Fragments of igneous rocks of between 4 and 32mm in size. Related Articles: Geo Junkets (Part 2): New Zealand, North IslandAlong the Chain of Craters Road, Big Island, Hawaii (Part 1)Along the Chain of Craters Road, Big Island, Hawaii (Part 4)An excursion to Krakatau (Part 1)Volcanoes in Garrotxa, Spain« Back to Glossary Index