The author visited in the autumn of 1950 the Lipari Islands to the north of Sicily in order to study especially the acid volcanic products of this region. The journey was limited to the islands Lipari and Vulcano which together with the quite insignificant island Basiluzzo are the only ones having acid volcanics. On Vulcano there is a still active volcano, the Fossa, from which in recent time obsidianio lava flows have extruded. The paper is a popular deseription of the geology of the islands.