Common in certain horse populations, enteroliths are mineral-based stones that gradually form in the large colon over several years. Composed primarily of struvite (magnesium ammonium phosphate), these stones develop around a central foreign object—such as a pebble, hair, baling twine, metal, or rubber—and often take on round, triangular, or flat shapes. Although they may remain undetected for long periods, enteroliths can shift and obstruct the intestinal tract, leading to episodes of colic in horses.