See hydrotalcite group.

A mining term, now obsolete and not used in the geologic literature, that refers to the palygorskite-sepiolite group (Brindley and Pedro, 1970; Bailey et al., 1971a).

A term used in industry referring to palygorskite and/or sepiolite. This term should not be used in the scientific literature.

A poorly defined material, found as infillings in cavities in basic igneous rocks, possibly an altered chlorite or a chlorite + smectite mixture.

Humic acids are chemically diverse acids that result from the decay of plants and microorganisms in some soils, sediments, peats, coals, shales, and surface waters. These acids are insoluble in water at low pH, can be precipitated at a pH = 1, and extracted from solids using a strong base, such as NaOH or KOH.
Cf., fulvic acid, humic substances, humification, humin

The general term that includes (large-molecule) humic acid, fulvic acid, and humin, all of which form the natural organic matter (NOM) of some soils, sediments, peats, coals, and shales. Non-humic materials, such as amino acids, peptides, and sugars, may also be present in some soils as NOM. Humic substances impart the brown or black color to some soils and surface waters as well as biological productivity. Humic substances do not further biodegrade readily. Humic substances are quite heterogeneous and complex, and studies often provide average properties and chemical compositions. However, Lehmann and Kleber (2015) have suggested that large-molecule humic substances do not actually exist in soils, and NOM form from a progressive breakdown of organic compounds.
Cf., fulvic acid, humic acid, humification, humin

Amount of water vapor contained in the atmosphere. “Relative humidity” is the ratio, usually expressed as a percent, of the amount of water vapor in the atmosphere to the maximum water vapor in the atmosphere possible at a specific temperature. “Absolute humidity” is the mass of water vapor per unit of dry air. When unspecified, reference is usually being made to relative humidity.

A process involving the decay of plant and microorganism matter to produce thenatural organic matter (NOM) as found in some soils, sediments, peats, coals, and shales. Plantlignin, related transformation phases, polysaccharides, melanin, cutin, proteins, lipids, nucleic acids, and fine char particles, are materials involved in humification.
Cf., fulvic acid, humic acid, humic substances, humin

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

See opal.