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 inter- stratification 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 min- eralogical 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 approxi- mately 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 calcu- lation 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.