Abstract
Nine samples of carbonate-free sodalite-group minerals, including those with abnormally high contents of polysulfide groups, fluoride anion and carbon dioxide molecules as well as synthetic fluoraluminate sodalite-type compound Na8(Si7Al5O24)(AlF6)3–·5H2O, have been studied by means of electron microprobe analyses, infrared and Raman spectroscopy; the CO2 content was determined using the selective sorption of gaseous ignition products. This article describes a semi-quantitative method for estimating the content of carbon dioxide molecules in these minerals, based on IR spectroscopy data. The data obtained demonstrate the existence of a sulfide sodalite-group mineral with the idealized formula Na7(Si6Al6O24)(S3−)·H2O, which differs significantly from the formula Na6Ca2(Si6Al6O24)S2–2 accepted for lazurite. According to single-crystal X-ray structural analysis, in the F-rich sodalite-group mineral from the Eifel paleovolcanic region, Germany with the idealized formula Na7(Si6Al6O24)F−·nH2O fluorine occurs as an isolated F− anion, unlike synthetic F-rich sodalite-type compounds.
Highlights
Natural aluminosilicates belonging to the sodalite group are feldspathoids whose crystal structures are based on the tetrahedral framework (Alx Si1−x O2 )x– with large cavities hosting large cations (Na+, K+, Ca2+ ), additional anions (Cl−, F−, SO4 2, S2, S3 −, etc.) and neutral molecules (H2 O, CO2 ) [1,2,3,4,5,6,7,8,9,10,11]
A combination of infrared and Raman spectroscopy was applied to the study of extra-framework anionic and neutral groups in nine samples of sodalite-group minerals with contrastingly different chemical compositions, including samples with abnormally high contents of polysulfide groups, fluoride anion and carbon dioxide molecules
This paper describes a semi-quantitative method for estimating the content of CO2 molecules in these minerals, based on IR spectroscopy data
Summary
Natural aluminosilicates belonging to the sodalite group are feldspathoids whose crystal structures are based on the tetrahedral framework (Alx Si1−x O2 )x– with large cavities (so-called β-cages) hosting large cations (Na+ , K+ , Ca2+ ), additional anions (Cl− , F− , SO4 2– , S2– , S3 − , etc.) and neutral molecules (H2 O, CO2 ) [1,2,3,4,5,6,7,8,9,10,11]. Vibrational (infrared and Raman) spectroscopy has proven to be an effective tool with which various anionic and neutral extra-framework groups in minerals of the sodalite group can be identified. Minerals 2020, 10, 363 writing of chemical formulae for members of the sodalite group with high sulfur and fluorine contents, as well as the present-day problem with the status of lazurite in the nomenclature of minerals. A combination of infrared and Raman spectroscopy was applied to the study of extra-framework anionic and neutral groups in nine samples of sodalite-group minerals with contrastingly different chemical compositions, including samples with abnormally high contents of polysulfide groups, fluoride anion and carbon dioxide molecules. This paper describes a semi-quantitative method for estimating the content of CO2 molecules in these minerals, based on IR spectroscopy data
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