Abstract
Three oxide minerals belonging to the columbite group, including columbite–(Mn) (MnNb 2 O 6 ), columbite–(Fe) (FeNb 2 O 6 ), and fersmite (CaNb 2 O 6 ), were found in specimens from gem placers in Ratnapura district, Sri Lanka. We present results of chemical, structural and spectroscopic analyses, including the first Raman spectrum for natural fersmite. For columbite–(Mn) and columbite–(Fe), analytical results obtained before and after dry annealing in air indicate low degrees of accumulated self-irradiation damage, which corresponds well with low actinide concentrations.