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Minerals
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The Rietveld Method in Geomaterials Characterisation
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The Rietveld Method in Geomaterials Characterisation

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Crystallography and Physical Chemistry of Minerals & Nanominerals".

Deadline for manuscript submissions: closed (5 February 2021) | Viewed by 19280

Special Issue Editor

Prof. Dr. Thomas N. Kerestedjian

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Guest Editor
Department of Mineralogy and Mineral Resources, Geological Institute, Bulgarian Academy of Sciences, 24 Acad. Georgi Bonchev str., 1113 Sofia, Bulgaria
Interests: mineralogy; ore geology; crystal growth; crystal structure; powder diffraction; crystal morphology; sector zoning; twining; environmental mineralogy; geochemistry; databases
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Geomaterials are essential to our technological society. In order to understand the properties of these materials and to improve them, their atomic structure has to be known. An effective way to do this is by means of diffraction techniques using neutrons or X-rays from X-ray tubes and synchrotrons. The single crystal diffraction technique, using relatively large crystals of the material, provides a set of data from which the structure can be obtained. However, many materials of geological or technical interest cannot grow large crystals or are obtained in powdery form, so one has to resort to the powder diffraction technique using material in the form of very small crystallites. The drawback of the conventional powder diffraction approach is that the data grossly overlap, thereby preventing proper determination of the structure.

The "Rietveld Method" creates an effective separation of these overlapping data, thereby allowing for an accurate determination of the structure. It employs a least squares approach to refine a theoretical line profile (calculated from a known or postulated crystal structure) until it matches the measured profile. The method has been so successful that nowadays the structure of powdery materials is routinely being determined, nearly as accurately as the results obtained by single crystal diffraction techniques. Introduced in 1969 by the famous Dutch crystallographer Hugo Rietveld, today the method is the de facto standard for whole pattern (full profile) refinement of powder diffraction data. Thousands of scientific papers have been published using the Rietveld method, and over 4200 unique diffraction data entries have been published in the ICDD® Powder Diffraction File™ (PDF®) with the Rietveld quality mark. The success of the method can be gauged by the publication of more than a thousand scientific papers yearly (over 15000 so far) using it.

An even more widely used application of the method is in determining the components of polyphase mixtures. Today, the Rietveld method is not only being used for structure refinement but it is also a key analytical method for quantitative phase analysis using powder diffraction techniques. In the field of geology, the last opportunity is especially important, because geological matter is most often polyphase, and quantitative characterization of the bulk composition, even of coarse-grain materials, is best done by grinding into powders, providing statistically representative quantification.

Powered with the capabilities of the Rietveld method, the geological community today has the chance not only to better characterize geomaterials of current industrial interest but also to revisit quantitative characteristics of the geological matter and widen our knowledge about generic natural processes.

Prof. Dr. Thomas N. Kerestedjian
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Rietveld method
  • powder diffraction
  • structural and crystallochemical characterization of minerals and industrial phases
  • quantitative characterization of poly-mineral and poly-phase matter
  • quantitative tailings, ore concentrate and wall-rock characterization
  • petrological and lithological quantification

Published Papers (7 papers)

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Editorial

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3 pages, 167 KiB  
Editorial
Editorial for the Special Issue “The Rietveld Method in Geomaterials Characterisation”
by Thomas N. Kerestedjian
Minerals 2021, 11(8), 814; https://doi.org/10.3390/min11080814 - 28 Jul 2021
Cited by 1 | Viewed by 1173
Abstract
The raw materials obtained from the Earth’s crust (Geomaterials) are of fundamental importance for a wide range of industries [...] Full article
(This article belongs to the Special Issue The Rietveld Method in Geomaterials Characterisation)

Research

Jump to: Editorial

19 pages, 14689 KiB  
Article
Maghemite in Brazilian Iron Ores: Quantification of the Magnetite-Maghemite Isomorphic Series by Χ-ray Diffraction and the Rietveld Method, and Confirmation by Independent Methods
by Renata Hiraga, Otávio da Fonseca Martins Gomes and Reiner Neumann
Minerals 2021, 11(4), 346; https://doi.org/10.3390/min11040346 - 26 Mar 2021
Cited by 8 | Viewed by 3748
Abstract
Maghemite (γ-Fe2O3) is a mineral formed from magnetite oxidation at low temperatures, an intermediate metastable term of the magnetite to hematite oxidation and could be mixed with both. It has magnetic susceptibility similar to magnetite, crystal structure close to [...] Read more.
Maghemite (γ-Fe2O3) is a mineral formed from magnetite oxidation at low temperatures, an intermediate metastable term of the magnetite to hematite oxidation and could be mixed with both. It has magnetic susceptibility similar to magnetite, crystal structure close to magnetite with which it forms a solid solution, while compositionally it equals hematite. Maghemite is thus easily misidentified as magnetite by Χ-ray diffraction and/or as hematite by spot chemical analysis in iron ore characterization routines. Nonstoichiometric magnetite could be quantified in samples of Brazilian soils and iron ores by the Rietveld method using a constrained refinement of the Χ-ray patterns. The results were confirmed by reflected light microscopy and Raman spectroscopy, thus qualitatively validating the method. Χ-ray diffraction with the refinement of the isomorphic substitution of Fe2+ by Fe3+ along the magnetite-maghemite solid solution could help to suitably characterize maghemite in iron ores, allowing for the evaluation of its ultimate influence on mineral processing, as its effect on surface and breakage properties. Full article
(This article belongs to the Special Issue The Rietveld Method in Geomaterials Characterisation)
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19 pages, 4688 KiB  
Article
Quantitative in Situ X-ray Diffraction Analysis of Early Hydration of Belite-Calcium Sulfoaluminate Cement at Various Defined Temperatures
by Maruša Borštnar, Christian L. Lengauer and Sabina Dolenec
Minerals 2021, 11(3), 297; https://doi.org/10.3390/min11030297 - 11 Mar 2021
Cited by 7 | Viewed by 2201
Abstract
The influence of temperature on the early hydration of belite-calcium sulfoaluminate cements with two different calcium sulfate to calcium sulfoaluminate molar ratios was investigated. The phase composition and phase assemblage development of cements prepared using molar ratios of 1 and 2.5 were studied [...] Read more.
The influence of temperature on the early hydration of belite-calcium sulfoaluminate cements with two different calcium sulfate to calcium sulfoaluminate molar ratios was investigated. The phase composition and phase assemblage development of cements prepared using molar ratios of 1 and 2.5 were studied at 25, 40 and 60 °C by in situ X-ray powder diffraction. The Rietveld refinement method was used for quantification. The degree of hydration after 24 h was highest at ambient temperatures, but early hydration was significantly accelerated at elevated temperatures. These differences were more noticeable when we increased the temperature from 25 °C to 40 °C, than it was increased from 40 °C to 60 °C. The amount of calcium sulfate added controls the amount of the precipitated ettringite, namely, the amount of ettringite increased in the cement with a higher molar ratio. The results showed that temperature also affects full width at half maximum of ettringite peaks, which indicates a decrease in crystallite size of ettringite at elevated temperatures due to faster precipitation of ettringite. When using a calcium sulfate to calcium sulfoaluminate molar ratio of 1, higher d-values of ettringite peaks were observed at elevated temperatures, suggesting that more ions were released from the cement clinker at elevated temperatures, allowing a higher ion uptake in the ettringite structure. At a molar ratio of 2.5, less clinker is available in the cement, therefore these differences were not observed. Full article
(This article belongs to the Special Issue The Rietveld Method in Geomaterials Characterisation)
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11 pages, 3197 KiB  
Article
Rietveld Study of the Changes of Phase Composition, Crystal Structure, and Morphology of BiFeO3 by Partial Substitution of Bismuth with Rare-Earth Ions
by Maria Kireva, Ventsislav Tumbalev, Vladislav Kostov-Kytin, Peter Tzvetkov and Daniela Kovacheva
Minerals 2021, 11(3), 278; https://doi.org/10.3390/min11030278 - 09 Mar 2021
Cited by 10 | Viewed by 2290
Abstract
BiFeO3 is an interesting material due to its multiferroic properties. It attracts attention due to its potential applications in spintronics and in microelectronics for data storage, among others. Single-phase bulk material from BiFeO3 is difficult to synthesize. The kinetics of perovskite [...] Read more.
BiFeO3 is an interesting material due to its multiferroic properties. It attracts attention due to its potential applications in spintronics and in microelectronics for data storage, among others. Single-phase bulk material from BiFeO3 is difficult to synthesize. The kinetics of perovskite phase formation most often leads to the presence of impurity phases. It has been shown that low levels of replacement of Bi with rare earth ions lead to stabilization of the perovskite phase. In the present work, Rietveld refinement of the crystal structure based on powder X-ray diffraction patterns was applied to study the influence of partial substitution of Bi by rare-earth (RE) elements with different ionic radii on structural and morphological properties of the ferrite phase. Substitution by large RE ions was found to preserve the rhombohedral symmetry of BiFeO3, whereas substitution by smaller RE ions led to the coexistence of two polymorphic perovskite phases with rhombohedral R3c and orthorhombic Pnma symmetries. The unit cell parameters as well as the interatomic distances and angles, not only around the A cation but also around the iron ions, were influenced by the substitution. The mean crystallite and particle size decreased with the decrease of ionic radius of substituting RE ion. Full article
(This article belongs to the Special Issue The Rietveld Method in Geomaterials Characterisation)
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16 pages, 5403 KiB  
Article
Powder XRD Structural Study of Ba2+ Modified Clinoptilolite at Different Stages of the Ion Exchange Process Conducted at Two Temperature Regimes—Room Temperature and 90 °C
by Louiza Dimowa, Yana Tzvetanova, Ognyan Petrov, Iskra Piroeva and Filip Ublekov
Minerals 2020, 10(11), 938; https://doi.org/10.3390/min10110938 - 22 Oct 2020
Cited by 4 | Viewed by 1618
Abstract
Partial and almost complete barium exchange on clinoptilolite is performed and structurally studied for different durations (2 h, 24 h, 72 h, 168 h, 12 d, 22 d) at room temperature and 90 °C of the ion exchange process. Continuing ion exchange up [...] Read more.
Partial and almost complete barium exchange on clinoptilolite is performed and structurally studied for different durations (2 h, 24 h, 72 h, 168 h, 12 d, 22 d) at room temperature and 90 °C of the ion exchange process. Continuing ion exchange up to the 22nd day is proved by EDS analyses data and powder XRD (intensity changes of 020 and 200 peaks). Rietveld structure refinement was first performed on the maximum Ba exchanged clinoptilolite at 90 °C for 22 days (3.04 atoms per unit cell). Four barium positions and 9 H2O sites were refined. The split positions Ba2 and BaK (around M3 site in channel C) were found mostly occupied by 2.23 atoms per unit cell. The rest of refined samples showed different occupations of the positions of incoming Ba2+ and outgoing cations (Na+, Ca2+, K+, Mg2+) during ion exchange, describing extra-framework cationic movements, which are released easily without preferable directions. The exchanges at 90 °C and room temperature were found proceeding similarly up to the 2nd hour, but then at room temperature the process is slowed and at 22nd day 1.64 barium atoms per unit cell are structurally refined. Full article
(This article belongs to the Special Issue The Rietveld Method in Geomaterials Characterisation)
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30 pages, 11646 KiB  
Article
Quantitative Phase Analysis of Skarn Rocks by the Rietveld Method Using X-ray Powder Diffraction Data
by Yana Tzvetanova, Ognyan Petrov, Thomas Kerestedjian and Mihail Tarassov
Minerals 2020, 10(10), 894; https://doi.org/10.3390/min10100894 - 09 Oct 2020
Cited by 4 | Viewed by 4716
Abstract
The Rietveld method using X-ray powder diffraction data was applied to selected skarn samples for quantitative determination of the present minerals. The specimens include garnet, clinopyroxene–garnet, plagioclase–clinopyroxene–wollastonite–garnet, plagioclase–clinopyroxene–wollastonite, plagioclase–clinopyroxene–wollastonite–epidote, and plagioclase–clinopyroxene skarns. The rocks are coarse- to fine-grained and characterized by an uneven [...] Read more.
The Rietveld method using X-ray powder diffraction data was applied to selected skarn samples for quantitative determination of the present minerals. The specimens include garnet, clinopyroxene–garnet, plagioclase–clinopyroxene–wollastonite–garnet, plagioclase–clinopyroxene–wollastonite, plagioclase–clinopyroxene–wollastonite–epidote, and plagioclase–clinopyroxene skarns. The rocks are coarse- to fine-grained and characterized by an uneven distribution of the constituent minerals. The traditional methods for quantitative analysis (point-counting and norm calculations) are not applicable for such inhomogeneous samples containing minerals with highly variable chemical compositions. Up to eight individual mineral phases have been measured in each sample. To obtain the mineral quantities in the skarn rocks preliminary optical microscopy and chemical investigation by electron probe microanalysis (EPMA) were performed for the identification of some starting components for the Rietveld analysis and to make comparison with the Rietveld X-ray powder diffraction results. All of the refinements are acceptable, as can be judged by the standard indices of agreement and by the visual fits of the observed and calculated diffraction profiles. A good correlation between the refined mineral compositions and the data of the EPMA measurements was achieved. Full article
(This article belongs to the Special Issue The Rietveld Method in Geomaterials Characterisation)
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17 pages, 2820 KiB  
Article
Rietveld Analysis of Elpidite Framework Flexibility Using in Situ Powder XRD Data of Thermally Treated Samples
by Vladislav V. Kostov-Kytin and Thomas N. Kerestedjian
Minerals 2020, 10(7), 639; https://doi.org/10.3390/min10070639 - 19 Jul 2020
Cited by 2 | Viewed by 2331
Abstract
The present study demonstrates the capabilities of the Rietveld procedure to track the structural transformations and framework flexibility on the example of the natural water-containing zirconosilicate elpidite, subjected (in bulk) to thermal treatment from room temperature to 300 °C. The methodological approach to [...] Read more.
The present study demonstrates the capabilities of the Rietveld procedure to track the structural transformations and framework flexibility on the example of the natural water-containing zirconosilicate elpidite, subjected (in bulk) to thermal treatment from room temperature to 300 °C. The methodological approach to the performed refinements and the obtained results are in accordance with the previously reported data from in situ single crystal X-ray diffraction studies on heated samples of the same mineral. More light has been drawn on the temperature interval in which the non-reconstructive topotactic phase transition occurs upon partial dehydration. The framework flexibility observed as a response to the water loss and subsequent thermal expansion was evaluated in terms of intentionally introduced set of geometric parameters characterizing the spatial orientation of symmetrically related zirconium octahedra in the structure, the coordination polyhedra volumes, their distortion indices, and bond angle variances. Full article
(This article belongs to the Special Issue The Rietveld Method in Geomaterials Characterisation)
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