Summary
The water content of nephelines from volcanic, subvolcanic and metamorphic parageneses of Somma-Vesuvio, Italy was studied by polarized FTIR microspectrometry on oriented (0001) crystal plates. The H(in2)O content varies from 0.05 to 0.39 wt% and is mainly controlled by the number of vacancies in the alkali site. Most samples show an inhomogeneous distribution of the H2O molecules, oriented with their H-H-axis perpendicular to [0001]. The absorption behaviour in the region of the OH-stretching fundamentals is characterized by four spectra types. The “high temperature spectrum” of a thermally treated nepheline reported by Beran and Rossman (1989) also occurs in some natural samples from the metamorphic paragenesis of Somma-Vesuvio.
Zusammenfassung
Variabler Wassergehalt im Nephelin vom Somma-Vesuvio, Italien Der Wassergehalt von Nephelinen aus vulkanischen, subvulkanischen and metamorphen Paragenesen vom Somma-Vesuvio, Italien wurde mittels polarisierter FTIRMikrospektrometrie an orientierten (0001) Kristallplatten untersucht. Der H2O-Gehalt variiert von 0.05 bis 0.39 Gew% and wird im wesentlichen durch die Anzahl der Leerstellen in der Alkali-Position bestimmt. Die meisten Proben zeigen eine inhomogene Verteilung der H2O-Molekiile, deren H-H-Achse senkrecht [0001] orientiert ist. Das Absorptionsverhalten im Bereich der OH-Streckschwingungen ist durch vier Spektrentypen charakterisiert. Das vonBeran andRossman (1989) beschriebene “Hochtemperatur-Spektrum” eines thermisch behandelten Nephelins zeigen auch einige natürliche Proben metamorpher Paragenesen vom Somma-Vesuvio.
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Balassone, G., Beran, A. & Lueger-Ring, K. Variable water content of nepheline from Somma-Vesuvio, Italy. Mineralogy and Petrology 52, 75–83 (1995). https://doi.org/10.1007/BF01163127
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DOI: https://doi.org/10.1007/BF01163127