gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1976.040.315.11 Cookeite and Diaspore in the Back Creek Pyrophyllite Deposit Near Pambula, New South Wales Loughnan F. C. School of Applied Geology, University of New South Wales, Kensington, N.S.W., Australia Steggles K. R. Australian Industrial Refractories Ltd., Mayfield, N.S.W., Australia 9 1976 40 315 765 772 15 10 1975 Copyright © 1976, The Mineralogical Society 1976 Summary

The occurrence of cookeite, a di/trioctahedral chlorite of composition (Al3·95Fe0·02Mg0·01Li0·81)(Al0·74Si3·26)O10(OH)8, in the Back Creek pyrophyllite deposit near Pambula is described. The mineral is restricted to a relatively narrow zone near the centre of the deposit and although diaspore is also present in this zone the two have not been found in intimate association, it is concluded that the introduction of lithium has been the principal factor controlling development of the cookeite.