Ab-initio synthesis and TEM confirmation of antigorite in the system MgO-SiO2H2O

Abstract

For the first time, chemically pure, nearly single-phase antigorite, Mg 48 Si 34 O 85 (OH) 62 , was synthesized directly without using seeds. Starting material was a stoichiometric mixture of previously synthesized talc and brucite. Synthesis conditions were 50 kbar, 500 degrees C, and 120 h. TEM studies show that the dominant wavelength for the structural modulation of antigorite is about 4.5 nm, which corresponds to m = 17 in the general antigorite formula M (sub 3m-1) T 2m O 5m (OH) (sub 4m-6) and thus to the structure of most natural antigorites. Selected-area electron diffraction patterns of single crystals exhibit the hkO reciprocal net diagnostic of antigorite.