Mixed-layer clay

Mixed-layer clays, particularly lUite—smectite, are very common minerals and illustrate the transitional nature of the 2 1 layered siHcates. The transition from smectite to iUite occurs when smectite, in the presence of potassium from another mineral such as potassium feldspar, or from thermal fluids, is heated and/or buried. With increasing temperature smectite plus potassium is converted to iUite (37,39). 

An alternative description of iUite—smectite mixed-layer clays begins with megacrystals of smectite that incorporate smaller packets of iUite (163). These constituents are observed as mixed-layer minerals in x-ray analysis. Diagenesis increases the percentage of iUite layer and with increasing alteration the mixed-layer mineral takes on the characteristics of an iUite dominated iUite—smectite. 

Chlorite is another mineral that is commonly associated with mixed-layered clays. Complete soHd solutions of chlorite mixed-layer minerals have not been identified. In contrast to iUite—smectite mixed-layer minerals, chlorite mixed-layer minerals occur either as nearly equal proportions of end-member minerals (Rl) or dominated by one end member (RO) (142). Mixed-layer chlorite may consist of any of the di—tri combinations of chlorite and chlorite mixed-layering occurs with serpentine, kaolinite, talc, vermicuhte, smectite, and mica. References of specific chlorite mixed-layer minerals of varied chemical compositions are available (142,156). 

Mixed layer clay mineral (sericite/smectite) is found in Kuroko ore bodies and altered dacitic rocks underlying the ore. This mineral is thought to have formed by the... 

Main gangue minerals of the Se-type deposits comprise quartz, adularia, illite/ smectite interstratified mixed layer clay mineral, chlorite/smectite interstratified mixed layer clay mineral, smectite, calcite, Mn-carbonates, manganoan caleite, rhodoehrosite, Mn-silicates (inesite, johannsenite) and Ca-silicates (xonotlite, truscottite). 

In eomparison, the Te-type deposits contain fine-grained quartz, chalcedonic quartz, sericite, barite, adularia, ehlorite/smectite interstratified mixed layer clay mineral and rarely anatase. Carbonates and Mn-minerals are very poor in the Te-type deposits and they do not coexist with Te-minerals. Carbonates are abundant and barite is absent in the Se-type deposits. The grain size of quartz in the Te-type deposits is very fine, while large quartz crystals are common in the Se-type deposits although they formed in a late stage and do not coexist with Au-Ag minerals. 

Principal gangue minerals in base-metal vein-type deposits are quartz, chlorite, Mn-carbonates, calcite, siderite and sericite (Shikazono, 1985b). Barite is sometimes found. K-feldspar, Mn-silicates, interstratified mixed layer clay minerals (chlorite/smectite, sericite/smectite) are absent. Vuggy, comb, cockade, banding and brecciated textures are commonly observed in these veins. 

Zeolite minerals (wairakite, laumontite etc.), mixed-layer clay minerals and sme-cite occur in the upper part of the propylitically altered rocks (e.g., Seigoshi, Fuke, Kushikino), but they are sometimes poor in amounts. Generally carbonates are more abundant in the mine area as in the Toyoha district. Temporal relationship between the formation of high temperature propylitic alteration minerals (epidote, actinolite, prehnite) and low temperature propylitic alteration minerals) (wairakite, laumontite, chlorite/smectite, smectite) in these areas (Seigoshi, Fuke, Kushikino) is uncertain. 

Seigoshi argentite electrum, pearceite, polybasite, pyrargyrite, stephanite, chalcopyrite, fahore, galena, sphalerite quartz, adularia, inesite, xonotlite, chlorite, mixed layer clay mineral, sericite. calcite, rhodochrosite... 

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... 

Over longer time scales, clay minerals can undergo more extensive reactions. For example, fossilization of fecal pellets in contact with a mixture of clay minerals and iron oxides produces an iron- and potassium-rich, mixed-layer clay called glauconite. This mineral is a common component of continental shelf sediments. Another example of an authigenic reaction is called reverse weathering. In this process, clay minerals react with seawater or porewater via the following general scheme ... 

This information is reported as the percentage that each of the clay mineral type contributes to total identifiable clay mineral content of the noncarbonate clay-sized fraction of the surface sediments. These percentages were determined by x-ray diffraction, which is luiable to identify noncrystalline solids. Using this technique, clay minerals were found to comprise about 60% of the mass of carbonate-free fine-grained fraction. Most of the noncrystalline soUds are probably mixed-layer clay minerals. Carbonate was removed to facilitate the x-ray diffraction characterization of the clay minerals. In some cases, roimd off errors cause the sum of the percentages of kaolinite, illite, montmorillonite, and chlorite to deviate slightly from 100%. 

Kaolin - Kaolinite 4, 5, 6, Dickite 16. 27 Mica - Biotite, Phologopite, Muscovite Illite - Illite 36, Illite-Bearing Shale Mixed-Layer Clays - Metabentonite 37, 42 Montmorillonite - 21. 22A, 22B, 24, 25, 26. 31 Feldspars - Albite, Anorthite, Orthoclase Chlorite - Chlorite... 

The problem with limited selectivity includes some of the minerals which are problems for XRD illite, muscovite, smectites and mixed-layer clays. Poor crystallinity creates problems with both XRD and FTIR. The IR spectrum of an amorphous material lacks sharp distinguishing features but retains spectral intensity in the regions typical of its composition. The X-ray diffraction pattern shows low intensity relative to well-defined crystalline structures. The major problem for IR is selectivity for XRD it is sensitivity. In an interlaboratory FTIR comparison (7), two laboratories gave similar results for kaolinite, calcite, and illite, but substantially different results for montmorillonite and quartz. 

Mixed layered clays, most often ordered, are present up to temperatures near 200°C at depths of 500 to 1500 meters. The minerals form in two distinct zones. At shallow depths (between 100 and 200°C) mixed layering is between 90 and 0% montmorillonite. Above 200°C or so no expandable minerals are present. In the second zone (1.5Km. depth) one finds ordered interlayering showing the superstructure reflection... 

Those chlorites associated with mixed layered clay minerals are most silica-rich and have the greatest compositional variations for grains in a single thin section they tend to be iron-rich and aluminous. One chlorite vein was found to transect a glauconite pellet. This chlorite was quite iron-poor indicating attainment of a local chemical equilibrium between chlorite and iron mica upon its crystallization. 

IIYAKA (J.T.) and ROY (R.), 1963. Controlled synthesis of heteropolytypic (mixed-layered) clay minerals. Clays and Clay Min. 10, 4-22. 

Clay Minerals. The clay minerals in coal all contain water bound within their lattices. Kaolinite contains 13.96%, illite 4.5%, and mont-morillonite 5% bound water. In addition, the montmorillonite in the mixed-layer clays also contains interlayer or adsorbed water. All of the water is lost during the high-temperature ashing. 

There is a large number of clays which are not pure mineral types but consist of interstratified units of different chemical composition. (In detail, this may include nearly all the 2 1 layer minerals.) These are called mixed-layer clays. The two or possibly three different units can be regularly interstratified ABABAB or more commonly randomly interstratified AABABBABA. The most common regularly interstratified clay mineral, corrensite (Lippman, 1954), consists of alternate layers of chlorite and vermiculite or chlorite and montmorillonite. 

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. 

Mg-rich chlorites do not seem to form readily in low-temperature marine environments. Mixed-layer chlorite-vermiculites form fairly easily in magnesium-rich environments but complete development of the brucite sheets must be considerably more difficult. Mixed-layer chlorite-vermiculite is the predominant clay in the Lower Ordovidian limestones and dolomites of southern United States, usually over a thousand feet thick and extending over 500,000 square miles, yet very little chlorite is present (Weaver, 1961a). These mixed-layer clays and others like them appear to have formed on extensive tidal flats where the clays were exposed to alternating evaporitic... 

The layers may be regularly or randomly interstratified. The latter are by far the more common and are probably the second most abundant clay mineral species, following illite (which in most cases is a mixed-layer clay). More regularly interstratified clay minerals have a definite periodicity and some are given specific mineral names. The randomly interstratified clay minerals are described in terms of the type and proportion of the two or more types of layers. Many of them exhibit some degree of regular interlayering. 

The most common type of mixed-layer clay is composed of expanded, waterbearing layers and contracted, non-water-bearing layers (i.e., illite-montmorillonite, chlorite-vermiculite, chloritc-montmorillonite). Most of these clays form by the partial leaching of K or Mg (OH)2 from between illite or chlorite layers and by the incomplete adsorption of K or Mg(OH)2 on montmorillonite- or vermiculite-like layers. They most commonly form during weathering or after burial but are frequently of hydro-thermal origin. 

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