[S-MP47_1PM1] Physics and Chemistry of Minerals

[SMP47-15] Mid- and far-infrared spectroscopy for Li-Al-Mg micas

*Masato MAKIO¹, Kiyotaka ISHIDA¹ (1.Graduate School of Social and Cultural Studies)

Keywords:Li-Al-Mg mica, hydrothermal synthesis, mid-infrared, far-infrared, Rietveld analysis

Mica is a one of the major rock forming minerals and widely spread in the earth crust. The hydrothermal synthetic Li-Al-Mg trioctahedral mica series were measured by mid- and far-infrared spectroscopy and X-ray powder diffraction Rietveld refinement: (a)Trilithionite: K(Li_1.5Al_1.5) (AlSi₃)O₁₀F₂- Phlogopite: KMg₃(AlSi₃)O₁₀F₂, (b)Polylithionite: K(Li₂Al)Si₄O₁₀F₂- Tainiolite: K (LiMg₂)Si₄O₁₀F₂, (c)Polylithionite- Eastonite: K(Mg₂Al)(Al₂Si₂)O₁₀F₂ and OD- F Mg- Masutomilite: K(LiAlMg)AlSi₃O₁₀(F, OD)₂ .The Li-Al-Mg micas synthesized hydrothermally at 600- 650 ^oC and 150- 200MPa in cold-seal externally heated Tuttle-type vessels. The starting materials were mixed and then sealed in Pt/Au capsules with 20 wt℅ D₂O (99.9℅ in purity). X-ray Rietveld analysis was done using Rietan- 2000 (Izumi and Ikeda 2000). Mid- and far-infrared spectra were measured with JASCO FTIR- 620 spectrometer. Each sample was scanned 256 times in an evacuated sample-chamber. All samples could refine monoclinic, C2/m (1M polytype). In the 250- 50cm^-1 far-infrared region , three kinds of bands are observed: these bands due to an in- plane tetrahedral torsional band between 170- 150cm^-1, an interlayer K- O_inner stretching band between 120- 140 cm^-1 and K- O_outer stretching band between 90- 100 cm^-1. With increasing< K- O_inner>, K- O_inner stretching band shifts higher frequency, while with increasing outer>, K- O_outer stretching band shifts lower frequency. In the 650- 250cm^-1 mid- and far-infrared region, two parts of bands are observed. With increasing ^[4]Si➞Al, (Si,Al)- O deformational band in the range of 600- 400cm^-1 became broad and merged.