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Pandaite from the Mrima Hill niobium deposit (Kenya)

Published online by Cambridge University Press:  14 March 2018

P. M. Harris
P. M. Harris*
Affiliation:
Warren Spring Laboratory, D.S.I.R., Stevenage, Herts
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Summary

A hydrated barium pyrochlore (pandaite) has been found at Mrima Hill (Kenya) in a residuum consisting mainly of goethite/limonite and gorceixite. The pandaite occurs as pale yellow or white octahedral crystals, which have a micro-crystalline interior. It is isotropic, the refractive index varies from 2·07 to 2·11. The calculated specific gravity is 4·07, and the unit cell dimension is 10·59 Å. After deduction of impurities the following formula was obtained (Na0·03 K0·02 Mg0·05 Ca0·09 Ba0·36 Ln0·05 Th0·01 Pb0·004) (Ti0·21 Nb1·78 Ta0·01) (H2O)1·64 O5·52.

Comparison of the calculated formula, essentially A0·614B2 (H2O)1·64 O5·52 with the ideal pyrochlore formula A2B2O6F indicates important deficiencies in the structure. Differential thermal analysis shows a large endothermic peak at 340° C and moderate exothermic peaks at 480 and 780° C. In its physical, chemical, X-ray, and thermal properties the Mrima pandaite is similar to pandaites described from other localities.

The nature of the alteration of primary pyrochlore to pandaite has been studied using an electron probe.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 35 , Issue 270 , June 1965 , pp. 277 - 290
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1965

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References

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