Formation of the high-pressure modification of hydrated talc at 450°C and 4 GPa: In situ diffraction study

Abstract

The formation of the high-pressure hydrous phase Mg₃Si₄O₁₀(OH)₂∙xH₂O (10 Å phase) through the reaction “talc + water” at 450°C and 4 GPa was studied using diamond anvil cell. The powder diffraction measurements in situ, performed at the Siberian Center of Synchrotron and Terahertz Radiation (SSTRC), were applied to refine the lattice parameters, atomic coordinates and the occupancy of interlayer H₂O site in the structure of 10 Å phase at 450°C and 4 GPa. The lattice parameters are a = 5.234(1) Å, b = 9.053(2) Å, c = 10.87(1) Å, β = 99.2(1)°, and V = 508.5(6) ų (space group C2/m). The results of Rietveld refinement show the best fit for the trioctahedral mica structure with split position Ow of the interlayer H₂O molecule. The half occupancy of the Ow site corresponds to one H₂O molecule per formula unit.