Mineral concretion formed anywhere in the gastrointestinal tract. Enteroliths frequently consist of the mineral struvite (ammonium magnesium phosphate) that is deposited in concentric layers around a nidus, usually a pebble or a sand corn.

Equine enterolithiasis is observed frequently in the southwestern regions of the USA, mainly in California. Proposed etiologic factors for enterolith formation include high mineral content (magnesium) of water supply and diet (alfalfa hay) and an alkaline pH within the large colon promoting excessive release of ammonium from a protein rich diet (e.g., alfalfa hay).