Multi-methodical study of the Ti, Fe and Fe distribution in chevkinite-subgroup minerals; X-ray diffraction, neutron diffraction, Fe Mssbauer spectroscopy and electron-microprobe analyses

Nagashima, Mariko*; Armbruster, T.*; Akasaka, Masahide*; Sano, Asami   ; Nishio-Hamane, Daisuke*; Malsy, A.*; Imaoka, Teruyoshi*; Nakashima, Kazuo*

Three non-metamict chevkinite-subgroup minerals, from Cape Ashizuri, Japan, Tangir Valley, Diamar District, Pakistan and Haramosh Mts., Skardu district, Pakistan, were studied by crystal chemical techniques. Powder X-ray diffraction and transmission electron microscopic observations confirmed well crystalline samples. Electron-microprobe analyses indicated the general composition known for chevkinite-(Ce). Site scattering values determined by single-crystal X-ray structure refinements suggested assignment of subordinate Nb to the octahedral M3 and M4 sites, minor Th to M1 for the Ashizuri sample and minor Mg to M1 for both samples from Pakistan. Neutron time-of-flight powder diffraction studies were applied to determine the Ti/Fe distribution among octahedral sites for all samples and Mossbauer spectroscopy served for the Fe valence assignment at the four octahedral sites. The dominant iron valence at M1 of the Haramosh sample is ferric whereas for samples Nos. 1 and 2 iron is ferrous.