Tephra's air-fall material produced by a volcanic eruption regardless of composition or fragment size. Tephra's typically rhyolitic in composition, as most explosive volcanoes are the product of the more viscous felsic or high silica magmas. Volcanologists also refer to airborne fragments as pyroclasts. These pyroclasts come mainly from pyroclastic flows which in turn (with cool air) turn into rock or pumice. Once clasts have fallen to the ground they remain as tephra unless hot enough to fuse… (More on Pyroclast)