Chlorite, layered silicate

Dixon, J. B. and M. L. Jackson. 1962. Properties of intergradient chlorite-expansible layer silicates of soils. Soil Sci, Soc. Am. Proc. 26 358-362. 

There are inconsistencies in the model for the calculation of activity products for the "clays. Exchangeable cations are disregarded for the low exchange capacity kaolinite, halloysite, chlorite, and moderate capacity illite. For certain expansible layer silicates and two zeolites, the logjo of the activity of selected cations is added into the sum of the activity products. 

There is not much resistance to weathering in these minerals because of the relative lack of Si—O—Si bonding, especially in island silicates such as olivine. Layer silicate minerals rich in Mg (e.g., trioctahedral smectites, chlorite, serpentine) may form from the siliceous residue if leaching does not deplete in the weathering zone. 

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. 

Chlorites occur extensively in soils and are 2 1 1 layer silicates (Fig. 5.6). The positively charged and substituted brucite sheet between the negatively charged mica-like sheets restricts swelling, decreases the effective surface area, and reduces the effec-... 

Despite the unlikelihood of secondary mineral formation by ion substitution into or movement within an existing solid, some secondary 2 1 layer silicates apparently are formed by solid-phase changes of mica fragments inherited from the parent material. Hydrous mica, for example, is a product of chemical weathering as well as mechanical breakdown of mica. Hydrous mica, in turn, can be modified directly to vermiculite, montmorillonite, or chlorite. The process is not completely understood, but seemingly involves the outward diffusion of K+ from between the layer lattices and a subsequent or simultaneous reduction of charge within the layer lattice. 

Clay minerals, the micas, chlorite, serpentine, talc, between them can also find within the group of minerals phyllosilicates or layered silicates. They all have different morphology, structure, and texture (Bergaya et al. 2009). The some representative layer silicates used mainly in nanocomposites-based starch are listed in Table 2. It is important to note that the some phyllosilicates do not display a normal layered strucmre, for example, the sepiolite shows a fibrous structure meanwhile halloysite has spheroidal aggregates morphology (Duquesque et al. 2007 Bergaya et al. 2009). 

Nanoclay fillers are categorized as platelet-like nanoclays or layered silicates and tubular nanoclays in terms of filler shape. With the configuration of two tetrahedral sheets of silicate and a sheet layer of octahedral alumina, platelet-like nanoclays or phyllosilicates are formed, which include smectite, mica, vermiculite, and chlorite. In particular, smectite clays are widely employed with further subcategories of MMT, saponite, hectorite, and nontronite. The typical MMT clays are regarded as one of the most effective nanofillers used in polymer/clay nanocomposites due to their low material cost and easy intercalation and modification (Triantafillidis et al., 2002). On the other hand, the fundamental structure of tubular nanoclays contains an aluminum hydroxide layer and a silicate hydroxide layer. They are also known as dio-ctahedral minerals with two different types of halloysite nanotubes (HNTs) and imo-golite nanotubes (INTs). Notwithstanding their material role as clay minerals, these two types of tubular nanoclays resemble the hollow tubular structure of carbon nanotubes (CNTs). In this section, three different types of clay nanofillers, namely MMTs, HNTs, and INTs are reviewed in detail along with the development of clay modification. 

Figure 3.4 Side views of the major types of layer silicate structures. The actual minerals shown are kaolinite, phlogopite IM, and chlorite IIb-2. The small circles are the actual hydrogen atom positions.

Mehra and Jackson [1959] showed, for a wide range of soil clays, that the sum of planar sorption surface of expandable 2 1 layer silicates and the mica unit-cell interlayer surface (as measured by potassium content), when corrected to exclude quartz, chlorite, and kaolinite in mixed clays, is constant within the experimental error of about 2%. 

Veitch and Radoslovich [1963] postulate that there should be two distinct octahedral hole sizes for most layer silicates and that octahedral ordering should exist as a general rule. This is only partly true for the chlorites whose structures are known. The llb-2 prochlorite shows cation ordering within both octahedral sheets. The la-4 kammererite and llb-4 corundophilite structures are ordered within the interlayer only. 

Brown and Jackson [1956], studying the Hiawatha Sandy Soils, find that the dominant layer silicate in all fractions of the B and C horizons is an interstratified vermiculite-chlorite (dominantly dioctahedral). This chlorite collapses on heating to 600° and is, therefore, relatively labile. Rich and Obenshain [1955] give evidence for an aluminum interlayer in dioctahedral vermiculite, which prevents the collapse of the mineral. 

Chlorites Hayashi and Oinuma [1965, 1967], Kodama and Oinuma [1963], Moenke [1962a]. 2 1 Layer Silicates... 

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