Leonardite is a low rank coal derived from prehistoric plant matter. It is found as outcropping of lignite deposits, usually very close to the surface. It differs from lignite by its high oxidation degree and the higher carboxy groups. Due to the large amount of living bacteria, Leonardite was formed instead of coal in certain sedimentation layers. Being a highly decomposed compressed natural organic humus that has been further processed by microbial activity, Leonardite has a high humic acid content which is one of the most bio-chemically active elements. The composition of Leonardite will show on average organic matter 75-90%, aluminum, nitrogen, phosphorus, potassium, sulfur, iron and calcium less than 1%. Since Leonardite is a naturally mined material, the composition of Leonardite differs slightly throughout the deposit and from deposit to deposit.
The sodium, potassium and ammonium salts of humic acids derived from Leonardite through alkaline extraction are referred to as humates. While sodium humates have usage in various industries such as printing inks, potassium humates are used extensively in agriculture. Only potassium humates are approved for organic agriculture by OMRI (Organic Materials Review Institute).
Humic acids are complex organic molecules formed by the breakdown of organic matter in soil. They are the main fraction, the biological center, of natural humic matter. It is the collective term for humic acid and fulvic acid.