In soil science, a coating is a layer of material, such as clay, organic material, mineral, non-crystalline material, etc., that partially or completely covers soil components (e.g., grains, voids). The term excludes b-fabrics.
Syn., cutan;
Cf., hypo-coating

Cohesion refers to the attractive forces (e.g., van der Waals, Coulombic) between two molecules of the same kind or two surfaces of similar material. For example, the shear strength of wet clayey soils involves both cohesive forces and friction. For wet clayey soils, the cohesion component of shear strength primarily results from the surface interactions between two clay particles (of similar composition and structure).
Cf., adhesion

An entity, either a solid or a liquid, dispersed in a medium. The entity must have one of its dimensions between 1 nm and 1 μm. A colloid dispersed in a liquid is also termed a “sol”. The term may be used also for the system as a whole. (after Lyklema 1991).
See gelling clay.

An obsolete term for roscoelite.

The relationship where a superstructure (or superlattice) is equal to an integral number of subcells (or sublattices). For example, some crystals of antigorite exist where the substructure a-cell dimension is 5.4 Å, and the superstructure of 32.4 Å, occurs from a wave-like curvature of the 1:1 along the [100] direction. Because the superstructure is 6 x 5.4 Å = 32.4 Å, the superstructure is commensurate with the substructure. In other crystals of antigorite, the superstructure may be related to the substructure by a non-integer number of subcells, and this is referred to as a non-commensurate relationship.

The relationship where a superstructure (or superlattice) is equal to an integral number of subcells (or sublattices). For example, some crystals of antigorite exist where the substructure a-cell dimension is 5.4 Å, and the superstructure of 32.4 Å (6 x 5.4 Å), occurs from a wave-like curvature of the 1:1 layers along the [100] direction. Because the superstructure is a multiple of the subcell dimension, the superstructure is commensurate with the substructure. In other crystals of antigorite, the superstructure may be related to the substructure by a non-integer number of subcells, and this is referred to as an incommensurate or non-commensurate relationship.

An obsolete term for muscovite.

a) In geology, compaction (= geological compaction) refers to the densification process caused by the gradual increase of overburden (weight) resulting from continuous deposition of sediments or by pressures from the movement of rock within the crust.

b) The geologic process of changing fine-grained sediment to consolidated rock, as in clay to shale.

c) In soils engineering, compaction is the artificial process to improve the engineering properties of a clay or soil by mechanical energy (e.g., vibration, static pressure). The clay or soil is usually partially saturated and thus contains mineral particles, air, and water. Compaction reduces the volume of air in the pores so that the dry density of the soil/clay increases. In practice, to maximize compaction, the water content is adjusted to a suitable value, called the optimal water content, so that the dry density approaches a maximum value.
See water, optimal content for compaction; consolidation, clay or soil

A complex is a dissolved or surface species that forms by association of a cation and either an anion or a neutral molecule, the latter anion or molecule is often referred to as a ligand. The complex may have an overall charge that is positive, negative, or neutral.

a) In soils engineering, compressibility is a mechanical property that defines the resistance of a water saturated clayey soil to compressional deformation under effective stress. The change in effective stress leads to the flow of porewater, resulting in the change in soil thickness or volume. Usually the compressibility of clay is measured by the one-dimensional (i.e., K0 condition) consolidation testing, and is defined by the compression index.

b) In geophysics, compressibility is defined as the reciprocal of the bulk modulus, which relates the change in volume of a material to the hydrostatic state of stress.
See also effective stress, void ratio, compression index