Illite-chlorite

The diagenetic effects are related to the alteration of rock mineral, shales in particular. Under certain conditions, montmorillonite clays change to illites, chlorites and kaolinites. The water of hydration that desorbs in the form of free water occupies a larger volume. This volume increase will cause abnormal pressures if the water cannot escape. 

Fine particle migration can occur in the absence of water-swelling clays. Migrating fines can include the migrating clays kaolinite, illite, chlorite, and some mixed layer clays and fine silica particles (162,163). Fine particle migration is promoted when the... 

Pyrophyllite is probably not stable below some 300°C at 1 Kb pressure. This temperature will be reduced at lower total water pressure but probably will remain at a substantial value (Velde and Kornprobst, 1969). Its existence in sedimentary rocks should be indicative of relatively high temperatures if it is stable. It is typically found with illite-chlorite or occasionally with allevardite (Dunoyer de Segonzac, 1969 Ehlmann and Sand, 1959). The reaction Kaolinite + quartz = pyrophyllite is an important marker in phyllosilicates parageneses when it can be observed. 

Above 200-220°C only illite or sericite is found, usually with chlorite. No dioctahedral mixed layered phase is present. This is the "illite-chlorite" zone. 

Figure 28. Depth-temperature plot of natural mineral assemblages for the fully expandable phases (Mo), random and ordered 30-80% mixed layered (ML) and superstructured, ordered 30-20% mixed layered (All) minerals. Data from Steiner (1968), S Muffler and White (1969), M Perry and Hower (1970, 1972), P Iijima (1970), I Browne and Ellis (1970), B Dunoyer de Segon-zac (1969), D and Weaver and Beck (1971), W. I-C illite, chlorite paragenesis. Tertiary or younger sediments are represented in these studies.

Figure 31b. Compositions of chlorites in the mixed-layered mineral facies of pelitic rocks (circles) and from the illite-chlorite facies (barred circles). Shaded area shows chlorite compositions from muscovite-chlorite metamorphic rocks.

Figure 31b indicates the compositional spread of chlorites from six rocks in the illite-montmorillonite mixed layered mineral facies and from the illite-chlorite zone in the French Alps (Velde, unpublished). The grains analyzed with the microprobe are chlorites replacing isolated grains of detrital mica or were newly formed grains. They are usually 15 microns in the smallest dimension. 

The stability conditions of corrensite then cover the low grade clay mineral facies (near 100°C) and extend well into the calcium zeolite-prehnite, muscovite-chlorite facies. In pelitic rocks the upper limit will be somewhat lower near the illite-chlorite zone. It is evident that composition of a rock governs the occurrence of corrensite. It can be... 

V is characterized by kaolinite-illite-chlorite assemblages beyond the stability of an expanding mixed layered potassic dioctahedral mineral and below the thermal stability of pyrophyllite. The establishment of such conditions will be difficult in that the non-appearance of a mineral is a poor diagnostic and, as we have seen, kaolinite is frequently eliminated from sediments before its upper stability limit in the presence... 

Once the illite-chlorite zone is entered, i.e., the facies where dioctahedral mica-montmorillonite mineral solid-solutions are no longer stable, how does the assemblage change into muscovite-chlorite The major... 

Most likely, the chemical system remains closed, as far as the other components in the silicate phases are concerned, as diagenesis or low grade metamorphism becomes more evident. Although there may be transfer of calcium, it seems, from bulk chemical analysis, that there is no systematic increase in potassium nor decrease in sodium content of argillaceous sediments. The transfer of Na and K is between the two size fractions—clay and coarse fraction—or between phyllosilicates and tectosilicates. Albitization of argillaceous rocks should be a common phenomenon where mixed layered phases are predominant in clay assemblages and especially evident in the illite-chlorite zone. 

DUNOYER DE SEGONZAC (G.) and HEDDEBAUT (C.), 1971. Paleozoique anchi-metamorphism a illite, chlorite, pyrophyllite, allevardite et paragonite dans les Pyrenees basques. Bull. Carte ser. Geol. Als. Lorr. 24, 277-90. 

The nodules are found in gray-black commercial slate having fine grain size, uniform color and texture, and well developed slaty cleavage. Such slate occurs in thick strata marked only by thin black bands ( ribbons ) of somewhat coarser texture, and by rare, disseminated knots, siliceous nodules of foreign material. The slate is a mixture of quartz, illite, chlorite, caldte, and muscovite, with minor amounts of pyrite, carbonaceous matter, and heavy mineral grains. The dark color is attributed to finely disseminated carbon and pyrite. An analysis of the slate is given in Table I. 

Clay minerals Kaolinite, illite, sericite, clay minerals with mixed-layer structure, Tonstein — Illite, chlorite... 

Mixed-layer illite-montmorillonite is by far the most abundant (in the vicinity 90%) mixed-layer clay. The two layers occur in all possible proportions from 9 1 to 1 9. Many of those with a 9 1 or even 8 2 ratio are called illites or glauconites (according to Hower, 1961, all glauconites have some interlayered montmorillonite) and those which have ratios of 1 9 and 2 8 are usually called montmorillonite. This practice is not desirable and js definitely misleading. Other random mixed-layer clays are chlorite-montmorillonite, biotite-vermiculite, chlorite-vermiculite, illite-chlorite-montmorillonite, talc-saponite, and serpentine-chlorite. Most commonly one of the layers is the expanded type and the other is non-expanded. 

At a temperature near 150°C kaolinite starts to decompose and the Al as hy-droxy-Al moves into the interlayer position increasing the proportion of dioctahedral chlorite layers. At this stage some of the chlorite layers form packets with a sufficient number of layers to diffract as the discrete mineral chlorite. Some additional Al may move into the tetrahedral sheet at this stage and some packets of 10A layers form (the K derived from K-feldspar). Thus, the amount of discrete 10A illite and dioctahedral chlorite has increased slightly but the majority of the clay consists of a mixed-layer illite-chlorite with a lesser amount of montmorillonite. 

K is obtained from associated K-feldspars and micas. The layer charge is increased by the reduction of iron in the octahedral sheet and incorporation of Al, entering through the ditrigonal holes in the basal oxygen plane, into the tetrahedral sheets (Weaver and Beck, 1971a Pollard, 1971). Weaver and Beck have presented evidence that indicates mixed-layer clays formed in this manner contain 20—30% chloritic layers and are actually mixed-layer illite-chlorite-montmorillonite clays. 

Of special significance with respect to their properties as sorbents are the clay minerals (e.g. kaolinite, montmorillonite, vermiculite, illite, chlorite), mainly due to their high exchange capacity. 

Continental detritus group samples contain minerals such as illite, chlorite, and probably polycrase [(Y,Ca,Ce,U,Th)(Ti,Nb,Ta)206] and chromite [FeO(Cr,V)203], supplied from the Himalayas region via the Ganges River (Fagel et al., 1997). Th and U are highly correlated, but several continental detritus group samples... 

Moderately Alkaline Weak-Leaching Environment Only a portion of the mobile weathering products (silica, base cations) is lost by leaching in this situation. Aluminum and iron hydroxide are the least soluble weathering products, so these react with the soluble silica and base cations to produce 2 1 layer silicates, including dioctahedral smectites and illites. Chlorites can be formed in this situation as well. 

Illite Chlorite and illite—smectite 1 trace trace trace... 

Explain the distribution pattern of clay minerals kaolinite, illite, chlorite and smectite in the world ocean. Why should be illite more common in the North Atlantic than in the South Atlantic ... 

A zonal distribution of clay minerals occurs in the East Hachimantai thermal area, characterized by smectite - illite/smectite - illite/chlorite, with the latter tending to occur in the vicinity of hot upflow zones. The smectite is characteristically Ca-smectite. The occurrence of Ca-bearing zeolite minerals, such as laumontite and wairakite correspond to the presence of hot hydrothermal fluids near in the center of the geothermal resource. In contrast, Na-smectite and Na-zeolite (e.g. clinoptilolite - mordenite - analcime) in marine sediments and pyroclastic sequences tend to envelope the main thermal area. Inoue et al. (2001) and Hara et al. (2001) have described the style and distribution of alteration in the Hachimantai area. The Na-enriched alteration zones contain higher Na concentrations than... 

Smectites Most clay minerals in deep-sea sediments are detrital phases from continental weathering. These minerals compose the bulk of the nonbiogenic sediments in the <2 pm fraction and include clay-sized quartz and the phyllosilicates kaolinite, illite, chlorite, and smectite. The smectite... 

The features of the adsorbed complex of the Cambrian argillites were intensely transformed by diagenetic reactions, making them unsuitable for any interpretations. The complex composition of the clays which consist of kaolinite, illite, chlorite and mixed-layer minerals, together with the absence of organic matter leads to the conclusion that the areas of denudation must have been of a local nature. At the same time, we may reconstruct a temperate to humid climate interrupted at times by periods of relative aridity. This explains the lack of laterites on the eruptive and metamorphic rocks. 

This category arises from two main sources either physically associated silicates, such as quartz-clay combinations derived from partings, or mixed-layer clays of variable compositions outside the compositional limits of the individual clay categories (kaolinite, illite, montmorilIonite, chlorite). For example, about 30 percent of the particles in the mixed-silicate category of the Massachusetts anthracite had compositions consistent with an illite-chlorite mixed-layer clay The weight percentages in this category can be further subdivided as needed ... 

---