Chemical compositions of euxenite and ilmenite from the Ippaiyama pegmatite, Fukushima Prefecture

Abstract

Main constituent minerals of the pegmatite are microcline perthite, plagioclase, quartz, muscovite and tourmaline. A considerable amount of platy crystal of ilmenite, sometimes attaining to 10cm in diameter and 1cm in thickness, occurs associating with pinkish microcline perthite of which composition is represented as Or_68.1 Ab_31.4 An_0.5. Euxenite, less than 1×3mm in size, is found in close association with ilmenite. The results of chemical analyses of ilmenite and euxenite are shown in the table 2 and 4 respectively. Ilmenite has excessive amounts of Fe₂O₃ and Ti0₂ which were derived from the mingling of unmixing hematite and titania mineral (rutile ?). The chemical formula of euxenite is calculated as (Ca_0.10 Mn_0.01 Th_0.02 Ce_0.04 Y_0.54 U_0.16 Fe+²_0.12)_0.99 (Mg_0.03 Fe+³_0.05 Al_0.02 Ti_1.20 Nb_0.43 Ta_0.25 Si_0.08)_2.06 (0, OH)_6.34.