Illite

Despite the fact that members of the illite family appear to be the most abundant clay minerals next to kaoUnite, their state has not yet been defined unequivocally by the Association Internationale pour L Etude des Argiles (AlPEA) (Jambor et al., 1998). Stubborn mysteries still surround the formation and transformation of this most abundant clay mineral, mostly related to its widely varying chemical composition, small crystal size, degree of crystallinity or lack thereof, as well as the complexity of transformation sequences in the geologic environment over time. It has been a longstanding agreement that illite sensu lato can form basically by 

Starting from an ideal muscovite lattice, three possible reaction paths have been su ested, as shown in Table 2.3 (i) K+ ions in the interlayer space will be replaced by H3O ions (ii) one K ion together with one OH group of the octahedral layer will be replaced by two H2O molecules and (iii) one Si ion in the tetrahedral 

The physical interpretation of KI is based on the mean number of layers in coherent scattering domains (i.e., illite particle size) and the smectite-layer 

1 From Clay Minerals Society s Source Clays Repository 

PZC/IEP of Illite from Clay Minerals Society s Source Clays Repository Description Electrolyte T Method Instrument pHo Reference 

7 From Hungary, Washed with Diluted HjOj 

Properties (Purihed and transferred into sodium form) BET specihc surface area 16.4 m7g [2242]. 

Properties traces of quartz and kaolinite [139], SiO2 47.2%, AIjO, 23.1%, 

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Table 4. Chemical Analysis of Illite, Glauconite, and Attapulgite, wt %...

Cs NMR results for Cs on the surfaces of illite, kaolinite, boehmite and silica gel (Figure 3) show that for this large, low charge cation the surface behavior is quite similar to the interlayer behavior. They also illustrate the capabilities of NMR methods to probe surface species and the effects of RH on the structural environments and dynamical behavior of the Cs. The samples were prepared by immersing 0.5 gm of powdered solid in 50 ml of O.IM CsCl solution at 2 5°C for 5 days. Final pHs were between 4.60 and 7.77, greater than the zero point of charge, except for boehmite, which has a ZPC... 

For illite (Figure 3B) the total amount of Cs adsorbed is two orders of magnitude larger (ca. 0.26 atoms/A2) due primarily to the permanent charge developed by substitution of Al for Si in the tetrahedral sites and to less efficient filtering of the solution caused by lower sample permeability. The maximum amount of hydrated Cs that can be accommodated on the illite surface is ca. 0.023 atoms/A, close to the amount... 

Figure 3. CS MAS NMR spectra of Cs- exchanged (A) silica gel, (B) illite, (C) kaolinite, and (D) boehmite collected at H = 11.7 T, room temperature and the indicated relative humidities. The peaks marked by are spinning sidebands. After reference 27.

For illite and kaolinite with decreasing solution concentration (Figure 5) there are two important changes. The relative intensity for inner sphere complexes increases, and the chemical shifts become substantially less positive or more negative due to the reduced Cs/water ratio, especially for the outer sphere complexes. Washing with DI water removes most of the Cs in outer sphere complexes and causes spectral changes parallel to those caused by decreasing solution concentration (data not shown). 

The surface behavior of Na is similar to that of Cs, except that inner sphere complexes are not observed. Although Na has the same charge as Cs, it has a smaller ionic radius and thus a larger hydration energy. Conseguently, Na retains its shell of hydration waters. For illite (Figure 6), outer sphere complexes resonate between -7.7 and -1.1 ppm and NaCl... 

Figure 5. Cs MAS NMR spectra of (A) illite and (B) kaolinite Cs-exchanged at the indicated CsCl solution concentrations and collected at room humidity (ca. 35% RH) and H = 11.7 T. After reference 27.

Figure 6. MAS NMR spectra of illite exchanged in 0.1 M NaCl solutions at 25°c. Spectra collected at = 11.7 T, room temperature, and room humidity ca. 35% RH).

The diagenetic effects are related to the alteration of rock mineral, shales in particular. Under certain conditions, montmorillonite clays change to illites, chlorites and kaolinites. The water of hydration that desorbs in the form of free water occupies a larger volume. This volume increase will cause abnormal pressures if the water cannot escape. 

Fig. 14. Compensation plot for dehydroxylation of kaolinite ( ) and other layer-type silicates (X = montmorillonite, illite and muscovite) data and sources given in Table 11. (Redrawn, with permission, from Advances in Catalysis, ref. 36).

Kodama and Brydon [631] identify the dehydroxylation of microcrystalline mica as a diffusion-controlled reaction. It is suggested that the large difference between the value of E (222 kJ mole-1) and the enthalpy of reaction (43 kJ mole-1) could arise from the production of an amorphous transition layer during reaction (though none was detected) or an energy barrier to the interaction of hydroxyl groups. Water vapour reduced the rate of water release from montmorillonite and from illite and... 

Free water is driven off between adjacent miceles of montmorillonite and illite clays... 

In their model they used a kaolinite-like clay for the degraded silicate and allowed Na, Mg, and K to react to form sodic montmorillonite, chlorite, and illite respectively. The balance is essentially complete with only small residuals for H4Si04 and HCOT The newly formed clays would constitute about 7% of the total mass of sediments. 

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). 

Gangue minerals Quartz (fine-large grained), adularia, illite/smectite, chlorite/smectite, calcite, rhodochrosite Quartz (very fine-grained), barite, illite, kaolinite, adularia... 

In the Se-type gangue minerals comprise quartz, adularia, illite/smectite inter-stratified mixed layer clay mineral, smectite, calcite, Mn carbonates (manganoan calcite, rhodochrosite), Mn silicates (inesite, johansenite) and Ca silicates (xonotlite, truscottite). In comparison, the Te-type contains fine-grained, chalcedonic quartz, sericite, barite, adularia and chlorite/smectite interstratified mixed layer clay mineral. Carbonates and Mn minerals are very poor in the Te-type and they do not coexist with Te minerals. Carbonates are abundant and barite is absent in the Se-type. Grain size of quartz in the Te-type is very fine, while large quartz crystals are common in the Se-type. 

The compositions of the Sumikawa discharge fluids are controlled by K-feldspar, illite, calcite and Ca-aluminosilicates (epidote, prehnite, wairakite). 

Dominant gangue minerals are quartz, muscovite, chlorite, actinolite, hornblende, epidote, and biotite (Table 2.22). Minor minerals are rutile, illite, sphene, and glauco-phane. It is interesting to note that silicate minerals such as chlorite, epidote, pumpellyite, and albite are common and actinolite has been reported from the basalt near the Ainai Kuroko deposits (Shikazono et al., 1995) and they are also common in the basic schist which host the Motoyama Kuno deposits (Yui, 1983). 

Basic studies on the kinetics of swelling have been performed [1699]. Pure clays (montmoiillonite, illite, and kaolinite) with polymeric inhibitors were investigated, and phenomenologic kinetic laws were established. 

Mahoney JJ, Langmuir D (1991) Adsorption of Sr on kaolinite, illite, and montmorillonite at high ionic strengths. Radiochim Acta 54 139-144... 

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