Infrared and Raman spectroscopic characterization of the carbonate bearing silicate mineral aerinite - Implications for the molecular structure

The mineral aerinite is an interesting mineral because it contains both silicate and carbonate units which is unusual. It is also a highly colored mineral being bright blue/purple. We have studied aerinite using a combination of techniques which included scanning electron microscopy, energy dispersive X-ray analysis, Raman and infrared spectroscopy. Raman bands at 1049 and 1072 cm(-1) are assigned to the carbonate symmetric stretching mode. This observation supports the concept of the non-equivalence of the carbonate units in the structure of aerinite. Multiple infrared bands at 1354, 1390 and 1450 cm(-1) supports this concept. Raman bands at 933 and 974 cm(-1) are assigned to silicon-oxygen stretching vibrations. Multiple hydroxyl stretching and bending vibrations show that water is in different molecular environments in the aerinite structure. (C) 2015 Elsevier B.V. All rights reserved.