Fluor-elbaite, lepidolite and Ta–Nb oxides from a pegmatite of the 3000 Ma Sinceni Pluton, Swaziland. Evidence for lithium–cesium–tantalum (LCT) pegmatites in the Mesoarchean
Mineral evolution is concerned with the timing of mineral occurrences, such as the earliest reported occurrences in the geologic record. Minerals containing essential Li have not been reported from rocks older than ca. 3000 Ma, thus the lithian tourmaline (fluor-elbaite) and mica (lepidolite) assemblage from a pegmatite near Zishineni associated with the ca. 3000 Ma Sinceni Pluton presents unusual interest. Fluor-elbaite (0.75-0.98 F per formula unit) forms green crystals up to 50 trim long. Spindle stage measurements give omega = 1.652(1), epsilon = 1.627(1) (589.3 nm).