Abstract
Stibiotantalite-group minerals were found from a lithium pegmatite, Nagatare, Fukuoka Prefecture, Japan. Two samples were examined; one is stibiotantalite, compositionally close to the ideal formula SbTaO4 and the other is a member of bismutotantalite-stibiotantalite series. The stibiotantalite grain is homogeneous in composition, and has high Ta/(Ta+Nb) values of 0.91-0.92. The bismutotantalite-stibiotantalite grain is very heterogeneous, and the ranges of Bi/(Bi+Sb) and Ta/(Ta+Nb) values are 0.26-0.54 and 0.71-0.81, respectively. This grain is heavily veined by Bi-poorer stibiotantalite. Compositional variation in Bi/(Bi+Sb) of this grain indicates the existence of solid solution between bismutotantalite and stibiotantalite with relatively wide range. The unit cell parameters of the stibiotantalite and the bismutotantalite-stibiotantalite are; orthorhombic a=4.916(1), b=11.811(1), c=5.536(1) Å and a=4.945(1), b=11.794(2), c=5.592(1) Å, respectively.
