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Illite

About: Illite is a(n) research topic. Over the lifetime, 8320 publication(s) have been published within this topic receiving 208519 citation(s). The topic is also known as: illite mica series.
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12 Oct 1989-
Abstract: The nature and production of x-rays diffraction effects structures, composition, properties and occurences of clay minerals sample preparation techniques for clay minerals sample preparation techniques for clay minerals identification of individual clay minerals and associated minerals identification of mixed layered clay minerals quantitative analysis.

4,424 citations


Journal ArticleDOI
01 Oct 1995-Geology
Abstract: Lutites are commonly metasomatized during diagenesis, but the analysis presented here accounts for most postdepositional change. Potassium metasomatism is particularly common, and typically involves the conversion of kaolin (residual weathering product) to illite by reaction with K + -bearing pore waters. Sandstones also undergo K metasomatism, which involves the replacement of plagioclase by potassium feldspar. These changes can be identified petrographically and are quantitatively accounted for by techniques discussed herein. Bulk chemical analyses and ternary diagrams are used to determine the amount of K addition, premetasomatized sediment composition, and composition of provenance areas. The premetasomatized mineralogy of paleosols can be compared with the mineralogy of recent soil profiles and thus, climate and topographic conditions determined for past weathering events. Some weathering indices lead to erroneous conclusions because, by excluding K 2 O from consideration, correction cannot be made for metasomatic effects.

1,660 citations


Journal ArticleDOI
Daniel J.K. Ross1, R. Marc Bustin1Institutions (1)
Abstract: The effect of shale composition and fabric upon pore structure and CH 4 sorption is investigated for potential shale gas reservoirs in the Western Canadian Sedimentary Basin (WCSB). Devonian–Mississippian (D–M) and Jurassic shales have complex, heterogeneous pore volume distributions as identified by low pressure CO 2 and N 2 sorption, and high pressure Hg porosimetry. Thermally mature D–M shales (1.6–2.5% VRo) have Dubinin–Radushkevich (D–R) CO 2 micropore volumes ranging between 0.3 and 1.2 cc/100 g and N 2 BET surface areas of 5–31 m 2 /g. Jurassic shales, which are invariably of lower thermal maturity ranging from 0.9 to 1.3% VRo, than D–M shales have smaller D–R CO 2 micropore volumes and N 2 BET surface areas, typically in the range of 0.23–0.63 cc/100 g (CO 2 ) and 1–9 m 2 /g (N 2 ). High pressure CH 4 isotherms on dried and moisture equilibrated shales show a general increase of gas sorption with total organic carbon (TOC) content. Methane sorption in D–M shales increases with increasing TOC and micropore volume, indicating that microporosity associated with the organic fraction is a primary control upon CH 4 sorption. Sorption capacities for Jurassic shales, however, can be in part unrelated to micropore volume. The large sorbed gas capacities of organic-rich Jurassic shales, independent of surface area, imply a portion of CH 4 is stored by solution in matrix bituminite. Solute CH 4 is not an important contributor to gas storage in D–M shales. Structural transformation of D–M organic matter has occurred during thermal diagenesis creating and/or opening up microporosity onto which gas can sorb. As such, D–M shales sorb more CH 4 per weight percent (wt%) TOC than Jurassic shales. Inorganic material influences modal pore size, total porosity and sorption characteristics of shales. Clay minerals are capable of sorbing gas to their internal structure, the amount of which is dependent on clay-type. Illite and montmorillonite have CO 2 micropore volumes of 0.78 and 0.79 cc/100 g, N 2 BET surface areas of 25 and 30 m 2 /g, and sorb 2.9 and 2.1 cc/g of CH 4 , respectively (dry basis) – a reflection of microporosity between irregular surfaces of clay platelets, and possibly related to the size of the clay crystals themselves. Mercury porosimetry analyses show that total porosities are larger in clay-rich shales compared to silica-rich shales due to open porosity associated with the aluminosilicate fraction. Clay-rich sediments (low Si/Al ratios) have unimodal pore size distributions

1,421 citations


Journal ArticleDOI
Abstract: A detailed mineralogical and chemical investigation has been made of shale cuttings from a well (Case Western Reserve University Gulf Coast 6) in Oligocene-Miocene sediment of the Gulf Coast of the United States. The 10-µm fractions from the 1,250- to 5,500-m stratigraphic interval were analyzed by x-ray diffraction. Major mineralogic changes with depth take place over the interval 2,000 to 3,700 m, after which no significant changes are detectable. The most abundant mineral, illite/smectite, undergoes a conversion from less than 20 percent to about 80 percent illite layers over this interval, after which the proportion of illite layers remains constant. Over the same interval, calcite decreases from about 20 percent of the rock to almost zero, disappearing from progressively larger size fractions with increasing depth; potassium feldspar (but not albite) decreases to zero; and chlorite appears to increase in amount. Variations in the bulk chemical composition of the shale with depth show only minor changes, except for a marked decrease in CaO concomitant with the decrease in calcite. By contrast, the <0.1-µm fraction (virtually pure illite/smectite) shows a large increase in K2O and Al2O3 and a decrease in SiO2 The atomic proportions closely approximate the reaction smectite + Al+3 + K+ = illite + Si+4. The potassium and aluminum appear to be derived from the decomposition of potassium feldspar (and mica?), and the excess silicon probably forms quartz. We interpret all the major mineralogical and chemical changes as the response of the shale to burial metamorphism and conclude that the shale acted as a closed system for all components except H2O, CaO, Na2O, and CO2. Compositional changes in the shale as a function of metamorphic grade closely parallel compositional changes in shale as a function of geologic age.

1,270 citations


Journal ArticleDOI
Abstract: Sandstones and shales of the Wilcox Group (lower Eocene) in southwest Texas were examined by X-ray powder diffraction, electron microprobe, and petrographically to interpret their diagenetic history. Samples analyzed are from depths of 975 to 4650 m, representing a temperature range of 55°C to 210°C. No consistent trend of depositional environments is recognized with increasing depth, and mineralogic changes observed are interpreted as diagenetic. Major mineral distribution patterns are (1) disappearance of discrete smectite at temperatures >70°C, (2) gradation of mixed-layer illite/smectite to less expandable (more illitic) illite/smectite over the entire temperature range, (3) disappearance of kaolinite from 150-200°C accompanied by an increase in chlorite, and (4) replacement of calcite cement at about 117 120°C by ankerite. Calculations based on data of Hower and others (1976) indicate that the stability of smectite layers may be a function of composition. Smectites with high ratios of octahedral (Fe + Mg)/Al appear to resist conversion to illite until temperatures high enough to produce ordering are attained. A diagenetic model is proposed which involves the breakdown of detrital K-feldspar and of some smectite layers in illite/smectite to convert other smectite layers to illite. Silica and calcium released by the illitization of smectite is transferred from shales to sandstones to produce quartz overgrowths and calcite cements at temperatures as low as 60°C. Iron and magnesium released by the illitization reaction are transferred from shales to sandstones at temperatures >100°C and react with kaolinite to produce high-alumina chlorite and/or with calcite to produce ankerite.

793 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202210
2021302
2020299
2019292
2018285
2017286