biogenic rock (bi-o-gen'-ic). An organic rock produced directly by the physiological activities of organisms, either plant or animal (Grabau, 1924, p.280); e.g. coral reefs, shelly limestone, pelagic ooze, coal, and peat. Cf: bioclastic rock; biolith. See also: phytogenic rock; zoogenic rock. Syn: biogenous rock; biogenetic rock.