Eifelite, KNa3Mg4Si12O30, a new mineral of the osumilite group with octahedral sodium

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Authors:Abraham, K.; Gebert, W.; Medenbach, O.; Schreyer, W.; Hentschel, G.
Author Affiliations:Primary:
Ruhr-Univ., Inst. Mineral, Bochum 4630, Federal Republic of Germany
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 82(2-3), p.252-258. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1983
Note:In English. 23 refs.; illus. incl. 5 anal., 5 tables, charts
Summary:Eifelite and roedderite occur in vesicles of contact-metamorphosed basement xenoliths ejected with the leucite tephrite lava of the Quaternary Bellerberg volcano in the Eifel, W Germany. They are considered to be precipitates of highly alkaline, MgSi-rich, but Al-deficient, gas phases. Eifelite, of variable composition, is uniaxial positive with omega approx 1.543 and epsilon approx 1.544, epsilon-omega 0.001-0.004; a 10.14-10.15 A, c approx 14.22 A; space group P6/m2/c2/c; strongest XRD lines 3.26(10), 3.75(9), 4.43(6) A. There is a complete series of solid solution between the eifelite end-member and roedderite, KNaMg5Si12O30, following the 2Na L/R arrows Mg substitution. Both eifelite and roedderite have milarite-type structures, but Na is always in six-coordinated sites. In roedderite Na occupies solely a newly defined B'(6) position, which is slightly displaced along c from the ideal B(9) position lying on the (001/2)-mirror plane in K2Mg5Si12O30. In eifelite Na is located both in B'(6) and in A(6) positions where it partially replaces Mg. Eifelite has the highest cation occupancy of all osumilite-group minerals known thus far. Chemical compositions of 2 eifelite crystals and 3 roedderite crystals are presented. [P.Br.]
Subjects:Alkali metals; Alkaline earth metals; Cell dimensions; Chemical composition; Collecting; Contact metamorphism; Crystal chemistry; Crystal structure; Geochemistry; Magnesium; Metals; Metamorphism; Milarite group; Mineral localities; Mineralogy; Minerals; New minerals; Optical properties; Osumilite; Physical properties; Properties; Ring silicates; Roedderite; Silicates; Sodium; Solid solution; Space groups; Substitution; X-ray data; Central Europe; Eifel; Europe; Germany; Rhenish Schiefergebirge; Rhineland-Palatinate Germany; Bellerberg; Eifelite; West Germany
Abstract Numbers:84M/0883
Record ID:1986065349
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from PASCAL, Institute de l'Information Scientifique et Technique
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