Allomelanins found in soils, coals, and peat, resulting from the decompn of organic matter, particularly dead plants. Consists of a mixture of complex macromolecules having polymeric phenolic structures with the ability to chelate with metals, esp iron. Review: R. A. Nicolaus, Melanins (Hermann, Paris, 1968) pp 147-153; W. Flaig et al. in Soil Components vol. 1, J. E. Gieseking, Ed. (Springer, New York, 1975) pp 1-211.