Abstract
Optical absorption spectra of synthetic (Ni, Mg)2SiO4 and (Co, Mg)2SiO4 olivines have been reexamined at room temperature in the near ultraviolet, visible and near infrared ranges, by the method of diffuse reflection attenuance. The samples were synthesized by sintering the pellets of NiO, MgO and SiO2 mixture and CoO, MgO and SiO2 mixture. Both of the spectra of the two kinds of olivines consist of three bands, which are consistent with the crystal field theory, and two kinds of bands which were assigned to transition metal in the distinct octahedra, are superposed on each three bands. The spectra of (Co, Mg)2SiO4 olivine series are more complicated, because two bands of high energy side are superposed on each others. High and low spin configurations of Ni2+ ion (3d8) have theoretically no difference. But it was revealed that the Co2+ ion in olivine has high spin state. After the assignments of these spectra, the value of Dq and Racah value B were determined as(Ni, Mg)2SiO4 Dq (cm-1) B (cm-1)M(1) 856 980M(2) 762 902(Co, Mg)2SiO4M(1) 940 920M(2) 720 820The excess CFSE is a few kcal/mole in M (1) site of both olivines.
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