Alice Taddei, P. Bonazzi, Hans-Jürgen Förster, Patrick Casey, D. Holtstam, Andreas Karlsson, Luca Bindi
{"title":"Multi-analytical characterization of an unusual epidote-supergroup mineral from Malmkärra, Sweden: Toward the new (OH)-analogue of dollaseite-(Ce)","authors":"Alice Taddei, P. Bonazzi, Hans-Jürgen Förster, Patrick Casey, D. Holtstam, Andreas Karlsson, Luca Bindi","doi":"10.2138/am-2024-9438","DOIUrl":null,"url":null,"abstract":"\n A study of a skarn sample from the Malmkärra iron mines, Norberg, Västmanland (Sweden) revealed the occurrence of a peculiar epidote-supergroup mineral. It was examined using electron microprobe, single-crystal X-ray diffraction, Mössbauer and Fourier-transform infrared spectroscopy techniques. Structure refinements combined with electron-microprobe data indicate the following cation populations: A1 = Ca0.96REE3+0.03Mn0.01; A2 = REE3+0.99Ca0.01; M1 = Mg0.40Al0.32Fe3+0.26Fe2+0.02; M2 = Al0.98Fe3+0.02; M3 = Mg0.72Fe2+0.17Fe3+0.11; T1,2,3 = Si2.93Al0.07, accounting for a total positive charge of 24.64. The presence of Fe2+ is confirmed by Mössbauer data. The remarkable amount of divalent cations at both M1 and M3 (> 1 pfu, per formula unit) demands more than one monovalent anion pfu in the structure. As the mineral lacks fluorine, charge neutrality must be achieved through additional H+ (about 0.4 apfu). Only one independent hydrogen atom is located within the structure, with O10 as donor and O4 as acceptor, as in other epidote-supergroup minerals. Nonetheless, another O–O distance is suitable for a hydrogen bond, namely O10–O2. Although the existence of the additional OH group was not directly proved by vibrational spectroscopy, FT-IR data provided information related to this potential O10–O2 bridge. In the IR-spectrum acquired, several bands are observed in the OH-stretching region, and a secondary peak at 2140 cm–1 could be assigned to the bending mode of the O10–H…O2 group. To shed light onto this puzzling observation, one single crystal was subjected to annealing experiments at temperatures from 500 to 700°C, in 50°C steps, while a second one has undergone a heat treatment at 700°C. After the heat treatment, the IR-spectrum showed a decrease in intensity of all observed bands, in agreement with a dehydrogenation occurring at high temperatures. Although the structural position of the second hydrogen is still uncertain, it is reasonable to describe the composition of the epidote-supergroup mineral from Malmkärra as a solid solution between dissakisite-(Ce) (32%), ferriallanite-(Ce) (28%) and a yet undescribed end-member (40%), the (OH)-analogue of dollaseite-(Ce) – ideally CaREE3+Mg2AlSi3O11(OH)2.","PeriodicalId":2,"journal":{"name":"ACS Applied Bio Materials","volume":"118 31","pages":""},"PeriodicalIF":4.6000,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"ACS Applied Bio Materials","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.2138/am-2024-9438","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATERIALS SCIENCE, BIOMATERIALS","Score":null,"Total":0}
引用次数: 0
Abstract
A study of a skarn sample from the Malmkärra iron mines, Norberg, Västmanland (Sweden) revealed the occurrence of a peculiar epidote-supergroup mineral. It was examined using electron microprobe, single-crystal X-ray diffraction, Mössbauer and Fourier-transform infrared spectroscopy techniques. Structure refinements combined with electron-microprobe data indicate the following cation populations: A1 = Ca0.96REE3+0.03Mn0.01; A2 = REE3+0.99Ca0.01; M1 = Mg0.40Al0.32Fe3+0.26Fe2+0.02; M2 = Al0.98Fe3+0.02; M3 = Mg0.72Fe2+0.17Fe3+0.11; T1,2,3 = Si2.93Al0.07, accounting for a total positive charge of 24.64. The presence of Fe2+ is confirmed by Mössbauer data. The remarkable amount of divalent cations at both M1 and M3 (> 1 pfu, per formula unit) demands more than one monovalent anion pfu in the structure. As the mineral lacks fluorine, charge neutrality must be achieved through additional H+ (about 0.4 apfu). Only one independent hydrogen atom is located within the structure, with O10 as donor and O4 as acceptor, as in other epidote-supergroup minerals. Nonetheless, another O–O distance is suitable for a hydrogen bond, namely O10–O2. Although the existence of the additional OH group was not directly proved by vibrational spectroscopy, FT-IR data provided information related to this potential O10–O2 bridge. In the IR-spectrum acquired, several bands are observed in the OH-stretching region, and a secondary peak at 2140 cm–1 could be assigned to the bending mode of the O10–H…O2 group. To shed light onto this puzzling observation, one single crystal was subjected to annealing experiments at temperatures from 500 to 700°C, in 50°C steps, while a second one has undergone a heat treatment at 700°C. After the heat treatment, the IR-spectrum showed a decrease in intensity of all observed bands, in agreement with a dehydrogenation occurring at high temperatures. Although the structural position of the second hydrogen is still uncertain, it is reasonable to describe the composition of the epidote-supergroup mineral from Malmkärra as a solid solution between dissakisite-(Ce) (32%), ferriallanite-(Ce) (28%) and a yet undescribed end-member (40%), the (OH)-analogue of dollaseite-(Ce) – ideally CaREE3+Mg2AlSi3O11(OH)2.
期刊介绍:
ACS Applied Bio Materials is an interdisciplinary journal publishing original research covering all aspects of biomaterials and biointerfaces including and beyond the traditional biosensing, biomedical and therapeutic applications.
The journal is devoted to reports of new and original experimental and theoretical research of an applied nature that integrates knowledge in the areas of materials, engineering, physics, bioscience, and chemistry into important bio applications. The journal is specifically interested in work that addresses the relationship between structure and function and assesses the stability and degradation of materials under relevant environmental and biological conditions.