is part of humus, and is a mixture of amorphous, polydispersed colloidal, yellow to brown-black organic substances. They are hydrophyllic, and high in molecular weights, which range from a few hundreds to thousands of daltons. They have originated from the decomposed, non-humic, organic fraction by "new formation," called humification. [Tan, Kim H. Humic matter in soil and the environment. Principles and controversies; 2003; Marcel Dekker.]