Complete analyses of two samples of blomstrandine and two samples of euxenite were carried out by chemical methods and by emission and fluorescent x-ray spectroscopy. Pure mineral samples were prepared by repeated treatment with heavy liquids and by magnetic separation. The major constituents were determined by chemical methods; niobium, tantalum, and titanium being separated and determined by precipitation with the organic reagent N-benzoyl-N-phenylhydroxylamine. Minor and trace elements were determined by emission spectroscopy and rare earths by fluorescent x-ray spectroscopy.