A process or phenomenon where a soil or clay mass has previously been subjected to pressures that were greater than the current overburden pressure.
A process or phenomenon where a soil or clay mass has previously been subjected to pressures that were greater than the current overburden pressure.
In soil science and soils engineering, the overconsolidation ratio (OCR) is the ratio of the preconsolidation effective stress to the current consolidation effective stress to which the soil is being subjected. For normally consolidated sediment the OCR = 1.0, thus for overconsolidated sediment the OCR >1.0.
A poorly defined material, possibly an altered iron-rich chlorite, from near Harper’s Ferry, West Virginia, USA.
A member of the brittle mica group, with an ideal chemical composition of Ba(Mg2Ti4+)Si2Al2O12. Oxykinoshitalite is the Ti and oxygenian dominant analogue of kinoshitalite. Oxykinoshitalite-1M forms in the C2/m space group with Ti primarily in the M2 site. It occurs in an olivine nephelinite from Fernando de Noronha Island, Pernambuco, Brazil (Kogarko et al., 2005).
An obsolete term for pyrophyllite or a mixture with dominant pyrophyllite.
Palliative refers to the relief of pain (or more generally, other side effects of an illness), but without treatment of the underlying condition. Clay baths (balnea) are commonly used as a palliative treatment for chronic pain (e.g., arthritis).
A member of the palygorskite-sepiolite group with a composition of approximately (Mg5-y-zR3+yvz) (Si8-xR3+x) O20 (OH)2 (OH2)4 . R2+(x-y+2x)/2 (H2O)4, where R are cations, v are vacancies, and x, y, and z are compositional parameters.
See palygorskite-sepiolite group
The palygorskite-sepiolite group consists of palygorskite, sepiolite, falcondoite, kalifersite, loughlinite, raite, tuperssuatsiaite, yofortierite, windhoekite, and an un-named species, ~NaCa(Fe2+, Al, Mn)5[Si8O19(OH)](OH)7.5H2O. Palygorskite and yofortierite are dioctahedral and all others are trioctahedral. The palygorskite-sepiolite group has infinitely extending tetrahedral sheets involving 6-fold rings of tetrahedra. Tetrahedral sheets have a continuous basal oxygen-atom plane, but the palygorskite-sepiolite group has apical oxygen atoms pointing in opposing directions within a continuous sheet. Each section of like-pointing tetrahedra form a strip or ribbon pattern, and each ribbon consists of a tetrahedral ring (or two pyroxene-like chains) in palygorskite and 1.5 rings (or three pyroxene-like chains) in sepiolite. In palygorskite and sepiolite, the octahedra, which are linked via edge sharing, form strips that are not continuous sheets. In sepiolite, the octahedral strips are eight octahedra wide, whereas strips that are five octahedra in width occur in palygorskite. The terminal anion at the edges of the octahedral strip involves four OH2 groups per formula unit and are required for charge balance. Because these groups are well bonded to the octahedral metal cation and not isolated, they are not referred to as H2O. Vacant regions, zeolitic H2O, and exchangeable cations may reside in the channels formed at the edges of the octahedral strips in palygorskite and sepiolite. Exchange reactions with organic molecules are possible if the size of the organic cations is appropriate, because steric constraints control what can enter this channel. Larger molecules also may be adsorbed by the structure, but this is probably because of defects. Environments of formation range from low-temperature aqueous solutions to high-temperature hydrothermal (< 350 oC) conditions, and natural solutions tend to be alkali-rich with (Na + K)/Al > 1. See individual species for chemical compositions.
A name introduced to replace palygorskite-sepiolite. This name has not been accepted by the International Mineralogical Association (or any nomenclature committee) and therefore should not be used.
A pedofeature formed by fragments of laminated clay coatings.
See pedofeature.