Abstract

Compositional data are presented for latrappite and other niobium-rich perovskite-group minerals from the Oka, Kaiserstuhl and Magnet Cove carbonatite complexes. Latrappite is shown to be a member of a continuous solid-solution involving CaTiO 3 , NaNbO 3 , Ca 2 NbFe (super 3+) O 6 and Ca 2 Nb 2 O 7 . 57 Fe Mossbauer spectrometry demonstrates that only ferric iron is present in latrappite. The crystal structure of latrappite, determined by Rietveld analysis, is similar to that of CaTiO 3 perovskite. It differs in that replacement of Ti by Nb and Fe (super 3+) results in greater distortion and tilting of the TiO 6 framework polyhedra relative to CaTiO 3 . Revised unit-cell parameters of latrappite are: a 5.4479(3), b 5.5259(3), c 7.7575(5) Aa, V 233.54 Aa 3 , space group Pbnm.

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