Abstract

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

\(oxygen\ atoms\ O(2A)\ {\mbox{--}}\ O(1\ A)\ and\ O(2B)\ {\mbox{--}}\ O(1B)\)
⁠.

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