A now-obsolete term first used by Schultz (1969) to define montmorillonite samples on the basis of chemical and thermal analysis with a total net layer charge of -0.85 to -1.20 per unit cell [O₂₀(OH)₄], with a layer-charge contribution from tetrahedral substitutions of between -0.15 to -0.50, although exceptions were noted. See Tatatila- type montmorillonite. Terms used in this obsolete classification are: Wyoming-type, Otay-type, Chambers-type, Tatatila-type, beidellite-type (ideal and non-ideal), and non-ideal montmorillonite. Current nomenclature for montmorillonite is that it is an Al-rich, dioctahedral smectite with an ideal structural formula of (Al_3.15Mg_0.85)Si₈O₂₀(OH)₄X_0.85.nH₂O with layer charge from primarily octahedral substitutions of Mg.
See also Part 2 of the Glossary.

The Fe-rich member of the chlorite group with a composition of ideally Fe²⁺₅Al(Si₃Al)O₁₀(OH)₈. There may be considerable substitutions of Mg, Fe³⁺, and Al for Fe²⁺. The common polytype is the IIb form, a one-layer form. Chamosite is an important constituent in oolitic and sedimentary iron formations and may be found as grain coatings in sandstones.
See chlorite

A ceramic raw material with a high silica and alumina composition typically produced by firing selected “fire clays” to high temperatures before grinding and screening to specific particle sizes. Chamotte is usually porous with a low bulk density.
Cf., fire clay

The state in which the rates of forward and reverse reactions are equal; thus, at equilibrium, the change in free energy ΔG = 0.

The study of reaction rates and mechanisms.

A thermodynamic term for the change of the Gibbs free energy of a system with respect to the change in the number of moles of a specific constituent. Chemical potential is equivalent to partial molar enthalpy, partial molar free energy, partial molar internal energy, and partial molar Helmholtz function. The chemical potential may be described as a force of energy change caused by a change of composition.

The process whereby chemical reactions alter or break down minerals or rocks under the influence of meteoric water at or near the Earth’s surface. Specific chemical weathering reactions include, but are not limited to, dissolution (congruent or incongruent), oxidation, hydrolysis, cation exchange, complexation, hydration, carbonation, and sulfation. Chemical weathering may be biologically influenced.
See weathering, physical weathering

A clay treated with chemical substances to improve properties or to increase reactivity. Chemical activation includes alkaline and acid activation.
Cf., acid activated clay, alkaline activated clay

A dioctahedral member of the brittle mica group. The end-member formula is: BaV₂□Al₂Si₂O₁₀(OH)₂, where □ = vacancy, but known samples are deficient in Ba (or K). Typical site substitutions primarily occur in the octahedral site by Al, Fe, and/or Mg. The 2M₁ polytype is the common polytype. Chernykhite is only known from southern Kazakhstan.
Cf., roscoelite

Chert is a rock term to describe an authigenic species of SiO₂ which consists of nanoscale intergrowths of quartz and moganite, a metastable SiO₂ polymorph (Heaney, 1994).
Cf., moganite, quartz