http://hdl.handle.net/20.500.12128/12198
Title: | Raman Spectroscopy and Single-Crystal High-Temperature Investigations of Bentorite, Ca6Cr2(SO4)3(OH)12.26H2O |
Authors: | Juroszek, Rafał Krüger, Biljana Galuskina, Irina Krüger, Hannes Tribus, Martina Kürsten, Christian |
Keywords: | bentorite; ettringite group; SC-XRD; Raman spectroscopy; Hatrurim Complex; Israel |
Issue Date: | 2020 |
Citation: | Minerals, Vol. 10 (2020), Art. No. 38 |
Abstract: | The crystal structure of bentorite, ideally Ca6Cr2(SO4)3(OH)12 26H2O, a Cr3+ analogue of ettringite, is for the first time investigated using X-ray single crystal di raction. Bentorite crystals of suitable quality were found in the Arad Stone Quarry within the pyrometamorphic rock of the Hatrurim Complex (Mottled Zone). The preliminary semi-quantitative data on the bentorite composition obtained by SEM-EDS show that the average Cr/(Cr + Al) ratio of this sample is >0.8. Bentorite crystallizes in space group P31c, with a = b = 11.1927(5) Å, c =21.7121(10) Å, V = 2355.60(18) Å3, and Z = 2. The crystal structure is refined, including the hydrogen atom positions, to an agreement index R1 = 3.88%. The bentorite crystal chemical formula is Ca6(Cr1.613Al0.387)S2[(SO4)2.750(CO3)0.499]S3.249(OH)11.502 ~25.75H2O. The Raman spectra of bentorite from two di erent localities exhibit the presence of the main stretching and bending vibrations related to the sulfate group at 983 cm1 ( 1), 1109 cm1 ( 3), 442 cm1 ( 2), and 601 cm1 ( 4). Moreover, the presence of bands assigned to the symmetric Cr(OH)6 3 stretching mode and hydroxyl deformation vibrations of Cr–OH units at ~540 cm1 and ~757 cm1, respectively, may be used to distinguish between ettringite and bentorite. In situ high temperature single crystal XRD experiments show that the decomposition of bentorite starts at ca. 45 C and that a dehydroxylation product similar to metaettringite is formed. |
URI: | http://hdl.handle.net/20.500.12128/12198 |
DOI: | 10.3390/min10010038 |
ISSN: | 2075-163X |
Appears in Collections: | Artykuły (WNP) |
File | Description | Size | Format | |
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Juroszek_Raman_spectroscopy_and_single_crystal.pdf | 3,86 MB | Adobe PDF | View/Open |
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