Physics and Chemistry of Minerals

, Volume 40, Issue 5, pp 425–437 | Cite as

Shock-induced formation mechanism of seifertite in shergottites

  • Ulrich W. Bläß
Original Paper


The Martian meteorites Shergotty, Zagami and Dhofar 378 have been re-investigated in order to elucidate the shock-induced formation of seifertite. The occurrence of orthorhombic seifertite (α-PbO2 structured SiO2) has been confirmed for the mesostasis of Shergotty and Zagami by transmission electron microscopy with lattice parameters of a = 4.05(1) Å, b = 5.05(1) Å and c = 4.45(1) Å. Seifertite crystals are interpreted as shock-induced transformation products occurring together with maskelynite of both plagioclase and alkali-feldspar composition in a largely preserved eutectic crystallisation texture. Shock-induced microstructures in accessory minerals demonstrate that these regions cannot have been completely re-molten. No further features indicating shock-pressures above ~30 GPa are detected. Hence, seifertite must have been formed below its stability field by a fast solid-state process. Significantly higher shock-pressures of Dhofar 378 indicate an inhibition of a potential seifertite crystallisation by resulting high post-shock temperatures. Crystallographic considerations reveal that a direct formation of seifertite from a high-pressure derivate of cristobalite is possible without breaking any silicon-oxygen bonds. Important implications arise from the existence of such a non-equilibrium pathway. Inferring shock-pressures from metastably formed phases appears implausible, and the transition pressure could be even below 30 GPa. Furthermore, the transformation product is determined by the precursor phase. Epitaxial intergrowth with other silica high-pressure polymorphs should be induced by certain features of the precursor, for example, planar defects, or heterogeneous strain conditions. Due to symmetrical considerations, seifertite will get amorphous during a potential back-transformation, which provides an explanation for the formation of numerous amorphous lamellae.


Silica High-pressure Polymorphism Metastability Shergottites Transmission electron microscopy 



The author thanks Falko Langenhorst, Friedrich-Schiller-Universität Jena, Germany, for providing samples of Shergotty and Zagami and together with Ahmed El Goresy, Bayerisches Geoinstitut, Universität Bayreuth, Germany, for several discussions. Hubert Schulze, Bayerisches Geosinstitut, Universität Bayreuth, Germany, is kindly acknowledged for the precise preparation of thin sections. The manuscript benefits from suggestions of Roman Scala and two further anonymous reviewers. The work was supported by Deutsche Forschungsgemeinschaft (grants BL 917/1-1).


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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.Institut für GeowissenschaftenFriedrich-Schiller-Universität JenaJenaGermany
  2. 2.Institut für Anorganische ChemieTU Bergakademie FreibergFreibergGermany

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