Infrared Spectroscopy of OD Vibrators in Minerals at Natural Dilution: Hydroxyl Groups in Talc and Kaolinite,and Structural Water in Beryl and Emerald

Abstract

An infrared (IR) study of natural deuteration is conducted on minerals containing hydroxyl groups (talc and kaolinite) and channel-water-bearing minerals (beryl and emerald). In talc, the OD valence vibration is located at 2710 cm⁻¹, corresponding to OD groups surrounded by 3 Mg atoms. In kaolinite, the OD valence vibrations are located at 2671 cm⁻¹ (inner OD group), 2712, 2706, and 2700 cm⁻¹ (three inner-surface OD groups). In beryl and emerald, natural deuteration of channel water is observed for the first time by infrared microspectroscopy. In beryl from Minas Gerais (Brazil), the OD profiles are characterized by four bands at 2735, 2686, 2672, and 2641 cm⁻¹. In emeralds from Colombia and Brazil, the OD profiles are characterized by five or four bands, respectively, at 2816, 2737, 2685, 2673, and 2641 cm⁻¹ (Colombia) and 2730, 2684, 2672, and 2640 cm⁻¹ (Brazil). The band at 2816 cm⁻¹ can be assigned to –OD or OD⁻, and bands at 2686–2684, 2673–2672, and 2641–2640 cm⁻¹ can be assigned to type-I and type-II HOD molecules. The band at 2737–2730 cm⁻¹ is partially disturbed by combination bands of the mineral. Such OD profiles are different from those obtained by artificial deuteration at higher OD dilution.