(MgFe)_2SiO_4 固溶体中の陽イオン配列について

Mossbauer spectra of some natural olivines have been measured as two mirror images at 310°C, 1x 1 0^-4 Torr in the oven, which was specially made of copper housing with the Mylar window to resolve the two superimposed doublets. And the Fe^2+ site occupancies (X_Mi.^Fe) in the crystallographically nonequivalent sites, Ml and M2 of olivine have been obtained from the equation (1). It is confirmed that olivines of plutonic or similar origins exhibit relative enrichment of Fes+ in Ml, whereas olivines of volcanic origin exhibit preferential ordering of Fe in M2. However, olivines that occurred as megacryst in calc-alkaline rock show the same site preference of Fe4^2+ to Ml as in plutonic origin. The annealing experiments show conflicting results: i.e., Fe^2+ enrichment occurs progressively as annealing temperature increases in the synthetic samples (SHINNO et al., 1974), and the reverse relation occurs mostly in naturals