Disordered kaolinite

Kaolins. The kaolin minerals include kaolinite. dickite. and nacrite which all have composition AUOi 2 SiO 2 FLO halloysite (7 At. AGO, 2 SiO, 2 H.O and halfoysile (10 A). Al 0, 2 SiO 4 H 0 The struclural formulas for kaolinite and halloysite tIO At. which are shown in Figure I, are AbSiaOiotOH)). and AljSi.iO, i(OH) -4 H,(). respectively. The so-called fire day mineral is a h-axis disordered kaolinite halloysite (7 A) and halloysite (10 A) are disordered along both the a- and h-Mcs Indeed, most variations in the kaolin group originate as structural polymorphs, related to variations in layer slacks. 

Worrall, W.E. and Cooper, A.E., 1966. Ionic composition of a disordered kaolinite. Clay Miner., 6 341-344. 

The intercalation capability of clay mineral decreases with increasing molecular volume of intercalated material [119]. The speed of intercalation of the MFA molecule decreases with increasing number of defects in the structure of mineral [120]. It corresponds with results of the study of Frost and coworkers [121] where highly ordered kaolinites easily intercalate which is in notable difference with high disordered kaolinites. The intercalation of formamide into kaolinite results in the changes in the vibrational spectra of both kaolinite and the target molecule [122-126]. The FA-intercalated kaolinite remains expanded after formamide desorption with a d(001) spacing of 10.09A [127-129]. 

PLA 75] PLANgON A., TCHOUBAR C., Study of stacking faults in partially disordered kaolinites. I. Stacking model allowing only translational faults , J. Appl. Cryst, vol. 8, p. 582-588, 1975. 

The kaolinite mineral species studied are kaolinite, kaolinite d (disordered kaolinite), dickite and nacrite. These polytypes have been described by Bailey (1963) on the basis of sense and degree of displacement of 1 1 layers and the position of vacant octahedral positions in the layer sequence. For the hydrated kaolinitic minerals, we have used the terminology of Keller and Johns (1976) which is based on endellite as the completely hydrated species and halloysite as the partly or completely dehydrated species. The polytypes of chlorite have been described by Bailey and Brown (1962) and Hayes (1970). In Fig. 8.3b it is shown that montmorillonite, the mixed-layer clays and illite are located between pyrophyllite without interfoliar charge and the dioctahedral... 

Livesite. A disordered kaolinite, particularly as found in some micaceous fireclays. The term is now little used it was proposed by K. Carr, R. W. Grimshaw and A. L. Roberts (Trans. 

The minerals exist as plates, laths, blocks, tubes, and hollow hexagonal prisms. Those with the most perfectly formed crystal structures— triclinic kaolinite, dickite and nacrite— occur as plates usually with many hexagonal angles [Figure l(above)]. Those with imperfect structures—halloysite and monoclinic disordered kaolinite—occur as laths, tubes, and hollow prisms [Figure 1 (below)]. 

Zvyagin [1967] is convinced that the halloysite structure is not merely disordered kaolinite. When the degree of disorder is great in either kaolinite or halloysite, there is little to distinguish between the two minerals, but the stacking sequence of the layers in halloysite cannot be derived from that of kaolinite. Souza Santos et al. [1965] have also commented that dried fiber bundles of halloysite from Brazil show some degree of regularity in their structures when examined by X-ray diffraction and selected-area electron diffraction. 

The powder pattern of disordered kaolinite (Table 7) has many fewer reflections than the... 

Table 7. X-Ray Powder Data for j5-Axis Disordered Kaolinite (Modified from Brindley [1961]).

If much well-ordered kaolinite is present, the assymmetric peaks are not prominent in the patterns from random samples, and the basal reflections are sharper and much enhanced in intensities in patterns from oriented samples. If much disordered kaolinite is present, the assymmetric peaks are prominent in the first patterns, and the basal reflections are much enhanced in the second. Chemical pretreatments prior to X-ray diffraction, such as those proposed by Wada [1965] and Alexiades and Jackson [1965], are sometimes useful in determining amounts of kaolinite and halloysite. Where the halloysite is tubular, it is easily detected in electron micrographs, although the amount can seldom be determined. Amounts of hydrated halloysite can be determined if allophane is not present in differential thermal analysis by calibrating and measuring the low-temperature endothermic peak. 

Figure 31. Differential thermal curves for A—dickite, Mexico nacrite, Germany C— kaolinite, Utah D—disordered kaolinite, Dorset metahalloysite, Kansas F—halloysite, North Carolina (Holdridge and Vaughan [1957]).

Study of hydrated kaolinites shows that water molecules adsorbed on a phyllosilicate surface occupy two different structural sites. One type of water, "hole" water, is keyed into the ditrigonal holes of the silicate layer, while the other type of water, "associated" water, is situated between and is hydrogen bonded to the hole water molecules. In contrast, hole water is hydrogen bonded to the silicate layer and is less mobile than associated water. At low temperatures, all water molecules form an ordered structure reminiscent of ice as the temperature increases, the associated water disorders progressively, culminating in a rapid change in heat capacity near 270 K. To the extent that the kao-linite surfaces resemble other silicate surfaces, hydrated kaolinites are useful models for water adsorbed on silicate minerals. 

Figure 4. A schematic representation of the tetrahedral surface of kaolinite (triangles) showing the position of the hole water molecules (open circles) keying into the ditrigonal holes. The associated water (filled circles in A) molecules are arranged in an ordered pattern which exists at low temperatures. Disorder in the associated water (filled circles in B) is created by increasing the temperature.

Kaolinite, ideally Al2Si205(OH)4, consists of 1 1 layers, alternating sequences of silicate and hydrated Al-octahedra (dioctahedral) sheets. There is potential for disorder in the specificity of the site occupied by Al and in the stacking of the sheets and layers, which give rise to the polymorphs dickite and halloysite. 

The ordering at the kaolinite surface is striking when compared with similar calculations for the amorphous silica surface (Figure 2c) which shows the ordering is substantially reduced relative to kaolinite. It is tempting to associate this disorder with the disorder at the silica surface this is consistent with the snapshot in Figure 4. 

Worral and Cooper (1966) analyzed a pure, poorly crystallized kaolinite from Jamaica (Table LXVII). The cation exchange capacity is 24.4 rrfequiv./lOO g. They suggest that substitution in the octahedral sheet is the cause of the high cation exchange capacity and may be the cause of the disorder. 

Fire clays, ball clays, flint clays are kaolinite-rich clays, usually of the 6-axis disordered variety, which contain a relatively high impurity content. Illite, montmoril-lonite, diaspore, boehmite, quartz, and organic material are the minerals usually associated with these deposits. Few, if any, of the kaolinite minerals in these clays have been concentrated enough to afford meaningful chemical data. 

Random displacements of nb/3 parallel to b are present in chamosite as in kaolinite (Brindley,1961). Youell (1955) has shown that in many chamosites there is disorder parallel to the a-axis. The better ordered chamosites are rich in iron, and the less well ordered contain less iron and more aluminum. Oxidation of Fe2+ to Fe3+ also increases the disorder. Both mechanisms cause a larger ion to be replaced by a smaller. This results in a decrease in the size of the octahedral sheet thus decreasing the misfit between the octahedral and tetrahedral sheets. Decreasing the strain within the layers apparently allows more shifting between layers. Youell (1955) noted that disordered chamosite is almost invariably accompanied by kaolinite, and ordered chamosite by siderite . 

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. 

Kaolinite is transformed into X-ray amorphous state when activated in air. According to authors [14,15], amorphization involves the destruction of bonds between tetrahedral and octahedral layers inside the package, till the decomposition into amorphous aluminium and silicon oxides. Other researchers [ 16,17] consider that amorphized kaolinite conserves the initial ordering of the positions of silicon atoms while disordering of the structure is due to the rupture of A1 - OH, Si - O - A1 bonds and the formation of molecular water. Endothermic effect of the dehydration of activated kaolinite is shifted to lower temperatures while intensive exo-effect with a maximum at 980°C still conserves. When mechanically activated kaolinite annealed at 1(X)0°C, only mullite (3Al20j-2Si0j) and X-ray amorphous SiOj are observed. In this case, the phase with spinel structure which is formed under thermal treatment of non-activated kaolinite is not observed thus, mechanical activation leads to the formation of other phases. 

Mineral composition, as determined by X-ray diffraction, shows a dominance of clay minerals, although quartz and opaline silica are persistent as sub-dominant and locally dominant or co-dominant (Table II). Of the clays, expandable lattice clay minerals, predominantly montmorillonite, occur in all the deposits with kaolinite or illite appearing as accessory or subdominant components. A marked contrast in the dominant clay species occurs between the brown oil shale unit and the two units below it at Condor. In these lower units, kaolinite is in greater abundance than other clays as well as quartz, an aspect already alluded to in the variations in Table I. (Loughnan (8) also noted that the structure of the kaolinite changes from ordered in the lower units to disordered in the brown oil shale unit). 

In the majority of British fireclays and ball clays, the clay mineral is usually kaolinite, but it is imperfectly crystalline, with some disorder in the stacking of the units. 

It had recently been shown that thermal disruption of the kaolinite mineral layer structure produced a highly reactive disordered aluminosilicate with a silica to alumina molar ratio of two. Higher calcination temperatures produced what is known as mullitized kaolin, which also contained some reactive free silica (86). This served to supply the additional silica needed for the synthesis of zeolite Y, which has a silica to alumina molar ratio in the 4.5 to 5.0 range. 

Clay plays an important role in medical science to prepare various medicines. This special aspect of clay is known as clay therapy. It is based on the ability of clays and clay minerals to adsorb and retain harmful and toxic substances. The beneficial effects of these materials to human health, notably in the treatment of gastrointestinal disorders, have been recognized. Among the variety of clays and clay minerals that were used by primitive tribes are bentonite, kaolinite, montmorillonite and smectite. The word medicine is derived from the Latin word ""medicind". Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness in human beings. Prehistoric medicine incorporated plants, animal parts and minerals. 

Clay. A natural material characterized by its plasticity, as taken from the clay-pit or after it has been ground and mixed with water. Clay consists of one or more clay minerals together with, in most cases, some free silica and other impurities. The common clay mineral is kaolinite most clays consist of kaolinite in various degrees of atomic disorder. 

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