Electron- and ion-microprobe analyses, and genetic inferences of tourmalines of the foitite-schorl solid solution, Elba Island (Italy)

The Li, B and H contents of foitite were investigated for the first time by means of secondary ion mass spectrometry (SIMS). The studied foitite occurs in the pockets of Elba pegmatites, not only as previously described, acicular and fibrous crystals, but also as black-violet, fibrous-to-prismatic overgrowth at the terminations of elbaitic, polychrome tourmalines. A variety of compositions, belonging to the foitite-schorl solid solution, were recognised. Foititic compositions observed as overgrowths of polychrome crystals are associated with the crystallisation of zeolites at the beginning of a zeolite hydrothermal stage. Morphologically similar overgrowths, but richer of schorlitic component. are associated with later hydrothermal circulation along late-stage fractures that crosscut the pegmatites and the host monzogranite.