It is not well understood how much water and other volatiles are really contained in different mantle rocks or minerals, and how these volatiles are transported down into the deeper mantle in subduction zones. Here we present new experimental data showing that a common mineral found in subduction zone rocks, the hydrated Mg-silicate clinohumite, is much more stable in the mantle than previously anticipated. We show that even small amounts of F– substituting for OH– are sufficient to stabilize clinohumite to temperatures well above the normal mantle geotherm. Based on this finding we propose that in subduction zones, clinohumite effectively transports water and other volatiles from shallow depths to the transition zone of the mantle. This can drastically increase the amount of fluorine and water recycled into the deep mantle.