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

  • K. Abraham
  • W. Gebert
  • O. Medenbach
  • W. Schreyer
  • G. Hentschel
Article

Abstract

Eifelite of variable composition is uniaxial positive withn0 near 1.543 andne near 1.544, a between 10.14 and 10.15 Å, andc about 14.22 Å, space groupP 6/m 2/c 2/c. There is a complete series of solid solution between the eifelite end member KNa3Mg4Si12O30 and roedderite, KNaMg5Si12O30, following the 2 Na⇌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 alongc from the ideal B[9]-position lying on the (001/2)-mirror plane in K2Mg5Si12O30. In eifelite Na is located both inB[6] and in theA[6]-positions, where it partially replaces Mg. Eifelite has the highest cation occupancy of all osumilite group minerals known thus far.

Both 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, West Germany. They are considered to be precipitates from highly alkaline, MgSi-rich, but Al-deficient gas phases that originated through interaction of gaseous igneous differentiates with the xenoliths.

Keywords

Sodium Solid Solution Mineral Resource Variable Composition Group Mineral 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag 1983

Authors and Affiliations

  • K. Abraham
    • 1
  • W. Gebert
    • 1
  • O. Medenbach
    • 1
  • W. Schreyer
    • 1
  • G. Hentschel
    • 2
  1. 1.Institut für MineralogieRuhr-UniversitätBochum 1
  2. 2.Hessisches Landesamt für BodenforschungLeberberg 9Federal Republic of Germany

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