Here's why:
* Composite cones are built up from layers of lava flows and pyroclastic material (ash, cinders, and blocks).
* Andesite is an intermediate extrusive igneous rock, meaning it forms from the cooling and solidification of lava on the Earth's surface.
* The magma that feeds stratovolcanoes typically has an intermediate composition, resulting in the production of andesite.
While other rock types can be found in stratovolcanoes, andesite is the most common due to the typical magma composition involved in their formation.
