Chlorite clay interlayers

Although partially organized dioctahedral chlorites form readily in soils, there are relatively few reported in sedimentary rocks. (More dioctahedral chlorites probably exist than have been recognized.) Swindale and Fan in 1967 reported the alteration of gibbsite deposited in Waimea Bay off the coast of Kauai, Hawaii, to chlorite but no data were obtained on its composition. Dioctahedral chloritic clays have been reported forming in recent marine sediments however, the identification is indirect and the interlayer material is relatively sparse (Grim and Johns, 1954). 

Chlorite (Mg-interlayer) Phyllosilicates Metamorphic or igneous rocks R vermiculite precursor Important precursor for 2 1 soil clay minerals... 

Montmorillonite has a high CEC value, but kaolinite and chlorite without interlayer cations have low CEC. Clays with high CEC play a leading role in the electrical conduction of shales and shaly sands (see Section 8.5). In case of radioactive ions , the abiUty of clay minerals to adsorb ions results in a contribution to natural radioactivity (see Section 5.2) (Table 1.2). 

Aluminum chlorite, (Al,Fe)4(Si,Al)402Q(0H)g, in which a gibbsitelike interlayer proxies in part for the bmcitelike interlayer, is being discovered in increasing occurrences and abundance (11,141). Chloritelike stmctures have been synthesi2ed by precipitation of Mg and Al between montmorillonite sheets (143). Cookite [1302-92-7], an aluminous chlorite containing lithium, has been found in high alumina refractory clays and bauxite [1318-16-7] (139). 

The CEC of clay minerals is partly the result of adsorption in the interlayer space between repeating layer units. This effect is greatest in the three-layer clays. In the case of montmorillonite, the interlayer space can expand to accommodate a variety of cations and water. This causes montmorillonite to have a very high CEC and to swell when wetted. This process is reversible the removal of the water molecules causes these clays to contract. In illite, some exchangeable potassium is present in the interlayer space. Because the interlayer potassium ions are rather tightly held, the CEC of this illite is similar to that of kaolinite, which has no interlayer space. Chlorite s CEC is similar to that of kaolinite and illite because the brucite layer restricts adsorption between the three-layer sandwiches. 

Chlorite and Vermiculite. Chlorite is a 1,4-nm (14 A) clay mineral that cannot be expanded or collapsed by traditional laboratory procedures. Structurally, the unit layer of chloride is composed of a 2 I layer combined with a ().4-nin Mg or Al interlayer or hydroxide sheet. 

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. 

Quite often Al, Fe, and Mg hydroxides partially fill the interlayer position of the derived vermiculites and decrease their exchange capacity and their ability to contract completely to 10 A when heated or when treated with a potassium solution. This material can usually be removed by treating the clay with a solution of sodium citrate (Tamura,1958). As the content of hydroxy interlayer material increases, the expandable clay tends to assume the character of a chlorite. Thus, in the weathering of a mica or illite it is not uncommon to form discrete vermiculite-like, beidellite-like, monf-morillonite-like and chlorite-like layers. These various layers can occur as discrete packets or interstratified in a wide variety of proportions. 

The negative relation between K2 O and Fe2 03 also occurs in the illites and has been discussed. Fe203 is positively correlated with H20+ and presumably negatively with layer charge. H20+ (greater than 110°C) and H20 (less than 110°C) are inversely related. These correlations suggest some of the H20+ may be trapped interlayer water not easily released (at 110°C) from the clays with a high proportion of contracted layers or that chloritic layers increase as the proportion of expandable layers decrease. 

When all the K is assigned to the contracted 10 A layers and a plot made of the amount of K per 10 A layer versus percent 10 A layers (Fig.18), a distinct positive relation is apparent. The data indicate that when there are no expanded layers the clay contains 0.8 K per O10(OH)2 the amount of K systematically decreases and for 40% contracted layers the concentration is 0.55 K per Oi 0(OH)2. If some K is present in the expanded layers the amount of K in the contracted layers would be even lower. These data may indicate the calculated proportion of contracted layers is high or, on the basis of Hower s (1967) reasoning, the amount of ordered interlayering increases with a decrease in the proportion of contracted 10 A layers (less average charge per layer is required to contract ordered interlayers than random interlayers). Another possibility is that approximately 20% of the contracted layers are chlorite. It is difficult to detect less than 40% illite layers interlayered with montmorillonite and it is probably equally difficult to detect 20% or so chloritic layers (Weaver and Beck, 1971a). 

Figure 2. Structure of a typical chlorite-like hydroxy-interlayered clay in which the galleries of a 2 1 smectite structure are filled, or nearly so, with brucite-like sheets of mainly edge-shared Mg(OH) octahedra. Aluminum occasionally substitutes for magnesium in the brucite sheet to provide the charge balance necessary for electrical neutrality.

Clay minerals are hydrous aluminum phyllosilicates made of sheets or layers composed of tetrahedra and octahedra. This mineral type includes the following groups kaolinite, smectite, illite, and chlorite. In the case of smectite, each layer comprises two sublayers of tetrahedra with an inserted octahedral layer, where, between layers, an interlayer space where the exchangeable cations are located is formed [131-133], In Figure 2.24... 

An additional structural variant for clay minerals is the chlorite-type structure. Chlorites are similar to the pyrophyllite-type structures with two tetrahedral sheets and an octahedral sheet making up each layer. Instead of alkali or alkaline earth interlayer cations, chlorites contain a brucite (Al-Mg hydroxide) layer between successive pyrophyllite-type layers [18]. 

X-ray diffraction analyses of the < 2-micron size fraction of suspended sediment and soils from the Mattole basin indicate that kaolinite, ver-miculite, and aluminum-interlayered vermiculite comprise the main clay minerals. Much smaller amounts of illite commonly are present. Chlorite is detectable in a few suspended-sediment samples. 

Rectorite is one of an almost infinite number of randomly mixed layer clays (411. collectively called illites, which include several other ordered interstratified varieties, including chlorite, corrensite and allevardite. Rectorite has the advantages of a mica and a smectite, in that alternate interlayers are expanding and non-expanding. It may be viewed as an ordered synthetic mica-montmorillonite (SMM) in the nomenclature familiar to catalytic... 

The 2 1 layer type with hydroxide interlayer is represented by dioc-tahedral chlorite in soil clays (Figs. 1,3). The unit cell chemical formula of this mineral can be expressed ... 

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%. 

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