Abstract
Crystal structure and cation distribution of “cleavable olivines” with distinctive partings on (010), (100), and (001) from two ultrabasic rock masses (Oeyama and Happo-O’ne) were investigated by X-ray diffraction method. Crystal structure of the cleavable olivine does not possess any peculiarity in contrary to the Kuroda and Shimoda’s claim that it has some structural anomaly on the basis of strong 020 diffraction intensity observed by them. Strong 020 reflection in powder X-ray patterns is merely due to the preferred orientation. Cation distribution of Fe and Mg between M1 and M2 sites is random for Happo-O’ne olivine, and Fe atom slightly prefers for the M2 site for Oeyama olivine, indicating that both of the cleavable olivines are equilibrated at low temperature, which is consistent with petrologic evidences.
