An occurrence of the rare mineral tuhualite (NaFe3+Fe2+Si6O15) is reported in a peralkaline rhyolitic ignimbrite from the island of Pantelleria, Italy. The mineral formed during devitrification of glassy fiamme and varies in form from anhedral plates to perfectly euhedral in open vesicles. There is significant replacement of Fe2+ by Mn (≤0.37 atoms per formula unit (apfu)) and Zn (≤0.11 apfu), and of Na by K (≤0.13 apfu). The tuhualite possibly formed at temperatures <580 °C at fO2>FMQ in the presence of a hydrous fluid.
Tuhualite in a peralkaline rhyolitic ignimbrite from Pantelleria, Italy
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Bogusław Bagiński, Ray Macdonald, John C. White, Lidia Jeżak; Tuhualite in a peralkaline rhyolitic ignimbrite from Pantelleria, Italy. European Journal of Mineralogy ; 30 (2): 367–373. doi: https://doi.org/10.1127/ejm/2018/0030-2711
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