A phacolith is a concordant, lens-shaped plutonic body that occupies the crests of anticlines or troughs of synclines, conforming to the folded structure. It differs from a laccolith (concordant, dome-shaped, arches overlying strata) and a lopolith (concordant, funnel- or saucer-shaped, depresses underlying strata). Phacoliths are fed by conduits from below and are relatively rare compared to laccoliths.