Physics and Chemistry of Minerals

, Volume 41, Issue 1, pp 1–16 | Cite as

Chemically induced fracturing in alkali feldspar

  • K. S. Scheidl
  • A. -K. Schaeffer
  • E. Petrishcheva
  • G. Habler
  • F. D. Fischer
  • J. Schreuer
  • R. Abart
Original paper

Abstract

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 Ic, is estimated as 2.30–2.72 MPa m1/2 (73–86 MPa mm1/2) 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.

Keywords

Alkali feldspar Cation exchange Coherency stress Chemically induced fracturing Stress intensity factor 

Notes

Acknowledgments

This work was funded by the Deutsche Forschungsgemeinschaft project AB 314/2-1 and by the Austrian Science foundation, FWF project I 474-N19, both in the framework of the research unit FOR 741-DACH. We are grateful to G. Giester and A. Wagner for their help in preparing oriented single crystal plates.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  • K. S. Scheidl
    • 1
  • A. -K. Schaeffer
    • 1
  • E. Petrishcheva
    • 1
  • G. Habler
    • 1
  • F. D. Fischer
    • 2
  • J. Schreuer
    • 3
  • R. Abart
    • 1
  1. 1.Department of Lithospheric ResearchUniversity of ViennaViennaAustria
  2. 2.Institute of Mechanics, Montanuniversität LeobenLeobenAustria
  3. 3.Institute for Geology, Mineralogy and GeophysicsRuhr-University BochumBochumGermany

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