SILICON K-EDGE XANES SPECTRA OF SILICATE MINERALS

Silicon K-edge x-ray absorption near-edge structure (XANES) spectra of a selection of silicate and aluminosilicate minerals have been measur ed using synchrotron radiation (SR). The spectra are qualitatively int erpreted based on MO calculation of the tetrahedral SiO44- cluster. Th e Si K-edge generally shifts to higher energy with increased polymeriz ation of silicates by about 1.3 eV, but with considerable overlap for silicates of different polymerization types. The substitution of Al fo r Si shifts the Si K-edge to lower energy. The chemical shift of Si K- edge is also sensitive to cations in more distant atom shells; for exa mple, the Si K-edge shifts to lower energy with the substitution of Al for Mg in octahedral sites. The shifts of the Si K-edge show weak cor relation with average Si-O bond distance (d(Si-O)), Si-O bond valence (s(Si-O)) and distortion of SiO4 tetrahedra, due to the crystal struct ure complexity of silicate minerals and multiple factors effecting the x-ray absorption processes.