Sound velocities of natural goethite across a-e phase transformation under dynamic compression

Goethite (a-FeOOH), a vital water- and hydrogen-bearing natural mineral, is extensively distributed on the Earth's surface and probably in the lower mantle. Laboratory measurements of its phase transition and sound velocities provide crucial data for a more rational understanding of the deep-water transportation and physical properties of the Earth's interior. Herein, the Hugoniot equation of state and sound velocities of natural goethite up to around 15 GPa are measured by dynamic compression. The discontinuities pertinent to the density and sound velocities of goethite are observed at 7.1 (2) GPa, in which a solid-solid phase transition occurs from a- (Pbnm) to e-FeOOH (P2(1)nm). Through this structural phase transition, the longitudinal and shear wave velocities in order, enhance by about 5% and 12%. We suggest that changes in the sound velocity due to the FeOOH phase transition may contribute to the discontinuity in the subduction zones.