High Resolution Electron Microscopy of Feldspar Weathering

Richard A. Eggleton and Peter R. Buseck
Geology Department, Australian National University P.O. Box 4, Canberra, ACT 2600, Australia
Departments of Chemistry and Geology, Arizona State University Tempe, Arizona 85281

Abstract: High resolution imaging by transmission electron microscopy has revealed a mechanism for the weathering of intermediate microcline in a humid, temperate climate. Dissolution of the feldspar begins at the boundary of twinned and untwinned domains and produces circular holes which enlarge to form negative crystals. Amorphous, ring-shaped structures develop, about 25 Å in diameter, within the larger holes. These rings, in turn, crystallize to an arcuate phase having a 10-Å basal spacing and then to crinkled sheets of illite or dehydrated montmorillonite. The 10-Å layer silicate shows an irregular stacking sequence, including 10-, 20-, and 30-Å sequences. Included plagioclase crystals show a similar mechanism of weathering and, moreover, are more intensely weathered.

Key Words: Feldspar • Illite/montmorillonite • Ion thinning • Microcline • Transmission electron microscopy • Weathering

Clays and Clay Minerals; June 1980 v. 28; no. 3; p. 173-178; DOI: 10.1346/CCMN.1980.0280302
© 1980, The Clay Minerals Society
Clay Minerals Society (www.clays.org)