A group name for platy phyllosilicates of 1:1 layer and a layer charge of ~ 0 per formula unit. Generally, the d(001) spacing is approximately 7.1-7.3 Å. The group is further divided into subgroups that are either trioctahedral (serpentine) or dioctahedral (kaolin), and these subgroups are further divided into mineral species based on chemical composition. The 1:1 layers are bonded by long hydrogen bonds (~2.9 Å) and possible coulombic interactions between the octahedral sheets of one layer and the tetrahedral sheet of the adjacent layer.
See “group names”.
A general term used to describe randomly interstratified layers (= “mixed layers”) of two types: 1:1 layers (i.e., serpentine-like, 7-Å spacing) and 2:1 layers + interlayer (i.e., chlorite-like, 14-Å spacing). The “random” (non-periodic) aspect is important because such a structure will not produce basal X-ray reflections expected by the Bragg equation. A non-periodic structure, i.e., a structure with random interstratifications, is not defined as a mineral (and cannot be given a mineral name). Serpentine-chlorite structures form most commonly under diagenetic conditions as authigenic material associated with pore-linings and fillings, peloids, and replacement phases.
An obsolete varietal term for clintonite.
A 2:1 hydrous phyllosilicate with continuous sheets of Mn and Na octahedra between two types of tetrahedral sheets. One sheet has isolated Si13(O,OH)37 islands whereas the other has similar islands with SiO3(OH) tetrahedra linkages between islands. The 2:1 layers are apparently not cross linked. The ideal chemical composition is K2Na3(Mn,Fe,Na)4[Si9(O,OH)27] (OH)2 . nH2O, with n ~ 2.33. Shafranovskite occurs in the pegmatites of the Khibiny and Lovozero alkaline complexes, Kola peninsula, Russia.
Shale is a mudrock with a high proportion of clay and silt sized particles, that usually exhibits lamination and fissility. When blocky and non-fissile the mudrock is named mudstone.
Cf., mudstone.
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.