Cu- and Mn-bearing tourmalines from Brazil and Mozambique: crystal structures, chemistry and correlations |
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Authors: | Andreas Ertl Gerald Giester Ulrich Schüssler Helene Brätz Martin Okrusch Ekkehart Tillmanns Hermann Bank |
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Institution: | 1. Institut für Mineralogie und Kristallographie, Geozentrum, Universit?t Wien, Althanstr. 14, 1090, Wien, Austria 2. Lehrstuhl für Geodynamik und Geomaterialforschung, Institut für Geographie und Geologie, Universit?t Würzburg, Am Hubland, D-97074, Würzburg, Germany 3. Geozentrum Nordbayern, Universit?t Erlangen, Schlossgarten 5a, 91054, Erlangen, Germany 4. Gebrüder Bank, Dietzenstrasse 1, 55743, Idar-Oberstein, Germany
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Abstract: | Cu- and Mn-bearing tourmalines from Brazil and Mozambique were characterised chemically (EMPA and LA-ICP-MS) and by X-ray single-crystal structure refinement. All these samples are rich in Al, Li and F (fluor-elbaite) and contain significant amounts of CuO (up to ~1.8 wt%) and MnO (up to ~3.5 wt%). Structurally investigated samples show a pronounced positive correlation between the <Y-O> distances and the (Li + Mn2+ + Cu + Fe2+) content (apfu) at this site with R 2 = 0.90. An excellent negative correlation exists between the <Y-O> distances and the Al2O3 content (R 2 = 0.94). The samples at each locality generally show a strong negative correlation between the X-site vacancies and the (MnO + FeO) content. The Mn content in these tourmalines depends on the availability of Mn, on the formation temperature, as well as on stereochemical constraints. Because of a very weak correlation between MnO and CuO we believe that the Cu content in tourmaline is essentially dependent on the availability of Cu and on stereochemical constraints. |
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