The number of reacting molecules, atoms, or ions in a single-step chemical reaction. For example, a unimolecular reaction may involve radioactive decay of a single atom, or one molecule producing other molecules. A bimolecular reaction involves the collision and reaction between two molecules, atoms or ions to form other products.
Cf., Transition State Theory

Between 2:1 layers of a phyllosilicate, a monolayer involves an arrangement within the interlayer of one single plane of H₂O molecules around interlayer cations (= hydration shell). Although the plane is only approximate, the spacing seems to suggest a planar feature. Because the H₂O molecules are in planar coordination around the cation, the spacing appears as an H₂O plane or “layer”.
Cf., bilayer; bilayer, phyllosilicate

An obsolete term for ferrian annite.

A trioctahedral member of the true mica group. The ideal formula is KFe²⁺_1.5Mn²⁺_0.5Mg_0.5 v_0.5Si₄O₁₀F₂ ( where v = vacancy) and this formula does not represent an end-member species. A typical range in composition is: Fe²⁺ > Mn²⁺ + Mg (Rieder et al., 1998). Robert and Maury (1979) originally described montdorite-1M from a peralkaline rhyolite of the Mont-Dore massif, France, in space group C2/m.

A classical molecular simulation approach, based on the Metropolis Monte Carlo algorithm, for calculating ensemble averages of structural properties. The model system evolves based on random moves (e.g., atom or molecular translation, system volume) that are accepted or rejected using a Boltzmann algorithm. System constraints (e.g., constant volume, temperature, pressure) usually correspond to a thermodynamic ensemble.
Cf., force field, Grand Canonical Monte Carlo simulation, molecular dynamics, quantum calculation

A dioctahedral member of the smectite group of minerals. A representative formula is: R0.33(Al1.67Mg0.33)Si4O10(OH)2^.nH2O. Montmorillonite is Al-rich and capable of cation exchange (the exchangeable cation is depicted as R in the formula, n is a rational number, not necessarily an integer). The origin of the layer charge is in the octahedral sheet. In older literature, montmorillonite was used as a group name, which is replaced by the group name, smectite.
See also Part 1 of the Glossary for terms that are obsolete: Wyoming-type, Otay-type, Chambers-type, Tatatila-type, beidellite-type (ideal and non-ideal), and non-ideal montmorillonite.
Cf., smectite

Old group name superceded by smectite. See also Part 2 of the Glossary.
Cf., smectite

See zeolite.

An obsolete term for nontronite from Morenci, Arizona, USA.

In soil science, the geometry and surface topology of a soil particle. The term may also be used as a study of soil horizons and soil properties.