A chemical substance formed from the bonding of compounds to metallic ions. Intense podzolization in humic-iron podzols is linked to mineral chelation (Dearing et al. (2001) Geophys. J. Int. 144). See Siebner-Freibach et al. (2004) Soil Sci. Soc. Am. J. 68 on the interaction of iron chelating agents with clay minerals. The leaching out of chelates is cheluviation. Chelation, the formation of chelates, is a process whereby relatively insoluble materials may become soluble, and be released into the soil, increasing nutrient availability to plants.