An obsolete term for a chocolate-brown saponite-rich material from Cathkin Hills, Scotland.

A process whereby a cation bound to a site on a surface is replaced by a cation from a solution. In both phyllosilicates and zeolites, the cation may be located on either external surfaces or internal surfaces; thus, the full process may involve cations from the interior that diffuse toward the surface, and are in turn replaced by cations from the solution which diffuse inward. The term differs from solid-state diffusion primarily by time scale, where cation exchange occurs relatively quickly and solid-state diffusion requires a much longer period.

The surface charge of a phyllosilicate that relates to a net negative imbalance of charges originating from the silicate layers of the mineral. The magnitude or capacity for exchange (see cation exchange) is related to the size of the net negative charge that occurs within the (commonly, 2:1) layer. Cation exchange occurs where a solution containing the exchangeable cations forms a concentration gradient with the exchangeable cation of the mineral. The charge on the mineral is operationally related to the magnitude of the number of exchanged cations. The net negative charge is considered “permanent charge”, and this originates from either (or both) tetrahedral or octahedral solid solutions, changes in oxidation state of constituent cations in the layer, substitutions involving anions [e.g., O2- for (OH)-], and other possible factors.

A poorly defined material, possibly muscovite and pyrophyllite.

A dioctahedral member of the true mica group. The ideal end-member formula is KFe³⁺(Mg, Fe²⁺)□Si₄O₁₀(OH)₂, where □ = vacancy. The typical range in composition is: ^viR²⁺/(^viR²⁺ + ^viR³⁺) ≥ 0.25, ^viAl/(^viAl + ^viFe³⁺) < 0.5, Mg/(Mg + ^viFe²⁺) > 0.5 (Rieder et al., 1998). Celadonite is commonly an alteration product of pyroxenes and other Fe,Mg minerals found in basalts either during low-grade metamorphism or hydrothermal activity.

The cell parameters define the edges of the smallest repeating parallelepiped of the atomic arrangement of a crystal. Values of the cell parameters are usually given as three scalar cell lengths (a, b, c) and three angles alpha (between b and c), beta (between a and c), and gamma (between a and b).
Cf., unit cell.

A Ba-dominated feldspar mineral, Ba(Si₂Al₂)O₈.
Cf., alkali feldspar, feldspar, plagioclase feldspar

A temperature scale based on a degree, ^oC, where the freezing point of pure water at one standard atmosphere is arbitrarily set at 0 and the boiling point at 100^oC. One Celsius degree equals one Kelvin. 0^oC equals 273.15 K.
Syn., centigrade
Cf., Fahrenheit, Kelvin

A solid binding agent between grains/particles of natural rocks (e.g., sandstones), soils, or synthetic construction materials (e.g., geopolymer, Portland cement, concrete).
Cf., binder

The process of forming the mineral matter that binds particles of a sedimentary rock together. The cementation process usually involves a chemical precipitate from solutions that may originate within the sediment or from outside the sediment body. The mineral matter is called “cement”. In general terms, the stiffness and strength of the sediment or soil is increased by the mineral matter. The mineral matter is often clay minerals, oxides, silica, carbonates, sulfides and others.