See hydrotalcite group.

See zeolite.

An obsolete term, possibly for nontronite or chlorite from Moravia.

A modulated 2:1 layer silicate with a continuous octahedral sheet and a modulated tetrahedral sheet (Eggleton, 1972). The tetrahedral sheet forms approximately hexagonal islands with 6-fold tetrahedral rings and island connectors are formed by an inverted single 6-fold ring with a near trigonal configuration. The islands are comprised of seven near- hexagonal tetrahedral 6-fold rings. The inverted rings also link adjacent layers across the interlayer. Trigonal rings also form by paired trigonal rings joined by the apical oxygen atoms along Z. The primarily ferrous form of stilpnomelane, often informally referred to as “ferrostilpnomelane”, has a structural formula of K₅Fe²⁺₄₈(Si₆₃Al₉)O₁₆₈(OH)₄₈ ^. 12H₂O, whereas the analogous “ferristilpnomelane” has a structural formula of K₅Fe³⁺₄₈(Si₆₃Al₉)O₂₁₆ ^. 36H₂O, although neither end-member forms have been found. The Mg-rich stilpnomelane is called lennilenapeite and the Mn-rich mineral is franklinphilite. Older literature incorrectly equates parsettensite as the Mn-rich version. Stilpnomelane occurs in many geological environments, including greenshist facies rocks, iron deposits, metal sulfide deposits, and in weathering profiles.

A mathematical expression that describes how a spherical particle, nominally less than 20 micrometers, settles in a viscous fluid. This equation is used in clay science, although clay particles are generally flat plates and not spherical, and thus fall at slower velocities than spheres of equal density as calculated using Stokes’ law.
Cf., equivalent spherical diameter

An obsolete local name for a mixture of smectite and a Ca-rich phase(?), or Ca-montmorillonite, from Stolpen, Saxony, Germany.

Plural of stratum.
See stratum.

A layer of sediment or sedimentary rock (pl. strata).

A process describing how a clay or soil experiences different loading or unloading conditions in the past. The maximum past effective stress is generally determined experimentally by measurement of one-dimensional elastic and plastic deformation that occurs during consolidation, or one-dimensional stress-strain compression curves, or from known events, such as specific sea-level changes, groundwater table fluctuations, etc. Usually, stress history is used in combination with overconsolidation or overconsolidation ratio.
Cf., overconsolidation, overconsolidation ratio

The graphical representation of the loading or unloading processes that a clay has experienced in a triaxial stress condition. The stress path is usually plotted in the coordinate system of mean effective stress and shear stress. The mean effective stress is the average of the vertical and horizontal effective normal stresses, whereas the shear stress is the difference between the vertical and horizontal effective normal stresses.