Abstract Detailed electron-microprobe analyses of zonal trends in the spinel mineral group in kimberlites show that the early formed spinels are either highly enriched in the series picrochromite-chromite, or alternatively in the series MgAl2O4FeAl2O4; in both compositional types, progressive enrichment trends induced by solid-liquid or solid-gas reaction result in an overall increase in Fe + Ti, and a specific increase in Fe+3. The range of primary spinel compositions previously reported in kimberlites has been widened towards higher ratios of Al Cr . Homogeneous and oscillatory zoned spinels, skeletal and subhedral, are present in garnet kelyphitic reaction mantles. The unique characterization of kimberlitic spinels is in high MgO, FeO(Fe2O3) and TiO2 contents; whereas kimberlitic ilmenites are fingerprinted by high MgO, intermediate Fe2O3 contents, and by the presence of Cr2O3. Accessory minerals identified are Fe, FeNi, pyrite, pyrrhotite, pentlandite and chalcopyrite. Compositional data on two new minerals are presented and the first occurrence of terrestrial armalcolite is reported.