A monolith is a geological feature such as a mountain, consisting of a single massive stone or rock, or a single piece of rock placed as, or within, a monument. Erosion usually exposes the geological formations, which are most often made of very hard and solid metamorphic or igneous rock. The word derives from the Latin word monolithus from the Greek word μονόλιθος (monolithos), derived from μόνος ("one" or "single") and λίθος ("stone").