Kaolinite sedimentary

Kaolin clays are naturally occuring sedimentary deposits composed largely of kaolinite mineral. Typical impurities in these deposits are iron oxides, titanifer-ous minerals, silica, feldspar, mica, sulfides and organic matter. The majority of kaolin clay produced in the world is used in the paper industry as coating and filler materials. This mineral also makes an excellent filler, carrier, opacifier and diluent in a variety of industrial products such as paints, plastics, cement, rubber, pharmaceuticals, etc. 

Figure 2. Illustration of the possible displacement of a sedimentary bulk composition upon reduction of Fe + to Fe + during diagenesis (after Velde, 1968). I = illite Chi = chlorite Kaol = Kaolinite M03 = expanding trioctahedral phases 1 = initial bulk composition 2 = reduced bulk composition. Upper diagram shows initial assemblage and the lower diagram those after reduction of Fe +.

Although gibbsite and kaolinite are important in quantity in some soils and hydrothermal deposits, they have diminishing importance in argillaceous sediments and sedimentary rocks because of their peripheral chemical position. They form the limits of any chemical framework of a clay mineral assemblage and thus rarely become functionally involved in critical clay mineral reactions. This is especially true of systems where most chemical components are inert or extensive variables of the system. More important or characteristic relations will be observed in minerals with more chemical variability which respond readily to minor changes in the thermodynamic parameters of the system in which they are found. However, as the number of chemical components which are intensive variables (perfectly mobile components) increases the aluminous phases become more important because alumina is poorly soluble in aqueous solution, and becomes the inert component and the only extensive variable. 

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. 

The AG between the assemblage of muscovite + chlorite at composition y and illite of this is likely to be relatively small and the tendency to recrystallize the muscovite from x to y compositions will be small at sedimentary conditions. However, as more thermal energy is added to the rock system, under conditions of deeper burial, the recrystallization will proceed more rapidly as temperature is increased. Evidence for such an effect can be found in Millot (1964) where sedimentary rocks coming from deeply buried or slightly metamorphosed series show the "chloritization" or kaolinitization" of detrital mica grains in splendid photographs. 

The effect is most marked in more mature sedimentary rocks where temperatures have been relatively high. The phenomenon represents not only the chloritization or kaolinitization of muscovite but also its illitization. 

Considering the compositions of the mixed layered minerals found in sedimentary rocks (Figure 25) it is obvious that magnesian-iron expandable dioctahedral minerals will be in equilibrium not uniquely with kaolinite but also in many instances with a magnesian-iron phase—either chlorite or an expanding trioctahedral mineral. In such a situation the slope in... 

However, both 7 and 14 8 chlorites are considered to be iron-rich when found in low temperature environments. Why are the diagenetic or authi-genic chlorites found in sedimentary rocks ferrous The answer can be found in the phase relations of the minerals common in sedimentary rocks. Basically, 14 8 chlorite is formed either through the destabilization of the montmorillonite-illite mixed layered mineral or kaolinite in the majority of argillaceous sedimentary rocks (Dunoyer de Segonzac, 1969 van Moort, 1971 Perry and Hower, 1970 Muffler and White, 1969). The increase in chlorite content is frequently observed in the presence of illite or a mixed layered mineral with a high non-expandable layer content. 

Two phase assemblages of any of these minerals are known. It should be noted that aluminous phases, such as kaolinite, have never been reported with corrensite neither are sedimentary phyllosilicates such as 7 8 chlorite or glauconite. Non-phyllosilicates in association with corrensite frequently include diagenetic quartz, albite and dolomite. Pelitic rocks, specially associated with those containing corrensite, contain allevardite and fully expanding montmorillonite (dioctahedral). 

In each of the different parageneses outlined here, the instability of a mineral can be denoted by its replacement with one or usually several minerals. The rocks in these facies are typified by multi-phase assemblages which can be placed in the K-Na-Al-Si system. This is typical of systems where the major chemical components are inert and where their masses determine the phases formed. The assumptions made in the analysis up to this point have been that all phases are stable under the variation of intensive variables of the system. This means that at constant P-T the minerals are stable over the range of pH s encountered in the various environments. This is probably true for most sedimentary basins, deep-sea deposits and buried sedimentary sequences. The assemblage albite-potassium feldspar-mixed layered-illite montmorillonite and albite-mixed layered illite montmorillonite-kaolinite represent the end of zeolite facies as found in carbonates and sedimentary rocks (Bates and Strahl,... 

Figure 42. Schematic sedimentary cross-section of a typical northwest Africa marginal sedimentary basin containing sepiolite-palygorskite bearing sediments (after the summary presented by Millot, 1964) K = Kaolinite ...

Large deposits of relatively pure kaolinite have developed from parent, feldspar-rich pegmatites, whereas others are secondarily deposited in sedimentary beds after transportation. 

From initial deposition and burial under overlying sedimentary materials through succeeding geological periods, coal beds are continually subject to the action of ground water. Thus, some coal beds have developed a system of essentially vertical fractures—thin cracks, often filled with coatings of pyrite. calcile. kaolinite and other minerals deposited from ground water. Impurities from these veins lower the quality of the coal. 

Aluminum is present in many primary minerals. The weathering of these primary minerals over time results in the deposition of sedimentary clay minerals, such as the aluminosilicates kaolinite and montmorillonite. The weathering of soil results in the more rapid release of silicon, and aluminum precipitates as hydrated aluminum oxides such as gibbsite and boehmite, which are constituents of bauxites and laterites (Bodek et al. 1988). Aluminum is found in the soil complexed with other electron rich species such as fluoride, sulfate, and phosphate. 

Clay minerals occur in all types of sediments and sedimentary rocks and are a common constituent of hydrothermal deposits. They are the most abundant minerals in sedimentary rocks perhaps comprising as much as 40% of the minerals in these rocks. Half or more of the clay minerals in the earth s crust are illites, followed, in order of relative abundance, by montmorillonite and mixed-layer illite-montmorillonite, chlorite and mixed-layer chlorite-montmorillonite, kaolinite and septachlorite, attapulgite and sepiolite. The clay minerals are fine-grained. They are built up of tetrahedrally (Si, Al, Fe3+) and octahedrally (Al, Fe3+, Fe2, Mg) coordinated cations organized to form either sheets or chains. All are hydrous. 

Most kaolinite is formed by the acid leaching of alkaline rocks, primarily the feldspars and micas however, practically any silicate rock or mineral will alter to kaolinite if leaching conditions are suitable for a sufficiently long period of time. Kaolinites that are formed by weathering and remain in place are called residual kaolinites. Those that are transported and sedimented are called sedimentary kaolinites... 

In the samples analyzed by Ross and Kerr (1931) the residual kaolinites have an average Fe203 content of 0.68% and the sedimentary kaolinites an average of... 

Amesite has more A1 substitution in the tetrahedral and octahedral sheets than has chamosite I (Table LXXV). In addition, the octahedral sheet is composed predominantly of Mg ions rather than Fe2+. Some samples show considerable disorder due to random displacement of layers by multiples of b/3 parallel to the y-axis (Deer et al., 1962). In both amesite and chamosite the negatively charged tetrahedral sheets and positively charged octahedral sheets allow ionic bonding between adjacent layers and a resulting contraction normal to the c-axis. The layer thickness is on the order of 7.00-7.11 as compared to 7.15 for kaolinite. This mineral is quite rare and has not been found in sedimentary deposits. 

In general, the minerals now identified as chamosite are found in iron ore bodies of sedimentary origin (e.g., Maynard, 1986 Fernandez and Moro, 1998 Wiewora et al, 1998 Kim and Lee, 2000). Chamosite associated with iron oxides appears to follow a compositional trend from iron oxides plus kaolinite to chlorite, as indicated in Figure 8, using the data of Velde (1989). The recombination of iron oxide in the presence of kaolinite gives an aluminous, ferrous mineral, chamosite. This mineral is formed under burial conditions where ferric iron oxide is reduced to feiTous iron which is rapidly incorporated into a 7 A chlorite mineral. Both chamosite and berthierine result from the reduction of ferric iron to ferrous iron. 

In an exploration area in northern Peru, igneous rocks cover an area of several square km within a metamorphosed series of quartzites and limestones. The younger sequence consists of ignimbrites, tuffs and tuffites of approximately 1000 m thickness. The metamorphism produced skams, which are connected with the ore body. A porphyry Cu deposit occurs in the metamorphosed rocks and is characterised by intense hydrothermal alteration (quartz-kaolinite-sericite) which makes determination and classification of magmatic and sedimentary rocks at the surface very difficult. A zone of propylitic alteration can locally be followed up to 500 m into the andesitic-dioritic wall rocks. 

Fluids can be released from solids by mineral dehydration thus adding fluids to the compaction-driven fluid flux in a sedimentary column undergoing burial. The relative contribution of such diagenetic processes to the compaction-driven flow, can be estimated. Dehydration of smectite may be important (Burst, 1969), but at greater depths illitization of kaolinite may be significant (Eq. (2)). Bjprlykke et al. (1986) and... 

Aggregation of dissolved humic substances can also occur with particulate materials in the estuarine water column. Preston and Riley (1982) showed that the adsorption of riverine humic substances onto kaolinite, montmorillonite, and illite increased with increasing salinity and dissolved humic substance concentration. Adsorption increased in the order kaolinite < illite < montmorillonite, which they ascribed to increasing cation-exchange capacity of the clays. They found considerable quantitative differences between the extent of adsorption of riverine versus extracted sedimentary humic substances, indicating the importance of using materials of proper origin in experiments of this type. 

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