A member of the palygorskite-sepiolite group with a composition of approximately (Mg8-y-zR3+yvz) (Si12-xR3+x) O30 (OH)4 (OH2)4 . R2+(x-y+2z)2 (H2O)8, where R are cations, v are vacancies, and x, y, and z are compositional parameters.
See palygorskite-sepiolite group
A group name for phyllosilicates with characteristics that are dominantly fiber-like, but with some plate-like character. The atomic structure has continuous planes of basal oxygen atoms (thus forming the plate-like character) with the apical oxygen atoms of the tetrahedra pointing alternatively in opposite directions away from the basal plane. The tetrahedral apices link to partial octahedral sheets, discontinuous along one direction but infinite in the other, to form a pattern of octahedral ribbons (thus forming the dominant fiber-like character). These minerals are classified as modulated phyllosilicates. The width of ribbons may vary, which leads to different numbers of octahedral cation sites per formula unit (5 for palygorskite, 8 for sepiolite).
An invalid term, use kaolin-serpentine group (Bailey, 1980).
A poorly defined term, commonly used in the past to describe an optical microscopic fine-grained aggregate of mica-like phases.
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.