The type of rock that primarily makes up the Appalachian Mountains is metamorphic rock .

The Appalachians were formed through geological processes that involved the alteration of pre-existing rocks due to heat and pressure over millions of years. This metamorphic activity has led to the formation of various rock types, including schist, gneiss, and quartzite, which are common in the region. While sedimentary rocks are also present, particularly in the valley areas, the dominant composition of the mountain ranges reflects their complex geological history. This diverse rock formation contributes to the rich ecosystems and unique landscapes found throughout the Appalachian region.