The breakdown of large soil or clay material aggregates (typically >2-5 mm) or fine-grained sedimentary rock rich in clay into small particles (<0.25 mm) when rapidly immersed in water. Slaking occurs when aggregates are not sufficiently strong to withstand internal stresses caused by rapid water uptake into the pore structure or fabric of the aggregate. Internal stresses result from differential swelling of clay particles, trapped and escaping air from pores, rapid release of heat during wetting, and the mechanical action of moving water. Slaking is influenced by the presence of smectitic clays (either smectite, especially Na-montmorillonite, or interstratified clay with a smectite component) that shrink when dry and swell when wet. Organic matter often reduces slaking by binding the particles or by slowing the rate of surface wetting.

A group name for platy phyllosilicates of 2:1 layer and a layer charge of ~ -0.2 to -0.6 per formula unit. Generally for natural samples, the d(001) spacing is approximately 14.4-15.6 Å, although other spacing may occur depending on H₂O retention and interlayer occupancy. The group is further divided into subgroups that are either trioctahedral (according to Bailey, 1980, this subgroup name is “saponite”) or dioctahedral (subgroup name of “montmorillonite”, according to Bailey, 1980), and these subgroups are further divided into mineral species based on chemical composition. Guggenheim et al. (2006) did not give subgroup names. Smectite minerals have large specific surface areas (10 – 700 m²/g) and exhibit a high expansion (swelling) capability in the presence of H₂O. Smectite and vermiculite minerals are often referred to as “swelling” or “expandable” clay minerals. Cation-exchange capacity or solvation of polar molecules is large. Smectite is commonly a primary constituent of bentonite (see bentonite forrespective genesis information) and pelitic sediments (e.g., shales) and occurs in soils. Prior to circa 1975, the smectite group was called the montmorillonite-saponite group, but this nomenclature was abandoned because of the confusion between the use of the same name for both a group and species. Very early (Kerr and Hamilton, 1949), smectite was used as a term for fuller’s earth (initially), montmorillonite, and certain bentonitic clay deposits.
See “group names”.

The group name for the 2:1 phyllosilicate minerals with a net negative layer charge between approximately -0.2 and -0.6 per formula unit on the layer. A generalized formula is X_0.3Y_2-3Z₄O₁₀(OH)₂ ^. nH₂O, where X is the exchangeable cation (e.g., Ca/2, Na, K, Mg/2), Y is a small to medium size cation (e.g., Al, Cr³⁺, Fe²⁺, Fe³⁺, Li, Mg, Ni, Zn), Z = Si, Al, and n is a rational number, not necessarily an integer). Smectite is often characterized by solvating polar organic molecules into the interlayer causing pronounced swelling between the layers [perpendicular to the (001) plane]. Smectite is commonly referred to as a “swelling clay”, as is vermiculite. The rock term, bentonite, refers to a smectite-rich material. See further discussion under Part 1, smectite and obsolete terms: Wyoming-type, Otay-type, Chambers-type, Tatatila-type, beidellite-type (ideal and non-ideal), and non-ideal montmorillonite.
Cf., bentonite, swelling clay, beidellite, hectorite, montmorillonite, nontronite, saponite, sauconite, stevensite, swinefordite, volkonskoite, yakhontovite

The conversion of smectite to illite involving a significant change in the chemical composition of the 2:1 layer from a smectite-like composition to an illite-like composition. The resulting net negative charge on the layer must become sufficiently large to preferentially fix potassium or other large cations and cause dehydration of the interlayer. The process of conversion may be one of apparent solid-state transformation or mostly in the solid state or apparent neoformation via a solution. The degree of conversion may be useful to understand crystallization parameters during burial diagenesis or metamorphism (e.g., Hower et al. (1976) or hydrothermal activity (e.g., Inoue et al., 1987).
Cf., illite/smectite

An obsolete varietal term for glauconite.

An obsolete term for calcic paragonite, calcic ephesite.

An obsolete term for paragonite.

An obsolete term for brammallite.

An obsolete term for aspidolite.

In soil science, plasma refers to fine-grained (too fine to resolve individual constituents by visible-light microscopy) crystalline or amorphous materials in soils, which includes saprolites.
Syn. pedoplasma
See saprolite, clay groundmass