Stabilization of trivalent Mn in natural tetragonal hydrogarnets on the join 'hydrogrossular'-henritermierite, Ca3Mn3+2 [SiO4]2[H4O4]

摘要

Four relatively intense and broad absorption bands centred at ~12500, ~19500, ~21500 and ~23000 cm–1 were recorded in polarized electronic single-crystal spectra of natural, optically uniaxial and pleochroic hydrogarnets with henritermierite contents ranging from 35 to 97 mol.%. These absorption bands arise from spin-allowed electronic d-d transitions in trivalent Mn located at the axially distorted six-coordinated site of the tetragonal hydrogarnet structure.