FIRST EVIDENCE OF SYNTHETIC POLYGONAL SERPENTINES

Hydrothermal syntheses on the stoichiometric composition 3MgO . 2SiO(2 ) plus excess H2O can reproduce the various rolled structures of natur al serpentines. However, synthetic polygonal serpentine has not been r eported yet, probably due to difficulties in TEM sample preparation. W e describe herein an embedding preparation technique followed by ion m illing, which allows HRTEM axial imaging of synthetic serpentine fibre s. Selected-area electron diffraction (SAED) patterns of single fibres could also be recorded. Like their natural counterparts synthetic fib res with a diameter greater than 100 nm unambiguously display polygona l arrangements of 15- and 30-sector types, and various stacking sequen ces including regular multi-layer polytypes. These results suggest tha t the origin of polygonization is probably controlled by temperature a nd/or growth (kinetic) parameters.