Hydrogen incorporation in enstatite

A series of synthetic enstatites containing up to 1000 ppm (wt) Al were analysed with FTIR-spectroscopy. Pure enstatite exhibits only two essential O-H absorption bands at 3070 and 3362 cm(-1). As Al is incorporated in the crystal the absorption band at 3362 cm(-1) is continuously split into two other peaks. In addition several new bands above 3400 cm(-1) progressively evolve with Al incorporation. The intensities of these peaks correlate well with the Al-content of the sample. The observations are consistent with a model, where hydrogen in pure, Al-free enstatite is linked to the oxygen atoms O(3A) and O(3B), which are located at the SiO4-tetrahedron faces pointing towards the cavity between two M2-positions along the crystallographic b-axis. In Al-bearing samples additional water is mainly incorporated between the oxygen atoms O(2A) - O(1A) and O(2B) - O(1B).