The phenomenon where a clay undergoes the transition from a purely elastic deformation stage to an elasto-plastic deformation stage. Yielding marks the onset of plastic deformation, and the stress at which yielding occurs is called yield stress or yield strength.
A member of the palygorskite-sepiolite group with a composition of approximately ~(R2+,R3+,v)5 Si8O20(OH, H2O)2(H2O)7, where Mn2+ dominates; R represents a cation and v are vacancies.
See palygorskite-sepiolite group
A measure of the response of a homogeneous material to uniaxial tension or compression, in units of pressure (usually gigapascals), obtained from the slope of the (linear) relationship of stress versus strain in the elastic regime.
Cf., elastic constants
A poorly defined term, fibrous in habit, possibly a serpentine or chlorite.
A family of hydrated aluminosilicate minerals with a three-dimensional Si, Al tetrahedral framework-type structure with molecular-size channels and cages. Rings of four, six and eight tetrahedra are common structural subunits of the framework. The “extra-framework” content includes cations and H2O; the cations are often exchangeable and the H2O may be dehydrated or partially dehydrated. The tetrahedra are occupied by >50% Si, as required by the Lowenstein Al- avoidance rule; in some cases, Be is present. Zeolites are used commercially in ion-exchange, molecular-sieve, and hydration-dehydration applications.
In general, zeolite structures are fine grained and are comprised of negatively charged, three dimensional (Si,Al)O4 corner-sharing tetrahedral networks (“framework”) which form structural cavities and “extraframework sites”. The tetrahedra, with Al substituting Si, have a negative charge that is balanced by exchangeable cations in the extraframework sites. H2O, which is polar, interacts with both the exchangeable cations and the framework, varying in number depending on relative humidity. Hydration and dehydration is generally continuous and reversible, and quite dynamic, although laumontite exhibits non-continuous behavior. Zeolites occur authigenicly, in low-temperature secondary alterations, such as in soils, as hydrothermal alteration products, in altered volcanics, in sediments, and many other environments. See also Part 1 of the Glossary. There are about 75 natural zeolites, and the more common species are given here:
chabazite (Ca0.5,Na,K)4(Al4Si8O24) . 12(H2O)
clinoptilolite (Na,K,Ca0.5)6(Al6Si30O72) . 20(H2O)
erionite K2(Ca0.5,Na)7(Al9Si27O72) . 28(H2O)
laumontite Ca4(Al8Si16O48) . 16(H2O)
mordenite Na3Ca2K(Al8Si40O96) . 28(H2O)
phillipsite K2(Na,Ca0.5)3(Al5Si11O32) . 12(H2O)
stilbite NaCa4(Al9Si27O72) . 30(H2O)
A platy serpentine mineral of ideal composition of Zn2Al(Si,Al)O5(OH)4. Zinalsite is the Zn analogue of amesite. Natural occurrences are rare. The type locality is from the oxidation zone of the Akdzhal deposit, Kazakhstan, and it is also known from Sterling Hill, New Jersey, USA.
Cf., amesite, kellyite
A series name for trioctahedral micas on or close to the siderophyllite-polylithionite join. Also used to describe dark micas with significant amounts of lithium.
An orthosilicate (= nesosilicate) mineral Zr(SiO4) that commonly occurs as an accessory mineral in igneous and metamorphic rocks. The mineral may be used for dating the age of its host rock because it contains radioactive U and Th.
See astrophyllite group.