Andesitic refers to a type of volcanic rock that is intermediate in composition between basalt and rhyolite. It is primarily composed of plagioclase feldspar, along with smaller amounts of biotite, hornblende, and other minerals. This rock is typically found in volcanic arcs, which are formed at convergent plate boundaries where an oceanic plate subducts beneath a continental plate. The name "andesitic" comes from the Andes Mountains, where this type of rock is commonly found. Andesitic lava tends to be more viscous than basaltic lava, leading to explosive volcanic eruptions. This characteristic makes andesitic volcanoes, such as Mount St. Helens and Mount Fuji, particularly hazardous.