A large number of studies of water in pyroxenes have confirmed that essentially all pyroxenes of terrestrial origin as a rule contain substantial amounts of OH, varying as a function of chemical composition and geological occurrence. The highest OH-concentrations are observed in mantle-derived samples, and it is now well established that both clino- and orthopyroxene can be considered as major host minerals for water in the mantle (e.g., Bell and Rossman 1992; Bell et al. 2004; Bolfan-Casanova 2005).

The first firm observations of OH in pyroxenes were made more than three decades ago. Even earlier, the “excess”...

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