Oxygen Isotope Changes during Mica Alteration

Sridhar Komarneni, Marion L. Jackson and David R. Cole
Materials Research Laboratory, The Pennsylvania State University University Park, Pennsylvania 16802
Department of Soil Science, University of Wisconsin Madison, Wisconsin 53706
Chemistry Division, Oak Ridge National Laboratory Oak Ridge, Tennessee 37830

Abstract: Oxygen isotope analyses (δO18) of micas that were artificially depleted in K+ indicate little or no isotope exchange during the transformation. The oxidation of iron in K-depleted, iron-rich micas by H2O2 treatment resulted in 1.6 to 4.6‰ decrease in δO18 due to the fact that the equilibrium fractionation factor is less than the initial difference between the starting δO18 of the fluid and micas. The oxygen isotope ratio of a saponite formed by the weathering of phlogopite showed a 9.7‰ increase in δO18 due to authigenic recrystallization. These results suggest that oxygen isotope ratios can be used to determine the nature of chemical transformation during the weathering of mica to vermiculite and/or smectite.

Key Words: Mica • Oxygen isotopes • Potassium • Recrystallization • Saponite • Weathering

Clays and Clay Minerals; June 1985 v. 33; no. 3; p. 214-218; DOI: 10.1346/CCMN.1985.0330307
© 1985, The Clay Minerals Society
Clay Minerals Society (www.clays.org)