Figure 1: Illite crystallinity classification chart showing the different metamorphic zones and facies corresponding to IC, adapted from Verdel 2012Figure 2: Illite structure
Illite crystallinity is a technique used to classify low-grade metamorphic activity in pelitic rocks.[1] Determining the "illite crystallinity index" allows geologists to designate what metamorphic facies and metamorphic zone the rock was formed in and to infer what temperature the rock was formed. Several crystallinity indices have been proposed in recent years, but currently the Kübler index is being used due to its reproducibility and simplicity.[2] The Kübler index is experimentally determined by measuring the full width at half maximum for the X-ray diffraction reflection peak along the (001) crystallographic axis of the rock sample.[3] This value is an indirect measurement of the thickness of illite/muscovite packets which denote a change in metamorphic grade.
The method can be used throughout the field of geology in areas such as the petroleum industry, plate tectonics.
^Verdel, Charles; Niemi, Nathan; van der Pluijm, Ben A. (2011). "Variations in the Illite to Muscovite Transition Related to Metamorphic Conditions and Detrital Muscovite Content: Insight from the Paleozoic Passive Margin of the Southwestern United States" (PDF). The Journal of Geology. 119 (4): 419–437. Bibcode:2011JG....119..419V. doi:10.1086/660086. S2CID 129686326. Retrieved 7 October 2013.
^Cite error: The named reference Abad was invoked but never defined (see the help page).
^Eberl, D. D.; Velde, B. (December 1989). "Beyond the Kübler index" (PDF). Clay Minerals. 24 (4): 571–577. Bibcode:1989ClMin..24..571E. doi:10.1180/claymin.1989.024.4.01.
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Illitecrystallinity is a technique used to classify low-grade metamorphic activity in pelitic rocks. Determining the "illitecrystallinity index" allows...
form of illite showing bands of red-purple and pale yellow-green. It may be carved into pendants and other ornaments. The crystallinity of illite has been...
accelerated chemical- and bio-degradation. Chemical changes affect crystallinity. Mechanisms of chemical change, such as the uptake of F− or CO2− 3 may...
the brittle crust. Gouges dominated by clay minerals (montmorillonite, illite, and chlorite) are consistently weaker. Those with a high concentration...
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Stráská, Jitka; Chmelík, František (January 2016). "Study of microcracking in illite-based ceramics during firing". Journal of the European Ceramic Society....
chlorite and illite, each adding distinct properties to the composition. Despite the chemical variation among clays, their prevailing crystalline phases primarily...
different crystallinity in the same sample from a low-pressure zone. Cookeites from high pressure always exhibit a high degree of crystallinity, but ordered...
interest in the release of water from illite clays in subducting sediments. The conversion of smectite to illite (illitization) in subduction zones is...
of feldspars happens by hydrolysis and produces clay minerals, including illite, smectite, and kaolinite. Hydrolysis of feldspars begins with the feldspar...
spectroradiometry. Illite, for instance, is commonly observed in the vicinity of hydrothermal ore bodies. Higher concentrations of illite may indicate areas...
parent rock. The common clay minerals are montmorillonite or smectite, illite, and kaolinite or kaolin. These minerals tend to form in sheet or plate...
evidence of alteration is bleaching, change in colour or change in the crystallinity of micaceous minerals. In such cases, characterising alteration often...
to calcium-rich clay (montmorillonite) rather than potassium-rich clay (illite). Further weathering, particularly in tropical climates, converts the montmorillonite...
have been found as well. Minerals identified include biotite, chlorite, illite, kaolinite, montmorillonite and muscovite, with varying colors depending...
nutrients, and the bulk of most nutrient elements in the soil is held in crystalline form within primary and secondary minerals, they weather too slowly to...
silicate hydroxide: Al2Si4O10(OH)2. It occurs in two forms (habits): crystalline folia and compact masses; distinct crystals are not known. The folia...
table is only a rough guide to order of weathering. Some minerals, such as illite, are unusually stable, while silica is unusually unstable given the strength...
micas". They include: Hydro-muscovite with H3O+ along with K in the X site; Illite with a K deficiency in the X site and correspondingly more Si in the Z site;...
smectite clays. The palygorskite component is an acicular bristle-like crystalline form that does not swell or expand. Attapulgite forms gel structures...
Allophane is an amorphous to poorly crystalline hydrous aluminium silicate clay mineraloid. Its chemical formula is Al2O3·(SiO2)1.3-2·(2.5-3)H2O. Since...
thick) are clay minerals, mainly smectites (beidellite, montmorillonite) and illite, amorphous silica and impregnation of sulfate minerals (mainly gypsum, alunite...
sepiolite. Some of the measured peaks end up broadened possibly due to poor crystallinity, so accurate d-values were difficult to obtain. Powder X-Ray Diffraction...
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