Summary: The occurrence of cookeite, a di/trioctahedral chlorite of composition (Al_3·95Fe_0·02Mg_0·01Li_0·81)(Al_0·74Si_3·26)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.