Abstract
Tapiolite hosted in lithium-caesium-tantalum (LCT)-type granitic pegmatite, near Arehalli, of Holenarsipur schist belt (HSB), occurs as euhedral crystals within the muscovite books or in association with columbite-tantalite. In this study, compositional and crystallographic characteristics of the tapiolite are presented. The tapiolite is Ta-rich (79.8% Ta2O5) and also Fe-rich (13.1% FeO) with minor amounts of Nb (3.80% Nb2O5) and Mn (0.30% MnO2), and is a Fe-end member of the FeTa2O6-MnTa2O6 series, ferrotapiolite. The tapiolite has very restricted compositional range. Calculated structural formula of the investigated tapiolite is [(Fe0.27 Mn0.66)0.93 (Nb0.45 Ta1.57 Ti0.004 Sn0.03)2.027O6].
The observed unit-cell dimension of studied tapiolite (aℴ = 4.7582Å and cℴ = 9.2186Å) matches with the value published in the international centre for diffraction data (ICDD) card for tapiolite standard (aℴ = 4.750 Å, cℴ = 9.205 Å), suggesting that the investigated mineral belongs to the category of ordered tapiolite. Furthermore, crystallographic data also reveal that studied tapiolite has not been affected by chemical substitutions. Restricted composition of tapiolite coupled with minor to trace content of Fe3+, Mn, Sn, Ti, Sc and REEs support this interpretation.
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Maithani, P.B., Singh, Y. Studies on tapiolite from Arehalli pegmatite, Hassan District, Karnataka. J Geol Soc India 78, 349–354 (2011). https://doi.org/10.1007/s12594-011-0096-2
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DOI: https://doi.org/10.1007/s12594-011-0096-2