In soil science, shear strength is a measure of the ability of a soil to resist failure along a surface when subjected to a critical combination of shearing and normal forces. The shear strength has cohesive (commonly related to clay content) and frictional components (related to the interaction of angular particles). Pore water pressures also play a role.

For phyllosilicates, a sheet refers to corner-sharing linkages of tetrahedral coordination polyhedra (i.e., tetrahedral sheet) or edge-sharing linkages of octahedral coordination polyhedra (i.e., octahedral sheet). For a tetrahedral sheet, three corners of a tetrahedron are shared with other tetrahedra and the fourth corner may point in any direction.
See Guggenheim et al. (2006) and references therein.
Cf., tetrahedral sheet, octahedral sheet, layer

A discredited name for a trioctahedral Mg-rich (Fe-poor), Si-poor chlorite.
See chlorite

An obsolete varietal term for ferroan muscovite, ferroan illite.

A trioctahedral member of the mica group characterized by Na occurring in the octahedral sheet in the M1 site. The ideal chemical composition is K(NaMg₂)Si₄O₁₀F₂. It is found in the apatite mine, Kukisvumchorr Mountain, Khibiny massif, Kola Peninsula, Russia, as a late hydrothermal phase in a small hyperalkaline pegmatite and it forms in the 1M polytype (Pekov et al., 2003).

A ceramics industry term describing the reduction in size of a solid body relating to dehydration during initial drying and/or devolatilization during the final firing stage of making the ceramic body (e.g., bricks, whiteware, sanitary articles, porcelain, and stoneware).

The shrinkage limit is the boundary water content that separates the semi-solid state of clay from its solid state in the classification of a fine-grained soil. At this water content, further drying of the clay does not cause a change in its total volume (i.e., no shrinkage). However, if the water content is greater than the shrinkage limit, drying causes the clay to shrink. The shrinkage limit is one of the three Atterberg Limits (i.e., liquid, plastic, and shrinkage limits).
Cf., Atterberg Limits

International System (of units); Système International d’Unités.

An obsolete term for lepidolite.

A trioctahedral member of the true mica group. The ideal end-member formula is KFe²⁺₂Al(Al₂Si₂)O₁₀(OH)₂, although such a chemical composition has not been reported. The siderophyllite composition is useful to describe solid solution series where there are Fe²⁺ + Al substitutions, whereas eastonite components involve Mg + Al substitutions. A Tschermak type substitution, which is common in some biotites, involves Al_oct + Al_tet = R²⁺ + Si.
Cf., eastonite