Perlites and obsidians of various composition were examined in this paper to determine the mobility of their minor and rare earth elements. Perlite samples from four deposits were collected from Trachilas and Provatas areas in Miles Island, the Kefalos area in Kos-Island and Kimolos Island. The analyses of Perlites show similar mineralogical features but distinguishable differentiation in their chemical composition. The main chemical variation between the perlites is present in alkalis, Ba and the rare earth elements (REE). The differences on the chemical composition indicate individual parent magmas, which produced the various perlites. The REE composition of obsidian provides evidence for the evolution of perlites from the hydration of obsidian.