Leonardite 
Naturally oxidised lignite, brown to black, mined near the surface in coal mines; one of the main sources of humic and fulvic acids.
Characteristics
- Formed by the slow oxidation of lignite: an intermediate stage between peat and coal.
- Analysis published by Ecoagro (Mexico): organic matter 61.5%, organic carbon 35.67%, total humic extract 37.7% (humic acids 15%, fulvic 22.7%), pH 5.85, C/N ratio 37.5, ash 34.5%.
- Advantages put forward by the maker: better soil structure, aeration and porosity, greater water retention, high cation exchange capacity, stimulation of microbial activity and better nutrient uptake.
- It is the raw material of most commercial humic acids, obtained by alkaline extraction.
Role in the preparation: Organic soil amendment, alone or mixed with compost, bokashi or rock dust; the maker gives 300 kg/ha.
Caution: Ask for a batch analysis (heavy metals, ash). Dusty: wear a mask when handling.
Sources: Ecoagro (Guamúchil, Sinaloa, México) — ficha técnica «Leonardita, ácidos húmicos y fúlvicos» · USDA AMS — Oxidized lignite / humic acids, Technical Evaluation Report (2012) · Wikipedia — Leonardite
Documentary information: this is neither a recommendation for use nor a plant-protection or veterinary claim. Check your country's regulations before any use.