The chemical composition of xenotime form fissures and pegmatites in the Alps

Eleven specimens of xenotime from the Alpine region (six from fissures, five from granitic pegmatites) have been analyzed by electron microprobe. Unit-cell parameters have been obtained from X-ray-diffraction data obtained on single crystals. The REE distribution is subject to important variation, some specimens being particularly rich in Gd, others in Dy or even in Yb. The Y2O3 content is nearly constant (average 46.5 wt.Yo), and there is little distinction between the pegmatite and the fissure samples. No substantial difference was found between the corresponding unit-cell parameters of all thpse crystals; the maximum variation does not exceed 0.02 A. Substitution of the actinides and Ca for the REE and of Si for P is very limited. The uranium content (average 0.96 wt.9o UO) is substantially higher than the thorium content (average 0.38 wt.9o Thor.