Polarized electronic absorption spectra and Ni-Mg partitioning in olivines (Mg1-xNix) (sub 2) (SiO (sub 4) )

Room-T spectra were fitted to homogeneous olivine crystals grown at 1173 K and 1 atm from Li (sub 2) MoO (sub 4) flux, with X (sub Ni) 1.00, 0.75, 0.31, 0.07 and 0.04 (as analysed by microprobe) and measured at room and liquid-nitrogen T by microscope spectrometric techniques. The 10 absorption bands could be assigned on the basis of their energy and relative intensity to spin-allowed and spin- forbidden transitions of Ni (super 2+ ) in M1 and M2 sites. The fractional Ni (super 2+) contents, Ni/(Ni + Mg), in M1 and M2 were calculated from the linear-absorption coefficient of the most intense Ni(M2) transition. The values obtained agree with those from crystal structure refinement [A.M. 66-770]. This opens up the systematic determination by spectroscopic techniques of Ni-Mg partitioning as a function of T.