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An experimental study of the replacement of leucite by analcime

¹ Institut für Mineralogie, University of Münster, D-48149 Münster, Germany
² Institut für Planetologie, University of Münster, D-48149 Münster, Germany
³ Dipartimento di Scienze Geologiche, Università degli Studi Roma Tre, 00146 Roma, Italy

Correspondence: ^* E-mail: putnisc{at}nwz.uni-muenster.de

Leucite and analcime have open framework aluminosilicate structures, where ion exchange by cation substitution has been previously used to explain the replacement of one phase by another. Using ¹⁸O-enriched NaCl solutions in hydrothermal reactions and run-product analyses using scanning electron microscopy, infrared and Raman spectroscopy, and time-of-flight secondary ion mass spectrometry, we show that the replacement of leucite by analcime is not a solid-state reaction involving cation exchange by volume diffusion. Textural features such as nano-pores and clusters, as well as the detection of high amounts of ¹⁸O in the framework of analcime, suggest that the reaction proceeds by dissolution of leucite and reprecipitation of analcime, where structural O atoms of the leucite framework are exchanged and a new analcime structure forms at a moving interface through the leucite parent crystal. The characteristic high porosity (on a nano-scale) in the analcime product phase results from some of the parent phase being lost to the solution to give a volume deficit reaction. However, external dimensions are maintained during the process to result in the pseudomorphic replacement of an open framework aluminosilicate structure by a coupled dissolution-reprecipitation mechanism.

Key Words: Dissolution-reprecipitation • pseudomorphism • analcime • Raman • TOF-SIMS • zeolite • replacement

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