Humic substances are a colloid and coat soil particles, acting as a cushion and an interface between the dead mineral of the soil and the living plant root. Without this coating the soil can become a gummy mass. With it, the soil becomes friable and granular in structure. These humic substances possess a high cation exchange capacity, which means that it helps hold the essential cation elements ammonium, potassium, calcium, et cetera. In the absence of the clay or humic colloid, the cations are either lost by fixation or leaching, and thereby they are lost to the plant root.
Humic substances are very complex and are different depending on conditions and minerals available.
In addition to the cations, the deposit contains very high levels of trace minerals in an organic form. That may be one of the keys to its beneficial properties. Plants and animals can absorb these elements readily in this humic form because it has already been assimilated and chelated by the microorganism which utilized parent organic matter eons ago. Trace elements are required in only minute amounts in this form. I know of no other natural product that has this mineral-organic makeup.