R1: Characterization and description of minerals (Joint Session with The Gemmological Society of Japan)

[R1-P-12] Re-examination of chemical compositions of W- and Nb-rich members of the columbite supergroup from Tahara, Gifu Prefecture, Japan

*Yasuyuki BANNO¹, Toshihiro KOGURE², Taiga OKUMURA² (1. AIST, 2. Waseda Univ.)

Keywords:

Ferberite,Columbite,FTIR,OH,Tahara

The chemical compositions of W- and Nb-rich members of the columbite supergroup, occurring as black prismatic crystals from Tahara, Gifu Prefecture, Japan, were re-examined. Back-scattered electron (BSE) images reveal that the crystals consist of a W-richer core and a W-poorer mantle. Combined results from electron microprobe analysis (EMPA), infrared (IR) spectroscopy, and electron energy-loss spectroscopy (EELS) suggest that the empirical formulae of the average compositions of the core and mantle are (Fe²⁺_0.582Mn_0.338Sc_0.055Zr_0.024Sn_0.008Ti_0.004Nb_0.230Ta_0.020W_0.741)_Σ2.00[O_3.838(OH)_0.162] and (Fe²⁺_0.392Mn_0.390Sc_0.028Zr_0.008Sn_0.005Ti_0.011Nb_0.740Ta_0.073W_0.353)_Σ2.00[O_3.927(OH)_0.073], respectively.