"Leonardite" and "humate" are terms to describe a variety of naturally occurring lithologies with high humic acid content, including weathered (oxidized) lignite, sub-bituminous coal and a variety of carbonaceous rocks, such as mudstones, shales and claystones. These raw materials are used mainly as soil conditioners but they also have applications in wood stains, drilling fluid additives and as a binder in iron pelletiing. To be of economic interest, raw humate or leonardite should contain a sufficient concentration of humic acid.