Far-infrared spectra of synthetic dioctahedral muscovite and muscovite–tobelite series micas: Characterization and assignment of the interlayer I–O_inner and I–O_outer stretching bands Available to Purchase

Far-infrared spectroscopy and X-ray powder diffraction Rietveld structure refinement for the hydrothermal synthetic muscovite series, (a) KAl₃(Si_3–yGe_y)O₁₀(OH,OD)₂, (b) KGa₃(Si_3–yGe_y)O₁₀(OH,OD)₂, and (c) K(Al_3–xGa_x)Ge₃O₁₀(OH,OD)₂, where x = 0.0–3.0, y = 0.0–3.0, and the muscovite–tobelite series, (d) [K_1–A(NH₄,ND₄)_A]Al₃Si₃O₁₀(OH,OD)₂, where A = 0.0–1.0, indicate that there is a complete solid-solution in each series. In the 200–50 cm⁻¹ far-infrared region, four kinds of bands are observed: two bands due to octahedral deformation coupled with OH deformational vibrations between 240 and 130 cm⁻¹, an in-plane tetrahedral torsional band between 175 and 130 cm⁻¹, an interlayer I–O_inner stretching band, and an I–O_outer stretching band. The weak and broad 140 cm⁻¹ band is assigned to K–O_inner stretching and the strong broad 110 cm⁻¹ band to K–O_outer stretching in muscovite. The broad 175 cm⁻¹ band is (NH₄/ND₄)–O_inner stretching and the 140 cm⁻¹ broad strong band is (NH₄/ND₄)–O_outer stretching in tobelite. With increasing Ga→Al substitution, the I–O_inner and I–O_outer stretching bands shift to lower frequency, while with increasing Ge→Si substitution, the I–O_inner stretching band shifts to higher frequency; the I–O_outer stretching bands do not change as a function of composition.