X-Ray Diffraction Line Profile of Glauconitic Clay from the Minamishiraoi Deposit and Evaluation of Its Mixedlayer Structure

$X-Ray Diffraction Line Profile of Glauconitic Clay from the Minamishiraoi Deposit and Evaluation of Its Mixedlayer Structure$

Clay Science 9, 53-63 (1994)

X-RAY DIFFRACTION LINE PROFILE OF GLAUCONITIC CLAY FROM THE MINAMISHIRAOI DEPOSIT AND EVALUATION OF ITS MIXED- LAYER STRUCTURE

TETSURO YONEDA Department of Mineral Resources Development Engineering, Hokkaido University, Sapporo 060, Japan

and TAKASHI WATANABE Department of Geoscience, Joetsu University of Education, Joetsu 943, Japan (Accepted Feb. 10, 1994)

ABSTRACT

X-ray diffraction experiment of a granular glauconitic clay and the computer simulation of the X-ray diffraction line profile of the clays from the Minamishiraoi Kuroko-type deposit, southwestern Hokkaido, Japan, were carried out to elucidate its mixed layer structure. The mixed layer structure which shows an intermediate property of glauconite and smectite were evaluated to be of a random-type interstratification somewhat deviated from random interstratification towards the direction of segregation structure of glauconite and smectite, through comparison of the measured and the calculated X-ray diffraction line profiles. It is suggested that the comparisons of the relative intensity ratio of the saddle peak and the (001) reflection corresponding to smectite, and the X-ray diffraction pattern between the measured and calculated ones, can be used efficiently as one of the methods to evaluate the mixed layer structure of glauconite-smectite series mineral in the clay.

Key words: Glauconitic clay, X-ray diffraction, Mixed-layer structure

INTRODUCTION

It has been known that the glauconite which occurs characteristically in marine sediments and sedimentary rocks, has usefulness as an indicator of the sedimentary conditions under marine environment (McRae, 1972; Van Houten and Puruker, 1984). While the glauconite is a ferriferous and potassic mica mineral of dioctahedral type in the narrow sense (Bailey, 1980), the mineral shows an extensive variation in mineralogical properties owing to the mixed layering with smectite layers (Hower, 1961). For example, the variation of the mineral is described as a glauconitic mineral series ranging from glauconitic mica to glauconitic smectite (Odin and Matter, 1981), and as a continuous mineralogical series analogous to that of aluminous mixed-layer illite-smectite (Thompson and Hower, 1975). This spread of the mineralogical property of the mineral is thought to be a characteristic controlled by formational environments, and caused by diagenesis 54 T. Yoneda and T. Watanabe after the formation (Odin and Matter, 1981; Odin and Morton, 1988). Knowledge of detailed mineralogical features in addition to the geological occurrence of the mineral becomes necessary to understand the genetic relation between the mineralogical property and the geological process for the glauconite, and the usefulness of the mineral mentioned above. In this paper, the result of the X-ray diffraction of glauconitic clay from the Minamishiraoi Kuroko-type barite deposit, Hokkaido, Japan, is described, with a view of making clear the mineralogical property of the clay that shows intermediate property of glauconite and smectite.

SAMPLE AND EXPERIMENTAL METHOD

Green clays occur widely in the hanging-wall rock composed of green sandstone and tuff on barite orebody of the Minamishiraoi deposit. The green clays are divided into three types of aggregation under petrographic observations: (1) granules less than approximately than 1 mm in diameter, (2) fillings of the matrix of grain, (3) stringlets replacing clastics or matrices of the rocks (Yoneda, 1993). In cases of (1) and (3), they are green and/or olive-colored, while they are brown-colored in case of (2) . The microscopic features of some granules are similar in shape to those of spheroidal glaucony after Triplehorn (1966) .

The granular clay (sample number: G37) (Figure 1-A) used for the X-ray diffraction experiment was sorted under the stereo-microscope from the sample of green sandstone. Observation by analytical transmitted electron microscope (ATEM) and scanning electron microscope (SEM) shows that the sorted sample is composed mainly of irregular flake- shape particles, and elongated lath- or needle-like particles determined as halloysite

(Figure 1-B,C,D). The electron microprobe analysis performed on polished sections of the rock sample show that the granular clay is potassic and ferriferous (Table 1). The Fe2O3 and K2O contents of the granular clay are lower than those of the New Jersey glauconite analyzed in this study. The K2O-content of the clay is corresponding to that of glauconitic smectite after Odin and Matter (1981) . Some of the sorted sample were prepared as randomly oriented powders mounted on Al-holder. The <2ƒÊm fractions separated from some sorted granules was prepared as the oriented powders mounted on a glass slide. Some of the oriented powders were saturated with ethylene glycol (EG) vapor. CuKƒ¿ radiations and measurements of diffraction patterns were carried out for these specimens using a Rigaku RU-300 and RAD-B system (tube voltages/tube currents 40 kV/200 mA; slit system 1•‹/2-0.3 mm-1•‹/2 and 1•‹/6-0.3 mm-1•‹/6). For a comparison to the G37, NJ-glauconite (New Jersey, USA) and nontronite (Hohen hagen, Germany) were also prepared similarly. In addition to the above-mentioned X-ray diffraction experiment, a computer simulation of X-ray diffraction was carried out using HITAC M-680 with the program (Watanabe, 1977) based on the expression of Kakinoki and Komura (Kakinoki and Komura, 1952) . X-Ray Diffraction Line Profile of Glauconitic 55

FIG. 1. Optical and electron microphotographs of glauconitic clay (G37) examined in this study . H:halloysite, B:barite. A. Optical photograph of granules sorted under stereomicroscope . B. SEM photograph showing particle aggregation at an inner part of granule . C and D. TEM photographs of the clay.

RESULT AND DISCUSSION

The X-ray diffraction (XRD) pattern of randomly oriented powder specimen of the clay sample (Figure 2) shows that the clay is dioctahedral smectite with impurities. The impurities in the sorted samples were determined as a small amount of kaolin mineral, mainly halloysite, and a minor amount of chlorite, feldspar, barite and quartz, by the ATEM observation and the XRD pattern of powder specimens. Allophane was not detected in the clay by the chemical staining test using NaF and C20H1404 solutions. The XRD pattern of the glycolated specimen of the clays (EG-G37) were shown together with those of NJ-glauconite (EG-NJG) and nontronite (EG-Nont) in Figure 3. While the XRD pattern of the EG-37 shows the basal 17 A-reflection and its higher order reflections similar to those of EG-Nont, it also exhibits a 10 A-reflection and its higher order reflections indicating existence of a mica mineral such as EG-NJG. In addition, the EG-G37 shows characteristically a higher saddle/001 peak intensity ratio (Figure 3), which is described later, as compared with that of the EG-Nont. This 56 T. Yoneda and T. Watanabe

TABLE1. Chemical composition (wt. %) of glauconitic granular clays. N:the number of analytical point, n:the number of analyzed granule. Numerals in the blanket are standard deviation

* :total Fe

characteristics of the XRD pattern suggests that mixed-layer mineral of smectite and mica may be exist in the clay, by analogy of the "saddle/001" method which is used to evaluate random interstratification of illite and smectite (Weir et al., 1975; Inoue et al . , 1989) . From these diffraction results and electron microprobe data, it is inferred that the mixed-layer phase is composed of smectite and glauconite, probably random type of interstratification in consideration of the X-ray line profiles calculated by Thompson and Hower (1975) . Meanwhile, it is difficult to obtain further informations from these X-ray diffraction results, such as the percentage of smectite layers and the interstratified structure. On the contrary, as for the aluminous illite/smectite mixed layer mineral, many workers have been studied in detailed the evaluation of interstratification of the mineral, and several methods on the estimation of interstratification structure of mica and smectite layers by the X-ray diffractometry werealready conducted (Srodon, 1980; Watanabe, 1981; Tomita and Takahashi, 12§5,t Inoue et al., 1989) . Therefore, the evaluation of interstratification of the glaucon., is clay is made in this study, by comparison of the theoretical and measured X-ray diffraction line profiles. The theoretical line profiles were calculated by Kakinoki and Komura (1952), on the basis of the structural models (Table 2) of glauconite and EG-smectite (Reynolds, 1981). In the calculation, the slit system of diffractometer and the particle size of the clay were made to be K = 10 and ƒ¢ƒÃ = 0.2 (Klug and Alexander, 1974), and N (the mean number of the layer) = 5(ƒÐ = 2.0:1 < N < 10) , respectively. This condition of the slit system is comparable to that (1•‹/2-0.3 mm-1•‹/2) of RAD-B diffractometer employed in this study

(Watanabe, 1988). The parameters of the interstratified structure employed in the calculation are plotted in Figure 4, showing a mixed layer structure of which arrangement is X-Ray Diffraction Line Profile of Glauconitic 57

FIG. 2. X-ray diffraction pattern of randomly oriented powder specimen of the clay sample. ch:chlorite, ko:kaolin.

affected by the kind of elementary layer before a preceding layer (Sato , 1965). That is, when the glauconite layer and smectite layer are denoted by G and S , respectively, it indicates that the interstratified structure is determined by a transition probability (a) from a G layer to a G layer, and a transition probability (16) from a S layer to a S layer . The transition probabilities of a and ƒÀ, and the existence probabilities , WG and Ws, of the G layer and S layer can be expressed as

= Kƒ¿ + (1-K) ƒÀ , where K = WG/Ws.

At first, the saddle peaks of the X-ray diffraction profiles are compared between the calculated and measured ones. In case of randomly interstratified illite/smectite mineral rich in aluminum, it is well known that the relative intensity ratio (Isaddle/I(001)) of the saddle peak and the (001) reflection is valid to a convenient evaluation of S% as 58 T. Yoneda and T. Watanabe

FIG. 3. Comparison of the X-ray diffraction patterns of the glycolated specimens of the clay (EG-G37) and nontronite (EG-Nont), and NJ-glauconite (EG-NJG) (left), and definition of the saddle peak of smectite (right). ch:chlorite, ko:kaolin, fd:feldspar.

TABLE2. Structure model of elementary layers (Reynolds, 1981) X-Ray Diffraction Line Profile of Glauconitic 59

FIG. 4. Transition probabilities of elementary layers employed in the calculation. When glauconite (mica) layer and smectite layer are denoted as G and S, respectively, the interstratified structure is determined by a transition probability (a) from a G layer to a G layer, and a transition probability (/) from a S layer to a S layer (Sato, 1965). Mixed-layer structure on the curves of a and b reveals the irregular and random interstratification of G and S, respectively. On the other hand, that on the curve c reveals the irregular interstratification with segregation of G and S. The degree of segregation in the mixed-layer structure increases from the diagonal line A-C towards the direction of segregation structure (B) in this diagram (Sato, 1975).

mentioned before. Relationship between S% and the intensity ratio of the calculation profiles of randomly interstratified glauconite/smectite was manifested by the same method to Inoue et al. (1989) in Figure 5. The intensity ratios in this calculation does not differ greatly from those calculated preliminary from the chemical composition (Si = 3.8, Al = 0.9, Fe = 0.9 and Mg = 0.4 per half cell unit (010(OH)2)) in consideration of the electron microprobe data of MS37 (Table 1). However, the intensity ratios shows con- siderable difference depending on the mean number of the layer (N). For a value of intensity ratio, the curve of N = 5 in Figure 5 gives a higher S% value (approximately 5% higher) as compared with that which was calculated preliminarily on the basis of N = 10 (5 < N < 15). This tendency of the effect of the number of the layer (the coherent domain size in the stacking direction) is concordant to that of randomly interstratified illite/ smectite which is discussed in detail by Inoue et al. (1989). As for the evaluation of Isaddle/I(001) ratio of the specimen (Figure 2-B), the peak height from the base line was 60 T. Yoneda and T. Watanabe

FIG. 5. Relationship between S% and the intensity ratio of the calculation profiles of randomly interstratified glauconite/smectite. Curves (a, b and c) are corresponding to those (a, b and c) in Figure 4.

determined using a glass slide without clay materials, similarly as Inoue et al. (1988). In addition, the influence of chlorite and discrete smectite possibly present in this specimen on the intensity ratio was ignored in this study. The X-ray intensity ratio of a saddle peak and (001) reflection peak increases with a decrease of S% in the structure (Figure 5). If the value (0.70) of Isaddle/I(001) ratio measured under the slit system of 1•‹/6-0.3 mm-1•‹/6 for the specimen EG-GS37 is applied to the relationship of the calculated line profiles (curve b of Figure 5), the S% can be presumed to be approximately 60% . However, the S% deviates greatly from the estimated value in case of the irregular types of interstratification somewhat disconnected from the random type shown in the curves a and c of Figure 5. Therefore, it is necessary to compare the measured profiles directly with the calculated ones in order to specify the S% and the interstratified structure of the clay. Besides, if the influence of chlorite and discrete smectite are taken into account, the value of S% may be smaller as compared with the value mentioned above. Some X-ray line profiles were calculated for the interstratified structures of which probability parameters were plotted on the curve a, b and c in Figure 4, and of which values of Isaddle/I(001) ratio were similar to that of the measured X-ray diffraction profile in Figure 5. And, a calculation line profile fitly corresponding to that of EG-GS37 was selected (Figure 6). As a result, the mixed-layer structure of EG-GS37 can be X-Ray Diffraction Line Profile of Glauconitic 61

FIG. 6. A comparison of the X-ray diffraction line profiles between a measured and a calculated ones for randomly interstratified glauconite/smectite . a:mcasured profile, b:calculated profile, ch:chlorite, ko:kaolin , fd:feldspar, q:quartz. evaluated to be random-type interstratification (S% = 35%) somewhat deviated from random interstratification toward the direction of segregation. As exemplified above, the measured and the theoretical line profiles of X-ray diffraction are corresponding well to one another. Consequently, it is suggested that the comparison of line profiles of X-ray diffraction between the measured and calculated ones , is valid also for the evaluation of mixed-layer of a glauconite-smectite series that is rich in iron 62 T. Yoneda and T. Watanabe and potassium, not only for that of an aluminous illite-smectite series. However, the comparison of XRD line profiles should be taken care, because the measured XRD line profile of a glauconite-smectite series is affected considerably by other minerals co- existing in the clay. For example, allohane and a small amount of regular-type mixed- layer mineral have a remarkable effect on the X-ray intensity of saddle peak. In this study, the constant iron-content in the octahedral sheet of the elementary layers is postulated. While, it is known that the iron-content of the glauconite-smectite series mineral frequently varies related with interlayer potassium and octahedral aluminum (Ireland et al., 1983; Iwasaki et al., 1989; Strickler and Ferrell, 1990; Yodena, 1993), so the iron-content of the glauconite-smectite series mineral may possibly vary related with S% of the interstratified structure. Subsequently, it may be necessary to make a comparison based on the theoretical X-ray line profiles in consideration of such variation of iron- content in the interstratified structure. Additionally, it is well known that mineral phases of which each property is somewhat different within a glauconite-smectite series, co-exist in a clay, even in a single grain of glauconite pellet (Odom, 1976; Odin and Morton, 1989), so the XRD line profile of the clay in such case should be considered hereafter, also.

CONCLUDING REMARKS

A potassic and ferriferous granular clay from the Minamishiraoi Kuroko-type deposit was determined to be mixed-layer mineral of glauconite and smectite by X-ray diffraction experiment and computer simulation. The mixed-layer structure of the glauconitic clay was evaluated to be a random-type interstratification (S% = 35%) somewhat deviated from random interstification toward the direction of segregation. Calculated XRD line profiles of the glauconite/smectite indicate that the X-ray intensity ratio of a saddle peak and (001) reflection peak increases with a decrease of S% in some irregular-type mixed-layer structures including random interstratification. The "Isaddle/ I001"relation which is used conveniently to evaluate random interstratification of aluminous illite-smectite series (Weir et al., 1975; Inoue et al., 1989) is valid also for a glauconite- smectite series. This relation can be used efficiently as one of the methods to elucidate a variation in mixed-layer structure and S% of the glauconitic clay.

ACKNOWLEDGEMENTS

The authors are indebted to associated professor T. Takama and staffs of the high brilliance X-ray laboratory, Hokkaido University for supports of X-ray experiments.

REFERENCES

BAILEY,S.W. (1980) Clay Miner., 15, 85-93. HOWER,J. (1961) Am. Mineral., 46, 313-334. INOUE,A., BOUCHET,A., VELDE,B. and MEUNIER,A. (1989) Clays and Clay Minerals, 37, 227-234. IRELAND,B.J., CURTIS,C.D. and WHITEMAN,J.A. (1983) Sedimentology, 30, 769-786. IWASAKI,H., MATSUEDA,H. and ISHIYAMA,D. (1989) Rept. Mining Col., Akita Univ., 10, 35-47 X-Ray Diffraction Line Profile of Glauconitic 63

(in Japanese with English abstract). KAKINOKI,J. and KOMURA,Y. (1952) J. Phys. Soc. Japan, 7, 30-35. KLUG, H.P. and ALEXANDER,E. (1974) X-ray Diffraction Procedure. Wiley, New York, 966pp. MCRAE, S.G. (1972) Earth-Sci. Rev., 8, 397-440. ODIN, G.S. and MATTER,A. (1981) Sedimentology, 28, 611-641. ODIN, G.S. and MORTON,A.C. (1988) Diagenesis, II (eds., Chilingarian, G.V. and Wolf, K.H.). Elsevier, 213-264. ODOM, I.E. (1976) Clays and Clay Minerals, 24, 232-238. REYNOLDS,R.C. (1981) Crystal structures and clay minerals and their X-ray identification (eds., Brindley, G.W. and Brown, G.). Min. Soc., London, 249-304. SATO,M. (1965) Nature, 208, 70-71. SATO,M. (1975) J. Cryst. Soc., Japan, 17, 165-180 (in Japanese with English abstract). SRODON,J. (1980) Clays and Clay Minerals, 28, 401-411. STRICKLER,M.E. and FERRELL,R.E. (1990) Clays and Clay Minerals, 38, 69-76. THOMPSON,G.R. and HOWER,J. (1975) Clays and Clay Minerals, 23, 289-300. TOMITA,K. and TAKAHASHI,H. (1985) Clays and Clay Minerals, 33, 379-390. TRIPLEHORN,D.M. (1966) Sedimentology, 6, 247-266. VAN HOUTEN,F.B. and PURUKER,M.E. (1984) Earth-Sci. Rev., 20, 211-243. WATANABE,T. (1977) Sci. Rept. Fac. Sci., Kyushu Univ., 12, 303-309. (in Japanese with English abstract) . WATANABE,T. (1981) Jour. Min. Soc. Japan, Spec. Issue, 15, 32-41 (in Japanese with English abstract) . WATANABE,T. (1988) Clay Science, 7, 97-114. WEIR, A.H., ORMEROD,E.G. and EL MANSEY,I.M.I. (1975) Clay Miner., 10, 369-386. YONEDA,T. (1993) Proc. 29th IGC'92 Selected Papers from Mineral Resources Symposia, Vol. C, 120-131.