  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.
