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Chemically induced fracturing in alkali feldspar

Autoren:Scheidl, K.S.Schäffer, Anne-KathrinPetrishcheva, E.Habler, G.Fischer, F.D.Schreuer, J. (Ruhr-Universität Bochum (RUB)) Abart, R.
Abstrakt:Fracturing in alkali feldspar during Na-K cation exchange with a NaCl-KCl salt melt was studied experimentally. Due to a marked composition dependence of the lattice parameters of alkali feldspar, any composition gradient arising from cation exchange causes coherency stress. If this stress exceeds a critical level fracturing occurs. Experiments were performed on potassium-rich gem-quality alkali feldspars with polished (010) and (001) surfaces. When the feldspar was shifted toward more sodium-rich compositions over more than about 10 mole %, a system of parallel cracks with regular crack spacing formed. The cracks have a general (h0l) orientation and do not correspond to any of the feldspar cleavages. The cracks are rather oriented (sub)-perpendicular to the direction of maximum tensile stress. The critical stress needed to initiate fracturing is about 325 MPa. The critical stress intensity factor for the propagation of mode I cracks, K, is estimated as 2.30-2.72 MPa m (73-86 MPa mm) from a systematic relation between characteristic crack spacing and coherency stress. An orientation mismatch of 18° between the crack normal and the direction of maximum tensile stress is ascribed to the anisotropy of the longitudinal elastic stiffness which has pronounced maxima in the crack plane and a minimum in the direction of the crack normal. © 2013 Springer-Verlag Berlin Heidelberg.
Anzahl der Seiten:16
Journal Titel:Physics and Chemistry of Minerals
Digital Object Identifier (DOI):http://dx.doi.org/10.1007/s00269-013-0617-1
Publikations Typ:Artikel
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