Vanadium in phyllosilicate ores: Occurrence, crystal chemistry, and leaching behavior

•We used TEM(-EELS) to examine vanadium occurrence in phyllosilicate ores.•Vanadium substitutes into crystal sites or forms discrete nanoscale V oxides.•The valence of crystallographic V averages 3.3 in V-chlorite, 3.8 in V-illite.•Leachability depends on the presence of nanoscale oxides, not oxidation state.•The results show the importance of nanoscopic phenomena in geometallurgy.