Lithium in NaBe-cordierites from El Peñón,Sierra de Córdoba,Argentina |
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| Authors: | Gordillo C E Schreyer W Werding G Abraham K |
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| Institution: | (1) Catedra de Petrologia, Universidad Nacional de Córdoba, Argentina;(2) Institut für Mineralogie, Ruhr-Universität, D-4630 Bochum 1, Federal Republic of Germany |
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| Abstract: | NaBe-cordierites (Fe/(Fe+Mn+Mg)=0.49–0.57) with BeO contents up to 1.16 weight % and additional Li2O contents up to 0.21 wt.% occur in cordierite-apatite-uraninite-muscovite-biotite-chlorite-feldspar-quartz nodules within pegmatites penetrating gneissic roof pendants of a lower Palaeozoic granite batholith. Occasional small crystals of beryl are interpreted to coexist stably with unaltered cordierite. Be and Li are incorporated in cordieriteaccording to the substitutions NaChannel] + Be4] Al4] and NaCh]+Li6]R2+6], respectively. The coexisting phyllosilicates do apparently not contain appreciable amounts of Li. According to powder IR-data, the analyzed water contents of the cordierites are dominantly of type II, and there is also little CO2. Their distortion indices  are rather low (0.121–0.145) and so are their optic angles (2V =50-51°). Considering all eleven NaBeLi-cordierites known thus far there is a strong positive correlation between Na and (Be+Li) with a slope close to 1.0. However, there is virtually no correlation between Be and Li, their incorporation into cordierite depending on the local geochemical environment. A strong negative correlation exists between the distortion indices of the NaBeLi-cordierites and their Be contents. Li has a disturbing influence on this relationship, and the versus Na correlation is also statistically worse than versus Be.Deceased December 20, 1984 |
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