Summary: A hydrated barium-strontium pyrochlore with only subordinate amounts of Ca and Na has been found in a weathered biotite rock (contact-rock of a carbonatite) from Panda Hill, Tanganyika, as small euhedral yellowish-grey cubic crystals (showing the combination of the octahedron and the cube) in a rock containing euhedral biotite, some orthoclase, and several other minerals. Hydrated Ba-Sr pyrochlore is isotropic, the refractive index varies from 2·07 to 2·10. The reflectivity (vertical illumination) is 13·2 %. H. 4 1 2 −5 –5 Poor {111} cleavage. The pyrochlore structure (space-group Oh7−Fd3m) and the unit-cell dimensions (a 10·562 Å.) are derived from X-ray powder and Weissenberg photographs. The calculated specific gravity is 4·01 (observed, 4·00 on dried material). Chemical analysis gives BaO 12·5, SrO 6·4, Na₂O 0·28, K₂O 0·25, CaO 1·35, rare earths (mainly Ce₂O₃) 2, ThO₂ 0·6, FeO 0·45, TiO₂ 3·9, Nb₂O₅ 67·0, Ta₂O₅ 0·22, H₂O+ 4·0, other constituents 2·21, total 101·16. After deduction for impurities the following formula resulted: (Ba_0·30Sr_0·22Ca_0·05Ce_0·04Na_0·03Fe_0·02K_0·01Th_0·01)(Nb_1·83Ta_0·004Ti_0·17)O_5·61(H₂O)_0·80.

The ideal formula for pyrochlore is A₂B₂O₆(F,OH). In the mineral described only a third of the A-positions are occupied by Ba, Sr, etc. Infra-red spectrophotometry does not indicate hydroxyl-groups. When the mineral is treated with TINO₃ solution the intensities of the X-ray diffraction lines 333/511, and 444 are changed; hydrated Ba-Sr pyrochlore shows a certain exchange-capacity.

The name pandaite, from Panda Hill, is proposed for the new mineral.