A poorly defined term, fibrous in habit, possibly a serpentine or chlorite.
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.
A modulated trioctahedral 2:1 phyllosilicate with an ideal chemical composition of RM13T18O42(OH)14, with R = Na and K, M = Mg, Mn, Fe2+, Fe3+, Al, and Ti, and T = Si and Al. The structure of zussmanite (Lopes-Vieira and Zussman, 1969) has a continuous octahedral sheet with islands of tetrahedral 6-fold rings on both sites of the octahedral sheet. Each island of 6-fold rings is laterally linked to other islands of six-fold rings by inverted three-fold rings, and these three-fold rings are linked also to the six-fold island tetrahedral rings of the adjacent 2:1 layer. The 6-fold rings align across the interlayer region and form a mica-like interlayer site where the large R cation can reside. Coombsite is the Mn analogue of zussmanite. Zussmanite occurs in blueschist facies metamorphic regimes at the Laytonville Quarry, Mendocino County, California.
An obsolete term for muscovite.