THE STRUCTURAL MODEL OF ILLITE/SMECTITE INTERSTRATIFIED MINERAL AND THE DIAGRAM FOR ITS IDENTIFICATION

Size: px

Start display at page:

Download "THE STRUCTURAL MODEL OF ILLITE/SMECTITE INTERSTRATIFIED MINERAL AND THE DIAGRAM FOR ITS IDENTIFICATION"

Dale Watkins
6 years ago
Views:

1 Clay Sicence 7, (1988) THE STRUCTURAL MODEL OF ILLITE/SMECTITE INTERSTRATIFIED MINERAL AND THE DIAGRAM FOR ITS IDENTIFICATION TAKASHI WATANABE Department of Geoscience, Joetsu University of Education, Joetsu, Niigata Pref., 943 Japan (Accepted March 7, 1988) ABSTRACT The structural model of I/S was proposed. The I/S structures are divided into some groups by the number of I which exists between S and S. The structural types were defined as 0, 1, 2, 3, n. In the case of type 0, the structural model is defined in the range of 0-50 S% and the SS sequence is allowed in the nearest neighbour case of S and S. The structural model of type 1 is allowed in the range of S% and the SIS sequence is recognized in the nearest neighbour case of S and S for 0-50 S%. The structural type 2 was defined in the range of 0-33 S% and the SIIS sequence exist in the nearest neighbour. The structural type 3 was defined in the range of 0-25 S% and the SIIIS sequence is recognized in the nearest neighbour case of S and S. Generally, the SI...IS sequence is recognized in the nearest neighbour case of S and S. The structural type of 1, 2, 3,...,n correspond to Reichweite 0,1,2,3,...n, respectively. The theoretical X-ray diffraction profile of I/S proposed by I/S structural model were calculated. By using of positions three characteristic X-ray profiles, the diagram for identification of I/S structure was obtained. Using the diagram for natural specimen of I/S, the good results were obtained. Key words: I/S, interstratified mineral, illite, smectite, structural model, Reichweite INTRODUCTION Recently, the interstratified illite/smectite (I/S) is the top of topics in the clay minerals world and many studies about the analysis of the formation process have been reported (Hower et al., 1976; Boles and Franks, 1979; Pollastro, 1985; Nadeau et al., 1985). The most interesting theme is how the structure of I/S converts in the formation process. However, the analytical method of interstratified structure is so complicated that the studies on the field have not developeḍ Sato et al. (1965) has reported for the first time the calculation method of the theoretical X-ray line profile using the stochastic process and its application to the natural samples, I/S. After that, Reynolds and Hower (1970) have calculated the theoretical profile by the different way based on MacEwan (1958). These theoretical data have been used by many other workers. Watanabe (1981) has proposed the diagram for structural identification of I/S. The method for the structural analysis of I/S is so

2 98 T. Watanabe simple and useful that this method is also applied to other interstratified minerals (Tomita & Takahashi, 1985, 1987). Inoue & Utada (1983) showed an actual proof that the conversion process S (smectite) I/S I (illite) exists in the hydrothermal environment by analyzing boring cores. In that report, they suggested that the interstratified structure of I/S is continually changing in the conversion process using the diagram for identification of I/S by Watanabe. The structural model of I/S proposed has become of interest lately. Bethke (1986, a, b) tried to catch the conversion process as the variation of the I/S structure. However, the systematic discussion about the structure model of I/S has never been done. The structural model of I/S and made the diagram for identification for g=0, 1, 2 has been already proposed by Watanabe (1981). Therefore, in this paper, the systematic structural model is proposed and the revised diagram for the structural identification of I/S for g >_ 3 is reported additionally. STRUCTURAL MODEL The structural models are identified by the type of the junction S (smectite layer) to S. That is, the type n 0 is defined as the number of I (iffite layer) between S and S as follows; structural type n (n _ 0) has the sequence SI IS in the nearest neighbour case. Therefore sequence SI -IS is allowed, but SI c IS is prohibited. In n<n structural type 0 of the structural model proposed, the all type of sequence i.e. II, SS, IS, SI are allowed. In the case of structural type 1, one S exists between I and I at least in the case of S >_ I% and on the contrary in the case I S%, one I exists between S and S at least. In other expression, sequences with more than one I between S and S such as SIS, SIIS, SIIIS, and SI...IS, exist, but S and S never contact directly in the case of I > S%, and vice versa in S? I%. In structural type 2, I-sequence between S and S is above 2 and SS, SIS sequences are prohibited. In the case of structural type 3 or more, the same manner as above is recognized, that is, in type n, the number of I between S and S is above n and under n is prohibited. Therefore, there is the important relation between the type n and S% range. Type 0, 1 is in the range of S%, type n _2 is defined in less than 50 S%. The more precise data of the structural models are summarized in Table 1. In other hand, there is not discontinuous but continuous relation between type n and n+1 in this structural model that are recognized as follows. For example, the minimum number of I between S and S is n in type n. When the number of I between S and S increases step by step without changing in ratio of I and S% and get to n+1 at the last, it will be interpreted that the structure type n changes completely into n+1. In the intermediate stage of n to n+1, the structure will be the mixed type of n and n+1. This structural model could be expressed by the mathematical representation using Markov stochastic theory and type n corresponds to Reichweite (Jagodzinski, 1949) as described in Appendix. Also, the probability matrix of type n=0, 1, 2, 3 is shown in Appendix.

3 The structure model of I/S 99 TABLE 1. The condition of structural model proposed. CALCULATION OF X-RAY LINE PROFILES X-ray line profiles of the structural model proposed here, were calculated by using the theory of Kakinoki and Komura (1952) (Watanabe, 1977). The process is shown as follows. At first, the structural model of elementary layer such as I and S and necessary parameters of interstratified structure based on the structural model proposed here were established. Using them, theoretical X-ray line profiles were calculated by Kakinoki & Komura (1952) and were, also, made correction for the particle size and the slit system of diffractometer. Elementary layer The structural parameter of EG-treated smectite layer and illite layer are listed up Table 2. Parameter of interstratified structure In the structural model of I/S proposed in the previous chapter, from Eq (A-4), (A-6), (A-11), and (A-16) shown in Appendix, the following equations hold. for g=0 Ws P12=P22 WI=P11 =P21 for g=-1,ws=-p12(1-ws)(i>s%) WI=P21(1-WI) (S>I%)

4 100 T. Watanabe TABLE 2. Structural data of elementary layers. Z; Z-parameter B; temperature factor for g=2, Ws=P14(1-2Ws) for g=3, Ws-P17(1-3Ws) and, considering Ws, WI, P12, P14, P17>0, the range of existence probability WS and WI are limited. The parameter of interstratified structure are summarized in Table 3-6. The theoretical X-ray profiles for each interstratified structure proposed are shown in Fig TABLE 3. The parameter of interstratified structure for type 0

5 The structure model of I%S 101 TABLE 4. The parameter of interstratified structure for type 1 TABLE 5. The parameter of interstratified structure for type 2 TABLE 6. The parameter of interstratified structure for type 3 Particle size and its distribution If the distribution of Ni elementary layer is P (Ni), the average number of layer, N is expressed as follows, In this paper, the distribution function P(Ni) is defined as next function.

6 102 T. Watanabe FIG. 1. Calculated diffraction profiles for structural type 0. The numbers (%) in right part show S%. In calculation, a = 2.0, N = 20 and used as the standard condition, and the function P(Ni) and Ni are listed in Table 7. Slit-condition In order to get good agreement between calculated and observed line profile, the line profile calculated was corrected for the slit condition. The convolution of the theoretical profile, f(20) and the slit-function, g(20) was calculated and the calculated line profile, I(20), was obtained. In this paper, the function I(20) is defined is follows,

7 The structure model of I/S 103 FIG. 2. Calculated diffraction profiles for structural type 1 (I>S%). The numbers (%) in right part show S%. I'(2ƒÆ+ƒÃ) is the theoretical intensity at 2ƒÆ+ƒÃ (degree) and exp (-K2 EƒÃ2) is the slit-function (Klug and Alexander, 1974). The constant K were defined experimentally as the value which gave good agreement to the line profile of the large sized muscovite. In calculation, K=10.0, d e =0.2 was used and this condition was setting for the slit system (1 /2-0.3mm-1 /2 ) of Rad-II diffractometer (RIGAKU Co. Ltd. JAPAN). THE DIAGRAM FOR IDENTIFICATION OF I/S STRUCTURE Watanabe (1981) has already reported the diagram for identification of I/S. In this paper, the new results about g>3 region are reported additionally. The modifications for g>3 of Watanabe's diagram were made by Srodon and Eberl (1984). However, the

8 104 T. Watanabe FIG. 3. Calculated diffraction profiles for structural type 2. The numbers (%) in right part show S%. modified diagram is differ from author's intention. The diagram for identificaon is formed by the plot of the difference angle among three characteristic X-ray line profile of I/S. Three X-ray line profiles appear at about 6, 9, and 17 (20 degrees, CuKƒ ), and represent the characteristic trend of I/S structure (Fig. 1-4). The position of three lines are indicated by l1,l2, and l3 (2ƒÆ ), and the differences are denoted as follows; 2ƒÆ1 =l2-l1, 2ƒÆ2 =l3-l2. The values of 2 01, 202 of Fig. 1-4 are plotted to get Fig. 5. The letter g = 0, 1, 2,..., noted on the plot lines correspond to the structural type and Reichweite g, and the numbers indexed on each triangle mark show S% The shaded zone between g = n and g = n-1 are when the intermediate structures of g = n and n-1 are plotted. It is expected almost I/S specimen in nature are plotted at this region.

9 The structure model of I/S 105 FIG. 4. Calculated diffraction profiles for structural type 3. The numbers (%) in right part show S%. TABLE 7. Number of component layers and its distribution

10 106 T. Watanabe Relation between n and n-1 (1) From type 1 to 0 The junction matrix P for type 1 is shown by Eq. (A-3). In the case of g=1 we can get P22 =0. If in the structure, the SS-sequence is found, the interstratified structure is apt to convert from 2 to 1. When we get P11=P21, P12=1)22 and the SS-sequence is increasing and get at maximum value, type 1 is transformed completely to 0. In the case of S > I%, the manner like this is developed, P11 = 0 at Eq. (A-5) and the II sequence in the structure is prohibited. If the II sequence is allowed in the structure, the structure is converted from 1 to 0, completely, when we can get P11= P21 P12=P22. The trend of transform 0 to 1 in case of 50%S and its X-ray line profiles were shown in Fig. 5 and (2) From type 2 to 1 The P matrix of type 2 is shown in Eq. (A-10). If SIS-sequences are changed by the sequence SII, the value of P24 starts from zero to get P14=P24 and p11=p21, this means that the structural type 2 is transformed by type 1. (3) Conversion from type 3 to 2 In type 3, P27 of (A-14) in Appendix is zero. Then, the SIIS-sequence is prohibited. FIG. 5. Identification diagram of I/S for Cu.ka radiation. Each triangle sign means S%. The dotted line means the disappearance of profile. A-B shows the tieline of 50%S and AB trends on increasing IS-sequence. The plots for g>_4 (A) were obtained from calculation of the supperlattice structure.

11 The structure model of VS 107 If the number of I in SIIIS decrease without changing in ratio of I and S%, the SIIS sequence increases in type 3 structure. It means that the structure type 3 is converting to type 2. This tendency is increasing and reaches at maximum value P 27=P17 i.e. P 11 =P21 then, the type 3 is completely transformed type 2.1 DISCUSSION Thickness of smectite layer (Ethylene glycolated) Srodorn (1980) has suggested that the position of line profiles of I/S are influe nced considerably by the d001 thickness of smectite. These influence for S% have been examined. The differences in the diagram for identification was very small fo r each cases of 16.9, 17.1, and 15.8A and three lines were mixed one another. Almost of natural specimens are plotted on the line of 16.9A as shown Fig. 7. Srodon (1980) has also indicated that smectite of 16.9A is verycommonin naturaloccurrences. Therefore, thi in s study, 16.9A is adopted as the thickness of smectite layer. FIG. 6. Calculated diffraction profiles for the variation along the tieline A -B on Fig. 5 (type 0-1, 50%S).

12 108 T. Watanabe FIG. 7. Plot of natural I/S samples. o: Inoue & Utada (1983), Ÿ: Srodon (1980). Particle size Srodon (1980) has pointed out that the X-ray profile positions depend on the particle size. In this study, the displacements of the lines in the identification diagram were examined. The lines of N=5 and 10, is placed under that of N=20, and for N>20, the lines did not change the position of N=20. Therefore, N=20 is adopted for the particle size in this study. The plots of natural I/S specimen are almost at upper side from line of N=20. This fact suggests that particle size is about more than N=20 and the I/S structure of natural sample has a tendency to be the intermediate structure between g=n and n+1. On the other side, it can be considered that the displacement of natural sample's plots is caused by the more randomly structure of the small particle specimens such as N=5, 10. Nevertheless, the I/S structure of S% is hardly disordered structure and the line profiles agree with the profiles of N = 20 and g = 1. It is very reasonable that the I/S structure is consist of the N=20 particles. Comparison with various I/S structure model reported The I/S structural model has been presented by Reynolds and Hower (1970). The I/S structural model as divided into some types, that is, S, IS, IIS, and IIIS separately. On the contrary, it is the important characteristic that the structural model proposed in the paper is treated as the structure with continuous variations from g=0 to n. The characteristic variations of the I/S structure cause the displacements of three special lines. The differences are plotted into the diagram and the identification of I/S structure

13 The structure model of I/S 109 is identified not independently but systematically. In Reynolds & Hower (1970) and Srodon (1980) method, at first, the decision of structural type (I, S, IS, IIS, IIIS) must be done, and the identification of I/S structure will be continued. The results of plotting of I/S in nature are shown in Fig. 7, and is plotted the expected zone. It is assumed that in reality more plot occur more concentrately in the shaded zone. It is concluded that close agreements between observed and calculated from the structural model were obtained, and the structure of I/S coincide with the structural model proposed in this paper. Also, from plot of natural I/S specimens, it is indicated that structural type 0, 1, 2 and 3 occur at , 0-50, and 0-25 S%. SUMMARY The structural models of I/S are represented by using n-th Markov theory and n-values response to Reichweite n by Jagodzinski (1949). In this paper, Reichweite g for I/S structure is extended from 0 to n. The diagram made from the structural model proposed in useful for identification of I/S structure of natural specimen. APPENDIX Letters used in appendix are defined as follows. P; the junction matrix whose element Pij means the transition probability from i-state to j-state. fi(xxx); the existence probability of xxx-sequence and i means i-kind of sequences. For example, Pis means the transition probability of illite to smectite and f 3(SSI) means the finding probability of SSI-sequence denoted by 3. Structural type 0 and 1 Case of type 0 and 1 are representated by simple Markov chain and correspond to Reichweite g=0 and 1, respectively. General formula of junction matrix P is as follows, (A-1), where Pi3 means junction probability of i to j and I, S correspond to illite and smectite, respectively. In the case of g=1, (A-2) In I S%, the SS-sequence is prohibited, and P22=0,

14 110 T. Watanabe (A-3) (A-4), where Ws means the existence probability of smectite. The sequences in the structure are SIS, SIIS,..., SI...IS. In S I%, the II sequence is not found and P11=0, (A-5) (A-6), where WI means the existence probability of illite. The sequences in the structure is ISI, ISSI,..., ISS csi. n>2 In the case of type 0, the SS-sequence are allowed and P22 in Eq. (A-1) is not zero. All elements of Eq. (A-1) are not zero and P11 P21=W1, P22 P12 =Ws' In the case of g=0, (A-7) This case corresponds to Reichweite g=0. The sequences in the structure are all kind such as IS, SI, SS and II.

15 The structure model of I/S 111 Structural type 2 This case is representated by 2nd Markov chain and correspond to Reichweite g=2. In this case, all kinds of. state are II, SI, SS, and IS. The geneal formula of the junction matrix is (A-9), where Pij means junction probability of i-state to j-state and the state of 1, 2, 3, and 4 corresponds to II, SI, SS, and IS, respectively. The sequences of SS, SIS, SSS, SSI, ISS are prohibited and P24=P32=P33=P42=P43=0,P21=1, then (A-10) (A-11) Structural type 3 The case is represented at 3rd Markov chain and correspond to Reichweite g=3. The general formula of junction matrix P is,

16 112 T. Watanabe (A-12) (A-13) (A-14)

17 The structure model of I/S 113 (A-15) (A-16) Therefore, structural type 0, 1, 2 and 3 be represented by n-th Markov chain. For g>4, the manner described above is developed. REFERENCES BETHKE, C.M., VERGO, N., and ALTANER, S.P.(1986, a) Pathways of smectite illitization: Clays & Clay minerals, 34, BETHKE, C.M. and ALTANER, S.P.(1986, b) Layer-by-layer mechanism of smectite illitization and application to a new rate law: Clays & Clay minerals, 34, BOLES, J.R. and FRANKS, S.G.(1979) Clay diagenesis in Wilcox sandstones of southwest Texas: Implications of smectite diagenesis on sandstone cementation: J. Sed. Petrol., 49, HOWER, J., ESLINGER, E., HOWER, M., and PERRY, E.(1976) The mechanism of burial diagenetic reactions in argillaceous sediments, 1. Mineralogical and chemical evidence: Geol. Soc. Amer. Bull., 87, INOUE, A. and UTADA, M.(1983) Further investigations of a conversion series of dioctahedral mica/smectites in the Shinzan hydrothermal alteration area, northeast Japan: Clays & Clay Minerals, 31, JAGODZINSKI, H.(1949) Eindimensionale Fehlordnung in Kristallen and ihr Einfluss auf die Rontgeninterferenzen. I. Berechnung des Fehlordnungsgrades aus der Rontgenintensitaten: Acta Crystallogr., 2, KAKINOKI, J. and KOMURA, Y.(1952) Intensity of X-ray by an one-dimensionally disordered crystal.: Jour. Phys. Soc. Japan, 7, KLUG, H.P. and ALEXANDER, L.E.(1973) X-ray diffraction procedures. John Wiley and Sons, New York (2nd. Ed.) 966p. MacEWAN, D.M.C.(1956) Fourier transform methods for studying scattering from lamellar systems. I. A direct method for analyzing interstratified mixtures.: Kolloidzeitschrift, 149, MacEWAN, D.M.C.(1958) Fourier transform methods for studying X-ray diffraction effects for various types of interstratification.: Kolloidzeitschrift, 156, NADEAU, P.H., WILSON, M.J., McHARDY, W.J., and TAIT, J.M.(1985) The conversion of smectite to illite during diagenesis: Evidence from some illitic clays from bentonites and sandstones: Mineral Mag., 49, POLLASTRO, R.M.(1985) Mineralogical and morphological evidence for the formation of illite at the expense of illite/smectite: Clays & Clay Minerals, 33, REYNOLDS, R.C. and HOWER, J.(1970) The nature of interlayering in mixed-layer illite-montmorillonites: Clays & Clay Minerals, 18,

18 114 T. Watanabe SATO M., OINUMA K. and KOBAYASHI K.(1965) Interstratified minerals of illite and montmorillonite. Nature, Lond., 208, RODOI^, J.(1980) Precise identification of illite/smectite interstratifications by X-ray powder diffraction: Clays & Clay Minerals, 28, SRODON, J. and EBERL, D.D.(1984) Illite: in Micas (Reviews in Mineralogy, vol 3), S.W. BEILEY, ed., Mineralogyical Society of America, TOMITA, K. and TAKAHASHI, H.(1985) Curves for the quantification of mica/smectite and chlorite/smectite interstratifications by X-ray powder diffraction: Clays & Clay Minerals, 33, TOMITA, K. and TAKAHASHI, H.(1986) Quantification curves for the X-ray powder diffraction analysis of mixed-layer kaolinite/smectite: Clays & Clay Minerals, 34, WATANABE, T.(1977) X-ray line profile of interstratified chlorite/saponite: Sci. Rept. Fac. Sci., Kyushu Univ., Geology, 12, (in Japanese, with English abstract). WATANABE, T.(1981) Identification of illite/montmorillonite interstratification by X-ray powder diffraction: J. Miner. Soc. Japan, Spec. Issue, 15, (in Japanese, with English abstract).

PATHWAYS OF SMECTITE ILLITIZATION

Clays and Clay Minerals, Vol. 34, No. 2, 125-135, 1986. PATHWAYS OF SMECTITE ILLITIZATION CRAIG M. BETHKE, NORMA VERGO, AND STEPHEN P. ALTANER Department of Geology, University of Illinois Urbana, Illinois