Shiprock, an example of a volcanic neck, is composed of fractured volcanic breccia and black dikes of igneous rock called minette, a type of lamprophyre. It is the erosional remnant of the throat of a volcano, and the volcanic breccia formed in a diatreme. The rock probably was originally formed 2,500–3,000 feet (750–1,000 meters) below the Earth's surface, but it was exposed after millions of