Holmite

An obsolete term for clintonite.

Homogeneous nucleation

Direct precipitation of a solid phase within a solution and not on the surface of another phase.

Homogeneous reaction

A reaction that involves only one physical state (i.e., solid, liquid, gas).
Cf., heterogeneous reaction

Honessite
Honeycomb microfabric
Hormite

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).

Hormite

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

Hullite

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

Humic acid

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