Infrared Emission Spectroscopic Study of Some Natural and Synthetic Paragonites

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-Al^VI 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.