Aluminous hydrous mineral δ ‐AlOOH as a carrier of hydrogen into the core‐mantle boundary

In‐situ X‐ray diffraction experiments were conducted to determine the stability field of the aluminous hydrous mineral δ ‐AlOOH over the entire conditions of the lower mantle. We observed δ ‐AlOOH at pressures from 33 to 134 GPa at 1350–2300 K, indicating that this hydrous mineral in the sediment layer of a subducting slab could transport hydrogen into the core‐mantle boundary (CMB).