Water in mantle minerals. In the aftermath of more than two decades of research, what have we discovered, what should we believe, and what are the unresolved questions ?

To comprehend the dynamic of the lithosphere, it is crucial to determine the extent of its “wetness” and its heterogeneity. Water concentration in the Nominally Anhydrous Minerals (NAMs) in xenoliths has been extensively employed in the past two decades to monitor the water content in the lithospheric mantle. Many experimental, numerical modelling and analytical studies of NAMs have been conducted in this lapse of time. The present state of knowledge on the subject, the major questions that remain unanswered, and the future of the topic will be examined through concrete examples.