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A hydrated barium-strontium pyrochlore in a biotite rock from Panda Hill, Tanganyika1

Published online by Cambridge University Press:  14 March 2018

E. Jäger ,
E. Niggli  and
A. H. Van der Veen
E. Jäger
Affiliation:
Min.-Petr. Inst., University of Berne, Switzerland
E. Niggli
Affiliation:
Min.-Petr. Inst., University of Berne, Switzerland
A. H. Van der Veen
Affiliation:
Min. Petr. Dept., Research Laboratory of the Billiton Maatschappij N.V., Hollandsche Metallurgische Bedrijven N.V., Arnhem, Netherlands.
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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. Poor {111} cleavage. The pyrochlore structure (space-group O7h–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: (Ba0·30Sr0·22Ca0·05Ce0·04Na0·03Fe0·02K0·01Th0·01)(Nb1·83Ta0·004Ti0·17)O5·61(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.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 32 , Issue 244 , March 1959 , pp. 10 - 25
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1959

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Footnotes

1

Published by permission of the N.V. Billiton Maatschappij and the Colonial Development Corporation.

References

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