Hydrothermal Synthesis of 1:1 and 2:1 Type Mg-Ni Layer Lattice Minerals, Their Structural Characterization by X-ray, Infra-Red and Optical Absorption Spectra

Hydrothermal synthesis of 1:1 type and 2:1 type trioctahedral hydrous layer lattice minerals covering the entire Mg-Ni compositional range is reported. Electronprobe microanalyses and X-ray diffraction data conform to the serpentine-type and talc-type chemistry and structure of these phases. Infra-red absorption spectra for the frequency range 4000-600 cm^-1 have been presented to characterize, their OH stretching vibrations, OH libration and the general lattice vibration modes. Optical absorption spectra between 2500 nm and 300 nm supplement the infra-red absorption data and clearly establish the d-d transition bands at about 1099 nm, 658 nm and 380 nm as caused by octahedrally coordinated Ni²⁺. Uniformity of the conditions- of synthesis between 250°C and 300°C and 350 bar P_H20 and the X-ray, infra-red and optical absorption spectra confirm the stability of the entire Mg-Ni compositional range under low pressure-temperature epizonal/hydrothermal conditions.