Cerotungstite, a cerian analogue to yttrotungstite, from Uganda

Abstract

This paper describes the mineral cerotungstite found as a secondary crystallization in some tungsten deposits in northern Rwanda and in the Kigezi District of south-western Uganda. Cerotungstite represents a cerian analogue to yttrotungstite known from the Kramat Pulai tin deposit in Malaysia. Therefore, some new data for the Kramat Pulai yttrotungstite are given for comparison. Cerotungstite is associated with anthoinite and with an aluminian analogue to ferritungstite. It occurs as radiated groups of orange yellow bladed crystals with intimate twinning on (001). Single crystal X-ray data indicate the monoclinic space group P21 or P21/m. Indexed powder pattern is given. The unit cell dimensions are a0 = 5.874 Å, b0 = 8.700 Å, c0 = 7.070 Å, ß = 105°27'. The chemical analysis reported yields the idealized formula (RE)W2O6(OH)3 with Z = 2. The relative abundances of the rare earth elements were determined. Ce and Nd strongly predominate over Y. The X-ray powder pattern and the single crystal data for the Kramat Pulai yttrotungstite are similar to those for the Uganda cerotungstite except that the unit cell deduced for yttrotungstite is slightly smaller: a0 = 5.774 Å, b0 = 8.643 Å, c0 = 6.957 Å, ß = 104°47'. In conjunction with the previous chemical data available for the Kramat Pulai mineral, a new chemical analysis indicates the same formula as that given for cerotungstite, with the difference that Y predominates over the cerium earth elements.