Wall rock is the rock that constitutes the wall of an area undergoing geologic activity. Examples are the rock along the neck of avolcano, on the edge of apluton that is being emplaced, along a fault plane, enclosing a mineral deposit, or where avein ordike is being emplaced.
In volcanoes, wall rock can often become broken off the wall and incorporated into the eruptedvolcanic rock asxenoliths. These xenoliths are important togeologists because they can come from rock units that are otherwise not exposed at the Earth's surface.
