The condition where the voids within a material are filled with water. The degree of water saturation is the ratio of pore water volume to the total pore volume, usually expressed as a percentage.

A measure of how far from equilibrium a solution is with respect to a given mineral. The saturation index, SI, is determined from SI = Q/K_eq, where Q is the reaction quotient and K_eq is the equilibrium constant, often given as log₁₀ (Q/K_eq). When SI = 0, then the system (water + mineral) is at equilibrium, if SI < 0, the mineral will dissolve, and if SI > 0, then the mineral will precipitate.

The Zn²⁺-rich trioctahedral smectite (Ross, 1946) with the ideal composition of (M⁺_x ^. nH₂O)Zn₃(Si_4-xAl_x)O₁₀(OH)₂ where M is the exchangeable cation in the interlayer (univalent example given here), x is the number of substitutions for Si by Al in the tetrahedral sites, and n is variable. Zn content may vary commonly from 1.48 to 2.89 atoms per O₁₀(OH)₂, and the octahedral site may contain vacancies. Mg, Fe³⁺, and Al are known to replace Zn (Faust, 1951).

An obsolete term for lepidolite.

See pyrosmalite.

An obsolete term for muscovite.

An obsolete term for what is believed to be a mixture of opal and allophane.

An obsolete term, probably a nickel-bearing chlorite.

An obsolete term for lepidolite.

Symmetry involving a rotation about an axis followed by a translation parallel to the axis. The rotations correspond to a 2-, 3-, 4- or 6-fold axis and requires a translation following each rotation. The symbol for a screw axis is n_m, where n is the rotation component and m/n is the translation component. For example, in a 4₁ screw axis, the translation is 1/4 of a unit cell and the rotation corresponds to a 4-fold axis. Thus, symmetry consistent with a 4₁ screw axis is generated by a 90^o rotation followed by a 1/4 cell translation, with the process continuing until closure.
Cf., rotation symmetry, rotoinversion axis, symmetry, unit cell