Preliminary report on metamict cerianite from Nesoya, Lutzow-Holmbunkta, East Antarctica

Mineralogical studies of a blackish mineral with strong radioactivity from microcline pegmatites of Nesoya, Lutzow-Holmbukta, East Antarctica, were performed. This mineral has been completely or almost completely transformed into a metamict state. However, in a heat treatment (1000℃, 7 hours), the powder pattern is identical with cerianite, and the unit cell dimension calculated from the powder X-ray diffraction data is α_0=5.451A. According to the qualitative analysis by an electron probe X-ray microanalyzer, the mineral consists of lanthanoids and other elements, such as La, Ce, Pr, Nd, Sm, Eu, Gd, Th, Xe, Cs, Pb, Rh, etc. Both the X-ray diffraction data and chemical analysis identify this mineral as a metamict cerianite [Ce(Th)O_2].