Anisotropic X-ray peak broadening and twin formation in hematite derived from natural and synthetic goethite

Löffler, Lars; Mader, W.

doi:10.1016/j.jeurceramsoc.2004.09.032

Cited by 46 publications

(17 citation statements)

References 22 publications

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“…The validity of the methodology based on the application of XRPD confirms the results of previous investigations carried out on synthetic goethite samples (Pomiès et al . ) and disagrees with the research carried out by Löffler and Mader (). These authors report the lack of selective broadening of heated natural goethite samples.…”

Section: Discussioncontrasting

confidence: 61%

“…Selective broadening during thermal treatment has been discussed and demonstrated by other authors for synthetic goethite (Pomiès et al . , ), even if no changes were observed for natural goethite due to the different surface‐to‐volume ratio existing between synthetic and natural goethite (Löffler and Mader ). This result is different from that obtained on natural goethite by Gialanella et al .…”

Section: Previous Studies On Thermally Induced Transformation Of Goetmentioning

confidence: 99%

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Heat Treatment of Mineral Pigment During the Upper Palaeolithic in North-East Italy

et al. 2018

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The use of red ochre for utilitarian, symbolic and artistic purposes is widely documented in prehistoric contexts. The absence of adequate red-coloured raw materials influenced the development of technological activities aimed at modifying the original physiochemical properties of yellow ochre. The heat treatment of goethite to obtain hematite was investigated in the western sector of the Lessini Mountains in north-east Italy, where red ochre was found in the (Proto)Aurignacian levels at Fumane cave and in the Late Epigravettian sequence at Tagliente rockshelter. The combination of X-ray powder diffraction (XRPD) and transmission electron microscopy (TEM) proved that heat treatment was a common practice in the studied archaeological sites due to the scarce availability of suitable hematite-based material in the region.

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Section: Discussioncontrasting

confidence: 61%

Section: Previous Studies On Thermally Induced Transformation Of Goetmentioning

confidence: 99%

Heat Treatment of Mineral Pigment During the Upper Palaeolithic in North-East Italy

et al. 2018

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“…Instead, they argue from TEM analysis that a nonstoichiometric microporous hematite "skin" forms on the surface of goethite grains during dehydration, and this skin moves inward during the transformation. Löffler and Mader (2006) attribute the non-uniform XRD peak broadening to nanoscale twinning in hematite, and they note that such broadening is absent in coarsely twinned hematite. Similarly, other scientists have ascribed non-uniform peak broadening to unusual behaviors with respect to particle morphology, size, microporosity, strain, and stacking faults (Watari et al 1979a(Watari et al , 1979b(Watari et al , 1983Jiang et al 2000;Fan et al 2006).…”

Section: Doubts Concerning Protohematite and Hydrohematitementioning

confidence: 99%

A refined monoclinic structure for a variety of "hydrohematite"

Peterson

Heaney

Post

et al. 2015

American Mineralogist

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In ferruginous soils, nano-to microscale hematite (a-Fe 2 O 3 ) plays a central role in redox processes and contaminant cycling. Hematite is known to incorporate structural OH -and water, and the requisite charge balance is achieved by iron vacancies. Prior researchers have suggested that the defective hematite structures form unique phases called "protohematite" and "hydrohematite." Infrared and Raman spectroscopic studies have assigned a lower-symmetry space group to "hydrohematite" (R3c) relative to that of stoichiometric hematite (R3c). However, the existence and structure of these phases have been contentious, largely due to the lack of in situ X-ray diffraction dataHere we present a new structure refinement for "hydrohematite" precipitated hydrothermally at 200 °C in a monoclinic space group (I2/a) using time-resolved synchrotron X-ray diffraction (TR-XRD) data collected during the in situ hydrothermal precipitation of akaganeite and its transformation to stoichiometric hematite. Distinct peak splitting was observed in the "hydrohematite" diffraction patterns, indicating a violation of the threefold rotational symmetry. A monoclinic unit cell with parameters of a = 7.3951(10), b = 5.0117(5), c = 5.4417(7) Å, b = 95.666(5)° provided a good fit and significant reduction in c 2 and R wp relative to space group R3c. Rietveld analyses revealed that water concentrations in the first-formed crystals of "hydrohematite" were comparable to water contents of akaganeite and goethite. Thus, the hydrothermal transformation of akaganeite to "hydrohematite" is promoted not by dehydration but by reconstruction of the oxygen framework.

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“…Loffler and Mader, 2006), which has a hexagonal structure with space group R 3c (Cox et al, 1962). The oxygen ions are approximately in a hexagonal close-packing arrangement, where the Fe(III) ions are located between the O layers and octahedrally coordinated to six O atoms (Fig.…”

Section: Hematite A-fe 2 Omentioning

confidence: 99%

Surface simulation studies of the hydration of white rust Fe(OH)2, goethite α-FeO(OH) and hematite α-Fe2O3

Leeuw

Cooper

2007

Geochimica et Cosmochimica Acta

107

106

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Anisotropic X-ray peak broadening and twin formation in hematite derived from natural and synthetic goethite

Cited by 46 publications

References 22 publications

Heat Treatment of Mineral Pigment During the Upper Palaeolithic in North-East Italy

Heat Treatment of Mineral Pigment During the Upper Palaeolithic in North-East Italy

A refined monoclinic structure for a variety of "hydrohematite"

Surface simulation studies of the hydration of white rust Fe(OH)2, goethite α-FeO(OH) and hematite α-Fe2O3

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