Crystal structure of lizardite 1T from electron diffractometry data

The crystal structure of the serpentine mineral lizardite 1T has been refin ed from electron diffractometry data (195 crystallographically nonequivalen t reflections from an oblique-texture electron diffraction patterns) up to R = 3.1%, The parameters of the hexagonal unit cell a = 5.317(2), c = 7.310 (2), sp. gr. P31m. The difference Fourier maps of the electrostatic potenti al clearly revealed the maxima characterizing the positions and potentials of hydrogen atoms. The interatomic O-H distances for hydrogen atoms of the internal and external hydroxyls are 0.93 and 0.95 Angstrom, respectively. A somewhat overestimated (Si-O)(av) distance indicates the stressed state of layers in lizardites. Under the action of hydrogen bonds, tetrahedra (T) i n lizardites are rotated by about 1.4 degrees with respect to strongly exte nded hexagonal configuration of the T-network in the direction toward the h exagonal packing of O, OH of the lizardite layer, OT (1 : 1). Under these c onditions, the partial substitution of Si by Al is a stabilizing factor pro moting commensurability of the octahedral and tetrahedral sheets.