An approximate method of incorporating quantum mechanics in calculating the electronic structure and related properties of a finite or periodic molecular model. This method differs from ab initio methods (i.e., a first principles method typically using a molecular orbital model) in that electron-electron interactions are approximated using functional mathematics in vector space.
Cf., molecular dynamics, quantum calculation

In geology, sedimentary deposits (or eluvium) derived by weathering, either with or without significant movement by the effects of gravity. In soil science, a soil horizon developed by the removal of soil material in suspension or solution (leaching) from a layer of a soil.

See hydrotalcite group.

The deviator stress is the difference between the major principal stress (σ₁) and minor principal stress (σ₃). The deviator stress usually defines the shear resistance of a clayey soil under triaxial shear loading.

See astrophyllite group.

Crystallization from a glass.

An obsolete term for a mixture of poorly crystalline phyllosilicates (1:1 and 2:1 types). When red, “deweylite” was called “eisengymnite”, and when found at Bare Hills, Maryland, USA, “deweylite” was called “gymnite”.

A species of the chlorite mineral group with a dioctahedral 2:1 layer and a trioctahedral interlayer (e.g., cookeite, sudoite).
Cf., trioctahedral chlorite, dioctahedral chlorite, dioctahedral sheet, trioctahedral sheet

A discredited term for a Si- and Fe-rich (clinochlore) chlorite.

The chemical, physical, and biological reactions incurred by sediment during burial, after initial accumulation. Diagenesis reactions may involve addition and removal of material, transformation by dissolution and recrystallization or replacement (authigenesis), or both, and phase changes (See Ostwald ripening). Weathering, incurred by sediments at the Earth’s surface under ambient conditions, is not part of the diagenesis process and represents the lower temperature limit of diagenesis. Hydrothermal, geothermal, and contact metamorphism are not considered part of the diagenesis process. The lowest grade of metamorphism limits the diagenesis process at high temperature and high pressure. In clay-rich rocks, the boundary between diagenesis and very low-grade metamorphism (anchizone is the transitional zone) has a Kübler index of 0.42 – 0.25 degrees two theta. Reduction of smectite interlayers in illite-smectite interstratifications to <10% is typical of the diagenetic zone-anchizone transformation (Merriman and Peacor, 1999). Weaver and Brockstra (1984) proposed a boundary between diagenesis and metamorphism as that point at which disordered illite (1Md) has been converted to ordered (1M, 3T or 2M1). “Retrograde” diagenesis was described by Nieto et al. (2005) as “fluid-mediated retrograde processes occurring under diagenetic conditions”. See anchizone, epizone, interstratification, Ostwald ripening, smectite-illite
Cf., Kübler index