Abstract: Muscovite samples were K-depleted with NaCl-NaTPB solutions. By varying the extraction period, samples that varied in total K from 219 to 15 meq per 100 g. were prepared. This treatment did not change the layer charge in the mineral, but it did increase the basal spacing of the mineral from 10 to 12.3 Å.
The changes in basal spacing that occurred when increasing amounts of interlayer K were replaced by Na and the effects of subsequent treatments for the removal of KTPB were determined with two size fractions. In each case, the interlayer K at the periphery of the muscovite particles was replaced by Na, and a fringe of K-depleted mineral with a basal spacing of 12.3 Å developed. In a <50µ sample the particles retained an inner core of 10 Å mineral as the weathered fringe increased. There was no evidence of interstratification. With this sample there was considerable Na trapping when the KTPB was removed with NH4Cl-acetone-water solutions. On the other hand, with a <2µ sample, mixed-layer structures developed as K was removed, and less Na trapping occurred. Na trapping was reduced by removing the KTPB with boiling NH4Cl.
Undried Na-degraded muscovite with only 15 meq K per 100 g did not expand beyond 12.3 Å. The NH4-degraded muscovite samples had a basal spacing of 10.4 Å.