Humin occurs as a result of the decay of plants and microorganisms in some soils, sediments, peats, coals, and shales, but not aquatic waters (humin is not soluble in water). Humin may be formed also in the dehydration of some sugars. Humin, along with fulvic acid and humic acid, is a humic substance. However, humin cannot be extracted from humic substances with either a strong base or a strong acid, whereas fulvic or humic acids can be extracted.
Cf., fulvic acid, humic acid, humic substances, humification