An atomic perspective on the serpentine-chlorite solid-state transformation.

Serpentine minerals are important components of metamorphic rocks and promising geo-materials for nanotechnology. Lizardite, the most abundant serpentine mineral, can be transformed into chlorite during metamorphism. This intriguing phase transformation should affect the deformation behavior during aseismic creep and slow slip at the base of the subduction zone, but has not been understood structurally and chemically at the atomic scale. Here we visualized cations and oxygen atoms using the state-of-the-art low-dose scanning transmission electron microscopy and found that restructuring mainly involves the synergistic migration of tetrahedral cations and oxygen anions, coupled with the migration of octahedral trivalent cations into the brucite-like interlayer. Further, we show that different serpentine polytypes result in distinct regular interstratifications of serpentine and chlorite. Our results clarify the long-standing puzzle of how solid-state layer silicate transformations occur and lead to long-period ordered structures.