First evidence of synthetic polygonal serpentines

Hydrothermal syntheses on the stoichiometric composition 3MgO2SiO (sub 2) plus excess H (sub 2) O can reproduce the various rolled structures of natural serpentines, but synthetic polygonal serpentine has not hitherto been reported, probably due to difficulties in TEM sample preparation. An embedding preparation technique followed by ion milling is described, which allows HRTEM axial imaging of synthetic serpentine fibres; selected-area electron diffraction (SAED) patterns of single fibres can also be recorded. Like their natural counterparts, synthetic fibres with a diameter >><$I> 100 nm unambiguously display polygonal arrangements of 150 and 30-sector types, and various stacking sequences including regular multi-layer polytypes. These results indicate that the origin of polygonization is probably controlled by T and/or growth (kinetic) parameters.