gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/002646199548303 Mn- and F-bearing Rasvumite in Natrocarbonatite at Oldoinyo Lengai Volcano, Tanzania Jago B. C. Lakefield Research Ltd. Postal Bag 4300, 185 Concession Street, Lakefield, Ontario, Canada K0L 2H0 Gittins J. Department of Geology, University of Toronto, Toronto, Canada M5S 3B1 2 1999 63 1 53 55 23 2 1998 12 3 1998 Copyright © 1999, The Mineralogical Society 1999 Abstract

Several K-Fe sulphide minerals have been described from natrocarbonatite lavas erupted from the Tanzanian volcano Oldoinyo Lengai but uncertainty remains about their exact identity. They do not appear to be any of the established K-Fe sulphides according to Dawson et al. (1995) and Mitchell (1997). Here, we describe yet another variant which is a Mn- and F-bearing variety of rasvumite. It appears to have formed by reaction of Fe alabandite grains with natrocarbonatite magma and occurs as minute rims on the alabandite. Its formula is: (K0.94Na0.06)(Fe1.91Mn0.13Ca0.01Sr0.01)(S2.06F0.24Cl0.04).

 Keywords K-Fe sulphide natrocarbonatite Oldoinyo Lengai rasvumite Tanzania manganese fluorine