient and often useful indicator of the presence and quantity of ferrihydrite in a soil, though it cannot be regarded as a means of positive identification.

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Kokowai Springs, Mount Egmont, New Zealand: Chemistry and mineralogy of the ochre (ferrihydrite) deposit and analysis of the waters

Cited by 28 publications

References 12 publications

Transmission Electron Microscopy of Synthetic 2- and 6-Line Ferrihydrite

Transmission Electron Microscopy of Synthetic 2- and 6-Line Ferrihydrite

The influence of silicate on transformation pathways of synthetic 2-line ferrihydrite

Ferrihydrite: A review of structure, properties and occurrence in relation to soils

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