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Open AccessArticle

Considerations About Bi and Pb in the Crystal Structure of Cu-Bearing Tourmaline

1
Institut für Mineralogie und Kristallographie, Universität Wien, Althanstrasse 14, 1090 Wien, Austria
2
Department of Mineralogy and Petrology, Faculty of Natural Sciences, Comenius University in Bratislava, Ilkovičova 6, 842 15 Bratislava, Slovakia
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(8), 706; https://doi.org/10.3390/min10080706
Received: 8 July 2020 / Revised: 3 August 2020 / Accepted: 7 August 2020 / Published: 10 August 2020
Copper- and Mn-bearing elbaitic tourmaline (“Paraíba tourmaline”) sometimes contains significant amounts of Pb and Bi. Their position in the tourmaline crystal structure was studied with correlation analysis and bond valence calculations. Correlations between the F content and the X-site charge allow predicting the X-site occupancy. Three sets of tourmaline analyses were studied: (1) Pb-rich tourmalines from the Minh Tien pegmatite, Vietnam; (2) Cu-, Pb- and Bi-bearing tourmalines from the Mulungu mine, Brazil; (3) Cu- and Bi-bearing tourmalines from the Alto dos Quintos mine, Brazil. Two correlations were plotted: (1) the charge by considering only Na1+, Ca2+ and K1+; (2) the charge by adding Pb2+ and Bi3+ to the X-site charge. When plotting correlations for the Minh Tien tourmalines, the correlation significantly improves by adding Pb2+ to the X site. For the Alto dos Quintos tourmalines, only a slight increase of the correlation coefficient is observed, while such a correlation for tourmalines from Mulungu interestingly shows a slight decrease of the correlation coefficient. Bond valence calculations revealed that Bi3+ and Pb2+ can indeed occupy the X site via BiLi(NaAl)−1, PbLi(NaCu)−1 and possibly PbCu(NaAl)−1 substitutions as seen in the investigated tourmaline samples. At the Y site, Pb4+ can be substituted via PbLi(AlCu)−1, and PbVO(AlVOH)−1, while Bi5+ does not have any stable arrangement in Cu-bearing fluor-elbaite. The occurrence of Pb4+ at the Y site could be one explanation for the results of the correlations of the Mulungu tourmalines. Another explanation could be that during the tourmaline crystallization some additional Bi and Pb came into the pegmatitic system and hence disturbed the correlation between the average X-site charge and the F content. Further plots of such correlations in “Paraíba tourmaline” samples might also help to distinguish between the worldwide localities of these rare and sought-after tourmalines. View Full-Text
Keywords: tourmaline; bismuth; lead; crystal structure; correlation analysis; bond valence calculation tourmaline; bismuth; lead; crystal structure; correlation analysis; bond valence calculation
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MDPI and ACS Style

Ertl, A.; Bačík, P. Considerations About Bi and Pb in the Crystal Structure of Cu-Bearing Tourmaline. Minerals 2020, 10, 706. https://doi.org/10.3390/min10080706

AMA Style

Ertl A, Bačík P. Considerations About Bi and Pb in the Crystal Structure of Cu-Bearing Tourmaline. Minerals. 2020; 10(8):706. https://doi.org/10.3390/min10080706

Chicago/Turabian Style

Ertl, Andreas; Bačík, Peter. 2020. "Considerations About Bi and Pb in the Crystal Structure of Cu-Bearing Tourmaline" Minerals 10, no. 8: 706. https://doi.org/10.3390/min10080706

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