gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1989.053.372.04 Mineralogy Niobian K-Ba-V Titanates from Micaceous Kimberlite, Star Mine, Orange Free State, South Africa Mitchell Roger H. Department of Geology, Lakehead University, Thunder Bay, Ontario P7B 5E1, Canada Meyer Henry O. A. Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana 47907, U.S.A. 9 1989 53 372 451 456 21 10 1988 3 1 1989 Copyright © 1987, The Mineralogical Society 1987 Abstract

Compositional data are presented for Nb-Ba-K-V titanates from micaceous kimberlite (Star mine, S. Africa). These data significantly extend the previously known range of solid solutions in naturally occurring members of the hollandite group. Two distinct suites of crystals occur. One is a suite of primary groundmass prismatic crystals that are Ba-K-V-rich and represent solid-solutions from the priderite series towards mannardite. The second suite consists of anhedral xenocrysts that are Ba-free. In this suite relatively Nb-rich varieties (>4.0% Nb2O5) represent solid-solution towards a niobian-bearing potassian analogue of mannardite, whereas relative Nb-poor (<3.0% Nb2O5) varieties are Nb-bearing vanadian priderites. These hollandite-group minerals have compositions that differ significantly from priderites found in lamproites.

 Keywods K-V-Ba titanate hollandite priderite kimberlite lamproites Star mine South Africa