We are grateful to the mineral collection of the Muséum National d’Histoire Naturelle in Paris for providing us with the kyanite crystal used for the calibration reported in this manuscript, as well as to Etienne Deloule for providing us with the amphibole standards. Thanks to Alessandro Guastoni at the Museum of Mineralogy, University of Padova, for supplying the staurolite sample from Pizzo Forno. We thank Paula Guira for helping to set up FTIR measurements and Roger Hewins for proofreading the manuscript and improving the English. We are grateful to Benoit Baptiste for access to the X-ray diffraction facility at IMPMC to check on the crystal orientations prior to FTIR and NanoSIMS analyses. Monika Koch-Müller, Richard L. Hervig and an anonymous reviewer are thanked for their constructive comments on earlier version of this manuscript. L.R. thanks the European Research Council for funding via the ERC project HYDROMA (grant agreement No. 819587). The NanoSIMS facility in Paris was established by funds from the CNRS, Région Ile de France, Ministère délégué à l’Enseignement Supérieur et à la Recherche, and the Muséum National d'Histoire Naturelle.

Staurolite is an important mineral that can reveal much about metamorphic processes. For instance, it dominates the Fe-Mg exchange reactions in amphibolite-facies rocks between about 550 and 700 °C, and can be also found at suprasolidus conditions. Staurolite contains a variable amount of OH in its structure, whose determination is a key petrological parameter. However, staurolite is often compositionally zoned, fine-grained, and may contain abundant inclusions. This makes conventional water analysis (e.g. FTIR or by chemical titration) unsuitable. With its high sensitivity at high spatial resolution, NanoSIMS is potentially a valuable tool for determining water contents in staurolite. However; a calibration with relevant standards covering a large range of water content is required to obtain accurate and reliable analyses, because matrix effects typically prevent direct quantification of water content by SIMS techniques.

Peer reviewed