Fergusonite and xenotime from the Nijünita pegmatite at Ohari, Marumori town, Miyagi Prefecture

Abstract

Fergusonite and xenotime occurred as single crystals, smaller than 4mm in size, associating with lepidomelane in plagioclase at the marginal part of the pegmatite. Fergusonite: the base {001} and the pyramid {111} are the dominant faces. Specific gravity G _??_=5.68₁ From the result of chemical analysis, shown in table 1, the chemical formula is calculated as (Y_0.97R_0.07)_1.04 ((Nb, Ta) _0.93R_0.07)_1.00O_4.03. Xenotime: the dominant face is z{101}, specific gravity G _??_=4.45₀. The chemical formula is given as (Y_0.90R_0.10) _1.00 (P_0.91Si_0.09) _1.00O_3.84'