Serpentinization of forsterite under hydrothermal conditions and controlled synthesis of lizardite

Abstract

Serpentinization is a widely observed hydration process in the earth’s crust. In this study, hydrothermal experiments were performed at different temperatures, times, and pH values to explore the geochemical processes of serpentinization in forsterite. The results indicated that forsterite converts to serpentine after reacting with SiO₂ at 200 °C and a pH of 13 for 20 days in a hydrothermal system. X-ray diffraction patterns showed that the serpentine is lizardite, with lamellar and leaf-like micro-morphology. Furthermore, hydroxyl absorption peaks, which represent the formation of lizardite, were observed in the Fourier-infrared spectroscopy spectra. The newly formed serpentine showed high crystallinity and a relatively perfect crystal form. High-resolution electron microscopy indicated that the serpentine crystal layer only appeared on the forsterite surface. The transformation was a process of the coupling of dissolution and precipitation where the forsterite was replaced from the surface; [SiO₄]⁴⁻ and [MgO₆]¹⁰⁻ units were attached in situ to the forsterite surface, reacted, and formed a serpentine structure. These results are of fundamental significance for exploring the transformation and controllable synthesis between olivine group and serpentine group minerals as well as understanding the genesis, geochemical behavior, and geological environment of ultrabafic rock alteration deposits.