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Illite TOT 2:1 layer clay

Illite TOT 2:1 layer clay. KAl 2 (AlSi 3 O 10 )(OH) 2 (Muscovite) Presented by Paul Sandlin. Illite Structure. Illite is a clay-grade mica resembling muscovite with more SiO 2 , less K 2 O, and more H 2 O

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Illite TOT 2:1 layer clay

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  1. IlliteTOT 2:1 layer clay KAl2(AlSi3O10)(OH)2 (Muscovite) Presented by Paul Sandlin

  2. Illite Structure • Illite is a clay-grade mica resembling muscovite with more SiO2, less K2O, and more H2O • Most Illites are dioctahedral with polytypes 2M1, 1M, 1Md, and 3T. However, trioctahedral illites are known • Difficult to determine chemical and structural characteristics, particularly 1Md types • Many illites are mixed-layer structures and the mixed-layering is not obvious when the proportion of admixed layers is small, 10% or less, usually montmorillonite • Weaver and Pollard (1973) -- chemical analyses data suggests that illites may resemble phengites rather than muscovites.

  3. Chemical Composition Srodon and Eberl (1984)

  4. Interlayer Cations • Interlayer stratification with montmorillonite will decrease the number of interlayer cations and increase the water content • sorbed water on surface replacing K+ at interlayer sites • Large surface area may account for excess sorption of H2O • Broken bonds may take up H2O, i.e., Si-O-Si may become Si-OH OH-Si to satisfy valence requirement • Alternatively, deficient K+ may be replaced by H3O+ • Aruja (1944)--chemical formula relative to 12(O + OH) is (K, Na)0.72(Al1.48Mg0.40)(Si3.19Al0.77Ti0.04)O9.18(OH)2.82 but the anion part is O10(OH)1.18(H2O)0.82 indicating that about 1/2 OH is replaced by water molecules

  5. 1. Yoder and Eugster (1955) 2. Levinson (1955) 3. Levinson (1955) 4. Levinson (1955) 5. Nagelschmidt and Hicks (1943)

  6. Srodon (1984)

  7. Interparticle Diffraction • McHardy et al. (1982), Nadeau et al. (1984) • Pure smectite is 10 Å thick corresponding to one 2:1 layer • Ordered I/S is composed primarily of particles 20 Å thick corresponding to two 2:1 layers coordinated by a single plane of K ions • ISII-ordered averaged four 2:1 layers coordinated by three planes of fixed K ions about 40 Å thick • Illite having no detectable expanding component averaged 70 Å thick • Evolution of I/S towards pure illite can be perceived as a growth of illite crystals parallel to c axis

  8. Polytypism • Yoder and Eugster (1955), Yoder (1959), and Velde (1965) • Found sequence of 1Md--1M--2M1 with increasing hydrothermal run time and temperature • In regional geologic studies, Reynolds (1963) and Maxwell and Hower (1967) showed 2M/1Md increases with increasing metamorphic grade in limestones and shales • Frey et al. (1983) found 3T, coarse-grained micas in regionally meta rocks from the Alps, but this polytype has not been found in diagenetic or low-grade meta sequences

  9. Illitization Processes • Detrital, diagenetic, and metamorphic processes • Illitization of smectite by wetting and drying process, Na replaced by K • Most marine illite is detrital, however, has been found in deeper sed cores and elevated temps of around 50°C • In lakes it is thought to be detrital smectite undergoing wetting and drying process • Kaolinite is illitized completely before smectite with no known reason • From muscovite with increasing temperature, the reaction sequence is detrital muscovitesericite (illite or I/S) phengite  muscovite which suggests that illite has a stability field with respect to muscovite • Neoformation of illite in sandstone pores (hairy illite) • Hydrothermal environments-- most studied from active geothermal fields-- • Horton (1983) documented a 1Md--1M--1M/3T--3T sequence evolution with decreasing expandibility • Shirozu and Higashi (1972) found 1Md--1M--2M1 set in similar geologic situation

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