Limits of Water Storage in Stishovite at Deep Mantle Conditions

The deep Earth water cycle is a key process in Earth's evolution. Stishovite has been proposed as a major carrier of water from the surface into the lower mantle. However, its role remains unclear because its water solubility is controversial. We investigated the water solubility of Al‐free stishovite at pressures of 33–38 GPa and temperatures of 700–1200 K using in situ X‐ray diffraction in an advanced multianvil apparatus. Water solubility is high, around 3 wt%, at 700 K but decreases rapidly with increasing temperature and becomes negligible (<1,000 ppm), at temperatures above 1000 K. These results suggest that pure stishovite is unlikely to transport significant amounts of water into Earth's lower mantle under comparable pressure‐temperature conditions. Previously reported high water contents in pure stishovite under deep Earth conditions likely reflect the solubility of post‐stishovite or experimental artifacts.