Abstract

The infrared emission spectra of a synthetic paragonite have been compared to natural paragonites from Monte Campione (Switzerland) and Williamstown (Australia). The OH stretching region is characterized by a silanol band around 3745 cm-1, two Al-OH stretching bands around 3650 and 3627 cm-1, and a water band around 3450 cm-1. The low-frequency region is characterized by bands at 1185, 1075, 993, 917, 883, 819, 803, 750, 725, 622, 545, and 486 cm-1 ascribed to different Si-O stretching, Al-OH libration and bending, and Si-O and Si-O-AlVI bending modes. The natural paragonites show minor differences in band positions. In the spectra of the paragonite from Williamstown (Australia), bands at 883 and 725 cm-1 are missing, while a new band is observed at 521 cm-1 and the Si-O stretching bands are shifted towards higher wavenumbers. This result is ascribed to the presence of a muscovite component in the crystal structure of the paragonite, as is possible in the continuous compositional series muscovite-paragonite. Heating causes the dehydroxylation of the paragonite, as is evidenced by broadening, a shift towards lower wavenumbers, and a diminishing intensity of the bands associated with the various OH modes. No new bands were observed indicating the restructuring of the octahedral layer.

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