Nature 210, 727 (14 May 1966); doi:10.1038/210727a0

Recrystallization of Mica in Crenulated Schists

N. RAST

Department of Geology, University of Liverpool.

DR. NICHOLSON, in his recent communication¹, quite rightly states that in strain-slipped phyllites micaceous minerals commonly concentrate on alternate limbs of crenulations. This observation has been made by Clough² and repeated by King and Rast³. In my more recent paper⁴ I was essentially concerned with the mechanics of growth of isolated matrix mica flakes under conditions involving annealing recrystallization, and not with the mechanism of chemical transport involved in chemical differentiation, which will be attempted elsewhere. My point, however, that in mimetic recrystallization mica flakes grow so as to become stain-free is amply illustrated by Dr. Nicholson's photographs. In particular his Fig. 2 shows clearly the completely stain-free mica flakes at the closures of microfolds. My other point that at a subsequent stage of recrystallization mica flakes grow parallel to axial planes of folds is again shown by Dr. Nicholson's Fig. 1. At no stage in my discussion did I claim that abundant new mica grows along the axial plane, but I did point out mica flakes growing parallel to axial planes. As my Fig. 4d shows, these micas, like Dr. Nicholson's Fig. 1, grow on the limbs of microfolds.

1. Nicholson, R. , Nature, 209, 68 (1966). | Article | ISI |
2. Clough, C. T. , in Geology of Cowal, Mem. Geol. Surv. Scotland, 9 (1897).
3. King, B. C. , and Rast, N. , Geol. Mag., 93, 191 (1956).
4. Rast, N. , in Controls of Metamorphism, edit. by Pitcher and Flinn, 89 (1965).