Water incorporation in rutile and stishovite: A review and perspective

<p indent="0mm"> A global water circulation can be observed in the Earth’s interiors. Stishovite and rutile can incorporate significant amounts of water and exist in the subducted slabs as important water carriers. In addition, stishovite is also expected to be a potential water reservoir in the topmost lower mantle at geotherm temperatures. Since rutile and stishovite have a same rutile-type structure, the mechanisms of water substitution in rutile and stishovite are also similar. Previously reported infrared spectroscopy investigations indicated that the water contents of rutile are mainly controlled by the concentrations of trivalent metal cation in the crystal structure. Although both Al-rich and Al-free stishovite can contain more than 0.01% H₂O, Al-rich samples are more hydrous in general. Further experimental studies are required to reveal the differences between infrared spectroscopy investigations and other analyses on the estimation of water solubility in stishovite and hydrogen partitioning between stishovite/rutile and coexisting mineral phases in various systems.