Nano-scale solution-reprecipitation responsible for altered near-surface zones during feldspar dissolution

HR: 0830h
AN: V51H-0369 [PDF]
TI: Nano-scale solution-reprecipitation responsible for altered near-surface zones during feldspar dissolution
AU: * Hellmann, R
EM: hellmann@obs.ujf-grenoble.fr
AF: LGIT-CNRS-OSUG, Maison des Geosciences BP 53X, Grenoble Cedex 9, 38041 France
AU: Penisson, J
EM: jpenisson@cea.fr
AF: DRFMC/SP2M, CEA-CENG, Ave. des Martyrs, Grenoble, 38000 France
AU: Hervig, R L
EM: hervig@asu.edu
AF: Center for Solid State Science, Arizona State University, Tempe, AZ 85287-1704 United States
AU: Thomassin, J
EM: Jean-Hugues.Thomassin@esip.univ-poitiers.fr
AF: UMR CNRS 6532, LMGE - ESIP, Universit‚ de Poitiers, Poitiers Cedex, 86022 France
AU: Abrioux, M
EM: Jean-Hugues.Thomassin@esip.univ-poitiers
AF: UMR CNRS 6532, LMGE - ESIP, Universit‚ de Poitiers, Poitiers Cedex, 86022 France
AB: The pH-dependency of the aqueous dissolution behavior of feldspar, the most abundant mineral in the Earth's crust, as well as many other alumino-silicate minerals, is generally modeled to invoke two distinct dissolution mechanisms: the formation of altered ('leached') near-surface layers at acid to neutral pH, and the absence of these layers at basic pH. Based on an approach combining transmission electron microscopy and spectroscopy methods with Ź to nm spatial resolution, the interfacial region between altered and non-altered zones after dissolution at acid pH conditions is characterized by extremely sharp and spatially coincident changes in structure and chemistry. Based on these new data, we propose that near-surface altered zones in feldspars result from interfacial solution-reprecipitation, and not preferential leaching. Therefore, the intrinsic dissolution process is congruent, whereby the release of all elements to solution is governed by a single mechanism that is invariant with pH. These results call into question prevailing dissolution models for feldspars and related alumino-silicate minerals.
DE: 8494 Instruments and techniques
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting