Abstract
Monazite from the Ebisu mine, Gifu Prefecture has been studied. The monazite from Ebisu is of yellowish or dark brown colour, with sp. gr.: 5, 20. The result of chemical analysis of the sample is as follows: P2O5 26.81, SiO2 2.24, Al2O3 0.36, ThO2 4.51, U3O8 0.21, Ce2O3 24.58, La2•O3 etc, 38.51, Fe2O3 0.48, CaO 0.86, PbO 0.026, ig. loss 0.91, total 99.49% Monazites from Ratnapura, Ceylon and Minas Geraias, Brazil are also analysed for comparison. The relationships between the cell dimensions, the relative abundances of rare earths and the ThO2 content are discussed. The chemical age of the Ebisu monazite is 108 m. y., while its thorium lead age on the basis of mass-spectrometric data is fifty million years, in accordance with the geological evidence.
