Evolution of chemically induced cracks in alkali feldspar: thermodynamic analysis

Rainer Abart, Elena Petrishcheva, Gerlinde Habler, Christoph Sutter, Franz-Dieter Fischer, Jozef Predan, Marko Kegl, Franz G. Rammerstorfer

Publikation: Beitrag in FachzeitschriftArtikelForschungBegutachtung


A system of edge cracks was applied to polished (010) surfaces of K-rich gem-quality alkali feldspar by diffusion-mediated cation exchange between oriented feldspar plates and a Na-rich NaCl–KCl salt melt. The cation exchange produced a Na-rich layer at and beneath the specimen surface, and the associated strongly anisotropic lattice contraction lead to a tensile stress state at the specimen surface, which induced fracturing. Cation exchange along the newly formed crack flanks produced Na-enriched diffusion halos around the cracks, and the associated lattice contraction and tensile stress state caused continuous crack growth. The cracks nucleated with non-uniform spacing on the sample surface and quickly attained nearly uniform spacing below the surface by systematic turning along their early propagation paths. In places, conspicuous wavy cracks oscillating several times before attaining their final position between the neighboring cracks were produced. It is shown that the evolution of irregularly spaced towards regularly spaced cracks including the systematic turning and wavyness along the early propagation paths maximizes the rate of free energy dissipation in every evolutionary stage of the system. Maximization of the dissipation rate is suggested as a criterion for selection of the most probable evolution path for a system undergoing chemically induced diffusion mediated fracturing in an anisotropic homogeneous brittle material.
FachzeitschriftPhysics and Chemistry of Minerals
PublikationsstatusVeröffentlicht - 3 Mai 2022

Bibliographische Notiz

Funding Information:
We gratefully acknowledge the constructive comments of two anonymous reviewers and by Richard Sack. Support by Gerald Giester and Andreas Wagner for orienting feldspar plates and by Franz Kiraly during EPMA analyses is gratefully acknowledged. Scanning electron microscopy was done on an FEI Quanta 3D FEG scanning electron microscope at the Laboratory for Scanning Electron Microscopy and Focused Ion Beam Applications of the Faculty of Geosciences, Geography and Astronomy at the University of Vienna. The electron probe micro analyses were done on a Cameca SXFiveFE electron probe micro analyzer at the Department of Lithospheric Research, University of Vienna.

Funding Information:
Open access funding provided by University of Vienna. This work was funded by the Austrian Science foundation, FWF Project I 4404-N.

Publisher Copyright:
© 2022, The Author(s).

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